An enhanced detection method based on reconfigurable intelligent surface assisted radar

Abstract

The application relates to an enhanced detection method based on a reconfigurable intelligent surface assisted radar, which comprises the following steps: an electromagnetic scattering characteristic model of an enhanced detection system comprising a radar, a target and an RIS array is established; a power ratio of a radar direct link and an RIS link is obtained based on the electromagnetic scattering characteristic model, and the power ratio of the radar direct link and the RIS link is used as an optimized objective function; the reflection coefficient matrix of the RIS array is optimized and solved to maximize the objective function, so that an optimal coding matrix is obtained; the reflection coefficient of each RIS unit is obtained according to the optimal coding matrix, and then the state of each unit of the RIS array is obtained, and an enhanced detection system integrating the RIS array and the radar is constructed. According to the application, a new autonomous controllable transmission link is constructed between the target and the radar receiver, and the radar system only needs to perform coherent processing on the double-link received echo signals in the back-end signal processing, so that the radar receiving echo power can be enhanced.

Description

Technical Field

[0001] This invention relates to the field of radar detection technology, and more specifically to an enhanced detection method based on reconfigurable smart surface-assisted radar. Background Technology

[0002] Radar detection technology plays a vital role in military, aerospace, and other fields. Its working principle involves detecting targets by receiving electromagnetic waves scattered by the target. In recent years, with continuous technological advancements, the performance of radar systems has significantly improved, particularly demonstrating strong advantages in high-precision target identification, complex environment monitoring, and long-range remote sensing. However, in scenarios involving the detection of small, long-range targets in complex electromagnetic environments, traditional radar systems still face limitations in detection range. This is mainly manifested in weak target echo signals, low signal-to-noise ratios, and difficulties in effective detection and stable tracking.

[0003] To overcome this bottleneck, Reconfigurable Intelligent Surfaces (RIS), as a novel electromagnetic control device with low profile, low cost, and easy deployment, show broad application prospects. By independently controlling the aperture units (e.g., the on / off state of the PIN diode or the voltage of the varactor diode loaded by the control unit), RIS can flexibly and in real time change the reflection phase and amplitude of the incident electromagnetic wave at each aperture unit, thereby achieving precise control of the phase and amplitude of electromagnetic waves throughout space, and thus completing various functions such as spatial beamforming and time-domain signal modulation.

[0004] In recent years, although some studies have proposed the concept of using reconfigurable smart surfaces to assist radar detection, related work has remained at the stage of theoretical analysis and numerical simulation verification, lacking joint experimental verification with radar systems. To date, no case has been reported that has achieved a significant improvement in radar system detection performance without modifying the existing radar system, simply by embedding external modules. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides an enhanced detection method based on a reconfigurable smart surface-assisted radar. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides an enhanced detection method based on reconfigurable smart surface-assisted radar, comprising: An electromagnetic scattering characteristic model is established for an enhanced detection system comprising radar, a target, and a RIS array. This model characterizes at least the signal propagation processes via the radar direct link and the RIS link. The RIS array includes... M × N One RIS unit; The power ratio of the radar direct link to the RIS link is obtained based on the electromagnetic scattering characteristic model, and the power ratio of the radar direct link to the RIS link is used as the objective function for optimization. With the objective function as the goal, the reflection coefficient matrix of the RIS array is optimized to obtain the optimal encoding matrix; The state of each unit of the RIS array is obtained based on the optimal coding matrix, and an enhanced detection system integrating the RIS array and radar is constructed to perform detection using the enhanced detection system.

[0006] In one embodiment of the present invention, an electromagnetic scattering characteristic model of an enhanced detection system including radar, a target, and a RIS array is established, including: In the radar direct link, the received power of the radar direct link is obtained from the backscatter power of the target after being illuminated by the electromagnetic waves emitted by the radar. In the RIS link, the power of the target scattered to the RIS unit is obtained based on the backscattering power; The reflected electric field of the RIS unit is obtained based on the power scattered from the target to the RIS unit; The electric field reflected from the RIS unit to the radar receiver is obtained based on the reflected electric field of the RIS unit. The total power of the RIS link received by the radar receiver is obtained from the electric field reflected from the RIS unit to the radar receiver.

[0007] In one embodiment of the present invention, in a radar direct link, obtaining the received power of the radar direct link based on the backscattering power of the target after being illuminated by the electromagnetic waves emitted by the radar includes: In the radar direct link, the backscattered power of the target after being illuminated by the electromagnetic waves emitted by the radar is obtained, and the backscattered power is expressed as:

[0008] in, This is the backscattering power. For radar transmission power, For the transmit antenna gain, This is the normalized radiation pattern of the transmitting antenna. The target's elevation angle relative to the radar. The target's azimuth angle relative to the radar. For the target scattering cross-section, For the target equivalent gain, The target scattering pattern. To reach the target distance; In the radar direct link, the received power of the radar direct link is obtained based on the backscattering power, and the received power of the radar direct link is expressed as:

[0009] in, This refers to the received power of the radar direct link. This refers to the effective aperture of the radar receiving antenna relative to the target. In one embodiment of the present invention, the power scattered by the target to the RIS unit is expressed as:

[0010]

[0011] in, For the target to scatter to the first The received power of each RIS unit, 1≤ m ≤ M ,1≤ n ≤ N , The distance from the target to the center of the RIS array. For the efficiency of the RIS unit, The projection factor of the RIS unit. For the first The pitch angle of each RIS unit relative to the target. For the first The azimuth angle of each RIS unit relative to the target. The size of the RIS unit, For RIS units in x Width in the axial direction, The length of the RIS unit along the y-axis; The reflected electric field of the RIS unit is expressed as:

