JP7141964B2 - Direction-of-arrival estimation device and direction-of-arrival estimation method - Google Patents

Description

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

A radar device emits radio waves and receives radio waves (reflected waves) reflected from a target, thereby estimating the direction of arrival of the reflected waves. The method of estimating the direction of arrival is a method of calculating the direction of arrival (angle) from information on the phase difference and amplitude difference of received signals obtained by a plurality of receiving antennas that receive reflected waves.

Japanese Unexamined Patent Application Publication No. 2011-33498

The number of antennas is very important in calculating the direction of arrival (angle), and greatly affects angle accuracy performance and angle separation performance. However, an increase in the number of antennas leads to an increase in cost of the radar device. Therefore, in recent years, attention has been paid to a technique of generating a virtual array antenna having virtual antennas in a number exceeding the number of reception antennas by combining a plurality of transmission antennas and a plurality of reception antennas.

In the virtual array antenna, errors that exist in one transmission antenna are reflected in errors in a plurality of virtual antennas, widening the range of error influence. For example, in a virtual array antenna VAx1 generated by combining two transmitting antennas Tx1 and Tx2 with an antenna spacing of 4d and four receiving antennas Rx1 to Rx4 with an antenna spacing of d shown in FIG. The errors present affect the four virtual antennas VRx5 to VRx8.

Similarly, in a virtual array antenna, errors that exist in one receiving antenna are reflected in errors in a plurality of virtual antennas, widening the range of error influence. For example, in a virtual array antenna VAx1 generated by combining four transmitting antennas Tx1 to Tx4 with an antenna spacing of d and two receiving antennas Rx1 and Rx2 with an antenna spacing of 4d shown in FIG. The errors present affect the four virtual antennas VRx1, VRx3, VRx5 and VRx7.

Therefore, multiple transmitting antennas and multiple receiving antennas are arranged so that multiple virtual antennas with the same round-trip path distance for signals to the same target can be obtained. There has been proposed a correction technique for correcting signals received by virtual antennas so as to cancel the difference between signals received by two virtual antennas (see Patent Document 1, for example).

However, random noise, such as thermal noise, occurs at each of the multiple transmit antennas and multiple receive antennas. Therefore, the noise included in each received signal of each virtual antenna is different. Therefore, in the above correction technique, the difference between the received signals of two virtual antennas having the same round-trip path distance of the signal to the same target is canceled while the received signals of the two virtual antennas contain different noises. Therefore, correct error correction cannot be performed. In particular, when the signal-to-noise ratio (SNR) is low, the influence of noise becomes large, and the accuracy of error correction becomes significantly degraded.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a direction-of-arrival estimation technique with high error correction accuracy.

A direction-of-arrival estimation apparatus according to the present invention includes a first virtual antenna and a second virtual antenna which are generated by combining a plurality of transmitting antennas and a plurality of receiving antennas, and which have the same round-trip path distance of a signal to the same target. and a correlation matrix of the received signal based on the received signal for each of a plurality of virtual antennas including the first virtual antenna and the second virtual antenna. a calculator for calculating an eigenvector based on eigenvalue decomposition of a correlation matrix of the received signal; an element of the eigenvector corresponding to the first virtual antenna; and an element of the eigenvector corresponding to the second virtual antenna and an estimating unit for estimating the direction of arrival of radio waves based on the eigenvector corrected by the correcting unit (first configuration).

In the direction-of-arrival estimation apparatus having the first configuration, the estimator corresponds to the element corresponding to the first virtual antenna and the element corresponding to the second virtual antenna in the eigenvector corrected by the corrector. A configuration (second configuration) that generates a joint eigenvector that summarizes the elements that good.

In the direction-of-arrival estimation apparatus having the second configuration, the calculation unit multiplies a feature matrix obtained by arranging the plurality of joint eigenvectors by a complex conjugate transposed matrix of the feature matrix to obtain a correlation matrix of the joint eigenvectors. It may be a configuration (third configuration) to generate.

In the direction-of-arrival estimation apparatus having the first configuration, the calculation unit calculates the single The correlation matrix of the received signal is calculated, and the correcting unit corrects the elements of the eigenvector corresponding to the virtual antenna generated by combining either the transmitting antenna that is the same as the second virtual antenna or the receiving antenna. A configuration (fourth configuration) may be used.

