A millimeter wave radar multi-target behavior perception multipath elimination method

Abstract

The application relates to a millimeter wave radar multi-target behavior sensing multi-path elimination method, relates to the technical field of radar multi-path elimination, and aims to solve the problem that, in the prior art, in the case of multi-target human body detection, too many targets exist and interfere with each other, thereby affecting the detection accuracy. The application utilizes the characteristics of ordered statistics, effectively suppresses and eliminates multi-path interference and clutter, thereby solving the problem that, in the case of multi-target human body detection, too many targets exist and interfere with each other, thereby affecting the detection accuracy. Meanwhile, the application further verifies multi-path elimination through a coherence coefficient, thereby improving the robustness of the method. The method can effectively improve the target detection and tracking performance of a radar system, and has high practical value for behavior sensing and other applications.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radar multipath elimination, in particular to a millimeter wave radar multi-target behavior perception multipath elimination method. BACKGROUND

[0002] Radar as a substitute sensing method for recognizing human posture has been proven to be successful in human posture recognition and has received more and more attention in civil fields. It can not only be applied in the fields of the elderly and hospitals, but also has great application prospects in prevention and control, security check, and smart home scenarios. In an indoor environment, radar detection has better comfort than wearable devices, and avoids the situation that the alarm is not timely due to forgetting to wear the device when the old people fall down. In addition, compared with computer vision detection, radar detection is not sensitive to light and obstacles, and privacy leakage is avoided.

[0003] In the application of millimeter wave radar-based vital sign detection, multi-target human detection has exploration value. In the case of multi-target human life detection, due to too many targets, interference exists between them, which affects the detection accuracy. For example, in the application of a family, there is a problem of separating multiple human bodies. Only when the target separation problem under multiple targets is handled well, and the multipath interference of millimeter wave radar in multi-target recognition is suppressed, can the application scenarios of millimeter wave radar-based vital sign detection be further expanded, and the foundation for the specific application of the millimeter wave vital sign detection system is laid. SUMMARY

[0004] The purpose of the present application is to solve the problem in the prior art that in the case of multi-target human detection, due to too many targets, interference exists between them, which affects the detection accuracy. A millimeter wave radar multi-target behavior perception multipath elimination method is proposed.

[0005] The technical scheme adopted by the present application to solve the above technical problem is:

[0006] A millimeter wave radar multi-target behavior perception multipath elimination method, comprising the following steps:

[0007] Step 1: Obtain the RD spectrum of the millimeter wave radar echo signal, and according to the RD spectrum and using the selected sorting constant false alarm detection, the number of targets is obtained, and then according to the size of the indoor space, the motion area of the target is evenly divided;

[0008] Step 2: For a target motion area, according to the motion area of the target, the energy maximum point is selected by spectrum peak search, which is determined as the real target, and is taken as the position of the current observation frame, and then according to the RD spectrum, the distance of the real target in the current motion area from the radar is obtained, and the inverse Fourier transform of the distance dimension where the real target is located in the RD spectrum is performed to obtain the micro-Doppler information of the target Finally, among the targets in the indoor space, the target with a distance to the radar smaller than the distance of the current target to the radar is obtained, and the micro-Doppler information of the target is obtained According to And The correlation coefficient r1 is obtained

[0009] Step three: for each real target, the distance to the radar of the highest point in the previous n frames is obtained, and the distance to the radar is sorted, and then the maximum value y in the sorting is removed min And the minimum value y max , and finally the mean value is taken to obtain the reference position y of the target mean , wherein n≥2;

[0010] Step four: the maximum detection speed v of the radar is obtained max , and the motion distance range X is obtained according to the frame time Tc configured by the radar pre_scope ;

[0011] Step five: according to the position y of the current observation frame n+1 And the reference position y mean , the displacement difference Δy is obtained, which is expressed as:

[0012] Δy=y n+1 -y mean

[0013] If Δy is greater than X pre_scope , the multi-path information in the RD spectrum is set to zero, and step six is executed, otherwise, it is ended, and the next frame is processed;

[0014] Step six: re-perform spectrum peak search to select the point with the maximum energy, update the position of the current observation frame, and then obtain the reset micro-Doppler information After that, among the targets in the indoor space, the target with a distance to the radar smaller than the distance of the current target to the radar is obtained, and the micro-Doppler information of the target is obtained According to And The correlation coefficient r2 is obtained

[0015] Step seven: if |r2|>|r1|, step eight is executed, otherwise, the multi-path elimination is completed;

[0016] Step eight: the position of the current observation frame and the positions of other targets in the motion region are set to zero, and spectrum peak search is performed again in the motion region of the target, so as to update the position of the current observation frame in step five, and repeat steps five and six to obtain the correlation coefficient r2', and take r2' as r2 to repeat step seven until the multi-path elimination is completed.

