Grâce à leur capacité de faire face à la sélectivité fréquentielle des canaux de transmission, les modulations multi-porteuses (MC) attirent de plus en plus d’attention. De nos jours, la modulation OFDM avec le préfixe cyclique (CP) est la plus utilisée, et cela grâce à sa simplicité et à sa robustesse. Cependant, la technique CP-OFDM présente une perte dans l’efficacité spectrale à cause de l’introduction du CP puisqu’il contient des informations redondantes. De plus, la réponse rectangulaire du filtre de mise en forme utilisé en OFDM a une mauvaise localisation fréquentielle. Afin de surmonter ces inconvénients, la modulation multi-porteuse à base des bancs de filtres (FBMC) a été proposée en tant qu’une approche alternative à la modulation OFDM. En effet, on n’a pas besoin d’insérer un intervalle de garde, tel que le CP, dans la modulation FBMC. D’autre part, la bonne localisation fréquentielle de la réponse du filtre de mise en forme permet un meilleur contrôle de la radiation hors-bande du système. Dans la littérature, on trouve plusieurs types de la modulations FBMC basés sur différentes structures. Dans cette thèse, nous ne nous intéressons que sur le schéma de Saltzberg appelé OFDM/OQAM ou FBMC/OQAM. Dans ce schéma, les symboles envoyés sur chaque sous-porteuse sont tirés d’une constellation PAM réelle, et les symboles réels sont envoyés à une cadence de 2/T . La condition d’orthogonalité est réduite sur l’ensemble des réels uniquement. En conséquence, le symbole démodulé et égalisé est infecté par un terme d’interférence purement imaginaire. Ce terme d’interférence est une combinaison linaire des symboles transmis dans le voisinage du symbole concerné. La présence de cette interférence inhérente cause des difficultés de détection dans certains schéma multi-antennes (MIMO).L’objectif de cette thèse est d’étudier l’association de la modulation FBMC aux techniques MIMO, à savoir le multiplexage spatiale avec détection de maximum de vraisemblance (ML). Dans un premier temps, nous proposons d’analyser différentes techniques d’annulation d’interférence que nous adaptons au contexte de MIMO-FBMC. Nous montrons que, dans certains cas, nous pouvons bien retirer l’interférence et appliquer la détection ML. Ensuite, nous proposons d’apporter une légère modification dans la modulation FBMC en transmettant des symbole QAM complexes. Évidement, cela brise la condition d’orthogonalité mais nous montrons qu’ainsi la puissance d’interférence sera considérablement réduite. Enfin, nous introduisons un nouveau schéma basé sur la modulation FBMC. Ce schéma, que nous avons baptisé FFT-FBMC, transforme le modèle du système à un modèle équivalent à celui de l’OFDM. Ainsi, n’importe quelle technique multi-antennes pourra être appliquée sans aucune difficulté. D’abord, nous développons le système FFT-FBMC dans un contexte SISO, et puis nous évaluons ces performances dans le contexte MIMO. / Multicarrier (MC) Modulation attracts a lot of attention for high speed wireless transmissions because of its capability to cope with frequency selective fading channels turning the wideband transmission link into several narrowband subchannels whose equalization, in some situations, can be performed independently and in a simple manner. Nowadays, orthogonal frequency division multiplexing (OFDM) with the cyclic prefix (CP) insertion is the most widespread modulation among all MC modulations, and this thanks to its simplicity and its robustness against multipath fading using the cyclic prefix. Systems or standards such as ADSL or IEEE802.11a have already implemented the CP-OFDM modulation. Other standards like IEEE802.11n combine CP-OFDM and multiple-input multiple-output (MIMO) in order to increase the bit rate and to provide a better use of the channel spatial diversity. Nevertheless, CP-OFDM technique causes a loss of spectral efficiency due to the CP as it contains redundant information. Moreover, the rectangular prototype filter used in CP-OFDM has a poor frequency localization. This poor frequency localization makes it difficult for CP-OFDM systems to respect stringent specifications of spectrum masks.To overcome these drawbacks, filter-bank multicarrier (FBMC) was proposed as an alternative approach to CP-OFDM. Indeed, FBMC does not need any CP, and it furthermore offers the possibility to use different time-frequency well-localized prototype filters which allow much better control of the out-of-band emission. In the literature we find several FBMC systems based on different structures. In this thesis, we focus on the Saltzberg’s scheme called OFDM/OQAM (or FBMC/OQAM). The orthogonality constraint for FBMC/OQAM is relaxed being limited only to the real field while for OFDM it has to be satisfied in the complex field. Consequently, one of the characteristics of FBMC/OQAM is that the demodulated transmitted symbols are accompanied by interference terms caused by the neighboring transmitted data in time-frequency domain. The presence of this interference is an issue for some MIMO schemes and until today their combination with FBMC remains an open problem.The aim of this thesis is to study the combination between FBMC and MIMO techniques, namely spatial multiplexing with ML detection. In the