The BeiDou satellite navigation system (BDS) is different from other global navigation satellite systems (GNSSs) because of its special constellation, which consists of satellites in geostationary earth orbit, inclined geosynchronous earth orbit (IGSO), and medium earth orbit (MEO). Compared to MEO satellites, the observations of IGSO satellites cover only a small range of nadir angles. Therefore, the estimation of phase center offsets (PCOs) suffers from high correlation with other estimation parameters. We have estimated the phase center offsets for BeiDou IGSO and MEO satellites with a direct PCO parameters model, and constraints are applied to cope with the correlation between the PCOs and other parameters. Validation shows that the estimated PCO parameters could be used to improve the accuracy of orbit and clock offset overlaps. Compared with the Multi-GNSS Experiment antenna phase center correction model, the average improvements of the proposed method for along-track, cross-track, and radial components are 19 mm (31%), 5 mm (14%), and 2 mm (15%) for MEO satellites, and 13 mm (17%), 12 mm (21%), and 5 mm (19%) for IGSO satellites. For clock offset overlaps, average improvements of standard deviation and root mean square (RMS) are 0.03 ns (20%) and 0.03 ns (12%), respectively. The RMS of precise coordinates in the BDS-only positioning was also improved significantly with a level of 24 mm (30%) in the up-direction. Finally, the overall uncertainty of the estimated results is discussed.
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Thanks for the data support of iGMAS and IGS. This research was partly supported by the National Natural Science Foundation of China (Grant Nos. 41731066, 41774025); the Program of the Grand Projects of the Beidou-2 System (Grant No. GFZX0301040308), the National Natural Science Foundation of Shaan Xi (Grant No. 2016JQ4011), and the Special Fund for Basic Scientific Research of Central Colleges (Grant Nos. 310826172006, 310826172202, 310826173101, Chang’an University). Finally, the authors are also grateful for the comments and remarks of the reviewers, who helped to improve the manuscript significantly.
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