JP2011191195A - Radar apparatus and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic scanning type radar apparatus distinguishing whether an object detected by the radar is low back type detection object. <P>SOLUTION: The radar apparatus includes: a transmission antenna 3 configured to transmit a radio wave; receiving antennas 11 to 1n receiving radio wave which is the transmitted radio wave reflected by an object; a distance detection section 24 detecting the distance to the object based on the received radio wave; a received power calculation section 22 calculating power of the received radio wave as a function of the detected distance; an area calculation section 28 calculating an area of the domain determined from an curve indicating the function as one boundary, at a predetermined distance section; and a detection processing section 29 deciding whether the object is a low back type detection object, based on the calculated area. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a radar apparatus and a computer program.

  Conventionally, a millimeter wave radar (hereinafter referred to as a radar) is usually mounted in front of the body of an automobile and used for inter-vehicle warning, vehicle speed control, and the like. As the in-vehicle radar, an electronic scanning type radar using a method such as FMCW (Frequency Modulated Continuous Wave) radar, multi-frequency CW (Continuous Wave) radar, and pulse radar is used.

  When there is an obstacle around the vehicle equipped with the radar, the on-vehicle radar uses the target data having information such as the relative distance, heading, and speed between the vehicle and the obstacle to generate an inter-vehicle warning and a vehicle speed control system. Output to. The inter-vehicle warning and speed control system maintains the distance between the vehicle and the obstacle according to the position information of the target, issues an alarm when a collision is expected, or decelerates the vehicle. Control of the own vehicle (hereinafter referred to as collision mitigation control) is performed (for example, see Patent Document 1). For this reason, the on-vehicle radar is required to have a capability of quickly and accurately detecting an object that may collide with the host vehicle.

  On the other hand, when there is no obstacle around the host vehicle, the radar does not detect anything, so the radar does not output the target data to the vehicle speed control system. In that case, the vehicle speed control system and the steering control system perform control so that the host vehicle travels at a preset vehicle speed and steering.

JP 2006-275840 A

  By the way, when there is an obstacle around the vehicle, but it is a detection object sufficiently lower than the vehicle floor height (hereinafter referred to as a low-profile detection object), the low-profile detection object The vehicle speed control system and the steering control system should be controlled so that the vehicle travels at a preset vehicle speed and steering, without issuing an inter-vehicle warning, since it does not hinder the progress of the host vehicle.

  However, in-vehicle radars that do not have resolution in the height direction have the problem of misidentifying low-profile detection objects as obstacles that hinder driving, depending on the antenna characteristics and the reflection intensity of the low-profile detection objects. . As a result, the vehicle control device determines that there is a risk of a collision due to the misrecognition of the radar in spite of a safe traveling situation in which no collision accident occurs physically. Due to this misjudgment, control such as sending out an unnecessary warning or undesired deceleration of the own vehicle is performed, causing discomfort to the driver. In addition, unnecessary deceleration of the host vehicle increases the risk of rear-end collision with the following vehicle.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a radar apparatus and a computer program that can determine whether an object detected by a radar is a low-profile detection object. To do.

In order to solve the above problems, a radar device according to one aspect of the present invention includes a transmission antenna that transmits radio waves, a reception antenna that receives radio waves reflected by an object, and the reception In a predetermined distance section, a distance detection unit that detects a distance to the object based on the received radio wave, a received power calculation unit that calculates power of the received radio wave as a function of the detected distance, An area calculation unit that calculates an area of a region that is defined with a curve representing the function as one boundary; a detection processing unit that determines whether or not the object is a low-profile detection object based on the calculated area; It is characterized by providing.
According to the radar apparatus, it is possible to determine whether or not the object detected by the radar is a low-profile object by expressing the received power as a function of the distance between the radar and the object.

The detection processing unit of the radar apparatus may calculate the area based on the intensity of the received wave only when the distance is within a predetermined range.
According to this, it is efficient to determine whether or not the object detected by the radar is a low-profile detection object, and the accuracy can be improved.

In order to solve the above problems, a radar apparatus according to one embodiment of the present invention includes a transmission antenna that transmits radio waves, a reception antenna that receives radio waves reflected by an object, As a function, a received power calculation unit that calculates the power of the received radio wave, an area calculation unit that calculates an area of a region defined by a curve representing the function as one boundary in a predetermined time interval, and the calculated And a detection processing unit that determines whether or not the object is a low-profile detection object based on an area.
According to the radar apparatus, it is possible to determine whether or not the object detected by the radar is a low-profile detection object by expressing the received power as a function of time.

The detection processing unit of the radar apparatus may calculate the area based on the intensity of the received wave only when the time is within a predetermined range.
According to this, it is efficient to determine whether or not the object detected by the radar is a low-profile detection object, and the accuracy can be improved.

The area calculation unit of the radar apparatus may calculate an area of a region defined by using the curve and a predetermined straight line as a boundary or an area determined by using the curve and the predetermined curve as a boundary.
According to this, by calculating the area of a region (closed space) defined with the curve and the predetermined straight line as a boundary in a predetermined section, the area calculated in the case of a low-profile detection object and normal detection Since the difference with the area calculated in a target object can be detected, it can be determined whether a target object is a low-profile detection target object.

The area calculation unit of the radar apparatus may calculate an area of a region determined by using the curve and a straight line determined based on an average value of the received radio wave power as a boundary.
According to this, since the difference between the area calculated in the case of the low-profile detection object and the area calculated in the normal detection object can be increased, the accuracy of whether the object is the low-profile detection object Can be judged well.

The detection processing unit of the radar apparatus may determine the target as a normal detection target when the sum of the plurality of sections of the area exceeds a predetermined threshold.
According to this, by using the sum of the section areas as a criterion for determination, the difference between the normal detection object and the low-profile detection object can be expressed more greatly, so that a margin can be given to the threshold setting. Can be determined with high accuracy.

