Multipath profile discrimination in TOA-based WLAN ranging with link layer frames

Indoor ranging and location in WLAN is possible through obtaining Round-Trip-Time (RTT) measurements at data link level. This procedure allows using the existing IEEE 802.11 WLAN infrastructure with minor changes in order to provide an accurate estimation of the position of the mobile terminal. In this paper, an approach to overcome the undesired impact of the indoor radio-channel multipath on the accuracy of the TOA estimation between the terminal and an Access Point is presented. Ranging errors caused by multipath are quantified for different channel profiles: Dominant Direct Path (DDP), Non Dominant Direct Path (NDDP) and Undetectable Direct Path (UDP). However, the main challenge corresponds to be able to identify this profile (i.e. the multipath condition) from the obtained RTT measurements at IEEE 802.11 link level. This allows applying a TOA estimation algorithm sensitive to the detected profile in order to minimize the TOA estimation error.