Coded data generation or conversion – Digital code to digital code converters – Adaptive coding
Reexamination Certificate
2001-03-22
2003-10-28
Huynh, Kim (Department: 2182)
Coded data generation or conversion
Digital code to digital code converters
Adaptive coding
C341S059000, C341S106000, C710S066000, C710S068000
Reexamination Certificate
active
06639524
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coding information, and more particularly, to a method and apparatus for coding information having improved information density. The present invention further relates to producing a modulated signal from the coded information, producing a recording medium from the coded information, and the recording medium itself. The present invention still further relates to a method and apparatus for decoding coded information, and decoding coded information from a modulated signal and/or a recording medium.
2. Description of the Background Art
When data is transmitted through a transmission line or recorded onto a recording medium such as a magnetic disc, an optical disc or a magneto-optical disc, the data is modulated into code matching the transmission line or the recording medium prior to the transmission or recording.
Run length limited codes, generically designated as (d, k) codes, have been widely and successfully applied in modern magnetic and optical recording systems. Such codes, and means for implementing such codes are described by K. A. Schouhamer Immink in the book entitled “Codes for Mass Data Storage Systems” (ISBN 90-74249-23-X, 1999). Run length limited codes are extensions of earlier non return to zero recording codes, where binary recorded “zeros” are represented by no (magnetic flux) change in the recording medium, while binary “ones” are represented by transitions from one direction of recorded flux to the opposite direction.
In a (d, k) code, the above recording rules are maintained with the additional constraints that at least d “zeros” are recorded between consecutive “ones”, and no more than k “zeros” are recorded between consecutive “ones”. The first constraint arises to obviate intersymbol interference occurring because of pulse crowding of the reproduced transitions when a series of “ones” are contiguously recorded. The second constraint arises to ensure recovering a clock from the reproduced data by “locking” a phase locked loop to the reproduced transitions. If there is too long an unbroken string of contiguous “zeros” with no interspersed “ones”, the clock regenerating phase-locked-loop will fall out of synchronism. In, for example, a (2,7) code there is at least two “zeros” between recorded “ones”, and there are no more than seven recorded contiguous “zeros” between recorded “ones”.
The series of encoded bits is converted, via a modulo-2 integration operation, to a corresponding modulated signal formed by bit cells having a high or low signal value. A “one” bit is represented in the modulated signal by a change from a high to a low signal value or vice versa, and a “zero” bit is represented by the lack of change in the modulated signal.
The information conveying efficiency of such codes is typically expressed as a rate, which is the quotient of the number of bits (m) in the information word to the number of bits (n) in the code word (i.e., m
). The theoretical maximum rate of a code, given values of d and k, is called the Shannon capacity.
FIG. 1
tabulates the Shannon capacity C(d,k) for d=2 versus k. As shown, for a (2,7) code, the Shannon capacity, C(2,7), has a value of 0.5174. This means that a (2,7) code cannot have a rate larger than 0.5174. The practical implementation of codes requires that the rate be a rational fraction, and to date the above (2,7) code has a rate ½. This rate of ½ is slightly less than the Shannon capacity of 0.5174, and the code is therefore a highly efficient one. To achieve the ½ rate, 1 unconstrained data bit is mapped into 2 constrained encoded bits.
(2,7) codes having a rate of ½ and means for implementing associated encoders and decoders are known in the art. U.S. Pat. No. 4,115,768 entitled “Sequential Encoding and Decoding of Variable Word Length, Fixed Rate Data Codes”, issued in the names of Eggenberger and Hodges, discloses an encoder whose output sequences satisfy the imposed runlength constraints.
However, a demand exists for even more efficient codes so that, for example, the information density on a recording medium or over a transmission line can be increased.
SUMMARY OF THE INVENTION
In the converting method and apparatus according to the present invention, m-bit information words are converted into n-bit code words at a rate greater than ½. Consequently, the same amount of information can be recorded in less space, and information density increased.
In the present invention, n-bit code words are divided into a first type, a second type and a third type, and into coding states of a first kind, a second kind and a third kind such that an m-bit information word is converted into an n-bit code word of the first, second or third kind if the previous m-bit information word was converted into an n-bit code word of the first type and is converted into an n-bit code word of the first or third kind, if the previous m-bit information word was converted into an n-bit code word of the second type and is converted into an n-bit code word of the first kind, if the previous m-bit information word was converted into an n-bit code word of the third type. Further, sets of code words belonging to the different coding states do not contain any code words in common. In one embodiment, n-bit code words of the first type end in “00”, n-bit code words of the second type end in “10”, n-bit code words of the third type end in “01”, n-bit code words belonging to the states of the first kind start with “00”, n-bit code words belonging to the states of the second kind start with “00”, “01” or “10”, and n-bit code words belonging to the states of the third kind start with “00” or “01”. Furthermore, in the embodiments according to the present invention, the n-bit code words satisfy a dk-constraint to (2,k) such that a minimum of 2 zeros and a maximum of k zeros falls between consecutive ones.
In other embodiments of the present invention, the coding device and method according to the present invention are employed to record information on a recording medium and create a recording medium according to the present invention.
In still other embodiments of the present invention, the coding device and method according to the present invention are further employed to transmit information.
In the decoding method and apparatus according to the present invention, n-bit code words created according to the coding method and apparatus are decoded into m-bit information words. The decoding involves determining the state of a next n-bit code word, and based on the state determination, the current n-bit code word is converted into an m-bit information word.
In other embodiments of the present invention, the decoding device and method according to the present invention are employed to reproduce information from a recording medium.
In still other embodiments of the present invention, the decoding device and method according to the present invention are employed to receive information transmitted over a medium.
REFERENCES:
patent: 4115768 (1978-09-01), Eggenberger et al.
patent: 4410877 (1983-10-01), Carrasso et al.
patent: 4517552 (1985-05-01), Shirota et al.
patent: 5696505 (1997-12-01), Schouhamer et al.
patent: 6084356 (2000-07-01), Arts
patent: 0745254 (1998-04-01), None
Birch & Stewart Kolasch & Birch, LLP
Huynh Kim
LG Electronics Inc.
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