JP2023120648A - Receiving device, on-vehicle device, and receiving method - Google Patents

Abstract

To provide a method for limiting an error correction ability without using a value like a syndrome.SOLUTION: A transmitting device 20 transmits to a rail R a transmission signal in which given transmission information has undergone error correction code processing and modulation. A receiving device 40 demodulates a reception signal received from the rail R to generate a reception word, further performs error correction decoding processing to generate reception information, and compares match of each bit between an assumed code word generated from the reception information and the reception word. The receiving device uses a result of the comparison to determine whether to adopt the reception information. For example, it is determined that the reception information is adopted when the number of mismatched bits satisfies a predetermined tolerance condition.SELECTED DRAWING: Figure 2

Description

Applied for application of Article 30, Paragraph 2 of the Patent Law The Institute of Electrical Engineers of Japan Transactions of the Institute of Electrical Engineers of Japan D Vol. 141 No. 3 2021 Industrial Application Division March 2021 issue

The present invention relates to a receiver and the like.

In information transmission in a railway train control device, error detection is performed by a CRC (Cyclic Redundancy Check) code on the receiving side, and if there is an error in the received information, the information is discarded. Further, if the received information continues to be erroneous, further safety-side control is performed in consideration of fail-safe, such as stopping the train. For this reason, if the quality of the communication channel is poor, the frequency of error detection becomes high, which may cause a problem that trains are frequently stopped.

In information transmission of railways, error detection is performed, but error correction using an error correction code is generally not performed. This is because a high level of safety is required for railways, and even if error correction is performed, there is a possibility that the error correction may not be complete, and as a result of the correction, there is a risk that control will be performed on the dangerous side.

Therefore, in railway information transmission, the amount of errors contained in the information received on the receiving side is grasped, and if the amount of errors does not exceed a predetermined error correction reference value, error-corrected information is adopted. A technique has been proposed to ensure reliability and security when using an error correction code by limiting the correction capability (see, for example, Patent Document 1).

JP 2012-138867 A

However, in the method of limiting the error correction capability described above, it is necessary for the receiving side to grasp the amount of errors in the received information. Therefore, error correction codes that can be used are limited to codes such as Reed-Solomon codes and BCH codes, which are capable of correcting errors of multiple bits and whose amount of errors can be grasped in the error correction decoding process. In the BCH code and Reed-Solomon code, a syndrome, which is a value indicating the position of an error in error correction decoding processing, is obtained. By referring to this syndrome, it is possible to grasp the error amount contained in the received information. .

Recently, the use of turbo codes and LDPC codes, which have higher error correction capabilities than Reed-Solomon codes, is being used. However, with turbo codes and LDPC codes, if the received word is decoded to obtain received information without determining the error position, the amount of errors contained in the received information cannot be grasped. A value like the syndrome obtained by BCH code or Reed-Solomon code cannot be obtained. Therefore, it cannot be used for the method of limiting the error correction capability described above. This is because the conventional method of limiting the error correction capability is realized by using a value such as a syndrome.

The problem to be solved by the present invention is to implement a method for limiting the error correction capability without using values such as the syndromes described above.

A first invention for solving the above problems is
A receiving apparatus for receiving a transmitted signal obtained by modulating a codeword obtained by performing error correction code processing on given transmission information, and decoding information from the received word obtained by demodulating the received signal,
a decoding unit that performs error correction decoding processing according to the error correction code processing on the received word to generate received information;
an encoding unit that generates an assumed codeword from the received information;
a comparison unit that compares the received word and the assumed codeword;
a determination unit that determines whether or not to adopt the received information using the comparison result of the comparison unit;
is a receiving device comprising

Another invention is
A receiving method for receiving a transmitted signal obtained by modulating a codeword obtained by performing error correction code processing on given transmission information, and decoding information from the received word obtained by demodulating the received signal,
performing error correction decoding processing according to the error correction code processing on the received word to generate received information;
generating an assumed codeword from the received information;
comparing the received word with the expected codeword;
determining whether to adopt the received information using the result of the comparison;
You may configure a receiving method including

