CN104717712A - Node selecting method for prolonging network lifetime of collaboration wireless sensor network - Google Patents

Abstract

The invention discloses a node selecting method for prolonging network lifetime of a collaboration wireless sensor network. By setting up the relation among channel state information, node rest energy and outage probability, which nodes serving as potential relays to transmit information are determined, the lifetime of the collaboration network can be effectively prolonged, and a more accurate method is adopted to define the lifetime of the collaboration network. Compared with an existing relay selecting scheme, the technical scheme prolongs the lifetime of a collaboration communication network.

Description

A kind of wireless sense network that cooperates strengthens the node selecting method of network lifecycle

Technical field

The present invention relates to the node selecting method that a kind of wireless sense network that cooperates strengthens network lifecycle, belong to wireless communications relay technology.

Background technology

Wireless sensor network (WSN, wireless sensor networks) is the network consisted of Ad hoc mode a large amount of microsensor nodes.These sensor node costs are low, power consumption is little and possess certain perception, computing capability and wireless communication ability.Wireless sensor network all has broad application prospects at numerous areas such as environment measuring, national defence anti-terrorism, earthquake relief work, medical treatment and nursing, Smart Home and deep space probings, is one of focus of academic circles at present research.The energy of sensor node is all generally rely on the built-in battery of node to provide, the energy that can node be supplied to carry out operational processes is limited, and sensor node is all generally sow the area in environmental condition complexity, how carrying out the supplementary of node energy is a great problem.Therefore, how to use energy efficiently, maximization network life cycle becomes wireless sensor network and applies the overriding challenge faced further.

According to the via node number participating in collaboration communication, relay selection scheme can be divided into two classes: a class is many trunk node selection scheme, namely requires that selecting multiple relaying to participate in cooperation forwards according to certain; Another kind of is single trunk node selection scheme, namely in multiple alternative relaying, only selects an optimum relaying to assist source node to carry out data retransmission according to a certain algorithm.To meet the SNR of destination node for index, when (or ratio be less than certain numerical value after) after the via node in system is less than certain quantity, definition cooperative communication network " death ", the duration before death is the life duration of cooperative communication network.

In the junction network shown in Fig. 1, information source S send information at the first time slot and reaches destination node D and each via node R, and each via node R selects a via node at second time slot forwarding information to destination node D after single trunk node selection scheme.In the prior art, conventional single trunk node selection scheme generally has two kinds: one is MTP scheme, and refer to choose needs the via node of minimum transmitting energy as cooperative transmission node at every turn; Another kind is MRE scheme, and refer to the via node selecting dump energy maximum, namely the present energy of via node deducts the energy needed for transmission, and the maximum is cooperative transmission node.

But there is following defect in MTP scheme and MRE scheme: 1, be inaccurate with the sensor node definition cooperation wireless sensor network life duration that there is specific quantity (ratio), because certain transducer can not participate in the spatial gain that forwarding information is only reduction of this system, the QoS demand of pedal system might not be discontented with; 2, the node that each transmitting energy of MTP Scheme Choice is minimum, likely makes certain relaying too early " death "; 3, MRE scheme makes the energy in relaying average, but the via node of forwarding information can be caused to consume macro-energy simultaneously, and therefore both are not of value to the prolongation of wireless sense network life duration.Therefore need a more excellent trunk node selection scheme to overcome these problems.

Abbreviation and Key Term definition

WSN wireless sensor networks wireless sense network

CSI channel state information channel condition information

REI residual energy information dump energy information

QOS quality of service service quality

AF amplify and forward amplification forwarding

MTP minimum transmission energy minimum transfer energy

MRE maximum residual energy maximum residual energy

The maximum energy efficiency index of MRI maximum energy-efficiency index

The OLS optimal lifetime strategy optimal network life-span

Summary of the invention

Goal of the invention: in order to overcome the deficiencies in the prior art, the invention provides the node selecting method that a kind of wireless sense network that cooperates strengthens network lifecycle, by setting up the relation of channel condition information (CSI), residue energy of node (REI) and outage probability, thus determine which node can as potential relay transmission message, effectively to extend the life duration of collaborative network, adopt the life duration of the collaborative network of method definition more accurately simultaneously.

