Full-duplex (FD) communication is becoming a key technology for future wireless systems, offering the potential to significantly improve spectral efficiency (SE) and overall system performance. This study explores how hardware impairments (HWIs) impact the performance of FD multiple-input multiple-output (MIMO) systems. We develop models to evaluate the achievable data rates for both uplink (UL) and downlink (DL) communications in the presence of hardware imperfections. Additionally, we address the challenge of optimizing power allocation to maximize FD SE using the Karush-Kuhn-Tucker (KKT) conditions. Our approach not only boosts system performance but also compensates for HWIs, even outperforming ideal systems operating at maximum power. Finally, extensive simulations validate our theoretical findings.

This paper investigates the threat of passive eavesdropping on downlink cell-free massive MIMO (CF-MaMIMO) systems, examining a particular system under the effects of both hardware impairments (HWIs) and pilot contamination. Physical layer security (PLS) techniques and power allocation algorithms are typically adopted to deteriorate the quality of eavesdropped signals. In the downlink stream, artificial noise (AN) is broadcasted simultaneously with the users’ data streams, with the aim of jamming the eavesdropper’s signal without sacrificing the quality of service (QoS). The obtained results prove that mitigating the impact of both pilot contamination and HWIs on both the system’s capacity and PLS is crucial for the deployment of practical CF-MaMIMO systems.

This work addresses two innovative and challenging aspects in the pursuit of an accurate localization process, which can be achieved through a complex and nonlinear approach such as neural networks (NNs). This study specifically focuses on developing a low-complexity localization method using NNs, along with presenting the associated Cramèr-Rao lower bound (CRB). The research considers real-world scenarios where system performance is corrupted by imperfect synchronization and hardware impairments (HWIs), which cause significant accuracy reduction when using traditional estimators. The NN approach offers a promising solution to counteract the effects of HWI and synchronization issues, by using substantial prior information during the training phase. However, incorporating this prior information and dealing with the nonlinearity of NNs presents challenges in deriving the CRB of the neural localization process. To overcome these challenges, the research utilizes the f-divergence function and the concept of mutual information to derive the CRB, making it applicable to various HWI, nonlinear activation functions in NNs and statistical models. The study further simplifies the optimization problem traditionally associated with this approach used in calculating the CRB. The simulation results demonstrate that the proposed approach achieves a low-complexity and accurate localization process even in asynchronous and impaired systems. Furthermore, the simulations validate the proposed CRB driving technique and provide the CRB values for various neural localization scenarios.

This paper investigates the problem of position estimation and tracking in indoor visible light communication (VLC) systems under a multiple-input single-output (MISO) configuration. The study specifically addresses the impact of signal-dependent shot noise (SDSN) and relative intensity noise (RIN), which significantly degrade localization accuracy in practical VLC scenarios. To establish a theoretical performance benchmark, a novel closed-form Bayesian Cramér-Rao lower bound (BCRLB) is derived for two-dimensional (2D) position estimation. The proposed extended Kalman filter (EKF) demonstrates superior localization accuracy by effectively accounting for motion dynamics through its recursive updates, unlike estimation methods that rely solely on noisy distance measurements. Our findings show that increasing the number of light sources improves spatial diversity, thereby enhancing positioning precision. Furthermore, analysis indicates that RIN has a more pronounced negative effect on tracking accuracy than SDSN. The EKF’s performance is validated against the proposed BCRLB, confirming its suitability for real-time and reliable indoor localization. Overall, this work provides meaningful insights into the design of robust and efficient VLC-based positioning systems.

Laser diode (LD) powered luminaires are already gaining traction in automotive applications and are expected to be increasingly deployed in homes and offices in the near future. This gives a unique opportunity to build visible light communication (VLC) systems with ultra-high-bandwidths offered by the LDs. However, LDs are subject to some inherent noise sources, notably signal-dependent shot noise (SDSN) and relative intensity noise (RIN). RIN basically describes the instability in the power level of a laser and quantifies the output power fluctuations. SDSN arises from variations in the photodetector’s response to optical signals. Our research explores the interplay between SDSN and RIN, revealing their combined adverse effect on channel estimation accuracy in a VLC system. Towards this direction, we first derive the Cramér-Rao lower bound (CLRB) in the presence of the SDSN and the RIN, which gives a lower estimate for the variance of an unbiased estimator. Then, we present the derivation of least square (LS) and maximum likelihood (ML) channel estimators. Furthermore, we present the optimal receiver in ML sense and compare it with a simple threshold detector as a sub-optimal solution, quantifying the impact of channel estimation accuracy on both receivers. Our study results reveal the adverse impact of the joint presence of SDSN and RIN on the channel estimation error; consequently, it degrades the BER of the two proposed receivers. Moreover, RIN emerges as the dominant noise source, especially at higher levels of transmitted power.

This work outlines a framework for full-duplex (FD) multiple-input multiple-output (MIMO) communication systems considering practical conditions, such as imperfect channel state information (CSI) and hardware impairments (HWIs). We analyze the performance of FD multi-user (MU) MIMO systems, specifically studying the effects of practical channel estimation errors and HWIs on the spectral efficiency (SE) performance of FD MU-MIMO systems. Maximum ratio combining/maximum ratio transmission (MRC/MRT) and zero-forcing reception/zero-forcing transmission (ZFR/ZFT) linear detectors/precoders are considered at the base station (BS). Moreover, linear minimum mean square error (LMMSE) and least square (LS) error estimation are used to estimate the channel at the BS. Mathematical derivations for the lower bounds of uplink (UL) and downlink (DL) SEs are presented in the context of imperfect CSI and HWIs. Computer simulations validate the analytical derivations. The results demonstrate the tightness of the obtained bounds.

Considering the current capability in hardware design, the wireless power transmission (WPT) enables the next stage in the current consumer electronics revolution by prolonging the lifetime of devices powered by batteries. Recently, Information Harvesting (IH) introduced a novel mechanism for wireless power and information transfer which differs from existing far-field wireless power transfer and simultaneous transmission of power and data protocols. In this paper, a new IH mechanism which relies on quadrature spatial modulation (QSM) is proposed and the simulation results demonstrate that the proposed mechanism improves the secrecy at information receiver and provide more harvested energy to the harvester.

This paper investigates the threat of passive eavesdropping on downlink cell-free massive MIMO (CF-MaMIMO) systems, examining in a particular system under the effects of imperfect channel estimation. Physical layer security (PLS) techniques and power allocation algorithms are typically adopted to deteriorate the quality of eavesdropped signals. In the downlink stream, artificial noise (AN) is broadcasted simultaneously with the users’ data streams, with the aim of jamming the eavesdropper’s signal without sacrificing the quality of service (QoS). However, imperfect channel estimation results in AN leakage to legitimate users. Our work considers this condition, and the power allocation algorithms we present determine the minimum power that is needed to maintain the user’s Qos even in the presence of leaked AN. We first propose the cooperative PLS algorithm (COP), which facilitates AN broadcasting via access point (AP) cooperation. Unfortunately, this cooperation wastes some of the power used to send the AN and, in most cases, increases the computational complexity. We then present the independent PLS algorithm (IND), where the goal is to regain this power by allowing each AP to broadcast AN independently. However, to meet the feasibility criterion, this occurs at the cost of increasing the number of used antennas. This technique reduces the power allocation complexity but increases the computational complexities of the precoder design and the channel estimation process. Our results reveal that the proposed algorithms enhance the security performance of CF-MaMIMO. We evaluate such performance from numerous angles including the number of users, number of APs, QoS, beamforming, AN leakage, and channel estimation techniques.

Full-duplex (FD) communications have been recognized as one of the promising wireless transmission candidates for the future of wireless communication and networking technologies, thanks to their ability to greatly improve spectral efficiency (SE) and dramatically enhance energy efficiency (EE). In this paper, we study the influence of hardware impairments (HWIs) on single-input single-output (SISO) FD access point (AP). More precisely, we study the EE when the system's terminals have impaired transceivers. Optimization problem for EE maximization is formulated to fulfill quality of service (QoS) and power budget constraints. We propose an algorithm to solve the optimization problem by using the fractional programming theory and Karush-Kuhn-Tucker (KKT) conditions technique. The results unveil that excellent power allocation is crucial in FD communication networks and the proposed algorithm outperforms the maximum power transmission scheme. The results also reveal that HWIs degrade both EE and SE performance. Moreover, at high power region, no further improvements can be obtained by increasing the transmission power. Finally, we assume that all fading channels demonstrate Nakagami-m distribution.

This work studies unmanned aerial vehicles (UAVs) as supporters of future wireless networks. We focus on channel assignment and study it as a joint optimization problem, where we pick from a pool of channels provided by a main core network. We find an optimal solution for the association problem between the wireless access points (WAPs) and UAVs, and this way we can maximize the total weighted sum rate by formulating a max-min optimization problem. This formulation is subject to quality of service (QoS), to a maximum number of links from the pool channel, and to available bandwidth constraints. The formulated problem is an NP-hard problem and requires exponential time to be solved as the number of WAPs increases. We propose a low-complexity centralized algorithm to solve the association problem. Our results demonstrate that the solution of the proposed algorithm approaches that of the exhaustive search technique with much less computational complexity.

Ful1-duplex (FD) communication stands out as a game-player for future wireless communication systems by the ability to increase spectral efficiency (SE) and improve system performance. In this paper, we study the effects of hardware impairments (HWIs) on the FD multiple-input multiple-output (MIMO) communication system’s performance. Mathematical frameworks for the lower bound of uplink (UL) and downlink (DL) SE are derived under imperfect hardware conditions. Furthermore, power allocation optimization problem is formulated to maximize the FD SE and then solved using the Karush-Kuhn-Tucker (KKT) conditions technique. Interestingly, using the proposed solution achieves a remarkable improvement. Moreover, it can compensate the impaired system, which can outperform the ideal system that transmits with maximum power. Finally, extensive computer simulations were conducted to validate the theoretical derivations.

