Carrier phase analysis to mitigate multipath effect.
Omer Mohsin Mubarak, Andrew Graham Dempster · UNSWorks (UNSW Sydney) · 2021
Although researchers have devised different methods to detect and correct effects of multipath, it remains one of the challenges in navigation receiver design. This paper explores the phase variations of the incoming carrier in the presence of multipath in GPS signals. Due to this change, while tracking an incoming signal, energy is shifted from the I channel to the Q channel. A novel technique has been presented to analyse the pattern of this energy shift in an ideal scenario to detect and accurately estimate the amplitude, delay and phase of the reflected signal. A perfect triangle has been used to depict ideal autocorrelation peak of a GPS signal. The algorithm is then applied to simulated GPS signals and it has been shown that errors are introduced in multipath estimates because GPS autocorrelation is not a perfect triangle. Tracking output from a software receiver is then used to detect and estimate multipath. A novel variable called Early late phase (ELP) has been proposed for multipath estimation. It has been shown that ELP performs better when carrier phase difference between line of sight and reflected signal is π/2 or its multiples. It gives worst performance when this difference is π or its multiples, because in this case there is no energy shift to Q-channel as the reflected signal is also matched to line of sight signal. However, this problem may be solved if the same technique is used for both L1 and L2C to aid each other. This paper provides background, explanation and initial results for the proposed algorithm. There are still few limitations in the algorithm, which needs to be addressed by more extensive experiments and analysis.