A RIS-assisted physical layer secure communication method for WPCN system

Abstract

The present invention discloses a RIS-assisted WPCN system physical layer secure communication method, which can realize secure communication of the WPCN system and unlimited energy replenishment of the terminal by adopting RIS-assisted and WPCN wireless energy supply technology. The communication method comprises the following steps: S1: constructing a RIS-assisted WPCN system network model; S2: determining the original problem of model optimization, and establishing an optimization problem with the goal of maximizing the system security transmission rate under the condition of fully considering the nonlinear energy collection model; S3: simplifying the original problem, and converting the original problem into several convex sub-problems by adopting AO, SCA and SDR methods; S4: establishing an iterative algorithm, and solving the several sub-problems by alternate iteration through the iterative algorithm to obtain the optimal base station beamforming factor, RIS energy and information reflection coefficient, and time allocation factor, so as to maximize the system security transmission rate.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a physical layer security communication method suitable for a Wireless Powered Communication Networks (WPCN) system. Background Art

[0002] Physical layer secure communication uses the randomness of wireless channels to achieve confidential communication, which is more secure than traditional encryption methods. WPCN uses collection technology to extract energy from received signals, which can provide a convenient solution to the energy limitation problem of wireless terminal nodes. Reconfigurable Intelligent Surface (RIS) is a passive reflective surface array composed of a large number of low-cost passive components. It can adjust the phase, amplitude and frequency of radio waves to optimize network performance and minimize losses. Applying RIS to physical layer security is expected to further improve the security of wireless networks.

[0003] At present, some scholars have conducted some research on the physical layer security of WPCN. The patent "A physical layer secure communication method based on a WPCN system with intelligent reflective surface" applied by Hu Kai et al. proposed a RIS-assisted physical layer secure communication method for WPCN systems, but it did not consider the energy consumption of the energy collection circuit itself, and considered a linear energy collection model, which is inconsistent with the actual energy collection circuit. In the paper "Cooperative Jamming-Aided Secure Wireless Powered Communication Networks: A Game Theoretical Formulation" published in "IEEE Communications Letters", Zhong Y proposed a method of using interference nodes to cooperate with the WPCN system to achieve secure transmission. The disadvantage is that this scheme also considers the linear energy collection model, and when the uplink user transmits information to the base station, the artificial noise generated by the interference source will interfere with both the eavesdropping end and the user end, thereby affecting the system's secure transmission rate. Summary of the invention

[0004] The purpose of the present invention is to solve the above defects in the prior art and provide a RIS-assisted WPCN system physical layer secure communication method. Taking into account the circuit hardware loss and nonlinear energy collection model, the base station beamforming factor, RIS energy and information reflection coefficient and time allocation factor are jointly optimized with the goal of maximizing the system's secure transmission rate, so as to provide wireless charging function for terminal nodes while improving the information transmission rate of legitimate terminals and reducing the eavesdropping ability of eavesdropping terminals, thereby achieving the purpose of secure communication.

[0005] The purpose of the present invention can be achieved by adopting the following technical solutions:

[0006] A RIS-assisted physical layer secure communication method for a WPCN system, the WPCN system comprising a base station equipped with N transmitting antennas forming a uniform linear array, a controller RIS equipped with M reflecting units forming a uniform rectangular array, a legitimate user User equipped with a single antenna, and an eavesdropping terminal Eve equipped with a single antenna. The implementation steps of the physical layer secure communication method are as follows:

[0007] S1. Before the transmission starts, the base station sends a broadcast instruction to all receiving ends including the user User and the controller RIS. After receiving the broadcast instruction, all receiving ends send training symbols to the base station.

[0008] S2: The base station estimates the legal uplink channel of the WPCN system based on the received training symbols and obtains the channel information between the base station and the controller RIS. Channel information between the base station and the user User in represents the channel information between the ith antenna of the base station and the controller RIS, h i represents the channel information between the i-th antenna of the base station and the user User, Represents a complex domain, and obtains the legal downlink channel between the base station and the user User through the symmetry of the channel information;

[0009] S3. Define the optimization problem of maximizing the system's secure transmission rate as follows

[0010] P1:

[0011] stC1:0≤τ k ≤1,k=0,1

[0012] C2:τ0+τ1=1

[0013] C3:||f|| 2 ≤P max

[0014] C4:

[0015] C5:

