JP7028715B2 - Arrival direction estimation device and arrival direction estimation method - Google Patents

Description

The present invention relates to a technique for estimating the arrival direction of radio waves.

The radar device estimates the arrival direction of radio waves (reflected waves from an object) by the ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) method or the like. The method of estimating the direction of arrival is a method of calculating the direction of arrival (angle) from signals received by a plurality of antennas. The angle calculation performance changes greatly depending on the distance between the antennas. Further, if the entire distance between the antennas is wider than the half wavelength of the incoming radio wave, phase folding occurs.

In order to reduce the half width MW of the main lobe of the angle spectrum and improve the angle separation performance, it can generally be dealt with by increasing the distance L1 between the antennas at both ends.

For example, when the one-dimensional antenna group shown in FIG. 10 (a) is used, the angle calculation result (angle spectrum) shown in FIG. 10 (b) can be obtained, whereas the one-dimensional antenna shown in FIG. 11 (a) can be obtained. When the arranged antenna group is used, the angle calculation result (angle spectrum) shown in FIG. 11B can be obtained. The angle calculation result shown in FIG. 10B and the angle calculation result shown in FIG. 11B are both the angle calculation result of the radio wave arriving from 0deg.

In both the one-dimensionally arranged antenna group shown in FIG. 10A and the one-dimensionally arranged antenna group shown in FIG. 11A, the antenna spacing is equal to L0. Since the one-dimensionally arranged antenna group shown in FIG. 11A has a larger number of antennas than the one-dimensionally arranged antenna group shown in FIG. 10A, the distance L1 between the antennas at both ends is longer. Therefore, the angle calculation result shown in FIG. 11B has a narrower half-value width MW of the main lobe than the angle calculation result shown in FIG. 10B.

Japanese Unexamined Patent Publication No. 2017-058359

However, increasing the number of antennas in order to lengthen the distance L1 between the antennas at both ends leads to an increase in cost. This tendency becomes more remarkable in the two-dimensionally arranged antenna group (see, for example, Patent Document 1) in which the angle can be estimated in two axes, and in the three-dimensionally arranged antenna group in which the angle can be estimated in three axes.

In order to suppress the increase in the number of antennas as much as possible and lengthen the distance L1 between the antennas at both ends while preventing phase wrapping, the distance between the antennas is unequal as in the one-dimensional arrangement antenna group shown in FIG. 12 (a). The interval (interval L0 ≠ interval L0'≠ interval L0 ") may be set.

However, in the angle calculation result shown in FIG. 12 (b) obtained when the one-dimensionally arranged antenna group shown in FIG. 12 (a) is used, the side lobe SH is higher than the angle calculation result shown in FIG. 11 (b). There is a problem that the height becomes high and it causes ghost detection.

In view of the above problems, the present invention provides an arrival direction estimation technique capable of suppressing the side lobe of the angle calculation result while improving the angle separation performance with a two-dimensionally arranged antenna group or a three-dimensionally arranged antenna group having a small number of antennas. The purpose is.

The arrival direction estimation device according to the present invention includes an acquisition unit that acquires a signal for each reception antenna based on a reception signal received by an antenna group in which an existing reception antenna and a non-existent virtual reception antenna are two-dimensionally arranged. A generation unit that generates a correlation matrix based on the signal for each receiving antenna acquired by the acquisition unit, and a first interpolation unit that performs a first interpolation process on the correlation matrix to generate a first extended correlation matrix. The arrival direction of the radio wave is estimated based on the second interpolation unit that generates the second extended correlation matrix by performing the second interpolation processing on the first extended correlation matrix and the second extended correlation matrix. The estimation unit is provided, and the adjacent antennas of the antenna group along the first axial direction are arranged at regular intervals, and the adjacent antennas of the antenna group along the second axial direction are constant. The first axial direction and the second axial direction are arranged at intervals and are different from each other, and the first interpolation process is the number of antennas arranged along the first axial direction × the said. A block matrix composed of the number of antennas arranged along the first axial direction is set as one unit, a division process for dividing the correlation matrix into a plurality of the block matrices, and a matrix element not related to the virtual receive antenna. In the block matrix including, the matrix element interpolation process of interpolating the matrix elements related to the virtual receive antenna with the matrix elements not related to the virtual receive antenna having the same antenna spacing is included, and the second interpolation process includes. In the first extended correlation matrix, there is a configuration (first configuration) having a block matrix interpolation process in which the block matrix is regarded as a matrix element and the same interpolation as the matrix element interpolation process is performed.

In the arrival direction estimation device of the first configuration, the receiving antenna may be arranged in a minimum redundant manner (second configuration).

