Analysis of Multi-GNSS PPP Initialization using Dual- and Triple-frequency Data

Abstract

With an increase in the number of satellite systems, redundant measurements, and improved satellite orbit and clock products, the initial convergence period of dual-frequency GNSS Precise Point Positioning (PPP) borders on tens of minutes to achieve an accuracy of a few centimetres. However, dual-frequency PPP still remains impractical for many real-time applications due to this relatively long convergence period. The introduction of a fully operational third frequency promised faster convergence and almost instantaneous integer resolution of ambiguities. However, the expectation of triple-frequency PPP has, so far, not been met with reliable quick fixing of float carrier-phase ambiguities. The objective of this work is to draw attention to the challenges and methods available for quickly attaining accurate position initialization for float PPP solutions, while analyzing the intricacies of issues that have to be dealt with in doing so. This paper concentrates on the first few minutes of PPP convergence in dual- and triple-frequency scenarios to analyze and contribute to improvements of the float solution before the resolution of ambiguities. L5 bias corrections from the Centre national d'etudes spatiales (CNES) were applied in the triple-frequency PPP float solutions, which improved the solution by 22% in the first 5 minutes. Three GNSS-based and two observable weighting schemes were investigated. Downweighting GLONASS and BeiDou observables gave the best results compared to the other schemes investigated. The weighting experiments confirmed that the appropriate choice of a weighting scheme impacts solution initialization.