CN104219026A - Joint Network Coding Relay Transmission Method Based on 3-D Turbo Codes - Google Patents

Abstract

The invention discloses a 3-D Turbo code-based joint network coding relay transmission method, which mainly solves the problem of low relay utilization rate of distributed 3-D Turbo codes in the prior art. The steps realized by the present invention are: (1) obtaining the modulation signal sequence; (2) broadcasting information; (3) the relay node performing Turbo decoding; (4) the relay node performing Turbo encoding; (5) selecting check bits; (6) The relay node performs network coding; (7) Obtains the third-dimensional coded modulation sequence; (8) The destination node jointly decodes. The present invention adopts network coding at the relay node to combine the two signals for transmission, which can effectively improve the utilization rate of the relay node. The invention can realize the effective trade-off between the decoding performance and the system complexity by changing the numerical value of the penetration coefficient, and is suitable for the wireless multiple access system.

Description

Joint Network Coding Relay Transmission Method Based on 3-D Turbo Codes

technical field

The invention belongs to the field of communication technology, and further relates to a multiple access technology, a joint network coding relay transmission method based on 3-D Turbo codes in the field of joint network-channel coding and relay cooperative communication technology. The present invention uses network coding at the relay node to combine two user data of multiple access and perform third-dimensional coding to form a relay transmission method of a 3-D Turbo code as a whole.

Background technique

Utilizing the relay cooperative transmission technology can obtain additional transmission gain, thereby improving the frame error rate performance of the destination end, and effectively improving the call quality at the cell edge of the mobile user.

In the traditional cooperative diversity communication, the relay node processes the received multi-channel signals separately in different time slots and then forwards them. Cooperative communication based on network coding allows the relay node to perform network coding combination on the data received from multiple source nodes, and then forward the coded data to the destination node.

A relay transmission method based on distributed 3-D Turbo codes is proposed in the patent "Relay transmission method based on distributed 3-D Turbo code" (application number: 201310030692.X) applied by Xidian University. The relay channel model of this method includes a source node, a relay node and a destination node, and two time slots are needed to complete the entire communication process: in the first time slot, the source node broadcasts data to the relay node R and the destination node Node D, in the second time slot, the relay node first decodes the received signal, then encodes it, and after encoding, performs third-dimensional encoding on part of the check bits of the codeword, and then forwards the codeword to the destination node. The destination node recovers the data information of the source node by using the signal sent by the direct link in the first time slot and the signal sent by the relay link in the second time slot. This method is suitable for a relay channel model containing a source node, a relay node and a destination node. The disadvantage of this method is that when a multiple access system composed of two source nodes or multiple source nodes uses this method to communicate, each source node needs a relay station, and too many relay stations will increase the overhead of the communication network , resulting in a waste of relay resources.

Contents of the invention

The purpose of the present invention is to address the deficiencies in the prior art above, to propose a new improved method, that is, to propose a relay transmission method based on a joint network coding of 3-D Turbo codes, which ensures the frame error rate at the destination Under the premise of high performance, the overhead of the communication network is reduced, and the relay station is fully utilized.

In order to achieve the above object, the technical idea of the present invention is: firstly, at the source node, the information of two independent source nodes is encoded using a traditional Turbo code; secondly, at the relay node, the received signal is decoded with a Turbo code to obtain two estimated information of a source node; re-encode the estimated information with Turbo code, and then select the parity bit by the penetration coefficient method, perform network coding on the selected parity bit, and then perform third-dimensional coding; finally, in the destination node Perform joint decoding.

The present invention is realized according to the following steps:

(1) Obtain the modulation signal sequence:

(1a) Two source nodes S ₁ and S ₂ carry out Turbo code encoding to their own original information sequences u ₁ and u ₂ respectively, and obtain encoded codewords T ₁ and T ₂ ;

(1b) Carry out binary shift keying BPSK modulation to encoded codewords T ₁ and T ₂ respectively, obtain modulated signal sequences C ₁ and C ₂ ;

(2) Broadcast information:

(2a) During the first time slot, the source node S ₁ broadcasts the signal sequence C ₁ to the destination node and the relay node;

(2b) During the second time slot, the source node S ₂ broadcasts the signal sequence C ₂ to the destination node and the relay node;

(3) The relay node performs Turbo decoding:

The relay node performs Turbo decoding on the received signal sequences C ₁ and C ₂ to obtain the estimated sequences of the original information sequences u ₁ and u ₂ and

(4) The relay node performs Turbo encoding:

(4a) The relay node estimates the sequence Perform Turbo encoding to obtain and estimate the sequence Two check sequences P ₁ and P ₂ with the same length;

(4b) The relay node estimates the sequence Perform Turbo encoding to obtain and estimate the sequence Two check sequences P ₃ and P ₄ with the same length;

(5) Select the parity bit:

Using the permeability coefficient selection method, respectively select the verification sequences P ₁ , P ₂ , P ₃ , and P ₄ to obtain the selected verification sequences D ₁ , D ₂ , E ₁ , and E ₂ ;

(6) The relay node performs network coding:

Using the method of bit alternation and combination, the relay node performs network coding on the selected check sequences D ₁ , D ₂ , E ₁ , and E ₂ to obtain the third-dimensional sequence D to be coded;

(7) Obtain the third-dimensional coded modulation sequence:

(7a) The relay node interleaves the third-dimensional coded sequence D and sends it to the third-dimensional encoder to obtain the third-dimensional coded check sequence P;

(7b) The relay node performs binary phase-shift keying BPSK modulation on the third-dimensional code check sequence P to obtain the third-dimensional code-modulated sequence P', and sends the third-dimensional code-modulated sequence P' to the destination node;

(8) Destination node joint decoding:

(8a) In the interval of [1, 1000], arbitrarily select the number of iterations of joint decoding;

(8b) After receiving the information P' of the relay node, the destination node uses the third-dimensional decoder to decode the external information sequence L';

(8c) The outer information sequence L' passes through the deinterleaver to obtain the outer information sequence L after deinterleaving;

(8d) The deinterleaved external information sequence L passes through a serial-to-parallel converter with one input terminal and four output terminals to obtain four check external information sequences L ₁ , L ₂ , L ₃ , L ₄ of equal length ;

(8e) The destination node performs Turbo decoding on the received signal of the signal sequence C ₁ , and obtains the two component verification external information sequences X ₁ and X ₂ of the source node S ₁ ;

(8f) The destination node performs Turbo decoding on the received signal of the signal sequence C ₂ , and obtains the two component verification external information sequences X ₃ and X ₄ of the source node S ₂ ;

(8g) The destination node merges the component verification external information sequences _X1 and _X2 with the external verification information sequences _L1 and _L2 respectively to obtain the two-dimensional verification information sequences _Y1 and _Y2 ;

(8h) The destination node merges the component verification external information sequence X ₃ and X ₄ with the verification external information sequence L ₃ and L ₄ respectively, to obtain the two-dimensional verification information sequence Y ₃ and Y ₄ ;

(8i) The destination node sends the two-dimensional check sequence Y ₁ and Y ₂ into the Turbo decoder of the signal sequence C ₁ , jointly decodes with the code word C ₁ , and decodes the component check external information sequence X ₁ and X ₂ 's update sequence;

(8j) The destination node sends the two-dimensional check sequence Y ₃ and Y ₄ into the Turbo decoder of the signal sequence C ₂ , jointly decodes with the code word C ₂ , and decodes the component check external information sequence X ₃ and X ₄ 's update sequence;

(8k) Using the permeability coefficient selection method, the destination node selects the updated component check sequences X ₁ , X ₂ , X ₃ , and X ₄ respectively, and obtains the selected component check sequences M ₁ , M ₂ , M ₃ , _M4 ;

(8l) The destination node alternately merges the bits in the component check sequences M ₁ , M ₂ , M ₃ , and M ₄ according to their arrangement order to obtain the merged check sequence M, and sends the check sequence M to the third dimension translation In the decoder, as the prior information of the third-dimensional decoder;

(8m) The destination node D judges whether the selected number of iterations of joint decoding has been reached, if yes, output the decoding result by the Turbo decoder, otherwise, execute step (8b).

Compared with the prior art, the present invention has the following advantages:

First, since the present invention performs network coding on the information from two source nodes at the relay node and then transmits the information through the same relay node, it overcomes the need for a relay station for each source node in the prior art. Collaboration results in the shortage of waste of relay resources, so that the present invention has lower communication network overhead.

