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  • 1.
    Bideberg, Glenn
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Construction of a secure clock location for alternative realization of UTC(SP)2014In: 2014 European Frequency and Time Forum (EFTF), 2014, p. 498-501, article id 7331545Conference paper (Refereed)
    Abstract [en]

    Swedish standard time is regulated by law to follow UTC as maintained by the BIPM. The atomic clocks that are used to implement UTC(SP), the realization of UTC in Sweden, are located at four different sites and are reported to TAI using data from TWSTFT and GNSS links. The activities in the Time and Frequency laboratory at SP are presently undergoing an expansion with the construction of a new additional secure site and the implementation of a distributed time scale.

  • 2.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Active detection of propagation delay variations in single way time transfer utilizing dual wavelengths in an optical fiber network2011In: Proceedings of 5th Joint Conference of the 65th IEEE International Frequency Control, 2011, , p. 5977328Conference paper (Refereed)
  • 3.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    One way time transfer utilizing active detection of propagation delay variations of dual wavelenghts in an optical fiber network2011In: 43rd Annual Precise Time and Time Interval Systems and Applications Meeting 2011, 2011, , p. 9-16Conference paper (Refereed)
  • 4.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Two-color One-Way Frequency Transfer in a Mtetropolitan Optical Fiber Data Network.2013In: NCSLI International Measure, Vol. 8, no 2, p. 10-Article in journal (Refereed)
  • 5.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. Chalmers University of Technology, Sweden.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. Chalmers University of Technology, Sweden.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Two-Color One-Way FrequencyTransfer in a Metropolitan OpticalFiber Data Network2013In: NCSLI Measure, ISSN 1931-5775, Vol. 8, no 2Article in journal (Refereed)
    Abstract [en]

    Two-color one-way frequency transfer through one strand of optical fiber is an alternative method to two-way frequencytransfer, and is useful if unknown asymmetries exist in the link due to different paths for each direction. The term “twocolor”refers to the ability to send signals at two different wavelengths utilizing the same fiber in one direction. The methodis suitable for implementation in existing urban Single Mode Fiber networks, for instance in networks that are utilized for dataand television communication. It is therefore able to coexist with data channels in wavelength-division multiplexing (WDM)systems. It performs as a dynamical control of transit time and simultaneously enables a real-time phase stabilized output signal.This paper presents results from a comparison of two cesium beam frequency standards separated by about 3 km over an opticalfiber network located in a metropolitan area in Sweden. The cesium standards were simultaneously compared to each other witha Global Positioning System (GPS) satellite link and over optical fibers, so that the optical fiber technique could be evaluatedwith respect to the GPS technique. The difference in frequency stability between the two methods is shown to be about 3 × 10-15over an averaging interval of 10 000 s.1. IntroductionThe need for high accuracy time and frequencytransfer has significantly increased over thelast decade. Users with the most demandingrequirements for the characterization of remotelylocated time and frequency standardsare investigating the use of optical fibers, asthe accuracy and stability of methods based onGNSS (Global Navigation Satellite Systems)such as Global Positioning System (GPS) appearto be reaching their limits. Recent workin the field of optical frequency transfer showsresults with potential accuracies below 10-17obtained in less than a day, demonstrating thatthe technique is useful for the comparison ofoptical frequency standards [1, 2]. Most of theoptical frequency transfer methods or laserstabilizations [3] focus on two-way frequencytransfer [4], whether it uses the optical phase[5-10] or intensity modulation at microwavefrequencies [11], dark fiber, or data protocolsutilized for timing in wavelength division multiplexingchannels [12-14]. When two-wayfrequency transfer methods are used, there is apresumption that the signals delays are equivalent(symmetrical) in both directions, but inmost cases the two counter wise transmissionpaths are asymmetrical and this introduces a

