Multi-source DoA estimation method based on power-amplified smart metasurface

Abstract

The present invention discloses a multi-source DoA estimation method based on a power amplifier intelligent metasurface, and its implementation scheme is: construct a power amplifier intelligent metasurface, which can amplify the power of radar received signals and improve the signal-to-noise ratio of radar received signals. The constructed power amplifier intelligent metasurface is used to realize DoA estimation, which, on the one hand, avoids the attenuation of radar received signals by traditional diode-based intelligent metasurfaces, and on the other hand, realizes two-dimensional DoA estimation of multiple sources. In addition, the present invention only uses part of the metasurface units for DoA estimation, and the remaining metasurface units can be designed to transmit radar signals, thereby hopefully realizing a full-duplex working mode. Therefore, the present invention can be applied to low-cost, high-precision, and multi-functional DoA estimation.

Description

Technical Field

[0001] The present invention belongs to the field of radar communication technology, and further relates to a multi-source DoA estimation method based on a power amplifier intelligent metasurface in the field of direction of arrival estimation technology. The present invention can be used to estimate the DoA of radar received signals. Background Art

[0002] As a new type of electromagnetic control and reception platform, smart metasurfaces have been widely studied for signal perception and DoA estimation. In traditional DoA estimation based on smart metasurfaces, the direction of the target is mainly obtained by receiving multiple random samples for compressed sensing. It is necessary to perform multiple random encodings on the metasurface units and obtain stray beams, which makes the existing methods not real-time, and the traditional direction of arrival estimation method based on smart metasurfaces is difficult to achieve two-dimensional positioning of multiple sources at the same time. In addition, traditional smart metasurfaces control each unit by loading diodes, so that the radar receiving signal will be attenuated after passing through the smart metasurface, thereby reducing the DoA estimation accuracy. How to use smart metasurfaces to achieve high-precision multi-source DoA estimation has become an important issue in this field.

[0003] Southeast University has published a multi-source DOA estimation method based on digital programmable metasurface in its patent application "A multi-source DOA estimation method based on digital programmable metasurface" (application number CN202111224815.4 application publication number CN 113871887 A). This method proposes to use a programmable metasurface to generate 40 groups of random dual-beam surface codes, each group of surface codes corresponds to a set of fixed dual-beam angles, and the 40 groups of sampling results are used to calculate the wave angle information through the OMP algorithm. However, the method still has the disadvantage that it uses one-dimensional dual-beam sampling and cannot achieve two-dimensional DoA estimation.

[0004] Mingtuan Lin, Ming Xu and others proposed a single-channel DoA estimation method based on metasurface in their paper "Single Sensor to Estimate DOA With Programmable Metasurface" (IEEE Internet of Things Journal, 2021, 8 (12): 10187-10197.). This method constructs a 20×20 programmable metasurface loaded with diodes, collects 100 random samples by generating 100 sets of random coding patterns, and uses the compressed sensing algorithm to realize the direction of arrival estimation. However, the method still has the following shortcomings: the diodes on the intelligent metasurface attenuate the radar received signal, deteriorate the signal-to-noise ratio of the radar received signal, and thus reduce the DoA estimation accuracy.

[0005] Junyan Dai, Wankai Tang and others proposed a method for DOA estimation using space-time coding metasurface in their paper “Simultaneous In-situ Direction Finding and Field Manipulation Based on Space-Time Coding Digital Metasurface” (IEEE Transactions on Antennas and Propagation, 2022). This method periodically adjusts the diodes on the coding metasurface unit to generate harmonics on the coding metasurface, and uses the amplitude ratio of the harmonics to estimate the DOA. However, the method still has the disadvantage that it is based on the amplitude ratio method of the harmonic component and can only perform one-dimensional estimation on a single source. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and propose a multi-source DoA estimation method based on a power amplifier intelligent metasurface, which is used to solve the problems that the existing wave direction estimation technology based on intelligent metasurface cannot realize two-dimensional DoA estimation of multiple sources, and the diode on the intelligent metasurface attenuates the radar receiving signal.

