Thèses sur le sujet « Adaptation du canal »

FundaÃÃo de Amparo à Pesquisa do Estado do CearÃ
Atualmente a internet à uma ferramenta largamente utilizada e o grande desenvolvimentoe popularidade de tecnologias de acesso sem-fio (wireless) nos levam a um futuro no qual uma conexÃo caracterizada por estar disponÃvel âanytime, anywhereâ, ou seja, a qualquer hora e em qualquer lugar, serà essencial. Tal caracterÃstica à considerada obrigatÃria em sistemas4G (quarta geraÃÃo), mas para uma experiÃncia satisfatÃria para o usuÃrio à necessÃrio que uma conexÃo segura e eficiente esteja disponÃvel. A fim de obter tal eficiÃncia, a comunidade de pesquisa tem gerado algumas soluÃÃes promissoras que obtÃm ganhos significativos no desempenho do sistema, tais como modulaÃÃo e codificaÃÃo adaptativas, codificaÃÃo espaÃo-temporal, mÃltiplas antenas e canais MIMO (Multiple Input Multiple Output ), modulaÃÃo multiportadora, detecÃÃo multiusuÃrio, etc. [1]. Dentre essas soluÃÃes, destaca-se a adaptaÃÃo do sistema, ou seja, o sistema deve estar em constante adaptaÃÃo para obter sempre o melhor desempenho possÃvel para cada situaÃÃo em que se encontra. No entanto, uma importante premissa para a adaptaÃÃo do sistema consiste em conhecer o estado atual em que o sistema se encontra (informaÃÃo sobre o canal de comunicaÃÃo). Para isso diversas tÃcnicas de estimaÃÃo de canal sÃo propostas na literatura, cada uma possuindo vantagens e desvantagens. Nesse trabalho o impacto da estimaÃÃo de canal na adaptaÃÃo de enlace à analisado atravÃs de simulaÃÃes computacionais1. Em particular, duas tÃcnicas de estimaÃÃo de canal com caracterÃsticas diferentes sÃo analisadas, para alguns cenÃrios especÃficos em um sistema MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing ), atravÃs de uma mÃtrica que considera tanto a redundÃncia introduzida para estimar o canal quanto o erro de estimaÃÃo de canal de cada tÃcnica. Os resultados encontrados constituem curvas que podem ser utilizadas para efetuar a adaptaÃÃo de enlace do sistema de maneira mais realista, ou seja, considerando o efeito da estimaÃÃo de canal, alÃm de incluir a prÃpria tÃcnica de estimaÃÃo de canal como um parÃmetro a ser adaptado.
Atualmente a internet à uma ferramenta largamente utilizada e o grande desenvolvimentoe popularidade de tecnologias de acesso sem-fio (wireless) nos levam a um futuro no qual uma conexÃo caracterizada por estar disponÃvel âanytime, anywhereâ, ou seja, a qualquer hora e em qualquer lugar, serà essencial. Tal caracterÃstica à considerada obrigatÃria em sistemas4G (quarta geraÃÃo), mas para uma experiÃncia satisfatÃria para o usuÃrio à necessÃrio que uma conexÃo segura e eficiente esteja disponÃvel. A fim de obter tal eficiÃncia, a comunidade de pesquisa tem gerado algumas soluÃÃes promissoras que obtÃm ganhos significativos no desempenho do sistema, tais como modulaÃÃo e codificaÃÃo adaptativas, codificaÃÃo espaÃo-temporal, mÃltiplas antenas e canais MIMO (Multiple Input Multiple Output ), modulaÃÃo multiportadora, detecÃÃo multiusuÃrio, etc. [1]. Dentre essas soluÃÃes, destaca-se a adaptaÃÃo do sistema, ou seja, o sistema deve estar em constante adaptaÃÃo para obter sempre o melhor desempenho possÃvel para cada situaÃÃo em que se encontra. No entanto, uma importante premissa para a adaptaÃÃo do sistema consiste em conhecer o estado atual em que o sistema se encontra (informaÃÃo sobre o canal de comunicaÃÃo). Para isso diversas tÃcnicas de estimaÃÃo de canal sÃo propostas na literatura, cada uma possuindo vantagens e desvantagens. Nesse trabalho o impacto da estimaÃÃo de canal na adaptaÃÃo de enlace à analisado atravÃs de simulaÃÃes computacionais1. Em particular, duas tÃcnicas de estimaÃÃo de canal com caracterÃsticas diferentes sÃo analisadas, para alguns cenÃrios especÃficos em um sistema MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing ), atravÃs de uma mÃtrica que considera tanto a redundÃncia introduzida para estimar o canal quanto o erro de estimaÃÃo de canal de cada tÃcnica. Os resultados encontrados constituem curvas que podem ser utilizadas para efetuar a adaptaÃÃo de enlace do sistema de maneira mais realista, ou seja, considerando o efeito da estimaÃÃo de canal, alÃm de incluir a prÃpria tÃcnica de estimaÃÃo de canal como um parÃmetro a ser adaptado.
Nowadays the internet is a widely used tool and the great development and popularity of wireless technologies leads us to a future where the connectivity will be characterized as âanywhere, anytimeâ. Such characteristic is considered essential in 4G systems. However, for a satisfactory user experience a secure and efficient connectivity has to be always available. To obtain such efficiency, the research community has generated a number of promising solutions that achieve significative improvements in system performance, such as adaptive modulation and coding, space-time coding, multiple antennas and MIMO (Multiple Input Multiple Output ) channels, multicarrier modulation, multiuser detection, etc. [1]. Among these solutions, the system adaptation is a particularly interesting one, there is, the system must constantly adapt itself to achieve the best performance for each situation. However, one important premise for the system adaptation is the knowledge of the channel state information (CSI). To obtain this knowledge, several channel estimation strategies were proposed in the literature, each one with advantages and disadvantages. In this work we analyze the impact of channel estimation in the link adaptation through computer simulations1. Two channel estimation techniques with different characteristics were analyzed for some specific scenarios in a MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing ) system. To perform the analysis it was used a metric that consider the redundancy introduced to estimate the channel and the channel estimation error of each technique. The obtained results constitute curves that can be used to perform link adaptation in a more realistic way, that is, considering the effect of channel estimation. Besides, it is shown that even the choice of the channel estimation strategy can be an adaptable parameter so that the most adequate channel estimation strategy for each system state is used.
Nowadays the internet is a widely used tool and the great development and popularity of wireless technologies leads us to a future where the connectivity will be characterized as âanywhere, anytimeâ. Such characteristic is considered essential in 4G systems. However, for a satisfactory user experience a secure and efficient connectivity has to be always available. To obtain such efficiency, the research community has generated a number of promising solutions that achieve significative improvements in system performance, such as adaptive modulation and coding, space-time coding, multiple antennas and MIMO (Multiple Input Multiple Output ) channels, multicarrier modulation, multiuser detection, etc. [1]. Among these solutions, the system adaptation is a particularly interesting one, there is, the system must constantly adapt itself to achieve the best performance for each situation. However, one important premise for the system adaptation is the knowledge of the channel state information (CSI). To obtain this knowledge, several channel estimation strategies were proposed in the literature, each one with advantages and disadvantages. In this work we analyze the impact of channel estimation in the link adaptation through computer simulations1. Two channel estimation techniques with different characteristics were analyzed for some specific scenarios in a MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing ) system. To perform the analysis it was used a metric that consider the redundancy introduced to estimate the channel and the channel estimation error of each technique. The obtained results constitute curves that can be used to perform link adaptation in a more realistic way, that is, considering the effect of channel estimation. Besides, it is shown that even the choice of the channel estimation strategy can be an adaptable parameter so that the most adequate channel estimation strategy for each system state is used.

Les systèmes de communication sans fil actuels évoluent vers un renforcement des réactivités des protocles de la gestion des ressources radio (RRM) et adaptation du lien radipe (FLA) afin d'optimiser conjointement les couches MAC et PHY. En parallèle, la technologie d'antenne multiples et turbo récepteurs avancés ont un grand potentiel pour augmenter l’efficacité spectrale dans les futurs systèmes de communication sans fil. Ces deux tendances, à savoir, l'optimisation inter couche et le traitement de turbo, nécessitent le développement de nouvelles abstractions de la couche PHY (aussi appelée méthode de prédiction de la performance) qui peuvent capturer les performances du récepteur itératif par itération pour permettre l'introduction en douceur de ces récepteurs avancés dans FLA et RRM.La thèse de doctorat revisite en détail l'architecture du turbo récepteur, plus particulièrement, la classe d'algorithme itératif effectuant la détection linéaire par minimisation d’erreur quadratique moyenne avec l'annulation d’interférence (LMMSE-IC). Ensuite, une méthode semi-analytique de prédiction de la performance est proposée pour analyser son l'évolution par la modélisation stochastique de chacun des composants. Intrinsèquement, la méthode de prédiction de la performance est subordonnée à la disposition de connaissance d’information d’état du canal au niveau du récepteur (CSIR), le type de codage de canal (code convolutif ou un code turbo), le nombre de mots de code ainsi que le type d’information probabilistic sur les bits codés réinjectée par le décodeur pour la reconstruction et l'annulation d'interférence à l'intérieur d’algorithme de LMMSE -IC itératif.Dans la deuxième partie, l’adaptation du lien en boucle fermée dans les systèmes MIMO codés basés sur les abstractions de la couche PHY proposées pour les récepteurs LMMSE -IC itératifs ont été abordés. Le schéma proposé d'adaptation de liaison repose sur un faible taux de rétroaction et exploite la sélection du précodeur spatiale (par exemple, la sélection d'antennes) et du schéma de modulation et de codage (MCS) de façon à maximiser le taux moyen soumis à une contrainte de taux d'erreur de bloc. Différents schémas de codage sont testés, tels qu’un codage parcourant tous les antennes où un codage par antenne. Les simulations montrent bien le gain important obtenu avec les turbo récepteurs comparée à celui d’un récepteur MMSE classique
Current wireless communication systems evolve toward an enhanced reactivity of Radio Resource Management (RRM) and Fast Link Adaptation (FLA) protocols in order to jointly optimize the Media Access Control (MAC) and Physical (PHY) layers. In parallel, multiple antenna technology and advanced turbo receivers have a large potential to increase the spectral efficiency of future wireless communication system. These two trends, namely, cross layer optimization and turbo processing, call for the development of new PHY-layer abstractions (also called performance prediction method) that can capture the iterative receiver performance per iteration to enable the smooth introduction of such advanced receivers within FLA and RRM. The PhD thesis first revisits in detail the architecture of the turbo receiver, more particularly, the class of iterative Linear Minimum Mean-Square Error (soft) Interference Cancellation (LMMSE-IC) algorithms. Then, a semi-analytical performance prediction method is proposed to analyze its evolution through the stochastic modeling of each of the components. Intrinsically, the performance prediction method is conditional on the available Channel State Information at Receiver (CSIR), the type of channel coding (convolutional code or turbo code), the number of codewords and the type of Log Likelihood Ratios (LLR) on coded bits fed back from the decoder for interference reconstruction and cancellation inside the iterative LMMSE-IC algorithms. In the second part, closed-loop FLA in coded MIMO systems based on the proposed PHY-layer abstractions for iterative LMMSE-IC receiver have been tackled. The proposed link adaptation scheme relies on a low rate feedback and operates joint spatial precoder selection (e.g., antenna selection) and Modulation and Coding Scheme (MCS) selection so as to maximize the average rate subject to a target block error rate constraint. The cross antenna coding (the transmitter employs a Space-Time Bit-Interleaved Coded Modulation (STBICM) ) and per antenna coding (Each antenna employs an independent Bit-Interleaved Coded Modulation(BICM)) cases are both considered. The simulations clearly show the significant gain obtained with turbo receivers compared to that of a conventional MMSE receiver

Les réseaux de capteurs suscitent un engouement croissant du fait du grand nombre d'applications mais également des défis inhérents à ce genre de réseaux. Le standard IEEE 802.15.4 a été proposé afin de standardiser les couches physique et MAC. Dans ce travail nous avons dans un premier temps proposé une variante multi-canal pour le standard 802.15.4 permettant de résoudre le problème de collisions de supertrames. Pour cela nous proposons de construire un réseau en arbre avec la particularité que chaque cellule du réseau utilise un canal différent permettant ainsi une réduction conséquente des interférences et augmente la capacité du réseau. Nous avons également introduit un nouveau mécanisme de construction de topologie, d'allocation de canal et d'ordonnancement de supertrames nécessaire au bon fonctionnement d'une telle solution. Dans un deuxième temps nous avons analysé l'impact des différents paramètres de la méthode d'accès du standard. Nous avons mis en exergue les faiblesses de la méthode d'accès dont les performances baissent drastiquement pour des réseaux trop importants. Partant de ce constat, nous avons proposé des mécanismes d'auto-adaptation pour la méthode d'accès du standard. Ces derniers permettent d'adapter dynamiquement la taille des fenêtres de contention en fonction des conditions de trafic observées sur le canal. Le calcul des valeurs optimales est exécuté par chaque coordinateur pour résoudre le problème de surdité. Ces mécanismes sont distribués et convergent rapidement même en cas de trafic en rafales
An increasing interest has been observed in Wirless Sensor Network that can be explained by wide range of WSN applications as well as by the challenges involving the constraints of this type of networks. The IEEE 802.15.4 standard has been proposed with the objective of standardizing the physical and MAC layers. In this work, we have firstly proposed an alternative multichannel scheme for the IEEE 802.15.4 standard. It is able to solve the problem of superframe collisions based on a cluster-tree topology approach in which each cluster uses a different channel allowing the reduction of the interference and increased network capacity. We have also difined a novel mechanism for topology construction, channel allocation, and superframe scheduling. Secondly, we have analyzed the impact of different parameters on the medium access control. We have shown the weakness of the medium access method proposed in the standard. For instance, we have observed a decrease in performance when the standard is applied in large networks. Motivated by the analysis and its results we have then proposed auto-adaptive mechanisms for the medium access control. They allow to dynamically adapt the size of the contention window according to the observed traffic conditions. Each coordinator computes the optimal values to avoid deafness. The proposed mechanisms rapidly converge even in the case of bursty traffic

Les algorithmes adaptatifs sont utilisés dans différentes applications de traitement du signal. Ainsi dans les applications telles que l'annulation d'écho acoustique, on utilise des algorithmes robustes et à faible complexité à cause des fortes contraintes imposées (temps réel, signaux complexes). Toutefois, les approches existantes de réduction de la complexité des moindres carrés concernent exclusivement les algorithmes issus du RLS, ils présentent, par conséquent, des problèmes d'instabilité numérique. Nous abordons dans cette thèse, la dérivation d'une nouvelle classe d'algorithmes adaptatifs. Ces algorithmes sont issus de l’algorithme QR-RLS par l'introduction de transformations itératives dans le schéma d'adaptation des matrices de l'algorithme. Ils présentent de ce fait d'excellentes propriétés numériques. Nous développons, également, des implémentations parallèles ainsi que des versions rapides de ces algorithmes. Les simulations dans le contexte de filtrage adaptatif multicanal, pour les applications : annulation d'écho acoustique stéréophonique et égalisation d'un canal numérique, permettent de mettre en évidence un comportement robuste des algorithmes bloc-GR. De même, cette approche s'applique au filtrage adaptatif à réponse impulsionnelle infinie (IIR), nous dérivons alors des algorithmes IIR rapides et efficaces. Finalement, nous définissons un cadre plus général d'algorithmes adaptatifs square-root qui intègre les algorithmes des moindres carrés, les algorithmes du gradient et les algorithmes bloc-QR. Ces derniers sont alors identifiés comme des intermédiaires entre les algorithmes des moindres carrés à convergence rapide et les algorithmes du gradient à convergence robuste.

Le nombre et la complexité croissante des applications qui sont intégrées dans des objets mobiles communicants sans fil (téléphone mobile, PDA, etc.) implique une augmentation de la consommation d'énergie. Afin de limiter l'impact de la pollution due aux déchets des batteries et des émissions de CO2, il est important de procéder à une optimisation de la consommation d'énergie de ces appareils communicants. Cette thèse porte sur l'efficacité énergétique dans les réseaux de capteurs. Dans cette étude, nous proposons de nouvelles approches pour gérer efficacement les objets communicants mobiles. Tout d'abord, nous proposons une architecture globale de réseau de capteurs et une nouvelle approche de gestion de la mobilité économe en énergie pour les appareils terminaux de type IEEE 802.15.4/ZigBee. Cette approche est basée sur l'indicateur de la qualité de lien (LQI) et met en œuvre un algorithme spéculatif pour déterminer le prochain coordinateur. Nous avons ainsi proposé et évalué deux algorithmes spéculatifs différents. Ensuite, nous étudions et évaluons l'efficacité énergétique lors de l'utilisation d'un algorithme d'adaptation de débit prenant en compte les conditions du canal de communication. Nous proposons d'abord une approche mixte combinant un nouvel algorithme d'adaptation de débit et notre approche de gestion de la mobilité. Ensuite, nous proposons et évaluons un algorithme d'adaptation de débit hybride qui repose sur une estimation plus précise du canal de liaison. Les différentes simulations effectuées tout au long de ce travail montrent l'efficacité énergétique des approches proposées ainsi que l'amélioration de la connectivité des nœuds.

L'augmentation des besoins en bande passante et la saturation du spectre en bande Ku (12 GHz) pour les nouveaux systèmes de communications par satellite géostationnaires, poussent à l'utilisation de fréquences plus élevées (bande Ka et Q/V, 20 à 50 GHz) où de plus grandes largeurs de bandes sont disponibles, mais où les effets atmosphériques sont importants. Il faut alors définir des techniques adaptatives (FMT : fade mitigation techniques) qui permettent d’optimiser la couche physique du système en prenant en compte les conditions de propagation qui sont variables dans le temps. La définition optimisée de ces techniques adaptatives fait l'objet de cette thèse. Le rapport décrit tout d’abord les caractéristiques principales de la propagation dans ces bandes de fréquences. Les techniques adaptatives sont ensuite analysées. L'analyse s’appuie sur un système de référence multifaisceaux pour l’accès distribué à l’lnternet. Une méthode originale d’évaluation des performances système a été développée pour quantifier l’efficacité de ces techniques et choisir leur meilleure combinaison. L'analyse a révélé le besoin de nouvelles procédures d'optimisation des bilans de liaison qui ont été mises au point. Ainsi l'introduction de l'adaptation du schéma de modulation-codage (utilisant le standard DVB-SZ et une proposition d'extension du DVB-RCS) permet une nette amélioration des résultats en termes de capacité. Après avoir quantifié l’apport de ces techniques de compensation de façon théorique, la dernière partie des travaux de recherche est dédiée à l'implémentation des techniques étudiées. La principale difficulté réside, selon la technique FMT concernée, dans l'obtention de mesures fiables et rapides de la magnitude de l'affaiblissement ou du SNIR, rapport puissance porteuse à puissance du bruit (y compris brouillages). Plusieurs architectures d'implantation des techniques FMT ont été proposées. Les sources d’erreurs associées aux différentes fonctions mises en œuvre dans l'architecture FMT ont été identifiées et quantifiées. À partir de cette analyse, une méthode de définition des seuils et des marges de décision d’activation de chaque technique est proposée. La thèse se termine par les résultats obtenus à partir d’un simulateur de la boucle de contrôle FMT. Les simulations confirment l'amélioration des performances du système grâce à l'introduction des FMT, et mettent aussi en évidence l'intérêt de la proposition de répartition non-uniforme des seuils et des marges pour optimiser la boucle de contrôle FMT.

