Cooperative communication has recently re-emerged as a possible paradigm shift to realize the promises of the ever increasing wireless communication market; how- ever, there have been few, if any, studies to translate theoretical results into feasi- ble schemes with their particular practical challenges. The multiple-input multiple- output (MIMO) technique is another method that has been recently employed in different standards and protocols, often as an optional scenario, to further improve the reliability and data rate of different wireless communication applications. In this work, we look into possible methods and algorithms for combining these two tech- niques to take advantage of the benefits of both. In this thesis, we will consider methods that consider the limitations of practical solutions, which, to the best of our knowledge, are the first time to be considered in this context. We will present complexity reduction techniques for MIMO systems in cooperative systems. Furthermore, we will present architectures for flexible and configurable MIMO detectors. These architectures could support a range of data rates, modulation orders and numbers of antennas, and therefore, are crucial in the different nodes of cooperative systems. The breadth-first search employed in our realization presents a large opportunity to exploit the parallelism of the FPGA in order to achieve high data rates. Algorithmic modifications to address potential sequential bottlenecks in the traditional bread-first search-based SD are highlighted in the thesis. We will present a novel Cooperative Partial Detection (CPD) approach in MIMO relay channels, where instead of applying the conventional full detection in the relay, the relay performs a partial detection and forwards the detected parts of the message to the destination. We will demonstrate how this approach leads to controlling the complexity in the relay and helping it choose how much it is willing to cooperate based on its available resources. We will discuss the complexity implications of this method, and more importantly, present hardware verification and over-the-air experimentation of CPD using the Wireless Open-access Research Platform (WARP). / NSF grants EIA-0321266, CCF-0541363, CNS-0551692, CNS-0619767, EECS-0925942, and CNS-0923479, Nokia, Xilinx, Nokia Siemens Networks, Texas Instruments, and Azimuth Systems.

This thesis aims to tackle the theoretical challenges of characterizing the fundamental performance limits of amplify-and-forward (AF) cooperative networks and to resolve the practical challenges in the receiver design for AF systems. First of all, we study the Shannon-theoretic channel capacity which serves as a benchmark for practical wireless communications systems. Specifically, we derive exact expressions of the ergodic capacity in a single-integral form for general multi-branch AF relay networks with/without the direct link (DL). Moreover, we derive closed-form and tight upper bounds on the ergodic capacity, which facilitate the evaluation of the ergodic capacity. These expressions provide useful theoretical tools for the design of practical wireless AF relaying systems. We then tackle the practical challenges involved in the design of AF receivers, aiming to substantially reduce the channel state information (CSI) signaling overhead yet achieving satisfactory error performance. We take the maximum-likelihood (ML) and generalized likelihood ratio test (GLRT) approaches to develop detectors under four typical wireless communications scenarios with little/no knowledge of the CSI. Firstly, for a semi-coherent scenario where only the product of channel coefficients of each relay branch is known, we develop the ML symbol-by-symbol (SBS) detector, which reduces the instantaneous CSI signaling overhead by 50% while achieving comparable performance to the ideal coherent receiver. Secondly, for the noncoherent scenario with only the (second-order) channel statistics and noise variances, we develop a noncoherent ML SBS detector for AF networks employing differential modulations. Thirdly, for AF networks with only the knowledge of the noise variance, we develop a sequence detector using GLRT. Lastly, for a completely blind scenario where the instantaneous CSI, channel statistics, and noise variances are all unknown, we develop a GLRT-based sequence detector. The proposed detectors achieve significant performance improvements over the state-of-the-art counterparts. The conducted theoretical analysis and practical design will facilitate the design of reliable communications over wireless AF networks with reduced CSI requirement. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2014-06-25 16:48:05.912

