JP2009017204A - Communication system, optical beacon, and onboard communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system, optical beacons, and an onboard communication apparatus which performs vehicle-to-vehicle wireless communications by a reservation system even if no road side wireless communication apparatus is installed. <P>SOLUTION: The communication system has onboard communication apparatuses mounted on vehicles which run on a road, and optical beacons which are installed on the road, and perform optical communications with the onboard communication apparatuses. The onboard communication apparatus has a wireless communication means which performs vehicle-to-vehicle wireless communications by the reservation system assigned beforehand so that a time slot for communication does not conflict with other apparatuses of a time division multiple access system between the onboard communication apparatuses mounted on other vehicles, and the wireless communication means starts the vehicle-to-vehicle wireless communication by the reservation system according to the optical communication performed with the optical beacon. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a communication system, an optical beacon, and an in-vehicle communication device for realizing an intelligent transport system (ITS).

  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 a system is mainly realized by a roadside wireless communication device as a communication device on the infrastructure side and an in-vehicle communication device that is a communication device mounted on each vehicle. Communication combinations include road-to-road communication between roadside wireless communication devices, road-to-vehicle (or roadway) communication between roadside wireless communication devices and vehicle-mounted communication devices, and vehicle-to-vehicle communication between vehicle-mounted communication devices. There is.

  In general, when a plurality of devices use the same frequency band at the same time in wireless communication, frequency division multiple access (FDMA) that communicates at different frequencies, or time division multiple that divides time into multiple time slots. Access (TDMA: Time Division Multiple Access) or the like can be used. There are also access methods that combine these.

  Among these access methods, in time division multiple access, there are a contention method in which transmission data collision may occur and a non-contention method in which transmission data collision is reliably avoided. The non-contention method includes a polling method and a reservation method. In order to prevent simultaneous transmission of transmission data in the same space, a time slot for wireless communication is exclusively assigned and the time Communicate using slots.

  In the contention method, transmission data may be transmitted at the same time in the same space. In such a case, the data is lost due to collision, and the data is resent in some way. Although it is necessary to prepare a method, it can be said that this method is suitable for a communication system in which the number of apparatuses that perform wireless communication is relatively small.

  Here, this contention method determines whether or not there is another device that is currently transmitting data by detecting the presence or absence of a carrier signal transmitted from another device before performing data transmission. (Hereinafter, this determination is referred to as carrier sense), regardless of whether other devices are performing data transmission, and an access method with carrier sense that starts data transmission only when it can be determined that it does not exist. It can be roughly divided into an access method without carrier sense for starting data transmission.

  As an access method with carrier sense, for example, CSMA (Carrier Sense Multiple Access), CSMA / CA (Carrier Sense Multiple Access / Collision Availidance), ISMA (Idle Signal Multiple SCT). As an access method without carrier sense, there are methods such as Pure ALOHA and Slotted ALOHA.

  The access method with carrier sense has an advantage that the probability of occurrence of collision is lowered and the certainty of arrival of data is improved because data transmission is started avoiding the timing at which other devices perform data transmission. However, since carrier sense is performed every time before the start of data transmission, there is a problem that overhead occurs and real-time performance is lowered.

  One access method without carrier sense performs data transmission regardless of other devices, so the overhead is smaller than the access method with carrier sense, but when data transmission is performed at the same timing as other devices Since the data is lost due to the occurrence of the collision, there is a problem that the certainty of reaching the destination is lowered. For this reason, in the access method without carrier sense, a backup procedure such as data retransmission is indispensable.

Japanese Patent No. 2806801

As described in Patent Document 1, if a wireless communication device is installed on the road side, a reservation method in which time slots are exclusively assigned to the in-vehicle communication device can be adopted. The reliability of wireless communication can be improved.
On the other hand, when a vehicle-mounted communication device transmits communication data with another vehicle-mounted communication device in a suburb where no roadside wireless communication device is installed, an access method with carrier sense such as CSMA may be adopted. Conceivable. This method is effective because the number of in-vehicle communication devices is relatively small, and in the suburbs where roadside wireless communication devices are not installed, it is considered that vehicle-to-vehicle communication will succeed with a very high probability.

On the other hand, even in the suburbs where infrastructure such as roadside wireless communication devices is not installed, there are areas with a large amount of traffic such as intersections where accidents frequently occur and points where sudden traffic congestion is likely to occur. In such a case, when an in-vehicle communication device tries to transmit data to another in-vehicle communication device by an access method with carrier sense such as CSMA, the real-time property of communication is impaired due to the overhead due to carrier sense. In addition, the carrier sense is repeated, and there is a possibility that data transmission cannot be completed within a limited period remaining in the communication area.
For this reason, even in the suburbs where the roadside wireless communication device is not installed, there has been a demand for a method that enables more reliable wireless communication between vehicles by a reservation method.

  The present invention has been made in view of such circumstances, and a communication system, an optical beacon, and an in-vehicle communication device capable of performing wireless communication between vehicles by a reservation method even when a roadside wireless communication device is not installed. The purpose is to provide.

  The present invention is a communication system including an in-vehicle communication device mounted on a vehicle traveling on a road, and an optical beacon installed on the road and performing optical communication with the in-vehicle communication device, The in-vehicle communication device is a vehicle-to-vehicle wireless communication based on a reservation method that is allocated in advance so that the communication time slot does not compete with other devices in the time-division multiple access with the in-vehicle communication device mounted on another vehicle. The wireless communication means is capable of starting inter-vehicle wireless communication by a reservation method in response to optical communication performed with the optical beacon. Yes.

