A secure communication method for intelligent reflective surface system based on pseudo-noise

Abstract

The present invention discloses a secure communication method based on a pseudo-noise intelligent reflection surface system, comprising: a base station obtains the statistical channel state information of a legitimate user, and designs a transmission precoding matrix and a pseudo-noise matrix according to the channel information; the base station traverses the lower bound of the security rate by a corresponding precoding matrix and pseudo-noise matrix calculation system, and transmits it to the intelligent reflection surface through a hardware link; finally, the base station and the intelligent reflection surface alternately optimize the pseudo-noise power allocation factor and the reflection phase shift beam of the transmitting end until the security rate converges. The optimization of the pseudo-noise power allocation factor and the reflection phase shift beam in the present invention only depends on the statistical channel information of the legitimate user, is suitable for scenarios where the channel state information of the eavesdropper cannot be obtained, and improves the security performance of the system.

Description

Technical Field

[0001] The invention relates to the field of wireless communication security, and in particular to a secure communication method of an intelligent reflection surface system based on pseudo-noise. Background Art

[0002] Intelligent Reflective Surfaces (IRS) are equipped with a large number of passive reflective elements to process the incident signal in real time, thereby changing the wireless channel between one or more pairs of transmitters and receivers to make it more conducive to communication. Since IRS does not need to connect to RF links, it can be densely deployed in wireless networks, making it one of the scalable solutions for sustainable capacity growth in the future. In particular, in IRS-assisted physical layer security communications, the signals reflected by the IRS can be designed to constructively interfere with each other by adjusting the programmable surface to increase the received signal power of legitimate users; at the same time, they can be destructively interfered to reduce the received signal power of eavesdroppers.

[0003] Many previous works consider instantaneous channel state information and adopt the method of alternately optimizing the transmitter signal precoding, pseudo noise (AN) matrix and IRS reflection beam. However, since the IRS is equipped with a large number of passive reflection elements, channel state information is difficult to obtain and the channel estimation overhead is huge. In addition, some works consider statistical channel state information and jointly optimize the transmitter precoding and IRS reflection phase shift beam, which greatly reduces the computational complexity. However, in actual systems, it is difficult for the base station to obtain the channel state information of the passive eavesdropper, and secure communication will be difficult to guarantee. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a secure communication method of an intelligent reflecting surface system based on pseudo-noise, so as to solve the problem of how to ensure secure communication in the scenario where the instantaneous channel state information of the legitimate user is difficult to obtain and the channel state information of the eavesdropper is unknown in the above scheme. The present invention considers introducing pseudo-noise into the IRS-assisted secure communication system when only the statistical channel state information of the legitimate user is known, and derives the closed form of the ergodic confidentiality rate, and jointly optimizes the IRS reflection beamforming and the pseudo-noise power allocation factor of the transmitting end, thereby improving the security of the system.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A secure communication method for an intelligent reflective surface system based on pseudo-noise, the secure communication method comprising the following steps:

[0007] Step S1: construct an intelligent reflector system based on pseudo-noise, which includes: a base station configured with M antennas, a front configured with N reflective units, a legitimate user with a single antenna, and a EAn eavesdropper with 1 antenna; wherein the eavesdropper eavesdrops on the signal transmitted by the base station to the legitimate user without being discovered, the transmission power of the base station is set to P, and ξ∈(0,1] is defined as the signal and pseudo-noise power allocation factor, then the useful signal power transmitted by the base station is expressed as ξP, and the pseudo-noise power is expressed as (1-ξ)P, wherein the useful signal and pseudo-noise are 1-dimensional and M-1-dimensional vectors respectively, and their elements obey a complex Gaussian distribution with a mean of 0 and a variance of 1;

[0008] Step S2, the base station first uses the null space of the channel matrix of the legal user as the precoding matrix of the pseudo-noise according to the channel of the legal user known to it, and then normalizes the channel matrix as the precoding matrix of the effective signal, and finally calculates the closed expression of the downlink ergodic safety rate according to the obtained precoding matrix of the pseudo-noise and the precoding matrix of the effective signal, and constructs an initial optimization problem;

[0009] Step S3, for the initial optimization problem constructed in step S2, an iterative solution is performed, and in each iteration, the base station designs the optimal pseudo-noise distribution factor according to the traversal safety rate, and the intelligent reflection surface designs the reflection phase shift beam according to the traversal safety rate. The two are performed alternately until the system's safety rate converges, and the optimal pseudo-noise distribution factor and reflection phase shift beam are obtained respectively.