Les réseaux de capteurs suscitent un engouement croissant du fait du grand nombre d'applications mais également des défis inhérents à ce genre de réseaux. Le standard IEEE 802.15.4 a été proposé afin de standardiser les couches physique et MAC. Dans ce travail nous avons dans un premier temps proposé une variante multi-canal pour le standard 802.15.4 permettant de résoudre le problème de collisions de supertrames. Pour cela nous proposons de construire un réseau en arbre avec la particularité que chaque cellule du réseau utilise un canal différent permettant ainsi une réduction conséquente des interférences et augmente la capacité du réseau. Nous avons également introduit un nouveau mécanisme de construction de topologie, d'allocation de canal et d'ordonnancement de supertrames nécessaire au bon fonctionnement d'une telle solution. Dans un deuxième temps nous avons analysé l'impact des différents paramètres de la méthode d'accès du standard. Nous avons mis en exergue les faiblesses de la méthode d'accès dont les performances baissent drastiquement pour des réseaux trop importants. Partant de ce constat, nous avons proposé des mécanismes d'auto-adaptation pour la méthode d'accès du standard. Ces derniers permettent d'adapter dynamiquement la taille des fenêtres de contention en fonction des conditions de trafic observées sur le canal. Le calcul des valeurs optimales est exécuté par chaque coordinateur pour résoudre le problème de surdité. Ces mécanismes sont distribués et convergent rapidement même en cas de trafic en rafales.

Cette thèse est consacrée à l'amélioration des performances de codage/décodage de systèmes de transmission d'images fixes sur des canaux bruités et réalistes. Nous proposons, à cet effet, le développement de méthodes de transmission d'images optimisées en se focalisant sur les deux couches application et physique des réseaux sans fil. Au niveau de la couche application et afin d'assurer une bonne qualité de service, on utilise des algorithmes de compression efficaces permettant au récepteur de reconstruire l'image avec un maximum de fidélité (JPEG2000 et JPWL). Afin d'assurer une transmission sur des canaux sans fil avec un minimum de TEB à la réception, des techniques de transmission, de codage et de modulation avancées sont utilisées au niveau de la couche physique (système MIMO-OFDM, modulation adaptative, CCE, etc). Dans un premier temps, nous proposons un système de transmission robuste d'images codées JPWL intégrant un schéma de décodage conjoint source-canal basé sur des techniques de décodage à entrées pondérées. On considère, ensuite, l'optimisation d'une chaîne de transmission d'images sur un canal MIMO-OFDM sans fil réaliste. La stratégie de transmission d'images optimisée s'appuie sur des techniques de décodage à entrées pondérées et une approche d'adaptation de lien. Ainsi, le schéma de transmission proposé offre la possibilité de mettre en oeuvre conjointement de l'UEP, de l'UPA, de la modulation adaptative, du codage de source adaptatif et de décodage conjoint pour améliorer la qualité de l'image à la réception. Dans une seconde partie, nous proposons un système robuste de transmission de flux progressifs basé sur le principe de turbo décodage itératif de codes concaténés offrant une stratégie de protection inégale de données. Ainsi, l'originalité de cette étude consiste à proposer des solutions performantes d'optimisation globale d'une chaîne de communication numérique pour améliorer la qualité de transmission
This work is devoted to improve the coding/ decoding performance of a transmission scheme over noisy and realistic channels. For this purpose, we propose the development of optimized image transmission methods by focusing on both application and physical layers of wireless networks. In order to ensure a better quality of services, efficient compression algorithms (JPEG2000 and JPWL) are used in terms of the application layer enabling the receiver to reconstruct the images with maximum fidelity. Furthermore, to insure a transmission on wireless channels with a minimum BER at reception, some transmission, coding and advanced modulation techniques are used in the physical layer (MIMO-OFDM system, adaptive modulation, FEC, etc). First, we propose a robust transmission system of JPWL encoded images integrating a joint source-channel decoding scheme based on soft input decoding techniques. Next, the optimization of an image transmission scheme on a realistic MIMO-OFDM channel is considered. The optimized image transmission strategy is based on soft input decoding techniques and a link adaptation approach. The proposed transmission scheme offers the possibility of jointly implementing, UEP, UPA, adaptive modulation, adaptive source coding and joint decoding strategies, in order to improve the image visual quality at the reception. Then, we propose a robust transmission system for embedded bit streams based on concatenated block coding mechanism offering an unequal error protection strategy. Thus, the novelty of this study consists in proposing efficient solutions for the global optimization of wireless communication system to improve transmission quality

Tradicionalmente, codificação de fonte e codificação de canal são tratados independentemente, no que se denomina sistema de codificação em dois passos. Isso ocorre porque o teorema da separação das codificações de fonte e canal garante que não há perdas em termos de confiabilidade da transmissão em assim fazê-lo quando o volume de dados gerados pela fonte cresce indefinidamente. No entanto, para seqüências finitas, foi mostrado que pode ser mais eficiente realizar a codificação em apenas um passo, denominada codificação conjunta fonte-canal, que faz uso das características da fonte ou do codificador de fonte para prover proteção contra erros. Este trabalho propõe uma técnica de codificação conjunta utilizando codificadores de fonte e canal consagrados e encontrados em aplicações práticas. São eles o codificador universal adaptativo LZW e o codificador de canal Reed-Solomon. O método proposto utiliza o fato do codificador de fonte não remover completamente a redundância dos arquivos originais para adicionar bits extras, sem perda de desempenho e sem distorção dos dados originais. A redundância remanescente no código é então utilizada para embutir os bits de paridade do código de canal. O desempenho do método é medido através de sua aplicação em arquivos dos corpos de Calgary e Canterbury. A exploração da redundância remanescente no código gerado pelo LZW pode ser aplicada aos codificadores universais LZ78 e suas variações que se baseiam no mesmo princípio de atualização do dicionário.

Već izvesno vreme u stručnoj literaturi vodi se rasprava o biokompatibilnosti materijala koji se koriste u periapikalnoj hirurgiji. Pored biokompatibilnosti, od materijala za retrogradnu opturaciju kanala korena zuba se očekuje da spreči prodor bakterija iz kanalnog sistema u okolna tkiva. Kvalitetno rubno zaptivanje, odnosno adekvatna marginalna adaptacija su među najznačajnijim faktorima za dugoročan uspeh tretmana. Cilj ovog istraživanja je bio ispitati biokompatibilnost i utvrditi da li postoji razlika u biokompatibilnosti između mineral-trioksid agregata, trikalcijum-silikatnog cementa i amalgama na osnovu tri standadna testa citotoksičnosti, kao i utvrditi marginalnu adaptaciju ispitivanih materijala za retrogradno zatvaranje kanala korena zuba. Materijali i metode: Eksperimentalni deo istraživanja je podeljen na dva dela. U prvom delu istraživanja je vršeno ispitivanje biokompatibilnosti materijala, dok je u drugom delu vršeno ispitivanje marginalne adaptacije na osnovu mikrofotografija dobijenih skening elektronskim mikroskopom. Ispitivanje biokompatibilnosti je izvršeno na dve ćelijske linije, liniji mišjih fibroblasta (L929) i liniji humanih fibroblasta (MRC-5). U eksperimentima su korišćene samo žive (vijabilne) ćelije. Broj ćelija i njihova vijabilnost je određena testom odbacivanja boje sa 0,1% tripan plavim. Vijabilnost ćelija korišćenih u eksperimentu je bila veća od 90%. Biokompatibilnost sve tri vrste materijala je ispitana na osnovu standardnih testova biokompatibilnosti: DET test, MTT test, Agar difuzioni test. Ispitivanje marginalne adaptacije je sprovedeno na 90 ekstrahovanih jednokorenih zuba interkaninog sektora gornje vilice sa intaktnom pulpom, završenim rastom korena, bez frakture i resorpcije korena zuba. Izvršena je endodontska obrada svih zuba i nakon toga su zubi ostavljeni u vlažnoj sredini na 48h, da bi se sprečile frakture prilikom sečenja. Nakon mehaničko medikamentozne obrade i opturacije kanala korena zuba je vršena resekcija vrha korena zuba 3mm, a nakon toga su svi zubi preparisani do dubine od 3 mm unutar kanala, ultrazvučnim nastavcima (EMS, miniMaster Piezon scaler). Zubi su naizmenično podeljeni u 3 grupe (30 zuba po grupi). Prvu grupu čine zubi kojima je apikalni kavitet biti ispunjen amalgamom, u drugoj grupi, apikalni kavitet je ispunjen MTA, a u trećoj trikalcijum-silikatnim cementom. Nakon retrogradne opturacije, zubi su ostavljeni u vlažnoj sredini 48h, do potpunog vezivanja ispitivanih materijala. Nakon vezivanja ispitivanih materijala, zubi su sečeni longitudinalno, finom dijamantskom šajbnom. Marginalna adaptacija ispitivanih materijala je procenjena skening elektronskim mikroskopom (SEM). Pripremljeni uzorci su posmatrani pod uvećanjima 30x, 40x, 80x i 100x. Uvećanje 30x je rađeno radi prikaza celokoupnog retrogradnog punjenja na jednom snimku, tj. spoja materijal-zub. Nakon toga je napravljeno više uzastopnih snimaka sauvećanjem 80x do pune dužine materijala. Na taj način je utvrđeno postojanje i izvršeno merenje marginalne pukotine u mikrometrima. Merenja ukupne dužine marginalne pukotine u mikrometrima u 5 tačaka sa obe strane preparata su vršena u softverskoj aplikaciji Image J software (National Institutes of Health, Bethesda, USA). Tačke su izabrane tako da tačka 1a i tačka 5a predstavljaju gornju i donju ivicu preparata. Tačka 3a predstavlja sredinu rastojanja između tačke 1a i tačke 5a. Tačka 2a i tačka 4a predstavljaju sredinu razmaka između tačke 1a i 3a, odnosno 3a i a5. Tačke 1b-5b su naspramne tačke. Rezultati biokompatibilnosti ukazuju na visok stepen ćelijske kompatibilnosti svih ispitivanih materijala. Međutim, DET testomnije utvrđena statistički značajna razlika u citotoksičnosti između istovetnih ispitivanih materijala u obe ćelijske linije, niti između sva tri ispitivana materijala u obe ćelijske kulture.Poređenjem rezultata MTT testa nakon 24h i 48h, kao i nakon 48h i 72h uočava se da su dobijene srednje vrednosti indeksa citotoksičnosti kod sva tri ispitivana materijala i na obe ćelijske linije manje nakon 48h, odnosno nakon 72h, što ukazuje na oporavak ćelijskog metabolizma. Poređenjem rezultata nakon 24h i nakon 72h, uočava se znatno veći pad vrednosti indeksa citotoksičnosti nakon 72h kod sva tri ispitivana materijala i na obe ćelijske linije. U kulturi ćelija MRC5, kod sva tri ispitivana materijala postoji statistički značajna razlika između indeksa citotoksičnosti izmerenog nakon 24h i nakon 72h, kao i u kulturi ćelija L929. Agar difuzionim testom nije uočena dekolorizacija, niti liza ćelija ispod ispitivanih materijala. Ćelijski odgovor je 0/0 što ukazuje da ovim testom nije utvrđeno postojanje citotoksičnog efekta ispitivanih materijala na ćelijske linije L929 i MRC-5. Ispitivanje marginalne adaptacije materijala je vršeno na osnovu mikrofotografija dobijenih skening elektronskim mikroskopom.. Najpre su testirane razlike na prvoj tački merenja. Rezultati ovog testa pokazuju da postoje značajne razlike između materijala i da amalgam ima značajno više vrednosti izmerenih pukotina u odnosu na preostala dva materijala, dok se vrednosti za MTA i biodentin međusobno značajno ne razlikuju. Kao još jedna referentna tačka uzeta je tačka merenja 5. I u odnosu na vrednosti u ovoj tački merenja zabeležene su značajne razlike između materijala. Post hoc Mann-Whitney test pokazuje da se amalgam značajno razlikuje od preostala dva materijala, dok nema značajnih razlika između MTA i biodentina. Na osnovu medijane može se videti da amalgam ima niže vrednosi u ovoj tački merenja u odnosu na preostala dva materijala. U tačkama 2-4, kao i u tačkama 1-5 (ukupno), ne postoji statistički značajna razlika u marginalnoj adaptaciji ispitivanih materijala. Rezultati biokompatibilnosti ukazuju na visok stepen ćelijske kompatibilnosti svih ispitivanih materijala. Rezultati sva tri testa pokazuju da ne postoji statistički značajna razlika u citotoksičnosti između ispitivanih materijala. MTT test pokazuje da u obe ćelijske kulture, kod istovetnih ispitivanih materijala postoji statistički značajna razlika između indeksa citotoksičnosti izmerenog nakon 24h i nakon 72h. Rezultati ispitivanja marginalne adaptacije pokazuju da u tački 1 najgore zaptiva amalgam, dok izmedju MTA i biodentina nema razlike. U tački 5 najbolje zaptiva amalgam.
Biocompatibility of materials, deployed in periapical surgery, has been a subject of debate in referential literature for some time now. Apart from biocompabillity, root end filling materials are expected to prevent bacteria from entering the surrounding tissue from canal system. The most important factors for successful long term treatment include marginal seal, i.e. adequate marginal adaptation. The aim of this research was to examine biocompatibility and establish the potential difference in biocompatibility between mineral trioxide aggregate, tricalcium silicate cement and dental amalgam according to three cytotoxicity tests, but also to corroborate marginal adaptation of the materials in question for retrograde seal of a root canal. Materials and methods: The experimental part of the research is divided in two parts. In the first part of the research biocompatibility of the materials was examined, while the examination of the marginal adaptation based on the micro images from scanning electron microscope was conducted in the second part. The examination of biocompatibility was executed on two cell lines, mouse fibroblast cell line (L929) and human cell line (MRC-5).Biocompatibility of all three types of material was examined based on three standard biocompatibility tests: DET test, MTT test, Agar diffusion test.The examination of marginal adaptation was carried out on 90 single-rooted tooth extractied human teeth of the intercanine sector of maxilla with intact pulp, mature apices, without root fractures or resorption. All teeth were endodontically treated. After the extirpation, irrigation and opturation, the resection of 3mm of root apex and retrograde preparation with ultrasonic instruments up to 3 mm depth inside the canal was done. Teeth were divided in three groups alternately. The First group include teeth which apical cavitation was filled with amalgam, in the Second group apical cavitation was filled with MTA, and in the Third group with tricalcium silicate cement. After the complete setting of the materials, teeth were cut in longitudinal manner, with fine, diamond tool. Marginal adaptation of the materials was assessed through scanning electron microscope (SEM). Software application Image J software was deployed to measure the total length of marginal fissure in micrometers in 5 pointson both sides of the preparation . The results of biocompatibility indicate high degree of cell compatibility of all tested materials. DET test did not assert any statistically significant difference in cytotoxicity between the same tested materials in both cell lines, nor between all three tested materials in both cell cultures. Comparing the results of MTT test after 24h and 48h, and 48h and 72h, it is noted that middle value of cytotoxicity index with all three tested materials and on both cell lines is lower after 48h, and after 72h, indicating the recovery of cell metabolism. In both cell cultures, with all three tested materials there is statistically significant difference between measured cytotoxicity indices after 24h and after 72h. Agar diffusion test did not show decolorization, nor cell lysis underneath the tested materials, which means that cytotoxic effect was not asserted on cell lines L929 i MRC-5. The examination of marginal adaptation was conducted according to micro images gained by scanning electron microscope. The results in the measure point 1 indicate there are significant differences between materials, and amalgam has significantly higher values of the measured fissures in relation to remaining two materials, whereas values for MTA and biodentine do not differ significantly. In measure point 5 significant differences were noted. Post hoc Mann-Whitney test shows that amalgam has lower values of the tested fissures in this measure point in relation to two other materials, while there were no significant differences between MTA i biodentine. In points 2-4, as well as points 1-5 (in total), there were no statistically significant differences in marginal adaptation of the examined materials. The results of all three tests show that there is no statistically significant difference in cytotoxicity between examined materials. MTT test shows that there is, in both cell cultures, with the same examined materials , statistically significant difference between cytotoxicity indices measured after 24h and after 72h. The results of the examination of marginal adaptation show that in point 1 amalgam has the worst seal, whereas between MTA and biodentine there is no difference. In point 5 amalgam has the best seal.

