JP4263019B2 - Wireless communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless communication system in which wireless communication devices mounted on a plurality of mobile bodies exist, and more particularly to a channel acquisition control technique when accessing a communication medium shared by each wireless communication device.
[0002]
[Prior art]
In an environment where many wireless communication devices (hereinafter referred to as terminals) share the same communication channel on the wireless communication means, efficient use of the communication channel is an important issue. In view of such a situation, there is an inter-vehicle communication system between a plurality of vehicle groups as shown in FIG. 8 as a wireless communication system in which a terminal mounted on each vehicle can communicate freely without a base station (for example, Patent Documents). 1). The patent document also discloses a means for improving communication efficiency by reconfiguring a special communication control frame and each vehicle into a communication network (hereinafter referred to as a group), a means for reconfiguring a group, and the like.
[0003]
[Patent Document 1]
JP-A-2001-118191 [0004]
[Problems to be solved by the invention]
However, because it is a mobile radio, channel acquisition control by fading or multipath may fail and a radio communication collision may occur. In particular, it is an important issue to avoid a phenomenon in which communication is continuously interrupted due to collision of wireless communication.
This is due to the fact that wireless communication collisions on the same wireless channel cannot be detected physically during wireless transmission. For this reason, no fundamental solution has been conventionally taken.
[0005]
Also in the invention disclosed in Patent Document 1, in a beacon random transmission procedure, a terminal that performs beacon transmission detects the presence or absence of another terminal that performs wireless transmission at the same timing and the same wireless channel as the terminal itself. It is not possible. In the invention disclosed in Patent Document 1 that employs a channel acquisition control unit that uses a beacon, this appears as a performance degradation in the data communication of the terminals in the group in the data period subsequent to the beacon period.
[0006]
A specific example of a communication channel acquisition procedure using a beacon control frame (hereinafter referred to as a beacon) in Patent Document 1 and problems thereof will be described below.
In the communication channel acquisition procedure using the beacon in Patent Document 1, the acquisition of the communication channel is performed by randomly transmitting the beacon during the beacon period shown in FIG. This beacon period is composed of a plurality of beacon slots, and contention control with other terminals (other groups) is realized by randomly selecting a slot to transmit. The basic concept of this beacon transmission procedure is shown in the following (1) to (7).
[0007]
(1) The beacon period is composed of slots shorter than the beacon. For example, the beacon period is set to beacon slots 1 to 30.
(2) The beacon is transmitted in one of the beacon slots in synchronization with the beacon slot.
(3) For beacon transmission, a beacon slot to be transmitted is determined from a random value (random numbers 1 to 30).
(4) If another terminal beacon is received before the beacon transmission, the beacon transmission is interrupted.
(5) A terminal (group) that has successfully transmitted a beacon acquires a communication channel and performs data transmission in the subsequent data period.
(6) The terminal (group) that has acquired the communication channel acquires a random value during the next beacon period.
(7) Terminals (groups) that have not acquired a communication channel subtract the time elapsed this time to obtain a random value for the next beacon period.
[0008]
Further, in the invention disclosed in the cited document 1, when a beacon is not transmitted by a terminal that does not transmit a beacon for a certain period, beacon transmission is started even if the beacon is not a beacon transmitting terminal. Built-in control for channel acquisition. With this function, it is avoided that communication of a terminal whose wireless environment has temporarily deteriorated is interrupted. This operation is continued until the wireless environment is improved and the beacon of the own group is received from the original beacon terminal.
[0009]
However, when a plurality of groups are arranged at a short distance and each other's wireless environment deteriorates (for example, when arranged in a wireless environment as shown in FIG. 10), each terminal stops without moving. In some cases, even if a plurality of beacons are transmitted, the wireless environment remains unimproved.
[0010]
FIG. 10 is a diagram illustrating an example of the position of each terminal and each communication area. Specifically, the communication area in each terminal can be assumed as follows.
(1) A wireless communication network consisting only of a group A beacon transmission terminal (A-1) and a subsequent terminal (A-2);
(2) Wireless communication comprising a group A terminal (A-2) and a front beacon transmission terminal (A-1), a group A terminal (A-2) and a rear B group terminal (B-1). network;
(3) A wireless communication network comprising a group B beacon transmission terminal (B-1) and a front terminal (A-2), and a group B beacon transmission terminal (B-1) and a rear terminal (B-2). ;
(4) A wireless communication network consisting only of group B terminals (B-2) and forward terminals (B-1).
