For high-resolution sensing in integrated sensing and communication (ISAC) systems, the deployment of extra-large antenna arrays (XLAAs) is essential. This, however, renders the traditional point target (PT) model inaccurate. Instead, targets must be considered as having a spatial extent over range and angle, necessitating their modeling as extended targets (ET) for accurate sensing, especially within the near-field propagation region. This shift to ET modeling often entails a significant increase in energy consumption, and reduced sum-rate and increased latency for the communication users compared to the simpler PT model. To address this critical trade-off, this paper proposes an antenna selection strategy for XLAA-based ISAC. By selectively activating antenna elements, the proposed ISAC design aims to maintain effective far-field PT operating conditions, thereby enhancing energy efficiency and communication sum-rate. The optimization ensures the communication quality-of-service by enforcing signal-to-interference-plus-noise power ratio constraints for the communication users, while inherently managing the sensing performance evaluated via the Cramer-Rao bound. This strategy provides a controllable operating point, balancing the ET model’s high sensing accuracy, which comes with higher signal processing time and lower communication sum-rate, against the PT model’s lower sensing accuracy but lower processing time and higher sum-rate. Numerical results validate the proposed approach, demonstrating substantial improvements in energy efficiency and sum-rate over pure ET modeling, achieved at a quantifiable cost in sensing accuracy.

This paper investigates the average achievable rate of reconfigurable intelligent surface (RIS) assisted point-to-point short-packet communication with multiple-antenna reception. First, using a random matrix theory based approach, closed-form upper bounds for the system’s average achievable rate are obtained for two asymptotic regimes: high and low transmit powers. Detailed performance analysis and insights based on the rate metric are provided. Then, a metric for quantifying the potential deterministic behavior of the system’s channels, specifically in the short-packet regime under consideration, is proposed. The hardening is studied, and key insights are provided, including the impact of the finite blocklength on the average achievable rate of the system, particularly for small numbers of receive antennas and in the high transmit power regime. The practical application of the hardening metric from a system design viewpoint is also discussed.

The advancement of industrial Internet of Things (IIoT) networks has brought challenges in terms of connectivity, efficient spectrum usage, and low latency. To tackle these challenges, advanced multiple access techniques have been developed. Non-orthogonal multiple access (NOMA) is a promising multiple access technique due to its high energy efficiency and fairness for devices. However, NOMA has inherent security issues due to wireless transmission and complex successive interference cancellation (SIC) based decoding, which can negatively impact system performance. Furthermore, achieving perfect SIC is also a challenging task due to implementation complexity. This study investigates the effects of imperfect SIC in a dual-device cooperative NOMA system. Our system includes direct links between the source and devices and uses both decode-and-forward and amplify-and-forward relays. The overall objective is to optimize decoding order and power allocation coefficients in order to maximize the near or priority device’s secrecy rate while meeting the quality-of-service (QoS) requirements of the far or normal device. Observing the underlying optimization problems to be non-convex, a low-complexity algorithm yielding optimal solutions is developed. Our findings reveal how imperfect SIC can impact massive access systems and secrecy performance. Extensive simulations provide novel design insights into the achievable secrecy rate and optimal power allocation coefficients. We also explore the trade-off between the priority device’s secrecy rate and the normal device’s rate, along with the impact of residual interference. Finally, our proposed solution has been shown to significantly improve the QoS-constrained secrecy rate of priority devices when compared to relevant benchmarks.

This work amalgamates spatial modulation (SM) with ambient backscattering (ABSc) to address the spectral and energy efficiency demands of the power constrained device-to-device (D2D) communications in the Internet-of-things. Though incorporating reconfigurable intelligent surfaces (RISs) in the communication process can help in extending the coverage of such power constrained devices, rich scattering in the operation environment, or broken links between the nodes involved in the end-to-end communication, can adversely affect the system performance. To cope up with this challenge, a selection-based cooperative RIS protocol is proposed, and the performance of the D2D communication system, founded on SM and ABSc at the transmitter and cooperative RISs, is evaluated in terms of the bit error rate, outage probability, and energy efficiency. A link budget analysis is conducted to comprehend the effects of the RIS sizes in countering the path loss effects, and the imperfection of the channel estimation and timing synchronization of multiple RISs are also analyzed. The results reveal that the proposed communication model with cooperative RISs can overcome the path loss effects and enhance the received power levels, thereby outperforming the baseline system where a single RIS intervenes in the end-to-end communication, with a signal-to-noise ratio gain of around 10 dB for the bit error rate, outage probability, and energy efficiency. Considering different prominent SM techniques for the system operation and comparing the performance in different set-ups, it is shown that the system implementing generalized SM performs the best.

In this paper, we focus on investigating the link-layer rate within a non-orthogonal multiple access (NOMA) system operating in the finite blocklength (FBL) regime, specifically designed for short-packet communications. By leveraging the effective capacity (EC) framework, latency and reliability in FBL, encompassing parameters such as the block error probability and the delay outage probability, are analyzed for two scenarios, namely, system operation with multiple NOMA pairs and the two-user NOMA operation. Closed-form expressions for the EC in the two cases are derived by assuming that transmissions are subject to Rayleigh fading and adopting a practical path-loss model. Numerical results are provided to validate the analytical findings, and to highlight the impact of the transmit signal-to-noise ratio, the blocklength, the delay exponent, and the block error probability, on the EC and the delay outage probability. Furthermore, various pairing configurations are investigated and demonstrate that the paired NOMA set attains the highest total EC for users experiencing substantial differences in their channel conditions.

In reconfigurable intelligent surface (RIS) aided communication implementing space-shift keying at the transmitter for index modulation, the RIS is proposed to perform the dual function of selecting the phases of the reflecting elements optimally according to the phases of the channel gains, and acting as a modulator by transmitting$M$-ary phase-shift keying (PSK) modulated symbols via reflection phase modulation. The target antenna at the receiver is chosen by utilizing the optimal maximum likelihood (ML) detection rule and a hardware- and energy-efficient greedy detector, which performs detection based on the maximum received energy. For these detection scenarios, closed-form expressions for the probability of erroneous detection (PED) of the target antenna are derived, considering Nakagami-$m$channel fading. Numerical results supporting the analytical framework show the role of the rotation of the$M$-PSKconstellation to improve the reliability of the system. In particular,$\pi/M{-}$rotated$M$-PSK constellation is optimal for the greedy detector, whereas the ML detector is not dependent on such rotation to yield minimum PED.

Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for enhanced spectral efficiency in the current and next-generation wireless networks. In this paper, we examine a realistic NOMA model where users, assisted by a regenerative relay, cannot be fully trusted. We address the challenge of ensuring secure access for these users while accounting for the error propagation in successive interference cancellation (SIC) during the decoding process. For such, we formulate and solve two optimization problems, viz. maximizing the minimum secrecy rate of the users and maximizing the sum secrecy rate of the users, while accounting for SIC errors and the constraint on the power budget. For each case, we derive the optimal power allocation solution to achieve positive secrecy rates despite imperfect SIC. Simulation results provide key insights on the obtained secrecy rates and power allocations, factoring in residual interference. The joint optimal solution for the decoding order and power allocation is compared with different benchmark schemes: optimal decoding order and equal power allocation, fixed decoding order and equal power allocation, fixed decoding order and optimal power allocation, and optimal decoding order and channel-based power allocation. Our proposed framework demonstrates average performance gains of about 47.62 dB, 50.79 dB, 54.02 dB and 39.83 dB over these schemes and, hence, the fact that the proposed framework can substantially improve the secrecy performance.

Each transmit antenna in spatial modulation (SM) based communication is uniformly activated, which can lead to poor channels for transmission, causing performance degradation. Though antenna selection can be used to tackle this problem caused by uniform antenna activation (U-AA), it requires additional antenna elements, high computational complexity, and signalling overhead. This paper proposes an irregular antenna activation (I-AA) technique, which activates an antenna with a probability that is proportional to a channel with the highest gain. In the proposed method, consecutive equal bits in a bit sequence are exploited to choose an antenna index for transmission. Since different numbers of consecutive equal bits occur with different probabilities, this makes each of the available antennas to be randomly activated with different probabilities. Taking advantage of available channel state information at the transmitter, we develop a rate-optimized I-AA method to utilize better channels for transmission. In prominent variants of SM, the use of I-AA is shown to yield higher throughput and smaller error rates compared to operations with the conventional U-AA. Moreover, a joint rate and Euclidean-distance optimized antenna selection (REAS) and a rate-optimized low-complexity AS (RLAS) for SM with I-AA are proposed. The use of I-AA without AS in prominent variants of the SM technique is shown to achieve better error rate performance compared to U-AA with AS. Also, the use of I-AA in REAS and RLAS yields improvements in the data rates and error rates compared to U-AA with AS, at a negligible extra complexity and signalling overhead.

This study proposes the utilization of quantum machine learning (QML) to maximize the energy efficiency of reconfigurable intelligent surface (RIS) assisted communication with rate-splitting multiple access (RSMA). The next-generation wireless communications are expected to yield significantly higher energy efficiency compared to that of the previous generations. In a multiuser system, energy efficiency can be defined as a benefit-to-cost ratio between the achievable sum-rate and the energy consumption, where enhancements in the former come at the expense of increases in the latter. Recently, the integration between RSMA and RISs has been advocated as a powerful mean to control this tradeoff. Indeed, RSMA can enhance the rate region while RISs can lead to reduced energy consumption thanks to the use of low-energy phase shifters. However, optimizing a RIS-aided RSMA communication system is faced with a computational burden given that the RIS enlarges the volume of the required channel information, which expands the information that needs to be processed by the optimization module, even when the optimization is based on conventional learning techniques. The proposed QML optimization framework, which orchestrates non-linear quantum unitary operations to compose the learning models, enjoys information processing gains thanks to state vector operations in multi-dimensional Hilbert space. It is composed of two trainable quantum-based learning models employed in an alternating manner: the first establishes the transmission precoding, and the second designs the RIS phase shifting. Numerical results show that the proposed QML delivers comparable performance to that of conventional optimization but with reduced complexity.

Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique to improve the spectral efficiency of the fifth-generation (5G) and beyond networks. However, the successive interference cancellation (SIC) based decoding used at the receivers makes NOMA prone to critical security risks. In this paper, we consider a regenerative relay-assisted dual-user downlink NOMA communication model. To ensure the robustness of the model, we also take into account the error propagation in SIC occurring in the decoding process. Our design goal being to provide security to both users, we propose an optimal power management strategy, so as to maximize the secrecy rate of the users under the impact of imperfect SIC. The optimal power allocation solution is obtained such that positive secrecy rate is achieved at both of the end receivers, while accounting for SIC errors. Analytical expressions of the secrecy rates are derived to analyze the secrecy performance. Simulation results are also presented, and provide key insights on the obtained secrecy rate and power allocation coefficients with residual interference. The achieved gains prove that the proposed model can substantially improve the secrecy performance.

This paper investigates the use of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) to assist the communication with multiple devices distributed according to a Poisson point process. First, using rate-splitting multiple access (RSMA) transmission scheme, the downlink STAR-RIS multi-user system is studied, and its fundamental statistics are provided. Then, by leveraging stochastic geometry tools, and adopting an approach based on the cumulative distribution function, the outage probability is obtained for the two types of devices, i.e., the ones in the transmission zone and those in the reflection zone. For such, the distributions of the channel gains and the devices’ distances are also characterized. The closed-form expressions with Meijer-G functions for the outage probability are provided in two cases for the STAR-RIS operation, energy splitting and mode switching. Simulation results and comparisons are provided, and the impact of various system parameters on the outage performance is analyzed. In particular, it is shown that as the RIS size, the RSMA power splitting factor, and the devices’ density, increase, the STAR-RIS aided RSMA helps achieve enhanced performance in both operation cases, i.e., energy splitting and mode switching.

This work employs modular quantum machine learning (QML) to estimate the wireless channels in simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RIS) aided communication systems. Although RISs, composed of low-energy phase-shifting elements, can enable controlled signal reflections to cover communication devices obstructed by blockages, the devices located behind the reflection-only surfaces cannot be covered as these structures now become blockages themselves. STAR-RISs solve this issue by allowing the transmission signals to be conveyed to the devices located behind the STAR-RIS structures. However, acquiring accurate channel information of devices in the reflection and transmission regions of a STAR-RIS is not a trivial task. To address this issue, this paper proposes a novel modular QML scheme that employs different quantum-based learning modules to (i) eliminate the noise from the coarse channel information, and (ii) estimate the channels of the devices in the reflection and transmission regions.

Keeping in mind the device size and power constraints of future wireless devices, transmitters free of radio frequency chains need to be designed using reconfigurable intelligent surfaces (RIS) as modulators. In this context, spatial modulation (SM) can be applied to selectively activate the desired RIS elements for fulfilling spectral- and energy-efficient communications with low error rates. In this paper, we deploy a RIS as a modulator and propose SM and generalized SM (GSM) based on irregular activation of the RIS elements, where the elements are activated with different probabilities. This can be further combined with element selection, where channel conditions are considered for element activation. It is shown that element selection based on channel conditions in conjunction with irregularly activated SM schemes perform better than conventional SM and GSM schemes in terms of error rates and energy efficiency while maintaining an acceptable signalling overhead and computational complexity.

Non-orthogonal multiple access (NOMA) has emerged as an enabling solution for 5th generation and beyond networks, but the often-neglected issues due to successive interference cancellation (SIC) based decoding might seriously hamper its performance. In this paper, we study a downlink NOMA system with cooperative half-duplex relaying with imperfect SIC, where the base station is communicating with two untrusted users with the aid of a trusted decode-and-forward relay while also considering the availability of direct links from the source. An optimization problem is formulated for maximizing the secrecy rate of the near user while fulfilling the quality-of-service requirements of the far user. The optimal power allocation solution is derived while considering the impact of SIC error. The simulation results illustrate the exactness of the theoretical analysis alongside insightful discussions to investigate the impact of imperfect SIC.

This paper proposes a joint broadcast-unicast downlink communication framework implementing layered-division multiplexing (LDM) and aerial reconfigurable intelligent surface (RIS), and develops a corresponding design with a focus on energy efficiency. Maximization of the energy efficiency is achieved by jointly designing the optimal active beamforming at the base station and the passive beamforming at the aerial RIS. The non-convex optimization is solved using a two-stage algorithm. The active beamforming is designed by using low-complexity zero-forcing for the unicasting service and successive convex approximation based on the first-order Taylor series expansion for the broadcasting service, and the RIS phase shifting is designed with semi-definite programming. Comparative results are provided, and show that the proposed LDM-based RIS-assisted joint broadcast-unicast communication framework is more energy efficient than the joint broadcast-unicast via time-division multiplexing or amplify-and-forward relaying.

In future wireless networks, device-to-device (D2D) communications are expected to play an important role to support a plethora of applications. To meet the target quality of service while ensuring high reliability, and high spectral and energy efficiencies, manipulation of the radio waves by reconfigurable intelligent surfaces (RIS) will be critical. In this context, leveraging concepts of polarization, this paper proposes a framework for bidirectional D2D communications, where the data exchange between a central node and devices operating in distinct polarization states, is multiple-input multiple-output in nature and takes place via a dual-polarized RIS, in the presence of hardware impairments and imperfect interference cancellation, as well as impairments caused by the spatial correlation and cross-polarization. Performance evaluation of such a framework is conducted in terms of key metrics, namely, bit error rate, outage probability, channel capacity, and energy efficiency, for which closed-form expressions are obtained considering transmissions over Nakagami fading channels. An asymptotic analysis is also conducted to evaluate the achievable diversity gains, by approximating the Nakagami model with a tractable Gamma model. Further, the impact of imperfect channel estimation on performance is also investigated. Comparative numerical results are provided, and the effects of the main system parameters on performance are analyzed. The proposed framework is shown to provide significant performance improvements as compared to D2D communications via non-polarized RIS.

Probabilistic flooding is an efficient information dissemination policy capable of spreading information to the network nodes by sending information messages according to a fixed forwarding probability in a per-hop manner starting from an initiator node. It is a suitable approach, especially in topologies where the number of information messages sent under traditional approaches is significantly increased. The analysis presented in this paper considers graph spectra properties such as the largest eigenvalue$\lambda _{1}$of the adjacency matrix, and the eigenvector centrality. Both are analytically investigated and$\frac {4}{\lambda _{1}}$is derived as a lower bound of the forwarding probability that allows for global coverage, i.e., all network nodes receive the information message, under certain conditions also investigated here (e.g., the condition of the binomial approximation). It is shown that for any value of the forwarding probability equal to or larger than$\frac {4}{\lambda _{1}}$: (i) coverage is proportional to the initiator node’s eigenvector centrality; (ii) the probability a node receives the information message is proportional to the node’s eigenvector centrality; (iii) termination time decreases as the initiator node’s eigenvector centrality increases. If knowledge of$\lambda _{1}$is not available, then the average node degree$\bar {d}$can be used for ensuring global coverage. If knowledge of both$\lambda _{1}$and$\bar {d}$is not available, a dissemination policy is proposed that forwards messages to$m$(randomly selected) neighbor nodes. It is analytically shown that any value of$m \geq 4$allows for global coverage. Simulation results demonstrate the effectiveness of the considered analytical approach and the introduced policy.

In this contribution, a novel framework for joint broadcast-unicast downlink transmissions using dual-polarized aerial reconfigurable intelligent surface (RIS) is proposed. The objective is to maximize the energy efficiency by jointly designing the active beamforming at the base station and the passive beamforming at the RIS. The optimization problem to maximize the system’s energy efficiency is formulated and solved using a two-stage algorithm. To tackle the non-convex nature of the problem, an alternating technique, where the optimization is decomposed into two sub-problems, is proposed. In the first stage, the passive beamforming matrix of the dual-polarized aerial RIS is designed based on the Gaussian randomization method, which relaxes the inhomogeneous non-convex quadratically constrained quadratic program (QCQP) into a semi-definite program. In the second stage, the active beamforming at the base station is designed based on a dual-structured beamforming approach, in which the interior point method is used to obtain the prebeamforming matrix, and the beamforming matrices pertaining to the unicasting and broadcasting are obtained based on low-complexity zero-forcing and successive convex approximation, respectively. Numerical results and comparisons are provided. In particular, it is shown that the polarization-based communication system yields higher energy efficiency gains as compared to a system implementing layered division multiplexing.

This paper investigates the performance of point-to-point communications in which the source node is capable of harvesting and storing energy from radio-frequency (RF) signals, and then using the harvested energy to communicate with its end destination. This operation is executed via a time-switching protocol at the source node while considering that the energy spent from its battery is fixed within a communication time interval. A mathematical framework is developed for the performance evaluation of the communication system subject to constraints on the allowable energy outage. A virtual energy queuing model is proposed and used to satisfy the assumptions of the large deviation principle, which is then used for the performance analysis. Considering all channels to be subject to Rayleigh fading, closed-form expressions are obtained for the energy used from the transmitter's battery and for the energy-outage probability of the system. Numerical results are also provided, and the effects of various parameters, including those of the time-switching protocol, the harvested energy, the distance between nodes, and the transmit power, on the performance of the RF energy-harvesting based communication systems are investigated.

Thanks to their capability in controlling the wireless channels in a dynamic way, metamaterial-based reconfigurable intelligent surfaces (RIS) can help in providing low error rates and high data rates, as per the requirements of future wireless applications. In many of the envisioned applications, devices need to interchange data within close proximity. In this context, this paper proposes a RIS-assisted full-duplex MIMO bidirectional model for communication between multiple devices, and analyzes its performance while considering a realistic model for the communication channels, which accounts for key physical charac-teristics and impairments. The system performance is evaluated in terms of the symbol error probability, outage probability, and channel capacity, for which closed-form expressions are derived while taking into account residual hardware impairments and residual self-interference at the devices, and considering operations in both indoor and outdoor environments. The results reveal that system operations in indoor environments yield better performance as compared to outdoor scenarios, and quantify the impacts of the hardware impairments and self-interferences.

Non-orthogonal multiple access (NOMA) has been considered as a promising solution to provide spectrally efficient communications in the 5th generation and beyond networks. Cooperative communication, on the other hand, helps in improving the coverage and reliability of the communications. In this paper, we consider a cooperative NOMA communication system with two untrusted users and a trusted amplify-and-forward relay. Maximization of the secrecy rate of the near user while considering the service requirements of the far user is tackled. Closed-form expressions are obtained for the optimal power sharing between the source and the relay, along with the optimal power allocation for both users. Numerical results are also provided, which verify the exactness of the theoretical analysis and provide insights on the design of secure NOMA-based cooperative communication networks.

We consider an ultra-reliable low-latency system in which a reconfigurable intelligent surface (RIS) is deployed to assist the simultaneous wireless information and power transfer between the access point and multiple devices. The data transmission, in the form of short packets, is performed using the rate splitting mechanism with chase-combining hybrid automatic repeat request error control. Using a realistic channel model and considering operation in the presence of hardware impairments at the RIS and the devices, the system performance is investigated in two folds. First, the average block error rate and the outage probability in the information transfer are evaluated. Then, the battery recharging time in the power transfer and its statistics are determined. Numerical results are provided to illustrate the system performance and quantify the impacts of key parameters including the packet size, the maximum number of packet retransmissions, and the RIS size.

This paper investigates the wireless power coverage in a network where intelligent reconfigurable surfaces (RISs), distributed according to a homogeneous Poisson point process, cooperate in the energy transfer from the power beacon to the harvesting devices. First, using energy beamforming and maximum ratio transmission, the harvested energy at a typical device is obtained. Then, leveraging stochastic geometry tools, and adopting an approach based on the moment generating function, the power coverage probability is obtained. For such, we also characterize the distributions of the channel gains and the device distances. Novel closed-form expressions for the coverage probability are provided for the cases when the wireless power transfer is assisted by multiple RISs, deployed in cascaded or distributed configurations, as well as when the power beacon is aided by a single RIS. The impact of the main network parameters on performance is analyzed. In particular, comparative results show the significant gains that can be achieved in the network coverage when multiple RISs cooperate in the wireless power transfer, as compared to the non-cooperative scheme.

Massive MIMO is an integral part of cellular communication systems in 5G and beyond. However, with the increase in the number of base station antennas, the need for radio-frequency chains to support parallel data streams also increases, leading to higher cost and lower energy efficiency. To address this issue, hybrid beam combining techniques have been devised, where constant phase shifters (CPSs) are used at the receiver to combine the signals coherently. Coherent combining requires a large number of CPSs and, as such, even a small amount of hardware impairment can lead to severe degradation in the combining performance. The use of these components needs to be done with practical consideration of non-linearities. In this paper, we consider a behavioral model for characterizing the impairments, and propose a CPS-based hybrid combining algorithm. Comparisons show that the proposed algorithm improves the throughput by utilizing a considerably lower number of CPSs. Considering both amplitude-to-amplitude modulation and amplitude-to-phase modulation distortions, it is shown that the proposed algorithm provides higher throughput than existing techniques. Error performance analysis also reveals that the proposed algorithm is robust to hardware impairments.

This paper investigates the power coverage probability in cooperative wireless powered communication networks, where multiple access points collaborate to meet the energy demands of low-power devices. Based on the theory of Poisson-Delaunay triangulation, the probability density functions (PDF) of the Euclidean distance between the access points of the Poisson-Delaunay triangular cell and typical devices are derived. By using the theory of stochastic geometry and the obtained PDFs, the closed-form expressions of the wireless power coverage probability are obtained for three typical locations of the devices. As the wireless power coverage probability expressions involve the extended generalized multivariate MeijerG function (EGMMGF), a new implementation enabling numerical calculation of the EGMMGF is also proposed. The impacts of the main network parameters on the performance of the proposed framework are analyzed. In particular, comparative results show the significant gains that can be achieved in the wireless power coverage when multiple access points participate in the wireless power transfer or when the density of the network’s access points is increased, as compared to the non-cooperative scheme.

We propose cooperative Han-Kobayashi (H-K) signaling schemes and investigate their performance in comparison with non-cooperative H-K signaling. In the cooperation scenario, the near user relays the base station (BS) common message or the far user’s message to increase the received signal-to-interference-plus-noise ratio of the far user. We evaluate the outage performance of the non-cooperative and cooperative signaling schemes. Specifically, we obtain the exact outage probability (OP) of the non-cooperative strategy, and closedform approximations for the OP of the cooperative schemes. As demonstrated in the comparative results, by setting an appropriate BS’s power budget and power allocation, the non-cooperative mechanism has the potential to excel in OP. Finding the best power allocation to achieve the least outage with non-cooperative H-K is not trivial, whereas allocating a small level of the BS’s transmit power to the far user’s message, and then relaying the said message with a suitable power can yield significant improvements in the outage performance and make the cooperative approach superior.

In wireless communications, reconfigurable intelligent surfaces (RIS) are emerging as a promising technology that is made possible by the advent of software controlled metamaterial sheets for controlling the wireless channels dynamically. In future applications, IoT devices will have small sizes and limited power supply. To make these devices spectrally and energy efficient in accordance with the advanced 5G and 6G specifications, we propose ambient backscattering (ABSc) technique along with spatial modulation (SM) and space shift keying (SSK) for data transfer assisted with RIS. We also conduct a thorough performance analysis of these schemes in terms of outage probability, and bit error rate, validated by Monte-Carlo simulations, and provide comparative results that illustrate the merits of the proposed techniques. In particular, it is shown that RIS-empowered SM and SSK along with ABSc perform much better than conventional communications.

Wireless communications via reconfigurable intelligent surfaces (RIS) are envisioned to offer unprecedented spectral efficiency gains by smartly inducing phase shifts on the impinging electromagnetic waves at the RIS to reconfigure the underlying propagation environment. This work investigates a multi-user downlink communication system in which the access point, equipped with multiple antennas, serves its associated single-antenna users equipments (UE) with the help of RIS. The proposal is a leakage-based design in which the transmit precoding, the power allocation, and the phase shifts of the RIS, are designed to maximize the minimum signal-to-Ieakage-plus-noise power ratio (SLNR) of the UEs subject to the constraint on the power budget of the access point. The merits of the SLNR-based approach are highlighted, e.g., reduced complexity, and simulation results show that the RIS-aided design can achieve massive MIMO gains with much fewer number of active antennas in the access point as compared to conventional relaying.

This paper tackles the energy efficiency optimization in wireless communication networks, where multiple unmanned aerial vehicles (UAVs) deploy power transfer towards several energy receivers (ERs) to enable their uplink data transmissions through non-orthogonal multiple access (NOMA). Utilizing a formulated closed-form expression for energy efficiency (EE), a resource allocation mechanism aiming to maximize the system's EE is developed. To address this optimization problem, two algorithms are proposed that use Lagrangian optimization and gradient descent methods. For the simulations, three different cases, depending on the ERs' service demands, are considered. Numerical results along with comparisons are given and illustrated. The results show an enhancement in the energy efficiency for the cases that consider the needs of the ERs. Moreover, in all cases, the NOMA scheme's EE results are better than OMA with respect to the optimal charging time.

