JP2001024717A - Turbo decoding device and reiterative decoding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration in error correction capability, even if a tail bit is included in an internal interleave when a turbo code on the code side the time of using SOVA as a decoding algorithm. SOLUTION: A tail bit is stored in a fixed value buffer 202, and switching of a changeover switch 203 is controlled to replace decoded information outputted from a SOVA decoder 201 with the tail bit stored in the fixed value buffer 202 in timing with decoding the tail bit. In the same manner, the tail bit is stored in a fixed value buffer 206, and switching of a changeover switch 207 is controlled to replace decoded information outputted from a SOVA decoder 205, with the tail bit stored in the fixed value buffer 206 in timing with decoding the tail bit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turbo decoding apparatus and an iterative decoding method used for decoding an error-correction-coded signal in the field of digital radio communication.

[0002]

2. Description of the Related Art At present, SOVA (Soft-Output Viterbi A) for softly outputting the reliability of information bits by improving the Viterbi algorithm which is a decoding algorithm for a convolutional code has been proposed.
lgorithm: soft output Viterbi algorithm) has been proposed.

[0003] Recently, as a decoding algorithm that can use the soft-output reliability, a turbo code / decoding (hereinafter simply referred to as "code") that can use the reliability of information bits generated in the decoding process in the next decoding is available. "Turbo code"). It is known that the error rate can be greatly improved by combining the turbo code and SOVA.

On the coding side of the turbo code, additional information (hereinafter referred to as “tail bits”) is inserted at the end of the block so that the internal state at the end of the block becomes a fixed value.

[0005] MAP (Maximum
A Posteriori Probability: When using a decoding method such as decoding, it is possible to decode without specifying the internal state at the end of the block. Therefore, the tail bits are included in the internal interleave of the turbo code on the code side. You can also.

[0006]

On the other hand, when SOVA is used as a decoding algorithm, the code side encodes all codewords by turbo code so that the internal state at the end of the block becomes a fixed value. , And tail bits are not included in the internal interleave of the turbo code.

[0007] When SOVA is used for the decoding algorithm, if the tail bits are included in the internal interleave of the turbo code on the code side, the internal state at the start of traceback, which is the end of the block, becomes undefined, and the assumed internal state This is because traceback is more performed, and if a bit error occurs immediately after traceback, the error correction capability is degraded during iterative decoding.

SUMMARY OF THE INVENTION The present invention has been made in view of the above point. In the case where SOVA is used as a decoding algorithm, even if tail bits are included in an internal interleave of a turbo code on the code side, turbo decoding which does not deteriorate error correction capability is performed. It is an object to provide an apparatus and an iterative decoding method.

[0009]

The gist of the present invention is to store tail bits on the decoding side and perform iterative decoding using the stored tail bits instead of the decoding information at the timing of decoding the tail bits. That is.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A turbo decoding apparatus according to the present invention includes decoding means for performing a soft output Viterbi algorithm on coded information by including fixed information in an internal interleave of a turbo code, and stores the fixed information. And a replacement unit that replaces the decoded information output from the decoding unit with the fixed information stored in the storage unit at the timing of decoding the encoded fixed information.

With this configuration, a bit error immediately after the start of the traceback can be corrected. Therefore, when SOVA is used as the decoding algorithm and the fixed information is included in the internal interleave of the turbo code on the code side, the bit error can be corrected immediately after the start of the traceback. Thus, even when a bit error occurs, the deterioration of the error correction capability can be suppressed.

The turbo decoding apparatus according to the present invention comprises a maximum value detecting means for detecting a maximum soft decision value output from a decoding means, and a multiplying means for multiplying fixed information stored in a storage means by the maximum value. Wherein the replacing means replaces the decoded information output from the decoding means with the multiplied value output from the multiplying means at the timing of decoding the encoded fixed information.

With this configuration, it is possible to repeatedly perform decoding using a value obtained by multiplying the fixed information stored on the decoding side by the maximum value of the soft decision value, so that the error correction capability can be further improved.

The turbo coding apparatus according to the present invention employs a configuration in which fixed information is included in an internal interleave of a turbo code at the time of encoding, and code information is transmitted to the turbo decoding apparatus according to the present invention.

[0015] The wireless communication apparatus of the present invention employs a configuration in which the turbo decoding apparatus of the present invention is mounted. The information processing device of the present invention employs a configuration in which the turbo decoding device of the present invention is mounted.

[0016] With these configurations, when using SOVA as a decoding algorithm and including fixed information in internal interleaving of a turbo code at the time of encoding, communication with high error correction capability can be performed.

In the iterative decoding method according to the present invention, the fixed information is included in the internal interleave of the turbo code at the time of encoding, a soft output Viterbi algorithm is performed on the encoded information, and the encoded fixed information is decoded. At this time, a method of replacing the decoded information with fixed information stored in advance is adopted.

