Some U.S. airwaves used for free, over-the-air TV signals must be repurposed for mobile broadband use to tackle a looming spectrum crisis, the top U.S. communications regulator said on Tuesday.

The Federal Communications Commission wants Congress to grant it authority to hold incentive auctions that would compensate television broadcasters for giving up some of their spectrum to wireless companies.

I believe the single most important step that will drive our mobile economy and address consumer frustration is authorizing voluntary incentive auctions, FCC Chairman Julius Genachowski told broadcasters at their annual convention in Las Vegas.

But broadcasters have been resistant to the agency's proposal, worried about the unintended consequences that parting with airwaves could have on their TV signals and the viewers they serve.

We're talking about putting the whole system at risk, Alan Frank, chief executive of Post-Newsweek Stations Inc, said earlier in the week at the conference.

Repacking the TV band, to clear large contiguous blocks of spectrum considered best for mobile broadband use, could increase interference and degrade the signal strength of broadcasters not parting with spectrum, said Frank.

We need to start defining not how the auction works, but what this is going to mean for the broadcasters who don't participate in the auction, Frank said.

Genachowski said he understood the concerns broadcasters had, and said he would work closely with them to implement policy that benefited them and the economy.

He noted that broadcasters, under the FCC proposal, would be fully compensated for any expenses related to repacking.

However, voluntary can't mean undermining the potential effectiveness of an auction by giving every broadcaster a new and unprecedented right to keep their exact channel location, Genachowski said, adding that doing so would give a single broadcaster veto power over the success of an auction.

He praised the industry for looking to take advantage of a multi-platform broadband world by introducing new technologies, platforms and business models to reach viewers.

But he made it clear that while the agency is working on multiple fronts to solve the spectrum crunch, the authority to hold voluntary incentive auctions is vital to meeting demand.

The FCC hopes to repurpose 120 megahertz of spectrum through incentive auctions where television broadcasters would voluntarily give up spectrum in exchange for a portion of the proceeds.

Some 25 million Americans watch video on their cell phones, and tablet computers like Apple Inc's iPad put 120 times more demand on spectrum than older phones.

This growing demand is not going away. The result is a spectrum crunch, Genachowski said. The only thing that can address the growing overall demand for mobile is increasing the overall supply of spectrum and the efficiency of its use.

Wireless carriers have lobbied for help, saying a spectrum shortage would mean clogged networks, more dropped calls and slower connection speeds for wireless customers.

AT&T Inc last month announced a $39-billion plan to buy Deutsche Telekom AG's T-Mobile USA, in part to deal with its impending spectrum shortage.

The National Association of Broadcasters (NAB) has questioned the existence of a nationwide spectrum shortage, but the group said they would only oppose the auctions if they appeared to harm broadcasters who opt not to part with spectrum or seemed to harm viewers.

Some 43 million Americans rely exclusively on over-the-air television.

(Reporting by Jasmin Melvin; Editing by Tim Dobbyn, Phil Berlowitz)

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