[0012] in, For the first The reflected electric field of each RIS unit For free space impedance, This represents the initial phase of the radar transmission. For the first The distance between each RIS unit and the target For wave number, It is a complex number. For the first The reflection coefficient of each RIS unit; The electric field reflected from the RIS unit to the radar receiver is represented as follows:

[0013] in, For the first The electric field reflected by each RIS element to the radar receiver For the radar receiver relative to the first The distance between RIS units, This is the reflection pattern of the unit cell. For the radar receiver relative to the first The pitch angle of each RIS unit. For the radar receiver relative to the first The azimuth angle of each RIS unit; The total power of the RIS link received by the radar receiver is expressed as:

[0014] in, This represents the total power of the RIS link received by the radar receiver. This is the effective aperture of the radar receiving antenna relative to the RIS array.

[0015] In one embodiment of the present invention, the power ratio of the radar direct link to the RIS link is obtained based on the electromagnetic scattering characteristic model, and the power ratio of the radar direct link to the RIS link is used as the objective function for optimization, including: The power ratio of the radar direct link to the RIS link is obtained based on the total power received by the radar receiver from the RIS link and the received power of the radar direct link. The power ratio of the radar direct link to the RIS link is expressed as follows:

[0016] in, The power ratio between the radar direct link and the RIS link. This represents the total power of the RIS link received by the radar receiver. This refers to the received power of the radar direct link; The power ratio of the radar direct link to the RIS link is used as the objective function for optimization. In one embodiment of the present invention, with the objective function as the goal, the reflection coefficient matrix of the RIS array is optimized to obtain the optimal encoding matrix, including: Step 3.1: Initialize scene parameters and initialize S A RIS array is initialized with parameters for an ant colony optimization algorithm, the parameters including... S Each ant corresponds to one of the following: M × NThe coding matrix of each coding unit, the pheromone of each coding unit, and the heuristic information; Step 3.2: With the goal of maximizing the objective function, perform iterations. Each ant selects an encoding value based on the probability calculated from the pheromone and heuristic information of each current encoding unit. Step 3.3: Evaluate each of the encoding matrices using the fitness function to obtain the fitness value for each ant, wherein the fitness function is consistent with the objective function; Step 3.4, according to the first k The maximum fitness value in the nth iteration and the 1st iteration k- The maximum fitness value in one iteration is the first... k The change in fitness value in the nth iteration, and the nth iteration k The change in fitness value in each iteration is compared with a preset threshold. If the change is continuous... E If the change in fitness value is less than the preset threshold, proceed to step 3.5; otherwise, perform evaporation and deposition on the pheromone to obtain the updated pheromone, and proceed to step 3.2. Step 3.2 is then performed based on the updated pheromone. Step 3.5, if continuous E If the maximum fitness change in each iteration is less than a preset threshold, a perturbation mechanism is triggered, randomly resetting a portion of the pheromones. Then, the process jumps to step 3.2, executing step 3.2 based on the reset pheromones. If the change continues... F If the maximum fitness change in each iteration is less than a preset threshold, then the iteration is considered to have converged sufficiently, the iteration stops, and the currently recorded globally optimal encoding matrix is ​​output as the final result. F > E . In one embodiment of the present invention, the maximization objective function is expressed as:

[0017] in, The power ratio between the radar direct link and the RIS link. This represents the total power of the RIS array. This refers to the received power of the radar direct link. To reach the target distance, The effective aperture of the radar receiving antenna relative to the RIS array. The effective aperture of the radar receiving antenna relative to the target. The size of the RIS unit, The wavelength of electromagnetic waves, For the efficiency of the RIS unit, For the target relative to the first The distance between RIS units, For the radar receiver relative to the first The distance between RIS units, The projection factor of the RIS unit. For the first The pitch angle of each RIS unit relative to the target. For the first The azimuth angle of each RIS unit relative to the target. This is the reflection pattern of the unit cell. For the radar receiver relative to the first The pitch angle of each RIS unit. For the radar receiver relative to the first The azimuth angle of each RIS unit. The symbol for the Hadamarda complex. For the first The reflection coefficient of each RIS unit. For wave number, For the radar receiver relative to the first The distance between RIS units, for M × N The reflection coefficient matrix, For the first The reflection coefficient of each RIS unit. In one embodiment of the present invention, each ant selects the encoding value of each encoding unit based on the probability calculated from the pheromone and heuristic information of each current encoding unit, including: Each ant obtains the probability of each coding state being selected based on the pheromone and heuristic information of each current coding unit; The encoding value is selected for each encoding unit based on the probability distribution.

[0018] In one embodiment of the present invention, the probability of the encoded state being selected is expressed as:

[0019] in, For the first s The first in each population The coding unit is the first q The probability of each encoded state. For the first s The first in each population The coding unit is the first q A pheromone encoding a state, For the first s The first in each population Heuristic information for each coding unit, For all populations, To control the weight of pheromones, To control the weights of heuristic information, 1 ≤ s ≤ S , 0≤ q ≤3. In one embodiment of the present invention, pheromones are subjected to evaporation and deposition processes to obtain updated pheromones, including: All pheromones are decayed according to a preset evaporation rate, and pheromones are added to the encoded path of the ant corresponding to the maximum fitness value to obtain all updated pheromones. Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Traditional radar systems rely on direct links for target detection, i.e., a single transmission link from radar to target to radar. The detection capability is limited by the system hardware performance and the characteristics of the spatial transmission link. However, the enhanced detection method provided by this invention embeds a reconfigurable smart surface in the near-field region of the radar receiver, creating a new, autonomous, and controllable transmission link between the target and the radar receiver. This is the reconfigurable smart surface link (RIS link), forming a dual-link transmission system for the enhanced detection system. The radar system only needs to perform coherent processing on the dual-link received echo signals in the back-end signal processing to enhance the signal-to-noise ratio of the radar received echo, thus breaking through the detection performance bottleneck of traditional radar systems.

