JP2006280010A - Decoding device and decoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decoding device capable of shortening the time for decoding processing, and to provide a decoding method. <P>SOLUTION: This decoding device is provided with a first decoder 11 for generating external information LE1, by performing first decoding on the basis of a first element code E and external information LE2, a second decoder 12 for generating external information LE2', by performing second decoding on the basis of a second element code E' and external information LE1', and a hard deciding section 15 for outputting a decoding sequence D, by applying hard decision to a logarithmic likelihood ratio L. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a decoding device and a decoding method, and more particularly, to a decoding device and a decoding method for repeatedly decoding first code data and second code data.

  In a digital communication system, an error correction code for correcting a code error that occurs in a transmission path is used. In particular, in a mobile communication system, since the strength of radio waves fluctuates greatly due to the influence of fading, a code error is likely to occur. Therefore, an error correction code is required to have a high correction capability. A turbo code, which is an example of an error correction code, has attracted attention as a code having an error correction capability close to the Shannon limit. For example, a third generation mobile communication system such as W-CDMA (Wideband Code Division Multiple Access) or CDMA Used in 2000.

  The block diagram of FIG. 8 shows a configuration of a general encoding device for generating a turbo code. For example, the encoding device 80 is provided on the transmission side of the communication system, encodes an information sequence U that is pre-encoded data into a turbo code of parallel concatenated convolutional codes (PCCCs), and transmits Output outside the road.

  As shown in the figure, the encoding device 80 includes a first encoder 81 and a second encoder 82 that are systematic convolutional encoders, and an interleaver 83 that interleaves (reorders) data. I have.

  The first encoder 81 encodes the input information series (organization part) U to generate redundant bits P, and outputs the redundant bits P to the outside. The interleaver 83 rearranges each bit of the input organizational unit U into a predetermined interleave pattern to generate an organizational unit U ′, and outputs this organizational unit U ′ to the second encoder 82. The second encoder 82 encodes the organization part U ′ to generate redundant bits P ′, and outputs the redundant bits P ′ to the outside.

  Therefore, the encoding unit 80 outputs the systematic part U, the redundant bit P, the systematic part U ′, and the redundant bit P ′ to the outside. A set (U, P) of the organization part U and the redundant bit P is referred to as a first element code (code data) E, and a set (U ′, P ′) of the organization part U ′ and the redundant bit P ′ is a second element code (code data) E. This is referred to as element code E ′. In the present specification, data without “′” indicates data relating to the first element code or non-interleaved data, and data with “′” is the second element code. Or the data regarding the interleaved data is shown.

  Decoding a turbo code encoded in this way is called turbo decoding. In turbo decoding, iterative decoding is performed while exchanging external information between a decoder that decodes the first element code E and a decoder that decodes the second element code E ′. For example, a conventional decoder used in turbo decoding is known from Patent Document 1.

  The block diagram of FIG. 9 shows the configuration of a conventional decoding device that performs turbo decoding. The conventional decoding apparatus 90 decodes the first element code E and the second element code E ′ output from the encoding apparatus 80 of FIG. As shown in the figure, the conventional decoding device 90 includes a first decoder 91 that decodes the first element code E, a second decoder 92 that decodes the second element code, and data Are provided, an interleaver 93 for interleaving, deinterleavers 94 and 95 for deinterleaving data (rearranging the interleave pattern to the original pattern), and a hard decision unit 96 for making a hard decision on soft output data.

  The first decoder 91 and the second decoder 92 perform decoding by the soft input / soft output decoding method. As soft input / soft output decoding methods, SOVA (Soft-Output Viterbi Algorithm) and MAP (Maximum A Postoriori) are known. For example, the first decoder 91 and the second decoder 92 perform decoding using a Max-Log-MAP algorithm that is an example of a MAP.

  In the Max-Log-MAP algorithm, Viterbi decoding is performed based on a state transition diagram called a trellis diagram. In the trellis diagram, the path connecting each state at each time point corresponds to the code sequence to be decoded. The likelihood (path metric) for the possible path is calculated, and the path with the highest likelihood is decoded as the surviving path. .

