WO2010090136A1 - 再生信号の評価方法および光ディスク装置 - Google Patents
再生信号の評価方法および光ディスク装置 Download PDFInfo
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- WO2010090136A1 WO2010090136A1 PCT/JP2010/051229 JP2010051229W WO2010090136A1 WO 2010090136 A1 WO2010090136 A1 WO 2010090136A1 JP 2010051229 W JP2010051229 W JP 2010051229W WO 2010090136 A1 WO2010090136 A1 WO 2010090136A1
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
- G11B20/10046—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
- G11B20/10046—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter
- G11B20/10055—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter using partial response filtering when writing the signal to the medium or reading it therefrom
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
- G11B20/10046—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter
- G11B20/10055—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter using partial response filtering when writing the signal to the medium or reading it therefrom
- G11B20/1012—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter using partial response filtering when writing the signal to the medium or reading it therefrom partial response PR(1,2,2,2,1)
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
- G11B20/10268—Improvement or modification of read or write signals bit detection or demodulation methods
- G11B20/10287—Improvement or modification of read or write signals bit detection or demodulation methods using probabilistic methods, e.g. maximum likelihood detectors
- G11B20/10296—Improvement or modification of read or write signals bit detection or demodulation methods using probabilistic methods, e.g. maximum likelihood detectors using the Viterbi algorithm
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
- H03M13/37—Decoding methods or techniques, not specific to the particular type of coding provided for in groups H03M13/03 - H03M13/35
- H03M13/39—Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
- H03M13/63—Joint error correction and other techniques
- H03M13/6343—Error control coding in combination with techniques for partial response channels, e.g. recording
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
- G11B20/10046—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter
- G11B20/10212—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter compensation for data shift, e.g. pulse-crowding effects
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
- G11B20/1816—Testing
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
- G11B20/1816—Testing
- G11B20/182—Testing using test patterns
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B2220/00—Record carriers by type
- G11B2220/20—Disc-shaped record carriers
- G11B2220/25—Disc-shaped record carriers characterised in that the disc is based on a specific recording technology
- G11B2220/2537—Optical discs
- G11B2220/2541—Blu-ray discs; Blue laser DVR discs
Definitions
- the present invention relates to a method for evaluating a reproduction signal obtained from an optical disk medium in which a recording mark having a physical property different from that of other parts is formed on the recording medium and storing information, and an optical disk apparatus using the method.
- optical disk media such as CD-R / RW, DVD-RAM, DVD ⁇ R / RW, Blu-ray Disc (hereinafter referred to as BD), and it is widely spread including media with two data layers. ing.
- BD Blu-ray Disc
- PRML Partial Response Maximum Likelihood
- a pattern including a virtual 1T run length is used as an error pattern in which an edge portion of a reproduction signal shifts to the left and right, and a sign is added based on the direction of edge shift.
- a reproduction signal evaluation technique for calculating a difference in sequence error and calculating an edge shift amount is disclosed.
- Patent Document 3 Japanese Patent Application Laid-Open No. 2005-196964
- Patent Document 4 Japanese Patent Application Laid-Open No. 2004-253114
- Patent Document 5 Japanese Patent Application Laid-Open No. 2003-151219 disclose an error corresponding to a correct pattern in advance.
- a method for evaluating the quality of a reproduced signal by using a table storing pattern combinations is disclosed.
- Patent Document 3 and Patent Document 4 the difference between the Euclidean distance between the reproduced signal and the correct pattern and the incorrect pattern is calculated, and the reproduced signal is calculated by the estimated bit error rate SbER (Simulated bit Error Rate) obtained from the average value and the standard deviation.
- SbER Simulated bit Error Rate
- Patent Document 5 discloses a technique for adjusting a recording condition so that a statistical error probability is minimized based on a difference in Euclidean distance between a reproduction signal and a correct pattern and an incorrect pattern.
- the bit error frequency can be ignored not only the edge shift but also the 2T shift and the 2T ball shift. Disappear.
- a plurality of error probabilities are processed into a positive pattern and an erroneous pattern, that is, the distribution is statistically processed for each evaluation bit string to be searched and extracted, and the quality of the reproduced signal is calculated using an average value and a standard deviation. Can be evaluated.
- JP 2003-141823 A JP 2005-346897 A JP 2005-196964 A JP 2004-253114 A JP 2003-151219 A
- Non-Patent Document 1 a PRML system with a constraint length of 5 or more is used in order to realize high-density recording equivalent to 30 GB or more in BD.
- the BD optical system conditions wavelength 405 nm, objective lens numerical aperture 0.85
- the amplitude of the 2T repetitive signal having the capacity of about 30 GB or more and the shortest run length becomes zero.
- a PR (1, 2, 2, 2, 1) method in which the target amplitude of the 2T repetition signal is zero is suitable as the PRML method.
- various evaluation techniques based on the error probability of the PRML method for example, the evaluation techniques described in Patent Documents 1 to 5 can be applied.
- the reproduction signal evaluation techniques described in Patent Documents 1 to 5 and the like have different configurations.
- the most probable evaluation bit string is searched and extracted from the binary bit strings output from the PRML decoder. A process is included.
- the most probable state transition sequence and the second most probable state transition sequence described in Patent Document 1, and the correct pattern and the incorrect pattern described in Patent Document 3 are target bit strings that should be spaced from the reproduction signal, respectively. It is the same thing in the meaning. Hereinafter, these will be collectively referred to as an evaluation bit string.
- N 2T is 0, 1, 2,. . . Is an integer.
- N 2T 0, 1, and 2 correspond to edge shift, 2T shift, and 2T ball shift, respectively, according to the above-described notation.
- N 2T is 0, 1, 2 , 3, 4, 5 and 6, the Hamming distances are 1, 2, 3, 4, 5, 6 and 7, respectively, and the first and second evaluation bit strings The Hamming distance between is (N 2T +1).
- the evaluation bit string is the relationship between the most probable first evaluation bit string and the second evaluation bit string corresponding to the target signal that minimizes the Euclidean distance from the target signal of the first evaluation bit string from among 2M bit strings. Can be easily enumerated by the mechanical operation of extracting.
- the accuracy of the binarized bit string obtained by the PRML system that is, the playback signal quality tends to improve as the constraint length increases. As the signal playback conditions such as multi-layer BD and high-speed playback become stricter in the future, the PRML system The restraint length is considered to be unavoidable.
- FIG. 2 is an example of an evaluation bit string corresponding to the PR (1, 2, 2, 2, 1) system with a constraint length of 5, and the same is described in Patent Document 4.
- the PRML system with a constraint length of 5 when used and the evaluation bit string is searched for and extracted from the binarized bit string of the PRML decoder and the quality evaluation of the reproduced signal is performed, there are 18 sets for each Hamming distance. A total of 54 sets, that is, 108 evaluation bit strings are listed. In the evaluation circuit that evaluates the reproduction signal, it is necessary to perform the search / extraction processing of these evaluation bit strings in parallel.
- FIG. 3 shows an evaluation bit string corresponding to PR (1, 2, 3, 3, 2, 1) having a constraint length of 6 according to the same notation.
- a set of evaluation bit strings corresponding to the Hamming distances 1, 2, and 3 is listed and classified for each Hamming distance, and it can be seen that there are 50 sets for each Hamming distance and a total of 300 evaluation bit strings.
