WO2020161968A1

WO2020161968A1 - Radar device

Info

Publication number: WO2020161968A1
Application number: PCT/JP2019/042290
Authority: WO
Inventors: 咲田中; 幸徳赤峰; 晃北山
Original assignee: 日立オートモティブシステムズ株式会社
Priority date: 2019-02-04
Filing date: 2019-10-29
Publication date: 2020-08-13
Also published as: DE112019006256T5; JP7023247B2; JP2020125948A

Abstract

Provided is a radar device that can mitigate lengthening of a measurement time. This radar device comprises: a plurality of transmission antennas that transmit a plurality of transmission signals; a plurality of reception antennas that receive, as signals, reflected waves generated as a result of transmission waves of the plurality of signals being reflected by a target; and a radar unit that adds chirp signals 101_S to 103_S received by the reception antennas such that the chirp signals are arranged in chronological order, and that, using a signal generated by adding the chirp signals, detects the relative speed of the target.

Description

Radar equipment

The present invention relates to a radar device, for example, a millimeter wave radar device mounted on an automobile.

ㆍThe millimeter-wave radar device installed in automobiles is used, for example, as a sensor for automatic driving, and is used to measure the distance, relative speed, and azimuth with the target object that is the measurement target. In this case, the distance to the target is estimated by the delay time of the signal, and the relative velocity is estimated by the frequency change of the signal due to the Doppler effect. The azimuth is estimated by the phase difference between the signals received between the antennas.

　In particular, radar devices for remote detection that aim for automated driving of level 3 or higher require high-resolution azimuth estimation. In order to increase the resolution of azimuth estimation, it is desirable to widen the antenna aperture length of the receiving antenna. In a radar device using a plurality of receiving antennas, it is possible to widen the antenna aperture length by widening the distance between the receiving antennas arranged most distant from each other. On the other hand, in order not to spoil the appearance of the automobile, downsizing of the radar device is required.

Virtual antenna technology based on MIMO (Multi-Input & Multi-Output) is important as a technology for achieving both miniaturization of radar equipment and high-resolution direction estimation.

A MIMO radar device using a virtual antenna technology by MIMO is described in Patent Document 1.

Japanese Patent Publication No. 2017-522576

In a MIMO radar device, signals can be transmitted from a plurality of transmitting antennas and received by a plurality of receiving antennas to multiplex the azimuth information of the target and virtually increase the number of receiving antennas. As a result, it is possible to suppress the actual number of receiving antennas, reduce the size of the radar device, and increase the resolution of the direction estimation.

In the MIMO radar device, the signals transmitted from the transmission antennas are required to be orthogonal to each other and separable. The orthogonality of signals can be achieved by code division, frequency division or time division. However, code division requires a high calculation cost, and frequency division makes it difficult to perfectly perform signal separation. Therefore, in this specification, a radar device that employs a time division method will be described.

The time division method can be realized by switching the transmission antenna that transmits the signal for each time. When the distance of a target having a relative speed is measured by a MIMO radar device adopting a time division method, the target moves while switching the transmission antenna, and a distance variation of about several mm occurs. .. However, the range resolution required for a millimeter wave radar device for automatic driving is about 0.1 m to several m. Therefore, in the distance measurement using the millimeter-wave radar device for automatic driving, the distance fluctuation that occurs while switching the transmission antenna can be ignored.

On the other hand, the distance variation of about several mm caused by switching the transmitting antenna is about the same as the wavelength of the transmitted signal. Therefore, the distance variation is detected as a phase variation when measuring the azimuth of the target. As described above, the azimuth of the target is estimated using the phase difference between the received signals. However, if the phase variation occurs due to the distance variation, the accuracy of the orientation estimation deteriorates. Since the distance variation has a value corresponding to the relative velocity of the target, it is possible to suppress the deterioration of the accuracy of the direction estimation by correcting the varied phase using the estimated relative velocity.

Patent Document 1 describes a technique for correcting the phase using the estimated relative speed. Patent Document 1 discloses that a chirp signal which is a transmission signal is transmitted at different time intervals for each transmission antenna in order to estimate the relative speed. In Patent Document 1, a chirp signal is transmitted at different time intervals for each transmitting antenna to uniquely estimate a relative velocity, the estimated relative velocity is used to correct the phase, and the corrected phase is used to estimate the direction. Is performed with high resolution.

However, in the MIMO radar device adopting the time division method, in order to secure the diversity of the chirp signal, a sufficient time is secured so that the chirp signals transmitted by the respective transmission antennas do not overlap in time. Is required. That is, it is required to secure sufficient time so that the chirp signals transmitted at different time intervals do not overlap in time. As a result, the technique disclosed in Patent Document 1 has a problem in that the period for transmitting the chirp signal becomes long, and the measurement time by the radar device and the time required for the calculation for performing the estimation become long.

