CN109085568B - Frequency modulation continuous wave multi-target detection method based on secondary frequency mixing - Google Patents
Frequency modulation continuous wave multi-target detection method based on secondary frequency mixing Download PDFInfo
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Abstract
The invention provides a frequency-modulated continuous wave multi-target detection method based on secondary frequency mixing, and belongs to the field of frequency-modulated continuous wave radar detection. The method mainly comprises the steps of firstly mixing radar echo and a transmitting signal to obtain a baseband signal, then mixing up and down frequency bands of the baseband signal, obtaining the speed of a first moving target and a radial distance parameter relative to the radar through Fourier transform, signal compensation and other modes, then filtering the moving target through a band elimination filter, multiplying the moving target by an inverse signal of the motion compensation signal to correct the moving target into an original baseband signal, and solving parameters of other targets in the same mode until no obvious target exists in a frequency spectrum. The method solves the coupling problem of speed-distance of a plurality of moving targets, realizes accurate measurement of target distance and speed, and can realize accurate detection of the plurality of moving targets by using the monocycle triangular wave on the premise of not increasing the complexity of the system.
Description
Technical Field
The invention belongs to the field of frequency modulated continuous wave radar detection, and particularly relates to a frequency modulated continuous wave multi-target detection method based on secondary frequency mixing.
Background
The linear frequency modulation continuous wave signal has a large bandwidth product, and a distance-speed coupling phenomenon exists when moving target detection is carried out, so that the moving target detection has deviation. In a multi-target environment, to accurately distinguish a plurality of targets, firstly, decoupling is carried out on echo signals, doppler frequency shift and distance difference frequency caused by target motion are separated, and then multi-target separation is carried out, so that multi-target detection is realized. Generally, symmetrical triangular frequency modulation continuous wave signals are adopted, and a triangular wave of each period is composed of two-section frequency modulation (namely, up/down frequency modulation) continuous wave signals of an up frequency band and a down frequency band, so that distance-speed decoupling of difference frequency signals can be realized, but in a multi-target environment, accurate matching of a plurality of spectral peaks of the up/down frequency bands is difficult to perform.
The traditional method adopts a multi-target identification method of a variable-period frequency modulation continuous wave radar, and real targets and false targets are distinguished through period change; or a method of estimating the target speed by combining fixed frequency with symmetrical triangular waves. In practical application, more time resources are occupied, the calculation amount is large, and the method is not suitable for occasions with high requirements of radar on data rate; and due to the inherent problem of high zero-frequency background noise of the frequency-modulated continuous wave radar system, the target is difficult to detect when the target speed is very low. Therefore, the traditional multi-target detection method cannot achieve the expected effect of accurately distinguishing a plurality of targets in the frequency modulation continuous wave radar detection.
Disclosure of Invention
The invention provides a frequency modulation continuous wave multi-target detection method based on secondary mixing, and aims to improve the frequency modulation continuous wave radar multi-target detection effect. The method adopts a symmetrical triangular wave frequency modulation continuous wave waveform, removes the problem of speed-distance coupling by mixing the baseband signals of the upper/lower frequency bands after mixing again, and can solve the speed of the target with the maximum echo energy according to the frequency of the maximum value in the frequency spectrum of the signals after mixing. And constructing a compensation function according to the target speed to obtain a one-dimensional range profile after motion compensation, thereby obtaining the distance of the target with the strongest echo energy. After the target with the strongest echo energy is detected, the remaining targets are sequentially detected by adopting a successive elimination method, so that the accurate detection of a plurality of moving targets is realized.
