Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2016-01-07T11:52:34Z No. of bitstreams: 2 Dissertacao - Darlyene Iviane da Costa Silva - 2015.pdf: 1555899 bytes, checksum: 72e56fb2419fd904a02d289126b62c0c (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-01-08T06:36:09Z (GMT) No. of bitstreams: 2 Dissertacao - Darlyene Iviane da Costa Silva - 2015.pdf: 1555899 bytes, checksum: 72e56fb2419fd904a02d289126b62c0c (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-01-08T06:36:09Z (GMT). No. of bitstreams: 2 Dissertacao - Darlyene Iviane da Costa Silva - 2015.pdf: 1555899 bytes, checksum: 72e56fb2419fd904a02d289126b62c0c (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-08-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The full-time school‟s expansion in Brazil, legitimized by various legal documents and juridical orders, set up an educational reform that has instigated constant studies and debates. The research that is presented in this dissertation, belongs to the research‟s line of “Fundaments of the Processes Educationals” and intent to address this issue with the perspective to learn the relations‟ specificity established in between time, space and pedagogical processes in four full-time public schools in Goiania and their possible consequences for teaching and learning. It is a study of comparative cases of Qualiquantitative nature which had as its main research tools: the political-pedagogical projects‟ analysis of the surveyed institutions; observations made on site in groups B and C of cycle I of each school; and analysis of the presented results by each group in diagnostic evaluations of writing appropriation, performed by the Evaluation and Research Center – NAP – of the City Department of Education in the first and second semester of 2014. The reflections made had as theoretical support, recent studies and research that discuss the issue in question (PARO, 1988; CAVALIERE, 2009; SANTOS, 2009; NUNES, 2011; SILVA, 2011 MAURICIO, 2013; among others) and also the studies that discuss about the educational reforms emerged in a political, economic, social and cultural context marked by a productive restructuring process that redefines, among others, the world relations of work, economics, politics, and education in which the school full-time is inserted (GENTILI, 1992; HARVEY, 1992; ARELARO 2000 ; CARVALHO, 2009; FRIGOTTO, 2010; SHIROMA; MORAES; EVANGELISTA, 2011; and others). The investigation determined that the extended daily journey, the spaces‟ reorganization inside the school and the extras activities that take place in the extra times (food, rest and workshops components of diversified curriculum) compose the specificities that belongs to the researched full time schools. It was observed that the absence of adequate space to meet the demands that emerge in expanded time, such as cafeteria, a rest room with conditions for body hygienization, such as bathing, themed rooms suitable for the workshops‟ development, among others, were revealed as one of the main challenges faced. Improving the conditions to ensure proper staying of students in school for more than eight hours proves to be so very important. Among the challenges faced in relation to space, resources, collective planning of difficulty for the achievement of a coordinated work between the knowledge, training, among others, the workshops revealed multiple possibilities potentiating the teaching-learning process to: 1) demonstrate to prosecute a complementary work to the regular disciplines of common national basis‟ curriculum, assisting in the contents‟ development exploited in them; 2) propose diversified contents that constitute the school news; 3) make possible more study time for some skills that were worked in a lightened form among many other content and activities developed by the school; 4) and propitiate classes conducted by teachers who use favorable relations to teaching and learning. / A expansão da escola de tempo integral no Brasil, legitimada por diversos documentos e ordenamentos jurídicos, configura uma reforma educacional que tem instigado constantes estudos e debates. A pesquisa que se apresenta na presente dissertação, inserida na linha de pesquisa “Fundamentos dos Processos Educativos”, objetiva abordar a temática da escola de tempo integral tendo em perspectiva apreender a especificidade das relações estabelecidas entre tempo, espaço e processos pedagógicos imbricados em quatro escolas de tempo integral da Rede Municipal de Educação em Goiânia e seus possíveis desdobramentos para o ensino-aprendizagem. Trata-se de um estudo de casos comparativos de natureza qualiquantitativa que