[0017] Further, the reference position ymean is expressed as:

[0018]

[0019] wherein y i represents the distance of the i-th frame target from the radar.

[0020] Further, the motion distance range X pre_scope is expressed as:

[0021] X pre_scope = v max · n / 2 · Tc.

[0022] Further, the specific step of setting the multi-path information in the RD spectrum to zero in step five is:

[0023] with the position y n+1 of the current observation frame as the center, the energy of the four distance gates close to the radar and far from the radar is set to zero.

[0024] Further, the real target distance from the radar is obtained according to the distance information in the RD spectrum, and the step of obtaining the distance information in the RD spectrum is:

[0025] Step 1: Obtain the center frequency of the intermediate frequency signal, and the center frequency of the intermediate frequency signal is expressed as:

[0026]

[0027] wherein c represents the speed of electromagnetic wave propagation in the air, c = 3 × 10 8 m / s, R represents the distance of the target from the radar, S represents the signal frequency modulation slope, and τ represents the time delay of the received signal relative to the transmitted signal;

[0028] Step 2: Obtain the distance information in the RD spectrum according to the center frequency of the intermediate frequency signal, and the distance information in the RD spectrum is expressed as:

[0029]

[0030] Further, the intermediate frequency signal is obtained by the following steps:

[0031] First, the transmitted signal of the radar is expressed as:

[0032] s T (t) = exp(j2π(f o t + 0.5St 2 ))

[0033] After the transmitted signal of the radar is reflected by the target, the received signal obtained, and the received signal is expressed as:

[0034] sR (t) = exp(j2pi(f o (t-τ) + 0.5S(t-τ) 2 ))

[0035] Wherein, f o Indicate signal carrier frequency, S indicates signal frequency modulation slope, t indicates transmission time, j indicates imaginary unit;

[0036] Finally, according to the transmitting signal and the received signal, the intermediate frequency signal is obtained.

[0037] Further, the radar maximum detection speed v max By the following steps:

[0038] The received signal is subjected to speed dimension FFT, and the speed of the target is obtained, and the speed of the target is represented as:

[0039]

[0040] Wherein, T indicates movement time, Indicate the phase difference of the transmitting signal and the received signal, and λ indicates the wavelength of electromagnetic wave; when The radar maximum detection speed v max The radar maximum detection speed v max Is represented as:

[0041]

[0042] Further, the RD spectrum of the millimeter wave radar echo signal is obtained by the following steps:

[0043] The time domain signal of the received signal is obtained, the time domain signal is read and framed, and the distance dimension FFT and the speed dimension FFT are performed on each frame signal after framing, to obtain the spatial distribution of multiple targets and the speed information of multiple targets, i.e. RD spectrum.

[0044] Further, the radar is a linear frequency modulation continuous wave radar, i.e. LFMCW.

[0045] Further, the n is 4.

[0046] The beneficial effects of the present application are:

[0047] The present application utilizes the characteristics of ordered statistics, effectively suppresses and eliminates multipath interference and clutter, and further solves the problem that in the case of multi-target human life detection, due to too many targets, interference exists between targets, and further affects the detection accuracy. Meanwhile, the present application further verifies the multipath elimination through the coherence coefficient, improves the robustness of the method. The method can effectively improve the target detection and tracking performance of the radar system, and has high practical value for behavior perception and other applications. Attached Figure Description

[0048] Figure 1 This is the overall flowchart of this application;

[0049] Figure 2 This is a schematic diagram illustrating the multipath phenomenon of targets in dual-target walking detection.

[0050] Figure 3 This is a schematic diagram illustrating the multipath suppression effect of the coherence coefficient method.

[0051] Figure 4 This is a schematic diagram illustrating the suppression effect of the multipath suppression method in this application. Detailed Implementation

[0052] It should be noted that, where there is no conflict, the various embodiments disclosed in this application can be combined with each other.

