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PTB providing Deutsche Telekom with time

Disseminating the PTB time scale with calibrated methods

PTB-News 2.2020
Especially interesting for

mobile telecommunications

manufacturers of 5G communications technology

Each mobile telecommunications network requires synchronization between its components. Deutsche Telekom Technik AG has decided to test a method developed by the AGH University of Science and Technology in Krakow, Poland, for the future monitoring of selected points in its network. It is based on optical time transmission (OTT), which has been tested in cooperation with PTB, among others, on glass fiber links of Deutsche Telekom AG (DTAG). The results exceed by far the requirements of the International Telecommunication Union (ITU-T) for 5G networks.

The OTT system uses terminals for feeding in the data and at the target location. For remote locations, a number of bidirectional, inline optical amplifiers are used to compensate for signal attenuation in the fiber.

The 5th generation of mobile networks (5G) requires extremely synchronous time stamps (which are not delayed differently, for example due to propagation times) at all positions in the network. Moreover, operating complex network architectures requires a suitable system that continuously monitors synchronization and identifies potential problems at an early stage.

OTT allows time scales such as UTC(PTB) to be transmitted to any location via optical fibers; thus, it also allows network synchronization. It is based on a bidirectional transmission of intensity-modulated laser radiation on a single fiber, as well as on the compensation of changes in the propagation times. OTT has allowed UTC(PTB)-referenced time signals to be transmitted via a cascaded, 300 km long glass fiber link to remote DTAG facilities with an uncertainty on the order of 50 ps. The time instability of less than 30 ps for averaging periods between 10 s and 106 s corresponds to that of the time scale fed in. All components of the link are connected with a terminal via a virtual private network (VPN). This terminal enables DTAG to manage, monitor and perform the initial calibration of the system.

Today, DTAG transmits the time signals from PTB to its own facilities in Frankfurt/Main and Bremen via a nodal point located in Hannover. In Germany, the DTAG network is supplied with its clock frequency from Frankfurt. A large facility for component testing is located in Bremen. PTB's time scale is available with an uncertainty on the order of 50 ps at both terminals.

Scientific publication

Ł. Śliwczyński, P. Krehlik, H. Imlau, H. Ender, H. Schnatz, D. Piester, A. Bauch: Fiber-based UTC dissemination supporting 5G telecommunications networks. IEEE Communications Magazine 58, 4, 67-73 (2020)


Harald Schnatz
Department 4.3
Quantum Optics and Unit of Length
Phone: +49 531 592-4300
Opens window for sending emailharald.schnatz(at)ptb.de

Andreas Bauch
Department 4.4
Time and Frequency
Phone: +49 531 592-4420
Opens window for sending emailandreas.bauch(at)ptb.de