[0010] Furthermore, in step S2, the channel between the base station and the smart reflective surface is represented by H1, which is an M×N dimensional matrix, and the phase shift matrix of the smart reflective surface is where θ i represents the phase shift of the i-th reflective element, i = 1, 2, ..., N, α represents the amplitude reflection coefficient;

[0011] The channel between the smart reflective surface and the legitimate user is expressed as The channel between the smart reflective surface and the eavesdropper is expressed as It is M E ×N-dimensional matrix, where β2 and β3 represent the large-scale fading of the channel, R I ,B, and R I,E is the channel correlation matrix, g B and G E represents the small-scale fading of the channel, and its elements obey a complex Gaussian distribution with a mean of 0 and a variance of 1;

[0012] The equivalent channels from the base station to the legitimate user and the eavesdropper are expressed as and in, The pseudo noise precoding matrix V satisfies h B V = 0, the effective signal precoding matrix satisfies w = h B / ||h B ||.

[0013] Furthermore, in step S2, the closed expression of the downlink traversal safety rate is expressed as:

[0014]

[0015] In this formula, tr(·) represents the trace of the matrix, is the channel noise variance from the base station to the legitimate user.

[0016] Furthermore, in step S2, the optimization goal of the initial optimization problem is:

[0017] Maximize R sec ;

[0018] The constraints are:

[0019] ξ∈(0,1];|φ n |=1,n=1,...,N

[0020] In the formula, φ n =αexp(jθ n ) represents the elements on the nth diagonal of the matrix φ.

[0021] Further, in step S3, according to the property that the initial optimization problem is a convex problem with respect to ξ, the solution is The optimal power allocation factor for the kth step is obtained as:

[0022]

[0023] in,

[0024]

[0025]

[0026]

[0027] Further, in step S3, the initial optimization problem is about φ n It is non-convex and is solved iteratively using the gradient projection method, which specifically includes:

[0028] Step S301, define vector

[0029] Step S302: In the kth iteration, define the ascending gradient And get the step size μ according to the line search k ;

[0030] Step S303, solving the projection problem min||vk -(v k-1 +μ k-1 q k-1 )||Satisfy the constraint condition|φ n |=1,n=1,...,N,then according to the result of step k, the value of step k+1 is v k+1 =exp(jarg(v k +μ k q k )), so the reflected phase shift beam is φ k+1 =αdiag(v k+1 );

[0031] Step S304: k+1 Substitute the closed expression of the safety rate into the equation to get the safety rate for the k+1th step The loop ends until the safe rate converges.

[0032] Furthermore, in step S302, the ascending gradient [q k ] n The expression is:

[0033]

[0034] In the formula, in, and The expressions are:

[0035]

[0036]

[0037] Among them, S E =ξM(M-1)M E tr(R B R E );

[0038] A E =(1-ξ)(M-1-M E )tr(R B )tr(R E );

[0039]

[0040]

[0041] The beneficial effects of the present invention are:

[0042] 1. The method of the present invention considers the actual communication scenario where the channel state information of the eavesdropping end is unknown, improves the system security by simply designing the pseudo-noise matrix and the transmission precoding, and derives the lower bound expression of the system ergodic security rate;

[0043] 2. The method of the present invention does not require instantaneous channel state information, performs alternate iterative optimization on the power allocation factor and the IRS reflection beam, and obtains a closed-form solution for the optimal pseudo-noise power allocation factor, effectively reducing the computational complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A system model diagram of a secure communication method of an intelligent reflective surface system based on pseudo-noise provided in Example 1;

[0045] Figure 2 This is a performance comparison chart of other solutions of the secure communication method provided in Example 1. DETAILED DESCRIPTION

[0046] 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.

