阅读说明：本技术 一种协作分集系统下最优中继节点选择及功率分配方法 (Optimal relay node selection and power distribution method under cooperative diversity system ) 是由 包建荣 亓凯梁 刘超 姜斌 吴俊� 唐向宏 邱雨 于 2020-12-29 设计创作，主要内容包括：本发明属于数字通信领域,具体涉及一种协作分集系统下最优中继节点选择及功率分配方法,主要通过以下步骤完成,S1：源节点发射信号；S2：将步骤S12所得调制后的信号作为输入参数,按备选中继节点集构建方法执行计算,得到从源节点到中继节点信道质量较好的备选中继节点集；S3：将步骤S2所得备选中继节点集作为输入参数,按协作判决方法执行计算,得到适合协作的中继节点集；S4：将S3所得适合协作的中继节点集作为输入参数,按最优中继节点选取及功率分配方法,执行计算,得到使源节点到目的节点信道容量最大的最优中继节点；S5：目的节点接收信号。本发明减小了系统中断概率,提高了系统能源利用率。(The invention belongs to the field of digital communication, and particularly relates to an optimal relay node selection and power distribution method under a cooperative diversity system, which is mainly completed by the following steps of S1: a source node transmits a signal; s2: taking the modulated signal obtained in the step S12 as an input parameter, and performing calculation according to a candidate relay node set construction method to obtain a candidate relay node set with good channel quality from the source node to the relay node; s3: taking the alternative relay node set obtained in the step S2 as an input parameter, and performing calculation according to a cooperation judgment method to obtain a relay node set suitable for cooperation; s4: taking the relay node set suitable for cooperation obtained in the step S3 as an input parameter, and executing calculation according to an optimal relay node selection and power distribution method to obtain an optimal relay node which enables the channel capacity from a source node to a destination node to be maximum; s5: the destination node receives the signal. The invention reduces the system interruption probability and improves the energy utilization rate of the system.)

1. A method for selecting optimal relay nodes and distributing power under a cooperative diversity system is characterized by comprising the following steps,

s1: the source node transmits a signal, comprising the steps of,

s11: the source node performs channel polarization coding on an original signal to be transmitted, namely binary bit data;

s12: executing an amplitude or phase modulation method on the coded code word obtained in the step S11 to obtain a modulation signal, and broadcasting the modulation signal to all relays and target nodes through a transmitting antenna;

s2: taking the modulated signal obtained in the step S12 as an input parameter, and performing calculation according to a candidate relay node set construction method to obtain a candidate relay node set with good channel quality from the source node to the relay node;

s3: taking the alternative relay node set obtained in the step S2 as an input parameter, and performing calculation according to a cooperation judgment method to obtain a relay node set suitable for cooperation;

s4: taking the relay node set suitable for cooperation obtained in the step S3 as an input parameter, and executing calculation according to an optimal relay node selection and power distribution method to obtain an optimal relay node which enables the channel capacity from a source node to a destination node to be maximum;

s5: the destination node receives the signal.

2. The method for optimal relay node selection and power allocation under a cooperative diversity system according to claim 1, wherein in step S2, the method for constructing the candidate relay node set comprises the following steps:

s21: in the multi-relay cooperative system, the system comprises a source node S, a destination node D and a plurality of nodesRelay node R_iI ranges from 1 to M; wherein M represents the number of all relay nodes; the source node broadcasts the signal to the relay and the destination node, the destination node D and the ith (i is more than or equal to 1 and less than or equal to M) relay node R_iThe received signals are respectively:

wherein x is_sA real number, representing the modulated signal obtained in step S12; p_sIs a real number and represents the transmitting power of the source node S; h is_sdAndis zero mean and the variance is respectivelyAndand mutually independent complex Gaussian random variables respectively representing S-D and S-R_iChannel coefficients of the link; wherein eta is_sdAndis a real number, representing S-D and S-R, respectively_iStandard deviation of link channel coefficients; and n is_sdAndis zero mean and variance is realAnd mutually independent complex Gaussian random variables respectively representing S-D and S-R_iAdditive white gaussian noise of the link; wherein σ_nIs a real number, representing the standard deviation of additive white gaussian noise;

s22: setting a threshold theta (can take 1) when S-R_iAnd when the square of the channel coefficient mode of the link is larger than a threshold value, selecting the relay node into an alternative relay node set omega.

