JP5012443B2 - COMMUNICATION SYSTEM, RADIO COMMUNICATION METHOD, AND COMMUNICATION DEVICE - Google Patents

Description

  The present invention relates to a communication system, a wireless communication method, and a communication apparatus that realize an intelligent transport system (ITS).

  The Intelligent Transport System is a system built for the purpose of safe driving support and improved transportation efficiency. It runs on multiple roadside communication devices, roadside sensors, and other infrastructure installed separately along the road. It is comprised from the vehicle-mounted communication apparatus mounted in each of the some vehicle to perform (for example, patent documents 1, 2).

The roadside communication device provides safe driving support information to the vehicle in real time by performing wireless communication using a time-division multiple access method with an in-vehicle communication device mounted on the vehicle (hereinafter referred to as road-to-vehicle communication). Safe driving support information includes, for example, information for preventing a driver's recognition error, information for assisting blind spots, obstacles on the road detected by road sensors, travel positions and speeds of surrounding vehicles collected from in-vehicle communication devices Etc. The in-vehicle communication device that has received the information supports safe driving by giving a warning to the driver when it is determined that there is a danger from the vehicle position, the inter-vehicle distance, the traveling speed, and the like. Information such as the speed of the vehicle, the traveling position, and the traveling direction is transmitted / received between the in-vehicle communication devices (hereinafter referred to as “between vehicles”), and safe driving is supported using the transmitted / received information.
The roadside communication device transmits / receives information for realizing smooth traffic between the roadside communication devices (hereinafter referred to as “roadside communication”), for example, information related to the control result of the signal lamp device. The lamp color switching control is performed.

In the time division multiple access method, a certain communication time (frame) in the same frequency band is time-divided into a plurality of time slots. This method is used alternately, and enables simultaneous communication using the band effectively (see FIG. 5).
Japanese Patent No. 3463102 JP 2000-124852 A

  However, in a conventional communication system that employs a time division multiple access method sharing the same frequency band, when the traffic volume of the vehicle increases, there are not enough time slots for road-to-vehicle or vehicle-to-vehicle communication, and a full and safe driving There is a risk that assistance cannot be provided.

  The present invention has been made in view of such circumstances, and provides a communication system, a wireless communication method, and a communication apparatus that can solve a shortage of time slots for road-to-vehicle or vehicle-to-vehicle communication and perform stable wireless communication. The purpose is to do.

  A communication system according to a first aspect of the present invention includes a plurality of roadside communication devices installed along a road, and an in-vehicle communication device mounted on each of a plurality of vehicles traveling on the road. A communication system in which a plurality of time slots for performing wireless communication by a time division multiple access method is assigned between roadside communication devices, between vehicle-mounted communication devices, and between the roadside communication device and the vehicle-mounted communication device. The roadside communication device is configured to acquire information indicating at least one of a traffic volume of the vehicle and a communication traffic of the in-vehicle communication device, and a traffic volume and a communication traffic indicated by the information acquired by the acquisition device. And changing means for changing the allocation of the time slot according to at least one of them.

  In the communication system according to the second invention, the changing means performs wireless communication between the roadside communication devices when at least one of the traffic volume and the communication traffic indicated by the information acquired by the acquiring means increases / decreases. Means for reducing / increasing the number of time slots for

  In the communication system according to a third aspect of the invention, the roadside communication device includes means for acquiring communication state information indicating whether the communication state of the in-vehicle communication device is good or bad, and the changing means is communication indicated by the acquired communication state information. When the state is bad / good, it is provided with means for increasing / decreasing the number of time slots for performing wireless communication between the roadside communication device and the in-vehicle communication device.

  In a communication system according to a fourth aspect of the present invention, the roadside communication device associates the priority of each of a plurality of types of information to be transmitted to the in-vehicle communication device with at least one of traffic volume and communication traffic, and Means for identifying the priority of each information according to the traffic volume based on at least one of the traffic volume and communication traffic indicated by the information acquired by the acquisition means, and the priority table; and information having high priority And means for transmitting in a larger number of time slots than information having a low priority.

  A wireless communication method according to a fifth aspect of the present invention is a wireless communication method in a communication system comprising a plurality of roadside communication devices installed along a road and an in-vehicle communication device mounted on each of a plurality of vehicles traveling on the road. A plurality of time slots for performing wireless communication by a time division multiple access method between each roadside communication device, between each vehicle-mounted communication device, and between the roadside communication device and the vehicle-mounted communication device. Time slot according to at least one of traffic and communication traffic indicated by the acquired information, acquiring information indicating at least one of traffic volume of the vehicle and communication traffic of the in-vehicle communication device It is characterized by changing the assignment.