  • 6.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jarlemark, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Time transfer between UTC(SP) and UTC(MIKE) using frame detection in fiber-optical communication networks2011In: 43rd Annual Precise Time and Time Interval Systems and Applications Meeting 2011, 2011, , p. 431-441Conference paper (Refereed)
  • 7.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jarlemark, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Emardson, Ragne
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Löthberg, Peter
    Measurements and Error Sources in Time Transfer Using Asynchronous Fiber Network2010In: IEEE Transactions on instrumentation and measurement, Vol. 59, no 7, p. 1918-1924Article in journal (Refereed)
  • 8.
    Emardson, Ragne
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Nilsson, Mattias
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jarlemark, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Johansson, Jan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Pendrill, Leslie
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Löthberg, Peter
    Nilsson, Håkan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Time Transfer by Passive Listening over 10 Gb/s Optical Fiber2008In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 57, no 11, p. 2495-2501Article in journal (Refereed)
  • 9.
    Hanssen, James L.
    et al.
    US Naval Observatory, USA.
    Ekström, Christopher R.
    US Naval Observatory, USA.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Evaluation of time transfer units for time and frequency transfer in optical fibers utilizing a passive technique based on SONET/SDH2012In: 44th Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting 2012, 2012, , p. 371-376p. 371-376Conference paper (Refereed)
    Abstract [en]

    The time transfer method of using passive listening and detection of SDH frame headers in fiberoptical networks has been presented earlier. Previous results, using commercialized equipment and commercial fiber-links, have shown that time transfer with a precision of the order of a few nanoseconds is possible over links with network distances exceeding 1100 km. The motivation of the work has been to develop an alternative and complementary time transfer method using existing infrastructure and to make it accessible to regular users of time keeping equipment. All previous reported experimental results were performed by SP Technical Research Institute of Sweden in commercial data communication networks in Sweden and Finland. This paper will report on the recent results from an experimental fiber test network implemented at the U.S. Naval Observatory. The fiber network is in a loop-back configuration with the two node elements in the same rack. The fiber link that connects the nodes is in an environmental chamber that allows a means to apply controlled fiber length fluctuations to the link. The performance of the Time Transfer Unit (TTU) was evaluated in this setting. This will be the first independent evaluation of the TTU equipment.

  • 10.
    Hedekvist, Per Olof
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Bideberg, Glenn
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Time and Frequency Activities at SP2013Conference paper (Other academic)
    Abstract [en]

    The national Time and Frequency laboratory of Sweden is a part of SP Technical Research Institute of Sweden since 1995. The laboratory is responsible for maintaining the official realization of Swedish standard time and the dissemination of it within Sweden. The objectives of the laboratory include supporting and making it accessible to Swedish industry and authorities with accurate measures of Time and Frequency by instrument calibration, knowledge-transfer, time dissemination, research and development. Swedish standard time is regulated by law to follow UTC as achieved and maintained by the BIPM. The atomic clocks that are used to implement UTC(SP), the realization of UTC in Sweden, are located at five different sites and are reported to TAI using data from TWSTFT and GNSS links. The activities in the Time and Frequency laboratory at SP is presently undergoing an expansion, with the construction of a new additional secure site, the implementation of a distributed time scale and the participation in the Galileo time scale.

  • 11.
    Hedekvist, Per Olof
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Backefeldt, Jan
    TeliaSonera AB, Sweden.
    Experimental data from NTP-monitoring and uncertainty estimation in nationwide network2014In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI, Institute of Electrical and Electronics Engineers Inc. , 2014, p. 52-56Conference paper (Refereed)
    Abstract [en]

    Using network-time-protocol, NTP, to synchronize electronics has its limitations. Even if the NTP-server is a Stratum 1 operated by a responsible agent and connected to a reliable source, the asymmetries in the network and the influence by data traffic congestions limit the accuracy to the order of 10 ms or worse. The large uncertainty of a single request can be compensated by repetition, but to be useful the local oscillator must be more stable than the occurrence of congestions in the network. Even then, there is a remaining doubt on the accuracy of the time received by the client. In principle the time achieved from an NTP-server is to be seen as unreliable for legal purposes, if no feedback estimates of the uncertainties are acquired of the transmission. Experimental data present how this limitation has improved, at least statistically, through the continuous upgrade of data bandwidth in one of Sweden's back-bone networks. Even though data over Internet also increases, it appears that the detrimental effects of the network on NTP accuracy have decreased. Since 2011, SP have monitored a number of NTP-servers operated by TeliaSonera and logged the response compared to the realization of the national timescale in Sweden (UTC(SP)). All NTP-servers used in this evaluation are commercial, off-the-shelf products with stratum 1 synchronization. The reference NTP-server and NTP-logger are located in SP premises in Borås, with a virtual private network connection to all servers, and thus sharing the bandwidth of the network between server and client. The NTP-logger is customized and includes equipment for independent measurements of the round-trip-delay. The uncertainty of each server, as achieved when polled from Borås, is calculated. The results present how the precision improves with an order of magnitude during the last three years by evaluating maximum daily variations. The improvements during the years have decreased the uncertainty and enhanced the accuracy to stable levels in ms to sub-ms range. This paper will further study and present the performance of the NTP-monitoring, with reported offset and uncertainty. It serves as an empirical reference on network improvements enabling better performance of NTP-synchronization.