An object of the present invention is to provide a radar device capable of suppressing a long measurement time.

The above and other objects and novel features of the present invention will be apparent from the description of the present specification and the accompanying drawings.

Among the inventions disclosed in the present application, a brief description of the outline of typical ones is as follows.

That is, the radar device, a plurality of transmission antennas for transmitting a plurality of transmission signals, a plurality of reception antennas for receiving as a signal a reflected wave generated by the transmission wave of the plurality of transmission signals being reflected by the target, A plurality of signals received by the receiving antenna are added together so that they are arranged in time series, and a signal processing unit that detects the relative speed of the target by using the signal generated by the addition is provided. ..

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

Since it is possible to suppress an increase in the time for measuring the relative speed of the target, it is possible to provide a radar device capable of suppressing an increase in the measurement time.

3 is a block diagram showing a configuration of a radar device according to the first embodiment. FIG. FIG. 3 is a diagram for explaining a radar device 1 according to the first embodiment. 3A to 3C are diagrams for explaining the process of the radar unit according to the first embodiment. 3 is a block diagram showing a configuration of a radar device according to the first embodiment. FIG. FIG. 3 is a diagram for explaining a rearrangement unit according to the first embodiment. FIGS. 6A and 6B are views for explaining the rearrangement unit according to the first embodiment. 7 is a block diagram showing a configuration of a radar device according to a modified example of the first embodiment. FIG. FIG. 6 is a waveform diagram for explaining the radar device according to the second embodiment. FIG. 6 is a waveform diagram for explaining the radar device according to the second embodiment. FIG. 9 is a diagram for explaining a radar device according to a third embodiment.

In the following embodiments, when there is a need for convenience, they will be described by dividing them into a plurality of sections or embodiments, but unless otherwise specified, they are not unrelated to each other, and one is not There are some or all of the modifications, details, supplementary explanations, and the like. Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, amount, range, etc.) of the elements, the case where it is particularly specified, and the case where the number is clearly limited to a specific number in principle, etc. However, the number is not limited to the specific number, and may be more than or less than the specific number.

Furthermore, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily essential unless otherwise specified or in principle considered to be essential. Needless to say. Similarly, in the following embodiments, when referring to shapes, positional relationships, etc. of constituent elements, etc., the shapes thereof are substantially the same unless explicitly stated otherwise or in principle not apparently. And the like, etc. are included. This also applies to the above numerical values and ranges.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, the same members are designated by the same reference symbols in principle, and their repeated description will be omitted in principle. Further, the embodiment will be described by taking a millimeter wave radar device used as a sensor for automatic driving as an example.
(Embodiment 1)
<Structure of radar device>

FIG. 1 is a block diagram showing the configuration of the radar device according to the first embodiment. In FIG. 1, reference numeral 1 denotes a radar device, and 100 denotes a target object to be measured. In FIG. 1, a wavy line 110 drawn between the radar device 1 and the target 100 indicates that the distance between the radar device 1 and the target 100 is large.

The radar device 1 includes a plurality of transmitting

antennas

101 and 103, a plurality of receiving antennas 104, and a radar unit 108 connected to the transmitting

antennas

101 and 103 and the plurality of receiving antennas 104. Further, in FIG. 1, a plurality of virtual receiving antennas (virtual receiving antennas) generated by the MIMO technique are shown by reference numeral 107. In the figure, the radar apparatus 1 having two transmitting antennas and three receiving antennas is shown, but the number of transmitting antennas and receiving antennas is not limited to this.

The radar unit 108 superimposes a chirp signal, which is a transmission signal, on a carrier wave of a predetermined frequency and supplies the chirp signal to the

transmission antennas

101 and 103. The transmission waves of the plurality of signals transmitted from the

transmission antennas

101 and 103 are reflected by the target 100 to generate reflected waves. The reflected waves are received by the receiving antennas as reflected signals, and the signals received by the respective receiving antennas are supplied to the radar unit 108.

Since the time division method is adopted, the radar unit 108 operates so that both the transmitting

antennas

101 and 103 do not transmit signals at the same time. That is, the radar unit 108 operates such that the transmission antenna 103 does not perform transmission while the transmission antenna 101 is transmitting a signal. Similarly, the radar unit 108 operates so that the transmitting antenna 101 does not transmit during the period when the transmitting antenna 103 is transmitting a signal.

