JP2001326577A - Device and method for directly connected convolutional encoding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a decoding delay without regard to an interleave size. SOLUTION: A recursive convolutional encoder 5 to which data signal systems 2 and u (t) are inputted has a first internal state S (t, 0). A first known signal 3 for restricting the first internal state is inputted to the encoder 5. The restriction of state transition like this corresponds to the restriction of state transition predicted by a decoder 101 when decoding a convolutional code and the restriction results in the restriction of a path to be searched. When the reliability of a signal received by the decoder 101 is low, the path to be searched is defined in comparison with officially known coding, which never add known information bit and the reliability of a survival path is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a directly concatenated convolutional encoder and a method for directly concatenated convolutional encoding.
The present invention relates to a direct concatenated convolutional encoder for correcting an error of a digital communication signal generated in a transmission medium by using an error correction code, and a direct concatenation convolutional encoding method.

[0002]

2. Description of the Related Art Digital transmission systems are required to reduce the required power. In order to reduce the required power, a technique of encoding a digital signal using an error correction code or a high-efficiency speech code having a high code gain is used. In particular, in a digital wireless communication system using direct sequence spectrum spreading such as CDMA, there is a demand for reduction of required power which directly leads to reduction of interference with other users. Reducing the required power promotes an increase in communication capacity. In deep space communication where the communication distance is very long and retransmission control is difficult, it is important to perform error correction using an error correction code.

Conventionally, a concatenated code in which a Reed-Solomon code is used as an outer code and a convolutional code is used as an inner code as an error correction code capable of greatly reducing bit errors under low S / N conditions. Has been widely used. On the other hand, parallel concatenated convolutional codes and serial concatenated convolutional codes have been proposed as other error correction codes that can greatly reduce bit errors under low S / N conditions. Encoders that perform such encoding commonly have an interleaver that rearranges the signal sequence, and drawing a trellis of the entire code has limitations in terms of the amount of calculation and the memory capacity. Therefore, it is difficult to perform maximum likelihood decoding by applying the Viterbi algorithm.

As a decoding other than the maximum likelihood decoding, iterative decoding has been proposed. Iterative decoding is a decoding method that reduces decoding errors by repeating decoding instead of increasing the complexity of the device. The iterative decoder inputs the soft output obtained as a result of performing the soft output decoding by one of the decoders for the recursive convolution decoding existing therein to the other decoder as external information, and An output and an input are repeated with each other, and when the number of repetitions reaches a specified number, a hard decision is made by a determiner to obtain an output as an iterative decoder.

As shown in FIG. 3, a repetition decoder using a serial concatenated convolutional code includes a first soft-input soft-output decoder 101 for decoding an inner code and a second soft-input soft-output decoder 101 for decoding an outer code. It comprises a soft output decoder 102, an interleaver 103 having the same permutation pattern as the encoder, an inverse interleaver 104 corresponding to the interleaver 103, and a decision unit. The received sequence obtained from the demodulator is input to a first soft-input / soft-output decoder 101 corresponding to the inner code, and is decoded with respect to the inner code. The prior likelihood of the first soft-input soft-output decoder 101 is zero when the first iteration is performed. The soft output sequence obtained from the first soft input / soft output decoder 101 is input to an inverse interleaver 104 and deinterleaved, and then input as a received sequence to a second soft input / soft output decoder 102 corresponding to the outer code. Then, the outer code is decoded. In the second soft-input soft-output decoder 102, the likelihood is zero regardless of the number of repetitions. The sequence of the extrinsic information likelihood obtained in this way is interleaved and then fed back to the first inner-code first soft-input soft-output decoder 101 again as prior likelihood. If the number of repetitions is 2 or more, the soft-input soft-output decoder 101 outputs the second soft-input soft-output decoder 102 corresponding to the outer code as the prior likelihood.
Is input, and a sequence obtained by the demodulator is input as a reception sequence. If such repetition reaches a specified number of times, a hard decision is made by the determiner,
A signal sequence as an iterative decoder is output. As shown in FIG. 4, the aforementioned sequence of external information likelihood is fed back as its prior likelihood and input to the soft-input soft-output decoder.

