CN118033626A

CN118033626A - Target tracking speed measurement method and system based on double radars

Info

Publication number: CN118033626A
Application number: CN202410430666.4A
Authority: CN
Inventors: 石宝勇; 魏强强; 杨洁; 潘仲倡; 胡琰敏; 赵玉玺
Original assignee: Jinan Zhuo Lin Intelligent Transportation Technology Co ltd
Current assignee: Jinan Zhuo Lin Intelligent Transportation Technology Co ltd
Priority date: 2024-04-11
Filing date: 2024-04-11
Publication date: 2024-05-14
Anticipated expiration: 2044-04-11
Also published as: CN118033626B

Abstract

The invention relates to the field of radar speed measurement, in particular to a target tracking speed measurement method and system based on double radars, wherein the method comprises the following steps: in the test stage, a test vehicle is driven through a monitoring road section for multiple times according to different driving modes, and the actual speed of the vehicle, the point cloud data of the monitoring road section and an intermediate frequency signal generated by a millimeter wave radar are obtained when the test vehicle drives through the monitoring road section each time and are used for constructing a vehicle path database and a frequency difference database; and in the actual measurement stage, determining the optimal Doppler shift according to the point cloud data and the intermediate frequency signal which are acquired in real time and the two databases, and further calculating the speed of the target vehicle by using the optimal Doppler shift. The invention realizes the combination of the combined speed measurement and the advantage combination of the three-dimensional laser radar and the millimeter wave radar, can provide enough detailed space information while improving the speed measurement of the curve, and improves the accuracy and the reliability of the speed measurement of the curve tracking of the vehicle.

Description

Target tracking speed measurement method and system based on double radars

Technical Field

The invention relates to the field of radar speed measurement, in particular to a target tracking speed measurement method and system based on double radars.

Background

With the rapid increase of the amount of automobile maintenance, road safety problems are increasingly prominent, wherein overspeed phenomenon is an important potential safety hazard. Therefore, the tracking and speed measuring technology for automobiles plays an increasingly important role in maintaining road traffic safety. In the prior art, millimeter wave radars are widely used for speed measurement of automobiles due to their unique advantages. The millimeter wave radar has excellent penetrating power, can keep stable performance under severe weather conditions such as fog, rain, snow and the like, and can realize continuous speed measurement of a target vehicle. In addition, the millimeter wave radar has a short wavelength, so that the millimeter wave radar has high resolution and measurement accuracy, and can accurately capture the speed and position information of the target vehicle.

Through years of development, when the vehicle runs normally, the millimeter wave radar speed measurement result is very accurate and reliable in most cases, but the problems are also highlighted. First, millimeter wave radar has a lower resolution than other detection technologies such as lidar, meaning that it may not provide sufficiently detailed spatial information in traffic scenarios, which is solved to some extent by combining millimeter wave radar with cameras to measure vehicle speed, but the detection capability of the cameras is compromised during night. Secondly, in a curve area, the vehicle moves in a curve, because the radar beam direction is not matched with the vehicle movement direction, the multipath effect and the dynamic environment are changed, the millimeter wave radar speed measurement based on the Doppler effect usually has larger error, a plurality of millimeter wave radars can be arranged in the same area, and further the measurement accuracy and reliability are improved by carrying out multi-angle speed measurement on the vehicle, however, the environment requirement of arranging the plurality of millimeter wave radars on a monitoring area is higher, and more public space can be occupied.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a target tracking speed measurement method and system based on double radars.

In order to achieve the above object, in a first aspect, the present invention provides a target tracking speed measurement method based on dual radars, the method comprising the steps of: analyzing possible driving modes of the vehicle on the monitoring road section in the test stage, and enabling the test vehicle to drive through the monitoring road section for multiple times according to different driving modes; when the test vehicle passes through the monitoring road section each time, acquiring the actual speed of the test vehicle, acquiring test point cloud data of the monitoring road section by using a three-dimensional laser radar, and acquiring a test intermediate frequency signal by using a millimeter wave radar; constructing a vehicle path database based on the test point cloud data, and further constructing a frequency difference database based on the test intermediate frequency signal and the actual speed; in an actual measurement stage, when a target vehicle runs on a monitoring road section, acquiring target point cloud data of the monitoring road section by using the three-dimensional laser radar, and acquiring a target intermediate frequency signal by using the millimeter wave radar; determining a reference driving path of the target vehicle according to the target point cloud data and the vehicle path database, and further determining a reference difference frequency change curve according to the frequency difference database; and determining optimal Doppler shift according to the target intermediate frequency signal and the reference difference frequency change curve, and calculating the target vehicle speed by using the optimal Doppler shift. The invention realizes the combination of the combined speed measurement and the advantage combination of the three-dimensional laser radar and the millimeter wave radar, can provide enough detailed space information while improving the speed measurement of the curve, and improves the accuracy and the reliability of the speed measurement of the curve tracking of the vehicle.

Optionally, the constructing a vehicle path database based on the test point cloud data, and further constructing a frequency difference database based on the test intermediate frequency signal and the actual speed includes the following steps:

Performing density reduction on the test point cloud data by using a voxel downsampling algorithm, and then performing point cloud segmentation on the test point cloud data with the reduced density to obtain standby point cloud data;

Acquiring two-dimensional position coordinates of the test vehicle according to the standby point cloud data, and further constructing the vehicle path database based on the two-dimensional position coordinates;

Performing one-dimensional FFT (fast Fourier transform) on the test intermediate frequency signals in different periods to obtain the frequency spectrum of the test intermediate frequency signals, and further estimating the frequency of the test intermediate frequency signals;

Drawing a speed change curve by using the actual speed, and performing time synchronization on the running track of the test vehicle and the speed change curve;

According to the result of time synchronization, calculating the test radial speed of the test vehicle according to the running track of the test vehicle and the actual speed, and further calculating the test Doppler frequency shift;

And acquiring a frequency difference change curve by using the test intermediate frequency signal frequency and the test Doppler frequency shift, and further constructing the frequency difference database.

