CN114666797A - Secure wireless power supply communication network system and communication method based on IRS - Google Patents
Secure wireless power supply communication network system and communication method based on IRS Download PDFInfo
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Abstract
The invention relates to the technical field of wireless communication, and discloses a safe wireless power supply communication network system based on IRS, which comprises: the IRS is composed of a plurality of passive elements; at least one eavesdropper; at least one legitimate user; a hybrid access point having both an energy signal transmission function and an information transmission function; the hybrid access point, the legal user and the eavesdropper are all provided with a single antenna, the IRS is used for enhancing the energy signal from the hybrid access point in the downlink from the hybrid access point to the legal user, and the IRS can assist the information transmission from the legal user to the hybrid access point while restricting the rate of the eavesdropper in the uplink from the legal user to the hybrid access point. The invention can limit the information transmission rate of the eavesdropper and realize the purpose of safe communication.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a safe wireless power supply communication network system and a communication method based on IRS.
Background
With the advent of the 21 st century, and the popularity of various mobile devices, wireless communication has become an indispensable part of this era, and to fulfill more of the practical needs of users, fifth generation wireless networks have proposed: high speed, low time delay and high reliability. By incomplete statistics, the network capacity increase goal of hundreds of times for fifth generation wireless networks, as compared to fourth generation wireless networks, and wireless connectivity of hardware devices on the order of at least billions, have been substantially realized. However, these problems have not been solved perfectly due to the use of the key technologies such as ultra-dense network, large-scale mimo and rf chain, which bring about the high complexity of the devices, the expensive hardware cost, the complex interference management between the hardware, and the energy consumption of the high-energy-consumption devices such as the rf chain. In order to solve the existing problems of the communication system, the researchers point out that a low-energy-consumption device should be adopted to artificially and intelligently control the propagation environment, and improve the transmission performance of the communication system at a lower cost as much as possible while eliminating interference. One of the schemes is to use the technology of IRS (Intelligent reflection Surface) to control the amplitude and phase of the reflection signal incident on the Surface, so as to realize artificial and Intelligent control of the propagation environment. Since the IRS does not use a transmit radio frequency chain and operates only over short distances, it can be deployed more objectively, cost and energy intensive, and does not require complex interference management between passive IRS.
In addition, because of the plasticity of the IRS, IRS conforming to any shape surface can be manufactured in practical application and can be installed at different positions, for example: walls, ceilings, building surfaces, advertising panels, and some objects that can provide sufficient area to satisfy the communication scenarios of different applications. In addition, because the IRS is a supplementary device, it is deployed in the existing network environment, it does not need to modify any hardware and standard in the existing network environment, the compatibility is very strong, and it also has high flexibility, for example, firstly, it can enhance the transmission of useful information by diversity gain, meanwhile, in millimeter wave communication, because the millimeter wave communication has serious path loss problem, it can establish the cascade link between the base station and the user and related to the IRS through the passive beam forming technology of the IRS, to bypass the "dead zone" between the base station and the user to realize the communication between the base station and the user. Secondly, when there is an eavesdropper in the communication system, the IRS may destroy the eavesdropped signal of the eavesdropper by passive beam forming using a phase superposition (interference) method at the eavesdropper.
With the arrival of 5G everything interconnection, the popularization of the internet of things has become a necessary trend, and in the internet of things, the application of a large number of sensors makes the Wireless Power Transfer (WPT) technology become very promising, however, because the WPT has the characteristics of low transmission efficiency, small coverage area and the like, the WPT is difficult to be widely applied in practice, and the passive beam forming of the IRS can well improve the energy transmission efficiency of the WPT and the coverage area thereof. Therefore, a need exists for designing a novel secure wireless power supply communication network system of the IRS, which can improve the WPT energy transmission efficiency and coverage area thereof, and can perform data transmission securely.
Disclosure of Invention
The invention provides a safe wireless power supply communication network system and a communication method based on IRS, which can well solve the problem of safe transmission of the system under the condition of the existence of an eavesdropper by jointly optimizing time allocation and a corresponding phase shift matrix at the IRS.
