CN1996765A - An iterative decoder and iterative decoding method - Google Patents

Abstract

This invention provides one integrate codes and its coding method, which comprises first coder, first cross device, second cross, second coder and decors device. The method comprises the following steps: using first known information to code first and added information sequence to get proximate information as first outside information; processing the first cross to get second outside information; processing the first information sequence to get second information sequence; using second outer information as first known information to code second information sequence and added to get proximately information as third outer information.

Description

A kind of iterative decoder and interative encode method

Technical field

The present invention relates to the decoder technical field, specifically, relate to a kind of iterative decoder and interative encode method.

Background technology

Channel coding technology is a ring important in the communication system, 802.16 in the agreement, provided the correlation technique of system channel coding, CTC (Convolutional Turbo codes, CTC) is wherein a kind of possibility, the basic principle that it adopts Turbo code realizes iterative decoding with dual input circulation RSC code (RecursiveSystematic Convolutional codes, recursive systematic convolutional code) as component code.

Iterative decoder is by two SISO (Soft Input Soft Output in the prior art, soft inputting and soft output) decoder is that a SISO decoder and the 2nd SISO decoder are composed in series, the one SISO decoder carries out optimal decoding to component code RSC1, even decoder output error probability minimum, generation is about the likelihood ratio information of each bit of information sequence, and general's external information wherein, promptly through the likelihood ratio information of each bit of the information sequence that obtains after the SISO decoder for decoding, send the 2nd SISO decoder to through after interweaving, the 2nd SISO decoder will be through the external information after interweaving as prior information, component code RSC2 is carried out optimal decoding, produce likelihood information through each bit of the information sequence after interweaving, send external information wherein to a SISO decoder through after the deinterleaving then, a SISO decoder is deciphered described external information to component code as prior information next time.Like this, through iteration repeatedly, the external information of the one SISO decoder and the 2nd SISO decoder tends towards stability, the likelihood ratio asymptotic value approaches the maximum-likelihood decoding to whole sign indicating number, then this likelihood ratio is carried out hard decision, can obtain the right optimum evaluation sequence of each bit of information sequence, the 2nd SISO decoder is exported the right optimum evaluation sequence of each bit of this information sequence.

At present, a kind of iterative decoder of the prior art, as shown in Figure 1, a SISO decoder receives prior information to information sequence ABY ₁W ₁Decipher, obtain information sequence ABY ₁W ₁First external information of each bit, described first external information is a likelihood ratio information, wherein information sequence W ₁Y ₁Be the additional information sequence of first encoder output of a SISO decoder correspondence, make data in the Channel Transmission process, reduce interference.

Wherein decoder carries out in the iterative decoding process, and the prior information that receives when a SIS0 decoder carries out deciphering for the first time is initial prior information, is preset value 0;

The first interleaver received information sequence AB at first exchanges the data in the sequence, is j=0 for sequence number for example, and 1 ..., the A of N-1 ₀, A ₁, B ₁..., A _N-1, B ₀, B ₁..., B _N-1Sequence is when j is odd number, with (the A among the sequence A B _j, B _j) exchange, make (A _j, B _j)=(B _j, A _j); First interleaver carries out output information sequence A after the interleaving treatment to data then ' B ' gives the 2nd SISO decoder.

Second interleaver receives first external information and handles back output second external information to the 2nd SISO decoder, the concrete processing with first interleaver.

Then, the 2nd SISO decoder receives second external information as prior information, to information sequence A ' B ' Y ₂W ₂Decipher, wherein information sequence Y ₂W ₂Be the additional information sequence of second encoder output of the 2nd SISO decoder correspondence, make data in the Channel Transmission process, reduce interference.Information sequence A ' B ' the Y that decoding is obtained ₂W ₂The likelihood ratio information of each bit export to deinterleaver as the 3rd external information, described external information equals information sequence A ' B ' Y ₂W ₂The log-likelihood ratio of each bit deduct described prior information and deduct channel value again, described prior information is the external information that a SISO decoder for decoding obtains, described channel value by a described SISO decoder to described information sequence A ' B ' Y ₂W ₂Decipher and obtain.

Described deinterleaver carries out deinterleaving to the 3rd external information of described second decoder output to be handled, exchange the data in the sequence after, first decoder is given in output the information all round.

