Method and System for Estimating Target Acceleration of Vehicle-mounted Radar Based on FrFT

Abstract

The present invention relates to a method and system for estimating the acceleration of a target of a vehicle-mounted radar based on the FrFT. The method includes: performing mixing processing and filtering on a plurality of continuously transmitted linear frequency modulation pulse signals and the received echo signals to obtain the beat signal of the echo, and sampling the beat signal to obtain a discrete beat signal; performing one-dimensional Fourier transform on each discrete beat signal to obtain the target distance, and acquiring the echo data corresponding to a plurality of discrete beat signals at the target distance; performing coherent accumulation on multiple groups of echo data, and according to the characteristics of the FrFT modulus function of the linear frequency modulation pulse signal, searching for the optimal rotation order to perform FrFT transform on the discrete beat signal after coherent accumulation, and determining the acceleration estimation value of the moving target according to the discrete beat signal after FrFT transform. Through the improved FrFT transform method, combined with the characteristics of the FrFT modulus function to search for the optimal rotation order, the acceleration estimation accuracy of the moving target is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of signal processing, and particularly to a method and system for estimating the target acceleration of a vehicle-mounted radar based on the FrFT. Background Art

[0002] With the development of technology, in the face of the increasingly congested urban traffic conditions in China, autonomous driving has gradually become an inevitable choice for future vehicle driving. The key technologies of autonomous vehicles include four core links: environmental perception, precise positioning, path planning, and drive-by-wire execution. Among them, environmental perception is not only the data basis for the other three key technologies but also the core of the four core links. Because only on the premise of accurately obtaining the perception information of the driving environment and other targets can the autonomous driving system make correct planning and control.

[0003] Environmental perception technology mainly includes target state perception and target recognition, which are often realized by using sensors such as cameras, millimeter-wave radars, and lidar. Among them, the millimeter-wave radar is mainly responsible for perceiving the distance, speed, acceleration, and azimuth angle information of moving targets. At present, the traditional millimeter-wave radar signal processing technology basically does not consider the acceleration information of the measured target, and at the same time, the offset error caused by acceleration is often ignored when estimating the target distance and speed. However, in fact, if the acceleration of a moving target can be accurately measured, not only can the estimation error caused by acceleration be compensated to obtain more accurate distance and speed information of the target, but also the motion state of the target can be judged more accurately, the motion of the target can be predicted, and measures can be automatically taken for obstacle avoidance and path planning to prevent traffic accidents and reduce the probability of accidents. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for estimating the target acceleration of a vehicle-mounted radar based on the FrFT, which can solve the problem that most current automotive millimeter-wave radars cannot measure the acceleration of moving targets and can more accurately judge the motion state of the target.

[0005] To achieve the above purpose, the present invention provides the following solutions:

[0006] The present invention provides a method for estimating the target acceleration of a vehicle-mounted radar based on the FrFT, and the method includes:

[0007] Continuously transmitting a plurality of linearly frequency-modulated pulse signals by using a millimeter-wave radar, and receiving the echo signals reflected by a moving target through a radar receiving antenna; the echo signals are the signals received by the radar receiving antenna after the linearly frequency-modulated pulse signals are reflected by the moving target;

[0008] Mix the echo signal with the chirp signal and perform low-pass filtering to obtain the beat signal of the echo; sample the beat signals of the echoes to obtain discrete beat signals;

[0009] Perform one-dimensional Fourier transform on each of the discrete beat signals to obtain the target distance, and acquire the echo data corresponding to multiple discrete beat signals at the target distance; the echo data is phase information;

[0010] Perform coherent integration on multiple groups of echo data received by multiple radar receiving antennas to obtain the discrete beat signal after coherent integration;

[0011] According to the characteristics of the FrFT modulus function of the chirp signal, search for the optimal rotation order to perform FrFT transform on the discrete beat signal after coherent integration, and determine the acceleration estimation value of the moving target based on the discrete beat signal after FrFT transform.

[0012] Optionally, the expression of the echo signal S t (t) is:

[0013] S r (t) = S t (t - τ) = exp{j[(2πf0(t - τ) + πK(t - τ) 2 )]}, t ∈ [0, T p ;

[0014] Wherein, S r (t) represents the echo signal, S t (t) represents the chirp signal, f0 is the initial frequency of the signal, τ is the echo time delay between the echo signal and the chirp signal, K is the frequency modulation slope, and T p is the chirp pulse width.

[0015] Optionally, the expression of the beat signal of the echo is:

[0016] t ∈ [0, T p , n ∈ [0, N - 1]

[0017] Wherein, S I (t) represents the beat signal of the echo, R0 is the radial distance between the moving target at the initial moment and the millimeter-wave radar, v is the radial velocity of the moving target at the initial moment, a is the radial acceleration of the moving target at the initial moment, f0 is the initial frequency of the signal, c is the speed of light, K is the frequency modulation slope, T p is the chirp pulse width, and n is the number of echoes.

