JP2013165338A - Decoding device and decoding method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain decoding characteristics of LDPC code in good shape depending on the condition of a propagation path, and also decode LDPC code with a small calculation amount.SOLUTION: A decoding device comprises: a decoder which decodes Low Density Parity Check (LDPC) code on the basis of a Sum-Product decoding method; a counter which, at decoding time, performs a count operation depending on whether an error was detected as the result of parity check by a check matrix; and an adjustment unit which adjusts the code length of LDPC code in an LDPC code encoder and decoder according to the count value of the counter.

Description

  The present invention relates to a decoding device, a decoding method, and a program, and more particularly, to a decoding device, a decoding method, and a program based on a low-density parity-check (LDPC) code.

  When decoding an LDPC code, increasing the code length is known to improve the decoding characteristics but increase the amount of calculation. An LDPC code having a sufficiently long code length has decoding characteristics close to the Shannon limit, but the amount of calculation becomes enormous as the code length increases. That is, there is a trade-off between decoding characteristics and calculation amount.

  Patent Document 1 describes a technique for reducing the calculation amount of the entire decoding apparatus by reducing the calculation amount of a check node for Sum-Product decoding of LDPC code data.

  Patent Document 2 describes a technique for performing LDPC code processing by dynamically changing a coding rate in accordance with a line state.

  Furthermore, Patent Document 3 describes a technique for determining the coding rate of a modulated signal to be transmitted based on the communication status.

JP 2008-167357 A JP 2008-153760 A JP 2010-252369 A

  The following analysis was made by the present inventors.

  The LDPC code not only has a decoding characteristic close to the Shannon limit, but also has an advantage that decoding can be performed in linear time with respect to the code length. However, decoding of an LDPC code only allows decoding in a linear time with respect to the code length based on parallel processing and a sparse matrix, so that the amount of calculation becomes enormous as the code length increases. Further, since the LDPC code has a better decoding characteristic as the code length is longer, the decoding characteristic and the calculation amount have a trade-off relationship with the code length. Therefore, it is necessary to set a code length in consideration of the balance between decoding characteristics and calculation amount.

  Patent Documents 2 and 3 also describe a technique for dynamically changing a coding rate based on a line state or a communication state. However, according to these techniques, there is a possibility that the quality of the line state and the communication state cannot be properly determined.

  Therefore, it becomes a problem to decode the LDPC code with a small amount of calculation while maintaining good decoding characteristics of the LDPC code according to the state of the propagation path. An object of the present invention is to provide a decoding device, a decoding method, and a program for solving such a problem.

The decoding device according to the first aspect of the present invention provides:
A decoder that decodes a low-density parity-check (LDPC) code based on a Sum-Product decoding method;
A counter that performs a counting operation according to whether or not an error is detected as a result of parity check using a check matrix during the decoding; and
And an adjustment unit that adjusts the code length of the LDPC code in the LDPC code encoder and the decoder in accordance with the count value of the counter.

The decoding method according to the second aspect of the present invention is:
Decoding a low density parity check (LDPC: Low-Density Parity-Check) code based on a Sum-Product decoding method;
A step of performing a counting operation according to whether an error is detected as a result of parity check by a check matrix during the decoding; and
Adjusting the code length of the LDPC code in the LDPC code encoder and decoder according to the count value of the counter.

The program according to the third aspect of the present invention is:
A process of decoding a low density parity check (LDPC: Low-Density Parity-Check) code based on a Sum-Product decoding method;
A process of performing a counting operation according to whether or not an error is detected as a result of parity check using a check matrix during the decoding;
Processing for adjusting the code length of the LDPC code in the encoder and decoder of the LDPC code according to the count value of the counter is executed by a computer.

  Here, the program may be recorded on a non-transient computer-readable recording medium.

  According to the decoding apparatus, the decoding method, and the program according to the present invention, it is possible to decode the LDPC code with a small amount of calculation while keeping the decoding characteristic of the LDPC code good according to the condition of the propagation path. .

