Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ROADSIDE BEACON SYSTEM
BACKGROUND OF THE INVENTIO~
F;eld of the Invention
This invention relates generally to a roadside
beacon system. More particularly~ this invention relates
to a roadside bearon system which is used to calibrate the
po.;ition of a vehicle and to perform data transmission in
a navigation system in w~ich, after data on a departure
po;int are inputted, vehicle speed data and direction data
arl~ inputted to enable the display o~ the present ~osition
of the vehicle~ .
Ba~kqround of_the Inven~ion
A so-called "navigation system" for vehicle~ has
bel~n known in the art. In the system, a small computer
and a small display unit are installed on a vehicle. A
road map is read out of memory means such as a compact
disk and displayed on the display unit. Qn the other
hand, the vehicle speed data outputted by a vehicle speed
sensor and the direction data provided by a direction
s~nsor are inputted, so that calculation of the posi~ion
of the vehicle and determination of the travelin~
direction of the vehicle are performed at all times.
According to the results of the calculation and the
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1 determination, the vehicle is marked on the road map
displayed on the display unit.
With the navigation system, the operator in the
vehicle can visually detect the present position and the
traveling direction o~ his vehicle. Therefore, he can
reach his destination withou~ losing his way.
However, the navigation system described above is
disadvantageous in the following point. In the system,
the errors inherent in the vehicle speed sensor and the
` 10 direction sensor are accumulated as the vehicle runs.
When the distance traveled by the vehicle exceeds a
predetermined value twhich is not always constant, being
determined by the errors of the vehicle speed sensor and
the direction sensor of each vehicle and by the
environmental conditions of the positions where the
sensors are installed), then the position of the vehicle
displayed on the display unit is great}y shifted ~rom the
true position. That is, the system becomes unreliable and
the vehicle operator may lose his way.
In order to overcome this difficulty, â SO~
called "roadside beacon system" has been proposed. In the
system, roadside antennas are installed a~ intervals
shorter than the distance with which the error accumulated
exceeds the above-described predetermined value. The
roadside antennas are used to transmit
RF (Radio Frequency) signals modulated by data including
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1 position data and road direction data to predetermined
relatively small areas, respectively. On the other hand,
the data thus transmitted are received through the
antenna and the receiver installed on a vehicle so thak the
the position and the traveling direction of the vhicle are
calibrated with a computer.
With the roadside beacon system, the error
accumulated is smaller than the predetermined value so
that the position of the vehicle can be displayed
according to the correct position data and the accurate
direction data at all times. This means the navigation
system is reliable. I~ the roadside antenna is installed
for instance near a railroad or a railroad crossing where
the magnetic direction sensor is liable to erroneously
operate, then errors attributed to external ~actors such
as the railroad can be effectively eliminated.
In the above-described roadside beacon system,
roadside antennas considerably high in directivity are
used to transmit RF signals modulated by the aforementioned
data including position data and road direction data at
all times. The vehicles receive the RF signals only when
passing through the areas converted by the RF signals and
the calibration is carried out according to the RF
signals thus received. Therefore, if the area
covered by the RF signal thus transmited
through each roadside antenna is increased,
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1 then the RF signal receiving position of ~he vhicle with
respect to the roadside antenna is greatly shi~ted. As a
result, the position and the traveling direction of the
vehicle cannot be effectively calibrated.
The roadside beacon system is provided primarily for
transmitting RF signals modulated by data including position
data and road direction data to vehicles having navigation
systems. However, it is desirable to give the following functions
to the system for more effective utilization:
(1) Traffic information such as traffic
congestion, construction work and road condition near a
roadside antenna are additionally transmitted to the
navigation system to allow the smooth movement of the
vehicle;
(2) Data concerning a detailed map including
buildings with names around a roadside antenna are added
to facilitate the navigation of the vehicle to a desired
destination near the antenna; and
(3) Information on a relatively wide road map
including the area where a roadside antenna is installed
is additionally transmitted to the naviyation system to
renew the road map displayed on the display unit so that
the operator can smoothly drive his vehicle to a distant
place.
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1 For these purposes, it is necessary to increase
the frequency band of the RF signals ~ransmi~ed through -the
roadside antennas and to increase the areas covered by the
RF signals thus transmitted.
However, if the frequency band of the RF signals
transmitted and the areas covered by the RF signals are
increased, then the RF signal receiving position will be
greatly separated from the position of the roadside
antenna. Therefore, the ~alibration of the vehicle
position, which is the original object of the navigatior
system, cannot be accurately achieved.
SUl~MARY OF THE INVENTION
In view of the foregoing, an object of this
invention is to provide a roadside beacon system in which
a variety of function can be readily performed and
calibration of a vehicle position can be achieved with
high accuracy.
