In this paper, we investigate a two-way backscatter communication system assisted by a dual-sided reconfigurable intelligent surface (RIS) which consists of active or passive elements. By altering the switch status within each RIS element, different transmission and reflection coefficients can be achieved, thus enabling a binary backscatter modulation. To begin with, we propose a maximum likelihood (ML) detector and a maximal-ratio-combining (MRC)-based detector for the proposed dual-sided RIS-assisted two-way communication system to decode the backscatter signal as well as the end-users’ respective signal. Moreover, we compare the underlying system with and without backscatter modulation at the dual-sided RIS. Subsequently, we analyze the corresponding symbol error rate (SER) and throughput to highlight the performance differences of the various communication modes under perfect channel state information (CSI) and imperfect CSI. Finally, numerical results reveal that: (1) the ML detector significantly outperforms the MRC-based detector in terms of SER and throughput; (2) the throughput performance can be significantly improved by adopting a backscatter modulation, especially in the medium and high signal-to-noise ratio regimes; (3) the phase shift of the dual-sided RIS element should be aligned with the signal to be decoded first, to guarantee an improvement in the SER performance.

This paper proposes an amplitude-phase decoupling scheme for reconfigurable intelligent surface (RIS)-enabled backscatter systems, which aims to achieve the standard quadrature amplitude modulation (QAM) constellation on the harmonics by considering the amplitude-phase coupling effects in the non-linear modulation procedure. To begin with, we derive closed-form expressions of the symbol error rate (SER) and throughput of the underlying system with and without decoupling. Moreover, we formulate the maximum amplitude expression of the lthorder harmonic for the coupling amplitude-phase curve. Finally, numerical results show that the proposed amplitude-phase decoupling scheme significantly improves the system performance in terms of SER and throughput, very close to the performance of the ideal one with perfect fitting function.

In this work, we investigate the secrecy performance of a wireless network that enables an aerial intelligent reflecting surface-unmanned aerial vehicle for non-orthogonal multiple access (NOMA) transmissions in the presence of a friendly jammer. For a practical NOMA-based system with imperfect successive interference cancellation, we develop a theoretical framework for the secrecy outage probability (SOP) and the strictly positive secrecy capacity. However, the derived expressions are complex and therefore, do not provide important insights into the system design. In this regard, explicit and simplified formulas of the asymptotic SOP are derived under high signal-to-noise ratio conditions for scenarios with and without jamming. Through extensive simulations, we verify the correctness of the proposed theoretical framework. Notably, numerical results reveal the superior performance of the jamming-enabled system over its non-jamming counterpart and demonstrate the efficacy of the proposed scheme.

This paper investigates the secrecy performance of a keyhole-aided multi-user communication network in the presence of multiple eavesdroppers. The communication happens through the same keyhole for legitimate users and eavesdroppers. In this context, the secrecy performance is evaluated for a user scheduling technique by obtaining the exact closed-form expression of secrecy outage probability (SOP). Further, a simplified asymptotic SOP expression is derived assuming high signal-to-noise ratio (SNR) scenario for a better understanding of the impact of system parameters. The effect of the keyhole parameters, number of users, number of eavesdroppers, and threshold secrecy rate on the SOP performance are also investigated for the considered system model. In the high-SNR regime, the asymptotic SOP saturates to a constant value and does not depend on the keyhole parameter and the channel parameter of the source-to-keyhole channel.

Existing reconfigurable intelligent surface (RIS)-enabled symbiotic systems generally rely on a dynamic adjustment of the amplitude of the RIS’s reflection coefficient to continuously change from 0 to 1 to support the underlying symbiotic trans-missions, which is however infeasible for practical RIS hardware. To address this, we propose a novel on-off digitalized symbiotic backscatter non-orthogonal multiple access (NOMA) system that employs an on-off mechanism of the RIS’s reflecting elements. In particular, the adjustment of the on-off state of reflecting elements in batches is adaptively invoked to control the power gain of the backscatter channel, thereby changing the amplitude of backscatter signals to establish symbiotic transmissions. In order to evaluate the practicability of the proposed on-off symbiotic mechanism, an analytical expression of coexistence outage probability at high SNR has been derived. Moreover, the adjustment of RIS’s elements on-off state is discussed and extended to the scenarios of one-shot and one-by-one activation modes. Finally, representative numerical results show that when a sufficient number of reflecting elements is deployed on the RIS, our proposed on-off mechanism can fully support the symbiotic transmissions of the underlying systems.