In this thesis new techniques are presented to achieve performance enhancement in wireless cooperative networks. In particular, techniques to improve transmission rate and maximise end-to-end signal-to-noise ratio are described. An offset transmission scheme with full interference cancellation for a wireless cooperative network with frequency flat links and four relays is introduced. This method can asymptotically, as the size of the symbol block increases, achieve maximum transmission rate together with full cooperative diversity provided the destination node has multiple antennas. A novel full inter-relay interference cancellation method that also achieves asymptotically maximum rate and full cooperative diversity is then designed for which the destination node only requires a single antenna. Two- and four-relay selection schemes for wireless cooperative amplify and forward type networks are then studied in order to overcome the degradation of end-to-end bit error rate performance in single-relay selection networks when there are feedback errors in the relay to destination node links. Outage probability analysis for a four-relay selection scheme without interference is undertaken. Outage probability analysis of a full rate distributed transmission scheme with inter-relay interference is also studied for best single- and two-relay selection networks. The advantage of multi-relay selection when no interference occurs and when adjacent cell interference is present at the relay nodes is then shown theoretically. Simulation results for outage probability analysis are included which support the theoretical expressions. Finally, outage probability analysis of a cognitive amplify and forward type relay network with cooperation between certain secondary users, chosen by best single-, two- and four-relay selection is presented. The cognitive amplify and forward relays are assumed to exploit an underlay approach, which requires adherence to an interference constraint on the primary user. The relay selection scheme is performed either with a max-min strategy or one based on maximising exact end-to-end signal-to-noise ratio. The outage probability analyses are again confirmed by numerical evaluations.

In this thesis new methods are presented to achieve performance enhancement in wireless cooperative networks. In particular, techniques to improve diversity gain, throughput and minimise the transmission delay are described. A buffer-aided amplify-and-forward max-link relay selection scheme for both symmetric and asymmetric channels is introduced. This approach shows that the max-link scheme is most effective over the traditional max-SNR scheme when the source-to-relay and relay-to-destination links are symmetric. The closed form expressions for the outage probability and average packet delay of the proposed scheme under both symmetric and asymmetric channel configurations is derived. The diversity order and the coding gain of the AF max-link scheme is analytically provided. Then a novel relay selection scheme with significantly reduced packet delay is proposed. Both the outage performance and average packet delay of the proposed scheme are analysed. The analysis shows that, besides the diversity and coding gains, the proposed scheme has average packet delay similar to that of a non buffer-aided relay system when the channel SNR is sufficiently high thereby. A novel buffer-aided link selection scheme based on network-coding in a multiple hop relay network is proposed. Compared with existing approaches, the proposed scheme significantly increases the system throughput. This is achieved by applying data buffers at the relays to decrease the outage probability and using network-coding to increase the data rate. The closed-form expressions of both the average throughput and packet delay are derived. The proposed scheme has not only significantly higher throughput than both the traditional and existing buffer-aided max-link scheme, but also smaller average packet delay than the max-link scheme. A decode-and-forward buffer-aided relay selection for the underlay cognitive relay networks in the presence of both primary transmitter and receiver is presented. A novel buffer aided relay selection scheme for the cognitive relay network is proposed, where the best relay is selected with the highest signal-to-interference-ratio among all available source-to-relay and relay-to-destination links while keeping the interference to the primary destination within a certain level. A closed-form expression for the outage probability of the proposed relay selection scheme is obtained. Finally, A novel security buffer-aided decode-and-forward cooperative wireless networks is considered. An eavesdropper which can intercept the data transmission from both the source and relay nodes is considered to threaten the security of transmission. Finite size data buffers are assumed to be available at every relay in order to avoid having to select concurrently the best source-to-relay and relay-to-destination links. A new max-ratio relay selection policy is proposed to optimise the secrecy transmission by considering all the possible source-to-relay and relay-to-destination links and selecting the relay having the link which maximises the signal to eavesdropper channel gain ratio. Two cases are considered in terms of knowledge of the eavesdropper channel strengths: exact and average gains, respectively. Closed-form expressions for the secrecy outage probability for both cases are obtained. The proposed max-ratio relay selection scheme is shown to outperform one based on max-min-ratio relay scheme.

