APAS-TR: a MATLAB-based open-source software package for multi-GNSS precise point positioning and its performance in strong ionospheric conditions

Abstract

The Precise Point Positioning (PPP) approach has recently acquired remarkable prominence within the GNSS community due to its ability to meet high-precision positioning requirements with only a single receiver. Moreover, the continuous development and evolution of GNSS satellites and signals have facilitated the implementation of various multi-GNSS integrations and led to significant improvements in convergence time and accuracy. This study introduces APAS-TR, an open-source software package based on MATLAB that provides multi-GNSS PPP solutions. APAS-TR can process GPS, GLONASS, Galileo, BDS-2/3, and QZSS observations, and it offers various statistical analysis and plotting options to promote the interpretation of solutions. Additionally, the increasing frequency of geomagnetic storms in recent years has made it necessary to update traditional methods of GNSS signal processing, particularly the cycle slip issue. In this regard, the software uses a rate of total electron content index (ROTI)-based threshold to avoid misjudgment of cycle slip detection during periods of geomagnetic storm-induced ionospheric disturbances. Indeed, the single and multi-GNSS kinematic PPP results obtained using 50 IGS MGEX stations demonstrate that the proposed methodologies substantially outperform the conventional approach, especially for stations located at high latitudes throughout strong geomagnetic storms. Besides, it was noticed that the performance of both single and multi-GNSS combinations for a geomagnetic storm day was comparable to that on quiet days, thanks to the new approaches. Lastly, the GREC3 combination has greatly enhanced the GPS-only solutions, producing less than 13 min of convergence time at the 95% quantile and consistent cm-level positioning accuracy across all days.