In this study, we present a unifying framework for future reconfigurable intelligent surface (RIS)-assisted space shift keying (SSK) systems; we additionally propose two novel transmission schemes. The key strategies surrounding this concept, namely power-sensing RIS-SSK and partitioned RIS-SSK, grant knowledge of the activated transmitter (Tx) antenna index at the RIS, which, when using SSK, allows us to adjust the reflection phases. The performance of the proposed scheme is investigated in terms of the theoretical average bit error rate (ABER), and the effect of non-ideal transceivers. The performance is then compared to that of a reference RIS-SSK scheme, and a complexity analysis is provided. The obtained results, verified by extensive computer simulations, demonstrate that the partitioned and power-sensing RIS-SSK schemes achieve a higher ABER than the reference one. Moreover, hardware impairments clearly have a critically degrading impact on the system performance for all schemes, and should be carefully taken into account in future communication systems.

Reconfigurable intelligent surfaces (RISs) are a recent yet revolutionary development in communications systems. Particularly applicable to millileter wave (mmWave) systems, these surfaces can increase localization performance and decrease vulnerability to environmental influences, all by adjusting the incoming signals’ phase. At the same time, manufacturing ideal hardware to be deployed at the transceivers is not feasible nor practical. These non-linearities in hardware, collectively known as hardware impairments (HWIs), cause signal degradation and adversely affect localization. In this paper, the effect of HWIs on RIS-aided localization is examined. Towards that, the mean squared error (MSE) of the user’s position is found through a maximum likelihood estimator (MLE) and its functionality is verified by the position error bounds (PEB), derived from Cramér-Rao lower bounds (CRLB). Our numerical results show that active RISs mitigate the deteriorating effect of HWIs on the user’s PEB. Based on our outcome, increasing the inter-RISs space generally creates more resolvable paths and leads to improved localization.

The paper studies the downlink of non-orthogonal multiple access (NOMA) under imperfect successive interference cancellation (SIC). In an effort to overcome the SIC imperfection problem, we propose to adopt improper Gaussian signaling (IGS) for the signal transmission of the NOMA users. In particular, we jointly optimize the IGS circularity coefficient and transmit power to maximize the spectral efficiency subject to minimum Quality-of-Service (QoS) per each user and total power budget. Simulations results show the effectiveness of IGS to compensate for the SIC imperfections compared with proper Gaussian signaling (PGS)-based NOMA systems.

Reconfigurable Intelligent Surface-based Space Shift Keying (RIS-SSK) was recently proposed as a promising transmission technique. In order to design strategic radio environments, this system takes advantage of RIS-based communication and adjusts the propagation channels. Furthermore, using SSK as a special case of the Spatial Modulation (SM) reduces the detection complexity by using only the index of the active antenna to transmit the data. However, when considering an effective RIS-SSK system, the transmit antenna is modeled by spatial constellation points with different weights. This requires the knowledge of Channel State Information (CSI), including the index of the activated antenna at each transmission which is impractical. In contrast, blind RIS-SSK does not require this information, decreasing its complexity and increasing its practicality. In this paper, a blind RIS-SSK system without phase-adjusting is studied in the presence of hardware impairments and compared to the standard SSK. Additionally, analytically error probability expressions based on the Maximum Likelihood (ML) detector are developed and proven with simulations. The results illustrate the negative effects of modeling the hardware impairments for robust RIS-SSK system implementation.

This paper investigates visible light positioning (VLP) systems in the presence of signal-dependent shot noise (SDSN). We consider both synchronous and asynchronous down-link communications when evaluating the Cramér–Rao lower bounds (CRLBs) of the distancing error. Performance assessment is based on time-of-arrival (TOA), received signal strength (RSS), and hybrid (TOA/RSS) based distance estimations. The results demonstrate that SDSN has a critical impact on the distancing bounds in all considered cases. Moreover, the level of degradation observed at higher SDSN levels is not uniform among all cases.

Location-awareness is expected to be one of the main services in 5G millimeter-wave (mmWave) communication systems. In mm-Wave, multiple-input multiple-output (MIMO) systems will be used, leading to the deployment of antenna arrays in both transmitter and receiver. Hardware components being used in transceiver are commonly modeled as linear filters; but practically, this linearity is not fully satisfied. Power amplifiers and filters applied in antennas mostly show nonlinear behavior, causing loss in spectral efficiency (SE) and signal quality. This non-linearity is referred to hardware impairments (HWIs). Under HWIs model at both the transmitter and receiver, 2D localization performance is examined. Towards that, we derive position and orientation error bounds and study the effect of HWIs on the derived bounds. The numerical results reveal that HWIs have a significant effect on localization and it causes more than 100% degradation in both the transmitter and receiver. Also, the rate of degradation stays the same for both position and orientation error bounds except for the oriented UE.

Large Intelligent Surfaces (LIS) are promising in terms of what they can offer to 6G and beyond communication networks. As such, they have recently attracted considerable attention in the research community. This technique allows the operators to control the environment in a strategic way so as to improve the communication system performance. This work studies the effect of hardware impairments (HWIs) on the LIS-Aided wireless communication system under correlated channel conditions. In specific, we look at the impact on the system performance. We also give a deterministic approximation function of the average bit error rate (ABER) for a large number of reflectors and a tight approximation of the outage probability (OP). Extensive Monte Carlo simulations are provided to verify the analytical results, which show that the system performance saturates at a high signal-to-noise ratio (SNR) due to the HWIs. Moreover, this degradation is exacerbated when the channels demonstrate strong correlation conditions. However, the HWIs have a dominant effect and the correlation impact diminishes with a larger number of reflectors.

Device-to-Device (D2D) communication underlying cellular networks was first introduced in the 3GPP Rel. 12 specifications, and was initially referred to as proximity services (ProSe). Its primary aim was to serve billions of Internet of Things (IoT) devices for 5G and beyond-5G networks. To enable D2D link establishment between various user equipments (UEs), the neighbor discovery process became crucial. This article investigates neighbor discovery for ProSe and Vehicle-to-Everything (V2X) communications through a SideLink interface, which is specifically introduced to support D2D communications over cellular networks. A single-user scenario is first considered to derive the probability of discovery in its closed-form and compare it with simulation results to validate its theoretical analysis. This scenario employs the demodulation reference signal (DMRS), where a power-normalized-correlation (PNC)-based metric is performed to determine the presence of active peers in the vicinity. Moreover, a multiuser scenario is considered to assess the impact of interference on the discovery probability in the cases of low and high vehicular mobility channel models. Then, group discovery is investigated using two strategies: 1) a distributed scheme incorporating out-of-coverage communications (modes 2 and 4) or 2) a network-assisted scheme applicable for supervised communications (modes 1 and 3). In this study, discovery periods are modeled as an Aloha-like protocol in the first case and a Polling-like protocol in the second case with either MAC layer or PHY layer collision models. Simulations are performed to evaluate the time required for group discovery completion as well as the collision rate in both low-mobility and high-mobility channels.

Spatial modulation (SM) is a promising low-complexity alternative to the state-of-art multiple-input multiple-output (MIMO) schemes due to its unique transmission approach. In this work, the impact of channel imperfections on the performance of SM-MIMO systems are investigated over generalized Beckmann fading channels, which introduce a versatile multipath fading model that includes several distributions such as Ricean, Nakagami-m and Beaulieu-Xie, as special cases. Specifically, an optimum maximum likelihood detection (MLD) method is proposed and the average pairwise error probability (APEP) is calculated by analytical derivations. Cramer-Rao bound approach is utilized for further improvement on decreasing the deteriorating effects that rise from estimation errors. The obtained results, confirmed by computer simulations, provide a comprehensive perspective to the performance of the SM-MIMO wireless communication systems.

Large propagation path loss and limited scattering of millimeter wave (mm-wave) channels create new challenges for physical layer signal processing. Hence, in this paper, we propose a photonic hybrid precoding model for mm-wave radio-over-fiber systems that overcomes hardware constraints on radio frequency precoding. With the help of analog photonic beamformers, the hybrid precoding strategy combats the large losses of mm-wave and mitigates inter-user interference, which in turn reduces the number of RF chains required to perform digital beamforming. The simulation results show that the proposed model can offer significant coding gains over conventional RF hybrid precoding systems. Unlike RF hybrid precoding systems, the photonic hybrid precoding systems can provide higher data rates and lower error rates in multi-user transmission scenarios.

Spatial modulation (SM) is a promising multiple- input multiple-output system used to increase spectral efficiency. The maximum likelihood (ML) decoder jointly detects the transmitted SM symbol, which is of high complexity. In this paper, a novel reliable sphere decoder (RSD) algorithm based on tree-search is proposed for the SM system. The basic idea of the proposed RSD algorithm is to reduce the size of the tree- search, and then, a smart searching method inside the reduced tree-search is performed to find the solution. The proposed RSD algorithm provides a significant reduction in decoding complexity compared to the ML decoder and existent decoders as well. Moreover, the RSD algorithm provides a flexible tradeoff between the bit error rate (BER) performance and decoding complexity, so as to be reliable for a wide range of practical hardware implementations. The BER performance and decoding complexity analysis for the RSD algorithm are studied, and Monte Carlo simulations are then provided to demonstrate the findings.

In this study, the authors secure the mixed radio frequency/free space optical (FSO) relay‐aided interference aligned system using a proposed physical layer security algorithm. This algorithm reduces the quality of the received signal at the eavesdropper through two procedures. First, it minimises the data transmission power from the legitimate users and the relays. Second, it jams the eavesdropper by broadcasting artificial noise from the users and the relays. Therefore, a joint optimisation problem is formulated to degrade the received signal at the eavesdropper from the users and the relays and to maximise the jamming artificial noise power, which is solved using an iterative optimisation algorithm beside a semi‐definitive programming algorithm. Furthermore, the pre‐coding and decoding matrices of the users and the relay are designed to enable the legitimate users to cancel the artificial noise, while the eavesdropper is disabled from distinguishing the artificial noise from the real streams. Moreover, the security performance of the proposed algorithm is analysed, and the impact of the FSO link's state on the security performance is studied. The extensive simulation results show the efficiency of the proposed algorithm and illustrate the role of the FSO link's state on the security performance.

