CN114252873B - Method and system for accurately estimating acceleration of millimeter wave radar target in real time - Google Patents
Method and system for accurately estimating acceleration of millimeter wave radar target in real time Download PDFInfo
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Abstract
The invention provides a millimeter wave radar target acceleration accurate real-time estimation method and a system thereof, the method comprises the steps of continuously transmitting a plurality of linear frequency modulation signals by using a millimeter wave radar, acquiring corresponding target echo signals through a receiving end of the millimeter wave radar, carrying out frequency mixing, low-pass filtering and distance FFT processing on the received target echo signals and transmission reference signals, carrying out time-frequency signal conversion on the target echo signals of different periods in the same distance, acquiring the Doppler conversion rate of the signals, and acquiring the real-time values of the speeds or accelerations of a plurality of target signals according to a self-adaptive multi-target instantaneous acceleration extraction algorithm, so that the accelerated or decelerated moving target signals can be accurately predicted. By applying the method and the device, the instantaneous acceleration of the automatic driving millimeter wave radar target can be accurately measured in real time, so that the problem of inaccurate position prediction of the acceleration target in the automatic driving path planning process is solved.
Description
Technical Field
The invention relates to the technical field of automatic driving safety assistance, in particular to a millimeter wave radar target acceleration accurate real-time estimation method and a system applying the method.
Background
With the popularization of private automobiles in China, the more serious urban traffic jam and the longer time for common salary people to drive vehicles in daily life, automatic driving has gradually become the inevitable choice for future automobile driving. The automatic driving comprises four core links of perception, cognition, planning and control, but the core in the core technology is perception technology, because the acquisition of perception information of complete and real-time driving environment and other targets is a necessary condition for the success of the automatic driving. If there are serious deficits in perception, automatic driving loses its automatic function even with perfect cognitive, planning and control techniques. The automatic driving perception is realized by sensors such as a main image collector, a millimeter wave radar, a laser radar and the like. The millimeter wave radar is mainly used for detecting and measuring a moving target, and moving target acceleration information has important significance in automatic driving path planning.
In the automatic driving perception technology, the millimeter wave radar is mainly used for detecting and measuring a moving target and is used for subsequent automatic driving path planning. Parameters that require measurement of important moving objects include object distance, position, doppler frequency or velocity, and even object acceleration. However, the existing automatic driving millimeter wave radar basically does not measure the acceleration of the target, or the existing millimeter wave radar system considers that the acceleration of the target is zero, so that the acceleration information of the target cannot be given.
Therefore, the problems of the prior art include the following:
1. at present, basically all the best automotive millimeter wave radars can only measure four-dimensional information of a target and an environment, namely three-dimensional position and speed, and cannot give a measured value of instantaneous acceleration of the target. There is evidence that many recent autodrive crashes are associated with unpredictable locations for other accelerated start vehicles.
2. Although the speed of a moving target in many automatic driving environments, such as a starting or accelerating vehicle, is not high, the acceleration is large, so that great deviation is brought to the position prediction of the target vehicle under a complex environment in automatic driving, and therefore, potential safety hazards are brought to path planning after automatic driving.
3. The millimeter wave radar of the existing automatic driving system cannot provide target acceleration, not because the acceleration is not important, and mainly no good measuring method exists. In theory, acceleration can be measured by the rate of change of velocity, but since the measurement time is too long, the acceleration values obtained are not only inaccurate, but also meaningless since the time is too long. Therefore, a new method for accurately measuring the instantaneous acceleration of the target in real time is required in the modern automatic driving millimeter wave radar.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a method and a system for accurately estimating the acceleration of a millimeter wave radar target in real time.
In order to solve the problems, the technical scheme adopted by the invention is as follows:
a method for accurately estimating the acceleration of a millimeter wave radar target in real time comprises the following steps: continuously transmitting a plurality of linear frequency modulation signals by using a millimeter wave radar, and collecting corresponding target echo signals through a receiving end of the millimeter wave radar; carrying out frequency mixing, low-pass filtering and distance FFT processing on the received target echo signal and the transmitting reference signal; the method comprises the steps of carrying out time-frequency signal conversion on target echo signals in different periods at the same distance to obtain the Doppler conversion rate of the signals, and obtaining the speed or real-time value of the acceleration of a plurality of target signals according to a self-adaptive multi-target instantaneous acceleration extraction algorithm, so that the accelerated or decelerated moving target signals can be accurately predicted.