The invention is realized by the following technical scheme:
an IRS-based secure wireless power communication network system, comprising:
the IRS consists of a plurality of passive elements;
at least one eavesdropper;
at least one legitimate user;
a hybrid access point having both an energy signal transmission function and an information transmission function;
the hybrid access point, the legitimate user and the eavesdropper are all equipped with a single antenna, and in the downlink from the hybrid access point to the legitimate user, the IRS is used to boost the energy signal from the hybrid access point, and in the uplink from the legitimate user to the hybrid access point, the IRS can assist the transmission of information from the legitimate user to the hybrid access point while constraining the eavesdropper rate.
As an optimization, the hybrid access point is a central control point, with the ability to coordinate the transmission capabilities between the IRS, eavesdroppers, and legitimate users, as well as the ability to perform computational off-load tasks and supply constant energy.
The invention also discloses a communication method of the safety wireless power supply communication network system based on the IRS, which comprises the following steps:
And 2, the legal user utilizes the energy signal collected in the step 1 to carry out information transmission, and meanwhile, the phase shift matrix, the energy signal transmission time and the information transmission time of the IRS are adjusted to ensure that the legal user carries out safe information transmission under the condition that an eavesdropper exists.
As an optimization, in step 1, the duration of time for which the hybrid access point sends an energy signal to the legitimate user is t1With power of transmitted energy signal phThe sending energy signal is E [ | x [ ]0(t)|2]Energy signal x of0(t), when the reflection phase shift matrix of the IRS is theta1＝diag(v1,1,...,v1,n,...,v1,N) Wherein, in the step (A),
v1,nn is the number of passive elements, theta is the phase shift corresponding to each element of the IRS,
gH,urespectively representing the downlink channel vectors from the hybrid access point to the IRS, from the IRS to the legal user and from the hybrid access point to the legal user, wherein the noise when the legal user receives signals is n(1)(t); at this time, the energy signal y received by the legal user(1)(t) is
The energy of the energy signal received by the legal user is as follows: e(1)＝ηE[|y(1)(t)|2]t1＝η|gH,rΘ1gR,u+gH,u|2pht1And 0 < eta < 1 represents the energy conversion efficiency of the legal user equipment at the receiving end.
As optimization, the specific implementation steps of the step 2 are as follows:
step 2.1, the legal user sends information, and the reflection phase shift matrix of the IRS is defined as theta at the moment2The time duration for the legal user to send information is defined as t2；
Step 2.2, respectively calculating the reachable rates of the information sent by the legal user to the mixed access point and the information sent by the legal user to the eavesdropper;
step 2.3, under the condition of ensuring that the reachable rate of the information reaching the eavesdropper is less than the constraint threshold, the reflection phase shift matrix theta of the IRS is subjected to the aim of maximizing the information transmission rate of the legal user1、Θ2And transmission time allocation t ═ t1,t2]And (6) optimizing.
As an optimization, the reflection phase shift matrix Θ of the IRS is optimized1、Θ2And transmission time allocation t ═ t1,t2]The method comprises the following steps: at fixed theta2、t2Obtaining a reflection phase shift moment of said IRS during an energy signal transmission phaseMatrix theta1Then at a fixed theta1And t1Under the condition of (2), the IRS phase shift matrix theta of the information transmission stage is obtained2And a duration of information transmission t2。
As an optimization, the reflection phase shift matrix Θ of the IRS is optimized1,Θ2And transmission time allocation t ═ t1,t2]The method comprises the following specific steps:
step 2.3.1, fixing theta2、t2Under the condition of (2), the IRS reflection phase shift matrix theta in the energy signal transmission stage is obtained in a phase alignment mode1；
Step 2.3.2, solving the IRS reflection phase shift matrix theta of the information transmission stage by adopting an alternative optimization algorithm2And time allocation t2。
As an optimization, the energy signal x transmitted by the hybrid access point0The mean value of (t) is 0 and the variance is 1.
As an optimization, the phase shift matrix of the IRS is:
and satisfy
The matrix coefficients are phase shifted for the corresponding IRS.
