WO2017141353A1

WO2017141353A1 - Fmcw radar device

Info

Publication number: WO2017141353A1
Application number: PCT/JP2016/054464
Authority: WO
Inventors: 三本　雅; 高橋　徹
Original assignee: 三菱電機株式会社
Priority date: 2016-02-16
Filing date: 2016-02-16
Publication date: 2017-08-24
Also published as: JP6415762B2; JPWO2017141353A1

Abstract

The present invention is provided with an observation unit (16) for obtaining an observation signal from a transmission signal radiated into space and a reception signal received as a result of the transmission signal being reflected and scattered by an object, a frequency analysis unit (152) for obtaining a spectrum of discrete frequencies from the obtained observation signal, a smoothed value calculation unit (153) for calculating a smoothed value for each discrete frequency from the obtained spectrum of discrete frequencies, a threshold value calculation unit (154) for calculating a detection threshold value for each discrete frequency by multiplying the calculated smoothed value for each discrete frequency by a threshold value coefficient, a comparison unit (155) for comparing the obtained spectrum of discrete frequencies with the calculated detection threshold values for each discrete frequency, a maximum value detection unit (156) for detecting, from the comparison results, the discrete frequency having the maximum spectral value from among the spectrum of discrete frequencies, and a distance and speed measurement unit (157) for measuring the distance and speed of the object on the basis of the detection result.

Description

FMCW radar equipment

This invention relates to an FMCW radar apparatus that estimates the distance and speed of an object to be observed.

Conventionally, an FMCW (Frequency Modulated Continuous Wave) type radar apparatus that can estimate the distance and speed of an object to be observed that is located within a range of several hundreds of meters or less from its own apparatus with a simple configuration compared to a pulse radar or the like. (Hereinafter referred to as FMCW radar device) is known. This FMCW radar apparatus measures the distance and relative velocity to an object from the frequency of an observation signal obtained by directly mixing a transmission signal and a reception signal.
In addition, when there are a plurality of objects, the observation signal includes a plurality of frequencies corresponding to each object. Therefore, the observation signal is analyzed to obtain a spectrum for each discrete frequency. Since the spectrum power reaches a peak (maximum value) at the discrete frequency corresponding to each object, the frequency corresponding to each object can be detected by detecting these peaks.

However, unless an appropriate detection threshold is provided for the spectrum power, a peak corresponding to an object to be detected may not be detected, or a peak that should not be detected may be detected.

Therefore, a method is known in which a spectrum waveform is acquired in the absence of an object to be detected in advance, and a detection threshold value that reflects temperature characteristics and the like is set based on the spectrum waveform (see, for example, Patent Document 1). .
A method is also known in which a peak is first detected with a first threshold value set from background noise and the like, and a second threshold value is provided according to the detected peak power to obtain a detection threshold value. (For example, refer to Patent Document 2).
In addition, a method of setting a detection threshold by a CFAR (Constant False Alarm Rate) technique is known (for example, see Non-Patent Document 1).

JP 2007-155728 A International Publication No. 2005/059588

However, in the prior art disclosed in Patent Document 1, for example, if there is a gentle convex waveform that changes with time as a spectrum waveform, there is a problem that a peak that should not be detected is detected.
In addition, in the conventional technique disclosed in Patent Document 2, once a peak that should not be detected is detected, detection by a threshold is performed again, so that a large amount of calculation resources such as calculation time and calculation memory are required. There is a problem.
In addition, in the prior art disclosed in Non-Patent Document 1, it is difficult to detect a peak corresponding to an object from spectral waveforms from a plurality of adjacent objects having different reflection intensities. Has the problem of requiring a lot of computing resources.

The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an FMCW radar apparatus that can suppress erroneous detection with a small amount of computation resources compared to the conventional configuration.

The FMCW radar apparatus according to the present invention includes: an observation unit that radiates a transmission signal to space, and obtains an observation signal from the transmission signal and a reception signal received by reflection and scattering of the transmission signal by an object to be observed; , A frequency analysis unit that obtains a spectrum for each discrete frequency from the observation signal obtained by the observation unit, and a smooth value calculation that calculates a spectrum smoothing value for each discrete frequency from the spectrum for each discrete frequency obtained by the frequency analysis unit A threshold value calculation unit that calculates a detection threshold value for each discrete frequency by multiplying a spectrum smoothing value for each discrete frequency calculated by the smoothing value calculation unit by a threshold coefficient, and a frequency analysis unit A comparison unit that compares the obtained spectrum for each discrete frequency with a detection threshold value for each discrete frequency calculated by the threshold value calculation unit, and a comparison unit. From the comparison result, out of the spectrum for each discrete frequency obtained by the frequency analysis unit, based on the detection result by the maximum value detection unit and the maximum value detection unit for detecting the discrete frequency at which the spectrum becomes the maximum value, the distance of the object And a distance / velocity measuring unit for measuring the velocity.