[0018] Optionally, according to the characteristics of the FrFT modulus function of the chirp pulse signal, the optimal rotation order is searched to perform FrFT transformation on the discrete beat signal after coherent accumulation, which specifically includes:

[0019] Set the FrFT rotation order range; the FrFT rotation order range is determined according to the maximum acceleration range of the moving target;

[0020] Under the condition of satisfying the FrFT rotation order range, set the first rotation order step size to search for the rotation order, and obtain the rotation order with the largest amplitude and the rotation order with the second largest amplitude;

[0021] Calculate the FrFT modulus function of the discrete beat signal after coherent accumulation, and according to the symmetry of the FrFT modulus function, set the second rotation order step size between the rotation order with the largest amplitude and the rotation order with the second largest amplitude to search for the rotation order, and obtain the optimal rotation order; the second rotation order step size is smaller than the first rotation order step size.

[0022] Optionally, determining the acceleration estimation value of the moving target according to the discrete beat signal after FrFT transformation specifically includes:

[0023] Based on the discrete beat signal after FrFT transformation, determine the peak value of the transformed discrete beat signal and the frequency corresponding to the peak value;

[0024] Judge whether the speed of the moving target exceeds the set threshold;

[0025] If not, determine the corresponding phase information according to the frequency, and according to the phase information, determine the frequency modulation slope of the signal, and according to the frequency modulation slope, determine the acceleration estimation value of the moving target;

[0026] If so, correct the frequency through Keystone transformation to obtain the corrected frequency, and according to the corrected frequency, determine the acceleration estimation value of the moving target.

[0027] Optionally, after performing coherent accumulation on the multi-group echo data received by multiple radar receiving antennas to obtain the discrete beat signal after coherent accumulation, it further includes:

[0028] Perform phase difference compensation on the discrete beat signal after coherent accumulation received by each radar receiving antenna; the phase difference is the phase difference related to the incident angle of the signal received by each antenna element and the echo signal.

[0029] Optionally, the expression of the discrete beat signal after phase difference compensation is:

[0030]

[0031] Among them, S I (t, n, p) represents the discrete beat signal after phase difference compensation, p represents the antenna number, R0 is the radial distance between the initial moment of the moving target and the millimeter-wave radar, v is the radial velocity of the moving target at the initial moment, a is the radial acceleration of the moving target at the initial moment, f0 is the initial frequency of the signal, c is the speed of light, K is the frequency modulation slope, T p is the linear frequency modulation pulse width, n is the number of echoes, d is the antenna spacing, and θ is the relative angle between the moving target and the antenna.

[0032] To achieve the above object, the present invention also provides the following solution:

[0033] A target acceleration estimation system for a vehicle-mounted radar based on FrFT, the system includes:

[0034] A signal transmitting and receiving unit, configured to continuously transmit a plurality of linear frequency modulation pulse signals by using a millimeter-wave radar, and receive an echo signal reflected by a moving target through a radar receiving antenna; the echo signal is a signal received by the radar receiving antenna after the linear frequency modulation pulse signal is reflected by the moving target;

[0035] A beat signal determination unit for the echo, configured to perform mixing processing and low-pass filtering on the echo signal and the linear frequency modulation pulse signal to obtain a beat signal for the echo; sampling the beat signals for each echo to obtain discrete beat signals;

[0036] A target distance and echo data determination unit, configured to perform one-dimensional Fourier transform on each of the discrete beat signals to obtain a target distance, and obtain echo data corresponding to a plurality of discrete beat signals at the target distance; the echo data is phase information;

[0037] A coherent accumulation unit, configured to perform coherent accumulation on multiple groups of echo data received by a plurality of radar receiving antennas to obtain a discrete beat signal after coherent accumulation;

[0038] An acceleration determination unit, configured to search for an optimal rotation order according to the characteristics of the FrFT modulus function of the linear frequency modulation pulse signal, perform FrFT transform on the discrete beat signal after coherent accumulation, and determine an acceleration estimation value of the moving target according to the discrete beat signal after FrFT transform.

[0039] Optionally, the acceleration determination unit includes:

[0040] A rotation order range determination module, configured to set a FrFT rotation order range; the FrFT rotation order range is determined according to the maximum acceleration range of the moving target;

[0041] A rotation order search module is used to perform rotation order search by setting a first rotation order step size under the condition of satisfying the FrFT rotation order range, and obtain the rotation order with the largest amplitude and the rotation order with the second largest amplitude.