Second, under the cooperation of the relay node, the present invention first combines the information network codes of the users of the two source nodes and then performs the third-dimensional coding, forming a 3-D Turbo code as a whole, and then forwards and transmits, and finally Joint iterative decoding at the destination node, on the premise of ensuring the frame error rate performance of the receiving end, overcomes the shortcomings of the existing technology that is only applicable to a communication system model of a source node, a relay node and a destination node, so that The present invention has wider application to multiple access systems.

Description of drawings

FIG. 1 is a schematic diagram of a wireless multiple access relay network model of the present invention.

Fig. 2 is a flow chart of the present invention.

Fig. 3 is a simulation diagram of the decoding performance of the distributed 3-D Turbo code transmission and the joint network coding transmission based on 3-DTurbo code at the destination node in the fixed relay node position of the present invention.

Fig. 4 is a simulation diagram of the decoding performance of the 3-D Turbo code joint network coding transmission at the destination node under the position of the fixed relay node and different penetration coefficients according to the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

The invention is realized in the wireless multiple access relay network. Referring to Figure 1, the multiple access relay network of the present invention is composed of two source nodes S ₁ , S ₂ , one relay node R and one destination node D. In the first time slot, the source node S ₁ sends messages to the destination node and the relay node. In the second time slot, the source node S ₂ sends messages to the destination node and the relay node. In the third time slot, the relay node processes the messages sent by the two source nodes and sends them to the destination node. The destination node performs joint decoding after receiving the messages sent by the source nodes S ₁ , S ₂ and the relay node R.

Referring to accompanying drawing 2, the implementation steps of the present invention are described in detail.

Step 1, obtain the modulated signal sequence.

Two source nodes S ₁ and S ₂ respectively perform Turbo code encoding on their original information sequences u ₁ and u ₂ to obtain encoded codewords T ₁ and T ₂ .

The implementation of this step is as follows.

The source node S ₁ performs Turbo coding on the original information sequence u ₁ to obtain the coded sequence T ₁ =(u ₁ ,p ₁ 1,p ₁ 2), where u ₁ is the information sequence of the coded sequence T ₁ of the source node S ₁ , p ₁ 1 is the check sequence of the first component code of the coded sequence T ₁ of the source node S ₁ ; p ₁ 2 is the check sequence of the second component code of the coded sequence T ₁ of the source node S ₁ .

The source node S ₂ performs Turbo coding on the original information sequence u ₂ , and the obtained coded sequence T ₂ =(u ₂ ,p ₂ 1,p ₂ 2), where u ₂ is the information of the coded sequence T ₂ of the source node S ₂ sequence, p ₂ 1 is the check sequence of the first component code of source node S ₂ encoding sequence T ₂ ; p ₂ 2 is the check sequence of the second component code of source node S ₂ encoding sequence T ₂ ; source node The Turbo coding method used can be selected from existing methods, and the specific method can be found in "Error Control Coding" (Shu Lin, Daniel J. Costello, Jr., Machinery Industry Press, 2007).

Perform binary direction shift keying BPSK modulation on encoded codewords T ₁ and T ₂ respectively to obtain modulated signal sequences C ₁ and C ₂ .

Step 2, broadcast information.

The source node S ₁ broadcasts the sending signal sequence C ₁ to the destination node and the relay node.

The source node S ₂ broadcasts the sending signal sequence C ₂ to the destination node and the relay node.

The signals received by the destination node and the relay node are expressed as:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}$

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}$

Among them, y _R,i represents the signal received by the relay node, i∈{1,2} represents the source nodes S ₁ and S ₂ , h _R,i represents the channel fading between the source node S _i and the relay node RN coefficient, E _s represents the transmit power of the source node, c _i represents the coded and modulated signal, n _R,i represents the channel additive white Gaussian noise between the relay node and the destination node; y _D,i represents the channel received by the destination node h _D,i represents the channel fading coefficient between the source node S _i and the destination node D, n _D,i represents the channel additive white Gaussian noise between the source node S _i and the destination node.

Step 3, the relay node performs Turbo decoding.

The relay node performs Turbo decoding on the received signals of the received signal sequences C ₁ and C ₂ to obtain the estimated sequences of the original information sequences u ₁ and u ₂ of the source nodes S ₁ and S ₂ and The Turbo decoding method can be selected from existing methods, and the specific method can be found in "Error Control Coding" (Shu Lin, Daniel J. Costello, Jr., Machinery Industry Press, 2007).

