JP2011097352A - Communication control device, and road-side communication instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication control device capable of securing a predetermined radio communication success rate by suppressing the occurrence of an error. <P>SOLUTION: The communication control device divides transmission information to be transmitted at a time slot Ta for a road side at which the road-side communication instrument 2 performs radio communication into a plurality of packets to be transmitted from the road-side communication instrument 2. The communication control device includes: a storage part 24 for storing reference information showing a relationship between a packet length and a radio communication success rate when the information is transmitted by the packet of the packet length; and a determination part 23E for determining a packet length L of unit being a unit for dividing the transmission information into the plurality of packets based on a data length possessed by the transmission information and the reference information. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to, for example, a communication control device used in an intelligent transport system (ITS) and a roadside communication device including the communication control device.

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

  In this case, the combination of communications performed between the respective communication subjects includes road-to-vehicle (or vehicle-road) communication performed by the roadside communication device and the vehicle-mounted communication device and vehicle-to-vehicle communication performed by the vehicle-mounted communication devices.

Japanese Patent No. 2806801

In an intelligent transportation system, when coexistence of road-to-vehicle communication and vehicle-to-vehicle communication coexists, there is a problem of what kind of communication control is to be performed by effectively using a band. In the case of an intelligent road traffic system, a standard for a communication band of approximately 10 MHz in the 700 MHz band is being studied. In such a relatively narrow bandwidth, there is a particular problem of how to effectively use the communication band in the communication area where the radio waves of the roadside communication device reach.
Therefore, it has been studied that multiple access is used in order to perform communication between road vehicles and between vehicles within such a limited frequency band.

  As this multi-access method, there are frequency division multiplexing (FDMA) and code division multiple access (CDMA), but communication with only a small number of in-vehicle communication devices is assumed in mountainous areas. As a multi-access method for inter-vehicle communication, it is preferable to adopt an autonomous random access method represented by CSMA (Carrier Sense Multiple Access), for example.

However, in areas where roadside communication devices exist, road-to-vehicle communication and vehicle-to-vehicle communication coexist.Therefore, in order to increase the priority of information handled by roadside communication devices on the infrastructure side, it is more important than vehicle-to-vehicle communication. A mechanism to preferentially perform road-to-vehicle communication is required.
Therefore, in order to preferentially transmit information on the roadside communication device, the frequency used for communication is time-divided at regular intervals to provide a time slot dedicated to transmission of the roadside communication device (TDMA: Time Division). Multiple access by Multiple Access is enabled.

  Therefore, for example, assuming a communication system composed of a plurality of roadside communication device groups installed at each intersection, a time slot transmitted by each roadside communication device is assigned by the TDMA method, and the remaining time slot is assigned to a vehicle by the CSMA method. It is considered to be a rational communication system to be used for inter-vehicle communication.

Here, the information transmitted by the roadside communicator in its own time slot includes signal display information indicating the scheduled time of the color of the traffic signal lamp installed at the intersection, and the length and slope of the road to a certain target point. There are road alignment information indicating the road structure, and the like, and such various information is transmitted from the roadside communication device.
In the intelligent transportation system, a method has been proposed in which such various information is divided into a plurality of packets and transmitted from a roadside communication device.

In road-to-vehicle communication using such a communication method, it is possible to estimate the propagation path using the signal at the beginning of the packet and to perform processing to compensate for the influence of the data portion due to the propagation path. However, as the packet length increases, the difference from the estimated propagation path may increase in the rear part of the packet. In this case, the in-vehicle communication device that has received the packet cannot successfully demodulate, and an error occurs. May occur.
SUMMARY OF THE INVENTION An object of the present invention is to provide a communication control device that can suppress occurrence of errors and ensure a predetermined wireless communication success rate, and a roadside communication device including the communication control device.

  (1) In order to achieve the above object, the present invention provides a communication control apparatus that divides transmission information transmitted in a roadside time slot in which a roadside communication device performs radio transmission into a plurality of packets and transmits the packet from the roadside communication device. A storage unit that stores reference information indicating a relationship between a packet length and a wireless communication success rate when the packet is transmitted in a packet of the packet length, a data length included in the transmission information, and the reference information And a determining unit that determines a unit packet length that is a unit for dividing the transmission information into a plurality of packets.

  According to the present invention, the determination unit divides the transmission information into a plurality of packets based on the data length of the transmission information transmitted in the roadside time slot and the reference information stored in the storage unit. A unit packet length as a unit is determined. For this reason, a unit packet length as a unit to be divided is obtained in consideration of the wireless communication success rate. If the transmission information is divided by the unit packet length and packets are transmitted, a predetermined wireless communication success rate can be secured.

  (2) That is, the reference information includes information on a wireless communication success rate in units of packets when the transmission information is divided and transmitted by a plurality of types of packet lengths, and the determination unit includes When the transmission information is divided and transmitted by dividing the plurality of types of packet lengths, among the plurality of types of packet lengths, the packet length with the highest wireless communication success rate in the transmission information unit is set as the unit packet. Can be determined as the length.