  According to a sixth aspect of the present invention, there is provided a communication apparatus comprising: a plurality of time slots for performing wireless communication by a time division multiple access method between a plurality of mobile communication apparatuses and between a fixed communication apparatus or the mobile communication apparatus. A communication device to be assigned to the mobile communication device and the fixed communication device, an acquisition unit for acquiring information indicating traffic volume of the mobile communication device or communication traffic of the mobile communication device, and And changing means for changing the allocation of time slots according to at least one of traffic and communication traffic indicated by the acquired information.

In the first, fifth and sixth inventions, the acquisition means of the roadside communication device acquires information indicating the traffic volume of the vehicle or the communication traffic of the in-vehicle communication device. Since the traffic volume and the communication traffic correspond to the shortage amount of the time slot, it is possible to determine the shortage of the time slot by acquiring the information. Then, the changing means of the roadside communication device changes the allocation of time slots for road-to-road, road-to-vehicle or inter-vehicle communication according to at least one of traffic and communication traffic indicated by the information acquired by the acquiring means. This eliminates the shortage of time slots for road-to-vehicle or vehicle-to-vehicle communication due to increased traffic.
The mobile communication device in the sixth invention is a superordinate concept of the in-vehicle communication device, and the fixed communication device and the communication device are superordinate concepts of the roadside communication device. In particular, the communication device according to the sixth invention functions as a roadside communication device by being installed on a road.
Further, the present invention includes not only a configuration in which the time slot assignment is changed according to traffic volume or communication traffic, but also a configuration in which the time slot allocation is changed according to both traffic volume and communication traffic.

  In the second invention, when the traffic volume increases, the number of time slots for road-to-road communication is decreased to eliminate the shortage of time slots for road-to-vehicle or vehicle-to-vehicle communication due to the increase in traffic volume. Further, when the traffic volume decreases again, the number of time slots of the roadside communication device is increased.

  In the third invention, the roadside communication device acquires communication state information indicating whether the communication state of the in-vehicle communication device is good or bad. Then, when the communication state indicated by the communication state information is bad, the roadside communication device enables stable road-to-vehicle communication by increasing the number of time slots for road-to-vehicle communication. When the communication state becomes good again, the number of time slots for road-to-vehicle communication is reduced.

  In the fourth invention, the specifying means of the roadside communication device specifies the priority of various types of information based on the priority table and at least one of the traffic and communication traffic indicated by the traffic information. Then, the roadside communication device transmits information having a high priority in a larger number of time slots than information having a low priority. Therefore, it is possible to increase the number of times of continuous transmission of information with high priority and transmit the information to the in-vehicle communication device more reliably.

  According to the present invention, the shortage of time slots for road-to-vehicle or vehicle-to-vehicle communication in a communication system can be solved by changing time slot allocation according to the traffic volume of a vehicle or the communication traffic of an in-vehicle communication device. Each communication device can perform stable wireless communication.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
FIG. 1 is an explanatory diagram conceptually showing a communication system according to an embodiment of the present invention. A communication system that implements the wireless communication method according to the present embodiment includes two roadside communication devices 1 and 1 (hereinafter referred to as roadside communication device 1) installed on the roadside of road R, for example, intersections B1 and B2, and roads (Hereinafter referred to as “vehicle C”) mounted on a plurality of vehicles C, C,... (Hereinafter referred to as “vehicle C”) and R (hereinafter referred to as “vehicle-mounted communication device 3”). The in-vehicle communication device 3 supports safe driving by transmitting and receiving various information related to safe driving support and traffic smoothing between roads, roads and vehicles, and vehicles between vehicles by time division multiple access wireless communication.

  In the time division multiple access method, a certain communication time (frame) in the same frequency band is time-divided into a plurality of time slots, and a plurality of roadside communication devices 1 and in-vehicle communication devices 3 use each time slot alternately. , Which enables simultaneous communication. According to the time division multiple access method, the same frequency band, for example, the UHF band, can be shared between roads, roads and vehicles, and vehicles can be used effectively. Note that the frequency band for wireless communication is not limited to UHF, and other bands may be used.

  FIG. 2 is an explanatory diagram conceptually illustrating an example of a data format of information transmitted and received by the roadside communication device 1 and the in-vehicle communication device 3 in a time slot. Information transmitted and received by the roadside communication device 1 and the in-vehicle communication device 3 is composed of a header part, a data part, and a footer part. In the header portion, for example, identification information indicating that the data is transmitted from the roadside communication device 1, an intersection number, and the like are stored. The data section stores information related to safe driving support and traffic smoothing transmitted to the in-vehicle communication device 3 or the roadside communication device 1.

