De nouveaux concepts d’imagerie permettent aux systèmes optiques d’être plus compacts et plus performants. Parmi ces nouvelles techniques, les systèmes d’imagerie hybrides par codage de pupille allient un système optique comprenant un masque de phase et un traitement numérique. La fonction de phase implantée sur le masque rend l’image insensible à un défaut du système optique, qui peut être une aberration ou de la défocalisation. Cet avantage est obtenu au prix d’une déformation connue de l’image qui est ensuite corrigée par un traitement numérique.L’étude des propriétés de ces systèmes a été effectuée en cherchant à augmenter la profondeur de champ d’un système d’imagerie. Un gain sur ce paramètre permet déjà d’envisager le relâchement de contraintes de conception optique telles que la courbure de champ, la défocalisation thermique, le chromatisme… Dans ces techniques d’imagerie, la prise en compte du bruit du capteur constitue l’un des paramètres critiques pour le choix et l’utilisation de méthodes de traitement d’image.Les travaux menés durant cette thèse ont permis de proposer une approche originale de conception conjointe de la fonction de phase du masque et de l’algorithme de restauration d’image. Celle-ci est basée sur un critère de rapport signal à bruit de l’image finale. Contrairement aux approches connues, ce critère montre qu’il n’est pas nécessaire d’obtenir une stricte invariance de la fonction de transfert du système optique. Les paramètres des fonctions de phase optimisés grâce à ce critère sont sensiblement différents de ceux usuellement proposés et conduisent à une amélioration significative de la qualité de l’image.Cette approche de conception optique a été validée expérimentalement sur une caméra thermique non refroidie. Un masque de phase binaire qui a été mis en œuvre en association avec un traitement numérique temps réel implémenté sur une carte GPU a permis d’augmenter la profondeur de champ de cette caméra d’un facteur 3. Compte-tenu du niveau de bruit important introduit par l’utilisation d’un capteur bolométrique, la bonne qualité des images obtenues après traitement démontre l’intérêt de l’approche de conception conjointe appliquée à l’imagerie hybride par codage de pupille. / New imaging techniques allow better and smaller systems. Among these new techniques, hybrid imaging systems with wavefront coding includes an optical system with a phase mask and a processing step. The phase function of the mask makes the system insensitive to a fault of the optical system, such as an aberration or a defocus. The price of this advantage is a deformation of the image acquired by a sensor, which is then processed. The study of the properties of these hybrid imaging systems has been completed by increasing the depth of field of an imaging system, which allows to relax some design constraints such as field curvature, thermal defocus, chromaticism… In these imaging techniques, the consideration the noise of the sensor is one the critical parameters when choosing the image processing method.The work performed during this thesis allowed to proposed an original approach for the cross-conception of the phase function of the mask and the processing step. This approach is based on a signal-to-noise criterion. Unlike known approaches, this criterion shows that a strict insensitivity of the modulation transfer function of the optics is not required. The parameters of the phase functions optimized thanks to this criterion are noticeably different from those usually proposed and lead to a significant increase of the image quality.This cross-conception approach has been validated experimentally on an uncooled thermal camera. A binary phase mask associated with a real-time processing implemented on a GPU allowed to increase the depth of field of this camera by a factor 3. Considering the important level of noise introduced by the use of a bolometric sensor, the good quality of the processed image shows the interest of the cross-conception for hybrid imaging system with wavefront coding.