According to the present invention, since it is configured as described above, it is possible to suppress erroneous detection with a smaller number of computing resources than in the conventional configuration.

It is a figure which shows the structural example of the FMCW radar apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows the function structural example of the control arithmetic unit in Embodiment 1 of this invention. It is a flowchart which shows the operation example of the control arithmetic unit in Embodiment 1 of this invention. It is a flowchart which shows the operation example of the smooth value calculation part in Embodiment 1 of this invention. 5A to 5C are diagrams for explaining the effect of the FMCW radar apparatus according to Embodiment 1 of the present invention (when a planar reflective object is present near the FMCW radar apparatus). 6A to 6C are diagrams for explaining the effect of the FMCW radar apparatus according to Embodiment 1 of the present invention (when there are a plurality of adjacent objects having different reflection intensities). 7A and 7B are diagrams showing an example of the hardware configuration of the control arithmetic unit according to the first embodiment of the present invention, showing a case where the processing circuit is dedicated hardware and a case where the processing circuit is a CPU. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of an FMCW radar apparatus 1 according to Embodiment 1 of the present invention.
The FMCW radar apparatus 1 estimates the distance and speed of an object to be observed. As shown in FIG. 1, the FMCW radar apparatus 1 includes a transmitter 11, a receiver 12, an analog / digital converter 13, a memory 14, and a control calculator 15.

The transmitter 11 emits a transmission signal to space. The transmitter 11 includes a voltage generation circuit 111, a voltage control oscillator 112, a distribution circuit 113, an amplification circuit 114, and a transmission antenna 115.

The voltage generation circuit 111 generates a predetermined modulation voltage for a transmission signal under the control of a control unit 151 described later of the control arithmetic unit 15. The modulation voltage generated by the voltage generation circuit 111 is output to the voltage controlled oscillator 112.

The voltage controlled oscillator 112 generates a transmission signal in accordance with the modulation voltage generated by the voltage generation circuit 111. The transmission signal generated by the voltage controlled oscillator 112 is output to the distribution circuit 113.

The distribution circuit 113 distributes and outputs the transmission signal generated by the voltage controlled oscillator 112 to a later-described mixer 122 of the amplifier circuit 114 and the receiver 12.

The amplification circuit 114 amplifies the transmission signal distributed and output by the distribution circuit 113. The transmission signal amplified by the amplifier circuit 114 is output to the transmission antenna 115.

The transmission antenna 115 radiates the transmission signal amplified by the amplification circuit 114 to space as an electromagnetic wave. Thereafter, the transmission signal radiated to the space is reflected and scattered by an object to be observed existing around the FMCW radar apparatus 1 (a range of several hundred meters or less), and a part of the transmission signal is received as a received signal. Return to.

The receiver 12 receives a reception signal from the space, and obtains an observation signal from the transmission signal from the distribution circuit 113 of the transmitter 11 and the reception signal. The receiver 12 includes a receiving antenna 121, a mixer 122, an amplifier circuit 123, and a filter circuit 124.

The reception antenna 121 receives a reception signal that is returned by the transmission signal radiated from the transmission antenna 115 being reflected and scattered by the object. The received signal received by the receiving antenna 121 is output to the mixer 122.

The mixer 122 mixes the reception signal received by the receiving antenna 121 and the transmission signal distributed by the distribution circuit 113 to generate an observation signal. The observation signal generated by the mixer 122 is output to the amplifier circuit 123.

The amplification circuit 123 amplifies the observation signal generated by the mixer 122. The observation signal amplified by the amplifier circuit 123 is output to the filter circuit 124.

The filter circuit 124 suppresses unnecessary frequency components from the observation signal amplified by the amplifier circuit 123. An observation signal in which unnecessary frequency components are suppressed by the filter circuit 132 is output to the analog-to-digital converter 13.

The analog-digital converter 13 converts an observation signal (analog signal) from the receiver 12 (filter circuit 124) into a digital signal (digital voltage data) under the control of a control unit 151 (to be described later) of the control arithmetic unit 15. It is. The observation signal converted into a digital signal by the analog-digital converter 13 is output to the memory 14.