Cette these vise l'obtention d'algorithmes ameliores d'egalisation autodidacte (sans sequence de reference) pour les futurs systemes radio-mobiles a hauts debits. Dans une premiere etape, nous donnons une methode generale permettant d'obtenir, a partir d'un algorithme adaptatif de gradient stochastique de type bussgang quelconque, un algorithme equivalent a faible charge de calcul et un algorithme a convergence amelioree. Ensuite, nous retravaillons deux algorithmes de depart: celui de godard et l'algorithme decision directed. Par une procedure de normalisation, et de normalisation par blocs, nous en ameliorons les performances et mettons en valeur leurs points communs. Ceci servira a proposer dans le chapitre v, un nouvel algorithme ayant les avantages des deux algorithmes initiaux. Ce travail est complete par une etude des etats stationnaires des algorithmes bussgang et par des simulations dans un contexte de communications radio-mobiles

La sécurité de la couche physique (PLS) est un paradigme émergent qui se concentre sur l'utilisation des propriétés de la communication sans fil, telles que le bruit, l'évanouissement, la dispersion, l'interférence, la diversité, etc. pour assurer la sécurité entre les utilisateurs légitimes en présence d'un espion. Comme le PLS utilise des techniques de traitement du signal et de codage, il intervient au niveau de la couche physique et peut donc garantir le secret quelle que soit la puissance de calcul de l'espion. Cela en fait une approche intéressante pour compléter la cryptographie traditionnelle dont le principe de sécurité est basé sur la dureté informatique de l'algorithme de cryptage qui ne peut pas être facilement cassé par un espion. En outre, les récents progrès rapides des technologies de communication sans fil ont permis l'émergence et l'adoption de technologies telles que l'internet des objets, les communications ultra-fiables et à faible latence, les communications massives de type machine, les véhicules aériens sans pilote, etc. La plupart de ces technologies sont décentralisées, limitées en ressources de calcul et de puissance, et sensibles aux délais. La plupart de ces technologies sont décentralisées, limitées en ressources de calcul et de puissance, et sensibles aux délais. Cela fait du PLS une alternative très intéressante pour assurer la sécurité dans ces technologies. À cette fin, dans cette thèse, nous étudions les limites de la mise en œuvre pratique de la PLS et proposons des solutions pour relever ces défis. Tout d'abord, nous étudions le défi de l'efficacité énergétique de la PLS par l'injection de bruit artificiel (AN) dans un contexte massif d'entrées multiples et de sorties multiples (MIMO). La grande matrice de précodage dans le contexte MIMO massif contribue également à un signal d'émission avec un rapport élevé entre la puissance de crête et la puissance moyenne (PAPR). Cela nous a incités à proposer un nouvel algorithme, appelé PAPR-Aware-Secure-mMIMO. Dans ce schéma, les informations instantanées sur l'état du canal (CSI) sont utilisées pour concevoir un AN tenant compte du PAPR qui assure simultanément la sécurité tout en réduisant le PAPR. Ensuite, nous considérons le PLS par adaptation du canal. Ces schémas PLS dépendent de la précision de la CSI instantanée et sont inefficaces lorsque la CSI est imprécise. Toutefois, la CSI peut être inexacte dans la pratique en raison de facteurs tels qu'un retour d'information bruyant, une CSI périmée, etc. Pour résoudre ce problème, nous commençons par proposer un schéma PLS qui utilise le précodage et la diversité pour fournir le PLS. Nous proposons ensuite un réseau neuronal autoencodeur peu complexe pour débruiter la CSI imparfaite et obtenir des performances PLS optimales. Les modèles d'autoencodeur proposés sont appelés respectivement DenoiseSecNet et HybDenoiseSecNet. Enfin, nous étudions les performances de la PLS dans le cas d'une signalisation à alphabet fini. Les signaux gaussiens ont une grande complexité de détection parce qu'ils prennent un continuum de valeurs et ont des amplitudes non limitées. Dans la pratique, on utilise des entrées de canal discrètes parce qu'elles permettent de maintenir une puissance de transmission de crête et une complexité de réception modérées. Cependant, elles introduisent des contraintes qui affectent de manière significative la performance du PLS, d'où la contribution de cette thèse. Nous proposons d'utiliser des clés dynamiques pour partitionner les espaces de modulation de manière à ce qu'ils profitent à un récepteur légitime et non à un espion. Ces clés sont basées sur le canal principal indépendant et leur utilisation pour la partition conduit à des régions de décision plus grandes pour le récepteur prévu et plus petites pour l'espion. Ce système est appelé modulation partitionnée par index (IPM)
Physical layer security (PLS) is an emerging paradigm that focuses on using the properties of wireless communication, such as noise, fading, dispersion, interference, diversity, etc., to provide security between legitimate users in the presence of an eavesdropper. Since PLS uses signal processing and coding techniques, it takes place at the physical layer and hence can guarantee secrecy irrespective of the computational power of the eavesdropper. This makes it an interesting approach to complement legacy cryptography whose security premise is based on the computational hardness of the encryption algorithm that cannot be easily broken by an eavesdropper. The advancements in quantum computing has however shown that attackers have access to super computers and relying on only encryption will not be enough. In addition, the recent rapid advancement in wireless communication technologies has seen the emergence and adoption of technologies such as Internet of Things, Ultra-Reliable and Low Latency Communication, massive Machine-Type Communication, Unmanned Aerial Vehicles, etc. Most of these technologies are decentralized, limited in computational and power resources, and delay sensitive. This makes PLS a very interesting alternative to provide security in such technologies. To this end, in this thesis, we study the limitations to the practical implementation of PLS and propose solutions to address these challenges. First, we investigate the energy efficiency challenge of PLS by artificial noise (AN) injection in massive Multiple-Input Multiple-Output (MIMO) context. The large precoding matrix in massive MIMO also contributes to a transmit signal with high Peak-to-Average Power Ratio (PAPR). This motivated us to proposed a novel algorithm , referred to as PAPR-Aware-Secure-mMIMO. In this scheme, instantaneous Channel State Information (CSI) is used to design a PAPR-aware AN that simultaneously provides security while reducing the PAPR. This leads to energy efficient secure massive MIMO. The performance is measured in terms of secrecy capacity, Symbol Error Rate (SER), PAPR, and Secrecy Energy Efficiency (SEE). Next, we consider PLS by channel adaptation. These PLS schemes depend on the accuracy of the instantaneous CSI and are ineffective when the CSI is inaccurate. However, CSI could be inaccurate in practice due to such factors as noisy CSI feedback, outdated CSI, etc. To address this, we commence by proposing a PLS scheme that uses precoding and diversity to provide PLS. We then study the impact of imperfect CSI on the PLS performance and conclude with a proposal of a low-complexity autoencoder neural network to denoise the imperfect CSI and give optimal PLS performance. The proposed autoencoder models are referred to as DenoiseSecNet and HybDenoiseSecNet respectively. The performance is measured in terms of secrecy capacity and Bit Error Rate (BER). Finally, we study the performance of PLS under finite-alphabet signaling. Many works model performance assuming that the channel inputs are Gaussian distributed. However, Gaussian signals have high detection complexity because they take a continuum of values and have unbounded amplitudes. In practice, discrete channel inputs are used because they help to maintain moderate peak transmission power and receiver complexity. However, they introduce constraints that significantly affect PLS performance, hence, the related contribution in this thesis. We propose the use of dynamic keys to partition modulation spaces in such a way that it benefits a legitimate receiver and not the eavesdropper. This keys are based on the independent main channel and using them to partition leads to larger decision regions for the intended receiver but smaller ones for the Eavesdropper. The scheme is referred to as Index Partitioned Modulation (IPM). The performance is measured in terms of secrecy capacity, mutual information and BER

Cette thèse s’articule autour d 'un dispositif dégalisation adaptatif autodidacte capable de transiter de façon réversible d'une structure linéaire à un ERD en fonction de la sévérité du canal. Létude de ce dispositif est tout d'abord réalisé dans un contexte mono-dimensionnel puis multi-dimensionnel. Cet égaliseur s'avère très robuste et présente d'excellentes performances en terme de temps de convergence et d'erreur résiduelle. Initialement introduit pour les transmissions à flot continu, la carte de légalisation adaptative paraissait inenvisageable pour les transmissions par blocs. Moyennant un traitement itératif éventuellement conjugué avec une approche basée sur le retournement temporel des séquences reçues, il est possible d'améliorer de façon notable les performances du dispositif de transmission sur des trames de longueur réduite. Cet égaliseur a du reste été implémenté sur un environnement DSP. Plusieurs campagnes d'essais en mer ont permis d'en valider le fonctionnement.

Cette thèse se propose pour objectif de caractériser la capacité théorique du canal ionosphérique et d'améliorer l'estimation du canal, dans une technique de réception numérique par voie ionosphérique, appelée turbo-égalisation. La capacité a été traitée par Lee et Ozarow pour les canaux radio-mobiles TDMA : ceux-ci supposent que l'atténuation d'amplitude de chaque trajet suit une loi de Rayleigh, sans toutefois, préciser les paramètres de cette loi. C'est pourquoi la première partie de ce travail présente une extension des travaux de Lee et d'Ozarow pour les canaux non-stationnaires, tel que le canal ionosphérique. Une expression théorique générale de la capacité a été mise en place en fonction de l'étalement Doppler, ce qui contribua, de façon fort intéressante, à la caractérisation des canaux ionosphériques. Elle permet, en effet, de donner une idée claire sur la limite théorique du débit transmissible par voie ionosphérique en présence d'étalement Doppler et d'interférences entre symboles, créés par les trajets multiples. Cette étude théorique a été finalisée par une application d'estimation de la capacité sur une réalisation réelle du canal ionosphérique, effectuée le jour de l'éclipse solaire du 11 août 1999. Une deuxième partie, étudie et caractérise les estimateurs susceptibles d'être utilisés dans une chaîne de réception ionosphérique à base de turbo-égalisation. En effet, les estimateurs du gradient stochastique (GS) Least Mean Squared (LMS), les algorithmes des moindres carrés récursifs (MCR) Recursive Least Squared (RLS) et le filtre de Kalman (KF) ont fait l'objet d'optimisations des paramètres et de comparaisons, dans un contexte ionosphérique réel et simulé. Ces optimisations et ces comparaisons, nous ont permis de retenir les estimateurs MCR et Kalman comme les plus performants dans un contexte ionosphérique non stationnaire. Enfin, la dernière partie de cette thèse concerne l'implémentation de la turbo-égalisation à base de l'égaliseur linéaire MMSE à entrées sorties souples Soft Input Soft Output (SISO) et des estimateurs MCR et Kalman sur le canal ionosphérique réel et simulé. Le format des trames utilisé a suivi les spécifications de la norme STANAG 4285, nécessaire dans la conception des modems hautes fréquences (HF). Les performances, mesurées en taux d'erreurs par bit et erreurs d'estimation, ont été évaluées par variation du rapport signal à bruit et de l'étalement Doppler. L'estimation par filtre de Kalman a favorisé la réception de façon plus performante que l'algorithme RLS
The aim of this thesis is to characterize the theoretical capacity of the HF ionospheric channels and to improve the estimate in a receiver based on turbo-equalization. The capacity was treated by Lee and Ozarow for TDMA radio-communications using the hypothesis that each path attenuation is a Rayleigh random variable. This hypothesis is used without specifying any parameter. In a first part, this thesis presents an extension of Lee and Ozarow results for the non-stationary environments such as the ionospheric channel. A general theoretical capacity formula versus the Doppler spread is developed and it is an interesting contribution for the non-stationary channels. This one makes it possible to give a clear idea on the theoretical achievable bit rate of an ionospheric link affected by Doppler spread and inter symbol Interferences (ISI). The theoretical approach was finalized by an application to a real ionospheric communications link realized during the eclipse day (August 11, 1999). In a second part of this thesis, we studied and characterize the estimators likely to be used in the ionospheric turbo-equalizer based on linear filtering. Indeed, the estimators, such as Least Mean Squared (LMS), Recursive Least Squared (RLS) and Kalman filters (KF), were the subject of optimizations and comparisons in a real and simulated ionospheric environments. The optimization and comparisons, enabled us to choose the RLS and the Kalman estimators as being most performant (powerful) in the non stationary ionospheric channel. In a second part of this thesis, we studied and characterize the estimators likely to be used in the ionospheric turbo-equalizer based on linear filtering. Indeed, the estimators, such as Least Mean Squared (LMS), Recursive Least Squared (RLS) and Kalman filters (KF), were the subject of optimizations and comparisons in a real and simulated ionospheric environments. The optimization and comparisons, enabled us to choose the RLS and the Kalman estimators as being most performant (powerful) in the non stationary ionospheric channel. The last part of this thesis relates to the implementation of MMSE turbo-equalizer based on Soft Input Soft Output SISO principal and on RLS and Kalman estimators in the real and simulated ionospheric channel. The transmission is continie in time and the frame pattern is based on the STANAG 4285 HF modem specifications. The performances in bit error rate and the Mean Squared Error (MSE) were evaluated versus signal to noise ratio and Doppler spread. With respect to bit error rate and mean squared error, the estimations based on Kalman filter was more powerful than that using RLS algorithm

Nous etudions le probleme de l'egalisation adaptative dans le cas du canal de transmission acoustique sous-marin, en nous interessant particulierement au comportement des algorithmes adaptatifs en regime non stationnaire. Nous montrons que les performances d'un egaliseur adaptatif restent tres liees a une certaine connaissance du milieu de propagation, particulierement en ce qui concerne ses variations en termes de degre de non-stationnarite. Nous montrons l'importance particuliere du choix du taux d'oubli de l'algorithme adaptatif utilise (correspondant a sa memoire), qu'il soit du type lms ou du type mcro (moindres carres recursifs avec oubli). Nous presentons une methode originale permettant de s'en affranchir dans le cas de l'algorithme lms; des simulations mettent en evidence son efficacite dans divers cas de poursuite; des exemples de traitement de donnees reelles montrent le potentiel d'un egaliseur adaptatif pour les transmissions de donnees sous-marines

Las técnicas de estimación de canal y de adaptación de la transmisión a las condiciones del entorno son temas de interés actual al estudiar la aplicación de técnicas de diversidad en transmisión en la tercera y cuarta generación de sistemas inalámbricos. En esta tesis se realiza un análisis del impacto del error de estimación de canal y la correlación en sistemas OFDM con diversidad en transmisión basados en codificación espacio-tiempo por bloques (STBC), se proponen técnicas de estimación de canal para estos sistemas y se propone una técnica de adaptación de la transmisión mediante la selección de código espacio-tiempo. En primer lugar, una técnica sencilla de mínimos cuadrados en el dominio de la frecuencia permite la estimación de canal en sistemas con dos antenas y constelaciones complejas, y con tres o cuatro antenas y constelaciones reales o complejas, utilizando STBCs ortogonales como bloques de entrenamiento. En segundo lugar, una representación 'sobre-completa' permite hacer una estimación diferencial de canal para un sistema con tres antenas transmisoras mediante la selección a partir de un banco de posibles estimadores, basándose en la redundancia provista por la matriz de transmisión no cuadrada del código ortogonal esporádico de tasa 3/4 para tres antenas transmisoras.En el contexto de sistemas con adaptación del transmisor, la técnica propuesta de diversidad por selección adaptativa de código espacio-tiempo se basa en el estado instantáneo del vector de canal y en un conjunto de niveles umbrales hallados fuera de línea en función del período de realimentación. Los resultados indican que esta técnica proporciona buenas prestaciones en canales correlados e incorrelados. Su aplicación a sistemas OFDM ha sido estudiada, superando a técnicas de selección de antena y a otras técnicas de transmisión adaptativa.
Channel estimation and adaptive transmission techniques are areas of increasing interest these days when considering transmit diversity systems for the 3G and 4G wireless communication systems. In this thesis an analysis of the channel estimation and channel correlation impact on transmit diversity OFDM systems based on space-time block coding (STBC) is presented, two channel estimation techniques are outlined and an adaptive space-time code selection technique is proposed. First, a simple frequency domain least square technique allows channel estimation for two transmitter systems with complex constellation, and three or four transmitter systems with real or complex constellation, using orthogonal STBCs as training blocks. Second, an 'overcomplete' representation allows a di.erential channel estimation for three transmitter systems through the instantaneous selection from a bank of estimators, based on the redundacy provided by the non-square transmission matrix of the sporadic 3/4-rate STBC for three transmitters.In the context of transmit adaptive systems, the proposed adaptive space-time code selection technique is based on both the instantaneous channel vector state and a set of predetermined threshold levels found o.-line as a function of the feedback period. Analytical and simulation results show that the proposed technique has a good performance in the presence of correlated and uncorrelated channels. Its application to OFDM systems has been considered, outperforming classical antenna selection techniques and other closed-loop adaptive transmission techniques.

En els darrers anys s'han dedicat grans esforços a l'estudi del control de la comunicació entre Elements de Procés de la Informació (per exemple, els computadors), principalment en els aspectes relacionats amb el suport de la comunicació (configuracions, topologies, protocols).

Dans la première partie de la thèse, on se concentre sur la conception d'un système de communication par satellite complet se basant sur la construction de faisceaux adaptatifs aux terminaux mobiles. Comparé à la construction classique de faisceaux fixes, le système à faisceaux adaptatifs peut considérablement améliorer la capacité du système en termes du nombre de STs desservies et de l'efficacité énergétique. Pour la conception du système à faisceaux adaptatifs, les informations sur l'état de canal (CSI) sont essentielles. Vu que le temps de propagation est trop long par rapport au temps de cohérence du canal, le CSI instantané est déjà périmé lorsqu'il est reçu pour la construction des faisceaux. Cependant, une partie de l'information du canal, plus particulièrement, les vecteurs de directivité ont une variation assez lente. On utilise cette connaissance partielle du CSI pour concevoir le système à base de faisceaux adaptatifs. Afin d'estimer les vecteurs de directivité, on propose un algorithme basé sur un critère de minimisation de l'erreur quadratique. Puis, basées sur l'estimation des vecteurs de directivité, on présente deux approches heuristiques pour la conception des faisceaux. En outre, on propose également deux approches qui reposent sur l'estimation de la directivité pour la détection des STs et la résolution possible des collisions sur le canal d'accès aléatoire au satellite. Comme la performance du système SDMA dépend fortement des positions spatiales des STs co-existants, on propose deux algorithmes de faible complexité pour l'attribution des fréquences dans le système de communication par satellite
In the first part of the thesis, we focus on the design of a complete satellite communication system adopting adaptive beamforming with mobile satellite terminals. Compared with conventional fixed beamforming, adaptive beamforming can signi_cantly improve the capacity of a satellite system in terms of served satellite terminals (ST) and power e_ciency. For the design of an adaptive beamforming system, channel state information (CSI) is critical. Since the propagation delay is too long compared to the coherence time of the channel, the instantaneous CSI is already stale when processed for beamforming. However, some parts of the channel, more speci_cally, directivity vectors change quite slowly. We utilize this partial knowledge of CSI to design an adaptive beamforming system. In order to estimate the directivity vectors, we propose an algorithm based on a least square error criterion. Then, based on the estimation of directivity vectors, we propose two heuristics approaches to the design of adaptive beamforming. Additionally, we also propose two approaches, based on directivity estimation for the detection of transmitting terminals and the possible resolution of collisions in the random access channel of the satellite system. Since SDMA system performance depends strongly on the spatial locations of co-existing terminals, we also propose two low complexity algorithms for frequency allocation in a satellite communication system. Finally, we simulate a complete satellite system, including a random access channel and a connection-oriented channel. We analyze the system performance and compare it to conventional fixed beamforming systems

En esta tesis doctoral se plantea la mejora de la capacidad de transmisión en las redes HDR-WPAN ( redes WPAN con elevada tasa binaria) empleando el estándar MB-OFDM (OFDM sobre múltiples bandas) en canales UWB con modulación adaptativa realizando una adaptación discreta de la tasa de bits transmitidos por subportadora. La tesis comienza con un análisis en el dominio del tiempo y de la frecuencia de los dos modelos de canal UWB propuestos en IEEE: IEEE 802.15.3a y 802.15.4a. El objetivo consiste en determinar la distribución estadística que mejor se aproxima a la amplitud de cada una de las subportadoras, para posteriormente definir la métrica a emplear en la evaluación del estado y dinámica del canal UWB. En la modulación adaptativa se requiere que el transmisor se adapte a la variabilidad del canal. El análisis se puede realizar de dos formas: - Asumiendo adaptación perfecta (estimación ideal), lo que implica que el transmisor siempre conoce la dinámica y estructura del canal. - Considerando un error (estimación imperfecta del canal) en la adaptación debido a la incertidumbre en el conocimiento del canal. El método de estimación del canal UWB empleado en la tesis se fundamenta en el conocimiento del coeficiente de correlación en potencia entre las subportadoras de datos y la subportadora piloto. A partir de la información sobre el estado del canal, u una vez definida la métrica que permite su evaluación, se calculan las prestaciones de la modulación adaptativa. Esta evaluación se realiza a través de expresiones cerradas para la capacidad media, la probabilidad de error de bit media y la probabilidad de bloqueo, así como la obtención de la distribución y estadísticos del error de estimación en el caso de estimación imperfecta del canal. Por otro lado, a partir de la distribución estadística de la amplitud de cada una de las subportadoras en frecuencia del canal UWB, se obtienen resultados respecto a la variación de potencia del canal en función del ancho de banda .
Llano Ramírez, G. (2010). Modelado en frecuencia del canal UWB y su aplicación en el análisis de técnicas de modulación adaptativa en sistemas MB-OFDM UWB para redes WPAN [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8429
Palancia

