Towards conflict-free switching in multihop wireless mesh networks

In wireless mesh networks, an important open problem is that of efficiently supporting end-to-end real-time flows such as voice, video or aggregated infrastructure traffic. The overall performance achieved by conventional layered approaches (802.11 MAC combined with independent ad hoc routing protocols) is significantly lower than the underlying network capacity due to interferences and poor interactions between MAC and routing layers. In this Ph.D. thesis, we propose a ``conflict-free switching'' framework to handle this challenge through a combination of techniques at the medium access control (MAC) and network (routing) layers. At first, we focus on the per-packet scheduling in MAC layer only and propose the D-LSMA MAC protocol as an enhancement of IEEE 802.11 MAC to solve the inefficiency of MAC problems in multi-hop wireless networks. Simulation results show that our D-LSMA protocol achieved 20-30% more throughput than the original IEEE 802.11 MAC. In dense wireless mesh environments, the communication complexity to establish conflict-free scheduling becomes very high due to extended interference range. In this case, per-flow optimization mechanisms are better than per-packet MAC scheduling solutions. Hence, to reduce control overhead and improve end-to-end performance further, we propose a clean-slated IRMA (Integrated Routing/MAC Scheduling) design to integrate the routing and MAC into a single protocol layer and use joint optimization techniques to establish end-to-end path and TDMA schedules for flows across the network. This approach achieves non-conflicting allocation of channel resources based on global or local traffic flow specifications and network conflict graphs. Two different joint routing/scheduling algorithms are presented. The first method solves min-hop routing, then optimizes link scheduling based on routing results and real-time flow demands. The second approach attempts to optimize routing and scheduling decisions simultaneously, using available MAC bandwidth information to route around congested areas. Both centralized and distributed algorithms based on these methods are proposed and evaluated with detailed simulations. Results show significant 2-3x improvements in network throughput when compared with baseline 802.11-based mesh networks using independent routing protocols.Ph.D.Includes bibliographical references (p. 90-94)