The transmitting

antennas

101 and 103 are installed apart from each other by a predetermined distance DIL. Since the installation positions are different, a route difference occurs between the route between the target 100 and the transmitting antenna 101 and the route between the target 100 and the transmitting antenna 103. In the figure, the path difference between the transmitting

antennas

101 and 103 is indicated by reference numeral 105. The path difference 105 is about the same as the wavelength of the transmission signal. The path difference 105 causes a phase difference between the signal transmitted from the transmission antenna 101 and the signal transmitted from the transmission antenna 103 with respect to the target 100. This is detected as the phase difference between the transmitting antennas by the antenna array 104AY configured by the plurality of receiving antennas 104.

In the antenna array 104AY, the path length between each receiving antenna 104 and the target 100 differs depending on the installation position where each receiving antenna 104 is installed and the azimuth between the target 100. This path difference is shown as 106 in FIG. When the path difference 106 occurs, a phase difference corresponding to the path difference 106 occurs between the reception signals received by the receiving antenna 104. That is, the azimuth of the target 100 is detected as the phase difference between the received signals.

By adding the path difference 105 caused by the installation positions of the

transmission antennas

101 and 103 and the path difference 106 generated between the reception antennas 104, the virtual reception antenna 107 is arranged at the position shown in FIG. Is considered Since the virtual reception antennas 107 are also plural, it can be considered that the antenna array 107YA is configured by the plural virtual reception antennas 107. In the radar device 1, the antenna array 104YA and the antenna array 107YA are added to each other to form an extended antenna array (extended antenna array), and based on the phase difference between the reception signals received by the extended antenna array, The direction of the target 100 is estimated.
<Target movement when switching the transmitting antenna>

FIG. 2 is a diagram for explaining the radar device according to the first embodiment. In FIG. 2, only the transmitting

antennas

101 and 103 and the target 100 shown in FIG. 1 are shown. The state of the

transmission antennas

101 and 103 and the target 100 at time T1 is shown on the upper side of the paper of FIG. 2, and at the lower side of the paper, the time has elapsed from time T1 and is time T2. The states of the transmitting

antennas

101, 103 and the target 100 when the target is turned on are shown. Further, in FIG. 2, the path difference 105 described in FIG. 1 is schematically shown as a block connected to the

transmission antennas

101 and 103.

At time T1, the transmitting antenna 101 is transmitting a signal. At this time, the target 100 is assumed to be at the position DI_T1 with respect to the radar device 1 shown in FIG. At time T1, the transmission signal from the transmission antenna 101 is reflected by the target 100 and is received by the extended antenna array shown in FIG.

The target 100 has a relative speed, and in the example of FIG. 2, it moves in a direction away from the radar device 1. Therefore, at the time T2, the target has moved by the distance 201 with respect to the position DI_T1 and is present at the position DI_T2. At time T2, the transmitting antenna 103 transmits a signal. Since the target 100 has moved by the distance 201, a path difference corresponding to the distance 201 occurs between the transmitting antenna and the target 100 as compared with the time T1. As for the route between the target 100 and the receiving antenna, a route difference corresponding to the distance 201 occurs as compared with the time T1. That is, the propagation path of the transmission signal from the transmission antenna to the reception antenna changes by twice the distance 201 as compared with the time T1.

-The change in the propagation path of the transmission signal appears as a phase difference in the reception signal received by the reception antenna because it is near the wavelength of the transmission signal. Since the azimuth of the target 100 is estimated by the phase difference between the received signals, the change in the propagation path of the transmission signal greatly affects the estimation of the azimuth. The propagation path difference between the propagation path of the transmission signal by the transmission antenna 101 at time T1 and the propagation path of the transmission signal by the transmission antenna 103 at time T2 is twice the distance 201, which is twice the distance 201. It is a value obtained by adding a route difference corresponding to.

The distance 201 is given by the product of the relative speed of the target 100 and the time interval of the signal that is the transmission signal. Therefore, it is possible to prevent the accuracy of the direction estimation from deteriorating by accurately obtaining the relative velocity of the target 100 and correcting the phase difference with the obtained relative velocity.
<Processing flow in radar unit>

FIG. 3 is a diagram for explaining processing in the radar unit according to the first embodiment. FIG. 3 shows a case where three transmitting antennas are used as the transmitting antennas. Here, for convenience of explanation, it is assumed that the transmission antenna 102 (not shown) is installed between the

transmission antennas

101 and 103 shown in FIG. Of course, the three transmitting antennas 101 to 103 are examples, and the number is not limited to this.

FIG. 3A shows a chirp signal which is a transmission signal transmitted by the radar unit 108 using three transmission antennas. 3B and 3C schematically show the processing of the radar unit 108 which processes the reception signal reflected by the target 100 and received by the reception antenna.

