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Method For DC Suppression without Violating the Run-Length Constraints

IP.com Disclosure Number: IPCOM000111598D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 106K

Publishing Venue

IBM

Related People

Ashley, J: AUTHOR [+3]

Abstract

A binary (d,k) run-length limited (RLL) sequence is a sequence over the alphabet [0,1], wherein any two consecutive occurrences of 1 are separated by at least d and, at most, k zeros. The running digital sum (RDS) of such a sequence 'b' sub 1 'b' sub 2 ellipsis 'b' sub 'n' is calculated as follows. The sequence is parsed as 'w' sub 0 'w' sub 1 ellipsis 'w' sub m, where 'w' sub 0 is a run of scriptl sub 0 'O' apos 's', and for 'i' gt O, 'w' sub i" is a 1 followed by scriptl sub 'i' - 1 O's. The RDS of the sequence is then given by sum sup 'm' above lparen emdash 1 rparen sup 'i' scriptl sub 'i'. As is well-known, keeping the RDS of a sequence bounded eliminates the DC content of the sequence. The smaller the bound on the absolute value of the RDS, the less power will the sequence have a low frequencies.

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Method For DC Suppression without Violating the Run-Length Constraints

      A binary (d,k) run-length limited (RLL) sequence is a sequence
over the alphabet [0,1], wherein any two consecutive occurrences of 1
are separated by at least d and, at most, k zeros.  The running
digital sum (RDS) of such a sequence 'b' sub 1 'b' sub 2 ellipsis 'b'
sub 'n' is calculated as follows.  The sequence is parsed as 'w' sub
0 'w' sub 1 ellipsis 'w' sub m, where 'w' sub 0 is a run of scriptl
sub 0 'O' apos 's', and for 'i' gt O, 'w' sub i" is a 1 followed by
scriptl sub 'i' - 1 O's.  The RDS of the sequence is then given by
sum sup 'm' above <sub 'i' eqsym 'o'> lparen emdash 1 rparen sup 'i'
scriptl sub 'i'.  As is well-known, keeping the RDS of a sequence
bounded eliminates the DC content of the sequence.  The smaller the
bound on the absolute value of the RDS, the less power will the
sequence have a low frequencies.

      A method of suppressing the DC content of run-length limited
sequences, without violating the run-length constraints, is proposed
in [*].  Specifically, it is proposed in [*] to insert two redundant
bits at regular intervals in a (1,7) RLL sequence.  The inserted bits
re-direct the RDS of the following block of data, while maintaining
the (1,7) run-length constraint.  Two alternative algorithms for this
purpose are presented herein.  The first algorithm inserts 4
redundant bits at regular intervals in the (1,7) sequence.  The
scheme is much simpler than the scheme of [*], and, furthermore, it
increases error propagation in the modulation decoder by, at most, 1
bit.  In [*]  only 2 bits are inserted, but as many as 8 data bits on
either side of the insertion are altered to maintain the (1,7)
run-length constraint.  This results in greater error propagation and
greater encoder and decoder complexity than the proposed scheme has.
The second algorithm inserts 6 bits, and so it is perhaps more suited
to a rate 2 :3 (1,7) code.  Furthermore, this second algorithm does
not increase decoder error propagation at all.  I should be pointed
out that the two insertion algorithms described below have the
additional advantage of being easily generalizable to any (d,k)
run-length constraints, whereas similar generalization of the method
of [*]  is not entirely obvious.

      The first algorithm which allows re-direction of the RDS by
inserting 4 redundant bits is now described.  The description of the
algorithm is put forth in the context of a practical situation common
to most magnetic and/or optical recording systems, wherein sectors of
data (the data area) are followed by resynchronization blocks.
Suppose the RDS of the (1...