JPH0724148B2 - Error correction method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an error correction method used when reproducing the above-mentioned data from a recording medium in which digital data having an error correction code is recorded as adjacent tracks.

[Outline of Invention]

According to the present invention, when the recording tracks of the digital signal are close to each other, the error correction cannot be performed focusing on the fact that the error generated in the reproduced digital signal due to the scratch or dust on the recording medium has the correlation between the tracks. The error data of a track is such that the error correction capability can be improved by referring to the error position information of an adjacent track in which the error of the data has been corrected and referring to the error position information. .

[Conventional technology]

An optical disc is an example of a storage device for storing digital data such as computer data.

In this optical disc, as shown in FIG. 3, the disc (1) is rotated at, for example, a constant angular velocity, and digital data forms one track (2) per revolution, forming concentric or spiral tracks. It is recorded optically and then reproduced.

As shown in FIG. 3, one track (2) of this optical disk (1) is composed of a plurality of sectors equally divided in the circumferential direction, and each sector is a block for a predetermined number of digital data that has been defined. It is composed of a data part in which a complete error correction code is formed and a header part including the track address and sector address of the sector.

When the disc (1) is rotated at a constant angular velocity, the same sector of each track can be recorded in the same rotation angle section as shown in FIG.

By the way, in an optical disc, a burst error occurs in reproduced data due to scratches or the like. Therefore, it is conceivable to use a so-called LDC (long distance code) having a relatively long burst error correction length.

An example of this LDC is shown in FIG.

That is, this means that the data size per sector is 51.
In the case of 2 bytes, this 512-byte information is arranged in a matrix with 4 bytes in the column direction and 128 bytes in the row direction. Also, an error detection CRC code generated for a header including block address data and the like, 512 bytes of information and a header is added as 4 × 2 = 8 bytes. And 128 bytes of information in the row direction and 2
Byte header + CRC code for a total of 130 bytes, for example, (146,130) 16 (16 by Reed-Solomon code)
Byte) check symbol is generated and added as shown.

In this case, the writing and reading of the data of the matrix structure as shown in the memory of the encoder and the decoder are sequentially performed from the left side of the drawing in the column direction as indicated by the arrow. Therefore, if there is a burst error in the data reproduced from the disc (1), the error data is continuously written into the memory from the middle of a certain column in the writing / reading direction to the certain column, as indicated by the mark X in the figure. This continues.

Meanwhile, if the minimum distance of the error correction code is d, the minimum distance d is, if satisfy _{d ≧ 2t 1 + t 2 +1} ...... (a), the code is also what t ₁ fold following error It corrected, also it is possible to detect the error from t ₁ +1 to t ₁ + t ₂ double (theorem).

Since the error correction code in the case of the example in FIG. 4 has the minimum distance 17, it is possible to perform octuple error correction in the row direction. Since the writing and reading directions are in the column direction, in the case of this example,
Burst errors up to a length of 4 × 8 = 32 bytes can be corrected.

[Problems to be solved by the invention]

By using LDC as described above, it is possible to correct a relatively long burst error. Then, if the minimum code distance is increased, it becomes possible to correct a burst error that is as long as that.
However, the length of the minimum distance is naturally limited due to the constraint of redundancy, and therefore, the burst error correction length also has a predetermined limit, and when a burst error occurs beyond that, it becomes uncorrectable.

Such a burst error occurs, for example, when the disc is scratched, but if error-correctable data occurs, in the case of computer data or the like, the information of that sector can no longer be used.

If the disc can be rewritten (recorded), it can be restored by rewriting the uncorrectable one, but it cannot be corrected with a read-only disc such as a CD-ROM. That is fatal.

An object of the present invention is to provide an error correction method capable of increasing the error correction capability without changing the redundancy of the error correction code.

[Means for solving problems]

According to the error correction method of the present invention, when reproducing digital data recorded as a track (2) adjacent to a recording medium (1) and having an error correction code, a predetermined sector portion ((i -1) When performing error correction processing on the data of track, m sector),
A sector ((i-2) corresponding to the predetermined sector part of a track adjacent to this track ((i-1) track)
An error data position where error detection and correction can be performed in the data recorded in the track (m sector) is detected, and the detected error data position in the predetermined sector ((i-1) track, m sector) of the track is detected. This is an error correction method that treats the data at the specified position as lost and corrects it.

