Effect of Contention Window on the Performance of IEEE 802.11 WLANs

In the IEEE 802.11, an exponential backoff has been adopted, which means whenever a collision occurs, the contention window (CW) of the station is doubled until it reaches the maximum value. The purpose of increasing CW is to reduce the collision probability by distributing the traffic into a larger time space. In this paper, we use a fixed contention window (FCW) scheme and then evaluate the performance of this scheme. Based on our analysis, we determine an optimal contention window (OCW). Furthermore, we apply the OCW scheme to 802.11e EDCF. The results show that the OCW scheme not only can effectively enhance the performance for high priority packets, but also can improve the overall system performance.