Дисертації: "Blind adaptation"

1

Duplessis-Beaulieu, François. "Fast convolutive blind speech separation via subband adaptation." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29535.

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Blind source separation (BSS) attempts to recover a set of statistically independent sources from a set of mixtures knowing only the structure of the mixing network, and the hypothesized probability distribution function of the sources. The case where the sources are immobile persons speaking in a reverberant room is of particular interest, because it represents a first step toward unlocking the so-called "cocktail party problem". Due to the reverberations, BSS in the time domain is usually expensive in terms of computations, but the number of computations can be significantly decreased if separation is carried out in subbands.
An implementation of a subband-based BSS system using DFT filter banks is described, and an adaptive algorithm tailored for subband separation is developed. Aliasing present in the filter bank (due to the non-ideal frequency response of the filters) is reduced by using an oversampled scheme. Experiments, conducted with two-input two-output BSS systems, using both subband and fullband adaptation, indicate that separation and distortion rates are similar for both systems. However, the proposed 32-subband system is approximately 10 times computationally faster than the fullband system.

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2

Saqr, Raneem. "Blind and Visually Impaired Users Adaptation to Web Environments: A Qualitative Study." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6380.

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Although much research exists on human behavior in online environments, research on users with disabilities is still rare. To draw more attention to this population, this dissertation explored browsing patterns and adaptive behaviors of people with visual disability across different online environments common in daily activities: social network, e-commerce, online information, and search engines’ websites. The main objective of this study is to propose a conceptual framework of how blind and visually impaired users browse and adapt to different web environments. We achieve this objective using a qualitative approach through three studies. In the first study, the researchers collect data by means of in-depth, semi-structured interviews with six users with different levels of visual impairment. In the second study, we use survey questionnaires with open-ended questions to reach a larger sample of study participants. Finally, we conduct a follow-up observational study as means to confirm our results. Open, axial, and selective coding are used for data reduction and analysis as part of the grounded theory method.

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3

Ben, Tourkia Slim. "L'enseignement de mal voyants en France et en Tunisie : de la défiance visuelle au déficit pédagogique : le cas de l'enseignement des mathématiques à l'école." Thesis, Paris 8, 2018. http://www.theses.fr/2018PA080009.

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L’instruction des ADV (Aveugles et Déficients visuels) sous-tend leur apprentissage et leur intégration aussi bien scolaire que sociale, et est fondée sur des politiques mises en œuvre dans divers pays. En France et dans d’autres pays, sont conçues au profit des ADV des politiques d’intégration dont celles en milieu ouvert et en milieu spécialisé. Les études de terrain en France et en Tunisie montrent, qu’avec de supports et de matériels spécifiques, les ADV ont pu apprendre les mathématiques en concrétisation de ces politiques d’intégration
Teaching the BVI (Blind and Visually Impaired) is the foundation of their learning and integration in both school and society, and is based on policies implemented in various countries. In France and in other countries, integration policies, in an open and specialized setting, are formed for the BVI. Field studies in France and in Tunisia show that with specific media and materials, the BVI were able to learn Math, thus concretizing these integration policies

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4

Pierre, Constance. "Conséquences fonctionnelles, comportementales et adaptatives d'une mutation de la MAO (MonoAmine Oxydase) chez le poisson cavernicole aveugle Astyanax mexicanus. A Mutation in Monoamine Oxidase (MAO) Affects the Evolution of Stress Behavior in the Blind Cavefish Astyanax Mexicanus." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS084.

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Le neurotransmetteur sérotonine contrôle une grande variété de mécanismes physiologiques et comportementaux. Chez les humains, les mutations qui affectent la monoamine oxydase (MAO), l’enzyme qui dégrade la sérotonine, sont hautement délétères. Pourtant, le morphotype cavernicole aveugle de l’espèce Astyanax mexicanus (téléostéens) porte une mutation (P106L) induisant une perte de fonction partielle de cette enzyme, et semble prospérer dans son habitat souterrain naturel. Cette thèse décrit les effets de cette mutation, depuis l’échelle moléculaire à l’échelle des populations, afin de mieux cerner sa contribution à l’évolution des traits neuro-comportementaux du poisson cavernicole lors de son adaptation au milieu souterrain.Dans une première publication, nous avons établi 4 lignées de poissons, correspondant aux deux morphotypes de l’espèce Astyanax mexicanus (poisson cavernicole et poisson vivant en surface), chacun porteur ou non de la mutation P106L. La mutation P106L affecte le stress en augmentant l’amplitude de la réponse aigue au stress, tout en diminuant l’anxiété. Nous avons aussi étudié la distribution des allèles mutés dans les populations naturelles au Mexique et trouvé que l’allèle mutant est présent dans plusieurs grottes. L’évolution de l’allèle muté sous sélection ou dérive génétique est discutée.Dans une seconde publication, nous avons étudié les conséquences structurelles et biochimiques de la mutation P106L. La réduction de l’activité enzymatique de la MAO mutée est probablement due à une réduction de la flexibilité de l’une des boucles formant l’entrée au site actif, limitant l’accès des substrats. Des mesures d’HPLC ont montré des perturbations majeures de taux de sérotonine, dopamine et noradrénaline (et métabolites) dans le cerveau des poissons mutants. La mutation P106L mao est donc entièrement responsable du déséquilibre monoaminergique observé dans le cerveau des poissons cavernicoles. Enfin, l’effet de la mutation est partiellement compensé par une réduction de l’activité de synthèse de la sérotonine par la TPH. Nos résultats en révèlent plus sur les spécificités des systèmes monoaminergiques des poissons.Enfin, pour aggraver l’inhibition de la MAO, nous avons généré le premier poisson mutant knockout pour la MAO. Les mutants KO homozygotes sont chétifs et meurent durant les premières semaines de développement. Contrairement au système dopaminergique, le système sérotoninergique des poissons KO homozygotes est très fortement altéré : aucun neurone positif à la sérotonine n’est détecté dans l’hypothalamus
The neurotransmitter serotonin controls a great variety of physiological and behavioral processes. In humans, mutations affecting the monoamine oxidase or MAO, the serotonin-degrading enzyme, are highly deleterious. Yet, blind cavefish of the species A. mexicanus carry a partial loss-of-function mutation in MAO (P106L) and seem to thrive in their subterranean environ-ment. This thesis describes the effects of this mutation, from the molecular level to the population level, in order to decipher the exact contribution of mao P106L in the evolution of cavefish neuro-behavioral traits, during their adaptation to the cave environment.In a first paper, we established 4 fish lines, corresponding to the blind cave-dwelling and the sighted river-dwelling morphs of this species, with or without the mutation. We found that mao P106L strongly affected anxiety-like behaviors. Cortisol measurements showed lower basal levels and an increased amplitude of stress response after a change of environment in fish carrying the mutation. Finally, we studied the distribution of the P106L mao allele in wild populations of cave and river A. mexicanus, and discovered that the mutant allele was present – and sometimes fixed - in all populations inhabiting caves of the Sierra de El Abra. The possibility that this partial loss-of-function mao allele evolves under a selective or a genetic drift regime in the particular cave environment is discussed.In a second paper, we assessed the structural and biochemical consequences of the mutation. We found that the reduction of enzymatic activity of mutant MAO is probably caused by a decrease of flexibility in one of the three loops forming the entrance of the active site, thus reducing the access of substrates. HPLC measurements in brains of mutant and non-mutant larvae and adult fish showed major disturbances in serotonin, dopamine and noradrenalin (and metabolites) contents, demonstrating that the P106L mao mutation is fully responsible for monoaminergic disequilibrium in the cavefish brain. We also discovered that the effects of the mutation were partially compensated by a decrease in activity of the TPH, the serotonin biosynthesis rate-limiting enzyme. Our results shade light on the specificities of fish monoaminergic systems.Finally in order to aggravate the MAO inhibition, we generated the first fish knockout MAO mutant. The KO homozygous mutants were stunted and died during the first weeks of development. Contrary to the dopaminergic system which seemed normal in the KO homozygous mutants, the serotonergic system was strongly impaired; no serotonin positive neuron was detected in the hypothalamus

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5

Silva, Magno Teófilo Madeira da. "Um estudo sobre técnicas de equalização autodidata." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-01042005-214250/.

