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Pour réduire la consommation d'énergie due aux transmissions radio dans les réseaux de capteurs sans fil, nous proposons une nouvelle approche associant les techniques de précodage MIMO et de relais, appelé précodage distribué max-dmin (DMP). Considérant une source et un relais avec une antenne chacun, et une destination disposant de deux antennes, nous déployons un système MIMO précodé virtuel 2 × 2. Dans ce contexte, nous étudions deux techniques de relais Amplify and Forward (AF) et Decode and Forward (DF). Des comparaisons en termes de taux d'erreur et d'efficacité énergétique par rapport aux systèmes plus classiques comme les codes spatio-temporels distribués ou les combinaisons à gain maximal montrent que notre système est intéressant pour des distances de transmission moyennes (à partir de 16 mètres). Toujours dans l'objectif de maximiser l'efficacité énergétique, nous proposons une allocation de puissance sur les nœuds source et relais. Pour cela, nous dérivons analytiquement les performances du système précodage distribué max-dmin selon le mode AF et DF. Enfin,pour améliorer les performances des systèmes avec décodage au relais (DF), nous proposons un nouveau récepteur (à la destination) qui tient compte des erreurs éventuelles au niveau du relais. / Among various cooperative techniques aiming to reduce power consumption for transmissions between Wireless Body Area Networks (WBAN) and base stations, we present a new approach, named distributed max-dmin precoding (DMP), combining MIMO precoding techniques and relay communications. This protocol is based on the deployment of a virtual 2 × 2 max-dmin precoding over one source, one forwarding relay, both equipped with one antenna and a destination involving 2 antennas. In this context, two kinds of relaying, amplify and forward (AF) or decode and forward (DF) protocols, are investigated. The performance evaluation in terms of Bit-Error-Rate (BER) and energy efficiency are compared with non cooperative techniques and the distributed space time block code (STBC) scheme. Our investigations show that the DMP takes the advantage in terms of energy efficiency from medium transmission distances (after 10 meters). In order to maximise the energy efficiency, we propose a power allocation over the source and the relay. Thus, we derive the performance of our system, both for AF and DF, analytically. To further increase the performance of DF cooperative schemes, we also propose to design a new decoder at the destination that takes profit from side information, namely potential errors at the relay.

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The Finite Difference Time Domain (FDTD) Method has been a powerful tool in numerical simulation of electromagnetic (EM) problems for decades. In recent years, it has also been applied to biomedical research to investigate the interaction between EM waves and biological tissues. In Wireless Body Area Networks (WBANs) studies, to better understand the localization problem within the body, an accurate source/receiver model must be investigated. However, the traditional source models in FDTD involve effective volume and may cause error in near field arbitrary direction. This thesis reviews the basic mathematical and numerical foundation of the Finite Difference Time Domain method and the material properties needed when modeling a human body in FDTD. Then Coincident Phase Centers (CPCs) point sources models have been introduced which provide nearly the same accuracy at the distances as small as 3 unit cells from the phase center. Simultaneously, this model outperforms the usual sources in the near field when an arbitrary direction of the electric or magnetic dipole moment is required.

This paper presents a scheduling algorithm for point to point wireless power transfer system (WPTS) to sensor nodes of wireless body area networks (WBAN). Since the sensors of wireless body area networks are continuously monitoring and sending data to remote central unit, power crisis for these sensor nodes degrades the data transfer of patient monitoring system. Although energy harvesting from ambient sources using electromagnetic induction enhances the longevity of sensor performance, continuous operation in the primary side decreases the overall efficiency. With such paradigm in sight, a framework is proposed for increasing the primary battery longevity and reducing the transmission loss, inductive power is transmitted from primary to secondary unit using medium access control (MAC) protocols for underlying the centralized scheduling opportunity in a collision free scheme for channel access of rare yet critical emergency situation. In a preliminary study, the proposed scheduling for charging sensor nodes in a wireless body area network (WBAN) is evaluated in a case consideration.

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The presented work considers a CDMA-based Wireless Body Area Network (WBAN) where multiple biosensors communicate simultaneously to a central node in an asynchronous fashion. The asynchronous nature of the WBAN introduces Multiple Access Interference (MAI). To combat this problem, presented is a methodology that uses a set of cyclically orthogonal spreading codes extracted from the Walsh-Hadamard matrix. When using the Cyclic Orthogonal Walsh-Hadamard Codes (COWHC) as spreading codes in the CDMA-based WBAN, the cyclic orthogonality property helps mitigate MAI amongst the on-body sensors. Presented is an ideal communication system that is most effective at mitigating MAI in proactive WBANs. The work illustrates the system optimality and effectiveness at mitigating MAI by studying the sensitivity to packet-loss through simulating the link Bit Error Rate (BER) performance. It is shown that the proposed design with COWHC, a Rayleigh flat-fading channel, BPSK modulation and a conventional receiver produce optimum MAI mitigation.