CN114236545B - Method for detecting vehicle-mounted millimeter wave radar non-direct-view front vehicle - Google Patents
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- G—PHYSICS
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Abstract
The invention discloses a vehicle-mounted millimeter wave radar non-direct-view front vehicle detection method, which is applied to the technical field of non-direct-view target detection and positioning, and solves the problem that the prior art lacks a non-direct-view front vehicle target detection scheme; according to the method, firstly, according to the propagation phenomenon of electromagnetic waves, the multipath signal propagation path of a front vehicle in a road under a detection scene is analyzed; then, an echo signal model is built based on the echo time delay of the ground primary reflection path; finally, target constant false alarm detection and a multichannel phase comparison positioning algorithm are applied to the echo signals to obtain a positioning result of a front vehicle target; the scheme of the invention can truly determine the electromagnetic propagation path of the front vehicle target, and effectively realize the detection and positioning functions of the front vehicle target.
Description
Technical Field
The invention belongs to the technical field of non-direct-view target detection and positioning, and particularly relates to a front vehicle target detection and positioning technology under a road non-direct-view scene.
Background
In road scenarios, traffic accidents caused by vehicle collisions can result in significant loss of property and casualties. In the worst case, a multiple vehicle collision occurs. Currently, vehicle collision avoidance systems (collision avoidance systems, cas) improve vehicle safety by detecting and predicting the motion characteristics of a vehicle in front in a Line of Sight (LOS) area. However, the existing collision avoidance system cannot detect the motion state of a Non-Line of Sight (NLOS) vehicle, and cannot avoid the occurrence of multiple vehicle collisions. In general, detecting non-looking vehicles is a challenging task, especially in complex road scenarios. Therefore, detection of a non-direct-view vehicle is one of the problems of current research in the field of vehicle-mounted radars.
Many research institutions abroad conduct detection and positioning research on non-direct-view vehicles. In 2014, swedish national defense research institute scholars can use multipath echoes of a wall body primary reflection path to detect NLOS moving vehicles (T.Johansson, A.Orbom, A.Sume, et al Radar measurements of moving objects around corners in a realistic scene [ C ]. In Radar Sensor Technology XVIII,2014, vol.9077.) behind corners by using the X-band radar, actual measurement experiments prove that the non-direct-view vehicles behind corners can be detected, but the experimental results are mainly applied to urban building environments and are limited by multiple attenuations of the building wall body reflection path, so that the range for detecting the non-direct-view vehicles is very limited. In 2021, the university of finnish tank peace sets up corner reflectors based on vehicle-mounted millimeter wave radar to detect moving vehicles behind a non-direct-view crossroad (D.Solomitckii, C.B.Barneto, M.Turunen, et al millimeter-Wave Radar Scheme with Passive Reflector for Uncontrolled Blind Urban Intersection [ J ]. IEEE Transactions on Vehicular Technology,2021,70 (8): 7335-7346.), and the article builds an analytical model on the basis of the object where the probability of detecting the moving vehicles is maximized, and thereby determines the measurement parameters of the corner reflectors when the moving vehicles are best detected at a specific crossroad geometry. The method needs to set an optimal reflecting surface for detecting the non-direct-view vehicles by oneself, and the research can only be applied to specific intersections and can not bring universal help to the detection of the road non-direct-view vehicles. In 2019, university of hong Kong specially researches the problem of non-direct-view front vehicle detection in road environment (Z.Zhang, S.W.Ko, R.Wang and K.Huang.Millifer-Wave Multi-Point Vehicular Positioning for Autonomous Driving [ C ].2019IEEE Global Communications Conference,Waikoloa,USA,2019,pp.1-6.), the article takes NLOS front vehicle target as a transmitting end, sets cooperative receiving signal vehicles, and then utilizes side vehicle reflection paths to position the front vehicle target in multiple scattering points.