According to this method, a bit error immediately after the start of the traceback can be corrected. Therefore, when SOVA is used as the decoding algorithm and the fixed information is included in the internal interleave of the turbo code on the code side, the bit error immediately after the start of the traceback is reduced. Thus, even when a bit error occurs, the deterioration of the error correction capability can be suppressed.

The iterative decoding method of the present invention performs a soft output Viterbi algorithm on encoded information by including fixed information in an internal interleave of a turbo code at the time of encoding, and performs a soft output Viterbi algorithm on the encoded information. A method of calculating a multiplication value with the maximum value of the determination value and replacing the decoded information with the multiplication value at the timing of decoding the encoded fixed information is adopted.

According to this method, it is possible to repeatedly perform decoding using a value obtained by multiplying the fixed information stored on the decoding side by the maximum value of the soft decision value, so that the error correction capability can be further improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a turbo decoder according to Embodiment 1 of the present invention and a turbo encoder for transmitting a signal to the turbo decoder. Here, tail bits known on both the code side and the decoding side are inserted at the end of the block. Also, transmission information u
Is transmitted in block units, the decoding side knows in advance the timing for decoding the tail bits.

In the turbo coding apparatus 100 shown in FIG. 1, a systematic coder 101 performs coding on transmission information u,
And it outputs a redundant bit y _1. Interleaver 102 performs column conversion (interleaving) on transmission information u and outputs an information symbol sequence different from transmission information u. Tissue encoder 103 performs encoding on the output information symbol sequence from interleaver 102, and outputs a redundant bit y _2.

As shown in FIG. 1, a turbo coding device 100
The transmission information u, the redundant bit y _1, and the redundant bit y ₂ transmitted from are transmitted to the turbo decoding device 200 after noise is added on the transmission path. Hereinafter, a signal obtained by adding noise to the transmission information u is denoted by U. Similarly, signals obtained by adding noise to the redundant bits y ₁ and y ₂ are referred to as Y ₁ and Y ₂ , respectively.

In the turbo decoding apparatus 200 shown in FIG.
The OVA decoder 201 uses the received signals U and Y ₁ and the output signal of the deinterleaver 208 to perform ACS (Add-Compare-
Select) Performs calculation and traceback to correct errors. The fixed value buffer 202 stores tail bits.

The changeover switch 203 is normally connected to the SOVA decoder 201, and is connected to the fixed value buffer 202 at the timing of decoding the tail bits. Thus, at the timing of decoding the tail bit, the SOVA decoder 2
01 can be replaced with the tail bits stored in the fixed value buffer 202.

The interleaver 204 is provided with the changeover switch 20
3 is column-converted into an order corresponding to the systematic encoder 103 and output to the SOVA decoder 205.

[0028] The SOVA decoder 205 is provided with the interleaver 2
Using the output signal of Y.04 and Y ₂ , ACS (Add-Compare-S
elect) Performs calculation and traceback to correct errors. The fixed value buffer 206 stores tail bits.

The changeover switch 207 is normally connected to the SOVA decoder 205, and is connected to the fixed value buffer 206 at the timing of decoding the tail bit. Thus, at the timing of decoding the tail bit, the SOVA decoder 2
05 can be replaced with the tail bits stored in the fixed value buffer 206.

The deinterleaver 208 has a switch 2
07 is again column-converted into an order corresponding to the systematic encoder 101, and the decoded information is converted to another device and the SOVA decoder 2
Output to 01.

Next, the turbo decoder 200 shown in FIG.
The traceback after the ACS calculation will be described with reference to FIGS. FIG. 2 is a block diagram showing an example of the internal configuration of the systematic encoder, and FIG. 3 is a trellis diagram of the systematic encoder of FIG.

The systematic encoder of FIG. 2 receives one bit of transmission information u, performs encoding using the constraint of trellis transition, and outputs one bit of redundant bit y.

In FIGS. 2 and 3, it is assumed that the input bits of the systematic encoder are (0, 0, 0, 0) and the bit at the timing of time n + 4 is a tail bit. The path 301 in FIG. 3 is an encoder path.

Since the state at the start of the traceback is unknown, assuming that the state (0,0) is the start state, the path 30
2, a bit error occurs at the timing of time n + 4, and the effect of the bit error immediately after the start of traceback deteriorates the error correction capability. On the other hand, as shown in FIG. 1, when the output of the fixed value buffer is used at the timing of time n + 4, the path to be traced back is the path 301, and the bit error immediately after the start of the traceback is corrected.

As described above, by storing the tail bits on the decoding side and performing the decoding repeatedly using the stored tail bits instead of the decoding information at the timing of decoding the tail bits, the tail bit immediately after the start of the traceback is obtained. Since a bit error can be corrected, the error correction capability can be improved.

(Embodiment 2) FIG. 4 is a block diagram showing a configuration of a turbo decoding apparatus according to Embodiment 2 of the present invention. In the block diagram of FIG. 4, components having the same operations and operations as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and description thereof is omitted. Further, the configuration of a turbo encoding device that transmits a signal to the turbo decoding device according to Embodiment 2 of the present invention is the same as that of Embodiment 1, and thus description thereof is omitted.

