Modeling and predicting inter-frequency clock bias of BDS-2 GEO, IGSO and MEO satellites for triple-frequency precise point positioning

[weisongwen]

Due to inter-frequency clock bias (IFCB), the dual-frequency precise clock products cannot be directly applied to BDS-2 triple-frequency precise point positioning (PPP). In this study, the datasets collected at 195 ground tracking stations for a whole year are employed to investigate the modeling and prediction of BDS-2 IFCB. The modeling periods of IFCB are consistent with orbital repeat periods, namely a week for medium earth orbit (MEO) satellites and a day for geostationary orbit (GEO) and inclined geosynchronous orbit (IGSO) satellites. The harmonic analysis results show that the IFCB of MEO satellites has seven significant periods of (168, 84, 56, 42, 33.6, 28, 12.9) h, while there are six obvious periods of (24, 12, 8, 6, 4.8, 4) h for GEO and IGSO satellites. Two function models composed of a linear term and a harmonic term with seven orders for MEO satellites and six orders for GEO and IGSO satellites are established to describe the IFCB variations, and the model coefficients are fitted by least squares. The IFCB modeling accuracies are 4 mm for MEO satellites and 2 mm for GEO and IGSO satellites. The established model can predict the IFCBs with single-day prediction accuracies of 5.0 and 3.9 mm for GEO and IGSO satellites and single-week prediction accuracies of 5.0 mm for MEO satellites, respectively. After applying these predicted IFCBs to BDS-2 triple-frequency PPP, the positioning accuracies are improved by 14–29%.