Long-Term Uncertainty in Time Transfer Using GPS and TWTFT Techniques

Published

April 13, 2015

Author(s)

Victor S. Zhang, Thomas E. Parker, Jian Yao

Abstract

The techniques of GPS time and frequency transfer (code based and carrier phase) and two-way satellite time and frequency transfer (TWSTFT) are widely used in remote clock comparison and in the computation of International Atomic Time (TAI). Many timing laboratories in the world utilize both techniques (GPS and TWSTFT transfer links) to compare each other's' clocks. The time transfer accuracy of these links is an important parameter, but in many cases calibration campaigns have been very infrequent due to the expense and lack of suitable equipment. In lieu of repeated calibrations, some information regarding the long-term stability of these links can be obtained through comparisons between the two links (a so called double difference). Without frequent calibrations it is impossible to tell where the instabilities originate, but information regarding the magnitude of the instabilities can be obtained from double difference data. We have been investigating the combined delay variations of GPS and TWSTFT links for a number of laboratory pairs, including both long and short base lines. Our preliminary results show that the relative delay change between GPS and TWSTFT transfer links can be as large as 2 to 3 ns over a few years and that all of the laboratory pairs that have been investigated show similar magnitudes in the double difference data. Currently the longest set of good double difference data is about 8 years. The data point out the need for frequent calibration campaigns if accuracies at the nanosecond level are required. In this paper, we will present the results of a study of the relative long-term delay changes between GPS and TWSTFT links for timing links between laboratories in Europe and the USA, as well as links within Europe, and in the USA.

Proceedings Title

Proceedings of the 2015 Joint Conference of the IEEE International Frequency Control Symposium & European Frequency and Time Forum

Conference Dates

April 12-16, 2015

Conference Location

Denver, CO

Conference Title

2015 Joint Conference of the IEEE International Frequency Control Symposium & European Frequency and Time Forum

Pub Type

Conferences

Download Paper

https://doi.org/10.1109/FCS.2015.7138943

Keywords

GPS time and frequency transfer, time and frequency transfer uncertainty, time transfer link calibration, TWSTFT

Citation

Zhang, V. , Parker, T. and Yao, J. (2015), Long-Term Uncertainty in Time Transfer Using GPS and TWTFT Techniques, Proceedings of the 2015 Joint Conference of the IEEE International Frequency Control Symposium & European Frequency and Time Forum, Denver, CO, [online], https://doi.org/10.1109/FCS.2015.7138943 (Accessed December 15, 2024)