Signal-scale cooperation is a class of techniques designed to harness the same gains offered by multi-antenna communication in scenarios where devices are too small to contain an array of antennas. While the potential improvements in reliability at the physical layer are well known, three key challenges must be addressed to harness these gains at the medium access layer: (a) the distributed synchronization and coordination of devices to enable cooperative behavior, (b) the conservation of energy for devices cooperating to help others, and (c) the management of increased inter-device interference caused by multiple spatially separate transmissions in a cooperative network. In this thesis, we offer three contributions that respectively answer the above three challenges. First, we present two novel cooperative medium access control protocols: Distributed On-demand Cooperation (DOC) and Power-controlled Distributed On-demand Cooperation (PDOC). These protocols utilize negative acknowledgments to synchronize and trigger cooperative relay transmissions in a completely distributed manner. Furthermore, they avoid cooperative transmissions that would likely be unhelpful to the source of the traffic. Second, we present an energy conservation algorithm known as Distributed Energy-Conserving Cooperation (DECC). DECC allows devices to alter their cooperative behavior based on measured changes to their own energy efficiency. With DECC, devices become self-aware of the impact of signal-scale cooperation -- they explicitly monitor their own performance and scale the degree to which they cooperate with others accordingly. Third and finally, we present a series of protocols to combat the challenge of inter-device interference. Whereas energy efficiency can be addressed by a self-aware device monitoring its own performance, inter-device interference requires devices with network awareness that understand the impact of their behavior on the devices around them. We investigate and quantify the impact of incomplete network awareness by proposing a modeling approximation to derive relaying policy behaviors. We then map these policies to protocols for wireless channels.

In recent years, relay communication has been proved to achieve the transmis-sion diversity order with space-time block coding (STBC). Most research assumedthat the relay nodes are in perfect synchronization. However, in actual, becausethe transmitting time at each relay is different, the signals from different relays received at destination will interfere with each other. Inter-symbol interference (ISI) iscaused. Besides, the time synchronization error will reduce orthogonality of space-time block coding and result in serious performance degrade. This thesis proposes a time delay compensation method by using Fourier transform and Least Square(LS)estimation method. The destination node can utilize the estimated time delay tosynchronize the received signal. Then, the space-time coding will maintain orthogonality at the receiver. Simulation results show that the proposed method caneffectively improve the performance of cooperative networks when imperfect timesynchronization exists.

No description available.

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.

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.

In a multihop cellular network, mobile terminals have the capability to transmit directly to other mobile terminals enabling them to use other terminals as relays to forward traffic towards the base station. Previous studies of networks consisting of a single cell found that the SINR in a multihop cellular network is slightly lower than in a traditional cellular network. However, multihop cellular networks may have a higher capacity than traditional cellular networks due to their potential for lower intercell interference. For this reason, the effects of intercell interference are investigated in this thesis. Our simulations of a network with many cells show that multihop cellular networks have a higher SINR than traditional cellular networks due to the near elimination of intercell interference. However, multihop cellular networks still suffer from large amounts of interference surrounding the base station because all traffic either emanates or is destined to the base station making it the capacity bottleneck. To resolve this problem, we propose a novel architecture called the autonomous infrastructure multihop cellular network where users can connect their mobile terminals to the backbone network giving them the functionality of an access point. Access points receive traffic from other terminals and send it directly onto the backbone, as would a base station. This reduces the traffic handled by the base station and increases network capacity. Our analysis and simulations show that in autonomous infrastructure multihop cellular networks, the SINR at the base station is higher, the power consumption is lower and the coverage is better than in normal multihop cellular networks. Access points require parameters like their transmission range to be adjusted autonomously to optimal levels. In this thesis, we propose an autonomous pilot power protocol. Our results show that by adjusting a parameter within the protocol, a required coverage level of terminals can be specified and achieved without knowledge of the location or density of mobile terminals. Furthermore, we show that the protocol determines the transmission range that is optimal in terms of SINR and power consumption that achieves the required coverage while effectively eliminating the bottleneck that existed at the base station.