Disclosure of Invention
In order to solve the technical problems, the invention provides a vehicle-mounted millimeter wave radar non-direct-view front vehicle detection method, which can accurately calculate the position of a non-direct-view front vehicle target shielded by an intermediate vehicle based on ground primary reflection path echo information and combined with a constant false alarm detection and multichannel phase comparison positioning method.
The invention adopts the technical scheme that: a vehicle-mounted millimeter wave radar non-direct-view front vehicle detection method is based on an application scene comprising the following steps: the vehicle comprises a radar vehicle O, an intermediate vehicle A and a front vehicle C, wherein the intermediate vehicle A is positioned in a direct-view area in front of the radar vehicle O, and the front vehicle C is positioned in a non-direct-view area of the radar vehicle O because of shielding of the intermediate vehicle A; the radar vehicle O is provided with a millimeter wave radar system, the radar includes 2 transmitting antennas, 4 receiving antennas,
when the radar vehicle O detects a front vehicle C in a non-direct-view area by utilizing a millimeter wave radar system, the front vehicle C comprises two electromagnetic propagation paths, wherein the first path is a direct path for detecting an intermediate vehicle A, the electromagnetic propagation process is that electromagnetic waves are emitted from the radar vehicle O to return to the radar vehicle O through a main body scattering path of the intermediate vehicle A, and the electromagnetic propagation paths are recorded as follows: O→A→O. The other path is a ground reflection path for detecting the front vehicle C, the electromagnetic propagation process is that electromagnetic waves are emitted from the radar vehicle O, a part of energy passes through the bottom of the intermediate vehicle A and is reflected at the ground B point to reach the front vehicle C, then the electromagnetic waves are scattered by a target and then returned to the radar vehicle O in a primary path, and the electromagnetic wave propagation path is marked as follows: o- & gt, B- & gt, C- & gt, B- & gt and O; the detection method comprises the following steps:
s1, obtaining radar echo signals according to respective time delays of two electromagnetic propagation paths;
s2, obtaining the distance between the radar vehicle O and the front vehicle C by adopting a one-dimensional unit average constant false alarm detection method;
s3, determining the azimuth angle of the front vehicle C by adopting a multichannel phase comparison method;
and S4, calculating the two-dimensional coordinates of the front vehicle C according to the distance between the radar vehicle O and the front vehicle C and the azimuth angle of the front vehicle.
The step S2 specifically comprises the following steps:
s21, performing digital sampling, MTI filtering and fast Fourier transform operation on the echo signals in the step S1 to obtain a target range profile, wherein the j-th periodic range profile is expressed as follows:
x j ＝[x j (1),…,x j (i),…,x j (N c )]
where x is j (i) Represents the i-th distance unit value, N c Is the number of distance units;
s22, accumulating all period target amplitude values in a frame by adopting a non-coherent superposition method, and obtaining a accumulated range profile by N T A period is a frame accumulation, expressed as:
where g (i) represents the i-th distance unit value of the accumulated range profile, h is the index number of the frame, and |·| represents the absolute value taking operation;
s23, detecting the accumulated distance image by adopting a one-dimensional unit average constant false alarm detection method, obtaining a distance unit index of a front vehicle target and further calculating a front vehicle target distance R.
The step S23 specifically includes: for the i-th distance cell, the detection threshold may be expressed as:
wherein P is f Represents the false alarm probability N r Represents the reference unit number g h (i) An ith distance cell value representing an h-frame accumulated range profile;
and comparing all the distance units with the corresponding detection threshold values to obtain the distance unit index of the front vehicle target so as to calculate the distance R of the front vehicle target.
The specific implementation process of the step S3 is as follows:
s312, for a uniform array receiving model, the expression of the phase difference phi between two adjacent antennas is as follows:
here, θ is the azimuth angle of the front vehicle target, d is the distance between two antennas, and λ is the wavelength of the transmitted signal;
s32, assuming that the echo signals of the two receiving antennas are y respectively 1 (t) and y 2 (t) applying Fourier transform processing to the echo signals to obtain signal spectrums Y 1 (ω)and Y 2 (ω), then the phase difference of the two receive antennas is denoted as:
im (-) represents the complex imaginary part and Re (-) represents the complex real part;
s33, combining the antenna phase difference formulas of the step S31 and the step S32, and calculating the azimuth angle theta of the front vehicle target as follows:
in step S4, the two-dimensional coordinate calculation formula of the preceding vehicle C is as follows:
x is the abscissa of the front vehicle C and y is the ordinate of the front vehicle C.
