FCC Kicks LightSquared Can Down the Road

 - September 15, 2011, 10:49 AM

On Tuesday, the FCC approved LightSquared’s fallback plan to move from a frequency close to that of GPS in the upper L-band–where tests had shown severe interference–to a lower 10-MHz portion of the same spectrum where reduced interference was expected. A new series of tests in this spectrum are expected to begin soon, and virtually every expert body has already predicted the tests will reveal some interference with GPS. The lower part of the L-band spectrum is essential to the more than 200,000 organizations of the true precision GPS community, from farmers to construction workers to earth crust scientists to building surveyors. To this exacting group, acceptable accuracy starts around an inch or two and quickly drops to fractions of centimeters. In previous tests even with lower-power transmitting stations than planned in final deployment, LightSquared’s 4G broadband transmissions still caused interference with high-precision GPS devices, including those for aviation. In its September 13 public notice, the FCC has apparently avoided facing up to the only solution to prevent any interference between the 4G broadband network and GPS, which is to move LightSquared to another frequency. Instead, the FCC chose to kick the can farther down the road.


LightSquared shuts down GPS receivers because the powerful signal (15,750 watts, or, maybe ½ that) just right near GPS receivers (up to many miles away) saturates the antenna amplifier in the GPS receiver trying to receive about 300 watts from about 11,000 miles away. No filter on LightSquared transmitters can prevent that. Need a filter on the GPS receiver after the patch before the gain stage to ground out the LightSquared off band signal. Our is $1200 and the size of a brick and NOT a complete solution. Sanjiv Ahuja has said he has one for 30 cents. We are waiting to see one. Javad says they have a better GPS. We are waiting to see one. Either way, you all get to buy a new GPS.

Another way is to alter the LightSquared protocol, to contain "holes" that GPS can listen through. Chief Network Officer for LightSquared says "…I do not intend to follow up with you regarding your proposal" and "Please understand we have received hundreds of offers to solve our issue and simply do not have time to engage everyone." That option does not have you all buying a new GPS.

Show comments (1)