CN102412930A - Method for decoding block product turbo code (BPTC) under 4-frequency-shift keying (4FSK) modulation mode - Google Patents

Method for decoding block product turbo code (BPTC) under 4-frequency-shift keying (4FSK) modulation mode Download PDF

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CN102412930A
CN102412930A CN2011103323006A CN201110332300A CN102412930A CN 102412930 A CN102412930 A CN 102412930A CN 2011103323006 A CN2011103323006 A CN 2011103323006A CN 201110332300 A CN201110332300 A CN 201110332300A CN 102412930 A CN102412930 A CN 102412930A
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soft information
bit soft
decoding
bptc
iteration
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戎骏
戴辉发
盛建峰
吴峰
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NEOLINK COMMUNICATION TECHNOLOGY (HANGZHOU) Co Ltd
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NEOLINK COMMUNICATION TECHNOLOGY (HANGZHOU) Co Ltd
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Abstract

The invention relates to the technical field of communication, in particular to a method for decoding a block product turbo code (BPTC) under a 4-frequency-shift keying (4FSK) modulation mode. The method for decoding the BPTC under the 4FSK modulation mode comprises the following steps of: 1) converting received sign soft information into bit soft information; 2) performing amplitude limitation processing on the bit soft information in the step 1); 3) performing 8-bit quantification on the bit soft information subjected to the amplitude limitation processing; and 4) iteratively decoding the bit soft information subjected to the 8-bit quantification, and when the iterated bit soft information is in accordance with an iteration stopping condition, stopping the iteration. Compared with the prior art, the decoding method has the advantages that: the performance is retained and the calculation amount can be reduced and the decoding delay time can be shorten.

