RADAR SIGNAL PROCESSING DEVICE, RADAR SIGNAL PROCESSING METHOD, RADAR DEVICE, AND IN-VEHICLE DEVICE

A radar signal processing device includes processing circuitry configured to repeatedly acquire a beat signal having a frequency of a difference between a frequency of a radar signal and a frequency of a reflected wave of the radar signal reflected by an observation target, repeatedly calculate a distance between a radar device and the observation target using the acquired beat signal, and repeatedly calculate a relative speed between the radar device and the observation target using the acquired beat signal; calculate an incident angle of the reflected wave to an array antenna by using the acquired beat signal and an arrangement interval between a plurality of reception antennas included in the array antenna; and determine whether the observation target is a detection target or a non-detection target due to electromagnetic noise based on the calculated incident angle, the plurality of distances and the plurality of relative speeds.

TECHNICAL FIELD

The present disclosure relates to a radar signal processing device and a radar signal processing method for calculating a distance between a radar device and an observation target, a radar device including the radar signal processing device, and an in-vehicle device including the radar device.

BACKGROUND ART

Among radar devices that calculate a distance between a radar device and an observation target and calculate a relative speed between the radar device and the observation target, there is a frequency modulated continuous wave (FMCW) radar device that transmits a radar signal whose frequency changes with the lapse of time. The FMCW radar device may erroneously detect a non-detection target due to electromagnetic noise as an observation target.

Patent Literature 1 below discloses a radar device capable of preventing erroneous detection of a non-detection target due to electromagnetic noise.

The radar signal transmitted from the radar device disclosed in Patent Literature 1 includes a first transmission wave whose frequency increases with the lapse of time and a second transmission wave whose frequency decreases with the lapse of time. The radar device generates a first beat signal having a frequency of a difference between a frequency of the first transmission wave and a frequency of a first reflection wave that is a reflection wave of the first transmission wave reflected by an observation target. In addition, the radar device generates a second beat signal having a frequency of a difference between a frequency of the second transmission wave and a frequency of a second reflection wave that is a reflection wave of the second transmission wave reflected by the observation target.

The radar device extracts, as a first peak frequency, a frequency at which a signal intensity is a maximum value among the frequencies included in the first beat signal. In addition, the radar device extracts, as a second peak frequency, a frequency at which a signal intensity is a maximum value among the frequencies included in the second beat signal.

The radar device performs noise determination processing of determining whether or not each of the first peak frequency and the second peak frequency is due to electromagnetic noise. In the noise determination processing, when the first peak frequency and the second peak frequency are substantially the same, it is determined that each of the first peak frequency and the second peak frequency is due to electromagnetic noise.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2018-80938 A

SUMMARY OF INVENTION

Technical Problem

In order for the radar device disclosed in Patent Literature 1 to perform noise determination processing, a radar signal including both a first transmission wave and a second transmission wave needs to be transmitted from the radar device.

Therefore, a radar device that transmits a radar signal having only the first transmission wave or a radar signal having only the second transmission wave cannot perform the noise determination processing. Therefore, a radar device that transmits a radar signal having only a first transmission wave or a radar signal having only a second transmission wave has a problem that a non-detection target due to electromagnetic noise may be erroneously detected as an observation target.

The present disclosure has been made to solve the above-described problems, and it is an object of the present disclosure to provide a radar signal processing device and a radar signal processing method capable of preventing erroneous detection of a non-detection target due to electromagnetic noise when a radar signal includes at least one of a transmission wave whose frequency increases with the lapse of time and a transmission wave whose frequency decreases with the lapse of time.

SOLUTION TO PROBLEM

A radar signal processing device according to the present disclosure includes: processing circuitry configured to repeatedly acquire a beat signal having a frequency of a difference between a frequency of a radar signal whose frequency changes with a lapse of time and a frequency of a reflected wave of the radar signal reflected by an observation target, repeatedly calculate at least one distance between a radar device and the observation target using the acquired beat signal, the at least one distance comprising a plurality of distances, and repeatedly calculate at least one relative speed between the radar device and the observation target using the acquired beat signal, the at least one relative speed comprising a plurality of relative speeds; calculate an incident angle of the reflected wave to an array antenna by using the acquired beat signal and an arrangement interval between a plurality of reception antennas included in the array antenna that receives the reflected wave; and determine whether the observation target is a detection target or a non-detection target due to electromagnetic noise on a basis of the calculated incident angle and the plurality of distances and the plurality of relative speeds having been calculated,. The processing circuitry performs determination processing of determining whether the observation target is the detection target or the non-detection target due to electromagnetic noise on a basis of the plurality of distances and the plurality of relative speeds only when an absolute value of the calculated incident angle is equal to or less than a first threshold.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present disclosure, a radar signal processing device is configured to include a determination unit that determines whether an observation target is a detection target or a non-detection target due to electromagnetic noise on the basis of an incident angle calculated by an angle calculating unit and a plurality of distances and a plurality of relative speeds calculated by a distance speed calculating unit. Therefore, the radar signal processing device according to the present disclosure can prevent erroneous detection of a non-detection target due to electromagnetic noise as long as the radar signal includes at least one of a transmission wave whose frequency increases with the lapse of time and a transmission wave whose frequency decreases with the lapse of time.

DESCRIPTION OF EMBODIMENTS

In order to explain the present disclosure in more detail, a mode for carrying out the present disclosure will be described below with reference to the accompanying drawings.

First Embodiment

FIG.1is a configuration diagram illustrating an in-vehicle device including a radar device1according to a first embodiment.

FIG.2is a configuration diagram illustrating the radar device1including a radar signal processing device22according to the first embodiment.

FIG.3is a hardware configuration diagram illustrating hardware of the radar signal processing device22according to the first embodiment.

The in-vehicle device is a device mounted on a vehicle such as an automobile, a motorcycle, or a bicycle. The in-vehicle device includes the radar device1that determines whether an observation target is a detection target or a non-detection target due to electromagnetic noise.

In a case where the radar device1is mounted on, for example, an automobile, the observation target corresponds to a vehicle such as another automobile, a pedestrian, a guardrail, or the like.

The radar device1includes a radar signal output unit11, a transmission and reception unit15, a beat signal generating unit18, and a radar signal processing device22.

The radar signal output unit11includes an output control unit12, a signal source13, and a divider14.

The radar signal output unit11intermittently and repeatedly outputs a frequency modulation signal whose frequency changes with the lapse of time to the transmission and reception unit15as a radar signal.

The output control unit12outputs a control signal indicating an output timing of the radar signal to each of the signal source13and a distance speed calculating unit23described later.

The signal source13intermittently and repeatedly outputs the frequency modulation signal as a radar signal to the divider14in accordance with the output timing indicated by the control signal output from the output control unit12.

The divider14divides each of the radar signals repeatedly output from the signal source13into two.

The divider14outputs one of the divided radar signals to a transmission antenna16to be described later, and outputs the other of the divided radar signals as a local oscillation signal to a frequency mixing unit19to be described later.

The transmission and reception unit15includes a transmission antenna16and an array antenna17.

