Localizing Low-power Backscatter Tags Using Commodity WiFi

Location information is crucial for enabling many applications in the era of Internet-of-Things (IoT). Localizing IoT devices using existing ubiquitous WiFi infrastructure enables rapid and universal deployment of IoT devices empowered with localization service. However, current WiFi-based localization systems require the target, that needs to be localized, to be equipped with a WiFi radio that actively transmits WiFi signals. Since a WiFi radio consumes lots of power for data transmission, such radio cannot be used in energy-impoverish IoT devices (for example, locating a pill bottle in an elder's apartment). This paper presents WiTag, the first system that reuses existing WiFi infrastructures for localizing low-power backscatter tags. We build upon recent work on low power tags that communicate via backscattering ambient WiFi signals and introduce novel modeling of the backscattered signal received at WiFi access points to localize the target IoT device. We prototype WiTag using off-the-shelf WiFi chips and a customized backscatter tag and show that it achieves sub-meter localization error. Thus, WiTag achieves localization error comparable to that of state-of-the-art WiFi based localization systems while consuming orders of magnitude lower power at the target IoT devices.