Abstract
The predicted navigation satellite clock offsets are crucial to support real-time global navigation satellite system (GNSS) precise positioning applications, especially for those applications difficult to access the real-time data stream, such as the low earth orbit (LEO) autonomous precise orbit determination. Currently, the clock prediction for the Chinese BeiDou system is still challenging to meet the precise positioning requirement. The onboard clocks of BeiDou satellites are provided by different manufacturers, and the clocks’ switch events are more frequent. Considering the satellite-specified and temporal variation of the BeiDou clocks characteristics, we intend to use an adaptive model for BeiDou clock prediction. During clock prediction, we identify different models for BeiDou clocks’ characteristics, and then address the optimal model with a cross-validation procedure. The model achieving the minimum variance in the cross-validation procedure is used for the final clock prediction. We compared the prediction results of our method with two well-recognized BeiDou ultra-rapid clock products, named GBU-P and ISU-P, respectively. The comparison results indicate that the adaptive model achieves about 1-ns precision for 3-h prediction, which corresponds to 47.3% and 32.1% precision improvement compared to the GBU-P and ISU-P products, respectively. The efficiency of the predicted clocks is further validated with the precise point positioning (PPP) data processing. The results indicate that the static PPP solution precision is improved by 21.6%–30.0% compared to the current predicted clock product. The precision improvement in kinematic PPP is even more significant, which reaches 46.7%–53.9% with respect to these GBU-P and ISU-P products. Therefore, the proposed adaptive model is a practical and an efficient way to improve the BeiDou clock prediction.
Highlights
Precise point positioning (PPP) is a popular satellite positioning technique providing a global scale, centimeter-level accuracy user position, becoming increasingly popular in global navigation satellite system (GNSS) communities [1,2,3]
According to extensive data analysis, we find that the key to improving BeiDou clock prediction is not the non-linear effects, since there is no substantial difference between the GPS and BeiDou clock in terms of stability
This study points out the uniqueness of the BeiDou clocks is that the clock characteristics are highly satellite-specified, and the characteristics may change by clock operations or clock events
Summary
Precise point positioning (PPP) is a popular satellite positioning technique providing a global scale, centimeter-level accuracy user position, becoming increasingly popular in GNSS communities [1,2,3]. The IGS ultra-rapid clock products (IGU-P) use a polynomial model with a sinusoid term for GPS clock offset prediction, which achieves about 1–4 ns precision for a 24-h prediction [21]. The BeiDou clock presents frequency clock steering or phase adjustment in operation, which causes many jumps and turning points [36] in the clock time series Another BeiDou clock characteristic is that the optimal clock model for a particular satellite may change over time.
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