The radar unit 108 operates so as to perform transmission by switching the three transmission antennas 101 to 103 for each corresponding transmission signal. In FIG. 3A, a solid line 101_S indicates a chirp signal which is a transmission signal transmitted from the transmission antenna 101, a two-dot chain line 102_S indicates a chirp signal transmitted from the transmission antenna 102, and a one-dot chain line 103_S indicates The chirp signal transmitted from the transmission antenna 103 is shown. The chirp signals 101_S to 103_S are the same signals. That is, the inclination of the frequency change and the center frequency when superposed on the carrier wave are the same between the chirp signals 101_S to 103_S.

Since it is a time division method, the radar unit 108 causes the transmission antenna to transmit the chirp signals 101_S to 103_S so that they do not overlap in time. In the first embodiment, the radar unit 108 operates so that the cycles of the chirp signals transmitted from the respective transmission antennas are the same. In the example of FIG. 3A, the radar unit 108 operates so that the chirp signals 101_S, 102_S, and 103_S are transmitted from the transmitting

antennas

101, 102, and 103, respectively, at the same period of 3 Tmm. In this case, the radar unit 108 switches the

transmission antennas

101, 102, and 103 so that the chirp signals are transmitted in the order of the chirp signals 101_S, 102_S, and 103_S.

Since the chirp signals 101_S, 102_S, and 103_S are repeatedly transmitted with the same period of 3 Tmm, as shown in FIG. 3A, each chirp signal, for example, the chirp signal 101_S, is a signal which is discontinuous in time. However, when the three chirp signals 101_S to 103_S are regarded as one combined chirp signal, the combined chirp signal is a temporally continuous signal. The transmitted combined chirp signal is reflected by the target 100, and the reflected combined chirp signal is received by the plurality of receiving antennas forming the antenna arrays 104YA and 107YA. In this case, the respective receiving antennas receive the combined chirp signals in the order of transmission, that is, in the order of the chirp signals 101_S, 102_S, and 103_S.

The radar unit 108 separates the combined chirp signal received by the receiving antenna 104 into chirp signals 101_S and 102_S103_S corresponding to the transmitting

antennas

101, 102 and 103. As a result, as shown in FIG. 3B, three chirp signals 101_S, 102_S and 103_S which are discontinuous in time are generated. Based on the phase difference between the generated chirp signals, the path difference 105 described in FIG. 1 is obtained, and the obtained path difference 105 and the phase difference 106 between the receiving antennas 104 (FIG. 1) are shown in FIG. The virtual receiving antenna 107 is formed.

The relative speed of the target 100 is estimated by the frequency change of the chirp signal due to the Doppler effect. In this case, as will be described later in detail in <<Problems related to relative velocity estimation>>, in the configuration in which the relative velocity is estimated by detecting the frequency changes of the chirp signals 101_S, 102_S, and 103_S by sampling. The problem arises that the maximum detectable relative speed decreases.

As shown in FIG. 3B, the radar unit 108 according to the first embodiment multiplies the separated chirp signals 101_S, 102_S, and 103_S by a predetermined coefficient described later in the second embodiment, and The chirp signals 101_S, 102_S, and 103_S are added so that the chirp signals are arranged in series. As a result, as shown in FIG. 3C, the chirp signals 101_S to 103_S are restored so as to be temporally continuous. By sampling the chirp signals 101_S to 103_S arranged so as to be continuous in time, a change in frequency in the recovered chirp signal is detected. In this case, since a chirp signal that is continuous in time is sampled, the sampling frequency can be increased. As a result, it is possible to suppress a decrease in the maximum detectable relative speed. In addition, since the sampling target is a chirp signal generated by adding three chirp signals together, it is possible to reduce the deterioration of the signal-to-noise ratio SNR, and it is possible to detect a distant target. ..

Since it is possible to suppress deterioration of the maximum detectable relative speed, it is possible to obtain the distance 201 (FIG. 2) caused by the movement of the target 100 with high accuracy. By correcting the phase difference using the obtained distance 201, it is possible to suppress deterioration of the orientation estimation of the target 100.
<<Issues of relative velocity estimation>>

Relative velocity is detected by the change in the center frequency of the chirp signal due to the Doppler effect. This change in center frequency is detected by sampling with each chirp signal as a sampling point. At this time, according to the Nyquist sampling theorem, the maximum detectable speed is determined by the time interval of the chirp signal. Of course, the shorter the time period in which the chirp signal is transmitted, the higher the maximum detection speed.