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Neste trabalho, investigam-se técnicas autodidatas baseadas em estatísticas de ordem superior, aplicadas à equalização de canais de comunicação. Inicialmente, obtém-se um intervalo do passo de adaptação que assegura a convergência do algoritmo do Módulo Constante com o gradiente exato. Algoritmos como o CMA (Constant Modulus Algorithm) e o SWA (Shalvi-Weinstein Algorithm) são revisitados e suas capacidades de tracking analisadas, utilizando-se uma relação de conservação de energia. Além disso, é proposto um algoritmo autodidata denominado AC-CMA (Accelerated Constant Modulus Algorithm) que utiliza a segunda derivada (aceleração) da estimativa dos coeficientes. Esse algoritmo pode apresentar um compromisso mais favorável entre complexidade computacional e velocidade de convergência que o CMA e o SWA. Esses resultados são estendidos para o caso multiusuário. Através de simulações, os algoritmos são comparados e as análises de convergência e tracking validadas. Considerando o DFE (Decision Feedback Equalizer) no caso monousuário com o critério do módulo constante, é proposto um algoritmo concorrente que evita soluções degeneradas e apresenta um desempenho melhor do que os existentes na literatura. Com o intuito de evitar propagação de erros, é proposta uma estrutura híbrida que utiliza uma rede neural recorrente na malha de realimentação. Resultados de simulações indicam que seu uso pode ser vantajoso para canais lineares e não-lineares.
The equalization of communication channels is addressed by using blind techniques based on higher order statistics. A step-size interval is obtained to ensure the convergence of Steepest-Descent Constant Modulus Algorithm. The Shalvi-Weinstein Algorithm (SWA) and Constant Modulus Algorithm (CMA) are revisited and their tracking capabilities are analyzed by using an energy conservation relation. Moreover, a novel blind algorithm named Accelerated Constant Modulus Algorithm (AC-CMA) is proposed. It adjusts the second derivative (acceleration) of the coefficient estimates and presents a more favorable compromise between computational complexity and convergence rate than CMA or SWA. These results are extended to the MIMO (Multiple-Input Multiple-Output) case. By means of simulations, the algorithms are compared and the convergence and tracking analysis are validated. The Decision Feedback Equalizer (DFE) is considered in the SISO (Single-Input Single-Output) case with the Constant Modulus criterion and a concurrent algorithm is proposed. It avoids degenerated solutions and shows better behavior than the others presented in the literature. In order to avoid error propagation, a hybrid DFE is also proposed. It includes a recurrent neural network in the feedback filter and may be advantageously used to equalize linear and nonlinear channels.

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6

Huuskonen, Maarit. "Identitet i kris : - identitet och anpassning bland invandrare i Sverige." Thesis, Karlstad University, Faculty of Social and Life Sciences, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-326.

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Abstract

When immigrants move to Sweden from their native country it is not unusual that they experience some kind of identity crises. Their own experience of their cultural identity can be very problematic and they often lose a part of what they previously saw as their own identity. To handle such crises the immigrants can use different strategies. They can for example accept their disparity, deny it or emphasize it. The aim of this study is to examine how immigrants in Sweden experience that their cultural identity has changed since they moved here from a country that has a culture that is different from the Swedish culture. To reach my goal with this study I interviewed immigrants/refugees from Chile, Lebanon and Thailand. Some of the results are that my presentation of the problem and the aim with the study were not profound enough. I intended to only write about cultural identity but I came to the conclusion that individual identity and different adaptation strategies were no less important. A further conclusion is that these three ingredients are completely different things; an immigrant can have one individual identity, another cultural identity and use a strategy that does not correspond with any of these. Moreover I also found that a person’s identity does not need to change when moving from their native country to Sweden. Finally I want to stress that my study is not about making sweeping statements, it is rather exemplifying. Identity and strategies are different from one person to another.

Keywords: individual identity, cultural identity, adaptation strategies

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7

Jay, Jason Chaw. "FOODWAYS OF THE VISUALLY-IMPAIRED: TRAVERSING THE BLIND KITCHEN." Scholarly Commons, 2018. https://scholarlycommons.pacific.edu/uop_etds/3125.

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In the United States, the number of visually impaired and blind Americans will rise drastically as the population continues to age; and, yet little is known about how the impact of blindness affects an individual when it comes to the experience of food provisioning and preparation. This thesis presents the study of how the blind and the visually impaired experience food provisioning and preparation. It explores how modern technology and sensory training help these groups of people traverse kitchen and grocery store environments. In thematically organized chapters, this thesis examines sensory education, nutrition and food related obstacles. This is the first study in the United States in which the experience of food provisioning, preparation of food, and consumption of food are described from the perspective of Blind and Visually Impaired Americans. In this qualitative study, food experience and the eating choices of the blind and visually impaired Americans were examined. Influential factors on the experience of food were also explored.

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8

Freitas, Mauro Lopes de. "Equalização adaptativa utilizando seleção de dados em transceptores em bloco com redundância reduzida." Universidade Federal do Amazonas, 2014. http://tede.ufam.edu.br/handle/tede/4503.

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
systems, mostly due to their welldefined structure and blockwise encoding. Among the main challenges encountered by mobile applications, there is an inherent interblock interference, due to superpositions of delayed signal copies, which is commonly eliminated with the addition of redundancy between adjacent data blocks. In addition to that, channel equalization is also usually employed, in order to further mitigate channel interferences. However, the amount of redundancy may be overestimated, which opens an opportunity for reduced-redundancy superfast transceivers, whose features include high spectral efficiency and low computational cost. Although the superfast approach aims at achieving low complexity, equalizer-coefficient updates are still very complex tasks due to channel variations, and most designs do not employ methodologies for computational-effort reduction. The present work addresses this problem and proposes a new design strategy for block-based transceivers, which provides semiblind equalization with data-selective update, besides the possibility of a generalized approach, based on the fast Fourier transform and diagonal matrices. Simulation results show that our approach updates less than 60% of the equalizer coefficients duringsupervised and blind period and maintain a competitive throughput for single-carrier and multicarrier transmissions.
Atualmente, os transceptores multicanais baseados em blocos são largamente utilizados em sistemas de comunicação sem fio, muito devido a sua estrutura bem definida e ao blockwise encoding. A respeito dos principais problemas encontrados em aplicações móveis, podemos destacar a interferência entre blocos, em decorrência da superposição de cópias atrasadas do sinal, a qual é usualmente eliminada com a adição de uma quantidade de redundância entre blocos de dados adjacentes. Adicionalmente, a equalização é comumente aplicada para mitigar o efeito do canal. Entretanto, a quantidade de redundância pode estar superestimada, abrindo oportunidade para a utilização de transceptores multicanais super-rápidos e com redundância reduzida, que possuem como característica uma alta eficiência espectral e baixa complexidade computacional. Entretanto, a abordagem super-rápida ainda possui uma alta complexidade para atualizar os coeficientes de equalização e a maioria das arquiteturas propostas não utilizam metodologias visando à redução do número de operações. O trabalho atual trata este problema e propõe uma nova arquitetura para tranceptores multicanais com transmissão em blocos, que se utiliza de uma equalização semi-cega com seleção de dados, além da abordagem generalizada, baseadas em transformadas rápidas de Fourier e matrizes diagonais. Os resultados das simulações demonstram que a abordagem permite atualizar menos de 60% dos coeficientes de equalização durante o período supervisionado e não supervisionado de equalização e manter a taxa de saída competitiva para sistemas monoportadora e multiportadora.

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9

Chira, Liviu-Teodor. "Déconvolution aveugle parcimonieuse en imagerie échographique avec un algorithme CLEAN adaptatif." Thesis, Tours, 2013. http://www.theses.fr/2013TOUR3311/document.

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L'imagerie médicale ultrasonore est une modalité en perpétuelle évolution et notamment en post-traitement où il s'agit d'améliorer la résolution et le contraste des images. Ces améliorations devraient alors aider le médecin à mieux distinguer les tissus examinés améliorant ainsi le diagnostic médical. Il existe déjà une large palette de techniques "hardware" et "software". Dans ce travail nous nous sommes focalisés sur la mise en oeuvre de techniques dites de "déconvolution aveugle", ces techniques temporelles utilisant l'enveloppe du signal comme information de base. Elles sont capables de reconstruire des images parcimonieuses, c'est-à-dire des images de diffuseurs dépourvues de bruit spéculaire. Les principales étapes de ce type de méthodes consistent en i) l'estimation aveugle de la fonction d'étalement du point (PSF), ii) l'estimation des diffuseurs en supposant l'environnement exploré parcimonieux et iii) la reconstruction d'images par reconvolution avec une PSF "idéale". La méthode proposée a été comparée avec des techniques faisant référence dans le domaine de l'imagerie médicale en utilisant des signaux synthétiques, des séquences ultrasonores réelles (1D) et images ultrasonores (2D) ayant des statistiques différentes. La méthode, qui offre un temps d'exécution très réduit par rapport aux techniques concurrentes, est adaptée pour les images présentant une quantité réduite ou moyenne des diffuseurs
The ultrasonic imaging knows a continuous advance in the aspect of increasing the resolution for helping physicians to better observe and distinguish the examined tissues. There is already a large range of techniques to get the best results. It can be found also hardware or signal processing techniques. This work was focused on the post-processing techniques of blind deconvolution in ultrasound imaging and it was implemented an algorithm that works in the time domain and uses the envelope signal as input information for it. It is a blind deconvolution technique that is able to reconstruct reflectors and eliminate the diffusive speckle noise. The main steps are: the estimation of the point spread function (PSF) in a blind way, the estimation of reflectors using the assumption of sparsity for the examined environment and the reconstruction of the image by reconvolving the sparse tissue with an ideal PSF. The proposed method was tested in comparison with some classical techniques in medical imaging reconstruction using synthetic signals, real ultrasound sequences (1D) and ultrasound images (2D) and also using two types of statistically different images. The method is suitable for images that represent tissue with a reduced amount or average scatters. Also, the technique offers a lower execution time than direct competitors

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10

Silva, Daniela Brasil. "Restauração cega de imagens: soluções baseadas em algoritmos adaptativos." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-27082018-143938/.

