JPH05129964A - Error correction device for digital data - Google Patents

Abstract

PURPOSE:To improve the error correction capability at decoding of a digital modulation code by applying weighting to a reference sample with an error incidence probability of configuration bits and selecting a reference sample whose distance to an input sample is closest so as to correct the error. CONSTITUTION:When a reproduced sample arrives in a data string comparison means 31, the matching between the sample and a reference sample in a ROM 32 is judged by the means 31. When they are unmatched, it is decided that an error takes place, and when plural reference samples whose minimum humming distance with respect to the inputted sample is equal are in existence, a weighting means 36 applies weighting arithmetic operation to the reference sample based on an error incidence probability of configuration bits. Then a selection means 38 obtains the distance between the input sample and the weighted reference samples and selects the reference sample whose distance is closest thereby correcting the error in the input sample. Thus, the error correction capability at decoding of the digital modulation code is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an error correction device for digital data.

[0002]

2. Description of the Related Art As is well known, when transmitting digital information, it is general to detect and correct an error occurring in a transmission line. According to the code theory, the basic principle of error correction is that the Hamming distance between codewords (symbol strings) is large.

The number of different pairs of symbols at corresponding positions of two symbol sequences u and v having the same length is called a Hamming distance of the symbol sequences u and v, and d _H (u,
v). Hereinafter, it may be simply referred to as distance. In a block code in which all codewords have finite length and are equal, the minimum value of the Hamming distance between different codewords is called the minimum (Hamming) distance of the code and is represented by d _min .

As shown in FIG. 7, a set of symbol strings having a distance of t or less from the codewords c _i and c _j is conceptually represented by a sphere having a radius t centered on c _i and c _j , respectively. , If they meet the following conditions, they have no common part. d _min ≧ 2t + 1

When the code word c _{i of the} block code is transmitted, an error of e (≦ t) occurs in the transmission path, and r
If is received, e is expressed as follows. e = d _H (c _i , r) ≦ t At this time, for any codeword c _j other than c _i , d _H (c _j , r)> t

Therefore, for the received word r, d _H (x,
If it is determined that the codeword x for which r) ≦ t is transmitted, t
Any number of errors (t or less) can be corrected. In general, a code whose d _min is 2t ₂ +1 or more is t
_{A single} error can be corrected and a t ₁ + t ₂ error can be detected.

Conventionally, in magnetic recording of digital signals, in consideration of electromagnetic conversion characteristics, individual original data has a DC component such as 8-10 modulation or 8-14 modulation, or a series of bits of the same polarity. It is converted into as few modulation codes as possible and recorded. Normally, this modulation code follows a predetermined modulation rule (rule), and sample data corresponding to all input data strings is stored in a ROM (Read Onl
yMemory) is installed.

When the sample data not included in the ROM table is obtained in violation of the modulation rule due to an error mainly occurring in the magnetoelectric conversion system during reproduction, the violation is performed with all the samples in this table as references. The Hamming distance from the reference sample is obtained by pair-wise comparison with the sample, and the violating sample is decoded into the sample having the closest Hamming distance. That is, the error is corrected by the minimum distance decoding method.

[0009]

In the magnetic recording of digital signals, however, the inter-code distance is generally small due to the above-mentioned restrictions on the modulation code. Therefore, the conventional minimum distance decoding method is not always sufficient. There was a problem that the correction ability was not obtained.

That is, as shown in FIG. 8, the modulation code space R
In addition to c, sample data e ₁ , e violating the modulation rule
_{When 2} and e ₃ are obtained, the violation sample e ₁ has one code c ₂ that has the minimum distance in the modulation code space Rc, and the error is corrected. However, since the violation sample e ₂ has two minimum distance codes c ₄ and c ₅ , the error cannot be corrected by the minimum distance decoding method.

For example, in a magnetic recording / reproducing system using 3-9 modulation as shown in Table 1 below, a sample S
It is assumed that pb = “011001001” is obtained. This sample Spb corresponds to the original signal “0” in Table 1 and is the reference sample Sr0 = “011001001” in the first column # 2.
Only the bits are different, and only the # 3 bit is different from the reference sample Sr1 = "011100001" corresponding to the original signal "1" in the second column. That is, in this case, the reproduced sample Spb has a Hamming distance of [1] with both the reference samples Sr0 and Sr1, so that the closest sample cannot be specified and only error detection is possible.

