JP2019027979A - Radar device and target detection method - Google Patents

Abstract

To suppress erroneous extraction of a noise peak based on phase noise.SOLUTION: A radar device pertaining to an embodiment of the present invention comprises a transmission unit, a reception unit, a conversion unit, a setting unit and a peak extraction unit. The transmission unit transmits a chirp wave by a transmission signal whose frequency continuously increases or decreases. The reception unit generates a beat signal for each reception antenna from the reception signal of the chirp signal reflected by a target and received by a plurality of reception antennas and the transmission signal. The conversion unit converts the beat signal generated by the reception unit into a frequency spectrum that indicates the distribution of signal strength to the distance from the target and relative speed. The setting unit sets a first threshold for extraction of peak to the relative speed for each distance on the basis of the average value of signal strength per distance in the frequency spectrum converted by the conversion unit. The peak extraction unit extracts a peak exceeding the first threshold set by the setting unit from the frequency spectrum as a peak of the target.SELECTED DRAWING: Figure 1B

Description

  The present invention relates to a radar apparatus and a target detection method.

  Recently, as a radar device for detecting a target, an FCM (Fast Chirp Modulation) type radar device that transmits a chirp wave whose frequency continuously increases or decreases to detect a distance and a relative speed from the target has been proposed. (For example, refer to Patent Document 1).

  In the FCM method, the distance and relative velocity between the target and the target are determined from the frequency and phase change of the beat signal generated by the transmission signal that generates the chirp wave and the reception signal that is obtained by receiving the reflected wave of the chirp wave from the target. This is a detection method.

JP, 2006-003873, A

  In such a radar apparatus, for example, when a peak of a strong reflector is present, the signal intensity of a noise peak based on phase noise or the like increases at the same distance as the peak, and the noise peak may be erroneously extracted.

  The present invention has been made in view of the above, and an object of the present invention is to provide a radar device and a target detection method that can suppress erroneous extraction of noise peaks based on phase noise.

  The radar apparatus according to the embodiment includes a transmission unit, a reception unit, a conversion unit, a setting unit, and a peak extraction unit. The transmission unit transmits a chirp wave by a transmission signal whose frequency continuously increases or decreases. The receiving unit generates a beat signal for each of the reception antennas from a reception signal obtained by receiving a reflected wave of the chirp wave by a target with a plurality of reception antennas and the transmission signal. The converting unit converts the beat signal generated by the receiving unit into a frequency spectrum indicating a signal intensity distribution with respect to a distance from the target and a relative speed. The setting unit sets, for each distance, a first threshold value for peak extraction with respect to a relative speed based on an average value of signal strength for each distance in the frequency spectrum converted by the conversion unit. The peak extraction unit extracts a peak exceeding the first threshold set by the setting unit from the frequency spectrum as a target peak.

  According to the radar apparatus and the target detection method according to an aspect of the embodiment, it is possible to suppress erroneous extraction of noise peaks based on phase noise.

FIG. 1A is a diagram illustrating an example of a positional relationship between a radar device mounted on a vehicle and a target. FIG. 1B is a diagram illustrating an outline of a target detection method. FIG. 2 is a block diagram of the radar apparatus. FIG. 3 is a diagram illustrating an example of a relationship among a transmission frequency, a reception frequency, and a beat frequency. FIG. 4 is a diagram illustrating a result of performing FFT processing on one beat signal. FIG. 5 is a diagram illustrating an example of FFT processing results of beat signals that are temporally continuous and a peak phase change between beat signals. FIG. 6 is a diagram showing a frequency spectrum at a specific distance. FIG. 7 is a diagram illustrating a specific example of processing by the calculation unit. FIG. 8A is a diagram (part 1) illustrating a specific example of a deviation threshold setting process. FIG. 8B is a diagram (part 2) illustrating a specific example of the first threshold value and the second threshold value. FIG. 9A is a flowchart (part 1) illustrating a processing procedure executed by the radar apparatus. FIG. 9B is a flowchart (part 2) illustrating a processing procedure executed by the radar apparatus. FIG. 10 is a diagram illustrating a specific example of a deviation calculation process according to the modification.

  Hereinafter, embodiments of a radar apparatus and a target detection method disclosed in the present application will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

  First, the outline of the target detection method by the radar apparatus according to the embodiment will be described with reference to FIGS. 1A and 1B. FIG. 1A is a diagram illustrating an example of a positional relationship between a radar device mounted on a vehicle and a target. FIG. 1B is a diagram illustrating an outline of a target detection method.