The transmission and reception unit15transmits each of the radar signals repeatedly output from the radar signal output unit11toward the observation target, and receives each of the radar signals reflected by the observation target as a reflected wave.

The transmission and reception unit15outputs a reception signal of each of the reflected waves to the beat signal generating unit18.

The transmission antenna16radiates each of the radar signals repeatedly output from the divider14into space.

The array antenna17includes a plurality of reception antennas17-1to17-N. N is an integer of 2 or more.

After each of the radar signals is radiated from the transmission antenna16into space, a reception antenna17-n(n=1,. . . , N) receives each of the radar signals reflected by the observation target as a reflected wave, and outputs a reception signal of each of the received reflected waves to a mixer19-nof the frequency mixing unit19.

In the transmission and reception unit15illustrated inFIG.2, the transmission antenna16is directly connected to the divider14. However, this is merely an example, and an amplifier may be connected between the divider14and the transmission antenna16, and the amplifier may amplify the radar signal output from the divider14and output the amplified radar signal to the transmission antenna16.

In addition, in the transmission and reception unit15illustrated inFIG.2, the reception antenna17-nis directly connected to the frequency mixing unit19. However, this is merely an example, and an amplifier may be connected between the reception antenna17-nand the mixer19-n, and the amplifier may amplify the reception signal output from the reception antenna17-nand output the amplified reception signal to the mixer19-n.

The beat signal generating unit18includes the frequency mixing unit19, a filter unit20, and an analog-to-digital converter21.

The beat signal generating unit18generates a beat signal having a frequency of a difference between a frequency of each of the radar signals output from the radar signal output unit11and a frequency of each of the reflected waves received by the transmission and reception unit15.

The beat signal generating unit18outputs each of the generated beat signals to the radar signal processing device22.

The frequency mixing unit19includes a plurality of mixers19-1to19-N.

The mixer19-n(n=1, . . . , N) mixes the local oscillation signal output from the divider14and the reception signal output from the reception antenna17-nto generate a beat signal having a frequency of a difference between a frequency of the local oscillation signal output from the divider14and a frequency of the reception signal.

The mixer19-noutputs the beat signal to a filter processing unit20-ndescribed later.

The filter unit20includes a plurality of filter processing units20-1to20-N.

The filter processing unit20-n(n=1, . . . , N) is implemented by a low pass filter (LPF), a band pass filter (BPF), or the like.

The filter processing unit20-nsuppresses an unnecessary component such as spurious included in the beat signal output from the mixer19-n, and outputs the beat signal after the suppression of the unnecessary component to an analog to digital converter (ADC)21-nto be described later.

The analog-to-digital converter21includes a plurality of ADCs21-1to21-N.

The ADC21-n(n=1, . . . , N) converts the beat signal output from the filter processing unit20-ninto digital data, and outputs the digital data to the distance speed calculating unit23described later.

The radar signal processing device22includes the distance speed calculating unit23, an angle calculating unit24, a determination unit25, and an observation target detecting unit26.

The distance speed calculating unit23is implemented by, for example, a distance speed calculating circuit31illustrated inFIG.3.

The distance speed calculating unit23repeatedly acquires the digital data output from the ADC21-n(n=1, . . . , N).

The distance speed calculating unit23integrates N pieces of digital data output from the ADCs21-1to21-N to calculate combined data of the N pieces of digital data.

Every time combined data is calculated, the distance speed calculating unit23calculates the distance between the radar device1and the observation target using the combined data, and calculates the relative speed between the radar device1and the observation target using the combined data.

The distance between the radar device1and the observation target is a distance between the transmission and reception unit15of the radar device1and the observation target. The relative speed between the radar device1and the observation target is a relative speed between the transmission and reception unit15of the radar device1and the observation target.

The distance speed calculating unit23outputs each of the calculated distance and relative speed to the determination unit25.

The angle calculating unit24is implemented by, for example, an angle calculating circuit32illustrated inFIG.3.

The angle calculating unit24calculates an incident angle of the reflected wave to the array antenna17using the digital data acquired by the distance speed calculating unit23and the arrangement interval of the reception antennas17-1to17-N.

The angle calculating unit24outputs the incident angle to the determination unit25.

The determination unit25is implemented by, for example, a determination circuit33illustrated inFIG.3.

The determination unit25determines whether the observation target is a detection target or a non-detection target due to electromagnetic noise on the basis of the incident angle calculated by the angle calculating unit24and the plurality of distances and the plurality of relative speeds calculated by the distance speed calculating unit23.

That is, only when the absolute value of the incident angle calculated by the angle calculating unit24is equal to or less than a first threshold, the determination unit25performs determination processing of determining whether the observation target is a detection target or a non-detection target due to electromagnetic noise on the basis of the plurality of distances and the plurality of relative speeds calculated by the distance speed calculating unit23.

The determination unit25outputs a determination result indicating whether the observation target is a detection target or a non-detection target due to electromagnetic noise to the observation target detecting unit26.

The electromagnetic noise is noise having a constant frequency. Note that, the electromagnetic noise is not limited to noise whose frequency does not change at all, and is assumed to include noise whose frequency slightly changes within a range in which there is no practical problem. As the electromagnetic noise, a continuous wave (CW) electromagnetic wave is assumed.

In the radar device1illustrated inFIG.2, a noise source present outside the radar device1is assumed as the noise source. As the noise source, for example, a wireless charging device for charging an electric vehicle is conceivable.

The observation target detecting unit26is implemented by, for example, an observation target detecting circuit34illustrated inFIG.3.

When the determination unit25determines that the observation target is the detection target, the observation target detecting unit26outputs the distance and the relative speed calculated by the distance speed calculating unit23and the incident angle calculated by the angle calculating unit24to the outside of the radar device1as the detection result of the observation target.

When the determination unit25determines that the observation target is the non-detection target, the observation target detecting unit26outputs information indicating that the non-detection target due to the electromagnetic noise has been detected to the outside of the radar device1.

InFIG.2, it is assumed that each of the distance speed calculating unit23, the angle calculating unit24, the determination unit25, and the observation target detecting unit26, which are components of the radar signal processing device22, is implemented by dedicated hardware as illustrated inFIG.3. That is, it is assumed that the radar signal processing device22is implemented by the distance speed calculating circuit31, the angle calculating circuit32, the determination circuit33, and the observation target detecting circuit34.

Each of the distance speed calculating circuit31, the angle calculating circuit32, the determination circuit33, and the observation target detecting circuit34corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof

The components of the radar signal processing device22are not limited to those implemented by dedicated hardware, and the radar signal processing device22may be implemented by software, firmware, or a combination of software and firmware.

The software or firmware is stored in a memory of a computer as a program. The computer means hardware that executes a program, and corresponds to, for example, a central processing unit (CPU), a central processing device, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a processor, or a digital signal processor (DSP).

FIG.4is a hardware configuration diagram of a computer in a case where the radar signal processing device22is implemented by software, firmware, or the like.

In a case where the radar signal processing device22is implemented by software, firmware, or the like, a program for causing a computer to execute each of processing procedures performed in the distance speed calculating unit23, the angle calculating unit24, the determination unit25, and the observation target detecting unit26is stored in a memory42. Then, a processor41of the computer executes the program stored in the memory42.

