A Subspace-Based Two-Way Ranging System Using a Chirp Spread Spectrum Modem, Robust to Frequency Offset

Herein, we propose and implement a subspace-based two-way ranging system for high resolution indoor ranging that is robust to frequency offset. Due to the frequency offset between wireless nodes, issues about sampling frequency offset (SFO) and carrier frequency offset (CFO) arise in range estimation. Although the problem of SFO is resolved by adopting the symmetric double-sided two-way ranging (SDS-TWR) protocol, the CFO of the received signals impacts the time-of-arrival (TOA) estimation, obtained by conventional subspace-based algorithms such as ESPRIT and MUSIC. Nevertheless, the CFO issue has not been considered with subspace-based TOA estimation algorithms. Our proposed subspace-based algorithm, developed for the robust TOA estimation to CFO, is based on the chirp spread spectrum (CSS) signals. Our subspace-based ranging system is implemented in FPGA with CSS modem using a hardware/software co-design methodology. Simulations and experimental results show that the proposed method can achieve robust ranging between the CSS nodes in an indoor environment with frequency offset.