GPS: primary tool for time transfer

Lewandowski, W.; Azoubib, J.; Klepczyński, W. J.

doi:10.1109/5.736348

Cited by 208 publications

(101 citation statements)

References 8 publications

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“…(1) terrestrial communications systems, such as television and telephones (MODEMS); (2) direct radio broadcasts (WWV and WWVH); (3) navigation systems, such as Loran-C and Global Positioning System (GPS); (4) satellite communications system such as two-way satellite time transfer (TWSTT). Most of all, GPS is a versatile and global tool which can be used to both distribute time to an arbitrary number of users and synchronize clocks over large distances with a high degree of precision and accuracy [6]. Since 1985 the Internet has had a well-known, widespread protocol for clock synchronization called NTP, the Network Time Protocol.…”

Section: Approaches For Time Synchronizationmentioning

confidence: 99%

“…Global Positioning System (GPS) is not only a navigation system, it is also a time-transfer system. As a time-transfer system it provides stability very close to one part in ten to the fourteenth over one day (1ns/day) [6]. GPS consists of 27 satellites maintained by the US Department of Defense (DoD), each transmitting coordinated "GPS Time" according to its onboard atomic clock.…”

Section: Functional Architecturementioning

confidence: 99%

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Embedded System Design for Network Time Synchronization

Hwang

2004

Embedded and Ubiquitous Computing

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Abstract. Every computer needs a timer mechanism to keep track of current time and also for various accounting purposes such as calculating the time spent by a process in CPU utilization, disk I/O, and so on, so that the corresponding user can be charged properly. In a distributed system, an application may have processes that concurrently run on multiple nodes of the system. For correct results, several such distributed applications require that the clocks of the nodes are synchronized with each other. Nowadays, time synchronization has been a compulsory thing as distributed processing and network operations are generalized. A network time server obtains, keeps accurate and precise time by synchronizing its local clock to a standard reference time source and distributes time information through a standard time synchronization protocol. This paper describes design issues and implementation of an embedded system for network time synchronization especially based on a clock model. Our system uses GPS (Global Positioning System) as a standard reference time source and offers UTC (Coordinated Universal Time) through the NTP (Network Time Protocol). Implementation results and performance evaluation are also presented.

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Section: Approaches For Time Synchronizationmentioning

confidence: 99%

Section: Functional Architecturementioning

confidence: 99%

Embedded System Design for Network Time Synchronization

Hwang

2004

Embedded and Ubiquitous Computing

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“…For our measurement, the largest frequency correction comes from the calibration of the frequency of the H-maser. To calibrate the frequency of the H-maser, a GPS time and frequency transfer receiver with an antenna (TTS-4, PikTime Systems) was used [25]. The receiver with reference to the 10 MHz and 1 pulse per second (p.p.s) signals from the H-maser received the GPS signals from 6~10 GPS satellites on average and generated and recorded the GPS measurement data.…”

Section: Camentioning

confidence: 99%

Hertz-level measurement of the40Ca+4s
Huang
¹
,
Cao
²
,
Liu
³

et al. 2012
Phys. Rev. A
60
0
42
0
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We report a frequency measurement of the clock transition of a single 40 Ca + ion trapped and laser cooled in a miniature ring Paul trap with 10 -15 level uncertainty. In the measurement, we used an optical frequency comb referenced to a Hydrogen maser, which was calibrated to the SI second through the Global Positioning System (GPS). Optical frequency standards have been developed rapidly in recent years thanks to the development of the cold atoms, the optical frequency comb technology [1,2] and the ultra-narrow-linewidth lasers. Optical frequency standards are expected to replace the Cs primary microwave standard as in the definition of the SI second in the near future. The measurement of the absolute optical frequency for the clock transition is an important step in the development of the optical frequency standards based on single ions and ultracold neutral atoms. The clock transition frequency had been measured using the optical frequency comb referenced to the Cs fountain and using GPS as a link to the SI second without a primary standard for direct calibration. The clock transition frequency had been measured referenced to the Cs fountain at uncertainties on the order of 10 level, which was referenced to the Cs atomic fountain clock [13].In this paper, we report on the first measurements of the 40 Ca + 4s 2 S 1/2 -3d 2 D 5/2 transition frequency with an uncertainty level of 10 -15 using an optical frequency comb referenced to a Hydrogen maser, which was calibrated through the Global Positioning System (GPS) as a link to the SI second. To approach a measurement of 10 -15 level accuracy, we performed the measurement for a very long time (7×10 5 s in May and 1.5×10 6 s in June) to reduce the statistical error and the frequency transfer error. At the same time, the systematic error had been reduced to be smaller than the previous work [14] by achieving the lower ion temperature and increasing the measurement precision on the electric quadrupole shift. Figure 1 is a schematic diagram of our experimental setup. Full details of the laser cooling, trapping detecting and probing system including the locking scheme of probe laser to the ion transitions used in this work were reported in previous works [14][15][16][17]. Briefly, a single 40 Ca + ion was trapped and cooled in a miniature Paul ring trap. The trap had an endcap-to-center distance of z 0  0.6mm with a center-to-

