CN102811116A - Distributed Turbo coding method in relay transmission system - Google Patents

Abstract

The invention discloses a novel distributed Turbo coding method in a relay transmission system, and mainly solves a problem of apparent decline of the performance of the system in case of the error decoding of a relay node. The method comprises the following steps of: 1) coding the information into the form of a serial cascade convolutional code by a source node; 2) deleting a code word by the source node and broadcasting; 3) calculating a log-likelihood ratio by the relay node depending on the received information; 4) calculating an information estimation value by the relay node depending on the log-likelihood ratio and a threshold; 5) sending the estimated information to a destination target by the relay node; 6) decoding by the destination node depending on the received broadcasting information and the information of the relay node, thereby obtaining a decoding estimation value; 7) implementing a cyclic redundancy check (CRC) to the estimation value, and finishing a frame of transmission. According to the distributed Turbo coding method, a better diversity gain and a better coding gain are obtained, and the error rate of the system is remarkably reduced; the method is applicable to a two-hop relay system under a quasi-static condition.

Description

Distributed T urbo coding method in the relay transmission system

Technical field

The invention belongs to wireless communication technology field, further relate to a kind of Distributed T urbo coding method in the wireless relay transmission field, can be used for the double bounce relay system under the quasistatic condition.

Background technology

The wireless relay transmission is an extremely promising information transmission technology, and it is used to help communicate by letter between source node and the destination node.In order to improve the performance of relay transmission system; Academia has proposed to have the distributed coding method of branch collection and coding gain in recent years; Comprise: distributed space time-code, distributed low density parity check code LDPC, Distributed T urbo product code; Distributed T urbo sign indicating number DTC etc., especially Distributed T urbo sign indicating number has been proved to be a kind of coding method that approaches the relay system capacity.However, as decoding to transmit DF the same because the decoding of the mistake of via node, error propagation also exists in the Distributed T urbo coding, this will cause the decline of relay system overall performance.

For the propagation that conquers erroneous ideas; People such as Li Y are at " Distributed turbo coding with soft information relaying in multihop relay networks " (IEEE J.Sel.Areas Commun.; Vol.24; No.11, pp.2040-2050 Nov.2006.) has proposed a kind of Distributed T urbo coding method based on soft information relay.This method is transmitted the log-likelihood ratio LLR of decoding bit to be transmitted through via node, error propagation is weakened, thereby improved the performance of relay transmission system.A few days ago, people such as Al-Habian G at " Threshold-based relaying in coded cooperative networks, " (IEEE Trans.Veh.Technol.; Vol.60; No.1, pp.123-135 Jan.2011.) has proposed a kind of distributed coding method based on thresholding.In the method, via node compares the LLR and the thresholding of decoding bit to be transmitted, as LLR during greater than thresholding; Via node thinks that bit to be transmitted is believable, with the hard decision value of transmitting LLR, otherwise; Via node will be kept silent; This method has reduced error propagation effectively, and the experiment show that its performance is superior to the Distributed T urbo coding method based on soft information relay, but since this method stoped the forwarding of via node to the lower correct decoding result of confidence level; Cause diversity gain low, can not satisfy the demand of wireless relay transmission system efficiently.

Summary of the invention

The objective of the invention is to deficiency to above-mentioned prior art; A kind of Distributed T urbo coding method of in the relay transmission system, using is provided; To have improved the performance of relay transmission system effectively, guarantee the demand of wireless relay transmission system to high efficiency of transmission.

Realize that the object of the invention technical thought is that via node compares through LLR and the thresholding to decoding bit to be transmitted, confirms the confidence level of decoding bit to be transmitted; In confidence level not simultaneously, via node is transmitted different information, promptly as LLR during greater than thresholding; Via node thinks that bit to be transmitted is believable; So transmit the hard decision value of bit to be transmitted, otherwise via node is transmitted a relative soft information.Implementation step is following:

1) to adopt code check be that 1/4 SCCC Serial Concatenated Convolutional Code SCCC is to a frame information b=[b to source node ₁, b ₂..., b _N] encode, obtain code word x=[u ₁, w ₁, u ₂, w ₂..., u _2N, w _2N], b wherein _iRepresent each bit among the frame information b, u _jBe each bit of the result that interweaves of b and its verification sequence, w _jBe u _jThe check bit position, j=1,2 ..., 2N, i=1,2 ..., N, N are the bit number that a frame information comprises;

2) source node is with the sequence u among the code word x ₁=[u ₂, u ₄..., u _2N] deletion, obtain code check and be 1/3 information x _s=[u ₁, w ₁, w ₂..., u _2N-1, w _2N-1, w _2N], and by source node it is broadcasted;