  FIG. 3 is a block diagram showing the configuration of the communication system. The roadside communication device 1 includes a communication unit 11 that performs wireless communication in a time-division multiple access method between the surrounding roadside communication device 1 and the in-vehicle communication device 3 using the antenna 10, and between roads, between roads, and between vehicles. A control unit 12 that performs various communication controls such as time slot allocation management and provision of safe driving support information, and a storage unit 13 that stores information necessary for various communication control processes.

  A roadside communication device 1 installed at an intersection B1 on the left side in FIG. 1 centrally manages wireless communication between road vehicles and between vehicles in a cross-shaped wireless communication area A1 indicated by a solid line. In the wireless communication area A1, by assigning different time slots prepared in advance so as not to compete with each in-vehicle communication device 3, the road-side communication device 1 and the in-vehicle communication device 3 can communicate with each other between roads and vehicles and between vehicles. Communicate. Similarly, the roadside communication device 1 installed at the intersection B2 on the right side in FIG. 1 centrally manages wireless communication between road vehicles and between vehicles in the wireless communication area A2.

  The road-to-vehicle communication method includes an individual communication method and a broadcast communication method. In this embodiment, a broadcast communication method that can effectively use a radio wave band is adopted. The individual communication method is a method in which a communication connection is established independently for each in-vehicle communication device 3, and since wireless communication is performed interactively between road vehicles, it is excellent in confidentiality and communication stability. On the other hand, the broadcast communication method is a communication method in which the roadside communication device 1 transmits the same information to all the vehicles C, and the vehicle-mounted communication device 3 selects the same information. Therefore, it is possible to effectively use the radio wave band.

  The control unit 12 is, for example, a microcomputer including a CPU and an interface, and a clock (not shown) for performing wireless communication by a time division multiple access method is connected to the control unit 12. The control unit 12 is connected to the optical beacon 4, the image sensor 5, the signal lamp 6, the computer of the traffic control center 2, and the like shown in FIG. Sending and receiving. For convenience of drawing, a communication line connecting the roadside communication device 1 to the optical beacon 4, the image sensor 5, the signal lamp 6, and the traffic control center 2 is not shown.

  The storage unit 13 stores various information transmitted from the optical beacon 4, the image sensor 5, the central government center, and the like. In addition, the storage unit 13 stores a priority table 13a for improving the reception probability of important information by the in-vehicle communication device 3.

  The optical beacon 4 includes a beacon head attached to a horizontal portion of a support frame installed on a road R near the outer edge of the wireless communication areas A1 and A2, and a beacon control device attached to a vertical portion of the support frame. Yes. The beacon head includes a projector / receiver for performing optical communication using near infrared rays between the in-vehicle communication devices 3. The installation position of the optical beacon 4 shown in FIG. 1 is an example, and the optical beacon 4 may be installed at another point.

  The optical beacon 4 projects a near-infrared optical signal toward the road R on which the vehicle C travels, and performs bi-directional optical communication with the vehicle C passing through the light projecting / receiving area. For example, when the in-vehicle communication device 3 that has entered the light emitting / receiving area transmits a time slot allocation request to the optical beacon 4 to perform wireless communication in a non-competitive manner, the optical beacon 4 The allocation request is received, and the received allocation request is transmitted to the roadside communication device 1. The roadside communication device 1 receives the assignment request transmitted from the optical beacon 4 and assigns the time slot corresponding to the traffic condition and the communication state of the in-vehicle communication device 3 to the in-vehicle communication device 3.

  The image sensor 5 is installed at the intersections B1 and B2 in a posture capable of capturing an image of the vehicle C traveling on the road R. The image sensor 5 includes a lens, an image sensor, an image processing circuit, a transmission unit, and the like. The image processing circuit calculates the traffic volume of the vehicle C traveling on the road R based on the image obtained by imaging with the imaging device, and the transmission unit displays the traffic volume information indicating the calculated traffic volume on the roadside communication device. 1 to send.

The traffic volume information may be transmitted from the traffic control center 2 to the roadside communication device 1. That is, the computer of the central control center collects image data from the image sensor 5, calculates the traffic volume based on the acquired image data, and transmits the traffic information indicating the calculated traffic volume to the roadside communication device 1. You may comprise.
Moreover, although the example which measures a traffic volume based on the image obtained by imaging was demonstrated, the vehicle which drive | works the road R by the vehicle detector which detects the vehicle C using an ultrasonic wave, a far infrared ray, etc., an optical beacon, etc. You may comprise so that the traffic volume of C may be measured.

