Active RIS-assisted jitter UAV air-ground safety communication method and active RIS-assisted jitter UAV air-ground safety communication system

Abstract

The invention provides an active RIS-assisted jitter UAV air-ground security communication method and system, and relates to the technical field of UAV communication. According to the active RIS-assisted jitter UAV air-ground safety communication method provided by the invention, the unmanned aerial vehicle airborne base station channel and the active RIS channel are constructed by constructing the coordinate of each communication node in the communication system and using the preset free space path loss model, and the active RIS channel is constructed based on the vibration characteristics of the unmanned aerial vehicle airborne base station. A pre-constructed uncertainty set of azimuth angles and elevation angles is utilized, jitter characteristics under the influence of random airflow and machine body vibration are considered for safe communication, unmanned aerial vehicle airborne base station channel errors and active RIS channel errors are determined, iterative solution is carried out on a constructed optimization problem, and therefore a communication decision of an active RIS-assisted UAV communication system is obtained. Therefore, the purpose of weakening the influence of the jitter characteristic on the safety communication of the unmanned aerial vehicle under the influence of random airflow and vehicle body vibration is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of UAV communication, and specifically relates to an active RIS-assisted jitter UAV-air-ground secure communication method and system. Background Art

[0002] The low-altitude economy is a comprehensive economic form driven by various low-altitude flight activities of manned or unmanned aerial vehicles, radiating and driving the integrated development of related fields, with characteristics such as a long industrial chain, a wide radiation range, strong growth potential and driving ability, mainly including low-altitude manufacturing, low-altitude flight, low-altitude guarantee and low-altitude operation services. Among them, the low-altitude flight industry is the core industry of the low-altitude economy, and the UAV industry is the forefront track of the low-altitude flight industry. A UAV is a flexible and fast mobile platform that can be widely used in various applications in smart cities, such as professional fields like mapping, aerial photography, evidence collection, and logistics. A large number of data processing behaviors are involved herein, and the electronic components such as cameras, environmental sensors, microphones, and GPS sensors carried by the UAV itself also enable it to collect and store data more conveniently and over a larger range, posing higher requirements for data security protection.

[0003] In the prior art, it is proposed to use Reconfigurable Intelligent Surface (RIS) technology to improve the secure communication performance of Unmanned Aerial Vehicles (UAVs). However, most of the current work ignores an inevitable problem in RIS-assisted UAV communication: Although RIS brings a new reliable reflection link for signal transmission outside the direct link, there is always a "double fading" effect in this reflection link, that is, the signal received via this link suffers from two large-scale fades. When the fading coefficient is large, the signal from the longer reflection link loses more power than the signal from the shorter direct link, resulting in limited secure performance gain compared to the link without RIS. On the other hand, the jitter characteristics caused by random airflows and the vibration of the UAV body itself have a non-negligible impact on establishing a robust and secure communication link. Different from the ground cellular network with fixed and stable infrastructure, UAVs are vulnerable to airflows and body vibrations, resulting in random vibrations, such as yaw jitter in the horizontal direction or pitch jitter in the vertical direction. Therefore, the vibration introduces non-negligible channel estimation errors, which lead to the deviation of the directional signal beam and further result in serious performance losses. Summary of the Invention

[0004] To solve the problem that the jitter characteristics of drones under the influence of random airflow and airframe vibration affect secure communication in the prior art, the present invention proposes an active RIS-assisted jitter UAV-air-to-ground secure communication method and system. In the active RIS-assisted jitter UAV-air-to-ground secure communication method provided by the present invention, the coordinates of each communication node in the communication system are constructed, and the free space path loss model preset is used to construct the UAV airborne base station channel and the active RIS channel. At the same time, based on the vibration characteristics of the UAV airborne base station, by using the pre-constructed uncertainty sets of azimuth and elevation angles, considering the jitter characteristics under the influence of random airflow and airframe vibration on secure communication, the UAV airborne base station channel error and the active RIS channel error are determined, and the constructed optimization problem is iteratively solved, so as to obtain the communication decision of the active RIS-assisted UAV communication system, thereby achieving the purpose of weakening the influence of the jitter characteristics under the influence of random airflow and airframe vibration on the secure communication of the drone.

[0005] On the one hand, the present invention provides an active RIS-assisted jitter UAV-air-to-ground secure communication method, including: Based on the communication nodes in the preset active RIS-assisted UAV communication system, using a three-dimensional coordinate system, the coordinates of each communication node in the communication system are obtained, and the communication nodes include a UAV airborne base station, an active RIS, a legitimate user, and an eavesdropper; Based on the coordinates of the communication nodes in the communication system, using the preset free space path loss model, the UAV airborne base station channel and the active RIS channel are constructed. The UAV airborne base station channel includes the channel between the UAV airborne base station and the active RIS, the channel between the UAV airborne base station and the legitimate user, and the channel between the UAV airborne base station and the eavesdropper. The active RIS channel includes the channel between the active RIS and the legitimate user and the channel between the active RIS and the eavesdropper; Based on the vibration characteristics of the UAV airborne base station, using the pre-constructed uncertainty sets of azimuth and elevation angles, the UAV airborne base station channel error and the active RIS channel error are determined; Based on the UAV airborne base station channel and the active RIS channel, the legitimate user received signal and the eavesdropper received signal are confirmed; Integrating the reflection coefficient matrix of the active RIS, the UAV airborne base station channel, the active RIS channel, the UAV airborne base station channel error, the active RIS channel error, the legitimate user received signal, and the eavesdropper received signal, taking the minimum transmit power of the active RIS-assisted UAV communication system as the optimization problem, using an iterative algorithm to solve the transmit beamforming matrix and the reflection coefficient matrix, obtaining the optimization result, and generating the communication decision of the active RIS-assisted UAV communication system.

