Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal gain processing
Reexamination Certificate
1998-03-27
2001-04-17
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal gain processing
Reexamination Certificate
active
06219320
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a recording and reproducing system for recording and reproducing digital information signal in a recording medium such as CD and an equalizing method for use in it. More particularly, it concerns a recording and reproducing system and an equalizing method for use in it that makes it possible to increase recording density of digital information signal without changing parameters inherent to a recording medium.
Conventionally, the art of such a technique has been disclosed in, for example, “Association of Television Technology”, Vol. 42, No. 4 (April, 1988), pp. 330-337. The prior art is described below.
A digital information signal to be recorded in a recording medium, such as a CD, is modulated by a run length limited (hereinafter referred to as the RLL) coder with use of the so-called (d, k) RLL code of minimum run length d and maximum run length k before being recorded. The signal reproduced from the recording medium is equalized by an equalizer before being decoded to the original digital information signal by a decoder to feed out.
FIG. 9
shows a frequency response M(f) of the RLL coder and a general overall transmission frequency response H(f) of the RLL decoder, the recording medium, and the equalizer. Curves (a) and (b) in the figure indicate the frequency response M(f) and the overall transmission frequency response H(f), respectively. Fb, Fn, and Fm in the figure indicate a recording bit rate after the modulation, a Nyquist frequency (=(Fb/d)/2), and a cut-off frequency of the recording medium 3, respectively. In general, the frequency response E(f) of the equalizer is set so that as shown by curve (b), the overall transmission frequency response H(f) should become a raised cosine characteristic (100% roll-off factor) of a Nyquist frequency Fn. The recording bit rate Fb therefore can be increased until bandwidth B (=2·Fn) of the overall transmission frequency response H(f) become the cut-off frequency Fm. Hence, the recording bit rate Fb is given with respect to the cut-off frequency Fm as
Fb=d·Fm (1)
FIG. 10
shows an eye pattern of the output signal of the equalizer
4
with the minimum run length d being 3. If the recording medium
3
is an optical disk, the cut-off frequency Fm of the recording medium
3
is given by an equation below:
Fm
≈
2
·
V
·
NA
λ
(
2
)
where &lgr; denotes a wavelength of laser, NA is a numerical aperture of an optical system, and V is a linear velocity of the recording medium.
As an example, a CD system with the minimum run length d of 3 can be made to have the recording bit rate Fb of around 4.32 Mbps and the bandwidth B of around 1.44 MHz. From Eq. 2, the cut-off frequency Fm becomes around 1.44 MHz that is equal to the bandwidth B if the wavelength &lgr; of the laser is 0.78 &mgr;m, the numerical aperture NA of the optical system is 0.45, and the linear velocity of the optical disk is 1.25 m/sec.
SUMMARY OF THE INVENTION
In general, the recording density of digital information signal can be increased by way of changing parameters of the recording medium, such as the wavelength &lgr; of the laser of the optical disk, and parameters of the RLL code, such as minimum run length d. However, it has not been known how to increase the recording density further, or how to increase it without changing those parameters.
If it is tried to increase the recording density without changing the parameters of the recording medium and those of the RLL code with use of the prior art described above, the following problems arise, which are described with reference to
FIGS. 11 and 12
.
In
FIG. 11
, curve (a′) indicates a frequency response M(f) of the RLL coder
2
, curve (b′) is an overall frequency response H(f), K is a coefficient of recording density increment, Fb′ is a recording bit rate (=K·Fb′), and Fn′ is a Nyquist frequency (=(Fb′/d)/2=K·Fn). Of course, the cut-off frequency Fm of the recording medium is constant since the parameters of the recording medium and the RLL code are unchangeable. With respect to the prior art, the frequency response E(f) of the equalizer is set so that as shown by curve (b′), the transmission frequency response H(f) should become a roll-off raised cosine characteristic of a Nyquist frequency Fn′. That is, the bandwidth B of the transmission frequency response H(f) is-limited by the cut-off frequency Fm, and the roll-off factor &bgr; is decreased with the coefficient K. Such relationships are given by
B=(1+&bgr;)·Fn′=(1+&bgr;)·K·Fn Fm=2·Fn
Hence,
∴
β
=
2
K
-
1
(
3
)
If the coefficient K in Eq. 3 above is 1.5, or if the recording density is increased 1.5 times, the roll-off factor &bgr; is decreased to 33.3%. If the minimum run length d is 3, the eye pattern of the output signal of the equalizer becomes the one as shown in
FIG. 12
, resulting in that an open area ratio of the eye pattern is deteriorated to a great extent.
As described above, the prior art has the open area ratio of the eye pattern deteriorated if trying to increase the recording density with the parameters of the recording medium and the RLL code made constant. This does not allow making a signal-to-noise ratio high. The system of the prior art therefore is likely affected by noises. That is, it is difficult that the prior art increases the recording density further with the parameters of the recording medium and the RLL code made constant.
In view of the foregoing, it is an object of the present invention to solve the problems of the prior art to provide a recording and reproducing system that makes it possible to increase recording density of digital information signal further without changing parameters of a recording medium and a RLL code and an equalizing method for use in it.
Briefly, the foregoing object is accomplished in accordance with aspects of the present invention by the recording and reproducing system, comprising a RLL coder for modulating a digital information signal to be recorded in a recording medium with use of a run length limited code having a minimum run length d, an equalizer for equalizing a signal reproduced from the recording medium, and a decoder for decoding a signal equalized by the equalizer to the original digital information signal, wherein a frequency response of the equalizer is set so that a transmission frequency characteristic H(f) of the RLL coder, the recording medium, and the equalizer to an impulse becomes the one given by Eq. 4 below
H
(
f
)
=
cos
(
π
2
·
f
Fm
)
(
4
)
where Fm denotes a cut-off frequency of the recording medium that is given by Eq. 5 below
Fm
=
Fb
d
·
k
(
5
)
With the frequency response of the equalizer is set as such, virtually all the isolated pulses are overlapped together from the minimum run length d to the maximum run length k. This gives little interference among the pulses even if the pulses come at random. The equalizing method of the present invention therefore provides sufficient open area ratio of eye pattern even with the recording density made high, or the recording density can be made high without lowering the signal-to-noise ratio.
REFERENCES:
patent: 5122912 (1992-06-01), Kanata et al.
patent: 5371771 (1994-12-01), Kim
patent: 5442615 (1995-08-01), Ohsato et al.
patent: 5488591 (1996-01-01), Kobayashi et al.
patent: 5537112 (1996-07-01), Tsang
patent: 5561647 (1996-10-01), Kayanuma
patent: 5563854 (1996-10-01), Kobunaya et al.
patent: 5563864 (1996-10-01), Kobayashi et al.
patent: 5579003 (1996-11-01), Hirayama et al.
patent: 5644307 (1997-07-01), Fukuda
patent: 5699061 (1997-12-01), Shimpuka
patent: 5740141 (1998-04-01), Sano et al.
patent: 5-28504 (1993-02-01), None
“AV Products with Digital Technology”, Corona Publishing Co., Ltd., Tokyo Japan, 1986.
“Development of a High Density Optical Disc System Employing Digital Compression MPEG1”, Pioneer Technical Report, No. 9, 1994, pp. 1-15.
“
Amada Nobutaka
Arai Takao
Takeuchi Toshifumi
Antonelli Terry Stout & Kraus LLP
Hindi Nabil
Hitachi , Ltd.
LandOfFree
Recording and reproducing system and equalizing method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Recording and reproducing system and equalizing method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Recording and reproducing system and equalizing method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2463166