Frequency modulated continuous wave radar measurement method based on false target echo learning

Abstract

The invention discloses a frequency-modulated continuous wave radar measurement method based on false target echo learning. The method comprises the steps that S1, a frequency-modulated continuous wave radar dechirps echo signals reflected by a target to obtain difference frequency echo signals; s2, performing distance dimension Fourier transform on the difference frequency echo signal to obtain a distance dimension frequency domain, speed dimension and time domain echo signal; s3, performing coherent accumulation on the distance-dimension frequency-domain speed-dimension time-domain echo signal, and performing speed-dimension Fourier processing to obtain a two-dimensional frequency-domain echo signal; s4, the frequency modulated continuous wave radar observes a target-free actual scene, and corresponding fixed detection signal-to-noise ratio thresholds are set in different distance sections; s5, setting a damping coefficient empirical value for local interference existing in the echo signal; s6, the frequency modulated continuous wave radar observes a target scene, and the target position is obtained through a constant false alarm detection method; and S7, calculating the distance and the speed of the target.

Description

Technical Field

[0001] This invention relates to the field of data processing, and in particular to a frequency-modulated continuous wave radar measurement method based on learning from false target echoes. Background Technology

[0002] Frequency-modulated continuous wave (FM-CHW) radar is a type of radar that uses frequency-modulated continuous waves as its transmitted signal. It features high accuracy in velocity and distance measurement, no near-range blind spots, low transmission power, simple structure, and small size. Considering the susceptibility of FM-CHW radar to environmental influences and its relatively high false alarm probability, measures are generally taken to mitigate the effects of strong clutter interference, including changes in signal format, filtering algorithms, and detection methods.

[0003] Domestic patent CN103698766A (“A Target Detection Method for Frequency-Modulated Continuous Wave Anti-Collision Radar under Strong Interference Conditions”) proposes a target detection method for frequency-modulated continuous wave anti-collision radar under strong interference conditions. It fully integrates the advantages of single-channel target reception, angle measurement, and miniaturization of the anti-collision radar using a time-division multiplexed receiving channel. Under interference conditions, adaptive beamforming provides significant zero-depth suppression of strong interference in the interference direction without affecting target detection, achieving the goal of miniaturized anti-collision radar target detection under interference conditions. However, the hardware system is relatively complex, and the signal processing flow is cumbersome.

[0004] Domestic patent CN109085568A (“A Frequency-Modulated Continuous Wave Multi-Target Detection Method Based on Secondary Frequency Mixing”) provides a frequency-modulated continuous wave multi-target detection method based on secondary frequency mixing. The method involves mixing the radar echo with the transmitted signal to obtain a baseband signal. This baseband signal is then mixed using up- and down-modulation bands. Fourier transform and signal compensation are used to obtain the velocity and radial distance parameters relative to the radar for the first moving target. A band-stop filter is used to filter out this moving target. The signal is then multiplied by the inverse of the motion compensation signal to correct the original baseband signal. The same method is used to calculate the parameters for other targets until no obvious targets are visible in the spectrum.

[0005] The paper "Research on Real-time Detection Algorithm of Object Motion State Based on Frequency Modulated Continuous Wave Radar" published in the October 2021 issue of the journal Acta Physica Sinica proposes a method for detecting dynamic targets. By performing a discrete Fourier transform on the beat signal of the moving object at a specific frequency, the real and imaginary parts of the transform are superimposed in two mutually perpendicular directions, and the synthesized trajectory is approximately an ellipse. The phase of each trajectory point is calculated to restore the motion state of the object. It has the ability to resist interference from stationary targets, but the calculation is relatively complex.

[0006] The article "Measurement of Target Parameters of Linear Frequency Modulated Continuous Wave Radar" published in the February 2021 issue of the journal "Radio Engineering" uses the radar to transmit a symmetrical triangular LFMCW signal. After the echo signal is reflected by different targets, the target motion parameters are solved by the beat signal information of the up and down frequency sweep. However, this method has good detection performance for moving targets but weak anti-interference ability.

