Improving decoding speed for parallel distributed video coding architectures

The research work disclosed in this publication is partially funded by the Strategic Educational Pathways Scholarship Scheme (Malta). The scholarship is part-financed by the European Union – European Social Fund. (ESF 1.25).The Distributed Video Coding (DVC) paradigm is suitable for devices which have limited encoding capabilities. However, it is characterized by excessive decoding delays which compromise their application for time constrained services. This limitation can be mitigated by adopting parallel DVC architectures. Yet, the traditional Gray-code or binary-code representations have a non-uniform distribution of mismatch across bit-planes, resulting in uneven decoding times which hinder parallel decoding. This work proposes an alternative indexing scheme, where mismatch is distributed more uniformly amongst bit-planes and thus comparable decoding delays are expected, facilitating parallel implementations. This method reduces decoding time by up to 32% compared to architectures using simple parallel techniques, with a slight loss of 0.06dB in RD performance.peer-reviewe

Etudes de récepteurs MIMO-LDPC itératifs

L objectif de cette thèse est l étude de récepteurs MIMO LDPC itératifs. Les techniques MIMO permettent d augmenter la capacité des réseaux sans fil sans la nécessité de ressources fréquentielles additives. Associées aux schémas de modulations multiporteuses CP-OFDM, les techniques MIMO sont ainsi devenues la pierre angulaire pour les systèmes sans fil à haute efficacité spectrale. La réception optimale peut être obtenue à l aide d une réception conjointe (Egalisation/Décodage). Étant très complexe, la réception conjointe n est pas envisagée et l égalisation et le décodage sont réalisés disjointement au coût d une dégradation significative en performances. Entre ces deux solutions, la réception itérative trouve son intérêt pour sa capacité à s approcher des performances optimales avec une complexité réduite. La conception de récepteurs itératifs pour certaines applications, de type WiFi à titre d exemple doit respecter la structure du code imposée par la norme. Ces codes ne sont pas optimisés pour des récepteurs itératifs. En observant l effet du nombre d' itérations dans le processus itératif, on montre par simulation que l ordonnancement des itérations décodage LDPC/Turbo-égalisation joue un rôle important dans la complexité et le délai du récepteur. Nous proposons de définir des ordonnancements permettant de réduire la complexité globale du récepteur. Deux approches sont proposées, une approche statique ainsi qu'une autre dynamique. Ensuite nous considérons un système multi-utilisateur avec un accès multiple par répartition spatiale. Nous étudions l intérêt de la réception itérative dans ce contexte tenant en compte la différence de puissance signale utile/interférence.The aim of this thesis is to address the design of iterative MIMO receivers using LDPC Error Correcting codes. MIMO techniques enable capacity increase in wireless networks with no additional frequency ressources. The associationof MIMO with multicarrier modulation techniques OFDM made them the cornerstone of emerging high rate wireless networks. Optimal reception can be achieved using joint detection and decoding at the expense of a huge complexity making it impractical. Disjoint reception is then the most used. The design of iterative receivers for some applications using LDPC codes like Wifi (IEEE 802.11n) is constrained by the standard code structure which is not optimized for such kind of receivers. By observing the effect of the number of iterations on performance and complexity we underline the interest of scheduling LDPC decoding iterations and turboequalization iterations. We propose to define schedules for the iterative receiver in order to reduce its complexity while preserving its performance. Two approaches are used : static and dynamic scheduling. The second part of this work is concerns Multiuser MIMO using Spatial Division Multiple Access. We explore and evaluate the interest of using iterative reception to cancel residual inter-user interference.PARIS-Télécom ParisTech (751132302) / SudocSudocFranceF

Intelligent Side Information Generation in Distributed Video Coding

Distributed video coding (DVC) reverses the traditional coding paradigm of complex encoders allied with basic decoding to one where the computational cost is largely incurred by the decoder. This is attractive as the proven theoretical work of Wyner-Ziv (WZ) and Slepian-Wolf (SW) shows that the performance by such a system should be exactly the same as a conventional coder. Despite the solid theoretical foundations, current DVC qualitative and quantitative performance falls short of existing conventional coders and there remain crucial limitations. A key constraint governing DVC performance is the quality of side information (SI), a coarse representation of original video frames which are not available at the decoder. Techniques to generate SI have usually been based on linear motion compensated temporal interpolation (LMCTI), though these do not always produce satisfactory SI quality, especially in sequences exhibiting non-linear motion. This thesis presents an intelligent higher order piecewise trajectory temporal interpolation (HOPTTI) framework for SI generation with original contributions that afford better SI quality in comparison to existing LMCTI-based approaches. The major elements in this framework are: (i) a cubic trajectory interpolation algorithm model that significantly improves the accuracy of motion vector estimations; (ii) an adaptive overlapped block motion compensation (AOBMC) model which reduces both blocking and overlapping artefacts in the SI emanating from the block matching algorithm; (iii) the development of an empirical mode switching algorithm; and (iv) an intelligent switching mechanism to construct SI by automatically selecting the best macroblock from the intermediate SI generated by HOPTTI and AOBMC algorithms. Rigorous analysis and evaluation confirms that significant quantitative and perceptual improvements in SI quality are achieved with the new framework

Anuário Científico – 2009 & 2010 Resumos de Artigos, Comunicações, Teses, Patentes, Livros e Monografias de Mestrado

O Conselho Técnico-Científico do Instituto Superior de Engenharia de Lisboa (ISEL), na senda da consolidação da divulgação do conhecimento e da ciência desenvolvidos pelo nosso corpo docente, propõe-se publicar mais uma edição do Anuário Científico, relativa à produção científica de 2009 e 2010. A investigação, enquanto vertente estratégica do Instituto Superior de Engenharia de Lisboa (ISEL), tem concorrido para o seu reconhecimento nacional e internacional como instituição de referência e de qualidade na área do ensino das engenharias. É também nesta vertente que o ISEL consubstancia a sua ligação à sociedade portuguesa e internacional através da transferência de tecnologia e de conhecimento, resultantes da sua atividade científica e pedagógica, contribuindo para o seu desenvolvimento e crescimento de forma sustentada. São parte integrante do Anuário Científico todos os conteúdos com afiliação ISEL resultantes de resumos de artigos publicados em livros, revistas e atas de congressos que os docentes do ISEL apresentaram em fóruns e congressos nacionais e internacionais, bem como teses e patentes. Desde 2002, ano da publicação da primeira edição, temos assistido a uma evolução crescente do número de publicações de conteúdos científicos, fruto do trabalho desenvolvido pelos docentes que se têm empenhado com afinco e perseverança. Contudo, nestes dois anos (2009 e 2010) constatou-se um decréscimo no número de publicações, principalmente em 2010. Uma das causas poderá estar diretamente relacionada com a redução do financiamento ao ensino superior uma vez que limita toda a investigação no âmbito da atividade de I&D e da produção científica. Na sequência da implementação do Processo de Bolonha em 2006, o ISEL promoveu a criação de cursos de Mestrado disponibilizando uma oferta educativa mais completa e diversificada aos seus alunos, mas também de outras instituições, dotando-os de competências inovadoras apropriadas ao mercado de trabalho que hoje se carateriza mais competitivo e dinâmico. Terminados os períodos escolar e de execução das monografias dos alunos, os resumos destas são igualmente parte integrante deste Anuário, no que concerne à conclusão dos Mestrados em 2009 e 2010.A fim de permitir uma maior acessibilidade à comunidade científica e à sociedade civil, o Anuário Científico será editado de ora avante em formato eletrónico. Excecionalmente esta edição contempla publicações referentes a dois anos – 2009 e 2010