The increasing reliance on GNSS signals for positioning, navigation and timing applications across different industries has raised questions about GNSS vulnerabilities and how to address them. We sat down with John Fischer, Spectracom’s chief technology officer, to talk to him about Resilient PNT (also known as Assured PNT and Alternative PNT) and its implications for today’s GPS/GNSS systems.

Q: “Resilient PNT” is a relatively new buzzword in the positioning, navigation and timing industry. What exactly does it mean?

Resilient PNT is about redundancy. To get PNT, you can use GPS, which is great, but it is vulnerable. So you need other reference sources. Keep in mind that no one source is perfect either. Hence, the answer lies in the combination of these things. Resilient PNT is a mix. It is the convergence of positioning, navigation and timing technology with non-traditional and emerging technologies to improve the reliability, performance and safety of mission-critical applications in the air, on land and at sea. RPNT solutions are used where even the smallest discrepancy in data accuracy, availability and stability can result in a mission failure, loss of life, battlefield disadvantages, or significant economic loss.

Q: What is the difference between “Assured PNT” and “Resilient PNT?”

The US Army uses the term “Assured.” The FAA uses the term “Alternative.” Otherwise, they are the same. The term “resilient PNT” is used by many organizations, including Orolia, the parent company of Spectracom, and the nonprofit Resilient Navigation and Timing Foundation, an educational and scientific organization.

Q: The world seems to rely more and more on GPS and other GNSS systems. What are the risks inherent in this heavy reliance on one technology?

Most of the world depends on satellite systems for precise navigation and timing services. These are exceptionally accurate and dependable, yet jamming, spoofing and other forms of interference are increasing, in both frequency and severity. And space systems aren’t immune to severe weather or cyber-attacks. The disruption created by any of these can have devastating effects on our lives and economy.

Q: How can I make my PNT equipment resilient against jamming, spoofing and other types of interferences? The key is Integrity and Trust: ensuring the integrity of GPS signals by making them trustworthy. This picture tells the story.

This image shows many references from the external world. But you can also use an internal reference – e.g., an inertial navigation system – to make your system resilient. An INS uses accelerometers to measure acceleration – integrating twice to get velocity and position – and gyroscopes to measure direction. This type of navigation is known as dead reckoning which cannot be spoofed or jammed, but over time errors build up. Occasional updates from external sources can correct these errors, but now you have reintroduced the possibility of spoofing.

Next Week: Part 2

John Fischer
John Fischer

For more than 15 years, John has been part of Orolia, where he works with global navigation satellite systems (GNSS), wireless, positioning navigation and timing (PNT),and specialized systems for our customers. Prior to joining Orolia, he specialized in wireless telecom as a founding member of two startups: Aria Wireless in 1990 and Clearwire Technologies in 1997. At Clearwire, he served as Chief Technology Officer in creating wireless broadband equipment for Internet connectivity. Early in his career, John worked as a systems engineer in radar, EW and command and control systems at Sierra Research and Comptek Research. He holds Masters and Bachelor of Science degrees in electrical engineering and computing engineering from the State University of New York at Buffalo.

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