Communications

New Spectrum from Old

The global switch from analog to digital television has created an unusual opportunity, opening up portions of the radio spectrum around the world that have been off limits to anyone but broadcasters for decades. These newly vacant “white spaces” can be found from 52 to 806 megahertz, and telecommunications companies hope to be able to use some of them for long-range broadband wireless connections. In the United States, the Federal Communications Commission announced rules for unlicensed use of white spaces in September, but a number of pilot systems have already been deployed. The first such public network, introduced in rural Virginia by Spectrum Bridge in October of last year, used white-space frequencies to connect Wi-Fi hot spots to the Internet.

White-space networks, such as Microsoft’s, must accommodate local TV stations.

One significant difficulty in opening up white spaces to mainstream consumer use is that the exact frequencies available vary from place to place, largely depending on the bands used by local TV stations.

Consequently, researchers are focusing on making wireless equipment smart enough to figure out which frequencies it should be using. At Microsoft Research, Ranveer Chandra (see TR35, September/October 2010) has developed a prototype system in which base stations determine their location using GPS and then check the Web to find out which radio bands are allocated to local broadcasters.

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