Coded data generation or conversion – Digital code to digital code converters – Coding by table look-up techniques
Reexamination Certificate
2001-10-26
2002-12-10
Young, Brian (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
Coding by table look-up techniques
C341S058000, C341S059000, C369S059240
Reexamination Certificate
active
06492920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a modulation method, modulator, transmission apparatus and recording medium, and more particularly to a modulation method and modulator in which a p-bit input data word is converted to a q-bit (q>p) code word using plural coding tables so as to intensify coding rate accompanied by increased density and a code word string is produced by coupling the code words directly, and a transmission apparatus for transmitting the code word string and a recording medium in which the code word string is recorded.
2. Description of the Related Art
Generally, the pit length to be recorded in an optical disk has a restriction about the minimum run length (minimum pit or land length) due to optical transmission characteristic for recording and reproduction and physical restraint relating to pit generation and further, a restriction about the maximum run length (maximum pit or land length) for the reason of facilitation of clock generation. Further, because of protection of a servo band and the like, it is necessary to modulate digital signals to be recorded so as to have a suppression characteristic for low-pass components thereof.
As a conventional modulation method which satisfies these restrictions in which the minimum run length is 3T (T is a period of channel bit herein after) and the maximum run length is 11T, EFM (
8
to
14
modulation) method used in compact disk (CD), EFM+ method used in digital versatile disk (DVD) and the like have been well known.
In the EFM modulation used for compact disk (CD), inputted 8-bit (1 byte) digital data is converted to 14-bit run length limited code (RLL code) which satisfies a run length restriction such that its minimum run length is 3T while its maximum run length is 11T and further, 3-bit connection bit for digital sum value (DSV) control and run length restriction rule holding is attached between the converted code words so as to generate EFM modulated signals.
Regarding the minimum run length of 3T, at least two “0”s (number d of “0”) are included between logical values “1” and “1” in code words, while regarding the maximum run length of 11T, 10 “0”s maximum (number k of “0”) are included between logical values “1” and “1” in code words. The 3-bit connection bit provided for DSV control and run length restriction rule holding in order to reduce DC component and low-pass component of the modulated signal is connected between the 14-bit code words, so that the EFM modulated signal can satisfy the run length restriction rule RLL(d, k)=RLL(
2
,
10
) that the minimum run length is 3T while the maximum run length is 11T.
Next, in the EFM+ method used for digital versatile disk (DVD), inputted 8-bit digital data is converted to a 16-bit code word and by connecting these code words directly without use of any connection bit, 8 to 16 modulation is executed so as to satisfy the run length restriction rule RLL(
2
,
10
) that the minimum run length is 3T while the maximum run length is 11T.
Further, such a modulation method which has a higher coding rate in order to achieve a higher density recording and satisfies a run length restriction rule that the minimum run length is 3T while the maximum run length is 11T has been proposed in Japanese Patent Application Laid-Open No.2000-286709 by this applicant. According to the modulation method proposed by this applicant, for example, seven coding tables are employed for an inputted digital signal (inputted data word) in order to convert the inputted digital signal to a code word. These seven coding tables have code words corresponding to the inputted digital signal and status information for selecting a coding table for encoding a next digital signal. Signals obtained by NRZI-modulating a code word based on a specific coding table for a predetermined input digital signal and a code word based on another specific coding table have opposite polarities (even/odd parities of “1” are different). Consequently, for example, it is possible to convert the 8-bit data to 15-bit code word while controlling its digital sum value (DSV).
FIG.1
shows major portions of the aforementioned seven coding tables. The seven coding tables corresponding to seven statuses, status “0” to status “6” shown in the same Figure store the code word (that is, output code word after conversion) and status information indicating a coding table for use in modulating next inputted data in order to obtain a next code word which satisfies a predetermined run length restriction rule (for example, minimum run length is 3T and maximum run length is 11T) even if it is coupled with the aforementioned code word directly, corresponding to an input word. Code words corresponding to each predetermined input word are determined such that signals obtained by NRZI-converting the respective code words have polarities opposite to each other. That is, the quantities of “1” in respective code words corresponding to a predetermined input word have an even/odd relation such that the number of “1” in one code word is even while that in the corresponding code word is odd, thereby enabling the DSV control.
Although the aforementioned 16-bit code word EFM+ method can increase the coding rate by about 6% as compared to the EFM method based on 17-bit code word including a margin bit, it is desirable to improve the coding rate further in order to achieve a higher density recording.
Accordingly, the applicant proposes a modulation method which achieves a higher coding rate than the aforementioned EFM+ method while suppressing the low-pass component of a recorded signal with allocation of the code words without use of the margin bit between the code words through the aforementioned Japanese Patent Application Laid-Open No.2000-286709. However, because the number of the coding tables affects the scale of hardware upon constructing the modulator, the conventional modulator mentioned in this publication has such a problem that the scale of the hardware is too large because the seven coding tables are employed.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been achieved in views of the above described problems and an object of the invention is to provide a modulation method, modulator, transmission apparatus and recording medium capable of achieving such modulation for obtaining a q-bit (q>p) code word from a p-bit inputted data word while a predetermined run length restriction rule is satisfied, with a small scale hardware using fewer coding tables than conventionally.
Further, another object of the present invention is to provide a modulation method, modulator, transmission apparatus and recording medium capable of further suppressing low-pass components in modulated signals in the 8-15 modulation method using no margin bit between the codes, by optimizing the coding table based on information about appearance frequency of input data words so as to achieve a DSV control with higher performance.
To achieve the above object, according to a first aspect of the present invention, there is provided a modulation method for performing a modulation to obtain a q-bit code word from a p-bit input data word (q>p) using plural coding tables, wherein the plural coding tables comprise six coding tables each storing a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; and in a specific coding table and another specific coding table of the six coding tables, code words stored corresponding to each predetermined input data word are determined to have an even/odd relation such that the number of “1” in a code word in the specific coding table is even while the number of “1” in a code word in the other specific coding table is odd so as to enable DSV control; and upon modulating the predetermined input data
Hayami Atsushi
Oki Tsuyoshi
Berkowitz Marvin C.
Nath Gary M.
Nguyen John
Novick Harold L.
Victor Company of Japan , Limited
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