Demonstrated interference to a wide variety of GPS-related devices has motivated 4G broadband wholesale company LightSquared to abandon at least part of its approved spectrum in the rollout of a nationwide network starting this year.
"Early test results indicated that one of LightSquared's 10MHz blocks of frequencies poses interference to many GPS receivers," the company wrote in a 20 June press release. "This block happens to be the specific set of frequencies that LightSquared planned to use for the initial launch of its nationwide wireless broadband network."
The US Federal Communications Commission earlier this year had cleared the company to use a block of frequencies adjacent to the GPS frequency block in the L1 band. The approval was conditional based on the results of a LightSquared and industry analysis and testing of a variety of land, air, space and sea GPS systems with an original completion deadline of 15 June.
LightSquared later requested and received a two-week extension from the FCC. LightSquared receives L band signals from telecommunication satellites and rebroadcasts the signal at much higher power from as a many as 40,000 ground based transmitters to cover the entire US with broadband capability.
However, tests showed significant impacts to airborne and land GPS units when operating in the higher of two frequency blocks LightSquared planned to use.
In addition to reducing its transmitter power by 50%, the company also forged an agreement with satellite provider Inmarsat to gain access to alternate L band spectrum that presumably would not interfere with GPS.
"This new plan will give LightSquared enough spectrum to serve its growing customer base for the next several years," says LightSquared. "During this time, LightSquared will not use the spectrum it originally planned to use for the launch of its network."
The company says it will work with the FCC and GPS user community "to explore mitigation possibilities and operational alternatives" that would allow it to eventually begin using some if not all of its approved spectrum.