When a target moving at a relative speed higher than the maximum detection speed is detected, the millimeter-wave radar device outputs a value obtained by subtracting a constant multiple of the maximum detection speed as a result of estimating the relative speed. In the time-division type MIMO radar device, the transmission antennas are switched and used at each time, so that the time interval of the chirp signal transmitted from the same transmission antenna becomes long in proportion to the total number of transmission antennas. Therefore, there is a problem that the maximum detection speed decreases in inverse proportion to the total number of transmitting antennas and decreases.

In Patent Document 1, by making the time interval of the chirp signal ambiguous, the maximum detection speed at which the aliasing display occurs is ambiguous, thereby improving the speed estimation accuracy. Due to the ambiguity of the maximum detection speed, the relative speeds displayed after being folded back have different values even for the same target. Therefore, the relative speed of the target above the maximum detected speed is estimated by performing matching processing on the speed estimation result obtained from the chirp signal from each transmitting antenna. However, in this method, it is necessary to lengthen the time interval between the chirp signals in order to maintain the orthogonality of the signals, which reduces the maximum detection speed. In addition, in the speed estimation by the matching process, there is a concern that the relative speed is not uniquely determined in addition to the increase in the calculation amount.

On the other hand, in the first embodiment, each of the chirp signals 101_S to 103_S has the same period 3Tmm, and the time interval of the chirp signals has no ambiguity and is constant. Therefore, when the same target is measured, the same relative velocity is obtained. Therefore, it is not required to perform the matching process, and it is possible to suppress an increase in the calculation amount in the radar unit 108.
<Structure of radar unit>

FIG. 4 is a block diagram showing the configuration of the radar device according to the first embodiment. In FIG. 4, one receiving antenna 104 among the receiving antennas forming the antenna array 104YA shown in FIG. 1 is shown as an example. The radar unit 108 includes a switch unit 200, a memory unit 207, and a signal processing unit. The signal processing unit includes a rearrangement unit 201, a correction unit 202, a time/frequency FFT (Fast Fourier Transform) unit 203, a distance/speed estimation unit 204, a correction unit 205, and an orientation estimation unit 206.

The operation of the radar unit 108 differs depending on whether the distance, relative speed, and azimuth of the target 100 (FIG. 1) have not been measured in advance, or when the relative speed of the target 100 has been measured in advance. Here, the case where the distance, the relative speed, and the azimuth are not measured in advance will be described as the first measurement, and the case where the relative speed is measured in advance will be described as the second measurement. For example, when the radar device 1 is powered on, the first measurement is executed, and at the next timing, the second measurement is executed.

At the first measurement, the switch unit 200 connects the receiving antenna 104 to the rearrangement unit 021. The rearrangement unit 201 rearranges the chirp signals received by the receiving antennas 104 into a two-dimensional data array, further divides the obtained two-dimensional data array into transmitting antennas, rearranges them, and outputs the two-dimensional data to each transmitting antenna. Form a dimensional data array. The rearrangement unit 201 will be described in detail with reference to the drawings. 5 and 6 are diagrams for explaining the sorting unit according to the first embodiment.

Although not shown in FIG. 4, a receiving unit 350 is connected between the receiving antenna 104 and the switch unit 200. The configuration of this receiving unit 350 is shown in FIG. The reception unit 350 includes a local oscillator circuit 352, a mixer 351, and an analog/digital conversion circuit (ADC) 353. Although not particularly limited, the local oscillator circuit 352 generates a local signal having a frequency corresponding to the carrier wave of the transmission signal. The mixer 351 mixes the received signal received by the receiving antenna 104 and the local signal. Due to this mixing, the mixer 351 outputs the chirp signal mixed with the carrier wave. Since the chirp signal output from the mixer 351 is analog, the ADC 353 converts the analog chirp signal into a digital chirp signal. The digital chirp signal obtained by the conversion is supplied to the rearrangement unit 201 via the switch unit 200.

FIG. 6 is a diagram for explaining sorting performed in the sorting unit 201. Digital chirp signals are sequentially supplied to the rearrangement unit 201 via the switch unit 200. That is, the plurality of chirp signals transmitted from the plurality of transmission antennas and reflected by the target 100 are supplied to the rearrangement unit 201 in time series. In FIG. 6A, the time series chirp signals from the ADC 353 are indicated by reference numerals 101_S to 103_S.

The rearrangement unit 201 converts the time-series chirp signals shown in FIG. 6A into a two-dimensional data array. That is, as shown in FIG. 6B, the chirp signals are arranged in the two-dimensional data array while changing the row in the two-dimensional data array for each chirp signal. In FIG. 6B, the row direction of the two-dimensional data array is shown as a distance, and the column direction is shown as a velocity.