- the bit length of each evaluation bit string is 11, 13 and 15, respectively.
- the Euclidean distances of the target signals of the evaluation bit string A and the evaluation bit string B are 28, 20 and 20, respectively.
- a total of 300 coincidence determination circuits are required to search and extract all evaluation bit strings from the binary bit string decoded from the reproduction signal by the PRML method.
- FIG. 5 summarizes the relationship shown in FIG. 4 in a table.
- a problem to be solved by the present invention is to provide a reproduction signal evaluation method and provision capable of evaluating the quality of a reproduction signal with a simple circuit configuration, preventing an increase in circuit scale when the PRML method is used, and an optical disk using the same. The provision of equipment.
- the present invention aims to increase the capacity of 30 GB or more on the basis of the BD system, the following description will be made assuming that the shortest run length of the modulation code is 2T.
- FIG. 1 A concept for simplifying the determination of whether or not a predetermined evaluation bit string exists in the binarized bit string output from the PRML decoder will be described with reference to FIG.
- This is a list of common terms extracted from the evaluation bit string corresponding to PR (1, 2, 2, 2, 1) having a constraint length of 5 shown in FIG.
- the 108 evaluation bit strings corresponding to the Hamming distances 1, 2, and 3 are a main bit string having bit lengths 5, 7, and 9, respectively, and a 2-bit sub-bit string XX, YY can be expressed.
- the main bit string is “00011”, “00111”, “11100”, and “11000”, and when the Hamming distance is 2, “0001100”, “0011000”, “1110011”, 4 for “1100111” and a Hamming distance of 3, “000110011”, “001100111”, “111001100”, and “110011000”, and the sub-bit string AA is “00”, “10”, or “ 11 ”and the sub-bit string BB is“ 00 ”,“ 01 ”, or“ 11 ”.
- organizing and describing the evaluation bit string is a foothold for simplifying the reduction in circuit scale.
- FIG. 7 shows the result of arranging the main bit string and the lucky bit string in the same manner.
- the main bit string is “00011”, “00111”, “11100”, and “11000”, and when the Hamming distance is 2, “0001100”, “0011000”,
- the sub bit string A is “0” or “1”
- the sub bit string B is also “0” or “1”.
- FIG. 8 shows the result of extracting and arranging common terms from the evaluation bit string corresponding to the constraint length 6 PR (1, 2, 3, 3, 2, 1).
- the main bit string is the same as that shown in FIG.
- the sub-bit string AAA is “000”, “011”, “100”, “110”, or “111”
- the sub-bit string BBB is “000”, “001”, “100”, “110”, or “111”
- the sub-bit string CCC is “000”, “001”, “011”, “110”, or “111”
- the sub-bit string DDD is “000”, “001”, “011”, “ 100 "or” 111 ".
- the main bit string is determined without depending on the constraint length of the PRML method.
- the shortest run length m is 2T
- the length of the main bit string is (2m + 1 + 2N 2T ).
- the main bit string means the shortest bit string that is determined according to the number of consecutive 2Ts included in the evaluation bit string.
- the length of the bit string necessary for calculating the Euclidean distance from the reproduction signal is (2N ⁇ 1 + 2N 2T ) using the PRML constraint length N.
- the shortest run length m 2 (N ⁇ 3).
- the length of the sub-bit string was 1, 2, and 3 corresponding to the constraint lengths 4, 5, and 6, respectively. From this, it can be seen that the length of the sub-bit string is equal to (N-3).
- the sub-bit string has a length of (N-3), is added to both sides of the main bit string, and is a bit string for determining boundary conditions necessary for calculating the Euclidean distance depending on the constraint length of the PRML method. It has a meaning as. This is the reason why the length of the sub-bit string does not depend on the Hamming distance.
- the evaluation bit string can be organized and expressed by using the main bit string that does not depend on the constraint length N of the PRML method and the sub-bit string having a length (N-3) added to both ends of the main bit string. Is possible.
- the sub-bit string plays a role of satisfying the shortest run length limit for calculating the Euclidean distance between the reproduction signal and the target signal and determining the boundary condition in the Euclidean distance calculation. It is added to the main bitstream to carry. Therefore, the corresponding portion of the binarized bit string output from the PRML decoder and the sub bit string need to be the same.
- a state less than the shortest run length does not exist inside, and the binary bit string output as a result does not include a bit string less than the shortest run length.
- the first and second evaluation bit strings generated including the sub bit string are automatically satisfied by an operation of extracting and copying the sub bit string from the corresponding portion from the binarized bit string. According to this idea, it can be seen that the bit string searched and extracted from the binarized bit string is only the main bit string shown above.
- the evaluation bit string can be expressed by the sum of the main bit string and the sub bit string provided on both sides of the main bit string (outside the first bit and the end bit of the main bit string).
- the length of the main bitstream is determined as (2m + 1 + 2N 2T ) by the shortest run length and the number of consecutive runs, and does not depend on the PRML constraint length N.
- the sub bit string is equal to the bit string of the corresponding part of the binarized bit string.
- the length of the evaluation bit string is (N ⁇ 3), where N is the constraint length.
- the evaluation bit string can be determined only by determining whether or not the inspection part in the binarized bit string matches the main bit string. In order to determine the most probable first evaluation bit string, it is determined whether or not a predetermined main bit string is present in the binarized bit string output from the PRML decoder.
- the bit string may be used by copying from the binarized bit string.
- FIG. 9 summarizes the operations for generating the second main bit string.
- the main bit string shown above is listed in the column of the main bit string (Main bit array). Based on the relationship between the main bit string and the sub bit string described above, the second main bit string in the first evaluation bit string is replaced with the second main bit string having the minimum Euclidean distance. Can be generated.
- the four main bit strings existing for each Hamming distance are referred to as a main bit string group, and a group number having the same value as the Hamming distance is assigned.
- the type numbers 1, 2, 3, and 4 are sequentially assigned to the four main bit strings included in the same main bit string group.
- the main bit string is identified by the relationship between the group number and the type number. This is performed as 1-1 and 1-2, and this is called a main bit string number.
- the method for generating the second main bit string can be easily realized by referring to the first main bit string number and the corresponding second main bit string number as shown in the figure.
- the generation of the second main bit string is realized by inversion of a predetermined bit in the main bit string. For example, no. When the third bit of the main bit string “00011” of 1-1 is inverted, It matches the main bit string “00111” of 1-2. No. When the third bit and the fifth bit of “0001100” of 2-1 are inverted, No. 2 is obtained. It matches with “0011000” in 2-2. Thus, the corresponding main bit string can be generated by the same bit inversion operation for each Hamming distance. In the figure, a bit string inversion mask indicating a bit string to be inverted is also shown. In the bit string inversion mask, the bit position to be inverted can be represented as 1, for example, “00100”, “0010100”.
- FIG. 10 schematically shows a method for simplifying the evaluation bit string determination in the binarized signal in accordance with the above description.
- the evaluation bit string determination according to the present invention is performed by the following steps as shown in the figure.
- Step-1 A non-negative integer i is used to open a detection window of 5 + 2i bits, that is, a bit length equal to the main bit string, in the binarized bit string output from the PRML decoder, and make a match determination with the main bit string.
