JP2020159980A - Radar device and target detection method - Google Patents

Abstract

To provide a radar device with which both short range and long range detections are achieved and a short range resolution is improved.SOLUTION: A radar device 1 pertaining to the present invention detects a target using an electromagnetic wave. This radar device comprises: a transmit unit 2 for transmitting a first pulse and a second pulse the amplitude and pulse width of which are larger than the first pulse; a receive unit 3 for receiving the reflected waves of the first and second pulses transmitted by the transmit unit 2 and reflected by a target; and a detection unit 4 for detecting the target on the basis of reflected wave signals of the reflected waves received by the receive unit 3. The transmit unit 2 forms the waveforms of the first and second pulses so that the rise time of the first pulse is smaller than the rise and fall times of the second pulse.SELECTED DRAWING: Figure 1

Description

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

In recent years, the use of radar devices for detecting surrounding objects (targets) such as peripheral monitoring for automobiles and ADAS (advanced driver assistance system) has been expanding. In particular, an automobile radar device is also required to detect a distant target and to detect a nearby target. When detecting a nearby target, an automobile radar device is required to accurately detect the position of a pedestrian or the like to prevent a collision, or to accurately detect the arrangement of surrounding obstacles when parking. Will be done. While it is required to be able to accurately detect the presence or absence of a long-distance target, it is necessary to identify the more accurate position and especially the recent contact point, especially for the position of a short-distance target.

Regarding a radar device that can be used for automobiles, Patent Document 1 describes data at a plurality of distance positions (distance bins) by transmitting a pulse signal having a small pulse width and performing equivalent sampling of this pulse waveform on the receiving side. The technology for disassembling and checking is disclosed. Further, Patent Document 2 discloses a technique in which a pulse signal having a high rising and falling speed is formed on the transmitting side and a target is detected on the receiving side by using a differential value of the received waveform. Further, in Patent Document 3, while keeping the pulse width on the transmitting side sufficiently wide, the receiving side performs an extremely narrow amplitude modulation on the order of 1/10 of the pulse width on the transmitting side, and shifts the timing on the receiving side. The technology to make it is disclosed.

Japanese Unexamined Patent Publication No. 2010-216980 JP-A-2002-365362 Japanese Unexamined Patent Publication No. 2016-516995

It is difficult to separate a plurality of targets, especially when the difference in the distances of the plurality of targets from the radar device is smaller than the resolution of the radar device. For example, when the radio wave reflection intensity of a distant target is high, the reflected wave of the near target is buried in the reflected wave of the distant target, and the near target cannot be separated and detected. there is a possibility. In particular, in the detection of nearby targets by a radar device for automobiles, the nearest target is reliably detected without being affected by the surroundings, such as obstacle detection when parking, and the distance to the target is determined. Accurate detection is often required.

The radar devices described in Patent Documents 1 to 3 are based on a single pulse pattern shaping, and problems are assumed regarding compatibility between saturation avoidance of nearby objects and detection of distant weak objects.

Further, it is possible to detect a weak object by making the rising edge of the transmission pulse steep, but this is not preferable because the frequency band of the transmission pulse is widened and there is a concern about the influence on peripheral devices.

Further, in Patent Documents 2 and 3, the transmission pulse width is set to be relatively wide with respect to the rise time, and when a plurality of targets are present in the vicinity of the vehicle, the separation of these targets, particularly It can be difficult to detect a distant target.

Further, when the receiving side is operated at high speed as disclosed in Patent Document 1 and the like, there is a concern about the influence of noise generation, which is not preferable.

In view of such circumstances, it is an object of the present invention to provide a radar device and a target detection method that achieve both long-distance and short-distance detection and improve short-distance resolution.

The radar device according to the present invention is a radar device that detects a target using radio waves, and has a transmission unit that transmits a first pulse and a second pulse having a larger amplitude and pulse width than the first pulse. The target is detected based on the receiving unit that receives the reflected wave by the target of the first pulse and the second pulse transmitted by the transmitting unit and the reflected wave signal of the reflected wave received by the receiving unit. The transmission unit includes a detection unit, and the transmission unit forms the waveforms of the first pulse and the second pulse so that the rise time of the first pulse is smaller than the rise and fall times of the second pulse. ..

The target detection method according to the present invention is a method of detecting a target using radio waves, and includes a step of transmitting a first pulse and a second pulse having a larger amplitude and pulse width than the first pulse. The target is detected based on the step of receiving the reflected wave by the target of the first pulse and the target of the second pulse transmitted in the transmission step and the reflected wave signal of the reflected wave received in the receiving step. The waveforms of the first pulse and the second pulse are formed so that the rise time of the first pulse is smaller than the rise and fall times of the second pulse in the transmission step. Target detection method.

According to the present invention, it is possible to provide a radar device and a target detection method that achieve both long-distance and short-distance detection and improve short-distance resolution.

