GPS Measurements Anomaly and Continuous GPS Carrier-Phase Time Transfer

The wide application of GPS carrier-phase (CP) time transfer is limited by the problem of boundary discontinuity (BD). The discontinuity has two categories. One is "day boundary discontinuity," which has been studied extensively and can be solved by a few methods [1-5]. The other category of discontinuity, called "anomaly boundary discontinuity (anomaly-BD)," comes from a GPS-measurements data anomaly. This paper focuses on the second category of discontinuity (i.e., anomaly-BD). We first demonstrate that a few minutes of GPS-measurements data anomaly are enough to lead to a discontinuity of more than 200 picoseconds in the GPS CP time transfer. To eliminate the anomaly-BD, we propose a simple, but powerful strategy, i.e., polynomial curve-fitting for the anomaly. The fitted phase measurement is typically less than 3 cm from the original phase measurement, in terms of the root mean square (RMS). And the fitted code measurement is typically less than 80 cm from the original code measurement. If we replace the anomaly with the fitted data, we can avoid the re-estimation of the phase ambiguities after the anomaly. Thus, the anomaly-BD at the anomaly should disappear. Tests show that the curve-fitting strategy works very well for up to 20 min of GPS-measurements data anomaly.