[0016] Where f=[f1,f2,...,f i ...,f N ] represents the base station beamforming factor, f i represents the beamforming factor of the ith antenna of the base station, τ=[τ0,τ1] T represents the time allocation factor, τ0 represents the time factor for the base station to transmit the energy signal, τ1 represents the time factor for the user to transmit the information signal, e=[e1,e2,...,e m ,...,e M ] T represents the controller RIS energy reflection coefficient vector, q=[q1,q2,...,q m ,...,q M ] T represents the controller RIS signal reflection coefficient vector, R=[τ1(R U -R E )] + =max{τ1(R U -R E ),0} represents the safe transmission rate of the WPCN system, R U =log2(1+γ U ) indicates the rate at which the base station receives information from the user User. represents the signal-to-noise ratio, It represents the total channel gain of the uplink user User sending information signals to the base station. represents the noise power of user User, represents the total channel gain of the downlink base station sending energy signals to the user User, μ r |h U f| 2 Represents the power consumption of the collection circuit itself, μ r Represents the circuit loss factor; R E =log2(1+γ E ) represents the information rate of the user User being eavesdropped by the eavesdropping end Eve, represents the signal-to-noise ratio of the eavesdropping end, It indicates the channel gain of the signal sent by the eavesdropping end Eve to the user User. represents the noise power of the eavesdropping end Eve; P max Indicates the maximum transmission power of the base station; P = min{|h Uf| 2 ,P sat} represents the received power of the user User, where P sat Indicates the maximum receiving power of the user User, |h U f| 2 represents the power transmitted by the base station to the user; constraints C1 and C2 represent the possible values ​​of the time allocation factor; constraint C3 represents the possible value of the base station beamforming factor f; constraints C4 and C5 represent e m and q m Possible values:

[0017] S4, the base station generates a signal s, which obeys a Gaussian distribution with a mean of 0 and a variance of 1. In the transmission time slot t0=τ0T, where T represents the time of a transmission time slot, the base station beamforming factor f is used to beamform the signal s. The energy signal transmitted by the base station to the user User is y U =(f·s).

[0018] Furthermore, the base station first sends training symbols to perform channel estimation and then obtains the channel information between the controller RIS and the user User Channel information between controller RIS and eavesdropping end Eve The channel information between the eavesdropping end Eve and the user User is calculated by using the quasi-static steady fading characteristics and the channel statistics.

[0019] Furthermore, in the physical layer secure communication method, the non-convex optimization problem described in step S3 is first decomposed into several convex sub-problems using AO, SCA and SDR methods;

[0020] Further, the optimization problem described in step S3 is iteratively solved using the convex optimization toolkit CVX;

[0021] Finally, the optimal base station beamforming factor is obtained where f i * represents the optimal beamforming factor of the ith antenna of the base station and the RIS energy reflection coefficient vector of the controller in Represents the mth optimal energy reflection factor of the controller RIS and the RIS signal reflection coefficient vector in, Represents the mth optimal information reflection factor and time allocation factor of the controller RIS in, represents the optimal time factor for the base station to transmit energy signals, It represents the optimal time factor for user User to transmit information signal. The process is as follows:

[0022] S3.1. Initialize the convergence tolerance ε, iteration variable k, and beamforming factor f = [f1, f2, ..., f i ...,f N ], controller RIS energy reflection coefficient vector e=[e1,e2,...,e m ,...,e M ] T 、Controller RIS signal reflection coefficient vector q=[q1,q2,...,q m ,...,q M ] T and time allocation factor τ = [τ0, τ1] T , get the initial value when k=1 where f i (1) represents the k=1 iteration value of the ith antenna of the base station, represents the k=1 iteration value of the mth energy reflection element of the controller RIS, represents the k=1 iteration value of the mth information reflection element of the controller RIS, in The time factor of the base station to transmit the energy signal k = 1 iteration value, Indicates the value of k=1 iterations of the information signal transmitted by the user User. Calculate the power collected by the user when k=1 in represents the power transmitted from the k=1 base station to the user User, P sat The maximum collected power of the user User is used to calculate the maximum safe transmission rate R of the system (1) ;

[0023] S3.2, fixed at k = 1 RIS energy reflection coefficient vector e (k) , RIS information reflection coefficient vector q (k) and the time allocation factor τ (k) ,make Use the CVX toolkit to solve the optimization problem of maximizing the system security transmission rate in step S3 and obtain the optimal solution f for the k+1th beamforming factor (k+1) ;