It is a block diagram which shows the structure of the radar apparatus of one Embodiment of this invention. It is a figure which shows the pulse waveform transmitted by the transmission part of the radar apparatus of FIG. It is a figure which illustrates the waveform of the reflected wave of the 1st pulse received by the receiving part of the radar apparatus of FIG. It is a figure which shows the formation process of the waveform signal of the 1st pulse in the transmission part of the radar apparatus of FIG. It is a figure which shows the change of the inclination of the reflected wave signal of FIG. It is a figure which illustrates the waveform of the reflected wave of the 1st pulse different from FIG. It is a figure which shows the change of the inclination of the reflected wave signal of FIG. It is a figure which shows the equivalent time sampling in the radar apparatus of FIG. It is a flowchart which shows the procedure of the target detection method of one Embodiment of this invention performed by the radar apparatus of FIG. It is a block diagram which shows the structure of the radar apparatus of the 2nd Embodiment of this invention. It is a figure which illustrates the intensity distribution for every angle and distance of the reflected wave signal in the radar apparatus of FIG. It is a figure which shows the angular peak in the intensity distribution of FIG. It is a figure which illustrates the intensity distribution for every angle and distance in the case where the angular resolution is lower than FIGS. 11 and 12 in the radar apparatus of FIG. It is a figure which shows the waveform of the reflected wave of the 1st pulse at the angle | angle peak of the intensity distribution of FIG. It is a figure which shows the intensity change and the determination index value for each reflected wave signal distance of FIG. It is a figure which shows the angle difference value at each angle peak of the intensity distribution of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a radar device 1 according to a first embodiment of the present invention.

The radar device 1 of the present embodiment is a device that detects a target using radio waves. The radar device 1 repeatedly transmits the first pulse P1 as shown in FIG. 2 and the second pulse P2 having a larger amplitude and pulse width than the first pulse P1 at the first timing having the first interval. A detection unit that detects a target based on a unit 2 and a reception unit 3 that receives the reflected waves of the first pulse and the second pulse targets transmitted by the transmission unit 2 and a reflected wave signal received by the reception unit 3. A control unit 5 for controlling a transmission unit 2, a reception unit 3, and a detection unit 4 is provided.

In the radar device 1, the first pulse P1 is used to detect a target existing at a relatively short distance, and the second pulse P2 is used to detect a target existing at a relatively long distance. Used. The first pulse P1 is detected as separate targets with resolution (when the distances of a plurality of targets from the radar device 1 are close, typically when a plurality of targets are close to each other). The pulse width is set to be relatively small so that the ability to perform) can be improved, and the pulse is set to have a relatively small amplitude so that the received intensity of the reflected wave of the target becomes large and is not saturated in the receiving system. On the other hand, the second pulse P2 has a relatively large amplitude and a relatively large pulse width in order to detect the existence of a distant target with high sensitivity while the distance attenuation is large and the reception intensity is small. It is said to be a pulse.

The transmission unit 2 includes an oscillation unit 21 that generates a local transmission signal having a predetermined carrier frequency, a waveform formation unit 22 that forms the waveform signals of the first pulse P1 and the second pulse P2, and a station transmission generated by the oscillation unit 21. It has a gain control unit 23 that amplifies the waveform signal formed by the waveform forming unit 22 by multiplying the number, and a transmitting antenna 24 that converts a signal output from the gain control unit 23 into radio waves and transmits the signal.

The oscillator 21 may have a well-known oscillator. Further, the oscillation unit 21 can generate a local signal according to the control of the control unit 5.

The waveform forming unit 22 forms a waveform signal that defines the waveforms of the first pulse P1 and the second pulse P2 so that the rise time of the first pulse P1 is smaller than the rise time and the fall time of the second pulse P2. Further, the waveform forming unit 22 sets a waveform signal that determines the waveforms of the first pulse P1 and the second pulse P2 so that the rising slope of the first pulse P1 becomes larger than the rising and falling slopes of the second pulse P2. It is preferable to form. The “rise time” and “fall time” mean the time when the value increases from 10% to 90% of the peak value and the time when the value decreases from 90% to 10% of the peak value. The slope of rising (falling) is divided by the time it takes to increase (decrease from 90% to 10%) the value of 80% (90% -10%) of the peak value from 10% to 90% of the peak value. It shall mean the value (absolute value).

As described above, since the pulse width of the first pulse P1 is relatively narrow, the first pulse P1 is a target even if there are a plurality of targets existing in the vicinity of the radar device 1 and the difference in distance between them is small. The radio waves reflected by the radar device can be received by the radar device and can be separated into electric signals as a plurality of targets. Further, by reducing the rise time of the first pulse P1, it is possible to prevent the target closer to the distant target from being buried and becoming indistinguishable.

Further, if the rise time and the fall time are reduced in the waveform of the transmitted radio wave, the frequency band of the radio wave transmitted from the oscillating unit 21 tends to be widened. However, for the purpose of accurately detecting the position (recent contact point) of the target closest to the radar device, it is relatively small only for the first pulse P1 whose output is relatively small, and only for the rise time. Since the spread of the frequency band can be suppressed, the influence on peripheral devices can be suppressed.

As shown in FIG. 4, the waveform forming unit 22 forms two original waveform signals having different rising times (the first original waveform signal U1 having a large rising time and the second original waveform signal V1 having a short rising time). Can be. The waveform forming unit 22 can form the waveform signal W1 that determines the waveform of the first pulse P1 by shifting and multiplying the two original waveform signals U1 and V1 having different rise times. The first original waveform signal U1 and the second original waveform signal V1 are staggered and multiplied so that the rising edge of the pulse of the second waveform signal is superimposed on the pulse of the first original waveform signal U1 and the falling edge is not superimposed. The waveform signal W1 for generating the first pulse P1 having a relatively short rise time and a large fall time can be formed relatively easily.

