Satellite networks have become central to the evolution of modern communications systems due to their potential for extensive global coverage. However, high latency in satellite systems poses critical challenges for delay-sensitive applications, underscoring the need for performance metrics that characterize ultra-reliable low-latency communications. To address these challenges, data-oriented approach, which is already widely studied in terrestrial networks, provides a fresh perspective by evaluating the transmission performance where it prioritizes both reliability and latency. This work introduces the data-oriented approach to uplink hybrid satellite-terrestrial networks (HSTNs), focusing on non-orthogonal multiple access (NOMA)-assisted semi-grant-free (SGF) transmission where terrestrial relays support the transmission between the satellite and users. Specifically, a novel grant-free user (GFU) admission protocol based on distributed contention control, the corresponding power allocation scheme for GFUs, and the relay selection procedure presented following the data-oriented approach. Then, the maximum number of GFUs that can be admitted under given data-oriented design requirements is determined. The analytical results are verified by extensive Monte-Carlo simulations, while a wide body of numerical results are also offered to understand and demonstrate the impacts of different system parameters. The proposed analytical framework offers useful insights toward the design of practical HSTNs, particularly in the context of delay-sensitive applications, by revealing the relationship between the amount of information data, the power consumption, and the satellite distance. The results demonstrate that the proposed scheme improves the DOR performance compared to conventional grant-free access and frequency division multiple access methods by dynamically selecting GFUs and allocating transmit power based on channel conditions. It is also shown that more GFUs can be admitted, especially with larger bandwidths and/or relaxed threshold settings.

Satellite networks have become central to advancing modern communication standards due to their potential for extensive global coverage. Despite this, high latency in satellite systems poses critical challenges for delay-sensitive applications, underscoring the need for reliable metrics that reflect ultra-reliable, low-latency communication. To address these challenges, data-oriented approaches, widely adopted in terrestrial networks, offer a fresh perspective by assessing transmission performance through delay outage rates. This work introduces the data-oriented approach to hybrid satellite-terrestrial networks (HSTNs), focusing on an uplink non-orthogonal multiple access (NOMA) scheme where grant-based and grant-free users coexist. The proposed analytical framework reveals the relationship between the amount of information data, power consumption, and the satellite distance, providing valuable pathway for optimizing the performance of HSTNs in the context of delay-sensitive applications.

In wireless body area networks (WBANs), ensuring energy efficiency while maintaining reliable transmission poses a significant and inherently conflicting design challenge. This paper presents a multi-objective optimization (MOO) design for wireless transmission in the finite blocklength (FBL) regime within a WBAN environment, aimed at minimizing both energy consumption and packet error rate (PER) for each transmission session. We propose to train an intelligent agent that can determine near-optimal transmission parameter values for different user preferences. Specifically, we reformulate the MOO problem as a multi-objective Markov decision process (MOMDP) and develop a multi-objective deep reinforcement learning (MODRL)-based solution to approximate the Pareto front, where the penalty-based boundary intersection (PBI) approach is utilized for reward scalarization. Simulation results demonstrate that our proposed solution can adapt transmission parameter values for each transmission session to balance energy efficiency and reliability requirements based on user preferences. Moreover, compared to the linear scalarization method, our solution with the PBI scalarization approach provides a more complete Pareto front.

Age of information (AoI) serves as a key metric for characterizing information freshness. In this article, we investigate the AoI minimization of a non-orthogonal multiple access (NOMA)-capable wireless-powered Internet of Things (WP-IoT) network, where a base station (BS) consistently sends radio frequency (RF) signals to power IoT sensors (IoT-Ss), and selected IoT-Ss are scheduled to transmit status update packets to the BS in each time slot. We first formulate a scheduling problem for average AoI (AAoI) minimization with NOMA transmission and solve for a near-optimal scheduling policy with a deep Q-network (DQN)-based solution. Next, we propose a novel joint transmission mode selection and scheduling (JTMSS) design to further minimize the AAoI of the network. Specifically, the system adaptively selects one of three transmission modes: NOMA, orthogonal multiple access (OMA), and no transmission and schedules two, one, or none sensors for transmission, respectively. Considering the discrete hierarchical action space of the JTMSS problem, we formulate a parameterized-action Markov Decision Process (PAMDP) and develop a deep transfer learning (DTL)-based solution with a two-tier DQN framework to find a near-optimal JTMSS policy. Besides, we present a partial tuning approach during online operation to alleviate the effects of environmental changes. Simulation results verify that the JTMSS design with DTL achieves a significant performance gain over the scheduling-only policy for NOMA transmission. Moreover, the online tuning with DTL converges quickly during online operation.

As modern wireless systems transit towards the sixth-generation (6G), uncrewed aerial vehicles (UAVs) are becoming essential in realizing ubiquitous coverage due to their fully controllable mobility and high transmission efficiency. To achieve max-min fairness among users, we aim to maximize the minimum throughput by optimizing the UAV trajectory and transmission scheduling in real-world scenarios where the UAV has access only tocausalchannel state information (CSI). However, max-min fairness is involved with the user-to-user dependency across the time horizon, which makes it challenging to maximize the minimum throughput without prior knowledge of the future CSI. To tackle this issue, we propose a bisection-integrated multi-step dueling double deep Q-network (Bi-D3QN) algorithm by combining a bisection method with a multi-step D3QN framework. The Bi-D3QN algorithm can solve the minimum throughput maximization problem by alternating between (1) finding optimal policies that minimize the UAV’s mission completion time for a given minimum throughput requirement through the multi-step D3QN and (2) evaluating the feasibility of the trained policy, followed by updating the minimum throughput requirement through the bisection method. Simulation results demonstrate that the proposed Bi-D3QN algorithm achieves a higher minimum throughput compared to existing benchmark schemes through real-time interaction with the environment.

Free-space optics (FSO) is slated as a promising solution to support extremely high data rates for future satellite communications (SatCom). Nonetheless, FSO transmission is susceptible to atmospheric turbulence impacts. Space-air-ground (SAG) FSO and hybrid single-hop (SH) FSO/radio frequency (RF) transmission systems are suggested to enhance the performance and reliability of FSO-based SatCom systems. They can also be integrated to further improve system performance. Previous work analyzed the performance of the resulting integrated SAG-FSO/SH-FSO/RF transmission system, assuming independent turbulence effects. In this paper, we perform a capacity analysis of the system in the presence of correlated turbulence. A novel analytical expression for the end-to-end ergodic capacity is derived and validated by Monte Carlo simulations. The numerical results demonstrate that, although the correlated turbulence adversely affects its performance, the integrated transmission system can still achieve a considerable capacity gain over existing solutions.

This article investigates the age of information (AoI) performance in a wireless powered communication network (WPCN), where a sensor node (SN) harvests energy from an energy transmitter (ET) and then transmits status information to its data receiver (DR) by using the harvested and accumulated energy. The AoI penalty is used as a performance metric to characterize the nonlinear feature of dissatisfaction with data obsolescence at the DR. We derive the closed-form expressions of the average AoI penalty and the average peak AoI (PAoI) penalty with the Rician fading model. To further explore the system performance limit in terms of AoI penalty, we formulate two optimization problems to minimize the average AoI penalty and the average PAoI penalty with respect to the battery discharge threshold. Particularly, we reveal the conditions for the existence of the average AoI penalty and average PAoI penalty. Simulation results show that there exists a unique optimal battery discharge threshold that minimizes the system’s average AoI penalty and a unique optimal battery discharge threshold that minimizes the system’s average PAoI penalty. Moreover, as expected, the average AoI penalty and the average PAoI penalty decrease with the increment of the Rician$K$-factor, and increase with the increment of the distance between ET and SN. Besides, the average AoI penalty and the average PAoI penalty first decrease with the increment of transmit power of ET and then tend to be flat. Additionally, a smaller data size of SN yields better system performance.

Energy-efficient transmission is essential to wireless body area networks (WBAN) as most biosensors in WBAN have limited energy supply. In this paper, we study the energy consumption minimization problem for each amplify-and-forward (AF) relay transmission session while satisfying a certain reliability requirement in WBAN. To minimize the energy consumption during successful transmission and wasted energy due to failed transmission attempts, over finite blocklength (FBL) regime, we design an intelligent agent that can determine: i) whether to transmit or not for given current channel state information (CSI) and available resources and ii) the best power levels and blocklength values for the current transmission session if the agent decides to transmit. To perform these two tasks simultaneously, we propose a novel hybrid supervised/reinforcement learning solution. Specifically, we design a classification network following the supervised learning approach to determine whether to transmit or not based on predicted minimal packet error probability. We then develop a deep reinforcement learning (DRL)-based solution that determines the optimal values of the transmission parameters. We also propose a DRL-based online parameter tuning (DRL-OPT) algorithm to minimize the impact of model inaccuracy and/or environment changes. Simulation results reveal that the performance of the proposed hybrid solution is almost identical to that of the exhaustive search. The DRL-OPT algorithm can follow environment variation and maintain a good performance with low computational complexity. Moreover, we numerically analyze the effect of slot duration on energy consumption and develop a guideline for practical WBAN design.

This article studies an intelligent reflecting surface (IRS)-assisted unmanned aerial vehicle (UAV) network, where the ground users (GUs) desire to receive information from a UAV. Downlink nonorthogonal multiple access (NOMA) is considered typically with two GUs being selected according to whether a Line-of-Sight (LoS) link between GUs and UAV exists. As the accurate channel information of LoS or Non-LoS (NLoS) links for multiple GUs is difficult to acquire, an approximate LoS region-based method is designed to select GUs as an alternative. In order to enhance the communication quality of the far GU, an IRS is deployed to assist the NLoS transmission. For such a system, we evaluate its outage performance in Nakagami-m fading. First, the central limit theorem (CLT) and Laplace transform (LT) are employed to derive the channel statistics of the UAV- IRS-user link. Then, asymptotic closed-form expressions of the outage probabilities are derived for the selected GUs based on Gaussian–Chebyshev quadrature approximation. Monte Carlo simulations validate the validness of our derived outage probabilities. It shows that the approximate LoS region-based scheme provides similar outage performance laws as the accurate LoS region-based one. Moreover, the outage probabilities of selected GUs in terms of NOMA-based protocol and orthogonal multiple access (OMA)-based protocol are analyzed. Simulation results confirm that the proposed NOMA-based protocol is capable of achieving superior performance compared with the OMA-based protocol by setting power allocation factor and targeted acrlong SINR thresholds of near GU and far GU properly. Specifically, when the rate threshold of near GU is relatively large or the rate threshold of far GU is relatively small, the outage performance derived by NOMA-based protocol performs better than OMA-based protocol in most of cases.

This paper explores the evolution of wireless communication networks from utilizing the sub-6 GHz spectrum and the millimeter wave frequency band to incorporating extremely high frequencies like optical and terahertz for 6G and beyond. While these higher frequencies offer broader bandwidths and extreme data rate capabilities, the transition from single-band and heterogeneous networks to multi-band networks (MBNs), where various frequency bands coexist introduces novel challenges in channel modeling, transceiver and antenna design, programmable simulation platforms, standardization, and resource allocation. This paper provides a tutorial overview from the communication design perspective of the various frequency bands, elaborating on the above issues. Then, we introduce and examine typical MBN architectures for future networks and provide a detailed overview of state-of-the-art resource allocation problems for existing MBNs that typically operate on two frequency bands. The considered resource allocation optimization problems and solution techniques are discussed comprehensively. We then identify key performance metrics and constraint sets that should be considered for resource allocation optimization in future MBNs and provide numerical results to depict how various system parameters and user behaviors can influence their performance. Finally, we present several potential research issues as future work for the design and performance optimization of MBNs.

Reliable and energy-efficient wireless transmission is of critical importance to the success of future advanced Internet of Things (IoT). Due to the sporadic nature of IoT transmissions, the energy consumption of the individual IoT transmission session varies dramatically with the instantaneous operating environment as well as the Quality of Service (QoS) requirements. In this article, we analyze and design the energy-efficient relay transmission systems from an individual data transmission session perspective. Specifically, we consider a dual-hop transmission system with a decode-and-forward relay that is solely powered by wireless power transfer from source node. For both time switching and power splitting modes of simultaneous power and information transmission, we analyze and minimize the total energy consumption of the system when transmitting a fixed amount of data, under a piecewise linear energy harvesting (EH) model. Closed-form expressions for optimal transmission parameters are obtained with and without the consideration of latency constraint. Through selected numerical results, we illustrate various design tradeoffs between energy consumption and latency constraint. We show that with optimal transmission parameters, relay transmission with energy transfer can achieve considerable energy saving compared to the direct transmission when the direct link quality is poor and the latency constraint is not stringent. We also show that with optimized parameters, power splitting mode leads to lower energy consumption and smaller transmission duration than time switching mode, at the cost of higher implementation complexity.

