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LightSquared points finger at GPS makers for interference problems

LightSquared SkyTerra 1

In a move that’s sure to win friends and admirers in the GPS industry, LTE network developer LightSquared today said that the reason its pending mobile broadband network might interfere with GPS systems is because GPS manufacturers never met Department of Defense and international standards. In a filing with the Federal Communications Commission, LightSquared laid the blame for its systems potentially interfering with GPS receivers at the feet of the GPS industry, asserting they failed to comply with required standards and “spurned” international recommendations for how GPS receivers should be designed.

“Had the GPS industry complied with DoD’s recommended filtering standards for GPS receivers, there would be no issue with LightSquared’s operations in the lower portion of its downlink band,” LightSquared’s executive VP for regulatory affairs and public police wrote in the FCC filing.

The issue is no small matter for LightSquared, which is seeking to build out a nationwide 4G LTE network using a number of satellite-linked terrestrial base stations. LightSquared’s LTE transmissions will operate in bands near frequencies close to frequencies reserved for the notoriously low-powered GPS signals sent from GPS satellites. The fear is that interference from LightSquared’s operations will interfere with passive GPS reception, potentially disrupting everything from vehicle navigation to emergency response systems.

According to LightSquared, the Department of Defense initially set aside 4MHz of frequency as a “guard band” that no one was supposed to use, effectively acting as a separator between spectrum used for GPS signals and spectrum that would (eventually) be used for other purposes. However, LightSquared says that the GPS industry is insisting on a 34MHz guard band—some eight and a half times wider—to ensure that LightSquared’s systems don’t interfere with GPS receivers.

LightSquared’s basic argument is that if GPS manufacturers had only designed their gear with that 4MHz guard band in mind—instead of accepting signals from well outside it—there wouldn’t be any issue with GPS interference. LightSquared characterizes the GPS industry’s insistence on a 34 MHz guard band as “squatting,” for free, on frequencies to which they have no license, and which can only be licensed for use in the U.S. by the government.

“Given the DoD’s clear recommendations and the long-standing ITU warnings, it is not credible for the GPS industry to now claim that it is not responsible for the flawed design of its receivers,” the company wrote in its statement. “The GPS industry has a responsibility to use its licensed spectrum in accordance with international and federal government standards—not for LightSquared’s sake, but for the sake of the American people who own the public airwaves and who fund the GPS satellite system.”

Strong words—we can’t imagine the GPS industry is going to take them lightly.

LightSquared recently announced a spectrum deal with Immarsat that would enable it to initially shift its LTE services to a frequency block further away from frequencies used by GPS systems.

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