first part, we propose to analyze different intersymbol interference (ISI) cancellation techniques that we adapt to the FBMC/OQAM with MIMO context. We show that, in some cases, we can cope with the presence of the inherent FBMC interference and overcome the difficulties of performing ML detection in spatial multiplexing with FBMC/OQAM. After that, we propose a modification in the conventional FBMC/OQAM modulation by transmitting complex QAM symbols instead of OQAM ones. This proposal allows to reduce considerably the inherent interference but at the expense of the orthogonality condition. Indeed, in the proposed FBMC/QAM,the data symbol and the inherent interference term are both complex. Finally, we introduce a novel FBMC scheme and a transmission strategy in order to avoid the inherent interference terms. This proposed scheme (that we call FFT-FBMC) transforms the FBMC system into an equivalent system formulated as OFDM regardless of some residual interference. Thus, any OFDM transmission technique can be performed straightforwardly to the proposed FBMC scheme with a corresponding complexity growth. We develop the FFT-FBMC in the case of single-input single-output (SISO) configuration. Then, we extend its application to SM-MIMO configuration with ML detection and Alamouti coding scheme.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2018-08-27T11:17:25Z No. of bitstreams: 2 Dissertação - Dalton Foltran de Souza - 2018.pdf: 3869661 bytes, checksum: 5fa93e5e35c983cbefa148826a07a3ef (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-08-27T11:20:32Z (GMT) No. of bitstreams: 2 Dissertação - Dalton Foltran de Souza - 2018.pdf: 3869661 bytes, checksum: 5fa93e5e35c983cbefa148826a07a3ef (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-08-27T11:20:32Z (GMT). No. of bitstreams: 2 Dissertação - Dalton Foltran de Souza - 2018.pdf: 3869661 bytes, checksum: 5fa93e5e35c983cbefa148826a07a3ef (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-07-04 / With the development of the next generation of mobile communications systems for 5G, several technologies are being studied aiming to reach the new requirements in new application scenarios. Among them, is the use of new modulations with higher spectral efficiency in substitution of OFDM, such as F-OFDM and UFMC, and also the scheduling algorithms which are in charge of sharing resources between users. In this work, we evaluated the application of F-OFDM and UFMC, 5G modulations candidates, on downlink LTE compared with OFDM and evaluated the schedulers Round Robin, QoS Guaranteed and PSO dealing with additional resources provided by the tested modulations. For that, we compared performance considering parameters like fairness, latency, throughput and spectral efficiency. The results showed that the downlink LTE improved performance in all evaluated parameters with UFMC modulation. In fact, there were a performance improvement in all schedulers evaluated. For example, PSO based scheduler improved latency and throughput while QoS Guaranteed reached the lowest loss, as the highest fairness were reached by QoS Guaranteed and Round Robin. Also, we propose a scheduling algorithm that takes into account the queue size in the user buffer and channel quality to maximize throughput and fairness in the LTE downlink network. The metrics evaluated were transmission efficiency, throughput, fairness, delay and losses. The proposed algorithm achieved better results for all evaluated metrics. / Com o desenvolvimento da próxima geração dos sistemas de comunicação móvel sem fio (5G) diversas tecnologias estão sendo estudadas com o objetivo de se atender aos novos requisitos de desempenho em diferentes cenários de aplicação. Dentre elas, está a utilização de modulações com maior eficiência espectral em substituição à OFDM, como F-OFDM e UFMC, como também os algoritmos de escalonamento que são responsáveis pelo compartilhamento dos recursos aos usuários. Neste trabalho, avaliamos a aplicação no downlink LTE das modulações F-OFDM e UFMC, candidatas ao 5G, comparadas a OFDM e avaliamos os escalonadores Round Robin, QoS Garantido e PSO ao lidar com recursos adicionais disponíveis proporcionados pelas modulações estudadas. Para tal, realizamos a análise de parâmetros de desempenho de tráfego, tais como vazão, índice de justiça, perda de dados e retardo médio. Os resultados mostraram que o enlace de descida do LTE apresentou melhor desempenho para todos os parâmetros analisados com a modulação UFMC. De fato, foram obtidas melhorias de desempenho para todos escalonadores avaliados. Como exemplo, o escalonador baseado em PSO apresentou melhorias no retardo e vazão, enquanto o escalonador QoS Garantido obteve menor taxa de perda de dados, sendo que índices de justiça mais elevados foram obtidos para os escalonadores QoS Garantido e Round Robin. Ainda, propusemos um escalonador que considera o tamanho da fila no buffer e a qualidade de canal visando maximizar a vazão e o índice de justiça no downlink da rede LTE. As métricas avaliadas foram eficiência de transmissão, vazão, índice de justiça, retardo e perda de dados. O algoritmo proposto alcançou melhores resultados em todas as métricas avaliadas em relação aos outros algoritmos considerados.

