A MIMO radar multi-target speed measurement extension method

Abstract

The present invention discloses a MIMO radar multi-target speed measurement expansion method, comprising the following steps: step 1, establishing a MIMO radar system model; step 2, designing an FMCW waveform in combination with sawtooth wave and triangle wave characteristics, and transmitting the FMCW wave; step 3, performing 2D-FFT processing on the sawtooth wave echo signal to obtain the search center of different targets in the triangle wave distance dimension spectrum; step 4, finding the spectrum peak of the moving target in the triangle wave echo for pairing and then resolving the speed ambiguity; step 5, performing moving target DOA estimation. The present invention combines the characteristics of the traditional symmetrical triangle wave and the classic multi-cycle sawtooth wave to design an FMCW waveform that can more accurately extract target information, simplify the calculation, and obtain a good MIMO radar angular resolution. Under the condition of ensuring the target DOA estimation accuracy, the speed measurement upper limit is improved, and the multi-target speed measurement expansion is realized. Compared with the classic triangle wave or multi-cycle sawtooth wave method, the MIMO radar can achieve better performance in moving target speed measurement and positioning.

Description

Technical Field

[0001] The invention belongs to the technical field of millimeter wave radar signal processing, and in particular relates to a MIMO radar multi-target speed measurement extension method. Background Art

[0002] Millimeter-wave radar is increasingly used in traffic safety systems due to its advantages such as large bandwidth, small size and low cost. To improve the angular resolution, millimeter-wave radar widely uses multiple-input multiple-output (MIMO) technology. Speed ​​measurement range and angular resolution are key indicators of MIMO radar. Due to hardware performance limitations, the unambiguous speed of MIMO radar is often very low.

[0003] In order to solve the speed ambiguity of MIMO radar, a method of measuring speed by transmitting symmetrical triangular wave is proposed in the literature "Zhang, Rong-quan, et al." Analysis of ambiguity function of symmetrical triangular linear frequency modulation continuous wave signal." Acta Electronica Sinica 32.3 (2004): 353-356.", in which the moving target is paired in the upper and lower sweep echoes to solve the distance speed coupling. In order to improve the pairing accuracy, the method usually has a long transmission time of the frequency modulation signal, and a group of signals contains two slopes of upper and lower sweep frequency. The PRF of the radar is very low, and it is difficult to find the target through 2D-FFT, that is, the number of detected targets is limited; in the literature "Wojtkiewicz, Andrzej, et al." Two-dimensional signal processing in FMCWradars." Proc. XX KKTOiUE (1997): 475-480.", a method of measuring speed by transmitting staggered slope frequency modulation signal is proposed, and the speed ambiguity is solved by the Chinese remainder theorem. Since this method transmits frequency modulated signals with different slopes or different pulse repetition frequencies, if the echo of the transmitted signal is to be used for beamforming and measuring the target angle, complex phase compensation of the receiving antenna echo is required, which is not convenient for engineering practice. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and design an FMCW waveform that combines the characteristics of a traditional symmetrical triangle wave and a classic multi-period sawtooth wave. Under the condition of ensuring the accuracy of target DOA estimation, the MIMO radar can achieve better performance in moving target speed measurement and positioning.

[0005] The object of the present invention is to achieve the following technical solution: a MIMO radar multi-target speed measurement extension method, comprising the following steps:

[0006] Step 1, establish a MIMO radar system model: adopt a MIMO radar system model based on FMCW transmission waveform, including a radio frequency front end composed of a transmitting antenna, a receiving antenna, a power amplifier, a power divider and a mixer, and a back-end processing part composed of an FMCW waveform generator, a filter amplifier circuit, an A / D sampling circuit and a signal processing module; the FMCW waveform signal generated by the FMCW waveform generator is divided into two signals through a power divider, one signal is amplified by the power amplifier and radiated from the transmitting antenna, and the other signal is used as a local oscillator and mixed with the echo signal received by the receiving antenna in the mixer to obtain a beat signal, and the beat signal enters the signal processing module after passing through the filter amplifier circuit and the A / D sampling circuit in turn, and the distance and speed information of the target are extracted through the signal processing module;

