JP4280005B2 - Error correction apparatus and receiver using the error correction apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is correcting device Ri erroneous that put the error correction, and a receiver using the error correction device.
[0002]
[Prior art]
In general, in order to cope with bit errors that occur when digital data is transmitted, a check code with error correction capability is added and transmitted, and a method of detecting and correcting the error position according to this check code is used on the receiving side. ing. In addition, in order to make the data after error correction more reliable, the check code is efficiently distributed to error correction capability and error detection capability to perform error correction processing that minimizes error correction. Then, a process for confirming whether or not erroneous correction has been performed on the data after error correction is performed.
[0003]
Here, after transmitting the data with error correction parity added as digital data of a shortened block code, the received codeword has an error as a method of determining whether the data after error correction has been completely corrected. For example, a correction process is performed, a syndrome is calculated again for the result, and it is confirmed whether or not it becomes “0”.
[0004]
This type of conventional example will be described with reference to the drawings.
[0005]
FIG. 1 is a configuration diagram of a detection apparatus that detects whether a conventional corrected signal is corrected beyond a block code correction capability.
[0006]
In FIG. 1, a conventional detection device for detecting whether a corrected signal has been corrected beyond the block code correction capability includes a syndrome calculation unit 11, an error value, an error position polynomial calculation unit 12, an error value, and an error. The position calculation unit 13, the data delay unit 14, the correction unit 15, the re-syndrome calculation unit 16, and the re-syndrome evaluation unit 17 are configured.
[0007]
The syndrome calculation unit 11 performs a syndrome calculation on the input codeword. The error value / error position polynomial calculator 12 obtains an error value polynomial and an error position polynomial from the syndrome. The error value / error position calculation unit 13 obtains an error value and an error position from a polynomial. The data delay unit 14 accumulates input data input from the syndrome calculation unit 11. The correction unit 15 corrects errors. The re-syndrome calculation unit 16 performs the syndrome calculation again on the code word after the error correction. The re-syndrome evaluation unit 17 evaluates whether or not error correction is correctly performed from the value of the re-syndrome.
[0008]
In the correction confirmation apparatus for error correction, a code word is input to the syndrome calculation unit 11 and the data delay unit 14. The data delay unit 14 is delayed until the error numerical value and the calculation result of the error position calculation unit 13 are output. A syndrome is obtained from the code word by the syndrome calculation unit 11 and output to the error numerical value and error position polynomial calculation unit 12. The error value / error position polynomial calculation unit 12 obtains an error value polynomial and an error position polynomial from the syndrome. The error value / error position calculation unit 13 obtains an error value and an error position using the error value polynomial and the error position polynomial. The correction unit 15 performs error correction on the code word data stored in the data delay unit 14 using the error numerical value and the error position. The re-syndrome calculation unit 16 obtains a syndrome again for the code word that has been subjected to error correction by the correction unit 15, and based on the result, the re-syndrome evaluation unit 17 evaluates whether the data after error correction is correct. I do.
[0009]
If the result of the re-syndrome is “0”, it is assumed that the correction is correct. If the result is other than “0”, there is an error correction in the error correction, and this is corrected beyond the code correction capability. means.
[0010]
[Problems to be solved by the invention]
However, the conventional detection device for detecting whether or not the corrected signal has been corrected beyond the block code correction capability needs to calculate the syndrome again, and there is a problem that the processing becomes complicated.
[0011]
Therefore, the present invention has been made in view of the above problems, and has a configuration of a detection device that can detect whether a corrected signal has been corrected beyond the block code correction capability by simple processing. An object of the present invention is to provide an error correction device and a receiver using the error correction device.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs means for solving the problems having the following characteristics.