A necessidade de transmissão de canais modulados a taxas a partir de 400 Gb/s tem motivado a pesquisa e os esforços relativos às tecnologias de camada física habilitadores desta alta capacidade. A atenção se volta, principalmente, aos frontends (transmissores e receptores), aliados aos processadores digitais de sinal (Digital Signal Processors, DSPs), às técnicas de amplificação óptica e a novos tipos de fibra óptica. Em particular a técnica baseada no emprego de filtros de Nyquist combinados à multiplexação de comprimentos de onda (Wavelength Division Multiplexing, DWM), conhecida como Nyquist-WDM, ou N-WDM, tem atraído grande interesse para geração de supercanais ópticos, hoje um dos elementos chave nos sistemas de redes ópticas. O estudo dos fundamentos e casos particulares dos filtros de Nyquist são aprofundados nesta dissertação para o controle de seus parâmetros, em especial o parâmetro conhecido como fator de roll-off, em aplicações que requerem flexibilidade na ocupação espectral e até o reaproveitamento das limitações do filtro para atenuar alguns efeitos lineares e não lineares na fibra. A técnica utiliza um tipo de formatação geométrica de pulso e é limitada pelo ajuste grosso do fator de roll-off, mas como abordagem inicial, permite estabelecer uma série de compromissos na concepção do circuito eletrônico de um transponder sintonizável. Uma investigação teórica foi feita em um sistema PM-16QAM de 21x256 Gb/s, a partir de dados experimentais obtidos com roll-off igual 0,1, para análise do efeito no desempenho sistêmico do ajuste do excesso de largura de banda (em relação à banda de Nyquist) de um filtro formatador de pulso. O fator de roll-off foi ajustado e seu impacto no desempenho do sistema, em termos de alcance, foi verificado. A partir dos resultados, foi observado que, desde que a taxa de erro de bit, BER, esteja dentro do limite do código corretor de erro (forward error corrector, FEC), o valor de roll-off pode ser ajustado para um valor ótimo de acordo com a configuração do sistema e as metas requeridas. Uma vez encontrada a relação entre a BER e o fator de roll-off, foi possível determinar um fator de mérito que relaciona a resolução do filtro de Nyquist, em função do número de taps que ele emprega, o consumo de energia da DSP e, consequentemente, a BER. O compromisso assim estabelecido entre o desempenho sistêmico, o consumo de energia e o fator de roll-off representa a principal contribuição desta dissertação. / The need for transmission of channels modulated at rates greater than 400 Gb/s has motivated the research and efforts related to the physical layer technologies that will enable this high capacity. The attention turns mainly to the frontends (transmitters and receivers), allied to digital signal processors (DSPs), optical amplification techniques and new types of optical fiber. The technique based on the use of Nyquist filters combined withWavelength Division Multiplexing (WDM), known as Nyquist-WDM, or N-WDM, has attracted great interest for the generation of optical super-channels, today one of the key elements in optical network systems. The study of the fundamentals and particular cases of the Nyquist filters are detailed in this dissertation for mastering the control of the parameters, especially the parameter known as roll-off factor, for applications that require flexibility in the spectral occupation and even the reutilization of the limitations of the filter to attenuate some linear and non-linear effects on the fiber. The technique uses a geometric type of pulse-shaping, and is limited by the roll-off factor tunning, but as an initial approach, it allows to establish a series of compensations in the design of the electronic circuit of a tunable transponder. A theoretical investigation was made on a 21x256 Gb/s PM-16QAM system, taken as reference the experimental data obtained with roll-off equal to 0.1, to analyze the effects of adjusting the excess bandwidth (relative to the Nyquist band) of a pulse-shaping filter. The roll-off factor was tunned and its impact on the system performance in terms of range effects was verified. From the results, it was observed that, as long as the bit error ratio, BER, is within the FEC limit, the roll-off parameter can be set to an optimum value according to the system configuration and required targets. Once the relationship between the BER and the roll-off factor was found, it was possible to determine a merit factor that relates the resolution of the Nyquist filter, as a function of the number of taps it uses, the energy consumption of the DSP and, consequently, the BER. The compromise thus established between system performance, energy consumption and roll off represents the main contribution of this work.

