In this dissertation, we study cross-layer design for cooperative wireless data communication networks. Based on the characteristics of cooperative wireless communications, and the requirement of Quality of Service (QoS) provisioning for data networks, we consider cross-layer system design for cooperative wireless networking. Three major design issues which cover cooperative link establishment, information security of cooperative communications, and cross-layer cooperative transmission scheduling, are investigated. Specifically, we follow the communication procedure in cooperative wireless systems and investigate several cross-layer design problems. Considering the queueing behavior of data buffers at the candidate relays, we study relay selection from a queue-aware perspective which takes into account the queueing systems at both the source and the potential relays. With the cooperative link established, we then study the secret key establishment problem by cross-layer cooperative discussion. Then cross-layer transmission scheduling is investigated from two perspectives. We first look at cross-layer adaptive modulation and coding (AMC), which takes both the channel condition and traffic intensity into consideration in the scheduling design. A more general queue-aware scheduler state selection mechanism based on buffer queue occupancy is studied, and optimization by nonlinear integer programming is presented. / Graduate / 0544

In this work, the problem of relay selection and resource power allocation in one- way and two-way cognitive relay networks using half duplex channels with different relaying protocols is investigated. Optimization problems for both single and multiple relay selection that maximize the sum rate of the secondary network without degrading the quality of service of the primary network by respecting a tolerated interference threshold were formulated. Single relay selection and optimal power allocation for two-way relaying cognitive radio networks using decode-and-forward and amplify-and-forward protocols were studied. Dual decomposition and subgradient methods were used to find the optimal power allocation. The transmission process to exchange two different messages between two transceivers for two-way relaying technique takes place in two time slots. In the first slot, the transceivers transmit their signals simultaneously to the relay. Then, during the second slot the relay broadcasts its signal to the terminals. Moreover, improvement of both spectral and energy efficiency can be achieved compared with the one-way relaying technique. As an extension, a multiple relay selection for both one-way and two-way relaying under cognitive radio scenario using amplify-and-forward were discussed. A strong optimization tool based on genetic and iterative algorithms was employed to solve the 
formulated optimization problems for both single and multiple relay selection, where discrete relay power levels were considered. Simulation results show that the practical and low-complexity heuristic approaches achieve almost the same performance of the optimal relay selection schemes either with discrete or continuous power distributions while providing a considerable saving in terms of computational complexity.

In-band full-duplex, by which radios may simultaneously transmit and receive over the same channel, has been always considered practically-unfeasible due to the prohibitively strong self-interference. Indeed, a freshly-generated transmit signal power is typically ten orders of magnitude higher than that of a naturally-attenuated received signal. While unable to manage such an overwhelming interference, wireless communications resorted to half-duplex operation, transmitting and receiving over orthogonal channel resources. Recent research has demonstrated the practical feasibility of full-duplexing via successive sophisticated stages of signal suppression/cancellation, bringing this long-held assumption down and reviving the promising full-duplex potentials. Full-duplex relaying (FDR), where intermediate nodes may now support source-destination communication via simultaneous listening/forwarding, represents one of two full-duplex settings currently recommended for deployment in future fifth-generation (5G) systems. Theoretically, it has been widely accepted that FDR potentially doubles the channel capacity when compared to its half-duplex counterpart. Although FDR doubles the multiplexing gain, the effective signal-to-noise ratio (SNR) can be significantly degraded due to the residual self-interference (RSI) if not properly handled. In this work, efficient protocols are devised for different FDR settings. Selective cooperation is proposed for the canonical three-terminal FDR channel with RSI, which exploits the cooperative diversity offered by the independently fading source/relay message replicas arriving at the destination. Closed-form expressions are derived for the end-to-end SNR cumulative distribution function (CDF) under Rayleigh and Nakagami-m fading. Further, the offered diversity gain is presented as a function of the RSI scaling trend with the relay power. We show that the existing diversity problem in simple FDR protocols can be considerably fixed via block transmission with selective cooperation. Beyond the single-relay setting, the outage performance of different opportunistic full-duplex relay selection (FDRS) protocols is also evaluated under Rayleigh and Nakagami-m fading. It is shown that, with state-of-the-art adaptive self-interference cancellation techniques, FDRS can offer the same diversity order of its half-duplex rival while supporting a higher level of spectral efficiency. FDRS is also analyzed when adopted by a spectrum-sharing secondary system while the primary spectrum user imposes an additional interference constraint. Finally, buffer-aided hybrid half-/full-duplex cooperation is addressed. To maximize the end-to-end throughput, joint duplexing mode and link selection is studied where the system leverages the buffer and outage state information at the transmitters. All theoretic findings are corroborated with numerical simulations, with comparisons to existing protocols.