Multi-user spatial modulation (SM) assisted by sparse code multiple access (SCMA) has been recently proposed to provide uplink high spectral efficiency transmission. The message passing algorithm (MPA) is employed to detect the transmitted signals, which suffers from high complexity. This paper proposes three low-complexity algorithms for the first time to the SM-SCMA. The first algorithm is referred to as successive user detection (SUD), while the second algorithm is the modified version of SUD, namely modified SUD (MSUD). Then, for the first time, the tree-search of the SM-SCMA is constructed. Based on that tree-search, another variant of the sphere decoder (SD) is proposed for the SM-SCMA, referred to as fixed-complexity SD (FCSD). SUD provides a benchmark for decoding complexity at the expense of bit-error-rate (BER) performance. Further, MSUD slightly increases the complexity of SUD with a significant improvement in BER performance. Finally, FCSD provides a near-optimum BER with a considerable reduction of the complexity compared to the MPA decoder and also supports parallel hardware implementation. The proposed algorithms provide flexible design choices for practical implementation based on system design demands. The complexity analysis and Monte-Carlo simulations of the BER are provided for the proposed algorithms.

Spatial modulation (SM) has been shown to be a promising low-complexity alternative to the state-of-art multiple-input multiple-output (MIMO) schemes due to its novel transmission approach. This paper investigates the performance of SM-MIMO systems in the presence of two practical undesirable effects, namely in-phase (I) and quadrature-phase (Q) imbalance (IQI) and imperfect channel state information (ICSI). An optimum maximum likelihood detection (MLD) method is proposed to tackle the effects of self-interference and signal distortion caused by IQI impairment by adapting the traditional MLD technique in accordance with the asymmetric characteristics of the IQI. More particularly, upper-bounds of the closed-form average pairwise error probability (APEP) and the average bit error rate (ABER) are derived for generalized Beckmann fading channels. As erroneously interpreted channel coefficients at the receiver (Rx) cause the error rate to increase and the detection to fall short, Cramer-Rao bound, which is a lower bound on the variance of the channel estimator, is utilized to assess the estimation accuracy. The system performance is evaluated by analytical derivations that are corroborated with computer simulations. The obtained results show that ICSI and IQI should be seriously considered while designing the future SM-based wireless communication systems.

The objective of health monitoring systems is to provide sustainable and high-quality service to subscribers, hence requiring that the system run without interruption for a sufficiently long time. In this paper, we investigate lifetime maximization in Wireless Body Sensor Networks (WBSN) to provide sustainable e-health service with energy harvesting enabled nodes. Maximizing the lifetime is equivalent to minimizing the energy budget within the whole network. To this aim, we optimize the time resource allocation for all involved sensor nodes in order to maintain a sufficient energy level for longer time after each packet transmission. Specifically, we model the energy harvesting process as a discrete-time Markov chain and evaluate the instantaneous energy budget in order to select the node that will occupy a specific time slot. The energy budget is presented as the net energy, which we quantify through the gap between the consumed and harvested energies. Therefore, to achieve sustainability, the idea of the proposed algorithm focuses on prioritizing nodes with a minimum net energy level while offering nodes with high net energy level the opportunity to harvest more energy and increase their capabilities to provide the required energy to continuously submit their data. The proposed algorithm is evaluated in terms of sensor uninterrupted lifetime and packet loss due to energy run out through simulations. The results demonstrate longer uninterrupted lifetime compared to the considered benchmark and low packet loss probability to subscribers.

By introducing the Proximity Services (ProSe) functionalities in its 12threlease, the 3rdGeneration Partnership Project (3GPP) made possible the ability to perform device-to-device (D2D) communication in Long Term Evolution-Advanced (LTE-A) cellular network. Direct communication between nearby User Equipments (UEs) is then enabled through the newly introduced sidelink. This paper investigates neighbor discovery for D2D communication exploiting Demodulation Reference Signals (DMRS), which are associated with physical sidelink channels for coherent demodulation. By simply listening to its sidelink signal, a ProSe-enabled UE can identify its peers and initiate a direct link without any additional overhead. The study examines the properties of DMRS sequences and proposes a robust neighbor discovery scheme tailored to DMRS structure based on a power normalized correlation process. A reduction in the computational load required to establish a link between two neighbors is proposed and evaluated. Simulation results show that nearby users can be discovered with a reasonable complexity while achieving a high discovery accuracy.

In this paper, a novel low-complexity detection algorithm for spatial modulation (SM), referred to as the minimum-distance of maximum-length (m-M) algorithm, is proposed and analyzed. The proposed m-M algorithm is a smart searching method that is applied for the SM tree-search decoders. The behavior of the m-M algorithm is studied for three different scenarios: 1) perfect channel state information at the receiver side (CSIR); 2) imperfect CSIR of a fixed channel estimation error variance; and 3) imperfect CSIR of a variable channel estimation error variance. Moreover, the complexity of the m-M algorithm is considered as a random variable, which is carefully analyzed for all scenarios, using probabilistic tools. Based on a combination of the sphere decoder (SD) and ordering concepts, the m-M algorithm guarantees to find the maximum-likelihood (ML) solution with a significant reduction in the decoding complexity compared with SM-ML and existing SM-SD algorithms; it can reduce the complexity up to 94% and 85% in the perfect CSIR and the worst scenario of imperfect CSIR, respectively, compared with the SM-ML decoder. The Monte Carlo simulation results are provided to support our findings as well as the derived analytical complexity reduction expressions.

Future wireless communication systems face several transceiver hardware imperfections that may significantly degrade their performance. In-phase (I) and quadrature-phase (Q) imbalance (IQI), which causes self-interference effects on the desired signal, is an important and practical example to these impairments. In this paper, a channel state information-assisted dual-hop amplify-and-forward (AF) relaying system in the presence of IQI is analyzed. The error performance of the relevant AF cooperative protocol is firstly studied by considering the traditional maximum likelihood detection (MLD) algorithm as a benchmark. Then, two compensation methods, weighting and zero-forcing, are proposed to mitigate the IQI effects. Finally, an optimal MLD solution is introduced by adapting the traditional MLD technique in compliance with the asymmetric characteristics of the IQI. The system performance is evaluated in terms of average symbol error probability (ASEP) through the computer simulations. The ASEP is calculated analytically for the optimal MLD method as well under the assumption of point-to-point communication, which has been envisioned as an allied technology of the fifth generation (5G) wireless systems, between the source and the relay nodes. A power allocation algorithm is provided for this specific case. The extensive computer simulations and analytical results prove that the proposed optimal MLD method provides the best results.

Error probability study of hardware impaired (HWI) systems highly depends on the adopted model. Considering the distinct improper Gaussian features of HWI systems, captured by recent models, HWI-aware receivers are designed. An optimal maximum likelihood (ML) receiver serves as a performance benchmark, and a sub-optimal linear minimum mean square error introduces a reduced-complexity implementation. Whereas, the conventional HWI-unaware minimum Euclidean distance receiver, based on the proper noise assumption, exhibits substandard performance. Next, the average error probability of the proposed optimal ML-receiver is analyzed, where several tight bounds and approximations are derived for various HWI systems. Motivated by the benefit of improper Gaussian signaling in mitigating HWI, which is proven in recent studies, asymmetric modulation is adopted and optimized for transmission. The numerical results demonstrate a bit error rate (BER) reduction up to 70% of the proposed HWI-aware receivers over HWI-unaware receivers. Moreover, the asymmetric modulation is shown to reduce the BER by 93%. These results signify the importance of incorporating accurate HWI models, designing appropriate receivers and optimizing signal transmission for the BER performance compensation.

Space shift keying (SSK) has many advantages through its unique transmission manner as compared to other multiple-input multiple-output (MIMO) techniques. Nevertheless, the practicality of SSK in the presence of real-time imperfections such as channel estimation errors and hardware impairments (HWIs) is still an open research problem. On the other hand, the effects of HWIs are assumed as zero-mean circularly-symmetric complex Gaussian random variable (RV) in the literature. However, this model does not reflect the asymmetric characteristics of different HWIs. Therefore, the aim of this paper is to shed light on the joint effect of improper Gaussian noise (IGN) and imperfect channel state information (ICSI) on the performance of SSK receiver. Particularly, an optimal maximum likelihood (ML) detector is designed, and pairwise error probability (PEP) expression is derived. Additionally, an exact closed-form Cramer-Rao bound expression is calculated for evaluating the channel estimation accuracy under the effect of IGN. The results obtained by using computer simulations prove that the proposed optimal detector is superior to the traditional ML detector in the presence of IGN and ICSI.

Full-dimensional (FD) channel state information at transmitter (CSIT) has always been a major limitation of the spectral efficiency of cellular multi-input multi-output (MIMO) networks. This letter proposes an FD-directional spatial channel estimation algorithm for frequency division duplex massive FD-MIMO systems. The proposed algorithm uses the statistical spatial correlation between the uplink (UL) and downlink (DL) channels of each user equipment. It spatially decomposes the UL channel into azimuthal and elevation dimensions to estimate the array principal receive responses. An FD spatial rotation matrix is constructed to estimate the corresponding transmit responses of the DL channel, in terms of the frequency band gap between the UL and DL channels. The proposed algorithm shows significantly promising performance, approaching the ideal perfect-CSIT case without UL feedback overhead.