In the direction-of-arrival estimation apparatuses having the first to third configurations, the calculator calculates a first correlation matrix based on the received signal for each of a plurality of virtual antennas including the first virtual antenna, and the second correlation matrix, A second correlation matrix based on the received signal for each of a plurality of virtual antennas including a virtual antenna is calculated as a separate correlation matrix of the received signal, and a first correlation matrix based on eigenvalue decomposition of the first correlation matrix An eigenvector and a second eigenvector based on eigenvalue decomposition of the second correlation matrix are calculated, and the correction unit calculates the element of the first eigenvector corresponding to the first virtual antenna and the second correcting the second eigenvector based on the elements of the second eigenvector corresponding to the virtual antenna of the estimating unit correcting the first eigenvector and the second eigenvector corrected by the correcting unit A configuration (fifth configuration) for estimating the direction of arrival of radio waves based on and may be used.

In the direction-of-arrival estimation apparatus having the fifth configuration, the estimating unit combines the first eigenvector and the second eigenvector corrected by the correcting unit to generate the combined eigenvector ( sixth configuration).

A direction-of-arrival estimation method according to the present invention includes a first virtual antenna and a second virtual antenna which are generated by combining a plurality of transmitting antennas and a plurality of receiving antennas, and which have the same round-trip path distance of a signal to the same target. and obtaining a correlation matrix of the received signals based on the received signals for each of a plurality of virtual antennas including the first virtual antenna and the second virtual antenna. calculating an eigenvector based on eigenvalue decomposition of a correlation matrix of the received signal; an element of the eigenvector corresponding to the first virtual antenna; and an element of the eigenvector corresponding to the second virtual antenna. and an estimating step of estimating the direction of arrival of radio waves based on the eigenvector corrected by the correcting step (seventh configuration).

According to the direction-of-arrival estimation technique according to the present invention, it is possible to improve the accuracy of error correction.

FIG. 1 is a diagram showing the configuration of a radar device according to first and second embodiments; The figure which shows the antenna arrangement|positioning in 1st and 2nd embodiment Flowchart showing schematic operation of the radar device according to the first embodiment Flowchart showing schematic operation of the radar device according to the second embodiment The figure which shows the modification of an antenna arrangement The figure which shows the other modified example of antenna arrangement The figure which shows the other modification of an antenna arrangement|positioning Diagram showing an example of general MIMO antenna arrangement Diagram showing another example of general MIMO antenna arrangement

Exemplary embodiments of the invention are described in detail below with reference to the drawings.

<1. First Embodiment>
<1-1. Configuration of Radar Device>
FIG. 1 is a diagram showing the configuration of a radar device 1 according to this embodiment. The radar device 1 is mounted on a vehicle such as an automobile. When the radar device 1 is mounted at the front end of the own vehicle, the radar device 1 acquires target object data related to a target existing in front of the own vehicle using transmission waves. 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, since the radar apparatus 1 according to this embodiment will be described as an example of a direction-of-arrival estimation apparatus, only the portion related to direction-of-arrival estimation will be described in the following description.

As shown in FIG. 1 , the radar device 1 mainly includes two transmitters 2 , a receiver 3 and a signal processor 4 . The radar device 1 is a so-called MIMO (Multi Input Multi Output) radar device.

The transmitter 2 includes a signal generator 21 and a transmitter 22 . The transmitter 22 modulates the signal generated by the signal generator 21 to generate a transmission signal. The two transmitting antennas 23 receive transmission signals from separate transmission units 2, convert the transmission signals into transmission waves TW, and output the transmission waves TW. The two transmission signals output from each of the two transmitters 2 are signals orthogonal to each other (orthogonal signals).

The receiving section 3 includes a plurality of receiving antennas 31 and a plurality of individual receiving sections 32 connected to the plurality of receiving antennas 31 . In this embodiment, the receiving section 3 includes, for example, four receiving antennas 31 and four individual receiving sections 32 . The four individual receivers 32 correspond to the four receiving antennas 31, respectively. The four receiving antennas 31 correspond to receiving channels ch1 to ch4, respectively. Each receiving antenna 31 receives a reflected wave RW from an object and acquires a received signal, and each individual receiving section 32 processes the received signal obtained by the corresponding receiving antenna 31 .

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

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 operated on in the memory 41, which is a storage device. The memory 41 is, for example, a RAM (Random Access Memory). The signal processing device 4 includes a transmission control section 42, a Fourier transform section 43, and a data processing section 44 as functions realized by software on a microcomputer. The transmission controller 42 controls each signal generator 21 of each transmitter 2 . The data processing section 44 includes a peak extraction section 45 , an acquisition section 46 , a calculation section 47 , a correction section 48 and an estimation section 49 .

Since the receiving antenna 31 receives the reflected waves from a plurality of targets in a state in which they overlap each other, the Fourier transform unit 43 extracts the frequency components based on the reflected waves from each target from the beat signal generated based on the received signal. are separated (for example, FFT (Fast Fourier Transfer) processing). In FFT processing, reception level and phase information are calculated for each frequency point (sometimes referred to as frequency bin) set at predetermined frequency intervals.