This paper proposes a reconfigurable intelligent surface (RIS) enabled symbiotic backscatter non-orthogonal multiple access (NOMA) system based on uniquely factorable constellation pair (UFCP) rule, where the RIS elements are used to passively modulate the backscatter signal over the primary NOMA signal. According to the coding design of UFCP, the backscatter signal modulated at the RIS and the primary NOMA signal emitted by the source, are jointly constructed to form a UFCP for each primary NOMA signal, thereby facilitating the decoding of the primary NOMA signal and backscatter signal at the receiver. To recover the backscatter signal modulated at the RIS as well as the primary NOMA signal, a successive interference cancellation (SIC) based detector is proposed and a closed-form expression of the symbol error rate (SER) is derived. Finally, extensive numerical results show that the proposed system possesses a signal-to-noise-ratio (SNR) gain of more than 10 dB at the SER level of 10−2in comparison with its counterpart without the UFCP design.

In this paper, we propose a two-way backscatter communication system assisted by an active and passive dualsided reconfigurable intelligent surface (RIS) where the active RIS element contains an amplifier while the passive one does not. By altering the switch status within each RIS element, different transmission and reflection coefficients can be achieved, enabling a binary backscatter modulation. Moreover, a maximal-ratio-combining (MRC)-based detector is proposed to decode the backscatter signal and the end-user's signal, and the corresponding symbol error rate (SER) and throughput are subsequently analyzed. Numerical results show that by avoiding the additive thermal noise within each RIS element, passive dual-sided RISenabled communications outperform the active dual-sided RISenabled communications in terms of SER, and it is also revealed that the throughput can be significantly improved through backscatter modulation.

In this paper, we investigate a novel representation of a band-limited and continuous-time signal using a sequence of impulses or events. To begin with, we evaluate the mean squared error between the original signal and its reconstructed version assuming that: (i) the signal samples are transmitted at the Shannon channel capacity; (ii) the signal representation using the cosine phase method is done before its transmission. The proposed approach is then compared with an existing approach based on the signal transmission of quantized samples. Finally, we provide some representative examples through Monte Carlo simulations, consistently revealing the superiority of the proposed signal representation approach over the existing one regarding transmission bandwidth and peak-to-peak value of the original signal.

This paper investigates the covert communication performance of a radio frequency underwater acoustic communication (RF-UAC) system deploying rate-splitting multiple access (RSMA). The proposed system aims to enhance the covertness of communication signals while maintaining reliable communications for legitimate users. In this context, we model the RF link using the Rayleigh distribution and the UAC link using the κ – μ shadow distribution. Moreover, We analytically evaluate key performance metrics for the proposed system, including the detection error probability, outage probability and covert communication rate under various system parameters, such as signal-to-noise ratio thresholds and power allocation between public and private streams. Our extensive numerical investigations validate the proposed analytical expressions, demonstrating the role of key system and channel parameters on the performance of RSMA-assisted RF-UAC communications.

This paper proposes a fast-decoding scheme based on the successive interference cancellation (SIC) framework for symbiotic backscatter multi-user non-orthogonal multiple access (NOMA) systems, which aims to decode the desired primary NOMA signal and the backscatter signal for the end-users in an efficient manner. Under the proposed decoding framework, we derive a closed-form expression of the coexistence outage probability (COP) with perfect SIC for the end-users over Nakagami-m fading channel. More importantly, the diversity order is determined by the bottleneck fading parameter of the two-hop backscatter channels in most general cases, but is dominated by the bottleneck fading parameter of the primary and backscatter channels in a rare special case. Due to the influence of the residual interference, the COP with imperfect SIC would converge to an error floor. Moreover, we formulate the symbiotic constraints to guarantee the minimum decoding times and a shorter decoding time than the conventional solutions, and further derive the corresponding successful fast-decoding probability at high transmit signal-to-noise ratio (SNR). The results show that by keeping a weak primary channel statistics or lowering the threshold to decode the backscatter signal, the proposed fast-decoding scheme outperforms conventional schemes in terms of decoding times.

