JP2018115930A - Radar device and method for detecting target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the accuracy of detecting a target.SOLUTION: The radar device according to an embodiment includes a sending unit, a generation unit, a conversion unit, a connection unit, and a distance calculation unit. The sending unit generates a chirp wave by a transmission signal having a continuously reducing or increasing frequency and sends the chirp wave. The generation unit generates a beat signal from a reception signal which received a reflection wave of the chirp wave by the target from a reception antenna or the transmission signal. The conversion unit performs a two-dimensional Fourier transform on the beat signal generated by the generation unit and converts the beat signal into a frequency spectrum showing the distance to the target and a relative speed. The connection unit generates a continuous beat signal by artificially connecting beat signals only when one peak alone exists at the same distance in a frequency spectrum converted by the conversion unit. The distance calculation unit performs a Fourier transform on the continuous beat signal generated by the connection unit and calculates the distance to 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 signal are determined from the frequency and phase change of the beat signal generated from the transmission signal that generates the chirp wave and the received signal that is obtained by receiving the chirp wave reflected by the target. This is a detection method.

JP, 2006-003873, A

  In such a radar apparatus, it may be difficult to separately detect and detect each of the plurality of targets when the distance and relative speed with the plurality of targets are close. For this reason, in the radar apparatus, it is desired to improve the detection accuracy of the target.

  The present invention has been made in view of the above, and an object of the present invention is to provide a radar apparatus and a target detection method capable of improving the detection accuracy of a target.

  The radar apparatus according to the embodiment includes a transmission unit, a generation unit, a conversion unit, a connection unit, and a distance calculation unit. The transmission unit generates a chirp wave by a transmission signal whose frequency continuously increases or decreases, and transmits the chirp wave. The generation unit generates a beat signal from a reception signal obtained by receiving a reflected wave of the chirp wave by a target with a reception antenna and the transmission signal. The conversion unit converts the beat signal into a frequency spectrum indicating a distance from the target and a relative speed by performing a two-dimensional Fourier transform on the beat signal generated by the generation unit. The connecting unit generates a connected beat signal by artificially connecting the beat signals when only one peak exists at the same distance in the frequency spectrum converted by the converting unit. The distance calculation unit calculates a distance from the target by performing a Fourier transform on the connection beat signal generated by the connection unit.

  According to the radar device and the target detection method according to one aspect of the embodiment, the detection accuracy of the target can be improved.

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. 6A is a diagram (part 1) illustrating an example of a condition for generating a connected beat signal by a connecting unit. FIG. 6B is a diagram (part 2) illustrating an example of a condition for generating a linked beat signal by the coupling unit. FIG. 7 is a diagram illustrating an example of the relationship between the number of beat signals to be connected and the distance. FIG. 8 is a flowchart showing a processing procedure executed by the radar apparatus.

  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, a radar apparatus 1 according to the embodiment is mounted on a host vehicle A such as an automobile, and detects a target in front (for example, another vehicle, a pedestrian, a stationary object such as 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, the distance resolution, which is the distance detection accuracy derived from the first FFT processing, can be improved by increasing the number of A / D (Analog / Digital) conversion samplings for the beat signal. .

  However, if the number of samplings is increased to improve the distance resolution, the result of the first FFT processing obtained per unit time is reduced. For this reason, the amount of data used for the second FFT processing is reduced, and the speed resolution, which is the accuracy of detecting the relative speed with the target, is lowered.

  Therefore, in the radar apparatus 1 according to the embodiment, the target resolution is improved by improving the distance resolution without reducing the velocity resolution. The radar apparatus 1 derives the distance and relative speed from the target by the two-dimensional FFT process, and then performs the FFT process again with an increased distance resolution for the target that satisfies the predetermined condition.

  Specifically, as shown in FIG. 1B, first, the radar apparatus 1 performs a two-dimensional FFT process on the beat signal, thereby converting the beat signal SB into a frequency spectrum indicating the distance and relative speed from the target. Conversion is performed (step S1).

