Time and frequency transfer system using GNSS receiver

Abstract

Global Positioning System (GPS) time and frequency transfer is one of the most useful ways for the comparison of remote clocks, and the comparison results are very important for the calculation of International Atomic Time and UTC (Coordinated Universal Time). For the timing laboratories, it is necessary to calibrate and periodically evaluate their time transfer system to ensure the accuracy and long-term stability of their time and frequency comparison results. Once the calibration is achieved, it can be used as a standard for traceable time and frequency measurements. In this paper, we demonstrate Global Navigation Satellite System receiver calibration campaign between the National Time and Frequency Standard Laboratory of Telecommunication Laboratories in Taiwan and the Measurement Standards Laboratory in New Zealand. Two calibration strategies, receiver calibration and the link calibration, are adopted in this work. The receiver calibration is used for evaluating the performance of the proposed system in domestic traceability network in Taiwan. The link calibration is used for minimizing the total uncertainty budget in calculating UTC. Experimental results indicate that the expanded time and frequency uncertainty of the proposed system (with a coverage factor of k = 2) are less than 25 ns and 1.1 × 10−13, respectively, after 1 day of averaging. The accuracy of GPS time link is reported to be better than 2 ns in long-baseline link (10,000 km) in Asia-Pacific Zone.