JPH10209881A - Method for encoding error correction and method for decoding the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve correcting capability and to prevent transition to an impossible encoding mode from being generated many times by using a code book in which code words are assigned so that humming distance between code words indicating a signal capable of transition can be made large. SOLUTION: Error correction encoding is operated by using a code book in which code words are assigned so that humming distance between code words indicating a signal capable of transition is made large. That is, in the code book in which different 11 bit code words are assigned to each of nine kinds of coding mode information, the code words are assigned so that each humming distance between one of code words indicating three kinds of coding mode information, that is, AA, AB and AC and the other two code words is made larger than each humming distance between one of those three kinds of code words and a code word indicating coding mode information different from the AA, AB and AC. Thus, strong error correcting capability is improved, and transition to an impossible coding mode is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to, for example, a mobile radio transmission line in which burst errors frequently occur, wherein a signal in a signal sequence is one of N elements in a finite space, and an adjacent signal A method in which a signal having M transitions (N> M) between them is subjected to error correction coding using a codebook, and
The present invention relates to the error correction decoding method.

[0002]

2. Description of the Related Art In a system for transmitting an acoustic signal using wireless communication, a voice / musical sound encoding method for digitizing an acoustic signal and compressing the signal efficiently is used for efficient use of a transmission path. . In order to efficiently encode audio signals at a low bit rate, TwinVQ (Transform-domain W
It has multiple encoding modes, such as a method called eighted Interleave Vector Quantization, extracts the characteristics of the audio signal for each time interval, and selects the encoding mode suitable for the audio signal in that time interval. An encoding method is suitable. For details of the TwinVQ encoding method, see, for example, “References: K. Ikeda, T. Moriya, N. Iwakami, S.
Miki, "A Design of TwinVQ Audio-Codec for Personal
Communication Aystems, "Proc. ICUPC '95, pp.803-80
7, 1995 ". TwinVQ is a fixed time interval
This is a fixed frame length / fixed bit rate coding method that generates a fixed number of bits for each (frame). However, since there are a plurality of coding modes, each coding mode has a bit representing the coding mode. The other bits indicate different information. Therefore, if an error occurs in a bit representing the coding mode in wireless transmission or the like, the bit representing a mode other than the coding mode is in an undecodable state, and a large distortion occurs in the decoded signal. For this reason, when TwinVQ is used in an environment where a code error is likely to occur, it is necessary to apply strong error protection to the coding mode information. The error correction encoding method and the error correction decoding method of the present invention are used, for example, for error correction encoding / decoding in the TwinVQ encoding mode.

FIG. 4 is a diagram showing the transition of the encoding mode of TwinVQ. TwinVQ is based on three types of encoding modes, types A, B and C. There are a total of nine types of encoding modes, including these three types and the transient state between these encoding modes. As shown in the figure, these encoding modes are AA, AB, AC, BA, BB, BC, CA, CB, and CC, respectively.

FIG. 5 is a diagram showing the transition of the encoding mode between the immediately preceding frame and the current frame. As shown in the figure, if the encoding mode of the immediately preceding frame is any of AA, BA, and CA, the encoding mode of the current frame is one of AA, AB, and AC, and the encoding mode of the immediately preceding frame is AB. , BB, or CB, the encoding mode of the current frame is BA, BB, or BC, and the encoding mode of the immediately preceding frame is AC, BC, or CC.
, The encoding mode of the current frame is CA, C
B or CC.

FIG. 6A is a diagram showing a conventional error correction encoding method of the encoding mode information of TwinVQ. A codebook storing nine types of coding mode information and nine codewords corresponding thereto is input to the error correction coding unit, and a codeword corresponding to the input coding mode information is output. . This is transmitted to the transmission line as a codeword after error correction coding. FIG. 6B is an example of a codebook of a conventional error correction coding method for coding mode information of TwinVQ. As shown in this figure, each of the nine types of TwinVQ coding mode information has 11
Assigns a codeword of bits. These codewords were arbitrarily assigned such that the minimum Hamming distance between the codewords was 5.

FIG. 7A is a diagram showing a conventional TwinVQ error correction decoding method for coding mode information. The received codeword is input to the error correction decoding unit. The codebook is the same as that used in the encoding, and is also input to the error correction decoding unit. The error correction decoding unit first calculates the Hamming distance between the received codeword and all codewords included in the codebook. Next, the coding mode represented by the code word with the minimum Hamming distance is selected, and this is output as post-decoding coding mode information. FIG. 7B shows the conventional Twin
5 shows a flowchart of an error correction decoding method for VQ coding mode information.

[0007]

In the conventional error correction coding method and decoding method of the coding mode information of TwinVQ, under a poor burst error transmission environment such as mobile radio, the correction capability is not sufficient. When bursts of code errors occur in a burst, there is a problem that transition to an impossible coding mode frequently occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide an error correction coding method and a decoding method which solve the two problems of the weak correction capability of the conventional method and the frequent occurrence of an impossible transition to the coding mode. Is to do.