The memory 14 stores an observation signal converted into a digital signal by the analog-to-digital converter 13 under the control of a control unit 151 (to be described later) of the control arithmetic unit 15. As the memory 14, for example, a RAM (Random Access Memory) is applicable.

The transmitter 11, the receiver 12, the analog-digital converter 13, and the memory 14 radiate a transmission signal to space, and the transmission signal and the transmission signal are reflected and scattered by an object to be observed and received. An observation unit 16 that obtains an observation signal from the received signal is configured. The configuration and operation of the observation unit 16 are basically the same as the configuration and operation of the conventional FMCW radar apparatus.

The control arithmetic unit 15 controls each part of the FMCW radar apparatus 1 and measures the distance and speed of the object to be observed using the observation signal stored in the memory 14. As shown in FIG. 2, the control calculator 15 includes a control unit 151, a frequency analysis unit 152, a smooth value calculation unit 153, a threshold value calculation unit 154, a comparison unit 155, a maximum value detection unit 156, and a distance speed measurement unit. 157.

The control unit 151 includes the voltage generation circuit 111 of the transmitter 11, the analog-digital converter 13, the memory 14, and each unit of the control arithmetic unit 15 (frequency analysis unit 152, smooth value calculation unit 153, threshold value calculation unit 154, comparison Unit 155, maximum value detection unit 156, and distance speed measurement unit 157).

The frequency analysis unit 152 obtains a spectrum for each discrete frequency by reading and analyzing the observation signal stored in the memory 14 under the control of the control unit 151. Data indicating the spectrum for each discrete frequency obtained by the frequency analysis unit 152 is output to the smooth value calculation unit 153, the comparison unit 155, and the maximum value detection unit 156.

The smooth value calculation unit 153 calculates a spectrum smooth value for each discrete frequency from the spectrum for each discrete frequency obtained by the frequency analysis unit 152 under the control of the control unit 151. The smooth value calculation unit 153 calculates a spectrum smooth value for each discrete frequency from the spectrum for each discrete frequency obtained by the frequency analysis unit 152 by using a feedback filter using a smooth filter coefficient. Data indicating the spectrum smooth value for each discrete frequency calculated by the smooth value calculation unit 153 is output to the threshold value calculation unit 154.

The threshold calculation unit 154 multiplies the spectrum smooth value for each discrete frequency calculated by the smooth value calculation unit 153 by a threshold coefficient under the control of the control unit 151, thereby detecting the detection threshold for each discrete frequency. Is calculated. Data indicating the detection threshold value for each discrete frequency calculated by the threshold value calculation unit 154 is output to the comparison unit 155.

The comparison unit 155 compares the spectrum for each discrete frequency obtained by the frequency analysis unit 152 with the detection threshold value for each discrete frequency calculated by the threshold value calculation unit 154 under the control of the control unit 151. Is. Data indicating the comparison result by the comparison unit 155 is output to the maximum value detection unit 156.

Under the control of the control unit 151, the maximum value detection unit 156 detects a discrete frequency at which the spectrum has a maximum value from the comparison results of the comparison unit 155 for each discrete frequency obtained by the frequency analysis unit 152. Is. At this time, the local maximum detection unit 156 has a spectrum that is larger than the detection threshold at the central discrete frequency among the three consecutive discrete frequencies, and the spectrum of the central discrete frequency is higher than the spectrum of the adjacent discrete frequencies. Is larger, the center discrete frequency is detected as a maximum value. Data indicating the detection result by the maximum value detection unit 156 is output to the distance speed measurement unit 157.

The distance / velocity measurement unit 157 measures the distance and speed of an object to be observed based on the detection result of the maximum value detection unit 156 and based on the known FMCW radar principle under the control of the control unit 151. It is.

Next, an operation example of the control arithmetic unit 15 in the first embodiment will be described with reference to FIGS. In addition, each part (frequency analysis part 152, smooth value calculation part 153, threshold value calculation part 154, comparison part 155, maximum value detection part 156, and distance speed measurement part 157) of the control calculator 15 is operated by the control part 151. Timing etc. are controlled.

In the operation of the control arithmetic unit 15, as shown in FIG. 3, first, the frequency analysis unit 152 reads out and analyzes the observation signal stored in the memory 14, thereby obtaining a spectrum for each discrete frequency (step ST301). . At this time, the frequency analysis unit 152 obtains a spectrum for each discrete frequency from the observation signal by, for example, a known FFT (Fast Fourier Transform) algorithm.

