Quality of service in wireless local area networks

Imad Aad 1
1 PLANETE - Protocols and applications for the Internet
Inria Grenoble - Rhône-Alpes, CRISAM - Inria Sophia Antipolis - Méditerranée
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.
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Imad Aad. Quality of service in wireless local area networks. Networking and Internet Architecture [cs.NI]. Université Joseph-Fourier - Grenoble I, 2002. English. ⟨tel-00406507⟩

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