According to the first invention and the like, an assumed codeword is generated based on received information generated by performing error correction decoding processing corresponding to error correction coding processing on a received word. When the error correction decoding process can output the entire codeword including the received information, the assumed codeword is generated as the assumed codeword, and when the error correction decoding process outputs only the received information, the received information An assumed code word is obtained by further performing error correction code processing based on this. The assumed codeword and the received word are compared, and the result of the comparison is used to determine whether or not to adopt the received information. That is, it is possible to limit the error correction capability according to the comparison result. Therefore, it is possible to realize a method of limiting the error correction capability without using a value such as the syndrome obtained by the BCH code or Reed-Solomon code.

More specifically, the received word may contain errors due to superposition of noise in the communication channel through which the signal was transmitted. Assuming that there is an error in the received word, the received information obtained by error correction decoding processing of the received word can have two cases: the information whose error has been completely corrected by the error correction decoding processing, and the information that has not been completely corrected. Two cases are conceivable. This is because whether or not the error can be corrected completely depends on the amount of error. In the case of complete correction, the received word containing the error does not match the assumed code word obtained by processing the corrected received information with the same error correcting code as that of the transmitting side. The amount of this mismatch can be estimated as the amount of error. On the other hand, even if it is not completely corrected, the expected codeword and the received word do not match. The amount of errors estimated from this mismatch increases by the amount of errors left uncorrected by the error correction decoding process. From the above, it is possible to realize a method of limiting the error correction capability by comparing an assumed codeword generated from received information and a received word and using the comparison result without using a value such as a syndrome. can be done.

A second invention is based on the first invention,
The comparison unit estimates an error amount by comparing each bit match between the received word and the assumed codeword.
It is a receiving device.

According to the second invention, the error amount contained in the received word can be estimated by the number of bits that do not match between the received word and the assumed codeword.

A third invention is, in the second invention,
The determination unit determines to adopt the received information when the error amount satisfies a predetermined allowable condition.
It is a receiving device.

According to the third invention, by setting the allowable condition to, for example, a condition such as a predetermined number of bits or less, if the number of mismatched bits between the received word and the assumed codeword is less than the predetermined number of bits, the received word is regarded as an error. Received information that has been corrected and decoded can be used. Also, when the number of non-matching bits exceeds a predetermined number of bits, the received information is not adopted, and the error correction capability can be limited. This makes it possible to ensure reliability and safety when using error correction codes.

A fourth invention is, in any one of the first to third inventions,
a hard-decision unit that hard-decides the received word and generates a hard-decision value of the received word;
further comprising
The comparison unit
comparing the hard decision value of the received word to the assumed codeword;
It is a receiving device.

The error correction decoding processing performed by the error correction decoding unit includes soft decision and hard decision, and soft decision provides higher error correction capability than hard decision. However, when soft decision is adopted for the error correction decoding process, the assumed codeword is a value corresponding to hard decision and cannot be directly compared with the received word. In this case, as in the fourth invention, by obtaining the hard decision value of the received word and comparing it with the assumed code word, while making use of the high error correction capability of the soft decision, errors occurring in the communication channel are evaluated, It is possible to reduce the probability of erroneous correction and ensure reliability and security when using the error correcting code.

A fifth invention is an on-board device equipped with the receiving device according to any one of the first to fourth inventions and mounted on a train,
The transmission information is information for controlling the train,
the modulated signal is transmitted over rails as a transmission medium;
the receiving device receives a signal transmitted on the rail;
It is an on-board device.

According to the fifth invention, in information transmission between the ground and on-board transmission of information for controlling the train to the on-board equipment using the rail as a transmission medium, high reliability and safety required for the railway. can ensure the integrity of the

The block diagram of an information transmission system. FIG. 2 is a configuration diagram of a transmitting device and a receiving device; Graph of experimental results. The block diagram of the modification of a receiving apparatus.

