Made available in DSpace on 2016-08-17T14:52:56Z (GMT). No. of bitstreams: 1 Juan Moises Mauricio Villanueva.pdf: 944458 bytes, checksum: 0b17f88c59a4149e61f4f3fa0969445e (MD5) Previous issue date: 2005-03-03 / In several applications in electronics, the generation of nonlinear function values using low-cost embedded systems is a problem. The nonlinear functions cannot be directly implemented due to restrictions of fixed-point calculations and limited resolution that are characteristics of the architecture of the processor employed. In this work, a procedure for determining piecewise linear approximation of nonlinear functions for a low-cost embedded system is presented. In order to solve this problem, a hierarchical evolutionary algorithm has been developed for determining the position and the minimal number of breakpoints and the minimal size of the look-up table for storing these breakpoints, for generating the approximated function values. The nonlinear function can be approximated using piecewise linear functions from the obtained breakpoints. The developed algorithm is tested using the case of approximating the first quadrant of a sine function, and the obtained results are presented for different resolutions for the input and output values generation. / Em diversas aplicações em eletrônica existe o problema de gerar valores de funções não lineares utilizando-se sistemas embarcados de baixo custo. Essas funções não lineares não podem ser implementadas diretamente devido às restrições de cálculo em ponto fixo e resolução limitada, características de arquitetura do processador empregado. Nesta dissertação, apresenta-se um procedimento para a determinação de aproximação linear por partes de funções não lineares para sistemas embarcados de baixo custo. Para resolver este problema, desenvolveu-se um algoritmo hierárquico evolutivo que determinará a posição e número mínimo de pontos de quebra e tamanho mínimo da tabela de equivalência para armazenar esses pontos de quebra, para gerar os valores da função aproximada. A função não linear pode então ser aproximada por funções lineares a partir dos valores dos pontos de quebra encontrados. O algoritmo desenvolvido é testado para o caso de aproximação da função seno no primeiro quadrante, e os resultados obtidos são apresentados para diversas resoluções de entrada e de geração dos valores de saída.

De nos jours, une forte croissance des objets connectés est constatée, dépassant même la population mondiale. Devant l'ampleur de ce phénoméne, l'efficacité énergétique des objets communicants est une sérieuse problématique. La maximisation de leur durée de vie est requise pour assurer une qualité de service. Dans cette optique, les travaux de cette thèse visent à optimiser la consommation énergétique des communications sans fil dans un réseau de capteurs. Le télé-réveil, un concept imaginé depuis une dizaine d'années, consiste au déclenchement du réveil du noeud communicant par un signal radio à distance. Par défaut, le noeud reste en mode veille de façon permanente à très basse consommation. Au besoin, il peut être réveillé à la demande par un signal radio spécifique. Ainsi, la consommation énergétique du module radio est grandement réduite par l'écoute passive du canal en mode veille. Ce principe de télé-réveil nécessite toutefois le développement de nouvelles architectures matérielles associées à des protocoles de communication adaptés et innovants. Malgré les propositions récentes, le niveau de maturité technologique n'a pas encore été atteint sur ce sujet. Par conséquent, un système de télé-réveil est proposé dans cette thèse, en incluant une caractérisation théorique de ses performances. Le récepteur de télé-réveil consomme 363 nW en mode veille contre 49,8 µW en mode de réception. De plus, deux nouveaux protocoles de télé-réveil DoRa et DC-DoRa sont proposés avec une évaluation de leurs performances par simulation. Les résultats obtenus montrent que ces protocoles de télé-réveil diminuent fortement l'énergie consommée par le module radio, en comparaison des protocoles MAC actuellement utilisés dans les réseaux de capteur. Enfin, la mise en œuvre expérimentale du système et des protocoles de télé-réveil a permis de mesurer les performances réelles de notre approche dans un environnement de surécoute et d'interférence. / Nowadays, a significant growth of connected things is observed, exceeding even the worldpopulation. Given the magnitude of this phenomenon, the energy efficiency of communicatingobjects is a crucial issue. Maximizing their lifetime is necessary to ensure a qualityof service. In this regard, the aim of this thesis is to optimize the energy consumption ofwireless communications in a wireless sensor network.The concept of wake-up radio was created a decade ago, which consists of waking up thecommunicating node by a remote radio signal. By default, the node remains in sleepingmode at a very low power consumption. If needed, the node can be woken up on demandthrough a specific radio signal. Thus, the energy consumption of the radio module is greatlyreduced by idle listening to the channel in sleeping mode. However, this wake-up radioprinciple requires the development of new hardware architectures associated with adaptedand innovative communication protocols. Despite recent proposals, the level of technologymaturity has not yet been reached on this subject.Therefore, a wake-up radio system is proposed in this thesis, including a theoreticalcharacterization of its performances. The wake-up receiver consumes 363 nW in sleepingmode and 49.8 µW in receiving mode. Moreover, two new protocols called DoRa and DC-DoRaare proposed with an evaluation of their performances by simulation. The resultsshow that these wake-up radio protocols greatly reduce the energy consumed by the radiomodule, compared to the MAC protocols currently used in wireless sensor networks. Finally,the experimental implementation of the wake-up radio system and protocols enabled thereal performance measurement of our approach in an environment with overhearing andinterference.