The peak extraction unit 45 detects peaks from the results of FFT processing, etc., performed by the Fourier transform unit 43 .

The acquisition unit 46 acquires the received signal of the virtual array antenna based on the peak value extracted by the peak extraction unit 45 . Details of the virtual array antenna will be described later.

The calculator 47 calculates a first eigenvector and a second eigenvector based on the received signal of the virtual array antenna. Details of the first eigenvector and the second eigenvector will be described later.

A corrector 48 corrects the second eigenvector. A specific example of correction will be described later.

The estimation unit 49 estimates the direction of arrival of radio waves based on the first eigenvector and the second eigenvector corrected by the correction unit 48 . A specific example of estimation will be described later.

<1-2. Antenna placement>
FIG. 2 is a diagram showing the antenna arrangement in this embodiment. As shown in FIG. 2(a), two transmitting antennas 23 are arranged in the horizontal direction with an antenna spacing of 3d, and as shown in FIG. 2(b), four receiving antennas 31 are arranged in the same horizontal direction. are arranged at an antenna spacing d of . Note that the three antenna intervals in the receiving antenna 31 may not be strictly the same, and it is sufficient if the three antenna intervals can be regarded as the same after considering design errors and variations. Also, the antenna spacing of the transmitting antenna 23 may not be strictly three times the antenna spacing of the receiving antenna 31, and is considered to be three times the antenna spacing of the receiving antenna 31 after considering design errors and variations. I wish I could.

A virtual array antenna shown in FIG. 2(c) is generated by combining the two transmitting antennas 23 shown in FIG. 2(a) and the four receiving antennas 31 shown in FIG. 2(b). The virtual array antenna shown in FIG. 2(c) is composed of eight virtual antennas VRx1 to VRx8.

By applying MIMO technology, it is possible to obtain virtual antennas that exceed the number of reception antennas. The virtual antennas VRx1 to VRx4 are arranged at an antenna interval d along the horizontal direction, and the virtual antennas VRx5 to VRx8 are arranged at an antenna interval d along the horizontal direction. The position of the virtual antenna VRx4 and the position of the virtual antenna VRx5 overlap. Note that the virtual antenna VRx4 and the virtual antenna VRx5, which are positioned at the same position, have the same round-trip path distance of the signal to the same target.

The received signal of the 1ch receiving antenna 31 includes the received signal of the virtual antenna VRx1 and the received signal of the virtual antenna VRx5 which are orthogonal to each other. Similarly, the received signal of the 2ch receiving antenna 31 includes the received signal of the virtual antenna VRx2 and the received signal of the virtual antenna VRx6 which are orthogonal to each other. Similarly, the received signal of the 3ch receiving antenna 31 includes the received signal of the virtual antenna VRx3 and the received signal of the virtual antenna VRx7 which are orthogonal to each other. Similarly, the received signals of the 4ch receiving antenna 31 include the received signals of the virtual antenna VRx4 and the virtual antenna VRx8 which are orthogonal to each other.

<1-3. General Operation of Radar Device>
FIG. 3A is a flowchart showing a schematic operation of the radar device 1. FIG. The radar device 1 periodically repeats the processing shown in FIG. 3A at regular time intervals.

First, the transmission antenna 23 outputs the transmission wave TW (step S10). Next, the reception antenna 31 receives the reception wave RW to obtain a reception signal (step S20). Next, the signal processing device 4 acquires a predetermined number of beat signals (step S30). Next, the Fourier transform unit 43 performs FFT calculation on the beat signal (step S40).

Then, the peak extraction unit 45 extracts a peak from the FFT calculation result (step S50).

In step S60 following step S50, the acquisition unit 46 acquires the received signal of the virtual array antenna shown in FIG. 2(c) based on the peak value extracted by the peak extraction unit 45. That is, the acquisition unit 46 acquires the reception signals x ₁ to x ₈ of the virtual antennas VRx1 to VRx8.

In step S70 following step S60, the calculator 47 calculates the first eigenvector and the second eigenvector based on the received signals x ₁ to x ₈ of the virtual antennas VRx1 to VRx8.

