JP2006252701A - Viterbi decoder, viterbi decoding method, and viterbi decoding program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately decode information recorded on a hologram recording medium without being affected by noise. <P>SOLUTION: A decoding processing section computes a reliability vector C. The reliability vector C represents which luminance value of two pixel images constituting difference modulation codes is higher and also represents the difference in these luminance values. Next, a length d1 from a unit vector [-1] representing "1" to the reliability vector C is computed, and further, a length d2 from a unit vector [1] representing "0" to the reliability C is computed. Then, the length d1 is defined as a soft decision value of "1", and the length d2 is defined as a soft decision value of "0", and soft decision Viterbi decoding is carried out by using these soft decision values. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a Viterbi decoding apparatus, method, and program, and more particularly to a Viterbi decoding apparatus, method, and program suitable for use in decoding a modulation code recorded on a hologram recording medium.

  In recent years, a recording / reproducing apparatus for a hologram recording medium has been proposed in which digital information is two-dimensionally recorded and reproduced using a hologram.

  In the case of recording digital information, the recording / reproducing apparatus spatially modulates a coherent signal laser beam based on digital information to be recorded, using a transmission type spatial light modulation element including a plurality of pixels, Two-dimensional diffracted light is generated by causing interference between the spatially light-modulated signal laser light and a separately emitted coherent reference laser light, and an image formed by the diffracted light is converted into two corresponding to digital information. It records on a hologram recording medium as dimension information (for example, refer patent document 1).

  On the other hand, when reproducing the digital information by reading the two-dimensional information from the hologram recording medium on which the two-dimensional information is recorded, a reproduction reference laser beam (recording reference laser) that is coherent to the two-dimensional information is recorded. The reflected light generated by irradiating the recording medium with the same incident angle as the light is received by a light receiving element having a plurality of pixels to generate an output signal, and the generated output signal is used. To reproduce the original digital information.

In addition, when digital information is reproduced, it has been studied to decode a convolutional code using a Viterbi decoding method (see, for example, Non-Patent Document 1).
JP 2000-228089 A Seungjune JEON, etc "Soft Decision Decoding for Holographic Memories with Intrapage Intensity Variations" Jpn. J. Appl. Phys. Vol.40 pp.1741-1746

  However, even if the techniques described in Patent Document 1 and Non-Patent Document 1 are used, each pixel of the image formed on the spatial light modulator does not match each pixel of the image received by the light receiving element. When noise is mixed in from the outside, information cannot be completely decoded and an error occurs.

  The present invention has been proposed to solve the above-described problems, and a Viterbi decoding apparatus, method, and method capable of decoding information recorded on a hologram recording medium with high accuracy without being affected by noise. The purpose is to provide a program.

  In order to solve the above-described problem, a Viterbi decoding device according to the present invention includes a luminance value detection unit that detects luminance values of a plurality of pixels constituting the modulation code from a hologram recording medium on which the modulation code is recorded, Based on each luminance value detected by the luminance value detecting means and each unit vector of a plurality of pixels constituting the modulation code, a reliability vector representing the relative relationship of each luminance value is calculated. And a soft decision value calculation for calculating a distance from the reliability vector calculated by the reliability vector calculation unit to a unit vector of a predetermined pixel constituting the modulation code as a soft decision value. Means, and decoding means for performing Viterbi decoding processing using the soft decision value calculated by the soft decision value calculation means.

  A modulation code is recorded as a hologram on the hologram recording medium. The modulation code represents binary data with a plurality of pixels. The hologram recording medium may be recorded with a first modulation code that represents 1 bit by two pixels having different luminance values, or a second that represents 2 bits by four pixels having different luminance values. May be recorded.

  The luminance value detecting means receives the diffracted light from the hologram recording medium and detects the luminance value of each of the plurality of pixels constituting the modulation code.

  The reliability vector calculation means calculates a reliability vector that represents the relative relationship of each luminance value based on each detected luminance value and each unit vector of a plurality of pixels constituting the modulation code. To do. This reliability vector represents the luminance deviation of the modulation code.

  The soft decision value calculation means calculates a distance from the reliability vector calculated by the reliability vector calculation means to a unit vector of a predetermined pixel constituting the modulation code as a soft decision value. And a decoding means performs a Viterbi decoding process using the calculated soft decision value.