Cooperative communication is a promising technique for wireless communication systems where wireless nodes cooperate together in transmitting their information. Such communication transmission technique, which realizes the multiple antenna arrays in a distributed manner over multiple wireless nodes, succeeds in extending the network coverage, increasing throughput, improving both link reliability and spectral efficiency. Available channel state information at the transmitting nodes can be used to design adaptive transmission schemes for improving the overall system performance. Throughout our work, we adaptively change loaded power and/or bit to the Orthogonal Frequency Division Multiplexing (OFDM) symbol in order to minimize bit error rate or maximize the throughput. In the first part of this dissertation, we consider single-relay OFDM system with amplify-and-forward relaying. We propose three algorithms to minimize the bit error rate under total power constraint and fixed transmission rate. These algorithms are optimal power loading, optimal bit loading and optimal bit and power loading. Through Monte Carlo simulations we study the proposed system performance and discuss the effect of relay location and channel estimation. This study shows that the proposed algorithms result in exploiting the multi-path diversity and achieving extra coding gain. In the second part, we extend the problem to a multi-relay OFDM network but with decode-and-forward relaying. We propose an adaptive power loading algorithm to minimize the bit error rate under total power constraint based on two relay selection strategies. The proposed system leads to achieve both multi-path and cooperative spatial diversity using maximal-ratio combiner for the detection. In the last part, we consider also multi-relay network but with amplify and forward relaying. We optimize the bit loading coefficients to maximize the throughput under target bit error rate constraint. The proposed algorithm is considered more practical since it takes into consideration the channel estimation quality. The considered adaptive system has less complexity compared with other adaptive systems through reducing the feedback amount. Furthermore, the full network channel state information is needed only at the destination.

In this thesis, we investigate partner selection schemes in multiuser cooperative networks. In networks, cooperative partners adopt coded cooperation to forward signals. Among the literature, two classes of two namely, centralized partner selections and distributed partner selections, have been proposed to select appropriate relays. Centralized partner selection is able to achieve the global optimization than distributed partner selection. However, centralized partner selections require high complexity, and global channel state information, which demands large amount of overhead and waste radio resources. Especially when the size of network increases, the cost to search appropriate relay for each user dramatically increases. Hence, we consider distributed partner selection scheme in the thesis. Among the existing work, fixed priority selection algorithm is a distributed partner selection algorithm strategy; where partner assignment is based on node indices do not include any channel information. To enhance performance, we exploit the geographical information of all users. Different from other distributed partner selection schemes, we adopt the method of Carrier Sense Multiple Access to exchange local information. We proposed coverage search algorithm, nearest source search algorithm and nearest middle-point search algorithm, the serve as the criteria of partner selection. The contributions of this thesis are to raise SNR, increase the probability that the achievable rate is great than the data rate in the distributed partner selection scheme, and enhance system performance.

Cooperative communication is a promising technique for wireless communication systems where wireless nodes cooperate together in transmitting their information. Such communication transmission technique, which realizes the multiple antenna arrays in a distributed manner over multiple wireless nodes, succeeds in extending the network coverage, increasing throughput, improving both link reliability and spectral efficiency. Available channel state information at the transmitting nodes can be used to design adaptive transmission schemes for improving the overall system performance. Throughout our work, we adaptively change loaded power and/or bit to the Orthogonal Frequency Division Multiplexing (OFDM) symbol in order to minimize bit error rate or maximize the throughput. In the first part of this dissertation, we consider single-relay OFDM system with amplify-and-forward relaying. We propose three algorithms to minimize the bit error rate under total power constraint and fixed transmission rate. These algorithms are optimal power loading, optimal bit loading and optimal bit and power loading. Through Monte Carlo simulations we study the proposed system performance and discuss the effect of relay location and channel estimation. This study shows that the proposed algorithms result in exploiting the multi-path diversity and achieving extra coding gain. In the second part, we extend the problem to a multi-relay OFDM network but with decode-and-forward relaying. We propose an adaptive power loading algorithm to minimize the bit error rate under total power constraint based on two relay selection strategies. The proposed system leads to achieve both multi-path and cooperative spatial diversity using maximal-ratio combiner for the detection. In the last part, we consider also multi-relay network but with amplify and forward relaying. We optimize the bit loading coefficients to maximize the throughput under target bit error rate constraint. The proposed algorithm is considered more practical since it takes into consideration the channel estimation quality. The considered adaptive system has less complexity compared with other adaptive systems through reducing the feedback amount. Furthermore, the full network channel state information is needed only at the destination.