Este trabalho tem como cenário as redes ópticas de próxima geração, por onde trafegarão supercanais flexíveis, sincronizados e modulados a taxas variáveis que podem chegar à ordem de Terabit por segundo. Mais especificamente, focaliza o supercanal óptico gerado a partir de um único laser (laser semente) composto por portadoras ortogonais entre si, travadas em frequência e moduladas de maneira síncrona. Tal arranjo constitui um sistema de transmissão conhecido como OFDM óptico (optical orthogonal frequency division multiplexing, O-OFDM). Este esquema não requer banda de guarda entre canais, o que proporciona uma melhor eficiência espectral, se mantidas as condições de ortogonalidade mútua, quando comparado à técnica Nyquist WDM (Nyquist wavelength division multiplexing, N-WDM), usualmente reconhecida como base para os sistemas de próxima geração. Muitos são os desafios a serem vencidos antes que a técnica O-OFDM possa ser efetivamente implantada comercialmente e esta tese busca, através de um estudo de seus princípios de funcionamento e módulos constituintes, elencar os principais obstáculos e as possíveis maneira de superá-los. Sem pretender ser exaustivo em termos de tecnologias disponíveis para alcançar este fim, o objetivo é propor novas configurações de subsistemas e arquitetura de nó para o transmissor, o nó intermediário e o receptor coerente, capazes de executar, de forma relativamente simples no domínio óptico, as principais funcionalidades de uma transmissão ponto a ponto com nós deriva/insere intermediários. Através de simulações sistêmicas e demonstrações experimentais, como prova de conceito, dois cenários são abordados: análise do desempenho numa transmissão ponto a ponto, e operação em rede, com derivação e inserção de canal em nós intermediários. Ao final, através de uma análise qualitativa, é feita uma estimativa de componentes e subsistemas necessários para tornar a transmissão de sinais O-OFDM implementável por tecnologias de fotônica integrada que atenda, com eficiência espectral e economia de energia, a sempre crescente demanda de capacidade em sistemas de transmissão óptica. / This work focuses on the scenario of next generation optical networking, where flexible optical superchannels will propagate modulated at variable rates that can reach terabits per second. More specifically, it focuses on the optical superchannel generated from a single laser (seed laser) composed of orthogonal carriers, which are frequency-locked and synchronously modulated. Such arrangement constitutes a transmission system known as optical orthogonal frequency division multiplexing (O-OFDM). This scheme does not require guard band between channels, which provides a better spectral efficiency, if the conditions of mutual orthogonality are maintained, when compared to the Nyquist wavelength dividing multiplexing (N-WDM) technique, usually recognized as the basis for the next generation systems. There are many challenges to overcome before O-OFDM technique can be effectively deployed commercially and this thesis seeks, through a study of its operating principles and constituent modules, to identify the main obstacles and the possible ways of overcoming them. Without intending to be exhaustive in terms of available technologies to achieve this aim, the objective is to propose new configurations of subsystems and node architecture for the transmitter, the intermediate node and the coherent receiver, able to perform in the optical domain, in a relatively simple way, the main features a point-to-point transmission with nodes drifting/inserting intermediates. Through systemic simulations and some experimental demonstrations, as proof of concept, two scenarios are addressed: performance analysis in a point-to-point transmission, and network operation, with channel derivation and insertion at intermediate nodes. At the end, through a qualitative analysis, an estimate of components and subsystems is made to make the transmission of O-OFDM signals implementable by integrated photonics technologies that meet, with spectral efficiency and energy savings, the ever increasing capacity demand in optical transmission systems.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-07T11:55:49Z No. of bitstreams: 1 robertomussideoliveira.pdf: 1293292 bytes, checksum: 78c6c9fd9415c0b3990a1aaf55b842a2 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-06-07T13:31:58Z (GMT) No. of bitstreams: 1 robertomussideoliveira.pdf: 1293292 bytes, checksum: 78c6c9fd9415c0b3990a1aaf55b842a2 (MD5) / Made available in DSpace on 2017-06-07T13:31:58Z (GMT). No. of bitstreams: 1 robertomussideoliveira.pdf: 1293292 bytes, checksum: 78c6c9fd9415c0b3990a1aaf55b842a2 (MD5) Previous issue date: 2015-03-11 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nesse trabalho, discutimos o uso de protocolos de cooperação na subcamada de controle de acesso ao meio (CMAC) para reduzir a taxa de perda de pacote e aumentar o goodput em um sistema de comunicação banda larga via rede elétrica (PLC) de ambientes residenciais. Para apoiar essa discussão, nós, pela primeira vez, apresentamos uma análise estatística da taxa de erro de pacote (PER) de canais PLC residenciais a partir de dados medidos em um modelo com um único relay. Adicionalmente, nós esboçamos um simples protocolo CMAC capaz de explorar a diversidade oferecida por uma rede elétrica doméstica. Usando esse protocolo, nosso objetivo é mostrar o impacto da variação da largura de banda, da variação da PER e da posição relativa do relay no desempenho do sistema. Sendo assim, nós mostramos que a taxa de perda de pacote e o goodput melhoram quando a largura de banda de frequência aumenta. Além disso, resultados mostram que a cooperação na camada de enlace não oferece vantagens caso os valores de PER do enlace direto e do enlace intermediado pelo relay sejam muito altos ou muito baixos. Nós também notamos que as melhorias estudadas dependem da posição do nó relay em relação ao nó fonte e ao nó destino (i.e., notamos melhoras na rede nos casos em que o relay estava situado próximo à fonte e no meio do caminho entre a fonte e o destino). Finalmente, uma comparação entre os esquemas de acesso múltiplo por divisão de frequências ortogonais - acesso múltiplo por divisão de tempo (OFDMA-TDMA) e acesso múltiplo por divisão de tempo - multiplexação por divisão ortogonal de frequência (TDMA-OFDM) mostra que o simples protocolo CMAC é mais eficaz quando usado juntamente com o primeiro esquema do que com o último. Em suma, a nossa contribuição é dividida em duas etapas: primeiramente, desenvolvemos um simples protocolo MAC de cooperação que traz melhorias de desempenho na rede quando comparado com um sistema sem a cooperação; em segundo lugar, nós realizamos uma análise sistemática de diferentes cenários, mostrando os benefícios e limitações da cooperação na camada de enlace de redes PLC. / In this work, we discuss the use of cooperative medium access control (CMAC) protocols to reduce packet loss rate and to improve goodput of in-home broadband power line communication (PLC) systems. To support this discussion, we, for the first time, present a statistical packet error rate (PER) analysis of measured in-home PLC channels by adopting a single relay model. Additionally, we outline a simple CMAC protocol that is capable of exploiting the diversity offered by in-home electric power grids. Using this protocol, we aim to show the impact of bandwidth variation, PER variation and of relative relay location on system performance. Thus, we show that packet loss rate and goodput improve when frequency bandwidth increases. Also, results show that cooperation at the link layer does not offer advantages if the PER values of direct and relayed links are very high or very low. Furthermore, we note that the improvements depend on the location of the node relay in relation to the nodes source and the destination (i.e., network improves if the relay is located near the source or in the midway between the source and the destination). Finally, a comparison between orthogonal frequency division multiple access - time division multiple access (OFDMA-TDMA) and time division multiple access - orthogonal frequency division multiplexing (TDMA-OFDM) schemes show that the simple CMAC protocol is more effective when it is used together with the former scheme than the latter.

