Study on Time Transfer using BDS Carrier Phase Observations

With developing of BDS, BDS-based time transfer has become an important research direction in BDS’s application fields. Currently, the main method of BDSbased time transfer is BDS common view (BDS CV), its accuracy is nanoseconds magnitude. But BDS common view method only adapts to short baseline. When baseline longer, it must select a relay station because it cannot observe the same satellite in a common horizon. In addition, the correlation of common error will decrease. Because BDS carrier phase (BDS CP) method can working with a single station, using a combination of code and phase observations, high accuracy of observations, and unaffected by distance, so more and more people began to study on time transfer using BDS carrier phase observations. According to the characteristics of Beidou navigation satellite systems and the limitations of the BDS CV method, reference the principle of time transfer by GPS carrier phase observations, this paper studied the method of BDS PPPbased time transfer by using the data of Beidou monitoring receive observational. The main steps of BDS CP are: (1) do preprocess for the observations, including cycle slip detection and repair and gross error reject; (2) various error correction and parameter estimation, such as the solid earth tide correction, the earth’s rotation correction, relativistic effects, zenith tropospheric delay parameter estimation etc. ; (3) use sequential least squares method or Kalman filtering method to solve the observations with the non-difference PPP mode, and output the relative receiver clock error; (4) comparative analysis the results of BDS CP and GPS CP. In order to verify the reliability of the algorithm, the experimental sets up two links to do the time transfer. Where the two stations of the first link are belonging to Gansu Continuously Operating Reference Station, the distance between them is about 62km; the two stations of the second link are belonging to Gansu Continuously Operating Reference Station too, the distance between them is about 70km. Simulation results show that, whether in first or second link, the accuracy of time transfer by BDS CP is almost same to the accuracy of time transfer by GPS CP, which proved the feasibility of BDS for precision timing.