3) broadcast message of via node reception sources node, and utilize the information y that receives _SrSequence of calculation u ₁Log-likelihood ratio L (u _k):

$L\left(u_k\right)=\ln \frac{P(u_k=1|y_{\mathrm{sr}},h_{\mathrm{sr}})}{P(u_k=-1|y_{\mathrm{sr}},h_{\mathrm{sr}})},$

In the formula, u _kExpression sequence u ₁In each bit, P (u _k=1|y _Sr, h _Sr) be meant at known y _SrAnd h _SrThe time check bit position u _k=1 posterior probability, P (u _k=-1|y _Sr, h _Sr) be meant at known y _SrAnd h _SrThe time check bit position u _k=-1 posterior probability, h _SrBe the fading coefficients of source node to channel between via node, h _SrObey average and be 0, variance is 1 multiple Gaussian distribution, k=2,4 ..., N;

4) according to log-likelihood ratio L (u _k) and set thresholding T, obtain the estimated sequence of u1:

Wherein, ${\hat{u}}_k=\left\{\begin{array}{cc}\mathrm{Sgn}\left(L\left(u_k\right)\right),& \left|L\left(u_k\right)\right|\&GreaterEqual;T\\ L\left(u_k\right)/T,& \left|L\left(u_k\right)\right|<T\end{array}\right.$

In the formula, k=2,4 ..., 2N,

Expression u _kEstimated value, L (u _k) expression u _kLikelihood ratio LLR, sign function is asked in sgn () expression, || it is to make system break probability value hour that absolute value operation, T are asked in expression, obtains through searching algorithm;

5) via node is sent to destination node with estimated sequence ;

6) estimated sequence that sends to of the broadcast message of destination node reception sources node and via node is designated as y respectively _SdAnd y _Rd, and with the complete codeword sequence of above-mentioned information merging composition, it is carried out iterative decoding obtain decoding information

7) decoding information

is carried out the cyclic redundancy CRC check; If verification is correct; The end of transmission of a frame then; Otherwise, return step 2).

The present invention compared with prior art has following advantage:

1) the present invention has fully excavated via node Reliability of Information to be transmitted, transmits a hard decision value for the information of high confidence level, transmits a relative soft information for the information of low confidence level, has therefore effectively weakened the mistake of via node and has relayed.

2) the present invention is because the length of estimated sequence

equals the length of frame information b; Therefore remedied the low shortcoming of Distributed T urbo coded diversity gain, thereby satisfied the demand of wireless relay system high efficiency of transmission based on thresholding.

Description of drawings

Fig. 1 is a coding flow chart of the present invention;

Fig. 2 is the performance simulation figure of the signal to noise ratio of the present invention's channel between source node and via node when being 10dB;

Fig. 3 is the performance simulation figure of the signal to noise ratio of the present invention's channel between source node and via node when being 20dB.

Embodiment

Through accompanying drawing and embodiment, technical method of the present invention is done further to describe below.

With reference to Fig. 1, concrete performing step of the present invention is following:

It is that 1/4 SCCC Serial Concatenated Convolutional Code SCCC is to a frame information b=[b that step 1, source node adopt code check ₁, b ₂..., b _N] encode:

Described code check is 1/4 SCCC Serial Concatenated Convolutional Code SCCC by two identical code checks is that 1/2 recursive systematic convolutional code is formed, and these two code checks are that the encoder of 1/2 recursive systematic convolutional code is designated as E respectively ₁And E ₂, code check is that the specific coding step of 1/4 SCCC Serial Concatenated Convolutional Code SCCC is following:

1.1) encoder E ₁To frame information b=[b ₁, b ₂..., b _N] encode, obtain the verification sequence p=[p of frame information b ₁, p ₂..., p _N]; B wherein _iRepresent each bit among the frame information b, p _iEach bit among the verification sequence p of expression b; I=1,2 ..., N, N are the bit number that a frame information comprises;

1.2) the verification sequence p of frame information b and b thereof is merged, obtain associating sequence c=[b ₁, p ₁, b ₂, p ₂..., b _N, p _N], associating sequence c interweaved obtains encoder E ₁Output sequence: u=[u ₁, u ₂..., u _2N], u wherein _jPresentation code device E ₁Output sequence u in each bit, j=1,2 ..., 2N;

1.3) with encoder E ₁Output sequence u as encoder E ₂Input, by encoder E ₂To encoder E ₁Output sequence u encode, obtain terminal check sequence w=[w ₁, w ₂..., w _2N], merge encoder E ₁Output sequence u and terminal check sequence w, obtain the code word x=[u of code check 1/4 ₁, w ₁, u ₂, w ₂..., u _2N, w _2N], w wherein _jEach bit among the expression terminal check sequence w, j=1,2 ..., 2N.

