Backpropagation Filter for GNSS Cycle Slip Mitigation and Ionosphere Monitoring

Abstract:

GNSS signals propagating through the ionosphere can provide important information about its state and turbulent structures. During strong ionosphere scintillation, the received coherent signal component displays fluctuations in phase and amplitude due to interference from scattered signal components. In addition, the measured unwrapped phase can be corrupted by many cycle slips, i.e. discrete one-cycle discontinuities, that in turn cause errors in estimation of total electron content (TEC) or phase scintillation indices such as sigma phi. The origins and effects of such slips on GNSS phase has been studied in our previous work in [1]. Various techniques have been developed for the detection and mitigation of cycle slips in GNSS phase, many of which attempt to detect cycle slip discontinuities in linear combinations of multi-frequency phase measurements. However, as we show in [2] ionosphere scintillation can be particularly challenging for such techniques, causing many false detections and inhibiting effective cycle slip correction.

In this work, we demonstrate cycle slip mitigation based on the principle of backpropagation of the received complex signal. It aims to recover the phase of the coherent signal component and thereby mitigate errors due to diffraction-induced cycle slips. We discuss the phase screen principle for modeling radio propagation through the ionosphere and the related backpropagation algorithm that can be used to recover the coherent signal phase. Real signals contain other phase components (e.g. clock variations) and noise that can cause backpropagation to fail. We present an augmentation of the algorithm to make it suitable for real signals. We then demonstrate the effectiveness of the technique using simulated and real multi-frequency GNSS scintillation data, with both cases showing a major reduction in the number of cycle slips in the filtered phase.

Breitsch, Brian, et al. "GNSS Carrier Phase Cycle Slips Due to Diffractive Ionosphere Scintillation: Simulation and Characterization." IEEE Transactions on Aerospace and Electronic Systems (2020).

Breitsch, Brian, and Y. Jade Morton. "Triple-Frequency GNSS Cycle Slip Detection Performance in the Presence of Diffractive Ionosphere Scintillation." 2020 IEEE/ION Position, Location and Navigation Symposium (PLANS). IEEE, 2020.