It is a block diagram which shows the structure of the decoding apparatus which concerns on 1st and 2nd embodiment as an example. It is a flowchart which shows the operation | movement of the decoding based on the Sum-Product decoding method. It is a flowchart which shows the operation | movement of the decoding apparatus which concerns on 1st Embodiment as an example. It is a flowchart which shows operation | movement of the decoding apparatus which concerns on 2nd Embodiment as an example.

  First, the outline of the present invention will be described. Note that the reference numerals of the drawings attached to this summary are merely examples for facilitating understanding, and are not intended to limit the present invention to the illustrated embodiment.

  The present invention changes the code length of an LDPC code based on a decoding result of a Sum-Product decoding method which is a decoding method of an LDPC (Low-Density Parity-Check) code.

  Specifically, the quality of the propagation path is estimated based on the result of parity check in the Sum-Product decoding method used for the LDPC code, and the propagation path is good (that is, the decoding characteristics may be reduced). The amount of calculation is reduced by shortening the code length. On the other hand, when the propagation path is inferior (that is, the decoding characteristic should be improved), the decoding characteristic is ensured by increasing the code length, although the calculation amount increases. In this manner, the code length is changed to an appropriate code length according to the propagation environment.

  Referring to FIG. 1, the decoding apparatus (10) includes a decoder (11) for decoding a low density parity check LDPC code based on a Sum-Product decoding method, and a parity check matrix in decoding. A counter (12) that performs a counting operation according to whether or not an error is detected as a result of the check, and a code length of the LDPC code in an LDPC code encoder (not shown) and decoder (11) And an adjustment unit (13) that adjusts according to the count value of (12).

Referring to FIG. 3, when no error is detected as a result of the parity check (OK in step S12), the counter (12) performs a counting operation on the first count value (C _S ) (step S15). ) When the parity check is repeated over the maximum number of iterations (L _max ) in the Sum-Product decoding scheme (YES in step S14), when an error is detected as a result of the parity check (NG in step S12), When the second count value (C _L ) is counted (step S18), the adjustment unit (13) has the first count value (C _S ) at the predetermined first value (C _Smax ). the (YES in step S16), and with a shorter code length (step S17), the second count value _{(C L)} is given If became second value _{(C Lmax)} may be (YES at step S19), and code length (step S20).

Referring to FIG. 3, when the first count value (C _S ) becomes a predetermined first value (C _Smax ) (YES in step S16), the counter (12) is configured to receive the second count value. When (C _L ) becomes a predetermined second value (C _Lmax ) (YES in step S19), the first count value (C _S ) and the second count value (C _L ) are initialized. You may make it carry out (step S17, S20).

Referring to FIG. 4, in the case where no error is detected as a result of the parity check (OK in step S25), the counter (12) has the number of repeated parity checks less than a predetermined third value (L _C ). (YES in step S28), the counting operation for the first count value (C _S ) may be performed (step S29).

According to the decoding device (10) of the present invention, the counter (12) performs a counting operation according to the result of the parity check by the decoder (11), so that the quality of the propagation path can be grasped properly. it can. The adjustment unit (13) shortens or lengthens the code length according to the count values (C _S , C _L ) of the counter (12). Therefore, according to the decoding apparatus (10), it is possible to decode the LDPC code with a small amount of calculation while maintaining good decoding characteristics of the LDPC code according to the condition of the propagation path. In addition, according to the decoding device (10) of the present invention, it is possible to properly grasp the quality of a propagation path by adding a count operation to a slight calculation load, that is, a flow of the Sum-Product decoding method. It becomes possible.