The invention relates to a frequency modulation continuous wave multi-target detection method based on secondary mixing, which mainly comprises the following steps:
step one, mixing a radar echo with a transmitting signal to obtain a baseband signal;
step two, mixing the up and down frequency bands of the baseband signal to obtain a first signal;
performing Fourier transform on the first signal to obtain a first frequency spectrum, judging whether the first frequency spectrum has an obvious target, and if so, continuing to execute backwards;
calculating the frequency of a sampling point corresponding to the maximum power value in the first frequency spectrum, and solving a target speed with the maximum echo energy according to the frequency;
fifthly, constructing a compensation signal capable of compensating the Doppler frequency shift of the moving target according to the target speed calculated in the fourth step, and multiplying the compensation signal by the up-down frequency band and the down-down frequency band of the baseband signal to obtain a second signal;
sixthly, performing Fourier transform on the second signal to obtain a second frequency spectrum;
step seven, calculating the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum, and calculating the radial distance between the target with the maximum echo energy and the radar according to the frequency;
step eight, constructing a band elimination filter, and filtering the second signal to obtain a third signal;
step nine, multiplying the third signal by the reciprocal of the compensation signal in the step five to obtain a fourth signal, mixing the up and down frequency bands of the fourth signal to obtain a new first signal, and repeatedly executing the steps three to eight until the first frequency spectrum does not have an obvious target;
the first frequency spectrum does not have obvious targets, and the corresponding power of all sampling points in the first frequency spectrum is lower than a threshold value, wherein the threshold value is a target echo power threshold under a corresponding detection scene, which is estimated according to radar parameters and system requirements.
Preferably, the compensation signal in the fifth step includes:
wherein, ± mu respectively represents the frequency modulation slope of the up and down frequency bands,
the speed of the ith target, c the speed of light, t the time,
is the doppler shift of the ith moving object.
Preferably, in the fifth step, multiplying the compensation signal by the up-down frequency band of the baseband signal to obtain a second signal includes:
and multiplying the compensation signal adopting the frequency modulation slope of the up-regulation frequency band by the up-regulation frequency band, and multiplying the compensation signal adopting the frequency modulation slope of the down-regulation frequency band by the down-regulation frequency band.
Preferably, in the sixth step, a part of the second signal in the fifth step is arbitrarily selected and subjected to fourier transform.
Preferably, the center frequency of the band-stop filter constructed in the step eight is the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum, and the stop band bandwidth is 1/8 to 1/12 of the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum.
The frequency modulation continuous wave multi-target detection method based on secondary frequency mixing obtains a baseband signal after radar echo frequency mixing, frequency mixing is carried out on the up/down frequency bands of the baseband signal again, the range difference frequency is removed, doppler frequency shift is reserved, the speed-range coupling problem is solved, and the speed of a target with the strongest echo energy is obtained according to a frequency spectrum after secondary frequency mixing. And constructing a motion compensation function according to the target speed, and obtaining a one-dimensional range profile after Doppler compensation of an up/down frequency band in the original echo, thereby obtaining the distance of the target with the strongest echo energy. When the target with the strongest echo energy is detected, the remaining targets are sequentially detected by adopting a successive elimination method. According to the method, the problem of speed-distance coupling is solved, the accurate measurement of the target distance and speed is realized, and the accurate detection of a plurality of moving targets can be realized by using the monocycle triangular wave on the premise of not increasing the complexity of the system.
Drawings
Fig. 1 is a flow chart of a preferred embodiment of a frequency modulated continuous wave multi-target detection method based on secondary mixing according to the present invention.
Fig. 2 is a schematic diagram of a multi-cycle triangular waveform according to the embodiment of the invention shown in fig. 1.
FIG. 3 is a first spectrum diagram illustrating processing of the first target according to the embodiment of FIG. 1.
FIG. 4 is a diagram of a second spectrum when processing the first target according to the embodiment of FIG. 1.
FIG. 5 is a diagram illustrating a first spectrum when processing a second target according to the embodiment of the invention shown in FIG. 1.
FIG. 6 is a diagram of a second spectrum when processing a second target according to the embodiment of the invention shown in FIG. 1.
