Understanding the effect of access point density on wireless LAN performance

In this paper, we present a systematic experimental study of the effect of inter-cell interference on IEEE 802.11 performance. With increasing penetration of WiFi into residential areas and usage in ad hoc conference settings, chaotic unplanned deployments are becoming the norm rather than an exception. These networks often operate many nearby access points and stations on the same channel, either due to lack of coordination or insufficient available channels. Thus, inter-cell interference is common but not well-understood. According to conventional wisdom, the efficiency of an 802.11 network is determined by the number of active clients. Surprisingly, we find that with a typical TCP-dominant workload, cumulative system throughput is characterized by the number of interfering access points rather than the number of clients. We find that due to TCP flow control, the number of backlogged stations in such a network equals twice the number of access points. Thus, a single access point network proved very robust even with over one hundred clients. Multiple interfering access points, however, lead to an increase in collisions that reduces throughput and affects volume of traffic in the network.