In the present invention, the following modes are possible.
[Form 1]
The decoding apparatus according to the first aspect is as described above.
[Form 2]
When no error is detected as a result of the parity check, the counter performs a count operation on the first count value and repeats the parity check for the maximum number of iterations in the Sum-Product decoding scheme. When an error is detected as a result of the parity check in, a count operation is performed on the second count value,
When the first count value becomes a predetermined first value, the adjustment unit shortens the code length and the second count value becomes a predetermined second value. Alternatively, the code length may be increased.
[Form 3]
When the first count value becomes the predetermined first value, or when the second count value becomes the predetermined second value, the counter The count value and the second count value may be initialized.
[Form 4]
The counter performs a counting operation on the first count value when the number of times the parity check is repeated is less than a predetermined third value when no error is detected as a result of the parity check. You may do it.
[Form 5]
The decoding method according to the second viewpoint is as described above.
[Form 6]
In the decoding method, when no error is detected as a result of the parity check, a count operation is performed on the first count value, and the parity check is repeated over the maximum number of iterations in the Sum-Product decoding scheme. In the case where an error is detected as a result of the parity check in the case, the count operation for the second count value is performed,
When the first count value becomes a predetermined first value, the code length is shortened, and when the second count value becomes a predetermined second value, the code The length may be increased.
[Form 7]
In the decoding method, when the first count value becomes the predetermined first value, or when the second count value becomes the predetermined second value, The count value of 1 and the second count value may be initialized.
[Form 8]
In the decoding method, when no error is detected as a result of the parity check, the count operation for the first count value is performed when the number of times the parity check is repeated is less than a predetermined third value. May be performed.
[Form 9]
The program is related to the third viewpoint.
[Mode 10]
In the above program, when no error is detected as a result of the parity check, a count operation is performed on the first count value, and the parity check is repeated over the maximum number of iterations in the Sum-Product decoding scheme. When an error is detected as a result of the parity check in, a count operation is performed on the second count value,
When the first count value becomes a predetermined first value, the code length is shortened, and when the second count value becomes a predetermined second value, the code The length may be increased.
[Form 11]
In the above program, when the first count value becomes the predetermined first value, or when the second count value becomes the predetermined second value, the first count value The count value and the second count value may be initialized.
[Form 12]
In the above program, when no error is detected as a result of the parity check, when the number of repetitions of the parity check is less than a predetermined third value, a count operation is performed on the first count value. You may do it.

(Embodiment 1)
A decoding apparatus according to the first embodiment will be described with reference to the drawings. FIG. 1 is a block diagram illustrating an example of the configuration of the decoding device 10 according to the present embodiment. Referring to FIG. 1, the decoding device 10 includes a decoder 11, a counter 12, and an adjustment unit 13.

The decoder 11 decodes the LDPC encoded data based on the Sum-Product decoding method. The Sum-Product decoding method is an iterative decoding method, and when the temporary estimated word obtained by the decoding process does not pass the parity check, a decoding method for deriving the temporary estimated word by calculating again using the calculation result in the decoding process It is. This repetition is performed up to the maximum number of repetitions L _max . If the parity check is passed in the middle of the repetition, the decoding process ends at that point.

The counter 12 performs a counting operation according to whether or not an error is detected as a result of parity check using a check matrix during decoding by the decoder 11. The decoding apparatus 10 feeds back the result of the parity check to the Sum-Product decoding method and changes the length of the code length. For this reason, the counter 12 holds count values C _L and C _S that count the success or failure of the parity check. Counter 12, if that failed parity check be performed repeatedly for the maximum iteration number counts the count value C _L. On the other hand, the counter 12, when passing through the parity check counts the count value C _S. Although the case where the counter 12 increments the count value will be described here, the counter 12 may decrement the count value. The counter 12 preferably resets the count values C _L and C _S to 0 at regular time intervals.

The adjusting unit 13 adjusts the code length of the LDPC code in the LDPC code encoder (not shown) and the decoder 11 according to the count value of the counter 12. When the count value _CL becomes equal to or greater than a certain value, the adjustment unit 13 determines that the propagation path is inferior and increases the code length. On the other hand, when the count value _CS becomes a certain value or more, the adjustment unit 13 determines that the propagation path is good and shortens the code length. The maximum code length is preferably set to a predetermined value in advance.

  Next, the operation of the decoding device 10 will be described with reference to the drawings.

  First, the operation of the decoder 11 will be described. FIG. 2 shows a flow of a decoding process based on the Sum-Product method by the decoder 11.

