U.S. patent application number 12/424850 was filed with the patent office on 2010-05-06 for radar device.
This patent application is currently assigned to Mitsubishi Electric Corporation. Invention is credited to Kado NAKAGAWA.
Application Number | 20100109939 12/424850 |
Document ID | / |
Family ID | 42130737 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100109939 |
Kind Code |
A1 |
NAKAGAWA; Kado |
May 6, 2010 |
RADAR DEVICE
Abstract
In a radar device including a transmitting unit for transmitting
a transmission signal having plural modulation sections, a
receiving unit for receiving a reflection signal obtained through
reflection of the transmission signal from a target by an array
antenna having plural channels, a mixing unit for mixing the
transmission signal with reception signals of the plural channels
to obtain beat signals of the plural channels, a frequency
analyzing unit for frequency-analyzing the beat signals of the
plural channels, and a direction calculating unit for calculating
the direction to the target on the basis of frequency analysis
results of the plural channels, the direction calculating unit adds
correlation matrixes generated from peak frequency spectra of the
plural modulation sections to obtain an summed correlation matrix,
and calculating the direction to the target on the basis of the
summed correlation matrix.
Inventors: |
NAKAGAWA; Kado; (Chiyoda-ku,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
42130737 |
Appl. No.: |
12/424850 |
Filed: |
April 16, 2009 |
Current U.S.
Class: |
342/157 |
Current CPC
Class: |
G01S 2013/0245 20130101;
G01S 3/74 20130101; G01S 13/584 20130101 |
Class at
Publication: |
342/157 |
International
Class: |
G01S 13/00 20060101
G01S013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2008 |
JP |
2008-283220 |
Claims
1. A radar device comprising: a transmitting unit for transmitting
a transmission signal having plural modulation sections; a
receiving unit for receiving a reflection signal obtained through
reflection of the transmission signal from a target by an array
antenna having plural channels; a mixing unit for mixing the
transmission signal with reception signals of the plural channels
to obtain beat signals of the plural channels; a frequency
analyzing unit for frequency-analyzing the beat signals of the
plural channels; and a direction calculating unit for calculating
the direction to the target on the basis of frequency analysis
results of the plural channels, wherein the direction calculating
unit sums correlation matrixes generated from peak frequency
spectrum of the plural modulation sections to obtain a summed
correlation matrix, and calculating the direction to the target on
the basis of the summed correlation matrix.
2. The radar device according to claim 1, wherein the modulation
sections of the transmission unit are subjected to frequency
modulation so that the frequency varies with time lapse.
3. The radar device according to claim 2, wherein the modulation
sections are subjected to the frequency modulation so that
frequency modulation width is different every modulation
section.
4. The radar device according to claim 2, wherein the modulation
sections are subjected to the frequency modulation so that
modulation time is different every modulation section.
5. The radar device according to claim 2, wherein the modulation
sections are subjected to the frequency modulation so that both
frequency modulation width and modulation time are different every
modulation section.
6. The radar device according to claim 2, wherein the modulation
sections of the transmission unit have an UP section in which the
frequency increases with time lapse and a DOWN section in which the
frequency decreases with time lapse.
7. The radar device according to claim 6, wherein the modulation
sections of the transmitting unit have alternately repetitive
arrangement of an UP section in which frequency increases with time
lapse and a DOWN section in which the frequency decreases with time
lapse.
8. The radar device according to claim 6, wherein the direction
calculating unit generates a summed correlation matrix by adding
correlation matrixes generated from UP-section peak frequency
spectra and a correlation matrixes generated from DOWN-section peak
frequency spectra, and calculates the direction to the target on
the basis of the summed correlation matrix.
9. The radar device according to claim 7, wherein the direction
calculating unit generates a summed correlation matrix by adding
correlation matrixes generated from UP-section peak frequency
spectra and a correlation matrixes generated from DOWN-section peak
frequency spectra, and calculates the direction to the target on
the basis of the summed correlation matrix.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a radar device for applying
a transmission signal (electronic waves) to a target object
(hereinafter referred to as "target"), receiving a reflection
signal based on the transmission signal from the target by plural
receiving units and calculating target information on the basis of
the reflection signal.
[0003] 2. Description of the Related Art
[0004] As a radar device for calculating the distance to a target
and the relative speed has been hitherto known a
frequency-modulation radar device in which a transmission signal
having continuously-modulated frequencies is transmitted to a
target, a reflection signal from the target is received and the
distance to the target and the relative speed are calculated.