  FIG. 10 shows an example of a trellis diagram used in the Max-Log-MAP algorithm. In the Max-Log-MAP algorithm, when data at time A is decoded, the path metric from the second position (starting point in the figure) before time A and the first position (end point in the figure) after time A are decoded. ) From the path metric. The process of calculating the path metric by performing Viterbi decoding in the direction from the start point to the end point on the trellis diagram (backward direction) is called forward processing, and the path metric calculated by the forward processing is called α path metric. Also, the process of calculating the path metric by performing Viterbi decoding in the reverse direction to the forward process (the direction from the end point to the start point: the forward direction) is called backward process, and the path metric calculated by the backward process is the β path It is called a metric.

  Further, in the Max-Log-MAP algorithm, after forward processing and backward processing, the likelihood (branch metric) of the branch connecting the α path metric and the β path metric is obtained, and the α path metric, β path metric, and branch metric are used. Log Likelihood Ratio (LLR) is calculated, and external information (Extrinsic Information) is calculated. The log likelihood ratio and the external information are soft output data (reliability) that is a decoding result of soft input / soft output decoding, and its calculation formula is described in Patent Document 1.

  FIG. 11 is a schematic diagram showing a conventional decoding method for performing turbo decoding. This conventional decoding method is a method performed in the conventional decoding device of FIG. In this conventional decoding method, first, after decoding the first element code E (1101), the second element code E ′ is decoded (1102). For example, the first decoder 91 performs decoding using the input first element code E and the external information LE2 deinterleaved by the deinterleaver 94, and outputs the external information LE1 to the interleaver 93. . Next, the second decoder 92 performs decoding using the input second element code E ′ and the external information LE1 ′ interleaved by the interleaver 93, and outputs the external information LE2 ′ to the deinterleaver 94. To do.

  In the decoding of the first element code E, the backward process (1104) is performed after the forward process (1103). Similarly, in the decoding of the second element code E, the backward process (1106) is performed after the forward process (1105). Then, the decoding of the first element code E and the decoding of the second element code E ′ are performed once, and this decoding is repeated N times (1107).

  After repeating N times, a deinterleaving process (1108) is performed, a hard decision is performed, and a decoded sequence D is output (1109). For example, the deinterleaver 95 deinterleaves the log likelihood ratio L ′ calculated by the second decoder 92, and the hard decision unit 96 makes a hard decision on the deinterleaved log likelihood ratio L and decodes it. The series D is output.

  However, in the conventional decoding device 90, after performing iterative decoding N times, the second decoder 92 outputs an interleaved log-likelihood ratio L ′, so that it is deinterleaved and a hard decision is made. There is a problem of having to. In addition, since the second decoder 92 performs backward processing after forward processing, the log-likelihood ratio L ′ is output in order from the end of the data to the top, and this is output in reverse order from the top. Must be sorted into

  On the other hand, in turbo decoding, a method is known in which the number of repetitions of decoding of the first element code E and decoding of the second element code E ′ is controlled (repeated control). The block diagram of FIG. 12 shows the configuration of a conventional decoding device that performs repetitive control. As shown in the figure, the conventional decoding device 120 includes a CRC (Cyclic Redundancy Check) determination unit 97 for iterative control in addition to the configuration of the conventional decoding device 90 of FIG.

  FIG. 13 is a schematic diagram showing a conventional decoding method for performing repetitive control. This conventional decoding method is a method performed in the conventional decoding device 120 of FIG. This conventional decoding method further performs CRC determination processing in addition to the decoding method of FIG.

  As shown in the figure, CRC determination is performed at the same timing as the forward processing (1103) in decoding the first element code E (1110). For example, the hard decision unit 96 makes a hard decision on the external information LE2 deinterleaved by the deinterleaver 94, and the CRC decision unit 97 makes a CRC decision on the decoded sequence D that is the result of the hard decision. If an error is detected as a result of the CRC determination, decoding is further repeated. When N iterations are performed, the log likelihood ratio L ′ is deinterleaved and the log likelihood ratio L is hard-decided as in FIG. 11, and then the CRC determination is performed again (1111).

  If no error is detected in the CRC determination result during the decoding iteration, the decoding iteration is terminated. Then, the external information LE2 used for the CRC determination is deinterleaved and a hard-decision decoded sequence D is output.

  However, in the conventional decoding device 120, when iterative control is performed by CRC determination, the CRC determination is performed on the result of hard determination of the external information LE2 deinterleaved by the deinterleaver 94. In general, external information is not data for making a hard decision and obtaining a decoded sequence, so there is a problem that the accuracy of iterative control is low. If the log-likelihood ratio L is used instead of the external information LE2, a memory for temporarily storing the log-likelihood ratio L is required, and the amount of memory increases.

