Quality evaluation and PPP performance analysis of GPS/BDS real-time SSR products

Objectives:  In recent years, with the rapid development of multi-system GNSS and the growing demand for real-time and high-precision applications, the State Space Representation (SSR) products provided by International GNSS Service (IGS) are more and more abundant. Evaluating GNSS real-time precise products and their positioning performance in different analysis centers is of important reference value for users. This paper aims to evaluate the availability and accuracy of real-time SSR products and their impact on real-time precise point positioning (RT-PPP) from six commonly-used ACs.   Methods:  After evaluating the epoch availability and satellite availability of SSR corrections and the accuracy of GPS/BDS precise orbit clock products, simulated kinematic GPS and GPS/BDS PPP positioning experiments were carried out to explore the relationship between SSR product accuracy and three-dimensional (3D) position accuracy.   Results:  CAS has the highest availability of GPS satellites, providing SSR corrections for all 32 GPS satellites; CAS, GFZ and WHU had the highest availability of BDS satellites, all of which provided SSR corrections for all 15+27 BDS satellites (excluding BDS-3 GEO). Among the SSR products of the six ACs, WHU's GPS satellite has the best 3D orbit accuracy (3D RMS was 3.3cm) and clock difference accuracy (STD was 0.05ns). The Signal-In-Space Ranging Errors (SISRE) of GPS satellites are generally better than 5cm in these six ACs. The SISREs of GPS satellites from six ACs are in the following order:WHU < GMV < CNE < DLR < GFZ < CAS. Compared with GPS, BDS orbit and clock accuracy is relatively poor, the SISRE values of MEO satellite precise products of BDS-2 and BDS-3 in WHU analysis center with the best performance were 8.83 cm and 5.91 cm, respectively. In GPSonly kinematic PPP mode, DLR has the slowest convergence speed (38.9 min), while GFZ has the fastest convergence speed (26.7 min). After adding BDS satellite, there is no significant difference in positioning accuracy, but it can effectively improve the convergence speed (6%-25%).   Conclusions:  Therefore, it can be concluded that SISRE can reflect the 3D position accuracy of GPS-only kinematic PPP. The addition of BDS satellite can significantly improve the convergence speed.