Introdução: O ruído é um dos principais agentes de poluição ambiental, que em intensidades elevadas, poderá causar a perda auditiva induzida por níveis de pressão sonora elevadas (PAINPSE). A PAINPSE é o segundo tipo de perda auditiva neurossensorial mais frequente, e considerada uma das principais doenças ocupacionais. Para evitar os prejuízos da exposição ao ruído ocupacional, legislações determinam o monitoramento e o desenvolvimento de ações para reduzir os efeitos da exposição, sendo o uso de dispositivos de proteção auditiva (DPA) a mais empregada. Contudo é comum que o trabalhador relate dificuldades para se comunicar com o DPA, o que pode induzi-lo ao uso inadequado. Os estudos já realizados apresentam discordâncias sobre os efeitos do DPA para a inteligibilidade da fala, além de serem poucos os que compararam participantes com perdas auditivas com normo-ouvintes. Objetivos: Avaliar a inteligibilidade de fala em trabalhadores expostos a ruído durante o uso de DPA. Métodos: Trata-se de um estudo transversal, aprovado pelo Comitê de Ética em Pesquisa da instituição nº 130/14, com amostra de 36 participantes, todos do sexo masculino e expostos ao ruído. Foram divididos em grupo normo-ouvintes (G1), com 20 participantes e com perda auditiva (G2), com 16 participantes. Todos os participantes realizaram avaliação da inteligibilidade de fala em campo acústico, utilizando listas de monossílabas e sentenças, em situações de uso do DPA no silêncio e no ruído e sem o uso do DPA no ruído. Resultados: Na avaliação da inteligibilidade de fala com DPA utilizando as monossílabas, ambos os grupos apresentaram porcentagens de acertos superiores à 95% na situação de silêncio. Na presença do ruído com o DPA, não foi detectado efeito de interação envolvendo grupo (p>=0,106) e nem efeito de grupo (p=0,182), mas houve efeito de interação entre intensidade de fala e relação sinal/ruído (S/R) (p=0,006). Na avaliação da inteligibilidade de fala no ruído sem o DPA, foi detectado efeito de interação entre uso do DPA e relação S/R (p=0,010) sobre a média das porcentagens de acertos. Na avaliação com listas de sentenças, a porcentagem de acertos com DPA foram superiores a 98% no silêncio; contudo, no ruído houve piora, com efeito de interação entre intensidade de fala e relação S/R (p=0,010) e entre grupo e relação S/R (p=0,039). Na comparação do uso/não uso do DPA, houve efeito de interação entre uso do DPA e as relações S/R (p=0,009) sobre a média das porcentagens de acertos. Conclusões: Para ambos os grupos, houve piora da inteligibilidade de fala com o aumento da intensidade do ruído; contudo, a dificuldade foi maior para o G2. Na comparação das situações com/sem o uso do DPA, o uso dificultou a inteligibilidade de fala, mas não houve diferença significante entre as situações. Por fim, ressalta-se a importância de realizar mais estudos dos efeitos do DPA na comunicação, além de inserir nas avaliações ocupacionais testes que avaliam a fala no ruído, para determinar as dificuldades que podem surgir no ambiente ocupacional, e assim desenvolver medidas que beneficiem os trabalhadores que necessitam se comunicar durante as atividades laborais / Introduction: Noise is one of the main agents of environmental pollution, and at high intensities, it may provoke noise-induced hearing loss (NIHL). NIHL is the second most frequent type of sensorineural hearing loss and it is considered one of the main occupational diseases. In order to avoid the effects of the exposition to occupational noise, legislation determines the monitoring and development of actions to reduce the effects of such exposure and one of the most applied measure is the mandatory use of hearing protection devices (HPD). However, workers often report difficulties to communicate when using the HPD, what may induce them to use it improperly. Previous studies showed divergences between the effects of HPD on speech intelligibility; besides, few studies compared participants with hearing loss to those with normal hearing. Purpose: To assess speech intelligibility of workers exposed to noise during the use of HPD. Methods: This is a cross-sectional study, approved by the Institution\'s Ethics Committee (nº 130/14) and counted on a sample of 36 participants, all males and exposed to noise. They were distributed into a normal hearing group (G1), with 20 participants and hearing loss group (G2), with 16 participants. All participants were submitted to an assessment of speech intelligibility in free field, using monosyllable and sentence lists, when using the HPD in silence and noise situation, and also without the use of HPD in noise. Results: In the assessment of speech intelligibility with HPD using the monosyllables, both groups presented percentages of correct answers above 95%. In the presence of noise with HPD, there was no interaction effect involving group (p>=0.106) or group effect (p=0.182), but there was found an interaction effect between speech intensity and signal-to-noise ratio (SNR) (p=0.006). In the assessment of speech intelligibility in noise without HPD, an interaction effect between HPD use and SNR (p=0.010) was detected over the