[0024] S3.3, using the k+1th beamforming factor f obtained above (k+1) , fixed f (k+1) ,q (k) ,τ (k) ,make The convex optimization toolkit CVX is used to solve the optimization problem of maximizing the system security transmission rate in step S3 to obtain the optimal solution e of the k+1th RIS energy reflection coefficient vector (k+1) ;

[0025] S3.4. Using the k+1th beamforming factor f obtained above (k+1) and the RIS energy reflection coefficient vector e (k+1) , fixed f (k+1) ,e (k+1) ,τ (k) ,make The convex optimization toolkit CVX is used to solve the optimization problem in step S3 to obtain the optimal solution q of the k+1th RIS information reflection coefficient vector (k+1) ;

[0026] S3.5. Using the k+1th beamforming factor f obtained above (k+1) ,RIS energy reflection coefficient vector e (k+1) and RIS information reflection coefficient vector q (k+1) ,make The convex optimization toolkit CVX is used to solve the optimization problem in step S3 to obtain the optimal solution τ of the k+1th time allocation factor (k+1) , calculate the maximum safe transmission rate R of the system when k+1 (k+1) ;

[0027] S3.6. Determine R (k+1) -R (k) ≤ε is true, if R (k+1) -R (k) ≤ε holds, stop the iteration and execute step S3.7; otherwise, let τ (k) =τ (k+1) ,e (k) =e (k+1) ,q (k) =q (k+1) ,f (k) =f (k+1) , k=k+1 return to step S3.2;

[0028] S3.7, through CVX solution, we finally get the optimal f corresponding to the maximum system safety rate of the WPCN communication system. * 、e * ,q * and τ * .

[0029] Compared with the prior art, the present invention has the following advantages and effects:

[0030] 1. The present invention proposes a RIS-assisted WPCN physical layer secure communication method under the condition of considering circuit hardware loss and nonlinear energy collection model. The system secure transmission rate is maximized by jointly optimizing the base station beamforming factor f, RIS energy reflection unit e and information reflection unit q and time allocation factor τ.

[0031] 2. The present invention uses WPCN technology to solve the problem of energy limitation in traditional networks. Nodes collect energy using a nonlinear energy collection model, and uses RIS technology to improve the security of the communication network at the physical layer security level. On this basis, a non-convex optimization problem is constructed. By splitting the non-convex multivariable optimization problem into multiple convex sub-problems containing a single optimization variable for solution, the implementation is simple and the complexity is low.

[0032] 3. The method proposed in the present invention, taking into account the limited and nonlinear energy collection situations of the user User, determines the actual collection power of the user User in actual application by comparing the base station transmission power and the user User's maximum receiving power, and then calculates a more practical WPCN system safe transmission rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0034] Figure 1 It is a schematic diagram of the RIS-assisted WPCN communication system model in the present invention;

[0035] Figure 2 It is a flow chart for implementing the RIS-assisted WPCN system physical layer secure communication method disclosed in the present invention;

[0036] Figure 3 It is a comparison diagram of the RIS-assisted WPCN nonlinear and linear energy harvesting models disclosed in the present invention;

[0037] Figure 4 The fixed base station transmission rate of the present invention is P max =30dBm, comparison of system security transmission rates under different implementations. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] This embodiment discloses a RIS-assisted physical layer secure communication method for a WPCN system, wherein the WPCN system includes a base station equipped with N transmitting antennas forming a uniform linear array, a controller RIS equipped with M reflecting units forming a uniform rectangular array, a legitimate user User equipped with a single antenna, and an eavesdropping terminal Eve equipped with a single antenna.

[0041] In this embodiment, the specific parameters are set as follows:

[0042] Assume that the WPCN system is in a three-dimensional coordinate system, with the base station located at (0m, 0m, 10m), the controller RIS located at (5m, 0m, 10m), the user User located at (5m, 2m, 10m) and the eavesdropping end Eve located at (2m, 5m, 10m); the base station is equipped with N = 6 antennas, with a maximum transmission power P max =30dBm, transmission time slot T = 1, user maximum receiving power P sat =10dBm; the controller RIS is equipped with M = 32 reflectors, and the convergence tolerance ε = 10 -4 , Noise Power All channels in this embodiment are Rice channels, and the channel model is: Where β represents the Rice factor, β = 10; G LoS Indicates the line-of-sight wireless transmission part, G NLoS Represents the non-line-of-sight wireless transmission part; PL is the path loss, which is calculated by PL = -30-10αlog 10 (d), where α is the path loss parameter, d is the Euclidean distance of the link, the path loss parameter α related to the controller RIS is 2.2, and the path loss parameter α from the base station to the user User and from the base station to the eavesdropping terminal Eve is 3.6.