Detailed Description
In order to make the implementation objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in the embodiments of the present invention. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are illustrative of some, but not all embodiments of the invention. The embodiments described below with reference to the accompanying drawings are illustrative and intended to explain the present invention and should not be construed as limiting the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
The invention provides a frequency-modulated continuous wave multi-target detection method based on secondary frequency mixing, which mainly comprises the following steps as shown in figure 1:
step one, mixing a radar echo with a transmitting signal to obtain a baseband signal;
step two, mixing the up and down frequency bands of the baseband signal to obtain a first signal;
performing Fourier transform on the first signal to obtain a first frequency spectrum, judging whether the first frequency spectrum has an obvious target, and if so, continuing to execute backwards;
calculating the frequency of a sampling point corresponding to the maximum power value in the first frequency spectrum, and solving a target speed with the maximum echo energy according to the frequency;
fifthly, constructing a compensation signal capable of compensating the Doppler frequency shift of the moving target according to the target speed calculated in the fourth step, and multiplying the compensation signal by the up-down frequency band and the down-down frequency band of the baseband signal to obtain a second signal;
sixthly, performing Fourier transform on the second signal to obtain a second frequency spectrum;
step seven, calculating the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum, and calculating the radial distance between the target with the maximum echo energy and the radar according to the frequency;
step eight, constructing a band elimination filter, and filtering the second signal to obtain a third signal;
step nine, multiplying the third signal by the reciprocal of the compensation signal in the step five to obtain a fourth signal, mixing the up and down frequency bands of the fourth signal to obtain a new first signal, and repeatedly executing the steps three to eight until the first frequency spectrum does not have an obvious target;
the first frequency spectrum does not have obvious targets, and the corresponding power of all sampling points in the first frequency spectrum is lower than a threshold value, wherein the threshold value is a target echo power threshold under a corresponding detection scene, which is estimated according to radar parameters and system requirements.
The respective steps are explained in detail below.
The transmitting signal adopts a symmetrical triangular waveform, and the waveform schematic diagram is shown in figure 2; setting a scene for detecting two uniform motion targets.
In the step 1, the received echo signal and the transmitting signal are mixed to obtain a baseband signal
Wherein s is R+ (t) and s R- (t) baseband time domain signals of up/down frequency bands, mu is the frequency modulation slope,
is a target i position time delay, r i And v i Respectively the initial distance and speed (uniform speed), f, of the target i di For moving objects i Doppler shift, C i J is the amplitude of the echo of the target in imaginary units.
In said step 2, up/down frequency band is divided intoThe band signals are mixed again to obtain the mixed signal, i.e. the first signal S mix_2 (t)：
In step 3, FFT transformation is performed on the first signal after the second mixing, and fig. 3 shows a spectrogram after FFT transformation, and as can be seen from the graph, except for two real targets (target numbers 1 and 2), two false targets (target numbers 1 'and 2') occur due to mutual coupling between target echoes, and the power is greater than 50dB. The doppler frequency shift of the target (target 1) with the maximum energy, which is the position of the maximum energy, is found from the frequency spectrum, and the velocity of the target can be calculated
In this embodiment, it is necessary to determine whether the first spectrum has an obvious target in this step, if so, the step is executed further backward, the speed of all targets and the radial distance from the radar are calculated, and if not, it is determined that the radar coverage area has no target or no other target, and the subsequent step is not necessary to be executed.
If a significant target is found, in step five, the speed is determined
The motion compensated signal is constructed (up/down frequency band chirp rate is opposite),
wherein, ± mu respectively represents the frequency modulation slope of the up and down frequency bands,
the speed of the ith target, c the speed of light, t the time,
is the doppler shift of the ith moving object.
Multiplying the formula (4) with baseband up/down frequency band signals respectively to obtain g 1± (t)＝s R± (t)·s com1 (t) the base band signal at this time has a speed of
The Doppler shift in the echo signal of target 1 is compensated for, leaving only the range difference frequency f (r) i ) The single-frequency sinusoidal signal of (a), and the echoes of other targets are still chirp signals;
then, fourier transform is carried out to calculate g 1± (t) frequency spectrum G 1 (f) As shown in FIG. 4, the position of the maximum value is searched for, i.e., the corresponding distance difference frequency f (r) i ) Thus obtaining the moving speed
The distance of the target 1 from the radar; it will be appreciated that when performing the fourier transform described above, a portion of the second signal in step five may be arbitrarily selected for calculation.