This paper proposes a simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) segmented symbiotic backscatter non-orthogonal multiple access (NOMA) system. Specifically, the STAR-RIS is divided into an enchancing primary signal (EP) zone and a backscatter device (BD) zone. To characterize the overall transmission effectiveness, the metric of sum ergodic capacity (EC) of the considered symbiotic system is established and the corresponding suboptimal approximation solutions are derived in closed-form for three typical NOMA channel conditions. Our results show that the sum EC obeys the scaling law of $\log \left(P_{s}\right)$ where $P_{s}$ is the total transmit power, and is dominated by the weaker one of the transmission and reflection channels. Moreover, our simulation results show that both the instantaneous sum rate and the sum EC derived by the proposed suboptimal solution are very close to the optimal one obtained through exhaustive search. More importantly, the transmission effectiveness of the proposed system is superior to the STAR-RIS-assisted NOMA system and the STAR-RIS-segmented symbiotic backscatter orthogonal multiple access (OMA) system. Additionally, it is shown that as the quantification order of the imperfect channel state information (ipCSI) increases, the sum EC performance gradually improves.

This paper puts forth a proposal for a reconfigurable intelligent surface (RIS) enabled symbiotic backscatter system riding over a multiuser non-orthogonal multiple access (NOMA) carrier, where the RIS is employed as a substitute for the conventional backscatter device (BD) with the objective of enhancing both primary NOMA transmission and backscatter communications. In particular, a symbiotic mechanism is proposed to control the mutual interference by means of an adaptive adjustment of the reflection coefficient at the RIS. Moreover, a novel and effective multiuser decoding scheme is proposed, based on successive interference cancellation (SIC), with the objective of ensuring the successful transmission of the symbiotic system. To this end, analytical expressions re derived for the closed-form outage lower bounds, asymptotic outage behavior and outage error floors are derived. Furthermore, the upper bounds of the ergodic capacity and its asymptote at high signal-to-noise ratio (SNR) are developed in order to illustrate the spectral efficiency of the proposed symbiotic system. Theoretical analysis and numerical results demonstrate that a stronger backscatter channel with a greater number of elements deployed on a segmented RIS results in a reduction in transmission outage and an increase in system capacity. Additionally, numerical results illustrate the spectral efficiency advantage of the proposed symbiotic system over the conventional solutions.

The acquisition of accurate channel state information (CSI) is of utmost importance since it provides performance improvement for wireless communication systems. However, acquiring accurate CSI, which can be done through channel estimation or channel prediction, is an intricate task due to the complexity of the time-varying and frequency selectivity of the wireless environment. To this end, we propose an efficient machine learning (ML)-based technique for channel prediction in orthogonal frequency-division multiplexing (OFDM) sub-bands. The novelty of the proposed approach lies in the training of channel fading samples used to estimate future channel behavior in selective fading.

In this paper, the privacy of wireless transmissions is improved through an efficient technique termed DDM and is subsequently assessed in terms of the measure of information leakage. Recently, a variation of DDM termed LPDDM has attracted significant attention as a prominent secure transmission method owing to its ability to improve the privacy of wireless communications. Roughly speaking, this modulation operates by randomly selecting the transmitting antenna from an antenna array whose radiation pattern is known. Thereafter, the modulator adjusts the constellation phase so as to ensure that only the legitimate receiver recovers the information. To begin with, we highlight some privacy boundaries inherent to the underlying system. In addition, we propose features that the antenna array must meet in order to increase the privacy of a wireless communication system. Last, we adopt a uniform circular monopole antenna array with equiprobable transmitting antennas in order to assess the impact of DDM on information leakage and the BER.

This paper proposes a simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) segmented symbiotic backscatter non-orthogonal multiple access (NOMA) system, where the STAR-RIS is composed of an enhancing primary signal (EP) zone and a backscatter device (BD) zone. To evaluate the overall system transmission reliability, we derive a tight lower bound of the coexistence outage probability (COP), where an imperfect/realistic successive interference cancellation (SIC) is considered. It is shown analytically that the error floor of the COP in both the near field and far field coverages would appear as long as the residual interference due to SIC is non-negligible, resulting in a diversity order of zero. Such an error floor is mainly dominated by the residual interference parameters, the decoding thresholds, and the power allocation ratios. More importantly, unlike the Gamma approximation approach, the adopted Laplace approach can capture the true diversity order with perfect SIC in the near-field/far-field coverage, which is dominated by the bottleneck number of the STAR-RIS elements belonging to the EP and BD zones, regardless of the dual-hop channel statistics. In addition, it is shown that the COP performance improves with either the quantification order or the concentration parameter of the imperfect channel state information.