[0007] Step 2: Design an FMCW waveform by combining the sawtooth wave and triangle wave characteristics, and transmit the FMCW waveform;

[0008] Step 3: Perform 2D-FFT processing on the sawtooth wave echo signal to obtain the search center of different targets in the triangular wave distance dimension spectrum;

[0009] Step 4: Find the spectral peak of the moving target in the triangle wave echo, match it, and resolve the velocity ambiguity;

[0010] Step 5: Estimate the DOA of the moving target.

[0011] Furthermore, the specific implementation method of step 2 is as follows: the FMCW waveform is two sets of identical triangle waves, and the waveform after the two sets of triangle waves is a sawtooth wave; the parameters of the MIMO radar system are:

[0012]

[0013]

[0014]

[0015] In the formula, Range max is the maximum measurement distance of the radar, f s is the radar transmission signal sampling rate, μ is the radar frequency modulation slope, and c is the speed of light; v t _acc is the speed corresponding to each unit frequency of the triangle wave, f s1 is the triangle wave sampling rate, N ADC1 is the number of triangle wave sampling points; N FFT is the number of Doppler FFT points, f0 is the carrier start frequency, PRF is the pulse repetition frequency, v s_acc is the velocity per unit frequency in the Doppler dimension of the sawtooth wave 2D-FFT graph;

[0016] The principle of designing the FMCW waveform is to increase the sawtooth wave PRF as much as possible while ensuring that the maximum measurement distance of the triangle wave and the sawtooth wave remains unchanged to meet the following requirements:

[0017]

[0018] in,

[0019] Furthermore, the specific implementation method of step 3 is as follows: after performing 2D-FFT processing on the sawtooth wave echo, the approximate distance of the target and multiple possible fuzzy speeds are obtained from the 2D-FFT graph, and the fuzzy speed is expressed as v s Indicates that the approximate position of the target in the triangular wave range-dimensional spectrum is determined by the approximate distance and multiple possible fuzzy speeds; the range-dimensional frequency point number corresponding to the known search center point is Range index Then, according to formula (5), the search center of different targets in the triangular wave distance dimension spectrum is calculated:

[0020]

[0021]

[0022] Where Range index_up and Range index_down are the center points of the distance dimension search windows of the upper and lower sweep echoes, N ADC2 is the number of sawtooth wave sampling points.

[0023] Furthermore, the specific implementation method of step 4 is: find the moving target in the range dimension search window of the upper and lower sweep echoes of the triangular wave, and pair the spectrum peaks of the moving target to obtain the decoupling speed v t , v t Represents the moving target velocity corresponding to the triangular wave search window; from all possible fuzzy velocities v s Select and v t The value with the smallest difference is taken as the measured speed v est .

[0024] Furthermore, the specific implementation method of step 5 is: phase compensation is performed on the echoes received by different transmitting antennas and DOA estimation is performed according to the following formula:

[0025]

[0026]

[0027] 0≤m≤N Tx-1,1≤n≤N Rx (9)

[0028] Where X(m,n) is the echo generated by the receiving antenna with serial number n receiving the transmitting antenna with serial number m+1, and X c (m,n) is the result after phase compensation, v r is the actual target speed, N Tx and N Rx are the number of transmitting antenna elements and receiving antenna elements respectively.