[0006] By applying the iterative decoding method to the serial concatenated convolutional code in this manner, under low S / N conditions,
Although a large coding gain can be obtained, in order to obtain a large code gain by the direct convolutional convolutional code, the size of the interleaver inside the encoder becomes large, and the decoding delay due to decoding with a large amount of calculation becomes large. Would. In a communication system in which the decoding delay must be reduced, the problem of the decoding delay remains in applying the serial concatenation code. Regardless of the size of the interleave size, it is desired to establish a direct concatenated convolutional coding method without increasing the decoding delay.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a direct concatenated convolutional encoder having a small decoding delay regardless of the interleave size and a direct concatenated convolutional coding method.

[0008]

Means for solving the problem are described as follows. The technical items appearing in the expression are appended with numbers, symbols, and the like in parentheses (). The numbers, symbols, and the like are technical items that constitute at least one embodiment or a plurality of the embodiments of the present invention, in particular, the embodiments or the examples. Corresponds to the reference numerals, reference symbols, and the like assigned to the technical matters expressed in the drawings corresponding to the above. Such reference numbers and reference symbols clarify the correspondence and bridging between the technical matters described in the claims and the technical matters of the embodiments or examples. Such correspondence / bridge does not mean that the technical matters described in the claims are interpreted as being limited to the technical matters of the embodiments or the examples.

A direct convolutional encoder according to the present invention includes a recursive convolutional encoder (5) to which a data signal sequence (2, u (t)) is input, and includes a recursive convolutional outer encoder (5). ) Has a first internal state (S (t, 0)), and a first known signal (3) for limiting the first internal state is input to the recursive outer convolutional encoder (5). Such a state transition restriction corresponds to the state transition restriction predicted by the decoder (101) when decoding a convolutional code. When the reliability of the signal received by the device (101) is low, the paths to be searched are more limited as compared with the known coding without adding the known information bits, and the reliability of the surviving path is high. Become.

[0010] A first interleaver (9) is further included.
The first interleaver (9) interleaves the first output sequence (8) output from the recursive convolutional outer encoder (5). The first puncture is a recursive convolutional outer coder (5)
And a first interleaver (9) for thinning out the redundant bits of the first output sequence (8) and the signal portion corresponding to the first known signal (3). By thinning out the first known signal (3), it is possible to prevent a decrease in the coding rate due to the insertion of the first known signal (3). Second signal sequence (12) interleaved by first interleaver (9)
Has a second inner state, and a second known signal (11) for limiting the second inner state is supplied to the recursive convolutional inner encoder (13). Is entered.

A second puncture (16) is further provided,
In the second puncture (16), the recursive convolutional inner encoder (1
The second signal sequence (15) output from 4) is input and
The puncturing (16) thins out a redundant bit of the second signal sequence (15) and a signal portion corresponding to the second known signal (11). The first known signal (3) is a data signal sequence (2)
Is preferably inserted at a constant interval with respect to. First output sequence (6) output from recursive convolutional outer encoder (5)
Is further provided on the receiving side for decoding by iterative decoding.