  According to the present invention, the wireless communication means of the in-vehicle communication device starts the inter-vehicle wireless communication by the reservation method by communicating with the optical beacon installed on the road. For this reason, vehicle-to-vehicle wireless communication by the reservation method can be performed without installing a roadside wireless communication device. Furthermore, the area on one side when the optical beacon installed on the road is used as a boundary can be an area where inter-vehicle wireless communication is performed by wireless communication using a reservation method.

In the communication system, the wireless communication unit may stop inter-vehicle wireless communication by the reservation method when at least one of the following applies.
(1) When the elapsed time from the start time exceeds a predetermined first threshold (2) When the travel distance from the start time exceeds a predetermined second threshold

  In this case, the in-vehicle communication device starts the inter-vehicle wireless communication by the reservation method according to the communication with the optical beacon, and stops the inter-vehicle wireless communication depending on the elapsed time from the start time, the travel distance, etc. An area where inter-vehicle wireless communication is performed according to the method can be defined in the vicinity of the optical beacon.

  On the other hand, when optical communication is performed with the in-vehicle communication device in order to demarcate an area in which the vehicle-to-vehicle wireless communication by the reservation method is performed, the vehicle-to-vehicle wireless communication by the reservation method performed by the wireless communication unit is stopped. A stop light beacon can also be provided.

In addition, the wireless communication means detects that a vehicle-mounted communication device that performs vehicle-to-vehicle wireless communication by a reservation method exists around itself by detecting a transmission signal from a vehicle-mounted communication device mounted on another vehicle. Then, the vehicle-to-vehicle wireless communication by the reservation method may be started.
In this case, the wireless communication means does not communicate with the optical beacon, but the reservation is performed by detecting that the in-vehicle communication device performing the inter-vehicle wireless communication by the reservation method exists around itself. It can be recognized that the vehicle is located in an area where vehicle-to-vehicle wireless communication is performed.

  In the communication system, the optical beacon assigns a time slot for inter-vehicle wireless communication according to the reservation method to an in-vehicle communication device that starts inter-vehicle wireless communication according to the reservation method according to the optical communication, Time slot allocating means for notifying time slot information related to the allocated time slot by the optical communication is provided, and the wireless communication means of the in-vehicle communication device performs vehicle-to-vehicle wireless communication by a reservation method based on the time slot information. It may be.

  The optical beacon can notify the time slot information about the assigned time slot to the in-vehicle communication device that starts the inter-vehicle wireless communication by the reservation method, so that the time slot can be dynamically allocated according to the demand. It becomes. The time slot information refers to information for the vehicle-mounted communication device to know the time slot that can be used by itself, and may be a timing that is a combination of the start time and end time of the usable time slot. It may be a time slot identification number.

In the communication system, the time slot allocating unit is configured such that the elapsed time from the time when the optical beacon performs optical communication with the in-vehicle communication device to which the time slot is allocated exceeds a predetermined third threshold. In addition, the assigned time slot may be an empty time slot.
In this case, the time slot once assigned can be made an empty time slot at an appropriate time.

In addition, when the wireless communication means stops vehicle-to-vehicle wireless communication according to the reservation method, time slot release information for notifying that the time slot assigned to the in-vehicle communication device becomes an empty time slot, It may be transmitted to other in-vehicle communication devices by wireless communication, or time slot release information received from other in-vehicle communication devices is transmitted to other in-vehicle communication devices by inter-vehicle wireless communication. Also good.
In this case, the time slot release information can be shared by a plurality of in-vehicle communication devices.

Further, in this case, the wireless communication unit transmits the time slot release information received from the other in-vehicle communication device to the stop optical beacon, and the time slot allocation unit transmits the stop optical beacon to the other optical beacon. When the time slot release information transmitted by the in-vehicle communication device is received, the time slot corresponding to the time slot release information may be an empty time slot.
Thus, in this system, the time slot release information transmitted by the in-vehicle communication device that stops the inter-vehicle wireless communication by the reservation method without communicating with the stop optical beacon is transmitted via the other in-vehicle communication device. Can be sent to an optical beacon. Furthermore, the assigned time slot can be released to make an empty time slot without directly communicating with the in-vehicle communication device that stops the inter-vehicle wireless communication by the reservation method.

Further, when the vehicle-to-vehicle wireless communication by the reservation method is stopped, the wireless communication means competes with other devices for a communication time slot with an in-vehicle communication device mounted on another vehicle. Communication using a possible contention method may be performed.
When the wireless communication means stops the vehicle-to-vehicle wireless communication by the reservation method, the wireless communication means is located outside the area where the vehicle-to-vehicle communication is performed by the wireless communication by the reservation method. For this reason, the contention system can be adopted for the wireless communication means.
The contention method is preferably a CSMA method.

  Moreover, the optical beacon of the present invention is used in the communication system, and according to this, as described above, inter-vehicle wireless communication can be performed by a reservation method without installing a roadside wireless communication device. .

  Further, the in-vehicle communication device of the present invention is an in-vehicle communication device that performs optical communication with an optical beacon installed on the road, and between the in-vehicle communication device mounted on another vehicle, In the divided multiple access, the communication time slot has wireless communication means capable of performing vehicle-to-vehicle wireless communication by a reservation method assigned in advance so as not to compete with other devices, and the wireless communication means includes the optical beacon. The vehicle-to-vehicle wireless communication by the reservation method is started according to the optical communication performed between the vehicle and the vehicle.

  According to the in-vehicle communication device having the above configuration, as described above, vehicle-to-vehicle wireless communication by the reservation method can be performed without installing a roadside wireless communication device.