The further scheme is that the method for continuously transmitting a plurality of linear frequency modulation signals by using the millimeter wave radar and acquiring corresponding target echo signals by a receiving end comprises the following steps: in a working period of the millimeter wave radar, continuously transmitting M linear frequency modulation signals through the millimeter wave radar, wherein the transmission waveform is defined as formula (1):
x 1 (t)＝sin[2π(f c +kt)t+φ 1 ][u(t)-u(t-T)] (1)
wherein f is c Is the transmit carrier modulation frequency, k is the chirp rate of the chirp signal, u (t) is the unit step function;
assuming that there is a target at the distance R, the resulting target echo signal is expressed as formula (2):
x 2 (t)＝Asin[2π(f c +kt-kτ)(t-τ)+φ 1 ][u(t-τ)-u(t-T)] (2)
wherein the content of the first and second substances,
in a further aspect, the mixing, low-pass filtering and range FFT processing the received target echo signal and the transmitted reference signal includes: after receiving the target echo signal, mixing the target echo signal with a transmitting frequency modulation reference signal, outputting low-pass filtering, and obtaining a frequency signal related to the target distance, wherein the frequency signal is expressed as a formula (4):
x(t)＝Asin(2πf 0 t+φ 0 )[u(t-τ)-u(t-T)] (4)
wherein the frequency of the output signal is f 0 K τ, which is FFT processed, the output frequency thereof is proportional to the target distance.
In a further aspect, the mixing, low-pass filtering, and range FFT processing the received target echo signal and the transmission reference signal include: judging whether the moving target has the acceleration B, if so, the instantaneous speed of the moving target is the formula (9):
v(t)＝v 0 +Bt (9)
the distance function of the respective target is formula (10):
therefore, when a moving target signal including the acceleration B is mixed and output to be low-pass filtered, a frequency signal related to the target distance is output as the following formula (11):
where h is the linear doppler shift rate, expressed as equation (12):
in a further aspect, the performing time-frequency signal transformation on target echo signals of different periods at the same distance includes: after the signals are subjected to frequency mixing, low-pass filtering and distance FFT processing, sampling output data points at a selected distance; selecting two-dimensional grid points of time and frequency of output data point time-frequency signal transformation; calculating the Wigner distribution function values of all frequency two-dimensional grid points; selecting a two-dimensional time-frequency low-pass function, and calculating two-dimensional function values of the two-dimensional grid points of all frequencies; and performing two-dimensional non-periodic convolution on the calculated Wigner distribution function value and the two-dimensional function value of the frequency two-dimensional grid point, outputting a time-frequency transformation result of the echo signal at the selected distance point, and generating a radar target signal time-frequency distribution graph.
In a further aspect, the performing time-frequency signal transformation on target echo signals of different periods at the same distance includes: selecting modified Wigner distribution transformation for target echo signals of different periods at the same distance to perform time-frequency signal transformation, assuming that the input echo signal is x (t), and defining the Wigner distribution transformation as a formula (13):
further, the radar target signal analysis is performed by using the modified wigner distribution transform as shown in formula (14):
where Φ (t, f) is the kernel function.
In a further aspect, the obtaining real-time values of a plurality of target signal speeds or accelerations according to an adaptive multi-target instantaneous acceleration extraction algorithm includes: randomly selecting a time point t on the acquired radar target signal time-frequency distribution diagram 1 Searching the maximum value points of all the time-frequency images at the time point; selecting a different time point t on the time-frequency distribution diagram of the radar target signal 2 Searching the maximum value points of all the time-frequency images at the time point; selecting t 1 And t 2 The maximum points of (a) are fitted to the following linear curve, represented by equation (17):
f-k 0 t＝f 0 (17)
wherein k is 0 ,f 0 Is a curve parameter which is uniquely determined by two selected maximum value points; and (4) clearing the pixel of the position of the fitted linear curve in the time-frequency image, simultaneously clearing all the two pixels attached to each curve pixel, and calculating the information entropy of the cleaned time-frequency image.
According to a further scheme, in a curve formed by combining all two maximum value points, the two maximum value points are selected to minimize the information entropy of the cleaned time-frequency imageIf the resulting curve parameter value is k 0 And f 0 Then the starting Doppler frequency of the radar moving target is f 0 The Doppler change rate of the target is k 0 Acceleration of k 0 Lambda; and repeating the steps by applying the cleaned time-frequency image until the Doppler change rate and the acceleration of all other moving targets are obtained and the information entropy after cleaning is not reduced any more.
Therefore, the method can measure the instantaneous acceleration values of a plurality of targets in real time through data acquisition, real-time high-speed time-frequency conversion, self-adaptive multi-target instantaneous acceleration extraction and other processing, so as to achieve the conversion of instantaneous tracking acceleration; the accuracy of the measured target acceleration value is high, and real-time acceleration can be provided for planning and using an automatic driving path; the method has no special requirements on the hardware environment of the radar, is mainly realized by signal processing algorithm software, and has low implementation cost.