In a multihop cellular network, mobile terminals have the capability to transmit directly to other mobile terminals enabling them to use other terminals as relays to forward traffic towards the base station. Previous studies of networks consisting of a single cell found that the SINR in a multihop cellular network is slightly lower than in a traditional cellular network. However, multihop cellular networks may have a higher capacity than traditional cellular networks due to their potential for lower intercell interference. For this reason, the effects of intercell interference are investigated in this thesis. Our simulations of a network with many cells show that multihop cellular networks have a higher SINR than traditional cellular networks due to the near elimination of intercell interference. However, multihop cellular networks still suffer from large amounts of interference surrounding the base station because all traffic either emanates or is destined to the base station making it the capacity bottleneck. To resolve this problem, we propose a novel architecture called the autonomous infrastructure multihop cellular network where users can connect their mobile terminals to the backbone network giving them the functionality of an access point. Access points receive traffic from other terminals and send it directly onto the backbone, as would a base station. This reduces the traffic handled by the base station and increases network capacity. Our analysis and simulations show that in autonomous infrastructure multihop cellular networks, the SINR at the base station is higher, the power consumption is lower and the coverage is better than in normal multihop cellular networks. Access points require parameters like their transmission range to be adjusted autonomously to optimal levels. In this thesis, we propose an autonomous pilot power protocol. Our results show that by adjusting a parameter within the protocol, a required coverage level of terminals can be specified and achieved without knowledge of the location or density of mobile terminals. Furthermore, we show that the protocol determines the transmission range that is optimal in terms of SINR and power consumption that achieves the required coverage while effectively eliminating the bottleneck that existed at the base station.

We investigate the effects of quantized channel state information (CSI) on the performance of resource allocation algorithms in wireless networks. The thesis starts with a brief overview of a specific type of quantizer, referred to as a conservative quantizer where we propose the optimality and sufficiency conditions as well as practical methods to find such quantizers. We apply this theory to the quantization of transmitter CSI in point-to-point Gaussian channels and transmission under short-term power constraints. Next, we show that in a multiple-node decode-and-forward (DF) cooperative network, the same structure for quantizer is close to op- timal for the sum-rate objective function. Based on a proposed upper bound on the rate loss in such scenarios, we also argue that the quantizer should assign uneven numbers of quantization bits to different links in the network. The simulation results show that given a target rate loss level, through quantization and bit allocation, there is, on average, 0.5−1 bits per link savings in CSI feedback requirements compared to the uniform and equal bit allocation approaches. Given the many benefits in non-uniform allocation of CSI rate in the network, we formulate a generalized bit allocation scheme which is extensible to arbitrary classes of network resource allocation problems. In the last part of this thesis, we focus on power control in an interference network and then, investigate the effects of CSI imperfections on the performance of power control algorithms. First, we propose an iterative power control algorithm based on a fixed-point iteration and prove its local convergence. Then, we show that for a centralized implementation of the power control algorithm, a uniform in dB (geometric) quantizer of channel power is efficient. Based on this choice of channel quantizer, we propose a bound on rate loss in terms of the resolution of the ii deployed quantizer, where a 3 dB in quantization error is shown to contribute to a maximum of 1 bit rate loss at each user. Similarly to the previous scenario, the upper bound suggests that an uneven assignment of numbers of quantization levels leads to smaller distortion. Based on this bound, we develop the corresponding bit allocation laws. We also investigate the effects of CSI errors on the performance of distributed power control algorithms and show that, compared to the centralized case, the distributed algorithm could lead to a further SINR loss of up to 3 dB for one or more transmitters. This error is due to the fact that because of CSI errors, the estimated interference level at each receiver is different from the induced interference wireless transmitters expect.