As an optimization, the size E [ | x ] of the energy signal sent by the hybrid access point is defined0(t)|2]＝1。
Compared with the prior art, the invention has the following advantages and beneficial effects:
the invention provides a novel IRS-based safe wireless power supply communication system, wherein the IRS is used for assisting the wireless power supply communication system to transmit energy and information in uplink and downlink, and can limit the information transmission rate of an eavesdropper, so that the aim of safe communication is fulfilled.
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In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and that for those skilled in the art, other related drawings can be obtained from these drawings without inventive effort. In the drawings:
fig. 1 is a system model diagram of an IRS-based secure wireless power communication network system according to the present invention;
fig. 2 is a simulation setup diagram of an IRS-based secure wireless power communication network system according to the present invention;
FIG. 3 is an algorithm convergence chart corresponding to the communication method of the IRS-based secure wireless power supply communication network system according to the present invention
Fig. 4 is a comparison diagram of the legal user rate and the number of IRS elements in different schemes.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
The IRS may play many roles in the communication system, for example, firstly it may enhance the transmission of useful information by spatial diversity gain, and secondly, in millimeter wave communication, because of the serious path loss problem of millimeter wave communication, the communication between the base station and the user may be realized by passive beam forming technology of the IRS by using the reflected signal on the IRS to bypass the "dead zone" between the base station and the user. Besides the functions, the invention also utilizes the passive beam forming function of the IRS to improve the transmission efficiency of the energy signal, and utilizes a phase superposition (interference) method at the eavesdropper to destroy the eavesdropping signal at the eavesdropper. In the embodiment, both the legitimate user and the eavesdropper are set to 1 for easy understanding.
Specifically, assume that the reflection phase shift matrix of the intelligent reflective surface IRS is theta, and the channel associated with the IRS is defined as hBIΘhIUWherein h isBIDenoted as channel from base station to IRS, hIUDenoted as IRS to user channel. In addition, the direct connection channel between the base station and the user can be regarded as hBU. Thus, the total channel can be considered as hBIΘhIU+hBU. By optimizing Θ, the cascade channel h can be changedBIΘhIUBy the interference principle of electromagnetic wave, change | | | hBIΘhIU+hBUThe size of the corresponding value of | may enable an enhancement or a de-emphasis of the channel link. The method and the device realize enhancement of the received signals of legal users, improve the energy transmission efficiency and the information transmission efficiency and weaken the received signals of eavesdroppers at the same time.
Therefore, as shown in fig. 1, embodiment 1 discloses an IRS-based secure wireless power communication network system, including:
the IRS is composed of a plurality of passive elements;
at least one eavesdropper;
at least one legitimate user;
a hybrid access point having both an energy signal transmission function and an information transmission function;
the hybrid access point, the legitimate user and the eavesdropper are all equipped with a single antenna, and in the downlink from the hybrid access point to the legitimate user, the IRS is used to boost the energy signal from the hybrid access point, and in the uplink from the legitimate user to the hybrid access point, the IRS can assist the transmission of information from the legitimate user to the hybrid access point while constraining the eavesdropper rate. In this embodiment, the hybrid access point is a central control point, and has a transmission capability of coordinating the IRS, the eavesdropper, and the legitimate user, and has a computing capability of performing a computation offload task and a capability of supplying a constant energy source. Here, a hybrid access point is understood to be a base station as mentioned above.
Example 2
The invention also discloses a communication method of the safety wireless power supply communication network system based on the IRS, which comprises the following steps:
Assuming that the CSI of all channels is known, all channel vectors are modeled as zero-mean independent identically distributed complex gaussian random variables whose variance depends on the path loss of the respective radio link. Let theta be [ theta ]1,....,θN]And simultaneously defining the phase shift matrix of the IRS as:
the matrix coefficients are phase shifted for the corresponding IRS. In the present invention, the reflectivity of IRS is maximally improved, so beta is assumedi1, satisfies
Meanwhile, the hybrid access point is assumed to be used as a central control point of the network, coordinates transmission among all devices in the system, and has computing capacity for executing computing unloading tasks and constant energy supply.
The wireless power supply communication network system works in two stages, wherein energy signal transmission is the first stage, and information transmission is the second stage.
