In addition to asking TV stations to give up spectrum, the FCC proposed to decrease distance-separation requirements between TV stations, create new spectrum licenses that allow multiple TV stations to operate in a single 6MHz band, and look at ways to reallocate, or repack, TV spectrum to clear up larger blocks of spectrum. TV stations that moved to new spectrum could have their expenses paid by the spectrum auction revenues, the FCC's plan said.

If the FCC does not get the 120MHz spectrum from TV stations voluntarily abandoning it, the agency should look into requiring over-the-air TV stations to broadcast using low-power cellular transmitters, look into selling spectrum licenses that overlay the TV spectrum, or consider requiring TV stations to share spectrum, the FCC plan said.

Some telecom experts have raised doubts that the FCC would get as much spectrum as it wants from voluntary efforts. The FCC's goals seem "completely unrealistic," said Daniel Hays, director of the telecom practice at PRTM, a management consultancy.

Some U.S. lawmakers have questioned whether broadcasters should give up additional spectrum.

It may be difficult to get broadcasters to voluntarily give up spectrum. said Rory Altman, director and co-founder of Altman Vilandrie & Co., a tech and telecom strategy consulting group. "The wireless industry needs more spectrum for all the mobile-device users out there, but broadcasters are hoarding the airwaves," he said. "The FCC's current proposal may not go far enough to convince broadcasters to give up their airwaves. The broadcasters hold the cards here."