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From: pa2aga
To: tcp_broadcast@pa2aga-10
Subject: TCP-Group Digest 96/189
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TCP-Group Digest Thu, 12 Sep 96 Volume 96 : Issue 189
Today's Topics:
high speed coders/decoders (2 msgs)
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Date: Wed, 11 Sep 1996 07:23:22 -0800 (PDT)
From: Glenn Elmore <glenne@hpsadr2.sr.hp.com>
Subject: high speed coders/decoders
Phil Karn <karn@qualcomm.com> wrote:
>
> Hi. Apropos the discussion of high speed RF hardware, I point out that
> digital video broadcasting is developing some neat stuff that may be
> usable for our purposes. LSI Logic (http://www.lsilogic.com) has a
> bunch of ICs intended for consumer DVB receivers that do QPSK
> demodulation, Viterbi decoding and Reed-Solomon decoding at data rates
> up to 50 megabits/sec. They seem to have a variety of packages, some
> highly integrated and others broken into more modular pieces.
The LSI parts do indeed look interesting to me. Particulary because of all
the built in FEC. From the initial blurb it appeared the would do >64Mbps
but it 5 wasn't clear how slow they could go.
At this point, figuring out how to deliver reasonable C/N across
several MHz in a typical amateur environment is the challenge. Most
amateurs don't seem willing to engineer the kind of path that is
generally required. Still, the parts look very attractive and it is the
possible that the price could become tolerable.
If anyone spends any extended time with them for any reason, I would
be interested in hearing about their experiences.
Glenn n6gn
------------------------------
Date: Wed, 11 Sep 1996 15:38:48 -0700 (PDT)
From: Phil Karn <karn@qualcomm.com>
Subject: high speed coders/decoders
> At this point, figuring out how to deliver reasonable C/N across
>several MHz in a typical amateur environment is the challenge. Most
>amateurs don't seem willing to engineer the kind of path that is
>generally required. Still, the parts look very attractive and it is the
>possible that the price could become tolerable.
Raw C/N in a metropolitan area is easy; it's C/multipath that's
hard. But power-efficient coding can alleviate the problem as
multipath can be made to look like thermal noise.
>The LSI parts do indeed look interesting to me. Particulary because of all
>the built in FEC. From the initial blurb it appeared the would do >64Mbps
>but it 5 wasn't clear how slow they could go.
Dunno. At some point if you're slow enough you can do it all in
software. I now have a r=1/2 K=7 Viterbi decoder running at 258kb/s on
a 133 MHz Pentium. More recently I've been tuning a (255,223) GF(256)
Reed-Solomon erasures-and-errors decoder routine that I found on the
net. I've gotten it up to 850-1600 kb/s on the same Pentium depending
on how many errors and erasures have to be corrected.
Because the LSI Logic parts are designed for consumer digital
broadcast receivers, the most integrated (and probably the cheapest)
parts do decoding only. But their product line does include a
stand-alone RS encoder, and it's pretty much trivial to encode a K=7
convolutional code and generate QPSK in your own hardware.
Phil
------------------------------
End of TCP-Group Digest V96 #189
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