In this paper, we present a resource allocation framework for uplink communication in cellular networks aided with aerial intelligent reflecting surface (IRS). The main focus is on maximizing the energy efficiency by jointly optimizing the transmit powers of the users, the active beamforming at the base stations, and the passive beamforming at the IRS, while maintaining the users' minimum rates and adhering to the power constraints. The formulated problem is a highly intractable non-convex one, with the optimization variables coupled with each other in an intricate manner. To tackle this, an iterative solution based on alternating techniques is proposed. In particular, the transmit beamforming and the phase-shift matrix are obtained by minimum mean square error and semidefinite relaxation techniques, respectively. Numerical results are provided and show that using aerial IRS has remarkable advantages compared to the system operation with conventional aerial relaying. In particular, significant energy efficiency gains are achieved when optimal transmit power and a large number of reflecting elements are implemented.

This paper investigates the wireless power coverage and the transmission probability in a network where multiple access points, distributed according to a homogeneous Poisson point process, cooperate in the energy transfer towards harvesting devices. Using distributed energy beamforming and maximum ratio transmission, and leveraging stochastic geometry tools, the power coverage probability and the transmission probability are obtained in closed-form for three types of devices, namely, inner-cell, cell-edge, and vertex-cell. Exact formulae for the coverage and transmission metrics when devices are serviced by single energy sources are also provided. The impact of the main network parameters on performance is analyzed. In particular, comparative results show the significant gains that can be achieved in the coverage and transmission probabilities when multiple access points participate in the wireless power transfer, as compared to the non-cooperative scheme.

Providing security guarantee is a critical concern in the ad-hoc networks relying on multi-hop channels, since their flexible topology is vulnerable to security attacks. To enhance the security of a spatial modulation (SM) assisted wireless network, various SM mapping patterns are activated by random channel quality indicator (CQI) patterns over the legitimate link, as a physical-layer secret key. The SM signals are encrypted by random mapping patterns to prevent eavesdroppers from correctly demapping their detections. This secret key is developed for multi-hop wiretap ad-hoc networks, where eavesdroppers might monitor all the transmitting nodes of a legitimate link. We substantially characterise the multi-hop wiretap model with receiver diversity techniques adopted by eavesdroppers. The security performance of the conceived scheme is evaluated in the scenarios where eavesdroppers attempt to detect their received signals using maximal-ratio combining or maximum-gain selection. The achievable data rates of both legitimate and wiretapper links are formulated with the objective of quantifying the secrecy rates for both Gaussian-distributed and finite-alphabet inputs. Illustrative numerical results are provided for the metrics of ergodic secrecy rate and secrecy outage probability, which substantiate the compelling benefits of the physical-layer secret key generation via CQI-mapped SM.

In the context of orthogonal frequency-division multiplexing with index modulation (OFDM-IM), this paper first presents an improved index modulation (IIM) technique to address the well-known low spectral efficiency problem of IM techniques in general and OFDM-IM in particular. OFDM-IIM is realized by deriving the minimum required number of subcarriers per group, and the minimum number of active subcarriers in each group, of the conventional OFDM-IM technique. It is proven that OFDM-IIM can deliver higher spectral and energy efficiencies than classical OFDM and OFDM-IM. The gains come at the expense of increased detection complexity. Therefore, a proposal of OFDM with generalized IM (OFDM-GIM) technique is presented, where a variable number of subcarriers per group are allowed to be activated. Two variants of OFDM-GIM are designed based on the activation pattern of the subcarriers: the first achieves superior spectral efficiency with reduced detection complexity as compared to OFDM-IIM, and the second is tailored for low data rate communications with higher energy efficiency requirements. Besides optimal maximum likelihood detection, a less-complex sub-optimal detector is proposed. A closed-form expression for the bit error rate (BER) of OFDM-IIM and the two variants of OFDM-GIM is derived, considering transmissions over Nakagami fading channels and multiple-antenna reception. Finally, OFDM-IIM and OFDM-GIM are compared with state-of-the-art techniques to validate their superiority in terms of BER, achievable rate, and energy efficiency.

This paper investigates the performance of dual-hop amplify-and-forward (AF) mixed radio frequency (RF)/free-space optical (FSO) transmissions with partial relay selection (PRS) based on outdated channel state information (CSI) estimates. Turbulence-induced fading, path loss, and pointing errors, are all considered in the FSO channel modeling. Both the fading and the path loss are described through general models which encompass the commonly used models. Novel expressions for the cumulative distribution function, probability density function, moment generating function, and moments of the end-to-end signal-to-noise ratio (SNR) are obtained in closed-form. Thereafter, novel closed-form expressions for key performance metrics, namely, outage probability, average bit error probability and spectral efficiency, are derived. The analysis is unified, applying to both types of detection techniques, intensity modulation/direct direction and heterodyne detection. Asymptotic analysis is further conducted, which open the door to additional important results. Monte Carlo simulation results confirm the effectiveness of the proposed analysis, and attest that in AF RF/FSO systems with PRS based on outdated CSI estimates, where implementing higher number of relays is highly difficult and costly, the low SNR regime may be prohibitive because it hinders the diversity advantages promised by the use of more relays in PRS systems.

Consider a multi-user wireless information transfer system where a multiple-antenna access point (AP) aims to sell its downlink radio access to the end users in an auction premise so that the social welfare is maximized. To this end, the AP holds auctions in which each user bids for its desired minimum signal-to-interference-plus-noise power ratio. Based on the user's channel state information, bids, and service demands, the AP seeks the optimal set of users for which information streams are to be allocated through beamforming. We formulate the optimization problem of finding the optimal allocation rule, apply brute-force search approach to find all the feasible allocation sets using uplink-downlink duality-based algorithm (UDD), and obtain the optimal allocation rule. To circumvent the time-greediness of conventional optimization methods such as semi-definite relaxation or UDD, we propose a deep neural network architecture, and use it to solve the optimization problem with a good accuracy. The training data is collected by solving offline plenty of network realizations via the application of the UDD algorithm.

This paper investigates the energy efficiency optimization in a wireless communication network in which an unmanned aerial vehicle (UAV) deploys information and power transfer towards co-located information and energy receivers to enable downlink and uplink data transmission through non-orthogonal multiple access (NOMA). Using a constructed closed-form expression for the energy efficiency, a resource allocation mechanism aiming at maximizing the energy efficiency of the system is developed. To this end, an algorithm which jointly takes into account the downlink and uplink stages is proposed, using Lagrangian optimization and gradient decent methods. Numerical results and comparisons are provided. In particular, the results show an enhancement in energy efficiency for the NOMA scheme compared with OMA, and that less wireless power transfer time will be needed from the UAV to simultaneously charge energy receivers when using NOMA.

In this paper, a high-efficiency CMOS rectifier circuit merged with a matched N-path filter is presented. The rectifier has a cross-coupled bridge configuration and is integrated by a tunable bandpass filter in 65 nm CMOS technology. A differential drive active gate bias mechanism at the same time enables both low ON-resistance and small reverse leakage of diode-connected CMOS transistors, in order to have a significant power conversion efficiency (PCE), specifically for low input-power levels. According to simulation results, at 1 GHz input RF signal, the designed rectifier has the PCE of 70% at -12.5 dBm input power for 10 kΩ load and 88% at -15 dBm input power for 100 kΩ load. Also, by using a larger load resistor, peak PCE can be obtained at smaller input power and better sensitivity. The designed CMOS circuit is a promising candidate for future wirelessly powering and energy harvesting applications.

In non-orthogonal multiple access (NOMA) systems, serving multiple users in shared resource blocks can allow untrusted users to overhear the messages of other users. In this context, we study a network consisting of a base station (BS), a near user and a far user, where the latter attempts to overhear the message of the former. The near user is a full-duplex (FD) node that can also act as a relay. Two operating scenarios are considered: 1) friendly jammer (FJ), where the FD node broadcasts noise for degrading the channel between the BS and the far user, while receiving data from the BS; and 2) friendly jammer relay (FJR), where, in addition to degrading the channel between the BS and the far user, the FD node relays the message of the far user. We investigate the secrecy performance of the network by characterizing the secrecy outage probability (SOP) in both scenarios. We obtain the exact SOP of the FJ case, and an approximation for the SOP of the FJR scenario, both expressed in closed-form. Numerical results confirm the accuracy of the analytical results. For a given BS power budget and power allocation to the users, it is demonstrated that the jamming and relaying powers are prominent factors to make the NOMA-FJR scheme superior to NOMA-FJ, as well as to conventional and cooperative NOMA schemes.

Finite blocklength (short packet) communications with non-orthogonal multiple access (NOMA) is regarded as an enabler for ultra-reliable and low-latency communications (URLLC). In this paper, we investigate the link-layer rate, i.e., the effective capacity, of a two-user NOMA in finite blocklength regime. The delay performance of the NOMA users is analyzed by taking into consideration the queueing delay violation probability and the transmission error probability. We further provide closed-form expressions for the individual effective capacity of the NOMA users in Rayleigh fading environment. Through simulations, we investigate the impact of the transmit signal-to-noise ratio and the delay exponent on the achievable effective capacity and the queueing delay violation probability of the NOMA weak and strong users. In particular, results show that when using short-packet communications, the queueing delay violation probability cannot be improved below a threshold.

In millimeter-wave (mmWave) massive MIMO systems, to decrease hardware cost and energy consumption, hybrid analog and digital precoding is preferred to pure digital precoding. In this paper, a hybrid precoding method for sub-connected mmWave MIMO systems is developed. To start with, we propose to formulate the hybrid precoding matrix as a Kronecker product of an analog precoding matrix and a digital precoding vector, by enforcing phase shifters connecting to each radio-frequency chain to share the same set of coefficients. Then, the optimal design of the digital and analog precoding matrices is formulated as the nearest Kronecker product (NKP) problem, which is analytically tractable. Finally, a low-complexity algorithm is developed to implement the proposed hybrid precoding method. Simulation results corroborate that the NKP-based hybrid precoding is near-optimal and achieves higher data rates than the successive interference cancellation method. Moreover, the energy efficiency of the proposed design is much higher than the fully-connected architecture.

Coordinated multi-point (CoMP) transmission is a cooperating technique among base stations (BSs) in a cellular network, with outstanding capability at inter-cell interference (ICI) mitigation. ICI is a dominant source of error, and has detrimental effects on system performance if not managed properly. Based on the theory of Poisson-Delaunay triangulation, this paper proposes a novel analytical model for CoMP operation in cellular networks. Unlike the conventional CoMP operation that is dynamic and needs on-line updating occasionally, the proposed approach enables the cooperating BS set of a user equipment (UE) to be fixed and off-line determined according to the location information of BSs. By using the theory of stochastic geometry, the coverage probability and spectral efficiency of a typical UE are analyzed, and simulation results corroborate the effectiveness of the proposed CoMP scheme and the developed performance analysis.

The performance of two wireless power transfer scheduling schemes, time sharing (TS) and spatial multiplexing (SM), in terms of provisioning fairness among energy receivers (ERs) is studied and compared while taking into account the nonlinearity of the energy harvesters circuits. In the network, the multiple-antenna energy transmitter (ET) attempts to maximize the harvested energy by the ER which has accumulated the minimum amount of energy among all single-antenna ERs during the wireless power transfer block T-hence the max-min fairness criterion. Two network scenarios are studied: homogeneous, where the channels power coefficients are assumed to be the same for all the well-apart ERs, and heterogeneous, where the said coefficients can take arbitrary values. It is proven analytically that in the homogeneous scenario, the optimal scheduling policy is to allocate each ER the full transmit power P with uniform distribution of charging times among ERs, rather than to allocate the full power transfer block T with uniform distribution of the power among ERs. Generalization of the network to the heterogeneous scenario aims to find the optimal beamforming vector for the SM scheme and the optimal time sharing vector for the TS scheme. It is shown through extensive Monte Carlo simulations that again TS outperforms SM in terms of max-min fairness as a result of taking into account the inherent non-linear characteristics of the harvesting devices.

This paper proposes a new power allocation scheme to jointly optimize energy efficiency (EE) and spectral efficiency (SE) of a point-to-point communication system in which the transmitter is equipped with fixed as well as energy harvesting batteries. Time switching protocol is used such that in each time frame the node either harvests energy or transmits information. Firstly, a multi-objective optimization problem which jointly optimizes EE and SE is formulated. An importance weight parameter is introduced to control the priority level between EE and SE. Secondly, the multi-objective problem is transformed into a single-objective optimization problem by using importance weight, and then solved through fractional programming. Using the Karush-Kuhn-Tucker conditions, the optimum power allocation scheme without input power constraint is developed. The ensuing solution is then generalized for system operation with average input power constraint. Closed-form expressions are derived and tested through simulations. Numerical results results are provided, and show the impact of the harvested power in improving the overall rate of the system. Also investigation is done to analyze the effect of system parameters on the achievable trade-off performance of the energy-harvesting based system.

This paper investigates the energy efficiency optimization in a wireless communication network where devices are wirelessly powered via unmanned aerial vehicle (UAV) to enable uplink data transmission. First, the path loss of the air-to-ground channels is minimized by optimizing the position of the UAV depending on the ground nodes' service demands. Then, using the optimized positioning and a closed-form expression for the energy efficiency, a resource allocation aiming at maximizing the energy efficiency is developed. To this end, two algorithms are proposed, using Lagrangian optimization and gradient decent methods. Numerical results and comparisons are provided. In particular, the results show an enhancement in energy efficiency and reduced wireless power charging time when the ground nodes' demands are taken into consideration.

In this paper, we consider minimum bit-error rate (BER) transceiver design for multiple-input multiple-output (MIMO) decode-and-forward (DF) relay systems employing single-carrier transmission with frequency-domain equalization (SC-FDE). The problem is formulated as the minimization of the end to-end (e2e) BER subject to a joint source and relay transmit power constraint. Since the e2e-BER is highly non-convex in terms of the complex matrix optimization variables, solving the optimization problem directly is challenging. By resorting to an upper bound on the e2e-BER and by assuming an optimal sum power budget splitting for the source and relay, we show that the problem can be reduced to the optimization of two equivalent point-to-point MIMO systems. This enables us to derive the optimal eigen-structure of the precoders and the matrix optimization problem simplifies into a convex power allocation problem involving real scalar variables. Primal decomposition is further applied to solve the resulting convex problem in a layered manner, where closed-form solutions are obtained for the inner subproblems. Simulation results are provided to confirm the BER performance of the proposed transceiver design for SC-FDE based MIMO DF relay systems.

Two-way massive MIMO amplify-and-forward relaying systems with non-ideal transceivers are investigated in this paper. To be general, multiple-antenna nodes and antenna correlation at both the user equipments (UEs) and the relay are considered, which differentiates the analysis from the prior ones. The achievable rate is analyzed and derived deterministically in closed-form. Joint scaling of the transmission powers and hardware impairments is then particularly investigated. Feasible scaling speeds for the transmission powers and hardware impairments are discovered when the number of relay antennas grows large. It is shown that down scaling of the transmission powers at the UEs and the relay and up scaling of the hardware impairment at the relay with the number of relay antennas are tolerable without reducing the expected rate. However, UE hardware impairment is a key limiting factor to the achievable rate and is not allowed to scale up with the number of relay antennas in order to achieve a non-vanishing rate. Moreover, ceiling effect on the achievable rate is still observable and the ceiling rate varies among different scaling cases. More interestingly, scalings of the UEs transmission power and the relay hardware impairment are found to be offsettable, which means that the relay hardware cost and the UE transmission power are tradable. It is found that the best tradeoff is achieved in the medium scalings of both the relay hardware impairment and UE transmission power. Numerical results are provided to verify the analysis and the tradability between the relay hardware cost and the UE transmission power. The analytical results thus provide solid foundation for flexible system designs under various cost and energy constraints.

This paper studies the performance of wireless power transfer (WPT) in millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems operating in rainy or non-rainy conditions. Accounting for rainfall effects, path loss, and small-scale fading, a comprehensive channel model suitable for modeling the energy propagation in mmWave massive MIMO systems is first developed. Based on this model, a framework for the channel estimation necessary at the hybrid data-and-energy access point (HAP) is provided, and various analytical results on the estimated channel matrix are obtained. Then, using the law of energy conservation, the downlink energy transferred by the HAP and harvested by the user equipments (UEs) is analyzed, and investigated in several important scenarios. The results reveal that the asymptotic harvested energy increases linearly with the number of HAP antennas and the number of UEs, whereas it decreases exponentially with the rain parameters which monotonically increase with the operating frequency. It is also demonstrated that severe rain attenuation can even make the WPT impossible. Afterwards, the scenario where UEs are randomly distributed is investigated, and important insights are gained. In particular, for a WPT system with coverage radius Rnand exclusion radius Re, the average asymptotic harvested energy significantly increases with decreasing Reand Rn, which confirms that small-cells configurations will be viable solutions for enhancing WPT performances in mmWave massive MIMO networks.

Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) promises superior bit error rate (BER) performance and transmit power savings compared to classical OFDM. The concept consists in dividing the available subcarriers into groups and activating a subset of subcarriers in each group for transmitting M-QAM/PSK symbols. The remaining subcarriers are kept idle. The transmitted symbols and the indexes of the active subcarriers both carry useful information. In the recent literature, OFDM-IM is conceived by activating half of the subcarriers in each group for transmission of M-QAM/PSK symbols, which results in low spectral efficiency (SE). This paper addresses the low SE problem in two ways. First, an inequality rule is developed by comparing the SE of classical OFDM and OFDM-IM. The rule is used to derive three limits on the group size and it is shown that OFDM-IM can overcome the SE limitation of classical OFDM for a group size of 2M or greater. Secondly, a new OFDM-IM scheme with a variable number of active subcarriers per group, termed OFDM-IM-VAS, is proposed. The optimal group size for a given M is obtained, and it is shown that OFDM-IM-VAS can achieve higher SE than classical OFDM with low BER and high power savings. The BER, bit level throughput, transmit power saving, and complexity of OFDM-IM and OFDM-IM-VAS are analyzed considering transmissions over Rayleigh fading channels and compared with classical OFDM. A closed-form BER expression is derived to support the simulation results.

Several critical operations such as, data collection, routing, service discovery, etc., employ various types of information dissemination in order to be carried out. To avoid costly flooding-based solutions reaching out to all nodes, it is frequently sufficient that only a proper subset of the nodes (or backbone network) be involved, i.e., the one ensuring that every other node will be at most d hops away from a node belonging to the said subset of nodes. Finding this subset is equivalent to the construction of a d-hop Connected Dominating Set (d-CDS). Given the high complexity (non-polynomial) and the requirement of global information for constructing a Minimum d-CDS (d-MCDS), in this paper a distributed algorithm that relies on local information (i.e., d hops away) to construct an approximation of the d-MCDS is developed. The proposed algorithm is studied and compared against a centralized one that is an approximate solution for the minimum d-MCDS problem, and a recently proposed distributed one. It is shown that the size of the constructed d-CDS under the proposed algorithm is (i) close and sometimes smaller than that under the recently proposed one; and (ii) close to the centralized one. In addition, the number of transmitted messages is significantly reduced under the proposed algorithm, which is important for preserving energy resources in wireless sensor networks.

This paper analyzes the performance of dual-hop amplify-and-forward hybrid radio-frequency/free-space optical (RF/FSO) transmissions with partial relay selection based on outdated channel state information estimates. The FSO channel modeling accounts for turbulence-induced fading, path loss, and pointing errors as well. Essential statistics of the system end-to-end signal-to-noise ratio (SNR) are derived in closed-form, yielding novel expressions for its cumulative distribution function and probability density function. Afterwards, novel closed-form expression for the system outage probability is obtained. High SNR approximation is applied to the obtained expression, yielding simple and easily tractable results, that, additionally, offer useful insights into the system performance. The analysis is unified, applying to both types of detection techniques, i.e., intensity modulation/direct direction and heterodyne detection. Monte Carlo simulation results corroborate the proposed analysis, and provide additional insights on the system performance.

Information dissemination plays a crucial role in modern network environments being an integral part of various vital processes (e.g., service discovery, data collection, routing). Probabilistic flooding has been proposed as a suitable alternative to blind flooding in order to reduce unnecessary transmissions and save valuable network resources. Under probabilistic flooding, an information message, initially located at some network node (i.e., the initiator node), is transmitted to neighbor nodes according to a forwarding probability attempting to reach all network nodes. This paper employs elements from algebraic graph theory to model probabilistic flooding behavior and derive analytical results regarding coverage (i.e., the number of nodes that have received the information message) and a lower bound of the forwarding probability allowing for global network outreach. It is also shown here, that for any value of the forwarding probability larger than this lower bound, (i) coverage under probabilistic flooding, is proportional to the initiator's node eigenvector centrality; and (ii) the probability for a node to receive the information message is proportional to the particular node's eigenvector centrality. Simulations performed for various topologies demonstrate the effectiveness of the proposed analytical model and support the analytical results.

In order to tackle the energy hole problem in wireless sensor networks, various recharging policies have been proposed attempting to keep the average energy level high and the recharging distance (i.e., the distance covered by a mobile recharger) low. As shown in the literature, the recharging distance is minimized when the basis of the mobile recharger is located at the solution of a median problem that takes into account both distance and traffic demands. In this paper, a novel on-demand recharging policy is proposed based on local information, where the mobile recharger moves-upon request-to a target node of reduced energy level and replenishes its battery. Under the proposed policy, the mobile recharger moves in a hop-by-hop manner to the neighbor nodes of the lowest energy level, starting from the target node. The effectiveness of this policy is investigated here using simulation results and compared against an existing well-known on-demand recharging policy that exploits global knowledge (i.e., knowledge of both the energy level of all nodes and the network topology). It is shown that the proposed policy, even though based on local information, maintain the average energy level and termination time higher than that under the existing one that exploits global knowledge. Furthermore, it is observed that the network's lifetime is maximized when the basis of the mobile recharger is located at the solution of the mentioned median problem for all studied policies.

We analyze the outage and throughput performance of full-duplex relay selection (FDRS) in underlay cognitive networks. Contrary to half-duplex relaying, full-duplex relaying (FDR) enables simultaneous listening/forwarding at the secondary relay(s), thereby allowing for higher spectral efficiency. However, due to simultaneous source/relay transmissions in FDR, the superimposed signal at the primary receiver should now satisfy the existing interference constraint, which can considerably limit the secondary network throughput. In this regard, FDRS can offer an adequate solution to boost the secondary throughput while satisfying the imposed interference limit. We first analyze the performance of opportunistic FDRS with residual self-interference (RSI) by deriving the exact cumulative distribution function of its end-to-end signal-to-interference-plus-noise ratio under Nakagami-m fading. We also evaluate the offered diversity gain of relay selection for different full-duplex cooperation schemes in the presence/absence of a direct source-destination link under Rayleigh fading. When the RSI link gain model is sublinear in the relay power, which agrees with recent research findings, we show that remarkable diversity can be recovered even in the presence of an interfering direct link. Second, we evaluate the end-to-end performance of FDRS with interference constraints due to the presence of a primary receiver. Finally, the presented theoretical findings are verified by numerical simulations.

This paper focuses on the performance evaluation of an energy harvesting (EH) equipped dual-hop relaying system for which the end-to-end signal-to-noise ratio (SNR) and the overall system throughput are analyzed. The transmitter and relay nodes are equipped with both fixed and EH batteries. The source for harvesting at the transmitter is the solar energy, and at the relay node, the interference energy in the radio frequency is the harvesting source. Time switching scheme is used at the relay to switch between EH and decoding information. Harvest-use approach is implemented, and we investigate the effects of the harvesting energy in enhancing the performance of the relaying system by deriving estimated closed-form expressions for the cumulative distribution function of each link's individual SNR and of the end-to-end SNR. The analytical expression for the ergodic capacity is also derived. These expressions are validated through Monte-Carlo simulations. It is also shown that with the additional EH at the transmitter (source and relay), a significant improvement in the system throughput can be achieved when fixed batteries are running on low powers.

Using a novel embedded Markov chain, we model and analyze a cognitive radio performing full-duplex spectrum sensing which is being carried out imperfectly-i.e., with errors-and asynchronously with primary traffic, from the perspective of energy efficiency. The effect of sensing frequency, which is varied by inserting sleeping periods between sensing processes is investigated, with focus on: 1) the energy efficiency of the device measured in terms of the number of successful transmissions under a limited battery budget; 2) the average throughput; and 3) the collision with the primary's traffic. We show analytically that, given false-alarm and mis-detection probabilities, the device's operation in lower-than-maximum sensing frequency may be more energy-efficient than that in maximum-frequency sensing case, while the radio is neither suffering throughput degradation nor disturbing the primary traffic seriously. We validate the deployment of such full-duplex cognitive radio (FDCR) along with the proposed sensing scheme for low-power short-range applications like wireless machine-to-machine communications and sensor networks, where the share of sensing power is comparable to that of transmission power. The merits of the proposed FDCR scheme are demonstrated through comparisons with a half-duplex cognitive radio scheme under different operating conditions and full-duplex self-interference cancellation factors.

For Poisson-Delaunay triangulations in d-dimensional Euclidean space ℝd, a structured and computationally efficient form of the probability density function (PDF) of the volume of a typical cell is analytically derived in this paper. In particular, the ensuing PDF and the corresponding cumulative density function are exact and unified, applicable to spaces of arbitrary dimension (d ≥ 1). Then, the special cases and shape characteristics of the resulting PDF are thoroughly examined. Finally, various applications of the obtained distribution functions are outlined and, in particular, a novel coordinated multi-point transmission scheme based on Poisson-Delaunay triangulation is developed and the pertinent void cell effect is precisely evaluated by using the obtained distribution functions.

This paper analyzes the performance of a relay- aided millimeter wave (mmWave) massive multiple- input multiple-output (MIMO) system, where the source node needs to harvest energy from the hybrid relay before transmitting its data. A comprehensive MIMO channel model is first developed, where rainfall effects, path loss and small-scale fading are all considered; which properly models the signal propagation on all links of the system. The expression of the asymptotic harvested energy is derived, and then used to assess the asymptotic spectral efficiency and system throughput for various important scenarios. Further, the optimal value of the harvesting time that maximizes throughput is investigated. In particular, it is shown that in operating conditions with light rain, the asymptotic spectral efficiency and throughput increase logarithmically with the number of relay antennas, and that both metrics decrease exponentially with the rain parameters.

In this paper, the performance of wireless energy transfer (WET) in millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems is analyzed. By accounting for rainfall effects, path loss and small-scale fading, a comprehensive MIMO channel model is first developed, which is suitable for modeling the energy propagation in WET mmWave massive MIMO systems operating in rainy or clear conditions. Based on this model, a framework for the channel estimation at the hybrid data-and-energy access point (HAP) is presented. Starting from the law of energy conservation, the downlink energy transferred by the HAP and harvested by the user equipments (UEs) is assessed, for several important scenarios. In particular, the results show that the asymptotic harvested energy increases linearly with the number of HAP antennas and the number of UEs, but decreases exponentially with the raining parameters which monotonically increase with the operating frequency.