The direct convolutional encoding method according to the present invention comprises the steps of outer-encoding a data signal sequence (2) by a first recursive convolution, and performing a data signal sequence (2) before the outer encoding. And transmitting the outer coded signal sequence (17) that is outer coded by outer coding. The outer coded signal sequence (6) is interleaved. The outer coded signal sequence (6) is punctured with respect to the first known signal (3). Outer encoding is used to inner-code the outer coded signal sequence (10) in which the data signal sequence (2) is outer-coded by the second recursive convolution, and to perform inner coding by performing the inner coding. Transmitting the encoded outer coded signal sequence. Before the inner encoding, the second known signal (11) is inserted into the outer encoded signal sequence (10). The outer coded signal sequence that is inner coded by inner coding is interleaved. Outer coded signal sequence inner-coded by inner coding (17)
Are punctured with respect to the second known signal (11). The outer coded signal sequence (17) is repeatedly decoded on the receiving side.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Corresponding to the drawings, an embodiment of a direct concatenated convolutional encoder according to the present invention is provided with a circuit array for error correction coding using a direct concatenated code.
The circuit sequence includes an inner encoder as well as an outer encoder. A transmission-side input signal data sequence 2 is input to the outer encoder 1. The first known bits 3 are inserted into the transmission-side input signal sequence 2 at specified intervals, particularly at regular intervals, with respect to the transmission-side input signal data sequence 2. The first known bit 3 is known on the receiving side. The first bit insertion signal sequence 4 in which the known bits 3 are inserted into the transmission side input signal data sequence 2 is input to the outer encoder 1.

The outer encoder 1 has a first recursive convolutional encoder 5
Built-in. The first bit insertion signal sequence 4 is convolutionally encoded by the outer encoder 1 of the first recursive convolutional encoder 5. The first convolutional coded signal sequence 6 output from the outer encoder 1 is
Input to the puncturing device 7. First puncturing device 7
Is a first convolutional encoded signal sequence 6 to be transmitted when encoding is performed.
Is decimated and its coding rate is converted.
The first puncturing device 7 also thins out the first known bits 3 when thinning out redundant bits. By thinning out the first known bits 3, it is possible to prevent a decrease in the coding rate (the ratio of the number of output bits to the number of input bits) due to the insertion of the first known bits 3.

The first puncturing device 7 includes a thinned signal sequence 8
Is output. The decimated signal sequence 8 is input to an interleaver 9. The interleaver means that a bit string is stored in a memory, and when the number of bits stored in the memory becomes a constant value, the bit string is output in an order different from the order at the time of input. The interleaver 9 rearranges the decimated signal sequence 8 after decimating the signal sequence 8 and outputs a rearranged signal sequence 10. The second known bits 11 are added to the rearranged signal sequence 10 at specified intervals with respect to the rearranged signal sequence 10, particularly, at regular intervals.
Is inserted. The second known bit 11 is known on the receiving side. The second bit insertion signal sequence 12 in which the second known bits 11 are inserted into the rearranged signal sequence 10 is input to the inner encoder 13.

The inner encoder 13 includes a second recursive convolutional encoder 14. The second recursive convolutional encoder 14 has a first
It need not be the same for the recursive convolutional encoder 5. The second bit insertion signal sequence 12 is convolutionally encoded by the second recursive convolutional encoder 14 of the inner encoder 13. The second convolutional encoded signal sequence 15 output from the inner encoder 13 is input to a second puncturing device 16. The second puncturing device 16 thins out the redundant bits of the second convolutional coded signal sequence 15 and converts the coding rate thereof. The second puncturing device 16 also thins out the inner encoder 13 when thinning out redundant bits. By thinning out the inner encoder 13, it is possible to prevent a decrease in the coding rate due to the insertion of the inner encoder 13.

FIG. 2 shows a first recursive convolutional encoder 5 and a first recursive convolutional encoder.
A second recursive convolutional encoder 14 which is the same as the recursive convolutional encoder 5 is shown. The first bit insertion signal sequence 4 or the second bit insertion signal sequence 12 is indicated by a signal sequence u (t). Hereinafter, u (t) is described as the first bit insertion signal sequence 4. Here, t indicates a time that is time-series. The first bit insertion signal sequence 4 shown in FIG. 2 has a coding rate of １ ／. The signal sequence u (t) is supplied to the first adder 2
1 to the first memory 22. First memory 22
Is called state 0 and is represented by S (t, 0). State 0 is held in the first memory 22, output from the first memory 22 as it is, and input to the second memory 23. The value held by the second memory 23 is called state 1,
It is represented by S (t, 1).