In this paper, we investigate the physical layer security (PLS) of an overlay cognitive non-orthogonal multiple access (NOMA) system with control-jamming (CJ) under Nakagami-m fading. Herein, a cooperative decode-and-forward (DF) relaying technique is adopted at the secondary transmitter, while a maximal ratio combining (MRC) scheme is employed at the primary destination in order to improve the secrecy performance of the underlying system. Under this setup, we derive analytical expressions for the secrecy outage probability (SOP) and the strictly positive secrecy capacity (SPSC). Moreover, we obtain simple and explicit expressions of the SOP in the high signal-to-noise ratio (SNR) region to get useful insights on the system design for both the cases of without and with jamming. Finally, Monte Carlo simulations are provided to: (i) demonstrate the effectiveness and superiority of the proposed system with jamming over its non-jamming counterpart in terms of security; (ii) verify the accuracy of the proposed analytical framework.

Wireless Body Area Networks (WBANs) comprise a network of sensors subcutaneously implanted or placed near the body surface and facilitate continuous monitoring of health parameters of a patient. Research endeavours involving WBAN are directed towards effective transmission of detected parameters to a Local Processing Unit (LPU, usually a mobile device) and analysis of the parameters at the LPU or a back-end cloud. An important concern in WBAN is the lightweight nature of WBAN nodes and the need to conserve their energy. This is especially true for subcutaneously implanted nodes that cannot be recharged or regularly replaced. Work in energy conservation is mostly aimed at optimising the routing of signals to minimise energy expended. In this article, a simple yet innovative approach to energy conservation and detection of alarming health status is proposed. Energy conservation is ensured through a two-tier approach wherein the first tier eliminates “uninteresting” health parameter readings at the site of a sensing node and prevents these from being transmitted across the WBAN to the LPU. The second tier of assessment includes a proposed anomaly detection model at the LPU that is capable of identifying anomalies from streaming health parameter readings and indicates an adverse medical condition. In addition to being able to handle streaming data, the model works within the resource-constrained environments of an LPU and eliminates the need of transmitting the data to a back-end cloud, ensuring further energy savings. The anomaly detection capability of the model is validated using data available from the critical care units of hospitals and is shown to be superior to other anomaly detection techniques.

The present work investigates the physical layer security of wireless communication systems over non-homogeneous fading environments, i.e., η-μ and λ-μ fading models, which are typically encountered in realistic wireless transmission scenarios in the context of conventional and emerging communication systems. This study considers a single-input multiple-output system that consists of a single-antenna transmitter, a multi-antenna legitimate receiver, and an active multi-antenna eavesdropper. To this end, novel exact analytical expressions are derived for the corresponding average secrecy capacity and secrecy outage probability, which are corroborated by respective results from computer simulations. Capitalizing on the offered results, the physical layer security is quantified in terms of different parameters, which leads to useful insights on the impact of non-homogeneous fading environment and the number of employed antennas on the achieved physical layer security levels of the underlying system configuration. The offered results and insights are useful for the design of such systems as well as for the computational requirements and sustainability relating to such systems, since emerging communications are largely characterized by stringent quality of service and complexity requirements.

In this paper, we consider an overlay cognitive satellite-terrestrial relay network comprising a primary satellite source-receiver pair and a secondary transmitter-receiver pair on the ground while taking into account the practical relay transceiver hardware impairments. Herein, a primary satellite source communicates with its terrestrial user by utilizing both direct and relay links, using an amplify-and-forward based cooperative communication technique. Considering distortion noises in relay signal processing, we obtain new closed-form expressions for the outage probability of primary satellite network and secondary terrestrial network and explicitly derive the asymptotic outage behaviour for primary network by adopting pertinent heterogeneous fading models. Both primary and secondary networks satisfy their quality-of-service criteria for the low data rate requirements only. However, for the high data rate requirements, a ceiling effect is shown to occur which eventually makes the spectrum sharing infeasible.

