Leveraging Multi-LEO Satellite Signals for Opportunistic Positioning

The study of navigation solutions other than GNSS is becoming increasingly important due to growing concerns about the vulnerability of GNSS to interference. The use of existing LEO satellite signals is a promising option in this respect. This study analyzes the accuracy of Doppler shift measurements for three satellite systems: Iridium-next, Orbcomm, and NOAA, based on actual signal acquisition, and evaluates the potential of their combination in positioning. The study takes advantage of Orbcomm’s dual frequency capability to reduce Doppler shift measurement noise, while highlighting the irrelevance of the ionosphere-free combination with Orbcomm. It proposes a method for obtaining unambiguous Doppler shifts from NOAA’s FM-AM signal, and introduces a smoothing technique to further improve Doppler shift measurement accuracy of LEO satellites. The positioning results show that positioning with three constellations is more accurate than positioning with one or two constellations, and that the effectiveness of passively combining several LEO systems for positioning is limited by the disparity between satellite constellations and the measurement quality inherent in each system.