Poster Abstract: LocTag: Passive WiFi Tag for Robust Indoor Localization via Smartphones

Indoor localization via smartphones has attracted many researchers' attention over the past few years. However, it still lacks a mature solution robust to complex indoor environments. In this paper we design LocTag, the first passive WiFi tag for localizing commercial off-the-shelf smartphones in arbitrary indoor environments with or even without APs (Access Points) deployment. Unlike conventional passive WiFi tags, LocTag backscatters ambient WiFi signals from APs or smartphones for localization instead of communications. To do so, we propose several techniques including triggering source selection, WiFi compatible modulation, and random multiple access. We prototype LocTag using a FPGA (Field Programmable Gate Array) and apply it in a typical indoor localization scenario. The experiment results show that sub-meter level accuracy is achieved via LocTag. Although our work is still at its early stage, it sheds new light on the robust indoor localization via passive WiFi tags.