The detection processing unit of the radar device may determine the target as a normal detection target when any of the areas of a plurality of sections exceeds a predetermined threshold.
According to this, since it can determine before calculating all the area of a section, even when the distance of a radar and a target object is separated, it can determine with a normal detection target object. As a result, the subsequent deceleration of the vehicle and the avoidance action of the object can be performed with sufficient time.

The detection processing unit of the electronic scanning radar apparatus may determine the object as a normal detection object when the number of times the area exceeds a predetermined threshold exceeds a preset number of times.
According to this, since it can determine before calculating all the area of a section, even when the distance of a radar and a target object is separated, it can determine with a normal detection target object. As a result, the subsequent deceleration of the vehicle and the avoidance action of the object can be performed with sufficient time.

In order to solve the above-described problem, a computer program according to an aspect of the present invention includes a first step of detecting a distance to the object based on a radio wave received by a receiving antenna, and the detected distance As a function, a second step of calculating the power of the received radio wave, a third step of calculating an area of a region defined by a curve representing the function as one boundary in a predetermined distance section, and the calculation And causing the computer to execute a fourth step of determining whether or not the object is a low-profile detection object based on the measured area.
According to this computer program, it is possible to determine whether the object detected by the radar is a low-profile detection object by expressing the received power as a function of distance.

In order to solve the above problem, a computer program according to one embodiment of the present invention includes a first step of calculating the power of the received radio wave as a function of time, and the function in a predetermined time interval. A second step of calculating an area of a region defined by a curve representing one boundary, and a third step of determining whether or not the object is a low-profile detection object based on the calculated area. A computer program for causing a computer to execute.
According to this computer program, it is possible to determine whether or not the object detected by the radar is a low-profile object by expressing the received power as a function of time.

  According to the present invention, it is possible to determine whether or not the object detected by the radar is a low profile detection object.

It is a block diagram which shows the structural example of the electronic scanning radar apparatus which is embodiment of this invention. It is a conceptual diagram explaining the production | generation of the beat signal in the rising area and falling area of a triangular wave with a transmission wave and a received wave. It is the figure which showed the method of calculating the arrival angle of the reflected wave with respect to the axis | shaft of a perpendicular direction with respect to the surface where the several antenna is arranged. It is a figure explaining the driving | running | working condition model in which an empty can exists in front of a vehicle. It is the figure which showed the relationship between the received electric power value of a radar, and an elevation angle. It is the figure which showed the distance characteristic of the reception power value of a normal detection target object, and the distance characteristic of the reception power value of a low profile detection target object. It is the figure which showed the distance characteristic of the path difference of a direct wave and an indirect wave, and the distance characteristic of the sine value of a phase difference. It is a figure for demonstrating the standardization value of the reception electric power value when detecting an arbitrary area and the low profile detection target object. It is the figure which showed the distance characteristic of standardization electric power. It is a figure for demonstrating extraction of the closed area and calculation of the area of the said closed area. It is the figure which showed the example of calculation of the area of a closed area. It is a figure for comparing the received power curve and section average value of a normal detection target object with the received power curve and section average value of a low profile detection target object. It is a figure for comparing the area of the standardization electric power of a normal detection target object with the area of the standardization electric power of a low profile detection target object. It is a figure for demonstrating the method to designate the integral range of the absolute value of standardization electric power. It is the figure which showed the distance characteristic of the integral value for every area. It is a flowchart of the whole target extraction process. It is a flowchart of the discrimination | determination process of a low profile detection target object.

  Hereinafter, an electronic scanning radar apparatus (FMCW millimeter wave radar) according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of the embodiment.

  In this figure, the electronic scanning radar apparatus according to the present embodiment includes receiving antennas 11 to 1n, mixers 21 to 2n, transmitting antenna 3, distributor 4, filters 51 to 5n, and SW (switch) 6. , ADC (A / D converter) 7, controller 8, triangular wave generator 9, VCO (Voltage Controlled Oscillator) 10, and signal processor 20.

  The signal processing unit 20 includes a memory 21, a received power calculation unit 22, a DBF detection unit 23, a distance detection unit 24, a speed detection unit 25, an orientation determination unit 26, a target takeover processing unit 27, The area calculation unit 28, the detection processing unit 29, and the target output processing unit 30 are configured.

Next, the operation of the electronic scanning radar apparatus according to the present embodiment will be described with reference to FIG.
The receiving antennas 11 to 1n receive a reflected wave, that is, a received wave, which is transmitted from the object, with the transmitted wave reflected by the object.
Each of the mixers 21 to 2n mixes a transmission wave transmitted from the transmission antenna 3 and a signal obtained by amplifying the reception wave received at each of the reception antennas 11 to 1n by an amplifier, and supports each frequency difference. Generated beat signal.

The transmission antenna 3 transmits a transmission signal obtained by frequency-modulating the triangular wave signal generated by the triangular wave generation unit 9 to the target as a transmission wave.
The distributor 4 distributes the frequency-modulated transmission signal from the VCO 10 to the mixers 21 to 2n and the transmission antenna 3.

Each of the filters 51 to 5n performs band limitation on the beat signals of Ch1 to Chn corresponding to the reception antennas 11 to 1n generated in the mixers 21 to 2n, respectively, and beats band-limited to the SW (switch) 6 Output a signal.
SW6 sequentially switches the beat signals of Ch1 to Chn corresponding to the respective receiving antennas 11 to 1n that have passed through the filters 51 to 5n in response to the sampling signal input from the control unit 8, and performs ADC (A / A D converter) 7.

  The ADC 7 A / D converts the beat signals of Ch1 to Chn corresponding to the receiving antennas 11 to 1n input from the SW6 in synchronization with the sampling signal into digital signals in synchronization with the sampling signal. The signal is converted and sequentially stored in the waveform storage area of the memory 21 in the signal processing unit 20.