[0013]
According to the first aspect of the present invention, a stuffing symbol having all bit values of “0” is inserted into the input shortened Reed-Solomon code, and a read having a data length of 238 bytes and a parity length of 16 bytes before shortening. A block code reproduction unit that reproduces a Solomon code (RS [255, 239]), an error correction unit that performs error correction using the reproduced Reed-Solomon code, and a Reed-Solomon code corrected by the error correction unit , In accordance with the number of “1” s in the bit values of the corrected stuffing symbol, it is checked whether or not the corrected Reed-Solomon code has been corrected beyond the block code correction capability, and the corrected stuffing If the bit value of the symbol contains “1” more than a preset number, the corrected read solo The inspection unit determines that the code has been corrected beyond the block code correction capability, the shortened block code storage unit that stores the input shortened Reed-Solomon code, and the inspection result obtained from the inspection unit corrects the correction. If it is determined that the Reed-Solomon code has been corrected beyond the block code correction capability, the data obtained from the shortened Reed-Solomon coding stored in the shortened block code storage unit is selected, and the other In some cases, the data processing apparatus includes a selection unit that selects and outputs error-corrected data obtained by the error correction unit.
[0014]
According to the first aspect of the present invention, the inspection unit detects whether or not the signal corrected based on the corrected stuffing symbol value has been corrected beyond the block code correction capability. In the processing, it is possible to detect whether or not the corrected signal has been corrected beyond the block code correction capability. In addition, by selecting one of the data after error correction obtained by the error correction unit and the data before error correction stored in the shortened block code storage unit based on the detection result, signal degradation in transmission data is selected. Can be reduced.
[0019]
The invention described in claim 2 is the receiver using the error correction device of claim 1, wherein.
[0020]
According to the invention described in claim 2, kill is possible to provide a receiver using the error correction device of claim 1, wherein.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Before describing embodiments of the present invention, the features of block codes will be described.
[0022]
In general, with a block code, only a code having a specific length can be obtained by its generation method. For example, in the case of a Reed-Solomon code, 8 bits (1 byte) are treated as one symbol, and when error correction is performed in units of symbols, the length of data and error correction parity (code word) is 255 bytes. Must be.
[0023]
The number of bits that can be corrected is determined in principle. For example, in RS [255,239] code (data length 239 bytes, parity length 16 bytes), which is a kind of Reed-Solomon code, 8 bytes, which is half the parity length. Corrections up to are possible. When the error correction processing (decoding processing) is performed on the data including the error exceeding the correction range, the bit error rate is deteriorated as compared with that before the error correction.
[0024]
Next, shortening of the block code will be described. As described above, the block code needs to be a codeword having a fixed length, and therefore, the length of data to be transmitted does not necessarily match the length of data suitable for the error correction code. In such a case, a technique called shortening is used. Hereinafter, a shortening method will be described with reference to FIG.
[0025]
FIG. 2 is a diagram for explaining an example of shortening.
[0026]
The Reed-Solomon code (RS [255, 239]) 21 in FIG. 2 includes an MPEG2 TS (Transport Stream) packet 22, a stuffing symbol 23, and an error correction parity 24.
[0027]
The shortened Reed-Solomon code (RS [204,188]) 25 is composed of an MPEG2 TS packet 22 excluding the stuffing symbol 23 and an error correction parity 24.
[0028]
In FIG. 2, a case is considered where error correction parity 24 is added to an 188-byte MPEG2 TS packet 22 which is data transmitted using an RS [255, 239] code 21, which is a kind of Reed-Solomon code. In this case, since the data length is fixed to 239 bytes, a predetermined value of data (stuff symbol 23) corresponding to the missing 51 bytes is added to generate a 16-byte error correction parity 24. The Reed-Solomon code 21 is created.
[0029]
However, since the stuffing symbol 23 has only the role of filling the shortage of the data length, it is not added when the data is actually transmitted, but is added before error correction on the receiving side, and the data length to be transmitted is set. The transmission capacity is reduced by making it as short as possible, and the band is used effectively. This is called shortening, and the data transmitted here is the shortened Reed-Solomon code (RS [204,188]) 25.
[0030]
Next, the principle of the present invention will be described with reference to FIG.
[0031]
FIG. 3 is a diagram illustrating an example of an error correction detection method in error correction.
[0032]
FIG. 3 shows a case where a shortened Reed-Solomon code (RS [204,188]) 25 is used as an error correction code to be added to digital data, and “0” for 51 bytes is used as the stuffing symbol 23.
[0033]
When the received data 31 contains only an error within 8 bytes, which is the error correction capability, the error correction is completely performed on both the 51-byte stuffing symbol 23 and the 188-byte data 31.