[0020] 2. Compared with traditional high-cost hardware upgrades that rely on increasing antenna aperture, increasing transmission power, or replacing low-noise devices, the enhanced detection method provided by this invention does not require modification of the existing radar system. It only requires the deployment of a reconfigurable smart surface in the near-field region of its receiver, thereby constructing a low-cost, low-system-complexity system architecture that upgrades the detection performance of traditional radar systems and is suitable for enhancing the detection performance of existing radar systems.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating an enhanced detection method based on a reconfigurable smart surface-assisted radar provided by the present invention. Figure 2 This is a schematic diagram illustrating the working principle of an enhanced detection system based on a reconfigurable intelligent surface-assisted radar provided by the present invention. Figure 3 This is a flowchart of a reconfigurable smart surface aperture encoding based on ACO optimization provided by the present invention; Figure 4 This is a schematic diagram of a reconfigurable smart surface aperture encoding based on ACO optimization provided by the present invention; Figure 5This invention provides a reconfigurable smart surface aperture reflection field distribution map based on ACO optimization; Figure 6 This invention provides a normalized slice of a reconfigurable smart surface aperture reflection field based on ACO optimization. Figure 7 This is a physical image of an enhanced detection system provided by the present invention; Figure 8a This is a schematic diagram of a direct link test for an enhanced detection system provided by the present invention; Figure 8b These are real-world test images of an enhanced detection system with a direct link provided by this invention. Figure 8c This is a graph showing the test results of the direct link echo power of an enhanced detection system provided by the present invention; Figure 9a This is a schematic diagram of a reconfigurable smart surface link test for an enhanced detection system provided by the present invention; Figure 9b This is a real-world test image of a reconfigurable smart surface link system for an enhanced detection system provided by this invention. Figure 9c This is a test result diagram of the reconfigurable smart surface link echo power of an enhanced detection system provided by the present invention; Figure 10 This is a graph showing the comparative analysis results of the echo power of the direct link and the reconfigurable smart surface link of an enhanced detection system provided by this invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0024] In current technologies, the main approach to improving the long-range detection capability of radar still relies on hardware upgrades, such as increasing transmitter power, improving receiver sensitivity, or increasing the aperture of the radio frequency transceiver antenna. Although these measures can improve the detection range to some extent, they lead to a significant increase in system cost and complexity. Specifically, such upgrades usually require replacing expensive high-power transmitters and low-noise receiver components, or redesigning and optimizing the entire radar system, thereby extending the development cycle and increasing maintenance costs. More importantly, due to the physical law that echo power is inversely proportional to the fourth power of the range in the radar range equation, the performance gain from simply relying on hardware upgrades exhibits a clear diminishing marginal effect: the increase in detection range obtained by investing a lot of resources is limited, the cost-effectiveness is low, and it is difficult to achieve efficient use of resources.

[0025] Please see Figure 1 and Figure 2 , Figure 1This is a flowchart illustrating an enhanced detection method based on reconfigurable smart surface-assisted radar provided by the present invention. Figure 2 This is a schematic diagram illustrating the working principle of an enhanced detection system based on a reconfigurable intelligent surface-assisted radar provided by the present invention. The present invention also provides an enhanced detection method based on a reconfigurable intelligent surface-assisted radar, which includes: Step 1: Establish an electromagnetic scattering characteristic model of the enhanced detection system, which includes radar, target and RIS array. The electromagnetic scattering characteristic model should at least characterize the signal propagation process of the radar direct link and the signal propagation process via the RIS link.

[0026] Here, the RIS array includes M × N One RIS unit.

[0027] Step 1.1: In the radar direct link, obtain the received power of the radar direct link based on the backscatter power after the target is illuminated by the electromagnetic waves emitted by the radar.

[0028] Step 1.11: In the radar direct link, obtain the backscatter power of the target after it has been illuminated by the electromagnetic waves emitted by the radar. The backscatter power is expressed as:

[0029] in, This is the backscattering power. For radar transmission power, For the transmit antenna gain, This is the normalized radiation pattern of the transmitting antenna. The target's elevation angle relative to the radar. The target's azimuth angle relative to the radar. For the target scattering cross-section, For the target equivalent gain, The target scattering pattern. To determine the distance at which the radar reaches the target.

[0030] Step 1.12: In the radar direct link, obtain the received power of the radar direct link based on the backscatter power. The received power of the radar direct link is expressed as:

[0031] in, This refers to the received power of the radar direct link. This refers to the effective aperture of the radar receiving antenna relative to the target.

[0032] Step 1.2: In the RIS link, the power scattered from the target to the RIS unit is obtained based on the backscattering power. The power scattered from the target to the RIS unit is expressed as:

[0033]

[0034] in, For the target to scatter to the first The power of each RIS unit, 1≤ m ≤ M ,1≤ n ≤ N , The distance from the target to the center of the RIS array. For the efficiency of the RIS unit, The projection factor of the RIS unit. For the first The pitch angle of each RIS unit relative to the target. For the first The azimuth angle of each RIS unit relative to the target. The size of the RIS unit, For RIS units in x Width in the axial direction, This represents the length of the RIS unit along the y-axis.

