JP2007265618A - Reproduced signal equalizing method for optical information media and optical information reproducing/recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To equalize stably a reproduced signal to a target partial response waveform even when reproduction conditions such as tilt or beam diameter are varied in PRML detection being effective for high density reproduction. <P>SOLUTION: Equalization is performed by the least square technique by using a predetermined number of data samples binarized by a viterbi decoder 3. Even when data written on an optical disk are unknown, the data can be equalized in a stable manner and can be reproduced at a low error rate without instability factors such as divergence due to interference. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of equalizing a reproduction signal obtained by irradiating an optical information recording medium with laser light, and an optical information reproducing apparatus having a function of equalizing the reproduction signal. In particular, using a reproduction signal equalization method and optical information recording / reproducing apparatus for an optical information medium related to a reproduction signal whose target waveform of equalization is a partial response waveform, and an equalized reproduction signal obtained by this equalization method The present invention relates to an evaluation method and an adjustment method for evaluating the quality of a reproduction signal and adjusting a recording condition based on the evaluation result.

  Normally, in reproducing information recorded at high density, a data signal recorded at a certain position on a recording medium is affected by data signals recorded before and after the data signal. Therefore, there is a problem that the read signal is subject to intersymbol interference that changes from the waveform intended for recording, and errors are likely to occur during decoding.

  For this reason, in an optical disc apparatus such as a DVD (Digital Versatile Disk), equalization that reduces intersymbol interference as much as possible has been used. However, in this method, when the density becomes very high, noise components are emphasized by equalization, so there is a certain limit to the improvement in detection performance.

  A data detection method called PRML (Partial Response Maximum Likelihood) is known as a reproduction method that can further increase the density compared with the conventional equalization method (see, for example, Patent Document 1). In PRML, a reproduced signal is equalized to a predetermined partial response waveform (hereinafter sometimes abbreviated as PR) having intersymbol interference, and data identification is performed by taking into account the influence of intersymbol interference by an algorithm called Viterbi decoding. It is carried out. Since some intersymbol interference defined by the partial response is equalized to a waveform that allows a waveform having intersymbol interference, an increase in noise due to equalization is suppressed. Further, since the influence of intersymbol interference is taken into account by Viterbi decoding, it is possible to realize a high recording density.

  In the partial response waveform, the time length in units of bit rate that takes a value other than zero (0) (time T in units of clocks in FIG. 3) is generally called a constraint length. FIG. 3 shows a partial response waveform having a constraint length of 4 as an example of the waveform. When the constraint length is long, a reproduced waveform with large intersymbol interference is assumed. Further, when the recording density is high, the intersymbol interference of a signal that is actually reproduced is large, so a partial response waveform having a long constraint length is selected. As a result, a reproduction signal close to the actual reproduction signal can be expressed by linear superposition (convolution operation) of partial response waveforms. When the difference between the actual reproduced waveform and the waveform expressed by the convolution calculation of the partial response waveform is small, it is possible to suppress noise amplification due to equalization.

  However, the conventional reproduction signal equalization method may not be able to equalize sufficiently close to the target waveform. That is, when equalization to a predetermined partial response waveform cannot be performed, a high error rate occurs in the Viterbi detector at the time of decoding. Therefore, there is a problem that it is difficult to discriminate binary information, and the error rate is deteriorated.

  The reason is that an FIR (Finite Impulse Response) filter usually composed of about 5 to 20 taps is used to equalize the reproduction signal to a partial response. And the signal after equalization will also change by changing the magnitude | size of each tap coefficient of a filter. Here, equalization can be performed using a predetermined fixed tap coefficient. However, even if the recording density is the same, the reproduction signal itself changes when the beam diameter of the optical head for reproduction, the tilt of the optical information medium, and the like change.

  Also, a technique called adaptive equalization is known as one of methods for changing the tap coefficient in accordance with the change of the reproduction signal (see, for example, Patent Document 2). In this adaptive equalization, an appropriate tap coefficient determined in advance is set as an initial value. Based on this initial value, the tap coefficient is obtained by performing convergence calculation while gradually changing the tap coefficient in a direction in which the difference between the waveform after equalization and the target waveform decreases most rapidly. However, this method has the advantage that equalization can be performed without knowing the data recorded in the information, but it is vulnerable to noise and the like, and there is a problem that the convergence calculation does not converge and diverges. This problem is particularly noticeable when the recording density is high and the signal quality of the reproduced signal is low.

