Vehicle-mounted millimeter wave radar anti-interference method and system based on slow time waveform coding

Abstract

The invention discloses a vehicle-mounted millimeter wave radar anti-interference method and system based on slow time waveform coding, and belongs to the technical field of vehicle-mounted millimeter wave radars, and the system comprises a pseudo-random number generator module, a modulation module, a transmitting module, a receiving module, a sampling module, a data processing module and a post-processing module. The three provided modulation methods dependent on three independent pseudorandom sequences are equivalent to performing random phase modulation on a transmitted signal, the method is realized through waveform modulation, waveform modulation interfaces provided by various platforms can be utilized, and the method is easy to realize technically; the method can achieve the flexible combination of waveforms, is better in adaptability for various observation scenes, does not need to detect an interference signal, is suitable for various interference conditions, does not need to add an interference signal detection module in an original signal processing flow, and is higher in adaptability. And the existing band-like signal processing flow can be reused to the greatest extent.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle-mounted millimeter-wave radar, and more specifically, to a vehicle-mounted millimeter-wave radar anti-interference method and system based on slow-time waveform coding. Background Art

[0002] In recent years, as millimeter-wave radars are widely used in automobile assisted driving, due to the same signal frequency band, it is easy for radar signals from different vehicles to interfere with each other, causing false alarms when radar detects interference signals or misses weak targets in the environment due to strong interference, which in turn leads to the system's misjudgment of the environment. In typical scenarios such as lane changes, intersections, and meeting and following vehicles, it is easy to be affected by similar active interference. If the interference signal is not effectively suppressed, it will affect the distance and speed measurement of targets in the environment, or cause false alarms and missed detection of targets, which will in turn affect subsequent decisions and even driving safety. Therefore, in order to solve the above problems, an anti-interference method for vehicle-mounted millimeter-wave radar based on slow-time waveform coding is necessary. Summary of the invention

[0003] The main technical problem solved by the present invention is to provide a vehicle-mounted millimeter-wave radar anti-interference method and system based on slow-time waveform coding, which can solve the problems raised by the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides the following technical solution: a vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding, comprising the following steps:

[0005] S1. Determine the modulation waveform according to the observation scene requirements, phase modulation, frequency hopping, start time delay or a combination of the three waveforms, and determine the frequency offset value Δf and time delay value δ when the code is 1;

[0006] S2, using a pseudo-random code generator to sequentially generate a phase modulation code sequence, a frequency modulation code sequence and a start time code sequence according to the selected modulation waveform;

[0007] S3, determine the starting frequency of the current transmission sequence according to the frequency coding sequence, determine the phase of the current chirp according to the phase coding sequence, and realize phase modulation through the phase shifter, and determine the starting time of the current chirp transmission according to the time coding sequence;

[0008] S4, transmitting a modulated waveform and receiving an echo signal, using the current chirp transmission signal as a reference signal to mix with the echo signal;

[0009] S5, sampling the intermediate frequency signal, performing distance dimension FFT on the sampled signal, and performing phase compensation according to the slow time series based on the distance index;

[0010] S6, performing Doppler dimension FFT on the compensated data, performing Doppler dimension FFT on the compensated data, and performing CFAR detection and DOA estimation on the 2dFFT results;

[0011] S7. Output target point cloud information.

[0012] Furthermore, the frequency offset value Δf in S1 is selected to be greater than half of the sampling frequency so that the interference signal with a code different from the target signal is moved outside the intermediate frequency bandwidth, and the accuracy Δf of the phase compensation satisfies:

[0013]

[0014] Where B is the sweep bandwidth of a single chirp, N r is the number of FFT points in the distance dimension, f s is the ADC sampling frequency, T p The upward sweep time of a single chirp. The time delay options are:

[0015]

[0016] Among them, when the phase modulation is coded as 1, the modulation phase is fixed to π.