In spatial modulation (SM) and quadrature SM (QSM), the maximum-likelihood (ML) decoder provides the optimum solution with high decoding complexity at the receiver side. This paper presents a novel low-complexity algorithm for decoding the SM and QSM symbols, referred to as the min-max algorithm. This is an intelligent searching algorithm, particularly designed for the tree-search of the SM and QSM decoders. The proposed algorithm expands the minimum Euclidean distance (ED) by adding a single node at each step, without considering the order of the branches. The expanding process stops if the minimum ED occurs at the end of a fully expanded branch. It is shown that the proposed algorithm achieves the optimum ML bit error rate performance with a significant reduction in the decoding complexity comparing with SM-ML and QSM-ML, as well as other existing sphere decoding algorithms. Simulations and mathematical analysis are provided to assess the decoding performance and complexity of the proposed algorithm.

In this paper, we have designed an optimal detector for the space shift keying (SSK) receiver in the presence of the improper Gaussian noise (IGN) with multiple antennas mounted the transmitter and receiver nodes. We have analyzed this optimal detector by finding the error probability and comparing the performance of this receiver with the suboptimal one which uses the traditional maximum-likelihood (ML) detector to detect the IGN as if it is a proper Gaussian noise (PGN). The analytical expressions obtained can be used under general complex fading channels. The analytically derived results have been validated using the simulation, where it is demonstrated that the importance of using the optimal receiver, in addition to the importance of considering the IGN over the (PGN) at the receiver.

In this paper, we accurately model the transceiver hardware impairments (HWIs) of multiple-input multiple-output (MIMO) systems considering different HWI stages at transmitter and receiver. The proposed novel statistical model shows that transceiver HWIs transform the transmitted symmetric signal to asymmetric one. Moreover, it shows that the aggregate self-interference has asymmetric characteristics. Therefore, we propose improper Gaussian signaling (IGS) for transmission in order to improve the achievable rate performance. IGS is considered as a general signaling scheme which includes the proper Gaussian signaling (PGS) as a special case. Thus, IGS has additional design parameters which enable it to mitigate the HWI self-interference. As a case study, we analyze the achievable rate performance of single-input multiple-output systems with linear and selection combiner. Furthermore, we optimize the IGS statistical characteristics for interference alignment. This improves the achievable rate performance as compared to the PGS, which is validated through numerical results.

The conventional minimum Euclidean distance (MED) receiver design is based on the assumption of ideal hardware transceivers and proper Gaussian noise in communication systems. Throughout this study, an accurate statistical model of various hardware impairments (HWIs) is presented. Then, an optimal maximum likelihood (ML) receiver is derived considering the distinct characteristics of the HWIs comprised of additive improper Gaussian noise and signal distortion. Next, the average error probability performance of the proposed optimal ML receiver is analyzed and tight bounds are derived. Finally, different numerical and simulation results are presented to support the superiority of the proposed ML receiver over MED receiver and the tightness of the derived bounds.

This paper proposes a novel physical layer security algorithm in interference alignment (IA) based multiuser communication system with a single amplify-and-forward (AF) relay in the coexistence of an eavesdropper that tries to hide its existence. Thus, the relay and the users cannot estimate the eavesdroppers channel state information (CSI). In the proposed algorithm, the users broadcasts artificial noise in the null of the relay at the multiple access (MAC) phase, and the relay jams the eavesdropper by broadcasting the artificial noise in the null of users at the broadcast (BC) phase. Therefore, the proposed algorithm is formulated as a joint optimization problem consisting of two semidefinite programming (SDP) problems aiming at maximizing the power of the artificial noise and preserving the quality- of-services (QoS) of the users. An iterative optimization algorithm is proposed to solve the joint problem. Extensive simulation results are provided to show the effectiveness of the proposed algorithm for IA based relaying networks.

Channel state information (CSI) acquisition is a crucial issue in downlink FDD-based massive multi-input multioutput (MIMO) networks, where the channel reciprocity is not applicable. Thus, users are expected to feedback the bestmatch quantized channels to serving transmitters. Hence, an extensively large size of the feedback overhead is needed, which is linearly scaled at each user with the number of transmit antennas at the base-station (BS). In turn, the uplink (UL) channel capacity may be consumed and the overall performance becomes fundamentally limited by the downlink (DL) channel quantization precision. An alternative CSI acquisition scheme is critically needed. In this paper, we propose a novel FDD massive MIMO system based on a spatial DL channel estimation scheme; it relies on the statistical spatial correlation of the UL and DL channel clusters, given an arbitrary frequency band gap between the UL and DL channels. A transformation matrix is constructed to precode the observed UL channel on the estimated dominant DL angles of departure. The proposed scheme significantly outperforms the recent state-of-the-art techniques, without the cost of user feedback overhead bits and prior knowledge of the channel statistics.

In this paper, the impact of co-channel interference (CCI) on the performance of an underlay cognitive radio (CR) network over Nakagami-m fading channels is presented and analyzed. More precisely, a decode-and-forward (DF) relay protocol for a dual-hop cognitive cooperative network is considered. In this study, the impact of both the primary transmitter and CCI on the secondary system performance are considered. First, an exact expression for the equivalent signal-to-interference-plus-noise ratio (SINR) of the secondary system is obtained. Then, the corresponding exact and asymptotic cumulative distribution function (CDF) are derived. From this, the exact outage performance for the secondary network is investigated. From the results, it can be inferred that the presence of the CCI and primary network interference severely degrades the system performance. Moreover, a higher value of the shape parameter of the desired channel gives better performance and diversity gain. Finally, the analytically derived results have been supported by providing numerical and Monte Carlo simulations results.

In this paper, we accurately model the hardware impairments (HWI) as improper Gaussian signaling (IGS) which can characterize the asymmetric characteristics of different HWI sources. The proposed model encourages us to adopt IGS scheme for transmitted signal that represents a general study compared with the conventional scheme, proper Gaussian signaling (PGS). First, we express the achievable rate of HWI systems when both PGS and IGS schemes are used when the aggregate effect of HWI is modeled as IGS. Moreover, we tune the IGS statistical characteristics to maximize the achievable rate. Then, we analyze the outage probability for both schemes and derive closed form expressions. Finally, we validate the analytic expressions through numerical and simulation results. In addition, we quantify through the numerical results the performance degradation in the absence of ideal transceivers and the gain reaped from adopting IGS scheme compared with PGS scheme.

In this work, the performance of spatial modulation (SM) for multiple-input multiple output (MIMO) underlay cognitive radio systems is studied under the effect of channel and hardware impairments. Specifically, a closed-form expression of the average pairwise error probability (APEP), an asymptotic APEP, and a tight upper bound of the average bit error rate (ABER) are derived for Rayleigh fading channels. Useful remarks are highlighted on the system diversity and on the impact of channel and hardware impairments. Numerical results, which are corroborated through simulations, show that the ABER performance saturates to a constant value in the high power region due to the effects of channel and hardware impairments.

Motivated by spectral efficiency improvement of the Quadrature Spatial Modulation (QSM), recent studies introduce the Orthogonal Frequency Division Multiplexing with Quadrature Index Modulation (OFDM-QIM), which includes the inphase and the quadrature dimensions in the index domain. Up to now, the performance analysis of this novel transmission technique assumes ideal hardware. For robust OFDM-QIM system implementation under realistic conditions, this paper derives a new analytical expression for the Pairwise Error Probability (PEP) over selective frequency Rayleigh fading channel and is used to calculate a tight upper bound of the Average Bit Error Probability (ABEP). The key of this derived expression is taking into account the impact of hardware impairments on the performance. Further, simple and generic asymptotic expression analysis is included. Numerical simulations are provided to prove the effectiveness of the proposed analysis.

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

In this paper, spatial modulation (SM) is used in a cooperative decode-and-forward (DF) cognitive radio system in order to enhance the overall spectral efficiency. In particular, a multi- antenna secondary transmitter communicates with a single antenna secondary receiver with the help of DF secondary relays in the presence of multiple primary users (PUs). To study the secondary system performance, we derive a closed-form expression for the average pairwise error probability (PEP) over Rayleigh fading channels assuming limited feedback from the PUs. A tight upper bounded average bit error rate is obtained using the PEP expression. Moreover, simple approximate expressions are obtained to get insights on the system diversity and estimation errors effects. Numerical results, which match simulations, show the effectiveness of SM in improving the overall secondary performance in the presence of channel estimation errors.

In this paper, we investigate the effects of shadowing and multi-path fading on a MIMO down-link amplify-and-forward (AF) dual-hop network. In the system, antenna selection is adopted at the first hop based on the shadowing information and we assume both hops undergo Generalized-K composite fading channel. For the considered model, approximate lower bound outage and error probability expressions are derived and asymptotic analysis is performed to investigate the effects of shadowing on the system performance. Moreover, the power allocation optimization problem is studied where optimal power values are obtained. Finally, the analytical findings are validated by the simulations.

This paper studies the recent novel multiple-input multiple-output transmission technique called quadrature spatial modulation (QSM), in underlay cognitive radio (CR) systems. In particular, a multi-antenna secondary transmitter (ST) communicates with a multi-antenna secondary receiver (SR) in the presence of a primary receiver (PR). Considering only the statistical knowledge of the ST-PR channel gain, the QSM-CR scheme is investigated using a mean value (MV)-based power allocation strategy referred to as MV-based scheme. Furthermore, assuming that the ST-PR channel gain is perfectly known, the QSM-CR scheme is investigated using a power allocation method based on instantaneous channel state information (CSI), referred to as CSI-based scheme. In each scheme, considering imperfect ST-SR channel estimation, we study the secondary system performance, where closed-form expressions for the average pairwise error probability (P̅E̅P̅) are derived over Rayleigh fading channels. A tight upper bounded average bit error rate is obtained using the derived P̅E̅P̅ expression. Moreover, simple approximate expressions are obtained to get insights on the system diversity and channel estimation errors' effects. Numerical results, which match with simulations, illustrate the robustness of QSM in enhancing the overall system performance in the presence of estimation errors.