  Therefore, according to the Viterbi decoding apparatus according to the present invention, the luminance values of the plurality of pixels constituting the modulation code are detected, and each detected luminance value and each of the plurality of pixels constituting the modulation code are detected. Based on the unit vector, a reliability vector representing the relative relationship of each luminance value is calculated, and the distance from the reliability vector to the unit vector of a predetermined pixel constituting the modulation code is calculated as a soft decision value In addition, by performing the Viterbi decoding process using the calculated soft decision value, the decoding process can be performed quickly and accurately without being affected by noise.

  In the above invention, the reliability vector calculation means may calculate the reliability vector using a unit vector arranged on the two-dimensional coordinate axis or a unit vector rotated by a predetermined angle with respect to the two-dimensional coordinate axis. Good.

  The present invention is also applied to the following Viterbi decoding method.

  That is, the Viterbi decoding method according to the present invention includes a luminance value detection step of detecting luminance values for a plurality of pixels constituting the modulation code from the hologram recording medium on which the modulation code is recorded, and the luminance value detection step. A reliability vector calculation step of calculating a reliability vector representing the relative relationship of each luminance value based on each detected luminance value and each unit vector of a plurality of pixels constituting the modulation code A soft decision value calculation step of calculating a distance from the reliability vector calculated in the reliability vector calculation step to a unit vector of a predetermined pixel constituting the modulation code as a soft decision value, and the soft decision A decoding step of performing a Viterbi decoding process using the soft decision value calculated in the value calculation step.

  In the present invention, the hologram recording medium may be recorded with a first modulation code representing 1 bit by two pixels having different luminance values, or 2 bits by four pixels having different luminance values. May be recorded.

  The reliability vector calculation step may calculate the reliability vector using a unit vector arranged on a two-dimensional coordinate axis or a unit vector rotated by a predetermined angle with respect to the two-dimensional coordinate axis.

  The Viterbi decoding apparatus, method, and program according to the present invention detect luminance values for a plurality of pixels constituting a modulation code, and detect each luminance value and each of the plurality of pixels constituting the modulation code. Based on the unit vector, a reliability vector representing the relative relationship of each luminance value is calculated, and the distance from the reliability vector to the unit vector of a predetermined pixel constituting the modulation code is calculated as a soft decision value In addition, by performing the Viterbi decoding process using the calculated soft decision value, the decoding process can be performed quickly and accurately without being affected by noise.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram showing a configuration of a recording / reproducing apparatus for a hologram recording medium according to the first embodiment of the present invention.

  The recording / reproducing apparatus includes a servo laser device 2 that is a servo light source, a half mirror 3 that reflects a servo return beam toward the position detector 6, and a servo laser beam as a signal laser beam (object And the half mirror 4 to be incident on the condensing lens 5, the converging lens 5 for converging the servo laser beam and the signal laser beam on the hologram recording medium 100, and the servo return beam. In response, the relative position relationship between the incident position of the servo laser beam on the hologram recording medium 100 and the marker on the hologram recording medium 100 is obtained from the light intensity distribution, and the position information is fed back to the servo mechanism. And a container 6.

  The recording / reproducing apparatus includes a recording / reproducing laser apparatus 7, a beam splitter 8 for dividing the light from the recording / reproducing laser apparatus 7 into a signal laser beam and a reference laser beam, and an optical path of the signal laser beam during reproduction. A shutter 11, a beam expander 12 that expands the beam so that the signal laser light is incident on the entire liquid crystal spatial light modulator 13, a liquid crystal spatial light modulator 13 in which a plurality of elements are arranged in a matrix, and a reference laser And an objective lens (a condensing lens for reference laser light) 14 that focuses the light onto the hologram recording medium 100.

  The liquid crystal spatial light modulator 13 forms an image pattern by operating each element according to input data. Each pixel of the liquid crystal spatial light modulator 13 has a one-to-one correspondence with each pixel of the CCD image sensor 16 described later.

  Further, in the recording / reproducing apparatus, the reproducing wavefront is necessary for reconstructing the image pattern on the liquid crystal spatial light modulator 13 on the imaging surface of the CCD image sensor 16 and the diffraction of the hologram recording medium 100. A CCD image sensor 16 that captures an image pattern that appears by light, a mirror 17 for changing the direction of the reference laser light, an A / D converter 18 that converts an imaging signal obtained by the CCD image sensor 16 into a digital signal, and A decoding device 19 for performing data decoding processing based on the digital signal output from the A / D converter 18 and encoding for performing data modulation processing on the recorded image and inputting the data to the liquid crystal spatial light modulator 13 The apparatus 20 is provided.