Japanese Patent Laying-Open No. 2003-151220 (paragraph 0004) JP 2001-14804 (paragraph 0004)

  The problem to be solved by the present invention is to solve the above-mentioned problems, when equalizing a reproduced signal of optical information recorded at a high density to a partial response waveform, the tilt or beam diameter It is to provide an equalization method capable of stably equalizing a reproduction signal to a partial response waveform even when the reproduction condition is changed or even when there is an influence of disturbance such as noise.

  The present invention is a method of equalizing a reproduction signal obtained by irradiating an optical information medium with laser light so as to approach a waveform having a predetermined characteristic, and an object of the present invention is to solve the above problems.

  The reproduction signal equalization method according to the present invention obtains a reproduction signal sampled at a predetermined cycle, and is one of the reproduction signals that is sufficiently smaller than the number of samples with respect to the data length to be subjected to binary identification and that is a certain number or more. The equalization coefficient calculation waveform sample is used as a sample, and the equalization coefficient that minimizes the difference between the equalized waveform of the sample and the target waveform with respect to the sample is calculated collectively by the least square method, The reproduction signal is equalized by the equalization coefficient.

  The number of samples of the waveform used for calculating the equalization coefficient is preferably 3000 or more. Further, a reproduction signal sampled at a predetermined period is input to a Viterbi decoder, and a target waveform is determined as an equalized waveform of the reproduction signal from binary identification data demodulated by the Viterbi decoder and a partial response waveform. be able to. In particular, it is desirable to use a PR value (1, 2, 2, 2, 1) as the target partial response waveform.

  An optical information reproducing apparatus according to the present invention has a function of equalizing a reproduction signal using the above equalization method.

  Further, according to the present invention, in the reproduction signal quality evaluation method, the reproduction signal can be equalized using the above equalization method, and the reproduction signal quality can be evaluated from the equalized reproduction signal and binary identification data.

  Further, according to the present invention, in the recording condition adjusting method for recording on the optical information recording medium, the recording condition can be adjusted based on the evaluation result of the signal quality evaluation method.

  The reproduction signal equalization method of the present invention obtains a reproduction signal sampled at a predetermined period, and is an example of the reproduction signal that is sufficiently smaller than the number of samples with respect to the data length to be subjected to binary identification and has a certain number or more. The waveform is used as an equalization coefficient calculation waveform sample, and the equalization coefficient that minimizes the difference between the waveform after equalization of the waveform sample and the target waveform with respect to the waveform sample is collectively calculated by the least square method and calculated. The reproduction signal is equalized by the equalization coefficient. For this reason, even if the information recorded on the optical disk is not known in advance, the reproduction signal can be accurately equalized to a predetermined partial response waveform without including instability factors such as divergence. Further, there is an effect that information can be reproduced at a low error rate even at the time of reproducing at a high recording density.

  In order to provide an equalization technique that can stably equalize the reproduction signal described above into a partial response waveform, the reproduction signal sampled at a predetermined period is acquired, and the number of samples with respect to the data length to be subjected to binary identification A part of the reproduction signal that is sufficiently smaller and more than a certain number is used as an equalization coefficient calculation waveform sample, and the difference between the equalized waveform of the waveform sample and the target waveform with respect to the waveform sample is minimized, etc. This is realized by calculating the equalization coefficients all at once by the method of least squares, and equalizing the reproduction signal using the calculated equalization coefficients.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an explanatory diagram showing an embodiment of the functional configuration of an optical information reproducing apparatus according to the present invention, particularly an equalizer. FIG. 2 is an explanatory diagram showing an embodiment of the configuration of the optical information reproducing apparatus according to the present invention.

In the optical information reproducing apparatus shown in FIG. 2, a signal recorded on an optical information medium, that is, an optical disk (not shown) is read out as an analog signal through an optical head device (not shown). This analog signal is amplified to an analog reproduction signal having a sufficiently large amplitude by the amplifier 11 and is digitally converted by an AD (analog-digital) converter 12. The digitally converted reproduction signal is output as a digital reproduction signal y _k for each bit rate, that is, in units of clock time by a PLL (phase locked loop) circuit, and is input to the equalizer 13. The reproduced signal y _k is equalized to a predetermined PR waveform by the equalizer 13 and input to the Viterbi decoder 14. The Viterbi decoder 14 binarizes data using a Viterbi algorithm.

