Responding to LightSquared's charge that interference was caused by GPS vendors that made receivers with inadequate filters, the Coalition said LightSquared itself offers GPS-related services outside the GPS band. These GPS augmentation services, which give users such as surveyors and farmers more accurate location data, are offered via satellite by both LightSquared and satellite operator Inmarsat. GPS manufacturers have to make devices that use LightSquared's spectrum so that they can take advantage of LightSquared's own services, the Coalition said.

On Monday, LightSquared acknowledged that it sells GPS augmentation services to OmniStar, a division of Trimble Navigation, which resells the services to users in construction, agriculture and other areas. Trimble has been a leading critic of LightSquared's plans.

The group also challenged LightSquared's view that the interference problem could be solved with inexpensive filters. "The only device LightSquared produced for testing was an antenna with filters so extreme that they would filter out more than 95 percent of the GPS signals as well, with an extremely severe penalty to receiver performance," the Coalition wrote. The group has said before that there are no filters available that could solve the interference problem. Retrofitting existing GPS receivers so they could work after LightSquared's launch would take at least 15 years, because devices such as in-car navigation systems are replaced on long cycles. LightSquared said there are already suitable filters for cell phones that cost about five cents each.

However, the Coalition laid the ultimate blame for the interference problem at the FCC's door. "It is and was the FCC's responsibility to identify and proactively address GPS interference issues to protect the substantial investment the federal government has in GPS," the paper said.

The IDG News Service