| 1. |
- Bergstrand, Sten, 1971, et al.
(författare)
-
Geometric Variations of a Geodetic Radio Telescope
- 2017
-
Ingår i: Proceedings of the 23rd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789188041104 ; , s. 61-64
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 2. |
- Dutta, Uttama, 1979, et al.
(författare)
-
Ionospheric Effects on GNSS RTK
- 2022
-
Ingår i: 35th International Technical Meeting of the Satellite Division of the Institute of Navigation, ION GNSS+ 2022. - : Institute of Navigation. ; 3, s. 1557-1566
-
Konferensbidrag (refereegranskat)abstract
- GNSS signals are influenced by free electrons as they propagate through the ionosphere. Studies have shown how the spatial variations of electron density in the ionosphere, affects measurements with network-Real Time Kinematic (NRTK) (Emardson et al 2011). This paper aims to predict what can be expected from measurements during the next solar maximum that is expected to occur around 2025 and discusses how it would affect RTK for automated transport applications. The ionospheric activity and its impact on positioning in the coming solar cycle maximum is discussed. This study focuses on data from Kiruna in northern Sweden (67.8N), mainly captured in January 2014 - in the middle of the most active time during the last cycle - which has been analyzed to predict the coming solar cycle. Based on the data, it was concluded that there is a risk of occasions with simultaneous signal slips on several satellites caused by the ionosphere which could cause temporary (minutes) loss of positioning ability for the RTK equipment. It is expected to occur a couple of times per month during the most active months of the solar cycle.
|
|
| 3. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
-
A fiber based frequency distribution system with enchanced output phase stability
- 2009
-
Ingår i: Proceedings EFTF-IFCS2009 joint conference 20-24 April 2009, IEEE catalog number:CFP09FRE-CDR. - 1075-6787. - 9781424435104 ; , s. 1061-1064
-
Konferensbidrag (refereegranskat)abstract
- Experimental results on the stability of the output phase of a frequency distribution system from several days of measurement is presented, in addition to a discussion regarding the influence of control loop parameters. The setup handles the issue that the output phase stability of a system depends on perturbations along the transmission length. This is especially critical if the signal is transmitted through optical fiber, at lengths of a few 100 m. An experimental evaluation using a laser based transmitter at a wavelength of 850 nm, and 625 m of multimode fiber where 575 m where placed outdoor, a temperature dependence of 100 ps/°C was detected. Tocompensate for these slow variations in real time, a setup using two-way transmission, in conjunction with an adjustable optical delay, was constructed. This device is adjusted to induce a delay variation of equal magnitude but opposite direction, in comparison to the delay change of the fiber. Calculating the modified Allan deviation of the transmitted signal, it is apparent that without active compensation, the deviation at τ below 1000 s is comparable to the values from the measurement system without transmission. At longer integration times, however, the slow variations in the fiber transmission will deteriorate the modified ADEV substantially. When activating the dynamic adjustment of pre-delay in the system, the deviation at shorter times will increase with a few dB, however, the modified ADEV decreases continuously with τ, eventually below the values for the uncompensated system. In conclusion, activating a dynamically controlled pre-delay in a fiber based frequency transmission system will induce a small penalty on fast variations of the output phase, however giving a remarkable improvement on slower variations. The usefulness of this added functionality must therefore be determined by the application of the signal.
|
|
| 4. |
- 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
|
|
| 5. |
- 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.
|
|
| 6. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
-
Time transfer using an asynchronous computer network: Results from three weeks of measurements
- 2007
-
Ingår i: European Frequency and Time Forum, 29/5 - 1/6, Geneva, CH.
-
Konferensbidrag (refereegranskat)abstract
- We have performed a time transfer experimentbetween two atomic clocks, over a distance of approximately 75km using an 10 Gbit/s asynchronous fiber-optic computernetwork. The time transfer was accomplished through passivelistening on existing data traffic and a pilot sequence in the SDHbit stream. In order to assess the fiber-link clock comparison, wesimultaneously compared the clocks using a GPS carrier phaselink. The standard deviation of the difference between the twotime transfer links over the three-week time period was 243 ps.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- 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
-
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.
|
|