The nature of cognitive radio is based on the co-existence of secondary users in the area of primary users. Co-channel interference (CCI), therefore, is a vulnerable phenomenon in such a system. Motivated by this, a more practical scenario has been considered for studying the performance of the single-input-multiple-output (SIMO) underlay cognitive cooperative network. In this investigation, the primary transceiver is considered as well as the impact of the CCI on the secondary network. For this practical scenario, the equivalent signal-to-interference-plus-noise ratio (SINR) of the secondary system is obtained by employing the selection combining (SC) technique at the receiver side. Then, the cumulative distribution function (CDF) of the equivalent SINR is derived. Using the derived CDF, exact outage probability for the secondary network is assessed. From the results, it can be deduced that using a multi-antenna scheme and applying the SC technique has the advantage of improving the system performance. Moreover, besides the impact of the interference power constraint, the presence of the primary transmitter and the CCI will severely reduce the system performance, especially when the CCI linearly increases with the secondary transmit powers. Finally, numerical results and Monte Carlo simulations have also been provided to support the correctness of the analytical derivations.

Quadrature spatial modulation (QSM) in cognitive radio (CR) is a new spectral efficient multiple-input multiple-output (MIMO) digital modulation technique. In QSM, the spatial constellation diagram of conventional spatial modulation (SM) system is extended to include both in-phase and quadrature components of the data symbol. As such, QSM combined with CR techniques achieve significant improvement in the overall spectral efficiency while the advantages of SM are retained. In this paper, we study the performance of QSM-MIMO-CR systems in the presence of mutual primary-secondary co-channel interference. A closed-form expression for the average pair-wise error probability (PEP) of the secondary system is derived and used to calculate a tight upper bound of the average bit error rate (ABER) over Rayleigh fading. In addition, a simple asymptotic expression is derived and analyzed. Simulation results, which corroborate the numerical ones, show the importance of QSM in improving the overall secondary performance.

In this study, the authors investigate the performance of opportunistic scheduling for the dual‐hop amplify‐and‐forward multi‐user cognitive relaying network. Expressions are derived for the cumulative distribution function (CDF) and probability density function of the equivalent signal‐to‐noise ratio (SNR). From the derived CDF, the outage performance of the cognitive network is investigated. Then, an expression for average error probability is derived. Furthermore, simple and generic asymptotic expressions for the outage and error probabilities are obtained and discussed. In addition, a closed‐form expression for the system's ergodic capacity is derived. Their asymptotic results show that opportunistic scheduling has no impact on diversity gain. It is confirmed that the array gain determines the SNR advantage of opportunistic scheduling over the single‐user scenario. Moreover, they study adaptive power allocation under the total transmit power constraint in order to minimise the average error probability. As expected, the results show that optimum power allocation improves system performance compared with uniform power allocation. Finally, numerical results and Monte Carlo simulations are also provided to support the correctness of the analytical calculations.

Quadrature spatial modulation (QSM) is proposed recently as an efficient multiple‐input–multiple‐output wireless communication technique. In QSM, spatial multiplexing gain is achieved through modulating a two‐dimensional spatial constellation diagram in addition to conventional signal modulation. It was demonstrated that QSM can be designed with single in‐phase and quadrature (IQ) transmitter. However, the impact of IQ modulator imperfections, which degrade signal fidelity and overall system performance, has not been studied in the literature. In this study, typical IQ modulator/demodulator is considered for QSM system and the performance of the system is analysed and discussed. In particular, IQ imbalance channel modelling, pair‐wise error probability, and average bit error ratio are discussed. Results reveal that IQ imbalance can lead to significant performance degradation of QSM system and should be carefully addressed for any future deployment.

In this paper, we provide a comprehensive analytical framework on the performance of multiple-input multiple-output (MIMO) mutlihop amplify-and-forward relay network employing transmit antenna selection (TAS) with receive maximal ratio combining (MRC) in the presence of randomly located interferers. The channel fading models per hop are assumed to be independent and follow exponential random distribution, and the interference is distributed according to the spatial Poisson point process PPP, which is further known as symmetric alpha stable distribution. The impact of spatial dependence across multiple antennas is facilitated by considering three different network interference models: 1) the isotropic model, where all receive antennas see interference belonging to the same Poisson point process (PPP); 2) the independent model, where each receive antenna sees interference belonging to a different independent PPP; and 3) the mixture model, where each receive antenna sees the superposition of the two previous models. The end-to-end transmission is performed using two TAS modes, which includes signal-to-noise ratio (SNR)-based selection, and signal-to-interference noise ratio (SINR)-based selection. The analysis provides new analytical results for the outage probability and symbol error rates (SER). In addition, the impact of feedback delay on the performance of the proposed system for SNR-based selection is investigated. We further study the optimum resource allocation strategies including power allocation, position allocation, and joint allocation for power and position. The obtained results are clarified through selected numerical and simulated examples.

In this paper, the performance of a multi-hop underlay cognitive radio network (UCRN) is thoroughly assessed. The co-existence of a primary transceiver and co-channel interference (CCI) is considered along with an uplink single-input multiple-output system utilizing selection combining and maximal ratio combining techniques at the receiver nodes. First, the equivalent per-hop signal-to-interference-plus-noise ratio (SINR) for the UCRN is formulated. Second, the exact cumulative distribution function (CDF) and the probability distribution function of the per-hop SINR are derived and discussed. Furthermore, approximate expressions exhibiting reduced complexity for the per hop equivalent CDF are derived to provide more insights. From the resulting CDF, the exact outage performance of the CR network is thoroughly assessed. In addition, mathematical formulas are derived for the average error probability and system ergodic capacity. Finally, the derived analytical expressions are validated by presenting numerical and simulation results for different network parameters. The results show that several factors contribute to the degradation of the system performance, namely, the interference power constraint, the primary transmitter power, and the presence of CCI, especially in the case where the CCI increases linearly with the secondary transmission powers.

In this paper, spatial modulation (SM) is used in multiple-input multiple-output (MIMO) spectrum sharing systems in order to enhance the overall spectral efficiency. In particular, a multi-antenna secondary transmitter, employing SM as a modulator, communicates with a multi-antenna secondary receiver in the presence of multiple primary users. To study the effect of estimation errors on the secondary system performance, we derive a closed-form expression for the average pairwise error probability (PEP) over Rayleigh fading channels assuming limited feedback from the PUs. A tight upper bounded average bit error rate is obtained using the PEP expression. Moreover, simple approximate expressions are obtained to get insights on the system diversity and estimation errors' effects. Numerical results, which match with simulations, show the efficacy of SM in improving the overall secondary performance in the presence of estimation errors.

This paper studies the use of spatial modulation (SM) in multiple-input multiple-output (MIMO) cognitive radio networks considering the primary receiver interference constraint and the maximum transmit power of the secondary transmitter. In particular, we investigate the effect of estimation errors on the secondary system performance, where a closed-form expression is derived for the average pairwise error probability (PEP) in Rayleigh fading environments. Based on this PEP expression, a tight upper bounded average bit error probability is obtained using the union bound formula. In addition, an asymptotic analysis is conducted and simple approximate expressions are derived to get useful insights on the system diversity and estimation errors' effects. Numerical results, which are validated through simulations, show that the SM is robust against estimation errors.

This paper considers a two-way relay system with time division broadcast (TDBC) protocol. In such protocol two end-sources exchange information with each other through help of a half-duplex decode- and-forward relay. To enhance the spectral efficiency in this system, we propose a novel scheme which incorporates signal space diversity with TDBC protocol. In the proposed scheme, original data symbols are rotated by a certain angle before being transmitted, and then the end- sources and the relay cooperate for transmitting in-phase and quadrature components of two consecutive rotated symbols. Thereby, the number of transmitted symbols are doubled over three time slots, which results in an increase in spectral efficiency. In particular, for this system we first derive a closed-form expression for the end- to-end (E2E) error probability with an arbitrary constellation to acquire all the resulting non- uniform constellation cases. Then, using the derived expression, we optimize the rotation angle at the different values of the signal-to-noise ratio to further improve the E2E error probability performance. Numerical results corroborate the theoretical analysis and show that the scheme proposed herein provides not only higher spectral efficiency, but also higher reliability transmission.

Cognitive radio allows secondary users to use the same existing frequency spectrum band as primary users. This co-existence has several impacts on the whole network. This has motivated us to study the performance of a more practical dual-hop underlay cognitive network, by considering the interference power constraint, the primary transceiver and the co-channel interference (CCI).We start by determining the equivalent signal-to-interference-plus-noise ratio (SINR) of the secondary network, then, we derive the cumulative distribution function (CDF) of the equivalent SINR. Using the derived CDF, system outage probability has been assessed. Furthermore, an approximate expression for the system average error probability has been derived. From the results it can be observed that besides the impact of the interference power constraint, the presence of the primary transmitter and the CCI will severely reduce the system performance especially when the CCI linearly increases with the secondary transmit power. Finally, numerical results and Monte Carlo simulations are also provided to sustain the correctness of the analytical derivations.

Quadrature spatial modulation (QSM) is a new multiple-input multiple-output (MIMO) transmission technique that enhances the overall spectral efficiency of conventional spatial modulation (SM). QSM extends the single dimension spatial constellation to another dimension by considering the inphase and the quadrature components of the data symbol. It has been shown that spectral efficiency can be significantly increased while most inherent advantages of SM are retained. In this paper, the impact of Gaussian imperfect channel estimation on the performance of QSM system is studied. A closed-form expression for the pair-wise error probability (PEP) of generic QSM system is derived and used to calculate a tight upper bound of the Average Bit Error Probability (ABEP) over Rayleigh fading. Also, simple asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results highlight the accuracy of the conducted analysis.