If the partial response waveform of the bit rate (clock time unit) is “h _i ” (subscript i corresponds to the time), and the binary data recorded on the optical disk is “a _k ”, the target waveform to be equalized is It will be represented by “Σa _k−i * h _i ”. In this equation, the sum of the subscript “i” depends on the constraint length of the partial response, but for example, if the response waveform has a constraint length of 5, the sum of “i” should be “1 to 5”. Just do it.

In the present invention, the tap coefficient of the equalizer is “w _i ”, and “w _i ” that minimizes the following equation ε = Σ (Σy _k−i * w _i −Σa _k−i * h _i ) ² is minimized. Obtained by the square method. In other words, take a variational δ _ε for "w _i" for the "ε", will be determined to "w _i" by solving the equation becomes "δ _ε = 0". In the present invention, since it is not necessary to perform convergence calculation, problems such as divergence do not occur.

The equation _where “δ _ε = 0” is reduced to the following linear equation. A matrix W expressed by tap coefficients to be obtained, a matrix C expressed by using the correlation of the actually reproduced signal as an element, and a matrix D expressed by using the correlation between the reproduced signal and the equalization target signal as an element , “Equalization coefficient W _i (each element of W corresponds to W _i ) can be obtained by performing a matrix calculation represented by“ W = C ⁻¹ D ”. Here, each element of “C” and “D” is defined as in the following formulas (1) and (2).

  Here, “N” is the number of taps of the FIR filter for performing a partial response, and “M” is the number of reproduction signal samples used to determine the tap coefficient.

  In the present invention, unlike the case of adaptive equalization, it is necessary to know information recorded on the optical disc in advance. However, it is difficult to know data recorded in advance on an optical disc that has been recorded in advance, such as a ROM (read only memory). The present inventors have found that even if a waveform that does not pass through an equalizer is used as it is and binarized by a Viterbi decoder, it is possible to perform equalization with high accuracy if there is a predetermined number of samples. I found it.

Before describing these embodiments, referring to FIG. 1, an equalizer 2 that receives a digital reproduction signal y _k sent from the AD converter 1, equalizes it, and then outputs a signal to the Viterbi decoder 3. The configuration will be described.

The equalizer 2 includes a target waveform generator 4, an equalization coefficient calculator 5, and a FIR (Finite Impulse Response) filter 6. The target waveform generator 4 receives the provisional identification data b _k output from the Viterbi decoder 3, generates a target waveform from the partial response waveform h _i to be equalized, and sends it to the equalization coefficient calculator 5. . The equalization coefficient calculator 5 receives the target waveform and receives the reproduction signal y _k from the AD converter 1 to calculate the equalization coefficient and send it to the FIR filter 6. Further, the FIR filter 6 adjusts equalization by changing a plurality of types of taps as described above.

  Next, Example 1 to Example 5 in the above embodiment will be specifically described in detail with reference to the drawings.

  A first embodiment of the present invention will be described with reference to FIG.

  Example 1 is an example in which a recording / reproduction evaluation was performed using a phase change optical disk.

The phase change optical disk is produced on a 0.6 mm thick polycarbonate substrate. The pitch of the guide grooves formed on the substrate was 0.68 μm. Data a _k modulated by the (1-7) modulation method under the conditions of a linear velocity of 5.6 m / s and a clock frequency of 64.6 MHz using an optical head having a wavelength of 405 nm and an objective lens numerical aperture of 0.65. Was recorded and played back. The recording density corresponds to 0.13 μm / bit. In the first embodiment, as shown in FIG. 1, the temporary binary data b _k obtained by directly inputting the reproduction signal y _k at each clock time to the Viterbi decoder 3 without being equalized is used. Equalization was performed by the method of least squares. In the first embodiment, the target partial response waveform is set to the PR value (1, 2, 2, 2, 1).

While changing the number of samples of the reproduction signal y _k used for the least square method, partial response equalization is performed, and finally “c _k ” and “a _k ” of the binary data demodulated by the Viterbi decoder 3 are obtained. The bit error rate (error rate) was calculated by comparison. A 9-tap FIR filter 6 was used for equalization. Although ¹⁰⁶ samples were used in the calculation of the error rate, for example, when calculating the equalization coefficient by the least square method using the 100 beginning of the reproduction signal samples of 10 ^6, the equalization All 10 ⁶ reproduction signal samples are equalized with coefficients, and the signal is input by the Viterbi decoder 3 to obtain one of the binary data “c _k ”.

  FIG. 4 shows the relationship between the number of samples and the finally obtained bit error rate. As shown in the figure, if the number of samples is 3000 or more, it can be seen that information can be reproduced at a low error rate. Moreover, since the error rate is almost constant when the number of samples is 3000 or more, 3000 is sufficient as the number of samples.

