From: Phiber Optik <phiber@eff.org>
Date: Tue, 9 Feb 93 01:39:03 PST
To: karn@qualcomm.com (Phil Karn)
Subject: Re:  Compressed/Encrypted Voice using Modems
In-Reply-To: <9302082123.AA00695@servo>
Message-ID: <199302090937.AA07958@eff.org>
MIME-Version: 1.0
Content-Type: text/plain


> 
> 
> >Shannon didn't consider intersymbol interference.
> 
> Sure he did. That's why the bandwidth term appears in his channel capacity
> equation.
> 
(stuff deleted)
I was probably being unclear.  According to my text, Shannon's capacity formula
does not account for intersymbol interference.  My text also states that 
Nyquist used intersymbol interference as a limit in his 2-bit rule.  I'm
considering my text to be correct, because the capacity formula doesn't account
for the imperfections (like intersymbol interference) and other problems
encountered in practice (envelope delay distortion, the need for echo cancell-
ation, etc.).  And in your words, it says that you can, but it doesn't say how.
For those who just tuned in, intersymbol interference refers to when the 
residual tail or bounce of a dying pulse interferes with a subsequent pulse.