Method for maximizing secrecy rate of IRS-assisted terahertz communication system under HIs

Abstract

The invention relates to a method for maximizing the secrecy rate of an IRS-assisted terahertz communication system under HIs, and belongs to the field of network security. A real communication system often has transceiver hardware damage and eavesdroppers, which may greatly reduce the safety performance of the communication system. In order to solve the problem, the invention provides a method for maximizing the secrecy rate of an IRS-assisted terahertz communication system under HIs in order to improve the utilization efficiency of system resources. According to the method, alternative optimization, continuous convex approximation, semi-definite programming and other convex optimization methods are used, HIs of a base station and IRS are considered, a base station beam forming vector, artificial noise and IRS phase shift are combined, the user secrecy rate is maximized, the optimal secure transmission performance is obtained, and the HIs resistance of the system is improved.

Description

Technical Field

[0001] The present invention belongs to the field of network security and relates to a method for maximizing the confidentiality rate of a terahertz communication system assisted by an intelligent reflecting surface (IRS) under hardware impairments (HIs). Background Art

[0002] With the commercialization of 5G, the sixth generation of mobile communications has gradually become a new round of research hotspots worldwide. As a popular technology of 6G, terahertz communication has the advantages of sufficient spectrum resources and strong anti-interference and anti-interception capabilities. However, it will still face some severe technical challenges in practical applications. The path loss and molecular absorption loss of terahertz waves are relatively serious, and the effective communication distance is limited to a very small range. In addition, the terahertz beam is narrower and more directional, which also makes terahertz communication easily blocked by obstacles. The IRS technology has the advantages of low cost, easy deployment, and active and intelligent control of the wireless propagation environment, which can effectively make up for the shortcomings of terahertz communication. Specifically, IRS uses digital coding to intelligently control electromagnetic waves to form an electromagnetic field with controllable amplitude, phase, and polarization, breaking through the uncontrollable characteristics of traditional wireless channels, realizing signal propagation direction control, enhancement, and elimination in three-dimensional space, suppressing interference and enhancing signals.

[0003] With the development of wireless network transmission, people increasingly rely on wireless networks to transmit important or private information. However, information leakage incidents occur frequently, and wireless secure communication has become an important issue for current and future wireless networks. Physical Layer Security (PLS), as an effective solution for wireless secure communication, has become a hot research topic in the industry. PLS technology uses the randomness and diversity of the channel to weaken the signal reception strength of the eavesdropper (Eve) by introducing artificial noise AN or cooperative jammers to achieve secure information transmission. However, these methods require the transceiver to perform complex signal processing to adapt the transmission signal to changes in the wireless environment, which will limit the system's secure transmission performance.

[0004] At present, the application of IRS in wireless communications has been widely studied. However, there are few studies on IRS-assisted terahertz communication systems, and they focus on channels. After searching, no research related to the physical layer security of IRS-assisted terahertz systems under HIS was found. Patent application number CN202010162635.7 discloses a design method for a terahertz secure communication system assisted by an intelligent reflective surface, but does not consider the impact of hardware damage on the system security performance in the actual communication system, and cannot cope with the situation where the system security performance is low due to hardware damage to the transceiver; In summary, this paper proposes a method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS.

[0005] The present invention considers the influence of HIs of transceivers in actual communication systems, and designs a reasonable resource allocation strategy to maximize the performance of the system in order to further ensure the fairness of user rates in the system, improve the system's anti-HIs capability and physical layer security. Therefore, the present invention designs an IRS-assisted terahertz communication system transmission optimization scheme, establishes a multi-input single-output (Multi-Input Single-Output, MISO) single-eavesdropping wireless communication system model of the IRS-assisted terahertz system, takes maximizing the system confidentiality rate as the goal, considers transceiver HIs, and models it as Gaussian distortion noise. At the same time, considering the influence of eavesdroppers on system security, artificial noise is used to weaken the signal reception strength of eavesdroppers, and under the constraints of the maximum transmission power of the base station, the minimum security rate of the user, and the IRS phase shift, a joint optimization problem about beamforming vectors, artificial noise, and IRS phase shift is constructed. Summary of the invention

[0006] In view of this, an object of the present invention is to provide a method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIs, the method comprising the following steps:

[0009] The system model consists of a base station, an IRS and K single-antenna legitimate users. At the same time, a single-antenna eavesdropper attempts to eavesdrop on the information transmitted to the legitimate user, considering the impact of hardware damage at the transceiver end on the system security performance. It includes the following steps:

[0010] 101. Consider a resource allocation model for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIs, construct an optimization problem, and determine whether the constructed problem has a feasible solution;

[0011] 102. After simplifying the original problem by variable substitution, the problem is decomposed into two sub-problems for optimization based on the alternating optimization algorithm. Variable substitution is to introduce auxiliary variables to simplify and replace the original objective function, and at the same time add constraints containing the introduced variables. Specifically, the base station beamforming vector and artificial noise optimization sub-problems are solved by continuous convex approximation and semi-positive relaxation, and the IRS phase shift optimization sub-problem is solved by using variable substitution and first-order Taylor approximation.

