U.S. spectrum agency finds there is no practical way to mitigate interference to GPS.

LightSquared Inc. holds mobile satellite licenses that it wants to use for delivering terrestrial (tower-based) broadband service. But probably not for much longer.

LightSquared’s proposal is controversial in part because its frequencies are close to those transmitted by GPS satellites, and so can threaten interference to GPS receivers. Two weeks ago, we reported on LightSquared’s request for an FCC ruling that GPS users are not entitled to protection from LightSquared’s interference. We noted then that the federal government, which both operates the GPS satellites and also uses GPS for many safety-critical operations, had not yet weighed in, and that when it did, its views could well settle the issue.

The federal government has now spoken. What it said was: No. In the FCC’s words, “NTIA, the federal agency that coordinates spectrum uses for the military and other federal government entities, has now concluded that there is no practical way to mitigate potential [LightSquared] interference at this time.”

LightSquared holds a provisional waiver that authorizes it to provide terrestrial service, conditioned on its first resolving the GPS interference issues. With NTIA having determined  that those issues cannot be resolved to its satisfaction, the FCC will soon release a formal proposal to terminate LightSquared’s authority.

The Fat Lady has not sung, quite yet. But she is warming up backstage.