Furthermore, because the running track of the vehicle has higher predictability in a specific monitoring road section, a corresponding frequency difference database can be established by establishing a vehicle path database and combining the principle of millimeter wave radar speed measurement and distance measurement, thereby providing reliable data support for the speed of the follow-up measurement target vehicle. The density of the test point cloud data is reduced through a voxel downsampling algorithm, the calculated amount is reduced, the point cloud data amount can be further reduced through point cloud segmentation, interference of unnecessary point clouds is eliminated, the running track of a test vehicle can be acquired more accurately, and time synchronization is beneficial to eliminating the influence of time deviation on the accuracy of the test radial speed.

Optionally, the acquiring the two-dimensional position coordinates of the test vehicle according to the backup point cloud data, and further constructing the vehicle path database based on the two-dimensional position coordinates includes the following steps:

detecting and removing ground point cloud data in the standby point cloud data to obtain test vehicle point cloud data;

Performing point cloud clustering on the point cloud data of the test vehicle to obtain two-dimensional position coordinates of the test vehicle, drawing a running track of the test vehicle in a rectangular coordinate system by using the two-dimensional position coordinates, and calibrating the positions of the three-dimensional laser radar and the millimeter wave radar in the rectangular coordinate system;

The vehicle path database is constructed using a plurality of the test vehicle travel trajectories.

Furthermore, the influence of irrelevant point clouds is eliminated by removing the ground point cloud data, so that the point cloud data of the test vehicle can be extracted more accurately, further, a more accurate vehicle running track is drawn, and the calculation of Doppler frequency shift of a subsequent test is facilitated by calibrating the radar position.

Optionally, said performing a one-dimensional FFT on said test intermediate frequency signal of different periods to obtain a spectrum of said test intermediate frequency signal, and estimating the test intermediate frequency signal frequency further comprises the steps of:

performing one-dimensional FFT conversion on the test intermediate frequency signals in different periods to obtain a frequency spectrum of the test intermediate frequency signals, and marking the frequency spectrum as a test frequency spectrum;

And estimating the frequency of the test intermediate frequency signal by using an A-I-Rife algorithm according to the test frequency spectrum.

Furthermore, the A-I-Rife algorithm is used, so that the frequency prediction accuracy is high, the calculated amount is low, and the speed measurement efficiency and accuracy are improved.

Optionally, the calculating the test radial speed of the test vehicle according to the running track of the test vehicle and the actual speed according to the result of time synchronization, and further calculating the test doppler shift comprises the following steps:

determining a test included angle between a connecting line of the millimeter wave radar and the test vehicle according to the running track of the test vehicle;

Calculating the test radial speed of the test vehicle according to the test included angle and the actual speed, and further calculating the test Doppler frequency shift, wherein the test Doppler frequency shift meets the following relation:

Wherein, For the test Doppler shift,/>For the actual speed,/>For the test angle,/>Is the wavelength of the electromagnetic wave emitted by the millimeter wave radar.

Furthermore, the vehicle running track obtained based on the three-dimensional laser radar is accurate and reliable, so that the obtained test included angle is also accurate and reliable, and the actual speed monitored by the vehicle is also accurate and reliable, so that the accurate and reliable test Doppler frequency shift can be finally obtained, and a reliable data base is provided for measuring the speed of the target vehicle.

Optionally, the obtaining a frequency difference variation curve by using the test intermediate frequency signal frequency and the test doppler shift, and further constructing the frequency difference database includes the following steps:

Drawing a test intermediate frequency signal frequency change curve by using the test intermediate frequency signal frequency, and drawing a test Doppler frequency shift change curve by using the test Doppler frequency shift;

Aiming at a test intermediate frequency signal frequency change curve and a test Doppler frequency shift change curve corresponding to the same test vehicle, performing time synchronization on the test intermediate frequency signal frequency change curve and the test Doppler frequency shift change curve, and then taking the difference between the test intermediate frequency signal frequency change curve and the test Doppler frequency shift change curve as the frequency difference change curve;

and constructing the frequency difference database by using the test intermediate frequency signal frequency change curve, the test Doppler frequency shift change curve and the frequency difference change curve.

Furthermore, a corresponding frequency difference database is established based on the principle of millimeter wave radar speed measurement and distance measurement, and reliable data support is provided for the speed of a subsequent measurement target vehicle.

Optionally, the determining the reference driving path of the target vehicle according to the target point cloud data and the vehicle path database, and further determining the reference difference frequency change curve according to the frequency difference database includes the following steps:

Acquiring a vehicle running path of the target vehicle according to the target point cloud data, selecting a plurality of target sampling points on the vehicle running path, and selecting a test sampling point corresponding to the target sampling point on a test vehicle running track according to the target sampling point, wherein the target sampling point and the corresponding test sampling point at least meet one of the same abscissa and the same ordinate;

based on the selected target sampling point and the test sampling point, calculating a consistency check value of a test vehicle running track and the vehicle running track in the vehicle path database by using a consistency check model;

Taking the test vehicle running track corresponding to the maximum consistency check value as a reference running path of the target vehicle;

inquiring a frequency difference change curve corresponding to the reference driving path in the frequency difference database, and recording the frequency difference change curve as a reference frequency difference change curve.

Optionally, the consistency check model satisfies the following relationship:

，

Wherein, For the consistency check value, N is the number of the target sampling points,/>For the abscissa of the ith target sampling point in a rectangular coordinate system,/>For the abscissa of the ith test sampling point in a rectangular coordinate system,/>Is the ordinate of the ith target sampling point in a rectangular coordinate system,/>And the ordinate of the ith test sampling point in the rectangular coordinate system.

Optionally, the determining the optimal doppler shift according to the target intermediate frequency signal and the reference difference frequency variation curve, and calculating the target vehicle speed using the optimal doppler shift includes the following steps:

estimating the target intermediate frequency signal frequency of the target intermediate frequency signal, drawing a target intermediate frequency signal frequency change curve, and performing time synchronization on the target intermediate frequency signal frequency change curve and the vehicle driving path;

calculating the optimal Doppler shift according to the target intermediate frequency signal frequency change curve and the reference difference frequency change curve, wherein the optimal Doppler shift meets the following relation:

Wherein, Time taken for the target vehicle to travel to the target sampling point,/>For the time taken for the test vehicle corresponding to the reference driving path to drive to the test sampling point corresponding to the target sampling point, B is the frequency modulation bandwidth, T is the frequency modulation period, c is the light speed,/>For optimal doppler shift when the target vehicle is traveling to the target sampling point,For the target intermediate frequency signal frequency when the target vehicle runs to the target sampling point,/>For the frequency difference value on the reference difference frequency change curve when the test vehicle runs to the test sampling point,/>Is of a certain value/>，/>For the test intermediate frequency signal frequency when the test vehicle runs to the test sampling point,/>A test Doppler shift when the test vehicle travels to the test sampling point;

and calculating the speed of the target vehicle by using the optimal Doppler frequency shift.