- Step-2 If a bit string that matches the main bit string appears in the detection window, the binarized bit string is cut out together with the portion that matches the main bit string and two sub-bit strings of (N-3) -bit length on both sides of the bit string to perform the first evaluation. Generate a bit string.
- the main bit string “00011” whose match is detected is cut out together with the sub bit string “11” on the left side and the sub bit string “11” on the right side to generate the first evaluation bit string “110001111”. It was. (Step-3) Next, a predetermined operation is performed on the portion of the first main bit string included in the first evaluation bit string to convert it into a corresponding second main bit string, thereby generating a second evaluation bit string.
- the main bit string “00011” in the first evaluation bit string “110001111” is converted into the main bit string “00111”, and the second evaluation bit string “110011111” is generated.
- the most probable first evaluation bit string and the second most probable second evaluation bit string generated in this manner are transferred to the Euclidean distance calculation circuit, whereby the Euclidean distance from the reproduction signal is calculated.
- the evaluation circuit according to the reproduction signal evaluation method of the present invention can be easily realized, and if this is used, an optical disk apparatus capable of evaluating the reproduction signal with a simple configuration can be provided.
- the present invention it is possible to greatly reduce the circuit scale and provide a reproduction signal evaluation method and provision capable of evaluating the quality of a reproduction signal with a simple circuit configuration, and an optical disk apparatus using the method. I was able to.
- a PRML system having a constraint length of 5 or more is necessary to ensure the necessary reproduction signal accuracy. Therefore, the present invention is considered to be particularly effective for signal reproduction processing using the PRML system having a constraint length of 5 or more, such as the PR (1, 2, 2, 2, 1) system.
- FIG. 6 is a schematic diagram for simplifying pattern determination of an evaluation bit string.
- FIG. 6 is a schematic diagram of a simplified method for determining a pattern of an evaluation bit string.
- FIG. 4 is a schematic diagram of a main bitstream determination method.
- FIG. 4 is a schematic diagram of a main bitstream determination method.
- FIG. 9 is a schematic diagram of a method for generating a second main bitstream.
- FIG. 9 is a schematic diagram of a method for generating a second main bitstream.
- FIG. 9 is a schematic diagram of a method for generating a second main bitstream. Schematic diagram of the run length violation inspection method.
- difference of a recording mark The figure which shows distribution of D value.
- the figure which shows the correlation of a bit error rate and SbER (classification according to shift direction).
- PR (1, 2, 2, 2, 1) correspondence evaluation bit string table The figure which shows the correlation of a bit error rate and SbER (classification of the front and back edges).
- PR (1, 2, 2, 2, 1) correspondence evaluation bit string table (group table).
- the figure which shows the experimental result of a bit error rate and SbER The figure which shows the experimental result of a bit error rate and SbER.
- the figure which shows the focus adjustment method using the evaluation method of a present Example. 1 is a schematic diagram showing an overall configuration of an optical disc apparatus. The flowchart of evaluation of a reproduction signal.
- the main bit string number is defined as a group number-type number
- the main bit string number is as shown in the figure as 1-1, 1-2, 1-3, 1-4, 2-1,.
- a unique identification number can be defined for each main bitstream.
- the second bit string operation is an operation for inverting all the values of the elements of the main bit string between “1” and “0”. This is called an all-bit inversion operation.
- the relationship between the main bit string type numbers can be organized.
- the bit string inversion mask operation for example, the main bit string numbers 1-2 and 1-4 can be obtained by performing the bit string inversion mask operation on the main bit string numbers 1-1 and 1-3, respectively.
- the all bit inversion operation for example, the main bit strings 1-3 and 1-4 can be obtained by performing the all bit inversion operation on the main bit strings 1-1 and 1-2, respectively.
- other main bit strings can be obtained using the operation based on the main bit string type number 1 of each group and the bit string inversion mask and the all bit inversion operation.
- FIG. 13 is a schematic diagram showing a main bit string search determination method. Using the same length detection window as the length M of the main bit string to be determined, that portion is extracted from the binarized bit string output from the PRML decoder.
- the aforementioned main bit string group number G is N 2T +1.
- the classification numbers 1, 3, 2, and 4 are used here because all bits are inverted. In the figure, the determination of the main bit string group 1 is shown.
- FIG. 14 is a schematic diagram showing another method of search determination of the main bit string.
- the value of two consecutive bits at both ends of the main bit string listed in FIG. 12 is “00” or “11”.
- the main bit string is not included if the continuous 2-bit values at both ends are neither “00” nor “11”.
- the value of two consecutive bits at both ends is “00” or “11”, it is possible to narrow down main bit string candidates that may match. This is because, as described above, the main bit string identification numbers 1, 3, 2, and 4 are in the relationship of all bit inversions.
- FIG. 1 the main bit string identification numbers 1, 3, 2, and 4 are in the relationship of all bit inversions.
- main bit string group 1 summarizes the relationship between the continuous 2-bit values at both ends and the main bit string that is a match candidate.
- main bit string group 1 if the value of 2 bits on the left side (the data side with the new time) is “00” and the 2 bits on the right side is “11”, the main bit string matches The candidate is the main bit string number 1-1 or 1-2. Conversely, when the left two bits are “00” and the right two bits are “11”, the match candidate is the main bit string number 1-3 or 1-4.
- this determination result can be shared by all main bit string groups.
- the scale of the determination circuit that determines whether there is a part that matches the main bit string in the binarized data string can be reduced.
- the most probable state transition that is, the first evaluation bit string
- the second most probable state transition that is, the Euclidean distance
- the constraint length of the PRML decoder is N, and the main bit string existing in the binarized data string is the first main bit string.
- the first evaluation bit string described above is a bit string having a length (2N ⁇ 1) including the first main bit string included in the binarized data.
- the second evaluation bit string corresponding to this is obtained by replacing the first main bit string in the first evaluation bit string with the second main bit string having the shortest Euclidean distance. Therefore, the main part of the method for generating the first and second evaluation bit strings is a process of generating a corresponding second main bit string from the first main bit string.
- the process of generating the second main bit string that minimizes the Euclidean distance from the first main bit string depends on the identification number of the first main bit string included in the binarized data string as shown in FIG. This can be implemented by selecting the corresponding second main bit string. If the identification number of the main bit string shown in FIG. 12 is used as address information or the like, as shown in FIG. 18, all the main bit strings are listed, and the main bit string of the address corresponding to the first main bit string is selected. Thus, the second main bit string can be uniquely determined. When such a method is implemented in a circuit, a reference table storing the value and address information of the main bit string and the address information of the corresponding second main bit string may be used.
- the relationship between the main bit string identification numbers 1 and 2, and 3 and 4 is the relationship of mutual conversion by the bit string mask inversion operation.
- FIG. 19 schematically shows a method of generating the second main bit string by the bit string mask inversion operation. Such an operation can be easily implemented in a circuit using a bitwise XOR operation or the like.
- FIG. 20 is another embodiment showing a method for generating the second main bit string.
- the bit shift operation is a kind of operation that can be processed at the highest speed among the numerical operations handled by the CPU.
- the second main bit string is generated by the CPU. Is often desirable. In such a case, it is possible to minimize the increase in processing time by generating the second main bit string based on the shift operation.