Spatial diversity is an effective technique to combat the effects of severe fading in wireless environments. Recently, cooperative communications has emerged as an attractive communications paradigm that can introduce a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. In this thesis, a new approach to cooperative communications via distributed extended orthogonal space-time block coding (D-EO-STBC) based on limited partial feedback is proposed for cooperative relay networks with three and four relay nodes and then generalized for an arbitrary number of relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain, and it has certain properties that make it alluring for practical systems such as orthogonality, flexibility, low computational complexity and decoding delay, and high robustness to node failure. Versions of the closed-loop D-EO-STBC scheme based on cooperative orthogonal frequency division multiplexing type transmission are also proposed for both flat and frequency-selective fading channels which can overcome imperfect synchronization in the network. As such, this proposed technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, this scheme is extended for two-way relay networks through a three-time slot framework. On the other hand, to substantially reduce the feedback channel overhead, limited feedback approaches based on parameter quantization are proposed. In particular, an optimal one-bit partial feedback approach is proposed for the generalized D-O-STBC scheme to maximize the array gain. To further enhance the end-to-end bit error rate performance of the cooperative relay system, a relay selection scheme based on D-EO-STBC is then proposed. Finally, to highlight the utility of the proposed D-EO-STBC scheme, an application to cognitive radio is studied.

Recently, cooperative relay networks have emerged as an attractive communications technique that can generate a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. To achieve cooperative diversity single-antenna terminals in a wireless relay network typically share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. However, there remain technical challenges to maximize the benefit of cooperative communications, e.g. data rate, asynchronous transmission, interference and outage. Therefore, the focus of this thesis is to exploit cooperative relay networks within two-way transmission schemes. Such schemes have the potential to double the data rate as compared to one-way transmission schemes. Firstly, a new approach to two-way cooperative communications via extended distributed orthogonal space-time block coding (E-DOSTBC) based on phase rotation feedback is proposed with four relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain. Then, distributed orthogonal space-time block coding (DOSTBC) is applied within an asynchronous two-way cooperative wireless relay network using two relay nodes. A parallel interference cancelation (PIC) detection scheme with low structural and computational complexity is applied at the terminal nodes in order to overcome the effect of imperfect synchronization among the cooperative relay nodes. Next, a DOSTBC scheme based on cooperative orthogonal frequency division multiplexing (OFDM) type transmission is proposed for flat fading channels which can overcome imperfect synchronization in the network. As such, this technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, a closed-loop EDOSTBC approach using through a three-time slot framework is proposed. A full interference cancelation scheme with OFDM and cyclic prefix type transmission is used in a two-hop cooperative four relay network with asynchronism in the both hops to achieve full data rate and completely cancel the timing error. The topic of outage probability analysis in the context of multi-relay selection for one-way cooperative amplify and forward networks is then considered. Local measurements of the instantaneous channel conditions are used to select the best single and best two relays from a number of available relays. Asymptotical conventional polices are provided to select the best single and two relays from a number of available relays. Finally, the outage probability of a two-way amplify and forward relay network with best and Mth relay selection is analyzed. The relay selection is performed either on the basis of a max-min strategy or one based on maximizing exact end-to-end signal-to-noise ratio. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of new algorithms and methods.

We study energy-efficient power allocation among relays for lifetime maximization in a dual-hop relay network operated by amplify-and-forward relays with battery limitations. Power allocation algorithms are proposed for three different scenarios. First, we study the relay cooperation case where all the relays jointly support transmissions for a targeted data rate. By exploring the correlation of time-varying relay channels, we develop a prediction-based relay cooperation method for optimal power allocation strategy to improve the relay network lifetime over existing methods that do not predict the future channel state, or assume the current channel state remains static in the future. Next, we consider energy-efficient relay selection for the single source-destination case. Assuming finite transmission power levels, we propose a stochastic shortest path approach which gives the optimal relay selection decision to maximize the network lifetime. Due to the high computational complexity, a suboptimal prediction-based relay selection algorithm, directly coming from previous problem, is created. Finally, we extend our study to multiple source-destination case, where relay selection needs to be determined for each source-destination pair simultaneously. The network lifetime in the presence of multiple source-destination pairs is defined as the longest time when all source-destination pairs can maintain the target transmission rate. We design relay-to-destination mapping algorithms to prolong the network lifeii time. They all aim at maximizing the perceived network lifetime at the current time slot. The optimal max-min approach and suboptimal user-priority based approach are proposed with different levels of computational complexity. / UOIT

