JP2011223162A - Radio receiver and road-to-vehicle communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio receiver capable of conveniently avoiding interference of a radio signal and a radio-to-vehicle communication system using the same.SOLUTION: The radio receiver comprises detector circuits 26a and 26b which detect RSSIs of received signals through first and second receiving antennas 20a and 20b, respectively, a determination unit 28a which determines whether or not the RSSIs detected by the detector circuits 26a and 26b are greater than a predetermined threshold value for each of the receiving antennas 20a and 20b, and an acquisition unit 28b which, when one of the RSSIs through the receiving antennas 20a and 20b is determined to be greater than the predetermined threshold value, acquires the received signal only through the receiving antenna corresponding to that RSSI.

Description

  The present invention relates to a radio receiver used in, for example, an intelligent transport system (ITS) and a road-vehicle communication system.

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, advanced road traffic systems that improve the safety of vehicles by receiving information from infrastructure devices installed on the road and utilizing this information have been studied. (For example, refer to Patent Document 1).
Such an intelligent road traffic system is mainly composed of a plurality of roadside communication devices which are wireless communication devices on the infrastructure side and a plurality of in-vehicle communication devices which are wireless communication devices mounted on each vehicle.

  In this case, a combination of communication performed between communication subjects includes road-to-road communication between road-side communication devices, road-to-vehicle (or vehicle-road) communication between road-side communication devices and vehicle-mounted communication devices, and vehicle-mounted communication. Vehicle-to-vehicle communication performed between aircraft. Thus, in a communication system in which a plurality of types of communication are performed, the transmission timing is divided between the roadside communication device and the vehicle-mounted communication device, thereby preventing mutual signals from colliding with each other. In the inter-vehicle communication and the inter-vehicle communication, wireless communication is performed by a carrier sense method (CSMA method). That is, when the in-vehicle communication device tries to transmit a signal to another device, it detects whether or not the wireless signal of the other device exists in the propagation path, and there is a state where the wireless signal does not exist. It is controlled to start transmission after being maintained for a predetermined time.

Japanese Patent No. 2806801

When one in-vehicle communication device detects a radio signal of another device so as to transmit a radio signal to another device, for example, other than transmitting a radio signal in the vicinity of the one in-vehicle communication device In some cases, the wireless signal cannot be detected in the one in-vehicle communication device.
For example, when the one in-vehicle communication device and the other in-vehicle communication device enter a certain intersection from different paths, there is an obstacle such as a building that blocks each other's propagation path between these in-vehicle communication devices. If present, even if the other in-vehicle communication device transmits a radio signal to the roadside communication device installed at the intersection, the one in-vehicle communication device does not reach the one in-vehicle communication device, There may be cases where the radio signal cannot be detected on the communication device side. In such a case, the one in-vehicle communication device may determine that there is no other radio signal in the propagation path and start transmitting the radio signal. Then, in the roadside communication device, radio signals from both the in-vehicle communication devices will reach, causing interference between the two signals, and may not be able to normally receive the radio signals from both in-vehicle communication devices. there were.
In this manner, the relationship between a plurality of in-vehicle communication devices that cannot detect each other's wireless signals and may transmit the wireless signals within the same period is hereinafter referred to as a hidden terminal relationship.

By the way, when a roadside communication device is installed at a certain intersection in the above-mentioned intelligent road traffic system, an area where the reception is not possible around the intersection only by installing one receiving antenna for receiving a radio signal from the vehicle-mounted communication device. May occur.
For example, at an intersection that forms a five-way intersection as shown in FIG. 10, a building 102 exists at a corner portion constituted by the route 100 and the route 101, and the roadside is on the side of the building 102. When the receiving antenna 103 of the communicator is installed, the wireless propagation path is blocked by the building 102, so that the radio wave transmitted from the area of the route 101 and the corner 104 of the route 101 is transmitted from the area. A non-receivable area 105 that cannot receive a signal occurs.
Furthermore, in the case of FIG. 10, the vehicle-mounted communication device 106 of the vehicle that is about to enter the intersection from the route 100 and the vehicle-mounted communication device 107 that is about to enter the intersection from the route 101 are hidden terminals due to the presence of the building 102. May be related.

  In the above case, even if the in-vehicle communication device 106 and the in-vehicle communication device 107 transmit wireless signals within the same period, if the in-vehicle communication device 107 is located in the unreceivable area 105, the in-vehicle communication device 107 The radio signal does not reach the reception antenna 103, and the reception antenna 103 receives only the radio signal from the in-vehicle communication device 104. As a result, both the in-vehicle communication devices 106 and 107 receive the radio signal in the same period. Even if they are transmitted, they do not interfere with each other.

On the other hand, as shown in FIG. 11, when the reception antenna 108 installed on the route 104 side is connected to the receiver of the roadside communication device in order to eliminate the unreceivable area X, the roadside communication device Although the radio signals from both the in-vehicle communication devices 106 and 107 can be received, the radio signals from both the in-vehicle communication devices arrive and cause interference between the two signals.
For example, a radio signal is transmitted from both in-vehicle communication devices 106 and 107 in the same period, a radio signal from the in-vehicle communication device 106 is received at −50 dBm at the receiving antenna 102, and a radio signal from the in-vehicle communication device 107 is received. If the antenna 106 is receiving at -55 dBm, the DU ratio (Desired to Unsigned signal ratio) at the receiver becomes 5 dB, and there is a possibility that neither of the radio signals of both the in-vehicle communication devices 104 and 105 can be normally received.

  In this way, if a plurality of antennas installed at different positions are connected to the receiver of the roadside communication device, the occurrence of the unreceivable area can be eliminated, but a plurality of antennas having a hidden terminal relationship can be eliminated. When an in-vehicle communication device is present, interference occurs between the radio signals transmitted by these in-vehicle communication devices, causing a problem that the radio signal from the in-vehicle communication device cannot be received normally.

  The present invention has been made in view of such circumstances, and a wireless signal resulting from the presence of a plurality of in-vehicle communication devices that have a plurality of antennas but cannot detect each other's wireless signals. It is an object of the present invention to provide a radio receiver and a road-to-vehicle communication system that can suitably avoid interference.

  (1) The present invention is a wireless receiver that receives received signals from a plurality of in-vehicle communication devices that communicate by the CSMA method and is received by a plurality of antennas, and receives the received signals by each of the plurality of antennas. A detection unit that detects a level; a determination unit that determines whether or not the reception level detected by the detection unit is greater than a predetermined threshold; and among the reception levels of each of the plurality of antennas, And an acquisition unit that acquires only a reception signal from an antenna corresponding to the one reception level when it is determined that any one of the reception levels is greater than the predetermined threshold.