The external information LE2 used for CRC determination is actually the output of decoding of the second element code E ′ in the previous iterative decoding. In order to perform CRC determination on the external information LE2, the external information LE2 is used. Deinterleaving is necessary, and this deinterleaving process (0.5 times for one decoding iteration) takes time.
JP 2004-80508 A

  As described above, in the conventional decoding device 90, after iterative decoding is performed N times, the interleaved log likelihood ratio L ′ must be deinterleaved or rearranged in the reverse order to perform a hard decision. For this reason, there is a problem that deinterleaving processing and rearrangement take time, and the time for decoding processing is long.

  The decoding apparatus according to the present invention generates first soft output data by performing first decoding based on first code data obtained by encoding pre-encoding data and second soft output data. The second soft output data by performing a second decoding based on the first decoder, the second code data encoded by interleaving the pre-encoding data and the first soft output data And a hard decision unit that outputs decoded data by making a hard decision on the first soft output data. This eliminates the need for deinterleaving and rearrangement processing, and shortens the time for decoding processing.

  A decoding apparatus according to the present invention includes a first decoder that generates first soft output data by performing decoding based on first code data obtained by encoding pre-encoding data, and the pre-encoding data. A second decoder for generating the second soft output data by performing decoding based on the second code data encoded by interleaving and the hard decision on the first soft output data A hard decision unit for outputting decoded data. This eliminates the need for deinterleaving and rearrangement processing, and shortens the time for decoding processing.

  The decoding method according to the present invention generates first soft output data by performing first decoding based on first code data obtained by encoding pre-encoding data and second soft output data, The second soft output data is generated by performing second decoding based on the second code data encoded by interleaving the pre-encoding data and the first soft output data, and the second soft output data is generated. Decoding data is output by making a hard decision on one soft output data. This eliminates the need for deinterleaving and rearrangement processing, thereby reducing the time for decoding processing.

  ADVANTAGE OF THE INVENTION According to this invention, the decoding apparatus and decoding method which can shorten the time of a decoding process can be provided.

Embodiment 1 of the Invention
First, the decoding apparatus and decoding method according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 3. In the decoding apparatus and the decoding method according to the present embodiment, decoding processing is repeated in the order of decoding of the second element code E ′ and decoding of the first element code E, and decoding is performed by forward processing in decoding of the first element code E. It is characterized in that the repetition of is terminated.

  Here, the configuration of the decoding apparatus according to the present embodiment will be described with reference to FIG. The decoding device 1 is a decoder that performs turbo decoding. For example, the decoding device 1 decodes the first element code E and the second element code E ′ output from the encoding device 80 illustrated in FIG. 8. That is, the decoding device 1 includes a first element code E (first code data) obtained by encoding the information sequence U (pre-encoding data) and a second element encoded by interleaving the information sequence U. The code E ′ (second code data) is input. The first element code E and the second element code E ′ are input to the decoding device 1 via a transmission line, and noise occurs in this transmission line, so that a code error occurs. The decoding device 1 turbo-decodes the first element code E and the second element code E ′, and corrects this code error with a high correction capability.

  As shown in the figure, the decoding device 1 includes a first decoder 11, a second decoder 12, an interleaver 13, a deinterleaver 14, and a hard decision unit 15.

  The first decoder 11 is provided corresponding to the first encoder 81 of the encoding device 80 and decodes the first element code E. The first decoder 11 is a soft input / soft output decoder and can be decoded by SOVA, MAP, or the like. The first decoder 11 performs decoding using, for example, a Max-Log-MAP algorithm. In this decoding, soft output data is generated. The soft output data is data indicating reliability and indicates the probability of “0” or “1”. For example, if the soft output data is a positively large value, it is more likely to be “0”, and if the soft output data is a negatively large value, it is more likely to be “1”. In the Max-Log-MAP algorithm, external information and a log likelihood ratio are generated as soft output data. External information is data exchanged between the first decoder 11 and the second decoder 12 in iterative decoding. The log likelihood ratio is data for making a hard decision and generating a decoded sequence.

  Also, the first decoder 11 performs decoding using the input first element code E and the external information LE2 deinterleaved by the deinterleaver 14, and outputs the external information LE1 calculated by decoding. Output. Further, the first decoder 11 repeats decoding a predetermined number of times together with the second decoder 12, and then outputs the log likelihood ratio L calculated by decoding to the hard decision unit 15. This decoding is repeated by performing decoding by the first decoder 11 after decoding by the second decoder 12 and repeating this N times.

