Understanding 802.11 performance in heterogeneous environments

The availability of unlicensed spectrum coupled with the increasing popularity of wireless communication has given rise to a diverse range of wireless technologies that compete for spectrum. In particular, 802.11 devices face a host of problems such as interference with other 802.11 devices (hidden terminals) as well as with technologies like Bluetooth and ZigBee. Understanding how the medium is utilized and inferring the cause of interference, based on observations from a single wireless node, is hard. Past work has used monitoring infrastructures to detect interference between 802.11 nodes in enterprise networks. In this paper, we try to answer the question: "how can we enable users to reason about wireless performance variations without requiring elaborate instrumentation and infrastructure support?". We propose WiMed, a tool that uses only local measurements from commodity 802.11 NICs (at the node being diagnosed) to construct a time map of how the medium is utilized. We have implemented a WiMed prototype using the MadWifi driver for Atheros NICs. Early results show that WiMed is useful and can characterize non-802.11 interference better than existing systems.