  According to the radio receiver configured as described above, when it is determined that any one of the reception levels of the plurality of antennas is greater than the predetermined threshold, the one reception level Since it has an acquisition unit that acquires only the received signal from the antenna corresponding to the case, even when a plurality of wireless signals are transmitted within the same period, it was first determined that the reception level was greater than the predetermined threshold Since only the reception signal received by the antenna is acquired, reception signals received by other antennas do not cause interference. As a result, a plurality of in-vehicle communication devices that are incapable of detecting each other's wireless signals, that is, a hidden terminal relationship, each transmit a wireless signal within the same period, and each of the plurality of antennas receives these as received signals. Even in the case of reception, at least one of the received signals can be acquired and interference can be suitably avoided.

(2) (3) Since the front signal is arranged at the head of the received signal and the data signal is arranged after that, in order to acquire at least all the data signals, the determination unit The determination is preferably performed for each unit period. More specifically, the predetermined unit period is preferably set according to the time length of the pre-signal.
In this case, by setting a predetermined unit period so that the determination is made in the range of the period in which the front signal is arranged, the data signal portion of the received signal can be suitably acquired.

  (4) In addition, since the data necessary for obtaining the data signal included in the reception signal is also included in the pre-signal, the predetermined unit period is equal to 1 of the time length of the pre-signal. / 2 or less is preferable, and in this case, the pre-signal can be acquired in the minimum necessary range.

(5) Since a reception signal received by a plurality of antennas may receive a noise signal, the acquisition unit determines that the one reception level when the acquired reception signal is determined to be noise. The acquisition of the received signal by the antenna corresponding to may be stopped.
In this case, it is possible to prevent unnecessary noise signals from being continuously received.

(6) Since the noise signal is often abrupt, the acquisition unit receives the one reception level after a predetermined time has elapsed when the acquisition of the reception signal by the antenna corresponding to the one reception level is stopped. The cancellation of the acquisition of the received signal by the antenna corresponding to may be canceled.
In this case, since the sudden reception of the noise signal is canceled by waiting for the elapse of the predetermined time, it is possible to appropriately cancel the cancellation of the reception of the reception signal by the antenna corresponding to the one reception level. .

(7) Since the noise signal may be acquired when the reception level exceeds a predetermined threshold due to the noise signal, the acquisition unit stops acquiring the reception signal by the antenna corresponding to the one reception level. After that, when it is determined that the reception level of the reception signal by the antenna corresponding to the one reception level is smaller than the predetermined threshold, the cancellation of the reception of the reception signal by the antenna corresponding to the one reception level is cancelled. It can also be configured as follows.
In this case, if it is determined that the reception level of the reception signal is smaller than the predetermined threshold, it can be determined that the reception level of the noise signal has decreased, and the reception signal by the antenna corresponding to the one reception level appropriately. Canceling the acquisition of can be canceled.

(8) According to the wireless receiver, as described above, even if there are a plurality of in-vehicle communication devices that have a so-called hidden terminal relationship, it is possible to preferably avoid the occurrence of interference. Among the antennas, at least one antenna and another antenna different from the one antenna have different reception areas and are transmitted from an in-vehicle communication device located in the reception area of the one antenna. The signal may be arranged so that the vehicle-mounted communication device located in the reception area of the other antenna may not be able to receive the signal.
In this case, even if there are a plurality of in-vehicle communication devices that have a so-called hidden terminal relationship, the reception range can be suitably ensured by the plurality of antennas without causing interference.

  (9) In addition, the present invention includes a plurality of in-vehicle communication devices that perform communication using the CSMA method, and a wireless receiver that receives reception signals from the plurality of in-vehicle communication devices that are received by a plurality of antennas. In the road-vehicle communication system, the radio receiver detects a reception level of a reception signal from each of the plurality of antennas, and whether the reception level detected by the detection unit is greater than a predetermined threshold. A determination unit that determines for each of the plurality of antennas, and when it is determined that any one of the reception levels of the plurality of antennas is greater than the predetermined threshold, the one reception level And an acquisition unit that acquires only a reception signal from an antenna corresponding to the above.

  According to the road-to-vehicle communication system having the above-described configuration, as described above, a plurality of in-vehicle communication devices having a hidden terminal relationship each transmit a radio signal within the same period, and each of the plurality of antennas receives these as reception signals. Even in the case of reception, at least one of the received signals can be acquired, and the occurrence of interference can be preferably avoided.

  According to the wireless receiver and the road-to-vehicle communication system of the present invention, a wireless signal caused by the presence of a plurality of in-vehicle communication devices that have a plurality of antennas but cannot detect each other's wireless signals. This interference can be preferably avoided.

1 is a schematic perspective view showing an overall configuration of an intelligent road traffic system (ITS) including a roadside communication device according to an embodiment of the present invention. It is a road top view which shows a part of jurisdiction area of the intelligent transport system shown in FIG. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a block diagram which shows the structure of a radio | wireless receiving part. It is a conceptual diagram which shows an example of a time slot. It is a figure which shows an example of the communication frame of the signal which a vehicle-mounted communication apparatus transmits. It is a flowchart which shows the aspect of the control which concerns on the reception process of each reception process sequence which a reception control part performs. It is the top view which showed typically an example of the installation position of each receiving antenna in the intersection where the roadside communication apparatus was installed. In the situation shown in FIG. 8, one in-vehicle communication device starts transmitting a radio signal, and then the other in-vehicle communication device starts transmitting a radio signal, so that both in-vehicle communication devices are wireless within the same period. It is the figure which showed the relationship between RSSI of both the receiving antennas of a roadside communication apparatus when transmitting a signal, and the mode of both receiving process sequences. It is the top view which showed typically an example of the installation position of the receiving antenna in the intersection where the conventional roadside communication apparatus was installed. It is the top view which showed typically the other example of the installation position of the receiving antenna in the intersection where the conventional roadside communication apparatus was installed.

[Overall system configuration]
FIG. 1 is a schematic perspective view showing an overall configuration of an intelligent road traffic system (ITS) including a roadside communication device according to an embodiment of the present invention. In this embodiment, as an example of the road structure, a grid structure in which a plurality of roads in the north-south direction and the east-west direction intersect with each other is assumed.
As shown in FIG. 1, the intelligent transportation system of this embodiment is equipped with a traffic signal 1, a roadside communication device 2, an in-vehicle communication device 3 (see FIGS. 2 and 3), a central device 4, and an in-vehicle communication device 3. A vehicle 5 and a roadside sensor 6 including a vehicle detector and a monitoring camera are included.

