Pulse or digital communications – Pulse code modulation – Length coding
Reexamination Certificate
1998-12-09
2002-03-19
Pham, Chi (Department: 2631)
Pulse or digital communications
Pulse code modulation
Length coding
C341S059000
Reexamination Certificate
active
06359930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a modulation device and method, and a distribution medium, and more particularly relates to a modulation device and method, and a distribution medium which are capable of data modulation and DSV control simultaneously so as to be suitable for data transmission and recording in recording media.
2. Description of Related Art
When data is transmitted to a desired transmission line, or for example, data is recorded in a recording medium such as a magnetic disc, optical disc, or magneto-optical disc, the data is modulated so as to be suitable for transmission and recording. The block code has been known as one of such modulation methods. In the block coding, a data string is divided into units composed of m×i bits (referred to as a data word hereinafter), and the data word is converted into the code word composed of n×i bits according to a suitable code rule. The code is a fixed length code if i=1, and the code is a variable length code if a plurality of i can be selected, that is, if a data string is converted using prescribed i in a range from 1 to i-max (maximum i). The block coded code is represented as a variable length code (d, k; m, n; r).
Herein i is referred as a limited length, i-max is r (maximum limited length). d is the minimum consecutive number of “t0” inserted between consecutive “1”, for example, the minimum run of 0, k is the maximum consecutive number of “0” inserted between consecutive “1”, for example, the maximum run of 0.
When the variable length code obtained as described herein above is recorded, for example, in an optical disc or magneto-optical disc, in the case of a compact disc or minidisc, NRZI (Non Return to Zero Inverted) modulation in which “1” of a variable length code is inverted and “0” is not inverted is performed, and recording is performed based on NRZI modulated variable length code (referred to as a recording waveform string hereinafter). Alternatively, like the magneto-optical disc of ISO standard, there is also provided a system in which recording modulated bit strings are recorded as it is without NRZI modulation.
Assuming that the minimum inversion interval of a recording waveform string is Tmin and the maximum inversion interval of a recording waveform string is Tmax, in order to perform high density recording in the linear speed direction, the longer minimum inversion interval Tmin is preferable, in other words, the smaller maximum run k is preferable, and various modulation method has been proposed.
In detail, there are provided variable length RLL (1-7), fixed length RLL (1-7), and variable length RLL (2-7) as the modulation system proposed, for example, for the optical disc, magnetic disc, or magneto-optical disc.
An example of the variable length RLL (1-7) conversion table is shown herein under:
TABLE 1
RLL (1, 7; 2, 3; 2)
data
code
i=1
11
00x
10
010
01
10x
i=2
0011
000 00x
0010
000 010
0001
100 00x
0000
100 010
The character x in the conversion table is 1 if the subsequent channel bit is 0; otherwise the character x is 0 if subsequent channel bit is 1. The limited length r is 2.
The parameter of the RLL (1-7) is (1, 7; 2, 3; 2), the bit interval of a recording waveform string is assumed as T, then the minimum inversion interval Tmin is 2 (=1+1) T. Further, the bit interval of a data string is assumed as Tdata, then the inversion interval Tmin is 33 (=(⅔)×2) Tdata, and the maximum inversion interval Tmax is 8T (5.33 Tdata). Further, the detection window width Tw is represented by (m
)×Tdata, the value is 0.67 (=⅔) Tdata.
As for the channel bit string modulated according to RLL (1-7), 2T namely Tmin most often occurs, followed by 3T and 4T. Often occurrence of edge information such as 2T and 3T with short period is favorable to clock reproduction, but often occurrence of 2T causes skew of the recording waveform. In other words, the waveform output is small and becomes sensitive to defocus and tangential tilt. Further, in the case of high density recording, recording in which the minimum mark occurs consecutively is sensitive to disturbance such as noise, data reproduction error is apt to occur.
The inventors of this invention proposed previously the code to limit the consecutive occurrence of Tmin in Japanese Patent Publication No. Hei 9-256745. This code is referred to as a RML code (Repeated Minimum run-length Limited code).
In this proposal, assuming that the variable length code (d, k; m, n; r) is a variable length code (1, 7; 2, 3; 3), in other words, the 0 minimum run d is 1 bit, the 0 maximum run k is 7 bits, the base data length m is 2 bits, the base code length n is 3 bits, and the maximum limited length r is 3, then the conversion table is shown in Table 2 herein under.
TABLE 2
RLL-P (1, 7; 2, 3; 3)
data
code
i=1
11
00x
10
010
01
10x
i=2
0011
000 00x
0010
000 010
0001
100 00x
0000
100 010
i=3
100110
100 000 010
Herein, the limited length is 3.
In the case that the data string is “10” in Table 2 as described herein above, particularly in the case that the total 6 data string is “100110” with reference to the following 4 data, by giving a special corresponding code as the code for limiting repetition of the minimum run, repetition of the minimum run is limited at most to 5 times in modulation according to Table 2.
By applying this method, processing for high linear density recording/reproduction of data is stabilized.
When data are recorded in a recording medium or data are transmitted, coding modulation suitable for each medium (transmission) is performed, in the case that a direct current component is included in these modulated codes, for example, fluctuation of various error signals such as tracking error in servo controlling of a disc device is apt to occur, and jitter is apt to occur. Therefore, it is desirable that the direct current component is contained as little as possible.
The modulated code in the variable length RLL (1-7) table and RML (1-7) table described herein above is not subjected to DSV control. In such case, DSV control is performed by inserting the prescribed DSV control bit in the coded string (channel bit string) with a prescribed interval.
A digital sum value (DSV) control means the sum obtained by the operation in which the channel bit string is subjected to NRZI modulation (namely level coding), and codes are added in the manner that “1” of a bit string (symbol of the data) is regarded as +1 and “0” is regarded as −1. DSV is a measure of direct current component of the code string, and the reduced absolute value of DSV indicates the suppressed direct current component of the code string.
The DSV control bit can be 2 (1+1)=4 bits in the case of 2×(d+1) namely d=1. When, the minimum run and the maximum run are maintained with an arbitrary interval, and perfect DSV control in which inversion and non inversion are possible is performed.
However, DSV control bit is basically the redundant bit. Therefore, the number of DSV control bits is desirably as small as possible in view of the code conversion efficiency.
For example, in the case that the control bit is 1×(d+1) namely d=1, 1×(1+1)=2 bits may be possible. In this case, perfect DSV control in which inversion and non inversion are possible is performed with an arbitrary interval. However, though the minimum run is maintained, the maximum run increases to (k+2). As for the code, the minimum run should be maintained without exception, but the maximum run is maintained not necessarily. Depending on the case, the format having the pattern which breaks the maximum run used as the sync signal has been known. For example, the maximum run of EFM plus of DVD is 11T, but 14T is allowed to be favorable for the format.
It is required that control bit for DSV control is inserted with an arbitrary interval in RLL (1-7) codes or RML (1-7) codes which are not subjected to DSV control out of RLL codes
Nakagawa Toshiyuki
Shimpuku Yoshihide
Frommer William S.
Frommer & Lawrence & Haug LLP
Kessler Gordon
Nguyen Dung X.
Pham Chi
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