The state 1 is held in the second memory 23, output from the second memory 23 as it is, and input to the second adder 24. State 0 is held in the first memory 22, output from the first memory 22 as it is, and input to the second adder 24. In the second adder 24, S (t, 0) in the state 0
And S (t, 1) in state 1 are added. The second adder 24 outputs S (t, 0) in state 0 and S (t, 0) in state 1
A first addition value 25 to (t, 1) is output. The first addition value 25 is input to the first adder 21. First adder 21
Is obtained by adding u (t) to the first addition value 25 to obtain a second addition value 2
6 is output.

S (t, output from the second memory 23)
1) and the second addition value 26 output from the first adder 21 are input to a third adder 27. The third adder 27 calculates S
(T, 1) and the second addition value 26 are added to obtain a third addition value 2
8 is output. The outer encoder 1 has w (t, 0) or w (t, 0)
(T, 1) is output. w (t, 0) = u (t) w (t, 1) = s (t, 0) + s (t, 1) + u (t) + s (t, 1) = s (t, 0) + u (t This addition is performed as an exclusive addition.

At time (t + 1), the states of the first memory 22 and the second memory 23 are as follows. s (t + 1,1) = s (t, 0) s (t + 1,0) = s (t, 0) + s (t, 1) + u
(T)

As described above, the convolutional coding is performed in the state s (t,
0) and the state s (t, 1), the values of the encoded outputs w (t, 0) and w (t, 1) are determined depending on these states. The value obtained by adding 1 to the numbers of the first memory 22 and the second memory 23 is called a constraint length.

In general, the smaller the coding rate, the more excellent the error correction code is in the error correction characteristics. On the other hand, if the coding rate is small, the transmission efficiency is deteriorated. Puncturing is performed to properly balance the error correction capability and the transmission efficiency. In particular, by puncturing redundant bits from the concatenated convolutional code, it is possible to suppress deterioration in characteristics. In the recursive convolutional encoder shown in FIG. 2, a code having a coding rate of 生成 is generated, but the coding rate is 2 by not transmitting redundant bits once every two bits. / 3. Puncture devices 7, 16
Can remove not only redundant bits but also known bits to be inserted, thereby increasing the coding rate.

When the output sequence 17 error-correction-coded by the serial concatenated code is applied to a wireless system, particularly CDMA, the output sequence 17 is re-interleaved and appropriately modulated as necessary before being transmitted to the receiving side. You. The output sequence 17 is demodulated and input to the first soft-input soft-output decoder 101 on the receiving side shown in FIG. The decoding of the output sequence 17 is performed by iterative decoding by the above-described known decoder shown in FIG.

The first known bit 3 is inserted into the first recursive convolutional encoder 5 and encoded. The internal states s (t, 0) and s (t, 1) of the first recursive convolutional encoder 5 are encoded. ) And state transitions are restricted. Such a restriction on the state transition corresponds to a restriction on the state transition predicted by the decoder when decoding the convolutional code. This restriction results in a restriction on the paths searched. For this reason, when the reliability of the signal received by the decoder is low, the paths to be searched are limited by comparison with the known coding without adding the known information bits, and the reliability of the surviving path is low. Get higher. Here, the surviving path corresponds to the information bit string estimated on the receiving side and its reliability.

As will be understood from the above description,
When serial concatenated convolutional coding, by inserting known bits before the outer encoder and the inner encoder, the reliability of the decoded output when the number of repetitions at the time of iterative decoding is small is high. , The reliability of the input of the next iterative decoding increases. For this reason, even when the number of repetitions at the time of performing iterative decoding is small, the bit error rate can be reduced as compared with a known encoding / decoding method in which known bits are not inserted.

The polynomials used for recursive convolutional coding are not limited to those described above. The reordering pattern of the interleaver can be freely adopted. The coding rate can also be freely adopted. Second known bit 11 input to inner encoder 13
Is not always necessary.

