399 research outputs found

    Dual-hop transmissions with fixed-gain relays over Generalized-Gamma fading channels

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    In this paper, a study on the end-to-end performance of dual-hop wireless communication systems equipped with fixed-gain relays and operating over Generalized-Gamma (GG) fading channels is presented. A novel closed form expression for the moments of the end-to-end signal-to-noise ratio (SNR) is derived. The average bit error probability for coherent and non-coherent modulation schemes as well as the end-to-end outage probability of the considered system are also studied. Extensive numerically evaluated and computer simulations results are presented that verify the accuracy of the proposed mathematical analysis.\u

    Optimal Power Allocation by Imperfect Hardware Analysis in Untrusted Relaying Networks

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    By taking a variety of realistic hardware imperfections into consideration, we propose an optimal power allocation (OPA) strategy to maximize the instantaneous secrecy rate of a cooperative wireless network comprised of a source, a destination and an untrusted amplify-and-forward (AF) relay. We assume that either the source or the destination is equipped with a large-scale multiple antennas (LSMA) system, while the rest are equipped with a single antenna. To prevent the untrusted relay from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as destination-based cooperative jamming (DBCJ). Given this system model, novel closed-form expressions are presented in the high signal-to-noise ratio (SNR) regime for the ergodic secrecy rate (ESR) and the secrecy outage probability (SOP). We further improve the secrecy performance of the system by optimizing the associated hardware design. The results reveal that by beneficially distributing the tolerable hardware imperfections across the transmission and reception radio-frequency (RF) front ends of each node, the system's secrecy rate may be improved. The engineering insight is that equally sharing the total imperfections at the relay between the transmitter and the receiver provides the best secrecy performance. Numerical results illustrate that the proposed OPA together with the most appropriate hardware design significantly increases the secrecy rate.Comment: 29 pages, 7 figures, Submitted to IEEE Transactions on Wireless Communication

    Performance Analysis, Resource Allocation and Optimization of Cooperative Communication Systems under Generalized Fading Channels

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    The increasing demands for high-speed data transmission, efficient wireless access, high quality of service (QoS) and reliable network coverage with reduced power consumption impose demanding intensive research efforts on the design of novel wireless communication system architectures. A notable development in the area of communication theory is the introduction of cooperative communication systems. These technologies become promising solution for the next-generation wireless transmission systems due to their applicability in size, power, hardware and price constrained devices, such as cellular mobile devices, wireless sensors, ad-hoc networks and military communications, being able to provide, e.g., diversity gain against fading channels without the need for installing multiple antennas in a single terminal. The performance of the cooperative systems can in general be signiïŹcantly increased by allocating the limited power efficiently. In this thesis, we address in detail the performance analysis, resource allocation and optimization of such cooperative communication systems under generalized fading channels. We focus ïŹrst on energy-efficiency (EE) optimization and optimal power allocation (OPA) of regenerative cooperative network with spatial correlation effects under given power constraint and QoS requirement. The thesis also investigates the end-to-end performance and power allocation of a regenerative multi-relay cooperative network over non-homogeneous scattering environment, which is realistic case in practical wireless communication scenarios. Furthermore, the study investigates the end-to-end performance, OPA and energy optimization analysis under total power constraint and performance requirement of full-duplex (FD) relaying transmission scheme over asymmetric generalized fading models with relay self-interference (SI) effects.The study ïŹrst focuses on exact error analysis and EE optimization of regenerative relay systems under spatial correlation effects. It ïŹrst derives novel exact and asymptotic expressions for the symbol-error-rates (SERs) of M -ary quadrature amplitude and M -ary phase-shift keying (M -QAM) and (M -PSK) modulations, respectively, assuming a dual-hop decode-and-forward relay system, spatial correlation, path-loss effects and maximum-ratio-combing (MRC) at the destination. Based on this, EEoptimization and OPA are carried out under certain QoS requirement and transmit power constraints.Furthermore, the second part of the study investigates the end-to-end performance and power allocation of MRC based regenerative multi-relay cooperative system over non-homogeneous scattering environment. Novel exact and asymptotic expressions are derived for the end-to-end average SER for M -QAM and M -PSK modulations.The offered results are employed in performance investigations and power allocation formulations under total transmit power constraints.Finally, the thesis investigates outage performance, OPA and energy optimization analysis under certain system constraints for the FD and half-duplex (HD) relaying systems. Unlike the previous studies that considered the scenario of information transmission over symmetric fading conditions, in this study we considered the scenario of information transmission over the most generalized asymmetric fading environments.The obtained results indicate that depending on the severity of multipath fading, the spatial correlation between the direct and relayed paths and the relay location, the direct transmission is more energy-efficient only for rather short transmission distances and until a certain threshold. Beyond this, the system beneïŹts substantially from the cooperative transmission approach where the cooperation gain increases as the transmission distance increases. Furthermore, the investigations on the power allocation for the multi-relay system over the generalized small-scale fading model show that substantial performance gain can be achieved by the proposed power allocation scheme over the conventional equal power allocation (EPA) scheme when the source-relay and relay-destination paths are highly unbalanced. Extensive studies on the FD relay system also show that OPA provides signiïŹcant performance gain over the EPA scheme when the relay SI level is relatively strong. In addition, it is shown that the FD relaying scheme is more energy-efficient than the reference HD relaying scheme at long transmission distances and for moderate relay SI levels.In general, the investigations in this thesis provide tools, results and useful insights for implementing space-efficient, low-cost and energy-efficient cooperative networks, speciïŹcally, towards the future green communication era where the optimization of the scarce resources is critical

