U.S. patent application number 09/797804 was filed with the patent office on 2001-12-27 for digital signal recording/reproducing method.
Invention is credited to Goto, Toshio, Yamaji, Takashi.
Application Number | 20010055259 09/797804 |
Document ID | / |
Family ID | 27614977 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010055259 |
Kind Code |
A1 |
Goto, Toshio ; et
al. |
December 27, 2001 |
Digital signal recording/reproducing method
Abstract
Digital signal sequences to be recorded in predetermined unitary
recording areas are transformed into blocks, a plurality of bit
data carrying all digit levels to be read and determined upon
reproduction are included in the resultant blocks, and sequences of
the data blocks are recorded in the recording medium in the unitary
recording areas. Upon reproduction, the blocks of the read signals
obtained from a recording medium are recognized, a threshold value
is determined for each block on the basis of the values of read
signals corresponding to bit data carrying all digit levels to be
read and determined, and each digit level of bit data in the read
signal are read and determined on the basis of the threshold
values.
Inventors: |
Goto, Toshio;
(Tsurugashima-shi, JP) ; Yamaji, Takashi;
(Tsurugashima-shi, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3202
US
|
Family ID: |
27614977 |
Appl. No.: |
09/797804 |
Filed: |
March 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09797804 |
Mar 5, 2001 |
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09270510 |
Mar 17, 1999 |
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6222754 |
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Current U.S.
Class: |
369/59.17 ;
369/59.24; 369/59.25 |
Current CPC
Class: |
G11B 7/0065 20130101;
G11C 13/042 20130101 |
Class at
Publication: |
369/59.17 ;
369/59.24; 369/59.25 |
International
Class: |
G11B 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 1998 |
JP |
10-72738 |
Claims
What is claimed is:
1. A method of recording a plurality of digital signal sequences at
predetermined unitary recording areas in a recording medium,
respectively, comprising the steps of: transforming each of said
digital signal sequences to be recorded into blocks; including a
plurality of bit data carrying all digit levels to be read and
determined upon reproduction within each of the resultant data
blocks; and recording a sequence of the data blocks at the
corresponding ones of said predetermined unitary recording areas in
said recording medium.
2. A method of reproducing digital signal sequences from a
recording medium, comprising the steps of: recognizing blocks in
each of read signal sequences obtained from said recording medium;
determining a threshold value for each block on the basis of read
values of bit data carrying all digit levels to be read and
determined; and reading and determining each digit level of bit
data of said read signal sequences on the basis of said threshold
value.
3. A method of recording a plurality of digital signal sequences at
predetermined unitary recording areas in a recording medium,
respectively, comprising the steps of: transforming each of said
digital signal sequences to be recorded into blocks; locating
reference bit data carrying at least first and second digit levels
to be read and determined upon reproduction at respective
predetermined positions in each of the resultant data blocks; and
recording a sequence of the data blocks at the corresponding ones
of said predetermined unitary recording areas in said recording
medium.
4. A method of reproducing digital signal sequences from a
recording medium, comprising the steps of: recognizing blocks in
each of read signal sequences obtained from said recording medium;
determining a threshold value for each of said blocks on the basis
of read values of reference bit data carrying at least first and
second digit levels to be read and determined, said reference bit
data being located at predetermined positions within each of said
block; and reading and determining each digit level of bit data of
said read signal sequences on the basis of said threshold
value.
5. A digital signal recording method according to claim 1, wherein
said data block is formed of the number of bits corresponding to a
vertical length by which a recording plane in said recording medium
is divided, and the number of bits corresponding to a horizontal
length by which the recording plane in said recording medium is
divided.
6. A digital signal recording method according to claim 1, wherein
said data block is formed of the number of bits corresponding to a
vertical length by which a recording plane in said recording medium
is divided, the number of bits corresponding to a horizontal length
by which the recording plane in said recording medium is divided,
and the number of bits corresponding to a recording time interval
for a recording area defined by both of said numbers of bits.
7. A method of recording a plurality of digital signal sequences at
predetermined unitary recording areas in a recording medium,
respectively, comprising the steps of: preparing correction digital
signals each corresponding to each of said predetermined unitary
recording areas and each including bit data carrying digit levels
to be determined upon reproduction and having a predetermined bit
position relationship corresponding to said digit levels; mixing
each of said correction digital signals with each of said digital
signal sequences; and recording the resultant digital signal
sequences at the corresponding ones of said predetermined unitary
recording areas in said recording medium.
8. A method of reproducing digital signal sequences from a
recording medium, comprising the steps of: recognizing correction
digital signals for each of predetermined unitary recording areas
from the read signal sequences obtained from said recording medium;
identifying bit data carrying digit levels to be read and
determined from said correction digital signals on the basis of a
predetermined bit position relationship thereof; detecting
deviation values from the respective expected values of the
identified bit data; and correcting each value of bit data of said
digital signal sequences on the basis of said deviation values.
9. A digital signal recording method according to claim 3, wherein
said data block is formed of the number of bits corresponding to a
vertical length by which a recording plane in said recording medium
is divided, and the number of bits corresponding to a horizontal
length by which the recording plane in said recording medium is
divided.
10. A digital signal recording method according to claim 3, wherein
said data block is formed of the number of bits corresponding to a
vertical length by which a recording plane in said recording medium
is divided, the number of bits corresponding to a horizontal length
by which the recording plane in said recording medium is divided,
and the number of bits corresponding to a recording time interval
for a recording area defined by both of said numbers of bits.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to an information
recording/reproducing method, and more particularly to a method of
recording a digital signal on a recording medium and reproducing
the digital signal therefrom.