When the waveform signal W1 of the first pulse P1 is formed by shifting and multiplying the first original waveform signal U1 and the second original waveform signal V1, the first pulse at the peak of the first original waveform signal U1 having a large rise time. It is preferable to multiply the two original waveform signals U1 and V1 so that the waveform signal W1 of P1 has a value (the second original waveform signal V1 has a value). More preferably, it is more preferable to multiply the two original waveform signals U1 and V1 so that the waveform signal W1 of the first pulse P1 becomes the maximum value at the peak of the first original waveform signal U1 having a large rise time. As a result, the asymmetric chevron waveform signal W1 whose rise time is smaller than the fall time can be formed relatively accurately and efficiently.

Further, the waveform forming unit 22 obtains a first original waveform signal U2 having a large rise time and a second original waveform signal V2 having a small rise time, which is the maximum value while at least the first original waveform signal U2 has a value. By multiplying, the waveform signal W2 of the second pulse P2 having a relatively large rise time and fall time can be formed.

The two original waveform signals U1 / V1 and U2 / V2 having different rise times can be formed by circuits having different time constants from each other. That is, the first original waveform signals U1 and U2 having a small rise time can be mountain-shaped or sine wave-shaped pulse signals output from a circuit having a large time constant, and the second original waveform signals V1 and V2 having a short rise time can be obtained. Can be a trapezoidal pulse signal output from a circuit having a small time constant. As a result, the waveform signal W1 having a small amplitude and a small pulse width for the vicinity and the first transmission generated based on the waveform signal W1 where the resolution is most required to be secured by adjusting the time control. A steep rise can be selectively formed in the pulse P1 relatively easily and accurately.

The gain control unit 23 forms a power signal to be supplied to the transmitting antenna 24 by amplifying the local signal generated by the oscillation unit 21 at an amplification factor proportional to the waveform signal formed by the waveform forming unit 22. A well-known amplifier circuit can be used as the gain control unit 23.

The transmitting antenna 24 transmits the power signals of the first pulse P1 and the second pulse P2 supplied from the gain control unit 23 as electromagnetic waves. A well-known antenna can be used as the transmitting antenna 24.

The receiving unit 3 passes through the receiving antenna 31 that receives electromagnetic waves, the mask unit 32 that can pass or block the received electric signal, the mixer unit 33 that downconverts the electric signal that has passed through the mask unit 32, and the mask unit 32. It also has an AD conversion unit 34 that converts the intensity signal extracted by the mixer unit 33 into a digital signal.

The receiving antenna 31 receives the reflected waves in the targets of the first pulse P1 and the second pulse P2 transmitted by the transmitting antenna 24 and uses them as electric signals (reflected wave signals). A well-known antenna can be used as the receiving antenna 31.

The mask unit 32 passes the reflected wave signal of the first pulse P1 for a limited time at regular time intervals (a part of the reflected wave signal of the first pulse P1 is synchronized with the second timing having the second interval). Let me. On the other hand, the mask unit 32 passes the reflected wave signal of the second pulse P2 as a whole. That is, as shown in the gain setting signal of FIG. 8, the mask unit 32 substantially receives the first pulse P1 from the start of the transmission of the first pulse P1 to the start of the transmission of the second pulse P2. During the period, the electric signal is passed at regular time intervals for a limited time (with a mask width equal to or less than the pulse width of the first pulse P1), and after the transmission of the second pulse P2 is started, the electric signal is continuously transmitted. Pass (pass the reflected wave signal of the second pulse P2). Such a mask unit 32 is configured so that the receiving antenna 31 can select whether to pass or block the electric signal due to the reflected wave received. As a result, the sensitivity is ensured by not losing the second pulse P2 at a long distance where the distance attenuation is large, and at a short distance where the SN is abundant, the resolution is increased by the blocking operation of the first pulse P1 and the mask portion 32 as described later. It can be secured.

Specifically, the mask unit 32 forms a gain control unit 321 that amplifies or attenuates the electric signal output from the receiving antenna 31, and a square wave or trapezoidal gain setting signal that sets the gain of the gain control unit 321. It can be configured to have a gain setting unit 322 to be used. The gain setting unit 322 forms a gain setting signal at an appropriate timing for the transmission of the first pulse P1 and the second pulse P2 of the transmission unit 2 by being controlled by the control unit 5. Further, a configuration in which the gain control unit 321 is directly controlled by a rectangular wave or a trapezoidal high-speed control signal directly from the control unit is also preferable.

The AD conversion unit 34, which will be described later, has an operating speed that is not sufficiently faster than the rate of change in the intensity of the first pulse P1. In addition, a low-pass filter may be loaded in any of the stages prior to the AD conversion unit 34 (for example, between the AD conversion unit 34 and the mixer unit 33). Therefore, when the reflected wave signal of the first pulse P1 is passed as it is, the band is limited by the action of the low-pass filter or the AD conversion unit 34, and the digital conversion is performed with the waveform in the state where the rising signal is blunted. .. That is, even if the signals are separated by a high-speed rise, the waveform may be blunted due to these band restrictions, and the signals of the peripheral time may be averaged, which may make separation difficult. Therefore, the signal separated by the mask unit 32 can be selected by cutting the electric signal in a limited time by the mask unit 32 at least in the previous stage under these band restrictions. As a result, the influence of the reflected wave signal of the first pulse P1 at a specific time (that is, a specific distance) is reduced by the reflected wave signal existing at the surrounding time (that is, the reflected wave signal caused by the target existing in the surrounding area). The AD conversion unit 34 can convert the data into digital data. In this way, the time resolution and the distance resolution can be maintained by performing the operation of cutting out the time in the mask unit 32 in a limited manner. There may be a delay in signal transmission from the mask unit 32 to the AD conversion unit 34 due to the intervention of a circuit such as a low-pass filter. In that case, the gain setting signal of the mask unit 32 and AD conversion shown in FIG. 8 may occur. The unit 34 is not synchronized in absolute time, but is synchronized in a state where the gain setting signal of the mask unit 32 is offset so that the detected value in the AD conversion unit becomes sufficiently large, more preferably the maximum, in consideration of the delay. Is preferable. As a result, the SN can be increased even when there is a circuit delay.