Description

The interpretation method of a kind of BPTC sign indicating number under the 4FSK modulation system
Technical field
The present invention relates to communication technical field, the interpretation method of particularly a kind of BPTC sign indicating number under the 4FSK modulation system.
Background technology
Chnnel coding is the marrow of whole communication theory with modulation, is widely used in the aerospace deep space communication, personal mobile communication, and public telephone network, various fields such as the Internet and DVD error correction are for social informatization provides efficiently, reliable guidance.
The Turbo product code is that Elias proposed in 1954; It is that first can realize not having the error correction coding of error code transmission after the Shannon information theory proposed when the non-zero code check; Be a kind of effective ways that can construct long codes with two or more short codes, can regard the serial concatenation of codes that row-column interleaver has been inserted in a centre as.Consider two system linear block code C 1(n 1, k 1, d 1), C 2(n 2, k 2, d 2), n wherein 1, k 1, d 1Be respectively code word size, information digit number and smallest hamming distance, then by C 1, C 2The product code P=C that forms 1* C 2Can obtain through following steps:
1) with (k 1* k 2) information bit lines up k 1Row k 2The matrix of row;
2) use C 2To k 1Row is encoded, and obtains (k 1* n 2) matrix;
3) to 2) matrix that obtains, use C 1To n 2Row are encoded, and obtain (n 1* n 2) code word matrix.
Structure such as Fig. 1 of product code show that the parameter that obtains the Turbo product code is n=n 1* n 2, k=k 1* k 2, d=d 1* d 2Code check R=R 1* R 2, R wherein iBe exactly C iCode check.No matter check digit to check digit among the product code P is to use C according to row 2Verification rule generate still and use C according to row 1Verification rule generate, its result is identical.Its component code is generally Hamming code, extended hamming code, parity check code, BCH code and expansion BCH code, linear block codess such as RS sign indicating number and expansion RS sign indicating number.In the world at present first three sign indicating number types that adopt, its coding and decoding is simple relatively more.
In the DMR agreement, the subcode of BPTC is a Hamming code, and the row subcode is Hamming (15,11,3), and the row subcode is Hamming (13,9,3), is BPTC (196,96) thereby obtain product code, and wherein extra 3bit information mends 0, mends 1bit 0 behind the coding again.
For its Hard decision decoding, can adopt the decoding of two steps, promptly carry out according to the order of (row) rank rear (OK) of going ahead of the rest; In this case; And if only if accomplish row and correct after, when the capable not correctable error pattern that stays was the repairable error pattern of row, whole error pattern was only repairable.
From information-theoretical angle, any hard decision all can lose partial information, therefore under the time allows, can adopt Soft decision decoding.1994; People such as Pyndiah have proposed a kind of soft inputting and soft output (Soft-In-Soft-Out, SISO) interative encode method of linear block codes on the basis of block code Chase interpretation method; Be applied to the decoding of product code subcode, be called Turbo product code (TPC).Concrete way is: establishing and receiving soft information matrix is [R], and to its hocket row decoding and column decoding, interpretation method is the Chase2 algorithm.See also Fig. 2, be the flow chart of SISO interative encode method.External information is provided between twice decoding each other, whenever carries out row decoding or column decoding and can regard iteration as half time.At first [R] carried out row decoding column decoding then, then the soft input information matrix of the m time half iteration does
[R(m)]＝[R]+α(m)[W(m)]
Wherein [W (m)] is external information.The scale factor of α for introducing; It is poor to be used for suppressing [R] sampling standard different with [W (m)], has reduced the influence of [W (m)] when the iteration initial stage, the error rate was higher simultaneously, and its value increases along with the increase of iterations; Scope is [0; 1], the error-correcting performance of BPTC there is bigger influence, can rule of thumb be worth and chooses.Soft output external information matrix does
[W(m+1)]＝[R′(m)]-[R(m)]
R ' is the soft output of the m time half iteration (m) in the formula.
An of paramount importance step is the calculating of external information W in the BPTC iterative algorithm, is without loss of generality, and considers certain delegation or row in the soft input matrix [R], then has
Figure BSA00000600852500021
p l = 0 c l = d l 1 c l ≠ d l
Wherein D is a soft-decision code word of utilizing the Chase2 algorithm to obtain, and C is the competition code word, is candidate codewords set C qIn satisfy c i≠ d iThe suboptimum code word.The confidence level of parameter beta representative judgement, span is [0,1], leans on the experience gained, changes along with iteration.But there is following defective in existing soft-decision decoding method:
Interpretation method is operated to real number, can cause the deterioration of real arithmetic and the increase of operand in actual applications.
Summary of the invention
The object of the invention is to provide the interpretation method of a kind of BPTC sign indicating number under the 4FSK modulation system; Operate to real number to solve in the prior art existing soft-decision decoding method, in practical application, can cause the technical matters of increase of deterioration and the operand of real arithmetic.
The object of the invention realizes through following technical scheme:
The interpretation method of a kind of BPTC sign indicating number under the 4FSK modulation system may further comprise the steps:
1) the soft information of symbol that receives is changed into bit soft information;
2) bit soft information in the step 1) is carried out amplitude limiting processing;
3) bit soft information after the amplitude limiting processing being carried out 8bit quantizes;
4) will carry out iterative decoding through the bit soft information that 8bit quantizes, when the bit soft information after the iteration satisfies stopping criterion for iteration, stop iteration.
Preferably, the amplitude limiting processing step 2) comprises:
Bit soft information is handled according to following formula:
r i = 1 r i > 1 r i | r i | &le; 1 - 1 r i < - 1
Wherein, r iBe bit soft information, when bit soft information is handled as 1 greater than 1 the time, when bit soft information is handled as-1 less than-1 the time, when the absolute value of bit soft information is handled according to the real information of bit soft information less than 1 the time.
Preferably, the stopping criterion for iteration described in the step 4) comprises:
Figure BSA00000600852500032
Wherein, d is a Hamming distance, and C is the competition code word, and R is a bit soft information, and Th is the broad sense thresholding, the level number of Q for quantizing; When Hamming distance d satisfied above-mentioned condition, bit soft information stopped iteration.
The interpretation method of a kind of BPTC sign indicating number under the 4FSK modulation system may further comprise the steps:
1) codeword sequence that receives is changed into code block;
2) 4 row check digit are carried out Hamming (13,9,3) decoding;