[0043] The steps for implementing the physical layer secure communication method are as follows:

[0044] S1. Before the transmission starts, the base station sends a broadcast instruction to all receiving ends including the user User and the controller RIS. After receiving the broadcast instruction, all receiving ends send training symbols to the base station.

[0045] S2: The base station estimates the legal uplink channel of the WPCN system based on the received training symbols and obtains the channel information between the base station and the controller RIS. Channel information between the base station and the user User in represents the channel information between the ith antenna of the base station and the controller RIS, h i represents the channel information between the i-th antenna of the base station and the User, Represents a complex domain, and obtains the legal downlink channel between the base station and the user User through the symmetry of the channel information;

[0046] S3. Define the optimization problem of maximizing the system's secure transmission rate as follows

[0047] P1:

[0048] stC1:0≤τ k ≤1,k=0,1

[0049] C2:τ0+τ1=1

[0050] C3:||f|| 2 ≤P max

[0051] C4:

[0052] C5:

[0053] where f=[f1,f2,...,f n ...,f6] is the base station beamforming factor, where f i represents the beamforming factor of the ith antenna of the base station, τ=[τ0,τ1] T represents the time allocation factor, where τ0 represents the time factor for the base station to transmit energy signals, τ1 represents the time factor for the user to transmit information signals, and e=[e1,e2,...,e m ,...,e 32 ] T is the controller RIS energy reflection coefficient vector, where q=[q1,q2,...,q m ,...,q 32 ] T is the RIS signal reflection coefficient vector, where R=[τ1(R U -R E )] + =max{τ1(R U -R E),0} represents the secure transmission rate of the WPCN system, where R U =log2(1+γ U ) indicates the rate at which the base station receives information from the user User. represents the signal-to-noise ratio, It represents the total channel gain of the uplink user User sending information signals to the base station. represents the noise power of user User, represents the total channel gain of the downlink base station sending energy signals to the user User, μ r |h U f| 2 Represents the power consumption of the collection circuit itself, μ r Represents the circuit loss factor; R E =log2(1+γ E ) represents the information rate of the user User being eavesdropped by the eavesdropping end Eve, represents the signal-to-noise ratio of the eavesdropping end, It indicates the channel gain of the signal sent by the eavesdropping end Eve to the user User. represents the noise power of the eavesdropping end Eve; P max Indicates the maximum transmission power of the base station; P = min{|h U f| 2 ,P sat} represents the received power of the user User, where P sat Indicates the maximum receiving power of the user User, |h U f| 2 represents the power transmitted by the base station to the user; constraints C1 and C2 represent the possible values ​​of the time allocation factor; constraint C3 represents the possible value of the base station beamforming factor f; constraints C4 and C5 represent e m and q m Possible values:

[0054] S3.1. Initialize the convergence tolerance ε, iteration variable k, and beamforming factor f = [f1, f2, ..., f i ...,f6], controller RIS energy reflection coefficient vector e=[e1,e2,...,e m ,...,e 32 ] T 、Controller RIS signal reflection coefficient vector q=[q1,q2,...,q m ,...,q 32 ] T and time allocation factor τ = [τ0, τ1] T , get the initial value when k=1 where f i(1) represents the k=1 iteration value of the ith antenna of the base station, in represents the k=1 iteration value of the mth energy reflection element of the controller RIS, in represents the k=1 iteration value of the mth information reflection element of the controller RIS, in Indicates the time factor k=1 iteration value of the base station transmission energy signal, Indicates the time factor k=1 iteration value of the user User transmitting the information signal, and calculates the power collected by the user when k=1 in represents the power transmitted from the k=1 base station to the user User, P sat The maximum collected power of the user User is used to calculate the maximum safe transmission rate R of the system (1) ;

[0055] S3.2, fixed at k = 1 RIS energy reflection coefficient vector e (k) , RIS information reflection coefficient vector q (k) and the time allocation factor τ (k) ,make Use the CVX toolkit to solve the optimization problem of maximizing the system security transmission rate in step S3 and obtain the optimal solution f for the k+1th beamforming factor (k+1) ;

