When the DTV transition happens in Feb. 2009, channels 2 through 51 will remain allocated for television transmission. Few of the nation’s television markets actually use 49 channels. Indeed, most use less than half of that number. The “white spaces” are these unused television channels, which amount to approximately 300 MHz of frequencies. According to Blair Levin, “[e]stimates vary, but most of the population (between 73% and 97%) lives in areas with access to 24 MHz or more of white space. Rural areas in particular, have a great deal of white space as they generally have fewer television broadcasters.” Rules for the “white spaces” are now on the Commission’s agenda.
Rather than being sold at auction to the highest bidder, unlicensed spectrum is useable by anyone with wireless equipment that has been certified by the FCC for unlicensed frequencies. A key advantage of unlicensed spectrum is that experiments in new technology can be carried out without asking the permission of spectrum licensees. To date, we have made very little spectrum available for unlicensed use and experimentation.
The FCC has the discretion to decide whether the digital television “white spaces” may be used on an unlicensed basis. Its own Spectrum Policy Task Force recommended in 2002 that such a step be taken. Indeed, in trying to stave off an auction rule in the 700 MHz proceeding that would have dedicated non-built-out spectrum to unlicensed uses, Verizon affirmatively argued that the Commission would be opening up the white spaces on an unlicensed basis – thus making such a rule for the 700 MHz auction unnecessary.
Beginning in 2004, the FCC asked for comments on uses of the white spaces, itself suggesting that unlicensed uses of these white spaces would be appropriate. The Commission recognized that the “significant growth of and consumer demand for unlicensed wireless broadband applications” supported opening up the white spaces for broad ranges of unlicensed use. Two years later, the FCC backtracked somewhat from its earlier wholehearted endorsements of unlicensed uses of the white spaces, saying (1) that, at the most, only “fixed” (non-portable) unlicensed uses should be allowed, and, even more disconcertingly, (2) that it is not confident any unlicensed uses are appropriate in the white spaces. The FCC is concerned about the possibility of interference among the transmissions of various users of the white spaces.
So this is a proceeding about almost 300 MHz of spectrum (and all the fighting over the C Block concerned just 22 MHz). It will be in “swiss cheese” (non-contiguous) form, but there will be a great deal of it. Using white space spectrum as a way to provide last-mile connectivity to wired Internet access nodes would be especially valuable in rural areas where those wired nodes are scarce and there is a great deal of vacant TV spectrum.
Today’s update is that Google is making concrete statements about its plans should the FCC allow for unlicensed use of some portion of the white spaces. (Here’s the company’s filing with the FCC.) Google suggests that there should be allocations for both portable and fixed unlicensed uses. (We need portable devices – they’ll be cheap and there’s a huge market for them. Without portable devices, this market just won’t take off.)
Google suggests that *all* devices for unlicensed use of the white spaces should be required to receive an “all clear” signal for the particular channel where they wish to operate, by using geolocation, checking a database of licensees in that location, and getting permission in advance. Wireless mics could send a signal (called a “beacon”) saying “don’t transmit here” that would be adhered to by these unlicensed devices. Google further suggests that no unlicensed device would be permitted to transmit at all in channels 36-38. The company makes the rural argument, pointing out that Android-powered handsets would be a good way of providing low-cost mobile broadband coverage for everyone. And it’s promising to provide technical assistance to people and manufacturers who want to exploit unlicensed white spaces.
Interestingly, the company is suggesting that this combination of geolocation, beacons, and databases will allow the FCC (eventually) to be comfortable with unlicensed devices that just use spectrum sensing. They’ll have so much data about interference successes etc. that they’ll see that interference can be dealt with just by spectrum sensing.
Once we’ve done all this experimentation with the white spaces, we may be in a better position to use *licensed* spectrum more wisely without causing interference. Google points out that they could use dynamic auctions to allocate spectrum on a real-time basis – the idea is that the licensee could grant the right to transmit an amount of power for a specified unit of time, subject to a cap.
Bottom line: This is a compromise proposal designed to assuage objectors and nudge the country down a path towards more efficient use of spectrum, both licensed and unlicensed. It will be interesting to see how the Commission responds. I’ve heard that there’s a welcoming mood over there for unlicensed uses.
*Cross-posted from [Susan Crawford blog](http://scrawford.net/blog).*