Orientador: Luís Geraldo Pedroso Meloni / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-23T18:38:54Z (GMT). No. of bitstreams: 1 BarraganGuerrero_DiegoOrlando_M.pdf: 4412718 bytes, checksum: fd7daf7712cace2d176bf47e3bd792dd (MD5) Previous issue date: 2013 / Resumo: Os sistemas OFDM são intrinsecamente sensíveis a erros de sincronismo de tempo e frequência. O sincronismo é uma etapa fundamental para a correta recepção de pacotes. Esta dissertação descreve como se implementar vários algoritmos de sincronismo para OFDM em FPGA usando os símbolos do preâmbulo definidos no padrão IEEE 802.11a. Além disso, foi implementado o algoritmo CORDIC (necessário para a etapa de estimação e compensação de desvio de portadora) em modo rotacional e vetorial para um sistema coordenado circular, comparando o desempenho de várias arquiteturas com o intuito de otimizar a frequência de operação e relacionar o erro do resultado com o número de iterações realizadas. Conforme mostrado nos resultados, são obtidas estimativas com boas aproximações para desvios de 0, 100 e 200 kHz. Os resultados obtidos constituem um instrumento importante para a melhor escolha de implementação de algoritmos de sincronismo em FPGA. Verificou-se que os diferentes algoritmos não apenas possuem valores de variância distintos, mas também frequências de operação diferentes e consumo de recursos da FPGA. Ao longo do projeto foi considerado um modelo de canal tapped-delay / Abstract: OFDM systems are intrinsically sensitive to errors of synchronization in time and frequency. Synchronization is a key step for correct packet reception. This thesis describes how to implement in FPGA several synchronization algorithms for OFDM using the symbols of the preamble defined in IEEE 802.11a. In addition, the CORDIC algorithm is implemented (step required for carrier frequency offset estimation and compensation) in rotational and vectoring mode for a circular coordinate system, comparing the performance of various architectures in order to optimize the operating frequency and relate the error of the result with the number of iterations performed. As shown in the results, estimates are obtained with good approximations for offsets of 0, 100 and 200 kHz. The obtained results are an important instrument for the best choice of synchronization algorithm for implementation in FPGA. It was found that the different algorithms have not only different values of variance, but also different operating frequency and consumption of the FPGA resources. Throughout the project a tapped-delay channel model was considered in the analysis / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

La radio cognitive (CR) est une radio entièrement reconfigurable qui permet de changer intelligemment ses paramètres de communication en réponse à l’activité des autres réseaux radios et demandes d’utilisateur. L’objectif ultime de la CR est de permettre à l’utilisateur secondaire (SU) d’utiliser la ressource de spectre disponible sans interférer sur l’utilisateur primaire (PU) en utilisant des trous de spectre. Par conséquent, la détection du PU est l’un des défis principaux dans le développement de la CR. Par rapport aux systèmes conventionnels de communication sans fil, le système CR introduit de nouveaux problèmes d’allocation de ressource (RA) en raison de l’interférence des canaux adjacents utilisés par le SU et le PU. Dans le contexte de la CR, la plupart des efforts ont été menés sur les systèmes de CR basés sur le multiplexage par division de fréquences orthogonales (OFDM). Toutefois, la technique de l’OFDM montre quelques points faibles dans l’application à cause des remontées significatives du spectre. Les modulations multiporteuses à base de bancs de filtre (FBMC) ont été récemment proposées pour des applications de CR. Dans cette thèse, trois points importants pour le développement d’un système de CR basé sur le FBMC sont discutés.Les trois points principaux peuvent être résumés ainsi: nous examinons premièrement les problèmes de détection de spectre des signaux OFDM et FBMC en employant le détecteur de signature de cyclostationnarité (CS). En outre, nous proposons une architecture de détection multi-bande basée sur le banc de filtre polyphasé (PFB), et montrons son avantage; deuxièmement, la comparaison entre l’OFDM et le FBMC du point de vue de l’efficacité spectrale est discutée; et enfin, nous proposons un algorithme stratégique d’allocation de ressource pour les systèmes cognitifs multi-cellulaires et multi-utilisateurs.Les algorithmes proposés dans cette thèse ont été testés par simulation. Les résultats numériques prouvent que le FBMC, par opposition à l’OFDM, pourrait réaliser une efficacité spectrale plus élevée et offre un avantage attrayant dans la détection de spectre. Les contributions de cette thèse ont accru l’intérêt d’appliquer FBMC dans les systèmes de CR à l’avenir. / Cognitive Radio (CR) is a fully reconfigurable radio that can intelligently change its communicationvariables in response to network and