[0042] An optimal rotation order determination module is used to calculate the FrFT modulus function of the discrete beat signal after coherent accumulation, and perform rotation order search by setting a second rotation order step size between the rotation order with the largest amplitude and the rotation order with the second largest amplitude according to the symmetry of the FrFT modulus function, so as to obtain the optimal rotation order; the second rotation order step size is smaller than the first rotation order step size.

[0043] Optionally, the acceleration determination unit further includes:

[0044] A frequency determination module is used to determine the peak value of the discrete beat signal after transformation and the frequency corresponding to the peak value based on the discrete beat signal after FrFT transformation.

[0045] A judgment module is used to judge whether the speed of the moving target exceeds a set threshold.

[0046] A first acceleration determination module is used to determine the corresponding phase information according to the frequency when the speed of the moving target does not exceed the set threshold, determine the frequency modulation slope of the signal according to the phase information, and determine the acceleration estimation value of the moving target according to the frequency modulation slope.

[0047] A second acceleration determination module is used to correct the frequency through Keystone transformation when the speed of the moving target exceeds the set threshold, obtain the corrected frequency, and determine the acceleration estimation value of the moving target according to the corrected frequency.

[0048] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0049] The present invention provides a method and system for estimating the acceleration of a target of a vehicle-mounted radar based on the FrFT. The method includes: continuously transmitting a plurality of linearly frequency-modulated pulse signals by a millimeter-wave radar, and receiving an echo signal reflected by a moving target through a radar receiving antenna; performing mixing processing and low-pass filtering on the echo signal and the linearly frequency-modulated pulse signal to obtain a beat signal of the echo; sampling each of the beat signals of the echo to obtain discrete beat signals; performing one-dimensional Fourier transform on each of the discrete beat signals to obtain a target distance, and acquiring echo data corresponding to a plurality of discrete beat signals at the target distance; performing coherent accumulation on multiple groups of echo data received by a plurality of radar receiving antennas to obtain a coherently accumulated discrete beat signal; searching for an optimal rotation order according to the characteristics of the FrFT modulus function of the linearly frequency-modulated pulse signal, performing FrFT transform on the coherently accumulated discrete beat signal, and determining an estimated value of the acceleration of the moving target according to the discrete beat signal after the FrFT transform. By means of the improved FrFT transform method and combining the characteristics of the FrFT modulus function to search for the optimal rotation order, the present invention improves the accuracy of estimating the acceleration of a moving target. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0051] Figure 1 It is a flowchart of the method for estimating the acceleration of a target of a vehicle-mounted radar based on the FrFT of the present invention;

[0052] Figure 2 It is a time-frequency diagram of a continuous linearly frequency-modulated pulse signal waveform;

[0053] Figure 3 It is a time-frequency diagram of a single Chirp pulse echo signal and a beat signal;

[0054] Figure 4 It is a schematic diagram of a situation where the distance FFT does not cross the range resolution unit;

[0055] Figure 5 It is a schematic diagram of a situation where the distance FFT crosses the range resolution unit;

[0056] Figure 6 It is a schematic diagram of receiving echo signals by multiple receiving antennas;

[0057] Figure 7 It is a schematic diagram of the result of roughly searching for the best rotation order;

[0058] Figure 8 Schematic diagram of the result for accurately searching the optimal rotation angle Detailed implementation manners

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0060] The object of the present invention is to provide a method and system for estimating the target acceleration of a vehicle-mounted radar based on the FrFT, which can solve the problem that most current automotive millimeter-wave radars cannot measure the acceleration of moving targets, more accurately judge the motion state of the target, and predict the motion of the target.

[0061] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0062] As Figure 1 shown, a method for estimating the target acceleration of a vehicle-mounted radar based on the FrFT of the present invention includes:

[0063] S1: Continuously transmit multiple linear frequency modulation pulse signals (also called Chirp) by using a millimeter-wave radar, and receive the echo signals reflected by the moving target through a radar receiving antenna; the echo signals are the signals received by the radar receiving antenna after the linear frequency modulation pulse signals are reflected by the moving target.

[0064] S2: Mix and process the echo signals with the linear frequency modulation pulse signals and perform low-pass filtering to obtain the beat signals of the echoes; sample the beat signals of each echo to obtain discrete beat signals.

[0065] S3: Perform one-dimensional Fourier transform on each of the discrete beat signals to obtain the target distance, and obtain the echo data corresponding to multiple discrete beat signals at the target distance; the echo data is phase information.

[0066] S4: Perform coherent accumulation on multiple groups of echo data received by multiple radar receiving antennas to obtain the discrete beat signals after coherent accumulation.

[0067] S5: According to the characteristics of the FrFT modulus function of the linear frequency modulation pulse signal, search for the optimal rotation order to perform FrFT transform on the discrete beat signals after coherent accumulation, and determine the acceleration estimation value of the moving target according to the discrete beat signals after FrFT transform.

