Opinions, Observations and Ramblings about media technology.

Tuesday, March 5, 2013

Filling in the White Spaces

Yesterday, Google launched the public trial of their new spectrum database, and it's pretty interesting.     First, a bit of background.

For at least the last 10 years, there has been much chatter about better utilizing scarce radio frequency (RF) spectrum to accommodate the billions of phones, tablets, laptops and other mobile devises connecting to the web wirelessly.  It turns out the much of the prime spectrum, from 470 MHz to 700MHz, known as the Ultra High Frequency band, has been allocated for broadcast television since the 1950's.  Early on, this spectrum was barely used since few TV's were able to receive UHF channels.  That all changed after 1962, when the All Channel Receiver Act (ACRA) was passed by Congress, requiring all television sets to receive UHF channels 14 through 83.   Channel 37 was the only exception, since that frequency (centered at 611 MHz) turns out to be very useful for radioastronomy.  Immediately, the value of UHF spectrum shot up.  There are now over 1,500 UHF television stations, and thousands more translators and low-power stations filling this chuck of bandwidth.

UHF has the advantage of using relatively short antennae, with a quarter wavelength of four to five inches.  In addition, this 470-700 MHz band has favorable propagation characteristics, since it can pass through walls and other obstructions more easily than higher frequencies.  So the question is: how to take advantage of the "white spaces" in the spectrum between operating TV stations.

I searched for available spectrum in my neighborhood.  Slim pickings...

Google and nine other companies -- including Microsoft -- submitted proposals to operate databases to identify available frequencies for new, unlicensed services operating in the UHF band.  A few of them, including a company call Spectrum Bridge began trials of their database a few months ago.  The generally picky National Association of Broadcasters has already kicked the tires on the Spectrum Bridge database, and gave it generally favorable reviews. 

The Google database is fun to use, and has good explanations.  Their party line is "Google is doing our part to free up spectrum. One way we are doing this is through dynamic spectrum sharing, one of the most promising ways to make more spectrum available to the public for broadband access. As part of our effort to improve connectivity globally, Google.org is working to promote dynamic spectrum sharing through a TV white spaces database."   Sounds very altruistic, doesn't it?

I'm a bit skeptical of how accurate and up to date these ten synchronized databases will be.  Any errors will cause problems in wireless service quality, not to mention wireless microphones at the Taylor Swift concerts...

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