The satellite communication (Satcom) community is exploring the license-free optical spectrum to support the growing traffic demand in a cost-effective manner. However, free-space optical (FSO) communications are vulnerable to atmospheric turbulence, pointing errors, and weather effects. Space-air-ground (SAG) FSO transmission and hybrid single-hop (SH) FSO/radio frequency (RF) transmission are promising solutions to improve the performance of FSO links and can be integrated into a Satcom system. In this work, we carry out a thorough error rate analysis of the resulting integrated SAG-FSO/SH-FSO/RF Satcom system, where Gamma-Gamma and Rician distributions are used to characterize FSO and RF links, respectively. The exact analytical expressions are derived and validated by Monte-Carlo simulations. The numerical results highlight the significant potential of the integrated SAG-FSO/SH-FSO/RF Satcom system over existing solutions.

In this work, we study the performance of reconfigurable intelligent surface (RIS)-aided communication systems over the sum of cascaded Rician fading channels. To facilitate the performance analysis of the practical scenario, we consider the case that imperfect channel state information (CSI) is available at the RIS. We derive the closed-form expressions of several performance metrics in terms of the exact outage probability, ergodic capacity and average bit error rate (BER). Through analytical and numerical results, we examine the effect of the number of reflecting elements at the RIS and different system parameters on the overall system performance.

With its low cost and high implementation flexibility, unmanned aerial vehicle (UAV) serves as an attractive solution for data collection from remote sensors. UAV can also power the transmission of resource-limited sensors through wireless energy transfer. In this article, we study the UAV energy consumption minimization during an individual sensor charging and data collection session. Specifically, considering the operation of the UAV at a particular sensor, we derive the closed-form expressions of optimal transmission parameters with/without latency constraint. We also analyze the probability of data collection failure due to poor channel condition. The validity of our theoretical analysis is verified by comparing with the results from exhaustive search. According to these results, optimal duration for sensor data transmission should be as short as possible for negligible circuit power, and latency constraint does not have significant impacts on minimum energy consumption for nonnegligible circuit power and channel gain.

This article studies the coverage performance of unmanned aerial vehicle (UAV)-assisted simultaneous wireless information and power transfer (SWIPT) networks under the nonlinear and linear energy harvesting (EH) models in the rich scattering scenarios, including smart farming and smart ranching, where the None-Line-of-Sight (NLoS) links are the dominate component of the wireless channel. Multiple UAVs are equipped with directional antennas to transfer information and energy to ground users (GUs). Power splitting (PS) or time switching (TS) architecture is employed at GUs. In order to evaluate the system performance in fading channels, the information and energy coverage probabilities of the system are discussed, and by using the stochastic geometry approach and the approximate scaling method, the general and lower bound explicit expressions of the coverage probabilities are derived. Numerical results show that the coverage performance of PS-based systems is superior to that of TS-based systems. Moreover, although the linear EH model yields better results than the nonlinear one, as the linear EH model is too ideal, its yielded results may mismatch practical EH circuits, and the ones yielded by the nonlinear EH model is much closer to practice, as the nonlinear EH model is based on real data measurement. Additionally, the nonlinear EH model has a relatively small effect on the harvested energy coverage probability, and the linear EH model introduces greater bias for the TS-based system than that for PS-based one.

Unmanned aerial vehicles (UAVs) with huge-capacity batteries could be employed to wirelessly charge the ground sensor users (GSUs) and enhance the coverage of aerial wireless networks in outdoor Internet of Things (IoT). This paper investigates the information and energy coverage of UAV-enabled simultaneous wireless information and power transfer (SWIPT) networks. Both power splitting (PS) and time switching (TS) receiver architectures are considered. By using stochastic geometry approach, the general and explicit expressions of the information coverage probability (ICP), the energy coverage probability (ECP) and the joint information and energy coverage probability (JIECP) are derived under the nonlinear and linear energy harvesting (EH) models, respectively. Particularly, the Laplace transform and the probability generating functional (PGFL) are used to derive the ICP. And, Campbell’s theorem and the maximum function are applied to obtain the ECP and the JIECP, respectively. To achieve the optimal UAVs’ deployment density, the maximization optimization problems are formulated for the PS-based and TS-based systems, respectively. By using the series expansion of$Q(x)$($Q$-function) with large$x$, the closed-form approximating optimal solutions to the formulated problems are obtained. Monte Carlo simulations validate the correction of our obtained theoretical results, and numerical results show that the performance of the PS-based system is superior to that of the TS-based one. Moreover, when the energy requirement of GSUs or the transmit power of UAVs is relatively large, or when the information requirement of GSUs or the UAV deployment density is relatively small, compared with the nonlinear EH model, the analysis bias caused by traditional linear EH model is relatively large and in these cases, traditional linear EH model cannot be used to replace the nonlinear EH one for the system performance analysis or optimal system design.

In symbiotic radio (SR), a secondary transmitter (STx) transmits messages by modulating its information over the radio frequency (RF) signals received from a primary transmitter (PTx), and in return, the secondary transmission provides multipath gain to the primary transmission. In this paper, we are interested in the fundamental mutualistic mechanism between the primary and secondary transmissions, which describes the condition through which the two systems can benefit each other. Since the symbol period ratio$K$between secondary and primary transmissions is an important system parameter that affects the mutualistic symbiosis, we first derive the theoretical performance in terms of bit error rate (BER) for both primary and secondary transmissions for arbitrary$K$by using QPSK modulation scheme at the PTx and BPSK modulation scheme at the STx as an example setup. Then we the obtain closed-form expressions for the condition on$K$to enable mutualistic symbiosis in SR, which is not related to the specific channel realizations but determined by the average strengths of the direct and backscatter links when the number of receiving antennas is large. Meanwhile, we analyze the average BER performance and the diversity orders for both transmissions in the high signal-to-noise-ratio (SNR) regime. Extensive simulations and numerical results are provided to verify the accuracy of our theoretical analysis and demonstrate the interrelationship between the primary and secondary transmissions.

In symbiotic radio (SR), also called cognitive backscatter communications, a secondary transmitter (STx) transmits messages by modulating its information over the RF signals from a primary transmitter (PTx), and in return, the secondary transmission provides multipath gain instead of interference to the primary transmission when the spreading factor$K$of SR is large enough. In this paper, we are interested in the fundamental mutualistic mechanism between the primary and secondary transmissions in SR, which describes the condition through which the two systems can benefit each other. We first derive the closed-form expressions for the bit error rates (BERs) for both primary and secondary transmissions for general$K$, then obtain the condition on$K$to enable mutualistic symbiosis in SR. It is observed that the critical point of$K$is related to the average strengths of the direct and backscatter links when the number of receiving antennas is large. Extensive simulation and numerical results are provided to verify the accuracy of theoretical analysis and demonstrate the interrelationship between primary and secondary transmissions.

In this letter, we study the interacting effects of the exclusion zone and eavesdropper colluding strategy on the secrecy performance of multiple-antenna transmission system. In particular, a base station (BS) applies random beamforming and user scheduling to enhance the legitimate user channel while multiple eavesdroppers try, either individually or jointly, to overhear the transmitted signal. We derive the closed-form expressions of secrecy outage probability (SOP) of the system with and without exclusion zone under different colluding strategies. Through selected numerical examples, we develop the design guideline on the size of the exclusion zone for a target security level subject to eavesdroppers' density and colluding strategy.

This paper presents and analyzes a novel multiuser network based on hybrid free-space optical (FSO)/radiofrequency (RF) transmission system, where every user is serviced by a primary FSO link. When more than one FSO link fail, the central node services these corresponding users of non-equal priority by using a common backup RF link according to a p persistence servicing protocol. A novel discrete-time Markov chain model is developed for the proposed network, where different transmission rates over RF and FSO links are assumed. We investigate the throughput from central node to the user, the average size of the transmit buffer allocated for every user, the frame queuing delay in the transmit buffer, the efficiency of the queuing system, the frame loss probability, and the RF link utilization. Numerical examples show that transmitting a data frame with probability p when using the common backup RF link achieves considerable network performance improvement while ensuring high-priority users enjoy better performance. Meanwhile, the performance of low-priority users approaches the performance when using equal priority protocol to serve all the remote users.

Ambient radio frequency (RF) energy harvesting is widely promoted as an enabler for self-powered wireless networks. This paper jointly characterizes the harvested energy and the packet transmission success probability in grant-free uplink IoT networks energized via harvesting downlink energy. To do that, a joint queueing theory and stochastic geometry model is exploited and a spatiotemporal analytical model is developed accordingly. Particularly, the harvested energy and packet transmission success probability are characterized using tools from stochastic geometry. Moreover, each device is modeled using a two-dimensional discrete-time Markov chain (DTMC) to track the time evolution of the joint states of the scavenged energy and the data buffer. Consequently, the adopted queueing model represents the devices as spatially interacting queues. To that end, the network performance is assessed in light of the packet throughput, the average waiting time, and the average buffer size which offer valuable insights for network design.

With adaptive transmission, the transmission rate and/or power are adaptively adjusted according to the channel realization, which leads to a variable amount of energy consumption for the transmission of the same amount of data. We propose an analytical framework to statistically characterize the transmitter energy consumption of adaptive transmission over fading channels. For slow fading scenario, we derive the probability density function (PDF) and cumulative distribution function (CDF) of energy consumption assuming continuous-time Markov channel model. For the fast fading case, we apply the statistical mixture model to obtain the approximate PDF of energy consumption. Selected numerical results are presented to illustrate and to validate the mathematical formulations.

Random unitary beamforming (RUB) can reduce the implementation complexity of massive multiple- input singleoutput (MIMO) downlink transmission by only requiring partial channel state information (CSI) at the transmitter. In this paper, we investigate the secrecy performance of a single- cell massive MIMO system with RUB in the presence of multiple noncolluding eavesdroppers. Specifically, we derive the closed-form expressions of the secrecy outage probability (SOP) for a massive MIMO transmission and its single legitimate user case. Numerical results are presented to illustrate the performance-complexity tradeoff among RUB based, zero-forcing (ZF) beamforming based, and maximum ratio transmission (MRT) based massive MIMO transmission schemes. We show that RUB based scheme can enhance secrecy performance of massive MIMO transmission with lower implementation complexity.

Conventional beamforming transmission techniques can enhance physical layer secrecy performance while requiring the full channel state information (CSI) of legitimate users and even that of eavesdroppers at the transmitter. However, providing full CSI of legitimate users at the transmitter can be challenging in practice. Thus, it is of considerable interest to enhance secrecy performance with partial CSI of legitimate users at the transmitter. Random unitary beamforming (RUB) is a low‐complexity multiple antennas transmission scheme requiring limited CSI. In this study, the authors investigate the secrecy performance of RUB transmission over multiple‐input single‐output single‐eavesdropper and multiuser multiple‐input multiple‐output single‐eavesdropper channels. They also propose a novel RUB‐based artificial noise (AN) method for multiple antennas communication system. They derive the closed‐form expressions of the exact and the asymptotic ergodic secrecy rate and the secrecy outage probability for these transmission scenarios. Numerical results are presented to illustrate the trade‐off between performance and complexity of the resulting physical layer security design. They show that the deployment of RUB and RUB‐based AN offers an attractive solution for enhancing the security of wireless transmission systems.

The authors study the optimal design of simultaneous wireless information and power transfer relaying in bidirectional non‐regenerative relay networks. They consider both power splitting relaying and time switching relaying. Since there are two opposite traffic flows between two sources, they characterise the transmission rate performance by the minimum rate of two opposite traffic flows. Specifically, they first obtain closed‐form expressions for the optimum power splitting and time switching coefficients to maximise the minimum transmission rate of bidirectional non‐regenerative relaying. They also derive the resulting maximum transmission rate expressions. Furthermore, they consider a minimum input radio frequency (RF) power level to turn on diodes, and derive the turn‐on probability of the RF energy harvesting circuit when two channels experience independent Rayleigh fading. Numerical results confirm that the authors' analyses exactly match with simulation results and that the two relaying strategies with optimum coefficients give almost the same transmission rate performance.

In one of the several manifestations, the future cellular networks are required to accommodate a massive number of devices, several orders of magnitude compared to today's networks. At the same time, the future cellular networks will have to fulfill stringent latency constraints. To that end, one problem that is posed as a potential showstopper is extreme congestion for requesting uplink scheduling over the physical random access channel (PRACH). Indeed, such congestion drags along scheduling delay problems. In this paper, the use of self-organized device-to-device (D2D) clustering is advocated for mitigating PRACH congestion. To this end, this paper proposes two D2D clustering schemes, namely, random-based clustering and channel-gain-based clustering. Accordingly, this paper sheds light on random access within the proposed D2D clustering schemes and presents a case study based on a stochastic geometry framework. For the sake of objective evaluation, the D2D clustering is benchmarked by the conventional scheduling request procedure. Accordingly, this paper offers insights into useful scenarios that minimize the scheduling delay for each clustering scheme. Finally, this paper discusses the implementation algorithm and some potential implementation issues and remedies.

We study the optimum design of an energy harvesting relay for two-way decode-and-forward (DF) relay networks. In the networks, the relay harvests energy as well as decodes information using the received signal from two sources with power splitting relaying (PSR) and time switching relaying (TSR) strategies. Since the two-way relay network has two opposite traffic flows, it can be considered as a special case of multi-user systems. Applying the max-min criterion for fairness and max-sum criterion for maximum resource utilization, we optimize the operations of the energy harvesting relay. Specifically, considering the transmission rate constraints of individual hops, we derive optimum power splitting coefficients and optimum time switching coefficients, respectively, for PSR-based and TSR-based networks under both criterions, and analytically calculate the resulting maximum transmission rates. Numerical results confirm that our analyses exactly match with exhaustive search simulations. The obtained optimum coefficients are given in closed-form, therefore, they can be easily adopted in simple two-way relay networks with limited computational power such as sensor/Internet of Things (IoT) networks and can help two-way DF relay networks.

