Tests Demonstrate GPS Backup Already Available

In their conference paper, the authors say the fiber network could be a partial backup to GPS, and GPS could be used for calibration to correct timing delays. Or, to provide a more reliable backup, two independent telecom network paths could be used.

The National Institute of Standards and Technology, a Commerce Department agency, and the U.S. Naval Observatory operate U.S. civilian and military time standards, respectively. They've been conducting tests with two companies—Monroe, La.-based CenturyLink and Aliso Viejo, Calif.-based Microsemi—to identify a practical backup for GPS systems, which "synchronize phone calls, time-stamp financial transactions, and support safe travel by aircraft, ship, train and car," in NIST's words.

Commercial fiber-optic telecommunications networks could be used, they've found. The agency reported an ongoing experiment is connecting the NIST time scales in Boulder, Colo., with the USNO alternate time scale at Schriever Air Force Base in Colorado Springs through CenturyLink's fiber-optic cables. "The two federal time scales, 150 kilometers apart, are ensembles of clocks that generate versions of the international standard for time, Coordinated Universal Time (known as UTC), in real time," according to NIST. "In this experiment, time signals were sent at regular intervals in both directions between the two locations. Researchers measured the differences between the remote (transmitted) and local time. The results, just presented at a conference, showed UTC could be transferred with a stability of under 100 nanoseconds (ns, or billionths of a second)—thus meeting the project’s original goal for this metric—as long as the connection remained unbroken."

"The 100 ns stability level is good enough to meet a new telecommunications standard," said lead author Marc Weiss, a mathematical physicist at NIST. "We'll continue trying to meet the 1 microsecond accuracy level, which is needed by critical infrastructure such as the power industry."

In their conference paper, the authors say the fiber network could be a partial backup to GPS, and GPS could be used for calibration to correct timing delays. Or, to provide a more reliable backup, two independent telecom network paths could be used.

The paper, by M. Weiss, L. Cosart, J. Hanssen and J. Yao. 2016, is "Precision Time Transfer using IEEE 1588 over OTN through a Commercial Optical Telecommunications Network" and was presented Sept. 7, 2016, at the 2016 International IEEE Symposium on Precision Clock Synchronization for Measurement, Control, and Communication in Stockholm, Sweden.

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