Coded data generation or conversion – Digital code to digital code converters – To or from run length limited codes
Reexamination Certificate
1998-09-17
2001-11-06
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from run length limited codes
C341S058000
Reexamination Certificate
active
06313764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a demodulating device, demodulating method and transmission medium, and in particular to a demodulating device, demodulating method and transmission medium which are suitable for demodulating a modulation code obtained by modulating data for application to data transmission or recording on a recording medium so as to reproduce data.
2. Description of the Related Art
When data is transmitted on a predetermined transmission path or recorded for example on recording media such as magnetic disks, optical disks, and magneto-optical disks, data modulation is performed which is suitable for the transmission or recording. One such type of modulation is known as block coding. This block coding converts a data sequence to blocks of m×i bit units (referred to hereafter as data words) , and this data word is converted to a code word comprising n×i bits according to a suitable code rule.
When i=1, this code is a fixed length code expressed by (d,k;m,n;1). When plural i are selected, a predetermined i is selected from the range 1 to imax (maximum value of i) and the conversion is performed, the code is a variable-length code. This block encoded code is represented by a variable length code (d,k;m,n;r).
Here, i is known as a restriction length, and imax is r (the maximum restriction length) . The minimum run d shows the minimum number of consecutive “0”s in repeated “1”s in the code sequence. The maximum run k shows the maximum number of consecutive “0”s in repeated “1”s in a code sequence.
In compact disks or mini-discs (trademark) etc., NRZI (Non Return to Zero Inverted) modulation, wherein “1” means inversion and “0” means non-inversion, is performed on the variable length code obtained as above, and the NRZI modulated variable length code (hereafter, referred to as a recorded waveform sequence) is recorded. This recorded waveform sequence will be referred to also as a level code.
When this level code is inverted so that “1” is replaced by “0” or “0” is replaced by “1”, i.e. when reverse NRZI modulation is performed wherein “1” indicates an edge, the same code sequence as the original EFM code or RLL(1-7) code can be obtained. This reverse NRZI code sequence will also be referred to as an edge code.
Various modulation techniques have been proposed. If the minimum inversion interval of the recorded waveform sequence is Tmin and the maximum inversion interval is Tmax, to record at a high density in a linear velocity direction, the minimum inversion interval Tmin should be long, that is, the minimum run d should be large. From the clock reproduction aspect, moreover, the maximum inversion interval Tmax should be short, that is, the maximum run k should be small.
For example, one modulation technique used by magnetic disks or magneto-optical disks, etc., isRLL(2-7) The parameters of this modulation method are (2,7;1,2;3) If the bit interval of the recording waveform sequence is T, the minimum inversion interval Tmin (=(d+1)T) is 3(=2+1)T. If the bit interval of the data sequence is Tdata, this minimum inversion interval Tmin is 1.5(=(m
)xTmin =(½)×3)Tdata. The maximum inversion interval Tmax (=(k+1)T) is 8(=7 +1)T (=((m
)×Tmax)Tdata=(½)×8Tdata =4.0Tdata). A detection window width Tw (=(m
)T)) is 0.5(=½)Tdata.
Another modulation technique used by magnetic disks or magneto-optical disks, etc., is RLL(1-7). The parameters of this modulation method are (1,7;2,3;2). The minimum inversion interval Tmin is 2(=1+1) T (=⅔×2Tdata=1.33Tdata). The maximum inversion interval Tmax is 8(=7+1) T(=(⅔)×8Tdata=5.33Tdata). Further, the detection window width Tw(=(m
)XT) is 0.67(=⅔ data.
Comparing RLL(2-7) and RLL(1-7), for example in a magnetic disk system or magneto-optic disk system, to increase recording density in the linear velocity direction, RLL (2-7) for which the minimum inversion interval Tmin is 1.5 data preferable to RLL(1-7) for which the minimum inversion interval Tmin is 1.33 data. In practice, however, RLL(2-7) which has a larger detection window width Tw than RLL(2-7) and which is said to have a large tolerance to jitter, widely used.