(3) Note that as the number of packets (number of divisions) increases, the DIFS (distributed inter frame space) also increases, and there is a possibility that roadside time slots allocated to a predetermined slot length cannot be effectively used for communication. is there.
Therefore, the determination unit divides the unit packet length so that a time required for transmitting the transmission information is within the time slot for the roadside having a prescribed slot length. It is preferred to determine the length. In this case, it is possible to limit the number of divisions from becoming too large, and the roadside time slot can be effectively used for communication.

(4) Since the wireless communication success rate varies depending on the relative position between the roadside communication device on the transmission side and the wireless communication device on the reception side, the wireless communication success rate is calculated based on the relationship between the roadside communication device and the reception position. It is preferable that the information is associated with the information on the relative position of.
In this case, the unit packet length can be determined according to the relative position between the roadside communication device and the reception position. The information on the relative position between the roadside communication device and the reception position may be information having a strong correlation with the distance in addition to the information on the distance between the roadside communication device and the reception position. can do.

  (5) In addition, when the storage unit stores the reference information for each communication parameter that affects the communication characteristics of the roadside communication device, the roadside communication device can perform communication such as a modulation scheme and a code error rate. Even when the transmission information is transmitted by changing the parameter, the reference information for each communication parameter can be used, and the unit packet length corresponding to the change of the communication parameter can be obtained. As a result, it is possible to divide transmission information according to changes in communication parameters and transmit packets.

(6) Further, the communication control device acquires a communication environment of the communication area based on transmission signals between a plurality of other wireless communication devices existing in the communication area of the roadside communication device, and sets the communication environment in the communication environment. It is preferable to further include a correction unit that corrects the reference information based on the information.
In this case, even if the communication environment in the communication area changes and the wireless communication success rate changes, the communication environment is acquired from the transmission signal between other wireless communication devices, and the reference information is corrected based on the communication environment. That's fine.

  (7) Although various types of information are included in the transmission information, the transmission information includes information that should be acquired with high probability by the surrounding wireless communication devices and other information. In this case, it is preferable that the determination unit varies a reference for determining the unit packet length according to the type of the transmission information.

  (8) Moreover, this invention is a roadside communication apparatus provided with the said communication control apparatus, This roadside communication apparatus can show | play the same effect | action as the said communication control apparatus.

  According to the present invention, a unit packet length as a unit to be divided can be obtained in consideration of a wireless communication success rate. If transmission information is divided and transmitted by the unit packet length, a predetermined wireless communication success is achieved. The rate can be secured. Thus, it is possible to improve communication performance by transmitting a packet by a suitable division method.

It is a schematic perspective view which shows one Embodiment of an intelligent road traffic system. It is a road top view which shows a part of jurisdiction area of an intelligent road traffic system. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a conceptual diagram which shows an example of a time slot. It is explanatory drawing explaining the structure of a packet. It is explanatory drawing of reference information, (a) is a 1st Example, (b) is a 2nd Example, (c) demonstrates the determination method of the unit packet length using reference information. FIG. It is explanatory drawing explaining the transmission packet in the time slot for roadsides. It is explanatory drawing explaining the other example (3rd Example) of reference information. It is explanatory drawing explaining the function of a correction | amendment part.

[Overall system configuration]
FIG. 1 is a schematic perspective view showing an embodiment of an intelligent road traffic system (ITS). The intelligent traffic system of this embodiment includes a traffic signal lamp 1, a roadside communication device 2, an in-vehicle communication device 3 (see FIGS. 2 and 3), a central device 4, a vehicle 5 equipped with the in-vehicle communication device 3, and a roadside. A sensor 6 is included.
The traffic signal lamp 1 and the roadside communication device 2 are installed at each of a plurality of intersections Ji (i = 1 to 12 in the figure), and are connected to the router 8 via a communication line 7 such as a telephone line. Yes. This router 8 is connected to the central device 4 in the traffic control center.

  The central device 4 constitutes a local area network (LAN) with the traffic signal lamp 1 and the roadside communication device 2 of each intersection Ji included in the area under its control. Therefore, bidirectional communication is possible among the central device 4, each traffic signal lamp 1, and each roadside communication device 2. The central device 4 may be installed on the road instead of the traffic control center.

  The roadside sensor 6 is composed of a sensor or a monitoring camera that detects an obstacle or a vehicle using ultrasonic waves or the like. For example, the roadside sensor 6 detects the number of vehicles flowing into each intersection Ji and grasps the traffic situation, Various locations on the road in the jurisdiction area for the purpose of grasping the presence of obstacles (for example, stopped vehicles) in Ji and grasping the position of the traveling vehicle (acquiring position information of the vehicle) Is installed. The sensor information acquired by the roadside sensor 6 is transmitted to the central device 4 via the communication line 7 and directly to the roadside communication device 2. The vehicle position information indicating the position of the traveling vehicle is transmitted from the roadside communication device 2 to the in-vehicle communication device 2 and is used for avoiding a vehicle collision, as will be described later.

  In FIG. 1 and FIG. 2, only one traffic signal lamp 1 is depicted at each intersection Ji for simplification of illustration, but the actual intersections Ji are used for ascending and descending roads intersecting each other. At least four traffic signal lamps 1 are installed. The group of traffic signal lamps 1 installed at each intersection Ji has a signal controller, from which signal display information indicating the scheduled time of the color of the traffic signal lamp 1 is communicated. The signal is transmitted to the central device 4 via the line 7 and directly to the roadside communication device 2.

