| 1. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
-
Time Transfer between UTC(SP) and UTC(MIKE) Using Frame Detection in Fiber-Optical Communication networks
- 2011
-
Ingår i: 43rd Precise Time and Time Interval (PTTI) Systems and Applications Meeting. - 9781622767953 ; , s. 431-441
-
Konferensbidrag (refereegranskat)abstract
- This paper presents recent results from a time transfer method using passive listening and detection of SDH frame headers in fiber-optical networks. The results are based on an experimental fiber-link that is implemented between the national time and frequency laboratories at SP in Borås, Sweden and at MIKES in Espoo, Finland with an intermediate connection at STUPI time and frequency facility in Stockholm, Sweden. The total fiber length exceeds 1129 km and is implemented in SUNET (Swedish University Network) and FUNET (Finnish University and Research Network). The two networks are connected via NORDUnet (Nordic Infrastructure for Research & Education) and the links are DWDM-based (Dense Wavelength Division Multiplexing).Both SP and MIKES maintains local representations of UTC and contributes with clock data to TAI, which gives the opportunity to compare the fiber-based method with those independent methods that are used regularly by the laboratories for the links to UTC. Preliminary results show that a time transfer stability of less than 10 picoseconds is obtained for averaging times of a few hundred seconds. The results also show that the method suffers from daily variations of a few nanoseconds, presumable due to temperature sensitive network equipment and asymmetric fiber paths. Nevertheless, a comparison to GPS carrier phase time transfer over three months shows an rms-agreement of less than 1 nanosecond.
|
|
| 2. |
- Jaldehag, R. T. Kenneth, 1962, et al.
(författare)
-
Time Transfer Using Frame Detection in Fiber-Optical Communication Networks: New Hardware
- 2011
-
Ingår i: Frequency Control and the European Frequency and Time Forum (FCS), Joint Conference of the IEEE International.
-
Konferensbidrag (refereegranskat)abstract
- In this paper, a new, recently developed hardware for time transfer using passive listening and detection of SDH frame headers in fiber-optical networks is described. The method has been presented earlier, and results, using prototype equipment and an experimental fiber-link, have shown that time transfer with a precision of the order of a few nanoseconds is possible over links with network distances exceeding 500 km. In order to further develop the method and make it available to regular users of time keeping equipment, it has been essential to minimize the space requirements of needed hardware and to make the implementation and installation more easily and straight forward. The new hardware is in this paper described in detail.
|
|
| 3. |
|
|
| 4. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Combining GPS and VLBI for inter-continental frequency transfer
- 2015
-
Ingår i: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 52:2, s. 251-261
-
Tidskriftsartikel (refereegranskat)abstract
- For decades the global positioning system (GPS) has been the only space geodetic technique routinely used for inter-continental frequency transfer applications. In the past very long baseline interferometry (VLBI) has also been considered for this purpose and the method's capabilities were studied several times. However, compared to GPS current VLBI technology only provides few observations per hour, thus limiting its potential to improve frequency comparisons. We therefore investigate the effect of combining GPS and VLBI on the observation level in order to draw the maximum benefit from the strength of each individual technique. As a test-bed for our study we use the CONT11 campaign observed in 2011. First we review the frequency transfer performance that can be achieved with independent technique-specific analyses, both with individual software packages and with the multi-technique software c5++. With this analysis approach both techniques, GPS and VLBI, show similar frequency link instabilities at the level of 10−14 to 10−15 (MDEV) on inter-continental baselines for averaging times of one day. Then we use the c5++ software for a combined analysis of GPS and VLBI data on the observation level. We demonstrate that our combination approach leads to small but consistent improvements for frequency transfer of up to 10%, in particular for averaging periods longer than 3000 s.
|
|
| 5. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Combining VLBI and GPS for inter-continental frequency transfer
- 2015
-
Ingår i: 22nd European VLBI for Geodesy and Astrometry (EVGA) Working Meeting.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For decades the Global Positioning System (GPS) has been the only space geodetic technique routinely used for inter-continental frequency transfer applications. In the past VLB) has also been considered for this purpose and the method's capabilities were studied several times. However, compared to GPS current VLBI technology only provides few observations per hour, thus limiting its potential to improve frequency comparisons. We therefore investigate the effect of combining VLBI and GPS on the observation level in order to draw the maximum benefit from the strength of each individual technique. As a test-bed for our study we use the CONT11 campaign observed in 2011. First we review the frequency transfer performance that can be achieved with independent technique-specific analyses. With this analysis approach both techniques, GPS and VLBI, show similar frequency link instabilities at the level of 1e-14 to 1e-15 (MDEV) on inter-continental baselines for averaging times of one day. We also perform a combined analysis of VLBI and GPS data on the observation level and demonstrate that our combination approach leads to small but consistent improvements for frequency transfer of up to 10%, in particular for averaging periods longer than 3000 s. We discuss the implications of these findings and present our ideas about how VLBI can contribute to international frequency transfer tasks.
|
|
| 6. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
-
Measurements and Error Sources in Time Transfer Using Asynchronous Fiber Network
- 2010
-
Ingår i: IEEE Transactions on Instrumentation and Measurement. - 1557-9662 .- 0018-9456. ; 59:7, s. 1918-1924
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed time transfer experiments basedon passive listening in fiber optical networks using Packet over synchronous optical networking (SONET)/synchronous digital hierarchy(SDH). The experiments have been performed with differentcomplexity and over different distances. For assessmentof the results, we have used a GPS link based on carrier-phase observations. On a 560-km link, precision that is relative to the GPS link of
|
|
| 7. |
|
|
| 8. |
- Hedekvist, Per Olof E, 1967, et al.
(författare)
-
Accurate time transfer utilizing the synchronization in an SDH-network
- 2006
-
Ingår i: 2006 Optical Fiber Communication Conference, and the 2006 National Fiber Optic Engineers Conference; Anaheim, CA; United States; 5 March 2006 through 10 March 2006. - 9781557528032 ; 2006
-
Konferensbidrag (refereegranskat)abstract
- A nationwide system for accurate time distribution is being developed, utilizing synchronization in an SDH-network. The first experimental results based on this technique are presented, performed on, but not limited to, STM-64.
|
|
| 9. |
- Jaldehag, R. T. Kenneth, 1962, et al.
(författare)
-
Time and frequency activities at SP in Sweden
- 2009
-
Ingår i: 41st Precise Time and Time Interval (PTTI) Systems and Applications Meeting, Santa Ana Pueblo. NM, November 16-19. - 9781617386541 ; , s. 231-251
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
|
|
| 10. |
- Jaldehag, R. T. Kenneth, 1962, et al.
(författare)
-
Time and frequency transfer using asynchronous fiber optical networks: progress report
- 2009
-
Ingår i: 41st Precise Time and Time Interval (PTTI) Systems and Applications Meeting, Santa Ana Pueblo. NM, November 16-19.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
|
|
