Long-Term Stability of GPS Time Transfer Link

The techniques of GPS Common-View (GPS CV) and GPS Precise Point Positioning (GPS PPP) are widely used in the computation of Coordinated Universal Time (UTC) for major international time-keeping laboratories. Long-term stability of the link is an important factor that affects the accuracy of time comparison at present. In order to ensure the long-term stability of time transfer, the link must be calibrated. However, in many cases, due to limited costs and lack of appropriate calibration equipment, frequent calibration is not possible. Instead of repeated calibration, some information about the long-term stability of these links can be obtained by comparing the two links. In this paper, the data of two years after the GPS travelling calibrator of the Bureau international des poids et mesures (BIPM) is used to perform the calibration measurement of the comparison link of the National Time Service Center (NTSC), based on the GPS receivers that use common reference signals from the same clock to carry out the zero-baseline common clock comparison. Then take the national standard time maintained by the NTSC and Physikalisch-Technische Bundesanstalt (PTB) as comparison objects, a long baseline GPS CV and PPP comparison test was carried out to directly investigate the long-term stability. The results show that the long-term stability of GPS time comparison is 1.88ns, which can meet the international time comparison requirements.