Les travaux decrits dans cette these concernent la validation experimentale d'un modele du canal de transmission ionospherique. L'expression generale de ce modele ainsi qu'un dispositif d'analyse experimentale de liaisons hf etablis dans le cadre d'etudes anterieures sont donc tout d'abord rappeles. Le modele se distingue de ceux actuellement disponibles par sa structure a deux composantes: l'une deterministe, l'autre statistique. La caracterisation de ces composantes a necessite la mise au point de techniques specifiques de traitement du signal et leur application a un grande nombre de cas experimentaux enregistres sur une liaison situee moyennes latitudes. Ces traitements a caractere adaptatif sont detailles ici. Ils permettent l'identification de parametres de propagation (amplitude, frequence) et le suivi de leurs evolutions a des echelles de temps de l'ordre de quelques dizaines de millisecondes. Le principe de base repose sur l'emploi successif de deux filtres de kalman etendus. Le premier identifie les valeurs moyennes des parametres et permet ainsi qu'une stationnarisation du signal de meme qu'une refjection du bruit de mesure. Le second filtre intervient pour separer en amplitude et frequence les deux modes magnetoioniques propages sur chaque trajet ionospherique, meme s'ils ne sont pas discernables en temps de groupe par le systeme de mesure. Il devient alors possible de caracteriser qualitativement et quantitativement la composante deterministe du modele. Apres extraction de cette derniere, on obtient la partie aleatoire qui est soumise a des analyses statistiques. On montre alors que lorsque la composante deterministe est bien identifiee, la partie statistique verifie les conditions d'un processus bivariant gaussien pouvant par ailleurs etre en bonne approximation represente a l'aide d'un modele autoregressif d'ordre faible. En conclusion le modele est considere valide sur la liaison etudiee et par extension sur des liaisons situees aux moyennes latitudes. Sa representativite pour d'autres zones geographiques ne sera acquise qu'apres des campagnes de mesures dans ces zones, alliees a une interpolation geophysique poussee des mesures

Dans la première partie de la thèse, on se concentre sur la conception d'un système de communication par satellite complet se basant sur la construction de faisceaux adaptatifs aux terminaux mobiles. Comparé à la construction classique de faisceaux fixes, le système à faisceaux adaptatifs peut considérablement améliorer la capacité du système en termes du nombre de STs desservies et de l'efficacité énergétique. Pour la conception du système à faisceaux adaptatifs, les informations sur l'état de canal (CSI) sont essentielles. Vu que le temps de propagation est trop long par rapport au temps de cohérence du canal, le CSI instantané est déjà périmé lorsqu'il est reçu pour la construction des faisceaux. Cependant, une partie de l'information du canal, plus particulièrement, les vecteurs de directivité ont une variation assez lente. On utilise cette connaissance partielle du CSI pour concevoir le système à base de faisceaux adaptatifs. Afin d'estimer les vecteurs de directivité, on propose un algorithme basé sur un critère de minimisation de l'erreur quadratique. Puis, basées sur l'estimation des vecteurs de directivité, on présente deux approches heuristiques pour la conception des faisceaux. En outre, on propose également deux approches qui reposent sur l'estimation de la directivité pour la détection des STs et la résolution possible des collisions sur le canal d'accès aléatoire au satellite. Comme la performance du système SDMA dépend fortement des positions spatiales des STs co-existants, on propose deux algorithmes de faible complexité pour l'attribution des fréquences dans le système de communication par satellite
In the first part of the thesis, we focus on the design of a complete satellite communication system adopting adaptive beamforming with mobile satellite terminals. Compared with conventional fixed beamforming, adaptive beamforming can signi_cantly improve the capacity of a satellite system in terms of served satellite terminals (ST) and power e_ciency. For the design of an adaptive beamforming system, channel state information (CSI) is critical. Since the propagation delay is too long compared to the coherence time of the channel, the instantaneous CSI is already stale when processed for beamforming. However, some parts of the channel, more speci_cally, directivity vectors change quite slowly. We utilize this partial knowledge of CSI to design an adaptive beamforming system. In order to estimate the directivity vectors, we propose an algorithm based on a least square error criterion. Then, based on the estimation of directivity vectors, we propose two heuristics approaches to the design of adaptive beamforming. Additionally, we also propose two approaches, based on directivity estimation for the detection of transmitting terminals and the possible resolution of collisions in the random access channel of the satellite system. Since SDMA system performance depends strongly on the spatial locations of co-existing terminals, we also propose two low complexity algorithms for frequency allocation in a satellite communication system. Finally, we simulate a complete satellite system, including a random access channel and a connection-oriented channel. We analyze the system performance and compare it to conventional fixed beamforming systems

Orientadores: Telma Teixeira Franco, Cecilia Sulzbacher Caruso
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: Material lignocelulósico, como bagaço de cana de açúcar, é matéria prima potencial para produção de biocombustíveis de segunda geração. Hidrolisado hemicelulósico (H-H) rico em xilose pode ser fermentado por leveduras oleaginosas para a produção de lipídeos. Nesse sentido, o objetivo deste trabalho foi adaptar a Lipomyces starkeyi DSM 70296 em meios de cultivo contendo H-H de bagaço de cana-de-açúcar. O H-H com 12 g/L de xilose, 2 g/L de glicose, 10 g/L de ácido acético, 0,7 g/L de furfural e 1,3 g/L de HMF foi obtido após sete etapas de sequenciais de extração de bagaço previamente explodido a vapor. A levedura foi adaptada por engenharia evolutiva em meio de cultivo contendo concentrações crescentes de H-H. Como resultado, obteve-se a levedura adaptada ao meio de cultivo contendo 30% de H-H, a qual apresentou maior produtividade celular (113,90 mg/L/h) e concentração celular (9,79 g/L) em relação à cepa não adaptada (73,54 mg/L/h e 5,21 g/L, respectivamente). Fermentações em biorreator em meio sintético e contendo 30% de H-H apresentaram velocidades especificas máximas de crescimento (?max) de 0,117 e 0,122 h-1, respectivamente. Através de planejamento experimental 23 foram determinados os efeitos do ácido acético, furfural e hidroximetilfurfural (HMF) no crescimento e produção de lipídeos da levedura. Resultados indicaram que o ácido acético apresentou efeito significativo sobre os parâmetros cinéticos aumentando a duração da fase lag até em 34 horas, além da redução da produtividade celular (Px) e da velocidade de consumo de substrato (rs). Adicionalmente foram verificados efeitos sinérgicos positivos entre ácido acético conjuntamente com furfural e HMF. Testes indicaram a possibilidade de altos níveis de inibição dos produtos gerados pela degradação da lignina em concentrações acima de 7,32 g/L
Abstract: Lignocellulosic materials, such sugar cane bagasse, as reported as potential feedstocks for production of second generation biofuels, through hemicellulose hydrolysates (H-H) extraction rich in xylose and the subsequent fermentation with oleaginous yeast for lipids production. In this regard, the objective of this study was to adapt the Lipomyces starkeyi DSM 70296 in culture media containing H-H of sugar cane bagasse. The H-H with 12 g/L of xylose, 2 g/L of glucose, 10 g/L acetic acid, 0.7 g/L of furfural and 1.3 g/L of HMF was obtained after seven sequential extraction steps of bagasse previously pretreated by steam explosion. The yeast was adapted by evolutionary engineering in culture medium containing increasing concentrations of H-H. As result, there was obtained the yeast adapted to culture medium containing 30% of H-H, which showed higher cell productivity (113.90 mg/L/h) and cell concentration (9.79 g/L) compared to not adapted strain (73.54 mg/L/h and 5.21 g/L, respectively). Fermentation in Bioreactor in synthetic medium and containing 30% of H-H medium showed maximum specific growth rate (?max) of 0.117 and 0.122 h-1, respectively. Through experimental design 23 was determined the effects of acetic acid, furfural and hydroxymethylfurfural (HMF) on growth and yield lipid yeast. As result, there was obtained that acetic acid had significant effect on kinetic parameters by increasing the duration of lag phase up to 34 hours, besides reduction of cell productivity (Px) and rate of substrate consumption (rs). Additionally positive synergistic effects were observed when acetic acid is found in culture media with furfural and HMF. Preliminary tests indicate the possibility of high levels of inhibition of products generated by lignin degradation at concentrations above 7.32 g/L
Mestrado
Engenharia de Processos
Mestra em Engenharia Química

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Fundação de Amparo à Pesquisa do Estado de Minas Gerais
Diferenças na taxa respiratória e morfologia do corpo gorduroso foram investigadas em populações resistentes e susceptível de Sitophilus zeamais. Os resultados do estudo de citomorfologia do corpo gorduroso e taxa respiratória mostraram que existe relação entre produção de CO2, área de trofócitos e massa corporal, independente do sexo e população. Também existe relação entre a citomorfologia do corpo gorduroso e resistência a inseticidas através de incremento no acúmulo de reservas disponíveis para a resistência a inseticidas. A capacidade de acúmulo de reservas energéticas e mobilização destas, possivelmente compensam o custo de energia associado à resistência a inseticidas na população resistente de Jacarezinho, já que esta não apresenta custo fisiológico associado à resistência. O mesmo não acontece com a população resistente de Juíz de Fora. O segundo estudo desta tese objetivou determinar a existência de assimetria flutuante (AF) nas populações de Sitophilus zeamais, e a relação entre AF e resistência a inseticidas e suas conseqüências potenciais. Os resultados mostram que as populações resistentes a inseticidas possuem valores menores de AF com relação à população susceptível. A população resistente de Jacarezinho apresentou o menor valor de AF. Esta população parece apresentar maior capacidade adaptativa por não apresentar custo fisiológico associado à resistência. Os resultados também mostram que fêmeas das populações de Sete Lagoas e Jacarezinho parecem usar AF como parâmetro para seleção sexual. Por fim, a pressão de seleção exercida pela aplicação de inseticidas possivelmente promoveu na população de Jacarezinho a fixação de genes modificadores de performance adaptativa, revertendo a desvantagem adaptativa.
Differences in respiration rate and fat body morphology were investigated in insecticide susceptible and resistant populations of Sitophilus zeamais. The results of fat body citomorphology and respiration rate showed that there is a relationship between Co2 production, area of trophocytes and body mass, regardless of sex and population. There is also a relationship between fat body citomorphology and insecticide resistance through the accumulation of energy reserves for insecticide resistance. The hability to store and mobilize energy reserves probably compensates the energy cost associated with the insecticide resistance of the Jacarezinho population, which did not show physiological cost associated with the resistance. This does not take place for the population from Juiz de Fora. The second study of the present thesis aimed to determine the fluctuating assimetry (FA) in the populations of Sitophilus zeamais, and the relationship between FA and insecticide resistance with its likely consequences. The results showed that the insecticide resistant populations have lower levels of FA compared with the susceptible population. The resistant population from Jacarezinho showed the lowest FA values. This population seems better adapted for not showing physiological costs associated with insecticide resistance. The results also showed that females from Sete Lagoas and Jacarezinho may use FA as a parameter for sexual selection. It seems that the selection pressure imposed upon the insects from Jacarezinho by the intense insecticide application for a long period of time probably favored the fixation of fitness modifier genes in this population mitigating the adaptative advantage usually associated with insecticide resistance.

La détection sans fil a évolué depuis la découverte de la détection radar en 1886. L’analyse des réflexions électromagnétiques d’objets a ouvert la voie à un large éventail d’applications allant de la localisation de cibles à longue distance pour la navigation civile et militaire à la surveillance du vent et des précipitations les prévisions météo à la détection de vitesse pour la sécurité routière. Cependant, pendant très longtemps, la détection sans fil a rarement été utilisée pour des applications centrées sur l’homme en raison de limitations techniques, d’impraticabilité ou de coût. L’introduction des réseaux sans fil a suscité́ un nouvel intérêt pour le développement de nouveaux services de détection sans fil en raison de leur souplesse et de leur polyvalence. L’intégration de ces fonctionnalités contribuerait à résoudre certains problèmes de société importants. La localisation, la détection de mouvements et la surveillance des signes vitaux ont un grand potentiel pour promouvoir le vieillissement en bonne santé, la sécurité publique et le commerce. La détection sans contact offre un degré de liberté appréciable, permettant de surveiller à distance les personnes âgées isolées sans entraver leur vie quotidienne. Elle pourrait aider les services de sécurité publique à dénombrer les foules et à détecter les survivants à l’intérieur des bâtiments en cas d’urgence. Les commerces de détail et les établissements publics tireraient parti d’une localisation active et passive pour offrir une expérience améliorée à leurs visiteurs et faciliter leurs efforts logistiques. Cette thèse aborde le problème de l’exploitation des réseaux sans fil commerciaux pour les applications de détection : L’un des défis de la surveillance sans fil consiste à détecter l’orientation d’une personne avec précision. Tandis que d’autres travaux fournissent des solutions à granularité grossière pour résoudre de tels problèmes, nous utilisons les techniques de radar MIMO pour fournir un système d’estimation d’orientation précis pour lesinfrastructures Wi-Fi. Plus précisément, nous analysons les informations de phase des signaux reçus sur le réseau d’antennes afin de calculer le cap d’un terminal Wi-Fi. Un deuxième défi consiste à fournir un système de positionnement précis aux systèmes LPWAN afin de maintenir la cohérence des informations des capteurs déployés. Les solutions actuelles sont complexes, coûteuses ou consomment beaucoup d’énergie. Pour résoudre ce problème, nous introduisons les fonctions MIMO dans les systèmes LoRa LPWAN afin de permettre une localisation précise avec des coûts de démarrage limités. Nous activons l’estimation de l’angle d’arrivée en utilisant une deuxième antenne sur la passerelle LoRaWAN. Nous prouvons également l’utilité de ces informations pour augmenter l’efficacité des communications sans fil. Un troisième défi pour la localisation sans fil est l’inefficacité des approches actuelles basées sur un modèle en cas de conditions de non-visibilité et la rigidité des approches basées sur les données en cas de changements d’environnement de propagation. Pour relever ce défi, nous proposons une nouvelle solution de localisation passive pilotée par les données afin de remédier aux limitations des techniques de localisation basées sur un modèle. Pour donner vie à de tels systèmes et leur donner une chance d’impact sur notre quotidien, nous devons promouvoir la réutilisabilité et la reproductibilité. Pour cela, nous essayons de relever le défi de la reproductibilité dans les réseaux sans fil enanalysant l’état actuel, en réalisant une étude de cas et en présentant les enseignements qui en découlent
Wireless sensing has evolved since the discovery of radio wave echo detection and radar in 1886. Analyzing electromagnetic reflections from objects opened the way for a wide range of applications spanning from locating long-range targets for navigation and military to monitoring wind and precipitation for weather-forecasting to velocity detection for public safety. However, for the longest time, its usefulness was seldom for human-centric applications because of technical limitations, impracticality or costliness. Introducing wireless networks awakened a newfound interest in developing new wireless sensing services for their seamlessness and versatility. Integrating such functionalities would contribute to resolving some prominent societal issues. Localization, motion detection, and vital signs monitoring have great potential for promoting healthy aging, public safety, and retail. Contactless sensing offers an appreciable degree of freedom, enabling remote monitoring of the isolated elderly without hampering their daily lives. It could assist public safety services for crowd counting and detection of survivors inside buildings during emergencies. Retail and public facilities would benefit from passive and active localization to offer an enhanced experience to their visitors and to help their logistical efforts. This thesis addresses the problem of leveraging commercial off-the-shelf wireless networks for sensing applications: One challenge for wireless monitoring is to detect the attitude of a person accurately. While other works provide coarse-grained solutions for resolving such issues, we use MIMO radar techniques to provide an accurate orientation estimation system for Wi-Fi infrastructures. To be more precise, we analyze the phase information of signals received on the antenna array to compute the heading of a Wi-Fi terminal. A second challenge is to provide an accurate positioning system for LPWAN systems to maintain the information consistency of deployed sensors. Current solutions are complex, costly, or not energy-efficient. To address this problem, we introduce MIMO capabilities to LoRa LPWAN systems that provide accurate localization with limited startup costs. We enable the angle of arrival estimation by leveraging a second antenna on the LoRaWAN gateway. We also prove the usefulness of such information for wireless communication efficiency. A third challenge for wireless localization is the inefficiency of current model-based approaches in case of non-line-of-sight conditions and the rigidity of data-driven approaches in case of propagation environment changes. To address this challenge, we propose a new data-driven solution for passive localization to address the limitations of model-based localization techniques. To give life to such systems and provide them with a chance of impacting our everyday lives, we should promote reusability and reproducibility. For that, we focus on the challenge of reproducibility in wireless networking by surveying the current state, performing a case study, and presenting the engendered lessons

Des nouveaux schémas de Codage Vidéo Linéaire (CVL) ont démontré ces dernières années un potentiel élevé pour la diffusion de contenus vidéo sur des canaux de transmission sans-fil sévères. SoftCast représente le pionnier des schémas CVL. Différent des standards de transmission vidéo actuels et particulièrement utile en situation de broadcast, SoftCast est un système de codage conjoint source-canal où les pixels sont traités par des opérations linéaires successives (transformée DCT, allocation de puissance, modulation quasi-analogique) et directement transmis sans quantification ni codage (entropique ou de canal). SoftCast permet ainsi d’offrir une qualité vidéo reçue directement proportionnelle à la qualité du canal de transmission, sans aucune information de retour et tout en évitant les mécanismes d’adaptation complexes des schémas classiques. Un premier objectif de ces travaux de thèse concerne l’étude des performances de bout en bout de SoftCast. Des modèles théoriques sont ainsi proposés prenant en compte les contraintes de bande passante de l’application, l’allocation de puissance, ainsi que le type de décodeur utilisé à la réception (LLSE, ZF). Une deuxième partie basée sur une campagne de tests subjectifs concerne une étude originale de la qualité vidéo et des artefacts spécifiques associés à SoftCast. Dans une troisième partie, des méthodes de prétraitement permettant d’accroître la qualité reçue sont proposées avec un gain moyen en PSNR de l’ordre de 3 dB. Finalement, un algorithme adaptatif modifiant la taille du groupe d’images (GoP) en fonction des caractéristiques du contenu vidéo transmis est proposé. Cette solution permet d’obtenir des gains supplémentaires en PSNR de l’ordre de 1 dB
Linear video coding (LVC) schemes have recently demonstrated a high potential for delivering video content over challenging wireless channels. SoftCast represents the pioneer of the LVC schemes. Different from current video transmission standards and particularly useful in broadcast situation, SoftCast is a joint source-channel coding system where pixels are processed by successive linear operations (DCT transform, power allocation, quasi-analog modulation) and directly transmitted without quantization or coding (entropic or channel). This allows to provide a received video quality directly proportional to the transmission channel quality, without any feedback information, while avoiding the complex adaptation mechanisms of conventional schemes. A first contribution of this thesis is the study of the end-to-end performances of SoftCast. Theoretical models are thus proposed taking into account the bandwidth constraints of the application, the power allocation, as well as the type of decoder used at the reception (LLSE, ZF). Based on a subjective test campaign, a second part concern an original study of the video quality and specific artifacts related to SoftCast. In a third part, preprocessing methods are proposed to increase the received quality in terms of PSNR scores with an average gain of 3 dB. Finally, an adaptive algorithm modifying the size of the group of pictures (GoP) according to the characteristics of the transmitted video content is proposed. This solution allows to obtain about 1 dB additional gains in terms of PSNR scores