The mask unit 32 controls the signal passage timing to be relatively shifted with respect to the plurality of first pulses P1 in synchronization with the AD conversion unit 34. In such a case, it is preferable to relatively shift the repeatedly transmitted transmission pulse with respect to the basic clock of the AD conversion unit. As a result, the waveforms of the reflected wave signals of the first pulse P1 are relatively shifted, signals at different timings are converted into digital data by the AD conversion unit 34, and the detection unit 4 combines these digital data to obtain the first pulse. Equivalent time sampling can be performed by using a sampling signal slower than the AD conversion speed of the pulse P1 as a more detailed time waveform, that is, a detailed distance waveform.

The gain rise time of the mask portion 32 is preferably equal to or less than the rise time of the first pulse P1, and the limited passing gain width of the mask portion is preferably equal to or less than the pulse width of the first pulse P1. .. It is more preferable that the gain waveform is rectangular wavy or trapezoidal. By doing so, it is possible to reduce the error in the intensity of the reflected wave signal sampled. Either the pulse operation on the transmitting side or the mask operation on the receiving side, whichever is slower and has a wider time width, may cause a decrease in resolution, but at least the operation of the mask unit 32 does not affect the emission of electromagnetic waves, so the gain The rise / fall time and gain width of the above can be increased in speed and resolution while reducing the influence on the surrounding equipment. That is, in order to obtain the same resolution, the rise time and pulse width of the first pulse P1 are set to be equal to or relatively larger than the rise and fall time and gain width of the gain of the mask portion 32, so that they are emitted as electromagnetic waves. Since the expansion of the frequency band of the first pulse P1 to be performed can be suppressed, the influence on surrounding devices can be suppressed.

The mixer unit 33 uses the local signal generated by the oscillating unit 21 to remove the frequency component of the carrier wave from the signal that has passed through the mask unit 32, so that the analog signal representing the intensity change of the reflected wave signal, that is, the envelope Extract the waves.

The AD conversion unit 34 converts the analog signal output from the mixer unit 33 into a digital signal and provides it to the detection unit 4. The AD conversion unit 34 can be configured by a well-known AD converter.

The detection unit 4 reflected the first pulse P1 and the second pulse P2 transmitted by the transmission unit 2 by accumulating the digital data input from the AD conversion unit 34 and analyzing the change over time of the reflected wave signal. Specify the position of the target (target detection process). The detection unit 4 can be configured by an arithmetic unit having a CPU, FPGA, memory and the like. The calculation procedure for the detection unit 4 to analyze the change over time of the reflected wave signal is described in the program and stored.

A specific example of the contents of the calculation is shown as a result of the phenomenon obtained by the above configuration and the detection result. In FIG. 3, the receiver 3 when there is only one target in the near area and when there are two targets in the near area and the target on the far side is larger (easily reflects radio waves). An actual measurement example of the intensity (amplitude) of the reflected wave signal received by is shown. As shown in the figure, due to the short rise time of the first pulse P1, the intensity of the reflected wave signal of the first pulse P1 by the target farther from the two targets existing in the vicinity region of the radar device 1 is large. Even in this case, a region having a small inclination near the peak of the waveform of the reflected wave by a nearby target (a region near the peak) is less likely to be obscured by the reflected wave by a distant target. As a result, the radar device 1 can detect a plurality of targets separately, so that the resolution at a short distance can be made particularly high.

As illustrated in FIG. 3, the detection unit 4 has the intensity of the reflected wave signal of the first pulse P1 equal to or higher than a predetermined intensity threshold value Sa, and the intensity change of the received wave signal of FIG. 3 (that is, the distance direction). As illustrated in the figure showing the slope in), it can be determined that the target exists when the slope of the reflected wave signal of the first pulse P1 is greater than 0 and equal to or less than the predetermined first slope threshold value Sg1. In FIG. 5, a distance position where the tilt of the received wave signal is equal to or less than the first tilt threshold value Sg1 (distance bin: the transmitting unit 2 transmits the first pulse P1 and then the receiving unit 3 transmits the reflected wave of the first pulse P1. The time until reception is converted into the distance from the radar device 1 to the target) corresponds to the front part of the peak vicinity region of the waveform due to the closer target in the reflected wave signal of FIG.

By setting the first inclination threshold value Sg1 to a value larger than 0 in this way, the presence of the target can be detected at a place where the reflected wave signal does not reach the peak before reaching the peak. The near side of the reflected wave signal is based on a steep rising waveform. In addition, this steepness, that is, the loss of a large inclination, is used as a judgment for detecting the presence of a target. As a result, even if the peak of the waveform due to the closer target in the reflected wave signal is covered by the waveform due to the far target, the portion immediately before the peak of the waveform due to the near target is due to the far target. If it is not covered by a waveform, the presence of a closer target can be detected. Therefore, the radar device 1 can separate the closest target from the farther target and detect it more reliably.