Au cours de cette dernière dizaine d’années, l’intérêt pour la diffusion en temps réel de séquences vidéo sur réseaux sans fil ad-hoc a grandi sans cesse, en raison de l'attrayante propriété d’être capable de déployer un système de communication visuelle à tout moment et en tout lieu, sans la nécessité d'une infrastructure préexistante. Une large gamme d'applications des opérations militaires et de sauvetage, jusqu'aux applications commerciales, éducatives, récréatives, a été envisagée, ce qui a crée un grand intérêt pour toutes les technologies concernées. L'objectif de cette thèse est de fournir un service efficace et robuste de diffusion vidéo en temps réel sur réseaux mobiles ad-hoc, avec un aperçu des solutions disponibles à ce moment, et de proposer de nouvelles solutions qui permettraient de surmonter les limites de celles actuelles. Nos contributions touchent à plusieurs aspects du paradigme mobile vidéo streaming : une nouvelle technique de codage vidéo par descriptions multiples, qui fournit une qualité vidéo acceptable, même en présence d'un taux élevé de pertes ; un protocole cross-layer pour la création et le maintien d'un réseau de overlay, qui, avec un échange de messages limité, géré de façon repartie un ensemble d'arbres de multicast, un pour chaque description du flux ; un cadre original de fonctions distribuées pour l'optimisation congestion-distorsion, qui, grâce à une représentation compacte des informations de topologie, permet aux nœuds d'apprendre la structure du overlay et d'optimiser leur comportement en conséquence ; et enfin, une intégration avec le paradigme émergent du codage réseau. / During the last decade, real-time video streaming over ad-hoc networks has gathered an increasing interest, because of the attractive property of being able to deploy a visual communication system anytime and anywhere, without the need for a pre-existing infrastructure. A wide range of target applications, from military and rescue operations, to business, educational, and recreational scenarios, has been envisaged, which has created great expectations with respect to the involved technologies. The goal of this thesis is to provide an efficient and robust real-time video streaming system over mobile ad-hoc networks, proposing cross-layer solutions that overcome the limitations of both the application and network solutions available at this time. Our contributions cover several aspects of the mobile video streaming paradigm: a new multiple description video coding technique, which provides an acceptable video quality even in presence of high loss rates; a novel cross-layer design for an overlay creation and maintenance protocol, which, with a low overhead, distributedly manages a set of multicast trees, one for each description of the stream; an original distributed congestion-distortion optimisation framework, which, through a compact representation of the topology information, enables the nodes to learn the structure of the overlay and optimise their behaviour accordingly; and, finally, an integration with the emerging network coding paradigm.