  FIG. 1B shows that the beat signal SB is converted into a frequency spectrum, and five peaks P1 to P5 are derived in the frequency spectrum. Subsequently, when only one peak exists at the same distance, the radar apparatus 1 generates a linked beat signal SL by simulating the beat signal SB (step S2).

  Here, when the beat signals SB are connected, the number of A / D conversion samplings increases according to the number of connected beat signals SB, so that the distance resolution can be improved.

  In addition, “only one peak at the same distance” means that if there are a plurality of peaks at the same distance, even if one of the plurality of peaks can be separated into two peaks, This is because it becomes difficult to assign these two peaks to the original peak.

  That is, “only one peak in the same distance bin” is set for the following reason. For example, suppose a peak is present in the 12BIN and 15BIN velocity bins in a 10BIN distance bin.

  In such a case, when the distance bin peak of 10 BIN is separated into a peak of 9.5 BIN (peak Pa) and a peak of 10.5 BIN (peak Pb), the velocity bins of peak Pa and peak Pb are 12 BIN and 15 BIN. This is because it is unclear which one corresponds.

  Therefore, the radar apparatus 1 performs this process when only one peak is detected in the velocity bin for a certain distance bin peak. In other words, the radar apparatus 1 improves the distance resolution of the peaks of targets having different distances and substantially the same relative speed.

  Thereby, the radar apparatus 1 travels at the same speed (relatively low speed) as the pedestrian, for example, at the peak distance bin value belonging to the pedestrian walking in front of the own vehicle A and at a position near the pedestrian. It is possible to accurately detect the peak distance bin value belonging to the vehicle.

  Subsequently, the radar apparatus 1 performs an FFT process on the connected beat signal SL (step S3). Thereby, a frequency spectrum can be analyzed more finely about a distance component.

  As a result, for example, as shown in FIG. 1B, when a plurality of peaks overlap with the peak P1, the peak P1 can be separated into two peaks P1a and P1b.

  Moreover, the relative speed of the peak P1 can be used as the relative speed of the peaks P1a and P1b. For this reason, the radar apparatus 1 can improve the distance resolution without reducing the speed resolution.

  Therefore, according to the radar apparatus 1 according to the embodiment, the detection accuracy of the target can be improved.

  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, a generation unit 30, and a processing unit 40. 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, which is a chirp signal whose frequency increases with the passage of time, every predetermined period Tc (hereinafter referred to as a chirp period Tc), based on the modulation signal generated by the signal generation unit 11. And output to the transmission antenna 13.

  The transmission antenna 13 converts the transmission signal ST from the oscillator 12 into a transmission wave SW, and outputs the transmission wave SW to the outside of the host vehicle A. The transmission wave SW output from the transmission antenna 13 is a chirp wave whose frequency increases with the passage of time every chirp period Tc. The transmission wave SW transmitted from the transmission antenna 13 to the front of the host vehicle A is reflected by a target such as another vehicle and becomes a reflected wave.

  The receiving unit 20 includes a plurality of receiving antennas 21 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 SR to the generating unit 30. The number of receiving antennas 21 shown in FIG. 2 is four, but it may be three or less or five or more.

  The generation unit 30 generates a beat signal SB from the transmission signal ST and the reception signal SR. The generation unit 30 includes a plurality of mixers 31 and a plurality of A / D converters 32. The mixer 31 and the A / D converter 32 are provided for each reception antenna 21.

  The received signal SR output from the receiving antenna 21 is amplified by an amplifier (not shown) (for example, a low noise amplifier) and then input to the mixer 31. The mixer 31 mixes a part of the transmission signal ST and the reception signal SR, removes unnecessary signal components, generates a beat signal SB, and outputs it to the A / D converter 32.

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 31 is converted into a digital signal by the A / D converter 32 and then output to the processing unit 40.

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 40 will be described. The processing unit 40 includes a transmission control unit 41 and a signal processing unit 42. The signal processing unit 42 includes a conversion unit 43, a peak extraction unit 44, an azimuth calculation unit 45, a distance / relative speed determination unit 46, a connection unit 47, and a distance calculation unit 48. The processing unit 40 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 41 and the signal processing unit 42 by reading and executing the program stored in the ROM. Note that the transmission control unit 41 and the signal processing unit 42 can all be configured by hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA).