3) Hamming (15,11,3) decoding is carried out in 4 performing check positions;
4) Hamming (13,9,3) decoding is carried out in 11 column information positions;
5) 9 row information bits are carried out Hamming (15,11,3) decoding.
Compared with prior art, interpretation method of the present invention is neither lost performance and can be reduced amount of calculation and decoding time-delay.
Description of drawings
Fig. 1 is the sketch map of existing Turbo product code coding;
Fig. 2 is the flow chart of SISO interative encode method;
Fig. 3 is the error performance comparison diagram of interpretation method of the present invention and existing interpretation method;
Fig. 4 is the error performance comparison diagram of interpretation method of the present invention and existing interpretation method;
Fig. 5 is the graph of a relation of signal to noise ratio and average half iterations in the interpretation method of the present invention.
Embodiment
Interpretation method of the present invention was carried out amplitude limiting processing earlier before bit soft information is carried out iteration; Can reduce because the performance loss that singular value is brought; And the setting stopping criterion for iteration, can make interpretation method of the present invention neither lose performance and can reduce amount of calculation and decoding time-delay.
The interpretation method of a kind of BPTC sign indicating number of the present invention under the 4FSK modulation system may further comprise the steps:
Earlier the soft information of symbol that receives is changed into bit soft information, then bit soft information is carried out amplitude limiting processing, amplitude limiting processing comprises:
The bit soft information of each iteration is handled according to following formula:
r i = 1 r i > 1 r i | r i | &le; 1 - 1 r i < - 1
Wherein, r iBe bit soft information, when bit soft information is handled as 1 greater than 1 the time, when bit soft information is handled as-1 less than-1 the time, when the absolute value of bit soft information is handled according to the real information of bit soft information less than 1 the time.This processing can be eliminated the singular value that indivedual samplings cause too greatly owing to the white noise fluctuation.Use this amplitude limit method but this formula emulation shows, the iterative decoding performance slightly improved when signal to noise ratio was low, slightly lost when signal to noise ratio is high.The present invention proposes a kind of BPTC interative encode method of the amplitude limit through integer quantisation, and small performance loss is only arranged by contrast, has solved in the practical application, real number is handled making operand increase, and is brought the problem of the deterioration of real arithmetic.
If receiving bit soft information is R=(r 1..., r l..., r n) | r l|≤1, corresponding reception signal hard decision is Y=(y 1..., y l..., y n), the bit soft information after the 8bit level quantizes does
S＝(s 1，…，s l，…，s n)
s l＝round((r l+1)/2*255)-127 s l∈[-127，128]
Then hard decision does
y l = 1 s l > 0 0 s l &le; 0
Wherein round (.) representes to round up computing.The soft input information matrix of the m time half iteration does
[S(m)]＝[S]+round(α(m)[W(m)])
s l ( m ) = 128 s l ( m ) > 128 - 127 s l ( m ) < - 127
Utilize the Chase2 algorithm that subcode is deciphered, with | s l(m) |-y l(m) measure as the bit confidence level, its value is more little, and confidence level is more little, and then optimum code word D does
Figure BSA00000600852500053
In kind obtain competing code word C, wherein c l, d l, c l' ∈ 1,1}.
The external information of the m+1 time iteration use is [W (m+1)], then has
Figure BSA00000600852500054
p l = 0 c l = d l 1 c l &NotEqual; d l
β wherein qParameter for after quantizing satisfies
β q＝round((β+1)/2*255)-127
To carry out iterative decoding through the bit soft information that 8bit quantizes again, when the bit soft information after the iteration satisfies stopping criterion for iteration, stop iteration.
Wherein, stopping criterion for iteration comprises:
Wherein, d is a Hamming distance, and C is the competition code word, and R is a bit soft information, and Th is the broad sense thresholding, the level number of Q for quantizing; When Hamming distance d satisfied above-mentioned condition, bit soft information stopped iteration.
To Hamming distance is the binary system linear block codes of d, and when Soft decision decoding was carried out in output to Q system channel with soft-decision decoding method, if obtain certain candidate codewords C, it satisfied with the soft-decision distance that receives hard decision sequence R
Then C is exactly the optimal decoding result, satisfies above-mentioned relation because only have a code word, and Th just is called as the broad sense thresholding.
Use 8bit to quantize, so Q=256 then is Th=382.Optimal conditions uses at all row or row, rather than whole BPTC sign indicating number, so can not guarantee that above broad sense thresholding is optimum.Based on analog simulation, the proposition optimal conditions is dis＜300, and the performance loss of this moment can be ignored, and has obviously reduced iterations simultaneously.Broad sense thresholding according to the linear block codes soft-decision provides the iteration stop criterion: when all row or column satisfied given optimal conditions, iteration stopped.
To the logic channel BPTC87CH among the DMR, promptly the 87bit information bit is carried out the CRC-9 coding, obtain 96bit, carry out the BPTC coding again, obtain BPTC (196,96).Use above-mentioned quantification iterative algorithm, and add stopping criterion for iteration, modulation system is 4FSK, under Gaussian channel, carries out emulation, simulation result such as Fig. 3, shown in Figure 4.
Fig. 3, Fig. 4 compare two kinds of Hard decision decoding methods simultaneously, can find out that improving algorithm has the gain of 0.2dB to improve approximately.For the Soft decision decoding that adopts iterative decoding, its performance is fairly good, and first three time iteration improvement in performance is remarkable, and during four iteration, gain only has small raising.Fig. 5 is for after adding stopping criterion for iteration, and half iterations is with the variation relation of signal to noise ratio, and visible its average iterations obviously reduces.
The interpretation method of a kind of BPTC sign indicating number of the present invention under the 4FSK modulation system may further comprise the steps:
1) codeword sequence that receives is changed into code block;
2) 4 row check digit are carried out Hamming (13,9,3) decoding;
3) Hamming (15,11,3) decoding is carried out in 4 performing check positions;
4) Hamming (13,9,3) decoding is carried out in 11 column information positions;
5) 9 row information bits are carried out Hamming (15,11,3) decoding.
This improves algorithm does not increase operand, and the coding gain of the 0.2dB that has an appointment improves.
Be relatively each time complexity soft, hard decoding, table 1 has provided clock cycle (clock) and the operation time (ms) of its c code under CCSStudio v3.3 environment, and frequency is 48MHz.
Table 1BPTC87CH compiles, the time complexity of decoding
Figure BSA00000600852500071
More than the disclosed several specific embodiments that are merely the application, but the application is not limited thereto, any those skilled in the art can think variation, all should drop in the application's the protection range.

