First Public White-Space Network Is Alive

An anonymous reader writes "The first public white space network officially launched on Wednesday in Claudville, Virginia. It uses sensing technology from Spectrum Bridge with software and Web cams supplied by Microsoft and PCs from by Dell. The project was funded the TDF Foundation. White space networks use unlicensed television spectrum and have been called 'WiFi on steroids.' They offer more bandwidth, over larger areas, than does WiFi. IT companies duked it out with broadcasters for years to get white spaces approved by the FCC. They finally got the FCC's nod in November, 2008."

Re:Is this statement misleading?

[spottedkangaroo]

It really doesn't matter what frequency when you're talking bandwidth. When you're talking size of the antenna or signal loss the wavelength might matter, but not for bandwidth. The reason you get more bandwidth here is because the spectrum is wider. The ISM spectrum is very very narrow and low power channels all bunched up around 2.4Ghz. With the new white spaces, they can use tons more and much louder. But, yes, they need longer antennas.

As far as the range? You can make a microwave signal go light years and a HAM signal go a few feet (although, there will be some distortion for transmitting a signal over a distance shorter than the wavelength). The range is more of a function of signal power.

Re:Webcams?

[John Hasler]

The school system is using them for "distance learning". They aren't really relevant to the story.

Re:Is this statement misleading?

[slifox]

I think the OP was referring to data transfer bandwidth (the throughput, or data rate), rather than the traditional electronics use of "bandwidth" (referring to the width of the transmitted signal in the frequency spectrum; though "channel width" is a more exact term).

Of course higher carrier frequencies don't have a higher bandwidth, because bandwidth is a property of the whole system, including the data signal and modulation method. You can make the bandwidth as big or small as your system's constraints allow (e.g. one constraint might be to keep most of your transmitted power inside the allocated bandwidth).

If your data signal is modulated in the exact same manner regardless of the carrier, varying the frequency of the carrier will not affect the transmitted signal's bandwidth. The carrier frequency imposes the upper limit on the data signal's frequency, and thus a higher carrier frequency will theoretically allow for a high data rate.

Practically, however, the data signal is almost always much smaller than the carrier signal, and the transmitted frequency is subject to many other important factors such as noise, signal propagation through the environment, etc... In the case of 2.4GHz vs. 800MHz carrier frequencies, there is no practical gain in potential data rate.

This is all based on my limited understanding of communication theory. Please correct me and/or provide further details if possible!

Re:Is this statement misleading?

[mwilliamson]

Uh, no. Range is not a function of signal power. It more is a function of the overall signal/noise ratio and the sensitivity of the receiver. This includes noise introduced in the transmitter, natural/other noise, and noise introduced in the receiver. An antenna system with gain can both concentrate and attenuate signals, depending on the directivity and where its pointed.

BTW, I got over 1400 miles out of a little 0.3 watt ham signal, but thats no where near as impressive as Earth still being able to receive signals from Voyager 1 and 2 nearly 10 billion miles away. That's impressive.

-Michael

Re:Is this statement misleading?

[niko9]

You can make a microwave signal go light years and a HAM signal go a few feet

Just for clarification, ham radio operators operate in the microwave region as well. They perform EME (earth-moon-earth) using microwave radios with regularity.

Some info here: http://www.dxzone.com/catalog/Operating_Modes/EME/ [dxzone.com]