Assessment on the Efficacy of Global Ionospheric Maps to Improve the Performance of Precise Point Positioning

This paper presents an application of global ionospheric maps (GIMs) for Global Navigation Satellite Systems (GNSS) Precise Point Positioning (PPP). PPP is a high- precision positioning technique that only requires a single GNSS receiver-operating similar to the standard positioning services mode. Currently the full potential of PPP is inhibited by a long initialisation time of approximately 20 minutes for the float ambiguity solution to converge to centimetre accuracy. In this assessment, positioning accuracy under different ionospheric conditions was analysed based on three types of convergence solution methods. Comprehensive experiments were carried out at eight continuous operating observation stations of the Australian Regional GNSS Network (ARGN) over a period of seven consecutive days. ARGN is an important part of the Australian National Positioning Infrastructure (ANPI). A review of the standard PPP algorithm and their enhancement is presented along with a brief summary of the recent advancements in using external ionospheric corrections to improve the performance of PPP based on the ANPI. Results of the experiment indicate that the ionospheric delay information derived from GIMs does not meet the required accuracy for fast ambiguity resolution. The convergence time to reach sub-decimetre level accuracies with the GIM aided ambiguity-resolved PPP is about 30 minutes. Improvements in precision can be expected if the external ionospheric corrections are better than that of code noise. The analysis could not identify sub-decimetre RMS accuracy for any of the satellites observed in this study. While the experiment complements the work in progress to navigate through current latency involved in ionospheric bias, methods to optimise ionospheric error modelling to enable fast ambiguity resolution for real-time PPP needs extensive research.