Step 4, the relay node performs Turbo encoding.

Relay node pair estimates sequence Perform Turbo encoding to obtain and estimate the sequence Two check sequences P ₁ and P ₂ with the same length.

Relay node pair estimates sequence Perform turbo encoding to obtain two check sequences P ₃ and P ₄ with the same length as the estimated sequence u ₂ .

Step 5, select parity bits.

Using the permeability coefficient selection method, respectively select the verification sequences P ₁ , P ₂ , P ₃ , and P ₄ to obtain the selected verification sequences D ₁ , D ₂ , E ₁ , and E ₂ .

The steps of the permeability coefficient selection method are as follows:

In the first step, the relay node randomly selects a value of the permeability coefficient λ in the interval [0,1].

In the second step, the four check sequences P ₁ , P ₂ , P ₃ , and P ₄ are equally divided into small check sequence blocks containing 1/λ bits, where λ represents the penetration coefficient.

The third step is to select a bit with the same arrangement position from the constituent bits of each small check sequence block in turn, arrange the selected bits in the selected order, and obtain the check sequence D ₁ after the four check sequences are selected. , D ₂ , E ₁ , E ₂ .

Step 6, the relay node performs network coding.

Using the method of bit alternation and combination, the relay node performs network coding on the selected check sequences D ₁ , D ₂ , E ₁ , and E ₂ to obtain the third-dimensional sequence D to be coded.

The steps of the bit alternation merging method are as follows:

The first step is to extract the first bit according to the arrangement order of the bits in the check sequence D ₁ , and advance the arrangement order of the remaining bits sequentially;

The second step is to extract the first bit according to the arrangement order of the bits in the check sequence _D2 , and advance the arrangement order of the remaining bits in turn;

The third step is to extract the first bit according to the arrangement order of the bits in the verification sequence E ₁ , and advance the arrangement order of the remaining bits successively;

The fourth step is to extract the first bit according to the arrangement order of the bits in the verification sequence _E2 , and advance the arrangement order of the remaining bits in turn;

The fifth step is to sequentially arrange the bits extracted in the above steps as the constituent bits of the sequence to be coded in the third dimension;

The sixth step is to judge whether the number of bits in the check sequence E ₂ is 0, and if so, the network coding performed by the relay node on the selected check sequences D ₁ , D ₂ , E ₁ , and E ₂ ends. Obtain the sequence D to be encoded in the third dimension, otherwise, perform the first step.

Step 7, obtaining the third-dimensional coded modulation sequence.

The relay interleaves the third-dimension to-be-encoded sequence D and sends it to the third-dimension encoder to obtain an encoding verification sequence P.

The relay node performs binary phase shift keying BPSK modulation on the code check sequence P to obtain the modulated sequence P', and sends the third-dimensional coded modulated sequence P' to the destination node.

Step 8, the destination node jointly decodes.

(8.1) In the interval of [1, 1000], the number of iterations of joint decoding is arbitrarily selected.

(8.2) After receiving the sequence P' sent by the relay node, the destination node uses the third-dimensional decoder to decode the external information sequence L'.

(8.3) The outer information sequence L' passes through the deinterleaver to obtain the outer information sequence L after deinterleaving.

(8.4) The deinterleaved external information sequence L passes through a serial-to-parallel converter with one input terminal and four output terminals to obtain four check external information sequences L ₁ , L ₂ , L ₃ , L ₄ of equal length .

(8.5) The destination node performs Turbo decoding on the received signal of the signal sequence C ₁ , and obtains the two component parity-external information sequences X ₁ and X ₂ of the source node S ₁ .

(8.6) The destination node performs Turbo decoding on the received code word C ₂ to obtain two component parity-external information sequences X ₃ and X ₄ of the source node S ₂ .

(8.7) The destination node merges the component check-external information sequences X ₁ and X ₂ with the check-external information sequences L ₁ and L ₂ respectively to obtain two-dimensional check information sequences Y ₁ and Y ₂ .

(8.8) The destination node merges the component check-external information sequences X ₃ and X ₄ with the check-external information sequences L ₃ and L ₄ respectively to obtain two-dimensional check information sequences Y ₃ and Y ₄ .