  ADVANTAGE OF THE INVENTION According to this invention, even if the roadside radio | wireless communication apparatus is not installed, the radio | wireless communication between vehicles by a reservation system can be performed.

[First embodiment]
[Overall configuration of communication system]
Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing an outline of a configuration of a communication system according to a first embodiment of the present invention as an example of an intelligent road traffic system. This communication system includes an in-vehicle communication device 10 mounted on a vehicle C traveling on a road, and an optical beacon 20 that is installed on the road and performs optical communication with the in-vehicle communication device 10. .

[Configuration of in-vehicle communication device and optical beacon]
FIG. 2 is a block diagram showing the internal configuration of the in-vehicle communication device 10 and the optical beacon 20.
The in-vehicle communication device 10 includes a wireless communication unit 12 connected to the antenna 11, a light projecting / receiving unit 13 for performing optical communication with the optical beacon 20, a control unit 14 for controlling both of these communications, and a later-described unit. And a storage unit 15 for storing information unique to the vehicle ID and the like. The in-vehicle communication device 10 can perform optical communication with the optical beacon 20 by the light projecting / receiving unit 13, and between the in-vehicle communication devices 10, wireless communication (vehicle) (Inter-vehicle wireless communication) can be performed, and the information about the traffic status of the vehicle can be exchanged with each other.

In addition, the wireless communication unit 12 of the in-vehicle communication device 10 can perform wireless communication in two types of communication modes. Specifically, the wireless communication unit 12 assigns in advance so that the communication time slot does not compete with other devices in the communication mode based on the CSMA method, which is a contention method for carrier sense, and time division multiple access. It is possible to switch to a communication mode based on the TDMA system, which is a reserved system.
This communication mode is switched according to optical communication performed with the optical beacon 20. That is, when the in-vehicle communication device 10 performs optical communication with the optical beacon 20, the vehicle-mounted communication device 10 receives information indicating a communication mode to be switched from the optical beacon 20. Based on information from the optical beacon 20, the control unit 14 of the in-vehicle communication device 10 controls the wireless communication unit 12 to switch to any one of the above communication modes.
As described above, the wireless communication unit 12 and the control unit 14 constitute a wireless communication unit capable of vehicle-to-vehicle wireless communication in a communication mode based on the TDMA method.

The switching of the communication mode is also performed based on surrounding received waves received via the antenna 11. That is, the control unit 14 constantly detects and measures the intensity of the transmission wave transmitted by the TDMA method received by the wireless communication unit 12 at the current location. Is switched to a communication mode based on the TDMA system (hereinafter also referred to as a TDMA mode), and the wireless communication unit 12 is controlled so as to switch to a communication mode based on the CSMA system (hereinafter also referred to as a CSMA mode) if the intensity is less than a predetermined level. As a result, the in-vehicle communication device 10 recognizes in which communication mode the other in-vehicle communication devices 10 existing around the device are communicating at the time, and sets the communication mode in the surroundings. The communication mode of the in-vehicle communication device 10 can be matched.
That is, the in-vehicle communication device 10 detects the transmission wave from the other in-vehicle communication device 10 existing around itself, so that the in-vehicle communication device 10 that performs vehicle-to-vehicle wireless communication in the TDMA mode exists in the vicinity of itself. When this is detected, inter-vehicle wireless communication in the TDMA mode is started.

  In the measurement of the transmission wave by the above TDMA system, if the number of transmission waves from the other in-vehicle communication device 10 received by the TDMA system during the predetermined time is equal to or more than the predetermined number, the mode is switched to the TDMA mode. The wireless communication unit 12 may be controlled to switch to the CSMA mode if the number of times is less than a predetermined number. In this way, the other in-vehicle communication devices 10 that are present in the vicinity of the self grasps in which communication mode the communication is performed at that time, and the communication mode of the self is changed to a plurality of surrounding communication modes. The communication mode of the in-vehicle communication device 10 can be matched, and the accuracy can be improved.

  The communication mode is basically a mode in which the CSMA mode is a normal mode and the TDMA mode is switched under the above-described conditions. Even if the TDMA mode is switched to the above-described conditions, For example, after the start of inter-vehicle wireless communication in the TDMA mode, when the elapsed time from the start time exceeds a predetermined value (predetermined first threshold), it is configured to return to the CSMA mode.

The optical beacon 20 includes one or a plurality of beacon heads 21 installed on the road by a support frame 5 (FIG. 1) installed on the road, a projector / receiver 22 incorporated therein, and a support frame 5 in the vicinity thereof, for example. And a beacon control unit 23 that collectively controls the beacon head 21 and is capable of bidirectional communication with the in-vehicle communication device 10 by optical communication using near infrared rays. is there.
The light projecting / receiving device 22 transmits a near-infrared light signal toward the vehicle C traveling on the road, and can communicate with the vehicle-mounted communication device 10 of the vehicle C passing through the light projecting / receiving area. it can. The light emitting / receiving area is relatively narrow and spot-like. Therefore, one-to-one communication between the optical beacon 20 and the in-vehicle communication device 10 is possible.

The beacon control unit 23 includes a microcomputer having a CPU, a memory (RAM), and a storage device (ROM), and performs communication control related to optical communication performed with the in-vehicle communication device 10.
The beacon control unit 23 has a function of comprehensively managing information exchanged with the in-vehicle communication device 10. The beacon control unit 23 is exchanged between the optical beacon 20 and the in-vehicle communication device 10, which will be described later, which is necessary for the inter-vehicle wireless communication of the in-vehicle communication device 10, information for supporting safe driving, etc. Is stored and managed in the storage device, and these pieces of information are provided to the in-vehicle communication device 10 as necessary.
For example, as shown in FIG. 4, when a plurality of optical beacons 20 are arranged at a predetermined location on a road in a predetermined area including an intersection, the beacon control unit 23 of these optical beacons 20 They are connected to each other and share the above information. At this time, the connection between the optical beacons 20 may be wired or wireless, or may be a method of mutual connection via a communication device such as a router.