  The traffic control center 2 collects and accumulates sensor information transmitted from a vehicle sensor (not shown) installed on the road side of the road R, a road surface condition sensor, and other various information. Based on the accumulated sensor information, the traffic control center 2 grasps the road R where the vehicle sensor is installed and the surrounding traffic conditions, and provides various information for safe driving support and traffic smoothing. It transmits to the roadside communication apparatus 1. For example, the traffic control center 2 provides the road-side communication device 1 with the color timing of the signal lamp 6, the traffic information of the intersections B1 and B2, and the like.

The information transmitted from the roadside communication device 1 that has collected various information to the in-vehicle communication device 3 includes the display lamp color of the signal lamp 6 and the duration of the display lamp color as information for supporting safe driving of the vehicle C. Information on road schedules, regulation information on traffic regulations on road R, road shape information on road R shapes such as the number of lanes and gradients, road surface information on road surface conditions on road R, administration such as traffic safety campaigns by administrative agencies Notification information and the like are included (see FIG. 4).
Further, the roadside communication device 1 communicates with the surrounding roadside communication devices 1 on the signal control result information regarding the control result of the signal lamp 6, the vehicle C flowing from the upstream intersections B1, B2 to the downstream intersections B1, B2. Traffic information related to the predicted traffic volume and traffic information around the roadside communication device 1 are shared by transmitting and receiving 5 minutes traffic information related to the traffic volume of the vehicle C traveling on the road R for 5 minutes.

FIG. 4 is an explanatory diagram conceptually showing the priority table 13a. The priority table 13a includes information items such as signal information, regulation information, road shape information, road surface information, and administrative notice information transmitted from the roadside communication device 1 to the in-vehicle communication device 3, and each item when the traffic volume is small. The transmission priority of each item is associated with the transmission priority of each item when the traffic volume is high. Note that the smaller the numerical value shown in the priority column, the higher the priority.
As shown in the priority table 13a, the priority of the information transmitted from the roadside communication device 1 to the in-vehicle communication device 3 changes according to the traffic volume. For example, when the traffic volume is large, the priority of traffic information such as traffic smoothness, comfort, environmental regulation information, signal information, etc. is high. When the traffic volume is low, the priority of sensor detection result information and roadside device state information related to safe driving support is high.
By using the priority table 13a as will be described later, it becomes possible to transmit information corresponding to changes in the priority of various types of information according to the traffic volume. That is, it is possible to improve the reception probability of important information by the in-vehicle communication device 3 by determining the content of the transmission information so that the number of continuous transmissions of information with high priority is optimized.
The priority may be determined by weighting based on traffic conditions or other communication means such as the optical beacon 4 or an information transmission request obtained from a mobile phone. For example, when the in-vehicle communication device 3 transmits an information transmission request for requesting transmission of restaurant information from the projector / receiver 34, the control unit 12 of the roadside communication device 1 transmits the information transmission request via the optical beacon 4. And the priority of the restaurant information may be increased according to the received information transmission request.

Next, the configuration of the in-vehicle communication device 3 will be described. The in-vehicle communication device 3 includes a communication unit 31 connected to the antenna 30, a control unit 32 that performs control related to communication, a storage unit 33 that stores information necessary for various processes such as communication processing and safe driving support processing, and the like. And a light projector / receiver 34 that performs optical communication with the optical beacon 4.
The control unit 32 of the in-vehicle communication device 3 has a function of self-diagnosis the communication state between road vehicles, particularly the reception state, and whether or not the information from the road side communication device 1 has been received or only a part of the information. Is configured to transmit communication status information indicating that it has been received. The communication status information can be included in, for example, a header portion of various information communicated between vehicles, and the roadside communication device 1 can acquire the communication status information by monitoring information communicated between vehicles. it can.
Note that the contents of the communication state information are examples. You may comprise so that the communication status information containing the time which received the information from the roadside communication apparatus 1 last time and a security code may be transmitted. Since the roadside communication device 1 knows the transmission time of information, the reception state of the in-vehicle communication device 3 can be grasped by referring to the communication state information transmitted by the in-vehicle communication device 3.

  In addition, when the in-vehicle communication device 3 enters the wireless communication areas A1 and A2, the on-vehicle communication device 3 requests time slot assignment via the light projector / receiver 34 and the optical beacon 4, and assigns the time slot transmitted from the roadside communication device 1. A result is received, and non-competing wireless communication is performed based on the received result. Outside the wireless communication areas A1 and A2, competitive wireless communication is performed with other in-vehicle communication devices 3.

Next, a time slot management method by the roadside communication device 1 will be described.
FIG. 5 is an explanatory diagram conceptually showing a time slot allocation changing method. The roadside communication device 1 is a time slot for road-to-vehicle communication, a time slot for road-to-road communication, and a vehicle for vehicle-to-vehicle communication in order to perform time-division multiple access wireless communication between roads and vehicles, between roads and between vehicles. A time slot is assigned to each roadside communication device 1 and in-vehicle communication device 3. The roadside communication device 1 always keeps track of the traffic volume of the vehicle C and the communication state of the in-vehicle communication device 3 in order to perform stable wireless communication, and assigns time slots according to the traffic volume and communication state. Make a change.

