Publication number | USRE34245 E |

Publication type | Grant |

Application number | US 07/578,178 |

Publication date | May 11, 1993 |

Filing date | Sep 6, 1990 |

Priority date | Dec 26, 1984 |

Fee status | Paid |

Also published as | DE3590661C2, DE3590661T, US4769819, WO1986003911A1 |

Publication number | 07578178, 578178, US RE34245 E, US RE34245E, US-E-RE34245, USRE34245 E, USRE34245E |

Inventors | Kiyoshi Matsutani, Ken Ohnishi |

Original Assignee | Mitsubishi Denki Kabushiki Kaisha |

Export Citation | BiBTeX, EndNote, RefMan |

Patent Citations (7), Referenced by (1), Classifications (11), Legal Events (2) | |

External Links: USPTO, USPTO Assignment, Espacenet | |

US RE34245 E

Abstract

Errors which arise in recording and reproducing data in a recording material are corrected with the use of an error correction code such as an RS (Reed-Solomon) code, and a two stage C_{2} and C_{1} coding method is conducted at an interval of repetition of a combination of [k_{2} /n_{2} ] and [k_{2} /n_{2} ]+1 on digital data having a two dimensional arrangement of k_{1} in the first direction and k_{2} in the second direction, whereby burst error correction ability is enhanced by the enhancement of error correction capacity.

Claims(4)

1. A two stage coding system for encoding digital information arranged in a matrix of k_{1} ×q digits in a first direction, and k_{2} digits in a second direction orthogonal to the first direction, wherein

K_{1}, q, and k_{2} are integers,

K_{1} <k_{2} ; q=the number of digits per data word, and

K_{1}, K_{2} =the number of data words in said first and second directions respectively, comprising:

C_{2} encoder means for encoding said digital information with a C_{2} code on a Galois Field GF (2^{q}), including means for .[.numbering.]. .Iadd.selecting .Iaddend.data words in said matrix diagonally from an arbitrary data word a_{1} and establishing a_{2} to a_{n2}, wherein n_{2} is the length of .[.code.]. .Iadd.the .Iaddend.C_{2} encoded data, such that ##EQU8## wherein h_{1} to h_{n2-1} satisfy the following

h_{2i-1}=[K_{2}/n_{2}]

h_{2i}=[k_{2}/n_{2}]+1 1≦i≦(n_{2}-1)/.Badd.2

.Iadd.said C_{2} encode means including .Iaddend.means for C_{2} encoding said .[.numbered.]. .Iadd.selected .Iaddend.data words, and means for adding the obtained C_{2} code to an end of said matrix in said first direction; and

C_{1} encoder means for encoding said C_{2} encoded matrix with a C_{1} code having a .Iadd.predetermined .Iaddend.length .[.of n_{1} .]. on a GF (2^{q}) for each row of data words in said first direction, and adding the obtained C_{1} code to an end of said matrix in said first direction. .Iadd.

2. The two stage coding system of claim 1 wherein said means for C_{2} encoding further encodes said selected data words in each said diagonal;

said means for adding a C_{2} code to the end of each said diagonal to form a C_{2} code field at the end of said matrix in said first direction. .Iaddend. .Iadd.3. The two stage coding system of claim 2 wherein said C_{2} encoder means subtracts n_{2} ×k_{2} from any initially calculated value of a_{2} to a_{n2} that exceed n_{2} ×k_{2} to select data words in said matrix diagonally. .Iaddend. .Iadd.4. The two stage coding system of claim 1 wherein said C_{2} encoder means subtracts n_{2} ×k_{2} from any initially calculated value of a_{2} to a_{n2} that exceed n_{2} ×k_{2} to select data words in said matrix diagonally. .Iaddend. .Iadd.5. The two stage coding system of claim 1 wherein additional data added to said rows of data words in said first direction prior to encoding of said C_{2} encoded matrix with a C_{1} code is also encoded with this C_{1} code by said C_{1} encoder means. .Iaddend. .Iadd.6. A two stage coding system for encoding digital information arranged in an information matrix of k_{1} ×q digits in a first direction, and k_{2} digits in a second direction orthogonal to the first direction, wherein

k_{1}, q, and k_{2} are integers,

k_{1} <k_{2} ; q=the number of digits per data word, and

k_{1}, k_{2} =the number of data words in said first and second directions respectively, comprising:

C_{2} encoder means for encoding said digital information with a C_{2} code on a Galois field GF(2^{2}), said C_{2} encoder means selecting data words in said information matrix diagonally from an arbitrary data word a_{1} and including a_{2} to a_{n2}, wherein n_{2} is the length of the C_{2} encoded data, such that

a_{2}=a_{1}+n_{2}×h_{1}+1

a_{3}=a_{2}+n_{2}×h_{2}+1

:

a_{k1}=a_{k1-1}+n_{2}×h_{k1-1}+1

:

a_{n2}=a_{n2-1}+n_{2}×h_{n2-1}+1,

h_{1} to h_{2n-1} each being selected from one of h_{A} and h_{B}, wherein,

h_{A}=[k_{2}/n_{2}],

h_{B}=[k_{2}/n_{2}]+1, and

h_{A}×l_{1}+h_{B}×l_{2}≦k_{2}, where

l_{1}+l_{2}=n_{2}

said C_{2} encoder means forming said C_{2} code from said selected data words and adding the obtained C_{2} code to an end of said information matrix in said first direction thereby forming a C_{2} encoded matrix; and

C_{1} encoder means for encoding each line in said first direction of said C_{2} encoded matrix with a C_{1} code having a predetermined length on a GF(2^{q}), and adding the obtained C_{1} code to an end of each said line of said matrix in said first direction to form a C_{2}

C_{1} encoded matrix. .Iaddend. .Iadd.7. The two stage coding system of claim 6 wherein a group of two or more adjacent lines h_{1}, h_{2}, . . . utilize a repetition pattern having at least one of each of h_{A} and h_{B} contained therein, said selection of data words a_{1} to a_{n} by said C_{2} encoder means utilizing said repetition pattern for selection of all said data words (a) in said information matrix. .Iaddend. .Iadd.8. The two stage coding system of claim 7 wherein said repetition pattern is selected from the group consisting of h_{A}, h_{B} ; h_{B}, h_{A} ; and h_{A}, h_{B}, h_{B}. .Iaddend. .Iadd.9. The two stage coding system of claim 6 wherein:

h_{2i-1}=h_{A},

h_{2i}=h_{B},

where 1<i<(n_{2} -1)/2. .Iaddend. .Iadd.10. The two stage coding system of claim 6 wherein:

h_{2i-1}=h_{B},

h_{2i}=h_{A},

where 1<i<(n_{2} -1)/2. .Iaddend. .Iadd.11. The two stage coding system of claim 6 wherein said C_{2} encoder means repeatedly selects data words in said information matrix from an arbitrary data word a_{1} and including a_{2} to a_{n2}, said C_{2} encoder means repeatedly forming said C_{2} code and adding said C_{2} to the end of the matrix, each repetition starting from a different arbitrary data word a_{1}. .Iaddend. .Iadd.12. The two stage coding system of claim 11 wherein said C_{2} encoder means selects k_{2} arbitrary data words from which to perform selecting, forming and adding to thereby form a complete C_{2} encoded matrix. .Iaddend. .Iadd.13. The two stage coding system of claim 6 wherein said means for C_{2} encoding further encodes said selected data words in each said diagonal;

said means for adding a C_{2} code to the end of each said diagonal to form a C_{2} code field at the end of said information matrix in said first direction. .Iaddend. .Iadd.14. The two stage coding system of claim 6 wherein additional data added to said rows of data words in said first direction prior to encoding of said C_{2} encoded matrix with a C_{1} code is also encoded with this C_{1} code by said C_{1} encoder means to thereby form said C_{2} C_{1} encoded matrix. .Iaddend. .Iadd.15. The two stage coding system of claim 14 wherein the length of said C_{2} C_{1} encoded data matrix in the first direction is (n_{1} +k_{3})×q digits, where k_{3} is an integer. .Iaddend. .Iadd.16. The two stage coding system of claim 6 wherein said C_{2} encoder means subtracts n_{2} ×k_{2} from any initially calculated value of a_{2} to a_{n2} that exceed n_{2} ×k_{2} to select data words in said matrix diagonally. .Iaddend. .Iadd.17. The two stage coding system of claim 6 wherein the length of said C_{2} C_{1} encoded data matrix in the first direction is n_{1} ×q digits. .Iaddend. .Iadd.18. A two stage coding system for encoding digital information arranged in an information matrix of k_{1} ×q digits in a first direction, and k_{2} digits in a second direction orthogonal to the first direction, wherein

k_{1}, q, and k_{2} are integers,

k_{1} <k_{q} ; q=the number of digits per data word, and

k_{1}, k_{2} =the number of data words in said first and second directions respectively,

said system further single stage coding additional information of k_{3} ×q digits in the first direction, where k_{3} is an integer and k_{2} digits in the second direction, comprising:

C_{2} encoder means for encoding said digital information with a C_{2} code on a Galois field GF(2^{q}), said C_{2} encoder means selecting data words in said information matrix diagonally from an arbitrary data word a_{1} and including a_{2} to a_{n2}, wherein n_{2} is the length of the C_{2} encoded data, such that

a_{2}=a_{1}+n_{2}×h_{1}+1

a_{3}=a_{2}+n_{2}×h_{2}+1

:

a_{k1}=a_{k1-1}+n_{2}×h_{k1-1}+1

:

a_{n2}=a_{n2-1}+n_{2}×h_{n2-1}+1

h_{1} to h_{n2-1} each being selected from one of h_{A} and h_{B}, wherein,

h_{A}=[k_{2}/n_{2}],

h_{B}=[k_{2}/n_{2}]+1, and

h_{A}×l_{1}+h_{B}×l_{2}≦k_{2}, where

l_{1}+l_{2}=n_{2}

said C_{2} encoder means forming said C_{2} code from said selected data words and adding the obtained C_{2} code to an end of said information matrix in said first direction to form a C_{2} encoded matrix; and

said additional data of k_{3} words and said C_{2} encoded matrix collectively forming an added data matrix having k_{2} lines;

C_{1} encoder means for encoding each of said k_{2} lines extending in said first direction of said added data matrix with a C_{1} code having a predetermined length on a GF(2^{q}), and adding the obtained C_{1} code to an end of each said line of said added data matrix in said first

direction to form a C_{2} C_{1} encoded matrix. .Iaddend. .Iadd.19. The two stage coding system of claim 18 wherein a group of two or more adjacent lines h_{1}, h_{2}, . . . utilize a repetition pattern having at least one of each of h_{A} and h_{B} contained therein, said selection of data words a_{1} to a_{n} by said C_{2} encoder means utilizing said repetition pattern for selection of all said data words (a) in said information matrix. .Iaddend. .Iadd.20. The two stage coding system of claim 19 wherein said repetition pattern is selected from the group consisting of h_{A}, h_{B} ; h_{B}, h_{A} ; and h_{A}, h_{B}, h_{B}. .Iaddend. .Iadd.21. The two stage coding system of claim 18 wherein:

h_{2i-1}=h_{A},

h_{2i}=h_{B},

where 1<i<(n_{2} -1)/2. .Iaddend. .Iadd.22. The two stage coding system of claim 18 wherein:

h_{2i-1}=h_{B},

h_{2i}=h_{A},

where 1<i<(n_{2} -1)/2. .Iaddend. .Iadd.23. The two stage coding system of claim 18 wherein said C_{2} encoder means repeatedly selects data words in said information matrix from an arbitrary data word a_{1} and including a_{2} to a_{n2}, said C_{2} encoder means repeatedly forming said C_{2} code and adding said C_{2} to the end of the matrix, each repetition starting from a different arbitrary data word a_{1}. .Iaddend. .Iadd.24. The two stage coding system of claim 23 wherein said C_{2} encoder means selects k_{2} arbitrary data words from which to perform selecting, forming and adding to thereby form a complete C_{2} encoded matrix. .Iaddend. .Iadd.25. The two stage coding system of claim 18 wherein said means for C_{2} encoding further encodes said selected data words in each said diagonal;

said means for adding a C_{2} code to the end of each said diagonal to form a C_{2} code field at the end of said information matrix in said first direction. .Iaddend. .Iadd.26. The two stage coding system of claim 18 wherein said C_{2} encoder means subtracts n_{2} ×k_{2} from any initially calculated value of a_{2} to a_{n2} that exceed n_{2} ×k_{2} to select data words in said information matrix diagonally. .Iaddend. .Iadd.27. The two stage coding system of claim 18 wherein the length of said C_{2} C_{1} encoded matrix in the first direction is (n_{1} +k_{3})×q digits. .Iaddend.

