JPS6412127B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an error correction method, and more specifically, to an error correction method used when transmitting, recording, or reproducing a digital signal with an error correction code added thereto. .

[Background of the invention]

Digital magnetic recording devices such as digital VTRs that record and reproduce PCM encoded television signals use error correction codes to correct code errors that occur during reproduction. Generally, in an error correction code, there is an upper limit to the number of code error bits that can be corrected, and if the code error exceeds this upper limit, operations such as uncorrectable or erroneous correction occur. In particular, digital
In VTRs, in addition to random code errors caused by noise, burst errors occur in which errors are concentrated in one place due to dropouts caused by scratches on the tape, etc. Many of these burst errors are code errors that exceed the correction range of the error correction code, but even for such errors, the redundancy of the television signal is used to correct the erroneous part of the previous line. It is necessary to perform so-called modification such as replacing the information with the information of However, in the case of an error that cannot be corrected using only an error correction code, it is also necessary to correct all information bits that do not contain the error contained in the code word.
If a mistake is made in the correction, the image will still contain the error, resulting in problems such as deterioration in image quality.

[Purpose of the invention]

An object of the present invention is to reduce the correction portion to be performed when a code error occurs and cannot be corrected in the digital signal processing circuit as described above, and to limit the correction portion to the area where the code error actually exists as much as possible. It is an object of the present invention to realize an error correction method that prevents erroneous corrections when performing correction using codes.

[Summary of the invention]

In order to achieve the above object, the present invention configures a code with error correction codes, and adds an error detection code to the code configuration for each code number that does not exceed the upper limit of code errors that can be corrected by the error correction code. When the recorded or transmitted code is reproduced, errors are detected using the error detection code, and if the code error exceeds at least the above correctable range, that part is corrected using a correction signal. and replace it with
Other parts of the erroneous part, ie, parts that do not exceed the above correctable range, are corrected using an error correction code.

As a particularly preferred form, as will be explained in detail in the following example, the code structure is such that the code words of a plurality of error correction codes are made into a block, and the codes within the block are temporally interleaved, and then the code can be corrected. An error detection code is added for each number of codes (number of bits) corresponding to a burst length, and the above-mentioned reproduction process is performed. In this way, even if there is a long dropout such as a burst error, the code error section in the error correction code word will be shortened during signal reproduction, and the shortened code error length will be used for correction of the error correction code. If it is longer than the maximum possible limit, it is corrected, and if it is shorter, it is corrected using an error correction code, so the correction part is limited to the part where the code error occurred.
Moreover, even if there is an error, if the error is short, it can be corrected to a correct code by the error correction code, and the image quality of the reproduced image is improved during image signal transmission or recording/reproduction.

[Embodiments of the invention]

Hereinafter, it will be explained in detail using the drawings.

FIG. 1 is a time chart for explaining the principle of the present invention. Figure a shows an error correction code in which four code words W ₁ , W ₂ , W ₃ , and W ₄ form one block. Here, the error correction code is assumed to be a code capable of correcting a single error. The codes included in this block are temporally interleaved to construct the code sequence shown in Figure b. In this case, since it is a single error correction code, the correctable burst length is 4, and burst errors up to length 4 can be corrected. Therefore, the number of information points in the added error detection code is four at most. Here, considering that an error detection code that enables the detection of code errors is added every code number equal to the correctable burst length, that is, every 4 in this case, as shown in Figure c. This code sequence is recorded. Assume that a burst error as shown in c in the figure occurs during reproduction. For the reproduction code,
When detecting the presence or absence of a code error using an error detection code added every 4 codes equal to the correctable burst length, a signal indicating the position of the code error as shown in e in the figure is obtained. . On the other hand, the code sequence shown in the figure d is obtained by removing the added code for error detection. When d and e are deinterleaved (reverse processing from a to b) and converted to the original time series code, signals f and g in the figure are obtained, respectively. Next, the decoder performs error correction on each code word, and during this correction, a signal indicating the position of the code error shown in FIG. 3G is used to control the error correction operation. That is, for each code word, if the number of code errors obtained from the signal indicating the position of code errors in g is less than the error correction range of each code word, error correction is performed using a normal error correction code. Do the following. On the other hand, if the number of code errors obtained from the signal of g exceeds the correction range, it cannot be corrected or the error correction operation will result in incorrect correction, so the correction operation is not performed and instead, the code error of g is Modify only the part that indicates the position. In the case of this drawing, each code word
Regarding W ₁ , W ₂ , W ₃ , and W ₄ , the number of code errors in all signals of g exceeds the correctable range (single error), so as shown in h of the figure, W ₁ , W ₂ ，
Only the codes corresponding to the error part of g in W ₃ and W ₄ are corrected. That is, in this embodiment, only the vicinity of the actual code error is corrected.
On the other hand, in the conventional method, a correction _operation is performed for each code word, and as _shown in Figure i, each code _word is All the contents will have to be corrected, and _W2 that was incorrectly corrected will remain in a state where the error remains.

