BACKGROUND OF THE INVENTION
This invention relates to an communication systems
on toll roads, including automatic toll gate systems.
This application is a counterpart application of
Japanese application Serial Number 302765/1996,filed
November 14, 1996, the subject matter of which is
incorporated herein by reference.
In the automatic toll gate system, this invention
relates to a vehicle identifier system that detects and
identifies vehicles which pass through the toll gate.
And this invention especially relates to the system
which is settled beside a road which comprises a plurality
of lanes on each way.
Fig. 1 shows elements of a typical automatic toll
gate system.
As shown in the figure, the automatic toll gate
system comprises a roadside system and a mobile station
including a transponder.
As shown in the figure, the roadside system
comprises an antenna assembly 1, a beacon 2, and a roadside
controller 4.
The antenna assembly 1 transmits and receives
information signals between the antenna assembly 1 and
mobile station (shown below) while a vehicle runs through
under the antenna assembly 1 along the road.
The beacon 2 has three functions. One function is to
detect vehicle. Another function is to communicate with the
mobile station while the vehicle runs through below the
antennas 1 or 2. And still another function is to detect
received signal level from the mobile station .
The roadside controller 4, in addition to general
control of popular beacon 2 functions, compares plural
received signal level.
The antenna assembly 1 comprises plane antennas 1a
and 1b. The antennas are located above each lanes of the
road. Each of the antennas 1a and 1b radiates a radio
frequency over service areas on each lanes. The service
areas are elongated along each lanes so that the beacon 2
can take a time period long enough to communicate with the
mobile station.
The roadside controller 4 detects vehicle when a
vehicle comes into the service area. The detection is
established by the beacon 2, through the radio communication
between the antenna 1 and the mobile station. Then, the
roadside controller 4 sends a request signal toward the
mobile station to request a response including a vehicle
identification signal.
On the other hand, the mobile station is set on each
vehicles.
On receiving the request signal from the roadside
controller 4, the mobile station transmits an identification
signal. The identification signal is unique with each
transponder.
This identification signal is utilized to identify a
vehicle from another. If the roadside controller 4 receive
two different identification signals, the roadside
controller 4is regarded to detect two different vehicles.
After that identification, the controlller
researches whether the vehicle is permitted to pas through
the toll gate without toll payment. If roadside controller 4
finds the vehicle is permitted, the roadside controller 4
tells a electronic banking system (not shown) that the
vehicle goes through the toll gate. Then the banking system
carries out the toll payment operation automatically.
Fig. 2 shows a sectional view of a roadside tollgate
utilizing the automatic toll gate system.
As shown in the figure, antennas 1a and 1b are
located straight above the lanes so that the vehicles go
through near one of those antennas. Each antenna
communicates with vehicles that go through the lanes stright
under the antenna.
Because the antenna has to identify each vehicle to
communicate individually, each antenna communicates with
vehicles on the lanes in pararell.
This pararell communication by each of the antennas
is indispensable in the case that two or more vehicles run
along each lane substantially side by side.
Because, in such a case, one antenna can communicate
with only one vehicle. This limitation is effective in order
to avoid communication failure caused by confusion.
In the toll gate communitcation, it is important to
assume communication accurcy at the toll gate. In order to
assume the communication accurcy, each datas received by the
antenna must be identified to be transmitted from the same
vehicle. To assume that, one effecive resolution is to join
each antenna to each lane (or vehicle on the lane) one by
one. In this case, each antenna never communicates with two
or more vehicles in pararell. As a result of the above
design, the communications between each antenna and each
vehicles are not interrupted by inaccurate communication
dates.
In the above case, there are two important technical
subjects. However, those technical subjects make a
contradiction, and will bring a system design of the system
into a technical dilemma.
The first subject is to lengthen a service area of
the antenna along the lanes. That is, to lengthen the
distance L shown in Fig. 3. The main purpose to lengthen the
service area is, to elongate a time period which allows data
communication between the antenna 1a or 1b and the vehicle
transmitter 3.
The first subject is an important subject in order
to assure communication accuracy between the antenna 1a or
1b and the vehicle transmitter, because the distance shown
in Fig.3 must be longer when the vehicle runs at higher
speed, in order to elongate the time period to complete the
data communication between the antenna 1a or 1b and the
vehicle transmitter 3. It is because, vehicle at higher
speed only needs less time to run through the distance L of
the service area .