Next, the smooth value calculation unit 153 calculates a spectrum smooth value for each discrete frequency from the spectrum for each discrete frequency obtained by the frequency analysis unit 152 (step ST302). Hereinafter, the smooth value calculation processing by the smooth value calculation unit 153 will be described with reference to the example shown in FIG.

In the smooth value calculation unit 153, as shown in FIG. 4, first, the number b of the discrete frequency that is the smooth value calculation target is set to the number 1 corresponding to the lowest discrete frequency in the spectrum obtained by the frequency analysis unit 152. (Step ST401).

Next, the smoothing value calculation unit 153 uses the discrete frequency spectrum P (b) of the number b (= 1) and the predetermined smoothing filter coefficient α1 as the smoothing coefficient Ps (b) of the discrete frequency of the number b. It calculates from Formula (1) (step ST402).
Ps (b) = α1 × P (b) (1)

Next, the smooth value calculation unit 153 increments the value of number b (step ST403).

Next, the smooth value calculation unit 153 determines whether the number b is larger than the highest discrete frequency number K in the spectrum obtained by the frequency analysis unit 152 (step ST404). In step ST404, when the smooth value calculation unit 153 determines that the number b is larger than the number K, the sequence ends.

On the other hand, in step ST404, when the smooth value calculation unit 153 determines that the number b is not greater than the number K, the spectrum P (b) of the discrete frequency with the number b is already calculated with the number b−. It is determined whether it is larger than the spectrum smoothing value Ps (b-1) of 1 discrete frequency (step ST405).

In step ST405, when the smooth value calculation unit 153 determines that the spectrum P (b) is larger than the spectrum smooth value Ps (b-1) of the previous discrete frequency, the smoothing filter coefficient αs is converted to the smoothing filter coefficient αs. The coefficient αu is set (step ST406). The smoothing filter coefficient αu is a filter coefficient that determines the degree of smoothness of the spectrum near the rising edge of the spectrum waveform, and is set to a value of 0.5 ≦ αu ≦ 1, for example. The smoothing filter coefficient αu is set (adjusted) using the frequency spectrum obtained from the actual data once for example of the number of states in which the object to be detected exists.

On the other hand, in step ST405, when the smooth value calculation unit 153 determines that the spectrum P (b) is not larger than the previous spectrum smooth value Ps (b-1), the smoothing filter coefficient αs is converted to the smoothing filter coefficient αs. The coefficient αd is set (step ST407). The smoothing filter coefficient αd is a filter coefficient that determines the degree of smoothness of the spectrum near the falling edge of the spectrum waveform, and is set to a value of 0 ≦ αd <0.5, for example. The smoothing filter coefficient αd is set (adjusted) by, for example, temporarily acquiring actual data for an example of the number of states in which an object to be detected exists and using a frequency spectrum obtained from the data.

After setting the smoothing filter coefficient αs, the smoothing value calculation unit 153 sets the discrete frequency spectrum smoothing value Ps (b) of number b, the discrete frequency spectral smoothing value Ps (b-1) of number b-1, and the number b. Is calculated from the feedback filter of the following equation (2) using the discrete frequency spectrum P (b) and the smoothing filter coefficient αs (step ST408).
Ps (b) = αs × Ps (b−1) + (1−αs) × P (b) (2)

Here, as described above, the smoothing filter coefficient αu is a filter coefficient that determines the degree of smoothing for the spectrum near the rising edge of the spectrum waveform, and the smoothing filter coefficient αd determines the degree of smoothing for the spectrum near the falling edge of the spectrum waveform. It is a filter coefficient. Then, by setting the smoothing filter coefficient αu to a large value (for example, 0.5 ≦ αu ≦ 1) in the range of 0 <αu ≦ 1, the waveform of the spectrum smoothing value rises gradually, and the spectrum smoothing value is The value is smaller than the spectrum. As a result, at the maximum point that should exist after the rise, the spectrum smooth value is always smaller than the spectrum, and by using the detection threshold obtained by multiplying this spectrum smooth value by the threshold coefficient, the maximum point is obtained. Is easy to detect. On the other hand, in the vicinity of the falling edge of the spectrum waveform, if the value of the smoothing filter coefficient remains large, the range in which the spectrum smooth value is larger than that of the original spectrum is expanded, and peak detection becomes difficult. Therefore, in order to avoid this, the smoothing filter coefficient αd is set to a small value (for example, 0 ≦ αd <0.5) in the range of 0 ≦ αd <1.

In equation (2), the smoothing filter coefficient to be multiplied by the discrete frequency spectrum smoothing value Ps (b-1) of number b-1 is αs, and the smoothing filter coefficient to be multiplied by the discrete frequency spectrum P (b) of number b is By setting (1-αs), the smoothing result is prevented from becoming unstable.
Through the above processing, the smooth value calculation unit 153 can calculate the spectrum smooth value Ps (b) for each discrete frequency.