3. The method for optimal relay node selection and power allocation under cooperative diversity system according to claim 2, wherein in step S3, the cooperative decision method is completed by the following steps:

s31: adopting the alternative relay node set selected in step S22, if the alternative relay node set Ω is empty, that is, the channel quality from the source node to the relay node does not meet the requirement, the system does not rely on the relay node, adopts the link to transmit directly, and all the power of the system is used for direct transmission:

wherein the content of the first and second substances,is a complex number representing the signal received by the destination node D in the case of direct transmission using a link, P_TotalReal number, representing the total power emitted by the system;

since no relay node participates, the channel capacity of the link direct transmission can be expressed as

Wherein, I_DTThe real number represents the channel capacity of the link direct transmission;

s32: if the candidate relay node set omega is not empty, for any relay node R in omega_iFor the relay node to correctly decode and forward the source node signal, S-R needs to be satisfied_iThe channel capacity of the link being greater than the transmission rate V of the system, i.e.

In order to ensure the source node transmitting power of the relay node for correct decoding, the following relationship is also required

Wherein the content of the first and second substances,and the real number represents the transmission power of the source node when the ith relay node can successfully decode. For the limited total system power, if the total system power P_TotalLess than satisfactory relay node R_iMinimum power required for correct decodingThe ith relay node does not participate in cooperation, i is a natural number and ranges from 1 to | omega |, and | omega | is the number of elements in the candidate relay node set omega;

s33: respectively calculate R_iSquaring of channel coefficient patterns for D-link and S-D link, ifIt indicates the ith relay node R_iThe channel quality of the D link is worse than that of the S-D link, and the ith relay node does not participate in cooperation; wherein the content of the first and second substances,is zero mean and variance ofIs a complex Gaussian random variable representing R_i-the channel coefficients of the D-link,is a real number, represents R_i-standard deviation of D link channel coefficients.

4. The method for optimal relay node selection and power allocation under cooperative diversity system according to claim 3, wherein in step S4, the method for optimal relay node selection and power allocation is completed by the following steps:

s41: for total system power P_TotalGreater than and equal to relay node R_iMinimum power required for correct decodingAnd isIn the case of a relay node R_iCan be correctly decoded and R_i-the channel quality of the D-link is stronger than the channel quality of the S-D link;

ith relay node R_iWith a transmission power of

The channel capacity from the source node to the destination node at this time can be expressed as

S42: comparing channels from source node to destination node of link direct transmissionCapacity I_DTAnd selecting the ith relay node R_iChannel capacity I from time source node to destination node_iThe size of (d);

the interrupt probability of the system is Pr (I < V), wherein I represents the channel capacity from the source node to the destination node, and Pr (.) is a real number and represents a probability value; selecting the channel capacity from the source node to the destination node to be maximum, so that the interruption probability of the system can be reduced;

selecting the node with the maximum channel capacity for decoding and forwarding or direct transmission;

I_max＝max(I_DT,I_i,i＝1～|Ω|) (10)

wherein, I_maxFor the selected maximum channel capacity, if I_max＝I_DTIf the channel capacity of the link direct transmission is the maximum, the step S31 is skipped to, the direct transmission link S-D transmission is preferentially selected, and the relay node does not participate in the cooperative transmission; if I_max＝I_iAnd i is 1 to omega, the selected ith relay node R_iAfter the received signal is processed by the polar code continuous deleting decoding method, the channel polar coding is executed again and the signal is forwarded to a destination node D; at R_iThe signal forwarded by coding can be represented asThen D received signalCan be expressed as

Wherein the content of the first and second substances,is zero mean and variance is realIndependent complex Gaussian random variationAmount, represents R_i-additive white gaussian noise for the D-link.

5. The method for optimal relay node selection and power allocation under cooperative diversity system according to claim 4, wherein in step S5, the step of receiving signal by destination node is:

after receiving the signals of the two stages in steps S21 and S42 or the signals forwarded only by link direct transmission in steps S31 and S41, the destination node performs a maximum ratio combining method to combine all the received signals, and then performs demodulation and decoding by a continuous erasure decoding method in sequence to obtain a signal sequence estimated by the destination node, which is the final result.

