Robust Positioning with LEO Satellites: Double-Difference Doppler Shift-Based Approach

Low Earth orbit (LEO) satellite-based positioning is emerging due to the available LEO constellation and high Doppler shift opportunity. However, positioning with LEO satellites utilizing signals of opportunity (SOPs)-based approach suffers from ephemeris error as the orbital element is estimated using two-line element (TLE) files that induce error over time. In the differential Doppler positioning method, an additional base receiver along with its known position with the user terminal (UT), is used to handle this erroneous measurement. The positioning accuracy of UT degrades significantly in the case of the long baseline (the distance between the base receiver and UT) scenario. Moreover, Doppler shift measurement errors also occur due to the clock synchronization issue between the base receiver and UT. Addressing these issues, we propose a robust positioning method, coined 3DPose, that can handle the clock synchronization issue between the base receiver and UT, as well as positioning degradation due to the long baseline. The proposed 3DPose method applies double-difference Doppler shift measurements to eliminate the clock synchronization issue, and a novel ephemeris error correction algorithm to improve UT positioning accuracy in case of the long baseline. To evaluate the performance of the proposed method, we perform a comparison with the existing differential Doppler positioning method. The comparison results show that the proposed 3DPose method outperforms the existing differential Doppler positioning in terms of positioning accuracy.