The LightSquared situation keeps getting more interesting. InfoWorld has another story on them attacking GPS manufacturers for not beingÂ moreÂ careful about filtering adjacent frequency bands (per a DoD recommendation from 2008).
LightSquared is at loggerheads with makers and users of GPS (Global Positioning System) over interference between the navigation system and its planned cellular LTE (Long-Term Evolution) network. That network would transmit on frequencies close to those used for GPS. The company has long argued that makers of GPS equipment are to blame for the interference because they don’t use strong enough filters to keep their receivers from searching for signals in LightSquared’s bands. But this is the first time LightSquared has accused the vendors of flouting a specific rule.
The DoD’s GPS Standard Positioning Service Performance Standard called for GPS receivers to filter out transmissions on frequencies adjacent to the GPS band, LightSquared told the FCC in a filing related to the agency’s ongoing consideration of the company’s network proposal. The standard, issued in September 2008, recommends that receivers reject all transmissions on frequencies that are more than 4MHz outside the GPS band, said Jeffrey Carlisle, LightSquared’s executive vice president for regulatory affairs and public policy. That 4MHz buffer is essentially a “guard band” to protect operations on either side, he said.
LightSquared plans eventually to use frequencies adjacent to the GPS band for its LTE network, but after mandatory tests earlier this year showed strong interference in that area, the company said it would start out in a slightly lower-frequency block.
Here’sÂ somethingÂ that’s a little disturbing, though:
There is no mandatory standard for filtering in GPS receivers, and the FCC does not certify the devices for this
In addition to the DoD recommendation, the International Telecommunication Union, a United Nations agency, has also warned since 2000 that stronger filtering might be necessary to protect GPS from nearby transmissions
The ‘Coalition to Save Our GPS’ had the following to say:
“GPS receivers incorporate filters that reject transmissions in adjacent bands that are hundreds of millions of times more powerful than those of GPS. What LightSquared is proposing, however, is to transmit signals that are at least one billion times more powerful,” the group said in a statement. “There has never been, nor will there ever be, a filter that can block out signals in an immediately adjacent frequency band that are so much more powerful, nor has LightSquared put forward any credible, independent expert opinion or other evidence that this is possible.”
I’m no expert, but “hundreds of millions” is distinctly not far-off from “one billion” (since one billion is equal to ten hundred million). I also acknowledge not having much domain expertise in radio signals, transmission, etc – but what LightSquared isÂ lookingÂ to do seems a lot more useful than worrying about some poorly-built GPS receivers.
The FCCÂ said earlier this week that it would not allow the LTE service to launchÂ unless the interference issue was resolved.
LightSquared has said it is confident the plan will be approved next month.