[0006] Optionally, by synthesizing the reflection coefficient matrix of the active RIS, the UAV airborne base station channel, the active RIS channel, the UAV airborne base station channel error, the active RIS channel error, the received signal of the legitimate user, and the received signal of the eavesdropper, taking the minimum transmit power of the active RIS-assisted UAV communication system as an optimization problem, using an iterative algorithm, solving for the transmit beamforming matrix and the reflection coefficient matrix, obtaining an optimization result, and generating a communication decision for the active RIS-assisted UAV communication system, including: By synthesizing the reflection coefficient matrix of the active RIS, the UAV airborne base station channel, the active RIS channel, the UAV airborne base station channel error, the active RIS channel error, the received signal of the legitimate user, and the received signal of the eavesdropper, taking the minimum transmit power of the active RIS-assisted UAV communication system as an optimization problem, constructing the constraints of the optimization problem; Based on the constructed optimization problem and the constraints of the optimization problem, using an iterative algorithm, solving for the transmit beamforming matrix and the reflection coefficient matrix, obtaining an optimization result; Based on the optimization result, using an equivalent transformation algorithm, generating a communication decision for the active RIS-assisted UAV communication system.

[0007] Optionally, the constraints of the constructed optimization problem satisfy the following expressions: , , , , , wherein, represents the power of the transmit beamforming matrix; represents the limit constraint of the transmit beamforming matrix; represents the minimum data rate received by the legitimate user; represents the preset data rate threshold received by the legitimate user; represents the maximum data rate received by the eavesdropper; represents the preset data rate threshold received by the eavesdropper; represents the reflection coefficient matrix; represents the channel fading between the UAV airborne base station and the active RIS; is the maximum amplification factor at the m th RE.

[0008] Optionally, the step of, based on the constructed optimization problem and the constraints, using an iterative algorithm to solve for the transmit beamforming matrix and the reflection coefficient matrix to obtain an optimization result includes: Based on the constructed optimization problem, decompose the optimization problem to generate optimization sub - problems regarding the transmit beamforming matrix and the reflection coefficient matrix; Based on the constraints of the optimization sub - problems, use the S - lemma algorithm to transform non - convex constraints into linear matrix inequalities, and use an iterative algorithm to iteratively solve the transmit beamforming matrix and the reflection coefficient matrix to determine the interference and noise power of legitimate users and the interference and noise power of eavesdroppers; Based on the linear matrix inequalities, by introducing slack variables and using the Schur complement lemma algorithm, perform equivalent transformation on the linear matrix inequalities to obtain the transformed optimization problem; Based on the transformed optimization problem, solve it through the CVX tool to obtain the optimization result.

[0009] Optionally, the decomposing the optimization problem based on the constructed optimization problem to generate optimization sub - problems includes: Based on the constructed optimization problem, by given the reflection coefficient matrix, obtain the optimization sub - problem of the transmit beamforming matrix; Based on the constructed optimization problem, by the transmit beamforming matrix, generate the optimization sub - problems of their respective reflection coefficient matrices.

[0010] Optionally, the constructing the UAV - mounted base station channel and the active RIS channel based on the coordinates of communication nodes in the communication system by using a preset free - space path loss model includes: Based on the coordinates of communication nodes in the communication system, use the uniform rectangular arrays of the UAV - mounted base station and the active RIS to obtain the reflection system matrix of the active RIS; Based on the LOS component and the NLOS component of the UAV - mounted base station channel and the preset free - space path loss model, obtain the UAV - mounted base station channel; Based on the LOS component and the NLOS component of the active RIS channel and the preset free - space path loss model, obtain the active RIS channel.

[0011] Optionally, after generating the communication decision of the active RIS - assisted UAV communication system by using the equivalent transformation algorithm based on the optimization result, it further includes: Based on the communication decision of the active RIS - assisted UAV communication system, combined with the channel uncertainty caused by the jitter of the UAV - mounted base station, calculate the changes of the transmit power with respect to the elevation angles of legitimate users and eavesdroppers, and generate an evaluation result for the active RIS - assisted UAV secure communication.

[0012] On the other hand, the present invention also provides an active RIS - assisted jitter UAV air - ground secure communication system, and the system includes: A coordinate determination module, configured to obtain the coordinates of each communication node in the communication system by using a three-dimensional coordinate system based on the communication nodes in a preset active RIS-assisted UAV communication system, where the communication nodes include a UAV airborne base station, an active RIS, a legitimate user, and an eavesdropper; A channel construction module, configured to construct a UAV airborne base station channel and an active RIS channel based on the coordinates of the communication nodes in the communication system by using a preset free space path loss model. The UAV airborne base station channel includes the channel between the UAV airborne base station and the active RIS, the channel between the UAV airborne base station and the legitimate user, and the channel between the UAV airborne base station and the eavesdropper. The active RIS channel includes the channel between the active RIS and the legitimate user and the channel between the active RIS and the eavesdropper; An error confirmation module, configured to determine the UAV airborne base station channel error and the active RIS channel error based on the vibration characteristics of the UAV airborne base station by using a pre-constructed uncertainty set of azimuth and elevation angles; A signal confirmation module, configured to confirm the received signal of the legitimate user and the received signal of the eavesdropper based on the UAV airborne base station channel and the active RIS channel; A decision generation module, configured to comprehensively consider the reflection coefficient matrix of the active RIS, the UAV airborne base station channel, the active RIS channel, the UAV airborne base station channel error, the active RIS channel error, the received signal of the legitimate user, and the received signal of the eavesdropper. Taking the minimum transmit power of the active RIS-assisted UAV communication system as the optimization goal, using an iterative algorithm to solve the transmit beamforming matrix and the reflection coefficient matrix, obtain the optimization result, and generate the communication decision of the active RIS-assisted UAV communication system.

[0013] On the other hand, the present invention also provides an electronic device, including: at least one processor and a memory; the memory and the processor are connected by a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, an active RIS-assisted jitter UAV air-ground secure communication method as described in the above technical solution is implemented.

[0014] On the other hand, the present invention also provides a readable storage medium, on which an execution program is stored. When the execution program is executed, an active RIS-assisted jitter UAV air-ground secure communication method as described in the above technical solution is implemented.

