| 11. |
- Jaldehag, R. T. Kenneth, 1962, et al.
(author)
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Time and frequency activities at SP in Sweden
- 2009
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In: 41st Precise Time and Time Interval (PTTI) Systems and Applications Meeting, Santa Ana Pueblo. NM, November 16-19. - 9781617386541 ; , s. 231-251
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Conference paper (other academic/artistic)abstract
- The national time and frequency laboratory of Sweden has since 1995 been a part of the measurement technology department at the SP Technical Research Institute of Sweden. The laboratory is responsible for maintaining a realization of Swedish standard time and the dissemination of this time scale in Sweden. The objective of the laboratory is to support and supply Swedish industry and authorities with accurate measures of time and frequency by instrument calibration, knowledge transfer, time dissemination, and research and development. Swedish standard time is connected by law to UTC as maintained by the BIPM. UTC (SP) is the realization of UTC in Sweden and is traceable to UTC via BIPM and time transfer using the GPS and TWSTFT techniques. This paper describes the generation and maintenance of UTC (SP) and the equipment, including clocks and time transfer equipment, needed for this task as well as the concept of a "Distributed Time Scale" using alternate versions of UTC (SP) maintained at sister laboratories in Sweden. The paper presents also activities related to the dissemination of Swedish standard time including GPS time transfer, Network Time Protocol (NTP), telephone time code, and a speaking clock. Finally, research activities including time transfer in optical fiber networks, continuous GNSS carrier-phase processing, and Kalman-filter-based ensemble clock generation are briefly presented.
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| 12. |
- Jaldehag, R. T. Kenneth, 1962, et al.
(author)
-
Time and frequency transfer using asynchronous fiber optical networks: progress report
- 2009
-
In: 41st Precise Time and Time Interval (PTTI) Systems and Applications Meeting, Santa Ana Pueblo. NM, November 16-19.
-
Conference paper (other academic/artistic)abstract
- SP Technical Research Institute of Sweden has since 2004 been running a project withthe aim of performing time and frequency transfer using commercial asynchronous fiberopticalnetworks. The project is motivated by the need for an alternative and complementarytime transfer method on a national basis with the goal of reaching accuracy and stabilitycomparable to satellite-based methods. Previous results using an OC-192/STM-64 10-Gb/spacket over SONET/SDH network, show that time transfer accuracy of the order of a fewnanoseconds is possible on baselines exceeding 500 km [1]. The method is based on passivelistening on existing data traffic and the detection of certain bit sequences in the SDH frameheaders continuously transmitted by the network routers. By using two-way time transfer, itis possible to estimate and compensate for symmetric delays in the optical fibers. The methodrelies on that time dependent residual delays are small or can be can be compensated forand constant residual delays can be calibrated.This paper briefly revises the method and presents new results in comparison with theGPS carrier-phase technique, with focus on residual effects due to temperature variationswhich have shown to have significant impact on the stability and accuracy. It also discusseshardware miniaturizations as well as new ideas for active time transfer using bit-sequencegenerators/transmitters in dedicated wavelength slots of the optical network. Finally, the useof a subset of the IEEE standard 1588-2008 (Precise Time Protocol, PTP) for data transportis briefly discussed.
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