[Satellite TODAY Insider 02-25-11] Engineers from satellite navigation systems manufacturer Garmin International filed a report in January with the U.S. Federal Communications Commission (FCC) claiming that LightSquared’s 4G LTE mobile infrastructure could create significant areas of signal interference, which would result in GPS dead zones across the United States.
    The report’s authors, Scott Burgett and Bronson Hokuf, told the FCC that the stronger signals created by the LightSquared mobile network base stations and the SkyTerra-1 satellite would "seriously limit GPS reception, causing widespread GPS jamming and depriving vast areas of the United States of GPS coverage."
    LightSquared’s satellite beams utilize the 1525 to 1559 MHz frequency range, which is next door to the GPS range of 1559 to 1610 MHz. The Garmin engineers said they conducted laboratory testing on a portable GPS device and a U.S. Federal Aviation Administration (FAA)-certified aviation receiver using a simulator to represent the 31-satellite GPS constellation. The LightSquared transmission signal was simulated with a signal generator and amplified to produce its expected signal strength.
    According to the report, the results of the test showed tha, "GPS signals began to experience interference [from the LightSquared signal] when 5.8 kilometers or closer to the simulated LightSquared transmitter and lost the fix altogether when 1.1 kilometers away. Interference started at 22.1 kilometers for the aviation receiver, and total loss of fix occurred at 9.0 kilometers from the transmitter."
    If accurate, the Garmin report would place LightSquared in violation of the provisional permit it received from the FCC, which stipulated that the network should not cause interference with other signals. The FCC also granted a LightSquared request in January to drop its requirement that mobile phones using satellite airwaves must be able to communicate with satellites. Over the past year, the FCC has auctioned satellite spectrum at much lower rates than other airwaves that are used for cellphone services. LightSquared is required to submit an initial plan to the FCC by Feb. 25 detailing how it would work with federal agencies and GPS companies to deal with potential interference.
    The Garmin report also received a mention from U.S. Air Force Space Command Director Gen. William Shelton at a Feb. 19 conference. Shelton called LightSquared’s potential impact on GPS jamming "unbelievable" and said the Air Force is hoping the FCC will deal with any issues if LightSquared cannot prove its network can operate without interfering with GPS.
    LightSquared spokesman Jeff Carlisle issued a Feb. 22 statement claiming that its base stations were not at fault and that the company spent $9 million on filters to prevent SkyTerra-1 and terrestrial signals from interfering with GPS signals. "If a problem exists with the new network only some highly sensitive GPS receivers will be affected," said Carlisle.
    The $8 billion LightSquared 4G broadband network, which aims to deliver 10 megabits-per-second download speeds to mobile phone users, is scheduled for completion by 2015.

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