A broadband target localization method and system based on reconfigurable holographic metasurfaces

Abstract

This application provides a broadband target localization method and system based on a reconfigurable holographic metasurface, belonging to the field of wireless positioning and sensing technology. The method includes: in a coarse estimation stage, adjusting the amplitude response of the reconfigurable holographic metasurface RHS antenna to generate a wide beam covering the region of interest, transmitting an OFDM signal through a single radio frequency link, and obtaining the coarse distance and coarse angle of the target based on the echo signal received from a single snapshot; in a fine estimation stage, adjusting the RHS antenna according to the coarse angle to generate a narrow beam pointing towards the target, transmitting the OFDM signal again, and obtaining the fine distance and fine angle of the target based on the echo signal. This application utilizes the amplitude modulation characteristics of the RHS antenna to adjust the beamwidth and utilizes the beam squint effect enhanced by its serial feeding structure to achieve frequency-angle mapping, thereby achieving high-precision broadband target localization under single radio frequency link conditions without beam scanning or the introduction of additional true time delay hardware.

Description

Technical Field

[0001] This application relates to the field of wireless positioning and sensing technology, specifically to a broadband target positioning method and system based on a reconfigurable holographic metasurface. Background Technology

[0002] In next-generation wireless communication systems (such as 5G-Advanced and 6G), integrating sensing functions (such as target localization and environmental imaging) into existing communication infrastructure has become an important development trend. This integrated sensing architecture enables communication networks to perform environmental sensing tasks while providing data transmission services.

[0003] However, in actual deployment, the sensing task faces the following strict constraints: First, in order to ensure the performance indicators of existing communication services, the radio frequency (RF) link resources and time domain symbol resources allocated by the system to the sensing task are extremely limited; Second, in order to control the hardware cost and power consumption of base station equipment, the introduction of additional dedicated hardware components should be avoided as much as possible.

[0004] In target localization tasks, range resolution is directly proportional to signal bandwidth; therefore, using broadband signals (such as orthogonal frequency division multiplexing (OFDM) signals) is essential for improving positioning accuracy. However, in broadband scenarios, traditional phased array antennas face severe beam squint, meaning the direction of the antenna beam's main lobe shifts spatially with the operating frequency. This effect is generally considered a harmful dispersion phenomenon, leading to energy dispersion of the received signal and deterioration of target localization performance.

[0005] In existing technologies, a representative approach for achieving broadband target localization under single-radio link constraints is based on True Time Delay (TDD) technology. This approach connects a TTD hardware component in series after each phase shifter in a traditional phased array. By adjusting the TTD, the delay of different frequency components is actively controlled, thereby compensating for or utilizing beam squint effects to achieve target angular differentiation. However, a significant drawback of this approach is that the large number of additional TTD components significantly increases the hardware cost of the wireless communication system, the integration complexity of the antenna array, and the overall power consumption, severely limiting its large-scale deployment in practical base station equipment.

[0006] To address the aforementioned issues, there is an urgent need for a new technical solution that can achieve efficient and high-precision broadband target positioning without the introduction of additional hardware components under single-radio link conditions. Summary of the Invention

[0007] The purpose of this application is to provide a broadband target localization method and system based on a reconfigurable holographic metasurface, in order to solve the technical problems of relying on time-consuming beam scanning process or requiring additional true time delay hardware to achieve high cost and power consumption when performing broadband target localization under single radio frequency link constraints.

[0008] In a first aspect, embodiments of this application provide a broadband target localization method based on a reconfigurable holographic metasurface. This method comprises two stages, including: Coarse estimation stage: The amplitude response of the reconfigurable holographic metasurface RHS antenna is adjusted to generate a wide beam covering the region of interest. An orthogonal frequency division multiplexing (OFDM) signal with multiple subcarriers is transmitted through a single radio frequency link, and the first echo signal reflected by the target is received. The coarse distance and coarse angle of the target are obtained based on the first echo signal received in a single snapshot. Fine estimation stage: Based on the coarse angle, the amplitude response of the RHS antenna is adjusted to generate a narrow beam pointing to the target. The OFDM signal is transmitted again through a single radio frequency link and the second echo signal reflected by the target is received. The fine distance and fine angle of the target are obtained based on the second echo signal received in a single snapshot.

