Time and Frequency Dissemination for Aerospace Industry using the White Rabbit Precision Time Protocol

Mura Alberto, Beretta Simone, Calonico Davide, Clivati Cecilia, Levi Filippo, Massare Maurizio, Sarcevic Sani, Sapia Adalberto

Abstract: Time synchronization and time stamping traceability are becoming rapidly a key enabling technology. Accurate time distribution is no more used only in navigation, but is becoming a key element in a large variety of industrial and scientific fields. E.g. telecommunications, mobile 5G technology, power grids, finance and trading, aerospace and research centers rely on accurate timing. Global Navigation Satellite Systems (GNSS) is today the most widespread timing source, although widely known problems such as spoofing, jamming, space weather vulnerability and lack of traceability to Universal Time Coordinated (UTC). Unlike GNSS, commercial telecommunication fiber-optic networks are intrinsically immune to the above mentioned problems and therefore represent a reliable, safer alternative distribution mean for Time and Frequency (TF) reference signal, for all those field that are do not require navigation and mobile devices. Since several years, INRIM has been developing a national fiber network to distribute a coherent frequency reference signal, spanning over 2000 km connecting several industrial and scientific research centers all over the country. This network is also reaching the Italian border with France, connecting INRIM to other European NMIs (SYRTE in Paris, and from there NPL in the UK and PTB in Germany), for accurate comparison of atomic clocks. On the same network we have recently started to distribute timing signal, on the same fiber cable, using bidirectional paths in single fiber, based on dense wavelength division multiplexing channels Different techniques were proposed in the last decade to address accurate timing on optical fibers. To compensate the delay and the variation of the fiber length due to thermal and mechanical stress two parallel fiber (TX and RX) are used. showing good level of stability, but some criticalities in the accuracy statement. In fact, on long hauls, one of the main limitation is always the non-reciprocity of the optical path at meter level. To overcome this problem, we implemented a modified White Rabbit set-up. White Rabbit is an open-source project for TF dissemination using fiber-optical links on Ethernet networks, combining Synchronous Ethernet and Precise Time Protocol to transport the traffic over medium, that was originally developed at CERN. We propose in-field deployment and performance demonstration of solution for TF dissemination, based on White-Rabbit Precision Time Protocol (WR-PTP), as extension of IEEE1588-2018 standard. The system was implemented on single shared fiber-optic link, utilized together with other data traffic and signals. This method allows to have a completely bidirectional optical path, making the delay compensation much more accurate and stable, being the chromatic differential group velocity the leading term in timing accuracy budget. The test bed for timing is a fiber haul spanning 230 km, connecting the Istituto Nazionale di Ricerca Metrologica in Turin and the final user, Leonardo S.p.A. in Nerviano (near Milan) – a global high technology company and key player in Aerospace, Defense and Security. At the conference, we will describe key system elements, network architecture, multiplexing technique and introduce coherent signal for frequency distribution applied on the same fiber. We will present solution for in-field calibration of link delays and results achieved in term of accuracy and showing our approach to evaluate performance in terms of stability.
Published in: Proceedings of the 51st Annual Precise Time and Time Interval Systems and Applications Meeting
January 21 - 24, 2020
Hyatt Regency Mission Bay
San Diego, California
Pages: 198 - 198
Cite this article: Alberto, Mura, Simone, Beretta, Davide, Calonico, Cecilia, Clivati, Filippo, Levi, Maurizio, Massare, Sani, Sarcevic, Adalberto, Sapia, "Time and Frequency Dissemination for Aerospace Industry using the White Rabbit Precision Time Protocol," Proceedings of the 51st Annual Precise Time and Time Interval Systems and Applications Meeting, San Diego, California, January 2020, pp. 198-198.
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