In addition, the invention provides a brand-new method for accurately measuring the acceleration of the target of the millimeter wave radar in real time, which can be used for the automatic driving millimeter wave radar, and is also suitable for estimating the acceleration of the ground moving target of an airborne radar, the acceleration of the ground moving target of an unmanned aerial vehicle, the acceleration of the sea surface or water surface target of a ship-borne radar, and the acceleration of the monitoring target of the internet of things based on a millimeter wave radar sensor.
A millimeter wave radar target acceleration accurate real-time estimation system is applied to the millimeter wave radar target acceleration accurate real-time estimation method to realize moving target detection and interference suppression, and comprises a target acceleration estimation unit, a target acceleration estimation unit and a target acceleration estimation unit; the signal receiving and transmitting unit is used for continuously transmitting a plurality of linear frequency modulation signals by using a millimeter wave radar and acquiring corresponding target echo signals through a receiving end of the signal receiving and transmitting unit; the processing unit is used for carrying out frequency mixing, low-pass filtering and distance FFT processing on the received target echo signal and the transmitting reference signal; and the output result unit is used for carrying out time-frequency signal conversion on the target echo signals of different periods in the same distance, acquiring the Doppler conversion rate of the signals, and acquiring the real-time values of the speeds or accelerations of a plurality of target signals according to the self-adaptive multi-target instantaneous acceleration extraction algorithm, so that the accelerated or decelerated moving target signals can be accurately predicted.
Therefore, the invention realizes the accurate estimation of the moving target acceleration through the target acceleration real-time estimation system consisting of the signal transceiving unit, the processing unit and the output result unit, can calculate the real-time planning acceleration, realizes the low-delay and high-accuracy acceleration estimation, further realizes the coupling planning of the automatic driving path and the acceleration, can meet the processing of complex working conditions, and simultaneously improves the platform adaptability and the safety performance of functions.
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Drawings
Fig. 1 is a block diagram of a flow chart of an embodiment of a method for accurately estimating acceleration of a millimeter-wave radar target in real time according to the present invention.
FIG. 2 is a schematic waveform diagram of M chirp signals transmitted by a millimeter wave radar in an embodiment of a method for accurately estimating the acceleration of a millimeter wave radar target in real time according to the present invention.
Fig. 3 is a schematic diagram of an output signal after frequency mixing and low-pass filtering of a target echo signal in an embodiment of a method for accurately estimating acceleration of a millimeter wave radar target in real time according to the present invention.
FIG. 4 is a schematic diagram of target distance and Doppler/velocity information extraction in an embodiment of a method for accurately estimating acceleration of a millimeter wave radar target in real time according to the present invention.
FIG. 5 is a schematic diagram of time-frequency signal transformation and Doppler transformation rate acquisition of echo signals in different periods at the same distance in an embodiment of a method for accurate real-time estimation of acceleration of a millimeter wave radar target according to the present invention.
FIG. 6 is a schematic diagram illustrating a principle of a maximum value point identification method in an embodiment of a method for accurately estimating acceleration of a millimeter wave radar target in real time according to the present invention.
FIG. 7 is a schematic waveform diagram of a moving target signal collected by a millimeter wave radar in an embodiment of a method for accurately estimating acceleration of a millimeter wave radar target in real time according to the present invention.
FIG. 8 is a schematic diagram illustrating a result of FFT processing of a moving target signal acquired by a millimeter wave radar in an embodiment of a method for accurately estimating acceleration of a millimeter wave radar target in real time according to the present invention.
FIG. 9 is a diagram illustrating results of radar signal time-frequency analysis implemented using modified Wigner distribution transform in an embodiment of a method for accurate real-time estimation of millimeter wave radar target acceleration according to the present invention.
FIG. 10 is a schematic diagram of a radar signal time-frequency distribution image after removing a uniform-velocity moving target signal in an embodiment of a method for accurately estimating acceleration of a millimeter wave radar target in real time according to the present invention.
FIG. 11 is a schematic diagram of a radar signal time-frequency distribution image after removing a uniform motion target and a deceleration target signal in an embodiment of a method for accurately estimating acceleration of a millimeter wave radar target in real time according to the present invention.
FIG. 12 is a flowchart illustrating data acquisition and preprocessing performed by a millimeter wave radar in an embodiment of the method for accurately estimating acceleration of a millimeter wave radar target in real time according to the present invention.
FIG. 13 is a flowchart of time-frequency transformation of radar target signals in an embodiment of a method for accurate real-time estimation of millimeter wave radar target acceleration according to the present invention.
FIG. 14 is a flowchart of an adaptive multi-target instantaneous acceleration extraction algorithm in an embodiment of a millimeter wave radar target acceleration accurate real-time estimation method of the invention.
Detailed Description
The embodiment of the method for accurately estimating the acceleration of the millimeter wave radar target in real time comprises the following steps:
referring to fig. 1, a method for accurately estimating acceleration of a millimeter wave radar target in real time executes the following steps when predicting speed or acceleration of a moving target:
first, step S1 is executed to continuously transmit a plurality of chirp signals using a millimeter wave radar, and collect corresponding target echo signals through a receiving end thereof.