[0012] 103. Solve the convex optimization problem after equivalent transformation of step 102, solve the beamforming vector w, artificial noise z and IRS phase shift vector q, obtain the maximum confidentiality rate based on all constraints, and perform resource allocation.

[0013] For the downlink of the terahertz communication system, considering that the base station is affected by HIs, the transmitted signal It is expressed as:

[0014]

[0015] Where w = w c ;w1;K;w K is the beamforming vector, is the AN vector at the base station, and Z±0 is the AN covariance matrix. Let is the Gaussian distortion noise caused by the base station HIs. The distortion noise power of each antenna is proportional to its transmitted signal power and can be expressed as in, is the HIs factor at the transmitting end, which represents the ratio of the transmitted distortion noise power to the transmitted signal power.

[0016] Considering the IRS-assisted transmission scheme and the influence of HIs at the receiving end, the received signal y of user k is k It can be expressed as

[0017]

[0018] in, represents the phase matrix of the IRS reflection model, is the reflection phase shift of the mth unit of IRS; n k is the additive white Gaussian noise at user k, satisfying d k is the Gaussian distortion noise caused by HIs at the receiving end, and its distribution is is the HIs factor of the kth legal user.

[0019] This paper assumes that the system cannot obtain all the state information of the eavesdropper and considers the worst case, that is, the eavesdropper uses high-quality eavesdropping equipment and is not affected by the receiving end HIs. The eavesdropper receives the signal ye Expressed as

[0020]

[0021] Among them, n e is the additive Gaussian white noise at the eavesdropper, satisfying

[0022] The signal-to-noise ratio of legitimate user k is:

[0023]

[0024] Among them, the first item in the denominator is the co-channel interference from other legitimate users, the second item is the HIs noise at the base station, the third item is the AN interference from the base station, the fourth item is the HIs noise interference of legitimate user k, and the fifth item is the Gaussian white noise of legitimate user k.

[0025] Similarly, the signal-to-noise ratio of the eavesdropper is expressed as:

[0026]

[0027] Therefore, the transmission rates of the legitimate user k and the eavesdropper are expressed as:

[0028] User k successfully decodes the public data stream s c After y k Subtract the reconstruction term e from H Y k w c s c . Then, user k decodes the private data stream s k The signal-to-interference-noise ratio is expressed as

[0029] R k =log2(1+γ k )

[0030] R e =log2(1+γ e )

[0031] To ensure the transmission performance of legitimate users, the security rate of legitimate users meets the following requirements:

[0032]

[0033] in,

[0034] Under the constraints of the maximum transmission power of the base station, the minimum security rate of the user and the IRS phase shift, the beamforming vector, artificial noise and IRS phase shift are optimized to maximize the system confidentiality rate. The optimization problem is expressed as

[0035]

[0036] in, is the confidentiality rate of user k; constraint C1 is the minimum security rate constraint used to overcome the influence of eavesdroppers on the secure transmission of legitimate user information; C2 is the maximum transmission power constraint at the base station; C3 is the IRS reflection phase shift constraint;

[0037] Since the optimization variables w, z, and θ in P1 are coupled, and the objective function and constraints are non-convex, this problem is difficult to solve directly. Therefore, this paper adopts the AO method to decouple the optimization variables w, z, and θ in P1 and divide P1 into two convex sub-problems for solution.

[0038] First, the IRS phase shift vector θ is fixed, and the transmit beamforming vector w and artificial noise z are optimized. Assume that the given θ is make M k =M H M, N e =N H N, W = ww H , at this time, the transmission rates of the legitimate user and the eavesdropper can be rewritten as:

[0039]

[0040] in

[0041]

[0042] At this time, the optimization problem can be simplified to:

[0043] (P2):

[0044]

[0045] C3:Rank(W k )=1

[0046]

[0047] Transform the above problem as follows:

[0048]

[0049]

[0050] At this point, the problem is still non-convex, and the optimal solution of w and z cannot be directly obtained. Use SCA to construct the global underestimate of E1 and E2 to obtain a strict convex upper bound of the objective function. It can be transformed into:

[0051]

[0052] At this time, the non-convex objective function is transformed into the following approximate convex function:

[0053]

[0054] And meet

[0055]

[0056] Then problem P2 can be rewritten as problem P3:

[0057] (P3):

[0058]

[0059] C3:Rank(W k )=1

[0060]

[0061] However, due to the existence of constraint C3, the problem is still non-convex. By relaxing the rank 1 constraint through SDR, it can be solved using the convex optimization toolbox CVX.

