The UK’s National Timing Centre programme

Helen Margolis, Head of Science for Time and Frequency, National Physical Laboratory, UK

Time is sometimes called the invisible utility.

We rely on increasingly accurate timing signals to sustain critical services such as telecommunications, power grids, banking and transportation.

However, many organizations are unaware of their dependence on time or lack an understanding of where that time comes from.

Over-reliance on GNSS

In most cases, timing signals come from global navigation satellite systems (GNSS). But those signals are weak, making them vulnerable to jamming or spoofing, or to natural interference from phenomena such as solar storms. This vulnerability, coupled with low awareness of the extent to which critical infrastructure depends on GNSS, poses a significant risk.

In the United Kingdom (UK), this risk was articulated in the 2018 Blackett review (Satellite-derived time and position: a study of critical dependencies) and added to the National Risk Register in 2020. Both the review and the register have made clear the necessity of taking steps to increase resilience to GNSS disruption, including the adoption of backup systems where appropriate.

UTC(NPL) — an alternative source of time

The National Physical Laboratory (NPL), as the UK’s National Metrology Institute, maintains the UTC(NPL) time scale — the only realization of coordinated universal time (UTC) in the UK — and disseminates this to users.

Our current services, though, are limited either in the accuracy they can deliver or in their geographical reach. The MSF radio time signal and Internet time service are relatively imprecise, while our fibre-based NPLTime® service for the financial sector is only available in a restricted area of the UK.

To meet increasingly demanding user requirements and reduce overreliance on GNSS in critical national infrastructure, NPL is leading a programme to significantly enhance timing infrastructure and capabilities across the UK.

The National Timing Centre programme

At the heart of this programme is the construction of a new, more resilient time scale, which once fully commissioned will become the source of UTC(NPL).

It is designed as a mesh of four geographically distributed, linked sites. Each will contain several hydrogen masers (electromagnetic wave emitters), together with associated signal measurement, frequency steering and distribution equipment, allowing for the implementation of several time-scale realizations. Inter-site time transfer links will keep all time-scale realizations aligned to the one designated as UTC(NPL), using multiple methods to ensure resilience.

UTC(NPL) itself will be steered to keep it within defined time and frequency offsets of UTC, assisted by caesium fountain primary standards within the mesh. Switching between different time-scale realizations will be possible when necessary either within the same site or at different sites. Software is being developed to monitor, control and automate the operation of the new infrastructure.

Stimulating innovation

Time and frequency signals from our existing UTC(NPL) time scale are also being made available to industrial and academic users through new innovation nodes located at the universities of Strathclyde, Surrey and Cranfield.

In partnership with Innovate UK, we are supporting research into time and frequency generation, dissemination and applications, as well as stimulating development of the industrial supply chain. The three innovation nodes, employing different time and frequency transfer methods for their connection to UTC(NPL), could serve as a blueprint for future UK distribution infrastructure.

A continuous time scale for a digital world

The new UK time scale is, of course, designed to handle leap seconds in accordance with international standards. This means it will provide the capability to disseminate leap second information to user access nodes. But not all time dissemination protocols deal properly with leap seconds, and the possibility of a negative leap second — something never experienced before — poses another risk to resilience.

For these reasons, key UK stakeholders think changing to a continuous UTC without leap seconds offers the best route to a resilient precision time scale that supports the modern digital economy.

Future vision

Our long-term ambition is to create a high-accuracy time and frequency backbone running the length of the country. Branches stemming off that backbone would deliver a range of services with different performance levels, some via fibre, some using broadcast technologies.

All these signals would be traceable to UTC(NPL) as the highest point of reference within the UK. The aim is to provide resilient time that users can trust — whoever they are and wherever they are.

This article first appeared in ITU News Magazine: The future of Coordinated Universal Time – part of a series of editions on topics to be discussed at the World Radiocommunication Conference (WRC-23), from 20 November to 15 December in Dubai, UAE.

Download your copy of the ITU News Magazine: The future of Coordinated Universal Time.

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