Furthermore, the speed of the target vehicle is calculated based on the reference difference frequency change curve, so that errors caused by mismatching of the radar beam direction and the vehicle moving direction, multipath effect and change of dynamic environment during curve movement of the vehicle can be avoided, and further accuracy of curve speed measurement is improved.

In a second aspect, the present invention further provides a target tracking speed measurement system based on dual radars, where the system uses the target tracking speed measurement method based on dual radars provided by the present invention, and the system includes: the data acquisition module is used for acquiring the actual speed of the test vehicle when the test vehicle passes through the monitoring road section each time, acquiring test point cloud data of the monitoring road section by using a three-dimensional laser radar and acquiring a test intermediate frequency signal by using a millimeter wave radar; in an actual measurement stage, when a target vehicle runs on a monitoring road section, acquiring target point cloud data of the monitoring road section by using the three-dimensional laser radar, and acquiring a target intermediate frequency signal by using the millimeter wave radar; the data processing module is used for constructing a vehicle path database based on the test point cloud data, and further constructing a frequency difference database based on the test intermediate frequency signal and the actual speed; determining a reference driving path of the target vehicle according to the target point cloud data and the vehicle path database, and further determining a reference difference frequency change curve according to the frequency difference database; determining optimal Doppler shift according to the target intermediate frequency signal and the reference difference frequency change curve, and calculating the target vehicle speed by using the optimal Doppler shift; the data storage module is used for storing all data generated by the data processing module; the data output and early warning module is used for outputting the speed of the vehicle and giving an alarm when the vehicle overspeed. The system provided by the invention has higher speed measuring efficiency and accuracy, can provide more choices for vehicle speed measuring, and promotes the development of radar speed measuring to a more accurate and reliable direction.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flow chart of a target tracking speed measuring method based on double radars according to an embodiment of the present invention;

FIG. 2 is a partial flow diagram of an embodiment of the present invention when the modified RANSAC algorithm is running;

fig. 3 is a schematic diagram of a target tracking speed measurement system frame based on double radars according to an embodiment of the present invention.

Detailed Description

Specific embodiments of the invention will be described in detail below, it being noted that the embodiments described herein are for illustration only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that: no such specific details are necessary to practice the invention. In other instances, well-known circuits, software, or methods have not been described in detail in order not to obscure the invention.

Throughout the specification, references to "one embodiment," "an embodiment," "one example," or "an example" mean: a particular feature, structure, or characteristic described in connection with the embodiment or example is included within at least one embodiment of the invention. Thus, the appearances of the phrases "in one embodiment," "in an embodiment," "one example," or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combination and/or sub-combination in one or more embodiments or examples. Moreover, those of ordinary skill in the art will appreciate that the illustrations provided herein are for illustrative purposes and that the illustrations are not necessarily drawn to scale.

It should be noted in advance that in an alternative embodiment, the same symbols or alphabet meaning and number are the same as those present in all formulas, except where separate descriptions are made.

In an alternative embodiment, please refer to fig. 1, the present invention provides a target tracking speed measurement method based on dual radars, the method comprising the steps of:

S1, analyzing possible driving modes of the vehicle on the monitoring road section in the test stage, and enabling the test vehicle to drive through the monitoring road section for multiple times according to different driving modes.

Specifically, in the present embodiment, during the test phase, it is a primary task to comprehensively analyze the driving modes that the vehicle may encounter on the monitored road section. This requires simple investigation and research on various aspects of road conditions, traffic flow, vehicle types, etc. of the monitored road section. For example, the monitored road section may be a junction of a busy city, a section of a highway, or a mountain area meandering road. The road conditions comprise the flatness of the road surface, friction coefficient, number of lanes, width, road marks and the like; the traffic flow includes traffic flow changes for different time periods; vehicle types include vehicles of different types and sizes, such as cars, trucks, buses, and the like. However, the road conditions and traffic rules of the road are limited, in the area where the radar can measure the speed, the subtle difference of the running track of the vehicle is eliminated, and the running track of the vehicle in normal running has extremely high predictability, so that all possible running modes of the vehicle in a monitored road section can be represented through limited tests, and data support is provided for the subsequent use of the radar.

Further, the monitoring road section is a curve, and the selection factor in the test stage is selected in a time period with good weather, so that the influence of the environment on the three-dimensional laser radar is reduced, the acquired point cloud data is ensured to have high accuracy, and a reliable data basis is provided for the analysis and calculation of the later data. In the test stage, the running mode can be planned and simulated in advance so as to perform the test more pertinently, avoid blind and repeated tests and improve the efficiency and accuracy of the test. In the test process, the test vehicle can be used for multiple times aiming at the same running mode, so that the accuracy and the effectiveness of data collection are ensured, and a solid data base is provided for the subsequent vehicle speed measurement.

S2, when the test vehicle passes through the monitoring road section each time, acquiring the actual speed of the test vehicle, acquiring test point cloud data of the monitoring road section by using a three-dimensional laser radar, and acquiring a test intermediate frequency signal by using a millimeter wave radar.

Specifically, in the present embodiment, the actual speed of the test vehicle is recorded by a speed sensor on the test vehicle. The test point cloud data acquired by using the three-dimensional laser radar comprises ground point and data of a detection road section and vehicle point cloud data; and transmitting the frequency modulation continuous wave and receiving the echo signal by using the millimeter wave radar, selecting a sawtooth wave by using a modulation mode, and carrying out mixing processing on the echo signal to obtain a test intermediate frequency signal. The actual speed of the test vehicle, the test point cloud data and the intermediate frequency signal are acquired simultaneously, which can provide an accurate basis for subsequent data analysis and evaluation.

