A Multi-Channel Approach and Testbed for Centimeter-Level WiFi Ranging

Latest advancements in WiFi ranging enable the use of both timestamps and channel frequency response (CFR) measurements supporting the recently released IEEE 802.11az Next Generation Positioning standard. However, resolution limitations are imposed by the single-channel bandwidth of operation, and WiFi devices that can only operate using 20 MHz channels on a given time instance suffer from limited ranging capabilities. While devices can frequency hop to multiple channels to obtain CFR measurements across larger bandwidths, changes in local oscillator phase offsets and time offsets per channel prevent direct stitching of the CFR. To overcome these challenges and achieve phase-coherent multi-channel (PCMC) CFR measurements, we propose a two-way CFR approach that embeds timestamp information in the phase. We develop a software-defined radio testbed to evaluate our proposed multi-channel ranging technique and answer hardware implementation challenges. For range estimation, we employ Multiple Signal Classification (MUSIC) and a complexity reduction strategy to accommodate large bandwidths with many subcarriers. Utilizing our proposed PCMC technique with 16 channels, we demonstrate a median error of 2.7 cm and a 90th percentile error of 9.5 cm in indoor line-of-sight conditions.