A common-view carrier phase frequency transfer based on PPP-derived parameters

The high-precision time and frequency transfer method, based on the global navigation satellite system (GNSS) precise point positioning (PPP), has high precision, wide range, and low cost, and the GNSS common-view (CV) can remove all satellite clock errors and partial satellite orbit errors. We conducted a study to select the best satellite and combined PPP and CV to eliminate satellite clock errors, weaken the impact of satellite orbit errors, and unmodeled atmospheric asymmetry in PPP frequency transfer, thus improving the performance of frequency transfer. This study uses conventional dual-frequency ionosphere-free PPP that does not solve for an azimuthal asymmetry in the troposphere. It uses international GNSS service (IGS) products to determine the carrier phase difference between each CV satellite time and the ground clock, for each epoch. Then, the comparison difference is obtained by directly subtracting the carrier phase differences between the CV satellite time and two ground clocks. For each hour, only the satellite that is fully visible at both sites and gives the smallest standard deviation in time comparison of the day between the two ground clocks is selected as the CV satellite. To evaluate the performance of PPP-CV, five stations connected to individual active hydrogen masers are selected to form four links, of which two stations (USN7 and USN8) are common-clock and common-antenna. The results show that the time comparison precision of PPP-CV improves by approximately 12% on average for the three European links compared to PPP with respect to IGS final clock products. For frequency transfer modified Allan deviation (MDEV) over 600,000 s, PPP-CV can reach 2 × 10–16 and 2 × 10–17 for the SPT0-IENG and USN7-USN8 links, respectively. In addition, the frequency transfer stability ranging from 1200 s to 60,000 s of PPP-CV improves by 7% on average compared to PPP, and its short-term stability is also better than that of PPP when the CV satellite does not change. However, the performance of PPP-CV is comparable to PPP when the link length reaches 5991 km and the short-term stability of PPP-CV is slightly worse than PPP when the CV satellite is constantly changing.