[0005] A method of mechanically turning a transmission unit to
sweep a transmission signal and calculating the direction to a
target is known as a method of calculating the target direction in
this type radar device. Furthermore, there is also known a
super-resolution incoming direction (arrival direction) estimation
processing such as Music (Multiple Signal Classification) method of
outputting a transmission signal without mechanically turning the
transmission unit and executing digital signal processing on a
reception signal received by an array antenna comprising plural
channels to calculate the direction to a target (for example, R. O.
Schmidt "Multiple Emitter Location and Signal Parameter Estimation"
IEEE Trans. Ap-34, No. 3, pp. 276-280 (1986); hereinafter referred
to as "non-patent document").
[0006] According to the MUSIC method disclosed in the non-patent
document, a correlation matrix of a peak frequency spectrum is
calculated, the correlation matrix is subjected to an
eigendecomposition, an angle spectrum is calculated from an
eigenvector and the direction to a target is calculated from the
angle spectrum. Furthermore, for example, according to a method
disclosed in JP-A-2006-145251 (hereinafter referred to as "patent
document"), a reception vector is not generated by using only the
peak frequency of a peak waveform, but reception vectors are also
generated by using other frequencies belonging to the same peak
waveform. In this case, the correlation matrixes thereof are
calculated and added, whereby the number of snapshots used to
calculate the correlation matrixes is secured.
[0007] The super-resolution incoming direction estimation
processing which is represented by the technique disclosed in the
non-patent document is based on the assumption that the respective
incoming waves are irrelevant to one another. Therefore, it cannot
be directly applied to land mobile communication or the like in
which the correlation among the respective incoming waves is very
high. In order to suppress the correlation among the incoming
waves, it is generally desired to increase the number of reception
signals used to generate the correlation matrix (the number of
snapshots).
[0008] Accordingly, a correlation matrix is obtained every
measurement in the radar device, and thus there is known a
so-called time averaging method in which the number of snapshots is
secured by utilizing correlation matrixes obtained through past
measurements executed over plural periods. With respect to the time
averaging method in which the number of snapshots is secured by
utilizing the correlation matrixes obtained through the past
measurements executed at plural periods, when it is applied to a
mobile object such as an in-vehicle mount radar device or the like,
the positional relationship with a target is varied in accordance
with the measurement timing, and thus the incoming direction of
electronic wave is varied. Therefore, when it takes long time to
secure the number of snapshots, the precision of the correlation
matrix (and thus the estimation precision of the incoming direction
of the electronic wave) is lowered.
[0009] On the other hand, according of the patent document
described above, in order to secure the number of snapshots, a
reception vector is not generated from only the peak frequency of a
peak waveform, but reception vectors are also generated from other
frequencies belonging to the same peak waveform, and the
correlation matrixes thereof are calculated. Therefore, the
calculation is complicated, and also the direction to a target
cannot be calculated with high precision because the frequencies
other than the peak frequency are used.
SUMMARY OF THE INVENTION
[0010] The present invention has been implemented to solve the
above problems, and has an object to provide a radar device that
can secure a snapshot number in short time and calculate the
direction to a target with high precision in a radar device for
calculating the direction to the target on the basis of a frequency
analysis result of plural channels.
[0011] In order to attain the above object, a radar device
according to the present invention is equipped with a transmitting
unit for transmitting a transmission signal having plural
modulation sections, a receiving unit for receiving reflection
signals obtained through reflection of the transmission signal from
targets by an array antenna having plural channels, a mixing unit
for mixing the transmission signal with reception signals of the
plural channels to obtain beat signals of the plural channels, a
frequency analyzing unit for frequency-analyzing the beat signals
of the plural channels; and a direction calculating unit for
calculating the direction to the target on the basis of frequency
analysis results of the plural channels, wherein the direction
calculating unit sums correlation matrixes generated from peak
frequency spectra of the plural modulation sections to obtain a
summed correlation matrix, and calculating the direction to the
target on the basis of the summed correlation matrix.
[0012] According to the present invention, the correlation matrixes
generated from the peak frequency spectra of the plural modulation
sections which are obtained at the same measurement period are used
to calculate the direction to the target, thereby securing a
snapshot number, and the direction to the target is calculated on
the basis of the summed correlation matrix obtained by adding the
plural correlation matrixes. Therefore, the snapshot number can be
secured in short time, and the angle can be calculated with higher
precision as the number of the modulation sections is larger.