In FIGS. 6 and 7, the change in the intensity of the reflected wave signal and the case where the two targets of FIGS. 3 and 5 are present and the distance between the two targets is smaller than that of FIGS. 3 and 5. Shows the change in tilt. In this case, there is a possibility that the closer target cannot be reliably detected due to the relationship between the slope of the reflected wave signal and the first slope threshold value Sg1. Therefore, the detection unit 4 determines that a target exists when the slope of the reflected wave signal of the first pulse P1 is continuously greater than 0 for a predetermined reference time Ts or more and becomes a predetermined second slope threshold value Sg2 or less. You may. Here, the reference time Ts is set to be equal to or greater than the time interval in equivalent sampling. That is, the detection unit 4 has a target when the inclination of the reflected wave signal of the first pulse P1 becomes a predetermined second inclination threshold value Sg2 or less for a predetermined number of times (twice in FIG. 7) in succession. Then, it may be determined (this distance position is determined as the point X0 where the target exists). In this case, the second inclination threshold value Sg2 is set to a value larger than the first inclination threshold value Sg1 which is determined to have a target when the value is equal to or less than the value even once.

In this way, by continuously checking the slope of the reflected wave signal, the target is detected from the region where the steepness, that is, the loss of the large slope continues, for the waveform based on the steep rise. be able to. Therefore, even if the waveform due to the closer target in the reflected wave signal is covered with the waveform due to the far target, the existence of the peak of the waveform due to the closer target can be estimated more reliably. ..

As described above, the detection unit 4 determines that a target exists in comparison with the first tilt threshold value Sg1 or the second tilt threshold value Sg2 of the tilt of the reflected wave signal of the first pulse P1 (FIGS. 3 and 3). The distance to the target may be calculated (distance calculation processing) with reference to the distance position X0) in 6 and FIG. 7, but the strength of the reflected wave signal of the first pulse P1 determines that the target exists. Even if the distance to the target is calculated with reference to the complementary point (distance position X1 in FIGS. 3 and 6) on the closer side, which is a value smaller than the intensity at (point X0) by a predetermined value ΔR. Good. At the point X0, the change in the intensity of the reflected wave signal with respect to the distance is small, so that the error between the point X0 where it is determined that the target exists and the actual distance position may become large. Therefore, the distance to the target is calculated more accurately by calculating the complementary point X1 which is a value smaller than the intensity at the point X0 by a predetermined value ΔR and performing the distance calculation process based on this. be able to.

The control unit 5 synchronizes the operation timings of the transmission unit 2, the reception unit 3, and the detection unit 4 so that the detection unit 4 can appropriately detect a target. The control unit 5 can be configured by, for example, an arithmetic unit having a CPU, FPGA, memory, etc., and its operation procedure is described in a program and stored. The control unit 5 is usually configured integrally with the detection unit 4. That is, the detection unit 4 and the control unit 5 are functionally distinct, and may not be clearly distinguishable in the physical configuration and the program configuration.

The control unit 5 controls the transmission unit 2 and the reception unit 3 in order for the reception unit 3 to appropriately perform equivalent time sampling of the reflected wave signal. That is, the control unit 5 causes the transmission unit 2 to repeatedly transmit the first pulse P1 and the second pulse P2, and causes the reception unit 3 to repeatedly transmit the reflected wave signals of the first pulse P1 and the second pulse P2, which are relatively different according to the repetition. AD conversion (sampling) is performed at the timing. In this way, by sampling the reflected wave signals of the first pulse P1 and the second pulse P2 in a plurality of different fields and combining the digital data of each field, the first pulse P1 and the second pulse P2 can be converted at an equivalently faster speed even in a slow AD conversion. The reflected wave signals of the 1st pulse P1 and the 2nd pulse P2 can be sampled, and more detailed time waveform information, that is, detailed distance waveform information can be obtained.

When such equivalent time sampling is performed, in the relative timing shift for that purpose, the interval of the timing shift of the first pulse is made finer than that of the timing shift of the second pulse, so that the second pulse is as shown in FIG. The first pulse is set so that the distance interval acquired by one pulse is finer than the distance interval acquired by the second pulse, and the number of signal acquisitions at the same distance is increased in the second pulse as compared with the first pulse. The timing of the transmission interval between the second pulse and the second pulse can be relatively shifted. As a result, in the pulse repeatedly transmitted in each field, the distance interval acquired by the detection unit 4 by the reflected wave of the first pulse P1 is made finer, the waveform is confirmed in detail, and the resolution of the target existing at a short distance is improved. At the same time, by confirming the signals at the same distance more times while making the distance interval acquired by the reflected wave of the second pulse P2 relatively coarse, for example, a plurality of signals are integrated or FFT processing at a relatively large number of points. By doing so, it becomes easy to distinguish from noise even when the intensity of the reflected wave of the second pulse P2 is small. In the first pulse P1 and the second pulse P2 by the transmission unit 2, the transmission is repeatedly transmitted while shifting the transmission interval, that is, by relatively shifting the first timing, the short-distance distance resolution and the distance accuracy are improved. It is possible to improve the detection sensitivity at a long distance at the same time.