[0007] The technical idea for achieving the purpose of the present invention is: the present invention utilizes a metasurface unit loaded with a power amplifier, which can amplify the power of the radar received signal and improve the signal-to-noise ratio of the radar received signal. Therefore, the power amplifier intelligent metasurface is constructed by using a metasurface unit loaded with a power amplifier, which avoids the attenuation of the radar received signal by the traditional diode-based intelligent metasurface. The present invention uses non-uniform time modulation technology to modulate the radar received signal, so that the harmonics generated by the radar received signal through different metasurface units will appear in different frequencies in the spectrum. By extracting the harmonic components in the spectrum from the single-channel signal to form an array signal, the present invention can use some metasurface units to achieve two-dimensional DoA estimation of multiple sources.

[0008] The specific steps of the present invention include the following:

[0009] Step 1, designing a metasurface unit loaded with a power amplifier;

[0010] Step 2, the designed metasurface units are periodically arranged to form a two-dimensional N×N power amplifier smart metasurface, where N represents the number of rows and columns of the two-dimensional structure;

[0011] Step 3, selecting at least three adjacent metasurface units from the power amplifier smart metasurface to form a two-dimensional array structure;

[0012] Step 4, modulating the selected metasurface unit using non-uniform time modulation technology;

[0013] Step 5, construct the signal model of the radar receiving signal after passing through each selected metasurface unit as follows:

[0014]

[0015] Among them, y (m,n) represents the signal model of the radar receiving signal after passing through the metasurface unit in the mth row and nth column in the two-dimensional array structure, G represents the gain generated by the power amplifier on each metasurface unit, ∑ represents the summation operation, q represents the order of the harmonics generated after the radar signal passes through each selected metasurface unit, k represents the sequence number of the target source to be measured, K represents the number of target sources to be measured, and s k represents the radar receiving signal of the kth target source to be detected, c q represents the Fourier coefficient of the qth harmonic generated by the radar receiving signal after passing through each selected metasurface unit, exp(.) represents the exponential operation with the natural constant e as the base, j represents the symbol of the imaginary unit, π represents pi, and f (m,n) represents the modulation frequency of the metasurface unit in the mth row and nth column in the two-dimensional array structure, t represents the time when the radar receives the signal, β represents the spatial wave number of the radar receiving signal, d represents the distance between each metasurface unit and each adjacent metasurface unit, sin represents the sine function, cos represents the cosine function, and θ k represents the pitch angle of the kth target source to be measured, φ k represents the azimuth of the kth target source to be measured;

[0016] Step 6: After the radar receiving signal passes through all the selected metasurface units, it is synthesized into a single-channel signal y as follows:

[0017] y=∑y (m,n) ;

[0018] Step 7, extracting the +1-order harmonic signal generated by the radar receiving signal after passing through each selected metasurface unit from the single-channel signal is as follows:

[0019]

[0020] in, represents the signal of +1-order harmonic generated by the radar receiving signal after passing through the metasurface unit of the mth row and the nth column in the two-dimensional array structure, and c1 represents the Fourier coefficient of +1-order harmonic generated by the radar receiving signal after passing through each metasurface unit;

[0021] Step 8, forming a harmonic vector R with +1-order harmonic components generated by all selected metasurface units;

[0022] Step 9: Use the obtained harmonic vector R to perform multi-source two-dimensional DoA estimation through a spatial spectrum estimation algorithm.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] First, since the present invention utilizes a metasurface unit loaded with a power amplifier to construct an amplified smart metasurface, it overcomes the defect of traditional diode-based smart metasurface in attenuating radar received signals, so that the present invention can significantly enhance the power of radar received signals, thereby improving the accuracy of DoA estimation.