[0056] S3.3, using the k+1th beamforming factor f obtained above (k+1) , fixed f (k+1) ,q (k) ,τ (k) ,make The convex optimization toolkit CVX is used to solve the optimization problem of maximizing the system security transmission rate in step S3 to obtain the optimal solution e of the k+1th RIS energy reflection coefficient vector (k+1) ;

[0057] S3.4. Using the k+1th beamforming factor f obtained above (k+1) and the RIS energy reflection coefficient vector e (k+1) , fixed f (k+1) ,e (k+1) ,τ (k) ,make The convex optimization toolkit CVX is used to solve the optimization problem in step S3 to obtain the optimal solution q of the k+1th RIS information reflection coefficient vector (k+1) ;

[0058] S3.5. Using the k+1th beamforming factor f obtained above(k+1) ,RIS energy reflection coefficient vector e (k+1) and RIS information reflection coefficient vector The convex optimization toolkit CVX is used to solve the optimization problem in step S3 to obtain the optimal solution τ of the k+1th time allocation factor (k+1) , calculate the maximum safe transmission rate R of the system when k+1 (k+1) ;

[0059] S3.6. Determine R (k+1) -R (k) ≤ε is true, if R (k+1) -R (k) ≤ε holds, stop the iteration and execute step S3.7; otherwise, let τ (k) =τ (k+1) ,e (k) =e (k+1) ,q (k) =q (k+1) ,f (k) =f (k+1) , k=k+1 return to step S3.2;

[0060] S3.7, through CVX solution, we finally get the optimal f corresponding to the maximum system safety rate of the WPCN communication system. * 、e * ,q * and τ * .

[0061] Figure 3 It is a comparison diagram of the RIS-assisted WPCN nonlinear and linear energy collection models; it can be seen from the figure that in the curve represented by Example 1, as the power of the base station gradually increases, the safe transmission rate of the WPCN system also gradually increases and finally tends to be flat, indicating that the transmission power of the base station has an impact on the safe transmission rate of the WPCN system, but when the transmission power of the base station exceeds a certain limit, the safe transmission rate of the WPCN system will not be affected by the base station power.

[0062] Example 2

[0063] This embodiment discloses a RIS-assisted physical layer secure communication method for a WPCN system, wherein the WPCN system includes a base station equipped with N transmitting antennas forming a uniform linear array, a controller RIS equipped with M reflecting units forming a uniform rectangular array, a legitimate user User equipped with a single antenna, and an eavesdropping terminal Eve equipped with a single antenna.

[0064] In this embodiment, the specific parameters are set as follows:

[0065] Assume that the WPCN system is in a three-dimensional coordinate system, with the base station located at (0m, 0m, 10m), the controller RIS located at (5m, 0m, 10m), the user User located at (5m, 2m, 10m) and the eavesdropping end Eve located at (2m, 5m, 10m); the base station is equipped with N = 6 antennas, with a maximum transmission power P max =30dBm, transmission time slot T = 1, user maximum receiving power P sat =10dBm; the controller RIS is equipped with M = 16 reflectors, and the convergence tolerance ε = 10 -4 , Noise Power All channels in this embodiment are Rice channels, and the channel model is: Where β represents the Rice factor, β = 10; G LoS Indicates the line-of-sight wireless transmission part, G NLoS Represents the non-line-of-sight wireless transmission part; PL is the path loss, which is calculated by PL = -30-10αlog 10 (d), where α is the path loss parameter, d is the Euclidean distance of the link, the path loss parameter α related to the controller RIS is 2.2, and the path loss parameter α from the base station to the user User and from the base station to the eavesdropping terminal Eve is 3.6.

[0066] The steps for implementing the physical layer secure communication method are as follows:

[0067] S1. Before the transmission starts, the base station sends a broadcast instruction to all receiving ends including the user User and the controller RIS. After receiving the broadcast instruction, all receiving ends send training symbols to the base station.