    Contributions to the Performance Analysis of Intervehicular Communications Systems and Schemes

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    RÉSUMÉ Le but des systĂšmes de communication intervĂ©hicule (Inter-Vehicle Communication – IVC) est d'amĂ©liorer la sĂ©curitĂ© de conduite en utilisant des capteurs et des techniques de communication sans fil pour ĂȘtre en mesure de communiquer mutuellement sans aucune intervention extĂ©rieure. Avec l'utilisation de ces systĂšmes, les communications vĂ©hicule Ă  vĂ©hicule (V2V) peuvent ĂȘtre plus efficaces dans la prĂ©vention des accidents et la dĂ©congestion de la circulation que si chaque vĂ©hicule travaillait individuellement. Une des solutions proposĂ©es pour les systĂšmes IVC est l’utilisation des systĂšmes de communication coopĂ©rative, qui en principe, augmentent l'efficacitĂ© spectrale et Ă©nergĂ©tique, la couverture du rĂ©seau, et rĂ©duit la probabilitĂ© de dĂ©faillance. La diversitĂ© d'antenne (entrĂ©es multiples sorties multiples « Multiple-Input Multiple-Output » ou MIMO) peut Ă©galement ĂȘtre une alternative pour les systĂšmes IVC pour amĂ©liorer la capacitĂ© du canal et la diversitĂ© (fiabilitĂ©), mais en Ă©change d’une complexitĂ© accrue. Toutefois, l'application de telles solutions est difficile, car les communications sans fil entre les vĂ©hicules sont soumises Ă  d’importants effets d'Ă©vanouissements des canaux appelĂ©s (canaux sujets aux Ă©vanouissements de n*Rayleigh, « n*Rayleigh fading channels»), ce qui conduit Ă  la dĂ©gradation des performances. Par consĂ©quent, dans cette thĂšse, nous proposons une analyse de la performance globale des systĂšmes de transmission coopĂ©ratifs et MIMO sur des canaux sujets aux Ă©vanouissements de n*Rayleigh. Cette analyse permettra d’aider les chercheurs pour la conception et la mise en Ɠuvre de systĂšmes de communication V2V avec une complexitĂ© moindre. En particulier, nous Ă©tudions d'abord la performance de la sĂ©lection du relais de coopĂ©ration avec les systĂšmes IVC, on suppose que la transmission via « Amplify-and-Forward» (AF) ou bien «Decode-and-Forward» (DF) est assurĂ©e par N relais pour transfĂ©rer le message de la source Ă  la destination. La performance du systĂšme est analysĂ©e en termes de probabilitĂ© de dĂ©faillance, la probabilitĂ© d'erreur de symbole, et la capacitĂ© moyenne du canal. Les rĂ©sultats numĂ©riques dĂ©montrent que la sĂ©lection de relais rĂ©alise une diversitĂ© de l'ordre de (d≈mN/n) pour les deux types de relais, oĂč m est un paramĂštre Ă©vanouissement de Rayleigh en cascade. Nous Ă©tudions ensuite la performance des systĂšmes IVC Ă  sauts multiples avec et sans relais rĂ©gĂ©nĂ©ratifs. Dans cette Ă©tude, nous dĂ©rivons des expressions approximatives pour la probabilitĂ© de dĂ©faillance et le niveau d’évanouissement lorsque la diversitĂ© en rĂ©ception basĂ©e sur le ratio maximum de combinaison (MRC) est employĂ©e. En outre, nous analysons la rĂ©partition de puissance pour le systĂšme sous-jacent afin de minimiser la probabilitĂ© globale de dĂ©faillance. Nous montrons que la performance des systĂšmes rĂ©gĂ©nĂ©ratifs est meilleure que celle des systĂšmes non rĂ©gĂ©nĂ©ratifs lorsque l’ordre de cascade n est faible, tandis qu’ils ont des performances similaires lorsque n est Ă©levĂ©. Ensuite, nous considĂ©rons le problĂšme de la dĂ©tection de puissance des signaux inconnus aux n* canaux de Rayleigh. Dans ce travail, de nouvelles expressions approximatives sont dĂ©rivĂ©es de la probabilitĂ© de dĂ©tection moyenne avec et sans diversitĂ© en rĂ©ception MRC. En outre, la performance du systĂšme est analysĂ©e lorsque la dĂ©tection de spectre coopĂ©rative (CSS) est considĂ©rĂ©e sous diverses contraintes de canaux (par exemple, les canaux de communication parfaits et imparfaits). Les rĂ©sultats numĂ©riques ont montrĂ© que la fiabilitĂ© de dĂ©tection diminue Ă  mesure que l'ordre n augmente et s’amĂ©liore sensiblement lorsque CSS emploie le schĂ©ma MRC. Il est dĂ©montrĂ© que CSS avec le schĂ©ma MRC maintient la probabilitĂ© de fausse alarme minimale dans les canaux d’information imparfaite plutĂŽt que d'augmenter le nombre d'utilisateurs en coopĂ©ration. Enfin, nous prĂ©sentons une nouvelle approche pour l'analyse des performances des systĂšmes IVC sur n*canaux de Rayleigh, en utilisant n_T antennes d'Ă©mission et n_R antennes de rĂ©ception pour lutter contre l'effet d’évanouissement. Dans ce contexte, nous Ă©valuons la performance des systĂšmes MIMO-V2V basĂ©s sur la sĂ©lection des antennes d'Ă©mission avec un ratio maximum de combinaison (TAS/MRC) et la sĂ©lection combinant (TAS/SC). Dans cette Ă©tude, nous dĂ©rivons des expressions analytiques plus prĂ©cises pour la probabilitĂ© de dĂ©faillance, la probabilitĂ© d'erreur de symbole, et l’évanouissement sur n*canaux Rayleigh. Il est montrĂ© que les deux rĂ©gimes ont le mĂȘme ordre de diversitĂ© maximale Ă©quivalent Ă  (d≈mn_T n_R /n) . En outre, TAS / MRC offre un gain de performance mieux que TAS/ SC lorsque le nombre d'antennes de rĂ©ception est plus que celle des antennes d’émission, mais l’amĂ©lioration de la performance est limitĂ©e lorsque n augmente.