The traffic signal 1 and the roadside communication device 2 are installed at each of a plurality of intersections Ji (i = 1 to 12 in the example), and are connected to the router 8 via a communication line 7 such as a telephone line. . This router 8 is connected to the central device 4 in the traffic control center.
The central device 4 constitutes a local area network (LAN) with the traffic signal device 1 and the roadside communication device 2 at each intersection Ji included in the area under its control. Therefore, the central device 4 can perform bidirectional communication with each traffic signal 1 and each roadside communication device 2. The central device 4 may be installed on the road instead of the traffic control center.

The roadside sensor 6 is installed in various places on the road in the jurisdiction area for the purpose of counting the number of vehicles flowing into each intersection Ji. The roadside sensor 6 includes a vehicle sensor that ultrasonically senses the vehicle 5 that passes underneath, or a monitoring camera that shoots traffic conditions on the road in time series. The sensing information S4 and the image data S5 are transmitted via the communication line 7. Is transmitted to the central device 4 via
In FIG. 1 and FIG. 2, only one signal lamp is depicted at each intersection Ji for the sake of simplicity of illustration, but each actual intersection Ji is used for ascending and descending roads that intersect each other. At least four signal lamps are installed.

[Central equipment]
The central device 4 has a control unit composed of a workstation (WS), a personal computer (PC), etc., and this control unit collects and processes various traffic information from the roadside communication device 2 and the roadside sensor 6. (Calculation)-Performs recording, signal control and information provision in an integrated manner.
Specifically, the control unit of the central device 4 performs system control for adjusting the traffic signal group 1 on the same road for the traffic signal 1 at the intersection Ji belonging to its own network, and this system control is applied to the road network. Extended wide area control (surface control) can be performed.

In addition, the central device 4 has a communication unit that is a communication interface connected to the LAN side via the communication line 7, and this communication unit includes a signal control command S1 relating to the lamp color switching timing of the signal lamp, Traffic information S2 including traffic jam information and the like is transmitted to the traffic signal device 1 and the roadside communication device 2 every predetermined time (see FIG. 1).
The signal control command S1 is transmitted every calculation period (for example, 1.0 to 2.5 minutes) of the signal control parameter when performing the system control and the wide area control, and the traffic information S2 is transmitted every 5 minutes, for example. Is done.

  Further, the communication unit of the central device 4 is generated when the vehicle passes through the vehicle information S3 including the current position of the vehicle 5 received by the communication device 2 from the in-vehicle communication device 3 from the roadside communication device 2 corresponding to each intersection Ji. Sensing information S4 of a vehicle sensor (not shown) consisting of a pulse signal and image data S5 consisting of digital information of a road photographed by a surveillance camera are received, and the control unit of the central device 4 Based on various information, the system control and the wide area control are executed.

[Wireless communication systems, etc.]
FIG. 2 is a road plan view showing a part of the jurisdiction area of the above intelligent road traffic system.
In FIG. 2, each of two roads intersecting each other is illustrated as one lane on one side in the up and down directions, but the road structure is not limited to this.
As shown also in FIG. 2, the intelligent transportation system of the present embodiment includes a plurality of roadside communication devices 2 capable of wireless communication with the in-vehicle communication device 3 and other communication using a carrier sense method (CSMA method). And an in-vehicle communication device 3 that is a kind of mobile wireless transceiver that performs wireless communication with the devices 2 and 3.

A plurality of roadside communication devices 2 are installed at each roadside intersection Ji. On the other hand, the in-vehicle communication device 3 is mounted on each vehicle 5 traveling on the road.
Each roadside communication device 2 has a reference area A (a range in which the transmission signal of the roadside communication device 2 can sufficiently reach) spreading around the roadside communication device 2, and the vehicle-mounted communication device 3 of the vehicle 5 traveling in its own reference area A Wireless signals can be transmitted.
Each roadside communication device 2 can also perform wireless communication with other roadside communication devices 2 in which the reference area A overlaps (partially or all overlap).

In the intelligent transport system of this embodiment, wireless communication is used between the roadside communication devices 2 (roadside communication), and between the roadside communication device 2 and the vehicle-mounted communication device 3 (from “road” to “car” Wireless communication is also used for both vehicle-to-vehicle communication and vehicle-mounted communication devices 3 (vehicle-to-vehicle communication).
As described above, the central device 4 provided in the traffic control center is capable of two-way communication with each roadside communication device 2 by wire, but wireless communication may be performed between these devices.

Each roadside communication device 2 assigns a time slot (first slot T1 in FIG. 5) for wireless transmission by the own device by the TDMA method, and a time slot other than this time slot (second slot T2 in FIG. 5). Does not perform wireless transmission. Therefore, the time zone other than the time slot for the roadside communication device 2 is opened as a transmission time by the CSMA method for the in-vehicle communication device 3.
The roadside communication device 2 has a time synchronization function with other roadside communication devices 2 in order to control its own transmission timing. The time synchronization of the roadside communication device 2 is performed by, for example, GPS synchronization that adjusts its own clock to the GPS time, air synchronization that adjusts its own clock to a transmission signal from another roadside communication device 2, or the like.

[Roadside communication device]
FIG. 3 is a block diagram showing the internal configuration of the roadside communication device 2 and the in-vehicle communication device 3.
The roadside communication device 2 includes a wireless reception unit (wireless receiver) 20, a wireless transmission unit 21, a wired communication unit 22 that performs bidirectional communication with the central device 4, and a control unit 23 that includes a CPU that performs communication control thereof. And a storage unit 24 composed of a storage device such as a ROM or a RAM connected to the control unit 23. The storage unit 24 stores a communication control program executed by the control unit 23, communication device IDs of the communication devices 2 and 3, and the like.

  The wireless transmission unit 21 includes a transmission antenna 21a, and sets its own reference area A by transmitting a wireless signal around its own device. The wireless transmission unit 21 also has a function of performing processing such as D / A conversion and amplification of the modulated transmission signal in addition to modulation of transmission data and transmission timing control given from the control unit 23. is doing.