- the bit elements of the second main bit stream are b [1], b [2], b [3],..., B [M-2], b [M-1], b [M] from the left, Referring to FIG.
- the bit elements of the second main bit string are b [1], b [1], b [2],..., B [M-3], b [ M-2], b [M], or b [1], b [3], b [4], ..., b [M-1], b [M], b based on the bit shift operation to the right Either [M].
- the former is when the bit string type numbers are 1 and 3, and the latter is when the bit string identification numbers are 2 and 4.
- FIG. 16 shows another embodiment showing the main bit string group of this embodiment.
- these non-matching bit elements are described as “X”.
- the value “Y” of the bit element represents bit inversion of “X”. If such a method is used, it is possible to detect common bit elements excluding mismatched bits.
- the method of generating the second main bit string using the first main bit string can also be schematically represented.
- FIG. 17 shows a case in which the mismatched bit elements “X” and “Y” in FIG. 16 are used, and the main bit strings having the smallest Euclidean distance and the values of the bit string elements being equal are represented by “aa” and “bb”.
- aa represents a 2-bit value
- bb is obtained by bit-inverting “aa”.
- the recognition of the main bit string type number can be uniquely determined by the value of the mismatch bit “X” and the value of the match bit “aa”.
- 2-bit address values it is possible to distinguish the four main bit strings by giving unique addresses respectively.
- the classification based on the main bit string is applied to the quality evaluation of the reproduction signal.
- quality evaluation by the SbER method estimatemated bit error rate: Simulated bit Error Rate
- the difference (D value) in the Euclidean distance between the reproduction signal and the target signal corresponding to these evaluation bit strings is obtained for the most likely first evaluation bit string and the second most likely second evaluation bit string.
- the distribution of the D value is obtained for each first evaluation bit string, and the bit error rate is calculated (estimated) using the average, standard deviation, and Hamming distance of each distribution.
- this estimated bit error rate is an index indicating the probability of state transition.
- the first evaluation bit string and the second most likely second evaluation bit string are held in the form of a table or the like. As described above, the number of evaluation bit strings increases exponentially when the constraint length of the PRML system to be used increases as the density of the optical disk increases.
- the circuit scale can be greatly reduced. If this is applied to the evaluation of the reproduction signal, the scale of the evaluation circuit can be greatly reduced while ensuring the same evaluation performance.
- the PRML system to be used is a PR (1, 2, 2, 2, 1) system with a constraint length of 5.
- the evaluation bit string is a combination of twelve main bit strings and two sub-bit strings represented by AA and BB of 2 bits on each side.
- the main bitstream type number 1 is “00011”, “0001100”, and “000110011”
- the main bitstream type number 2 is “00111”, “0011000”, and “1110011”
- the main bitstream type number 3 is “11100”.
- the 2-bit sub-bit string AA is “00”, “10”, or “11”, and the sub-bit string BB is either “00”, “01”, or “11”.
- a bit string inversion mask operation using the bit inversion masks “00100”, “0010100”, and “001010100” is performed for each group,
- the converted main bit string may be used as the second evaluation bit string.
- the main bit string type number is 1
- the evaluation corresponds to the evaluation of the error probability from the main bit string No. 1 to No. 2, and represents a shift to the left edge (negative side in the time direction) of the front edge of the mark or the 2T mark.
- the evaluation with the main bitstream type number 2 corresponds to the evaluation of the error probability from the main bitstream number 2 to the first, to the front edge of the mark or to the right side of the 2T mark (positive side in the time direction). Represents the shift.
- the evaluation with the main bit string type number 3 corresponds to the evaluation of the error probability from the main bit string number 3 to 4, and represents a shift to the left edge of the mark or the 2T space to the left.
- the evaluation of the main bit string type number 4 corresponds to the evaluation of the error probability from the main bit string number 4 to 3, and represents the shift of the mark to the right side of the trailing edge or 2T space.
- the evaluation is related to the front and rear edges of the mark
- the group number is an even number
- the evaluation is related to the mark or space shift.
- Information stored in the optical disk medium is stored as physically different states such as pits and spaces or crystals and amorphous. At this time, for various reasons, it is well known that the state in which the reliability of recorded information is the highest is not necessarily symmetrical in the level direction and the time direction as in the PRML target signal. As a result, asymmetry and edge shift remain in the reproduction signal obtained from the optical disk medium.
- FIG. 23 is a schematic diagram showing an edge (broken line) of a mark recorded with an optimum recording power and an edge (filled) of a mark recorded with a power lower than the optimum recording power.
- the recording power is insufficient, both the front edge and the rear edge of the mark are shifted in the direction of shortening the mark. That is, the front edge is shifted to the right in the figure, and the rear edge is shifted to the left.
- recording marks are formed by irradiating with a focused laser beam, so that the edge shift amount caused by the influence of fluctuations in recording power differs between the front and rear edges.
- the shift amount of the leading edge is directly affected by the decrease in recording power, whereas the shift amount of the trailing edge is less than the leading edge because of heat accumulation during mark recording. This is because it is not easily affected.
- the difference in the residual shift of the front and rear edges with respect to the power fluctuation has been described.
- the time increment of the recording pulse is a discrete value such as T / 16 or T / 32. Therefore, staying at the edge shift is inevitable.
- the formation of the mark becomes unstable, and as a result, edge fluctuation increases and the reproduction signal quality may deteriorate.
- the stability of the system is improved by forming the recording marks short in advance. In this way, edge shifts remain in marks recorded on an actual optical disk medium depending on fluctuations in recording power, residual recording pulse adjustment errors, differences in characteristics of recording materials, etc. Is different.
- the optical system conditions of the linear diffraction optical simulator are a wavelength of 405 nm, an objective lens numerical aperture of 0.85, and the recording mark conditions are a mark width of 0.22 ⁇ m, a mark part reflectance of 1%, and a space part reflectance of 10. %, And the length corresponding to the detection window width T was 56 nm (corresponding to a BD line recording density of 33 GB).
- the SNR of the reproduction signal was changed by applying white noise to the reproduction signal obtained from the linear diffraction optical simulator.
- a conventional equalizer defined in the BD standard is used, the boost amount is 12 dB, PR (1, 2, 2, 2, 1) is used as the PRML system, A 21-tap FIR (Finite Impulse Response) filter was used as an automatic equalizer.
- each hamming distance can be grouped in a direction in which the mark becomes larger and smaller in order to evaluate by error type. This corresponds to the case where the reproduction signal has asymmetry.
- the influence is examined by giving a phase shift in the time direction to the reproduction signal. That is, the influence of SNR is evaluated by applying white noise, the influence of asymmetry is evaluated as an offset in the level direction, and the influence of edge shift is evaluated as a phase shift in the time direction.
- the coefficient of each tap is a value symmetrical with respect to the center in order to prevent the applied phase shift from being canceled by the automatic equalizer described above.
- FIGS. 24A to 24C show the results of calculating the distribution of D values when there is an SNR, an offset, and a phase shift.
- the SNR is the ratio of the one-side amplitude of the reproduction signal and the standard deviation of the applied white noise, and was set to ⁇ 22 dB.
- the Hamming distance is 1, “Edge” is included, and when the Hamming distance is 2, 2T is included, so “2T (1)”. When the Hamming distance is 3, 2T is included, so “2T (2 ) ”.