[0068] Specifically, in step S2, the beat signal S of the echo I (t) has the following expression:

[0069]

[0070] S r (t) is the echo signal, and S t (t) is the linear frequency modulation pulse signal.

[0071] The specific sampling method is as follows: For each Chirp echo in the beat signals of N Chirp echoes, sampling is performed with a sampling period T s and the number of sampling points M, to obtain a two-dimensional discrete signal matrix of M*N (i.e., the discrete beat signal).

[0072] Furthermore, in step S2, the linear frequency modulation pulse signal can be expressed as:

[0073] S t (t) = exp[j(2πf0t + πKt 2 )], t ∈ [0, T p ; (2)

[0074] where S t (t) is the linear frequency modulation pulse signal, f0 is the initial frequency of the signal, K is the frequency modulation slope, and T p is the Chirp pulse width.

[0075] Assume that there is a moving target directly in front of the radar. The radial distance between the moving target and the radar at the initial moment is R0. The moving target is moving away from the radar with a radial velocity v and a radial acceleration a. And consider using the "Stop-and-Go" model for target echo signal modeling. This model assumes that the target remains stationary within one Chirp time and only moves between adjacent Chirps. Based on this model, there is an echo time delay τ between the single Chirp echo signal and the transmitted linear frequency modulation pulse signal, which is expressed as:

[0076]

[0077] where c is the speed of light. Then, in step S2, the Chirp echo signal can be regarded as a version of the linear frequency modulation pulse signal after a time delay τ. The echo signal S r (t) is expressed as:

[0078] S r (t) = S t (t - τ) = exp{j[(2πf0(t - τ) + πK(t - τ) 2 )]}, t ∈ [0, T p ; (4)

[0079] f0 is the initial frequency of the signal, τ is the echo time delay between the echo signal and the chirp signal, K is the frequency modulation slope, and T p is the chirp pulse width.

[0080] Furthermore, the beat signal of the Chirp pulse echo in step S2 can be obtained by substituting (2) and (4) into (1):

[0081] S I (t) = exp{j[2π(f0τ + Kτt) - πKτ 2} t ∈ [0, T p ; (5)

[0082] Then substitute the echo time delay into the above formula (5), and considering that τ 2 is very small, so the πKτ 2 term in the above formula is ignored, and we can get

[0083]

[0084] Furthermore, considering that N Chirps are continuously transmitted in step S3, based on the "Stop-and-Go" echo model, the echo time delay of the nth Chirp is:[[]]

[0085]

[0086] Substitute the time delay τ n into formula (5), and also ignore the πKτ 2 term in the formula, we get:

[0087]

[0088] In the above formula the term is much smaller than So it can be omitted, and finally the beat signal formula of the echo of N Chirp pulses can be obtained as:

[0089]

[0090] where c is the speed of light, K is the frequency modulation slope, T p is the chirp pulse width, and n is the number of echoes.

[0091] Furthermore, considering the data of multiple antennas, since there is still a phase related to the antenna array at the peak after the data between each antenna channel is corrected by range Fourier transform and Keystone transform, in order to coherently accumulate the echoes of each receiving antenna channel, it is necessary to first estimate the DOA of the target to obtain the incident angle of the target, and then compensate for the phase difference brought by the antenna array After that, coherent accumulation of data between multiple channels can be performed, and the result is used as the input of the FrFT to estimate the frequency modulation slope.

[0092] Therefore, after performing coherent accumulation on multiple sets of echo data received by multiple radar receiving antennas in step S4 to obtain the discrete beat signal after coherent accumulation, it further includes:

[0093] Performing phase difference compensation on the discrete beat signal after coherent accumulation received by each radar receiving antenna; the phase difference is the phase difference related to the incident angle of the signal received by each antenna element and the echo signal.

[0094] Further, the expression of the discrete beat signal after completing phase difference compensation is:

[0095]

[0096] where p represents the antenna number, n is the number of echoes, d is the antenna spacing, usually half a wavelength, and θ is the relative angle between the moving target and the antenna.

[0097] Further, in step S5, according to the characteristics of the FrFT modulus function of the linear frequency modulation pulse signal, searching for the optimal rotation order to perform FrFT transformation on the discrete beat signal after coherent accumulation specifically includes:

[0098] Setting the FrFT rotation order range; the FrFT rotation order range is determined according to the maximum acceleration range of the moving target.

[0099] Under the condition of satisfying the FrFT rotation order range, setting the first rotation order step size to perform rotation order search to obtain the rotation order with the largest amplitude and the rotation order with the second largest amplitude.

[0100] Calculating the FrFT modulus function of the discrete beat signal after coherent accumulation, and according to the symmetry of the FrFT modulus function, setting the second rotation order step size between the rotation order with the largest amplitude and the rotation order with the second largest amplitude to perform rotation order search to obtain the optimal rotation order; the second rotation order step size is smaller than the first rotation order step size.

