JP2007281867A - Wireless communication method, roadside machine, and vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology to appropriately switch over between road-to-vehicle communications and vehicle-to-vehicle communications. <P>SOLUTION: The wireless communication system performs road-to-vehicle communication and vehicle-to-vehicle communication by time division by periodically switching over between a road-to-vehicle communication mode and a vehicle-to-vehicle communication mode. In this system, a roadside machine transmits an existence notification for notifying the vehicle of the existence of the roadside machine at time intervals of the time assigned to road-to-vehicle communication or less. The vehicle knows that it is going into a communication range of the roadside machine by receiving the existence notification from the roadside machine, and continues the road-to-vehicle communication mode until it receives a synchronization signal from the roadside machine. Thus, the vehicle can immediately knows that it is going into the communication range of the roadside machine. Moreover, synchronization control between the road and the vehicle can be surely performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless communication method in a wireless communication system that performs road-to-vehicle communication and vehicle-to-vehicle communication by time division.

  Conventionally, a wireless communication system using a wireless communication device (on-vehicle terminal) mounted on a vehicle is known. Such a wireless communication system includes two types of communication: road-to-vehicle communication for communication between a base station (roadside machine) provided on the roadside and a vehicle (on-vehicle terminal), and vehicle-to-vehicle communication for communication between vehicles. There is a form.

  When the vehicle performs both road-to-vehicle communication and vehicle-to-vehicle communication, and there is only one wireless device mounted on the vehicle, it is necessary to avoid collision of these communications. Specifically, it is conceivable that road-to-vehicle communication and vehicle-to-vehicle communication are separated in time and performed at different timings.

When multiple access is realized by time division in this way, it is necessary to perform time synchronization between the roadside machine and the vehicle. In road-to-vehicle communication, it is common to perform synchronous control with a roadside machine as a reference. That is, the roadside device periodically transmits a synchronization signal to the vehicle, and the vehicle that has received the synchronization signal synchronizes its own clock with the roadside device according to the synchronization signal. By such a method, time synchronization can be performed between the roadside machine and the vehicle, and both road-to-vehicle communication and vehicle-to-vehicle communication can be performed by time division.
JP-A-8-98253

  However, in the case of the prior art as described above, the following problems have occurred. That is, road-to-vehicle communication is premised on the presence of roadside machines, but roadside machines are not installed at all locations on the road. In a place where there is no roadside machine, road-to-vehicle communication cannot be performed, and only vehicle-to-vehicle communication is performed.

  Even when only vehicle-to-vehicle communication is performed, communication between vehicles is performed only at the time slot assigned to vehicle-to-vehicle communication so that road-to-vehicle communication can be performed when the vehicle enters the installation range of the roadside unit. Thus, in order to maintain time-division multiple access even in places where there are no roadside units, synchronous control between vehicles is required. This synchronization control is performed when another vehicle synchronizes its own clock with the reference vehicle with a certain vehicle (reference vehicle) as a reference.

  In such a case, the vehicle cannot perform time synchronization with the roadside device, and there is a possibility that a time difference occurs between the road vehicles. A situation in which the vehicle has entered the communicable area of the roadside machine in a state where the time is shifted between the road vehicles will be described with reference to FIG. FIG. 5 is a communication timing chart when the clock timing is shifted between the roadside machine and the vehicle. As shown in the figure, the roadside device transmits information to the vehicle for a certain period of time at a predetermined cycle. When the roadside device transmits information to the vehicle, a reference signal (synchronization signal) is transmitted first.

On the other hand, the vehicle performs communication while periodically switching between a road-vehicle communication mode in which a signal from a roadside device is received and a vehicle-to-vehicle communication mode in which communication is performed between vehicles. The vehicle does not transmit information in the road-to-vehicle communication mode, and therefore can receive information from the roadside machine. However, in the inter-vehicle communication mode, since information can be transmitted, there is a case where information from the roadside device cannot be received. As shown in the figure, when the clock timing is shifted between the vehicle and the roadside machine, it may be impossible to receive the reference signal transmitted from the roadside machine. When the vehicle cannot receive the reference signal, the vehicle cannot detect transmission from the roadside device, and there is a problem that information from the roadside device cannot be received.