Described first decoder with described all round information as prior information again to information sequence ABY ₁W ₁Decipher.Through iteration repeatedly, the external information of a SISO decoder and the 2nd SISO decoder tends towards stability, and the likelihood ratio asymptotic value approaches the maximum-likelihood decoding to whole sign indicating number, and then the 2nd SISO decoder utilizes second external information, and conversion obtains information sequence A ' B ' Y ₂W ₂The likelihood information of each bit, obtain posterior probability by likelihood information, and decipher judgement according to maximum posteriori criterion, and can obtain the right optimum evaluation sequence of each bit of information sequence, the 2nd SISO decoder is exported the right optimum evaluation sequence of each bit of this information sequence

The likelihood ratio information of each bit of the information sequence that the upper level decoder obtains decoding in the interative encode method that prior art adopts is exported as external information, the next stage decoder receives the external information of upper level decoder output, after being likelihood ratio information, likelihood ratio information is deciphered as prior information, likelihood ratio information need be converted operation during decoding and obtain likelihood information, could obtain posterior probability by likelihood information, decipher judgement and obtain deciphering output sequence.This has increased the workload of decoder, and in product development process, need carry out fixed point, promptly need the floating-point variable in the floating-point emulation in the development process is converted into integer variable in the fixed-point simulation product, have some losss of significance like this, influence the performance of iterative decoder.

Summary of the invention

The invention provides a kind of iterative decoder and interative encode method, when the next stage decoder adopts the external information of upper level decoder transmission to decipher as prior information, do not need to convert operation and just can obtain likelihood information, reduced the workload of decoder.

The present invention is achieved in that a kind of iterative decoder, comprises first decoder, second decoder, first interleaver, second interleaver and deinterleaver;

Described first decoder receives prior information the first information sequence and the additional information sequence thereof of input is deciphered, and the described first information sequence that decoding is obtained and the likelihood information of additional information sequence thereof are exported to second interleaver as first external information;

After described second interleaver carries out interleaving treatment to described first external information, export second external information and give second decoder;

After described first interleaver carries out interleaving treatment to described first information sequence, export second information sequence and give second decoder;

Described second decoder receives described second external information and as prior information described second information sequence and the additional information sequence thereof of input is deciphered, described second information sequence that decoding is obtained and the likelihood information of additional information sequence thereof are exported to deinterleaver as the 3rd external information, and when the external information of first decoder and second decoder tends towards stability, likelihood information is carried out hard decision, obtain the optimum evaluation sequence and the output of first information sequence;

After described deinterleaver carried out deinterleaving and handles described the 3rd external information, output the information all round gave first decoder as the prior information that first information sequence and additional information sequence thereof are deciphered.

The prior information that receives when described first decoder carries out deciphering for the first time is initial prior information.

Described initial prior information is a preset value 0.

Described interleaver comprises order Switching Module and interleaving block;

The data that described order Switching Module is used for receiving are carried out the internal order exchange of data;

Described interleaving block is used for the data of handling through described order Switching Module are carried out interleaving treatment.

Described deinterleaver comprises order Switching Module and de-interleaving block;

Described de-interleaving block is used for that the data that receive are carried out deinterleaving to be handled;

Described order Switching Module is used for the data of handling through described deinterleaver are carried out the internal order exchange of data.

Described decoder is the SISO decoder.

A kind of interative encode method may further comprise the steps:

Utilize prior information that the first information sequence and the additional information sequence thereof that receive are deciphered, the first information sequence that decoding is obtained and the likelihood information of additional information sequence thereof are as first external information;

Described first external information is carried out interleaving treatment obtain second external information;

Described first information sequence is carried out interleaving treatment obtain second information sequence;

Utilize described second external information as prior information second information sequence and the additional information sequence thereof that receive to be deciphered, described second information sequence that decoding is obtained and the likelihood information of additional information sequence thereof are as the 3rd external information;

Described the 3rd external information is carried out deinterleaving handle the information all round that obtains.

With described all round information as the prior information that described first information sequence and additional information sequence thereof are deciphered;

When each external information tends towards stability, the likelihood information of described second information sequence and additional information sequence thereof is carried out hard decision, obtain the optimum evaluation sequence and the output of first information sequence.