[0015] Compared with the prior art, the beneficial effects of the present invention are: In an active RIS-assisted jitter UAV air-ground secure communication method provided by the present invention, by constructing the coordinates of each communication node in the communication system and using a preset free space path loss model, the UAV airborne base station channel and the active RIS channel are constructed. At the same time, based on the vibration characteristics of the UAV airborne base station, by using the pre-constructed uncertainty sets of azimuth and elevation angles, considering the jitter characteristics under the influence of random airflow and airframe vibration on secure communication, the UAV airborne base station channel error and the active RIS channel error are determined, and the constructed optimization problem is iteratively solved, so as to obtain the communication decision of the active RIS-assisted UAV communication system, thereby achieving the purpose of weakening the influence of the jitter characteristics under the influence of random airflow and airframe vibration on the secure communication of the UAV. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flowchart of an active RIS-assisted jitter UAV air-ground secure communication method of the present invention; Figure 2 It is a schematic diagram of an active RIS-assisted UAV communication system constructed by the present invention; Figure 3 It is the number of RIS units of an active RIS-assisted jitter UAV air-ground secure communication method of the present invention M And the maximum change in transmission power Relative to the AOD of the legitimate user Alice Schematic diagram of the relationship between ratios; Figure 4 It is the number of RIS units of an active RIS-assisted jitter UAV air-ground secure communication method of the present invention M And the maximum change in transmission power Relative to the AOD of the eavesdropper Eve Schematic diagram of the relationship between ratios; Figure 5 It is a schematic diagram of the relationship between the transmission power and the maximum amplification factor of RIS of an active RIS-assisted jitter UAV air-ground secure communication method of the present invention Between; Figure 6 It is a schematic diagram of the structure of an electronic device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Example 1: Referring to Figure 1 , the present invention provides an active RIS-assisted jitter UAV air-ground secure communication method, including: S1. Based on the communication nodes in the preset active RIS-assisted UAV communication system, using a three-dimensional coordinate system, obtain the coordinates of each communication node in the communication system. The communication nodes include an airborne UAV base station, an active RIS, a legitimate user, and an eavesdropper. S2. Based on the coordinates of the communication nodes in the communication system, use a preset free-space path loss model to construct the airborne UAV base station channels and the active RIS channels. The airborne UAV base station channels include the channel between the airborne UAV base station and the active RIS, the channel between the airborne UAV base station and the legitimate user, and the channel between the airborne UAV base station and the eavesdropper. The active RIS channels include the channel between the active RIS and the legitimate user and the channel between the active RIS and the eavesdropper. S3. Based on the vibration characteristics of the airborne UAV base station, use the pre-constructed uncertainty sets of azimuth and elevation angles to determine the airborne UAV base station channel error and the active RIS channel error. S4. Based on the airborne UAV base station channels and the active RIS channels, confirm the received signals of the legitimate user and the eavesdropper. S5. Considering comprehensively the reflection coefficient matrix of the active RIS, the airborne UAV base station channels, the active RIS channels, the airborne UAV base station channel error, the active RIS channel error, the received signal of the legitimate user, and the received signal of the eavesdropper, take the minimum transmit power of the active RIS-assisted UAV communication system as an optimization problem, and use an iterative algorithm to solve for the transmit beamforming matrix and the reflection coefficient matrix to obtain the optimization result, and generate the communication decision of the active RIS-assisted UAV communication system.

[0018] Referring to Figure 2 , for the convenience of studying the air-ground secure communication method, the air-ground secure communication scenario of the UAV generally includes an airborne UAV base station, an active RIS, a legitimate user, and an eavesdropper. To assist the secure communication of the UAV, the active RIS is usually fixedly deployed on the facade of a ground building or other ground devices. The UAV hovers in the air at a fixed height and realizes the air-to-ground communication service through the airborne base station carried by itself. In addition, since UAV communication may be interfered with or hacked, a physical layer secure transmission method needs to be adopted to ensure the security of the communication of legitimate users.

[0019] In S1, the present invention constructs an active RIS-assisted UAV communication system, which includes a single-antenna legitimate user Alice and a single-antenna eavesdropper Eve. The active RIS additionally integrates a reflective power amplifier on each RIS unit, which not only regulates the reflected signal but also amplifies the reflected signal with high gain, so as to be able to compensate for the path loss caused by multiplicative fading.

[0020] Exemplarily, in S2, the present invention provides an A2G wireless channel model, where the unmanned aerial vehicle (UAV)-borne base station (UBS) and the active reconfigurable intelligent surface (RIS) can be regarded as being respectively equipped with uniform rectangular arrays (URAs) of sizes and respectively.

[0021] denotes the number of antennas of the UAV-borne base station along the axis; denotes the number of antennas of the UAV-borne base station along the axis; denotes the number of reflecting elements (REs) of the RIS along the axis; denotes the number of reflecting elements (REs) of the RIS along the axis.

[0022] All communication nodes are placed in a three-dimensional Cartesian coordinate system. In this case, the coordinates of the UAV, Alice, and Eve are ([[]]END]] ), ([[]]END]] ), and ([[]]END]] ), respectively.

[0023] The reflection coefficient matrix of the active RIS is expressed as: , wherein, denotes the amplitude, which can be greater than 1 in an active load; denotes the phase; in contrast, a passive RIS cannot amplify the incident signal. Therefore, the amplitude of each RE is limited to ; denotes the identity matrix; denotes the imaginary unit; denotes the set of matrices with M rows and M columns.

[0024] In addition, the first element of the active RIS is regarded as the reference point, and its coordinates are represented by ([[]]END]] ), where respectively represent the x , y and z coordinates of the active RIS.

[0025] Exemplarily, in S2 provided by the present invention, it includes: Based on the coordinates of the communication nodes in the communication system, using the uniform rectangular arrays of the UAV-borne base station and the active RIS, obtaining the reflection system matrix of the active RIS; Based on the LOS component and NLOS component of the UAV airborne base station channel and the preset free space path loss model, the UAV airborne base station channel is obtained; Based on the LOS component and the NLOS component of the active RIS channel and a preset free space path loss model, the active RIS channel is obtained.

