Distributed MAC Strategy for Exploiting Multi-user Diversity in Multi-rate IEEE 802.11 Wireless LANs

Fast rate adaptation has been established as an effective way to improve the PHY-layer raw date rate of wireless networks. However, within the current IEEE 802.11 legacy, MAC-layer throughput is dominated by users with the lowest data rates, resulting in underutilization of spectrum bandwidth. In this paper, we propose a novel distributed MAC strategy, referred to as rate-aware DCF (R-DCF), to leverage the potential of rate adaptation in IEEE 802.11 WLANs. The key feature of R-DCF is that by introducing different mini slots according to the instantaneous channel conditions, only contending stations with the highest data rate can actually access the channel. In this way, the R-DCF protocol not only effectively exploits multi-user diversity in a fully distributed manner but also drastically reduces the loss of throughput due to collisions. Through analysis, we derive a closed-form network throughput expression for R-DCF. Based on the analysis, we further derive the maximal throughput that can be achieved by R-DCF. For practical implementation, an offline adaptive backoff method is developed for R-DCF to achieve a close-to-optimal performance at low runtime complexity. The superiority of R-DCF is proven by extensive analyses and simulations.