Returning to the description of the operation of the control arithmetic unit 15 shown in FIG. 3 again, the threshold value calculation unit 154 multiplies the spectrum smoothing value for each discrete frequency calculated by the smoothing value calculation unit 153 by the threshold coefficient, A detection threshold value for each discrete frequency is calculated (step ST303). That is, the threshold value calculation unit 154 calculates the detection threshold value Th (b) for each discrete frequency from the following equation (3) using the spectrum smoothing value Ps (b) and the threshold coefficient γ for each discrete frequency. calculate. Note that the threshold coefficient γ is set (adjusted) using, for example, frequency data obtained from the actual data once for a number of states in which there are objects to be detected.
Th (b) = γ × Ps (b) (3)

In place of the threshold coefficient γ, a threshold coefficient γ (b) whose value is changed for each discrete frequency may be used. The threshold coefficient γ (b) is, for example, more likely to be an object at a longer distance as the frequency is higher (number b is larger), and the intensity of the received electromagnetic wave is smaller at an object at a longer distance. You may set (adjust) so that a value may become small, so that b is large. In addition, when a planar reflecting object exists and the distance (interval) between the FMCW radar apparatus 1 and the planar reflecting object is known in advance as in the example of FIG. 5, the convexity corresponding to the moving speed of the FMCW radar apparatus 1 is obtained. Since the shape pattern can be predicted to some extent, the threshold coefficient γ (b) may be set (adjusted) based on the pattern. The threshold coefficient γ (b) may be set (adjusted) by combining the above two setting methods.

Next, the comparison unit 155 compares the spectrum for each discrete frequency obtained by the frequency analysis unit 152 with the detection threshold value for each discrete frequency calculated by the threshold value calculation unit 154. Next, the maximum value detection unit 156 detects, from the comparison result by the comparison unit 155, a discrete frequency at which the spectrum has a maximum value among the spectra for each discrete frequency obtained by the frequency analysis unit 152. Hereinafter, an example of processing performed by the comparison unit 155 and the maximum value detection unit 156 will be described with reference to FIG.

First, the comparison unit 155 sets the number b of the discrete frequency to be compared to the number 1 corresponding to the lowest discrete frequency in the spectrum obtained by the frequency analysis unit 152 (step ST304).

Next, comparison section 155 determines whether spectrum P (b) obtained by frequency analysis section 152 is greater than detection threshold Th (b) calculated by threshold calculation section 154 (step ST305). .

In step ST305, when the comparison unit 155 determines that the spectrum P (b) is larger than the detection threshold Th (b), the spectrum P (b) is converted into the spectrum P (b-1) and the spectrum P (b). b + 1) is determined (step ST306).

In step ST306, when the comparison unit 155 determines that the spectrum P (b) is larger than the spectrum P (b-1) and the spectrum P (b + 1), the maximum value detection unit 156 sets the discrete frequency of number b to the maximum. It detects as a value (step ST307). Thereafter, the sequence proceeds to step ST308.

On the other hand, when the comparison unit 155 determines in step ST305 that the spectrum P (b) is not larger than the detection threshold Th (b), or in step ST306, the comparison unit 155 determines that the spectrum P (b) is the spectrum. If it is determined that it is not larger than P (b−1) and spectrum P (b + 1), the sequence proceeds to step ST308.
In step ST308, the comparison unit 155 increments the number b of the discrete frequency to be compared.

Next, the comparison unit 155 determines whether the number b is larger than the number K of the highest discrete frequency in the spectrum obtained by the frequency analysis unit 152 (step ST309). In step ST309, when the comparison unit 155 determines that the number b is not greater than the number K, the sequence returns to step ST305 and repeats the above processing.

On the other hand, if the comparison unit 155 determines in step ST309 that the number b is greater than the number K, the distance / velocity measurement unit 157 knows from the detection result (the discrete frequency that is the maximum value) by the maximum value detection unit 156. Based on the principle of the FMCW radar, the distance and speed of the object to be observed are measured (step ST310).

Next, the effect of the FMCW radar apparatus 1 according to the first embodiment will be described with reference to FIGS. 5 and 6, the horizontal axis indicates the discrete frequency, and the vertical axis indicates the spectrum power.
For example, when a planar reflecting object such as a road surface exists in the vicinity of the FMCW radar apparatus 1, the spectrum of the discrete frequency obtained by the frequency analysis unit 152 is as shown by a solid line in FIGS. 5A to 5C. However, the convex pattern of the spectrum waveform changes with time depending on the moving speed of the FMCW radar apparatus 1.