The control unit 8 is configured by a microcomputer or the like, and controls the entire electronic scanning radar apparatus shown in FIG. 7 based on a control program stored in a ROM (not shown) or the like.
The memory 21 in the signal processing unit 20 stores the digital signal digitally converted by the A / D converter 7 for each channel corresponding to each of the receiving antennas 11 to 1n.

<Principle to detect distance, relative speed, horizontal angle (azimuth)>
Next, the principle of detecting the distance, relative speed, and angle (azimuth) between the electronic scanning radar apparatus and the object used in the signal processing unit 20 in this embodiment will be briefly described with reference to FIG.

2 shows a transmission signal obtained by frequency-modulating the signal generated by the triangular wave generation unit 9 of FIG. 1 with a center frequency f ₀ and a modulation width Δf in the VCO 10, and the transmission signal is reflected by an object and input as a reception signal. Indicates the state to be performed. The example of FIG. 2 shows a case where there is one object.

  As shown in FIG. 2 (a), a received signal that is a reflected wave from an object is received with respect to a signal to be transmitted, delayed in the right direction (time delay direction) according to the distance between the radar and the object. Is done. Furthermore, the Doppler effect varies in the vertical direction (frequency direction) with respect to the transmission signal in accordance with the relative speed with the object.

  The reception power calculation unit 22 performs a Fourier transform on the beat signal for each channel corresponding to the reception antennas 11 to 1n stored in the memory 21 (the lower diagram in FIG. 2A). Here, the amplitude of the complex data after Fourier transform is referred to as a signal level.

  The reception power calculation unit 22 converts the complex number data of any antenna or the sum of complex number data of all antennas into a frequency spectrum, thereby obtaining an object depending on the beat frequency corresponding to each peak value of the spectrum, that is, the distance. Can be detected. Here, by adding the complex number data of all antennas, the noise components are averaged and the S / N ratio is improved.

  As a result of the Fourier transform, as shown in FIG. 2 (b), when there is one object, each of the ascending region and the descending region has one peak value. Here, in FIG. 8B, the horizontal axis represents frequency and the vertical axis represents signal intensity.

  Then, the received power calculation unit 22 detects the signal level exceeding the preset numerical value (threshold value) from the signal level for each beat frequency shown in FIG. Determine. Here, the peak value of the signal level is referred to as the intensity of the received wave.

  When the peak of the signal level is detected, the reception power calculation unit 22 outputs the beat frequency of the peak value (both ascending and descending portions of the beat signal) as the object frequency to the distance detecting unit 24 and the speed detecting unit 25. . The received power calculation unit 22 outputs the frequency modulation width Δf to the distance detection unit 24 and outputs the center frequency f0 to the speed detection unit 25.

  The reception power calculation unit 22 calculates the square of the peak value of the downlink part of the signal level as reception power. The received power is output to the area calculation unit 28 as a function of the distance from the object input from the distance detection unit 24 described later.

The reception power calculation unit 22 outputs information that there is no target candidate to the target output processing unit 30 when the signal level peak cannot be detected.
The peak value of the upstream part of the beat signal or the average of the peak value of the upstream part of the beat signal and the peak value of the downstream part of the beat signal may be used as the signal level.

  When there are a plurality of objects, after the Fourier transform, the same number of peaks as the number of objects appear in each of the upstream portion of the beat signal and the downstream portion of the beat signal. Since the received signal is delayed in proportion to the distance between the radar and the object, and the received signal at the upper stage of FIG. 2A is shifted to the right, the distance between the radar and the object increases as the distance between the radar and the object increases. The frequency of the beat signal in the lower part of) increases.

  When a plurality of signal level peaks corresponding to a plurality of objects are detected, numbers are assigned in order starting from the lowest frequency for each peak value of the upstream portion and downstream portion, and the detection processing unit 29 Output. Here, in the up and down portions, the peaks with the same number correspond to the same object, and each identification number is the number of the object.

Next, the distance detection unit 24 calculates the distance r from the object frequency f _u of the rising portion and the object frequency f _d of the falling portion input from the reception power calculation unit 22 by the following formula, and receives power The data is output to the calculation unit 22 and the target takeover processing unit 27.
r = {C · T / (2 · Δf)} · {(f _u + f _d ) / 2}

Further, the speed detection unit 25 calculates the relative speed v by the following equation from the ascending portion object frequency f _u and the descending portion object frequency f _d input from the received power calculation unit 22, and the target. The data is output to the takeover processing unit 27.
v = {C / (2 · f ₀ )} · {( _fu −f _d ) / 2}

In the formula for calculating the distance r and the relative velocity v, C is the speed of light, T is the modulation period (rising portion / descending portion), f _u is the object frequencies in the rising portion, f _d is the object frequencies in the falling portion is there.

  Next, the receiving antennas 11 to 1n in the present embodiment are array antennas arranged at intervals d as shown in FIG. The receiving antennas 11 to 1n are incident waves (incident waves, that is, transmitted waves transmitted from the transmitting antenna 3) that are incident from an angle φ direction with respect to an axis perpendicular to the antenna array surface. Wave reflected from the object).

At this time, the incoming wave is received at the same angle φ by the receiving antennas 11 to 1n. The phase difference of the received signal generated between the receiving antenna at one end and the other end is determined from the frequency f of the received signal, the interval dn _-1 between the receiving antenna at the other end and the angle φ, It is calculated by 2πf · (dn ₋₁ · sinφ / C).

  Using the above phase difference, a DBF (digital beam forming) processing unit 23 further performs Fourier transform on complex data obtained by Fourier transform on the time axis corresponding to each input antenna in the antenna arrangement direction, that is, a space. Perform axial Fourier transform. Then, the DBF processing unit 23 calculates spatial complex number data indicating the intensity of the spectrum for each angle channel corresponding to the angular resolution, and outputs it to the direction detection unit 26 for each beat frequency.

