JP4643866B2 - Wireless communication system and in-vehicle wireless terminal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless communication technology between vehicles in a mobile body, for example, a road traffic system, and an in-vehicle wireless terminal.
[0002]
[Prior art]
As a communication environment in which wireless communication is performed between a plurality of networks and within the same network without a base station, for example, there is a wireless communication system between vehicles, and contention is performed to perform communication between vehicles without using a base station. It is common to adopt a method.
[0003]
[Problems to be solved by the invention]
The possibility of wireless communication between mobile bodies (vehicles) by developing wireless communication technology between mobile bodies is highly expected to be applied to, for example, road traffic systems and railway vehicle systems. Specifically, reporting the speed and position of the preceding vehicle on the same route to the following vehicle and obtaining the abnormality information of the other vehicle is very valuable information for vehicle control during traveling.
[0004]
If the contention method is introduced as it is for communication between vehicles without using a base station, there is a problem that it becomes impossible to design a system in consideration of the number of vehicles and the operation mode.
[0005]
On the other hand, as a communication means between vehicles, it is desired to construct a wireless system that can be easily used without requiring an advanced backbone such as a device that performs wireless communication control with each vehicle on the track or road side. In the construction of such a wireless communication system, since it is wireless communication, a wireless communication system that considers communication reliability, effective use of frequency, hidden terminal problem, securing of communication channel, etc. must be taken into consideration. There is a demand in wireless communication technology that it must not.
[0006]
As a technique for solving such a problem, the applicant of the present invention filed on October 20, 1999 (Japanese Patent Application No. 11-298386), that is, between vehicles disclosed in Japanese Patent Application Laid-Open No. 2001-118191. There is a wireless communication system.
[0007]
In the wireless communication system disclosed in the above publication, for example, in the inter-vehicle wireless communication system 200 shown in FIG. 10, the vehicles 1-1,. The wireless communication devices of the vehicles belonging to the vehicle groups 1, 2, 3,... Composed of the vehicles 3-1, 3-2 are in a group called a beacon (reference signal) control frame (beacon packet). Each data slot period in which each wireless communication device (slave station) in the group is assigned by acquiring a communication channel using a control frame having a function of assigning a communication channel for each wireless communication device. In this case, only certain wireless communication devices have the right to transmit data frames, and data frame (data packet) collisions with other wireless communication devices occur. It is configured so as not.
[0008]
Further, as a protocol, a unit including a time-divided beacon period 91 and a data period 92 as shown in the explanatory diagram of the communication protocol of the wireless communication system using the beacon shown in FIG. It is used as one channel (FIG. 11 (a)). The beacon period and the data period are each composed of a plurality of slots 93 as shown in FIG.
[0009]
Here, when it is desired to perform communication by acquiring a channel within the same network (that is, within the same group), one beacon station existing in each network randomly selects one slot from the beacon period. The selected slot is set as a transmission slot, and preparations for transmitting a beacon packet are made.
[0010]
In a slot not selected as a transmission slot, a reception operation is performed to check whether a beacon station of another network has transmitted a beacon packet. Here, if the beacon station of the own network receives a beacon of another network before transmitting a beacon packet, this channel becomes a channel of another network. On the other hand, if a beacon packet can be transmitted before receiving a beacon of another network, this channel becomes a channel of its own network. That is, if a channel can be acquired by transmitting or receiving a beacon of its own network, data communication is performed in the data period 92 following the beacon period 91.
[0011]
In the above data packet transmission method, each slot in the data period 92 is individually assigned to each of the beacon station and the slave station existing in the network, so that the data packets transmitted by the beacon station and the slave station do not collide. . That is, in the wireless communication system disclosed in the above publication, the wireless communication timing between the different groups is executed without collision.
[0012]
However, when communication is interrupted in the same group due to shielding or the like, a subgroup is formed, and this overlap occurs when the wireless communication areas 10-A and 10-B of each subgroup partially overlap. There was a problem that the influence on vehicles existing in the area was not fully considered.
[0013]
For example, as shown in the example of FIG. 3, when the vehicle group 10 is traveling, the vehicle 13 is divided into the subgroup A including the vehicles 11, 12, and 13 and the subgroup B including the vehicles 14 and 15. Despite being in a position where both wireless communications can be received, according to the wireless channel procedure by the wireless communication system disclosed in the above publication, the beacon transmission vehicles of subgroups A and B receive each other's wireless communications. Since the synchronization control of the wireless device is not performed because it is not possible, the transmission timing as shown in FIG. 4, that is, the vehicle 11 of the subgroup A and the vehicle 14 of the subgroup B are transmitting beacons. There is.