[0035] Step 1.3: Obtain the reflected electric field of the RIS cell based on the power scattered from the target to the RIS cell. The reflected electric field of the RIS cell is expressed as:

[0036] in, For the first The reflected electric field of each RIS unit For free space impedance, This represents the initial phase of the radar transmission. For the first The distance between each RIS unit and the target For the first The reflection coefficient of each RIS unit. It is a complex number. For wave number. Step 1.4: Obtain the electric field reflected from the RIS element to the radar receiver based on the reflected electric field of the RIS element. The electric field reflected from the RIS element to the radar receiver is expressed as:

[0037] in, For the ( m , n The electric field reflected by the RIS unit to the radar receiver. For the radar receiver relative to the first The distance between RIS units, This is the reflection pattern of the unit cell. For the radar receiver relative to the first The pitch angle of each RIS unit. For the radar receiver relative to the first The azimuth angle of each RIS unit.

[0038] Step 1.5: Obtain the total RIS link power received by the radar receiver based on the electric field reflected from the RIS unit to the radar receiver. The total RIS link power received by the radar receiver is expressed as:

[0039] in, This represents the total power of the RIS link received by the radar receiver. This is the effective aperture of the radar receiving antenna relative to the RIS array.

[0040] Step 2: Based on the electromagnetic scattering characteristic model, obtain the power ratio of the radar direct link and the RIS link, and use the power ratio of the radar direct link and the RIS link as the objective function for optimization.

[0041] Step 2.1: Based on the total power received by the radar receiver from the RIS link and the received power of the radar direct link, obtain the power ratio of the radar direct link to the RIS link. The power ratio of the radar direct link to the RIS link is expressed as:

[0042] in, This represents the power ratio between the radar direct link and the RIS link.

[0043] Step 2.2: Use the power ratio of the radar direct link to the RIS link as the objective function for optimization, in order to optimize the coding of the reconfigurable smart surface.

[0044] Step 3: Optimize the reflection coefficient matrix of the RIS array to maximize the objective function and obtain the optimal encoding matrix.

[0045] This embodiment aims to optimize the phase configuration of a RIS array, which includes... M Line × N List several RIS units, each of which can select four discrete phase modulation states, for example, a 20×20 RIS array.

[0046] The optimization problem of RIS arrays has the following characteristics: Discrete combinatorial optimization: The phase state of each RIS unit is discrete, therefore the solution space has a size of 4. 400 Traditional analytical methods are difficult to solve directly.

[0047] Complex objective function: The objective function comprehensively considers the peak field strength and energy focusing degree of the target region, involves complex electromagnetic field calculations, and the function may be non-convex, making it difficult to apply traditional gradient optimization methods.

[0048] Global and local search requirements: Due to the nonlinear phase superposition of electromagnetic waves, the optimization problem may have multiple local optima. To obtain a global or near-global optimal solution, the algorithm needs to have strong global search capabilities, while simultaneously improving the solution quality through local fine-tuning.

[0049] Therefore, this problem is an NP-hard problem, similar to a large-scale traveling salesman problem, and a metaheuristic algorithm should be considered to solve it. Based on the characteristics of this problem mentioned above, this embodiment of the invention preferentially selects the Ant Colony Optimization (ACO) algorithm to optimize this problem.

[0050] Ant Colony Optimization (ACO) is a metaheuristic optimization algorithm based on swarm intelligence, proposed by Italian scholar Marco Dorigo in 1992. It is inspired by the behavior of ants using pheromones to choose paths during foraging. ACO simulates the cooperative mechanism of ants searching for the optimal path and is particularly suitable for solving discrete combinatorial optimization problems, such as the Traveling Salesman Problem, scheduling problems, and network routing optimization. Its core idea is to guide a group of "ants" to gradually converge to the global or near-global optimum by using the accumulation and evaporation of pheromones in parallel search of the solution space.

[0051] The advantages of ACO lie in its global search capability, parallelism, and adaptability to complex nonlinear problems. Through dynamic updates of pheromones, the algorithm can explore a broad solution space in the early stages and focus on high-quality solutions in the later stages through pheromone accumulation. In addition, ACO does not depend on the mathematical properties of the objective function (such as differentiability), making it suitable for handling discrete, combinatorial, or non-convex optimization problems, namely the optimization problem proposed in this embodiment.

[0052] The algorithm simulation platform is MATLAB, version R2024b, developed by MathWorks. The simulation code implements a program for optimizing the reflection coefficient of a reconfigurable smart surface based on ant colony optimization. This program aims to optimize the encoded distribution of reflections from the reconfigurable smart surface to achieve electromagnetic wave focusing in a specific direction, such as... Figure 3 As shown, the specific implementation process is as follows: Step 3.1: Initialize scene parameters and initialize S A RIS array is initialized with parameters for an ant colony optimization algorithm, the parameters including... S Each ant corresponds to one of the following: M × N The coding matrix of each coding unit, the pheromone of each coding unit, and the heuristic information.

[0053] Specifically, the key parameters required are first initialized according to the actual application scenario, including electromagnetic environment parameters such as incident wave angle, target direction angle, and operating frequency.

[0054] Before implementing the method of this embodiment, electromagnetic simulation software was used to simulate the RIS cells of the RIS array in four phase modulation states, and an S11 data table was established accordingly. The S11 data table records the four reflection coefficients (including amplitude and phase) of the RIS cells under different incident wave angles and different operating frequencies. Each reflection coefficient corresponds to a coding state, which is denoted as code 0, 1, 2, and 3, respectively.