More specifically, in this embodiment, the working frequency of the millimeter wave radar is 23.8GHz, the sampling frequency is 10kHz, the sampling point number is 1024, and the three-dimensional laser radar selects the graminearum XT32 laser radar. The three-dimensional laser radar and the millimeter wave radar are arranged at the circle center corresponding to the curve circular arc and are positioned on the same vertical line, the installation height is selected to be between 3 meters and 6 meters, and the installation height of the three-dimensional laser radar is lower than that of the millimeter wave radar, so that the influence on the speed measurement precision caused by shielding of the three-dimensional laser radar by the millimeter wave radar is avoided. In other alternative examples, the relevant personnel can also select other types of three-dimensional laser radars and millimeter wave radars according to actual needs.

And S3, constructing a vehicle path database based on the test point cloud data, and further constructing a frequency difference database based on the test intermediate frequency signal and the actual speed.

Wherein, S3 specifically includes the following steps:

And S31, performing density reduction on the test point cloud data by using a voxel downsampling algorithm, and then performing point cloud segmentation on the test point cloud data with the density reduced to obtain standby point cloud data.

Specifically, in this embodiment, this step is the prior art, so it is not described in detail here.

Further, the density of the test point cloud data is reduced through a voxel downsampling algorithm, the calculated amount is reduced, the point cloud data amount can be further reduced through point cloud segmentation, interference of unnecessary point clouds is eliminated, and the method is beneficial to more accurately acquiring the running track of the test vehicle.

S32, acquiring two-dimensional position coordinates of the test vehicle according to the standby point cloud data, and further constructing the vehicle path database based on the two-dimensional position coordinates.

Wherein, S32 further comprises the following steps:

S321, detecting and removing ground point cloud data in the standby point cloud data to obtain test vehicle point cloud data.

Specifically, in the present embodiment, the identification of the ground point cloud data is achieved using the modified RANSAC algorithm. Referring to fig. 2, the modified RANSAC algorithm specifically performs the following steps when running:

1. And inputting standby point cloud data, a plane model and algorithm confidence, wherein the plane model is ax+by+cz+d=0, a, b, c and d are model parameters, and (x, y, z) represents three-dimensional coordinates of points.

2. And randomly selecting local points in the standby point cloud data to fit the plane model, and further calculating model parameters to determine a reference plane.

3. And traversing the rest points in the standby point cloud data by using the reference plane, classifying the rest points as local points if the distance between the points and the reference plane is not more than 2cm, classifying the rest points as external points if the distance between the points and the reference plane is not more than 2cm, and counting the number of the local points after traversing all the points.

4. If the number of the local points exceeds the point threshold k, re-fitting the plane model by using all the local points to obtain new model parameters, further determining a standby reference plane, and otherwise returning to the step 2.

5. Calculating the matching degree of the local points and the standby reference plane, comparing the matching degree with the last calculation result, reserving the standby reference plane and the corresponding local points with the largest matching degree, recording the standby reference plane and the corresponding local points as standby output data, outputting the standby output data when the iteration times are reached, taking the local points output at the time as the first ground points, and returning to the step 2 if the set iteration times are not reached.

6. And (3) re-executing the steps 1 to 5 on the basis of the outlier obtained in the step S3 to obtain a second batch of ground points.

More specifically, in step 5, the method for calculating the matching degree between the local point and the standby reference plane and the method for setting the iteration number may refer to the RANSAC algorithm. In the steps 1 to 6, the first batch of ground points and the second batch of ground points are obtained to identify the horizontal plane and the gradient plane, so that the point cloud data of the test vehicle are accurately extracted, and the accurate identification and tracking of the test vehicle are facilitated.

Further, the point cloud data corresponding to the first batch of ground points and the second batch of ground points, namely the ground point cloud data, are removed from the standby point cloud data, and finally the test vehicle point cloud data are obtained. The influence of irrelevant point clouds is eliminated by removing the ground point cloud data, so that the point cloud data of the test vehicle can be extracted more accurately, and further, a more accurate vehicle running track is drawn.

S322, performing point cloud clustering on the point cloud data of the test vehicle to obtain two-dimensional position coordinates of the test vehicle, drawing a running track of the test vehicle in a rectangular coordinate system by using the two-dimensional position coordinates, and calibrating positions of the three-dimensional laser radar and the millimeter wave radar in the rectangular coordinate system.

Specifically, in this embodiment, a DBSCAN clustering algorithm is used to perform point cloud clustering on point cloud data of a test vehicle to distinguish which point cloud data belong to the same test vehicle, three-dimensional dimensions of the test vehicle can be extracted after clustering is completed, the test vehicle is wrapped by using a spatial hexahedron, and in a radar coordinate system of the three-dimensional laser radar, a center of the spatial hexahedron is a radar coordinate system coordinate of the test vehicle.

Further, an intersection point of a vertical line where the three-dimensional laser radar is located and a horizontal plane is taken as an origin, the vertical line where the three-dimensional laser radar is located is taken as a z axis, a space rectangular coordinate system is established, an xOy plane of the space rectangular coordinate system is parallel to the horizontal plane, an x axis and a y axis of the space rectangular coordinate system are the x axis and the y axis of the rectangular coordinate system, the rectangular coordinate system is marked as a first rectangular coordinate system for convenience in distinguishing, and the positions of the three-dimensional laser radar and the millimeter wave radar are the positions where the origin of the first rectangular coordinate system is located. The radar coordinate system coordinates of the test vehicle are converted into a space rectangular coordinate system, the position coordinates of the test vehicle in the space rectangular coordinate system are obtained, the position coordinates are projected onto an xOy plane of the space rectangular coordinate system to obtain a projection point, the projection point is the two-dimensional position coordinates of the test vehicle, and the smooth curve is used for connecting all the two-dimensional position coordinates of the test vehicle to obtain the running track of the test vehicle, so that the tracking of the test vehicle is realized.

S323, constructing the vehicle path database by using a plurality of test vehicle driving tracks.

S33, performing one-dimensional FFT conversion on the test intermediate frequency signals in different periods to obtain the frequency spectrum of the test intermediate frequency signals, and further estimating the frequency of the test intermediate frequency signals.

Wherein S33 further comprises the following steps:

s331, performing one-dimensional FFT conversion on the test intermediate frequency signals in different periods to obtain a frequency spectrum of the test intermediate frequency signals, and marking the frequency spectrum as a test frequency spectrum.

S332, estimating the frequency of the test intermediate frequency signal by using an A-I-Rife algorithm according to the test frequency spectrum.