[0014]
In such a case, since the vehicle 13 located in the overlapping area of the subgroups A and B can receive the beacons of both subgroups, the beacons collide and the beacon reception fails, and the wireless communication procedure is not executed. It will be.
[0015]
That is, according to the communication procedure disclosed in the above publication, as long as the wireless channel is free, a beacon is transmitted to try to acquire the communication channel, so this state continues continuously, and the overlapping areas of subgroups A and B In the vehicle 13 located in the position, both beacons collide, and there is a problem that the channel acquisition of the own group cannot be confirmed.
[0016]
Further, since the beacon transmission vehicles of the subgroups A and B cannot confirm each other, the avoidance means is not executed, and the vehicle 13 located in the overlapping area of the subgroups A and B cannot be communicated. There was a problem that it included sex.
[0017]
The present invention has been made to solve the above-described problems, and even when subgroups are configured in the same vehicle group, collision of wireless communication of vehicles in the group is avoided and effective use of wireless communication channels is achieved. An object of the present invention is to provide a wireless communication system and an in-vehicle wireless terminal that can realize the above.
[0018]
[Means for Solving the Problems]
In order to solve the above problems, a wireless communication system according to a first aspect of the present invention is a wireless communication system in which there is at least one group that performs wireless communication among a plurality of wireless terminals, and one of each group A beacon signal is generated with a wireless terminal as a beacon station, and other wireless terminals in the same group are in a specific data slot assigned to each wireless terminal in a data frame following the beacon signal emitted by the beacon station. In a wireless communication system having a communication protocol for transmission, When a wireless terminal in which the wireless link is disconnected in each group is detected and a wireless terminal in which the wireless link is disconnected is detected, a subgroup is formed in the group. A process of determining, a process of setting one wireless terminal in each subgroup as a beacon station when the subgroup is formed, and Each wireless terminal set in the beacon station of each subgroup Calculate the number of pauses at random And Stop beacon signal generation for the number of times equivalent to the calculated number of pauses. And a step of avoiding collision of beacon signals emitted by each beacon station of each sub-loop at a wireless terminal that has belonged to each sub-group simultaneously with the formation of the sub-group. It is characterized by that.
[0020]
The second 2 The invention of the above 1's In the wireless communication system of the invention, prior to the step of determining whether or not a subgroup has been formed, the method includes a step of detecting the number of pauses by a group other than the own group. The step of generating a beacon signal from a beacon station includes a step of adding the number of pauses by a group other than the own group detected to the number of pauses calculated at random, and the number of pauses by a group other than the own group is added. The generation of the beacon signal is paused for the number of times corresponding to the number of times.
[0021]
The second 3 The invention of the first aspect Or 2 The wireless communication system according to any one of the inventions is characterized in that the wireless terminal is mounted on a mobile body.
[0022]
The second 4 The invention of the first to the above 3 In the wireless communication system of any one of the inventions, the moving body is a vehicle.
[0023]
The second 5 The in-vehicle wireless terminal of the invention is a wireless communication system in which there is at least one vehicle group that performs wireless communication between a plurality of vehicles equipped with wireless terminals.
A beacon signal is generated using a wireless terminal mounted on one vehicle in each vehicle group as a beacon station, and a wireless terminal mounted on another vehicle in the same group is after a beacon signal emitted by the beacon station. A wireless communication means having a communication procedure for transmitting in a specific data slot assigned to each wireless terminal in a subsequent data frame and a wireless link state is detected in a vehicle group to which the vehicle in which the vehicle is mounted belongs. Sub-group determination means for determining that a sub-group is formed by separating a vehicle group to which a vehicle equipped with the radio terminal belongs when a radio terminal having a broken radio link is detected; Signal collision avoidance control means for performing collision avoidance control of beacon signals between subgroups when formed, The signal collision avoidance control means includes a beacon station setting means for setting a wireless terminal mounted on one vehicle in each subgroup as a beacon station when the subgroup is formed, and the beacon station setting means The number of times of beacon signal generation of each beacon station set by the beacon station is randomly calculated, and the number of times corresponding to the number of pauses calculated by the number of times of pause calculated by the beacon stations in the subgroup Beacon signal generation that avoids collision of beacon signals emitted by each beacon station in each sub-loop at a wireless terminal that has belonged to each sub-group simultaneously with the formation of the sub-group by pausing the generation of the beacon signal Including pause control means, It is characterized by that.