contou como principais instrumentos de investigação: a análise dos Projetos Político-Pedagógicos das instituições pesquisadas; observações realizadas in loco nos agrupamentos B e C do ciclo I de cada escola; e análise dos resultados apresentados por cada agrupamento nas avaliações diagnósticas de apropriação escrita realizadas pelo Núcleo de Avaliação e Pesquisa – NAP – da Secretaria Municipal de Educação no primeiro e segundo semestre do ano de 2014. As reflexões tecidas tiveram como aporte teórico, recentes estudos e pesquisas que discutem a temática em questão (PARO, 1988; CAVALIERE, 2009; SANTOS, 2009; NUNES, 2011; SILVA, 2011, MAURICIO, 2013; entre outros) e também os estudos que discorrem sobre as reformas educacionais emergidas em um contexto político, econômico, social e cultural marcado por um processo de reestruturação produtiva que redefine, entre outras, as relações no mundo do trabalho, da economia, da política, e da educação na qual a escola de tempo integral está inserida (GENTILI, 1992; HARVEY, 1992; ARELARO, 2000; CARVALHO, 2009; FRIGOTTO, 2010; SHIROMA; MORAES; EVANGELISTA, 2011; e outros). A investigação definiu que a jornada diária ampliada, a reorganização dos espaços no interior da escola e as atividades que se realizam a mais no tempo que se tem a mais (alimentação, descanso e oficinas componentes do currículo diversificado) constituíram as especificidades inerentes às escolas de tempo integral pesquisadas. Observou-se que a ausência de espaços adequados para o atendimento das demandas que emergem no tempo ampliado como refeitório, ambiente para descanso com condições para higienização do corpo como banho, salas temáticas apropriadas para o desenvolvimento das oficinas realizadas, entre outros, se revelaram como um dos principais desafios enfrentados. A melhoria das condições para garantir a adequada permanência dos alunos na escola por mais de oito horas diárias revela-se assim de suma importância. Em meio aos desafios enfrentados em relação ao espaço, recursos, dificuldade de planejamento coletivo para realização de um trabalho articulado entre os conhecimentos, formação, entre outros, as oficinas revelaram múltiplas possibilidades potencializadoras do processo de ensino-aprendizagem ao: 1) demonstrarem exercer um trabalho complementar as disciplinas regulares do currículo de base nacional comum, auxiliando no desenvolvimento dos conteúdos explorados nelas; 2) proporem conteúdos diversificados que se constituem em novidades da escola; 3) possibilitarem mais tempo de estudo para alguns conhecimentos que antes eram trabalhados de forma aligeirada em meio a tantos outros conteúdos e atividades desenvolvidos pela escola; 4) e propiciarem aulas conduzidas por professores que empregam relações favoráveis ao ensino-aprendizagem.

Nesta pesquisa procuramos estabelecer as bases teóricas e práticas da Internacional Situacionista e de dois de seus principais teóricos, Guy Debord e Raoul Vaneigem. Para aprofundar a compreensão, fomos em busca das origens desse grupo no Letrismo, na Internacional Letrista e Movimento por uma Bauhaus Imaginista, em uma tentativa de estabelecer uma trajetória. O início, no Letrismo, se estabelece como vanguarda artística, para logo quebrar com a perspectiva de uma proposta estética e realizar um aprofundamento de caráter marxista na crítica à cultura e ao urbanismo, na forma metodológica do desvio e da deriva e na construção de situações, a partir dos anos da Internacional Letrista. O processo de Decomposição da cultura faz com que alguns grupos se reúnam em uma nova internacional, desta vez Situacionista, com uma proposta inicial de revolução cultural, na e contra Decomposição. O envolvimento de Guy Debord com outros teóricos marxistas como Henri Lefebvre, radicaliza uma crítica da vida cotidiana e tira do foco uma discussão sobre cultura. O resultado é desenvolvimento do conceito de espetáculo, forma mais desenvolvida da sociedade produtora de mercadorias, e a centralização da questão do fetiche na crítica. Uma possibilidade de debate entre uma práxis revolucionária da vida cotidiana e a centralidade do fetiche da mercadoria nos parece necessária no momento atual da Geografia. / This research sought to establish the theoretical and practical bases of the Situationist International and two of its leading theorists, Guy Debord and Raoul Vaneigem. To deepen understanding, we were in search of the origins of this group in Lettrism, Lettrist International and the International Movement for an Imaginist Bauhaus, in an attempt to establish a trajectory. The beginning, in Lettrism, establishes himself as the artistic vanguard, soon to break with the prospect