In this embodiment, step 1 belongs to an energy signal transmission phase, and the duration of time for the hybrid access point to send an energy signal to the legitimate user is defined as t1With power of transmitted energy signal phThe sending energy signal is E [ | x [ ]0(t)|2]Energy signal x of0(t), when the reflection phase shift matrix of the IRS is theta1＝diag(v1,1,...,v1,n,...,v1,N) Wherein, in the process,
v1,nis the corresponding IRS phase shift matrix coefficient, theta is the phase shift corresponding to each unit of IRS, N is the number of passive elements,
gH,urespectively representing the downlink channel vectors from the hybrid access point to the IRS, from the IRS to the legal user and from the hybrid access point to the legal user, wherein the noise when the legal user receives signals is n(1)(t); at this time, the energy signal y received by the legal user(1)(t) is
(1) Since the noise power is negligible for the energy signal, the energy level of the energy signal received by the legitimate user is: e(1)＝ηE[|y(1)(t)\2]t1＝η|gH,rΘ1gR,u+gH,u|2pht1(2) Wherein 0 < eta < 1 represents the energy conversion efficiency of the legal user equipment at the receiving end.
And 2, the legal user utilizes the energy signal collected in the step 1 to carry out information transmission, and meanwhile, the phase shift matrix, the energy signal transmission time and the information transmission time of the IRS are adjusted to ensure that the legal user carries out safe information transmission under the condition that an eavesdropper exists.
The specific implementation steps of the step 2 are as follows:
step 2.1, the legal user sends information, and the reflection phase shift matrix of the IRS is defined as theta at the moment2The time duration for the legal user to send information is defined as t2；
Step 2.2, respectively calculating the reachable rates of the information sent by the legal user to the mixed access point and the information sent by the legal user to the eavesdropper;
step 2.3, under the condition of ensuring that the reachable rate of the information reaching the eavesdropper is less than the constraint threshold, the reflection phase shift matrix theta of the IRS is subjected to the aim of maximizing the information transmission rate of the legal user1、Θ2And transmission time allocation t ═ t1,t2]And (6) optimizing.
In the second stage of information transmission, a legal user utilizes the energy collected in the first stage to perform information transmission, and meanwhile, the IRS adjusts the phase shift matrix to ensure that the legal user performs safe information transmission under the condition that an eavesdropper exists. With the energy collected in the first stage, the power transmitted by the legitimate user is: p is a radical of formulau＝E(1)/t2＝η|gH,rΘ1gR,u+gH,u\2pht1/t2(3) By E [ | x1(t)|2]Defining information transmission signal x as 11(t), the received signal at the hybrid access point at this time may be represented as:
the received signal at the eavesdropper can be expressed as:
wherein Θ is2＝diag(v2,1,...,v2,n,...,v2,N) A reflection phase shift matrix defined as the second stage of IRS, wherein,
n is the number of passive elements in the IRS for the corresponding IRS phase shift matrix coefficients. Equivalently, σH (2)(t)，σE (2)(t) is defined as the noise at the receiving end hybrid access point and at the eavesdropper, respectively, and σH (2)(t)，σE (2)(t) are mutually opposite and are desirably zero, with variance σ2Gaussian noise. Thus, the rate of reachability from the legitimate user to the hybrid access point and the reachability to the eavesdropper at this timeThe rates can be expressed as:
optimizing the reflection phase shift matrix theta of the IRS with the aim of maximizing the information transmission rate of a legal user under the condition of ensuring that the eavesdropper is smaller than a constraint threshold value1,Θ2And a transmission time allocation t ═ t1,t2]The established optimization problem is as follows:
first constraint t1+t2T ≦ ensures that the sum of the energy information transfer times does not exceed the total time duration T, a second constraint RE≤r0Ensuring that the rate of the eavesdropper is below a set threshold ensures secure communication by the system. The detailed expression of the optimization problem is:
in the above optimization problem, T is assumed to be 1 for no loss of generality, and the energy transmission time and the information transmission time T are made to be the same for maximum utilization of the time T1，t2The sum of (1) is equal to T.