[0009]

According to the error correction encoding method and the error correction decoding method of the present invention, a signal in a signal sequence or a signal represented by a code word in a code word sequence has N signals in a finite space. It is assumed that the signal is one of the elements and the number of transitions between adjacent signals is M (N> M), and the encoding uses a codebook composed of codewords corresponding to all the elements. Are sequentially error-correction-encoded, and in decoding, the input codeword is sequentially decoded using the same codebook as the encoding, and in the encoding method of the present invention, an encoded codeword for the immediately preceding signal, The Hamming distance between the coded codeword for the other signal that can transition from the signal and the coded codeword for the signal that cannot transition from the previous signal and the coded codeword for the signal that cannot transition from the signal is larger than the hamming distance. Codebook is required Code words are allocated for.

[0010] According to the error correction decoding method of the second aspect of the present invention, error correction decoding is performed using only code words of M signals (N> M) that can transition from the immediately preceding signal as candidates. The signal obtained by this is a decoded signal. According to a third aspect of the present invention, in the second aspect of the present invention, only the decoding result when all codewords (N) are candidates and error-correction decoding is performed and only codewords of transitionable signals are set as candidates. The decoding result is compared with the decoding result. If the comparison result is not coincident, for the decoding of the signal immediately after that, all the codewords (N) are subjected to error correction decoding as candidates to obtain a decoded signal.

[0011]

The error correction encoding method and the decoding method according to the present invention are used for error correction encoding and decoding of a signal whose transition between adjacent signals is limited, such as encoding mode information of TwinVQ. In error correction coding, error correction coding is performed using a codebook to which codewords are assigned so that the Hamming distance between codewords indicating transitionable signals becomes large, and between adjacent signals in error correction decoding. By applying transition-limited decoding, a strong error correction capability is realized even in burst error transmission, and a transition between coding modes that cannot be achieved is reduced.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 (Embodiment of Encoding Method) An embodiment in which the invention of claim 1 of the present invention is applied to an error correction encoding method of encoding mode information of TwinVQ will be described. In this case, the content of the code book is different from that of the conventional encoding method, and the other parts are exactly the same as the conventional method shown in FIG. 6A. FIG. 1 shows an example of a codebook in the case where the invention of claim 1 is applied to an error correction coding method for coding mode information of TwinVQ. As shown in this codebook, 11-bit different codewords are assigned to each of the nine types of coding mode information. Here, each Hamming distance between one of the codewords representing the three types of coding mode information of AA, AB, and AC and the other two codewords is one of these three types of codewords, and A
A, AB, AC codewords representing the three types of coding mode information of BA, BB, and BC so as to be greater than each Hamming distance between the codewords and the codewords representing different coding mode information. Is larger than the Hamming distance between one of BA, BB, and BC from one of the BA, BB, and BC to a different codeword from CA, CB, and CC. The Hamming distance between one of the codewords representing the type of coding mode information and the other two codewords is larger than the Hamming distance between one of CA, CB, and CC and a different codeword. Code words as follows. As a result, the minimum Hamming distance between all codewords in the codebook is 5, but the minimum Hamming distance between codewords representing two types of encoding modes that can transition from the encoding mode of the immediately preceding frame is 7.

When this error correction coding method is used, the Hamming distance between a plurality of coding modes that can transition from the coding mode of the immediately preceding frame becomes large. If this error correction encoding method is used in combination with the error correction decoding method described in the second embodiment described below, high error correction capability can be realized. Embodiment 2 (Embodiment of Decoding Method) FIG. 2A is a block diagram in which the invention of claim 2 is applied to an error correction decoding method for encoding mode information of TwinVQ. The difference from FIG. 7A showing the conventional decoding method is that the decoded coding mode information of the immediately preceding frame is input to the error correction decoding unit. FIG. 2B shows a flowchart in which the decoding method of the present invention is applied to the error correction decoding method of the encoding mode information of TwinVQ. Hereinafter, the error correction decoding method will be described according to this flowchart. First, a codeword received by the error correction decoding unit, a codeword from the codebook,
The decoded coding mode information of the immediately preceding frame is input. The codebook is the same as that used in the encoding.
Next, three kinds of codewords corresponding to three kinds of coding mode candidates of the current frame determined from the decoded coding mode information of the immediately preceding frame are selected from the codebook, and the received codeword and each of the selected codes are selected. The Hamming distance between the word and the word is calculated, and the encoding mode represented by the code word with the minimum Hamming distance is selected. This is output as decoded coding mode information of the current frame. In this error correction decoding method, by limiting the candidates for the encoding mode information of the current frame to the encoding modes that can transition from the decoded encoding mode information of the immediately preceding frame, an erroneous encoding mode can be set when a code error occurs. The possibility of being selected as decoded encoding mode information can be reduced. Further, since the Hamming distance between the encoding mode candidates is large, it is possible to realize a higher error correction capability than the conventional method.

