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From: rab@well.UUCP
Newsgroups: comp.dcom.modems
Subject: Re: Network protocols questions
Message-ID: <2849@well.UUCP>
Date: Tue, 31-Mar-87 02:57:21 EST
Article-I.D.: well.2849
Posted: Tue Mar 31 02:57:21 1987
Date-Received: Wed, 1-Apr-87 07:04:12 EST
References: <12289499503.24.SY.FDC@CU20B.COLUMBIA.EDU> <2160@cit-vax.Caltech.Edu>
Reply-To: rab@well.UUCP (Bob Bickford)
Distribution: world
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
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In a previous article a System Mangler writes:
  (in answer to a question about what codes are used in space)
+ They use convolutional codes, often with a rate of 1/2 (i.e. half of
+ the bits sent are data, the rest are error correction).  These are
+ serial codes, with the next error correction bit depending on the last
+ N data bits.  As N gets large, the code can handle longer error bursts,
+ and a higher percentage of errors, at immense decoding cost.  With such
+ codes you can approach the Shannon limit, which is why they're used in
+ deep-space communications, where transmission power is dear.

+ Don Speck   speck@vlsi.caltech.edu  {seismo,rutgers,ames}!cit-vax!speck

   Could you post some references, where I might find a good but not
too technical explanation of such codes?  I don't want to get too deeply
into the math, I'd just like to find out about some typical ways of
implementing them.


-- 
Robert Bickford         {hplabs, ucbvax, lll-lcc, ptsfa}!well!rab
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