A method for resolving velocity ambiguity of millimeter wave radar

Abstract

The application provides a millimeter wave radar velocity ambiguity resolving method, which comprises the following steps: transmitting a set of staggered time delay waveforms in each system cycle; performing two-dimensional FFT processing on the received signals corresponding to the two waveforms respectively at the receiving end; calculating the target distance and ambiguous velocity according to the target detection result; and then resolving the unambiguous velocity by using the phase difference of the target in the two range-Doppler data. The staggered time delay waveform is easy to implement, the velocity resolving algorithm is simple, the occupied computing power resource is small, the unambiguous velocity of the target can be obtained in a single system cycle, and the velocity measurement range of the radar is greatly expanded.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of millimeter wave radar, in particular to a millimeter wave radar velocity ambiguity resolution method. BACKGROUND

[0002] Compared with cameras and laser radars, millimeter wave radars can obtain higher resolution at lower cost, and are less affected by surrounding environment such as rain, fog, snow and light, and can work all day and all year round, gradually becoming one of the indispensable sensors in the ADAS field and being widely used.

[0003] The vehicle-mounted millimeter wave radar generally adopts the frequency-modulated continuous wave (FMCW) system, periodically transmits a group of sequences containing multiple linear frequency modulation waveforms (chirp waveforms), and uses two-dimensional fast Fourier transform (FFT) for distance-Doppler joint processing in signal processing to measure the target distance and velocity parameters. This method can distinguish multiple targets in the distance-velocity two dimensions, has stronger distinguishing ability and higher precision, but generally has the problem of velocity ambiguity. This is because, in real situations, due to the limitation of the hardware conditions of the automotive radar, the repetition period of the chirp waveform generally cannot directly meet the requirements of the automotive radar application scene for the velocity measurement range. When the velocity of the target exceeds the non-ambiguous velocity measurement range, Doppler ambiguity will be caused, resulting in incorrect measurement of the target velocity. This problem seriously limits the measurable velocity range of the frequency-modulated sequence automotive radar. The most typical velocity ambiguity resolution method is to use multiple frequency waveforms, transmit chirp waveforms with different repetition periods, and use the Chinese remainder theorem to solve the non-ambiguous velocity. This method needs to use the target information list of the current period and the previous period (or several previous periods), and performs target matching processing in two (or multiple) measurement periods. If there is target missing or false alarm in the current period or the previous period, target matching error may occur in adjacent periods, resulting in incorrect velocity measurement. On the other hand, when the radial velocity of the same target changes greatly between two periods, the target velocity is easily calculated incorrectly. In addition, in the patent US 2015 / 0084806, a frequency-modulated waveform sequence based on staggered frequency shift is proposed, which uses the phase difference of the same target after two-dimensional FFT processing of different waveforms to resolve the velocity ambiguity. However, since the transmission waveform contains two different center frequency waveform sequences, for different waveform sequences, the same target may be located in different distance-velocity units after two-dimensional FFT, so target matching processing is needed. If target matching error occurs, the target velocity will be calculated incorrectly. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a method for extending the speed measurement range of vehicle-mounted millimeter wave radar, which transmits a set of staggered time delay frequency modulation waveforms, and eliminates the speed ambiguity of the target through a signal processing algorithm at the receiving end to solve the speed ambiguity problem, thereby improving the speed measurement range of the radar.

[0005] Specifically, the present application proposes a millimeter wave radar speed ambiguity resolution method, comprising the following steps:

[0006] comprising the following steps:

[0007] S1: a set of staggered time delay chirp waveforms are transmitted in each system cycle, the first kind of transmission waveform is denoted as A wave, and the second kind of transmission waveform is denoted as B wave;

[0008] S2: the radar receiving signal is subjected to ADC sampling to obtain the ADC data of the current system cycle; according to the transmission sequence of the A wave and the B wave, all the ADC data are reorganized to obtain the ADC data corresponding to sequence 1 and sequence 2; the ADC data corresponding to sequence 1 and sequence 2 are subjected to windowed FFT processing along the distance dimension with a point number of N1 and along the speed dimension with a point number of N2, respectively, to obtain the distance-Doppler two-dimensional matrix data after two-dimensional FFT, which are denoted as F1 and F2, respectively;

[0009] S3: the distance-Doppler two-dimensional matrix data corresponding to the sequence 1 and the sequence 2 are subjected to target detection processing to obtain the distance-Doppler unit where the target peak value is located, denoted as ;

[0010] S4: according to the detection result of the target peak value position, the ambiguous Doppler frequency of the target is calculated, denoted as ;

[0011] S5: the unambiguous speed is calculated using the phase difference of the target in the two distance-Doppler data.