  Further, when the number of samples for calculating the equalization coefficient is increased from 3000, the error rate is slightly improved, but the error rate is constant even when the number is increased to 10,000 or more. Therefore, even if a large number of samples are taken, it is sufficient if 10,000.

  A second embodiment of the present invention will be described with reference to FIG.

  Example 2 is an example in which a recording / reproduction evaluation was performed using a ROM disk.

The ROM disk is made on a 0.6 mm thick polycarbonate substrate. A known data string _ak was formed on the substrate with a pitch of 0.4 μm in the radial direction of the pits and a pitch of 0.2 μm in the laser scanning direction. (1-7) Since the pits are formed using the modulation method, the linear density corresponds to 0.15 μm / bit. Reproduction evaluation was performed at a linear velocity of 6.6 m / s using an optical head having a wavelength of 405 nm and an objective lens numerical aperture of 0.65. Also in this embodiment, as shown in FIG. 3, as in the first embodiment, the minimum self- _timer is obtained using temporary binary data b _k obtained by inputting the reproduction signal y _k at each clock time to the Viterbi decoder 3. Equalization was performed by multiplication. A 9-tap FIR filter 6 was used for equalization, and the target partial response waveform was a PR value (1, 2, 2, 2, 1).

While changing the number of samples of the reproduction signal y _k used for the least square method, partial response equalization is performed, and finally “c _k ” and “a _k ” of the binary data demodulated by the Viterbi decoder 3 are obtained. The bit error rate (error rate) was calculated by comparison. 10 ⁶ samples were used to calculate the error rate. However, for example, when calculating the equalization coefficient by the least square method using the 100 beginning of the reproduction signal samples of ^106, equalizes the ¹⁰⁶ of the reproduction signal samples in total that equalization coefficient, its The signal was input by the Viterbi decoder 3 and one of the binary data “c _k ” was obtained.

  FIG. 5 shows the relationship between the number of samples and the finally obtained bit error rate. Although the recording density in the second embodiment is different from that in the first embodiment, as in the first embodiment, if the number of samples is 3000 or more, it can be seen that information can be reproduced at a low error rate. . Moreover, since the error rate is almost constant when the number of samples is 3000 or more, 3000 is sufficient as the number of samples.

In Example 1 or Example 2 described above, had been calculated binary data b _k provisional enter the Viterbi decoder 3 without equalizing the sampled reproduction signal has been properly set such A signal equalized by the equalization coefficient may be input to the Viterbi decoder 3 to calculate provisional binary data.

That is, the reproduction signal is filtered (equalized) using a fixed coefficient as the initial equalization coefficient of the FIR filter, and the provisional identification signal b _k is generated from the equalized signal using the Viterbi decoder 3. . Next, the target waveform generator 4 and the equalization coefficient calculator 5 calculate the equalization coefficient of the FIR filter from the provisional identification data and the reproduced signal y _{k in the same} manner as in the first and second embodiments. The initial equalization coefficient can be obtained by an experiment using, for example, an optical head and an optical disk similar to an actual drive product, and stored in a predetermined area of the recording medium. As the initial equalization coefficient W (iT) (i = −4, −3, −2, −1, 0, 1, 2, 3, 4), the following can be used.

Example 1 of the initial equalization coefficient is
W (−4T) = W (4T) = 0.0259,
W (−3T) = W (3T) = − 0.1023
W (−2T) = W (2T) = 0.1276,
W (-T) = W (T) = 0.0011, or W (0T) = 0.6974.

Example 2 of the initial equalization coefficient is
W (−4T) = W (4T) = 0.1634,
W (−3T) = W (3T) = − 0.0903,
W (−2T) = W (2T) = − 0.2099,
W (−T) = W (T) = 0.0968, or W (0T) = 1.0800.

In the third embodiment, an equalizer 2 in which equalization coefficients are fixed in advance may be placed between the reproduced signal y _k and the Viterbi decoder 3 in FIG. However, as another method, a fixed equalization coefficient set in the FIR filter 6 of FIG. 1 can be supplied from a memory or the like.

  Further, after the equalization coefficient is calculated at a certain time point, the equalization coefficient may be calculated again at a time point when the reproduction condition changes. In this case, the equalization coefficient obtained in the first embodiment or the second embodiment or the equalization coefficient obtained using the initial equalization coefficient according to the third embodiment is stored in a memory or the like. It is burned. When re-calculating the equalization coefficient, the reproduction signal equalized by the previous equalization coefficient is input to the Viterbi decoder, the provisional binary discrimination data is calculated, and the target equalization waveform is obtained. You may ask for it.