  • 12.
    Jaldehag, Kenneth
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation. Chalmers University of Technology, Sweden.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation. Chalmers University of Technology, Sweden.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Two color one-way frequency transfer in an urban optical fiber network2013In: 2013 Joint European Frequency and Time Forum and International Frequency Control Symposium, EFTF/IFC, 2013, , p. 1010-1013p. 1010-1013, article id 6702163Conference paper (Refereed)
    Abstract [en]

    SP Technical Research Institute of Sweden has previously presented results with a two color one-way method. This method is an alternative method to two-way time and frequency transfer that is useful if there are unknown asymmetries in the connection. The method is possible to use in existing infrastructure and is able to coexist with data channels for example in WDM systems, which make it possible to broadcast to multiple users and enables the user to be anonymous to the time or frequency transfer. This paper will present the results from the analysis when implementing the technique in an urban commercial optical fiber data communication WDM network between two clock labs in Sweden connecting two cesium clocks to each other for frequency comparison. The evaluation is performed with two wavelengths 8 nm apart on 6 km of installed fiber in an urban city network. The transmitter and the receiver are installed in an electromagnetically shielded room several meters below ground, and the fiber runs to a building at a distance of 3 km, and then back again. The comparison will be within the laboratory, eliminating any errors from a reference system. Results and conclusion from this evaluation reveals the propagation delay variations in the propagation distance and will display the need of compensation for these variations.

  • 13.
    Jaldehag, Kenneth
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Time transfer using frame detection in fiber-optical communication networks: New hardware2011In: 5th Joint Conference of the 65th IEEE International Frequency Control Symposium, IFCS 2011, 2011, , p. 5977323Conference paper (Refereed)
  • 14.
    Jaldehag, Kenneth
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Active optical pre-compensation in short range frequency transfer in optical single-mode fiber2011In: Proceedings of the IEEE International Frequency Control Symposium and Exposition; 5th Joint Conf. of the 65th IEEE Int. Frequency Control Symposium,, 2011, , p. 5977329Conference paper (Refereed)
  • 15.
    Jaldehag, Kenneth
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Jarlemark, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Clock models for Kalman filtering2016Report (Other academic)
    Download full text (pdf)
    fulltext
  • 16.
    Jaldehag, Kenneth
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Jarlemark, Per
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Rieck, Carsten
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Further Evaluation of CGGTTS Time Transfer Software2019In: IFCS/EFTF 2019 - Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019Conference paper (Refereed)
    Abstract [en]

    A new software tool for GNSS time transfer implementing the Common GNSS Generic Time Transfer Standard (CGGTTS) was developed by the time and frequency group at RISE Research Institutes of Sweden. The software is called RISEGNSS and converts RINEX observational data into CGGTTS data. It handles codes and carriers of the satellite navigation systems GPS, GLONASS, Galileo and BeiDou including the most important ranging codes for time transfer applications. The software is also prepared for single-frequency applications, and for the use of non-standard codes and carriers such as Galileo PRS and those from SBAS. The aim of the development is to provide an alternative to existing software and to support time transfer with new GNSS. This paper presents a full comparison of new versions of RISEGNSS and the well-established software R2CGGTTS, developed by the Royal Observatory of Belgium. The evaluation includes the linear combinations recommended in the CGGTTS standard for time transfer applications using GPS, GLONASS, Galileo and BeiDou. The aim of the evaluation is to support the development in making CGGTTS data compatible between different stand-alone software as well as those implemented in receivers, which is important to make Common-View (CV) time transfer results precise and accurate. The paper also presents CV time transfer results for three different baselines based on CGGTTS data obtained from the RISEGNSS software. The results include those obtained from dual-frequency code combinations of the four GNSS: GPS, Galileo, GLONASS and BeiDou. The results also include those of using standard single-frequency code observables as well as nonstandard codes and carriers such as L5 for GPS, E5b and E5 (Alt-BOC) for Galileo, G3 for GLONASS, and B3 for BeiDou. It finally studies the possibility and quality of using SBAS for time transfer. 