[0055] Then, initialize S Each RIS array is used. For each RIS cell in each RIS array, four reflection coefficients corresponding to the current incident angle and operating frequency are loaded from the S11 data table. Simultaneously, based on the near-field propagation formula of electromagnetic field, the field distribution of the incident electromagnetic wave on the RIS array is calculated, and combined with parameters such as cell size, cell efficiency, and projection factor, the received power and incident electric field distribution of the RIS array are calculated.

[0056] This invention employs an ant colony optimization algorithm to optimize the coding distribution (0, 1, 2, 3) of a reconfigurable smart surface to maximize the electric field intensity in the target region. Therefore, the parameters of the ant colony optimization algorithm are initialized, including... S Each ant corresponds to one of the following: M × N The encoding matrix of each encoding unit, the pheromone of each encoding unit, and the heuristic information. Each encoding unit is initialized to correspond to four encoding states (0, 1, 2, 3). The size of the encoding matrix is, for example, 20×20.

[0057] Step 3.2: With the goal of maximizing the objective function, perform iterations. Each ant selects the encoding value of each encoding unit based on the probability calculated by the pheromone and heuristic information of each encoding unit at the current time.

[0058] Here, the objective function is maximized as follows:

[0059] in, The wavelength of electromagnetic waves, For the goal and the first The distance between RIS units, The symbol for the Hadamard product. for M × N The reflection coefficient matrix, For the first The reflection coefficient of each RIS unit. In one specific embodiment, each ant selects the encoding value of each encoding unit based on the probability calculated from the pheromone and heuristic information of each current encoding unit, including: S3.21. Each ant obtains the probability of each coding state being selected based on the pheromone and heuristic information of each current coding unit.

[0060] Here, the probability of the encoded state being selected is expressed as:

[0061] in, For the first s The first in each population The coding unit is the first q The probability of each encoded state. For the first s The first in each population The coding unit is the first q A pheromone encoding a state, For the first s The first in each population Heuristic information for each coding unit, For all populations, To control the weight of pheromones, To control the weights of heuristic information, 1 ≤ s ≤ S , 0≤ q ≤3.

[0062] S3.22. Determine the coding value for each coding unit based on the probability distribution.

[0063] After obtaining the selection probabilities of the four coding states (0, 1, 2, 3) for each coding unit in step S3.21, a weighted random sampling method is used to assign coding values ​​to the unit. Specifically, the probabilities of the four states are converted into cumulative probability intervals. By generating uniform random numbers between [0,1], it is determined which interval the number falls into, i.e., the corresponding coding state is selected, thereby constructing the complete coding matrix for each ant in this round of iteration.

[0064] Step 3.3: Evaluate each encoding matrix using the fitness function to obtain the fitness value for each ant, where the fitness function is consistent with the objective function.

[0065] Step 3.4, according to the first k The maximum fitness value in the nth iteration and the 1st iteration k- The maximum fitness value in one iteration is the first... k The change in fitness value in the nth iteration, and the nth iteration k The change in fitness value in each iteration is compared with a preset threshold. If the change is continuous... E If the change in fitness value is less than the preset threshold, proceed to step 3.5; otherwise, perform evaporation and deposition on the pheromone to obtain the updated pheromone, and proceed to step 3.2. Step 3.2 is then executed based on the updated pheromone.

[0066] Specifically, the maximum fitness value is selected from all the fitness values ​​calculated in step 3.3. This maximum fitness value is then subtracted from the maximum fitness value obtained in the previous round. This difference is used as the change in fitness value between two adjacent iterations. This change in fitness value is then compared with a pre-set threshold. If the changes are consecutive... E If the change in fitness value is less than a preset threshold in all comparisons, then proceed to step 3.5; otherwise, perform evaporation and deposition processing on the pheromone to obtain an updated pheromone, and jump to step 3.2. Step 3.2 is then executed based on the updated pheromone. It should be noted that this embodiment does not specify a preset threshold and... E Specific limitations can be set by those skilled in the art according to actual needs, for example, a preset threshold of 10. -3 , E It is 10.

[0067] In one specific embodiment, pheromones undergo evaporation and deposition processes to obtain updated pheromones, including: All pheromones are decayed according to a preset evaporation rate, and pheromones are added to the coding path of the ant with the highest fitness value to obtain all updated pheromones. In this embodiment, only the ant with the highest fitness in the current iteration is allowed to release pheromones on its selected coding path to achieve positive feedback updates.

[0068] Specifically, the preset evaporation rate is denoted as... Then the decayed pheromone , The pheromone after decay, For example, the pheromone before decay. Next, the encoding path of the ant corresponding to the maximum fitness value is selected, and additional pheromones are randomly added to this encoding path, with the increment being proportional to the maximum fitness value. Step 3.5, if continuous E If the maximum fitness change in each iteration is less than a preset threshold, a perturbation mechanism is immediately triggered. A portion of the coding units in the RIS array are randomly selected, and their pheromones are reset to enhance the algorithm's global exploration capability. After the perturbation, the process jumps to step 3.2, executing step 3.2 based on the reset pheromones. If the perturbation continues... F If the maximum fitness change in each iteration is less than a preset threshold, the algorithm is considered to have converged sufficiently, the iteration stops, and the currently recorded globally optimal encoding matrix is ​​output as the final result. F > E .