  The second decoder 12 is provided corresponding to the second encoder 82 of the encoding device 80 and decodes the second element code E ′. The second decoder 12 is a soft input / soft output decoder similar to the first decoder 11. Also, the second decoder 12 performs decoding using the input second element code E ′ and the external information LE1 ′ interleaved by the interleaver 13, and the external information LE2 ′ calculated by decoding. Is output.

  The interleaver 13 interleaves the data into a predetermined interleave pattern. For example, the interleaver 13 has a memory, and can perform interleaving by a writing process and a reading process for the memory. When writing to the memory, the data may be rearranged and written according to the interleave pattern, and when reading the memory, the data may be read sequentially from the top. Further, when writing to the memory, the data may be sequentially written from the top, and when reading the memory, the data may be read according to the interleave pattern. The interleaver 13 interleaves the external information LE1 output from the first decoder 11 and outputs the external information LE1 ′ to the second decoder 12.

  The deinterleaver 14 deinterleaves the interleaved data into the original sequence of data. Similar to the interleaver 13, the deinterleaver 14 can perform deinterleaving by writing processing and reading processing to the memory. When writing to the memory, the data may be rearranged and written according to the deinterleave pattern opposite to the interleave pattern, and when reading the memory, the data may be read sequentially from the top. In addition, when writing to the memory, the data may be sequentially written from the top, and when reading the memory, the data may be read according to the deinterleave pattern. The deinterleaver 14 deinterleaves the external information LE2 ′ output from the second decoder 12 and outputs the external information LE2 to the first decoder 11.

  The hard decision unit 15 makes a hard decision on the soft output data and generates a decoded sequence. In the hard decision, predetermined data such as “0” or “1” is selected based on data having an arbitrary value such as soft output data. For example, if the soft output data is a little “0”, it is determined as “0”, and if it is a little “1”, it is determined as “1”.

  Further, after iterative decoding is performed, hard decision section 15 makes a hard decision on log likelihood ratio L output from first decoder 11 and outputs the result of the hard decision as decoded sequence D. In this embodiment, since the log likelihood ratio L output from the first decoder 11 instead of the second decoder 12 is hard-decided as it is, it is not necessary to rearrange the log likelihood ratios L by deinterleaving. .

  Next, the configuration of the decoder according to the present embodiment will be described with reference to FIG. FIG. 2A shows the configuration of the first decoder 11, and FIG. 2B shows the configuration of the second decoder 12.

  As shown in FIG. 2A, the first decoder 11 includes a forward processing unit 21, a backward processing unit 22, a memory 23, and an external information calculation unit 24. The memory 23 stores information necessary for processing by the forward processing unit 21, backward processing unit 22, and external information calculation unit 24.

  The backward processing unit 22 performs backward processing using the input first element code E and the external information LE2 deinterleaved by the deinterleaver 14. The backward processing unit 22 refers forward from a position (end point) after the position where the external information LE2 and the first element code E are decoded, and obtains a β path metric from the end point in the trellis diagram. . Then, the backward processing unit 22 stores the first element code E and the external information LE2 used for the backward processing and the β path metric calculated by the backward processing in the memory 23.

  The forward processing unit 21 performs forward processing using the first element code E and the external information LE2 stored in the memory 23 by the backward processing unit 22. The forward processing unit 21 refers backward from a position (start point) before the position where the external information LE2 and the first element code E are decoded, and obtains an α path metric from the start point in the trellis diagram. Then, the forward processing unit 21 stores the α path metric calculated by the forward processing in the memory 23.

  The external information calculation unit 24 calculates the log likelihood ratio L and the external information LE1 using the α path metric and β path metric stored in the memory 23 by the backward processing unit 22 and the forward processing unit 21. For example, the external information calculation unit 24 obtains a branch metric connecting an α path metric and a β path metric, calculates a log likelihood ratio L from the α path metric, the β path metric, and the branch metric, and calculates the log likelihood ratio L from the log likelihood ratio L. External information LE1 is calculated. Then, the external information calculation unit 24 outputs the calculated log likelihood ratio L or the external information LE1.