The prior information that receives when first decoder carries out deciphering for the first time is initial prior information.

Described initial prior information is a preset value 0.

Described interleaving treatment is specially: after the data that receive are carried out the internal order exchange of data, data are carried out interleaving treatment respectively.

Described deinterleaving is handled and is specially: after the data that receive are carried out the deinterleaving processing respectively, data are carried out the internal order exchange of data.

The present invention exports as external information by the likelihood information of the information sequence that the upper level decoder obtains decoding, the next stage decoder directly utilizes through the external information behind the interleaving/deinterleaving and deciphers as prior information, need be when making decoder for decoding through the conversion operation, reduced the workload of decoder, and when fixed point, made the stable performance of iterative decoder.

Description of drawings

Fig. 1 is the structural representation of the iterative decoder of prior art;

Fig. 2 is the structural representation of the embodiment of the invention.

Embodiment

The invention provides a kind of iterative decoder and interative encode method, make the likelihood information of the information sequence that the upper level decoder obtains decoding export to the next stage decoder as external information, the next stage decoder is deciphered this external information as prior information, reduced the workload of decoder.

Adopt the SISO decoder below in conjunction with Fig. 2 with first decoder and second decoder, receiving four tunnel prior informations is concrete iterative decoder provided by the invention and the interative encode method of setting forth of example.Adopting four tunnel priori is preferred version of the present invention, because the number of bits of the each input coding device of CTC is two bits in 802.16 agreements, these two than peculiar four kinds of possible values, has determined that the each likelihood information number of transmitting of decoder is four.The each likelihood information number of transmitting of decoder also can be other numbers.

As shown in Figure 2, a kind of iterative decoder provided by the invention comprises a SISO decoder, the 2nd SISO decoder, first interleaver, second interleaver and deinterleaver.Wherein a SISO decoder, second interleaver, the 2nd SISO decoder, deinterleaver, a SISO decoder are connected successively.

A described SISO decoder receives prior information L _E0 L _E1 L _E2 L _E3 is to information sequence ABY ₁W ₁Decipher, and the information sequence ABY that decoding is obtained ₁W ₁The likelihood information of each bit export to second interleaver as first external information, information sequence Y wherein ₁W ₁Be the additional information sequence of first information sequence A B, by corresponding first encoder output of a SISO decoder, additional information sequence Y ₁W ₁Main effect be to make data in the Channel Transmission process, reduce interference;

Decoder carries out in the iterative decoding process, and the prior information that receives when a SISO decoder carries out deciphering for the first time is initial prior information, is preset value 0;

Described second interleaver is to the first external information L of described first decoder output _E0L _E1L _E2L _E3After carrying out interleaving treatment, export the second external information L _E0' L _E1' L _E2' L _E3' to described the 2nd SISO decoder;

After described first interleaver carries out interleaving treatment to first information sequence A B, export the second information sequence A ' B ' and give second decoder;

Described the 2nd SISO decoder receives the second external information L of described second interleaver output _E0' L _E1' L _E2' L _E3' as prior information, to the information sequence A'B ' Y of input ₂W ₂Decipher, wherein information sequence Y ₂W ₂Be the additional information sequence of the second information sequence A ' B ', by corresponding second encoder output of the 2nd SISO decoder, additional information sequence Y ₂W ₂Main effect be to make data in the Channel Transmission process, reduce interference, the information sequence A'B ' Y that decoding is obtained ₂W ₂The likelihood information of each bit as the 3rd external information L _E0" L _E1" L _E2" L _E3" export to deinterleaver, and when the external information of a SISO decoder and the 2nd SISO decoder tended towards stability, the likelihood information that the 2nd SISO decoder for decoding is obtained carried out hard decision, obtained the optimum evaluation sequence of information sequence AB And output

Described deinterleaver is to the 3rd external information L of described second decoder output _E0" L _E1" L _E2" L _E3" after carrying out deinterleaving and handling, output the is information L all round _E0 L _E1 L _E2 L _E3 gives first decoder;

Described first decoder receives the information L all round of described deinterleaver output _E0 L _E1 L _E2 L _E3 as prior information to information sequence ABY ₁W ₁Decipher.

