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An Almost Symmetric (0,3/6) PRML Code

IP.com Disclosure Number: IPCOM000036640D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 100K

Publishing Venue

IBM

Related People

Marcus, B: AUTHOR [+2]

Abstract

Partial-response signaling with maximum-likelihood sequence estimation (which we denote by PRML) is a technique, using amplitude detection, which has been investigated for high density magnetic recording of digital data. The technique combines partial-response class IV signaling with maximum likelihood detection in the form of a Viterbi (Image Omitted) decoder. There is a need for constrained codes in this context: to improve timing and gain control, as well as to limit the path memory of the Viterbi decoder. In the presence of an inverse-channel precoder, the input sequences are the same as the output constrained sequences, and hence the simple run-length constraints at the output directly transfer to the input sequences.

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An Almost Symmetric (0,3/6) PRML Code

Partial-response signaling with maximum-likelihood sequence estimation (which we denote by PRML) is a technique, using amplitude detection, which has been investigated for high density magnetic recording of digital data. The technique combines partial-response class IV signaling with maximum likelihood detection in the form of a Viterbi

(Image Omitted)

decoder. There is a need for constrained codes in this context: to improve timing and gain control, as well as to limit the path memory of the Viterbi decoder. In the presence of an inverse-channel precoder, the input sequences are the same as the output constrained sequences, and hence the simple run-length constraints at the output directly transfer to the input sequences. The PRML channel constraints, in that case, take the form of limiting the maximum run length of zeros in two ways: the maximum run length of zeros is k in the over-all recorded sequence, and is k1 in the sequences of all-odd or all-even digit positions. The corresponding code is called a (d,k/ k1) code where the minimum run length d of zeros is usually 0 in case of a partial-response class IV channel. Further discussion of constrained codes for PRML can be found in 1.

In 2, logic equations are given for a rate 8/9 (0,4/4) code and a rate 8/9 (0,3/6) code. Both of these codes are block codes. The (0,4/4) code has the property that the code is "read-backward" symmetric, which is reflected in the fact that the logic equations are symmetric with respect to reversal of the order of the input variables x1, ..., x8 and the output variables y1, ..., y9 . Symmetry in the logic equat...