The performance of reactive decode-and-forward multi-branch relaying in the presence of co-channel interference and Nakagami fading is analytically investigated. Intermediate relays that successfully decode the received signals from the source node form a decoding set, from which the relay whose corresponding branch results in the highest signal-to-interference-plus-noise ratio (SINR) at the destination node is chosen to serve as the best relay. The selected relay re-encodes the source message and forwards it to the destination while the remaining relays keep idle. For this relaying scheme, we first obtain the exact end-to-end SINR expression by considering the general case of Nakagami-m fading channels. Then, the exact unconditional probability density function (PDF) of the end-to-end SINR is explicitly derived. With the resulting PDF, exact closed-form expressions for the outage and error probabilities are obtained. Moreover, to gain insights into the system performance, asymptotic analysis of the error probability is performed. Finally, Monte-Carlo simulation results are presented to corroborate the analysis, and comparative numerical results are discussed.

We analyze a wireless power charging network to find the best users' admission policy and power allocation by the wireless power charger (WPC). The objective of the WPC is to maximize its utility while keeping the users' satisfaction up to their required level. This optimum strategy depends on the users' bids and on the WPC's knowledge about the users' requests and the network parameters. Here, the network is modeled by an M/M/N/N queue. The competition of users is modeled using game theory, and the game model is embedded in a continuous-time Markov process model. If a user is admitted by the WPC, the latter broadcasts its new budgeted allocation, after which the users compete for the power in a non-cooperative game by broadcasting their bids. Knowing other bids, users renew and then broadcast their own bids until convergence to the Nash Equilibrium strategy. When a new user places an admission request, the WPC - desiring to maximize its profit with regard to the current users' utilities - decides to whether admit or reject the request by solving a constrained non-linear optimization problem. The performance of the proposed admission and power charging policy is analyzed.

This paper investigates the performance and optimization of a relaying system operating in practical environments with co-channel interferers. The relaying system implements signal space diversity technique, which involves constellation rotation and interleaving of the signal points at the source node. Detection at the destination node is dependant to correct or incorrect decoding at the relay. The performance of the system is evaluated in terms of outage probability and asymptotic error probability, assuming the channels, for both the desired and the interfering signals, to experience Rayleigh fading. Furthermore, a two-fold system optimization is presented, whereby we obtain the optimum rotation angle and the optimum source and relay energies to minimize the error probability under constraint on the energy budget. Applying the two-phase optimization, the system performance increases considerably. Moreover, an optimization procedure aiming at minimizing the total energy expenditure at the transmit nodes subject to error probability constraint is presented. Results pertaining to the interference-free system operation are also provided.

In integrated mobile satellite systems (MSSs) with ancillary terrestrial component (ATC), seamless handoff techniques will be fundamental for allowing users to switch between the space segment and the terrestrial component. On the other hand, introducing multiple-input multiple-output (MIMO) antenna technology in next-generation MSS-ATC systems promises the well-known advantages related to the MIMO implementation. For performing handoff analysis, the single-input single-output (SISO) channel model equivalent to the MIMO model needs to be developed, which is challenging in MSS-ATC networks because of the high complexity of the satellite channel, and the vast difference in the nature of the MSS and the ATC links. This challenge is tackled in this paper, where an optimal user-driven handoff algorithm for MSS-ATC systems is presented, with both types of links implementing MIMO. Furthermore, for a better signal prediction, Kalman filtering is proposed, which significantly increases the performance. Notably, the application of multi-antenna technology in MSS-ATC systems reveals significant gains in terms of handoff performance.

In this paper, we propose a robust distributed relay beamformer design for cognitive radio network operating under uncertainties in the available channel state information. The cognitive network consists of a pair of transceivers and a set of non-regenerative two-way relays that assist the communication between the transceiver pair. The secondary nodes share the spectrum with a licensed primary user node while ensuring that the interference to the primary receiver is maintained below a certain threshold. The proposed robust design maximizes the worst-case signal-to-interference-plus-noise ratio at the secondary transceivers while satisfying constraints on the interference to the primary user and on the total relay transmit power. Though the robust design problem is not a convex problem in its original form, we show that it can be reformulated as a convex optimization problem, which can be solved efficiently. Numerical results are provided and illustrate the merits of the proposed design for various operating conditions and parameters.

We consider a network comprised of multiple primary users (PUs) and multiple secondary users (SUs), where the SUs seek access to a set of orthogonal channels each occupied by one PU. Only one SU is allowed to coexist with a given PU. We propose a distributed matching algorithm to pair the network users, where a Stackelberg game model is assumed for the interaction between the paired PU and SU. The selected secondary is given access in exchange for monetary compensation to the primary. The PU optimizes the interference price it charges to a given SU and the power allocation to maintain communication. The SU optimizes its power demand so as to maximize its utility. Our algorithm provides a unique stable matching. Numerical results indicate the advantage of the proposed algorithm over other reference schemes.

This paper analyzes the spectral efficiency of massive multiple-input multiple-output (MIMO) systems in both centralized and distributed configurations, referred to as C-MIMO and D-MIMO, respectively. By accounting for real environmental parameters and antenna characteristics, namely, path loss, shadowing effect, multipath fading, and antenna correlation, a novel comprehensive channel model is first proposed in closed-form, which is applicable to both types of MIMO schemes. Then, based on the proposed model, the asymptotic behavior of the spectral efficiency of the MIMO channel, under both the centralized and distributed configurations is analyzed and compared in exact forms, by exploiting the theory of very long random vectors. Afterwards, a case study is performed by applying the obtained results into MIMO networks with circular coverage. In such a case, it is attested that for the D-MIMO of cell radius rcand circular antenna array of radius ra,the optimal value of rathat maximizes the average spectral efficiency is accurately established by raopt= rc/1.31. Monte Carlo simulation results corroborate the developed spectral-efficiency analysis.

It is now indisputable that the performance of cognitive radio networks is closely subject to the accuracy and reliability of the inherent spectrum sensing process. In this regard, the development of an efficient sensing mechanism is an imperative task, the performance of which not only relies on the choice of the sensing function, but it substantially depends on the efficiency of the sensing data fusion, i.e. the combining of outputs from individual sensing functions. Due to its importance as well as the lack of efficient algorithms, the spectrum sensing data fusion was left as open issue in the cognitive radio IEEE 802.22 standard for wireless regional area networks (WRANs). In this research, we address this open issue by proposing a novel distributed sensing algorithm for WRANs, named single-channel learning-based distributed sensing (SC-LDS). This algorithm is self-trained, stable, and compensates for fault reports using a reward-penalty approach. Moreover, it exhibits more uniform performance in all traffic regimes, is fair (reduces the false-alarm/mis-detection gap), adjustable to different application needs, and bandwidth efficient. Simulation results unanimously corroborate that the proposed SC-LDS algorithm outperforms other techniques such as the AND, OR and VOTING rules.

In coverage areas overlapped by the mobile satellite system (MSS) and the ancillary terrestrial component (ATC) of integrated MSS/ATC networks, users can suffer severe co-channel interference (CCI) due to the coexistence of MSS and ATC signals. The vast difference between the characteristics of the desired channels for a user, depending on whether it is connected to the satellite or to the terrestrial station, makes the corresponding performance evaluation very challenging. This paper tackles this issue by using the powerful generalized-K distribution, and offers a unified closed-form analysis for the system performance of both types of connections. In particular, it is revealed that the user's diversity gain depends only upon the minimum between the fading parameter and the shadowing parameter of the desired channel, regardless of the CCI. Also, the coding gain increases with the diversity gain. The effectiveness of the analysis is corroborated by Monte Carlo simulations.

To account for antenna physical parameters and real propagation conditions encountered by large-scale multipleinput multiple-output (MIMO) antenna systems in practical deployment, this paper develops a comprehensive MIMO channel model in an analytical way. In particular, major parameters including path loss, shadowing effect, multi-path fading, channel polarization, channel correlations, antenna cross-polarization discrimination and environmental cross-polar coupling, are integrated in a mathematically tractable way. Then, an upper bound on the ergodic capacity of the comprehensive MIMO channel is derived asymptotically, i.e. as the number of transmit and/or receive antennas of the MIMO system approaches infinity. Finally, Monte Carlo simulation results corroborate the effectiveness of the proposed model and the accuracy of the resulting capacity bound. Thanks to its high generality and compactness, the proposed model can serve as the kernel for the design and performance evaluation of large-scale MIMO in real propagation environments.

In this paper, we investigate half-duplex two-way dual-hop channel state information (CSI)-assisted amplify-andforward (AF) relaying in the presence of high-power amplifier (HPA) nonlinearity at relays. The expression for the end-toend signal-to-noise ratio (SNR) is derived as per the modified system model by taking into account the interference caused by relaying scheme and HPA nonlinearity. The system performance of the considered relaying network is evaluated in terms of average symbol error probability (SEP) in Nakagami-m fading channels, by making use of the moment-generating function (MGF) approach. Numerical results are provided and show the effects of several parameters, such as quadrature amplitude modulation (QAM) order, number of relays, HPA parameters, and Nakagami parameter, on performance.

In this paper, a new detector is proposed for an amplify-and-forward (AF) relaying system. The detector is designed to minimize the symbol-error-rate (SER) of the system. The SER surface is non-linear and may have multiple minimas, therefore, designing an SER detector for cooperative communications becomes an optimization problem. Evolutionary based algorithms have the capability to find the global minima, therefore, evolutionary algorithms such as particle swarm optimization (PSO) and differential evolution (DE) are exploited to solve this optimization problem. The performance of proposed detectors is compared with the conventional detectors such as maximum likelihood (ML) and minimum mean square error (MMSE) detector. In the simulation results, it can be observed that the SER performance of the proposed detectors is less than 2 dB away from the ML detector. Significant improvement in SER performance is also observed when comparing with the MMSE detector. The computational complexity of the proposed detector is much less than the ML and MMSE algorithms. Moreover, in contrast to ML and MMSE detectors, the computational complexity of the proposed detectors increases linearly with respect to the number of relays.

Radio-frequency energy harvesting constitutes an effective way to prolong the lifetime of wireless networks, wean communication devices off the battery and power line, benefit the energy saving and lower the carbon footprint of wireless communications. In this paper, an interference aided energy harvesting scheme is proposed for cooperative relaying systems, where energy-constrained relays harvest energy from the received information signal and co-channel interference signals, and then use that harvested energy to forward the correctly decoded signal to the destination. The time-switching scheme (TS), in which the receiver switches between decoding information and harvesting energy, as well as the power-splitting scheme (PS), where a portion of the received power is used for energy harvesting and the remaining power is utilized for information processing, are adopted separately. Applying the proposed energy harvesting approach to a decode-and-forward relaying system with the three-terminal model, the analytical expressions of the ergodic capacity and the outage capacity are derived, and the corresponding achievable throughputs are determined. Comparative results are provided and show that PS is superior to TS at high signal-to-noise ratio (SNR) in terms of throughput, while at low SNR, TS outperforms PS. Furthermore, considering different interference power distributions with equal aggregate interference power at the relay, the corresponding system capacity relationship, i.e., the ordering of capacities, is obtained.

We propose a three-message superposition coding scheme in a cognitive radio relay network exploiting active cooperation between primary and secondary users. The primary user is motivated to cooperate by substantial benefits it can reap from this access scenario. Specifically, the time resource is split into three transmission phases. The first two phases are dedicated to primary communication, while the third phase is for the secondary's transmission. We formulate two throughput maximization problems for the secondary network subject to primary user rate constraints and per-node power constraints with respect to the time durations of primary transmission and the transmit power of the primary and the secondary users. The first throughput maximization problem assumes a partial power constraint such that the secondary power dedicated to primary cooperation, i.e. for the first two communication phases, is fixed apriori. In the second throughput maximization problem, a total power constraint is assumed over the three phases of communication. The two problems are difficult to solve analytically when the relaying channel gains are strictly greater than each other and strictly greater than the direct link channel gain. However, mathematically tractable lowerbound and upperbound solutions can be attained for the two problems. For both problems, by only using the lowerbound solution, we demonstrate significant throughput gains for both the primary and the secondary users through this active cooperation scheme. We find that most of the throughput gains come from minimizing the second phase transmission time since the secondary nodes assist the primary communication during this phase. Finally, we demonstrate the superiority of our proposed scheme compared to a number of reference schemes that include best relay selection, dual-hop routing, and an interference channel model.

In this work, efficient protocols are studied for full-duplex relaying (FDR) with loopback interference over Nakagami-m block fading channels. Recently, a selective decode-and-forward (DF) protocol was proposed for FDR, and was shown to outperform existing protocols in terms of outage over Rayleigh-fading channels. In this work, we propose an incremental selective DF protocol that offers additional power savings, yet yields the same outage performance. We evaluate their outage performance over independent non-identically distributed Nakagami-m fading links, and study their relative performance in terms of the signal-to-noise ratio cumulative distribution function via closed-form expressions. The offered diversity gain is also derived. In addition, we study their performance relative to their half-duplex counterparts, as well as known non-selective FDR protocols. We corroborate our theoretical results with simulation, and confirm that selective cooperation protocols outperform the known non-selective protocols in terms of outage. Finally, we show that depending on the loopback interference level, the proposed protocols can outperform their half-duplex counterparts when high spectral efficiencies are targeted.

The concept of a multi-interface multi-channel cognitive radio is both novel and promising. Indeed, such opportunistic access to the spectrum, over multiple channels in a simultaneous manner, will provide much higher data rates and better seamless communication while decreasing the possibility of interference to licensed users. In this vein, this paper proposes a detailed modeling and analysis of multi-interface multi-channel cognitive radio networks. The analytical efforts lead to the representation of each cognitive node with a 2-D Markov chain. Among the findings of the proposed modeling and analysis is the probability mass function of the secondary user (SU)'s queue length, from which any higher moment can be extracted. In addition, the stability condition, beyond which the network cannot be considered operative any longer, is derived. Statistical tests are conducted to determine the characteristics of the queue length's tail distribution. The accuracy of the analytical results is corroborated with simulation experiments. The proposed modeling is fairly practical as it takes into account issues such as sensing faults and channel imperfections, asynchronism among SUs, distance, and the primary activity level. In addition, the model is useful for the performance analysis and design of other types of cognitive networks as well, including cognitive-radio-based wireless regional area networks.

Abstract Information‐guided channel hopping (IGCH) is a promising technique for high‐data‐rate communications using multiple antennas for information mapping at the transmitter and optional antenna diversity at the receiver. Compared with some popular multi‐antenna techniques, the advantage of this scheme is proven in ideal channel conditions, where the channel is spatially white and the perfect channel state information is assumed available at the receiver. The main objective of this paper is to present an information theoretical study on IGCH in realistic propagation environments with channel degeneracy due to spatial correlation and keyhole phenomena as well as imperfect channel estimation. It is proven that good performance promised by IGCH can be achieved in a variety of non‐ideal channel conditions. Moreover, the analysis in this paper provides a convenient tool for the corresponding system design in practical operating environments. Copyright © 2013 John Wiley & Sons, Ltd.

Far-field wireless power transfer (WPT) is a promising technique to resolve the painstaking power-charging of wireless user terminals (UTs). However, the main issue hindering the implementation of this technique in practice is its limited efficiency. This paper aims to improve WPT efficiency in terms of the time-average direct current (DC) output power at UTs in support of simultaneous data and power transfer. In particular, the power scaling law when opportunistic scheduling strategy is performed among N UTs is analytically attained, by using the extreme value theory. Our results reveal that, the opportunistic technique has a scheduling gain of N times that of the round-robin scheduling policy, thereby improving the power transfer efficiency significantly.

In this paper, a hierarchical cell structure is considered, where public safety broadcasting is fulfilled in a femtocell located within a macrocell. In the femtocell, also known as local cell, an access point broadcasts to each local node (LN) over an orthogonal frequency sub-band independently. Since the local cell shares the spectrum licensed to the macrocell, a given LN is interfered by transmissions of the macrocell user (MU) in the same sub-band. To improve the broadcast performance in the local cell, a novel scheme is proposed to mitigate the interference from the MU to the LN while achieving diversity gain. For the sake of performance evaluation, ergodic capacity of the proposed scheme is quantified and a corresponding closed-form expression is obtained. By comparing with the traditional scheme that suffers from the MU's interference, numerical results substantiate the advantage of the proposed scheme and provide a useful tool for the broadcast design in hierarchical cell systems.

Wireless energy harvesting is an effective way to prolong the lifetime of wireless networks. In this paper, a novel interference aided energy harvesting scheme is proposed for decode-and-forward relaying systems. In this scheme, the energy-constrained relays harvest energy from the received information signal and co-channel interference (CCI) signals and then use that harvested energy to decode the source signal and forward it to the destination node. A time switching scheme, in which the receiver switches over time between decoding information and harvesting energy, is adopted due to its circuit simplicity and availability. Applying the proposed interference aided energy harvesting approach to a decode-and-forward relaying system with the three-terminal model, the analytical expression of the ergodic capacity is derived in order to determine the achievable throughput at the destination node. Furthermore, the optimal value of the energy harvesting ratio, which maximizes the throughput of the system, is investigated. The CCI signals can provide energy for relay recharging and hence effectively reduce the optimal value of the energy harvesting ratio. Furthermore, by lowering the noise variance or applying some interference cancellation schemes at the information decoder, the utilization of the CCI signals can be enhanced to improve the system performance further.

This paper develops a general and unified multi-input multi-output (MIMO) channel model applicable to both mobile satellite systems (MSS) and ancillary terrestrial component (ATC) links of integrated MSS with ATC. Major channel parameters pertaining to the MSS and ATC links, such as large-scale path loss, shadowing effect, small-scale multi-path fading, satellite elevation angle, channel polarization and temporal correlations, antenna cross-polarization discrimination and environment cross-polar coupling, are all taken into account in a compact, flexible and fully parameterized way. Moreover, a step-by-step methodology used for Monte-Carlo simulation of the proposed channel model is explicitly provided. Further, numerical results illustrating the effects of several channel parameters are presented. The proposed model is general and constitutes a fundamental kernel for the design and performance evaluation of MSS-ATC networks, and is also suitable for the modeling of other hybrid networks such as heterogeneous networks.

A cognition scheme, whereby nodes are enabled with the full-duplex technology at the PHY layer in conjunction with packet fragmentation at the MAC layer, is proposed to increase the performance of cognitive radio networks. As full-duplex allows doubling the throughput by equipping secondary users (SUs) with the capability to sense and transmit simultaneously, it also enables them to inflict considerably less interference to primary users (PUs), and to discover spectrum holes for transmission opportunities more efficiently. On the other hand, fragmentation technique at the MAC layer provides better quality-of-service for the SUs by empowering the information forwarding in the unpredictable PUs' channels in a progressive manner. Selecting the effective data transfer, the successful packet transmission time and the energy efficiency as metrics, we assess the performance of this cognition scheme and demonstrate its overall merits in cognitive radio networks, in comparison with conventional schemes that use half-duplex and no packet fragmentation.

This paper investigates the performance of a two-way cognitive relaying network in Rayleigh fading environment. We consider that two secondary users (SUs) are allowed to access a licensed portion of the frequency spectrum and share it with a primary user (PU) provided that their transmission power meet interference constraints dictated by the primary receiver. Considering that the SUs are unable to directly communicate with each other, a set of L terminals intervene to relay the information between the source nodes. For efficiency regarding the utilization of the licensed spectrum, only the “best” relay is selected, by means of opportunistic selection, to process and relay the received signals. We derive closed-form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) of each of the links between the “best” relay and the source nodes, followed by the average bit error rate (ABER), the outage probability and the ergodic capacity. We also provide numerical results to assess the theoretical analysis.

We propose a three-message superposition coding scheme in a cognitive radio relay network exploiting active cooperation between primary and secondary networks. The time resource is split into three transmission phases. The first two phases are dedicated to primary communication, while the third phase is for the secondary's transmission. We formulate a throughput maximization problem for the secondary network subject to primary user rate constraints and per-node power constraints with respect to the time durations of primary transmission and the power allocation at the primary and the secondary users. We provide an analytical solution to our problem and validate it by numerical optimization. We demonstrate significant throughput gains for both the primary and the secondary users through this active cooperation scheme. We find that most of the throughput gains come from minimizing the second phase transmission time. Finally, we demonstrate the superiority of our proposed scheme compared to best relay selection.

Recent advances in wireless communications promised the realisation of a revolutionary technique, called full‐duplex (FD), which allows communication in both directions at the same time and over the same channel. However, the viability of FD in the physical layer requires the support of the MAC layer to fully spread the advantages of this technology to the whole wireless network. In this study, the authors introduce a distributed MAC protocol, termed distributed‐access FD MAC, suitable for multi‐hop communications whereby nodes are FD enabled. Using this protocol, a data packet can be forwarded by a number of nodes along a multi‐hop path with un‐contented access to the channel at each hop except for the head node. After detailing the specifications of this protocol, they establish a finite‐state discrete‐time Markov model to evaluate its performance. Using probabilistic mathematical methods, they derive important quantitative metrics such as path delay and throughput. Numerical results are provided and demonstrate the considerable improvement in network performance that the proposed protocol achieves compared with CSMA/CA half‐duplex access mechanism.

This paper studies the performance of a two‐way relay‐based communication system with opportunistic relay selection in Nakagami‐ m fading environments. The authors consider a two‐way wireless communication system where two nodes, acting as sources and using different modulation schemes for transmission, are unable to exchange data because of deep fading on their direct link and proceed via L relay terminals. They provide closed‐form expression for the probability density function of the link between the ‘selected’ best relay and each source, and use this result to derive a closed‐form expression for the average symbol error probability which, to the best knowledge of the authors, has never been done before. This result is further approximated for the high signal‐to‐noise ratio regions and used to develop closed‐form expressions for the optimised power allocated to each node involved in the communication process. The authors asset their formulae with numerical results and interpretations to complete this work.

In this study, dual‐hop channel state information‐assisted amplify‐and‐forward (AF) cooperative systems in the presence of in‐phase and quadrature‐phase (I/Q) imbalance, which refers to the mismatch between components in the I and Q branches, are investigated. First, the authors analyse the performance of the considered AF cooperative protocol without compensation for the I/Q imbalance as the benchmark. Then, a compensation algorithm for the I/Q imbalance is proposed, which makes use of the received signals at the destination, from the source and the relay nodes, together with their conjugations to detect the transmitted signal. Moreover, the authors study the considered AF cooperative system implemented with the opportunistic relay selection and the proposed compensation mechanism for the I/Q imbalance. The performance of the AF cooperative system under study is evaluated in terms of average symbol error probability, which is derived by considering transmission in a Rayleigh fading environment. Numerical results are provided and show that the proposed compensation algorithm can efficiently mitigate the effect of the I/Q imbalance. On the other hand, it is observed that the AF cooperative system with opportunistic relay selection acquires a performance gain beyond that without relay selection.

In this study, the authors develop a transmission protocol for cognitive radio networks, whereby fountain codes are exploited in the broadcast channels and secondary users help with the broadcast from the base station (BS) to primary users (PUs). With fountain codes, the BS broadcasts to the secondary transmitter (ST) as well as PUs simultaneously, and stops broadcasting once the ST has received sufficient codeword to decode the original information reliably. Then, the ST will resume the broadcasting to PUs until all of them can decode the original information successfully. While broadcasting, the ST transmits information over its own link, that is, to the secondary receiver, based on dirty paper coding technique. As such, the energy expenditure at the BS is reduced and, moreover, secondary links have more opportunities to access the licensed spectrum band. To evaluate the performance of the developed scheme, they analyse its energy expenditure, broadcast time as well as the throughput over secondary links, and achieve the corresponding closed‐form expressions. Compared with the traditional broadcast protocol without the secondary's help, illustrative numerical results substantiate the validity of the author's derivations, which also demonstrate the efficiency of the developed scheme both on the energy savings and on the spectrum utilisation.

In this contribution, we establish a model for multi-channel cognitive radio networks (CRNs) using the theory of priority queues. This model enables us to conduct a performance analysis in the most general form by the derivation of the probability mass function (PMF) of queue length at the secondary users (SUs). In the second part, a reverse problem is considered to answer the important top-down question of whether a service requirement can be satisfied in a multi-channel CRN knowing the network parameters and traffic situation with respect to the SUs and the primary users (PUs). Terming this problem as the network synthesis, a precise conservation law is obtained, which relates the packet waiting times of both types of users, and based on which the achievable region of the network is also determined. Lastly, by the introduction of a mixed strategy, the conditions for the existence of an optimal trade-off between the interference onto the PUs and the quality-of-service of the SUs is shown, and the optimal mixed strategy is obtained when those conditions are satisfied.

The ever growing demand of higher data rates can now be addressed by exploiting cooperative diversity. This form of diversity has become a fundamental technique for achieving spatial diversity by exploiting the presence of idle users in the network. This has led to new challenges in terms of designing new protocols and detectors for cooperative communications. Among various amplify-and-forward (AF) protocols, the half duplex non-orthogonal amplify-and-forward (NAF) protocol is superior to other AF schemes in terms of error performance and capacity. However, this superiority is achieved at the cost of higher receiver complexity. Furthermore, in order to exploit the full diversity of the system an optimal precoder is required. In this paper, an optimal joint linear transceiver is proposed for the NAF protocol. This transceiver operates on the principles of minimum bit error rate (BER), and is referred as joint bit error rate (JBER) detector. The BER performance of JBER detector is superior to all the proposed linear detectors such as channel inversion, the maximal ratio combining, the biased maximum likelihood detectors, and the minimum mean square error. The proposed transceiver also outperforms previous precoders designed for the NAF protocol.

A new cost efficient automated planning and optimization method is proposed for OFDMA future-generation cellular networks targeting throughput maximization. The mathematical formulation is a non-linear multi-objective optimization problem subject to minimum interference, cost and similar resource constraints at each cell within a defined heterogeneous traffic environment. The fundamental objective is to maximize the individual cell throughput without deteriorating it over other cells, which results in a throughput equilibrium maximization over multiple cells. This implicitly implies traffic and co-channel interference congestion avoidance across the network whilst maintaining both cost efficiency and quality of service (QoS) policies. Optimal solution existence is subject to the network size, traffic and computational complexity constraints which converges to a throughput equilibrium or alternatively to the well known Nash Equilibrium (NE).

Sensing with equal gain combining (SEGC), a novel cooperative spectrum sensing technique for cognitive radio networks, is proposed. Cognitive radios simultaneously transmit their sensing results to the fusion center (FC) over multipath fading reporting channels. The cognitive radios estimate the phases of the reporting channels and use those estimates for coherent combining of the sensing results at the FC. A global decision is made at the FC by comparing the received signal with a threshold. We obtain the global detection probabilities and secondary throughput exactly through a moment generating function approach. We verify our solution via system simulation and demonstrate that the Chernoff bound and central limit theory approximation are not tight. The cases of hard sensing and soft sensing are considered and we provide examples in which hard sensing is advantageous to soft sensing. We contrast the performance of SEGC with maximum ratio combining of the sensors' results and provide examples where the former is superior. Furthermore, we evaluate the performance of SEGC against existing orthogonal reporting techniques such as time division multiple access (TDMA). SEGC performance always dominates that of TDMA in terms of secondary throughput. We also study the impact of phase and synchronization errors and demonstrate the robustness of the SEGC technique against such imperfections.

