JPS60186940A - Code error correction system - Google Patents

Abstract

PURPOSE:To decrease the number of correction unable error patterns by making use of a bit corresponding to an error flag showing the presence or absence of a code error as well as a bit corresponding to data. CONSTITUTION:The error detection of X direction is carried out over an entire code block and then the error correction of Y direction is carried out over the entire code block. Then the error detection of X direction is carried out again, and the error correction of Z direction is carried out over the entire code block. These correction processings are carried out J times, and the error detection of X direction is carried out once more to finish corrections. In this system, the value of an error flag showing the presence or absence of an error is decided by the error position information obtained from another error correction code and the result of detection of an error detection code before an error correction is carried out. Thus it is possible to correct errors after addition of an accurate error flag.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention provides a method for converting a plurality of data words including bits corresponding to data and bits corresponding to an error flag indicating the presence or absence of a code error using an error detection code and two error correction codes. This invention relates to a method for correcting code errors in code blocks obtained by encoding.

BACKGROUND ART One error detection code and two error correction codes are added to correct code errors in a plurality of data words forming a code block as shown in FIG. 1 using a conventional code error correction method. Let's explain the case. In Figure 1, 44
l block of data words WO-W4 consisting of 0 words
3g are arranged in the shape of a rectangular parallelepiped with KIO words in the X direction, 4 words in the Y direction, and 11 words in the Z direction. x, y,
In each direction of z, each data word sequence is encoded as a subblock, with two additional words, check words P and Q, formed by a Reed-Solomon code VcL.

The subscripts x, y, and zi of P and Q indicate the expansion direction of the subblock containing the check word, and the numerical subscript corresponds to the number of the first word of the subblock in the expansion direction. The word expressed as PXPYO is defined by the check word Px in the X direction, and is also the check word PY in the Y direction, and the numbers of Px and PY at the beginning of each direction are 0.
It shows that. Further, a word expressed as QxQYQz is a test word Qx in the X direction, a test word QY in the Y direction, and a test word Qz in two directions. The same applies to other words expressed by the combination of P or HQ and the subscript f. The reason why one word can serve as a check word in multiple directions at the same time is because the Reed-Solomon code is a linear code.

Here, it is assumed that each word of data and check consists of 8 bits, and that the Reed-Solomon code is a code on the Galois field GF(28). Data word WO-W43g
The subscript represents the order before 3-dimensional arraying, and this
et W. -W2B5 are arranged as shown in FIG. 1, test words are added, and then words are taken out one by one in the order of x, y, and z and recorded or transmitted. That is, the word order at this time is Wo.

Wlt + -W2O1Pxor Qxo + Wt
io + °" W220 + -W3ao +...W4
291PX3301Qx33010°pyol "'
PY99 + pxpyo IQxPyo + Qy
o + °°' QYgg + PxQyo・QxQy
o + Wl + °'“w2.

”'”'3 + ”' W4 r ”°W5* ”'
W6 + °"Wlt・°'W8...°W9゜"
'Wio + "'Wiog r PXlo l Qx
to + H0QX3401°QxP2a3o+゛°'
QXQYIO+ Pzo + ”' P2O3+ P
XPZO+ QXPZO+-QXPZ330 r ”・
QxPyPz + ”' QxQyPz + ”' Q
zo + ”'Qzgg.

PzQzo + QxQzo + ”' QxQz3s
o + "" QxPyQz + -QxQyQz.

On the regeneration or receiving side, the frame word series is arranged again as shown in the zi diagram, and after correction of errors that occurred during recording or transmission, only the data words are arranged in the order of z, x, and y. Take out the original W. , wl... Obtain a data word sequence of W439.

As described above, changing the order of words during recording or transmission is to disperse erroneous words in the original data word sequence when an uncorrectable burst error occurs in the regenerated or received data. It's for a reason.

Check words PU and QU (U=X, Y, or 2) consisting of Reed-Solomon codes in the code block of FIG. 1 are generated so as to satisfy the following equation.

■ However, the addition is modulo 2, and α is a primitive element on GF(28). Further, V assumes values of 10 and 4.11 for U=X, Y, and Z, respectively, and the subscript kid of W indicates the position in the subblock of the data word, and is assumed to be the leading i1.

(1), (The following equation is obtained from equation 21.

At the time of regeneration, if the xp order t is known for the subblocks in each direction in the code block shown in FIG. 1, errors in data and check words within 2 words can be corrected, and errors can be If the location is not known, errors in l-word data and check words can be corrected. These corrections are performed in one line as follows, and gf is defined by the following formula for data and check words that first contain errors.
Calculate L syndrome 8vv r SQU k.