[0025] Second, since the present invention uses non-uniform time modulation technology to modulate the radar received signal, it avoids the deficiency of the prior art that only one-dimensional estimation of the target source can be performed, so that the present invention realizes two-dimensional DoA estimation of multiple sources and broadens the application scenarios of the present invention.

[0026] Third, the present invention only uses some units on the power amplifier intelligent metasurface for DoA estimation, and the remaining metasurface units can be designed to transmit radar signals, which overcomes the shortcoming of low real-time performance in the prior art and enables the intelligent metasurface of the present invention to receive and transmit radar signals without interfering with each other, thereby realizing a full-duplex working mode and improving the real-time performance of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of the present invention;

[0028] Figure 2 It is a structural diagram and electrical schematic diagram of the super surface unit used in the present invention;

[0029] Figure 3 It is a schematic diagram of two-dimensional DoA estimation using the constructed power amplifier intelligent metasurface in the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0031] Reference Figure 1 The specific implementation steps of the present invention are further described in detail with reference to the accompanying drawings.

[0032] Step 1: Design a metasurface unit loaded with a power amplifier.

[0033] The metasurface unit loaded with the power amplifier is either a transmission type or a reflection type. The control end on the power amplifier is connected to a field-programmable gate array (FPGA) to achieve time modulation of the power amplifier.

[0034] Refer to the attached Figure 2 , the metasurface unit structure loaded with the designed power amplifier is further described.

[0035] The metasurface unit used in the embodiment of the present invention is a transmission structure. The top surface of the metasurface unit includes a receiving patch antenna, a power amplifier circuit and a radio frequency via. The receiving patch antenna is connected to the input port of the power amplifier circuit through a microstrip line, and the output port of the power amplifier circuit is connected to the radio frequency via through a microstrip line. Figure 2 (a) shows that the RF vias on the bottom surface of the metasurface unit are connected to the transmitting patch antenna through a phase delay line, as shown in Figure 2 (b) As shown. Therefore, the radar signal received by the receiving patch antenna can be amplified by the power amplifier, transmitted from the top surface of the metasurface unit to the bottom surface of the metasurface unit through the RF via, and re-radiated by the transmitting patch antenna on the bottom surface. Compared with the traditional metasurface unit loaded with a diode, the metasurface unit loaded with a power amplifier can enhance the power of the radar received signal, thereby improving the signal-to-noise ratio of the radar received signal and significantly improving the accuracy of DoA estimation.

[0036] The electrical schematic diagram of the metasurface unit is shown in Figure 2 (c) shows that the DC power supply V dc , field effect transistor D1, resistor R1 and resistor R2 together constitute the bias circuit of the power amplifier circuit on the metasurface unit, wherein the input end of resistor R1 is connected to the field programmable gate device FPGA as a control port to realize time modulation of the power amplifier. Inductor L and C1 together constitute a low-pass filter to prevent the RF signal from leaking into the DC power supply. The input end of the low-pass filter is connected to the field effect transistor D1 in the bias control circuit through a wire.

[0037] The transmissive structure metasurface unit is referred to in "Wang X, Han J, Tian S, et al. Amplification and Manipulation of Nonlinear Electromagnetic Waves and Enhanced Nonreciprocity using Transmissive Space-Time-Coding Metasurface" (Advanced Science, 2022, 9(11): 2105960.)

[0038] Step 2: The designed metasurface units are periodically arranged to form a two-dimensional N×N power amplifier intelligent metasurface. In the embodiment of the present invention, N=6. Figure 3 The power amplifier smart metasurface is shown in Figure 2.

[0039] Step 3: modulate the metasurface unit using non-uniform time modulation technology.

[0040] At least three adjacent metasurface units in the power amplifier smart metasurface are selected to form a two-dimensional array structure, and the two-dimensional array structure refers to any one of an L-shaped structure, a circular structure, a cross structure and a square structure. In an embodiment of the present invention, an L-shaped array structure composed of 11 metasurface units located at the edge of the power amplifier smart metasurface is selected, such as Figure 3 The advantage of selecting some metasurface units for DoA estimation is that the complexity of the system is reduced, and the remaining metasurface units can be designed to transmit radar signals, so that the receiving and transmitting radar signals do not interfere with each other, realizing a full-duplex working mode.