[0011]
Furthermore, in such a wireless environment, a wireless communication procedure as shown in FIG. 11 is performed, and a channel contention procedure using a beacon is not established, and a situation in which communication is interrupted occurs. This situation will be described below with reference to FIG.
[0012]
(1) The beacon transmission terminal (A-1) of group A judges that only the own group exists in the vicinity because only the subsequent terminal (A-2) can receive normally in rare cases. . As a result, continuous communication channels are acquired without considering other groups in the vicinity.
[0013]
(2) The terminal (A-2) of the group A transmits data during the data period of the own terminal because it can rarely receive the beacon of the own group. However, data from the front terminal (A-1) collides with a terminal (B-1) in another group and cannot communicate normally. At this time, the data of the terminal (B-1) cannot be received.
[0014]
(3) The beacon transmission terminal (B-1) of group B judges that only the own group exists in the vicinity because only the subsequent terminal (B-2) can receive normally in rare cases. . As a result, continuous communication channels are acquired without considering other groups in the vicinity. In addition, data from the subsequent terminal (B-2) collides with a terminal (A-2) in another group A, and cannot be received normally.
[0015]
(4) Since the terminal (B-2) of the group B can normally receive the beacon of the own group, it transmits data during the data period of the own terminal. In addition, data from the front terminal (B-1) can be received well without colliding.
[0016]
That is, the invention disclosed in Patent Document 1 is a wireless communication system (an inter-vehicle wireless communication system) for a mobile body (vehicle), but each terminal stops in a state where the communication environment within the group has deteriorated. Since the response to the situation is not sufficient, the above-mentioned problems have arisen.
[0017]
Therefore, when communication is interrupted due to radio interference or propagation path conditions, it can be expected that the detection and recovery of communication interruption will greatly contribute to the efficient use of the communication channel.
[0018]
The present invention has been made to solve the above-described problems of the prior art, and in a wireless communication system between wireless communication devices mounted on a plurality of mobile objects, a communication interruption state can be avoided. An object is to provide a radio channel cycle changing procedure that realizes efficient use.
[0019]
[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 a plurality of networks configured by performing wireless communication between a plurality of mobile bodies are set. , One mobile unit is assigned to a beacon station, and another mobile unit belonging to the network is assigned to a client station, and the communication protocol includes a beacon period consisting of a plurality of beacon slots and a data period consisting of a plurality of data slots. Each data slot is assigned to each mobile unit, and a beacon packet is transmitted from the beacon station of each network during the beacon period, and each mobile unit receives a beacon packet of the network to which the mobile unit belongs. Sometimes during the data slot period allocated to the mobile In a wireless communication system using a controlled Ru communication protocol to transmit data packets of its own mobile, communication protocol, when the collectively one period of one data period and subsequent one beacon period, each network After transmitting the beacon packet, the beacon station sets a counter for the number of beacon pauses corresponding to the number of networks other than its own network plus one. 1 to suspend transmission of a beacon packet by subtracting, characterized in that when the value of the counter is zero, including a radio channel cycle changing procedure so as to change the radio channel periodically by sending the bi over Con packet .
[0020]
The second invention is the wireless communication system of the first invention, and further, in each network, when the beacon packet of the beacon station is not received by the client station for a certain time or more, the client station belonging to the network of the beacon station In a wireless communication system configured to transmit beacon packets from one of the wireless communication systems, the radio channel period changing procedure is performed when a beacon station of each network receives a beacon packet from one of the client stations. When transmitting a beacon packet from a station, the method includes a procedure of pausing the transmission of a beacon packet by one more period than the pause period of the beacon packet.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
[Overview]
The present invention provides a wireless communication system between mobile units in which a plurality of networks (hereinafter referred to as groups) configured by performing wireless communication between a plurality of mobile units is provided, as shown in FIG. A plurality of mobile bodies A-1, A-2, B-1, and B-2 arranged at short distances are wireless channel cycle changing means between the mobile bodies grouped in a plurality of networks A and B. Is to provide. In addition, the conditions of the mobile bodies constituting the group are that at least two vehicles equipped with the wireless communication devices exist in a short distance (communication range) and move in substantially the same direction (the destination destination is the same). ).
[0022]
FIG. 1 is a block diagram showing a configuration of an embodiment of a wireless communication device mounted on each vehicle in a wireless communication system between vehicles of the present invention. A wireless communication device (hereinafter referred to as a terminal) 100 includes an antenna 11 and a wireless communication unit. 12, a control unit 13, a memory 14, and a vehicle interface 15.