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O objetivo da desconvolução cega de imagens é restaurar uma imagem degradada sem usar informação da imagem real ou da função de degradação. O mapeamento dos níveis de cinza de uma imagem em um sinal de comunicação possibilita o uso de técnicas de equalização cega de canais para a restauração de imagens. Neste trabalho, propõe-se o uso de um esquema para desconvolução cega de imagens baseado na combinação convexa de um equalizador cego com um equalizador no modo de decisão direta. A combinação também é adaptada de forma cega, o que possibilita o chaveamento automático entre os filtros componentes. Dessa forma, o esquema proposto é capaz de atingir o desempenho de um algoritmo de filtragem adaptativa supervisionada sem o conhecimento prévio da imagem original. O desempenho da combinação é ilustrado por meio de simulações, que comprovam a eficiência desse esquema quando comparado a outras soluções da literatura.
The goal of blind image deconvolution is to restore a degraded image without using information from the actual image or from the point spread function. The mapping of the gray levels of an image into a communication signal enables the use of blind equalization techniques for image restoration. In this work, we use a blind image deconvolution scheme based on the convex combination of a blind equalizer with an equalizer in the decision-directed mode. The combination is also blindly adapted, which enables automatic switching between the component filters. Thus, the proposed scheme is able to achieve the performance of a supervised adaptive filtering algorithm without prior knowledge of the original image. The performance of the combination is illustrated by simulations, which show the efficiency of this scheme when compared to other solutions in the literature.

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11

Pivré, Caroline, and Mimmi Roos. "Marknadsföringsaktiviteter på sociala medier : En undersökande studie om varumärkeskännedom bland konsumenter inom generation X." Thesis, Högskolan i Gävle, Avdelningen för ekonomi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-35158.

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Sammanfattning Titel: Marknadsföringsaktiviteter på sociala medier – En undersökande studie om varumärkeskännedom bland konsumenter inom generation X Nivå: Examensarbete på grundnivå (kandidatexamen) inom företagsekonomi Författare: Caroline Pivré och Mimmi Roos Handledare: Anna Ljung Datum: 2021 - januari Syfte: Syftet med denna studie är att undersöka om marknadsföringsaktiviteter på sociala medier leder till ökad varumärkeskännedom bland konsumenter som tillhör generation X. Metod: En kvantitativ metod med en deduktiv ansats tillämpades. Populationen som studerades var konsumenter som tillhör generation X. Ett slumpmässigt urval användes. Data samlades in genom en enkät som delades ut på Facebook. Data analyserades i det statistiska programmet SPSS där faktoranalys, test av Cronbachs Alfa, korrelationsanalys och multipel regressionsanalys genomfördes. Data har redovisats i löpande text och i tabellform. Resultat och slutsats: Resultatet visade att varumärkeskännedom ökar bland konsumenter inom generation X när marknadsföringsaktiviteter på sociala medier används, samt att anpassning av marknadsföring till generation X som ett segment inte har någon betydelse för ökad varumärkeskännedom. Studiens slutsats är att ett varumärkes sociala plattformar ska vara intressanta och underhållande för att varumärkeskännedomen ska öka samt att det finns begränsad kunskap om generation X som ett segment jämfört med generation Y. Examensarbetets bidrag: Uppsatsen bidrar med kunskap om att marknadsföringsaktiviteter på sociala medier leder till ökad varumärkeskännedom för konsumenter inom generation X, samt att anpassning till generationen som ett segment inte har betydelse för ökad varumärkeskännedom. Studien bidrar med praktiska bidrag om betydelsen av att skapa intressanta och underhållande plattformar. Förslag till fortsatt forskning: Förslag till fortsatt forskning är att undersöka hur personligheter, värderingar och kön påverkar upplevd varumärkeskännedom bland konsumenter inom generation X. Nyckelord: Varumärkeskännedom, marknadsföringsaktiviteter på sociala medier, traditionella marknadsföringsaktiviteter och anpassning till ett segment.
Abstract Title: Marketing activities on social media - A study that examines brand awareness among consumers within generation X Level: Final assignment for bachelor’s degree in Business Administration Author: Caroline Pivré and Mimmi Roos Supervisor: Anna Ljung Date: 2021 - January Aim: The purpose of this study is to investigate if social media marketing activities lead to increased brand awareness among consumers within generation X. Method: A quantitative method with a deductive approach was applied. The population studied was Generation X consumers. A random sample was used. Data was collected through a survey distributed on Facebook. Data was analysed in the statistical program SPSS where factor analysis, test of Cronbach's Alpha, correlation analysis and multiple regression analysis were performed. Data has been reported in linear form and in table form. Result and Conclusions: The results showed that brand awareness increases among consumers within generation X when marketing activities on social media are used, and that marketing adaptation to generation X as a segment, has no significance for increased brand awareness. The study concludes that a brand's social platforms should be interesting and entertaining in order for brand awareness to increase, and that there is limited knowledge about generation X as a segment compared to generation Y. Contribution of the thesis: The thesis contributes with knowledge that marketing activities on social media lead to increased brand awareness for consumers within generation X, and that adaptation to the generation as a segment has no significance for increased brand awareness. The study provides practical contributions on the importance of creating interesting and entertaining platforms. Suggestions for future research: Suggestions for further research are to investigate how personalities, values and gender affect perceived brand awareness among consumers within generation X. Key words: Brand awareness, marketing activities on social media, traditional marketing activities and adaptation to a segment.

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12

Pavan, Flávio Renê Miranda. "Sobre a desconvolução multiusuário e a separação de fontes." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-22092016-103501/.

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Os problemas de separação cega de fontes e desconvolução cega multiusuário vêm sendo intensamente estudados nas últimas décadas, principalmente devido às inúmeras possibilidades de aplicações práticas. A desconvolução multiusuário pode ser compreendida como um problema particular de separação de fontes em que o sistema misturador é convolutivo, e as estatísticas das fontes, que possuem alfabeto finito, são bem conhecidas. Dentre os desafios atuais nessa área, cabe destacar que a obtenção de soluções adaptativas para o problema de separação cega de fontes com misturas convolutivas não é trivial, pois envolve ferramentas matemáticas avançadas e uma compreensão aprofundada das técnicas estatísticas a serem utilizadas. No caso em que não se conhece o tipo de mistura ou as estatísticas das fontes, o problema é ainda mais desafiador. Na área de Processamento Estatístico de Sinais, soluções vêm sendo propostas para resolver casos específicos. A obtenção de algoritmos adaptativos eficientes e numericamente robustos para realizar separação cega de fontes, tanto envolvendo misturas instantâneas quanto convolutivas, ainda é um desafio. Por sua vez, a desconvolução cega de canais de comunicação vem sendo estudada desde os anos 1960 e 1970. A partir de então, várias soluções adaptativas eficientes foram propostas nessa área. O bom entendimento dessas soluções pode sugerir um caminho para a compreensão aprofundada das soluções existentes para o problema mais amplo de separação cega de fontes e para a obtenção de algoritmos eficientes nesse contexto. Sendo assim, neste trabalho (i) revisitam-se a formulação dos problemas de separação cega de fontes e desconvolução cega multiusuário, bem como as relações existentes entre esses problemas, (ii) abordam-se as soluções existentes para a desconvolução cega multiusuário, verificando-se suas limitações e propondo-se modificações, resultando na obtenção de algoritmos com boa capacidade de separação e robustez numérica, e (iii) relacionam-se os critérios de desconvolução cega multiusuário baseados em curtose com os critérios de separação cega de fontes.
Blind source separation and blind deconvolution of multiuser systems have been intensively studied over the last decades, mainly due to the countless possibilities of practical applications. Blind deconvolution in the multiuser case can be understood as a particular case of blind source separation in which the mixing system is convolutive, and the sources, which exhibit a finite alphabet, have well known statistics. Among the current challenges in this area, it is worth noting that obtaining adaptive solutions for the blind source separation problem with convolutive mixtures is not trivial, as it requires advanced mathematical tools and a thorough comprehension of the statistical techniques to be used. When the kind of mixture or source statistics are unknown, the problem is even more challenging. In the field of statistical signal processing, solutions aimed at specific cases have been proposed. The development of efficient and numerically robust adaptive algorithms in blind source separation, for either instantaneous or convolutive mixtures, remains an open challenge. On the other hand, blind deconvolution of communication channels has been studied since the 1960s and 1970s. Since then, various types of efficient adaptive solutions have been proposed in this field. The proper understanding of these solutions can suggest a path to further understand the existing solutions for the broader problem of blind source separation and to obtain efficient algorithms in this context. Consequently, in this work we (i) revisit the problem formulation of blind source separation and blind deconvolution of multiuser systems, and the existing relations between these problems, (ii) address the existing solutions for blind deconvolution in the multiuser case, verifying their limitations and proposing modifications, resulting in the development of algorithms with proper separation performance and numeric robustness, and (iii) relate the kurtosis based criteria of blind multiuser deconvolution and blind source separation.