  The recording / reproducing apparatus configured as described above operates as follows during recording and during reproduction.

[Recording operation]
At the time of recording, the liquid crystal spatial light modulator 13 forms an image pattern based on the differential modulation code input from the encoding device 20.

  FIG. 2 is a block diagram illustrating a configuration of the encoding device 20. The encoding device 20 includes a recording image input unit 31 that inputs a recording image from the outside, and a modulation encoding unit 32 that performs an encoding process after performing a modulation process on the recording image input to the recording image input unit 31. I have.

  The modulation encoding unit 32 performs a convolutional encoding process on the recorded image to generate a convolutional code. The convolutional coding process is a coding method in which signal bits for error correction / detection are generated retroactively to past data. A convolutional code is a code in which information is sequentially folded into a code.

  The most commonly used decoding method for convolutional codes is the Viterbi decoding method described later. The convolutional code is used in combination with Viterbi decoding in the error correction circuit to detect and correct transmission errors from past data values instead of a fixed information block unit, thus providing powerful error correction. Demonstrate power. Then, the modulation encoding unit 32 performs differential modulation processing on the convolutional code to generate a differential modulation code.

  FIG. 3 is a diagram for explaining the differential modulation code. The differential modulation code is a modulation code in which the number of bits of the output bit string is 1 bit. For example, when no modulation is performed, a white pixel image represents “1” of binary data, and a black pixel image represents “1”. On the other hand, the differential modulation represents 1-bit binary data by arranging pixel images of white and black one by one in the one-dimensional (horizontal direction) direction. Specifically, the differential modulation code in which the white pixel image is “left” (the black pixel image is right) represents binary data “1”. A differential modulation code in which a white pixel image is “right” (a black pixel image is left) represents “0”. The modulation encoding unit 32 supplies the differential modulation code thus processed to the liquid crystal spatial light modulator 13 to cause the liquid crystal spatial light modulator 13 to form an image pattern.

  On the other hand, the laser beam emitted from the recording / reproducing laser device 7 is divided into a signal laser beam and a reference laser beam by the beam splitter 8. The signal laser light is spread by the beam expander 12, passes through the liquid crystal spatial light modulator 13, is collected by the condenser lens 5, and is applied to the hologram recording medium 100. An image pattern is formed on the liquid crystal spatial light modulator 13 based on the input data from the encoding device 21. Further, the reference laser light is reflected by the mirror 17 and enters the hologram recording medium 100.

  FIG. 4 is a diagram illustrating a state in which a hologram image is recorded on the hologram recording medium 100. FIG. 5 is a diagram illustrating a state in which optical interference occurs between the signal laser beam and the reference laser beam. θ is an incident angle of the reference laser beam with respect to the normal direction of the hologram recording medium 100.

  The signal laser light and the reference laser light cause optical interference in the hologram recording layer of the hologram recording medium 100, and the image pattern formed by the liquid crystal spatial light modulator 13 is recorded as interference fringes. And this interference fringe becomes a hologram image. When the wavelength of the reference laser beam is λ, the interference fringe spacing Λ is expressed by the following equation.

  The focusing lens 5 shown in FIG. 1 is applied with a Z-axis servo (automatic focus position adjustment, the Z-axis is parallel to the optical axis) (not shown). The laser beam emitted from the servo laser device 2 passes through the same optical path as the signal laser beam by the half mirror 4 and is incident so as to be focused by the marker of the hologram recording medium 100.

  In addition, tracking sampling servo (automatic radial position adjustment of the disk-shaped hologram recording medium 100) is always applied, and even if the hologram recording medium 100 is eccentric, recording is performed at a predetermined position with good reproducibility. The recording / reproducing laser device 7 uses a high coherency laser, but the servo laser device 2 uses a low coherency laser (short in coherence distance).

  FIG. 6 is a diagram showing a rectangular hologram image recorded on the hologram recording medium 100. The image pattern formed by the liquid crystal spatial light modulator 13 is recorded on the hologram recording medium 100 as it is. Markers are attached to the four corners near the outer periphery of the hologram image. The position of each marker is set in advance.

