Real-time multi-GNSS precise point positioning with ambiguity resolution based on the BDS-3 global short-message communication function

Real-time precise point positioning (PPP) with ambiguity resolution (PPP-AR) has been realized with the provision of various precise correction parameters from IGS multi-GNSS experiment (MGEX) centers via the Internet and commercial services via communication satellites. For users in remote regions with no access to the Internet, e.g., oceans and deserts, BDS-3 provides an open and free prototype for global users to receive precise positioning services through its global short-message communication (GSMC) function. However, limited by the bandwidth and parameter update frequency, the set of precise correction parameters from MGEX or other resources cannot be fully transmitted to users. To address this issue and improve the positioning performance of the BDS GSMC service, we propose a real-time multi-GNSS PPP-AR method based on real-time state space representation (SSR) corrections, where a novel strategy for the generation, encoding and broadcast of the correction parameters is developed. The new model maintains the accuracy of the correction parameters to the largest extent while meeting the interface requirement of BDS GSMC regarding the bandwidth and parameter update frequency. Experiments show that the new strategy effectively improves positioning performance compared to conventional GSMC-based float-ambiguity PPP. Specifically, in a kinematic experiment, the positioning precision improved by 10%, and the convergence time was shortened by 15%, with an average 71% successfully fixed rate. Beyond that, with the proposed extrapolatable corrections, the validity time of corrections is significantly prolonged from 2.5 to 7.5 min when a centimeter-level accuracy is needed. Thus, the continuity of the positioning service is guaranteed even if an unexpected short-term interruption occurs in the GSMC.