Multi-constellation GNSS PPP instantaneous ambiguity resolution with precise atmospheric corrections augmentation

Precise point positioning (PPP) can be significantly improved with the multi- multi-GNSS constellation, but it still takes more than 10 min to obtain positioning results at centimeter-level accuracy. We develop a multi-constellation (GPS + GLONASS + Galileo + BDS) PPP ambiguity resolution (AR) method augmented by precise atmospheric corrections to achieve instantaneous centimeter-level positioning. In the proposed method, multi-constellation PPP fixed solutions are carried out at the reference network. The precise tropospheric delays are derived from the ionospheric-free (IF) phase observations while the slant ionospheric delays are extracted from the raw phase observations after the ambiguities are fixed. Afterward, they are provided to user stations for correcting the raw observations. Using these precise atmospheric corrections, one can achieve an instantaneous ambiguity resolution (IAR) with an accuracy of several centimeters. This method is validated experimentally with the Australian Regional GPS Network (ARGN), the South Pacific Regional GNSS Network (SPRGN) and the Hong Kong CORS. The ambiguity resolution can be achieved in several seconds with regionally computed atmospheric corrections, and the convergence time of positioning is significantly shortened compared to the PPP float and PPP-AR solution. Besides, the regional augmentation PPP (RA-PPP) also provides an advantage over network real-time kinematic (NRTK); the time to first ambiguity resolution can be shortened from 3 epochs to 1 epoch. The results also demonstrate the contribution of multi-constellation fusion to the PPP IAR in terms of positioning accuracy and reliability. The percentage of IAR can be up to 90.0% for multi-GNSS solutions, while the percentage for GPS-only solution is 7.2% when the cutoff elevation angle is 40°.