FIG. 5A shows a case where CA (Cell Averaging) -CFAR, which is one of the conventional techniques, is applied to the spectrum (solid line) for each discrete frequency obtained by the frequency analysis unit 152. In FIG. 5A, a dotted line shows the result of calculating the sum of eight discrete frequencies as a reference range, and a white broken line shows a detection threshold value obtained by multiplying the sum by a threshold coefficient 0.6. .
In this case, there is no spectrum that exceeds the detection threshold in a gentle convex portion that does not need to be detected, and unnecessary detection is not performed.

Further, FIG. 5B is obtained by applying Ordered Statistics (OS) -CFAR, which is one of the conventional techniques, to the spectrum (solid line) for each discrete frequency obtained by the frequency analysis unit 152. In FIG. 5B, a dotted line indicates the fourth spectrum from the smaller value of eight discrete frequencies as a reference range, and a white broken line indicates a detection threshold obtained by multiplying the spectrum by a threshold coefficient 4.5. The value is shown.
In this case, there is no spectrum that exceeds the detection threshold in a gentle convex portion that does not need to be detected, and unnecessary detection is not performed. However, since it is necessary to rearrange the eight spectra for each discrete frequency in ascending order, a lot of calculation resources are required.

On the other hand, FIG. 5C shows a case where the smoothed value calculation unit 153 calculates the spectrum smooth value for the spectrum (solid line) for each discrete frequency obtained by the frequency analysis unit 152. In FIG. 5C, the dotted line indicates the spectrum smooth value calculated with the smoothing filter coefficient α1 = 0.5, the smoothing filter coefficient αu = 0.9, and the smoothing filter coefficient αd = 0.1, and the white broken line indicates the spectrum. The detection threshold value obtained by multiplying the smooth value by the threshold coefficient γ = 4 is shown.
In this case, as in FIG. 5A and FIG. 5B, there is no spectrum exceeding the detection threshold in a gentle convex portion that does not need to be detected, and unnecessary detection is not performed. Further, the smooth value calculation processing by the smooth value calculation unit 153 is as shown in FIG. 4, for example, and the processing can be performed with fewer calculation resources than when OS-CFAR is applied.

In addition, when there are two objects having a smaller distance difference and an object on the near side having a lower radio wave reflection and lower received signal intensity, the spectrum of the discrete frequency obtained by the frequency analysis unit 152 is shown in FIG. It becomes like the solid line shown in FIG. 6C. The peak frequencies corresponding to the two objects are denoted by

reference numerals

601 and 602.

FIG. 6A shows a case where CA-CFAR, which is one of the conventional techniques, is applied to the spectrum (solid line) for each discrete frequency obtained by the frequency analysis unit 152. In FIG. 6A, a dotted line indicates a result of calculating the sum of eight discrete frequencies as a reference range, and a white broken line indicates a detection threshold value obtained by multiplying the sum by a threshold coefficient 0.6. .
In this case, it can be seen that the detection threshold is high for the peak of the object on the near side, making detection difficult.

FIG. 6B shows a case where OS-CFAR, which is one of the conventional techniques, is applied to the spectrum (solid line) for each discrete frequency obtained by the frequency analysis unit 152. In FIG. 6B, a dotted line indicates the fourth spectrum from the smaller value of eight discrete frequencies as a reference range, and a white broken line indicates a detection threshold obtained by multiplying the spectrum by a threshold coefficient 4.5. The value is shown.
In this case, both two objects can be detected. However, since it is necessary to rearrange the eight spectra for each discrete frequency in ascending order, a lot of calculation resources are required.

On the other hand, FIG. 6C shows a case where the smoothed value calculation unit 153 calculates the spectrum smooth value for the spectrum (solid line) for each discrete frequency obtained by the frequency analysis unit 152. In FIG. 6C, the dotted line indicates the spectrum smooth value calculated with the smoothing filter coefficient α1 = 0.5, the smoothing filter coefficient αu = 0.9, and the smoothing filter coefficient αd = 0.1, and the white broken line indicates the spectrum. The detection threshold value obtained by multiplying the smooth value by the threshold coefficient γ = 4 is shown.
In this case, both two objects can be detected. Further, the smooth value calculation processing by the smooth value calculation unit 153 is as shown in FIG. 4, for example, and the processing can be performed with fewer calculation resources than when OS-CFAR is applied.