The invention has the beneficial effects that: according to the invention, a vehicle-mounted millimeter wave radar is utilized to detect and position a front vehicle target ahead on a road without direct vision; according to the propagation phenomenon of electromagnetic waves, the main propagation path of the electromagnetic waves of the front vehicle target before detection is analyzed to be a ground primary reflection path; in addition, the invention effectively utilizes the constant false alarm detection and the multichannel phase comparison method to realize the detection and positioning of the front vehicle target without direct vision. The actual measurement result shows that the method can obtain a good detection positioning result of the target in the detection scene of the front vehicle before the non-direct vision in the reply road.
Drawings
FIG. 1 is a model of electromagnetic wave propagation in a front vehicle detection scene;
wherein (a) is a side view and (b) is a top view;
FIG. 2 is a front vehicle detection actual measurement scenario;
FIG. 3 is a flow chart of an embodiment of the present invention;
FIG. 4 is a front truck detection raw range profile;
fig. 5 is a front vehicle target positioning result.
Detailed Description
The present invention will be further explained below with reference to the drawings in order to facilitate understanding of technical contents of the present invention to those skilled in the art.
According to the method for detecting the front vehicle with the vehicle-mounted millimeter wave radar and the non-direct-view front vehicle, disclosed by the invention, a scene of the blocked front vehicle is shown as shown in fig. 1, the scene comprises a radar vehicle O, an intermediate vehicle A and a front vehicle C, the intermediate vehicle A can be found to be positioned in a direct-view area in front of the radar vehicle A, and the front vehicle C is positioned in the non-direct-view area because of the blocking of the intermediate vehicle A.
The hidden front vehicle target is detected by adopting a millimeter wave radar system, the radar comprises 2 transmitting antennas and 4 receiving antennas, and the radar is defined as an origin O detection target. The front vehicle detection scene can be seen to mainly comprise two electromagnetic propagation paths, wherein the first path is a direct path for detecting a middle vehicle, the electromagnetic propagation process can be described as that electromagnetic waves return to the radar from the radar vehicle through a middle vehicle body scattering original path, and the electromagnetic wave propagation path is as follows: O→A→O. The other path is a ground reflection path for detecting a front vehicle target, electromagnetic wave is emitted from a radar vehicle in the electromagnetic propagation process, a part of energy passes through the middle vehicle bottom and is reflected at a ground point B to reach a front vehicle C, then the electromagnetic wave is returned to the radar in an original path after being scattered by the target, and the electromagnetic wave propagation path is as follows: O→B→C→B→O.
The processing flow of the method comprises the following steps:
step 1: echo signal modeling
Millimeter wave radar transmitting carrier frequency f 0 S (t), the transmit signal expression is:
s(t)＝A 0 exp(j2πf 0 t+jπμt 2 )u(t)
wherein the method comprises the steps of
A 0 Representing the amplitude of the transmitted signal, T representing time, the signal bandwidth denoted B, the pulse time denoted T, i.e. having a chirp rate denoted μ=b/T, the expression of the moment function u (T) is as follows:
by analyzing an electromagnetic multipath propagation model in a front vehicle detection scene, a radar receiving echo contains direct path information and ground primary reflection path information, and the direct path echo time delay is set as tau path-1 The time delay of the primary reflection path of the ground is tau path-2 The specific expression of time delay is
Where C represents the propagation speed of electromagnetic waves, |OA| represents the distance between the radar O and the intermediate vehicle A, |OB| represents the distance between the radar O and the intermediate vehicle bottom reflection point B, |BC| represents the distance between the intermediate vehicle bottom reflection point B and the preceding vehicle C, l path-1 =2|oa| stands for direct path propagation length, l path-2 =2 (|ob|+|bc|) represents the ground primary reflection path propagation distance.
