JP2007318666A - Wireless communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system in which information frames of adjacent groups can be prevented from colliding with each other and thereby causing communication blackout. <P>SOLUTION: There is provided a radio communication system in which a plurality of groups are formed as constituted by enabling radio communications between a plurality of mobile objects. In each group, one mobile object is defined as a mobile object in a state of transmitting a control frame, and the remaining mobile objects are defined as the mobile objects in a state of not transmitting a control frame. The mobile object of each group in the state of transmitting the control frame receives the control frames transmitted from the mobile objects in the state of not transmitting the control frame of the other group existing about, and performs synchronization within its own group. Then, the mobile object of each group in the state of transmitting the control frame transmits the control frames to the mobile objects in the state of not transmitting each control frame of its own group, and thereby sets transmitting timing of information frame of the mobile object in the state of not transmitting each control frame. In the radio communication system, a communication capability of the mobile object in the state of transmitting the control frame is set at a lower level than that of the mobile object in the state of not transmitting the control frame. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless communication system and a mobile body thereof, and more particularly to a wireless communication system in which a plurality of groups configured by performing wireless communication between a plurality of mobile bodies are formed and the mobile body thereof.

  2. Description of the Related Art In recent years, road traffic systems have been developed that form a platoon by electronically connecting self-driving vehicles through inter-vehicle communication and respond flexibly and quickly to fluctuations in passenger demand.

In Patent Document 1, one vehicle in a group is assigned to a beacon station, and the remaining vehicles are assigned to client stations. The beacon station synchronizes with the communication timing of other surrounding groups, and the client station of its own group. A wireless communication system for controlling the communication timing is described.
JP 2005-223509 A

  FIG. 1 shows a state where groups 1 and 2 exist in a conventional wireless communication system. Group 1 is composed of beacon station B1 and client stations S1-1 and S1-2 existing within a wireless communication range indicated by a broken circle, and group 2 is within a wireless communication area indicated by beacon station B2 and a broken circle. Are comprised of client stations S2-1 and S2-2.

  In this case, since the groups 1 and 2 are sufficiently separated from each other, the client stations S1-1 and S1-2 of the group 1 do not receive the beacon frame transmitted from the beacon station B2 of the group 2. For this reason, the networks of the groups 1 and 2 cannot synchronize with each other, and the beacon frame and data frame transmitted by the beacon station and the data frame transmitted by the client station are transmitted asynchronously between the networks.

  FIG. 2 shows a state in which group 3 is inserted between groups 1 and 2. Since the beacon stations B2 and B3 of the groups 2 and 3 are within the radio communication range of each other, the networks of the groups 2 and 3 are synchronized, and the beacon frames of the groups 1 and 2 are shown in FIG. There is no collision between B and data frame D.

  However, since the beacon stations B1 and B3 of the groups 1 and 3 are out of each other's wireless communication range, the networks of the groups 1 and 3 are asynchronous. In this case, since the client station S3-2 of the group 3 is within the wireless communication range of the beacon stations B1 and B3, the client station S3 of the group 3 is located at the position of the client station S3-2 as shown in FIG. There may be a collision between the data frame D transmitted by -1 and the data frame D transmitted by the beacon station B1 of group 1. In this case, the client station S3-2 cannot normally receive the frame. Although the groups 1 and 3 transmit frames asynchronously, each group transmits a frame at the same cycle. Therefore, the data frame collision occurs every time and the client station S3-2 is in a communication interruption state. There was a problem of becoming.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a radio communication system and a mobile unit thereof that can prevent an information frame of an adjacent group from colliding to cause a communication interruption state. .

