Enhancing Efficiency and Effectiveness of 802.11 MAC in Wireless Mesh Networks

The 802.11 MAC protocol is widely used in wireless mesh networks. However, with multi-hop transmissions prevalent in such networks, neither the current 802.11 DCF basic scheme nor the RTS/CTS scheme can achieve full utilization of network capacity for various reasons. First, the 802.11 MAC provides low spatial reuse (low parallelism of transmissions). Second, the collision avoidance mechanism in 802.11 becomes less effective for multi-hop scenarios. In this article, we review two types of 802.11-based MAC enhancements to improve the efficiency and effectiveness in wireless mesh networks. One class of schemes focus on tuning transmission power and carrier sense threshold. In static strategies, the interference model is introduced and a static optimal strategy is derived for the worst case scenarios. In dynamic strategies, transmission power and carrier sensing threshold are tuned adaptively to various network conditions and access patterns. Another class of schemes exploit the channel-state diversity among the receivers of a specific sender by scheduling the frames based on the receivers’ conditions.