In addition,FIG.3illustrates an example in which each of the components of the radar signal processing device22is implemented by dedicated hardware, andFIG.4illustrates an example in which the radar signal processing device22is implemented by software, firmware, or the like. However, this is merely an example, and some components in the radar signal processing device22may be implemented by dedicated hardware, and the remaining components may be implemented by software, firmware, or the like.

FIG.5is a configuration diagram illustrating the distance speed calculating unit23of the radar signal processing device22.

The distance speed calculating unit23includes a first spectrum calculating unit51, a second spectrum calculating unit52, and a distance speed calculation processing unit53.

The first spectrum calculating unit51repeatedly acquires the digital data output from the ADC21-n(n=1, . . . , N) in synchronization with the output timing indicated by the control signal output from the output control unit12.

The first spectrum calculating unit51repeatedly calculates a first frequency spectrum fs1,aby performing Fourier transform on each repeatedly acquired digital data in a distance direction.

The first spectrum calculating unit51outputs each of the first frequency spectra fs1,arepeatedly calculated using the digital data output from the ADC21-nto the second spectrum calculating unit52.

The first spectrum calculating unit51calculates combined data of N pieces of digital data by adding the N pieces of digital data output from the ADCs21-1to21-N in synchronization with the output timing indicated by the control signal output from the output control unit12.

Every time the combined data is calculated, the first spectrum calculating unit51calculates first frequency spectra fs1,bby the number of N reception antennas17-nby performing Fourier transform on the combined data in the distance direction.

The first spectrum calculating unit51outputs each of the first frequency spectra fs1,brepeatedly calculated using the combined data to the second spectrum calculating unit52.

The second spectrum calculating unit52repeatedly acquires K (K is an integer of 2 or more) first frequency spectra fs1,arelated to the ADC21-nfrom the first spectrum calculating unit51.

Every time the K first frequency spectra fs1,aare acquired, the second spectrum calculating unit52calculates a second frequency spectrum fs2,aby performing Fourier transform on the K first frequency spectra fs1,ain a Doppler direction.

The second spectrum calculating unit52outputs the second frequency spectrum fs2,arelated to the ADC21-nto the angle calculating unit24. The second frequency spectrum fs2,aoutput from the second spectrum calculating unit52to the angle calculating unit24is not the relative speed itself, but includes information on the relative speed. Therefore, information on the relative speed is output from the second spectrum calculating unit52to the angle calculating unit24.

The second spectrum calculating unit52integrates the K first frequency spectra fs1,arelated to the ADC21-n, and outputs an integrated first frequency spectrum fs1,ato the angle calculating unit24. The first frequency spectrum fs1,aoutput from the second spectrum calculating unit52to the angle calculating unit24is not the distance itself, but includes information on the distance. Therefore, information on the distance is output from the second spectrum calculating unit52to the angle calculating unit24.

The second spectrum calculating unit52repeatedly acquires K first frequency spectra fs1,bcalculated using the combined data from the first spectrum calculating unit51.

Every time the K first frequency spectra fs1,bare acquired, the second spectrum calculating unit52calculates a second frequency spectrum fs2,bby performing Fourier transform on the K first frequency spectra fs1,bin the Doppler direction.

The second spectrum calculating unit52outputs the second frequency spectra fs2,bto the distance speed calculation processing unit53.

The second spectrum calculating unit52integrates the K first frequency spectra fs1,b, and outputs an integrated first frequency spectrum fs1,b′ to the distance speed calculation processing unit53.

The distance speed calculation processing unit53acquires the integrated first frequency spectrum fs1,b′ from the second spectrum calculating unit52.

Every time the integrated first frequency spectrum fs1,b′ is acquired, the distance speed calculation processing unit53detects a beat frequency which is a frequency corresponding to a peak value of the integrated first frequency spectrum fs1,b′.

The distance speed calculation processing unit53calculates the distance between the radar device1and the observation target on the basis of the detected beat frequency.

The distance speed calculation processing unit53acquires the second frequency spectrum fs2,bfrom the second spectrum calculating unit52.

Every time the second frequency spectrum fs2,bis acquired, the distance speed calculation processing unit53detects a Doppler frequency, which is a frequency corresponding to the peak value of the second frequency spectrum fs2,b.

The distance speed calculation processing unit53calculates the relative speed between the radar device1and the observation target on the basis of the detected Doppler frequency.

Every time the distance and the relative speed are calculated, the distance speed calculation processing unit53outputs each of the calculated distance and relative speed to the determination unit25.

FIG.6is a configuration diagram illustrating the angle calculating unit24of the radar signal processing device22.

The angle calculating unit24includes a third spectrum calculating unit61and an angle calculation processing unit62.

The third spectrum calculating unit61acquires N first frequency spectra fs and N second frequency spectra fs2,afrom the second spectrum calculating unit52of the distance speed calculating unit23.

The third spectrum calculating unit61generates N Range-Doppler maps including the first frequency spectra fs1,aand the second frequency spectra fs2,a, and calculates a third frequency spectrum fs3by performing Fourier transform on the N Range-Doppler maps.

The third spectrum calculating unit61outputs the third frequency spectrum fs3to the angle calculation processing unit62.

The angle calculation processing unit62detects a frequency corresponding to a peak value of the third frequency spectrum fs3output from the third spectrum calculating unit61.

The angle calculation processing unit62calculates an incident angle of the reflected wave to the array antenna17using the frequency corresponding to the detected peak value and the arrangement interval of the reception antennas17-1to17-N.

The angle calculating unit24outputs the incident angle to the determination unit25.

Next, the operation of the radar device1illustrated inFIG.2will be described.

FIG.7is an explanatory diagram illustrating a radar signal, a reception signal, a beat signal, and signal processing performed in the distance speed calculating unit23.

FIG.8is an explanatory diagram illustrating a radar signal, a reception signal, a beat signal, and signal processing performed in the distance speed calculating unit23in a case where electromagnetic noise is input to the ADC21-n(n=1, . . . , N).

The radar signal Tx(k) (k=1, . . . , K) is a frequency modulation signal whose frequency decreases with the lapse of time. T is a sweep time of the radar signal Tx(k) and is a time on the order of microseconds. BW is a frequency bandwidth of the radar signal Tx(k).

InFIGS.7and8, the radar signal Tx(k) is a frequency modulation signal whose frequency decreases with the lapse of time. However, this is merely an example, and the radar signal Tx(k) may be a frequency modulation signal whose frequency increases with the lapse of time. In addition, the radar signal Tx(k) may include a frequency modulation signal whose frequency increases with the lapse of time and a frequency modulation signal whose frequency decreases with the lapse of time.

First, the output control unit12outputs a control signal indicating an output timing of the radar signal Tx(k) to each of the signal source13and the distance speed calculating unit23.

As illustrated inFIGS.7and8, the output timing of the radar signal Tx(k) is a time interval longer than the sweep time T.

The signal source13repeatedly outputs the radar signal Tx(k) to the divider14in accordance with the output timing indicated by the control signal output from the output control unit12.

Every time the radar signal Tx(k) is received from the signal source13, the divider14divides the radar signal Tx(k) into two.

