BDS-2 and BDS-3 combined precise orbit determination with hybrid ambiguity resolution

The BeiDou Regional Navigation Satellite System (BDS-2) and BeiDou Global Navigation Satellite System (BDS-3) satellites will be utilized in conjunction to provide positioning, navigation and timing (PNT) services. Precise orbit products are essential preconditions and guarantees for providing PNT services. To improve the quality of the BeiDou Navigation Satellite System (BDS) orbits determination, a method for eliminating the biases caused by code inter-system biases (ISBs) between the BDS-2 and BDS-3 at overlapping frequencies on BDS double-difference (DD) ambiguity resolution (AR) is proposed. To validate the contribution of the proposed method, the dataset spanning from day of year (DOY) 170, 2019, to DOY 170, 2020 is analyzed in the BDS precise orbit determination (POD) with different processing strategies. The results show that the fractional cycle biases (FCBs) in wide-lane and narrow-lane ambiguities are related to the receiver types, which are stable and can be estimated as constants in a POD arc length. After applying the proposed calibration method, the success fixing rate for the BDS-2/3 inter-system wide-lane ambiguities is improved by more than 25%, and that of the narrow-lane ambiguities by approximately 6%. Compared with that for BDS-2/2 and BDS-3/3 intra-system AR independently, the overlapping accuracy is improved by 13.7%, 4.8% in the along-track, cross-track directions, respectively, after adding BDS-2/3 inter-system AR.