Technical Field

The invention belongs to the field of digital communication, and particularly relates to an optimal relay node selection and power distribution method in a cooperative diversity system.

Background

In recent years, in the field of wireless communication, obtaining performance gain by diversity in a Multiple Input Multiple Output (MIMO) system has been receiving extensive attention and research in the industry. And cooperative communication is to allow users in the system to complete cooperation by relaying messages between each other to a destination. This effectively forms a distributed antenna array to achieve the spatial diversity gain achieved by a centralized MIMO system. The common relay method for cooperative communication includes: amplify-and-forward (AF), decode-and-forward (DF), Selective Relay (SR), Coding Cooperation (CC), and compress-and-forward (CF), among others. The Laneman J N et al analyzes a distributed space-time coding method in cooperation, reduces loss of frequency spectrum efficiency, and the Bletsas A et al provides an optimal relay method in a multi-relay system, selects a relay node with optimal performance from a plurality of relay nodes for forwarding, and proves that the performance is superior to that of distributed space-time coding under the condition of equal power. However, the prior art still has the defects that the system has low energy utilization rate under the condition of limited total power and the system is easy to interrupt.

The invention provides an optimal relay node selection and power distribution method under a cooperative diversity system based on a polarization code coding and decoding method, a modulation method and a Maximum Ratio Combining (MRC) method in the prior art. Wherein the content of the first and second substances,

1. polarization code coding and decoding method

An information sequence with length bit K is constructed into an information code word vector u with the length of 1 multiplied by L through a channel polarization theory (u is equal to₁,u₂,…,u_L). Wherein K and L are natural numbers and have K<And L. The u element includes K information bits and L-K bitsThe frozen bits, which do not convey information, may all be represented by codeword 0. Then, a polar code P (L, K) with a code length L and an information bit length K is coded into a codeword x by a polar coding method, and the codeword x can be decoded by a successive erasure coding (SC) method. The Channel Polarization Theory, Polarization coding and continuous deletion decoding Method are concretely described in 'E.Arikan, Channel Polarization: A Method for transforming Capacity-Achieveying Codes for symmetry Binary-Input memory Channels, IEEE Transactions on Information Theory, vol.55, No.7, pp.3051-3073, July 2009'.

2. Modulation method

The source node polarization channel coding obtains a code word x ═ (x)₁,x₂,…,x_L) Modulation is accomplished through variations in amplitude, frequency, phase, etc. See specifically "H · morkar, jing, a · Y · golhoff, et al. Such as Binary Phase Shift Keying (BPSK) modulation, is achieved by: s_i＝1-2x_iI is a natural number ranging from 1 to L, L represents a codeword length, s_iIs x_iCorresponding BPSK modulation symbols, s_iE { -1,1 }. Other modulation methods are similar, see the above references.

3. Maximal Ratio Combining (MRC) method

To fully exploit the spatial diversity gain provided by multipath reception, MRC selects a weighting factor that maximizes the received SNR, thereby reducing outage probability. See in particular "D G Brennan, On the maximum signal-to-noise ratio conversion from partial noise signals, Proc IRE, vol 43, p1530, Oct 1955". In particular, the weight factor for MRC, given instantaneous channel state information, is given by:

wherein, i is a natural number,for the link channel coefficient h_iConjugation of (1).

Disclosure of Invention

Based on the defects that the system energy utilization rate is not high and the system is easy to interrupt under the condition that the total power is limited in the prior art, the invention provides an optimal relay node selection and power distribution method under a cooperative diversity system, and the system performance is improved by combining a channel polarization coding and selection decoding forwarding mode; the relay node which enables the channel capacity from the source node to the destination node to be maximum is selected for forwarding, and the system interruption probability is reduced.