[0009] In one possible implementation, the RHS antenna has a serial feeding structure to enhance the broadband beam squint effect, so that targets at different spatial angles form frequency and angle mapping characteristics on the spectrum of the received signal. In the coarse estimation stage, multiple subcarriers of the first echo signal are jointly processed based on the frequency-angle mapping characteristics to obtain the coarse angle; In the fine estimation stage, multiple subcarriers of the second echo signal are jointly processed based on the frequency-angle mapping characteristics to obtain the fine angle.

[0010] In one possible implementation, the step of generating a wide beam covering the region of interest during the coarse estimation stage includes: Based on the angular range of the region of interest to be covered, determine the number N of radiating elements N of the RHS antenna required for the effective antenna aperture. a ; The serial number is greater than The normalized radiation amplitude of some radiating elements is set to zero to disable some radiating elements. The goal is to maximize the antenna gain in the direction corresponding to the center angle of the region of interest. An optimization problem is solved under the constraint of radiation amplitude values ​​to determine the remaining top N elements. a The normalized radiation amplitude of each radiation unit, to utilize the first N a Each radiating element forms a wide beam covering the region of interest.

[0011] In one possible implementation, the number N of radiating elements required for the effective antenna aperture is... a Determined by the following formula: ; in, For wavelength, The distance between adjacent radiating elements. and These are the upper and lower boundary angles of the region of interest, respectively.

[0012] In one possible implementation, the step of generating a narrow beam during the fine estimation stage includes: Activate all radiating elements of the RHS antenna; With the goal of maximizing the antenna gain in the direction corresponding to the rough angle, an optimization problem is solved under the constraint of radiation amplitude values ​​to determine the normalized radiation amplitude of each radiating element.

[0013] In one possible implementation, The optimization problem in the coarse estimation stage or the fine estimation stage is solved using a binary iterative search algorithm, the steps of which include: In the coarse estimation stage, the target orientation angle is initialized to the center angle of the region of interest; in the fine estimation stage, the target orientation angle is initialized to the coarse angle. The amplitude of each radiating element is randomly initialized; In each iteration, the radiating cells to be optimized are traversed sequentially. For the current radiating cell, the objective function value is calculated when taking the lower limit and upper limit of the feasible region. The value that makes the objective function value larger is retained, while the amplitude of other radiating cells remains unchanged. Repeat the iterative process until the objective function value converges.

[0014] In one possible implementation, obtaining the coarse distance and coarse angle of the target based on the first echo signal received from a single snapshot, and / or obtaining the fine distance and fine angle of the target based on the second echo signal received from a single snapshot, includes: A dictionary matrix is ​​constructed based on the beamforming matrix and steering vector of the RHS antenna, where each column of the dictionary matrix corresponds to a discrete grid point in the range and angle domains; The received signal vector is modeled as the sum of the product of the dictionary matrix and the sparse reflection coefficient vector and the noise; By solving the sparse recovery optimization problem, the sparse vector is recovered from the received signal vector, where the grid positions corresponding to the non-zero elements are the estimated distance and angle values ​​of the target.

[0015] In one possible implementation, the sparse recovery optimization problem is solved using the orthogonal matching pursuit (OMP) algorithm.

[0016] Secondly, embodiments of this application provide a broadband target localization system based on a reconfigurable holographic metasurface, comprising: A transmitter used to generate OFDM signals with multiple subcarriers; A reconfigurable holographic metasurface RHS transmitting antenna, connected to the transmitter, includes multiple radiating elements arranged along a dielectric integrated waveguide (SIW), and the radiation amplitude of each radiating element can be independently adjusted. A reconfigurable holographic metasurface RHS receiving antenna comprises multiple radiating elements arranged along a dielectric integrated waveguide (SIW). The radiation amplitude of each radiating element can be independently adjusted to receive signals reflected from a target. A receiver, connected to the RHS receiving antenna, is used to process the received signal; A controller, connected to the RHS transmitting antenna and the RHS receiving antenna, is configured to perform the method described in the first aspect to configure the radiation amplitude of each radiating element.

[0017] In one possible implementation, both the RHS transmitting antenna and the RHS receiving antenna adopt a one-dimensional serial feeding structure, the plurality of radiating elements are arranged alternately in two rows along the signal propagation direction, and each radiating element is provided with a diode for independently adjusting the radiation amplitude.