  The transmission control unit 41 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 43 performs two-dimensional fast Fourier transform (FFT) processing (hereinafter referred to as FFT processing) on the beat signal SB output from each A / D converter 32.

  The conversion unit 43 performs a two-dimensional FFT process on the beat signal SB generated for each reception antenna 21 by the generation unit 30 during a predetermined period, thereby converting the beat signal SB into a frequency spectrum indicating a distance and a relative speed (FIG. 1B). See).

  Then, the converting unit 43 outputs the frequency spectrum to the peak extracting unit 44, and outputs the beat signal SB used for deriving the frequency spectrum to the connecting unit 47.

  Here, although it is a well-known technique, the detection principle of the distance and relative velocity with the target in the radar apparatus of the FCM system will be briefly 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 period from when the transmission wave SW is transmitted from the transmission antenna 13 until the reception signal SR is output increases or decreases in proportion to the distance between the target and the radar apparatus 1, and the frequency of the beat signal SB is It is proportional to the distance between the target and the radar apparatus 1 (hereinafter referred to as the distance to the target).

  For this reason, by performing FFT processing on the beat signal SB, a peak appears in a frequency bin corresponding to the distance from the target (hereinafter sometimes referred to as a 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 illustrated in FIG. 4, a peak appears in the distance bin fr <b> 10, indicating that a target exists at a distance corresponding to the distance bin fr <b> 10.

  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 a frequency bin with respect to the Doppler frequency can be obtained by arranging the frequency spectrum obtained by performing FFT processing on each beat signal SB in time series and performing the second FFT processing. By detecting the frequency bin in which such a peak appears (hereinafter sometimes referred to as a 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, the distance bin fr10 has a peak, and the phase of the peak is changed.

  As described above, the distance and relative speed with respect to the target can be detected by performing the FFT processing twice on the beat signal SB and detecting the distance bin and the velocity bin where the peak exists.

  Returning to the description of FIG. 2, the description of the processing unit 40 will be continued. The peak extraction unit 44 extracts a peak whose power is a predetermined value or more from the frequency spectrum input from the conversion unit 43, and outputs information regarding the peak to the azimuth calculation unit 45.

  Here, when only one peak exists in the same distance bin, that is, when there is no peak indicating a different speed bin in the same distance bin, the peak extraction unit 44 generates the connection beat signal SL in the connection unit 47. Instruct. Hereinafter, a single peak in the same distance bin is referred to as a single peak.

  By the way, even if the connecting unit 47 generates the connected beat signal SL and increases the distance resolution, the peak to be detected separately may be one peak in the first place.

  For this reason, the peak extraction part 44 can also reduce the process by the connection part 47 by narrowing down conditions and extracting a single peak. Details of this point will be described later with reference to FIGS. 6A and 6B.

  The azimuth calculation unit 45 separates information about a plurality of targets existing in the same distance bin from the signal of each distance bin of the peak extracted by the peak extraction unit 44 by a predetermined angle calculation process. Estimate the angle of each target.

  The azimuth calculation unit 45 pays attention to signals of the same peak 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 21, and these peak signals The angle of the target is estimated based on the phase information. The azimuth estimation in the azimuth calculation unit 45 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 distance / relative velocity determination unit 46 calculates the distance and relative velocity with respect to the target based on the combination of the peak distance bin and the velocity bin extracted by the peak extraction unit 44.

  Then, the distance / relative speed determination unit 46 generates target information including the target distance, relative speed, direction, and the like, and outputs the target information to the vehicle control device 2. Here, when the distance information is input from the distance calculation unit 48, the distance / relative speed determination unit 46 replaces the part corresponding to the distance information of the target information and outputs it to the vehicle control device 2.

  Next, the connecting portion 47 will be described. When the generation instruction of the connected beat signal SL is input from the peak extracting unit 44, the connecting unit 47 generates the connected beat signal SL that is artificially connected.

