JP5258690B2 - Roadside radio equipment - Google Patents

Description

  The present invention relates to a roadside apparatus for performing communication with an ETC on-board unit using a dedicated short-range communication system (DSRC).

Conventionally, in the non-stop toll collection system (hereinafter referred to as ETC: Electronic Toll Collection System) applied to expressways and parking lots, ETC on-board equipment installed in vehicles and roadside radio installed on the toll gate side Road-to-vehicle communication is performed between devices using a narrow-area wireless communication system (DSRC) (see Patent Documents 1 and 2).
This roadside wireless device transmits a radio wave to the vehicle when the vehicle enters the communication range, and receives a signal from the ETC on-board unit with an antenna and transmits / receives a data signal between the two. is there.

  The ETC vehicle-mounted device is configured to return a radio wave when the vehicle-mounted device enters the communication range and the radio wave emitted from the roadside radio device exceeds the no response level (−70.5 dBm). That is, when the no-response level is set as a threshold and the vehicle-mounted device receives a radio wave exceeding the threshold, the vehicle is regarded as having entered the communication range, and communication with the roadside apparatus is started. ing.

On the other hand, if the radio wave emitted from the roadside radio device is in a free space like an outdoor toll booth, the reflection of the radio wave is hardly affected by only the reflection from the road surface toward the sky. If the received power of the vehicle-mounted device exceeds the non-response level, the position is about 5 m before the antenna, and this may be set as the communication range.
However, at toll gates in tunnels called digging toll gates and toll gates in buildings, etc., there are ceilings and left and right wall surfaces that form a sealed space with a rectangular cross section. The radio wave emitted from the antenna of the roadside wireless device installed near the ceiling of the road travels while being reflected in multiple directions such as primary reflection, secondary reflection, tertiary reflection,.

  As a result of measurement using a simulation technique based on the cell space method (this method will be described later) in the case where there is this multiple reflection, the received power of the vehicle-mounted device is about −57 dBm even at a position 14 m before the antenna, for example. It was found that the level of no response of ETC onboard equipment was greatly exceeded. For this reason, even though it is originally an area outside the communication range at a position of 14 m, the vehicle-mounted device recognizes that it has entered the toll gate area and starts a response, which is an incorrect road-to-vehicle communication. There was a problem of being connected.

  On the other hand, as a method for preventing such multiple reflection, for example, as disclosed in Patent Document 3, a radio wave absorber is installed on the ceiling and the left and right wall surfaces, and the radio wave reflected by the radio wave absorber is absorbed. Elimination of the effects of reflection is being done. However, this radio wave absorber has a problem that it is very expensive and requires a large installation cost. In addition, where it is most efficient to install this wave absorber is not fully elucidated, and technology for efficiently constructing with as few wave absorbers as possible has not been established. There was a problem that it was necessary to install a lot.

JP 2004-302738 A JP 2002-42191 A JP 2002-245499 A

  The present invention solves the above-described problems, and even if the vehicle-mounted device starts to respond due to the influence of multiple reflection at a toll booth or the like in the tunnel, the vehicle does not actually enter the communication range area. As long as it can be controlled so that road-to-vehicle communication is not performed, it is possible to improve only the roadside wireless device without any changes to the on-vehicle equipment, and furthermore, electromagnetic waves can be reduced by using as few radio wave absorbers as possible. It was completed for the purpose of providing a roadside radio device capable of performing environmental improvement construction.

The invention according to claim 1 to solve the above-mentioned problem is a roadside wireless device in ETC, and is referred to as an activation channel (ACTC) from the vehicle-mounted device among the received signals from each vehicle-mounted device received by the antenna. An RSSI detector that detects the signal strength (hereinafter referred to as RSSI) for the signal to be processed, an RSSI determiner that determines whether or not the detected RSSI value exceeds a predetermined threshold, and the RSSI value has a threshold A calculation result using a simulation technique based on a cell space method as a predetermined threshold is provided as a communication controller that determines that a received signal is valid only when the signal exceeds the threshold and starts signal transmission / reception with the on-vehicle device. To -52 dBm is set as the roadside wireless device.