For a receiving antenna, the echo signal may be represented as
y(t)＝σ 1 s(t-τ path-1 )+σ 2 s(t-τ path-2 )+n(t)
Here σ 1 For intermediate train target scattering coefficient, sigma 2 For the front vehicle target scattering coefficient, n (t) represents background noise and environmental interference.
Step 2: non-direct view target detection
In order to eliminate the influence of the environmental clutter in the radar echo, a moving target indication (Moving Target Indicator, MTI) method is adopted to eliminate the static clutter in the environment, and the echo of a dynamic target is reserved. The target range profile can be obtained by digitally sampling the echo signal y (t), MTI filtering and FFT operation, and the jth period range profile can be expressed as
x j ＝[x j (1),…,x j (i),…,x j (N c )]
Where x is j (i) Represents the ith distance element value, and N c Is the number of distance units.
Then, in order to enhance the energy at the target, the incoherent superposition method is adopted to accumulate the target amplitude values of all periods in one frame, and the accumulated range profile is N T A period is a frame accumulation, which can be expressed as:
where g (i) represents the i-th distance unit value of the accumulated range profile, h is the index number of the frame, and |·| represents the absolute value taking operation.
In order to obtain the distance of the target, a one-dimensional unit average constant false alarm detection (Cell Averaging-Constant False Alarm Rate, CA-CFAR) method is adopted to detect the accumulated range profile. For the i-th distance cell, the detection threshold may be expressed as:
wherein P is f Represents the false alarm probability N r Represents the reference unit number g h (i) And the ith distance unit value representing the accumulated range profile of the h frame.
And then comparing the values of all the distance units and the detection threshold through the self-adaptive judgment criteria to obtain the index of the target distance unit of the front vehicle, wherein the judgment criteria are as follows:
wherein H is 1 Representing the targeted hypothesis, H 0 Indicating that there is no target hypothesis, performing the judgment criterion of the above formula on all the distance units, and if the target hypothesis is present, reserving a distance unit index i. Calculating the target distance according to the distance unit index i first calculates the length R of each distance unit min The calculation formula is as follows:
wherein N is a For Fourier transform points, R max For the maximum distance that the radar can detect, the expression is as follows
R can be seen here max Mainly related to the setting of the parameters of the chirped continuous wave, wherein f s For radar sampling rate, k is the chirp rate of the chirped continuous wave. It is assumed that the object of the front vehicle has the ith distance unit after CFAR detection, and the distance R thereof can be calculated as r=r min ·i。
It should be noted that, in practical experiments, since the radar height is much smaller than the distance of the electromagnetic propagation path o→b, we approximate the path length of the once-through ground reflection to the distance R of the radar O to the front vehicle target C, i.e., having |ob|+|bc|c|oc| according to the mathematical geometry. Thus, the target distance obtained by CFAR detection at this time is a one-way ground primary reflection path distance, and is also equivalent to the front vehicle target distance R.
Step 3: non-direct view target positioning
After the distance R of the non-direct view front truck is obtained, a multichannel phase comparison method is used to determine the azimuth of the front truck target. The method calculates the azimuth angle of the target through the phase difference information of any two channels.
For a uniform array reception model, the phase difference Φ between two adjacent antennas can be expressed as:
where θ is the azimuth of the front vehicle target, d is the spacing of the two antennas, and λ is the wavelength of the transmitted signal.
Assume that the echo signals of the two receiving antennas are y respectively 1 (t) and y 2 (t) applying Fourier transform processing to the echo signals, respectively, to obtain a signal spectrum Y 1 (ω)and Y 2 (ω), then the phase difference of the two receive antennas can be expressed as:
im (-) represents the complex imaginary part and Re (-) represents the complex real part.