[0018] The advantages of this application compared to existing technologies are: 1. Low hardware cost and power consumption: The beam control and slant-look utilization are achieved by utilizing the amplitude modulation and serial feeding structure of the RHS itself, without the need to introduce additional hardware components such as TTD. The system structure is simple and significantly reduces the hardware cost and power consumption of the RF link.

[0019] 2. Low time overhead: The coarse estimation stage only requires a single snapshot, while the fine estimation stage requires K signal transmissions and receptions (K is the number of targets), for a total of K+1 times, which can cover the entire region of interest (RoI) and obtain the approximate location of the targets, completely avoiding the time-consuming full-space beam scanning process in traditional schemes.

[0020] 3. High positioning accuracy: The two-stage strategy combines the rapid discovery capability of wide beams with the high-precision measurement capability of narrow beams; at the same time, the enhanced beam squint effect provides rich frequency diversity information for joint distance and angle estimation, effectively improving the accuracy of parameter estimation. Attached Figure Description

[0021] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A schematic diagram of a broadband positioning system based on a reconfigurable holographic metasurface provided in this application is shown. Figure 2 A schematic diagram illustrating the structure and working principle of the reconfigurable holographic metasurface provided in this application is shown. Figure 3 The curve showing the root mean square error of the distance estimation provided in this application as a function of the signal-to-noise ratio is illustrated. Figure 4 The curve showing the root mean square error of the angle estimation provided in this application as a function of the signal-to-noise ratio is illustrated. Figure 5 The graphs showing the root mean square error of the angle estimation corresponding to different numbers of activated radiative elements in the coarse estimation stage provided in this application are illustrated as a function of the signal-to-noise ratio. Figure 6 The graph shows the root mean square error of the angle estimation corresponding to different numbers of activated radiative elements during the fine estimation stage provided in this application, as a function of the signal-to-noise ratio. Detailed Implementation

[0022] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of this application. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0023] The accompanying drawings illustrate various structural schematics according to embodiments of this application. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0024] In the context of this application, when a layer / element is referred to as being "above" another layer / element, the layer / element may be directly above the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "above" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0025] This application proposes a two-stage broadband positioning method and system by utilizing two inherent physical characteristics of reconfigurable holographic metasurface (RHS) antennas: adjustable beamwidth and beam squint effect enhanced by serial feeding structure.

[0026] On one hand, the RHS antenna consists of a feed and a large number of subwavelength radiating elements, the radiation amplitude of each element can be independently adjusted by controlling the bias voltage of its integrated diode. By setting the amplitude of some radiating elements to zero (i.e., in the off state), the effective aperture of the antenna can be flexibly reduced, thereby conveniently generating a wide beam to cover the observation area of ​​interest; conversely, activating all elements can generate a high-gain narrow beam to accurately point to the target. This mechanism avoids complex beamforming algorithms or mechanical scanning mechanisms.

[0027] As can be seen, this application relies on the amplitude modulation characteristics of RHS, which enables the beamwidth to be adjustable by turning off specific radiating elements, thereby achieving flexible coverage of the target without scanning.

[0028] On the other hand, the RHS antenna employs a serially fed structure composed of integrated dielectric waveguides (SIW). After the signal is fed from the feed source, it sequentially excites each radiating element along the waveguide. Since the propagation constant of the signal within the waveguide is a function of frequency, subcarriers of different frequencies will produce different cumulative phase delays when arriving at the same radiating element. This physical mechanism significantly enhances the beam squint effect in broadband systems, causing the direction of the transmit / receive beam to shift drastically and regularly with changes in the subcarrier frequency. This application transforms the beam squint effect, which is considered a defect in conventional schemes, into a powerful tool for frequency-angle mapping: targets at different spatial angles will map unique energy distribution characteristics onto the spectrum of the received signal.

[0029] As can be seen, the enhanced beam squint effect caused by the serial feeding structure of RHS in this application makes the target at different spatial angles form frequency and angle mapping characteristics on the spectrum of the received signal, which can be used to estimate the angle based on the echo signal.

