Performance Analysis of LEO Multi-Constellation Aided GNSS Positioning Under Weak Signals Environments

This research assesses the feasibility and conducts performance analysis of an LEO-aided GNSS-based navigation system under weak GNSS signal environments. The Doppler measurements are extracted from the Iridium NEXT and Orbcomm constellations to increase the LEO satellite signals availability. The simplex signals of Iridium Next are received to extract Doppler frequency. Since the simplex signal is a pure tone, the fast Fourier transform method is adopted to search for the received carrier frequency and obtain Doppler shift measurement. The Doppler shift of Orbcomm can be extracted the same way as Iridium NEXT. The Doppler extraction from Iridium NEXT and Orbcomm will be combined with global positioning system (GPS) Doppler acquisition and tracking procedure to conduct the experiments. After extracting the Doppler measurements from Iridium NEXT, Orbcomm, and GPS, the measurements will input an extended Kalman filter to generate navigation solutions. The experiments will compare the impact of including the LEO satellite signal in weak GNSS signal environments in which less than four GPS signals are available, then add the LEO satellite signals to manifest the effect of opportunistic navigation through space-based SOPs. Two environments will be the trial fields, including the deep urban canyons, the dense forest, and the indoor environments, which make discontinuous position solutions. Two main contributions of the paper are as follows. 1) Combination of Doppler and pseudorange measurements of GPS signals and Doppler measurements from two LEO constellations at receiver level and 2) verification and analysis of the performance of an LEO-aided GNSS under weak GNSS signal environments.