WLAN Fairness with Idle Sense

Idle Sense (IS) is a simple yet efficient access method to provide optimized throughput and fairness in wireless local area networks (WLAN). Each station dynamically controls its contention window (CW) size by monitoring the mean number of idle slots between transmission attempts. In general this quantity is subject to estimation error that is related to the number of transmissions, M, over which it is measured. Previous works in IS assumed all stations use similar CW sizes to contend the channel; an assumption that is not always valid in reality. Therefore, this paper studies the behaviour of the scheme when stations have different CW sizes. An analysis shows that bias caused by the additive increase multiplicative decrease (AIMD) algorithm used to control the CW sizes, combined with varying lengths of M can cause a fairness problem. Two classes of stations develop, with the first class gaining most of the channel bandwidth while the second class stays idle.