The invention adopts the following technical scheme:

a method for selecting optimal relay nodes and distributing power under a cooperative diversity system is characterized by comprising the following steps,

s1: the source node transmits a signal, comprising the steps of,

s11: the source node performs channel polarization coding on an original signal to be transmitted, namely binary bit data;

s12 executing amplitude or phase modulation method to the code word obtained from S11 to obtain modulation signal, then broadcasting to all relay and destination nodes through transmitting antenna;

s2: taking the modulated signal obtained in the step S12 as an input parameter, and performing calculation according to a candidate relay node set construction method to obtain a candidate relay node set with good channel quality from the source node to the relay node;

s3: taking the alternative relay node set obtained in the step S2 as an input parameter, and performing calculation according to a cooperation judgment method to obtain a relay node set suitable for cooperation;

s4: taking the relay node set suitable for cooperation obtained in the step S3 as an input parameter, and executing calculation according to an optimal relay node selection and power distribution method to obtain an optimal relay node which enables the channel capacity from a source node to a destination node to be maximum;

s5: the destination node receives the signal.

Preferably, in step S2, the method for constructing an alternative relay node set includes the following steps:

step S21: in the multi-relay cooperative system, the system comprises a source node S, a destination node D and a plurality of nodesRelay node R_iAnd i ranges from 1 to M. Where M represents the number of all relay nodes. The source node broadcasts the signal to the relay and the destination node, the destination node D and the ith (i is more than or equal to 1 and less than or equal to M) relay node R_iThe received signals are respectively:

wherein x is_sIs a real number, representing a modulated signal; p_sIs a real number and represents the transmitting power of the source node S; h is_sdAndis zero mean and the variance is respectivelyAndand mutually independent complex Gaussian random variables representing S-D and S-R_iChannel coefficients of the link. Wherein eta is_sdAnd η_sriIs a real number, representing S-D and S-R, respectively_iStandard deviation of the link channel coefficients. And n is_sdAndis zero mean and variance is realAnd mutually independent complex Gaussian random variables respectively representing S-D and S-R_iAdditive white gaussian noise of the link. Wherein σ_nIs a real number and represents the standard deviation of additive white gaussian noise.

Step S22: in order to obtain a relay node set with better channel quality from a source node to a relay node, the method includesSetting a threshold theta (can take 1) when S-R_iAnd when the square of the channel coefficient mode of the link is larger than a threshold value, selecting the relay node into an alternative relay node set omega.

Preferably, the method for determining cooperation in step S3 includes the following steps:

step S31: adopting the alternative relay node set selected in the step 2.2, if the alternative relay node set Ω is empty, that is, the channel quality from the source node to the relay node does not meet the requirement, the system does not depend on the relay node, adopts the link to transmit directly, and all the power of the system is used for direct transmission:

wherein the content of the first and second substances,is a complex number representing the signal received by the destination node D in the case of direct transmission using a link, P_TotalAnd is a real number representing the total power transmitted by the system.

Since no relay node participates, the channel capacity of the link direct transmission can be expressed as

Wherein, I_DTAnd the real number represents the channel capacity of the link direct transmission.

Step S32: if the candidate relay node set omega is not empty, for any relay node R in omega_iFor the relay node to correctly decode and forward the source node signal, S-R needs to be satisfied_iThe channel capacity of the link being greater than the transmission rate V of the system, i.e.

In order to ensure the source node transmitting power of the relay node for correct decoding, the following relationship is also required

Wherein the content of the first and second substances,and the real number represents the transmission power of the source node when the ith relay node can successfully decode. For the situation that the total power of the system is limited, if the total power of the system is: p_TotalLess than satisfactory relay node R_iThe minimum power required to be correctly decoded:the ith relay node does not participate in the cooperation, i is a natural number and ranges from 1 to | Ω |, and | Ω | is the number of elements in the candidate relay set Ω.

Step S33: respectively calculate R_iSquaring of channel coefficient patterns for D-link and S-D link, ifThis indicates the ith relay node R_iAnd the channel quality of the D link is worse than that of the S-D link, and the ith relay node does not participate in the cooperation. Wherein the content of the first and second substances,is zero mean and variance ofIs a complex Gaussian random variable representing R_i-the channel coefficients of the D-link,is a real number, represents R_i-D linkStandard deviation of channel coefficients.