[0003] 2. Description of the Related Art
[0004] A holographic memory system, which is one of information
recording/reproduction systems mentioned above, records a digital
signal (hereinafter called "data") on a holographic memory medium
(a photo-refractive crystal material such as LiNbO.sub.3 or the
like) and reproducing the data therefrom. The system is capable of
recording and reproducing data in a form of two-dimensional plane
page, and moreover capable of recording and reproducing over a
large number of pages. An exemplary configuration of the system is
illustrated in FIG. 1.
[0005] Referring to FIG. 1, an encoder 11 converts time series
recording data sequences to be recorded into a "page" in a
holographic memory medium 1. In other words, the encoder 11
rearranges the time series recording data into a data matrix
corresponding to a two-dimensional unitary plane page as a
predetermined unitary recording region, for example, in a matrix of
vertically 480 bits and horizontally 640 bits (480.times.640) to
produce unitary page data sequence. The unitary page data sequence
is sent to a spatial light modulator (SLM) 12.
[0006] The SLM 12 optically modulates an irradiated signal beam in
accordance with the unitary page data sequence from the encoder 11
in modulation processing units of vertically 480
pixels.times.horizontally 640 pixels corresponding to the unitary
page, and leads a modulated beam resulting therefrom to a lens 13.
More specifically, the SLM 12 passes a signal beam therethrough in
response to a logical value "1" in the unitary page data sequence,
which is an electrical signal, and blocks the signal beam in
response to a logical value "0," to achieve electrical-optical
transducing in accordance with the respective bit contents in the
unitary page data to produce a modulated signal beam as an optical
signal representing the unitary page sequence.
[0007] Such a modulated signal beam is input to the holographic
memory medium 1 through the lens 13. The holographic memory medium
1 is also irradiated with a reference beam having an angle from a
predetermined reference line (hereinafter, called the "incident
angle .beta.") orthogonal to the optical axis of the beam carrying
the optical signal, other than the modulated signal beam.
[0008] When the modulated signal beam and the reference beam are
simultaneously incident on the holographic memory medium 1, both
beams interfere with each other within the holographic memory
medium 1 to produce an interference pattern which is recorded in
the holographic memory medium 1, thereby recording the data in the
holographic memory medium 1. Also, by inputting the reference beam
with a different incident angle .beta., data can be recorded in the
holographic memory medium 1 in units of predetermined
three-dimensional recording regions including a plurality of pages
of two-dimensional data.
[0009] For reproducing recorded data from the holographic memory
medium 1, unlike recording, no signal beam is input to the
holographic memory medium 1, but the reference beam only is input
at the same incident angle .beta. as that used during the
recording. In this way, diffracted light from an interference
pattern recorded in the holographic memory medium 1 is led to a
lens 21.
[0010] The diffracted light reaching the lens 21 passes through the
lens 21, and impinges on a CCD (Charge-Coupled Device) 22 having a
light receiving area of vertically 480 pixels.times.horizontally
640 pixels. Each of the pixels in the light receiving area of the
CCD 22 corresponds to each pixel on a recording plane in the
holographic memory medium 1, so that the CCD 22 transduces the
brightness of the incident light in each pixel area into the
magnitude of an electrical signal level, i.e., generates an analog
electrical signal indicative of a level corresponding to the
luminance of incident light, and supplies the analog electrical
signal to a decoder 23 as a read signal.
[0011] The decoder 23 has a function of digitizing the read signal
or performing binary determination, and recognizes a logical value
"1" when the read signal has a level higher than a slice level
serving as a threshold value, and a logical value "0" when lower
than the level to produce a digital signal which carries the values
thus recognized. In addition, the decoder 23 performs a reverse
conversion of conversion performed in the encoder 11 to the digital
signal to produce time series reproduced signal.
[0012] The holographic memory system thus configured is capable of
recording and reproducing three-dimensional data including a
temporal element to and from the holographic memory medium 1 by
changing an incident angle .beta. of a reference beam at arbitrary
time intervals, as well as recording and reproducing planar
two-dimensional data in vertical and horizontal dimensions.
[0013] However, a variety of factors such as dust and stain on each
optical elements, crosstalk, interference fringes and so on may
cause the light intensity to spatially and temporally fluctuate,
resulting in fluctuations due to noise in amplitude occurring in
the output of the CCD, i.e., a read signal, other than a change in
amplitude due to data itself. When the output of the CCD 22 is
converted to data of "1" or "0" based on a fixed slice level in the
decoder 23, data read errors may occur owing to amplitude
fluctuations.
[0014] By way of example, assume that an image carrying a
two-dimensional data matrix as illustrated in FIG. 2 is recorded in
the holographic memory medium 1.
[0015] In FIG. 2, a white portion represents data "1," while a
black portion represents data "0." If an irregular luminance
illustrated in FIG. 3 is superimposed on the pattern image carrying
such data, a read signal is produced on the basis of a pattern
image as illustrated in FIG. 4. In this case, an amplitude value of
a read signal in a data "1" portion is affected by "dark" or lower
luminance irregularity to become smaller.
[0016] In FIG. 4, when a portion free from a "dark" region due to
the irregular luminance indicated by an arrow A is sliced in the
horizontal direction, and is represented as a change in the output
level of light received by the CCD 22 corresponding to the sliced
portion, i.e., a change in the level of the read signal, a waveform
as shown in FIG. 5 is derived.