The conversion table for the RLL(1-7) code is, for example, as follows.
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
Herein, the symbol x in the conversion table is given the value 1 when the following channel bit is 0, and given the value 0 when the following channel bit is 1 (same hereafter). The restriction length r is 2.
The conversion table for the RLL(2-7) code for which the minimum run d=2 and the maximum inversion interval Tmax is 8T (maximum run 7), is for example as shown below.
TABLE 2
RLL (2, 7; 1, 2; 3)
Data
Code
i = 1
11
1000
10
0100
i = 2
011
001000
010
100100
000
000100
i = 3
0011
00001000
0010
00100100
The restriction length r is 3.
However, in a channel bit sequence which is modulated by RLL(1-7), the occurrence frequency of 2T which is Tmin is the greatest, followed by 3T and 4T. In general, if many periods occur wherein a large amount of edge information occurs early as in the case of 2T and 3T, this is advantageous for clock reproduction. However, if 2T occurs repeatedly, distortion of the recorded waveform occurs more easily. Specifically, the output waveform amplitude of 2T is small, and easily affected by defocusing or tangential tilt. Further, at a high linear density, recordings wherein the minimum mark is repeated are easily affected by external disturbances such as noise so that data reproduction errors tend to occur.
RLL(1-7) is often combined with PRML (Partial Response Maximum Likelihood), to improve S/N during playback of a high density recording. This method comprises, for example, Viterbi decoding equalized by PR(1,1) or PR(1,2,1) by matching the RF reproduction waveform to media characteristics. For example, a desirable reproduction output when equalization is performed by PR(1,1) is as follows.
1
0
1
0
0
1
0
(channel bit data sequence)
1
1
0
0
1
0
0
(after NRZI conversion)
. . .
. . .
1
1
1
1
−1
−1
−1
−1
1
1
1
1
−1
−1
. . .
. . .
. . .
+2
0
−2
0
+2
0
. . .
(reproduction output)
The data after this NRZI conversion is level data. When the channel bit data is 1, it is given a different value (0 or 1) from the immediately preceding value (1 or 0) , and when the channel bit data is 0, it is given the same value (0 or 1) as the immediately preceding value (0 or 1). In this example, when the value after NRZI conversion is 1, “11” is decoded, and when the value after NRZI conversion is “0”, “-1-1” is decoded. Waveform equalization when 2T which is Tmin is repeated, is performed to obtain this reproduction output. In general, waveform interference becomes longer the higher the linear density, therefore, waveform equalization also becomes longer as in PR(1,2,2,1) or PR(1,1,1,1).
However when the minimum run d=1 and a suitable waveform equalization is PR (1,1,1,1) as a result of high linear density, considering a situation when 2T which is Tmin occurs repeatedly, the reproduced signal at that time is
1
0
1
0
1
0
1
0
1
0
(channel bit data
sequence)
1
1
0
0
1
1
0
0
1
1
(after NRZI conversion)
. . .
. . .
1
1
1
1
1
1
1
1
−1
−1
−1
−1
−1
−1
−1
−1
1
1
1
1
1
1
1
1
−1
−1
−1
−1
. . .
. . .
. . .
0
0
0
0
. . .
(reproduction output).
and the zero level will be traced for a long time.
This shows that a situation when practically no signal level is output after waveform equalization continues, and therefore Viterbi decoding does not merge. This also causes considerable loss of data reproduction or clock reproduction stability.
This kind of channel bit data sequence, for exa
Nakagawa Toshiyuki
Narahara Tatsuya
Shinpuku Yoshihide
Frommer William S.
Frommer & Lawrence & Haug LLP
Jean-Pierre Peguy
Smid Dennis M.
Sony Corporation
LandOfFree
Demodulating device, demodulating method and transmission... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Demodulating device, demodulating method and transmission..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Demodulating device, demodulating method and transmission... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2614151