  As shown in FIG. 1A, the radar apparatus 1 according to the embodiment is mounted on a host vehicle MC such as an automobile, and detects a target ahead (for example, a stationary object such as another vehicle, a pedestrian, or a guardrail). To do.

  The radar apparatus 1 is an FCM (Fast Chirp Modulation) type radar apparatus that transmits a chirp wave whose frequency continuously increases or decreases to detect the distance and relative velocity with each target existing in the detection range L. is there.

  The radar apparatus 1 performs a two-dimensional fast Fourier transform (Fast Fourier transform) on a beat signal for each chirp wave generated from a transmission signal for generating a chirp wave and a reception signal obtained by receiving a reflected wave of a chirp wave by a target. A Fourier Transform process (hereinafter referred to as a two-dimensional FFT process) is performed to derive the distance from the target and the relative velocity.

  Specifically, in the two-dimensional FFT processing, the distance from the target is derived by the first fast Fourier transform (hereinafter referred to as FFT processing), and the relative velocity with the target is derived by the second FFT processing. To do.

  Here, in the second FFT processing, the relative speed with respect to the target is derived based on the phase difference for each beat signal. For this reason, for example, when phase noise (random noise inherent in the device; for example, thermal noise or deviation in the transmission timing of the chirp wave) occurs during the transmission of the chirp wave, A phase difference based on phase noise appears in addition to a phase difference based on the relative velocity with respect to the target.

  Then, a relatively strong signal strength peak (a peak related to a large vehicle (for example, a truck or a bus) having a large reflected wave power) in which the signal strength is equal to or higher than a predetermined value in a beat signal related to a relative speed at a certain distance BIN is detected. If this is the case, the signal strength (power) of the beat signal with respect to this relative speed is relatively increased. For this reason, in the prior art, the signal intensity of the noise peak based on the phase noise in the beat signal related to the relative speed also increases, and there is a possibility that the noise peak is erroneously extracted as the peak of the target.

  Therefore, in the target detection method according to the embodiment, paying attention to the point that a noise peak occurs in the beat signal related to the relative speed derived for each predetermined distance frequency (for each distance BIN) due to the influence of phase noise, the predetermined distance The first threshold Th1 for peak extraction in the beat signal related to the relative speed is set for each frequency.

  Hereinafter, the outline of the target detection method according to the embodiment will be described with reference to FIG. 1B. FIG. 1B shows a frequency spectrum as a result of the two-dimensional FFT process, and shows a spectrum at a specific distance where the target exists in a cross-section.

  Moreover, in FIG. 1B, the case where the peak P1 of a strong reflector exists in this frequency spectrum is shown by a solid line, and the frequency spectrum when the peak P1 does not exist is shown by a broken line for comparison.

  As shown in FIG. 1B, when the peak P1 based on the strong reflector is present, the power of the frequency spectrum is relatively increased as compared with the case where the peak P1 is not present.

  That is, when the peak P1 exists, the power of the frequency spectrum at a distance near the peak P1 relatively increases due to the influence of the phase noise. For this reason, the average value of the power of the distance BIN in the vicinity distance becomes high. Note that 1BIN is 468 Hz.

  On the other hand, in contrast to the case where the peak P1 exists, when there is no strong reflector such as the peak P1 in the vicinity distance, the power of the noise peak affected by the phase noise does not increase as shown by the broken line. . For this reason, such noise peaks have low power and are difficult to be extracted as target peaks.

  Therefore, in the object detection method, the first threshold Th1 is set for each distance based on the average value of the power for each distance. As a result, even if the peak P1 exists and the power in the vicinity of the peak P1 (for example, a frequency range of ± 5 BIN) increases, only the peak P1 is extracted while eliminating the noise peak based on the phase noise. It is possible to set the first threshold Th1a.

  Thus, in the target detection method according to the embodiment, by setting the first threshold value Th1 for peak extraction with respect to the relative speed (speed BIN) for each distance BIN, erroneous extraction of noise peaks based on phase noise is suppressed. It becomes possible.

  Next, the configuration of the radar apparatus 1 according to the embodiment will be described with reference to FIG. FIG. 2 is a block diagram of the radar apparatus 1. FIG. 2 shows the vehicle control device 2 in addition to the radar device 1.

  The vehicle control device 2 performs vehicle control such as PCS (Pre-crash Safety System) and AEB (Advanced Emergency Braking System) based on the detection result of the target by the radar device 1. The radar device 1 may be used for various purposes other than the on-vehicle radar device (for example, monitoring of an airplane or a ship).

