Overhearing the Wireless Interface for 802.11-Based Positioning Systems

Not only the communication capabilities of 802.11, but also the capability to determine the position of mobile devices make 802.11 highly appealing for many application areas. Typically, a mobile device that wants to identify its position regularly performs active or passive scans to obtain the signal strength measurements of neighboring access points. However, so far, no investigations are known to have been launched into how regular scanning affects concurrent data transmissions from an end-user point of view. In this paper, we explore how common data communication is affected while actively or passively scanning at the same time. Furthermore, we present a novel scan scheme called monitor sniffing. Monitor sniffing exploits the fact that 802.11 operates on overlapping channels by overhearing the wireless interface. We have implemented our monitor sniffing algorithm using commodity 802.11g hardware, and we demonstrate that it does not disturb concurrent data communication