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Implementing Resilient PNT in the Real World: The Challenges of Standardisation


The IEEE is in the process of defining technical standards for PNT resilience – but creating standards that work everywhere and for everyone will be a difficult task.

Critical infrastructure has become heavily dependent on positioning, navigation and timing (PNT) services provided by global navigation satellite systems (GNSS) like GPS.

From the clocks that keep energy grids in sync to the steering systems of automated cranes in busy container ports, precise time and position data from GNSS is a key element that keeps many vital operations running smoothly and safely.

GNSS has become so vital that a major outage would have a significant impact not just on safety and productivity, but on whole economies. A report produced for the UK government in 2017, for example, calculated a £5.2bn loss to the UK economy if GNSS were unavailable for five days.

That’s clearly a worst-case scenario, but it does highlight the modern world’s growing reliance on the “invisible utility”, and it’s causing more and more concern for lawmakers and regulators.

The past few years have seen a steady stream of government guidance aimed at protecting critical PNT systems and their users from threats like radio frequency (RF) jamming, RF signal spoofing, and adjacent band interference (ABI). Threats like these are becoming increasingly prevalent: the intergovernmental aviation organisation EUROCONTROL received more than 3,500 reports of GPS jamming in the Central and Eastern Mediterranean in 2019 alone.

First moves towards technical standards for resilient PNT

Now, consensus is emerging that technical standards are needed to ensure that critical PNT systems can adequately withstand such threats. In December 2020, the US Department of Homeland Security took an important step towards that goal, drawing up a five-level framework to classify the resilience of PNT systems.

While the Resilient PNT Conformance Framework is a solid basis for thinking about resilience, it does not define how resilience should be practically measured. That task was taken up in August 2021 by the IEEE, but it’s not a straightforward one. Three big challenges will need to be tackled to make the framework practically implementable by developers and user of PNT systems:

Challenge 1: Defining parameters and designing relevant tests

The IEEE and its industry partners will need to define test methodologies that allow the resilience of any given PNT system to be reliably measured. That’s a major undertaking, as the function and design of PNT systems vary enormously. The navigation integrity requirements of a self-driving vehicle, for example, are very different from the specific timing needs of a modern electricity grid.

While both systems may be able to detect, mitigate and recover from a threat with no loss of performance, that resilience has very different characteristics in each one, and the mechanisms by which they achieve it will vary significantly. Test methodologies will therefore need to be applicable to a wide range of very specific types of system.

Challenge 2: Keeping pace with the evolving threat landscape

The task of standardisation is made even more difficult by the fact that threats to PNT systems are highly variable and constantly evolving.

As an example, we’ve recently seen a new form of RF spoofing, so-called ‘circle spoofing’, in geopolitical hotspots like China and Iran. Will it be possible to design a framework that can take unforeseen threat evolutions into account? And will systems need to be retested every time a new threat emerges?

From our own testing at Spirent, we also know that spoofing attacks and radio frequency interference (RFI) disruptions are highly stochastic in nature, with even small variations in starting conditions producing very different effects in the receiver. This suggests that a level of repeat testing will be required if receivers are to be certified resilient to a certain level.

Challenge 3: Achieving international harmonisation

A third challenge will be gaining international consensus on resilience standards and test methodologies. As many critical PNT systems will be used internationally – in maritime freight, for example, or commercial aviation – a level of harmonisation on standards will be necessary.

The alternative is that individual countries or regions put significant amounts of effort into protecting their own critical infrastructure, resulting in diverging standards that will create confusion and complexity for manufacturers, integrators and buyers of PNT systems.

Get ready for resilient PNT standards with our webinar series

Given the challenges involved, it will require a period of well-focused work to develop the first technical standards for PNT resilience. But the rapidly evolving threat landscape means that developers and integrators of critical PNT systems need to start designing and implementing appropriate mitigations now.

In Spirent’s webinar series, Implementing Resilient PNT in the Real World, we’ll look at why and how standards are evolving – and how you can achieve resilience in your critical PNT systems today.

The first webinar, The Challenges of Standardising PNT Resilience, features Spirent PNT Security Technologist Guy Buesnel with special guest Duke Buckner, Head of Strategy and Business Development at Microchip. They review the evolving threat landscape for critical systems, the progress towards standardisation, and mitigations available today to developers, integrators and buyers of PNT systems. The on-demand link will be available after the completion of the series.

The Implementing Resilient PNT in the Real World webinar series is now available on demand.

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Guy Buesnel
Guy Buesnel

CPhys, FRIN, Product Manager – GNSS Vulnerabilities

Guy has more than 16 years experience in working on Robust and Resilient Position Navigation and Timing, having started his career as a Systems Engineer involved in developing GPS Adaptive Antenna Systems for Military Users. Guy has been involved in GPS and GNSS Receiver System Design with the aim of designing a new generation of Rugged GNSS Receivers for use by Military and Commercial Aviation Users. Guy is a Chartered Physicist, a Member of the Institute of Physics and an Associate Fellow of the Royal Institute of Navigation