of an aesthetic proposal and make a deeper exploration in the marxist ideas, in order to make a critique of culture and urbanism with the methodological form of the detournement, the dérive and the construction of situations, since the years of the Lettrist International. The process of Decomposition of the culture causes some groups to join in a new International, Situationist this time, with an initial proposal of cultural revolution, inside and against Decomposition. Guy Debord\'s involvement with other marxist theorists such as Henri Lefebvre, the radical critique of everyday life takes the focus from the discussion about culture. The result is the development of the concept of spectacle, most developed form of commodity-producing society, and centered on the critical question of the fetish. A possibility for discussion between a revolutionary praxis of everyday life and the centrality of the fetish seems necessary at this moment in Geography.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-27T15:09:07Z No. of bitstreams: 1 brunogoncalves.pdf: 703613 bytes, checksum: d575219a1a60c3df43cb9c15e5bc8fd8 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-07T21:05:05Z (GMT) No. of bitstreams: 1 brunogoncalves.pdf: 703613 bytes, checksum: d575219a1a60c3df43cb9c15e5bc8fd8 (MD5) / Made available in DSpace on 2017-08-07T21:05:05Z (GMT). No. of bitstreams: 1 brunogoncalves.pdf: 703613 bytes, checksum: d575219a1a60c3df43cb9c15e5bc8fd8 (MD5) Previous issue date: 2010-03-15 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / A tese está composta de duas partes principais. Na primeira parte, o férmion de Dirac foi considerado interagindo com diferentes campos externos. Uma abordagem extremamente eficiente para se extrair informações físicas da Hamiltoniana, é fazer uma transformação Foldy-Wouthuysen nela. Além da transformação Foldy-Wouthuysen perturbativa, existe a versão exata, que não é baseada em séries de potências no parâmetro 1/m. Nesta tese foi desenvolvida uma maneira de se fazer a transformação Foldy-Wouthuysen exata com os campos de interesse. Foi tomado o campo espinorial de Dirac no fundo de ondas gravitacionais e um campo magnético constante. A Hamiltoniana transformada mostra que o efeito da onda gravitacional no campo espinorial e na correspondente partícula pode ser, em princípio, intensificado por um campo magnético suficientemente forte. Cálculos análogos foram realizados para a componente temporal do campo de torção gravitacional. Além disso, foi feita uma classificação geral dentre os possíveis termos que violam as simetrias CPT e Lorentz, selecionando aqueles que admitem esta transformação. Foi desenvolvida uma nova abordagem para estudar, qualitativamente, os casos para os quais a transformação exata não é permitida. Esta técnica foi chamada de transformação semi-exata. A vantagem desta técnica em relação à transformação padrão é de ser muito mais econômica na parte de cálculos. Como exemplo de aplicação foram considerados os casos de campo elétrico externo e a parte vetorial do campo de torção gravitacional. Na segunda parte da tese, foram calculadas as correções de um laço para o setor do fóton da eletrodinâmica quântica no fundo de um campo gravitacional. O cálculo foi realizado utilizando a técnica do "heat-kernel"de duas maneiras diferentes e uma nova ambiguidade nos resultados foi encontrada. Este resultado representa o primeiro exemplo conhecido da chamada anomalia multiplicativa. Realizando os cálculos para diferentes dimensões do espaço-tempo, encontramos uma explicação qualitativa desta anomalia. Além dos fatores de forma não-locais do campo eletromagnético, foi calculada a função beta de um laço física, que descreve a variação desta grandeza em relação à energia do processo e é válida para todas as escalas de energia. Usando esta função beta encontramos a forma mais completa do famoso teorema de Appelquist e Carazzone. / This thesis is composed by two main parts. On the first one, the Dirac fermion was considered interacting with different external fields. A very efficient approach to extract physical information from the Hamiltonian is to perform a Foldy-Wouthuysen transformation on it. There are, on the literature, two versions of this transformation. The standard and the exact ones. The main difference between them is that the last is not based on a power series low in the parameter l/m. On this thesis, we developed a method to perform the exact Foldy-Wouthuysen with the fields of interest. The Dirac field was described in a constant magnetic field plus gravitational wave background. The transformed Hamiltonian shows that the effect of the gravitational