The calculator 47 calculates a first correlation matrix R1 based on the received signals x ₁ to x ₄ of the virtual antennas VRx1 to VRx4, and a second correlation matrix R2 based on the received signals x ₅ to x ₈ of the virtual antennas VRx5 to VRx8. , is calculated. The first correlation matrix R1 can be calculated by the following formula (1), and the second correlation matrix R2 can be calculated by the following formula (2). Here, X1 ₌ [x1,x2 _{, x3} , _x4 ] ^T , X2=[ _x5 , _x6 , _x7 , _x8 ] ^T , and E[.] indicates time averaging process. and [·] ^H represents the complex conjugate transpose.
R1=E[ ^X1X1H ] (1)
R2=E[ ^X2X2H ] (2)

The calculator 47 performs eigenvalue decomposition on the first correlation matrix R1 and the second correlation matrix R2. Signal and noise can be separated by eigenvalue decomposition. Since the first correlation matrix R1 and the second correlation matrix R2 are each a matrix of 4 rows and 4 columns, 4 eigenvalues of the first correlation matrix R1 are obtained, and 4 eigenvalues of the second correlation matrix R2 are also obtained. .

In this embodiment, the calculator 47 calculates first eigenvectors corresponding to each specific eigenvalue of the first correlation matrix R1, and calculates second eigenvectors corresponding to each specific eigenvalue of the second correlation matrix R2. Calculate A specific eigenvalue means an eigenvalue whose absolute value is greater than or equal to a predetermined value.

Hereinafter, among the eigenvalues of the first correlation matrix R1, only the eigenvalue Φ ₁₁ with the largest absolute value and the eigenvalue Φ ₁₂ with the second largest absolute value correspond to specific eigenvalues, and the eigenvalues of the second correlation matrix R2 A case where only the eigenvalue Φ ₂₁ with the largest absolute value and the eigenvalue Φ ₂₂ with the second largest absolute value among them correspond to specific eigenvalues will be described as an example.

The calculator 47 calculates a first eigenvector e ₁₁ corresponding to the eigenvalue Φ ₁₁ , a first eigenvector e ₁₂ corresponding to the eigenvalue Φ ₁₂ , a second eigenvector e ₂₁ corresponding to the eigenvalue Φ ₂₁ , and an eigenvalue Φ ₂₂ . Calculate the second eigenvector e ₂₂ for The first eigenvectors _e11 and _e12 and the second eigenvectors _e21 and _e22 calculated by the calculator 47 are not affected by noise. The first eigenvectors e ₁₁ and e ₁₂ and the second eigenvectors e ₂₁ and e ₂₂ calculated by the calculator 47 are represented by the following equations (3) to (6).
_e11 =[ _e111 , _{e112, e113, e114 ] T} ⁽ 3)
_e12 =[ _e121 , _e122 , _e123 , _e124 ] ^T (4)
_e21 = [ _e211 , _e212 , _e213 , _e214 ] ^T (5)
_e22 = [ _e221 , _e222 , _e223 , _e224 ] ^T (6)

In step S80 following step S70, the correction unit 48 corrects the second eigenvectors _e21 and _e22 .

If there is no error between the two transmit antennas 23, the element e ₁₁₄ of the first eigenvector e ₁₁ corresponding to the virtual antenna VRx4 and the element e ₂₁₁ of the second eigenvector e ₂₁ corresponding to the virtual antenna VRx5 are coincident. should be. Therefore, the _correction unit _{48 adjusts} the first 2 eigenvector e ₂₁ is corrected.

Similarly, if there is no error between the two transmit antennas 23, the element e ₁₂₄ of the first eigenvector e ₁₂ corresponding to the virtual antenna VRx4 and the element e ₂₂₁ of the second eigenvector e ₂₂ corresponding to the virtual antenna VRx5 and should match. Therefore, the _correction unit _{48 adjusts} the second Correct the eigenvector e ₂₂ of 2.

The corrected second eigenvectors e′ ₂₁ and e′ ₂₂ are represented by the following equations (7) to (8).
e′ ₂₁ =(e ₁₁₄ /e ₂₁₁ )×[e ₂₁₁ , e ₂₁₂ , e ₂₁₃ , e ₂₁₄ ] ^T (7)
e′ ₂₂ =(e ₁₂₄ /e ₂₂₁ )×[e ₂₂₁ , e ₂₂₂ , e ₂₂₃ , e ₂₂₄ ] ^T (8)

_In step S90 following step S80, the estimating unit 49 generates a combined eigenvector e _C1 by combining the first eigenvector e ₁₁ and the corrected second eigenvector e′ ₂₁ , Generate a combined eigenvector e _C2 that is combined with the subsequent second eigenvector e′ ₂₂ . In addition, in the above connection, matching elements are grouped into one element.