Step 2, source node carries out broadcasting after the deletion action to code word x.

2.1) source node is to code word x=[u ₁, w ₁, u ₂, w ₂..., u _2N, w _2N] carry out deletion action by code check 1/4, the information x after obtaining deleting _s=[u ₁, w ₁, w ₂..., u _2N-1, w _2N-1, w _2N], the sequence of being left out is u ₁=[u ₂, u ₄..., u _2N];

2.2) information x after source node will be deleted _sBroadcast.

Step 3, the information y that the via node utilization receives _SrUse maximum a posteriori probability MAP algorithm, the sequence u that the calculation sources node is left out ₁Log-likelihood ratio:

$L\left(u_k\right)=\ln \frac{P(u_k=1|y_{\mathrm{sr}},h_{\mathrm{sr}})}{P(u_k=-1|y_{\mathrm{sr}},h_{\mathrm{sr}})},$

In the formula, u _kThe sequence u that expression is left out ₁In each bit, k=2,4 ..., 2N, P (u _k=1|y _Sr, h _Sr) be meant at known y _SrAnd h _SrThe time check bit position u _k=1 posterior probability, P (u _k=-1|y _Sr, h _Sr) be meant at known y _SrAnd h _SrThe time check bit position u _k=-1 posterior probability, y _Sr={ y _Sr[1], y _Sr[2] ..., y _Sr[3N] } broadcast message of the source node that receives of expression via node, it embodies formula and is:

$y_{\mathrm{sr}}\left[n\right]=\sqrt{E_{\mathrm{sr}}}{h}_{\mathrm{sr}}s\left[n\right]+n_{\mathrm{sr}}\left[n\right],$

In the formula, n=1,2 ..., 3N, E _Sr=E _s(G _Sr) ²The energy of each symbol that the expression via node receives, E _sThe energy of each symbol of expression source node broadcasting, G _SrBe the gain coefficient of source node to channel between via node, h _SrBe the fading coefficients of source node to channel between via node, h _SrObey average and be 0, variance is 1 multiple Gaussian distribution, the information x after s [n] the expression deletion _sIn each bit, n _Sr[n] is the being added with property white Gaussian noise that source node produces to channel between via node.

Step 4 is set thresholding T, with log-likelihood ratio L (u _k) compare with thresholding T, obtain step 2.1) the middle sequence u that is left out ₁Estimated sequence:

${\hat{u}}_1=[{\hat{u}}_2,{\hat{u}}_4,...,{\hat{u}}_{2N}],$

Wherein,

Expression u _kEstimated value, ${\hat{u}}_k=\left\{\begin{array}{cc}\mathrm{Sgn}\left(L\left(u_k\right)\right),& \left|L\left(u_k\right)\right|\&GreaterEqual;T\\ L\left(u_k\right)/T,& \left|L\left(u_k\right)\right|<T\end{array}\right.,$

L (u _k) expression u _kLog-likelihood ratio LLR, sign function is asked in sgn () expression, || absolute value operation is asked in expression, k=2,4 ..., 2N.

Step 5, via node sends to destination node with estimated sequence

.

Step 6, the estimated value information that the broadcast message of destination node reception sources node and via node send to is designated as respectively: y _Sd={ y _Sd[1], y _Sd[2] ..., y _Sd[3N] } and y _Rd={ y _Rd[3N+1], y _Rd[3N+2] ..., y _Rd[4N] }, and above-mentioned information merged form complete codeword sequence:

y _d＝{y _sd[1],y _sd[2],y _sd[3],y _rd[3N+1],…，y _sd[3N-2]，y _sd[3N-1],y _sd[3N],y _rd[4N]}，

Wherein, y _SdThe broadcast message y of the source node that [n] expression destination node receives _SdIn each bit, y _RdThe estimated value information y that the via node that [m] expression destination node receives sends to _RdIn each bit, n=1,2 ..., 3N, m=3N+1,3N+2 ..., 4N, y _Sd[n] and y _RdThe expression formula of [m] is distinguished as follows:

$y_{\mathrm{sd}}\left[n\right]=\sqrt{E_{\mathrm{sd}}}{h}_{\mathrm{sd}}s\left[n\right]+n_{\mathrm{sd}}\left[n\right],$