Usually, the errors have two-dimensional spreads, although there is a difference in size. Especially, in the case of a burst error due to a defect such as a scratch, when the adjacent tracks are adjacent to each other, the adjacent tracks are adjacent to each other. The same error is observed on the track.

FIG. 2 is a schematic view in the case of considering an optical disk rotating at a constant angular velocity. In the figure, a curve (3) indicates a track, and here, five tracks from a track number (i-2) to (i + 2) are shown. ing. Further, (m-1), m, (m + 1) are sector numbers. Defects (4) are shown by hatching, and in this example, there are defects (4) in five sectors in m sectors.

In the case of an optical disc, the track spacing is, for example, 1.6 μ, the width of scratches or the like is usually 300 μ, and the length is longer than this, as shown in the figure.

From this schematic diagram, it can be seen that, in the tracks from number (i-2) to (i + 2), a burst error occurs at almost the same position in the m sector and the error correlation is strong between the tracks.

Now, for example, it is assumed that the error correction is possible for the m sector of the (i-2) track, but the error correction is not possible for the i track outside the (i-1) track and the m sector of the (i + 1) track.

(I-2) The fact that error correction is possible in the m sector of the track makes it possible to know the byte position in error. When the error cannot be corrected in the m sector of the (i-1) track, it is considered that the error in the m sector of the (i-1) track is larger than the error in the m sector of the (i-2) track. , (I-2) The byte data at the same position as the error byte in the m sector of the track can be considered to be included in the burst error.

Therefore, using the byte position information of the correctable burst error detected on the (i-2) track, the error at the same byte position on the (i-1) track is regarded as disappearance on this (i-1) track. , And erasure correction is performed, and error detection and correction is performed on an error byte that is larger than the error portion regarded as erasure in the m sector of (i-1) track.

By doing so, it becomes possible to correct an error that could not be corrected, and the correction capability is expanded.

If all the burst errors in the (i-1) track can be corrected as described above, the error byte is regarded as an error in the i-track and the byte at the same position as the error byte position in the (i-1) track is considered to be lost. There is a possibility that the error can be corrected by performing the correction operation. Thereafter, even if the burst error is considerably long, it is possible that the burst error can be corrected by sequentially performing the same error correction method on the outer track in which the burst error length increases.

〔Example〕

Hereinafter, one embodiment of the method of the present invention will be described by taking as an example the case where the recording medium is an optical disk which is rotationally driven at a constant angular velocity and the LDC of FIG. 4 is adopted as the structure of the data portion of each sector.

That is, this example is a case where the Reed-Solomon code with the minimum distance of 17 is used, but t ₂ > rather than performing only detection and correction, that is, not t ₂ = 0 in the equation (a) above. 2 is used for error detection,
The erasure correction is also used by using the error information of the adjacent track before the correction process is completed.

Now, for example, as shown in FIG. 2, a defect (4) occurs (i-
2) Consider a state in which a burst error occurs in a state where there is an error correlation between tracks in m sectors from track to (i + 2) track.

Then, from (i-1) track of this m sector, (i
The burst error that occurs up to +1) track can be represented as shown in FIG. 1 when displayed on the memory array of LDC data.

Here, in FIG. 1, it is assumed that all the errors including the burst error of the (i-1) track m sector can be corrected.

That is, when the minimum distance is 17, up to 8 errors in the row direction can be detected and corrected, so the burst error length is 4 ×.
This is the case where 8 = 32 bytes or less. The fact that the error detection and correction was successful means that the error position of the (i-1) track can be known. Therefore, this error position is stored. The burst error position can be known from this error position, but if modulation such as so-called 8-10 conversion is performed when data is recorded on the disc, it is converted to byte unit data by 10-8 conversion during reproduction. When performing processing, when so-called out-of-rule 10-bit data that is not in the conversion map of 10-8 conversion continues, that period may be detected as a burst error occurrence position, and this detection information may also be used. .