It is also important because the communication must
be repeated between the antenna 1a or 1b and the vehicle
transmitter in case the communication failed by some
reasons. The repeated communications take a considerably
long time. In order to complete the communication by
repetition, the time period which allows data communication
must be elongated enough.
The communication accuracy is a critical problem in
the toll gate system case, because the toll gate system
handles money transaction.
And, the second subject is to sharpen the service
area of the antenna across the lanes. That is, to contract
the width W shown in Fig. 4. The main purpose to sharpen the
service area is, to keep the antenna from communication with
improper vehicles on the other lanes.
In case the improper communication occurs, a
plurality of antennas 1s will try to communicate with only
one vehicle transmitter. As a result, the beacon 2
misdetects the one vehicle as a plurality of vehicles. If
two antennas communicate with one vehicle, the beacon
misdetects the vehicle as two vehicles.
In this case, the system will request for fee
payment twice.
On the contrary, another case of misdetection could
occur. It is to overlook a vehicle when two or more vehicle
come along substantially side by side. In this case, one or
more antennas communicate with a n improper vehicles, and
ignore another proper vehicle which should have been
detected, because the antenna fully spends its limited
communication capacity to the wrong communication with the
improper vehicle, and never keeps its capacity for
communication with the proper vehicle.
In addition to the two main subjects cited above,
still another extra subject to sharpen the service area is,
to keep the communication from radiowave or electromagnetic
noize.
Moreover, there is still another technical problem
that the antenna tends to be larger and heavier. It will be
inevitable because directional antennas are utilized in
order to sharpen the service area. The directional antennas
are relatively large and heavy.
SUMMARY OF THE INVENTION
Reviewing the above cited technical problems, this
invention will try to provide a suitable solution against
the dilemma. Objectively, this invention will keep the toll
gate system free from the misdetection of vehicles when the
service area is elongated.
In order to prevent the misdetection, the system
observes the received radiowave signals from the mobile
station, and detects signal levels from the radiowave
signals. If the plurality of antennas receive radiowave
signals from one mobile station, the beacon compares the
signal levels from each antennas, and employs only one
signal that shows higher (or highest) signal level. Then,
the following signals from the antenna which received the
higher (or highest) level signal will be employed by the
beacon.
The higher (or highest) signal level shows a
relatively closer (or closest) communication between an
antenna and a mobile station. It means that the antenna than
brings a higher (or highest) signal level is one the
antennas which is positioned straight above the lane along
which the vehicle is running.
At the same time, other signals which show
relatively lower signal levels are cancelled to be improper,
and the following signals are as well.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a driver's view when a vehicle comes up
to an automatic toll gate.
Fig. 2 shows a summarized sectional view of an
automatic toll gate system.
Fig. 3 shows a conceptional view of a service area
length.
Fig. 4 shows a conceptional view of a service area
width, and also of a misdetection of vehicles.
Fig. 5 shows a conceptional view that the plurality
of antennas request an ID signal for a mobile station.
Fig. 6 shows a conceptional view that the mobile
station transmits ID signal in response to the request.
Fig. 7 shows a conceptional view that the beacon
detects signals and compares the signal levels.
DESCRIPTION OF THE PREFFERED EMBODIMENTS
The following description will explain an desirable
embodiment of this invention.
Fig. 5 shows a conceptional view of the toll gate
system from the driver's position. As shown in the fig. 5,
antennae 1a and 1b are held aloft above the road. Each of
the antennas are positioned substantially straight above
each lane, so that each of the antennas correspond with each
lanes one by one.
These antennas 1a and 1b communicate with the
vehicle transmitter (cited as 3 below) being kept under
control of beacon 2. Under the control of the beacon 2, the
antennas 1a and 1b synchronize with each other in
communication process between the antennas and the vehicle
transmitter.
On the other hand, a vehicle comprises a mobile
station 3. The transponder has a radiowave transceiver that
can exchange digital dates between the antennas 1a and 1b.
The datas include vehicle ID data, which is unique to each
transponder 3.