[0101] Further, in step S5, determining the acceleration estimation value of the moving target according to the discrete beat signal after FrFT transformation specifically includes:

[0102] Based on the discrete beat signal after FrFT transformation, determining the peak value of the transformed discrete beat signal and the frequency corresponding to the peak value.

[0103] Judging whether the speed of the moving target exceeds the set threshold.

[0104] If not, determine the corresponding phase information according to the frequency, determine the frequency modulation slope of the signal according to the phase information, and determine the acceleration estimation value of the moving target according to the frequency modulation slope.

[0105] If so, correct the frequency through Keystone transform to obtain the corrected frequency, and determine the acceleration estimation value of the moving target according to the corrected frequency.

[0106] Specifically, perform Fourier transform on the echo S I (t,n) of N Chirp pulses along the distance dimension (fast time) t to obtain Equation (11):

[0107]

[0108] Equation (11) shows that the central spectrum of the spectral envelope obtained by performing Fourier transform on S I (t,n) along the fast time is located at f t , and f t can be expressed as

[0109]

[0110] It can be seen from Equation (12) that the value of f t is not fixed and is related to the Chirp period n. Therefore, it can be said that the fast time t and the slow time n are coupled. Perform one-dimensional Fourier transform (range FFT) on each Chirp echo. If the target speed is not large, peaks will appear at the same frequency after FFT. At this time, the phases at the peaks of the N Chirp range FFTs can be directly extracted to obtain a data sequence (N*1) related to the target speed and acceleration. If the target speed is large, the frequency at the peak will shift after range FFT. At this time, KeyStone transform needs to be used to correct the frequency shift so that the peak is corrected back to the same frequency, and then the phase at the peak is extracted. The following is discussed in two cases.

[0111] Case 1: Assume that the speed of the moving target is not large and the target does not exceed one range resolution cell (range resolution cell is the range resolution or an index interval of the discrete Fourier transform), that is, the peaks of the fast time discrete Fourier transform of N Chirp pulses are at the same frequency index. At this time, the phase at the peak after Fourier transform can be expressed as:

[0112]

[0113] This equation can be regarded as a linear frequency modulation signal with as the initial frequency and as the slope. The data can be directly input into the FrFT algorithm to estimate the frequency modulation slope.

[0114] Case 2: Assume that the target speed is relatively large and the target spans multiple range resolution units, that is, there is an offset in the frequency index at the peak of the fast-time discrete Fourier transform of N Chirp pulses. At the offset, there will also be an additional phase error caused by the offset in the phase at the peaks of the fast-time Fourier transforms of two adjacent Chirps. Therefore, the Keystone transform is used to correct the phenomenon of peak frequency offset in the fast-time Fourier transform caused by the relatively large target speed.

[0115] Perform the following transformation on Equation (10):

[0116]

[0117] After the transformation, we get:

[0118]

[0119] At this time, the fast time t and the slow time n are no longer coupled, and there is no peak index offset phenomenon after the fast-time Fourier transform. Therefore, the phase at the peak can be extracted to obtain a set of chirp signals related to the target speed and acceleration.

[0120] Furthermore, for the numerical calculation of the FrFT, the Ozaktas sampling-type algorithm is adopted. This numerical calculation method converts the continuous and complex integral transform of the FrFT into the convolution calculation of the chirp. Therefore, it can be implemented by the fast Fourier transform, which can greatly reduce the calculation amount. At the same time, the Ozaktas sampling-type algorithm requires the signal to be dimensionally normalized. Here, the discrete scaling method is used to directly perform the scaling transformation on the discrete signal. Using the scaling factor for scaling, the time-frequency domain width is normalized to where T is the time for transmitting N chirps, and f d is 1 / T c , that is, the reciprocal of the time interval between two adjacent chirps.

[0121] In the traditional medium and long-distance waveform parameter configuration of 77GHZ vehicle-mounted millimeter-wave radar, after the signal is normalized, the value of the slope will become smaller accordingly. To obtain an acceleration estimation accuracy of 0.2m / s 2 , the step size of the FrFT rotation order needs to be set to 0.0001. Therefore, simply searching for the peak in the two-dimensional plane to determine the optimal rotation order is very time-consuming and requires a more efficient search strategy.

[0122] In the present invention, an improved FrFT is used to perform the FrFT transformation on the discrete beat signal after coherent accumulation. The improved FrFT is expressed as:

[0123]

[0124] It is expressed as:

[0125]

[0126] The optimal rotation angle of FrFT needs to be obtained by two-dimensional search in the rotation angle range and the frequency domain of the rotated FrFT. If the rotation angle step size is set very small or the signal length is long, a long search time is required, which is very unfavorable for the real-time estimation of target acceleration by the vehicle-mounted millimeter-wave radar system. Therefore, the search strategy needs to be improved. The FrFT modulus function of the linear frequency modulation signal has a symmetrical property, so this property can be used to improve the search efficiency by using a coarse search plus a fine search method.