[0069] Specifically, in satisfying continuity E When the change in fitness value is less than a preset threshold, a perturbation mechanism is immediately triggered: a portion of the coding units in the RIS array are randomly selected (e.g., 10% to 30% of the units and their corresponding states are randomly selected), and their pheromone values ​​are reset to uniformly small random numbers (e.g., values ​​uniformly randomly generated within the range of [0.1, 0.5]) to enhance the algorithm's global exploration capability and prevent premature entrapment in local optima. After the perturbation, the process jumps to step 3.2 to continue iterating. If continuous F If the change in fitness value is less than a preset threshold for all iterations, the iteration stops, and the optimal encoding matrix is ​​output. For example, in E For 10, F When the fitness value is 15, if the fitness value has changed less than the preset threshold for 10 consecutive times, a portion of the pheromones is immediately reset randomly, and the process returns to step 3.2 to continue iterating. If the fitness value has changed less than the preset threshold for 15 consecutive times, convergence is determined, iteration stops, and the optimal encoding matrix is ​​output. The encoding state corresponding to this optimal encoding matrix is ​​the final encoding state, thus completing the phase configuration of each unit in the RIS array.

[0070] Based on the above modeling, the simulation was performed with the incident point elevation angle at 0°, azimuth angle at 0°, and distance at 2.91m; the reflection point elevation angle at 30°, azimuth angle at 180°, and distance at 0.69m; and the frequency at 10 GHz for encoding optimization. The optimized reconfigurable smart surface code is as follows: Figure 4 As shown.

[0071] A slice is plotted on a plane 0.59m from the reconfigurable smart surface aperture (i.e., the plane containing the target point), and the amplitude information of the electric field on the slice is plotted as follows: Figure 5 As shown in the figure, the black rectangle represents the receiving antenna area. Calculations show that in the simulation scenario, an antenna with an area of ​​0.11m x 0.08m (the antenna used in the actual measurement) can receive 67% of the total energy of the reflected field. The field at the target point is normalized and sliced ​​along the X-axis and Y-axis respectively, as shown... Figure 6As shown in the figure. Analysis reveals that the 3dB main lobe width of the reflected field along the X-axis is 0.084m, and the 3dB main lobe width along the Y-axis is 0.066m. The side lobes are also relatively low, indicating a significant near-field focusing effect.

[0072] Step 4: Obtain the state of each RIS unit in the RIS array based on the optimal coding matrix, and construct an enhanced detection system integrating the RIS array and radar to perform detection using the enhanced detection system, and conduct detection verification experiments using the enhanced detection system.

[0073] Specifically, after determining the optimal coding matrix in step 3, the phase modulation of each unit of the RIS array is configured according to the coding state (0, 1, 2 or 3) of each coding unit in the matrix, so as to realize the near-field focusing optimization of the RIS reflection field, and then build an enhanced detection system of RIS array and monostation radar.

[0074] The physical embodiment of the enhanced detection system built in this example is shown below. Figure 7 As shown, the enhanced detection system consists of a radar simulator and a RIS array. The radar simulator can transmit various waveforms, including single-carrier, LFM, PCM, and custom-defined slice waveforms, with a sampling rate reaching 1.2 GHz and operating in the X-band. A 20×20 broadband reconfigurable smart surface aperture is deployed in the near-field region of the radar receiver. The two are integrated to form the enhanced detection system, as illustrated in the schematic diagram. Figure 2 As shown. The reconfigurable smart surface aperture of this embodiment has X-band broadband operation capability and full-aperture fast coding switching capability, without requiring any modifications to the original radar's RF front-end, transceiver antenna, or operating system.

[0075] This invention proposes an enhanced detection method integrating a broadband reconfigurable smart surface and a monostation radar. This enhanced detection method can significantly improve the detection performance of existing radar systems without requiring upgrades. Specifically, based on the constructed enhanced detection system, after the radar emits electromagnetic waves to illuminate the target, the target's scattered signal returns to the radar receiver along the inherent direct link, and a portion of the target's scattered signal can also be received by the broadband reconfigurable smart metasurface deployed in the near-field region of the radar receiver. By independently adjusting the reflection phase of each unit of the reconfigurable smart surface aperture, the received target echo signal can be focused and transmitted to the radar receiver. By performing coherent processing on the radar's dual-link echo signal, the signal-to-noise ratio of the received radar echo is significantly improved, achieving enhanced detection performance without modifying the radar system. The proposed enhanced detection system architecture has advantages such as low cost, low system complexity, convenient deployment, and compatibility with radar operating modes, providing an effective and feasible low-cost, low-complexity path for improving the detection performance of existing radar systems.

[0076] In addition, embodiments of the present invention also conducted a dual-link echo power comparison verification experiment of the enhanced detection system to verify the effectiveness of reconfigurable smart surfaces in assisting radar enhanced detection.

[0077] To verify the performance improvement of the proposed enhanced detection system compared to traditional radar systems, the experiment was set up as follows: Figure 8a , Figure 8b , Figure 8c , Figure 9a , Figure 9b , Figure 9c The scene shown Figure 8a , Figure 8b , Figure 8c The diagram shows the test results of the direct link echo power of the enhanced detection system of this invention. Figure 9a , Figure 9b , Figure 9c This is an experimental diagram showing the echo power test results of the reconfigurable smart surface link in the enhanced detection system of this invention. The reconfigurable smart surface is located directly in front of the target, and the radar receiving antenna is positioned at an elevation of 30° and an azimuth of 180° on the reconfigurable smart surface. Due to limitations in the experimental environment and conditions, the direct link and the RIS reflection link of the enhanced detection system were tested separately. The direct link's two-way distance was 3.89m, and the RIS reflection link's two-way distance was 5.42m. The radar system's transmitted waveforms are shown in Table 1 below.