[0017] Furthermore, the pseudo-random code generator in S2 is implemented using a linear feedback shift register. A suitable primitive polynomial is selected according to the maximum number of chirps supported to generate a pseudo-random sequence of the corresponding period. The seeds used in generating the three phase modulation sequences are different and not 0. In addition, whether a random sequence is generated by a pseudo-random encoder is determined based on the modulation enable. If a certain modulation is not enabled, the corresponding sequence is set to 0.

[0018] Furthermore, when the current chirp code in S3 is 0, the corresponding phase, frequency, and start time are not modulated, and the basic waveform is transmitted;

[0019] When the code is 1, the corresponding modulation is performed: the modulation phase is π, and the starting frequency is changed to f c +Δf, the reference clock edge is transmitted after a delay of δ after arrival, and any combination of modulations may be performed within a chirp.

[0020] Furthermore, the reference waveform used for the mixing in S4 is the waveform after the current chirp modulation.

[0021] Furthermore, the phase compensation in S5 refers to compensation for the chirp when the code is 1, including compensation for phase modulation, frequency modulation and time delay. For the phase modulation mode, the compensation phase is θ ps =π;

[0022] In frequency modulation mode, each distance unit is compensated, and the compensation phase is:

[0023]

[0024] The compensation phase in random delay mode is:

[0025]

[0026] Where m represents the distance index value of the current compensation.

[0027] Furthermore, during the CFAR detection in S6, the interference signal cannot be accumulated in the Doppler dimension and appears as a random noise spectrum. After the noise floor detection is performed at the corresponding distance index, the CFAR threshold value should be appropriately raised to avoid false alarms.

[0028] According to another aspect of the present invention, there is provided a vehicle-mounted millimeter wave radar anti-interference system based on slow-time waveform coding, comprising a pseudo-random number generator module, a modulation module, a transmitting module, a receiving module, a sampling module, a data processing module and a post-processing module;

[0029] The pseudo-random number generator module is used to generate three groups of modulation sequences for waveform modulation;

[0030] The modulation module is used to modulate the transmission waveform, including phase modulation, starting frequency modulation and transmission time modulation;

[0031] The transmitting module is used to transmit the modulated waveform;

[0032] The receiving module is used to receive the echo signal of the target and mix it with the reference signal;

[0033] The sampling module is used to sample the echo analog signal for subsequent digital signal processing;

[0034] The data processing module includes performing FFT operation on the sampled signal and demodulation operation between two-dimensional FFT;

[0035] The post-processing module is used to perform CFAR detection and DOA estimation on the two-dimensional spectrum of the echo and output point cloud information.

[0036] Furthermore, the pseudo-random number generator of the pseudo-random number generator module may have multiple primitive polynomials built in to generate sequences of different lengths, or may use a primitive polynomial with a longer period to extract a portion of the sequence;

[0037] The modulation module realizes phase modulation through a phase shifter. When using the phase shifter, the phase shifter should be calibrated, and only the relative value of the two phase points needs to be calibrated as π. There is no need to select the absolute phase 0 and phase π. The time delay operation is completed by counting the clock cycles. After the reference clock edge arrives, the number of clock cycles calculated according to the configured delay time is counted, and the transmission is performed after the counting is completed.

[0038] The beneficial effects of the vehicle-mounted millimeter-wave radar anti-interference method and system based on slow-time waveform coding of the present invention are:

[0039] Through waveform modulation, the waveform modulation interface provided by each platform can be used, which is technically simple to implement; flexible combined waveforms can be realized, which has good adaptability to various observation scenarios, and the proposed anti-interference method does not need to detect interference signals, which is applicable to various interference situations. Therefore, there is no need to add an interference signal detection module to the original signal processing process, and the existing class-band signal processing process can be reused to the greatest extent;