[0030] Based on the above principles, this application provides a broadband target localization method based on a reconfigurable holographic metasurface, comprising two consecutively executed stages: Coarse estimation stage: The amplitude response of the RHS antenna is adjusted to generate a wide beam covering the region of interest. An OFDM signal with multiple subcarriers is transmitted via a single radio frequency link, and the first echo signal reflected from the target is received. Based on the first echo signal received in a single snapshot, the coarse range and coarse angle of the target are obtained by jointly processing multiple subcarriers using frequency-angle mapping characteristics.

[0031] Fine estimation stage: Based on the coarse angle, the amplitude response of the RHS antenna is adjusted to generate a high-gain, precisely pointed narrow beam at that coarse angle. The OFDM signal is transmitted again via a single radio frequency link, and the second echo signal reflected from the target is received. Based on the second echo signal received in a single snapshot, joint processing is performed again to obtain the fine range and fine angle of the target.

[0032] Accordingly, this application also provides a broadband target localization system based on a reconfigurable holographic metasurface, see [link to relevant documentation]. Figure 1 The system includes: a transmitter (not shown), an RHS transmitting antenna 10, an RHS receiving antenna 20, a receiver (not shown), and a controller (not shown). The controller is used to perform the above method, configure the amplitude response of the RHS antenna, and process the received signal.

[0033] See Figure 1 The RHS-based broadband positioning system provided in this application mainly consists of two parts: a transmitter and a receiver. The origin of the coordinate system can be set as the center position of the transmitter and the receiver.

[0034] Transmitter: Used to generate an OFDM baseband signal containing M subcarriers and upconvert it to the radio frequency carrier band.

[0035] RHS transmit antenna (Tx RHS): Connected to the single-RF link output of the transmitter. For example... Figure 2 As shown, the Tx RHS is an ultrathin planar antenna consisting of a feed, a dielectric integrated waveguide (SIW), and... It consists of several radiating elements. After the signal is fed in from the feed source, it propagates along the SIW and excites each radiating element in series. Each radiating element integrates a diode. The controller can independently control the amplitude of the electromagnetic wave radiated by the element by adjusting the bias voltage of the diode. The electromagnetic waves radiated by all elements are superimposed to form the target beam.

[0036] RHS receiving antenna (Rx RHS): Its structure is symmetrical to Tx RHS, including... Each radiation element is used to receive space electromagnetic waves reflected by the target and couple them to the SIW, which are then converged to the feed output.

[0037] Receiver: Connected to the feed output of Rx RHS, it performs low-noise amplification, down-conversion, and analog-to-digital conversion on the received signal to obtain a digital baseband received signal vector on M subcarriers.

[0038] Controller: Connected to the control interfaces of Tx RHS and Rx RHS respectively, used to execute amplitude optimization algorithms and generate and issue commands to control the state of each radiation unit diode.

[0039] To better illustrate the implementation process of this application, the mathematical model of the RHS antenna will be explained first.

[0040] 1. Reconfigurable holographic metasurface (RHS) like Figure 2 As shown, the RHS is an ultra-thin planar antenna composed of a feed source and radiating elements. After the signal is fed into the feed source, it propagates along the integrated dielectric waveguide (SIW) and sequentially excites the RHS radiating elements. At each RHS radiating element, the amplitude of the radiated electromagnetic wave can be independently controlled by adjusting the voltage of a diode. The superposition of the electromagnetic waves radiated by all elements forms the target beam.

[0041] Consider RHS based on one-dimensional SIW. The elements are arranged alternately in two rows. When the RHS is used as a transmitting antenna, its effect on electromagnetic waves can be represented by a holographic beamforming matrix. This indicates that the first... The units are: ; in, Indicates the RHS transmitting antenna number The normalized radiation amplitude of each unit, It is the magnitude vector; For feed to the first The power of each unit, of which This indicates the total power fed into the RHS transmitting antenna; Denotes the propagation constant of RHS, where This represents the frequency of the m-th subcarrier; Indicates the first x-axis coordinates of each transmit RHS unit; The phase difference caused by the alternating arrangement of two rows can be expressed as:

[0042] When the RHS is used as the receiving antenna, based on the reciprocity of the antenna, the holographic beamforming matrix is... The Each unit can be represented as: ; in, Indicates the RHS receiving antenna number The normalized magnitude of each unit, ; Indicates the first The x-axis coordinates of each receiving RHS unit; Indicates the first The ratio of the power received by each unit to the incident power, without loss of generality, assumes that the signal reflected by the target is small enough that it can be fully received by the RHS unit. .