  FIG. 5A shows an example of a time slot allocation method when the communication state of the in-vehicle communication device 3 is good when it is not crowded. Arrows indicate the time axis, and rectangular cells arranged in the vertical direction indicate time slots. As shown in FIG. 5A, when the communication state of the in-vehicle communication device 3 is good when there is no congestion, two time slots for road-to-vehicle communication and one time slot for road-to-road communication are present in one cycle. Three are assigned, and three timeslots for inter-vehicle communication are assigned.

FIG. 5B shows an example of a time slot allocation method when the in-vehicle communication device 3 is in a busy state and the communication state is good. As shown in FIG. 5 (b), when there is a lot of traffic, the number of time slots for inter-vehicle communication is insufficient, so the number of time slots for inter-road communication is reduced from three to two, and the open time Assign the slot to a time slot for inter-vehicle communication.
In general, when the traffic volume increases, the traffic conditions at surrounding intersections B1 and B2 do not change much. For example, the content of signal control information transmitted and received between the roadside communication devices 1 often does not change. For this reason, when the traffic volume increases, there is no adverse effect even if the number of time slots for road-to-road communication is reduced to reduce the communication speed. The present invention focuses on this point, and when the traffic volume increases, the time slot for road-to-road communication is released and assigned to the time slot for vehicle-to-vehicle communication. The shortage can be resolved.
If the traffic volume changes abruptly, that is, if the change in traffic volume per unit time is greater than or equal to a predetermined value, the allocation of the time slot for inter-road communication is not changed and the traffic volume per unit time is changed. When the amount of change is less than a predetermined value, the allocation of the time slot for inter-road communication may be changed. When configured in this way, the assignment of time slots can be changed in accordance with a stable traffic volume, so communication between roads, roads and cars, and cars can be further stabilized.
In addition, when the number of time slots for road-to-road communication is decreased, when there is information with high priority to be communicated between roads, the information is transmitted using the time slot for road-to-vehicle communication. One roadside communication device 1 may be configured, and another roadside communication device 1 may be configured to receive the time slot for road-to-vehicle communication. One roadside communication device 1 can interrupt and transmit high-priority and highly urgent information for road-to-road communication in a time slot for road-to-vehicle communication, and as a result, monitors road-to-vehicle communication. The information can be transmitted to another roadside communication device 1.
Further, when the number of time slots for road-to-road communication is reduced, the roadside communication device 1 stores information to be communicated between roads in the storage unit 13 so that the traffic volume decreases and When the number of communication time slots increases, the information stored in the storage unit 13 may be communicated between roads.

FIG. 5C shows an example of a time slot allocation method when the communication state of the in-vehicle communication device 3 is bad at the time of congestion. As shown in FIG. 5C, when the communication state is bad at the time of congestion, the number of time slots for road-to-road communication is reduced, and free time slots are assigned to time slots for road-to-vehicle communication.
The roadside communication device 1 refers to the communication state information transmitted by the in-vehicle communication device 3, measures the ratio of the vehicle C that has failed to receive information from the roadside communication device 1, and determines the vehicle C that has failed to receive the information. When the ratio is large, the number of time slots for road-to-vehicle communication is increased from two to four, and the frequency of continuous transmission is increased to increase the information reception probability from the roadside communication device 1. By increasing the number of time slots for road-to-vehicle communication, that is, increasing the number of times of continuous information transmission, the probability of information reception by the in-vehicle communication device 3 is improved, and stable wireless communication can be performed. If necessary, slots allocated between vehicles may be thinned out.

FIG. 5D shows an example of a time slot allocation method when the communication state of the in-vehicle communication device 3 is bad at the time of non-congestion. When the communication state is poor as shown in FIG. 5D, the number of time slots for road-to-vehicle communication is increased. By increasing the number of time slots for road-to-vehicle communication, the information reception probability by the in-vehicle communication device 3 is improved, and stable wireless communication can be performed.
As shown in FIG. 5, the time slot is assigned in a fixed predetermined time length, but the time slot may be assigned in a variable predetermined time length.

FIG. 6 is a flowchart illustrating a processing procedure of the control unit 12 related to the wireless communication of the roadside communication device 1.
First, the control unit 12 determines whether or not the timing unit has counted a predetermined information collection period, for example, 100 msec (step S11). When it determines with having measured the predetermined period (step S11: YES), the control part 12 acquires traffic volume information, communication status information, and other various information (step S12).