The central device 4 has a control unit including a workstation (WS), a personal computer (PC), and the like. This control unit comprehensively collects / processes (calculates) / records various information, controls signals, and provides various information to each roadside communication device 2 and each traffic signal lamp 1.
That is, the central device 4 has a communication unit that is a communication interface connected to the LAN side via the communication line 7. The communication unit includes the signal display information received from the traffic signal lamp 1, the traffic Various provision information D1 such as a signal control command related to the switching timing of the signal lamp 1 and the sensor information received from the roadside sensor 6 is transmitted to the traffic signal lamp 1 and the roadside communication device 2 (see FIG. 1).

[Wireless communication systems, etc.]
FIG. 2 is a road plan view showing a part of the jurisdiction area of the intelligent transportation system. The road structure is not limited to this. The intelligent transportation system of the present embodiment includes a plurality of roadside communication devices 2 capable of wireless communication with an in-vehicle communication device 3, and mobile wireless transmission / reception that performs wireless communication with other communication devices 2 and 3 using a carrier sense method. And an in-vehicle communication device 3 which is a kind of a communication device (mobile communication device).

Each of the roadside communication devices 2 is installed at a roadside intersection Ji, and is attached to a column of the traffic light 1 in FIG. On the other hand, the in-vehicle communication device 3 is mounted on each vehicle 5 traveling on the road.
Each roadside communication device 2 has a communication area A (a range in which a transmission signal of the roadside communication device 2 can sufficiently reach) spreading around the roadside communication device 2 and wirelessly communicates with the vehicle-mounted communication device 3 of the vehicle 5 traveling in its own communication area A. Communication is possible. Each roadside communication device 2 can also perform wireless communication with other roadside communication devices 2 in which the communication area A overlaps (partially overlaps or all overlaps).

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

The roadside communication device 2 assigns roadside time slots for wireless transmission by itself by the TDMA method, and does not perform wireless transmission in a time zone other than the roadside time slots. Therefore, the time zone other than the time slot for the roadside communication device 2 is opened as a transmission time by the CSMA method for the in-vehicle communication device 3.
Further, as will be described later, the roadside communication device 2 divides the provision information (transmission information) D1 to be transmitted in its own roadside time slot into a plurality of packets and transmits it in its communication area A.
Each roadside communication device 2 has a time synchronization function with other roadside communication devices 2 in order to control its own transmission timing. The time synchronization of the roadside communication device 2 is performed by, for example, GPS synchronization that adjusts its own clock to the GPS time, air synchronization that adjusts its own clock to a transmission signal from another roadside communication device 2, or the like.

  In the present embodiment, one parent device is selected in advance from the plurality of roadside communication devices 2 and includes a determination unit 23E, an information classification unit 23C, an information allocation unit 23D, and the like described later. The control device "is illustrated as being mounted on each of the plurality of roadside communication devices 2 serving as a parent device and a child device. However, the communication control device is provided only in the parent device, and the determining unit 23E of the parent device, It may be configured to function for other slave units, and a communication control device is provided in the central device 4 so that the determination unit 23E and the like function for the master unit and the slave units. May be. The determination unit 23E, the information classification unit 23C, and the information allocation unit 23D may be provided in separate devices, or a communication system in which only one of them is provided in another device. May be configured.

  Further, in this embodiment, the “communication control device” provided in the parent device has a slot assignment unit 23A described later, autonomously assigns slots to the own device, and a plurality of devices managed by the parent device. A case will be described in which general time slot allocation is performed so as to achieve transmission timing that does not cause radio wave interference including the slave units. Note that the locations of the slot allocating unit 23A and a later-described notification unit 23B may also include a slave unit or the central device 4 as described above.

[Configuration of roadside communication device]
FIG. 3 is a block diagram showing the internal configuration of the roadside communication device 2 and the in-vehicle communication device 3.
The roadside communication device 2 includes a wireless communication unit 21 to which an antenna 20 for wireless communication is connected, a wired communication unit 22 that performs bidirectional communication with the central device 4, and a processor (CPU: Central Processing Unit) that performs communication control thereof. ) And a storage unit 24 including a storage device such as a ROM or a RAM connected to the control unit 23.

  The storage unit 24 of the roadside communication device 2 stores a computer program for communication control and the like executed by the control unit 23, communication device IDs of the communication devices 2 and 3, and reference information described later. The control unit 23 of the roadside communication device 2 includes a slot allocation unit 23A, a notification unit 23B, an information classification unit 23C, an information allocation unit 23D, a determination unit 23E, and a correction unit as functional units achieved by executing the computer program. 23F.

Among them, the notification unit 23B includes the signal display information received by the wired communication unit 22 from the central device 4 and the like, provided information D1 such as sensor information and road alignment information described later, and a slot allocation unit 23A described later. The generated slot information D2 is temporarily stored in the storage unit 24, and broadcast transmission is performed from the wireless communication unit 21 to the in-vehicle communication device 3.
In addition, the notification unit 23B temporarily stores the vehicle information (the position, speed, direction, and the like of the vehicle 5) of the in-vehicle communication device 3 received by the wireless communication unit 21 in the storage unit 24. Transfer to device 4.