[0026] Therefore, the distance between RIS and a certain communication node can be approximated as the distance between the reference point and the corresponding node. It is assumed that both the UBS-Alice / Eve link and the UBS-RIS link contain line-of-sight (LOS) and non-line-of-sight (NLOS) wireless transmission components, which follow the free-space path loss model. It is assumed that all channels are defined by large-scale fading and small-scale fading, and the small-scale fading in the A2G link can be assumed to be Ricean fading. In particular, , and Can be modeled as: , , , (1) In the formula, represents the UBS-Alice channel; Indicates UBS-Eve channel; Indicates UBS-RIS channel; , and The Rice channels of UBS-Alice, UBS-Eve and UBS-RIS are represented respectively. factor; and are the path loss factors of LOS and NLOS respectively; and are the path loss coefficients of LOS and NLOS, respectively; and They are represented as the distances between UBS-Alice, UBS-Eve and UBS-RIS respectively.

[0027] The distances between UBS-Alice, UBS-Eve and UBS-RIS satisfy the following expressions: , , , (2) In addition, the channel fading between RIS-Alice and RIS-Eve also follows the Rice distribution, which can be generated by a similar process and is denoted as and .

[0028] In equation (1), the LOS and NLOS components of the UBS-Alice channel are respectively denoted as and , and the UBS-Eve and UBS-RIS channels can be expressed similarly.

[0029] In addition, the NLOS component both follow the circularly symmetric complex Gaussian distribution with zero mean and unit variance, that is .

[0030] The LOS components and can be expressed as: , , (3) where represents the azimuth angle of the path between the URA at the UBS and Alice; represents the elevation angle AOD of the path between the URA at the UBS and Alice; represents the azimuth angle of the path between the URA at the UBS and Eve; represents the elevation angle AOD of the path between the URA at the UBS and Eve; is the distance between two adjacent UBS antennas; λ represents the wavelength of the carrier center frequency; represents the identity matrix; represents the imaginary unit; represents the transpose matrix.

[0031] can be expressed as: , where, represents the array response at the RIS; represents the array response at the UBS.

[0032] Among them, and both satisfy the following expressions: , (4) , (5) where, represents the array response at the RIS; represents the array response at UBS; represents the azimuth of the path between RIS and Alice; represents the elevation angle AOD of the path between RIS and Alice; It represents the azimuth between URA and RIS at UBS; represents the arrival angle between URA and RIS at UBS; is the antenna spacing of URA during RIS; represents the azimuth between URA and RIS at UBS; It represents the elevation angle AOD between URA and RIS at UBS.

[0033] Exemplarily, in S3 provided by the present invention, the present invention also provides a CSI error model taking into account UAV jitter. Since the vibration characteristics of the UAV are caused by multiple factors, these random vibration characteristics will lead to imperfect CSI estimation and unstable wireless transmission, especially when equipped with a large antenna array.

[0034] For URA, the varying elevation angle captures the jitter of the UAV in pitch and roll, while the varying azimuth angle captures the jitter in yaw. , and and azimuth , and They satisfy the following expressions respectively: , , , , , , , , , (6) In the formula, represents the uncertainty of the estimated azimuth angle AOD of the path between UBS and Alice; represents the uncertainty of the estimated azimuth angle AOD of the path between UBS and Eve; represents the uncertainty of the estimated azimuth angle AOD of the path between UBS and RIS; represents the uncertainty of the azimuth angle AOD of the path between UBS and Alice; Denote the uncertainty of the azimuth angle AOD of the path between UBS and Eve; Denote the uncertainty of the azimuth angle AOD of the path between UBS and RIS; Denote the uncertainty of the estimated elevation angle of the path between UBS and Alice; Denote the uncertainty of the estimated elevation angle of the path between UBS and Eve; Denote the uncertainty of the estimated elevation angle of the path between UBS and RIS; Denote the uncertainty of the elevation angle of the path between UBS and Alice; Denote the uncertainty of the elevation angle of the path between UBS and Eve; Denote the uncertainty of the elevation angle of the path between UBS and RIS; 、 and All represent the set of all possible AOD uncertainties including Alice, Eve, and RIS; Denote the set of real numbers; The uncertainties of the azimuth angle AOD and elevation angle AOD of Alice are bounded by the maximum variations and respectively. The uncertainties of the azimuth angle AOD and elevation angle AOD of Eve are bounded by the maximum variations and respectively. The uncertainties of the azimuth angle AOD and elevation angle AOD of RIS are bounded by the maximum variations and respectively.

[0035] Since is a non - linear function of and ; To solve this problem, this paper approximates by applying Taylor expansion, that is, satisfying the following expression: , (7) where x 、 y represent the estimated values of two independent variables in the function, . Therefore, each exponential term in Equation (3) and Equation (5) can be approximated as the following expression: , (8) Denote the x -th element of the UAV - mounted base station antenna along the n axis, Denote the y -th element of the UAV - mounted base station antenna along the n axis; and respectively represent the estimated value and the error value of the azimuth angle AOD, + and respectively represent the estimated value and the error value of the elevation angle AOD. For the convenience of analysis and calculation, the following auxiliary variables are defined : , (9) , (10) Then, in the formula (1) , and . Among them, the formula (3) and the formula (5) can be expressed as: , , , (11) In the formula, , , are respectively substituted into the formula (9) and the formula (10), and we can get , , , (12) Among them, , and are respectively used to represent the channel components in the corresponding channel state information that are not affected by the UAV jitter, and satisfy the following expressions: , , , (13) In the formula, , , , , , , , , (14) In addition, the channel change caused by the UAV jitter will lead to channel estimation error, but this channel error cannot be modeled by the bounded channel error model or the statistical channel error model. Here, , and satisfy the following expressions: , , , (15) where Therefore, in equations (1) and (2), , and can be rewritten as the following expressions: , , , (16) To evaluate the bounded uncertainty of the channel caused by UAV jitter, the CSI error models of and are further derived to satisfy the following expressions: , , (17) To further simplify the expressions, by introducing auxiliary variables and making variable substitutions, , , , and (6), (17) can be rewritten as the following expressions: , , (18) wherein, both represent correction coefficients; represents an auxiliary variable; and both represent correction coefficients; represents an auxiliary variable.