Next, step S2 is executed to perform mixing, low-pass filtering, and range FFT processing on the received target echo signal and the transmitted reference signal.
Then, step S3 is executed to perform time-frequency signal transformation on the target echo signals of different periods in the same distance, so as to obtain the doppler transformation ratio of the signals, and obtain the real-time values of the speeds or accelerations of multiple target signals according to the adaptive multi-target instantaneous acceleration extraction algorithm, so as to accurately predict the moving target signals with acceleration or deceleration.
In the above step S1, the autopilot radar of the present embodiment is a general Frequency Modulated Continuous Wave (FMCW) radar, and M Chirp signals (as shown in fig. 2) (also called Chirp signals, where the time width of a single signal is T and the bandwidth is B) are continuously transmitted by the millimeter wave radar in the working cycle of the millimeter wave radar as shown in fig. 12, and the transmission waveform thereof is defined as formula (1):
x 1 (t)＝sin[2π(f c +kt)t+φ 1 ][u(t)-u(t-T)] (1)
wherein f is c Is the transmit carrier modulation frequency, k is the chirp rate of the chirp signal, and u (t) is a unit step function.
Then, assuming that there is an object at the distance R, the resulting object echo signal is expressed as formula (2):
x 2 (t)＝Asin[2π(f c +kt-kτ)(t-τ)+φ 1 ][u(t-τ)-u(t-T)] (2)
wherein the content of the first and second substances,
in the above step S2, after the target echo signal is received, it is mixed with the transmitted frequency modulation reference signal, and after the low-pass filtering is output, a frequency signal related to the target distance is obtained, as shown in fig. 3.
Thus, the mixed, low-pass filtered output signal is represented by equation (4):
x(t)＝Asin(2πf 0 t+φ 0 )[u(t-τ)-u(t-T)] (4)
wherein f is 0 ＝kτ (5)
Wherein the content of the first and second substances,
wherein the frequency of the output signal of equation (4) is f 0 And if multiple targets exist, the echo signals of multiple time delays can be reflected by the frequency spectrum component output by the FFT.
In this embodiment, if it is considered that the target moves relative to the radar at a constant velocity v, the distance between the radar and the target is also continuously changed, and the phase in equation (6) is also continuously changed along with time, i.e. the doppler frequency of the moving target, as shown in equation (7):
for a uniformly moving object, the output after mixing and filtering (4) becomes equation (8):
x(t)＝Asin(2π(f 0 +f d )t+φ 0 '),τ≤t≤T (8)
if the chirp signal echo receives the mixing and filtering process, N points are sampled to perform FFT processing to obtain the range information of the target, and then M periodic data points at the same range point are subjected to FFT processing to obtain the doppler information of the target at the range point, as shown in fig. 4.
In the above step S2, it is determined whether the moving object has an acceleration B, and if so, the instantaneous speed of the moving object is expressed by the following formula (9):
v(t)＝v 0 +Bt (9)
the distance function of the respective target is formula (10):
therefore, when a moving target signal including the acceleration B is mixed and output to the low-pass filter, a frequency signal related to the target distance is output as the following formula (11):
where h is the linear doppler transform rate, expressed as equation (12):
if the Doppler conversion rate h of the signal can be estimated in real time, the acceleration B of the target can be measured. In this embodiment, a real-time-frequency transform is used to estimate the doppler transform rate, specifically, a similar radar target doppler velocity estimation may be used, and on the basis of frequency mixing, filtering and distance FFT processing, time-frequency signal transformation is performed on echo signals in different periods in the same distance, and finally the doppler transform rate is obtained, as shown in fig. 5.
In step S3, after the signal is subjected to frequency mixing, low-pass filtering and distance FFT processing, the output data point of the selected distance is sampled; selecting two-dimensional grid points of time and frequency of output data point time-frequency signal transformation; calculating the Wigner distribution function values of all frequency two-dimensional grid points; selecting a two-dimensional time-frequency low-pass function, and calculating two-dimensional function values of the two-dimensional grid points of all frequencies; and performing two-dimensional non-periodic convolution on the calculated Wigner distribution function value and the two-dimensional function value of the frequency two-dimensional grid point, outputting a time-frequency transformation result of the echo signal at the selected distance point, and generating a radar target signal time-frequency distribution graph.
Specifically, as shown in fig. 13, the specific steps of implementing acceleration information analysis by time-frequency transformation of the radar target signal according to this embodiment are as follows:
step 1: the range position of the radar target to be measured is selected.
Step 2: m linear frequency modulation wave signals (the fixed period is T) which are sequentially transmitted through a millimeter wave radar, frequency mixing and low-pass filtering are carried out on echo signals and reference signals, and output data points at a selected distance are sampled after digital-to-analog conversion and FFT processing.