The rearrangement unit 201 further generates a two-dimensional data array corresponding to each transmitting antenna from the two-dimensional data array shown in FIG. 6(B). The two-dimensional data array corresponding to the transmitting antenna is also similar to the two-dimensional data array shown in FIG. The difference is that in the two-dimensional data array corresponding to the transmitting antennas, a plurality of chirp signals discontinuously transmitted from the same transmitting antenna are sequentially arranged in the transmission order along the column direction of the two-dimensional data array. It is that you are.

The time/frequency FFT unit 203 performs a fast Fourier transform on the chirp signal of the two-dimensional data array generated by the rearrangement unit 201, and the distance/speed estimation unit 204 detects a peak to detect the target 100. Distance and relative velocity can be estimated. The estimated distance and relative velocity are recorded in the memory unit 207. If the estimated relative velocity of the target 100 is not “0”, the correction unit 205 corrects the phase of the chirp signal for each transmitting antenna using the previously estimated relative velocity. The orientation estimation unit 206 estimates the orientation of the target 100 using the corrected phase. The estimated azimuth is recorded in the memory 207.

In the second measurement in which the relative speed of the target 100 has been measured, the reception antenna 104 is connected to the correction unit 202 via the switch unit 200. The correction unit 202 reads the azimuth of the target 100 recorded in the memory unit 207 and multiplies the chirp signal for each transmitting antenna by the correction term shown in Expression (1) to update the phase of the chirp signal. .. In Expression (1), i is an imaginary number, and k is a number that specifies the transmitting antenna. Further, in Expression (1), φ is represented by Expression (2). In this equation (2), Nrx is the number of receiving antennas, d is the distance between the receiving antennas, λ is the wavelength of the transmission signal, and θ is the azimuth of the target.

In the second measurement, the time/frequency FFT unit 203 performs calculation and the distance/speed estimation unit 204 performs peak detection on the chirp signal updated by the correction unit 202, and the distance and relative distance of the target 100 are measured. Speed estimation is performed. That is, in the second measurement, the orientation recorded in the memory 207 is fed back to the correction unit 202. Using the fed-back bearing, the correction unit 202 updates the chirp signal to a state corresponding to the maximum detected speed. The distance and the relative speed of the target 100 are estimated based on the updated chirp signal.

The addition of the chirp signals and the sampling of the chirp signals described in FIG. 3 are performed in the time/frequency FFT 203. As a result, the decrease in the maximum speed detected by the distance/speed estimation unit 204 is suppressed. As a result, it is possible to suppress a decrease in the accuracy of orientation estimation. Further, since the matching process is not required, it is possible to reduce the amount of calculation in the time/frequency FFT unit 203 and suppress the measurement time from becoming long. Here, it is described that the addition of the chirp signals and the sampling of the chirp signals are performed in the time/frequency FFT unit 203, but the present invention is not limited to this.
<Modification>

FIG. 7 is a block diagram showing the configuration of the radar device according to the modification of the first embodiment. The radar device 108_1 includes a signal processing unit and a memory unit 207. The signal processing unit includes a correction unit 202, a time/frequency FFT speed estimation unit 203_4, a speed result correction unit 205, and an orientation estimation unit 206. The correction unit 205 performs the correction by multiplying the value of the expression (3).

In Equation (3), i is an imaginary unit, c is the speed of light, Vest is the center frequency of the transmission signal including the carrier wave, fc is the center frequency of the chirp signal, and Tm is the sampling period.

The correction unit 205 based on the speed result corrects the phase of each transmission antenna based on the relative speed of the target 100 output from the speed estimation unit 203_4 based on the time/frequency FFT. The azimuth estimation unit 206 estimates the azimuth of the target 100 using the corrected phase, as in FIG. 4. The estimated azimuth is recorded in the memory 207.

In the modification, the orientation of the target 100 recorded in the memory unit 207 or the orientation of the target 100 from the outside 208 is supplied to the correction unit 202. The correction unit 202 updates the chirp signal to a state corresponding to the maximum detection speed, using the supplied orientation, as in FIG. 4.

In the modification, for example, the azimuth of the target 100 is externally supplied to the correction unit 202 at the time of the first measurement, and the azimuth recorded in the memory unit 207 at the time of the second measurement is the correction unit 202. Is supplied to. The addition and sampling of the chirp signal described in FIG. 3 is performed in the speed estimation unit 203_4 by the time/frequency FFT.

In the radar devices 108 and 108_1 described with reference to FIGS. 4 and 7, the units except the memory unit 207 may be realized by software, or may be realized by a combination of hardware and software.
(Embodiment 2)
In the second embodiment, the predetermined coefficient described in FIG. 3B will be described.