By combining the two antenna phase difference formulas, the azimuth angle theta of the front vehicle target can be calculated as follows:
after the target distance R is obtained through the detection of the front vehicle target and the target azimuth angle theta is obtained by applying the multichannel phase comparison method, the two-dimensional position coordinates of the target can be calculated as follows:
the coordinates (x, y) of the front vehicle target can be obtained according to the calculation formula of the above formula.
The following gives specific embodiments of the present invention based on actual measurement tests.
The detection of a front vehicle target is shown in fig. 2 as an actual scene. A front vehicle target is detected by adopting a linear frequency modulation continuous wave millimeter wave radar, the radar frequency is 77GHz, and the bandwidth is 0.9GHz. Here the radar position is assumed to be the central origin (0, 0) m and the radar system height is 0.35m. In the initial stage of the experiment, the distance between the radar and the middle vehicle is 6.5m, and the initial distance between the radar and the front vehicle is 14m. In the whole experimental stage, the intermediate vehicle keeps a static state, and the front vehicle target moves in a non-direct vision area in front of the intermediate vehicle, and the range of motion of the distance radar is 15-35m. As shown in fig. 3, the processing steps of the present invention include:
step 1: target distance detection
First, an original target range profile is obtained through fourier transform operation, as shown in fig. 4. It can be seen that the range profile includes the range trajectories of the intermediate vehicle and the front vehicle target, and the intermediate vehicle target amplitude energy is stronger than the front vehicle, and the range profile extends from 6.5m to 9.5m, because the vehicle body target is a surface scatterer, and no shielding exists, and all scattered electromagnetic waves of the surface target can directly return to the radar. The range profile of the front vehicle target is not expanded, which indicates that the echo path is a non-direct-view ground reflection path, and the energy loss is large and the path is single. And then MTI filtering is applied to the original range profile to eliminate the static intermediate vehicle target information, and then the real-time range value of the front vehicle target can be obtained through non-coherent superposition and CFAR detection.
Step 2: and calculating the target arrival angle of the front vehicle by adopting a multichannel phase comparison method.
Step 3: and calculating real-time position coordinates of the target by combining the distance and azimuth angle of the front vehicle target.
According to the steps 1 and 2, the target distance and the arrival angle can be calculated, then the target position is obtained through a coordinate calculation formula, and the obtained positioning result is shown in fig. 5. It can be seen that the ground primary reflection path is utilized to detect and locate the front vehicle target in the non-direct vision, the effective detection of the front vehicle target can be completed, the locating point trace is consistent with the real motion track of the front vehicle target, and the actual measurement practice proves the feasibility and effectiveness of the front vehicle detection method in the non-direct vision.
The method for detecting the non-direct-view front vehicle target in the road scene can accurately detect and position the front vehicle target, and verifies the accuracy and the effectiveness of the method.
Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (5)
1. The detection method for the vehicle-mounted millimeter wave radar non-direct-view front vehicle is characterized by comprising the following steps of: the vehicle comprises a radar vehicle O, an intermediate vehicle A and a front vehicle C, wherein the intermediate vehicle A is positioned in a direct-view area in front of the radar vehicle O, and the front vehicle C is positioned in a non-direct-view area of the radar vehicle O because of shielding of the intermediate vehicle A; the radar vehicle O is provided with a millimeter wave radar system, the radar includes 2 transmitting antennas, 4 receiving antennas,
when the radar vehicle O detects a front vehicle C in a non-direct-view area by utilizing a millimeter wave radar system, the front vehicle C comprises two electromagnetic propagation paths, wherein the first path is a direct path for detecting an intermediate vehicle A, the electromagnetic propagation process is that electromagnetic waves are emitted from the radar vehicle O to return to the radar vehicle O through a main body scattering path of the intermediate vehicle A, and the electromagnetic propagation paths are recorded as follows: O-A-O, wherein the other path is a ground reflection path for detecting the front vehicle C, the electromagnetic propagation process is that electromagnetic waves are emitted from the radar vehicle O, a part of energy passes through the bottom of the intermediate vehicle A and is reflected at the ground B point to reach the front vehicle C, and then the electromagnetic waves are scattered by a target and returned to the radar vehicle O in the original path, and the electromagnetic wave propagation path is recorded as follows: o- & gt, B- & gt, C- & gt, B- & gt and O; the detection method comprises the following steps:
s1, obtaining radar echo signals according to respective time delays of two electromagnetic propagation paths;
s2, obtaining the distance between the radar vehicle O and the front vehicle C by adopting a one-dimensional unit average constant false alarm detection method;
s3, determining the azimuth angle of the front vehicle C by adopting a multichannel phase comparison method;
and S4, calculating the two-dimensional coordinates of the front vehicle C according to the distance between the radar vehicle O and the front vehicle C and the azimuth angle of the front vehicle.