The arrival direction estimation method according to the present invention includes an acquisition step of acquiring a signal for each receiving antenna based on a receiving signal received by an antenna group in which an existing receiving antenna and a non-existing virtual receiving antenna are two-dimensionally arranged. A generation step of generating a correlation matrix based on the signal for each receiving antenna acquired by the acquisition step, and a first interpolation step of performing a first interpolation process on the correlation matrix to generate a first extended correlation matrix. The arrival direction of the radio wave is estimated based on the second interpolation step of performing the second interpolation process on the first extended correlation matrix to generate the second extended correlation matrix and the second extended correlation matrix. The estimation process is provided, and the adjacent antennas along the first axial direction of the antenna group are arranged at regular intervals, and the adjacent antennas along the second axial direction of the antenna group are constant. The first axial direction and the second axial direction are arranged at intervals and are different from each other, and the first interpolation process is the number of antennas arranged along the first axial direction × the said. A block matrix composed of the number of antennas arranged along the first axial direction is set as one unit, a division process for dividing the correlation matrix into a plurality of the block matrices, and a matrix element not related to the virtual receive antenna. In the block matrix including, the matrix element interpolation process of interpolating the matrix elements related to the virtual receive antenna with the matrix elements not related to the virtual receive antenna having the same antenna spacing is included, and the second interpolation process includes. In the first extended correlation matrix, there is a configuration (third configuration) having a block matrix interpolation process in which the block matrix is regarded as a matrix element and the same interpolation as the matrix element interpolation process is performed.

According to the arrival direction estimation technique according to the present invention, it is possible to suppress the side lobe of the angle calculation result while improving the angle separation performance with the two-dimensionally arranged antenna group or the three-dimensionally arranged antenna group having a small number of antennas.

Diagram showing a configuration example of a radar device Figure showing an example of antenna arrangement in two-dimensional arrangement antenna group Figure showing another example of antenna arrangement in two-dimensional arrangement antenna group Flow chart showing the operation of the signal processing device Conceptual diagram showing the correlation matrix of received signals Conceptual diagram showing the first extended correlation matrix Conceptual diagram showing the second extended correlation matrix Diagram showing the angle spectrum The figure which shows the angle spectrum of the comparative example. The figure which shows the one-dimensional arrangement antenna group and the angle spectrum The figure which shows the one-dimensional arrangement antenna group and the angle spectrum The figure which shows the one-dimensional arrangement antenna group and the angle spectrum

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings.

<1. Radar device configuration>
FIG. 1 is a diagram showing a configuration of a radar device 1 according to the present embodiment. The radar device 1 is mounted on a vehicle such as an automobile. When the radar device 1 is mounted on the front end of the own vehicle, the radar device 1 acquires the target data related to the target existing in front of the own vehicle by using the transmitted wave. The target data includes the distance to the target, the relative speed of the target with respect to the radar device 1, and the like. However, in order to explain the radar device 1 according to the present embodiment as an example of the arrival direction estimation device, only the part related to the arrival direction estimation will be described in the following description.

As shown in FIG. 1, the radar device 1 mainly includes a transmitting unit 2, a receiving unit 3, and a signal processing device 4.

The transmission unit 2 includes a signal generation unit 21 and a transmitter 22. The transmitter 22 modulates the signal generated by the signal generation unit 21 to generate a transmission signal. The transmission antenna 23 converts the transmission signal into a transmission wave TW and outputs it.

The receiving unit 3 includes a plurality of receiving antennas 31 forming a two-dimensionally arranged antenna group together with the plurality of virtual receiving antennas, and a plurality of individual receiving units 32 connected to the plurality of receiving antennas 31. The virtual receiving antenna is a non-existent antenna, and the receiving antenna 31 is an existing antenna. In the present embodiment, the receiving unit 3 includes, for example, 12 receiving antennas 31 and 12 individual receiving units 32. The twelve individual receiving units 32 correspond to the twelve receiving antennas 31, respectively. Each receiving antenna 31 receives the reflected wave RW from the object and acquires a received signal, and each individual receiving unit 32 processes the received signal obtained by the corresponding receiving antenna 31.

FIG. 2 is a diagram showing an example of antenna arrangement in a two-dimensional arrangement antenna group. In the arrangement example shown in FIG. 2, 4 × 3 receiving antennas (ch1, ch2, ch5, ch7, ch8, ch9, The receiving antennas of ch12, ch14, ch22, ch23, ch26, and ch28) are arranged in a minimum redundant manner. Then, the virtual receiving antenna is arranged at the grid point where the receiving antenna is not arranged.

