A small cell band would mean a dedicated swathe of spectrum in which carriers could deploy tiny cell sites, mounted on light poles or inside buildings, layering enormous amounts of capacity onto their 3G and 4G networks. Operators like Sprint and AT&T plan to deploy their first small cell systems in the coming years.

But it’s not a done deal. By unanimous vote, the commission issued a notice for proposed rulemaking (NPRM), which means a lengthy commentary and response period going well into spring, and no timeline has been set for a final decision. But the FCC is did offer details on what shape the final band will take.

Basically the FCC would set aside 100 MHz of spectrum in the 3.5 GHz band currently used by government agencies and satellite providers, and the give different sets of users priority in using the spectrum:

• The incumbent government and satellite users would make up the first tier. Whenever they’re online in a particular portion of the band everyone else is offline.
• The second tier is reserved for hospitals, utilities, government facilities and public safety agencies, which would be given priority access in specific geographic areas.
• The third tier is basically anyone else. Established carriers and anyone who cared to set up a network would be able to deploy small cells in the geographic and spectral gaps that remain. Those carriers would have to tap into a dynamic spectrum database that would tell them when and where spectrum is available so they could stay away from the incumbent and priority users.

Generally carriers aren’t fond of sharing spectrum with anyone, particularly each other. We’ll find out what mobile operators really think about the proposal in the coming months as they file their comments, but the initial reaction from the industry is positive. Telecommunications Industry Association President Grant Seiffert issued this statement:

“The FCC’s adoption of the NPRM is a commendable and significant step towards addressing the looming spectrum crunch and meeting National goal of making 500 MHz newly available for broadband use within 10 year. After careful and exhaustive planning to avoid harmful interference occurrences within and surrounding it, we believe that the 3.5 GHz band could be used advantageously for small cell use, and that more efficient use of this band could help decrease congestion in other bands.”

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The National Telecommunications and Information Administration (NTIA) proposed that 95 MHz currently being used by 20 different federal agencies be made available to carriers, but that a good portion of be turned into what is effectively an airwave time share. The military and other agencies would use it for their communications needs at certain times and specific locations, but whenever and wherever they were offline, carriers would be free to use the spectrum for mobile broadband.

CTIA VP of regulatory affairs Chris Guttman-McCabe said that sharing spectrum is a great idea in principle, but logistically it will be very difficult to pull off. Carriers simply can’t turn capacity on and off on a schedule or leave big gaping bandwidth holes in their coverage if they’re going to adequately serve their customers, Guttman-McCabe said.

He did concede there would be some circumstances where sharing would work. For instance, a government satellite network with a dozen ground stations in remote locations would be easy to work around, Guttman-McCabe said. In a such a scenario, carriers would create exclusion zones around the satellite uplink sites to prevent interference, but as long as zones weren’t located near metropolitan areas – where capacity is most needed – it wouldn’t be a problem, he said.

The big problem, Guttman-McCabe said, is time-based sharing. Unless the government limited its use to the wee hours of the night, carriers couldn’t depend on using that spectrum when they most need it. While CTIA is definitely willing to work with government where sharing is a logistically feasible, Guttman-McCabe said, it wants it to be the option of last resort.

“We want to make sure that the balance is in favor of clearing rather than sharing spectrum, with the recognition that some sharing is inevitable,” Guttman-McCabe said. “We understand that there are some government services that need to remain in the band. … I do have a fear, though, that the default approach is going to be to leave government users in place and have us work around them.”

Slicing and dicing the airwaves

The NTIA administrator Larry Strickling has pointed out that the carriers aren’t the only ones who need spectrum. Just as the consumer and business demand for mobile broadband skyrocketed so has the government’s, and everyone is clamoring for the same scarce airwaves. Clearing entirely the 95 MHz block,  which spans 1755-1850 MHz, could cost as much as $18 billion, could take as much as decade, and would require the relocation of highly sensitive military applications such as the air combat training systems. While Strickling said there are some frequencies that would be easier to clear — such as the microwave transmission bands — for much of that spectrum, sharing would be a much more cost-efficient way of alleviating the capacity crunch.

The NTIA is proposing that emerging technologies such as LTE-Advanced would make such sharing possible. LTE-Advanced uses a technique called carrier aggregation, which lashes together frequencies from all over the band map, while still preserving the integrity of government systems interleaved among them. The technology could even be used dynamically, grabbing government bandwidth when not in use by the feds and adding that capacity temporarily to the network. An NTIA spokesperson told us via email:

“This forward-looking approach, involving a combination of sharing spectrum and relocating federal users, will enable spectrum to be put to commercial use more quickly and in a more cost-efficient manner than the old method for making spectrum available. NTIA will convene industry and federal agencies, as quickly as possible, to move forward with making this spectrum commercially available while protecting critical federal missions.”

CTIA, however, isn’t questioning whether sharing is technically possible, but rather its commercially feasible, given the constraints operators would work under. According to Guttman-McCabe, CTIA would rather the NTIA try to consolidate as many government users as possible into specific blocks and give the remaining spectrum up for commercial use. The debate is likely to play out as the first block the government has identified for clearance: the 1755-1780 MHz, which must be auctioned off by 2015.

Tower Image courtesy of Flickr user Nikhil Verma; Washington Image courtesy of humbertomoreno flickr creative commons.

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