Cognitive radio (CR) systems can improve radio spectrum utilization by allowing secondary access of underutilized spectrum resources. With interweave cognitive implementation, secondary users have to wait for spectrum opportunities before their transmission. Therefore, the total delivery time of secondary transmission consists of both waiting slots and transmission slots. In this work, we study the resulting extended delivery time (EDT) of secondary transmission for a fixed amount of data over multiple primary channels. In particular, a birth-death process is introduced to model the number of available primary channels, based on which, we derive the distribution function of the EDT for both continuous and periodic sensing cases. We also present selected numerical results to illustrate the mathematical formulation.

Random unitary beamforming (RUB) is a multiple antenna transmission scheme requiring limited channel state information (CSI) with low computational complexity. In this paper, we investigate the security performance of RUB over a multiple-input single-output single-eavesdropper (MISOSE) broadcast channel. We derive the closed-form expressions of ergodic secrecy rate and the secrecy outage probability (SOP) of the resulting design. Meanwhile, the effect of artificial noise (AN) on physical layer (PHY) security performance of RUB-based MISOSE transmission is also investigated. Numerical results are presented to illustrate the tradeoff between performance and complexity of the proposed PHY security design. We show that the deployment of RUB offers an attractive solution for enhancing the security of wireless transmission systems.

Radio frequency (RF) energy harvesting provides wireless sensors with permanent and convenient energy supply. In this paper, we study the statistics of harvested RF energy of secondary wireless sensor over quasi-static fading channels. We also investigate the performance of secondary sensor transmission with harvested RF energy. Specifically, assuming that the sensor uses all the harvested RF energy for transmission, we derive the exact statistics of received signal-to-noise ratio (SNR) over Nakagami fading channel. We also investigate the statistics of received SNR under a primary interference constraint. The statistics are applied to performance evaluation in term of outage probability and average error rate. Selected numerical results are presented to illustrate the mathematical formulation.

In cognitive radio communication system, unlicensed secondary user (SU) can opportunistically transmit over underutilized primary user's (PU) spectrum. With interweave implementation, SU performs spectrum sensing on the target frequency band to explore transmission opportunity. Sensing errors can greatly affect the performance of secondary transmission. In this paper, we propose a seven-state discrete-time Markov model to characterize slotted secondary transmission process with imperfect spectrum sensing. A two-dimensional Markov model is also developed to study the queueing performance of slotted secondary transmission with adaptive modulation and coding. We show that false alarm has significant effect on the secondary throughput, whereas miss detection only notably reduces the secondary throughput when the traffic intensity is low.

This paper considers the problem of reducing the broadcast decoding delay of wireless networks using instantly decodable network coding- based device-to-device communications. In contrast with the previous works that assume a fully connected network, this paper investigates a partially connected configuration in which multiple devices are allowed to transmit simultaneously. To that end, different events occurring at each device are identified so as to derive an expression for the probability distribution of the decoding delay. Afterward, the joint optimization problem over the set of transmitting devices and packet combination of each is formulated. The optimal solution of the joint optimization problem is derived using a graph-theoretic approach by introducing the cooperation graph in which each vertex represents a transmitting device with a weight translating its contribution to the network. This paper solves the problem by reformulating it as a maximum weight clique problem which can efficiently be solved. Numerical results suggest that the proposed solution outperforms state-of-the-art schemes and provides significant gain, especially for poorly connected networks.

The Internet-of-Things (IoT) is the paradigm where anything will be connected. There are two main approaches to handle the surge in uplink (UL) traffic that the IoT is expected to generate, namely, scheduled UL (SC-UL) and random access uplink (RA-UL) transmissions. SC-UL is perceived as a viable tool to control quality-of-service levels while entailing some overhead in the scheduling request prior to any UL transmission. On the other hand, RA-UL is a simple single-phase transmission strategy. While this obviously eliminates scheduling overheads, very little is known about the scalability of RA-UL. At this critical junction, there is a dire need to analyze the scalability of these two paradigms. To that end, this paper develops a spatiotemporal mathematical framework to analyze and assess the performance of SC-UL and RA-UL. The developed paradigm jointly utilizes stochastic geometry and queuing theory. Based on such a framework, we show that the answer to the scheduling versus random access paradox actually depends on the operational scenario. Particularly, the RA-UL scheme offers low access delays but suffers from limited scalability, i.e., cannot support a large number of IoT devices. On the other hand, SC-UL transmission is better suited for higher device intensities and traffic rates.

In this paper, we investigate the transmission time of a large amount of data over fading wireless channel with adaptive modulation and coding (AMC). Unlike traditional transmission systems, where the transmission time of a fixed amount of data is typically regarded as a constant, the transmission time with AMC becomes a random variable, as the transmission rate varies with the fading channel condition. To facilitate the design and optimization of wireless transmission schemes for big data applications, we present an analytical framework to determine statistical characterizations for the transmission time of big data with AMC. In particular, we derive the exact statistics of transmission time over block fading channels. The probability mass function and the cumulative distribution function of transmission time are obtained for both slow and fast fading scenarios. We further extend our analysis to the Markov channel, where transmission time becomes the sum of a sequence of exponentially distributed time slots. Analytical expression for the probability density function of transmission time is derived for both fast fading and slow fading scenarios. These analytical results are essential to the optimal design and the performance analysis of future wireless transmission systems for big data applications.

This paper presents and analyzes a point-to-multi-point (P2MP) network that uses a number of free-space optical (FSO) links for data transmission from the central node to the different remote nodes. A common backup radio-frequency (RF) link is used by the central node for data transmission to any remote node in case of the failure of any one of FSO links. We develop a cross-layer Markov chain model to study the throughput from central node to a tagged remote node. Numerical examples are presented to compare the performance of the proposed P2MP hybrid FSO/RF network with that of a P2MP FSO-only network and show that the P2MP Hybrid FSO/RF network achieves considerable performance improvement over the P2MP FSO-only network.

Cognitive radio communications can opportunistically access underutilized spectrum for emerging wireless applications. With interweave cognitive implementation, secondary user transmits only if primary user does not occupy the channel and waits for transmission otherwise. Therefore, secondary packet transmission involves both transmission time and waiting time. The resulting extended delivery time (EDT) is critical to the throughput analysis of secondary system. In this paper, we study the EDT of secondary packet transmission with adaptive modulation under interweave implementation to facilitate the delay and throughput analysis of such cognitive radio system. In particular, we propose an analytical framework to derive the probability density functions of EDT considering random-length transmission and waiting slots. We also present selected numerical results to illustrate the mathematical formulations and to verify our analytical approach.

In this paper, we investigate the statistics of packet transmission time of wireless transmission systems employing adaptive modulation. Unlike traditional transmission systems, where the transmission time of a fixed-size packet is typically regarded as a constant, the transmission time of adaptive modulation systems depends on the channel realization as the transmission rate varies with the fading channel conditions. In this paper, we derive the exact statistical distribution of packet transmission time for adaptive modulation systems over block fading channels. The exact expressions of the probability mass function (PMF) and cumulative distribution function (CDF) of packet transmission time are obtained for both slow and fast fading scenarios. We further present an approximate PMF for fast fading scenario to reduce the computation complexity. Selected numerical results are presented to illustrate the mathematical formulation.

Massive multiple‐input multiple‐output (MIMO) systems bring manifold improvements in the system spectral efficiency but result in high hardware and processing complexity at the base station. Employing hybrid precoding at the base station can reduce such complexity. In this study, unlike most existing work on hybrid precoding design, the authors consider a sub‐connected analogue combining structure to reduce the complexity. Starting from an important observation on the effect of sequentially designed analogue phased arrays on users' sum rate, the authors develop three low‐complexity hybrid precoding schemes for a multi‐user massive MIMO system. The proposed schemes apply equal gain transmission (EGT) based analogue beamforming to reap the diversity benefit of an analogue phased array and employ zero‐forcing (ZF) beamforming for nullifying inter‐user interference. The authors carry out an extensive computational complexity analysis and simulation study on the proposed schemes. The proposed singular‐value decomposition based EGT scheme outperforms all others but incurs the highest computational burden. On the other hand, the sequential‐EGT scheme is the least computationally intensive scheme but shows the worse performance amongst them.

The high hardware cost associated with multiple antennas at the secondary transmitter of an underlay cognitive radio (CR) can be reduced by antenna selection. This paper analyzes different power adaptive transmit antenna selection (TAS) schemes for an underlay CR, which ensure that the instantaneous interference caused by the secondary transmitter to the primary receiver is below a predetermined level. We consider the optimal continuous power adaptive TAS and present a low-complexity antenna and power level selection scheme, named sequential antenna and power level selection scheme (SAPS), for discrete power adaptation. Exact statistical characterizations of the signal-to-interference plus noise ratio at the secondary receiver are derived for the considered schemes. Based on the newly derived statistics, we prove that the considered schemes achieve the highest diversity order equaling the number of antennas at the secondary transmitter. Further, we also derive a closed-form expression of the ergodic capacity for the underlay CR with SAPS scheme. Finally, we show that the proposed scheme outperforms existing schemes in terms of ergodic capacity.

This paper investigates the optimal resource allocation in wireless powered communication network with user cooperation, where two single-antenna users first harvest energy from the signals transmitted by a multi-antenna hybrid access point (H-AP) and then cooperatively send information to the H-AP using their harvested energy. To explore the system information transmission performance limit, an optimization problem is formulated to maximize the weighted sum-rate (WSR) by jointly optimizing energy beamforming vector, time assignment, and power allocation. Besides, another optimization problem is also formulated to minimize the total transmission time for given amount of data required to be transmitted at the two sources. Because both problems are non-convex, we first transform them to be convex by using proper variable substitutions and then apply semi-definite relaxation to solve them. We theoretically prove that our proposed methods guarantee the global optimum of both problems. Simulation results show that system WSR and transmission time can be significantly enhanced by using energy beamforming and user cooperation. It is observed that when the total amount of information of two users is fixed, with the increase of the information amount of the user relatively farther away from the H-AP, the transmission time of the user cooperation scheme decreases while that of the direct transmission increases. Besides, the effects of user position on the system performances are also discussed, which provides some useful insights.

Cognitive radio transceiver can opportunistically access the underutilized spectrum resource of primary systems for new wireless services. With interweave cognitive implementation, secondary transmission may be interrupted by primary transmission. To facilitate the packet delay analysis of such secondary transmission, we study the extended delivery time of secondary packet transmission. In particular, we derive the exact distribution function of extended delivery time of a fixed-size secondary packet with non-work-preserving strategy, where interrupted packets must be repeated. We also analyze the effect of imperfect periodic sensing, i.e., the secondary user periodically senses the spectrum for availability, with a chance of missing an available channel on a certain sensing attempt. These results complement previous work on work-preserving strategy with perfect sensing. Selected numerical and simulation results are presented for verifying the mathematical formulation.

We present a transmit antenna subset selection scheme for an underlay cognitive system serving multiple secondary receivers. The secondary system employs zero-forcing beamforming to nullify the interference to multiple primary users and eliminate inter-user interference to the secondary users simultaneously. Simulation results show that the proposed scheme achieves near-optimal performance with low computational complexity. Lastly, an optimal power allocation strategy is also introduced to improve the secondary network throughput.

Random unitary beamforming (RUB) achieves multiuser diversity gain over multiple-input multiple-output (MIMO) broadcast channels with channel state information (CSI). In this paper, we optimize RUB schemes in terms of energy efficiency (EE) which is defined as "capacity/power consumption". The key idea of our approach is to derive EE-optimal number of antennas and transmit power based on mathematical analysis. Using simple approximation expression, we derive efficient approach to find global optimum. Simulation results demonstrate that analytical results are accurate.

In this study, the authors investigate the downlink area spectral efficiency (ASE) of infrastructure relay enhanced cellular systems. ASE for cellular systems is defined as the maximum achievable data rate per unit bandwidth per unit area supported by a base station. In relay enhanced systems, ASE can serve as an attractive performance metric by capturing the benefit of the relatively smaller spatial footprint of relay transmission and the resulting lower co‐channel interference. In this study, by applying a moment generating function based approach, the authors first derive the general closed‐form statistics of the total interference from dominant co‐channel cells over Rayleigh fading channels. These interference statistics are readily applied to the calculation of the resulting ASE. The authors also propose a novel in‐cell frequency reuse scheme to further exploit the smaller transmission power of relay stations (RSs). Through selected numerical examples, the authors show that in relay enhanced systems, the cell size, transmission power and RS positions should be properly selected to gain better ASE performance than the conventional systems without relays.

Free-space optical (FSO) communication systems are negatively affected by two physical phenomenon, namely, scintillation due to atmospheric turbulence and pointing errors. To quantify the effect of these two factors on FSO system performance, we need an effective mathematical model for them. In this paper, we propose and study a generalized pointing error model based on the Beckmann distribution. We then derive a generic expression of the asymptotic capacity of FSO systems under the joint impact of turbulence and generalized pointing error impairments. Finally, the asymptotic channel capacity formula is extended to quantify the FSO systems performance with selection and switched-and-stay diversity.

