This thesis present a new receiver framework for the cyclic-prefix free (CP-free) MIMO-OFDM system, equipped with the space-time block coded (ST-BC) uplink transmission over (slowly) time varying multipath channels. Usually, without CP in the OFDM system the inter-carrier interference (ICI) could not be removed, effectively, at the receiver, when the inter-symbol-interference (ISI) has to be taken into account. In this thesis, by exploiting the spatial and frequency resources, we propose a novel frequency-domain decision-feedback equalizer, associated with the oblique projection (OB), to combat the effects of ISI and ICI, simultaneously. The OB is a non-orthogonal projection and is very useful to deal with the structure noise (e.g., the ISI term). From computer simulations, we observe that the performance of propose scheme can perform very close to the conventional CP-based MMO-OFDM with the ST-BC.

As the Internet becomes the ubiquitous infrastructure for various applications, demands on the reliability, availability and security of routing protocols in the Internet are becoming more stringent. Unfortunately, failures are still common in the daily operation of a network. Service disruption for even a short time can seriously affect the quality of real-time applications, such as VoIP and video on demand applications. Moreover, critical business and government applications require routing protocols to be robust against malicious attacks, such as denial of Service attacks. This dissertation proposes three techniques to address some reliability and security concerns in intra-domain (distance vector) routing protocols and inter-domain (path vector) routing protocols. The first technique addresses the problem of service disruption that arises from sudden link failures in distance vector routing protocols. We consider two types of link failures: single link failures and shared risk link group failures. For single link failures, we propose an IP fast reroute mechanism to reroute packets around the failed links. This fast reroute mechanism is the first that does not require complete knowledge of the network topology and does not require changing of the original routing protocol. This mechanism proactively computes a set of relay nodes that can be used to tunnel the rerouted packets immediately after the detection of a link or node failure. The mechanism includes an algorithm for a node to automatically identify itself as a candidate relay node for a reroute link and notify the source node of the reroute link of its candidacy. The source node can then decide the validity of a candidate relay node. The mechanism also includes an algorithm to suppress redundant notification messages. We then extend our IP fast reroute mechanism for single link failures to accommodate shared risk link group failures. We achieve this goal by introducing one more bit information. Through simulations, I show that the proposed mechanisms succeed in rerouting around failed links about 100% of the time, with the length of the reroute path being comparable to the length of the re-converged shortest path. The second technique addresses the problem that arises from allowing any node to route data packets to any other node in the network (and consequently allow any adversary node to launch DoS attacks against other nodes in the network). To solve this problem, we propose a blocking option to allow a node u to block a specified set of nodes and prevent each of them from sending or forwarding packets to node u. The blocking option intends to discard violating packets near the adversary nodes that generated them rather than near their ultimate destinations. We then discuss unintentionally blocked nodes, called blind nodes and extend the routing protocols to allow each node to communicate with its blind nodes via some special nodes called joint nodes. Finally, I show, through extensive simulation, that the average number of blind nodes is close to zero when the average number of blocked nodes is small. The third technique addresses the problem that arises when a set of malicious ASes in the Internet collude to hijack an IP prefix from its legitimate owner in BGP. (Note that none of previous proposals for protecting BGP against IP prefix hijacking is effective when malicious ASes can collude.) To solve this problem, we propose an extension of BGP in which each listed AS in an advertised route supplies a certified full list of all its peers. Then I present an optimization where each AS in an advertised route supplies only a balanced peer list, that is much smaller than its full peer list. Using real Internet topology data, I demonstrate that the average, and largest, balanced peer list is 92% smaller than the corresponding full peer list. Furthermore, in order to handle the dynamics of the Internet topology, we propose algorithms on how to issue certificates to reflect the latest changes of the Internet topology graph. Although the results in this dissertation are presented in the context of distance vector and path vector routing protocols, many of these results can be extended to link state routing protocols as well. / text