Description

The present invention relates to a two stage coding method having a high burst error correction ability and also a random error correction ability equivalent to that of the prior art when an error correction code such as a Reed Solomon code (hereinafter referred to as "RS code") is used in order to correct data errors which arise in reproducing data recorded in a recording material such as a magnetic disk.

Generally, in recording and reproducing data into and from a recording material such as a magnetic disk a data error may arise dependent on the state of the recording material. A data error may be a burst error caused by a signal drop out .[.on.]. .Iadd.or .Iaddend.a random error caused by a deterioration in SN ratio. In order to correct these errors a two stage coded error correction code is used. As an example, a two stage code using RS codes on a GF .[.(2^{8}).]. (.Iadd.2^{q}) .Iaddend.where q=8 will be considered. A two stage encoder is shown in FIG. 3. In FIG. 3, reference numeral 1 designates an input terminal, reference numeral 2 designates a C_{2} encoder, reference numeral 3 designates an interleaving circuit, reference numeral 4 designates a C_{1} encoder, the reference numeral 5 designates an output terminal. First of all, C_{2} encoding is performed on the original data, interleaving is executed thereto, and thereafter C_{1} encoding is conducted, and the resulting code signal is output to the output terminal. A two stage decoder is shown in FIG. 4. In FIG. 4, reference numeral 6 designates an input terminal, reference numeral 7 designates a C_{1} decoder, reference numeral 8 designates a deinterleaving circuit, reference numeral 9 designates a C_{2} decoder, and reference numeral 10 designates an output terminal. In this decoder deinterleaving is executed after the C_{1} decoding, and thereafter C_{2} decoding is conducted. There is a prior art two stage coding method which, assuming that data obtained by arranging .[.k_{1} ×9.]. .Iadd.k_{1} ×q .Iaddend.digits in a first direction and k_{2} digits (k_{1} <k_{2}) in a second direction as shown in FIG. 5 is arranged into 8 .[.data.]. .Iadd.digit .Iaddend.words in the first direction, consists of adding a first check code of n_{2} -k_{1} digits, and thereafter adding a second check code of n_{1} -n_{2} digits as shown in FIG. 2, (n_{2}, k_{1}) RS code is used as the C_{2} code, and (n_{1}, n_{2}) RS code is used as the C_{1} code.

A specific coding example will be described with reference to FIGS. 5 and 2. When it is established that k_{1} =32, k_{2} =128, n_{1} =40, n_{2} =36, and h_{1} =h_{2} = . . . =h_{35} =h=3, the data region comprising the data and the first check code becomes data of n_{2} ×k_{2} =4608 digits as shown in FIG. 5, and when a_{1} is set to 1, a_{2} to a_{36} become as follows: ##EQU1## and C_{2} encoding is conducted on the data corresponding to the a_{1} -th, a_{2} -th, . . . , a_{32} -th data .Iadd.selected .Iaddend.with use of the following generation polynomial of C_{2} code ##EQU2## where α is a root of a primary polynomial (for example, such as x^{8} +x^{4} +x^{3} +x^{2} +1 on GF (2^{8})). The generated check codes are arranged at the positions corresponding to the a_{33} -th, a_{34} -th, . . . , a_{36} -th data. Next, a_{1} is set as follows:

a_{1}=a_{1}+n_{2}=a_{1}+36,

and similarly check codes are added to the data successively. Herein, if the calculated result of a_{2} to a_{36} exceeds n_{2} ×k_{2} =4608, a number obtained by subtracting 4608 therefrom is made the result. The encoding is repeated k_{2} times thereby to conclude the C_{2} encoding.

Next, C_{1} encoding is conducted on the data of n_{2} digits in each column arranged in the first direction as shown in FIG. 2 with the use of the following generation polynomial of C_{1} code ##EQU3## The generated check code is added to the end portion of the data and the encoding is repeated k_{2} times. In the recording of the data onto the recording material data of n_{1} =40 digits arranged in the first direction is sent out k_{2} times successively. In the reproduction of the same the sent out data are arranged in a column in the first direction by 40 digits successively.