$y_{\mathrm{rd}}\left[m\right]=\sqrt{E_{\mathrm{rd}}}{h}_{\mathrm{rd}}s\left[m\right]+n_{\mathrm{rd}}\left[m\right],$

In the formula, E _Sd=E _s(G _Sd) ²And E _Rd=E _r(G _Rd) ²Represent the energy of destination node respectively, E from each symbol of source node and via node reception _sThe energy of each symbol of expression source node broadcasting, E _rThe energy of each symbol that the expression via node sends, G _SdAnd G _RdRepresent the gain of source node respectively, h to the gain of via node channel and via node to the destination node channel _SdAnd h _RdRepresent the fading coefficients of source node respectively, h to the fading coefficients of via node channel and via node to the destination node channel _Sr, h _SdSeparate and obey all that average is 0, variance is 1 multiple Gaussian distribution, the information x after s [n] the expression deletion _sIn each bit, s [m] representes estimated sequence In each bit, n _Sd[n] and n _Rd[m] representes the being added with property white Gaussian noise that source node produces to channel between destination node to channeling and trunking node between via node respectively.

Step 7 is to becoming complete codeword sequence y _dCarry out the maximum a posteriori probability iterative decoding, obtain deciphering estimated information:

$\hat{y}=\{{\hat{b}}_1,{\hat{b}}_2,...,{\hat{b}}_N\},$

Wherein

is each bit in the decoding estimated information

; I=1; 2;, N.

Step 8; Decoding estimated information

is carried out CRC check; If the error pattern of gained is 0 after the verification, think that then message transmission is correct, then the end of transmission of a frame; Otherwise, return step 2).

CRC check is to utilize the principle of division and remainder to carry out error detection.During practical application, dispensing device calculates crc value and together sends to receiving system with data, and receiving system recomputates crc value to the data of receiving and compares with the crc value of receiving, if two crc value differences, then mistake appears in the declarative data communication.Crc value is that two byte datas stream adopts the binary divisions resulting remainder that is divided by.Wherein dividend be need calculation check and the binary representation of inter-area traffic interarea, divisor is the predefined binary number that a length is.

Effect of the present invention can further specify through following emulation.

1) simulated conditions: the definition source node is γ to the signal to noise ratio of destination node channel _Sd=E _Sd/ N ₀, via node is γ to the signal to noise ratio of destination node channel _Rd=E _Rd/ N ₀, source node is γ to the signal to noise ratio of via node _Sr=E _Sr/ N ₀, N ₀The power of white Gaussian noise makes γ in the expression channel _Rd=2 γ _Sd, N=80, E ₁And E ₂Adopting identical generator polynomial is G=(7,5) ₈Recursive systematic convolutional code, interleaver is selected twice replaced polynomial interleaver for use, the MAP algorithm is adopted in decoding, iterations is 6 times.In addition, thresholding T of the present invention selects optimum thresholding for use P _bIt is the bit error rate of decoding.

2) emulation content and result:

With Distributed T urbo coding method Proposed DTC of the present invention with based on the Distributed T urbo coding method DTC-DF of simple DF, based on the Distributed T urbo coding method DTC-SIR of soft information relay, satisfying under the situation of above-mentioned simulated conditions and γ based on the Distributed T urbo coding method DTC-TR of thresholding relaying, perfect Distributed T urbo coding method Perfect-DTC _SrDuring=10dB, bit error rate is arrived the signal to noise ratio γ of destination node channel with source node _SdSituation of change is carried out emulation relatively, result such as Fig. 2.

With Distributed T urbo coding method Proposed DTC of the present invention with based on the Distributed T urbo coding method DTC-DF of simple DF, based on the Distributed T urbo coding method DTC-SIR of soft information relay, satisfying under the situation of above-mentioned simulated conditions and γ based on the Distributed T urbo coding method DTC-TR of thresholding relaying, perfect Distributed T urbo coding method Perfect-DTC _SrDuring=20dB bit error rate is arrived destination node channel signal to noise ratio γ with source node _SdSituation of change is carried out emulation relatively, its result such as Fig. 3.

Can know by Fig. 2; The bit error rate of Distributed T urbo coding method of the present invention is lower than the bit error rate based on the Distributed T urbo coding method of thresholding relaying, far below based on the Distributed T urbo coding method of simple DF with based on the bit error rate of the Distributed T urbo coding method of soft information relay.

