Quality of service in wireless local area networks. (Qualité de service dans les réseaux locaux sans-fil)

Qualité de service dans les réseaux locaux sans-fil (Quality of service in wireless local area networks) Date de soutenance: 7 octobre 2002 Composition du jury: Thèse préparée au sein du projet PLANETE de l'INRIA Rhône-Alpes Abstract IEEE 802.11 wireless networks are widely used to connect to the Internet due to their low cost, easy deployment and mobility support. In this thesis we deal with four different aspects of QoS support in these networks: • Service differentiation: The current IEEE 802.11 protocol has no QoS support. Therefore, all terminals equally share the available data rate. We propose mechanisms for service differentiation on the MAC level. We develop several differentiation mechanisms and evaluate their performance through simulation. • Noisy environments: IEEE 802.11 use contention windows to resolve multiple terminals' access to the channel. A terminal doubles its contention window size upon each packet loss. This mechanism reduces collisions on the channel. However, it increases packet overhead, thus reducing the throughput. Packet losses can be due to collisions or to noise on the channel as well. In the latter case, increasing the contention window size decreases the system performance; contention windows should be decreased upon packet collisions only. We propose a mechanism to adapt contention window sizes according to the estimation of the packet loss cause. • Congested environments: After each successful packet transmission, IEEE 802.11 resets its contention window size. However, in congested environments, the channel load may vary so fast, and a terminal takes the risk of observing the same collisions and retransmissions rate for each packet. We propose a mechanism to decrease contention windows slowly, avoiding further collisions and retransmissions. This showed considerable throughput enhancements and reduced energy consumption. • Ad-hoc networks: In ad-hoc networks, packets are routed on multi-hop path routes. Routing is therefore a cooperative work between nodes, and the average available data rate to each node depends on the number of nodes, on interference and on collisions. We propose a mechanism to control data rates at the sources, based on estimations of the throughputs and delays, aiming to optimize the useful throughputs and to reduce battery power consumption. Mots-clés: Contrôle d'accès au medium, différentiation de services, qualité de service, réseaux sans-fil. Acknowledgment While I was enjoying my time preparing my Ph.D., many volunteers were offering their humanitarian help somewhere in the " unknown " world, trying to compensate my negligence.