  The connecting unit 47 connects the beat signals SB after multiplying the beat signal SB input from the converting unit 43 by a window function. Thereby, it is possible to generate the linked beat signal SL in which the discontinuity of each beat signal SB is reduced. In addition, the connecting unit 47 outputs the generated connected beat signal SL to the distance calculating unit 48. In addition, the connection part 47 can use predetermined window functions, such as a square window function, a Hanning window function, a Gaussian window function, for example as a window function.

  By the way, the connection part 47 can also suppress the increase in a processing load by adjusting the number connected according to the distance bin of a single peak. Details of this point will be described with reference to FIG.

  The distance calculation unit 48 performs an FFT process on the connected beat signal SL input from the connecting unit 47 to convert the connected beat signal SL into a frequency spectrum indicating the distance from the target, and based on the frequency spectrum, the object is calculated. Calculate the distance to the mark. Further, the distance calculation unit 48 outputs distance information as a calculation result to the distance / relative speed determination unit 46.

  Next, conditions for the peak extraction unit 44 to instruct the connection beat signal SL to the connection unit 47 will be described using FIG. 6A. FIG. 6A is a diagram illustrating an example of conditions for generating the linked beat signal SL by the linking unit 47.

  In FIG. 6A, the previous frequency spectrum and the current frequency spectrum are superimposed. Further, in the figure, the previous frequency spectrum peaks P6 and P7 are indicated by white circles, and the current frequency spectrum peak P8 is indicated by black circles.

  As shown in the figure, when two peaks P6 and P7 extracted in the previous frequency spectrum move in the direction of the dashed arrow shown in the figure, they are extracted as one peak P8 in the current frequency spectrum. There is a case.

  In the peak P8, there is a high possibility that two peaks derived from the peaks P6 and P7 are extracted as one peak. For this reason, only in such a case, the peak extraction unit 44 can instruct the connection unit 47 to generate the connected beat signal SL.

  For example, the peak extraction unit 44 predicts a peak position (distance bin, velocity bin) in the current frequency spectrum based on the history of the frequency spectrum, and a plurality of peaks overlap one peak in the current frequency spectrum. When it is determined that the possibility is high, an instruction to generate the linked beat signal SL is issued.

  Thereby, the peak extraction part 44 can operate the connection part 47 and the distance calculation part 48 efficiently. Therefore, it is possible to improve the distance resolution of the target while suppressing an increase in processing load.

  Next, the target range of the single peak will be described with reference to FIG. 6B. FIG. 6B is a diagram illustrating an example of a generation condition of the connected beat signal SL by the connecting unit 47, and shows a frequency spectrum in which the vertical axis is a speed bin and the horizontal axis is a distance bin.

  The peak extraction unit 44 can instruct the connection unit 47 to generate the connected beat signal SL only when a single peak is extracted in the target region. Moreover, the peak extraction unit 44 can dynamically set the target region.

  For example, the peak extraction unit 44 sets the target area based on information on the traveling speed input from a speed sensor (not shown). When the speed bin corresponding to the traveling speed of the host vehicle A (hereinafter referred to as the host vehicle speed) is y [Hz], the peak extraction unit 44 has a speed bin frequency between y + a and y−b [Hz]. Set the area as the target area.

  y + a to y−b [Hz] corresponds to, for example, a speed bin corresponding to ± 10 [km / h] from the vehicle speed. This is because detection is performed by improving the distance resolution by narrowing down the target to pedestrians and stationary objects (for example, stationary vehicles).

  The relative speed of the stationary vehicle is y [Hz] equal to the own vehicle speed. Moreover, it can be considered that the moving speed of a pedestrian is approximately within 10 [km / h].

  The relative speed when the pedestrian approaches the own vehicle A increases within a range of 10 [km / h], and the relative speed when the pedestrian approaches the own vehicle A is within a range of 10 [km / h]. It is assumed that it will become smaller.

  For this reason, by limiting the target range to a speed range of ± 10 [km / h] from the speed of the host vehicle A, the pedestrian and the stationary object can be separated efficiently. The above-described target area is an example, and is not limited to this, and can be arbitrarily changed.

  In addition, as illustrated in FIG. 6B, the peak extraction unit 44 can limit the target region based on the distance bin. For example, a section on the side closer to the host vehicle A where the distance bin is x [Hz] (a side where the distance bin is smaller) is set as the target area, and a side far from the host vehicle A (the side where the distance bin is larger) is set outside the target area. You can also.