  Further, the apparatus main body may be installed in a place where multiple reflection of radio waves occurs, and this is the invention according to claim 2.

Furthermore, the apparatus main body can be installed at a toll booth in the tunnel, and this is the invention according to claim 3 .

In the invention according to claim 1, in the ETC roadside radio apparatus, an RSSI detector, an RSSI determiner, and a communication controller are provided, and only when the received signal strength (RSSI) from each vehicle-mounted device exceeds a threshold value. Since it is determined that the received signal is valid and signal transmission / reception is started with the vehicle-mounted device, erroneous road-to-vehicle communication can be reliably prevented even if there is multiple reflection of radio waves.
In addition, by setting -52 dBm as a predetermined threshold value, it is possible to reliably prevent erroneous communication at the toll gate in the tunnel and to secure a communication distance required by ETC.

  In the invention which concerns on Claim 2, the apparatus main body is installed in the place where the multiple reflection of an electromagnetic wave generate | occur | produces, The influence of multiple reflection can be eliminated and correct road-to-vehicle communication can be ensured.

  In the invention according to claim 3, the apparatus main body is installed at the toll gate in the tunnel, and it has become possible to reliably prevent erroneous communication that has conventionally occurred frequently due to the influence of multiple reflection.

It is a block diagram which shows embodiment of this invention. It is explanatory drawing which shows the communication sequence of this invention. It is a graph which shows the relationship between the received signal strength (dBm) from the roadside apparatus by onboard equipment, and approach direction distance (m). It is a graph which shows the relationship between the received signal strength (dBm) from onboard equipment in a roadside apparatus, and approach direction distance (m). It is the schematic which shows an ETC system.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 5 shows a schematic diagram of the ETC system. The illustrated one shows a system provided in a digging toll gate in a tunnel, and a road surface 30, a ceiling 31, and left and right wall surfaces (not shown) are present to form a sealed space having a rectangular cross section. . An example of the specifications of the tunnel is a space with a ceiling height of 8.3 m and a distance between the left and right side walls of 14 m, and the antenna of the roadside apparatus is installed at a height of 5 m from the road surface.
In the figure, 1 is a device body of an ETC roadside wireless device installed near the ceiling on the toll gate side, 2 is an antenna provided in the ETC roadside wireless device, 20 is a vehicle, and 21 is an ETC on-board unit. Further, 32 is an entrance-side vehicle sensor that detects that the vehicle 20 has entered the toll gate and communicates it to the apparatus body 1, and 33 is an exit-side vehicle sensor that detects that the vehicle 20 has passed through the toll gate. It is.

An outline of road-to-vehicle communication in such an ETC system will be described.
When the vehicle 20 enters the toll gate, the vehicle sensor 32 detects and communicates a signal (S1) to the apparatus main body 1, receives this signal (S1), and the apparatus main body 1 performs frame control at a cycle of 3.9 msec. Continue to fire a signal (S2) called Message Channel (FCMC). Next, when the vehicle-mounted device 21 receives a signal (S2) exceeding the no-response level, a signal (S3) called an activation channel (ACTC) is emitted. When the apparatus main body 1 receives this signal (S3), road-to-vehicle communication is started between the apparatus main body 1 and the vehicle 20.
In this case, in an enclosed space such as a digging toll booth, the vehicle-mounted device 21 recognizes that the vehicle-mounted device 21 has entered the toll gate area even though it is an area outside the communication range due to the influence of multiple reflection. As described above, this causes erroneous road-to-vehicle communication.