[0062] Given w, z, optimize the phase shift vector q. Introduce auxiliary variables make θ=θ H θ, we can get:

[0063]

[0064] in

[0065] The first-order Taylor approximation of (1b) and (2a) is:

[0066]

[0067] At this point, the target problem can be expressed as P4:

[0068] (P4):

[0069]

[0070] (1a),(1c),(1d),(2b),(2c),(2d),(3a),(3c)

[0071] Apply the SDR method P4 to further relax it into a convex SPD, and then use the CVX toolbox to solve the convex problem P4;

[0072] According to the above two sub-problems, the optimal beamforming vector w, the optimal IRS phase shift vector q, and the optimal artificial noise z are output, and the maximum confidentiality rate is updated until convergence to obtain the solution to the problem.

[0073] The beneficial effects of the present invention are:

[0074] The present invention takes into account the situation that there are transceiver hardware damage and eavesdroppers in the actual terahertz communication system, and studies the problem of maximizing the confidentiality rate of the IRS-assisted terahertz system under the condition of hardware damage.

[0075] The present invention considers the impact of transceiver hardware damage and eavesdroppers on the security performance of the actual communication system, takes maximizing the confidentiality rate as the goal, considers transceiver HIs, and models it as Gaussian distortion noise. At the same time, the impact of eavesdroppers on system security is considered, artificial noise is used to weaken the signal reception strength of eavesdroppers, and under the constraints of the maximum transmission power of the base station, the minimum security rate of the user, and the IRS phase shift, a joint optimization problem about the beamforming vector, artificial noise, and IRS phase shift is constructed. Through auxiliary variable replacement and AO alternating optimization method, the original non-convex problem is converted into two convex sub-problems and solved, and the beamforming vector, artificial noise, and IRS phase shift are optimized to obtain the maximum confidentiality rate of the system under all constraints.

[0076] Compared with other traditional IRS-assisted terahertz systems, the present invention has the advantages of simple solution and low complexity. The system's ability to resist hardware damage and confidentiality performance are improved from the perspective of the physical layer. The present invention innovatively considers the impact of transceiver hardware damage and eavesdroppers on system security performance in actual communication systems, making it more in line with actual conditions and having good feasibility.

[0077] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0079] Figure 1 The IRS-assisted terahertz communication system model under the hardware damage condition provided by the present invention;

[0080] Figure 2 It is a flow chart of a method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0081] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0082] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0083] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0084] See also Figure 1 The technical solution of the present invention to solve the above technical problems is:

[0085] A method for maximizing the confidentiality rate of an IRS-assisted terahertz system under hardware damage conditions includes the following steps:

[0086] Step 1: Calculate the feasibility of the problem and ensure that the problem has a feasible solution under the constraints of the problem;

[0087] Step 2: Establish a system model, such as Figure 2 The system consists of a base station, an IRS and multiple single-antenna legitimate users. The direct link is blocked by obstacles. The base station transmits information to the single-antenna legitimate user through a cascade link. At the same time, a single-antenna eavesdropper attempts to eavesdrop on the information transmitted to the legitimate user. The IRS reflection unit is a set of User Sets

[0088] Step 3: The channel model from the terahertz base station to the IRS can be expressed as:

[0089]

[0090] in, is the composite path gain, f is the center frequency, d is the distance from the terahertz base station to the center of the IRS, c is the speed of light, τ(f) is the medium absorption factor, It represents the channel matrix from the terahertz base station to the IRS. Assuming that the channel state information is known, the transmitter and the legitimate user receiver are affected by hardware damage, and considering the worst case, that is, the eavesdropper is not affected by the hardware damage of the receiver.

[0091] Step 4: The problem of maximizing the confidentiality rate of the IRS-assisted terahertz system under hardware damage conditions is stated as:

[0092] (P1):

[0093]

[0094]

[0095]

[0096] in, is the confidentiality rate of user k; constraint C1 is the minimum security rate constraint used to overcome the influence of eavesdroppers on the secure transmission of legitimate user information; C2 is the maximum transmission power constraint at the base station; C3 is the IRS reflection phase shift constraint.

[0097] Step 5: Fix the IRS phase shift θ, optimize the beamforming vector w and artificial noise z, and reformulate P1 as P2, that is,

[0098] (P2):

[0099]

[0100] C3:Rank(W k )=1

[0101]

[0102] Use SCA to construct the global underestimates of E1 and E2 to obtain a strictly convex upper bound of the objective function. At this time, the non-convex objective function is transformed into an approximate convex function, and problem P2 is transformed into P3:

[0103] (P3):

[0104]

[0105] C3:Rank(W k )=1

[0106]

[0107] Step 6: Optimize the IRS phase shift q, fix the beamforming vector w and artificial noise z. Problem P1 is transformed into P4:

[0108] (P4):

[0109]