  The radar apparatus 1 includes a transmission unit 10, a reception unit 20, and a processing unit 30. The transmission unit 10 includes a signal generation unit 11, an oscillator 12, and a transmission antenna 13. The signal generator 11 generates a modulated signal whose voltage changes in a sawtooth waveform and supplies the modulated signal to the oscillator 12. The oscillator 12 generates a transmission signal ST that is a chirp signal based on the modulation signal generated by the signal generation unit 11 and outputs the transmission signal ST to the transmission antenna 13.

  The transmission antenna 13 converts the transmission signal ST input from the oscillator 12 into a transmission wave SW, and outputs the transmission wave SW to the outside of the host vehicle MC. The transmission wave SW output from the transmission antenna 13 is a so-called chirp wave. The transmission wave SW transmitted from the transmission antenna 13 to the front of the host vehicle MC is reflected by a target such as another vehicle and becomes a reflected wave.

  The receiving unit 20 includes a plurality of receiving antennas 21a to 21d, mixers 22a to 22d, and A / D converters 23a to 23d that form an array antenna. Each receiving antenna 21 receives a reflected wave from a target as a received wave RW, converts the received wave RW into a received signal SR, and outputs the received signal RW to a mixer 22 provided for each receiving antenna 21. The number of receiving antennas 21 shown in FIG. 2 is four, but it may be three or less or five or more.

  The reception signal SR output from each reception antenna 21 is amplified by an amplifier (not shown) (for example, a low noise amplifier) and then input to the mixer 22. The mixer 22 mixes a part of the transmission signal ST and the reception signal SR, removes unnecessary signal components, generates a beat signal SB, and outputs the beat signal SB to the A / D converter 23.

Thereby, the beat frequency f _SB (which is the difference between the frequency f _ST of the transmission signal ST (hereinafter referred to as the transmission frequency f _ST ) and the frequency f _SR of the reception signal _SR (hereinafter referred to as the reception frequency f _SR ). = F _ST −f _SR ) is generated. The beat signal SB generated by the mixer 22 is converted to a digital signal by the A / D converter 23 and then output to the processing unit 30.

FIG. 3 is a diagram illustrating an example of the relationship among the transmission frequency _fST , the reception frequency _fSR, and the beat frequency _fSB . As shown in FIG. 3, the beat signal SB is generated for each chirp wave.

Further, in the example shown in FIG. 3, the transmission frequency _{f ST,} for each chirp wave, along with the reference frequency f0 time increases at a gradient θ (= (f1-f0) / Tm), reaching the maximum frequency f1 A sawtooth waveform that returns to the reference frequency f0 in a short time. The transmission frequency _{f ST} is reached in a short time from the reference frequency f0 to the maximum frequency f1 for each chirp wave, decreases with a slope with the take up frequency f1 in the time θ (= (f0-f1) / Tm) Sawtooth wave shape may be sufficient.

  Returning to the description of FIG. 2, the processing unit 30 will be described. The processing unit 30 includes a transmission control unit 31 and a signal processing unit 32. The signal processing unit 32 includes a conversion unit 33, a calculation unit 35, a peak extraction unit 36, a distance / relative speed calculation unit 37, and an azimuth calculation unit 38.

  The processing unit 30 is a microcomputer including, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output port, and the like, and controls the entire radar apparatus 1.

  The CPU of the microcomputer functions as the transmission control unit 31 and the signal processing unit 32 by reading and executing the program stored in the ROM. Note that at least a part or all of the transmission control unit 31 and the signal processing unit 32 can be configured by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

  The transmission control unit 31 controls the signal generation unit 11 of the transmission unit 10 and causes the signal generation unit 11 to output a modulation signal whose voltage changes in a sawtooth shape to the oscillator 12. As a result, the transmission signal ST whose frequency changes with the passage of time is output from the oscillator 12 to the transmission antenna 13.

  The conversion unit 33 performs a two-dimensional fast Fourier transform process on the beat signal SB output from each A / D converter 23. That is, the converting unit 33 converts the beat signal generated by the receiving unit 20 into a frequency spectrum indicating a distribution of signal strength (power) with respect to the distance to the target and relative speed.

  Further, the converter 33 averages the signal strength of the frequency spectrum obtained for each reception antenna 21 and outputs the averaged frequency spectrum to the setting unit 34. Further, the conversion unit 33 performs a process of outputting each frequency spectrum for each reception antenna 21 before averaging to the calculation unit 35.

