Optimization of IEEE 802.11 Multirate Wireless LAN

IEEE 802.11 standards support multiple data transmission rates with dynamic rate switching capability to improve the performance. With multirate enhancement, data transmission from wireless LAN (WLAN) stations can take place at various rates according to channel conditions. This paper investigates the problem of optimizing aggregate saturation throughput of a multirate WLAN. Analytical expressions for transmission rate specific optimal minimum Contention Window (CWmin) values that simultaneously maximize aggregate saturation throughput and provide proportional throughput differentiation among different stations are determined. It is demonstrated that, with these optimal CWmin values, the achievable aggregate throughput is much greater than that of the basic configuration in which competing stations use the same MAC parameters. Further, every station gets a throughput proportional to its data rate. We also derive analytical expression for the maximum aggregate saturation throughput assuming very large number of active stations.