[0012] The bandwidth, slope and initial phase of the A wave and the B wave are the same; the initial transmission time of the B wave relative to the A wave is constant with a phase difference of T+a.

[0013] Further, the sequence 1 and the sequence 2 each contain L chirp waveforms; the chirp repetition frequencies of the sequence 1 and the sequence 2 are equal, denoted as ;

[0014] The window function of the distance dimension and the speed dimension is selected according to the actual application scenario, and the window function is at least any one of a rectangular window, a Hamming window and a Chebyshev window.

[0015] Further, the target detection further comprises: if there are multiple receiving channel data, the distance-Doppler two-dimensional matrix data corresponding to sequence 1 or sequence 2 can be processed by digital beam forming first, and then target detection is performed; or only the distance-Doppler two-dimensional matrix data of one receiving channel is selected for target detection; the target detection processing adopts CA-CFAR detection or OS-CFAR detection.

[0016] The calculation of the ambiguous Doppler frequency of the target further comprises:

[0017] ,

[0018] wherein, is the ambiguous Doppler frequency of the target, is the Doppler unit sequence number corresponding to the target peak in the two-dimensional distance-Doppler spectrum, is the number of FFT points in the velocity dimension, is the chirp repetition frequency of sequence 1 and sequence 2.

[0019] The S5 further comprises a calculation process:

[0020] The signals at the target peak in the distance-Doppler two-dimensional matrix data corresponding to sequence 1 and sequence 2 are extracted respectively, and the corresponding phase values are extracted, denoted as and ;

[0021] Let ,

[0022] wherein, , is the rounding operation following the rounding principle, is the defined residual amount, is the distance unit sequence number corresponding to the target peak in the two-dimensional distance-Doppler spectrum, is the Doppler unit sequence number corresponding to the target peak in the two-dimensional distance-Doppler spectrum, is the phase value of the distance-Doppler unit wherein the target peak is located in the distance-Doppler two-dimensional matrix data corresponding to sequence i, is the ambiguous Doppler frequency of the target, is the chirp time length of sequence 1, and a is the time delay of B wave relative to the previous A wave;

[0023] The Doppler unambiguous number of the target is calculated, ;

[0024] The unambiguous velocity of the target is calculated. .

[0025] wherein, The residual amount calculated in claim 7, The chirp repetition frequency of sequence 1 and sequence 2, The chirp repetition frequency period of sequence 1, and a is the time delay of B wave relative to the previous A wave, The minimum and maximum values of the Doppler unambiguous number calculated according to system requirements, respectively, The wavelength of the electromagnetic wave radiated by the radar, The ambiguous Doppler frequency of the target.

[0026] Further, the velocity measurement range required by the system is recorded as According to the system waveform parameters and the velocity measurement range requirement, the value range of the target Doppler unambiguous number . .

[0027] Further, the qmin and qmax are calculated by the following formula:

[0028] ,

[0029] Wherein, And respectively represent the floor and ceiling, The chirp repetition frequency of sequence 1 and sequence 2, The wavelength of the electromagnetic wave radiated by the radar.

[0030] In summary, the present application provides a millimeter wave radar velocity ambiguity resolution method, by transmitting a set of staggered time delay waveforms in each system cycle; The two-dimensional FFT processing is carried out on the received signals corresponding to the two waveforms at the receiving end respectively; And according to the target detection result, the target distance and ambiguous velocity are calculated; Then the unambiguous velocity is calculated by using the phase difference of the target in the two distance-Doppler data. The staggered time delay waveform proposed by the present application is easy to realize, the velocity calculation algorithm is simple, and the occupied computing resources are small; And the unambiguous velocity of the target can be obtained in a single system cycle, which greatly expands the velocity measurement range of the radar. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The waveform diagram of A wave of the present application.

[0032] Figure 2 The waveform diagram of B wave of the present application.

[0033] Figure 3 The staggered time delay transmission waveform diagram of AB wave of the present application.

[0034] Figure 4 The distance-velocity two-dimensional FFT processing diagram of the present application.

[0035] Figure 5 This is a schematic diagram of the BA wave interleaved delay transmission waveform of the present invention. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention proposes a method for resolving velocity ambiguity in millimeter-wave radar, comprising the following steps:

[0038] S1: Transmit a set of interleaved signal chirp waveforms with interleaved time delays in each system cycle. The first transmitted waveform is denoted as wave A, and the second transmitted waveform is denoted as wave B.