[0068] S2: The base station estimates the legal uplink channel of the WPCN system based on the received training symbols and obtains the channel information between the base station and the controller RIS. Channel information between the base station and the user User in represents the channel information between the ith antenna of the base station and the controller RIS, h i represents the channel information between the i-th antenna of the base station and the User, Represents a complex domain, and obtains the legal downlink channel between the base station and the user User through the symmetry of the channel information;

[0069] S3. Define the optimization problem of maximizing the system's secure transmission rate as follows

[0070] P1:

[0071] stC1:0≤τ k ≤1,k=0,1

[0072] C2:τ0+τ1=1

[0073] C3:||f|| 2 ≤P max

[0074] C4:

[0075] C5:

[0076] where f=[f1,f2,...,f n ...,f6] is the base station beamforming factor, where f i represents the beamforming factor of the ith antenna of the base station, τ=[τ0,τ1] T represents the time allocation factor, where τ0 represents the time factor for the base station to transmit energy signals, τ1 represents the time factor for the user to transmit information signals, and e=[e1,e2,...,e m ,...,e 16 ] T is the controller RIS energy reflection coefficient vector, where q=[q1,q2,...,q m ,...,q 16 ] T is the RIS signal reflection coefficient vector, where R=[τ1(R U -R E )] + =max{τ1(R U -R E ),0} represents the secure transmission rate of the WPCN system, where R U =log2(1+γ U ) indicates the rate at which the base station receives information from the user User. represents the signal-to-noise ratio, It represents the total channel gain of the uplink user User sending information signals to the base station. represents the noise power of user User, represents the total channel gain of the downlink base station sending energy signals to the user User, μ r |h U f| 2 Represents the power consumption of the collection circuit itself, μ r Represents the circuit loss factor; R E =log2(1+γ E ) represents the information rate of the user User being eavesdropped by the eavesdropping end Eve, represents the signal-to-noise ratio of the eavesdropping end, It indicates the channel gain of the signal sent by the eavesdropping end Eve to the user User. represents the noise power of the eavesdropping end Eve; P max Indicates the maximum transmission power of the base station; P = min{h U f| 2 ,P sat} represents the received power of the user User, where P sat Indicates the maximum receiving power of the user User, |h U f| 2 represents the power transmitted by the base station to the user; constraints C1 and C2 represent possible values ​​of the time allocation factor; constraint C3 represents possible values ​​of the base station beamforming factor f; constraints C4 and C5 represent e m and q m Possible values:

[0077] S3.1. Initialize the convergence tolerance ε, iteration variable k, and beamforming factor f = [f1, f2, ..., f i ...,f6], controller RIS energy reflection coefficient vector e=[e1,e2,...,e m ,...,e 16 ] T 、Controller RIS signal reflection coefficient vector q=[q1,q2,...,q m ,...,q 16 ] T and time allocation factor τ = [τ0, τ1] T , get the initial value when k=1 where f i (1) represents the k=1 iteration value of the ith antenna of the base station, in represents the k=1 iteration value of the mth energy reflection element of the controller RIS, in represents the k=1 iteration value of the mth information reflection element of the controller RIS, in Indicates the time factor k=1 iteration value of the base station transmission energy signal, Indicates the time factor k=1 iteration value of the user User transmitting the information signal, and calculates the power collected by the user when k=1 in represents the power transmitted from the k=1 base station to the user User, P sat The maximum collected power of the user User is used to calculate the maximum safe transmission rate R of the system (1) ;

[0078] S3.2, fixed at k = 1 RIS energy reflection coefficient vector e (k) , RIS information reflection coefficient vector q (k) and the time allocation factor τ (k) ,make Use the CVX toolkit to solve the optimization problem of maximizing the system security transmission rate in step S3 and obtain the optimal solution f for the k+1th beamforming factor (k+1) ;

[0079] S3.3, using the k+1th beamforming factor f obtained above (k+1) , fixed f (k+1) ,q (k) ,τ (k) ,make The convex optimization toolkit CVX is used to solve the optimization problem of maximizing the system security transmission rate in step S3 to obtain the optimal solution e of the k+1th RIS energy reflection coefficient vector (k+1) ;

[0080] S3.4. Using the k+1th beamforming factor f obtained above (k+1) and the RIS energy reflection coefficient vector e (k+1) , fixed f (k+1) ,e (k+1) ,τ (k) ,make The convex optimization toolkit CVX is used to solve the optimization problem in step S3 to obtain the optimal solution q of the k+1th RIS information reflection coefficient vector (k+1) ;

