Multipath Mitigation Analysis using Hatch Filter and DTW in Single Frequency RTK

Abstract

Multipath being a stochastic GNSS error is hard to eliminate. For two receivers operating in differential GNSS mode with a short baseline (below 10 km in this case), it is possible to mitigate geographically common errors to both receivers but not multipath. Real Time Kinematic (RTK) uses carrier-phase observations to form differences in real time. The single frequency (SF) code observations for receivers functioning in RTK are filtered through code-carrier combination of observations. The Hatch filter algorithm is often utilized in SF-GNSS based applications to detect cycle slips and also to mitigate multipath. However, choosing an effective smoothing window is important to ensure that the Hatch filtered output matches closely to that of the input raw signal. Dynamic Time Warping (DTW) was used to get appropriate smoothing constant value for the Hatch filter by measuring the squared Euclidean distances of corresponding points of the two signals. Using dynamic data collected for 906 epochs from two receivers configured in RTK mode, a bespoke SF-RTK software was used to compare the positioning results of the Hatch filtered output to that of the widely used RTKLIB software. The results showed that the standard deviation of the differences of the ECEF coordinates between the two software are within centimetre levels.