Non-intrusive, dynamic interference detection for 802.11 networks

In densely packed 802.11 environments, access-point domains significantly overlap and wireless hosts interfere with each other in complex ways. Knowing which devices interfere is an essential first step to minimizing this interference, improving efficiency and delivering quality connectivity throughout the network. This knowledge, however, is extremely difficult to obtain without either taking a running network offline for measurements or having client hosts monitor and report airspace anomalies, something typically outside the control of network administrators. In this paper we describe a technique we have developed to reveal wireless-network interference relationships by examining the network traffic at wired routers that connects wireless domains to the Internet. This approach, which we call VOID (Vvirless Online Interference Detection), searches for correlated throughput changes that occur when traffic from one node causes a throughput drop at other nodes in its radio range. In one analysis round we identify each node's interference neighbours using a single set of performance data collected from a wired-network router. We have evaluated VOID in Emulab testbeds consisting of tens of nodes as well as a six-node testbed in a live wireless network. The initial results have shown the promise of VOID to accurately correlate interfering devices together and effectively discriminate interfering devices from non-interfering ones.