Cognitive radio (CR) technology addresses the problem of spectrum under-utilization. In underlay CR mode, the secondary users are allowed to communicate provided that their transmission is not detrimental to primary user communication. Transmit antenna selection is one of the low-complexity methods to increase the capacity of wireless communication systems. In this article, we propose and analyze the performance benefit of a transmit antenna selection scheme for underlay secondary system that ensures the instantaneous interference caused by the secondary transmitter to the primary receiver is below a predetermined level. Closed-form expressions of the secondary link outage probability, higher order amount of fading, and ergodic capacity are derived for the proposed scheme. Monte-carlo simulations are also carried out to confirm various mathematical results presented in this article.

Free-space optical (FSO) communication systems are negatively affected by two physical phenomenon, namely, scintillation due to atmospheric turbulence and pointing errors. To quantize the effect of these two factors on FSO system performance, we need an effective mathematical model for them. Scintillations are typically modeled by the log-normal and Gamma-Gamma distributions for weak and strong turbulence conditions, respectively. In this paper, we propose and study a generalized pointing error model based on the Beckmann distribution. We then derive the asymptotic ergodic capacity of FSO systems under the joint impact of turbulence and generalized pointing error impairments.

In this paper, we investigate the performance of a green mobile operator collaborating with other traditional mobile operators. Its goal is to minimize its CO2emissions, maximize its profit or achieve or tradeoff between both objectives by offloading its users to neighbor networks and exploiting renewable energies. On the other hand, traditional mobile operators aim to maximize their profits by attracting the maximum number of roamed users. The problem is modeled as a two-level Stackelberg game and its equilibrium is derived. A green mobile operator level that determines how many users per each base station to offload to each neighbor network, and a non-green mobile operator level where operators focus on finding the optimal roaming price. Our simulation results show a significant saving in terms of CO2emissions compared to the non-cooperation case and that roaming decision depends essentially on the availability of renewable energy in base station sites.

RF energy harvesting is a promising potential solution for providing convenient and perpetual energy supply to low-power wireless sensor networks. In this paper, we investigate the performance of overlaid wireless sensor transmission powered by RF energy harvesting from existing wireless system. Specifically, we derive the exact closed-form expression for the distribution function of harvested energy over a certain number of channel coherence time over Rayleigh fading channels with the consideration of hardware limitation, such as energy harvesting sensitivity and harvesting efficiency. We also obtain the exact distribution of the number of coherence time needed for fully charging the sensor. Based on these analytical results, we analyze the average packet delay and packet loss probability of sensor transmission subject to interference from existing system, for delay insensitive traffics and delay sensitive traffics, respectively. Finally, we investigate the optimal design of energy storage capacity of the sensor nodes to minimize the average packet transmission delay for delay insensitive traffics with two candidate transmission strategies.

Receive antenna selection is a low complexity scheme to reap diversity benefits. We analyze the performance of a receive antenna selection scheme in spectrum sharing systems where the antenna that results in highest signal-to-interference plus noise ratio at the secondary receiver is selected to improve the performance of secondary transmission. Exact and asymptotic behaviours of the received SINR are derived for both general and interference limited scenarios over general fading environment. These results are then applied to the outage and average bit error rate analysis when the secondary transmitter changes the transmit power in finite discrete levels to satisfy the instantaneous interference constraint at the primary receiver.

Cognitive radio transceiver can opportunistically access the underutilized spectrum resource of primary systems for new wireless services. With interweave implementation, the secondary transmission may be interrupted by the primary user's transmission. To facilitate the delay analysis of such secondary transmission for fixed-size secondary packets, we study the resulting extended delivery time that includes both transmission time and waiting time. In particular, we derive the exact distribution functions of extended delivery time of secondary transmission for both continuous sensing and periodic sensing cases. Selected numerical and simulation results are presented for illustrating the mathematical formulation. Finally, we consider an M/G/1 queueing set-up at the secondary transmitter and formulate the closed-form expressions for the expected delay with Poisson traffic. The analytical results will greatly facilitate the design of the secondary system for particular target application.

Opportunistic relaying in cooperative communication depends on careful relay selection. However, the traditional centralized method used for opportunistic amplify-and-forward protocols requires precise measurements of channel state information at the destination. In this paper, we adopt the max-min criterion as a relay selection framework for opportunistic amplify-and-forward cooperative communications, which was exhaustively used for the decode-and-forward protocol, and offer an accurate performance analysis based on exact statistics of the local signal-to-noise ratios of the best relay. Furthermore, we evaluate the asymptotical performance and deduce the diversity order of our proposed scheme. Finally, we validate our analysis by showing that performance simulation results coincide with our analytical results over Rayleigh fading channels, and we compare the max-min relay selection with their centralized channel state information-based and partial relay selection counterparts.

Hybrid free space optical (FSO)/ radio frequency (RF) systems have emerged as a promising solution for high data rate wireless back haul.We present and analyze a switching based transmission scheme for hybrid FSO/RF system. Specifically, either FSO or RF link will be active at a certain time instance, with FSO link enjoying a higher priority. Analytical expressions have been obtained for the outage probability, average bit error rate and ergodic capacity for the resulting system. Numerical examples are presented to compare the performance of the hybrid scheme with FSO only scenario.

Cognitive radio transceiver can opportunistically access the underutilized channels of primary systems for new wireless services. The secondary transmission may be interrupted by the primary user's transmission. To facilitate the delay analysis of such secondary packet transmission, we study the resulting extended delivery time for a fixed-size secondary packet that includes both transmission time and waiting time. In particular we derive the exact distribution functions of extended delivery time of secondary transmission for both continuous sensing and periodic sensing cases. Selected numerical results are presented for illustrating the mathematical formulation.

This paper studies the performance of a RUB-based cognitive radio (CR) network, which coexists with a primary network with single primary transmitter (PT) and single primary user (PU). It is assumed that the PU can control the availability of each beam of the secondary base station (SBS) over a feedback link. The PU only needs to feed back to the SBS the index of the usable beams, which lead to the received SINR at the PU larger than a predefined beam selection threshold, and the outage probability of the primary system can be limited to a tolerable level. The SBS then selects one from the usable beams to achieve the largest throughput of the secondary system. We derive the accurate upper bound of the outage probability of the primary system and the exact throughput of the secondary system. Numerical examples show that to avoid the burst increase of the outage probability of the primary system, as well as achieve the maximal throughput of the secondary system, the beam selection threshold should be equal to the outage threshold of the primary system.

We consider in this paper, a spectrum sharing cognitive radio system with a ratio selection scheme; where one out of N independent-and-identically-distributed transmit antennas is selected such that the ratio of the secondary transmitter (ST) to the secondary receiver (SR) channel gain to the interference from the ST to the primary receiver (PR) channel gain is maximized. Although previous works considered perfect, outdated, or partial channel state information at the transmitter, we stress that using such assumptions may lead to a feedback overhead for updating the SR with the ST-PR interference channel estimation. Considering only statistical knowledge of the ST-PR channel gain, we investigate a ratio selection scheme using a mean value (MV)-based power allocation strategy referred to as MV-based scheme. We first provide the exact statistics in terms of probability density function and cumulative distribution function of the secondary channel gain as well as of the interference channel gain. Furthermore, we derive exact cumulative density function of the received signal-to-noise ratio at the SR where the ST uses a power allocation based on instantaneous perfect channel state information (CSI) referred to as CSI-based scheme. These statistics are then used to derive exact closed form expressions of the outage probability, symbol error rate, and ergodic capacity of the secondary system when the interference channel from the primary transmitter (PT) to the SR is ignored. Furthermore, an asymptotical analysis is also carried out for the MV-based scheme as well as for the CSI-based scheme to derive the generalized diversity gain for each. Subsequently, we address the performance analysis based on exact statistics of the combined signal-to-interference-plus-noise ratio at the SR of the more challenging case; when the PT-SR interference channel is considered. Numerical results in a Rayleigh fading environment manifest that the MV-based scheme outperforms the CSI-based scheme provided that a low interference power constraint is deployed, implying that the MV-based scheme is more suitable for practical systems.

Area spectral efficiency (ASE) was introduced as a metric to quantify the spectral utilization efficiency of cellular systems. Unlike other performance metrics, ASE takes into account the spatial property of cellular systems. In this paper, we generalize the concept of ASE to study arbitrary wireless transmissions. Specifically, we introduce the notion of affected area to characterize the spatial property of arbitrary wireless transmissions. Based on the definition of affected area, we define the performance metric, generalized area spectral efficiency (GASE), to quantify the spatial spectral utilization efficiency as well as the greenness of wireless transmissions. After illustrating its evaluation for point-to-point transmission, we analyze the GASE performance of several different transmission scenarios, including dual-hop relay transmission, three-node cooperative relay transmission and underlay cognitive radio transmission. We derive closed-form expressions for the GASE metric of each transmission scenario under Rayleigh fading environment whenever possible. Through mathematical analysis and numerical examples, we show that the GASE metric provides a new perspective on the design and optimization of wireless transmissions, especially on the transmitting power selection. We also show that introducing relay nodes can greatly improve the spatial utilization efficiency of wireless systems. We illustrate that the GASE metric can help optimize the deployment of underlay cognitive radio systems.

In this paper, we propose a novel relaying scheme for packet transmission over fading channels, which improves the spectral efficiency of cooperative diversity systems by utilizing limited feedback from the destination. Our scheme capitalizes on the fact that relaying is only required when direct transmission suffers deep fading. We calculate the packet error rate for the proposed efficient incremental relaying (EIR) scheme with both amplify and forward and decode and forward relaying. We compare the performance of the EIR scheme with the threshold-based incremental relaying (TIR) scheme. It is shown that the efficiency of the TIR scheme is better for lower values of the threshold. However, the efficiency of the TIR scheme for higher values of threshold is outperformed by the EIR. In addition, three new threshold-based adaptive EIR are devised to further improve the efficiency of the EIR scheme. We calculate the packet error rate and the efficiency of these new schemes to provide the analytical insight.

Space time network coding (STNC) is a recently proposed time-division multiple-access (TDMA)-based cooperative relaying scheme for multi-relay wireless systems, which can achieve full diversity order with low transmission delay by taking advantage of the concepts of network coding and distributed space time coding. However, STNC does not fully exploit the benefit of the broadcast nature of wireless channels, since it only allows relays to receive signals from the sources. To explore the potential capacity of STNC-based systems, in this paper, we propose a new cooperative relaying scheme, termed space-time network coding with overhearing relays (STNC-OR), by allowing each relay to collect the signals transmitted from not only the sources but also its previous relays. Then, we derive some explicit expressions for the outage probability and symbol error rate (SER) for STNC-OR with decode-and-forward relaying over independent non-identically distributed (i.n.i.d) Rayleigh fading channels. For comparison, we also derive the explicit expression of the outage probability for STNC. To further improve the performance of STNC-OR, we investigate the effect of relay ordering on the performance of STNC-OR and then present the optimal relay ordering algorithm. Further, a suboptimal relay ordering is also designed to reduce the complexity. Extensive simulation and numerical results are presented finally to validate our theoretical analysis. It is shown that the proposed STNC-OR achieves much lower outage probability and SER than STNC and traditional pure TDMA relaying schemes.

Area spectral efficiency (ASE) was introduced as a metric to quantify the spectral efficiency of cellular systems. Unlike other performance metrics, ASE takes into account the spatial property of cellular wireless system. In this paper, we generalize the ASE metric for arbitrary wireless transmission. Specifically, we introduce the concept of affected area, based on which we evaluate the spectral and power efficiency of three different transmission scenarios, namely single user point-to-point transmission, two-user X channel transmission and two-hop relay transmission. We derive the closed-form expressions of resulting generalized ASE (GASE) metric for each transmission scenario over Rayleigh fading environment. We show through mathematical analysis and numerical examples that there is an optimal choice of transmitting power value in terms of maximizing the area spectrum efficiency.

A closed-form expression of the capture probability of generalized selection combining (GSC) RAKE receivers was introduced in [1]. The idea behind this new performance metric is to quantify how the remaining set of uncombined paths affects the overall performance both in terms of loss in power and increase in interference levels. In this previous work, the assumption was made that the fading is both independent and identically distributed from path to path. However, the average strength of each path is different in reality. In order to derive a closed-form expression of the capture probability over independent and non-identically distributed (i.n.d.) fading channels, we need to derive the joint statistics of ordered non-identical exponential variates. With this motivation in mind, we first provide in this paper some new order statistics results in terms of both moment generating function (MGF) and probability density function (PDF) expressions under an i.n.d. assumption and then derive a new exact closed-form expression for the capture probability GSC RAKE receivers in this more realistic scenario.

