The forthcoming transition to digital TV transmissions will free up about half the spectrum currently allocated to TV broadcasters. This freed-up spectrum was the subject of the FCC’s just-concluded 700MHz Auction, which yielded about $20 billion in license fees to the government. The fate of the other half of the TV spectrum, the part that will remain assigned to TV broadcasts after the digital transition, remains in contention.

This spectrum will be shared by licensed TV broadcast channels and wireless microphones, but even so much of it will remain mostly unused. These chunks of spectrum left idle by their licensees are called “White Spaces.” The advent of “spectrum sensing” radio technology means that it is now theoretically possible for transmitters to identify and use White Spaces without interfering with the licensed use of the spectrum.

The FCC has issued a Notice of Proposed Rulemaking and a First Report and Order to explore whether this is a good idea, and if so, how to handle it.

The potential users of the White Spaces have formed roughly two camps, those who see it best suited for fixed broadband access (similar to the first version of WiMAX), and those who see it as also suited for “personal/portable” applications (similar to Wi-Fi).

Google, along with Microsoft and some other computer industry companies, advocates the personal/portable use. The FCC’s Office of Engineering and Technology (OET) is currently lab-testing some devices from Microsoft and others to see if their spectrum-sensing capabilities are adequate to address the concerns of the broadcast industry, which fears that personal/portable use will cause interference.

Google filed an ex-parte letter with the FCC on March 24th, weighing in on the White Spaces issue. The letter is well worth reading. It concedes that in the introductory phases it makes sense to supplement spectrum sensing with other technologies, like geo-location databases and beacons. The letter asserts that these additional measures render moot the current squabble over a malfunction in the devices in the first round of FCC testing, and that the real-world data gathered in this introductory phase would give the FCC confidence ultimately to repeal the supplemental measures, and perhaps to extend open spectrum-sensing uses to the entire radio spectrum, leading to a nirvana of effectively unlimited bandwidth for everybody.

The kicker is in the penultimate paragraph, where Google recycles an earlier proposal it made for the 700MHz spectrum auction, suggesting a real-time ongoing “dynamic auction” of bandwidth. Google now suggests applying this dynamic auction idea to the white spaces:

For each available spectrum band, the licensee could bestow the right to transmit an amount of power for a unit of time, with the total amount of power in any location being limited to a specified cap. This cap would be enforced by measurements made by the communications devices. For channel capacity efficiency reasons, bands should be allocated in as large chunks as possible. The airwaves auction would be managed via the Internet by a central clearinghouse.

Current expectations are for spectrum-sensing use of the whites spaces to be unlicensed (free, like Wi-Fi). Now Google appears to be proposing “sub-licensed” rather than unlicensed spectrum use. The word “auction” implies that this could be a revenue producer for TV broadcast licensees, who received their licenses free from the government. This is a very different situation than the original context of the dynamic auction proposal, which applied to spectrum for which licensees paid $20 billion. Depending how it is implemented, it could fulfill the telcos’ dream of directly charging content providers for bandwidth on a consumer’s Internet access link, a dream that Google has opposed in the network neutrality wars. Google may ultimately regret opening the door to this one, even though it presumably sees itself cashing in as the ideal candidate to operate the “central clearinghouse.”

Update April 10th: Interesting related posts from Michael Marcus and Sascha Meinrath.

It took a while, and 261 rounds of bidding, but its over. Click here for the write-up from Wired.

The attractive thing about the 700 MHz spectrum that was freed up by the move to digital TV broadcasting is that transmissions at these frequencies pass through walls. The unusual thing about the “C Block” of this spectrum is that the FCC attached “open access” conditions to the license. This was at the behest of the computer industry, spearheaded by Google, who may even have made a bid on this block. But as the Wired story points out, Google had already won their victory with the imposition of the open access rules - winning the spectrum would have been more of a headache for them than losing it.

Don’t confuse the spectrum licensed in this auction with the White Spaces spectrum. The White Spaces spectrum is the spectrum that the TV broadcasters retained for their transition to digital transmissions in February 2009. The White Spaces issue is still unresolved by the FCC. The FCC is deliberating over whether to allow unlicensed use of the digital TV spectrum when it is not being used by a TV broadcast (hence “White Spaces.”) This use depends on effective functioning of “cognitive radio,” which lets transmitters sense by listening (and other means) when spectrum is available for use. If the FCC allows it, they still have to decide whether to allow only fixed broadband replacement like 802.22, or to allow “Personal and Portable” use as well.