In this paper, we investigate the effect of co-channel interference on the performance of cooperative diversity networks with amplify-and-forward (AF) relaying. We consider both conventional and opportunistic relaying. First, we obtain a tight upper-bound for the equivalent signal-to-interference-plus-noise ratio (SINR) at the destination. Subsequently, the cumulative distribution function (CDF), probability density function (PDF) and moment generating function (MGF) of the effective SINR are determined based on the upper-bound. Expressions for the error probabilities in both conventional and opportunistic relaying are derived utilizing the statistical characterization of the effective SINR. We also derive an approximate PDF of the equivalent instantaneous SINR at the destination. This leads to a simple and general asymptotic error probability expression which facilitates better insight into the effect of different system parameters on the error probability. Furthermore, we investigate the problem of optimum resource allocation in the network aiming at improving performance in the presence of resource constraints. We present numerical results that illustrate the excellent match between the analytical results and the simulation results, and the performance enhancement resulting from the proposed optimal resource allocation.

We present various robust precoder designs for two-way relaying in a cognitive radio network, where a pair of cognitive (or secondary) transceiver nodes communicate with each other assisted by a set of cognitive two-way relays. The secondary nodes share the spectrum with a licensed primary user (PU) node while keeping the interference to the PU below a specified threshold. The PU node and the cognitive transceivers employ single transmit/receive antennas whereas the secondary relay nodes employ multiple transmit/receive antennas. The proposed precoder designs ensure robust performance in the presence of errors in the channel state information (CSI). Such robust designs are of significant interest since in practice it is very difficult to obtain perfect CSI. We consider CSI errors with two different types of characterization and corresponding robust designs. First, we consider robust relay precoder designs that are applicable when CSI errors have known first and second moments. Next, we consider robust designs that are applicable when the CSI error can be characterized in terms of spherical uncertainty region. We show that the proposed designs can be reformulated as convex optimization problems that can be solved efficiently. Through numerical simulations and comparisons we illustrate the performance of the proposed designs.

In spectrum-sharing cognitive radio systems, the transmit power of secondary users has to be very low due to the restrictions on the tolerable interference power dictated by primary users. In order to extend the coverage area of secondary transmission and reduce the corresponding interference region, multi-hop amplify-and-forward (AF) relaying can be implemented for the communication between secondary transmitters and receivers. This paper addresses the fundamental limits of this promising technique. Specifically, the effect of major system parameters on the performance of spectrum-sharing multi-hop AF relaying is investigated. To this end, the optimal transmit power allocation at each node along the multi-hop link is firstly addressed. Then, the extreme value theory is exploited to study the limiting distribution functions of the lower and upper bounds on the end-to-end signal-to-noise ratio of the relaying path. Our results disclose that the diversity gain of the multi-hop link is always unity, regardless of the number of relaying hops. On the other hand, the coding gain is proportional to the water level of the optimal water-filling power allocation at secondary transmitter and to the large-scale path-loss ratio of the desired link to the interference link at each hop, yet is inversely proportional to the accumulated noise, i.e. the product of the number of relays and the noise variance, at the destination. These important findings do not only shed light on the performance of the secondary transmissions but also benefit system designers improving the efficiency of future spectrum-sharing cooperative systems.

In this paper, we propose optimal linear detectors for non-orthogonal amplify-and-forward cooperative protocol when considering a single-relay scenario. Two types of detectors are proposed based on the principles of minimum mean square error (MMSE) and minimum bit error rate (MBER). The MMSE detector minimizes the mean square error, while the MBER minimizes the system bit error rate (BER). Both detectors exhibit excellent BER performance with relatively low complexity as compared to the maximal likelihood (ML) detector. The BER performance of both detectors is superior to the channel inversion, the maximal ratio combining, and the biased ML detectors.

In this paper, multi-hop cooperative networks implementing channel state information (CSI)-assisted amplify-and-forward (AF) relaying in the presence of in-phase and quadrature-phase (I/Q) imbalance are investigated. We propose a compensation algorithm for the I/Q imbalance. The performance of the multi-hop CSI-assisted AF cooperative networks with and without compensation for I/Q imbalance in Nakagami-m fading environment is evaluated in terms of average symbol error probability. Numerical results are provided and show that the proposed compensation method can effectively mitigate the impact of I/Q imbalance.

In this paper, we consider a broadcast channel in spectrum-sharing networks, where the base station schedules licensed primary users (PUs) and cognitive secondary users (SUs) simultaneously. Based on such a framework, we present a transmission strategy in the light of dirty paper coding. In order to promise the PUs' quality of service (QoS) in the broadcasting, the base station chooses codewords for the users by taking into account that the codewords pertaining to SUs can be pre-subtracted from those pertaining to PUs as if there were no interference from the secondary's data to the primary's data. For the purpose of performance evaluation, by taking capacity behavior and bit error rate (BER) as metrics, we study the achievable data rate regions for both types of users with the introduced design, and analyze the BER performance in corresponding systems implemented with hierarchical modulation. Numerical results substantiate that with flexible management of the spectrum resources, our proposed scheme provides more communication opportunities for SUs while maintaining PUs' QoS at an acceptable level.

This paper derives the error probability of a two-way relay-based communication system with opportunistic selection in Rayleigh fading environments. We consider a two-way wireless communication system where two nodes, acting as sources, are unable to exchange data directly and, thus, proceed via L intermediate relay terminals. We investigate a single-relay selection scheme wherein only the best among the L relays is chosen. Since the communication is two-way, the analyzed scheme aims at optimizing the worse performance of the two communication tasks between the pair of users. In particular, we derive closed-form expressions of the probability density functions (PDFs) of the signal-to-noise ratios (SNRs) at both users. This result is then used to derive novel closed-form expressions for the average symbol error probabilities (ASEPs) at both users' nodes. Results on the asymptotic error probability in the high-SNR range completes the performance evaluation part. Then, we provide closed-form expressions for the transmit power optimization at the two source nodes before corroborating the analysis with numerical results.

In this work, we consider a cooperative network where multiple relay nodes having different modulation capabilities assist the end-to-end communication between a source and its destination. Firstly, we evaluate the effective capacity (EC) performance of the network under study. According to the analysis, an EC-based relay selection criterion is proposed. Based on the proposed selection rule and half-duplex decode-and-forward protocol, the activated relays cooperatively help with the packet transmission from the source. At the destination, packet combining is taken into account to improve the quality of service. Compared to the popular scheme, opportunistic relay selection, numerical results are provided to prove the validity and advantages of our proposed scheme in certain scenarios. Moreover, the analysis presented herein offers a convenient tool to the relaying transmission design, specifically on which relay selection scheme should be used as well as how to choose the receiving strategy between with and without packet combining at the destination.

Throughput maximization is generally the major objective when allocating resources in orthogonal frequency division multiple access (OFDMA)networks. Traditionally, dynamic allocation methods were developed to exploit multi-user diversity in these networks. These techniques achieved significant gain in throughput by adopting relaxed convex models to define system upper bound capacity. Frequency diversity, on the other hand, is only considered to a certain extent in order to meet user service constraints. The vast majority of existing research relies on these techniques. Separately, research considering combining frequency diversity and multi-user diversity in full has been scarce. The results of our research in this paper show that using this dual diversity combining can substantially maximize system capacity and resource efficiency, and minimize outage probability whilst users' quality of service (QoS) demands are maintained.

In this paper, we present a robust joint relay precoder design and transceiver power allocation for a cognitive radio network under imperfect channel state information. The secondary (or cognitive) network consists of multiple pairs of single-antenna transceiver nodes and a non-regenerative two-way relay with multiple antennas which aids the intra-pair communication process of the transceiver nodes. The secondary nodes share the spectrum with a licensed primary user (PU) while guaranteeing that the interference to the PU receiver is maintained below a specified threshold. The proposed robust design is based on the minimization of the sum mean-square error (MSE) of the transceiver nodes under constraints on the secondary users' transmit powers and interference to PU the receiver. Though the original problem is non-convex, we show that the proposed design can be solved using alternating optimization of convex subproblems which have analytic or efficient numerical solutions. We illustrate the performance of the proposed designs through some selected numerical simulations.

In this paper, we investigate half-duplex two-way dual-hop channel state information (CSI)-assisted amplify-and-forward (AF) relaying in the presence of in-phase and quadrature-phase (I/Q) imbalance. A compensation approach for the I/Q imbalance is proposed, which employs the received signals together with their conjugations to detect the desired signal. We also derive the average symbol error probability of the considered half-duplex two-way dual-hop CSI-assisted AF relaying networks with and without compensation for I/Q imbalance in Rayleigh fading channels. Numerical results are provided and show that the proposed compensation method mitigates the impact of I/Q imbalance to a certain extent.

In this paper, we present robust joint relay precoder designs and transceiver power allocations for a cognitive radio network under imperfect channel state information (CSI). The secondary (or cognitive) network consists of a pair of single-antenna transceiver nodes and a non-regenerative two-way relay with multiple antennas which aids the communication process between the transceiver pair. The secondary nodes share the spectrum with a licensed primary user (PU) while guaranteeing that the interference to the PU receiver is maintained below a specified threshold. We consider two robust designs: the first is based on the minimization of the total transmit power of the secondary relay node required to provide the minimum quality of service, measured in terms of mean-square error (MSE) of the transceiver nodes, and the second is based on the minimization of the sum-MSE of the transceiver nodes. The robust designs are based on worst-case optimization and take into account known parameters of the error in the CSI to render the performance immune to the presence of errors in the CSI. Though the original problem is non-convex, we show that the proposed designs can be reformulated as tractable convex optimization problems that can be solved efficiently. We illustrate the performance of the proposed designs through some selected numerical simulations.

This study investigates the capacity of multiple relay channels in different fading and shadowing environments under spectrum‐sharing constraints. The authors consider that a secondary user (SU) is allowed to share the spectrum band with a primary user (PU) provided that the SU's transmit power remains below an interference power threshold set by the PU. Considering a scenario where the SU's transmitter and receiver cannot communicate directly, a relay node, chosen among a set of K terminals, helps transmitting data from the SU's transmitter to the destination. The SU's transmitter and chosen relay node adapt their corresponding transmission parameters so as to satisfy the interference‐power constraint at the PU's receiver. The authors derive closed‐form expressions for the ergodic capacity of the SU's channel in Rayleigh fading, Nakagami‐ m fading and lognormal shadowing environments. They further obtain the outage capacity assuming the aforementioned environments and the above‐mentioned spectrum‐sharing limitations. Numerical results are provided to reinforce our theoretical derivations.

In this letter, a new detector is proposed for amplify-and-forward (AF) relaying system when communicating with the assistance of$L$relays. The major goal of this detector is to improve the bit error rate (BER) performance of the receiver. The probability density function is estimated with the help of kernel density technique. A generalized Gaussian kernel is proposed. This new kernel provides more flexibility and encompasses Gaussian and uniform kernels as special cases. The optimal window width of the kernel is calculated. Simulations results show that a gain of more than 1 dB can be achieved in terms of BER performance as compared to the minimum mean square error (MMSE) receiver when communicating over Rayleigh fading channels.

In vehicular ad hoc networks (VANETs), because all vehicles in range are shown as destination nodes and less time is spent for the medium access process, broadcast communication is considered a highly appropriate technique for the dissemination of safety messages in such networks. However, the lack of request-to-send/clear-to-send handshaking and packet acknowledgment makes the communication more vulnerable to interferences, thus resulting in lower communication reliability. In this paper, we present an analytical model for the performance evaluation of safety message dissemination in vehicular ad hoc networks with two priority classes. In particular, considering the IEEE 802.11 broadcast protocol and using 2-D Markov modeling, we derive the joint distribution of the numbers of low-priority periodic messages, which are in transmission mode and in a backoff process in a highway. Then, the result is used to derive the average dissemination delay of high-priority event-driven messages in the presence of the low-priority traffic in the network. The results are helpful in determining a good tradeoff between network parameters such as vehicles' transmission range, safety traffic generation rate, and medium access control (MAC) parameters to satisfy the required delay bounds for the critical high-priority traffic.

The recent emergence of the cognitive radio standard IEEE 802.22 is finally empowering network operators with a new platform for their abundant services. Likewise previous wireless standards, where the modeling helped in a better understanding of the concepts and played an important role in extending the outreach of the technology and subsequent innovations, the modeling of IEEE 802.22 wireless regional area networks (WRANs) is a necessity. In this work, we accomplish this task using the theory of queues. To that end, we model the dynamics of each cognitive user, termed customer premises equipments (CPE) according to the standard terminology, with a 2-D Markov chain. Given this model, we show that a WRAN cell can be modeled as a Jackson network. We also find the probability mass function (PMF) and cumulative distribution function (CDF) of the CPE queue length, from which any higher moment can be derived. Notable is the fact that said PMF is expressed in an exact closed-form. In addition to the nodal analysis, a WRAN cell-level discussion is conducted by finding the stability condition and peer-to-peer delay. Moreover, we provide preliminary results on the resource allocation in WRANs, which is a very important area of focus and discovery for an efficient deployment and operation of future WRANs.

ABSTRACT Mobile‐to‐mobile (M‐to‐M) communications are expected to play a crucial role in future wireless systems and networks. In this paper, we consider M‐to‐M multiple‐input multiple‐output (MIMO) maximal ratio combining system and assess its performance in spatially correlated channels. The analysis assumes double‐correlated Rayleigh‐and‐Lognormal fading channels and is performed in terms of average symbol error probability, outage probability, and ergodic capacity. To obtain the receive and transmit spatial correlation functions needed for the performance analysis, we used a three‐dimensional (3D) M‐to‐M MIMO channel model, which takes into account the effects of fast fading and shadowing. The expressions for the considered metrics are derived as a function of the average signal‐to‐noise ratio per receive antenna in closed‐form and are further approximated using the recursive adaptive Simpson quadrature method. Numerical results are provided to show the effects of system parameters, such as distance between antenna elements, maximum elevation angle of scatterers, orientation angle of antenna array in the x–y plane, angle between the x–y plane and the antenna array orientation, and degree of scattering in the x–y plane, on the system performance. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, dual-hop amplify-and-forward (AF) cooperative systems in the presence of high-power amplifier (HPA) nonlinearity at semi-blind relays, are investigated. Based on the modified AF cooperative system model taking into account the HPA nonlinearity, the expression for the output signal-to-noise ratio (SNR) at the destination node is derived, where the interference due to both the AF relaying mechanism and the HPA nonlinearity is characterized. The performance of the AF cooperative system under study is evaluated in terms of average symbol error probability (SEP), which is derived using the moment-generating function (MGF) approach, considering transmissions over Nakagami-m fading channels. Numerical results are provided and show the effects of some system parameters, such as the HPA parameters, numbers of relays, quadrature amplitude modulation (QAM) order, Nakagami parameters, on performance.

Small-world phenomenon is an important property of many complex networks possessing small average shortest path lengths and high clustering coefficients. On the other side, wireless ad-hoc networks are highly clustered having large average shortest path length caused by the locality of their physical connections. Since the average shortest path length (number of hops) traversed by data packets has a tight interplay with the level of quality of service experienced in the network, efforts have recently focused on the creation of small-world property in wireless networks. In this study, the concept of small world is investigated in the context of wireless ad-hoc networks in a Rayleigh fading environment. In particular, we prove that the extension of few wireless links to farther located nodes (using the concept of rewiring) can reduce the average shortest path length to a decent extent, even in the presence of severe channel fading. Simulation results show that a reduction of up to 23.3% in clustering coefficient and up to 25.6% in average shortest path length can be achieved for a low-density network in the presence of fading.

In this paper, the performance of opportunistic amplify-and-forward multi-hop multi-branch relaying systems operating in the presence of co-channel interferences is investigated. Considering transmissions over independent non-identical Rayleigh fading channels, exact and upper-bound expressions for the end-to-end signal-to-interference-plus-noise ratio (SINR) are obtained. Then, the cumulative distribution function (CDF) and the probability density function (PDF) of the upper bounded SINR are studied. Based on these statistics, the system's outage probability is analyzed in closed form. Moreover, we derive an approximate expression for the PDF of the instantaneous end-to-end SINR. Following that, simple expressions for the approximate error and outage probabilities are presented and discussed. The accuracy of the analysis is validated by comparing the numerical results with Monte Carlo simulations, and insightful discussions are provided.

In this paper, we study the error performance of two-way amplify-and-forward (AF) relaying over independent but not necessarily identically distributed Rayleigh fading channels, in the presence of co-channel interfering signals affecting the network nodes. Closed-form expressions for the cumulative distribution function (CDF) of the signal-to-interference-plus-noise ratio (SINR) and for the error probability are presented. Furthermore, an approximate expression for the error probability is provided and analyzed. Simulations are performed to confirm the exactness of our theoretical analysis, and discussed along with numerical results based on said analysis.

Wireless network nodes, recently powerful enough to assume sophisticated roles, have changed the angle of studying service communication costs in modern, typically large-scale and inherently dynamic, network environments. Communication cost minimization for using a certain service, is one of the challenging issues in these environments. Its ensuing optimization problem is not only difficult (NP-hard and requires global information), but also its centralized solution is non-scalable. The approach followed in this paper is a distributed one based on local information. First, a facility replication method ensuring overall communication cost reduction is proposed and analyzed. No additional overhead is introduced and the cost of hosting a new facility is also taken into account. Second, and aiming at reducing the communication cost for using a service, a policy that employs facility replication in conjunction with facility migration, is introduced. This policy is easy to implement since it relies on information locally available at the facility node, and its efficiency and limitations are also analyzed and discussed here. Simulation results are presented, supporting the analytical findings and demonstrating a significant overall cost reduction when the proposed policy is implemented.

This paper presents a locally optimal handoff algorithm for integrated satellite/ground communication systems. We derive the handoff decision function and present the results in the form of tradeoff curves between the number of handoffs and the number of link degradation events in a given distance covered by the mobile user. This is a practical receiver-controlled handoff algorithm that optimizes the handoff process from a user perspective based on the received signal strength rather than from a network perspective.

In this contribution, two-way cooperative amplify-and-forward (AF) relaying technique is integrated into spectrumsharing wireless systems to improve spectral efficiency of secondary users (SUs). In order to share the available spectrum resources originally dedicated to primary users (PUs), the transmit power of a SU is optimized with respect to the average tolerable interference power at primary receivers. By analyzing outage probability and achievable data rate at the base station and at a cell-edge SU, our results reveal that the uplink performance is dominated by the average tolerable interference power at primary receivers, while the downlink always behaves like conventional one-way AF relaying and its performance is dominated by the average signal-to-noise ratio (SNR). These important findings provide fresh perspectives for system designers to improve spectral efficiency of secondary users in next-generation broadband spectrum-sharing wireless systems.

In this paper, we focus on a cognitive radio network where adaptive modulation is adopted in primary links. The gap between the primary user (PU)'s received signal-to-noise ratio (SNR) and the lower SNR boundary of the modulation mode that is being used, provides an interference-tolerable zone. Based on this gap, a secondary user (SU) has an increased opportunity to access the licensed spectrum and to determine the transmit power it should use to keep the PU's quality-of-service (QoS) unaffected. However, since the SU cannot obtain perfect information on the PU's received SNR, it has to choose an SNR point between the lower and upper boundaries of the PU's current modulation mode as if this point were the real SNR received by the PU. Considering this issue, in order to quantify the effect of the SU's transmissions on the PU's QoS, we define the PU's service outage probability and obtain its closed-form expressions by taking into account whether the peak transmit power constraint is imposed on the secondary's transmission or not. Subsequently, we derive the SU's achievable data rate in closed form for counterpart scenarios. Numerical results provided here quantify the relation between the PU's service outage probability and the SU's achievable data rate, which further demonstrate that the higher the peak transmit power a secondary transmitter can support, the better performance the cognitive radio network can achieve.

In this paper, a new detector is being proposed for amplify-and-forward (AF) relaying system when communicating with the assistance of L number of relays. The major goal of this detector is to improve the bit error rate (BER) performance of the system. The complexity of the system is further reduced by implementing this detector adaptively. The proposed detector is free from channel estimation. Our results demonstrate that the proposed detector is capable of achieving a gain of more than 1-dB at a BER of 10-5as compared to the conventional minimum mean square error detector when communicating over a correlated Rayleigh fading channel.

This paper investigates and compares the performance of wireless sensor networks (WSN) when sensors operate on the principles of cooperative communications. We consider a scenario where the source transmits signals to the destination with the help of L sensors. As the destination has the capacity of processing only U out of these L signals, U strongest signals are selected while the remaining (L - U) signals are suppressed. A preprocessing block similar to channel-shortening (CS) is proposed in this contribution. However, this preprocessing block employs rank-reduction technique instead of CS. This detector operates on the principles of principal components (PC). From our simulations it can be observed that this detector is capable of achieving a similar bit error rate (BER) performance as the full-rank MMSE detector with significantly lower complexity. It outperforms the CS-based detector in terms of BER performance when using fixed amplification factor. However, for variable gain amplification factor a tradeoff between the diversity gain and the receiver complexity can be observed. From the simulations it can be concluded that the BER performance of the PC-based detector when using variable gain amplification factor are better than that of the CS-based detector for lower signal to noise ratio.

In this paper, we obtain the resource allocation policies pertaining to the ergodic and outage capacity notions in spectrum-sharing cognitive radio systems where the transmission parameters of the secondary users are adaptively changed based on the availability of channel state information (CSI) of the secondary user link, and soft-sensing information (SSI) about the activity of the licensed-band (primary) user as obtained from the sensing detector at the secondary user's transmitter. Assuming availability of SSI and CSI statistics at the secondary transmitter and considering operation under constraints on average received-interference and peak transmit-power, we investigate two different capacity notions of spectrum-sharing fading channels, namely, ergodic and Outage, and obtain their corresponding optimal power allocation policies. We also sustain our theoretical results by numerical and simulation analysis.

Adaptive traffic ratio control (ATRC) with hybrid network coding and cooperative relaying is proposed to improve the overall throughput in an asymmetric data traffic network. The scheme is used in conjunction with adaptive transmission protocol and relay selection based on instantaneous channel state information. Simulation results show that (i) ATRC provides better trade-off between achieved throughput and traffic ratio and (ii) both maximum throughput and guaranteed traffic ratio can be simultaneously achieved by ATRC as offered traffic approaches symmetric.

In this paper, we present a distributed relay beamformer design for a cognitive radio network in which a cognitive (or secondary) transmit node communicates with a secondary receive node assisted by a set of cognitive non-regenerative relays. The secondary nodes share the spectrum with a licensed primary user (PU) node, and each node is assumed to be equipped with a single transmit/receive antenna. The interference to the PU resulting from the transmission from the cognitive nodes is kept below a specified limit. The proposed robust cognitive relay beamformer design seeks to minimize the total relay transmit power while ensuring that the transceiver signal-to-interference-plus-noise ratio and PU interference constraints are satisfied. The proposed design takes into account a parameter of the error in the channel state information (CSI) to render the performance of the beamformer robust in the presence of imperfect CSI. Though the original problem is non-convex, we show that the proposed design can be reformulated as a tractable convex optimization problem that can be solved efficiently. Numerical results are provided and illustrate the performance of the proposed designs for different network operating conditions and parameters.

In this paper, a new network planning framework is proposed for orthogonal frequency-division multiple access (OFDMA) cellular systems based on co-channel interference and traffic congestion avoidance. The network planning is formulated as a non-linear multi-objective optimization problem subject to minimum interference and related resource constraints at each cell under heterogeneous traffic. The multi-objective problem is represented by the throughput maximization of each single cell without penalizing the remaining cells, which results in a throughput equilibrium over the whole network. The fundamental objective is to maximize the throughput balance and, hence, traffic and co-channel interference congestions are avoided across the network. In order to maximize the equilibrium, the optimization problem is decomposed into a positioning problem and a resource allocation problem, which are solved by parallel heuristics and convex optimization. Additionally, a novel rotated polarization assignment method is proposed to minimize further the effect of the co-channel interference.

In the context of primary/secondary spectrum sharing, we propose a randomized secondary access strategy with access probabilities that are a function of both the primary automatic repeat request (ARQ) feedback and the spectrum sensing outcome. The primary terminal operates in a time slotted fashion and is active only when it has a packet to send. The primary receiver can send a positive acknowledgment (ACK) when the received packet is decoded correctly. Lack of ARQ feedback is interpreted as erroneous reception or inactivity. We call this the explicit ACK scheme. The primary receiver may also send a negative acknowledgment (NACK) when the packet is received in error. Lack of ARQ feedback is interpreted as an ACK or no-transmission. This is called the explicit NACK scheme. Under both schemes, when the primary feedback is interpreted as a NACK, the secondary user assumes that there will be retransmission in the next slot and accesses the channel with a certain probability. When the primary feedback is interpreted as an ACK, the secondary user accesses the channel with either one of two probabilities based on the sensing outcome. Under these settings, we find the three optimal access probabilities via maximizing the secondary throughput given a constraint on the primary throughput. We compare the performance of the explicit ACK and explicit NACK schemes and contrast them with schemes based on either sensing or primary ARQ feedback only.

Efficient energy consumption is a challenging problem in wireless sensor networks (WSNs) and closely related to extending network lifetime. The usual way of tackling this issue for topologies with fixed link weight and fixed sink location, has been shown to be severely affected by the energy hole problem. In this paper, the energy consumption problem is initially studied for WSNs with fixed sink assignment and it is analytically shown that energy consumption is minimized when the sink is assigned to the node that is the solution of a suitably formulated 1-median problem. This motivates the introduction of a dynamic environment where link weights change based on the energy level and the aggregate traffic load of the adjacent nodes. Then, the sink is adaptively allowed to move among neighbor nodes, according to a scalable sink migration strategy. Simulation results support the analytical claims demonstrating energy consumption reduction and an additional network lifetime increment when migration is employed in the dynamic environment.

In this paper, dual-hop amplify-and-forward (AF) cooperative systems in the presence of in-phase and quadrature-phase (I/Q) imbalance, which refers to the mismatch between components in I and Q branches, are investigated. First, we analyze the performance of the considered AF cooperative protocol without compensation for I/Q imbalance as the benchmark. Furthermore, a compensation algorithm for I/Q imbalance is proposed, which makes use of the received signals at the destination, from the source and relay nodes, together with their conjugations to detect the transmitted signal. The performance of the AF cooperative system under study is evaluated in terms of average symbol error probability (SEP), which is derived considering transmission over Rayleigh fading channels. Numerical results are provided and show that the proposed compensation algorithm can efficiently mitigate the effect of I/Q imbalance.