- FIG. 24A when neither an offset nor a phase shift is added to the reproduction signal, “Edge”, “2T (1)”, and “2T (2)” are each distributed in one Gaussian distribution. .
- FIG. 24B shows a distribution when there is an offset in the level direction.
- a case where the offset amount is 0.02 with respect to the amplitude of the reproduction signal is schematically shown.
- the symbol “LeL” in the figure indicates the leftward shift of the front edge
- “LeR” indicates the rightward shift of the front edge
- “TeL” indicates the leftward shift of the rear edge
- “TeR” Each shift of the trailing edge to the right is shown.
- the distribution of “Edge” and “2T (2)” is split into two distributions in the direction of increasing the mark (LeL and TeR) and the direction of decreasing the mark (LeR and TeL).
- the distribution of “2T (1)” remains one distribution without splitting.
- the four groups included in the Hamming distance 2 are evaluated when the 2T mark and the 2T space are shifted to the left and right, respectively, and the change in the size of the mark or space is evaluated. This is due to not being a thing. In the SbER method, six distributions are formed, but it can be seen that this is not the case in the method of this embodiment.
- FIG. 24C shows a distribution when there is a phase shift in the time direction.
- the case where the detection window width T is 10% as the phase shift amount is shown.
- the symbol “ ⁇ L” represents a shift in the left direction
- “ ⁇ R” represents a shift in the right direction.
- all of “Edge”, “2T (1)”, and “2T (2)” are split into two distributions of “ ⁇ L” and “ ⁇ R”, respectively. .
- the six distributions obtained here have different grouping conditions from the distribution obtained in FIG. 24B.
- FIG. 25 shows the result of the simulation.
- the bit error rate and SbER have a good correlation with respect to all of (a) SNR, (b) offset, and (c) phase shift.
- (2) Independent evaluation of 6 evaluation bit strings depending on changes in mark size As described above, two groups per hamming distance are grouped into a group with a large mark and a group with a small mark. is there. The circuit scale is reduced to 1/18 of the case where all evaluation bit strings are handled independently.
- FIG. 26 shows the result of the simulation.
- SNR and (b) the bit error rate and SbER have a good correlation with respect to the offset, but (c) the SbER is about 1000 times maximum with respect to the phase shift. It turns out that it has an error.
- This reason reflects the result of FIG. 24C, and the grouping focusing on the size of the mark depends on obtaining the average and standard deviation by combining two distributions split by phase shift into one. Is.
- This method is very effective for simplifying the circuit scale, but when there is a phase shift (corresponding to the residual edge shift) and the quality of the reproduced signal is evaluated, the bit error rate and SbER The error will increase.
- FIG. 27 shows the result of the simulation.
- the bit error rate and SbER have a good correlation with respect to all of (a) SNR, (b) offset, and (c) phase shift.
- the error between the first evaluation bit string and the second evaluation bit string corresponds to the shift of the edge or mark to the left and right. This is because the average and the standard deviation are calculated with the distribution split with respect to the phase shift as one distribution.
- 12 group independence according to main bit string This is the main point of the grouping method of the present embodiment, and based on the contents organized in FIG. 22, a total of 12 corresponding to the four main bit strings for each Hamming distance.
- SbER is calculated independently for each group. As shown in FIGS. 24A to 24C, it can cope with offset and phase shift (corresponding to asymmetry and residual edge shift). The circuit scale is reduced to 1/9 of the case where all evaluation bit strings are handled independently.
- This grouping method focusing on the main bit string of this embodiment is expected to have a good correlation between the bit error rate and SbER for all of (a) SNR, (b) offset, and (c) phase shift.
- Figure 28 shows the simulation results. As can be seen from the figure, it was confirmed that the bit error rate and SbER have a good correlation with respect to all of (a) SNR, (b) offset, and (c) phase shift. Although the circuit scale is reduced to 1/9, it can be seen that the correlation performance equivalent to the case where all 108 evaluation bit strings are calculated independently can be obtained.
- the effect of the present embodiment has been described in the case where the Hamming distance is 1, 2, 3, that is, the number of 2T included in the evaluation bit string is 0, 1, 2.
- the number of continuous 2Ts in the modulation code including the BD format is limited, there are cases where 2Ts are continuous up to about 6 in some cases. Therefore, it is necessary to clarify how many consecutive 2T evaluations are appropriate in order to provide an excellent evaluation method of a reproduction signal.
- FIG. 29 is a simulation result summarizing the relationship between SNR and SbER.
- the simulation conditions were as described above, and the calculation was performed for 2T continuous numbers 0, 1, 2, 3, 4, 5, and 6 included in the evaluation bit string.
- grouping by the main bit string was not performed, and the total value obtained by calculating SbER independently for all (36 ⁇ 6) evaluation bit strings was obtained.
- the number of consecutive 2Ts is 2 or more, and the SbER value gradually approaches a constant value. Therefore, it can be said that evaluating up to two continuous 2Ts is excellent from the balance between the evaluation performance of the reproduced signal and the circuit scale for realizing the reproduction signal.
- the evaluation bit string shown in FIG. 30 was used. This is an extension of the evaluation bit string table of FIG. According to the present embodiment, when the reproduction signal is evaluated and when the reproduction performance is important, the 2T continuous numbers 3, 4, 5, 6, that is, the Hamming distances 4, 5, 6 are used by using the evaluation bit string table of FIG. , 7 can also be evaluated.
- FIG. 31 shows the result of calculating the relationship between the bit error rate and SbER with respect to SNR, offset, and phase shift as described above, and examining the relationship between the 2T consecutive numbers included in the evaluation bit string to be used.
- the results of comparing four methods for grouping SbER calculations are shown.
- the error of the bit error rate and the error of SbER are continuous 2T included in the evaluation bit string to be evaluated. It can be seen that the number decreases as the number increases. It can also be seen that evaluating the number of continuous 2Ts up to two is superior from the balance between the evaluation performance of the reproduced signal and the circuit scale to be realized.
- the evaluation bit string discrimination method of this embodiment is as described with reference to FIG.
- the binarized signal generated by the PRML method corresponding to the shortest run length 2T automatically satisfies the run length limit.
- This assumption is correct in the general case of assessing the quality of the playback signal.
- a reproduction signal is evaluated including a defect on the optical disk medium, it is considered that the path merge is not completed according to the path memory length of the PRML circuit.
- 1T may be included in the binarized signal, and even if the main bit strings match, the run length restriction will not be satisfied if sub-bit strings at both ends are included.
- the SbER calculation circuit it may cause a malfunction.
- FIG. 32 is an evaluation bit string table when the left shift and the right shift are grouped with respect to FIG. As described above, when the main bit string is classified into the left shift and the right shift based on the meaning, the total number of groups is six.
- FIG. 33 shows simulation results showing the relationship between the bit error rate and SbER. (B) Although the error is large when there is an offset, it can be seen that the relationship between the bit error rate and SbER is relatively good as a whole.
- FIG. 34 is an evaluation bit string table when the front edge and the rear edge are grouped with respect to FIG. Similarly, the total number of groups is six.
- FIG. 35 is a simulation result showing the relationship between the bit error rate and SbER. (C) Although the error is large in the case of phase shift, it can be seen that the relationship between the bit error rate and SbER is relatively good as a whole.