▽ In the signal transmitted from each transmitting antenna, the difference in the position of the transmitting antenna appears as a phase difference. Due to this phase difference, a virtual receiving antenna can be realized in MIMO technology. In the time division type MIMO radar device, the transmission antennas are switched for each time, so that the reception antenna receives the signal of each transmission antenna at each time. Since there is a phase difference according to the path difference 105 (FIG. 1) between the chirp signals transmitted from each transmitting antenna, it is necessary to separate the chirp signals for each transmitting antenna for processing.

On the other hand, in a time division MIMO radar device, when the Doppler effect is used to estimate the relative velocity of a target, the radar device detects the frequency change of the chirp signal caused by the Doppler effect. The period of the sampling pulse for detecting the frequency change decreases in inverse proportion to the number of transmitting antennas as described above, and the maximum detection speed decreases.

As described in the first embodiment, by adding the chirp signals 101_S to 103_S so that the chirp signals 101_S to 103_S are time-series data, it is possible to prevent the cycle of the sampling pulse from becoming long. However, a phase difference corresponding to the path difference 105 exists between the chirp signals. Due to the existence of the phase difference, the amplitude of the chirp signal obtained at the time of sampling changes irregularly, which affects the estimation of the relative velocity of the target.

An example in which the amplitude of the chirp signal obtained when sampling changes irregularly will be explained using the drawings. FIG. 8 is a waveform diagram for explaining the radar device according to the second embodiment. FIG. 8 shows a case where there is a phase difference between the chirp signals according to the path difference 105. When the chirp signals 101_S to 103_S are sampled in the cycle of the sampling pulse, that is, the sampling cycle Tm, the chirp signals at the sampling timings indicated by the marks become signals that change in amplitude different from 101_S to 103_S, and different from 101_S to 103_S It becomes a wave containing frequency components. Therefore, it is not suitable for detecting the frequency change with the passage of time.

In the second embodiment, as shown in FIG. 3B, the separated chirp signals 101_S, 102_S and 103_S are multiplied by a predetermined coefficient so that the chirp signals are arranged in time series. The addition of 101_S, 102_S, and 103_S is being performed. Specifically, for the two-dimensional data array of the chirp signals 101_S, 102_S, and 103_S, a column including the coefficient CK and the coefficient “1” represented by the equation (2) is used as a predetermined coefficient. There is. By obtaining the product of this coefficient string and the two-dimensional data array, the time series data of the chirp signal adjusted by the coefficient can be obtained.

FIG. 9 is a waveform diagram for explaining the radar device according to the second embodiment. 9 is similar to FIG. 8, but shows the waveforms of the chirp signals 101_S to 103_S in which the phase difference between the chirp signals due to the path difference 105 is adjusted by multiplying by a predetermined coefficient. Since the waveforms of 101_S to 103_S are superposed, as shown in FIG. 9, the change in the amplitude at the sampling timing indicated by X is regular, and even if the chirp signals are transmitted from the transmitting antennas whose installation positions are different from each other. , It is possible to treat as a chirp signal transmitted from the same transmitting antenna. Thus, by adopting the time division method, the sampling period can be shortened even if the time interval between the chirp signals becomes long. Furthermore, at the sampling timing, it is possible to handle the chirp signals from the same transmitting antenna as if they were being sampled, and the maximum detection speed can be improved.
<Test method>

A test method for testing whether or not the time/frequency FFT unit 203 that performs addition of chirp signals and sampling of chirp signals is operating normally will be described. In the test of the time/frequency FFT unit 203, a predetermined test signal is supplied to the time/frequency FFT unit 203, and it is checked whether or not the estimated relative speed is equal to or higher than the maximum detection speed Vmax shown in the equation (4). By doing so, it is possible to execute. When the estimated relative speed is equal to or higher than the maximum detection speed Vmax when the predetermined test signal is supplied, it is possible to determine that the time/frequency FFT unit 203 is operating normally.

The predetermined test signal is a signal corresponding to a state where the velocity is V and the bearing is not “0”. The speed V at this time is set so as to satisfy the condition of Expression (5).

In equations (4) and (5), N _Tx is the number of transmit antennas and Nc is the number of chirp signals in one frame.
(Embodiment 3)

In the third embodiment, a case will be described in which the radar device described in the first or second embodiment is used to perform tracking for estimating the relative speed of the target 100. Tracking estimates the relative speed of a target that moves faster than the maximum detection speed of the radar device.

First, we will explain the outline of tracking. In tracking, the relative speed of the target is estimated using the past detection results.