  Here, the detection principle of the distance to the target and the relative speed in the FCM radar device will be described. As described above, the transmission wave SW based on the transmission signal ST is transmitted from the transmission antenna 13, and the transmission wave SW is reflected by the target to become a reflected wave, and the reflected wave is received by the reception antenna 21 as the reception wave RW. And output as a received signal SR.

  The frequency of the beat signal SB increases or decreases in proportion to the distance between the target and the radar apparatus 1 and is proportional to the distance between the target and the radar apparatus 1 (hereinafter referred to as the distance to the target). To do.

  For this reason, by performing FFT processing on the beat signal SB, a peak appears at a frequency BIN corresponding to the distance from the target (hereinafter sometimes referred to as distance BIN). By specifying the distance BIN where such a peak exists, the distance to the target can be detected.

  FIG. 4 is a diagram showing the result of performing FFT processing on one beat signal SB, with the horizontal axis representing frequency and the vertical axis representing power magnitude. In the example shown in FIG. 4, a peak appears at the distance BINfr10, indicating that a target exists at a distance corresponding to the distance BINfr10.

  By the way, when the relative velocity between the target and the radar apparatus 1 is zero, no Doppler component is generated in the received signal SR, and the phase is the same between the received signals SR corresponding to each chirp wave. The phase of the signal SB is also the same.

  On the other hand, when the relative velocity between the target and the radar apparatus 1 is not zero, a Doppler component is generated in the received signal SR, and the phase is different between the received signals SR corresponding to each chirp wave. A phase change corresponding to the Doppler frequency appears between the signals SB.

  Thus, when the relative velocity between the target and the radar apparatus 1 is not zero, a phase change corresponding to the Doppler frequency appears at the peak of the same target between the beat signals SB. Therefore, a frequency spectrum in which a peak appears in the frequency BIN with respect to the Doppler frequency can be obtained by arranging the frequency spectrum obtained by performing the FFT processing on each beat signal SB in time series and performing the second FFT processing. By detecting the frequency BIN at which such a peak appears (hereinafter sometimes referred to as velocity BIN), the relative velocity with respect to the target can be detected.

  FIG. 5 is a diagram illustrating an example of the phase change of the peak between the beat processing result of the beat signal SB that is temporally continuous and the beat signal SB. In the example shown in FIG. 5, there is a peak at the distance BINfr10, and the phase of the peak is changed.

  Thus, the distance and relative speed from the target can be detected by performing FFT processing twice on the beat signal SB and detecting the distance BIN and the speed BIN where the peak exists.

Returning to the description of FIG. 2, the setting unit 34 will be described. The setting unit 34 sets the first threshold Th1 for peak extraction with respect to the relative speed based on the average value of the signal intensity for each distance in the frequency spectrum converted by the conversion unit 33.
The setting unit 34 sets a second threshold Th2 that is lower than the first threshold Th1 for each distance. The setting unit 34 outputs information regarding the set first threshold Th1 and second threshold Th2 to the calculation unit 35.

  Here, a specific example of processing by the setting unit 34 will be described with reference to FIG. FIG. 6 is a diagram showing a frequency spectrum at a specific distance.

  As shown in FIG. 6, first, the setting unit 34 calculates the average value Av of the power at each speed BIN. For example, the setting unit 34 calculates the total value of power at each speed BIN, and calculates the average value Av for each distance BIN by dividing the total by the number of speed BINs. The average value Av may be a value obtained by dividing the power for each distance BIN of the spectrum obtained by the first FFT processing by the number of speeds BIN.

  Subsequently, the setting unit 34 sets the first threshold Th1 by adding a predetermined value α1 to the average value Av. Here, the predetermined value α1 is a value set based on the variation in floor noise. For example, the floor noise is noise generated even when no signal is input in the radar apparatus 1. For this reason, such a noise value is experimentally calculated and added to the average value Av as a predetermined value α1.

  Assume that the predetermined value α1 is not added and the average value Av is set as it is to the first threshold value Th1. In this case, when the floor noise is large, the power of the noise peak may rise above the first threshold Th1 due to the floor noise, and this noise peak may be erroneously extracted as the target peak.

  That is, the setting unit 34 sets the value obtained by adding the predetermined value α1 to the average value Av as the first threshold value Th1, so that even if the noise peak power is increased by floor noise, It becomes possible to suppress erroneous extraction of peaks.