user demands. The ultimate goal of CR is to allowthe Secondary User (SU) to utilize the available spectrum resource on a non-interfering basis to thePrimary User (PU) by sensing the existence of spectrum holes. Therefore, the detection of PU isone of the main challenges in the development of the CR technology. Moreover, compared to conventionalwireless communication systems, CR system poses new challenges to Resource Allocation(RA) problems because of the Cross-Channel Interference (CCI) from the adjacent channels used bySU to PU. In the CR context, most past efforts have been spent on Orthogonal Frequency DivisionMultiplexing (OFDM) based CR systems. However, OFDM technique exhibits some shortcomingsin application due to its significant spectrum leakage. Filter Bank based Multi-Carrier (FBMC), asanother promising Multi-Carrier Modulation (MCM) candidate, has been recently proposed for CRapplications. In this dissertation, three important issues in developing a FBMC based CR system arediscussed.The three prime issues can be summarized: we firstly survey the spectrum sensing problemsof OFDM and FBMC signals by using Cyclostationary Signature (CS) detector. Furthermore, wepropose a Polyphase Filter Bank (PFB) based multi-band sensing architecture, and argue for its advantage;secondly, the comparison of OFDM and FBMC from the spectral efficiency point of viewis discussed; and lastly, our emphasis is placed on the strategic resource allocation algorithms fornon-cooperative multi-cell CR systems.The overall proposed algorithms have been verified by simulation. Numerical results show thatFBMC, as opposed to OFDM, could achieve higher spectrum efficiency and attractive benefit inspectrum sensing. The contributions of this dissertation have heighten the interest in applying FBMCin the future CR systems.

La croissance exponentielle du trafic de données sans fils, causée par l'Internet mobile et les smartphones, contraint les futurs systèmes radio à inclure des modulations/formes d'ondes plus avancées offrant un débit plus élevé et une utilisation efficace des ressources spectrales. Les transmissions dites Faster-Than-Nyquist (FTN), introduites en 1975, sont parmi les meilleurs candidates pour répondre à ces besoins. En transmettant les symboles à une cadence plus rapide que celle définie par le critère de Nyquist, FTN peut théoriquement augmenter le débit mais en introduisant des interférences en contrepartie. Dans cette thèse, nous explorons le concept des transmissions FTN à travers un canal AWGN (Additive White Gaussian Noise) dans le contexte des modulations OFDM/OQAM (Orthogonal Frequency Division Multiplexing with Offset Quadrature Amplitude Modulation).L'objectif principal de cette thèse est de présenter un système OFDM/OQAM qui permet de transmettre l'information au-delà de la cadence de Nyquist tout en tenant en compte la complexité globale du système. Tout d'abord, nous proposons une nouvelle implémentation efficace des systèmes OFDM/OQAM appliquant le concept FTN, désignée ici par FTN-OQAM, qui garde la même complexité que les systèmes OFDM/OQAM et qui permet un gain en débit très proche du gain théorique. Vu que la condition de Nyquist n'est plus respectée, le signal transmis est maintenant perturbé par des interférences. Pour remédier à ce problème, nous proposons un récepteur basé sur le principe de l'égalisation linéaire sous le critère minimum erreur quadratique moyenne avec annulation d'interférences appelé MMSE LE-IC. Le but de notre système est d'augmenter le débit de transmission, ce qui signifie que des constellations d'ordres élevés seront ciblées. Dans ce contexte, le MMSE LE-IC, dont la complexité est indépendante de la constellation, représente un bon compromis entre efficacité et complexité. Puisque la modulation OFDM/OQAM utilise différents types de formes d'ondes, nous proposons pour plusieurs d'entre elles un algorithme pour déterminer la valeur minimale du facteur d'accélération, en fonction de l'ordre de constellation, qui apporte un gain en efficacité spectrale tout en gardant les mêmes performances que les systèmes respectant le critère de Nyquist à un SNR fixé. Ensuite, nous étudions l'amélioration du traitement itératif de l'émetteur-récepteur. La méthode proposée consiste à combiner un précodeur avec le système FTN-OQAM afin de réduire les interférences causées par du FTN à l'émission. Nous proposons un modèle de précodage dispersé, car il est difficile de précoder conjointement tous les symboles transmis. Nous présentons trois familles de précodeurs avec les récepteurs correspondants. En outre, nous modifions différents blocs de l'émetteur FTN-OQAM tels que le codage canal, le mappage des bits et le mappage des symboles afin d'améliorer davantage le transmetteur FTN-OQAM. Les résultats présentés révèlent le potentiel important des systèmes proposés. / The exponential growth of wireless data traffic driven by mobile Internet and smart devices constrains the future radio systems to include advanced modulations/waveforms