[0043] 2. RHS-based target positioning system like Figure 1 As shown, the system consists of a transmitter and a receiver, each equipped with an RHS antenna as the transmitting and receiving antennas, respectively. The origin of the coordinate axis is located at the midpoint between the two RHS antennas. The RHS transmitting antenna is connected to the transmitter, and the transmitter generates [data / signals]. The OFDM signal of each subcarrier is fed into the RHS transmitting antenna (Tx RHS) through a feed hood. This signal is radiated into free space by the RHS, reflected by the target, and received by the RHS receiving antenna (Rx RHS), then transmitted to the receiver through the feed hood. The receiver... The received signal of each subcarrier can be represented as: ; in, Indicates the first The normalized transmitted signal of each subcarrier satisfies ; This represents the Gaussian white noise at the Rx RHS cell, assuming its mean is 0 and its variance is... ; Indicates passing through Tx RHS cell The target is reflected into the Rx RHS unit. The channel matrix of the nth subcarrier, its nth Each unit satisfies , and These represent the cell indices of Rx RHS and Tx RHS, respectively; Indicates the first The reflection coefficient of the target; and Let Tx RHS and Rx RHS be the steering vectors, respectively, satisfying the following conditions: ; .

[0044] 3. The adjustable beamwidth of RHS and the beam slant enhancement effect Unlike traditional solutions, the proposed solution based on a reconfigurable holographic surface aims to achieve efficient target localization using only a single radio frequency link, without the need for beam scanning or the introduction of additional hardware.

[0045] The implementation method is as follows: The adjustable beamwidth of the reconfigurable holographic surface provides flexible spatial coverage for the target, and the beam-slant enhancement effect of the reconfigurable holographic surface is combined to distinguish the target angle. Specifically: a) Adjustable beamwidth: In practical applications, the target location is usually unknown beforehand; only the region of interest (RoI) can be obtained. To avoid beam scanning, a wide-coverage beam is needed to cover the RoI initially. Once a rough target location is obtained, a high-gain narrow beam is required to improve estimation accuracy. Therefore, adaptive beamwidth control is required. Traditionally, phased arrays with fixed antenna apertures can achieve adjustable beamwidth by introducing additional hardware or employing complex beamforming optimizations. However, these methods often introduce additional hardware overhead, increased computational complexity, and undesirable beam pattern jitter.

[0046] In contrast, RHS, thanks to its amplitude modulation capabilities, offers a simple and efficient method for beamwidth control. Specifically, the amplitude response of each RHS element can be controlled independently. By setting the amplitude response of a specific element to zero, these elements are effectively disabled, contributing neither to radiation nor reception. Therefore, the effective antenna aperture is determined by the number of effective elements, denoted as . At this point, the half-power beamwidth (HPBW) is... Inversely proportional to the effective antenna aperture, it can be expressed as: ; in, Indicates wavelength. Indicates the spacing between adjacent units. This can be adjusted... The number of beams required can be conveniently generated during the rough estimation stage.

[0047] b) Beam-squinting enhancement effect A single, full-coverage beam supported by a single radio frequency chain lacks the spatial diversity needed to distinguish echo signals from different angles. Traditional positioning schemes typically address this limitation by employing multiple radio frequency chains or utilizing sequential beam scanning. In contrast, by utilizing the beam angle-shifting effect, the echo signals on different subcarriers exhibit angle-dependent variations. Therefore, each spatial angle maps a unique spectral characteristic in the received signal distribution. Through this frequency-angle mapping, the target angle can be distinguished using only a single radio frequency chain in a single snapshot.

[0048] Due to the beamforming vector of RHS and guide vector These are all frequency-dependent, which exacerbates the beam-squinting effect of the RHS in broadband applications. Specifically, the amplitude response of the RHS... Designed to operate at a frequency of The steering vector is towards the direction angle The desired beam pattern is achieved by directional control. However, when the frequency changes from... Offset to The beam direction deviates from a different direction Angle This is known as beam squint. Furthermore, due to the series-fed structure of the RHS, the phase of the reference wave differs at each unit, resulting in a stronger beam squint effect.