  By the way, when there is a low reflection object such as a pedestrian having a relative speed different from that of the strong reflection object at a distance BIN in the vicinity of the strong reflection object, the peak power corresponding to the pedestrian is smaller than the first threshold Th1. There is a case. In other words, when there is a low reflection object having a relative speed different from that of the strong reflection object at a nearby distance BIN, the peak of the low reflection object may not be extracted as the peak of the target.

  Therefore, the setting unit 34 sets a second threshold Th2 obtained by adding a value α2 that is smaller than the predetermined value α1 to the average value Av. A peak that exceeds the first threshold Th1 is likely to be a target peak, and a peak that is greater than or equal to the second threshold Th2 and less than the first threshold Th1 may be either a noise peak or a low-reflector peak. is there.

  For this reason, the radar apparatus 1 individually determines whether the peak is a low-reflector or a noise peak for peaks that are greater than or equal to the second threshold Th2 and less than the first threshold Th1. Details of this point will be described later with reference to FIG.

  As described above, the radar apparatus 1 sets the thresholds (first threshold Th1 and second threshold Th2) in consideration of the phase noise at the speed BIN for each distance BIN. That is, the threshold is set high for the speed BIN where the influence of the phase noise is large, and the threshold is set low for the speed BIN where the influence of the phase noise is small. This makes it possible to extract the target peak while eliminating the noise peak.

  In the above example, the case where one first threshold Th1 and second threshold Th2 are set for one speed BIN has been described. However, for each speed BIN of a plurality of adjacent distances BIN. One first threshold Th1 and second threshold Th2 may be set respectively.

  Returning to the description of FIG. 2, the calculation unit 35 will be described. The calculating unit 35 calculates the deviation of the signal intensity in the frequency spectrum for each of the receiving antennas 21a to 21d for a peak whose power is smaller than the first threshold Th1 and larger than the second threshold Th2 in the frequency spectrum averaged by the converting unit 33. calculate.

  That is, the calculating unit 35 calculates the power deviation of the same distance BIN and the same speed BIN in each frequency spectrum for each of the reception antennas 21a to 21d for the peak that is greater than or equal to the second threshold Th2 and less than the first threshold Th1.

  FIG. 7 is a diagram illustrating a specific example of processing by the calculation unit 35. In the following description, the peak of the frequency spectrum derived based on the reception signal of the reception antenna 21a is described as the peak of the channel ch1, and the peaks of the frequency spectrum based on the reception signals of the reception antennas 21b to 21d are the channels ch2 to ch4. Are described as peaks.

  As shown in FIG. 7, the calculation unit 35 calculates the deviation of the peak powers of the channels ch1 to ch4 with respect to the peak that is not less than the second threshold Th2 and not more than the first threshold Th1 in the frequency spectrum averaged by the conversion unit 33. To do. In the example shown in FIG. 7, the peaks with the speed BIN of x [BIN] and y [BIN] are applicable.

  Here, the averaged frequency spectrum is obtained by averaging the power of the same distance BIN and the same speed BIN of the frequency spectrum of each channel ch.

  Further, the deviation indicates a variation in peak power of each channel ch (ch1 to ch4) that constitutes the peak of the averaged frequency spectrum. If the noise peak is based on phase noise, the deviation is large, indicating that the variation is large.

  In other words, if the peak of the target, the power of the reflected wave received by the receiving antenna will be substantially the same for each antenna, the deviation will be small, and if it is a noise peak, the beat signal of the relative speed at each receiving antenna Since the signal intensity affecting the signal is random, the deviation becomes large. Therefore, the radar apparatus 1 can determine whether the target peak or the noise peak is based on the deviation.

  For example, the calculation unit 35 calculates the sum of the differences in peak power of each channel ch as a deviation. That is, the difference between the peak power differences of channel ch1 and channel ch2 to ch4, the difference between the peak powers of channel ch2 and channel ch3 and ch4, and the difference between the peak powers of channel ch3 and channel ch4 is the deviation. Become.

  Returning to the description of FIG. 2, the peak extraction unit 36 will be described. The peak extraction unit 36 extracts peaks that exceed the first threshold Th1 set by the setting unit 34 from the averaged frequency spectrum. Such a peak is processed as a target peak.

  In addition, the peak extraction unit 36 determines whether the peak of the target is a noise peak based on the deviation calculated by the calculation unit 35 for peaks that are equal to or greater than the second threshold Th2 and less than the first threshold Th1 in the averaged frequency spectrum. Do it individually.

