Algorithm and Assessment of Ambiguity-Fixed PPP with BeiDou Observations and Regional Network Augmentation

Abstract

In precise point positioning (PPP) applications, uncalibrated phase delays (UPD) are applied to retrieve the ambiguity integers for achieving precise solutions over a short period. Also, the atmospheric corrections obtained from a dense reference network are applied to accomplish this task of shorter convergence time or even instantaneous ambiguity resolution. The combined BeiDou Navigation Satellite System (BDS) and Global Positioning System (GPS) PPP with regional network augmentation is presented with threefold contributions. First, in order to overcome the UPD-inherent unmodeled errors in undifferenced ambiguity resolution at reference stations, it is proposed to fix the single-differenced ambiguities and use them as a constraint to fix the undifferenced ambiguities. Second, the performance of combined GPS+BDS PPP are fully evaluated with various indicators specified by single and combined satellite systems and several ratio test thresholds for ambiguity resolution. The BDS observations can provide the user with a significant improvement on the position solutions. The fix rate and correct fix rate are found to be increased by more than 7% and 11%, respectively. Third, the GPS+BDS regional augmented PPP is assessed in a highly occluded urban canyon. The experiments show the unfix rates of the combined system are decreased by more than 40%, and the correct fix rates can be improved by up to 55% compared with a GPS-only scenario.