In this study, the authors investigate different capacity notions in cognitive radio systems where the transmission parameters of the cognitive users are adaptively changed based on the availability of (i) channel state information (CSI) pertaining to the cognitive (secondary) user link, and (ii) soft-sensing information (SSI) about the activity of the licensed-band (primary) user as obtained from the sensing detector at the secondary user's transmitter. Using statistics of available SSI and CSI at the secondary transmitter, the cognitive user adopts a transmission policy that maximises the achievable capacity under appropriate system constraints. Assuming above considerations in a cognitive radio system operating under average received-interference and peak transmit-power constraints, the authors study three different capacity notions of spectrum-sharing fading channels – namely, ergodic, delay-limited and service-rate with/without outage – and obtain their corresponding optimal power allocation policies. In particular, in this study, the authors obtain the optimal power allocation policies to achieve the channel capacity of the secondary link for the appropriate transmission policy which satisfies the spectrum-sharing system requirements in each of the above-mentioned scenarios, and further provide expressions for the capacity metrics. They also provide illustrative numerical simulations sustaining our theoretical results.

Amplify-and-forward (AF) relaying with multi-branch dual-hop relays in independent non-identical Weibull fading channels with multiple antennas at the destination is addressed. The authors consider orthogonal relaying and study conventional cooperative systems where all relays participate in the relaying phase as well as opportunistic cooperative systems where only the best relay participates in the relaying phase. An expression for the approximate probability density function (PDF) of the total instantaneous signal-to-noise ratio (SNR) at the destination is derived. Subsequently, expressions for the asymptotic average error rate and the outage probability are presented. The results provided are fairly simple and general for arbitrary values of the fading severity parameters. It is shown that opportunistic relaying does not necessarily outperform the conventional approach in terms of coding gain under equal energy allocation as in the Rayleigh fading case. Simulation results verify the tightness of the proposed analytical expressions in the high SNR region.

In this study, the authors investigate the effect of co-channel interference on the performance of dual-hop communications with amplify-and-forward relaying. First, the exact equivalent signal-to-interference-plus-noise ratio (SINR) at the destination is formulated and upper bounded. Then, the cumulative distribution function, probability density function (PDF) and moment generating function of the upper bounded SINR are determined. Further, expressions for the error and the outage probabilities are obtained. Moreover, an approximate PDF of the dual-hop link's instantaneous SINR is derived. In particular, simple expressions for the error and outage probabilities are presented and discussed. Numerical and simulation results are provided and confirm the tightness of the presented asymptotic expressions. Besides, optimisation of the power allocation and relay positioning are addressed. Specifically, the authors study adaptive power allocation with fixed relay location, optimal relay location with fixed power allocation, and joint optimisation of the power allocation and relay location under total transmit power constraint, in order to minimise the asymptotic average error probability and outage probability. Results show that optimum power allocation, optimum relay location and joint optimisation significantly improve the system performance in terms of error and outage probabilities compared to uniform power allocation and mid-point distance location of the relay node.

Emergence of new wireless technologies has facilitated the way to higher data rates and more robust communication links. Ultra wideband (UWB) is one of these promising technologies that, despite its several outstanding benefits, can cause interference to other networks operating in the same frequency range because of its large bandwidth. In this study, the authors introduce a solution for interference management in heterogeneous UWB networks. The analysis can be generalised for other coexistence scenarios where we have wireless networks with different specifications. Game theory is used to study the joint power and rate control problem under mutual interference between two UWB standards, namely, multiband orthogonal frequency division multiplexing UWB and direct-sequence UWB. A non-cooperative joint rate and power control game with pricing (NRPGP) in which each node seeks to choose its possible transmit power and rate in order to maximise its own utility while satisfying its target signal-to-interference-and-noise ratio as quality-of-service requirement is introduced. Simulation results are provided to evaluate the performance of the proposed game, NRPGP.

When analyzing system performance of conventional one-way relaying or advanced two-way relaying, these two techniques are always dealt with separately and, thus, their performance cannot be compared efficiently. Moreover, for ease of mathematical tractability, channels considered in such studies are generally assumed to be subject to Rayleigh fading or to be Nakagami-m channels with integer fading parameters, which is impractical in typical urban environments. In this paper, we propose a unified moments-based framework for general performance analysis of channel-state-information (CSI) assisted amplify-and-forward (AF) relaying systems. The framework is applicable to both one-way and two-way relaying over arbitrary Nakagami-m fading channels, and it includes previously reported results as special cases. Specifically, the mathematical framework is firstly developed under the umbrella of the weighted harmonic mean of two Gamma-distributed variables in conjunction with the theory of Padé approximants. Then, general expressions for the received signal-to-noise ratios of the users in one-way/two-way relaying systems and the corresponding moments, moment generation function, and cumulative density function are established. Subsequently, the mathematical framework is applied to analyze, compare, and gain insights into system performance of one-way and two-way relaying techniques, in terms of outage probability, average symbol error probability, and achievable data rate. All analytical results are corroborated by simulation results as well as previously reported results whenever available, and they are shown to be efficient tools to evaluate and compare system performance of one-way and two-way relaying.

This paper investigates the ergodic capacity and outage probability performance of multihop relaying networks subject to independent non-identically distributed Nakagami-m fading. Particularly, we exploit a typical amplify-and-forward relaying system with an arbitrary number of cooperative intermediate relays and no direct link between the source and destination nodes. In our analysis, channel state information is assumed to be known only at the receiving nodes and the cooperative links may have distinct fading parameters and distinct average signal-to-noise ratio (SNR) levels. In this context, a tight closed-form upper bound expression for the ergodic capacity is derived. For this, firstly the moment generating function (MGF) of the inverse of the end-to-end SNR is obtained in closed-form. Then, making use of this expression, an upper bound for the ergodic capacity is attained. Thereafter, we investigate the end-to-end outage probability performance of the multihop relaying channels in Nakagami-m fading by making use of the aforementioned MGF expression. Finally, Monte-Carlo simulation results are provided and show the tightness of the proposed bounds.

The performance of two-way amplify-and-forward (AF) relaying networks, considering transmissions over independent but not necessarily identically distributed Rayleigh fading channels in the presence of a finite number of co-channel interferers, is studied. Specifically, closed-form expressions for the cumulative distribution function (CDF) of the equivalent signal-to-interference-plus-noise ratio (SINR), the error probability, the outage probability and the system's achievable rate, are presented. Furthermore, an asymptotic expression for the probability density function (PDF) of the equivalent instantaneous SINR is derived, based on which simple and general asymptotic formulas for the error and outage probabilities are derived and analyzed. Numerical results are also provided, sustained by simulations which corroborate the exactness of the theoretical analysis.

In this paper, single-carrier multiple-input multiple-output (MIMO) transmit beamforming (TB) systems in the presence of high-power amplifier (HPA) nonlinearity are investigated. Specifically, due to the suboptimality of the conventional maximal ratio transmission/maximal ratio combining (MRT/MRC) under HPA nonlinearity, we propose the optimal TB scheme with the optimal beamforming weight vector and combining vector, for MIMO systems with nonlinear HPAs. Moreover, an alternative suboptimal but much simpler TB scheme, namely, quantized equal gain transmission (QEGT), is proposed. The latter profits from the property that the elements of the beamforming weight vector have the same constant modulus. The performance of the proposed optimal TB scheme and QEGT/MRC technique in the presence of the HPA nonlinearity is evaluated in terms of the average symbol error probability and mutual information with the Gaussian input, considering the transmission over uncorrelated quasi-static frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects on the performance of several system parameters, namely, the HPA parameters, numbers of antennas, quadrature amplitude modulation modulation order, number of pilot symbols, and cardinality of the beamforming weight vector codebook for QEGT.

Since the electromagnetic spectrum resource is becoming more and more scarce, improving spectral efficiency is becoming extremely important for the sustainable development of wireless communication systems and services. Integrating cooperative relaying techniques into spectrum-sharing cognitive radio systems sheds new light on higher spectral efficiency. In this paper, we analyze the end-to-end performance of cooperative amplify-and-forward (AF) relaying in spectrum-sharing systems. In order to achieve the optimal end-to-end performance, the transmit powers of the secondary source and the relays are optimized with respect to average interference power constraints at primary users and Nakagami-m fading parameters of interference channels (for mathematical tractability, the desired channels from secondary source to relay and from relay to secondary destination are assumed to be subject to Rayleigh fading). Also, both partial and opportunistic relay-selection strategies are exploited to further enhance system performance. Based on the exact distribution functions of the end-to-end signal-to-noise ratio (SNR) obtained herein, the outage probability, average symbol error probability, diversity order, and ergodic capacity of the system under study are analytically investigated. Our results show that system performance is dominated by the resource constraints and it improves slowly with increasing average SNR. Furthermore, larger Nakagami-m fading parameter on interference channels deteriorates system performance slightly. On the other hand, when interference power constraints are stringent, opportunistic relay selection can be exploited to improve system performance significantly. All analytical results are corroborated by simulation results and they are shown to be efficient tools for exact evaluation of system performance

For cooperative amplify-and-forward (AF) relaying in spectrum-sharing wireless systems, secondary users share spectrum resources originally licensed to primary users to communicate with each other and, thus, the transmit power of secondary transmitters is strictly limited by the tolerable interference powers at primary receivers. Furthermore, the received signals at a relay and at a secondary receiver are inevitably interfered by the signals from primary transmitters. These co-channel interferences (CCIs) from concurrent primary transmission can significantly degrade the performance of secondary transmission. This paper studies the effect of CCIs on outage probability of the secondary link in a spectrum-sharing environment. In particular, in order to compensate the performance loss due to CCIs, the transmit powers of a secondary transmitter and its relaying node are respectively optimized with respect to both the tolerable interference powers at the primary receivers and the CCIs from the primary transmitters. Moreover, when multiple relays are available, the technique of opportunistic relay selection is exploited to further improve system performance with low implementation complexity. By analyzing lower and upper bounds on the outage probability of the secondary system, this study reveals that it is the tolerable interference powers at primary receivers that dominate the system performance, rather than the CCIs from primary transmitters. System designers will benefit from this result in planning and designing next-generation broadband spectrum-sharing systems.

In this paper, we investigate a cooperative spectrum sensing scheme in which the local sensors at the secondary users perform an M-level quantization on the local decision statistic, and the quantized data are reported through erroneous channels, to be fused under Neyman-Pearson (N-P) criterion. The local quantization can be as fine as the bandwidth limitations permit; thus, the idea behind our effort is to smooth up the path towards the challenge of cooperative spectrum sensing under bandwidth constraints. We initially aim at formulating the N-P fusion rule with M-level quantization of the decision statistic. In this vein, we derive the required randomized test for the N-P fusion that represents the total performance of our spectrum sensing scheme. We further introduce a tight lower bound for the optimal performance of the primary user signal detection. An analytical procedure towards the bound and its relevant quantization setup at the local sensors are proposed and examined through case studies. The proposed near optimal bound gets closer to the optimal performance as the channel probability of error decreases, such that for ideal channels, it is seen to provide the exact optimal performance.

This paper investigates the performance of using cooperative relaying technique in spectrum-sharing cognitive radio (CR) systems while considering constraints on the average received-interference at the primary receivers. Specifically, we consider that the communication between a secondary source and its destination nodes is assisted by an intermediate relay that uses amplify-and-forward (AF) strategy. In this context, we obtain closed-form expressions for the probability density function (PDF) of the received signal-to-noise ratio (SNR) at the secondary destination node for different channel fading distributions, namely, Nakagami and Rayleigh. Then, the end-to-end performance of the proposed cooperative relaying spectrum-sharing system is investigated in terms of the overall achievable capacity and outage probability of the secondary user communication. Finally, simulation results sustaining our theoretical analysis are provided and comparisons illustrating the overall performance of the cooperative spectrum-sharing system are drawn for different propagation conditions.

This article focuses on the performance of a relay system in spectrum-sharing context. We consider that a secondary user (SU) is allowed to share the spectrum band with a primary user (PU) as long as it meets predefined interference constraints set by the PU. We suppose that the SU's transmitter and receiver are unable to communicate directly and, thus, are helped by a set of intermediate terminal nodes to deliver the data from the source to the destination. The relay nodes function using amplify-and-forward (AF) and a single "best" intermediate node is selected among a cluster by means of partial relay selection (PRS) technique to relay the information to the destination. Statistics for the end-to-end signal-to-noise ratio (SNR), namely, the probability density function (PDF) and the moment generating function (MGF), are derived and used next to evaluate the bit error rate (BER) of several modulation schemes. Numerical results and interpretations complete the study.

In this paper, we present an analytical study for the performance of a two-tier primary-secondary network based on IEEE 802.11 DCF mechanism. It is assumed that multiple primary users (PUs) and secondary users (SUs) coexist in the radio environment and share a single band such that the SUs are allowed to contend only if they sense the channel idle for a certain period of time. First, we derive the PUs' medium access delay in the presence of SUs. Then, assuming an exponential packet inter-arrival time for the primary network, and using M/G/1 queue modeling, we determine the collision probability and throughput for the primary and secondary networks, as well as the PUs' average total delay including the queuing delay. Numerical along with simulation results show how the performance in the primary network, with given packet arrival rate, can be affected as functions of the sensing time, packet payload size and population size of the SUs. The findings of this work can be used effectively to study the performance of any IEEE 802.11 based primary-secondary network, such as cognitive radio networks where SUs may exploit a primary channel opportunistically based on a predefined policy, as well as to optimize the performance of distributed cognitive radio MAC protocols.

Aiming to achieve the sum-rate capacity in multi-user multi-antenna systems where Ntantennas are implemented at the transmitter, opportunistic beamforming (OBF) generates Ntorthonormal beams and serves Ntusers during each channel use, which results in high scheduling delay over the users, especially in densely populated networks. Non-orthogonal OBF with more than Nttransmit beams can be exploited to serve more users simultaneously and further decrease scheduling delay. However, the inter-beam interference will inevitably deteriorate the sum-rate. Therefore, there is a tradeoff between sum-rate and scheduling delay for non-orthogonal OBF. In this context, system performance and implementation of non-orthogonal OBF with N >; Nt beams are investigated in this paper. Specifically, it is analytically shown that non-orthogonal OBF is an interference-limited system as the number of users K → ∞. When the inter-beam interference reaches its minimum for fixed Ntand N, the sum-rate scales as N In (N/(N-Nt)) and it degrades monotonically with the number of beams N for fixed Nt. On the contrary, the average scheduling delay is shown to scale as1/NK ln K channel uses and it improves monotonically with N. Furthermore, two practical non-orthogonal beamforming schemes are explicitly constructed and they are demonstrated to yield the minimum inter-beam interference for fixed Ntand N. This study reveals that, if user traffic is light and one user can be successfully served within a single transmission, non-orthogonal OBF can be applied to obtain lower worst-case delay among the users. On the other hand, if user traffic is heavy, non-orthogonal OBF is inferior to orthogonal OBF in terms of sum-rate and packet delay.

ABSTRACT The mutual interference between the two ultra wideband (UWB) technologies, which use the same frequency spectrum, will be a matter of concern in the near future. In this context, we present a performance analysis of direct‐sequence (DS) UWB communication in the presence of multiband orthogonal frequency division multiplexing (MB‐OFDM) UWB interfering transmissions. The channel fading is modeled according to Nakagami‐m distribution, and multi‐user interference is taken into account. The DS‐UWB system performance is evaluated in terms of bit error rate (BER). Specifically, using the characteristic function approach, an analytical expression for the average BER is derived conditioned on the channel impulse response. Numerical and simulation results are provided and compared for different coexistence scenarios. Copyright © 2011 John Wiley & Sons, Ltd.

We introduce closed-form lower bounds for the performance of multi-hop wireless networks with non-regenerative relays over Rayleigh fading channels in the presence of co-channel interference. The analysis assumes an arbitrary number of independent and identically distributed Rayleigh interferers. Novel closed-form expressions are obtained for the probability density function (PDF) and cumulative distribution function of the upper bounded end-to-end signal-to-interference-plus-noise ratio (SINR) at the destination node. These results are then used to study the average error probability. Furthermore, an approximate expression for the PDF of the instantaneous end-to-end SINR is derived, based on which general asymptotic expression for the error probability is presented and discussed. Moreover, analytical comparison of the error probability achieved by amplify-and-forward and decode-and-forward multi-hop transmissions is provided. Using these expressions, the effect of co-channel interference on system performance is investigated.

In this paper, a design for the multiple-input-multiple-output~(MIMO) multiuser transmission in the cognitive radio network is developed and its end-to-end performance is investigated under spectrum-sharing constraints. Firstly, the overall average packet error rate is analyzed by considering the channel state information feedback delay and the multiuser scheduling. Then, we provide corresponding numerical results to measure the performance evaluation for several separate scenarios, which presents a convenient tool for the cognitive radio network design with multiple secondary MIMO users.

Aiming to achieve the sum-rate capacity in multi user multi-input multi-output (MIMO) channels with Ntantennas implemented at the transmitter, opportunistic beamforming (OBF) generates Ntorthonormal beams and serves Nt users during each transmission, which results in high scheduling delay over the users, especially in densely populated wireless networks. Non-orthogonal OBF with more than Nttransmit beams can be exploited to serve more users simultaneously and further decreases scheduling delay. However, the inter-beam interference will inevitably deteriorate the sum-rate. Therefore, there is a tradeoff between the sum-rate and the increasing number of transmit beams. In this context, the sum-rate of non-orthogonal OBF with N >; Ntbeams are studied, where the transmitter is based on the Grassmannian beamforming. Our results show that non-orthogonal OBF is an interference-limited system. Moreover, when the inter-beam interference reaches its minimum for fixed Nt and N, the sum-rate scales as N ln (N/N-Nt) and it decreases monotonically with N for fixed Nt. Numerical results corroborate the accuracy of our analyses.

In this paper, we consider an underlay cognitive relaying network consisting of multiple secondary users and introduce a cooperative transmission protocol using a common relay to help with the communications between all secondary source-destination pairs for higher throughput and lower realization complexity. A whole relay-assisted transmission procedure is composed of multiple access phase and broadcast phase, where the relay is equipped with multiple antennas, and the secondary sources and destinations are single-antenna nodes. Considering the spectrum-sharing constraints on the secondary sources and the relay, we analyze the capacity behaviors of the underlay cognitive relaying network under study. The corresponding numerical results provide a convenient tool for the presented network design and substantiate a distinguishing feature of introduced design in that multiple secondary users' communications do not rely on multiple relays, hence allowing for a more efficient use of the radio resources.

We consider a cooperative spectrum sensing scenario where the local sensors at the secondary users are viewed as one-level quantizers, and the quantized data are to be fused under Neyman-Pearson (N-P) criterion. We demonstrate how the N-P fusion results in a randomized test, which represents the total performance of our spectrum sensing scheme. We further introduce an upper performance bound for the overall primary user signal detection. An analytical procedure towards the upper bound and its relevant quantization setup at the local sensors are proposed and examined through simulations.

The performance of dual-hop transmission system operating over independent and non-identical Nakagami-m fading channels in the presence of co-channel interference is studied. Exact and upper-bound expressions for the signal-to-interference-plus-noise-ratio (SINR) at the destination are formulated. Then, the cumulative distribution function (CDF) and probability density function (PDF) of the upper bounded SINR are determined. Furthermore, closed-form expressions for the error and outage probabilities are obtained and discussed. Moreover, an approximate PDF of the dual-hop link's instantaneous SINR is derived. Based on said PDF, simple, yet general, asymptotic expressions for the error and outage probabilities are presented and discussed. Numerical and simulation results are provided to verify the tightness of the presented analysis.

We consider power allocation and relay positioning with the objective to minimize system error probability in a dual-hop regenerative relaying system operating under co-channel interference. First, assuming fixed relay location, adaptive power allocation at the source and the relay nodes under joint power constraint is presented. Then considering fixed power allocation scheme, the optimal relay position is obtained. Results show that optimum power allocation, optimum relay location and joint optimization of the power allocation and relay positioning significantly improve the system performance in terms of error probability compared to uniform power allocation and mid-point distance location for the relay node.

Two-way relaying is generally designed assuming the availability of perfect channel state information (CSI) at the network nodes. However, perfect CSI is not available in practice. This paper investigates the impact of Gaussian estimation errors on the two-way relaying performance in independent and non identically distributed Rayleigh fading channels. Specifically, we derive the cumulative distribution function (CDF) and the probability density function (PDF) of the two-way relaying output signal-to-noise ratio (SNR) under imperfect CSI, enabling the evaluation of some useful performance metrics such as the average error probability and outage probabilities in practical operating environments. Furthermore, numerical and simulation results are provided and the impact of imperfect CSI on the two-way relaying performance is investigated.

In this paper, we study the performance of a network comprised of a primary user and a secondary user with the latter having cognitive radio capabilities. The secondary node uses the empty slots of the primary user to transmit its own traffic as well as to relay the primary's traffic in a cooperative fashion. Taking a queuing theory approach, we find the probability generating functions of the numbers of packets in the queues of the primary and secondary users. Subsequently, we determine a number of performance measures such as the average queues' lengths, average packet transmission delays and secondary user's queue surcharge due to cooperation. The numerical results along with the simulations show the importance of controlling the number of primary user packets admitted by the secondary user for cooperation and its impacts on the other performance measures.

In this paper, we propose a compensation method for the joint effect of high-power amplifier (HPA) nonlinearity, in-phase/quadrature-phase (I/Q) imbalance and crosstalk in multiple-input multiple-output (MIMO) orthogonal space-time block coding (OSTBC) systems. The performance of the MIMO OSTBC equipped with the proposed compensation mechanism is evaluated in terms of average symbol error probability and system capacity, in Rayleigh fading channels. Numerical results are provided and show the effects on performance of several system parameters, namely, the HPA parameters, image-leakage ratio, crosstalk, numbers of antennas, and phase-shift keying modulation order.

In this paper, we present distributed two-way relay beamformer designs for a cognitive radio network (CRN) in which a pair of cognitive (or secondary) transceiver nodes communicate with each other assisted by a set of cognitive two-way relay nodes. The secondary nodes share the spectrum with a licensed primary user (PU) node, and each node is assumed to be equipped with a single transmit/receive antenna. The interference to the PU resulting from the transmission from the cognitive nodes is kept below a specified limit. First, we consider relay beamformer designs assuming the availability of perfect channel state information (CSI). For this case, a mean-square error (MSE)-constrained beamformer that minimizes the total relay transmit power, and an MSE-balancing beamformer with a constraint on the total relay transmit power are proposed. Next, we consider relay beamformer designs assuming that the available CSI is imperfect. For this case too, we consider the same problems as those in the case of perfect CSI, and propose beamformer designs that are robust to the errors in the CSI. We show that the proposed designs can be reformulated as convex optimization problems that can be solved efficiently. Through numerical simulations, we illustrate the performance of the proposed designs.

Several attractive features of ultra wideband (UWB) communications make it a good candidate for physical-layer of wireless sensor networks (WSN). These features include low power consumption, low complexity and low cost of implementation. In this paper, we present an opportunistic power assignment strategy for distributed detection in parallel fusion WSNs, considering a Nakagami-m fading model for the communication channel and time-hopping (TH) UWB for the transmitter circuit of the sensor nodes. In a parallel fusion WSN, local decisions are made by local sensors and transmitted through wireless channels to a fusion center. The fusion center processes the information and makes the final decision. Simulation results are provided for the global probability of detection error and relative performance gain to evaluate the efficiency of the proposed power assignment strategy in different fading environments.

In MIMO-OFDM multiuser systems, user scheduling is employed as a means of multiple access. In a downlink scenario, users that share the same subcarriers of an OFDM symbol are separated through precoding in order to achieve space division multiple access (SDMA). User scheduling techniques rely on channel knowledge at the transmitter, namely, the so-called channel quality indicator (CQI). In this paper, we implement a leakage-based precoding algorithm whose purpose is twofold. First, it is used to compute a reliable CQI based on a group of precoding vectors that are adapted to the channel. Then, it implements user scheduling through using the optimum vectors for precoding, thus minimizing interference among users. We also introduce the concept of resource block size adaptivity. The resource block (RB) is defined as the least unit in an OFDM symbol that a user can be assigned to. We propose a variable RB size that adapts to the channel conditions.

With the purpose of improving the performance of next generation wireless networks, cooperative relaying (CoR) and network coding (NC) are promising techniques for bi-directional or two-way transmissions. Compared to CoR, NC can reduce the number of bi-directional transmission slots, which results in higher total throughput. However, the asymmetric traffic condition has significant impact on the bi-directional throughput of NC. CoR is robust against asymmetric traffic conditions when adaptive transmission direction switching (TDS) based on channel and traffic condition is applied. In order to improve the throughput of NC even under asymmetric traffic condition, two hybrid NC and CoR schemes with opportunistic scheduling are proposed in the present paper. In the proposed schemes, adaptive resource allocation is realized for each transmission protocol, and the impact of the traffic ratio and the relay position on the throughput is investigated. Simulation results reveal that the proposed schemes not only achieve higher throughput than the conventional scheme but are also robust against asymmetric traffic conditions. Moreover, the results can contribute to the development of relay selection and routing schemes for practical networks.

In this paper, we study the performance of a two-tier primary-secondary network based on IEEE 802.11 broadcast scheme. We assume that a number of primary and secondary users coexist in the radio environment and share a single band. To protect the primary users' priority, the secondary users are allowed to contend for the channel only if they sense it idle for a certain sensing time. Considering an exponential packet inter-arrival time for the primary network, we model each primary user as an independent M/G/1 queue. Subsequently, we determine the primary users' average medium access delay in the presence of secondary users as well as the hybrid network's throughput. Numerical results and discussions show the effects of parameters pertaining to the secondary users, such as as sensing time, packet payload size and population size, on the performance of the primary network. Furthermore, we provide simulation results which confirm the accuracy of the proposed analysis.

In this paper, we investigate the joint effects of high-power amplifier (HPA) nonlinearity, in-phase/quadrature-phase (I/Q) imbalance and crosstalk, on the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems, and propose a compensation method for the three impairments together. The performance of the MIMO TB system equipped with the proposed compensation scheme is evaluated in terms of average symbol error probability and capacity when transmissions are performed over uncorrelated Rayleigh fading channels. Numerical results are provided and show the effects on performance of several system parameters, namely, the HPA parameters, image-leakage ratio, crosstalk, numbers of antennas, length of pilot symbols and phase-shift keying modulation order.

In this study, we propose a practical adaptive multiple-input multiple-output (MIMO) transmission approach for broadband wireless multiuser systems. The presented scheme adaptively switches between open-loop and closed-loop MIMO modes depending on the users’ channel conditions and required rates as a means to enhance the system throughput and performance. Each mode is a combination of a transmission technique (space-time block coding and/or spatial multiplexing or beamforming) and a modulation/coding scheme. We first evaluate the spectral efficiency of each mode and provide a simple way to select adaptively the best combination of code rate and modulation scheme for open-loop and closed-loop transmission modes in a Rayleigh/composite fading environment. Based on these results, we propose a simple and practical switching criterion that is shown to yield significant spectral efficiency improvements over independent adaptive open-loop or closed-loop schemes for typical multiuser system scenarios. Simulations in an IEEE 802.16e framework are provided and illustrate significant improvements in throughput performance and service fairness.