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Brazil is the world's largest producer of sugarcane (Saccharum spp.), whose culture interacts with the most varied environments. The replacement of varieties has contributed greatly to an effective increase in productivity. Thus it studies of genotype x environment (G x E) interaction, the analysis of phenotypic adaptability and stability, and the selection of parents for hybridization are essential for the indication of varieties suited to different soil and climatic conditions. The objective of this research was to evaluate the agribusiness behavior, adaptability and phenotypic stability of 11 RB sugarcane clones in the final phase of the trial, in sugarcane micro regions in the State of Pernambuco, Brazil Northeast, for three consecutives harvests, as well as assisting the selection of potential parents to be used in future crossings by conducted by Sugarcane Breeding Program (PMGCA) of Network for the Development of Alcohol and Sugar (RIDESA) of Experimental Station Sugarcane Carpina (EECAC) of Federal Rural University of Pernambuco (UFRPE). The experiments were carried out in five Pernambuco sugar mills, in the months of july and august 2006, using the experimental design of randomized blocks with four replications and plots with five eight-meter furrows and spacing of 1.0 m. The results were subjected to analysis of variance, comparison of averages by Scott & Knott test and studies of adaptability, stability and genetic divergence. In each section the variables were measured as ton of pol per hectare (TPH), ton of cane per hectare (TCH); fibre (FIB), Pol% corrected (PCC), purity (PZA), soluble solids (BRIX) and total recoverable sugar (TRS). Based on the results, the best RB genotypes of sugarcane were G1, G6 and G9 in environment I, G1 and G11 in environment II, G1 and G9 in environment III, G3 for environment IV and G1 the environment V. Among the best clones, those with wide adaptability are: G1 and G11, and those with adaptability to environments are: G6 and G9. The genotypes most indicated for use in hybridizations are G1 and G6, as they showed the greatest genetic dissimilarity.
O Brasil é o maior produtor mundial de cana-de-açúcar (Saccharum spp.), cuja cultura interage com os mais variados ambientes. A substituição de variedades tem contribuído bastante para um eficiente aumento na produtividade. Neste sentido, os estudos da interação genótipo x ambiente (G x A), as análises de adaptabilidade e estabilidade fenotípica, e a seleção de parentais para cruzamentos são imprescindíveis para a indicação de variedades adequadas às diversas condições edafoclimáticas. Objetivou-se com esta pesquisa avaliar o comportamento agroindustrial, a adaptabilidade e a estabilidade fenotípica de 11 clones RB de cana-de-açúcar, na fase final da experimentação, em microrregiões canavieiras do Estado de Pernambuco, por três colheitas consecutivas, bem como auxiliar a seleção de progenitores potenciais a serem utilizados em futuros cruzamentos pelo Programa de Melhoramento Genético da Cana-de-açúcar (PMGCA) da Rede Interuniversitária para o Desenvolvimento do Setor Sucroalcooleiro (RIDESA) conduzido pela Estação Experimental de Cana-de-açúcar (EECAC) da Universidade Federal Rural de Pernambuco (UFRPE). Os experimentos foram instalados em cinco usinas de Pernambuco, nos meses de julho e agosto de 2006, utilizando-se o delineamento experimental de blocos casualizados, com quatro repetições e parcelas com cinco sulcos de oito metros com espaçamento de 1,0 m. Os resultados foram submetidos à análise de variância, à comparação de médias pelo teste de Scott & Knott e a estudos de adaptabilidade, estabilidade e divergência genética. Em cada corte foram mensuradas as variáveis tonelada de pol por hectare (TPH), tonelada de cana por hectare (TCH); Pol% corrigido (PCC), fibra (FIB), pureza (PZA), teor de sólidos solúveis (BRIX) e açúcar total recuperável (ATR). Com base nos resultados, os genótipos RB de cana-de-açúcar mais produtivos foram G1, G6 e G9; para o ambiente I, G11 e G1 para o ambiente II, G9 e G1 para o ambiente III, G3 para o ambiente IV e G1 para o ambiente V. Dentre os melhores clones, aqueles com adaptabilidade ampla são: G1 e G11; e aqueles com adaptabilidade para ambientes favoráveis são: G6 e G9. Os genótipos mais indicados para utilização em hibridações são G1 e G6, pois estes apresentaram a maior dissimilaridade genética.

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Em um sistema de comunica c~oes, os sinais s~ao transmitidos atrav es de canais de comunica c~ao que, idealmente, deveriam transportar os dados de maneira a n~ao causar distor c~ao alguma. Por em, em sistemas reais, existem limita c~oes que interferem neste processo causando degrada c~ao nas informa c~oes transmitidas, podendo comprometer sua recep c~ao. Tais limita c~oes ocorrem devido a presen ca de ru do aditivo, e principalmente por interfer^encia intersimb olica, esta caracterizada pela sobreposi c~ao de s mbolos gerados por uma mesma fonte transmissora. A equaliza c~ao de canal e uma das t ecnicas existentes que reduzem os efeitos da interfer^encia intersimb olica, dando maior con abilidade e robustez aos sistemas de comunica c~oes. Dentre as t ecnicas utilizadas para equaliza c~ao de canal, o uso de algoritmo adaptativos vem sendo amplamente utilizados devido as suas propriedades de se auto-ajustarem as varia c~oes que ocorrem ao longo do tempo. Este trabalho tem como objetivo veri car o comportamento de diferentes tipos de algoritmos adaptativos cegos ou semicegos, assim denominados por n~ao utilizarem sequ^encias de treinamento, aplicados a equaliza c~ao de canais esparsos. Canais esparsos s~ao encontrados em diversos sistemas de comunica c~oes como, por exemplo, na comunica c~ao sem o (telefonia m ovel, transmiss~ao de r adio e TV), ou, ainda, em canais subaqu aticos. Os algoritmos foram escolhidos com base em recentes estudos desta aplica c~ao, que operam em modo cego ou semicego e utilizam estat sticas de alta ordem, como os algoritmos Bussgang e Matching Pursuit. Os algoritmos foram implementados em ambiente de simula c~ao computacional no qual foram utilizados canais esparsos simples e de resposta ao impulso conhecida, permitindo comparar o comportamento dos diferentes algoritmos, em termos do sinal recuperado, e da inversa da resposta ao impulso do canal original.
In communications systems, information signals are transmitted through communications channels that, ideally, are delivered without distortions. However, on real communications channels there are limitations that interferes on the process, reducing the probability to recover the original signal at receiver. These distortions are basically thermal noise and Intersymbol Interference (ISI), caused by superposition on the received symbols received from the same source. Channel Equalization acts reducing these distortions, bringing more reliability to communications systems. The objective of this work is to verify di erent adaptive algorithms behavior, applied to sparse channel equalization problem. Many communications systems have sparse channels, like broadcast radio, television, mobile telephony and underwater communications. The selected algorithms used in this work includes high order statistics algorithms family, like Bussgang and Matching Pursuit. This kind of algorithms are widely used, with high relevance, for blind channel equalization. The selected algorithms were submitted to computer simulations using simple sparse channels and knowledge about their impulse response, in order to analyze their behavior in therms of bit error rate and the inverse impulse response of the channel.

In order to verify the productive potential of new varieties of sugar cane for the central region of Rio Grande do Sul, it was installed an experimental area at Polytechnic School of Universidade Federal de Santa Maria. The study began in 2007. We evaluated eleven varieties of sugar cane to check their adaptation in the State s Central Region. Thereunto, morpho-physiological characteristics were evaluated, such as: cane weight, weight of the edges, weight of the culms, base diameter, number of culms, useful culms s height, length of the base culm, length of the tip culm, base ºbrix, edge ºbrix, maturation index, total sample weight, pre-drought mass weight, total residue weight, broth volume, ºbrix, temperature, pH, total production (t/ha) and frost resistance. Cane was used for animal feed, production of molasses, jaggery, brown sugar, alcohol and rum. The bagasse was used as ground covering and in the boiler, and the vinasse was utilized as fertilizer for crops. The experiment was conducted by randomized blocks, with three repetitions of each variety, and area of 56 m² each. Data were submitted to variance analysis via Tukey s test at 5% probability and SAS. The varieties Tucumã (average), IAC 311 (average), SP 701143 (average), Preta Torta (late), Napa 5679 (late), 3X (precocious), and RB 76 5418 (precocious) obtained higher productivity (t/ha) than national average. The varieties Branca Mole (average), Napa 7696 (precocious) and RB 78 5750 (late) higher productivity than State average and the only variety which didn t reach the State s average productivity was the RB 85 1011 (precocious).
Com o objetivo de verificar o potencial produtivo de novas variedades de cana-deaçúcar para a região central do Rio Grande do Sul foi instalada uma área experimental no Colégio Politécnico da Universidade Federal de Santa Maria (UFSM). O trabalho iniciou em 2007. Foram avaliadas onze variedades de cana-deaçúcar para a verificação de sua adaptação na Região Central do Estado. Para isso, foram avaliadas as características morfofisiológicas da planta tais como: peso das canas, peso das pontas, peso das palhas, peso dos colmos, o diâmetro da base, o diâmetro da ponta, o número de colmos, a altura dos colmos úteis, o comprimento do colmo da base, o comprimento do colmo da ponta, ºbrix da base, ºbrix da ponta, o índice de maturação (IM), peso da amostra integral (AI), peso da massa pré-seca (MPS), o peso total do bagaço, o volume do caldo, ºbrix, temperatura, o pH, a produção total (t/ha) e a resistência à geada. A cana foi utilizada para a alimentação animal, produção de melado, açúcar mascavo, rapadura, álcool e cachaça. O bagaço foi utilizado como cobertura de solo e na caldeira e, o vinhoto foi utilizado como adubo para as lavouras. O experimento foi conduzido por blocos ao acaso, com três repetições de cada variedade selecionada e cada parcela teve 56 m2 de área. Os dados foram submetidos à análise de variância pelo Teste de Tukey ao nível de 5% de probabilidade e o programa SAS. As variedades Tucumã (média), IAC 311 (média), SP 701143 (média), Preta Torta (tardia), Napa 5679 (tardio), 3X (precoce) e RB 76 5418 (precoce) obtiveram produtividade (t/ha) maior que a média nacional. As variedades Branca Mole (média), Napa 7696 (precoce) e RB 78 5750 (tardio) obtiveram produtividade maiores que a média do estado e a única variedade que não atingiu a produtividade média do estado foi a variedade RB 85 1011 (precoce).

O desenvolvimento de alternativas aos combustíveis fósseis como fonte de energia é uma prioridade global. A biomassa celulósica representa uma alternativa para satisfazer a procura de bicombustíveis renováveis. O bagaço de cana-de-açúcar é um abundante subproduto proveniente da produção atual de etanol no Brasil. Tal subproduto pode ser hidrolisado a fim de se obter açúcares fermentáveis para a produção do etanol de segunda-geração. Porém, no processo de pré-tratamento são gerados diversos inibidores como ácido acético, furfural e hidroximetilfurfural que causam efeitos adversos para a levedura no processo de fermentação alcoólica. A adição de melaço ao hidrolisado é uma forma de diminuir os efeitos dos inibidores no metabolismo das leveduras e também permite uma fermentação com maior teor alcoólico contribuindo para um balanço energético favorável da destilação, contribui também com o fornecimento de nutrientes minerais e orgânicos necessários a levedura para um processo empregando reciclo de células. Assim, objetivou-se selecionar linhagens de Saccharomyces cerevisiae com melhores características de multitolerância ao hidrolisado a partir de cruzamento direcionado e cruzamento massal seguido de evolução adaptativa. Para tal, linhagens S. cerevisiae industriais CAT-1, BG-1, PE-2 e SA-1 foram esporuladas e mediante micromanipulação foram obtidos 604 haploides, que foram avaliados quanto ao crescimento (DO570nm) em substrato constituído por hidrolisado e melaço. Os haploides selecionados (25) tiveram o \"mating type\" determinado permitindo a realização de 51 cruzamentos direcionados, gerando 398 zigotos, que foram igualmente avaliados para o crescimento no meio seletivo. Paralelamente, foram realizados cruzamentos massais, resultando em 7 diferentes populações, as quais foram submetidas à evolução adaptativa por 25 gerações, sendo que os isolados selecionados de cada cruzamento foram avaliados em fermentação com reciclo de células. Quatro linhagens se destacaram como superiores aos parentais, evidenciando que a estratégia utilizada permitiu a obtenção de linhagens de S. cerevisiae com maior tolerância aos estresses impostos por um substrato para produção do etanol de segunda geração.
The development of alternatives to fossil fuels as a source of energy is a global priority. Cellulosic biomass is an alternative to meet the demand for renewable biofuels. The sugarcane bagasse, an abundant byproduct generated from ethanol production in Brazil, can be hydrolysed to obtain fermentable sugars to produce second-generation ethanol. However, inhibitors produced in the pre-treatment process such as acetic acid, furfural and hydroxymethylfurfural, cause adverse effects to the yeast in the fermentation process. Addition of molasses in the bagasse hydrolyzate is one way to reduce the effects of inhibitors in the metabolism of yeast and also could allow fermentation with higher alcohol content contributing to a favorable energy balance in the distillation, as well as providing minerals and organic nutrients for the yeast. The main goal of this study was to select strains of Saccharomyces cerevisiae with better features of multi-tolerance to the bagasse hydrolyzate by directed crossing and mass mating followed by adaptive evolution. For that S. cerevisiae lineages CAT-1, BG-1, PE-2 e SA-1 were sporulated and 604 haploid cultures were obtained by micromanipulation and evaluated for growth (OD 570nm) in the substrate consisting of hydrolyzate and molasses. Selected haploids (25) were identified regarding their \"mating type\" (a and α) and used in. 51 directed crossings generating 398 zygotes, which were rescued by micromanipulation and also evaluated for growth in the same selective medium. Mass mating were performed with 7 different haploid populations from the parental strains, followed by an adaptive evolution for 25 generations. The selected zygotes were then subjected to fermentation trails with cell recycling, resulting in 4 strains with superior traits when compared with the parentals, allowing to conclude that the used strategy was successful in obtaining hybrids of Saccharomyces cerevisiae with increased profile of tolerance towards a substrate for second-generation ethanol production.

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES
Introduction: the PAJ inventory study the path of young love, from the perspective of analyzing the relationship between violent events and relationships with family, friends and lovers. This th?me has mobilized researchers in different social contexts, regions and countries, considering the violence`s impact. Researchers in this area requires the use of validated instruments, with multidimensional approach, regardless of source context, based on the experience of literature. Objective: submit the inventory PAJ "Parcour Amoreux des Jeunes" to the cross-cultural adaptation and validation of content. Methodology: protocol steps recommended were the ones that follow: (1) translation and back-translation - translation and back-translation - the translation was attended by two Brazilian researchers , skilled in French , and later , two young native Canadian researchers fluent in Portuguese, ending Pilot II version . (2) Analisys by the Expert Committee - ten professionals from different backgrounds participated (researchers in validation , adolescence and violence) , who analyzed individually , the clarity and equivalence for each question according to the characteristics of clarity (1) It is not clear , (2) It is a little unclear , (3) almost everything is clear , (4) it is clear and I have no doubt , and equivalence : (1) not equivalent , (2) Partially equivalent; " (3) equivalent . After analysis , the percentages of clarity and equivalence and Content Validity Index / general question for IVC were calculated, obtaining Pilot III version , (3) Pre -test - Pilot III was assessed by a sample of 36 young people , 14-24 years old, both genders , with the same characteristics as the target of the later stages (psychometric analysis and application to the target population) population. In the pre -test interpretive questions were analyzed , in order to obtain cultural, conceptual, semantic and idiomatic equivalence, improving, thus, the instrument comprehension. After analysis of experts and young people , proportions relative to clarity and equivalence and Content Validity Index ( CVI ) were calculated , considering as appropriate issues with grades 3 and 4 for clarity, with value above 0.78 , according literature recommendations. Results: in general, the inventory PAJ had adequate content validity (0.97), considering the recommended limit value for adequacy (0.78). All sections of the instrument showed good performance (adequacy to clarity and equivalence), except the first section (general information, sociodemographic questions the cultural context of young parents' ethnicity, education, language spoken, among others) whose items and issues experienced cross-cultural adaptation and adjustment to match the Brazilian reality. Conclusions: PAJ showed suitable validity of content. The stages of cultural adaptation, and validation of content of instrument becomes appropriate for the procedures that follow - steps of reliability assessment (psychometrics) and applicability to the youth population in the brazilian context.
Introdu??o: o invent?rio PAJ busca estudar o percurso amoroso de jovens, na perspectiva de analisar a rela??o entre os eventos violentos e relacionamentos com familiares, amigos e amores. Esse tema tem mobilizado estudiosos, nos distintos contextos sociais, regi?es e pa?ses, considerando o impacto da viol?ncia Pesquisar nesta ?rea requer a utiliza??o de instrumentos validados, com abordagem multidimensional, independente do contexto de origem, tendo como base a experi?ncia da literatura. Objetivo: submeter o invent?rio PAJ ?Parcours Amourex des Jeunes?, ? adapta??o transcultural e ? valida??o de conte?do, para utiliza??o em contexto nacional. Metodologia: foram obedecidas etapas protocolares recomendadas: : (1) Tradu??o e Retrotradu??o ? para tradu??o participaram dois pesquisadores brasileiros, habilitados na lingua francesa, obtendo duas vers?es em protugu?s; na retradu??o, dois novos pesquisadores nativos do Canad? com flu?ncia no portugu?s, finalizando vers?o Piloto II. (2) An?lise por Comit? de Especialistas ? participaram dez profissionais de diferentes forma??es, pesquisadores nas ?reas de (valida??o, adolesc?ncia e viol?ncia), os quais analisaram, individualmente, o grau de clareza e de equival?ncia para cada quest?o, segundo as caracter?sticas de clareza (1) N?o est? claro; (2) Est? um pouco claro; (3) Est? quase tudo claro; (4) Est? claro e n?o tenho d?vidas; e de equival?ncia: (1) N?o equivalente; (2) Pouco equivalente; ?(3) Equivalente. Ap?s an?lise, foram calculadas as porcentagens de clareza e de equival?ncia e o Indice de Validade de Conte?do/IVC geral por quest?o, obtendo-se vers?o Piloto III; (3) Pr?-teste ? o Piloto III foi avaliado por uma amostra de 36 jovens, de 14 a 24 anos, ambos os sexos, com as mesmas caracter?sticas da popula??o alvo das etapas posteriores (an?lise psicom?trica e aplicabilidade na popula??o alvo). No pr?-teste foram analisadas quest?es de ordem interpretativa, visando obter equival?ncias cultural, conceitual, sem?ntica, idiom?tica, na perspectiva de aprimorar a compreens?o do instrumento. Ap?s an?lise dos especialistas e dos jovens, foram calculadas propor??es relativas ao grau de clareza e equival?ncia e o ?ndice de Validade de Conte?do (IVC), considerando como adequadas quest?es com graus 3 e 4, para clareza, com valor acima de 0,78, segundo recomenda??es da literatura. Resultados: de maneira geral, o invent?rio PAJ apresentou adequada validade de conte?do (0,97), considerando o valor limite para adequa??o recomendado (0,78).Todas as se??es do instrumento apresentaram bom desempenho (adequa??o para clareza e equival?ncia), exceto a primeira se??o (informa??es gerais, quest?es sociodemogr?ficas do contexto cultural do jovem, etnia dos pais, escolaridade, l?ngua mais falada, entre outros aspectos) cujos itens e quest?es sofreram a adapta??o transcultural e adequa??o para corresponder ? realidade brasileira. Conclus?es: o PAJ mostrou adequada validade de conte?do. Os est?gios de adapta??o cultural e valida??o de conte?do torna o instrumento apropriado para os procedimentos que se seguem - medidas de avalia??o da confiabilidade (psicometria) e aplicabilidade para a popula??o jovem no contexto brasileiro.