And step 3: time and frequency two-dimensional grid points of data time-frequency transformation are selected.
And 4, step 4: the value of the vignette distribution function for a frequency two-dimensional grid point is calculated according to equation (13).
And 5: and repeating the step 4 until Wigner distribution function values of all the two-dimensional grid points are calculated.
Step 6: and selecting a two-dimensional time-frequency low-pass function, and calculating function values of the two-dimensional time-frequency low-pass function at all two-dimensional grid points.
And 7: and (4) performing two-dimensional non-periodic convolution on the two-dimensional functions calculated in the step (5) and the step (6), wherein the final result is the time-frequency transformation result of the radar signal at the distance point.
In step S3, the time-frequency signal transformation is performed on the target echo signals of different periods at the same distance by using modified wigner distribution transformation, assuming that the input echo signal is x (t), the wigner distribution transformation is defined as formula (13):
in the present embodiment, there are various time-frequency transform methods such as short-time fourier transform (STFT), wavelet transform, Gabor transform, wavelet packet change, discrete cosine transform, and the like. However, although these orthogonal transforms are easy to reconstruct, they have poor resolution and it is difficult to extract the target acceleration information in real time. Therefore, the invention selects Modified Wigner distribution transformation.
Specifically, the wigner distribution transform is similar to a time-varying power spectrum analysis, and is a non-orthogonal transform or signal decomposition, that is, the original signal x (t) cannot be reconstructed from the coefficients of the wigner distribution in formula (13), but it is very effective in analyzing the signal components, especially the signal contains a time-varying signal, that is, the signal spectrum varies with time. The frequency of the chirp signal increases linearly with time, so the chirp signal is typically a time-varying signal. Therefore, the wigner distribution can be used for analyzing the chirp signals, but the basic wigner distribution is nonlinear transformation, and if the input signal contains a plurality of time-varying signals, the analysis result has the problem of mutual interference among the signals. This is quite possible in the working environment of millimeter wave radar, and typically in the case of simultaneous acceleration of multiple targets, the input signal may contain multiple chirps, and there is a possibility of mutual interference in signal analysis, so the present invention proposes to perform radar target signal analysis using the following modified wigner distribution transformation, as in the above step S3, which is expressed as formula (14):
where Φ (t, f) is a kernel function, typically a two-dimensional low-pass filter, one possible choice is the following decaying exponential function, as in equation (15):
Φ(t,f)＝exp(-αt 2 f 2 ),α＞0 (15)
another possible form of kernel function is as in equation (16):
Φ(t,f)＝q(t)Q(f) (16)
where q (t) is the low pass filter window function and q (f) is its fourier transform.
In the step S3, obtaining real-time values of the speeds or accelerations of the plurality of target signals according to the adaptive multi-target instantaneous acceleration extraction algorithm includes:
randomly selecting a time point t on the acquired radar target signal time-frequency distribution diagram 1 And searching the maximum value points of all the time-frequency images at the time point.
Selecting a different time point t on the time-frequency distribution diagram of the radar target signal 2 And searching the maximum value points of all the time-frequency images at the time point.
Selecting t 1 And t 2 The maximum points of (a) are fitted to the following linear curve, represented by equation (17):
f-k 0 t＝f 0 (17)
wherein k is 0 ,f 0 Is a curve parameter uniquely determined by the two maximum points selected.
And (4) clearing the pixel of the position of the fitted linear curve in the time-frequency image, simultaneously clearing all the two pixels attached to each curve pixel, and calculating the information entropy of the cleaned time-frequency image.
Selecting two maximum value points from a curve formed by combining the two maximum value points to minimize the information entropy of the cleaned time-frequency image, and if the finally obtained curve parameter value is k 0 And f 0 Then the starting Doppler frequency of the radar moving target is f 0 The Doppler change rate of the target is k 0 Acceleration of k 0 Lambda; and repeating the steps by applying the cleaned time-frequency image until the Doppler change rate and the acceleration of all other moving targets are obtained and the information entropy after cleaning is not reduced any more.
Specifically, the time-frequency transformation of the radar data only gives partial information of the target acceleration, and the accurate estimation of the real-time value of the multi-target acceleration needs to be realized by an additional self-adaptive multi-target instantaneous acceleration extraction algorithm. As shown in fig. 14, the algorithm searches a mathematical expression form of a possible target signal source, such as a single frequency signal or a chirp signal, on a completed time-frequency transformation graph, and further estimates a velocity or acceleration value of the target signal, and specifically includes the following steps:
step 1: randomly selecting a time point t on the acquired radar target signal time-frequency distribution diagram 1 And searching all maximum value points at the time point, namely requiring that the reciprocal of the function of the point must be zero, or that the three function values at the left of the point (including the maximum value point) are sequentially increased and the three function values at the right (including the maximum value point) are sequentially decreased (as shown in fig. 6). The maximum points found by the method are as follows from big to small: p is a radical of 11 (t 1 ,f 11 ),p 12 (t 1 ,f 12 ),…,p 1R (t 1 ,f 1R ) Where R is the number of maxima, the location of the maxima in the time-frequency plane in bracketsAnd (4) marking.