[0025]
The second 6 The invention of the above 5 In the in-vehicle wireless terminal according to the present invention, it is provided with a pause number detecting means for detecting the number of pauses by a group other than the own vehicle group before the presence / absence of sub-group formation. Means for adding the number of pauses detected by the pause count detection means to the number of pauses generated by the pause count detection means, and the number of times in the subgroup corresponding to the number of times after the pause count addition detected by the pause count detection means The generation of a beacon signal by a beacon station is suspended.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
(In-vehicle wireless terminal)
FIG. 1 is a block diagram showing a configuration of an embodiment of a wireless communication device (hereinafter referred to as an in-vehicle wireless terminal) installed in each vehicle in a wireless communication system between vehicles of the present invention. A wireless communication unit 112, a control unit 113, a memory 114, and a vehicle interface 115.
[0027]
Under the control of the control unit 113, the wireless communication unit 112 receives a beacon control frame and transmits / receives a data frame via the antenna 111 according to a predetermined communication procedure (for example, the communication procedure of the wireless communication channel shown in FIG. 2). In the case where the in-vehicle wireless terminal 100 is a representative wireless communication device to be described later, transmission / reception of a beacon control frame and transmission / reception of a data frame are performed.
[0028]
The control unit 113 has a computer configuration including a CPU (or MPU) 116, a program storage memory such as a ROM 117, a RAM 118, and peripheral circuits such as an internal clock 119.
[0029]
The memory 114 stores the beacon control frame and data frame received via the wireless communication unit 112 and the vehicle data (vehicle speed, direction of travel, current position (coordinates), etc.) acquired via the vehicle interface 115. Remember me under the control of
[0030]
A CPU (or MPU) 116 executes overall control of the apparatus according to a control program recorded in the ROM 117. In addition, a beacon communication procedure with another group is executed by a communication control program recorded in the ROM 117, and a signal collision avoidance procedure (beacon station setting means, beacon pause when a subgroup occurs in the same group according to the present invention). A wireless communication procedure including a beacon communication procedure including a frequency calculation means and a beacon signal generation suspension control means is performed.
[0031]
The ROM 117 stores a control program, a communication control program including the wireless communication procedure, beacon information, various setting values, and other processing programs. The RAM 118 is used as a work memory, and when the in-vehicle wireless terminal 100 is activated, the control program stored in the ROM 117 is made resident, and the communication control program, the beacon information, etc. described above, or other processing programs are stored as appropriate. Read from the program storage memory and stay for as long as necessary for execution.
The memory 114 also controls storage of beacon control frames and data frames received via the wireless communication unit 112 and vehicle data (vehicle speed, direction of travel, current position (coordinates), etc.) acquired via the vehicle interface 115. Store under the control of the unit 113.
[0032]
The vehicle interface 115 converts vehicle data such as vehicle speed, direction of travel, current position (coordinates), and the like acquired by sensors provided in the vehicle into digital data and stores it in the memory 114 under the control of the control unit 113. Or the data read from the memory 114 is converted into a signal and sent to the vehicle side (for example, when the drive system control data is read from the memory 114, a drive system control unit (not shown) provided in the vehicle) To send).
[0033]
FIG. 2 is an explanatory diagram of the communication procedure of the wireless communication channel, and shows the intra-group wireless communication procedure when a formation is formed as shown in FIG. In this case, intra-group communication means communication between in-vehicle wireless terminals of vehicles belonging to groups 1, 2, 3, 4,... (Group 2 vehicles in this example) as shown in FIG. The period during which the channel is acquired (FIG. 2C) is shown. The communication channels of each group 1, 2, 3, 4,... Acquire a communication channel using a special control frame called a beacon (reference signal) control frame.
[0034]
This beacon control frame has a function of assigning a communication channel (slot) to each in-vehicle wireless terminal in the group (FIG. 2B). The communication channel assignment function is a data slot assigned to a wireless terminal mounted on the own vehicle wireless terminal that has received a beacon control frame having a group ID to which the wireless terminal mounted on the own vehicle belongs. This is a function indicating a reference time for calculating an allocation time for transmitting a data frame in a period of (data slot) (in the example of FIG. 2B, 10 slots slot1 to slot10).
