Coded data generation or conversion – Digital code to digital code converters – To or from run length limited codes
Reexamination Certificate
2002-09-03
2003-10-28
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from run length limited codes
C341S050000
Reexamination Certificate
active
06639525
ABSTRACT:
SUMMARY OF THE INVENTION
Method of converting a stream of databits of a binary information signal into a stream of databits of a constrained binary channel signal, device for encoding, signal comprising a stream of databits of a constrained binary channel signal, record carrier and device for decoding.
The invention relates to a method of converting a stream of databits of a binary information signal into a stream of databits of a constrained binary channel signal, wherein the stream of databits of the binary information signal is divided into n-bit information words, said information words being converted into m
1
-bit channel words in accordance with a channel code C
1
, or m
2
-bit channel words, in accordance with a channel code C
2
, where m
1
, m
2
and n are integers for which it holds that m
2
>m
1
≧n, wherein the m
2
-bit channel word is chosen from at least two m
2
-bit channel words, at least two of which have opposite parities, the concatenated m
1
-bit channel words and the m
2
-bit channel words complying with a runlength constraint of the binary channel signal.
The invention also relates to a device for encoding a stream of databits of a binary information signal into a stream of databits of a constrained binary channel signal. The invention also relates to a signal comprising a stream of databits of a constrained binary channel signal. The invention further relates to a record carrier and to a device for decoding the constrained binary channel signal.
The invention is in the field of channel coding, in particular in runlength limited channel coding. The length of time, expressed in channel bits, between consecutive signal transitions is usually called the runlength. Different constraints can be imposed on a channel code, e.g. resulting in a runlength limited channel code. In such a code, a sequence of channel words is characterized by two parameters, a d-constraint and a k-constraint. In (d,k) domain a logical “one” indicates a transition in the signal waveform. A (d,k) sequence satisfies the following two conditions: due to the d-constraint, two logic “ones” are separated by a run of at least d consecutive “zeroes”; due to the k-constraint two logic “ones” are separated by a run of at most k consecutive “zeroes”. The (d,k) sequence is converted from the (d,k) domain into a runlength-limited (RLL) sequence of the type (d,k) in the RLL domain upon precoding in a 1T precoder. This RLL sequence comprises elements with runlengths (either an array of consecutive zeroes or an array of consecutive ones) of d+1 at minimum and k+1 at maximum between subsequent signal reversals in the information signal. The values of (d+1) and (k+1) indicate the minimum and maximum runlengths of the element allowed in the sequence. It is noted that the term element can be used to indicate both an element of a (d,k) sequence or an element of an RLL sequence. An element is considered to be extending over a runlength in the RLL domain or (d,k) domain.
In runlength limited channel coding, each information word is converted into a channel word according to predefined rules of conversion, these channel words forming a modulated signal.
Research Disclosure,
January 1992, page 32, 33340, discloses a coding method according to which n-bit information words are alternately converted into m
1
-bit channel words and m
2
-bit channel words, where n, m
1
and m
2
are integers and n≦m
1
<m
2
. For each n-bit information word, there are two m
2
-bit channel words available having mutually different disparities. A channel word is selected so that the current running digital sum in the channel signal shows a behaviour in accordance with a desired pattern as a function of time, for example a DC-free coding in the channel signal.
In other words, there are two channel codes involved in the Research Disclosure, one with an n-to-m
1
mapping of information words into channel words, which can be referred to as the main code C
1
, and the other with an n-to-m
2
mapping, with two m
2
-bit channel words, which can be referred to as the dual code C
2
.
The efficiency of a channel code can be expressed by using the (information) rate of the channel code. This rate R of a channel code is defined as the quotient n/m, in which the code translated n binary user (or information) symbols into m binary channel symbols. As explained above, in runlength limited channel coding, the channel words must comply with certain constraints, for example a d-constraint and a k-constraint. Due to these restrictions, the number of bit combinations which may represent the information words is lowered and therefore the rate will decrease.
It is an object of the invention to realize an efficient method of encoding a stream of information words into a constrained stream of channel words.
The method in accordance with the invention is characterized in that the method comprises the repetitive and/or alternate steps of:
selecting the m
1
-bit channel word from a set out of a plurality of sets of m
1
-bit channel words, each set comprising only m
1
-bit channel words having a beginning part out of a subset of beginning parts of the m
1
-bit channel words, each set being associated with a coding state of channel code C
1
, the coding state being established in dependence upon an end part of the preceding channel word,
or:
selecting the m
2
-bit channel word from a set out of a plurality of sets of m
2
-bit channel words, each set comprising only m
2
-bit channel words having a beginning part out of a subset of beginning parts of the m
2
-bit channel words belonging to said set, each set being associated with a coding state of channel code C
2
, the coding state being established in dependence upon an end part of the preceding channel word,
the end parts of the m
1
-bit channel words in a coding state of channel code C
1
and the beginning parts of the m
2
-bit channel words in a set of channel code C
2
being arranged to comply with said runlength constraint.
By repetitively or alternately performing said steps and by arranging the end parts of the m
1
-bit channel words in a coding state of channel code C
1
and the beginning parts of the m
2
-bit channel words in a coding state of channel code C
2
, the beginning parts of the m
2
-bit channel words can be applied to the coding states of channel code C
1
, thereby realizing the constrained binary channel signal; and vice versa when arranging the end parts of the m
2
-bit channel words and the beginning parts of the m
1
-bit channel words.
The invention is based on the recognition that the coding states of two different channel codes can be combined by arranging the beginning parts and the end parts of the channel words of the channel codes, so that end parts in the channel code C1 match with beginning parts of the sets of m
1
-bit channel words, but also with the beginning parts of the sets of m2-bit channel words. A multiple-state description of encoder and decoder yields channel codes with high efficiency or information rate.
Another method according to the invention is characterized in that the number of coding states of channel code C
1
is equal to the number of coding states of channel code C
2
.
In the case where for the dual code C
2
, two m
2
-bit channel words with opposite parity can be used for each n-bit information word, it is possible to use these channel words for influencing predetermined properties of the binary channel signal. In order to be able to comply with the constraints of the constrained stream of channel words, it is advantageous that the end parts of the m
1
-bit channel words in a coding state of channel code C
1
and the beginning parts of the m
2
-bit channel words in a coding state of channel code C
2
are arranged that the number of coding states of channel code C
1
is equal to the number of coding states of channel code C
2
. In this way, the coding tables can be limited. Parts of the coding states of channel code C
1
can for example be similar or equal to parts of the coding states of channel code C
2
. This results in an
Belk Michael E.
Jean-Pierre Peguy
Koninklijke Philips Electronics , N.V.
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