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Accurate TWSTFT time transfer with indirect links



Victor S. Zhang, Zhiheng Jiang, Thomas E. Parker, Jian Yao, Yi-Jiun Huang, Shinn-Yan Lin


The conventional wisdom suggests a direct Two-Way Satellite Time and Frequency Transfer (TWSTFT or TW) time link should result in a smaller uncertainty than that of an indirect TW link over the same baseline [12]. This is why all Coordinated Universal Time (UTC) TW links are direct and therefore assumed to be the most precision. This paper shows an exception to this logic. Following the use of the Global Positioning System (GPS) all-in-view [1], the UTC links, including Global Navigation Satellite Systems (GNSS) and TWSTFT, became the direct links between Lab(k) and the PTB (Physikalisch-Technische Bundesanstalt, Germany), which is the single pivot laboratory of the international UTC network. Currently, the daily variation (diurnal) in TW differences is the dominant source of instability in TWSTFT. This, at least in the case of the inner-European network, may be significantly reduced by an indirect link through a third intermediate laboratory in the USA [2,3]. In this study, we examined the direct and indirect Europe-Europe TW links with data collected by SATRE† modems and using the NIST (National Institute of Standards and Technology) or the USNO (US Naval Observatory) laboratory as an intermediate laboratory. We applied the Time Deviation (Tdev), triangle closures, comparisons to the results of the GPS Precise Point Positioning (GPSPPP) [4] and the TW software-defined radio (SDR) receiver [5,6,7] as indicators to verify the improvements in the indirect links versus the direct links. A factor of 2 or 3 uncertainty improvement was obtained from the diurnal and time transfer noise reduction. On the same TW baselines, we further investigated the TW SDR indirect links and gains continued to be observed. In addition, the rapidly developing new time and frequency transfer techniques, such as optical fibres, are often not linked directly with the present pivot laboratory, the PTB. Therefore, indirect links or the multi-pivot UTC time transfer network configuration for fu
Proceedings Title
Proceedings of PTTI 2017
Conference Dates
January 31-February 2, 2017
Conference Location
Monterey, CA
Conference Title
Precise Time and Time Interval Meeting (PTTI) 2017


Direct link and Indirect links, Diurnal, GPSPPP, SDR, Stability, Time Deviation, TWSTFT or TW


Zhang, V. , Jiang, Z. , Parker, T. , Yao, J. , Huang, Y. and Lin, S. (2017), Accurate TWSTFT time transfer with indirect links, Proceedings of PTTI 2017, Monterey, CA (Accessed April 16, 2024)
Created January 31, 2017, Updated July 3, 2017