wave on the magnetic field could be, in principle, enforced by a sufficient strong magnetic field. Similar calculations was performed to the temporal component of the gravitational torsion field. Furthermore, it was done a general classification of the possible terms the violate the CPT and Lorentz symmetries, selecting those of them wich allow the exact transformation. A new approach to qualitatively study the cases for wich this kind of transformation is not allowed, was developed. This technique was called semi-exact transformation and has the advantage to the standard transformation of being much more economic in the calculations part. As examples of application it was considered the cases of external electric field and the vectorial component of the torsion gravitational field. On the second part of the thesis, it was calculated the one loop quantum corrections to the photon sector of the quantum electrodynamics in a gravitational background. The calculation was done using the "heat-kernel" technique in two different ways and an ambiguity on the results was found. This fact represents the first known example of the so called multiplicative anomaly. The calculations were performed to different space-time dimensions and a qualitative explanation of this anomaly was found. The non local formfactors to the electromagnetic field was obtained and also the one loop complete beta function, that describes the energy variation of it in relation to the energy of the process and it is valid to all energy scales. Using this beta function, the more complete form of the famous Appelquist e Carazzone theorem was obtained.

We live in an information hungry age, we generate and process information at a rate never before recorded in the history of mankind. Today’s computing platforms are run on Gigahertz multi-core processors churning out Gigabits streams of data that need to be transmitted as quickly as possible. Often times the source and the destination are mobile which means wired connections are not a choice. This has led to an ever increasing need to develop wireless access technologies that support high throughput regardless of the transmission environment. Till date, many proprietary solutions exist that seek to bridge this gap with little or no support for interoperability. For the sheer scale of development that is required, a standard based solution is the key. The IEEE 802.1x committee oversees the development of standards for wireless systems, it formed the 802.16 working group to develop a standards-based Wireless Metropolitan Area Network (MAN) solution. One of the fruits of this effort is the 802.16e standard fondly referred to as mobile WiMAX and it is the subject of study in this thesis. This thesis seeks to analyze the transmission characteristics of two of the antenna systems defined in the standard i.e. Adaptive Beamforming Systems and Multiple-Input Multiple-Output Systems. Multiple-Input Multiple-Output (MIMO): utilizes multiple antennas at the transmitter and receiver to provide diversity gain, multiplexing gain or both. Adaptive Antenna Systems (AAS): Adaptive array system uses an antenna array to generate in real-time radiation patterns with the main lobes and/or nulls dynamically tuned to specific directions in order to increase or suppress signal power in that direction. / Worldwide Interoperability for Microwave Access (WiMAX) is the acronym for Institute of Electrical and Electronics Engineers (IEEE) 802.16 set of standards governing Air Interface for Fixed Broadband Wireless Access Systems. In the history of wireless systems, WiMAX is revolutionary technology as affords its users the Wi-Fi grade throughput and cellular system level of mobility. With WiMAX, broadband technology (traditionally ADSL and Fiber) goes wireless and WiMAX users can basically enjoy triple-play application, and split-second download and upload rates. WIMAX also offers full mobility much as traditional cellular systems do with features like seamless hand-over and roaming at vehicular speed; this is made possible because the system design covers the access network to core network. For the operator, WiMAX is a welcome development because it merges traditional cellular networks with broadband technology thus opening them to more business offerings and a larger client base and all this at a reduced cost of deployment. Base stations are comparatively cheaper and do not require extensive planning typical of other cellular systems thus WiMAX is aptly suited for emerging markets where infrastructure cost is a major issue; little wonder a lot of 3rd world countries have signified interest in the technology.