  For example, the external information calculation unit 24 obtains the log likelihood ratio L and the external information LE1 in the order in which both the α path metric and the β path metric are generated, and outputs the log likelihood ratio L or the external information LE1 in the generation order. To do. Since the first decoder 11 performs the forward processing of the forward processing unit 21 after the backward processing of the backward processing unit 22, all the β path metrics are generated, and then the α path metric is converted into a trellis diagram. It is generated in the order from the start point to the backward direction. Then, the log likelihood ratio L and the external information LE1 are obtained in order from the start point to the backward direction, and the log likelihood ratio L or the external information LE1 is output in this order. Accordingly, since the log likelihood ratio L is output in order from the top of the data, it is possible to make a hard decision in that order without rearranging the data.

  As shown in FIG. 2B, the second decoder 12 includes a forward processing unit 21 ′, a backward processing unit 22 ′, a memory 23 ′, and an external information calculation unit 24 ′. Each component of the second decoder 12 is the same as each component of the first decoder 11. However, in the second decoder 12, the input / output relationship of data in the forward processing unit 21 and the backward processing unit 22, that is, the order of the forward processing and the backward processing is different.

  The forward processing unit 21 ′ refers to the input second element code E ′ and external information LE1 ′ in the backward direction from the start point to obtain an α path metric, and obtains the second element code E ′ and external information LE1 ′. And the α path metric are stored in the memory 23 ′. The backward processing unit 22 ′ refers to the external information LE1 ′ and the second element code E ′ stored in the memory 23 ′ by the forward processing unit 21 ′ in the forward direction from the end point, obtains a β path metric, The β path metric is stored in 23 ′. The external information calculation unit 24 ′ calculates the external information LE2 ′ in the same manner as the external information calculation unit 24.

  Since the second decoder 12 performs the backward processing of the backward processing unit 22 ′ after the forward processing of the forward processing unit 21 ′, the β path metric is converted into the trellis after all the α path metrics are generated. Generated in order from the end point of the diagram to the front. Accordingly, the external information LE2 ′ is obtained in order from the end point in the forward direction, and the external information LE2 ′ is output in this order.

  Next, the decoding method according to the present embodiment will be described with reference to FIG. This decoding method is performed by the decoding device 1 in FIG. That is, this decoding method is a method of iteratively decoding the first element code E and the second element code E ′ that are turbo-encoded.

  In this decoding method, first, the second element code E ′ is decoded (301). In this decoding, backward processing (304) is performed after forward processing (303). For example, when the second element code E ′ and the external information LE1 ′ are input to the second decoder 12, the forward processing unit 21 ′ performs the forward processing and then the backward processing unit 22 ′ performs the backward processing. Perform word processing. Then, the external information calculation unit 24 ′ calculates the log likelihood ratio L and the external information LE2 ′ based on the path metrics obtained by the forward process and the backward process. Note that the decoding of the second element code E ′ is performed. The order of processing is not limited to this, and forward processing may be performed after backward processing.

  Further, when the decoding of the second element code E ′ is the first decoding, since the external information LE1 ′ is not calculated, the initial value is used, and in the second and subsequent decodings, the first decoder The external information LE1 ′ calculated by 11 is used.

  Next, the first element code E is decoded (302). In this decoding, forward processing (306) is performed after backward processing (305). For example, when the first element code E and the external information LE2 are input to the first decoder 11, the backward processing unit 22 performs backward processing and then the forward processing unit 21 performs forward processing. . Then, the external information calculation unit 24 calculates the log likelihood ratio L and the external information LE1 based on the path metrics obtained by the backward process and the forward process.

  Next, the decoding of the second element code E ′ and the decoding of the first element code E are performed once, and this decoding is repeated N times (307). The code correction capability improves each time this decoding is repeated, but the number of repetitions is, for example, 8 to 10 times.

  Next, after decoding is repeated N times, a hard decision is made (308). For example, the first decoder 11 counts the number of decoding times of the first element code E, and when this count value reaches N, outputs the log likelihood ratio L at that time to the hard decision unit 15. . The hard decision unit 15 makes a hard decision on the log likelihood ratio L output from the first decoder 11 and outputs a decoded sequence D.

  As described above, in the present embodiment, the log likelihood ratio is output from the first decoder after the decoding iterative process, so that the hard decision can be made without rearranging the log likelihood ratio. That is, unlike the log likelihood ratio output from the second decoder, no deinterleaving is required. Further, since the first decoder performs forward processing after backward processing and outputs a log likelihood ratio, it is not necessary to rearrange the log likelihood ratio in reverse order. Therefore, since deinterleaving and rearrangement processing are not required, the time for decoding processing can be shortened, and power consumption can be further reduced. In particular, it is more effective in an electronic device such as a cellular phone that requires low power consumption.

