Improved performance of BDS-3 time and frequency transfer based on an epoch differenced model with receiver clock estimation

The carrier-phase (CP) technique based on the BeiDou global satellite navigation system (BDS-3) has proven to be an important spatial tool for remote time and frequency transfer. The current CP technique models the receiver clock offset as a white noise stochastic process, and easily absorbs some unmodeled errors, which compromises time and frequency transfer performance. To further improve the performance of time and frequency transfer, a new BDS-3 receiver clock estimation algorithm based on the epoch-difference (ED) model is presented, and the mathematical principle and applied mode are discussed. The algorithm makes full use of both observation of current epoch and practical variation of receiver clock offset, further improving the performance of time and frequency transfer. Five MGEX network stations equipped with various types of receivers and antennas with dual-frequency BDS-3 signals were used to establish four time transfer links (i.e., AMC4–PTBB, BRUX–PTBB, OP71–PTBB, and WTZS–PTBB) to evaluate their effectiveness. The ED model improved all four time links in terms of noise level, with improvements of 17.0%, 18.3%, 20.3%, and 5.9% for AMC4–PTBB, BRUX–PTBB, OP71–PTBB, and WTZS–PTBB, respectively, when compared with the results from a non-ED model. ED model outputs were better than raw solutions in terms of frequency stability at all time links, particularly for average time intervals (tau) < 1,000 s. The mean improvement was 8.1% for AMC4–PTBB, 16.1% for BRUX–PTBB, 10.0% for OP71–PTBB, and 18.6% for WTZS–PTBB when the average time (tau) was less than 1,000 s.