[About optical communication between in-vehicle communication devices and optical beacons]
Here, the outline | summary of the optical communication performed between the optical beacon 20 and the vehicle-mounted communication apparatus 10 is as follows. The light emitter / receiver 22 of the optical beacon 20 continuously transmits downlink information including lane notification information at a predetermined cycle. The in-vehicle communication device 10 receives the downlink information when it enters an optically communicable area, and transmits uplink information including the vehicle ID information of the in-vehicle communication device 10 to the optical beacon 20 accordingly. When the optical beacon 20 receives the uplink information, the optical beacon 20 is necessary for lane notification information that associates the number of the lane that received the uplink information with the vehicle ID information, information related to safe driving support, and inter-vehicle wireless communication. And the like are stored in the downlink information and transmitted to the in-vehicle communication device 10. Thereby, the in-vehicle communication device 10 can acquire information necessary for inter-vehicle wireless communication while recognizing the number of the lane in which the in-vehicle communication is running.

The vehicle ID information indicates a character string or a numerical string uniquely assigned to the in-vehicle communication device or a combination thereof. Information necessary for inter-vehicle wireless communication includes information indicating whether the communication mode of the in-vehicle communication device 10 that has performed optical communication is switched to the TDMA mode or the CSMA mode, and a time slot such as a timing and an identification number. Time slot information which is information for setting is included.
Next, inter-vehicle wireless communication between in-vehicle communication devices will be described.

[About inter-vehicle wireless communication]
The inter-vehicle wireless communication of the in-vehicle communication device 10 is performed in two communication modes, the CSMA mode and the TDMA mode, as described above. In the CSMA mode, each of a large number of in-vehicle communication devices 10 performs communication while searching for a frame transmission time by performing carrier sense.
On the other hand, in the TDMA mode, one communication frame is divided into a number of time slots divided at a predetermined timing on the time axis, and each of these time slots is reserved as a data transmission timing of the in-vehicle communication device 10. Assign.
FIG. 3A is an example of a TDMA mode communication frame configuration between the in-vehicle communication devices 10. This communication frame is composed of a predetermined number of time slots divided at predetermined timing on the time axis. One in-vehicle communication device 10 is assigned to one time slot so as not to compete with other devices. The self data is transmitted using the assigned time slot. Similarly, a different in-vehicle communication device 10 can be assigned to each of the predetermined number of time slots, and the inter-vehicle wireless communication can be performed without colliding data.

This time slot allocation management is performed by the beacon control unit 23 of the optical beacon 20. The time slot allocated to the in-vehicle communication device 10 is released when the in-vehicle communication device 10 communicates with the exit side beacon 20b, as will be described later.
Further, the optical beacon 20 stores the time at which the time slot is allocated, and releases the time slot even when a predetermined time (predetermined third threshold) has elapsed since that time. If the time slot is not released for a long time, the in-vehicle communication device 10 to which the time slot is assigned does not already exist in the vicinity, or the communication of the exit side beacon 20b cannot be performed properly and the time slot is released. It is conceivable that the information for this cannot be acquired. Therefore, by setting the optical beacon 20 so as to release the time slot when a predetermined time elapses, the assigned time slot can be made an empty time slot at an appropriate time, and the time slot can be made effective. Can be used.
The light projector / receiver 22 and the beacon control unit 23 having the time slot information and the like in the optical beacon 20 assign a time slot to the in-vehicle communication device 10 that starts inter-vehicle wireless communication in the TDMA mode. Time slot allocation means for notifying time slot information regarding the allocated time slot by optical communication is configured.

  Moreover, FIG.3 (b) is an example of the data format which the vehicle-mounted communication apparatus 10 transmits. This data format includes a header, reception quality, vehicle position, direction (traveling direction), speed, mode, and data. The header includes a preamble, the vehicle ID information, and the like. The reception quality is C / N (Carrier to Noise Ratio), RSSi (Receive Signal Strength Indication), etc. as seen from the in-vehicle communication device. The mode is information indicating whether the current mode of the in-vehicle communication device 10 is the above-described TDMA mode or CSMA mode.

FIG. 4 is a diagram showing a state in which the present system is applied to a road in an urban area where roads intersect with east, west, south, and north, for example. In the drawing, an optical beacon is arranged at a predetermined distance from the intersection K on each road extending from the central intersection K to the east, west, south, and north. This optical beacon is arranged for each lane of the road. The beacon 20a is in the lane through which the vehicle C about to enter the intersection K passes, and the exit side is in the lane through which the vehicle C leaving the intersection K passes. A beacon 20b is arranged.
Here, in the present embodiment, when the vehicle C (the in-vehicle communication device 10) performs optical communication by passing through the approaching beacon 20a, the in-vehicle communication device 10 switches the communication mode to the TDMA mode according to the optical communication. , TDMA communication is set to start. Further, when the vehicle C (the in-vehicle communication device 10) passes through the leaving beacon 20b and performs optical communication, the in-vehicle communication device 10 switches the communication mode to the CSMA mode according to the optical communication and performs communication by the TDMA method. It is set to stop.
Accordingly, the communication mode of the in-vehicle communication device 10 is switched to the CSMA mode outside the intersection K and the TDMA mode inside the intersection K with the two optical beacons 20a and 20b as a boundary.

