

FCC votes unanimously in favor of using whitespace for 'super WiFi' - lotusleaf1987
http://www.engadget.com/2010/09/23/fcc-votes-unanimously-in-favor-of-using-whitespace-for-super-wi/

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rkowalick
From the title I thought that the FCC ruled on 'super WiFi' over 'superWiFi'

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coin
So what exactly is "Whitespace airwaves"?

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mikemol
Area in the spectrum normally reserved for television, but not intentionally
actively used by television broadcasters.

Simplified (it _used_ to work this way, now it's slightly more complicated),
each television channel frequency required a certain small range (the tuner
frequency +/- a certain number of MHz) to carry its signal. Ideally, the
affected range of spectrum wouldn't exceed that specced amount, but
electronics aren't perfect, and RF is a tricky matter.

In practice, you tend to see splatter near a particular channel, outside its
allotted frequency range. Furthermore, receivers have to filter out any signal
not within the frequency range for the channel they want to watch, but the
filtering circuitry (called a bandpass filter) will tend to cause distortions
within the intended frequency range the better they are at filtering
frequencies outside that range. There are also other complicating factors,
like signal overloading receivers, and mis-tuned transmitters.

This resulted in a margin space between channels, so that adjacent channels
would interfere with each other less. As receiver electronics have gotten
better, more selective and more error tolerant, these margin spaces became
less necessary, and we have space in the spectrum that's no longer required
for its original purpose of providing a margin.

That space is your 'whitespace'.

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InclinedPlane
_" As receiver electronics have gotten better, more selective and more error
tolerant, these margin spaces became less necessary..."_

More to the point, as the technology used to broadcast has completely changed
from analog to digital the margin spaces have become completely unnecessary.
Additionally, digital television does not use the entire spectrum previously
allocated to analog broadcasts.

Edit: additionally, in locations where there aren't local television
broadcasts on certain channels those channels can be used for wifi.

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mikemol
Digital signal transmission tends to include an increase in error tolerance,
which I mentioned. The margin reduces the strain on the error tolerance, which
is also needed to cope with signal loss issues.

So, no, the margin spaces aren't completely unnecessary with digital
signaling.

Furthermore, I'll pick a couple nits and point out that it's only television
broadcasting which has completely switched to digital in the US. AM/FM radio
is still analog by definition, and there are large swaths of spectrum which
use those and other signaling methods.

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tocomment
Where does the rest of the world fit into this? Do other countries copy the
FCC restrictions? If not, why haven't "super WiFi" devices already been built
in countries that already had this spectrum open?

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kd0amg
There is some degree of international coordination under the International
Telecommunication Union (radio waves don't really recognize national borders),
but individual countries still have leeway to make their own internal rules.
There is also some international cooperation aimed at keeping people from
stepping on each others toes (e.g. I cannot use part of the 70cm amateur
allocation because I am too close to Canada who makes different use of those
frequencies). That said, as far as I can tell, it seems rules adopted by a
significant number of countries (or a number of significant countries) are
likely to become international.

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dangrossman
Opening up the 2.4ghz spectrum to everyone didn't create ubiquitous free
internet, nor even ubiquitous free-with-ads internet. Why are some postulating
that this will mean the end of cellular carriers and that phones will somehow
use this spectrum for free?

In terms of utilizing frequencies that can provide connections over longer
range than 2.4GHz, that's exactly what WiMax already is. And WiMax specs
aren't leading us towards any kind of free internet, they're the new high
priced 4G service you now buy from the same cell companies as always.

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InclinedPlane
I wish I had the expertise or the time to give a better rebuttal to this,
instead I'll just point out a few things:

First, the 2.4ghz spectrum is not the best for wireless comms, there were many
reasons for opening up that spectrum and very few of those reasons were
because it was an optimal signal frequency.

Second, bandwidth. The 2.4ghz spectrum is confined within an 82mhz band. The
available whitespace spectrum has a significantly larger bandwidth.

Third, technology. 802.11b and g are based on technology that is now stale by
more than a decade. Today's wireless broadband tech makes those protocols look
like a 56k modem.

The combination of these factors allows for stunning possibilities. More
efficient broadband technologies, better broadcast frequencies, more
bandwidth. These allow for more users with higher data rates at farther
distances from base stations. It also makes things like bridging access points
a lot easier. There's little reason to believe that in 10 years whitespace
broadband access points won't be utterly ubiquitous.

As for WiMax, that's not open spectrum, consumers can't buy a WiMax AP on
newegg. That makes it an entirely different beast.

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wmf
In large cities there is less than 82 MHz of white space available AFAIK.
Also, white space channels are 6 MHz wide while 802.11 channels are 20 MHz.

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aresant
If Google runs Android, and builds out an ad-supported "super wifi" network
what value do traditional carriers bring? Infrastructure for relays?

