Criminal jamming of GPS
We need to guard against the increasing threat to global infrastructure due to the criminal jamming of GPS signals, says Bob Cockshott of the Digital Systems Knowledge Transfer Network
Much of the infrastructure we take for granted uses signals from the Global Positioning System (GPS) to make it work. Satellite navigation underpins not only the device in your car but also systems as varied as air traffic communications, electricity transmission, telecoms networks and emergency services fleet management. Also, the precise time reference GPS provides is used in many applications including the scientific study of earthquakes and as a time synchronization source for cellular networks and banking. That's why it is crucial that those that take an overview of contingency are aware of the potential affects of GPS jamming and how it can be countered.
Although GPS is extremely prevalent, it is surprisingly delicate. The strength of a GPS signal is about as strong as viewing a 25 watt light bulb shining down from a satellite 10,000 miles away. It's no surprise then that GPS signals are vulnerable to natural and, increasingly, criminal interruptions.
Specific natural interruptions are impossible to predict, but broadly higher levels of radio emissions and atomic particles from the sun in the coming few years will cause inaccurate data to be sent to GPS devices. The consequences of this could highlight just how reliant society has become on GPS.
A full solar cycle occurs every 11 years. During the cycle the level of radio emissions and particle ejections from the sun varies. There is currently a low level of activity but this is expected to peak by 2012. Usually, the upper layers of the atmosphere (the ionosphere) behave like a fine glass coating, allowing GPS signals to pass straight through. During a peak of activity from the sun the ionosphere can become rough, which disrupts GPS signals. There is important work going on at the University of Bath now which is exploring these issues.
A less benign cause for interference with the GPS signal is the increasing use of "jammers" in criminal activity. A quick google search on "GPS jammer" returns 227,000 hits – many of them offering cheap devices from China or Russia that can be bought from as little as £50. Far from being insignificant items for ineffectual pranks – even these small wattage jammers can have significant implications. A portable jammer in a tall building like the Gherkin could cover most of London and planes approaching its airports.
A recent trial by the General Lighthouse Authority used a relatively low-power jamming signal off the east coast of England, and found that ships coming into the jamming area suddenly read locations anywhere from Ireland to Scandinavia. GPS performance was unpredictable in these conditions and varied between different receivers.
There are three main reasons why someone would buy a jammer. Organised crime syndicates use them for specific reasons like preventing being tailed on getaways in stolen lorries, and the Police have already seized very powerful jammers capable of causing widespread disruption to GPS. There is also a potential threat from terrorist organisations trying to disrupt the country's infrastructure. Thirdly there exist individuals who might want to make an attack simply because they can. We are currently in a situation akin to IT before the first virus. Unfortunately we won't be able to keep it that way.
The implications of GPS vulnerability are being investigated by the Technology Strategy Board funded GAARDIAN project that brings together industry and academia. The project, led by Chronos Technology Ltd, creates a network of sensors deployed at sites in the vicinity of applications that rely on the GPS signal. It is then able to monitor any change in the signal due to natural, accidental or criminal activity. The project also monitors complementary signals and systems such as the ground based eLoran.
Deploying eLoran is probably our best chance of countering the problem at the moment. It is a terrestrial radio navigation system that uses high power low frequency radio transmissions to determine the location and speed of the receiver. Because it is a completely different signal to GPS (and other satnav systems such as Galileo) it can be used as a backup and redundancy for when other critical services are affected by GPS outage. We need to think how we can address this problem as a matter of urgency and this is one solution needing further investigation.
Bob Cockshott, Location and Timing Director, Digital Systems Knowledge Transfer Network.
