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Rate 8/10 Code for Dicode Channels

IP.com Disclosure Number: IPCOM000123972D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2005-Apr-05
Document File: 1 page(s) / 59K

Publishing Venue

IBM

Related People

Fredrickson, LJ: AUTHOR

Abstract

A rate 8/10 code for use on dicode channels is described having a minimum number of states in a Viterbi detection scheme. It is a DC free code in which the running digital sum of the channel input sequence takes on five distinct values. Because of this limitation, the code has a k constraint of four. In Fig. 1, paths considered by a five state Viterbi detector, which is assumed to be synchronized with channel byte boundaries, are shown.

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Rate 8/10 Code for Dicode Channels

A rate 8/10 code for use on dicode channels is described
having a minimum number of states in a Viterbi detection scheme.  It
is a DC free code in which the running digital sum of the channel
input sequence takes on five distinct values.  Because of this
limitation, the code has a k constraint of four.  In Fig. 1, paths
considered by a five state Viterbi detector, which is assumed to be
synchronized with channel byte boundaries, are shown.

   Although there is a sufficient number of sequences
originating from each of the states 0, 1, 2, and 3 to create a rate
8/10 block code, repeated use of some of these sequences would reduce
the minimum distance between sequences as seen by a Viterbi detector
(shown Fig. 1) with a finite length of path memory.  In Fig. 1, the
set of all sequences which originate in states 0 or 1 and remain in
states 2, 3, or 4 is the same as the set of sequences which originate
in states 0 or 1 and remain in states 0, 1, or 2, so that long
parallel paths which do not accumulate distance can degrade the
detector's performance.  If all these sequences were eliminated from
the code, there would be an insufficient number of sequences from
states 0 and 1 to create an 8/10 block code.

   A modified Viterbi detector is shown in Fig. 2 where the
detector effectively partitions the quasi-catastrophic sequences by
eliminating from consideration the set of all sequences which
originate in states 2 or 3 and remain in states...