Telco Fiber Optics Could Back Up GPS Time Synchronization, NIST Says

Commercial fiber-telco networks could be a backup to the GPS system in transmitting precision time signals used in synchronization, the National Institute of Standards and Technology said in a news release Thursday. NIST said it and the U.S. Naval Observatory (USNO) worked with CenturyLink and Microsemi to find backup possibilities for when GPS signals are disrupted by radio interference or weather. That work includes an ongoing experiment that connects NIST time scales in Colorado with a USNO alternate time scale elsewhere in Colorado via CenturyLink fiber, with time signals sent in regular intervals between the two locations and researchers measuring the differences between the transmitted and local times. The results, presented this month at the International IEEE Symposium on Precision Clock Synchronization for Measurement, Control and Communication in Stockholm, indicated the signals experienced "significant unequal delays," resulting in an accuracy that didn't meet goals, but that using GPS to calibrate the unequal delays could allow for time transfer within the 100 nanosecond goal if GPS were to be disrupted, said NIST. If the fiber network or its power source were to go down and then be re-established, GPS or some other time reference would be needed to recalibrate the fiber circuit, NIST said. The experiment is to run through the end of this year, and there's a possibility of a nationwide time-transfer experiment, it said.