In the prior art two stage coding method with such a construction, the C_{2} code is concerned with burst error correction ability, and the C_{1} and C_{2} codes are concerned with random error correction ability. In the stage of conducting C_{2} encoding the h must be made large in order to enhance the burst error correction ability, and h is set as follows:

h=[k_{2}/n_{2}]=[128/36]=3

.Iadd.where [A] denotes an integer which does not exceed A .Iaddend.The C_{2} codes are gathered at the right end portion of the data region in FIG. 5, and the C_{2} and the C_{1} code are arranged adjacent to each other in the first direction subsequent to the data of k_{1} =32 digits when the C_{1} encoding is completed.

The prior art two stage coding method is constructed in such a manner, and the error correction ability by one code amounts to n_{2} -k_{1} digits when forfeiture correction is conducted by the C_{2} decoding. Accordingly, the burst error correction ability becomes as follows for data of n_{2} ×k_{2} =4608 digits comprising all the data and the C_{2} code

(n_{2}-k_{1})×n_{2}×h=432,

but h becomes as follows:

h=[k_{2}/n_{2}]=[128/36]=3<128/36,

and k_{2} /n_{2} does not equal an integer, thereby resulting in deterioration of error correction capability.

The present invention is directed to solve the problems pointed out above and an object is to provide a two stage coding method in which the above-described deterioration in a burst error correction ability is improved and a higher burst error correction ability than that of the prior art device is obtained.

According to the coding method of the present invention, assuming that data of k_{1} ×8×k_{2} digits are arranged in a matrix of k_{1} ×8 digits in a first direction and k_{2} digits(s) in a second direction and the data is divided into words of 8 digit(s) in the first direction, in conducting C_{2} encoding by taking out n_{2} data words from the data of .[.n_{2} .]. .Iadd.n_{2} -k_{1} .Iaddend.words in the first direction and k_{2} words in the second direction with no duplication of data in either of the first and second directions, a C_{2} code of .[.code.]. length .[.n_{2} .]. .Iadd.n_{2} -k_{1} .Iaddend.is produced by establishing a_{1} at an arbitrary data number word, and establishing h_{1}, h_{2}, . . . , h_{n2-1} such that they become a repetition of a combination satisfying the condition that [k.sub. 2 /n_{2} ] and [k_{2} /n_{2} ]+1 may be

[k_{2}/n_{2}]×1_{1}+([k_{2}/n_{2}]+1)×1_{2}≦k_{2}

(herein, l_{1} +l_{2} =n_{2} (l_{1}, 1_{2} : integer) and a_{2} to a_{n2} exceeding n_{2} ×k_{2} are obtained by subtracting n_{2} ×k_{2} therefrom) for a_{2} to a_{n2} as in the following: ##EQU4## when numbering is conducted successively in the first direction on the data of n_{2} words in the first direction and k_{2} words in the second direction, and this is repeated k_{2} words in the second direction, and thereafter C_{1} encoding of each n_{2} ×q digits in the first direction .[.into a.]..Iadd., forming an C_{1} C_{2} encoded data matrix having a total .Iaddend.code length n_{1} is conducted.

In the two stage coding method of the present invention, C_{2} codes are constructed to be effective for error correction at the portion of n_{2} -k_{1} in the first direction and at the portion of k_{2} in the second direction against the data obtained by arranging k_{1} digits in the first direction and k_{2} digits in the second direction, as shown in FIG. 1. According to the present invention, the burst error correction ability against the data of n_{2} ×k_{2} =4608 digits comprising all the data, and the C_{2} codes becomes

(n_{2}-k_{1})×n_{2}×(h_{4}+h_{B})/2=504.

and this exceeds 432 which is the burst error correction ability of the prior art device against the same number of data and the same number of check codes.

In this way, it is possible to conduct a two stage coding having a higher burst error correction ability than that of the prior art, and having a random error correction ability equivalent to that of the prior art due to the C_{1} and C_{2} codes.

FIG. 1 is a diagram showing a data arrangement for conducting a C_{2} encoding method as one embodiment of the present invention;

FIG. 2 is a diagram showing a data arrangement for conducting a prior art two stage coding method and a C_{1} encoding method as an embodiment of the present invention;

FIG. 3 is a block diagram showing a two stage encoding circuit;

FIG. 4 is a block diagram showing a two stage decoding circuit; and

FIG. 5 is a diagram showing a data arrangement for conducting the C_{2} encoding method of the prior art two stage coding method.

