The FCC seems to have quietly approved the rules necessary to allow 11 more 802.11a channels to the 5 gigahertz (GHz) band: Joanie Wexler of Network World reports the 255 megahertz (MHz) chunk added to unlicensed 5 GHz use comes as a result of compromise between the Department of Defense and the "industry," which wasn't well defined. Public process doesn't seem to have been broadly involved here, but it may just be less transparent to someone not trained in the intricacies of FCC interaction with other parts of government.
The new rules went into effect Jan. 20, and allow the use of 5.47 to 5.725 GHz--11 channels in the 802.11a version of Wi-Fi--with a couple of key signal usage modifiers. The rule also changes the requirements for the next-down stretch of spectrum, 5.25 to 5.35 GHz to conform to those modifiers.
(Update: It turns out this story is incorrect: the 5.47 to 5.2725 GHz band was available about a year ago. This new order adds the signal modifiers below to the 5.25 to 5.35 GHz band. There was a lag of some kind between these new channels being available for legal use and chips and equipment supporting them, but no regulation gap.)
Both bands must now use dynamic frequency selection (DFS) to avoid in-use spectrum, and transmit power control (TPC), which throttles power to the minimum necessary for given communication. Older equipment using 5.25 to 5.35 GHz is exempt, although one might expect manufacturers to push out firmware upgrades. These requirements are part of 802.11h, which extended 802.11a for legal European operation.
Interest in 5 GHz has increased in the last year or so with the recognition that having no 802.11b devices to support in that band makes voice over IP over WLAN (VoWLAN) easier to operate in corporations. The band is also being used for backhaul on mesh networks and will be one of the early profiles for WiMax.
Even though 5 GHz has restrictions on omnidirectional signal strength that makes it propagate less far than the highest-powered 2.4 GHz omni-driven gateways, the rules for directional antennas for the top four channels (highest frequencies) in the band give it parity. The lack of competing signals and now a total of 23 channels (some with limitations on outdoor vs. indoor use) make 5 GHz very appealing for these specific applications.