In step 8, the above-mentioned target that has participated in the calculation and output the speed and distance information needs to be filtered out, so as to perform the calculation and output of the next target, and for this reason, a band-stop filter needs to be constructed, in this embodiment, the center frequency of the constructed band-stop filter is the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum, and the bandwidth of the stop band is 1/8 to 1/12, for example, 1/10, of the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum, as shown in fig. 5. The range frequency difference and doppler shift of the target 1 in the baseband echo are now all compensated.
By the above process, the speed in the baseband is
Target 1 is filtered out. For the next object, it is first necessary to multiply the filtered signal by the motion compensated signalThe inverse signal is corrected to be an original baseband signal, then the frequency mixing of up and down frequency bands is carried out on the corrected original baseband signal, the steps 3-8 are repeated, and the rest targets (speed and distance parameters) are output.
In this embodiment, the inverse of the motion compensated signal is
In this embodiment, until no significant target is detected. Fig. 6 shows a diagram of echo spectra after two repetitions of cancellation, from which it can be seen that the maximum is much lower than the echo energy of the target (fig. 3), and no target is considered to be apparent.
Finally, it should be pointed out that: the above examples are only for illustrating the technical solutions of the present invention, and are not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (4)
1. A frequency modulation continuous wave multi-target detection method based on secondary frequency mixing is characterized by comprising the following steps:
step one, mixing a radar echo with a transmitting signal to obtain a baseband signal;
step two, mixing the up and down frequency bands of the baseband signal to obtain a first signal;
performing Fourier transform on the first signal to obtain a first frequency spectrum, judging whether the first frequency spectrum has an obvious target, and if so, continuing to execute backwards;
calculating the frequency of a sampling point corresponding to the maximum power value in the first frequency spectrum, and solving a target speed with the maximum echo energy according to the frequency;
step five, constructing a compensation signal capable of compensating the Doppler frequency shift of the moving target according to the target speed calculated in the step four, and multiplying the compensation signal with the up and down frequency bands of the baseband signal to obtain a second signal, wherein the constructing of the compensation signal comprises the following steps:
wherein, ± mu respectively represents the frequency modulation slope of the up and down frequency bands,
the speed of the ith target, c the speed of light, t the time,
doppler frequency shift for the ith moving target;
sixthly, performing Fourier transform on the second signal to obtain a second frequency spectrum;
step seven, calculating the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum, and calculating the radial distance between the target with the maximum echo energy and the radar according to the frequency;
step eight, constructing a band-elimination filter, and filtering the second signal to obtain a third signal;
step nine, multiplying the third signal by the reciprocal of the compensation signal in the step five to obtain a fourth signal, mixing the up and down frequency bands of the fourth signal to obtain a new first signal, and repeatedly executing the steps three to eight until the first frequency spectrum does not have an obvious target;
the first frequency spectrum does not have obvious targets, and the corresponding power of all sampling points in the first frequency spectrum is lower than a threshold value, wherein the threshold value is a target echo power threshold under a corresponding detection scene, which is estimated according to radar parameters and system requirements.
2. A frequency modulated continuous wave multi-target detection method based on secondary mixing as claimed in claim 1, wherein in the fifth step, the step of multiplying the compensation signal by the up and down frequency bands of the baseband signal to obtain a second signal comprises:
and multiplying the compensation signal adopting the frequency modulation slope of the up-regulation frequency band by the up-regulation frequency band, and multiplying the compensation signal adopting the frequency modulation slope of the down-regulation frequency band by the down-regulation frequency band.
3. A frequency modulated continuous wave multi-target detection method based on secondary mixing as claimed in claim 2, characterized in that in the sixth step, a part of the second signal in the fifth step is arbitrarily selected to be fourier transformed.
4. A frequency modulated continuous wave multi-target detection method based on secondary mixing as claimed in claim 1, wherein the center frequency of the band-stop filter constructed in the eighth step is the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum, and the stop band bandwidth is 1/8-1/12 of the frequency of the sampling point corresponding to the maximum power value in the second frequency spectrum.
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