[0049] Assuming Tx RHS at frequency The direction is designed according to the holographic principle. The amplitude response, when the number of RHS components is sufficient, the frequency shifts to... Beam direction generated at time It can be approximated as: ; in, It represents the refractive index by which the signal propagates within the RHS. This is the speed of light in free space. This effect causes the beams of different subcarriers to point in a scanning effect in space. Therefore, beams located at different angles... The target, whose echo energy is in different subcarriers The distribution on it will exhibit a unique pattern, namely, the realization of frequency-angle mapping.

[0050] 4. A two-stage localization scheme based on reconfigurable holographic metasurfaces Based on the adjustable beamwidth characteristic of RHS and the beam squint enhancement effect, a two-stage broadband positioning scheme is proposed, as follows: a) Coarse estimation stage: Generate a wide beam to cover the entire Rol with a single transmission, providing a coarse estimate of the target's range and angle.

[0051] Wide beam design: Activation One RHS unit to generate a wide beam, covering Rol ,in and These represent the angles corresponding to the boundaries of the RoI. The magnitude response of the RHS cell is obtained through the RHS magnitude response optimization algorithm described below; Signal transmission: Tx RHS transmits a single symbol, which is reflected by the target and received by Rx RHS, represented as... ; Coarse estimation: Using the joint range-angle estimation algorithm described below, the received signals of different subcarriers exhibiting beam-squinting effects are processed to obtain the target range. and angle A rough estimate.

[0052] b) Fine estimation stage: Generate a high-gain narrow beam to improve the estimation accuracy of each detected target.

[0053] Fine beam design: For each coarsely estimated target Activating all RHS cells to generate a high-gain narrow beam, providing a coarse estimate of the angle of the target. The amplitude response of the RHS cell is obtained through the RHS amplitude response optimization algorithm described below; Signal transmission: For each coarsely estimated target, the Tx RHS transmits a single symbol, which is reflected by the target and received by the RxRHS. The received signal of each target is represented as ; Detailed estimation: Using the joint range-angle estimation algorithm described below, the received signals of different subcarriers exhibiting beam-squinting effects are processed to obtain the target range. and angle A detailed estimate.

[0054] 5. RHS Amplitude Response Optimization Algorithm Taking Tx RHS as an example, given the center frequency is and angle The optimization problem of Tx RHS can be expressed as:

[0055] in, This indicates the maximum value of the RHS amplitude. The propagation factor within the waveguide. It is the nth component of the free space guide vector.

[0056] The above optimization problem can be solved using a binary iterative search. Specifically, the optimization algorithm consists of two parts: Initialization: Calculate angles In the rough estimation stage, Depend on Calculations show that, in the detailed estimation stage, The coarsely estimated angle result set as the target, i.e. In addition, the amplitude response of the RHS is randomly initialized; Iteration: In a given In this case, the amplitude response of the RHS cell is iteratively optimized. In each iteration, the two ends of the feasible set are compared... and The algorithm selects a better RHS cell magnitude based on the corresponding objective function value, while keeping the magnitudes of other cells unchanged. The algorithm terminates when the objective function value converges.

[0057] 6. Joint distance-angle estimation algorithm In both the coarse and fine estimation stages, the receiver needs to obtain the received signal vector. The position parameters of the target are recovered from the data, and this application models it as a sparse signal recovery problem.

[0058] Assuming to adopt If there are 1 subcarrier, then Received signals of each subcarrier It can be represented as: ; in, Represents a dictionary matrix, where Indicates the number of grid points in the division, the first... Each unit can be represented as , and They represent the first The distance and angle of the grid points , , Indicates the Kronecker product; It is a sparse target reflection coefficient vector, only The non-zero elements correspond to... One goal, namely If and only if ; This represents the noise vector.