Accordingly, each in-vehicle wireless terminal in the group has a right to transmit a data frame only to a specific in-vehicle wireless terminal in each assigned data slot period slot 1 to slot 10, so that a data frame with another in-vehicle wireless terminal No collision occurs. By using the beacon control frame in this way, it is possible to secure a communication channel and realize a data communication environment in which no collision occurs.
[0035]
FIG. 3 is a diagram showing an example of subgroups generated in the same group. FIG. 4 is an explanatory diagram of a communication collision example at the time of group separation.
[0036]
Here, if the group is not separated and the sub group is not generated while the vehicles 11 to 15 of the group 10 are traveling, the above-described wireless communication procedure of FIG. 2 is executed. However, as described above, when communication is interrupted in the same group due to a shield or the like, a subgroup is generated, and there is a partial overlap in the radio communication areas 10-A and 10-B of each subgroup. Furthermore, in the vehicle 13 existing in this overlapping area, when both beacons collide, the group channel acquisition cannot be confirmed, and the beacon transmission vehicles of the subgroups A and B confirm each other. Therefore, the avoidance means is not executed and the vehicles 13 in the overlapping areas of the subgroups A and B have a risk of being unable to communicate.
[0037]
Based on such a situation, a beacon transmission procedure when subgroups are formed in the same group will be described below.
[0038]
<Beacon transmission procedure>
FIG. 5 is a flowchart showing an embodiment of a beacon transmission procedure according to the present invention. The following steps F3 to F5 are signal collisions for avoiding a beacon signal when a subgroup occurs in the same group according to the present invention. This corresponds to the avoidance procedure (step F3 corresponds to the operation of the beacon station setting means, step F4 corresponds to the operation of calculating the number of beacon pauses, and step F5 corresponds to the operation of the beacon signal generation stop means).
[0039]
In FIG. 5, the control unit 111 executes a communication channel suspension procedure (described later: FIG. 8) for avoiding a collision with a beacon of another group when another group other than the own group exists during beacon transmission. , Get the number of pauses by neighboring groups. The communication channel procedure is included in the beacon communication procedure with the other group of the communication control program recorded in the ROM 117 described in FIG. 1, and is read from the ROM 117 and executed by the CPU 116 (step F1).
[0040]
Next, the control unit 113 determines whether or not a subgroup is formed in its own group based on information detected by the radio link state detection procedure. If a subgroup is formed, the process proceeds to step F3. If not, the process proceeds to step F6. Here, the radio link state detection procedure is included in the beacon communication procedure with the other group of the communication control program recorded in the ROM 117 described in FIG. 1, and is read from the ROM 117 by the CPU 116 and executed. In the wireless link state detection procedure, as will be described later (FIG. 9), for example, in the vehicle 11 shown in FIG. 3, the vehicle 14 and the vehicle 15 are in a state incapable of communication. And it determines with the link with the vehicle 15 having been cut | disconnected. Conversely, the wireless link information of the vehicle 14 and the vehicle 15 determines that the link with the vehicle 11 and the vehicle 12 is disconnected, and as a result, the vehicle in which the link is disconnected within the own group for the vehicle 11, that is, The presence or absence of subgroup formation can be determined (step F2).
[0041]
When subgroups exist in the same group, first, the subgroups are separated. The separation procedure is executed when the beacon control frame cannot be received for a predetermined time or more as described above, or when the data from each corresponding in-vehicle wireless terminal cannot be received. That is, the inability to receive the beacon control frame indicates that communication with each vehicle in the group to which the vehicle on which the vehicle is mounted belongs is disconnected and separated from the group. Therefore, the wireless terminal mounted on the separated vehicle spontaneously transmits a beacon control frame to form a group using a new subgroup ID. That is, in each subgroup, a wireless terminal mounted on one vehicle in each subgroup is set as a beacon station. For example, in the example of FIG. 3, a wireless terminal mounted on the vehicle 11 of the subgroup A and a wireless terminal mounted on the vehicle 14 of the subgroup B are beacon stations (step F3).
Next, the channel acquisition stop count is obtained. The channel pause count is calculated at random using a beacon pause count calculation program (step F4).