[0029] The beneficial effects of the present invention are as follows: the present invention proposes a MIMO radar multi-target speed measurement expansion method. Combining the characteristics of the traditional symmetrical triangle wave and the classic multi-cycle sawtooth wave, an FMCW waveform that can more accurately extract target information is designed, which simplifies the calculation and obtains a good MIMO radar angular resolution. Under the condition of ensuring the accuracy of target DOA estimation, the speed measurement upper limit is improved and the multi-target speed measurement expansion is realized. Compared with the classic triangle wave or multi-cycle sawtooth wave method, the MIMO radar can achieve better performance in moving target speed measurement and positioning, and has good engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the MIMO radar multi-target speed measurement expansion method of the present invention;

[0031] Figure 2 A schematic diagram of the working mechanism of the MIMO radar system model of the present invention;

[0032] Figure 3 Schematic diagram of a transmitting antenna unit and a receiving antenna unit of this embodiment;

[0033] Figure 4 It is a traditional FMCW symmetrical triangle wave waveform;

[0034] Figure 5 It is a classic multi-cycle sawtooth waveform;

[0035] Figure 6 FMCW waveform diagram designed for the present invention;

[0036] Figure 7 Simulated FMCW waveform designed for this embodiment;

[0037] Figure 8 2D-FFT image and CFAR detection results of moving targets during simulation;

[0038] Fig. 9 Schematic diagram of searching for target spectrum peaks in the distance dimension of the upper and lower sweep echoes of the triangle wave;

[0039] Fig.10This is a schematic diagram of the DOA estimation results of the moving target;

[0040] Fig.11 Schematic diagram of all moving target detection results in this embodiment. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0042] like Figure 1 As shown, a MIMO radar multi-target speed measurement expansion method of the present invention comprises the following steps:

[0043] Step 1: Establish a MIMO radar system model: Use a MIMO radar system model based on FMCW transmission waveform. The entire working mechanism is as follows: Figure 2 As shown, it includes a radio frequency front end consisting of a transmitting antenna, a receiving antenna, a power amplifier, a power divider and a mixer, and a back-end processing part consisting of an FMCW waveform generator, a filter amplifier circuit, an A / D sampling circuit and a signal processing module; the FMCW waveform signal generated by the FMCW waveform generator is divided into two signals by a power divider, one signal is amplified by the power amplifier and radiated from the transmitting antenna, and the other signal is used as a local oscillator and mixed with the echo signal received by the receiving antenna in the mixer to obtain a beat signal, the frequency of the beat signal is related to the distance and speed of the target, the beat signal passes through the filter amplifier circuit and the A / D sampling circuit in turn and enters the signal processing module, and the distance and speed information of the target are extracted through the signal processing module; for the convenience of analysis and description, this embodiment takes 2 transmitting antenna units and 4 receiving antenna units as an example for research, and the MIMO radar antenna model is as follows Figure 3 As shown. Assume that the antenna arrays are uniform linear arrays, consisting of two transmitting antenna elements Tx1 and Tx2 and four receiving antenna elements Rx1, Rx2, Rx3, and Rx4, where the spacing between the transmitting antenna elements is 2λ and the spacing between the receiving antenna elements is λ / 2. Assume that the mixing and sampling processes are completed by the radar hardware.

[0044] Step 2: Design an FMCW waveform by combining the sawtooth wave and triangle wave characteristics, and transmit the FMCW waveform;

[0045] The traditional FMCW symmetrical triangle wave waveform is as follows Figure 4 As shown, f0 is the carrier start frequency, f1 is the carrier maximum frequency, and f r is the frequency shift caused by the target with echo delay τ, and the Doppler frequency shift of the moving target is f d The moving target echo contains f r and f d The coupling is shown by the dotted line in the figure, and is calculated by formula (1):

[0046]

[0047] Where R is the distance between the moving target and the radar, v is the speed of the target, μ is the radar frequency modulation slope, and the speed of light is c.

[0048] The difference frequency between the transmitted signal and the received echo is usually called the beat. In the figure, the upper and lower sweep beats are f + and f - ,Right now

[0049]

[0050] By sweeping up the frequency difference f + and the down sweep frequency difference f - The distance and speed information of the moving target can be inversely solved by processing.