The divider14outputs one of the divided radar signals Tx(k) to the transmission antenna16, and outputs the other of the divided radar signals Tx(k) as a local oscillation signal Lo(k) to each of the mixers19-1to19-N in the frequency mixing unit19.

Every time the radar signal Tx(k) is received from the divider14, the transmission antenna16radiates the radar signal Tx(k) into space.

The reception antenna17-n(n=1, . . . , N) of the array antenna17receives, as a reflected wave, the radar signal Tx(k) reflected by the observation target after the radar signal Tx(k) is radiated from the transmission antenna16into space, and outputs a reception signal Rx(k) of the received reflected wave to the mixer19-n.

Every time the mixer19-nreceives the local oscillation signal Lo(k) from the divider14and every time the mixer receives the reception signal Rx(k) from the reception antenna17-n, the mixer mixes the local oscillation signal Lo(k) and the reception signal Rx(k).

The mixer19-nmixes the local oscillation signal Lo(k) and the reception signal Rx(k) to generate a beat signal having a frequency of a difference between the frequency of the local oscillation signal Lo(k) and the frequency of the reception signal Rx(k).

Every time the beat signal is generated, the mixer19-noutputs the generated beat signal to the filter processing unit20-n.

Note that, during a period in which the local oscillation signal Lo(k) is not output from the divider14, the mixer19-ndoes not generate a beat signal and does not output the beat signal to the filter processing unit20-n.

Every time the beat signal is received from the mixer19-n, the filter processing unit20-nsuppresses an unnecessary component such as spurious included in the beat signal, and outputs the beat signal after the suppression of the unnecessary component to the ADC21-n.

Every time the beat signal is received from the filter processing unit20-n, the ADC21-nconverts the beat signal into digital data, and outputs the digital data to the distance speed calculating unit23of the radar signal processing device22.

When the electromagnetic noise is input to the ADC21, the electromagnetic noise may be superimposed on the beat signal as illustrated inFIG.8.

The operation period of the ADC21-ncorresponds to a period in which the mixer19-noutputs the beat signal to the filter processing unit20-n.

Hereinafter, the operation of the radar signal processing device22will be described.

FIG.9is a flowchart illustrating a radar signal processing method which is a processing procedure performed in the radar signal processing device22.

FIG.10is a flowchart illustrating a processing procedure performed in the distance speed calculating unit23.

FIG.11is a flowchart illustrating a processing procedure performed in the angle calculating unit24.

FIG.12is a flowchart illustrating a processing procedure performed in the determination unit25.

The distance speed calculating unit23repeatedly acquires the digital data output from the ADC21-n(n=1, . . . , N).

Every time digital data is acquired from the ADC21-n, the distance speed calculating unit23calculates the distance between the radar device1and the observation target using the digital data (step ST1inFIG.9).

In addition, the distance speed calculating unit23calculates the relative speed between the radar device1and the observation target using the digital data (step ST1inFIG.9).

Every time each of the distance and the relative speed is calculated, the distance speed calculating unit23outputs each of the calculated distance and relative speed to the angle calculating unit24.

The distance speed calculating unit23calculates combined data of a plurality of pieces of digital data output from the ADCs21-1to21-N.

Every time combined data is calculated, the distance speed calculating unit23calculates the distance between the radar device1and the observation target using the combined data (step ST1inFIG.9).

In addition, the distance speed calculating unit23calculates the relative speed between the radar device1and the observation target using the combined data (step ST1inFIG.9).

Every time each of the distance and the relative speed is calculated, the distance speed calculating unit23outputs each of the calculated distance and relative speed to the determination unit25.

Hereinafter, calculation processing of the distance speed calculating unit23will be specifically described.

The first spectrum calculating unit51repeatedly acquires the digital data output from the ADC21-n(n=1, . . . , N) during the period in which the local oscillation signal Lo(k) is output from the divider14in synchronization with the output timing indicated by the control signal output from the output control unit12.

Every time digital data is acquired from the ADC21-n, the first spectrum calculating unit51calculates the first frequency spectrum fs1,aby performing Fourier transform on the digital data in the distance direction (step ST11inFIG.10).

InFIGS.7and8, FFT(1) represents the Fourier transform in the distance direction by the first spectrum calculating unit51.

As the digital data is Fourier-transformed in the distance direction, the spectrum value of the reception signal Rx(k) (k=1, . . . , K) of the reflected wave from the observation target is integrated into the beat frequency Fsb_rshown in the following Formula (1).

In Formula (1), R is a distance between the radar device1illustrated inFIG.2and the observation target, and c is the speed of light.

Furthermore, the digital data is Fourier-transformed in the distance direction, whereby the spectrum value of the electromagnetic noise is integrated into the frequency Fn_rof the electromagnetic noise.

Every time K first frequency spectra fs1,aare calculated, the first spectrum calculating unit51outputs the K first frequency spectra fs1,ato the second spectrum calculating unit52.

In addition, the first spectrum calculating unit51calculates combined data of N pieces of digital data by integrating the N pieces of digital data output from the ADCs21-1to21-N in synchronization with the output timing indicated by the control signal output from the output control unit12.

Every time the combined data is calculated, the first spectrum calculating unit51calculates first frequency spectra fs1,bby the number of N reception antennas17-nby performing Fourier transform on the combined data in the distance direction.

Every time K first frequency spectra fs1,bare calculated, the first spectrum calculating unit51outputs the K first frequency spectra fs1,bto the second spectrum calculating unit52.

The second spectrum calculating unit52repeatedly acquires K first frequency spectra fs1,arelated to the ADC21-nfrom the first spectrum calculating unit51.

Every time the K first frequency spectra fs1,aare acquired, the second spectrum calculating unit52calculates the second frequency spectrum fs2,aby performing Fourier transform on the K first frequency spectra fs1,ain the Doppler direction (step ST12inFIG.10).

InFIGS.7and8, FFT(2) represents the Fourier transform in the Doppler direction by the second spectrum calculating unit52.

As the K first frequency spectra fs1,aare Fourier-transformed in the Doppler direction, the spectrum value of the reception signal Rx(k) of the reflected wave from the observation target is integrated into a Doppler frequency Fsb_vexpressed by the following Formula (2) corresponding to the relative speed between the radar device1illustrated inFIG.2and the observation target.

In Formula (2), f represents the center frequency of the local oscillation signal Lo(k), and v represents the relative speed between the radar device1illustrated inFIG.2and the observation target.

In addition, as the K first frequency spectra fs1,aare Fourier-transformed in the Doppler direction, the spectrum value of the electromagnetic noise is integrated into the Doppler frequency Fn_vcorresponding to the sum of the phase difference corresponding to the relative speed between the radar device1illustrated inFIG.2and the noise source and the phase difference between the noise source and the radar signal.

Every time the second frequency spectrum fs2,ais calculated, the second spectrum calculating unit52outputs the second frequency spectrum fs2,ato the angle calculating unit24.

In addition, the second spectrum calculating unit52integrates the K first frequency spectra fs1,a, and outputs the integrated first frequency spectrum fs1,a′ to the angle calculating unit24.