[0040] The three proposed modulation methods that rely on three independent pseudo-random sequences are equivalent to performing random phase modulation on the transmitted signal. Therefore, the transmitted signal of this system can be correctly demodulated, while the interference signal not from this system cannot be correctly demodulated, so that in the signal processing process, only the target signal of interest can be coherently accumulated to form a target peak, while the interference signal cannot be accumulated into a peak, and appears in the form of a random noise floor in the Doppler dimension. Furthermore, since the frequency hopping and randomly delayed waveforms can move part of the interference signal out of the intermediate frequency band, the energy of part of the interference signal can be reduced, effectively reducing the influence of the interference signal on target detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0042] Figure 1 The present invention is a flow chart of the vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding;

[0043] Figure 2 A schematic diagram of a vehicle-mounted millimeter-wave radar anti-interference system based on slow-time waveform coding provided by the present invention;

[0044] Figure 3 A schematic diagram of a pseudo-random number generator provided in Example 1 of the present invention;

[0045] Figure 4 A schematic diagram of a decoding phase compensation method provided in Embodiment 1 of the present invention;

[0046] Figure 5A schematic diagram of a phase (PS) modulation waveform provided in an embodiment of the present invention;

[0047] Figure 6 A schematic diagram of a frequency hopping (FH) modulation waveform provided in Embodiment 1 of the present invention;

[0048] Figure 7 A schematic diagram of a delay (CS) modulation waveform provided in Example 1 of the present invention;

[0049] Figure 8 A schematic diagram of a combined modulation waveform provided in Embodiment 1 of the present invention;

[0050] Fig. 9 A schematic diagram of a radar signal waveform subjected to interference provided in Embodiment 1 of the present invention;

[0051] Fig.10 The 2D-FFT result of the radar signal subjected to interference provided in Embodiment 1 of the present invention;

[0052] Fig.11 A schematic diagram of a frequency hopping (FH) anti-interference 1DFFT result provided in Example 1 of the present invention;

[0053] Fig.12 A schematic diagram of a frequency hopping (FH) anti-interference 1DFFT result provided in Example 1 of the present invention;

[0054] Fig.13 A schematic diagram of a frequency hopping (FH) anti-interference 2D-FFT result provided in Example 1 of the present invention;

[0055] Fig.14 A schematic diagram of the delay (CS) anti-interference 2D-FFT result provided in Example 1 of the present invention;

[0056] Fig.15 This is a schematic diagram of the phase (PS) anti-interference 2D-FFT results provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0057] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] Example 1

[0059] As shown in the figure, according to one aspect of the present invention, a technical solution is provided: for phase coding (PS) anti-interference, the transmission waveform is as follows: Figure 5As shown; consider the phase difference between two chirps with different codes. In order to enable the target to be coherently accumulated through FFT in slow time, we need to ensure the phase continuity on the full-time shoulder. Since the modulation phase when the code is 1 is fixed to , the compensation phase of PS anti-interference is fixed to , that is, directly multiply -1 on the chirp with code 1.

[0060] In one embodiment, for frequency hopping (FH) anti-interference, the transmission waveform is as follows: Figure 6 As shown, consider the effect of frequency variation on the echo phase of a target:

[0061] θ=2πΔf·t r

[0062] Among them, t r is the round-trip time from the echo to the target. Therefore, the phase that needs to be compensated in the frequency hopping mode is:

[0063]

[0064] Since the distance information of the target cannot be known before detection, it is necessary to traverse and compensate all distance grid points in the 1DFFT result. The compensation value of each grid point is calculated as follows:

[0065]

[0066] Where B is the frequency sweep bandwidth of a single chirp, is the number of FFT points in the distance dimension, and f s is the ADC sampling frequency, T p is the upward sweep time of a single chirp.

[0067] It should be noted that since the distance obtained by the FFT result is a discretized grid point, there may be a certain error between it and the actual target, which will cause an error in phase compensation. The distance error noticed is half of the distance of a single grid point:

[0068]

[0069] In order to ensure the accuracy of compensation phase calculation, it is necessary to ensure In this example, we select So we have:

[0070]

[0071] In practical applications, the threshold can be flexibly set according to the requirements of compensation accuracy to determine the selection range of the frequency hopping value.