Step 2: selecting a different time point t on the time-frequency distribution diagram of the radar target signal 2 ,t 2 ≠t 1 Searching for maximum points of all time-frequency images at the time point, wherein the maximum points found according to the method in the step 1 are as follows from large to small: p is a radical of 21 (t 2 ,f 21 ),p 22 (t 2 ,f 22 ),…,p 2S (t 2 ,f 2S ) Where S is the number of maxima, S and R are not necessarily the same due to noise effects.
And step 3: selection of p 11 (t 1 ,f 11 ) And one maximum point of step 2 is fitted to the following linear curve, as shown in equation (17).
And 4, step 4: and (3) clearing the pixel of the position of the fitted curve in the time-frequency image, simultaneously clearing all the two pixels of the pixel accessory of each curve, and calculating the information entropy of the cleared time-frequency image according to the following formula (18):
in this embodiment, if the quantization between the maximum and minimum values of the image pixels is L uniform intervals, p i The number of pixels representing the pixel amplitude value in the quantization interval i is a proportion of the number of all image pixels.
Selecting two maximum value points in a curve formed by combining all two points possibly to minimize the entropy of the cleaned image information, and if the finally obtained curve parameter value is k 0 And f 0 The starting Doppler frequency of a radar moving target is f 0 The Doppler change rate of the target is k 0 And its acceleration is k 0 λ。
And then, repeating the steps 3-4 by applying the cleaned time-frequency image until the Doppler change rate and the acceleration of all other moving targets are obtained and the cleaned information entropy is not reduced any more.
In practical application, the radar target data sampling test results are as follows:
in this embodiment, the multi-cycle radar target echo waveform sampling data (1ms period) output in the same distance in the time domain includes three moving targets, a uniform moving target, an accelerating target and a decelerating target (the signal is the data collected after mixing, filtering and distance FFT). Where the signal-to-noise ratio SNR is 12 dB.
As shown in fig. 7, if the signals in fig. 7 are directly transformed by FFT, as a result, as shown in fig. 8, the doppler frequency of the moving object with uniform speed can be identified, but the moving object signal with acceleration or deceleration cannot be identified.
In practical applications, the real-time frequency conversion processing test results are as follows:
in this embodiment, since the chirp target signal generated by the acceleration target cannot be identified and measured according to the conventional FFT, the echo signal of the target can be accelerated by time-frequency transformation. The time-frequency transformation adopted by the invention is modified Wigner distribution transformation, and the result is shown in figure 9, so that three time-frequency curves generated by three targets can be clearly seen. The characteristic of the Wigner distribution is that the resolution is high, the data does not need to be large, but the Wigner distribution is nonlinear transformation, and the transformation result cannot directly generate target parameters, so that additional target parameter extraction algorithm processing is required.
In practical application, the test result of the self-adaptive multi-target instantaneous acceleration extraction algorithm is as follows:
in this embodiment, according to the adaptive multi-target instantaneous acceleration extraction algorithm provided by the present invention, firstly, the signal parameter of a strongest target is tentatively estimated, and if the estimation is correct, the target signal after identification and parameter extraction is removed from the image, and the entropy of the image information after cleaning the correct target signal should be reduced. The first signal selected to be clear from the image is a uniformly moving object, and the cleaned time-frequency image is shown in fig. 10, with only two signals of the moving object being accelerated/decelerated.
Then, the same method is adopted to remove the next strongest radar target signal from the target signal time-frequency image, and the final result is shown in fig. 11. The chirp signal identifying the deceleration motion is the target signal, which is also removed from the time-frequency image after the signal parameters are extracted. The final result is only one acceleration target signal. The target signal parameters can also be correctly identified and estimated. The results of the estimation of all three moving target signal parameters are listed in table 1, the target parameter estimation is accurate (certainly, the table shows the doppler and doppler conversion rate parameters of the target, and the velocity and acceleration of the target need to be converted according to the wavelength of the radar transmitted signal), and this test result also proves the correctness of the method for estimating the acceleration of the target in real time at a high speed provided by the present invention.
Table 1: radar target parameter value estimated in real time at high speed
Therefore, the instantaneous acceleration values of a plurality of targets can be measured in real time through data acquisition, real-time high-speed time-frequency conversion, self-adaptive multi-target instantaneous acceleration extraction and other processing, and the conversion of instantaneous tracking acceleration is achieved; the measured target acceleration value has high accuracy, and real-time acceleration can be provided for planning and using an automatic driving path; the method has no special requirements on the hardware environment of the radar, is mainly realized by signal processing algorithm software, and has low implementation cost.