In this paper, we present an analytical study for the performance of message dissemination in vehicular ad hoc networks (VANETs) with two priority classes. It is assumed that the message traffic generated by event-driven safety applications has higher priority compared to the remaining network traffic. First, we derive the distribution of the number of concurrent transmissions of lower priority messages in the system at the steady state, through a birth-death process analysis. The distribution has a simple product form solution. We also derive the percentage of destination node population which cannot receive the message error free due to interference. Subsequently, we determine the average forwarding distance and the number of nodes which receive a high-priority message in the presence of low-priority traffic. Numerical results are provided along with simulation results that confirm the accuracy of the proposed analysis. The distribution of the number of concurrent transmissions is shown to have a bell-shape curve. Results also show that larger transmission ranges do not necessarily improve the per hop safety-message forwarding distance as more nodes may be exposed to interference, especially in networks with higher node densities.

In this paper, we consider a primary/secondary spectrum-sharing system, and study adaptive resource management in cognitive radio (CR) fading broadcast channels (BC). Specifically, we propose utilizing spectrum sensing information about the primary's activity at the secondary base station for an efficient allocation of the resources, namely, transmission time and power, to the secondary users. Spectrum sensing information about the primary user, and secondary channel side information, are assumed available at the base station and receivers of the secondary CR network. The sensing information is obtained using spectrum-aware sensors deployed in the secondary network coverage area. Based on this information, we present an optimal time-sharing and power allocation policy to maximize the achievable capacity of fading cognitive radio broadcast channels, where transmission is limited by appropriate constraints on the average received-interference at the primary receiver and peak transmit-power pertaining to the secondary transmitter. Furthermore, considering that availability of full soft-sensing information at the CR transmitter may result in a severe load of feedback data and high system complexity, we present a quantized spectrum sensing mechanism wherein only restricted levels of primary activity are considered for the sensing observations. Our theoretical results are sustained by numerical and simulation analyses, and insightful discussions are provided.

This paper presents an optimal adaptive modulation (AM) algorithm designed using a cross-layer approach which combines truncated automatic repeat request (ARQ) protocol and packet combining. Transmissions are performed over multiple-input multiple-output (MIMO) Nakagami fading channels, and retransmitted packets are not necessarily modulated using the same modulation format as in the initial transmission. Compared to traditional approach, cross-layer design based on the coupling across the physical and link layers, has proven to yield better performance in wireless communications. However, there is a lack for the performance analysis and evaluation of such design when the ARQ protocol is used in conjunction with packet combining. Indeed, previous works addressed the link layer performance of AM with truncated ARQ but without packet combining. In addition, previously proposed AM algorithms are not optimal and can provide poor performance when packet combining is implemented. Herein, we first show that the packet loss rate (PLR) resulting from the combining of packets modulated with different constellations can be well approximated by an exponential function. This model is then used in the design of an optimal AM algorithm for systems employing packet combining, truncated ARQ and MIMO antenna configurations, considering transmission over Nakagami fading channels. Numerical results are provided for operation with or without packet combining, and show the enhanced performance and efficiency of the proposed algorithm in comparison with existing ones.

In downlink multi-user multiple-input multiple-output (MIMO) transmissions, several precoding schemes have been proposed to decrease interference among users. Notable among these precoding schemes is one that uses the signal-to-leakage-plus-noise ratio (SLNR) as an optimization criterion. In this paper, leveraging the efficiency of the SLNR optimization, we generalize this precoding scheme to MIMO orthogonal frequency division multiplexing (OFDM) multi-user systems where the OFDM is used to overcome the inter-symbol-interference (ISI) introduced by multipath channels. We also introduce a channel compensation technique that reconstructs the channel at the transmitter for every time instant given a significantly lower channel feedback rate by the receiver.

Relay transmission is promising for future wireless systems due to its significant cooperative diversity gain. The performance of dual-hop semi-blind amplify-and-forward (AF) relaying systems was extensively investigated, for transmissions over Rayleigh fading channels or Nakagami-m fading channels with integer fading parameter. For the general Nakagami-m fading with arbitrary m values, the exact closed-form system performance analysis is more challenging. In this paper, we explicitly derive the moment generation function (MGF), probability density function (PDF) and moments of the end-to-end signal-to-noise ratio (SNR) over arbitrary Nakagami-m fading channels with semi-blind AF relay. With these results, the system performance evaluation in terms of outage probability, average symbol error probability, ergodic capacity and diversity order, is conducted. The analysis developed in this paper applies to any semi-blind AF relaying systems with fixed relay gain, and two major strategies for computing the relay gain are compared in terms of system performance. All analytical results are corroborated by simulation results and they are shown to be efficient tools to evaluate system performance.

In addressing the issue of achieving high throughput in half-duplex relay channels, we exploit a concept of information-guided transmission for the network consisting of a source node, a destination node, and multiple half-duplex relay nodes. For further benefiting from multiple relay nodes, the relay-selection patterns are defined as the arbitrary combinations of given relay nodes. By exploiting the difference among the spatial channels states, in each relay-help transmission additional information to be forwarded is mapped onto the index of the active relay-selection pattern besides the basic information mapped onto the traditional constellation, which is forwarded by the relay node(s) in the active relay-selection pattern, so as to enhance the relay throughput. With iterative decoding, the destination node can achieve a robust detection by decoupling the signals forwarded in different ways. We investigate the proposed scheme considering "decode-and-forward" protocol and establish its achievable transmission rate. The analytical results on capacity behaviors prove the efficiency of the proposed scheme by showing that it achieves better capacity performance than the conventional scheme.

In this paper, we investigate the effect of co-channel interference on the performance of dual-hop communications with amplify-and-forward relaying. Based on the derivation of the effective signal-to-interference-plus-noise ratio (SINR) at the destination node of the system, taking into account co-channel interference, we obtain expressions for the error and outage probabilities. Moreover, we study the performance of the system in the high SINR regime. Monte-Carlo simulations are further provided and confirm the accuracy of the analytical results.

Information-guided channel-hopping technique employing multiple transmit antennas was previously proposed for supporting high data rate transmission over fading channels. This scheme achieves higher data rates than some mature schemes, such as the well-known cyclic transmit antenna selection and space-time block coding, by exploiting the independence character of multiple channels, which effectively results in having an additional information transmitting channel. Moreover, maximum likelihood decoding may be performed by simply decoupling the signals conveyed by the different mapping methods. In this paper, we investigate the achievable spectral efficiency of this scheme in the case of having channel estimation errors, with optimum pilot overhead for minimum mean-square error channel estimation, when transmitting over block-fading channels. Our numerical results further substantiate the robustness of the presented scheme, even with imperfect channel state information.

In this contribution, we address the resource allocation problem in cognitive radio (CR) broadcast channels (BC) when the radio resources are shared between the primary user of the spectrum band and the CR-BC secondary network. Specifically, we propose utilizing spectrum sensing information about the primary's activity at the secondary base station for an efficient allocation of the resources, namely, transmission time and power, to the secondary users. For this purpose, we assume that the spectrum sensing information, obtained using spectrum-aware sensors deployed in the secondary transmission range, and secondary channel side information, are available at the CR-BC secondary transmitter and receivers. Based on this information, we obtain an optimal time and power allocation policy to maximize the achievable capacity of fading cognitive radio broadcast channels, where the spectrum-sharing requirements are specified by appropriate constraints on the average received-interference at the primary receiver and on the peak transmit-power of the secondary base station. Finally, we sustain our theoretical results by numerical and simulation analysis.

We propose using cooperative relaying technique in spectrum-sharing systems to more effectively and efficiently use the available transmission resources, such as power, rate and bandwidth, while adhering to the spectrum-sharing resource requirements of the licensed (primary) user. Specifically, we consider that the secondary user of the spectrum is assisted by a decode-and-forward (DF) relay to help in the communication between its source and destination nodes. In this context, we obtain the end-to-end performance of the proposed spectrum-sharing cooperative relaying system in terms of the average symbol error rate (SER) of the secondary's communication under appropriate constraints on the interference power at the primary receiver. We further analyze our theoretical results through simulations and comparisons illustrating the SER performance of the proposed spectrum-sharing cooperative system for different operating scenarios.

In this paper, multiple-input multiple-output (MIMO) transmit beamforming (TB) systems under the consideration of nonlinear high-power amplifiers (HPAs) are investigated. The optimal beamforming scheme, with the optimal beamforming weight vector and combining vector, is proposed for MIMO systems with HPA nonlinearity. The performance of the proposed MIMO beamforming scheme in the presence of HPA nonlinearity is evaluated in terms of average symbol error probability (SEP), outage probability and system capacity, considering transmission over uncorrelated quasi-static frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects of several system parameters, namely, parameters of nonlinear HPA, numbers of transmit and receive antennas, and modulation order of phase-shift keying (PSK), on performance.

This paper addresses the power allocation and relay positioning problems in Amplify-and-forward cooperative networks over Weibull fading channels. We study adaptive power allocation (PA) with fixed relay location, optimal relay location with fixed power allocation, and joint optimization of the PA and relay location under total transmit power constraint, in order to minimize the outage probability and average error probability at high signal-to-noise ratios (SNR). Analytical results are validated by numerical simulations and comparisons between the different optimization schemes and performance are provided. Results show that optimum PA brings only coding gain, while optimum relay location yields, in addition to the latter, diversity gains as well. Also, joint optimization improves both, the diversity gain and coding gain. Furthermore, results illustrate that the analyzed adaptive algorithms outperform uniform schemes.

The task of multicast is to deliver common information to all users in a group. However, these users' different channel qualities result in their decoding capabilities being different. Therefore, the multicast design faces a dilemma to convey common information in terms of different decoding capabilities. Motivated by this, a multicast transmission scheme is proposed in this paper. In the proposed scheme, the base station transmitter prescribes the modulation and coding scheme to be used, considering the difference between the better channel-case and worse channel-case users' decoding capabilities, and the adaptive hierarchical modulation promises that each users can process the received signals according to his own decoding capabilities. Compared to the traditional multicast transmission with fixed data rate, the numerical results prove the efficiency of the proposed scheme in exploiting the users' decoding capabilities.

In this paper, we derive closed-form expressions for the average symbol error probability (SEP) of arbitrary rectangular I × J-ary quadrature amplitude modulation (QAM) in cooperative amplify-and-forward (A&F) relaying systems, when no direct line-of-sight exists between the source and the destination nodes and when the links between the K successive nodes forming the multihop cooperation chain (including the source and the destination nodes) follow independent but not-necessarily identical Nakagami-m fading distributions with arbitrary real indexes {mk}k=1Knot less than 1/2 and arbitrary average power levels {γ̅k}k=1K. The average SEP of rectangular QAM for this set-up is provided in closed-form as a linear combination of the first Lauricella's multivariate hypergeometric function, FA(K+1), K being the number of multihop links, which can be efficiently evaluated using standard numerical softwares. Simulation results sustaining our analysis are provided, and the impacts of various parameters on the overall multihop system performance are investigated.

In this paper, we present a practical adaptive multiple-input multiple-output (MIMO) transmission approach for broadband wireless multiuser systems. The proposed scheme adaptively switches between open-loop and closed-loop MIMO modes, depending on the users' channel conditions and required rates, as a means to enhance the system throughput and performance. Each mode is a combination of a MIMO transmission technique (space-time block coding and/or spatial multiplexing or beamforming) and a modulation/coding scheme. We first evaluate the spectral efficiency of each mode and provide a simple way to select adaptively the best mode among the open-loop and closed-loop available transmission modes in a Rayleigh/composite fading environment. Based on these results, we propose a simple and practical switching criterion that is shown to yield significant spectral efficiency improvements over independent adaptive open-loop or closed-loop schemes for typical multiuser system scenarios. Simulations in an IEEE 802.16e framework illustrate significant improvements in throughput performance.

This paper proposes a novel routing protocol for multi-service wireless mesh networks (WMNs). Our protocol provisions quality of service (QoS) using bandwidth reservation and bandwidth splitting mechanisms in the network layer and enhanced distributed contention access mechanism in the MAC layer. A performance analysis is conducted and the results show that the proposed resource management mechanism enables high-priority traffics to better access network resources and achieve lower delays. Low-priority traffics, on the other hand, may be routed through higher number of hops and may experience more delays or lower bandwidth resources. The proposed bandwidth offer mechanism results in an efficient traffic load distribution in the network and eliminates bottle-neck situations. The results also show the interaction between the MAC and routing protocols in terms of joint QoS provisioning.

In this paper, we investigate the effects of high-power amplifier (HPA) nonlinearity and in-phase and quadrature-phase (I/Q) imbalance on the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems. Specifically, we propose a compensation method for HPA nonlinearity and I/Q imbalance together in MIMO TB systems. The performance of the MIMO TB system under study is evaluated in terms of the average symbol error probability (SEP) and system capacity, considering transmission over uncorrelated frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects of several system parameters, such as the HPA parameters, image-leakage ratio, numbers of transmit and receive antennas, length of pilot symbols, and modulation order of phase-shift keying (PSK), on performance.

In this letter, we study the performance of two promising relay selection techniques, namely selection cooperation (SC) and opportunistic relaying (OPR), under a clustered fixed-gain relay setting. Such relay configuration finds applicability in practical ad-hoc and sensor networks, although it considers independent identically distributed channels among the links of each hop. Assuming Rayleigh fading and that all nodes are single-antenna devices, a comparative analysis between the selection strategies is performed in terms of the outage probability and average bit error rate. With this aim, closed-form expressions for the probability density function, cumulative distribution function, and moment generating function of the end-to-end signal-to-noise ratio (SNR) are derived. Our theoretical results are validated by means of Monte Carlo simulations, and show that, irrespective on the metric analyzed, OPR always yields higher performance than SC. Such conclusions differ from recent results reported in the open literature for decode-and-forward relays.

In wireless communication systems, all in-phase and quadrature-phase (I/Q) signal processing receivers face the problem of I/Q imbalance. In this paper, we investigate the effect of I/Q imbalance on the performance of multiple-input multiple-output (MIMO) maximal ratio combining (MRC) systems that perform the combining at the radio frequency (RF) level, thereby requiring only one RF chain. In order to perform the MIMO MRC, we propose a channel estimation algorithm that accounts for the I/Q imbalance. Moreover, a compensation algorithm for the I/Q imbalance in MIMO MRC systems is proposed, which first employs the least-squares (LS) rule to estimate the coefficients of the channel gain matrix, beamforming and combining weight vectors, and parameters of I/Q imbalance jointly, and then makes use of the received signal together with its conjugation to detect the transmitted signal. The performance of the MIMO MRC system under study is evaluated in terms of average symbol error probability (SEP), outage probability and ergodic capacity, which are derived considering transmission over Rayleigh fading channels. Numerical results are provided and show that the proposed compensation algorithm can efficiently mitigate the effect of I/Q imbalance.

In this paper, we investigate the capacity gains offered by cognitive radio in a spectrum-sharing system where the transmit power and rate of the secondary user are adjusted based on the channel variations of the secondary link and spectrum-sensing information pertaining to the activity of the licensed user. We assume a primary/secondary spectrum-sharing system where the secondary users may have access to the spectrum band originally assigned to the primary (licensed) user, as long as the interference power inflicted on the primary receiver is considered unharmful. In this context, considering joint average interference-power and peak transmit-power constraints, we first obtain the optimal power allocation scheme, namely variable power, for maximizing the achievable capacity of the secondary user over fading channels. Thereafter, we look into the variable rate and power adaptation policy by maximizing the achievable capacity under said power constraints and bit error rate requirements in multilevel quadrature amplitude modulation (M-QAM). Finally, the benefits of using soft-sensing information about the primary user's activity on the power and rate adaptation strategies are assessed, and numerical results and comparisons illustrating the performance of our spectrum-sharing system in different operating scenarios are provided.

This paper offers a new insight to the fundamental problem of efficient admission control in arbitrary power-controlled wireless networks with an unknown call arrival distribution. Active transmitter-receiver pairs are assumed to (i) communicate simultaneously over shared channels, (ii) define target signal-to-interference and noise ratios (SINRs) by nonlinear functions of channel interference, and (iii) use adaptive power control to maintain the actual SINR at the target level in response to interference variations. Unlike other studies, in this study, power control with limited dynamic range and both the discrete-time and the continuous-time dynamics is explicitly considered, as well as the effects of stochastic radio propagation phenomena. Without relying on a priori assumptions, we first define sufficient conditions for a channel allocation mechanism to ensure the SINR constraints in cooperation with the deployed power control mechanism. We use the concept of Lyapunov stability as a cross-layer optimization criterion. Subsequently, we focus on the widely assumed case of SINR targets being defined by linear functions of interference, and show that such targets can be achieved if hii> |Ai|¿ j¿i hij¿i, where hijis the channel gain between the transmitter of link j and the receiver of link i, and Ai is the slope of the linear definition of the target SINR. This knowledge allows us to propose a simple distributed algorithm for implementing an admission control mechanism that (i) uses interference and pilot signal measurements as its only decision-making input, and (ii) allows links to adaptively adjust the SINR targets within the system stability bounds. This mechanism is shown to outperform the carrier sensing approach (CSMA/CA) for admission control.

In this paper, we consider coexistence of secondary and primary users who share particular portions of the spectrum and propose a delay-constrained power and rate allocation scheme for the secondary user link. Secondary users are allowed to access the spectrum occupied by a primary user subject to satisfying interference-power limitations imposed by the primary user. Applying this limitation, we obtain the maximum arrival-rate supported by the secondary channel in Nakagami-m block-fading environment subject to satisfying a given statistical delay quality-of-service (QoS) constraint. In this respect, we derive the optimal rate and power adaptation policy that maximizes the effective capacity of the channel, and provide closed-form expressions for the power allocation and the effective capacity. In addition, we obtain closed-form expressions for the expenditure-power that is required at the secondary transmitter to achieve the above-mentioned capacity metric. Moreover, for comparison purposes, we consider two widely deployed power allocation strategies, namely, optimal power and rate allocation (opra) and channel inversion with fixed rate (cifr), and investigate the effective capacity of the channel under these power transmission techniques. Numerical simulations are conducted to corroborate our theoretical results.

This paper investigates delay constrained performance of a cognitive radio relay network when the cognitive (secondary) user transmission is subject to satisfying spectrum-sharing restrictions imposed by a primary user. The primary user allows a secondary user to gain access to its allocated spectrum band as long as certain thresholds on the interference power, on the peak or average values, inflicted on the primary receiver are not exceeded by the transmission of the secondary users. In addition, we assume that the secondary transmitter benefits from an intermediate node, chosen from K terminals, to relay its signal to the destination. Considering that the transmission of the secondary user is subject to satisfying a statistical delay quality-of-service (QoS) constraint, we study the maximum arrival rate of the secondary user's relay link while the interference limitations required by the primary user are satisfied. Particularly, we obtain the effective capacity of the secondary network and determine the power allocation policies that maximize the effective capacity of the secondary user's relaying channel. In addition, we derive closed-form expressions for the effective capacity of the channel in Rayleigh block-fading environment under peak or average interference-power constraints. Numerical simulations are provided to endorse our theoretical results.

Cross-layer design is a generic designation for a set of efficient adaptive transmission schemes, across multiple layers of the protocol stack, that are aimed at enhancing the spectral efficiency and increasing the transmission reliability of wireless communication systems. In this paper, one such cross-layer design scheme that combines physical layer adaptive modulation and coding (AMC) with link layer truncated automatic repeat request (T-ARQ) is proposed for multiple-input multiple-output (MIMO) systems employing orthogonal space--time block coding (OSTBC). The performance of the proposed cross-layer design is evaluated in terms of achievable average spectral efficiency (ASE), average packet loss rate (PLR) and outage probability, for which analytical expressions are derived, considering transmission over two types of MIMO fading channels, namely, spatially correlated Nakagami-m fading channels and keyhole Nakagami-m fading channels. Furthermore, the effects of the maximum number of ARQ retransmissions, numbers of transmit and receive antennas, Nakagami fading parameter and spatial correlation parameters, are studied and discussed based on numerical results and comparisons. Copyright © 2009 John Wiley & Sons, Ltd.

We propose rate and power adaptation strategies to optimize data transmission over fading channels in a spectrum sharing system operating under average received-interference constraint at the licensed user (primary user). Specifically, considering availability of the channel state information (CSI) pertaining to the secondary link and spectrum-sensing information about the activity state of the primary user, we investigate two adaptation policies at the secondary user's transmitter, namely, variable power and variable rate and power, over Rayleigh fading channels. The adaptation policies are obtained by maximizing the achievable capacity under said constraint and bit error rate (BER) requirements in multilevel quadrature amplitude modulation (M-QAM). We asses the benefits of using soft-sensing information about the primary user's activity on rate and power adaptation in spectrum sharing systems, and provide numerical results and comparisons illustrating performance for different operating scenarios.

The performance of beamforming in dual-hop cooperative networks with fixed-gain relays is investigated. These kinds of relays offer low complexity and ease of deployment when compared with variable-gain relays. In our analysis, the source and destination nodes are equipped with multiple antennas, whereas the relay is assumed to be a single-antenna device. Closed-form expressions for the outage probability (OP), probability density function (PDF), moment generating function (MGF), and generalized moments of the end-to-end signal-to- noise ratio (SNR) are obtained. It is shown that when the same antenna configurations are considered at the source and destination sides, the power imbalance between the hops may be either beneficial or detrimental for the overall system performance. In addition, depending on whether the average SNR of the second hop is equal, lower, or higher than that of the first hop, an increase of the number of antennas may not necessarily result in a substantial improvement in performance.

By enhancing diversity, cooperation in wireless networks allows increasing the transmission reliability and extending the radio coverage, without the need of implementing multiple antennas at the terminals. In this context, this paper proposes a general approach for analyzing the performance of dual-hop cooperative diversity networks with nonregenerative variable-gain relays. Such a strategy allows for the use of both equal-gain combining (EGC) and maximal-ratio combining (MRC) techniques at the destination. In our analysis, closed-form approximations for the outage probability (OP) and average symbol error rate (SER) of linear modulations are presented. These expressions yield results instantaneously, regardless the number of relays used, in contrast with exact solutions which are rather intricate and difficult to evaluate, especially when the number of relays increases. The inherent simplicity of our methodology makes it attractive to serve as a benchmark in the design and performance evaluation of cooperative networks with variable-gain relays and employing either EGC or MRC. Numerical results are provided and compared with Monte Carlo simulations to illustrate the accuracy of the proposed expressions.

In this paper, we consider variable-rate variable-power MQAM modulation employed under delay quality-of-service (QoS) constraints over spectrum-sharing channels. In particular, we assume two users sharing the spectrum with one of them having a primary access to the band, and the other, known as secondary user, constrained by interference limitations imposed by the former. We study the performance of the secondary user's link employing adaptive MQAM modulation scheme when, on top of the above-mentioned interference constraint, the secondary user is also required to satisfy a statistical delay QoS constraint. Considering two modulation schemes, namely, continuous MQAM and discrete MQAM with restricted constellations, we obtain the effective capacity of the secondary user's link, and derive the optimum power allocation scheme that maximizes the effective capacity in each case. Numerical simulations are conducted to corroborate our theoretical results.

Nonlinearity of high-power amplifier (HPA) plays a crucial role in the performance of multiple-input multiple-output (MIMO) systems. In this paper, we investigate the performance of MIMO orthogonal space-time block coding (STBC) systems in the presence of nonlinear HPA. Specifically, we assess the impact of HPA nonlinearity on the average symbol error probability (SEP), total degradation (TD), and system capacity of orthogonal STBC in uncorrelated Nakagami-m fading channels. Numerical results are provided and show the effects of several system parameters, such as the output back-off (OBO) of nonlinear HPA, numbers of transmit and receive antennas, and modulation order of quadrature amplitude modulation (QAM), on performance.

In this paper, making use of the relaying concept, which enables single-antenna devices to benefit from spatial diversity, a statistical analysis of dual-hop cooperative links using semi-blind (fixed gain) relays and partial relay selection, is provided. The selection scheme considers that the source monitors the connectivity among the nodes (relays) of the first hop only; an interesting assumption which finds applicability in practical ad-hoc and sensor networks. In our analysis, compact closed-form expressions are obtained for the outage probability (OP), probability density function (PDF), moment generating functions (MGFs), and generalized moments of the end-to-end signal-to-noise ratio (SNR). Furthermore, the influence of the relay selection on the system performance is analyzed and discussed. The analysis is also sustained by numerical results and comparisons. In particular, it is shown that the power imbalance between the hops may have positive or negative effects on the overall system performance, irrespective of the number of selected relays.

Next generation wireless networks are foreseen to be heterogeneous in nature.Wireless networks consisting of different access technologies with different bandwidth and coverage area will coexist to provide roaming users with their requirements. Handoff among heterogeneous networks, i.e. vertical handoff (VHO), has attracted enormous attention from researchers over the last couple of years. Absence of symmetry is the core distinction between homogeneous and heterogeneous networks, as one network has preference over the other network. Therefore a proficient handoff mechanism is crucial for making the experience seamless to the user, trim down the number of unnecessary handoffs, as well as to capitalize on the underlay network utilization. In this article, we propose an advanced filtering based VHO algorithm in 3G/WLAN and discuss its performance. Performance criteria are based on the number of handoffs.

IEEE 802.11 based wireless networks are widely deployed in densely populated areas such as university campuses, airports, offices, cafeterias, etc. Their popularity is rising because of their low cost and high bandwidth except that they cover small coverage areas. In order to cover large areas several access points (AP) are required, which makes it disruptive technology. During roaming, the mobile station (STA) makes frequent handoffs (HO) between APs. Scanning delay during the HO process is quite high, which makes it unsuitable for real-time applications such as VoIP (voice over internet protocol). In this article, we present a technique to reduce the MAC layer HO delay. Using an analytical model, we discuss our technique along with numerical results, and show that the scanning delay is within VoIP constraint which is a major obstacle for WLANs to be used for real-time applications.

In this paper, we investigate the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems in the presence of nonlinear high-power amplifiers (HPAs). Due to the suboptimality of maximal ratio transmission/maximal ratio combining (MRT/MRC) under HPA nonlinearity, quantized equal gain transmission (QEGT) is suggested as a feasible TB scheme. The effect of HPA nonlinearity on the performance of MIMO QEGT/MRC is evaluated in terms of the average symbol error probability (SEP) and system capacity, considering transmission over uncorrelated quasi-static frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects of several system parameters, such as the parameters of nonlinear HPA, cardinality of the beamforming weight vector codebook, and modulation order of quadrature amplitude modulation (QAM), on performance.