The joint eigenvectors e _C1 and e _C2 are represented by the following equations (9) to (10).
e _C1 = [e ₁₁₁ , e ₁₁₂ , e ₁₁₃ , e ₁₁₄ , (e ₁₁₄ /e ₂₁₁ )×e ₂₁₂ , (e ₁₁₄ /e ₂₁₁ )×e ₂₁₃ , (e ₁₁₄ /e ₂₁₁ )×e ₂₁₄ ] ^T ... (9)
_eC2 = [ _e121 , _e122 , _e123 , _e124 , ( _e124 / _e221 ) x _e222 , ( _e124 / _e221 ) x _e223 , ( _e124 / _e221 ) x _e224 ] ^T (10)

Furthermore, the estimating unit 49 multiplies the feature matrix A obtained by arranging the joint eigenvector e _C1 and the joint eigenvector e _C2 in order by the complex conjugate transposed matrix of the feature matrix A to generate the correlation matrix _Rev of the joint eigenvector. . The correlation matrix _Rev is represented by the following equation (11).
_Rev = AA ^H
_Rev =[ _{eC1eC2 ]} ^{* [} _{eC1HeC2H ]} (11)

Finally, the estimation unit 49 uses a known direction-of-arrival estimation method such as MUSIC (Multiple Signal Classification) and ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) to calculate the angle spectrum based on the correlation matrix _Rev. , the direction of arrival of radio waves (target angle) is estimated based on the calculated angular spectrum.

By executing the operation shown in the flowchart of FIG. 3A described above, the signal and the noise can be separated, and the error correction can be performed without being affected by the noise. Therefore, it is possible to improve the accuracy of error correction.

<2. Second Embodiment>
Next, a second embodiment of the invention will be described. Note that the description of the portions that overlap with the first embodiment will be omitted. In the second embodiment, the processing of the calculator 47, the corrector 48, and the estimator 49 is different.

The calculator 47 calculates one correlation matrix based on the received signal of the virtual array antenna, and calculates an eigenvector from the correlation matrix.

A correction unit 48 corrects the eigenvectors.

The estimator 49 estimates the direction of arrival of radio waves based on the eigenvector corrected by the corrector 48 .

A schematic operation of the radar device 1 according to the second embodiment will be described below with reference to FIG. 3B. The second embodiment differs from the first embodiment in that steps S70' to S80' are executed instead of steps S70 to S80.

In step S70′ following step S60, the calculation unit 47 calculates eigenvectors based on the received signals x ₁ to x ₈ of the virtual antennas VRx1 to VRx8.

The calculator 47 calculates a single correlation matrix R based on the received signals x ₁ to x ₈ of the virtual antennas VRx1 to VRx8. The correlation matrix R can be calculated by the following formula (12). where X ₌ [x1,x2 _{, x3} , _x4 , _x5 , _x6 , _x7 , _x8 ] ^T .
R=E[ ^XXH ] (12)

The calculator 47 performs eigenvalue decomposition on the correlation matrix R. FIG. Signal and noise can be separated by eigenvalue decomposition. Since the correlation matrix R is a matrix of 8 rows and 8 columns, eight eigenvalues of the correlation matrix R are obtained.

In this embodiment, the calculator 47 calculates an eigenvector corresponding to each specific eigenvalue of the correlation matrix R. FIG. A specific eigenvalue means an eigenvalue whose absolute value is greater than or equal to a predetermined value.

A case will be described below where only the eigenvalue Φ ₁ with the largest absolute value and the eigenvalue Φ ₂ with the second largest absolute value among the eigenvalues of the correlation matrix R correspond to specific eigenvalues.

The calculator 47 calculates an eigenvector e ₁ corresponding to the eigenvalue Φ ₁ and an eigenvector e ₂ corresponding to the eigenvalue Φ ₂ . The eigenvectors e ₁ and e ₂ calculated by the calculator 47 are not affected by noise. The eigenvectors e ₁ and e ₂ calculated by the calculator 47 are represented by the following equations (13) to (14).
e1=[ _e11 , _e12 , e13, _e14 , _e15 , _e16 , _e17 , _e18 ] ^T _{( 13} )
e2 ₌ [ _e21 , _e22 , _e23 , _e24 , e25, _e26 , _e27 , _e28 ] ^T ₍ 14)

_In step S80' following step S70', the correction unit 48 corrects the eigenvectors _e1 and e2.

If there is no error between the two transmitting antennas 23, the element e14 of the eigenvector e1 corresponding to the virtual antenna _VRx4 should _match the element _e15 of the eigenvector e1 corresponding to the virtual antenna _VRx5 . In other words, each element e ₁₅ to e ₁₈ of the eigenvector e ₁ corresponding to virtual antennas VRx5 to VRx8, which are virtual antennas generated using the same transmit antenna as virtual antenna VRx5, is the difference between e ₁₄ and e ₁₅ . have corresponding errors. Therefore, the correction unit 48 corrects the eigenvector e1 so that the element e14 of the eigenvector e1 corresponding to the virtual antenna _VRx4 and the element of the corrected eigenvector _e'1 corresponding to the virtual antenna _{VRx5 match} . Specifically, each element e ₁₅ to e ₁₈ of the eigenvector e ₁ corresponding to the virtual antennas VRx5 to VRx8 is corrected.