The foregoing object of the invention has been
achieved by the provision of a roadside beacon system in
which according to the invention, a navigator device is
installed on a vehicle and is adapted to receive RF signals
transmitted through each of several roadside ~ntennas to
calibrate and display vehicle position da~a. The
navigator device includes data receiving means for
receiving a transmitted RF signal when the level of the
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1 transmitted R~ signa] is higher than a relatively low level.
Position determining means receive a transmitted RF signal
when the level of the transmitted ~F signal is higher tharl a
relatively high level in order to output a position
5 determination siynal. Calibrating means calibrates
position data based on data representing positions of
antennas, for instance, which has been stored in navigator
devices and direction data accordiny to the position
determination signal and data received.
In the system, the relatively low level should be
set to a value with which the RF signals transmitted through
the roadside antennas can be received without being
affected by noise or the like. On the other hand, the
relatively high level should be set to a value which is
close to the peak value in level of a signal received by
the navigator device when the vehicle confronts the
roadside antenna.
Furthermore in the system, data transmitted for a
relatively long period of time which is determined by the
relatively low level are applied to a communication data
terminal.
Therefore, a variety of data including position
data and direction data are transmitted to the vehicles ~hrough
the roadside antennas insta-lled along r~ads at predetermined
positions. In the roadside beacon system thus organized,
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1 of the RF signals transmitted through the roadside antennas, the
RF- signal whose level is higher than the relatively low
level can be received by the data receiving means and the RF
signal whose level is higher than the relatively high
level can be received by the position determining means
thus providing the position determination signal. The
calibrating means, receiving the data received by the data
receiving mPans and the position determination signal
outputted by the position determining means, calibrates
the position data and the direction data. Then,
navigation of the vehicle is continued by using the output
signals of a vehicle speed sensor and a direction sensor.
Thereafter, the above-described calibration and
navigation are repeatedly carried out so that the vehicle
can smoothly travel.
In the above roadside beacon system, the
relatively low level is set ~o the value with which the RF
signals transmitted through the roadside antennas can be
received without being affected by noise or the like.
Then, the navigation system on the vehicle can receive
the RF signals modulated by data necessary for additional functicns
as well as the position data and the road direction da~a
which are absolutely required for the original position
finding function.
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1 Furthermore, in the above roadside beacon system,
the relatively high level is set to the value which is
close to the peak level value of the RF signal rec~ived by
the navigator device when the vehicle confronts anyone of
the roadside antennas. Thereby, the position data and the
road direction data can be calibrated when the vehicle has
approached the roadside antenna.
Moreover, in the above roadside beacon system, the
data transmitted for a relatively long period of time
which is determined by the relatively low level are
applied to the communication data terminal, necessary
communication data can be read with means connected to the
communication data terrninal.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing one example of a
navigator dev~ce according to this invention.
Fig. 2 is a graphical representation indicating
the relation between the variation in level of a signal
received by a mobile antenna and reference levelsv
Figs. 3 and 4 are a plan view and a perspective
view, respectively, outlining the roadside beacon system.
Fig. 5 is a schematic diagram showing one example
of a road map displayed on a display unit in the system of
the invention.
DETAILED DBSCRIPTION OF THE PREFEERRED EMBODIMENTS
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1 One embodiment of this invention will be described
with reference to the accompanying drawings.
Fi~. 5 is a diagram showing one example of a road
map displayed on a display unit. The present position and
traveling direction of the vehicle is indicated by the
arrow A. The positions of roadside antennas Pl, P2,...
and Pn are also indicated (the indication of these
roadside antennas not always being required)~ In
addition, buildings or the like (not shown in Fig. 5)
which can be used a guides are indicated.
Figs. 3 and 4 are sch~ematic diagrams for à
description of the road-side beacon system according to
the invention. A roadside antenna 2 is installed at a
predetermined position near a road 1. The roadside
antenna 2 is connected to a navigation data transmitter 2a
to transmit an RF signal modulated by data including position
data and road direction data. On the other hand,a mobile an-
tenna 4 for receiving the aforementioned signal is installed at
a predetermined position on a vehicle 3 which runs ~l.on~ t.hR
road 1. The signal received by the mobile antenna 4 is
supplied to a navigation device (not shown in FigsO 3 and
4). The roadside antenna 2 is so high in directivity that
it covers o~ly a relatively small area R in ~ig. 4. In
addition, the roadside antenna 2 is such that it is non-
directional for instance in a horizontal direction.
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l Fig. l is a block diagram showing one example of
the roadside beacon system according to the invention.
The RF signal received by the mobile antenna 4, after
being amplified by an amplifier S, is supplied to a high level
determining circuit 6, a low level determining circuit 7 and a
demodulating circuit 8. The demodulated data passed through the
gate circuit 8 which is opened by the output signal of the second
level determining circuit 7 is tempor~rily stored in a memory 9.