Embodiments of the present invention will be described with reference to the drawings. In FIGS. 1 and 2, the constants are established that q=8, k_{1} =32, k_{2} =128, n_{1} =40, n_{2} =36, and data are divided into words of 8 digits in the first direction. FIG. 1 shows a C_{2} encoding method. Data of k_{1} ×k_{2} =4096 data words are arranged sequentially in the first direction and in a matrix of k_{1} =32 words in the first direction and k_{2} =128 words in the second direction, and when h_{2i-1} and h_{2i} are set as follows

h_{2i-1}=h_{A}=]k_{2}/n_{2}]=3

h_{2i}=h_{B}=[k_{2}/n_{2}]+1=4,

(i: integer, 1≦i≦(n_{2} -1)/2)

and a_{1} is set 1, a_{2} to a_{36} become ##EQU5## and, C_{2} encoding is performed on the data corresponding to the a_{1} -th, a_{2} -th, . . . , and a_{32} -th data with the use of the generation polynomial of the C_{2} code ##EQU6## Herein, α is a root of a primary polynomial. The generated check codes are arranged at the positions corresponding to the a_{33} -th, a_{34} -th, . . . , a_{36} -th data. Next, a_{1} is set as follows

a_{1}=a_{1}+n_{2}=a_{1}+36

and similarly inspection codes are added to the data successively. a_{2} to a_{36} exceeding n_{2} ×k_{2} =4608 are made by subtracting 4608 therefrom. When this encoding operation is repeated k_{2} times the C_{2} encoding is completed.

Next, C_{1} encoding is performed on the data of n_{2} words in each column arranged in the first direction as shown in FIG. 2 with the use of the generation polynomial of C_{1} code ##EQU7## The generated check codes are added to the data, and the encoding is repeated k_{2} times. The recording of the data on a recording material is conducted by sending out data of n_{1} =40 words arranged in the first direction successively k_{2} times. The data format reproduction is conducted by arranging the sent out data by 40 words successively in a column in the first direction.

In the two stage coding method of the present invention, the C_{2} code is concerned with burst error correction ability and both C_{1} and C_{2} codes are concerned with random error correction ability. In conducting the C_{2} encoding, C_{2} codes of n_{2} -k_{1} in the first direction and k_{2} in the second direction can be used effectively for the error correction of the data arranged in a matrix of k_{1} in the first direction and k_{2} in the second direction.

In the above-illustrated embodiment a repetition pattern of (h_{A}, h_{B}) is adopted for h_{1}, h_{2}, . . . , h_{n2-1}, but other combinations using h_{A} and h_{B} such as (h_{B}, h_{A}) or (h_{A}, h_{B}, h_{B}) can be used if they comply with the following conditions

h_{A}×l_{1}+h_{B}×l_{2}≦k_{2}

l_{1}+l_{2}=n_{2}

Furthermore, an RS code on GF (2^{q}) is used as an error correction code, but another code such as a BCH code can be used as an error correction code. Furthermore, the number of data, the construction of information lengths in the first and second directions, and the C_{2} and C_{1} code lengths can be arbitrarily established. Furthermore, in the illustrated embodiment the region occupied by the check codes of the C_{2} code and the C_{1} code is shown in FIG. 2, but this occupied region can be arbitrarily established by establishing a_{1} at an arbitrary number.

Furthermore, it is possible to add the additional information of k_{3} ×q digits in the second direction k_{2} times precedent to the C_{1} encoding, and thereafter to conduct C_{1} encoding on GF (2^{q}) having the (n_{1} +k_{3})×q digits in the first direction, and to conduct a coding k_{2} times repeatedly in the second direction.

The present invention is applicable not only to a magnetic disk apparatus but also to an optical recording and reproducing apparatus, and an optical magnetic recording and reproducing apparatus.

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Referenced by

Citing Patent | Filing date | Publication date | Applicant | Title |
---|---|---|---|---|

US5537429 * | Feb 5, 1993 | Jul 16, 1996 | Mitsubishi Denki Kabushiki Kaisha | Error-correcting method and decoder using the same |

Classifications

U.S. Classification | 714/761, 714/763, 714/784 |

International Classification | H03M13/27, H03M1/24, G11B20/18, H03M13/29 |

Cooperative Classification | H03M13/29, H03M13/27 |

European Classification | H03M13/29, H03M13/27 |

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