Specifically, in this embodiment, the specific procedure for estimating the frequency of the intermediate frequency signal of the test using the a-I-life algorithm is as follows:

a1, determining an amplitude maximum value point k ₀ of a test frequency spectrum, and sequentially recording the frequency spectrum amplitude values of the amplitude maximum value point, the left adjacent point and the right adjacent point of the amplitude maximum value point 、/>And/>。

A2, sequentially and respectively calculating the amplitude of the midpoint between the maximum amplitude point and the left and right adjacent points by utilizing a frequency spectrum thinning technologyAnd/>And by comparison/>And/>The small judgment correction direction e of (1), if/>E=1, otherwise e= -1.

A3, calculatingWhen/>When the frequency shift factor/>, is calculated using the first relationOtherwise calculate the frequency shift factor/>, using the second relationThe first relation and the second relation respectively satisfy the following relations in turn:

a4, calculating the amplitude value after the frequency shift of the left adjacent point and the right adjacent point by using a frequency spectrum refinement technology AndFurther calculate the frequency/>, of the test intermediate frequency signal。

Further, the frequency spectrum refinement technique used in step a2 and step a4, and the method of calculating the frequency of the test intermediate frequency signal in step a4 may refer to the I-Rife algorithm. The A-I-Rife algorithm used in the embodiment not only has higher frequency prediction precision, but also has lower calculated amount, which is beneficial to improving the speed measurement efficiency and accuracy.

And S34, drawing a speed change curve by using the actual speed, and performing time synchronization on the running track of the test vehicle and the speed change curve.

Specifically, in this embodiment, a second rectangular coordinate system is established with time as a horizontal axis and actual speed as a vertical axis, so as to draw a speed change curve; the abscissa of any point on the test vehicle travel path represents the distance of the point projected onto the origin of coordinates on the x-axis, and the ordinate represents the distance of the point projected onto the vertical axis on the y-axis. For the same test vehicle, an actual speed corresponds to any point of the test vehicle running track, and the speed change curve and the vehicle running track have a starting point and an ending point due to the limited length of the monitored road section.

Further, the vertical axis of the test vehicle running track and the vertical axis of the speed change curve are in the same straight line, the horizontal axis of the test vehicle running track and the horizontal axis of the speed change curve are in different straight lines which are parallel but not overlapped, the starting points of the speed change curve and the vehicle running track are on the vertical axis, and the ending points are on the same straight line perpendicular to any one horizontal axis, so that the time synchronization of the test vehicle running track and the speed change curve is realized, and at the moment, as long as any point is taken on the test vehicle running track, the straight line perpendicular to the horizontal axis corresponding to the speed change curve can be intersected with the speed change curve through the point, and the actual speed of the test vehicle at the point and the time taken by the test vehicle running to the point can be rapidly determined. The time synchronization also helps to eliminate the effect of time deviation on the accuracy of the calculated test radial velocity.

S35, according to the result of time synchronization, calculating the test radial speed of the test vehicle according to the running track of the test vehicle and the actual speed, and further calculating the test Doppler frequency shift.

Wherein, S35 further comprises the following steps:

S351, determining a test included angle between a connecting line of the millimeter wave radar and the test vehicle according to the running track of the test vehicle.

Specifically, in this embodiment, the position of the millimeter wave radar is unchanged, the measured vehicle speed is a radial vehicle speed, that is, the actual speed is a speed component on the connection line between the test vehicle and the radar, and the direction points to the millimeter wave radar, so that under the condition that the actual speed of the test vehicle is known, the accurate radial vehicle speed can be calculated only by obtaining the magnitude of the included angle between the connection line between the millimeter wave radar and the test vehicle, that is, the magnitude of the test included angle, so that the measuring error caused by multipath effect, mismatching of the vehicle moving direction and change of the dynamic environment when the millimeter wave radar measures the speed can be eliminated, thereby providing a reliable data base for subsequently obtaining the speed of the target vehicle, and improving the accuracy and reliability of the speed measurement.

S352, calculating the test radial speed of the test vehicle according to the test included angle and the actual speed, and further calculating the test Doppler frequency shift, wherein the test Doppler frequency shift meets the following relation:

Wherein, For the test Doppler shift,/>For the actual speed,/>For test included angle,/>Is the wavelength of electromagnetic waves emitted by millimeter wave radar.

Specifically, in this embodiment, the vehicle driving track obtained based on the three-dimensional laser radar is accurate and reliable, so that the obtained test included angle is also accurate and reliable, and the actual speed monitored by the vehicle is also accurate and reliable, so that the accurate and reliable test doppler shift can be finally obtained, and a reliable data base is provided for measuring the speed of the target vehicle.

S36, acquiring a frequency difference change curve by using the test intermediate frequency signal frequency and the test Doppler frequency shift, and further constructing the frequency difference database.

Wherein, S36 further comprises the following steps:

s361, drawing a test intermediate frequency signal frequency change curve by using the test intermediate frequency signal frequency, and drawing a test Doppler frequency shift change curve by using the test Doppler frequency shift.

Specifically, in this embodiment, when the fm continuous wave is used for speed measurement, due to the coupling between the speed and the distance, the radial speed of the test vehicle cannot be calculated by using the test intermediate frequency signal in one period, so that the radial speed of the test vehicle can be calculated by analyzing the test intermediate frequency signals in at least two periods, therefore, in step S331, the one-dimensional FFT conversion is actually performed on the test intermediate frequency signals in different periods, which are adjacent to each other, and finally, one test intermediate frequency signal frequency is estimated, and because the test vehicle is continuously moving, the test intermediate frequency signals in different periods are continuously obtained by the millimeter wave radar, a plurality of test intermediate frequency signal frequencies can be finally obtained, and the test intermediate frequency signal frequency is used as a vertical axis to establish a third rectangular coordinate system by using the time as a horizontal axis, and then, a test intermediate frequency signal frequency change curve is drawn by using the test intermediate frequency signal frequency.

Further, after the test vehicle driving track is determined, 99 points are taken at equal intervals on the test vehicle driving track based on the abscissa of the first rectangular coordinate system, and test doppler shift corresponding to the 99 points is calculated, and according to step S34, the time taken for the test vehicle to travel to the 99 points can be obtained, so that a fourth rectangular coordinate system can be established based on the time as the horizontal axis and the test doppler shift as the vertical axis, and further a test doppler shift change curve can be drawn in the fourth rectangular coordinate system.