  For example, the deinterleaving process requires a processing time of 0.5 times for one decoding iteration, but this process is not necessary in this embodiment. If the number of repetitions of the decoding process is 8, in the conventional example (FIG. 9), the processing time for 8.5 repetitions is required. In this embodiment (FIG. 1), the processing time for 8 repetitions is required. Thus, the processing time for 0.5 repetitions (about 6%) can be reduced.

Embodiment 2 of the Invention
Next, a decoding apparatus and a decoding method according to the second embodiment of the present invention will be described with reference to FIGS. The decoding device and the decoding method according to the present embodiment are characterized in that a hard decision of the decoding result of the first element code E is CRC-determined and repeatedly controlled.

  Here, the configuration of the decoding apparatus according to the present embodiment will be described with reference to FIG. In FIG. 4, the same reference numerals as those in FIG. 1 are the same elements, and the description thereof is omitted.

  As shown in the figure, the decoding device 1 includes a CRC determination unit 16 in addition to the configuration of FIG. The CRC determination unit 16 performs CRC detection on the decoded sequence D and performs error detection.

  Next, the decoding method according to the present embodiment will be described with reference to FIG. This decoding method is performed by the decoding device 1 of FIG. Further, this decoding method further performs CRC determination processing in addition to the decoding method of FIG. Other than the CRC determination process is the same as in FIG.

  In this decoding method, similarly to FIG. 3, the second element code E ′ is decoded (301) and the first element code E is decoded (302), and this decoding is repeated N times (307). In this embodiment, every time decoding is repeated, CRC determination is performed based on the decoding result of the first element code E (309). For example, the first decoder 11 performs backward processing (305) and forward processing (306) each time decoding is performed, outputs the external information LE1 to the interleaver 13, and makes a hard decision on the log likelihood ratio L. To the unit 15. Hard decision unit 15 makes a hard decision on log-likelihood ratio L and outputs decoded sequence D to CRC decision unit 16. The CRC determination unit 16 performs CRC calculation on the decoded sequence D and performs error detection.

  If no error is detected as a result of the CRC determination, the decoding sequence D is output without repeating the decoding. If an error is detected as a result of the CRC determination, the decoding is further repeated. For example, when the CRC calculation value matches the CRC value included in the decoded sequence D, the CRC determination unit 16 outputs the decoded sequence D as no error. If the CRC calculation value and the CRC value do not match, the fact that an error has been detected is output to the first decoder 11. Then, the first decoder 11 and the second decoder 12 further repeat decoding while an error is detected.

  Next, after decoding is repeated N times, similarly to FIG. 3, a hard decision is made on the log likelihood ratio L output from the first decoder 11, the decoded sequence D is CRC-determined, and the decoded sequence D Is output.

  As described above, in this embodiment, the logarithmic likelihood ratio L output by decoding the first element code E in the first decoder is hard-decided and CRC-determined, so that external information is stored as in the conventional case. Compared with the case of hard decision and CRC decision, the accuracy of repeated control is improved. That is, since CRC determination is performed based on the log likelihood ratio L for actually obtaining a decoded sequence, the reliability of error detection by CRC determination is increased, and the number of decoding iterations can be more accurately reduced. Therefore, it is possible to shorten the time for decoding processing and reduce power consumption.

  Further, since the log likelihood ratio L output from the first decoder is hard-decided as it is and the CRC decision is made, deinterleaving processing is unnecessary, and the decoding processing time can be further shortened. In particular, the CRC determination in the repetitive control is performed each time it is repeated, so that the greater the number of repetitions, the greater the effect of time reduction.

  Here, simulation results of the decoding device and the decoding method according to the present embodiment will be described with reference to FIGS. 6 and 7.

  FIG. 6 shows the code error rate characteristics of the decoding apparatus. The horizontal axis in FIG. 6 indicates Eb / N0. Eb / N0 is a signal-to-noise ratio (SNR), which is a ratio of signal energy Eb per bit to white noise power density N0 per band. When Eb / N0 is a small value, the noise component is larger, and when Eb / N0 is a large value, the noise component is smaller. The vertical axis in FIG. 6 indicates a bit unit error rate (Bit Error Rate) and a block unit error rate BLER (BLOCK Error Rate) including a plurality of bits.