[0042]
Next, the beacon collision between the subgroups can be avoided by stopping the acquisition of the continuous communication channel for the number of times corresponding to the calculation result (the number of pauses) in step F4. That is, the generation of the beacon signal is paused for the number of times corresponding to the calculation result (pause number) in step F4, and then the process proceeds to step F6. Thereby, the beacon reception success probability of the vehicle 13 belonging to the overlapping area of the subgroup can be increased. FIG. 6 shows the result of the simulation of the reception success probability by the signal collision avoidance procedure (steps F3 to F5) (the reception success probability every 100 msec in the vehicle 13 in the overlapping area of the subgroup). It should be noted that the number of pauses by the peripheral group acquired in step F1 is added to the calculation result (number of pauses) in step F4, and the generation of the beacon signal is paused for the number of times corresponding to the addition result, and then the process proceeds to step F6. You may make it (step F5).
[0043]
The beacon period is started and the control unit 113 starts a timer. At this time, the random delay time Tr held in the RAM 118 (the initial value is held in the memory 14 but the value calculated in step F8 is held from the next cycle) is set. The elapsed time Tw from the start of the beacon period is calculated, and the random delay time Tr is updated as delay time Tr from the start of the beacon period = previous delay time Tr−elapsed time Tw (step F6).
[0044]
After the random delay time Tr has elapsed, the control unit 113 controls the wireless communication unit 112 to transmit the beacon control frame of this group, and acquires a communication channel (step F7).
[0045]
Next, when the beacon transmission is not completed, the control unit 113 transitions to step F9, and when the beacon transmission is completed, the control unit 113 returns to the operation of acquiring the number of pauses by the peripheral group in step F1 (step F8).
[0046]
The control unit 113 calculates the random delay time Tr again, overwrites the previous random delay time held in the RAM 118, and returns to step F7 (step F9).
[0047]
According to the beacon transmission procedure shown in the flowchart of FIG. 5 above, it is determined whether or not a subgroup is formed in step F2, and when a subgroup is formed, acquisition of continuous communication channels is stopped in steps F4 and F5. Since the beacon collision is avoided and the beacon reception success probability of the vehicles in the overlapping area of the subgroup is increased, the beacon reception of the vehicle 13 is possible, and the vehicle 13 is not disabled.
[0048]
(Simulation result of beacon frame reception success probability)
FIG. 6 is a diagram showing a simulation result of a beacon frame reception success probability by the signal collision avoidance means (FIG. 5: Steps F3 to F5), and FIG. 7 is a diagram showing simulation parameters at the time of the simulation of FIG. In this simulation, the following conditions (1) to (4) are used to simplify the calculation.
(1) Do not consider propagation delay time, transmission / reception switching time, etc .;
(2) The propagation path model assumes an ideal propagation path and there are no communication errors other than the occurrence of a collision;
(3) If communication collides, it shall be said that communication has failed;
(4) There is no other group.
[0049]
From the simulation result of FIG. 6, it can be seen that the beacon reception success rate in the vehicle 13 increases when the maximum random value, that is, the maximum value Smax of the number of random pauses is increased.
[0050]
(Communication channel suspension procedure)
FIG. 8 is a flowchart showing a detailed operation of step F1 of FIG. 5, that is, an embodiment of a communication channel suspension procedure for avoiding a collision with a beacon of another group when another group other than the own group exists. .
[0051]
Here, the beacon control frame reception request processing is performed by making a beacon control frame transmission request every beacon period. At this time, the control unit 113 uses the pause counter to select whether or not to start transmission of a beacon control frame. That is, when acquiring the group ID from the received beacon control frame, the control unit 113 checks the value of the pause counter. If the pause counter = 0, the process proceeds to step S2, and if the pause counter ≠ 0, the process proceeds to step S4 ( Step S1).
When the pause counter = 0 in step S1, the control unit 113 counts the type of group ID acquired. That is, the number of peripheral groups is counted, and the number of other groups existing in the periphery is acquired every update time (for example, 1 second) (step S2).
[0052]
Next, this acquired value is set in the pause counter as the number of beacon control frame transmission pauses, and the process proceeds to step F2 (FIG. 5) (step S3).