[0013] The foregoing and other object, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram showing a radar device according
to an embodiment of the present invention;
[0015] FIG. 2 is a flowchart showing the operation of a target
detector according to the embodiment of the present invention;
[0016] FIG. 3 is a diagram showing the amplitude of each complex
spectrum every channel and every modulation section in the
embodiment of the present invention; and
[0017] FIG. 4 is a diagram showing the processing of an MUSIC
spectrum in the embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] A preferred embodiment according to the present invention
will be described hereunder with reference to the accompanying
drawings.
[0019] FIG. 1 is a block diagram showing a radar device according
to an embodiment of the present invention.
[0020] In FIG. 1, a radar device has a target detector 1 comprising
a microcomputer, a control voltage generator 2 for outputting a
control voltage under the control of the target detector 1, VCO
(Voltage Controlled Oscillator) 3 for outputting a transmission
signal whose frequency is subjected to UP/DOWN modulation on the
basis of the control voltage, a distributor 4 for distributing a
transmission signal, and a transmission antenna 5 (transmission
unit) for emitting a transmission signal W1 to a target 40.
[0021] The radar device also has array type reception antennas 6 to
11 (reception unit) of plural channels (for example, 6 channels)
for receiving a reflection signal W2 which is obtained through
reflection of the transmission signal W1 from the target 40, mixers
12 to 17 (mixing unit) for mixing the transmission signal
distributed by the distributor 4 with the reception signals of the
plural channels to obtain beat signals of the plural channels, A/D
converters 18 to 23 for A/D-converting the beat signals of the
plural channels, and FFT (Fast Fourier Transform) operators 24 to
29 (frequency analysis unit) for executing frequency analysis on
the A/D-converted beat signals of the plural channels.
[0022] The frequency analysis results of the beat signals of the
plural channels (the beat frequency spectra of the plural channels)
from the FFT operators 24 to 29 are input to the target detector 1.
The target detector 1 calculates the distance to the target 40, the
relative speed of the target 40 or the direction to the target 40,
and outputs it as target information to an external device (not
shown).
[0023] In order to attain the target information, the target
detector 1 has a peak detector 30 for detecting the peak frequency
from the frequency analysis results of the beat signals, a
distance/relative speed calculator 31 for calculating the distance
R to the target 40 and the relative speed V of the target 40 on the
basis of the peak frequency, and a direction calculator 32 for
calculating the direction .theta. to the target 40 on the basis of
the beat frequency spectra of the plural channels, the distance R
and the relative speed V.
[0024] The operation of the embodiment according to the present
invention shown in FIG. 1 will be described.
[0025] When a modulation start instruction is output from the
target detector 1 to the control voltage generator 2, a control
voltage of a modulation section (for example, triangular UP/DOWN)
is applied from the control voltage generator 2 to VCO (Voltage
Controlled Oscillator) 3, and a transmission signal which is
subjected to frequency modulation in the UP section/Down section
according to the control voltage is output from VCO 3.
[0026] The transmission signal is distributed through the
distributor 4 to the transmission antenna 5 and the mixers 12 to
17, and emitted from the transmission antenna 5 to the target
40.
[0027] Furthermore, a reflection signal W2 reflected from the
target 40 is received as reception signals of six channels (CH1 to
CH6) by plural (for example, six) reception antennas 6 to 11, and
each of the reception signals is mixed with the transmission signal
by each of the mixers 12 to 17.
[0028] Accordingly, beat signals corresponding to the six channels
are generated from the mixers 12 to 17, and each beat signal is
converted to digital data in each of the A/D converters 18 to 23
with respect to each of the UP section in which the frequency
increases with time lapse and the DOWN section in which the
frequency decreases with time lapse.
[0029] The digital data generated from the A/D converters 18 to 23
are individually subjected to frequency analysis using FFT by the
FFT operators 24 to 29 (frequency analysis unit). The frequency
analysis results of the six channels (the beat frequency spectra)
calculated by the FFT operators 24 to 29 are input to the target
detector 1 with respect to each of the UP section and the DOWN
section.
[0030] In the target detector 1, the peak detector 30 first detects
the peak frequency from the frequency analysis results of the six
channels. Subsequently, the distance/relative speed calculator 31
calculates the distance to the target 40 and the relative speed of
the target 40 on the basis of the detected peak frequency. At this
time, the calculation value of impossible distance or relative
speed is not regarded as information of the target 40 and thus it
is excluded.