[0078] Table 1. Test waveforms of echo power analysis for reconfigurable smart surface apertures

[0079] After the radar acquires the echo, the baseband echo data is processed. First, it is precisely segmented according to the pulse repetition period, and coherent accumulation is performed on multiple pulses to enhance the target echo intensity. Next, using the pure noise segment as a benchmark, the actual noise power is calculated, and a normalization factor is applied to unify it to the theoretical reference level, thereby ensuring the comparability of the echo power between the direct link and the RIS reflection link. Then, phase estimation and correction are performed on the echoes under "target present" and "target absent" scenarios respectively, and the vector cancellation method is used to process the echo data to effectively suppress background clutter and system bias, extracting the true target echo signal. Finally, the average power is statistically calculated within the range window corresponding to the target to obtain the echo power levels of the direct link and the RIS link and calculate... This allows for quantitative verification of the impact of the enhanced detection system's RIS reflection link on the target echo power.

[0080] like Figure 10As shown, the experimental results indicate that the average echo power received by the enhanced detection system via the direct link is -2.59 dBm, while the average echo power received via the RIS reflection link is 0.9 dBm. Compared to the direct link, the average echo power received via the RIS reflection link is increased by 3.49 dB, demonstrating that the reconfigurable smart surface aperture can effectively assist in enhancing radar detection performance.

[0081] This invention places a broadband reconfigurable smart surface in the near-field region of a radar receiver. By loading specific optimized aperture coding, the backscattered echo signal of the target received by the reconfigurable smart surface is focused onto the radar receiver in its near-field region, thereby establishing a new transmission link between the target and the radar receiver. Additional target echoes are fed back to the radar receiver, improving the radar's received echo power and extending the radar's detection range.

[0082] For near-field focusing scenarios, this invention establishes an optimization function with the objective of maximizing the electric field strength of the reconfigurable smart surface reflection focusing at the radar receiver, and uses an ant colony optimization algorithm to globally optimize the discrete phase state of each unit of the reconfigurable smart surface to obtain the optimal aperture coding sequence for a given scenario.

[0083] The enhanced detection system proposed in this invention does not require improvements to the radio frequency front-end, antenna, and signal processor of existing radars. It only requires embedding a broadband reconfigurable smart surface aperture in the near-field region of the radar receiver and applying specific aperture coding to achieve a significant increase in the radar received echo power. This provides existing radars with a low-cost, low-complexity, and rapidly deployable extended-range detection solution.

[0084] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0085] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, disclosure, and appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0086] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, any modifications made without departing from the inventive concept should be considered within the scope of protection of the present invention.

Claims

1. An enhanced detection method based on reconfigurable intelligent surface-assisted radar, characterized in that, include: An electromagnetic scattering characteristic model of an enhanced detection system comprising a radar, a target, and a RIS array is established, wherein the electromagnetic scattering characteristic model at least characterizes a radar direct link and a signal propagation process via a RIS link, and the RIS array comprises M × N RIS units The power ratio of the radar direct link to the RIS link is obtained based on the electromagnetic scattering characteristic model, and the power ratio of the radar direct link to the RIS link is used as the objective function for optimization. With the objective function as the goal, the reflection coefficient matrix of the RIS array is optimized to obtain the optimal encoding matrix; The state of each RIS unit in the RIS array is obtained based on the optimal coding matrix, and an enhanced detection system integrating the RIS array and radar is constructed to perform detection using the enhanced detection system.

2. The method of claim 1, wherein, An electromagnetic scattering characteristic model of an enhanced detection system, including radar, target, and RIS array, is established, including: In the radar direct link, the received power of the radar direct link is obtained from the backscatter power of the target after being illuminated by the electromagnetic waves emitted by the radar. In the RIS link, the power of the target scattered to the RIS unit is obtained based on the backscattering power; The reflected electric field of the RIS unit is obtained based on the power scattered from the target to the RIS unit; The electric field reflected from the RIS unit to the radar receiver is obtained based on the reflected electric field of the RIS unit. The total power of the RIS link received by the radar receiver is obtained from the electric field reflected from the RIS unit to the radar receiver.

3. The method of claim 2, wherein, In a direct radar link, the received power of the direct radar link is obtained based on the backscattered power of the target after being illuminated by the electromagnetic waves emitted by the radar. This includes: In the radar direct link, the backscattered power of the target after being illuminated by the electromagnetic waves emitted by the radar is obtained, and the backscattered power is expressed as: wherein, is the backscatter power, is the radar transmit power, is the transmit antenna gain, is the transmit antenna normalized pattern, is the target elevation angle relative to the radar, is the target azimuth angle relative to the radar, is the target scattering cross section, is the target equivalent gain, is the target scattering pattern, is the radar range to the target; In the radar direct link, the received power of the radar direct link is obtained based on the backscattering power, and the received power of the radar direct link is expressed as: in, This refers to the received power of the radar direct link. This refers to the effective aperture of the radar receiving antenna relative to the target.