[0053]
When the pause counter is not equal to 0 in step S1, the control unit 113 subtracts 1 from the pause counter, ends the beacon control frame transmission request, and transitions to step F2 (FIG. 5) (step S4).
With the above operation, if a beacon control frame is transmitted and a communication channel is acquired, the acquisition of the communication channel can be stopped for a time corresponding to the beacon period corresponding to the number of beacon control frame transmission suspensions.
[0054]
(Radio link status detection procedure)
FIG. 9 is an explanatory diagram of the detailed operation of step F2 of FIG. 5, that is, the radio link state detection procedure. According to the above-described wireless communication procedure (FIG. 2), a communication channel can be acquired at certain intervals using a beacon control frame. Therefore, in order to grasp the wireless status of each vehicle in the group with the in-vehicle wireless terminal, each in-vehicle wireless terminal has: a: presence / absence of channel acquisition within a certain time range and the vehicle on which the own device is mounted. It detects that the elapsed time after receiving the beacon control frame of the group to which it belongs has exceeded the time set by the system. This is important information related to the beacon transmission function validation procedure and the group configuration procedure.
[0055]
b: The reception status of the data frame of the in-vehicle wireless terminal corresponding to each data slot (data slot) in the acquired channel is grasped. For example, a link counter 31 is provided for each in-vehicle wireless terminal in the group, and processing is performed such that the counter is cleared when there is reception from the corresponding in-vehicle wireless terminal, and the counter is incremented by 1 when there is no reception. Here, only the link counter 31 is shown in FIG. 9, but the link counter is equal to the number of in-vehicle wireless terminals in the same group for each in-vehicle wireless terminal minus 1 (the link counter for the own wireless terminal is unnecessary). Only).
[0056]
In the wireless communication procedure described above, the maximum channel acquisition interval assumed in the system is determined by the beacon control frame. This is determined from the amount of data required by the system for wireless communication, the frequency of data generation, etc., and determines system parameters such as the beacon interval and the amount of random delay when transmitting a beacon control frame. The channel acquisition interval is determined from these parameters. If a limit time (link counter value) is set based on this parameter, communication with the corresponding in-vehicle wireless terminal is impossible if this limit value is exceeded. It can be detected. That is, from this link counter 31, each in-vehicle wireless terminal acquires reception status information with each in-vehicle wireless terminal in the group, and from this reception status information, the communication status within the group, that is, the radio link status Can be judged.
[0057]
In summary, an in-vehicle wireless terminal can communicate with an in-vehicle wireless terminal in the group based on wireless link information (elapsed time after receiving the beacon control frame of the group to which the vehicle on which the vehicle is mounted belongs). When it is detected that communication has been interrupted, this indicates that the in-vehicle wireless terminal has been separated from the group. That is, the wireless link information is effective information indicating the in-vehicle wireless terminals constituting the current group, and becomes system operation information.
[0058]
As mentioned above, although the Example of this invention was described, this invention is not limited to the said Example, It cannot be overemphasized that various deformation | transformation implementation is possible.
[0059]
【The invention's effect】
As described above, according to the radio communication systems of the first to fifth inventions, even when the same group is separated and subgroups are formed, collision of beacon control frames between subgroups can be suppressed. The probability of successful beacon reception within the subgroup is increased, and an efficient wireless communication procedure can be provided. Further, when there is a vehicle in an overlapping area in the sub group, beacon reception is possible, and the vehicle does not become incapable of communication.
[0060]
In addition, according to the on-vehicle wireless terminals of the sixth to eighth inventions, when the same group is separated and the subgroup is formed, the beacon generation by the beacon station in the subgroup is stopped at random. Therefore, the beacon control frame collision in the subgroup is avoided by controlling to make it stop according to the above, so that the beacon reception success probability in the subgroup is increased, and an efficient inter-vehicle wireless communication means can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of an in-vehicle wireless terminal installed in each vehicle in a wireless communication system between vehicles of the present invention.
FIG. 2 is an explanatory diagram of a communication procedure of a wireless communication channel.
FIG. 3 is a diagram showing an example of subgroups generated in the same group.
FIG. 4 is an explanatory diagram of a communication collision example at the time of group separation.
FIG. 5 is a flowchart showing an embodiment of a beacon transmission procedure according to the present invention.
FIG. 6 is a diagram showing a simulation result of a probability of successful reception of a beacon frame by a signal collision avoidance procedure.