- FIG. 36 is an evaluation bit string table in the case of grouping with respect to FIG. The simulation results are shown in FIG.
- the average value and the standard deviation are calculated as a1, a2 and ⁇ 1, ⁇ 2 for any two main bit strings
- the average value a and the standard deviation ⁇ when these are grouped are represented by a Gaussian distribution. According to the synthesis, it can be obtained approximately by the following equation.
- the SbER value with high accuracy is calculated by grouping into four main bit strings per Hamming distance and adding all the results by the method of obtaining the average and variance of the D values.
- (Equation 1) shows the case where the number of measurement events of the two distributions is substantially equal.
- the average value and the standard deviation of the composite distribution are obtained in consideration of the number of events. This is a well-known matter as a composition of Gaussian distribution.
- FIG. 37 shows experimental results showing the relationship between the bit error rate and SbER.
- five consecutive tracks were recorded so as to include the influence of crosstalk, and various stresses were applied to the central track for experiments.
- Specific stresses include radial tilt (R-tilt), tangential tilt (T-tilt), focus shift (AF), spherical aberration (SA) due to operation of the optical head beam expander, and changes in recording power ( Pw) and radial tilt are cases where the residual shift of the 2T mark is large due to the recording strategy (R-tilt (2T Shift)).
- the grouping by the main bit string is the four classifications shown in FIG.
- bit error rate and SbER are in good agreement, and it has been verified that the performance of the evaluation of the reproduced signal by this method is necessary and sufficient.
- the bit error rate is in the vicinity of 10 ⁇ 5
- the cause of the large variation is mainly the influence of the defect of the medium.
- FIG. 38 shows the experimental results when two classifications regarding the shift direction are performed in accordance with the evaluation bit string table of FIG. Although the error is slightly larger than the result of FIG. 37, the correlation between the bit error rate and SbER is good.
- FIG. 39 shows the experimental results when two classifications for the front and rear edges are performed according to the evaluation bit string table of FIG. Similarly, the error is slightly larger than the result of FIG. 37, but the correlation between the bit error rate and SbER is good.
- the ⁇ value of the synthesized Gaussian distribution can be obtained from the average value and the standard deviation value of four distributions obtained for each Hamming distance by the evaluation method of this embodiment.
- FIG. 40 shows experimental results showing the relationship between the bit error rate and the ⁇ value of the combined distribution. This can also be used as one of indexes having a high correlation with bit errors.
- FIG. 41 shows the experimental results showing the relationship between the focus offset amount and the SbER obtained by this embodiment. By using this relationship and minimizing SbER, an appropriate focus offset value learning process can be realized. The same method can be applied to various learning processes such as radial tilt, tangential tilt, spherical aberration, and recording power.
- the binary signal output from the PRML decoder is compared with the main bit string (S201). It is determined whether or not any main bit string is included in the binarized signal (S202). If not included (No), the process returns to S201 and the process is continued (Yes), as described in FIG. Processing is performed to generate a first evaluation bit string and a second evaluation bit string (S203). Next, the Euclidean distance between the equalized reproduction signal and the target signal of the first evaluation bit string and the second evaluation bit string is calculated, and a D value that is the difference between the two is obtained (S204).
- the D value obtained here is stored according to the determined main bit string, and the average value and the standard deviation are calculated (S205). It is determined whether or not acquisition of a predetermined amount of data has been completed (S206). If it has not been completed (No), the process returns to S201 to continue processing (Yes), and is calculated for each main bit string in S205.
- the evaluation value of the reproduction signal is calculated by synthesizing the average value and standard deviation of the D values (S207).
- FIG. 1 is an embodiment showing a configuration of a reproduction signal evaluation circuit for realizing the optical disk apparatus of the present embodiment.
- a reproduction signal 51 reproduced from an optical disk medium and subjected to analog filter processing (not shown) is converted into 6 to 8-bit digital data by an A / D converter 21 and equalized by an automatic equalizer 22. Thereafter, the signal is binarized by the PRML decoder 23 and a binarized signal 52 is output.
- the reproduction signal quality evaluation circuit 30 of this embodiment includes a main bit discrimination circuit 31, an evaluation bit string generation circuit 32, an Euclidean distance calculation circuit 33, a group-specific D value memory 34, and an evaluation value totaling circuit 35.
- the main bit string discriminating circuit 31 stores main bit string data, and determines whether or not the main bit string is included in the binarized signal 52.
- the evaluation bit string generation circuit 32 performs the processing described in FIG. 11 and generates the first evaluation bit string and the second evaluation bit string.
- the Euclidean distance calculation circuit 33 calculates the Euclidean distance between the target signal of the first evaluation bit string and the second evaluation bit string and the equalized reproduction signal 53 output from the automatic equalizer 22, and the difference between the two is calculated. A certain D value is obtained.
- the D value obtained here is sent to the group-specific D value memory 34 and stored according to the main bit string determined by the main bit determination circuit 31, and the average value and the standard deviation are calculated.
- the evaluation value totaling circuit 35 combines these results, calculates the evaluation result of the reproduction signal, and transfers the result to the CPU 140 in accordance with the instruction.
- the evaluation result SbER or the like can be used.
- the CPU 140 evaluates the quality of the reproduction signal while changing the focus offset, for example, and performs a focus offset learning process or the like so that this is the best. With such a configuration, it is possible to manufacture a circuit that implements the reproduction signal evaluation method of this embodiment.
- FIG. 42 is a schematic diagram showing a configuration example of an optical disc apparatus equipped with the reproduction signal evaluation method of this embodiment.
- the optical disk medium 100 mounted on the apparatus is rotated by a spindle motor 160.
- the laser power / pulse controller 120 controls the current flowing to the semiconductor laser 112 via the laser driver 116 in the optical head 110 so that the light intensity instructed by the CPU 140 is generated, and the laser light 114 is generated.
- the laser beam 114 is condensed by the objective lens 111 to form the light spot 101 on the optical disc medium 100.
- the reflected light 115 from the light spot 101 is detected by the photodetector 113 via the objective lens 111.
- the photodetector is composed of a plurality of photodetecting elements.
- the reproduction signal processing circuit 130 reproduces information recorded on the optical disc medium 100 using the signal detected by the optical head 110.
- This embodiment is built in the reproduction signal processing circuit 130 as the circuit block shown in FIG. With such a configuration, the optical disk apparatus of the present embodiment can implement a reproduction signal evaluation and various learning processing functions using the reproduction signal as an apparatus for realizing a BD of 30 GB or more.
- This embodiment relates to a method for evaluating a reproduction signal of a large-capacity optical disc and an optical disc apparatus, and is used for an optical disc apparatus having a capacity of 30 GB or more per layer.
