Instrumentation & Measurement Magazine 25-6 - 23

Table 3 - Statistics of DCD results
time to critical infrastructure systems in the United States, " NIST
Technical Note 2187, pp. 86-92, 2021.
Link
NTSC-PTB
KRISS-PTB
PL-PTB
KRISS-NTSC
Mean (ns)
-0.058
-0.014
0.064
0.084
Standard
deviation (ns)
0.341
0.228
0.323
0.379
of the TWSTFT results. The DCD statistics results are given in
Table 3.
From the statistics listed for DCD results in Table 3, it can be
seen that the maximum mean value of the DCD results is 0.084
ns on the KRISS-NTSC baseline, which is completely within
the calibration uncertainty of GPS PPP link, indicating that the
TWSTFT results are consistent with the GPS PPP results. The
standard deviation of the DCD results for all baselines is less
than 0.5 ns, which is the statistical uncertainty of TWSTFT released
by BIPM. It is indicated that the Asia-Europe TWSTFT
link can be used for international time comparison for UTC
calculation. Considering that the reference GPS PPP is not errorless,
the true precision may be higher.
Conclusion
We calculate the monthly TWSTFT results for Asia-Europe link
over long and short baselines and use MDEV and DCD analysis
to evaluate the stability and accuracy of TWSTFT results.
The evaluation with real UTC data of inner-continental and inter-continental
links shows that the Asia-Europe TWSTFT links
have been stable and reliable since their establishment, and the
TWSTFT results have a good agreement with the GPS PPP solutions.
In terms of the MDEV index, the stability of TWSTFT
results on the long and short baselines can reach E-15 at averaging
time of 1 d, and the link stability of KRISS-PTB baseline is
the best among the four selected baselines. The long-term stability
is better than GPS PPP when the averaging time is greater
than 3 d. In terms of the DCD index, the mean value between
the TWSTFT results and PPP is less than 0.1 ns, and the standard
deviation is less than 0.4 ns, which meets the precision of
international UTC time comparison. After the link is calibrated
and tested for a period of time, the Asia-Europe TWSTFT link
may be formally adopted by BIPM in UTC generation.
Acknowledgments
We thank the Asia-Europe TWSTFT community for providing
TWSTFT and GPS PPP measurements and BIPM for sharing
the data.
References
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IEEE Frequency
Weixiong Wang (wangweixiong@ntsc.ac.cn) is a Research
Assistant at the National Time Service Center at the Chinese
Academy of Sciences in Xi'an, China. His main
research interests include timekeeping techniques, high
precision time and frequency transfer. He received his
Ph.D. degree from the University of Chinese Academy of
Sciences in 2021.
Shaowu Dong (sdong@ntsc.ac.cn) is a Researcher and Ph.D.
candidate supervisor at the National Time Service Center at
the Chinese Academy of Sciences in Xi'an, China. He became
Head of the Timekeeping Laboratory at NTSC in 2004. His
main research fields are timekeeping techniques and GNSS
IEEE Instrumentation & Measurement Magazine
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