[0027]

According to the direct convolutional encoder and the direct convolutional encoding method of the present invention, the number of times of iterative decoding can be reduced, and the delay due to the iterative decoding can be suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment of a direct concatenation convolutional encoder according to the present invention.

FIG. 2 is a circuit diagram for performing convolutional coding;

FIG. 3 is a circuit diagram showing a known iterative decoder applied to the present invention.

FIG. 4 is a circuit diagram showing a transmission / reception signal sequence of a known device.

[Explanation of symbols]

 2, u (t) ... data signal sequence 3 ... first known signal 5 ... recursive convolutional outer coder 6 ... first output sequence 9 ... first interleaver 8 ... first output sequence 10 ... outer coded signal sequence 11 ... second known signal 12 ... second signal sequence 13 ... recursive convolutional inner encoder 14 ... recursive convolutional inner encoder 15 ... second signal sequence 16 ... second puncture 17 ... outer coded signal sequence 101 ... decoding S (t, 0): first internal state S (t, 1): second internal state

Claims (15)

[Claims] 1. A recursive convolutional coder to which a data signal sequence is input, wherein the recursive convolutional outer coder has a first inner state; (1) A directly concatenated convolutional encoder to which a first known signal for limiting an internal state is input. 2. The concatenated convolutional encoder according to claim 1, further comprising a first interleaver, wherein the first interleaver interleaves a first output sequence output from the recursive convolutional outer encoder. 3. The method according to claim 1, further comprising a first puncture, wherein the first puncture is interposed between the recursive convolutional outer coder and the first interleaver, and wherein the first puncture includes the first output sequence. 3. The concatenated convolutional encoder according to claim 2, wherein said redundant bits and a signal portion corresponding to said first known signal are decimated. 4. A recursive convolutional inner encoder to which a second signal sequence interleaved by the first interleaver is inputted, wherein the recursive convolutional inner encoder has a second inner state, The direct concatenated convolutional encoder according to claim 3, wherein a second known signal for limiting the second internal state is input to the recursive convolutional inner encoder. 5. A second puncturer, wherein a second signal sequence output from the recursive convolutional inner encoder is input to the second puncture, and the second puncture is a redundant signal of the second signal sequence. 5. The concatenated convolutional encoder of claim 4, wherein bits and a signal portion corresponding to the second known signal are decimated. 6. The direct convolutional encoder according to claim 1, wherein said first known signal is inserted at a constant interval into said data signal sequence. 7. A direct concatenated tatami according to claim 1, further comprising a decoder for decoding the first output sequence output from said recursive convolutional outer encoder by iterative decoding on a receiving side. Embedded encoder. 8. An outer encoding of a data signal sequence by a first recursive convolution, and a first signal encoding is performed on the data signal sequence before the outer encoding.
A directly concatenated convolutional coding method, comprising: inserting a known signal; and transmitting an outer-coded outer coded signal sequence by performing the outer coding. 9. The direct convolution coding method according to claim 8, wherein said outer coded signal sequence is interleaved. 10. The coded signal sequence is punctured with respect to the first known signal.
Direct convolutional encoding method. 11. An outer coded signal sequence in which the data signal sequence is outer coded by the outer coding is inner coded by a second recursive convolution. 9. The method of claim 8, further comprising transmitting the encoded outer coded signal sequence. 12. The method of claim 11, further comprising inserting a second known signal into the outer coded signal sequence before performing the inner coding. 13. The direct convolutional coding method according to claim 12, wherein said outer coded signal sequence inner-coded by said inner coding is interleaved. 14. The direct convolutional coding method according to claim 12, wherein said outer coded signal sequence inner-coded by said inner coding is punctured with respect to said second known signal. 15. The direct concatenated convolution coding method according to claim 8, further comprising iteratively decoding said outer coded signal sequence on a receiving side.