As described above, according to the first embodiment, a transmission signal is radiated to a space, and an observation signal is received from the transmission signal and a reception signal received by being reflected and scattered by an object to be observed. From the observation signal obtained by the observation unit 16, the frequency analysis unit 152 for obtaining a spectrum for each discrete frequency from the observation signal obtained by the observation unit 16, and the spectrum for each discrete frequency obtained by the frequency analysis unit 152. A smoothing value calculation unit 153 that calculates a spectrum smoothing value, and a threshold value coefficient is multiplied by the spectrum smoothing value for each discrete frequency calculated by the smoothing value calculation unit 153, thereby calculating a detection threshold value for each discrete frequency. The spectrum for each discrete frequency obtained by the threshold calculation unit 154 and the frequency analysis unit 152 is used as the separation calculated by the threshold calculation unit 154. From the comparison result by the comparison unit 155 that compares the detection threshold value for each frequency and the comparison unit 155, the discrete frequency at which the spectrum has a maximum value is detected from the spectrum for each discrete frequency obtained by the frequency analysis unit 152. Since the maximum value detection unit 156 and the distance speed measurement unit 157 for measuring the distance and speed of the object based on the detection result by the maximum value detection unit 156 are provided, the error is reduced with less calculation resources than the conventional configuration. Detection can be suppressed. In this way, by setting the detection threshold according to the change in the original spectrum waveform, it is possible to detect a peak that should not be detected in a gently convex spectrum waveform that changes over time with a small amount of computing resources. In addition, a peak corresponding to an object can be detected from spectral waveforms from a plurality of adjacent objects having different reflection intensities.

In the example shown in FIG. 3, the comparison unit 155 notifies the local maximum value detection unit 156 that the spectrum of the discrete frequency to be compared is larger than the detection threshold and larger than the spectrum of the adjacent discrete frequencies. The case where the maximum value is detected by the maximum value detector 156 is shown. However, the present invention is not limited to this. For example, the comparison unit 155 generates detection information by comparing a spectrum for each discrete frequency with a detection threshold value for each discrete frequency, and uses the detection information as a maximum value detection unit 156. You may make it output to. The detection information includes a discrete frequency, a spectrum of the discrete frequency, and a comparison result between the spectrum and a detection threshold value. For example, the comparison unit 155 sets the comparison result to 1 when the spectrum is larger than the detection threshold, and sets the comparison result to 0 when the spectrum is equal to or lower than the detection threshold. Then, the maximum value detection unit 156 detects the maximum value using the detection information from the comparison unit 155.

Finally, with reference to FIG. 7, a hardware configuration example of the control arithmetic unit 15 according to the first embodiment of the present invention will be described.
The functions of the control unit 151, the frequency analysis unit 152, the smoothing value calculation unit 153, the threshold value calculation unit 154, the comparison unit 155, the maximum value detection unit 156, and the distance speed measurement unit 157 in the control arithmetic unit 15 are the processing circuit 51. It is realized by. As shown in FIG. 7, even if the processing circuit 51 is dedicated hardware, a CPU (Central Processing Unit, a central processing unit, a processing unit, an arithmetic unit, a microprocessor, and the like that executes a program stored in the memory 53. It may be a microcomputer, a processor, or a DSP (Digital Signal Processor) 52.

When the processing circuit 51 is dedicated hardware as shown in FIG. 7A, the processing circuit 51 includes, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit). , FPGA (Field Programmable Gate Array), or a combination thereof. The processing circuit 51 implements the functions of the control unit 151, frequency analysis unit 152, smooth value calculation unit 153, threshold value calculation unit 154, comparison unit 155, maximum value detection unit 156, and distance speed measurement unit 157. Alternatively, the function of each unit may be integrated and realized by the processing circuit 51.

As shown in FIG. 7B, when the processing circuit 51 is the CPU 52, the control unit 151, the frequency analysis unit 152, the smooth value calculation unit 153, the threshold value calculation unit 154, the comparison unit 155, the maximum value detection unit 156, and the distance speed measurement unit The function 157 is realized by software, firmware, or a combination of software and firmware. Software and firmware are described as programs and stored in the memory 53. The processing circuit 51 implements the functions of each unit by reading and executing the program stored in the memory 53. That is, the control arithmetic unit 15 includes a memory 53 for storing a program that, when executed by the processing circuit 51, for example, results in the steps shown in FIGS. In addition, these programs are used to calculate the procedures and methods of the control unit 151, the frequency analysis unit 152, the smooth value calculation unit 153, the threshold value calculation unit 154, the comparison unit 155, the maximum value detection unit 156, and the distance speed measurement unit 157. It can be said that this is what is executed. Here, the memory 53 is, for example, a nonvolatile or volatile semiconductor memory such as a RAM, a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), an EEPROM (Electrically EPROM), a magnetic disk, A flexible disk, an optical disk, a compact disk, a mini disk, a DVD (Digital Versatile Disc), and the like are applicable.

