Doppler-Only Wireless Positioning for High-Speed Railway Based on Fractional Doppler Estimation

Fractional Doppler is always treated as a technical barrier in Orthogonal Time Frequency Space (OTFS) transmission, for it will lead to extra Doppler spread. In this paper, we view fractional Doppler from a new perspective that it can be utilized for high-resolution Doppler-only positioning and adopt it in high-speed railway scenarios for positioning and velocity detection. The proposed method uses only Doppler shifts for positioning, instead of delay or any other angle-related measurement, and can effectively work without massive antenna arrays or large bandwidth. Correlation-based Doppler estimation, which is adopted for OTFS channel estimation, is adopted to obtain high-resolution fractional Doppler measurement. Then the Doppler-only positioning problem is transformed into a non-linear equation and solved by the Halley method. The simulation results verify that the proposed method, with just normal bandwidth as commercial communication systems, shows better performance than integer Doppler-based positioning and ultra-wide-band (UWB) time-of-arrival (TOA)-based method.