[0031] Finally, the direction calculator 32 executes
super-resolution incoming direction estimation processing on the
beat frequency spectrum corresponding to the peak frequency used to
calculate the distance and the relative speed, thereby calculating
the direction .theta. of the target 40. In this case, the MUSIC
method described above is used as the super-resolution incoming
direction estimation processing.
[0032] Specifically, as described later, the direction calculator
32 generates a summed correlation matrix by adding a correlation
matrix generated from the UP-section peak frequency spectrum and a
correlation matrix generated from the DOWN-section peak frequency
spectrum, and calculates the direction to the target 40 or the
number of targets on the basis of an eigenvalue and an
eigenvector.
[0033] The operation of the target detector 1 shown in FIG. 1 will
be described with reference to FIGS. 2 to 4.
[0034] FIG. 2 is a flowchart showing the operation procedure of the
target detector 1. FIG. 3 is a diagram showing the processing of
step S101 in FIG. 2, and shows the amplitudes of input beat
frequency spectra of six channels. FIG. 4 is a diagram showing the
processing of step S106 in FIG. 2, and shows an example of a MUSIC
spectrum.
[0035] In FIG. 2, the peak detector 30 first detects the peak with
respect to the amplitudes of the beat frequency spectra of the six
channels (step S101). Specifically, as shown in FIG. 3, a detection
threshold value is provided for the amplitudes of the beat
frequency spectra of the six channels, and the amplitude of a beat
frequency which is above the detection threshold value and also
larger than the amplitude of each of beat frequencies before and
after the beat frequency concerned is judged as the peak.
[0036] In FIG. 3, (a) to (f) show the amplitudes of the beat
frequency spectra of the six channels at UP, and (g) to (l) shows
the amplitudes of the beat frequency spectra of the six channels at
DOWN. In each graph, the abscissa axis represents the beat
frequency, and the ordinate axis represents the amplitude.
Furthermore, the peak frequency having the peak amplitude is
represented by "fbu" in the UP section and by "fbd" in the DOWN
section.
[0037] Returning to FIG. 2, the distance/relative speed calculator
31 calculates the distance R to the target 40 and the relative
speed V of the target 40 on the basis of the peak frequencies fbu
and fbd obtained in step S1 according to the principle of general
FM-CW (Frequency Modulation Continuous Wave) radar (step S102).
That is, the distance R is calculated according to the following
equation (1).
R = cT 4 f m ( f bu + f bd ) ( 1 ) ##EQU00001##
Furthermore, the relative speed V is calculated according to the
following equation (2).
V = - c 4 f c ( f bu - f bd ) ( 2 ) ##EQU00002##
[0038] In the equation (1) and the equation (2), c represents
velocity of light, T represents one modulation time, fm represents
frequency modulation width and fc represents the frequency of
carrier wave. Subsequently, the distance/relative speed calculator
31 counts and stores the number K of the targets 40 (step
S103).
[0039] Next, the direction calculator 32 generates a correlation
matrix to be used for the MUSIC method (step S104). The summed
correlation matrix Rc obtained by adding the correlation matrix
generated from the UP-section peak frequency spectrum and the
correlation matrix generated from the DOWN-section peak frequency
spectrum is 6.times.6 order, and it is represented by the following
equation (3).
R c = [ X 1 X 1 * X 1 X 2 * .LAMBDA. X 1 X 6 * X 2 X 1 * X 2 X 2 *
.LAMBDA. X 2 X 6 * M M O M X 6 X 1 * X 6 X 2 * .LAMBDA. X 6 X 6 * ]
+ [ Y 1 Y 1 * Y 1 Y 2 * .LAMBDA. Y 1 Y 6 * Y 2 Y 1 * Y 2 Y 2 *
.LAMBDA. Y 2 Y 6 * M M O M Y 6 Y 1 * Y 6 Y 2 * .LAMBDA. Y 6 Y 6 * ]
( 3 ) ##EQU00003##
In the above equation (3), Xi represents the beat frequency
spectrum of the peak frequency fbu at the i-th (i=1, . . . , 6)
channel (CHi), and Yi represents the beat frequency spectrum of the
peak frequency fbd at i-th (i=1, . . . , 6) channel (CHi). Xi*
represents the complex conjugate of Xi, and Yi* represents the
complex conjugate of Yi.