S, υ = five towns ten P, ten Q.・・・・・・・・・・・・
...(5) However, each subscript UP for U, V, and so on. +QoO
It is the same as the subscript of the expression.

Now, if an error occurs at each position of two words (=i,) and the error pattern is ei + e), then the syndromes Spg and SQU n will be as shown in the following equations.

SP, J = ei + eノ ・・・・・・・・・・・・
・・・・・・・・・・・・(7) SqU=αv+z−i, 10αV+2−noeノ ・・・・・・・・・(8)(7)
, (81 equation ei+e) becomes as shown in the following equation.

(9) It can be seen that if , (located from equation 1) is known and can be solved, error correction is possible by 1 in the above equation 19e z and ei.

Next, if the error pattern of l word occurs at position i and the error pattern is feei, Kundrotum S,. rS
QU is as shown in the following equations.

5PLI = ei ・Mountain/river・・・・・・・River・・
(II) S = αv + 2-iei ・・・・・・・・・
・・・・・・・・・・・・(13U Qυ, the following equation is obtained from equation 03.

Even if the formula 03 position i is not known, spul sQ,
I am hesitant to increase αi more, but ex is sPU
It can be seen that error correction is possible because it becomes the same.

In the code block shown in Figure 1, each word in the X direction is continuous on the recording or transmission system, so errors of 3 or more words often occur consecutively in the X direction, and correction is more difficult than in the Y and Z directions. There is a high probability that it will be impossible. Therefore, in the X direction, the Reed-Solomon code must be used as an error detection code, 5Px=sQx=.

If it is correct, there is no error, and if it is other than n, it is judged that there is an error, and only the value of the bit corresponding to the error flag indicating the presence or absence of an error in the word can be determined.

When correction of code errors in code blocks as described above is carried out by the conventional method, the following processing is performed in accordance with the procedure shown in the flowchart of FIG. 2 in 1c. That is, first, error detection is performed for each sub-block in the Add to. Next, error correction is performed for each subblock in the Y direction with reference to the error flag, and then error correction is performed in the same manner in the two directions.

Repeat this number of times to complete the correction. Note that although the value of J is usually l in many cases, it is not particularly limited here and may be set to 3, for example. In addition, when three or more error flags of words in a sub-block are 'l' in Y-direction correction, the Y-direction syndrome S,...,5QYK,C
Find the error position, and if the error flag at that position is '1', correct only that l word and then perform the correction.
Set all error flags in the subblock containing the word to 10
''.Also, not only when one word is corrected in this way, but also when both SPY + sQY are 10゛ and no correction is made, and when two or f11 error flags are ``l°'', SPY , 5QYVc, all error flags are reset to 10. Similar corrections are made in the two directions as well.

If the conventional code error correction method described above is used, it becomes possible to correct the error pattern shown in Figure 3.
Error patterns such as those shown in K become uncorrectable. In the same figure and in the same figure (Bl), one Y-2 plane of the code block of FIG. 1 is shown, and '-' indicates an incorrect word. Because other words in the subblock in the X direction are incorrect,
Error flag is # l 1 even though it is correct for itself
It shows the word that is 1. Figure 3 (sub-block B in the Y direction in AIIC)
,, even if the error in subblock B2 is not corrected, the error flag is reset to "OII" at the same time as the l word error in subblock B3 is corrected, so subblock B
3, the two words indicated by It X 11 are both normal words. Then, the error in each subblock in the Z direction becomes 2 words or less, and the errors in the other 4 words are also corrected.

However, sub-block B1. When the error flag is 3 or more 'l'' and two words are incorrect, as in B2, if cpl word correction is performed on the syndrome SPY l s, Y, a false correction may be made. In sub-block B4 in Figure 3+B], a false correction is made to the word whose error flag is incorrectly set to g111, and as a result, all three words of U...XII become incorrect υ. Yes, and since the error flag of these 3 words is reset to #011, these 3 words are reset.
The three erroneous words in word and sub-blocks B5&C are no longer corrected by subsequent corrections in the Z direction or in the Y direction.