Similarly, if there is no error between the two transmit antennas 23, the element e ₂₄ of the eigenvector e ₂ corresponding to the virtual antenna VRx4 and the element e ₂₅ of the eigenvector e ₂ corresponding to the virtual antenna VRx5 should match. . Therefore, the correction unit 48 corrects the eigenvector e2 so that the element _e24 of the eigenvector e2 corresponding to the virtual antenna _VRx4 and the element of the corrected eigenvector _e'2 corresponding to the virtual antenna _VRx5 match.

The corrected eigenvectors e' ₁ and e' ₂ are represented by the following equations (14) to (17).
k1=(e14/ _e15 ) _{( 14} )
k2 ₌ ( _e24 /e25) ( ₁₅ )
e′ ₁ =e ₁ ^T ×[1, 1, 1, 1, k ₁ , k ₁ , k ₁ , k ₁ ] (16)
e′ ₂ =e ₂ ^T ×[1, 1, 1, 1, k ₂ , k ₂ , k ₂ , k ₂ ] (17)

In step S90 following step S80', the estimator 49 generates a joint eigenvector e _C1 . The combined eigenvector e _C1 is a vector that integrates the elements corresponding to the virtual antennas VRx4 and _VRx5 in the corrected eigenvector e′1. This is because the correction unit 48 made corrections so that the elements of both of them match each other. Similarly, the estimator 49 also generates a joint eigenvector e _C2 . The combined eigenvector e _C2 is a vector that integrates the elements corresponding to the virtual antennas VRx4 and _VRx5 in the corrected eigenvector e′2.

The joint eigenvectors e _C1 and e _C2 are represented by the following equations (18) to (19).
_eC1 =[ _e11 , _e12 , _e13 , _e14 , k1* _e16 , k1* _e17 , _k1 * _e18 ] ^T _{( 18} )
_{eC2 =} [ _e21 , _e22 , _e23 , _e24 , _k2xe26 , _k2xe27 , _{k2xe28 ]} ^T ₍ 19)

Furthermore, the estimating unit 49 multiplies the feature matrix A obtained by arranging the joint eigenvector e _C1 and the joint eigenvector e _C2 in order by the complex conjugate transposed matrix of the feature matrix A to generate the correlation matrix _Rev of the joint eigenvector. . The correlation matrix _Rev is represented by the following equation (20).
_Rev = AA ^H
_Rev =[ _{eC1eC2 ]} ^{* [} _{eC1HeC2H ]} (20)

Finally, the estimation unit 49 uses a known direction-of-arrival estimation method such as MUSIC (Multiple Signal Classification) and ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) to calculate the angle spectrum based on the correlation matrix _Rev. , the direction of arrival of radio waves (target angle) is estimated based on the calculated angular spectrum.

The radar device 1 according to this embodiment has a unique effect that cannot be achieved by the radar device 1 according to the first embodiment.

In the radar device according to the first embodiment, when the eigenvalues have approximately the same magnitude, there is a possibility that the combination is uncertain. For example, consider the situation Φ ₁₁ ≈Φ ₁₂ and Φ ₂₁ ≈Φ ₂₂ . At this time, the eigenvectors corresponding to Φ ₁₁ and Φ ₂₁ and the eigenvectors corresponding to Φ ₁₂ and Φ ₂₂ are a correct combination. However, due to the influence of noise or the like, there is a possibility that the eigenvectors corresponding to _Φ11 and _Φ22 are erroneously combined, and the eigenvectors corresponding to _Φ12 and _Φ21 are erroneously combined. If the eigenvectors are erroneously combined in this way, the estimator 49 cannot calculate the correct angle.

Such a situation can occur, for example, when there are similar targets with the same distance and speed but different angles. For example, this is the case where vehicles of the same model run side by side in the same position on both adjacent lanes.

On the other hand, in the radar apparatus 1 according to the present embodiment, since a single correlation matrix is generated using the received signals of all virtual antennas, there is no risk of uncertainty in combination in principle. Therefore, the radar device 1 according to this embodiment can stably estimate the correct angle even in the above state.

<3. Others>
Various modifications can be made to the various technical features disclosed in this specification without departing from the gist of the technical creation in addition to the above-described embodiments. In addition, multiple embodiments and modifications shown in this specification may be implemented in combination to the extent possible.

In the above-described embodiment, the errors between the transmitting antennas are corrected. error may be corrected.