[0017] In FIG. 5, by determining whether the read signal is "1" or
"0" based on a slice level defined by a median value between a
maximum value and a minimum value of the read signal, recorded data
"1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1" can be correctly
reproduced as reproduced data "1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
1, 0, 1."
[0018] However, if a portion including a "dark" region due to
irregular luminance indicated by an arrow B is sliced in the
horizontal direction, and a read signal from that portion is
determined whether it is "1" or "0" with the same slice level as
FIG. 5, recorded data is not correctly reproduced because a level
corresponding to the "dark" region is lower than the slice level as
shown in FIG. 6, so that the reproduced data represents "1, 0, 1,
0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1," thus resulting in a read
error.
[0019] While FIG. 6 shows an example where the level of a read
signal corresponding to data "1" becomes lower due to a "darky"
region of the irregular luminance to result in a read error, the
level of a read signal corresponding to data "0" may become higher
due to a "light" region of irregular luminance to cause a read
error, as shown in FIG. 7.
[0020] Also, as shown in FIGS. 8 and 9, data cannot be correctly
reproduced if the entire level of a read signal fluctuates with an
offset due to the irregular luminance to cause a read error.
[0021] In the case shown in FIGS. 8, 9, while a large offset may
result in the level of a read signal exceeding an upper limit of
data "1" or falling below a lower limit of data "0," the level is
limited by the respective upper limit or the lower limit.
OBJECT AND SUMMARY OF THE INVENTION
[0022] The present invention has been made in view of the problem
mentioned above, and its object is to provide a digital signal
recording method, reproducing method and recording/reproducing
method which are capable of reliably reproducing a recorded digital
signal even if a read signal is experiencing level level
fluctuations due to noise.
[0023] To achieve the above object, a method of recording a
plurality of digital signal sequences at predetermined unitary
recording areas in a recording medium, respectively, according to
the present invention comprises the steps of transforming each of
the digital signal sequences to be recorded into blocks, including
a plurality of bit data carrying all digit levels to be read and
determined upon reproduction within each of the resultant data
blocks, and recording a sequence of the data blocks at the
corresponding ones of the predetermined unitary recording areas in
the recording medium.
[0024] A method of reproducing digital signal sequences from a
recording medium according to the present invention comprises the
steps of recognizing blocks in each of read signal sequences
obtained from the recording medium, determining a threshold value
for each block on the basis of read values of bit data carrying all
digit levels to be read and determined, and reading and determining
a digit level of each bit of the read signal sequences on the basis
of the threshold value.
[0025] Another method of recording a plurality of digital signal
sequences at predetermined unitary recording areas in a recording
medium, respectively, according to the present invention comprises
the steps of transforming each of the digital signal sequences to
be recorded into blocks, locating reference bit data carrying at
least first and second digit levels to be read and determined upon
reproduction at respective predetermined positions in each of the
resultant data blocks, and recording a sequence of the data blocks
at the corresponding ones of the predetermined unitary recording
areas in the recording medium.
[0026] Another method of reproducing digital signal sequences from
a recording medium according to the present invention comprises the
steps of recognizing blocks in each of read signal sequences
obtained from the recording medium, determining a threshold value
for each of the blocks on the basis of read values of reference bit
data carrying at least first and second digit levels to be read and
determined, the reference bit data being located at predetermined
positions within each of the block, and reading and determining a
digit level of each bit of the read signal sequences on the basis
of the threshold value.
[0027] In one embodiment of the recording method, the data block
may be formed of the number of bits corresponding to a vertical
length by which a recording plane in the recording medium is
divided, and the number of bits corresponding to a horizontal
length by which the recording plane in the recording medium is
divided.
[0028] Alternatively, the data block may be formed of the number of
bits corresponding to a vertical length by which a recording plane
in the recording medium is divided, the number of bits
corresponding to a horizontal length by which the recording plane
in the recording medium is divided, and the number of bits
corresponding to a recording time interval for a recording area
defined by both of the numbers of bits.
[0029] A further method of recording a plurality of digital signal
sequences at predetermined unitary recording areas in a-recording
medium, respectively, according to the present invention comprises
the steps of preparing correction digital signals each
corresponding to each of the predetermined unitary recording areas
and each including bit data carrying digit levels to be determined
upon reproduction and having a predetermined bit position
relationship corresponding to the digit levels, mixing each of the
correction digital signals with each of the digital signal
sequences, and recording the resultant digital signal sequences at
the corresponding ones of the predetermined unitary recording areas
in the recording medium.
