[MLB-WIRELESS] Theoretical limits of 2.4 GHz band

[Robert Graham Merkel]

A topic that has come up with some regularity in discussions about
wireless networking is that the network could never supply the kind 
of data bandwidth that people would like.  It's clear that 802.11b,
wonderful as it is, can't do the real heavy lifting that we'd like.
However, the existence of gear like the new 22mbps Dlink range, and
the upcoming 802.11g standard, demonstrates that we technology can
get us more carrying capacity out of the 2.4 Ghz band than we currently
get.


However, there is an ultimate theoretical limit to how much data you
can carry with a certain amount of radio spectrum and the signal/noise
ratio.  From what I recall from my computer networking class (I'm a
CS guy, not an electronic engineer), and a bit of research, the formula
(called Shannon's Theorem) is:

<discussion of Shannon's Theorem, skip if you already understand it>

Channel Capacity = (Hardware Bandwidth) * LOG2(1 + Signal/Noise ratio).

Now, the hardware bandwidth is simply the chunk of spectrum allocated
to the communication.  If we used the entire 2.4 Ghz band that's 100
Mhz, so hardware bandwidth = 10^8 for this calculation.

The signal/noise ratio, for this formula, has to be the actual ratio, 
not the decibel ratio.  The decibel ratio is 10 log10(S/N), so the actual
signal to noise ratio is 10^((signal-to noise in db/10))
<end discussion>

Anyway, the point of all this, is given the signal-noise ratio and the 
amount of the 2.4 Ghz band you want to use, you can determine how much
data could ultimately be carried on the band.  

However, I'm not sure what values to use for the signal-noise ratio.  
Has anybody got some measured or calculated data on S/N ratios for 
interesting configurations
that we could plug into Shannon's Theorem and see what technology might
ultimately give us?


-- 
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                                           Robert Merkel
                                          rgmerk at mira.net
I know the human being and fish can coexist peacefully.
  -- George W. Bush.
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