[0047] Example 1

[0048] See also Figure 1-Figure 2 This embodiment provides a secure communication method for an intelligent reflective surface system based on pseudo-noise, and the secure communication method includes:

[0049] The base station obtains the statistical channel state information of the legitimate user and designs the transmit precoding matrix and pseudo noise matrix based on the channel information;

[0050] The base station traverses the lower bound of the safety rate through the corresponding precoding matrix and pseudo noise matrix calculation system, and transmits it to the intelligent reflection surface through the hardware link;

[0051] Finally, the base station and the intelligent reflection surface alternately optimize the pseudo-noise power allocation factor of the transmitter and the reflection phase shift beam until the safe rate converges.

[0052] Specifically, in this embodiment, the secure communication method is based on an intelligent reflective surface system, the structure of which is as follows: Figure 1 As shown, the base station has M antennas and the eavesdropper has M EThe single-antenna legitimate user is served by an intelligent reflective surface equipped with N reflective array elements. Eavesdroppers can eavesdrop on the signals transmitted by the base station to the legitimate user without being discovered. First, the base station designs the transmit precoding and pseudo-noise matrix based on the statistical channel state information of the legitimate user, and calculates the downlink traversal security rate. The base station and the intelligent reflective surface optimize the pseudo-noise power allocation factor and the reflection phase shift beam according to the rate expression, respectively, and the two are performed alternately to maximize the system's secure transmission rate.

[0053] More specifically, based on the above-mentioned intelligent reflecting surface system, this embodiment provides a secure communication method of an intelligent reflecting surface system based on pseudo noise, comprising the following steps:

[0054] (1) The lower bound of the ergodic safety rate of the system is calculated as follows:

[0055]

[0056] where tr(·) represents the trace of the matrix, is the channel noise variance from the base station to the legitimate user.

[0057] (2) The optimization goal of the initial optimization problem is:

[0058] Maximize R sec

[0059] The constraints of the initial optimization problem are:

[0060] ξ∈(0,1];|φ n |=1,n=1,...,N

[0061] In the formula, φ n =αexp(jθ n ) represents the elements on the nth diagonal of the matrix φ.

[0062] (3) According to the property that the optimization objective is convex with respect to ξ, solve The optimal power allocation factor for the kth step is:

[0063]

[0064] The expressions of A, B and C are

[0065]

[0066]

[0067]

[0068] (4) The optimization problem is about φ nIt is non-convex and is solved iteratively using the gradient projection method:

[0069] Defining vectors

[0070] In the kth iteration, define the ascending gradient And get the step size μ according to the line search k ;

[0071] Solve the projection problem min||v k -(v k-1 +μ k-1 q k-1 )||Satisfy the constraint condition|φ n |=1,n=1,...,N,then according to the result of step k, the value of step k+1 is v k+1 =exp(jarg(v k +μ k q k )), and then the reflected phase shift beam is φ k+1 =αdiag(v k+1 );

[0072] φ k+1 Substituting the expression in step 2, we can get the safe rate of the k+1th step: The loop ends until the safe rate converges.

[0073] In the above process, the rising gradient [q k ] n The expression is:

[0074]

[0075] in and The expressions are

[0076]

[0077]

[0078] S E =ξM(M-1)M E tr(R B R E )

[0079] A E =(1-ξ)(M-1-M E )tr(R B )tr(R E )

[0080]

[0081]

[0082] (5) After the safe rate of the system converges, the optimal pseudo-noise distribution factor and reflected phase shift beam are obtained respectively.

[0083] Figure 2 The performance variation diagram of the traversal safety rate of the present invention and the other three schemes with the number of reflective elements is shown in FIG. The benchmark scheme is a random phase shift setting and a fixed selected power allocation factor. Figure 2 The base station is equipped with 16 antennas and the eavesdropping end is equipped with 8 antennas. The proposed scheme outperforms the other three schemes and further improves with the increase of the number of reflective elements. In addition, the proposed scheme only requires the statistical channel state information of the legitimate users, which reduces the channel estimation overhead and algorithm complexity.

