An Open Source GPS/GNSS Vector Tracking Loop - Implementation, Filter Tuning, and Results

TL;DR: Test results show that the vector tracking loops have definite advantages over traditional scalar loops including better position accuracy and higher robustness under low signal-to-noise ratios, however, to obtain these benefits, the vector loop parameters should be carefully tuned depending on different scenarios the receiver is going through.

Abstract: This paper first briefly introduces the advantages of vector tracking loops (or vector lock loops - VLL) over traditional scalar tracking loops (or scalar lock loops - SLL) in a GNSS receiver. Then, some principles and the mechanism of how VLL works are illustrated. Based on an open source GPS software-defined receiver code, the VLL is implemented and tested with three different data sets including two from a GPS simulator and one from a drive test. To compare the performance, a traditional SLL is also used to process these three datasets. Their results are included. Comparisons between scalar loop and vector loop observables including carrier frequency results and position/velocity results are presented. Based on the details illustrated in this paper, one can easily understand the mechanism of the vector tracking algorithm and incorporate this in their receiver code. The tests carried out in this paper are not exhaustive but provide solid insights into the implementation and tuning associated with the vector loops. Test results show that the vector tracking loops have definite advantages over traditional scalar loops including better position accuracy and higher robustness under low signal-to-noise ratios. However, to obtain these benefits, the vector loop parameters should be carefully tuned depending on different scenarios the receiver is going through. Meanwhile, some criteria of tuning these parameters are given empirically in this work.