[0040] Furthermore, the direction calculator 32 analyze the
eigenvalue and the eigenvector for the correlation matrix Rc to
determine eigenvalues .lamda.1 to .lamda.6 and corresponding
eigenvectors e1 to e6 (step S105).
[0041] Subsequently, the direction calculator 32 calculates an
angle spectrum Pm(.theta.) (MUSIC spectrum) on the basis of the
general MUSIC method by using the eigenvalues .lamda.1 to .lamda.6
and the eigenvectors e1 to e6 according to the following equation
(4) (step S106).
P m ( .theta. ) = a ( .theta. ) 2 i = K + 1 6 e i H a ( .theta. ) 2
, a ( .theta. ) = [ 1 exp ( j.DELTA..phi. ) exp ( j2.DELTA..phi. )
exp ( j3.DELTA..phi. ) exp ( j4.DELTA..phi. ) exp ( j5.DELTA..phi.
) ] , .DELTA..phi. = 2 .pi. d .lamda. sin .theta. ( 4 )
##EQU00004##
[0042] In the equation (4), eiH represents the complex conjugate
transposition of eigenvector ei, K represents the number of
incident signals, .lamda. represents the wavelength and d
represents the element interval of the reception antennas 6 to 11.
Subsequently, the direction calculator 32 extracts a direction
.theta. at which the MUSIC spectrum is peak (step S107).
Specifically, when the MUSIC spectrum of the direction being noted
is larger than the MUSIC spectra before and after the MUSIC
spectrum concerned, the direction concerned is calculated as the
peak direction.
[0043] The thus-extracted peak directions are successively set as
the direction .theta. of the target 40 in the decreasing order of
the MUSIC spectrum. In the example of FIG. 4, .theta.1, .theta.2
are calculated as the directions .theta. of the two targets.
[0044] The steps S105 to S107 correspond to the basic processing of
MUSIC, and the detailed description thereof is omitted because it
is made open to public in various well-known documents.
[0045] Finally, the target detector 1 determines whether the
calculation of targets whose number K is counted in step S103
calculation of targets whose number K is counted in step S103 is
completed or not (step S108). If the calculation is not completed
(that is, NO), the processing returns to step S104 to repetitively
execute the processing of the steps S104 to S107.
[0046] On the other hand, in step S108, if it is determined that
the calculation has been executed at the frequency corresponding to
the number of the targets (that is, Yes), the distance R, the
relative speed V or the direction .theta. of all the targets 40 are
output as target information to the external device (not
shown).
[0047] As described above, according to the embodiment 1 of the
present invention, the direction calculator 32 secure the snapshot
number by utilizing the correlation matrix generated from the
UP-section peak frequency spectrum and the correlation matrix
generated from the DOWN-section peak frequency spectrum, and the
direction of the target is calculated on the basis of the summed
correlation matrix obtained by adding both the correlation
matrixes, so that the snapshot number can be secured in short time
and the direction to the target can be calculated with high
precision.
[0048] In the above embodiment, the six reception antennas 6 to 11
(see FIG. 1) are used. However, the present invention can be
likewise applied even when reception antennas of a different number
are used.
[0049] Furthermore, in the above embodiment, two sections of the
UP-section and the DOWN-section are used as the modulation section.
However, the present invention is likewise applicable even when the
number of the modulation sections is equal to three or more, the
modulation sections are combined with another modulation section
such as non-modulation or the like or the frequency modulation
width or the modulation time is changed every section.
[0050] Still furthermore, in order to suppress the correlation of
the incoming waves, a so-called spatial averaging method for
determining an average value of correlation matrixes obtained by
properly moving the reception position may be used.
[0051] Furthermore, the MUSIC method is used as the direction
calculation processing of the target 40 by the direction calculator
32. However, the present invention may be applied to a radar device
using another method such as unitary MUSIC method, ESPRIT method,
unitary ESPRIT method or the like. Particularly, when the unitary
method is used, only the real number portion of the correlation
matrix may be used, and thus the operation load can be further
reduced.
[0052] Still furthermore, the FM-CW system is used as a system for
detecting the distance R and the relative speed V of the target 40.
However, the present invention is applicable to a radar device in
which the transmission signal is modulated to be sectioned in the
form of pulse.
[0053] Various modifications and alterations of this invention will
be apparent to those skilled in the art without departing from the
scope and spirit of this invention, and it should be understood
that this is not limited to the illustrative embodiments set forth
herein.
* * * * *