Although a method based on a GPS (Global Positioning System) satellite signal is also conceivable as a method of time synchronization, in this case, all vehicles need to be equipped with a GPS satellite signal receiver. Also, it must be possible to receive GPS satellite signals at all locations. Therefore, it is desirable to perform time synchronization without relying on GPS satellite signals.

  The present invention has been made in view of the above circumstances, and an object thereof is to appropriately perform road-to-vehicle communication and vehicle-to-vehicle communication in a wireless communication system that performs road-to-vehicle communication and vehicle-to-vehicle communication in a time-sharing manner. It is to provide a technology for switching.

  In order to achieve the above object, the present invention realizes compatibility between road-to-vehicle communication and vehicle-to-vehicle communication by the following means or processing.

  The wireless communication method according to the present invention is a wireless communication method in a wireless communication system in which a road-to-vehicle communication mode and a vehicle-to-vehicle communication mode are periodically switched, and wireless communication is performed in a time-sharing manner between roads and vehicles. In the road-to-vehicle communication mode, information is transmitted from the roadside device to the vehicle, and information is not transmitted from the vehicle. In the inter-vehicle communication mode, information is transmitted between vehicles. The roadside machine and the vehicle synchronize with each other, switch the timing for performing road-to-vehicle communication and vehicle-to-vehicle communication, and realize both communication.

  The roadside device in the present invention transmits a presence notification for notifying the vehicle of the presence of the roadside device to the vehicle at a predetermined interval. The information included in the presence notification may be only information indicating that a roadside device exists, and includes information such as a communicable range of the roadside device and a range (service provision range) in which information transmitted from the roadside device should be used. It may be. By receiving this presence notification, the vehicle can detect that its own vehicle enters the communicable range of the roadside machine.

  The roadside device in the present invention transmits this presence notification at intervals equal to or less than the time allocated for road-to-vehicle communication. The presence notification is not necessarily transmitted periodically, and may be transmitted at any timing as long as the maximum interval is equal to or less than the time allocated for road-vehicle communication. By transmitting the presence notification in this manner, the roadside machine can receive the presence notification at least once when the vehicle is in the road-vehicle communication mode.

  Further, the roadside device transmits a synchronization signal for synchronizing with the vehicle at a predetermined cycle. The roadside machine preferably adds this synchronization signal before data to be transmitted to the vehicle. With this synchronization signal, the vehicle can detect the start timing of road-to-vehicle communication and can synchronize with the roadside machine.

  The vehicle in the present invention determines entry into the communication range of the roadside device by receiving the presence notification from the roadside device. When it is determined that the vehicle has entered the communication range of the roadside machine, the vehicle continues in the road-vehicle communication mode until a synchronization signal is received from the roadside machine. That is, until the synchronization signal is received after entering the communication range of the roadside unit, the road-to-vehicle communication and the vehicle-to-vehicle communication are not switched by time division, and the state where the information from the roadside unit can be received is maintained. And a vehicle performs synchronous control between roadside machines based on the synchronous signal received from the roadside machine.

In this way, since the presence notification transmitted from the roadside device is transmitted at a cycle equal to or shorter than the time allotted to road-to-vehicle communication, the vehicle immediately sends this presence notification after entering the communicable range of the roadside device. Can be received. In addition, since the vehicle that has received the presence notification continues the road-to-vehicle communication mode until it receives the synchronization signal from the roadside unit, it is possible to reliably synchronize between the vehicle and the roadside unit. And switching of inter-vehicle communication is performed appropriately.

  In addition, this invention can be grasped | ascertained as a roadside machine or vehicle which has at least one part of the said means. The present invention can also be understood as a program for realizing at least a part of the above processing. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention.

  For example, a roadside machine as one aspect of the present invention periodically switches between a road-vehicle communication mode for transmitting information from a roadside machine to a vehicle and an inter-vehicle communication mode for transmitting information between vehicles, A roadside unit in a wireless communication system that performs time-division communication between road vehicles and between vehicles, and a presence notification for notifying the vehicle of the presence of the road side device is transmitted at intervals equal to or less than the time allocated for road-to-vehicle communication It has a notification transmission means and a synchronization signal transmission means for transmitting a synchronization signal for synchronization control in a predetermined cycle.

