Precise Carrier-Phase-Based Ranging and Motion Detection by Reusing OFDM Data Subcarriers: Analysis and Demonstration

Carrier-phase-based ranging can achieve highly accurate ranging at the sub-wavelength level. This paper explores and experimentally demonstrates the reuse of orthogonal frequency division multiplexing (OFDM) communication signals for precise carrier-phase-based ranging. The approach involves leveraging a large number of phases extracted from OFDM subcarriers, including both pilot and data subcarriers, to suppress phase noise. For the best outcome, optimal selection of subcarrier frequencies is considered. The selection is formulated as a max-min optimization problem and studied with consideration of measurement error tolerance, along with analysis and quantitative assessment of range ambiguity defined in pairwise error probability. A decision-assistance phase extraction method is introduced to make use of data subcarriers in addition to the pilots. An iterative algorithm is proposed for ultra-accurate carrier frequency offset (CFO) correction, which is essential to measure the range-related phase polluted by phase noise for precise ranging. Laboratory proof-of-concept prototyping and experiments are conducted based on a bi-static setup in the fashion of simultaneous communication and sensing (a subcategory of integrated sensing and communication (ISAC)), which can be extended to a multi-static configuration. The simulation and experimental results demonstrate that, by using four or more data subcarriers in addition to the four pilots in a WiFi signal centered at 2 GHz, the proposed scheme can effectively mitigate the impact of phase noise to achieve millimeter-level accuracy without interrupting communication. This suggests that the proposed method is promising for detecting and estimating micro-motion.