S362, time synchronization is carried out on the test intermediate frequency signal frequency change curve and the test Doppler frequency shift change curve corresponding to the same test vehicle, and then the difference between the test intermediate frequency signal frequency change curve and the test Doppler frequency shift change curve is used as the frequency difference change curve.

Specifically, in this embodiment, since the third rectangular coordinate system and the fourth rectangular coordinate system are both time on the horizontal axis, and the test doppler shift is the difference between the transmitting frequency and the receiving frequency of the millimeter wave radar and is directly related to the frequency, the test doppler shift change curve can be drawn in the third rectangular coordinate system, so that the time synchronization of the test intermediate frequency signal frequency change curve and the test doppler shift change curve is realized, and the subsequent operation of subtracting the curves is facilitated.

Further, in the third rectangular coordinate system, the frequency difference change curve obtained by subtracting the test doppler shift change curve from the test intermediate frequency signal frequency change curve is easily found that the frequency difference change curve is located between the test intermediate frequency signal frequency change curve and the doppler shift change curve.

S363, constructing the frequency difference database by using the test intermediate frequency signal frequency change curve, the test Doppler frequency shift change curve and the frequency difference change curve.

Specifically, in this embodiment, a frequency variation curve of the intermediate frequency signal, a doppler shift variation curve of the intermediate frequency signal, and a frequency variation curve of the doppler shift are obtained by one test and used as a set of curve data, and multiple sets of curve data can be obtained through multiple tests, so that a frequency variation database can be established, and a data base is provided for the subsequent measurement of the speed of the target vehicle.

And S4, in an actual measurement stage, when the target vehicle runs on the monitored road section, acquiring target point cloud data of the monitored road section by using the three-dimensional laser radar, and acquiring a target intermediate frequency signal by using the millimeter wave radar.

Specifically, in the present embodiment, this step may be described with reference to step S2.

S5, determining a reference driving path of the target vehicle according to the target point cloud data and the vehicle path database, and further determining a reference difference frequency change curve according to the frequency difference database.

Wherein, S5 further comprises the following steps:

S51, acquiring a vehicle driving path of the target vehicle according to the target point cloud data, selecting a plurality of target sampling points on the vehicle driving path, and selecting a test sampling point corresponding to the target sampling point on a test vehicle driving track according to the target sampling point, wherein the target sampling point and the corresponding test sampling point at least meet one of the same abscissa and the same ordinate.

In particular, in the present embodiment, the time factor is not considered when the target sampling point is selected on the vehicle driving path and when the test sampling point is selected on the test vehicle driving track, because the time when different vehicles drive through the monitored road section is almost impossible to be identical, which means that the positions of the test vehicle and the target vehicle on the monitored road section are not identical in the same time, which is disadvantageous for the subsequent calculation of the consistency check value.

Further, considering that after the test vehicle and the target vehicle drive through the monitored road section, if the vehicle driving path is also drawn in the first right-angle coordinate system, the starting points of the vehicle driving path and the test vehicle driving track are on the vertical axis, and the ending points are on the same straight line passing through the origin of coordinates, if at this time, a straight line passing through the origin of coordinates and intersecting the vehicle driving path and the test vehicle driving track at the point g and the point h respectively, the point g is a target sampling point, the h is a test sampling point corresponding to the g, the test sampling point is acquired at equal intervals with the horizontal axis of the first right-angle coordinate system, and the target sampling point and the test sampling point are acquired in such a way, so that the subsequent calculation of the consistency check value is facilitated.

S52, based on the selected target sampling points and the test sampling points, calculating a consistency check value of the test vehicle running track and the vehicle running track in the vehicle path database by using a consistency check model.

Specifically, in the present embodiment, based on the description of S51, it is not difficult to obtain the magnitude of the consistency check value, which actually reflects the similarity between the test vehicle running track and the vehicle running track, and the greater the consistency check value, the greater the similarity between the test vehicle running track and the vehicle running track, and the consistency check model satisfies the following relationship:

，

Wherein, For consistency check value, N is the number of target sampling points,/>For the abscissa of the ith target sampling point in the rectangular coordinate system,/>For the abscissa of the ith test sample point in a rectangular coordinate system,/>Is the ordinate of the ith target sampling point in a rectangular coordinate system,/>Is the ordinate of the ith test sample point in the rectangular coordinate system. Number of target sampling points is taken/>，/>For the time it takes for the target vehicle to travel to the target sampling point, T is the frequency modulation period, t=0.001 s.

Further, when the frequency modulation continuous wave radar measures the vehicle speed by adopting a sawtooth wave as a modulation mode, the distance between the vehicle and the radar is coupled with the vehicle speed, and according to the prior art, the vehicle speed and the distance between the vehicle and the radar respectively satisfy the following relations:

Wherein, For vehicle speed,/>Wavelength of electromagnetic wave emitted by radar,/>For Doppler shift, c is the speed of light, B is the frequency modulation bandwidth, in this embodiment B is 1000MHz,/>Is the frequency of the intermediate frequency signal,/>Is of frequency difference and/>. It can be seen from these two relations that when the millimeter wave radar is fixed in the curve, when two vehicles travel through the monitoring area of the millimeter wave radar in a similar track, the difference of the distances between the two vehicles and the radar can be regarded as a fixed value, and the fixed value is recorded as a fixed distance value, so that when the target vehicle speed is calculated later, the target vehicle speed can be calculated only by calculating the fixed distance value, and the calculation mode refers to step S6.

And S53, taking the test vehicle running track corresponding to the maximum consistency check value as a reference running path of the target vehicle.

Specifically, in this embodiment, the degree of similarity between the vehicle travel path and the test vehicle travel path is limited, and since the distance constant is not strictly a constant value, the accuracy of the target vehicle speed calculated based on a reference travel path needs to be improved, and it is considered that the speed measurement error caused by using the distance constant is reduced by continuously obtaining the test vehicle travel path most similar to the vehicle travel path, and the accuracy of the speed measurement is improved. As can be seen from the description of step S52, the calculation of the consistency check value is not stopped when the target vehicle is traveling on the monitored road section, and the maximum consistency check value may not be a constant value because the vehicle travel path is changing, so that the reference travel paths obtained at different points in time are not necessarily the same test vehicle travel track. Therefore, after the distance constant value is calculated based on the first reference driving path, the distance constant value can still be used even if different reference driving paths are obtained later, and the accuracy of speed measurement is further improved to the greatest extent.