Cette thèse est une description des marqueurs verbaux de lètὲɣὲ (téké) langue bantu parlée au Gabon (B71a). Les marqueurs verbaux étudiés sont : le préfixe verbal (marque d’accord), le marqueur de négation kâ…ŋí, les particules énonciatives mâ et mí et la finale verbale. De nombreux linguistes bantouistes considèrent ce domaine d’étude (marqueurs verbaux) comme étant complexe, c’est le cas de Guarisma (2000). Le nombre de marqueurs verbaux en est une des raisons de cette complexité. Il est difficile d’assigner un rôle à certains morphèmes. Elle s’inscrit dans le cadre Théorique des Opérations Prédicatives et Enonciatives (TOPE), élaboré par Culioli et ses collaborateurs, voir Culioli (1990,1999a). L’étude de ces morphèmes montre que chacun marque une opération linguistique spécifique. / This thesis is a description of verbal markers in lètὲɣὲ (Téké), a Bantu language spoken in Gabon (B 71a). The verbal markers studied are: the verbal prefix (mark of agreement), the negation marker kâ ... ŋí, the enunciating particles mâ and mí and the verbal final. Many Bantuist linguists consider this field of study (verbal markers) to be complex, as is the case with Guarisma (2000). The number of verbal markers is one of the reasons for this complexity. This work is conducted within the framework of the Theory of the Predicative and Enunciative Operations developed by Culioli (1990) and his collaborators. The enunciative study of these elements shows that each of them marks a specific linguistic operation.

A síntese de imagens com alta faixa dinâmica é uma prática cada vez mais comum em computação gráfica. O desafio consiste em relacionar o grande conjunto de intensidades da imagem sintetizada com um sub-conjunto muito inferior suportado por um dispositivo de exibição, evitando a perda de detalhes contrastivos. Os operadores locais de reprodução de tons (local tone-mapping operators) são capazes de realizar tal compressão, adaptando o nível de luminância de cada pixel com respeito à sua vizinhança. Embora produzam resultados significativamente superiores aos operadores globais, o custo computacional é consideravelmente maior, o que vem impedindo sua utilização em aplicações em tempo real. Este trabalho apresenta uma técnica para aproximar o operador fotográfico local de reprodução de tons. Todas as etapas da técnica são implementadas em GPU, adequando-se ao cenário de aplicações em tempo real, sendo significativamente mais rápida que implementações existentes e produzindo resultados semelhantes. A abordagem é baseada no uso de tabelas de áreas acumuladas (summed-area tables) para acelerar a convolução das vizinhanças, usando filtros da média (box-filter), proporcionando uma solução elegante para aplicações que utilizam imagens em alta faixa dinâmica e que necessitam de performance sem comprometer a qualidade da imagem sintetizada. Uma investigação sobre algoritmos para a geração de somatórios pré-fixados (prefix sum) e uma possível melhoria para um deles também são apresentada. / High dynamic range (HDR) rendering is becoming an increasingly popular technique in computer graphics. Its challenge consists on mapping the resulting images’ large range of intensities to the much narrower ones of the display devices in a way that preserves contrastive details. Local tone-mapping operators effectively perform the required compression by adapting the luminance level of each pixel with respect to its neighborhood. While they generate significantly better results when compared to global operators, their computational costs are considerably higher, thus preventing their use in real-time applications. This work presents a real-time technique for approximating the photographic local tone reproduction that runs entirely on the GPU and is significantly faster than existing implementations that produce similar results. Our approach is based on the use of summed-area tables for accelerating the convolution of the local neighborhoods with a box filter and provides an attractive solution for HDR rendering applications that require high performance without compromising image quality. A survey of prefix sum algorithms and possible improvements are also presented.