Technical scheme: for achieving the above object, the technical solution used in the present invention is:

The wireless sense network that cooperates strengthens a node selecting method for network lifecycle, comprises the steps:

(1) initialization relaying number N, the primary power of N number of via node is timing step lifetime=0 is set;

(2) system break probability is judged whether be less than setting threshold η, η is cooperative relay system largest tolerable outage probability value:

$P_{\mathrm{out}}\left(\stackrel{\→}{e}\right[m\left]\right)=\underset{k=1}{\overset{N}{\mathrm{\Π}}}{P}_{\mathrm{out}}\left(e_k\right[m\left]\right)$

$\begin{array}{c}{P}_{\mathrm{out}}\left(e_k\right[m\left]\right)=P_r(P_s{\left|h_{\mathrm{sd}}\right|}^2+\frac{P_s{e}_k\left[m\right]{\left|h_{\mathrm{sk}}{h}_{\mathrm{kd}}\right|}^2}{1+P_s{\left|h_{\mathrm{sk}}\right|}^2+e_k\left[m\right]{\left|h_{\mathrm{kd}}\right|}^2}<\mathrm{\&gamma;})\\ =1-\left[e^{-(\frac{\mathrm{\&gamma;}}{P_s{\mathrm{\&sigma;}}_{\mathrm{sk}}^2}+\frac{\mathrm{\&gamma;}}{e_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{kd}}^2})}\sqrt{\frac{4\mathrm{\&gamma;}}{P_s{e}_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{sk}}^2{\mathrm{\&sigma;}}_{\mathrm{kd}}^2}}{K}_1\left(\sqrt{\frac{4\mathrm{\&gamma;}(\mathrm{\&gamma;}+1)}{P_s{e}_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{sk}}^2{\mathrm{\&sigma;}}_{\mathrm{kd}}^2}}\right)\right]\end{array}$

Wherein, γ is the threshold value of the received signal to noise ratio of destination node, if the received signal to noise ratio of destination node is greater than threshold gamma, then thinks that destination node proper reception of information; e _k[m] is the primary power of a kth via node when m time slot; P _r() represents the probability asking for bracket content; P _sfor the transmitting power of information source node S; h _sdrepresent that information source node is to the channel gain of destination node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; h _skrepresent that information source node is to the channel gain of via node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; h _kdrepresent that via node is to the channel gain of destination node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; K ₁() represents the Bessel function of the second kind of single order;

As can be seen from the above equation, system break probability only relevant with the dump energy of via node; If then enter step (3); Otherwise record lifetime also terminates;

(3) h that cooperative relay system stochastic generation is new _sd, h _skand h _kd;

(4) judge whether via node belongs to set R _e, namely judge whether via node meets following condition:

1. the signal to noise ratio that accepts of destination node needs to be greater than threshold gamma, the minimum transmission power P that therefore a kth via node is required under m time slot meets this condition _k-min[m] is:

$P_{k-\min }\left[m\right]=\min \left\{P_k\right[m]:P_s{\left|h_{\mathrm{sd}}\right|}^2+\frac{P_s{P}_k\left[m\right]{\left|h_{\mathrm{sk}}{h}_{\mathrm{kd}}\right|}^2}{1+P_s{\left|h_{\mathrm{sk}}\right|}^2+P_k\left[m\right]{\left|h_{\mathrm{kd}}\right|}^2}\&GreaterEqual;\mathrm{\&gamma;}\}$

Wherein, P _k[m] represents the through-put power of a kth via node at m time slot; Set information is a unit interval in the time of each slot transmission, then the power consumption of via node transmission is numerically equal to the power of transmission, requires that a kth via node meets P based on this _k-min[m]≤P _k-maxand P _k-min[m]≤e _k[m] these two conditions, namely require when m time slot, the minimum transmission power P of a kth via node _k-min[m] is less than its maximum transmission power P _k-max, the minimal consumption energy P of a kth via node _k-min[m] is less than its primary power e at m time slot _k[m];

2. when m time slot, the received signal to noise ratio of a kth via node is greater than γ, ensures that the information of relay forwarding can not too distortion, namely $R_t=\{k:P_s{\left|h_{\mathrm{sk}}\right|}^2\&GreaterEqual;\mathrm{\&gamma;}\};$

