LightSquared blames GPS industry for inadequate filters in interference debate

LightSquared ratcheted up its battle with the GPS industry, accusing the GPS industry of not complying with GPS receiver filtering standards and being the cause of the interference concerns posed by LightSquared's wholesale LTE network.

In a filing with the FCC, Jeff Carlisle, LightSquared's vice president of regulatory affairs, said the GPS industry is at fault for failing to comply with a Department of Defense filtering standard issued in September 2008. "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," Carlisle said in the FCC filing.

The FCC is currently evaluating a revised proposal from LightSquared to use the lower 10 MHz of its L-Band spectrum for its network, which has shown fewer interference concerns with GPS receivers. The GPS industry has said that the new plan still poses problems, especially for precision GPS.

Carlisle said the Defense Department recommendation calls for GPS receivers to filter out transmissions from adjacent bands. He said the standards effectively offer GPS receivers a 4 MHz protective guard band.

"Had the GPS manufacturers been responsible, they could have built to these standards, as other spectrum users have built to much tighter standards in heavily used frequency bands," he said. "But most of them avoided that responsibility. They are now also turning their back on LightSquared's offer to observe what basically amounts to a 23 MHz guard band, by shifting its terrestrial operations to the lower 10 MHz of its downlink band."

Additionally, Carlisle said that GPS receiver manufacturers are not in compliance with filtering standards proposed by the International Telecommunications Union.

In response, the Coalition to Save Our GPS, a group of GPS device manufacturers opposed to LightSquared's plans, said the company's filing was an act of "desperation."

"LightSquared has completely mischaracterized the 2008 DoD GPS Signal in Space (SIS) standards, which according to DoD's own language, define ‘the levels of performance the U.S. Government makes available to users of the Global Positioning System,' but in no way addresses standards for commercial GPS receivers," the group said in a statement to FierceWireless. "In fact, DoD specifically said that the receiver characteristics it detailed ‘are not intended to impose any minimum requirements on receiver manufacturers or integrators,' and they do not specify commercial GPS receiver performance standards."

"In fact, today's GPS receivers incorporate state-of-the-art filters that reject transmissions in adjacent bands that are hundreds of millions of times more powerful than those of GPS," the group continued. "But LightSquared is proposing is to transmit signals that are at least one billion times more powerful. There has never been, nor will there ever be, a filter that can block out signals one billion times more powerful than those transmitted in an immediately adjacent frequency - regardless of which shifting policy target LightSquared next tries to blame."

Earlier this week, FCC officials said they have no timetable for evaluating LightSquared's revised proposal, and that finding a solution that protects GPS is a top priority. They said more testing may be needed, but declined to say how long that might take. 

A report issued in June that was commissioned by the FCC found LightSquared's initial LTE network design interfered with GPS signals. In response, LightSquared released a revised network design, which uses the the lower 10 MHz of its L-Band spectrum.

For more:
- see this LightSquared letter (PDF)
- see this release
- see this IDG News Service article

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