Dynamic information storage or retrieval – Binary pulse train information signal – Including sampling or a/d converting
Reexamination Certificate
2001-05-22
2004-08-03
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Binary pulse train information signal
Including sampling or a/d converting
C369S047350
Reexamination Certificate
active
06771580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to data reproduction apparatuses for reproducing recorded data from media such as optical disks, and more particularly to a data reproduction apparatus for reproducing data from a reproduced signal from a recording medium recorded with data in accordance with a recording signal of a partial response waveform.
2. Description of the Related Art
For instance, attempts have been made to use a magneto-optical disk unit, which is a data reproduction apparatus, in a variety of fields such as the recording and reproduction of image information and various code data for computers because of its large capacity, low price, and high reliability. Such a magneto-optical disk unit is expected to have a larger capacity, and is required to record data with high density and reproduce the data with high accuracy.
Proposed as a method of recording and/or reproducing data with high accuracy is a technique to detect maximum likelihood (ML) data by using a maximum likelihood data detector such as a Viterbi detector after sampling at a given sampling frequency a reproduced signal from a magneto-optical disk recorded with a recording signal obtained by modulating data to be recorded into a so-called partial response (PR) waveform.
Such a Viterbi detector has a structure shown in FIG.
1
.
In
FIG. 1
, a Viterbi detector
100
includes a branch metric calculation unit (hereinafter referred to simply as a BM)
101
, an Add-Compare-Select unit (hereinafter referred to simply as an ACS)
102
, a path metric memory (hereinafter referred to simply as a PMM)
103
, and a path memory (hereinafter referred to simply as a PM)
104
.
In the Viterbi detector
100
that is applied to the data reproduction system of a magneto-optical disk unit, a sampled value yt of a reproduced signal from the magneto-optical disk is supplied to the BM
101
, and the BM
101
calculates a branch metric value (hereinafter referred to simply as a BM value) that is a difference between the sampled value yt and each expected value. The expected values, which depend on a partial response waveform used in data recording, are values that the reproduced signal is expected to take correctly. The BM value is calculated with respect to each expected value when the one sampled value yt is supplied to the BM
101
.
The ACS
102
adds the BM values to path metric values (hereinafter referred to simply as PM values) of a preceding clock timing, and compares each given two of obtained PM values. Then, as a result of the comparisons, the ACS
102
selects the smaller of each given two PM values as a new PM value, and stored the selected PM values in the PMM
103
. As a result of such a process, BM values are accumulated to be the PM values. Selecting the smaller of each given two PM values as previously described corresponds to selecting a state transition path. That is, the ACS
102
always selects a state transition path that minimizes the PM value.
Data (binary data) corresponding to the paths selected in the above-described manner is supplied from the ACS
102
to the PM
104
. The PM
104
shifts the data corresponding to the selected paths successively, and in the process, discards data corresponding to paths determined unselected based on the continuity of state transition. Then, the PM
104
outputs data corresponding to a survivor path as detected data.
As previously described, by detecting the maximum likelihood data by using the Viterbi detector
100
as well as modulating recording data into a recording signal having a partial response waveform and recording the recording signal on the magneto-optical disk, data recorded with high density on the magneto-optical disk is reproduced therefrom with high accuracy. Such a recording and reproduction technique is called a partial response maximum likelihood (hereinafter referred to simply as PRML) technique.
For instance, in the case of recording, in accordance with a PR(1, 1) waveform, a magneto-optical disk with a signal obtained by modulating data of the 1T sequential pattern “10101010 . . . ”, sampled values of a signal reproduced from the magneto-optical disk are as shown in FIG.
2
. That is, since a recording signal based on PR(1, 1) corresponds to a bit string obtained by adding the bit string of the data and the bit string of the data shifted by one bit (1+D), the sampled values of the reproduced signal corresponding to the recording signal are “00001111110000000” as shown in
FIG. 2
when the data is “00001010100000000”.
In the case of inputting the sampled values shown in
FIG. 2
to the Viterbi detector
100
of
FIG. 1
, the paths selected in the ACS
102
and states has a relation shown in FIG.
3
.
In
FIG. 3
, the states are indicated by circles and the state transition paths are indicated by arrows. In this case, each state is either 0 or 1, and the state transition paths are classified into four types: state 0 to state 0, 0 to 1, 1 to 0, and 1 to 1. A solid arrow indicates a path to state 1, and a dotted arrow indicates a path to state 0.
In the PM
104
, the paths selected in the ACS
102
are discarded one after another so that a survivor path is determined. For instance, in (2) through (9) of a time series shown in
FIG. 3
, neither solid nor broken arrow can be defined as a path (no-merge), and, thereafter in the time series, if such state is entered that paths can be determined (merge), either solid or broken arrows are defined as paths. As a result, for instance, arrows enclosed by a dotted line in
FIG. 4
become the survivor path, and data “0000101010000000” corresponding to the arrows enclosed by the dotted line is obtained as detected data, which matches the original data.
In some cases, the sampled values shown in
FIG. 2
are deviated by the effect of noise. Suppose that the reproduced signal (sampled values) that should be obtained correctly as shown in
FIG. 2
is obtained as shown in
FIG. 5
in which the level of the reproduced signal is lowered by a noise at a time (9). In this case, if sampled values shown in
FIG. 5
are input to the Viterbi detector
100
one after another, the paths selected in the ACS
102
and states has a relation shown in FIG.
6
. In
FIG. 6
, only a path at the time (9) is different from that in FIG.
3
. However, detected data includes more than one error bit.
If the sampled values shown in
FIG. 5
are input to the Viterbi detector
100
, paths enclosed by a dotted line in
FIG. 7
are defined as a survivor path in the PM
104
. Paths in (3) through (9) of the time series in
FIG. 7
are different from paths corresponding to the data shown in
FIG. 4
which data should correctly be detected. That is, the above-described error path (at the time (9)) causes the detected data to include six error bits.
As described above, since the conventional Viterbi detector determines paths based on the continuity of state transition, a determined (survivor) path may includes sequential errors if a sampled value has an error to change a corresponding path. As a result, detected value corresponding to the determined path may include sequential bit errors.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a data reproduction apparatus having a high data detection capability and good noise immunity.
The above object of the present invention is achieved by a data reproduction apparatus claimed in claim
1
sampling at a given rate a reproduced signal complying with a partial response waveform, calculating branch metric values in accordance with the Viterbi decoding algorithm by employing expected values defined by the partial response waveform and each of sampled values, calculating path metric values based on the branch metric values, selecting paths corresponding to data state transition in accordance with a given rule based on comparison results of the path metric values, and reproducing data based on the selected paths, the reproduced signal being obtained from a recording medium, which data reproduction apparatus include
Taguchi Masakazu
Uchida Akiyoshi
Greer Burns & Crain Ltd.
Huber Paul W.
LandOfFree
Data reproduction apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Data reproduction apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Data reproduction apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3293853