The second spectrum calculating unit52repeatedly acquires K first frequency spectra fs1,bcalculated using the combined data from the first spectrum calculating unit51.

Every time the K first frequency spectra fs1,bare acquired, the second spectrum calculating unit52calculates the second frequency spectrum fs2,bby performing Fourier transform on the K first frequency spectra fs1,bin the Doppler direction.

Every time the second frequency spectrum fs2,bis calculated, the second spectrum calculating unit52outputs the second frequency spectrum fs2,bto the distance speed calculation processing unit53.

The second spectrum calculating unit52integrates the K first frequency spectra fs1,bcalculated using the combined data, and outputs the integrated first frequency spectrum fs1,b′ to the distance speed calculation processing unit53.

In the radar device1illustrated inFIG.2, the second spectrum calculating unit52calculates the second frequency spectrum fs2,bby performing Fourier transform in the Doppler direction on the K first frequency spectra fs1,bcalculated using the combined data, and outputs the second frequency spectrum fs2,bto the distance speed calculation processing unit53. However, this is merely an example, and the second spectrum calculating unit52may output the second frequency spectrum fs2,aoutput to the angle calculating unit24to the distance speed calculation processing unit53. In addition, the second spectrum calculating unit52may output the integrated first frequency spectrum fs1,a′ output to the angle calculating unit24to the distance speed calculation processing unit53.

Every time the integrated first frequency spectrum fs1,b′ is received from the second spectrum calculating unit52, the distance speed calculation processing unit53detects the beat frequency Fsb_rcorresponding to the peak value of the first frequency spectrum fs1,b′.

Specifically, the distance speed calculation processing unit53compares the plurality of spectrum values included in the first frequency spectrum fs1,b′ with a beat frequency detection threshold Thb.

The distance speed calculation processing unit53detects a spectrum value larger than the threshold Thbamong the plurality of spectrum values as a peak value. The beat frequency detection threshold Thbmay be stored in the internal memory of the distance speed calculation processing unit53or may be provided from the outside of the radar device1.

When detecting the peak value, the distance speed calculation processing unit53detects a frequency corresponding to the peak value as the beat frequency Fsb_rin the first frequency spectrum fs1,b′.

The beat frequency Fsb_rdetected by the distance speed calculation processing unit53may be a frequency related to the observation target, but may be the frequency Fn_rof the electromagnetic noise in a case where the electromagnetic noise is input to the ADC21.

When detecting the beat frequency Fsb_rcorresponding to the peak value of the first frequency spectrum fs1,b′, the distance speed calculation processing unit53substitutes the beat frequency Fsb_rinto the following Formula (3) to calculate the distance R between the radar device1illustrated inFIG.2and the observation target (step ST13inFIG.10).

The distance R calculated by the distance speed calculation processing unit53may be a distance between the radar device1and the observation target, but may be a false detection distance due to electromagnetic noise in a case where the electromagnetic noise is input to the ADC21-n.

Every time the second frequency spectrum fs2,bis received from the second spectrum calculating unit52, the distance speed calculation processing unit53detects the Doppler frequency Fsb_vcorresponding to the peak value of the second frequency spectrum fs2,b.

Specifically, the distance speed calculation processing unit53compares the plurality of spectrum values included in the second frequency spectrum fs2,bwith the Doppler frequency detection threshold THd.

The distance speed calculation processing unit53detects a spectrum value larger than the threshold Thdamong the plurality of spectrum values as a peak value. The Doppler frequency detection threshold Thdmay be stored in the internal memory of the distance speed calculation processing unit53or may be provided from the outside of the radar device1.

When detecting the peak value, the distance speed calculation processing unit53detects a frequency corresponding to the peak value as the Doppler frequency Fsb_vin the second frequency spectrum fs2,b.

The Doppler frequency Fsb_vdetected by the distance speed calculation processing unit53may be a frequency related to the observation target, but may be the Doppler frequency Fn_vof the electromagnetic noise in a case where the electromagnetic noise is input to the ADC21-n.

When detecting the Doppler frequency Fsb_vcorresponding to the peak value of the second frequency spectrum fs2,b, the distance speed calculation processing unit53substitutes the Doppler frequency Fsb_vinto the following Formula (4) to calculate the relative speed v between the radar device1illustrated inFIG.2and the observation target (step ST13inFIG.10).

The relative speed v calculated by the distance speed calculation processing unit53may be a relative speed between the radar device1and the observation target, but may be a relative speed due to electromagnetic noise in a case where the electromagnetic noise is input to the ADC21-n.

Every time each of the distance R and the relative speed v is calculated, the distance speed calculation processing unit53outputs each of the distance R and the relative speed v to the determination unit25.

FIG.13is an explanatory diagram illustrating signal processing performed in the angle calculating unit24.

The third spectrum calculating unit61of the angle calculating unit24acquires N first frequency spectra fs1,a′ and N second frequency spectra fs2,afrom the second spectrum calculating unit52of the distance speed calculating unit23.

The third spectrum calculating unit61generates a Range-Doppler map (n) related to the ADC21-nincluding a first frequency spectrum fs1,a′(n) related to the ADC21-namong the N first frequency spectra fs1,aand a second frequency spectrum fs2,a(n) related to the ADC21-namong the N second frequency spectra fs2,a. The third spectrum calculating unit61generates N Range-Doppler maps (1) to (N) in total.

The third spectrum calculating unit61calculates a third frequency spectrum fs3as illustrated inFIG.13by performing Fourier transform on the N Range-Doppler maps (1) to (N) (step ST21inFIG.11).

The third spectrum calculating unit61outputs the third frequency spectrum fs3to the angle calculation processing unit62.

The angle calculation processing unit62acquires the third frequency spectrum fs3from the third spectrum calculating unit61.

The angle calculation processing unit62detects a frequency Fsb_θcorresponding to the peak value of the third frequency spectrum fs3.

The angle calculation processing unit62calculates an incident angle θ of the reflected wave to the array antenna17using the frequency Fsb_θcorresponding to the detected peak value and the arrangement interval d of the reception antennas17-1to17-N as expressed in the following Formula (5) (Step ST2inFIG.9and step ST22inFIG.11).

In Formula (5), λ represents a wavelength of a radar signal.

FIG.14is an explanatory diagram illustrating an incident angle λ of a reflected wave to the array antenna17.

InFIG.14, the reception antenna17-1is disposed at the origin of the x-y coordinate system, and the reception antennas17-1to17-N are arranged in a direction parallel to the y axis.

The angle calculating unit24outputs the incident angle θ to the determination unit25.

The angle θ calculated by the angle calculation processing unit62may be an incident angle of the reflected wave to the array antenna17, but may be an angle due to electromagnetic noise in a case where the electromagnetic noise is input to the ADC21-n.

The determination unit25determines whether the observation target is a detection target or a non-detection target due to the electromagnetic noise on the basis of the incident angle θ calculated by the angle calculating unit24and the plurality of distances R and the plurality of relative speeds v calculated by the distance speed calculation processing unit53of the distance speed calculating unit23.

Hereinafter, the noise determination processing by the determination unit25will be specifically described.