Therefore, in the present invention, an RSSI detector that detects the received signal strength (hereinafter referred to as RSSI) from the vehicle-mounted device received by the antenna, and an RSSI determiner that determines whether or not the detected RSSI value exceeds a predetermined threshold value. The roadside wireless device is provided with a communication controller that determines that the received signal is valid only when the RSSI value exceeds the threshold and starts signal transmission / reception with the vehicle-mounted device.
FIG. 1 shows a block diagram of the apparatus main body 1. In the figure, 2 is an antenna, 3 is a duplexer, 4a is a transmitter, 4b is a receiver, and the above configuration is the same as that of the conventional one. In introducing the received signal strength (RSSI), an RSSI detector 5 for detecting the RSSI value is provided, and an RSSI determiner 6 for determining whether or not the detected RSSI value exceeds a predetermined threshold value. Furthermore, only when the RSSI value exceeds the threshold value, the received signal is determined to be valid and signal transmission / reception is started with the vehicle-mounted device 21. Otherwise, even if RSSI is received from the vehicle-mounted device 21 The communication controller 7 to be ignored is provided.
In addition, 8 is a lane server for calculating a charge based on the information from onboard equipment.

A communication sequence of the ETC roadside apparatus of the present invention configured as described above will be described with reference to FIG.
First, when the vehicle 20 enters the toll gate, the vehicle sensor 32 detects and communicates a signal (S1) to the apparatus main body 1. When receiving this signal (S1), the apparatus body 1 continues to emit a signal (S2) called a frame control message channel (FCMC) at a cycle of 3.9 msec. The upper part of FIG. 2 is out of the communication range. Here, the vehicle-mounted device 21 does not respond to the signal (S2) received from the device body 1 because the level does not exceed the no-response level. Accordingly, road-to-vehicle communication is not performed in this region.

Next, the middle part in FIG. 2 is outside the communication range, but is affected by multiple reflections, and the vehicle-mounted device 21 is an area for receiving a signal (S2) exceeding the no-response level. For this reason, the vehicle-mounted device 21 emits a signal (S3) called an activation channel (ACTC). Conventionally, communication is immediately started with the apparatus main body 1 by the emission of this signal (S3), and erroneous road-to-vehicle communication has occurred.
On the other hand, in the present invention, when the apparatus body 1 receives the signal (S3) from the vehicle-mounted device 21, it passes through the RSSI detector 5 and then the detected RSSI value exceeds a predetermined threshold value (T). Whether or not the RSSI value exceeds the threshold value (T) by the communication controller 7 and determines that the received signal is valid, and transmits and receives signals to and from the vehicle-mounted device 21. In other cases, the RSSI from the vehicle-mounted device 21 is ignored. Therefore, since the RSSI value does not exceed the threshold value (T) in this region, the signal (S3) from the vehicle-mounted device 21 is ignored, and road-to-vehicle communication with the vehicle 20 is not performed. As a result, erroneous road-to-vehicle communication as in the prior art is not generated.
In the above process, the timing at which the signal (S3) from each vehicle-mounted device 21 is emitted can be predicted by the communication controller 7 according to the communication protocol. Therefore, the detection operation of the RSSI detector 5 is instructed by the communication controller 7. Implemented at the timing.

Next, when entering the communication range in the lower part of FIG. 2, the vehicle-mounted device 21 emits a signal (S3) called an activation channel (ACTC) in order to receive the signal (S2) exceeding the non-response level.
When the apparatus body 1 receives the signal (S3) from the vehicle-mounted device 21, it passes through the RSSI detector 5 and then determines whether or not the detected RSSI value exceeds a predetermined threshold value (T). In this region, since the RSSI value exceeds the threshold (T), the communication controller 7 determines that the received signal is valid and starts signal transmission / reception with the vehicle 20.

Next, the threshold value (T) will be described.
FIG. 3 is a graph showing the relationship between the received signal strength (dBm) from the roadside apparatus in the downlink, that is, the vehicle-mounted device, and the approach direction distance (m). A point with an approach direction distance of 0 m corresponds to a position directly below the antenna of the roadside apparatus. In FIG. 3, the broken line B shows the transition of only the direct wave that does not consider the reflection of the radio wave. On the other hand, a solid line A shows a transition when a multiple reflected wave is added to a direct wave in consideration of multiple reflection of radio waves.
The solid line A is the result of calculation using a simulation technique based on the cell space method. This cell space method is a calculation method for simulating the transition of radio waves that are reflected by multiple reflections up to a higher-order reflection called 12th-order reflection, and it has been confirmed that it is very close to the graph of the actual measurement values (Matsuumi Oyama). : "Electromagnetic environment in road traffic system", monthly EMC No. 210, 29-37, 2005).