  This is because a target that is close to the vehicle A needs to be detected with higher accuracy than a target that is far away. In other words, it is sufficient to detect a target far from the host vehicle A with high accuracy after the distance is short.

  For this reason, by limiting the target region for the distance bin, it is possible to accurately detect a target with high priority to be detected while suppressing the processing load.

  For example, x [Hz] corresponds to a distance of 20 [m] from the own vehicle A. However, when the traveling speed of the own vehicle A is high, the distance is set to a longer distance than when the own vehicle A is slow. It can also be changed according to the traveling state of the vehicle A.

  Next, the relationship between the number of beat signals SB to be connected and the distance will be described with reference to FIG. FIG. 7 is a diagram illustrating an example of the relationship between the number of beat signals SB to be connected and the distance. In FIG. 7, the vertical axis represents the number connected by the connecting portion 47, and the horizontal axis represents the single peak distance bin.

  As described above, when the number of beat signals SB to be linked to the linked beat signal SL is increased, the number of A / D conversion samplings for the beat signal SB is increased, and the distance resolution is improved.

  For this reason, as shown in FIG. 7, the connecting unit 47 connects a larger number of beat signals SB as the single peak distance bin is smaller. On the other hand, the connecting unit 47 generates a connected beat signal SL by connecting a smaller number of beat signals SB as the distance bin becomes larger.

  In other words, the connecting unit 47 detects the target with higher detection accuracy as the distance from the target is shorter, and suppresses an increase in processing load as the distance from the target increases.

  Accordingly, it is possible to detect a target with high priority to be detected with improved detection accuracy while suppressing an increase in processing load. Although FIG. 7 shows the case where the number of beat signals SB and the distance bin are in a proportional relationship, the present invention is not limited to this. As the distance bin increases, the number of beat signals SB is decreased stepwise, or when the distance bin is less than or equal to a predetermined value, the number of beat signals SB is set to a fixed number and gradually decreased after exceeding the predetermined value. It can be arbitrarily changed.

  Next, a processing procedure executed by the radar apparatus 1 according to the embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing a processing procedure executed by the radar apparatus 1.

  As shown in FIG. 8, first, the converting unit 43 converts the beat signal SB into a frequency spectrum by two-dimensional FFT processing (step S101). Subsequently, the peak extraction unit 44 performs a peak extraction process from the frequency spectrum (step S102).

  Next, the peak extraction unit 44 determines whether or not there is a single peak in the peak extraction process (step S103). In this determination, when there is a single peak (step S103, Yes), the connecting unit 47 generates a connected beat signal SL (step S104).

  Subsequently, the distance calculation unit 48 calculates a distance by FFT processing on the connected beat signal SL (step S105). In addition, when there is no single peak in the determination of step S103 (step S103, No), the processing unit 40 omits the processes of step S104 and step S105.

  Next, the azimuth calculation unit 45 performs azimuth calculation processing based on the processing result of the peak extraction processing (step S106), and the distance / relative speed determination unit 46 executes distance / relative speed determination processing (step S107). The process is terminated.

  As described above, the radar apparatus 1 according to the embodiment includes the transmission unit 10, the generation unit 30, the conversion unit 43, the connection unit 47, and the distance calculation unit 48. The transmission unit 10 generates a chirp wave by the transmission signal ST whose frequency continuously increases or decreases, and transmits the chirp wave. The generation unit 30 generates a beat signal SB from the reception signal SR and the transmission signal ST received by the reception antenna 21 as a reflected chirp wave from the target.

  The conversion unit 43 performs a two-dimensional Fourier transform on the beat signal SB generated by the generation unit 30, thereby converting the beat signal SB into a frequency spectrum indicating a distance from the target and a relative speed. When there is only one peak at the same distance in the frequency spectrum converted by the converting unit 43, the connecting unit 47 artificially connects the beat signal SB to generate a connected beat signal SL. The distance calculation unit 48 calculates the distance from the target by performing Fourier transform on the connection beat signal SL generated by the connection unit 47. Therefore, according to the radar apparatus 1 according to the embodiment, the detection accuracy of the target can be improved.

