Objectives In recent years, the rapid development of multi-system global navigation satellite systems (GNSS) and the growing demand for real-time,high-precision applications have led to an increasing variety of state space representation (SSR) products provided by the International GNSS Service (IGS). Evaluating the accuracy and availability of GNSS real-time precise products and their positioning performance across different analysis centers is of great importance for users. We aim to assess the availability and accuracy of real-time SSR products and their impact on real-time precise point positioning (PPP) from six commonly used analysis centers.
Methods We evaluated the epoch availability and satellite availability of SSR corrections, as well as the accuracy of GPS and BeiDou satellite navigation system (BDS) precise orbit and clock products. Simulated kinematic GPS and GPS/BDS PPP experiments were conducted to investigate the relationship between SSR product accuracy and three-dimensional (3D) position accuracy.
Results The Chinese Academy of Sciences (CAS) exhibited the highest availability for GPS satellites, providing SSR corrections for all 32 GPS satellites. CAS, Deutsches GeoForschungsZentrum (GFZ), and Wuhan University (WHU) demonstrated the highest availability for BDS satellites, with all three providing SSR corrections for all 15 BDS-2 and 27 BDS-3 satellites, excluding BDS-3 geostationary Earth orbit (GEO) satellites. Among the SSR products from the six analysis centers, WHU's GPS satellites achieved the best 3D orbit and clock accuracy. The signal-in-space ranging errors (SISRE) for GPS satellites across all six centers were generally better than 5 cm. The SISRE ranking for GPS satellites was as follows: WHU < GMV Aerospace and Defense (GMV) < Centre National d’Études Spatiales (CNE) < Deutsches Zentrum für Luft- und Raumfahrt (DLR) < GFZ < CAS. In contrast, the orbit and clock accuracy of BDS satellites was comparatively lower. For WHU, the best-performing analysis center, SISRE values for medium Earth orbit satellites of BDS-2 and BDS-3 were 8.83 cm and 5.91 cm, respectively. In GPS-only kinematic PPP, DLR exhibited the slowest convergence speed, while GFZ achieved the fastest. Adding BDS satellites did not significantly improve positioning accuracy but effectively enhanced convergence speed.
Conclusions SISRE is shown to reliably reflect the 3D position accuracy of GPS-only kinematic PPP. Moreover, incorporating BDS satellites can significantly improve convergence speed, even if their impact on positioning accuracy is minimal.
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