Communications: directive radio wave systems and devices (e.g. – Determining velocity – Combined with determining distance
Reexamination Certificate
2002-10-23
2004-09-07
Lobo, Ian J. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
Combined with determining distance
C342S070000, C342S128000
Reexamination Certificate
active
06788247
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a signal processing apparatus for a radar installed on a movable object such as, for instance, a vehicle, etc., and more particularly, to a distance and speed measuring method for detecting an object in the form of a target, and measuring the relative distance and relative speed of the object, as well as to a radar signal processing apparatus using such a method.
BACKGROUND ART
In radars installed on vehicles, etc., the distance of a target which is able to be measured thereby is generally in the range of about several m to about 200 m. As a radar system for detecting objects to be measured lying in such a range, there has often been used a well-known FMCW (Frequency Modulated Continuous Wave) method which is described for example in a book entitled “Introduction to Radar Systems” by M. I. SKOLNIK, McGRAW-HILL BOOK COMPANY, INC., (1962), a book entitled “RADAR HANDBOOK” by M. I. SKOLNIK, McGRAW-HILL BOOK COMPANY, INC., (1970), a book entitled “Radar Technologies” compiled under the supervision of Takashi Yoshida and edited by the Japanese Electronic Information Communications Society (1989), etc.
FIG. 3
shows the frequency characteristics of respective signals relative to time in an FMCW radar.
In
FIG. 3
,
1
designates a transmission signal,
2
a reception signal, and
3
a beat signal. Assuming that a frequency sweep width is B; a frequency sweep time is T; the speed of light is c: a wavelength is &lgr;; the relative distance to a target is r; and the relative speed of the target is v, the frequency U of the beat signal
3
in the up phase and the frequency D of the beat signal in the down phase are represented by the following expression:
U
=
-
2
B
cT
r
+
2
λ
v
(
1
)
D
=
2
B
cT
r
+
2
λ
v
(
2
)
From these relations, the relative distance r and the relative speed v of the target are obtained from the following expressions (5), (6) by using the results according to the subtraction and addition of the beat frequencies U and D, as shown by the following expressions (3), (4).
D
-
U
=
4
B
cT
r
(
3
)
U
+
D
=
4
λ
v
(
4
)
r
=
cT
4
B
(
D
-
U
)
(
5
)
v
=
λ
4
(
U
+
D
)
(
6
)
Moreover, when there are (N) targets, the frequency Ui{i=Nu, Nu≦N}of the beat signal in the up phase and the frequency Dj{j=Nd, Nd≦N}of the beat signal in the down phase are obtained. Therefore, a frequency pair (Ux, Dy) is selected based on a criterion set beforehand. The relative distance and the relative speed of each target are obtained by substituting the frequency pair for the expressions (5) and (6).
For such a selection criterion, for example, peak strengths in the frequency spectrum of the beat signal may be employed. In Japanese Patent Application Laid-Open No. 5-142337, pairs are determined in order of the magnitude of strength thereof. In addition, in Japanese Patent Application Laid-Open No. 11-337635, there are used strength patterns which are obtained some different directions by scanning a beam.
These relative distance and relative speed of a target are generally measured repeatedly at preset time intervals.
However, in actuality, there arises a problem that the frequency of the beat signal measured in a time series manner is varied according to the state of reflection from a target in the form of a vehicle, the characteristics of the components of a transmit and receive device, etc., thus resulting in unstable measurements of the distance and speed of the vehicle.
As solutions for such a problem, Japanese Patent Application Laid-Open No. 5-142338, Japanese Patent Application Laid-Open No. 5-150035, Japanese Patent Application Laid-Open No. 5-249233, etc., disclose the use of information in a time series direction with respect to the frequency of the beat signal.
For instance,
FIG. 4
shows the configuration of a signal processing part of a millimeter wave radar system disclosed in Japanese Patent Application Laid-Open No. 5-249233. The signal processing part
10
illustrated is provided with an A/D (Analog to Digital) conversion part
11
, a frequency analysis part
12
, a switching part
13
, comparison parts
14
,
18
, reference value forming parts
15
,
19
, storage parts
16
,
20
, variation removing parts
17
,
21
, and a distance and speed deriving part
22
.
Next, the operation will be described below. In the signal processing part
10
shown in
FIG. 4
, a beat signal
3
for a target is input as an analog signal, and this beat signal is converted into a digital signal by the A/D conversion part
11
. In the frequency analysis part
12
, frequency analysis is performed through the use of an FFT (Fast Fourier Transform), etc., and the frequency U of the beat signal in an up phase and the frequency D of the beat signal in a down phase are extracted.
These frequencies are associated through the switching part
13
with the point in time t at which they are measured. The frequency U is stored as U(t) in the storage part
16
, and the frequency D is also stored as D(t) in the storage part
20
.
At time point t, the reference value forming part
15
sets a reference value Uref(t) by using the past data stored in the storage part
16
. For instance, the reference value Uref(t) is set according to the following expression (7) while assuming that an measurement interval is &Dgr;t.
Uref
(
t
)
=
U
(
t
-
Δ
t
)
+
U
(
t
-
2
·
Δ
t
)
+
⋯
+
U
(
t
-
5
·
Δ
t
)
5
(
7
)
Similarly, the reference value forming part
19
sets a reference value Dref(t) by using the past data stored in the storage part
20
. For instance, the reference value Dref(t) is set according to the following expression (8).
Dref
(
t
)
=
D
(
t
-
Δ
t
)
+
D
(
t
-
2
·
Δ
t
)
+
⋯
+
D
(
t
-
5
·
Δ
t
)
5
(
8
)
The comparison part
14
compares the frequency U(t) of the beat signal in the up phase input thereto via the switching part
13
with the reference value Uref(t) set by the reference value forming part
15
, and determines whether the frequency U(t) of the beat signal in the up phase is data without any variation. For instance, whether the relationship of the following expression (9) is satisfied for a preset allowance or allowable width Wu is used as a criterion for such a determination.
|
U
(
t
)−
Uref
(
t
)|≦
Wu
(9)
Similarly, the comparison part
18
compares the frequency D(t) of the beat signal in the down phase input thereto via the switching part
13
with the reference value Dref(t) set by the reference value forming part
19
, and determines whether the frequency D(t) of the beat signal in the down phase is data without any variation. For instance, whether the relationship of the following expression (10) is satisfied for a preset allowance or allowable width Wd.
|
D
(
t
)−
Dref
(
t
)≦
Wd
(10)
The frequency U(t) of the beat signal in the up phase, for which the presence or absence of a variation was determined by the comparison part
14
, is removed by the variation removing part
17
if determined as including a variation, whereas it is stored in the storage part
16
and input to the distance and speed deriving part
22
if determined as including no variation.
Similarly, the frequency D(t) of the beat signal in the down phase, for which the presence or absence of a variation was determined by the comparison part
18
, is removed by the variation removing part
21
if determined as including a variation, whereas it is stored in the storage part
20
and input to the distance and speed deriving part
22
if determined as including no variation.
Here, note that the frequency data U(t−&Dgr;t) and D(t−&Dgr;t) of the last beat signal may be used instead of the frequencies U(t) and D(t) of the current beat signal when the frequencies of the beat sign
Fujisaka Takahiko
Kai Koichi
Kosuge Yoshio
Mitsumoto Masashi
Okada Takamitsu
Lobo Ian J.
Mitsubishi Denki & Kabushiki Kaisha
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