LocRa: Enable Practical Long-Range Backscatter Localization for Low-Cost Tags
Jinyan Jiang, Jiliang Wang, Yijie Chen, Yihao Liu, Yunhao Liu
Abstract
Long-range backscatter localization is a promising technology for the Internet of Things. Existing works cannot work well for distributed base stations and low-cost tags. We present LocRa, which provides accurate localization for long-range backscatter with distributed base stations. We present a novel method to extract accurate channel information and synchronize the phase of different base stations. To compensate for the frequency and phase error on low-cost tags, we combine multiple channel measurements and eliminate the error by aligning different channels. Finally, we exploit frequency domain characteristics of the backscatter signal to extend its bandwidth and improve the SNR, thereby enhancing the localization accuracy. We prototype LocRa tags using custom low-cost hardware and implement LocRa base stations on USRP. Through extensive experiments, we show that the localization error of LocRa is 6.8 cm and 88 cm when the tag is 5m and 50m away from the base station, which is 3.1× and 2.3× better than the state-of-the-arts methods.