  The azimuth detection unit 26 outputs the angle φ having the largest value among the calculated values of the spatial complex number data for each beat frequency to the target takeover processing unit 27 as the azimuth in which the object exists.

The target takeover processing unit 27 compares the object distance, relative speed, and azimuth values calculated this time with the object distance, relative speed, and azimuth values calculated one cycle before read out from the memory 21. If the absolute value of each difference is smaller than the value determined for each value, the object detected one cycle before and the object detected this time are determined to be the same.

  In that case, the target takeover processing unit 27 increments the target takeover processing count of the target object read from the memory 21 by one. Otherwise, the target takeover processing unit 27 considers that a new object has been detected. In addition, the target takeover processing unit 27 stores the distance, relative speed, direction, and the number of times of target takeover processing for the target object in the memory 21 at this time. In addition, the target takeover processing unit 27 outputs the identification number of the object to the detection processing unit 29.

The area calculation unit 28 receives the power of the received radio wave as a function of the detected distance from the reception power calculation unit 22.
The area calculation unit 28 calculates an area of a region defined by a curve representing the function and a straight line determined based on an average value of the received radio wave power in a predetermined distance section.
The area calculation unit 28 adds the area to the sum of the areas calculated so far, and stores the sum of the areas after the addition in the memory 21.

  The detection processing unit 29 reads the sum of the areas after the addition from the memory 21, and uses a low-profile detection target discrimination algorithm to be described later to determine whether the target is a normal detection target with a risk of collision. Whether the object is a low-profile detection object that does not interfere with the operation, and the determination result is output to the target output processing unit 30. As a result, when the object is a normal detection object with a risk of collision, the vehicle can be decelerated to avoid the collision, or an alarm can be issued to alert the driver.

  When the target is a normal detection target, the target output processing unit 30 outputs the identification number of the target as a target. The target output processing unit 30 receives the discrimination results of a plurality of objects from the detection processing unit 29, and when both of them are normal detection objects, the target number identification number of the object on the own vehicle lane is obtained. Output as a mark.

  In addition, the target output processing unit 30 receives the determination results of a plurality of objects, both of which are normal detection objects, and when two or more objects are on the lane of the own vehicle Then, the identification number of the object having a large number of target takeover processes read from the memory 21 is output as a target. When the target is a low-profile detection target or when information indicating that there is no target candidate is input from the received power calculation unit 22, the target output processing unit 30 displays information indicating that there is no target. Output.

<Simulation results of radar detection of low-profile objects>
Before describing the simulation results of radar detection of a low-profile detection object, the conditions will be described first. FIG. 4 is a model of traveling conditions on the yz plane assuming that there is an empty can 42 directly in front of the vehicle 41. d1 is a direct distance between the vehicle 41 and an empty can 42 as an example of a low-profile detection object, r1 is a direct wave propagation path of electromagnetic waves to the object, and r2 and r3 are indirect wave propagation paths of electromagnetic waves to the object. is there. h1 is the height of the in-vehicle radar, h2 is the height of the empty can, and h3 is the vehicle floor height.

  As shown in FIG. 5, with respect to the antenna conditions, the full width at half maximum 43 is 4 [deg], and the ratio of the main lobe received power to the side lobe received power (hereinafter referred to as the side lobe ratio) 44 is 45 [dB]. I decided to.

  Next, simulation conditions in the case where a normal detection target that has a risk of collision with the vehicle exists in front of the vehicle will be described. The simulation conditions are as follows. The in-vehicle radar in FIG. 4 uses millimeter wave band radio waves, and the radar installation height h1 is 0.55 [m]. Since the radar propagating wave is highly linear, the height h2 of the reflection surface of the target object is set to 0.55 [m], which is the same height as the radar installation height h1. RCS (Radar Cross Section, radar reflection cross section) is 0 [dB].

  FIG. 6A is a simulation result showing the distance characteristics of the radar received power when a normal detection target that has a risk of collision with the vehicle exists in front of the vehicle. The horizontal axis is the linear distance d1 between the host vehicle and the detection target shown in FIG. 4, and the vertical axis is the received power, which is calculated to be 0 [dBm] when the received power is 1 [mW].

  Further, −70 [dBm] is the detection threshold value THa, and in the region (detection region 63a) equal to or greater than the detection threshold value THa, the radar can detect the received wave, but the region smaller than the detection threshold value THa (non-detection region). In 64a), the radar cannot detect the received wave. In the case of a normal detection target, the received power curve 61a varies drastically according to the direct distance d1.

  Next, a description will be given of simulation conditions when a low-profile object to be detected that does not collide with a vehicle exists in front of the vehicle. The simulation conditions are as follows. The in-vehicle radar in FIG. 4 uses millimeter wave band radio waves, and the radar installation height h1 is 0.55 [m]. The height h2 of the target object from the road surface is set to 0.1 [m]. Assuming an empty can or the like, the RCS is set to a sufficiently smaller value (−10 [dB]) than in the case of FIG.

  FIG. 6B is a simulation result showing the distance characteristics of the radar received power in the case where a low-profile detection object without a risk of collision with the vehicle exists in front of the vehicle. The horizontal axis is the linear distance d1 between the host vehicle and the detection target shown in FIG. 4, and the vertical axis is the received power, which is calculated to be 0 [dBm] when the received power is 1 [mW].

  In addition, −70 [dBm] is the detection threshold value THb, and in the region (detection region 63b) equal to or greater than the detection threshold value THb, the radar can detect the received wave, but the region (non-detection region) smaller than the detection threshold value THb. In 64b), the radar cannot detect the received wave. In the case of a low-profile detection object, the received power curve 61b changes less in accordance with the direct distance d1 than the reception power curve 61a in the case of a normal detection object.