The radio reception unit 20 includes a first reception antenna 20a and a second reception antenna 20b, and each is installed at a predetermined position of an intersection Ji where the roadside communication device 2 is installed.
FIG. 4 is a block diagram illustrating a configuration of the wireless reception unit 20. The radio reception unit 20 includes both reception antennas 20a and 20b and reception processing sequences R1 and R2 to which both the reception antennas 20a and 20b are connected.
Each reception processing sequence R1, R2 includes RF units 25a, 25b, detection circuits 26a, 26b, and changeover switches 27a, 27b, respectively. In addition, the wireless reception unit 20 includes a reception control unit 28 for controlling the reception processing sequences R1 and R2 and demodulating the reception signal.

The RF units 25a and 25b have functions of performing amplification processing, A / D conversion processing, and the like of reception signals received by the reception antennas 20a and 20b. 26b and the changeover switches 27a and 27b.
The detection circuits 26a and 26b perform envelope detection based on the reception signals given from the RF units 25a and 25b, respectively, and detect the detected voltage values of the reception signal strengths (Received Signal Strength Indication, Hereinafter, it is also output to the reception control unit 28 as RSSI).
The changeover switches 27a and 27b have a function of switching the output destination of the reception signals from the RF units 25a and 25b to either the reception control unit 28 side or the ground side. The changeover switches 27 a and 27 b are controlled by the reception control unit 28.

  The reception control unit 28 acquires a reception signal given from the RF units 25a and 25b via the determination unit 28a that performs determination on the RSSI output from the detection circuits 26a and 26b and the changeover switches 27a and 27b. Part 28b. The determination unit 28a determines whether or not the reception antenna is receiving a signal by determining whether or not the RSSI exceeds a predetermined threshold value. The acquisition unit 28b acquires the reception signals given from the RF units 25a and 25b, demodulates the acquired reception signals, and outputs the demodulated data to the control unit 23.

In addition, the acquisition unit 28b controls the changeover switches 27a and 27b based on the determination result by the determination unit 28a, so that the reception processing for each reception processing sequence R1 and R2 to which the reception antennas 20a and 20b are connected is performed. Control is performed by selecting one of the standby mode, the acquisition mode, and the cancel mode.
Each mode and control related to the reception processing of each reception processing sequence R1 and R2 performed by the reception control unit 28 will be described in detail later.

  Returning to FIG. 3, the control unit 23 has a function of comprehensively controlling wireless communication performed by the wireless reception unit 20 and the wireless transmission unit 21. Specifically, it performs code conversion for data transmission / reception with the in-vehicle communication device 3a, and processing such as aggregation, accumulation, transfer, and editing of transmission / reception data exchanged by each wireless communication unit 20-23. The relay process of data between other devices is performed.

  Further, the control unit 23 temporarily stores the traffic information S2 and the like received from the central device 4 received by the wired communication unit 22 in the storage unit 24, and broadcasts it from the first wireless communication unit 20 to its own reference area A. To do. In addition, the control unit 23 temporarily stores the vehicle information S3 received by the reception units of the wireless communication units 20 to 23 in the storage unit 24 and transfers the vehicle information S3 to the central device 4 via the wired communication unit 22.

  Further, the control unit 23 broadcasts the allocation information S6 related to the time slot stored in the storage unit 24 to its own reference area A via the wireless transmission unit 21. This allocation information S6 is for notifying the in-vehicle communication device 3 of the transmission time of the roadside communication device 2. The in-vehicle communication device 3 of the vehicle 5 traveling in the reference area A performs radio transmission by the carrier sense method in a time zone when the roadside communication device 2 does not transmit.

[Time slot allocation information]
FIG. 5 is a conceptual diagram showing an example of a time slot included in the allocation information S6.
As shown in FIG. 5, the time slot includes a first slot T1 and a second slot T2, and these total periods are repeated at a constant period C.
The first slot T1 is a time slot for the roadside communication device 2, and wireless transmission by the roadside communication device 2 is permitted in this time zone. A slot number i is assigned to the first slot T1, and the slot number i is periodically incremented or decremented.

The second slot T2 is a time slot for the in-vehicle communication device 3. Since this time zone is opened for wireless transmission by the in-vehicle communication device 3, the roadside communication device 2 does not perform wireless transmission in the second slot T2.
In the time slot shown in FIG. 5, the dots ● marked in the first slot T1 of each slot number i = 1 to 3 indicate that the transmission times of the plurality of roadside communication devices 2 are assigned to the first slot T1. Show.

  That is, in the example shown in FIG. 5, the transmission times of the two roadside communication devices 2 at the intersections J1 and J5 (see FIG. 1) are allocated to the first slot T1 of the slot number (1), and the slot number (2 ) Is assigned to the transmission times of the three roadside communication devices 2 at the intersections J2, J6 and J8, and the first slot T1 of the slot number (3) is assigned to one roadside at the intersection J3. The transmission time of the communication device 2 is assigned.

Thus, the transmission time of each roadside communication device 2 is not assigned to the first slot T1 in a one-to-one correspondence, but is installed at the intersection Ji (i = 1 to 12) where no radio wave interference occurs. The roadside communication devices 2 can be assigned to the same slot number i.
Such slot allocation can be performed collectively by the central device 4, or each roadside communication device 2 can autonomously perform using the installation position and slot information acquired from other devices. Also, one master unit is selected in advance from a plurality of roadside communication devices 2, and this parent device is a transmission timing at which radio interference does not occur between the slave devices that are the other roadside communication devices 2 that it manages. It is also possible to perform slot allocation so that

[In-vehicle communication device]
Returning to FIG. 3, the in-vehicle communication device 3 includes a communication unit (transmission / reception unit) 31 connected to the antenna 30 for wireless communication, a control unit 32 including a CPU that performs communication control on the communication unit 31, and the like. A storage unit 33 including a storage device such as a ROM or a RAM connected to the control unit 32 is provided. The storage unit 33 stores a communication control program executed by the control unit 32, communication device IDs of the communication devices 2 and 3, and the like.

The control unit 32 of the in-vehicle communication device 3 has a function of causing the communication unit 31 to perform wireless communication by the carrier sense method for inter-vehicle communication, and in the time division multiplexing method with the roadside communication device 2 It does not have a communication control function.
Accordingly, the communication unit 31 of the in-vehicle communication device 3 always senses the reception level of a predetermined carrier frequency, and when the value is equal to or greater than a certain threshold, wireless transmission is not performed, and when the value is less than the threshold Only intended to perform wireless transmission.

