  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 bandwidth. In this paper, we propose
and analyze 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 access the channel. In this way, the R-DCF protocol not only
exploits multi-user diversity in a fully distributed manner but also reduces
the loss of throughput due to collisions. Through analysis, we develop an
analytical model to derive the throughput of R-DCF in general multi-rate WLANs.
Using the analytical model we investigate the performance of R-DCF protocol in
various network settings with different rate adaptation strategies and channel
variations. Based on the analysis, we further derive the maximal throughput
achievable by R-DCF. For practical implementation, an offline adaptive backoff
method is developed to achieve a close-to-optimal performance at low runtime
complexity. The superiority of R-DCF is proven via extensive analyses and
simulations.