The wireless communication system of the present invention is a wireless communication system in which a plurality of groups configured by performing wireless communication between a plurality of mobile bodies are formed, and each group transmits a control frame to one mobile body. The remaining mobile units are mobile units that do not transmit control frames, and the mobile units that transmit control frames for each group are mobile units that transmit control frames for other groups around them. Of the mobile unit in a state in which the control frame transmitted from the mobile station is received, the synchronization of the own group is performed, and the control frame is transmitted to the mobile unit in the state where the control frame is not transmitted in the own group. In a wireless communication system for setting transmission timing of an information frame,
By setting the communication capability of a mobile unit that does not transmit a control frame to be lower than the communication capability of a mobile unit that is transmitting a control frame, information frames of adjacent groups collide, resulting in a communication disruption state. Can be prevented.

In the wireless communication system,
The communication capability is reception sensitivity and transmission power, and the reception sensitivity and transmission power of a mobile body that does not transmit the control frame are set lower than the reception sensitivity and transmission power of the mobile body that transmits the control frame. be able to.

In the wireless communication system,
The mobile unit that does not transmit the control frame has an attenuator between the wireless communication device and the antenna,
The reception sensitivity can be set by setting the attenuation amount of the attenuator according to the distance from the moving body in a state of transmitting the control frame.

The mobile body of the present invention is a mobile body that transmits / receives information to / from another mobile body by wireless communication, and includes means for switching between a state in which a control frame for synchronizing with the other mobile body is transmitted and a state in which the control frame is not transmitted. In the moving body,
By setting the communication capability when the control frame is not transmitted to be lower than the communication capability when the control frame is transmitted, the information frames of adjacent groups collide and the communication is interrupted. Can be prevented.

  ADVANTAGE OF THE INVENTION According to this invention, it can prevent that the information frame of an adjacent group collides and it will be in a communication interruption state.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Vehicles applied to wireless communication systems>
FIG. 4 shows a configuration diagram of an embodiment of a vehicle applied to the wireless communication system of the present invention. In the figure, each of vehicles 10A and 10B is provided with a wireless communication device 11 and a vehicle control device 12. The wireless communication device 11 of each vehicle performs information communication with the wireless communication device 11 of another vehicle using the antenna 13. The content of the data communication is, for example, control information for the vehicles 10A and 10B to travel in groups.

  The vehicle control device 12 is supplied with the control information received by the wireless communication device 11 to control the drive system and the control system of the vehicle, and generates control information for other vehicles and transmits the control information to the wireless communication device 11. .

  An attenuator 14 is provided between the wireless communication device 11 and the antenna 13. In a client station vehicle, the wireless communication device 11 uses the attenuator 14 to control transmission / reception signal attenuation, that is, reception sensitivity and transmission power attenuation control. It is carried out. In FIG. 4, a beacon station that is a mobile body in a state where the vehicle 10A transmits a control frame and a client station that is a mobile body in a state where the vehicle 10B does not transmit a control frame are set.

<One Embodiment of Wireless Communication Device>
FIG. 5 shows a configuration diagram of an embodiment of the wireless communication device 11 mounted on each vehicle in the wireless communication system of the present invention. The wireless communication apparatus has the same configuration in the beacon station and the client station. In the figure, the wireless communication device 11 includes a wireless communication unit 22, a control unit 23, a memory 24, and a vehicle interface 25.

  The wireless communication unit 22 transmits / receives a beacon frame as a control frame and a data frame as an information frame using the antenna 13 according to a predetermined communication procedure under the control of the control unit 23. In the client station vehicle, the attenuation of the attenuator 14 with respect to the transmission / reception signal is varied under the control of the controller 23. In the beacon station vehicle, the attenuator 14 does not attenuate the transmission / reception signal.

  The control unit 23 includes a microcomputer including a CPU 23a, a ROM 23b for storing programs, a RAM 23c serving as a work area, an internal clock 23d, and peripheral circuits (not shown), and controls the entire apparatus, compares group IDs, and gives priority. Processing such as determination of the degree, correction of the internal clock 23d, time synchronization with other groups, attenuation amount control of the attenuator, and the like are executed. The ROM 23b stores the above control program and communication protocol.

  The memory 24 stores beacon frames and data frames received via the wireless communication unit 22, and stores vehicle data (vehicle speed, direction of travel, current position, etc.) acquired via the vehicle interface 25.