FIG. 3 is a diagram showing an example of antenna arrangement in a two-dimensional arrangement antenna group. In the arrangement example shown in FIG. 3, 4 × 3 receiving antennas (ch1, ch2, ch5, ch7, ch8, ch9, The receiving antennas of ch12, ch14, ch22, ch23, ch26, and ch28) are arranged in a minimum redundant manner. Then, the virtual receiving antenna is arranged at the grid point where the receiving antenna is not arranged.

Returning to FIG. 1, each individual receiving unit 32 includes a mixer 33 and an A / D converter 34. The received signal obtained by the receiving antenna 31 is amplified by a low noise amplifier (not shown) and then sent to the mixer 33. A transmission signal from the transmitter 22 of the transmission unit 2 is input to the mixer 33, and the transmission signal and the reception signal are mixed in the mixer 33. As a result, a beat signal having a beat frequency that is the difference between the frequency of the transmission signal and the frequency of the reception signal is generated. The beat signal generated by the mixer 33 is converted into a digital signal by the A / D converter 34 and then output to the signal processing device 4.

When the radar device 1 is an FMCW (Frequency Modulation Continuous Wave) type radar device, the frequency difference between the transmitted wave TW and the received wave RW increases / decreases in proportion to the distance between the target and the radar device. Is the variable component of the distance. On the other hand, when the radar device 1 is an FCM (First Chirp Modulation) type radar device, the phase difference (phase shift) between the transmitted wave TW and the received wave RW increases / decreases in proportion to the distance between the target and the radar device. Therefore, the fluctuation component of the beat signal due to this phase difference becomes the fluctuation component of the distance. In addition, when reflected by the target, the received wave RW is affected by the speed of the target, and the frequency difference between the pulses increases or decreases in proportion to the relative speed (Doppler frequency) between the target and the radar device. The fluctuation component of the beat signal due to the frequency difference between the pulses becomes the fluctuation component of the velocity. When there are a plurality of targets having different relative velocities and distances, each receiving antenna 31 receives a plurality of reflected waves having different phase shift amounts and doppler shift amounts, and the beat signal obtained from the mixer 33 receives each target. It will contain various ingredients corresponding to.

The signal processing device 4 includes a microcomputer including a CPU (Central Processing Unit), a memory 41, and the like. The signal processing device 4 stores various data to be calculated in the memory 41 which is a storage device. The memory 41 is, for example, a RAM (Random Access Memory) or the like. The signal processing device 4 includes a transmission control unit 42, a Fourier transform unit 43, and a data processing unit 44 as functions realized by software in a microcomputer. The transmission control unit 42 controls the signal generation unit 21 of the transmission unit 2. The data processing unit 44 includes a peak extraction unit 45, an extended calculation unit 46, and an orientation calculation unit 47.

Since the Fourier transform unit 43 is received by the receiving antenna 31 in a state where the reflected waves from a plurality of targets are overlapped with each other, the frequency component based on the reflected waves of each target is obtained from the beat signal generated based on the received signal. (For example, FFT (Fast Fourier Transfer) processing) is performed. In the FFT process, reception level and phase information are calculated for each frequency point (sometimes called a frequency bin) set at a predetermined frequency interval.

The peak extraction unit 45 detects a peak from the result of FFT processing or the like by the Fourier transform unit 43. The extended calculation unit 46 calculates an extended correlation matrix based on the signal of the frequency bin in which the peak is generated. The direction calculation unit 47 estimates the direction (angle) in which the target exists based on the extended correlation matrix. The direction calculation unit 47 outputs the estimated direction (angle) in which the target exists to the memory 41, the vehicle control ECU 51, or the like.

<2. Operation of signal processing device>
Next, the operation of the signal processing device 4 will be described. FIG. 4 is a flowchart showing the operation of the signal processing device 4. The signal processing device 4 periodically repeats the process shown in FIG. 4 at regular time intervals.

The signal processing device 4 acquires a predetermined number of beat signals (step S10). Next, the Fourier transform unit 43 executes the FFT operation on the beat signal (step S20).

Next, the peak extraction unit 45 extracts a peak from the result of the FFT calculation (step S30). Then, the extended calculation unit 46 calculates the extended correlation matrix based on the signal of the frequency bin in which the peak is generated (step S40). Finally, the azimuth calculation unit 47 calculates the angle spectrum based on the extended correlation matrix, and estimates the azimuth (angle) in which the target exists based on the calculated angle spectrum (step S50).

<3. Calculation of extended correlation matrix>
The extended arithmetic unit 46 sets the received signal of the virtual receiving antenna to 0.

