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Australian Government: National Measurement InstituteAustralian Government: National Measurement Institute
National Measurement Institute

Time and Frequency Research

Our research program is centred on dissemination of time and frequency signals and is focused on three key techniques, broadly characterised by their accuracy: Network Time Protocol, GPS time-transfer and optical fibre. We regularly collaborate with Australian universities and science organisations in support of this program.

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Dissemination via the Internet

Time can be transmitted via the internet using the Network Time Protocol (NTP) with an accuracy typically better than a hundredth of a second. Our research in this area is targeted on improving the legal traceability of NTP, at both the point of transmission (the server) and reception (the user).

We also operate a test network for Precise Time Protocol (PTP). PTP is a next-generation network synchronisation technology that can transmit time with an accuracy of a hundred billionths of a second where the network is specifically designed to support it.

NMI's time-transfer systemDissemination via GPS Common-view Time-transfer

We have been developing GPS common-view time-transfer systems for many years. These systems support time-transfer at an accuracy of better than 50 billionths of a second and provide traceability to the Australian standard UTC(AUS).

Our current activities are focused on the use of new GNSS (Global Navigation Satellite System) signals, such as those from the Russian system GLONASS, to improve the integrity of our GPS-based time-transfer system.

Dissemination via Optical Fibre

Optical fibre can be used to transmit time and frequency signals at the highest level of accuracy and precision.

We have developed both digital and analogue techniques for transmitting radio frequencies up to 80 MHz over optical fibre and have tested these over distances of up to hundreds of kilometres. We are also working on techniques for transmitting time with an accuracy of better than 100 trillionths of a second.

Recent Publications

He, YB et al (2013) Stable radio-frequency transfer over optical fiber by phase-conjugate frequency mixing Optics Express 21(16), 18754–18764

Hsu, MTL et al (2012) All-digital radio-frequency signal distribution via optical fibers IEEE Photonics Technology Letters 24(12), 1015–1017