MobiCom 2011 poster: AirTrack: locating non-WiFi interferers using commodity WiFi hardware

Abstract

Recent studies [1, 4, 5] have shown that interference due to non-WiFi RF devices has become a major problem in today’s 802.11 networks. In our own experiments, we observed that high powered interferers like analog cordless phones, video cameras can cause an 802.11 link to experience complete loss of connectivity. Figure 1 shows an example of non-WiFi RF activity in a university cafe, where a FHSS cordless phone and a Microwave oven caused increased interference. Knowledge about the active non-WiFi RF devices and their physical locations can help the WLAN administrators take corrective actions (e.g., bringing down rogue non-WiFi transmitters, or by altering some of the operational wireless parameters). In this paper, we focus on the problem of locating the non-WiFi interferers in a WLAN without using any specialized hardware. Specifically, we try to answer the following question: “How can a system using only WiFi nodes accurately locate non-WiFi RF devices? Further, how can it do this in real-time, in a non-intrusive manner, and without the help of any additional sensors or hardware?" In our attempt to answer the above question, we present AirTrack — a system to locate non-WiFi devices using commodity WiFi hardware. AirTrack is non-intrusive, as it employs a passive approach (i.e., it does not introduce any additional traffic into the wireless medium) and localizes nonWiFi devices in real-time. Goals and challenges. Locating non-WiFi transmitters using only WiFi hardware is particularly challenging because WiFi nodes cannot decode the transmissions from these devices (e.g., Microwaves, video cameras, Xbox). While it is possible to equip each WiFi node with additional hardware (e.g., a Bluetooth interface to detect Bluetooth devices, a ZigBee interface to detect ZigBee devices), such a solution is clearly not scalable. In some cases, doing so might not even help detect the interferer because the received interference power might be simply due to unintended radiations from the device (e.g., Microwave ovens). With AirTrack, we first wish to detect and uniquely identify the presence of multiple, simultaneously operating non-WiFi devices using limited signal information (e.g., RSS per sub-carrier) provided by commodityWiFi cards. For example, if two Bluetooth devices and an analog phone are operating simultaneously, AirTrack should be able to detect all the three device instances. We note that detecting the presence