GPS Carrier-Phase Time and Frequency Transfer With Different Versions of Precise Point Positioning Software

摘要

The GPS carrier-phase technique (GPSCP) allows one to compare the frequencies of remote clocks with similar accuracy as with two-way satellite time and frequency transfer. Thus, GPSCP enables a relatively cheap and easy method to compare a remote frequency source at any site with the primary frequency standards at PTB. For this reason, a Dicom GTR50 time and frequency transfer receiver has been combined with a transportable passive hydrogen maser. This mobile unit can be placed at institutes or companies that are interested in a highly accurate frequency link to PTB. In this contribution, we focus on the software aspects, because the accuracy of GPSCP time and frequency transfer depends both on the performance of the receivers and the quality of the used precise point positioning (PPP) software. We use the NRCan-PPP software and the Concerto software package developed at NICT, which are based on different numerical models. These two packages were chosen because they allow processing of longer data than provided in one daily measurement data file. Even in case of a quasi-zero-baseline and common-clock configuration, the solutions of the both software concepts for comparison of two receivers show sometimes small divergences. Thus, this is definitely induced by the software due to the different filter and processing methods. In the case of clock comparisons, the solutions can differ from each other up to 1 nanosecond in 1 day, depending on the starting point and the length of the processed epoch. We demonstrate that processing over long epochs strongly reduces this error. Therefore, we propose the new approach of continuous processing without resetting the ambiguities every 24 h as the best way to obtain proper results. With the Concerto software, the process can continue without limitation.