GPS/BDS/GLONASS Real-Time Precise Point Positioning using RTCM-SSR for Kinematic Maritime Positioning

Real-time precise point positioning (PPP) has been evolved as a powerful technique to achieve globally homogenous decimeter or even centimeter positioning accuracy, which plays a significant role for maritime positioning. With the rapid development of GNSS, the positioning accuracy and convergence time of the real-time PPP using multi-GNSS can be further improved, compared with single constellation. However, the navigation performance of maritime positioning based on PPP heavily depends on not only the real-time availability and quality of satellite orbits and satellite clocks, but also the estimation accuracy of wet zenith troposphere delay (ZWD) under the complex fluctuations of marine atmospheric weather. In this contribution, by using the State Space Representation correction products based on Radio Commission for Maritime Services (RTCM-SSR), we develop the GPS/BDS/GLONASS real-time PPP based on the ionosphere-free combination. Regarding to the issue of ZWD estimation, based on the performance comparison between the real-time widely-used tropospheric mapping models, i.e., the Niell Mapping Function (NMF), the Vienna Mapping Function 1 -Forecast (VMF1-FC), and the Global Mapping Function (GMF), a piece-wise method is adopted to estimate the ZWD and the horizontal gradient. Regarding to the issue of the gross unmolded errors, especially for the poor quality of correction products, a robust sequential least squares (RSLSQ) is proposed based on IGG-III model. Based on the 6h maritime data, the results show that the NMF, GMF and VMF1-FC have the similar effect on estimation ZWD and position coordinates, and the VMF1-FC with 0.5 h window length makes the accuracy of up direction improve 30%. In addition, the horizontal accuracy of real-time single BDS and GPS using RTCM-SSR can achieve the accuracy of decimeter level when the positioning is convergence, and the single BDS has a longer convergence time. Compared with the single constellation, the positioning accuracy of the real-time GPS/BDS/GLONASS using RTCM-SSR improves by 33% and the convergence time improves by 31%. Meanwhile, the convergence time improves 16.7% for GPS/BDS/GLONASS based on RSLSQ.