[0007] Compared with domestic and foreign literature, there are many detection and testing methods for frequency modulated continuous wave radar. In view of the strong interference problem faced by frequency modulated continuous wave radar, the clutter parameter estimation method is basically adopted, which results in a large amount of computation and insufficient robustness to different working scenarios. Summary of the Invention

[0008] The purpose of this invention is to provide a frequency-modulated continuous wave radar measurement method based on false target echo learning. For different radar operating scenarios, this invention eliminates the influence of strong interference by learning the echo of false targets in targetless scenarios. This invention is applicable to relatively complex operating scenarios, and the method has low computational load, making it easy to apply to practical engineering.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution: A frequency-modulated continuous wave radar measurement method based on spurious target echo learning, characterized by the following steps: Step S1: The frequency-modulated continuous wave radar delinearly modulates the echo signal reflected from the target to obtain the difference frequency echo signal. Step S2: Perform a distance-dimensional Fourier transform on the difference frequency echo signal to obtain a distance-dimensional frequency domain velocity-dimensional time domain echo signal; Step S3: After coherently accumulating the distance-dimensional frequency domain echo signal and velocity-dimensional time domain echo signal, perform velocity-dimensional Fourier processing to obtain a two-dimensional frequency domain echo signal. Step S4: The frequency-modulated continuous wave radar observes the actual scene without targets and sets corresponding fixed detection signal-to-noise ratio thresholds for different distance segments; Step S5: Set an empirical value for the damping coefficient for the local interference present in the echo signal; Step S6: The frequency-modulated continuous wave radar observes the target scene, and after learning the false target echo using the damping coefficient and joint detection with multiple thresholds, the target position is obtained through the constant false alarm rate detection method. Step S7: Calculate the target's distance and speed.

[0010] Furthermore, in step S1: Assuming the radar transmits a signal as follows: In the formula, For carrier frequency, For frequency modulation slope, The bandwidth of the transmitted linear frequency modulated signal. Given the frequency modulation period, assume a uniformly moving target is located at the range radar. At that location, the speed is The target echo, after being amplified by the receiver, mixed, filtered, and normalized, becomes the difference frequency signal. In the formula, the difference frequency signal mainly consists of three parts. The first term is the initial distance from the target. The first term, representing the time delay of the echo signal, is related to the phase term; the second term is the Doppler phase term caused by the target motion, which increases with slow time. The change in frequency will modulate the amplitude of the moving target's echo; the third term is the main body of the difference frequency signal, which can be regarded as having a center frequency of 100 Hz. A single-carrier frequency complex exponential signal; where Indicates a fast time. Indicates slow time. Indicates wavelength. Indicates wave speed.

[0011] Further, step S2 includes: ; In the formula, This represents the frequency after distance-dimensional Fourier transform processing. Since the Fourier transform operation is equivalent to adding a rectangular window to the signal, the spectrum of the difference frequency signal has the shape of the Sink function, with the spectral peak located at... .

[0012] Further, step S3 includes: In the formula, Equivalent to distance, Doppler frequency Equivalent to velocity, the target's range-Doppler frequency domain two-dimensional spectrum is obtained through two-dimensional FFT operations.

[0013] Further, step S5 includes: To address the issue of local interference in the echo substrate, a damping coefficient is set to make the noise substrate of the echo signal flat at different distance segments, so that it does not affect the target detection in subsequent distance segments; When the radar's operating environment changes, false target echo learning is performed again, and a new damping coefficient is set to enable the radar to adapt to different operating environments.

[0014] Further, step S6 includes: Frequency-modulated continuous wave radar observes target scenarios. After learning from false target echoes using damping coefficients and joint detection with multiple thresholds, it uses frequency domain constant false alarm rate detection to find pseudo-target points in different distance frequency domain bands. The target position is obtained by associating it with data from the preceding and following frames.

[0015] Step S7 includes: For the target motion For targets smaller than one distance unit, the two-dimensional spectrum of the echo signal is further simplified for processing: The formula calculates the target distance and speed: .

[0016] Compared with the prior art, the present invention has the following advantages: 1. This invention enables high-precision distance and velocity measurement in complex working environments by learning the echoes of false targets in targetless scenarios to eliminate the influence of strong interference, targeting different radar operating scenarios.

[0017] 2. This invention is applicable to relatively complex working scenarios, and the method involves little computation, making it easy to apply to practical engineering projects. Attached Figure Description

[0018] Figure 1 This is a flowchart of a frequency-modulated continuous wave radar measurement method based on false target echo learning according to the present invention; Figure 2 This is a block diagram illustrating the constant false alarm rate (CFAR) detection principle of the present invention. Figure 3 Two-dimensional frequency domain echo signal diagram of frequency-modulated continuous wave radar with interference in a targetless scene; Figure 4 Two-dimensional frequency domain echo signal diagram of frequency-modulated continuous wave radar in a targetless scene after interference removal; Figure 5 Two-dimensional frequency domain echo signal diagram of frequency modulated continuous wave radar with interference in a target scene; Figure 6 Frequency domain echo signal diagram of a frequency-modulated continuous wave radar with a target scene after interference removal. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and by providing a detailed description of a preferred embodiment.