  The vehicle according to one aspect of the present invention periodically switches between a road-to-vehicle communication mode in which information is transmitted from the roadside machine to the vehicle and a vehicle-to-vehicle communication mode in which information is transmitted between the vehicles. A vehicle in a wireless communication system that performs time-division communication between vehicles and between vehicles, and based on the presence notification that notifies the presence of the roadside device transmitted from the roadside device, entering the communication range of the roadside device A roadside machine area entry detecting means for detecting the roadside vehicle, and a control means for continuing the road-to-vehicle communication mode until receiving a synchronization signal transmitted from the roadside machine when entering the communicable range of the roadside machine, It is characterized by having.

  ADVANTAGE OF THE INVENTION According to this invention, in the radio | wireless communications system which performs road-to-vehicle communication and vehicle-to-vehicle communication by time division, it becomes possible to switch road-to-vehicle communication and vehicle-to-vehicle communication appropriately.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

<System overview>
FIG. 1 is a diagram illustrating a system overview of a wireless communication system according to the present embodiment. The roadside device 1 notifies the vehicle 2 entering the intersection that there is an oncoming vehicle. The vehicle 2 notified of the presence of the right turn vehicle by road-to-vehicle communication can issue a warning to the driver. Note that the information transmitted by the roadside machine is not limited to information related to the oncoming vehicle at the intersection, but may be information related to traffic jams or information related to obstacles (such as falling rocks and accident vehicles) on roads with poor visibility.

  The communicable range of radio waves transmitted from the roadside device 1 is shown as a communicable area 4 in the figure. The vehicle 2 uses information transmitted from the roadside device 1 when the vehicle is located in the service providing area 3 that is a part of the communicable area 4. This is because at a point far from the intersection, there is little advantage of using information related to the oncoming vehicle transmitted from the roadside machine 1. The roadside machine 1 periodically transmits an area notification signal for notifying the presence of the roadside machine, and a vehicle that has entered the communicable area 4 detects the presence of the roadside machine 1 by receiving this area notification signal. Is possible.

In the present embodiment, the service providing area 3 is part of the communicable area 4, but the service providing area 3 and the communicable area 4 may be the same range. Further, the area notification signal for notifying the presence of the roadside device 1 is transmitted not only by the roadside device 1 itself but also by a communication device (base beacon) different from the roadside device 1 provided in front of the service providing area 3. May be. In this case, synchronization control is required between the roadside device 1 and the base point beacon. However, since the roadside device 1 and the base point beacon can be configured to always communicate with each other by wire or wirelessly, the synchronization control is easy.

  Further, the vehicle 2 not only receives information from the roadside machine as described above, but also performs communication between the vehicles. In the inter-vehicle communication, for example, a subsequent brake is notified to the following vehicle, or information for cooperative traveling is notified.

  The vehicle and roadside machine in this wireless communication system have a hardware configuration such as a CPU (Central Processing Unit), a main memory (RAM), an auxiliary memory (ROM), a communication interface, etc. connected via a bus. Configured to provide. Each processing described below is realized by the CPU executing various programs stored in the auxiliary storage device. Note that some or all of the processing performed by the vehicle and the roadside machine may be executed by a dedicated chip.

The vehicle in this wireless communication system uses the same wireless device for both road-to-vehicle communication and vehicle-to-vehicle communication. The wireless communication system used in this wireless communication system is 5.8 GHz band DSRC (Dedicated Short Range Communication) for both road-to-vehicle communication and vehicle-to-vehicle communication. However, IEEE802.11 wireless LAN,
Any other wireless communication method such as IEEE 802.16, IEEE 802.20, or Bluetooth (registered trademark) may be used.

<Time division multiple access>
As described above, road-to-vehicle communication and vehicle-to-vehicle communication are compatible with each other by time division multiple access (TDMA). FIG. 2 is a diagram illustrating a communication sequence performed while switching between road-to-vehicle communication and vehicle-to-vehicle communication. As shown in the figure, the timing for performing road-to-vehicle communication and the timing for performing vehicle-to-vehicle communication are periodically switched to achieve both road-to-vehicle communication and vehicle-to-vehicle communication.