[Playback operation]
During reproduction, the signal laser beam is blocked by the shutter 11 and only the reference laser beam is incident on the hologram recording medium 100. When the reference laser beam is incident on the hologram image recorded on the hologram recording layer of the hologram recording medium 100, the focused spherical wave of the signal laser beam at the time of recording is reproduced as a divergent spherical wave (in the direction opposite to that at the time of recording). Is done. The reproduction wavefront passes through the reproduction lens 15 and forms image pattern data formed by the liquid crystal spatial light modulator 13 at the time of recording as an image pattern on the imaging surface of the CCD image sensor 16. The CCD image sensor 16 converts the imaged image pattern into an electric signal and supplies it to the decoding device 19 via the A / D converter 18.

  FIG. 7 is a block diagram showing the configuration of the decoding device 19. The decoding device 19 includes a two-dimensional image position detection unit 41, an image distortion correction unit 42 that corrects the distortion of the hologram image, an image extraction unit 43 that extracts a hologram image portion, and a decoding process based on the extracted hologram image. And a decoding processing unit 44 to be applied. Note that the decoding device 19 may be configured by a computer, for example, and execute processing to be described later according to a predetermined program.

  The two-dimensional image position detection unit 41 detects markers at the four corners of the hologram image detected by the CCD image sensor 16 and detects the positions of these markers.

  The image distortion correction unit 42 compares the marker position detected by the two-dimensional image position detection unit 41 with a preset marker position, detects the distortion amount of the hologram image, and corrects the distortion of the hologram image. To do. The image cutout unit 43 cuts out the distortion-corrected hologram image.

  The decoding processing unit 44 calculates a soft decision value based on the differential modulation code of the extracted hologram image, and performs a Viterbi decoding process using the soft decision value.

  First, the decoding processing unit 44 calculates the reliability vector C using the luminance values of the two pixel images constituting the differential modulation code. The reliability vector C is represented by a one-dimensional vector obtained by combining the two vectors when the luminance of the two pixel images is represented by a vector.

FIG. 8 is a diagram showing two pixel images corresponding to the differential modulation code read from the hologram recording medium 100. FIG. 9 is a vector diagram showing the reliability vector C. On the one-dimensional vector axis, the luminance unit vector of the left pixel image is [−1], its luminance value is C ₁ , the luminance unit vector of the right pixel image is [1], and its luminance value is C _2. And In the present embodiment, the range of C ₁ and C ₂ is [0, 1], but is not limited to this. At this time, the reliability vector C indicating the relative relationship between the luminance values is obtained by Expression (1).

  The reliability vector C represents which of the two pixel images constituting the differential modulation code has a higher luminance value and the difference between the luminance values. In other words, the reliability vector C is represented by the luminance deviation of the differential modulation code, and indicates the reliability (certainty) of the binary data obtained from the differential modulation code. That is, the greater the bias of the reliability vector C, the higher the reliability of the binary data.

  Next, a case will be described as an example where one of the branches represented by “1” and “0” is selected in selecting the surviving path.

  After calculating the reliability vector C, the decoding processing unit 44 calculates a length d1 from the unit vector [−1] representing “1” to the reliability vector C as shown in FIG. The length d2 from the unit vector [1] representing “to the reliability vector C is calculated. The length d1 is a soft decision value of “1” and the length d2 is a soft decision value of “0”.

  Using these soft decision values, the decoding processing unit 44 performs decoding (soft decision Viterbi decoding) to search for a code sequence with the highest likelihood from the received sequence. Here, the decoding processing unit 44 compares the length d1 and the length d2, and selects the unit vector “1” corresponding to the smaller one (the one closer to the reliability vector C).

  In narrowing down the code sequences, it is only necessary to invert the bits in order from the one with the lowest reliability (the absolute value of the two soft decision values described above), and to set the combination of these as code sequence candidates. Thereby, even if the code sequence is long, the amount of calculation can be reduced.

  10A and 10B are diagrams for explaining the demodulation processing by the decoding processing unit 44. FIG. 10A shows a case where the state of the reproduced image is good, FIG. 10B shows a case where the state of the reproduced image is bad, and FIG. This is a pixel image corresponding to 1 ″. Here, “the state of the reproduced image is good” means that the pixel image of the hologram corresponds to the light receiving pixel of the CCD image sensor 16.

  In the case of (A), the pixel image of the hologram corresponds to one light receiving pixel (pixel match), and the luminance value of the left light receiving element is much larger than the luminance value of the right light receiving element. In the case of (B), the pixel image of the hologram extends over two light receiving pixels, and the luminance value of the left light receiving element is slightly larger than the luminance value of the right light receiving element. In addition, it may become like (B) when noise mixes.