Based on above-mentioned condition, R _e=R _t∩ { k:P _k-min[m]≤e _k[m] } ∩ { k:P _k-min[m]≤P _max; If R _efor empty set, then keep current relay state constant, return step (3); Otherwise, enter step (5);

(5) adopt MEI scheme or OLS scheme from R _emiddle selection via node is as assistance transmission node;

1. MEI scheme is select the energy efficiency via node of maximum ratio as assistance transmission node, is specially: for R _ein each via node, calculate following formula:

$k_{\mathrm{MEI}}^{*}=\arg \underset{k\&Element;R_E}{\max }\frac{e_k\left[m\right]}{w_k\left[m\right]}$

Choose be worth minimum via node as assistance transmission node, the via node selected like this is the minimum via node of energy relative surplus node energy ratio of consumption;

2. OLS scheme is for choosing system break probability is minimum after the complete current information of node-node transmission via node as assistance transmission node: for R _ein each via node, calculate following formula:

$\begin{array}{c}{k}_{\mathrm{OLS}}^{*}=\arg \underset{k\&Element;R_E}{\min }{P}_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m]-w_k[m\left]1_k\right)\\ =\arg \underset{k\&Element;R_E}{\min }\frac{P_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m]-w_k[m\left]1_k\right)}{P_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m\left]\right)}\\ =\arg \underset{k\&Element;R_E}{\min }\frac{P_{\mathrm{out}}\left(e_k\right[m]-w_k[m\left]\right)}{P_{\mathrm{out}}\left(e_k\right[m\left]\right)}\end{array}$

Wherein 1 _kfor N × 1 vector, the value in kth position is 1, and the value of all the other positions is 0;

Choose be worth minimum via node as assistance transmission node; Because the life duration definition of the wireless sense network that cooperates is relevant with outage probability, therefore this energy distribution scheme is equivalent to extend network life duration steppingly;

(6) cooperative transmission node selected according to step (5) changes relay state, and lifetime=lifetime+1, returns step (2).

Based on the inventive method, we can define grid life duration be: represent the maximum transmitted time slot that all via nodes can reach under initial energy; Namely step (2) is in confirmation the lifetime value recorded in situation.

Beneficial effect: cooperation wireless sense network provided by the invention strengthens the node selecting method of network lifecycle, by setting up the relation of channel condition information, residue energy of node and outage probability, thus determine which node can as potential relay transmission message, effectively can extend the life duration of collaborative network, have employed the life duration of the collaborative network of method definition more accurately simultaneously; Compared with existing relay selection scheme, technical solution of the present invention improves the life duration of cooperative communication network.

Accompanying drawing explanation

Fig. 1 is the system model of cooperation wireless sense network;

Fig. 2 is realization flow figure of the present invention;

The network duration contrast of the various relay selection scheme of Fig. 3.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further described.

Be illustrated in figure 1 a kind of system model of the wireless sense network that cooperates, at the first time slot, information source sends information to via node and destination node by broadcast channel, and adopt AF pass-through mode, the received signal to noise ratio of via node is:

SNR＝P _s|h _sk| ²

At the second time slot, all relayings receiving information therefrom select optimum relay transmission information to destination, and the received signal to noise ratio of destination node is:

$\mathrm{SNR}=P_s{\left|h_{\mathrm{sd}}\right|}^2+\frac{P_s{P}_k{\left|h_{\mathrm{sk}}{h}_{\mathrm{kd}}\right|}^2}{1+P_s{\left|h_{\mathrm{sk}}\right|}^2+P_k{\left|h_{\mathrm{kd}}\right|}^2}$

The wireless sense network that cooperates strengthens a node selecting method for network lifecycle, comprises the steps:

(1) initialization relaying number N, the primary power of N number of via node is timing step lifetime=0 is set;

(2) system break probability is judged whether be less than setting threshold η, η is cooperative relay system largest tolerable outage probability value:

$P_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m\left]\right)=\underset{k=1}{\overset{N}{\mathrm{\&Pi;}}}{P}_{\mathrm{out}}\left(e_k\right[m\left]\right)$