[0030] A further A method of reproducing digital signal sequences
from a recording medium according to the present invention
comprises the steps of recognizing correction digital signals for
each of predetermined unitary recording areas from the read signal
sequences obtained from the recording medium, identifying bit data
carrying digit levels to be read and determined from the correction
digital signals on the basis of a predetermined bit position
relationship thereof, detecting deviation values from the
respective expected values of the identified bit data, and
correcting values of each bit of the digital signal sequences on
the basis of the deviation values.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a block diagram illustrating the basic
configuration of an information recording/reproducing system common
to a prior art and respective embodiments of the present
invention;
[0032] FIG. 2 is a schematic diagram illustrating an example of a
data pattern image for a recording page;
[0033] FIG. 3 is a schematic diagram illustrating a pattern of
irregular luminance which can be superimposed on the data pattern
image of FIG. 2;
[0034] FIG. 4 is a schematic diagram illustrating an example of the
irregular luminance pattern of FIG. 3 superimposed on the data
pattern image of FIG. 2;
[0035] FIG. 5 is a time chart showing an example of level
fluctuations of a read signal in a normal operation;
[0036] FIG. 6 is a time chart showing an example of level
fluctuations of a read signal when an irregular luminance is
present;
[0037] FIG. 7 is a time chart showing another example of level
fluctuations of a read signal when an irregular luminance is
present;
[0038] FIG. 8 is a time chart showing an example of level
fluctuations of a read signal when an offset component is included
in the read signal;
[0039] FIG. 9 is a time chart showing another example of level
fluctuations of a read signal when an offset component is included
in the read signal;
[0040] FIG. 10 is a flow chart illustrating a procedure for data
reproduction processing performed in accordance with a first
embodiment of the present invention;
[0041] FIG. 11 is a diagram illustrating an example of a data
pattern for a unitary recording page for explaining in detail the
data reproduction processing of FIG. 10;
[0042] FIG. 12 is a time chart for explaining data reproduced by
the data reproduction processing of FIG. 10;
[0043] FIG. 13 is a diagram illustrating another example of a data
pattern for a unitary recording page for explaining in detail the
data reproduction processing of FIG. 10;
[0044] FIG. 14 is a flow chart illustrating a procedure for the
data reproduction processing performed in accordance with a second
embodiment of the present invention;
[0045] FIG. 15 is a diagram illustrating an example of a data
pattern for a unitary recording page for explaining in detail the
data reproduction processing of FIG. 14;
[0046] FIG. 16 is a time chart for explaining data reproduced by
the data reproduction processing of FIG. 14;
[0047] FIG. 17 is a diagram illustrating another example of a data
pattern for a unitary recording page for explaining in detail the
data reproduction processing of FIG. 14;
[0048] FIG. 18 is a diagram showing a corresponding relationship of
recording page data sequence composed by encoding processing
according to a third embodiment of the present invention; and
[0049] FIG. 19 is a flow chart illustrating a procedure for data
reproduction processing performed in accordance with the third
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] Several embodiments of the present invention will
hereinafter be described in detail with reference to the
accompanying drawings.
[0051] A general configuration of an information
recording/reproducing system according to first embodiment of the
present invention is the same as that illustrated in FIG. 1.
[0052] However, the encoder 11 does perform processing unique to
this embodiment. Specifically, data to be recorded, corresponding
to a single unitary page or a predetermined number of unitary
pages, is divided into two-dimensional or three-dimensional
predetermined blocks such that at least one data bit "1" and at
least one data bit "0" are included in each block. In other words,
the data block includes a plurality of data bits which generally
carry all digit levels to be read and determined upon reproduction.
The unitary page data sequences to be recorded thus composed are
sent to the SLM 12.
[0053] The data sent to the SLM 12 is recorded in the holographic
memory medium 1 by a signal beam and a reference beam.
[0054] The data recorded in the holographic memory medium 1 is read
by using the reference beam. In this event, diffracted light from
the holographic memory medium 1 reaches the CCD 22 through the lens
21. The CCD 22 supplies its output indicative of the received light
to the decoder 23 as a read signal.
[0055] The decoder 23 performs data reproduction processing unique
to this embodiment. A flow chart of the processing is illustrated
in FIG. 10.
[0056] Specifically, as the decoder 23, for example, A/D-converts
the read signal to fetch digital signal data sequences (step S11),
it divides each of the digital data sequences into predetermined
blocks as a block recognition step (step S12).
[0057] Next, the decoder 23 compares each level of the read data
(i.e., value of each bit) in each block with a preliminary slice
level arbitrarily determined for the block (for example, an average
value of all the read data in the block may be used as the slice
level), and once determines "1" or "0" for the level of the read
data by checking whether it is higher or lower than the slice level
to produce a data carrying "1" or "0" (step S13).
[0058] Then, the decoder 23 calculates an average value of the read
data corresponding to data determined as "1" (at least one) within
the block produced by the processing at Step S13, and an average
value of the read data corresponding to data determined as "0" (at
least one) within the block produced by the processing at Step S13
(step S14).
[0059] The decoder 23 newly determines a slice level from the two
average values so as to minimize a read error in the read data
(step S15). Then, the decoder 23 compares the read data with the
newly obtained slice level to determine "1" or "0" again for the
level of the read data by checking whether it is higher or lower
than the slice level, and newly produces determined data which
carries "1" or "0" (step S16). As a new slice level determined at
Step S15, an average of the two average values for "1" and "0"
derived at Step S14 may be employed.
[0060] Subsequent to Step S16, the decoder 23 determines whether or
not the slice level should be changed (step S17). If it should be
changed, i.e., if it is determined that the read error in data can
be further reduced, an average value of the read data corresponding
to data determined as "1" and an average value of the read data
corresponding to data determined as "0" are again calculated for
each block of the determined data which have been finally derived
to determine the slice level. Then, the procedure proceeds to Step
S14 to determine "1" or "0" for the level of the read data
[0061] If it is determined at Step S17 that the slice level need
not be changed, the decoder 23 combines the blocks (step S18), and
outputs the finally derived determined data as decoded data or
reproduced data in time series (step S19).
[0062] The foregoing processing performed by the encoder 11 and the
decoder 23 may be implemented by a personal computer or the like
either in software or in hardware.