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Frasson, Felipe. "Análise comparativa de algoritmos adaptativos que usam estatísticas de alta ordem para equalização de canais esparsos." Niterói, 2017. https://app.uff.br/riuff/handle/1/3934.

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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.

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Fernandes, Carlos Alexandre Rolim. "EqualizaÃÃo adaptativa e autodidata de canais lineares e nÃo-lineares utilizando o algoritmo do mÃdulo constante." Universidade Federal do CearÃ, 2005. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=2041.

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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
Este trabalho trata da proposiÃÃo de algoritmos para equalizaÃÃo cega de canais lineares e nÃao-lineares inspirados no Algoritmo do MÃdulo Constante (CMA). O CMA funciona de maneira bastante eficiente com constelaÃÃes nas quais todos os pontos possuem a mesma amplitude, como em modulaÃÃes do tipo Phase Shift Keying (PSK). Entretanto, quando os pontos da constelaÃÃo podem assumir diferentes valores de amplitudes, como em modulaÃÃes do tipo Quadrature Amplitude Modulation (QAM), o CMA e seus derivados muitas vezes nÃo funcionam de forma satisfatÃria. Desta forma, as tÃcnicas aqui propostas sÃo projetadas para melhorar a performance do CMA em termos de velocidade de convergÃncia e precisÃo, quando operando em sinais transmitidos com diversos mÃdulos, em particular para a modulaÃÃo QAM. Assim como o CMA, para possuir um bom apelo prÃtico, essas tÃcnicas devem apresentar bom compromisso entre complexidade, robustez e desempenho. Para tanto, as tÃcnicas propostas utilizam o Ãltimo sÃmbolo decidido para definir uma estimaÃÃo de raio de referÃncia para a saÃda do equalizador. De fato, esses algoritmos podem ser vistos como generalizaÃÃes do CMA e de alguns derivados do CMA para constelaÃÃes com mÃltiplos raios. A proposiÃÃo de algoritmos do tipo gradiente estocÃstico Ã concluÃda com o desenvolvimento de tÃcnicas originais, baseadas no CMA, para equalizaÃÃo de canais do tipo Wiener, que consiste em um filtro linear com memÃria, seguido por um filtro nÃo-linear sem memÃria. As expressÃes para a adaptaÃÃo do equalizador sÃo encontradas com o auxÃlio de uma notaÃÃo unificada para trÃs diferentes estruturas: i) um filtro de Hammerstein; ii) um filtro de Volterra diagonal; e iii) um filtro de Volterra completo. Um estudo teÃrico acerca do comportamento do principal algoritmo proposto, o Decision Directed Modulus Algorithm (DDMA) Ã realizado. SÃo analisadas a convergÃncia e a estabilidade do algoritmo atravÃs de uma anÃlise dos pontos de mÃnimo de sua funÃÃo custo. Outro objetivo Ã encontrar o valor teÃrico do Erro MÃdio QuadrÃtico MÃdio em Excesso - Excess Mean Square Error (EMSE) fornecido pelo DDMA considerando-se o caso sem ruÃdo. Ao final, Ã feito um estudo em que se constata que o algoritmo DDMA possui fortes ligaÃÃes com a soluÃÃo de Wiener e com o CMA. VersÃes normalizadas, bem como versÃes do tipo Recursive Least Squares (RLS), dos algoritmos do tipo gradiente estocÃstico estudados sÃo tambÃm desenvolvidas. Cada famÃlia de algoritmos estudada fie composta por quatro algoritmos com algumas propriedades interessantes e vantagens sobre as tÃcnicas clÃssicas, especialmente quando operando em sinais QAM de ordem elevada. TambÃm sÃo desenvolvidas versÃes normalizadas e do tipo RLS dos algoritmos do tipo CMA estudados para equalizaÃÃo de canais nÃo-lineares. O comportamento de todas as famÃlias de algoritmos desenvolvidos Ã testado atravÃs de simulaÃÃes computacionais, em que Ã verificado que as tÃcnicas propostas fornecem ganhos significativos em desempenho, em termos de velocidade de convergÃncia e erro residual, em relaÃÃo Ãs tÃcnicas clÃssicas.
This work studies and proposes algorithms to perform blind equalization of linear and nonlinear channels inspired on the Constant Modulus Algorithm (CMA). The CMA works very well for modulations in which all points of the signal constellation have the same radius, like in Phase Shift Keying (PSK) modulations. However, when the constellation points are characterized by multiple radii, like in Quadrature Amplitude Modulation (QAM) signals, the CMA does not work properly in many situations. Thus, the techniques proposed here are designed to improve the performance of the CMA, in terms of speed of convergence and residual error, when working with signals transmitted with multiple magnitude, in particular with QAM signals. As well as for the CMA, these techniques should have a good compromise among performance, complexity and robustness. To do so, the techniques use the last decided symbol to estimate reference radius to the output of the equalizer. In fact, they can be seen as modifications of the CMA and of some of its derivatives for constellations with multiple radii. The proposition of stochastic gradient algorithms is concluded with the development of new adaptive blind techniques to equalize channels with a Wiener structure. A Wiener filter consists of a linear block with memory followed by a memoryless nonlinearity, by using the CMA. We develop expressions for the adaptation of the equalizer using a unified notation for three different equalizer filter structures: i) a Hammerstein filter, ii) a diagonal Volterra filter and iii) a Volterra filter. A theoretical analysis of the main proposed technique, the Decision Directed Modulus Algorithm (DDMA), is also done. We study the convergence and the stability of the DDMA by means of an analysis of the minima of the DDM cost function. We also develop an analytic expression for the Excess Mean Square Error (EMSE) provided by the DDMA in the noiseless case. Then, we nd some interesting relationships among the DDM, the CM and the Wiener cost functions. We also develop a class of normalized algorithms and a class of Recursive Least Squares (RLS)-type algorithms for blind equalization inspired on the CMA-based techniques studied. Each family is composed of four algorithms with desirable properties and advantages over the original CM algorithms, specially when working with high-level QAM signals. Normalized and RLS techniques for equalization of Wiener channels are also developed. The behavior of the proposed classes of algorithms discussed is tested by computational simulations. We verify that the proposed techniques provide significative gains in performance, in terms of speed of convergence and residual error, when compared to the classical algorithms.

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Andersson, Beatrice, Emilia Lundblad, and Thitti Wiking. "Har elevernas vikt någon betuýdelse för idrottsläraren? : En studie som beskriver om idrottslärare gör något för att förebygga övervikt bland elever i år 3 och år 5." Thesis, Halmstad University, School of Social and Health Sciences (HOS), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-3833.

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Larmrapporterna om barns övervikt blir allt fler, det har blivit ett stort hälsoproblem i såväl Sverige som i resten av västvärlden. Ett sätt att få barn, både överviktiga och icke överviktiga, att bli mer aktiva är att engagera dem på lektionerna i idrott och hälsa i skolan. Syftet med denna studie var att ta reda på om det sker något förebyggande arbete för de eleverna med övervikt, på idrottslektionerna. Data samlades in genom att skicka ut enkäter till rektorer, på grundskolor i Skåne, med uppmaning att de skulle vidarebefordra enkäten till idrottslärarna i år 3 och år 5. Sammanlagt deltog 57 idrottslärare i studien. Resultatet visade att 43 respondenter anpassar sina lektioner i ämnet idrott och hälsa så att elever med övervikt kan vara med i samma utsträckning som övriga elever. 28 svarar att de försöker motverka övervikt bland sina elever. Utifrån vad resultatet visade engagerar sig de flesta lärarna i elevernas övervikt, vilket är bra. Men det kan bli bättre!

The reports about overweight among children are increasing by day and it has developed into a large health problem in Sweden as well as in the rest of the western world. One way to inspire children to be more physically active is to stimulate them at the physical education classes in school. The aim of this study was to find out if the physical education teachers are working actively to prevent weight gain in overweight children. Data was collected through a questionnaire sent to headmasters at primary schools in Skåne, Sweden. The respondents were physical education teachers working with children in grade three and five. A total of 57 teachers participated in the study. The result was that 43 respondents adapt their lessons to make overweight children as involved as not overweight children. 28 teachers reported that they actively try to prevent overweight. The result shows that most of these teachers are committed to preventing overweight among children.

