Communications: electrical – Traffic control indicator – Combined
Reexamination Certificate
2001-02-27
2002-08-20
Trieu, Van (Department: 2632)
Communications: electrical
Traffic control indicator
Combined
C340S917000, C340S933000
Reexamination Certificate
active
06437706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electronic toll collection system based on radio communications for a tollgate, and particularly relates to a communication method suitable for the radio environment of a tollgate.
2. Description of Related Art
An electronic toll collection system (ETCS) is an electronic system that enables drivers at a tollgate on a turnpike such as an expressway to receive tickets or pay their tolls without stopping their cars.
FIGS. 2A and 2B
show an outline of a tollgate which uses an ETCS.
FIG. 2A
is a perspective view and
FIG. 2B
is a top view. The tollgate
300
is demarcated from the neighboring gate zone by an island
311
. A roadside communication antenna
21
is installed on the tollgate
300
. As a car
31
with a vehicle-mounted communication antenna enters a designed communication area
350
, necessary information for charging is exchanged between the roadside communication antenna
21
and the vehicle-mounted communication antenna
22
through radio signals and the car
31
can pass through the tollgate without a stop.
If a car which has no vehicle-mounted communication antenna
22
enters the tollgate area, a car sensor
321
detects its entry and, if no communication with the roadside communication antenna
21
occurs, the car is considered as having no vehicle-mounted communication antenna
22
and the driver must receive a ticket from toll collection personnel in the tollgate booth
301
or pay the toll to him or her.
In this system, if a car with a vehicle-mounted communication antenna enters the tollgate area and no communication is established, the car must stop temporarily. Conversely, if a car without a vehicle-mounted communication antenna enters the zone and a communication between the roadside antenna and the vehicle-mounted communication antenna of another car is established, the former car can pass through the tollgate without paying the toll. Therefore, in order to ensure that tolls are collected without fail, it is proposed that the designed communication area should be set to allow only one car to enter it and there should be a means to enable communication only with the vehicle-mounted communication antenna which is present in it, or disable communication with any vehicle-mounted communication antenna outside it.
For example, the toll collection system disclosed in J-P-A-No.40433/1998 uses a roadside communication antenna which irradiates electromagnetic wave beams with high directivity; and J-P-A-No. 214359/1998 discloses a system in which a car type detector is installed at the front of the tollgate and the directional pattern of electromagnetic wave beams of the roadside communication antenna is varied depending on the car type for the purpose of suppressing communication area variation caused by variation in the position (vertical) of a vehicle-mounted communication antenna.
Another type of proposal is that the roadside antenna should be selected depending on the car's position or height, or depending on the car's height and speed (J-P-A-No.315283, 5/1992 and J-P-A-No.239954/1995).
In the conventional toll collection systems, in order to ensure that each communication is established with only one car at a tollgate, attention is paid only to the directional range of direct electromagnetic wave beams but the influence of reflected waves in the communication area is not taken into consideration.
As shown in
FIG. 2A
, actually there are structures such as a sound-proof wall
201
and a roof
221
in the tollgate area. As the roadside communication antenna
21
irradiates an electromagnetic wave beam, not only direct radio wave
210
which comes directly from the antenna
21
reaches the vehicle-mounted communication antenna
22
in the car
31
, but also reflected wave
211
from the roof
221
and reflected wave
212
from the sound-proof wall
201
may be generated. Since the vehicle-mounted communication antenna
22
receives a radio signal as the direct wave combined with the reflected waves, the direct wave
210
may be offset by the reflected waves
211
and
212
even within the directional range of the electromagnetic wave beam and thus there may be a zone where the radio signal cannot be received. Such a zone momentarily changes depending on the position, speed and other factors of the car
31
and the next car
32
.
Besides, even when the vehicle-mounted communication antenna
23
in the next car
32
is outside the directional range of the roadside communication antenna
21
, the next car
32
may receive reflected waves from the structures in the tollgate area and/or the car
31
ahead, generating a path of reflected waves
213
, which means establishment of communication with a car outside the designed communication area. In this case, because the roadside communication equipment cannot distinguish between the car
31
and the next car
32
, if the communication with the latter is established before establishment of communication with the former, the equipment would mistake the communicating car
32
for the car
31
and, therefore, may allow the car
31
to pass through the gate without communication with it or without charging it. The frequency of such mistakes will be higher if there are more cars without vehicle-mounted communication antennas which enter the designed communication area.
As mentioned above, the communication area in conventional ETCSs is designed on the premise of transmission and reception of direct radio waves or at most once reflected wave from the ground, so reflected waves which vary depending on the entering car or other factors may make communication in the designed communication area impossible or make communication outside the area possible. This leads to the problem of low stability and low reliability in radio wave transmission and reception for toll collection.
Also, a special tollgate structure and a wide gate are required to decrease reflected waves. In addition, a specific communication means for each tollgate may be needed because different tollgates have different electromagnetic field environments. This results in a higher construction or operating cost.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and provides a toll collection system which electronically collects tolls with accuracy using special software to ensure stable communication with a car in the designed communication area while the radio environment in the tollgate area varies depending on the car position, and also provides its communication method.
The present invention concerns a toll collection system which charges cars which pass through a tollgate without a stop, by means of radio communication. The system is composed of the following devices installed at the tollgate: a roadside antenna whose directional pattern is variable; roadside communication equipment including a communication controller, which communicates with cars and the host system; and a car sensor which detects the position and profile of the car going to pass through the gate. In the system, taking it into consideration that the radio communication environment as mentioned above is influenced by reflected waves which vary depending on the car's position and profile, the environment for communication between the roadside antenna and the vehicle-mounted antenna in the designed communication area is maintained suitable for automatic toll collection.
For this purpose, the system is characterized in that plural paths of direct and reflected waves which connect the roadside antenna with the antenna in the car present in a given area (car detection area) including the communication area are found and one path which maximizes the sensitivity of communication with the car in the communication area is selected from among them, then the directional pattern of the roadside antenna is so adjusted as to suit the direction of radiation (radiation direction 1) for the selected radio wave path. Also the directional pattern is controlled so tha
Kato Manabu
Sato Yoshihito
Kenyon & Kenyon
Trieu Van
LandOfFree
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