Cooperative relaying systems aim to improve weak communication links by exploiting the spatial diversity obtained by the statistically independent channels between relays and the destination. In this thesis a cooperative relaying scheme called the Opportunistic Multiple Relaying (OMR) is proposed with its special receiver structure. Unlike most relaying schemes in the literature, multiple relay nodes are allowed to transmit in nonorthogonal channels in OMR without requiring any control overhead for relay coordination. OMR is compared to a benchmark scheme called the Selection Relaying (SR) in which the relay node is preselected by the source before transmission according to the average channel quality information. It is observed that OMR performs significantly better than SR in terms of error performance.

The trend towards personalized ubiquitous computing has led to the advent of a new generation of wireless technologies, namely wireless body area networks (WBANs), which connect the wearable devices into the Internet-of-Things. This thesis considers the problems of relay selection and power control in fading WBANs with energy-efficiency and security considerations. The main body of the thesis is formed by two papers. Ideas from probability theory are used, in the first paper, to construct a performance measure signifying the energy efficiency of transmission, while in the second paper, information-theoretic principles are leveraged to characterize the transmission secrecy at the wireless physical layer (PHY). The hypothesis is that exploiting spatial diversity through multi-hop relaying is an effective strategy in a WBAN to combat fading and enhance communication throughput. In order to analytically explore the problems of optimal relay selection and power control, proper tools from game theory are employed. In particular, non-cooperative game-theoretic frameworks are developed to model and analyze the strategic interactions among sensor nodes in a WBAN when seeking to optimize their transmissions in the uplink. Quality-of-service requirements are also incorporated into the game frameworks, in terms of upper bounds on the end-to-end delay and jitter incurred by multi-hop transmission, by borrowing relevant tools from queuing theory. The proposed game frameworks are proved to admit Nash equilibria, and distributed algorithms are devised that converge to stable Nash solutions. The frameworks are then evaluated using numerical simulations in conditions approximating actual deployment of WBANs. Performance behavior trade-offs are investigated in an IEEE 802.15.6-based ultra wideband WBAN considering various scenarios. The frameworks show remarkable promise in improving the energy efficiency and PHY secrecy of transmission, at the expense of an admissible increase in the end-to-end latency.

Les réseaux de télécommunications sont soumis à des processus d'amélioration et d'optimisation continue. Chaque nouvelle itération apporte son lot de défis et limites. En effet, la croissance exponentielle des appareils de télécommunication, des stations de base aux équipements utilisateurs conduisent à de sérieux problèmes d'economie d'énergie. En plus des menaces à la vie privée, en particulier pour les réseaux sans fil car les canaux utilisés par les opérateurs peuvent également être utilisés par une oreille indiscrète quelconque. L'optimisation de l'utilisation du spectre est également un défi en raison du fait que le spectre disponible dans les systèmes de communication sans fil est devenu une ressource très rare en raison de la demande croissante. Les réseaux émergents, tels que les femtocells, souffrent également des défis mentionnés précédemment. Le travail de thèse actuel se concentre sur la proposition de solutions aux défis cités précédemment: l'efficacité énergétique, le partage du spectre et la sécurité. Le travail de recherche présenté dans cette thèse a porté sur trois axes principaux: Premièrement, trouver un moyen de réduire au minimum la consommation d'énergie des femtocellules dans les reseaux BWA femto/macro-cellulaire en diminuant le nombre d'événements de mobilité non désirées et l'introduction de nouveaux états de puissance pour la femtocellule. En second lieu, proposer une solution qui vise à réduire le temps de transmission prévu dans le temps de séjour de l'utilisateur secondaire (SU) dans la couverture d'une femtocellule en utilisant un algorithme basé sur le temps minimum prévu de transmission dans le temps de séjour de l'équipement utilisateur (UE). Enfin, introduire un nouveau modèle qui basé sur la sélection du meilleur relais qui maximise le taux de confidentialité et les avantages de l'augmentation du nombre de relais sous la contrainte de qualité de service à la destination. / Telecommunications networks are subject to continuous improvement and enhancement processes. Every new iteration brings its set of challenges and limitations. In fact, the exponential growth in telecommunication devices, from base stations to user equipments lead to serious energy efficiency issues. Along with the privacy threats, especially for wireless networks as the channels used by operators can also be used by any eavesdropper. Spectrum usage optimization is also a challenge due to the fact that the available spectrum in wireless communications systems has been a very rare resource because of the increasing demand. Emerging networks, such as femtocells, suffer also from the previously mentioned challenges. The current thesis work focuses on proposing several solutions to the previously cited challenges: energy efficiency, spectrum sharing and security. The research work introduced in this thesis has focused on three main axes: First, find a way to minimize the energy consumption of femtocells in macro/femto-cellular BWA networks by decreasing the number of unwanted mobility events and introducing new power states for the femtocell device. Second, propose a solution that aims to reduce the expected transmission time within the dwell time of Secondary User (SU) in the coverage of a femtocell using an algorithm based on the minimum expected transmission time within the dwell time of the User Equipment (UE) in the coverage of the femtocell. Finally, introduce a new scheme that is based on best relay selection method that maximizes the secrecy rate and benefits from increasing the number of relays under QoS constraint at the destination.