In this paper, we investigate the performance gains of cognitive radio relay networks under delay quality of service (QoS) limitations at the secondary users, and spectrum-sharing restrictions imposed by the primary users of the channel. In particular, we assume that the primary user allows secondary users to gain access to its allocated spectrum band as long as a certain threshold on its corresponding outage probability is satisfied. Using this constraint, we find the maximum limit on the interference-power inflicted on the primary receiver that should not be exceeded by the transmission of the secondary users. In addition, we assume that the secondary transmitter benefits from an intermediate node, chosen from K terminals, to relay its signal to the destination. Considering that the transmission of the secondary user is subject to satisfying a statistical delay QoS constraint, we obtain the maximum arrival-rate supported by the secondary user's relaying link. In this respect, we derive closed-form expressions for the effective capacity of the channel in Rayleigh block-fading environment. Numerical simulations are provided to endorse our theoretical results.

In practice, all I/Q signal processing receivers face the problem of I/Q imbalance. In this paper, we investigate the effect of I/Q imbalance on the performance of MIMO maximal ratio combining (MRC) systems that perform the combining at the radio frequency (RF) level, thereby requiring only one RF chain. Based on a system modeling that takes the I/Q imbalance into account, we evaluate the performance in terms of average symbol error probability (SEP), outage probability and system capacity, which are derived considering transmission over uncorrelated Rayleigh fading channels. Numerical results are provided to illustrate the effects of system parameters, such as the image- leakage ratio, numbers of transmit and receive antennas, and modulation order of quadrature amplitude modulation (QAM), on the system performance.

The wide spectrum of ultra wideband (UWB) communications makes it inevitable to consider strategies for avoiding and mitigating interference from narrowband wireless systems such as GPS, UMTS, and WLAN, or other UWB wireless technologies. In this paper, we provide a performance analysis of multiband orthogonal frequency division multiplexing (MB-OFDM) UWB in the presence of binary phase-shift keying time-hopping (BPSK-TH) UWB or BPSK-DS UWB interfering transmissions under Nakagami-m fading. In the bit-error rate (BER) analysis, several UWB interferers are considered to affect the MB-OFDM signal. A Gaussian approximation is considered for the UWB interferers and used in the analysis of the BER performance of the MB-OFDM UWB system. The Nakagami-m distribution is applied to characterise the amplitude of the fading channels for both the reference signal and the interference signals. Furthermore, a waveforming technique is considered for mitigating the effect of interference and its efficiency is illustrated in terms of BER improvement. Numerical and simulation results are provided and compared for different coexistence scenarios.

In this contribution, we derive exact closed-form expressions for the average symbol error probability (SEP) of arbitrary rectangular quadrature amplitude modulation (QAM) for single- and multichannel diversity reception over independent but not-necessarily identically distributed Nakagami-m fading channels. The diversity branches may hence exhibit identical or distinctive power levels and their associated Nakagami indexes need not be the same. Our work extends previous results pertaining to nondiversity reception of M-ary rectangular QAM over Rayleigh fading channels and multichannel reception of M-ary square QAM over Nakagami-m fading channels. For a given number L of diversity branches and a corresponding set of arbitrary real-valued Nakagami indexes not less than 1/2, our SEP results are expressed in terms of Gauss's hypergeometric function2F1and Lauricella's multivariate hypergeometric function FD(L)of L variables, both of which can be efficiently evaluated using standard numerical softwares.

The impact of imperfect channel state information (CSI) on the performance of transmit-beamforming (TB) over multiple-input multiple-output (MIMO) Rayleigh fading channels when using constant-power rate-adaptive pilot symbol assisted modulation (PSAM) is investigated. Specifically, imperfect CSI is accounted for with respect to both estimation and prediction errors, thereby allowing to quantify the performance degradation of the adaptive PSAM-based TB system due to both channel estimation and prediction errors. Such errors entail a mismatch between the optimal transmit/receive beamforming weights and the transmission rate implied by the true CSI on the one hand, and the actual values of these quantities as determined based on the estimated and predicted CSI, on the other hand. The compound effect of both estimation and prediction errors on the overall system performance is assessed in terms of the achievable average spectral efficiency, average bit error probability and outage probability, for which approximate closed-form expressions are derived for arbitrary numbers of transmit and receive antennas. Furthermore, the latter metrics are used to optimize the PSAM parameters, namely the power allocation between data and pilot symbols as well as the pilot spacing in order to maximize the achievable average spectral efficiency while adhering to a fixed target bit error probability.

In this paper, we analyze the capacity gains of opportunistic spectrum-sharing channels in fading environments with imperfect channel information. In particular, we consider that a secondary user may access the spectrum allocated to a primary user as long as the interference power, inflicted at the primar's receiver as an effect of the transmission of the secondary user, remains below predefined power limits, average or peak, and investigate the capacity gains offered by this spectrum-sharing approach when only partial channel information of the link between the secondaryiquests transmitter and primary's receiver is available to the secondary user. Considering average received-power constraint, we derive the ergodic and outage capacities along with their optimum power allocation policies for Rayleigh flat-fading channels, and provide closedform expressions for these capacity metrics. We further assume that the interference power inflicted on the primaryiquests receiver should remain below a peak threshold. Introducing the concept of interference-outage, we derive lower bounds on the ergodic and outage capacities of the channel. In addition, we obtain closedform expressions for the expenditure-power required at the secondary transmitter to achieve the above-mentioned capacity metrics. Numerical simulations are conducted to corroborate our theoretical results.

In this paper, we investigate the end-to-end performance of dual-hop relaying systems with beamforming over Nakagami-m fading channels. Our analysis considers semiblind (fixed-gain) relays with single antennas, and source and destination nodes equipped with multiple antennas. Closed-form expressions for the outage probability (OP), moment generating function (MGF), and generalized moments of the end-to-end signal-to-noise ratio (SNR) are derived. The proposed expressions apply to general operating scenarios with distinct Nakagamim fading parameters and average SNRs between the hops. The influence of the power imbalance, fading parameters, and antenna configurations on the overall system performance are analyzed and discussed through representative numerical examples. Furthermore, the exactness of our formulations is validated by means of Monte Carlo simulations.

The end-to-end performance of dual-hop cooperative links using semi-blind (fixed gain) relays and partial relay selection is investigated. The selection scheme considers that the source monitors the connectivity among the nodes (relays) of the first hop only. This scheme is interesting in practical ad-hoc and sensor networks. In our analysis, compact closed-form expressions are obtained for the outage probability, probability density function, moment generating functions, and generalized moments of the end-to-end signal-to-noise ratio(SNR), from which other relevant statistics that well-describe the distribution of the end-to-end SNR, such as mean, variance, kurtosis, skewness, and amount of fading, can also be deduced. Furthermore, the dynamic behavior of the end-to-end envelope is investigated, and the corresponding level crossing rate and average fade duration are obtained in an exact manner. Also, tight lower and upper bounds for these second-order statistics are presented in closed-form. Numerical results illustrating the system's performance in terms of the above metrics are provided, and the influence of the relay selection on performance is analyzed and discussed. For instance, it is shown that the power imbalance between the hops may have positive or negative effects on the overall system performance irrespective of the number of selected relays.

This paper investigates the fundamental capacity limits of opportunistic spectrum-sharing channels in fading environments. The concept of opportunistic spectrum access is motivated by the frontier technology of cognitive radio which offers a tremendous potential to improve the utilization of the radio spectrum by implementing efficient sharing of the licensed spectrum. In this spectrum-sharing technology, a secondary user may utilize the primary user's licensed band as long as its interference to the primary receiver remains below a tolerable level. Herein, we consider that the secondary user's transmission has to adhere to limitations on the ensuing received power at the primary's receiver, and investigate the capacity gains offered by this spectrum-sharing approach in a Rayleigh fading environment. Specifically, we derive the fading channel capacity of a secondary user subject to both average and peak received-power constraints at the primary's receiver. In particular, considering flat Rayleigh fading, we derive the capacity and optimum power allocation scheme for three different capacity notions, namely, ergodic, outage, and minimum-rate, and provide closed-form expressions for these capacity metrics. Numerical simulations are conducted to corroborate our theoretical results.

Abstract Selective space‐time coding and selection diversity can be viewed as practical means to reduce the implementation complexity of multiple‐input multiple‐output (MIMO) systems while still taking benefit of the use of multiple antennas. In this paper, we evaluate the performance of selective space‐time block coding (selective‐STBC) and antenna selection diversity, and analyze the performance of both techniques under perfect and imperfect channel state information (CSI) available at both ends of the transmission link. Our performance analysis reveals that, under perfect or imperfect CSI and ideal feedback channel, selective‐STBC yields a loss in selection diversity gains and that selecting just a single antenna at the transmitter side is the best transmission strategy. We also show that selective‐STBC and antenna selection diversity have different behaviors when the feedback channel is imperfect. Indeed, it is shown that selection diversity outperforms selective‐STBC when the feedback channel is of high quality, while selective‐STBC yields better performance when the feedback channel is of low quality. Copyright © 2008 John Wiley & Sons, Ltd.

Cognitive radio technology offers tremendous potential to improve the utilization of the radio spectrum by efficiently reusing and sharing the licensed spectrum bands, as long as the interference power inflicted on the primary users of the band remains below a predefined threshold level. In this paper, we investigate the outage capacity gains offered by cognitive radio in Rayleigh fading environment where the transmit power of the secondary user can be adjusted based on soft-sensing information pertaining to the primary user. Specifically, considering joint average interference and peak transmit power constraints, we derive lower bound on the outage capacity of the secondary user's channel. We propose a power allocation policy for achieving a constant-power at the secondary's receiver and provide closed- form expressions for the outage capacity and its associated power allocation policy. Furthermore, we illustrate our analysis through numerical results and comparisons.

In this paper, we propose a quality-of-service (QoS) constrained power and rate allocation scheme for spectrum sharing systems. In particular, we assume existence of secondary users, who are allowed to access the spectrum occupied by a primary user subject to satisfying interference-power limitations. Specifically, we assume that the successful operation of the primary user requires a minimum-rate to be supported by its channel for a certain percentage of time, and obtain an average interference-power constraint that is required to be fulfilled by the secondary user. Applying this limitation, we obtain the maximum arrival-rate supported by a Rayleigh block- fading channel subject to satisfying a given statistical delay QoS constraint. In this respect, we derive an optimal adaptation policy that maximizes the effective capacity of the channel, and provide closed-form expressions for the power allocation and the effective capacity. In addition, we obtain closed-form expressions for the expenditure-power that is required at the secondary transmitter to achieve the above-mentioned capacity metric.

In this paper, we consider multiple-input multiple- output (MIMO) maximal ratio combining (MRC) systems and assess the system performance in terms of average symbol error probability (SEP), outage probability and ergodic capacity in double-correlated Rayleigh-and-Lognormal fading channels. In order to derive the receive and transmit correlation functions needed for the performance analysis, a three-dimensional (3D) MIMO mobile-to-mobile (M-to-M) channel model, which takes into account the effects of fast fading and shadowing is used. Numerical results are provided to show the effects of system parameters, such as maximum elevation angle of scatterers, orientation angle of antenna array in the x-y plane, angle between x-y plane and the antenna array orientation, and degree of scattering in the x-y plane, on the system performance.

In cognitive radio technology, secondary users may be granted access to the spectrum bands occupied by a primary user as long as the interference-power, inflicted on the primary receiver as an effect of the transmission of the secondary user, is deemed unharmful. In this paper, we assume that the successful operation of the primary user requires a minimum-rate to be guaranteed by its channel for a certain percentage of time, and obtain the interference-power constraint that is required to he fulfilled by the secondary user. We investigate the capacity gains offered by this spectrum-sharing approach when the input transmit power of the secondary user is limited. In particular, we assume that only partial channel information of the link between the secondary's transmitter and primary's receiver is available to the former, and derive lower bounds on the capacity of a Rayleigh flat-fading channel with different transmission techniques, namely, channel inversion and constant-power transmission. Closed-form expressions for these capacity metrics are provided, and numerical simulations are conducted to corroborate our theoretical results.

Cognitive radio technology has been recently proposed for sharing and utilising the spectrum in order to satisfy the increasing demands for spectrum access. In this radio technology, secondary users may be granted access to the spectrum bands occupied by a primary user as long as the interference power, inflicted on the primary receiver as an effect of the transmission of the secondary user, is deemed unharmful. In this paper the authors assume that the successful operation of the primary user requires a minimum rate to be guaranteed by its channel for a certain percentage of time and obtain the interference-power constraint that is required to be fulfilled by the secondary user. Considering the input transmit-power constraint, on average or peak power, for the secondary user, the authors investigate the capacity gains offered by this spectrum-sharing approach when only partial channel information of the link between the secondary's transmitter and primary's receiver is available to the former. In particular, the lower bounds on the capacity of a Rayleigh flat-fading channel with two different transmission techniques, namely channel inversion and optimum rate allocation with constant power transmission, are derived. Closed-form expressions for these capacity metrics are provided, and numerical simulations are conducted to corroborate the theoretical results.

We analyze the bit error rate (BER) performance of M-ary quadrature amplitude modulation (M-QAM) when using space-time block coding (STBC) along with packet combining triggered by automatic repeat request (ARQ) retransmission over multiple-input multiple-output (MIMO) fading channels. Specifically, adopting a log-likelihood ratio (LLR) based approach and considering the 16-QAM case of study, we provide an exact formulation for the aggregate LLR distribution in the case the STBC codeword can be transmitted twice, and derive the resulting BER. For higher number of retransmissions, an approximation of the error function is used to derive the LLR distributions and the system's ensuing BER. Considering different values of combined transmissions and M-QAM with possible constellation rearrangement (CoRe), validation of the proposed BER analytical model through simulations and assessment of the advantages of packet combining are provided for transmissions over additive white Gaussian noise (AWGN) channel and orthogonalized MIMO Rayleigh fading channels with different STBC mappings.

This paper analyzes distributed asynchronous power and rate control for wireless ad hoc networks. Importantly, all network transmitters are considered to be independent of any management infrastructure and to have the freedom to choose their own arbitrary control rules, using as input only information on local interference and achieved carrier signal-to-interference ratio (CIR). Such an approach respects diverse user preferences of on quality of service (QoS) and allows them to adapt to local network conditions in contrast with conventional cellular systems, whose users must follow centralized control commands from serving base stations. For this purpose, we develop a general non-cooperative game-theoretic framework and characterize the resulting power and rate allocation dynamics in terms of its convergence to network-wide acceptable equilibrium states under stochastic communication channels. Chief among the attractive features of our proposed framework is the fact that it is developed in an entirely abstract way without any particular technological or architectural assumptions, which are typically made in related works. Numerical simulations prove the potential of our approach to provide for fair, robust and comparably better CIR allocation in ad hoc networks with varying topology and user density.

This paper investigates the capacity of multiple- input multiple-output (MIMO) wireless communication systems when instantaneous channel state information (CSI) is available at both the transmitter and the receiver in a line-of-sight Rician fading environment. Specifically, an infinite series representation for the ergodic capacity of MIMO channels subject to uncorrected Rician fading (URiF) is derived, assuming both transmitter and receiver CSI. The ergodic capacity and its associated outage probability are expressed as a function of a cutoff value capturing the optimal power allocation scheme. Moreover, an equation for evaluating the cutoff value using standard numerical search techniques is derived, along with closed-form expressions for the capacity of the URiF MIMO channel when the so-called eigen-mode channel inversion technique and its truncated variant are implemented. We then provide numerical results showing the effects of Ricianness on the capacity of the eigen-mode optimal power and rate adaptation, and the sub-optimal channel inversion techniques and compare the achievable spectral efficiencies with and without channel knowledge at the transmitter thereby highlighting the capacity gains enabled by channel side information in a Rician fading environment.

This paper investigates the impact of spatial fading correlation and keyhole (pinhole) condition on the capacity of multiple-input multiple-output (MIMO) channels when instantaneous channel state information (CSI) is available at the transmitter and receiver sides. A separable correlation model is considered, whereby spatial fading correlation is accounted for at either or at both sides of the collocated MIMO wireless channel. Two extreme scenarios of a double scattering environment are analyzed: (i) an extremely rich scattering environment corresponding to a conventional semi-correlated Rayleigh fading channel and (ii) a double-correlated rank-deficient keyhole channel with a single degree of freedom. In the case of semi-correlated Rayleigh fading, the capacity expressions are derived for two types of correlation structures among the transmitting or the receiving antennas, namely, a constant correlation model and an arbitrary correlation model, the latter being induced by a full-rank Hermitian covariance matrix with non-repeating distinct eigenvalues. On the other hand, the capacity expressions pertaining to the double-correlated keyhole channel are derived given arbitrary Hermitian covariance matrices at the transmitter and the receiver. For all channel types and correlation structures, closed-form expressions for the capacity of the eigen-mode optimal power and rate adaptation policy as well as for the sub-optimal eigen-mode channel inversion and its truncated variant are derived. Monte Carlo simulations are also carried out thereby upholding our theoretical analysis.

We study upper and lower bounds on the achievable sum-rate of a correlated MIMO MAC with channel estimation error at the receiver when the correlation information is available to the users' transmitters, and prove that, for Gaussian input signals with arbitrary input covariance matrices, the gap between these bounds does not exceed a limiting value at any input transmit power. We further prove that in systems with uniform input power utilization over the transmit antennas, the gap between the mutual information bounds increases monotonically as the input power of each user increases. Furthermore, we show that in the absence of correlation, the gap between the mutual information bounds is maximum for beamforming and minimum for uniform input power allocation over the transmit antennas. We further prove that utilizing the input power of each user towards the directions of the eigenvectors of its transmit correlation matrix maximizes the mutual information lower bound. Moreover, we derive the transmit directions that maximize the mutual information lower and upper bounds in an uncorrelated MIMO MAC with delayed feedback from the receiver to the transmitters, and characterize the power allocation of this system in terms of its beamforming range. Numerical simulations are conducted to corroborate our theoretical results.

Abstract In this paper, we propose a method for evaluation of the bit error rate (BER) for packet combining based on constellation rearrangement (CoRe). Such mapping diversity scheme, adopted in the high speed downlink packet access (HSDPA), uses Gray‐mapped constellations and is based on suboptimal accumulation of the reliability metrics generated in each of the transmissions. We present an exact model for the logarithmic likelihood ratios (LLR) obtained by means of the so‐called max‐log approximation, and we show that their conditional probability density functions (pdf) are piecewise Gaussian. We then present the derivation of the uncoded BER and illustrate it with simulation results that confirm our formulation. Finally, we propose simplifications which significantly reduce the complexity of the evaluation method and provide results with a very good accuracy; an extension to transmissions over faded channel is also presented. Copyright © 2007 John Wiley & Sons, Ltd.

This paper theoretically analyzes cross-layer optimized design of transmit power allocation in distributed interference-limited wireless networks with asynchronously acting links and stochastic communication channels, whereby the network link's architecture is abstracted into three layers - a physical, a data link and a network layer. We treat the transmit power allocation process as a result of coupled interaction, in which all the three layers try to satisfy their individual requirements on power control, admission control and routing respectively. Using a best-response approach for system modeling and the notion of network's stability for its cross-layer optimization, we present simple power control and admission control algorithms for convergent iterative allocation of equilibrium transmit powers, which optimally balance the network-wide trade-off between allocated transmit powers and resulting interference. Numerical simulations evaluate the achievable stability of our scheme with theoretical bounds.

Ultra wideband (UWB) technology is one of the promising solutions for future short-range communication which has recently been receiving increasing attention by many researchers. So far, two standards have been proposed to the IEEE 802.15.3a task group (TG3a) as high-speed physical technologies for next-generation wireless personal area networks (WPAN). These standards are based on multiband orthogonal frequency division multiplexing (MB-OFDM) UWB or direct-sequence (DS) UWB, two different technologies that will have to coexist in the near future. In this paper, we provide a performance analysis of MB-OFDM UWB communication in the presence of binarv phase-shift keying time-hopping (BPSK-TH) UWB or BPSK-DS UWB interfering transmissions. In the bit error rate (BER) analysis, it is considered that there are multiple UWB interferers affecting the MB-OFDM signal. A Gaussian approximation is considered for the DS-UWB and TH-UWB interferers under consideration and used in the analysis of the BER performance of a MB-OFDM UWB system. Furthermore, a waveforming technique is suggested for mitigating the effect of interference and its efficiency is illustrated in terms of BER improvement. Numerical and simulation results are provided and compared for different coexistence scenarios.

In this paper, we focus on opportunistic spectrum- sharing channels, whereby a secondary user may access the spectrum owned by a primary user as long as the average interference power, inflicted at the primary's receiver as an effect of the transmission power of the secondary user, remains below a predefined threshold, and investigate the effect of imperfect feedback on the capacity gains offered by this spectrum-sharing approach in fading environments. In particular, we assume that the secondary user is only provided with partial channel information of the link between its transmitter and the primary's receiver and derive the ergodic and outage capacities achieved by the secondary user's channel, modeled as Rayleigh flat-fading, and provide closed-form expressions for these capacity metrics along with their optimum power allocation policies. We further obtain closed-form expressions for the outage probability and the expenditure-power required at the secondary transmitter to achieve the channel capacity. Numerical simulations are conducted to corroborate our theoretical results and quantify the effect of imperfect channel estimation.

In this paper, we study upper and lower bounds on the achievable sum-rate of an uncorrelated multiple-input multiple-output (MIMO) multiple access channel (MAC) for Gaussian input signals and with channel estimation error at the receiver. We prove that the gap between the mutual information bounds does not exceed a certain value for arbitrary input covariance matrices and at any input transmit power. We also prove that in a MIMO MAC with uniform input power utilization over the transmit antennas, the gap between the mutual information bounds increases monotonically as the input power of each user increases. Furthermore, we show that the gap between the bounds is maximum when beamforming is applied at the transmitters of all users. We also derive the transmit directions that maximize the mutual information lower and upper bounds when delayed feedback is available from the receiver to the transmitters, and characterize the power allocation of this system in terms of its beamforming range. Numerical simulations are conducted to corroborate our theoretical results and quantify the effect of imperfect channel estimation.

In this fast growing technology world, where communications play a major rule for connecting people and machines together, the growth in wireless applications have caused an increasing demand for gaining access to the radio spectrum. However, the outdated spectrum utilization policies, imposed by the regulatory bodies in the past century, have caused the spectrum to look over-saturated. Recently, the concept of opportunistic spectrum access has been introduced as a tool to overcome the scarcity of the spectrum. The latter technology offers a tremendous potential to improve the utilization of the radio spectrum by implementing an efficient sharing of the licensed spectrum, whereby a secondary user may utilize the primary user's licensed band as long as its interference to the primary receiver remains below a tolerable level. In this paper, we investigate the capacity gains offered by this spectrum-sharing approach in Rayleigh fading environments. In particular, we derive the fading channel capacity of a secondary user subject to both average and peak received-power constraints at the primary's receiver. Considering both constraints, we derive the ergodic and outage capacities along with their optimum power allocation policies for Rayleigh flat-fading channel, and provide closed-form expressions for these capacity metrics. Furthermore, numerical simulations are conducted to corroborate our theoretical results.

Using a cross-layer approach, two enhancement techniques applied for adaptive modulation and coding (AMC) with truncated automatic repeat request (T-ARQ) are investigated, namely, aggressive AMC (A-AMC) and constellation rearrangement (CoRe). Aggressive AMC selects the appropriate modulation and coding schemes (MCS) to achieve higher spectral efficiency, profiting from the feasibility of using different MCSs for retransmitting a packet, whereas in the CoRe-based AMC, retransmissions of the same data packet are performed using different mappings so as to provide different degrees of protection to the bits involved, thus achieving mapping diversity gain. The performance of both schemes is evaluated in terms of average spectral efficiency and average packet loss rate, which are derived in closed-form considering transmission over Nakagami-m fading channels. Numerical results and comparisons are provided. In particular, it is shown that A-AMC combined with T-ARQ yields higher spectral efficiency than the AMC-based conventional scheme while keeping the achieved packet loss rate closer to the system's requirement, and that it can achieve larger spectral efficiency objectives than that of the scheme using AMC along with CoRe.

This paper investigates the impact of fading correlation and channel degeneracy alias keyhole condition on the capacity of multiple-input multiple-output (MIMO) spatial multiplexing systems when instantaneous channel state information is available at the transmitter and receiver sides. Two special scenarios of a double scattering channel model are analyzed: (i) an extremely rich scattering environment corresponding to a conventional semi-correlated Rayleigh fading channel whereby correlation is accounted for either among the transmitting or the receiving antennas and (ii) a rank-deficient keyhole channel with a single degree of freedom and zero correlation at both sides of the wireless link. For both fading scenarios, closed-form capacity expressions are derived in terms of a cut-off signal- to-noise ratio which must be solved for numerically. In the case of semi-correlated Rayleigh fading, the capacity expressions are obtained for two kinds of correlation structures, namely, a constant correlation model and an arbitrary correlation model, the latter being induced by a full-rank covariance matrix with non-repeating distinct eigenvalues. Monte Carlo simulations are also carried out thereby upholding our theoretical analysis.

This paper analyzes distributed asynchronous power and rate control for wireless ad hoc networks with stochastic channels. In contrast to conventional cellular systems, all network transmitters are assumed to be independent of any management infrastructure and, importantly, to have the freedom to choose their own arbitrary control rules, using as input only the information on local interference and achieved signal-to-interference and noise ratio (SINR). This approach respects link's different local network conditions and preferences on quality of service. With the purpose of finding network-wide acceptable equilibria for such an individually defined power/rate allocation dynamics, the authors discuss an entirely general asynchronous and distributed algorithm, whereby stochastic channels are assumed. Moreover, optimum admission scheme for linear/linearized models is given. Numerical simulations show the efficiency of our approach to allocate comparably higher SINRs in random ad hoc networks with changing topologies and user density.

In this work, we derive exact closed-form expressions for the average symbol error probability (SEP) of arbitrary rectangular quadrature amplitude modulation (QAM) when used along with orthogonal space-time block coding (OSTBC) over independent but not necessarily identically distributed multiple-input multiple-output (MIMO) Nakagami-m fading channels. The derived SEP expressions account for diversity branches which may exhibit identical or distinctive power levels while their associated Nakagami indexes can take arbitrary real values not less than 1/2. Our work extends previous results pertaining to the performance analysis of OSTBC using M-ary rectangular QAM over Rayleigh fading channels and M-ary square QAM over Nakagami-m fading channels. For a MIMO diversity system with nTtransmit and nRreceive antennas and a corresponding set of arbitrary real-valued Nakagami indexes, our rectangular QAM SEP results are expressed in terms of Lauricella's multivariate hypergeometric functions FD(L)and FD(L + 1)where L = nTnRis the total number of diversity branches.

This paper investigates the effects of channel estimation error at the receiver on the achievable rate of distributed space-time block coded transmission. The authors assume that multiple transmitters cooperate to send the signal to the receiver and derive lower and upper bounds on the mutual information of STBCs when the sub-channel gains and error variances between different transmitter-receiver links are unequal. The authors prove that the gap between these two bounds can not exceed a certain value at high transmit powers. The authors further prove that the gap between the mutual information bounds increases monotonically as a function of the input transmit power, and show that the gap is minimum if the receiver can estimate the channels pertaining to different transmitters with the same accuracy. The authors further derive closed-form expressions for the outage probability lower bound of distributed-STBCs (D-STBCs) with arbitrary number of transmitters. Numerical simulations are conducted to corroborate the analysis and quantify the effect of imperfect channel estimation.