Abstract
Description
(Step-1)
負でない整数iを用いて,PRMLデコーダから出力される2値化ビット列に5+2iビット,すなわち主ビット列と等しいビット長の検出窓を開いて,主ビット列との一致判定を行う。ここで,iは前述のN2Tに等しい意味をもち,ハミング距離を用いて,i=(ハミング距離)-1である。
(Step-2)
検出ウィンドウに主ビット列と一致するビット列が出現した場合,2値化ビット列から,主ビット列に一致した部分と,その両隣の(N-3)ビット長の2つの副ビット列と共に切り出して第1の評価ビット列を生成する。
(Step-3)
次に,第1の評価ビット列に含まれる第1の主ビット列の部分に所定の操作を施すことによって,対応する第2の主ビット列に変換し,第2の評価ビット列を生成する。
本発明の他の目的,特徴及び利点は添付図面に関する以下の本発明の実施例の記載から明らかになるであろう。
(1)全108評価ビット列独立
108(36×3)個の評価ビット列のそれぞれについて独立にSbERを算出し,それらの加算値として合計のSbERを求めるものである。回路規模は大きいがビットエラー率とSbERの相関には最も優れていると考えられる。
(2)マークの大きさ変化に依存した6評価ビット列独立
前述のように,マークが大きくなるグループとマークが小さくなるグループに分けて,ハミング距離当たり2つ,合計6つのグループ化を行なうものである。回路規模は全評価ビット列を独立に扱う場合の1/18に削減される。
(3)54評価ビット列独立
評価ビット列のグループ化手法として,第1の評価ビット列から第2の評価ビット列への評価と,その逆の評価をまとめて扱う方法が考えられる。これらは評価ビット列の相関が強いため,良好な評価値が得られると考えられるからである。回路規模は全評価ビット列を独立に扱う場合の1/2に削減される。
(4)主ビット列に応じた12グループ独立
これは本実施例のグループ化方法の主眼であり,図22に整理した内容に基づいて,ハミング距離ごとの4つの主ビット列に対応して合計12のグループに分けて独立にSbERを算出する方法である。図24A-24Cに示したように,オフセットと位相シフト(アシンメトリと残留エッジシフトに対応)に対して,対応可能なものである。回路規模は全評価ビット列を独立に扱う場合の1/9に削減される。本実施例の主ビット列に着目したこのグループ化方法は(a)SNR,(b)オフセット,(c)位相シフトの全てに対して,ビットエラー率とSbERは良好な相関を持つことが期待される。
上記記載は実施例についてなされたが,本発明はそれに限らず,本発明の精神と添付の請求の範囲の範囲内で種々の変更および修正をすることができることは当業者に明らかである。
22 自動等化器
23 PRMLデコーダ
30 再生信号の評価回路
31 主ビット列判別回路
32 パターン生成回路
33 ユークリッド距離計算回路
34 グループ別D値メモリ
35 SbER算出回路
51 再生信号
52 2値化信号
53 等化再生信号
100 光ディスク
101 光スポット
110 光ヘッド
111 対物レンズ
112 半導体レーザ
113 光検出器
114 レーザ光
115 反射光
116 レーザドライバ
120 レーザパワー/パルス制御器
130 再生信号処理器
140 CPU
160 スピンドルモータ
Claims (14)
- 情報が記録された記録媒体から得られる再生信号と複数の状態遷移における目標信号とを比較して,最も確からしい状態遷移を選択するPRML方式によって,前記再生信号を復号し時系列的に2値化ビット列を得る工程と,
前記再生信号の品質を,前記状態遷移における最も確からしい第1の状態遷移と2番目に確からしい第2の状態遷移との所定の組み合わせを検出する工程と,
前記第1の状態遷移の確からしさを表す指標Paと,前記第2の状態遷移の確からしさを表す指標Pbとして,|Pa-Pb|を用いて前記再生信号の品質を評価する再生信号評価方法において,
前記所定の組み合わせを検出する工程は,
前記記録媒体に記録された情報が最短ラン長2Tの符号を用いて変調されたものであるとき,
前記PRML方式の拘束長をN,0以上の整数をiとして,該iごとに長さL=5+2iの4個の特定の主ビット列からなる主ビット列群を用い,
該主ビット列と前記2値化ビット列の一部と比較して,前記主ビット列群の中から第1の主ビット列を選択する工程と,
前記第1の主ビット列を前記iによって定まる特定の演算によって定まる第2の主ビット列を生成する工程と,
前記第1の主ビット列を含む状態遷移を前記第1の状態遷移として定める工程と,
前記第2の主ビット列を含む状態遷移を前記第2の状態遷移として定める工程と,
を含むことを特徴とする再生信号の評価方法。 - 請求項1に記載の再生信号の評価方法であって,
前記4個の主ビット列は,
特定の主ビット列要素Aとの不一致ビットの数が前記iを用いて(i+1)である主ビット列要素Bと,
前記主ビット列要素Aに含まれる“0”と“1”を反転した主ビット列要素Cと,
該主ビット列要素Cとの不一致ビットの数が前記iを用いて(i+1)である主ビット列要素Dと,
であること,
を特徴とする再生信号の評価方法。 - 請求項1に記載の再生信号の評価方法であって,
前記主ビット列群の中から第1の主ビット列を選択する工程は,
前記4個の主ビット列と前記2値化ビット列の連続する5時刻の値の一致判定を行う工程,
または
前記長さMの範囲で前記主ビット列と前記2値化ビット列との一致ビット数を実質的に計数し,前記一致ビット数が0または前記Mであることを判定する工程,
または
任意の整数をkとして,時刻kにおける前記2値化ビット列の値をa[k]としたとき,
前記Mを用いて,連続する2ビットa[k],a[k+1]の値が“11”または“00”であることを判定する工程,
または
任意の整数をkとして,時刻kにおける前記2値化ビット列の値をa[k]としたとき,
前記Mを用いて,a[k]の値とa[k+M-1]の値に基づいて,前記第1の主ビット列群の中から前記2値化ビット列と比較するものを選び出す工程,
のうち少なくとも1つの工程を含むことを特徴とする再生信号の評価方法。 - 請求項1に記載の再生信号の評価方法であって,
前記第1の主ビット列のビット要素を左からb[1],b[2],...,b[M-1],b[M]としたとき,
b[3+2i]の値の“1”と“0”を反転した主ビット列を前記第2の主ビット列として用いる工程,
または
請求項2記載の主ビット列要素を含む主ビット列群を用い
前記第1の主ビット列が主ビット列要素Aを含む場合には前記第2の主ビット列として主ビット列要素Bを含むものを選択し,
かつ,前記第1の主ビット列が主ビット列要素Bを含む場合には前記第2の主ビット列として主ビット列要素Aを含むものを選択し,
かつ,前記第1の主ビット列が主ビット列要素Cを含む場合には前記第2の主ビット列として主ビット列要素Dを含むものを選択し,
かつ,前記第1の主ビット列が主ビット列要素Dを含む場合には前記第2の主ビット列として主ビット列要素Cを含むものを選択する工程,
または
前記iが奇数のとき,
左からb[M],b[M-1],...,b[2],b[1]なるビット要素を持つ主ビット列を前記第2の主ビット列として用いる工程,
または
該第1の主ビット列を左または右に1ビットだけシフトして得られるビット列の
左から1番目,2番目,M-1番目,およびM番目のビット要素をそれぞれb[1],b[2],...,b[M-1],b[M]で置き換え,
かつ全ビット長さをMとする主ビット列を前記第2の主ビット列として用いる工程,