  Referring to FIG. 2, after receiving the LDPC code, the decoder 11 initializes parameters used for decoding calculation (step S1). For example, the decoder 11 sets the number of iterations L = 0.

  Next, after performing row processing (step S2) and column processing (step S3), the decoder 11 calculates a temporary estimated word using these results (step S4).

  Next, the decoder 11 performs a parity check on the obtained temporary estimated word using a parity check matrix (step S5). If the result of the parity check is OK (OK in step S5), the decoder 11 outputs the temporary estimated word as an estimated word.

On the other hand, when the result of the parity check is NG (NG in step S5), the decoder 11 increments (+1) the number of iterations L (step S6), and then the number of iterations L is the maximum number of iterations L _max. (Step S7).

When the number of iterations L has not reached the maximum number of iterations _{L max} (NO in step S7), and returns to the decoder 11 the row processing (step S2), and performs the calculations again. On the other hand, if the parity check is not passed even if the maximum number of repetitions L _max is repeated (YES in step S7), the decoder 11 gives up decoding and outputs the temporary estimated word at that time as an estimated word. To do.

  Next, the overall operation of the decoding apparatus 10 will be described with reference to the drawings. FIG. 3 is a flowchart showing an operation of the decryption apparatus 10 as an example. FIG. 3 corresponds to the flow of the Sum-Product decoding method shown in FIG. 2 with a process of feeding back the result of parity check and changing the length of the code length.

The operations in steps S8 to S14 in FIG. 3 are the same as the operations in steps S1 to S7 in FIG. The counter 12 sets the count values C _L and C _S to 0 in advance. These two count values C _L and C _S are not manipulated in the initialization of step S8.

Referring to FIG. 3, when passing through the check in the parity check (OK in step S12), the counter 12 counts the count value C _S (step S15), and the count value C _S becomes constant value greater than or equal In this case (YES in step S16), the adjustment unit 13 shortens the LDPC code length and resets the count values C _L and C _S to 0 (step S17).

On the other hand, (YES in step S14) if the number of iterations L has reached the maximum number of iterations _{L max,} the counter 12 counts the count value _{C L} (step S18), and the count value _{C L} constant value greater than or equal If it becomes (YES in step S19), the adjustment unit 13 increases the LDPC code length and resets the count values C _L and C _S to 0 (step S20).

  According to the decoding apparatus 10 of the present embodiment, by using the result of the parity check, the decoding characteristic is improved by increasing the code length when the propagation path environment is bad, and the code length is shortened when the propagation path environment is good. By doing so, it is possible to reduce the amount of calculation.

(Embodiment 2)
A decoding apparatus according to the second embodiment will be described with reference to the drawings.

As in the decoding device 10 of the first embodiment, when the communication path is determined to be good only after passing the parity check, the propagation environment is as in the case where the iteration close to the maximum number of iterations L _max is performed. Even if it is somewhat deteriorated, the communication path is determined to be good, and the adjustment unit 13 may shorten the code length. At this time, there is a possibility that the decoder 11 fails to decode due to the deterioration of the decoding characteristics due to the shortening of the code length, and the code length is increased again by the adjustment unit 13. When such a situation occurs, the transmission rate also decreases due to retransmission or the like due to decoding failure. The decoding apparatus according to the present embodiment avoids such a situation.

  FIG. 4 is a flowchart showing an example of the operation of the decoding apparatus according to this embodiment. The operations in steps S21 to S27 in FIG. 4 are the same as the operations in steps S1 to S7 shown in FIG. Further, the operations in steps S29 to S31 in FIG. 4 are the same as the operations in steps S15 to S17 shown in FIG.

In FIG. 4, the conditions for shortening the code length of the LDPC code of the method shown in FIG. 3 are changed. More specifically, only when the number of iterations L is less than a predetermined number of times _{L c} (YES in step S28), and is changed to proceed to the procedure of Step S29～S31. Therefore, in the decoding device 10 of this embodiment, the counter 12 determines that the propagation path is good when the number of repetitions is less than L _c and passes the parity check (YES in step S28). As long as the count operation is performed (step S29).

