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The FCC kicked off its inaugural incentive spectrum auction at the end of June, and broadcasters are asking for a lot of money. In the just-concluded reverse portion of the auction, broadcasters bid against one another to offer spectrum at the lowest price they're willing to accept from the FCC. In the next stage, the forward auction, wireless carriers will bid against one another for the highest price they're willing to pay.

The FCC says carriers will have to bid $86.4 billion total on the 126 MHz of spectrum available at auction. If the bids don't reach that mark, the FCC will have to go back to broadcasters for another round of reverse bidding with less spectrum on the block.

It's likely the auction will be extended another round. Here's why.

There's just not enough demand

Between Verizon (NYSE:VZ), AT&T (NYSE:T), and T-Mobile (NASDAQ:TMUS), analysts don't expect them to bid nearly as much as broadcasters want. AT&T is expected to pick up two 10 MHz nationwide bands, which analysts expect to cost around $10 billion. Verizon isn't expected to spend nearly as much, with analysts saying it could spend up to $5 billion. T-Mobile could spend up to $10 billion, but its CFO believes he can get the job done with as little as $1 billion.

That would leave the difference to be made up by smaller carriers and other parties such asDISH Network (NASDAQ:DISH) and Comcast (NASDAQ:CMCSA). DISH Network could be a dark horse, but the sheer amount of spectrum available could leave it to bid low on the spectrum causing the total to fall short of broadcaster's price. Comcast has said that it's looking to buy spectrum only if it can get it at a value price, and it has a mobile virtual network operator agreement with Verizon to fall back on if it plans to launch a wireless service.

On top of that, there's 30 MHz of reserved spectrum in each region for carriers with less than 45 MHz of low-band spectrum (less than 1000 MHz). That leaves out AT&T and Verizon in most areas, but T-Mobile and DISH should be able to snatch most of what they need on the cheap thanks to less competition from the big spenders. Comcast will also be able to participate in the reserve.

Additionally, Verizon and AT&T are unlikely to increase their spectrum budgets. Recon Analytics analyst Roger Entner says it's unlikely either carrier will raise additional debt to bid on spectrum. That's especially true considering it's "an election year with a lot of uncertainty, with Brexit making the debt markets jittery."

All this points to the FCC's eventual need to go back to the broadcasters and ask them to lower the clearing costs, probably reducing the amount of spectrum available for auction. That could extend the auction well into 2017.

Who gets hurt the most?

T-Mobile may get hurt the most from the extension of the incentive auction. T-Mobile customers use much more data on average compared with other carriers, and its spectrum position lags every major competitor. While T-Mobile does have more spectrum per customer compared with AT&T and Verizon, according to CFO Braxton Carter, almost half of that spectrum is dedicated to 3G or older technology. Currently, 80% of T-Mobile's data usage is on 4G LTE.

Carter is relying on the incentive auction to add capacity, and he figures he'll be able to deploy the spectrum it buys at auction before the end of next year. That's ambitious to begin with, considering broadcasters will have the right to hold on to their spectrum for up to 39 months after the auction closes. With the likely extension, T-Mobile could find itself even more crunched for spectrum capacity. Investors should hope that won't cause T-Mobile to overextend itself in the auction to buy spectrum it doesn't need.

AT&T and Verizon are in much better positions, comparatively, after spending big in the FCC's previous spectrum auction for AWS-3 spectrum. While that higher-band spectrum isn't as good for transmitting signals long distance or penetrating buildings, its deployment will help fill in dead spots on each of their coverage maps, which is just about all that's left for either of the larger nationwide carriers to do.

T-Mobile has been resourceful in getting the most out of its spectrum holdings and has shown a willingness to acquire spectrum in the private market when it's appropriate. Carter probably has some contingency plans if the auction extends -- possibly including a tie-up with DISH Network -- but AT&T and Verizon can afford to wait it out.