Viavi targets GNSS disruption threats with Cesium-Free ePRTC360+

Viavi Solutions has launched its patent-pending Cesium-less ePRTC360+ holdover solution, designed to protect critical infrastructure from the growing risk of Global Navigation Satellite Sysytem (GNSS) timing disruptions. The technology is intended for use in power grids, transport, aviation, public safety systems, 5G mobile networks and AI data centres. According to the company, it is the only non-Cesium alternative that meets the International Telecommunication Union Telecommunication Standardization Sector G.8272.1 standard.

The ITU-T G.8272.1 standard specifies that an Enhanced Primary Reference Time Clock (ePRTC) must demonstrate a short-term drift of less than 30 nanoseconds when entering holdover, and a long-term drift of less than 100 nanoseconds over 14 days, with both traceable to UTC. These requirements have previously been met only by Cesium atomic clocks. VIAVI states that the ePRTC360+ also satisfies these criteria.

Doug Russell, Senior Vice President and General Manager, Aerospace and Defense at VIAVI, said the Cesium-less ePRTC360+ delivers holdover performance comparable to advanced Cesium clocks at a lower cost, enabling wider deployment across synchronisation networks, including at edge sites where Cesium-based solutions have typically been considered too expensive.

The ePRTC360+ has been tested in live-sky defence and commercial jamming and spoofing environments, and has been integrated into Viavi’s SecurePNT 6200 product series. The company says the system can maintain 100 nanoseconds accuracy during GNSS-denied conditions by using the altGNSS GEO-L service, without a time limit. It also incorporates the VIAVI SecureTime GEO anti-jamming antenna and an enhanced GNSS anti-spoofing antenna, both of which receive eGNSS GEO services with GPS/GNSS-NMA authentication for spoofing detection and mitigation.

Unlike conventional omni-directional GNSS signals, which are vulnerable to low-power interference, Viavi’s GNSS-independent GEO-L service uses encrypted, highly directional L-band signals transmitted from geostationary satellites. Combined with the SecureTime GEO antenna, this service is intended to provide a resilient timing reference for the ePRTC360+’s internal Rubidium oscillator and support smooth switchover between timing sources, even when primary GNSS frequencies are jammed, spoofed or subject to meaconing attacks.

Viavi says the lower cost of the ePRTC360+, compared with Cesium clocks, enables deployment beyond the network core. The clocks can also operate alongside non-RF Cesium systems at the core, strengthening overall synchronisation resilience through meshed Precision Time Protocol (PTP) feeds between clocks, particularly in the event of local or regional jamming or spoofing incidents.

The company adds that the ePRTC360+ addresses several operational constraints associated with Cesium clocks, including sensitivity to shock, complex start-up procedures that can take several days, export licence requirements under ECCN 3A001.i, extended GNSS learning periods of up to 40 days, and strict shipping and storage conditions. Cesium tubes typically require replacement approximately every seven years, and the dismantling and disposal of Cesium clocks are classified as hazardous due to their material content.

Viavi states that the ePRTC360+ is designed for straightforward integration into third-party grandmaster clock systems, with the aim of meeting ePRTC requirements while lowering total cost of ownership.