When correcting the error between receiving antennas, for example, as shown in FIG. As shown, two receiving antennas 31 may be arranged with an antenna spacing of 3d along the horizontal direction. Then, the calculation unit 47 calculates the first correlation matrix R1 based on the received signals x ₁ , x ₃ , x ₅ , and x ₇ of the virtual antennas VRx1, VRx3, VRx5, and VRx7, the virtual antennas VRx2, VRx4, VRx6, and a second correlation matrix R2 based on the received signals x ₂ , x ₄ , x ₆ and x ₈ of VR x8.

In this case, the received signal of the receiving antenna 31 of 1ch includes the received signal of the virtual antenna VRx1, the virtual antenna VRx3, the virtual antenna VRx5, and the virtual antenna VRx7 which are orthogonal to each other. Similarly, the received signals of the 2ch receiving antenna 31 include the received signals of the virtual antenna VRx2, the virtual antenna VRx4, the virtual antenna VRx6, and the virtual antenna VRx8, which are orthogonal to each other.

Further, in the above-described embodiment, only the position of the virtual antenna VRx4 and the position of the virtual antenna VRx5 overlap, but a plurality of pairs of virtual antennas may overlap. For example, when the antennas are arranged as shown in FIG. 5, the positions of the virtual antennas VRx3 and VRx5 overlap, and the positions of the virtual antennas VRx4 and VRx6 overlap. In this case, for example, the first correction is performed such that the element e ₁₁₃ of the first eigenvector e ₁₁ corresponding to the virtual antenna VRx3 and the element of the corrected second eigenvector e′ ₂₁ corresponding to the virtual antenna VRx5 match. A second correction amount such that the element e ₁₁₄ of the first eigenvector e ₁₁ corresponding to the virtual antenna VRx4 matches the element of the corrected second eigenvector e′ ₂₁ corresponding to the virtual antenna VRx6 , and based on the first correction amount and the second correction amount, the final correction amount of the second eigenvector _e21 can be determined. For example, a simple average of the first correction amount and the second correction amount may be used as the final correction amount, and a weighted average of the first correction amount and the second correction amount considering the characteristics of each receiving antenna may be used. It may be the final correction amount. The same is true for the final correction amount of the second eigenvector _e22 .

Also, by providing three or more transmitting antennas, a plurality of pairs of virtual antennas having overlapping positions may be provided. For example, when the antennas are arranged as shown in FIG. 6, the positions of the virtual antennas VRx4 and VRx5 overlap, and the positions of the virtual antennas VRx8 and VRx9 overlap. In this case, for example, the calculation unit 47 also calculates a third correlation matrix R3 based on the received signals x ₉ to x ₁₂ of the virtual antennas VRx9 to VRx12, and eigenvalue decomposes the third correlation matrix R3 to obtain a third eigenvector Also calculate e ₃₁ and e ₃₂ . Then, the first correction amount is obtained such that the element e114 of the first eigenvector _e11 corresponding to the virtual antenna _VRx4 and the element of the corrected second eigenvector _e'21 corresponding to the virtual antenna VRx5 match. , to obtain a second correction amount such that the element e ₁₁₈ of the first eigenvector e ₁₁ corresponding to the virtual antenna VRx8 and the element of the corrected third eigenvector e′ ₃₁ corresponding to the virtual antenna VRx9 match, The third eigenvector _e31 can be corrected with a correction amount obtained by multiplying the first correction amount by the second correction amount. The same is true for the correction of the third eigenvector e ₃₂ .

Further, in the above-described embodiment, an on-vehicle radar system has been described, but the present invention can also be applied to an infrastructural radar system installed on a road or the like, a ship monitoring radar system, an aircraft monitoring radar system, and the like.

In the above-described embodiment, the estimation unit 49 multiplies the feature matrix A obtained by arranging the combined eigenvector e _C1 and the combined eigenvector e _C2 in order by the complex conjugate transposed matrix of the feature matrix A to obtain the correlation of the combined eigenvector A matrix R _ev was generated. This makes it possible to improve the accuracy of target angle estimation even when two targets exist at very similar angles.

For example, in the case of a radar system that does not assume a scene in which two targets exist at very similar angles, such as a ship surveillance radar system, the estimator 49 determines the combined eigenvector e _C1 and the combined eigenvector e _C1 and the complex conjugate transposed vector to generate the correlation matrix _Rev1 of the combined eigenvector e _C1 , and the combined eigenvector e _C2 and the complex conjugate transposed vector of the combined eigenvector e _C2 to generate the correlation matrix _Rev2 of the combined eigenvector e _C2 Then, an angular spectrum may be calculated based on each of the correlation matrices _Rev1 and _Rev2 , and the direction of arrival of radio waves (target angle) may be estimated based on the calculated angular spectrum.