offering higher data rates with more efficient bandwidth usage. One possibility is to violate the well known Nyquist criterion by transmitting faster than the Nyquist rate, i.e., using a technique also known as Faster-Than-Nyquist (FTN) signaling. Nyquist-based systems have the advantage of simple transmitter and receiver architectures at the detriment of bandwidth efficiency. The idea of signaling beyond the Nyquist rate to trade the interference-free transmission for more throughput goes back to 1975. In this dissertation, we investigate the concept of FTN signaling over Additive White Gaussian Noise (AWGN) channel in the context of Orthogonal Frequency Division Multiplexing with Offset Quadrature Amplitude Modulation OFDM/OQAM modulation.The main objective of our work is to present an OFDM/OQAM system signaling faster than the Nyquist one and explore its potential rate improvement while keeping under consideration the overall system complexity. First, we propose a new efficient FTN implementation of OFDM/OQAM systems, denoted by FTN-OQAM, that has the same complexity as OFDM/OQAM systems, while approaching very closely the FTN theoretical rate improvement. As the Nyquist condition is no longer respected, severe interference impacts the transmitted signals. To deal with the introduced interferences, we propose a turbo-like receiver based on Minimum Mean Square Error Linear Equalization and Interference Cancellation, named MMSE LE-IC. The aim of our system is to boost the transmission rate, which means that high constellation orders will be targeted. In this respect, the MMSE LE-IC, whose complexity is independent of the constellation, turns out to be a good candidate. Since OFDM/OQAM modulation can be equipped with different types of pulse shapes, we propose an algorithm to find, for different constellation orders, the minimum achieved FTN packing factor for various pulse shapes. Then, we aim at improving the iterative processing of the introduced transceiver. The proposed method involves combining a precoder with the FTN-OQAM system in order to remove FTN-induced interference at the transmitter. We also present a sparse precoding pattern as it is difficult to jointly precode all the transmitted symbols. We introduce three families of precoders along with the corresponding receivers. Furthermore, we propose several modifications of the FTN-OQAM transmitter concerning different blocks such as channel coding, bits mapping and symbols mapping to further enhance the FTN-OQAM transceiver design. Presented results reveal the significant potential of the proposed methods.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this master s thesis, a wireless communication scheme with a single transmit and single receive antenna, SISO case, with use of the OFDM multicarrier technique and application of LDPC coding was considered. It is well known that one of the biggest challenge related to OFDM system refers to the reduction of the peak-to-average power ratio (PAPR) factor. Thus this master s thesis proposes the use of 16-APSK and 16-QAM modulations by aiming to mitigate the PAPR factor. It is also considered the use of LDPC codes to evaluate the performance of bit error rate (BER) versus signal-to-noise ratio (SNR) performance for the 16-QAM, A16- QAM and 16-APSK constellations. The LDPC codes were adopted since they are one of the most effective methods of channel coding presented in the literature. Monte Carlo simulations were performed in AWGN and Rayleigh fading channels in order to evaluate the system performance in terms of BER × SNR and the PAPR factor analysis from the perspective of CCDF curves. Results reveal that with the use of LDPC codes associated with the use of 16-APSK constellations in multicarrier systems promotes BER performance gain and also reduction of the PAPR factor. / Nesta dissertação foi considerado um esquema de comunicação sem fio, com uma antena transmissora e uma antena receptora, caso SISO, com uso da técnica multiportadora OFDM e aplicação de codificação LDPC. Sabe-se que um dos maiores desafios na utilização do sistema OFDM refere-se à redução do fator razão de potência de pico e potência média (PAPR). Assim, nesta dissertação de mestrado propõe-se o emprego de modulações 16-APSK e A16-QAM com intuito de mitigar esse fator. Considera-se também o emprego de códigos LDPC para melhorar o desempenho de taxa de erro de bit (BER) versus razão sinal-ruído (SNR) para as constelações 16-QAM, A16-QAM e 16-APSK. Os códigos LDPC foram adotados por serem um dos mais eficazes métodos de codificação de canal apresentados na literatura. Foram realizadas simulações do tipo Monte Carlo em canais AWGN e com desvanecimento do tipo Rayleigh para se avaliar o desempenho do sistema em termos de curvas de BER × SNR e o fator PAPR sob a perspectiva de curvas de CCDF. Os resultados revelam que o emprego de códigos LDPC associados ao uso de constelacões 16-APSK em sistemas multiportadora promovem ganhos na taxa de erros e redução no fator PAPR.

