I. Introduction
The ieee 802.11 standards currently specify wireless local area networks (WLANs) with bit rates up to 54 Mbps. The ongoing development of the new IEEE 802.11n standard promises bit rates over 100 Mbps. With these bit rates, it is expected that an access point will serve a large number of stations for scenarios such as large conference halls or lecture theaters. However, the throughput of the IEEE 802.11 WLANs at these high bit rates is much lower than their specified bit rates because of the medium access control (MAC) and physical overheads [1]. Moreover, collision overheads in the IEEE 802.11 distributed coordination function (DCF) could cause performance degradation with a high number of stations [2].