  Specifically, the peak extraction unit 36 determines that the peak of the peak that is greater than or equal to the second threshold Th2 and less than the first threshold Th1 is less than the deviation threshold Thd, and that the deviation is greater than or equal to the deviation threshold Thd. For example, it is determined as a noise peak. The deviation threshold Thd is a value set based on the calculation result of the azimuth calculation unit 38 described later. For this reason, the peak extraction unit 36 once extracts all peaks that exceed the second threshold Th <b> 2 and outputs them to the distance / relative speed calculation unit 37.

  Thereafter, the peak extraction unit 36 sets a deviation threshold Thd based on the calculation result of the azimuth calculation unit 38, and determines whether the peak of the target is the peak of the target or the noise peak for the second threshold Th2 or more and less than the first threshold Th1. Details of this point will be described later with reference to FIGS. 8A and 8B.

  The distance / relative velocity calculation unit 37 derives the distance and relative velocity with respect to the target based on the combination of the distance BIN and the velocity BIN specified by the peak extraction unit 36 as having a peak. Further, the distance / relative speed calculation unit 37 outputs information on the derived distance to the target and relative speed and information on the peak input from the peak extraction unit 36 to the direction calculation unit 38.

  The azimuth calculation unit 38 separates information about a plurality of targets existing at the same distance BIN from a signal of each distance BIN where the peak specified by the peak extraction unit 36 exists by a predetermined angle calculation process, Estimate the angle of each of these multiple targets.

  The azimuth calculation unit 38 pays attention to signals of the same frequency BIN (hereinafter referred to as peak signals) in all frequency spectra of the four beat signals SB based on the reception signals SR of the four reception antennas 21a to 21d, and the peak signals The angle of the target is estimated based on the phase information. The azimuth estimation in the azimuth calculation unit 38 is performed using a predetermined azimuth estimation method such as ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques), DBF (Digital Beam Forming), or MUSIC (Multiple Signal Classification). Is called.

  The azimuth calculation unit 38 outputs information (distance / relative speed, angle, etc.) regarding the peak exceeding the first threshold Th1 to the vehicle control device 2. In addition, the azimuth calculation unit 38 outputs a calculation result for a peak not less than the second threshold Th2 and less than the first threshold Th1 to the peak extraction unit 36.

  As a result, the peak extraction unit 36 sets the deviation threshold Thd and determines whether the peak is greater than or equal to the second threshold Th2 and less than the first threshold Th1 and is a target peak or a noise peak.

  Here, a specific example of the deviation threshold Thd will be described with reference to FIGS. 8A and 8B. 8A and 8B are diagrams illustrating a specific example of the setting process of the deviation threshold Thd.

  8A and 8B indicate that the center of the fan is the front of the host vehicle MC (radar apparatus 1). For example, as shown in FIG. 8A, the peak extraction unit 36 sets the deviation threshold Thd to a smaller value as it is in front of the host vehicle MC, and increases the deviation threshold Thd as the angle is wider from the front of the host vehicle MC. Set.

  In the case of a peak of a target, the closer to the front of the host vehicle MC, the less likely the peak power of each channel ch varies, and the more likely the power of each channel ch varies as it goes to the wide angle side. Because. In other words, even if it is the peak of the target, the deviation is lower as it is in front of the host vehicle MC, and the deviation is likely to be larger toward the wide angle side.

  As described above, the peak extraction unit 36 can cancel the variation based on the angle included in the deviation by setting the deviation threshold Thd based on the angle at which the peak exists. Then, the peak extraction unit 36 determines a peak at which the above deviation is less than the deviation threshold Thd as a target peak, and a peak at which the deviation is equal to or greater than the deviation threshold Thd as a noise peak.

  That is, the peak extraction unit 36 can accurately determine whether the peak is a target or a noise peak by setting the deviation threshold Thd based on the angle at which the peak exists.

  Incidentally, as shown in FIG. 8B, the peak extraction unit 36 can also set the deviation threshold Thd according to the number of targets. Specifically, when the peak having the same distance and relative speed is separated into a plurality of peaks by the azimuth calculation unit 38, the peak extraction unit 36 sets the deviation threshold Thd of the peak to a large value.

  This is because when there are a plurality of targets having the same distance and relative speed, that is, when a plurality of peaks overlap the same distance BIN and the same speed BIN, the peak power of each channel ch varies. This is because it is likely to occur.

  On the other hand, if there is a single peak having the same distance and relative speed according to the calculation result of the azimuth calculation unit 38, the peak extraction unit 36 sets the peak deviation threshold Thd to the same distance BIN and the same speed BIN. Set to a smaller value than when the peaks of have overlapped.

