Could defence sector help avert GPS disaster?

Senior Reporter

Ships colliding at sea, stock markets crashing, transport networks in chaos: these are some of the nightmare scenarios that researchers studying GPS-jamming techniques this week warned we could be facing if suitable countermeasures aren’t produced.

The newspapers gave substantial coverage on Wednesday to a conference at the National Physical Laboratory (NPL) in west London, which highlighted the dangers society is facing as we become increasingly dependent on global navigation satellite systems (GNSS) like America’s GPS and the forthcoming European Galileo.

The problem is that GNSS satellite transmissions, which are used not just for navigation but also to provide time stamps for transactions at the stock market and to alert trains when to stop at specific stations, can easily be jammed or falsified (spoofed) with fake signals.

Doing so might be illegal but jammers are cheaply and easily available over the internet and can be small enough to plug into a car’s cigarette lighter. A recent Technology Strategy Board-funded study led by Chronos Technology estimated that between 60 and 450 jamming incidents occur every day in the UK.

Many of these probably came from portable devices in vehicles, maybe from drivers who wanted to take a break without their boss tracking them or maybe from criminal gangs stealing shipments of goods.

As Dr Todd Humphreys of the University of Texas warned, criminals interfering with GNSS signals at a stock exchange in order to manipulate the market, could cause trading algorithms that monitor unusual activity to pull large amounts of money out and cause a crash.

With GNSS being such an established technology integrated so deeply into our infrastructure, it seems amazing that authorities seem so unprepared for these scenarios.

But in the defence sector the problem is well understood and technology already exists for preventing jamming or spoofing attacks. In fact, industry delegates at the conference told me how frustrated they were that civil sectors were still dwelling on the scale of the issue instead of focusing on the solutions.

The problem is that current anti-jamming technology is very expensive. Not a problem when you’re building a billion-pound jet fighter, but different for the small delivery firm trying to monitor its fleet.

However, defence firms are looking at producing products for the commercial market and there are plenty of ideas out there about other solutions to the jamming and spoofing problem that need to be explored.

The best place to address the problem is in the satellite system itself, said Lyn Dutton, a GNSS specialist for Thales. Military GPS signals are already encrypted and so difficult to spoof, while new signals are being designed that use multiple frequencies and so require much more powerful equipment to jam.

Todd Humphreys has also proposed creating an authentication signal inside the public GPS transmission that would only require a software update for existing receivers to use it – but says authorities have shown little interest in this idea so far.

One solution to at least detecting when GNSS is being jammed could be based on the fact that most jammers are very simple pieces of equipment that blast out signals far stronger than those coming from satellites.

Receiving devices make internal measurements in order to correctly set their signal gain control, which means they could detect these ‘loud’ jamming signals but this information isn’t currently used.

‘GPS receiver designs need to be tweaked to allow this simple piece of information to be made available to the end user or tracking device to help warn of jamming or log jamming activity,’ said Dr Ramsey Faragher from BAE Systems, who remained tight-lipped on whether the company was developing this idea commercially.

Although these loud signals account for the vast majority of jamming signals, as Lyn Dutton pointed out, the really dangerous ones therefore are the quieter ones that only just cover up the real transmissions, and more sophisticated technology would be needed to detect them.

Spoofing signals are more difficult to detect but this is commonly done with expensive multiple-element antennas that can determine whether the signal is coming from the expected direction (satellites in the sky).

Michael Jones of Roke Manor Research said the company was developing the world’s first true anti-spoofing technology that would locate and block out false signals, and that there were several ways of detecting spoofing although he declined to say which the firm was using.

What he did reveal was that the blocking method was the same as for existing anti-jamming equipment, which Roke Manor is also working on turning from an expensive defence technology into a commercial one.

Most GNSS antennas receive signals from all directions, but devices such as the Gajt produced by Qinetiq and Canadian firm Novatel use multiple antenna elements to nullify all signals except those coming from the sky (the real satellite ones).

The alternative to these solutions is to use other radio signals to triangulate positions and compare them to GNSS readings to see if they are accurate. Mobile phones already do this to a degree but BAE has developed more sophisticated radio positioning technologies that take different signal measurements to learn about the signal environment.

The dangers of GNSS jamming have ignited a debate about how much we should depend on the technology and the importance of having alternatives should it go down. This has led to renewed interest in the terrestrial radio navigation system LORAN that was used by ships in North America until 2010, and its enhanced successor eLORAN, which is curently used in the UK.

But as some delegates at the NPL conference pointed out, GNSS has provided an incredible leap in our navigation capabilities and we should be careful not to over-exaggerate its problems.

‘When computer viruses first appeared we didn’t go back to pen and paper, we created solutions,’ said Michael Jones. These solutions to GNSS-jamming now exist but we currently face a trade-off in how much risk we’re willing to accept because of their high costs.

It’s now up to engineers in both the defence and civil sectors to take on the challenge of developing cheaper countermeasures to stop GNSS being abused and enable its full potential to be maintained.