TV and radio signals take over when GPS goes wrong

Paul Marks, chief technology correspondent

We all take GPS for granted: but what happens if we lose the signal or it's jammed?

BAE Systems has developed a positioning system that it claims will work even when GPS is unavailable. Its trick is to use the miasma of radio frequency signals we are all bathed in from TV, radio and cellphone masts, and even WiFi routers, to work out where we are.

GPS is a weak, highly jammable signal, equivalent, it is said, to trying to see a car's headlights from 20,000 kilometres away. And as New Scientist has revealed before, the availability of illegal handheld jammers online is indeed allowing people to block GPS signals.

Once jammed, a spoof GPS-format signal can be created to direct a vehicle (car, aircraft or ship say) in the wrong direction. Just two weeks ago, the radio navigation department at the University of Texas at Austin showed how an attacker could spoof GPS?to force a small helicopter drone off course?in a trial in a football stadium. And after a man died in May when an Austrian drone lost GPS and crashed in South Korea, the need for a backup positioning system became crystal clear - especially as drones prepare for mass civilian applications.

BAE's answer is dubbed Navigation via Signals of Opportunity (NAVSOP) and it?interrogates the airwaves for the ID and signal strength of local digital TV and radio signals, plus air traffic control radars, with finer grained adjustments coming from cellphone masts and WiFi routers.

In any given area, the TV, radio, cellphone and radar signals will be at constant frequencies and power levels as they are are heavily regulated - so positions can always be triangulated from them. It's like the way Google Maps on a cellphone uses local WiFi signals from homes and offices to improve positioning calculations based on cellphone mast and GPS signals.?

"The real beauty of NAVSOP is that the infrastructure required to make it work is already in place," says a BAE spokesman - and "software defined radio" microchips that run NAVSOP routines can easily be integrated into existing satnavs. The firm believes the technology will work in urban concrete canyons where GPS signals cannot currently reach.

Amusingly, perhaps, BAE says that even the signals from GPS jammers (if they are on all the time) can be used to build a radio picture of an area. The system will be demonstrated at the Farnborough International Airshow in the UK on 9 July, where BAE hopes to show it calculating user locations to within a few metres.

Source: http://feeds.newscientist.com/c/749/f/10897/s/20d628fa/l/0L0Snewscientist0N0Cblogs0Conepercent0C20A120C0A60Cgps0Ejammed0Bhtml0DDCMP0FOTC0Erss0Gnsref0Fonline0Enews/story01.htm

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