An Improvement of RINEX-Shift Algorithm for Continuous GPS Carrier-Phase Time Transfer

The wide application of GPS carrier-phase (CP) time transfer is limited by the problem of boundary discontinuity. The RINEX-Shift (RS) algorithm was designed to solve this problem [1]. However, if there are GPS data anomalies, the time transfer result computed by this algorithm oscillates around the true value. The deviation from the true value can be as large as a few nanoseconds. The origin of this oscillation behavior lies in the fact that the precise point positioning (PPP) technique needs some time (e.g., 2 hours) to converge. If there are only a short segment (e.g., < 2 hours) of valid data before or after the missing data, PPP does not have enough time to converge so that the solution for this short segment deviates from the true value. We propose the “revised RINEX-Shift” (RRS) algorithm to solve the oscillation problem in the RS algorithm. RRS extracts the result at the middle epoch, rather than the first epoch as in the RS algorithm. In this way, PPP has enough time to converge. Tests of the RRS algorithm show that the oscillation problem is solved successfully and there is a 10–55% improvement of fractional frequency stability over the RS algorithm. Thus, the RRS algorithm provides the best GPS time transfer result.