Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!purdue!gatech!prism!ce1zzes
From: ce1zzes@prism.gatech.EDU (Eric Sheppard)
Newsgroups: sci.electronics
Subject: Re: MODEM SPEED INCREASE
Keywords: 300 to 1200+
Message-ID: <1556@hydra.gatech.EDU>
Date: 22 Aug 89 01:08:08 GMT
References: <1436@esunix.UUCP> <3194@scolex.sco.COM> <1166@tukki.jyu.fi>
Organization: Georgia Institute of Technology
Lines: 26

>
>I've also seen the CCITT V.22bis (that's 2400 b/s for all americanos out
>there) called "Quadrature Amplitude Modulation", is this just techno-talk
>hype for PSK with the 4-bit codings ?

Quadrature Amplitude Modulation is the combination of both FSK and PSK
modulation methods.  The data stream is both phase AND frequency shifted.
Sounds confusing?  You bet it is!  The main difficulty in detecting the
QAM signal lies in regenerating the original carrier; both the frequency of
the originating system's carrier and its phase must be recovered from the
transmitted signal.
 
I've only started studying digital communications systems, and I'm overwhelmed
by their complexity, both in design and implementation.  Could anyone tell me
which systems today's modems use?  Is it QPSK, 8PSK, or 8QAM?

Eric Sheppard
Georgia Institute of Technology, Atlanta Georgia, 30332
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-- 
ERIC SHEPPARD
Georgia Institute of Technology, Atlanta Georgia, 30332
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