Preferred embodiments of the present invention will be described below with reference to the drawings. In addition, the present invention is not limited by the embodiments described below, and the forms to which the present invention can be applied are not limited to the following embodiments. Also, in the description of the drawings, the same reference numerals are given to the same elements.

[overall structure]
FIG. 1 is a diagram showing a configuration example of an information transmission system including a receiving device 40 and an on-board device 30 according to this embodiment. According to FIG. 1, the information transmission system includes a ground device 10 installed in a command center, a maintenance area, a station equipment room, etc., and an on-board device 30 mounted on a train 3. ) from the ground equipment 10 to the on-board equipment 30 via the rail R.

The ground equipment 10 includes a ground control device 12 and a transmitter 20 . The ground control device 12 generates information for controlling the train 3 such as speed limit information and track information. The transmission device 20 performs error correction code processing and modulation on transmission information, which is information for controlling the train 3 generated by the ground control device 12, to generate a transmission signal, and transmits the generated transmission signal to the rail R.

The on-board device 30 includes a receiving device 40 and an on-board control device 32 . The receiving device 40 receives the transmission signal transmitted to the rail R via the power receiver 5 provided at the bottom of the train 3, demodulates the received signal and performs error correction decoding processing to generate reception information. The on-board control device 32 performs running control of the train 3 using the information for controlling the train 3 which is the received information generated by the receiving device.

[Transmitting device and receiving device]
FIG. 2 is a diagram showing a configuration example of the transmitting device 20 and the receiving device 40. As shown in FIG. According to FIG. 2, the transmitter 20 has an error correction encoder 21 and a modulator 22 .

The error correction coding unit 21 performs error correction code processing on transmission information, which is information for controlling the train 3 generated by the ground control device 12, and generates a code word. The error correction code used by the error correction coding unit 21 is, for example, a code capable of correcting multiple-bit errors, such as an LDPC (Low Density Parity Check) code or turbo code.

The modulator 22 modulates the codeword generated by the error correction encoder 21 to generate a transmission signal, and transmits the generated transmission signal to the rail R, which is a transmission medium. The modulation scheme used by the modulator 22 is, for example, OFDM (Orthogonal Frequency Division Multiplexing) modulation or QPSK (Quadrature Phase Shift Keying) modulation.

The receiver 40 has a demodulator 41 , an error correction decoder 42 , an error correction encoder 43 , a comparator 45 and a decision unit 46 .

The demodulator 41 demodulates the received signal to generate a received word. The demodulation method used by the demodulation unit 41 is a demodulation method according to the modulation method used by the modulation unit 22 of the transmission device 20 .

The error correction decoding unit 42 performs error correction decoding processing on the received word generated by the demodulation unit 41 to generate received information. The error correction decoding used by the error correction decoding section 42 is error correction decoding according to the error correction code used by the error correction encoding section 21 of the transmission device 20 .

The error correction coding unit 43 performs error correction coding processing on the received information generated by the error correction decoding unit 42 to generate assumed codewords. The error correction code used by the error correction encoder 43 is the same as the error correction code used by the error correction encoder 21 of the transmission device 20 .

If the error correction decoding unit 42 can generate not only received information but also codewords by error correction decoding processing, the error correction encoding unit 43 can be omitted by using the codewords as assumed codewords.

The comparator 45 compares the assumed codeword generated by the error correction encoder 43 and the received word generated by the demodulator 41 . Specifically, each bit match between the assumed codeword and the received word is compared, and the number of bits that do not match (the number of mismatched bits) is estimated as the amount of error in the received word.

The determination unit 46 uses the comparison result of the comparison unit 45 to determine whether or not to adopt the received information generated by the error correction decoding unit 42 . Specifically, when the error amount (number of mismatched bits) estimated by the comparison unit 45 satisfies a predetermined allowable condition, it is determined to adopt the received information. The permissible condition can be, for example, that the number of bits is less than or equal to a predetermined number.

