The Method of BDS PPP Time Transfer Considering Clock Modeling

GPS Precise Point Positioning (PPP) time transfer has been applied to the international time comparison at BIPM, while BDS PPP time transfer has not been applied at BIPM. With the rapid development of China’s international GNSS continuous Monitoring and Assessment System (iGMAS), this work, supported by iGMAS products, has carried out the BDS PPP time transfer method and experimental research. The traditional PPP algorithm takes the receiver clock offset parameter as independent white noise, while ignoring the correlation of between-epoch clock offset. For this problem, this contribution proposed the BDS PPP time transfer method which is constrained by the receiver clock model. Using the final (ISC) precise orbit and clock products released by iGMAS, the paper selected the stations of the timing laboratories such as the National Timing Center (NTSC), the Physikalisch Technische Bundesanstalt (PTB) and the GNSS station with external hydrogen atomic clock, and forms 5 time-links with NTSC station as the center node to investigate the experiment. The GPS PPP solutions using IGS final products were regarded as the reference. The experimental results demonstrated that the standard deviation (STD) values of traditional BDS PPP time transfer based on iGMAS products is about 0.7 ns in Eurasian links, and about 0.5 ns in Asia-Pacific links. Compared with the traditional BDS PPP time transfer, the STD value of BDS PPP based on the between-epoch constraint model is reduced significantly, range from 1.53% to 16.6%, especially in the Eurasian links. In addition, the frequency stability of traditional BDS PPP based on iGMAS products is comparable to that of GPS PPP under good observation conditions. BDS PPP using clock model has been significantly improved in the Eurasian link, both in terms of long-term and short-term stability, and the max improvement is about 80%. In the Asia-Pacific region, short-term stability is significantly improved. The maximum stability at 120 s is increased to 57%, while the 15360 s stability is increased by 19%. At the same time, with the development of iGMAS global tracking station and BDS, BDS PPP time transfer performance can be further improved.