[0041] Each selected metasurface unit is modulated using non-uniform time modulation technology. Non-uniform time modulation technology refers to the use of multiple modulation functions with different frequencies to modulate each selected metasurface unit at the same time, and the different modulation frequencies are mutually prime. Each modulation function is modulated to the corresponding metasurface unit through FPGA. Therefore, after the radar receiving signal passes through each modulated metasurface unit, all the first-order harmonics generated will not be aliased in the spectrum and appear at different frequencies in the spectrum. All first-order harmonic components in the spectrum can be extracted and applied to DoA estimation.

[0042] Step 4: Generate a single-channel signal model.

[0043] Step 4.1, construct the signal model of the radar receiving signal after passing through each selected metasurface unit as follows:

[0044]

[0045] Among them, y (m,n) represents the signal model of the radar receiving signal after passing through the metasurface unit in the mth row and nth column in the two-dimensional array structure, G represents the gain generated by the power amplifier on each metasurface unit, ∑ represents the summation operation, q represents the order of the harmonics generated after the radar signal passes through each selected metasurface unit, k represents the sequence number of the target source to be measured, K represents the number of target sources to be measured, and s k represents the radar receiving signal of the kth target source to be detected, c qrepresents the Fourier coefficient of the qth harmonic generated by the radar receiving signal after passing through each selected metasurface unit, exp(.) represents the exponential operation with the natural constant e as the base, j represents the symbol of the imaginary unit, π represents pi, and f (m,n) represents the modulation frequency of the metasurface unit in the mth row and nth column in the two-dimensional array structure, t represents the time when the radar receives the signal, β represents the spatial wave number of the radar receiving signal, d represents the distance between each metasurface unit and each adjacent metasurface unit, sin represents the sine function, cos represents the cosine function, and θ k represents the pitch angle of the kth target source to be measured, φ k represents the azimuth of the kth target source to be measured, and the positions of the two angles are as follows: Figure 3 shown.

[0046] Step 4.2: After the radar receiving signal passes through all the metasurface units in the L-shaped array, it is synthesized into a single-channel signal y:

[0047]

[0048] Among them, y (1,n) represents the signal of the radar receiving signal after passing through the first row and nth column of the metasurface unit in the two-dimensional array structure, y (m,1) Represents the signal after the radar receiving signal passes through the metasurface unit in the mth row and the first column in the two-dimensional array structure.

[0049] Step 5, extract the +1-order harmonic generated by each selected metasurface unit from the single-channel signal:

[0050]

[0051] in, represents the signal of +1-order harmonic generated by the radar receiving signal after passing through the metasurface unit of the mth row and the nth column in the two-dimensional array structure, and c1 represents the Fourier coefficient of +1-order harmonic generated by the radar receiving signal after passing through each metasurface unit. The size of c1 is determined by the duty cycle of the modulation function. In the embodiment of the present invention, the duty cycle of the modulation function is 25%.

[0052] Step 6: According to the following formula, extract the +1-order harmonic components generated by all the metasurface units in the L-shaped array to form the harmonic vector R:

[0053]

[0054] Among them, n1, n2 and n K They represent the noise in the radar signals reflected by the first, second and Kth target sources to be measured respectively.

[0055] Step 7, using the harmonic vector R obtained in a single channel, a spatial spectrum estimation algorithm, such as "Multiple signal classification algorithm MUSIC (Multiple signal classification algorithm)" and "Estimating signal parameter via rotational invariance techniques ESPRIT (Estimating signal parameter via rotational invariance techniques)", is used to perform two-dimensional DoA estimation of multiple sources.