  Using the phase change optical disk and the optical head used in Example 1 above, information recorded in advance is reproduced while changing the defocus, and equalization is performed by calculating an equalization coefficient under each defocus condition. Thereafter, the error rate was measured. In the third embodiment, equalization is performed using the tap coefficient calculated in the first embodiment (this is the same under each defocus condition), and a reproduction signal is input to the Viterbi decoder, and the target waveform is based on the provisional binary discrimination data. And the final equalization coefficient was obtained. Also in this embodiment, the number of taps in the FIR filter for equalization is “9”.

  FIG. 6 shows the relationship between the number of samples used for equalization and the error rate for each defocus condition. Since the condition of the defocus amount of 0 μm is substantially the same as that of the first embodiment, reproduction with a low error rate is possible with a small number of samples and coefficients obtained by the least square method. The error rate is degraded with a very small number of samples of about 100 because the influence of random noise is not completely the same even if the playback conditions are the same. It is done.

  Under the condition that the defocus is ± 0.2 μm, as in the case of the first and second embodiments, it can be seen that reproduction with a low error rate is possible if there are about 3000 samples. The reason why the error rate is degraded compared to 0 μm under the condition of ± 0.2 μm is not due to the calculation accuracy of the equalization coefficient, but because the reproduction performance itself is degraded due to defocusing.

  In the above embodiment, the number of taps of the FIR filter 6 is “9”. However, when equalizing the PR value (1, 2, 2, 2, 1) of the constraint length 5, the number of taps is “7 or more”. Since it has been confirmed that the equalization error is almost constant, any number of taps may be used as long as the number of taps is “7 or more”. However, an unnecessarily large number of taps increases the computation scale of the least squares method and causes problems such as an increase in circuit scale or a decrease in operation speed, and therefore the number of taps is preferably about 7 to 15.

  FIG. 7 is a diagram showing a configuration of an optical information recording / reproducing apparatus according to Example 4 of the present invention. The illustrated equalizer 22 is the same as the equalizer described in the first to third embodiments. First, the tap coefficient of the equalizer 22 is obtained according to the procedure of the first to third embodiments. Subsequently, the reproduction signal is equalized using the tap coefficients, and binary identification data is obtained from the equalized reproduction signal by the Viterbi decoder 23. Finally, the quality of the reproduced signal is evaluated by the signal evaluator 24 from the equalized reproduced signal and binary identification data.

  FIG. 8 is a diagram showing the configuration of the optical information recording / reproducing apparatus according to Example 5 of the present invention. In the figure, an equalizer 22 is the same as the equalizers of the first to third embodiments. An initial value for generating a recording waveform is stored in the internal memory of the recording waveform generator 33. Here, the recording waveform represents a temporal change (power and pulse width are parameters) of the laser beam irradiated to the optical disc during recording, which is generally called a recording strategy. The initial set value may be recorded in advance on the optical disc 31, read out from the corresponding location, and then stored in the internal memory.

  First, the recording waveform generator 33 generates an initial recording waveform from binary recording data based on the initial setting value of the recording waveform. Information is recorded on the optical disk 31 through the optical head 32 using the initial recording waveform. This recorded information is read out as a reproduction signal via the optical head 32 and converted into digital data by the AD converter 21. From the reproduced signal, the tap coefficient of the equalizer 22 is obtained in accordance with the procedure of the first to third embodiments. The reproduction signal from the information is read again, the reproduction signal is equalized using the tap coefficient, and binary identification data is obtained from the equalized reproduction signal by the Viterbi decoder 23. From the equalized reproduction signal and binary identification data, the signal evaluator 24 calculates a quality evaluation value of the reproduction signal. Based on the calculated quality evaluation value, the set value of the recording waveform stored in the internal memory of the recording waveform generator 33 is corrected.

  Correction of the set value of the recording waveform can be repeatedly executed. That is, a recording waveform is generated from binary recording data based on the corrected setting value of the recording waveform. Thereafter, the quality evaluation value of the reproduction signal is calculated according to the same procedure as described above. Based on the calculated quality evaluation value, the set value of the recording waveform stored in the internal memory of the recording waveform generator 33 is corrected.