[0051]

[0052] The classic multi-cycle sawtooth waveform is as follows Figure 5 As shown, different transmitting antennas transmit frequency modulation signals with the same slope, and the target distance and speed can be solved by performing 2D-FFT processing on the moving target echo.

[0053] Without considering the fuzzy speed, the speed v range that the classic sawtooth wave MIMO radar can measure is:

[0054] -v max <v<v max (4)

[0055]

[0056] PRF is the pulse repetition frequency, T s is the frequency modulation period. Due to the limitation of radar hardware, PRF has an upper limit. When the target moves too fast, spectrum overlap will occur in the Doppler dimension. The target speed measured at this time is usually called fuzzy speed.

[0057] Combining the characteristics of triangle wave and sawtooth wave, the present invention designs a FMCW waveform, such as Figure 6 As shown in the figure, the FMCW waveform is two sets of identical triangle waves, and the waveform after the two sets of triangle waves is a sawtooth wave; this can cancel the up-sweep and down-sweep echo signals in the time domain, thereby reducing the impact of stationary targets. The waveform parameters of the FMCW waveform can be used for radar positioning, speed measurement and other functions. The parameters of the MIMO radar system are:

[0058]

[0059]

[0060]

[0061] In the formula, Range max is the maximum measurement distance of the radar, f s is the radar transmission signal sampling rate; v t _acc is the speed corresponding to each unit frequency of the triangle wave, f s1 is the triangle wave sampling rate, N ADC1 is the number of triangle wave sampling points; N FFT is the number of Doppler FFT points, f0 is the carrier start frequency, v s _acc is the velocity per unit frequency in the Doppler dimension of the sawtooth wave 2D-FFT graph;

[0062] The principle of designing the FMCW waveform is to increase the sawtooth wave PRF as much as possible while ensuring that the maximum measurement distance of the triangle wave and the sawtooth wave remains unchanged to meet the following requirements:

[0063]

[0064] The simulated FMCW waveform designed in this embodiment is as follows Figure 7 As shown, the simulation parameters of the FMCW waveform are shown in Table 1. Multiple point targets are set in the simulation scene, including 3 moving targets and 2 static targets. The information parameters of the targets are shown in Table 2.

[0065] Table 1

[0066] parameter value parameter value <![CDATA[f0]]> 77GHz <![CDATA[T 1+ ,T 1- ]]> 1024us <![CDATA[T i1 ]]> 12us <![CDATA[T1]]> 1036us <![CDATA[μ1]]> 2.993MHz / us <![CDATA[μ2]]> 6.25MHz / us <![CDATA[N ADC1 ]]> 3072 <![CDATA[N ADC2 ]]> 256 <![CDATA[T d ]]> 40.96us <![CDATA[T i2 ]]> 9.04us <![CDATA[T2]]> 50us <![CDATA[N chirps ]]> 128

[0067] Table 2

[0068] Target number x(m) y(m) speed(m / s) 1 8 30 0 2 -12 60 -40 3 8 70 0 4 0.1 70 15 5 3.5 100 30

[0069] Step 3: Perform 2D-FFT processing on the sawtooth wave echo signal and obtain the search center of different targets in the triangular wave distance dimension spectrum; the specific implementation method is: after performing 2D-FFT processing on the echo signal obtained by the transmitted sawtooth wave, a 2D-FFT diagram is obtained, such as Figure 8 As shown in (a), in the figure, the vertical axis Range Index is the frequency point number, and the horizontal axis DopplerIndex is the Doppler frequency point number. In the 2D-FFT graph, CFAR is used to detect the approximate distance and multiple possible fuzzy speeds of the moving target. The fuzzy speed is expressed as v s Represented by, and the approximate position of the target in the triangular wave distance dimension spectrum is determined by the approximate distance and multiple possible fuzzy speeds. The result is as follows Figure 8 (b) as shown.