[0063] As an example of two-dimensional division of recording data
into blocks, explanation will be given of a two-dimensional data
matrix of FIG. 4 which is divided into 3 bits by 3 bits blocks 1-a,
2-a, . . . , 5-e as illustrated in FIG. 11.
[0064] A block is composed to satisfy a condition that it must
include one or more data bits "1" and one or more data bits "0."
Here, one bit located at the upper left corner of the data in the
3.times.3 block is used as an adjusting bit for satisfying the
condition, so that the remaining eight bits, excluding the upper
left one bit, are used as normal information data. As a specific
method of determining the value for the adjusting bit, the smaller
one of the numbers of "1" and "0" of information data in the block
is assigned to the adjusting bit. If the number of "1" is the same
as the number of "0" in information data of a block, either of
them, for example, "1" may be selected.
[0065] In this way, it is possible to compose a block which
includes both data "1" and "0" without fail.
[0066] According to this embodiment, when the blocked data as
illustrated in FIG. 11 is read, the read data is divided into
3.times.3 blocks identical to those upon encoding at Step S12.
Then, at Step S13, each bit of the read data is determined whether
it is "1" or "0" with an arbitrary slice level for each block, and
an average value of the read data corresponding to "1" data thus
determined and an average value of the read data corresponding to
"0" data thus determined are again averaged to determine a slice
level at Steps S14 and S15. Then, each bit of the read data is
again determined whether it is "1" or "0" with the newly determined
slice level.
[0067] Therefore, neighboring data on a recording format, here, in
a unitary plane page of data to be read, i.e., data "1" and "0"
within a previously defined block are used to set a slice level to
determine "1" or "0" of the data. Therefore, even if the level of
read signal fluctuates due to noise caused by a variety of factors,
the values of data within the block, which is referenced for the
slice level, also fluctuates to cause the slice level to fluctuate
in a manner similar to the data, thereby making it possible to
correctly determine whether the read data is "1" or "0."
[0068] FIG. 12 shows level fluctuations of the data corresponding
to a portion of the read data, indicated by an arrow B in FIG. 11,
which has been sliced in the horizontal direction.
[0069] Referring specifically to FIG. 12, in blocks free from the
influence of irregular luminance such as blocks 1-c, 2-c or the
like, data can be correctly determined whether it is "1" or "0"
based on a slice level determined by the average values for the
read data "1" and for the read data "0" without errors.
[0070] In blocks influenced by irregular luminance such as a block
3-c, on the other hand, the read data "1" in the block is
influenced by the irregular luminance. The read data "1" and the
read data "0" are determined with a new threshold value changed as
appropriate, and the slice level determined in accordance with
these read data also follow the change, so that the read data
having levels fluctuating due to a noise component such as
irregular luminance can also be determined for "1" or "0" without
errors.
[0071] Next, a three-dimensional division of recording data into
blocks will be explained with reference to an example. In this
example, the two-dimensional data matrix of FIG. 4 is processed
such that not only a plane A as a unitary recording page is divided
into 3 bits by 3 bits areas 1-a, 2-a, . . . , 5-e, but also a plane
B as a unitary recording page produced by changing an incident
angle .beta. of a reference beam over a time T is also divided
corresponding to each of divided areas of the plane A, as shown in
FIG. 13, to produce a block having a thickness of the time T and a
volume of 2 bits of plane dimension by 3 bits of vertical dimension
by 3 bits of horizontal dimension.
[0072] In such a division of recording data into blocks, it can be
generally said that a data block is formed by the number of bits
corresponding to a vertical length by which a recording plane on
the medium 1 is divided; the number of bits corresponding to a
horizontal length by which the recording plane is divided; and the
number of bits corresponding to a recording time interval for a
recording area defined by both of the numbers of bits.
[0073] More specifically, in FIG. 13, the encoding is performed,
for example, on a virtually three-dimensional cubic block of 2 bits
by 3 bits by 3 bits formed by an area 1-a on a plane A and an area
1-a on a plane B, both of which are recording pages. The cubic
block is the unit of the encoding.
[0074] A block is composed to satisfy a condition that it must
include one or more data bits "1" and one or more data bits "0".
Here, one bit at the upper left corner of data in a 3.times.3 area
on the plane A is chosen to be an adjustment bit, and a total of 17
bits including eight bits in this area excluding the upper left bit
and all nine bits of data in the 3.times.3 area on the plane B are
used as information data. For the adjusting bit, the smaller one of
the numbers of "1" and "0" of information data in the block is
assigned. If the number of "1" is the same as the number of "0" in
information data of a block, either of them, for example, "1" may
be selected.
[0075] According to the embodiment, when blocked data as
illustrated in FIG. 13 is read, the read data is divided into
2.times.3.times.3 blocks identical to those upon encoding at Step
S12, and determination is made as to whether the read data is "1"
or "0" based on an arbitrary slice level for each block at Step
S13. An average value of the read data corresponding to data
determined as "1" and an average value of the read data
corresponding to data determined as "0" are further averaged at
Step S14 to determine the slice level at Step S15. Then, the read
data is again determined whether it is "1" or "0" based on the
newly determined slice level.
[0076] Thus, the "0" determination is performed by using
neighboring data on a three-dimensional recording format of data to
be read, i.e., other data within a three-dimensional block over a
previously set time interval T to determine a slice level.
