Iterative method for signal path delay difference estimation of two-way satellite time and frequency transfer

The signal path delay difference due to satellite motion relative to the ground stations adds non-reciprocity to Two-way Satellite Time and Frequency Transfer (TWSTFT). For the availability of broadcast ephemeris for the geostationary satellite for TWSTFT in BeiDou navigation system, an iterative method for signal path delay difference estimation due to the satellite motion is proposed, which is compared with the ranging method. The one day TWSTFT experiment data with BeiDou GEO satellite at 140°E experiment between Beijing and Sanya has been analyzed, which show that the signal path delay difference is less than 0.14ns and the difference of the results using these two methods is less than 0.11ps. This implies that there is no need to conduct ranging when the broadcast ephemeris is available for the estimation signal path delay difference.