Decimeter-Level Passive Human Tracking with a Single Wi-Fi Link

This chapter presents Widar2.0, the first Wi-Fi-based system that enables passive human localization and tracking using a single link on commodity off-the-shelf devices. Previous works based on either specialized or commercial hardware all require multiple links, preventing their wide adoption in scenarios like homes where typically only one single AP is installed. The key insight underlying Widar2.0 to circumvent the use of multiple links is to leverage multi-dimensional signal parameters from one single link. To this end, we build a unified model accounting for Angle-of-Arrival, Time of Flight, and Doppler shifts together and devise an efficient algorithm for their joint estimation. We then design a pipeline to translate the erroneous raw parameters into precise locations, which first finds parameters corresponding to the reflections of interests, then refines range estimates, and ultimately outputs target locations. Our implementation and evaluation on commodity Wi-Fi devices demonstrate that Widar2.0 achieves better or comparable performance to state-of-the-art localization systems, which either use specialized hardware or require 2 to 40 Wi-Fi links. (This chapter is based on our previously published paper. Widar2.0: Passive Human Tracking with a Single Wi-Fi Link. Proceedings of the 16th Annual International Conference on Mobile Systems, Applications, and Services (MobiSys ’18), Pages 350–361, Ⓒ2018 ACM, Inc. https://doi.org/10.1145/3210240.3210314.)