Method of Precise Common-View frequency transfer based on BeiDou GEO satellite

At present, many Beidou tracking stations over the world have been set up for international GNSS Monitoring and Assessment System (iGMAS) and a pilot project named Multi-GNSS Experiment (MGEX) is implemented. Each station was equipped with the Multi-GNSS receivers which are able to track BeiDou as well as GPS signals. Furthermore some of stations were equipped with high-precision atomic clocks as external frequency reference. Based on the BeiDou Geostationary (GEO) satellite and the BeiDou tracking stations, a method of Precise Common-View (PCV for short) frequency transfer is proposed, which use high-precision carrier phase and iGMAS precise orbit. Firstly, data preprocess are carried out for both of the carrier phase and the code for BeiDou B1 and B2 frequencies. The process includes cycle slip and repair as well as outlier removal. Secondly, to calculate clock offset ionosphere-free linear combination of BeiDou B1 and B2 for the phase observations is used. Finally, the frequency transfer is implemented by epoch-difference, which cancelled the initial phase ambiguity. The PCV method is advantageous over others. First, BeiDou GEO satellites can been observed all day, which is enable for continuous frequency transfer between stations; Second, only the initial phase ambiguity, which is present in the carrier phase measurements of GEO satellites, can be cancelled out by epoch-difference; Third, the effect on multipath for GEO satellites also can be cancelled out by epoch-difference. In October 2013, PCV frequency transfer experiment was carried out between MGEX station CEBR and NNOR with hydrogen masers and the Multi-GNSS receivers. The BeiDou-G5 satellite was used. The precise orbit of BeiDou satellites was calculated with iGMAS and MGEX data by dynamic orbit determination method. The station coordinates were computed by GPS PPP with the position accuracy better than 1centimeter. The troposphere error was corrected using Neil model. In order to verify the method, the comparison to Precise Point Position (PPP) using GPS observation and IGS final product shows that: the method of PCV frequency transfer has a frequency accuracy of 2 parts in 10
¹⁵
for the duration of a day and the performance of the PCV method is consistent with that of GPS PPP. With the improvement of the precision of iGMAS precise orbit, the performance of the PCV method can be further enhanced.