[0036] Similarly, the CSI error model of , (19) wherein, and both represent correction coefficients.

[0037] For the convenience of analysis, the channels UBS-RIS-Alice and UBS-RIS-Eve are respectively represented by the cascaded channels and .

[0038] Let and respectively represent the cascaded channels through the RIS at the user Alice and the eavesdropper Eve, and be the conjugate transposes of the channels between RIS - Alice and RIS - Eve, where H represents the conjugate transpose. The cascaded channels and 's CSI error model is expressed as: , wherein, and are both correction factors, is an auxiliary variable.

[0039] , (20) is an auxiliary variable. Wherein, , , , , (21) In S4 provided by the present invention, the present invention can, through a pre - constructed signal model, represent the signals received at Alice from both the UBS - Alice and UBS - RIS - Alice channels as: , (22) The signal received at Eve can be represented as: , (23) wherein, represents Gaussian white noise with variance at the RIS, where ; represents Gaussian white noise with variance at Alice; represents Gaussian white noise with variance at Eve; represents a data symbol vector with unit power; represents a transmit beamforming matrix; represents the multiplication of two matrices; also represents the multiplication of two matrices.

[0040] is represented as a vector containing the diagonal elements of the matrix , wherein, anym An element is represented as .

[0041] Therefore, the achievable rates of Alice and Eve satisfy the following expressions: , , (24) where , , (25) where denotes the conjugate transpose of; and respectively denote the estimated value and the error value of; and respectively denote the estimated value and the error value of; and respectively denote the estimated value and the error value of; and respectively denote the estimated value and the error value of; and respectively denote the estimated value and the error value of.

[0042] In practical applications, the transmission power of the UAV is strictly limited. On the premise of ensuring the requirements of secure communication, it is necessary to reduce the transmission power as much as possible. Therefore, to reduce the transmission power of the active RIS-assisted UAV system under a given ASR constraint, that is, the worst case is that Alice reaches its required minimum data rate and Eve reaches its maximum data rate. To ensure secure transmission between the UBS and Alice, the secrecy rate in the worst case should be greater than 0, which is given by and satisfies the following expression: , (26) where denotes the minimum data rate accepted by the legitimate user; denotes the maximum data rate accepted by the eavesdropper.

[0043] Since the active RIS will amplify the received signal and noise at each RE, in addition, due to the total power budget and amplification power of the RIS being limited, assuming PF represents the maximum amplification power of the active RIS, which is actually much smaller than that of the traditional RF amplifier, the following expression is satisfied: , (27) In S5 provided by the present invention, it includes: S501. Based on the reflection coefficient matrix of the active RIS, the channel of the UAV airborne base station, the channel of the active RIS, the channel error of the UAV airborne base station, the channel error of the active RIS, the received signal of the legitimate user, and the received signal of the eavesdropper, taking the minimum transmit power of the active RIS-assisted UAV communication system as an optimization problem, and constructing the constraints of the optimization problem; S502. Based on the constructed optimization problem and its constraints, using an iterative algorithm to solve the transmit beamforming matrix and the reflection coefficient matrix to obtain the optimization result; S503. Based on the optimization result, using an equivalent transformation algorithm to generate the communication decision of the active RIS-assisted UAV communication system.

[0044] Exemplarily, the constructed optimization problem is as follows: (P1):

[0045] Optionally, the constraints of the constructed optimization problem satisfy the following expressions: , (28a) , (28b) , (28c) , (28d) , (28e) In the formula, represents the power of the transmit beamforming matrix; represents the limit constraint of the transmit beamforming matrix; represents the minimum data rate received by the legitimate user; represents the preset data rate threshold received by the legitimate user; represents the maximum data rate received by the eavesdropper; represents the preset data rate threshold received by the eavesdropper; represents the reflection coefficient matrix; represents the channel fading between the UAV airborne base station and the active RIS; is the m maximum amplification factor at the

[0046] According to formula (28a), it can be known that is limited by the peak power constraint; at the same time, according to formula (28d), it can be observed that , It is highly coupled with the change of AOD. Therefore, the optimization problems in Eqs. (28a)-(28e) are non-convex and difficult to solve.

[0047] To solve the defect that the optimization problem is non-convex, the present invention proposes an AO method to sequentially optimize in an iterative manner and . Specifically, the optimization problem P1 is divided into the following two sub-problems: 1), the optimization of the transmit beamforming matrix under the given reflection coefficient matrix ; 2), the optimization of the reflection coefficient matrix under the given transmit beamforming matrix .

[0048] Exemplarily, S502 is specifically implemented as: Based on the constructed optimization problem, decompose the optimization problem to generate optimization sub-problems regarding the transmit beamforming matrix and the reflection coefficient matrix; Based on the constraints of the optimization sub-problems, use the S-lemma algorithm to transform the non-convex constraints into linear matrix inequalities, and use the iterative algorithm to iteratively solve the transmit beamforming matrix and the reflection coefficient matrix to determine the interference and noise power of the legitimate users and the interference and noise power of the eavesdropper; Based on the linear matrix inequalities, by introducing slack variables and using the Schur complement lemma algorithm (Schur complement theorem), perform equivalent transformation on the linear matrix inequalities to obtain the transformed optimization problem; Based on the transformed optimization problem, solve it through the CVX tool to obtain the optimization result.

[0049] Optionally, the decomposing the optimization problem based on the constructed optimization problem to generate optimization sub-problems includes: Based on the constructed optimization problem, obtain the optimization sub-problem of the transmit beamforming matrix by giving the reflection coefficient matrix; Based on the constructed optimization problem, generate the optimization sub-problem of each reflection coefficient matrix by the transmit beamforming matrix.

[0050] To achieve the purpose of alternately solving the two sub-problems to minimize the transmission power of the UBS. For non-convex constraints, use the S-lemma to transform the worst-case secrecy rate constraint into a linear matrix inequality. Since the logarithmic function is a monotonically increasing function, consider the channel uncertainty in Eqs. (18) and (20) and define the following expressions: , , Equations (28b) and (28c) can be rewritten as the following expressions: , (29) , (30) where represents the interference plus noise power of Alice; represents the interference plus noise power of Eve.