[0034]
However, when an error exceeding 8 bytes exceeding the error correction capability is included, both the stuffing symbol 23 and the data 31 are erroneously corrected.
[0035]
That is, when the stuffing symbol 23 which is all “0” is not detected as all “0”, it can be confirmed that at least error correction has been corrected beyond the block code correction capability.
[0036]
Note that, when the stuffing symbol 23 that should originally be “0” is erroneously corrected, the probabilities of being detected as “0” or “1” are equal and can be considered to be ½ respectively. Although the 51-byte all- “0” static symbol 23 of the embodiment is erroneously corrected, the probability that it will be detected as all “0” is as high as 1/2 to the 408th power (51 bytes × 8 bits). It is possible to detect that the error correction has been corrected almost completely beyond the correction capability of the block code.
[0037]
Therefore, if error correction is performed correctly, the corrected data is output. If error correction is not performed correctly, the data part before error correction is output, thereby reducing the bit error rate of the data. Can be prevented.
[0038]
Next, an embodiment of the present invention will be described with reference to FIG.
[0039]
FIG. 4 is a diagram of an example of a detection device and an error correction device.
[0040]
4 includes an error correction device 41, a detection device 42, a shortened block code storage unit 43, and a selection unit 44. The detection device 42 includes a block code reproduction unit 45, an error correction unit 46, and an inspection unit 47.
[0041]
The block code reproduction unit 45 adds a stuffing symbol to the input shortened Reed-Solomon code (RS [204,188]) and reproduces the Reed-Solomon code (RS [255,239]) before the shortening. The error correction unit 46 performs error correction of the code word, and the inspection unit 47 detects whether correction is performed beyond the error correction capability of the block code from the data after error correction. The shortened block code storage unit 43 stores the shortened block code input to the error correction device 41, and the selection unit 44 controls the data to be output under the control of the error correction flag output from the check unit 47. Select and output.
[0042]
The shortened Reed-Solomon code (RS [204,188]) input to the error correction device 41 is obtained by adding error correction parity (16 bytes) to MPEG2 TS packet data (188 bytes).
[0043]
The shortened Reed-Solomon code (RS [204,188]) is input to the detection device 42 and the shortened block code storage unit 43.
[0044]
The shortened block code storage unit 43 stores the input data as it is.
[0045]
The block code reproduction unit 45 adds a 51-byte stuffing symbol that is all “0” to the shortened Reed-Solomon code (RS [204,188]) to reproduce the Reed-Solomon code (RS [255,239]). . The Reed-Solomon code is subjected to error correction by an error correction unit 46, and the error-corrected data is output to the selection unit 44 and the error-corrected stuffing symbol is output to the inspection unit 47.
[0046]
The inspection unit 47 compares the stuffing symbol after error correction with the stuffing symbol (all “0”) added by the block code reproduction unit 45 and compares it with the selection unit 44 when it matches. If the values do not match, an error correction flag such as “0” is output.
[0047]
Based on the result of the error correction flag, the selector 44 selects a corrected MPEG2 TS packet output from the error corrector 46 when the flag is “1” (match), and when the flag is “0” (not match). Outputs a TS packet of MPEG2 before error correction from the shortened block code stored in the shortened block code storage unit 43.
[0048]
In the inspection unit 47 according to the present invention, a flag can be output in accordance with the number of errors in the compared data. In the selection unit 48, data is edited using the flag output from the inspection unit 47. be able to.
[0049]
Next, a configuration example of the receiver is shown in FIG.
[0050]
The receiver in FIG. 5 includes a digital decoding unit 51, an error correction device 41, a video / audio decoding unit 52. The error correction device 41 includes a detection device 42, a shortened block code storage unit 43, and a selection unit 44.
[0051]
FIG. 5 is a satellite digital broadcast receiving system.
[0052]
The digital modulation wave that has passed through the transmission path is decoded by the digital decoding unit 41 into a shortened Reed-Solomon code (RS [204, 188]). The shortened Reed-Solomon code is output to the detection device 42 and the shortened block code storage unit 43. The detection device 42 performs block code reproduction, error correction, and detection of whether or not the correction exceeds the block code correction capability described above. The error correction flag and the MPEG2 TS packet (data part) after error correction are detected. The data is output to the selection unit 44.