----------Abstract The purpose of intervehicular communication (IVC) systems is to enhance driving safety, in which vehicles use sensors and wireless communication techniques to talk to each other without any roadside intervention. Using these systems, vehicle-to-vehicle (V2V) communications can be more effective in avoiding accidents and traffic congestion than if each vehicle works individually. A potential solution can be implemented in this research area using cooperative communications systems which, in principle, increase spectral and power efficiency, network coverage, and reduce the outage probability. Antenna diversity (i.e., multiple-input multiple output (MIMO) systems) can also be an alternative solution for IVC systems to enhance channel capacity and diversity (reliability) but in exchange of an increased complexity. However, applying such solutions is challenging since wireless communications among vehicles is subject to harsh fading channels called ‘n*Rayleigh fading channels’, which leads to performance degradation. Therefore, in this thesis we provide a comprehensive performance analysis of cooperative transmission and MIMO systems over n*Rayleigh fading channels that help researchers for the design and implementation of V2V communication systems with lower complexity. Specifically, we first investigate the performance of cooperative IVC systems with relay selection over n*Rayleigh fading channels, assuming that both the decode-and-forward and the amplify-and-forward relaying protocols are achieved by N relays to transfer the source message to the destination. System performance is analyzed in terms of outage probability, symbol error probability, and average channel capacity. The numerical results have shown that the best relay selection approach achieves the diversity order of (d≈mN/n) where m is a cascaded Rayleigh fading parameter. Second, we investigate the performance of multihop-IVC systems with regenerative and non-regenerative relays. In this study, we derive approximate closed-form expressions for the outage probability and amount of fading when the maximum ratio combining (MRC) diversity reception is employed. Further, we analyze the power allocation for the underlying scheme in order to minimize the overall outage probability. We show that the performance of regenerative systems is better than that of non-regenerative systems when the cascading order n is low and they have similar performance when n is high. Third, we consider the problem of energy detection of unknown signals over n*Rayleigh fading channels. In this work, novel approximate expressions are derived for the average probability of detection with and without MRC diversity reception. Moreover, the system performance is analyzed when cooperative spectrum sensing (CSS) is considered under various channel constraints (e.g, perfect and imperfect reporting channels). The numerical results show that the detection reliability decreases as the cascading order n increases and substantially improves when CSS employs MRC schemes. It is demonstrated that CSS with MRC scheme keeps the probability of false alarm minimal under imperfect reporting channels rather than increasing the number of cooperative users. Finally, we present a new approach for the performance analysis of IVC systems over n*Rayleigh fading channels, using n_T transmit and n_R receive antennas to combat fading influence. In this context, we evaluate the performance of MIMO-V2V systems based on the transmit antenna selection with maximum ratio combining (TAS/MRC) and selection combining (TAS/SC) schemes. In this study, we derive tight analytical expressions for the outage probability, the symbol error probability, and the amount of fading over n*Rayleigh fading channels. It is shown that both schemes have the same maximum diversity order equivalent to (d≈mn_T n_R /n). In addition, TAS/MRC offers a better performance gain than TAS/SC scheme when the number of receive antennas is more than that of transmit antennas, but the performance improvement is limited as n increases