The control unit 32 of the in-vehicle communication device 3 broadcasts and wirelessly transmits vehicle information S3 including the current position, direction, speed, vehicle type, etc. of the vehicle 5 (in-vehicle communication device 3) to the outside via the communication unit 31. To do.
In addition, the control unit 32 of the in-vehicle communication device 3 has the position, speed, and direction included in the vehicle information S3 received directly from the other vehicle 5 or the vehicle information S3 of the other vehicle 5 received from the roadside communication device 2. Based on this, it is possible to perform safe driving support control for avoiding a right-handed collision or a head-on collision.

FIG. 6 is a diagram illustrating an example of a communication frame of a signal transmitted by the in-vehicle communication device 3.
As shown in FIG. 6, the communication frame of the transmission signal of the in-vehicle communication device 3 includes a preamble (prefix signal), a header, data, and a CRC (Cyclic Redundancy Check).
As shown in the figure, among the above data, the preamble is arranged at the head of the frame and is a signal for allowing the receiving side to recognize the head of the frame.
The header stores the contents of data stored in the frame and information necessary for communication.
The data includes the position, direction (traveling direction), and speed of the vehicle 5, but can also include a reception level when a transmission signal is received from the roadside communication device 2. The information on the position and direction of the vehicle 5 is usually information autonomously measured by sensors on the vehicle 5 side such as GPS, but it may be acquired from the infrastructure side such as an optical beacon. The speed is information based on a speed sensor or the like mounted on the vehicle 5.

[About Control Modes Related to Reception Processing of Each Reception Processing Sequence Performed by Reception Control Unit 28]
Next, an aspect of control related to the reception processing of each of the reception antennas 20a and 20b performed by the reception control unit 28 (FIG. 4) will be described.
As described above, the reception control unit 28 selects any one of the standby mode, the acquisition mode, and the cancel mode for the reception processing of the reception processing sequences R1 and R2 to which the reception antennas 20a and 20b are connected. Select and control.
The standby mode is a mode in which each of the reception antennas 20a and 20b waits to receive a signal based on the RSSI of the detection circuits 26a and 26b with the changeover switches 27a and 27b switched to the ground side. In this standby mode, when the determination unit 28a determines that any of the reception antennas is receiving a signal, it is allowed to change the reception processing sequence to which the reception antenna is connected to the acquisition mode. In the reception processing sequence set to the standby mode, the reception antenna to which the reception processing sequence is connected is connected to the ground side, and thus no reception signal is acquired.

In addition, the acquisition mode means that one of the changeover switches 27a and 27b is connected to the reception control unit 28 side and the other is connected to the ground side, so that only one reception processing sequence is received by the reception antenna. This is a mode for acquiring a signal. Note that when one reception processing sequence is in the acquisition mode, the other reception processing sequences are in the cancel mode.
The cancellation mode is a mode in which the changeover switch 27a (27b) is maintained in the state of being switched to the ground side, and the state is maintained even if the RSSI of the detection circuit 26a (26b) exceeds a predetermined threshold. . In the reception processing sequence set to the cancel mode, the reception antenna is not acquired because the reception antenna is connected to the ground side.

FIG. 7 is a flowchart showing an aspect of control related to the reception processing of each reception processing sequence R1, R2 performed by the reception control unit 28.
First, the reception control unit 28 sets each reception processing sequence (hereinafter, the reception processing sequence is also simply referred to as a sequence) to the standby mode (step S101), and sets the value K of the clock counter provided therein to itself. It is set to 0 (step S102).
Next, the reception control unit 28 proceeds to steps S103 and S104. These processes are processes for the series set to the stop mode in step S111 described later, and will be described in detail later.

When the reception control unit 28 finishes the processes in steps S103 and S104, the reception control unit 28 determines whether or not the value K of the clock counter is equal to or greater than a predetermined value k1 (step S105).
If it is determined in step S105 that the value K of the clock counter is not greater than or equal to the predetermined value k1, the reception control unit 28 returns to step S103 again, and proceeds to step S105 via step S104. On the other hand, if it is determined in step S105 that the value K of the clock counter is equal to or greater than the predetermined value k1, the reception control unit 28 proceeds to step S106.
Therefore, the reception control unit 28 repeats the process between steps S103 to S105 until the value K of the clock counter reaches the predetermined value k1 or more. That is, the reception control unit 28 proceeds from step S102 to step S106 after a period determined by the value K of the clock counter being equal to or greater than the predetermined value k1.

In step S105, when it is determined that the value K of the clock counter is equal to or greater than the predetermined value k1 and the process proceeds to step S106, the determination unit 28a of the reception control unit 28 determines that the RSSI of each series set in the standby mode is It is determined whether or not the value is larger than a predetermined threshold value Th (step S106).
Here, the threshold value Th is set to a value of RSSI that can be determined that the corresponding receiving antenna is receiving a radio signal from the in-vehicle communication device 3, and the determination unit 28 a determines that the RSSI is greater than the threshold value Th. By determining that it is large, it is determined that the receiving antenna corresponding to the RSSI is receiving a radio signal from the in-vehicle communication device 3.

If it is determined in step S106 that none of the RSSIs of each series is greater than the threshold value Th, the determination unit 28a has not received the radio signal from the in-vehicle communication device 3 by each reception antenna. It returns to step S102 again.
Here, from step S102 to step S106, as described above, there is a period determined by the value K of the clock counter being equal to or greater than the predetermined value k1. That is, the determination performed in step S106 is periodically performed for each period. In the present embodiment, the predetermined value k1 is set such that the period is equal to or less than ½ of the time length of the preamble included in the transmission signal of the in-vehicle communication device 3.

On the other hand, when it is determined in step S106 that at least one of the RSSIs of each series is a value larger than the threshold Th, the acquisition unit 28b of the reception control unit 28 first sets the RSSI value to the threshold Th. Is exceeded, only the sequence determined to be receiving the radio signal from the in-vehicle communication device 3 is set to the acquisition mode, and the other sequence is set to the stop mode (step S107).
As a result, the acquisition unit 28b first acquires a reception signal from a sequence that is determined to be receiving a radio signal from the in-vehicle communication device 3 because the RSSI value exceeds the threshold Th, and acquires the acquired reception. Demodulate the signal. Note that sequences other than those determined to be receiving radio signals are set to the cancel mode, so even if the receiving antenna connected to these sequences receives the radio signal from the in-vehicle communication device 3, The reception signal is not acquired by the reception control unit 28.

  If it is determined in step S106 that the RSSI values of a plurality of sequences (sequences R1, R2) are substantially larger than the threshold value Th at the same time (to the extent that it is not possible to determine which sequence was first), acquisition is performed. The unit 28b sets the series having the largest RSSI value to the acquisition mode.