Claims (4)

1. the interpretation method of a BPTC sign indicating number under the 4FSK modulation system is characterized in that, may further comprise the steps:
1) the soft information of symbol that receives is changed into bit soft information;
2) bit soft information in the step 1) is carried out amplitude limiting processing;
3) bit soft information after the amplitude limiting processing being carried out 8bit quantizes;
4) will carry out iterative decoding through the bit soft information that 8bit quantizes, when the bit soft information after the iteration satisfies stopping criterion for iteration, stop iteration.
2. a kind of interpretation method of BPTC sign indicating number as claimed in claim 1 under the 4FSK modulation system is characterized in that step 2) in amplitude limiting processing comprise:
Bit soft information is handled according to following formula:
r i = 1 r i > 1 r i | r i | &le; 1 - 1 r i < - 1
Wherein, r iBe bit soft information, when bit soft information is handled as 1 greater than 1 the time, when bit soft information is handled as-1 less than-1 the time, when the absolute value of bit soft information is handled according to the real information of bit soft information less than 1 the time.
3. a kind of interpretation method of BPTC sign indicating number as claimed in claim 1 under the 4FSK modulation system is characterized in that the stopping criterion for iteration described in the step 4) comprises:
Figure FSA00000600852400012
Wherein, d is a Hamming distance, and C is the competition code word, and R is a bit soft information, and Th is the broad sense thresholding, the level number of Q for quantizing; When Hamming distance d satisfied above-mentioned condition, bit soft information stopped iteration.
4. the interpretation method of a BPTC sign indicating number under the 4FSK modulation system is characterized in that, may further comprise the steps:
1) codeword sequence that receives is changed into code block;
2) 4 row check digit are carried out Hamming (13,9,3) decoding;
3) Hamming (15,11,3) decoding is carried out in 4 performing check positions;
4) Hamming (13,9,3) decoding is carried out in 11 column information positions;
5) 9 row information bits are carried out Hamming (15,11,3) decoding.
CN2011103323006A 2011-10-27 2011-10-27 Method for decoding block product turbo code (BPTC) under 4-frequency-shift keying (4FSK) modulation mode Pending CN102412930A (en)

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CN111147157A (en) * 2019-12-30 2020-05-12 浙江大学 Soft interference elimination Turbo equalization method for orthogonal signal division multiplexing on underwater acoustic channel

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CN111147157A (en) * 2019-12-30 2020-05-12 浙江大学 Soft interference elimination Turbo equalization method for orthogonal signal division multiplexing on underwater acoustic channel

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Application publication date: 20120411