Second interleaver in the wherein said iterative decoder comprises order Switching Module and interleaving block; The data that described order Switching Module is used for receiving are carried out the internal order exchange of data; Described interleaving block is used for the data of handling through described order Switching Module are carried out interleaving treatment.

Deinterleaver in the described iterative decoder comprises order Switching Module and de-interleaving block; Described de-interleaving block is used for that the data that receive are carried out deinterleaving to be handled; Described order Switching Module is used for the data of handling through described deinterleaver are carried out the internal order exchange of data.

Following mask body is set forth interative encode method provided by the invention.

The decoding principle of at first introducing SISO component code decoder is:

If k two bits of input coding device constantly is d _k=(d _1k, d _2k), promptly decoding output result should be d when decoder for decoding is entirely true _k=(d _1k, d _2k), other establishes the decoder received signal is R _k={ x _1k, x _2k, y _1k, y _2k, wherein, x _1k, x _2kBe information bits, y _1k, y _2kBe check bit.Consider AWGN (Additive WhiteGaussian Noise, additive white Gaussian noise) channel, the noise average is 0, and variance is σ ²Under BPSK (Binary Phase Shift Keying, two-phase PSK) modulation system, decoder receives bit and is:

$x_{1k}=\sqrt{E_s}{u}_{1k}+n_1$

$x_{2k}=\sqrt{E_s}{u}_{2k}+n_2$

$y_{1k}=\sqrt{E_s}{v}_{1k}+n_3$

$y_{2k}=\sqrt{E_s}{v}_{2k}+n_4$

In the formula, u _1k, u _2kBe information bit x _1k, x _2kAverage, v _1k, v _2kBe respectively check bit y _1k, y _2kAverage.For representing conveniently to suppose signal energy normalization, i.e. E _s=1.

In order to obtain the likelihood information of each bit, at first define following three metric function:

Forward metrics: ${\stackrel{\‾}{\mathrm{\α}}}_k\left(S_k\right)\stackrel{\mathrm{\Δ}}{=}\ln P(R_k^{-},S_k)$

Back to tolerance: ${\stackrel{\‾}{\mathrm{\β}}}_{k+1}\left(S_{k+1}\right)\stackrel{\mathrm{\Δ}}{=}\ln P\left(R_k^{+}\right|S_{k+1})$

Branch metric: ${\stackrel{\‾}{\mathrm{\γ}}}_{k,k+1}(S_k,S_{k+1})\stackrel{\mathrm{\Δ}}{=}\ln P(S_{k+1},R_k|S_k)$

If joint probability is: APPi=lnP (d _k=i, R)

Joint probability ratio and posterior probability ratio are of equal value herein, because

APPi＝lnP(d _k＝i，R)＝lnP(d _k＝i|R)P(R)

In the formula, d _k=i, i=0,1,2,3 represent respectively current by d _1kd _2kFour kinds of possible binary system values 00,01,10,11 that are arranged in.Be expressed as follows with form:

d k	d 1kd 2k
		0	00
1	01
		2	10
3	11

Then can obtain four kinds of possible decoding output probability APP ₀, APP ₁, APP ₂, APP ₃,

At first, a SISO decoder receives prior information L _E0 L _E1 L _E2 L _E3 is to the information sequence ABY of input ₁W ₁Decipher, wherein information sequence Y ₁W ₁Be the additional information sequence of first information sequence A B, by corresponding first encoder output of a SISO decoder, additional information sequence Y ₁W ₁Main effect be to make data in the Channel Transmission process, reduce interference, and the external information in the likelihood information that decoding is obtained, the i.e. first external information L _EiExport to second interleaver;

Decoder carries out in the iterative decoding process, and the prior information that receives when a SISO decoder carries out deciphering for the first time is initial prior information, is preset value 0;

Second interleaver receives the first external information L of described SISO decoder output _E0L _E1L _E2L _E3And it is carried out the output second external information L after the interleaving treatment _E0' L _E1' L _E2' L _E3' be specially: at first, described interleaver carries out the internal order exchange of data to first external information, and promptly working as k is 1,3, and interleaver is with (L during odd numbers such as 5... _E1 ^k, L _E2 ^k) exchange, then, each circuit-switched data is carried out interleaving treatment respectively, promptly

