Microsoft details a fix for 'white space' interference

ronjor · Aug 19, 2009

by Marguerite Reardon

Microsoft researchers may have taken a step closer to finally turning unused analog TV spectrum, known as "white spaces," into unlicensed spectrum that can be used to deliver new wireless broadband services.

"White space" spectrum is unused wireless spectrum that sits between analog TV channels. Because much of this spectrum operates at lower frequencies, it can travel longer distances, much longer distances than the unlicensed frequencies used for Wi-Fi devices. Most Wi-Fi devices operate at 2.4 GHz, whereas, white space spectrum between analog TV channels 21 and 51 operate in the 512 megahertz and 698 megahertz range. (Signals transmitted over lower frequencies tend to travel longer distances at slower speeds, while signals transmitted at higher frequencies tend to be faster over shorter distances.)
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Article

Bill_Bright · Aug 20, 2009

As noted in a couple comments there is some misinformation presented there.

the article's author said:

Signals transmitted over lower frequencies tend to travel longer distances at slower speeds, while signals transmitted at higher frequencies tend to be faster over shorter distances
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That is not correct at all. Radio waves travel at the same speed, regardless the frequency: ~186,000 miles per second, or the speed of light. This is a Law of Physics. And Radio waves, regardless the frequency will travel the same distance (forever!) unless blocked. However different frequencies will behave differently. Some travel in straight lines only (line of sight), some bounce off objects or the atmosphere.

However, higher frequencies, as with CPUs, means more information can be processed in the same amount of time. So in terms of data "bandwidth" higher frequencies can support more. This results in "faster" data transfer but not faster radio waves or signals.

ronjor · Aug 20, 2009

Law of Physics.
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Of course, you are right Bill.

The really interesting concept is here --

Microsoft has designed a set of protocols it calls "White-Fi," which it claims will be able to avoid interference to make the best use of the spectrum. One of the biggest challenges with avoiding interference is that new devices using the same frequency can be introduced to the network at any time. For example, a wireless microphone can be turned on and off. And the tiniest bit of interference can cause interference problems.

To avoid this problem, Microsoft's White-Fi protocol is designed so that each device measures the spectrum conditions around it, finds available frequencies, and is able keep searching for interference. And if interference is detected, it can move to a different sliver of spectrum at anytime, the article said.

The way it works is that the device connects to the available "white space" frequency. But it will also maintain a backup radio frequency channel, so that if another device that uses the same frequency comes into range, it could switch to the backup frequency.
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Bill_Bright · Aug 20, 2009

It will be interesting to see what the FCC allows as the government owns the frequencies and allocates when, how and who will use it.

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Microsoft details a fix for 'white space' interference

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