  At the time of road-to-vehicle communication, the roadside device transmits information, and the vehicle receives the information. Therefore, the vehicle does not transmit information during road-to-vehicle communication. On the other hand, during vehicle-to-vehicle communication, the vehicle can transmit information. At this time, a vehicle that transmits information performs communication according to a CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) method.

  In this embodiment, both communication is implement | achieved by time-sharing the communication period of road-to-vehicle communication and vehicle-to-vehicle communication in this way. In addition, road-to-vehicle communication cannot be performed outside the roadside machine communicable area 4, but only vehicle-to-vehicle communication can be performed. However, when entering the roadside machine communicable area 4, the road-to-vehicle communication can be performed immediately as described above. Communication is performed while always assigning a communication period for road-to-vehicle communication.

<Treatment of roadside machine>
Next, the processing of the roadside machine will be described based on FIG. In the period _TRV allocated for road-to-vehicle communication, the roadside machine transmits an area notification signal 10 for notifying the service providing area 3 of the base station, a reference signal 11 (reference burst) for performing synchronization control between road vehicles, and a vehicle. The information 12 to be transmitted is transmitted in order. The reference signal 11 stores an identification code that notifies the start of road-to-vehicle communication, and the vehicle that has received the reference signal 11 can synchronize with the roadside machine. That is, the reference signal 11 corresponds to the synchronization signal in the present invention.

The roadside device periodically transmits the area notification signal 10 and the cycle thereof is set to be equal to or shorter than the period _TRV allocated for road-to-vehicle communication. Figure has a T _RV the transmission period of 2 the area information signal 10 in principle, and so that also transmit the area information signal 10 at the beginning of the timing allocated to the road-vehicle communication.

<Vehicle processing>
In the period _TRV assigned to road-to-vehicle communication, the vehicle shifts to the reception mode so that the information 12 from the roadside device can be received. Further, in the period _{T IV} assigned to the inter-vehicle communication, and transmits the information in accordance with CSMA / CA scheme.

Since the transmission cycle of the area notification signal 10 transmitted from the roadside machine is equal to or less than the time _TRV assigned to road-to-vehicle communication, the vehicle receives the area notification signal 10 at least once during the reception mode. be able to. That is, the vehicle can reliably detect the presence of the roadside machine.

  A specific process of the vehicle when receiving the area notification signal 10 will be described with reference to FIG. Based on the area notification signal 10, the vehicle determines whether or not the vehicle has entered the service providing area 3 of the roadside machine (S01). The vehicle may determine that the area notification signal 10 is received as entering the service providing area 3. Further, when the communicable area 4 and the service providing area 3 of the roadside machine are different, the relative position between the own vehicle and the service providing area 3 is acquired based on the area notification signal 10, and the service is determined based on the travel distance of the own vehicle. You may grasp | ascertain the approach timing to the provision area 3. FIG.

  If it has not entered the service providing area 3 (S01-NO), the process is terminated. Even when the area notification signal 10 is received again when already located in the service providing area 3, the process ends without being determined to enter the service providing area 3.

  When the vehicle enters the service providing area 3 (S01-YES), the vehicle continues the road-to-vehicle communication mode in order to receive information from the roadside machine. That is, the switching between the road-vehicle communication mode and the vehicle-vehicle communication mode according to the clock in the vehicle is temporarily stopped.

  Since the vehicle continues in the road-to-vehicle communication mode, the vehicle can receive the reference signal 11 next time the roadside device transmits the reference signal 11 (S03). By this reference signal 11, the vehicle performs synchronous control with the roadside machine (S04).

Thus, after receiving the area notification signal 10 transmitted at a period equal to or less than the time _TRV assigned to road-to-vehicle communication, the road-to-vehicle communication mode is continued, so the reference signal 11 from the roadside device is reliably received. be able to.