[0023]
The wireless communication unit 12 receives a beacon control frame and transmits / receives a data frame via the antenna 11 according to a predetermined communication procedure under the control of the control unit 13. When terminal 100 is a beacon transmitting terminal, beacon control frames (hereinafter referred to as beacons) are transmitted and received and data frames (hereinafter referred to as data) are transmitted and received.
[0024]
The control unit 13 has a microcomputer configuration including a CPU, a ROM (not shown), a program storage memory such as a ROM, an internal clock 131 and peripheral circuits. The control unit 13 controls the entire apparatus and means described below (in the embodiment, a program). Configuration) performs execution control such as comparison of group ID information, determination of priority, correction based on the beacon time of the internal clock, and time synchronization with other groups. In addition to the control program and communication protocol for controlling the entire terminal, the program storage memory, the program for performing communication control and necessary processing in the inter-vehicle wireless communication system of the present invention, and the number of pauses as shown in FIG. A setting table 30 and various setting values are stored.
[0025]
The memory 14 stores beacons and data received via the wireless communication unit 12 and vehicle data (vehicle speed, direction of travel, current position (coordinates), etc.) acquired via the vehicle interface 15 under the control of the control unit 13. Remember me.
[0026]
The vehicle interface 15 converts vehicle data such as vehicle speed, direction of travel, current position (coordinates), and the like acquired by a sensor provided in the vehicle into digital data and stores it in the memory 14 under the control of the control unit 13. Or data converted from the data read from the memory 14 and sent to the vehicle side (for example, when driving system control data is read from the memory 14, a driving system control unit (not shown) provided in the vehicle) To send).
[0027]
FIG. 2 is a flowchart showing a channel acquisition cycle change procedure for each mobile unit between a plurality of mobile groups arranged at a short distance according to the present invention, and FIG. 3 is used in the channel acquisition cycle change procedure of FIG. FIG. 4 is a diagram illustrating a setting example of the suspension frequency control table, and FIG. 4 is an explanatory diagram of a communication channel acquisition state of each terminal according to the channel acquisition cycle changing procedure of FIG.
[0028]
As shown in FIG. 10, when there are a plurality of mobile groups arranged at a short distance in a wireless communication area, it is most efficient for each group to acquire a communication right in order. . In such a situation, in order to acquire the optimal communication right, as shown in the flowchart of FIG. 2, the number of groups other than the own group existing in the wireless communication area is monitored, and a certain group acquires the communication right once. In the beacon period that follows, it is effective to pause beacon transmission once. That is, when the group that has acquired the communication right pauses the communication right acquisition work after the end of the communication, the other group can execute beacon transmission independently, and the communication right can be acquired. This is because even when there are three or more groups in a wireless communication area, if one of those groups suspends beacon transmission, the number of competitors will be reduced for other groups. To reduce the communication channel acquisition collision probability and increase the communication channel acquisition probability.
[0029]
A specific procedure example of the above processing will be described with reference to the flowchart of FIG. 2 with reference to the transmission suspension frequency control table of FIG. 3 and the communication channel acquisition state of each terminal of FIG. Here, the beacon transmission terminal (A-1) and the beacon transmission terminal (B-1) use the pause counter to determine whether or not to transmit a beacon.
That is, in FIG. 2, when the control unit 13 of the beacon transmission terminal (A-1) obtains the group ID from the received beacon, the control unit 13 checks the value of the pause counter. If the pause counter = 0, the process proceeds to step S2, and the pause counter ≠ When it is 0, the process proceeds to step S5 (step S1).
When the pause counter = 0 in step S1, the control unit 13 of the terminal (A-1) counts the types of acquired group IDs. That is, the number of groups other than the own group is counted, and the number of other groups existing in the vicinity is obtained every update time (for example, 1 second) (in the example of FIG. 10, the number of groups = 2, and other than the own group) Group number = group number-1 = 1) (step S2), the number of pauses is obtained from the pause count setting table 30 as shown in FIG. 3 based on this acquired value, and the pause count is set as the beacon transmission pause count. The counter is set (in the example of FIG. 10, since the number of groups other than the own group = 1, the number of pauses 1 is obtained from the pause count setting table and set in the pause counter) (step S3).
[0030]
Then, the beacon is transmitted to the wireless communication unit 12, and the beacon transmission process is terminated (step S4). When the pause counter is not 0 in step S1, the control unit 13 subtracts 1 from the pause counter and ends the beacon transmission process (step S5).
[0031]
With the above operation, if a beacon is transmitted and a communication channel is acquired, acquisition of the communication channel can be stopped for a time corresponding to the beacon period corresponding to the number of beacon transmission suspensions. That is, in the example of the group of FIG. 10, the beacon transmission terminal (A-1) transmits a beacon every other time as shown in FIG.