[0012]

[Table 1]

In view of the above point, an object of the present invention is to decode a digital modulation code in a digital signal transmission system,
An object of the present invention is to provide an error correction device for digital data, which has significantly improved error correction capability.

[0014]

SUMMARY OF THE INVENTION The present invention is a data string comparing means for comparing, for each constituent bit, an input data string that has passed through a predetermined transmission system and a group of reference data strings having the same length as this input data string. In a digital data error correction device including 31 and a data string selection unit 34 that selects a reference data string having a minimum distance from an input data string based on the output of the data string comparison unit, a group of reference data Weighting means 36, 37 for weighting the error occurrence probability of a predetermined transmission system for each constituent bit of the column,
When a plurality of reference data strings are selected by the data string selecting means, a data string corresponding to each of the plurality of reference data strings and having a minimum distance from the input data string among the plurality of data strings weighted by the weighting means. Second to select
And an error correction device for digital data provided with the data string selection means 38.

[0015]

According to this structure, in the digital signal transmission system, the error correction capability is significantly improved when decoding the digital modulation code.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A digital data error correction device according to the present invention will now be described with reference to FIGS.
An embodiment applied to R will be described.

FIG. 2 shows the overall construction of an embodiment of the present invention, and FIG. 1 shows the construction of the essential parts. In FIG. 2, 10 is a recording system, and an analog video signal or the like from a terminal 11 is supplied to a data generating circuit 13 via an AD converter 12 to generate recording data conforming to the system format. It Reference numeral 14 is a digital modulation (data conversion) circuit, which is provided with a ROM table storing conversion codes as shown in Table 1 above. The output of the generation circuit 13 is supplied to a digital modulation circuit (ROM) 14, and the sample data output from the modulation circuit 14 is recorded amplifier 15
Is supplied to the magnetic head 1 via the recording medium and recorded directly on the magnetic tape MT.

Reference numeral 20 is a reproducing system, in which an RF signal reproduced from the magnetic tape MT by the magnetic head 2 is passed through a reproducing amplifier 21 and a waveform equalizing circuit 22 to a binary comparator 2
3 and the sample data is reproduced. Comparator 2
3 is supplied to the PLL circuit 24 and the synchronization detection circuit 25, and the synchronization detection circuit 25 is supplied with the output of the PLL circuit 24.

Reference numeral 30 is an error correction circuit, the detailed construction of which will be described later. The output of the synchronization detection circuit 25 is supplied to the error correction circuit 30, the corrected sample data is supplied to the digital demodulation circuit 26, is converted into original data, and is output to the output terminal 27. A system control circuit (microprocessor) 40 includes a data bus 41.
Via the digital modulation circuit 14 and the digital demodulation circuit 2
6. Control the error correction circuit 30.

As shown in FIG. 1, the data string comparison means 31 of the error correction circuit 30 is supplied with a series of sample data from the input terminal 30i and compares it with the reference sample stored in the ROM 32 for each constituent bit. To be done. The output of the comparison means is led to the output terminal 30o via the movable contact of the switch 33 and the c-side fixed contact, and is supplied to the minimum distance selection means 34 via the d-side fixed contact. The output of the minimum distance selection means 34 is led to the output terminal 30o via the movable contact of the switch 35 and the s-side fixed contact, and is also supplied to the weighting means 36 via the p-side fixed contact.

In the weighting means 36, the selection means 3
The weighting coefficient stored in the ROM 37 is multiplied for each constituent bit of the output of No. 4, and the multiplication result is supplied to the second minimum distance selecting means 38. The weighting factor will be described later. The output of the second selecting means 38 is led to the output terminal 30o via the movable contact of the switch 39 and the s-side fixed contact, and is also led to the output terminal 30e via the p-side fixed contact.

