Multi-Frequency Combined Processing for Direct and Multipath Signals Tracking Based on Particle Filtering

Multipath propagation inflicts tracking biases on the code delay and carrier parameters that lead to a degradation in the positioning accuracy in challenging environments, such as indoor and urban areas. The modernized GPS signals, although more robust than the legacy GPS C/A signal, they still suffer from attenuation and multipath reflection errors. This paper introduces a particle filtering-based tracking algorithm that has the ability to separate the line-of-sight signal from the multipath signals, and track their parameters. The algorithm is designed to exploit the benefits of combining the processing of same-satellite signals when operating in dual or multi-frequency receivers. Same-satellite signals are broadcast on different carrier frequencies from the same satellite. The relationships between the corresponding signals parameters are functions in two factors, which are the relative motion between the GPS satellite and the receiver, and the ionospheric effects on the signals propagation. Those relationships are derived and utilized to increase the tracking robustness. The performance of the algorithm is evaluated by examining the multipath detection capability, the tracking of multipath parameters variations, and the tracking accuracy for signals with different carrier to noise rations (C/N-0). Several multipath scenarios are conducted in the evaluation. The results verify the ability of the proposed algorithm to mitigate multipath errors under strong and weak signals conditions. The advantage of combining the processing of same-satellite signals is also demonstrated in the results.