Therefore, even if the level of read signal fluctuates due to noise
caused by a variety of factors, the values of data within the
block, which is referenced for the slice level, also fluctuates to
cause the slice level to fluctuate in a manner similar to the data,
thereby making it possible to correctly determine whether the read
data is "1" or "0." The approach for setting a slice level using
three-dimensional blocks as mentioned is advantageously resistant
to fluctuations in a recording form and a reproduction form on the
time base, and capable of performing efficient processing because
of a large amount of data contained in each block.
[0077] As described above, even if the level of the read data
arranged in two-dimensional or three-dimensional recording format
spatially or temporally fluctuates due to a variety of factors, the
slice level for determining "1" or "0" is determined from the read
data "1" and "0" which are similarly affected by the fluctuations,
thereby making it possible to determine whether each bit of the
read data is "1" or "0" even if level fluctuations due to noise is
present in the read data.
[0078] Moreover, fluctuations exceeding an upper limit of "1" and
falling below a lower limit of "0," as illustrated in FIGS. 8 and 9
may cause the level of a read signal to saturate, resulting in the
lack of linearity in the level change and a significantly distorted
waveform of the read signal. Even in such a case, the slice level
is determined utilizing information of both the read data "1" and
"0" the slice level can be appropriately determined because even if
one is saturated, the other remains unsaturated.
[0079] While the foregoing explanation has been made referring to
an example where the shape of block for determining the slice level
is 3.times.3 for a two-dimensional block, and 2.times.3.times.3 for
a three-dimensional block, any shape of block may be used as long
as it includes both of data "1" and "0." Alternatively, a variety
of blocks may be combined without limiting the shape. Further, a
block having a different shape may be provided for determining the
slice level for extracting data "1" and "0" separately from the
block for determining "1" or "0" for data.
[0080] Also, while an adaptive slice level is calculated after each
bit of data in block is determined whether it is "1" or "0" based
on an arbitrary slice level for each block, the slice level may be
calculated by first determining the read data as to whether data is
"1" or "0" based on a single slice level before it is divided into
blocks, and then dividing the read data into blocks.
[0081] An information recording/reproducing system according to
another embodiment of the present invention can be basically
realized in a similar manner to that illustrated in FIG. 1.
[0082] The encoder 11, however, does perform processing unique to
this embodiment. More specifically, recording data corresponding to
a unitary page or a predetermined number of unitary pages is
divided into predetermined two-dimensional or three-dimensional
blocks, each of which is composed to include at least one reference
data "1" specified at an assigned location, and at least one
reference data "0" similarly specified at an assigned location. In
other words, the reference data bits, each carrying at least first
and second digit levels ("0" and "1" in this embodiment) to be read
and determined upon reproduction, are arranged at the respective
predetermined locations in a resulting data block. A unitary page
recording data sequence thus composed is sent to the SLM 12.
[0083] The data sent to the SLM 12 is recorded in the holographic
memory medium 1 by a signal beam and a reference beam.
[0084] The data recorded in the holographic memory medium 1 is read
by using the reference beam. In this event, diffracted light from
the holographic memory medium 1 reaches the CCD 22 through the lens
21. The CCD 22 supplies its output indicative of received light to
the decoder 23 as a read signal.
[0085] The decoder 23 performs data reproduction processing unique
to this embodiment as illustrated in FIG. 14.
[0086] Specifically, as the decoder 23, for example A/D-converts a
read signal to fetch digital signal data sequences (step S21), it
divides each of the digital data sequences into predetermined
blocks as a block recognition step (step S22).
[0087] Next, the decoder 23 extracts reference data "1" and "0"
within the block (step S23), and determines a slice level so as to
minimize read errors in the read data from both reference data
(step S24). As the slice level, an average value of the reference
data "1" and "0" may be employed.
[0088] After the slice level has been determined, the decoder 23
determines "1" or "0" for the level of the read data by checking
whether it is higher or lower than the slice level (step S25). The
data "1" and "0" obtained by the determination are output as
decoded data, i.e., reproduced data in time series (step S26).
[0089] The processing performed by the encoder 11 and the decoder
23 may also be implemented by a personal computer or the like
either in software or in hardware.
[0090] As an example of two-dimensional division of recording data
into blocks, explanation will be given of a two-dimensional data
matrix of FIG. 4 which is divided into 3 bits by 3 bits blocks 1-a,
2-a, 5-e as illustrated in FIG. 15.
[0091] A block is composed to satisfy a condition that it must
include one or more reference data bits "1" and one or more
reference data bits "0" respectively specified at particular
locations in the block. Here, one bit located at the upper left
corner of the data in each 3.times.3 block is used as the reference
data bit "1" and the next one bit to the right as the reference
data bit "0," and the remaining portion except for the two
locations is assigned for normal information data.
[0092] According to the embodiment, when the blocked data as
illustrated in FIG. 15 is read, the read data is divided into
3.times.3 blocks identical to those upon encoding at Step S22. At
Step S23, the reference data "1" recorded at the upper left corner
and the reference data "0" recorded at the next location to the
right of the reference data "0" are extracted in each block at Step
S23. Then, at Step S24, the slice level is determined by the
extracted reference data, and each bit of the read data is
determined whether it is "1" or "0" based on the determined slice
level.
[0093] Therefore, neighboring data on a recording format of data to
be read, i.e., the reference data positioned at previously
specified locations in a block are used to set a slice level to
determine "1" or "0" of the data. Therefore, even if the level of
read signal fluctuates due to noise caused by a variety of factors,
the values of the reference data within the block, which is
referenced for the slice level, also fluctuates to cause the slice
level to fluctuate in a manner similar to the reference data,
thereby making it possible to correctly determine whether the read
data is "1" or "0."
