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Jamming may leave GPS in the wilderness
Australian researchers have raised concern over the growing vulnerability of global positioning system devices to accidental and intentional attack.

Professor Andrew Dempster from the School of Surveying and Spatial Information Systems at the University of New South Wales says the global positioning system (GPS) has become an integral part of our lives.

"Most people wouldn't be aware of how many of their daily systems require GPS to work," says Dempster. "It is not just a system to provide you with position in fact each GPS satellite is an atomic clock."

"Those clocks are used to synchronise a whole range of things, from radar for air traffic control ... to the official time for Australia."

Dempster spoke this week at a workshop in Canberra on GPS vulnerability organised by UNSW's Australian Centre for Space Engineering Research. The workshop discussed threats to GPS including jamming and 'spoofing' devices.

Dempster says the weak radio signals used by GPS receivers makes them vulnerable to interference and attack.

"The satellites are 20,000 to 26,000 kilometres away and the power that they're transmitting is not much more than a light bulb," he says. "By the time they get to the surface of the Earth they are very weak."

A recent survey by UNSW researchers found radio signals from a television transmission tower in the northern suburbs of Sydney disrupted GPS receivers, despite it using a different frequency.

"The SBS transmission tower in Artarmon has a transmission frequency about one third of the GPS central frequency," he says. "The third harmonic falls in or near the GPS band and we have observed that there is interference to GPS."

Dempster says electronic devices such as computer and portable music players can also interfere with GPS receivers.
Future impact on GPS

Recently, there have been claims radio waves coming from 4G transmission towers - the next phase of mobile telephone and internet services - are interfering with GPS signals.

"In 2010, the FCC (Federal Communications Commission) in the US approved a company called Light Squared to use LTE equipment - the next generation of mobile phone technologies," says Dempster. "It will be operating in a band right next to GPS and those transmissions will be relatively strong."

"The lesson we need to learn from the US experience is not to use spectrum right next to satellite navigation."

But Dempster says the biggest threat to GPS could come from criminal or terrorist activities.

His says UNSW is working with the University of Adelaide and GPSat Systems to develop jammer-detection technology that should reduce the threat.

"We are looking at setting up a system where we [can] identify the location of a jammer," says Dempster. "By using various techniques we are hoping that we'll be able to say 'OK, that jammer is at point X,Y'."

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