[0072] In one embodiment, for frequency hopping (FH) anti-interference, the transmission waveform is as follows: Figure 7 As shown in the figure, the time delay causes different codes to have different corresponding transmission frequencies at the sampling starting point, which is similar to the analysis of the frequency hopping waveform. It is noted that the delay causes the phase lag and the phase difference between different codes can be obtained as follows:

[0073]

[0074] Similarly, phase compensation needs to be performed on all distance grid points in the 1D-FFT result. The compensation phase is calculated as follows:

[0075]

[0076] Similarly, the threshold is set to 0.1 due to the accuracy of the distance grid points. The following conditions must be met when selecting the delay time:

[0077]

[0078] In one embodiment, the combined modulated waveform is transmitted as Figure 8 As shown; select the corresponding compensation phase according to the three modulation codes of the current chirp, as shown in the following table:

[0079] Table 1 Decoding phase corresponding to the combined waveform

[0080]

[0081] Phase compensation operation between 1D-FFT and 2D-FFT is performed as follows Figure 4 shown.

[0082] In another embodiment, the pseudo-random number generator is implemented by a linear feedback shift register, such as Figure 3 As shown, it consists of ten delay modules, where the taps are located at the 7th and 10th bits, and the 4th bit is used for output. The generated sequence period is 1024. Designers can also use other primitive polynomials to generate pseudo-random number generators with different structures.

[0083] In another embodiment, the echo signal interfered by other radars such as Fig. 9 As shown in Figure 2, if no anti-interference processing is performed, the 2D-FFT result is as follows: Fig.10 As shown, it can be seen that there is an obvious interference peak at a distance of 20-60m, and the interference intensity is basically consistent with the height of the weak target at 90m, causing multiple target false alarms in CFAR detection. Fig.11 , Fig.12The 1D-FFT results of FH anti-interference and CS anti-interference are shown respectively. It can be seen that in the slow time, the interference signal in the chirp is moved outside the intermediate frequency bandwidth, so the total energy of the interference signal is reduced by half; Fig.13 , Fig.14 , Fig.15 The performance of the FH, CS, and PS anti-interference methods on 2DFFT is shown respectively. The peak of the interference signal decreases to varying degrees, but the target peak height also decreases due to the phase compensation error in the FH and CS methods. In order to evaluate the anti-interference effect, the signal-to-interference ratio (SIR) is defined as the ratio between the target signal peak and the maximum interference peak:

[0084]

[0085] In this example, the target peak at 90m is used as the reference signal. The signal-to-interference ratios of different anti-interference methods are as follows:

[0086] Table 2 Comparison of signal-to-interference ratio of different anti-interference methods

[0087]

[0088]

[0089] The above results show that the anti-interference waveforms of the present invention can effectively suppress interference signals, among which the combination of the three waveforms has the best suppression effect on interference signals, and the effect of PS is best when used alone.

[0090] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding, characterized in that: The following steps are involved: S1. Determine the modulation waveform according to the observation scene requirements, phase modulation, frequency hopping, start time delay or a combination of the three waveforms, and determine the frequency offset value Δf and time delay value δ when the code is 1; S2, using a pseudo-random code generator to sequentially generate a phase modulation code sequence, a frequency modulation code sequence and a start time code sequence according to the selected modulation waveform; S3, determine the starting frequency of the current transmission sequence according to the frequency coding sequence, determine the phase of the current chirp according to the phase coding sequence, and realize phase modulation through the phase shifter, and determine the starting time of the current chirp transmission according to the time coding sequence; S4, transmitting a modulated waveform and receiving an echo signal, using the current chirp transmission signal as a reference signal to mix with the echo signal; S5, sampling the intermediate frequency signal, performing distance dimension FFT on the sampled signal, and performing phase compensation according to the slow time series based on the distance index; S6, performing Doppler dimension FFT on the compensated data, performing Doppler dimension FFT on the compensated data, and performing CFAR detection and DOA estimation on the 2dFFT results; S7. Output target point cloud information.