  For example, if the differential modulation codes shown in (A) and (B) are subjected to hard decision decoding (binarization), a value of “1” is obtained. The Viterbi decoding is performed without considering that the reliability of the value “1” in (A) is high and the reliability in (B) is low.

  On the other hand, since the decoding processing unit 44 performs soft decision Viterbi decoding using the above soft decision value, for example, the states (A) and (B) are finely quantized and their reliability is taken into consideration. Therefore, Viterbi decoding can be performed with high accuracy.

  As described above, the recording / reproducing apparatus according to the first embodiment calculates the reliability vector C in which the luminance deviation of the differential modulation code is expressed as a vector, and each pixel is calculated from the reliability vector C. The distance to the unit vector corresponding to is calculated as a soft decision value. Since soft decision Viterbi decoding is performed using this soft decision value, data decoding processing can be performed at high speed and accurately without being affected by noise. In particular, the recording / reproducing apparatus can perform the Viterbi decoding while considering the reliability of the differential modulation code by performing the soft decision Viterbi decoding using the soft decision value indicating the degree of deviation of the luminance value of the differential modulation code. As a result, the decoding accuracy can be improved while reducing the calculation load.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the site | part same as 1st Embodiment, and the detailed description is abbreviate | omitted.

  The hologram recording medium recording / reproducing apparatus according to the second embodiment is configured as shown in FIGS. 1, 2, and 7 as in the first embodiment. A / 4 modulation code is used.

  In the present embodiment, the modulation encoding unit 32 shown in FIG. 2 performs a convolutional encoding process on the recorded image to generate a 2/4 modulation code.

  FIG. 11 is a diagram for explaining a 2/4 modulation code. The differential modulation code is a modulation code in which the number of bits of the output bit string is 2 bits. The 2/4 modulation code represents two bits depending on a two-dimensional (vertical and horizontal direction) arrangement of a total of four pixel images, one white and three black, that is, the position of a white pixel image. Specifically, a 2/4 modulation code in which the white pixel image is “upper left” represents “00”. The 2/4 modulation code with the white pixel image “upper right” represents “01”. A 2/4 modulation code with a white pixel image “bottom left” represents “10”. A 2/4 modulation code with a white pixel image “bottom right” represents “11”. The modulation encoding unit 32 supplies the differential modulation code thus processed to the liquid crystal spatial light modulator 13 to cause the liquid crystal spatial light modulator 13 to form an image pattern.

  In this embodiment, the decoding processing unit 44 shown in FIG. 7 calculates a soft decision value based on the 2/4 modulation code of the hologram image cut out by the image cutout unit 43, and uses the soft decision value to perform Viterbi decoding. Process.

  First, the decoding processing unit 44 calculates the reliability vector C using the luminance values of the four pixel images constituting the 2/4 modulation code. The reliability vector C is represented by a two-dimensional vector obtained by synthesizing the four vectors when the luminance of the four pixel images is represented by a vector.

FIG. 12 is a diagram showing four pixel images corresponding to a 2/4 modulation code read from the hologram recording medium 100. Here, the densities of the upper left, upper right, lower left, and lower right pixel images are C ₁ , C ₂ , C ₃ , and C ₄ , respectively. In the present embodiment, the range of C ₁ , C ₂ , C ₃ , and C ₄ is [0, 1], but is not limited to this.

  FIG. 13 is a vector diagram showing the reliability vector C. Here, the unit vector of “00” is [−1 / √2, 1 / √2], the unit vector of “01” is [1 / √2, 1 / √2], and the unit vector of “10” is [ −1 / √2, −1 / √2], and the unit vector of “11” is [1 / √2, −1 / √2]. At this time, the reliability vector C indicating the relative relationship between the luminance values is obtained by Expression (2).

  The reliability vector C represents which of the luminance values of the four pixel images is relatively high. In other words, the reliability vector C is represented by the luminance deviation of the 2/4 modulation code, and indicates the reliability (certainty) of the binary data obtained from the 2/4 modulation code.

  Next, a case will be described as an example where one of the branches represented by “00” and “11” is selected in selecting the surviving path.