A síntese de imagens com alta faixa dinâmica é uma prática cada vez mais comum em computação gráfica. O desafio consiste em relacionar o grande conjunto de intensidades da imagem sintetizada com um sub-conjunto muito inferior suportado por um dispositivo de exibição, evitando a perda de detalhes contrastivos. Os operadores locais de reprodução de tons (local tone-mapping operators) são capazes de realizar tal compressão, adaptando o nível de luminância de cada pixel com respeito à sua vizinhança. Embora produzam resultados significativamente superiores aos operadores globais, o custo computacional é consideravelmente maior, o que vem impedindo sua utilização em aplicações em tempo real. Este trabalho apresenta uma técnica para aproximar o operador fotográfico local de reprodução de tons. Todas as etapas da técnica são implementadas em GPU, adequando-se ao cenário de aplicações em tempo real, sendo significativamente mais rápida que implementações existentes e produzindo resultados semelhantes. A abordagem é baseada no uso de tabelas de áreas acumuladas (summed-area tables) para acelerar a convolução das vizinhanças, usando filtros da média (box-filter), proporcionando uma solução elegante para aplicações que utilizam imagens em alta faixa dinâmica e que necessitam de performance sem comprometer a qualidade da imagem sintetizada. Uma investigação sobre algoritmos para a geração de somatórios pré-fixados (prefix sum) e uma possível melhoria para um deles também são apresentada. / High dynamic range (HDR) rendering is becoming an increasingly popular technique in computer graphics. Its challenge consists on mapping the resulting images’ large range of intensities to the much narrower ones of the display devices in a way that preserves contrastive details. Local tone-mapping operators effectively perform the required compression by adapting the luminance level of each pixel with respect to its neighborhood. While they generate significantly better results when compared to global operators, their computational costs are considerably higher, thus preventing their use in real-time applications. This work presents a real-time technique for approximating the photographic local tone reproduction that runs entirely on the GPU and is significantly faster than existing implementations that produce similar results. Our approach is based on the use of summed-area tables for accelerating the convolution of the local neighborhoods with a box filter and provides an attractive solution for HDR rendering applications that require high performance without compromising image quality. A survey of prefix sum algorithms and possible improvements are also presented.

A síntese de imagens com alta faixa dinâmica é uma prática cada vez mais comum em computação gráfica. O desafio consiste em relacionar o grande conjunto de intensidades da imagem sintetizada com um sub-conjunto muito inferior suportado por um dispositivo de exibição, evitando a perda de detalhes contrastivos. Os operadores locais de reprodução de tons (local tone-mapping operators) são capazes de realizar tal compressão, adaptando o nível de luminância de cada pixel com respeito à sua vizinhança. Embora produzam resultados significativamente superiores aos operadores globais, o custo computacional é consideravelmente maior, o que vem impedindo sua utilização em aplicações em tempo real. Este trabalho apresenta uma técnica para aproximar o operador fotográfico local de reprodução de tons. Todas as etapas da técnica são implementadas em GPU, adequando-se ao cenário de aplicações em tempo real, sendo significativamente mais rápida que implementações existentes e produzindo resultados semelhantes. A abordagem é baseada no uso de tabelas de áreas acumuladas (summed-area tables) para acelerar a convolução das vizinhanças, usando filtros da média (box-filter), proporcionando uma solução elegante para aplicações que utilizam imagens em alta faixa dinâmica e que necessitam de performance sem comprometer a qualidade da imagem sintetizada. Uma investigação sobre algoritmos para a geração de somatórios pré-fixados (prefix sum) e uma possível melhoria para um deles também são apresentada. / High dynamic range (HDR) rendering is becoming an increasingly popular technique in computer graphics. Its challenge consists on mapping the resulting images’ large range of intensities to the much narrower ones of the display devices in a way that preserves contrastive details. Local tone-mapping operators effectively perform the required compression by adapting the luminance level of each pixel with respect to its neighborhood. While they generate significantly better results when compared to global operators, their computational costs are considerably higher, thus preventing their use in real-time applications. This work presents a real-time technique for approximating the photographic local tone reproduction that runs entirely on the GPU and is significantly faster than existing implementations that produce similar results. Our approach is based on the use of summed-area tables for accelerating the convolution of the local neighborhoods with a box filter and provides an attractive solution for HDR rendering applications that require high performance without compromising image quality. A survey of prefix sum algorithms and possible improvements are also presented.