[0094] FIG. 16 shows level fluctuations of the read data
corresponding to a portion of the read data , indicated by an arrow
B in FIG. 15, which has been sliced in the horizontal
direction.
[0095] Referring specifically to FIG. 16, in blocks free from the
influence of irregular luminance such as a block 1-d or the like,
data can be correctly determined that it is "1" or "0" based on a
slice level determined by the reference data "1" and the reference
data "0" without errors.
[0096] In blocks influenced by irregular luminance such as a block
3-d, on the other hand, the reference data "1" in the block is
influenced by the irregular luminance in a manner similar to other
data. Thus, the reference data "1" and the reference data "0" are
determined with a new threshold value changed as appropriate, and
the slice level determined in accordance with these read data also
follow the change, so that the read data having level fluctuations
can also be determined for "1" or "0" without errors.
[0097] Next, a three-dimensional division of recording data into
blocks will be explained with reference to an example. In this
example, the two-dimensional data matrix of FIG. 4 is processed
such that planes A and B, which are recording pages, are both
divided into 3 bits.times.3 bits areas 1-a, 2-a, . . . , 5-e, and
an interval between both planes is defined by changing an incident
angle .beta. of a reference beam over a time T, as shown in FIG.
17, i.e., a block having two planes spaced by the time T and a
volume of 2 bits of plane dimension by 3 bits of vertical dimension
by 3 bits of horizontal dimension.
[0098] More specifically, in FIG. 17, encoding is performed, for
example, in units of a three-dimensional cubic block of 2 bits by 3
bits by 3 bits formed by an area 1-a on the plane A and an area 1-a
on the plane B, both of which are recording pages.
[0099] A block is composed to satisfy a condition that it must
include one or more reference data bits "1" and one or more
reference data bits "0" respectively specified at particular
locations in the block. Here, one bit at the upper left corner of
data in a 3.times.3 area on the plane A is used as the reference
data "1," and one bit at the upper left corner of data in a
corresponding 3.times.3 area on the plane B is used as the
reference data "0." The remaining 16 bit locations are assigned for
information bit data.
[0100] According to the embodiment, when the blocked data as
illustrated in FIG. 17 is read, the read data is divided into
2.times.3.times.3 blocks identical to those upon encoding at Step
S22. At Steps S23, the reference data "1" recorded at the upper
left corner on the plane A and the reference data "0" recorded at
the upper left corner on the plane B are extracted in each block.
Then, at Step S24, the slice level is determined from the extracted
reference data with which each bit of the read data is determined
as to whether it is "1" or "0."
[0101] Thus, the "1"/"0" determination is performed by using
neighboring data on a three-dimensional format of data to be read,
i.e., the reference data within a three-dimensional block over a
previously set time interval T to set a slice level. Therefore,
even if the level of read signal fluctuates due to noise caused by
a variety of factors, the values of data within the block, which
are referenced for the slice level, also fluctuate to cause the
slice level to fluctuate in a manner similar to the data, thereby
making it possible to correctly determine whether the read data is
"1" or "0." The approach for setting a slice level using
three-dimensional blocks as mentioned is advantageously capable of
correcting fluctuations in a recording form and a reproduction form
on the time base, and capable of processing a large amount of data
in blocks.
[0102] As described above, even if the amplitude of
two-dimensionally or three-dimensionally arranged data spatially or
temporally fluctuates due to a variety of factors, the reference
signals "1" and "0," which are simultaneously affected by the
fluctuations are located in the vicinity of other data within the
blocks, thereby making it possible to determine correctly whether
data is "1" or "0" from the reference signals "1" and "0".
[0103] The embodiment also provides a proper slice level and
"1"/"0" determination in cases shown in FIGS. 8 and 9, in a manner
similar to the first embodiment.
[0104] While the foregoing explanation has been made referring to
an example where the shape of block for determining the slice level
is 3.times.3 for a two-dimensional block, and 2.times.3.times.3 for
a three-dimensional block, any shape of block may be used as long
as it includes the reference data "1" and "0" which are specified
at determined locations (strictly, the locations of which are
recognizable upon decoding). Alternatively, a variety of blocks may
be combined without limiting the shape. Further, a block having a
different shape may be provided for extracting the reference data
"1" and "0" separately from the block for determining whether the
data is "1" or "0".
[0105] Also, the block may include a plurality of reference data
"1" and "0," respectively. Further, the reference data "1" and "0"
may be placed at different locations from block to block.
[0106] Furthermore, while the foregoing embodiment uses binary data
consisting of "1" and "0" as data to be recorded and reproduced,
multi-value data having three values or more may also be recorded
and reproduced. In this case, a plurality of slice levels may be
calculated from the reference data "1" and "0" to determine the
multi-value data. Alternatively, other reference data indicative of
any intermediate value may be recorded other than the reference
data "1" and "0" to determine the multi-value data.
[0107] While the respective embodiments described above cope with
irregular luminance in unitary recording page for each block, a
third embodiment described below provides a method which can cope
with irregular luminance in a unitary recording page without the
need for dividing the unitary recording page into blocks.
