Experimental Analysis of Backpressure Scheduling in IEEE 802.11 Wireless Mesh Networks

Transmission scheduling to improve the capacity in wireless mesh networks (WMNs) is challenging. One promising candidate solution is backpressure scheduling, which was shown to provide throughput optimality and queue stability. Several recent practical systems that implement approximations of backpressure scheduling show performance benefits in WMNs that are based on IEEE 802.11, which is the most widely adopted MAC protocol. However, a detailed analysis of the queuing behavior is still missing for practical systems. In this paper, we experimentally show that backpressure scheduling over IEEE 802.11 presents significant queue instability due to the delayed interaction between MAC and network layers. To understand how and when queue instability occurs, we present a weighted backpressure scheduling (WBS), which uses two additional weight factors β and γ for the queue lengths of a node and its next-hop node when computing the backpressure value. By using WBS, we experimentally investigate the interactions between the components of backpressure scheduling implementations, i.e packet scheduling and link scheduling, and show that, usually, β >; γ leads to queue stabilization.