Abstract The thesis is an investigation into the spatio-temporal knowledge creation of international research groups. Knowledge is spatial: it is created in geographical places, shared in communicative space and analyzed in the cognitive space of the mind. Knowledge is a process that evolves in the interactions and interpretations of people. It is created in the tempo of working days that is experienced as flowing or disrupted time. These dimensions of spaces and times come together as the contexts of knowledge creation. In current internationalizing universities, work groups increasingly consist of members from different countries and with varying professional backgrounds. In their endeavor to create globally renowned results, the international research groups are both challenged and enabled by their diversity. Multiple views can benefit the creation of novelty, but reaching a common understanding in a diverse group might not be easy. Current research calls for a more detailed understanding of the processes and contexts of knowledge creation in international groups. The empirical part of the thesis is comprised of two case study compilations. Case A focuses on the University of Oulu, with its foreign employees and three international research groups from the humanist, scientific and technical fields. Four international research groups from the fields of science and technology, led by top foreign professors and funded by the Finland Distinguished Professor Programme, form case B. Altogether, the main materials include 37 interviews, 123 weekly diaries, observation and a survey (67 replies). The main methods applied are mental mapping, discourse analysis and content analysis. According to the results, knowledge creation is a complex spatio-temporal process that often leads to unexpected results. Processes of interaction and interpretation enable the group to reach cognitive friction. This fertile ground of knowledge creation can be reached when a group possesses enough common understanding and enough diversity in their individual interpretations. Humanist, scientific and technical knowledges are created in multiple contexts through group-specific discourses. Knowledge itself is a spatio-temporal process of stages, flows and disruptions towards the not-yet-known. Knowledge is inseparable from individuals, groups, the processes and contexts of creation. / Tiivistelmä Väitöskirjassa tarkastellaan tiedon jalostamista tilassa ja ajassa kansainvälisissä tutkimusryhmissä. Tieto on tilallista: sitä jalostetaan maantieteellisissä paikoissa, jaetaan kommunikaation tilassa ja analysoidaan mielen kognitiivisessa tilassa. Tieto on prosessi, jota ihmiset jalostavat vuorovaikutuksen ja tulkinnan kautta. Tietoa jalostetaan aikarajojen ja työpäivien määrittelemässä ajassa, joka voi tuntua virtaavan tai pysähtelevän. Nämä tilan ja ajan ulottuvuudet yhdistyvät tiedon jalostamisen kontekstiksi. Kansainvälistyvissä yliopistoissa työryhmät koostuvat enenevissä määrin jäsenistä, jotka edustavat eri kansallisuuksia ja joiden ammatilliset taustat ovat erilaiset. Monimuotoisuus on sekä haaste että mahdollisuus ryhmien tavoitteelle luoda kansainvälisesti merkittäviä tuloksia. Monipuoliset näkökulmat voivat edesauttaa tiedon jalostamista, mutta yhteisymmärryksen muodostaminen ryhmässä voi olla haastavaa. Nykytutkimuksessa tarvitaan syvällisempää ymmärrystä tiedon jalostamisen prosesseista ja konteksteista kansainvälisissä ryhmissä. Väitöskirjan empiirinen osa sisältää kaksi tapaustutkimuskokonaisuutta. Tapaus A koskee Oulun yliopiston ulkomaalaisia työntekijöitä ja kolmea kansainvälistä tutkimusryhmää humanistiselta, luonnontieteelliseltä ja tekniseltä alalta. Tapauksen B muodostavat neljä kansainvälistä luonnontieteen ja tekniikan alan tutkimusryhmää, joiden johtajat ovat ulkomaalaisia huippuprofessoreita ja jotka ovat Finland Distinguished Professor -ohjelman rahoittamia. Yhteensä pääaineisto koostuu 37 haastattelusta, 123 viikkopäiväkirjasta, havainnoinnista ja kyselystä (67 vastausta). Aineiston käsittelyn päämenetelmät ovat mentaalikartta-, diskurssi- ja sisällönanalyysi. Tulosten mukaan tiedon jalostaminen on monimutkainen prosessi, joka usein johtaa odottamattomiin tuloksiin. Vuorovaikutuksen ja tulkitsemisen prosessit mahdollistavat kognitiivisen kitkan muodostumisen, joka on hedelmällinen maaperä tiedon jalostamiselle. Sen saavuttamiseksi ryhmässä tarvitaan riittävästi yhteisymmärrystä ja riittävästi monimuotoisuutta jäsenten yksilöllisissä tulkinnoissa. Humanistiset, luonnontieteelliset ja tekniset tiedot jalostetaan ryhmän sisäisissä diskursseissa monipuolisissa konteksteissa. Tieto on tilallinen ja ajallinen prosessi kohti toistaiseksi tietämätöntä. Tieto on erottamaton osa ihmisiä, ryhmiä ja jalostamisen prosesseja ja konteksteja.

