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USAF concerned about GPS interference from LightSquared

The head of the US Air Force Space Command expressed concern that a new mobile phone service in the US could interfere with GPS signals for military and non-military users.

Speaking at the Air Force Association's Air Warfare Symposium in Orlando, Gen William Shelton says the 4G mobile broadband network in the works from LightSquared would spread 40,000 towers - and interference - across the US.

"Within three to five miles on the ground and within 12 miles in the air, GPS is jammed by those towers," Shelton says. "If we allow that system to be fielded and it does indeed jam GPS, think about the impact. We're hopeful we can find a solution, but physics being physics we don't see a solution right now. LightSquared has got to prove that they can operate with GPS and we're hoping the FCC does the right thing."

The company was issued a provisional permit by the Federal Communications Commission in late 2010 is already testing the system for GPS interference. One of the conditions of the provisional permit is that LightSquared's network does not interfere with other signals.

The FCC told the company to work with the federal government and the GPS industry to find answers to jamming questions. The FCC process starts with a 25 February initial report - which Jeff Carlisle, LightSquared's executive vice president for regulatory affairs says the company is currently working on - followed by monthly reports and a 15 June final report. After that, the FCC will confer with other agencies, including the Defense Department and the Federal Aviation Administration, on the results.

Carlisle says LightSquared has invested $9 million to keep its L-band signals from interfering with the already-weak GPS signal through a series of filters, and that the problem - if it even exists - would only be with certain, highly sensitive GPS receivers.

"There's a wall between us and GPS," he says. Independent tests by GPS receive companies, to which Shelton may have been referring, likely used only a simulation of the filters and not the actual protections in which LightSquared has invested, Carlisle says.

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