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Implementation of SDR TWSTFT in UTC Computation



Zhiheng Jiang, Felicitas Arias, Victor S. Zhang, Yi-Jiun Huang, Joseph Ackhar, Dirk Piester, Shinn-Yan Lin, Wenjun Wu, Andrey Naumov, Sung-hoon Yang, Jerzy Nawrocki, Ilaria Sesia, Christian Schlunegger, Kun Liang


Two-Way Satellite Time and Frequency Transfer (TWSTFT or TW for short) is a primary technique for the realization of Coordinated Universal Time (UTC), which is computed by the International Bureau of Weights and Measures (BIPM). TWSTFT is carried out continuously by about 20 timing laboratories around the world. It is capable of performing frequency comparisons with an uncertainty at the level of 10-15 at averaging times of one day and time comparisons with a combined standard uncertainty of 1 ns. One limiting factor of the TWSTFT performance is the daily pattern (diurnals) in the TWSTFT difference, of which the peak-to-peak variation could be up to 2 ns in some extreme cases. In 2014 and 2015, it was demonstrated in the Asia to Asia links that the use of Software-Defined Radio (SDR) receivers for TWSTFT could considerably reduce the diurnals and also the TWSTFT measurement noise. In 2016, BIPM and the Consultative Committee for Time and Frequency (CCTF) working group (WG) on TWSTFT launched a pilot study on the application of SDR receivers in the Asia to Asia, Asia to Europe, Europe to Europe and Europe to USA TWSTFT networks. So far, 15 timing laboratories have installed SDR receivers and participate in daily SDR TWSTFT. The participants include: TL, NICT, KRISS (KRIS), NTSC and NIM in Asia; PTB, OP, VNIIFTRI (SU), INRIM (IT), METAS (CH), AOS, RISE (SP), ROA and NPL in Europe; and NIST in USA. Three satellites have been used in the pilot study, they are: Eutelsat 172B for the Asia to Asia links, Express AM22 for the Asia to Europe links until June 2017 and Telstar 11N for the Europe to Europe and the Europe to USA links. At the time of this writing, the successor of AM22 satellite has been selected and the Asia to Europe TWSTFT links will soon be reinstated. The very first results of the pilot study have been reported to the PTTI 2017. The results show, 1) for continental (short) links: SDR TWSTFT demonstrates a significant gain in reducing the diurnals by a fac
Conference Dates
January 29-February 1, 0018
Conference Location
Reston, VA, US
Conference Title
Proceedings of ITM/PTTI 2018


Coordinated Universal Time (UTC), software defined radio (SDR) receivers, Two-Way Satellite Time and Frequency Transfer (TWSTFT)


Jiang, Z. , Arias, F. , Zhang, V. , Huang, Y. , Ackhar, J. , Piester, D. , Lin, S. , Wu, W. , Naumov, A. , Yang, S. , Nawrocki, J. , Sesia, I. , Schlunegger, C. and Liang, K. (2018), Implementation of SDR TWSTFT in UTC Computation, Proceedings of ITM/PTTI 2018, Reston, VA, US, [online], (Accessed June 24, 2024)


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Created January 29, 2018, Updated October 12, 2021