Poisson point process has been widely adopted in the analysis of co-channel interference in dense frequency reuse systems. With the decaying power law, the aggregate co-channel interference in Poisson field can be viewed as the output of a shot noise process. In this paper, we first consider the wireless transmission of a single transmitter- receiver pair with a guard zone centered at the receiver. Other interfering transmitters are randomly distributed outside the guard zone according to a spatial Poisson process. We derive the generic closed-form moment generating function (MGF) of the aggregate interference over Rayleigh fading channels. Then we show that the ergodic capacity of wireless transmission in Poisson field over Rayleigh fading channels can be expressed as function of the MGF of the aggregate interference. Through numerical examples, we examine the accuracy of the Gaussian approximation on the aggregate interference in terms of ergodic capacity calculation. Finally we introduce the Matern point process to model the spatial distribution of multiple transmitter-receiver pairs with guard zones centered at respective receivers.

Cognitive radio is a promising technology to improve the spectrum utilization by allowing the unlicensed (secondary) user share a frequency bandwidth with the licensed (primary) owner under the condition that no harmful interference is imposed on the licensee. In this paper, we analyze the spatial spectrum utilization efficiency of underlay cognitive radio transmission. In particular, we apply the performance metric, generalized area spectral efficiency (GASE), to the performance evaluation and design of underlay cognitive radio transmission. Closed-form expressions are given on the ergodic capacity of the primary and secondary user in underlay cognitive radio transmission over Rayleigh fading channels, which are then utilized to evaluate GASE metric. Mathematical analysis and numerical examples show the asymptotic GASE performance of the underlay cognitive radio transmission with respect to the interference constraint on the primary receiver. We show that GASE performance metric provides a new perspective to the design of underlay cognitive radio transmission.

ABSTRACT In this paper, we proposed several antenna selection schemes for cooperative diversity systems with adaptive transmission. The proposed schemes were based on dual‐hop relaying where a relay with multiple‐antenna capabilities at reception and transmission is deployed between the source and the destination nodes. We analyzed the performance of the proposed schemes by quantifying the average spectral efficiency and the outage probability. We also investigated the trade‐off of performance and complexity by comparing the average number of active antennas, path estimations, and signal‐to‐noise ratio comparisons of the different proposed schemes. Copyright © 2011 John Wiley & Sons, Ltd.

ABSTRACT In this paper, we consider the effect of feedback error on the performance of the joint adaptive modulation and diversity combining (AMDC) scheme which was previously studied with an assumption of perfect feedback channels. We quantify the performance of two joint AMDC schemes in the presence of feedback error, in terms of the average spectral efficiency, the average number of combined paths, and the average bit error rate. The benefit of feedback error compensation with adaptive combining is also quantified. Selected numerical examples are presented and discussed to illustrate the effectiveness of the proposed feedback error compensation strategy with adaptive combining. Copyright © 2011 John Wiley & Sons, Ltd.

Multiple input multiple output (MIMO) relay channels has great application potentials in wireless communication systems and therefore attracts both academia and industrial attentions recently. In this paper, we consider the MIMO relay channels where both source node and relay node are equipped with multiple antennas and the destination node has a single antenna. We address the optimal beamforming design when decode-and-forward half-duplex relaying protocol is deployed. Specifically, we develop an efficient algorithm to determine the optimal beamforming vector at the source when transmitting to relay and destination at the same time. Based on the exact channel capacity formulation, the proposed algorithm can achieve arbitrarily high accuracy with low computational complexity.

In this paper, we present and study the performance of a coordinated random beamforming transmission strategy for dual-cell multiple-input single-output (MISO) systems. The strategy under consideration has low complexity as the coordinating base stations need to share only the indices of the qualified beamforming vectors. Focusing on single-user scheduling in each cell, we analyze exact sum-rate of the resulting system. Based on selected numerical examples, we develop important design guidelines for coordinated random beamforming schemes. We also consider an adaptive implementation approach of the proposed strategy where the number of qualified beamforming vectors are determined based on a certain predetermined threshold.

In this paper, we investigate the area spectral efficiency (ASE) in a three-node cooperative network with opportunistic relaying. On one hand, in conventional cellular network, ASE is defined to be the average data rate per unit bandwidth per unit area supported by a base station. On the other hand, in cooperative network, since there is no such a central base station, we redefine ASE to be the average data rate per unit bandwidth within a particular area, in which simultaneous transmissions are not allowed. In addition, to maximize the instantaneous capacity between the source and the destination, we apply a transmission mode selection criterion to determine whether the direct transmission or the multi-hop relay transmission is utilized. We derive the mathematical expression of ASE with the consideration of the relay node location and the impact of path-loss and fading effects. We show through selected numerical examples the effect of relay node position on the performance metric of ASE.

We investigate the performance of a multiuser downlink access scheme based on a post-selection switch and examine algorithm. The studied scheme sequentially switches over the users that experience independent and non-identically distributed fading conditions, and selects a single user with an acceptable channel quality as compared to a pre-selected signal-to-noise ratio (SNR) threshold. If no one of the users can satisfy the target channel quality, the base station (BS) takes the advantage of the knowledge of all users channels and serves the user with the best channel quality among all users. This scheme reduces considerably the feedback load but offers a lower average spectral efficiency (ASE) as compared to that of the full feedback system with instantaneous best user selection. On the other hand, it improves the system performances, such as outage probability and average bit error rate (BER), as compared to a system that is based on a standard switching scheme without post-selection. Numerical results for the ASE average BER, and average feed back load, are presented for the cases of outdated and non-outdated rate-adaptive modulation scheme operating over independent and non-identically distributed users.

A dynamic decode-&-forward (DDF) is redesigned to meet the crucial requirements for type-2 user equipment (UE) relays which are being considered for next-generation cellular standards (e.g., LTE-Advanced). Toward this, the proposed modified DDF (M-DDF) realizes a fast jump-in relaying and sequential decoding where a subframe decoding is employed to yield a combination of energy/information/mixed combining, in conjunction with the random codeset for encoding and re-encoding at source and multiple UE relays, depending on their channel conditions. These additional features existing in the M-DDF circumvent the need of exchanging control messages between multiple relays and end user near cell boundary, which is not allowed for type-2 UE relays. Through comparison among the DDF with single and multiple orthogonal channels and M-DDF, the M-DDF bridges the gap between former relaying protocols with application to type-2 UE relays, offering reliable rate capacity with less channel usage and further improvement, if the early termination of decoding is made available.

In this paper, we investigate a relay enhanced cellular system, where a relay station is located in the overlap area served by two base stations. We propose cooperative joint precoding schemes for the downlink transmission of such relay enhanced cellular system to maximize the system capacity while minimizing the interference at both the relay station and the mobile stations. We formulate the optimization problems to maximize the system capacity and design the multiuser precoding vectors at each base station and the relay station. We quantify the ergodic rate performance of the proposed multiuser precoding schemes through statistical analysis. The extensively derived ergodic expressions will facilitate the accurate performance evaluation of the proposed transmission schemes. Numerical results show that the proposed schemes can effectively cancel the interference and improve the sum rate and the outage performance for cell edge users.

In conventional multiuser parallel scheduling schemes, every scheduled user is interfering with every other scheduled user, which limits the capacity and performance of multiuser systems, and the level of interference becomes substantial as the number of scheduled users increases. Based on the above observations, we investigate the trade-off between the system throughput and the number of scheduled users through the exact analysis of the total average sum rate capacity and the average spectral efficiency. Our analytical results can help the system designer to carefully select the appropriate number of scheduled users to maximize the overall throughput while maintaining an acceptable quality of service under certain channel conditions.

In this paper, we consider a low complexity symbol-wise beamforming for MIMO-OFDM systems. We propose a non-iterative algorithm for the symbol-wise beamforming, which can provide the performance approaching that of the conventional symbol-wise beamforming based on the iterative algorithm. We demonstrate that our proposed scheme can reduce the computational complexity significantly. From our simulation results, it is evident that our proposed scheme leads to a negligible performance loss compared to the conventional symbol-wise beamforming regardless of spatial correlation or presence of co-channel interference.

In this paper, we propose a reduced-complexity beamforming coordination method for the emerging two-tier MIMO-femtocell systems. With a small overhead signaling, the proposed scheme implements the cross-tier interference control between the macrocell and the femtocell. Furthermore, we develop the exact analytical expressions of the ergodic capacity of selected users in both tiers. We show through selected numerical examples that our proposed beamforming coordination achieves significant performance gain over conventional systems while only requiring beam index and an angle information sharing between the two heterogeneous cells.

In this paper, we introduce the notion of a relay enhanced cellular system, where a relay station is located in the overlap area served by two base stations, and propose a cooperative joint precoding scheme for the relay enhanced cellular system. We consider a system in which two base stations apply linear precoding to minimize the interference at the relay station and the mobile stations and formulate the optimization problem to maximize the system capacity and design the multiuser precoding vector for each base station. We quantify the ergodic rate performance of the proposed multiuser precoding scheme through statistical analysis. Numerical results show that the proposed scheme can effectively cancel the interference and improve the sum rate performance for cell edge users.

In this paper, we investigate an opportunistic relaying scheme where the selected relay assists the source-destination (direct) communication. In our study, we consider a regenerative opportunistic relaying scheme in which the direct path may be considered unusable, and the destination may use a selection combining technique. We first derive the exact statistics of each hop, in terms of probability density function (PDF). Then, the PDFs are used to determine accurate closed form expressions for end-to-end outage probability for a transmission rate R. Furthermore, we evaluate the asymptotical performance analysis and the diversity order is deduced. Finally, we validate our analysis by showing that performance simulation results coincide with our analytical results over different network architectures.

Dual-cast transmission appears naturally in network coding-based two-way relay systems, where the relay terminal needs to send network coded information to both end users simultaneously. In this paper, we investigate the optimal beamforming design for wireless dual-cast channels. Specifically, we present an efficient closed-form solution of the optimal beamforming vectors and their achievable maximal dual-cast rate for both orthogonal and nonorthogonal user channel cases. Comparison with conventional non-network-coding based schemes shows that the proposed design of dual-cast beamforming with network coding can best explore the capacity benefit of multiple antennas at the relay terminal.

In this paper, we investigate an opportunistic relaying scheme where the selected relay assists the source-destination (direct) communication. In our study, we consider a regenerative opportunistic relaying scheme in which the direct path can be considered unusable, and takes into account the effect of the possible erroneously detected and transmitted data at the best relay. We first derive the exact statistics of each hop, in terms of probability density function (PDF). Then, the PDFs are used to determine accurate closed form expressions for end-to-end bit-error rate (BER) of binary phase-shift keying (BPSK) modulation where the detector may use maximum ration combining (MRC) or selection combining (SC). Finally, we validate our analysis by showing that performance simulation results coincide with our analytical results over linear network (LN) architecture and considering Rayleigh fading channels.

In this paper, we introduce the notion of a relay enhanced cellular system, where a relay station is located in the overlap area served by two base stations. We propose a cooperative joint precoding scheme in the downlink of the relay enhanced cellular system to maximize the system capacity while eliminating the interference at the mobile stations. We formulate an optimization problem to maximize the system capacity and design the multiuser precoding vectors for each base station and the relay station. We analyze the ergodic rate performance of the proposed multiuser precoding scheme over Nakagami-m fading channels. Numerical results show that the proposed scheme can effectively cancel the interference and improve the sum rate and outage performance for cell edge users.

In this paper, we propose an adaptive beam deactivation scheme for the coordinated multi-cell multiuser multiple-input multiple-output (MU-MIMO) downlink system with limited feedback. In the proposed scheme, each user feeds back the indices of a desired beam and multiple undesired beams from its codebook and some channel quality indicators to its base station (BS). Based on the feedback information and the proposed transmitting user set selection algorithm, the coordinating BSs select one user for each BS to serve. Through the numerical example, we show that the proposed scheme achieves comparable sum rate gain compared to the conventional zeroforcing based coordinated multi-cell system with reduced feedback load.

In this paper, we investigate an incremental opportunistic relaying scheme where the selected relay chooses to cooperate only if the source-destination channel is of an unacceptable quality. In our study, we consider regenerative relaying in which the decision to cooperate is based on a signal-to-noise ratio (SNR) threshold and takes into account the effect of the possible erroneously detected and transmitted data at the best relay. We derive a closed-form expression for the end-to-end bit-error rate (BER) of binary phase-shift keying (BPSK) modulation based on the exact probability density function (PDF) of each hop. Furthermore, we evaluate the asymptotic error performance and the diversity order is deduced. We show that performance simulation results coincide with our analytical results.

Random unitary beamforming (RUB) is an attractive transmission scheme for MIMO broadcast channels because of its ability to achieve high sum-rate capacity with limited feedback. In this letter, we derive the exact analytical expressions for the ergodic sum rate of MIMO broadcast channels with RUB. The analysis is facilitated by the development of the complete statistical characterization of ordered beam SINRs for a user, which can find their application in many related problems.

In this paper, we propose a new amplify-and-forward (AF) cooperative transmission scheme with adaptive modulation to maximize overall system spectral efficiency. We quantify the average spectral efficiency performance of the proposed scheme through statistical analysis based on an upper bound of the combiner output signal-to-noise ratio (SNR) and obtain the closed-form solutions for some practical scenarios of interest.

In this paper, we investigate a dual-hop decode-and-forward opportunistic relaying scheme where the selected relay chooses to cooperate only if the source-destination channel is of an unacceptable quality. We first derive the exact statistics of received signal-to-noise (SNR) over each hop with co-located relays, in terms of probability density function (PDF). Then, the PDFs are used to determine very accurate closed-form expression for the outage probability for a transmission rate R. Furthermore, we perform asymptotic analysis and we deduce the diversity order of the scheme. We validate our analysis by showing that performance simulation results coincide with our analytical results over different network architectures.