[0032]
Similarly, the beacon transmission terminal (B-1) also transmits a beacon every other time, and the beacon transmission terminal (A-1) and the beacon transmission terminal (B-1) change the channel acquisition cycle alternately. Since beacons are transmitted, communication channels can be obtained alternately as shown in FIG. That is, beacon collision does not occur between a plurality of mobile groups arranged at a short distance, and normal communication is possible. In the above example, the number of groups is 2, but the same applies to the case of 3 or more.
[0033]
The above-described channel acquisition cycle changing procedure is to provide a guard-free vacant channel, which is considered to be a factor that reduces the channel usage efficiency as a system. It will not be a major factor and will not have a significant impact. Furthermore, the realization of avoidance of a situation in which wireless communication is interrupted provides a stable communication channel, which is more advantageous than a decrease in channel utilization efficiency due to an increase in the number of pauses for one time.
[0034]
(Embodiment 2)
In the first embodiment described above, the channel acquisition cycle changing procedure is configured such that a plurality of groups alternately acquire communication channels. However, in this embodiment, two groups (not limited to two) have the same timing. The case where a communication channel is acquired will be described.
[0035]
FIG. 5 is a flowchart showing an example of the procedure for switching between valid / invalid of the beacon transmission function. When the beacon of the own group cannot be received for a predetermined time or more, separation processing (beacon transmission processing by a terminal other than the beacon transmission terminal) Migrate to In other words, if for some reason the beacon control frame cannot be received for a certain time or longer, communication becomes impossible, and it is necessary to try to acquire the communication channel by itself.
[0036]
In FIG. 5, the control unit 13 of each terminal 100 pays attention to the beacon reception for the own group, and when the beacon control frame is received within the scheduled beacon reception time of the own group, the control unit 13 proceeds to step T2 and passes the scheduled time. Even if it cannot be received, the process proceeds to step T4 (step T1). If a beacon is received within the scheduled time in step T1, it is checked whether it is a beacon of its own group. If it is a beacon of its own group, the process proceeds to step T3. Otherwise, the process returns to step T1 (step S1). T2).
[0037]
When the own group beacon is received in step T2, the scheduled reception time of the own group beacon is updated, and the process returns to step T1 (step T3). When the beacon cannot be received within the scheduled time in step T1, the beacon transmission function is enabled (for example, the beacon transmission flag is turned on) (step T4).
Moreover, when the beacon of the own group is received when the beacon transmission function is valid, the process returns to step T1. Otherwise, the process proceeds to beacon transmission by a terminal other than the beacon terminal. In addition, beacon transmission by terminals other than a beacon terminal is performed similarly to the case of beacon transmission by a beacon transmission terminal (step T5).
[0038]
When the terminal cannot receive the beacon of its own group for a predetermined time or more by the operation shown in the flowchart of FIG. 5 above, in the beacon transmission process of the channel acquisition cycle changing procedure described above (that is, step S4 of the flowchart of FIG. 2), Since a beacon is transmitted from one of the terminals other than the beacon transmitting terminal (for example, the terminal (A-1)) (for example, the terminal (A-2)), The beacon transmission terminal transmits a beacon in the subsequent beacon period. The beacon transmission terminal that receives the beacon of its own group (here, the terminal (A-1)), As shown in the flowchart of FIG. 7, beacon transmission is paused for one more period than normal beacon pause control. Please is carried out.
[0039]
FIG. 6 is a flowchart showing an example of a procedure for changing the channel acquisition cycle of each mobile unit between a plurality of mobile unit groups arranged at a short distance, and the number of pauses in the process at the time of wireless reception in the beacon transmission terminal The procedure related to control is shown. FIG. 7 is an explanatory diagram of the communication channel acquisition state of each terminal according to the channel acquisition cycle changing procedure of FIG. In the following description, the “neighboring group ID table” means a table storing IDs of groups existing around the own group.
[0040]
In FIG. 6, when the beacon transmission terminal (A-1) receives a new beacon, it acquires the group ID of the transmission source terminal of the beacon (step U1), checks the peripheral group ID table developed in the memory 14, and stores it in the table. If there is no ID that matches the newly acquired group ID, the process proceeds to step U3, and if there is a matching ID, the beacon reception process ends (step U2). If there is no ID that matches the acquired group ID, the group ID on the new beacon is additionally registered in the peripheral group ID table (step U3), and the number of registered IDs is updated by adding 1 to the group ID counter. (Step U4).