  When the process of step S12 is completed, or when it is determined in step S11 that the predetermined information collection cycle has not been timed (step S11: NO), the control unit 12 receives a time slot allocation request from the in-vehicle communication device 3. It is determined whether or not there is (step S13).

  When it is determined that there is a time slot allocation request (step S13: YES), the control unit 12 calls a subroutine related to time slot allocation change and changes the time slot allocation (step S14).

FIG. 7 is a flowchart showing a processing procedure of a subroutine related to time slot assignment change.
The control unit 12 determines whether or not the time slot is insufficient, for example, whether or not the traffic volume is equal to or greater than a predetermined traffic volume and the traffic volume has increased (step S31). When it is determined that the time slots are insufficient (step S31: YES), the control unit 12 decreases the number of time slots for inter-road communication (step S32).

  When the process of step S32 is completed, or when it is determined that there are not insufficient time slots (step S31: NO), the control unit 12 determines whether or not there are remaining time slots, for example, the traffic volume is a predetermined traffic volume. It is determined whether it is less than (step S33). If it is determined that the traffic volume is less than the predetermined traffic volume (step S33: YES), the control unit 12 changes the number of time slots for inter-road communication to the standard number of time slots (step S34). The predetermined traffic volume and the standard number of time slots are stored in the storage unit 13 of the roadside communication device 1.

  When the process of step S34 is completed, or when it is determined that the number of time slots is equal to or greater than the predetermined traffic volume (step S33: NO), the control unit 12 is based on the communication state information acquired by monitoring the inter-vehicle communication. Then, the quality of the communication state by the in-vehicle communication device 3 is determined (step S35). When it is determined that the communication state is poor (step S35: YES), the control unit 12 increases the number of time slots for road-to-vehicle communication (step S36).

  Preferably, in step S36, the number of time slots is increased so that the optimal time slot interval at which the in-vehicle communication device 3 can easily receive the information transmitted from the roadside communication device 1 is obtained.

  When the process of step S36 is completed, or when it is determined that the communication state is not defective (step S35: NO), the control unit 12 is in a good state in which the communication state of the in-vehicle communication device 3 is normalized. Is determined (step S37). If it is determined that the communication state is good (step S37: YES), the number of time slots for road-to-vehicle communication is changed to the standard number of time slots (step S38).

  When the process of step S38 is completed or when it is determined that the wireless communication state is not good (step S37: NO), the control unit 12 determines time slot allocation, and determines the determined time slot allocation result. The in-vehicle communication device 3 and the roadside communication device 1 are notified (step S39), and the subroutine processing relating to the time slot assignment change is completed.

  As shown in FIG. 6, when the process of step S14 is completed or when it is determined in step S13 that there is no time slot request (step S13: NO), the control unit 12 prioritizes the traffic volume indicated by the traffic volume information. The priority of the information to be transmitted is specified based on the degree table 13a (step S15), and the transmission information to be transmitted to the in-vehicle communication device 3 or the roadside communication device 1 is created (step S16).

Specifically, the transmission information is created so that the number of continuous transmissions of information with high priority is large and the number of continuous transmissions of information with low priority is small. That is, information with high priority is transmitted in a large number of time slots, and information with low priority is transmitted in a small number of time slots.
Preferably, time slots are allocated so as to obtain the optimum number of continuous transmissions from items with high priority. Time slots are allocated so that information items with low priority, for example, information items with the sixth or higher priority are assigned once per cycle, for example, once every 100 msec.

FIG. 8 is an explanatory diagram conceptually showing the content of transmission information according to priority. FIG. 8A shows the transmission information when the communication state of the in-vehicle communication device 3 is good when it is not crowded. As in FIG. 5, the arrows indicate the time axis, and the rectangular cells arranged in the vertical direction indicate time slots. A case where one cycle is 150 msec and wireless communication is performed using a 10 msec time slot will be described. If the communication status of the in-vehicle communication device 3 is good even if the traffic volume is small and the number of continuous transmissions is small, for example, information with a priority of 1 to 8 is transmitted in one time slot and prioritized in another time slot. Information with a degree of 9 to 17 may be transmitted.
FIG. 8B shows transmission information when the communication state of the in-vehicle communication device 3 is bad at the time of congestion. When there is a lot of traffic and the communication state of the in-vehicle communication device 3 is poor, information of 1 to 6 with high priority is transmitted at an optimal time slot interval, for example, 30 msec. That is, information with a priority of 1 to 6 is repeatedly transmitted in one period in all time slots for road-to-vehicle communication. And information of 7-17 which is low in importance is transmitted at a time slot interval of 150 msec. In this way, by assigning time slots so as to obtain the optimum number of continuous transmissions from items with high priority, the reception probability of information with high priority can be improved.
In addition, although the case where it transmits also about information with low priority was illustrated, you may comprise so that all or one part of information with low priority may not be transmitted.