  From the results shown in FIGS. 6A and 6B, if all the objects exceeding the detection threshold value are the collision risk objects, the radar is both the object when the direct distance d1 is 90 [m] or less. Is judged as a collision risk object, and unnecessary collision mitigation control is performed. Therefore, the detection processing unit 29 does not perform unnecessary collision mitigation control, so that a normal detection target with a risk of collision is detected with respect to a low-profile detection target that does not interfere with traveling using the algorithm described below. Identify things.

<Principle of low-profile detection object discrimination algorithm>
Next, the principle of the low-profile detection target discrimination algorithm in the area calculation unit 28 and the detection processing unit 29 will be described.
As shown in FIG. 4, the electromagnetic wave swept from the radar is reflected through two routes, a direct wave propagation route r1 and an indirect wave propagation route (a route combining r2 and r3, hereinafter collectively referred to as r4). It reaches a detection object that is a point and is synthesized. Further, the composite wave is re-swept at the reflection point, propagates through the route r1 and the route r4, and is again synthesized by the on-vehicle radar as the arrival point.

  Due to the synthesis of two propagation waves with different paths, a “point to strengthen” and a “point to cancel” occur in the received power that changes according to the direct distance d1 between the radar and the detection target. In such a phenomenon, the height h1 of the radar and the height h2 of the detection object shown in FIG. 4 are the main factors that determine the number of occurrences (hereinafter referred to as the number of occurrences) of the points to be strengthened and the points to be canceled. It has become.

Specifically, the difference between the direct wave propagation path r1 and the indirect wave propagation path r4 causes a phase difference between the direct wave and the indirect wave observed at the arrival point. By synthesizing two waves having such a phase difference, a “strengthening point” and a “spotting point” are generated in the received power characteristics.
The amount of change in the path difference between the direct wave and the indirect wave when the distance d1 changes is larger for the normal detection target than for the low-profile detection target.

Here, as the path difference Δr (where Δr = r4−r1) changes according to the distance d1, the phase difference also changes. Therefore, the position of the direct wave and the indirect wave when the distance d1 changes. The amount of change in the phase difference is larger for the normal detection object than for the low-profile detection object.
Further, the greater the number of occurrences in a certain distance section, the smaller the distance (hereinafter referred to as bandwidth) between the adjacent points to be strengthened and the points to be canceled.

  In order to specifically show the number of occurrences and bandwidths of the above “strengthening points” and “points to cancel”, FIG. 7 shows the propagation path difference Δr and the phase difference Δφ under the same conditions as FIG. This is a comparison between “detection object” and “low-profile detection object”. In FIG. 7A, the magnitude of Δr is “normal detection target” >> “low profile detection target”. Inevitably, the fluctuation amount of Δφ is also “normal detection target” >> “low profile detection target”.

  Accordingly, in FIG. 7B, the variation amount of sin (Δφ) when the distance is changed is “normal detection target” >> “low profile detection target”. The number of occurrences of “strengthening points” and “points to cancel” is determined by the amount of change in Δr when the distance changes, that is, the amount of change in the phase difference Δφ when the distance changes.

  In particular, in the range where d1 is about 30 [m], which is the main use range of on-vehicle radars, and the maximum value of d1 is about a few hundred tens of meters, in the case of normal detection objects, “strengthening points” and “cancellation” The “matching point” occurs several times and has a bandwidth of several meters and tens of meters. On the other hand, in the low-profile detection object, the “strengthening points” and “spotting points” occur once each and have a bandwidth of several tens of meters and several hundreds of meters. As mentioned above, a remarkable difference is recognized. The discrimination algorithm for the low-profile detection object of the present invention is based on the principle of discriminating the difference between the number of occurrences and the bandwidth.

<Distinguishing algorithm for low-profile objects>
Next, an outline of a discrimination algorithm for the low-profile detection object will be described. As a method for discriminating between a normal detection object and a low-profile detection object, a method using an area of an area determined by using a reception power curve and a straight line having a vertical axis value as a section average value of reception power will be described. .

First, as shown in FIG. 8, the area calculation unit 28 divides the direct distance d1 between the radar and the detection target into arbitrary N sections (Δd ₁ ,..., Δd _N ). For example, the section is divided at an interval of a distance of 5 [m].
The area calculation unit 28 calculates the area of a region defined by the boundary between the reception power curve 81 and a straight line having the value of the vertical axis as the average value of the reception power in each section. Specifically, for example, in the section 82, the sum of the areas of the region 83 and the region 84 is calculated.

As shown in FIG. 8, the area calculation unit 28 calculates an average power Mean within each section, and calculates a power obtained by subtracting the average power from the received power for each section (hereinafter referred to as normalized power). For example, if there are n points of received power P (Δd _{k, i} ) (i is an integer from 1 to n) in the interval Δd _k (k is an integer from 1 to N), the normalized power p (Δd _{k, i} ) [dB] is expressed by the following equation (1) using subtraction in decibel notation (division for linear values).

Next, FIG. 9 shows the distance characteristics of the normalized power. As shown in FIG. 9, the normalized power curve 91 crosses zero [dB]. Here, in FIG. 10A, focusing on the Δd _k section, the normalized power includes a positive region 101 and a negative region 102.
As shown in FIG. 10B, the area calculation unit 28 calculates the absolute value | p (Δd _{k, i} ) | of the standardized power, and integrates the absolute value of the standardized power within the interval. A closed section (for example, areas 103 and 104 filled in FIG. 10B) is defined.

  FIG. 11 is an enlarged view of the area 103 in FIG. The absolute value 111 of the normalized power can be approximated by a quadratic function 112. The area calculation unit 28 calculates the approximate area of the region 103 in FIG. 11 using the Simpson formula.