In general radar equipment, the distance and relative speed of the target are estimated by discretely executing digital signal processing at regular time intervals. Therefore, the measured time and the estimated distance and relative velocity are also discretized, and the minimum unit exists. When the minimum unit of distance measurement is ΔR and the minimum unit of measured time is Tc, the relative speed is given by a value obtained by dividing time by distance change. The past relative speed can be calculated by using the minimum unit ΔR and Tc which are the past measurement results, but the calculated relative speed is also discretized, and the minimum unit exists.

In the past, the result of distance measurement at any time can be used, and the time to see the distance change is given by the product nTc of an arbitrary integer n and the minimum unit Tc. The minimum unit of distance change is the minimum unit of distance measurement ΔR. Therefore, when the relative speed is estimated using the past measurement result, the minimum unit of the estimated relative speed is ΔVr=ΔR/n, and the accuracy of the speed can be improved by increasing n. That is, it is possible to improve the maximum detection speed.

Comparing the speed estimation using the past measurement results with the speed estimation using the Doppler effect, the maximum detection speed is larger in the speed estimation using the past measurement results, but the minimum unit of the estimated speed. However, the speed estimation value using the past measurement result is larger. Therefore, considering the minimum unit of the estimated speed, a general radar device has a problem in terms of accuracy.

In the radar device according to the third embodiment, velocity estimation using past measurement results and velocity estimation using Doppler effect are used complementarily. Thereby, the above-mentioned problems can be solved. FIG. 10 is a diagram for explaining the radar device according to the third embodiment. In FIG. 10, the horizontal axis indicates the relative speed of the target. In the third embodiment, the rough relative velocity MVmax of the target is estimated by the velocity estimation using the above-described past measurement result, and then the relative velocity V of the target is estimated by the velocity estimation using the Doppler effect. To be done. The relative speed Vest of the target is obtained by adding the relative speed estimated by the speed estimation using the past measurement result and the relative speed estimated by the speed estimation using the Doppler effect. This makes it possible to accurately obtain a wide range of speeds with a fine minimum unit. At this time, it is necessary to satisfy the equation (6) in order to uniquely obtain the relative speed. As described in the first and second embodiments, the maximum detection speed of the radar device 1 according to the embodiments is improved. Therefore, in the speed estimation using the past measurement result, the equation (6) can be established even if the integer n that determines the time to see the distance change is small. That is, it is possible to uniquely obtain the relative speed of the target in a short time nTc.

Here, M is an integer indicating the number of turns, Vmax is the maximum detection speed of the radar device, Tm is the time taken to measure one chirp signal, and N is an arbitrary integer. Further, Rset represents an estimated value of the distance, and, for example, Rest(t0) represents an estimated value of the distance at time t0.

Although the invention made by the inventor has been specifically described based on the embodiment, the invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

1 radar device 100

target

101, 103 transmission antenna 101_S to 103_S chirp signal 104 reception antenna 108 radar unit 200 switch unit 201

rearrangement unit

202, 205 correction unit 203 time/frequency FFT unit 204 distance/speed estimation unit 206 azimuth estimation unit 207 Memory unit CK coefficient

Claims

A plurality of transmission antennas for transmitting a plurality of transmission signals,
A plurality of receiving antennas for receiving as a signal a reflected wave generated by the transmission wave by the plurality of transmission signals being reflected by the target,
Signal processing in which the signals received by the plurality of receiving antennas are added together so that they are arranged in time series, and the signals generated by the addition are used to estimate the relative speed of the target. Department,
A radar device equipped with.
The radar device according to claim 1,
The signal processing unit is supplied with the azimuth of the target estimated based on the phase difference between the signals received by the plurality of receiving antennas,
The signal processing unit is a radar device that estimates a relative velocity of the target using the supplied azimuth of the target and the signals received by the plurality of receiving antennas.
The radar device according to claim 2,
The signal processing unit estimates the orientation of the target by using the phase difference between the signals received by the plurality of receiving antennas, records the estimated orientation of the target in a memory, and records the orientation in the memory. The radar device, wherein the azimuth of the target is supplied to the signal processing unit.
The radar device according to claim 3,
The signal processing unit uses the estimated relative velocity of the target to correct the phase of the signal received by the plurality of receiving antennas, and uses the corrected phase to estimate the azimuth of the target, Radar equipment.
The radar device according to claim 3,
The said signal processing part is a radar apparatus which updates the phase of the signal received by the said receiving antenna using the direction of the said target recorded on the said memory.
The radar device according to claim 1,
The radar device, wherein the addition of the received signals is performed by multiplying the received signals by a predetermined coefficient sequence.