In this paper, we consider the scheduling problem in multiple-input multiple-output (MIMO) wireless networks. The main important characteristic of an optimal scheduler is to maximize throughput while servicing users in a fair manner. Herein, we formulate MIMO scheduling as a generalized assignment problem (GAP) and propose a general solution for the GAP, namely, a cross-layer MIMO scheduler (CMS), which uses a novel adaptive proportional fairness (APF) mapping approach in conjunction with a new fast transmit antenna selection (FTAS) technique, to determine the set of users to transmit to and the antenna over which the data associated to each user should be transmitted. The proposed scheduler is applied for packet transmission in high-speed downlink packet access (HSDPA), taking advantage of the use of adaptive modulation and coding while coping with the constraints on the maximum number of simultaneous codes a user equipment can support, the limited uplink signalling, and the absence of fast power control. Numerical results show that the proposed CMS provides up to 70% increase in total throughput compared to other scheduling schemes

In this paper, we characterize the eigenvalue distribution of Hermitian matrices generated from a set of independent zero-mean proper complex Gaussian random (PCGR) vectors with an arbitrary common covariance matrix. Such random matrices follow the so-called Wishart-type distribution, a generic designation for both Wishart and pseudo-Wishart distributions. More specifically, we propose new simple expressions for the probability density function (PDF) and derive the cumulative distribution function (CDF) of any subset of unordered eigenvalues of Wishart-type random matrices with arbitrary finite dimensions. Many interesting results can be deduced from the foregoing distributions. In particular, one can straightforwardly deduce the statistics of the largest eigenvalue of Wishart-type random matrices, thereby paving the way for the second contribution of this paper, namely, analyzing the average error probability of dual multiple-input multiple-output (MIMO) systems using maximum-ratio transmission (MRT), subject to frequency-nonselective semicorrelated Rayleigh fading. Furthermore, Monte Carlo simulations are carried out and shown to be in perfect match with the corresponding analytical results, thereby illustrating their validity.

This paper characterizes the eigenvalue distributions of full-rank Hermitian matrices generated from a set of independent (non)zero-mean proper complex Gaussian random vectors with a scaled-identity covariance matrix. More specifically, the joint and marginal cumulative distribution function (CDF) of any subset of unordered eigenvalues of the so-called complex (non)central Wishart matrices, as well as new simple and tractable expressions for their joint probability density function (PDF), are derived in terms of a finite sum of determinants. As corollaries to these new results, explicit expressions for the statistics of the smallest and largest eigenvalues, of (non)central Wishart matrices, can be easily obtained. Moreover, capitalizing on the foregoing distributions, it becomes possible to evaluate exactly the mean, variance, and other higher order statistics such as the skewness and kurtosis of the random channel capacity, in the case of uncorrelated multiple-input multiple-output (MIMO) Ricean and Rayleigh fading channels. Doing so bridges the gap between Telatar's initial approach for evaluating the average MIMO channel capacity (Telatar, 1999), and the subsequently widely adopted moment generating function (MGF) approach, thereby setting the basis for a PDF-based framework for characterizing the capacity statistics of MIMO Ricean and Rayleigh fading channels.

We propose three different dynamic resource allocation algorithms using adaptive beamforming for multiple-input multiple-output (MIMO) OFDM systems, and investigate their performance over multipath fading channels under perfect and imperfect channel state information (CSI). These approaches involve the use of adaptive modulation, adaptive frequency-domain power allocation, and/or adaptive sub-channel allocation. By employing the proposed approaches in MIMO/OFDM systems, significant performance improvement can be achieved compared to the conventional adaptive antenna array based OFDM. The investigation of the effects of imperfect CSI reveals that the adaptive-modulation based approach is too sensitive to channel estimation errors, and that its performance is worse than the adaptive frequency-domain power allocation and/or adaptive sub-channel allocation approaches. The performance analysis also shows that combining adaptive power allocation with sub-channel allocation yields the best performance under imperfect CSI while being robust to channel estimation errors.

Closed-form expressions for the bit error rate (BER) performance of space-frequency block coded OFDM (SFBC-OFDM) systems are derived and evaluated for frequency-selective fading channels. In the performance analysis, both M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) are considered, and the effects of channel estimation errors on the BER performance are studied. Numerical results and comparisons are provided for several forms of SFBC-OFDM. It is shown that the results obtained from the closed-form formulae are very close to the ones using the exact expressions and to simulation results of the SFBC-OFDM model. The BER deterioration that results from channel estimation errors in the SFBC-OFDM systems is also illustrated. Using the provided results, the amount of degradation can be quantified.

Adopting a log-likelihood ratio (LLR) based approach, we analyze the bit error rate (BER) performance of orthogonal space-time block coding (STBC) using M-ary quadrature amplitude modulation (M-QAM) along with packet combining triggered by automatic repeat request (ARQ) retransmission over multiple-input multiple-output (MIMO) Rayleigh fading channels. Specifically, considering the 16-QAM case of study, we provide an exact formula for the aggregate LLR distribution in the case the STBC codeword can be transmitted twice, and derive an exact expression for the BER. For higher number of retransmissions, an approximation of the error function, erf(.), is used to derive the LLR distributions and the system's ensuing BER. The proposed BER analytical model is validated through simulations considering transmission over additive white Gaussian noise (AWGN) and MIMO Rayleigh fading channels, for different STBC mappings, different values of combined transmissions, and possible constellation rearrangement (CoRe).

In this paper, we propose a method to evaluate analytically the bit error rate (BER) for packet combining with Gray mapping and constellation rearrangement (CoRe) between retransmissions - a mapping diversity scheme adopted in the high speed downlink packet access (HSDPA) standard. We first develop the model for the logarithmic likelihood ratios (LLR) and show that their conditional probability density functions (pdf) are piecewise Gaussian. We then present the derivation of the BER and illustrate it with simulation results that validate our formulation.

This paper investigates the capacity of multiple-input multiple-output (MIMO) wireless systems when instantaneous channel state information (CSI) is available at both the transmitter and the receiver in a line-of-sight Rician fading environment. Specifically, an infinite series representation for the ergodic capacity of uncorrelated Rician fading MIMO channels is derived, assuming both transmitter and receiver CSI and a specular component of arbitrary rank. The ergodic capacity and its associated outage probability are expressed in terms of a cutoff level capturing the optimal eigen-mode power and rate adaptation. Moreover, an equation from which the cutoff value can be solved for numerically is derived for arbitrary numbers of transmit and receive antennas.

A resource allocation policy using transmit Beam- forming is proposed for the downlink of multiuser systems. Users to be selected for transmission in a given time slot are examined from groups of users to which the proposed algorithm determines the resources to be allocated in terms of antennas and power. The transmit beam-vectors are computed according to a zero-forcing criterion. Users are selected from different groups so as to achieve a desired balance between maximizing throughput and achieving a high degree of fairness among groups of users as well as between users within a group. Such grouping allows the proposed algorithm to make full usage of the resources and to dynamically allocate these while avoiding the complexity of the NP-complete resource reservation and users' scheduling. Computational complexity is reduced by first estimating the resources to be allocated to the groups of users and then distributing these fairly among the selected users in each group. Such an approach allows the base station to assign its antenna and power resources to groups of users for which transmission would alleviate the interference that would result in neighboring cells, or to direct the resources toward overloaded regions in the cell. Simulation results and comparisons show that the proposed dynamic resource allocation strategy achieves multiuser diversity and a high efficiency in terms controlling the tradeoff between throughput and fairness.

In this paper we consider the problem of maximizing the multi-user capacity of Gaussian multiple-input multiple-output (MIMO) broadcast channels (BC). This problem consists in finding the optimal users' covariance matrices that maximize the multiuser capacity. These covariances represent, in the same time, the selection of users to transmit to, and their corresponding allocated power. To deal with this problem, many papers use iterative algorithms to provide the optimal solution. However, when the number of active users is high, these algorithms introduce a high order of complexity and suffer from memory drawback. Herein, we show that in a multi-user multi-antenna system, there exists a subset of active users that achieves a capacity close to the maximum, and that such iterative algorithms can be utilized considering a group of users instead of all active users. In addition, we present a new algorithm which makes a suboptimal selection of such group, referred to as the Best Group (BG). The proposed algorithm can be used jointly with any optimal power allocation algorithm in order to provide the covariances which maximize the multiuser capacity. Numerical results are provided and show that the BG selection is at least 5 times faster than other algorithms with a negligible reduction in the BC capacity.

In this paper, we characterize the eigenvalue distribution of Hermitian matrices generated from a set of independent zero-mean proper complex Gaussian random vectors with an arbitrary common covariance matrix. Such random matrices follow the so-called Wishart-type distribution, a generic designation for both Wishart and pseudo-Wishart distributions. More specifically, we propose new simple expressions for the joint probability density function and cumulative distribution function of any subset of unordered eigenvalues of Wishart-type random matrices with arbitrary finite dimensions. We further show how one can extract many interesting results from the foregoing distributions such as the statistics of the extreme eigenvalues. In particular, we focus on the statistics of the largest eigenvalue of Wishart-type random matrices, thereby paving the way for the second contribution of this paper, namely, analyzing the average bit/symbol error probability of dual multiple-input multiple-output systems employing maximum-ratio transmission, subject to frequency-nonselective semicorrelated Rayleigh fading.

In this work, we provide a new framework for the analysis of the multiple-input multiple-output (MIMO) Ricean and Rayleigh fading channel capacity statistics under the assumption of perfect channel knowledge at the receiver, no channel state information at the transmitter and isotropic Gaussian distributed inputs. More specifically, we show that by deriving the marginal densities of the unordered eigenvalues of (non) central Wishart matrices, it is possible to generalize Telatar's approach for evaluating the average channel capacity, to derive the capacity variance as well as its higher order statistics, such as its skewness and kurtosis, for a class of MIMO fading environments, including the uncorrelated Rician and Rayleigh fading and the semicorrelated Rayleigh fading, thereby alleviating the need to resort to the moment generating function approach so far used in the open literature. Numerical results are also provided and sustained by Monte Carlo simulations in order to show the perfect match between the theoretical and simulation results.

In this paper, a study of the effect of channel estimation error on the capacity, outage probability, and bit error rate (BER) performance of multiple-input multiple-output OFDM (MIMO-OFDM) systems, is provided. First, a lower bound for the mutual information of MIMO-OFDM in the presence of channel estimation error is derived. Then, we derive an outage probability expression under imperfect channel information for MIMO-OFDM systems in general and for space-frequency block coded OFDM (SFBC-OFDM) in particular. Furthermore, we consider SFBC-OFDM used in conjunction with adaptive modulation, and evaluate the spectral efficiency of the adaptive SFBC-OFDM system under imperfect channel information at the transmitter. Simulation results are provided to analyze the performance of the MIMO-OFDM systems under study, and quantify the amount of degradation that imperfect channel information yields on the channel capacity, BER, outage probability and system throughput.

The impact of imperfect channel state information (CSI) on the performance of transmit-beamforming (TB) over multiple-input multiple-output (MIMO) Rayleigh fading channels when using constant-power rate-adaptive pilot-symbol-assisted modulation (PSAM), is investigated. Specifically, imperfect CSI is accounted for with respect to both estimation and prediction errors. Such errors entail a mismatch between the optimal transmit and receive beamforming weight vectors and the constellation size for adaptive modulation as implied by the true CSI and the actual values of these parameters as determined according to the predicted CSI, thereby degrading the performance of the adaptive PSAM-based TB system. The compound effect of both estimation and prediction errors on the overall system performance is assessed in terms of the achievable average spectral efficiency, average bit error probability and outage probability, for which approximate closed-form expressions are derived for arbitrary numbers of transmit and receive antennas

In this paper, we study the effect of channel estimation error at the receiver on the mutual information of a multi user multiple input multiple output (MIMO) channel obeying Rayleigh fading. We assume that imperfect knowledge of the channel is available at the receiver and find the upper bound and the lower bound on mutual information for Gaussian input signals for the uplink of this system. We prove that when the input power at each user is uniformly distributed over its transmit antennas, the bounds on the mutual information are asymptotically tight for Gaussian input signals and this tightness increases when the number of users increases. Numerical simulations are conducted to corroborate theoretical results.

Exact evaluation of the bit- and symbol-error rates in a 2-D constellation has closed solutions for particular modulations and/or bits-to-symbol mapping. To solve this fundamental problem of digital communications, we propose a general method which yields the exact results for arbitrary modulation symbols' set, arbitrary bits-to-symbol mapping, and deals with the case of nonuniform signaling. These three conditions define any digital transmission using memoryless modulation, so the proposed method is a general tool solving all problems tackled in the literature, under constraints imposed on one or more of the parameters defining the modulation or signaling type. Such an evaluation tool is of practical importance during the design of the modulation. Our analysis and numerical simulations show the advantages offered by the new method when compared with the bounding techniques.

Exact evaluation of bit- and symbol-error rates in a 2-D constellation is a fundamental problem of digital communications, which only for particular modulations and/or bits-to-symbol mapping has closed-form solutions. Here, we propose a general, numerically efficient algorithmic method, which yields the exact results for arbitrary modulation symbols' set and arbitrary bits-to-symbol mapping, and which deals with the case of nonuniform signaling. These three conditions define any digital transmission using memoryless modulation, so the proposed method is a general tool solving all problems tackled in the literature under constraints imposed on one or more of the parameters defining the modulation or signaling type. Such an evaluation tool is of practical importance during the design of the modulation. Our analysis and numerical simulations show the advantages offered by the new method when compared with the bounding techniques

The exact closed-form expression for the bit-error rate (BER) of rectangular quadrature amplitude modulation (QAM) is given. The presented formula is independent of the bit mapping and it is thus particularly useful in the design and analysis of modulation schemes employing non-Gray mapping. Compared with the so-called expurgated bound and the union bound, our expression is shown to accurately predict the BER in the low signal-to-noise ratio range where the bounding techniques fail.

Orthogonal space-time block coding (STBC) is an open-loop transmit diversity scheme that decouples the multiple-input multiple-output (MIMO) channel, thereby reducing the space-time decoding into a scalar detection process. This characteristic of STBC makes it a powerful tool, achieving full diversity over MIMO fading channels, and requiring little computational cost for both the encoding and decoding processes. In this paper, we exploit the single-input single-output equivalency of STBC in order to analyze its performance over nonselective Nakagami fading channels in the presence of spatial fading correlation. More specifically, we derive exact closed-form expressions for the outage probability and ergodic capacity of STBC, when the latter is employed over spatially correlated MIMO Nakagami fading channels. Moreover, we derive the exact symbol error probability of coherent M-PSK and M-QAM, when these modulation schemes are used along with STBC over such fading channels. The derived formulae are then used to assess the robustness of STBC to spatial correlation by considering general MIMO correlation models and analyzing their effects on the outage probability, ergodic capacity, and symbol error probability achieved by STBC.

This paper formulates the scheduling problem in MIMO networks as a generalized assignment problem (GAP), and advances a new cross-layer design for the scheduling of users and the assignment of their corresponding data to the available transmit antennas. The proposed scheduling and antenna sharing method, referred to as fast transmit antenna selection (FTAS), uses adaptive proportional fairness (APF) mapping as a means to determine the user-antenna assignment that maximizes the network performance both in terms of throughput and fairness. The proposed scheduler is applied in a high speed downlink packet access (HSDPA) network, taking advantage of an inherent HSDPA characteristic, namely, the use of adaptive modulation and coding, while coping with the imposed maximum number of simultaneously supported codes and the absence of fast power control. Numerical results show that our scheduler provides up to 70% increase in total throughput compared to other scheduling schemes applied to HSDPA

In this paper, we exploit the single-input single-output equivalency of orthogonal space-time block coding (STBC) in order to analyze its performance over nonselective Nakagami-m fading channels, in the presence of spatial correlation. More specifically, we derive the exact average symbol error probability (SEP) of coherent M-PSK and M-QAM, when such modulation schemes are used along with STBC over correlated Nakagami-m fading channels. Besides, for integer values of the Nakagami parameter m, closed-form expressions for the derived SEP formulae are provided. Moreover, in the latter case, we also derive exact closed-form expressions for the ergodic Shannon capacity of STBC, when used in the presence of spatially correlated Nakagami-m fading channels. Numerical results are provided to assess the robustness of STBC to spatial correlation, by analyzing the effects of specific correlation parameters on the achievable symbol error probability

Exact evaluation of the bit- and symbol error rates in two dimensional constellation is a fundamental problem of digital communications which has closed-form solutions for particular modulations and/or bits-to-symbol mapping. In this paper we propose a general method which yields the exact results for arbitrary modulation constellation, arbitrary bits-to-symbol mapping and deals with the case of non-uniform signalling. These three conditions define any digital transmission using memoryless modulation thus, our method is a general tool solving all problems tackled in the literature under constraints imposed on one or more of the parameters defining the modulation or signalling type. Such evaluation tool is of practical importance during the design of the modulation. Through numerical simulations we illustrate the advantages offered by the new method when compared to the bounding technique.

In this paper, we capitalize on some recently derived results yielding the probability density function (PDF) of the largest eigenvalue of complex central Wishart matrices with independent and identically distributed entries, to derive a closed-form expression for the capacity of adaptive transmission with the so-called multiple-input multiple-output (MIMO) maximal ratio combining systems, also known as transmit-beamforming (TB) systems, under Rayleigh fading. The achievable spectral efficiency by this type of MIMO systems is derived for two power and rate allocation policies, namely, the optimal power and rate adaptation policy (opra) and the channel inversion with fixed rate policy (cifr). The spectral efficiency of these adaptive transmission policies when used along with TB is evaluated and compared for different MIMO antenna configurations.

MIMO systems can provide significant increases in capacity and bandwidth efficiency as well as improvement in the QoS in wireless communications. However, multiple RF chains connected to multiple antennas are usually more expensive and complex than antenna elements themselves. Selective space-time coding and selection diversity can be viewed as practical means to reduce the implementation complexity of MIMO systems while still taking benefit of the use of multiple antennas. In this paper, we evaluate the performance of selective space-time block coding and antenna selection diversity and analyze the performance of both schemes under perfect and imperfect channel state information (CSI) available at both ends of the transmission link. Our performance analysis reveals that, under perfect CSI, selective space-time coding diversity yields a loss in selection diversity gains when combined with space-time coding, and that selecting just a single antenna at the transmitter side to transmit data is the best strategy in this CSI case of operation. We also show that selection diversity still outperforms selective space-time coding diversity when the channel estimation is imperfect.

In this paper, we derive general closed-form expressions for the Shannon capacity achieved by orthogonal space-time block coding (STBC) over Rayleigh fading channels under adaptive transmission and channel estimation errors. Adaptive transmission can be performed on a frame-by-frame basis provided that a channel state information (CSI), consisting of the SNR level as estimated by the receiver, is fed back to the transmitter, thereby allowing for different compromises between the achievable capacity and the corresponding implementation complexity. The closed-form capacity formulae, derived for different power and rate allocation policies, are expressed in terms of the number of transmit and receive antennas, the code-rate of the STBC mapping, the average SNR per receive antenna, and a single parameter capturing Gaussian channel estimation errors. Numerical results showing the effects of the estimation errors on the capacity of STBC subject to the adaptive transmission policies under consideration are provided.

Transmit-beamforming (TB) over multiple-input multiple-output (MIMO) fading channels steers the transmit power in the receiver's direction, so as to maximize the output signal-to-noise ratio (SNR) after maximal ratio combining (MRC) at the receiver. This letter proposes a simple algorithm that allows evaluating an exact and tractable expression for the probability density function of the SNR at the output of the TB receiver, subject to Rayleigh fading. The latter enables the derivation of closed-form expressions for the outage and ergodic capacity of MIMO MRC systems under Rayleigh fading, thereby avoiding the need for time-consuming numerical integrations or Monte Carlo simulations.

This paper considers packet scheduling in high speed downlink packet access (HSDPA) networks. One of the main features of HSDPA is the capability of tracking fast channel variations and the use of a large set of discrete rate values, which should be used to conduct fast scheduling of packets while ensuring fairness between users. We consider the operating environment where the scheduling is performed in heterogeneous channels. In this case, proportional fairness (PF) scheduling fails to achieve the goal of providing fair throughput to the users. We propose, in this paper, an approach that resolves this shortcoming. The proposed scheduling algorithm, called adaptive proportional fairness (APF) is shown to ensure proportional fairness even under different QoS requirements for users experiencing different channel conditions. Taking into consideration the system's constraints on the available rates, simulation results and comparisons show the high efficiency of our approach compared to PF scheduling.

In this paper, we investigate the capacity of orthogonal space-time block coding (STBC) in Rayleigh fading, subject to different power and rate adaptation policies. These policies can be performed on a frame-by-frame basis provided that partial channel state information (CSI), consisting of the signal-to-noise ratio (SNR) level as estimated by the receiver, is fed back to the transmitter. This allows for adapting the transmit power and rate to the variations of the fading channel using different policies that provide for different compromises between the achievable capacity and the corresponding implementation complexity. In particular, we derive exact closed-form expressions for the Shannon capacity of three power and rate adaptation policies, namely, the optimal power and rate adaptation, the total channel inversion with fixed rate policy, and its variant, the so-called truncated channel inversion with fixed rate policy.

The aim of this paper is to provide a framework for cross-layer management of packet-data transmissions in MIMO systems employing orthogonal space-time block coding (STBC) over Nakagami fading channels. The framework integrates physical layer adaptive modulation and link layer truncated automatic repeat request (T-ARQ), in an attempt to maximize the system's spectral efficiency under prescribed quality of service requirements such as delay and error rate constraints. The performance of the proposed scheme is assessed via three metrics for which we derive closed-form expressions. These metrics consist of the average packet error rate, the average spectral efficiency and the outage probability. We illustrate our analysis through numerical results showing how the combined cross-layer design significantly outperforms both physical layer adaptive modulation and link layer T-ARQ when solely one of these adaptive techniques is used in conjunction with STBC.

In this contribution, we first derive the Shannon capacity of MIMO orthogonal space-time block coding (STBC) in Rayleigh fading, expressing it in closed-form as function of the number of transmit and receive antennas, and the average received signal-to-noise ratio (SNR). We then assess the performance of M-ary quadrature amplitude modulation (M-QAM) used in conjunction with STBC. The performance of this rate adaptive policy is evaluated in terms of its induced average bit error rate and average spectral efficiency, the latter being compared to the derived Shannon capacity which represents the upper bound on the achievable spectral efficiency for any practical approach to adaptive modulation (AM) using STBC.

We consider the problem of call admission and resource management in a code-division multiple-access (CDMA) wireless network supporting several types of services over a range of transmission rates and offering possibly different grades of service. Resource requirements are considered separately for the uplink and downlink. The high-level objective is to design a simple admission scheme that ensures adequate signal-to-interference ratios for both the incoming call (if accepted), as well as previously admitted calls. Our approach is based on two key ideas: 1) an integrated measure of resource utilization that is agnostic to the details of the traffic mix and 2) an estimate of the additional resources required to accommodate the new call seeking admission. The current work considers estimation of the total received power distribution on the uplink and the total transmitted power distribution on the downlink, and prediction of their displacements as a result of admitting a new call. The total received/transmitted power distributions are estimated based on data obtained from the power control module. The displacement of total received/transmitted power is predicted based on the characteristics of the incoming call and the current resource utilization. Dynamic call capacities are compared with static capacities to indicate the effectiveness of the proposed algorithm in achieving high network utilization with low probability of overload.

We proposed a method to control the downlink packet flow at the base stations of CDMA wireless networks where we maximize data throughput while ensuring fairness among users. In this work, we investigate important issues for realistic implementations. Firstly, we evaluate the network performance when cell subdivision is utilized for the purpose of complexity reduction. We obtain up to 50% reduction for a minimal loss in total throughput. Secondly, a modified algorithm is proposed to support multi-class users. The results show that priority for distant users requesting high data rates can be maintained with no significant decrease in throughput. The compromise between short-term fairness ensured by our algorithm and long-term fairness taking benefit of mobility is also studied and compared. Moreover, to be able to support high priority users even when they undergo bad channel conditions, we implement two transmit diversity schemes, an open-loop method and a closed-loop method. Simulations show that the closed-loop technique provides up to 29% gain in throughput.

We consider packet scheduling and rate assignment on the uplink of a packet data wireless CDMA network in the presence of imperfect interference cancellation (IC) and limited user transmission rates, and subject to in-cell and out-of-cell resource limitations. The objective is to propose and implement a system level position-based flow control algorithm that accounts for a limited IC capability provided by power control for multi-user detection. The proposed algorithm assigns packets to be transmitted to separate queues, one for each spatial zone within which packets generate roughly the same in-cell interference and impose equal interference on a neighboring base station. Given the cell partitioning into zones, the algorithm dynamically adapts to the resource constraints and efficiently uses IC to provide for fairness in serving the various queues without giving up the objective of maximizing data throughput. Throughput and fairness are two conflicting objectives to be optimized. We show that the joint use of IC and location-based scheduling is able to achieve complete fairness with negligible loss in throughput even under stringent resource limitations.

Abstract We consider packet scheduling and rate assignment on the uplink of a packet data wireless CDMA network in the presence of imperfect interference cancellation (IC) and limited user transmission rates, and subject to in‐cell and out‐of‐cell resource limitations. The objective is to propose and implement a system level position‐based flow control algorithm that accounts for a limited IC capability provided by power control for multi‐user detection. The proposed algorithm assigns packets to be transmitted to separate queues, one for each spatial zone within which packets generate roughly the same in‐cell interference and impose equal interference on a neighboring base station. Given the cell partitioning into zones, the algorithm dynamically adapts to the resource constraints and efficiently uses IC to provide for fairness in serving the various queues without giving up the objective of maximizing data throughput. Throughput and fairness are the two conflicting objectives to be optimized. We show that the joint use of IC and location‐based scheduling is able to achieve complete fairness with negligible loss in throughput even under stringent resource limitations. The IC technique implemented is based on the interference subspace rejection (ISR) technique. We investigate both successive and group cancellation modes of ISR. Through the zone‐based grouping of users, the flow control algorithm provides a high flexibility in taking advantage of IC and is general enough to adapt to situations with constraints on the transmission rates. Results provided show how group‐based scheduling with group‐cancellation can provide for high fairness even under stringent out‐of‐cell resource limitations. Copyright © 2003 John Wiley & Sons, Ltd.

We present a block-oriented method for design of a finite set of linear predictors using a clustering algorithm on a training set. The predictors are tested with DPCM and 2-D code excited linear prediction (2-D-CELP) coding systems using switched prediction. An improved 2-D-CELP system using variable block size (VB 2-D-CELP) is proposed.