  Thus, in the radar apparatus 1, the deviation threshold Thd is set based on the calculation result of the azimuth calculation unit 38. Thereby, the variation based on the angle included in the deviation and the variation based on the overlap of a plurality of peaks can be offset.

  Therefore, the peak extraction unit 36 can accurately determine whether the target peak or the noise peak based on the phase noise. The deviation threshold Thd may be a constant value regardless of the calculation result of the azimuth calculation unit 38. In this case, the deviation threshold Thd can be derived by experiments or the like. In such a case, since the process of setting the deviation threshold Thd for each peak can be omitted, the processing load on the radar apparatus 1 can be reduced.

  In addition, the radar apparatus 1 does not perform the above-described determination processing on all peaks, but only determines a peak that is suspected of being a target peak or a noise peak (second threshold Th2 or more and less than the first threshold Th1). Process. As a result, the processing load can be reduced as compared with the case where the above-described determination processing is performed on all peaks.

  Next, a processing procedure executed by the radar apparatus 1 according to the embodiment will be described with reference to FIGS. 9A and 9B. FIG. 9A and FIG. 9B are flowcharts showing a processing procedure executed by the radar apparatus 1. Note that this processing procedure is repeatedly executed by the processing unit 30.

  First, an overall processing procedure executed by the radar apparatus 1 will be described with reference to FIG. 9A. As shown in FIG. 9A, first, the conversion unit 33 converts the beat signal into a frequency spectrum (step S101).

  Subsequently, the setting unit 34 sets the first threshold Th1 and the second threshold Th2 for each distance (step S102). Next, the peak extraction unit 36 performs peak extraction processing (step S103).

  Subsequently, the processing unit 30 determines whether or not there is a peak greater than or equal to the second threshold Th2 and less than the first threshold Th1 (step S104). When there is the peak in the determination (step S104, Yes), the processing unit 30 performs a peak determination process (step S105). Note that the processing procedure of the peak determination processing in step S105 will be described later with reference to FIG. 9B.

  Subsequently, the distance / relative speed calculation unit 37 performs distance / relative speed calculation (step S106), and the azimuth calculation unit 38 performs azimuth calculation processing (step S107), and ends the process.

  Further, when there is no peak that is equal to or greater than the second threshold Th2 and less than the first threshold Th1 in the determination of Step S104 (No in Step S104), the processing unit 30 omits the process of Step S105 and performs the process of Step S106. .

  Next, a processing procedure related to peak discrimination processing will be described with reference to FIG. 9B. Note that this predetermined procedure corresponds to step S106 illustrated in FIG. 9A and is performed on a peak that is equal to or greater than the second threshold Th2 and less than the first threshold Th1.

  As shown in FIG. 9B, first, the calculation unit 35 calculates the deviation of the peak power of each channel ch (step S201). Subsequently, the peak extraction unit 36 sets a deviation threshold Thd for each peak based on the calculation result of the azimuth calculation unit 38 (step S202).

  Subsequently, the peak extraction unit 36 determines whether or not the deviation is less than the deviation threshold Thd for each peak (step S203). In this determination, when the deviation is less than the deviation threshold Thd (step S203, Yes), the peak extraction unit 36 determines the peak as a target peak (step S204) and ends the process.

  On the other hand, when the deviation is equal to or greater than the deviation threshold Thd (step S203, No), the peak extraction unit 36 determines the peak as a noise peak (step S205) and ends the process.

  As described above, the radar apparatus 1 according to the embodiment includes the transmission unit 10, the reception unit 20, the conversion unit 33, the setting unit 34, and the peak extraction unit 36. The transmitter 10 transmits a chirp wave by a transmission signal whose frequency continuously increases or decreases. The receiving unit 20 generates a beat signal for each of the reception antennas 21a to 21d from the reception signal and the transmission signal that are received by the reception antennas 21a to 21d of the chirp wave reflected by the target.

  The conversion unit 33 converts the beat signal generated by the reception unit 20 into a frequency spectrum indicating a signal intensity distribution with respect to the distance to the target and relative speed. The setting unit 34 sets, for each distance, a first threshold Th1 for peak extraction with respect to the relative speed based on the average value Av of the signal intensity for each distance in the frequency spectrum converted by the conversion unit 33. The peak extraction unit 36 extracts a peak exceeding the first threshold Th1 set by the setting unit 34 from the frequency spectrum as a target peak. Therefore, according to the radar apparatus 1 according to the embodiment, it is possible to suppress erroneous peak extraction based on phase noise.