mean percentage of correct answers. In the evaluation with lists of sentences, the percentage of correct answers with HPD were superior to 98% in the silence; however, in noise, there was a decrease on the interaction effect between speech intensity and SNR (p = 0.010) and between group and SNR (p = 0.039). In the comparison with/without use of HPD, there was found an interaction effect between hearing protection use and SNR (p = 0.009) on the mean percentage of correct answers. Conclusions: For both groups, it was noticed that speech intelligibility decrease with the increasing of noise intensity; nevertheless, the difficulty was greater for the group with hearing loss. In the comparison of situations with and without the use of HPD, its use made speech intelligibility more challenging, but no significant difference between the situations was found. Finally, it is important to highlight the importance of further studies regarding the effects of HPD on communication and, besides, inserting speech-in-noise tests in occupational examination in order to determine the difficulties that may arise in the occupational environment and thus, develop measures that benefits the workers who need communicate during their labor activities

Submitted by Kelren Mota (kelrenlima@ufpa.br) on 2018-06-14T18:39:25Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_MetodologiaPredicaoPerda.pdf: 3699343 bytes, checksum: 3b43522af593666187f8aef07927421f (MD5) / Approved for entry into archive by Kelren Mota (kelrenlima@ufpa.br) on 2018-06-14T18:39:41Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_MetodologiaPredicaoPerda.pdf: 3699343 bytes, checksum: 3b43522af593666187f8aef07927421f (MD5) / Made available in DSpace on 2018-06-14T18:39:41Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_MetodologiaPredicaoPerda.pdf: 3699343 bytes, checksum: 3b43522af593666187f8aef07927421f (MD5) Previous issue date: 2018-02-27 / Esta dissertação apresenta uma metodologia que visa auxiliar o planejamento de sistemas de redes sem fio indoor, que requerem o conhecimento prévio dos ambientes nos quais serão implantados. Assim, é necessário precisão na análise do sinal por meio de uma abordagem empírica estatística, que leva em consideração alguns fatores que influenciam na propagação do sinal indoor: arquitetura dos prédios; disposição de móveis no interior dos compartimentos; números de paredes e pisos de diversos materiais, além do espalhamento das ondas de rádio. A metodologia adotada é baseada em medições com uma abordagem cross-layer, que demonstra o impacto da camada física em relação à camada de aplicação, com o objetivo de prever o comportamento da métrica de Qualidade de Experiência (QoE), chamada de Peak signal-to-noise ratio (PSNR), em transmissões de vídeo em 4k em redes sem fio 802.11ac, no ambiente indoor. Para tanto, foram realizadas medições, que demonstram como o sinal/vídeo se degrada no ambiente estudado, sendo possível modelar esta degradação por meio de uma técnica de inteligência computacional, chamada Redes Neurais Artificiais (RNA), na qual são inseridos parâmetros de entrada como, por exemplo, a distância do transmissor ao receptor e o número de paredes atravessadas a fim de predizer perda de propagação e perda de PSNR. Para avaliar a capacidade de predição dos métodos propostos, foram obtidos os valores dos erros Root Mean Sqare (RMS) entre os dados medidos e os preditos, pelo os métodos de predição perda de propagação e perda de PSNR, sendo os valores respectivos 2,17 dB e 2,81 dB. / This dissertation presents a methodology that aims to assist the planning of indoor wireless network systems, which require prior knowledge of the environments in which they will be deployed. Thus, accurate signal analysis is necessary by means of a statistical empirical approach, which takes into account some factors that influence the propagation of the indoor signal: architecture of the buildings; arrangement of furniture inside the compartments; numbers of walls and floors of various materials, and the spread of radio waves. The methodology adopted is based on measurements with a cross-layer approach, which demonstrates the impact of the physical layer in relation to the application layer, in order to predict the behavior of the Quality of Experience (QoE) metric, called Peak signal- to-noise ratio (PSNR), in 4K video streams on 802.11ac wireless networks in the indoor environment. In order to do so, measurements were performed, which demonstrate how the signal / video degrades in the studied environment. It is possible to model this degradation by means of a computational intelligence technique, called Artificial Neural Networks (RNA), in which input parameters are inserted as, for example, the distance from the transmitter to the receiver and the number of walls crossed in order to predict loss of propagation and loss of PSNR. In order to evaluate the predictive capacity of the proposed methods, the values of the Root Mean Sqare (RMS) errors between the measured and predicted data were obtained by the prediction methods loss of propagation and loss of PSNR, with respective values of 2.17 dB and 2.81 dB.