[0053]
The selection unit 44 outputs the MPEG2 TS packet after the error correction to the video / audio decoding unit 52 if they match according to the result of the error correction flag, and shortens if the flags do not match. From the shortened block code stored in the block code storage unit 47, the MPEG2 TS packet before correction is output to the video / audio decoder 52.
[0054]
The video / audio decoder 52 can reduce degradation of data in transmission by decoding the selected MPEG2 TS packet data input from the selection unit 44.
[0055]
FIG. 6 shows the effect of using the detection apparatus, error correction apparatus, and receiver using the same in the error correction of the present invention.
[0056]
FIG. 6 is a graph plotting the bit error rate of transmission data against the required C / N (ratio of signal power to noise power at the receiver input terminal).
[0057]
In FIG. 6, the horizontal axis indicates the required C / N, the vertical axis indicates the bit error rate, and (1) indicates the plot value when error correction processing is performed on the Reed-Solomon code.
[0058]
{Circle over (2)} shows plot values when error correction processing is not performed on the Reed-Solomon code.
[0059]
By implementing the present invention, it is possible to obtain a plot value as shown in (3) of FIG. 6, improve the required C / N, and reduce signal deterioration in transmission data.
[0060]
The input data used in the description of the present invention is not limited to the shortened Reed-Solomon code, and may be any signal to which specific data can be added.
[0061]
Further, the number of bytes of the stuffing symbol varies depending on the type of the block code to be shortened, and the value of the data is not limited to “0”.
[0062]
【The invention's effect】
As described above, according to the present invention, in the case it was corrected erroneous data after error correction, by using the data before the error correction processing, that Do is possible to reduce signal degradation in the transmission data mis Ri correction device, and it is possible to provide a receiver using the error correction device.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a detection device in conventional error correction.
FIG. 2 is a diagram for explaining an example of shortening.
FIG. 3 is a diagram illustrating an example of an error correction detection method in error correction.
FIG. 4 is a diagram for explaining an example of a detection device and an error correction device.
FIG. 5 is a diagram for explaining a configuration example of a receiver.
FIG. 6 is a diagram for explaining an effect example of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Syndrome calculation part 12 Error value, error position polynomial calculation part 13 Error value, error position calculation part 14 Data delay part 15 Correction part 16 Re-syndrome calculation part 17 Re-syndrome evaluation part 21 Reed-Solomon code (RS [255,239])
22 MPEG2 TS packet 23 Stuffing symbol 24 Error correction parity 25 Shortened Reed-Solomon code (RS [204, 188])
31 Data 41 Error correction device 42 Detection device 43 Shortened block code storage unit 44 Selection unit 45 Block code reproduction unit 46 Error correction unit 47 Inspection unit 51 Digital decoding unit 52 Video and audio decoding unit

Claims (2)

A stuffing symbol having all bit values of “0” is inserted into the input shortened Reed-Solomon code, and a Reed-Solomon code (RS [255, 239]) having a data length of 238 bytes and a parity length of 16 bytes before shortening. A block code reproduction unit for reproducing
An error correction unit that performs error correction using the reed-Solomon code reproduced above;
For the Reed-Solomon code corrected by the error correction unit, the corrected Reed-Solomon code exceeds the block code correction capability according to the number of “1” s in the bit values of the stuffing symbol after correction. The corrected Reed-Solomon code has a block code correction capability when the bit value of the corrected stuffing symbol includes “1” more than a preset number. An inspection unit that determines that the correction has been made beyond
A shortened block code storage unit for storing the input shortened Reed-Solomon code;
If it is determined that the corrected Reed-Solomon code has been corrected beyond the block code correction capability based on the inspection result obtained from the inspection unit, the shortened Reed-Solomon stored in the shortened block code storage unit An error correction apparatus comprising: a selection unit that selects data obtained from encoding, and otherwise selects and outputs error-corrected data obtained by the error correction unit.   A receiver using the error correction apparatus according to claim 1.

Images