First, the determination unit25compares the absolute value of the incident angle θ with the first threshold Th1. The first threshold Th1is, for example, a value of ½ of the resolution of the incident angle θ. The first threshold Th1may be stored in the internal memory of the determination unit25or may be provided from the outside of the radar signal processing device22.

If the absolute value of the incident angle θ is equal to or smaller than the first threshold Th1(step ST3inFIG.9: YES), the determination unit25performs noise determination processing described below (step ST4inFIG.9).

If the absolute value of the incident angle θ is larger than the first threshold Th1(step ST3inFIG.9: NO), the determination unit25does not perform the noise determination processing described below.

In a case where the electromagnetic noise is input to each of the ADCs21-1to21-N, since the arrangement of the signal wirings of the ADCs21-ncorresponding to the reception antennas17-1to17-N is very short compared to the wavelength of the electromagnetic noise, the noise induced in each of the signal wirings can be regarded as the same phase. In a state in which the output signals of the ADCs21-1to21-N are in the same phase, the frequency Fsb_θ=0, that is, the incident angle θ is 0 degrees. Therefore, erroneous detection of a non-detection target due to electromagnetic noise occurs when the incident angle θ is near 0 degrees. That is, the erroneous detection of the non-detection target due to the electromagnetic noise occurs when the absolute value of the incident angle θ is equal to or less than the first threshold Th1. In other words, when the absolute value of the incident angle θ is larger than the first threshold Th1, there is a low possibility that erroneous detection of a non-detection target due to electromagnetic noise occurs.

FIG.15is an explanatory diagram illustrating a range of the incident angle θ on which the noise determination processing by the determination unit25is performed.

The range of the incident angle θ on which the noise determination processing is performed is a range of—the first threshold Th1to +the first threshold Th1.

The range of the incident angle θ on which the detection processing of the observation target is performed is wider than the range of the incident angle θ on which the noise determination processing is performed, and includes the range of the incident angle θ on which the noise determination processing is performed.

The determination unit25performs the noise determination processing only in a case where the absolute value of the incident angle θ is equal to or less than the first threshold Th1, and does not perform the noise determination processing described below in a case where the absolute value of the incident angle θ is larger than the first threshold Th1(in a case of step ST3inFIG.9: NO). Therefore, it is possible to suppress an increase in the processing load or an increase in the memory amount due to the noise determination processing.

The determination unit25acquires M (M is an integer of 2 or more) distances R and M relative speeds v from the distance speed calculation processing unit53(step ST31inFIG.12).

Here, in order to simplify the description, it is assumed that all of the M distances R repeatedly calculated by the distance speed calculation processing unit53are distances between the radar device1and the observation target or false detection distances due to electromagnetic noise.

In addition, it is assumed that all of the M relative speeds v repeatedly calculated by the distance speed calculation processing unit53are relative speeds between the radar device1and the observation target or relative speeds due to electromagnetic noise.

The determination unit25calculates an absolute value |ΔRM| of a difference ARM between the first calculated distance and the Mth calculated distance among the M distances R.

The determination unit25compares the absolute value |ΔRM| of the difference ΔRMwith a second threshold Th2. As the second threshold Th2, for example, a value of the resolution+r of the distance R calculated by the distance speed calculating unit23is used. r is, for example, twice the resolution of the distance R. The second threshold Th2may be stored in the internal memory of the determination unit25or may be provided from the outside of the radar signal processing device22.

The frequency of the electromagnetic noise output from the noise source is a constant frequency. Therefore, if the distance R calculated by the distance speed calculating unit23is a false detection distance due to electromagnetic noise, it is conceivable that the change in the M distances R repeatedly calculated by the distance speed calculating unit23is very small, and the absolute value |ΔRM| of the change in the distances R is equal to or less than the second threshold Th2.

For example, in a case where the observation target is stationary, if the radar device1illustrated inFIG.2is moving, the distance between the radar device1illustrated inFIG.2and the observation target changes. As the stationary observation target, for example, a guardrail can be considered.

Therefore, in a case where the observation target is a stationary object, if the radar device1illustrated inFIG.2is moving, the absolute value ARM of the change in the M distances R repeatedly calculated by the distance speed calculating unit23is considered to be larger than the second threshold Th2.

For example, in a case where the observation target is an oncoming vehicle of the vehicle on which the radar device1illustrated inFIG.2is mounted, if the radar device1illustrated inFIG.2is moving, the distance between the radar device1illustrated inFIG.2and the observation target greatly changes.

Therefore, in a case where the observation target is an oncoming vehicle, if the radar device1illustrated inFIG.2is moving, the absolute value |ΔRM| of the change in the M distances R repeatedly calculated by the distance speed calculating unit23is considered to be larger than the second threshold Th2.

For example, in a case where the observation target is a preceding vehicle of the vehicle on which the radar device1illustrated inFIG.2is mounted, even if the radar device1illustrated inFIG.2is moving, the distance between the radar device1illustrated inFIG.2and the observation target may hardly change. In a case where the vehicle on which the radar device1illustrated inFIG.2is mounted is traveling in the same direction at substantially the same speed as that of the preceding vehicle, the distance between the radar device1illustrated inFIG.2and the observation target hardly changes.

Therefore, in a case where the observation target is the preceding vehicle, even if the radar device1illustrated inFIG.2is moving, the absolute value |ΔRM| of the change in the M distances R repeatedly calculated by the distance speed calculating unit23may not be larger than the second threshold Th2.

If the absolute value |ΔRM| of the difference ΔRMis larger than the second threshold Th2(step ST32inFIG.12: YES), the determination unit25determines that the observation target is a detection target and is not a noise source (step ST35inFIG.12).

Other than the case where the observation target is a stationary object such as a guardrail, in a case where the observation target is, for example, an oncoming vehicle, the determination unit25determines that “the observation target is not a noise source”.

If the absolute value ΔRMof the difference ΔRMis equal to or less than the second threshold Th2(step ST32inFIG.12: NO), the determination unit25compares the absolute values of the M relative speeds v with a third threshold Th3. As the third threshold Th3, for example, 1 km/h is used. However, this is merely an example, and the third threshold Th3may be 2 km/h, 3 km/h, or the like. The third threshold Th3may be stored in the internal memory of the determination unit25or may be provided from the outside of the radar signal processing device22.

The relative speed v due to electromagnetic noise varies depending on the relative speed between the radar device1and the noise source, as well as the frequency of the electromagnetic noise, the sweep time of the radar signal, and the output timing of the radar signal. Therefore, the relative speed v due to the electromagnetic noise is likely to be a value other than zero. Therefore, when the third threshold Th3is a value sufficiently smaller than the maximum value of the relative speed between the radar device1and the observation target, if the relative speed v calculated by the distance speed calculating unit23is a relative speed due to electromagnetic noise, there is a high possibility that all the absolute values of the M relative speeds v repeatedly calculated by the distance speed calculating unit23are larger than the third threshold.