Thereafter, necessary communication data are
lO read out by a CRT display device lla connected to a
communication data terminal 11. On the other hand, data
such as road direction data and map data are transferred
into a navigation device. The present position data is
applied to a navigator 10 in response to a position determining
15 signal (or timing pulse signal) outputted by the high level
determining circuit 6, so that the present position is calibrat~d.
The determining reference levels of the level
determining circuits ~ and 7 are set, to Ll and L2 ~Ll>h2)
respectively.
The operation of the roadside beacon system thus
organi~ed will be described with reference to Fig. 2.
Let us consider the case where the vehicle 3 comes
nearer to the roadside antenna 2 and then goes away it,
i.e., the vehicle 3 passes by the roadside antenna 2.
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1 First, the level of RF signal received by the mobile
antenna 4 is substantially zero (0). Therefore, RF signals
whose levels are lower than the determining reference
levels Ll and L2 are applied to both the level determining
circuits S and 7. Therefore, the gate circuit 8 is
maintained closed and no data is transferred to the me~ory
9, e.g., during the period Tl in Fig. 2.
As the vehicle 3 approaches the roadside antenna
2, the level of the RF sisnal received by the antenna 4
gradually increases. However, the above-described
operation is continued until the level of ~he RF signal
applied to the low level determining circuit 7 becomes
higher than the determining reference level L2, (e.g.,
during the period T2 in Fig. 2).
That is, during the above~described operation, no
data is transferred to the navigator 10 from the memory 9,
and the navigator 10 calculates and determines the present
direction and the traveling direction of the vehicle
according to the vehicle speed data outputted by a vehicle
speed sensor ~not shown) and the traveling direction data
provided by a direction sensor (not shown~, so that the
present position and traveling direction of the vehicle
together with the road map are displayed on the display
unit (not shown~.
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l As the vehicle 3 further approaches the roadside
antenna 2, the level of the RF signal received by the antenna
becomes higher. When the level of the RF s~gnal supplied ~o
the low level determining circuit 7 exceeds the lower
reference level L2~ the gate circuit 8 is opened by the
data-transmitting-area determination signal outputted by the
low level determining circuit 7. As a result, data modulated
by the demodulator 12 from the RF signal received by the
mobile antenna 4 and amplified by the amplifier 5 are stored
in the memory 9, (e.g., during the period T3 in Fig. 2) and
predetermined data are applied to the communication data
terminal 11 and the necessary data are inputted into the navigator lO.
When the vehicle 3 substantially confronts the
roadside antenna 2, the level of the RF~ signal received by
the mobile antenna 4 is further increased and the level of
the RF signalsupplied to the high level determining circuit
6 exceeds the high reference level Ll so that the high
level determining ~ircuit 6 outputs a position
determination signal which is applied to the navigator lO.
At the same time, of the data stored in the memory 9, the
position data is transferred to the navigator 10, so the
present position stored in the navigator lO is calibrated.
Thus, ~he position data and the traveling direction data
have been calibrated. That is, the correct present
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1 position and traveling direction can be displayed on the
display unit.
Thereafter, with the present position and
traveling direction thus calibrated as references, the
position and the traveling direction of the vehicle 3 can
be displayed as a function of time with the arrow A on the
display unit lla together with the road map using the
vehicle speed data outputted by the vehicle speed sensor
and the traveling direction data provided by the direction
sensor.
Fig. 2 shows the variation in level of the RF signal
received by the vehicle 3 which runs at a constant speed.
In the case when the vehicle moves at different speeds,
the periods Tl, T2 and T3 are merely varied, shortened or
lengthened, according to the speeds, which will not change
the effect of the invention.
As was described above, in the roadside beacon
system with the navigation device according to the invention,
when the level of the ~ignal received by the bile an~enna exceeds
the relatively low level, i~e.,the data transmission can be
effectively carried out, the necessary data are stored in
the memory 9 temporarily, and the predetermined data are
store in the navigator 10. Only when the vehicle has
sufficiently approached the roadside antenna 2 is the
position data transferred to the navigator 10 so that the
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1 present position and the traveling direct.ion of the
vehicle are calibrated. Therefore, even if the number o~
pieces of data transmitted th~ough the roadside antenna 2
increasesV the data can be positively written in the
.navigator lOo Therefore~ the system can perform a variety
o ~unctions (such as displaying road conditions and
traffic congestion)c Furthermore~ other necessar~
communication data can be transmitted to the communication
- data ~erminal 11. Since the position detection of the
vehicle 3 is carried out when the vehicle come~
sllfficiently close to the roadside antènna 2 and the
received signal level reaches the peak value, the position
of. the vehicle 3 can be detected with high accuracy.
In the system of the invention, the threshold
level for storing data transmitted through the roadside
antenna- is set at a low level and the treshould level for
detecting the position of the vehicle i5 ~et to a high
level with the result that the position detection is
carried out wi~h high accuracy and the number of pieces o~
data ~ransmit cd can be increased.
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