[0051] Furthermore, a linear approximation of the useful signal power in Equation (29) is given in the following lemma.

[0052] Assume and are the optimal solutions obtained at iteration , then the left side of Equation (29) has the following linear lower bound at ( ): , (31) where represents the independent variable.

[0053] , , , , (32) where, in the equation , ,

[0054] , , , , , , , (33) where represents the conjugate operation in a certain vector form.

[0055] Therefore, Equation (29) is equivalently rewritten as: , (34) Similarly, Equation (30) can be equivalently rewritten as: , (35) where ; , , ,(36)

[0056] wherein, , , , , ,(37) Lemma 2 (S - lemma): Let the functions , , then it is defined as: ,(38) wherein , the condition holds if and only if there exists such that: ,(39) is On the contrary, the condition holds if and only if there exists such that: ,(40) Rewrite as the following quadratic expression: ,(41)

[0057] Then, after introducing and as slack variables, Equation (34) can be transformed into the following equivalent LMI by Lemma 1: ,(42) ,(43) After introducing and as slack variables, Equation (35) can be converted into the following equivalent LMI: ≥0,(44) , (45) Then, the Schur complement theorem is used to equivalently transform Equation (45) into a matrix inequality, satisfying the following expression: , (46) . In summary, for the given and sub - problem, it satisfies the following expression:

[0058] s.t . (28a), (42), (44) and (46)(47) The problem corresponding to Equation (47) is a convex problem and can be directly solved by the CVX tool.

[0059] Since solving the sub - problem for the given and is a feasibility - checking problem. To improve the convergence solution in the optimization, by introducing a slack variable to rewrite the useful signal power inequality in Equation (29), it satisfies the following expression: , (48) Subsequently, the LMI Equation (42) is rewritten as: , (49) By introducing a slack variable to modify the Eve signal power inequality in Equation (30) and rewrite it as: (50) And the LMI Equation (44) is rewritten as: ≥0, (51) Let , where , respectively represent M elements; then Equation (27) can be expressed as .

[0060] Therefore, the sub - problem can be expressed as:

[0061] s.t . (47), (49) , , (52) where, representation Problem (52) is a convex optimization problem, which can also be solved efficiently and optimally by the tool CVX.

[0062] In the active RIS-assisted jitter UAV air-ground secure communication method provided by the present invention, by constructing the coordinates of each communication node in the communication system and using the preset free space path loss model, the UAV airborne base station channel and the active RIS channel are constructed. At the same time, based on the vibration characteristics of the UAV airborne base station, using the pre-constructed uncertainty sets of azimuth and elevation angles, by considering the jitter characteristics under the influence of random airflow and airframe vibration on secure communication, the UAV airborne base station channel error and the active RIS channel error are determined, and the constructed optimization problem is iteratively solved, so as to obtain the communication decision of the active RIS-assisted UAV communication system, thereby achieving the purpose of weakening the influence of the jitter characteristics under the influence of random airflow and airframe vibration on the secure communication of the UAV.

[0063] Optionally, after generating the communication decision of the active RIS-assisted UAV communication system by using the equivalent transformation algorithm based on the optimization result, it further includes: Based on the communication decision of the active RIS-assisted UAV communication system, combined with the channel uncertainty caused by the jitter of the UAV airborne base station, calculate the changes of the transmission power with respect to the elevation angles of the legitimate user and the eavesdropper, and generate an evaluation result for the active RIS-assisted UAV secure communication.

[0064] Exemplarily, assume that the UAV coordinates are (10, 20, 10), the RIS coordinates are (10, 0, 10), the Alice coordinates are (20, 20, 0), and the Eve coordinates are (10, 40, 0). Assume that the UBS is equipped with = 2 transmit antennas, = , = 30 dB, = 4.5, = 1, environmental parameter = 5, = . At the same time, in the simulation, assume that the maximum transmission power = , path loss factor = -2.14 , = -3.14 , path loss exponent = 2.09, = 3.75. The noise power is -10 . The CSI error bound caused by UAV jitter can be defined as and In addition, the setting error tolerance .

[0065] To demonstrate the superiority of the proposed scheme (denoted as "active RIS"), the results are compared with a benchmark scheme, i.e., a similar scheme assisted by passive RIS.

[0066] To evaluate the impact of channel uncertainty caused by UAV jitter on active RIS-assisted UAV secure communication, Figure 3 shows the maximum change in transmit power with respect to the AOD of Alice ratio of Figure 4 shows the maximum change in transmit power with respect to the AOD of Eve ratio of

[0067] Due to the elevation angle analysis is similar to that of the azimuth angle Here, the elevation angle is taken as an example. Figure 3 in , similarly Figure 4 in . It can be seen that the transmit power at the UBS increases with the increase of AOD uncertainty, which means that the more severe the UAV jitter is, the more transmit power is required to meet the requirements of the effectiveness of the legitimate link and the security of the confidential signal. In addition, the active RIS scheme can achieve an improvement in secrecy performance with only a small number of REs, that is, reducing the UAV transmit power under the same ASR. As the number of REs of the active RIS increases, the required transmit power also increases because the amplification effect of the active RIS on noise and channel error also increases.

[0068] Assume and , Figure 5 compares the relationship between the transmit power of the RIS-assisted system and the number of REs. In this setting, the passive RIS can use up to 90 REs to reflect the incident signal. However, even with 90 REs, the transmit power of the passive RIS is greater than that equipped with pieces (optimal The transmit power of the active RIS of the antenna, as the active RIS can directly amplify the incident signal. On the contrary, the active RIS only requires a small number of REs (about 15 - 20) at different amplitude gains to achieve its optimal secrecy performance. Different from the passive RIS where the thermal noise can be ignored when reflecting signals passively, the active RIS will additionally introduce and amplify non-negligible thermal noise while amplifying the reflected signal. Therefore, when the number of REs of the active RIS increases, the resulting performance gain does not continue to rise. In practice, the active RIS is usually designed with a small number of REs. Due to the small number of REs, the active RIS also has a small surface size, which is more suitable for UAV secrecy communication with limited payloads.