As a preferred scheme, the optimal relay node selecting and power allocating method in step S4 includes the following steps:

step S41: for total system power P_TotalGreater than and equal to relay node R_iMinimum power required for correct decodingAnd isIn the case of a relay node R_iCan be correctly decoded and R_iUnder the condition that the channel quality of the D link is stronger than that of the S-D link, in order to maximize the signal-to-noise ratio of the destination node, the relay node R is required to be_iTransmitting with as much power as possible. Therefore, the ith relay node R_iThe transmission power of (a) is:

then the channel capacity from the source node to the destination node at this time can be expressed as:

step S42: comparing channel capacity I from source node to destination node of link direct transmission_DTAnd selecting the ith relay node R_iChannel capacity I from time source node to destination node_iThe size of (2).

Because the outage probability of the system is Pr (I < V), wherein I represents the channel capacity from the source node to the destination node, and Pr (.) is a real variable and represents a probability value. The choice of maximizing the channel capacity from the source node to the destination node reduces the outage probability of the system.

The node with the largest channel capacity is then selected for decoding forwarding or direct forwarding.

I_max＝max(I_DT,I_i,i＝1～|Ω|) (11)

Wherein, I_maxFor the selected maximum channel capacity, if I_max＝I_DTIf the channel capacity of the link direct transmission is the maximum, the step S31 is skipped to, the direct transmission link S-D transmission is preferentially selected, and the relay node does not participate in the cooperative transmission; if I_max＝I_iAnd i is 1 to omega, the selected ith relay node R_iAfter the received signal is processed by the polar code continuous deleting decoding method described in the background technology, the channel polar code described in the background technology is executed again and forwarded to the destination node D. At R_iThe signal forwarded by coding can be represented asThen D received signalCan be expressed as

Wherein the content of the first and second substances,is zero mean and variance is realIs a complex Gaussian random variable representing R_i-additive white gaussian noise for the D-link.

Preferably, in step S5, the step of receiving the signal by the destination node is: after receiving the signals of the two stages in steps S21 and S42 or the signals forwarded only by link direct transmission in steps S31 and S41, the destination node performs a maximum ratio combining method to combine all the received signals, and then performs demodulation and decoding by a continuous erasure decoding method in sequence to obtain a signal sequence estimated by the destination node, which is the final result.

Compared with the prior art, the invention has the beneficial effects that:

the invention combines the channel polarization coding and decoding forwarding method, and realizes the optimal relay node selection and power distribution method scheme under a cooperative diversity system; aiming at the problem of low energy utilization rate of the system under the condition that the total power of the system is limited at present, a power distribution scheme between a source node and a selected relay node is provided; the relay node which enables the channel capacity from the source node to the destination node to be maximum is selected for forwarding, and the system interruption probability is reduced; and the system performance is improved by combining advanced channel polarization coding and selective decoding forwarding.

Drawings

Fig. 1 is a flowchart of an optimal relay node selection and power allocation method in a cooperative diversity system according to an embodiment of the present invention;

FIG. 2 is a flowchart illustrating a step of a source node transmitting a signal according to an embodiment of the present invention;

fig. 3 is a flowchart of a method for constructing an alternative relay node set according to an embodiment of the present invention;

FIG. 4 is a flowchart of a method for determining collaboration in accordance with an embodiment of the present invention;

fig. 5 is a flowchart of an optimal relay node selection and power distribution method according to an embodiment of the present invention;

FIG. 6 is a flowchart illustrating a signal receiving procedure of a destination node according to an embodiment of the present invention;

Detailed Description

The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto.

The embodiment of the invention provides an optimal relay node selection and power distribution method in a cooperative diversity system, which comprises the following steps:

s1: the source node transmits a signal.

The method for transmitting the signal by the source node comprises the following steps:

s11: the source node performs channel polarization coding on the original signal to be transmitted as described in the background.

S12: the coded code word obtained in step S11 is subjected to the modulation method described in the background art, and then broadcast to all relays and destination nodes via the transmitting antenna.

S2: and taking the modulated signal obtained in the step S12 as an input parameter, and performing calculation according to a candidate relay node set construction method to obtain a candidate relay node set with good channel quality from the source node to the relay node.