$\begin{array}{c}{P}_{\mathrm{out}}\left(e_k\right[m\left]\right)=P_r(P_s{\left|h_{\mathrm{sd}}\right|}^2+\frac{P_s{e}_k\left[m\right]{\left|h_{\mathrm{sk}}{h}_{\mathrm{kd}}\right|}^2}{1+P_s{\left|h_{\mathrm{sk}}\right|}^2+e_k\left[m\right]{\left|h_{\mathrm{kd}}\right|}^2}<\mathrm{\&gamma;})\\ =1-\left[e^{-(\frac{\mathrm{\&gamma;}}{P_s{\mathrm{\&sigma;}}_{\mathrm{sk}}^2}+\frac{\mathrm{\&gamma;}}{e_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{kd}}^2})}\sqrt{\frac{4\mathrm{\&gamma;}}{P_s{e}_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{sk}}^2{\mathrm{\&sigma;}}_{\mathrm{kd}}^2}}{K}_1\left(\sqrt{\frac{4\mathrm{\&gamma;}(\mathrm{\&gamma;}+1)}{P_s{e}_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{sk}}^2{\mathrm{\&sigma;}}_{\mathrm{kd}}^2}}\right)\right]\end{array}$

Wherein, γ is the threshold value of the received signal to noise ratio of destination node, if the received signal to noise ratio of destination node is greater than threshold gamma, then thinks that destination node proper reception of information; e _k[m] is the primary power of a kth via node when m time slot; P _r() represents the probability asking for bracket content; P _sfor the transmitting power of information source node S; h _sdrepresent that information source node is to the channel gain of destination node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; h _skrepresent that information source node is to the channel gain of via node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; h _kdrepresent that via node is to the channel gain of destination node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; K ₁() represents the Bessel function of the second kind of single order;

As can be seen from the above equation, system break probability only relevant with the dump energy of via node; If then enter step (3); Otherwise record lifetime also terminates;

(3) h that cooperative relay system stochastic generation is new _sd, h _skand h _kd;

(4) judge whether via node belongs to set R _e, namely judge whether via node meets following condition:

1. the signal to noise ratio that accepts of destination node needs to be greater than threshold gamma, the minimum transmission power P that therefore a kth via node is required under m time slot meets this condition _k-min[m] is:

$P_{k-\min }\left[m\right]=\min \left\{P_k\right[m]:P_s{\left|h_{\mathrm{sd}}\right|}^2+\frac{P_s{P}_k\left[m\right]{\left|h_{\mathrm{sk}}{h}_{\mathrm{kd}}\right|}^2}{1+P_s{\left|h_{\mathrm{sk}}\right|}^2+P_k\left[m\right]{\left|h_{\mathrm{kd}}\right|}^2}\&GreaterEqual;\mathrm{\&gamma;}\}$

Wherein, P _k[m] represents the through-put power of a kth via node at m time slot; Set information is a unit interval in the time of each slot transmission, then the power consumption of via node transmission is numerically equal to the power of transmission, requires that a kth via node meets P based on this _k-min[m]≤P _k-maxand P _k-min[m]≤e _k[m] these two conditions, namely require when m time slot, the minimum transmission power P of a kth via node _k-min[m] is less than its maximum transmission power P _k-max, the minimal consumption energy P of a kth via node _k-min[m] is less than its primary power e at m time slot _k[m];

2. when m time slot, the received signal to noise ratio of a kth via node is greater than γ, ensures that the information of relay forwarding can not too distortion, i.e. R _t={ k:P _s| h _sk| ²>=γ };

Based on above-mentioned condition, R _e=R _t∩ { k:P _k-min[m]≤e _k[m] } ∩ { k:P _k-min[m]≤P _max; If R _efor empty set, then keep current relay state constant, return step (3); Otherwise, enter step (5);

(5) adopt MEI scheme or OLS scheme from R _emiddle selection via node is as assistance transmission node;

1. MEI scheme is select the energy efficiency via node of maximum ratio as assistance transmission node, is specially: for R _ein each via node, calculate following formula:

$k_{\mathrm{MEI}}^{*}=\arg \underset{k\&Element;R_E}{\max }\frac{e_k\left[m\right]}{w_k\left[m\right]}$