Abstract The development of wireless telecommunication systems has been rapid during the last two decades and the data rates as well as the quality of service (QoS) requirements are continuously growing. Multiple-input multiple-output (MIMO) techniques in combination with orthogonal frequency-division multiplexing (MIMO–OFDM) have been identified as a promising approach for high spectral efficiency wideband systems. The optimal detection method for a coded MIMO–OFDM system with spatial multiplexing (SM) is the maximum a posteriori (MAP) detector, which is often too complex for systems with high order modulation. Suboptimal linear detectors, such as the linear minimum mean square error (LMMSE) criterion based detection, offer low complexity solutions, but have poor performance in correlated fading channels. A list sphere detector (LSD) is a tree search based soft output detector that can be used to approximate the MAP detector with a lower computational complexity. The benefits of the more advanced detectors can be realized especially in a low SNR environment by, e.g., increasing the cell coverage. In this thesis, we consider the linear minimum mean square error (LMMSE) criterion based detectors and more advanced LSDs for detection of SM transmission. The LSD algorithms are not as such feasible for hardware implementation. Therefore, we identify the design choices that relate to the performance and implementation complexity of the LSD algorithms. We give guidelines to the LSD algorithm design and propose the proper trade-off solutions for practical wireless systems. The more stringent requirements call for further research on architectures and implementation. In particular, it is important to address the parallelism and pipelining factors in the architecture design to enable an optimal trade-off between used resources and operating speed. We design pipelined systolic array architecture for LMMSE detector algorithms and efficient architectures with given algorithm properties for the LSD algorithms. We consider the VLSI implementation of the algorithms to study the true performance and complexity. The designed architectures are implemented on a field programmable gate array (FPGA) chip and CMOS application specific integrated circuit (ASIC) technology. Finally, we present some measurement results with a hardware testbed to verify the performance of the considered algorithms. / Tiivistelmä Langattoman tietoliikenteen kehitys on ollut nopeaa viimeisien vuosikymmenien aikana ja järjestelmiltä vaaditaan yhä suurempia datanopeuksia ja luotettavuutta. Multiple-input multiple-output (MIMO) tekniikka yhdistettynä monikantoaaltomodulointiin (MIMO-OFDM) on tunnistettu lupaavaksi järjestelmäksi, joka mahdollistaa tehokkaan taajuusalueen hyödyntämisen. Optimaalinen ilmaisumenetelmä tilakanavoituun (SM) ja koodattuun MIMO-OFDM järjestelmään on maximum a posteriori (MAP) ilmaisin, joka on tyypillisesti liian kompleksinen toteuttaa laajakaistajärjestelmissä, joissa käytetään korkean asteen modulointia. Alioptimaaliset lineaariset ilmaisimet, kuten pienimpään keskineliövirheeseen (LMMSE) perustuvat ilmaisimet, ovat suhteellisen yksinkertaisia toteuttaa nykyteknologialla, mutta niiden suorituskyky on varsin heikko korreloivassa radiokanavassa. Listapalloilmaisin (LSD) on puuhakualgoritmiin perustuva pehmeän ulostulon ilmaisin, joka pystyy jäljittelemään MAP ilmaisinta sitä pienemmällä kompleksisuudella. Kehittyneemmät ilmaisimet, kuten LSD, voivat parantaa langattoman verkon suorituskykyä erityisesti ympäristössä, jossa on matala signaalikohinasuhde, esimerkiksi mahdollistamalla suuremman toiminta-alueen. Tässä väitöskirjassa on tutkittu kahta LMMSE ilmaisinta ja kolmea LSD ilmaisinta SM lähetyksen ilmaisuun. Yleisesti LSD algoritmit eivät ole sellaisenaan toteutuskelpoisia kaupallisiin järjestelmiin. Väitöskirjassa on tämän vuoksi tutkittu LSD:n toteutukseen liittyviä haasteita ja toteutusmenetelmiä ja annetaan suosituksia LSD algorithmien suunnitteluun sekä ehdotetaan sopivia toteutuskompromisseja käytännön langattomiin järjestelmiin. Haastavammat suorituskyky- ja latenssivaatimukset edellyttävät lisätutkimuksia toteutusarkkitehtuureihin ja toteutuksiin. Erityisesti rinnakkaisten resurssien käyttö ja liukuhihnatekniikka toteutusarkkitehtuureissa mahdollistavat optimaalisen kompromissin löytämisen toteutuksessa käytettyjen resurssien ja laskentanopeuden väliltä. Väitöskirjassa suunnitellaan tehokkaat arkkitehtuurit tutkituille LMMSE ja LSD algoritmeille ottaen huomioon niiden ominaisuudet. Väitöskirjassa tutkitaan algoritmien toteutusta VLSI tekniikalla ja pyritään saamaan realistinen arvio algoritmien kompleksisuudesta ja suorituskyvystä. Algoritmeille suunnitellut arkkitehtuurit on toteutettu sekä FPGA piirille että erillisenä toteutuksena ASIC teknologialla. Väitöskirjassa esitetään myös testilaitteistolla tehtyjä mittaustuloksia ja varmistetaan toteutettujen algoritmien suorituskyky.