<Operation example>
An example of the operation when the vehicle enters the communicable area 4 of the roadside machine in a situation where the vehicle and the roadside machine are not synchronized will be described with reference to FIG. Since the road-to-vehicle is not synchronized, at time A, the roadside machine transmits information for road-to-vehicle communication, but the vehicle is in the vehicle-to-vehicle communication mode. Therefore, the vehicle cannot receive the area notification signal 10 and the reference signal 11 from the roadside machine.

Thereafter, the vehicle shifts to the road-to-vehicle communication mode according to the clock in the host vehicle, and can receive information from the roadside machine (period R1). Since the roadside device transmits the area notification signal 10 at a period equal to or less than the period allocated for road-to-vehicle communication, the vehicle can receive the area notification signal 10 from the roadside device during this period R1. In the figure, the vehicle receives the area notification signal 10 at time B.

  A vehicle that has received the area notification signal 10 can detect that its own vehicle has entered the service providing area 3 of the roadside machine. Therefore, this vehicle forcibly continues the road-vehicle communication mode without following the timing switching based on the clock timing of the own vehicle (period R2). Thus, since the vehicle continues in the road-to-vehicle communication mode, it is possible to receive the reference signal 11 at the time point C and to synchronize with the roadside machine.

<Effect of embodiment>
As described above, in the present embodiment, even when the time synchronization between the roadside machine and the vehicle is shifted, the entry of the roadside machine into the service providing area 3 is immediately detected, and the time between the roadside car is detected. Appropriate communication can be performed by synchronizing.

It is a figure which shows the system outline | summary of the radio | wireless communications system which concerns on this embodiment. It is a figure which shows the sequence of the communication process in this embodiment. It is a flowchart which shows the flow of the process at the time of area notification signal reception of the vehicle in this embodiment. It is a figure which shows the sequence of the communication process in this embodiment. It is a figure which shows the sequence of the communication process in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Roadside machine 2 Vehicle 3 Service provision area 4 Communication possible area 10 Area notification signal 11 Reference signal 12 Road-to-vehicle communication timing 13 Vehicle-to-vehicle communication timing

Claims (3)

Radio that performs road-to-vehicle and vehicle-to-vehicle communication in a time-sharing manner by periodically switching between the road-to-vehicle communication mode for transmitting information from the roadside machine to the vehicle and the vehicle-to-vehicle communication mode for transmitting information between vehicles. A wireless communication method in a communication system, comprising:
The roadside machine
A presence notification for notifying the vehicle of the presence of the roadside device is transmitted at intervals equal to or less than the time allotted for road-to-vehicle communication,
A synchronization signal for synchronization control is transmitted at a predetermined cycle,
Vehicle
By receiving the presence notification from the roadside machine, determine the approach to the communication range of the roadside machine,
When entering the communication range of the roadside machine, continue the road-vehicle communication mode until the synchronization signal is received,
A wireless communication method, wherein synchronization control is performed based on the received synchronization signal. Radio that performs road-to-vehicle and vehicle-to-vehicle communication in a time-sharing manner by periodically switching between the road-to-vehicle communication mode for transmitting information from the roadside machine to the vehicle and the vehicle-to-vehicle communication mode for transmitting information between vehicles. A roadside device in a communication system,
Presence notification transmitting means for transmitting the presence notification for notifying the vehicle of the presence of the roadside device at intervals equal to or less than the time allotted to road-to-vehicle communication;
Synchronization signal transmitting means for transmitting a synchronization signal for synchronization control in a predetermined cycle;
A roadside machine characterized by comprising: Radio that performs road-to-vehicle and vehicle-to-vehicle communication in a time-sharing manner by periodically switching between the road-to-vehicle communication mode for transmitting information from the roadside machine to the vehicle and the vehicle-to-vehicle communication mode for transmitting information between vehicles. A vehicle in a communication system,
Roadside machine area entry detection means for detecting entry into the communication range of the roadside machine based on the presence notification that notifies the existence of the roadside machine transmitted from the roadside machine;
Control means for continuing the road-to-vehicle communication mode until receiving a synchronization signal transmitted from the roadside machine when entering the communicable range of the roadside machine,
Synchronization means for performing synchronization control based on the received synchronization signal;
The vehicle characterized by having.

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