Choose be worth minimum via node as assistance transmission node, the via node selected like this is the minimum via node of energy relative surplus node energy ratio of consumption;

2. OLS scheme is for choosing system break probability is minimum after the complete current information of node-node transmission via node as assistance transmission node: for R _ein each via node, calculate following formula:

$\begin{array}{c}{k}_{\mathrm{OLS}}^{*}=\arg \underset{k\&Element;R_E}{\min }{P}_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m]-w_k[m\left]1_k\right)\\ =\arg \underset{k\&Element;R_E}{\min }\frac{P_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m]-w_k[m\left]1_k\right)}{P_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m\left]\right)}\\ =\arg \underset{k\&Element;R_E}{\min }\frac{P_{\mathrm{out}}\left(e_k\right[m]-w_k[m\left]\right)}{P_{\mathrm{out}}\left(e_k\right[m\left]\right)}\end{array}$

Wherein 1 _kfor N × 1 vector, the value in kth position is 1, and the value of all the other positions is 0;

Choose be worth minimum via node as assistance transmission node; Because the life duration definition of the wireless sense network that cooperates is relevant with outage probability, therefore this energy distribution scheme is equivalent to extend network life duration steppingly;

(6) cooperative transmission node selected according to step (5) changes relay state, and lifetime=lifetime+1, returns step (2).

Below in conjunction with embodiment, the present invention is made further instructions.

Embodiment adopts network topology as shown in Figure 1, and sensor node is positioned on the perpendicular bisector of information source node and destination node, and information source node and destination node distance are 20m.The emulation platform of embodiment is Matlab R2012b.Scene setting is: the through-put power of information source is the threshold gamma of 12dB, SNR is 14dB, and the threshold value η of outage probability is 0.1, information source node and via node h _skand the channel coefficients h of via node and destination node _kdmeet 0 average, variance is the multiple Gaussian Profile of Cyclic Symmetry of 1.Via node quantity is 4, and the maximum transmission power of via node is 82.25mW, and the primary power excursion of via node is 100 ~ 500mJ.

Under the same experiment scene that this embodiment is arranged, emulated by Monte Carlo, the sensor network life duration under more each relay selection scheme, as shown in Figure 3.

By Fig. 3, as compared to existing relay selection scheme (MRE with MTP), MEI and OLS relay selection scheme all extends the life duration of cooperative communication network, and the line style of MEI and OLS almost overlaps in the drawings.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (1)

1. the wireless sense network that cooperates strengthens a node selecting method for network lifecycle, it is characterized in that: comprise the steps:

(1) initialization relaying number N, the primary power of N number of via node is timing step lifetime=0 is set;

(2) system break probability is judged whether be less than setting threshold η, η is cooperative relay system largest tolerable outage probability value:

$P_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m\left]\right)=\underset{k=1}{\overset{N}{\mathrm{\&Pi;}}}{P}_{\mathrm{out}}\left(e_k\right[m\left]\right)$

$\begin{array}{c}{P}_{\mathrm{out}}\left(e_k\right[m\left]\right)=P_r(P_s{\left|h_{\mathrm{sd}}\right|}^2+\frac{P_s{e}_k\left[m\right]{\left|h_{\mathrm{sk}}{h}_{\mathrm{kd}}\right|}^2}{1+P_s{\left|h_{\mathrm{sk}}\right|}^2+e_k\left[m\right]{\left|h_{\mathrm{kd}}\right|}^2}<\mathrm{\&gamma;})\\ =1-\left[e^{-(\frac{\mathrm{\&gamma;}}{P_s{\mathrm{\&sigma;}}_{\mathrm{sk}}^2}+\frac{\mathrm{\&gamma;}}{e_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{kd}}^2})}\sqrt{\frac{4\mathrm{\&gamma;}(\mathrm{\&gamma;}+1)}{P_s{e}_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{sk}}^2{\mathrm{\&sigma;}}_{\mathrm{kd}}^2}}{K}_1\left(\sqrt{\frac{4\mathrm{\&gamma;}(\mathrm{\&gamma;}+1)}{P_s{e}_k\left[m\right]{\mathrm{\&sigma;}}_{\mathrm{sk}}^2{\mathrm{\&sigma;}}_{\mathrm{kd}}^2}}\right)\right]\end{array}$