In order to correctly correct the error pattern in 031 of the same figure, when performing correction processing when the error flag is 3 or more & l 11, set the error flag to 11 of ic ' l ' instead of setting it to 10''. However, if this is done, the error recovery shown in (5) of the same figure becomes uncorrectable. Furthermore, in order to avoid false corrections, if no correction processing is performed when the error flag is 3 or more Rl 11, an error pattern as shown in [A] of the same figure becomes uncorrectable. Therefore, the conventional code error υ correction method vc, r
, it is not possible to correctly correct error patterns such as those shown in FIG. 3 (N and fBl in the same figure).
The errors in each subblock in each direction are two words or less. Therefore, all errors can be corrected if the error positions are correctly identified before performing the correction process. In the conventional code error correction method, the information on the error position before correction is only an error flag due to error detection in the X direction, and since there is no error detection in the X direction after that, some error flag correction is required after correction. However, it is not possible to accurately detect the error position. For this reason, in the conventional code error correction system, the original correction ability of the code cannot be fully utilized, and there are many error patterns that cannot be corrected. Summary of the Invention Therefore, the purpose of the present invention is to It is an object of the present invention to provide a code error correction method capable of fully utilizing the original correction ability of a code and reducing uncorrectable error patterns.

The code error correction method according to the present invention includes a plurality of data words formed by bits corresponding to data and bits corresponding to an error flag indicating the presence or absence of a code error, an error p detection code, and a first and second error Ic. A method for correcting code errors in a code block consisting of a plurality of check words formed by correction codes, wherein immediately after error correction by one of the first and second error correction codes, an error caused by one of the first and second error correction codes is corrected. After performing a process of determining the value of the error flag based on the error position information obtained at the time of correction and the detection result by the error detection code, the error flag is referred to and the error position information detected by the error detection code is determined. The feature is that the other party corrects any mistakes at least once.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 4 to 9.

When correcting errors in a code block as shown in FIG. 1 using the code error correction method according to the present invention, the following processing is performed according to the procedure shown in the flowchart of FIG. That is, first, error detection in the X direction is performed over the entire code block.

Next, error correction in the X direction is performed over the entire code block. Next, error detection in the X direction is performed again, and then error correction in two directions is performed over the entire code block.

After performing the above correction process iJ times, the error detection in the X';+5 direction is performed again, and the correction is completed.

The first error detection in the X direction in the flowchart of FIG. 4 is performed in the same way as the error detection in the X direction in the conventional error correction method, and an error flag is added to each word according to the detection result. . Further, the error correction in the Y direction is performed in accordance with the procedure shown in the flowchart of FIG. 5 as follows. That is, first, for subblocks whose error flags are all 60'' among subblocks extending in the X direction, if the syndrome Spy and SQY are both O, it is assumed that no error exists and all error flags are reset. .The reset error flag remains 0 even if an error is detected f' in the next error detection in the X direction.
”. Also, at this time, spy l sQy are both 0.
In cases other than ``,'' the error flag is 0 but there is an erroneous word, that is, an erroneous word that was not detected. Therefore, when the error position determined by SPY and SQY corresponds to any word in the sub-block, that word is determined to be an undetected error word and corrected. After this correction, all error flags are reset to "0" as if no error exists. If the erroneous position determined by Spy+SQY does not correspond to any word in the subblock, there is an undetected error of two or more words, which cannot be corrected using only spy and sQy.

Therefore, at this time, all error flags are set to "1", and the set error flags remain "1" even if no error is detected in the next error detection in the X direction.

Next, for a sub-block with only one error flag "]", if spy l 5ciy are both "O", the error flag is "1" even though it is a correct word.
, and set all error flags to “0”.
Reset to . Unless both spy l SQY are "0", use spy l SQY to find the incorrect position, and if the obtained incorrect position corresponds to a word whose error flag is "l", that word is incorrect. If the detected error position does not correspond to the word with the error flag "l", there must be n other errors detected. AjLsp
If correction is made using y and sQY, there is a high possibility that the correction will be false, so no correction is made and all error flags are set.

In addition, for a sub-block with two error flags "1", if both SPY and SQY are "O", the error flag is "1" even though the two words with the error flag "1" are both correct. , and resets all error flags. spy.

2 with error flag 61" unless both sqy are O.
It is assumed that one word is incorrect, and the Spy*SQY correction is performed using the positions of these two words as the error positions. Note that at this time, the error flag is not set or reset, but is changed in accordance with the result of the next error detection in the X direction.