FIG. 5 is a diagram illustrating operations of the in-vehicle communication device 10 and the optical beacon 20 according to the present embodiment. Hereinafter, with reference to FIG. 4 and FIG. 5, the inter-vehicle wireless communication between the in-vehicle communication devices 10 will be described based on the mode when the vehicle C1 in FIG. 4 enters and exits the intersection K. To do.
First, in Fig.4 (a), the vehicle C1 is moving toward the intersection K, and is going through the approach side beacon 20a. At this time, the in-vehicle communication device 10 of the vehicle C1 is in the CSMA mode (step S1 in FIG. 5), and can communicate with the other in-vehicle communication devices 10 in the CSMA mode.

Next, when the vehicle C1 travels in the direction of the arrow, the vehicle C1 passes through the approaching beacon 20a. At this time, the in-vehicle communication device 10 performs optical communication with the approaching beacon 20a (steps S2 and S3). The in-vehicle communication device 10 switches the communication mode to the TDMA mode according to this optical communication (step S4).
On the other hand, the approaching side beacon 20a determines a time slot to be assigned to the in-vehicle communication device 10, and stores the time slot information related to the assigned time slot in the downlink information together with the lane notification information and information related to safe driving support. (Step S5).
The in-vehicle communication device 10 receives the time slot information and the like from the entry side beacon 20a (step S6), and recognizes the timing at which the vehicle communication device 10 can transmit data. Then, after passing the approach side beacon 20a (FIG. 4 (b)), based on this time slot information, another vehicle set in the TDMA mode in the vicinity of the intersection K, for example, approach to the left side of the page The vehicle-to-vehicle wireless communication by the reservation method becomes possible with the vehicle C2 that has passed through the side beacon 20a and entered the intersection K (step S7).
Note that switching to the TDMA mode (step S4) of the in-vehicle communication device 10 may be executed when time slot information can be received from the optical beacon (after step 6).

Thereafter, when the vehicle C1 further travels in the intersection K and passes through the exit side beacon 20b, the in-vehicle communication device 10 performs optical communication with the exit side beacon 20b (steps S8 and S9). The in-vehicle communication device 10 switches the communication mode to the CSMA mode according to this optical communication (step S10). On the other hand, the leaving beacon 20b recognizes that the in-vehicle communication device 10 switches from the TDMA mode to the CSMA mode by the optical communication. Then, the time slot assigned to the in-vehicle communication device 10 is released, and the slot is set as an empty time slot (step S11). At this time, when the exit-side beacon 20b receives at least the vehicle ID of the in-vehicle communication device 10 from the in-vehicle communication device 10, the leaving beacon 20b releases the time slot assigned to the in-vehicle communication device 10.
In addition, each beacon control part 23 of each entrance side beacon 20a and exit side beacon 20b shares each information by being mutually connected as mentioned above, and the time in step S5 and step S11 in FIG. The slot allocation process is also performed based on shared information.

  The in-vehicle communication device 10 that has passed the exit side beacon 20b is in the CSMA mode (FIG. 4C), and can communicate with a vehicle in another CSMA mode, for example, the vehicle C3 that is about to pass the entrance side beacon 20a. Become.

As described above, in the communication system according to the present embodiment, the in-vehicle communication device 10 that moves together with the vehicle C1 communicates with the approaching beacon 20a installed on the road, so that the vehicle by the TDMA method that is the reservation method is used. Start inter-vehicle wireless communication. Therefore, vehicle-to-vehicle wireless communication in the TDMA mode can be performed without installing a roadside wireless communication device on the road side.
Furthermore, the area on the intersection K side when this approach side beacon 20a is used as a boundary can be set as an area where inter-vehicle wireless communication is performed by the TDMA method. That is, this area surrounding the intersection K by the entry side beacon 20a and the exit side beacon 20b defines a communication area A in which vehicle-to-vehicle wireless communication is performed in the TDMA mode. As a result, in this communication area A, even if vehicle traffic is concentrated, the probability of data transmission / reception in inter-vehicle wireless communication can be increased.

  In this embodiment, since the optical beacon 20 transmits the time slot information to the in-vehicle communication device 10 that starts the TDMA mode, the time slot can be dynamically allocated according to demand. it can.

  As described above, the in-vehicle communication device 10 according to the present embodiment can observe surrounding reception waves and grasp the communication mode of the in-vehicle communication device 10 located in the vicinity. For example, the in-vehicle communication device 10 enters the communication area A. In doing so, even if the optical communication with the approaching side beacon 20a is not successful and the communication mode is not switched, it can be determined whether or not it is located in the communication area A, The own communication mode can be matched with the communication mode of the other in-vehicle communication device 10 located around. Further, even when the in-vehicle communication device 10 moves outside the communication area A, the communication mode (CSMA mode) of other surrounding in-vehicle communication devices 10 can be matched in the same manner as described above.

  Furthermore, even if the switch to the TDMA mode is performed, the in-vehicle communication device 10 is configured to return to the CSMA mode when a predetermined time elapses as described above. For this reason, after the in-vehicle communication device 10 enters the communication area A, even if the communication with the leaving beacon 20b is not successful and the communication mode is not switched (from TDMA mode to CSMA mode), the final Can return to CSMA mode.

