Enhancing BDS-3 precise time transfer with DCB modelling

Abstract

This article is the first report of BDS-3 differential code bias (DCB) correction models. Satellite differential code biases (SDCBs) were regarded as a source of error; if there was no correction, the quality of the GNSS Position & Navigation & Timing service deteriorated. As a newly built global system, the BDS-3 satellite broadcasted B1I, B3I, B1C and B2a signals. To fully exploit all the BDS-3 signals, DCB correction models related to multiple Dual-Frequency (DF) Ionosphere-Free (IF) combinations were developed for BDS-3 application. Two prevailing global navigation satellite system positioning technologies, namely, standard point positioning (SPP) and precise point positioning (PPP), were utilized to validate the efficacy of the DCB parameters provided by the Multi-GNSS Experiment (MGEX). Our numerical analyses clarified how the DCB model performed when it was applied to positioning and time transfer events under the B1C&B3I, B1I&B2a, B1C&B2a cases. With the use of DCB correction in three combinations, the positioning accuracy and frequency stability were significantly improved. The E, N and U position accuracies of the ondcb scheme compared to those of the offdcb scheme were enhanced in the range of 39.51–86.24%, 35.44–78.64% and 41.84–78.64%, respectively. In particular, we observed that the long-term stability of the time link was obviously better than the short-term stability. The stability percentages were improved by at least 3%, and some were improved by up to 66.5%. The frequency stability obtained by B1I&B3I is equivalent to that obtained by B1C&B3I and B1I&B2a. Finally, all the statistics indicate that the B1C&B2a combination recommended as the optimal option is applicable to time transfer communities. The result agrees with our expectation that the appropriate modelling of DCB is vital, which allows for more precise positioning and a stable time link.