[0108] In the following, explanation is given of multiplex
recording which records a modulated signal beam at the same
location in the holographic memory medium 1 for each page by
changing the incident angle .beta. of the reference beam in
predetermined steps. In this case, separate from normal recording
pages for carrying normal information data patterns, a data pattern
serving as the basis of correcting for irregular luminance is
recorded as a reference page. Upon reading data, the reference page
is read to detect irregular luminance in the reference page based
on a known pattern, and the value of information data in a
recording page is corrected in accordance with the detection
result.
[0109] FIG. 18 shows a relationship between a normal recording page
and the reference page.
[0110] It can be seen from FIG. 18 that the first reference page is
assigned to the first page, and subsequently a reference page is
assigned to every ten normal recording pages. The reference page on
Page 1 functions to correct the values of information data on
recording pages on Page 2 to 5; a reference page on Page 11
functions to correct the values of information data on recording
pages on pages 6 to 15; and so on. A reference page on the
{10(n-1)+1}th page functions to correct the values of information
data on normal recording pages on Pages (10n-4) to (10n+5).
[0111] The reference page on Page 1 is an initial reference page
which belongs to a different category from the other reference
pages. This page has the responsibility of identifying this page as
the first recording page in the holographic memory medium 1.
[0112] Each of the reference pages is coded in the same manner as
data patterns recorded on a normal recording page, and recorded
therein is a random pattern having a known bit position
relationship.
[0113] The encoder 11 inserts the reference page for correcting
irregular luminance as mentioned into normal recording pages to
compose a data sequence to be recorded.
[0114] Each of the pages recorded in the holographic memory medium
1 is read therefrom by sequentially changing the incident angle
.beta. of the reference beam, and a read signal is supplied to the
decoder 23. In this event, the decoder 23 corrects irregular
luminance based on the read reference page. FIG. 19 is a flow chart
illustrating a data reproducing procedure including such
correction.
[0115] Referring to FIG. 19, the decoder 23, upon detecting the
initial reference page by identifying it (step S31), reads a normal
page (step S32), and then reads data on a corresponding reference
page (step S33).
[0116] When reading data on the reference page, the decoder 23
calculates a correction coefficient (step S34), and corrects data
on the normal recording page using the correction coefficient (step
S35). If no data on the reference page is read, the decoder 23
corrects data on the normal recording page using a previously
calculated correction coefficient corresponding thereto (step
S35).
[0117] The data correction as mentioned is followed by the data
reproduction processing explained in the respective embodiments in
connection with FIG. 10 or 11 (step S36). In this way, a correct
slice level is set after data on the entire page have been
corrected, with the result that a digital signal is reliably
reproduced.
[0118] After Step S36, it is determined whether or not necessary
pages have been read (step S37). If not, the procedure returns to
Step S32 to continue to read other pages.
[0119] If necessary pages have been read, the decoder 32 performs
decoding including the processing for releasing the paged
configuration (step S38), followed by the termination of the
processing illustrated in the flow chart.
[0120] Next, the data correcting method conducted at Steps S34 and
S35 will be described in detail.
[0121] A data pattern on a reference page have their black portions
and white portions arranged at bit positions which have previously
been recognized on the decoder side. Therefore, the decoder 23 can
recognize whether each of bits arranged in a two-dimensional matrix
carries black or white, in other words, which of the digit levels
is assigned to.
[0122] In a white portion, the value of the read data corresponding
to the white portion itself corresponds to the amount of irregular
luminance. In other words, this is comparable to detection of a
deviation from an expected value with respect to the value of a
read signal corresponding to data bit which has been identified as
"1."
[0123] In a black portion, on the other hand, the amount of
irregular luminance therein is estimated from irregular luminance
of a while portion adjacent to or surrounding the black
portion.
[0124] It is therefore possible to detect the amount and
distribution of irregular luminance over the entire page including
all of white and black portions. For example, irregular luminance
including a "dark" portion as illustrated in FIG. 3 can be detected
as the amount and distribution with respect to the entire page.
[0125] The irregular luminance thus detected may be represented in
the form of two-dimensional data in units of pages. Then, the
two-dimensional data carrying the irregular luminance is
standardized, a correction coefficient (i.e., corresponding to a
coefficient for reducing the deviation to zero) is calculated and
stored for each pixel, and data on a corresponding normal recording
page is multiplied by the correction coefficient to remove the
irregular luminance.
[0126] According to this embodiment, irregular luminance is
detected in a page, and the value of corresponding data is
corrected to remove the irregular luminance. Thus, irregular
luminance between holograms caused by an uneven light source,
interference fringes remaining in optics, and the characteristics
of recording materials is removed, so that reproduced data can be
reliably provided while reducing read errors. Furthermore, by
combining the data reproduction processing unique to the respective
embodiments described above, such as that at Step S36, the
irregular luminance can be processed such that a rough compensation
is first made and then followed by a fine compensation, thereby
making it possible to more reliably reproduce a digital signal.
[0127] While the respective embodiments described above have
employed only a holographic memory medium as a recording medium,
the present invention is not necessarily limited to this particular
recording medium.
[0128] While a variety of means and steps have been explained in a
limited manner in the respective embodiment described above, they
may be appropriately modified within a scope in which those skilled
in the art may design.
[0129] According to the present invention as described above in
detail, a recorded digital signal can be reliably reproduced even
if a read signal is experiencing level fluctuations due to
noise.
[0130] The present invention has been described with reference to
the preferred embodiments thereof. It should be understood that a
variety of alterations and modifications may be contemplated by
those skilled in the art. It is intended that all such variations
and modifications are encompassed in the appended claims.
* * * * *