Conception d'une interface inter-couches pour les reseaux ad hoc a detection multi-utilisateurs

For the next generations of wireless systems, ad hoc networks are needed to solve the coverage problems, where wired lines and cellular systems cannot be deployed. In this kind of networks, the major loss of performance is due to the wireless medium which introduces fading in the radio waveform. The behaviour of the wireless medium also introduces errors on the data received at physical layer. The different layers of the protocols stack are seriously affected trough the packets received, the data flows and the services.;To cope with these degradations, the layers architecture is limited by its lack of flexibility. In this work cross-layer methodology is used to increase the capacity of ad hoc networks. We adopted the principle according to which the knowledge of the wireless channel characteristics and the mathematical structure of the modulator are important sources of gain for MAC layers mechanisms such as, the rate control, the scheduling, and the quality of service provided. To achieve this goal, we designed and implemented a framework which provides some synergy between MAC and physical layers. The wireless channels of the connected users are predicted and the data packets are sent at different rate according to the predicted gains. Least mean square algorithm is preferred for the prediction, to reduce the system complexity. The novelty of the work is the high capacity of network addressed and the multiuser context. Physical layer is chosen to implement a software defined radio based multi-users detectors platform, which integrates the linear multi-user detectors and the matched filter receiver. MAC layer implements a full multi-user detection protocol, designed to support in the nodes position of reception several users' signals and packets detection at the same time.;Different wireless channels and two scenarios of mobility are used to evaluate the performances of the framework by computer simulations. We demonstrate that the knowledge of the channel state information at MAC layer increases the performance. Important gain of performance is achieved by multi-rates transmissions schemes among which multi-processing gain schemes gives globally the higher throughput, and the decorrelating multiuser detector, the better quality of reception. Variable slot duration is beneficial for the system and the node MAC layers resist to multiple access interferences. Also, the different schemes and the detection platform are used to achieve fixed QoS transmissions which outperform the single rate system transmission.;Firstly, the scheme proposed, increases the user capacity and network quality of service. It gives a wide range of high data rates and low target bit error rates. It is well fitted to support high-quality multi-media transmissions, and to improve the performance of applications that require high quality of service (QoS). Secondly, it fills the need of reconfigurability of ad hoc network. In particular for the multiuser detection based ad hoc network the framework could be implemented as software on the radios. Thirdly it could adapt itself to the environment of the deployment of the different ad hoc networks, and future cognitive radios networks.