The turbo decoder 400 shown in FIG. 4 is different from the turbo decoder 200 shown in FIG.
A configuration in which a multiplier 402, a maximum value detector 403, and a multiplier 404 are added is adopted.

The maximum value detector 401 is connected to the SOVA decoder 2
The soft decision value of each state outputted from 01 is inputted, and the largest one is detected and outputted. The multiplier 402 multiplies the output of the fixed value buffer 202 and the output of the maximum value detector 401 and outputs the multiplied value to the changeover switch 203.

Thus, at the timing of decoding the tail bits, the soft decision value can be used as information to replace the decoded information output from SOVA decoder 201, and interleaver 204 always outputs the soft decision value. I do.

The maximum value detector 403 is the SOVA decoder 2
The soft decision value of each state output from 05 is input, and the largest one is detected and output. The multiplier 404 multiplies the output of the fixed value buffer 206 and the output of the maximum value detector 403, and outputs the multiplied value to the changeover switch 207.

Thus, at the timing of decoding the tail bits, the soft decision value can be used as information to replace the decoding information output from SOVA decoder 205, and deinterleaver 208 always uses the soft decision value. Output.

As described above, by repeatedly performing decoding using the value obtained by multiplying the maximum value of the soft decision value by the tail bit stored on the decoding side, the stored tail bit is used instead of the decoded information. In this case, an optimal soft decision value can be used, so that the error correction capability can be further improved as compared with the first embodiment.

Note that the maximum value detectors 401 and 403
The maximum absolute value of the soft decision value may be detected. In this case, a more accurate soft decision value can be detected.

Further, table data may be prepared, and the soft decision value may be estimated based on the received power, the received quality, the number of times of turbo decoding, or the like. In this case, the process of detecting the largest soft decision value is not required, so that the maximum value detector can be deleted.

[0045]

As described above, according to the turbo decoding apparatus and the iterative decoding method of the present invention, when the tail bit is included in the internal interleave of the turbo code at the time of encoding using SOVA as the decoding algorithm, Even when a bit error occurs immediately after the start of the back, the error correction capability does not deteriorate.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a turbo decoder according to Embodiment 1 of the present invention and a turbo encoder that transmits signals to the turbo decoder.

FIG. 2 is a block diagram showing an example of an internal configuration of a systematic encoder.

FIG. 3 is a trellis diagram of the systematic encoder of FIG. 2;

FIG. 4 is a block diagram showing a configuration of a turbo decoding device according to Embodiment 2 of the present invention.

[Explanation of symbols]

 101, 103 Systematic encoder 102 Interleaver 201, 205 SOVA decoder 202, 206 Fixed value buffer 203, 207 Changeover switch 204 Interleaver 208 Deinterleaver 401, 403 Maximum value detector 402, 404 Multiplier

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 14/04 H04B 14/04 Z (72) Inventor Takaaki Sato 4-3 Tsunashima Higashi, Kohoku-ku, Yokohama-shi, Kanagawa No. 1 Matsushita Communication Industrial Co., Ltd. F term (reference) 5J065 AD10 AE06 AF02 AG06 AH23 5K004 AA01 BB05 5K041 AA02 BB01 BB08 CC01 FF32 GG03 HH32 JJ24

Claims (7)

[Claims] 1. A decoding means for performing a soft output Viterbi algorithm on information encoded by including fixed information in an internal interleave of a turbo code; a storage means for storing the fixed information; A turbo decoding apparatus, comprising: replacement means for replacing the decoded information output from the decoding means with the fixed information stored in the storage means at a timing of decoding the fixed information. 2. A system comprising: a maximum value detecting means for detecting a maximum value of a soft decision value output from a decoding means; and a multiplying means for multiplying fixed information stored in a storage means by the maximum value. 2. The turbo decoding apparatus according to claim 1, wherein the means replaces the decoded information output from the decoding means with a multiplied value output from the multiplying means at a timing of decoding the encoded fixed information. . 3. A turbo coding apparatus characterized in that fixed information is included in an internal interleave of a turbo code at the time of encoding, and code information is transmitted to the turbo decoding apparatus according to claim 1 or 2. 4. A wireless communication device equipped with the turbo decoding device according to claim 1. 5. An information processing apparatus equipped with the turbo decoding device according to claim 1. 6. A soft output Viterbi algorithm is performed on the encoded information by including the fixed information in an internal interleave of the turbo code at the time of encoding, and the decoded information is decoded at a timing at which the encoded fixed information is decoded. Is replaced with fixed information stored in advance. 7. A soft output Viterbi algorithm is performed on coded information by including fixed information in an internal interleave of a turbo code during coding, and fixed information stored in advance and a maximum value of a soft decision value are calculated. The iterative decoding method characterized in that at the timing of calculating the multiplied value of (i) and decoding the encoded fixed information, the decoded information is replaced with the multiplied value.