Cette thèse consiste en une description du Fang-Nzaman, langue bantoue parlée au Gabon en Afrique Centrale. Le travail présente la phonologie en commençant par l'identification des phonèmes, avec la mise en relief des paires minimales qui permettent d'opposer les phonèmes : /mb/ vs /b/ et de les classer comme unités distinctives. Le choix des oppositions qui sont présentées a été fait en fonction des éléments nécessaires à l'identification dans certaines positions. Pour les phonèmes, le lexème permet les oppositions dans les structures les plus usitées. Les phonèmes sont ainsi définis dans leur fonctionnement et dans leur classement.Les unités discrètes sont indispensables au fonctionnement de langues, mais les éléments majeurs suprasegmentaux de la prosodie que sont les tons dans le fang-nzaman le sont aussi. Ils sont répertoriés en tons ponctuels et tons modulés.L'organisation de ces unités a permis l'identification de différentes positions occupées par les catégories grammaticales ou lexicales dans le syntagme ; après la définition des éléments du système dans le cadre syntaxique, on a procédé à l'analyse des classes nominales. L'étude des catégories grammaticales permet également d'envisager la morphologie dans le cadre d'un paradigme nominal et dans un aperçu du paradigme verbal. Le paradigme nominal inventorie les indices de classe, les détermine à partir de trois critères, la forme du préfixe nominal, l'appariement des classes et les accords de classe. La langue permet aussi d'étudier le fonctionnement des indices de classe avec les pronoms dans les énoncés. / This thesis is a description of Fang-Nzaman, a Bantu language spoken in Gabon, in Central Africa. This work identifies the phonemes of Fang-Nzaman, highlighting the existence of minimal pairs opposing the phonemes /mb/ and /b/, which shows that they are distinctive units.The oppositions presented were chosen according to the representativeness of the elements necessary to identification in certain positions. For phonemes, the lexeme allows for oppositions in the most commonly used structures. Phonemes are thus defined in terms of their behaviour and their classification.Discrete units are key to the understanding of languages, but major suprasegmental elements of prosody, such as the tones of Fang-Nzaman, are also crucial. They are classified into punctual tones and contour tones.The organization of those units has made it possible to identify the various positions occupied by the grammatical or lexical categories in the syntactic unit and to define the elements of the system within a syntactic framework, prior to the analysis of noun classes.Thus, the study of grammatical categories makes it possible to analyze morphology in terms of a noun paradigm and, briefly, a verb paradigm. The noun paradigm lists the class affixes, identifying them on the basis of three criteria: form of the noun prefix, pairing and class inflection. The language also makes it possible to show how class affixes are used with pronouns in speech.

This diploma thesis takes a comprehensive look at the matter of prefixation in contemporary Spanish and it is therefore divided into two parts. In the first one, we occupy ourselves with the area of constructional morphology and tackle theoretical matters. From the more general topics of word formation we then proceed to prefixation itself which we then attempt to define and describe in more detail. We outline the issues of concept delimitations, definition of prefixation, classification of prefixes and other controversial matters related to this process in the Spanish language. The second part of the thesis is of a more practical nature. There, we focus on the semantic meanings (locative and gradative) some prefixes may acquire. We then concentrate on specific prefixes (entre-, inter-, sobre-, super-), their distribution among word classes, and finally, using InterCorp, a parallel language corpus, we study Czech equivalents of selected elements.

Cognitive radios are the radios which use spectrum licensed to other users. For this, they perform Radio Environment Analysis, identify the Spectral holes and then operate in those holes. We consider the problem of Spectrum Sensing in Cognitive Radio Networks. Our Algorithms are based on Sequential Change Detection techniques. In this work we have used DualCUSUM, a distributed algorithm developed recently for cooperative spectrum sensing. This is used by cognitive (secondary) nodes to sense the spectrum which then send their local decisions to a fusion center. The fusion center again sequentially processes the received information to arrive at the final decision. We show that DualCUSUM performs better than all other existing spectrum sensing algorithms. We present a generalized analysis of DualCUSUM and compare the analysis with simulations to show its accuracy. DualCUSUM requires the knowledge of the channel gains for each of the secondary users and the receiver noise power. In Cognitive Radio setup it is not realistic to assume that each secondary user will have this knowledge. So later we modify DualCUSUM to develop GLRCUSUM algorithms which can work with imprecise estimates of the channel gains and receiver noise power. We show that the SNR wall problem encountered in this scenario by other detectors is not experienced by our algorithm. We also analyze the GLRCUSUM algorithms theoretically. We also apply our algorithms for detecting the presence of the primary in an Orthogonal Frequency Division Multiplexing (OFDM) setup. We first consider the Cyclic Prefix (CP) detector, which is considered to be robust to uncertainties in noise power, and further modify the CPdetector to take care of some of the common impairments like Timing offset, Frequency offset and IQ imbalance. We further modify the CPdetector to work under frequency selective channel. We also consider the energy detector under different impairments and show that the sequential detection based energy detectors outperform cyclic prefix based Detectors.