The above problem can be translated into the problem P1:
the optimization problem is a non-convex optimization problem due to the modulus constraints and the coupling between the optimization variables due to the multiplicative terms. To solve the above optimization problem, first fix Θ2Obtaining IRS phase shift moment of energy transmission stage by mathematically deriving phase alignment under condition of tMatrix theta1Then at a fixed theta1Under the condition of (2), an alternative optimization mode is adopted to obtain an IRS phase shift matrix theta at an information transmission stage2And a time allocation t. The detailed solving steps are as follows:
the first step is as follows: designing IRS phase shift matrix theta of energy transfer phase by phase alignment1
First fix theta2T, because the eavesdropper does not have the problem of eavesdropping the information of the legal user in the energy transmission stage, and the eavesdropping of the eavesdropper only occurs in the information transmission stage, the optimization problem constraint can be ignored
A constraint for eavesdroppers. Meanwhile, the equality constraint is brought into other constraints and the objective function, and then the problem P1 is reduced to P2:
at the same time, since we fix Θ2T, so we can compare Θ2T is considered as a constant and thus neglects its effect on the optimization. The optimization problem P2 now turns into P3:
although by fixing theta2、t2Coupling influence caused by multiplication of optimization variables is eliminated, but due to the existence of modulus constraint, the optimization problem P3 is still a non-convex problem which can be solved by a continuous convex approximation or a semi-positive definite relaxation algorithm in the conventional method, but the problem of high complexity often exists, and the optimal phase matrix theta of the energy transmission stage IRS can be obtained in a closed form by a mathematical derivation method1。
Let vi＝[vi,1,...,vi,n,...,vi,N]i＝1,2，v1＝[v1,1,...,v1,n,...,v1,N]At this time we have, gH,rΘ1gR,u+gH,u＝v1diag(gH,r)gR,u(14) Let us order diag (g)H,r)gR,u＝a (15)， |gH,rΘ1gR,u+gH,u|＝|v1a+gH,uI (16) optimization problem P3 at this time is transformed into P4
According to the triangle inequality, the objective function of (P4) satisfies the following inequality:
wherein [ a ]]iThe ith element representing a, it is noted that only when θ1,i＝arg(gH,u)-arg([a]i) When, | v1a+gH,uL satisfies the upper bound of the inequality. Where arg (.) denotes the operation of phase extraction. Solving the optimal solution v of P41Denoted as v1 *. Through the mathematical derivation method, the optimal phase shift matrix theta corresponding to the energy transmission stage IRS can be obtained1 *。
Secondly, solving the IRS phase shift matrix theta of the information transmission stage by adopting an alternative optimization algorithm2And an allocation time t2
1) For a given time allocation t, the IRS phase shift matrix Θ1 *Problem p1 is reduced to:
further, (P1-a-1) can be simplified to: (P1-a-2)
Wherein, the first and the second end of the pipe are connected with each other,
for the objective function, | hU,rΘ2hR,h+hU,h|2＝|v2diag(hU,r)hR,h+hU,h|2(21) Let Diag (h)U,r)hR,hThe objective function in β (22), (p 1-a-2) is converted to: | v2β+hU,h|2 (23)
For constraint, similarly, | hU,rΘ2hR,e+hU,e|2＝|v2diag(hU,r)hR,e+hU,e|2(24) Let Diag (h)U,r)hR,e＝γ (25)
The constraints in (P1-a-2) are converted into: | v2β+hU,h|2 (27)
So the equivalent of (P1-a-2) can be converted into (P1-a-3):
order:
|v2β+hU,h|2is equivalent to
Order:
|v2γ+hU,e|2is equivalent to
By the above-mentioned variable replacement, (P1-a-3) can be converted into (P1-a-4)
Note that V is in the optimization problem (P1-a-4)2Need to satisfy
And rank (V)2) 1. Since the rank-one constraint belongs to the non-convex constraint, (P1-a-4) is relaxed to (P1-a-5) by the semi-definite relaxation algorithm
After solving the rank-one constraint by a semi-definite relaxation algorithm, it is clear (p 1-a-4) becomes the classic SDP problem. The optimization problem can be solved well by CVX, and the optimization solution in (P1-a-4) is defined as V2 *However, the relaxation solution obtained in the (p 1-a-5) problem is often not an optimal solution to the (p 1-a-4) problem that includes a rank-one constraint, which means that the optimal solution obtained in (p 1-a-5) only satisfies the upper bound of the optimal solution in (p 1-a-4), and therefore the rank-one optimal solution in (p 1-a-4) is to be reconstructed from the high-rank optimal solution in (p 1-a-5) by an additional step.