As is apparent from this graph, the vehicle-mounted device is configured to return a radio wave when the radio wave emitted from the roadside radio device exceeds the no-response level (−70.5 dBm). The response is started even in the section of about 5.5 m to 14 m before the receiving antenna. Originally, this area is an area outside the communication range, and is a section in which it is not desired to respond.
On the other hand, FIG. 4 is a graph showing the relationship between the received signal strength (dBm) from the vehicle-mounted device in the uplink, that is, the roadside apparatus, and the approach direction distance (m). As described above, when receiving the influence of multiple reflection, the vehicle-mounted device starts a response even in a section of about 5.5 m to 14 m before the antenna, but the reception sensitivity of the roadside wireless device is −65 dBm. The roadside wireless device receives the signal from, which causes erroneous road-to-vehicle communication.
Therefore, when RSSI is introduced as in the present invention and −52 dBm is set as the threshold (T), the threshold (T) is not exceeded in the section of about 5 m to 14 m before the antenna. Does not start transmission / reception. As a result, it is possible to reliably eliminate erroneous communication in this section as in the past.
Note that the threshold value of −52 dBm is set as a threshold value that can secure an effective communication distance even when fluctuation factors in line design overlap at the digging toll gate.

In the above description, the roadside wireless device is used in a sealed space having wall surfaces on all sides, such as a digging toll gate. However, other radio waves such as a toll gate having only a ceiling or a toll gate having only left and right wall surfaces can be used. Of course, it can be installed and used in any place where multiple reflection occurs. Also, the threshold value (T) can be arbitrarily selected according to the environment.
Moreover, although the above description demonstrated the case where one vehicle carrying an ETC onboard equipment entered the ETC toll booth, it is needless to say that it can be applied to the case where a plurality of vehicles enter.

  As described above, in the present invention, even in the section where multiple reflections of radio waves shown in the middle part of FIG. 2 occur, it is possible to execute correct road-to-vehicle communication without being affected by multiple reflections by introducing RSSI. Since there is no need to change anything, only the roadside wireless device can be improved, so that the vehicle-mounted device can be used as it is. Furthermore, since it is not necessary to construct a radio wave absorber in the section where multiple reflections of radio waves shown in the middle part of FIG. 2 described above, it is possible to perform improvement of the electromagnetic environment with as few radio wave absorbers as possible, There is also an advantage that construction costs can be greatly reduced.

DESCRIPTION OF SYMBOLS 1 Apparatus main body 2 Antenna 3 Duplexer 4a Transmitter 4b Receiver 5 RSSI detector 6 RSSI determination device 7 Communication controller 8 Lane server 20 Vehicle 21 Vehicle-mounted device 30 Road surface 31 Ceiling 32 Entrance side vehicle sensor 33 Exit side vehicle sensor

Claims (3)

A roadside wireless device in ETC, which detects a signal strength (hereinafter referred to as RSSI) for a signal called an activation channel (ACTC) from a vehicle-mounted device among signals received from each vehicle-mounted device received by an antenna. An RSSI detector, an RSSI determiner that determines whether or not the detected RSSI value exceeds a predetermined threshold value, and determines that the received signal is valid only when the RSSI value exceeds the threshold value. A roadside radio apparatus comprising: a communication controller that starts signal transmission / reception between the first and second terminals, and -52 dBm is set as a predetermined threshold value based on a calculation result using a simulation technique based on a cell space method.   2. The roadside apparatus according to claim 1, wherein the apparatus main body is installed in a place where multiple reflection of radio waves occurs.   The roadside radio apparatus according to claim 2, wherein the apparatus main body is installed at a toll gate in the tunnel.

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