Cette thèse étudie la problématique de l’indexation et de la recherche dans les tables de hachage distribuées –Distributed Hash Table (DHT). Elle propose un système de stockage distribué des résumés de documents en se basant sur leur contenu. Concrètement, la thèse utilise les Filtre de Blooms (FBs) pour représenter les résumés de documents et propose une méthode efficace d’insertion et de récupération des documents représentés par des FBs dans un index distribué sur une DHT. Le stockage basé sur contenu présente un double avantage, il permet de regrouper les documents similaires afin de les retrouver plus rapidement et en même temps, il permet de retrouver les documents en faisant des recherches par mots-clés en utilisant un FB. Cependant, la résolution d’une requête par mots-clés représentée par un filtre de Bloom constitue une opération complexe, il faut un mécanisme de localisation des filtres de Bloom de la descendance qui représentent des documents stockés dans la DHT. Ainsi, la thèse propose dans un deuxième temps, deux index de filtres de Bloom distribués sur des DHTs. Le premier système d’index proposé combine les principes d’indexation basée sur contenu et de listes inversées et répond à la problématique liée à la grande quantité de données stockée au niveau des index basés sur contenu. En effet, avec l’utilisation des filtres de Bloom de grande longueur, notre solution permet de stocker les documents sur un plus grand nombre de serveurs et de les indexer en utilisant moins d’espace. Ensuite, la thèse propose un deuxième système d’index qui supporte efficacement le traitement des requêtes de sur-ensembles (des requêtes par mots-clés) en utilisant un arbre de préfixes. Cette dernière solution exploite la distribution des données et propose une fonction de répartition paramétrable permettant d’indexer les documents avec un arbre binaire équilibré. De cette manière, les documents sont répartis efficacement sur les serveurs d’indexation. En outre, la thèse propose dans la troisième solution, une méthode efficace de localisation des documents contenant un ensemble de mots-clés donnés. Comparé aux solutions de même catégorie, cette dernière solution permet d’effectuer des recherches de sur-ensembles en un moindre coût et constitue est une base solide pour la recherche de sur-ensembles sur les systèmes d’index construits au-dessus des DHTs. Enfin, la thèse propose le prototype d’un système pair-à-pair pour l’indexation de contenus et la recherche par mots-clés. Ce prototype, prêt à être déployé dans un environnement réel, est expérimenté dans l’environnement de simulation peersim qui a permis de mesurer les performances théoriques des algorithmes développés tout au long de la thèse. / This thesis examines the problem of indexing and searching in Distributed Hash Table (DHT). It provides a distributed system for storing document summaries based on their content. Concretely, the thesis uses Bloom filters (BF) to represent document summaries and proposes an efficient method for inserting and retrieving documents represented by BFs in an index distributed on a DHT. Content-based storage has a dual advantage. It allows to group similar documents together and to find and retrieve them more quickly at the same by using Bloom filters for keywords searches. However, processing a keyword query represented by a Bloom filter is a difficult operation and requires a mechanism to locate the Bloom filters that represent documents stored in the DHT. Thus, the thesis proposes in a second time, two Bloom filters indexes schemes distributed on DHT. The first proposed index system combines the principles of content-based indexing and inverted lists and addresses the issue of the large amount of data stored by content-based indexes. Indeed, by using Bloom filters with long length, this solution allows to store documents on a large number of servers and to index them using less space. Next, the thesis proposes a second index system that efficiently supports superset queries processing (keywords-queries) using a prefix tree. This solution exploits the distribution of the data and proposes a configurable distribution function that allow to index documents with a balanced binary tree. In this way, documents are distributed efficiently on indexing servers. In addition, the thesis proposes in the third solution, an efficient method for locating documents containing a set of keywords. Compared to solutions of the same category, the latter solution makes it possible to perform subset searches at a lower cost and can be considered as a solid foundation for supersets queries processing on over-dht index systems. Finally, the thesis proposes a prototype of a peer-to-peer system for indexing content and searching by keywords. This prototype, ready to be deployed in a real environment, is experimented with peersim that allowed to measure the theoretical performances of the algorithms developed throughout the thesis.