For example, when the observation target is a preceding vehicle, if the vehicle on which the radar device1illustrated inFIG.2is mounted is traveling in the same direction at substantially the same speed as that of the preceding vehicle, the relative speed v between the radar device1illustrated inFIG.2and the preceding vehicle becomes a relative speed close to 0. Therefore, if the relative speed v calculated by the distance speed calculating unit23is the relative speed between the radar device1and the preceding vehicle, there is a high possibility that one or more relative speeds v among the M relative speeds v repeatedly calculated by the distance speed calculating unit23will be equal to or less than the third threshold Th3.

If all the absolute values of the M relative speeds v are larger than the third threshold Th3(step ST33inFIG.12: YES), the determination unit25determines that the observation target is a non-detection target and is a noise source (step ST34inFIG.12).

If one or more relative speeds v among the absolute values of the M relative speeds v are equal to or less than the third threshold Th3(step ST33inFIG.12: NO), the determination unit25determines that the observation target is a detection target and is not a noise source (step ST35inFIG.12).

For example, in a case where the observation target is a preceding vehicle, there is a high possibility that the determination unit25determines that “the observation target is not electromagnetic noise”.

When determining that the observation target is the detection target and is not the noise source (step ST5inFIG.9: NO), the determination unit25outputs each of the M distances R, the M relative speeds v, and the incident angle θ to the observation target detecting unit26.

The observation target detecting unit26outputs each of the M distances R, the M relative speeds v, and the incident angle θ to the outside of the radar device1(step ST6inFIG.9).

When determining that the observation target is a non-detection target and is a noise source (step ST5inFIG.9: YES), the determination unit25discards each of the M distances R, the M relative speeds v, and the incident angle θ.

When the determination unit25determines that the observation target is the non-detection target, the observation target detecting unit26outputs information indicating that the non-detection target due to the electromagnetic noise has been detected to the outside of the radar device1.

Note that the observation target detecting unit26may output each of the false detection distance R due to the electromagnetic noise, the relative speed v, and the incident angle θ due to the electromagnetic noise to the outside of the radar device1.

Here, in order to simplify the description, it is assumed that all of the M distances R repeatedly calculated by the distance speed calculating unit23are distances between the radar device1and the observation target or false detection distances due to electromagnetic noise.

In addition, it is assumed that all of the M relative speeds v repeatedly calculated by the distance speed calculating unit23are relative speeds between the radar device1and the observation target or relative speeds due to electromagnetic noise.

However, in a case where the electromagnetic noise output from the noise source is input to the ADC21-nat the timing when the reflected wave from the observation target is received by the reception antenna17-n, for example, if the number of observation targets is one, the distance speed calculating unit23calculates two distances R in each of the M times of calculation processing. Among the two distances R, one distance R is a distance R between the radar device1and the observation target, and the other distance R is a false detection distance R due to electromagnetic noise. Note that, the distance speed calculating unit23cannot determine which of the two calculated distances R is the distance R between the radar device1and the observation target and which of the distances R is the false detection distance R due to electromagnetic noise.

In addition, the distance speed calculating unit23calculates two relative speeds v in each of the M times of calculation processing. Among the two relative speeds v, one relative speed v is a relative speed v between the radar device1and the observation target, and the other relative speed v is a relative speed v due to electromagnetic noise. Note that, the distance speed calculating unit23cannot determine which of the two calculated relative speeds v is the relative speed v between the radar device1and the observation target and which of the relative speeds v is the relative speed v due to the electromagnetic noise.

The determination unit25acquires (2×M) distances R and (2×M) relative speeds v from the distance speed calculating unit23as processing results of the M times of calculation processing.

When acquiring (2×M) distances R from the distance speed calculating unit23, the determination unit25classifies the (2×M) distances R into a group related to the observation target and a group related to the noise source. Here, for convenience of description, it is assumed that the group related to the observation target is a group (1) and the group related to the noise source is a group (2).

Further, when acquiring (2×M) relative speeds v from the distance speed calculating unit23, the determination unit25classifies the (2×M) relative speeds v into a group (1) related to the observation target and a group (2) related to the noise source.

The processing of classifying the (2×M) distances R into two groups (1) and (2) and the processing of classifying the (2×M) relative speeds v into two groups (1) and (2) are known techniques, and thus detailed description thereof will be omitted.

The determination unit25determines whether or not the observation target is a noise source by performing the above-described determination processing for each of the two groups (1) and (2) (step ST5inFIG.9).

Since the group (1) is determined to be a group related to the observation target by performing the above determination processing, the determination unit25outputs the distance R belonging to the group (1) to the observation target detecting unit26as the distance R between the radar device1and the observation target. In addition, the determination unit25outputs the relative speed v belonging to the group (1) to the observation target detecting unit26as the relative speed v between the radar device1and the observation target. In addition, the determination unit25outputs the incident angle θ belonging to the group (1) to the observation target detecting unit26as the incident angle θ.

Since the group (2) is determined to be a group related to a noise source by performing the above determination processing, the determination unit25discards the distance R belonging to the group (2) as the false detection distance R due to electromagnetic noise. In addition, the determination unit25discards the relative speed v belonging to the group (2) as the relative speed v due to the electromagnetic noise. In addition, the determination unit25discards the incident angle θ belonging to the group (2).

In the first embodiment described above, the radar signal processing device22includes the distance speed calculating unit23to repeatedly acquire a beat signal having a frequency of a difference between the frequency of the radar signal whose frequency changes with the lapse of time and the frequency of the reflected wave of the radar signal reflected by the observation target, repeatedly calculate the distance between the radar device1and the observation target using the acquired beat signal, and repeatedly calculate the relative speed between the radar device1and the observation target using the acquired beat signal, and the angle calculating unit24to calculate the incident angle of the reflected wave to the array antenna17using the beat signal acquired by the distance speed calculating unit23and the arrangement intervals of the plurality of reception antennas17-1to17-N included in the array antenna17that receives the reflected wave. Furthermore, the radar signal processing device22is configured to include the determination unit25to determine whether the observation target is a detection target or a non-detection target due to electromagnetic noise on the basis of the incident angle calculated by the angle calculating unit24and the plurality of distances and the plurality of relative speeds calculated by the distance speed calculating unit23. Therefore, the radar signal processing device22can prevent erroneous detection of a non-detection target due to electromagnetic noise when the radar signal includes at least one of a transmission wave whose frequency increases with the lapse of time and a transmission wave whose frequency decreases with the lapse of time.

In the radar signal processing device22illustrated inFIG.2, the noise induced in the signal wiring in each of the ADCs21-ncan be regarded as having the same phase. However, since there is a difference in the wiring lengths of the respective signal wirings, noise induced in the respective signal wirings may not be regarded as having the same phase. In addition to the reception antennas17-1to17-N, the transmission antenna16includes a plurality of antennas. Then, since the radar device1has a configuration of multiple input multiple output (MIMO) and corrects the phase at the time of angle calculation, the angle due to the electromagnetic noise may be a value near the correction value corresponding to the frequency Fsb_θ=0.

In these cases, instead of determining whether or not the absolute value of the incident angle θ is equal to or less than the first threshold Th1, the determination unit25may determine whether or not the absolute value of the incident angle θ is equal to or less than the correction value corresponding to the frequency Fsb_θ=0.