In this paper, we present a low-complexity coordinated beamforming transmission scheme for multiuser multiple-input-single-output (MISO) systems. With a minimum overhead signaling, the proposed scheme selects the beamforming vector and users while considering the interference from other cells. We develop the exact analytical expressions of the ergodic sum-rate for the resulting system for dual-cell scenario. Based on the analytical results, we compare the performance of the proposed scheme with other MISO transmission schemes in multiple cell environment, and then analyze their respective superiority and shortcomings. We show through selected numerical examples that our proposed coordinated beamforming scheme achieves tremendous performance gain over conventional schemes while only requiring beam index sharing between base stations.

In this paper, we propose and study a cooperative transmission scheme for amplify-and-forward (AF) relaying system with adaptive modulation. Unlike the conventional incremental relaying with adaptive modulation (IR-AM) scheme, which improves the spectral efficiency with the minimum usage of relaying, our proposed scheme adaptively utilizes cooperative relaying to maximize the system spectral efficiency. We quantify the average spectral efficiency performance of the proposed scheme through statistical analysis and obtain the closed-form solutions for some practical scenarios of interest. Selected numerical results demonstrate that the spectral efficiency gain of the proposed scheme over the IR-AM scheme occurs mainly over the median signal-to-noise ratio range.

In this paper, we present the sum-rate analysis of multiuser multiple-input multiple-output (MIMO) downlink systems with incremental beamforming (IB). We develop the analytical expressions of the ergodic sum-rate for the dual-transmit-antenna scenario. Based on the analytical results, we compare the performance of the proposed IB scheme with popular random beamforming techniques, such as random unitary beamforming (RUB) and conventional random beamforming (CRB), and analyze their respective superiority and shortcomings. We show through selected numerical examples that our approach achieves similar performance as RUB but with much lower feedback load and system complexity. Ultimately, we introduce a modified version of our scheme that adaptively selects a second user for sum-rate benefit.

In multicell wireless systems with insufficient frequency reuse, user transmission will suffer other-cell interference (OCI). Cell cooperation is an effective way to mitigate OCI and increase the system sum rate. An adaptive scheme for serving one user in each cell was proposed in. In this paper, we generalize that scheme by serving more than one user in each cell with adaptive zeroforcing beamforming (ZF) strategies. Based on our derived statistics of the signal-to-noise plus interference ratios, we choose the scheme to maximize the total ergodic sum-rate based on user locations. Through the numerical examples, we show that the total system sum rate can be improved by selecting appropriate transmitting strategy adaptively. As a result, our proposed system can explore spatial multiplexing gain without additional power and thus improves total system sum rate significantly.

Order statistics find applications in various areas of communications and signal processing. In this paper, we introduce an unified analytical framework to determine the joint statistics of partial sums of ordered random variables (RVs). With the proposed approach, we can systematically derive the joint statistics of any partial sums of ordered statistics, in terms of the moment generating function (MGF) and the probability density function (PDF). Our MGF-based approach applies not only when all theKordered RVs are involved but also when only theKs(KsK) best RVs are considered. In addition, we present the closed-form expressions for the exponential RV special case. These results apply to the performance analysis of various wireless communication systems over fading channels.

We propose and analyze two different approaches for performing adaptive modulation and coding (AMC) in dual-hop transmission systems, where a source node S communicates with a certain destination node D via an intermediate decode-and- forwarding relay station R. In this regard, we consider the most general case, where the AMC on the S-R and R-D links might be performed independently of each other, thus requiring a potential buffering of data packets at the relay station before they can be forwarded to the destination D. With our first approach, AMC is performed solely based on the instantaneous channel realizations, without considering the current buffer level at the relay station, what consequently might result in packet losses due to potential buffer overflows. Our second approach eliminates this problem by taking the current buffer level into account in the AMC transmission over the first hop and reducing the transmission rate accordingly if the buffer would overflow otherwise. Both schemes are analyzed analytically based on a finite-state Markov chain model of our system. Building upon this model, we derive analytical closed-form expressions for a variety of different key performance indicators, which are illustrated for various practical cases by means of selected numerical results.

Mobile ad-hoc networks (MANETs) usually contain sparse or even empty regions called holes. The local optimum problem will occur when routing packets meet holes in the network. In this paper, we propose a novel hole-reshaping routing protocol (HRR) in large-scale MANETs. It effectively solves the hole problem by regularizing a hole with an ellipse, and then locally broadcasting the hole information away from the hole. Simulation results show that the proposed protocol guarantees finding a short routing path with a small routing delay, which is a prerequisite to achieve scalability in large-scale networks.

We consider the design and performance analysis of adaptive modulation and coding (AMC) applied to regenerative dual-hop transmission systems, where a source node communicates with a corresponding destination node only indirectly via an intermediate relay station operating in the well-known decode-and-forward mode. Specifically, we consider the general case where the AMC over both hops is performed independently of each other. As such, a buffer is required at the relay station to buffer certain data packets received from the source node before they can be forwarded to the actual destination. The proposed scheme is especially suitable for systems operating in time division duplex (TDD) mode, where channel state information is readily available at the transmitter-side. We analyze the performance of our approach based on a finite-state Markov chain model of our system and we derive exact analytical closed-form expressions for a variety of different performance measures, which are illustrated for various cases by means of selected numerical results.

Joint channel-aware and queue-aware scheduling has been studied widely for direct downlink transmission in cellular networks. In this paper, we combine this cross-layer scheduling concept with opportunistic relaying for slotted multiuser packet transmissions. Cooperative relaying can bring additional degree of freedom, resulting in the system performance improvement in terms of throughput and fairness. Specifically, we propose two scheduling algorithms for selecting the destination user and its assistant user based on the instantaneous channel information and buffer status. Through simulation, we show that the proposed algorithms expand the system stable load region and reduce the average delay while improving the fairness among users with heterogeneous channel conditions compared to conventional schemes.

In this paper, we consider the effect of feedback error on the performance of the joint adaptive modulation and diversity combining (AMDC) scheme which was previously studied with an assumption of perfect feedback channels. In order to compensate for the performance degradation due to feedback error, we propose the path adjustment algorithm for diversity combining. We quantify the performance of the joint AMDC scheme in the presence of feedback error, in terms of the average spectral efficiency, the average number of combined paths, and the average bit error rate. Selected numerical examples are presented and discussed to illustrate the effectiveness of the proposed feedback error compensation strategy with adaptive combining.

We consider the problem of performing adaptive modulation and coding (AMC) in dual-hop transmission systems with regenerative relaying. In particular, we consider a scenario where the AMC on both hops is done independently of each other, thus requiring a potential buffering of data packets at the relay station before they can be forwarded to the actual destination. In this regard, we propose that both the current channel conditions as well as the current buffer filling level are taken into account in the AMC mode selection, so that buffer overflows at the relay station can be completely avoided. We thoroughly analyze our scheme by means of a finite-state Markov model, based on which we derive various different performance measures, such as the average transmission efficiency or the average transmission delay.

In this paper, we propose several relay selection schemes for cooperative diversity systems with adaptive transmission. The proposed schemes are based on dual-hop relaying with multiple relays. We analyze the performance of the proposed schemes by quantifying the average spectral efficiency and the outage probability. We also investigate the tradeoff of performance and complexity among proposed schemes by evaluating the average number of active relays, path estimations, and signal- to-noise ratio comparisons. Our proposed schemes and analysis are also applicable to single relay systems with multiple antennas.

This letter investigates the effect of feedback error on the performance of the joint adaptive modulation and diversity combining (AMDC) scheme which was previously studied with an assumption of error-free feedback channels. We also propose to utilize adaptive diversity to compensate for the performance degradation due to feedback error. We accurately quantify the performance of the joint AMDC scheme in the presence of feedback error, in terms of the average number of combined paths, the average spectral efficiency, and the average bit error rate. Selected numerical examples are presented and discussed to illustrate the effectiveness of the proposed feedback error compensation strategy with adaptive combining. It is observed that the proposed compensation strategy can offer considerable error performance improvement with little loss in processing power and spectral efficiency in comparison with the no compensation case.

In this letter, we present the exact sum-rate analysis of the multiuser multiple-input multiple-output (MIMO) systems with zero-forcing transmit beamforming (ZFBF). We develop the analytical expressions of the ergodic sum-rate for two low-complexity user selection strategies for the dual-transmit-antenna scenario. Based on the analytical results, we examine the parameter optimization problem to properly trade off between channel power gain and directional gain in term of maximizing the ergodic sum rate.

In this paper, we propose two new threshold based parallel multiuser scheduling schemes, namely (i) an on-off based scheduling (OOBS) scheme and (ii) a switched based scheduling (SBS) scheme. The objective is to reduce the complexity of implementation without a considerable performance loss in comparison with conventional selection based scheduling. While the OOBS scheme schedules all the users with an SNR above a fixed preselected signal to noise ratio (SNR) threshold, the SBS scheme schedules only the Ksusers with an acceptable SNR if there are enough acceptable users. Otherwise, the scheduler selects the best Ksusers. We analyze statistical characteristics and performances of these proposed schemes. Numerical results show that the proposed schemes can offer some decrease in the average feedback load without an important degradation in average bit error rate and average spectral efficiency.

In this paper, we propose threshold-based power allocation algorithms for a recently proposed down-link parallel multiuser scheduling (SBS) scheme. The proposed algorithms re-allocate the extracted excess transmit power from some acceptable users to those unacceptable users among scheduled users. After the power allocation process, more unacceptable users will enjoy acceptable link reliability as the number of effective acceptable users with an acceptable receive SNR level among the scheduled users is increased without any additional down-link transmit power. Some selected numerical results, show that the proposed power allocation algorithms offer a certain improvement in average spectral efficiency (ASE) and an increase in the average number of effective acceptable users. Although the average bit error rate (BER) performance degrades, especially when the average SNR is close to the SNR threshold, this average BER performance still meets the average BER requirement.

Random unitary beamforming (RUB) is an attractive low-complexity transmission scheme for multiuser MIMO broadcast channel. When there are a moderate number of users in the system, the sum rate performance of this signaling scheme becomes mainly interference-limited over high signal-to-noise ratio (SNR) region. In this paper, we study the performance of RUB-based multiuser MIMO systems when optimum combining is employed at mulitple-antenna mobile receivers to suppress multiuser interference. We adopt a geometric approach to derive the statistics of the output signal-to-interference ratio (SIR) of the optimum combiner, based on which a sum rate upper bound is obtained over high SNR region. We show through selected numerical examples that the proposed RUB with optimal combining achieves much better sum rate performance while maintaining low feedback load.

In this paper, we study the asymptotic performance of absolute-threshold and normalized-threshold- based generalized selection combining (AT-GSC and NT-GSC) schemes over generalized fading channels for high average signal-to-noise ratio (ASNR). By evaluating the asymptotic moment generating function (MGF) of the threshold-based GSC (T-GSC) output SNRs, we derive the diversity and combining gains for AT- and NT-GSCs with a large class of modulation formats and versatile fading conditions, including different types of fading channels and non-identical SNR statistics across diversity branches. Our analytical results reveal that the diversity gains of AT- and NT-GSC are equivalent to that of maximum ratio combining (MRC), and the differences in the combining gains for different threshold values, and modulation and diversity formats, are derived using the concept of the modulation factor.

In this paper, we present the exact sum-rate analysis of the multiuser multiple-input multiple-output (MIMO) broadcast channel with zero-forcing transmit beamforming. We develop the analytical expressions of the ergodic sum-rate for two low-complexity user selection strategies for the important dual- transmit-antenna scenario. Based on the analytical results, we examine the parameter optimization problem to properly trade off between channel power gain and directional gain in term of maximizing the ergodic sum rate offered by multiuser diversity.

There is a continuing interest in low-complexity multiuser MIMO transmission techniques based on random unitary beamforming (RUB). Different RUB schemes mandate different amount of feedback to exploit the multiuser diversity gain for sum-rate capacity benefits. In this paper, we investigate the tradeoff of sum-rate capacity versus feedback load between different RUB schemes through accurate statistical analysis. Specifically, we derive the exact sum-rate expressions for two RUB schemes based on quantized signal-to-interference-plus- noise ratio (SINR) feedback. These analysis are accompanied by the development of the complete statistical characterizations of ordered SINRs for a user, which can find their application in many other related problems. We show through selected numerical examples that the additional feedback of the quantized values of best beam SINR from each user can help considerably improve the sum-rate performance of RUB systems.

This paper investigates the effect of feedback error on the performance of the joint adaptive modulation and diversity combining (AMDC) scheme which was previously studied with an assumption of error-free feedback channels. We also propose to utilize adaptive diversity to compensate for the performance degradation due to feedback error. We accurately quantify the performance of the joint AMDC scheme in the presence of feedback error, in terms of the average number of combined paths, the average spectral efficiency, and the average bit error rate. Selected numerical examples are presented and discussed to illustrate the effectiveness of the proposed feedback error compensation strategy with adaptive combining. It is observed that the proposed compensation strategy can offer considerable error performance improvement with little loss in processing power and spectral efficiency in comparison with the no compensation case.