Specifically, using the Simpson formula, the area s _{Δd (k, i)} of the region 103 includes the end point 113 (d1 = Δd _{k, i} ), the end point 115 (d1 = Δd _{k, i + 1} ), and An approximation can be made using the distance d1 of the intermediate point 114 (d1 = (Δdk _{, i} + Δdk _{, i + 1} ) / 2) and the value of each normalized power p (d1). Therefore, the area calculation unit 28 approximates the area of the region 103 using only the values of the three coordinates, and calculates using the following equation (2).

The area calculation unit 28 repeats the series of processes described above _, and sequentially adds the calculated area s _{Δd (k, i)} to the received power integral value S to calculate the received power integral value S. The above processing is expressed by the following formula (3).

The area calculation unit 28 stores the received power integral value S that is sequentially updated in the memory 21.
FIG. 12A shows the received power 121 of the normal detection target and the average value Ma of the section. The area of the region determined by the straight line of the reception power curve 121 of the normal detection object and the average value Ma of the section increases as the reception power of the normal detection object changes steeply.

  The above will be described with a specific example. For example, the area calculated in the section 122 is compared with the area calculated in the section 123. The area calculated in the section 122 is the sum of the area of the region 122a and the area of the region 122b. On the other hand, the area calculated in the section 123 is the sum of the area of the region 123a and the area of the region 123b.

As apparent from FIG. 12, the region 123a is longer in the vertical axis direction than the region 122a, and thus the region 123a has a larger area than the region 122a. Similarly, since the region 123b is longer in the vertical axis direction than the region 122b, the region 123b has a larger area than the region 122b.
As described above, in the section where the received power changes sharply, the calculated area increases because the change range of the received power is large.

  On the other hand, FIG. 12A shows the received power 124 of the low-profile object and the average value Mb of the section. The received power of the low-profile object is smoothly changed in all the sections and is not abruptly changed. Therefore, in any section, the curve of the received power 124 of the low-profile object and the average value Mb of the sections. The area of the region defined by the straight line becomes smaller.

Therefore, the sum of the areas of the areas determined by the straight line of the received power curve of the normal detection object and the average value Ma of the section, and the area of the area determined by the straight line of the received power curve of the low detection object and the average value Mb of the section When the sum of the areas is compared, the sum of the areas of the areas determined by the curve of the received power of the normal detection object and the straight line of the average value Ma of the sections becomes larger.
From the above, the number of occurrences is represented by an index called the area of the region determined by the straight line of the received power curve of the normal detection object and the average value of the section.

In the above embodiment, the area is calculated using the horizontal axis as the distance, but the area may be calculated by replacing the horizontal axis with time.
Further, in the above embodiment, a straight line having the vertical axis value as the average value of the received power section is used as one boundary when calculating the area, but the boundary line is the vertical axis value. Any straight line with a predetermined value may be used. For example, the straight line may be a straight line having the vertical axis value as the minimum value of the section, a straight line having the vertical axis value as the maximum value of the section, or a straight line having the vertical axis value as the median value of the section.

  For the verification, as an example, the area of the region defined by the boundary between the received power curve and the straight line with the vertical axis value as the minimum value of the interval in a certain section is compared with the case of the normal detection object and the low profile detection object. Compare in case of things. In FIG. 13A, the area of the received power 131 in the case of the normal detection target in a certain section is represented by a region 132.

  On the other hand, in FIG. 13B, the area of the received power 133 in the case of a low profile detection target in a certain section is represented by a region 134. Since the change amount of the standardized power in the case of the normal detection target is larger than the change amount of the standardization power in the case of the low-profile detection target, the area of the region 132 is larger than the area of the region 134.

  Therefore, the number of occurrences is represented by an index called an area of an area determined by using a reception power curve and a straight line having a value on the vertical axis as the minimum value of the section. In addition, the area of the region defined by the boundary between the received power curve and a straight line having another predetermined value (for example, the maximum value of the section or the median value of the section) is also generated based on the same principle. An index that reflects the number.

  In the above-described embodiment, a straight line having the vertical axis value as the average value of the received power is used as one boundary when calculating the area. However, the boundary line may be a curve. For example, the curve may be a free space propagation attenuation curve. For the verification, the area of the region defined by the reception power curve and the free space propagation attenuation curve as a boundary in a certain section is compared between the case of the normal detection object and the case of the low-profile detection object.

  In FIG. 13C, in the case of a normal detection target, the area of the region defined by the reception power curve 136 and the free space propagation attenuation curve 135 as a boundary in a certain section is the sum of the area of the region 136a and the area of the region 136b. expressed. On the other hand, in the case of a low-profile detection object, the area of a region determined by using the received power curve 137 and the free space propagation attenuation curve 135 as a boundary in a certain section is represented by the sum of the area of the region 137a and the area of the region 137b.

  As is clear from FIG. 13C, the area calculated for the normal detection object is larger than the area calculated for the low-profile detection object. Therefore, when calculating the area, the boundary line may be a curve.

The curve serving as the boundary is not limited to the free space propagation attenuation curve, but may be an approximate curve for the received power characteristic of a certain object using a several-order least square method. Further, the line serving as the boundary may be a predetermined downward-sloping line (including straight lines and curves).
Therefore, when calculating the area, the line serving as the boundary may be a straight line or a curved line, and may be a predetermined line determined in advance.

<Integration range during low-profile detection object discrimination processing>
Next, the specification of the integration range will be described with reference to FIG. 14 in order to improve the efficiency and accuracy of the low-profile detection target discrimination process. In FIG. 14, 141 is a detection threshold value, 142 is a reception power curve of a normal detection object, 143 is a theoretical curve of reception power due to free space propagation attenuation, 144 is a reception power curve of a low-profile object, and 145a is from Δd ₁ to Δd. The integration range up to _N , 145b is the area that cancels over the widest range, and 145c is the neighborhood.