[0127] For a single-component linear frequency modulation signal

[0128]

[0129] The improved p-order FrFT module function is:

[0130]

[0131] Among them, the rotation angle (rotation order) α = p*π / 2. From the above formula, we can see that the modulus function has symmetry and unilateral monotonicity, so this property can be used to optimize the search strategy. First, determine the rough estimate p1 through a rough search with a larger rotation order step w1, then judge the FrFT modulus function values ​​at p1-w1 and p1+w1, and determine whether the optimal rotation order is on the left or right side of p1, and then use a smaller step size to further search between p1 and max(p1-w1,p1+w1), and repeat the above steps to achieve the desired accuracy.

[0132] To achieve the above object, the present invention also provides the following solution:

[0133] A target acceleration estimation system of a vehicle-mounted radar based on FrFT, the system comprising:

[0134] The signal transmitting and receiving unit is used to continuously transmit multiple linear frequency modulation pulse signals using a millimeter wave radar, and receive the echo signal reflected by the moving target through the radar receiving antenna; the echo signal is a signal received by the radar receiving antenna after the linear frequency modulation pulse signal is reflected by the moving target.

[0135] The echo beat signal determination unit is used to perform mixing processing and low-pass filtering on the echo signal and the linear frequency modulation pulse signal to obtain the echo beat signal; and sample the beat signal of each echo to obtain a discrete beat signal.

[0136] A target distance and echo data determination unit for performing one-dimensional Fourier transform on each of the discrete beat signals to obtain the target distance, and acquiring echo data corresponding to a plurality of discrete beat signals at the target distance; the echo data is phase information.

[0137] A coherent accumulation unit for performing coherent accumulation on multiple sets of echo data received by multiple radar receiving antennas to obtain discrete beat signals after coherent accumulation.

[0138] An acceleration determination unit for searching for an optimal rotation order according to the characteristics of the FrFT modulus function of the linear frequency modulation pulse signal, performing FrFT transform on the discrete beat signals after coherent accumulation, and determining an acceleration estimation value of the moving target according to the discrete beat signals after FrFT transform.

[0139] Further, the acceleration determination unit includes:

[0140] A rotation order range determination module for setting a FrFT rotation order range; the FrFT rotation order range is determined according to the maximum acceleration range of the moving target.

[0141] A rotation order search module for performing rotation order search by setting a first rotation order step size under the condition of satisfying the FrFT rotation order range to obtain the rotation order with the largest amplitude and the rotation order with the second largest amplitude.

[0142] An optimal rotation order determination module for calculating the FrFT modulus function of the discrete beat signals after coherent accumulation, and performing rotation order search by setting a second rotation order step size between the rotation order with the largest amplitude and the rotation order with the second largest amplitude according to the symmetry of the FrFT modulus function to obtain the optimal rotation order; the second rotation order step size is smaller than the first rotation order step size.

[0143] Further, the acceleration determination unit further includes:

[0144] A frequency determination module for determining the peak value of the discrete beat signals after transformation and the frequency corresponding to the peak value based on the discrete beat signals after FrFT transform.

[0145] A judgment module for judging whether the speed of the moving target exceeds a set threshold.

[0146] A first acceleration determination module for determining the corresponding phase information according to the frequency when the speed of the moving target does not exceed the set threshold, determining the frequency modulation slope of the signal according to the phase information, and determining the acceleration estimation value of the moving target according to the frequency modulation slope.

[0147] A second acceleration determination module, configured to, when the speed of a moving target exceeds a set threshold, correct the frequency through Keystone transform to obtain a corrected frequency, and determine an acceleration estimation value of the moving target according to the corrected frequency. Specific embodiments

[0149] Reference Figure 2 and Figure 3 , where TX is the transmitted chirp pulse signal and RX is the echo signal. The millimeter-wave radar continuously transmits multiple chirp pulses, and collects corresponding echo signals through its receiving end. The received target echo signal and the transmitted signal are mixed and low-pass filtered to obtain a beat signal.

[0150] Perform Fourier transform on each pulse sequence to obtain the target distance under each pulse. Reference Figure 3 , if the target distance does not cross the range resolution cell, directly select the slow-time dimension data of this range cell. Reference Figure 4 , if the target distance crosses the range resolution cell, KeyStone transform needs to be used for correction.