When the error contained in the received word is completely corrected by the error correction processing of the error correction decoding unit 42 and the received information is "correct" information, an assumed code word generated from this received information (that is, the received information is equal to the codeword after error correction coding processing of the transmission information by the error correction coding unit 21 in the transmitting device 20 . However, since the received word itself contains errors, the assumed code word and the received word do not match, and the number of mismatched bits corresponds to the amount of errors contained in the received word. This is because the expected codeword and the received word match when the received word contains no error.

Then, what happens when the amount of errors contained in the received word is large and the received information is "incorrect" information without being completely corrected by the error correction processing of the error correction decoder 42? Also in this case, the expected codeword and the received word do not match. It is estimated that the number of mismatched bits increases by the amount of errors left uncorrected by the error correction decoding process. This estimation will be described later with reference to experimental results. For this reason, the received word is compared with an assumed code word generated by performing error correction coding processing again on the received information after the received word has been subjected to error correction decoding processing, and the degree of discrepancy obtained by comparison is calculated as the received word. can be estimated as the amount of error contained in

[Experimental result]
FIG. 3 shows experimental results of the information transmission system of this embodiment. In this experiment, transmission information generated as random data was modulated and subjected to error correction code processing, and noise was superimposed on the transmission signal to obtain a reception signal. went. The error amount was obtained as an error rate (BER: Bit error rate). Also, QPSK modulation was used as the modulation method, and LDPC code was used as the error correction code.

FIG. 3 shows a graph of error rate characteristics with the horizontal axis representing the S/N ratio and the vertical axis representing the error rate. FIG. 3 shows a graph of error rate characteristics calculated from the number of mismatched bits obtained by the processing of this embodiment as "this embodiment". As a comparative example, a graph of the error rate characteristics of the received information itself subjected to QPSK demodulation and LDPC decoding processing is referred to as "first comparative example", and only QPSK modulation is performed at the time of transmission and only QPSK demodulation is performed at the time of reception (i.e. A graph of error rate characteristics in the case where error correction code processing is not performed is shown as a “second comparative example”. It can be said that the second comparative example exhibits, so to speak, correct error rate characteristics.

First, as for the error rate characteristics of the received information itself (first comparative example), the error rate is improved against the deterioration of the S/N ratio. , it was impossible to calculate the error rate with the S/N ratio in the error-free region in which the error was corrected by the LDPC decoding process. The error rate characteristics of this embodiment show characteristics that substantially match those of the second comparative example in the entire S/N ratio range. This indicates that the amount of errors occurring in the process of transmission can be estimated almost accurately.

[Effect]
According to this embodiment, an assumed codeword is generated from received information generated by performing error correction decoding processing corresponding to error correction coding processing on a received word. When the error correction decoding process can output the entire codeword including the received information, the assumed codeword is generated as the assumed codeword, and when the error correction decoding process outputs only the received information, the received information An assumed code word is obtained by further performing error correction code processing based on this. The assumed codeword and the received word are compared, and the result of the comparison is used to determine whether or not to adopt the received information. That is, it is possible to limit the error correction capability according to the comparison result. Therefore, it is possible to realize a method of limiting the error correction capability without using a value such as the syndrome obtained by the BCH code or Reed-Solomon code.

More specifically, there is a possibility that an error is included in the received word due to superposition of noise on the rail R, which is the transmission medium (communication path). Assuming that there is an error in the received word, the received information obtained by error correction decoding processing of the received word can have two cases: the information whose error has been completely corrected by the error correction decoding processing, and the information that has not been completely corrected. Two cases are conceivable. This is because whether or not the error can be corrected completely depends on the amount of error. In the case of complete correction, the received word containing the error does not match the assumed code word obtained by processing the corrected received information with the same error correcting code as that of the transmitting side. The amount of this mismatch can be estimated as the amount of error. On the other hand, even if it is not completely corrected, the expected codeword and the received word do not match. The amount of errors estimated from this mismatch increases by the amount of errors left uncorrected by the error correction decoding process. In this way, by comparing the expected codeword generated from the received information with the received word, the amount of errors contained in the received word can be estimated regardless of the error correction code system. A method can be implemented to limit the error correction capability without using a value.

