Title: Phase Cycle Slip Mitigation by Piecewise Polynomial Doppler FIT
Author(s): Tsvi G. Dvorkind
Published in: Proceedings of the 29th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2016)
September 12 - 16, 2016
Oregon Convention Center
Portland, Oregon
Pages: 2101 - 2106
Cite this article: Dvorkind, Tsvi G., "Phase Cycle Slip Mitigation by Piecewise Polynomial Doppler FIT," Proceedings of the 29th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2016), Portland, Oregon, September 2016, pp. 2101-2106.
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Abstract: Continuous phase tracking within a GPS receiver is vital for precise positioning applications. Automatic landing systems, agricultural and industrial applications are just a few examples of fields where differential GPS (DGPS) utilizes carrier phase tracking for centimeter level positioning accuracy. Precise positioning algorithms that perform integer ambiguity resolution rely on continuous phase tracking without cycle slips in order to calculate sub-wavelength range measurements. As phase information is cycle ambiguous, a phase locked loop (PLL) assisted by a frequency locked loop (FLL) is usually employed in order to obtain continuous phase tracking results. Unfortunately, occasional signal loss which might occur due to line of sight blockage, dynamic stress, or RF interference might cause disruptions in Doppler and phase tracking. With current receiver designs, even a single epoch which results in signal loss, or one erroneous outlier in a Doppler and phase estimate, might lead to a phase cycle slip and disrupt any continuous phase tracking results obtained thus far. In order to improve continuous phase tracking robustness, we suggest fitting a piecewise polynomial model to several Doppler measurements at a time. Then, by analytically integrating the obtained model, we also obtain a closed form expression for the continuous-phase function. In this contribution we simulate noisy Doppler and phase measurements with occasional signal loss. We show that the suggested approach can cope with such measurements and produce continuous phase tracking despite the data gaps. We also suggest a method for continuous phase tracking along several piecewise polynomial fits, allowing for integer ambiguity resolution algorithms to be applied based on very long phase tracking results. Simulation of the suggested approach demonstrates the effectiveness of the piecewise continuous-time model for phase tracking with low probability of cycle slips.