[0020] like Figure 1 As shown, a frequency-modulated continuous wave radar measurement method based on false target echo learning includes the following steps: Step S1: The frequency-modulated continuous wave radar dechirps the echo signal reflected from the target to obtain the difference frequency echo signal. Step S2: Perform a distance-dimensional Fourier transform on the difference frequency echo signal to obtain a distance-dimensional frequency domain velocity-dimensional time domain echo signal; Step S3: After coherent accumulation of the distance-dimensional frequency domain echo signal and velocity-dimensional time domain echo signal, velocity-dimensional Fourier processing is performed to obtain a two-dimensional frequency domain echo signal. Step S4: The frequency-modulated continuous wave radar observes the actual scene without targets and sets corresponding fixed detection signal-to-noise ratio thresholds for different distance segments; Step S5: After multiple tests, an empirical value for the damping coefficient is set to eliminate the impact of local interference on target detection. Step S6: The frequency-modulated continuous wave radar observes the target scene, and after learning the false target echo using the damping coefficient and joint detection with multiple thresholds, the target position is obtained through the constant false alarm rate detection method. Step S7: Calculate the target's distance and speed.

[0021] In step S1: Assuming the radar transmits a signal as follows: In the formula, For carrier frequency, For frequency modulation slope, The bandwidth of the transmitted linear frequency modulated signal. Given the frequency modulation period, assume a uniformly moving target is located at the range radar. At that location, the speed is The target echo is then amplified by the receiver. Indicates a fast time. Indicates slow time. Indicates wavelength. Representing wave velocity, the difference frequency signal after normalization following mixing and filtering: In the formula, the difference frequency signal mainly consists of three parts. The first term is the initial distance from the target. The first term, representing the time delay of the echo signal, is related to the phase term; the second term is the Doppler phase term caused by the target motion, which increases with slow time. The change in frequency will modulate the amplitude of the moving target's echo; the third term is the main body of the difference frequency signal, which can be regarded as having a center frequency of 100 Hz. A single-carrier frequency complex exponential signal.

[0022] Step S2 includes: ; In the formula, This represents the frequency after the distance is processed by the FFT. Since the Fourier transform operation is equivalent to adding a rectangular window to the signal, the spectrum of the difference frequency signal follows the shape of the Sinkfeld function, with the spectral peak located at... .

[0023] Step S3 includes: In the formula, Equivalent to distance, Doppler frequency Equivalent to velocity, the target's range-Doppler frequency domain two-dimensional spectrum is obtained through two-dimensional FFT operations.

[0024] In step 4, the frequency-modulated continuous wave (FM-CVW) radar employs separate transmitting and receiving antennas. A frequency sensitivity control capacitor bank is typically added to the radar front-end to reduce the impact of transmitted signal leakage on receiver sensitivity. This causes the floor power of the FM-CVW radar echo signal to vary with distance. Furthermore, this radar operates at close range and is susceptible to near-field environmental factors; the actual floor noise power of the echo signal in a target-free environment varies. Figure 3 The image shows a two-dimensional frequency domain echo signal diagram of a frequency-modulated continuous wave radar with interference in a targetless scene. Therefore, the overall detection range is segmented in the frequency domain and different fixed intercept signal-to-noise ratio thresholds are set.

[0025] Step S5 includes: To address the issue of localized interference within the echo substrate, a damping coefficient is set to ensure a flat noise substrate in different range segments of the echo signal, preventing it from affecting target detection in subsequent range segments. Figure 4 The image shows the two-dimensional frequency domain echo signal of a continuous wave radar in a target-free scenario after interference removal, with the damping coefficient set. When the radar's operating environment changes, false target echo learning is performed again, and a new damping coefficient is set to enable the radar to adapt to different operating environments.

[0026] Step S6 includes: Frequency-modulated continuous wave radar observation of target scenarios. Figure 5 This diagram shows the two-dimensional frequency domain echo signal without a damping coefficient. As can be seen from the diagram, the two-dimensional echo spectrum of the frequency-modulated continuous wave radar is subject to interference, making it impossible to detect targets with high accuracy using the constant false alarm rate (CFAR) detection method. Figure 2 This is a schematic diagram of the horizontal false alarm detection method. After learning from the false target echo using the damping coefficient and joint detection with multiple thresholds, constant false alarm rate (CFAR) detection in the frequency domain is used to find the target point at different distance frequency bands; the target position is obtained by correlation processing with the data of the preceding and following frames. Figure 6 The image shows the frequency domain echo signal of a frequency-modulated continuous wave radar with a target scene after interference has been removed. The interference around the target scene has been removed.