Abstract Medium access control (MAC) in wireless ad hoc networks has received considerable attention for almost a couple of decades; however, there are still open problems which deserve thorough study in order to facilitate migration to the next generation broadband wireless communication systems. In ad hoc networks, a detected frame collision can be due to the so-called unreachability problem, where the destination station is situated either in the transmission or interference range of an emitting station and is unable to receive connection establishment frames from any of its neighboring stations. Unreachability might also be due to the inability of a radio station to respond to any connection establishment request, though when the unreachable station receives the connection establishment requests, however, it is prohibited from responding to the requests due to being situated in the interference range of the emitting neighbor. To investigate the impact of this problem, we have to be equipped with a proper analytical framework; therefore, as the first part of this thesis, a scalable framework called Parallel Space – Time Markov chain (PSTMC) is proposed, through which a finite load non-saturated ad hoc network can be easily modeled. At the first step, a single-hop ad hoc network is considered and the accuracy of the model is evaluated using extensive numerical results. Subsequently, the proposed framework is further extended to model multi-hop ad hoc networks. Several discussions are also given on how the framework can be deployed for an arbitrary network topology. One of the main key features of the PSTMC model is its remarkable scalability in modeling complex network configurations. In fact, it is shown that multi-hop ad hoc networks have bounded complexity in being modeled by the PSTMC framework due to its spectacular specifications. These features lead us to a powerful tool by which an arbitrary network topology can be studied. In addition, the proposed models clearly facilitate demonstrating the impact of the unreachability problem on the performance of multi-hop networks. The introduced framework shows how the unreachability problem degrades the achieved throughput and channel capacity by the contending radio stations depending on the deployed network topology. In the remainder of the thesis the unreachability problem in mobile ad hoc networks is tackled and a new MAC protocol to enhance the performance of the network is proposed. This MAC scheme is equipped with smart decision-making algorithms as well as adaptive management mechanisms to reduce the impact of the unreachability problem in single channel scenarios. Subsequently, the problem of concurrent radio resource management and contention resolution in multi-channel cognitive ad hoc networks is considered. In particular, a multi-channel technique for traffic distribution among a set of data channels without centralized control, which is enabled by a probabilistic channel selection algorithm as well as a multi-channel binary exponential backoff mechanism, is proposed. It is shown through simulations that the suggested scheme outperforms the existing MAC protocols in multi-channel environments as well as cognitive networks coexisting with primary users. A mathematical model is also introduced to study the performance of the multi-channel MAC protocol in a single-hop non-saturated wireless network.