Despite the rich literature on cooperative networks, employment of different modulation levels by the source and relay terminals has not been investigated thoroughly from the physical layer perspective. In this paper, we investigate the bit error rate (BER) performance of selective relaying in a multi-relay decode-and-forward cooperative network where the source and the relays transmit using different modulation levels. Specifically, we derive a closed form expression for the end-to-end (uncoded) BER. To draw further insights on the BER performance, we also provide a simpler approximate BER expression that is accurate in the high signal-to-noise ratio regime. Finally, simulation results are presented to verify the analytical results. The derived BER expressions can be utilized in various other scenarios in which the destination selects the best signal (in terms of minimizing BER) among a set of signals which use different modulation levels. The set of signals to choose from may have already been received through orthogonal channels (selection combining), or this signal set may correspond to a set of “candidate” transmissions. The latter scenario is often referred to as selective transmission; applications of this scenario include selective relaying (the setting in this paper), fast base-station selection, and coordinated multipoint transmission and reception (CoMP).

This paper analyzes the performance of space modulation techniques over generalized fading channels with imperfect channel estimation. In particular, a unified approach for calculating the pairwise error probability (PEP) of spatial modulation (SM) and space shift keying (SSK) modulation techniques for multiple-input multiple-output (MIMO) wireless communication systems is presented. A new, simple, and exact closed-form expression for the PEP over generalized α-μ fading channels under imperfect channel state information (CSI) is derived. The PEP expression considers the joint distributions of the envelope and the phase of the fading channel. Furthermore, the derived PEP and the union bound technique are used to obtain a closed-form expression for the average bit error rate (BER). The influence of the fading parameters α and μ and the channel estimation error on the system performance is analyzed and discussed through representative numerical examples. The correctness of our derivations is validated by means of MonteCarlo simulations.

A high spectral efficiency multiple-input multiple- output (MIMO) technique called Quadrature Spatial Modulation (QSM) is proposed in this work. QSM enhances the overall spectral-efficiency of conventional SM systems by using an extra spatial modulation dimension. The conventional SM technique uses only the real part of the spatial modulation constellation and QSM extends this to in-phase and quadrature dimensions. It is shown that significant performance enhancements as compared to conventional SM can be achieved without any extra cost. Also, a closed-form expression for the pair-wise error probability (PEP) of generic QSM system is derived and used to calculate a tight upper bound of the Average Bit Error Probability (ABEP) over Rayleigh fading channels. Additionally, simple and general asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results corroborate the accuracy of the conducted analysis and demonstrate the significant enhancements of the QSM scheme.

A high spectral efficiency cooperative communication system is proposed in this paper. The concept of signal space diversity (SSD) is utilized to double the spectral efficiency of opportunistic cooperative communication networks. SSD rotates the transmitted symbols by a certain angle at the source, before transmission, such that each in-phase and quadrature component of the rotated symbol contains enough information to retrieve the entire original data symbol. As such, parts of the rotated symbols are transmitted by the source and the other parts are transmitted by a relay. In opportunistic relaying, the best relay among all relays that decode the source signals correctly participates in forwarding a message to the destination. Optimum receiver along with detailed performance analysis are presented in this paper. Also, asymptotic analysis and optimum power allocations at the source and the active relay are given. It is shown that the proposed technique enhances the performance by about 2dB over the conventional opportunistic relaying. As well, optimum power allocation is shown to further enhance the error probability performance.

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

Performance analysis of multi‐hop wireless networks with non‐regenerative relays over Nakagami‐ m fading channels in the presence of co‐channel interference is presented in this paper. In the analysis, an arbitrary number of independent and identically distributed Nakagami‐ m interferers will be considered. Closed‐form expression for the cumulative distribution function (CDF) of the upper bounded end‐to‐end signal‐to‐interference‐plus‐noise ratio (SINR) at the destination is given. The obtained CDF is then considered to study the average bit error probability (ABEP). Furthermore, an approximate expression for the CDF of the instantaneous end‐to‐end SINR is derived, based on which simple and general asymptotic expression for the error probability is presented and discussed. The derived asymptotic equation is shown to reduce to the already published equation in Rayleigh fading, which corroborate the exactness of the derived analysis. Besides, analytical comparison between amplify‐and‐forward and decode‐and‐forward multi‐hop systems in terms of ABEP is provided. Optimisation of the power allocation at the network's transmit nodes and the positioning of the relays are studied as well. It is shown that optimum power allocation achieves only coding gain, whereas optimising relay locations yields diversity gains as well as coding gain.

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

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

In this paper, spatial modulation (SM) is considered in a cooperative communication system and the effect of imperfect channel estimation on the overall system performance is analyzed. SM is a multiple-input multiple-output (MIMO) technique that considers the multiple transmit antennas as an added constellation points and utilizes them to boost the spectral efficiency. In our analysis, a wireless communication system, where a source communicating with a destination through a direct link and multiple decode and forward (DF) relays, is considered. Imperfect channel knowledge is assumed at each relay and at the destination node. In cooperative mode, only the relays that correctly decode the source signal forward the decoded message to the destination. A closed form expression of the pair wise error probability (PEP) is obtained for a system consisting of two transmit antennas, multiple DF relays and single receive antenna and a tight upper bound is given for the average error probability. As well, asymptotic expression for the PEP at high signal to noise ratio (SNR) is derived.

In this paper, performance and optimization study of multi-hop wireless system with amplify and forward (AF) relays over Nakagami-m fading channels and in the presence of co-channel interference is considered. Arbitrary number of independent and identically distributed Nakagami-m interferers is assumed in the analysis. The cumulative distribution function (CDF) of the upper bounded end-to-end signal-to-interference-plus-noise ratio (SINR) at the destination is calculated in closed-form. The obtained CDF is then used to study the end-to-end average bit error probability (ABEP). As well, approximate expression for the CDF of the instantaneous end-to-end SINR is derived. Based on this, simple and general asymptotic expression for the error probability is presented and discussed. Finally, optimizing power allocation at the transmit nodes and the positioning of the relays are studied. Obtained results revealed that optimum power allocation slightly enhances the performance, whereas optimizing relay locations yields significant performance enhancement. Further improvement is shown to be achieved through joint power and positions optimization.

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

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

Space modulation techniques, such as spatial modulation (SM) and space shift keying (SSK), are efficient low complexity implementation of multiple input multiple output (MIMO) systems. In such techniques, a single transmit-antenna is activated during each time instant and the activated antenna index is used to convey information. Due to the novel method of conveying information, a major criticism arises on the practicality of such techniques in the presence of real-time imperfections such as channel estimation errors. Therefore, the aim of this paper is to shed light on this issue. The performance of such systems are analyzed in the presence of Gaussian imperfect channel estimations. More specifically, the performance of SSK system consisting of Nttransmit and Nrreceive antennas with maximum-likelihood (ML) detection and imperfect channel state information (CSI) at the receiver is studied. The exact average bit error probability (ABEP) over Rayleigh fading channels is obtained in closed-form for Nt= 2 and arbitrary Nr; while union upper bound is used to compute the ABEP when Nt>; 2 and arbitrary Nr. Furthermore, simple and general asymptotic expression for the ABEP is derived and analyzed. Besides, the effect of imperfect CSI on the performance of SM, Alamouti and SSK schemes considering different number of channel estimation pilots are studied and compared via numerical Monte Carlo simulations. It is shown that, on the contrary to the raised criticism, space modulation techniques are more robust to channel estimation errors than Alamouti since the probability of error is determined by the differences between channels associated with the different transmit antennas rather than the actual channel realization.

In this paper, single amplify and forward (AF) relay is placed between the source and the destination in space shift keying (SSK) multiple-input single output (MISO) system. In SSK, transmit-antenna indices form a spatial constellation diagram where each group of base two logarithm of the input data bits are mapped to one spatial constellation point. Hence, at each time instant, only single transmit antenna is active, which transmits certain energy that contains no data symbol, and all other antennas are off. The receiver, with single receive antenna, decodes the received signal from the single antenna AF relay and estimates the index of the active transmit-antenna to retrieve the transmitted information bits. Closed-form bit error ratio (BER) is derived for the considered system in correlated and uncorrelated channels assuming a transmitter with two transmit antennas. The analytical framework is generalized for an arbitrary number of transmit antennas and a tight upper bound on the BER performance is derived. Additionally, asymptotic analysis are carried out to investigate the effect of the different system parameters on the overall system performance. The analytical results are validated through Monte-Carlo simulation results.

In this study, the authors introduce an adaptive bit loading scheme for an amplify-and-forward orthogonal frequency division multiple cooperative system with relay selection. The proposed bit loading scheme maximises the throughput for a target error rate taking into account the quality of imperfect channel estimation. It relies on estimated channel state information (CSI) at the destination node and partial CSI (which involves the number of loaded bits) at the source node. The authors provide extensive Monte Carlo simulation results to demonstrate the throughput and the no-transmission probability performance of the proposed scheme and discuss the effect of various system and channel parameters on the performance.

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

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

In this study, the authors examine the effect of a channel-estimation error on the error and outage probabilities of a multi-relay system with amplify-and-forward relaying over a frequency-flat Rician fading channel. The authors consider orthogonal relaying and study both conventional cooperative systems (i.e. all relays participate in the relaying phase) and opportunistic cooperative systems (i.e. only the best relay participates in the relaying phase). Based on the derivation of an effective signal-to-noise ratio (SNR) at the destination node taking into account channel-estimation error, the authors obtain closed-form expressions for error and outage probabilities in a high SNR regime. Such closed-form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. Computer simulations are used to validate the authors’ analytical results.