  In FIG. 6, (a-1) is the BER characteristic of Conventional Example 1 (FIGS. 9 and 11), that is, the BER characteristic when the number of repetitions is fixed. (B-1) is the BER characteristic of Conventional Example 2 (FIGS. 12 and 13), and (c-1) is the BER characteristic of the present embodiment (FIGS. 4 and 5). (A-2) is the BLER characteristic of Conventional Example 1, (b-2) is the BLER characteristic of Conventional Example 2, and (c-2) is the BLER characteristic of this embodiment.

  As shown in the figure, in the conventional example 1, the conventional example 2, and the present embodiment, the BER characteristic and the BLER characteristic show substantially the same characteristics. This is because the error rate characteristic improves each time decoding is repeated, and therefore, when decoding is repeated to some extent, all examples exhibit similar characteristics.

  FIG. 7 shows the number of repetitions of the decoding process in the code error rate characteristic of FIG. That is, the number of repetitions at each Eb / N0. In FIG. 7, (a) shows the number of repetitions of Conventional Example 1, (b) shows the number of repetitions of Conventional Example 2, and (c) shows the number of repetitions of this embodiment.

In FIG. 6, all examples showed similar characteristics. However, as shown in FIG. 7, the number of decoding iterations is different in each example. As shown in FIG. 7, in Conventional Example 1, the number of repetitions is fixed to 8 times for any Eb / N0. Conventional example 2 has a smaller number of repetitions than conventional example 1, and decreases from about 8 times to about 4.5 times as Eb / N0 increases. In the present embodiment, the number of repetitions is the smallest, and the number of repetitions decreases from about 7.5 to about 3.5 as Eb / N0 increases. For example, if BLER = 10 ⁻² is used as a reference, Eb / N0 at this time is 0.8 from FIG. From FIG. 7, the number of repetitions of Eb / N0 = 0.8 dB is about 5.5 in Conventional Example 2, whereas this embodiment is about 4 times. That is, it can be seen that the average 1.5 times (about 27%) of decoding processing can be reduced.

Other Embodiments of the Invention
In the above example, the example in which the decoding of the second element code E ′ and the decoding of the first element code E are repeated has been described. However, the present invention is not limited to this, and the logarithmic likelihood output from the first decoder is not limited. Any configuration may be used as long as the degree ratio is determined hard.

  Further, in the above-described example, the example of iterative decoding using two decoders has been described. However, the present invention is not limited to this, and it may be repeatedly decoded using an arbitrary number of decoders.

  In addition, various modifications and implementations are possible without departing from the scope of the present invention.

It is a block diagram which shows the structure of the decoding apparatus concerning this invention. It is a block diagram which shows the structure of the decoder concerning this invention. It is a figure for demonstrating the decoding method concerning this invention. It is a block diagram which shows the structure of the decoding apparatus concerning this invention. It is a figure for demonstrating the decoding method concerning this invention. It is a graph which shows the simulation result of the decoding apparatus concerning this invention. It is a graph which shows the simulation result of the decoding apparatus concerning this invention. It is a block diagram which shows the structure of a general encoding apparatus. It is a block diagram which shows the structure of the conventional decoding apparatus. It is a figure which shows an example of the trellis diagram used with a general decoder. It is a figure for demonstrating the conventional decoding method. It is a block diagram which shows the structure of the conventional decoding apparatus. It is a figure for demonstrating the conventional decoding method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Decoding apparatus 11 1st decoder 12 2nd decoder 13 Interleaver 14 Deinterleaver 15 Hard decision part 16 CRC decision part 21, 21 'Forward process part 22, 22' Backward process part 23, 23 'Memory 24, 24 'external information calculation unit

Claims (3)

Perform first decoding by calculating α and β path metrics,
Perform the second decoding by calculating the α and β path metrics,
A decoding method in which the first decoding and the second decoding are alternately repeated,
In the first decoding, after calculating the β path metric, the α path metric is calculated;
In the second decoding, the α path metric is calculated before calculating the β path metric.   The decoding method according to claim 1, wherein a hard decision is made based on the soft output data generated by the first decoding. In the first decoding, a first element code obtained by encoding an information sequence is decoded,
3. The decoding method according to claim 2, wherein in the second decoding, a second element code obtained by interleaving the encoded information sequence is decoded.

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