[pt] Em redes sem fio, o desvanecimento do sinal causado pela propagação por caminhos múltiplos pode ser mitigado através do uso de diversidade cooperativa [1–3]. Neste contexto, esquemas de seleção de repetidores são essenciais por causa de seu alto desempenho [4–6]. Esta tese é focada no desenvolvimento de técnicas de seleção de repetidores, que utilizam buffers. Como primeira contribuição, apresentamos uma estrutura de chaveamento para sistemas de repetidores MIMO em que um nó de origem pode transmitir diretamente para um nó de destino ou auxiliado por repetidores. Em particular, apresentamos uma nova técnica de seleção de repetidores baseada no chaveamento e seleção do melhor canal, denominada Switched Max-Link, que faz uso do critério de seleção Maximum Minimum Distance (MMD). Como segunda contribuição, apresentamos uma estratégia de seleção de repetidores para sistemas cooperativos de múltiplas antenas que são auxiliados por um nó processador central, em que um cluster formado por dois usuários é selecionado para transmitir simultaneamente um ao outro com a ajuda de repetidores. Em particular, apresentamos uma nova estratégia de seleção de repetidores Multi-Way com base na seleção do melhor link, explorando o uso de buffers e codificação de rede em camada física (PLNC), denominada Multi-Way Buffer-Aided Max-Link (MW-Max-Link). Como terceira contribuição, apresentamos uma estrutura de uplink dirigida por nuvem para sistemas de repetidores Multi-Way de múltiplas antenas, que ajuda na detecção conjunta de símbolos na nuvem, onde os usuários são selecionados para transmitir simultaneamente uns aos outros auxiliados por repetidores. Em particular, desenvolvemos um novo protocolo de seleção de repetidores Multi-Way com base na seleção do melhor link, explorando o uso de buffers em nuvem e PLNC, denominado Multi-Way Cloud-Driven Best-User-Link (MWC-Best-User-Link). É realizada uma análise das técnicas propostas e existentes em termos de custo computacional, probabilidade de erro de pareamento, soma das taxas e atraso médio e simulações são empregadas para avaliar o desempenho dessas técnicas. / [en] In wireless networks, signal fading caused by multipath propagation can be mitigated through the use of cooperative diversity [1–3]. In this context, relay selection schemes are key because of their high performance [4–6]. Thus, this thesis is focused on developing relay selection techniques, that uses buffers. In this work, as a first contribution, we present a switched relaying framework for multiple-input multiple-output (MIMO) relay systems where a source node may transmit directly to a destination node or aided by relays equipped with buffers. In particular, we develop a novel relay selection protocol based on switching and the selection of the best link, denoted as Switched Max-Link, that uses the novel Maximum Minimum Distance (MMD) relay selection criterion. After that, as a second contribution, we present a relay-selection strategy for multi-way cooperative multi-antenna systems that are aided by a central processor node, where a cluster formed by two users is selected to simultaneously transmit to each other with the help of relays. In particular, we present a novel multi-way relay selection strategy based on the selection of the best link, exploiting the use of buffers and physical-layer network coding (PLNC), that is called Multi-Way Buffer-Aided Max-Link (MW-Max-Link). Moreover, as a third contribution, we present a cloud-driven uplink framework for multi-way multiple-antenna relay systems which aids joint symbol detection in the cloud and where users are selected to simultaneously transmit to each other aided by relays. In particular, we develop a novel multi-way relay selection protocol based on the selection of the best link, exploiting the use of cloud buffers and PLNC, denoted as Multi-Way Cloud- Driven Best-User-Link (MWC-Best-User-Link). An analysis of the proposed and existing techniques in terms of computational cost, pairwise error probability, sum-rate and average delay is carried out. Simulations are then employed to evaluate the performance of these techniques.