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When the U.S. Digital Television Transition (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, telecom and technology regulatory analyst, "[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.

This is a proceeding about almost 300 MHz of spectrum (and all the fighting over the 700 MHz C Block concerned just 22 MHz). It will be in "swiss cheese" (non-contiguous) form, but there will be a great deal of it.

Today, with Congress in recess, leaving less room for last-minute-Lucy-with-the-football lobbying gambits, the Federal Communications Commission (FCC) appears to be poised to release a report saying the white spaces can be used without necessarily causing interference to existing broadcasts.

There are still many questions to be answered—

(1) Will permitted uses of the white spaces have to be licensed, or can they be unlicensed? Unlicensed uses could unleash the creation of an entire ecosystem of new devices and new uses, as we've seen in the "junk band" use of wireless hotspots. With machines making their own etiquette decisions (subject to power-level certification by the FCC), the capacity of the white spaces (potentially enormous) could be used far more effectively. This could provide a much-needed end-run around last-mile bottlenecks, particularly for mobile and rural users.

(2) Will devices have to be fixed, or can they be portable? If portable devices are allowed, a much larger market for these new gadgets will be created—which means they'll be cheaper (because they'll be sold in enormous numbers), which means that innovation will move much more quickly, which means many more interesting mobile uses will be possible. You can't use a fixed device in a car moving at 60mph down the highway.

(3) What kind of spectrum sensing will be required? Will devices be permitted to carry out their own sensitive etiquette so as to avoid interference? Or will they need to check against authoritative databases and/or send out foghorn-like "beacons" so that existing actors will know they're interested in transmitting? Google has proposed a hybrid solution that includes the use of databases and beacons (and protects those holy wireless mics); other groups are more interested in pure spectrum sensing.

More coming, but this is a very interesting first step.

By Susan Crawford, Professor, University of Michigan Law School. Visit the blog maintained by Susan Crawford here.

Related topics: Access Providers, Broadband, Policy & Regulation, Telecom, White Space, Wireless