    Outage Probability Analysis of Full-Duplex Amplify-and-Forward MIMO Relay Systems

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    abstract: Multiple-input multiple-output systems have gained focus in the last decade due to the benefits they provide in enhancing the quality of communications. On the other hand, full-duplex communication has attracted remarkable attention due to its ability to improve the spectral efficiency compared to the existing half-duplex systems. Using full-duplex communications on MIMO co-operative networks can provide us solutions that can completely outperform existing systems with simultaneous transmission and reception at high data rates. This thesis considers a full-duplex MIMO relay which amplifies and forwards the received signals, between a source and a destination that do not a have line of sight. Full-duplex mode raises the problem of self-interference. Though all the links in the system undergo frequency flat fading, the end-to-end effective channel is frequency selective. This is due to the imperfect cancellation of the self-interference at the relay and this residual self-interference acts as intersymbol interference at the destination which is treated by equalization. This also leads to complications in form of recursive equations to determine the input-output relationship of the system. This also leads to complications in the form of recursive equations to determine the input-output relationship of the system. To overcome this, a signal flow graph approach using Mason's gain formula is proposed, where the effective channel is analyzed with keen notice to every loop and path the signal traverses. This gives a clear understanding and awareness about the orders of the polynomials involved in the transfer function, from which desired conclusions can be drawn. But the complexity of Mason's gain formula increases with the number of antennas at relay which can be overcome by the proposed linear algebraic method. Input-output relationship derived using simple concepts of linear algebra can be generalized to any number of antennas and the computation complexity is comparatively very low. For a full-duplex amplify-and-forward MIMO relay system, assuming equalization at the destination, new mechanisms have been implemented at the relay that can compensate the effect of residual self-interference namely equal-gain transmission and antenna selection. Though equal-gain transmission does not perform better than the maximal ratio transmission, a trade-off can be made between performance and implementation complexity. Using the proposed antenna selection strategy, one pair of transmit-receive antennas at the relay is selected based on four selection criteria discussed. Outage probability analysis is performed for all the strategies presented and detailed comparison has been established. Considering minimum mean-squared error decision feedback equalizer at the destination, a bound on the outage probability has been obtained for the antenna selection case and is used for comparisons. A cross-over point is observed while comparing the outage probabilities of equal-gain transmission and antenna selection techniques, as the signal-to-noise ratio increases and from that point antenna selection outperforms equal-gain transmission and this is explained by the fact of reduced residual self-interference in antenna selection method.Dissertation/ThesisMasters Thesis Electrical Engineering 201
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