Blogs

1. The reliance we have on satellite navigation systems
2. The confidence we can place in our Position, Navigation and Timing (PNT) solutions. In particular, how close we are to being able to always rely on a PNT solution, irrespective of the weather, terrain or hostile environment in which we might find ourselves.

There has been an exponential growth in the reliance on GNSS (Global Navigation Satellite Systems) as a PNT tool since the introduction of GPS (Global Positioning System) in the 1980s. PNT - using GNSS technology - can be found in the very fabric of our critical national infrastructures, including the electrical power grid, financial services, transportation and emergency services.

The use of PNT through GNSS has become so ubiquitous in our lives that we have often neglected considerations of the potential risks and impact associated with a loss of access to the required satellite signals. However, over the last decade we have seen an increased focus on the topic and a number of published reports1 highlight our reliance on the technology, the potential risks and what we might do to mitigate them.

The critical importance of PNT in the commercial and defence arena has drawn up a wealth of terms around the ability to rely on it in a variety of operational environments. Operators can refer to assured, secure, resilient or robust PNT, depending on the application the solution addresses. Assured PNT is often presented as an all-encompassing phrase that pulls in a number of these terms.

Each of the terms make sense within the context of delivering an assured PNT solution and we will return to them in more detail in later blogs. As an initial introduction, however, I indicate below what these elements might contain:

• Performance is the ability to deliver results to an acceptable standard and could include the accuracy of positioning, timing or the sensitivity of a receiver;
• Security is generally considered as the ability for the PNT solution to be “tamper proof” and not compromised by nefarious operators;
• Robustness is typically the ability to operate in adverse and hostile environments which could include signal interference and spoofing;
• Resilience by a dictionary definition is the ability to return quickly to a previous good condition after problems.

However, the US National Institute of Standards and Technology (NIST) Special Publication 800-160 Vol2 on Developing Cyber-Resilient Systems describes resiliency as “the ability to anticipate, withstand, recover from and adapt to adverse conditions, stresses, attacks, or compromises on systems” and notes that this definition can be applied to a variety of entities, including:

• A system;
• A mechanism, component, or system element;
• A system-of-systems in a critical infrastructure sector or sub-sector.

Another organisation - RIN (Royal Institute of Navigation)2 – wrote in a recent white paper 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.)

Within the context of resilience and as with assured PNT, there are typically levels and/or categories that need to be achieved to satisfy a particular risk factor and/or application requirement. The resilience levels are defined in a number of documents (3), typically as:

• Level 1 – Ensure recoverability after removal of the threat 
• Level 2 – Provides a solution (possibly with unbounded degradation) during threat
• Level 3 – Provides a solution (with bounded degradation) during threat 
• Level 4 – Provides a solution without degradation during threat 

We now have available to us a variety of technologies that can assist in delivering a system of systems approach to desired level 4 solutions. On the input side to GNSS receivers we can have Controlled Reception Pattern Antennas (CRPAs); specialised antennas that help protect the receiver from jamming and interference.

GNSS receivers themselves can come with varying high levels of anti-jam and anti-spoof capability. Anti-jamming encompasses detection through to detection with full mitigation, while anti-spoofing encompasses detection only to detection with mitigation. These, more advanced capabilities, can be offered by receivers with multi-constellation (GPS, Galileo, Glonass, Beidou) and multiple frequency band support – a feature that enables the selection of the best combination of GNSS signals to deliver a suitable PNT solution.

So, there is a lot that makes the receiver very resilient in a variety of application spaces, however if satellite signals are completely blocked then there are still alternative technologies that can deliver PNT solutions and these can include Simultaneous Location and Mapping (SLAM), inertial navigation systems, audio or visual based systems and Light Detection and Ranging (LIDAR). Combining these technologies in a system of systems approach can – as indicated – deliver the resilience required for a particular hostile environment.

However, despite the indication of a potential solution for assured PNT, it is not easy for a system integrator to make the decisions around what is required to deliver the desired level of assured PNT/resilience. Often, they are not experts in the PNT arena and really require some guidance or direction on what components might deliver a particular category of assurance and/or group of components combined might deliver a top level assurance, as part of a system of systems approach.

So, coming back to the initial question of: “are we there yet?” and able to deliver solutions that will offer the desired assurance for a particular application, I would have to say well yes and no, in that like Steve Austin – showing age now – we certainly have the parts and ability to build any desired assured PNT solution required but not, at this juncture, the clear guidance on how to combine them.

1. Blackett Report on global navigation by Govt office for Science (2018), Space based PNT programme by UK space agency (2020), Resilient Positioning, Navigation and Timing (PNT) Conformance Framework Version 2.0 (2022).
2. “Recommendations to Promote the Adoption of Resilient Position, Navigation and Timing in the UK – With Growing Capabilities Come Growing Threats” – The Royal Institute of Navigation White Paper (2023)
3. FEDERAL POSITIONING, NAVIGATION, AND TIMING (PNT) SERVICES ACQUISITIONS GUIDANCE (Version 1.0) (2024), Resilient Positioning, Navigation and Timing (PNT) Conformance Framework Version 2.0 (2022).