  • 17.
    Jaldehag, Kenneth
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Rieck, Carsten
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Jarlemark, Per
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Evaluation of CGGTTS time transfer software using multiple GNSS constellations2018Conference paper (Refereed)
    Abstract [en]

    A new software tool for GNSS time transfer implementing the Common GNSS Generic Time Transfer Standard (CGGTTS) has been developed by the time and frequency group at RISE Research Institutes of Sweden. The software handles signals from the satellite navigation systems GPS, GLONASS, Galileo and BeiDou including the most important ranging codes for time transfer applications. The aim of the development is to provide an alternative to existing software and to support time transfer with new GNSS. The paper presents an evaluation of CGGTTS data calculated with the new software tool in comparison with those calculated using two other, independently developed software tools. It is shown that the results obtained from the different software agree to the sub-nanosecond level. Specifically, the agreement seen between individual GPS, Galileo and BeiDou CGGTTS data is at the 100- to 200-picosecond level. Similarly, GLONASS CGGTTS data agree to the sub-nanosecond level. Further, the paper presents a comparison between time transfer links for both long baselines and short, common-clock baselines obtained from a common view analysis of CGGTTS data from the four mentioned GNSS, as well as a combination of them. It finally discusses other features available from the RISE software, such as non-smoothed CGGTTS data, adoption of satellite orbit and clock products from the IGS as well as the results of an evaluation using linear combinations with non-standard CGGTTS codes and signals.

  • 18.
    Johansson, Jan
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Nilsson, Håkan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Korrekt tid och säker tidsangivning.2005Report (Refereed)
  • 19.
    Rieck, Carsten
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Haas, Rüdiger
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Johansson, Jan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    VLBI and GPS-based Time-Transfer Using Cont08 Data2010In: 6th IVS General Meeting, 2010, , p. 365-369Conference paper (Other academic)
  • 20.
    Rieck, Carsten
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Haas, Rüdiger
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Johansson, Jan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    VLBI time-transfer using Cont08 Data2010Conference paper (Other academic)
  • 21.
    Rieck, Carsten
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. Chalmers University of Technology, Sweden.
    A hardware accelerated 10GbE primary NTP-server2012In: European Frequency and Time Forum, EFTF 2012, 2012, , p. 387-391p. 387-391, article id 6502408Conference paper (Refereed)
    Abstract [en]

    In this paper we present a primary NTP server design that provides a full line rate packet stream handling with about 50 ns internal timing accuracy independent from packet throughput. The provided solution is replay proof and is intended for NTP services close to backbone of the Internet.

  • 22.
    Rieck, Carsten
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. Chalmers University of Technology, Sweden.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Time transfer with nanosecond accuracy using ethernet2014In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI, Institute of Electrical and Electronics Engineers Inc. , 2014, p. 74-78Conference paper (Refereed)
    Abstract [en]

    Hardware aided time stamping of Ethernet frames is used to implement a two way time transfer. The method is capable to either operate actively by initiating or relaying frames, or passively by utilization the traffic on, preferably, optical links. Time stability of unfiltered measurements taken on local links is about 3.5 ns @ 1s TDEV, reaching below 1 ns for time intervals of about 100s. The presented method is specific to a family of commercial traffic analyzers, but can be generalized for any similar capable hardware.

  • 23.
    Rieck, Carsten
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Jaldehag, Kenneth
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Ebenhag, Sven-Christian
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Jarlemark, Per
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Hedekvist, Per Olof
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Time and frequency laboratory activities at RISE2020In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI, Institute of Electrical and Electronics Engineers Inc. , 2020, p. 169-180Conference paper (Refereed)
    Abstract [en]