[0053] Specific implementation method one: Refer to Figure 1 This embodiment describes a multipath cancellation method for multi-target behavior sensing using millimeter-wave radar, comprising the following steps:

[0054] Step 1: Obtain the RD spectrum of the millimeter-wave radar echo signal. Based on the RD spectrum and using selection sort constant false alarm rate detection, obtain the number of targets. Then, divide the target movement area into equal parts according to the size of the indoor space.

[0055] Step 2: For a target's moving region, perform a spectral peak search to select the point with the highest energy within the moving region. This point is identified as the true target and used as its position in the current observation frame. Then, based on the RD spectrum, obtain the distance between the true target and the radar in the current moving region. Perform an inverse Fourier transform on the distance dimension of the true target in the RD spectrum to obtain the target's micro-Doppler information. Finally, among the targets in the indoor space, those whose distance from the radar is less than the current distance from the radar are acquired, and their micro-Doppler information is obtained. according to and The correlation coefficient r1 was obtained;

[0056] Step 3: For each real target, obtain the distance from the radar to the point with the highest energy in the previous n frames, sort the distances to the radar, and then remove the maximum value y from the sorted list. min and minimum value y max Finally, the average value is taken to obtain the reference position y of the target. mean where n≥2;

[0057] Step 4: Obtain the radar's maximum detection speed v max, and according to the radar configuration, each frame time Tc, the motion distance range X is obtained pre_scope ;

[0058] Step five: according to the position y of the current observation frame n+1 and the reference position y mean , the displacement difference Δy is obtained, which is expressed as:

[0059] Δy = y n+1 - y mean

[0060] If Δy is greater than X pre_scope , the multipath information in the RD spectrum is set to zero, and step six is executed, otherwise, it is ended, and the next frame is processed;

[0061] Step six: re-perform spectrum peak search to select the point with the maximum energy, update the position of the current observation frame, and further obtain the reset micro-Doppler information Then, among the targets in the indoor space, the target with a distance from the radar less than the distance of the current target from the radar is obtained, and the micro-Doppler information of the target is obtained According to and , the correlation coefficient r2 is obtained;

[0062] Step seven: if |r2| > |r1|, step eight is executed, otherwise, the multipath elimination is completed;

[0063] Step eight: set the position of the current observation frame and the positions of other targets in the motion region to zero, and re-perform spectrum peak search in the motion region of the target, thereby updating the position of the current observation frame in step five, and repeating steps five and six to obtain the correlation coefficient r2' and take r2' as r2 to repeat step seven until the multipath elimination is completed.

[0064] The present application is aimed at the problem in the prior art that in the case of multi-target human life detection, due to too many targets, interference exists between the targets, thereby affecting the detection accuracy. Figure 2 As shown in FIG. 1, it is a target multipath phenomenon in double-target walking detection.

[0065] The present application has two stages:

[0066] Stage one, target detection based on echo energy

[0067] The transmission signal of the LFMCW radar can be expressed as:

[0068] s T (t) = exp(j2π(f o t + 0.5St 2 )) (1)

[0069] where fo f is the signal carrier frequency, S is the signal frequency modulation slope, t is the transmission time, and j is the imaginary unit.

[0070] After the target reflection, the received signal is obtained:

[0071] s R (t) = exp(j2π(f o (t-τ) + 0.5S(t-τ) 2 )) (2)

[0072] where f o is the signal carrier frequency, S is the signal frequency modulation slope, t is the transmission time, and j is the imaginary unit, τ is the time delay of the received signal relative to the transmitted signal.

[0073] The intermediate frequency signal is obtained by the transmitted signal and the received signal.

[0074] Step one, distance estimation

[0075] The center frequency of the intermediate frequency signal is:

[0076]

[0077] where c = 3 x 10 8 m / s represents the speed of electromagnetic wave propagation in the air. R represents the distance between the target and the radar, v represents the target speed, and λ represents the wavelength of the electromagnetic wave.

[0078] The human body motion target considered in this application moves relatively slowly, so the Doppler shift generated is relatively weak. If the influence of the Doppler shift on the intermediate frequency signal frequency is ignored, the intermediate frequency signal frequency of the moving target can be approximately represented as:

[0079]

[0080] Therefore, the distance of the target can be represented as:

[0081]

[0082] In this application, the radar may detect multiple targets at different distances, and due to different time delays, the receiving end will correspondingly generate multiple intermediate frequency signals with different frequencies.