Dans cette thèse, nous nous intéressons aux espaces temps dit globalement hyperboliques Cauchy compacts. Ce sont des espaces temps qui admettent une fonction, dite fonction temps de Cauchy, propre qui croit strictement le long des courbes causales inextensibles. Les niveaux de telles fonctions sont des hypersurfaces de type espace appelées hypersurfaces de Cauchy. La donnée d'une fonction temps définit naturellement une famille à 1-paramètres d'espaces métriques. Notre but est d'étudier le comportement asymptomatique de ces familles d'espaces métriques Il y a deux cas de figure à considérer : le premier étant le comportement asymptomatique dans le passé ; le deuxième est celui du comportement asymptomatique dans le futur. Plus de conditions géométriques sur l'espace temps et les fonctions temps à considérer seront nécessaires / In this thesis we're interested in globally hyperbolic Cauchy compact space-times. These are space-times that possess a proper function, called Cauchy time function, which ist strictly increasing along inextensible causal curves. A Cauchy time function defines naturally a 1-parameter family of metric spaces. One asks the natural and important question of the asymptomatic behaviour of this family with respect to the time : when time goes to 0 and when it goes towards infinity. Of course additional geometric condition on the space-ime and the time function will be necessary for a more appropriate study

Cette thèse étudie la technique dite de ‘Retournement Temporel’ afin d’améliorer l’efficacité énergétique des futurs réseaux mobiles d’une part, et réduire le coût des futurs terminaux mobiles, d’autre part. Le retournement temporel consiste à utiliser l’inverse temporel de la réponse impulsionnelle du canal de propagation entre un émetteur et un récepteur pour préfiltrer l’émission d’un signal de données. Avantageusement, le signal ainsi préfiltré est reçu avec une puissance renforcée (c’est la focalisation spatiale) et un écho principal qui est renforcé par rapport aux échos secondaires (c’est la compression temporelle). Lors d’une étape préalable d’apprentissage, l’émetteur estime le canal en mesurant un signal pilote provenant du récepteur. La focalisation spatiotemporelle n’est obtenue qu’à condition que la propagation demeure identique entre la phase d’apprentissage et la phase de transmission de données : c’est la condition de ‘réciprocité du canal’. De nombreux travaux montrent que la focalisation spatiale permet de réduire la puissance émise nécessaire pour atteindre une puissance cible au récepteur d’une part, et que la compression temporelle permet de réduire la complexité du récepteur nécessaire pour gérer l’effet des échos multiples, d’autre part. Cependant, les études sur la réduction de la complexité du récepteur se limitent à l’ultra large bande. Des travaux de cette thèse (basés sur des simulations et des mesures expérimentales) montrent que pour des bandes de fréquences plus typiques des futurs réseaux mobiles (fréquence porteuse à 1GHz et spectre de 30 MHz à 100 MHz), grâce au retournement temporel, un récepteur simple et un signal monoporteuse suffisent pour atteindre de hauts débits. En outre, la condition de réciprocité du canal n’est pas vérifiée dans deux scénarios typiques des réseaux mobiles. Tout d’abord, dans la plupart des réseaux mobiles européens, le mode de duplex en fréquence est utilisé. Ce mode implique que l’émetteur et le récepteur communiquent l’un avec l’autre sur des fréquences porteuses distinctes, et donc à travers des canaux de propagations différents. De plus, lorsqu’on considère un récepteur sur un véhicule connecté en mouvement, l’émetteur et le récepteur communiquent l’un avec l’autre à des instants distincts, correspondants à des positions distinctes du véhicule, et donc à travers des canaux de propagations différents. Des travaux de cette thèse proposent des solutions pour obtenir la focalisation spatio-temporelle dans ces deux scenarios. Enfin, des travaux de la thèse explorent la combinaison du retournement temporel avec d’autres techniques de traitement de signal récentes (la modulation spatiale, d’une part, et une nouvelle forme d’onde multiporteuse, d’autre part), ou des scenarios de déploiement nouveaux (ondes millimétriques et très grands réseaux d’antennes pour inter-connecter les noeuds d’un réseau ultra dense) ou de nouvelles applications (guidage et navigation) envisageables pour les futurs réseaux mobiles. / This thesis studies the time reversal technique to improve the energy efficiency of future mobile networks and reduce the cost of future mobile devices. Time reversal technique consists in using the time inverse of the propagation channel impulse response (between a transceiver and a receiver) as a prefilter. Such pre-filtered signal is received with a stronger power (this is spatial focusing) and with a strong main echo, relatively to secondary echoes (this is time compression). During a