A busca por soluções sustentáveis, levando a um processo energético mais eficiente induziu a novas tecnologias e esforços estão sendo realizados para viabilizar o etanol de segunda geração, com o aproveitamento da biomassa celulolítica como substrato para a fermentação alcoólica. Contudo, durante a hidrólise do bagaço, muitos compostos tóxicos à levedura são formados como o furfural, hidroximetilfurfural, ácido acético, e compostos fenólicos com efeitos depressivos sobre a fermentação. A adição de melaço no hidrolisado de bagaço poderia permitir uma fermentação com maior teor alcoólico, contribuindo para um balanço energético favorável da destilação, além de propiciar nutrientes minerais e orgânicos para a levedura. Tais nutrientes poderiam permitir um processo fermentativo com reciclo de células de leveduras aproveitando assim uma estrutura e conhecimentos já existentes na destilaria de etanol de primeira geração. O reciclo de células permitiria fermentações rápidas, porém impõe repetidas condições estressantes, o que torna um grande desafio a obtenção de linhagens com o perfil de tolerância desejado. Assim este trabalho se propôs a selecionar linhagens de Saccharomyces cerevisiae com múltiplas tolerâncias em relação aos inibidores tanto presentes no hidrolisado como no melaço. Para tal, foram impostas condições estressantes sobre culturas da linhagem SA-1 e de leveduras isoladas de destilarias brasileiras durante cerca de 62 gerações, forçando uma evolução adaptativa ou mesmo um enriquecimento/seleção de indivíduos mais tolerantes. Paralelamente a biodiversidade de linhagens isoladas de destilarias foi avaliada quanto aos atributos de tolerância aos compostos tóxicos presentes no hidrolisado do bagaço. As linhagens com maiores desempenhos foram avaliadas em fermentações com reuso de células empregando-se substrato constituído de hidrolisado e melaço, sendo que 4 linhagens se mostraram superiores às linhagens referenciais. Destas, dois isolados (242 e 408) foram esporulados e os conjuntos dos haploides foram empregados em cruzamentos massais. Simultaneamente, 273 haploides isolados das linhagens 242 e 408 foram avaliados quanto ao crescimento (DO600nm) em substrato constituído por hidrolisado e melaço, sendo que 32 foram selecionados. Após a tipificação segundo o \"mating type\" os mesmos foram utilizados em cruzamentos direcionados mediante micromanipulação, resultando em 35 cruzamentos. Cinco híbridos de cada cruzamento direcionado foram resgatados (155 isolados), que juntamente com 80 isolados oriundos do cruzamento massal, foram novamente avaliados quanto ao crescimento (DO600nm) e a seguir em fermentações com reciclo de células. Cinco linhagens se destacaram como superiores aos parentais, demonstrando que mediante o protocolo empregado foi possível incrementar o perfil de tolerância de Saccharomyces cerevisiae para suportar os estresses impostos por um substrato para produção do etanol de segunda geração.
The search for sustainable solutions to improve process efficiency has promoted the development of new technologies, and the use of cellulolytic biomass as the substrate for fermentation has emerged as a promising second-generation ethanol production strategy. However, the hydrolysis of this material results in the formation of toxic compounds to yeast such as furfural, hydroxymethylfurfural, acetic acid and phenolic compounds, with deleterious effects on fermentation. Addition of molasses in the bagasse hydrolysate could allow fermentation with higher alcohol content contributing to a favorable energy balance in the distillation, as well as providing minerals and organic nutrients for the yeast. These nutrients could allow a fermentative process with yeast cell recycle, utilizing the structure and knowledge already existing in first generation process. The cell recycle enables a rapid fermentation, but imposes repeated stress conditions, making it challenging to obtain strains with the desired tolerance profile. The purpose of this study was to select Saccharomyces cerevisiae strains with multiple tolerances to inhibitors present in the hydrolysate and molasses. Stressful conditions were imposed on cultures of SA-1 strain and indigenous strains from Brazilian distilleries for around 62 generations, forcing an adaptive evolution or even an enrichment / selection of more tolerant individuals. In parallel, the biodiversity of the strains from Brazilian distilleries were evaluated with respect to their tolerance to the toxic compounds present in bagasse hydrolysate. The strains that showed higher performance were assessed in fermentations with cell reuse employing substrate composed by hydrolyzate and molasses. Four of the analyzed strains exhibited better performance than the reference strain. Of these, two isolates (242 and 408) were sporulated and the haploids were subjected to mass mating. Simultaneously, 273 haploids rescued from the strains 242 and 408 were evaluated for growth (OD 600 nm) in the substrate consisting of hydrolysate and molasses, and among them 32 were selected. After the characterization according to the \"mating type\", the haploids were utilized in direct mating induced by micromanipulation, totaling 35 crossings. Five hybrids from each direct mating were rescued (totaling 155 isolates), which together with 80 isolated from the mass mating, were evaluated for growth (OD 600 nm) and then in fermentation with cell recycle. 5 strains have excelled as superiors to the reference strain showing that by the protocol employed was possible to increase profile of tolerance of Saccharomyces cerevisiae to resist pressures imposed by a substrate for second-generation ethanol production.

Les applications de vidéosurveillance pour les transports publics s’appuient sur des systèmes de communication sans fil qui requièrent des débits élevés entre les véhicules et le sol et des critères de qualité de service élevés. Afin de répondre à ces contraintes, dans ce travail nous avons proposé de tenir compte à la fois des paramètres de transmission et de d’encodage vidéo en combinant les techniques de codage MDC (Multiple Description Coding) et de codage par zone d'intérêt (ROI, Region Of Interest) avec différentes schémas MIMO (Mulitple Input Multiple Output) sur la base de la couche PHY du standard Wifi IEEE802. 11n dans un environnement de type métro (tunnel). Dans un premier temps, nous avons montré qu'il est possible d'améliorer les performances d'un système MIMO en optimisant l'allocation des bits et des puissances indépendamment de l'information à transmettre. Nous proposons deux approches aboutissant à la répartition optimale des ressources qui permettent d'atteindre un ordre de diversité maximal et offrent de meilleures performances que le précodeur max-SNR dans le cas d’un canal corrélé ou non. Nous montrons ensuite que l’association d’un codage MDC avec des schémas MIMO constitue une stratégie intéressante afin d’adapter le contenu vidéo à la structure multi-antennes, en particulier lorsqu’aucune connaissance de l’état du canal n’est pas disponible en émission. En outre, il est possible d'améliorer les performances en utilisant un lien retour à faible débit grâce aux techniques OSM (Orthogonalized Spatial Multiplexing) et à l’OSM précodé. Enfin, dans le cas où la connaissance du canal à l’émission est parfaite, pour un lien retour offrant un débit suffisant, nous avons associé les techniques MIMO et un mécanisme de codage vidéo hiérarchique qui consiste en la séparation de la scène en régions d'intérêt. Le flux correspondant à la zone d’intérêt maximal est transmis sur le canal propre de plus grand gain. Ceci permet d'assurer une meilleure robustesse de transmission et garantit ainsi un niveau acceptable pour la QoS perçue par le centre de contrôle. La création des différentes régions d’intérêt s’appuie sur l’outil FMO (Flexible Macroblock Ordering) introduit dans le nouveau standard de compression H. 264/AVC. Ainsi, les différents schémas de transmission proposés permettent d’accroître la qualité de service d’un flux vidéo sans augmenter la puissance émise ni multiplier le nombre de points d’accès radio de l’infrastructure
Video monitoring applications in the Public Transport field rely on wireless telecommunication systems which require high data rate between vehicles and the ground and high Quality of Service (QoS). In order to satisfy these constraints we have proposed to take into account both transmission parameters and video coding by combining Multiple Description Coding (MDC) and Region Of Interest coding with different MIMO (Mulitple Input Multiple Output) schemes on the basis of the PHY layer of IEEE802. 11n Wifi standard in a metro environment (tunnel). First, we have shown that it is possible to increase the performance of a MIMO system by optimizing bits and power allocation independently of the type of information to be transmitted. Two approaches are proposed. They lead to an optimal repartition of resources, reach maximal diversity order and they outperform the max-SNR precoder performances. Secondly, the association of MDC with MIMO schemes is introduced to adapt the video content to the multi antenna structure particularly when the channel knowledge is not available at transmitter side. Furthermore, the performances can be enhanced using a low data rate return link and considering the Orthogonalized Spatial Multiplexing (OSM) and the precoded OSM. When perfect channel information is available at transmitter side thanks to a high data rate return link, MIMO schemes are associated with hierarchic video coding consisting in the separation of regions of interest in the scene. The stream associated to the area with the maximal interest is transmitted on the eigen channel with the higher gain. This strategy allows to guaranty better robustness and acceptable QoS of the video streams observed in the control-center. The creation of the different regions of interest is based on the Flexible Macroblock Ordering (FMO) technique introduced in the new compression standard H. 264/AVC. We have shown the interest of the different transmission schemes proposed in order to enhance the QoS of a video stream with no increase of the transmitted power and of the number of radio access points along the infrastructure

O cenário atual do estado de São Paulo reflete o cenário de degradação observado na Floresta Atlântica do país, onde os remanescentes florestais estão muito fragmentados, degradados e imersos em uma paisagem agrícola, dominada predominantemente por matrizes de cana de açúcar e pastagens. Neste contexto, objetivamos investigar se a regeneração natural da borda de fragmentos florestais tem características distintas nessas duas matrizes agrícolas dominantes. Nossa hipótese foi que de a regeneração natural em fragmentos inseridos em matrizes de cana de açúcar e pastagem são distintas, porque essas matrizes definem diferentes trajetórias de degradação sobre a flora de fragmentos naturais. Este trabalho foi desenvolvido na bacia do rio Corumbataí, onde indivíduos de espécies arbustivo e arbóreas do estrato regenerante (mínimo de 30cm de altura até 15 cm de perímetro à altura do peito) foram amostrados em 60 transectos de 30x2m (subdivididos em transectos contíguos de 10x2m) sistematicamente distribuídas a partir da borda de 12 fragmentos selecionados na bacia. Primeiramente, foi feita uma caracterização florística geral da regeneração natural das bordas de fragmentos florestais inseridos nas duas matrizes agrícolas. Posteriormente, foram utilizadas as variáveis número de indivíduos.hectare-1 (RN_HA) e número de espécies/m2 (NESP_M2) e diversidade florística (ISHANNON) para analisar as diferenças da estrutura e composição da regeneração natural nas duas matrizes. Essas mesmas variáveis foram utilizadas para analisar estatisticamente o efeito de indicadores de conservação dos fragmentos, como entrada de gado, presença de eucaliptos no dossel e abundância de gramíneas e lianas, sobre a regeneração natural. A similaridade florística entre remanescentes das paisagens foi calculada através do Índice de Similaridade de Jaccard. Em todos os transectos, foram amostrados 5886 regenerantes, divididos em 58 famílias, 220 espécies e 18 morfoespécies. O índice de Jaccard mostrou que houve similaridade florística (45%) entre os regenerantes dos fragmentos da matriz de pastagem e cana de açúcar. Nos fragmentos inseridos na matriz de pastagem, a entrada de gado foi o indicador de conservação de fragmentos que apresentou maior interferência sobre a regeneração natural, diminuindo tanto o número de indivíduos por unidade de área quanto a diversidade florística. Para a paisagem de cana, a fonte de variação que mais interferiu na estrutura da regeneração foi a presença de eucaliptos no dossel, que aumentou o número de indivíduos por unidade de área. A abundância de gramíneas e lianas e a presença de epífitas não apresentaram influência sobre a regeneração quando analisados tipo de matriz ou tamanho do fragmento. Entre os sub-transectos contíguos de 10m, não houve variação na estrutura e composição da regeneração natural, indicando que nesta profundidade de borda a vegetação regenerante é homogênea quanto à florística, diversidade e classificação sucessional. Os resultados indicam que, mesmo inseridos em paisagens agrícolas profundamente antropizadas, os remanescentes florestais ainda detém elevada diversidade florística. A regeneração natural mostrou-se um bom indicador de qualidade atual e futura dos remanescentes florestais, e demonstrou, juntamente com os indicadores de conservação, que os fragmentos são passíveis de manejo, o que poderá potencializar o papel de conservação da biodiversidade exercido pela regeneração natural.
At São Paulo state, Brazil, the scenario of the Atlantic Forest reflects the scenario of degradation of the biome in the country, where forest remnants are embedded in an agricultural landscape, dominated by sugar cane fields and pasture fields. In this context, we aimed to investigate if natural forest regeneration responds differently to each agricultural matrix. Our hypothesis was that forest regeneration composition in remnants surrounded by sugar cane fields is different of forest regeneration composition in remnants surrounded by pasture fields, because these agricultural matrices impact differently forest biota. The present research was developed in Corumbataí river basin, in the countryside of São Paulo state. Shrub and tree individuals, from regeneration layer, were sampled in 60 plots 30x2 meters long (subdivided in plots 10x2 meters long) systematically distributed on the edges of 12 fragments. Firstly, we characterized the natural regeneration of the edges of forest remnants embedded in agricultural landscapes. Then we used the variables number of individuals.ha-1 (RN_HA), number of species/m2 (NESP_M2) and floristic diversity (ISHANNON) to analyze the differences in structure and composition of forest natural regeneration between sugar cane fields and pasture fields. These variables were used to analyze the statistical effects of conservation indicators, such as cattle entrance on forest remnants, abundance of woody-vines and grasses, and presence of eucalyptus trees on forest canopy, on natural regeneration. Floristic similarity between forest remnants was assessed by Jaccard Similarity Index. 5886 saplings were sampled among the 60 plots, divided in 57 families, 214 species and 31 morphospecies. Jaccard index indicated floristic similarity (45%) among the fragments inserted in sugar cane field and pasture field. Among the fragments inserted in pasture field, cattle entrance was the conservation indicator with the strongest interference over natural regeneration, decreasing both the number of plants per area and the floristic diversity. At sugar cane landscape, presence of eucalyptus on forest canopy increased the number of individuals per area. Grass and woody-vines abundance and presence of epiphytes were not significant for any variable, when analyzed with matrix type or fragment size. Among the subplots of 10m long, there was no variation of structure and composition of natural regeneration, what indicates that, in relation to floristic, diversity and sucessional classification, the regenerant vegetation is homogeneous in the first 30 meters of the edge. The results indicate that, even embedded in anthropogenic agricultural landscapes, the remnants studied still retain high floristic diversity. Natural regeneration has shown to be a good indicator of actual and future quality of forest remnants, and, together with conservation indicators, demonstrated that the fragments studied are subject to management actions, which may improve the role of biodiversity conservancy developed by natural regeneration

La technologie OFDMA (Orthogonal frequency division multiple access) a été adoptée par les systèmes de télécommunications de 4ème génération (4G) comme technique de transmission et d'accès multiple pour ses performances supérieures en termes d'efficacité spectrale. Dans ce type de systèmes, l'adaptation dynamique du débit en fonction de la qualité du canal CQI (Channel Quality Indicator) constitue une problématique de recherche d'actualité qui attire l'attention de plusieurs acteurs académiques et industriels. Ce problème d'adaptation dynamique est encore plus complexe à gérer dans des environnements multi-utilisateurs hétérogènes et à ressources limitées tels que les systèmes OFDMA comme WiMAX Mobile et Long-term Evolution (LTE). Dans cette thèse, nous nous intéressons au problème d'allocation de ressources de l'information de feedback relative au CQI dans le cadre de systèmes OFDMA multi-porteuses multi-utilisateurs. Dans le but de réduire la charge (overhead) du feedback, nous proposons une méthode de prédiction du CQI basée sur l'exploitation de la corrélation temporelle de ce dernier et d'une solution inter-couches. L'objectif est de trouver des schémas d'allocation de ressources adaptatifs respectant les contraintes de qualité de service (QoS) applicatives.Nous proposons en premier lieu un algorithme de réduction de feedback PBF (Prediction Based Feedack) qui permet à la station de base (BS) à prédire certaines occurrences du CQI en se basant sur l'algorithme des moindres carrés récursif RLS (Recursive least-square). Les résultats de simulation montrent que l'outil de prédiction du CQI réduit sensiblement l'overhead du feedback et améliore par conséquent le débit de la liaison montante. Nous proposons, par la suite, une version opportuniste de PBF pour atténuer les éventuels effets de sur et sous estimations liées à l'algorithme de prédiction. Dans ce mécanisme, nous exploitons les informations inter-couches pour améliorer les performances des mécanismes de feedbacks périodiques dont PBF fait partie. L'approche opportuniste améliore sensiblement les performances du système pour les cas de mobilité élevée comparés aux cas de faible mobilité.Dans un second temps, nous proposons une plateforme (FEREP : feedback resource allocation and prediction) basée sur une approche inter-couches. Implémentée au niveau de la station BS, FEREP intègre les fonctionnalités de prédiction, d'adaptation dynamique du CQI et d'ordonnancement des demandes de feedback. Elle comporte trois modules. Le module FWA (feedback window adaptation) gère dynamiquement la fenêtre de feedbacks de chaque station mobile (MS) en se basant sur les messages ARQ (Automatic Repeat Request) reçus qui reflètent l'état actuel des canaux respectifs. Le module PBFS (priority-based feedback scheduling) effectue ensuite l'ordonnancement des feedbacks en tenant compte de la taille de la fenêtre de feedback, du profil de l'utilisateur sous la contrainte de la limitation des ressources globales du systèmes réservées au feedback. Afin de choisir les paramètres de transmission MCS (modulation and coding schemes), le module PBF (prediction based feedback) est utilisé pour les utilisateurs dont le feedabck n'a pas pu être ordonnancé dans la trame courante. Les résultats de simulation ont montré un gain significatif des performances de FREREP en comparaison à un mécanisme de référence, en particulier, sous de fortes contraintes de limitation des ressources du feedback.Le protocole ARQ génère un accusé de réception uniquement si l'utilisateur est sélectionné par l'ordonnanceur pour envoyer des données sur la liaison descendante. Dans le cas où la fréquence d'ordonnancement des utilisateurs sur le lien descendant est réduite, les messages ARQ s'en trouvent également réduits, dégradant par conséquent les performances de la plateforme FEREP proposée ci-dessus. En effet, dans ce cas la signalisation ARQ devient insuffisante pour adapter efficacement la fenêtre de feedback de chaque utilisateur. Pour pallier à ce problème, nous proposons l'algorithme DCRA (dynamic CQI resource allocation) qui utilise deux modes d'estimation de la fenêtre de feedback. Le premier est un mode hors-ligne basé sur des études empiriques permettant d'estimer la fenêtre moyenne optimale de feedback en utilisant les profils applicatif et de mobilité de l'utilisateur. Notre analyse de performance par simulation montre que la fenêtre de feedback peut être estimée en fonction de la classe de service des utilisateurs et de leurs profils de mobilité pour un environnement cellulaire donné. Le second mode de fonctionnement de DCRA effectue une adaptation dynamique de la fenêtre en temps réel dans le cas où la signalisation ARQ est suffisante. Une étude comparative avec les mécanismes DFS (deterministic feedback scheduling) et OFS (opportunistic feedback scheduling), a montré que DCRA arrive à réaliser un meilleur gain en ressources montantes grâce à la réduction de l'overhead des feedbacks, sans pour autant trop dégrader le débit descendant des utilisateurs. Du point de vue des utilisateurs, DCRA améliore les contraintes de QoS tels que le taux de perte de paquets et réduit la consommation énergétique des terminaux grâce à la réduction de feedback.

