GPS signals easy to jam with $150 equipment

Growing menace from jammers, say experts


A meeting held at the National Physics Laboratory in Teddington, UK, pointed out that equipment is easily and cheaply available off the internet that can cripple satellite navigational signals, including those widely used in GPS systems at sea.



Although the conference was not particularly looking at marine systems, experts warn that growing reliance on GPS signals by navigators can have disastrous consequences. Even more dangerous than jamming the GPS signal are sophisticated methods that let jammers hack into programs and decide what to display on your shipboard receiver.


Consultant David Last, former President of the Royal Institute of Navigation, says, "You can consider GPS a little like computers before the first virus - if I had stood here before you then and cried about the risks, you would've asked 'why would anyone bother?'.

But hackers do, and this is a clear and present danger to shipping, where GPS signals are used directly for position determination and also fed to other critical equipment. Additionally, many observers fear that navigating officers are now less competent to go back to older traditional methods of navigation in any such eventuality.


In 2008, Alan Grant of the General Lighthouse Authorities carried out an experiment to assess the degree to which ships would be affected by a jamming signal (see diagram).

Using a low power jamming signal off the eastern English coast, he could have their receivers show positions almost anywhere in Europe. Much depended on the strength of the jamming signal and the ship’s equipment, but seafarers will agree with Grant when he says that a jamming signal causing smaller errors would be infinitely more dangerous at sea, as navigators would not be able to easily identify the error.


 New Year Day failure of a single satellite in 2004 created huge confusion in GPS readings. Professor Last says that "Satellite failures, though dramatic, are not the main problem. The Achilles heel of GPS is the extremely weak signals that reach the receiver."

The weak signals can be swamped by other stronger signals on earth; the armed forces have been doing this for a long time in an attempt to disrupt enemy missile and other capabilities. However, cheap and low power jamming devices are easily available on the internet today; one can get hand held versions that run on batteries and interfere with satellite signals miles away. More powerful ones can do much more.


"You can now buy a low-cost (100 GBP) simulator and link it to Google Earth, put on a route and it will simulate that route to the timing that you specify," said Professor Last. "A GPS receiver overcome by it will behave as if you're travelling along that route." This simulator, although more expensive, can easily be used by criminals or terrorists.


It is not just marine systems that are under threat, of course. High value cargo and armoured cars are being regularly monitored using GPS systems, and missiles are increasingly using these to lock into targets. Even in cases of clear civilian use, the potential for mischief is huge. GPS systems are widely used across the world in areas as diverse as rental car tracking, toll usage charges, logistics handling, distribution, just in time logistics, emergency services, farming and road building, just to name a few.

And, critically, GPS also keeps our telephone networks, internet systems, banking and trading systems- and our power systems up and running.


"Navigation is no longer about how to measure where you are accurately - that's easy," says Professor Last. "It’s all about how to do so reliably, safely and robustly."

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