Rapid frequency transfer by BDS-3/GPS PPP with tropospheric augmentation

Precise point positioning (PPP) can currently achieve time transfer to a precision of one hundred picoseconds. However, the long convergence time is the main drawback of this popular time and frequency transfer method. It is well known that the convergence of position and receiver clock offset parameters in PPP solution is related to the satellite geometry, in which the receiver clock offset is the key parameter in time and frequency transfer and its performance could be reflected by the time dilution of precision (TDOP). This study applies tropospheric augmentation to accelerate PPP initialization and improve PPP frequency transfer performance during the convergence period. With the tropospheric augmentation applied to BDS-3 PPP, the convergence speed of receiver clock offset has been greatly improved when there are few visible satellites. Since GPS and BDS-3/GPS combined PPP, the satellite geometry and TDOP are better than that of BDS-3, the improvement in convergence speed is limited correspondingly. In addition, due to a more stable receiver clock offset estimated with the tropospheric information constraints, the short-term stability of frequency transfer during the convergence period has been greatly improved for GPS, BDS-3 and BDS-3/GPS combined PPP. For the two time links selected in this study, the short-term stability has been improved by more than 60, 45 and 40% in BDS-3, GPS and BDS-3/GPS combined PPP frequency transfer, respectively. However, the contribution of tropospheric augmentation to PPP frequency transfer is no longer significant after convergence.