[0110] (1a),(1c),(1d),(2b),(2c),(2d),(3a),(3c)

[0111] Step 7: Maximum confidentiality rate The specific steps are as follows: according to the two sub-problems, output the optimal beamforming vector w, the optimal IRS phase shift vector q, the optimal artificial noise z, and update the maximum confidentiality rate until convergence to find the solution to the problem

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS, wherein the system consists of a base station, an IRS and multiple single-antenna legal users, wherein: The direct link is blocked by obstacles, and the base station transmits information to the single-antenna legitimate user through the cascade link. At the same time, a single-antenna eavesdropper attempts to eavesdrop on the information transmitted to the legitimate user. The system considers HIs, and there are corresponding hardware impairment noises at the base station and IRS. Among them, the IRS reflection unit set M 31, User Set K 32, characterized in that the method comprises the following steps:

101. Initialize the maximum transmission power of the base station, the artificial noise power, the HIs coefficients of the transmitting and receiving ends, and the number of users, establish a mathematical model for the original optimization problem of the confidentiality rate, and find that the original optimization problem is a non-convex problem; 102. After simplifying the original problem by variable substitution, the problem is decomposed into two sub-problems for optimization based on the alternating optimization algorithm. Variable substitution is to introduce auxiliary variables to simplify and replace the original objective function, and at the same time add constraints containing the introduced variables; the base station beamforming vector and artificial noise optimization sub-problems are solved by continuous convex approximation and semi-positive relaxation, and the IRS phase shift optimization sub-problem is solved by using variable substitution and first-order Taylor approximation; 103. Solve the convex optimization problem after equivalent transformation of step 102, solve the beamforming vector w, artificial noise z and IRS phase shift vector q, and obtain the maximum confidentiality rate based on all constraints.

2. According to claim 1, a method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS, characterized in that: The channel state information of the system is known, and the channel gains of BS-IRS, IRS-user k, and IRS-eavesdropper are expressed as For the downlink of the terahertz communication system, considering that the base station is affected by HIs, the transmitted signal f∈￡ N′1 Expressed as Where w = w c ;w1;K;w K is the beamforming vector, is the artificial noise (AN) vector at the base station, and Z±0 is the AN covariance matrix; let is the Gaussian distortion noise caused by the base station HIs. The distortion noise power of each antenna is proportional to its transmitted signal power and can be expressed as in, is the HIs factor at the transmitting end, which represents the ratio of the transmitted distortion noise power to the transmitted signal power.

3. The method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS according to claim 2, characterized in that: A mathematical model for the maximization problem is established for the confidentiality rate of the system, and the maximization objective function is: in, is the confidentiality rate of user k; constraint C1 is the minimum security rate constraint, which is used to overcome the influence of eavesdroppers on the secure transmission of legitimate user information; C2 is the maximum transmission power constraint at the base station; C3 is the IRS reflection phase shift constraint.

4. The method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS according to claim 3, characterized in that: P1 is solved by the AO method. The solution steps are: fix θ, optimize the beamforming vector w and artificial noise z; fix w and z, optimize the IRS phase shift vector θ; perform alternately until Converge and obtain the solution to the problem.

5. The method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS according to claim 4, characterized in that: The optimized beamforming vector w and artificial noise z are specifically: Fixed phase shift vector θ, assuming the given θ is M k =M H M, N e =N H N,W=ww H ,make At this time, the transmission rates of the legitimate user and the eavesdropper are rewritten as: At this time, the optimization problem is simplified to: C3:Rank(W k )=1 C4:W k ±0 C5:Z±0 Transform the above problem as follows: At this point, the problem is still non-convex, and the optimal solution of w and z cannot be directly obtained. Use SCA to construct the global underestimate of E1 and E2 to obtain the strict convex upper bound of the objective function; transform it into: At this time, the non-convex objective function is transformed into the following approximate convex function: And meet Then problem P2 can be rewritten as problem P3: C3:Rank(W k )=1 C4:W k ±0 C5:Z±0 There is a constraint C3, and the problem is non-convex; by relaxing the rank-1 constraint through SDR, it is solved by the convex optimization toolbox CVX.

6. The method for maximizing the confidentiality rate of an IRS-assisted terahertz communication system under HIS according to claim 5, characterized in that: The phase shift vector q is optimized as follows: Given w and z, introduce auxiliary variables make θ=θ H θ, we get: in The first-order Taylor approximation of (1b) and (2a) is: At this point, the target problem is expressed as P4: (1a),(1c),(1d),(2b),(2c),(2d),(3a),(3c) Apply the SDR method to further relax P4 into a convex SPD, and then use the CVX toolbox to solve the convex problem P4; According to P3 and P4, the optimal beamforming vector w, the optimal IRS phase shift vector q, and the optimal artificial noise z are output, and the maximum confidentiality rate is updated until convergence, and the solution to the problem is obtained.

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