[0081] S3.5. Using the k+1th beamforming factor f obtained above (k+1) ,RIS energy reflection coefficient vector e (k+1) and RIS information reflection coefficient vector q (k+1) ,make The convex optimization toolkit CVX is used to solve the optimization problem in step S3 and obtain the k+1 The optimal solution of the sub-time allocation factor τ (k+1) , calculate k+1 The maximum safe transmission rate of the system is R (k+1) ;

[0082] S3.6. Determine R (k+1) -R (k) ≤ε is true, if R (k+1) -R (k) ≤ε holds, stop the iteration and execute step S3.7; otherwise, let τ (k) =τ (k+1) ,e (k) =e (k+1) ,q(k) =q (k+1) ,f (k) =f (k+1) , k=k+1 return to step S3.2;

[0083] S3.7, through CVX solution, we finally get the optimal f corresponding to the maximum system safety rate of the WPCN communication system. * ,e * ,q * and τ * .

[0084] Figure 4 The fixed base station transmission rate of the present invention is P max =30dBm, a comparison chart of the system security transmission rate under different embodiments is shown; it can be seen from the figure that when the maximum transmission power of the base station is fixed, the security transmission rate of the WPCN system gradually increases with the increase of the number of iterations and eventually tends to be flat, indicating that the method proposed in the present invention is convergent. It can be seen from the figure that after about 6 iterations, the security transmission rate of the WPCN system has become flat, indicating that the method proposed in the present invention converges quickly.

[0085] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. A RIS-assisted WPCN system physical layer security communication method, characterized in that: The WPCN system includes a base station equipped with N transmitting antennas forming a uniform linear array, a controller RIS equipped with M reflecting units forming a uniform rectangular array, a legitimate user User equipped with a single antenna, and an eavesdropping terminal Eve equipped with a single antenna. The implementation steps of the physical layer secure communication method of the WPCN system are as follows: S1. Before the transmission starts, the base station sends a broadcast instruction to all receiving ends including the user User and the controller RIS. After receiving the broadcast instruction, all receiving ends send training symbols to the base station. S2: The base station estimates the legal uplink channel of the WPCN system based on the received training symbols and obtains the channel information between the base station and the controller RIS. Channel information between the base station and the user User in represents the channel information between the ith antenna of the base station and the controller RIS, h i represents the channel information between the i-th antenna of the base station and the User, Represents a complex domain, and obtains the legal downlink channel between the base station and the user User through the symmetry of the channel information; S3. Define the optimization problem of maximizing the system's secure transmission rate as follows s.t.C1:0≤τ k ≤1,k=0,1 C2:τ0+τ1=1 C3:||f|| 2 ≤P max Where f=[f1,f2,...,f i ...,f N ] represents the base station beamforming factor, f i represents the beamforming factor of the ith antenna of the base station, τ=[τ0,τ1] T represents the time allocation factor, τ0 represents the time factor for the base station to transmit the energy signal, and τ1 represents the time factor for the user to transmit the information signal. e=[e1,e2,...,e m ,...,e M ] T represents the controller RIS energy reflection coefficient vector, q=[q1,q2,...,q m ,...,q M ] T represents the controller RIS signal reflection coefficient vector, R=[τ1(R U -R E )] + =max{τ1(R U -R E ),0} represents the safe transmission rate of the WPCN system, R U =log2(1+γ U ) indicates the rate at which the base station receives information from the user User. represents the signal-to-noise ratio, It represents the total channel gain of the uplink user User sending information signals to the base station. represents the noise power of user User, represents the total channel gain of the downlink base station sending energy signals to the user User, μ r |h U f| 2 Represents the power consumption of the collection circuit itself, μ r Represents the circuit loss factor; R E =log2(1+γ E ) represents the information rate of the user User being eavesdropped by the eavesdropping end Eve, represents the signal-to-noise ratio of the eavesdropping end, It indicates the channel gain of the signal sent by the eavesdropping end Eve to the user User. Indicates the channel information between the controller RIS and the eavesdropping end Eve, represents the noise power of the eavesdropping end Eve; P max Indicates the maximum transmission power of the base station; P = min{|h U f| 2 ,P sat } represents the received power of the user User, where P sat Indicates the maximum receiving power of the user User, |h U f| 2 represents the power transmitted by the base station to the user; constraints C1 and C2 represent the possible values ​​of the time allocation factor; constraint C3 represents the possible value of the base station beamforming factor f; constraints C4 and C5 represent e m and q m Possible values: S4, the base station generates a signal s, which obeys a Gaussian distribution with a mean of 0 and a variance of 1. In the transmission time slot t0=τ0T, where T represents the time of a transmission time slot, the base station beamforming factor f is used to beamform the signal s. The energy signal transmitted by the base station to the user User is y U =(f·s).

