Impact of BeiDou satellite-induced code bias variations on precise time and frequency transfer

Abstract

The Chinese BeiDou navigation satellite system (BDS) is an emerging global navigation satellite system similar to the global positioning system (GPS), which provides positioning, navigation and timing services. The typical character of BDS code bias variation has received greater attention in relation to positioning and navigation in comparison with its underlying mechanism and effects on BDS carrier-phase time and frequency transfer. This study developed a code bias variation correction model. The improvements in the model correction results from nine time transfer stations were observed at two satellite frequencies (i.e. B1 and B2) and for both inclined geostationary orbit (IGSO) and medium earth orbit (MEO) satellite constellations. At frequency B1, the IGSO and the MEO variation improved by 43.64% and 46.39%, respectively. At frequency B2, the IGSO and the MEO variation improved by 52.14% and 51.08%, respectively. Raw and corrected scenarios were compared in an experiment investigating time and frequency transfer. Consequently, the impact of BDS code bias variation on time and frequency transfer was mainly concentrated on the value of the time and frequency transfer. It was not a constant value (mean time transfer value of −0.41 ns), and the corresponding amplitude is closely related to the geodetic distance of the time links. Moreover, the BDS code bias variation showed no obvious effect on the frequency stability of the time links. Therefore, the satellite-induced code bias variation is a crucial error term in practical time transfer work, which needs to be corrected to improve the accuracy of the time transfer value, particularly for a long geodetic distance time link.