Doppler Positioning Based on Globalstar Signals of Opportunity

As one of the early low Earth orbit (LEO) communication satellite constellations, Globalstar provides voice communication, Internet of Things (IoT), and cooperative positioning services. In this paper, considering the unknown signal specifications of Globalstar signals, we first examine the common characteristics of LEO constellation signals affected by high-speed motion. We then analyze the complicated modulation scheme of Globalstar pilot signals. By adequately processing the sampled signals of opportunity from Globalstar, we successfully extract the Doppler frequency. Finally, we perform Doppler positioning, achieving a non-cooperative horizontal positioning capability for Globalstar with an accuracy superior to 300 meters.