  The vehicle interface 25 converts the vehicle data supplied from the vehicle into wireless communication data and sends it to the memory 24, and sends the data in the data frame read from the memory 24 to the vehicle side as vehicle data.

<Vehicle-to-vehicle communication>
Inter-vehicle communication by vehicles in each group will be described. Each group acquires a communication channel using a beacon frame as shown in FIG. After receiving the beacon frame having the group ID of the own device, the wireless communication device of each group transmits the data frame during the data slot period assigned to each wireless communication device.

  The beacon frame and the data frame are composed of a header part and a data part as shown in FIG. In the header part is a frame type indicating whether it is a beacon frame or a data frame, a beacon slot at the time of transmission, a destination address, a source address, a frame sequence number, a sequence number at the time of retransmission, a subgroup ID, a frame data length, a frame check code, etc. Is provided.

  In the case of a data frame that is an information frame, vehicle data such as the vehicle speed, the direction of travel, and the current position are set in the data portion. In the case of a beacon frame that is a control frame, the time (the time of the internal clock of the beacon station), the beacon transmission interval, the period during which the own group can communicate, the group ID of the beacon station, the subgroup ID of the beacon station, and other various controls Data is set.

  Which wireless communication device in the group is a beacon station is determined by the priority of the subgroup ID of the wireless communication device. When the wireless communication device in the group receives the beacon frame of the own group, the time of the beacon frame is set in the internal clock of the own device and the time is set. Thereby, it is possible to synchronize the time of the wireless communication devices belonging to the group and to predict the reception time of the next beacon frame.

  The wireless communication device of the beacon station of each group compares the group ID of the received beacon frame with the group ID of the own device, and when the priority of the group ID of the received beacon frame is high, the time of the received beacon frame is The time is set by setting the internal clock, and when it is low, the scheduled time for transmitting the next beacon frame is calculated. Next, the communication allocation time of the group of the own apparatus is calculated from the time of the received beacon frame and the group ID, and the beacon station of each group calculates the scheduled time for transmitting the beacon frame next from the calculated value. As a result, time synchronization of each group is performed, and communication time allocation of each group is prevented from overlapping.

<One Embodiment of Wireless Communication Device>
FIG. 8 shows a flowchart of the reception sensitivity control process executed by the control unit 23 in the client station vehicle.

  In the figure, the current position of the vehicle of the beacon station is extracted from the beacon frame received in step S11. Next, in step S12, an inter-vehicle distance r between the own vehicle and the vehicle of the beacon station is calculated. In step S 13, the radio wave propagation loss Los corresponding to the inter-vehicle distance r is calculated by the equation (1), and this is set in the attenuator 14 as the attenuation amount of the attenuator 14.

Los = 20 × log (4πr / λ) (1)
Where λ is the wavelength of the radio wave (= speed of light / frequency of the radio wave).

  Here, as shown in FIG. 9, when the beacon station B1 and the client station S1 are separated by a distance r, the reception area of the beacon station B1 is a circle with a radius L centered on the beacon station B1 (a circle indicated by a solid line). ) If the reception sensitivity is not attenuated at the client station S1, the reception area of the client station S1 is a circle with a radius L (circle indicated by a broken line) centered on the client station S1.

  In this embodiment, by setting the radio wave propagation loss Los corresponding to the inter-vehicle distance r to the attenuator 14 as an attenuation amount, the reception area of the client station S1 is a circle with a radius (Lr) centered on the client station S1 (one point). A circle indicated by a chain line) and inscribed in the reception area (circle indicated by a solid line) of the beacon station B1.

  As shown in FIG. 10, even when the beacon station B1 and the client stations S1, S2, and S3 form a group A and the group B exists adjacent to the group A, the present invention similarly applies to the client station S1. , S2 and S3 are inscribed in the reception area of the beacon station B1. For comparison, FIG. 11 shows reception areas of conventional client stations S1, S2, and S3 that do not control the attenuator.