  When the correction of the set value of the recording waveform is repeatedly executed, the tap coefficient calculated from the second time onward may be used. By doing so, since the time for calculating the tap coefficient is omitted after the second time, the set value of the recording waveform can be corrected at high speed.

  The reproduction signal obtained by irradiating the optical information medium with laser light is sampled at a predetermined cycle, and the equalization coefficient that minimizes the difference between the target waveform and the waveform after equalization is equal to or greater than a certain number of samples. By using the least square method and the equalization coefficient, the playback signal is equalized to the partial response waveform by the calculated equalization coefficient, thereby reproducing the playback signal from a recording medium having a very high recording density with high quality. It can be applied to the use of recording / playback to acquire

It is a figure which shows one Embodiment of the function structure in the optical information reproducing | regenerating apparatus in this invention, especially an equalizer. It is a figure which shows one form of a function structure of the optical information reproducing | regenerating apparatus in this invention. It is a figure explaining a partial response waveform. It is a figure which shows the relationship between the number of reproduction signal samples, and a final error rate with respect to a phase change optical disk. It is a figure which shows the relationship between the number of reproduction signal samples, and a final error rate with respect to a reproduction-only optical disk. It is a figure which shows the relationship between the number of reproduction signal samples, and a final error rate about the case where defocusing is changed. It is a figure which shows one form of a function structure of the optical information reproducing | regenerating apparatus concerning Example 4 of this invention. It is a figure which shows one form of a function structure of the optical information recording / reproducing apparatus concerning the 5th Example of this invention.

Explanation of symbols

1, 12, 21 AD converter 2, 13, 22 Equalizer 3, 14, 23 Viterbi decoder 4 Target waveform generator 5 Equalization coefficient calculator 6 FIR filter 11 Amplifier 24 Signal evaluator 31 Optical disc 32 Optical head 33 Recording waveform generator

Claims (8)

  A method of equalizing a reproduction signal obtained by irradiating a laser beam to an optical information medium so as to approach a waveform having a predetermined characteristic, acquiring a reproduction signal sampled at a predetermined period, and performing binary identification A part of the reproduction signal that is sufficiently smaller than the number of samples corresponding to the target data length and that is equal to or greater than a certain number is used as a sample of the equalization coefficient calculation waveform, A reproduction signal equalization method for an optical information medium, wherein equalization coefficients that minimize the difference between the two are calculated all at once by the least square method, and the reproduction signal is equalized by the calculated equalization coefficients.   2. The method for equalizing a reproduction signal of an optical information medium according to claim 1, wherein the number of samples of the waveform used for equalization coefficient calculation is 3,000 or more.   3. The reproduction signal sampled according to claim 1, wherein the reproduction signal sampled at a predetermined period is input to a Viterbi decoder, and the reproduction signal is equalized from the binary data demodulated by the Viterbi decoder and the partial response waveform. A method for equalizing a reproduction signal of an optical information medium, wherein a target waveform is determined as a waveform.   4. The method for equalizing a reproduction signal of an optical information medium according to claim 3, wherein a partial response value (1, 2, 2, 2, 1) is used as the partial response waveform.   5. An optical information reproducing apparatus having a function of equalizing a reproduction signal by using the reproduction signal equalization method according to claim 1.   A reproduction signal is equalized using the reproduction signal equalization method according to any one of claims 1 to 4, and the quality of the reproduction signal is evaluated from the equalized reproduction signal and binary identification data. A signal quality evaluation method characterized by the above.   A method for equalizing a reproduction signal obtained by irradiating a laser beam to an optical information medium so as to approach a waveform having a predetermined characteristic, when reading information recorded on the optical information medium, A reproduction signal sampled at a period is acquired, and the reproduction signal is equalized using a predetermined initial filter coefficient to generate a first equalization signal, and the first equalization signal is converted into a Viterbi identification result. The target signal is generated from the provisional identification result and a predetermined partial response waveform by identifying and obtaining with a decoder. The target signal is sufficiently smaller than the number of samples for the data length to be subjected to binary identification, and consists of a certain number or more. A part of the reproduction signal is used as a sample of an equalization coefficient calculation waveform, and filter coefficients that reduce the difference between the equalized signal of the sample and the target signal with respect to the sample are collectively obtained. An optical information medium characterized in that the reproduced signal is equalized using the obtained filter coefficient to generate a second equalized signal, and the second equalized signal is identified using the Viterbi decoder Playback signal equalization method.   8. The method for equalizing a reproduction signal of an optical information medium according to claim 7, wherein the number of samples of the waveform is a number selected from 3,000 to 10,000.

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