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“…When message delivery times between the two clocks is uncertain, O(2 2n ) classical messages must be exchanged between the clocks to determine n digits of ∆. On the other hand, as we show, there exists a quantum algorithm to obtain n digits of ∆ while communicating only O(n) quantum messages.Clock synchronization is an important problem with many practical and scientific applications [1,2]. Accurate timekeeping is at the heart of many modern technologies, including navigation, (the global positioning system), electric power generation (synchronization of generators feeding into national power grids), and telecommunication (synchronous data transfers, financial transactions).…”

mentioning

confidence: 99%

“…Clock synchronization is an important problem with many practical and scientific applications [1,2]. Accurate timekeeping is at the heart of many modern technologies, including navigation, (the global positioning system), electric power generation (synchronization of generators feeding into national power grids), and telecommunication (synchronous data transfers, financial transactions).…”

mentioning

confidence: 99%

Quantum Algorithm for Distributed Clock Synchronization

2000

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The clock synchronization problem is to determine the time difference ∆ between two spatially separated clocks. When message delivery times between the two clocks is uncertain, O(2 2n ) classical messages must be exchanged between the clocks to determine n digits of ∆. On the other hand, as we show, there exists a quantum algorithm to obtain n digits of ∆ while communicating only O(n) quantum messages.Clock synchronization is an important problem with many practical and scientific applications [1,2]. Accurate timekeeping is at the heart of many modern technologies, including navigation, (the global positioning system), electric power generation (synchronization of generators feeding into national power grids), and telecommunication (synchronous data transfers, financial transactions). Scientifically, clock synchronization is key to projects such as long baseline interferometry (distributed radio telescopes), gravitational wave observation (LIGO), tests of the general theory of relativity, and distributed computation.The basic problem is easily formulated: determine the time difference ∆ between two spatially separated clocks, using the minimum communication resources. Generally, the accuracy to which ∆ can be determined is a function of the clock frequency stability, and the uncertainty in the delivery times for messages sent between the two clocks. Given the stability of present clocks, and assuming realistic bounded uncertainties in the delivery times (e.g. satellite to ground transmission delays), protocols have been developed which presently allow determination of ∆ to accuracies better than 100 ns (even for clock separations greater than 8000 km); it is also predicted that accuracies of 100 ps should be achievable in the near future.However, these protocols fail if the message delivery time is too uncertain, because they rely upon the law of large numbers to achieve a constant average delivery time (thus, also requiring O(2 2n ) messages to obtain n digits of ∆). If the required averaging time is longer than the stability time of the local clocks, then these protocols must be replaced. A simple, different, protocol, which succeeds independent of the delivery time, is to just send a clock which keeps track of the delivery time. For example, if Alice mails Bob a wristwatch synchronized to her clock, then when Bob receives it he can clearly calculate the ∆ for their two clocks from the difference between his time and that given by the wristwatch. This wristwatch protocol is generally impractical, but it suggests another scheme which is intriguing. A quantum bit (qubit) behaves naturally much like a small clock. For example, a nuclear spin in a magnetic field precesses at a frequency given by its gyromagnetic ratio times the magnetic field strength. And an optical qubit, represented by the the presence or absence of a single photon in a given mode, oscillates at the frequency of the electromagnetic carrier. The relative phase between the |0 and |1 states of a qubit thus keeps time, much like a clock, and ticks ...

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GPS: primary tool for time transfer

Cited by 208 publications

References 8 publications

Embedded System Design for Network Time Synchronization

Embedded System Design for Network Time Synchronization

Hertz-level measurement of the40Ca+4s
Huang
¹
,
Cao
²
,
Liu
³

et al. 2012
Phys. Rev. A
60
0
42
0
View full text Add to dashboard Cite

Quantum Algorithm for Distributed Clock Synchronization

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GPS: primary tool for time transfer

Cited by 208 publications

References 8 publications

Embedded System Design for Network Time Synchronization

Embedded System Design for Network Time Synchronization

Hertz-level measurement of the40Ca+4sHuang1, Cao2, Liu3 et al. 2012Phys. Rev. A600420View full textAdd to dashboardCite

Quantum Algorithm for Distributed Clock Synchronization

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Product

Resources

About

Hertz-level measurement of the40Ca+4s
Huang
¹
,
Cao
²
,
Liu
³

et al. 2012
Phys. Rev. A
60
0
42
0
View full text Add to dashboard Cite