Mes travaux de thèse portent sur l’application de l’imagerie fUS (functional ultrasound imaging) à l’imagerie cérébrale préclinique chez le petit animal. Le but était de transformer cette technique d’imagerie cérébrale récente en un véritable outil de quantification de l’état cérébral. Les objectifs principaux ont été de démontrer la faisabilité de l’imagerie fUS chez le petit animal non anesthésié ainsi que de passer du modèle rat au modèle souris - modèle de choix en imagerie préclinique en neurosciences - de surcroît de façon non invasive. J’ai tout d’abord mis au point une nouvelle séquence d’imagerie ultrasonore ultrarapide (Multiplane Wave imaging), permettant d’améliorer le rapport signal-à-bruit des images grâce à l’augmentation virtuelle de l’amplitude du signal émis, sans diminuer la cadence ultrarapide d’acquisition. Dans un deuxième temps j’ai démontré la possibilité d’imager le cerveau de la souris et du jeune rat anesthésiés par échographie Doppler ultrarapide, de manière transcrânienne et complètement non invasive, sans chirurgie ni injection d’agents de contraste. J’ai ensuite mis au point un montage expérimental, une séquence ultrasonore et un protocole expérimental permettant de réaliser de l’imagerie fUS de manière minimalement invasive chez des souris éveillées et libres de leurs mouvements. Enfin, j’ai démontré la possibilité d’utiliser le fUS pour étudier la connectivité fonctionnelle du cerveau au repos (sans stimulus) chez des souris éveillées ou sédatées. L’imagerie fUS et la combinaison « modèle souris » + « minimalement invasif » + « animal éveillé » + « connectivité fonctionnelle » constituent un outil précieux pour la communauté des neuroscientifiques travaillant sur des modèles animaux pathologiques ou de nouvelles molécules pharmacologiques / My work focuses on the application of fUS (functional ultrasound) imaging to preclinical brain imaging in small animals. The goal of my thesis was to turn this recent vascular brain imaging technique into a quantifying tool for cerebral state. The main objectives were to demonstrate the feasibility of fUS imaging in the non-anaesthetized small rodents and to move from rat model imaging to mouse model imaging –most used model for preclinical studies in neuroscience-, while developing the least invasive imaging protocols. First, I have developed a new ultrafast ultrasonic imaging sequence (Multiplane Wave imaging), improving the image signal-to-noise ratio by virtually increasing emitted signal amplitude, without reducing the ultrafast framerate. Then, I have demonstrated the possibility to use ultrafast Doppler ultrasound imaging to image both the mouse brain and the young rat brain, non-invasively and through the intact skull, without surgery or contrast agents injection. Next, I have developed an experimental setup, an ultrasound sequence and an experimental protocol to perform minimally invasive fUS imaging in awake and freely-moving mice. Finally, I have demonstrated the possibility to use fUS imaging to study the functional connectivity of the brain in a resting state in awake or sedated mice, still in a transcranial and minimally invasive way. fUS imaging and the combination of "mouse model" + "minimally invasive" + "awake animal" + "functional connectivity" represent a very promising tool for the neuroscientist community working on pathological animal models or new pharmacological molecules

Processing of broadband signals induced on an antenna array using a tapped delay line filter and a set of steering delays has two problems. Firstly one needs to manipulate large matrices to estimate the filter coefficients. Secondly the use of steering delays is not only cumbersome but implementation errors cause loss of system performance. This thesis looks at both of these problems and presents elegant solutions by developing and studying a design method referred to as the DFT method, which does not require steering delays and is computationally less demanding compared to existing methods. Specifically the thesis studies and compares the performance of a time domain element space beamformer using the proposed method and that using an existing method, and develops the DFT method when the