The control unit 5 causes the transmission unit 2 to transmit two or more types of first pulses having different carrier frequencies, and causes the detection unit 4 to make a difference or phase difference of the complex amplitude vector of the reflected wave signals of the two or more types of first pulses. The target may be detected based on the above. The phase of the reflected wave signal transmitted from the transmitting unit 2 and reflected by the target and received by the receiving unit 3 changes according to the distance of the target and the carrier frequency. On the other hand, the phase of the received signal transmitted from the transmitting unit 2 and directly reaching the receiving unit 3 with a propagation distance of almost zero does not change substantially depending on the carrier frequency. Therefore, when receiving two or more types of first pulses having different carrier frequencies, it is possible to remove the component that has reached the receiving unit 3 directly from the transmitting unit 2 by calculating the difference or phase difference of the complex amplitude vector of the signal. it can. Further, by calculating such a difference, in addition to the radar wraparound signal that is not derived from the target, the wraparound signal in the installed installation environment, the noise component that wraps around from the transmitting unit 2 to the receiving unit 3, high-speed control for the transmission pulse can be performed. Additional noise generated by high-speed mask control in the receiving unit can also be removed. Therefore, by using two or more types of first pulses having different carrier frequencies, noise can be reduced and the target detection accuracy can be improved. The number of types of the first pulse having different carrier frequencies is at least two, and three or more types of carrier frequencies may be used stepwise. Further, the difference value may be acquired after the complex amplitude vector of the reflected wave signal at one carrier frequency is slightly phase-rotated by a predetermined propagation distance without setting the propagation distance to exactly zero.

As described above, the radar device 1 according to the present embodiment uses the first pulse P1 having a small rise time and the mask portion 32 passing through for a limited time to relatively set a plurality of targets existing at a short distance. It can be separated with high accuracy and detected separately. When the radar device 1 having such a high resolution at a short distance is mounted on an automobile and checks surrounding obstacles when parking, for example, the nearest target can be reliably detected, so that the automobile can be detected. It is possible to park safely without touching obstacles.

The target detection method performed by the radar device 1 of FIG. 1 described above is itself a target detection method according to an embodiment of the present invention. As shown in FIG. 9, the target detection method performed by the radar device 1 of FIG. 1 is a step of transmitting a first pulse P1 and a second pulse having a larger amplitude and pulse width than the first pulse (step S1: Based on the transmission step), the step of receiving the reflected waves of the first and second pulse targets transmitted in the transmission step (step S2: reception step), and the reflected wave signal of the reflected waves received in the reception step. It includes a step of detecting a target (step S3: detection step).

In the target detection method of the present embodiment, the waveforms of the first pulse P1 and the second pulse P2 are arranged so that the rise time of the first pulse P1 is larger than the rise and fall times of the second pulse P2 in the transmission step. To form. In this way, by using the first pulse P1 having a small rise time, it is possible to separate a plurality of targets existing at a short distance with relatively high accuracy and detect them separately. Further, the waveform forming method and the reflected wave signal processing method described for the radar device 1 of FIG. 1 all have a configuration that can be adopted in the target detection method of the present embodiment.

Subsequently, the radar device of the second embodiment of the present invention will be described. FIG. 10 is a block diagram showing a configuration of a radar device 1A according to a second embodiment of the present invention. The radar device 1A of the present embodiment has a transmitting unit 2A that transmits the first pulse P1 and the second pulse P2, and a receiving unit that receives the reflected waves of the first pulse and the second pulse transmitted by the transmitting unit 2A. It includes a 3A, a detection unit 4A that detects a target based on the reflected wave signal received by the reception unit 3A, and a control unit 5A that controls the transmission unit 2, the reception unit A3, and the detection unit 4A. In the description of the radar device 1A of FIG. 10, the same components as those of the radar device 1 of FIG. 1 are designated by the same reference numerals, and duplicate description will be omitted.

The transmission unit 2A uses the oscillation unit 21 that generates a locally-generated signal of the carrier frequency, the waveform-forming unit 22 that forms the waveform signals of the first pulse P1 and the second pulse P2, and the locally-generated signal generated by the oscillation unit 21. A gain control unit 23 that multiplies the waveform signals formed by the waveform forming unit 22, a plurality of transmitting antennas 24 that transmit signals output from the gain control unit 23 as radio waves, and one of a plurality of transmitting antennas 24. A transmission selection unit 25 for selection is provided. That is, the transmission unit 2A has a plurality of transmission channels.

The transmission selection unit 25 can be configured by a well-known selector that switches the electric circuit so that the signal output from the gain control unit 23 is transmitted to only one of the transmission antennas 24 according to the control unit 5A.

The receiving unit 3 has a plurality of receiving antennas 31 that receive electromagnetic waves and convert them into electric signals, a reception selection unit 35 that selects any one of the plurality of reception antennas, and a reception antenna selected by the reception selection unit 35. A mask unit 32 that can pass or block the electric signal of 31, a mixer unit 33 that extracts an amplitude component from the electric signal that has passed through the mask unit 32, and an AD conversion unit 34 that converts the signal extracted by the mixer unit 33 into a digital signal. And have. That is, the receiving unit 3A has a plurality of receiving channels.

The reception selection unit 35 can be configured by a well-known selector that switches the electric path so as to supply only the signal of any one of the reception antennas 31 to the mixer unit 33 via the mask unit 32 according to the control unit 5A.

