Abstract
The carrier-phase (CP) technique based on the Global Navigation Satellite System (GNSS) has proved to be a useful spatial tool for remote and precise time transfer. In order to improve the robustness and stability of the time transfer solution for a time link, a new CP approach based on a combination of GPS, BeiDou (BDS), and Galileo satellite systems is proposed in this study. The mathematical model for the obtained unique time transfer solution is discussed. Three GNSS stations that can track GPS, BeiDou, and Galileo satellites were used, and two time links are established to assess the performance of the approach. Multi-GNSS time transfer outperforms single GNSS by increasing the number of available satellites and improving the time dilution of precision. For the long time link, with a geodetic distance of 7537.5 km, the RMS value of the combined multi-system solution improves by 18.8%, 59.4%, and 35.0% compared to GPS-only, BDS-only, and Galileo-only, respectively. The average frequency stability improves by 12.9%, 62.3%, and 36.0%, respectively. For the short time link, with a geodetic distance of 4.7 m, the improvement after combining the three GNSSs is 6.7% for GPS-only, 52.6% for BDS-only, and 38.2% for Galileo-only.
Highlights
Time and frequency transfer is a basic issue for the comparison of remote time and frequency laboratories
Since the 1980s, the Global Positioning System (GPS) operated by the United States has been used for time and frequency transfer based on the common view (CV) approach, which provides impetus to the application in the field of time and frequency [1,2]
With development of the International Global Navigation Satellite System (GNSS) Service (IGS) products, for satellite orbit and clock products [3,4], all in view (AV) and carrier phase (CP) approaches have been proposed for time and frequency transfer using GPS code and carrier phase observations [5,6]
Summary
Time and frequency transfer is a basic issue for the comparison of remote time and frequency laboratories. With development of the International GNSS Service (IGS) products, for satellite orbit and clock products [3,4], all in view (AV) and carrier phase (CP) approaches have been proposed for time and frequency transfer using GPS code and carrier phase observations [5,6]. These approaches exhibit a better performance compared to the CV approach.
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