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, LightSquared said.
The Coalition to Save Our GPS, which has led the fight against LightSquared's proposed network, defended the filters used in GPS devices and called the latest filing a sign of "desperation" by LightSquared.
"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."
The FCC is still accepting comments on LightSquared's proposal, which includes operating both a satellite and an LTE network and selling capacity wholesale to other carriers. The FCC said earlier this week that it would not allow the LTE service to launch unless the interference issue was resolved. LightSquared has said it is confident the plan will be approved next month. Opponents say the carrier should be required to operate the network on other frequencies.