On the accuracy of two-way satellite time and frequency transfer: A study of triplet closures

Bauch, A.; Breakiron, Lee A.; Matsakis, Demetrios; Piester, D.

doi:10.1109/cpem.2008.4574928

Cited by 4 publications

(3 citation statements)

References 4 publications

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“…between time laboratories: two-way satellite time and frequency transfer (TWSTFT), and reception of global navigation satellite system (GNSS) signals. TWSTFT is based on a signal exchange between the two stations using a transponder on-board a geostationary satellite as a relay [2]. GNSS is based on measurements of signals broadcast by GNSS satellites, which allow the determination of the time offset between the local clock and a common reference time scale available through the GNSS satellite clocks [3].…”

Section: Study Of the Gps Inter-frequency Calibration Of Timing Recei...mentioning

confidence: 99%

Study of the GPS inter-frequency calibration of timing receivers

Defraigne¹,

Huang²,

Bertrand³

et al. 2017

Metrologia

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When calibrating Global Positioning System (GPS) stations dedicated to timing, the hardware delays of P1 and P2, the P(Y)-codes on frequencies L1 and L2, are determined separately. In the international atomic time (TAI) network the GPS stations of the time laboratories are calibrated relatively against reference stations. This paper aims at determining the consistency between the P1 and P2 hardware delays (called dP1 and dP2) of these reference stations, and to look at the stability of the inter-signal hardware delays dP1-dP2 of all the stations in the network. The method consists of determining the dP1-dP2 directly from the GPS pseudorange measurements corrected for the frequency-dependent antenna phase center and the frequencydependent ionosphere corrections, and then to compare these computed dP1-dP2 to the calibrated values.Our results show that the differences between the computed and calibrated dP1-dP2 are well inside the expected combined uncertainty of the two quantities. Furthermore, the consistency between the calibrated time transfer solution obtained from either singlefrequency P1 or dual-frequency P3 for reference laboratories is shown to be about 1.0 ns, well inside the 2.1 ns uB uncertainty of a time transfer link based on GPS P3 or Precise Point Positioning. This demonstrates the good consistency between the P1 and P2 hardware delays of the reference stations used for calibration in the TAI network.The long-term stability of the inter-signal hardware delays is also analysed from the computed dP1-dP2. It is shown that only variations larger than 2 ns can be detected for a particular station, while variations of 200 ps can be detected when differentiating the results between two stations. Finally, we also show that in the differential calibration process as used in the TAI network, using the same antenna phase center or using different positions for L1 and L2 signals gives maximum differences of 200 ps on the hardware delays of the separate codes P1 and P2; however, the final impact on the P3 combination is less than 10 ps.

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Section: Study Of the Gps Inter-frequency Calibration Of Timing Recei...mentioning

confidence: 99%

Study of the GPS inter-frequency calibration of timing receivers

Defraigne¹,

Huang²,

Bertrand³

et al. 2017

Metrologia

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“…Because ionospheric delay is inversely proportional to the square of the signal frequency, it is not cancelled out in TWSTFT because of the frequency difference between the uplink and downlink. In TWCode, it is assumed that the impact of the ionospheric delay is negligible [25]. On the other hand, it should be considerable in the TWCP link taking the high performance into account.…”

Section: Compensation For Ionospheric Delaymentioning

confidence: 99%

Carrier-phase two-way satellite frequency transfer over a very long baseline

et al. 2014

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In this paper we report that carrier-phase two-way satellite time and frequency transfer (TWSTFT) was successfully demonstrated over a very long baseline of 9,000 km, established between the National Institute of Information and Communications Technology (NICT) and the Physikalisch-Technische Bundesanstalt (PTB). We verified that the carrier-phase TWSTFT (TWCP) result agreed with those obtained by conventional TWSTFT and GPS carrier-phase (GPSCP) techniques. Moreover, a much improved short-term instability for frequency transfer of 2 × 10 −13 at 1 s was achieved, which is at the same level as previously confirmed over a shorter baseline within Japan. The precision achieved was so high that the effects of ionospheric delay became significant which are ignored in conventional TWSTFT even over a long link. We compensated for these effects using ionospheric delays computed from regional vertical total electron content maps. The agreement between the TWCP and GPSCP results was improved because of this compensation.Carrier-phase Two-Way Satellite Frequency Transfer over a Very Long Baseline

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“…For a complete network, there are (N 2 − 3N + 2)/2 redundant links composing the same number of independent triangle conditions. A non-zero closure is a true error and is a good index of the time link quality (figure 2 [8]). In 2006, [1] proposed a mathematical model to adjust the closures to zero by a global network processing.…”

Section: Introductionmentioning

confidence: 99%

Towards a TWSTFT network time transfer

Jiang

2008

Metrologia

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TWSTFT (Two Way Satellite Time and Frequency Transfer, TW hereafter) is a major technique used in TAI (International Atomic Time) generation. More than two-thirds of TAI clocks and almost all the primary frequency standards are transferred using TW. Up to now, the only geometry in TAI time transfer is single-link. However, the TAI TW time transfer data are highly redundant. In general, for an N -point network, there are N(N − 1)/2 independently measured links. Among them, only N − 1 will be used. We then have (N 2 − 3N + 2)/2 redundant links. As a function of N , the redundant measurements increase quickly (cf figure 1 and table 1). At present, for the European-American network N = 13, but only 12 out of a total of 78 measured links are used in TAI. For the Asia-Pacific regions, N = 8. Full use of the high redundancy is an effective way to improve TAI without new cost.The sum of three TW links that form a closed triangle is the triangle closure. Theoretically a closure is expected to be zero if there are no measurement errors, namely the triangle closure condition. A non-zero closure is a true error and an index of the time link quality. A redundant link sets a geometric constraint. There are (N 2 − 3N + 2)/2 independent conditions in a network. In 2006, Jiang and Petit (Proc. EFTF 2006 pp 468-75) proposed a mathematical model to adjust the closures to zero by global network processing. In consequence, time transfer between any two points through any link(s) in the network gives exactly the same result with the same uncertainty. This is the so-called network time transfer.In this paper, the author introduces his recent works on completing the network model by adding the calibration, the uncertainty estimation and the quality assessment using GPS PPP (time transfer by precise point positioning (PPP hereafter)) (

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On the accuracy of two-way satellite time and frequency transfer: A study of triplet closures

Cited by 4 publications

References 4 publications

Study of the GPS inter-frequency calibration of timing receivers

Study of the GPS inter-frequency calibration of timing receivers

Carrier-phase two-way satellite frequency transfer over a very long baseline

Towards a TWSTFT network time transfer

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