[0059] In the above formula, each grid point corresponds to A column vector and An element. If The If an element is not 0, it means that at the corresponding grid point There exists a target. Therefore, the distance and angle estimation problem can be transformed into a sparse recovery problem, i.e., from the received signal... Recovery of sparse vectors The optimization problem can then be expressed as: ; in, express -norm, This is a predefined threshold parameter related to noise power. The above optimization problem can be solved using the Orthogonal Matching Pursuit (OMP) algorithm to obtain estimates of distance and angle. The OMP algorithm iteratively selects the dictionary column vector most relevant to the current residual at each iteration and updates the residual using the least squares result of the selected column vectors. Iteration After that ( (where the number of targets is 0), the algorithm outputs the grid coordinates corresponding to the non-zero elements, which are the estimated distance and angle values ​​of the targets.

[0060] 7. Performance simulation verification To verify the technical effectiveness of this application, a Monte Carlo simulation experiment was conducted. The simulation parameters were set as follows: carrier frequency 27 GHz, bandwidth 2 GHz, subcarrier spacing for positioning 20 MHz, and RHS cell number... = =128. The two-stage scheme of this application is compared with the traditional beam scanning-based scheme and the TTD-based scheme.

[0061] Figure 3 This demonstrates the root mean square error of the distance estimation ( ) with signal-to-noise ratio ( (The curve of change) Figure 4 This demonstrates the root mean square error of the angle estimation ( ) with signal-to-noise ratio ( The curves show the changes. As can be seen from the figure, under the same signal-to-noise ratio, the distance and angle estimation errors of the proposed scheme are significantly lower than those of the traditional TTD scheme. Moreover, it only requires far fewer time-domain symbols than the traditional scanning scheme to achieve similar positioning accuracy. This verifies that the proposed scheme can achieve higher-precision broadband target positioning under a single radio frequency link by utilizing the beam squint effect enhanced by RHS and a two-stage strategy.

[0062] Figure 5 This demonstrates the root mean square error of angle estimation corresponding to different numbers of activated radiative units during the coarse estimation stage. ) with signal-to-noise ratio ( (The curve of change) Figure 6 This demonstrates the root mean square error of angle estimation corresponding to different numbers of activated radiative units during the fine estimation stage. ) with signal-to-noise ratio ( The graph shows the change in the radiative unit count. As can be seen from the graph, under the same signal-to-noise ratio, the more activated radiative units, the smaller the root mean square error.

[0063] The advantages of this application compared to existing technologies are: 1. Low hardware cost and power consumption: The beam control and slant-look utilization are achieved by utilizing the amplitude modulation and serial feeding structure of the RHS itself, without the need to introduce additional hardware components such as TTD. The system structure is simple and significantly reduces the hardware cost and power consumption of the RF link.

[0064] 2. Low time overhead: The coarse estimation stage only requires a single snapshot to cover the entire region of interest (RoI) and obtain the rough location of the target, completely avoiding the time-consuming full-space beam scanning process in traditional schemes.

[0065] 3. High positioning accuracy: The two-stage strategy combines the rapid discovery capability of wide beams with the high-precision measurement capability of narrow beams; at the same time, the enhanced beam squint effect provides rich frequency diversity information for joint distance and angle estimation, effectively improving the accuracy of parameter estimation.

[0066] To achieve the same structure, those skilled in the art can also devise methods that are not entirely identical to those described above. Furthermore, although various embodiments have been described separately above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination.

[0067] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0068] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. The scope of this application is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this application, and all such substitutions and modifications should fall within the scope of this application.

Claims

1. A broadband target localization method based on a reconfigurable holographic metasurface, characterized in that, The method consists of two stages, including: Coarse estimation stage: The amplitude response of the reconfigurable holographic metasurface RHS antenna is adjusted to generate a wide beam covering the region of interest. An orthogonal frequency division multiplexing (OFDM) signal with multiple subcarriers is transmitted through a single radio frequency link, and the first echo signal reflected by the target is received. The coarse distance and coarse angle of the target are obtained based on the first echo signal received in a single snapshot. Fine estimation stage: Based on the coarse angle, the amplitude response of the RHS antenna is adjusted to generate a narrow beam pointing to the target. The OFDM signal is transmitted again through a single radio frequency link and the second echo signal reflected by the target is received. The fine distance and fine angle of the target are obtained based on the second echo signal received in a single snapshot.