processor is implemented in partitioned form. The study presented in the thesis shows that the processors using the DFT method are robust to look direction errors and require less computation than that using the existing method for comparable performance. The thesis further introduces a broadband beamformer design which does not require any steering delays between the sensors and the tapped delay line section as is presently the case. It has the capability of steering the array in an arbitrary direction with a specified frequency response in the look direction while canceling unwanted uncorrelated interferences. The thesis presents and compares the performance of a number of techniques to synthesize an antenna pattern of a broadband array. These techniques are designed to produce isolated point nulls as well as broad sector nulls and to eliminate the need for the steering delays. Two of the pattern synthesis techniques presented in the thesis allow optimization against unwanted interferences in unknown directions. The techniques allow formulation of a beamforming problem such that the processor is not only able to place nulls in specified directions but also able to cancel directional interferences in unknown directions along with a specified frequency response in the look direction over a band of interest. The thesis also presents a set of directional constraints such that one does not need steering delays and an array can be constrained in an arbitrary direction with a specified frequency response. The constraints presented in the thesis are simple to implement. Based on these constraints a pattern synthesis technique for broadband antenna array is also presented.

Η διαμόρφωση με πολύπλεξη συχνότητας ορθογωνίων φερουσών (Orthogonal Frequency Division Multiplexing - OFDM) έχει εδραιωθεί ως μία από τις επικρατέστερες μεθόδους διαμόρφωσης για την υψηλού ρυθμού μετάδοση πληροφορίας μέσω ασύρματων μέσων. Σε ένα σύστημα OFDM, ένα από τα βασικότερα και υπολογιστικά πολυπλοκότερα τμήματα είναι ο υπολογισμούς του Ταχύ Μετασχηματισμού Fourier. Αντικείμενο της εργασίας αυτής είναι η μελέτη της χρήσης εναλλακτικής αριθμητικής για την υλοποίηση κυκλωμάτων FFT. Τυπικά, τέτοιου είδους κυκλώματα υλοποιούνται χρησιμοποιώντας κάποια γραμμική αναπαράσταση σταθερής υποδιαστολής. Στη βιβλιογραφία έχουν προταθεί υλοποιήσεις του FFT με χρήση του Λογαριθμικού Συστήματος Αρίθμησης (Logarithmic Numbering System – LNS) και έχουν αναφερθεί κέρδη για συγκεκριμένους παράγοντες όπως το σφάλμα κβαντισμού, η επιφάνεια ολοκλήρωσης και η κατανάλωση ισχύος. Η αποδοτικότητα αυτών των λύσεων ερευνάται για τη συγκεκριμένη περίπτωση της εφαρμογής του FFT σε OFDM modems. Εστιάζοντας στην περίπτωση του FFT 64 σημείων για OFDM modem για ασύρματα δίκτυα 802.11a, μία από τις πλέον επιτυχημένες αρχιτεκτονικές που έχουν προταθεί για την υλοποίηση του, στηρίζεται στη λογική του FFT γραμμής – στήλης και παρουσιάζει έναν τρόπο πραγματοποίησης του υπολογισμού χωρίς κανένα ψηφιακό πολλαπλασιαστή. Με το βασικό πλεονέκτημα της λογαριθμικής αναπαράστασης να είναι η απλοποίηση των κυκλωμάτων πολλαπλασιασμού (με ταυτόχρονη όμως αύξηση του κόστους για την πραγματοποίηση προσθέσεων), δείχνεται ότι τελικά η υλοποίηση ενός FFT αμιγώς σε LNS δεν είναι προτιμητέα. Αν και η αρχιτεκτονική του FFT γραμμής – στήλης μπορεί να προσφέρει υψηλή απόδοση με χαμηλό κόστος υλοποίησης, παρουσιάζει μια σειρά από αδυναμίες, που σχετίζονται κυρίως με τη χρήση ειδικών κυκλωμάτων για την εκτέλεση των πολλαπλασιασμών με τις σταθερές που εμφανίζονται στον FFT (twiddle factors). Για την αντιμετώπιση αυτών των περιορισμών προτείνεται η εισαγωγή του LNS σε κάποια τμήματα του κυκλώματος του FFT, οδηγώντας έτσι στη δημιουργία ενός συστήματος μικτής αναπαράστασης. Σε τέτοιου είδους υβριδικά συστήματα τίθενται δύο βασικά ζητήματα. Το πρώτο αφορά τον ορισμό της ισοδυναμίας μεταξύ των διαφορετικών αναπαραστάσεων και το δεύτερο τον αποδοτικό τρόπο υλοποίησης των κυκλωμάτων μετατροπής από το ένα αριθμητικό σύστημα στο άλλο. Τυπικά, τα κριτήρια ισοδυναμίας που επιλέγονται είναι αυστηρά μαθηματικά ορισμένα, όπως για παράδειγμα ο Λόγος Σήματος προς Θόρυβο (Signal-to-Noise Ratio - SNR) ή το Μέσο Σχετικό Σφάλμα Αναπαράστασης (Average Relative Representation