  The time slot interval that is the optimum number of times of continuous transmission is obtained by the roadside communication device 1 accumulating communication state information and traffic volume information.

  FIG. 9 is a graph showing the relationship between the traffic density and the optimal time slot interval. The horizontal axis represents the traffic density (units / km), and the vertical axis represents the time slot interval (msec) at which the information reception probability by the in-vehicle communication device 3 is substantially maximized. The roadside communication device 1 measures the time slot interval at which the reception probability of the in-vehicle communication device 3 is substantially maximum based on the communication state information transmitted from the in-vehicle communication device 3, and the time slot interval at which the reception probability is approximately maximum. And the relationship with the traffic density is stored in the storage unit. According to FIG. 9, for example, when the traffic density is 90 [vehicles / km], the optimum time slot interval is 30 msec. The traffic density can be calculated or estimated based on the traffic volume.

  Next, the control unit 12 determines whether or not it is a predetermined transmission timing based on the timing result of the timing unit (step S17). When it determines with it not being a transmission timing (step S17: NO), the control part 12 returns a process to step S11. When it determines with it being a transmission timing (step S17: YES), the control part 12 transmits the information produced in step S16 to the vehicle-mounted communication apparatus 3 or the roadside communication apparatus 1 (step S18), and a process is set to step S11. return.

  In the communication system configured as described above, when the traffic volume increases, the number of time slots for road-to-road communication is reduced, and the opened time slot is used as a time for vehicle-to-vehicle communication or road-to-vehicle communication. By allocating to slots, the shortage of time slots for vehicle-to-vehicle or road-to-vehicle communication due to increased traffic volume can be resolved, and wireless communication using the band can be performed effectively. Even if traffic volume increases, it is safe. Can support driving.

  Further, when the communication state of the in-vehicle communication device 3 deteriorates, the communication state of the in-vehicle communication device 3 is maintained well by increasing the number of time slots for road-to-vehicle communication, and stable wireless communication and safety support are performed. be able to.

  Furthermore, the priority of transmission information that changes according to the traffic volume is specified, and information that has high priority is configured to be transmitted in a larger number of time slots than information with low priority. The reception probability of highly important information by the communication device 3 can be improved.

In the embodiment, the time slot shortage is determined based on the traffic information indicating the traffic of the vehicle. However, the information indicating the communication traffic of the in-vehicle communication device is acquired. The time slot shortage may be determined. Each in-vehicle communication device transmits the information amount of information to be transmitted, specifically storing the information amount of information to be transmitted in the header part, and the road-side communication device is transmitted and received by each in-vehicle communication device By monitoring the information to be performed, information indicating communication traffic of a plurality of in-vehicle communication devices traveling on the road can be obtained. Moreover, you may comprise so that this traffic information may be acquired from the memory | storage part which memorize | stored the number of time slots allocated to the vehicle-mounted communication apparatus as traffic information.
FIG. 10 is a graph showing the relationship between traffic volume and communication traffic. The horizontal axis indicates the traffic volume of the vehicle (unit / 5 minutes), and the vertical axis indicates the communication traffic (Erlang). When 10% of the vehicle C traveling on the road R is equipped with the in-vehicle communication device 3, the traffic volume and the communication traffic have a correlation as shown in FIG. The traffic used for processing can be replaced by communication traffic.
Specifically, as in the priority table shown in FIG. 4, the storage unit of the roadside communication device stores various items of information to be transmitted from the roadside communication device to the in-vehicle communication device, and transmission of each item when communication traffic is low. A priority table in which the priority and the priority of each item when communication traffic is high is associated is stored. The order of priority is the same as in FIG.
And the control part of a roadside communication apparatus acquires the information which shows communication traffic by step S12 of FIG. 6, and it is comprised so that allocation of a time slot may be changed according to the communication traffic which the acquired information shows. Specifically, the control unit of the roadside communication device determines whether the time slot is excessive or insufficient based on the communication traffic in steps S31 and S33, and if the number of time slots decreases and is insufficient, it is for roadside communication. When the number of time slots is decreased and the number of time slots is excessively increased, the number of time slots for communication between roads is increased. Further, the control unit of the roadside communication device specifies the priority of the information to be transmitted based on the communication traffic and the above-described priority table in steps S15 and S16, and transmits it to the in-vehicle communication device or the roadside communication device. Configure to create information.
In addition, although the structure which changes allocation of a time slot according to traffic volume or communication traffic was demonstrated, you may comprise so that allocation of a time slot may be changed according to traffic volume and communication traffic.

