Multi-GNSS real-time precise point positioning using BDS-3 global short-message communication to broadcast corrections

The real-time precise point positioning (RTPPP) based on real-time service (RTS) products has attracted much interest with the increasing demand for real-time applications. It is difficult to achieve RTPPP for some areas where the available communication links for transmitting RTS products are limited, such as marine and desert areas. The global short-message communication (GSMC) function of the BeiDou global navigation satellite system (BDS-3) provides an option to transmit corrections for global RTPPP. However, the maximum size of each BDS-3 global short message is 560 bits, and the communication frequency is limited to 1 min, which brings challenges for broadcasting precise corrections using BDS-3 GSMC. In this contribution, based on dual-frequency GNSS data, we present a global RTPPP technique with BDS-3 GSMC. To overcome the limitations of communication bandwidth and frequency, at the server, the real-time precise orbits and clocks are predicted for 1 min, and then, the orbit and clock corrections of each satellite are converted into an equivalent range correction based on the user's approximate position obtained through BDS-3 GSMC. The range corrections for a maximum of 22 visible GPS, Galileo and BDS satellites are encoded into a BDS-3 global short message in accordance with the designed encoding strategy and are broadcast to users once per minute via BDS-3 GSMC. At the user, the range corrections of the observation moment are obtained by interpolating the corrections of the two adjacent epochs for RTPPP. Both simulated experiments using observations from IGS stations and field experiments using GNSS receivers with the BDS-3 GSMC function are conducted to evaluate the RTPPP performance. The results show that the proposed RTPPP scheme with GSMC can reach a positioning accuracy of better than 10 cm with GPS + BDS + Galileo observations.