  The slot allocating unit 23A time-divides roadside time slots in which the roadside communication device 2 performs radio transmission in each frame (time domain) repeated at a predetermined cycle (for example, a constant cycle of 100 milliseconds). Allocate and generate a predetermined time slot. FIG. 4 is a conceptual diagram showing an example of time slots assigned by the slot assignment unit 23A. The slot allocation unit 23A generates a time slot Ta for wireless transmission by its own roadside communication device 2 (master device R1) and other roadside communication devices 2 (child devices R2 to R8) for each frame Δt.

  Further, the slot assignment unit 23A sets the road time slot Ta of each of the plurality of roadside communication devices 2 to have a predetermined (constant) slot length. That is, the slot length of one roadside communication device 2 may be different from the slot length of another roadside communication device 2, but the slot length of one roadside communication device 2 is the same in any frame Δt. Is set to For example, in the case of FIG. 4, the slot length of the parent device R1 is set to 4 milliseconds in any frame Δt, and the slot length of the child device R2 is set to 3 milliseconds in any frame Δt. .

  In each time slot for roadside Ta, wireless transmission by the roadside communication device 2 is allowed in this time zone. The time zone other than the time slot Ta for the roadside communication device 2 is the time slot Tb for the in-vehicle communication device 3, and the time zone of the in-vehicle time slot Tb is opened for wireless transmission by the in-vehicle communication device 3. Therefore, the roadside communication device 2 does not perform radio transmission in the in-vehicle time slot Tb.

  In order for the slot allocation unit 23A to execute such slot allocation processing, the slot allocation unit 23 generates slot information D2 indicating the time of each road-side time slot Ta included in each frame Δt. The slot information D2 includes information on the start time and slot length of the roadside time slot Ta of each of the plurality of roadside communication devices 2.

When the slot information D2 is generated, the notification unit 23B (see FIG. 3) functions to cause the in-vehicle communication device 3 to acquire the slot information D2. That is, the notification unit 23 b transmits slot information from the wireless communication unit 21.
In each roadside time slot Ta, transmission information is transmitted as a packet. That is, the provision information D1 is assigned to a plurality of packets for each roadside time slot Ta and transmitted.
FIG. 5 is an explanatory diagram for explaining the structure of a packet transmitted from the wireless communication unit 21. The standard header includes address information and the like, and the extension header includes the slot information D2. Then, the provision information D1 is included in the data portion.

In such transmission, in order to determine how information to be transmitted in the roadside time slot is allocated (packed) to the packet, the information classification unit 23C and the information allocation unit of each roadside communication device 2 23D (see FIG. 3) functions.
That is, the information classification unit 23C has a function of classifying the provided information D1 transmitted in the roadside time slot Ta into first information and second information. This classification is performed based on the level of frequency of updating and transmitting information.

  Here, the provided information D1 transmitted from the roadside communication device 2 includes the first information and the second information, and the first information has a high update frequency, for example, every frame Δt set to 100 milliseconds. The second information is transmitted at a lower update frequency than the high frequency update information, for example, every second (or more). Good information (hereinafter also referred to as infrequently updated information).

The roadside communication device 2 can obtain the provision information D1 directly from another communication device in addition to obtaining the provision information D1 from the central device 4. The provided information D1 is information useful for safe driving support control for the vehicle 5 on which the in-vehicle communication device 3 is mounted.
Specifically, the provided information D1 includes the signal display information and the sensor information. The vehicle position information based on the signal display information and the sensor information is temporally dynamic information that changes every moment, and such information becomes high-frequency update information that should be transmitted at a high update frequency.
In particular, since the signal display information may be changed according to the traffic congestion state of the road where the traffic signal lamp 1 is installed under the control of the signal controller or the central device 4, such signal display information is The information to be transmitted at a high update frequency.

  Furthermore, since the signal display information is information indicating the scheduled time of the color of the traffic signal lamp 1, it is meaningful to transmit from the roadside communication device 2 at the installation position (near) of the traffic signal lamp 1. Similarly, the sensor information is meaningfully transmitted from the roadside communication device 2 in the detection target area (near). The vehicle position information may be information based on the sensor information, but may be information transmitted from the in-vehicle communication device 2 and received by the roadside communication device 2.

Other provision information D1 includes road alignment information indicating the shape of the road. The road alignment information is information indicating a road structure from an information providing point to a certain target point or a certain target section, and is information such as a road length, a slope, and a degree of a curve, for example. The road alignment information is information that can be stored in advance by the roadside communication device 2 or acquired from the central device 4.
The road alignment information does not need to be continuously updated because the information is valid until it passes through a certain target point (intersection or curve) of the road. For this reason, such road alignment information is static information in time, and is low-frequency update information that may be transmitted at a low update frequency.
Furthermore, since the road alignment information is information indicating the road structure up to a certain target point or a certain target section, it may be transmitted from the roadside communication device 2 existing up to the target point or the target section.

Each of such signal display information, vehicle position information, and road alignment information is assigned with a unique identifier in advance, for example.
Therefore, the information classification unit 23C can determine whether the provided information D1 is high-frequency update information or low-frequency update information based on the identifier, and by this determination, in the road time slot Ta. The provided information D1 to be transmitted can be classified into high-frequency update information and low-frequency update information.