のうち少なくとも1つの工程を含むことを特徴とする再生信号の評価方法。 - 請求項1に記載の再生信号の評価方法において,
前記4個の主ビット列群は
長さが5ビットのとき,「00011」,「00111」,「11100」,「11000」,
長さが7ビットのとき,「0001100」,「0011000」,「1110011」,「1100111」,
長さが9ビットのとき,「000110011」,「001100111」,「111001100」,「110011000」,
であることを特徴とする再生信号の評価方法。 - 請求項1に記載の再生信号の評価方法であって,
前記主ビット列ごとに前記|Pa-Pb|を独立に計算する工程,
を含むことを特徴とする再生信号の評価方法。 - 情報が記録された記録媒体から得られる再生信号と複数の状態遷移における目標信号とを比較して,最も確からしい状態遷移を選択するPRML方式によって,前記再生信号を復号し時系列的に2値化ビット列を得る手段と,
前記再生信号の品質を,前記状態遷移における最も確からしい第1の状態遷移と2番目に確からしい第2の状態遷移との所定の組み合わせを検出する手段と,
前記第1の状態遷移の確からしさを表す指標Paと,前記第2の状態遷移の確からしさを表す指標Pbとして,|Pa-Pb|を用いて前記再生信号の品質を評価する機能を備えた光ディスク装置において,
前記所定の組み合わせを検出する手段は,
前記記録媒体に記録された情報が最短ラン長2Tの符号を用いて変調されたものであるとき,
前記PRML方式の拘束長をN,0以上の整数をiとして,該iごとに長さL=5+2iの4個の特定の主ビット列からなる主ビット列群を用い,
該主ビット列と前記2値化ビット列の一部と比較して,前記主ビット列群の中から第1の主ビット列を選択する手段と,
前記第1の主ビット列を前記iによって定まる特定の演算によって定まる第2の主ビット列を生成する手段と,
前記第1の主ビット列を含む状態遷移を前記第1の状態遷移として定める手段と,
前記第2の主ビット列を含む状態遷移を前記第2の状態遷移として定める手段と,
を具備することを特徴とする光ディスク装置。 - 請求項7に記載の光ディスク装置であって,
前記4個の主ビット列は,
特定の主ビット列要素Aとの不一致ビットの数が前記iを用いて(i+1)である主ビット列要素Bと,
前記主ビット列要素Aに含まれる“0”と“1”を反転した主ビット列要素Cと,
該主ビット列要素Cとの不一致ビットの数が前記iを用いて(i+1)である主ビット列要素Dと,
であること,
を特徴とする光ディスク装置。 - 請求項7に記載の光ディスク装置であって,
前記主ビット列群の中から第1の主ビット列を選択する手段は,
前記4個の主ビット列と前記2値化ビット列の連続する5時刻の値の一致判定を行う手段,
または
前記長さMの範囲で前記主ビット列と前記2値化ビット列との一致ビット数を実質的に計数し,前記一致ビット数が0または前記Mであることを判定する手段,
または
任意の整数をkとして,時刻kにおける前記2値化ビット列の値をa[k]としたとき,
前記Mを用いて,連続する2ビットa[k],a[k+1]の値が“11”または“00”であることを判定する手段,
または
任意の整数をkとして,時刻kにおける前記2値化ビット列の値をa[k]としたとき,
前記Mを用いて,a[k]の値とa[k+M-1]の値に基づいて,前記第1の主ビット列群の中から前記2値化ビット列と比較するものを選び出す手段,
のうち少なくとも1つの手段を具備することを特徴とする光ディスク装置。 - 請求項7に記載の光ディスク装置であって,
前記第1の主ビット列のビット要素を左からb[1],b[2],...,b[M-1],b[M]としたとき,
b[3+2i]の値の“1”と“0”を反転した主ビット列を前記第2の主ビット列として用いる手段,
または
請求項2記載の主ビット列要素を含む主ビット列群を用い
前記第1の主ビット列が主ビット列要素Aを含む場合には前記第2の主ビット列として主ビット列要素Bを含むものを選択し,
かつ,前記第1の主ビット列が主ビット列要素Bを含む場合には前記第2の主ビット列として主ビット列要素Aを含むものを選択し,
かつ,前記第1の主ビット列が主ビット列要素Cを含む場合には前記第2の主ビット列として主ビット列要素Dを含むものを選択し,
かつ,前記第1の主ビット列が主ビット列要素Dを含む場合には前記第2の主ビット列として主ビット列要素Cを含むものを選択する手段,
または
前記iが奇数のとき,
左からb[M],b[M-1],...,b[2],b[1]なるビット要素を持つ主ビット列を前記第2の主ビット列として用いる手段,
または
該第1の主ビット列を左または右に1ビットだけシフトして得られるビット列の
左から1番目,2番目,M-1番目,およびM番目のビット要素をそれぞれb[1],b[2],...,b[M-1],b[M]で置き換え,
かつ全ビット長さをMとする主ビット列を前記第2の主ビット列として用いる手段,
のうち少なくとも1つの手段を具備することを特徴とする光ディスク装置。 - 請求項7に記載の光ディスク装置において,
前記4個の主ビット列群は
長さが5ビットのとき,「00011」,「00111」,「11100」,「11000」,
長さが7ビットのとき,「0001100」,「0011000」,「1110011」,「1100111」,
長さが9ビットのとき,「000110011」,「001100111」,「111001100」,「110011000」,
であることを特徴とする光ディスク装置。 - 請求項7に記載の光ディスク装置において,
前記主ビット列ごとに前記|Pa-Pb|を独立に計算する手段,
を具備することを特徴とする光ディスク装置。 - 情報が記録された記録媒体から得られる再生信号から生成される2値化ビット列に対し,現在の2値化ビット列が次に遷移する状態を記述する評価ビット列を複数生成し,前記現在の2値化ビット列から前記複数の評価ビット列への遷移の確からしさを各々評価することにより状態遷移後の2値化ビット列を決定し,当該決定を繰り返すことにより前記再生信号の復号を行うPRML方式により復号演算を実行する際における再生信号の評価方法において,
前記評価ビット列は,PRMLの拘束長によっては変化しない部分として定義される主ビット列と,当該主ビット列の先頭ビットと終端ビットの両側に付加される副ビット列との結合として表現され,
前記復号の実行時には,
前記状態遷移における最も確からしい第1の状態遷移に対応する第1の評価ビット列と,2番目に確からしい第2の状態遷移に対応する第2の評価ビット列とを生成し,
当該第1の評価ビット列および第2の評価ビット列を生成するに際し,
前記主ビット列を記述するビットパターンをあらかじめ複数準備し,
当該主ビット列と前記現在の2値化ビット列の一部を比較して,前記複数のビットパターンの中から,前記第1の評価ビットに適用する第1の主ビット列を選択し,
前記第1の評価ビットに適用する主ビット列に対して所定の演算を実行することにより前記第2の評価ビットに適用する第2の主ビット列を生成し,
前記第1の主ビット列および第2の主ビット列に対して,前記副ビット列を各々結合することにより,前記第1の評価ビット列および第2の評価ビット列を生成することを特徴とする再生信号の評価方法。 - 請求項13に記載の再生信号の評価方法において,
前記主ビット列は,
前記2値化ビット列の最短ラン長の連続数と,前記状態遷移の前後での前記2値化ビット列間のハミング距離に応じて定まることを特徴とする再生信号の評価方法。
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