(8.9) The destination node sends the two-dimensional check sequence Y ₁ and Y ₂ into the Turbo decoder of the signal sequence C ₁ , jointly decodes with the code word C ₁ , and decodes the component check external information sequence X ₁ and X ₂ 's update sequence.

(8.10) The destination node sends the two-dimensional check sequence Y ₃ and Y ₄ into the Turbo decoder of the signal sequence C ₂ , jointly decodes with the code word C ₂ , and decodes the component check external information sequence X ₃ and X ₄ 's update sequence.

(8.11) The destination node uses the permeability coefficient selection method to select the component verification sequences X ₁ , X ₂ , X _{3 ,} and X ₄ respectively, and obtain the selected component verification sequences M ₁ , M ₂ , M ₃ , and M ₄ .

The steps of the permeability coefficient selection method are as follows:

In the first step, the four check sequences X ₁ , X ₂ , X ₃ , and X ₄ are equally divided into small check sequence blocks containing 1/λ bits, where λ represents the penetration coefficient.

The second step is to sequentially select a bit with the same arrangement position from the constituent bits of each small check sequence block, arrange the selected bits according to the selected order, and obtain the check sequence M ₁ of the four check sequences after selection , M ₂ , M ₃ , M ₄ .

(8.12) The destination node alternately merges the bits in the component check sequences M ₁ , M ₂ , M ₃ , and M ₄ according to their arrangement order to obtain the merged check sequence M, and sends the check sequence M to the third dimension translation In the decoder, as the prior information of the third-dimensional decoder.

(8.13) The destination node D judges whether the number of iterations of the selected joint decoding has been reached, if yes, the Turbo decoder outputs the decoding result, otherwise, execute step (8.2).

The effect of the present invention will be further described in conjunction with the simulation diagram below.

1. Simulation conditions:

Set the information length of users S1 and S2 to be 1024, the source node encoder adopts the Turbo code standard in LTE, and the generation matrix is G(D)=[1,(1+D ² +D ³ )/(1+D +D ³ )], the code rate is 1/2, wherein the parameters f1=465 and f2=224 of the binomial permutation QPP interleaver are used in Turbo coding. The third-dimensional encoder at the relay node adopts a circular convolution RSC encoder with a code rate of 1 to generate a matrix ] Wherein, the parameters of the binomial permutation QPP interleaver used at the relay are f1=71, f2=172. Assuming that the sending power of each node is the same, all channels are Rayleigh slow fading channels, and the number of iterations of the decoder is 16.

2. Simulation content:

Simulation experiment 1 of the present invention. The position of the fixed relay node is 1/2 from the source node to the destination node, and the decoding performance of the destination node is simulated for the distributed 3-D Turbo code relay transmission method and the 3-D Turbo code joint network coding relay transmission method .

Fig. 3 is a simulation diagram of the decoding performance of the distributed 3-D Turbo code transmission and the joint network coding transmission based on 3-DTurbo code at the destination node in the fixed relay node position of the present invention. The results of the simulation experiment are shown in Fig. 3. The abscissa in Fig. 3 represents the signal-to-noise ratio from the source node to the destination node, and the ordinate represents the frame error rate FER of the destination node. The solid line with triangles in FIG. 3 represents the frame error rate performance simulation curve of the present invention. The solid curve with a circle represents the frame error rate performance simulation curve of the distributed 3-D Turbo code relay transmission method.

As can be seen from Fig. 3, the solid line with triangles is obviously located under the solid line with circles, indicating that under the same SNR, the frame error rate of the present invention at the destination node is better than that of the distributed 3-D Turbo code relay The frame error rate of the transmission method at the destination node

Simulation experiment 2 of the present invention. The position of the relay node is fixed so that it is located at 1/2 of the source node to the destination node, and different penetration coefficients are selected to simulate the decoding performance of the destination node of the 3-D Turbo code joint network coding relay transmission method. Fig. 4 is a simulation diagram of the decoding performance of the 3-D Turbo code joint network coding transmission at the destination node under the position of the fixed relay node and different penetration coefficients according to the present invention. The simulation results are shown in Figure 4. The abscissa represents the signal-to-noise ratio from the source node to the destination node, and the ordinate represents the frame error rate of the destination node for decoding. The meanings of the curves in Figure 4 are as follows: the circled curve represents the simulation curve of the frame error rate performance of the 3-D Turbo code joint network coding relay transmission method with a penetration coefficient of 0.25. The curve with triangles represents the frame error rate performance simulation curve of the 3-D Turbo code joint network coding relay transmission method with a penetration coefficient of 0.5.