The method for constructing the alternative relay node set comprises the following steps:

s21: in the multi-relay cooperative system, the system comprises a source node S, a destination node D and a plurality of relay nodes R_iAnd i ranges from 1 to M. Where M represents the number of all relay nodes. The source node broadcasts the signal to the relay and the destination node, the destination node D and the ith (i is more than or equal to 1 and less than or equal to M) relay node R_iThe received signals are respectively:

wherein x is_sThe real number represents the modulated signal obtained in the step 1.2; p_sIs a real number and represents the transmitting power of the source node S; h is_sdAndis zero mean and the variance is respectivelyAndand mutually independent complex Gaussian random variables representing S-D and S-R_iChannel coefficients of the link. Wherein eta is_sdAndis a real number, representing S-D and S-R, respectively_iStandard deviation of the link channel coefficients. And n is_sdAndis zero mean and variance is realAnd mutually independent complex Gaussian random variables respectively representing S-D and S-R_iAdditive white gaussian noise of the link. Wherein σ_nIs a real number and represents the standard deviation of additive white gaussian noise.

S22: in order to obtain a relay node set with better channel quality from a source node to a relay node, a threshold theta (can be 1) is set, when S-R is used_iAnd when the square of the channel coefficient mode of the link is larger than a threshold value, selecting the relay node into an alternative relay node set omega.

S3: and taking the alternative relay node set obtained in the step S2 as an input parameter, and performing calculation according to a cooperation judgment method to obtain a relay node set suitable for cooperation.

The cooperative judgment method is completed by adopting the following steps:

s31: adopting the alternative relay node set selected in step S22, if the alternative relay node set Ω is empty, that is, the channel quality from the source node to the relay node does not meet the requirement, the system does not rely on the relay node, adopts the link to transmit directly, and all the power of the system is used for direct transmission:

wherein the content of the first and second substances,is a complex number representing the signal received by the destination node D in the case of direct transmission using a link, P_TotalAnd is a real number representing the total power transmitted by the system.

Since no relay node participates, the channel capacity of the link direct transmission can be expressed as

Wherein, I_DTAnd the real number represents the channel capacity of the link direct transmission.

S32: if the candidate relay node set omega is not empty, for any relay node R in omega_iFor the relay node to correctly decode and forward the source node signal, S-R needs to be satisfied_iThe channel capacity of the link being greater than the transmission rate V of the system, i.e.

In order to ensure the source node transmitting power of the relay node for correct decoding, the following relationship is also required

Wherein the content of the first and second substances,and the real number represents the transmission power of the source node when the ith relay node can successfully decode. For the situation that the total power of the system is limited, if the total power of the system is: p_TotalLess than satisfactory relay node R_iThe minimum power required to be correctly decoded:the ith relay node does not participate in the cooperation, i is a natural number and ranges from 1 to | Ω |, and | Ω | is the number of elements in the candidate relay set Ω.

S33: respectively calculate R_iSquaring of channel coefficient patterns for D-link and S-D link, ifThis indicates the ith relay node R_iAnd the channel quality of the D link is worse than that of the S-D link, and the ith relay node does not participate in the cooperation. Wherein the content of the first and second substances,is zero mean and variance ofIs a complex Gaussian random variable representing R_i-the channel coefficients of the D-link,is a real number, represents R_i-standard deviation of D link channel coefficients.

S4: and taking the relay node set suitable for cooperation obtained in the step S3 as an input parameter, and executing calculation according to an optimal relay node selection and power distribution method to obtain an optimal relay node which enables the channel capacity from the source node to the destination node to be maximum.

The optimal relay node selection and power distribution method is completed by adopting the following steps:

s41: for total system power P_TotalGreater than and equal to relay node R_iMinimum power required for correct decodingAnd isIn the case of a relay node R_iCan be correctly decoded and R_iUnder the condition that the channel quality of the D link is stronger than that of the S-D link, in order to maximize the signal-to-noise ratio of the destination node, the relay node R is required to be_iTransmitting with as much power as possible. So the ith relay node R_iWith a transmission power of

The channel capacity from the source node to the destination node at this time can be expressed as

S42: comparing channel capacity I from source node to destination node of link direct transmission_DTAnd selecting the ith relay node R_iChannel capacity I from time source node to destination node_iThe size of (2).