$L_{e,i}^k=L_{e,P\left(i\right)}^k,i=\mathrm{0,1,2,3},$

Wherein P (i) is the position that interweaves;

First interleaver carries out output information sequence A after the interleaving treatment to information sequence AB ' B ' gives the 2nd SISO decoder, and be specially: at first exchanging the data in the sequence, is j=0 for sequence number for example, 1 ..., the A of N-1 ₀, A ₁, B ₁..., A _N-1, B ₀, B ₁..., B _N-1Sequence is when j is odd number, with (the A among the sequence A B _j, B _j) exchange, make (A _j, B _j)=(B _j, A _j); First interleaver carries out output information sequence A after the interleaving treatment to data then ' B '.

Then, the 2nd SISO decoder receives the second external information L of described second interleaver output _E0' L _E1' L _E2' L _E3' as prior information to information sequence A ' B ' Y ₂W ₂Decipher, wherein information sequence Y ₂W ₂Be the additional information sequence of the second information sequence A ' B ', by corresponding second encoder output of the 2nd SISO decoder, additional information sequence Y ₂W ₂Main effect be to make data in the Channel Transmission process, reduce interference.Obtain information sequence A ' B ' Y ₂W ₂The likelihood information of each bit, and described likelihood information exported to deinterleaver as the 3rd external information.Be specially: L _Ei=L _Ai, i.e. L _Ai=APPi-L _Ai-L _Ci, obtain information sequence A ' B ' Y thus ₂W ₂The likelihood information of each bit.

Deinterleaver receives the 3rd external information L of the 2nd SISO decoder output _E0" L _E1" L _E2" L _E3" and it is carried out deinterleaving handle back output the information L all round _E0 L _E1 L _E2 L _E3 gives a SISO decoder, is specially: at first, described deinterleaver carries out deinterleaving respectively to each circuit-switched data to be handled, promptly

$L_{e,p\left(i\right)}^k=L_{e,i}^k,i=\mathrm{0,1,2,3},$

Wherein P (i) is the position that interweaves,

Then, the 3rd external information is carried out the internal order exchange of data, promptly working as k is 1,3, and deinterleaver is with (L during odd numbers such as 5... _E1 ^k, L _E2 ^k) exchange;

The one SISO decoder is again with the information L all round of deinterleaver output _E0 L _E1 L _E2 L _E3, as the prior information of a SISO decoder to information sequence ABY ₁W ₁Decipher, obtain information sequence ABY ₁W ₁The posterior probability of each bit, posterior probability described herein is likelihood information,

APPi，i＝0，1，2，3，

And obtain first external information of a described SISO decoder thus

L _ei＝APPi-L _ai-L _ci， i＝0，1，2，3，

Wherein prior information is

L _ai＝lnP(d _k＝i)， i＝0，1，2，3，

Channel value is

L _ci＝lnP(x _1kx _2k|d _k＝i)， i＝0，1，2，3，

External information in the likelihood information that the one SISO decoder obtains decoding, the i.e. first external information L _EiExport to second interleaver; Repeat above-mentioned iterative decoding process, like this, through iterative decoding repeatedly, be generally iterative decoding in the practical application 6 to 8 times, the external information of a SISO decoder and the 2nd SISO decoder tends towards stability, the 2nd SISO decoder is posterior probability APPi to the likelihood information of second information sequence and additional information sequence thereof, i=0,1,2,3 carry out hard decision, can obtain the optimum evaluation sequence of first information sequence The 2nd SISO decoder output optimum evaluation sequence

Concrete hard decision process is as follows:

At APPi, i=0, of selecting the value maximum in 1,2,3, APPi=lnP (d _k=i R), makes d _k=i finds out and d according to following table _kCorresponding d _1kAnd d _2k,

d k	d 1kd 2k
		0	00
1	01
		2	10
3	11

Enter a judgement according to maximum posteriori criterion, promptly

${\hat{d}}_{1k}=\left\{\begin{array}{ccc}1,& \mathrm{if}& L\left(d_{1k}\right)\&GreaterEqual;0\\ 0,& \mathrm{if}& L\left(d_{1k}\right)<0\end{array}\right.$

${\hat{d}}_{2k}=\left\{\begin{array}{ccc}1,& \mathrm{if}& L\left(d_{2k}\right)\&GreaterEqual;0\\ 0,& \mathrm{if}& L\left(d_{2k}\right)<0\end{array}\right.$

Can obtain the optimum evaluation sequence of information sequence.