[0083] Step two, speed estimation, and the speed of the target can be obtained by doing a speed dimension FFT on the echo pulse of formula (2):

[0084]

[0085] where T is the motion time, is the phase difference between the transmitted signal and the received signal

[0086] Step 3, Maximum Detection Speed

[0087] When measuring speed using the phase difference of two consecutive frequency-modulated waves, if the phase difference does not meet the requirements... This will result in blurriness, therefore, when using it, this condition must be met: when | The maximum detection speed can be obtained:

[0088]

[0089] Therefore, there is a maximum detection speed used in millimeter-wave radar detection. From the steps described above, multiple targets in space can be detected based on radar echoes, and their distance and velocity information relative to the radar can be obtained. The maximum detection speed can then be determined based on the velocity information.

[0090] Step 4: Calculate the RD spectrum of the echo.

[0091] Based on the received signal, the time-domain signal is read and segmented into frames to obtain time-domain information with a certain resolution and continuity. Each frame is windowed and subjected to an FFT to obtain its frequency-domain information. For the FFT result of each frame, its instantaneous power spectral density (i.e., amplitude squared) and the time position of the instantaneous peak in each frequency band are calculated. The time positions of the instantaneous peaks and their corresponding frequency bands are plotted as a 2D image, which is the RD spectrum.

[0092] The RD spectrum can display the position information of the real target in the current frame, as well as the Doppler information at each position.

[0093] Phase Two: Inter-frame tracking based on ordered statistics and multipath suppression based on Doppler coherence coefficients

[0094] Step 1: Determine the location of multiple targets. Starting from the unprocessed data, the number of targets is obtained using the RD spectrum and by selecting and sorting constant false alarm rate (CFAR) detection. Then, based on the size of the indoor space, the target movement areas are evenly divided.

[0095] The point with the highest energy is selected by spectral peak search based on the region, and it is determined to be the real target. The RD spectrum includes the target's distance information from the radar. The RD spectrum is processed to obtain the distance of the real target from the radar in each target's movement area. An inverse Fourier transform is performed on the distance dimension of the real target in the RD spectrum to obtain the target's micro-Doppler information. The distance of each real target to the radar and its micro-Doppler information are recorded. Finally, targets whose distance to the radar is less than the current target's distance to the radar are identified, and their micro-Doppler information is obtained. according to and The correlation coefficient r1 is obtained.

[0096] However, the target extracted at this time may be a false multipath target, so multipath decision needs to be performed.

[0097] Step two involves using statistically based inter-frame tracking to determine if it is multipath propagation. The radar's echo signal-to-noise ratio decreases with distance from the radar. Compared to the real target, multipath propagation closer to the radar can affect the identification of the real target.

[0098] For each real target, obtain the distance from the radar to the point with the highest energy in the previous n frames, sort them, and remove the closest point y. min and the farthest distance y max The average of the intermediate distances is used to obtain the reference position y of the target. mean .

[0099] Where n≥2.

[0100]

[0101] The average difference between this mean and the current frame is N = n / 2 frames, with Tc time per frame, y i Let represent the distance between the target and the radar in the i-th frame, and let be the maximum radar detection velocity obtained from equation (7). That is, the range of movement distance

[0102] X pre_scope =v max ·n / 2·Tc (9)

[0103] Where n is the total number of selected forward tracking records, v max Tc represents the maximum detection speed of the radar, and Tc represents the frame time configured for the radar.

[0104] Calculate whether the current frame is within the actual reachable motion range.

[0105] Δy=y n+1 -y mean (10)

[0106] Among them, y n+1 y represents the position of the current observation frame. mean As a reference position, if Δy is greater than X pre_scope This indicates that the current frame's position information is multipath information, not true information, and the multipath information in the RD spectrum will be set to zero (based on the multipath position y). n+1 Centered on the radar, the energy of the four range gates (closest and furthest from the radar) is set to zero. A new spectral peak search is performed to select the point with the highest energy, updating the position of the current observation frame, thereby obtaining the reset micro-Doppler information. Repeat step one to obtain the correlation coefficient r2.

[0107] Therefore, to eliminate the information of the close position of the multipath on the RD chart, the target search is re-performed to search for the real target.

[0108] Step three, if |r2|>|r1|, then repeat step two to update the position of the current observation frame, otherwise, the multipath elimination is effective and the multipath elimination is completed.