In addition, the invention provides a brand-new method for accurately measuring the acceleration of the target of the millimeter wave radar in real time, which can be used for automatically driving the millimeter wave radar, and is also suitable for estimating the acceleration of the ground moving target of an airborne radar, the acceleration of the ground moving target of an unmanned aerial vehicle, the acceleration of the sea surface or water surface target of a ship-borne radar, and the acceleration of the monitoring target of the internet of things based on a millimeter wave radar sensor.
The embodiment of the system for accurately estimating the acceleration of the millimeter wave radar target in real time comprises the following steps:
a millimeter wave radar target acceleration accurate real-time estimation system is applied to the millimeter wave radar target acceleration accurate real-time estimation method to realize moving target detection and interference suppression, as shown in FIG. 14, and comprises;
and the signal receiving and transmitting unit is used for continuously transmitting a plurality of linear frequency modulation signals by using a millimeter wave radar and acquiring corresponding target echo signals through a receiving end of the signal receiving and transmitting unit.
And the processing unit is used for carrying out frequency mixing, low-pass filtering and range FFT processing on the received target echo signal and the transmitting reference signal.
And the output result unit is used for carrying out time-frequency signal conversion on the target echo signals of different periods in the same distance, acquiring the Doppler conversion rate of the signals, and acquiring the real-time values of the speeds or accelerations of a plurality of target signals according to the self-adaptive multi-target instantaneous acceleration extraction algorithm, so that the accelerated or decelerated moving target signals can be accurately predicted.
Therefore, the invention realizes the accurate estimation of the moving target acceleration through the target acceleration real-time estimation system consisting of the signal transceiving unit, the processing unit and the output result unit, can calculate the real-time planning acceleration, realizes the low-delay and high-accuracy acceleration estimation, further realizes the coupling planning of the automatic driving path and the acceleration, can meet the processing of complex working conditions, and simultaneously improves the platform adaptability and the safety performance of functions.
The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.
Claims (8)
1. A method for accurately estimating the acceleration of a millimeter wave radar target in real time is characterized by comprising the following steps:
continuously transmitting a plurality of linear frequency modulation signals by using a millimeter wave radar, and collecting corresponding target echo signals through a receiving end of the millimeter wave radar;
carrying out frequency mixing, low-pass filtering and distance FFT processing on the received target echo signal and the transmitting reference signal;
carrying out time-frequency signal transformation on target echo signals of different periods at the same distance to obtain the Doppler transformation rate of the signals, and obtaining the real-time values of the speeds or accelerations of a plurality of target signals according to a self-adaptive multi-target instantaneous acceleration extraction algorithm, so that accelerated or decelerated moving target signals can be accurately predicted;
the obtaining of the real-time values of the speeds or accelerations of a plurality of target signals according to the self-adaptive multi-target instantaneous acceleration extraction algorithm comprises the following steps: randomly selecting a time point t on the acquired radar target signal time-frequency distribution diagram 1 Searching for maximum value points of all time-frequency images at the time point;
selecting a different time point t on the time-frequency distribution diagram of the radar target signal 2 Searching the maximum value points of all the time-frequency images at the time point;
selecting t 1 And t 2 The maximum points of (a) are fitted to the following linear curve, expressed as equation (17):
f-k 0 t＝f 0 (17)
wherein k is 0 ,f 0 Is a curve parameter which is uniquely determined by two selected maximum value points;
clearing pixels at positions of the fitted linear curves in the time-frequency image, simultaneously clearing two pixels attached to each curve pixel, and calculating the information entropy of the cleared time-frequency image;
selecting two maximum value points from a curve formed by combining the two maximum value points to minimize the information entropy of the cleaned time-frequency image, and if the finally obtained curve parameter value is k 0 And f 0 Then the starting Doppler frequency of the radar moving target is f 0 The Doppler change rate of the target is k 0 Acceleration of k 0 λ；
And repeating the steps by applying the cleaned time-frequency image until the Doppler change rate and the acceleration of all other moving targets are obtained and the cleaned information entropy is not reduced.