It can also be seen that by Fig. 2 and Fig. 3 contrast, along with the link signal to noise ratio γ between source node and the via node _SrThe bit error rate of increase Distributed T urbo coding method of the present invention bit error rate can be more near Distributed T urbo coding method the time, therefore, Distributed T urbo coding method of the present invention has certain use value.

Claims (3)

1. the Distributed T urbo coding method in the relay transmission system comprises the steps:

1) to adopt code check be that 1/4 SCCC Serial Concatenated Convolutional Code SCCC is to a frame information b=[b to source node ₁, b ₂..., b _N] encode, obtain code word x=[u ₁, w ₁, u ₂, w ₂..., u _2N, w _2N], b wherein _iRepresent each bit among the frame information b, u _jBe each bit of the result that interweaves of b and its verification sequence, w _jBe u _jThe check bit position, j=1,2 ..., 2N, i=1,2 ..., N, N are the bit number that a frame information comprises;

2) source node is with the sequence u among the code word x ₁=[u ₂, u ₄..., u _2N] deletion, obtain code check and be 1/3 information x _s=[u ₁, w ₁, w ₂..., u _2N-1, w _2N-1, and by source node it is broadcasted;

3) broadcast message of via node reception sources node, and utilize the information y that receives _SrSequence of calculation u ₁Log-likelihood ratio on L (u _k):

$L\left(u_k\right)=\ln \frac{P(u_k=1|y_{\mathrm{sr}},h_{\mathrm{sr}})}{P(u_k=-1|y_{\mathrm{sr}},h_{\mathrm{sr}})},$

In the formula, u _kExpression sequence u ₁In each bit, P (u _k=l|y _Sr, h _Sr) be meant at oneself and know y _SrAnd h _SrThe time check bit position u _k=1 posterior probability, P (u _k=-1|y _Sr, h _Sr) be meant at oneself and know y _SrAnd h _SrThe time check bit position u _k=-1 posterior probability, h _SrBe the fading coefficients of source node to channel between via node, h _SrObey average and be 0, variance is 1 multiple Gaussian distribution, k=2,4 ..., 2N;

4) according to L (u on the log-likelihood ratio _k) and set thresholding T, obtain u ₁Estimated sequence:

Wherein, ${\hat{u}}_k=\left\{\begin{array}{cc}\mathrm{Sgn}\left(L\left(u_k\right)\right),& \left|L\left(u_k\right)\right|\&GreaterEqual;T\\ L\left(u_k\right)/T,& \left|L\left(u_k\right)\right|<T\end{array}\right.$

In the formula,

Expression u _kEstimated value, L (u _k) expression u _kLikelihood ratio LLR, sign function is asked in sgn () expression, || it is to make system break probability value hour that absolute value operation, T are asked in expression, obtains through searching algorithm;

5) via node is sent to destination node with estimated sequence

;

6) estimated sequence that sends to of the broadcast message of destination node reception sources node and via node is designated as y respectively _SdAnd y _Rd, and with the complete codeword sequence of above-mentioned information merging composition, it is carried out iterative decoding obtain decoding information

7) decoding information is carried out the cyclic redundancy CRC check; If verification is correct; The end of transmission of a frame then; Otherwise, return step 2).

2. the Distributed T urbo coding method in the relay transmission according to claim 1 system, wherein to adopt code check be that 1/4 SCCC Serial Concatenated Convolutional Code SCCC is to a frame information b=[b to the described source node of step 1) ₁, b ₂..., b _N] encode, carry out as follows:

1a) encoder E ₁To frame information b=[b ₁, b ₂..., b _N] encode, obtain the verification sequence p=[p of b ₁, p ₂..., p _N], the verification sequence p of frame information b and b is merged, obtain associating sequence c=[b ₁, p ₁, b ₂, p ₂..., b _N, p _N], associating sequence c interweaved obtains encoder E ₁Output sequence: u=[u ₁, u ₂..., u _2N];

1b) with encoder E ₁Output sequence u as encoder E ₂Input, by encoder E ₂To encoder E ₁Output sequence u encode, obtain terminal check sequence w=[w ₁, w ₂..., w _2N], merge encoder E ₁Output sequence u and terminal check sequence w, obtain the code word x=[u of code check 1/4 ₁, w ₁, u ₂, w ₂..., u _2N, w _2N], p wherein _iBe b _iThe check bit position, i=1,2 ..., N, E ₁And E ₂Represent that two identical code checks are the encoder of 1/2 recursive systematic convolutional code.

3. the Distributed T urbo coding method in the relay transmission according to claim 1 system, the iterative decoding in the wherein said step 6) adopts the maximum posteriori decoding mode.

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