2. The vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding according to claim 1 is characterized in that: The frequency offset value Δf in S1 is selected to be greater than half of the sampling frequency so that the interference signal with a different encoding from the target signal is moved outside the intermediate frequency bandwidth, and the phase compensation accuracy Δf satisfies: Where B is the sweep bandwidth of a single chirp, N r is the number of FFT points in the distance dimension, f s is the ADC sampling frequency, T p The upward sweep time of a single chirp. The time delay options are: Among them, when the phase modulation is coded as 1, the modulation phase is fixed to π.

3. The vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding according to claim 1 is characterized in that: The pseudo-random code generator in S2 is implemented using a linear feedback shift register. A suitable primitive polynomial is selected according to the maximum chirp number supported to generate a pseudo-random sequence of the corresponding period. The seeds used in generating the three phase modulation sequences are different and not 0. In addition, whether to generate a random sequence through a pseudo-random encoder is determined based on the modulation enable. If a certain modulation is not enabled, the corresponding sequence is set to 0.

4. The vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding according to claim 1 is characterized in that: When the current chirp code in S3 is 0, the corresponding phase, frequency, and start time are not modulated, and the basic waveform is transmitted; When the code is 1, the corresponding modulation is performed: the modulation phase is π, and the starting frequency is changed to f c +Δf, the reference clock edge is transmitted after a delay of δ after arrival, and any combination of modulations may be performed within a chirp.

5. The vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding according to claim 1 is characterized in that: The reference waveform used for the mixing in S4 is the waveform after the current chirp modulation.

6. The vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding according to claim 1 is characterized in that: The phase compensation in S5 refers to the compensation of the chirp when the code is 1, including compensation of phase modulation, frequency modulation and time delay. For the phase modulation mode, the compensation phase is θ ps =π; In frequency modulation mode, each distance unit is compensated, and the compensation phase is: The compensation phase in random delay mode is: Where m represents the distance index value of the current compensation.

7. The vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding according to claim 1 is characterized in that: During the CFAR detection in S6, the interference signal cannot be accumulated in the Doppler dimension and is manifested as a random noise spectrum. After the noise floor detection is performed at the corresponding distance index, the CFAR threshold value should be appropriately raised to avoid false alarms.

8. A vehicle-mounted millimeter-wave radar anti-interference system based on slow-time waveform coding, comprising the vehicle-mounted millimeter-wave radar anti-interference method based on slow-time waveform coding according to any one of claims 1-1, characterized in that: It includes a pseudo-random number generator module, a modulation module, a transmitting module, a receiving module, a sampling module, a data processing module and a post-processing module; The pseudo-random number generator module is used to generate three groups of modulation sequences for waveform modulation; The modulation module is used to modulate the transmission waveform, including phase modulation, starting frequency modulation and transmission time modulation; The transmitting module is used to transmit the modulated waveform; The receiving module is used to receive the echo signal of the target and mix it with the reference signal; The sampling module is used to sample the echo analog signal for subsequent digital signal processing; The data processing module includes performing FFT operation on the sampled signal and demodulation operation between two-dimensional FFT; The post-processing module is used to perform CFAR detection and DOA estimation on the two-dimensional spectrum of the echo and output point cloud information.

9. The vehicle-mounted millimeter-wave radar anti-interference system based on slow-time waveform coding according to claim 8 is characterized in that: The pseudo-random number generator of the pseudo-random number generator module can be built with multiple primitive polynomials to generate sequences of different lengths, or a primitive polynomial with a longer period can be used to intercept a part of the sequence; The modulation module realizes phase modulation through a phase shifter. When using the phase shifter, the phase shifter should be calibrated, and only the relative value of the two phase points needs to be calibrated as π. There is no need to select the absolute phase 0 and phase π. The time delay operation is completed by counting the clock cycles. After the reference clock edge arrives, the number of clock cycles calculated according to the configured delay time is counted, and the transmission is performed after the counting is completed.

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