Next, the operation of one embodiment of the present invention will be described with reference to FIGS.

According to the present invention, based on the finding that the error occurrence probability of each constituent bit of the reproduced sample depends on the length of the bit inversion interval of each reproduced sample, that is, the bit pattern, as shown in Table 1 above. It is apparent that the probability that an error will occur in the transmission system to be used is calculated in advance for each of the constituent bits of all the reference samples, and the weight corresponding to this error occurrence probability is applied to each of the constituent bits of the reference sample. The distance is expanded so that sufficient correction ability can be obtained.

In this embodiment, when a reproduction sample arrives at the data string comparing means 31 of FIG. 1, it is judged whether or not the reproduction sample and the reference sample of the ROM 32 match (steps S11 and S12). Since no error has occurred, the process returns to step S11 again. In this case, the switch 33 is connected in a state opposite to that shown.

If they do not match, the switch 33 is connected to the state shown in the figure, and the selecting means 34 determines how many reference samples with the minimum Hamming distance from the input sample are present (step S13). As shown by e _{1 in FIG.} 8 above, when there is one reference sample of the minimum Hamming distance, this reference sample is selected and the switch 35 is set to the opposite of that shown in the figure, as in the conventional minimum distance decoding method. After being connected to the state, the error is introduced to the output terminal 30o and the error of the input sample is corrected (step S14).

In this embodiment, as shown by e _{2 in} FIG. 8 above, when there are a plurality of reference samples having the same minimum Hamming distance from the input sample, the switch 35 is used.
Is connected to the state shown in the figure, and in the weighting means 36,
Based on the error occurrence probability of each constituent bit, the constituent bits of a plurality of reference samples are weighted (step S21). Then, the second selecting means 38 finds the distance between the weighted reference sample and the input sample, and determines how many reference samples having the minimum Hamming distance from the input sample exist (step S22).

If there is one minimum distance weighted reference sample, this reference sample is selected, switch 39 is connected to the state shown, and the error in the input sample is corrected (step S14). This significantly improves the error correction capability.

On the other hand, when there are a plurality of weighted reference samples with the minimum distance, an error flag is set, the switch 39 is connected in the opposite state to that shown, and an error in the input sample is detected (step S23).

For example, as shown in FIG. 4, the above-mentioned error occurrence probability has the same transmission system as shown in FIG. 2, which is composed of the recording amplifier 15, the magnetic heads 1 and 2, the tape MT, and the reproduction amplifier 21 to the comparator 23. The known data is sent from the computer CMP through the computer CMP, and the received data including an error is fetched into the computer CMP by an appropriate means such as a digital storage oscilloscope DSS and compared with the original data.

In this embodiment, as shown in Table 1 above,
The bit inversion interval of each reference sample falls within the range from the minimum 1 bit to the maximum 5 bits, and for example, as shown in FIG.
It is represented as E. Further, as shown in the figure, the probability that an error will occur in the transmission system is P11; P21, P22; P31 to P33; P41 for each constituent bit in each inversion interval.
-P44; P51-P55.

In the case of a digital VTR, the error occurrence probabilities P11 to P55 can be obtained by the measurement shown in FIG. 4, for example, as shown in Table 2 below.

[0032]

[Table 2]

Since the reproduction sample is obtained by shaping the reproduction RF signal by the binary comparator, as is clear from Table 2, the error occurrence probability at the inversion bit is high. Also, in magnetic recording, the shorter the recording wavelength, the reproduction RF
Since the signal level decreases and the S / N deteriorates, the error occurrence probability increases when the bit inversion interval is short. Further, when the recording wavelength is long, the amount of edge jitter is large and the error occurrence probability is high.

In this embodiment, the reciprocal of the above-described error occurrence probability Pij (P11 to P55) is set as the weighting coefficient αxy of the #y bit of the reference sample corresponding to the original signal "x", and the result shown in FIG. It is stored in the ROM 36. Then, in the weighting means 35, each of the constituent bits of the reference sample is multiplied by this weighting coefficient.