1 radar device 2 transmitting unit 23 transmitting antenna 3 receiving unit 31 receiving antenna 4 signal processing unit 46 acquiring unit 47 calculating unit 48 correcting unit 49 estimating unit VRx1 to VRx12 virtual antenna

Claims (8)

Acquisition of received signals of a virtual array antenna including a first virtual antenna and a second virtual antenna generated by combining a plurality of transmitting antennas and a plurality of receiving antennas and having the same round-trip path distance of signals to the same target an acquisition unit that
calculating a correlation matrix of the received signal based on the received signal for each of the plurality of virtual antennas including the first virtual antenna and the second virtual antenna, and calculating an eigenvector based on eigenvalue decomposition of the correlation matrix of the received signal; a calculation unit that calculates
a correction unit that corrects the eigenvector based on the eigenvector element corresponding to the first virtual antenna and the eigenvector element corresponding to the second virtual antenna;
an estimating unit that estimates the direction of arrival of radio waves based on the eigenvector corrected by the correcting unit;
A direction-of-arrival estimation device comprising: The estimation unit
In the eigenvector after being corrected by the correction unit,
generating a combined eigenvector that combines elements corresponding to the first virtual antenna and elements corresponding to the second virtual antenna;
generating a correlation matrix for the joint eigenvectors;
estimating the direction of arrival of radio waves based on the correlation matrix of the combined eigenvectors;
A direction-of-arrival estimation apparatus according to claim 1 . The calculation unit
multiplying a feature matrix obtained by arranging a plurality of the joint eigenvectors by a complex conjugate transposed matrix of the feature matrix to generate a correlation matrix of the joint eigenvectors;
A direction-of-arrival estimation apparatus according to claim 2 . The calculation unit
calculating a correlation matrix of the single received signal based on the received signals for each of a plurality of virtual antennas including both the first virtual antenna and the second virtual antenna;
The correcting unit corrects the element of the eigenvector corresponding to the virtual antenna generated by combining either the transmitting antenna that is the same as the second virtual antenna or the receiving antenna,
A direction-of-arrival estimation apparatus according to claim 1 . The calculation unit
A first correlation matrix based on the received signal for each of the plurality of virtual antennas including the first virtual antenna and a second correlation matrix based on the received signal for each of the plurality of virtual antennas including the second virtual antenna and are calculated as correlation matrices of the separate received signals,
a first eigenvector based on eigenvalue decomposition of the first correlation matrix;
calculating a second eigenvector based on eigenvalue decomposition of the second correlation matrix;
The correction unit is
correcting the second eigenvector based on the first eigenvector element corresponding to the first virtual antenna and the second eigenvector element corresponding to the second virtual antenna;
The estimation unit
estimating the direction of arrival of radio waves based on the first eigenvector and the second eigenvector corrected by the correction unit;
A direction-of-arrival estimation apparatus according to claim 1 . The calculation unit
A first correlation matrix based on the received signal for each of the plurality of virtual antennas including the first virtual antenna and a second correlation matrix based on the received signal for each of the plurality of virtual antennas including the second virtual antenna and are calculated as correlation matrices of the separate received signals,
a first eigenvector based on eigenvalue decomposition of the first correlation matrix;
calculating a second eigenvector based on eigenvalue decomposition of the second correlation matrix;
The correction unit is
correcting the second eigenvector based on the first eigenvector element corresponding to the first virtual antenna and the second eigenvector element corresponding to the second virtual antenna;
The estimation unit
estimating the direction of arrival of radio waves based on the first eigenvector and the second eigenvector corrected by the correction unit;
4. A direction-of-arrival estimation apparatus according to claim 2 or 3. The estimation unit
combining the first eigenvector and the second eigenvector corrected by the correction unit to generate the combined eigenvector;
A direction-of-arrival estimation apparatus according to claim 6 . Acquisition of received signals of a virtual array antenna including a first virtual antenna and a second virtual antenna generated by combining a plurality of transmitting antennas and a plurality of receiving antennas and having the same round-trip path distance of signals to the same target an obtaining step for
calculating a correlation matrix of the received signal based on the received signal for each of the plurality of virtual antennas including the first virtual antenna and the second virtual antenna, and calculating an eigenvector based on eigenvalue decomposition of the correlation matrix of the received signal; a calculating step of calculating
a correcting step of correcting the eigenvector based on the eigenvector element corresponding to the first virtual antenna and the eigenvector element corresponding to the second virtual antenna;
an estimating step of estimating the direction of arrival of radio waves based on the eigenvector corrected by the correcting step;
A direction-of-arrival estimation method comprising:

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