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From: tnixon@hayes.uucp
Newsgroups: comp.dcom.modems
Subject: Re: V32bis
Message-ID: <3728.278db272@hayes.uucp>
Date: 11 Jan 91 12:41:22 GMT
References: <6596.27880099@zswamp.fidonet.org>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 26

In article <6596.27880099@zswamp.fidonet.org>,
root@zswamp.fidonet.org (Geoffrey Welsh) writes: 

>  >V.32 and V.32bis use Quadrature Amplitude Modulation.
> 
>    Is it still kosher to refer to them as QAM, even when the coding
> constellation (is that the proper term?) is more complex than the
> one described in V.22bis?  I was under the impression that QAM was
> so called because amplitude was used to differentiate between the
> two possible shifts at the 90 degree angles, while the other angles
> represented only one bit pair each and did not require aimplitude
> for differentiation.

The standards themselves refer to the modulation technique as QAM.
My understanding is that the Quadrature part refers to the division
of the constellation into quadrants, with the two low-order bits
being differentially encoded to select the quadrant of the next
signal.  The Amplitude part refers to, simply, that the signal is
not of constant amplitude; V.22bis uses three different amplitudes,
and V.32 at 9600 has five.

-- 
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