The low-profile detection object has a low feedback power value because the radar reflection cross-sectional area is narrow. In order to suppress the calculation amount as much as possible, the area calculation unit 28 sets a starting point at a position estimated to exceed the detection threshold in advance. For example, assume that the integration start position is Δd ₁ in FIG.
The area calculation unit 28 refers to the result calculated under the maximum height condition assumed for the low-profile detection object, and from the portion 145b that cancels over the widest range existing in the longest distance assumed in the field of view of the radar. Determine the end point at a distance.

For example, the integration end position and [Delta] d _N of FIG. Therefore, the area calculation unit 28 calculates the area of the normalized power in the integration range 145a from Δd ₁ to Δd _N.
Further, in the vicinity region 145c where the distance is 20 [m] or less, the antenna directivity starts to appear remarkably, and the aspect of the propagation characteristics changes greatly, so it is excluded from the integration interval.

<Integration result of low-profile detection target discrimination process>
FIG. 15 is an example of an integration result of the low-profile detection target discrimination process. When attention is paid to a section indicated by an arrow near the distance d1 of 47 [m], it can be seen that there is a sufficiently large difference (up to 10 to 30 times) even in a numerical comparison limited to one closed section.

  The area calculation unit 28 sequentially adds the section area to the sum of the section areas, and stores the sum of the added section areas in the memory 21. The detection processing unit 29 reads the sum of the section areas from the memory 21. When the sum of the section integration values exceeds a predetermined threshold, the detection processing unit 29 determines the target object as a normal detection target and uses the determination result as a target output process. To the unit 30.

  Thus, by making a determination based on the sum of the interval integral values, the difference between the normal detection object and the low-profile detection object can be expressed more greatly, so that it is possible to make a highly accurate determination with a large margin.

The detection processing unit 29 may determine that the object is a normal detection object when any of the interval integral values exceeds a predetermined threshold.
Thereby, since it can determine before calculating all the integral values of a section, even when the distance of a radar and a target object is separated, it can determine with a normal detection target object. As a result, the subsequent deceleration of the vehicle and the avoidance action of the object can be performed with sufficient time.

Moreover, the detection process part 29 may determine the said target object as a normal detection target, when the frequency | count that the said area integral value exceeds a predetermined threshold value exceeds the preset frequency | count.
Thereby, since it can determine before calculating all the integral values of a section, even when the distance of a radar and a target object is separated, it can determine with a normal detection target object. As a result, the subsequent deceleration of the vehicle and the avoidance action of the object can be performed with sufficient time.

  Next, the target extraction process will be described with reference to the flowchart of FIG. The signal processing unit 20 stores the beat signal for each channel corresponding to each of the receiving antennas 11 to 1n subjected to the AD conversion in the memory 21 (step S161). Next, the reception power calculation unit 22 performs Fourier transform on the beat signal for each channel corresponding to each of the reception antennas 11 to 1n, and calculates the signal level (step S162).

  The received power calculation unit 22 outputs a value obtained by performing Fourier transform in the time direction for each antenna to the DBF processing unit 23. The received power calculation unit 22 outputs the frequency modulation width Δf, the rising object frequency, and the falling object frequency to the distance detection unit 24. Also, the received power calculation unit 22 outputs the center frequency f0, the object frequency of the rising portion, and the object frequency of the falling portion to the speed detection unit 25. The received power calculation unit 22 outputs the received power as a function of distance to the area calculation unit 28. Further, when the received power intensity cannot be detected, the received power calculation unit 22 outputs to the target output processing unit 30 that there is no target candidate.

  Next, the DBF processing unit 23 further performs a Fourier transform in the time direction of the antenna for each antenna input from the received power calculation unit 22, and further performs a Fourier transform in the antenna arrangement direction, for each angle channel corresponding to the angular resolution. A spatial complex number is calculated and output to the bearing detection unit 26 for each beat frequency (step S163).

  Next, the distance detection unit 24 calculates the distance from the frequency modulation width Δf input from the received power calculation unit 22, the target frequency of the rising portion, and the target frequency of the lowering portion (step S164). Further, the speed detector 25 calculates a relative speed from the center frequency, the rising object frequency, and the falling object frequency input from the received power calculator 22 (step S164).

  Next, the direction detection unit 26 outputs the angle having the largest amplitude among the calculated spatial complex numbers for each beat frequency to the target takeover processing unit 27 as the direction in which the target exists (step) S165).

  Next, the target takeover processing unit 27 calculates the object distance, relative speed, and azimuth value calculated this time, and the object distance, relative speed, and azimuth value calculated one cycle before read out from the memory 21. If the absolute value of each difference is smaller than the value determined for each value, the object detected one cycle ago and the object detected this time are determined to be the same, and the object in the memory Are updated, and the identification number of the object is output to the area calculation unit 28 (step S166).

  Next, the area calculating unit 28 receives received power that is a function of the distance output from the received power calculating unit 22. The area calculation unit 28 calculates an area of a region defined by a curve representing the function and a straight line determined based on an average value of the received radio wave power in a predetermined distance section. The area calculation unit 28 sequentially adds the section area to the sum of the section areas calculated so far, and stores the sum of the section areas after the addition in the memory 21.

  The detection processing unit 29 reads the sum of the section areas from the memory 21, determines whether or not the object is a low-profile object based on the sum of the areas, and the object is a low-profile object. Or information indicating whether the object is a normal detection object is output to the target output processing unit 30 (step S167).

  Next, when the target is a normal detection target, the target output processing unit 30 outputs the identification number of the target as a target (step S168). The target output processing unit 30 receives the determination results of a plurality of objects, and when both of them are normal detection objects, outputs the identification number of the object on the lane of the own vehicle as a target.

  Further, the target output processing unit 30 receives the determination results of a plurality of objects, both of which are normal detection objects, and when two or more objects are on the lane of the own vehicle, The identification number of the target with a large number of target takeover processes read from the memory 21 is output as a target. Above, this flowchart is complete | finished.