  Further, not only the traffic volume of the vehicle traveling on the road but also the vehicle type may be determined and the traffic volume for each vehicle type may be acquired. Higher vehicles are more likely to interfere with wireless communications than low-priced regular vehicles, so there are more high-volume vehicles with more traffic than normal vehicles with more traffic. It is good to increase or decrease the number of time slots. In this case, it is possible to change the allocation of the time slot that more accurately grasps the shortage of the time slot.

  Furthermore, the transmission from the roadside communication device to the in-vehicle communication device employs broadcast communication that can effectively use the radio wave band, but is not necessarily limited thereto.

  Furthermore, although the communication system which employ | adopted the broadcast communication system as a communication system between road vehicles was demonstrated, you may employ | adopt an individual communication system, when there is room in a radio wave band.

  Furthermore, it should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is explanatory drawing which shows notionally the communication system which concerns on embodiment of this invention. It is explanatory drawing which shows notionally an example of the data format of the information which a roadside communication apparatus and a vehicle-mounted communication apparatus transmit / receive in a time slot. It is a block diagram which shows the structure of a communication system. It is explanatory drawing which shows a priority table notionally. It is explanatory drawing which shows notionally the allocation change method of a time slot. It is a flowchart which shows the process sequence of the control part which concerns on the radio | wireless communication of a roadside communication apparatus. It is a flowchart which shows the process sequence of the subroutine which concerns on the allocation change of a time slot. It is explanatory drawing which shows notionally the content of the transmission information according to a priority. It is a graph which shows the relationship between traffic density and the optimal time slot interval. It is a graph which shows the relationship between traffic volume and communication traffic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Roadside communication apparatus 2 Traffic control center 3 In-vehicle communication apparatus 4 Optical beacon 5 Image sensor 6 Signal lamp 10, 30 Antenna 11, 31 Communication part 12, 32 Control part 13, 33 Storage part 13a Priority table B1, B2 Intersection C Vehicle R road

Claims (6)

A plurality of roadside communication devices installed along a road, and a vehicle-mounted communication device mounted on each of a plurality of vehicles traveling on the road, the roadside communication device between each roadside communication device, each vehicle-mounted communication device A communication system configured to allocate a plurality of time slots for performing wireless communication by a time division multiple access method between the roadside communication device and the in-vehicle communication device,
The roadside communication device is
Obtaining means for obtaining information indicating at least one of traffic volume of the vehicle and communication traffic of the in-vehicle communication device;
And a changing unit that changes the allocation of time slots in accordance with at least one of traffic and communication traffic indicated by the information acquired by the acquiring unit. The changing means is
And means for decreasing / increasing the number of time slots for performing wireless communication between the roadside communication devices when at least one of the traffic volume and communication traffic indicated by the information acquired by the acquisition means increases / decreases. The communication system according to claim 1. The roadside communication device is
Means for acquiring communication state information indicating whether the communication state of the in-vehicle communication device is good or bad;
The changing means is
A means for increasing / decreasing the number of time slots for performing wireless communication between the roadside communication device and the in-vehicle communication device when the communication state indicated by the acquired communication state information is poor / good. The communication system according to claim 1 or 2. The roadside communication device is
A priority table in which the priority of each of a plurality of types of information to be transmitted to the in-vehicle communication device is associated with at least one of traffic volume and communication traffic;
Means for identifying the priority of each information according to traffic based on at least one of traffic and communication traffic indicated by the information acquired by the acquisition means, and the priority table;
The communication system according to any one of claims 1 to 3, further comprising: means for transmitting information having a higher priority in a larger number of time slots than information having a lower priority. A wireless communication method in a communication system comprising a plurality of roadside communication devices installed along a road and an in-vehicle communication device mounted on each of a plurality of vehicles traveling on the road,
A plurality of time slots for performing wireless communication by a time division multiple access method between each roadside communication device, between each vehicle-mounted communication device, and between the roadside communication device and the vehicle-mounted communication device, the roadside communication device and the vehicle-mounted communication. Assigned to the device,
Obtaining information indicating at least one of traffic volume of the vehicle and communication traffic of the in-vehicle communication device;
A wireless communication method, characterized in that time slot assignment is changed according to at least one of traffic and communication traffic indicated by the acquired information. A plurality of time slots for performing wireless communication by a time division multiple access method between a plurality of mobile communication devices and between a fixed communication device or the mobile communication device, and the mobile communication device and the fixed type A communication device assigned to the communication device,
Obtaining means for obtaining information indicating traffic volume of the mobile communication device or communication traffic of the mobile communication device;
A communication device comprising: changing means for changing time slot allocation in accordance with at least one of traffic and communication traffic indicated by the information acquired by the acquisition means.

Images