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

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

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

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

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

Cooperative-diversity has recently been proposed as an efficient technique to form virtual antenna arrays without using collocated multiple antennas at the transmitters or receivers. Cooperative-diversity networks use the neighbour nodes to assist the source by sending the source information to the destination for achieving spatial diversity. Regular cooperative-diversity networks make an inefficient use of the channels because relays forward the source signal to the destination every time regardless of the channel conditions. Incremental-relaying cooperative-diversity has been proposed to save the channels by restricting the relaying process to the bad channel conditions only. Incremental-relaying cooperative-diversity networks exploit limited feedback from the destination terminal, for example, a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback, in this case only, the relay retransmits the source signal in an attempt to exploit spatial diversity by combining the signals received at the destination from the source and the relay. In this study, the authors study the end-to-end performance of un-coded incremental-relaying cooperative-diversity networks using decode-and-forward and amplify-and-forward relaying over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate, the signal-to-noise ratio (SNR) outage probability and average achievable rate are determined. Results show that the un-coded incremental-relaying cooperative-diversity can achieve the maximum possible diversity, compared with the regular cooperative-diversity networks, with higher channel utilisation.

In this study, the performances analysis of cooperative-diversity networks using adaptive decode-and-forward (DF) relaying over independent non-identical flat Nakagami-m fading channels is investigated. The authors derive exact and approximate closed-form expressions for the error probability, outage probability and average channel capacity, and analyse their dependence on the channel parameters. In adaptive DF relaying, among M relays that can participate, only C relays (C≤M), with good channels to the source, DF (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using maximum ratio combining technique. The authors derive a closed-form expression for the the moment generating function of the total signal-to-noise ratio (SNR) at the destination node. Then, the authors find an exact closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the exact closed-form expressions of the performance metrics. Such closed-form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. Since exact expressions are complicated, the authors have introduced simple approximate expressions for the error and outage probabilities where these expressions explicitly show the diversity order. Computer simulations are used to validate our analytical results. Results show the significant performance improvement because of the use of the adaptive DF cooperative diversity. Also, results indicate that increasing the number of relays will not always decrease the outage probability.

In this paper, we introduce a comprehensive analysis of the incremental-best-relay cooperative diversity, in which we exploit limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the best relay among M available relays retransmits the source signal in an attempt to exploit spatial diversity by combining the signals received at the destination from the source and the best relay. Furthermore, we study the end-to-end performance of the incremental-best-relay cooperative-diversity networks using decode-and-forward and amplify-and-forward relaying over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate, the outage probability and average channel capacity are determined. Results show that the incremental-best-relay cooperative diversity can achieve the maximum possible diversity order, compared with the regular cooperative-diversity networks, with higher channel utilization. In particular, the incremental-best-relay technique can achieve M+1 diversity order at low signal-to noise ratio (SNR) and considerable virtual array gain at high SNR.

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

Performance analysis of cooperative multiple-input multiple-output (MIMO) relaying system with a single relay is discussed in this paper. The MIMO scheme is based on Alamouti space-time block coding (STBC) over Rayleigh flat fading channels. The source node, equipped with two transmit antennas, simply broadcasts each STBC code to the relay and the destination nodes. Then, the relay node, equipped with multiple antennas, amplifies-and-forwards (AF) the received STBC codes. Finally, the destination node uses maximum ratio combining (MRC) and exploits the diversity gain obtained through the direct and the indirect links simultaneously. Lower bounds of the symbol error probability (SEP) and the outage probability are derived using the moment generating function (MGF) of the total signal-to-noise ratio (SNR) for a particular signal of M-ary-quadrature-amplitude modulation (M-QAM). Subsequently, simulation results are provided to verify the validity of the analytical results.

In this paper, we investigate the performance of a cooperative network with adaptive decode-and-forward (DF) relaying over time-selective frequency-flat Rayleigh fading channels. In adaptive DF relaying, only a subset of the available relays with "good" channels are allowed to participate in the relaying phase. The destination combines the direct and the relayed signals using maximal ratio combining technique. Pilot-symbol-assisted modulation (PSAM) is used for the estimation of time-varying fading channel coefficients. For the system under consideration, we derive an exact closed-form expression for the average bit error rate. Such closed form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. We further present computer simulations to validate our analytical results.

In this paper, we investigate the effect of channel estimation error on the error rate performance of a multi-relay system with amplify-and-forward relaying. We consider orthogonal relaying and study both conventional cooperative systems (i.e., all relays participate in the relaying phase) and opportunistic cooperative systems (i.e., only the best relay participates in the relaying phase). Based on the derivation of effective signal-to-noise ratio at the receiver taking into account channel estimation error, we obtain closed-form expressions for bit error rate. Monte-Carlo simulations are further provided to confirm the analytical results.

Outage analysis of cooperative space-time block coding (STBC) multiple-input multiple-output (MIMO) relaying system with a single relay is discussed in this paper. The source node, equipped with two transmit antennas, broadcasts each STBC code to the relay and the destination nodes. Then, the relay node also equipped with multiple antennas, amplifies-and-forwards (AF) the received STBC codes. Finally, the destination node uses maximum ratio combining (MRC) and exploits the diversity gain obtained through the direct and the indirect links simultaneously. Lower bounds of the outage probability is derived using the moment generating function (MGF) of the total signal-to-noise ratio (SNR) for a particular signal of M-ary-quadrature-amplitude modulation (M-QAM). Simulation results are provided to verify the validity of the analytical results.

In this paper, the use of adaptive source transmission with amplify-and-forward best relaying selection scheme is proposed. Three different adaptive techniques are considered: (i) optimal simultaneous power and rate adaptation; (ii) constant power with optimal rate adaptation; (iii) channel inversion with fixed rate. The capacity upper bounds of these adaptive protocols are derived for the relay-selection amplify-and-forward cooperative network over independent and identical (i.i.d) and independent and non-identical (i.n.d) Rayleigh fading channels. The capacity analysis is based on an upper bound on the effective received signal-to-noise ratio (SNR). It is shown that at high SNR the optimal simultaneous power and rate adaptation and the optimal rate adaptation with constant power provide roughly the same capacity. Channel inversion is shown to suffer from a deterioration in capacity relative to the other adaptive techniques.

We consider adaptive decode-and-forward (DF) cooperative-diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). In this paper, we analyze the system where N multiple relays that have the strongest signal strength at the destination are selected out of M relays and forward their received data from the source node to the destination node. We derive closed-form expressions for the average symbol error probability, the outage probability and the average channel capacity. In particular, closed-form expression for the moment generating function of the SNR at the destination node is determined. Then, we find a closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the closed-form expressions of the performance metrics. Simulation results are also given to verify the analytical results.

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

In this paper, we investigate the performance of constant-power adaptive L-ary quadrature modulation (L-QAM) for an opportunistic decode-and-forward (DF) relaying scheme. Specifically, we adopt adaptive five-mode L-QAM with fixed and optimum switching and derive expressions for the error rate, outage probability and spectral efficiency over both independent and identical (i.i.d.) and independent and non-identical (i.n.d.) Rayleigh fading channels.

Cooperative diversity is a relatively new technique that can be used to improve the performance of the wireless networks. The main advantage of this technique is that the diversity gain can be achieved without the need to install multiple antennas at the transmitter or the receiver. In this paper, we investigate the performance of the best-relay selection scheme where the "best" relay only participates in the relaying. Therefore, two channels only are needed in this case (one for the direct link and the other one for the best indirect link) regardless of the number of relays (M). The best relay is selected as the relay node that can achieve the highest signal-to-noise ratio at the destination node. A general mathematical probability model is developed to study the outage performance of the best-relay selection adaptive decode-and-forward cooperative networks. In particular, closed-form expressions for the outage probability and average channel capacity are derived. Results show that the best-relay selection not only reduces the amount of required resources but also can maintain a full diversity order.

In this letter, we consider the adaptive decode-and-forward (DF) and amplify-and-forward (AF) cooperative-diversity systems with the Nthbest-relay selection scheme. In the best-relay selection scheme, from the set of M relays the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally the Nth best relay. We derive closed-form expressions for the symbol error probability, outage probability and asymptotic error probability. In particular, we derive a closed-form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function (MGF) of the output SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. All these expressions are derived over identical and non-identical Rayleigh fading channels. Results show that with the Nthbest relay the diversity order is equal to (M - N + 2) where M is the number of relays.

Cooperative-diversity networks have recently been proposed as an effective technique to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider the adaptive decode-and-forward (DF) cooperative-diversity system with the Nth best-relay selection scheme. In the best-relay selection scheme, from the set of M relays the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally the Nth best relay. We derive closed-form expressions for the symbol error probability, outage probability and channel capacity. In particular, we derive a closed-form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function (MGF) of the output SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. Results show that with the Nth best relay the diversity order is equal to (M - N + 2) where M is the number of relays. Simulation results are also given to verify the analytical results.

We consider power allocation (PA) and relay positioning in a dual-hop decode-and-forward relaying system over Nakagami-m fading channels. We investigate adaptive power allocation (PA) with fixed relay location, optimal relay location with fixed power allocation and joint optimization of the PA and relay location under transmit power constraint in order to minimize outage probability and average error probability upper bound. Results show that the analyzed adaptive algorithms outperform uniform algorithms and direct transmission. It is also found that as the source destination channel is getting better, the less power will be needed to allocate to the relay node in order to satisfy the optimization criteria. Numerical results are presented to verify our analysis.

In this paper, we investigate amplify-and-forward (AF) incremental-best-relay cooperative diversity to make efficient use of the channel spectrum by exploiting a limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the best relay among M available relays retransmits the source signal in an attempt to exploit spatial diversity by combining the signals received at the destination from the source and the best relay. Closed-form expressions for the bit error rate, the outage probability and average channel capacity are determined over independent non-identical Rayleigh fading channels. Results show that the AF incremental-best-relay cooperative diversity can achieve the maximum possible diversity order, compared with the conventional cooperative-diversity networks, with higher channel utilization. In particular, the AF incremental-best-relay technique can achieve M + 1 diversity order at low signal-to noise ratio (SNR) and and exhibits a 20 to 30 dB gain relative to direct transmission, assuming single-antenna terminals at high SNR.