In this paper, the performance of a digital communication system subject to $\kappa-\mu$ Extreme fading conditions is investigated. Specifically, exact and novel analytical expressions for the normalized average channel capacity and average error rate are derived assuming arbitrary fading parameters. An asymptotic error analysis is also performed in order to get further insights for the system performance. Finally, our analytical results are corroborated through Monte Carlo simulations. Although the derived expressions of the exact performance metrics include an infinite series, it is worth noting that they all converge rapidly and steadily after a few terms. In light of this, a truncation error analysis on one of the underlying performance metrics under investigation is provided and it is shown that the relative error is less or equal to 0.001% for as many as 10 terms.

This study investigates the performance of a cooperative non‐orthogonal multiple access cognitive network with imperfect successive interference cancellation under Rayleigh fading conditions. Specifically, the authors consider an underlay cognitive network that consists of a primary transmitter–receiver pair and a secondary system where a source node communicates with two destinations nodes directly and indirectly through a relay node selected from a set of decode‐and‐forward relays. A partial relay selection scheme is used to determine the best relay. The authors present an analytical framework, with closed‐form analytical expressions for the outage probabilities at the two destinations as well the primary destination. Moreover, to simplify the analysis and to provide further insights into the impact of key system parameters, asymptotic studies of the outage probabilities were carried out. To this end, the authors focus on two cases: (i) the maximum allowable transmit power of the secondary network grows sufficiently large and (ii) the interference power approaches infinity. Finally, Monte Carlo simulations are provided in an effort to assess the accuracy of the proposed mathematical framework.

We introduce the α-κ-μ shadowed (α-KMS) fading distribution as a natural generalization of the versatile α-κ-μ and α-η-μ distributions. The α-KMS fading distribution unifies a wide set of fading distributions, as it includes the α-κ-μ, αη-μ, α-μ, Weibull, κ-μ shadowed, Rician shadowed, κ-μ and ημ distributions as special cases, together with classical models like Rice, Nakagami-m, Hoyt, Rayleigh and one-sided Gaussian. Notably, the α-KMS distribution reduces to a finite mixture of α-μ distributions when the fading parameters μ and m take positive integer values, so that performance analysis over αKMS fading channels can be tackled by leveraging previous (existing) results in the literature for the simpler α-μ case. As application examples, important performance metrics like the outage probability and average channel capacity are analyzed.

Two sequential relay selection strategies are investigated for a cooperative relay-assisted device-to-device (D2D) communication underlaying cellular network over mixed fading channels. The relay selection schemes aim to improve the D2D communication performance and the wireless physical layer security of the cellular network. In this paper, the study is conducted analytically by obtaining an expression for the secrecy outage probability (SOP) of the cellular network. Moreover, in an effort to assess the usefulness of the cooperation between the two networks, an expression for the mutual outage probability (MOP) - which represents the true outage probability across both the D2D and cellular networks - is derived. Also, an asymptotic analysis of the MOP in the high signal-to-noise ratio regime is obtained and the diversity order is evaluated. Monte-Carlo simulations are provided to validate the accuracy of our proposed analytical framework.

In this paper, the error performance of binary and quaternary phase-shift keying signals with imperfect carrier phase recovery is investigated assuming a flat slow α-μ fading channel and the presence of thermal noise. The phase noise is considered to be Tikhonov and Gaussian distributed. More specifically, an analytical expression for the exact average bit error rate is obtained, as well as its corresponding asymptotic expression for large signal-to-noise ratio (SNR) values. The derived expressions are valid for arbitrary values of the fading parameters, namely α and μ, and they are validated through Monte Carlo simulations. Several important conclusions concerning the system performance as a function of the channel parameters, namely, non-linearity, clustering, and loop SNR, are drawn.

This paper investigates the secrecy performance of a multiple-input multiple-output (MIMO) system with transmit antenna selection (TAS) and maximal-ratio combining (MRC) over generalized α-μ fading. In the underlying wireless communication system, a single antenna is selected to transmit confidential messages to a multi-antenna receiver in the presence of a passive multi-antenna eavesdropper. In our analysis, new closed-form expressions are obtained for the secrecy outage probability (SOP) and the probability of strictly positive secrecy capacity (SPSC), and are subsequently corroborated through Monte Carlo simulations to assess their validity. Moreover, asymptotic studies of the secrecy outage probability are derived and explicitly show the effects of various system parameters on the secrecy diversity gain.