We investigate the effects of quantized channel state information (CSI) on the performance of resource allocation algorithms in wireless networks. The thesis starts with a brief overview of a specific type of quantizer, referred to as a conservative quantizer where we propose the optimality and sufficiency conditions as well as practical methods to find such quantizers. We apply this theory to the quantization of transmitter CSI in point-to-point Gaussian channels and transmission under short-term power constraints. Next, we show that in a multiple-node decode-and-forward (DF) cooperative network, the same structure for quantizer is close to op- timal for the sum-rate objective function. Based on a proposed upper bound on the rate loss in such scenarios, we also argue that the quantizer should assign uneven numbers of quantization bits to different links in the network. The simulation results show that given a target rate loss level, through quantization and bit allocation, there is, on average, 0.5−1 bits per link savings in CSI feedback requirements compared to the uniform and equal bit allocation approaches. Given the many benefits in non-uniform allocation of CSI rate in the network, we formulate a generalized bit allocation scheme which is extensible to arbitrary classes of network resource allocation problems. In the last part of this thesis, we focus on power control in an interference network and then, investigate the effects of CSI imperfections on the performance of power control algorithms. First, we propose an iterative power control algorithm based on a fixed-point iteration and prove its local convergence. Then, we show that for a centralized implementation of the power control algorithm, a uniform in dB (geometric) quantizer of channel power is efficient. Based on this choice of channel quantizer, we propose a bound on rate loss in terms of the resolution of the ii deployed quantizer, where a 3 dB in quantization error is shown to contribute to a maximum of 1 bit rate loss at each user. Similarly to the previous scenario, the upper bound suggests that an uneven assignment of numbers of quantization levels leads to smaller distortion. Based on this bound, we develop the corresponding bit allocation laws. We also investigate the effects of CSI errors on the performance of distributed power control algorithms and show that, compared to the centralized case, the distributed algorithm could lead to a further SINR loss of up to 3 dB for one or more transmitters. This error is due to the fact that because of CSI errors, the estimated interference level at each receiver is different from the induced interference wireless transmitters expect.

[pt] A brusca transição que levou os mercados da América Latina à sua atual configuração, exerceu uma forte pressão sobre as Pequenas e Médias Empresas (PMEs) industriais e colocou em xeque a sua competitividade. Entornos cada vez mais turbulentos e competitivos ameaçam seriamente as PMEs que atuam de forma isolada e chamam, sobretudo, à adoção de formas de organização industrial baseadas no cooperativismo e aproveitamento da similaridade e complementaridade de competências entre firmas. Os clusters regionais de PMEs e as redes de cooperação produtivas representam alternativas organizacionais que contemplam a cooperação inter-empresarial como um meio para conseguir uma maior eficiência na administração dos recursos das firmas, a redução dos seus custos de transação e a geração dinâmica de processos inovativos. Esses fatos motivaram o autor desta dissertação a estudar experiências bem sucedidas de clusters regionais de PMEs e redes de cooperação produtiva no Brasil, e tirar delas lições na forma de propostas factíveis e transferíveis à realidade do seu país de origem, a Nicarágua. São analisadas as características estruturais e operacionais de dois clusters regionais envolvendo os ramos madeira/móveis e couro/calçados. O presente trabalho pretende servir como uma guia referencial para agentes envolvidos em tarefas de promoção, estruturação e dinamização de clusters regionais de PMEs industriais e redes de cooperação produtiva na Nicarágua. / [en] The abrupt transition that brought Latin American markets to their actual configuration, laid a great amount of stress upon the Small and Medium sized Enterprises (SMEs) and put their competitiveness in check. Increasingly turbulent and competitive environments threaten SMEs when operating in an isolated manner, and call for the adaptation of new forms of industrial organization based on cooperation and on the utilization of similarities and complementarities of competencies between firms. Regional clusters of SMEs and cooperative networks represent organizational alternatives that aim to use inter-firm cooperation as a means to achieve higher efficiency on the administration of the firms resources, the reduction of their transaction costs and the dynamic generation of innovative processes. These facts motivated the author of this dissertation to study well succeeded experiences of SMEs regional clusters and cooperative networks in Brazil, and extract from them lessons in the form of feasible proposals that could be transferred to the reality of his own country, Nicaragua. The study focuses on the structural and operational characteristics of two regional clusters in the wood/furniture and leather/shoe industry. This work intends to serve as a reference guide for agents involved in tasks related to promoting and structuring SMEs regional clusters and cooperative networks in Nicaragua.