Abstract: In IEEE 802. 11/a/b/g Wireless Local Area Networks, the physical layers support multiple transmission rates. Since the wireless channel varies over time due to such factors as station mobility, time-varying interference, signal fading, and so on, it is very important for the transmitting station to assess channel conditions and accordingly adjust the rate in order to yield higher throughout Rate adjustment mechanism can be classified into open-loop schemes based on statistics information and closcloop schemes based on the RTS/CTS information feedback. We summaried the performance of the rate adjustment schemes,analyzed the key issues which include initial rate,packet loss distinction and adjustment strategies, and pointed out the present problems and future research interests.

Key words: Wireless networks, Multiple rates, Data rate, Loss differentiation, SNR