In this paper, we investigate the performance of a relay selection scheme in a buffer-aided multi-relay network with coded transmissions. We consider: (1) two different coding schemes, i.e., Turbo codes and distributed Turbo codes (DTC) and (2) quasi-static Rayleigh fading channels, where all the links are independent but asymmetric. For each of the aforementioned schemes, we analyze the performance of the system in terms of the average throughput and average delay. In addition, simple and explicit approximations of the asymptotic throughput for infinite buffer size and the high signal-to-noise ratio (SNR) regime are obtained. Our analysis of the asymptotic throughput provides the maximum achievable diversity gain of the system, and the accuracy of the derived analytical framework is assessed when compared to the Monte-Carlo simulations.

This paper investigates the secrecy performance of multiple-input multiple-output systems under generalized α - μ fading conditions. To this end, we focus on two distinct scenarios: 1) the transmitter has knowledge of the channel state information (CSI) of the eavesdropper channel and 2) the transmitter is not aware of the CSI of the wiretap link. By considering transmit antenna selection in the underlying system, we develop closedform analytical expressions for the lower bound of the secrecy outage probability (SOP) and the probability of the strictly positive secrecy capacity. Furthermore, two novel approaches are proposed to derive an analytical expression of the average secrecy capacity (ASC). First, the ASC is expressed as a function of the average capacity of the desired link and an interaction term regarded as the ASC loss. Second, the ASC is expressed in terms of the average capacities of the desired and eavesdropper links, plus an interaction term that can be regarded as some sort of ASC gain due to the statistical independence between the desired and eavesdropper links. In addition, asymptotic studies of the SOP and the ASC at high signal-to-noise ratio are carried out, which precisely reveal the secrecy diversity and array gains.

In this paper, we analyze the performance of the generalized selection combining with Gaussian distributed weighting errors for physical-layer security of a wireless communication system. Exact closed-form expressions for the secrecy performance in terms of the secrecy outage probability and the probability of non-zero secrecy capacity are derived. Moreover, asymptotic expressions are obtained and provide insights on how the channel parameters affect the secrecy performance. Monte-Carlo simulations are conducted to assess the accuracy of our analytical framework.

In this paper, we investigate the physical-layer (PHY) security problem of a wireless communication system over mixed generalized fading channels. We consider the transmission of confidential information between a transmitter and a legitimate receiver over an α-μ fading channel in the presence of an eavesdropper who is subject to κ-μ fading. Both the α-μ and κ-μ distributions have been considered in the literature to model the generalized small-scale fading and such a mixed fading propagation environment can be encountered in practical systems where one channel is described for its non-linearity and clustering properties whereas the other has a line-of-sight (LOS) component. In particular, novel analytical expressions for the exact and asymptotic average secrecy capacity (ASC) are derived. Finally, Monte-Carlo simulations are performed to assess the accuracy of the proposed mathematical analysis.

This paper provides an analytical study on the bit-error rate (BER) of the turbo-coded cooperative relaying in spectrum-sharing systems subject to Rayleigh fading. It is assumed that a single relay that maximizes the received signal- to-noise ratio (SNR) is selected in a secondary multi-relay network. We consider that the transmit power conditions of the underlay system is controlled by the joint power constraint of the interference in the primary network and the maximum allowable transmission power at the secondary network. Moreover, the proposed scheme takes into account the effect of primary user (PU) interference on the neighboring secondary network. First, we derive an expression of a tight upper bound for the BER of the secondary network. Then, we investigate the cooperative diversity gain of the underlying scheme. Finally, the proposed analysis is validated by Monte-Carlo simulations.

In this paper, we study the outage probability of the amplify-and-forward (AF) cognitive relaying in spectrum-sharing environments with outdated channel state information (CSI) over Rayleigh fading channels. A selection of the best relay in the secondary system with outdated channel information is considered. We derive a closed-form expression for the tight lower bound on the end-to-end outage probability using the cumulative density function (CDF) approach. Furthermore, the asymptotic behavior of the outage performance is investigated and reveals the diversity order of the underlying scheme. Finally Monte-Carlo simulations are provided to verify the analytical framework.