In addition, in the present invention, the reason why an error detection code is added for each number of codes corresponding to the maximum correctable burst length is that the error correction operation using the error correction code is performed for errors smaller than the correctable burst length. This is to make them do it.

Next, an embodiment of an error correction circuit according to the present invention is shown in FIG. A plurality of code words to which error correction codes have been added in encoder 1 are treated as one block,
The interleave processing circuit 2 converts the code into a code sequence as shown in FIG. 1b. Then, in the parity addition circuit 3, an error detection code having one or more check points is added for each code having a burst length that can be corrected at most, and a code as shown in FIG. 1c is recorded. On the other hand, during reproduction, the error detection circuit 4 detects the presence or absence of errors in the reproduced code using error detection codes added for each code having a maximum correctable burst length. One output of the error detection circuit 4 is a code obtained by removing the code of the check point added for error detection, as shown in FIG.
becomes the input. As shown in FIG. 1e, the remaining output is a signal that is, for example, "1" when a code error is detected, and "0" otherwise, and is input to the deinterleave processing circuit 6. . The deinterleave processing circuits 5 and 6 have exactly the same configuration and convert the code into the original code sequence. Therefore, the output of the deinterleave processing circuit 5 is shown in FIG. 1 f, and the output of the deinterleave processing circuit 6 is shown in g. The error correction circuit 7 performs an error correction operation, and this operation is controlled by one output of the counting circuit 8. That is, the counting circuit 8 uses the output of the deinterleave processing circuit 6 to count the number of detected code errors for each code word of the error correction code, and determines whether this number can be corrected by the error correction code. If the number is less than a certain number, the error correction circuit 7 generates a control signal to perform a correction operation. On the other hand, if the number of code errors counted exceeds the number that can be corrected by the error correction circuit, a control signal is generated to inhibit the correction operation of the error correction circuit 7. Further, the other output of the counting circuit 8 is only when the number of counted code errors exceeds the number that can be corrected by the error correction code. The selection circuit 9 is controlled so as to replace the modified code, for example, with the information of the previous line of the television signal. Therefore, as shown in FIG. 1h, the output of the selection circuit 9 provides an output code with a limited modification area.

As mentioned above, an error detection code is added for each code with a burst length that can be corrected at most, and this error detection code is used to count the number of errors included in the error correction code. Therefore, according to the present invention, which controls the operation of error correction,
Even if the number of code errors exceeds the number that can be corrected by the error correction code, it is possible to perform corrections limited to the vicinity of the actual code errors.

Note that depending on the selection of the error detection code to be added, the probability of overlooking an error may be quite large, but in such cases, for example, A similar effect can be obtained by expanding the number of codes corresponding to the information points of the error detection code and using this expanded error range as a new code error area.

Furthermore, so far, a case has been described in which a plurality of error correction codes are treated as one block, the codes within this block are interleaved, and then an error detection code is added. However, even if an error detection code is added directly to the error correction code without interleaving, the erroneous correction can be removed for code errors that exceed the correction range, and correction can also be performed in the vicinity of the actual error. Needless to say, it is limited to.

[Brief explanation of drawings]

FIG. 1 is a time chart for explaining the principle of the present invention, and FIG. 2 is a block diagram showing the configuration of an embodiment of an error correction circuit according to the present invention. 1... Encoder, 2... Interleave processing circuit, 3
...Parity addition circuit, 4...Error detection circuit, 5, 6
... Deinterleave processing circuit, 7... Error correction circuit,
8... Counting circuit, 9... Selection circuit.

Claims (1)

[Scope of Claims] 1. In an image signal error correction system, a plurality of code words to which error correction codes are respectively added are treated as one block, and code errors within the one block that can be corrected by the error correction codes are The codes in the block are interleaved so that code sequences with the number of codes less than or equal to the upper limit of After detecting an error using the error detection code, deinterleaving is performed, and if the detected code error does not exceed the correctable range of the error correction code, each code word is corrected using the error correction code. If the error exceeds the error range, the error correction method is characterized in that after detecting the error, the code error part of each deinterleaved code word is replaced with a corrected code that correlates with that part. 2. In the error correction method described in paragraph 1, when an error exceeding the above correctable range is detected, the error correction method replaces the code portion near the code error portion with a corrected code.