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Batany, Yves-Marie. "Séparation de signaux en mélanges convolutifs : contributions à la séparation aveugle de sources parcimonieuses et à la soustraction adaptative des réflexions multiples en sismique." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM093/document.

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La séparation de signaux corrélés à partir de leurs combinaisons linéaires est une tâche difficile et possède plusieurs applications en traitement du signal. Nous étudions deux problèmes, à savoir la séparation aveugle de sources parcimonieuses et le filtrage adaptatif des réflexions multiples en acquisition sismique. Un intérêt particulier est porté sur les mélanges convolutifs : pour ces deux problèmes, des filtres à réponses impulsionnelles finies peuvent être estimés afin de récupérer les signaux désirés.Pour les modèles de mélange instantanés et convolutifs, nous donnons les conditions nécessaires et suffisantes pour l'extraction et la séparation exactes de sources parcimonieuses en utilisant la pseudo-norme L0 comme une fonction de contraste. Des équivalences entre l'analyse en composantes parcimonieuses et l'analyse en composantes disjointes sont examinées.Pour la soustraction adaptative des réflexions sismiques, nous discutons les limites des méthodes basées sur l'analyse en composantes indépendantes et nous soulignons l'équivalence avec les méthodes basées sur les normes Lp. Nous examinons de quelle manière les paramètres de régularisation peuvent être plus décisifs pour l'estimation des primaires. Enfin, nous proposons une amélioration de la robustesse de la soustraction adaptative en estimant les filtres adaptatifs directement dans le domaine des curvelets. Les coûts en calcul et en mémoire peuvent être atténués par l'utilisation de la transformée en curvelet discrète et uniforme
The recovery of correlated signals from their linear combinations is a challenging task and has many applications in signal processing. We focus on two problems that are the blind separation of sparse sources and the adaptive subtraction of multiple events in seismic processing. A special focus is put on convolutive mixtures: for both problems, finite impulse response filters can indeed be estimated for the recovery of the desired signals.For instantaneous and convolutive mixing models, we address the necessary and sufficient conditions for the exact extraction and separation of sparse sources by using the L0 pseudo-norm as a contrast function. Equivalences between sparse component analysis and disjoint component analysis are investigated.For adaptive multiple subtraction, we discuss the limits of methods based on independent component analysis and we highlight equivalence with Lp-norm-based methods. We investigate how other regularization parameters may have more influence on the estimation of the desired primaries. Finally, we propose to improve the robustness of adaptive subtraction by estimating the extracting convolutive filters directly in the curvelet domain. Computation and memory costs are limited by using the uniform discrete curvelet transform

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Suyama, Ricardo. "Proposta de metodos de separação cega de fontes para misturas convolutivas e não-lineares." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260846.

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Orientador: João Marcos Travassos Romano
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
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Resumo: O problema de separação cega de fontes (BSS - Blind Source Separation) vem despertando o interesse de um número crescente de pesquisadores. Esse destaque é devido, em grande parte, à formulação abrangente do problema, que torna possível o uso das técnicas desenvolvidas no contexto de BSS nas mais diversas áreas de aplicação. O presente trabalho tem como objetivo propor novos métodos de solução do problema de separação cega de fontes, nos casos de mistura convolutiva e mistura não-linear. Para o primeiro caso propomos um método baseado em predição não-linear, cujo intuito é eliminar o caráter convolutivo da mistura e, dessa forma, separar os sinais utilizando ferramentas bem estabelecidas no contexto de misturas lineares sem memória. No contexto de misturas não-lineares, propomos uma nova metodologia para separação de sinais em um modelo específico de mistura denominado modelo com não-linearidade posterior (PNL - Post Nonlinear ). Com o intuito de minimizar problemas de convergência para mínimos locais no processo de adaptação do sistema separador, o método proposto emprega um algoritmo evolutivo como ferramenta de otimização, e utiliza um estimador de entropia baseado em estatísticas de ordem para avaliar a função custo. A eficácia de ambos os métodos é verificada através de simulações em diferentes cenários
Abstract: The problem of blind source separation (BSS) has attracted the attention of agrowing number of researchers, mostly due to its potential applications in a significant number of different areas. The objective of the present work is to propose new methods to solve the problem of BSS in the cases of convolutive mixtures and nonlinear mixtures. For the first case, we propose a new method based on nonlinear prediction filters. The nonlinear structure is employed to eliminate the convolutive character of the mixture, hence converting the problem into an instantaneous mixture, to which several well established tools may be used to recover the sources. In the context of nonlinear mixtures, we present a new methodology for signal separation in the so-called post-nonlinear mixing models (PNL). In order to avoid convergence to local minima, the proposed method uses an evolutionary algorithm to perform the optimization of the separating system. In addition to that, we employ an entropy estimator based on order-statistics to evaluate the cost function. The effectiveness of both methods is assessed through simulations in different scenarios
Doutorado
Telecomunicações e Telemática
Doutor em Engenharia Elétrica

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Lima, Marcelo Antonio Alves. "Uma nova metodologia para análise da qualidade da energia elétrica sob condições de ocorrência de múltiplos distúrbios." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18154/tde-14112013-102931/.

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Um Sistema Elétrico de Potência (SEP) está susceptível à presença de diversas fontes de distúrbios que prejudicam a Qualidade da Energia Elétrica (QEE). Desta forma, as suas tensões e/ou correntes podem conter m´múltiplos distúrbios com ocorrência simultânea. Este trabalho apresenta uma metodologia para decomposição do sinal medido em componentes que estimem as formas de onda dos distúrbios individuais quando da ocorrência de m´múltiplos distúrbios, com o posterior reconhecimento de cada um deles. A Análise de Componentes Independentes (ICA) é utilizada como principal ferramenta na etapa de decomposição dos distúrbios. A ICA é originalmente uma t´técnica aplicada em análise multivariada de dados, o que significa que ela necessita de medições realizadas por múltiplos sensores dispostos em diferentes posições de um sistema. No entanto, este trabalho propõe a sua aplicação tendo disponível apenas um sinal medido. Para tanto, são propostos dois métodos para produzir a diversidade necessária para a t´técnica funcionar adequadamente. É demonstrado que ambos os métodos equivalem a um banco de filtros lineares adaptativos capaz de realizar a separação não-supervisionada de múltiplos distúrbios independentes e que sejam espectralmente disjuntos. Por fim, é proposto um sistema de classificação que utiliza Redes Neurais Artificiais (RNAs) para identificar os distúrbios decompostos pela etapa anterior. A metodologia completa é avaliada por meio de testes utilizando dados sintéticos e reais, alcançando resultados altamente satisfatórios para decomposição de sinais contendo múltiplos distúrbios e taxas de acerto globais dos classificadores superiores a 97%
The power system is susceptible to the presence of several sources of disturbances that harm the power quality. In this sense, its voltages and/or currents may contain multiple disturbances with simultaneous occurrence. This work presents a methodology that decomposes the measured signal in components which estimate the waveforms of the individual disturbances followed by their recognition when a multiple disturbance situation occurs. The Independent Component Analysis (ICA) is the main tool in the disturbance decomposition stage. The ICA is originally a technique applied in multivariate data analysis, which means that it requires measurements from multiple sensors allocated in different positions of the system. However, this work proposes its application for a single measured signal available. For this, two methods were developed in order to provide the required diversity to the ICA technique. It is demonstrated that both methods are equivalent to an adaptive linear filter bank capable to perform an unsupervised separation of multiple independent disturbances, if they are spectrally disjoint. A classification system based on artificial neural networks is proposed to identify the disturbances decomposed by the previous stage. The complete system is tested using synthetic and actual data, presenting highly satisfactory results for the decomposition of signals containing multiple disturbances, and precision for the classification task above 97%

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Lassami, Nacerredine. "Représentations parcimonieuses et analyse multidimensionnelle : méthodes aveugles et adaptatives." Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2019. http://www.theses.fr/2019IMTA0139.

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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

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Filho, João Mendes. "Algoritmos eficientes para equalização autodidata de sinais QAM." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-15032012-122010/.

