Wireless protos- 11a 11b 11g ....11x?

[Jeff Kinz]

On Wed, Jan 12, 2005 at 02:42:30PM -0500, Bill Freeman wrote:
> Jeff Kinz writes:
>  > I just got asked what the differences are between the various wireless 
>  > protoccols and I'm realizing I don't have a good summary available.  Does
>  > anyone know of a website or document that explains what is special about
>  > "11n" (possibly vs 11g)?

Hi Bill, A good summary, thanks  Rob Flickenger Wireless Hacks
book covers much of the same ground.  I'm hoping to find a quick
description of the 802.11n stuff, and whatever else is forward looking
right now.

> 	If you're an IEEE member you can get PDF's of the specs free.
        Read specs? - not until I have to code something! 

> 	802.11b is an 11Mbps (max, with fall baxk) scheme using "channels"
> around 2.4GHz.  There are, I believe, 14 channels, where almost no country
> allows the use of all of them.  The US authorizes 11 of them.
> 
> 	802.11g uses the same spectrum as b, but uses wider bandwidth
> signals to allow 54Mbps (max).  The wider bandwidth means that these
> signals don't fit in a 802.11b channel: each g uses several of the b
> channels, allowing only 3 channels of g in the "band".

11g devices are also backwards compatible w/11b's, naturally they have
to slow down to do this.

> 
> 	802.11a uses a separate band around 5GHz, where more spectrum is
> available, allowing a more reasonable number of 54Mbps channels (I don't
> remember exactly, but I think that it's on the order of 10 of them).

And its range as slightly less than half of 11b at the same power
levels.  some people call 11a the "betamax" of wireless. :)

> 
> 	I believe that these are all spread spectrum schemes.  I don't
> know if a and g are similar modulation schemes that are just on
> different frequencies.  Because the RF stuff is compatible between b
> and g, most g designs allow communication in b as well, with
> essentially no extra hardware.


11g uses OFDM, just like 11a, but in the 2.4GHz band, but it also falls
back to DSSS to maintain compatibility w/11b.  11g looks like a very
good bet for the near term, but I still want to understand 11n.

> 	The g stuff came in at the same time as it became comfortable
> to produce somewhat software defined radios.  The channel set and more
> is determined by software controls, and these radios are capable of
> operating well outside the allowed (in any given country) frequency
> ranges, etc.  The manufacturer's lawyers have told them that folks
> like the FCC will hold them accountable if they make it too easy for
> users to set them up to operate illegally, which is the main reason
> that they won't give sufficient hardware info for Linux folks to write
> device drivers.


-- 
Linux/Open Source:  Your infrastructure belongs to you, free, forever.
Idealism:  "Realism applied over a longer time period"
http://www.scaled.com/projects/tierone/
http://kinz.org
http://www.fedoratracker.org http://www.fedorafaq.org
http://www.fedoranews.org
Jeff Kinz, Emergent Research, Hudson, MA.
~
~
~
~