Contributions to the Performance Analysis of Intervehicular Communications Systems and Schemes

RÉSUMÉ Le but des systèmes de communication intervéhicule (Inter-Vehicle Communication – IVC) est d'améliorer la sécurité de conduite en utilisant des capteurs et des techniques de communication sans fil pour être en mesure de communiquer mutuellement sans aucune intervention extérieure. Avec l'utilisation de ces systèmes, les communications véhicule à véhicule (V2V) peuvent être plus efficaces dans la prévention des accidents et la décongestion de la circulation que si chaque véhicule travaillait individuellement. Une des solutions proposées pour les systèmes IVC est l’utilisation des systèmes de communication coopérative, qui en principe, augmentent l'efficacité spectrale et énergétique, la couverture du réseau, et réduit la probabilité de défaillance. La diversité d'antenne (entrées multiples sorties multiples « Multiple-Input Multiple-Output » ou MIMO) peut également être une alternative pour les systèmes IVC pour améliorer la capacité du canal et la diversité (fiabilité), mais en échange d’une complexité accrue. Toutefois, l'application de telles solutions est difficile, car les communications sans fil entre les véhicules sont soumises à d’importants effets d'évanouissements des canaux appelés (canaux sujets aux évanouissements de n*Rayleigh, « n*Rayleigh fading channels»), ce qui conduit à la dégradation des performances. Par conséquent, dans cette thèse, nous proposons une analyse de la performance globale des systèmes de transmission coopératifs et MIMO sur des canaux sujets aux évanouissements de n*Rayleigh. Cette analyse permettra d’aider les chercheurs pour la conception et la mise en œuvre de systèmes de communication V2V avec une complexité moindre. En particulier, nous étudions d'abord la performance de la sélection du relais de coopération avec les systèmes IVC, on suppose que la transmission via « Amplify-and-Forward» (AF) ou bien «Decode-and-Forward» (DF) est assurée par N relais pour transférer le message de la source à la destination. La performance du système est analysée en termes de probabilité de défaillance, la probabilité d'erreur de symbole, et la capacité moyenne du canal. Les résultats numériques démontrent que la sélection de relais réalise une diversité de l'ordre de (d≈mN/n) pour les deux types de relais, où m est un paramètre évanouissement de Rayleigh en cascade. Nous étudions ensuite la performance des systèmes IVC à sauts multiples avec et sans relais régénératifs. Dans cette étude, nous dérivons des expressions approximatives pour la probabilité de défaillance et le niveau d’évanouissement lorsque la diversité en réception basée sur le ratio maximum de combinaison (MRC) est employée. En outre, nous analysons la répartition de puissance pour le système sous-jacent afin de minimiser la probabilité globale de défaillance. Nous montrons que la performance des systèmes régénératifs est meilleure que celle des systèmes non régénératifs lorsque l’ordre de cascade n est faible, tandis qu’ils ont des performances similaires lorsque n est élevé. Ensuite, nous considérons le problème de la détection de puissance des signaux inconnus aux n* canaux de Rayleigh. Dans ce travail, de nouvelles expressions approximatives sont dérivées de la probabilité de détection moyenne avec et sans diversité en réception MRC. En outre, la performance du système est analysée lorsque la détection de spectre coopérative (CSS) est considérée sous diverses contraintes de canaux (par exemple, les canaux de communication parfaits et imparfaits). Les résultats numériques ont montré que la fiabilité de détection diminue à mesure que l'ordre n augmente et s’améliore sensiblement lorsque CSS emploie le schéma MRC. Il est démontré que CSS avec le schéma MRC maintient la probabilité de fausse alarme minimale dans les canaux d’information imparfaite plutôt que d'augmenter le nombre d'utilisateurs en coopération. Enfin, nous présentons une nouvelle approche pour l'analyse des performances des systèmes IVC sur n*canaux de Rayleigh, en utilisant n_T antennes d'émission et n_R antennes de réception pour lutter contre l'effet d’évanouissement. Dans ce contexte, nous évaluons la performance des systèmes MIMO-V2V basés sur la sélection des antennes d'émission avec un ratio maximum de combinaison (TAS/MRC) et la sélection combinant (TAS/SC). Dans cette étude, nous dérivons des expressions analytiques plus précises pour la probabilité de défaillance, la probabilité d'erreur de symbole, et l’évanouissement sur n*canaux Rayleigh. Il est montré que les deux régimes ont le même ordre de diversité maximale équivalent à (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 réception est plus que celle des antennes d’émission, mais l’amélioration de la performance est limitée 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

Performance study of an underlay cognitive radio network in the presence of co-channel interference