Further, in other alternative embodiments, in order to reduce the data processing amount, 20 marking points may be taken at equal intervals on the abscissa of the first coordinate system, and when the target vehicle travels to the marking points, the reference travel path is acquired again to calculate the target vehicle speed.

S54, inquiring a frequency difference change curve corresponding to the reference driving path in the frequency difference database, and recording the frequency difference change curve as a reference frequency difference change curve.

And S6, determining optimal Doppler shift according to the target intermediate frequency signal and the reference difference frequency change curve, and calculating the target vehicle speed by using the optimal Doppler shift.

Wherein, S6 further comprises the following steps:

S61, estimating the target intermediate frequency signal frequency of the target intermediate frequency signal, drawing a target intermediate frequency signal frequency change curve, and performing time synchronization on the target intermediate frequency signal frequency change curve and the vehicle driving path.

Specifically, in the present embodiment, the method for estimating the frequency of the target intermediate frequency signal refers to step S33, the method for drawing the frequency variation curve of the target intermediate frequency signal refers to step S361, and the method for time-synchronizing the frequency variation curve of the target intermediate frequency signal with the vehicle running path refers to step S34.

S62, calculating the optimal Doppler shift according to the target intermediate frequency signal frequency change curve and the reference difference frequency change curve, wherein the optimal Doppler shift meets the following relation:

Wherein, Time taken for target vehicle to travel to target sampling point,/>For the time taken for the test vehicle corresponding to the reference travel path to travel to the test sampling point corresponding to the target sampling point,/>For optimal Doppler shift when the target vehicle is driving to the target sampling point,/>For the target intermediate frequency signal frequency when the target vehicle runs to the target sampling point,/>For the frequency difference value on the reference difference frequency change curve when the test vehicle runs to the test sampling point,/>Is of a certain value/>In particular a distance constant,/>，/>For the test medium frequency signal frequency when the test vehicle runs to the test sampling point,/>Is the test Doppler shift when the test vehicle is traveling to the test sampling point.

Specifically, in the present embodiment, according to the description of step S52, a distance constant value needs to be calculated before calculating the optimal doppler shift, and after the first reference travel path is obtained, the distance constant value is the difference between the ordinate of the start point of the reference travel path and the ordinate of the start point of the travel path of the vehicle.

Further, after the distance constant value is obtained, there areIn determiningIn the case of/>The value of (2) can be determined directly by reference to the difference frequency curve, while/>It is known that/>, can be directly calculated. Therefore, speed measurement errors caused by mismatching of radar beam directions and vehicle movement directions, multipath effects and changes of dynamic environments during curve movement of the automobile can be avoided, and accuracy of curve speed measurement is improved.

And S63, calculating the speed of the target vehicle by using the optimal Doppler frequency shift.

Specifically, in the present embodiment, after obtaining the optimal Doppler frequency, the calculation is performed using step S52The target vehicle speed is calculated.

In an alternative embodiment, referring to fig. 3, the present invention further provides a dual-radar-based target tracking speed measurement system, where the dual-radar-based target tracking speed measurement method provided by the present invention is used, and the system includes a data acquisition module A1, a data processing module A2, a data storage module A3, and a data output and early warning module A4.

The data acquisition module A1 is used for acquiring the actual speed of the test vehicle when the test vehicle passes through a monitoring road section each time, acquiring test point cloud data of the monitoring road section by using a three-dimensional laser radar and acquiring a test intermediate frequency signal by using a millimeter wave radar; and in the actual measurement stage, when the target vehicle runs on the monitored road section, acquiring target point cloud data of the monitored road section by using the three-dimensional laser radar, and acquiring a target intermediate frequency signal by using the millimeter wave radar.

Specifically, in the present embodiment, the data acquisition module A1 includes a three-dimensional laser radar, a millimeter wave radar, and a speed sensor. The data acquisition module A1 specifically executes the content described in step S2 and step S4.

The data processing module A2 is used for constructing a vehicle path database based on the test point cloud data, and further constructing a frequency difference database based on the test intermediate frequency signal and the actual speed; determining a reference driving path of the target vehicle according to the target point cloud data and the vehicle path database, and further determining a reference difference frequency change curve according to the frequency difference database; and determining optimal Doppler shift according to the target intermediate frequency signal and the reference difference frequency change curve, and calculating the target vehicle speed by using the optimal Doppler shift.

Specifically, in this embodiment, the data processing module A2 is wirelessly connected to the data acquisition module A1, including but not limited to using bluetooth connection and using internet of things connection, and the content executed by the data processing module A2 may be described with reference to steps S3 to S6.

The data storage module A3 is configured to store all data generated by the data processing module.

Specifically, in the present embodiment, the data storage module A3 is electrically connected to the data processing module A2, and the data specifically generated by the data processing module A2 can refer to the contents described in steps S3 to S6.

The data output and early warning module A4 is used for outputting the vehicle speed and giving an alarm when the vehicle overspeed.

Specifically, in this embodiment, the data output and early warning module A4 is wirelessly connected with the data storage module A3 and the data processing module A2, including but not limited to using bluetooth connection and using internet of things connection, the data output and early warning module A4 includes a data output sub-module and an early warning sub-module, the data output sub-module includes an electronic display screen for displaying the vehicle speed, and the early warning sub-module sends out an alarm when the vehicle speed exceeds a speed threshold, where the speed threshold is set according to the speed limit condition of the monitored road section.

It should be noted that, in some cases, the actions described in the specification may be performed in a different order and still achieve desirable results, and in this embodiment, the order of steps is merely provided to make the embodiment more clear, and it is convenient to describe the embodiment without limiting it.

In summary, the method provided by the invention is based on constructing a vehicle path database and a frequency difference database, uses a three-dimensional laser radar to acquire target point cloud data of a monitored road section, uses a millimeter wave radar to acquire a target intermediate frequency signal, then determines a reference driving path of a target vehicle according to the target point cloud data and the vehicle path database, further determines a reference difference frequency change curve according to the frequency difference database, and finally determines optimal Doppler shift and calculates the speed of the target vehicle according to the target intermediate frequency signal and the reference difference frequency change curve.

Firstly, the three-dimensional laser radar can provide enough detailed spatial information to accurately track and position the target vehicle, and simultaneously provides a reliable data base for measuring the speed of the target vehicle.