First, for V2Carrying out eigenvalue decomposition, V2＝UΣUHWherein U ═ U1,...,uN+1]，∑＝diag(λ1，...，λN+1) Is a unitary matrix and a diagonal matrix having matrix dimensions of (N +1) × (N +1), wherein the order is
Wherein
Is composed of a mean value of 0 and a covariance matrix of IM×1Of a circle pairThe random variable generated by the complex Gaussian distribution is called, and r is independently generated, and the corresponding best variable in all r is passed
The optimal value of the objective function (P1-a-4) can be approximated to the optimal value of the objective function found in (P1-a-5). Last in (p 1-a-3)
Wherein [ x ]](1:N)Representing the first N vectors in x, it has been demonstrated that using the SDR algorithm, when sufficient r is used for Gaussian randomization, it is possible to ensure that the solution obtained is able to reach the optimal solution
The phase shift matrix Θ for a given IRS1 *The IRS phase shift matrix theta2Problem p1 is reduced to:
because, the IRS phase shift matrix Θ is fixed1 *The IRS phase shift matrix theta2. Therefore, can order
|hU,rΘ2hR,h+hU,h|2η|gH,rΘ1gR,u+gH,u|2ph/σ2＝d (33)
|hU,rΘ2hR,e+hU,e|2η|gH,rΘ1gR,u+gH,u|2ph/σ2＝e (34)
In this case (P1-b-1) is reduced to (P1-b-2)
Further, t may be1+t 21 as t2By t1To show, rewrite as: t is t2＝1-t1And simultaneously carrying in the objective function and the rest of the constraints for simplification, (P1-b-2) for simplification:
obviously, the optimization problem is a non-convex optimization problem due to log constraints, and in order to solve the optimization problem, a new algorithm is proposed to find t2The value of (a). The specific algorithm is as follows:
step 1: setting a speed threshold lambda of an eavesdropper, and respectively solving an objective function and a constraint in the problem of (P1-b-3) with respect to t2Stagnation point h*，e*And corresponding legal user rate Rh(h*) And eavesdropper rate Re(e*)
Step 2: comparison of Re(e*) The magnitude of λ.
If R ise(e*) < lambda (i.e. the rate representing the eavesdropper is below the set threshold), the feasible domain t2Is all times in the range of 0 to 1, when the maximum user rate is Rh(e*) Corresponding t2＝h*。
Otherwise Re(e*) More than or equal to lambda, let us let Re(e) Solving e of e reversely1，e2(e1＜e2) At this time, the possible field t2In the range of 0. ltoreq. t2＜e1，e2＜t2And (4) the algorithm enters the step 3.
And step 3: comparison e2And h*The magnitude relationship of (1).
If e2≤h*，h*At t2Within the feasible region of (1), the maximum legal user rate is Rh(h*) Corresponding to t2＝h*。
Otherwise e2＞h* Algorithm step ofStep 4
And 4, step 4: comparison e1And h*Size relationship of
If e1＞h*Then h*T is less than or equal to 02＜e1Within the range of (3), the maximum legal user rate is Rh(e1)
Otherwise e1≤h*Then h*Is not at t2Within the feasible region of (3), the algorithm proceeds to step 5
And 5: comparison of Rh(e1) And Rh(e2) The magnitude relationship of (1).
If R ish(e2)＞Rh(e1) Then the maximum legal user rate is Rh(e2) Corresponding time t2＝e2。
Otherwise Rh(e2)≤Rh(e1) Then the maximum legal user rate is Rh(e1) Corresponding time t2＝e1。
By the method, we can well find t2The value of (a). We optimize t by alternating2，Θ2The value of (d) can be finally obtained, and the optimal solution of the optimization problem is recorded as t2 *，Θ2 *。
Through simulation verification, the alternating optimization algorithm can be converged finally.