This paper presents an analytical study on the outage probability (OP) of cognitive amplify-and-forward (AF) with underlay spectrum-sharing systems subject to Rayleigh fading. In the underlying scheme, we consider a partial relay selection with outdated channel state information (CSI) and a spectrum-sharing system where the transmit power conditions are controlled by the combined interference power in the primary network and the maximum allowable transmission power at the secondary network. We first derive the end-to-end OP in closed form and then present asymptotic analysis for the high signal-to-noise ratio (SNR). Finally, Monte-Carlo simulations are provided to verify the accuracy of the theoretical analysis.

Abstract Recently, cooperative relaying techniques have been integrated into spectrum‐sharing systems in an effort to yield higher spectral efficiency. Many investigations on such systems have assumed that the channel state information between the secondary transmitter and primary receiver used to calculate the maximum allowable transmit secondary user transmit power to limit the interference is known to be perfect. However, because of feedback delay from the primary receiver or the time‐varying properties of the channel, the channel information may be outdated, which is an important scenario to cognitive radio systems. In this paper, we investigate the impact of outdated channel state information for relay selection on the performance of partial relay selection with amplify and forward in underlay spectrum‐sharing systems. We begin by deriving a closed‐form expression for the outage probability of the secondary network in a Rayleigh fading channel along with peak received interference power constraint and maximum allowable secondary user transmit power. We also provide a closed‐form expression for the average bit‐error rate of the underlying system. Moreover, we present asymptotic expressions for both the outage probability and average bit‐error rate in the high signal‐to‐noise ratio regime that reveal practical insights on the achievable diversity gain. Finally, we confirm our results through comparisons with computer simulations. Copyright © 2016 John Wiley & Sons, Ltd.

In this paper, the best relay selection in CSI-assisted variable gain amplify-and-forward (AF) with outdated channel state information (CSI) in the presence of co-channel interference (CCI) over Rayleigh fading channels is investigated. We first derive the cumulative density function (CDF) of the effective signal-to-interference-plus-noise ratio (SINR) of both the best source-to-relay and relay-to-destination links. Subsequently, a closed-form expression for the lower bound on the end-to-end outage probability (OP) of the system under study is obtained. Moreover, we present and discuss asymptotic expressions of the OP, which reveal the diversity gain of the underlying system. In particular, it is shown that for varying interference-to-noise ratio (INR), the diversity order is reduced to zero regardless of the nature of the desired CSI (i.e., outdated or ideal), and to full diversity or diversity one for fixed INR with ideal CSI or outdated CSI, respectively. Finally, Monte-Carlo simulation results are presented to validate the accuracy of the proposed analytical framework.

In this paper, we study the performance of relay selection in variable-gain amplify-and-forward (AF) turbo-coded cooperative network in the presence of channel estimation errors. In particular, we assume M-ary phase shift keying (MPSK) modulation and consider a dual multi-relay cooperative scenario where the relay selection requires global knowledge (end-to-end) of the relaying link. We derive the probability density function (PDF) of the received signal-to-noise ratio (SNR) for the underlying relaying link, and an upper bound expression of the average pairwise error probability (PEP). Furthermore, we present the diversity analysis study in which we show that the effect of erroneous channel estimates reduce the diversity order at high SNR to zero. Using these results, we evaluate the performance of the coded cooperation scenario under study in terms of bit-error rate (BER). Monte-Carlo simulation results are presented to validate the accuracy of the analytical results.

In this paper, we consider a cognitive radio network (CRN) with multiple primary users (PUs) and multiple SUs and propose a cooperative spectrum sensing and transmission for some selected SUs in order to avoid interference with PUs. The distributed collaboration strategy is done through a coalitional game and we present a distributed algorithm for the coalition formation. In the proposed scheme, the SUs that sense a particular channel with non-identical sensing times, form a coalition in which a coalition head is selected to determine whether or not the channel is idle. If a channel is not active, then the SU chosen as coalition head can transmit its packets through a cooperative scheme in the data transmission slot. Our simulation results show that the proposed scheme can significantly improve the average throughput compared to its non-cooperative counterpart. Moreover, it is shown that the proposed scheme is energy efficient in comparison to a scheme with fixed and identical sensing times.