And secondly, the millimeter wave radar can realize all-weather data acquisition, can meet the requirement of 24-hour speed measurement, and when the frequency of an intermediate frequency signal is acquired, the used A-I-Rife algorithm not only has higher frequency prediction precision, but also has lower calculated quantity, and improves the speed measurement efficiency and accuracy.

And thirdly, based on the theoretical basis that the frequency modulation continuous wave radar adopts sawtooth waves as a modulation mode to measure the speed, a consistency check model is used for acquiring a reference driving path, and further a reference frequency difference change curve is acquired for calculating the speed of a target vehicle, so that the combination speed measurement and the advantage combination of the three-dimensional laser radar and the millimeter wave radar are realized, the speed measurement error caused by the mismatching of the radar beam direction and the vehicle movement direction, the multipath effect and the change of the dynamic environment when the vehicle moves in a curve is avoided, and the accuracy of the speed measurement of the curve is further improved.

Finally, the invention can provide more choices for vehicle speed measurement and provide reference for speed measurement of vehicles moving in a curve.

In addition, the system provided by the invention has higher speed measuring efficiency and accuracy, can provide more choices for vehicle speed measurement, and promotes the development of radar speed measurement to a more accurate and reliable direction.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention, and are intended to be included within the scope of the appended claims and description.

Claims

1. The target tracking speed measuring method based on double radars is characterized by comprising the following steps of:

analyzing possible driving modes of the vehicle on the monitoring road section in the test stage, and enabling the test vehicle to drive through the monitoring road section for multiple times according to different driving modes;

When the test vehicle passes through the monitoring road section each time, acquiring the actual speed of the test vehicle, acquiring test point cloud data of the monitoring road section by using a three-dimensional laser radar, and acquiring a test intermediate frequency signal by using a millimeter wave radar;

Constructing a vehicle path database based on the test point cloud data, and further constructing a frequency difference database based on the test intermediate frequency signal and the actual speed;

In an actual measurement stage, when a target vehicle runs on a monitoring road section, acquiring target point cloud data of the monitoring road section by using the three-dimensional laser radar, and acquiring a target intermediate frequency signal by using the millimeter wave radar;

determining a reference driving path of the target vehicle according to the target point cloud data and the vehicle path database, and further determining a reference difference frequency change curve according to the frequency difference database;

And determining optimal Doppler shift according to the target intermediate frequency signal and the reference difference frequency change curve, and calculating the target vehicle speed by using the optimal Doppler shift.

2. The method for measuring the speed of a target tracking system based on double radars according to claim 1, wherein the step of constructing a vehicle path database based on the test point cloud data, and further constructing a frequency difference database based on the test intermediate frequency signal and the actual speed comprises the steps of:

3. The method for tracking and measuring speed of a target based on double radars according to claim 2, wherein the step of obtaining two-dimensional position coordinates of the test vehicle according to the backup point cloud data, and further constructing the vehicle path database based on the two-dimensional position coordinates comprises the following steps:

4. The method for tracking and measuring speed of a target based on double radars according to claim 2, wherein said performing one-dimensional FFT on said test intermediate frequency signals of different periods to obtain a spectrum of said test intermediate frequency signals, and further estimating the frequency of the test intermediate frequency signals comprises the steps of:

5. The method for tracking and measuring speed of a target based on double radars according to claim 2, wherein the calculating the test radial velocity of the test vehicle according to the running track of the test vehicle and the actual velocity according to the result of time synchronization, and further calculating the test doppler shift comprises the following steps:

，

6. The method for tracking and measuring speed of a target based on double radars according to claim 2, wherein the step of obtaining a frequency difference change curve by using the test intermediate frequency signal frequency and the test doppler shift, and further constructing the frequency difference database comprises the steps of:

7. The method for tracking and measuring speed of a target based on double radars according to claim 6, wherein the step of determining the reference travel path of the target vehicle according to the target point cloud data and the vehicle path database, and further determining the reference difference frequency change curve according to the frequency difference database comprises the steps of:

8. The dual radar-based target tracking speed measurement method according to claim 7, wherein the consistency check model satisfies the following relationship:

，

9. The method for tracking and measuring speed of a target based on double radars according to claim 2, wherein said determining an optimal doppler shift according to said target intermediate frequency signal and said reference difference frequency variation curve, and calculating a target vehicle speed using said optimal doppler shift comprises the steps of:

，

Wherein, Time taken for the target vehicle to travel to the target sampling point,/>For the time taken for the test vehicle corresponding to the reference driving path to drive to the test sampling point corresponding to the target sampling point, B is the frequency modulation bandwidth, T is the frequency modulation period, c is the light speed,/>For optimal Doppler shift when the target vehicle is traveling to the target sampling point,/>For the target intermediate frequency signal frequency when the target vehicle runs to the target sampling point,/>For the frequency difference value on the reference difference frequency change curve when the test vehicle runs to the test sampling point,/>Is of a certain value/>，/>For the test intermediate frequency signal frequency when the test vehicle runs to the test sampling point,/>A test Doppler shift when the test vehicle travels to the test sampling point;

10. A dual radar-based target tracking speed measurement system using a dual radar-based target tracking speed measurement method according to any one of claims 1 to 9, comprising:

The data acquisition module is used for acquiring the actual speed of the test vehicle when the test vehicle passes through the monitoring road section each time, acquiring test point cloud data of the monitoring road section by using a three-dimensional laser radar and acquiring a test intermediate frequency signal by using a millimeter wave radar; in an actual measurement stage, when a target vehicle runs on a monitoring road section, acquiring target point cloud data of the monitoring road section by using the three-dimensional laser radar, and acquiring a target intermediate frequency signal by using the millimeter wave radar;

The data processing module is used for constructing a vehicle path database based on the test point cloud data, and further constructing a frequency difference database based on the test intermediate frequency signal and the actual speed; determining a reference driving path of the target vehicle according to the target point cloud data and the vehicle path database, and further determining a reference difference frequency change curve according to the frequency difference database; determining optimal Doppler shift according to the target intermediate frequency signal and the reference difference frequency change curve, and calculating the target vehicle speed by using the optimal Doppler shift;

The data storage module is used for storing all data generated by the data processing module;

The data output and early warning module is used for outputting the speed of the vehicle and giving an alarm when the vehicle overspeed.