  According to the decoding device 10 of the present embodiment, it is possible to avoid the phenomenon that the code length is shortened more than necessary as described above.

  Various modifications can be made to the decoding device 10 according to the first embodiment and the second embodiment described above. As an example, it is possible not only to reflect the result of the parity check in the code length but also to reflect in the coding rate or the like, thereby selecting the decoding characteristic and transmission rate according to the propagation path environment.

  It should be noted that the disclosures of prior art documents such as the above patent documents are incorporated herein by reference. Within the scope of the entire disclosure (including claims) of the present invention, the embodiments and examples can be changed and adjusted based on the basic technical concept. Further, various combinations or selections of various disclosed elements (including each element of each claim, each element of each embodiment, each element of each drawing, etc.) are possible within the scope of the claims of the present invention. It is. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the entire disclosure including the claims and the technical idea.

DESCRIPTION OF SYMBOLS 10 Decoding apparatus 11 Decoder 12 Counter 13 Adjustment part

Claims (10)

A decoder that decodes a low-density parity-check (LDPC) code based on a Sum-Product decoding method;
A counter that performs a counting operation according to whether or not an error is detected as a result of parity check using a check matrix during the decoding; and
A decoding apparatus comprising: an LDPC code encoder; and an adjustment unit that adjusts a code length of the LDPC code in the decoder according to a count value of the counter. When no error is detected as a result of the parity check, the counter performs a count operation on the first count value and repeats the parity check for the maximum number of iterations in the Sum-Product decoding scheme. When an error is detected as a result of the parity check in, a count operation is performed on the second count value,
When the first count value becomes a predetermined first value, the adjustment unit shortens the code length and the second count value becomes a predetermined second value. The decoding apparatus according to claim 1, wherein the code length is increased.   When the first count value becomes the predetermined first value, or when the second count value becomes the predetermined second value, the counter The decoding apparatus according to claim 2, wherein a count value and the second count value are initialized.   The counter performs a counting operation on the first count value when the number of times the parity check is repeated is less than a predetermined third value when no error is detected as a result of the parity check. The decoding device according to claim 2 or 3, wherein Decoding a low density parity check (LDPC: Low-Density Parity-Check) code based on a Sum-Product decoding method;
A step of performing a counting operation according to whether an error is detected as a result of parity check by a check matrix during the decoding; and
Adjusting the code length of the LDPC code in the encoder and decoder of the LDPC code in accordance with the count value of the counter. If no error is detected as a result of the parity check, a count operation is performed on the first count value, and the parity check is performed when the parity check is repeated over the maximum number of iterations in the Sum-Product decoding scheme. When an error is detected as a result of the above, the count operation for the second count value is performed,
When the first count value becomes a predetermined first value, the code length is shortened, and when the second count value becomes a predetermined second value, the code 6. The decoding method according to claim 5, wherein the length is increased.   When the first count value becomes the predetermined first value, or when the second count value becomes the predetermined second value, the first count value and the The decoding method according to claim 6, wherein the second count value is initialized.   When no error is detected as a result of the parity check, a count operation is performed on the first count value when the number of times the parity check is repeated is less than a predetermined third value. The decoding method according to claim 6 or 7. A process of decoding a low density parity check (LDPC: Low-Density Parity-Check) code based on a Sum-Product decoding method;
A process of performing a counting operation according to whether or not an error is detected as a result of parity check using a check matrix during the decoding;
A program for causing a computer to execute a process of adjusting a code length of an LDPC code in an encoder and a decoder of the LDPC code according to a count value of the counter. If no error is detected as a result of the parity check, a count operation is performed on the first count value, and the parity check is performed when the parity check is repeated over the maximum number of iterations in the Sum-Product decoding scheme. When an error is detected as a result of the above, the count operation for the second count value is performed,
When the first count value becomes a predetermined first value, the code length is shortened, and when the second count value becomes a predetermined second value, the code The program according to claim 9, wherein the length is increased.

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