Abstract
Because modernized global navigation satellite systems (GNSSs) carry high-performance atomic clocks onboard, a new problem has arisen regarding whether the clock estimation approach is good enough to reflect the true performance of onboard atomic clocks. This paper proposes a new and novel centimeter-level clock synchronization approach for BDS-3 satellites based on two-way comparisons using inter-satellite link measurements. The proposed approach estimates satellite clock offsets by adjusting satellite clock offsets obtained from inter-satellite ranging measurements, and measurement noise is greatly reduced. The noise level of clock offsets estimated by the new approach is 0.7 cm, which is 41% of that of clock offsets estimated by ISL direct two-way comparisons. Compared to the ODTS approach, the new approach efficiently eliminates orbit errors in clock offsets. On this basis, the paper presents a space-borne timescale (SPBT) using high-performance atomic clocks onboard BDS-3 satellites. The frequency stability of the SPBT is 8.6E-16 at a 1-day interval; this result is superior to ground GNSS timescales such as BDT. Based on the SPBT, this paper evaluates the performance of the BDS-3 onboard atomic clock. The 2-h and 24-h prediction uncertainties for the BDS-3 PHM are 0.04 and 0.12 m, and the frequency stabilities are 1.6e-14 and 3.4e-15 at 10,000-s and 1-day intervals, respectively. The 2-h and 24-h prediction uncertainties of the BDS-3 RAFSs are 0.05 and 0.37 m, and the frequency stabilities are 1.9E-14 and 8.1E-15 at 10,000-s and 1-day intervals. This study contributes to autonomous navigation and signal-in-space accuracy improvements for GNSSs.
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Data availability
The test data used in this contribution including the ISL measurements and the L-band measurements. At present, the test data are not available to the scientific community openly because they are still under test process. But they are available from the corresponding author upon request. The other data used in this contribution including precise clock provided by GFZ, which can be download from ftp://ftp.gfz-potsdam.de/.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant Nos. 41804030, 41874039, 41574029 and 41674041). And the authors wish to thank the editor and the reviewers, whose valuable comments and suggestion helped improve this paper enormously.
Funding
The study was funded by the National Natural Science Foundation of China with the Grants Nos. 41804030; Grants Nos. 41874039, Grants Nos. 41574029, Grants Nos. 41674041.
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YJH, TCP and HXG provided the initial idea for this study. LL, GR and LS collected the original measurements. YJH, PJY and YYF preprocessed the original measurements. YJH and LS conducted the experiments and performed data analysis. YJH and TCP wrote the article. SYZ and GR helped with the data analysis. ZSS, LL and HXG gave helpful suggestions and improved the quality of the article during the revision process.
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Yang, J., Tang, C., Hu, X. et al. Centimeter-level clock synchronization and space-borne timescale generation for BDS-3 using inter-satellite link measurements. J Geod 97, 77 (2023). https://doi.org/10.1007/s00190-023-01765-7
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DOI: https://doi.org/10.1007/s00190-023-01765-7