[0109] The Doppler coherence coefficient is used to detect the multipath suppression effect. The coherence coefficient is usually applied to the feature recognition of different types of targets by radar. In the present application, the Doppler information carried by the multipath signal has a strong correlation with the Doppler information of the real target generating the multipath, and the Doppler information of the posture also has correlation between different individuals. However, the coherence coefficient of the multipath and the real target generating the multipath is larger.

[0110] Therefore, the Doppler correlation coefficient is used as an index for testing the multipath suppression effect. It is tested whether the coherence coefficient is reduced before and after the multipath elimination. If the coherence coefficient after the multipath elimination is greater than the coherence coefficient before the multipath elimination, the multipath elimination has omissions and needs to be re-performed in step two. If the coherence coefficient after the multipath elimination is less than the coherence coefficient before the multipath elimination, the multipath elimination is effective. Note that the coherence coefficient here is the absolute value of the coherence coefficient.

[0111] Embodiment:

[0112] The effect of multipath elimination is displayed by the real measurement of the walking of two targets to show the multipath suppression effect of the present application.

[0113] The radar working parameters are set as follows: the radar starting frequency is 60 GHZ, the frequency modulation bandwidth is 2.1 GHZ, the frame time is 36 ms, the maximum detection speed is 8.9 m / s, the distance gate size is 7 cm, the detection frame is the 22nd frame, and the forward tracking frame number is 4 frames.

[0114] The steps of the present application are as follows:

[0115] (1) The position of target 1 is displayed at the 13th distance gate, each distance gate is 7 cm, which is 0.84 m, the position of target 2 is at the 49th distance gate, which is 3.37 m, and the cross-correlation coefficient r1 of the two is 0.9422;

[0116] (2) The position of target 2 in the 21st frame is at the 76th distance gate, the position of target 2 in the 20th frame is at the 54th distance gate, the position of target 2 in the 19th frame is at the 79th distance gate, and the position of target 2 in the 18th frame is at the 79th distance gate;

[0117] (3) The data is sorted from small to large as follows: 54, 76, 79, 79;

[0118] (4) The extreme minimum value and the extreme maximum value are removed, and the average value y is taken mean77.5;

[0119] (5) At this time, the average value and the current 22 frame position distance, by formula (9) is Δy = 77.5-49 = 28.9;

[0120] (6) Using formula (8), the motion range at this time, X pre_scope is 9.15 distance gates;

[0121] (7) At this time, Δy>X pre_scope , it is judged that this time is multipath;

[0122] (8) Eliminate the current position information, and re-search the spectrum peak;

[0123] (9) At this time, the updated position information is 81 distance gates, and at this time Δy = 81-77.5 = 3.5;

[0124] (10) At this time ΔyX pre_scope , and at this time the coherence coefficient is r2 = 0.7657 < r1;

[0125] (11) At this time, the multipath is correctly eliminated.

[0126] Effect comparison: compared with the single coherence coefficient multipath suppression method, the application is suitable for multi-target indoor attitude recognition perception; the multipath interference can be accurately eliminated, and the real target position information can be obtained. The multipath suppression effect of the prior art is as shown in Figure 3 , and the multipath suppression effect of the application is as shown in Figure 4 .

[0127] It should be noted that the specific embodiments are only an explanation and description of the technical solutions of the application, and cannot limit the protection scope. Any partial change according to the claims and the specification of the application shall still fall within the protection scope of the application.