The detection unit 4A calculates the intensity information at the angle (angle bin) and the distance (distance bin) by performing angle calculation processing for each distance of the reflected wave signal of the first pulse P1 in the above-mentioned plurality of channels. Can be done (angle measurement processing). FIG. 11 shows an example of mapping this intensity information data with the angular position and the distance position as the horizontal axis and the vertical axis. Here, the noise of each of the multiple channel signals is random by synthesizing the signals of multiple channels by the angle calculation process, whereas the reflected wave signal is coherent with respect to the direction in which the target exists. An integration effect is obtained in the angular peak direction. With respect to the composite signal itself, as shown by an arrow in FIG. 11, it is possible to detect a target at each angle based on the intensity change with respect to the same distance as in FIGS. 5 and 7 described above. As a result, the target has azimuth information, and the position of the target can be detected with high resolution at a distance as described above.

Further, instead of the distance axis processing in all the angle bins as shown in FIG. 11, the distance axis processing as described above may be performed only on the angle peak acquired by the angle calculation processing. Specifically, as shown in FIG. 12, as a result of peak detection by the angle axis, the angle peak amplitudes on each distance axis are connected to obtain the distance amplitude information. Further, in the case where a plurality of targets exist as shown in FIGS. 11 and 12, when the targets can be separated as a plurality of peaks, the reflected wave signals from the same target and the relatively angular peaks assumed to be at each distance are close to each other. The amplitudes of are connected to obtain a plurality of distance amplitude information. As a result, it is possible to have azimuth information in the target, realize separation of a plurality of targets in the azimuth information, and realize detection with high resolution at a distance as described above. While it is possible to have abundant information in FIG. 11, it is possible to reduce the calculation load by handling only the angle peak in FIG.

Next, FIG. 13 shows a case in which the number of antenna channels is smaller and the angular resolution is lower than in FIG. In this case, even if a plurality of targets exist, it may be difficult to separate them as two peaks on the angle axis as shown in FIG. Even in such a situation, it is possible to realize detection with high resolution at a distance by acquiring amplitude distance information at an angle peak.

Specifically, as shown in addition to FIG. 13, the detection unit 4A specifies an angle at which the intensity of the reflected wave signal is maximized for each distance (extracts the maximum intensity for each distance position). FIG. 15 shows the change in the extracted maximum intensity with respect to the distance. As shown in FIG. 14, the maximum intensity may be extracted only when the intensity of the reflected wave signal at the peak at each angle of distance is equal to or higher than the intensity threshold value Sa. FIG. 15 shows the intensity change in the reflected wave signal of FIG. 14 in the same manner as in FIGS. 5 and 7, but in this case, the distance between the two targets is smaller than that of FIG. 6, and only the above-described processing is performed. That is, it is difficult to detect the value (intensity change before correction) because the value (intensity change before correction) does not reach the detection threshold by simply calculating the intensity change (slope) between the distance bins. Here, the angle information obtained based on the angle calculation process is used. FIG. 16 shows the absolute value of the difference between the angle values that are the angle peaks for each distance. It is confirmed that the angle value changes sharply in the map of FIG. 13 and FIG. 16 at a specific distance, and in particular, the angle difference (angle inclination) as shown in FIG. 16 can be extracted as a quantitative value. In the normal angle calculation process, the existence angle of the target may be calculated stepwise including various calibrations. At that time, the angle value used here may not be the final detection angle, but may be the difference between the index values related to the angle, which is the intermediate information in the angle calculation result.

Then, as shown in FIG. 15, the detection unit 4A calculates a value obtained by multiplying the amount of change (slope) between the distance bins of the angle (peak angle) at which the maximum intensity is obtained as shown in FIG. 16 by a certain coefficient. , Calculate the judgment index value (intensity change after correction) subtracted from the slope of the maximum intensity. The detection unit 4A can determine that the target exists when the determination index value becomes a predetermined third inclination threshold value Sg3 or less. Further, as in FIG. 7, when the determination index value is continuously equal to or less than a predetermined threshold value among the plurality of distance bins, it may be determined that the target exists (this time position is determined to be the point X0). .. By using the amount of change in angle, it is possible to more reliably detect a target that was difficult to detect in the past. It should be noted that the method of acting the amount of change in the angle here is not limited to the above means.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and modifications can be made. For example, in the present invention, the first pulse may have at least a small rise time, and the fall time may have a waveform as small as the rise time. Specifically, the first pulse may have a rectangular wavy or trapezoidal waveform. Further, the second pulse may be one having a relatively large pulse width, for example, a frequency-modulated continuous wave whose pulse width is on the order of 10 times or more that of the first pulse and whose carrier frequency continuously changes.

In the radar device according to the present invention, the transmission unit may be different from the configuration of the above-described embodiment as long as it can transmit the first pulse and the second pulse as described above. As a specific example, a locally generated signal may be amplified to form a symmetric power signal, and this power signal may be amplified by an amplifier whose gain changes with time to form a power signal of the first pulse having a small rise time. .. Further, even in the case of forming a waveform signal having a small rise time in the above-described embodiment, the method for forming the waveform signal is arbitrary.

In the radar device according to the present invention, in FIG. 8, the transmission interval between the first pulse P1 and the second pulse P2 is once shifted by the shift amount of the signal passage timing of the mask portion, and then returned to the original transmission interval. Therefore, the reflected wave of the second pulse is AD-converted twice at the same timing, but the transmission interval may be shifted so that the reflected wave of the second pulse is AD-converted three times or more at the same timing. ..

