Path: utzoo!utgpu!watserv1!maytag!xenitec!zswamp!root
From: root@zswamp.fidonet.org (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: Re: PEP vs. v.32
Message-ID: <6927.27D24513@zswamp.fidonet.org>
Date: Mon, 04 Mar 91 00:50:30 EST
Organization: Izot's Swamp BBS - Kitchener, Ontario

In a letter to All, Greg Andrews (gandrews@netcom.COM ) wrote:

 >In article <6895.27CDE02A@zswamp.fidonet.org> 
 >root@zswamp.fidonet.org (Geoffrey Welsh) writes:
>
>   For instance, I've noticed that the trend in 9600+ bps modems is to 
>increase the resolution in the coding constellation.  PEP still uses sixteen 
>point QAM; has DSP technology not improved enough to enable us to code more 
>than four bits per baud in a multicarrier scheme?
>

 >PEP isn't limited to a 16 point constellation.  In the 
 >cleanest parts
 >of the line you'll see carriers using a 64 point (6 bit) 
 >constellation.

 >Unless the modem decides the line won't support that kind of 
 >signal resolution...

   My disappointment has doubled.  At first I believed that Telebit & co. were 
simply not pushing the technology.  Now I that I have reason to believe that 
they are, I can't avoid the conclusion that they are doing so poorly!

   If there are 511 carriers operating at a maximum of 8 baud with 4 bit QAM, 
the maximum possible raw throughput is in the vicinity of 16000 bps, a figure 
which I have seen Telebit modems approach on clean lines.  If, as you say, 
they're using a 64 point constellation, the maximum raw throughput should 
be around 24000 bps, and I've never seen a TB come even close to that.
 

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