[0069] Embodiment 2: Based on the same inventive concept, the present invention also provides an active RIS-assisted jitter UAV air-ground secure communication system, which includes: A coordinate determination module, configured to obtain the coordinates of each communication node in the communication system by using a three-dimensional coordinate system based on the communication nodes in the preset active RIS-assisted UAV communication system, where the communication nodes include an airborne UAV base station, an active RIS, a legitimate user, and an eavesdropper; A channel construction module, configured to construct an airborne UAV base station channel and an active RIS channel based on the coordinates of the communication nodes in the communication system by using a preset free space path loss model. The airborne UAV base station channel includes the channel between the airborne UAV base station and the active RIS, the channel between the airborne UAV base station and the legitimate user, and the channel between the airborne UAV base station and the eavesdropper. The active RIS channel includes the channel between the active RIS and the legitimate user and the channel between the active RIS and the eavesdropper; An error confirmation module, configured to determine the airborne UAV base station channel error and the active RIS channel error based on the vibration characteristics of the airborne UAV base station by using a pre-constructed uncertainty set of azimuth and elevation angles; A signal confirmation module, configured to confirm the received signal of the legitimate user and the received signal of the eavesdropper based on the airborne UAV base station channel and the active RIS channel; A decision generation module, configured to comprehensively consider the reflection coefficient matrix of the active RIS, the airborne UAV base station channel, the active RIS channel, the airborne UAV base station channel error, the active RIS channel error, the received signal of the legitimate user, and the received signal of the eavesdropper, take the minimum transmit power of the active RIS-assisted UAV communication system as the optimization objective, use an iterative algorithm to solve for the transmit beamforming matrix and the reflection coefficient matrix, obtain the optimization result, and generate the communication decision of the active RIS-assisted UAV communication system.

[0070] Embodiment 3: AsFigure 6 As shown in Figure 6 , the present invention further provides an electronic device, which may be a computer device, a single-chip microcomputer device, a smart mobile device, etc. The electronic device in this embodiment may include a processor, a memory, a transceiver component, etc. The memory, the processor, and the transceiver component are connected through a bus; the memory can be used to store an execution program, and an exemplary execution program may include instructions; the processor is used to execute the instructions stored in the memory. The memory can also be used to store data, and this data can be called and / or modified when the instructions are executed.

[0071] The processor may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of an active RIS-assisted jitter UAV air-ground secure communication method in the above embodiment.

[0072] Embodiment 4: Based on the same inventive concept, the present invention further provides a readable storage medium, specifically an electronic device-readable storage medium (Memory). The electronic device-readable storage medium is a memory device in the electronic device, and is used to store programs and data. It can be understood that the storage medium here can include both the built-in storage medium in the electronic device, and of course can also include the extended storage medium supported by the electronic device. The storage medium provides a storage space, and the operating system of the terminal is stored in this storage space. And, one or more instructions suitable for being loaded and executed by the processor are also stored in this storage space. These instructions can be one or more execution programs (including program codes). It should be noted that the storage medium here can be a high-speed RAM memory, or a non-volatile memory, such as at least one disk memory. By loading and executing one or more instructions stored in the storage medium by the processor, the steps of an active RIS-assisted jitter UAV air-ground secure communication method in the above embodiment can be implemented.

[0073] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0074] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, as well as the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for realizing the functions specified in Figure 1 one or more of the flows Figure 1 or a plurality of flows and / or blocks

[0075] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means realizes the functions specified in Figure 1 one or more of the flows Figure 1 or a plurality of flows and / or blocks

[0076] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for realizing the functions specified in Figure 1 one or more of the flows Figure 1 or a plurality of flows and / or blocks

[0077] The above are only embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention pending approval.

Claims

1. An active RIS-assisted jitter UAV air-to-ground safe communication method, characterized in that: include: Based on the communication nodes in the preset active RIS-assisted UAV communication system, the coordinates of each communication node in the communication system are obtained using a three-dimensional coordinate system, wherein the communication nodes include the UAV airborne base station, the active RIS, the legitimate user and the eavesdropper; Based on the coordinates of the communication nodes in the communication system, a preset free space path loss model is used to construct a UAV airborne base station channel and an active RIS channel, wherein the UAV airborne base station channel includes a channel between the UAV airborne base station and the active RIS, a channel between the UAV airborne base station and a legitimate user, and a channel between the UAV airborne base station and an eavesdropper, and the active RIS channel includes a channel between the active RIS and the legitimate user and a channel between the active RIS and the eavesdropper; Based on the vibration characteristics of the UAV airborne base station, the UAV airborne base station channel error and active RIS channel error are determined using the pre-constructed uncertainty set of azimuth and elevation angles. Based on the drone airborne base station channel and the active RIS channel, confirm that the legitimate user receives the signal and the eavesdropper receives the signal; The reflection coefficient matrix of the active RIS, the UAV airborne base station channel, the active RIS channel, the UAV airborne base station channel error, the active RIS channel error, the legitimate user received signal and the eavesdropper received signal are comprehensively considered, and the minimum transmission power of the UAV communication system assisted by the active RIS is taken as an optimization problem. The transmit beamforming matrix and the reflection coefficient matrix are solved by an iterative algorithm to obtain the optimization result, and the communication decision of the UAV communication system assisted by the active RIS is generated.