Similarly to the above, during reproduction, the sample Spb =
Assuming that “011001001” is obtained, this sample Spb is the reference sample Sr0 = “011001001”; Sr1 = corresponding to the original signal “0”;
For "011100001", # 2 and # 3 respectively
Of the reference samples Sr0 and Sr1 are both [1]. The error occurrence probabilities of the respective constituent bits of both reference samples Sr0 and Sr1 are shown in FIG.
As shown in A and B.

Therefore, the weighted Hamming distances dwp0 and dw between the reproduction sample Spb and both reference samples Sr0 and Sr1.
The p1s are remarkably different from each other as follows, and the reference sample closest to the reproduction sample Spb is Sr0. dwp0 = α02 = 1 / P22 = 1 × 10 ⁷ dwp1 = α13 = 1 / P53 = 5 × 10 ¹²

Similarly, the reproduction sample Spb and each of the reference samples Sr2 to Sr7 having a normal Hamming distance of [2] or more.
The weighted Hamming distances dwp2 to dwp7 of and are expressed by the following equation 1, respectively.

[0038]

[Equation 1]

For example, as shown in FIG. 8 above, there are two minimum distance codes c ₄ and c ₅ for the violation sample e ₂ outside the modulation code space Rc, and these codes c ₄ and c ₅ are respectively When the reference samples Sr2 and Sr4 correspond to the original signals “2” and “4” in Table 1 above, or when the reference samples Sr5 and Sr7 correspond to the original signals “5” and “7”. As is clear from the above formula 1, the weighted Hamming distances dwp2, dwp4; dwp5, dwp7 with each reference sample pair Sr2, Sr4; Sr5, Sr7 become equal, and FIG.
An error is detected, as also shown in step S23 of.

In the above embodiment, for convenience of explanation,
Although the weighting coefficient ROM and the weighting calculation circuit are provided separately, values determined in advance for all data outside the modulation code space may be stored in the digital demodulation ROM. Further, in the above-described embodiment, the 3-9 conversion is illustrated for the sake of simplicity, but other 8-
The present invention can be similarly applied to 10 modulation, 8-14 modulation, and the like.

[0041]

As described above in detail, according to the present invention,
In the minimum distance decoding method, when there are a plurality of reference samples having the same minimum Hamming distance with the input sample, based on the error occurrence probability of each constituent bit, weighting the constituent bits, among the plurality of reference samples By correcting the error by selecting the reference sample with the closest distance to the input sample, when decoding the digital modulation code in the digital signal transmission system,
An error correction device for digital data having a significantly improved error correction capability can be obtained.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a configuration of a main part of an embodiment in which an error correction device for digital data according to the present invention is applied to a digital VTR.

FIG. 2 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 3 is a flowchart for explaining the operation of the main part of the embodiment of the present invention.

FIG. 4 is a block diagram for explaining the operation of the main part of the embodiment of the present invention.

FIG. 5 is a waveform diagram for explaining the operation of the main part of the embodiment of the present invention.

FIG. 6 is a waveform diagram for explaining the operation of the main part of the embodiment of the present invention.

FIG. 7 is a conceptual diagram for explaining the present invention.

FIG. 8 is a conceptual diagram for explaining the present invention.

[Explanation of symbols]

 14 Digital Modulation Circuit 26 Digital Demodulation Circuit 30 Error Correction Circuit 34, 38 Minimum Distance Selection Means 36, 37 Weighting Means 40 System Control Circuit (Microprocessor)

Claims (1)

[Claims] 1. A data string comparing means for comparing, for each constituent bit, an input data string passing through a predetermined transmission system and a group of reference data strings having the same length as the input data string, and a data string comparing means of the data string comparing means. In a digital data error correction device comprising a data string selecting means for selecting the reference data string having the minimum distance from the input data string based on the output, for each of the constituent bits of the group of reference data strings. A weighting means for performing weighting based on the error occurrence probability of the predetermined transmission system; and when a plurality of reference data strings are selected by the data string selecting means, the weighting means respectively correspond to the plurality of reference data strings. Second data string selecting means for selecting a data string having a minimum distance from the input data string among the plurality of data strings weighted by. Error correction device for digital data, characterized in that the.