previous learning phase, the transceiver estimates the channel by measuring the pilot signal emitted by the receiver. Space-time focusing is obtained only at the condition that the propagation remains identical between the learning phase and the data transmission phase: this is the ‘channel reciprocity’ condition. Numerous works show that spatial focusing allows for the reduction of the required transmit power for a given target received power, on the one hand, and that time compression allow for the reduction of the required complexity at the receiver side to handle multiple echoes, on the other hand. However, studies on complexity reduction are limited to ultra wideband. Some works of this thesis (based on simulations and experimental measurements) show that, for bands which are more typical for future networks (a carrier frequency of 1GHz and a spectrum of 30 MHz to 100 MHz), thanks to time reversal, a simple receiver and a mono-carrier signal are sufficient to reach high data rates. Moreover, the channel reciprocity condition is not verified in two scenarios which are typical from mobile networks. Firstly, in most European mobile networks, the frequency division duplex mode is used. This mode implies that the transceiver and the receiver communicate on distinct carriers, and therefore through different propagation channels. Secondly, when considering a receiver on a moving connected vehicle, the transceiver and the receiver communicate one with each other at distinct instants, corresponding to distinct positions of the vehicles, and therefore through different propagation channels. Some works of this thesis propose solutions to obtain space-time focusing for these two scenarios. Finally, some works of this thesis explore the combination of time reversal with other recent signal processing techniques (spatial modulation, on the one hand, a new multi-carrier waveform, on the other hand), or new deployment scenarios (millimeter waves and large antenna arrays to interconnect the nodes of an ultra dense network) or new applications (guidance and navigation) which can be envisaged for future mobile networks.

Les codes espace-temps sont des codes correcteurs dédiés aux transmissions MIMO. Mathématiquement, un code espace-temps est un ensemble fini de matrices complexes. Ses performances dépendent de plusieurs critères, dont la distance minimale en métrique rang. Les codes de Gabidulin sont des codes dans cette métrique, connus pour leur optimalité et pour l'existence d'algorithmes de décodage efficaces. C'est pourquoi ils sont utilisés pour concevoir des codes espace-temps. La principale difficulté est alors de construire des matrices complexes à partir de matrices binaires. Les travaux présentés dans ce documents consistent à généraliser les codes de Gabidulin à des corps de nombres, en particulier des extensions cyclique. Nous verrons qu'ils ont les mêmes propriétés que leurs analogues sur les corps finis. Nous étudierons plusieurs modèles d'erreurs et d'effacements et présenterons un algorithme qui permettra de retrouver l'information transmise avec une complexité quadratique. En calculant dans des corps infinis, nous serons confrontés au problème de la taille des éléments, qui augmente exponentiellement au gré des calculs. Pour éviter ce désagrément, nous verrons qu'il est possible de réduire le code afin de calculer dans un corps fini. Enfin, nous proposerons une famille de codes espace-temps dont la construction est basée sur les codes de Gabidulin généralisés. Nous verrons que leurs performances sont similaires à celles des codes existants, et qu'ils disposent d'une structure supplémentaire. / Space-time codes are error correcting codes dedicated to MIMO transmissions. Mathematically, a space-time code is a finite family of complex matrices. Its preformances rely on several parameters, including its minimal rank distance. Gabidulin codes are codes in this metric, famous for their optimality and thanks to efficient decoding algorithms. That's why they are used to design space-time codes. The main difficulty is to design complex matrices from binary matrices. The aim of the works collected here is to generalize Gabidulin codes to number fields, especially cyclique extesnions. We see that they have the same properties than Gabidulin codes over finite fields. We study several errors and erasures models and introduce a quadratic algorithm to recover transmitted information. When computing in finite fields, we are faced with the growing size problem. Indeed, the size of the coefficients grows exponentielly along the algorithm. To avoid this problem, it is possible to reduce the code, in order to compute in a finite field. Finally, we design a family of space-time codes, based on generalised Gabidulin codes. We see that our codes have performances similar to those of existing codes, and that they have additional structure.

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