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Neste trabalho, são propostos e analisados algoritmos autodidatas eficientes para a equalização de canais de comunicação, considerando a transmissão de sinais QAM (quadrature amplitude modulation). Suas funções de erro são construídas de forma a fazer com que o erro de estimação seja igual a zero nas coordenadas dos símbolos da constelação. Essa característica os possibilita ter um desempenho similar ao de um algoritmo de equalização supervisionada como o NLMS (normalized least mean-square), independentemente da ordem da constelação QAM. Verifica-se analiticamente que, sob certas condições favoráveis para a equalização, os vetores de coeficientes dos algoritmos propostos e a correspondente solução de Wiener são colineares. Além disso, usando a informação da estimativa do símbolo transmitido e de seus símbolos vizinhos, esquemas de baixo custo computacional são propostos para aumentar a velocidade de convergência dos algoritmos. No caso do algoritmo baseado no critério do módulo constante, evita-se sua divergência através de um mecanismo que descarta estimativas inconsistentes dos símbolos transmitidos. Adicionalmente, apresenta-se uma análise de rastreio (tracking), que permite obter expressões analíticas para o erro quadrático médio em excesso dos algoritmos propostos em ambientes estacionários e não-estacionários. Através dessas expressões, verifica-se que com sobreamostragem, ausência de ruído e ambiente estacionário, os algoritmos propostos podem alcançar a equalização perfeita, independentemente da ordem da constelação QAM. Os algoritmos são estendidos para a adaptação conjunta dos filtros direto e de realimentação do equalizador de decisão realimentada, levando-se em conta um mecanismo que evita soluções degeneradas. Resultados de simulação sugerem que a utilização dos esquemas aqui propostos pode ser vantajosa na recuperação de sinais QAM, fazendo com que seja desnecessário o chaveamento para o algoritmo de decisão direta.
In this work, we propose efficient blind algorithms for equalization of communication channels, considering the transmission of QAM (quadrature amplitude modulation) signals. Their error functions are constructed in order to make the estimation error equal to zero at the coordinates of the constellation symbols. This characteristic enables the proposed algorithms to have a similar performance to that of a supervised equalization algorithm as the NLMS (normalized least mean-square), independently of the QAM order. Under some favorable conditions, we verify analytically that the coefficient vector of the proposed algorithms are collinear with the Wiener solution. Furthermore, using the information of the symbol estimate in conjunction with its neighborhood, we propose schemes of low computational cost in order to improve their convergence rate. The divergence of the constant-modulus based algorithm is avoided by using a mechanism, which disregards nonconsistent estimates of the transmitted symbols. Additionally, we present a tracking analysis in which we obtain analytical expressions for the excess mean-square error in stationary and nonstationary environments. From these expressions, we verify that using a fractionally-spaced equalizer in a noiseless stationary environment, the proposed algorithms can achieve perfect equalization, independently of the QAM order. The algorithms are extended to jointly adapt the feedforward and feedback filters of the decision feedback equalizer, taking into account a mechanism to avoid degenerative solutions. Simulation results suggest that the proposed schemes may be advantageously used to recover QAM signals and make the switching to the decision direct mode unnecessary.

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Assis, Fábio Ferreira de. "Algoritmos set-membership para equalização autodidata aplicados a redes de sensores sem fio." reponame:Repositório Institucional da UFABC, 2018.

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Orientadora: Profa. Dra. Aline de Oliveira Neves Panazio
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia da Informação, Santo André, 2018.
Este trabalho dedica-se ao estudo de algoritmos de filtragem adaptativa autodidata no modo difusão, com aplicações em redes de sensores sem fio (RSSF). No modo difusão, os nós sensores da rede possuem poder de processamento local e trocam informações com seus vizinhos. Neste trabalho, propomos dois algoritmos utilizando como base o algoritmo CMA no modo Difusão (CMAD), com duas abordagens distintas da técnica Set-Membership. O primeiro baseia-se no algoritmo Set-Membership Least Mean Squares (SM-LMS), desenvolvido também no modo difusão. Estendemos o algoritmo para o contexto não supervisionado, denotando por Algoritmo Set-Membership CMA no modo Difusão (SM-CMAD). Mostramos que este algoritmo apresenta desempenho melhor ou similar ao CMAD, em termos de velocidade de convergência, patamar de interferência intersimbólica (IIS) e possuindo a importante vantagem de reduzir as trocas de informações entre os nós, economizando energia e recursos da rede. O segundo algoritmo proposto se baseia no Set-Membership do Módulo Constante (SM-CM), o qual estendemos para o contexto de redes de sensores sem fio no modo difusão. Tal algoritmo é denotado por Algoritmo Set-membership CMA no modo Difusão Square-root Gamma (SM-CMAD-SG). Novamente o algoritmo apresenta um bom desempenho quando comparado com o CMAD e, quando comparado ao SM-CMAD, vemos que sua principal vantagem está na economia em termos de atualizações dos coeficientes do filtro, que chega a valores acima de 70% em diversos cenários de simulação, sem grandes perdas de desempenho economizando energia.
This work is devoted to the study of unsupervised adaptive filtering algorithms in diffusion mode, with applications in wireless sensor networks (WSNs). In diffusion mode, network sensing nodes have local processing power and exchange information with their neighbors. In this work, we propose two algorithms based on the CMA algorithm in Diffusion mode (CMAD), with two different approaches to the Set-Membership technique. The first one is based on the Set-Membership Least Mean Squares (SM-LMS) algorithm, also developed in the diffusion mode. We extend the algorithm to the unsupervised context, denoting by Set-Membership CMA in Diffusion mode (SM-CMAD). We show that this algorithm presents better or similar performance to CMAD, in terms of convergence speed, intersymbol interference threshold (IIS), and has the important advantage of reducing the exchange of information between nodes, saving energy and network resources. The second proposed algorithm is based on the Set-Membership of the Constant Modulus (SM-CM), which we extend to the context of wireless sensor networks in the diffusion mode. This algorithm is denoted by the Set-membership CMA in Diffusion mode Square-root Gamma (SM-CMAD-SG). This algorithm performs well when compared to CMAD and, when compared to SM-CMAD, we see that its main advantage lies in the economy in terms of the update of the filter coefficients, which reaches values above 70% in several scenarios without loss of performance, saving energy.

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Gandar, Benoît. "Apprentissage actif pour l'approximation de variétés." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2012. http://tel.archives-ouvertes.fr/tel-00954409.

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L'apprentissage statistique cherche à modéliser un lien fonctionnel entre deux variables X et Y à partir d'un échantillon aléatoire de réalisations de (X,Y ). Lorsque la variable Y prend un nombre binaire de valeurs, l'apprentissage s'appelle la classification (ou discrimination en français) et apprendre le lien fonctionnel s'apparente à apprendre la frontière d'une variété dans l'espace de la variable X. Dans cette thèse, nous nous plaçons dans le contexte de l'apprentissage actif, i.e. nous supposons que l'échantillon d'apprentissage n'est plus aléatoire et que nous pouvons, par l'intermédiaire d'un oracle, générer les points sur lesquels l'apprentissage de la variété va s'effectuer. Dans le cas où la variable Y est continue (régression), des travaux précédents montrent que le critère de la faible discrépance pour générer les premiers points d'apprentissage est adéquat. Nous montrons, de manière surprenante, que ces résultats ne peuvent pas être transférés à la classification. Dans ce manuscrit, nous proposons alors le critère de la dispersion pour la classification. Ce critère étant difficile à mettre en pratique, nous proposons un nouvel algorithme pour générer un plan d'expérience à faible dispersion dans le carré unité. Après une première approximation de la variété, des approximations successives peuvent être réalisées afin d'affiner la connaissance de celle-ci. Deux méthodes d'échantillonnage sont alors envisageables : le " selective sampling " qui choisit les points à présenter à un oracle parmi un ensemble fini de candidats et l'" adaptative sampling " qui permet de choisir n'importe quels points de l'espace de la variable X. Le deuxième échantillonnage peut être vu comme un passage à la limite du premier. Néanmoins, en pratique, il n'est pas raisonnable d'utiliser cette méthode. Nous proposons alors un nouvel algorithme basé sur le critère de dispersion, menant de front exploitation et exploration, pour approximer une variété.

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Vaerenbergh, Steven Van. "Kernel Methods for Nonlinear Identification, Equalization and Separation of Signals." Doctoral thesis, Universidad de Cantabria, 2010. http://hdl.handle.net/10803/10673.