2. According to claim 1, a RIS-assisted WPCN system physical layer security communication method is characterized in that: In the physical layer secure communication method of the WPCN system, the channel information between the controller RIS and the user User is continuously acquired by sending training symbols for channel estimation. Channel information between controller RIS and eavesdropping end Eve The channel information between the eavesdropping end Eve and the user User is calculated by using the quasi-static steady fading characteristics and the channel statistics.

3. According to claim 1, a RIS-assisted WPCN system physical layer security communication method is characterized in that: In the physical layer secure communication method of the WPCN system, the convex optimization toolkit CVX is used to solve the optimization problem of maximizing the system secure transmission rate in step S3 to obtain the optimal base station beamforming factor where f i * represents the optimal beamforming factor of the ith antenna of the base station and the RIS energy reflection coefficient vector of the controller in Represents the mth optimal energy reflection factor of the controller RIS and the RIS signal reflection coefficient vector in, Represents the mth optimal information reflection factor and time allocation factor of the controller RIS in, represents the optimal time factor for the base station to transmit energy signals, Indicates the optimal time factor for user User to transmit information signals.

4. A RIS-assisted WPCN system physical layer security communication method according to claim 1, characterized in that: The process of step S3 is as follows: S3.

1. Initialize the convergence tolerance ε, iteration variable k, and beamforming factor f = [f1, f2, ..., f i ...,f N ], controller RIS energy reflection coefficient vector e=[e1,e2,...,e m ,...,e M ] T 、Controller RIS signal reflection coefficient vector q=[q1,q2,...,q m ,...,q M ] T and time allocation factor τ = [τ0, τ1] T , get the initial value when k=1 where f i (1) represents the k=1 iteration value of the ith antenna of the base station, represents the k=1 iteration value of the mth energy reflection element of the controller RIS, represents the k=1 iteration value of the mth information reflection element of the controller RIS, in The time factor of the base station to transmit the energy signal k = 1 iteration value, Indicates the value of k=1 iterations of the information signal transmitted by the user User. Calculate the power collected by the user when k=1 in represents the power transmitted from the k=1 base station to the user User, P sat The maximum collected power of the user User is used to calculate the maximum safe transmission rate R of the system (1) ; S3.2, fixed at k = 1 RIS energy reflection coefficient vector e (k) , RIS information reflection coefficient vector q (k) and the time allocation factor τ (k) ,make Use the CVX toolkit to solve the optimization problem of maximizing the system security transmission rate in step S3 and obtain the optimal solution f for the k+1th beamforming factor (k+1) ; S3.3, using the k+1th beamforming factor f obtained above (k+1) , fixed f (k+1) ,q (k) ,τ (k) ,make The convex optimization toolkit CVX is used to solve the optimization problem of maximizing the system security transmission rate in step S3 to obtain the optimal solution e of the k+1th RIS energy reflection coefficient vector (k+1) ; S3.

4. Using the k+1th beamforming factor f obtained above (k+1) and the RIS energy reflection coefficient vector e (k+1) , fixed f (k+1) ,e (k+1) ,τ (k) ,make The convex optimization toolkit CVX is used to solve the optimization problem and obtain the optimal solution q of the k+1th RIS information reflection coefficient vector (k+1) ; S3.

5. Using the k+1th beamforming factor f obtained above (k+1) ,RIS energy reflection coefficient vector e (k+1) and RIS information reflection coefficient vector q (k+1) ,make The convex optimization toolkit CVX is used to solve the optimization problem and obtain the optimal solution τ of the k+1th time allocation factor. (k+1) , calculate the maximum safe transmission rate R of the system when k+1 (k+1) ; S3.

6. Determine R (k+1) -R (k) ≤ε is true, if R (k+1) -R (k) ≤ε holds, stop the iteration and execute step S3.7; otherwise, let τ (k) =τ (k+1) ,e (k) =e (k+1) ,q (k) =q (k+1) ,f (k) =f (k+1) , k=k+1 return to step S3.2; S3.7, through CVX solution, finally get the optimal f when the WPCN communication system reaches * ,e * ,q * and τ * .

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