The rise of Satellite Based Positioning and Timing

Over the past twenty years, satellite navigation systems have been providing the world with accurate positioning and timing data.  The proliferation of devices that use the information from free of direct charge systems, such as GPS and Galileo has been astonishing – in those two decades, we have got to a point where there are said to be more GNSS receivers on the planet than human beings.

Accuracy and Convenience of GNSS

The very high accuracy of GNSS combined with the amazingly low cost of devices that can receive the signals has resulted in the use of PNT data becoming ubiquitous in many application areas where precise positioning or timing data are required. Some of those application areas are in use cases where safety or security are important considerations in addition to the convenience of a low-cost commercial solution.

Critical dependencies emerge

This has led to a growing and high dependence on Space based PNT data that is often not fully understood by the owners, operators and users of the dependent systems and services.  This is particularly true of timing data provided by GNSS, where often the use of satellite derived timing data in dependent systems is not even known about, let alone understood. The concern of many of these users remains accuracy and precision (i.e., repeatable accuracy), without regard to the other important PNT metrics of availability, integrity, and coverage.  This can and has led to unusual and sometimes alarming consequences when GNSS services have been disrupted.  The belief that by simply increasing the number of constellations and satellites this problem can be mitigated has led to significant investments in space-based PNT, while resilient ground-based PNT solutions have been ignored or, even worse, decommissioned. 

John Pottle, Director of the Royal Institute of Navigation (RIN) maintains that “used naïvely or in an “unprotected” way, there are risks to accuracy and trust of the information that comes from satellite navigation systems. Alongside the growing dependencies on PNT information, it can be argued that there is an uncomfortable over-reliance in many critical areas.”

RIN White paper identifies no standard set of test cases or approaches  to assessing resilience

In 2023 the RIN published a White Paper looking at existing standards for resilient PNT.  Titled “Recommendations to Promote the Adoption of Resilient Position, Navigation and Timing in the UK - With Growing Capabilities Come Growing Threats” it concluded that there is no current standard (or set of standards) that identifies the performance requirements needed to ensure resilient PNT to satisfy the needs of all UK Critical National Infrastructure (CNI) stakeholders. 

This finding is significant as it is not straightforward to assess the resilience of PNT systems - there is no standard set of test cases or test approaches; and that the concept of a simple “resilience score”, while compelling in theory, can be difficult to achieve in practice at application level, due to the divergence of specific requirements between stakeholder types.  However, there are obviously some general principles and guidelines that will have general applicability.

RIN to establish a “Best Practices”  Working Group

To help address this pressing need to improve guidance on Resilient PNT in the UK, the RIN intend to set up a Working Group to address the issues and work on developing a set of effective guidance and best practices, that can be used by regulators, operators, owners and users in critical application areas to improve the resilience of their systems and equipment.

The co-authors of the white paper,  Mitch Narins and Ramsey Farragher, have this to say on the need for general principles and guidelines that can improve PNT Resilience.

Ramsey Farragher said “Aside from the main actions out of the study, there were two really interesting findings for me from the stakeholder discussions and other background research for the paper. One was the realisation that people in different sectors and parts of the PNT value chain can mean quite different things when they use terms like resilient, robust and assured. Common language across the supply chain and among end users is critical and we will be able to help to establish that. The second realisation was that there will be so much benefit derived from a relatively simple and succinct set of best practice guidelines for each CNI that it will be a crucial “quick win” in advance of any major future undertaking involving legislation and standardisation.”

Mitch Narins highlighted that there is no current standard (or set of standards) that identifies the performance requirements needed to ensure resilient PNT to satisfy the needs of all UK Critical National Infrastructure (CNI) stakeholders (i.e., services providers, users, and use cases).  He also points out that over the past two decades many manufacturers and users throughout the world have migrated to using PNT services derived from GNSS without needing to determine their PNT requirements or having a thorough understanding of the impact that loss or degradation of the service would have to them.  Whilst creating a single universal standard to cover all sectors and use cases would be a huge and lengthy undertaking, the idea of the RIN working group is to develop a set of recommended best practices which will inform, influence, and motivate users to adopt resilient PNT services and solutions.

Andy Proctor, Chair of the RIN PNT Advisory Group said, “This key activity will take the initial steps forward to improve the PNT System resilience of our critical infrastructure. Forming the team and setting the short- and medium-term objectives and outputs will be crucial to ensuring adoption and success of the principles and practices identified.”

To learn more about the Royal Institute of Navigation's UK PNT Advisory Group or to sign up to its non-member mailing list, please click here.