[0041]
Next, when the acquired beacon is not the beacon of the own group, the beacon receiving process is terminated (step U5). When the acquired beacon is the beacon of the own group, 1 is added to the suspension counter and the beacon receiving process is terminated (step U6). .
[0042]
The beacon transmitting terminal (A-1) transmits a beacon every other time by the operation shown in the flowchart of FIG. Similarly, the beacon transmission terminal (B-1) also transmits a beacon every other time, and the beacon transmission terminal (A-1) and the beacon transmission terminal (B-1) change the channel acquisition cycle alternately. Since beacons are transmitted, communication channels can be obtained alternately as shown in FIG. That is, beacon collision does not occur between a plurality of mobile groups arranged at a short distance, and normal communication is possible. In the above example, the number of groups is 2, but the same applies to the case of 3 or more.
That is, as shown in FIG. 7, the acquisition of the communication channel after the channel acquisition cycle change (after the cycle indicated by the symbol β) is executed alternately by each group, and a wireless communication environment without collision can be realized.
[0043]
As mentioned above, although one 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.
[0044]
【The invention's effect】
As described above, according to the present invention, even in a radio communication system based on a random access scheme, by changing the channel acquisition cycle, radio signal collision can be avoided and communication channel utilization efficiency can be improved. I can expect.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of a wireless communication device installed in each vehicle in a wireless communication system between vehicles of the present invention.
FIG. 2 is a flowchart showing an embodiment of a procedure for changing the channel acquisition cycle of each mobile unit between a plurality of mobile unit groups arranged at a short distance.
FIG. 3 is a diagram showing an example of a pause count control table used in the channel acquisition cycle changing procedure of FIG. 2;
4 is an explanatory diagram of a communication channel acquisition state of each terminal according to the channel acquisition cycle changing procedure of FIG. 2;
FIG. 5 is a flowchart showing an embodiment of a procedure for switching beacon transmission function valid / invalid.
FIG. 6 is a flowchart illustrating an example of a procedure for changing a channel acquisition cycle of each mobile unit between a plurality of mobile unit groups arranged at a short distance.
7 is an explanatory diagram of a communication channel acquisition state of each terminal according to the channel acquisition cycle changing procedure of FIG. 6;
FIG. 8 is an explanatory diagram of a radio communication system between mobile units in a plurality of mobile unit groups.
FIG. 9 is a diagram illustrating an example of a communication channel acquisition procedure according to a conventional example.
FIG. 10 is a diagram illustrating an example of a wireless communication network in the case where a plurality of mobile body groups are arranged at a short distance.
FIG. 11 is an explanatory diagram of deterioration of the wireless communication state in the wireless communication network as shown in FIG.
[Explanation of symbols]
1, 2, 3 Mobile group (network)
1-1 to 3-1, 2-1, 2-2, 3-1 to 3 Mobile 12 Wireless communication unit 13 Control unit 100 Wireless communication device 131 Internal clock A, B Mobile group (network)
A-1, B-1, A-2, B-2 Mobile

Claims (2)

A wireless communication system in which a plurality of networks configured by performing wireless communication between a plurality of mobile bodies is set, and in each network, one mobile body is assigned to a beacon station and another mobile belonging to the network is assigned. The communication protocol is configured such that a beacon period consisting of a plurality of beacon slots and a data period consisting of a plurality of data slots are alternately repeated, and each data slot is assigned to each mobile station. The beacon packet is transmitted from the beacon station of each network during the beacon period, and each mobile unit receives the beacon packet of the network to which the mobile unit belongs only during the data slot period allocated to the mobile unit. controlled Ru communication professional to transmit data packets In a wireless communication system using Col
In the communication protocol, when one beacon period and a subsequent data period are combined into one cycle, the beacon station of each network transmits a beacon packet and then sets 1 to the number of networks other than its own network. If the counter of the beacon number of pauses, corresponding to a number obtained by adding, counter frequency period of the beacon number of pauses is to suspend transmission of a beacon packet by subtracting 1 from the counter, when the value of the counter is zero wireless communication system comprising a radio channel cycle changing procedure so as to change the radio channel periodically by sending the bi chromatography con packet. Further, in each of the networks, when the beacon packet of the beacon station is not received by the client station for a certain time or more, the wireless is set to transmit the beacon packet from one of the client stations belonging to the beacon station network. In a communication system,
When the beacon station of each network receives a beacon packet from one of the client stations, the radio channel cycle changing procedure is performed when the beacon packet is transmitted from the beacon station. The wireless communication system according to claim 1, further comprising a procedure for pausing the transmission of the beacon packet by one period more than the minute.

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