The information allocating unit 23D allocates the high-frequency update information and the low-frequency update information to the plurality of packets included in each roadside time slot Ta and transmits the packets to the low-frequency update information. It has a function of assigning to packets in preference to information and assigning the infrequent update information to the remainder.
That is, as described above, high-frequency update information such as signal display information is transmitted from a predetermined roadside communication device 2 (for example, the parent device R1) existing at the installation position (near) of the predetermined traffic signal lamp 1. Since there is significance, the high-frequency update information is assigned to a packet included in the road-side time slot Ta of the predetermined roadside communication device 2 (master device R1), and the high-frequency update information is more than the low-frequency update information. Is also preferentially assigned.

  Then, if there is a margin in this roadside time slot Ta to which the high-frequency update information is assigned with priority, low-frequency update information such as road alignment information is assigned to the remainder (packet). Since the road alignment information that is the low-frequency update information may be transmitted from the roadside communication device 2 existing up to the target point or the target section as described above, the low-frequency update information includes all or a part thereof, Even if transmission is not possible in the predetermined roadside time slot Ta, transmission may be performed in a later (other) roadside time slot Ta.

Provided information D1 to be transmitted in the roadside time slot Ta is allocated to each packet by the information allocating unit 23D and transmitted from the roadside communication device 2. In executing this processing, the determining unit 23E Based on the total data length of the information D1 and reference information to be described later, a unit packet length that is a unit for dividing the provided information D1 into a plurality of packets is determined. That is, the determination unit 23E performs a process of determining the packet lengths of a plurality of packets included in the roadside time slot Ta.
A specific example of information allocation by the information allocation unit 23D and unit packet length determination by the determination unit 23E will be described later.

[Reference information]
FIG. 6 is an explanatory diagram of the reference information. The reference information is stored in the storage unit 24 (see FIG. 3), the packet length of the packet for transmitting the provision information D1, and the packet when the packet of the packet length is transmitted in the communication area A This is information indicating the relationship with the wireless communication success rate (packet arrival rate) in units. The packet length of the packet has the same meaning as the data length included in the packet, and the wireless communication success rate is a value when a packet having this data length is transmitted.

  The reference information (first embodiment) shown in FIG. 6A includes a plurality of types (three types in the example) of packet length values, packet arrival rates when packets of each packet length are transmitted, and It is information about the relationship. According to this reference information, for example, the packet arrival rate in the in-vehicle communication device 3 of a single packet transmitted with a packet length of 500 bytes means 0.95.

  The reference information (second embodiment) shown in FIG. 6B also includes information on the relative position between the roadside communication device 2 and the reception position of the in-vehicle communication device 3. In addition, the information regarding the relative position illustrated in FIG. 6B is the received signal strength (RSSI) having a strong correlation with the distance between the roadside communication device 2 and the reception position. That is, this reference information indicates the relationship between a plurality of types of packet length values (three types in the figure) and the packet arrival rate associated with the received signal strength when packets of each packet length are transmitted. Information.

  According to the reference information in FIG. 6B, for example, in the area where the received signal strength is −80 or more in the communication area A, the packet in the in-vehicle communication device 3 of a single packet transmitted with a packet length of 500 bytes. This means that the arrival rate is 0.95. This reference information is acquired by measuring the wireless communication success rate (packet arrival rate) in the communication area A in advance. The wireless communication success rate is a probability that the in-vehicle communication device 3 can receive and demodulate, and may be other than the packet arrival rate or may be a packet error rate.

As described above, the reference information is created in advance when the roadside communication device (communication control device) 2 is installed, and is stored in the storage unit 24. For example, the reference information increases with the passage of time due to increase or decrease of surrounding buildings. Thus, the communication environment of the communication area A may change. In this case, the packet arrival rate of the reference information may change compared to the original.
Therefore, the correction unit 23F acquires the communication environment of the communication area A based on transmission signals between the plurality of in-vehicle communication devices 3 existing in the communication area A of the roadside communication device 2, and based on the communication environment It has a function of correcting reference information.

The function of the correction unit 23F will be specifically described.
Within the communication area A of the roadside communication device 2, a plurality of in-vehicle communication devices 3 communicate with each other using vehicle time slots. The information transmitted by the in-vehicle communication device 3 includes vehicle information about its current position. For this reason, the position of the vehicle-mounted communication device 3 (vehicle) can be grasped by the roadside communication device 2 receiving (intercepting) the vehicle information. That is, it is possible to grasp that the wireless information transmitted from the position of the in-vehicle communication device 3 has been received.

  The information transmitted by the in-vehicle communication device 3 is also transmitted by being divided into a plurality of packets, and the packet length may be different from the packet length of the packet transmitted by the roadside communication device 2, for example, the in-vehicle communication device Assume that the packet length of the packet transmitted from 3 is fixed to 200 bytes. In this case, the packet arrival rate for the same packet length as the packet length of the in-vehicle communication device 3 is obtained in advance, and the storage unit 24 includes information indicating the relationship (relation at the start of operation) in the reference information. I remember it.

  As shown in FIG. 9, for example, at a position 25 m away from the roadside communication device 2, although the roadside communication device 2 can receive packets from 10 in-vehicle communication devices 3, these When 10 in-vehicle communication devices 3 are 50 m away from the roadside communication device 2, when the roadside communication device 2 can receive packets from 9 instead of all 10 devices, a position 50 m away from the roadside communication device 2 The packet arrival rate at can be estimated to be 90%.