7 is a diagram showing simulation parameters during the simulation of FIG. 6; FIG.
FIG. 8 is a flowchart showing an embodiment of a communication channel suspension procedure for avoiding a collision with a beacon of another group.
FIG. 9 is an explanatory diagram of a radio link state detection procedure.
FIG. 10 is an explanatory diagram of an inter-vehicle wireless communication system.
FIG. 11 is an explanatory diagram of a communication protocol of a wireless communication system using a beacon.
[Explanation of symbols]
1-1, 1-2, 1-3, 11-15 vehicles
1, 2, 3, 4, 10 Vehicle group
100 In-vehicle wireless terminal (communication terminal)
112 Wireless communication unit
113 Collision avoidance control means (control unit)
A, B subgroup

Claims (6)

In a wireless communication system in which there is at least one group that performs wireless communication between a plurality of wireless terminals, and a beacon signal is generated using one wireless terminal in each group as a beacon station, In a wireless communication system with a communication protocol, other wireless terminals transmit in a specific data slot assigned to each wireless terminal in a data frame following a beacon signal emitted by the beacon station.
Detecting a wireless terminal in which the wireless link is disconnected in each group, and determining that a subgroup is formed in the group when the wireless terminal in which the wireless link is disconnected is detected ;
A process of setting one wireless terminal in each subgroup as a beacon station when a subgroup is formed;
Each of the sub-group wireless terminal set to the beacon station is to calculate the number of pauses after random, by Rukoto rested the generation of only the beacon signal the number of times corresponding to the calculated number of pauses, the subgroup A wireless communication system comprising: a step of avoiding collision of beacon signals emitted by beacon stations in each sub-loop at wireless terminals that have simultaneously belonged to each sub-group along with the formation . Before the step of determining whether or not the subgroup is formed, comprising the step of detecting the number of pauses by a group other than the own group,
When subgroups are formed, the step of generating a beacon signal from the beacon station of each subgroup is a step of adding the number of pauses by a group other than the detected own group to the number of pauses calculated at random. The beacon signal generation is paused a number of times corresponding to the number of times the pause number by the group other than the own group is added,
Claim 1 Symbol placement of the wireless communication system, characterized in that. The wireless terminal is a wireless communication system according to claim 1 or 2, wherein the mounted on the moving body. The wireless communication system according to any one of claims 1 to 3, wherein the moving body is a vehicle. In a wireless communication system in which there is at least one vehicle group performing wireless communication between a plurality of vehicles equipped with wireless terminals,
A beacon signal is generated using a wireless terminal mounted on one vehicle in each vehicle group as a beacon station, and a wireless terminal mounted on another vehicle in the same group is after a beacon signal emitted by the beacon station. Wireless communication means comprising a communication procedure for transmitting in a specific data slot assigned to each wireless terminal in the subsequent data frame;
When a wireless link state is detected in a vehicle group to which the vehicle on which the vehicle is mounted belongs and a wireless terminal with a disconnected wireless link is detected, the vehicle group to which the vehicle on which the wireless terminal is mounted is separated. Subgroup determining means for determining that a subgroup has been formed,
Signal collision avoidance control means for performing collision avoidance control of beacon signals between subgroups when a subgroup is formed ,
The signal collision avoidance control means is set by a beacon station setting means for setting a wireless terminal mounted on one vehicle in each subgroup as a beacon station when the subgroup is formed, and the beacon station setting means. The beacon signal generation pause number of each beacon station is calculated at random, and the number of beacon signals by the beacon stations in the subgroup is equal to the number of pauses calculated by the pause number calculator. Beacon signal generation suspension control means for avoiding collision of beacon signals emitted by each beacon station in each sub-loop at a wireless terminal that has belonged to each sub-group simultaneously with the formation of the sub-group by pausing the generation An in-vehicle wireless terminal characterized by including: Prior to determining whether or not a sub-group has been formed, there is provided a pause number detecting means for detecting the number of pauses by a group other than the own vehicle group, wherein the beacon signal generation pause control means generates a beacon signal calculated by the pause number calculating means Including a means for adding the number of pauses detected by the pause count detection means to the number of pauses, and a beacon by a beacon station in the subgroup by a number corresponding to the number of times after addition of the pause count detected by the pause count detection means 6. The in-vehicle wireless terminal according to claim 5 , wherein generation of a signal is suspended.

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