Claims

1. A multi-source DoA estimation method based on power amplifier intelligent metasurface, characterized in that: A power amplifier intelligent metasurface is constructed by using a metasurface unit loaded with a power amplifier, and each selected metasurface unit is modulated using a non-uniform time modulation technique. DoA estimation is performed by extracting the harmonics generated during the modulation process. The steps of the DoA estimation method include the following: Step 1, designing a metasurface unit loaded with a power amplifier; Step 2, the designed metasurface units are periodically arranged to form a two-dimensional N×N power amplifier smart metasurface, where N represents the number of rows and columns of the two-dimensional structure; Step 3, selecting at least three adjacent metasurface units from the power amplifier smart metasurface to form a two-dimensional array structure; Step 4, modulating the selected metasurface unit using non-uniform time modulation technology; Step 5, construct the signal model of the radar receiving signal after passing through each selected metasurface unit as follows: Among them, y (m,n) represents the signal model of the radar receiving signal after passing through the metasurface unit in the mth row and nth column in the two-dimensional array structure, G represents the gain generated by the power amplifier on each metasurface unit, ∑ represents the summation operation, q represents the order of the harmonics generated after the radar signal passes through each selected metasurface unit, k represents the sequence number of the target source to be measured, K represents the number of target sources to be measured, and s k represents the radar receiving signal of the kth target source to be detected, c q represents the Fourier coefficient of the qth harmonic generated by the radar receiving signal after passing through each selected metasurface unit, exp(.) represents the exponential operation with the natural constant e as the base, j represents the symbol of the imaginary unit, π represents pi, and f (m,n) represents the modulation frequency of the metasurface unit in the mth row and nth column in the two-dimensional array structure, t represents the time when the radar receives the signal, β represents the spatial wave number of the radar receiving signal, d represents the distance between each metasurface unit and each adjacent metasurface unit, sin represents the sine function, cos represents the cosine function, and θ k represents the pitch angle of the kth target source to be measured, φ k represents the azimuth of the kth target source to be measured; Step 6: After the radar receiving signal passes through all the selected metasurface units, it is synthesized into a single-channel signal y as follows: y=∑y(m,n); Step 7, extracting the +1-order harmonic signal generated by the radar receiving signal after passing through each selected metasurface unit from the single-channel signal is as follows: in, It represents the signal of +1-order harmonic generated by the radar receiving signal after passing through the metasurface unit of the mth row and the nth column in the two-dimensional array structure, and c1 represents the Fourier coefficient of +1-order harmonic generated by the radar receiving signal after passing through each metasurface unit; Step 8, forming a harmonic vector R with +1-order harmonic components generated by all selected metasurface units; Step 9: Use the obtained harmonic vector R to perform multi-source two-dimensional DoA estimation through a spatial spectrum estimation algorithm.

2. The multi-source DoA estimation method based on power amplifier intelligent metasurface according to claim 1 is characterized in that: The metasurface unit loaded with the power amplifier described in step 1 is a transmission type or a reflection type, and the control end on the power amplifier is connected to the field programmable gate device FPGA to achieve time modulation of the power amplifier.

3. The multi-source DoA estimation method based on power amplifier intelligent metasurface according to claim 1 is characterized in that: The selecting of at least three adjacent supersurface units to form a two-dimensional array structure in step 3 refers to any one of an L-shaped structure, a circular structure, a cross structure and a square structure.

4. The multi-source DoA estimation method based on power amplifier intelligent metasurface according to claim 1 is characterized in that: The specific steps of using the non-uniform time modulation technology to modulate the selected metasurface unit described in step 4 are as follows: In the first step, a group of square wave signals with different frequencies and the same duty cycle are selected as modulation functions. The number of modulation functions is equal to the number of selected metasurfaces, and different modulation frequencies are mutually prime. In the second step, the modulation function corresponds to the selected metasurface unit one by one, and each modulation function is modulated to the corresponding metasurface unit through FPGA.

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