Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2000-11-22
2002-08-06
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S071000, C342S072000, C342S099000, C342S123000, C342S128000, C342S146000, C340S903000, C340S435000, C340S436000
Reexamination Certificate
active
06429804
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor-vehicle-mounted radar apparatus mounted on a vehicle and used to explore obstacles such as other vehicles traveling around the vehicle, for example, ahead of the vehicle, as targets thus securing safety of driving.
2. Description of the Related Art
Conventionally, motor-vehicle-mounted radar apparatus that explores obstacles of a vehicle in the direction of traveling has been developed. As motor-vehicle-mounted radar apparatus, the FM-CW system is employed in which an exploration wave as a continuous sending wave frequency-modulated using a triangular wave as a modulating wave and a beat component caused by a reflected wave from a target are extracted as a beat signal, and the relative velocity and relative range to the target are obtained based on the frequency of the beat signal. Related arts concerning the FM-CW system radar apparatus are disclosed, for example, in the Japanese Patent Laid-Open No. 111395/1977, the Japanese Patent Laid-Open No. 120549/1995, the Japanese Patent Laid-Open No. 80184/1997 and the Japanese Patent Laid-Open No. 145824/1997. Especially in the Japanese Patent Laid-Open No. 120549/1995, a configuration is disclosed whereby the radiation direction of a beam-shaped radio wave transmitted from motor-vehicle-mounted radar apparatus can be changed in order to correctly explore a target such as a vehicle traveling diagonally ahead for example in curvilinear traveling.
FIG. 16
shows a schematic configuration of conventional motor-vehicle-mounted radar apparatus of the FM-CW system
1
. The motor-vehicle-mounted radar apparatus
1
explores a target
2
and transmits a radio wave for exploration from an antenna
3
in order to calculate the range to the target
2
and the relative velocity to the target
2
. The antenna
3
receives the reflected radio wave reflected off the target
2
. The antenna
3
is formed in a beam shape having a sharp range whose gain is high. Thus it is possible to execute scanning with beam direction changed via a scanning mechanism
4
and to detect the direction of the target
2
from the direction of beam in receiving a reflected signal from the target
2
. With the range to and direction of the target
2
obtained, the position of the target
2
can be relatively obtained based on the position of the vehicle.
In the exploration according to FM-CW system, a transmitter circuit
5
is used to give an exploration signal frequency-modulated by a triangular wave to the antenna
3
for transmission, a reflected signal received by the antenna
3
is amplifier and frequency-converted by a receiver circuit
6
and converted to a digital signal by an analog-to-digital (hereinafter referred to as A/D) converter circuit
7
, then converted to a frequency component by a fast Fourier Transform (hereinafter referred to as FFT) circuit
8
. An object detection circuit
9
, based on the range R and the relative velocity V to the target
2
based on the frequency component from the FFT circuit
8
.
Each of
FIGS. 17A and 17B
show a principle in which the object detection circuit shown in
FIG. 16
explores the target
2
and calculates the range R and the relative velocity V in accordance with the FM-CW system. From the antenna
3
in
FIG. 16
, an exploration signal
10
for frequency-modulated continuous wave (CW) is transmitted so that frequencies maybe continuously varied on the triangular wave at a constant variation velocity. An exploration
10
wave reflects off the target
2
and a resulting reflected signal
11
that is received by the antenna
3
is delayed as long as the period corresponding to the range R from the exploration signal
10
. This causes difference in frequencies for the exploration signal
10
whose frequency is in variation. The relative velocity V is generated to the target
2
. Thus the Doppler shift effect is generated on the reflected signal
11
, causing difference in frequency from the exploration signal
10
.
In the FM-CW system, as shown in
FIG. 17B
, variation in frequency caused by the Doppler shift effect is reflected differently on an upbeat signal
12
as a beat signal in the frequency rise section where the frequency shift amount of frequency modulation is increasing, and on a downbeat signal
13
as a beat signal in the frequency drop section where the frequency shift amount of frequency modulation is decreasing. Thus the frequency fub of the upbeat signal
12
and the frequency fdb of the downbeat signal
13
can be represented as the following expressions
1
and
2
using the range frequency fr and the Doppler shit frequency fd that are standard beat signal frequencies.
fub=fr−fd
(1)
fdb=fr+fb
(2)
Here, the range frequency fr is in proportion to the range R to the target
2
and can be represented by the following expression
3
assuming the frequency shift amplitude of the exploration signal of the FM-CW system
10
as a triangular wave as &Dgr;f, modulating frequency as a triangular wave fm, and the velocity of light C. The Doppler shift frequency fd can be represented by the following expression
4
assuming the relative velocity to the target
2
as V and the wavelength of the exploration signal as &lgr;. It is also possible to calculate the range R and the relative velocity V respectively from the range frequency fr and the Doppler shift frequency fd by using the expressions
3
and
4
.
fr=
4×&Dgr;
f×fm×
R/C (3)
fd=
2V/&lgr; (4)
As shown in
FIG. 16
, related arts concerning the motor-vehicle-mounted radar apparatus that scans the beam direction of the antenna
3
are disclosed, for example, in the Japanese Patent Laid-Open No. 64499/1999, the Japanese Patent Laid-Open No. 72651/1999, the Japanese Patent Laid-Open No. 84001/1999 and the Japanese Patent Laid-Open No. 121053/1999. In the Japanese Patent Laid-Open No. 82673/1996, a configuration whereby the short range and long range are switched over for exploring a target. In the Japanese Patent Laid-Open No. 282220/1998, a related technology is disclosed whereby part of data obtained in radar exploration is used to identify a target for a radar for an airframe. In the Japanese Patent Laid-Open No. 38141/1999, a related art is disclosed whereby a mobile-vehicle-mounted radar is used to recognize an obstacle in a three-dimensional image.
Of the related arts that scan the beam direction of an antenna, for example in the Japanese Patent Laid-Open No. 84001/1999 and the Japanese Patent Laid-Open No. 231053/1999, a philosophy is described that a plurality of explorations are carried out in a single scan period and the target direction is estimated from the peak of the reflected signal level obtained according to the variation in beam direction. In order to upgrade the exploration accuracy of the exploration in the target direction using such a philosophy in the related arts, it is necessary to explore a target in more directions and to increase of the frequency of exploration. Such a method suffers from high load of operation processing so that special hardware for high-speed signal processing is required to process data at a high speed. High-speed signal processing has a problem of heat as well as costs. Smooth operation requires a corresponding circuit scale thus upsizing the system configuration.
A method is also available whereby the limits of angle of exploration in a specific section where a target is present is narrowed. This approach requires a complicated hardware configuration and has few merits in terms of costs.
In recognizing a target, it is necessary to prepare a complicated logic in order to extract a true target in case reflected signals from a guard rail, tunnel, or sound-proof wall is received. In the case of a guard rail, the relative velocity calculated after paring processing in which the frequency in the frequency rise section and the frequency in the frequency drop section according to the FM-CW system are combined does to
Higashida Hirofumi
Kishida Masayuki
Ono Daisaku
Fujitsu Ten Limited
Sotomayor John B.
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