Claims

1. A multipath cancellation method for multi-target behavior sensing in millimeter-wave radar, characterized in that... Includes the following steps: Step 1: Obtain the RD spectrum of the millimeter-wave radar echo signal. Based on the RD spectrum and using selection sort constant false alarm rate detection, obtain the number of targets. Then, divide the target movement area into equal parts according to the size of the indoor space. Step 2: For a target's moving region, perform a spectral peak search to select the point with the highest energy within the moving region. This point is identified as the true target and used as its position in the current observation frame. Then, based on the RD spectrum, obtain the distance between the true target and the radar in the current moving region. Perform an inverse Fourier transform on the distance dimension of the true target in the RD spectrum to obtain the target's micro-Doppler information. Finally, among the targets in the indoor space, those whose distance from the radar is less than the current distance from the radar are acquired, and their micro-Doppler information is obtained. according to and The correlation coefficient r1 was obtained; Step 3: For each real target, obtain the distance from the radar to the point with the highest energy in the previous n frames, sort the distances to the radar, and then remove the maximum value y from the sorted list. min and minimum value y max Finally, the average value is taken to obtain the reference position y of the target. mean where n≥2; Step 4: Obtain the radar's maximum detection speed v max And based on the time Tc of each frame configured by the radar, the range of motion X is obtained. pre_scope ; Step 5: Based on the current observation frame position y n+1 and reference position y mean The displacement difference Δy is obtained, and Δy is expressed as: Δy = y n+1 -y mean If Δy is greater than X pre_scope If the multipath information in the RD spectrum is zeroed, then step six is ​​executed; otherwise, the process ends and the next frame is processed. Step Six: Re-perform the spectral peak search, select the point with the highest energy, update the position of the current observation frame, and thus obtain the reset microDoppler information. Next, targets within the indoor space whose distance from the radar is less than the current target's distance from the radar are acquired, and their micro-Doppler information is obtained. according to and The correlation coefficient r² was obtained; Step 7: If |r2| > |r1|, then proceed to step 8; otherwise, complete multipath elimination. Step 8: Set the position of the current observation frame and the positions of other targets within the moving area to zero, and re-perform the spectral peak search in the moving area of ​​the target to update the position of the current observation frame in Step 5. Repeat Step 5 and Step 6 to obtain the correlation coefficient r2' and use r2' as r2 to repeat Step 7 until multipath elimination is completed.

2. The multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 1, characterized in that... The reference position y mean Represented as: Among them, y i This represents the distance between the target and the radar in the i-th frame.

3. The multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 2, characterized in that... The range of movement distance X pre_scope Represented as: X pre_scope =v max ·n / 2·Tc。 4. The multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 3, characterized in that... The specific steps for setting the multipath information in the RD spectrum to zero in step five are as follows: At the current observation frame position y n+1 Centered on the radar, the energy of the four range gates, one near the radar and one far from the radar, is set to zero.

5. The multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 4, characterized in that... The actual target distance from the radar is obtained based on the range information in the RD spectrum. The steps for obtaining the range information in the RD spectrum are as follows: Step 1: Obtain the center frequency of the intermediate frequency (IF) signal. The center frequency of the IF signal is expressed as: Where c represents the speed of electromagnetic wave propagation in the air, c = 3 × 10 8 m / s, R represents the distance between the target and the radar, S represents the signal frequency modulation slope, and τ represents the time delay of the received signal relative to the transmitted signal; Step 2: Obtain the distance information in the RD spectrum based on the center frequency of the intermediate frequency signal. The distance information in the RD spectrum is represented as follows:

6. The multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 5, characterized in that... The intermediate frequency signal is obtained through the following steps: First, the radar's transmitted signal is represented as: s T (t)=exp(j2π(f o t+0.5St 2 )) The received signal obtained after the radar's transmitted signal is reflected by the target is represented as follows: s R (t)=exp(j2π(f o (t-τ)+0.5S(t-τ) 2 )) Among them, f o The signal carrier frequency is represented by S, the frequency modulation slope is represented by t, the transmission time is represented by j, and the imaginary unit is represented by j. Finally, the intermediate frequency signal is obtained based on the transmitted and received signals.

7. The multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 6, characterized in that... The radar's maximum detection speed v max It is obtained through the following steps: Perform a velocity-dimensional FFT on the received signal to obtain the target's velocity, which is expressed as: Where T represents the motion time. The phase difference between the transmitted and received signals is represented by λ, where λ represents the wavelength of the electromagnetic wave. when The maximum detection speed v of the radar is obtained. max Radar maximum detection speed v max Represented as:

8. The multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 7, characterized in that... The RD spectrum of the millimeter-wave radar echo signal is obtained through the following steps: The time-domain signal of the received signal is acquired, the time-domain signal is read and segmented into frames, and the range dimension FFT and velocity dimension FFT are performed on each frame of the signal after segmentation to obtain the spatial distribution of multiple targets and the velocity information of multiple targets, i.e., the RD spectrum.

9. A multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 8, characterized in that... The radar is a linear frequency modulated continuous wave radar, i.e., LFMCW.

10. A multipath cancellation method for multi-target behavior sensing in millimeter-wave radar according to claim 9, characterized in that... The value of n is 4.

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