Also, for sub-blocks where three or more error flags are "1", if both SPY and SQY are 0, nothing will be done.
In other cases, use spy l sQy to find the wrong position. When this incorrect 9th position corresponds to one of the words with the error flag "l", it is determined that that word is an error and the error flag is set to "l" even though the other words are correct. 1 corresponding to the incorrect position of the request
Correct one word. ib position has error flag “1”
If it does not correspond to the word "chair n", there is an error of 2 or more words, and even if the error is 2 words, its position is unclear and correction is impossible.In this case, Spy does not set or reset the error flag regardless of the 5QYO value and whether it is correctable or not, and all follow the result of the next X-direction error detection.This means that if there are three or more error flags If it is ``1'', it is natural that there is an error of 3 words or more, in which case 'SPY
* This is because it is possible that both SQYs may become "0" by chance, or that the requested erroneous position may coincidentally correspond to any n word whose error flag is "1".

In the above correction processing, the processing of error flags after correction is changed depending on the number of "l"s in the error flag before correction and the correction situation. Distinguish between those that have a very low probability of being detected, those that are definitely due to errors in detection, and those that are not, and then reset the error flag, set the error flag, or set the error flag. This is to make the reset and set representation processing correspond to each other. Also, since the sub-blocks extending in the X direction and the sub-blocks extending in the Y direction intersect with each other, the sub-blocks extending in the X direction are Error flags processed independently will be added to each word in the sub-block.

In addition, in the X-direction error detection that follows the Y-direction error re-correction in the flowchart of FIG. Let's set the value. In other words, the reset error flag and the set error flag in Y-direction error correction are "0" and "0" regardless of the result of the next X-direction error detection.
l”.

If an error flag is not reset or set during error correction in the Y direction, if an error flag is detected during the next error correction in the X direction, it becomes "l". If f'L is not detected, it becomes 0''.

After such error detection in the X direction is performed, compared to after error correction in the Y direction in the conventional error correction power formula, words with error flags "l" and errors are detected even though they are correct. In spite of the fact that the error flag is "0", the number of words is reduced.1 In the Z-direction error re-correction in the flowchart of Fig. 4, effective error re-correction can be performed based on accurate error flags. By performing error re-correction in the Z direction in the same manner as error re-correction in the Y direction, if error detection in the X direction and error correction in the Y direction are not performed again after the error correction in the Z direction, this Directional error re-correction can also be performed based on accurate error flags.

After performing error re-correction f′LJ times in the Y direction and Z direction as described above, error detection in the X direction is performed once again in order to detect errors that cannot be corrected in the end. to finish the correction.

When the error code turn shown in the third section is corrected using the above code error correction power formula, the erroneous l word in sub-block B8 is corrected by the first error re-correction in the Y direction.
Due to the primary X-direction error detection, the word with the error flag ``l'' is not a normal word even though it is correct, and the next 2-direction error correction causes 4-word errors to be sent. In addition, when the error pattern shown in FIG. However, as the error flags of these three words become "l" due to the next detection of the error code in the X direction, all of them are corrected along with the error flags of the three words of sub-block B5 by the next error recorrection in the Z direction. Explode.

In the correction processing procedure shown in the flowchart of Fig. 4, the detection of false marks in the X direction is always performed before the correction of false marks in the Y direction and the Z''5 direction. It is possible to partially omit the error detection in the X direction except for the error detection in the X direction. Before,
In the same figure ([1], error detection in the X direction is omitted before the second and subsequent error re-correction in the Y direction. If error detection in the X direction is omitted f', the value of the error flag is It must be determined after the previous error correction. Therefore, in the Y-direction error correction in the procedure shown in the flowchart of FIG. It is necessary to perform the correction process according to a procedure obtained by changing the process of ``None'' to the process of ``holding the value of the error flag before correction.''

By doing so, all the values of the error flags are determined at the time when the error correction in the Y direction is completed. Also, Figure 6 (
Similarly, in the Z-direction error 9 correction in the procedure shown in the flowchart of Figure 5, the processing of "no error flag reset/set" in the procedure shown in the flowchart of Figure 5 is replaced with the processing of "maintaining the value of the error flag before correction". It is necessary to carry out the correction process according to the procedure obtained by changing to ”1
Since the number of words ``increases, the effect of error correction immediately thereafter becomes small, but this does not pose a practical problem as long as the number of times correction is repeated is large.

