GPS Carrier-Phase Time Transfer Boundary Discontinuity Investigation

We report on a study of the carrier-phase time transfer boundary discontinuity by the use of the precise point positioning (PPP) technique. Carrier-phase time transfer is first compared with two-way satellite time and frequency transfer (TWSTFT) between the same stations. It matches TWSTFT quite well and provides better short-term stability. Later, we extract 1-day data-arc boundary discontinuity jump values for 151 days. The distribution of jump values is almost Gaussian. Different GPS receivers have different mean jump values (-200 ps to +200 ps) and different standard deviations (100 ps to 300 ps). Among the receivers at NIST (USA), USNO (USA), and PTB (Germany), USNO has the smallest absolute mean jump value (14.2 ps) and the smallest deviation (105.1 ps). In addition, with the increase of data-arc from 1-day to 4-days, both mean value and deviation increase. For receivers at the same station, the correlation varies. At PTB, the correlation between the jumps for receivers PTBB and PTBG is only -0.064. At NICT (Japan), the correlation between receivers SEPA and SEPB is 0.47, while that between receivers SEPB and SEPT is 0.10. The above variation in the correlation between receivers at the same location suggests that the boundary discontinuity does not mainly come from satellite-path-related noise. Further investigation reveals that multipath also contributes little to boundary discontinuity. Comparison between PPP and network method shows that the algorithm of fixing phase ambiguity plays an important role in boundary discontinuity.