Countering the threat of GPS disruption with more resilient PNT sources

In light of the recent increase in state-sponsored cyberattacks, there has been much speculation around spoofing global navigation satellite systems and the susceptibility of these systems. Alex Love explores how this has led defence departments to consider more resilient sources of position, navigation and time signals.

A surge in electronic attacks against global navigation satellite systems (GNSS) in recent years has highlighted the need for more robust protection against disruption to position, navigation and time (PNT) data.

GNSS or GPS spoofing is one of the most commonly deployed attacks and involves broadcasting signals with false information that imitate those from genuine satellites. Other methods of attack include carrier jamming, signal jamming, and rebroadcasting.

With so much of the world’s critical infrastructure dependent on GNSS, organisations need to be prepared for unexpected interruptions to services. If a ship or vehicle relies on false navigation data, the results could be disastrous. Governments around the world are taking such threats seriously.

It's very cheap and simple to interfere with the signals, not just jamming but spoofing as well. 

"GNSS signals are very, very weak because they come from low Earth orbit. And they are free at the point of delivery. Therefore, we've become addicted to them and use them so much in our daily lives that they are a very, very tempting thing to interfere with,” says Richard Hoptroff, founder and chief technology officer of Hoptroff. His company has developed a highly accurate, resilient network solution for timing that is delivered by software.

"It's very cheap and simple to interfere with the signals, not just jamming but spoofing as well. And it can be mostly for defensive reasons. If you are concerned that somebody is relying on GPS to attack you, then one of your best points of counter-attack is to interfere with that signal, which is the weakest link in the chain,” adds Hoptroff. "Part of what I'm trying to do is address that by strengthening that weak link by backing it up with terrestrially-based signalling.”

Rising threats

Russia is understood to possess large-scale GNSS disruption capabilities at a state level. It has reportedly accelerated its development of electronic warfare systems in an attempt to counter NATO's considerable C4ISR capabilities.

A report by C4ADS linked Russia with as many as 9,883 spoofing incidents between February 2016 and early 2019. The authors obtained information from sensors on the International Space Station. Events occurred throughout ten locations and influenced 1,311 vessel navigation platforms used by civilians. In addition, the report claimed that Russia has been using spoofing and jamming technologies to hide its operations in Syria.

These activities are not limited to Russia. The UK Ministry of Defence has been known to interfere with GPS signals through jamming exercises. Ofcom publishes times, dates, locations, and other information such as frequencies on its website. And, in the US, Federal Aviation Authority files reveal that private and commercial aircraft have had instruments disrupted by GPS jamming carried out by the US military.

While military systems typically have higher levels of protection and encryption, it has become remarkably simple for civilians to buy equipment online to launch a DIY cyberattack at the lower end. This has the potential to cause significant disruption to civilian infrastructure such as airports, telecoms, and power stations.  

"[At the lower end] you can buy something for £150 that will spoof or jam a signal. It's a Raspberry Pi circuit board with a software-defined radio and appropriate open-source code that you can get from the internet. If you know what you're doing, it's easy,” explains Dr Simon Harwood, director of defence and security at Cranfield University.

Yet it is not just deliberate attacks that cause a GNSS failure. Outdated equipment and solar weather can also cause disruption.

US Air Force GPS III satellite on orbit. Credit: Lockheed Martin

Providing backup

Hoptroff originally established his eponymous company in 2015 to serve the finance sector, as precise timestamps are vital for the stock exchange. If the timestamp is out of sync by even a few milliseconds, then the fixed rates are rejected, and it is marked down as a lost trade.

When developing the resilient timing system, he initially thought he would need antennae that rely on GPS on roofs or would have to place clocks everywhere. However, it soon became apparent that this plan would be expensive. So, his team had a rethink and came up with something that turned out to also address the troubles facing GNSS.

“We developed a terrestrial network of time delivery over internet protocol. And that was back in 2016 when I wasn't aware of this kind of GPS threat issue. But it now turns out that this is a strength of what we have,” he says.

“In terms of the potential damage that can be done in financial services, the problem is you lose the causality and therefore the absolute record of events that took place. The world won't blow up as a result of that, but it does make the financial world very difficult to regulate without it.

The way to develop resilience against an untrustable satellite source is to have some alternative.

“But in other fields such as power generation, every substation has a GPS receiver, which it uses to synchronise AC. If that was manipulated, then you would have very serious problems in terms of synchronising to different power sources. Similarly, every cell phone tower relies on GPS for handover between cells and also for frequency generation, so the damage you could do in terms of communications and power distribution is equally very significant.”

Increasing resilience

As most deliberate GNSS disruptions are caused by systems on the ground, that’s also where the solution lies. Richard Hoptroff says that the best way to achieve resilience in sources of time is to have a reliable alternative to satellites.

"The time distribution technologies are generally made resilient by being able to switch over between sources because you never know which bit of it's going to break down,” explains Hoptroff. “The way to develop resilience against an untrustable satellite source is to have some alternative and that's the direction we're taking. What we have is a terrestrially-based time distribution network. It's not as accurate as GPS, but it's a lot more resilient, so it's like your backup.” 

With the potential threats of GNSS disruptions only expected to grow in the long term, defence organisations will need to be certain that their information is reliable. To address this, Hoptroff is collaborating with Cranfield University to examine ways that the defence sector could use the technology to gain operational advantage. 

“It's a matter of simply measuring risk versus being resilient. You can say something’s a risk but if you don't do anything about it, it'll continue to be a threat. If you understand the threat, if you play with the threat, if you then try and build things to counter it then you will,” adds Harwood.

“But as we move into the world of artificial intelligence, quantum, autonomy, and supercomputing, as they get advanced, then the size, weight and power of things changes. When you get more high-end power with computer systems, things become technically easier to do. But you can either use them for good or for bad. So as things become easier to do, it becomes easier to defend against them; it's a never-ending cycle.”

// Main image: An artist’s rendering of the GPS III satellite. Credit: Lockheed Martin