In the iterative decoder disclosed by the invention, the one SISO decoder utilization through deinterleaving handle all round information as prior information information sequence is deciphered, directly decoding being obtained likelihood information then exports as first external information, the 2nd SISO decoder utilization is deciphered information sequence as prior information through second external information of interleaving treatment, do not obtain likelihood information and need in decode procedure, not convert operation, decoding directly obtains likelihood information and posterior probability, decipher judgement and obtain the optimal decoding output sequence, reduced the workload of SISO decoder.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (11)

1, a kind of iterative decoder is characterized in that, comprises first decoder, second decoder, first interleaver, second interleaver and deinterleaver;

Described first decoder receives prior information the first information sequence and the additional information sequence thereof of input is deciphered, and the described first information sequence that decoding is obtained and the likelihood information of additional information sequence thereof are exported to second interleaver as first external information;

After described second interleaver carries out interleaving treatment to described first external information, export second external information and give second decoder;

After described first interleaver carries out interleaving treatment to described first information sequence, export second information sequence and give second decoder;

Described second decoder receives described second external information and as prior information described second information sequence and the additional information sequence thereof of input is deciphered, described second information sequence that decoding is obtained and the likelihood information of additional information sequence thereof are exported to deinterleaver as the 3rd external information, and when the external information of first decoder and second decoder tends towards stability, likelihood information is carried out hard decision, obtain the optimum evaluation sequence and the output of first information sequence;

After described deinterleaver carried out deinterleaving and handles described the 3rd external information, output the information all round gave first decoder as the prior information that first information sequence and additional information sequence thereof are deciphered.

2, iterative decoder according to claim 1 is characterized in that, the prior information that receives when described first decoder carries out deciphering for the first time is initial prior information.

3 iterative decoders according to claim 2 is characterized in that, described initial prior information is a preset value 0.

4, iterative decoder according to claim 1 is characterized in that, described interleaver comprises order Switching Module and interleaving block;

The data that described order Switching Module is used for receiving are carried out the internal order exchange of data;

Described interleaving block is used for the data of handling through described order Switching Module are carried out interleaving treatment.

5, iterative decoder according to claim 1 is characterized in that, described deinterleaver comprises order Switching Module and de-interleaving block;

Described de-interleaving block is used for that the data that receive are carried out deinterleaving to be handled;

Described order Switching Module is used for the data of handling through described deinterleaver are carried out the internal order exchange of data.

6, iterative decoder according to claim 1 is characterized in that, described decoder is the SISO decoder.

7, a kind of interative encode method is characterized in that, may further comprise the steps:

Utilize prior information that the first information sequence and the additional information sequence thereof that receive are deciphered, the first information sequence that decoding is obtained and the likelihood information of additional information sequence thereof are as first external information;

Described first external information is carried out interleaving treatment obtain second external information;

Described first information sequence is carried out interleaving treatment obtain second information sequence;

Utilize described second external information as prior information second information sequence and the additional information sequence thereof that receive to be deciphered, described second information sequence that decoding is obtained and the likelihood information of additional information sequence thereof are as the 3rd external information;

Described the 3rd external information is carried out deinterleaving handle the information all round that obtains.

With described all round information as the prior information that described first information sequence and additional information sequence thereof are deciphered;

When each external information tends towards stability, the likelihood information of described second information sequence and additional information sequence thereof is carried out hard decision, obtain the optimum evaluation sequence and the output of first information sequence.

8, method according to claim 7 is characterized in that, the prior information that receives when first decoder carries out deciphering for the first time is initial prior information.

9, method according to claim 8 is characterized in that, described initial prior information is a preset value 0.

10, according to claim 7 or 8 or 9 described methods, it is characterized in that described interleaving treatment is specially: after the data that receive are carried out the internal order exchange of data, data are carried out interleaving treatment respectively.

11, method according to claim 10 is characterized in that, described deinterleaving is handled and is specially: after the data that receive are carried out the deinterleaving processing respectively, data are carried out the internal order exchange of data.

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