A new user scheduling strategy is proposed for multiuser MIMO system with random unitary beamforming (RUB) in this paper. This strategy imposes a threshold on the signal to interference and noise ratio (SINR) of mobile users to reduce the feedback load. The basestation only uses those beams that are requested by feedback users. The exact analytical expression of the sum rate of proposed strategy is developed, based on which the threshold is optimized to maximize the sum rate. With optimal thresholds, we demonstrate through numerical examples that the proposed strategy achieve a better sum-rate performance than existing scheduling strategies over high SNR region.

In this paper, we present the exact sum-rate analysis of the multiuser MIMO system with random unitary beamforming (RUB). Specifically, with the derived statistics of ordered beam signal to interference and noise ratio, we obtain the analytical expression of system sum rate for arbitrary number of users. The effects of system parameters, including the number of users, the number of transmit antennas and the signal to noise ratio (SNR), on the sum rate are examined through numerical methods. Besides, we develop an upper bound for the sum rate, which reveals that the sum rate with RUB benefits mainly from multiuser directional diversity gain when SNR is high.

In this paper, we introduce a new zero-forcing beamforming (ZFBF) transmission scheme for multi-user MIMO Gaussian channel with finite rate feedback. With this transmission scheme, the base station adaptively utilizes transmit antennas according to the channel status and the number of active users to control the multiuser interference. We show through selected numerical results that our proposed scheme can achieve remarkable sum-rate improvement compared to other schemes with fixed transmit antennas.

We propose and analyze in this paper a new finger assignment technique that is applicable for RAKE receivers when they operate in the soft handover (SHO) region. This scheme employs a new version of generalized selection combining (GSC). More specifically, in the SHO region, the receiver uses by default only the strongest paths from the serving base station (BS) and only when the combined signal-to-noise ratio (SNR) falls below a certain pre-determined threshold, the receiver uses more resolvable paths from the target BS to improve the performance. Hence, relying on some recent results on order statistics we attack the statistics of two correlated GSC stages and provide the approximate but accurate closed-form expressions for the statistics of the output SNR. By investigating the tradeoff among the error performance, the path estimation load, and the SHO overhead, we show through numerical examples that the new scheme offers commensurate performance in comparison with more complicated GSC-based diversity systems while requiring a smaller estimation load and SHO overhead.

We propose and analyze new finger assignment techniques that are applicable for RAKE receivers in the soft handover (SHO) region. Specifically, extending the results for the case of two-base station (BS), we consider the multi-BS situation, attack the statistics of several correlated generalized selection combining (GSC) stages, and provide closed-form expressions for the statistics of the output signal-to-noise ratio (SNR). By investigating the tradeoff among the error performance, the average number of required path estimations/comparisons, and the SHO overhead, we show through numerical examples that the new schemes offer commensurate performance in comparison with more complicated GSC-based diversity systems while requiring a smaller estimation load and SHO overhead.

We propose and analyze a new finger replacement technique that is applicable for RAKE receivers in the soft handover (SHO) region. More specifically, the receiver uses in the SHO region by default the strongest paths from the serving base station (BS) and only when the combined signal-to-noise ratio falls below a certain pre-determined threshold, the receiver uses more resolvable paths from the target BS to improve the performance. Instead of changing the configuration for all fingers, the receiver just compares the sum of the weakest paths out of the currently connected paths from the serving BS with the sum of the strongest paths from the target BS and selects the better group. Using accurate statistical analysis, we investigate in this letter the tradeoff between error performance, average number of required path comparisons, and SHO overhead offered by this newly proposed scheme.

Generalized switch and examine combining (GSEC) was recently proposed as a low-complexity diversity combining scheme for diversity-rich environment. In this paper, we present and analyze a modified version of GSEC scheme, termed as GSEC with post-examine selection (GSECps). The GSECps scheme operates in the same way as GSEC when channel conditions are favorable and becomes equivalent to the generalized selection combining (GSC) scheme otherwise. We show, through a thorough and accurate tradeoff analysis of performance versus complexity, that GSECps can deliver a better performance-complexity tradeoff than both GSEC and GSC schemes.

Adaptive diversity combining techniques aim to provide the desired performance by adaptively utilizing the resources of wireless communication systems. These schemes offers different tradeoffs between performance and power consumption. In this paper we present a new adaptive combining scheme that takes advantage of the existing combiner structure and transits directly to the appropriate combining mode for subsequent data reception. We carry out a thorough performance and complexity analysis on the proposed scheme based on a properly developed Markov model. Through numerical examples, we show the proposed scheme offers a better tradeoff of performance versus complexity than conventional OT-MRC.

We propose and analyze new finger replacement techniques for RAKE reception in the soft handover (SHO) region with multiple base stations. The proposed schemes are basically based on the block comparison among groups of resolvable paths and lead to the reduction of complexity while offering commensurate performance in comparison with previously proposed schemes. Relying on the newly derived analytical expressions, we investigate not only the complexity in terms of the average number of required path estimations/comparisons and the SHO overhead but also the error performance of the proposed scheme over independent and identically distributed fading channels.

In this paper, we propose two new threshold based parallel multiuser scheduling schemes, namely (i) an on-off based scheduling (OOBS) scheme and (ii) a switched based scheduling (SBS) scheme. The objective is to reduce the complexity of implementation without a considerable performance loss in comparison with selection based scheduling. While the OOBS scheme schedules all the users with an SNR above a fixed preselected signal to noise ratio (SNR) threshold, the SBS scheme schedules only the Ks users with an acceptable SNR if there are enough acceptable users. Otherwise, the scheduler selects the best Ks users. We analyze statistical characteristics and performances of these proposed schemes. Numerical results show that the proposed schemes can offer some decrease in the average number of feedback load without an important degradation in average bit error rate and average spectral efficiency.

The authors propose and analyze new finger assignment techniques that are applicable for rake receivers in the soft handover (SHO) region. More specifically, in the SHO region, the receiver uses by default only the strongest paths from the serving base station (BS) and only when the combined signal-to-noise ratio (SNR) falls below a certain pre-determined threshold, the receiver uses more resolvable paths from the target BSs to improve the performance. Relying on the previous results for the case of two-BS case, the authors consider the multi-BS situation by attacking the statistics of several correlated generalized selection combining (GSC) stages and provide closed-form expressions for the statistics of the output SNR. By investigating the tradeoff among the error performance, the path estimation load, and the SHO overhead, the authors show through numerical examples that the new schemes offer commensurate performance in comparison with more complicated GSC-based diversity systems while requiring a smaller estimation load and SHO overhead.

We consider the problem of finding low-complexity, bandwidth-efficient, and processing-power efficient transmission schemes for a downlink scenario under the framework of diversity combining. Capitalizing on recent results for joint adaptive modulation and diversity combining schemes (AMDC), we design and analyze two AMDC schemes that utilize power control to reduce the radiated power, and thus the potential interference to other systems/users. Based on knowledge of the channel fading, the proposed schemes adaptively select the signal constellation, diversity combiner structure, and transmit power level. We show that the novel schemes also provide significant average transmit power gains compared to existing joint adaptive QAM and diversity schemes. In particular, over a large signal to noise ratio range, the transmitted power is reduced by 30-50%, yielding a substantial decrease in interference to co-existing systems/users, while maintaining high average spectral efficiency, low combining complexity, and compliance with bit error rate constraints.

Both adaptive modulation and diversity combining represent important enabling techniques for future generations of wireless communication systems. In this paper, capitalizing on recent developments in adaptive combining, we propose three joint adaptive modulation and diversity combining (AMDC) schemes. With these schemes, the modulation mode and diversity combiner structure are adaptively determined based on the fading channel condition and error-rate requirement. We accurately analyze these three AMDC schemes in terms of processing power consumption, spectral efficiency, and error-rate performance. Selected numerical examples show that the proposed AMDC systems meet the target error-rate requirement while achieving high spectral efficiency with low processing power consumption

This paper introduces and analyzes a new adaptive minimum-estimation minimum-combining switched-combining based scheme that reduces considerably the average receiver channel estimation complexity and the power drain from the battery while satisfying a certain desired performance requirement. The mathematical formalism is supported by some selected numerical examples that show that the newly proposed combining scheme can essentially achieve the same performance as competing schemes such as generalized selection combining (GSC) while offering 50 % channel estimation and 75 % processing power savings for some system parameters of interest

In this paper, we propose a combined adaptive modulation transmission and output threshold MRC diversity reception scheme for high spectral and power efficiency wireless transceiver design. The modulation constellation size and the number of combined diversity paths are jointly determined to achieve the highest spectral efficiency but with low combining complexity, given the fading channel conditions and the required error rate performance. We derive the statistics of the resulting output signal-to-noise ratio (SNR) and then use it to analyze the proposed system (i) performance in terms of outage probability and average bit error rate, (ii) complexity in terms of the average number of path estimation and the average number of combined paths, and (iii) spectral efficiency. Some selected numerical examples are finally presented and discussed to illustrate the tradeoff offered by this scheme.

Generalized selection combining (GSC) is one of the most widely investigated low-complexity diversity techniques. Recently, output-threshold GSC (OT-GSC) was proposed as a power-saving variant of traditional GSC scheme. In this paper, we present an exact performance analysis of OT-GSC over Rayleigh fading channels. In particular, we derive the cumulative distribution function (CDF), probability density function (PDF) and moment generation function (MGF) of the combined SNR with OT-GSC. Then, we apply these results to study the outage probability and average error rate performance of OT-GSC. This analysis allows for a thorough and accurate comparison of OT-GSC with other variants of GSC, such as minimum selection GSC.

Global flooding and expanding ring search are two commonly used methods in search for an interested object in multi-hop wireless networks. While global flooding is simple, it is not scalable for large networks. To take advantage of expanding ring search, a critical question must be answered: what is the best initial TTL (time-to-live) value for the expanding ring search? Although an accurate answer to this question depends on specific application scenarios and system configurations, via mathematical analysis and numerical validation, we illustrate that pessimistic search (i.e., search with an initial range that just covers the object in the worst case) is mostly the best for expanding ring search.

We consider the energy-efficient transmission of traffics with hard delay constraint over wireless ad hoc networks. We adopt a cross-layer design approach and develop a route configuration method such that the average energy cost for packet delivery is minimized while maintaining the required delivery ratio. In particular, we allow the intermediate nodes to drop a packet when the node has performed certain number of unsuccessful retransmissions. Based on the physical channel state information, we formulate and solve an optimization problem to jointly configure the transmitting power for each transmitting node and the retransmission limit over each hop. The resulting route configuration solution achieves minimum energy consumption for message delivery while guaranteeing an acceptable quality of service (QoS) level. Numerical results demonstrate the effectiveness and efficiency of our route configuration algorithm regarding both energy saving and statistical QoS guarantee

Both adaptive modulation and diversity combining represent important enabling techniques for future generations of wireless communication systems. In this paper, we present a new joint adaptive modulation and diversity combining (AMDC) scheme, termed as bandwidth efficient and power greedy AMDC. With this scheme, the modulation mode and diversity combiner structure are adaptively determined based on the fading channel condition and error rate requirement. We accurately analyze this AMDC scheme in terms of processing power consumption, spectral efficiency, and error rate performance. Selected numerical examples show that the proposed AMDC scheme satisfy the target error rate requirement while achieving high spectral efficiency with low processing power consumption

Both adaptive modulation and diversity combining represent important enabling techniques for future generations of wireless communication systems. In this paper, capitalizing on recent developments in adaptive combining, we propose two joint adaptive modulation and diversity combining (AMDC) schemes. With these schemes, the modulation mode and diversity combiner structure are adaptively determined based on the fading channel condition and error rate requirement. We accurately analyze these AMDC schemes in terms of processing power consumption, spectral efficiency and error rate performance. Selected numerical examples show that the proposed AMDC systems meet the target error rate requirement while achieving high spectral efficiency with low processing power consumption.

In this paper, we propose a combined adaptive modulation transmission and output threshold MRC diversity reception scheme for high spectral and power efficiency wireless transceiver design. The modulation constellation size and the number of combined diversity paths are jointly determined based on the fading channel conditions and the required error rate performance. We derive the statistics of the resulting output signal-to-noise ratio (SNR) and then use it to analyze the proposed system in terms of performance, complexity, and spectral efficiency. Some selected numerical examples are finally presented to illustrate the mathematical formulism.