  In the above-described embodiment, the case where the deviation threshold value Thd is set based on the calculation result of the azimuth calculation unit 38 has been described. However, the present invention is not limited to this.

  That is, the radar apparatus 1 can change the calculation method of the deviation itself based on the calculation result of the azimuth calculation unit 38. Here, details of this point will be described with reference to FIG. FIG. 10 is a diagram illustrating a specific example of a deviation calculation process according to the modification.

  Here, the case where the target is detected at the position of the peak P shown in FIG. 10 based on the calculation result of the azimuth calculation unit 38 is shown, and the peak P is composed of the peaks of the channels ch1 to ch4 shown in FIG. Shall. For example, the calculation unit 35 calculates the deviation after correcting the peak power value of the channel ch far from the peak P (target) based on the calculation result of the azimuth calculation unit 38.

  In the example illustrated in FIG. 10, the peak P is present on the right side of the front, the channel ch corresponding to the reception antenna 21 closest to the peak is the channel ch4, and the channel ch3 to ch1 are in the order of distance from the peak P. ing.

  The power of the channel ch4 closest to the peak P is more easily observed than the power of the other channel ch, and the power of the channel ch1 farthest from the peak P is the weakest and easily observed.

  That is, in the above example, a power difference is likely to occur between the channel ch4 and the channel ch1. For this reason, the calculation unit 35 corrects, for example, the power of the channel ch1 and the channel ch2 far from the peak P.

  For example, the calculation unit 35 adds the correction value d1 to the power of the channel ch1 and adds a correction value d2 smaller than the correction value d1 to the power of the channel ch2, and then calculates the power deviation of each channel ch.

  That is, the power variation generated between the channels ch based on the distance difference between the target and each receiving antenna 21 is corrected. Then, the deviation is calculated based on the corrected power of each channel. Thereby, the deviation based on the phase noise is more remarkably reflected in the deviation.

  Therefore, the radar apparatus 1 can improve the accuracy of the determination by determining whether the target peak or the noise peak is based on the deviation.

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Radar apparatus 10 Transmission part 20 Reception part 21 Reception antenna 30 Processing part 31 Transmission control part 33 Conversion part 34 Setting part 35 Calculation part 36 Peak extraction part 37 Distance / relative speed calculation part 38 Direction calculation part Th1 1st threshold value Th2 2nd Threshold Thd Deviation threshold

Claims (4)

A transmitter that transmits a chirp wave by a transmission signal whose frequency continuously increases or decreases;
A reception unit that generates a beat signal for each of the reception antennas from a reception signal received by a plurality of reception antennas and a reflected signal of the chirp wave by a target; and
A conversion unit that converts the beat signal generated by the reception unit into a frequency spectrum indicating a distribution of signal intensity with respect to a distance and a relative speed with respect to a target;
A setting unit that sets, for each distance, a first threshold value for peak extraction with respect to relative speed based on an average value of signal strength for each distance in the frequency spectrum converted by the conversion unit;
A radar apparatus, comprising: a peak extraction unit that extracts a peak exceeding the first threshold set by the setting unit from the frequency spectrum as a target peak. The setting unit
A second threshold value smaller than the first threshold value is set for each distance;
A calculation unit that calculates a deviation of the signal strength in the frequency spectrum for each of the receiving antennas for a peak in which the signal strength is larger than the second threshold and smaller than the first threshold;
The peak extraction unit
The radar apparatus according to claim 1, wherein a peak whose deviation is smaller than a predetermined deviation threshold is extracted as a peak of the target among the peaks whose deviation is calculated by the calculation unit. An azimuth calculation unit that estimates an angle at which the target exists based on the peak extracted by the peak extraction unit;
The peak extraction unit
The radar apparatus according to claim 2, wherein the deviation threshold is set based on a calculation result by the azimuth calculation unit. A transmission step of transmitting a chirp wave by a transmission signal whose frequency is continuously increased or decreased;
A reception step of generating a beat signal for each of the reception antennas from the reception signal and the transmission signal received by a plurality of reception antennas of the chirp wave reflected by a target;
A conversion step of converting the beat signal generated by the reception step into a frequency spectrum indicating a distribution of signal intensity with respect to a distance and a relative speed with respect to a target;
A setting step for setting, for each distance, a first threshold value for peak extraction with respect to a relative speed based on an average value of signal strength for each distance in the frequency spectrum converted by the conversion step;
And a peak extraction step of extracting from the frequency spectrum a peak that exceeds the first threshold set in the setting step as a target peak.

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