As described above, when the roadside communication device 2 acquires transmission information from the in-vehicle communication device 3 at various reception positions, the packet length when the packet length is 200 bytes and the packet with the packet length are transmitted. In this case, the correction unit 23F can obtain the relationship with the packet arrival rate (the relationship during system operation).
Therefore, the correction unit 23F compares the information indicating the relationship during the system operation with the reference information including the information indicating the relationship at the start of operation stored in the storage unit 23, and increases or decreases the wireless communication success rate. Get the trend.

Since the tendency of the increase / decrease in the wireless communication success rate is considered to be common with packet communication with other packet lengths within the same communication area A, the correcting unit 23F, for example, uses FIG. The reference information shown in b) is corrected.
That is, the correction unit 23F corrects the wireless communication success rate illustrated in FIG. 6B according to the change tendency of the communication environment estimated by intercepting the transmission packet from the in-vehicle communication device 3.
Thus, even if the packet arrival rate changes due to the change in the communication environment of the communication area A, the reference information can be corrected according to the change, and the determination unit 23E determines the unit packet length. Accuracy can be maintained.

[In-vehicle communication device]
Returning to FIG. 3, the in-vehicle communication device 3 is configured to be able to wirelessly communicate with the roadside communication device 2 (communication control device). For this purpose, the in-vehicle communication device 3 is connected to an antenna 30 for wireless communication, and the provided information D1 and A communication unit 31 that receives information including slot information D2 and the like, a control unit 32 including a processor that performs communication control on the communication unit 31, and a storage device such as a ROM and a RAM connected to the control unit 32 And a storage unit 33.
The storage unit 33 stores a computer program for communication control executed by the control unit 32, communication device IDs of the communication devices 2 and 3, and the like.

  The control unit 32 of the in-vehicle communication device 3 includes a communication control unit 32A, a transmission unit 32B, and a restoration unit 32C as functional units achieved by executing the computer program.

Based on the slot information D2 directly received from the roadside communication device 2 or the slot information D2 notified from the other vehicle-mounted communication device 3, the communication control unit 32A performs the roadside time slot Ta and the vehicle-mounted time slot Tb (see FIG. 4) and has a function of controlling execution and stop of its own wireless transmission.
Further, in the in-vehicle time slot Tb, the communication control unit 32A can cause the communication unit 31 to perform wireless communication based on the carrier sense method for inter-vehicle communication, and the time-division multiplexing method with the roadside communication device 2 It does not have a communication control function.
Therefore, the communication control unit 32A always senses the reception level of the predetermined carrier frequency, and does not perform wireless transmission when the value is equal to or higher than a certain threshold value, and performs wireless transmission only when the value is less than the threshold value. To do.

Further, the communication control unit 32 </ b> A can wirelessly transmit vehicle information including the current position, speed, direction, and the like of the vehicle 5 (the in-vehicle communication device 3) by broadcast to the outside via the communication unit 31. The position and direction of the vehicle 5 are usually information autonomously measured by sensors on the vehicle 5 side such as GPS, but may be acquired from the infrastructure side such as an optical beacon. The speed is information based on a speed sensor of the vehicle 5.
The transmission unit 32B has a function of notifying (transferring) the slot information D2 and the provision information D1 received by the communication unit 31 to the other mobile communication devices 3 via the communication unit 31. Yes.

  The communication unit 31 receives vehicle information about the speed and position of the vehicle 5 transmitted by the other vehicle 5, and the provision information D1 and the slot information D2 transmitted by the roadside communication device 2. When the communication unit 31 receives these pieces of information, the communication control unit 32A can execute processing for safe driving support control based on these pieces of information. That is, when the in-vehicle communication device 3 receives such information, based on the information, the in-vehicle communication device 3 performs a process for safe driving support control for avoiding a right-right collision or a head-on collision, etc. This is performed in cooperation with the mechanism of the vehicle 5.

  As will be described later, when one or both of the high-frequency update information and the low-frequency update information are divided and assigned for each packet, the communication unit 31 divides the high-frequency update information into pieces. When the communication unit 31 receives the division information, the restoration unit 32C uses the original high-frequency update information and the original low-frequency update information. It has a function to restore to frequency update information.

[Specific example of information allocation by the information allocation unit]
FIG. 7 is an explanatory diagram for explaining a transmission packet in the roadside time slot Ta (see FIG. 4) of the roadside communication device 2 (master device R1). The provided information D1 transmitted in the roadside time slot Ta includes the high-frequency update information and the low-frequency update information. The classification between the high-frequency update information and the low-frequency update information is performed by the information classification unit 23C as described above.
In FIG. 7, the high-frequency update information is indicated as “high”, and the low-frequency update information is indicated as “low”.

When the high-frequency update information and the low-frequency update information are classified by the information classification unit 23C, the information allocation unit 23D first assigns the high-frequency update information to the packet with priority over the low-frequency update information.
In performing this assignment process, based on a predetermined decision logic, the decision unit 23E is a unit packet length L (see FIG. 7), which is a unit for dividing the provision information D1 transmitted in the roadside time slot Ta into a plurality of packets. ). This determination is made based on the total data length of the provision information D1 and the reference information stored in the storage unit 24.
In FIG. 7, by determining the unit packet length L, the provision information D1 transmitted in the roadside time slot Ta is divided into three. The determination logic for determining the unit packet length L will be described later.