Adaptive modulation and coding (AMC) and automatic repeat request (ARQ) are two of the most important techniques for high performance wireless communications. In this paper, we develop a novel cross-layer design of joint AMC/ARQ transmission for TDMA systems. We also carry out an accurate performance analysis of the proposed systems for different traffic types based on Markov chain theory. Our design and analysis differs from previous works by considering different ARQ strategies and the size limitation of transmitter buffer. Selected numerical results show that the proposed AMC/ARQ system can offer considerable performance improvement over traditional systems even with a limited buffer size

Generalized selection combining (GSC), also known as hybrid selection/maximum ratio combining, is one of the most widely investigated low-complexity diversity techniques. Recently, output-threshold GSC (OT-GSC) was proposed as a power-saving variant of traditional GSC scheme. In this paper, we present an exact performance analysis of OT-GSC over Rayleigh fading channels. In particular, we obtain the cumulative distribution function (CDF), probability density function (PDF) and moment generation function (MGF) of the combined SNR with OT-GSC. Then, we apply these results to study the outage probability and average error rate performance of OT-GSC. These analysis allows for a thorough comparison of OT-GSC with other variants of GSC, such as minimum selection GSC

Diversity combining techniques improve the performance of wireless communication systems at the cost of increased power consumption. Minimum-selection generalized selection combining (MS-GSC) scheme has been proposed as a power saving implementation of conventional generalized selection combining (GSC) scheme. In this paper, noting that previous analytical results on the error rate of MS-GSC are approximate, we carry out a thorough and exact analysis for MS-GSC. In particular, based on a new result on order statistics, we obtain the statistics of the combined SNR with MS-GSC and we then apply these results to analyze the performance of MS-GSC over fading channels. We derive the closed-form expressions of important performance measures, including outage probability and average error rate, for the Rayleigh fading scenario. In addition, we investigate the average number of active MRC branches with MS-GSC, as a quantification of the power saving

Switched diversity offers one of the lowest complexity solution for fading mitigation. The receiver employing switched combining schemes. seeks and uses an acceptable diversity path for data reception. However, when no acceptable path is found after all paths have been examined, the receiver ends up randomly choosing an unacceptable path. In this paper, we consider the performance improvement of switched combining schemes. In particular, we modify conventional multi-branch switch and examine combining (SEC) schemes in a way that the best path is selected when no acceptable path is found after all paths have been examined. We carry out a thorough performance versus complexity tradeoff study on the resulting scheme: SEC with post-examining selection and illustrate the study with some selected numerical examples.

This paper proposes and analyzes an alternative form of switch and examine combining, namely one that waits for a channel coherence time if all the available diversity paths fail to meet a predetermined minimum quality requirement. This scanning through the available diversity paths followed by waiting process is repeated indefinitely until a path with an acceptable quality is found. The performance of the resulting "scan and wait" combining (SWC) scheme is studied in terms of its average probability of error and ergodic capacity. The paper looks also into (i) the delay associated with SWC by deriving the statistics of the waiting time needed before satisfactory transmission occurs and (ii) the underlying complexity by studying the statistics of the number of diversity paths estimated per channel access. Selected numerical examples show that, for a fixed average number of channel estimates per channel access, SWC outperforms traditional diversity combining schemes at the expense of a negligible time delay.

To efficiently take advantage of the potential diversity benefits of diversity-rich environments, we need combining schemes that can achieve good performance-complexity tradeoff. In this paper, noting the performance limitation of the recently proposed generalized switch and examine combining (GSEC) scheme over the low signal to noise ratio (SNR) region, we develop a new low-complexity combining scheme. The new scheme, termed as GSEC with post-examine selection (GSECps), can offer improved performance over GSEC by operating in the same way as generalized selection combining (GSC) when fading condition is unfavorable. Through thorough performance and complexity analysis of GSECps over i.i.d. Rayleigh fading channels, we show that GSECps can obtain a better performance-complexity tradeoff than both GSEC and GSC schemes.

Diversity combining techniques improve the performance of wireless communication systems at the cost of increased processing power consumption. Minimum-selection generalized selection combining (MS-GSC) scheme has been proposed as a power saving implementation of conventional generalized selection combining (GSC) scheme. In this paper, noting that previous analytical results on the error rate of MS-GSC are approximate, we carry out a thorough and exact analysis for MS-GSC. In particular, based on a new result on order statistics, we obtain the statistics of combined SNR with MS-GSC and we then apply these results to analyze the performance of MS-GSC over fading channels. We derive closed-form expressions for important performance measures, including outage probability and average error rate, for the Rayleigh fading scenario.

This paper introduces a new adaptive minimum-estimation minimum-combining switched-combining based scheme that reduces considerably the average receiver channel estimation complexity and the power drain from the battery while satisfying the desired performance requirement. More specifically, analysis supported by numerical results show that the newly proposed combining scheme can achieve essentially the same performance as competing schemes such as generalized selection combining (GSC) and minimum selection GSC while offering 50% channel estimation and 75% processing power savings for some system parameters of interest

In this paper we consider the performance of a RAKE receiver in a code division multiple access (CDMA) system employing maximal-ratio combining. A simple select and combine algorithm is introduced in which the RAKE receiver combines only the synchronization path and those resolvable paths with a signal-to-noise ratio (SNR) larger than a given threshold. We analyze its performance based on moment generating functions of the SNR of the combined signal. We study the cases with equal and unequal average SNR for different diversity paths. In particular, closed-form expressions for the average combined SNR and symbol error probability with the proposed RAKE receiver over block fading channels are derived. We also study the outage probability of the system and the number of channels estimated. Numerical results are given to illustrate the analytical results.

A generalized switch-and-examine combining (GSEC) scheme was previously proposed by the authors as a low-complexity diversity technique for diversity-rich environments. In this letter, we extend the study of GSEC to independent and nonidentically distributed (i.n.d.) fading environments. In particular, after presenting the mode of operation of the GSEC scheme over i.n.d. fading paths, we analyze its error performance based on the moment generating function of combined signal-to-noise ratios. We then study its complexity in terms of the average number of path estimations. We finally investigate the effect of path examination order on the performance and complexity of GSEC over i.n.d. paths.

Switched diversity offers one of the lowest complexity solutions for fading mitigation. The receiver employing switched combining schemes seeks and uses an acceptable diversity path for data reception. When no acceptable path is found after all paths have been examined, however, the receiver randomly chooses an unacceptable path. In this paper, we consider the performance improvement of switched combining schemes. In particular, we modify the conventional switch and examine combining (SEC) scheme in a way such that the best path is selected when there is no acceptable path. For the resulting SEC with post-examining selection (SECps) scheme, we carry out a thorough performance analysis over fading channels. Noting that SECps can be viewed as selection combining (SC) with an output threshold scheme, we perform a tradeoff study of performance versus complexity between SECps and SC. The analytical results are illustrated with some selected numerical examples.

Generalized selection combining (GSC) delivers the largest possible diversity benefit for a given hardware-complexity constraint. However, it also increases the power consumption of the receiver with the path selection and the maximum ratio combining (MRC) operations. In this paper, we investigate a variant of GSC, termed output thresholded GSC (OT-GSC). More specifically, to reduce the power consumption of the GSC scheme, we introduce a threshold check at the GSC combiner output. The resulting OT-GSC combiner tries to raise the signal to noise ratio of the combined signal above a threshold by using the least combiner resources (in terms of path estimations and active MRC branches) possible. The tradeoff between power consumption and performance is illustrated with selected numerical examples.

Diversity combining technique greatly improves the performance of wireless communication systems in fading environment. However, it also increases the power consumption of the receiver. In this paper, we investigate a variant of the classical maximum ratio combining (MRC) scheme that minimizes the processing power at the receiver while still providing considerable performance improvement. In particular, we carry out a thorough performance versus power consumption tradeoff analysis of the output-thresholded MRC scheme. Numerical examples show that the output thresholded combining scheme leads to considerable less average power consumption than conventional MRC scheme while providing nearly the same performance.

Switch-and-stay combining (SSC) diversity systems have the advantage of offering one of the least complex solutions to mitigating the effect of fading. In this paper, we present a Markov chain-based analytical framework for the performance analysis of various switching strategies used in conjunction with SSC systems. The resulting expressions are quite general, and are applicable to dual-branch diversity systems operating over a variety of correlated and/or unbalanced fading channels. The mathematical formalism is illustrated by some selected numerical examples, along with their discussion and interpretation. As a result, this paper presents a thorough comparison and highlights the main differences and tradeoffs between the various SSC switching strategies.

In diversity-rich environments, there is a tradeoff between performance and complexity. While combining a large number of diversity paths improves the system performance, it also increases the receiver complexity. With this in mind, we propose generalized switch and examine combining (GSEC) as a good candidate combining scheme for such environments. Description of the GSEC mode of operation shows that this scheme conserves a fixed complexity as the number of diversity paths increases, and offers a considerable complexity savings over traditional maximum ratio combining and even other low-complexity schemes, such as generalized selection combining. In this paper, we look into the design and performance analysis of GSEC over independent and identically distributed diversity paths. As an illustration of the mathematical formalism, selected numerical examples are provided, together with some related discussions and interpretations.

Abstract We investigate the performance of non‐coherent frequency shift keying (NCFSK) with multi‐branch post‐detection switched diversity systems. After an appropriate statistical description of the square‐law detector output, we derive generic formulas for the symbol/bit error probability of NCFSK for both switch and stay combining (SSC) and switch and examine combining (SEC) schemes. We show that while the SSC scheme does not benefit from more than two diversity paths when the paths are identically distributed, the error performance of SEC improves as the number of antenna paths increases. We consider two detection schemes for NCFSK, one for M‐ary FSK and another limited to only BFSK. We show that the second scheme leads to lower error probability performance when both are used to detect binary signals. The mathematical formalism is illustrated with a number of selected numerical examples. Copyright © 2004 John Wiley & Sons, Ltd.

In diversity-rich environments, there is a tradeoff between performance and complexity. While combining a high number of paths improves the performance, it also increases the receiver complexity. With this in mind, we look into the performance of generalized switch and examine combining (GSEC): a low-complexity scheme suitable for diversity-rich environments. More specifically, after deriving the statistics of the combiner output, including the moment generating function and probability density function, we analyze the performance of of GSEC in independent and identically distributed Rayleigh fading environment in terms of average combiner signal-to-noise ratio, outage probability, and average error probability. As an illustration of the mathematical formalism, selected numerical examples and provided together with some related discussions and result interpretations.

We investigate the performance of multibranch switched diversity systems. Specifically, we first derive generic formulas for the cumulative distribution function, probability density function, and moment-generating function of the combined signal power for both switch-and-stay combining (SSC) and switch-and-examine combining (SEC) schemes. We then capitalize on these expressions to obtain closed-form expressions for the outage probability and average error rate for various practical communication scenarios of interest. As a byproduct of our analysis we prove that for SSC with identically distributed and uniformly correlated branches, increasing the number of branches to more than two does not improve the performance, but the performance can be different in the case the branches are not identically distributed and/or not uniformly correlated. We also show that, in general, the SEC performance improves with additional branches. The mathematical formalism is illustrated with a number of selected numerical examples.

Outage probability of two low-complexity dual-branch diversity schemes with the consideration of both minimum carrier-to-interference ratio and the carrier-to-noise ratio constraints is investigated. More specifically, closed-form expressions for this outage probability for selection combining and switch and stay combining in single-interferer Rayleigh fading environment are derived, first under the assumption of perfectly estimated independent diversity paths, then by taking into account the effect of branch correlation and outdated/imperfect channel estimates. When applicable, the results obtained as special cases of the offered generic closed-form expressions are compared with those previously reported in the literature. In addition, some numerical examples are provided and discussed.

Outage probability of two low-complexity dual-branch diversity schemes with the consideration of both minimum carrier-to-interference ratio and the carrier-to-noise ratio constraints is investigated. More specifically, closed-form expressions for this outage probability for selection combining and switch and stay combining in a single-interferer Rayleigh fading environment are derived, first under the assumption of perfectly estimated independent diversity paths, then by taking into account the effect of branch correlation and outdated/imperfect channel estimates. Some selected numerical examples are also provided and discussed.

A novel model for slowly varying shadowed fading channel based on Markov chain theory is proposed. It not only leads to accurate first-order statistical description of the composite process but also captures the memory effect of the channel. Following a hierarchical approach, the shadowing/fading process is modeled as a nested Markov chain, where the macrostate variation is assumed to be caused by the shadowing process while microstate transitions is initialized by the fading effect with macrostate-dependent transition probabilities. As an illustration of the mathematical formalism, some simulation results are provided and discussed.

We investigate the performance of both switch and stay combining (SSC) and switch and examine combining (SEC) multi-branch diversity schemes. We first derive generic formulas for the cumulative distribution function, probability density function, and moment generating function of the combiner output signal for both schemes. We then capitalize on these expressions to obtain closed-form expressions for the outage probability and average error rate for various communication scenarios of interest. As a byproduct of our analysis we prove that for SSC with identically distributed and uniformly correlated branches, increasing the number of branches to more than two does not improve the performance but the performance can be different in the case the branches are not identically distributed. We also show that, in general, the SEC performance improves with additional branches. The mathematical formalism is illustrated with a number of selected numerical examples.

The throughput of slotted Aloha in a fading environment is investigated with the consideration of both minimum carrier-to-interference ratio and minimum carrier-to-noise ratio constraints. In particular, Nakagami/Rician and Rician/Nakagami fading combinations with the assumption of independent identical distributed (i.i.d.) interferers are studied. After representing the throughput of slotted Aloha in terms of outage probability, closed-form expressions of outage probability for the chosen fading scenarios are derived. These expressions are given in terms of the Marcum Q-function and modified Bessel functions, and therefore readily allow numerical evaluation for various cases of practical interest. In addition, numerical examples of the throughput of the slotted Aloha system under both fading combinations with a minimum power constraint have been provided and discussed.