Second Embodiment

In a second embodiment, a radar signal processing device22will be described in which a determination unit27determines whether or not the observation target is a non-detection target due to electromagnetic noise on the basis of an average value vaveof the M relative speeds v, a transmission time interval ΔT of a radar signal group necessary for single calculation of the distance and the speed by the distance speed calculating unit23, and the absolute value |ΔRM| of the difference ΔRM.

FIG.16is a configuration diagram illustrating the radar device1including the radar signal processing device22according to the second embodiment. InFIG.16, the same reference numerals as those inFIG.2denote the same or corresponding parts, and thus description thereof is omitted.

The hardware of the radar signal processing device22according to the second embodiment is similar to the hardware of the radar signal processing device22according to the first embodiment, and a hardware configuration diagram illustrating the hardware of the radar signal processing device22according to the second embodiment isFIG.3.

In the radar signal processing device22illustrated inFIG.16, each of the number of distances R calculated by the distance speed calculating unit23and the number of relative speeds v calculated by the distance speed calculating unit23is M (M is an integer of 2 or more).

The determination unit27is implemented by, for example, the determination circuit33illustrated inFIG.3.

The determination unit27determines whether the observation target is a detection target or a non-detection target due to electromagnetic noise on the basis of the incident angle θ calculated by the angle calculating unit24and the M distances and the M relative speeds calculated by the distance speed calculating unit23.

That is, the determination unit27calculates the average value vaveof the M relative speeds v calculated by the distance speed calculating unit23.

The determination unit27multiplies the average value vaveof the M relative speeds v, the transmission time interval ΔT (seeFIG.18) of the radar signal group necessary for single calculation of the distance and the speed by the distance speed calculating unit23, (M−1), and a positive constant a of less than 1.FIG.18is an explanatory diagram illustrating the transmission time interval ΔT of a radar signal group radiated from the radar device1.

When a multiplication result G of the average value vave, the time interval ΔT, (M−1), and the constant a is equal to or larger than the absolute value |ΔRM| of the difference ΔRM, the determination unit27determines that the observation target is a non-detection target due to electromagnetic noise.

InFIG.16, it is assumed that each of the distance speed calculating unit23, the angle calculating unit24, the determination unit27, and the observation target detecting unit26, which are components of the radar signal processing device22, is implemented by dedicated hardware as illustrated inFIG.3. That is, it is assumed that the radar signal processing device22is implemented by the distance speed calculating circuit31, the angle calculating circuit32, the determination circuit33, and the observation target detecting circuit34.

The components of the radar signal processing device22are not limited to those implemented by dedicated hardware, and the radar signal processing device22may be implemented by software, firmware, or a combination of software and firmware.

In a case where the radar signal processing device22is implemented by software, firmware, or the like, a program for causing a computer to execute each of processing procedures performed in the distance speed calculating unit23, the angle calculating unit24, the determination unit27, and the observation target detecting unit26is stored in the memory42illustrated inFIG.4. Then, the processor41illustrated inFIG.4executes the program stored in the memory42.

Next, the operation of the radar device1illustrated inFIG.16will be described. Note that, since the components other than the determination unit27are similar to those of the radar device1illustrated inFIG.2, only the operation of the determination unit27will be described here.

FIG.17is a flowchart illustrating a processing procedure performed in the determination unit27.

Similarly to the determination unit25illustrated inFIG.2, the determination unit27compares the absolute value of the incident angle θ calculated by the angle calculating unit24with the first threshold Th1.

If the absolute value of the incident angle θ is equal to or less than the first threshold Th1, the determination unit27acquires M distances R and M relative speeds v from the distance speed calculation processing unit53of the distance speed calculating unit23(step ST41inFIG.17).

Here, in order to simplify the description, it is assumed that all of the M distances R repeatedly calculated by the distance speed calculating unit23are distances between the radar device1and the observation target or false detection distances due to electromagnetic noise.

In addition, it is assumed that all of the M relative speeds v repeatedly calculated by the distance speed calculating unit23are relative speeds between the radar device1and the observation target or relative speeds due to electromagnetic noise.

Next, the determination unit27calculates an average value vaveof the M relative speeds v, and calculates G as a multiplication result by multiplying the average value vave, the transmission time interval ΔT of the radar signal group, (M−1), and a positive constant a of less than 1 as expressed in the following Formula (6).

In a case where the observation target is not a noise source, the absolute value ΔRMof the difference ΔRM, which is the change in distance, is represented by the product of the speed and the time. Therefore, the change in distance should take a value corresponding to the product of the average value vaveof the relative speed v and the time ΔT×(M−1) required for transmitting the M radar signal groups.

On the other hand, in a case where the observation target is a noise source, since the distance R is a value close to a constant value, the change in the distance is a value significantly smaller than the product of the average value vaveof the relative speeds v and the time ΔT×(M−1) required for transmitting the M radar signal groups. Therefore, in Formula (6), by setting a to an appropriate value less than 1, it is possible to determine whether or not the observation target is a non-detection target due to electromagnetic noise. As the value of α, for example, α=½ is used. Note that the value of a is desirably set in consideration of the resolution of the distance R, the resolution of the relative speed v, the change in the relative speed v, the variation in the frequency of the assumed electromagnetic noise, and the like.

The determination unit27compares the multiplication result G with the absolute value |ΔRMof the difference ΔRM.

If the multiplication result G is equal to or larger than the absolute value ARM of the difference ΔRM(step ST42inFIG.17: YES), the determination unit27determines that the observation target is a non-detection target and is a noise source (step ST43inFIG.17).

When the multiplication result G is less than the absolute value |ΔRM| of the difference ΔRMand one or more relative speeds v among the M relative speeds v are equal to or less than the third threshold Th3, the determination unit27determines that the observation target is a detection target and is not a noise source.

When the multiplication result G is less than the absolute value ΔRMof the difference ΔRMand all of the M relative speeds v are larger than the third threshold Th3, the determination unit27determines that the observation target is a non-detection target and is a noise source.

In the second embodiment described above, the radar signal processing device22illustrated inFIG.16is configured in such a way that the determination unit27determines that the observation target is a non-detection target due to electromagnetic noise when the multiplication result of the average value of the M relative speeds calculated by the distance speed calculating unit23, the time interval of the radar signal radiated from the radar device1, (M−1), and the positive constant of less than 1 is equal to or greater than the absolute value of the difference between the distance calculated first by the distance speed calculating unit23and the distance calculated Mth. Therefore, similarly to the radar signal processing device22illustrated inFIG.2, the radar signal processing device22illustrated inFIG.16can prevent erroneous detection of a non-detection target due to electromagnetic noise as long as the radar signal includes at least one of a transmission wave whose frequency increases with the lapse of time and a transmission wave whose frequency decreases with the lapse of time.

It should be noted that the present disclosure can freely combine the embodiments, modify any component of each of the embodiments, or omit any component in each of the embodiments.

INDUSTRIAL APPLICABILITY

The present disclosure is suitable for a radar signal processing device and a radar signal processing method for calculating a distance from a radar device to an observation target.

The present disclosure is suitable for a radar device including a radar signal processing device and an in-vehicle device including the radar device.

REFERENCE SIGNS LIST