Because the outage probability of the system is Pr (I < V), where I represents the channel capacity from the source node to the destination node, and Pr (.) is a real number, representing a probability value. The choice of maximizing the channel capacity from the source node to the destination node reduces the outage probability of the system.

The node with the largest channel capacity is then selected for decoding forwarding or direct forwarding.

I_max＝max(I_DT,I_i,i＝1～|Ω|) (22)

Wherein, I_maxFor the selected maximum channel capacity, if I_max＝I_DTIf the channel capacity of the link direct transmission is the maximum, the step S31 is skipped to, the direct transmission link S-D transmission is preferentially selected, and the relay node does not participate in the cooperative transmission; if I_max＝I_iAnd i is 1 to omega, the selected ith relay node R_iAfter the received signal is processed by the polar code continuous deleting decoding method described in the background technology, the channel polar code described in the background technology is executed again and forwarded to the destination node D. At R_iThe signal forwarded by coding can be represented asThen D received signalCan be expressed as

Wherein the content of the first and second substances,is zero mean and variance is realIs a complex Gaussian random variable representing R_i-additive white gaussian noise for the D-link.

S5: the destination node receives the signal, comprising the steps of,

s51: after receiving the two-stage signals of step S21 and step S42 or the signals forwarded only by link-directed forwarding of step S31 and step S41, the maximum ratio combining method reception described in the background is performed.

S52: the demodulation and polar code decoding methods described in the background art are sequentially performed on the received signal obtained in S51 to obtain an estimated signal, i.e., the final result of the method.

As shown in fig. 1, a method for selecting an optimal relay node and allocating power in a cooperative diversity system according to an embodiment of the present invention is mainly completed through the following steps: step one, a source node transmits signals: the source node sequentially executes channel polarization coding and modulation on an original signal to be transmitted, and broadcasts the original signal to all relay and target nodes through a transmitting antenna; step two, a method for constructing an alternative relay node set: selecting a relay node with better channel quality from a source node to the relay node as a standby relay node set; step three, the cooperation judging method comprises the following steps: judging whether a relay node participates in cooperation or not according to the condition that the total power of a system is limited and the channel state information; step four, the optimal relay node selection and power distribution method comprises the following steps: selecting a relay with the largest channel capacity from a source node to a destination node as an optimal relay node, and distributing power between the selected relay node and the source node; step five, the step of receiving signals by the destination node: after the signal reaches the destination node, the maximum ratio combining method is adopted for receiving, and then the signal is demodulated and polarized decoded to obtain an estimated original signal.

Fig. 2 is a flow chart of the steps of the source node transmitting a signal. The source node performs channel polarization coding on the signal sequence to be transmitted as described in the background. The coded codeword is then subjected to the modulation method described in the background art and broadcast in free space to all relay and destination nodes via the transmit antennas.

Fig. 3 is a flowchart of an alternative relay node set construction method. In the multi-relay cooperative system, the system comprises a source node S, a destination node D and a plurality of relay nodes R_iAnd i ranges from 1 to M. Where M represents the number of all relay nodes. The source node broadcasts the signal to the relay and the destination node, the destination node D and the ith (i is more than or equal to 1 and less than or equal to M) relay node R_iThe received signals are respectively:

wherein x is_sIs a real number, representing a modulated signal; p_sIs a real number and represents the transmitting power of the source node S; h is_sdAndis zero mean and the variance is respectivelyAndand mutually independent complex Gaussian random variables representing S-D and S-R_iChannel coefficients of the link. Wherein eta is_sdAndis a real number, representing S-D and S-R, respectively_iStandard deviation of the link channel coefficients. And n is_sdAndis zero mean and variance is realAnd mutually independent complex Gaussian random variables respectively representing S-D and S-R_iAdditive white gaussian noise of the link. Wherein σ_nIs a real number and represents the standard deviation of additive white gaussian noise.

In order to obtain a relay node set with better channel quality from a source node to a relay node, a threshold theta (can be 1) is set, when S-R is used_iAnd when the square of the channel coefficient mode of the link is larger than a threshold value, selecting the relay node into an alternative relay node set omega.