In step S107, after setting only the sequence determined to be receiving a radio signal to the acquisition mode, the acquisition unit 28b or the control unit 23 determines that the reception signal acquired and demodulated by the acquisition unit 28b is noise (noise signal). ) Is determined (step S108).
Next, the acquisition unit 28b determines whether or not the determination result of the determination performed in step S108 is noise (step S109). If the determination result is not noise, the acquisition unit 28b proceeds to step S110 and checks whether or not acquisition of the received signal is completed (step S110). When acquisition of the reception signal is not completed, the acquisition unit 28b continues the acquisition mode for the sequence determined to be receiving the radio signal, and continuously acquires the reception signal. Whether or not the demodulated received signal is noise is determined as needed during the acquisition mode (step S108), and the acquisition unit 28b of the reception control unit 28 repeats the determination of the determination result (step S109).
If it is confirmed in step S110 that reception signal acquisition has been completed, the reception control unit 28 returns to step S101 and repeats the above-described processing again.

  On the other hand, if the determination result for the demodulated received signal is noise in step S109, the acquisition unit 28b of the reception control unit 28 sets the sequence set to the acquisition mode to the stop mode and sets other sequences to The standby mode is set (step S111), and the process returns to step S102.

When the process returns from step S111 to step S102, after setting the value K of the clock counter to 0 in step S102, the determination unit 28a of the reception control unit 28 sets the series (reception signal) set in the stop mode in step S111. It is determined whether or not the RSSI of the series determined as noise is smaller than the threshold Th (step S103). As a result, the reception control unit 28 can confirm whether or not the reception signal received as noise has been received by the reception antenna.
If it is determined in step S103 that the RSSI is smaller than the threshold value Th, the reception control unit 28 sets a sequence corresponding to the RSSI (a sequence in which the received signal is determined to be noise) as a standby mode (step S103). S104). In this case, at least under the present circumstances, since it is not determined that a signal is received, it can be considered that a signal such as noise is not received. For this reason, the reception control unit 28 sets the sequence to the standby mode so that the wireless signal from the in-vehicle communication device 3 can be received.

On the other hand, if it is determined in step S103 that the RSSI is not smaller than the threshold Th, the reception control unit 28 proceeds to step S105. In this case, since there is still a possibility that the noise is still received in the sequence, the reception control unit 28 proceeds to step S105 in a state where the sequence is continuously set to the stop mode.
In this manner, the reception control unit 28 performs determination for setting the mode for the sequence set from the acquisition mode to the stop mode during steps S102 to S105 that determine the determination period of step S106.

  As described above, the reception control unit 28 controls each series, and the reception antenna that is determined to have received the radio signal from the in-vehicle communication device 3 when the RSSI value first exceeds the threshold Th is connected. Control is performed so as to acquire only the received signals of the received sequences.

[Installation mode at the intersection of each receiving antenna]
Next, an installation mode at the intersection of the reception antennas 20a and 20b of the wireless reception unit 20 will be described.
FIG. 8 is a plan view schematically showing an example of the installation positions of the receiving antennas 20a and 20b at the intersection where the roadside communication device 2 is installed. In FIG. 8, for the sake of easy understanding, the signal lamps installed in each direction of the road intersecting each other are omitted.

In FIG. 8, the building B exists in the corner | angular position comprised by the path H1 and the path H2 among each path which comprises the intersection J, and the 1st receiving antenna 20a is the path H1 side. It is installed on the side of Building B.
Further, the second receiving antenna 20b is disposed on the side of the building B on the side of the route H2 and at a position sandwiching the route H2.
For this reason, in FIG. 8, the radio signal propagation path is blocked by the building B, so that the non-receivable area X1 is an area where the radio signal transmitted from the area cannot be received by the first receiving antenna 20a. It occurs on the path H2.
Similarly, the radio signal propagation path is blocked by the building B, so that the non-receivable area X2, which is an area in which the second antenna 20b cannot receive a radio signal transmitted from the area, is located on the path H1. Has occurred.
Therefore, the first receiving antenna 20a and the second receiving antenna 20b are arranged in such a relationship that their reception areas are different from each other and an unreceivable area is generated.

However, the first receiving antenna 20a can receive signals transmitted from the non-receivable area X2 of the second receiving antenna 20b, and the second receiving antenna 20b is transmitted from the non-receivable area X1 of the first receiving antenna 20a. The signal can be received. For this reason, the radio reception unit 20 can receive radio signals around the intersection J by interpolating the non-receivable areas X1 and X2 that occur between the reception antennas 20a and 20b.
As described above, the radio receiving unit 20 according to the present embodiment is configured so that the first and second receiving antennas 20a and 20b ( A plurality of receiving antennas).

  The roadside communication device 2 and the wireless reception unit 20 included in the roadside communication device 2 are installed, for example, on a support column on which the second reception antenna 20b is installed. Both receiving antennas 20a and 20b are connected to the wireless receiving unit 20 by wire. Further, the wireless transmission unit 21 and the transmission antenna 21a are not shown.

  Hereinafter, as shown in FIG. 8, when both receiving antennas 20a and 20b are installed, the vehicle 5a equipped with the in-vehicle communication device 3a to enter the intersection J from the route H1 and the intersection J from the route H2 are installed. A more specific operation of the wireless reception unit 20 (reception control unit 28) when there is a vehicle 5b equipped with the in-vehicle communication device 3b about to enter the vehicle will be described.

[Specific Example of Operation of Wireless Reception Unit 20]
In FIG. 8, the in-vehicle communication device 3a located in the route H1 is located in the incapable reception area X2, and the in-vehicle communication device 3b located in the route H2 is located in the incapable reception area X1. Further, the vehicle-mounted communication devices 3a and 3b are in a hidden terminal relationship because their radio propagation paths are blocked by the building B. For this reason, when it is going to approach the intersection J, the vehicle-mounted communication apparatuses 3a and 3b may transmit a radio signal together within the same period.

  FIG. 9 shows that, in the situation shown in FIG. 8, the in-vehicle communication device 3b starts transmitting a radio signal, and then the in-vehicle communication device 3a starts transmitting a radio signal, so that both the in-vehicle communication devices 3a and 3b It is the figure which showed the relationship between the RSSI of both the receiving antennas 20a and 20b of the roadside communication apparatus 2 when transmitting a radio signal within the same period, and the modes of both receiving processing sequences R1 and R2.

