BDS Real-time Satellite Clock Offsets Estimation with Three Different Datum Constraints

Abstract

A clock offset datum should be selected to separate the satellite and receiver clock offset when estimating the Global Navigation Satellite System (GNSS) satellite clock offset. However, the applicable conditions and performance of the estimated satellite clock offset vary for different clock offset datums. In this paper, the BeiDou Navigation Satellite System (BDS) real-time satellite clock offset is estimated by using the undifferenced (UD) model with three datum constraints: receiver clock datum, satellite clock datum, and zero-mean condition (ZMC) datum. The constraint conditions of three clock offset datums are discussed, the transformation relationship among the three datums constraints is derived, and the characteristics of three clock offset datums are analyzed. One hundred stations were used to perform the experiments, and the results show mean standard deviation (STD) values of ±0.118, ±0.124, and ±0.101 ns for the receiver clock, satellite clock, and ZMC datum, respectively. The mean clock offset model precisions with the three datum are ±0.497, ±0.646, and ±0.442 ns, respectively. The frequency stability with ZMC datum results showed the best performance when the integration time is less than 10,000 s. For precise point positioning (PPP), the ZMC datum results show better performance among the three datum constraints. This study can provide a reference for clock offset datum selection for GNSS satellite clock offset estimation.