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En la última década, los métodos kernel (métodos núcleo) han demostrado ser técnicas muy eficaces en la resolución de problemas no lineales. Parte de su éxito puede atribuirse a su sólida base matemática dentro de los espacios de Hilbert generados por funciones kernel ("reproducing kernel Hilbert spaces", RKHS); y al hecho de que resultan en problemas convexos de optimización. Además, son aproximadores universales y la complejidad computacional que requieren es moderada. Gracias a estas características, los métodos kernel constituyen una alternativa atractiva a las técnicas tradicionales no lineales, como las series de Volterra, los polinómios y las redes neuronales. Los métodos kernel también presentan ciertos inconvenientes que deben ser abordados adecuadamente en las distintas aplicaciones, por ejemplo, las dificultades asociadas al manejo de grandes conjuntos de datos y los problemas de sobreajuste ocasionados al trabajar en espacios de dimensionalidad infinita.En este trabajo se desarrolla un conjunto de algoritmos basados en métodos kernel para resolver una serie de problemas no lineales, dentro del ámbito del procesado de señal y las comunicaciones. En particular, se tratan problemas de identificación e igualación de sistemas no lineales, y problemas de separación ciega de fuentes no lineal ("blind source separation", BSS). Esta tesis se divide en tres partes. La primera parte consiste en un estudio de la literatura sobre los métodos kernel. En la segunda parte, se proponen una serie de técnicas nuevas basadas en regresión con kernels para resolver problemas de identificación e igualación de sistemas de Wiener y de Hammerstein, en casos supervisados y ciegos. Como contribución adicional se estudia el campo del filtrado adaptativo mediante kernels y se proponen dos algoritmos recursivos de mínimos cuadrados mediante kernels ("kernel recursive least-squares", KRLS). En la tercera parte se tratan problemas de decodificación ciega en que las fuentes son dispersas, como es el caso en comunicaciones digitales. La dispersidad de las fuentes se refleja en que las muestras observadas se agrupan, lo cual ha permitido diseñar técnicas de decodificación basadas en agrupamiento espectral. Las técnicas propuestas se han aplicado al problema de la decodificación ciega de canales MIMO rápidamente variantes en el tiempo, y a la separación ciega de fuentes post no lineal.
In the last decade, kernel methods have become established techniques to perform nonlinear signal processing. Thanks to their foundation in the solid mathematical framework of reproducing kernel Hilbert spaces (RKHS), kernel methods yield convex optimization problems. In addition, they are universal nonlinear approximators and require only moderate computational complexity. These properties make them an attractive alternative to traditional nonlinear techniques such as Volterra series, polynomial filters and neural networks.This work aims to study the application of kernel methods to resolve nonlinear problems in signal processing and communications. Specifically, the problems treated in this thesis consist of the identification and equalization of nonlinear systems, both in supervised and blind scenarios, kernel adaptive filtering and nonlinear blind source separation.In a first contribution, a framework for identification and equalization of nonlinear Wiener and Hammerstein systems is designed, based on kernel canonical correlation analysis (KCCA). As a result of this study, various other related techniques are proposed, including two kernel recursive least squares (KRLS) algorithms with fixed memory size, and a KCCA-based blind equalization technique for Wiener systems that uses oversampling. The second part of this thesis treats two nonlinear blind decoding problems of sparse data, posed under conditions that do not permit the application of traditional clustering techniques. For these problems, which include the blind decoding of fast time-varying MIMO channels, a set of algorithms based on spectral clustering is designed. The effectiveness of the proposed techniques is demonstrated through various simulations.

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Piccinini, Giulio Francesco Bianchi. "Drivers behavioural adaptation to the use of Advanced Cruise Control (ACC) And Blind Spot Information System (BLIS)." Doctoral thesis, 2014. https://repositorio-aberto.up.pt/handle/10216/74327.

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Piccinini, Giulio Francesco Bianchi. "Drivers behavioural adaptation to the use of Advanced Cruise Control (ACC) And Blind Spot Information System (BLIS)." Tese, 2014. https://repositorio-aberto.up.pt/handle/10216/74327.

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Jansenberger, Martha. "Legally blind people’s experiences of stigma in the context of the labour market: Stories of adaptation and resistance." Thesis, 2014. http://hdl.handle.net/1828/5594.

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This thesis examines the labour market experiences of a purposive sample of legally blind people in a medium-sized Canadian city. Relevant literature on disability, employment and stigma is reviewed, providing context for the thesis. Thematic analysis of qualitative data gathered from 18 in-depth face-to-face interviews of legally blind working-age participants provide rich narratives of their experiences in the labour market and society at large. The participants’ current and past employment situations are described and barriers to acceptance of their disability in the workforce are identified. Findings suggest that while perceived, enacted, and felt stigma constitute significant barriers to meaningful employment for the participants, many employ effective strategies to adapt to or resist stigmatizing treatment by others. Policy suggestions are provided to mitigate the impact of stigma on the lives of legally blind Canadians. The thesis concludes with suggestions for future directions of research in the area.
Graduate
0629
0630
0626
martha.jansenberger@gmail.com

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HSIN-YA, YEH, and 葉欣雅. "A study on the learning process and vocational adaptation of female massager who becomes blind in the mid life." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/98471662020018465290.

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碩士
國立高雄師範大學
成人教育研究所
96
Abstract This study focuses on the learning process and vocational adaptation of female massager who becomes blind in the mid life. Semi-structural qualitative study method is adopted and six female massagers who become blind in the mid life are selected as the research target; meanwhile, in-depth interview method is used to collect the data and to perform data analysis and arrangement. The study conclusions are as in the followings: 1.The learning motivation of massage might be just for living or for the reception of encouragement from friends and social group. The learning content is mainly based on massage because of the inferior situation encountered in other learning. 2.The learning processes are divided into three stages which are the beginning stage, the intermediary stage and the latter stage. The curriculum classification or planning of massage training is not based on physical capability or visional level, and there is no reinforcement on the incubation of specific teachers. 3.The work achievement comes from the feedback of customers and confidence.What he/she gets from massage is the main income for living, yet it has great meaning to a person to rely on himself/herself. 4.There is few trust among colleagues, competition relationship dominates partner relationship. 5.The vocational harassment experience is not uncommon. Female massager should develop self handling strategy. 6.Develop professional capability to fulfill the need to match up with the vocational environment. 7.It is hoped that employment related assistance can be provided. 8.The enhancement of lifelong learning is helpful to vocational adaptation. Based on the above study conclusions, the following suggestions are proposed: 1. Suggestions to the vocational education of those who are blind in the mid life (1) We have to pay attention to the vocational education and long life learning of those who are blind in the mid life and help them to conquer the handicap of learning.. (2) Different massage training projects should be planned by considering physical capability and visional status. (3) The vocational harassment issue of the female massager in the vocational site should be paid attention to. (4)Enhance the vocational rehabilitation service for massager who become blind in the mid life。 (5)Using empower program to encourage self-perceive and the energy of improvement. 2. Suggestions for future study In the future study, it is suggested to prepare survey questionnaire to perform survey on female massagers who have massage certificates; it is suggested that the research target can cover all the visional disabled people with massage as the main job; meanwhile, further study should be performed on the life style and difficulties encountered by visional disabled people when they work in other type of occupation. Key words: Becomes blind in the mid life, female massager, learning process, vocational adaptation

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Samarasinghe, Devanarayanage Pradeepa. "Efficient methodologies for real-time image restoration." Phd thesis, 2011. http://hdl.handle.net/1885/9859.

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In this thesis we investigate the problem of image restoration. The main focus of our research is to come up with novel algorithms and enhance existing techniques in order to deliver efficient and effective methodologies, applicable in real-time image restoration scenarios. Our research starts with a literature review, which identifies the gaps in existing techniques and helps us to come up with a novel classification on image restoration, which integrates and discusses more recent developments in the area of image restoration. With this novel classification, we identified three major areas which need our attention. The first developments relate to non-blind image restoration. The two mostly used techniques, namely deterministic linear algorithms and stochastic nonlinear algorithms are compared and contrasted. Under deterministic linear algorithms, we develop a class of more effective novel quadratic linear regularization models, which outperform the existing linear regularization models. In addition, by looking in a new perspective, we evaluate and compare the performance of deterministic and stochastic restoration algorithms and explore the validity of the performance claims made so far on those algorithms. Further, we critically challenge the ne- cessity of some complex mechanisms in Maximum A Posteriori (MAP) technique under stochastic image deconvolution algorithms. The next developments are focussed in blind image restoration, which is claimed to be more challenging. Constant Modulus Algorithm (CMA) is one of the most popular, computationally simple, tested and best performing blind equalization algorithms in the signal processing domain. In our research, we extend the use of CMA in image restoration and develop a broad class of blind image deconvolution algorithms, in particular algorithms for blurring kernels with a separable property. These algorithms show significantly faster convergence than conventional algorithms. Although CMA method has a proven record in signal processing applications related to data communications systems, no research has been carried out to the investigation of the applicability of CMA for image restoration in practice. In filling this gap and taking into account the differences of signal processing in im- age processing and data communications contexts, we extend our research on the applicability of CMA deconvolution under the assumptions on the ground truth image properties. Through analyzing the main assumptions of ground truth image properties being zero-mean, independent and uniformly distributed, which char- acterize the convergence of CMA deconvolution, we develop a novel technique to overcome the effects of image source correlation based on segmentation and higher order moments of the source. Multichannel image restoration techniques recently gained much attention over the single channel image restoration due to the benefits of diversity and redundancy of the information between the channels. Exploiting these benefits in real time applications is often restricted due to the unavailability of multiple copies of the same image. In order to overcome this limitation, as the last area of our research, we develop a novel multichannel blind restoration model with a single image, which eliminates the constraint of the necessity of multiple copies of the blurred image. We consider this as a major contribution which could be extended to wider areas of research integrated with multiple disciplines such as demosaicing.

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Abiri, Behrooz. "High Speed Clock and Data Recovery Techniques." Thesis, 2011. http://hdl.handle.net/1807/30162.

