Cooperative Relay Mechanism On IEEE802.11WLAN

Rate anomaly is a common phenomenon at wireless LAN based on IEEE802.11protocols. The STA nodes associated with a same AP usually have different transmissionrate, so the STA nodes with lower transmission rate will consume more medium time thanthe ones with higher rate, and then rate anomaly happened. Rate anomaly will bring abouta severe decrease of network throughput.In order to alleviate the performance loss causedby rate anomaly, many methods have been proposed,which can be classified as threecategories including: changing the fairness transmission strategy, proposing multi-hoprelay anddeploying repeater devices.Based on the survey on related work and the analysis on the features of WLAN andIEEE802.11protocols, this paper proposed a cooperative relaymechanism (CRM) whichsubstitute one-hop direct link with two-hop relay link only if the latter link has a betterperformance than the former link. This mechanism doesn’t only overcome the shortcuts ofthe solutions discussed above, but also effectively alleviate the rate anomaly occurred inWLAN. During the research and implementation process, a contention-aware mediumtime metric, which takes account of physical features, protocol expense and channelcontention, has been proposed to more precisely indicate link performance. Meanwhile, anerror compensation of link performance evaluation has also been proposed, which useszero pause link switchover to re-evaluate the link performance with practical data traffic.Testing result showed that the new link performance evaluation can effectivelyindicate both one-hop and two-hop link performance and cooperative relay mechanismcan alleviate the rate anomaly problem of WLAN.