And finally, a simulation result is given to verify the superiority of the system in eavesdropping prevention and the feasibility of the optimization algorithm scheme.
Fig. 2 is a simulation setup diagram corresponding to the present invention, and in fig. 2, the simulation location setup is considered, where the IRS is located in the middle of the system, the distance between the hybrid access point and the IRS is 5m, the distance between the IRS and the legitimate user is 5m, the distance between the hybrid access point and the legitimate user is 8m, the distance between the eavesdropper and the legitimate user is 6m, the eavesdropper and the hybrid access point are located in the same orientation, and the eavesdropper is closer to the legitimate user than the hybrid access point. Such an emulation arrangement may better illustrate the theft protection of the systemListening ability. For large scale fading of a system, there is the following path loss model.
C0＝30dB，d0＝1m， C0Denotes a reference distance d0λ represents a path loss coefficient. The path loss coefficient of the cascade channel related to the IRS is set to be 2.2, and the path loss coefficients of all the other direct channels unrelated to the IRS are set to be 3.6
For small-scale fading of the system, the base station to IRS channel can be a LOS channel by artificially intentionally deploying the position of the IRS first, because in actual deployment, the IRS is usually deployed with the known AP position. And the rest cascaded links related to the IRS are considered as Lass fading channels, the corresponding Lass factor is 3, and the rest direct-link links are considered as Rayleigh fading channels.
FIG. 3 is a corresponding algorithm convergence diagram of the present invention, and in FIG. 3, the constraint threshold of the eavesdropper is considered to be 1.5bit/s/Hz, the transmission power of the hybrid access point is 30dBm, and the noise is Gaussian white noise with a power of-110 dBm. The energy conversion efficiency is 0.8, the rice factor is 3, and the channel realization times is 1000. From the view of convergence times, the algorithm has good convergence by changing the number N of the intelligent reflection surface elements (which is consistent with the M in the foregoing. It can also be seen that as the number of N increases, the performance of the system becomes better.
Fig. 4 is a comparison diagram of the legal user rate and the number of IRS elements under different schemes, and in fig. 4, the constraint threshold of the eavesdropper is considered to be 1.5bit/s/Hz, the transmission power of the hybrid access point is 30dBm, and the noise is gaussian white noise power of-110 dBm. The energy conversion efficiency is 0.8, the rice factor is 3, and the channel realization times is 1000. In the scheme 1, a one-dimensional search method is adopted to solve the time allocation of the system, and IRS is solved by the method used in the scheme, so that the relatively best optimization result can be obtained and is recorded as the upper optimization bound of the system. Scheme 2 adopts an IRS phase shift matrix with the same uplink and downlink, and the whole is solved by adopting an SDR algorithm. And for time allocation, the method provided by the scheme is adopted for solving. For the scheme 1, although a good optimization result can be obtained, the complexity of the scheme is too high because a one-dimensional search method is adopted to solve the time allocation. And for scheme 2, the same IRS phase shift matrix is used for the uplink and downlink. The restriction of an eavesdropper can affect the optimization of the IRS phase shift matrix in the downlink energy transmission stage, so that the performance of the system is greatly affected. Although the solving step of the phase alignment of the IRS phase shift matrix in the downlink stage is omitted, the complexity of the solving is low due to the phase alignment, and the complexity is not greatly influenced. Therefore, from the simulation result, the performance of the scheme provided by the invention approaches the upper optimization limit of the system under the condition of low complexity, and the scheme has good optimization performance. In contrast, the proposed solution has significant advantages.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. An IRS-based secure wireless powered communication network system, comprising:
the IRS consists of a plurality of passive elements;
at least one eavesdropper;
at least one legitimate user;
a hybrid access point having both an energy signal transmission function and an information transmission function;
the hybrid access point, the legitimate user and the eavesdropper are all equipped with a single antenna, and in the downlink from the hybrid access point to the legitimate user, the IRS is used to boost the energy signal from the hybrid access point, and in the uplink from the legitimate user to the hybrid access point, the IRS can assist the transmission of information from the legitimate user to the hybrid access point while constraining the eavesdropper rate.