  After calculating the reliability vector C, the decoding processing unit 44 calculates the length from the unit vector [−1 / √2, 1 / √2] representing “00” to the reliability vector C as shown in FIG. d1 is calculated, and the length d2 from the unit vector [1 / √2, −1 / √2] representing “11” to the reliability vector C is calculated. Note that the length from the other unit vector to the reliability vector C may be obtained. The length d1 is a soft decision value of “00”, and the length d2 is a soft decision value of “11”.

  Then, the decoding processing unit 44 performs soft decision Viterbi decoding using these soft decision values. Here, the decoding processing unit 44 compares the length d1 and the length d2, and selects the unit vector “00” corresponding to the smaller one (the one closer to the reliability vector C).

  In narrowing down the code sequences, it is only necessary to invert the bits in order from the one with the lowest reliability (the absolute value of the two soft decision values described above), and to set the combination of these as code sequence candidates. Thereby, even if the code sequence is long, the amount of calculation can be reduced.

  In FIG. 13, the four unit vectors are arranged at positions shifted by 45 degrees with respect to the xy axis, but these four unit vectors may be arranged on the xy axis by rotating 45 degrees.

  FIG. 14 is a vector diagram showing the reliability vector C when the unit vectors are arranged on the xy axis. Here, the unit vector of “00” is [0, 1], the unit vector of “01” is [1, 0], the unit vector of “10” is [−1, 0], and the unit vector of “11” is [0, -1]. At this time, the reliability vector C indicating the relative relationship between the luminance values is obtained by Expression (3).

  Then, the decoding processing unit 44 obtains the length from an arbitrary unit vector to the reliability vector C in the same manner as described above, and may use this as a soft decision value, but it may also be as follows.

  For example, when obtaining the soft decision values “00” and “11”, the decoding processing unit 44 may use the y component of the reliability vector C, and obtaining the soft decision values “10” and “01”. May use the x component of the reliability vector C. Thereby, the decoding process part 44 can reduce the calculation load of a soft decision value, As a result, a soft decision Viterbi decoding process can be performed at high speed.

  As described above, the recording / reproducing apparatus according to the second embodiment calculates the reliability vector C that represents the four luminance deviations constituting the 2 / 4-tone code as a vector, The distance to the unit vector corresponding to the four pixels is calculated as a soft decision value. And since it decodes using this soft decision value, a data decoding process can be performed at high speed and correctly, without being influenced by noise. The recording / reproducing apparatus performs Viterbi decoding while considering the reliability of the differential modulation code by performing soft decision Viterbi decoding using a soft decision value that represents the degree of deviation of the luminance value of the 2/4 modulation code. As a result, it is possible to improve the decoding accuracy while reducing the calculation burden.

  Further, when the unit vector corresponding to each of the four pixels is arranged on the two-dimensional coordinate axis, the recording / reproducing apparatus can reduce the calculation load of the soft decision value, so that the data decoding process can be performed at a higher speed. it can.

  Note that the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can also be applied to a design modified within the scope of the claims.

  In the present invention, for example, even when using a modulation code in which the number of bits of the output bit string is 3 bits, by representing the reliability with a three-dimensional vector, the soft decision is made as in the first and second embodiments. The value can be calculated and this soft decision value can be decoded.

It is a figure which shows the structure of the recording / reproducing apparatus of the hologram recording medium which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of an encoding apparatus. It is a figure explaining a differential modulation code. It is a figure which shows the state in which a hologram image is recorded on a hologram recording medium. It is a figure which shows the state which has caused the optical interference of a signal laser beam and a reference laser beam. It is a figure which shows the square-shaped hologram image recorded on the hologram recording medium. It is a block diagram which shows the structure of a decoding apparatus. It is a figure which shows two pixel images corresponding to the differential modulation code read from the hologram recording medium. 3 is a vector diagram showing a reliability vector C. FIG. It is a figure explaining the demodulation process by a decoding process part, (A) is when the state of a reproduced image is good, (B) is when the state of a reproduced image is bad, (C) respond | corresponds to binary data "1". It is a pixel image. It is a figure explaining a 2/4 modulation code. It is a figure which shows four pixel images corresponding to the 2/4 modulation code read from the hologram recording medium. 3 is a vector diagram showing a reliability vector C. FIG. It is a vector diagram showing the reliability vector C when a unit vector is arrange | positioned on xy axis.