Fig. 4 is a flowchart of a cooperation deciding method. Adopting an alternative relay node set, if the alternative relay node set omega is empty, namely the channel quality from a source node to a relay node does not meet the requirement, the system does not depend on the relay node, adopting a link for direct transmission, and using all power of the system for direct transmission:

wherein the content of the first and second substances,is a complex number representing the signal received by the destination node D in the case of direct transmission using a link, P_TotalAnd is a real number representing the total power transmitted by the system.

Since no relay node participates, the channel capacity of the link direct transmission can be expressed as

Wherein, I_DTAnd the real number represents the channel capacity of the link direct transmission.

If the candidate relay node set omega is not empty, for any relay node R in omega_iFor the relay node to correctly decode and forward the source node signal, S-R needs to be satisfied_iThe channel capacity of the link being greater than the transmission rate V of the system, i.e.

In order to ensure the source node transmitting power of the relay node for correct decoding, the following relationship is also required

Wherein, P_SiAnd the real number represents the transmission power of the source node when the ith relay node can successfully decode. For the situation that the total power of the system is limited, if the total power of the system is: p_TotalLess than satisfactory relay node R_iThe minimum power required to be correctly decoded:the ith relay node does not participate in the cooperation, i is a natural number and ranges from 1 to | Ω |, and | Ω | is the number of elements in the candidate relay set Ω.

Respectively calculate R_iSquaring of channel coefficient patterns for D-link and S-D link, ifThis indicates the ith relay node R_iAnd the channel quality of the D link is worse than that of the S-D link, and the ith relay node does not participate in the cooperation. Wherein the content of the first and second substances,is zero mean and variance ofIs a complex Gaussian random variable representing R_i-the channel coefficients of the D-link,is a real number, represents R_i-standard deviation of D link channel coefficients.

Fig. 5 is a flowchart of an optimal relay node selection and power allocation method. For total system power P_TotalGreater than and equal to relay node R_iMinimum power required for correct decodingAnd isIn the case of a relay node R_iCan be correctly decoded and R_iUnder the condition that the channel quality of the D link is stronger than that of the S-D link, in order to maximize the signal-to-noise ratio of the destination node, the relay node R is required to be_iTransmitting with as much power as possible. So the ith relay node R_iWith a transmission power of

The channel capacity from the source node to the destination node at this time can be expressed as

Comparing channel capacity I from source node to destination node of link direct transmission_DTAnd selecting the ith relay node R_iChannel capacity I from time source node to destination node_iThe size of (2).

Because the outage probability of the system is Pr (I < V), where I represents the channel capacity from the source node to the destination node, and Pr (.) is a real number, representing a probability value. The choice of maximizing the channel capacity from the source node to the destination node reduces the outage probability of the system.

The node with the largest channel capacity is then selected for decoding forwarding or direct forwarding.

I_max＝max(I_DT,I_i,i＝1～|Ω|) (33)

Wherein, I_maxFor the selected maximum channel capacity, if I_max＝I_DTIf the channel capacity of the link direct transmission is the maximum, the step S31 is skipped to, the direct transmission link S-D transmission is preferentially selected, and the relay node does not participate in the cooperative transmission; if I_max＝I_iAnd i is 1 to omega, the selected ith relay node R_iAfter the received signal is processed by the polar code continuous deleting decoding method described in the background technology, the channel polar code described in the background technology is executed again and forwarded to the destination node D. At R_iThe signal forwarded by coding can be represented asThen D received signalCan be expressed as

Wherein the content of the first and second substances,is zero mean and variance is realIs a complex Gaussian random variable representing R_i-additive white gaussian noise for the D-link.

Fig. 6 is a flow chart of the steps of the destination node receiving a signal. For the signal transmitted to the destination node, the maximum ratio combining method described in the background art is performed to combine all the received signals. Then, the combined signal sequence is sequentially subjected to demodulation and polar code decoding methods described in the background art to obtain a signal estimated by a target node, namely a final result of the method.

While the embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that variations may be made in the embodiments without departing from the spirit of the invention, and such variations are to be considered within the scope of the invention.