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From: earle@smeagol.UUCP
Newsgroups: comp.dcom.modems
Subject: Re: Network protocols questions
Message-ID: <1094@smeagol.JPL.NASA.GOV>
Date: Mon, 30-Mar-87 21:28:30 EST
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Posted: Mon Mar 30 21:28:30 1987
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>Does anybody know what kind of protocols and error control techniques are used
>to send back data from space (like from Uranus and Neptune), where corruption
>is very likely, and retransmission is very expensive?

All (forseeable) future spacecraft will use Reed-Solomon encoders on board the
spacecraft for telemetry transmissions.

The best reference I can come up with is
	Reed-Solomon Encoders -
	Conventional vs. Berlekamp's
		Architecture

	Authors: Marvin Perlman
		 Jun-ji Lee

	JPL Publication 82-71
	December 1, 1982

You should write to either the Publications Office (or, as a default,
the Office Of Public Affairs) at JPL and enquire about obtaining the
above booklet.

	Jet Propulsion Laboratory
	Public Information Office
	M/S 180-200
	4800 Oak Grove Drive
	Pasadena, CA  91109

The beginning of the first chapter reads:

				I. BACKGROUND

	Reed-Solomon (RS) codes are a special case of the nonbinary
generalization of Bose-Chaudhuri-Hocquenghem (BCH) codes.  They are among the
Maximum Distance Seperable (MDS) codes which realize the `maximum' minimum
Hamming distance possible for a linear code (Refs. 1 and 2).  The interest in
RS codes was primarily theoretical until the concept of concatenating coding
was formulated and first introduced in Ref. 3.  Concatenated coding has been
adopted by the U.S. National Aeronautics and Space Administration (NASA) for
interplanetary space missions (see Fig. 1).  The application of concatenated
coding to NASA's Jet Propulsion Laboratory (JPL) spacecraft telemetry with a
convolutional inner code and an RS outer code was first proposed and analyzed
in Ref. 4.
...

`Figure 1' shows the pathway through a telemetry encoding and downlink, and
looks approximately like this:

info->RS encoder & symbol interleave->convolutional encoder->modul.->downlink
									|
									|
 ------------------------------------------------------------------------
 |
 |
 --> demodulator->viterbi decoder->RS symbol deinterl'ving buf->RS decode->info

(Where `RS' == Reed-Solomon)

Hope this helps.

-- 
	Greg Earle	UUCP: sdcrdcf!smeagol!earle; attmail!earle
	JPL		ARPA: elroy!smeagol!earle@csvax.caltech.edu
AT&T: +1 818 354 4034	      earle@jplpub1.jpl.nasa.gov (For the daring)
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