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Use of software-defined radio receiversin two-way satellite time and frequencytransfers for UTC computation
BIPM Bureau International des Poids et Mesures, France.
NIST National Institute of Standards and Technology, USA.
Telecommunication Laboratories, Chinese Taipei.
Sorbonne Université, France.
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2018 (English)In: Metrologia, ISSN 0026-1394, E-ISSN 1681-7575, Vol. 55, p. 685-698Article in journal (Refereed) Published
Abstract [en]

Two-way satellite time and frequency transfer (TWSTFT) is a primary technique for thegeneration of coordinated universal time (UTC). About 20 timing laboratories around theworld continuously operate TWSTFT using satellite time and ranging equipment (SATRE19)modems for remote time and frequency comparisons in this context. The precision of theSATRE TWSTFT as observed today is limited by an apparent daily variation pattern (diurnal)in the TWSTFT results. The observed peak-to-peak variation have been found as high as 2 nsin some cases. Investigations into the origins of the diurnals have so far provided no completeunderstanding about the cause of the diurnals. One major contributor to the diurnals, however,could be related to properties of the receive part in the modem. In 2014 and 2015, it wasdemonstrated that bypassing the receive part and the use of software-defined radio (SDR) receivers in TWSTFT ground stations (SDR TWSTFT) instead could considerably reduce boththe diurnals and the measurement noise.In 2016, the International Bureau of Weights and Measures (BIPM) and the ConsultativeCommittee for Time and Frequency (CCTF) working group (WG) on TWSTFT launched a pilotstudy on the application of SDR receivers in the TWSTFT network for UTC computation.The first results of the pilot study were reported to the CCTF WG on TWSTFT annualmeeting in May 2017, demonstrating that SDR TWSTFT shows superior performancecompared to that of SATRE TWSTFT for practically all links between participating stations.In particular, for continental TWSTFT links, in which the strongest diurnals appear, the useof SDR TWSTFT results in a significant suppression of the diurnals by a factor of betweentwo and three. For the very long inter-continental links, e.g. the Europe-to-USA links wherethe diurnals are less pronounced, SDR TWSTFT achieved a smaller but still significant gainof 30%. These findings are supported by an evaluation of some of the links with an alternatetechnique based on GPS signals (GPS IPPP) as reported in this paper.Stimulated by these results, the WG on TWSTFT prepared a recommendation for the 21stCCTF meeting, which proposed the introduction of SDR TWSTFT in UTC generation. WithCCTF approval of the recommendation, a roadmap was developed for the implementationof SDR TWSTFT in UTC generation. In accordance with the roadmap, most of the stationsthat participated in the pilot study have updated the SDR TWSTFT settings to facilitatethe use of SDR TWSTFT data in UTC generation. In addition, the BIPM conducted a finalevaluation to validate the long-term stability of SDR TWSTFT links, made test runs using theBIPM standard software for the calculation of UTC, now including SDR TWSTFT data, andstarted to calculate SDR TWSTFT time links as backup from October 2017. The use of SDRTWSTFT in UTC generation will begin in 2018.

Place, publisher, year, edition, pages
2018. Vol. 55, p. 685-698
Keywords [en]
UTC, TWSTFT, SDR, diurnal, uncertainty, time transfer
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-35175DOI: 10.1088/1681-7575/aacbe6OAI: oai:DiVA.org:ri-35175DiVA, id: diva2:1247447
Available from: 2018-09-12 Created: 2018-09-12 Last updated: 2019-05-29Bibliographically approved

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Publisher's full texthttp://iopscience.iop.org/article/10.1088/1681-7575/aacbe6/pdf

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Rieck, Carsten

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