2. The method according to claim 1, characterized in that, The RHS antenna has a serial feeding structure to enhance the broadband beam squint effect, so that targets at different spatial angles form frequency and angle mapping characteristics on the spectrum of the received signal. In the coarse estimation stage, multiple subcarriers of the first echo signal are jointly processed based on the frequency-angle mapping characteristics to obtain the coarse angle; In the fine estimation stage, multiple subcarriers of the second echo signal are jointly processed based on the frequency-angle mapping characteristics to obtain the fine angle.

3. The method according to claim 1, characterized in that, The steps for generating a wide beam covering the region of interest in the coarse estimation stage include: Based on the angular range of the region of interest to be covered, determine the number N of radiating elements N of the RHS antenna required for the effective antenna aperture. a ; The serial number is greater than The normalized radiation amplitude of some radiating elements is set to zero to disable some radiating elements. The goal is to maximize the antenna gain in the direction corresponding to the center angle of the region of interest. An optimization problem is solved under the constraint of radiation amplitude values ​​to determine the remaining top N elements. a The normalized radiation amplitude of each radiation unit, to utilize the first N a Each radiating element forms a wide beam covering the region of interest.

4. The method according to claim 3, characterized in that, The number of radiating elements required for the effective antenna aperture Determined by the following formula: ； in, For wavelength, The distance between adjacent radiating elements. and These are the upper and lower boundary angles of the region of interest, respectively.

5. The method according to claim 1, characterized in that, The steps for generating a narrow beam in the fine estimation stage include: Activate all radiating elements of the RHS antenna; With the goal of maximizing the antenna gain in the direction corresponding to the rough angle, an optimization problem is solved under the constraint of radiation amplitude values ​​to determine the normalized radiation amplitude of each radiating element.

6. The method according to claim 1, characterized in that, The optimization problem in the coarse estimation stage or the fine estimation stage is solved using a binary iterative search algorithm, the steps of which include: In the coarse estimation stage, the target orientation angle is initialized to the center angle of the region of interest; in the fine estimation stage, the target orientation angle is initialized to the coarse angle. The amplitude of each radiating element is randomly initialized; In each iteration, the radiating cells to be optimized are traversed sequentially. For the current radiating cell, the objective function value is calculated when taking the lower limit and upper limit of the feasible region. The value that makes the objective function value larger is retained, while the amplitude of other radiating cells remains unchanged. Repeat the iterative process until the objective function value converges.

7. The method according to claim 1, characterized in that, The process of obtaining the coarse distance and coarse angle of the target based on the first echo signal received from a single snapshot, and / or the process of obtaining the fine distance and fine angle of the target based on the second echo signal received from a single snapshot, includes: A dictionary matrix is ​​constructed based on the beamforming matrix and steering vector of the RHS antenna, where each column of the dictionary matrix corresponds to a discrete grid point in the range and angle domains; The received signal vector is modeled as the sum of the product of the dictionary matrix and the sparse reflection coefficient vector and the noise; By solving the sparse recovery optimization problem, the sparse vector is recovered from the received signal vector, where the grid positions corresponding to the non-zero elements are the estimated distance and angle values ​​of the target.

8. The method according to claim 7, characterized in that, The sparse recovery optimization problem is solved using the orthogonal matching pursuit (OMP) algorithm.

9. A broadband target localization system based on a reconfigurable holographic metasurface, characterized in that, include: A transmitter used to generate OFDM signals with multiple subcarriers; A reconfigurable holographic metasurface RHS transmitting antenna, connected to the transmitter, includes multiple radiating elements arranged along a dielectric integrated waveguide (SIW), and the radiation amplitude of each radiating element can be independently adjusted. A reconfigurable holographic metasurface RHS receiving antenna comprises multiple radiating elements arranged along a dielectric integrated waveguide (SIW). The radiation amplitude of each radiating element can be independently adjusted to receive signals reflected from a target. A receiver, connected to the RHS receiving antenna, is used to process the received signal; A controller, connected to the RHS transmitting antenna and the RHS receiving antenna, is configured to perform the method as described in any one of claims 1 to 8 to configure the radiation amplitude of each radiating element.

10. The system according to claim 9, characterized in that, Both the RHS transmitting antenna and the RHS receiving antenna adopt a one-dimensional serial feeding structure. The multiple radiating elements are arranged alternately in two rows along the signal propagation direction, and each radiating element is equipped with a diode for independently adjusting the radiation amplitude.

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