Next, details of the low-profile detection target discrimination process in the area calculation unit 28 and the detection processing unit 29 will be described with reference to the flowchart of FIG.
First, the area calculation unit 28 designates an integration range for the direct distance d1 between the radar and the object (step S171). Next, the area calculation unit 28 divides the direct distance d1 between the radar and the object into arbitrary sections (step S172).

Next, steps S163 to S167 shown below are repeated as long as the direct distance d1 between the radar and the object is within the integration range specified in step S161.
First, the area calculation unit 28 calculates an average of received power in the section (hereinafter referred to as average received power) (step S173). Next, the area calculation unit 28 calculates the normalized power by subtracting the average received power from the received power in the section (step S174).

  Next, the area calculating unit 28 converts the normalized power into an absolute value, and extracts a closed section surrounded by the curve of the normalized power of the normalized power and the axis of the distance d1 (step S175). Next, the area calculation unit 28 calculates the area of the extracted closed section (step S176). Next, the area calculation unit 28 reads the sum of the areas calculated up to the previous loop from the memory 21, adds the calculated area to the sum of the areas calculated up to the previous loop, The sum of the areas is stored in the memory 21 (step S177). When the area calculation unit 28 finishes adding the areas calculated in all the sections to the sum of the areas, this loop ends.

When the calculated area sum is larger than a predetermined threshold (step S178 YES), the detection processing unit 29 determines that the detected object is a normal detection object (step S179a) and is a normal detection object. Information is output to the target output processing unit 30.
On the other hand, when the sum of the calculated areas is equal to or less than a predetermined threshold (NO in step S178), the detected object is determined as a low-profile object (step S179b), and information indicating that the object is a low-profile object is obtained. The data is output to the mark output processing unit 30. Above, this flowchart is complete | finished.

  In this embodiment, the received power is calculated as a function of distance, but the present invention is not limited to this and may be a function of time. For example, when the target object is stopped, the distance between the radar and the target object decreases with time. As a result, when the received power is expressed as a function of time, the sum of the areas of the areas defined by the received power curve from the low-profile detection object as one boundary is equal to the received power curve from the normal detection object. It becomes smaller than the sum of the areas of the regions determined as the boundaries. Therefore, the detection processing unit 29 can determine whether the object is a low-profile object based on the difference in the sum of the areas.

  In this embodiment, the electronic scanning radar apparatus has been described. However, the present invention is not limited to this, and a mechanically operated radar apparatus may be used. This is because the change in the received power with respect to the distance when using the mechanically operated radar device is equivalent to the change in the received power with respect to the distance when using the electronic scanning radar device.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design etc. of the range which does not deviate from the summary of this invention are included.

11, 1n receiving antenna 21, 2n mixer
3 Transmitting antenna
4 distributor
51, 5n filter
6 SW
7 ADC
8 Control unit
9 Triangular wave generator 10 VOC
20 Signal processing unit 21 Memory 22 Received power calculation unit 23 DBF processing unit 24 Distance detection unit 25 Speed detection unit 26 Direction detection unit 27 Target takeover processing unit 28 Area calculation unit 29 Detection processing unit 30 Target output processing unit

Claims (11)

A transmitting antenna that transmits radio waves,
A receiving antenna that receives the radio wave reflected by the object,
A distance detector for detecting a distance to the object based on the received radio wave;
A received power calculation unit that calculates power of the received radio wave as a function of the detected distance;
An area calculation unit that calculates an area of a region that is defined with a curve representing the function as one boundary in a predetermined distance section;
A detection processing unit for determining whether or not the object is a low-profile detection object based on the calculated area;
A radar apparatus comprising:   The radar apparatus according to claim 1, wherein the detection processing unit calculates the area based on the intensity of the received wave only when the distance is within a predetermined range. A transmitting antenna that transmits radio waves,
A receiving antenna that receives the radio wave reflected by the object,
A received power calculation unit that calculates the power of the received radio wave as a function of time;
An area calculating unit that calculates an area of a region that is defined with a curve representing the function as one boundary in a predetermined time interval;
A detection processing unit for determining whether or not the object is a low-profile detection object based on the calculated area;
A radar apparatus comprising:   The radar apparatus according to claim 3, wherein the detection processing unit calculates the area based on the intensity of the received wave only when the time is within a predetermined range.   5. The area calculation unit calculates an area of a region determined by using the curve and a predetermined straight line as a boundary, or an area of a region determined by using the curve and the predetermined curve as a boundary. The radar device according to any one of the above.   6. The area calculation unit according to claim 1, wherein the area calculation unit calculates an area of a region determined by using the curve and a straight line determined based on an average value of the received radio wave power as a boundary. The radar device described in 1.   The said detection process part determines the said target object as a normal detection target, when the sum of the several area of the said area exceeds a predetermined threshold value, The said detection object is any one of Claims 1-6 characterized by the above-mentioned. Radar device.   The said detection process part determines the said target object as a normal detection target, when either of the said areas of several areas exceeds a predetermined threshold value, The said target object is any one of Claims 1-7 characterized by the above-mentioned. Radar equipment.   9. The detection unit according to claim 1, wherein the detection processing unit determines that the object is a normal detection object when the number of times that the area exceeds a predetermined threshold exceeds a preset number of times. A radar device according to claim 1. A first step of detecting a distance to the object based on radio waves received by a receiving antenna;
A second step of calculating the power of the received radio wave as a function of the detected distance;
A third step of calculating an area of a region defined by a curve representing the function as one boundary in a predetermined distance section;
A fourth step of determining whether or not the object is a low-profile detection object based on the calculated area;
A computer program for causing a computer to execute. A first step of calculating the power of the received radio wave as a function of time;
A second step of calculating an area of a region defined by a curve representing the function as one boundary in a predetermined time interval;
A third step of determining whether or not the object is a low-profile detection object based on the calculated area;
A computer program for causing a computer to execute.

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