  By the way, the radar apparatus 1 does not need to perform the FFT process on the connected beat signal SL in the entire range. For example, the radar apparatus 1 can also perform FFT processing in a limited range based on the single bin distance bin for the connected beat signal SL. In such a case, it is possible to reduce the processing load of the FFT processing for the connected beat signal SL.

  Further, in the present embodiment, the case where the peak extraction unit 44 instructs the connection unit 47 to generate the connected beat signal LS based on the history of the position of each peak has been described (see FIG. 6A), but the present invention is not limited thereto. It is not something.

  The peak extraction unit 44 can also instruct the connection unit 47 to generate the connected beat signal LS based on the power history of each peak. For example, when the power of a peak in the previous frequency spectrum has increased beyond a predetermined value in the current frequency spectrum, there is a high possibility that a plurality of peaks have overlapped with this peak.

  For this reason, the peak extraction part 44 can also instruct | indicate the production | generation of the connection beat signal LS to the connection part 47, when the peak whose power exceeds a predetermined value from the last time exists. Thereby, the detection accuracy of the target can be improved while suppressing an increase in processing load.

  In addition, the peak extraction unit 44 may instruct the connection unit 47 to generate a connected beat signal LS when a broad peak is extracted. This is because there is a high possibility that a plurality of peaks overlap the broad peak.

  Therefore, the peak extraction unit 44 instructs the connection unit 47 to generate a connected beat signal LS when, for example, a peak having a spread of 3 BIN or more is extracted in at least one of the distance bin and the speed bin in the frequency spectrum. . Thereby, the detection accuracy of the target can be improved while suppressing an increase in processing load.

  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 21 Reception antenna 30 Generation part 43 Conversion part 44 Peak extraction part 45 Direction calculation part 46 Distance and relative speed determination part 47 Connection part 48 Distance calculation part SB Beat signal SL Connection beat signal

Claims (6)

A transmitter that generates a chirp wave by a transmission signal whose frequency continuously increases or decreases, and transmits the chirp wave;
A generation unit that generates a beat signal from the reception signal and the transmission signal received by the reception antenna of the chirp wave reflected by the target;
A conversion unit that converts the beat signal into a frequency spectrum indicating a distance and a relative velocity with respect to a target by performing a two-dimensional Fourier transform on the beat signal generated by the generation unit;
When there is only one peak at the same distance in the frequency spectrum converted by the conversion unit, a connection unit that artificially connects the beat signal to generate a connected beat signal;
A radar apparatus comprising: a distance calculation unit that calculates a distance from the target by performing a Fourier transform on the connection beat signal generated by the connection unit. The connecting portion is
The radar apparatus according to claim 1, wherein the number of beat signals to be connected is increased as the distance in which only one peak exists in the frequency spectrum is shorter. The connecting portion is
The radar apparatus according to claim 1, wherein the connected beat signal is not generated when a relative speed corresponding to the peak is outside a speed range corresponding to a moving speed of a pedestrian. The connecting portion is
The beat signal is connected only when a plurality of the peaks in the frequency spectrum previously converted by the conversion unit overlap with each other in the frequency spectrum converted this time to become one peak. The radar apparatus according to 1, 2, or 3. The connecting portion is
The radar according to any one of claims 1 to 4, wherein the generation of the connected beat signal is not performed when a distance where only the one peak exists in the frequency spectrum is a predetermined value or more. apparatus. Generating a chirp wave by a transmission signal whose frequency continuously increases or decreases, and transmitting the chirp wave;
A generation step of generating a beat signal from a reception signal received by a reception antenna and a reflected wave of the chirp wave by a target, and the transmission signal;
A conversion step of converting the beat signal into a frequency spectrum indicating a distance and a relative velocity with respect to a target by performing a two-dimensional Fourier transform on the beat signal generated by the generation step;
When there is only one peak at the same distance in the frequency spectrum converted by the conversion step, a connecting step of generating a connected beat signal by artificially connecting the beat signals;
A target detection method comprising:

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