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This thesis presents two contributions in the area of high speed clock and data recovery systems. These contributions are focused on the fast phase recovery and adaptive equalization techniques. The first contribution of this thesis is an adaptive engine for a 2x blind sampling receiver. The proposed adaptation engine is able to find the phase-dependent DFE coefficients of the receiver on the fly. The second contribution is a burst-mode clock and data recovery architecture which uses an analog phase interpolator. The proposed burst-mode CDR is capable of locking to the first data transition it receives. The phase interpolator uses the inherent timing information in the data transition to rotate the phase of a reference clock and align it with the incoming data edge. The feasibility of the concept is demonstrated through fabrication and measurements.

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Silva, Catarina Santos. "A proporção corporal como factor adaptativo : comprimento relativo do membro inferior e o gasto energético de repouso." Master's thesis, 2016. http://hdl.handle.net/10400.5/13188.

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A presente tese contempla dois estudos e baseou-se nos dados recolhidos no âmbito do projecto de investigação Impacto do desporto federado, do desporto escolar e da actividade física regular feita após o horário escolar no estilo e qualidade de vida das crianças e dos adolescentes (6 a 11 anos) em função da sua idade óssea, um estudo transversal com duração de 3 anos, financiado pela Fundação para a Ciência e Tecnologia (FCT) (PTDC/DES/113156/2009). O primeiro estudo investigou o papel do comprimento relativo do membro inferior na relação entre a massa livre de gordura e o gasto energético de repouso numa amostra de adolescentes (n = 611, 13.63 ± 1.87 anos). Estimou-se o comprimento relativo do membro inferior através da estatura e altura sentado [CRMI = (estatura - altura sentado)/estatura] e o gasto energético de repouso utilizando a equação de Müller. Identificou-se um efeito moderador do comprimento relativo do membro inferior através de um modelo de regressão linear múltipla (β = - 0.016; SE = 0.005; p = .003). A análise de covariância mostrou que adolescentes com um comprimento relativo do membro inferior superior têm um maior gasto energético de repouso por quilograma de massa livre de gordura [F(2,607) = 6.001; R2 = .114; p = .003]. O segundo estudo focou-se na validação relativa do Nível de Actividade Física (PAL) obtido através do Questionário Biossocial e para Avaliação das Rotinas de Vida Diárias em Crianças e Adolescentes, utilizando o ActiGraph GT3X como método de comparação. Analisou-se, igualmente, o impacto da inclusão das actividades durante os períodos de não utilização na qualidade dos dados da acelerometria. Uma amostra de 127 adolescentes (14.24 ± 1.95 anos) utilizou o ActiGraph durante cinco dias consecutivos (dois de fim-de-semana) e registou a duração e percepção de esforço de actividades realizadas fora dos períodos de utilização do acelerómetro. A mesma amostra preencheu o questionário RAPIL II, que incluía a duração e frequência de um largo conjunto de actividades semanais. A análise Bland-Altman baseada na regressão mostrou que a diferença média entre métodos foi de - 1.050 + 0.689PALmédio (LOA = - 0.71298 + 0.18962PALmédio, - 1.38702 + 1.18838PAL médio) e - 1.031 + 0.654PALmédio (LOA = - 0.33236 - 0.11106PALmédio, - 1.72964 + 1.41906PALmédio), incluindo ou excluindo da análise as actividades nos períodos de não utilização. O RAPIL II é válido em contexto populacional, apresentando uma boa concordância com o ActiGraph GT3X, mas não em contexto de avaliação individual. Deve ser considerada a inclusão das actividades em períodos de não utilização do acelerómetro. Ambos os estudos abrem novos caminhos para futura investigação, quer no respeitante ao papel da proporção corporal na estimação das necessidades energéticas, quer na avaliação epidemiológica do Nível de Actividade Física, através de um método acessível e pouco dispendioso.
The present thesis comprises two studies and was based on the data collected under the research project The impact of regular competitive sport, extracurricular school-based sport and out-of-school time physical activities on lifestyle and quality of life of children and adolescents (11 to 16 years old) considering their bone age, a 3-year cross-sectional study sponsored by the Science and Technology Foundation (FCT) (PTDC/DES/113156/2009). The first study investigated the role of relative leg length on resting energy expenditure-to-fat-free mass relationship in a sample of adolescents (n = 611, 13.63 ± 1.87 years). Relative leg length was estimated through height and sitting height [RLL = (height - sitting height)/height], and resting energy expenditure using Müller equation. A moderation effect of relative leg length was identified through a multiple linear regression model (β = - 0.016; SE = 0.005; p = .003). Analysis of covariance showed that adolescents with higher relative leg length have higher resting energy expenditure by kilogram of fat-free mass [F(2,607) = 6.001; R2 = .114; p = .003]. The second study focused on the relative validation of Physical Activity Level (PAL) obtained with the Biosocial and Daily Life Routines Questionnaire for Children and Youth (RAPIL II), using ActiGraph GT3X as comparison method. It was also analyzed the impact of including non-wear time activities on the accelerometry data quality. A sample of 127 adolescents (14.24 ± 1.95 years) used the ActiGraph GT3X during five consecutive days (two weekend days), and recorded the duration and perceived exertion of non-wear time activities. The same sample completed the RAPIL II questionnaire, which included the duration and frequency of a large set of week activities. Bland-Altman regression analysis showed a mean difference between methods of -1.050+0.689MeanPAL (LOA = -0.71298+0.18962MeanPAL, -1.38702+1.18838MeanPAL) and -1.031+0.654MeanPAL (LOA = -0.33236-0.11106MeanPAL, - 1.72964+1.41906MeanPAL) when non-wear time activities were included or excluded from analysis. RAPIL II is valid on a population basis, presenting good agreement with ActiGraph GT3X, but not for individual evaluation purposes. Consideration should be given to the inclusion of non-wear time activities. Both studies open new paths for future research, either regarding the role of body proportion in energy requirements estimation, or the epidemiological assessment of Physical Activity Level through an accessible and low-cost method.

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Billette, Marc-Olivier. "Analyse en composantes indépendantes avec une matrice de mélange éparse." Thèse, 2013. http://hdl.handle.net/1866/9921.

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Анотація:

L'analyse en composantes indépendantes (ACI) est une méthode d'analyse statistique qui consiste à exprimer les données observées (mélanges de sources) en une transformation linéaire de variables latentes (sources) supposées non gaussiennes et mutuellement indépendantes. Dans certaines applications, on suppose que les mélanges de sources peuvent être groupés de façon à ce que ceux appartenant au même groupe soient fonction des mêmes sources. Ceci implique que les coefficients de chacune des colonnes de la matrice de mélange peuvent être regroupés selon ces mêmes groupes et que tous les coefficients de certains de ces groupes soient nuls. En d'autres mots, on suppose que la matrice de mélange est éparse par groupe. Cette hypothèse facilite l'interprétation et améliore la précision du modèle d'ACI. Dans cette optique, nous proposons de résoudre le problème d'ACI avec une matrice de mélange éparse par groupe à l'aide d'une méthode basée sur le LASSO par groupe adaptatif, lequel pénalise la norme 1 des groupes de coefficients avec des poids adaptatifs. Dans ce mémoire, nous soulignons l'utilité de notre méthode lors d'applications en imagerie cérébrale, plus précisément en imagerie par résonance magnétique. Lors de simulations, nous illustrons par un exemple l'efficacité de notre méthode à réduire vers zéro les groupes de coefficients non-significatifs au sein de la matrice de mélange. Nous montrons aussi que la précision de la méthode proposée est supérieure à celle de l'estimateur du maximum de la vraisemblance pénalisée par le LASSO adaptatif dans le cas où la matrice de mélange est éparse par groupe.
Independent component analysis (ICA) is a method of statistical analysis where the main goal is to express the observed data (mixtures) in a linear transformation of latent variables (sources) believed to be non-Gaussian and mutually independent. In some applications, the mixtures can be grouped so that the mixtures belonging to the same group are function of the same sources. This implies that the coefficients of each column of the mixing matrix can be grouped according to these same groups and that all the coefficients of some of these groups are zero. In other words, we suppose that the mixing matrix is sparse per group. This assumption facilitates the interpretation and improves the accuracy of the ICA model. In this context, we propose to solve the problem of ICA with a sparse group mixing matrix by a method based on the adaptive group LASSO. The latter penalizes the 1-norm of the groups of coefficients with adaptive weights. In this thesis, we point out the utility of our method in applications in brain imaging, specifically in magnetic resonance imaging. Through simulations, we illustrate with an example the effectiveness of our method to reduce to zero the non-significant groups of coefficients within the mixing matrix. We also show that the accuracy of the proposed method is greater than the one of the maximum likelihood estimator with an adaptive LASSO penalization in the case where the mixing matrix is sparse per group.

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Дисертації з теми "Blind adaptation"

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