Error – ARRE). Στη συγκεκριμένη εργασία ακολουθείται μια λιγότερο δεσμευτική προσέγγιση, ορίζοντας την ισοδυναμία δύο αναπαραστάσεων με βάση την τελική απόδοση του συστήματος OFDM όσον αφορά το ρυθμό λαθών στο δέκτη (Bit Error Rate - BER). Με βάση αυτή τη λογική, αποδεικνύεται ότι μπορούν να χρησιμοποιηθούν αναπαραστάσεις πολύ μικρού μεγέθους λέξης και οι προσεγγίσεις που χρειάζεται να γίνουν κατά τις μετατροπές μεταξύ των δύο συστημάτων δεν είναι ανάγκη να είναι ιδιαίτερα ακριβείς. Έτσι, τα σχετικά κυκλώματα μπορούν να υλοποιηθούν αποδοτικά και με μικρό κόστος. Η υλοποίηση δύο συστημάτων για τον FFT 64 σημείων, ένα βασισμένο αποκλειστικά σε γραμμική αναπαράσταση σταθερής υποδιαστολής και ένα υβριδικό που χρησιμοποιεί γραμμική και λογαριθμική αναπαράσταση, δείχνει ότι χωρίς διαφορές όσον αφορά το BER και την καθυστέρηση (delay), η υβριδική προσέγγιση απαιτεί μικρότερη επιφάνεια ολοκλήρωσης και παρουσιάζει σημαντικά χαμηλότερη κατανάλωση ισχύος. / Orthogonal Frequency Division Multiplexing (OFDM) has been established as one of the most prevalent methods for high data rate transmission through wireless channels. In an OFDM communication system, one of the fundamental and most computationally intensive parts is the computation of the Fast Fourier Transform (FFT). The subject of this thesis is to investigate the use of alternative arithmetic representation systems for the implementation of FFT circuits. Typically, these circuits are implemented using linear fixed-point representations. In literature, implementations of the FFT using the Logarithmic Numbering System (LNS) have been proposed and significant gains in quantization errors, chip area and power consumption have been reported. The effectiveness of these proposals in the case of the FFT for OFDM systems is investigated. Focusing on the case of the 64-point FFT for an OFDM modem for an 802.11a wireless network, one of the most efficient architectures proposed is based on the concept of row-column FFT and presents a way of implementing the computation without using any digital (non-fixed input) multiplier. The most important feature of the LNS representation is the fact that multiplication operations turn to mere additions, thus there are significant implementation gains. On the downside though, addition in LNS is very expensive. Combining the aforementioned, it is shown that the implementation of the whole FFT computation in LNS is not a preferable solution. Although the row-column FFT architecture may offer high performance and low implementation cost, it presents a number of deficiencies mainly due to the fact that special purpose circuits are used to perform the multiplications with the complex constants (twiddle factors) that appear in the computation. In order to alleviate these deficiencies, it is proposed to use the LNS representation in some parts of the FFT circuit, thus forming a hybrid-representation system. In hybrid-representation systems two major issues are raised. The first one is how to define equivalence between the arithmetic representation systems used and the second one is related to the cost of the circuits required to perform the conversions between the numbers of the different arithmetic systems. Typically, the equivalence criterion used is mathematically defined and metrics like the Signal-to-Noise Ratio (SNR) or Average Relative Representation Error (ARRE) are commonly used. In this report, a less restrictive metric is used: two arithmetic representations are defined to be equal if the Bit Error Rate (BER) performance of the overall OFDM system is equal. Using this approach, it is shown that short word-length representations may be used and the conversions between the linear and logarithmic systems need not be very accurate. This results in great simplification of the conversion process and the respected circuits can be implemented with low cost. For comparison, two 64-point FFT systems have been implemented, one using a linear fixed-point 2’s complement representation and one using both linear and LNS representation. Without any differences in BER performance and circuit delay, the hybrid-representation system requires less chip area and consumes significantly lower power.