It goes without saying that the embodiments to which the present invention can be applied are not limited to the above-described embodiments, and can be changed as appropriate without departing from the scope of the present invention.

(A) Hard Decision of Received Word For example, the hard decision value of the received word may be compared with the assumed codeword. Specifically, as shown in FIG. 4, a receiving device 40A is configured that further includes a hard decision section 44 that generates a hard decision value of a received word. The hard decision unit 44 makes a hard decision on the received word generated by the demodulator 41 to generate a hard decision value of the received word. A hard decision is the process of determining whether a bit is "1" or "0". If the bit string contained in the received word is not "1" or "0" but has a series of analog values, the received word can be converted to digital data of the bit string by hard decision.

Then, the comparison unit 45A compares the assumed codeword generated by the error correction coding unit 43 and the hard decision value of the received word generated by the hard decision unit 44 . That is, each bit match between the assumed codeword and the hard decision value of the received word is compared, and the number of bits that do not match (the number of mismatched bits) is estimated as the amount of error in the received word.

The error correction decoding processing performed by the error correction decoding unit includes soft decision and hard decision, and soft decision provides higher error correction capability than hard decision. However, when soft decision is adopted for the error correction decoding process, the assumed codeword is a value corresponding to hard decision and cannot be directly compared with the received word. In such a case, by obtaining the hard decision value of the received word and comparing it with the expected code word, it is possible to evaluate the error that occurred in the communication channel while taking advantage of the high error correction capability of the soft decision, and to estimate the probability of miscorrection. to ensure reliability and security when using error correcting codes.

(B) Information transmission system Also, in the above-described embodiment, an example in which the present invention is applied to an information transmission system between the ground and on-board trains has been described. However, the present invention can be applied to other information transmission systems as well as railways.

DESCRIPTION OF SYMBOLS 10... Ground equipment 12... Ground control apparatus 20... Transmission apparatus 21... Error correction coding part 22... Modulation part 3... Train 5... Power receiver 30... On-board apparatus 40 (40A)... Reception apparatus 41... Demodulation part 42... Error Correction decoding unit 43 Error correction encoding unit 44 Hard decision unit 45 (45A) Comparison unit 46 Decision unit 32 On-board controller R Rail

Claims (6)

A receiving apparatus for receiving a transmitted signal obtained by modulating a codeword obtained by performing error correction code processing on given transmission information, and decoding information from the received word obtained by demodulating the received signal,
a decoding unit that performs error correction decoding processing according to the error correction code processing on the received word to generate received information;
an encoding unit that generates an assumed codeword from the received information;
a comparison unit that compares the received word and the assumed codeword;
a determination unit that determines whether or not to adopt the received information using the comparison result of the comparison unit;
receiving device. The comparison unit estimates an error amount by comparing each bit match between the received word and the assumed codeword.
The receiving device according to claim 1. The determination unit determines to adopt the received information when the error amount satisfies a predetermined allowable condition.
3. The receiving device according to claim 2. a hard-decision unit that hard-decides the received word and generates a hard-decision value of the received word;
further comprising
The comparison unit
comparing the hard decision value of the received word to the assumed codeword;
The receiving device according to any one of claims 1-3. An on-board device equipped with the receiving device according to any one of claims 1 to 4 and mounted on a train,
The transmission information is information for controlling the train,
the modulated signal is transmitted over rails as a transmission medium;
the receiving device receives a signal transmitted on the rail;
on-board equipment. A receiving method for receiving a transmitted signal obtained by modulating a codeword obtained by performing error correction code processing on given transmission information, and decoding information from the received word obtained by demodulating the received signal,
performing error correction decoding processing according to the error correction code processing on the received word to generate received information;
generating an assumed codeword from the received information;
comparing the received word with the expected codeword;
determining whether to adopt the received information using the result of the comparison;
Receiving method including.