[0027] Step S7 includes: For the target motion For targets smaller than one distance unit, the two-dimensional spectrum of the echo signal is further simplified for processing: The formula calculates the target distance and speed: .

[0028] In summary, this invention provides a frequency-modulated continuous wave radar measurement method based on false target echo learning. It addresses different radar operating scenarios by learning the echoes of false targets in targetless scenarios to eliminate the impact of strong interference. This invention is applicable to relatively complex operating scenarios, and the method has low computational complexity, making it easy to apply in practical engineering.

[0029] It should be noted that, in the embodiments of the present invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the embodiments. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0031] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A frequency-modulated continuous wave radar measurement method based on false target echo learning, characterized by, The method comprises the following steps: Step S1, a frequency-modulated continuous wave radar linearly demodulates a target reflected echo signal to obtain a difference frequency echo signal; Step S2, a distance dimension Fourier transform is performed on the difference frequency echo signal to obtain a distance dimension frequency domain speed dimension time domain echo signal; Step S3, after coherent accumulation of the distance dimension frequency domain speed dimension time domain echo signal, a speed dimension Fourier transform is performed to obtain a two-dimensional frequency domain echo signal; Step S4, the frequency-modulated continuous wave radar observes a target-free actual scene, and sets a corresponding fixed detection signal-to-noise ratio threshold in different distance segments; Step S5, an empirical value of a damping coefficient is set for local interference existing in the echo signal; Step S6, the frequency-modulated continuous wave radar observes a target scene, and after false target echo learning with a damping coefficient and multi-threshold joint detection, a target position is obtained through a constant false alarm detection method; Step S7, a target distance and speed are calculated.

2. The false target echo learning based frequency modulated continuous wave radar measurement method of claim 1, wherein, In the step S1, the step S2 comprises: Assume the radar transmits a signal As follows: wherein is the carrier frequency, is the frequency modulation slope, is the bandwidth of the transmitted chirp, is the frequency modulation period, assuming a uniformly moving target at a distance of from the radar with a velocity of The target echo after the receiver amplification, mixing and filtering, and the normalized difference frequency signal is: In the equation, the difference frequency signal is mainly composed of three parts, the first term is the phase term related to the initial distance of the target , representing the time delay of the echo signal; the second term is the Doppler phase term caused by the target motion, which will be modulated by the Doppler frequency as the slow time changes; the third term is the main body of the difference frequency signal, which can be regarded as a single carrier frequency complex exponential signal with the center frequency of ; wherein represents the fast time, represents the slow time, represents the wavelength, represents the wave speed.

3. The false target echo learning based frequency modulated continuous wave radar measurement method of claim 2, wherein, In the step S2, the step S3 comprises: ； In the formula, represents the frequency after distance dimension Fourier processing. Since the Fourier transform operation is equivalent to adding a rectangular window to the signal, the frequency spectrum of the difference frequency signal is in the shape of a sinc function, and the spectrum peak is located at .

4. The false target echo learning-based frequency-modulated continuous wave radar measurement method of claim 3, wherein, In the step S3, the step S5 comprises: In the formula, Equivalent to the distance, Doppler frequency Equivalent to the velocity, after two-dimensional FFT operation, the target's range-Doppler frequency domain two-dimensional spectrum is obtained. 5.The false target echo learning based frequency-modulated continuous wave radar measurement method of claim 1, wherein, For the problem of local interference existing in an echo base, a damping coefficient is set to make the echo signal have a flat noise base in different distance segments, so that the echo signal does not affect subsequent target detection in the distance segments; When the radar working environment is changed, false target echo learning is performed again, a new damping coefficient is set, and the radar is adapted to different working environments. In the step S6, the step S6 comprises: 6.The false target echo learning based frequency-modulated continuous wave radar measurement method of claim 1, wherein, The frequency-modulated continuous wave radar observes a target scene, and after false target echo learning with a damping coefficient and multi-threshold joint detection, a target position is obtained through a constant false alarm detection method. In the step S6, the step S6 comprises: In the step S7, the step S7 comprises:

7. The false target echo learning based frequency modulated continuous wave radar measurement method of claim 1, wherein, In the step S7, the step S7 comprises: For target motion For targets smaller than one range cell, the echo signal two-dimensional spectrum further simplifies processing: In the step S7, the step S7 comprises: 。

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