It can be seen from Figure 4 that the solid line with triangles is obviously below the solid line with circles, indicating that when the penetration coefficient is 0.5, the frame error rate performance of the destination node of the 3-D Turbo code joint network coding relay transmission method is better than that of When the penetration coefficient is 0.25, the frame error rate performance of the destination node of the 3-D Turbo code combined network coding relay transmission method, and the decoding performance of the destination node with a larger penetration coefficient will be greatly improved. Although the transmission rate is reduced and the complexity of the relay is increased, the performance is improved.

To sum up the above, the present invention uses network coding to combine the two user data of multiple access and perform third-dimensional coding, forming a 3-D Turbo code as a whole for transmission. Compared with the transmission method of the distributed 3-D Turbo code in the prior art, the present invention has obvious performance gain, and with the increase of the SNR, the performance gain is continuously expanded. This proves that the present invention makes full use of the relay channel under the premise of ensuring the frame error rate performance of the destination, and achieves different performance gains by changing the size of the penetration coefficient, which can realize the complexity of the relay node and the translation of the destination node. Effective tradeoff of code performance.

Claims (5)

1. A joint network coding relay transmission method based on 3-D Turbo code, comprising steps as follows: (1) Obtain the modulation signal sequence: (1a) Two source nodes S ₁ and S ₂ respectively perform Turbo code encoding on their original information sequences u ₁ and u ₂ to obtain encoded codewords T ₁ and T ₂ ; (1b) Carry out binary shift keying BPSK modulation to encoded codeword T ₁ and T ₂ respectively, obtain modulated signal sequence C ₁ and C ₂ ; (2) Broadcast information: (2a) During the first time slot, the source node S ₁ broadcasts the signal sequence C ₁ to the destination node and the relay node; (2b) During the second time slot, the source node S ₂ broadcasts the signal sequence C ₂ to the destination node and the relay node; (3) The relay node performs Turbo decoding: The relay node performs Turbo decoding on the received signal sequences C ₁ and C ₂ to obtain the estimated sequences of the original information sequences u ₁ and u ₂ and (4) The relay node performs Turbo encoding: (4a) The relay node estimates the sequence Perform Turbo encoding to obtain and estimate the sequence Two check sequences P ₁ and P ₂ with the same length; (4b) The relay node estimates the sequence Perform Turbo encoding to obtain and estimate the sequence Two check sequences P ₃ and P ₄ with the same length; (5) Select the parity bit: Using the permeability coefficient selection method, respectively select the four calibration sequences P ₁ , P ₂ , P ₃ , and P ₄ to obtain the selected calibration sequences D ₁ , D ₂ , E ₁ , and E ₂ ; (6) The relay node performs network coding: By adopting the method of alternate bit combination, the relay node performs network encoding on the selected check sequences D ₁ , D ₂ , E ₁ , and E ₂ to obtain the third-dimensional sequence D to be encoded; (7) Obtain the third-dimensional coded modulation sequence: (7a) The relay node interleaves the third-dimensional coded sequence D and sends it to the third-dimensional encoder to obtain the third-dimensional coded check sequence P; (7b) The relay node performs binary phase-shift keying BPSK modulation on the third-dimensional code check sequence P to obtain the third-dimensional code-modulated sequence P', and sends the third-dimensional code-modulated sequence P' to the destination node; (8) Destination node joint decoding: (8a) In the interval of [1, 1000], arbitrarily select the number of iterations of joint decoding; (8b) After receiving the sequence P' sent by the relay node, the destination node uses the third-dimensional decoder to decode the external information sequence L'; (8c) The outer information sequence L' passes through the deinterleaver to obtain the outer information sequence L after deinterleaving; (8d) The deinterleaved external information sequence L passes through a serial-to-parallel converter with one input terminal and four output terminals to obtain four check external information sequences L ₁ , L ₂ , L ₃ , L ₄ of equal length ; (8e) destination node carries out Turbo decoding to received code word C ₁ , obtains the two component check outer information sequences X ₁ and X ₂ of source node S ₁ ; (8f) destination node carries out Turbo decoding to received codeword C ₂ , obtains the two component check outer information sequences X ₃ and X ₄ of source node S ₂ ; (8g) The destination node merges the component verification external information