The extended calculation unit 46 defines a received signal vector X of 28 rows and 1 column. Each component of the received signal vector X is a peak value extracted by each receiving antenna and the peak extracting unit 45 of each receiving antenna. The row components of the received signal vector X are arranged in the order of ch1 to ch28.

The extended arithmetic unit 46 generates a correlation matrix of received signals. The correlation matrix _RXX is expressed as follows. Here, [・] ^H represents a complex conjugate transpose. The correlation matrix _RXX is a 28-by-28 matrix.
R _XX = XX ^H

The extended calculation unit 46 performs the first interpolation process on the correlation matrix to generate the first extended correlation matrix. The first interpolation process includes a division process and a matrix element interpolation process. The division process is the number of antennas arranged along the first axial direction (total number of receiving antennas and virtual receiving antennas) × the number of antennas arranged along the first axial direction (total number of receiving antennas and virtual receiving antennas). ) Is a unit, and the correlation matrix is divided into a plurality of block matrices. Here, the direction of the straight line connecting the receiving antenna of ch1, the receiving antenna of ch2, the receiving antenna of ch5, and the receiving antenna of ch7 is defined as the first axial direction. In addition, unlike this embodiment, the direction of the straight line connecting the receiving antenna of ch1, the receiving antenna of ch8, and the receiving antenna of ch22 may be the first axial direction.

FIG. 5 is a conceptual diagram showing a correlation matrix. Each thick frame of 7 × 7 is each block matrix. Each cell is each matrix element of the correlation matrix. The plain matrix element represents a matrix element associated with the virtual receive antenna and has a value of 0.

In the matrix element interpolation processing, in a block matrix containing matrix elements not related to the virtual receiving antenna (a block row example including a non-plain matrix element in FIG. 5), the matrix elements related to the virtual receiving antenna are subjected to virtual receiving antennas having the same antenna spacing. It is a process of interpolating with matrix elements that are not related to. FIG. 6 is a conceptual diagram showing the first extended correlation matrix.

Here, the above interpolation will be described by taking the block matrix B1 in the 1st to 7th rows and the 1st to 7th columns of the correlation matrix as an example. The block matrix B1 is represented by the number 1 shown below. Here, [・] ^* represents a complex conjugate.

In the block matrix B1, the diagonally arranged matrix elements correspond to the matrix elements having the same antenna spacing. Therefore, by replacing "matrix elements that are 0" with "matrix elements that are not 0" in the matrix elements that are arranged diagonally, the matrix elements related to the virtual receiving antenna are replaced with the matrix elements not related to the virtual receiving antenna having the same antenna spacing. Can be interpolated with.

In the block matrix B1, since there are a plurality of "non-zero matrix elements" in the diagonal lines shown by the dotted lines, a plurality of interpolation methods can be considered.

For example, the average value a of a plurality of "non-zero matrix elements" may be obtained, and all the matrix elements of the diagonal lines shown by the dotted lines may be a. In this case, the block matrix B11 of the first extended correlation matrix corresponding to the block matrix B1 is represented by the number 2 shown below.

Further, for example, the average value a of a plurality of “non-zero matrix elements” may be obtained, and the “zero matrix element” of the diagonal line shown by the dotted line may be replaced with a. In this case, the block matrix B11 of the first extended correlation matrix corresponding to the block matrix B1 is represented by the number 3 shown below.

Also, for example, even if one of a plurality of "non-zero matrix elements" is selected and the "zero matrix element" of the diagonal line shown by the dotted line is replaced with the selected "non-zero matrix element". good. In this case, the block matrix B11 of the first extended correlation matrix corresponding to the block matrix B1 is represented by the number 4 shown below.

Finally, the extended calculation unit 46 performs a second interpolation process on the first extended correlation matrix to generate a second extended correlation matrix. The second interpolation process includes a block matrix interpolation process. The block matrix interpolation process is a process in which the block matrix is regarded as a matrix element and the same interpolation as the matrix element interpolation process is performed in the first extended correlation matrix. FIG. 7 is a conceptual diagram showing the second extended correlation matrix. The second extended correlation matrix is the extended correlation matrix finally calculated in step S40 described above.

By applying the second extended correlation matrix in the estimation process of the arrival direction, the intervals between adjacent antennas have changed from unequal intervals to pseudo-equal intervals. It is possible to suppress the side lobe of the angle calculation result while improving.

FIG. 8 shows an angle spectrum when the second extended correlation matrix (see FIG. 7) is applied, and FIG. 9 shows an angle spectrum when a correlation matrix (see FIG. 5) is applied as a comparative example. .. In FIGS. 8 and 9, the shaded area indicates a region where the signal level is −7 [dB] or higher. By applying the second extended correlation matrix (see FIG. 7), the side lobe of the angle calculation result can be suppressed.