  In the figure, the upper part shows the time-dependent change of RSSI of the first receiving antenna 20a and the mode of the series R1, and the middle part shows the time-dependent change of RSSI of the second receiving antenna 20b and the mode of the series R2. Further, the lower part shows the timing for executing the determination (step S106 in FIG. 7) whether or not the RSSI value performed by the determination unit 28a of the reception control unit 28 exceeds the threshold Th. In each of these drawings, the horizontal axis indicates time, and the time relationships are shown to match each other. In the figure, a diagram L1 shows a change in the RSSI value of the first receiving antenna 20a, and a diagram L2 shows a change in the RSSI value of the second receiving antenna 20b.

  In the illustrated example, at the timing u2, the in-vehicle communication device 3b starts transmitting the radio signal, so the second receiving antenna 20b starts receiving the radio signal, and the timing u4 is a time point after the timing u2. FIG. 3 shows a case where the first receiving antenna 20a starts receiving the radio signal because the in-vehicle communication device 3a starts transmitting the radio signal.

  In the figure, since both in-vehicle communication devices 3a and 3b have not started transmitting radio signals at a time prior to timing u2, both receiving antennas 20a and 20b have RSSI values exceeding the threshold Th. No radio signal is received. Therefore, the reception control unit 28 sets both the series R1 and R2 to the standby mode.

In addition, while both series R1 and R2 are set to the standby mode, the determination unit 28a of the reception control unit 28 periodically determines whether the RSSI value exceeds the threshold Th at intervals of the period W. (Steps S102 to S106 in FIG. 7).
In the determination performed at the timing u1 immediately before the timing u2 at which the second receiving antenna 20b starts receiving the radio signal, both the receiving antennas 20a and 20b have not received the signal, and the RSSI value is the threshold Th. Therefore, the reception control unit 28 continues the mode of both the series R1 and R2 in the standby mode, and performs the determination again at the timing u3 that is the timing after the period W from the timing u1.

At timing u3, as shown in the figure, the second receiving antenna 20b starts receiving a radio signal from the in-vehicle communication device 3b, and since the RSSI value exceeds the threshold Th, the determination unit 28a In the determination at the timing u3, it is determined that the RSSI value of the second receiving antenna 20b exceeds the threshold Th, and the second receiving antenna 20b recognizes that a radio signal is received (in FIG. 7, Step S106).
Then, the acquisition unit 28b of the reception control unit 28 sets the reception processing sequence R2 to which the second reception antenna 20b is connected to the acquisition mode, and starts acquiring the reception signal received by the second reception antenna 20b. On the other hand, the reception processing sequence R1 to which the first reception antenna 20a is connected is set to the cancel mode (step S107 in FIG. 7). Note that the determination unit 28a does not execute the determination while the acquisition mode is being executed.

For this reason, as shown in the figure, at the timing u4 when the reception processing sequence R2 is still executing the acquisition mode, the in-vehicle communication device 3a starts transmitting the radio signal, so that the first receiving antenna 20a transmits the radio signal. Even if reception is started and the RSSI value exceeds the threshold Th, the acquisition unit 28b does not switch to the acquisition mode for the reception processing sequence R1 in the cancellation mode, and continues the cancellation mode.
Therefore, the acquisition unit 28b of the reception control unit 28 acquires only the reception signal from the reception processing sequence R2 even if the radio signals are transmitted from both the in-vehicle communication devices 3a and 3b within the same period after the timing u4. Therefore, the reception signal received by the first receiving antenna 20a does not cause interference.

Note that the period W, which is a cycle for determining whether or not the RSSI value exceeds the threshold Th, is equal to or less than ½ of the time length of the preamble included in the transmission signal of the in-vehicle communication device 3b as described above. It is set to be. For this reason, when switching from the standby mode to the acquisition mode, the determination is made at least within the range from the beginning of the preamble to half the time length of the preamble, so when acquiring the received signal in the acquisition mode In addition, the acquisition unit 28b can acquire the preamble at least in a range corresponding to ½ of the time length of the preamble. Thereby, the minimum necessary information required for communication included in the preamble can be acquired.
As described above, since the preamble is arranged at the head of the received signal and the signal constituting the data such as the position and speed of the vehicle is arranged thereafter, in order to obtain at least all of the data, the determination unit 28a The determination is preferably performed for each period set in accordance with the time length of the preamble, whereby the portion of the received signal constituting the data can be suitably acquired.

The reception control unit 28 continues to acquire the reception signal by setting the mode of the sequence R2 as the acquisition mode until acquisition of the reception signal is completed (step S110 in FIG. 7).
Assuming that the in-vehicle communication device 3b has finished transmitting the radio signal at the timing u5, the RSSI value of the second receiving antenna 20b is lower than the threshold Th at the timing u5. At this time, the acquisition unit 28b recognizes that the reception signal acquisition is completed from the information indicating the length of the signal included in the acquired reception signal or the RSSI value (step S110 in FIG. 7).
Then, the reception control unit 28 sets both the modes R1 and R2 to the standby mode (step S101 in FIG. 7), and the RSSI values of the receiving antennas 20a and 20b again exceed the threshold Th. The determination of whether or not there is started.

  Here, when the transmission of the radio signal of the in-vehicle communication device 3a is completed, if the determination unit 28a restarts the determination at the timing u6, the RSSI values of the receiving antennas 20a and 20b do not exceed the threshold Th. The reception control unit 28 continues the modes of both series R1 and R2 to enter the standby mode, and waits for a radio signal to be transmitted next.

  On the other hand, when the determination unit 28a restarts the determination at the timing u6, the in-vehicle communication device 3a still continues to transmit the wireless signal, and the wireless signal is received by the first receiving antenna 20a. As shown in FIG. 8, since the RSSI value of the first receiving antenna 20a still exceeds the threshold Th, the acquisition unit 28b sets the reception processing sequence R1 to the acquisition mode and the reception processing sequence R2 to the stop mode. (Steps S106 and S107 in FIG. 7).

However, in this case, since the reception signal acquired from the reception processing sequence R1 is acquired from the middle of the entire reception signal, all necessary data cannot be acquired and may not be used as information. In such a case, the acquisition unit 28b or the control unit 23 can acquire and demodulate the reception signal to some extent and determine whether or not all necessary data can be acquired based on the content of the reception signal.
Therefore, if the acquiring unit 28b acquires the received signal to some extent and determines that the acquired received signal is a received signal that cannot acquire all of the necessary data (for example, at the timing u7), the acquired received signal is converted into noise. (Steps S108 and S109 in FIG. 7). Then, the reception processing sequence R1 set to the acquisition mode is set to the cancellation mode, and the reception processing sequence R2 set to the cancellation mode is set to the standby mode (step S111 in FIG. 7).