Similarly, in the above embodiment, the first error correction is performed immediately after the first error detection in the X direction, but the first error detection is performed in two directions and then the first error correction is performed. You can do it like this. For example, after detecting an error in the X direction,
It is also possible to perform error detection in the direction and start error correction in the Y direction. At this time, the value of the error flag is determined after erroneous detection in two directions.
Figure) Syndrome SPY, SQ at 70-f yard
Change Y to t'Lspz I sQz, remove the syndrome correction processing step, and change the "No error flag reset/set" processing step to 1X
Error flag processing when moving to the L word correction processing step due to syndrome when the number of error flags of "1" is less than or equal to 1. This can be done by changing the procedure to "holding the value of the error flag for error detection in the X direction" and following a flowchart such as n. Also,
In the above embodiment, the error correction is all started from the Y direction, but the error correction may also start from the Z direction. '
! J fCs In the flowcharts of Figures 4 and 6, the detection of false marks in the X direction before the end of correction is for detecting residual false marks after error detection. It can be omitted if it is not required.

In addition, in the above embodiment, a Reed-Solomon code with a check word count of 2 is used as the error detection code and the error correction code, but other than the Reed-Solomon code can be used as the error detection code and the error correction code. Similar effects can be expected when codes are used.

The correction of code errors in a rectangular parallelepiped code block as shown in FIG. 1 has been explained above. The present invention can be applied to code error correction in any code block. For example, as shown in Figure 7, a code block of infinite length with crossed codes, or a code block of finite length extracted from the code block shown in Figure 7 and connected at both ends to circulate the code. It is clear that the present invention can also be applied to code blocks as shown in FIG.

Incidentally, a code block as shown in FIG. 7 is obtained by an encoding circuit as shown in FIG. In FIG. 9, zero data words forming a subblock extending in the Z direction are provided to a Z direction error correction encoder 30. The Z-direction error correction encoder 30 is configured to output the supplied f'L7nα data words as they are, and at the same time generate and output a check word of the Z-direction error correction code.

The Z-direction error correction encoder 30 outputs multiple data words and Z-direction check words through delay circuits DIl'' DIα,Dt(a
10+) to D1h, a sub-block extending in the Y direction is formed and supplied to the Y-direction error correction encoder 31. The Y-direction error correction encoder 31 includes a delay circuit Do.
=Dxh output as is, and at the same time generates and outputs a check word of an error correction code in the Y direction. This Y direction 1IQ41) Correction encoder 31
The outputs of the delay circuits Dgt' having different delay times are
D2a + D*(a+l)'DzblD2(b+1'
) and l) i+C to form a complete long block extending in the X direction and supply it to the X direction error detection encoder 32. The X-direction error detection encoder 32 includes a delay circuit D21
.about.D2c is output as is, and at the same time, a check word of the X-direction error detection code is generated and output. An infinite length code block is formed by the output of the X-direction error detection encoder 32.Effects As detailed above, in the code error correction system according to the present invention, other error correction codes are used before error correction. obtained from f
Since the value of the error flag indicating the presence or absence of an error is determined based on the error position information and the detection result of the error detection code,
By monitoring errors in two crossed codes (#), we can reduce the number of words that are incorrect even though the error flag is 0'' and words that are not incorrect even though the error flag is l''. , it is possible to perform error correction after adding an accurate error flag. Therefore, the original correction ability of the error correction code is fully utilized, and errors such as the one shown in Fig. 3, which could not be corrected with conventional methods, can be corrected. Detection using a pattern or an error detection code can also correct error patterns including t, and even error patterns for which a false correction would be made with a single error correction code.

[Brief explanation of the drawing]