When the unit packet length L is determined, the information allocation unit 23D divides the information (high frequency update information and low frequency update information) transmitted in the roadside time slot Ta for each unit packet length L.
That is, in the case of FIG. 7, since the total data length of the high frequency update information is larger than the unit packet length L, the high frequency update information includes the information “high (1/2)” contained in the first packet P1. ”And“ high (2/2) ”. “High (½)” in which the packet length is the unit packet length L is assigned to the first packet P1. Then, the remaining “high (2/2)” is allocated to the second packet P2. In this way, high-frequency update information is first assigned to packets with priority.

Since the second packet P2 still has a margin with respect to the unit packet length L, “low (1/2)” is divided so that the margin becomes a part, and the packet P2 Also, “low (1/2)” which is the part of the low-frequency update information is also assigned. The remaining “low (2/2)” is allocated to the packet P3.
As described above, the low-frequency update information is divided and assigned to the remainder of the packets in the roadside time slot Ta.

In this embodiment, since high-frequency update information is assigned to packets with priority, the amount of high-frequency update information is large, and there is no room for transmitting low-frequency update information in the time slot Ta for the roadside. Only the high-frequency update information may be transmitted in the roadside time slot Ta. In this case, the low-frequency update information that should have been transmitted in the roadside time slot Ta may be transmitted in another (later) roadside time slot Ta.
According to this embodiment, since each packet is divided into a certain unit packet length L, the in-vehicle communication device 3 that has received these slots can be easily processed without being affected by the packet length at the MAC layer level, for example. .

[About decision logic]
The unit packet length L is determined by the determination unit 23E based on the total data length of the provision information D1 and the reference information (see FIG. 6) stored in the storage unit 24.
That is, as shown in FIG. 6 (b), the reference information includes packets when packets of a plurality of types (three types in the example) of packet length (500 bytes, 750 bytes, 1500 bytes) are transmitted. Information on the arrival rate is included. Therefore, when the determination unit 23E transmits the provision information D1 by dividing each of the packet lengths, the wireless communication success rate in units of the provision information D1 (units of roadside time slots Ta) is included in the packet lengths. A process of determining the highest packet length as a unit packet length is performed. The wireless communication success rate in units of the provision information D1 is a total of packet arrival rates, and will be described below as a total packet arrival rate.

An upper limit is set for the unit packet length L to be determined. For example, the maximum packet length (maximum data length) is set to 1500 bytes from a practical viewpoint.
Further, the unit packet length L can be of two types, that is, a case where the high frequency update information is divided and a case where the low frequency update information is divided, and these may be different values.

The determination process of the unit packet length L will be specifically described.
Assume that the total data length of the provided information D1 is 1500 bytes. When this provision information D1 is divided by a packet length of 500 bytes, it is divided into three. In this case, according to FIG. 6 (b), since the packet arrival rate of the single packet in the vehicle-mounted communication device 3 is 0.95, all the vehicle-mounted communication devices 3 of the provided information D1 to be transmitted in three divisions. The total packet arrival rate is 0.95 × 0.95 × 0.95 = 0.86 (see FIG. 6C).

  On the other hand, when the provided information D1 is divided into two parts with a packet length of 750 bytes, the total packet arrival rate is 0.9 × 0.9 = 0.81. When the packet length is 1500 bytes, the total packet arrival rate is 0. .8 (see FIG. 6C). Thus, “(total packet arrival rate) = (packet arrival rate) ^ (number of divisions)”.

  From the above, the packet length with the highest total packet arrival rate is determined as the unit packet length L that is a unit for actual division. In the case of FIG. 6C, 500 bytes is determined as the unit packet length L, and it is determined to be divided into three.

When the unit packet length L is shortened and the number of divisions is increased, in FIG. 7, the DIFS (distributed inter frame space) also increases, and the road side time slot Ta may not be effectively used for communication. Therefore, in this embodiment, it is preferable that the determination of the unit packet length L by the determination unit 23E satisfies the following condition.
That is, the unit packet length is set so that the time required to transmit the provision information D1 divided by the unit packet length L falls within the roadside time slot Ta having the specified slot length. L is determined.

More specifically, the number of divisions based on the unit packet length L must satisfy the condition of the following formula <1>.
<1> (number of divisions + 1) × (DIFS) + (total number of transmission times in each packet) <(slot length ΔTL of road time slot Ta)
According to this formula <1>, it is possible to prevent the DIFS from increasing and not being able to fit within the constant slot length ΔTL.

As described above, the provision information D1 includes high-frequency update information and low-frequency update information. The high-frequency update information is information that should be acquired with higher probability by the in-vehicle communication device 3 existing in the communication area A than the low-frequency update information.
Here, as shown in FIG. 6 (c), as a criterion for determining the unit packet length L, a threshold value α indicating a minimum criterion for the total packet arrival rate is further set. In this case, as described above, even if the packet length has the highest total packet arrival rate, if the total packet arrival rate does not exceed the threshold value α, the determination unit 23E determines the packet length as the unit packet length L. Instead, the number of divisions is further increased to increase the packet arrival rate.