After setting the reception processing sequence R2 to the standby mode, the determination unit 28a of the reception control unit 28 starts determining whether or not the RSSI value of each reception antenna exceeds the threshold Th (step in FIG. 7). S102 to S106).
If the first determination after the reception processing sequence R2 is set to the standby mode is made at the timing u8, the RSSI value of the second reception antenna 20b is smaller than the threshold Th at this time, so that the reception control unit 28 The acquisition unit 28b continues the mode of the reception processing sequence R2 in the standby mode. On the other hand, since the reception processing sequence R1 is the cancel mode, the cancel mode is continued regardless of the RSSI value.
Here, the reception control unit 28 determines whether or not the RSSI of the first reception antenna 20a is smaller than the threshold value Th between two successive determination timings (step S103 in FIG. 7).
As shown in the figure, if the RSSI value of the first receiving antenna 20a becomes smaller than the threshold Th at timing u9, the acquisition unit 28b of the reception control unit 28 at the timing u10 when the next determination is performed Recognizing that the reception antenna 20a is not receiving a reception signal regarded as noise, the mode of the reception processing sequence R1 is changed from the stop mode to the standby mode (step S104 in FIG. 7).

In the above, a case has been described in which when a received signal that cannot receive the entire data is acquired, the received signal is regarded as noise and processing is performed. In the present embodiment, reception received by either of the receiving antennas 20a and 20b. Even when it is determined that the signal is noise, the corresponding sequence is set to the stop mode until it is recognized that the received signal determined to be noise is not received. As a result, it is possible to prevent unnecessary noise from being continuously received.
Further, in this case, if it is determined that the RSSI value of the received signal is smaller than the threshold Th, it can be determined that the noise reception level has decreased, and the corresponding sequence mode is set to the standby mode as described above. Since the change is made, it is possible to appropriately cancel the suspension mode of the relevant series.

  In addition, since there are many unexpected noises, the reception control unit 28 waits for the cancel mode of the corresponding sequence after a predetermined time has elapsed when the sequence corresponding to the receiving antenna that received the noise is set to the cancel mode. You may comprise so that it may change into a mode. Also in this case, it is possible to appropriately cancel the cancellation mode of the series.

According to the radio receiving unit 20 of the present embodiment configured as described above, when it is determined that one of the RSSI values of the two receiving antennas 20a and 20b is larger than the predetermined threshold Th. Since the acquisition unit 28b that acquires only the reception signal from the reception antenna corresponding to the RSSI value is provided, even when a plurality of wireless signals are transmitted within the same period, the RSSI value is first set to the threshold Th. Since only the reception signal received by the reception antenna determined to be larger is acquired, the reception signals received by other reception antennas do not cause interference.
As a result, as shown in FIG. 8, even when in-vehicle communication devices that are in a hidden terminal relationship transmit radio signals within the same period and each antenna receives these as received signals, these receptions are also received. Among the signals, at least one received signal can be acquired, and interference can be suitably avoided.

The present invention is not limited to the above embodiments. In the above-described embodiment, the case where the present invention is applied to an intersection that forms a four-way with four routes is illustrated, but the present invention can also be applied to an intersection of another aspect such as a three-way.
Moreover, in the said embodiment, although the case where the radio | wireless receiving part 20 was provided with two receiving antennas, the 1st receiving antenna 20a and the 2nd receiving antenna 20b, it shall be set as the structure provided with many receiving antennas. You can also.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

2 Roadside communication devices 3a and 3b Car-mounted communication device 20 Wireless reception unit 20a First reception antenna 20b Second reception antennas 26a and 26b Detection circuit (detection unit)
28a determination unit 28b acquisition unit

Claims (9)

A wireless receiver that receives received signals from a plurality of in-vehicle communication devices that communicate with a CSMA system and that are received by a plurality of antennas,
A detection unit for detecting a reception level of a reception signal by each of the plurality of antennas;
A determination unit that determines, for each of the plurality of antennas, whether the reception level detected by the detection unit is greater than a predetermined threshold;
An acquisition unit that acquires only a reception signal from an antenna corresponding to the one reception level when it is determined that any one of the reception levels of the plurality of antennas is greater than the predetermined threshold; And a wireless receiver.   The wireless receiver according to claim 1, wherein the determination unit performs determination for each predetermined unit period.   The radio receiver according to claim 2, wherein the predetermined unit period is set according to a time length of a front signal included in the reception signal.   The radio receiver according to claim 3, wherein the predetermined unit period is ½ or less of a time length of the front signal.   The acquisition unit according to any one of claims 1 to 4, wherein when the acquired reception signal is determined to be noise, the acquisition unit stops acquisition of the reception signal by the antenna corresponding to the one reception level. Wireless receiver.   The acquisition unit cancels the cancellation of the reception of the reception signal by the antenna corresponding to the one reception level after a predetermined time has elapsed when the acquisition of the reception signal by the antenna corresponding to the one reception level is stopped. 5. The radio receiver according to 5.   The acquisition unit determines that the reception level of the reception signal by the antenna corresponding to the one reception level is smaller than the predetermined threshold after stopping the acquisition of the reception signal by the antenna corresponding to the one reception level. The wireless receiver according to claim 5, wherein cancellation of acquisition of a reception signal by an antenna corresponding to the one reception level is canceled.   At least one of the plurality of antennas and another antenna different from the one antenna have different reception areas and are transmitted from an in-vehicle communication device located in the reception area of the one antenna. The radio receiver according to any one of claims 1 to 7, wherein the received signal is arranged so that an in-vehicle communication device located in a reception area of the other antenna may not be able to receive the signal. A road-to-vehicle communication system comprising: a plurality of in-vehicle communication devices that communicate with each other using a CSMA method; and a wireless receiver that receives reception signals from the plurality of in-vehicle communication devices that are received by a plurality of antennas.
The wireless receiver
A detection unit for detecting a reception level of a reception signal by each of the plurality of antennas;
A determination unit that determines, for each of the plurality of antennas, whether the reception level detected by the detection unit is greater than a predetermined threshold;
An acquisition unit that acquires only a reception signal from an antenna corresponding to the one reception level when it is determined that any one of the reception levels of the plurality of antennas is greater than the predetermined threshold; A road-to-vehicle communication system comprising:

Images