2. A secure wireless power communication network system of IRS according to claim 1, characterized by that, the hybrid access point is a central control point, with transmission capability to coordinate between the IRS, eavesdropper and legitimate users, with computing capability to perform computation offload tasks and with the capability to supply constant energy.
3. A communication method of a secure wireless powered communication network system based on the IRS according to any of claims 1-2, characterized by comprising the steps of:
step 1, transmitting an energy signal x by the hybrid access point0(t) giving the legal user a received signal y(1)(t)；
And 2, the legal user utilizes the energy signal collected in the step 1 to carry out information transmission, and meanwhile, the phase shift matrix, the energy signal transmission time and the information transmission time of the IRS are adjusted to ensure that the legal user carries out safe information transmission under the condition that an eavesdropper exists.
4. A communication method of an IRS-based secure wireless power communication network system according to claim 3, wherein in step 1, the hybrid ap sends energy signal to the legal user for t duration1With power of transmitted energy signal phThe sending energy signal is E [ | x [ ]0(t)|2]Energy signal x of0(t), when the reflection phase shift matrix of the IRS is theta1＝diag(v1,1,...,v1,n,...,v1,N) Wherein, in the step (A),
v1,nn is the number of passive elements, theta is the phase shift corresponding to each element of the IRS,
gH,urespectively representing the downlink channel vectors from the hybrid access point to the IRS, from the IRS to the legal user and from the hybrid access point to the legal user, wherein the noise when the legal user receives signals is sigma(1)(t); at this time, the energy signal y received by the legal user(1)(t) is
The energy of the energy signal received by the legal user is as follows: e(1)＝ηE[|y(1)(t)|2]t1＝η|gH,rΘ1gR,u+gH,u|2pht1And 0 < eta < 1 represents the energy conversion efficiency of the legal user equipment at the receiving end.
5. The communication method of the IRS-based secure wireless power supply communication network system according to claim 3, wherein the step 2 is implemented by the following steps:
step 2.1, the legal user sends information, and the reflection phase shift matrix of the IRS is defined as theta at the moment2The time duration for the legal user to send information is defined as t2；
Step 2.2, respectively calculating the reachable rates of the information sent by the legal user to the hybrid access point and the information sent by the legal user to the eavesdropper;
step 2.3, under the condition of ensuring that the reachable rate of the information reaching the eavesdropper is less than the constraint threshold, the reflection phase shift matrix theta of the IRS is subjected to the aim of maximizing the information transmission rate of the legal user1、Θ2And transmission time allocation t ═ t1,t2]And (6) optimizing.
6. Root of herbaceous plantA communication method of an IRS-based secure wireless power communication network system according to claim 5, wherein the reflection phase shift matrix Θ of the IRS is optimized1、Θ2And transmission time allocation t ═ t1,t2]The method comprises the following steps: at fixed theta2、t2Obtaining a reflection phase shift matrix theta of the IRS at an energy signal transmission stage1Then at a fixed theta1And t1Under the condition of (2), the IRS phase shift matrix theta of the information transmission stage is obtained2And a duration of information transmission t2。
7. A communication method of a secure wireless power communication network system based on IRS according to claim 6, characterized in that the reflection phase shift matrix Θ of the IRS is optimized1,Θ2And transmission time allocation t ═ t1,t2]The method comprises the following specific steps:
step 2.3.1, fixing theta2、t2Under the condition of (2), the IRS reflection phase shift matrix theta in the energy signal transmission stage is obtained in a phase alignment mode1；
Step 2.3.2, solving the IRS reflection phase shift matrix theta of the information transmission stage by adopting an alternative optimization algorithm2And time allocation t2。
8. A communication method of an IRS-based secure wireless power communication network system according to claim 3, wherein the energy signal x transmitted by the hybrid access point0The mean value of (t) is 0 and the variance is 1.
9. A communication method of an IRS-based secure wireless power communication network system according to claim 3, wherein the phase shift matrix of the IRS is:
and satisfy
N is the number of passive elements for the corresponding IRS phase shift matrix coefficients.
10. The communication method of the IRS-based secure wireless power communication network system according to claim 4, wherein the size E [ | x ] of the energy signal transmitted by the hybrid access point is defined0(t)|2]＝1。
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