[Second Embodiment]
FIG. 6 is a diagram illustrating a state in plan view of an intersection to which the communication system according to the second embodiment of the present invention is applied. In FIG. 6, the road extending from east to west is the priority road D1, and the road extending from north to south is the non-priority road D2.
The difference between the present embodiment and the first embodiment is that the optical beacon 20 (the entry side beacon 20a and the exit side beacon 20b is provided only at one place (the right side of the page) of the priority road D1 among the four roads extending from the intersection K. ) And when the travel distance of the vehicle C from the time when the TDMA mode is started exceeds a predetermined distance (predetermined third threshold), the TDMA mode is stopped and the CSMA mode is set. The in-vehicle communication device 10 controls the communication mode.

Hereinafter, the operation of the communication system when the vehicle C1 in the drawing enters and leaves the intersection K will be described with reference to FIG.
FIG. 6A is a diagram showing the operation of the communication system when the vehicle C1 travels along the solid line L1 along the priority road D1 in the figure, and enters the intersection K through the approach side beacon 20a. Shows when to do.
First, when the vehicle C1 (the in-vehicle communication device 10) travels from the position c10 to the position c11 and passes through the entry side beacon 20a, the communication mode is set to the TDMA mode and, for example, “time slot 1” is assigned from the entry side beacon 20a. . As a result, the vehicle C1 can perform inter-vehicle wireless communication using the TDMA method with other vehicles. Next, when the vehicle C1 moves to the position c12, the in-vehicle communication device 10 determines to stop the TDMA mode. That is, as described above, the in-vehicle communication device 10 controls the communication mode so that the CSMA mode is set when the traveling distance of the vehicle C from the time when the TDMA mode is started exceeds a predetermined distance. This predetermined distance is set, for example, to a distance when traveling to the edge of the communication area A shown in the figure. Accordingly, the vehicle that has passed through the approaching side beacon 20a performs inter-vehicle wireless communication in the TDMA mode in the range of the communication area A. In this way, the inter-vehicle wireless communication in the TDMA mode is started in response to the communication with the approaching beacon 20a, and the communication area A is made to stop by stopping the TDMA mode in accordance with the travel distance of the vehicle from the start time. Can be defined.
Further, the in-vehicle communication device 10 always performs communication in the TDMA mode within a predetermined time from the time when the time slot is assigned from the ingress beacon 20a. The in-vehicle communication device 10 may grasp in which communication mode the communication is performed at that time. By doing so, the precision which defines the communication area A can be improved.

When the in-vehicle communication device 10 determines to stop the TDMA mode, the in-vehicle communication device 10 determines that the time slot to which the in-vehicle communication device 10 is assigned to the other in-vehicle communication device 10 or the leaving beacon 20b is an empty time slot. Generate and transmit time slot release information to notify This time slot release information includes information indicating a time slot to be released and a time to release (or a time at which release information is generated). In FIG. 6A, the time slot release information of the vehicle C1 includes information such as “time slot 1” as the time slot to be released and “15:00:00” as the release time.
In FIG. 6A, the in-vehicle communication device 10 of the vehicle C1 located at the position c12 transmits time slot release information to the vehicle C4 located in the vicinity thereof.

Thereafter, the vehicle C1 leaves the communication area A and sets the communication mode to the CSMA mode.
On the other hand, when the vehicle C4 that has received the time slot release information of the vehicle C1 goes straight in the right direction on the paper and passes through the exit side beacon 20b, the vehicle C4 transmits the time slot release information of the vehicle C1 to the exit side beacon 20b. . As a result, “time slot 1” assigned to the vehicle C1 is released, and the optical beacon 20 sets this “time slot 1” as an empty time slot.
The vehicle C4 can also transmit time slot release information of the vehicle C1 to another vehicle, for example, the vehicle C5. Therefore, even when the vehicle C4 turns without going straight through the intersection K and does not pass the exit side beacon 20b, the vehicle C5 that receives the time slot release information of the vehicle C1 from the vehicle C4 receives the exit side beacon 20b. If it passes, “Time Slot 1” is released.

As described above, the wireless communication unit 12 and the control unit 14 of the in-vehicle communication device 10 have a function of transmitting time slot release information to other in-vehicle communication devices 10 when stopping the inter-vehicle wireless communication in the TDMA mode. is doing. Furthermore, the in-vehicle communication device 10 has a function of transmitting the time slot release information received from the other in-vehicle communication device 10 to the other in-vehicle communication device 10 by inter-vehicle wireless communication.
Thereby, the time slot release information can be relayed and shared by a plurality of in-vehicle communication devices 10.

In addition, the time slot release information includes information related to the number of times the information is relayed by inter-vehicle communication, and if the number of times of relaying is a predetermined number or more, the time slot release information may be discarded. Good. When the time slot release information received from the other in-vehicle communication device 10 is communicated to the other in-vehicle communication device 10 by inter-vehicle wireless communication, and this is repeated, any of the in-vehicle communication devices 10 traveling in the communication area A It is assumed that it is sent and received permanently. By providing the number of relays in the time slot release information, it is possible to prevent such permanent information from remaining.
Further, the elapsed time from the release time in the time slot release information may be calculated, and if the elapsed time is equal to or longer than a predetermined time, the time slot release information may be discarded. Even in this case, the same effect can be obtained.

Further, the wireless communication unit 12 and the control unit 14 of the in-vehicle communication device 10 transmit the time slot release information received from the other in-vehicle communication device 10 to the exit side beacon 20b, and the exit side beacon 20b receives the time slot release information. When the time slot is received, the time slot corresponding to the time slot release information is set as an empty time slot.
Thereby, in this embodiment, the time slot release information transmitted by the in-vehicle communication device 10 that stops the TDMA mode without communicating with the exit-side beacon 20b is sent to the exit-side beacon 20b via the other in-vehicle communication device 10. Can be sent.
As a result, the leaving beacon 20b can release the assigned time slot without directly communicating with the in-vehicle communication device 10 that stops the TDMA mode, and can make the time slot an empty time slot.