Next, since it became uncorrectable in the m sector of the i track, an error of 32 bytes or more occurred. However, in the burst error part due to the defect (4), as shown by the one-dot chain line in FIG. It can be predicted that the error has expanded from the burst error portion of the (i-1) track.

Therefore, in this i-track, the error portion position surrounded by the one-dot chain line is known from the error position information of the (i-1) track, and the error surrounded by the one-dot chain line on the i-track is regarded as disappearance and is corrected. .

The maximum value of the disappearance information considered here is 8 in the row direction.
(Byte). Therefore, if the erasure information is 8, and if t ₂ = 8 from the above equation (a), the error position of the i track is detected in combination with the error position information of the (i-1) track. You can correct the disappearance. On the other hand, t ₁ = 4 bytes can be detected and corrected. Therefore, in the example of FIG. 1, since the error is expanded by 2 bytes in the row direction, it can be completely corrected.

In other words, it is known that the part surrounded by the one-dot chain line is the burst error part, and since the error detection up to t ₂ = 8 bytes can be detected by the inspection point in the row direction, the error position can be specified, so this is regarded as disappearance. Can be corrected by erasing, and the part surrounded by the one-dot chain line can be erased and corrected.

In this way, if all the errors in the m sectors of the i track can be corrected, this error position information is stored.
Then, in FIG. 1, using the information on the corrected error position surrounded by the chain double-dashed line, the error at the same position on the (i + 1) track is regarded as disappearance, and correction is performed in the same manner as above.

In the example shown in the figure, the lost information may be set to 10, and at this time, error detection and correction of up to 3 bytes are possible.
There is a possibility that all +1) track errors can be corrected.

Thus, it becomes possible to correct an error that could not be corrected only by detection and correction, and it becomes possible to recover a sector that cannot be used due to a scratch or the like.

In the example of the figure, it is explained that all the error positions of the previous error-corrected tracks are regarded as lost.
It may be considered that only the exact position of the error is lost, not all the error positions. For example, when the (i + 1) track is corrected, the portion surrounded by the alternate long and short dash line, rather than the portion surrounded by the alternate long and two short dashes line, may be regarded as erasure, and the erasure information 8 may be detected and corrected.

In short, erasure correction may be performed in consideration of the number of bytes that can be error-detected and corrected, instead of all error detection positions in the previous track.

Further, as in the above example, even if t ₁ and t ₂ in the equation (a) are set and the number of bytes for detection correction and erasure correction is set according to the maximum value of the number of errors in the previous track that can be corrected. However, t ₁ and t ₂ may be fixedly set in consideration of the number of possible correctable errors.

If the data is computer data, etc.,
For sectors with erasure correction, CRC is applied after the correction is completed.
It is okay to detect the error by the code, judge whether there is an error, and do not use the data of the sector when the error remains.

It should be noted that the above is an example of the case where the recording medium is a disk, but it is needless to say that the present invention can be applied to the case of a tape and other recording media.

〔The invention's effect〕

As described above, according to the present invention, the burst error between the adjacent tracks has the correlation between the tracks, and the position information of the error data which is capable of the error detection and correction of the adjacent tracks is used. Since the correction is performed by regarding the same position on the track as the erasure, the error correction capability can be expanded as compared with the case where only the detection correction is performed.

Especially in the case of read-only CD-ROM,
There is a merit that it is possible to restore the sector data that cannot be read due to scratches on the disk.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the method of the present invention, FIG. 2 is an explanatory diagram for inter-track correlation of an error in the case of an optical disc, FIG. 3 is an explanatory diagram of a recording data format of the optical disc, and FIG. 4 is an error. It is a figure which shows the example of the data block which used an example of a correction code.

Claims (1)

[Claims] 1. When reproducing digital data recorded as adjacent tracks on a recording medium and having an error correction code, the error correction processing is performed on the data of a predetermined sector portion of a certain track. Data at a position corresponding to the detected error data position in a predetermined sector of the track is detected by detecting an error data position where error detection and correction can be performed in data recorded in a sector corresponding to the predetermined sector portion of an adjacent track. An error correction method that treats as an erasure and corrects it.