Communications: electrical – External condition vehicle-mounted indicator or alarm
Reexamination Certificate
2000-08-09
2002-01-15
Tweel, Jr., John (Department: 2632)
Communications: electrical
External condition vehicle-mounted indicator or alarm
C340S928000
Reexamination Certificate
active
06339381
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DSRC (dedicated short-range communication) car-mounted equipment used for an ETC (electronic toll collection) system in an ITS (intelligent transport system). More particularly, the invention relates to a DSRC car-mounted equipment which prevents communication error relative to an on-the-road equipment by setting an optimum communication area depending upon the vehicle speed data.
2. Prior Art
There has heretofore been known a DSRC car-mounted equipment (hereinafter also referred to simply as “car-mounted equipment”) for transmitting and receiving a variety of data through communication with an on-the-road equipment installed on a road on which a vehicle travels, and has been used as, for example, an ETC car-mounted equipment.
FIG. 4
is a block diagram schematically illustrating the constitution of a conventional DSRC car-mounted equipment and illustrating, here, an ETC car-mounted equipment.
FIG. 5
is a diagram of characteristics showing electric field intensities received by the conventional DSRC car-mounted equipment, and
FIG. 6
is a flowchart illustrating the communication operation between the on-the-road equipment and the car-mounted equipment using the conventional DSRC car-mounted equipment.
In
FIG. 4
, the car-mounted equipment
1
includes a microcomputer
10
for processing data received from the on-the-road equipment, a communication control unit
11
that operates in relation to the microcomputer
10
, a radio detector unit
12
controlled by the communication control unit
11
, and a storage medium interface
13
for sending and receiving a variety of data (such as toll collection data) to and from an external storage medium
2
.
The external storage medium
2
may be an IC card having a car-mounted interface
20
, and sends and receives data related to the toll collection to and from the microcomputer
10
in the car-mounted unit
1
through the storage medium interface
13
.
Here, through not diagramed, the storage medium interface
13
interposed relative to the external storage medium
2
includes a physically mounted unit and a control unit (not shown) for reading data, and is allowed to be connected to various external equipment.
The conventional car-mounted equipment is constituted as shown in FIG.
4
and in which the microcomputer
10
controls the communication control unit
11
to transmit and receive real radio data to and from the on-the-road equipment (not shown) through the radio detector unit
12
.
That is, the microcomputer
10
fetches the data received from the on-the-road equipment through the radio detector unit
12
, and sends transmission data to the on-the-road equipment through a transmission unit (not shown).
The radio detector unit
12
in the car-mounted equipment
1
detects the radio electric field intensity transmitted from the on-the-road equipment, and informs the microcomputer
10
of the fact that the car is entering the area for communicating radio data for toll collection.
In the automatic toll collection system as is widely known, the state in which the external storage medium
2
is normally mounted on the car-mounted equipment
1
and the toll collection conformance of the external storage medium
2
are confirmed and, then, the radio communication is executed relative to the on-the-road equipment using the data within the communication area, in order to automatically collect the toll.
In the DSRC car-mounted equipment
1
of this kind, in general, the sensitivity for reception has been set constant irrespective of whether it is within the communication area or not. Therefore, the electric field intensity of the electromagnetic waves received from the on-the-road equipment varies depending upon the distance (position in a direction in which the vehicle is traveling) as shown in FIG.
5
.
In
FIG. 5
, the abscissa represents the position (distance in the direction in which the vehicle is traveling) of the car-mounted equipment with respect to an antenna ANT of the on-the-road equipment, and the ordinate represents the intensity of electric field received by the car-mounted equipment
1
. The communication start area (communication area) is set relying upon a relationship between the electric field intensity determined by the distance from the antenna ANT of the on-the-road equipment and a predetermined level (threshold) TH corresponding to the sensitivity for reception.
Here, the antenna ANT of the on-the-road equipment is installed at a toll collection gate of a toll expressway.
The communication area in which the data are exchanged after the vehicle has entered into the communication start area is set within about 4 meters from the antenna ANT of the on-the-road equipment.
Further, the communication area set by the predetermined level TH (sensitivity for reception) may include areas A, B where the electric field intensity so drops that the communication cannot be accomplished and unstable boundary areas due to side lobes in the output from the antenna ANT of the on-the-road equipment.
As the vehicle approaches the on-the-road equipment, the communication is repeated a plural number of times between the on-the-road equipment and the car-mounted equipment
1
, and the on-the-road equipment repetitively transmit communication signals to the car-mounted equipment
1
at all times.
Next, the communication operation of the conventional DSRC car-mounted equipment will be described with reference to
FIGS. 4
,
5
and
6
.
FIG. 6
illustrates the flow of the toll collection communication by taking into consideration the areas A, B where the electric field intensity drops.
In
FIG. 6
, first, the car-mounted equipment
1
approaches the on-the-road equipment
1
and enters into the system start area and where the electric field intensity received from the antenna ANT of the on-the-road equipment becomes greater than a system drive level (<predetermined level TH). Then, the system in the car-mounted equipment
1
is driven in response thereto (step S
11
).
Then, the car-mounted equipment
1
further approaches the antenna ANT of the on-the-road equipment, whereby the intensity of the received electric field exceeds the predetermined level TH and a first communication signal is received. Then, in response thereto, the car-mounted equipment
1
transmits communication signals to the antenna ANT of the on-the-road equipment and executes the initial communication for receiving the toll (step S
12
).
Then, it is judged whether the communication for receiving the toll is all completed between the on-the-road equipment and the car-mounted equipment
1
(step S
13
). When the communication signals are normally exchanged and it is judged that the communication has completed (i.e., YES), the routine normally ends in a state where the communication for collecting the toll has been finished (step S
14
).
When it is judged at step S
13
that the communication for receiving the toll has not all been completed (i.e., NO), the on-the-road equipment repetitively transmits retrial communication signals for collecting the toll to the car-mounted equipment
1
(step S
15
).
Next, it is judged whether the communication is normal between the on-the-road equipment and the car-mounted equipment
1
(step S
16
). When it is judged that the communication is normal during the above retrial period (i.e., YES), the routine returns back to the step S
13
and the processing is repetitively executed until it is confirmed that the toll collection communication has normally ended (step S
14
).
Here, the retrial communication operation by the on-the-road equipment is repeated about 100 to 200 times for every 2 milliseconds, and it is judged that the communication condition is normal when the vehicle enters into the communication-possible area (or when the vehicle leaves the boundary area).
At step S
16
, on the other hand, when the vehicle enters into the area A or B (or boundary area) where the electric field intensity drops and it is judged that the communication condi
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