Wherein, γ is the threshold value of the received signal to noise ratio of destination node, if the received signal to noise ratio of destination node is greater than threshold gamma, then thinks that destination node proper reception of information; e _k[m] is the primary power of a kth via node when m time slot; P _r() represents the probability asking for bracket content; P _sfor the transmitting power of information source node S; h _sdrepresent that information source node is to the channel gain of destination node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; h _skrepresent that information source node is to the channel gain of via node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; h _kdrepresent that via node is to the channel gain of destination node, meet that average is 0, variance is the multiple Gaussian Profile of Cyclic Symmetry; K ₁() represents the Bessel function of the second kind of single order;

If then enter step (3); Otherwise record lifetime also terminates;

(3) h that cooperative relay system stochastic generation is new _sd, h _skand h _kd;

(4) judge whether via node belongs to set R _e, namely judge whether via node meets following condition:

1. the signal to noise ratio that accepts of destination node needs to be greater than threshold gamma, the minimum transmission power P that therefore a kth via node is required under m time slot meets this condition _k-min[m] is:

$P_{k-\min }\left[m\right]=\min \left\{P_k\right[m]:P_s{\left|h_{\mathrm{sd}}\right|}^2+\frac{{P_s{P}_k\left[m\right]\left|h_{\mathrm{sk}}{h}_{\mathrm{kd}}\right|}^2}{1+P_s{\left|h_{\mathrm{sk}}\right|}^2+P_k\left[m\right]{\left|h_{\mathrm{kd}}\right|}^2}\&GreaterEqual;\mathrm{\&gamma;}\}$

Wherein, P _k[m] represents the through-put power of a kth via node at m time slot; Set information is a unit interval in the time of each slot transmission, then the power consumption of via node transmission is numerically equal to the power of transmission, requires that a kth via node meets P based on this _k-min[m]≤P _k-maxand P _k-min[m]≤e _k[m] these two conditions, namely require when m time slot, the minimum transmission power P of a kth via node _k-min[m] is less than its maximum transmission power P _k-max, the minimal consumption energy P of a kth via node _k-min[m] is less than its primary power e at m time slot _k[m];

2. when m time slot, the received signal to noise ratio of a kth via node is greater than γ, ensures that the information of relay forwarding can not too distortion, i.e. R _t={ k:P _s| h _sk| ²>=γ };

Based on above-mentioned condition, R _e=R _t∩ { k:P _k-min[m]≤e _k[m] } ∩ { k:P _k-min[m]≤P _max; If R _efor empty set, then keep current relay state constant, return step (3); Otherwise, enter step (5);

(5) adopt MEI scheme or OLS scheme from R _emiddle selection via node is as assistance transmission node;

1. MEI scheme is: for R _ein each via node, calculate following formula:

$k_{\mathrm{MEI}}^{*}=\arg \underset{k\&Element;R_E}{\max }\frac{e_k\left[m\right]}{w_k\left[m\right]}$

Choose be worth minimum via node as assistance transmission node;

2. OLS scheme is: for R _ein each via node, calculate following formula:

$\begin{array}{c}{k}_{\mathrm{OLS}}^{*}=\arg \underset{k\&Element;R_E}{\min }{P}_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m]-w_k[m\left]1_k\right)\\ =\arg \underset{k\&Element;R_E}{\min }\frac{P_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m]-w_k[m\left]1_k\right)}{P_{\mathrm{out}}\left(\stackrel{\&RightArrow;}{e}\right[m\left]\right)}\\ =\arg \underset{k\&Element;R_E}{\min }\frac{P_{\mathrm{out}}\left(e_k\right[m]-w_k[m\left]\right)}{P_{\mathrm{out}}\left(e_k\right[m\left]\right)}\end{array}$

Wherein 1 _kfor N × 1 vector, the value in kth position is 1, and the value of all the other positions is 0;

Choose be worth minimum via node as assistance transmission node;

(6) cooperative transmission node selected according to step (5) changes relay state, and lifetime=lifetime+1, returns step (2).