No description available.

Secret key generation from reciprocal multi-antenna channels is an interesting alternative to cryptographic key management in wireless systems without infrastructure access. In this work, we study the secret key rate for the basic source model with a MIMO channel. First, we derive an expression for the secret key rate under spatial correlation modelled by the Kronecker model and with spatial precoding at both communication nodes. Next, we analyze the result for uncorrelated antennas to understand the optimal precoding for this special case, which is equal power allocation. Then, the impact of correlation is characterized using Majorization theory. Surprisingly for small SNR, spatial correlation increases the secret key rate. For high SNR, the maximum secret key rate is achieved for uncorrelated antennas. The results indicate that a solid system design for reciprocal MIMO key generation is required to establish the secret key rate gains.

Thesis (Master').

Ce travail de thèse a pour but de suivre le comportement du liant ionomère après vieillissement en condition réelle d'utilisation de la pile. Dans un premier temps, diverses techniques de caractérisation en phase solide ont été utilisées afin d'étudier le ionomère présent dans les électrodes. La majeure partie de ces techniques se sont avérées insatisfaisantes pour le suivi du vieillissement du ionomère. Seule l'analyse par diffraction rayon X (DRX) a mis en avant un changement d'organisation structurale du ionomère dans les électrodes. Par la suite, nous avons choisi de caractériser le ionomère en solution après extraction par l'eau. Préalablement, un protocole de quantification en 2 à 3 étapes, dans lequel intervient une quantification via le rapport signal-sur-bruit (S/N), a été mis en place afin de quantifier le Nafion® et autres petites molécules fluorés. L'extraction Soxhlet a ensuite été réalisée sur les électrodes permettant de révéler la présence d'un produit de dégradation hydrosoluble après fonctionnement en pile, à la fois en cathode et en anode. Enfin, la macération des électrodes dans le diméthylacétamide (DMAc) a permis d'extraire le polymère Nafion® ainsi que deux acides : l'acide trifluoroacétique (TFA) et l'acide triflique (TFI). En conclusion, la corrélation de l'ensemble des observations nous a permis de proposer un mécanisme de dégradation du liant ionomère présent dans les électrodes. / The purpose of this study was to follow the behavior of ionomer binder after fuel cell operation. First, a series of techniques were used to investigate to characterize ionomer in electrode at solid state. Most of them were inefficient to study ionomer degradation. Only X-Ray Diffraction (XRD) pointed out a structural change of the binder in electrodes. Second, it has been decided to characterize ionomer in liquid state after water extraction. But first of all, a quantitative 19F NMR protocol composed of two to three steps, with a first step using a quantification through signal-to-noise ratio (S/N), was establish in order to quantify Nafion® and degradation products. Soxhlet extraction performed on electrodes allowed to detect a degradation product water-soluble. Finally, extraction with organic solvent (Dimethylacetamide) allowed to extract Nafion® and two acid: trifluoroacetic acid (TFA) and triflic acid (TFI) from electrodes. In conclusion, correlation between observation and literature allowed us to propose a degradation mechanism of ionomer in electrodes.