[0039] like Figures 1-2 The figures shown are waveform diagrams for wave A and wave B, respectively. Waves A and B have the same bandwidth, slope, and initial phase. The only difference is that wave B always has a fixed time delay relative to the preceding wave A, denoted as 'a'. That is, the initial transmission times of two adjacent transmitted waveforms are constantly differing by (T+a), where T is the total duration of wave A. Figure 3 The diagram shown is a schematic of the AB wave interleaved delay transmission waveform.

[0040] S2: Perform ADC sampling on the radar received signal to obtain the ADC data for the current system period; according to the transmission order of A-wave and B-wave, reorganize all ADC data to obtain the ADC data corresponding to sequence 1 and sequence 2; perform windowed FFT processing with N1 points along the range dimension and windowed FFT processing with N2 points along the velocity dimension on the ADC data corresponding to sequence 1 and sequence 2 respectively to obtain the range-Doppler two-dimensional matrix data after two-dimensional FFT (e.g., Figure 4 (as shown), denoted as F1 and F2 respectively;

[0041] Within each system cycle, the frequency modulation sequence composed of all A waves is denoted as Sequence 1, and the frequency modulation sequence composed of all B waves is denoted as Sequence 2. Both Sequence 1 and Sequence 2 contain L chirp waveforms, and the chirp repetition frequencies of Sequence 1 and Sequence 2 are equal, denoted as Li. .

[0042] Furthermore, the window functions for the distance and velocity dimensions are selected according to the actual application scenario, and the window function is at least any one of the following: rectangular window, Hamming window, and Chebyshev window.

[0043] S3: target detection processing is performed on the distance-Doppler two-dimensional matrix data corresponding to the sequence 1 and the sequence 2 to obtain a distance-Doppler cell where a target peak value is located, denoted as ;

[0044] The target detection further includes: if there are multiple receiving channel data, the distance-Doppler two-dimensional matrix data corresponding to the sequence 1 or the sequence 2 can be first subjected to digital beamforming processing, and then subjected to target detection; or only the distance-Doppler two-dimensional matrix data of one receiving channel is selected for target detection; and the target detection processing adopts CA-CFAR detection or OS-CFAR detection.

[0045] S4: according to the detection result of the target peak value position, a fuzzy Doppler frequency of the target is calculated, denoted as ;

[0046] Further, the calculation of the fuzzy Doppler frequency of the target further includes:

[0047] ,

[0048] wherein, is the fuzzy Doppler frequency of the target, is a Doppler cell serial number corresponding to the target peak value in the two-dimensional distance-Doppler spectrum, is a velocity dimension FFT point number, is a chirp repetition frequency of the sequence 1 and the sequence 2.

[0049] S5: the unambiguous velocity is solved by using the phase difference of the target in the two distance-Doppler data.

[0050] Specifically, the S5 further includes a calculation process:

[0051] The signal at the target peak value in the distance-Doppler two-dimensional matrix data corresponding to the sequence 1 and the sequence 2 is extracted respectively, and the corresponding phase values are extracted, denoted as and ;

[0052] Let ,

[0053] wherein, , is an integral operation following the rounding principle, is a defined residual amount, is a distance cell serial number corresponding to the target peak value in the two-dimensional distance-Doppler spectrum, is a Doppler cell serial number corresponding to the target peak value in the two-dimensional distance-Doppler spectrum, a phase value of a distance-Doppler cell where a target peak value is located in a distance-Doppler two-dimensional matrix data corresponding to the sequence i, a blurring Doppler frequency of the target, a chirp duration of the sequence 1, and a is a time delay of the B wave relative to the previous A wave.

[0054] a Doppler unblurring number of the target,

[0055] an unblurring velocity of the target,

[0056] wherein, a residual amount calculated in claim 7, a chirp repetition frequency of the sequence 1 and the sequence 2, a chirp repetition frequency period of the sequence 1, and a is a time delay of the B wave relative to the previous A wave, respectively a minimum and a maximum value of the Doppler unblurring number calculated according to system requirements, a wavelength of the electromagnetic wave radiated by the radar, a blurring Doppler frequency of the target.

[0057] Further, a velocity measurement range required by the system is denoted as , and a value range of the Doppler unblurring number of the target is calculated according to the system waveform parameters and the velocity measurement range requirement .

[0058] Then, the qmin and the qmax are calculated by the following formula:

[0059] ,

[0060] wherein, and respectively represent a floor function and a ceiling function, a chirp repetition frequency of the sequence 1 and the sequence 2, a wavelength of the electromagnetic wave radiated by the radar.