4. The enhanced detection method according to claim 3, characterized in that, The power scattered from the target to the RIS unit is expressed as: in, For the target to scatter to the first The received power of each RIS unit, 1≤ m ≤ M ,1≤ n ≤ N , The distance from the target to the center of the RIS array. For the efficiency of the RIS unit, The projection factor of the RIS unit. For the first The pitch angle of each RIS unit relative to the target. For the first The azimuth angle of each RIS unit relative to the target. The size of the RIS unit, For RIS units in x Width in the axial direction, The length of the RIS unit along the y-axis; The reflected electric field of the RIS unit is expressed as: in, For the first The reflected electric field of each RIS unit For free space impedance, This represents the initial phase of the radar transmission. For the first The distance between each RIS unit and the target For wave number, It is a complex number. For the first The reflection coefficient of each RIS unit; The electric field reflected from the RIS unit to the radar receiver is represented as follows: in, For the first The electric field reflected by each RIS element to the radar receiver For the radar receiver relative to the first The distance between RIS units, This is the reflection pattern of the unit cell. For the radar receiver relative to the first The pitch angle of each RIS unit. For the radar receiver relative to the first The azimuth angle of each RIS unit; The total power of the RIS link received by the radar receiver is expressed as: in, This represents the total power of the RIS link received by the radar receiver. This is the effective aperture of the radar receiving antenna relative to the RIS array.

5. The enhanced detection method according to claim 1, characterized in that, Based on the electromagnetic scattering characteristic model, the power ratio of the radar direct link to the RIS link is obtained, and the power ratio of the radar direct link to the RIS link is used as the objective function for optimization, including: The power ratio of the radar direct link to the RIS link is obtained based on the total power received by the radar receiver from the RIS link and the received power of the radar direct link. The power ratio of the radar direct link to the RIS link is expressed as follows: in, The power ratio between the radar direct link and the RIS link. This represents the total power of the RIS link received by the radar receiver. This refers to the received power of the radar direct link; The power ratio of the radar direct link to the RIS link is used as the objective function for optimization.

6. The enhanced detection method according to claim 1, characterized in that, With the objective function as the goal, the reflection coefficient matrix of the RIS array is optimized to obtain the optimal encoding matrix, including: Step 3.1: Initialize scene parameters and initialize S A RIS array is initialized with parameters for an ant colony optimization algorithm, the parameters including... S Each ant corresponds to one of the following: M × N The coding matrix of each coding unit, the pheromone of each coding unit, and the heuristic information; Step 3.2: With the goal of maximizing the objective function, perform iterations. Each ant selects an encoding value based on the probability calculated from the pheromone and heuristic information of each current encoding unit. Step 3.3: Evaluate each of the encoding matrices using the fitness function to obtain the fitness value for each ant, wherein the fitness function is consistent with the objective function; Step 3.4, according to the first k The maximum fitness value in the nth iteration and the 1st iteration k- The maximum fitness value in one iteration is the first... k The change in fitness value in the nth iteration, and the nth iteration k The change in fitness value in each iteration is compared with a preset threshold. If the change is continuous... E If the change in fitness value is less than the preset threshold, proceed to step 3.5; otherwise, perform evaporation and deposition on the pheromone to obtain the updated pheromone, and proceed to step 3.

2. Step 3.2 is then performed based on the updated pheromone. Step 3.5, if continuous E If the maximum fitness change in each iteration is less than a preset threshold, a perturbation mechanism is triggered, randomly resetting a portion of the pheromones. Then, the process jumps to step 3.2, executing step 3.2 based on the reset pheromones. If the change continues... F If the maximum fitness change in each iteration is less than a preset threshold, then the iteration is considered to have converged sufficiently, the iteration stops, and the currently recorded globally optimal encoding matrix is ​​output as the final result. F > E .

7. The enhanced detection method according to claim 6, characterized in that, The maximization objective function is expressed as: in, The power ratio between the radar direct link and the RIS link. This represents the total power of the RIS array. This refers to the received power of the radar direct link. To reach the target distance, The effective aperture of the radar receiving antenna relative to the RIS array. The effective aperture of the radar receiving antenna relative to the target. The size of the RIS unit, The wavelength of electromagnetic waves, For the efficiency of the RIS unit, For the target relative to the first The distance between RIS units, For the radar receiver relative to the first The distance between RIS units, The projection factor of the RIS unit. For the first The pitch angle of each RIS unit relative to the target. For the first The azimuth angle of each RIS unit relative to the target. This is the reflection pattern of the unit cell. For the radar receiver relative to the first The pitch angle of each RIS unit. For the radar receiver relative to the first The azimuth angle of each RIS unit. The symbol for the Hadamarda complex. For the first The reflection coefficient of each RIS unit. For wave number, For the radar receiver relative to the first The distance between RIS units, for M × N The reflection coefficient matrix, For the first The reflection coefficient of each RIS unit.

8. The enhanced detection method according to claim 6, characterized in that, Each ant selects the encoding value for each encoding unit based on the probability calculated from the pheromone and heuristic information of each current encoding unit, including: Each ant obtains the probability of each coding state being selected based on the pheromone and heuristic information of each current coding unit; The encoding value is selected for each encoding unit based on the probability distribution.

9. The enhanced detection method according to claim 8, characterized in that, The probability of the encoded state being selected is expressed as: in, For the first s The first in each population The coding unit is the first q The probability of each encoded state. For the first s The first in each population The coding unit is the first q A pheromone encoding a state, For the first s The first in each population Heuristic information for each coding unit, For all populations, To control the weight of pheromones, To control the weights of heuristic information, 1 ≤ s ≤ S , 0≤ q ≤3.

10. The enhanced detection method according to claim 6, characterized in that, The pheromones are subjected to evaporation and deposition processes to obtain updated pheromones, including: All pheromones are decayed according to a preset evaporation rate, and pheromones are added to the encoded path of the ant corresponding to the maximum fitness value to obtain all updated pheromones.

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