In addition, unlike the present embodiment, even when the actual receiving antenna arrangement is not the minimum redundant arrangement, the side lobe of the angle calculation result can be suppressed while improving the angle separation performance with the two-dimensional arrangement antenna group having a small number of antennas. However, the "matrix element that is 0" remains in the second extended correlation matrix. Therefore, it is desirable that the arrangement of the existing receiving antennas is the minimum redundant arrangement.

<4. Others>
In addition to the above embodiments, the various technical features disclosed herein can be modified in various ways without departing from the spirit of the technical creation. In addition, a plurality of embodiments and modifications shown in the present specification may be combined and implemented to the extent possible.

For example, in the radar device, instead of the FCM method and the FMCW method described above, for example, a pulse Doppler method that detects Doppler shift as a phase change between a plurality of pulse signals instead of the frequency of the beat signal may be adopted.

In the above-described embodiment, the arrival direction estimation device processes the received signal received by the two-dimensional arrangement antenna group, but the arrival direction estimation device may process the reception signal received by the three-dimensional arrangement antenna group.

Further, although the in-vehicle radar device has been described in the above-described embodiment, the present invention can also be applied to an infrastructure radar device, an aircraft surveillance radar device, etc. installed on a road or the like.

1 Radar device 2 Transmitter 3 Receiver 31 Receive antenna 4 Signal processing device 46 Extended arithmetic unit 47 Directional arithmetic unit

Claims (3)

An acquisition unit that acquires a signal for each receiving antenna based on a receiving signal received by a group of antennas in which an existing receiving antenna and a non-existing virtual receiving antenna are two-dimensionally arranged.
A generation unit that generates a correlation matrix based on the signal for each receiving antenna acquired by the acquisition unit, and a generation unit.
A first interpolation unit that performs a first interpolation process on the correlation matrix to generate a first extended correlation matrix, and a first interpolation unit.
A second interpolation unit that performs a second interpolation process on the first extended correlation matrix to generate a second extended correlation matrix, and a second interpolation unit.
An estimation unit that estimates the arrival direction of radio waves based on the second extended correlation matrix, and
Equipped with
Adjacent antennas along the first axial direction of the antenna group are arranged at regular intervals.
Adjacent antennas along the second axial direction of the antenna group are arranged at the fixed intervals.
The first axial direction and the second axial direction are different from each other.
The first interpolation process is
A block matrix composed of the number of antennas arranged along the first axial direction × the number of antennas arranged along the first axial direction is set as one unit, and the correlation matrix is divided into a plurality of the block matrices. Blocking process and
In the block matrix including the matrix element not related to the virtual receiving antenna, the matrix element interpolation processing for interpolating the matrix element related to the virtual receiving antenna with the matrix element not related to the virtual receiving antenna having the same antenna spacing is provided. death,
The second interpolation process is
The first extended correlation matrix has a block matrix interpolation process in which the block matrix is regarded as a matrix element and the same interpolation as the matrix element interpolation process is performed.
Arrival direction estimation device. The arrival direction estimation device according to claim 1, wherein the receiving antenna is arranged in a minimum redundant manner. An acquisition process of acquiring a signal for each receiving antenna based on a receiving signal received by a group of antennas in which an existing receiving antenna and a non-existing virtual receiving antenna are two-dimensionally arranged, and
A generation step of generating a correlation matrix based on the signal for each receiving antenna acquired by the acquisition step, and a generation step.
The first interpolation step of applying the first interpolation process to the correlation matrix to generate the first extended correlation matrix, and
A second interpolation step of performing a second interpolation process on the first extended correlation matrix to generate a second extended correlation matrix.
An estimation process for estimating the arrival direction of radio waves based on the second extended correlation matrix, and
Equipped with
Adjacent antennas along the first axial direction of the antenna group are arranged at regular intervals.
Adjacent antennas along the second axial direction of the antenna group are arranged at the fixed intervals.
The first axial direction and the second axial direction are different from each other.
The first interpolation process is
A block matrix composed of the number of antennas arranged along the first axial direction × the number of antennas arranged along the first axial direction is set as one unit, and the correlation matrix is divided into a plurality of the block matrices. Blocking process and
In the block matrix including the matrix element not related to the virtual receiving antenna, the matrix element interpolation processing for interpolating the matrix element related to the virtual receiving antenna with the matrix element not related to the virtual receiving antenna having the same antenna spacing is provided. death,
The second interpolation process is
The first extended correlation matrix has a block matrix interpolation process in which the block matrix is regarded as a matrix element and the same interpolation as the matrix element interpolation process is performed.
Arrival direction estimation method.

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