2. The active RIS-assisted jitter UAV air-to-ground safe communication method as claimed in claim 1, characterized in that: The reflection coefficient matrix of the active RIS, the UAV airborne base station channel, the active RIS channel, the UAV airborne base station channel error, the active RIS channel error, the legitimate user received signal and the eavesdropper received signal are integrated, and the minimum transmission power of the UAV communication system assisted by the active RIS is taken as an optimization problem. The transmission beamforming matrix and the reflection coefficient matrix are solved by an iterative algorithm to obtain the optimization result, and the communication decision of the UAV communication system assisted by the active RIS is generated, including: Taking into account the reflection coefficient matrix of the active RIS, the UAV airborne base station channel, the active RIS channel, the UAV airborne base station channel error, the active RIS channel error, the legitimate user receiving signal and the eavesdropper receiving signal, the minimum transmission power of the active RIS-assisted UAV communication system is taken as an optimization problem, and the constraints of the optimization problem are constructed; Based on the constructed optimization problem and its constraints, the transmit beamforming matrix and the reflection coefficient matrix are solved by using an iterative algorithm to obtain the optimization result. Based on the optimization result, an equivalent conversion algorithm is used to generate a communication decision of the active RIS-assisted UAV communication system.

3. The active RIS-assisted jitter UAV air-to-ground safe communication method as claimed in claim 2, characterized in that: The constraints of the optimization problem constructed above satisfy the following expression: ， ， ， ， ， In the formula, represents the power of the transmit beamforming matrix; represents the restriction constraints of the transmit beamforming matrix; Indicates the minimum data rate accepted by legitimate users; Indicates the data rate threshold accepted by the preset legal users; Indicates the maximum data rate accepted by the eavesdropper; Indicates the data rate threshold accepted by the preset eavesdropper; represents the reflection coefficient matrix; represents the channel fading between the UAV airborne base station and the active RIS; It is m The maximum amplification factor at each RE.

4. The active RIS-assisted jitter UAV air-to-ground safe communication method as claimed in claim 2, characterized in that: Based on the constructed optimization problem and constraints, the transmit beamforming matrix and the reflection coefficient matrix are solved by an iterative algorithm to obtain the optimization results, including: Based on the constructed optimization problem, the optimization problem is decomposed to generate optimization sub-problems about the transmit beamforming matrix and the reflection coefficient matrix; Based on the constraints of the optimization subproblem, the non-convex constraints are converted into linear matrix inequalities using the S-lemma algorithm, and the transmit beamforming matrix and the reflection coefficient matrix are iteratively solved using an iterative algorithm to determine the interference and noise power of the legitimate user and the interference and noise power of the eavesdropper; Based on the linear matrix inequality, by introducing slack variables and using the Schur complement lemma algorithm, the linear matrix inequality is equivalently transformed to obtain a transformed optimization problem; Based on the transformed optimization problem, the CVX tool is used to solve it and obtain the optimization result.

5. The active RIS-assisted jitter UAV air-to-ground safe communication method as claimed in claim 4, characterized in that: The optimization problem based on the construction, decomposing the optimization problem to generate optimization sub-problems includes: Based on the constructed optimization problem, the optimization sub-problem of the transmit beamforming matrix is ​​obtained by giving the reflection coefficient matrix; Based on the constructed optimization problem, the optimization sub-problems of the respective reflection coefficient matrices are generated by transmitting the beamforming matrix.

6. The active RIS-assisted jitter UAV air-to-ground safe communication method as claimed in claim 1, characterized in that: The method of constructing a UAV airborne base station channel and an active RIS channel based on the coordinates of the communication nodes in the communication system and using a preset free space path loss model includes: Based on the coordinates of the communication nodes in the communication system, the reflection system matrix of the active RIS is obtained by using the uniform rectangular array of the UAV airborne base station and the active RIS; Based on the LOS component and NLOS component of the UAV airborne base station channel and the preset free space path loss model, the UAV airborne base station channel is obtained; Based on the LOS component and the NLOS component of the active RIS channel and a preset free space path loss model, the active RIS channel is obtained.

7. The active RIS-assisted jitter UAV air-to-ground safe communication method as claimed in claim 2, characterized in that: After generating the communication decision of the active RIS-assisted UAV communication system based on the optimization result by using an equivalent conversion algorithm, the method further includes: Based on the communication decision of the active RIS-assisted UAV communication system and the channel uncertainty caused by the jitter of the UAV airborne base station, the change of the transmission power relative to the elevation angle of the legitimate user and the elevation angle of the eavesdropper is calculated to generate an evaluation result of the active RIS-assisted UAV secure communication.

8. An active RIS-assisted jitter UAV air-to-ground safety communication system, characterized in that: The system comprises: A coordinate determination module, for obtaining the coordinates of each communication node in a preset active RIS-assisted UAV communication system using a three-dimensional coordinate system, wherein the communication nodes include a UAV airborne base station, an active RIS, a legitimate user, and an eavesdropper; A channel construction module, used to construct a UAV airborne base station channel and an active RIS channel based on the coordinates of the communication nodes in the communication system and using a preset free space path loss model, wherein the UAV airborne base station channel includes a channel between the UAV airborne base station and the active RIS, a channel between the UAV airborne base station and a legitimate user, and a channel between the UAV airborne base station and an eavesdropper, and the active RIS channel includes a channel between the active RIS and a legitimate user and a channel between the active RIS and an eavesdropper; An error confirmation module is used to determine the UAV airborne base station channel error and the active RIS channel error based on the vibration characteristics of the UAV airborne base station and using a pre-built uncertainty set of azimuth and elevation angles; The signal confirmation module is used to confirm the legitimate user receiving the signal and the eavesdropper receiving the signal based on the UAV airborne base station channel and the active RIS channel; The decision generation module is used to comprehensively consider the reflection coefficient matrix of the active RIS, the UAV airborne base station channel, the active RIS channel, the UAV airborne base station channel error, the active RIS channel error, the legitimate user received signal and the eavesdropper received signal, and take the minimum transmission power of the UAV communication system assisted by the active RIS as the optimization goal, use the iterative algorithm to solve the transmission beamforming matrix and the reflection coefficient matrix, obtain the optimization result, and generate the communication decision of the UAV communication system assisted by the active RIS.

9. An electronic device, characterized in that: include: at least one processor and memory; The memory and the processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, an active RIS-assisted jitter UAV air-to-ground safety communication method as described in any one of claims 1 to 7 is implemented.

10. A readable storage medium, characterized in that: An execution program is stored thereon, and when the execution program is executed, an active RIS-assisted jitter UAV air-to-ground safety communication method as described in any one of claims 1 to 7 is implemented.

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