O objetivo geral desta tese foi avaliar o Procad, desde a sua criação, em 2000, até o lançamento da última edição, ocorrida em 2013, refletindo em que medida foram alcançados seus objetivos de promoção da melhoria da qualidade dos programas de pós-graduação stricto sensu, por meio do estímulo à formação de redes cooperativas. Apesar de o Programa ter mais de 15 anos de existência e o Plano Nacional de Pós-Graduação – PNPG 2011-2020 ter recomendado sua continuidade, ele não conta ainda com um processo permanente de avaliação. A metodologia proposta caracteriza-se como um estudo exploratório e descritivo, quanto a sua natureza e utilizou tanto a abordagem qualitativa, quanto a quantitativa, levando em consideração a complementaridade de tais abordagens (MINAYO, 2012). Os dados qualitativos foram estudados por meio da Análise de Conteúdo, de acordo com Bardin (2011). Com relação aos meios, foram elaborados dois instrumentos de consulta, que foram enviados, por correio eletrônico, aos coordenadores gerais dos projetos Procad e aos avaliadores dos referidos projetos. O primeiro instrumento objetivou à avaliação do Programa sob o ponto de vista de seus executores e o segundo teve o propósito de avaliar o Procad sob o ponto de vista de seus avaliadores. Além disso, foram tratados os resultados da análise dos pareceres emitidos pelos avaliadores de projetos Procad, por ocasião da avaliação intermediária. Os resultados obtidos nesta tese estão sendo apresentados em dois artigos e um manuscrito. No primeiro artigo foi abordado o levantamento das respostas obtidas por meio do questionário enviado aos 603 coordenadores gerais dos projetos Procad das Edições de 2005 a 2009. Responderam à pesquisa 236 coordenadores. Verificou-se que 79% dos respondentes consideraram que o Procad tinha alcançado os principais objetivos que nortearam a sua criação. Apesar disso, esses coordenadores apontaram dois aspectos que merecem maior atenção por parte da Capes: a superestimação de metas por parte dos beneficiários de projetos e a morosidade da Capes na divulgação dos resultados da análise das prestações de contas. No segundo artigo, os dados apresentados expressaram as respostas dos avaliadores de projetos, integrantes das comissões avaliativas relativas às edições Procad, lançadas no período de 2005 a 2009. Responderam à consulta 100% dos avaliadores consultados, o que demonstrou o reconhecimento, por parte desses respondentes, da importância de tal política pública. Observou-se que 91% dos respondentes consideraram que o Procad tem atingido os principais objetivos que orientaram a sua criação. Entretanto, indicaram a necessidade de rever os prazos de duração das missões de estudo e de instituir um processo de acompanhamento e avaliação do Programa. No manuscrito foram apresentados os dados relativos à análise dos 706 pareceres emitidos pelos consultores que participaram de processos avaliativos intermediários do Procad, correspondentes às edições de 2000 a 2009. Desse total, 646 (91,5%) foram favoráveis à renovação dos projetos e 60 (8,5%) foram desfavoráveis à renovação do apoio concedido pela Capes, demonstrando que a maior parte dos projetos teve sucesso no desenvolvimento das atividades propostas para os dois primeiros anos de execução. Observaram, entretanto, que houve a implementação de uma quantidade maior de missões de trabalho em relação às missões de estudo. Sugeriram a flexibilização da duração das missões de estudo para estimular a ampliação dessas missões. Com base na pesquisa realizada, verificou-se que é preciso instituir um processo sistemático de acompanhamento e avaliação do Procad e de outras ações e linhas de apoio da Capes, aumentando a eficiência dessas políticas e a transparência na execução dos gastos públicos. São propostos, também, outros possíveis caminhos para o aperfeiçoamento do Programa. / The purpose of this thesis was to evaluate the Procad since its creation in 2000 until the release of the latest edition in 2013, reflecting on in its objectives for promoting quality improvement of graduate programs, through the incentive of formation of cooperative networks. Although the program has over 15 years of existence and the National Graduate Plan - PNPG 2011-2020 PNPG have recommended its continuation, he still has not a permanent process of evaluation. The proposed methodology is characterized as an exploratory and descriptive study, as its nature and used both qualitative approach, as the quantitative nature taking into account the complementarity of these approaches (MINAYO, 2012). Qualitative information was studied through content analysis, according to Bardin (2011). It was developed two research instruments which were sent by e-mail, the projects general coordinators of Procad and evaluators of these projects. The first instrument aimed to assess the program from the point of view of its managers and the second aimed to evaluate the Procad from the point of view of their evaluators. In addition, were analyzed the opinions issued by the projects evaluators of Procad, at the intermediate evaluation. The results obtained in this thesis are presented in two articles and a manuscript. In the first article was approached the survey responses obtained through the questionnaire sent to 603 project general coordinators of Procad of 2005 to 2009. 236 project coordinators answered the research. It was found that 79% of respondents consider that the Procad has achieved the main objectives. Nevertheless, these coordinators considered that two aspects deserve more attention from the Capes: the establishment of goals too optimistic by the project beneficiaries and the delay of Capes in disseminating the analysis results of accountability. In the second article, the data presented express the responses of project evaluators, members of evaluation committees concerning Procad editions, released from 2005 to 2009. The questionnaire was responded to 100% of project evaluators consulted, which demonstrated the recognition by these respondents the importance of such public policy. It was observed that 91% of respondents considered that the Procad have achieved the main objectives. However, they pointed out the need to review the long periods of study missions and the need to create the monitoring and evaluation of Procad. In the manuscript were presented data on the analysis of 706 opinions issued by the consultants who participated in the intermediate Procad evaluation processes, corresponding to the 2000 editions to 2009. Of this total, 646 (91.5%) were favorable to renovation projects and 60 (8.5%) were unfavorable to the renewal of support by Capes, showing that most of the projects had success in the development of the proposed activities for the first two years of implementation. They observed, however, that there was an implementation of an increased amount of work missions in relation to the study missions. They suggested that the duration of study missions might be more flexible to encourage the expansion of such missions. Based on this research, it was found that it is necessary to establish a systematic process for monitoring and evaluation of Procad and other actions and support lines Capes, increasing the efficiency of these policies and transparency in the execution of public spending. Proposed are also other possible ways to improve the program.

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