Therefore, since the provided information D1 includes information that should be acquired by the surrounding in-vehicle communication device 3 with high probability and other information, the determination unit 23E determines the reference for determining the unit packet length L. In order to make it differ according to the type of the provided information D1, two types of the threshold value α are set.
For example, when only high-frequency update information is transmitted in a certain time slot for roadside Ta, a higher value is selected as the threshold value α, and when only low-frequency update information is transmitted, the threshold value α is set to a lower value. The threshold α corresponding to the type of information is selected and the unit packet length L is determined by the same processing as in the above embodiment.

Moreover, FIG. 8 is explanatory drawing explaining the other example (3rd Example) of the reference information which the memory | storage part 24 has memorize | stored.
In this embodiment, the reference information stored in the storage unit 24 includes information for each communication parameter that affects the communication characteristics of the roadside communication device 2.
That is, the control unit 23 of the roadside communication device 2 is configured to change the communication parameters such as the modulation scheme and the code error rate according to the communication environment and transmit the provision information D1. Accordingly, the storage unit 24 stores reference information for each communication parameter so that the determination unit 23E can divide the provision information D1 according to the change of the communication parameter and transmit the packet. Yes. In FIG. 8, reference information for each modulation method is stored.

  Then, for example, when the modulation scheme in the roadside communication device 2 is changed, reference information corresponding to the changed modulation scheme is selected by the determination unit 23E, and the unit is processed by the same processing as in the above embodiment according to the reference information. The packet length L is determined.

As described above, according to the roadside communication device 2 having the function of the communication control device of the present invention, the total data length of the provision information D1 transmitted in the roadside time slot Ta is stored in the storage unit 24. Based on the reference information, a unit packet length L that is a unit for dividing the provided information D1 into a plurality of packets can be determined. Since the unit packet length is obtained in consideration of the wireless communication success rate, if the provided information D1 is divided and transmitted by dividing the unit packet length, a predetermined wireless communication success rate is secured. Is possible.
Thus, the best division method is determined according to the communication environment of the communication area A, and packet transmission is performed by this division service, so that communication performance is improved regardless of the installation environment and communication environment of the roadside communication device 2. Is possible.

  In addition, since the communication performance can be enhanced on the side of the roadside communication device 2 having each function of the communication control device, the communication reliability can be improved even with the in-vehicle communication device 3 that does not have the reception performance improvement function. Can be increased. As a result, the in-vehicle communication device 3 can acquire the provision information D1, and the acquisition probability can be improved, which can be used for traffic safety support.

The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, 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.
FIG. 6 illustrates the case where three types of packet lengths of 500 bytes, 750 bytes, and 1500 bytes are employed to determine the optimum unit packet length. However, these values are examples, and three or more types of packet lengths are used. Reference information about the packet length may be used.

  FIG. 6B shows reference information in which the relationship between the packet length and the packet arrival rate is continuous according to the change in the signal reception strength. In order to acquire such reference information in advance, it is not necessary to acquire all the relationships every time the signal reception intensity increases, for example, by 1. For example, a plurality of specific points are acquired, and other points are acquired from the acquired information. Reference information may be acquired by estimation.

2: roadside communication device, 3: in-vehicle communication device (mobile communication device), 23: control unit, 23A: slot allocation unit, 23B: notification unit, 23C: information classification unit, 23D: information allocation unit, 23E: determination unit, 23F: Correction unit, 24: Storage unit, L: Unit packet length, Ta: Roadside time slot, Tb: In-vehicle time slot

Claims (8)

A communication control device for transmitting transmission information to be transmitted in a time slot for a roadside where a roadside communication device performs wireless transmission, and dividing the information into a plurality of packets and transmitting from the roadside communication device,
A storage unit that stores reference information indicating a relationship between a packet length and a wireless communication success rate when the packet is transmitted in a packet of the packet length;
A communication control device comprising: a determination unit that determines a unit packet length that is a unit for dividing the transmission information into a plurality of packets based on a data length of the transmission information and the reference information . The reference information includes information on a wireless communication success rate in units of packets when the transmission information is divided and transmitted by a plurality of types of packet lengths.
When the transmission unit divides the transmission information by each of the plurality of types of packet lengths and transmits the packet, the wireless communication success rate in the transmission information unit is the highest among the plurality of types of packet lengths. The communication control apparatus according to claim 1, wherein a packet length is determined as the unit packet length.   The determining unit determines the unit packet length so that a time required for transmitting the transmission information divided by the unit packet length is within the time slot for the roadside having a prescribed slot length. The communication control device according to claim 1, wherein the communication control device is determined.   The communication control apparatus according to any one of claims 1 to 3, wherein the wireless communication success rate is associated with information on a relative position between the roadside communication device and the reception position.   The communication control device according to any one of claims 1 to 4, wherein the storage unit stores the reference information for each communication parameter that affects communication characteristics of the roadside communication device.   A correction unit that acquires a communication environment of the communication area based on transmission signals between a plurality of other wireless communication devices existing in the communication area of the roadside communication device, and corrects the reference information based on the communication environment. The communication control device according to any one of claims 1 to 5, further comprising:   The communication control apparatus according to any one of claims 1 to 6, wherein the determination unit changes a reference for determining the unit packet length according to a type of the transmission information.   The roadside communication apparatus provided with the communication control apparatus as described in any one of Claims 1-7.

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