[0151] Reference Figure 5 , when the transmitting antenna transmits a Chirp pulse, it is transmitted by an object and received by multiple receiving antennas. The data phases between these receiving antenna channels only have a phase difference caused by the target incident angle. Therefore, after distance Fourier transform and correct compensation of the incident angle phase difference, the data phase of each channel is only affected by the target speed and acceleration. Therefore, coherent integration can be performed on this data.

[0152] The estimation of the chirp signal parameters first requires setting a suitable range of FrFT orders. To reduce the calculation amount, the maximum acceleration range of the target can be estimated in advance. For example, in urban traffic, the maximum acceleration of a vehicle is expected not to exceed a m / s 2 , the rotation order p corresponding to the acceleration a can be calculated, so the order range is set to (-p, p). Set a larger rotation order step size for rough search to obtain the rotation order with the largest amplitude and the rotation order with the second largest amplitude. According to the symmetry of the modulus function, set a more accurate step size between the two for search to obtain the optimal rotation order p opt . The schematic diagrams of the results of rough search for the best rotation angle and accurate search for the best rotation angle are shown in Figure 7 and Figure 8 .

[0153] Due to the dimensional normalization method using the discrete scale method, the frequency modulation slope k est and the optimal rotation order p opt are no longer

[0154] From the relationship, the relationship between the actual tuning frequency and the estimated value can be deduced as

[0155] k = k est *f D / T; (21)

[0156] Converting the Doppler frequency to velocity and T to time, the estimated value of acceleration acc is finally obtained as:

[0157]

[0158] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the system disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section.

[0159] In this article, specific examples are used to elaborate on the principles and implementation manners of the present invention. The descriptions of the above embodiments are only used to help understand the method of the present invention and its core idea. At the same time, for those of ordinary skill in the art, based on the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for estimating the target acceleration of a vehicle-mounted radar based on the FrFT, characterized in that, The method includes: Continuously transmitting multiple chirp pulse signals by a millimeter-wave radar, and receiving the echo signals reflected by a moving target through a radar receiving antenna; the echo signals are the signals received by the radar receiving antenna after the chirp pulse signals are reflected by the moving target; Mixing and low-pass filtering the echo signals with the chirp pulse signals to obtain the beat signals of the echoes; sampling the beat signals of the echoes to obtain discrete beat signals; Performing one-dimensional Fourier transform on each of the discrete beat signals to obtain the target distance, and acquiring the echo data corresponding to multiple discrete beat signals at the target distance; the echo data is phase information; Performing coherent integration on multiple groups of echo data received by multiple radar receiving antennas to obtain the discrete beat signals after coherent integration; According to the characteristics of the FrFT modulus function of the chirp pulse signal, searching for the optimal rotation order to perform FrFT transform on the discrete beat signals after coherent integration, and determining the acceleration estimation value of the moving target according to the discrete beat signals after FrFT transform.

2. The method for estimating the target acceleration of the vehicle-mounted radar based on the FrFT according to claim 1, wherein The expression of the echo signal is: S r s(t) = S t s(t - τ) = exp{j[(2πf0(t - τ) + πK(t - τ) 2 )]}, t ∈ [0, T p ; Among them, S r (t) represents the echo signal, S t (t) represents the chirp pulse signal, f0 is the initial frequency of the signal, τ is the echo time delay between the echo signal and the chirp pulse signal, K is the frequency modulation slope, T p is the chirp pulse width.

3. The method for estimating the target acceleration of the vehicle-mounted radar based on the FrFT according to claim 1, wherein, The expression of the beat signal of the echo is: Among them, S I (t, n) represents the beat signal of the echo, R0 is the radial distance between the initial moment of the moving target and the millimeter-wave radar, v is the radial velocity of the moving target at the initial moment, a is the radial acceleration of the moving target at the initial moment, f0 is the initial frequency of the signal, c is the speed of light, K is the frequency modulation slope, T p is the linear frequency modulation pulse width, and n is the number of echoes.

4. The method for estimating the target acceleration of the vehicle-mounted radar based on FrFT according to claim 1, wherein The specific steps of searching for the optimal rotation order according to the characteristics of the FrFT modulus function of the chirp pulse signal to perform FrFT transform on the discrete beat signals after coherent integration include: Setting the FrFT rotation order range; the FrFT rotation order range is determined according to the maximum acceleration range of the moving target; Searching for the rotation order within the FrFT rotation order range with a first rotation order step size to obtain the rotation order with the largest amplitude and the rotation order with the second largest amplitude; Calculating the FrFT modulus function of the discrete beat signals after coherent integration, and searching for the rotation order with a second rotation order step size between the rotation order with the largest amplitude and the rotation order with the second largest amplitude according to the symmetry of the FrFT modulus function to obtain the optimal rotation order; the second rotation order step size is smaller than the first rotation order step size.