Note that some of the functions of the control unit 151, the frequency analysis unit 152, the smoothing value calculation unit 153, the threshold value calculation unit 154, the comparison unit 155, the maximum value detection unit 156, and the distance speed measurement unit 157 are dedicated hardware. It may be realized by hardware and a part may be realized by software or firmware. For example, the function of the control unit 151 is realized by the processing circuit 51 as dedicated hardware, and the frequency analysis unit 152, the smooth value calculation unit 153, the threshold value calculation unit 154, the comparison unit 155, and the maximum value detection unit 156. As for the distance / velocity measuring unit 157, the processing circuit 51 can read out and execute the program stored in the memory 53, thereby realizing its function.

As described above, the processing circuit 51 can realize the above-described functions by hardware, software, firmware, or a combination thereof.

In the present invention, any component of the embodiment can be modified or any component of the embodiment can be omitted within the scope of the invention.

The FMCW radar apparatus according to the present invention can suppress erroneous detection with less computation resources than the conventional configuration, and is suitable for use in the FMCW radar apparatus 1 that estimates the distance and speed of an object to be observed. ing.

1 FMCW radar device, 11 transmitter, 12 receiver, 13 analog-digital converter, 14 memory, 15 control arithmetic unit, 16 observation unit, 51 processing circuit, 52 CPU, 53 memory, 111 voltage generation circuit, 112 voltage controlled oscillator 113 distribution circuit, 114 amplification circuit, 115 transmission antenna, 121 reception antenna, 122 mixer, 123 amplification circuit, 124 filter circuit, 151 control unit, 152 frequency analysis unit, 153 smooth value calculation unit, 154 Threshold value calculation unit, 155 comparison unit, 156 maximum value detection unit, 157 distance speed measurement unit.

Claims

An observation unit that radiates a transmission signal to space, and obtains an observation signal from the transmission signal and a reception signal received by reflection and scattering of the transmission signal by an object to be observed;
A frequency analysis unit for obtaining a spectrum for each discrete frequency from the observation signal obtained by the observation unit;
From the spectrum for each discrete frequency obtained by the frequency analysis unit, a smooth value calculation unit for calculating a spectrum smooth value for each discrete frequency,
A threshold value calculation unit for calculating a detection threshold value for each discrete frequency by multiplying the spectrum smooth value for each discrete frequency calculated by the smooth value calculation unit by a threshold coefficient;
A comparison unit that compares the spectrum for each discrete frequency obtained by the frequency analysis unit with a detection threshold value for each discrete frequency calculated by the threshold value calculation unit;
From the comparison result by the comparison unit, among the spectrum for each discrete frequency obtained by the frequency analysis unit, a maximum value detection unit for detecting a discrete frequency at which the spectrum is a maximum value;
A FMCW radar apparatus comprising: a distance / velocity measurement unit that measures a distance and a velocity of the object based on a detection result by the maximum value detection unit.
The smoothing value calculation unit calculates a spectrum smoothing value for each discrete frequency from a spectrum for each discrete frequency obtained by the frequency analysis unit by a feedback filter using a smoothing filter coefficient. Item 2. The FMCW radar apparatus according to Item 1.
The FMCW radar apparatus according to claim 2, wherein the smoothing value calculation unit calculates a spectral smoothing value from a spectrum having a low discrete frequency.
The smoothing value calculation unit switches the smoothing filter coefficient used for the spectrum that is a smoothing value calculation target according to a magnitude relationship between the spectrum and a spectrum smoothing value of a discrete frequency immediately before the spectrum. 4. The FMCW radar apparatus according to claim 3, wherein
The smoothing value calculation unit sets the value of the smoothing filter coefficient to 0.5 or more and 1 or less when the spectrum that is the smoothing value calculation target is larger than the spectrum smoothing value of the previous discrete frequency, and the spectrum is The FMCW radar apparatus according to claim 4, wherein the smoothing filter coefficient value is 0 or more and less than 0.5 when the spectrum smoothing value is less than or equal to the spectrum smoothing value.
The FMCW radar apparatus according to claim 1, wherein the threshold value calculation unit changes the threshold coefficient for each discrete frequency.