We investigate the incremental relaying protocol in conjunction with relay-selection cooperative diversity networks with an aim to make efficient use of the degrees of freedom of the channels by exploiting a limited feedback signal from the destination. In particular, whenever the direct link from the source to the destination is not favorable to decoding, the destination will request the help from the best relay. The performance of the incremental-relay-selection decode-and-forward technique over independent non-identical Rayleigh fading channels is derived in terms of average bit error probability, outage probability and average channel capacity. The analytic results show that the system assisted by the selection relaying can achieve full diversity at low SNR regime and exhibits a 20 to 30 dB gain relative to direct transmission, assuming single-antenna terminals.

Cooperative-diversity networks have been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider the amplify-and-forward cooperative-diversity system with theNthbest-relay selection scheme. In the best-relay selection scheme, the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally theNthbest relay. We derive closed-form expressions for the symbol error probability, outage probability and channel capacity. In particular, we derive a closed-form expression for the probability density function of the signal-to-noise ratio of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function of the total SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. Results show that with theNthbest relay the diversity order is equal to (M-N+ 2) whereMis the number of relays. Simulation results are also given to verify the analytical results.

We consider an amplify-and-forward (AF) cooperative-diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays), in this paper, we analyze the system where N multiple relays that have the strongest signal strength at the destination are selected out of M relays and forward their received data from the source node to the destination node. We derive closed-form expressions for the average symbol error probability, the outage probability, the average channel capacity, the average signal-to-noise ratio (SNR), the amount of fading, and the SNR moments. In particular, closed-form expression for the moment generating function of the SNR at the destination node is determined. Then, we find a closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the closed-form expressions of the performance metrics. Simulation results are also given to verify the analytical results. Results show that increasing N will slightly improves the error performance and degrade the outage probability and average channel capacity. In particular, N = M gives the best performance in terms of error performance and N = 1 (the best relay) gives the best performance in terms of outage probability and average channel capacity.

In this paper, the performances analysis of cooperative-diversity networks using adaptive decode-and-forward (DF) relaying over independent non-identical flat Nakagami-m fading channels is investigated. We derive closed-form expressions for the error probability, outage probability and average channel capacity, and analyze their dependence on the channel parameters. In adaptive DF relaying, among M relays that can participate, only C relays (C les M), with good channels to the source, decode and forward (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using maximum ratio combining (MRC) technique. We derive a closed-form expression for the the moment generating function (MGF) of the total signal-to-noise ratio (SNR) at the destination node. Then, we find a closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the closed-form expressions of the performance metrics. Computer simulations are used to validate our analytical results. Results show the significant performance improvement due to the use of the adaptive DF cooperative diversity. Also, results indicate that increasing the number of relays will not always decrease the outage probability.

Cooperative-diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. Cooperative-diversity networks use the neighbor nodes to assist the source by sending the source information to the destination for achieving spatial diversity. Regular cooperative-diversity networks make an inefficient use of the channel resources because relays forward the source signal to the destination every time regardless of the channel conditions. Incremental relaying cooperative diversity has been proposed to save the channel resources by restricting the relaying process to the bad channel conditions only. Incremental relaying cooperative relaying networks exploit limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the relay retransmits in an attempt to exploit spatial diversity by combining the signals that the destination receives from the source and the relay. In this paper, we study the end-to-end performance of incremental relaying cooperative-diversity networks using decode-and-forward relays over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate and the signal-to-noise ratio (SNR) outage probability are determined. Results show that the incremental relaying cooperative diversity can achieve the maximum possible diversity, compared with the regular cooperative-diversity networks, with higher throughput.

Cooperative diversity is a promising technology for future wireless networks. In this paper, we derive the average bit error rate (BER) and outage probability (Pout) for differential equal gain combining (EGC) in cooperative diversity networks. The considered network uses adaptive decode-and-forward (DF) relaying over independent non-identical Nakagami-m fading channels. In adaptive DF relaying among M relays, that can participate, only C relays (C les M), with good channels to the source, decode and then forward (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using differential EGC. We first derive a simple exact expression for the equivalent SNR at the destination. Second, we derive the expressions of the PDF and the MGF of this equivalent total SNR at the destination. Then the MGF is used to determine the error and outage probabilities of adaptive DF with an arbitrary number of relays. Furthermore, we found (in terms of MGF) the SNR moments, the average signal-to-noise ratio (SNR) and the amount of fading. Computer simulations are used to validate our analytical results. Results show the significant performance improvement due to the use of the adaptive DF cooperative diversity. Also, results show that the performance of the adaptive DF differential EGC is comparable to the adaptive DF maximum ratio combining (MRC) performance.

In this paper, we present closed form expressions for tight lower bounds of the performance of dual-hop non- regenerative relaying over independent non-identical Weibull fading channels. Since it is hard to find a closed form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) for the Weibull fading distribution, we use an approximate value instead. Novel closed form expressions for the PDF, outage probability and the moments of the approximate value of the SNR at the destination are derived. Also, the average SNR and amount of fading are determined. Moreover, closed form expressions (in terms of the tabulated Meijer's G-function) are found for the average symbol error probability (for several modulations schemes) as well as the Shannon capacity. It should be noted that the Meijer's G-function is widely available in many scientific software packages, such as MATHEMATICAL and MAPLEreg. Finally, simulations results are also shown to verify the analytical results.

Cooperative diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider adaptive decode-and-forward cooperative diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). In this letter, we investigate the performance of the best-relay selection scheme where the best relay only participates in the relaying. Therefore, two channels only are needed in this case (one for the direct link and the other one for the best indirect link) regardless of the total number of relays. The best relay is selected as the relay node that can achieve the highest signal-to-noise ratio at the destination node. We developed a general analytical model to analyze the performance of the adaptive decode-and-forward cooperative networks with best-relay selection. In particular, exact closed-form expressions for the error probability and Shannon capacity are derived over independent and nonidentical Rayleigh fading channels. Results show that the best-relay selection not only reduces the number of required channels but also can maintain a full diversity order.

Cooperative diversity is a promising technology for future wireless networks. In this paper, we derive exact closed-form expressions for the average bit error rate (BER) and outage probability (Pout) for differential equal gain combining (EGC) in cooperative diversity networks. The considered network uses amplify-and-forward relaying over independent non-identical Nakagami-m fading channels. The performance metrics (BER and Pout) are derived using the moment generating function (MGF) method. Furthermore, we found (in terms of MGF) the SNR moments, the average signal-to-noise ratio (SNR) and amount of fading. Numerical results show that the differential EGC can benefit from the path-loss reduction and outperform the traditional multiple-input single output (MISO) system. Also, numerical results show that the performance of the differential EGC is comparable to the maximum ratio combining (MRC) performance.

Cooperative diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. Cooperative diversity networks use the neighbor nodes to assist the source by sending the source information to the destination for achieving spatial diversity. Regular cooperative diversity networks make an inefficient use of the channel resources because relays forward the source signal to the destination every time regardless of the channel conditions. Incremental relaying cooperative diversity has been proposed to save the channel resources by restricting the relaying process to the bad channel conditions only [1]. Incremental relaying cooperative relaying networks exploit limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the relay retransmits in an attempt to exploit spatial diversity by combining the signals that the destination receives from the source and the relay. In this paper, we study the end-to-end performance of incremental relaying cooperative diversity networks using amplify-and-forward relays over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate and the signal-to-noise ratio (SNR) outage probability are determined. Results show that the incremental relaying cooperative diversity can achieve the maximum possible diversity, compared with the regular cooperative diversity networks, with higher channel utilization.

In this paper, we present closed form expressions for tight lower bounds of the performance of dual-hop non- regenerative relaying over independent non-identical generalized gamma fading channels. The generalized gamma distribution is very versatile and accurately approximates many of the commonly used channel models for multi-path, shadow, and composite fading. Since it is hard to find a closed form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) for the generalized gamma distribution, we use an approximate value instead. Novel closed form expressions for the PDF, outage probability and the moments of the approximate value of the SNR at the destination are derived. Also, the average SNR and amount of fading are determined. Moreover, closed form expressions (in terms of the tabulated Meijer's G-function) are found for the average symbol error probability (for several modulations schemes) as well as the Shannon capacity. It should be noted that the Meijer's G-function is widely available in many scientific software packages, such as MATHEMATICAreg and MAPLEreg. Finally, simulations results are also shown to verify the analytical results.

This paper analyzes the end-to-end bit error rate performance of cooperative diversity networks using decode-and-forward (DF) relaying over independent non-identical flat Nakagami-m fading channels. We derive a closed-form expression for the error rate and analyze its dependence on the channel parameters. In DF cooperative diversity, a relay detects the received signal and then relays the signal to the destination. The destination combines the two signals received from the source and relay. We assume here that the relay decides independently (based on the received signal quality at the relay) whether or not to forward the signal to the destination. Computer simulations are used to validate our analytical results. Results show the significant performance improvement due to the use of the DF cooperative diversity. Also, results indicate that the source-relay channel has the most influence on the error performance.

Cooperative diversity is a promising technology for future wireless networks. In this paper, based on the moment generating function (MGF), we derive exact closed-form expressions for the average bit error rate (BER), the amount of fading (AF), and outage probability (Pout) for cooperative diversity networks withamplify-and-forwardrelaying overRayleigh-fading channel using differentially- non-coherent equal gain combining (EGC) technique. We show that this scheme (differentially-non-coherent EGC) achieves a diversity order of 2 at highSNR. The main advantage of this scheme is that it does not need channel state. information of the transmission links at the relay and destination nodes. This feature reduces the design and implementation complexity. Furthermore, we study in this paper the impact of the relay location on the system performance.