[0084] The parts not described in detail in the present invention are all known technologies to those skilled in the art. The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A secure communication method for an intelligent reflective surface system based on pseudo-noise, characterized in that: The secure communication method comprises the following steps: Step S1: construct an intelligent reflector system based on pseudo-noise, which includes: a base station configured with M antennas, a front configured with N reflective units, a legitimate user with a single antenna, and a E An eavesdropper with 1 antenna; wherein the eavesdropper eavesdrops on the signal transmitted by the base station to the legitimate user without being discovered, the transmission power of the base station is set to P, and ξ∈(0,1] is defined as the signal and pseudo-noise power allocation factor, then the useful signal power transmitted by the base station is expressed as ξP, and the pseudo-noise power is expressed as (1-ξ)P, wherein the useful signal and pseudo-noise are 1-dimensional and M-1-dimensional vectors respectively, and their elements obey a complex Gaussian distribution with a mean of 0 and a variance of 1; Step S2, the base station first uses the null space of the channel matrix of the legal user as the precoding matrix of the pseudo-noise according to the channel of the legal user known to it, and then normalizes the channel matrix as the precoding matrix of the effective signal, and finally calculates the closed expression of the downlink ergodic safety rate according to the obtained precoding matrix of the pseudo-noise and the precoding matrix of the effective signal, and constructs an initial optimization problem; Step S3, for the initial optimization problem constructed in step S2, iteratively solve, and in each iteration, the base station designs the optimal pseudo-noise allocation factor according to the traversal safety rate, and the intelligent reflection surface designs the reflection phase shift beam according to the traversal safety rate, and the two are alternately performed until the safety rate of the system converges, and the optimal pseudo-noise allocation factor and reflection phase shift beam are obtained respectively; In step S2, the closed expression of the downlink traversal safety rate is expressed as: In the closed-form expression for the downlink ergodic safety rate, tr(·) represents the trace of the matrix, is the channel noise variance from the base station to the legitimate user, Among them, β2 and β3 represent the large-scale fading of the channel, R I,B , and R I,E is the channel correlation matrix, H1 is the channel between the base station and the smart reflection surface, and φ is the phase shift matrix of the smart reflection surface; In step S2, the optimization goal of the initial optimization problem is: Maximize R sec ; The constraints are: ξ∈(0,1];|φ n |=1,n=1,...,N In the formula, φ n =αexp(jθ n ) represents the elements on the nth diagonal of the matrix φ; In step S3, according to the property that the initial optimization problem is a convex problem with respect to ξ, the solution is The optimal power allocation factor for the kth step is obtained as: in, In step S3, the initial optimization problem is about φ n It is non-convex and is solved iteratively using the gradient projection method, which specifically includes: Step S301, define vector Step S302: In the kth iteration, define the ascending gradient And get the step size μ according to the line search k ; Step S303, solving the projection problem min||v k -(v k-1 +μ k-1 q k-1 )||Satisfy the constraint condition|φ n |=1,n=1,…,N, then according to the result of step k, the value of step k+1 is v k+1 =exp(jarg(v k +μ k q k )), so the reflected phase shift beam is φ k+1 =αdiag(v k+1 ); Step S304: k+1 Substitute the closed expression of the safety rate into the equation to get the safety rate for the k+1th step The loop ends until the safe rate converges.

2. The secure communication method of a pseudo-noise-based intelligent reflective surface system according to claim 1, characterized in that: In step S2, the channel between the base station and the smart reflective surface is represented by H1, which is an M×N dimensional matrix, and the phase shift matrix of the smart reflective surface is where θ i represents the phase shift of the i-th reflective element, i=1,2,...,N, α represents the amplitude reflection coefficient; The channel between the smart reflective surface and the legitimate user is expressed as The channel between the smart reflective surface and the eavesdropper is expressed as It is M E ×N-dimensional matrix, where β2 and β3 represent the large-scale fading of the channel, R I,B , and R I,E is the channel correlation matrix, g B and G E Represents the small-scale fading of the channel, and its elements obey a complex Gaussian distribution with a mean of 0 and a variance of 1; The equivalent channels from the base station to the legitimate user and the eavesdropper are expressed as and in, The pseudo noise precoding matrix V satisfies h B V = 0, the effective signal precoding matrix satisfies w = h B / ||h B ||.

3. The secure communication method of a pseudo-noise-based intelligent reflective surface system according to claim 1, characterized in that: In step S302, the ascending gradient [q k ] n The expression is: In the formula, in, and The expressions are: Among them, S E =ξM(M-1)M E tr(R B R E ); AND E =(1-ξ)(M-1-M E )tr(R B )tr(R E );

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