PhD ThesisMassive innovation in all aspects of the wireless communication network has been witnessed over the last few decades. The demand for data throughput is continuously growing, as such, the current regulations for allocating frequency spectrum are not able to respond to this exponential growth. Cognitive radio (CR), has been proposed as a solution to this problem. One of the possible scenarios of the implementation of CR is underlay cognitive radio. In this thesis the performance of an underlay cognitive radio network (UCRN) in the presence of the co-channel interference (CCI) is assessed. Firstly, the impact of CCI on the dual-hop cooperative UCRN is investigated over Rayleigh fading channels. In order to do this, the exact outage probability (OP), average error probability (AEP) and the ergodic capacity (EC) are studied. In addition, simple and asymptotic expressions for the OP and AEP are derived. Furthermore, the optimal power allocation is investigated to enhance the network performance. Moreover, the performance of a multi-user scenario is studied by considering the opportunistic SNR-based selection technique. Secondly, the effect of both primary network interference and CCI on the dual-hop UCRN over Rayleigh fading channels are studied. The equivalent signal-to-interference-plus-noise ratio (SINR) for this network scenario is obtained by considering multi-antenna schemes at all receiver nodes. The different signal combinations at the receiver nodes are investigated and compared, such as selection combining (SC) and maximum ratio combining (MRC) techniques. Then, the equivalent probability density function (PDF) and cumulative distribution function (CDF) of the network’s equivalent SINR are derived and discussed. Furthermore, expressions for the exact OP, AEP, and EC are derived and reviewed. In addition, asymptotic OP expressions are obtained for different case scenarios to gain an insight into the network parameters. Thirdly, multiple-input multiple-output (MIMO) UCRN is investigated under the influence of primary transmitter interference and CCI over Rayleigh fading channels. The transmit antenna selection and maximum ratio combining (TAS/MRC) techniques are considered for examining the performance of the secondary network. At first the equivalent SINR for the system is derived, then the exact and approximate expressions for the OP are derived and discussed. Fourthly, considering Nakagami-m fading channels, the performance of the UCRN is thoroughly studied with the consideration of the impact of primary network interference and CCI. The equivalent SINR for the secondary system is derived. Then, the system equivalent PDF and CDF are derived and discussed. Furthermore, the OP and AEP performances are investigated. Finally, for the cases mentioned above, numerical examples in conjunction with MatLab Monte Carlo simulations are provided to validate the derived results. The results show that CCI is one of the factors that severely reduces the UCRN performance. This can be more observable when the CCI power increases linearly with the transmission power of the secondary transmitter nodes. Furthermore, it was found that in a multi-user scenario the opportunistic SNR-based selection technique consideration can improve the performance of the network. Moreover, adaptive power allocation is found to give better results than equal power allocation. In addition, cooperative communication can be considered to be an effective way to combat the impact of transmission power limitation of the secondary network and interference power constraint. The multi-antenna schemes are another important consideration for enhancing the overall performance. In fact, despite the interference from the CCI and primary user sources, the multi-antennas scheme does not lose its advantage in the UCRN performance improvementHigher Committee for Education Development in Iraq (HCED). I am also grateful to the Ministry of Transportation and Communication, Kurdistan Regional Government-Iraq

Diversity techniques for broadband wireless communications: performance enhancement and analysis

The diversity techniques have been proven to be effective for next generation broadband wireless communications, and are the focus of this thesis. The diversity techniques can be broadly categorized into three types: Space, Time, and Frequency. In this thesis, we are mainly concerned with frequency and space diversity techniques. Orthogonal Frequency Division Multiplexing (OFDM) is a frequency diversity technique which offers several benefits such as easier digital implementation, immunity to multipath channels, low complexity channel equalization, etc. Despite these desirable features, there are few inherent problems in OFDM such as high peak-to-average power ratio (PAPR). High PAPR demands large dynamic range in the transmitted chain such as digital to analog converter (DAC) and power amplifier (PA). Unless pre-processed, the transmitted signal gets distorted due to quantization errors and inter-modulation. In the initial stage of PhD candidature, the author focused on PAPR reduction techniques. A simple modification on conventional iterative clipping and filtering (ICF) technique was proposed which has less computational complexity. The power savings achievable from clipping and filtering method was considered next. Furthermore the ICF is compared with another distortion-less PAPR reduction technique called Selective Mapping (SLM) based on power savings. Finally, impact of clipping and filtering on the channel estimation was analyzed. Space diversity seeks to exploit the multi-path characteristics of wireless channels to improve the performance. The simplest form of the space diversity is the receive diversity where two or more antennas with sufficient spacing collect independent copies of the same transmitted signal, which contributes to better signal reception. In this thesis new analytical expressions for spectral efficiency, capacity, and error rates were presented for adaptive systems with channel estimation error. Beamforming (steering signal towards desired receiver) is another useful technique in multiple-antenna systems to further improve the system performance. MRT (Maximal Ratio Transmission) or MIMO-MRC is such system where the transmitter, based on channel feedback from the receiver, uses weighting factors to steer the transmitted signal. Closed form expressions for symbol error rates were derived for MRT system with channel estimation error. The results were extended to evaluate closed form expressions of error rates for Rectangular QAM. Antenna correlation was considered in another contribution on MRC systems. Relay and Cooperative networks represent another form of spatial diversity and have recently attracted significant research attention. These networks rely on intermediate nodes called "relays" to establish communication between the source and the destination. In addition to coverage extension, the relay networks have shown to offer cooperative diversity when there is a direct link or multiple relays. The first contribution is to analyze a dual-hop amplify-forward relay networks with dissimilar fading scenarios. Next error rates of Rectangular QAM for decode-forward selection relay system are derived. Multiple antenna at relay is included to analyze the benefits of dual spatial diversity over Rayleigh and Nakagami fading channels. Antenna selection is a cost-effective way to exploit the antenna diversity. General Order Antenna Selection (GOAS), based on Ordered Statistics, is used to evaluate signal statistics for a MIMO relay network

A Study Of Cooperative Spectrum Sharing Schemes For Internet Of Things Systems

The Internet of Things (IoT) has gained much attention in recent years with the massive increase in the number of connected devices. Cognitive Machine-to-Machine (CM2M) communications is a hot research topic in which a cognitive dimension allows M2M networks to overcome the challenges of spectrum scarcity, interference, and green requirements. In this paper, we propose a Generalized Cooperative Spectrum Sharing (GCSS) scheme for M2M communication. Cooperation extends the coverage of wireless networks as well as increasing their throughput while reducing the energy consumption of the connected low power devices. We study the outage performance of the proposed GCSS scheme for M2M system and derive exact expressions for the outage probability. We also analyze the effect of varying transmission powers on the performance of the system