An accurate, CFO-free, phased-based ranging solution using the round-trip CSI.

The presence of the carrier frequency offset (CFO) in WiFi systems not only interferes with communication but also hampers the use of the channel state information (CSI) derived from the WiFi signals for ranging. In this paper, we aim to remove the error caused by the CFO and then present an accurate, phased-based ranging solution using the round-trip CSI measurements. Concretely, we first investigate the errors of the CFO that contaminate CSI and model the effects mathematically. Then, we propose the sparse recovery method to estimate the amount of the CFO error and derive a stable calibration parameter based on the linear fitting method to compensate for the CFO error. To validate the proposed method, we finally prototype the ranging system using the software defined radio (SDR) platform. The extensive experimental results show that the ranging accuracy is significantly improved provided that we