  Thereby, the client station S1 does not receive a signal from the beacon station B2 of the group B existing outside the reception area of the beacon station B1. For this reason, it is possible to avoid a collision between a beacon frame or data frame transmitted from its own group and a beacon frame or data frame transmitted from another group at each client station S1, S2, S3.

  In the above-described embodiment, the communication capacity of the client station is set lower than the communication capacity of the beacon station by variably setting the attenuation amount of the transmission / reception signal of the client station according to the inter-vehicle distance r with the beacon station. If the communication capability of the client station is set lower than the communication capability of the beacon station by variably setting at least the attenuation of the received signal of the client station according to the inter-vehicle distance r with the beacon station, the client station S1 A signal from the beacon station B2 of the group B existing outside the reception area of the station B1 is not received.

  However, if the attenuation of the transmission / reception signal is variably set according to the distance r between the beacon station and the beacon station, it is possible to prevent the occurrence of data frame collisions in other groups of beacon stations and client stations due to radio waves transmitted from the client station. Is more effective.

  Furthermore, the communication capacity of the client station may be set lower than the communication capacity of the beacon station by variably setting the amplification amount of the transmission / reception signal of the beacon station according to the inter-vehicle distance r with the beacon station. It is not limited to.

It is a figure for demonstrating the conventional radio | wireless communications system. It is a figure for demonstrating the conventional radio | wireless communications system. It is a figure which shows the transmission timing of the conventional radio | wireless communications system. It is a block diagram of one Embodiment of the vehicle applied to the radio | wireless communications system of this invention. It is a block diagram of one Embodiment of the radio | wireless communication apparatus mounted in each vehicle by the radio | wireless communications system of this invention. It is a figure which shows the communication timing of a beacon frame and a data frame. It is a figure which shows a frame format. It is a flowchart of reception sensitivity control processing. It is a figure which shows the reception area of a beacon station, and the reception area of a client station. It is a figure which shows the reception area of the beacon station of this invention, and the reception area of a client station. It is a figure which shows the reception area of the conventional beacon station, and the reception area of a client station.

Explanation of symbols

10A, 10B Vehicle 11 Wireless communication unit 12 Vehicle control device 13 Antenna 14 Attenuator 22 Wireless communication unit 23 Control unit 24 Memory 25 Vehicle interface

Claims (4)

A wireless communication system in which a plurality of groups configured by performing wireless communication between a plurality of mobile bodies is formed, and in each group, one mobile body is a mobile body in a state of transmitting a control frame, and the remaining mobile The mobile unit that is not transmitting control frames is a mobile unit that is transmitting control frames of each group, and the control unit that is transmitting the control frames of other groups around it receives control frames transmitted from other groups. Then, synchronize the own group, and transmit the control frame to the mobile body that does not transmit the control frames of the own group, and set the transmission timing of the information frame of the mobile body that does not transmit the control frames. In a wireless communication system,
A wireless communication system, characterized in that a communication capacity of a mobile body that does not transmit a control frame is set lower than a communication capacity of the mobile body that transmits a control frame. The wireless communication system according to claim 1, wherein
The communication capability is reception sensitivity and transmission power, and the reception sensitivity and transmission power of a mobile body that does not transmit the control frame are set lower than the reception sensitivity and transmission power of the mobile body that transmits the control frame. A wireless communication system. The wireless communication system according to claim 2, wherein
The mobile unit that does not transmit the control frame has an attenuator between the wireless communication device and the antenna,
A wireless communication system, wherein the reception sensitivity is set by setting an attenuation amount of the attenuator in accordance with a distance from a moving body in a state of transmitting the control frame. In a mobile that transmits and receives information by wireless communication with another mobile, and has a means for switching between a state of transmitting a control frame for synchronizing with the other mobile and a state of not transmitting,
A mobile unit characterized in that the communication capability when the control frame is not transmitted is set lower than the communication capability when the control frame is transmitted.

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