Calibration of TWSTFT Links through the Triangle Closure Condition

Z. Jiang, W. Lewandowski, and D. Piester

Abstract:	Nanosecond uncertainty TWSTFT (Two-Way Satellite Time and Frequency Transfer, TW for short) is, together with GPS time transfer, the primary technique used for UTC generation. The high accuracy of TW with a potential sub-nanosecond uncertainty is based on a metrological calibration which is, however, not only labor- and cost-intensive, but also limited by the complexity of the organization and the availability of equipment. TW is operated in a network of which every link is measured independently. For an N-point network, there are N(N-1)/2 independent links, of which N-1 are UTC links and (N2-3N+2)/2 redundant links. In this network, only a limited number of links were calibrated to enable true time transfer for UTC or other scientific applications. In this paper, we present a strategy to calibrate the whole TW network by transferring the existing TW calibrations to the uncalibrated links using the so called triangle-closure condition. The uncertainty of a TW calibration is typical uB=1 ns. The uncertainty of the triangle calibration is increased by a factor of about v2, corresponding to an effective uncertainty of about 2 ns for the redundant links, which is satisfactory at present for the metrological time transfer necessities. Applying the triangle-closure condition, we computed all the non-UTC link calibrations and the results have been implemented in the European-American TW network since MJD 54677 (30 July 2008).
Published in:	Proceedings of the 40th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 4, 2008 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	467 - 484
Cite this article:	Jiang, Z., Lewandowski, W., Piester, D., "Calibration of TWSTFT Links through the Triangle Closure Condition," Proceedings of the 40th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 2008, pp. 467-484.
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