Communications: directive radio wave systems and devices (e.g. – Presence detection only
Reexamination Certificate
2001-06-01
2002-07-23
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Presence detection only
C342S028000, C342S052000, C342S058000, C342S070000, C375S130000, C375S140000, C375S146000, C375S147000, C375S150000
Reexamination Certificate
active
06424289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an obstacle detection device using a leaky transmission path such as a leaky coaxial cable, a leaky wave guide and the like, and more particularly relates to an obstacle detection device and obstacle detection system precisely detecting the presence and position of an obstacle utilizing spread spectrum technology regardless of whether the obstacle is motionless or moving.
2. Description of the Related Art
A fallen object from a traveling vehicle, a vehicle performing an emergency stop operation or the like are considered as examples of an obstacle on ordinary roads and railroad lines. Since these obstacles in a state of being motionless on the ordinary roads and railroad lines are factors causing the occurrences of a rear end collision and a double rear end collision accident, in order to prevent these occurrences, it is also necessary to promptly detect these obstacles and perform removal operations for these obstacles.
As an obstacle detection device for detecting an obstacle on the ordinary roads and railroad lines arising from the above-described request, there are obstacle detection devices which use leakage transmission paths such as a leakage coaxial cable, a leakage wave guide and the like. A brief explanation of the configurations of these leakage transmission paths will be given hereafter. A leakage wave guide is one in which multiple slots leaking and radiating a radio wave in the longitudinal direction of a wave guide comprising a conductor are provided at suitable intervals. A leakage coaxial cable has a configuration based on a principle similar to that of the leakage wave guide. A related-art obstacle detection device using a leakage coaxial cable (hereafter, referred to as LCX) will be described below.
FIG. 6
is a block diagram showing a configuration of a related-art obstacle detection device disclosed in Japanese Laid-Open Patent Application No. 10-95338. In
FIG. 6
, reference numeral
1
′ denotes a transmission LCX which is laid on one side of a road or a railroad line and provided with a plurality of slots leaking and radiating a pulse modulated signal for detection at suitable intervals in the longitudinal direction, reference numeral
2
′ denotes a receiving LCX which is laid on the opposing side of the transmission LCX
1
′ laid on the road or the railroad line and receives the radiated pulse signal from the transmission LCX
1
′ by a plurality of slots provided at suitable intervals in the longitudinal direction. Matched terminations are connected at far ends of the transmission LCX
1
′ and the receiving LCX
2
′ opposite to a transmitter
63
and a receiver
64
, respectively. Reference numeral
63
denotes a transmitter connected to one end (near end) of the transmission LCX
1
′ and generating a pulse modulated signal for detecting an obstacle; reference numeral
64
denotes a receiver connected to one end (near end) of the receiving LCX
2
′, which end is opposite to the near end of the transmission LCX
1
′, and receiving the pulse modulated signal for detection from the transmission LCX
1
′; reference numeral
65
denotes a portion of the receiver
64
operating as a low pass filter (hereafter, referred to as LPF) for extracting an envelope from a waveform of the pulse modulated signal for detection which has been received by the receiver
64
; reference numeral
66
denotes a portion of the receiver
64
operating as a memory device for storing an envelope extracted from the waveform of pulse modulated signal for detection when an obstacle does not exist; and reference numeral
67
denotes a portion of the receiver
64
operating as a computing unit in which the difference between an envelope from a waveform of the pulse modulated signal for detection extracted by the LPF
65
and an envelope stored in the memory device
66
when an obstacle does not exist is found and the position of the obstacle is detected from the difference waveform.
A description will now be given of the operation according to the related art.
A signal for detecting an obstacle which has been pulse modulated in the transmitter
63
is outputted to the transmission LCX
1
′. The inputted pulse signals in the transmission LCX
1
′ are in turn radiated as a radio wave from the respective slots aligned in the longitudinal direction of the transmission LCX
1
′. This radio wave enters the respective slots provided in the longitudinal direction of the receiving LCX
2
′ opposed to the transmission LCX
1
′, and received by the receiver
64
with a delay corresponding to the positions of the slots. When the receiver
64
receives a radio wave from the transmission LCX
1
′, the LPF
65
in the receiver
64
extracts an envelope from a waveform of the pulse signal for detecting an obstacle received as a radio wave from the transmission LCX
1
′ and transmits the extracted envelope to the computing unit
67
. The computing unit
67
reads the envelope (reference waveform) previously measured when an obstacle does not exist from the memory device
66
whenever the LPF
65
extracts an envelope from a waveform of the received signal and finds a difference waveform between the read envelope and the envelope of the waveform of the pulse modulated signal for detection which the LPF
65
has extracted. At this time, if an obstacle exists on the road or the railroad line, which intervenes between the transmission LCX
1
′ and the receiving LCX
2
′, the radio wave from the transmission LCX
1
′ is interrupted at its position. Therefore, if an obstacle exists, a reception level of a radio wave received by the receiving LCX
2
′ from the transmission LCX
1
′ is reduced by a certain degree, irrespective of the field intensity provided by the transmission LCX
1
′. Owing to this, since a change corresponding to the obstacle appears in the difference waveform calculated by the computing unit
67
, the presence of the obstacle can be detected.
Since the related-art obstacle detection device is configured as described above, and because the coupling loss of a signal transmitted via a LCX is large, the received S/N ratio of the pulse modulation signal that the receiver
64
receives is small and the reference waveform used during the detection of an obstacle varies, resulting in a problem that an obstacle could not be detected with the sufficient precision to satisfy reliability demands.
The above-described problem will be concretely described below.
FIGS. 7A-7H
are graphical representations showing a transmitted waveform and received waveform of a related-art obstacle detection device described above.
FIG. 7A
shows a waveform of a pulse modulated signal for detecting an obstacle outputted to the transmitting LCX
1
′ by the transmitter
63
.
FIG. 7B
shows an ideal waveform of a signal received by the receiver
64
via the receiving LCX
2
′ without considering factors such as the coupling loss and noise of LCX,
FIG. 7C
shows a waveform of a signal received by the receiver
64
via the receiving LCX
2
′ in consideration of the coupling loss of LCX,
FIG. 7D
shows an envelope extracted from a signal waveform of
FIG. 7C
,
FIG. 7E
shows an observed waveform of a received signal by the receiver
64
via the receiving LCX
2
′,
FIG. 7F
shows an envelope extracted from the waveform of
FIG. 7E
,
FIG. 7G
shows a waveform when the noise is added to a signal received by the receiver
64
, and
FIG. 7H
shows an envelope from the signal waveform of FIG.
7
G.
A signal outputted from the transmitter
63
to the receiving LCX
1
′ is pulse modulated and shows a sinusoidal waveform as shown in FIG.
7
A. This signal is radiated as a radio wave and inputted into the receiver
64
via the receiving LCX
2
′. A radio wave from the receiving LCX
1
′ is a waveform as shown in
FIG. 7B
when factors such as the coupling loss and no
Fukae Tadamasa
Kawakami Takashi
Morihara Kenji
Somiya Hiroyuki
Gregory Bernarr E.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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