Embodiment 3 (Another Example of Decoding Method) A decoding apparatus in which the invention of claim 3 is applied to the error correction decoding method of the coding mode information of TwinVQ is an error correction decoding method of the invention of claim 2. 2A to which FIG. 2 is applied, but the processing inside the error correction decoding is different from the error correction decoding method to which the invention of claim 2 is applied. FIG.
5 shows a flowchart applied to an error correction decoding method for encoding mode information of inVQ. Hereinafter, an embodiment of the error correction decoding method will be described according to this flowchart. First, the codeword received by the error correction decoding unit, the codeword from the codebook, and the decoded mode information of the immediately preceding frame are input. The codebook is the same as that used in the encoding. Next, it is selected from the transition limitation information obtained from the decoding of the immediately preceding frame whether or not to perform the transition limitation in the current frame (S1).

When the transition limitation is not performed, the Hamming distance is calculated in the same manner as the conventional error correction decoding method, that is, all codewords in the codebook are used as candidates (S2), and the codeword having the minimum distance is calculated. After decoding the encoding mode represented by, the encoding mode information is obtained, and transition limitation is performed in the next frame.
(S3). When the transition is limited in step S1, the post-decoding encoding mode information is obtained by the same method as the error correction decoding method described in the second embodiment. That is, the Hamming distance between each code word that can transition from the decoded coding mode information of the immediately preceding frame is calculated (S4), and the coding mode represented by the code word having the smallest distance is used as the decoding result (S5). . At the same time, coding mode information is obtained by the same method as the conventional error correction decoding method (S6, S7), and is compared with the post-decoding coding mode information obtained in step S5 (S8). If they are equal, the transition is limited in the next frame (S9), and if they are different, the transition is not restricted in the next frame (S10).

In this error correction decoding method, decoding is performed while adaptively controlling the presence / absence of transition limitation. Therefore, errors in one encoding mode cause errors in the encoding mode over many frames. The possibility of occurrence (the possibility of error propagation) can be reduced. In the above description, the minimum value of the Hamming distance between the coded code word for the immediately preceding signal and the coded code word for another signal to which the signal can transit cannot be changed from the coded code word for the immediately preceding signal and the signal. The fact that the signal is larger than the maximum value of the Hamming distance between the signal and the encoded codeword may be such that the minimum value is not less than the maximum value, that is, the minimum value may be the same value as the maximum value. Further, in the above description, the present invention is applied to the encoding and decoding of the encoding mode information of TwinVQ.
The number of signals that can transition from the immediately preceding signal, which is one of the elements, is limited to M (N> M). The invention can be applied.

[0017]

As described above, according to the error correction encoding method and the decoding method of the present invention, when error correction encoding and decoding of state information with limited state transitions is performed, error correction is performed. Strong error correction even in burst error transmission by assigning code words so that the Hamming distance between code words indicating transitionable states in coding is large and applying transition-limited decoding in error correction decoding The capability can be realized, and the transition between the impossible encoding modes can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a codebook used in the encoding method of the present invention.

FIG. 2A is a block diagram showing an error correction decoding method of the coding mode information of TwinVQ to which the invention of claim 2 is applied;
Is a flowchart for explaining an error correction decoding method for the encoding mode information.

FIG. 3 shows an encoding mode of TwinVQ to which the invention of claim 3 is applied.
4 is a flowchart for explaining an error correction decoding method of the block information.

FIG. 4 is a diagram showing a transition of an encoding mode of TwinVQ.

FIG. 5 is a diagram showing a transition between encoding modes of a previous frame and a current frame.

FIG. 6A is a diagram showing a conventional TwinVQ error correction coding method for coding mode information, and FIG. 6B is a diagram showing a codebook thereof.

7A is a diagram showing a conventional TwinVQ encoding mode information error correction decoding method, and FIG. 7B is a diagram showing a conventional TwinVQ encoding mode.
9 is a flowchart for explaining an error correction decoding method of the code information.

Claims (3)

[Claims] 1. A signal in a signal sequence is one of N elements in a finite space, and transitions between adjacent signals are M (N> M), corresponding to the N elements. Error-correction encoding method for sequentially performing error-correction encoding on a signal using a codebook made up of encoded codewords to obtain a codeword, comprising: The codebook encodes each element so that the Hamming distance between the encoded codeword and the encoded codeword for the immediately preceding signal and the encoded codeword for the signal that cannot transition from that signal are greater than the Hamming distance between the encoded signal and the encoded signal. An error correction encoding method, wherein words are assigned. 2. A signal represented by a codeword in a codeword string is one of N elements in a finite space, and M transitions between adjacent signals (N> M) are performed. In an error correction decoding method for sequentially decoding and error-correcting an input signal using a codebook consisting of codewords corresponding to a number of elements, a codeword of a signal that can transition from a signal immediately before being decoded is provided. An error correction decoding method characterized in that error correction decoding is performed using only the candidate as a candidate. 3. An input signal is error-correction-decoded using all codewords in the codebook as candidates, and only a decoding result obtained when all codewords are candidates and codewords of transitionable signals are used as candidates. 3. A decoding result is compared with the decoding result of the above-mentioned case, and if the comparison is not the same, a signal immediately after that is subjected to error correction decoding with all codewords as candidates, thereby obtaining a decoded signal. Error correction decoding method as described in the above.