    RISE Research Institutes of Sweden is since 2018 the result of a rebranding of SP Technical Research Institute of Sweden and several other national research facilities and test beds in Sweden. This also comprises most national metrology institute (NMI) activities, including time and frequency that is still located at its Borås facilities in the southwest of Sweden since 1995. UTC(SP) remains the official designation of the Swedish UTC(k) realization. It is realized in a classical master clock and phase stepper setup and is locally distributed to different users and time transfer applications. The most recent local clock ensemble consists of four hydrogen masers and three high performance 5071A Cs standards. UTC(SP) is linked to TAI using TWSTFT and GNSS. The primary link is a combination TWGPPP with current calibration uncertainties of 1.1 ns. The time scale is regularly kept within ±5 ns of UTC. RISE has also established several distributed UTC(SP) copies, with both local backups in Borås and facilities at remote sites linked together by GNSS time transfer. Network time distribution at those sites make UTC(SP) publicly available. Additionally, RISE offers several calibration services for the distribution of UTC-traceable time and frequency signals. Time and frequency related metrological research at RISE is mostly concentrated on further refinement of GNSS and TWSTFT methods, their calibration and the dissemination using those methods. We are also active in research on fiber based optical time and frequency transfer. Outside the metrological responsibilities, many research projects focus on establishing metrological aspects of time and frequency within for instance the automotive and maritime domain.

  • 24.
    Rieck, Carsten
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jarlemark, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Haas, Rüdiger
    VLBI Frequency Transfer using CONT112012In: European Frequency and Time Forum (EFTF 2012), 2012, , p. 163-165p. 163-165, article id 6502358Conference paper (Refereed)
    Abstract [en]

    Geodetic VLBI is an independent technique, which does not rely on third parties. This makes it a viable future alternative for time- and frequency transfer over long baselines. Frequency link instabilities in the order of 1.5e-15 for time periods of one day are comparable to those achievable with methods using GNSS carrier-phase observations. Data of the continuous VLBI campaign CONT11 were analyzed and compared to results from GPS PPP analysis on collocated/common clock stations.

  • 25.
    Rieck, Carsten
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Jarlemark, Per
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Jaldehag, Kenneth
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Passive utilization of the TWSTFT technique2018Conference paper (Refereed)
    Abstract [en]

    As an active technique TWSTFT is limited in the number of concurrent users on the same communication channel. Using the transmissions of the reference network, passive users can observe the signals in a common view sense and by knowing the orbit of the relaying satellite, corrections describing the dynamic path delay can be used to estimate the clock difference between passive stations. Reliable orbit determination can be achieved using all the active measurements performed by the regular active users. For the EU/US network using Telesat Telstar 11N, the orbit estimation uncertainty is in the order of 1m for the area spanned by the contributing stations. The corresponding time uncertainty for a passive user is about 1 ns, slightly larger than achievable by active links. A passive use of TWSTFT may provide increased timing resiliency for a number of applications. The design of a passive ground station based on a SDR receiver is suggested.

  • 26.
    Rieck, Carsten
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Jarlemark, Per O.J.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Jaldehag, Kenneth
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Utilizing TWSTFT in a passive configuration2017In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI, Institute of Electrical and Electronics Engineers Inc. , 2017, p. 219-234Conference paper (Refereed)
    Abstract [en]

    In this paper we suggest the passive usage of Two Way Satellite Time and Frequency Transfer (TWSTFT). In a passive configuration a receiver observes, possibly multiple, codes sent by the active users of a TWSTFT-network. Common view observations of the same signals by a pair of observers can be used to compare their local clocks. Similar to GNSS, the users need to know their local coordinates and the orbit of the satellite in order to reduce the measurements by the geometry. As the orbit is usually poorly known, it is essential to establish an infrastructure that provides the users with satellite ephemerides and appropriated correction models. In this initial study we use the ranging measurements performed by the active European network to TELSTAR 11N in order to estimate precise satellite positions. Residual ranges of the position estimates are well below 1 m. Based on the precise satellite positions and other regular TWSTFT measurements an extended Kepler description of the orbit is determined, which can be used to estimate ranges from the satellite to a passive user at arbitrary station positions and arbitrary epochs. A passive use of TWSTFT will enable us to increase the number of measurements without increasing the noise level on the transponder. It will also reach out to a new group of users, both commercial and scientific, which will benefit from current and future developments of TWSTFT. NMIs will be able to offer an independent method for robust distribution of their national time scales. © 2017 Institute of Electrical and Electronics Engineers Inc. All rights reserved.

1 - 26 of 26
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