In the radar device according to the present invention, target detection processing may be performed on one or more angle peaks acquired by performing angle measurement processing based on the slope of each peak amplitude in the distance direction. The target detection process may be performed based on the slope of each peak amplitude in the distance direction and the slope of each peak angle.

1,1A Radar device 2,2A Transmitter 3,3A Receiver 4,4A Detector 5,5A Control 21 Oscillator 22 Waveform formation 23 Gain control 24 Transmit antenna 25 Transmit selection 31 Receive antenna 32 Mask 33 Mixer unit 34 AD conversion unit 35 Reception selection unit 321 Gain control unit 322 Gain setting unit

Claims (15)

A radar device that detects targets using radio waves.
A transmitter that transmits the first pulse and a second pulse having a larger amplitude and pulse width than the first pulse.
A receiving unit that receives reflected waves from the target of the first pulse and the second pulse transmitted by the transmitting unit, and a receiving unit.
A detection unit that detects the target based on the reflected wave signal of the reflected wave received by the receiving unit, and a detection unit.
With
The transmission unit is a radar device that forms waveforms of the first pulse and the second pulse so that the rise time of the first pulse is smaller than the rise and fall times of the second pulse. The detection unit
Based on the reflected wave signal of the first pulse, the target existing at a relatively short distance is detected, and the target is detected.
The radar device according to claim 1, wherein the target is detected at a relatively long distance based on the reflected wave signal of the second pulse. The first pulse and the second pulse are repeatedly transmitted at the first timing having the first interval, and are transmitted repeatedly.
The receiving unit has a mask unit and an AD conversion unit that repeatedly samples a signal that has passed through the mask unit at a second timing having a second interval and converts it into a digital signal.
The mask portion passes a part of the reflected wave signal of the first pulse for a certain period of time in synchronization with the second timing, and also passes through the reflected wave signal of the second pulse.
The radar device according to claim 1 or 2, wherein the reflected wave signals of the first pulse and the second pulse are sampled for equivalent time by relatively shifting the first timing and the second timing. The transmission unit makes the distance interval acquired by the first pulse smaller than the distance interval acquired by the second pulse, and increases the number of signal acquisitions at the same distance by the second pulse more than the first pulse. The radar device according to claim 3, wherein the first timing is relatively shifted. The radar device according to claim 3 or 4, wherein the gain rise time of the mask portion is equal to or less than the rise time of the first pulse, or the mask width is equal to or less than the pulse width of the first pulse. In the detection unit, the intensity of the reflected wave signal of the first pulse is equal to or more than a predetermined intensity threshold value, and the inclination of the reflected wave signal of the first pulse in the distance direction is greater than 0 and equal to or less than a predetermined first inclination threshold value. The radar device according to any one of claims 1 to 5, wherein the target is determined to exist when the target becomes The detection unit determines that the target exists when the inclination of the reflected wave signal of the first pulse in the distance direction is continuously greater than 0 and equal to or less than a predetermined second inclination threshold value for a predetermined reference time or longer. The radar device according to any one of claims 1 to 6. The detection unit uses the complement point on the closer side as a reference, which is a value smaller than the intensity of the reflected wave signal at the point where the target is determined to exist by the first pulse by a predetermined value. The radar device according to claim 6 or 7, which calculates the distance to. Any of claims 1 to 8, wherein the transmission unit forms two original waveform signals having different rise times, and forms the waveform of the first pulse by shifting and multiplying the two original waveform signals. Radar device described in Crab. The radar device according to claim 9, wherein the transmission unit multiplies the two original waveform signals so that the first pulse becomes a value at the peak of the original waveform signal having a larger rise time. The transmitter transmits two or more types of the first pulses having different carrier frequencies.
The radar according to any one of claims 1 to 10, wherein the detection unit detects the target based on the difference or phase difference of the complex amplitude vectors of the two or more types of reflected wave signals of the first pulse. apparatus. At least one of the transmitting unit and the receiving unit has a plurality of channels.
The detection unit performs target detection processing on the composite signal acquired by performing angle measurement processing from the reflected wave signal of the first pulse based on the slope of the amplitude in the distance direction, and with respect to the composite signal. The radar device according to any one of claims 1 to 11, wherein the distance calculation process is performed. At least one of the transmitting unit and the receiving unit has a plurality of channels.
The detection unit performs target detection processing on one or more angle peaks acquired by performing angle measurement processing from the reflected wave signal of the first pulse based on the slope of each peak amplitude in the distance direction. The radar device according to any one of claims 1 to 12, wherein the distance calculation process is performed for each peak amplitude. At least one of the transmitting unit and the receiving unit has a plurality of channels.
The detection unit is based on the slope of each peak amplitude in the distance direction and the slope of each peak angle with respect to one or more angle peaks acquired by performing angle measurement processing from the reflected wave signal of the first pulse. The radar device according to any one of claims 1 to 12, wherein the target detection process is performed, and the distance calculation process is performed for each peak amplitude. It is a method of detecting a target using radio waves,
The step of transmitting the first pulse and the second pulse having a larger amplitude and pulse width than the first pulse, and
The step of receiving the reflected wave by the target of the first pulse and the second pulse transmitted in the transmission step, and
A step of detecting the target based on the reflected wave signal of the reflected wave received in the receiving step, and a step of detecting the target.
With
A target detection method in which waveforms of the first pulse and the second pulse are formed so that the rise time of the first pulse is smaller than the rise and fall times of the second pulse in the transmission step.

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