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Improving Two-Way Satellite Time and Frequency Transfer with Redundant Links for UTC Generation

Published

Author(s)

Zhiheng Jiang, Victor S. Zhang, Thomas E. Parker, Gerard Petit, Yi-Jiun Huang

Abstract

Two-Way Satellite Time and Frequency Transfer (TWSTFT) is a primary technique for the generation of Coordinated Universal Time (UTC). About 12 timing laboratories around the world use SAtellite Time and Ranging Equipment (SATRE†) modems in TWSTFT operation (SATRE TWSTFT) and contribute the data for the realization of UTC. In principle, the advantages of TWSTFT is its small calibration uncertainty (≤ 1.0 ns if the link is calibrated with a TWSTFT mobile station) and its long-term link stability. However, the precision of the SATRE TWSTFT is degraded by a daily variation pattern (diurnal) in the TWSTFT results. The diurnal with varying amplitude exists in all the SATRE TWSTFT links. The observed peak-to-peak variation of the diurnals can reach 2.0 ns in some case. The diurnal can be caused by many different sources. Studies of the sources of the diurnal provided no conclusive understanding of the dominant origin of the diurnal. Therefore, efforts have been made to reduce the impact of the diurnal in SATRE TWSTFT for UTC computation. The BIPM has been using the combination of SATRE TWSTFT results and GPS carrier- phase Precise Point Positioning solutions (GPSPPP) for UTC computation since 2010. The combination effectively removes the diurnal from the TWSTFT. The use of Software-Defined Radio receivers (SDR) in receiving TWSTFT signals has shown the diurnals in most of the inner- continental SATRE TWSTFT links are reduced by a factor of two to three and a gain in stability for all UTC SDR TWSTFT links. There has been research on the full use of the redundancy in the TWSTFT network to improve the TWSTFT link stability. Recent studies on the indirect links found that it is possible to apply a simplified procedure to use the redundancy, in a most effective way, to reduce the diurnal in the Europe-to-Europe SATRE TWSTFT links by a factor of three to five.The methods of the combination of SATRE TWSTFT and GPSPPP as well as the indirect SATRE TWSTFT links u
Citation
Metrologia

Keywords

Combination of TWSTFT and GPS, Diurnal, GPS, Indirect Link, Redundancy, Robustness, Stability, Time Transfer, TWSTFT, Uncertainty
Created February 21, 2019, Updated October 6, 2020