Fiber-Optic Time Transfer for UTC-Traceable Synchronization for Telecom Networks

A robust and reliable synchronization network, able to distribute signals traceable to a recognized standard, is crucial for the operation of future 5G telecommunication networks. In this article we present the results of time transfer using optical fibers. The main goal is to test the long-term capability of ELSTAB technology (developed by AGH) to deliver time and frequency signals traceable at the sub-nanosecond level to UTC in a real telecommunication environment. In an ongoing cooperation between Deutsche Telekom (DTAG), the Physikalisch- Technische Bundesanstalt (PTB) and AGH University of Science and Technology, we deliver UTC -- as realized by PTB in Braunschweig -- to a test center of DTAG located in Bremen. For this purpose, a fiber optic link has been operated since July 2015. The results obtained show that the operator of a telecom network may use such a stabilized fiber optic link as a reliable source for synchronization signals with a precision and accuracy superior to those obtained using a state-of-the-art GNSS time receiver. Moreover, a fiber optic link delivering UTC traceable signals increases the robustness and reliability of the network's synchronization chain by making it less dependent on GNSS.