[0070] In this embodiment, three moving targets are detected, and their coordinate numbers are (34,172), (48,121), and (59,106), respectively. The format is (Doppler index ,Range index ). Taking the moving target at (34,172) as an example, the range of the moving target in the sawtooth wave 2D-FFT graph is index =172 Substitute into formula (11) and calculate the search center of the target in the triangular wave distance dimension spectrum:

[0071]

[0072]

[0073] Where Range index_up and Range index_down are the center points of the distance dimension search windows of the upper and lower sweep echoes, N ADC2 is the number of sawtooth wave sampling points.

[0074] Step 4: Find the spectral peaks of the moving target in the triangular wave echo, pair them, and then resolve the velocity ambiguity. The specific implementation method is: find the moving target in the distance dimension search window of the upper and lower sweep frequency echoes of the triangular wave obtained in formula (11), and pair the spectral peaks of the moving target, such as Fig. 9 As shown in the figure, (a) is the search in the upper sweep echo, and (b) is the search in the lower sweep echo. In the figure, Magnitude represents the amplitude, Range MTI up represents the range-dimensional spectrum after the upper sweep beat cancellation, and Range MTI down represents the range-dimensional spectrum after the lower sweep beat cancellation. The target is searched at 2067 and 1038 in the range dimension of the upper and lower sweep echoes. The decoupling speed v can be obtained by formula (3): t , v t Indicates the speed of the moving target corresponding to the triangle wave search window.

[0075]

[0076] Due to errors in pairing and other reasons, the speed measured by the triangle wave is often not accurate enough. t _acc>v s _acc, the sawtooth wave speed measurement accuracy is higher than the triangle wave, from all possible fuzzy speeds v s Select and v t The value with the smallest difference is taken as the measured speed v est .

[0077] The possible speeds in the sawtooth wave 2D-FFT plot are

[0078] v s=-48.02;-28.57;-9.11;10.33;30.08;49.23(m / s) (13)

[0079] In formula (13), v s =30.08 (m / s) is closest to v t , then the measured speed v est =30.08(m / s).

[0080] Step 5: Estimation of DOA of moving targets. The specific implementation method is: According to formula (14), phase compensation is performed on the echoes received by different transmitting antennas and DOA estimation is performed. The result is as follows: Fig.10 As shown in the figure, Angle represents the azimuth. If the accurate target speed is measured, the phase compensation between the transmitting antennas will be more accurate, and the MIMO radar DOA estimation can ensure accuracy.

[0081]

[0082]

[0083] 0≤m≤1,1≤n≤4 (16)

[0084] Where X(m,n) is the echo generated by the receiving antenna with serial number n receiving the transmitting antenna with serial number m+1, and X c (m,n) is the result after phase compensation, v r is the actual target speed, N Tx and N Rx are the number of transmitting antenna elements and receiving antenna elements respectively.

[0085] The results of using the classic sawtooth wave and the FMCW waveform designed by the present invention are compared. Fig.10 As shown in (a) and (b), the DOA estimation angles are 7.29° (sawtooth wave) and 1.90°, respectively, and the measurement speeds are v est =10.33(m / s)(sawtooth wave) and v est =30.08 (m / s), indicating that the FMCW waveform designed by the present invention has better angle and speed measurement effects than the sawtooth waveform.

[0086] The above steps are performed on all moving targets, and the distance, direction and speed information of the three moving targets are obtained as follows: Fig.11As shown, they are (3.32, 99.96, 30.38), (0, 69.81, 14.89), (-12.00, 59.64, -40.42), and the coordinate format is (x(m), y(m), speed(m / s)). Through simulation, it can be verified that the multi-target speed measurement extension method proposed in the present invention can efficiently realize multi-target positioning and speed measurement, and improve the speed measurement upper limit while ensuring the accuracy of DOA estimation.