Fig. 1 shows a code block obtained by encoding a plurality of data words using an error correction code and an error detection code, and Fig. 2 shows an error correction processing procedure using a conventional code error correction method. FIG. 3 is a flowchart showing an example of an error pattern that cannot be corrected by the conventional method. FIGS. 4 and 5 are a flowchart showing an embodiment of the present invention. FIG. FIGS. 7 and 8 are flowcharts showing other embodiments of the code block to which the present invention can be applied. FIG. 9 is a flowchart showing an example of a code block to which the present invention can be applied. FIG. 2 is a block diagram showing an encoding circuit. Applicant: Pioneer Co., Ltd. Agent Motohiko Fujimura, Patent Attorney Motohiko Fujimura Book 7 Leap County 2 Figure 3 Book Lo Figure fA l (B) Book 7 Leap County Figure 25 L q Lean Procedure Neho (self-proposal) April 12, 1985 Commissioner of the Japan Patent Office 1. Indication of the case Patent Application No. 014039 of 1982 2. Name code error correction method of the invention 3. Relationship with the person making the amendment Patent applicant address 1-4 Meguro, Meguro-ku, Tokyo Number 1 Name (5
01) Pioneer Co., Ltd. 4, Agent 104 Address Kyodo Building, 3-10-9 Ginza, Chuo-ku, Tokyo (
Ginza 3-chome) Phone: 543-7369 Name (7911)
) Patent Attorney Motohiko Fujimura5, Date of amendment order Voluntary6, Number of inventions increased by amendment None8, Contents of amendment (1) The scope of claims will be amended as shown in the attached sheet. (2) From line 14 on page 2 of the specification to line 16 on the same page, delete j that includes a pit corresponding to data and a bit corresponding to an error flag indicating the presence or absence of a code error. (3) Correct the J in the F word on page 8, line 19 of specification a with ``J added to each word. (4) Delete the pit J corresponding to `` on page 9, line 1 of specification a. (5) Delete "the bit corresponding to" on the 8th line of page 9 of the specification. (6) Delete the bit corresponding to "Reset" on the 1st line of page 10 of the specification. Syndrome Spy in the Y direction when three or more word error flags are ``1''
, the error flag of the error position set by Say is °゛0''
In the case of , for example, all error flags in the sub-block containing the corrected word are set to ``1''.'' is inserted. (7) From line 4 of page 12 of the specification to line 5 of the same page, r 11
1. The same applies if you do not perform the correction process in case of II.
If we simply do not perform the correction process when r II I II, the error pattern shown in FIG. 2B can be corrected.'' (8) Delete "formed by a pit corresponding to data and a bit corresponding to an error flag indicating the presence or absence of a code error" from line 8 to line 10 of page 13 of the specification. (9) "Change" on page 18, line 7 of the specification is amended to "determination." (10) Next to "..." on page 19, line 8 of the specification, [Note that the error flag is formed of, for example, 2 bits, and is "11" (hereinafter abbreviated as "1"). ) corresponds to the set state, that is, there is an error, and 00 (hereinafter abbreviated as “0゛′) corresponds to the reset state, that is, there is no error.
1101 Insert "II or 'io" corresponds to the initial state 'TJ, that is, the state without set reset. No reset]. (12) From line 12 on page 20 of the specification to line 13 on the same page [
"Reset and Set" is corrected to "Set and Reset". (13) In the 16th line of page 22 of the specification, next to “...omitted.” There is, but not one.”
Insert. (14) "No reset/set" in the second line of page 23 of the specification is corrected to "no set/reset". (15) Insert [(sets the error flag to the initial state) J next to the process j in the second line of page 23 of the Mei St+ book. (16) QQillini! page 23, page 1017 (7)
F') Correct J with no set/set as J with no set/reset. (17) Change "infinite length" in line 6 of page 27 of the specification to
Correct J as shown in the figure. (Attachment) [2.Claims] Out of a plurality of υ blocks obtained by dividing a code block consisting of a plurality of data words and a plurality of check words by each of the first, second and third division methods. any two words of the plurality of data words and check words included in one of the first, second and third division methods for obtaining a sub-block in which these two words exist; an error detection code formed for each subblock obtained by the first division method when the error detection code is not simultaneously present in any of the subblocks obtained by the other two except one; A method for correcting code errors in the code block when the plurality of check words are formed by first and second error correction codes respectively formed for each sub-block obtained by a dividing method, the method comprising: Ichiichi Tower°
By adding an error flag to each of the scanning words to eliminate the error in the code, one of the first and second correction codes is used to calculate the error position obtained when the error is corrected by one of the first and second correction codes. After performing a process of determining the value of the error flag based on the information and the detection result by the error detection code, at least one of the first and second error correction codes performs error correction by referring to the error flag. A code@error correction method that is characterized by being performed once. J

Claims (1)

[Claims] A code block consisting of a plurality of data words and a plurality of check words formed by a bit corresponding to data and a bit VCL corresponding to an error flag indicating the presence or absence of a code error is first. Any two words among the plurality of data words and check words included in one of the plurality of sub-blocks obtained by dividing by each of the second and third division methods are these two. The first . Of the second and third division methods, when f''Lvc of the sub-blocks obtained by the other two except 1''':) does not exist at the same time, the first division method is reversed. n false detection codes formed for every n sub-blocks obtained by
A method for correcting a code error in the code block when the plurality of check words are formed by using the first and second error correction codes formed, the method comprising:
Immediately after error correction by one of the second error correction codes, determining the value of the error flag based on the error position information obtained during error correction by the one and the detection result by the error detection code. 1. A code error correction method characterized in that after performing a process of performing the above error flag, error correction is performed at least once using the other of the i1 and the second error correction code with reference to the error flag.