Quality of service and routing in wireless mesh networks. (Qualité de service et routage dans les réseaux maillés sans fil)

Wireless mesh networks are a promising technology for providing last-mile broadband wireless Internet to a large number of users spread across large geographical regions. Due to their peculiar limitations and the increasing demand of users for high performance (high throughput, low delays etc), mesh networks have attracted the attention of researchers world-wide. Towards this goal, this dissertation contributes in several areas of Routing and Quality-ofService provisioning in IEEE 802.11-based wireless mesh networks. Chapter 1 introduces wireless mesh networks and their architectural and functional components. The difference between mesh networks and traditional wireless multi-hop networks is emphasized. A comprehensive background study of routing and QoS solutions for multi-hop wireless networks is presented with an emphasis on mesh-specific solutions. Chapter 2 presents our first contribution : route selection in wireless mesh networks. A primary research problem in mesh networks is to find the "best" available route between a pair of mesh routers. Recent research shows that selecting the shortest path is a poor decision as it does not take into account other factors pertaining to link quality. We propose an efficient routing metric Expected Link Performance metric (ELP) which considers a number of factors including link loss ratio, link interference, and link capacity to find the ”best” route between a pair of mesh routers. Performance evaluation of ELP is carried out against contemporary routing metrics. A part of metric is also evaluated on a mesh testbed. An extension of the metric is proposed for the special case of mesh traffic directed at gateways. A gateway discovery protocol is also proposed which integrates the extended metric and performance evaluation is carried out against traditional gateway and gateway-route selection schemes. Chapter 3 presents our second contribution : route maintenance in mesh networks. After route selection, the next research problem that we consider is the maintenance of that route. The route maintenance mechanism of on-demand routing protocols in 802.11-based mesh networks is inaccurate and results in frequent route breakages which cause route instability and performance degradation. The chapter discusses the problem of route stability for ondemand protocols in detail. The Efficient Route Maintenance (ERM) scheme is proposed which improves route maintenance for on-demand routing protocols in wireless mesh networks by using cross-layering to get information from lower layers. The ERM scheme is then extended for multi-radio multi-channel mesh scenarios. ERM is evaluated against classical route maintenance mechanism of the on-demand routing protocols. Chapter 4 presents the final contribution of the thesis : QoS framework for bandwidth guarantees in multi-radio multi-channel mesh networks. Providing QoS guarantees is particularly important for users who use the mesh network to access the Internet. The framework provides flow-specific reservation-based bandwidth guarantees in mesh networks. Link diversity (the availability of multiple redundant links between neighbors) is exploited for proposing a novel QoS provisioning solution which can provide better load-balancing in the network and provide a higher flow admittance ratio.