[0087] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A MIMO radar multi-target speed measurement extension method, characterized in that: The following steps are involved: Step 1: Establish a MIMO radar system model: Use a MIMO radar system model based on FMCW transmission waveform, including the RF front end consisting of a transmitting antenna, a receiving antenna, a power amplifier, a power divider and a mixer, and the back end processing part consisting of an FMCW waveform generator, a filter amplifier circuit, an A / D sampling circuit and a signal processing module; The FMCW waveform signal generated by the FMCW waveform generator is divided into two signals through a power divider. One signal is amplified by a power amplifier and radiated from the transmitting antenna. The other signal is used as a local oscillator and mixed with the echo signal received by the receiving antenna in a mixer to obtain a beat signal. The beat signal passes through the filter amplifier circuit and the A / D sampling circuit in turn and enters the signal processing module. The signal processing module extracts the distance and speed information of the target. Step 2: Design the FMCW waveform by combining the sawtooth wave and triangle wave characteristics, and transmit the FMCW wave; Step 3: Perform 2D-FFT processing on the sawtooth wave echo signal to obtain the search center of different targets in the triangular wave distance dimension spectrum; Step 4: Find the spectral peak of the moving target in the triangle wave echo, match it, and resolve the velocity ambiguity; Step 5: Estimate the DOA of the moving target.

2. A MIMO radar multi-target speed measurement extension method according to claim 1, characterized in that: The specific implementation method of step 2 is: the FMCW waveform is two sets of identical triangle waves, and the waveform after the two sets of triangle waves is a sawtooth wave; the parameters of the MIMO radar system are: In the formula, Range max is the maximum measurement distance of the radar, f s is the radar transmission signal sampling rate, μ is the radar frequency modulation slope, and c is the speed of light; v t _acc is the speed corresponding to each unit frequency of the triangle wave, f s1 is the triangle wave sampling rate, N ADC1 is the number of triangle wave sampling points; N FFT is the number of Doppler FFT points, f0 is the carrier start frequency, PRF is the pulse repetition frequency, v s _acc is the velocity per unit frequency in the Doppler dimension of the sawtooth wave 2D-FFT graph; The principle of designing the FMCW waveform is to increase the sawtooth wave PRF as much as possible while ensuring that the maximum measurement distance of the triangle wave and the sawtooth wave remains unchanged to meet the following requirements: in, 3. The MIMO radar multi-target speed measurement extension method according to claim 1, characterized in that: The specific implementation method of step 3 is as follows: after performing 2D-FFT processing on the sawtooth wave echo, the approximate distance of the target and multiple possible fuzzy speeds are obtained from the 2D-FFT graph, and the fuzzy speed is expressed as v s Indicates that the approximate position of the target in the triangular wave range-dimensional spectrum is determined by the approximate distance and multiple possible fuzzy speeds; the range-dimensional frequency point number corresponding to the known search center point is Range index Then, according to formula (5), the search center of different targets in the triangular wave distance dimension spectrum is calculated: Where Range index_up and Range index_down are the center points of the distance dimension search windows of the upper and lower sweep echoes, N ADC2 is the number of sawtooth wave sampling points.

4. A MIMO radar multi-target speed measurement extension method according to claim 3, characterized in that: The specific implementation method of step 4 is: find the moving target in the range dimension search window of the upper and lower sweep echoes of the triangular wave, and pair the spectrum peaks of the moving target to obtain the decoupling speed v t , v t Represents the moving target velocity corresponding to the triangular wave search window; from all possible fuzzy velocities v s Select and v t The value with the smallest difference is taken as the measured speed v est .

5. The MIMO radar multi-target speed measurement extension method according to claim 1, characterized in that: The specific implementation method of step 5 is: perform phase compensation on the echoes received by different transmitting antennas and perform DOA estimation according to the following formula: 0≤m≤N Tx -1,1≤n≤N Rx (9) Where X(m,n) is the echo generated by the receiving antenna with serial number n receiving the transmitting antenna with serial number m+1, and X c (m,n) is the result after phase compensation, v r is the actual target speed, N Tx and N Rx are the number of transmitting antenna elements and receiving antenna elements respectively.

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