  The time slot release information includes information on the time at which the time slot is released. Therefore, even if the time slot release information is duplicated and transmitted to the egress beacon 20b, it can be determined that the time slot is duplicated. A beacon can be prevented from accidentally releasing a time slot.

FIG. 6B is a diagram showing a mode when the vehicle C1 travels along the solid line L2 along the priority road D1 in the drawing, and enters the intersection K without passing through the entry side beacon 20a. Is shown.
In this case, the in-vehicle communication device 10 of the vehicle C1 determines whether or not it has entered the communication area A by the above-described function of detecting the communication mode of the surrounding vehicle. That is, the transmission wave of the surrounding vehicle, for example, the vehicle C6 in the figure is in the TDMA mode, and the presence or absence of the vehicle communicating in the TDMA mode in the vicinity of itself depending on the transmission intensity of the radio wave transmitted from the vehicle C6. Judging. When it is determined that the vehicle in the TDMA mode is located in the vicinity, it is determined that the vehicle has entered the communication area A, and communication in the TDMA mode is started.

  FIG. 7 is an example of a communication frame configuration in the inter-vehicle wireless communication in the TDMA mode in the present embodiment. The communication frame of this embodiment has a time slot used for the TDMA mode as a reservation method and a time slot used for vehicle-to-vehicle wireless communication using the contention method in one frame. In the present embodiment, when a time slot is assigned to the in-vehicle communication device 10 that has passed the optical beacon, the reservation method slot in the figure is used, and the communication area A is entered without passing the optical beacon, and in the TDMA mode. The in-vehicle communication device 10 that attempts to communicate uses a contention time slot.

This contention time slot is reserved for contention communication in a frame conforming to the TDMA method, and as shown in FIG. 6B, the communication area A does not communicate with an optical beacon. The vehicle-mounted communication device 10 that has entered the vehicle is configured to perform inter-vehicle wireless communication in the TDMA mode using this time slot.
With this configuration, the time slots of the in-vehicle communication device 10 to which the time slot is assigned by the entry side beacon 20a and the in-vehicle communication device 10 that has entered the communication area A without communicating with the optical beacon overlap. Can be avoided, and collision of transmission data can be prevented.
Further, the ratio of the time slot used in the TDMA mode that is a reservation method and the time slot used in the inter-vehicle wireless communication by the contention method may be made variable according to the system.
In that case, if information related to this ratio is included in the information transmitted from the optical beacon, more flexible communication can be realized.

  Further, in the case of the in-vehicle communication device 10 of the vehicle C1 shown in FIG. 6B that has entered the communication area A without communicating with the optical beacon, the time slot for the contention method is used. It is not always necessary to transmit time slot release information or the like to another in-vehicle communication device 10 or an optical beacon. However, when the time slot release information of another vehicle is received in the communication area A, the information is transmitted to the other vehicle and transmitted to the leaving beacon 20b.

As described above, in the communication system of the present embodiment, the optical beacon 20 is arranged on one of the four roads extending from the intersection K, so that the roadside wireless communication device is not particularly installed on the road side. The communication area A in which the inter-vehicle wireless communication around K is set to the TDMA mode can be configured, and the probability of data transmission / reception can be increased.
Moreover, the system of this embodiment is applied to the intersection where the priority road D1 with a relatively large vehicle traffic volume intersects with the priority road D2 with a small vehicle traffic volume compared to the road as in the above-described present embodiment. In this case, if an optical beacon is installed on the priority road D1, the communication area A can be configured without installing an optical beacon on the non-priority road D2.
As a result, reliable inter-vehicle wireless communication can be realized on the priority road D1 where the amount of traffic of the vehicle is large, and more effective operation such as preventing an encounter collision with a vehicle coming out from the non-priority road D2 can be realized. It can be performed.

In addition, as described above, this communication system only needs to have at least one optical beacon. Therefore, for example, it is particularly effective when applied to an intersection where infrastructure such as a suburban roadside wireless communication device is not established. It is.
In the above embodiment, the optical beacon 20 (the entry side beacon 20a and the exit side beacon 20b) is arranged only at one place on the priority road side among the four roads with respect to the intersection K. In this case, the function as the TDMA mode can be used more effectively, and the probability of data transmission / reception can be further increased.

Moreover, in the said embodiment, although the vehicle-mounted communication apparatus 10 was comprised so that the vehicle-to-vehicle wireless communication by a TDMA system might be performed based on communication with the optical beacon installed in the road side, when it sees from another viewpoint, for example, The following configuration can also be adopted.
That is, a communication system having an in-vehicle communication device mounted on a vehicle traveling on a road and a communication device installed on the road and communicating with the in-vehicle communication device, wherein the in-vehicle communication device is Radio that enables vehicle-to-vehicle wireless communication using a reservation method that is assigned in advance so that communication time slots do not compete with other devices in time-division multiple access with in-vehicle communication devices installed in other vehicles The wireless communication means starts communication between vehicles according to the reservation method according to communication performed with the communication device, and further, the vehicle-to-vehicle communication according to the reservation method. When the wireless communication is stopped, the time slot release information for notifying that the time slot assigned to the in-vehicle communication device becomes an empty time slot is indicated by the inter-vehicle wireless communication. Therefore, it is intended to be sent to another vehicle-mounted communication device can be characterized.