2. The method for detecting the front vehicle without direct vision by the vehicle-mounted millimeter wave radar according to claim 1, wherein the step S2 is specifically:
s21, performing digital sampling, MTI filtering and fast Fourier transform operation on the echo signals in the step S1 to obtain a target range profile, wherein the j-th periodic range profile is expressed as follows:
x j ＝[x j (1),…,x j (i),…,x j (N c )]
wherein x is j (i) Represents the i-th distance unit value, N c Is the number of distance units;
s22, accumulating all period target amplitude values in a frame by adopting a non-coherent superposition method, and obtaining a accumulated range profile by N T A period is a frame accumulation, expressed as:
where g (i) represents the i-th distance unit value of the accumulated range profile, h is the index number of the frame, and |·| represents the absolute value taking operation;
s23, detecting the accumulated distance image by adopting a one-dimensional unit average constant false alarm detection method, obtaining a distance unit index of a front vehicle target and further calculating a front vehicle target distance R.
3. The method for detecting the front vehicle with the vehicle-mounted millimeter wave radar and the non-direct-view method according to claim 2, wherein the step S23 is specifically: for the i-th distance cell, the detection threshold may be expressed as:
wherein P is f Represents the false alarm probability N r Represents the reference unit number g h (i) An ith distance cell value representing an h-frame accumulated range profile;
and comparing all the distance units with the corresponding detection threshold values to obtain the distance unit index of the front vehicle target so as to calculate the distance R of the front vehicle target.
4. The method for detecting the front vehicle without direct vision by using the vehicle-mounted millimeter wave radar according to claim 3, wherein the specific implementation process of the step S3 is as follows:
s312, for a uniform array receiving model, the expression of the phase difference phi between two adjacent antennas is as follows:
wherein θ is the azimuth of the front vehicle target, d is the distance between two antennas, and λ is the wavelength of the transmitted signal;
s32, assuming that the echo signals of the two receiving antennas are y respectively 1 (t) and y 2 (t) applying Fourier transform processing to the echo signals to obtain signal spectrums Y 1 (ω)and Y 2 (ω), then the phase difference of the two receive antennas is denoted as:
wherein Im (·) represents the complex imaginary part and Re (·) represents the complex real part;
s33, combining the antenna phase difference formulas of the step S31 and the step S32, and calculating the azimuth angle theta of the front vehicle target as follows:
5. the method for detecting a front vehicle with no direct vision by using a vehicle-mounted millimeter wave radar according to claim 4, wherein in step S4, the two-dimensional coordinate calculation formula of the front vehicle C is as follows:
where x is the abscissa of the front vehicle C and y is the ordinate of the front vehicle C.
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| CN106877992A (en) * | 2017-04-14 | 2017-06-20 | 南京林业大学 | A kind of recessive blind area cognitive method based on Vehicular virtual radar, system and vehicle |
| CN109087503A (en) * | 2018-09-04 | 2018-12-25 | 惠州市德赛西威智能交通技术研究院有限公司 | A kind of collaborative truck system and method based on V2X |
| CN109946648A (en) * | 2019-03-06 | 2019-06-28 | 东南大学 | Vehicle high-precision localization method based on ultra wide band under a kind of collaboration of bus or train route |
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