sequences _X1 and _X2 with the external verification information sequences _L1 and _L2 respectively to obtain the two-dimensional verification information sequences _Y1 and _Y2 ; (8h) The destination node merges the component verification external information sequence X ₃ and X ₄ with the verification external information sequence L ₃ and L ₄ respectively, to obtain the two-dimensional verification information sequence Y ₃ and Y ₄ ; (8i) The destination node sends the two-dimensional check sequence Y ₁ and Y ₂ into the Turbo decoder of the code word C ₁ , jointly decodes with the code word C ₁ , and decodes the component check external information sequences X ₁ and X ₂ 's update sequence; (8j) The destination node sends the two-dimensional check sequence Y ₃ and Y ₄ into the Turbo decoder of the code word C ₂ , jointly decodes with the code word C ₂ , and decodes the component check external information sequence X ₃ and X ₄ 's update sequence; (8k) Using the permeability coefficient selection method, the destination node selects the updated component check sequences X ₁ , X ₂ , X ₃ , and X ₄ respectively, and obtains the selected component check sequences M ₁ , M ₂ , M ₃ , _M4 ; (8l) The destination node alternately merges the bits in the component check sequences M ₁ , M ₂ , M ₃ , and M ₄ according to their arrangement order to obtain the merged check sequence M, and sends the check sequence M to the third dimension translation In the decoder, as the prior information of the third-dimensional decoder; (8m) The destination node D judges whether the selected number of iterations of joint decoding has been reached, if yes, output the decoding result by the Turbo decoder, otherwise, execute step (8b). 2. the joint network coding relay transmission method based on 3-D Turbo code according to claim 1, is characterized in that, the step of the penetration coefficient selection method described in the step (5) is as follows: In the first step, the relay node randomly selects a value of the permeability coefficient λ in the interval [0,1]; In the second step, the four check sequences P ₁ , P ₂ , P ₃ , and P ₄ are equally divided into small check sequence blocks containing 1/λ bits, where λ represents the penetration coefficient; The third step is to select a bit with the same arrangement position from the constituent bits of each small check sequence block in turn, arrange the selected bits in the selected order, and obtain the check sequence D ₁ after the four check sequences are selected. , D ₂ , E ₁ , E ₂ . 3. the joint network coding relay transmission method based on 3-D Turbo yards according to claim 1, is characterized in that, the step of the bit alternate merging method described in the step (6) is as follows: The first step is to extract the first bit according to the arrangement order of the bits in the selected check sequence _D1 , and advance the arrangement order of the remaining bits successively; The second step is to extract the first bit according to the arrangement order of the bits in the selected check sequence _D2 , and to advance the arrangement order of the remaining bits successively; The third step is to extract the first bit according to the arrangement order of the bits in the selected check sequence _E1 , and advance the arrangement order of the remaining bits successively; The fourth step is to extract the first bit according to the arrangement order of the bits in the selected check sequence _E2 , and advance the arrangement order of the remaining bits successively; The fifth step is to sequentially arrange the bits extracted in the above steps as the constituent bits of the sequence to be coded in the third dimension; The sixth step is to judge whether the number of bits in the check sequence E ₂ is 0, and if so, the network coding performed by the relay node on the selected check sequences D ₁ , D ₂ , E ₁ , and E ₂ ends. Obtain the sequence D to be encoded in the third dimension, otherwise, perform the first step. 4. the joint network coding relay transmission method based on 3-D Turbo code according to claim 1, is characterized in that, the third dimension coder described in step (7a) adopts the circular convolution RSC of code rate 1 Encoder. 5. the joint network coding relay transmission method based on 3-D Turbo code according to claim 1, is characterized in that, the step of the penetration coefficient selection method described in the step (8k) is as follows: In the first step, divide the four check sequences X ₁ , X ₂ , X ₃ , and X ₄ into small check sequence blocks containing 1/λ bits, where λ represents the penetration coefficient; The second step is to sequentially select a bit with the same arrangement position from the constituent bits of each small check sequence block, arrange the selected bits according to the selected order, and obtain the check sequence M ₁ of the four check sequences after selection , M ₂ , M ₃ , M ₄ .