The present invention is not limited to the above embodiments. For example, in each of the above embodiments, after the in-vehicle communication device 10 starts the inter-vehicle wireless communication in the TDMA mode in response to the communication with the optical beacon, the elapsed time from the start time or the travel distance of the vehicle from the start time The vehicle-to-vehicle wireless communication in the TDMA mode is configured to be stopped. For example, the position where the TDMA mode can be stopped may be specified by acquiring information on the position of the in-vehicle communication device 10 using GPS or the like. it can.
In each of the above embodiments, the case where the present invention is applied to an intersection where a traffic signal as shown in FIG. 1 is installed is exemplified, but the present invention can also be applied to an intersection where there is no signal.

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

It is a figure which shows the outline of a structure of the communication system by 1st embodiment of this invention. It is a block diagram which shows the internal structure of a vehicle-mounted communication apparatus and an optical beacon. (A) is an example of a TDMA mode communication frame configuration between the in-vehicle communication devices 10, and (b) is an example of a data format transmitted by the in-vehicle communication device 10. It is a figure which shows the state which applied this system to the road of the urban area where the road crossed east, west, south, and north, (a)-(c) has shown progress of the vehicle over time. It is a figure which shows operation | movement of a vehicle-mounted communication apparatus and an optical beacon. It is a figure which shows the state which planarly viewed the intersection which applied the communication system by 2nd embodiment of this invention, (a) is operation | movement of a communication system when a vehicle drive | works along the solid line L1 in the figure. (B) is a figure which shows a mode when a vehicle drive | works along the solid line L2 in the figure. It is an example of the communication frame structure in the TDMA mode vehicle-to-vehicle wireless communication in this embodiment.

Explanation of symbols

10 on-vehicle communication device 12 wireless communication unit (wireless communication means)
14 Control unit (wireless communication means)
20 optical beacon 20a entry side beacon 20b exit side beacon (stop optical beacon)
22 Projector / Receiver (Time slot allocation means)
23 Beacon control unit (time slot allocation means)
4e Exit light beacon C Vehicle

Claims (13)

An in-vehicle communication device mounted on a vehicle traveling on a road;
A communication system including an optical beacon installed on the road and performing optical communication with the in-vehicle communication device,
The in-vehicle communication device is a vehicle-to-vehicle radio based on a reservation method that is assigned in advance so that a communication time slot does not compete with other devices among time-division multiple access with an in-vehicle communication device mounted on another vehicle. It has wireless communication means capable of communication, and this wireless communication means starts vehicle-to-vehicle wireless communication by a reservation method in response to optical communication performed with the optical beacon. A communication system. The communication system according to claim 1, wherein the wireless communication unit stops vehicle-to-vehicle wireless communication based on the reservation method when at least one of the following applies.
(1) When the elapsed time from the start time exceeds a predetermined first threshold (2) When the travel distance from the start time exceeds a predetermined second threshold   The communication according to claim 1, further comprising: a stop optical beacon that stops the inter-vehicle wireless communication by the reservation method performed by the wireless communication unit when performing optical communication with the in-vehicle communication device. system.   By detecting the transmission signal from the in-vehicle communication device mounted on another vehicle, the wireless communication means detects that the in-vehicle communication device that performs inter-vehicle wireless communication by the reservation method exists around itself, The communication system as described in any one of Claims 1-3 which starts the vehicle-to-vehicle wireless communication by a reservation system. The optical beacon assigns a time slot for vehicle-to-vehicle wireless communication according to the reservation method to an in-vehicle communication device that starts vehicle-to-vehicle wireless communication according to the reservation method according to the optical communication, and relates to the assigned time slot Time slot allocation means for notifying time slot information through the optical communication,
The communication system according to any one of claims 1 to 4, wherein the wireless communication means of the in-vehicle communication device performs inter-vehicle wireless communication by a reservation method based on the time slot information. The time slot allocating means includes
When the elapsed time from the time when the optical beacon performs optical communication with the in-vehicle communication device to which the time slot is allocated exceeds the predetermined third threshold, the allocated time slot is defined as an empty time slot. The communication system according to claim 5. The wireless communication means includes
When stopping the vehicle-to-vehicle wireless communication according to the reservation method, the time slot release information for notifying that the time slot assigned to the vehicle-mounted communication device becomes an empty time slot is transmitted to the other vehicle-mounted communication device through the vehicle-to-vehicle wireless communication. The communication system according to any one of claims 1 to 6, wherein the communication system is transmitted to. The wireless communication means includes
The communication system according to claim 7, wherein the time slot release information received from another in-vehicle communication device is transmitted to the other in-vehicle communication device by inter-vehicle wireless communication. The wireless communication means includes
Send the time slot release information received from other in-vehicle communication devices to the stop optical beacon,
The time slot allocating means includes
The communication according to claim 7 or 8, wherein when the stop optical beacon receives time slot release information transmitted by the other in-vehicle communication device, the time slot corresponding to the time slot release information is set as an empty time slot. system. The wireless communication means includes
When the inter-vehicle wireless communication by the reservation method is stopped, it is based on the contention method that the communication time slot may compete with other devices with the in-vehicle communication device mounted on the other vehicle. The communication system according to any one of claims 1 to 9, which performs inter-vehicle wireless communication.   The communication system according to claim 10, wherein the contention method is a CSMA method.   An optical beacon used in the communication system according to any one of claims 1 to 11. An in-vehicle communication device that performs optical communication with an optical beacon installed on the road,
Wireless communication that enables vehicle-to-vehicle wireless communication based on a reservation method that is assigned in advance so that communication time slots do not compete with other devices in time-division multiple access with in-vehicle communication devices installed in other vehicles Has means,
The wireless communication means starts vehicle-to-vehicle wireless communication according to a reservation method in response to optical communication performed with the optical beacon.

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