Acta Geodaetica et Cartographica Sinica ›› 2021, Vol. 50 ›› Issue (12): 1738-1750.doi: 10.11947/j.AGCS.2021.20200580

• Navigation Satellite System • Previous Articles     Next Articles

Evaluation of multi-GNSS orbit and clock extrapolating error and their influence on real-time PPP during outages of SSR correction

SHU Bao1,2,3, WANG Li1,2,3, ZHANG Qin1,2,3, HUANG Guanwen1,2   

  1. 1. College of Geological Engineering and Geomatics, Chang'an University, Xi'an 710054, China;
    2. State Key Laboratory of Geographic Information Engineering, Xi'an 710054, China;
    3. Key Laboratory of Western China's Mineral Resources and Geological Engineering, Ministry of Education, Xi'an 710054, China
  • Received:2020-12-07 Revised:2021-08-19 Published:2022-01-08
  • Supported by:
    The National Natural Science Foundation of China (Nos. 42004024;41877289);The China Postdoctoral Science Foundation (No. 2020M673321);The Natural Science Basic Research Program of Shanxi (No. 2021JQ-230);The Fundamental Research Funds for the Central Universities,CHD (No. 300102261305)

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Abstract: For real-time precise point positioning (PPP) users, the State Space Representation (SSR) messages from the server are usually transmitted by wireless data link. Due to unstable communication links in practical applications, it is common that the real-time orbit and clock streams are delivered to the users at certain time delays. For multi-GNSS combined positioning, the satellite orbit and clock types for GPS, GLONASS, BDS, and Galileo are different, the ability to maintain orbit and clock accuracy will be of different characteristics when SSR delay occurs. In this condition, it is difficult to maintain the real-time precision positioning accuracy and availability with conventional models. In this study, the orbit and clock extrapolating errors are evaluated based on GPS, GLONASS, BDS-2, BDS-3, and Galileo SSR products from CNES; and the performance of real-time positioning during outages of SSR correction are also analyzed for these four systems. The experiment results show that the accuracy of the orbital clock extrapolation decreases with the increase of the SSR delay time. However, significant differences in the orbital clock extrapolation errors are observed for different GNSS satellites under the same SSR delay. For 10 minutes SSR delay, the GLONASS signal-in-space range errors (SISREs) caused by orbit and clock offset extrapolation can reach 20.9 and 7.3 cm, respectively, while the BDS and Galileo SISREs caused by orbit and clock offset extrapolation can be kept within 2.2 cm, the clock offset has been converted to distance by the light speed. The performance of BDS and Galileo real-time positioning under SSR delays are significantly better than that of GLONASS and GPS. Compared with the traditional model, the four-system combined real-time positioning performance under SSR delay situation is significantly improved when ultra-rapid precise orbits are used and the clock extrapolation error characteristics for different satellites are considered. Using this new model, the positioning accuracy in the horizontal and vertical directions can maintain at 1.7 and 2.1 cm under 10 minutes SSR delay. This research has important reference value for improving the robustness of real-time positioning and optimizing the SSR update rate.

Key words: multi-GNSS, SSR time delay, real-time positioning, orbit extrapolating error, clock extrapolating error

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