2. The method of claim 1, wherein the continuously transmitting a plurality of chirp signals by using the millimeter wave radar and collecting corresponding target echo signals through a receiving end thereof comprises:
in a working period of the millimeter wave radar, M linear frequency modulation signals are continuously transmitted by the millimeter wave radar, and a transmission waveform is defined as a formula (1):
x 1 (t)＝sin[2π(f c +kt)t+φ 1 ][u(t)-u(t-T)] (1)
wherein f is c Is the transmit carrier modulation frequency, k is the chirp rate of the chirp signal, u (t) is the unit step function;
assuming that there is a target at the distance R, the resulting target echo signal is expressed as formula (2):
x 2 (t)＝Asin[2π(f c +kt-kτ)(t-τ)+φ 1 ][u(t-τ)-u(t-T)] (2)
wherein the content of the first and second substances,
3. the method of claim 2, wherein the mixing, low-pass filtering and range-FFT processing the received target echo signal and the transmitted reference signal comprises:
after receiving the target echo signal, mixing the target echo signal with a transmitting frequency modulation reference signal, outputting low-pass filtering, and obtaining a frequency signal related to the target distance, wherein the frequency signal is expressed as a formula (4):
x(t)＝Asin(2πf 0 t+φ 0 )[u(t-τ)-u(t-T)] (4)
wherein the frequency of the output signal is f 0 K τ, it is FFT processed, and its output frequency is proportional to the target distance.
4. The method of claim 2, wherein the mixing, low-pass filtering and range-FFT processing the received target echo signal and the transmitted reference signal comprises:
judging whether the moving target has the acceleration B, if so, the instantaneous speed of the moving target is the formula (9):
v(t)＝v 0 +Bt (9)
the distance function of the respective target is formula (10):
therefore, when a moving target signal including the acceleration B is mixed and output to the low-pass filter, a frequency signal related to the target distance is output as the following formula (11):
where h is the linear doppler shift rate, expressed as equation (12):
5. the method of claim 4, wherein the transforming the time-frequency signals of the target echo signals of different periods at the same distance comprises:
sampling an output data point of a selected distance after frequency mixing, low-pass filtering and distance FFT processing are carried out on the signal;
selecting two-dimensional grid points of time and frequency of output data point time-frequency signal transformation;
calculating the Wigner distribution function values of all frequency two-dimensional grid points;
selecting a two-dimensional time-frequency low-pass function, and calculating two-dimensional function values of the two-dimensional grid points of all frequencies;
and performing two-dimensional non-periodic convolution on the calculated Wigner distribution function value and the two-dimensional function value of the frequency two-dimensional grid point, outputting a time-frequency transformation result of the echo signal at the selected distance point, and generating a radar target signal time-frequency distribution graph.
6. The method of claim 5, wherein the transforming the time-frequency signals of the target echo signals of different periods at the same distance comprises:
selecting modified Wigner distribution transformation for target echo signals of different periods at the same distance to perform time-frequency signal transformation, assuming that the input echo signal is x (t), and defining the Wigner distribution transformation as a formula (13):
7. the method of claim 6, wherein:
radar target signal analysis was performed using the modified wigner distribution transform, expressed as equation (14):
where Φ (t, f) is the kernel function.
8. A system for accurately estimating the acceleration of a millimeter wave radar target in real time, which is applied to the method for accurately estimating the acceleration of a millimeter wave radar target in real time according to any one of claims 1 to 7 to accurately estimate the acceleration of a moving target in real time, the system comprising:
the signal receiving and transmitting unit is used for continuously transmitting a plurality of linear frequency modulation signals by using a millimeter wave radar and acquiring corresponding target echo signals through a receiving end of the signal receiving and transmitting unit;
the processing unit is used for carrying out frequency mixing, low-pass filtering and distance FFT processing on the received target echo signal and the transmitting reference signal;
an output unit for outputting the target echoes of different periods at the same distanceThe signals are subjected to time-frequency signal transformation to obtain the Doppler transformation rate of the signals, and real-time values of the speeds or accelerations of a plurality of target signals are obtained according to a self-adaptive multi-target instantaneous acceleration extraction algorithm, so that the accelerated or decelerated moving target signals can be accurately predicted; wherein, a time point t is arbitrarily selected on the acquired radar target signal time-frequency distribution diagram 1 Searching for maximum value points of all time-frequency images at the time point;
selecting a different time point t on the time-frequency distribution diagram of the radar target signal 2 Searching the maximum value points of all the time-frequency images at the time point;
selecting t 1 And t 2 The maximum points of (a) are fitted to the following linear curve, represented by equation (17):
f-k 0 t＝f 0 (17)
wherein k is 0 ,f 0 Is a curve parameter which is uniquely determined by two selected maximum value points;
clearing pixels at positions of the fitted linear curves in the time-frequency image, simultaneously clearing two pixels attached to each curve pixel, and calculating the information entropy of the cleared time-frequency image;
selecting two maximum value points from a curve formed by combining the two maximum value points to minimize the information entropy of the cleaned time-frequency image, and if the finally obtained curve parameter value is k 0 And f 0 Then the starting Doppler frequency of the radar moving target is f 0 The Doppler change rate of the target is k 0 Acceleration of k 0 λ；
And repeating the steps by applying the cleaned time-frequency image until the Doppler change rate and the acceleration of all other moving targets are obtained and the cleaned information entropy is not reduced.
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