[0061] As shown in Figure 5 , the millimeter wave radar velocity unblurring method of the present application is also applicable to a scenario where the transmission sequence of the A wave and the B wave is opposite, that is, the unblurring velocity value of the target is calculated when the BA wave is transmitted in an interlaced time delay manner.

[0062] ​​​The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be based on the appended claims.

Claims

1. A millimeter wave radar range rate ambiguity resolution method, characterized by, The method comprises the following steps: S1: transmitting a set of staggered time delay staggered signal chirp waveforms in each system cycle, a first transmission waveform is denoted as A wave, and a second transmission waveform is denoted as B wave; S2: performing ADC sampling on the radar receiving signal to obtain ADC data of the current system cycle; reorganizing all the ADC data according to the transmission sequence of the A wave and the B wave to obtain ADC data corresponding to sequence 1 and sequence 2; performing windowed FFT processing with a point number of N1 along the distance dimension and windowed FFT processing with a point number of N2 along the velocity dimension on the ADC data corresponding to sequence 1 and sequence 2 respectively to obtain two-dimensional FFT distance-Doppler two-dimensional matrix data, which are denoted as F1 and F2 respectively; S3: using the sequence 1 and sequence 2 corresponding distance-Doppler two-dimensional matrix data to carry out target detection processing, obtaining the distance-Doppler unit where the target peak value is located, denoted as ; S4: According to the detection result of the target peak position, the fuzzy Doppler frequency of the target is calculated, denoted as ; S5: calculating the unambiguous velocity by using the phase difference of the target in the two distance-Doppler data; The target detection further comprises: if there are multiple receiving channel data, performing digital beam forming processing on the distance-Doppler two-dimensional matrix data corresponding to sequence 1 or sequence 2 before target detection; or only selecting the distance-Doppler two-dimensional matrix data of one receiving channel for target detection; the target detection processing adopts CA-CFAR detection or OS-CFAR detection; The calculation of the ambiguous Doppler frequency of the target further comprises: , wherein, is the target Doppler frequency, is the Doppler bin number corresponding to the target peak in the two-dimensional range-Doppler spectrum, is the number of velocity dimension FFT points, is the chirp repetition frequency of sequence 1 and sequence 2.

2. The millimeter wave radar range resolution ambiguity resolving method of claim 1, wherein, The bandwidth, slope and initial phase of the A wave and the B wave are all the same; the initial transmission time of the B wave relative to the A wave is constant with a phase difference of T+a, T is the chirp time length of sequence 1, and a is the time delay of the B wave relative to the previous A wave.

3. The millimeter wave radar range resolution ambiguity resolving method of claim 1, wherein, The sequence 1 and the sequence 2 both contain L chirp waveforms; the chirp repetition frequencies of the sequence 1 and the sequence 2 are equal, denoted as .

4. The millimeter wave radar range resolution method of claim 1, wherein, The window function of the distance dimension and the velocity dimension is selected according to the actual application scene, and the window function is at least any one of a rectangular window, a Hamming window and a Chebyshev window.

5. The millimeter wave radar range resolution method of claim 1, wherein, The S5 further comprises a calculation process: The signal at the target peak in the distance-Doppler two-dimensional matrix data corresponding to sequence 1 and sequence 2 is extracted respectively, and the corresponding phase value is extracted, denoted as and ; Let , wherein, , is a rounding operation following the rounding rule, is a defined residual quantity, is a distance unit sequence number corresponding to the target peak in the two-dimensional distance-Doppler spectrum, is a phase value of the target peak in the distance-Doppler unit of the distance-Doppler two-dimensional matrix data corresponding to the sequence i, T is the chirp duration of the sequence 1, and a is the time delay of the B wave relative to the previous A wave.

6. The millimeter wave radar range resolution ambiguity resolving method of claim 5, wherein, The S5 further comprises a calculation process: calculating a Doppler unambiguity number for the target, ; unambiguous speed of the calculation target, ; wherein q min , q max are the minimum and maximum values of the Doppler unambiguity number calculated according to the system requirements, respectively, is the wavelength of the radar radiated electromagnetic wave.

7. The millimeter wave radar range resolution deambiguity method according to claim 6, characterized in that, The velocity measurement range required by the system is recorded as , and the q value range is calculated according to the system waveform parameters and the velocity measurement range requirement .

8. The millimeter wave radar range resolution deambiguity method according to claim 7, characterized in that, The q min , q max is calculated using the following formula: , wherein and denote the floor and ceiling functions, respectively.

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