When a vehicle approaches the toll gate, the beacon
2 detects the vehicle. Then the beacon 2 generates a request
signal (not shown), and transmits the request signal from
the antennas 1a and 1b toward the vehicle. In this
condition, the beacon 2 does not recognize whether the
vehicle is on the right lane (above which the antenna 1a is
held aloft) or on the left lane (above which the antenna 1b
is held aloft).
This request signal should be synchronized, because
the mobile station 3 should correctly regard that the
request signal was transmitted only once, not twice.
When the request signal is transmitted from the
antenna 1a or 1b, the mobile station 3 receives the request
signal. In this condition, the mobile station 3 does not
distinguish from which antenna 1a or 1b the request signal
was received.
Regardless of which antenna has transmitted the
request signal that is received by the mobile station 3, the
mobile station 3 transmits a response signal (not shown)
toward both of the antennas 1a and 1b. The mobile station 3
does not specify a transmission object as the antenna 1a or
1b but radiates the radiofrequency response signal broadly
forward.
On receiving the response signal from the mobile
station 3, the beacon 2 interrupts the signal transmission
temporally. During the interruption, the beacon 2 analyses
the response signals received by the antennas 1a and 1b.
The analysis contains two sequential processes; a
first process to find vehicle IDs contained in the response
signals both from the antennas 1a and 1b, and a second
process to compare whether the vehicle IDs from the antenna
1a and the one from the antenna 1b are the same or not.
If each vehicle IDs from the antenna 1a and the one
from the antenna 1b are different, the beacon 2 resumes each
communication utilizing the antennas 1a and 1b. In this
condition, the antennas 1a and 1b are communicating with
respective mobile station 3s. That is, two (or more)
vehicles are approaching the toll gate substantially side by
side. So, the beacon 2 must continue communication with each
mobile station 3s, in order to settle account on each
vehicle respectively.
If the vehicle IDs from the antenna 1a and one from
the antenna 1b are the same, the two response signals from
the antennas 1a and 1b are transmitted from the same
vehicle, and the response signals are all the same. In this
condition, the beacon 2 utilizes only one response signal
for fee account.
In order to determine which response signal to
utilize for account, the beacon 2 measures signal levels of
each response signals. Then the beacon 2 translates the
signal levels into additional level signals.
These additional level signals indicate distances
between antennas 1a or 1b and mobile station 3, because the
signal levels of the response signals fluctuate on the
distances. The response signal recedes when it is radiated
from the mobile station 3.
Then, the beacon 2 transmits the additional level
signals to the beacon controller.
On receiving the additional level signals, the
beacon controller 4 compares the singnal levels of the
response signals each received by the antenna 1a and
received by the antenna 1b.
As cited above, each of the signal levels indicate
the distances between the mobile station 3 and each antennas
1a and 1b.
The distances inform that along which lane the
vehicle is going. By comparing the distance, it is
identified which antenna was of the shortest distanse from
the mobile station 3.
Then, the antenna of the shortest distance should
continue communication with the mobile station 3. The other
antenna should cease their communication, because it has
been communicating with improper vehicle on the lane that =`X
not positioned straight below the antennas.
After that identification, the antenna 1a, of the
shortest distance, resumes the communication process.
Accorcding to the identifidation, the beacon
controller 4 registers the ID of the mobile station 3. Then
the vehicle corresponding to the ID is regarded to run along
the lane which is straight below the antenna 1a.
Following to the charge processing, the beacon 2
transmits following signals. The following signals show that
the beacon controller 4 has registered the vehicle ID to the
system.
On the other hand, the antenna 1b, of the longer
distsance, keeps the following communication process in
suspend.
Instead of the following communication process, the
antenna 1b transmits the request signal repeatedly, because
the antenna 1b must communicate with another vehicle that
approaches the toll gate along the lane below the antenna
1b.
By this cease of the communication and repetition of
the request signal, the antenna 1b is free from wasting
communication ability.
According to the process as cited above, the
communication between the antenna 1a or 1b and the mobile
station 3 is completed only once for one mobile station 3.
This process is effective for fee transaction accuracy,
because the toll gate system can avoid double charge of the
fee. And this process is also effective for accuracy,
because the beacon will not overlook any vehicles which have
mobile stations.