Explanation of symbols

2 Laser device for servo 7 Laser device for recording / reproducing 8 Beam splitter 13 Liquid crystal spatial light modulator 16 CCD image sensor 19 Decoder 20 Encoder 31 Recorded image input unit 32 Modulation encoder 41 Two-dimensional image position detector 42 Image Distortion correction unit 43 Image cutout unit 44 Decoding processing unit 100 Hologram recording medium

Claims (12)

A luminance value detecting means for detecting a luminance value for a plurality of pixels constituting the modulation code from a hologram recording medium on which the modulation code is recorded;
Based on each luminance value detected by the luminance value detecting means and each unit vector of a plurality of pixels constituting the modulation code, a reliability vector representing the relative relationship of each luminance value is calculated. A reliability vector calculation means to perform,
Soft decision value calculation means for calculating a distance from a reliability vector calculated by the reliability vector calculation means to a unit vector of a predetermined pixel constituting the modulation code as a soft decision value;
Decoding means for performing a Viterbi decoding process using the soft decision value calculated by the soft decision value calculation means;
A Viterbi decoding device. 2. The Viterbi decoding apparatus according to claim 1, wherein a first modulation code representing one bit is recorded on the hologram recording medium with two pixels having different luminance values. 2. The Viterbi decoding apparatus according to claim 1, wherein a second modulation code representing 2 bits is recorded on the hologram recording medium by four pixels having different luminance values. The reliability vector calculating means calculates the reliability vector using a unit vector arranged on a two-dimensional coordinate axis or a unit vector rotated by a predetermined angle with respect to the two-dimensional coordinate axis. 4. The Viterbi decoding device according to 3. A luminance value detecting step for detecting a luminance value for a plurality of pixels constituting the modulation code from a hologram recording medium on which the modulation code is recorded;
Based on each luminance value detected by the luminance value detection step and each unit vector of a plurality of pixels constituting the modulation code, a reliability vector representing a relative relationship between the luminance values is calculated. A reliability vector calculation process,
A soft decision value calculation step of calculating a distance from a reliability vector calculated in the reliability vector calculation step to a unit vector of a predetermined pixel constituting the modulation code as a soft decision value;
A decoding step of performing a Viterbi decoding process using the soft decision value calculated by the soft decision value calculation step;
A Viterbi decoding method comprising: The Viterbi decoding method according to claim 5, wherein a first modulation code representing one bit is recorded on the hologram recording medium by two pixels having different luminance values. 6. The Viterbi decoding method according to claim 5, wherein a second modulation code representing 2 bits is recorded on the hologram recording medium with four pixels having different luminance values. The reliability vector calculation step calculates the reliability vector using a unit vector arranged on a two-dimensional coordinate axis or a unit vector rotated by a predetermined angle with respect to the two-dimensional coordinate axis. 8. The Viterbi decoding method according to 7. On the computer,
Detecting a luminance value for a plurality of pixels constituting the modulation code from the hologram recording medium on which the modulation code is recorded;
Based on each detected luminance value and each unit vector of a plurality of pixels constituting the modulation code, a reliability vector representing a relative relationship of each luminance value is calculated,
A distance from the calculated reliability vector to a unit vector of a predetermined pixel constituting the modulation code is calculated as a soft decision value,
A Viterbi decoding program for executing a Viterbi decoding process using the calculated soft decision value. A luminance value detecting means for detecting a luminance value for a plurality of pixels constituting the modulation code from a hologram recording medium on which the modulation code is recorded;
Based on each luminance value detected by the luminance value detecting means, soft decision calculating means for calculating the degree of bias of each luminance value in the modulation code as a soft decision value;
Decoding means for performing Viterbi decoding processing of the modulation code using the soft decision value calculated by the soft decision value calculation means;
A Viterbi decoding device. A luminance value detecting step for detecting a luminance value for a plurality of pixels constituting the modulation code from a hologram recording medium on which the modulation code is recorded;
Based on each luminance value detected by the luminance value detection step, a soft decision calculation step for calculating a degree of bias of each luminance value in the modulation code as a soft decision value;
A decoding step of performing a Viterbi decoding process of the modulation code using the soft decision value calculated in the soft decision value calculation step;
A Viterbi decoding method comprising: On the computer,
Detecting a luminance value for a plurality of pixels constituting the modulation code from the hologram recording medium on which the modulation code is recorded;
Based on each detected luminance value, the degree of bias of each luminance value in the modulation code is calculated as a soft decision value,
A Viterbi decoding program that executes a Viterbi decoding process of the modulation code using the calculated soft decision value.