Cooperation with channel coding also known as coded cooperation has been shown to be an efficient scheme for providing significant performance gains. However, relay selection in coded cooperation systems is seldom available in the existing literature. It is widely known that relay selection schemes in cooperative communications are dependent on the quality of the channel state information (CSI). In this paper, we study the impact of using outdated channel state information (CSI) for opportunistic relay selection (ORS) in turbo-coded cooperation over Rayleigh fading channels. A closed-form expression for the exact outage probability as a function of the correlation between the actual and delayed or outdated CSI is derived. Furthermore, diversity analysis is presented and it is noted that the diversity order is reduced to two regardless of the number of available relays, when the correlation factor is not equal to unity.

In this paper, we consider relay selection for turbo coded cooperative networks subject to Nakagami-m fading when the channel state information (CSI) is known at the receiver but is not necessarily ideal. This non-ideality may be due to a feedback delay caused by the difference between the instantaneous CSI during the transmission and the CSI at the time of relay selection, resulting in outdated CSI phenomena. The impact of the outdated CSI on the proposed scheme is well investigated. A closed-form expression for the exact outage probability is derived as well as its asymptotic expression in the high signal-to-noise (SNR) regime. Moreover, upper bounds on the bit-error rate (BER) are presented and a study of the diversity order reveals that for ideal CSI, full diversity in the number of relays and fading parameters m is achieved as opposed to outdated CSI where the achievable diversity is equivalent to the diversity of a coded cooperative network with a single relay.

We study the performance of distributed turbo-coded cooperative networks with multiple dual-hop relays over both identical and non-identical Nakagami-m slow fading channels. All the relays are equipped with error detection capabilities and only the reliable relays retransmit to the destination. In this paper, we derive the union bounds on the bit-error rate (BER) of the proposed scheme using the transfer function bounding and the limit-before-average techniques. Moreover, through the derived pairwise-error probability (PEP), we analyze the asymptotic behavior of this system at high signal-to-noise ratio (SNR). It is noted that the achievable diversity order depends on the number of cooperating relays and the fading parameters. Finally, performance evaluation of the proposed scheme is presented via error bounds and Monte Carlo simulations.

We investigate a power assignment scheme in multi-relay adaptive decode-and-forward (DF) cooperative-diversity networks over non-identical Rayleigh fading channels, that integrates truncated automatic repeat-request (ARQ) at the link layer. At the cooperative level, only the reliable relays participate in the retransmission phase if necessary. In this paper, we aim at maximizing the system throughput via power optimization and we show that this can be done by minimizing the symbol-error rate (SER) of the retransmission. We derive the closed- form expressions for the exact SER of the multi-relay adaptive DF over non-identical Rayleigh fading channels as well as the asymptotic bounds for the SER. Results show that the analytical bounds for the SER corroborate with the simulated SER at high signal-to-noise ratio (SNR) and maximum throughput is achieved through optimal power allocated at the source and various reliable relays.

In this paper, we investigate a cross-layer relay selection approach for cooperative-diversity networks that employ the truncated automatic repeat request (ARQ) protocol. The key feature of the proposed scheme is that the criterion for the selection of relay subsets is the maximization of the link-layer throughput that takes into account both the physical and link layers characteristics. Results show that the proposed cross-layer approach which assigns transmission to relay combination that sees better channel conditions, outperforms the capacity-based cooperative transmission with the same number of reliable relays in terms of throughput gain. Furthermore, a joint optimization of constellation size and packet length is included to enhance the system throughput for both the cross-layer relay selection and capacity-based relay selection.

Recently, cooperative diversity has been introduced where single-antenna mobiles achieve uplink transmit diversity helping each other by relaying one another's messages. A variation of this principle is coded cooperation which partitions the codeword of each mobile and transmits portions of each codeword through independent fading channels. Coded cooperation framework has been easily extended using turbo codes. In this paper we propose a new cooperative protocol that improves the performance of turbo coded cooperation from moderate to high signal-to-noise ratios. This method uses the forced symbol method in which the basic encoder structure remains unchanged. We present computer simulation results of the proposed scheme under various inter-user channel SNRs and compare to the union bound analysis.

This paper presents a new method that improves the performance of coded cooperation, especially in the error floor region. This method uses a modified repeat-punctured turbo code or double repeat-punctured turbo code with the cooperative scheme, where the modified repeat-punctured turbo code uses a repeater and an interleaver for both the first and second recursive systematic encoders. The analysis and simulation results of the proposed scheme are given and a comparison is made with the conventional turbo coded cooperative diversity scheme and the coded cooperation with repeat-punctured turbo code.