Study On IEEE 802.11 Rate Adaptation For Wireless Network

With the development of the technologies of computer networks and wireless communication,Wireless LAN(WLAN) is widely used nowadays.IEEE 802.11 standard become one of the most popular standards,promoting the development of WLAN.IEEE 802.11 standard family specified physical(PHY) layer and media access control(MAC) layer,and support the transmission rate up to 54Mbps and even higher.IEEE 802.11 PHY supports multiple transmission rates.For example,802.11a specifies 8 rates(6Mbps～54Mbps),802.11b specifies 4 rates(1～11Mbps),and 802.11g specifies 12 rates(1Mbps～54Mbps).However 802.11 did not specify the rate adaptations.How to select the best transmission rate and dynamically adapt its decision to the time-varying and channel quality is a hot topic.Until now,many rate adaptation algorithms follow the intuitive framework that specifies two FLR(frame Loss Rate)thresholds Th_up and Th_down,when the FLR at the current transmission rate exceeds Th_down,lower the transmission rate;when that below than Th_up,increase the transmission rate;otherwise keep transmitting at the current rate.These algorithms seem reasonable,and get better performance,but because of the difficulty in choosing parameters,which is set by empirical value,they may lead to an undesirable repeat rate jump(RRJ) phenomenon.This paper proposed a rate adaptation based on comparing real throughput.It starts with the comparison of real throughput,and deduces the threshold formula for throughput maximization.It calculates FLR and thresholds in real-time.NS2 simulation results show that our algorithm outperforms other state-of-the-art methods on both Rayleigh and Ricean channel.