Cette thèse a pour but de proposer toutes les avancées possibles dans l’utilisation du modèle de propagation Multi-Resolution Frequency-Domain ParFlow (MR-FDPF). Etant un modèle de propagation radio déterministe, le modèle MR-FDPF possède un haut niveau de précision, mais souffre des limitations communes à tous les modèles déterministes. Par exemple, un canal radio réel n’est pas déterministe, mais un processus aléatoire à cause par exemple des personnes ou objets mobiles, et ne peut donc être décrit fidèlement par un modèle purement déterministe. Dans cette thèse, un modèle semi-déterministe est proposé, basé sur le modèle MR-FDPF, qui introduit une part stochastique pour tenir compte des aspects aléatoires du canal radio réaliste. La partie déterministe du modèle est composée du path loss (atténuation d’espace), et la partie stochastique venant du shadow fading (masquage) et du small scale fading (évanouissement). De même, de nombreux simulateurs de propagation radio ne proposent que la prédiction de la puissance moyenne. Mais pour une simulation précise de la propagation radio il convient de prédire également des informations de fading permettant dès lors une prédiction précise du taux d’erreur binaire (BER) potentiel. Dans cette thèse, l’information de fading est déduite des simulations MR-FDPF et par la suite des valeurs réalistes de BER sont données. Enfin, ces données réalistes de BER permettent d’évaluer l’impact de schémas de modulation adaptatifs. Des résultats sont présentés dans trois configurations : systèmes SISO (mono-antenne à l’émission et à la réception), systèmes à diversité de type MRC, et systèmes large bande de type OFDM
This thesis aims at proposing all the possible enhancements for the Multi-Resolution Frequency-Domain ParFlow (MR-FDPF) model. As a deterministic radio propagation model, the MR-FDPF model possesses the property of a high level of accuracy, but it also suffers from some common limitations of deterministic models. For instance, realistic radio channels are not deterministic but a kind of random processes due to, e.g. moving people or moving objects, thus they can not be completely described by a purely deterministic model. In this thesis, a semi-deterministic model is proposed based on the deterministic MR-FDPF model which introduces a stochastic part to take into account the randomness of realistic radio channels. The deterministic part of the semi-deterministic model is the mean path loss, and the stochastic part comes from the shadow fading and the small scale fading. Besides, many radio propagation simulators provide only the mean power predictions. However, only mean power is not enough to fully describe the behavior of radio channels. It has been shown that fading has also an important impact on the radio system performance. Thus, a fine radio propagation simulator should also be able to provide the fading information, and then an accurate Bit Error Rate (BER) prediction can be achieved. In this thesis, the fading information is extracted based on the MR-FDPF model and then a realistic BER is predicted. Finally, the realistic prediction of the BER allows the implementation of the adaptive modulation scheme. This has been done in the thesis for three systems, the Single-Input Single-Output (SISO) systems, the Maximum Ratio Combining (MRC) diversity systems and the wideband Orthogonal Frequency-Division Multiplexing (OFDM) systems

Orientadores: Maria Imaculada Zucchi, Anete Pereira de Souza
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: A associação entre subpopulações de insetos e plantas-hospedeiras pode ocorrer por adaptação e esta, pode ser uma etapa anterior ao surgimento de raças-hospedeiras e especialização. Pouco se sabe sobre o papel da mudança da composição da paisagem, mediada pela atividade agrícola recente, na divergência adaptativa e fluxo gênico de insetos fitófagos. Dessa forma, o presente trabalho teve como objetivos: i) desenvolver marcadores moleculares microssatélites para o estudo genético de um inseto fitófago, Diatraea saccharalis; ii) quantificar e caracterizar a estrutura genética, o fluxo gênico e os fatores que contribuem para a divergência genética das subpopulações da espécie; iii) identificar variação genética sob seleção natural que possa estar contribuindo para a divergência genética de subpopulações associadas a cana-de-açúcar e milho e; iv) desenvolver recurso genômico através de bibliotecas genômicas RADtag para a busca, desenvolvimento e caracterização de marcadores moleculares associados a genes candidatos. Dos 20 locos microssatélites, dez foram selecionados para serem utilizados no estudo de ecologia molecular. Os índices de diferenciação mostraram que, tanto a estruturação genética espacial, quanto a determinada pelo hospedeiro, foram significativas. Dos 301 locos AFLP utilizados para a genotipagem de quatro subpopulações, 19 foram identificados como outliers nas comparações par-a-par e desses, cinco locos foram identificados pelos dois métodos empregados na detecção de outliers, e podem, desta forma, estar associados à adaptação à planta-hospedeira. Os resultados das análises de agrupamento utilizando os locos outliers mostraram o agrupamento dos indivíduos em grupos que representam a planta-hospedeira onde foram coletados. Os mesmos resultados foram obtidos com uma amostra dos SNPs isolados através do protocolo de RADtag. Os dados genômicos obtidos até o momento estão sendo utilizados, juntamente com o estudo de genômica comparativa, na identificação e desenho de primers específicos para genes candidatos. Os resultados mostraram os efeitos da expansão e mudança recente da paisagem agrícola na diversidade genética de uma espécie de inseto fitófago. A atividade agrícola pode ser fonte de seleção divergente suficiente para levar à especialização e especiação de insetos. Os resultados deste trabalho sugerem estar havendo divergência ecológica entre as subpopulações de D. saccharalis coletadas em milho e cana-de-açúcar e que esta divergência, por ser recente, não é completa. Além disso, esses resultados mostram a necessidade de estudos complementares para isolar as fontes de seleção divergente, os mecanismos de isolamento reprodutivo, e a arquitetura genética que liga a seleção divergente ao isolamento reprodutivo
Abstract: The association between subpopulations of insects and their host plants can occur by adaptation and this may lead to host-races formation and specialization. Little is known about the role of the changing landscape composition mediated by recent agricultural activity in adaptive divergence and gene flow of phytophagous insects. This study aimed to: i) develop microsatellite markers for the genetic study of a phytophagous insect, Diatraea saccharalis; ii) quantify and characterize the genetic structure, gene flow and the factors that contribute to the genetic divergence of subpopulations of the species; iii) identify genetic variation that may be experiencing natural selection and thus be contributing to genetic divergence of subpopulations associated with sugarcane and maize; iv) develop genomic resource through RADtag libraries to search, characterize and develop molecular markers linked to candidate genes. Ten of 20 microsatellite loci were selected for use in the study of molecular ecology. The genetic differentiation showed that both spatial genetic structure and that determined by the host-plant were significant. Of the 301 AFLP loci used for genotyping four subpopulations, 19 were identified as outliers in pairwise comparisons and five were identified by the two methods employed for outliers detection and thus, can be associated with host-plant adaptation. Cluster analysis using outlier loci showed the grouping of individuals into groups that represent the host plant where they were collected. Data from a sample of SNPs isolated by RADtag protocol showed the same results. The genomic data obtained so far are being used together with the study of comparative genomics for the identification and design of specific primers for candidate genes. The results showed the effects of expansion and recent changes in agricultural landscape in genetic diversity of phytophagous insect species. Farming can generate enough source for ecologically based divergence that could lead to specialization and speciation in insects species. The results of this study suggest that there is ecological divergence between subpopulations of D. saccharalis collected from corn and sugarcane, but it is not complete. In addition, these results showed the need for further studies to isolate the sources of divergent selection, the mechanisms of reproductive isolation, and the genetic architecture linking the divergent reproductive isolation with selection
Doutorado
Genetica Animal e Evolução
Doutor em Genetica e Biologia Molecular

Au cours de la dernière décennie, l’étude mathématique et statistique des représentations parcimonieuses de signaux et de leurs applications en traitement du signal audio, en traitement d’image, en vidéo et en séparation de sources a connu une activité intensive. Cependant, l'exploitation de la parcimonie dans des contextes de traitement multidimensionnel comme les communications numériques reste largement ouverte. Au même temps, les méthodes aveugles semblent être la réponse à énormément de problèmes rencontrés récemment par la communauté du traitement du signal et des communications numériques tels que l'efficacité spectrale. Aussi, dans un contexte de mobilité et de non-stationnarité, il est important de pouvoir mettre en oeuvre des solutions de traitement adaptatives de faible complexité algorithmique en vue d'assurer une consommation réduite des appareils. L'objectif de cette thèse est d'aborder ces challenges de traitement multidimensionnel en proposant des solutions aveugles de faible coût de calcul en utilisant l'à priori de parcimonie. Notre travail s'articule autour de trois axes principaux : la poursuite de sous-espace principal parcimonieux, la séparation adaptative aveugle de sources parcimonieuses et l'identification aveugle des systèmes parcimonieux. Dans chaque problème, nous avons proposé de nouvelles solutions adaptatives en intégrant l'information de parcimonie aux méthodes classiques de manière à améliorer leurs performances. Des simulations numériques ont été effectuées pour confirmer l’intérêt des méthodes proposées par rapport à l'état de l'art en termes de qualité d’estimation et de complexité calculatoire
During the last decade, the mathematical and statistical study of sparse signal representations and their applications in audio, image, video processing and source separation has been intensively active. However, exploiting sparsity in multidimensional processing contexts such as digital communications remains a largely open problem. At the same time, the blind methods seem to be the answer to a lot of problems recently encountered by the signal processing and the communications communities such as the spectral efficiency. Furthermore, in a context of mobility and non-stationarity, it is important to be able to implement adaptive processing solutions of low algorithmic complexity to ensure reduced consumption of devices. The objective of this thesis is to address these challenges of multidimensional processing by proposing blind solutions of low computational cost by using the sparsity a priori. Our work revolves around three main axes: sparse principal subspace tracking, adaptive sparse source separation and identification of sparse systems. For each problem, we propose new adaptive solutions by integrating the sparsity information to the classical methods in order to improve their performance. Numerical simulations have been conducted to confirm the superiority of the proposed methods compared to the state of the art

En environnements hostiles, les signaux GNSS (Global Navigation Satellite System)peuvent être soumis à des risques de brouillages intentionnels. Basées sur un réseau d'antennes adaptatif, les solutions spatio-temporelles (STAP) ont déjà montré de bonnes performances de réjection des interférences. Toutefois, lorsque le module GNSS est placé sous les pales d'un hélicoptère, des effets non-stationnaires, appelés Rotor Blade Modulation (RBM), créés par les multiples réflexions du signal sur les pales du rotor, peuvent dégrader les techniques usuelles d’antibrouillage. Le signal utile GNSS n’est alors plus accessible. Le travail de la thèse consiste donc à élaborer un système de protection des signaux GNSS adapté à la RBM. Pour cela, un modèle innovant de multitrajets, adapté à ce type de phénomène, a été développé. La comparaison de simulations électromagnétiques représentatives et de mesures expérimentales sur hélicoptère EC-120 a permis de valider ce modèle. Celui-ci permet d'estimer, par maximum de vraisemblance, les paramètres de la contribution non-stationnaire du signal reçu. Enfin, l'association d'un algorithme de filtrage des multitrajets par projection oblique et d'un traitement STAP permet d'éliminer la contribution dynamique puis statique de l'interférence. Les simulations montrent que le signal utile GNSS est alors de nouveau exploitable
In hostile environments, Global Navigation Satellite System (GNSS) can be disturbed by intentional jamming. Using antenna arrays, space-time adaptive algorithm (STAP) isone of the most efficient methods to deal with these threats. However, when a GNSS receiver is placed near rotating bodies, non-stationary effects called Rotor Blade Modulation (RBM) are created by the multipaths on the blades of the helicopter. They can degrade significantly the anti-jamming system and the signal of interest could belost. The work of the thesis is, consequently, to develop a GNSS protection system adapted to the RBM. In this way, an innovative multipath model, adapted to this phenomenon, has been developed. The model is then confirmed by comparison with a symptotic electromagnetic simulations and experiments conducted on an EC-120helicopter. Using a Maximum Likelihood algorithm, the parameters of the non-stationary part of the received signal have been estimated. And finally, the RBM anti-jamming solution, combining oblique projection algorithm and academic STAP, can mitigate dynamic and static contributions of interferences. In the end, the navigation information is available again

La technologie OFDMA (Orthogonal frequency division multiple access) a été adoptée par les systèmes de télécommunications de 4ème génération (4G) comme technique de transmission et d'accès multiple pour ses performances supérieures en termes d'efficacité spectrale. Dans ce type de systèmes, l'adaptation dynamique du débit en fonction de la qualité du canal CQI (Channel Quality Indicator) constitue une problématique de recherche d'actualité qui attire l'attention de plusieurs acteurs académiques et industriels. Ce problème d'adaptation dynamique est encore plus complexe à gérer dans des environnements multi-utilisateurs hétérogènes et à ressources limitées tels que les systèmes OFDMA comme WiMAX Mobile et Long-term Evolution (LTE). Dans cette thèse, nous nous intéressons au problème d'allocation de ressources de l'information de feedback relative au CQI dans le cadre de systèmes OFDMA multi-porteuses multi-utilisateurs. Dans le but de réduire la charge (overhead) du feedback, nous proposons une méthode de prédiction du CQI basée sur l'exploitation de la corrélation temporelle de ce dernier et d'une solution inter-couches. L'objectif est de trouver des schémas d'allocation de ressources adaptatifs respectant les contraintes de qualité de service (QoS) applicatives.Nous proposons en premier lieu un algorithme de réduction de feedback PBF (Prediction Based Feedack) qui permet à la station de base (BS) à prédire certaines occurrences du CQI en se basant sur l'algorithme des moindres carrés récursif RLS (Recursive least-square). Les résultats de simulation montrent que l'outil de prédiction du CQI réduit sensiblement l'overhead du feedback et améliore par conséquent le débit de la liaison montante. Nous proposons, par la suite, une version opportuniste de PBF pour atténuer les éventuels effets de sur et sous estimations liées à l'algorithme de prédiction. Dans ce mécanisme, nous exploitons les informations inter-couches pour améliorer les performances des mécanismes de feedbacks périodiques dont PBF fait partie. L'approche opportuniste améliore sensiblement les performances du système pour les cas de mobilité élevée comparés aux cas de faible mobilité.Dans un second temps, nous proposons une plateforme (FEREP : feedback resource allocation and prediction) basée sur une approche inter-couches. Implémentée au niveau de la station BS, FEREP intègre les fonctionnalités de prédiction, d'adaptation dynamique du CQI et d'ordonnancement des demandes de feedback. Elle comporte trois modules. Le module FWA (feedback window adaptation) gère dynamiquement la fenêtre de feedbacks de chaque station mobile (MS) en se basant sur les messages ARQ (Automatic Repeat Request) reçus qui reflètent l'état actuel des canaux respectifs. Le module PBFS (priority-based feedback scheduling) effectue ensuite l'ordonnancement des feedbacks en tenant compte de la taille de la fenêtre de feedback, du profil de l'utilisateur sous la contrainte de la limitation des ressources globales du systèmes réservées au feedback. Afin de choisir les paramètres de transmission MCS (modulation and coding schemes), le module PBF (prediction based feedback) est utilisé pour les utilisateurs dont le feedabck n'a pas pu être ordonnancé dans la trame courante. Les résultats de simulation ont montré un gain significatif des performances de FREREP en comparaison à un mécanisme de référence, en particulier, sous de fortes contraintes de limitation des ressources du feedback.Le protocole ARQ génère un accusé de réception uniquement si l'utilisateur est sélectionné par l'ordonnanceur pour envoyer des données sur la liaison descendante. Dans le cas où la fréquence d'ordonnancement des utilisateurs sur le lien descendant est réduite, les messages ARQ s'en trouvent également réduits, dégradant par conséquent les performances de la plateforme FEREP proposée ci-dessus. En effet, dans ce cas la signalisation ARQ devient insuffisante pour adapter efficacement la fenêtre de feedback de chaque utilisateur. Pour pallier à ce problème, nous proposons l'algorithme DCRA (dynamic CQI resource allocation) qui utilise deux modes d'estimation de la fenêtre de feedback. Le premier est un mode hors-ligne basé sur des études empiriques permettant d'estimer la fenêtre moyenne optimale de feedback en utilisant les profils applicatif et de mobilité de l'utilisateur. Notre analyse de performance par simulation montre que la fenêtre de feedback peut être estimée en fonction de la classe de service des utilisateurs et de leurs profils de mobilité pour un environnement cellulaire donné. Le second mode de fonctionnement de DCRA effectue une adaptation dynamique de la fenêtre en temps réel dans le cas où la signalisation ARQ est suffisante. Une étude comparative avec les mécanismes DFS (deterministic feedback scheduling) et OFS (opportunistic feedback scheduling), a montré que DCRA arrive à réaliser un meilleur gain en ressources montantes grâce à la réduction de l'overhead des feedbacks, sans pour autant trop dégrader le débit descendant des utilisateurs. Du point de vue des utilisateurs, DCRA améliore les contraintes de QoS tels que le taux de perte de paquets et réduit la consommation énergétique des terminaux grâce à la réduction de feedback
Orthogonal frequency division multiple access (OFDMA) technology has been adopted by 4th generation (a.k.a. 4G) telecommunication systems to achieve high system spectral efficiency. A crucial research issue is how to design adaptive channel quality indicator (CQI) feedback mechanisms so that the base station can use adaptive modulation and coding (AMC) techniques to adjust its data rate based on the channel condition. This problem is even more challenging in resource-limited and heterogeneous multiuser environments such as Mobile WiMAX, Long-term Evolution (LTE) networks. In this thesis, we consider CQI feedback resource allocation issue for multiuser multicarrier OFDMA systems. We exploit time-domain correlation for CQI prediction and cross-layer information to reduce feedback overhead for OFDMA systems. Our aim is find resource allocation schemes respecting the users QoS constraints.Our study begins with proposing prediction based feedback (PBF) which allows the base station to predict the CQI feedbacks based on recursive least-square (RLS) algorithm. We showed that it is useful to use channel prediction as a tool to reduce the feedback overhead and improve the uplink throughput. Then, we propose an opportunistic periodic feedback mechanism to mitigate the possible under and over estimation effects of CQI prediction. In this mechanism, we exploited the cross-layer information to enhance the performance of periodic feedback mechanisms. The opportunistic mechanism improves the system performance for high mobility cases compared to low mobility cases.For OFDMA systems with limited feedback resource, we propose an integrated cross-layer framework of feedback resource allocation and prediction (FEREP). The proposed framework, implemented at the BS side, is composed of three modules. The feedback window adaptation (FWA) module dynamically tunes the feedback window size for each mobile station based on the received ARQ (Automatic Repeat Request) messages that reflect the current channel condition. The priority-based feedback scheduling (PBFS) module then performs feedback allocation by taking into account the feedback window size, the user profile and the total system feedback budget. To choose adapted modulation and coding schemes (MCS), the prediction based feedback (PBF) module performs channel prediction by using recursive least square (RLS) algorithm for the user whose channel feedback has not been granted for schedule in current frame. Through extensive simulations, the proposed framework shows significant performance gain especially under stringent feedback budget constraint.ARQ protocol receives users acknowledgement only if the user is scheduled in the downlink. The reduction in users scheduling frequency also reduces the rate of ARQ hints and degrades the performance of above contributions. In this case, it is difficult to exploit the ARQ signal to adapt the feedback window for that user. To address this issue, we propose a cross-layer dynamic CQI resource allocation (DCRA) algorithm for multiuser multicarrier OFDMA systems. DCRA uses two modes for feedback window estimation. The first one is an off-line mode based on empirical studies to derive optimal average feedback window based on user application and mobility profile. Our experimental analysis shows that the feedback window can be averaged according to users service class and their mobility profile for a given cell environment. DCRA performs a realtime dynamic window adaptation if sufficient cross-layer hints are available from ARQ signaling. DCRA increases uplink resource by reducing feedback overhead without degrading downlink throughout significantly compared to deterministic feedback scheduling (DFS) and opportunistic feedback scheduling (OFS). From the users perspective, DCRA improves QoS constraints like packet loss rate and saves users power due to feedback reduction

