Multi-GNSS real-time clock estimation using sequential least square adjustment with online quality control
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Real-time satellite orbit and clock product is a key prerequisite for real-time precise positioning service based on precise point positioning (PPP). With the rapid development of the multiple global navigation satellite systems (Multi-GNSS), about 120 satellites will be processed for Multi-GNSS real-time clock estimation. Unfortunately, the computation is very time-consuming, especially for quality control since problematic observations are inevitable. Taking advantage of computer technology, sequential least square adjustment with an adapted online quality control procedure is developed to rapidly estimate Multi-GNSS real-time clocks, although various filtering estimators are commonly used now. A globally distributed network including 70 stations tracking mostly satellites of GPS, GLONASS, BDS, and Galileo is employed for experimental validation. The results show that the computation time per epoch is less than 3 s in average and can meet the 5 s update rate of the IGS real-time clock product. Compared to the GeoForschungsZentrum MGEX (GBM) final clock product, the averaged STD values of the estimated clocks of the four GNSS systems are 0.089 ns and 0.153 ns, respectively, for the clock solutions with and without the online quality control, which also confirms the importance of the quality control procedure. The Multi-GNSS kinematic PPP experiment using the estimated clocks with quality control shows that the positioning RMS is about 4 cm and generally 2 cm in vertical and horizontal components, respectively, and the corresponding convergence time is about 15 min.
KeywordsMulti-GNSS Real-time clock estimation Online quality control Sequential least square adjustment
This work was supported partly by the scholarship program of China Scholarship Council (CSC), the Program of the National Natural Science Foundation of China (41731066, 41774025), the Special Fund for Basic Scientific Research of Central Colleges (Grant Nos. 310826165014, 310826171004, Chang’an University), and the Grand Projects of the Beidou-2 System (GFZX0301040308). We also thank the MGEX and GFZ for providing the data and products for this study.
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