5. The method for estimating the target acceleration of the vehicle-mounted radar based on FrFT according to claim 1, wherein The specific steps of determining the acceleration estimation value of the moving target according to the discrete beat signals after FrFT transform include: Based on the discrete beat signals after FrFT transform, determining the peak value of the discrete beat signals after transformation and the frequency corresponding to the peak value; Judging whether the speed of the moving target exceeds a set threshold; If not, determining the corresponding phase information according to the frequency, determining the frequency modulation slope of the signal according to the phase information, and determining the acceleration estimation value of the moving target according to the frequency modulation slope; If so, correcting the frequency through Keystone transform to obtain the corrected frequency, and determining the acceleration estimation value of the moving target according to the corrected frequency.

6. The method for estimating the target acceleration of the vehicle-mounted radar based on the FrFT according to claim 5, wherein After performing coherent integration on multiple groups of echo data received by multiple radar receiving antennas to obtain the discrete beat signals after coherent integration, it further includes: Performing phase difference compensation on the discrete beat signals after coherent integration received by each radar receiving antenna; the phase difference is the phase difference related to the incident angle of the signals received by each antenna element and the echo signal.

7. The method for estimating the target acceleration of the vehicle-mounted radar based on the FrFT according to claim 6, wherein, The expression of the discrete beat signal after completing phase difference compensation is as follows: Among them, S I (t, n, p) represents the discrete beat signal after phase difference compensation, p represents the antenna number, R0 is the radial distance between the moving target at the initial moment and the millimeter-wave radar, v is the radial velocity of the moving target at the initial moment, a is the radial acceleration of the moving target at the initial moment, f0 is the initial frequency of the signal, c is the speed of light, K is the frequency modulation slope, T p is the linear frequency modulation pulse width, n is the number of echoes, d is the antenna spacing, and θ is the relative angle between the moving target and the antenna.

8. A target acceleration estimation system for a vehicle-mounted radar based on the FrFT, characterized in that, The system includes: A signal transmitting and receiving unit, which is used to continuously transmit multiple chirp pulse signals by using a millimeter-wave radar and receive the echo signals reflected by a moving target through a radar receiving antenna; the echo signal is the signal received by the radar receiving antenna after the chirp pulse signal is reflected by the moving target; A beat signal determination unit for the echo, which is used to mix and low-pass filter the echo signal and the chirp pulse signal to obtain the beat signal of the echo; sample each beat signal of the echo to obtain a discrete beat signal; A target distance and echo data determination unit, which is used to perform one-dimensional Fourier transform on each discrete beat signal to obtain the target distance and acquire the echo data corresponding to multiple discrete beat signals at the target distance; the echo data is phase information; A coherent integration unit, which is used to perform coherent integration on multiple groups of echo data received by multiple radar receiving antennas to obtain a discrete beat signal after coherent integration; An acceleration determination unit, which is used to search for the optimal rotation order according to the characteristics of the FrFT modulus function of the chirp pulse signal, perform FrFT transform on the discrete beat signal after coherent integration, and determine the acceleration estimation value of the moving target according to the discrete beat signal after FrFT transform.

9. The target acceleration estimation system of the vehicle-mounted radar based on FrFT according to claim 8, wherein, The acceleration determination unit includes: A rotation order range determination module, which is used to set the FrFT rotation order range; the FrFT rotation order range is determined according to the maximum acceleration range of the moving target; A rotation order search module, which is used to search for the rotation order by setting the first rotation order step size under the condition of satisfying the FrFT rotation order range to obtain the rotation order with the largest amplitude and the rotation order with the second largest amplitude; An optimal rotation order determination module, which is used to calculate the FrFT modulus function of the discrete beat signal after coherent integration, and search for the rotation order by setting the second rotation order step size between the rotation order with the largest amplitude and the rotation order with the second largest amplitude according to the symmetry of the FrFT modulus function to obtain the optimal rotation order; the second rotation order step size is smaller than the first rotation order step size.

10. The target acceleration estimation system of the vehicle-mounted radar based on FrFT according to claim 8, wherein, The acceleration determination unit further includes: A frequency determination module, which is used to determine the peak value of the discrete beat signal after transformation and the frequency corresponding to the peak value based on the discrete beat signal after FrFT transform; A judgment module, which is used to judge whether the speed of the moving target exceeds a set threshold; A first acceleration determination module, which is used to determine the corresponding phase information according to the frequency when the speed of the moving target does not exceed the set threshold, determine the frequency modulation slope of the signal according to the phase information, and determine the acceleration estimation value of the moving target according to the frequency modulation slope; A second acceleration determination module, which is used to correct the frequency through Keystone transform when the speed of the moving target exceeds the set threshold to obtain the corrected frequency, and determine the acceleration estimation value of the moving target according to the corrected frequency.

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