Compared with the free atmosphere, the aquatic environment is oxygen poor. As a result many secondarily aquatic organisms have adaptations that allow them to continue to use the atmosphere, directly or indirectly, to supply their oxygen requirements. This thesis examines how diving insects use bubbles of air collected at the surface of the water as oxygen reserves, gills and flotation devices, and how an aquatic angiosperm channels convective flows of air from its emergent leaves to its submerged organs. 1. Backswimmers (Anisops spp.) begin a dive positively buoyant, but rapidly enter a protracted period of near neutral buoyancy. A bubble of air held on the insect’s abdomen shrinks as respiration consumes its oxygen, while at the same time highly soluble carbon dioxide dissolves into the surrounding water. The reduced air volume confers neutral buoyancy. In response to low oxygen partial pressure (PO2) in the bubble, oxygen is released from large haemoglobin cells in the abdomen. The haemoglobin’s sensitivity to falling PO2 maintains the oxygen tension between 5.1 and 2.0 kPa. This stabilises the volume and buoyancy of the bubble. During a dive the haemoglobin and air-store supply 0.25 and 0.26 μL of oxygen, respectively. 2. The oxygen affinity of backswimmer haemoglobin determines the stability of the neutrally buoyant phase as well as its ability to satisfy the insect’s respiration. An oxygen equilibrium curve (OEC) determined in vivo has a highly sigmoid shape and an oxygen affinity of 3.9 kPa. In comparison with OEC made in vitro, the in vivo measurements show increased cooperativity and oxygen affinity, consistent with the presence of cationic effectors. Models strongly support the accuracy of the in vivo OEC method. 3. It has long been assumed that a bubble of air held over the spiracles of an insect enables the uptake of oxygen from the surrounding water and thus acts as a ‘gas gill’. Oxygen diffuses into a bubble of air when its PO2 is lower than the surrounding water, but a coincident higher nitrogen partial pressure causes it to dissolve. Several models have been produced to describe the gas exchange process, but all are based on untested assumptions of gill parameters. Measurements of gas gill volume and PO2 made on water bugs (Agraptocorixa eurynome) demonstrate that both drop quickly at the beginning of a dive, but PO2 reaches a stable level while the gas gill continues to dissolve. The importance of ventilation in maintaining an acceptable rate of oxygen consumption is also shown. 4. Interconnected gas spaces within the leaves, stems and rhizomes are a common feature of many emergent aquatic plants. Pressurised air from the leaves and culms of these plants ventilate these lacunae, flowing back to the atmosphere through efflux points. Unlike most aquatic plants, which have simple interconnected pith spaces, sacred lotus, Nelumbo nucifera, possess discrete gas canals which only interconnect where a leaf grows from the rhizome. Silicone casts and pneumatic tests of the gas canals reveal a complex repeating pattern of interconnections which channel air from specific regions of the leaf blade to the rhizome and out through efflux points on adjacent leaves. 5. Lotus, Nelumbo nucifera, possess in the centre of their leaves a specialised efflux organ which connects the gas canals in the leaves and stems with the atmosphere through the apertures of large stomata. Measurements made on excised lotus leaves and in situ reveal that the large stomata act as exhaust valves, opening and closing in a diurnal pattern to regulate the flow of pressurised gas from the leaf lamina and gas canals. This behaviour is shown to regulate gas flow rate and direction. The aquatic environment offers similar respiratory challenges to both plants and insects. While the oxygen uptake and transport mechanisms evolved by these groups are markedly different, they all function according to the same physical laws. Diving insects are separated from the atmosphere while underwater, forcing them to rely on oxygen either carried with them from the surface or extracted from the surrounding water. Emergent aquatic plants have permanent access to atmospheric oxygen, but must transport it long distances from their aerial leaves and stems to their roots and rhizomes. This thesis examines the uptake and storage of oxygen by diving insects and the gas transport system of the sacred lotus.
Thesis(Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008

Ce travail de thèse se cadre autour de la thématique d'identification / égalisation aveugle (autodidacte) de canaux de transmission, dont l'atout majeur est, incontestablement, la suppression de la séquence d'apprentissage. Néanmoins, une telle démarche présente certains inconvénients, par rapport à un traitement classique (avec séquence d'apprentissage) du problème, à savoir, un niveau de performance plus faible, un coût de calcul plus élevé et une sensibilité plus importante aux incertitudes sur certains paramètres, tel l'ordre du canal. Ce qui joue en défaveur d'une large application des schémas d'identification / égalisation aveugle dans la pratique. Tenant compte de cette problématique et afin d'améliorer les performances des systèmes d'identification / égalisation aveugle et de palier à leurs carences, cette étude vient, dans un premier temps, résumer, clarifier et évaluer un certain nombre de travaux déjà existants, et dans un deuxième temps, proposer deux nouvelles approches adaptatives et rapides d'égalisation du type erreur quadratique moyenne minimale (MMSE: Minimum Mean Square Error), aveugle du second ordre, pour des systèmes multicanaux à réponse impulsionnelle finie. La première approche, destinée à des systèmes à entrées multiples sorties multiples (MIMO: Multiple Input Multiple Output), est robuste aux erreurs de surestimation de l'ordre du canal. Tandis que la deuxième approche, destinée à des systèmes à une entrée plusieurs sorties (SIMO: Single Input Multiple Output), est totalement indépendante de l'ordre du canal.

Este trabalho enquadra-se na área da propagação na faixa das ondas milimétricas, nomeadamente, na modelação do canal em banda larga e seu impacto no desempenho de transmissão do sistema rádio móvel e acesso sem fios, capaz de suportar a gama de serviços prevista para a B-ISDN. Inicia-se pela identificação da banda de frequências mais adequada para implementar o sistema de comunicações móveis de banda larga e/ou acesso sem fios em ambientes interiores, tendo-se revelado a faixa das ondas milimétricas a mais apropriada. Assim, após uma caracterização teórica de canais lineares e variantes no tempo são discutidas as vantagens e desvantagens dos modelos determinísticos e estatísticos e é apresentada uma descrição matemática detalhada do modelo determinístico desenvolvido. Este modelo permite estimar a resposta impulsiva do canal de propagação num dado ambiente, tendo em conta qualquer tipo de antenas a serem usadas pela estação móvel bem como pela estação base. É também apresentado um modelo analítico recursivo que permite obter a função de transferência do canal sem recorrer a complexas rotinas de software. A comparação entre os resultados dos modelos com medidas experimentais em diferentes ambientes, demonstra a validade dos modelos desenvolvidos. Utilizando o simulador que implementa o modelo desenvolvido, é estudada a influência da configuração celular, tipos de antenas e suas características (p.e., diagrama de radiação e polarização) nos parâmetros que caracterizam a resposta impulsiva do canal, indicando-se a configuração mais adequada para cada cenário. É feita uma avaliação do impacto que os aspectos de propagação, incluindo as configurações celulares, têm no desempenho de transmissão do sistema, recorrendo a técnicas de equalização adaptativa e diversidade como forma de combater os efeitos da propagação multipercurso. Por último são apresentados resultados de simulação Monte-Carlo que permitem estimar a máxima taxa de transmissão por portadora em diferentes cenários, consoante a configuração celular e o esforço de equalização empregue, bem como um método geral para estimar a referida taxa de transmissão com base na dispersão temporal do canal.
This thesis deals with wide-band propagation channel modelling in the millimetre-wave band and its impact on the transmission performance of a mobile radio communication system intended to support the range of services envisioned for the B-ISDN. First, it is identified the appropriate frequency band to implement a mobile broadband system and/or a broadband wireless access for indoor environments. The millimetre-wave band has shown to be the most appropriate. After a theoretical characterisation of a linear time variant channels and a discussion concerning the advantages and disadvantages of deterministic and statistical models, a detailed mathematical description of the developed deterministic model is presented. This model is able to estimate the propagation channel impulse response in a given environment, taking into account the characteristics of the mobile and base station antennas. A site-specific analytical model, able to estimate the propagation channel transfer function, without the need of developing complex software packages, is also proposed. The comparison between the results of the models with experimental measurements in different environments, demonstrates the validation of the developed models. The influence of the cellular configuration, type of antennas and their characteristics (e.g. radiation patterns and polarisation) on the channel impulse response parameters is studied through the use of the simulator that implements the developed deterministic model, being the most appropriate configuration for each scenario also indicated. The impact of the propagation aspects, including the cellular configurations, on the transmission performance of a mobile broadband communications system is evaluated making use of adaptive equalisation and diversity techniques to mitigate the effects of the multipath propagation. Finally, results of Monte-Carlo simulation that allow to estimate the carrier bit rate in different environments based on the cellular configurations and equalisation effort are presented, as well as, a general method to estimate the carrier bit rate based on the channel time dispersion.
Junta Nacional de Investigação Científica e Tecnológica e PRAXIS XXI
Programa Doutoral em Engenharia Eletrotécnica

Tese de doutoramento em Psicologia, especialização em Psicologia Clínica, área temática de Psicologia da Família e Intervenção Familiar, apresentada à Faculdade de Psicologia e de Ciências da Educação da Universidade de Coimbra
Introdução: O nascimento do primeiro filho em idade materna avançada (IMA, ≥ 35 anos) é uma tendência reprodutiva cada vez mais comum na maioria dos países da Europa. Além de constituir uma preocupação social e de saúde emergente, este comportamento reprodutivo é complexo e associa-se a desafios e recursos específicos que podem conferir contornos particulares às mudanças potencialmente indutoras de stress que a transição para a parentalidade comporta. Com base numa perspetiva desenvolvimental e ecológica e no contributo específico dos modelos traços-desejos-intenções-comportamentos e de stress familiar, esta investigação teve como objetivos gerais conhecer os antecedentes do nascimento do primeiro filho em IMA e compreender o processo de adaptação dos casais nesta fase do ciclo de vida, desde o terceiro trimestre de gravidez até aos seis meses de vida do bebé. Metodologia: Esta investigação baseou-se num desenho prospetivo longitudinal, composto por quatro momentos de avaliação: diagnóstico pré-natal, terceiro trimestre de gravidez, um mês e seis meses após o parto. Dos 128 casais colaboraram no momento do diagnóstico pré-natal, 58 participaram em todos os momentos de avaliação. Foi igualmente constituído um grupo de controlo, composto por casais que experienciaram a transição para a parentalidade em idades maternas mais jovens (20-34 anos). Além de dados sociodemográficos e clínicos, foi recolhida informação acerca dos antecedentes motivacionais da gravidez (motivações para a parentalidade e perceções acerca do seu momento) e do conhecimento acerca dos riscos reprodutivos relacionados com a idade materna. Foram igualmente avaliados os recursos dos casais (competências pessoais e recursos sociais) e a sua adaptação individual (sintomatologia psicopatológica e qualidade de vida), conjugal (ajustamento diádico) e parental (dificuldade, competência e gratificação parental). Resultados: Destacamos os seguintes resultados: 1) o nascimento do primeiro filho em IMA enquadrou-se num contexto profissional mais estável do que em idades mais jovens mas associou-se a percursos conjugais e reprodutivos mais complexos que coexistem com fortes lacunas no conhecimento acerca dos riscos relacionados com a idade materna; 2) embora os casais tenham atribuído menor importância à parentalidade (nomeadamente aos benefícios para a realização pessoal e relação conjugal) em IMA, os fatores mais influentes no planeamento (desejo partilhado de ter filhos e relação certa, independência e segurança financeira) e na satisfação com o momento da gravidez (expectativas sociais e licença parental, problemas de saúde reprodutiva) foram semelhantes em ambas as faixas etárias; 3) porém, o momento da parentalidade foi menos satisfatório em IMA e cerca de metade dos casais referiu que gostaria que a gravidez atual tivesse ocorrido mais cedo; 4) foram identificados dois perfis de casais que experienciaram a parentalidade em IMA (com ou sem história de infertilidade) cujos percursos se associam a diferentes padrões motivacionais (realista ou desligado) face à parentalidade; 5) a adaptação individual, conjugal e parental dos casais de ambas as faixas etárias foi comparável ao longo do tempo mas os casais com história de infertilidade descreveram mais dificuldades de adaptação parental no pós-parto imediato em IMA; 6) embora as semelhanças e diferenças de género tenham sido comparáveis em ambas as faixas etárias, o conhecimento dos homens acerca dos riscos influenciou a adaptação de ambos os membros dos casais durante a gravidez em IMA e as competências pessoais masculinas revestiram-se de maior relevância para a sua adaptação no pós-parto imediato nesta fase do ciclo de vida. Conclusões: Estes resultados sublinham que o nascimento do primeiro filho em IMA é um comportamento reprodutivo pouco informado e resulta de uma diversidade de influências que nem sempre estão sob o controlo dos casais e nem sempre possibilitam que o momento da parentalidade seja congruente com as suas preferências. As políticas sociais e de saúde devem ser ajustadas, de modo a minimizar os obstáculos à concretização mais precoce do projeto de parentalidade e a promover decisões informadas acerca do seu momento. Durante a transição para a parentalidade, os profissionais de saúde devem reconhecer que a adaptação em IMA é comparável àquela que se verifica em idades mais jovens e que a sua variabilidade depende dos percursos conducentes à sua ocorrência e dos recursos dos casais. As especificidades da experiência masculina em IMA devem ser objeto de investigação futura e de atenção por parte dos profissionais de saúde. As intervenções psicoeducativas focadas no casal podem facilitar a adaptação à transição para a parentalidade nas diferentes faixas etárias e constituir-se como um contexto privilegiado para a identificação de casais com maior risco de inadaptação e/ou com dificuldades suscetíveis de legitimar uma intervenção psicológica estruturada.
Background: First childbirth at advanced maternal age (AMA, ≥ 35 years) is an increasing reproductive trend in most European countries. Beyond being an emerging social and health concern, this reproductive behaviour is complex and has been associated with specific challenges and resources that may influence the stressful nature of the changes related to the transition to parenthood. Based on a developmental and ecological approach and on the specific contribution of traits-desires-intentions-behaviours and family stress models, this study aimed to clarify the antecedents of first childbirth at AMA and to understand couples’ adaptation at this stage of the lifecycle, from the third trimester of pregnancy to six months post-birth. Methods: This study was based on a longitudinal prospective design with four assessment times: prenatal diagnosis, third trimester of pregnancy, one and six months post-birth. From the 128 couples who collaborated at the timing of prenatal diagnosis, 58 participated in all assessment times. A comparison group (couples who experienced the transition to parenthood at younger maternal ages, that is, between 20 to 34 years) was also recruited. Beyond sociodemographic and clinical data, information was gathered on motivational antecedents of pregnancy (childbearing motivations and perceptions about the timing of childbearing) and on knowledge about maternal age-related risks. Couples’ resources (personal competences and social resources) and individual (psychopathological symptoms and quality of life), marital (dyadic adjustment) and parental (parental difficulty, competence and gratification) were also assessed. Results: We highlight the following findings: 1) first childbirth at AMA occurred in a more stable professional context than at younger maternal ages but was related to more complex marital and reproductive trajectories that coexisted with knowledge gaps on maternal age-related risks; 2) although couples attributed less importance to parenthood at AMA (namely to its benefits for personal fulfillment and marital relationship), the factors that had a higher influence on the planning (shared desire to have children and suitable relationship, independence and financial security) and on the satisfaction with the timing of childbearing (social expectations and parental leave, reproductive health problems) were similar at both age ranges; 3) however, the timing of childbearing was less satisfactory at AMA e nearly half of the couples would have liked that the current pregnancy has occurred earlier; 4) two profiles of couples who experienced parenthood at AMA were identified (with or without infertility history) whose trajectories were associated with different motivational patterns (realistic or disengaged) towards childbearing; 5) the individual, marital and parental adaptation of couples was comparable at both age ranges across time but couples with infertility history described more difficulties in the adaptation to the parental role during early postpartum at AMA; 6) although the gender similarities and differences were comparable at both age ranges, men’s risk knowledge influenced the adaptation of both members of the couples at AMA and male personal competences were more relevant for their adaptation during early postpartum at this stage of the lifecycle. Conclusions: These findings highlight that first childbirth at AMA is a relatively uninformed reproductive behaviour and results from a diversity of influences that are sometimes beyond couples’ control, so that the timing of childbearing is not always congruent with their preferences. Social and health policies should be adjusted to minimize the barriers that inhibit the earlier consecution of the childbearing project and to promote informed decisions about its timing. During the transition to parenthood, healthcare providers should recognize that the adaptation is comparable at AMA and at younger maternal ages and that its variability depends on the trajectories that precede its occurrence and on couples’ resources. The specificities of men’s experience at AMA should be better investigated and should deserve the attention from healthcare providers. Couple-focused psychoeducative interventions may ease the adaptation to the transition to parenthood at different age ranges and may be a privileged context for the identification of couples at higher risk of adaptation difficulties and/or who face difficulties that may deserve a structured psychological intervention.
FCT - SFRH/BD/68912/2010