JP4260035B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a radio communication technique between mobile bodies such as mobile bodies, and more particularly to a data slot allocation method and a radio communication system that do not cause a decrease in radio channel.

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, a special communication control frame (beacon control frame) between a plurality of vehicle groups as shown in FIG. 6 as a wireless communication system in which a terminal mounted on each vehicle without a base station can freely communicate. Means and the like for improving communication efficiency by forming each vehicle into a communication network (hereinafter referred to as a group) are disclosed (for example, see Patent Document 1).

  In the communication channel acquisition procedure using the beacon in Patent Document 1, communication channel acquisition control is performed by randomly transmitting a beacon during the beacon period shown in FIG. This beacon period is composed of a plurality of beacon slots (slot1-slot10), and contention control with other terminals (other groups) is realized by randomly selecting a slot to be transmitted. The basic concept of this beacon transmission procedure is shown in the following (1) to (7).

(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) When the other 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) A terminal (group) that has not acquired a communication channel subtracts the time elapsed this time to obtain a random value in the next beacon period.

  Next, user data is processed in the data period after acquisition of the wireless channel. In FIG. 7, ten data slots from slot 1 to slot 10 are prepared and assigned to terminals belonging to the same group. For example, if the terminals in the group are terminal 1 to terminal 10, they are assigned to slot 1 to slot 10, respectively.

  Further, in a wireless communication system between wireless communication devices mounted on a plurality of mobile units, a wireless channel cycle changing procedure for avoiding a communication interruption state and realizing efficient use of a communication channel is as follows. In the beacon period that continues after a certain group has acquired the communication right once, the channel period is changed so as to pause the transmission of the beacon once (for example, a group). , See Patent Document 2).

JP 2001-118191 A Japanese Patent Application No. 2003-135614

  The communication system disclosed in Patent Document 1 is intended to achieve wireless communication with no collision within the channel obtained by the above procedure, but in mobile communication, the reception level is increased as the terminal moves. This causes a decrease in the reliability of the transmission signal due to fading such as Rayleigh distribution.

  Specifically, when a plurality of groups are arranged and the wireless environment of each other deteriorates due to a road shape or fading due to terminal movement, for example, when arranged in a wireless environment as shown in FIG. There may be a case where wireless communication between terminals is not normally performed.

  FIG. 8 shows the position of each terminal and each wireless communication area. In FIG. 8, each wireless communication area can be assumed as follows.

(A) Group A beacon transmission terminal (A-1): Only subsequent terminal (A-2).
(B) Group A terminal (A-2): Front terminal (A-1) and rear group B terminal (B-1).
(C) Group B beacon transmission terminal (B-1): a front group A terminal (A-2) and a group B terminal (B-2).
(D) Group B terminal (B-2): Only the front terminal (B-1).

  However, in the situation as described above, the reception performance of the other group terminals at the terminal (A-2) and the terminal (B-1) may deteriorate due to the influence of road topography, structures, and fading.

  In this case, the communication procedure is as shown in FIG. 9 (FIGS. 9A and 9B), and the channel synchronization and channel contention procedures using the beacons are not established, and a situation in which some communication is interrupted occurs. To do.

FIG. 9 shows an embodiment of a wireless communication procedure when wireless communication timing overlaps.
First, the data from the subsequent terminal (A-2) can be normally received normally in the beacon transmission terminal (A-1) of group A. However, since the peripheral group number information of the own terminal and the rear terminal is 0 (zero), as shown in the radio channel cycle change procedure described in Patent Document 2, the pause period = 0 + 1 = 1, The radio channel acquisition control is executed with the pause period as one time.

  Next, the data from the subsequent terminal (B-2) can be normally received normally at the beacon transmission terminal (B-1) of group B. However, since the number of surrounding vehicles in the peripheral group number information of the own terminal and the rear terminal is 0 (zero), the suspension period = 0 + 1 = 1, and the wireless channel acquisition control is executed with the suspension period as one time.

  Here, FIG. 9A and FIG. 9B show a state in which the wireless communication timing of each group is different. In particular, in FIG. 9B, since the data transmission timings of the terminal (A-1) and the terminal (B-1) coincide with each other, even if the radio wave propagation path state is improved, a radio signal collision occurs as a result. It is shown that. Thus, the state of wireless communication changes depending on the state of the radio wave propagation path, and communication between terminals that are normally capable of normal communication is impossible.

  In general, as an improvement measure in such a case, it is often considered to employ selection diversity reception after detection or maximum ratio combining diversity. However, for example, as a means for selective diversity reception after detection, a radio signal is always received by two systems using two antennas and two receiving circuits, and a good reception signal is received from the result. Become. The maximum ratio combining diversity means performs combining so that the CNR (Carrier Noise Ratio) of the received signal is maximized instead of selecting a good received signal.

  In both cases, the antenna and the receiving circuit are two systems, and an optimum design of the selection or synthesis unit is required. In addition, there are problems such as an increase in power consumption and an obstacle to miniaturization.

  The present invention has been made to solve the above-described problem, and a data slot allocation method that reduces the occurrence of a disruption state without causing a decrease in channel utilization efficiency by changing only the slot allocation in the data period. And a wireless communication system.

In order to solve the above-mentioned problem, in the invention according to claim 1, a wireless communication system in which a plurality of groups configured by performing wireless communication between a plurality of mobile bodies is set, and in each group, One mobile unit is assigned to a beacon station, and another mobile unit belonging to the group is assigned to a client station, and the communication protocol alternates between 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 signal is transmitted from each group of beacon stations in the beacon period, and each mobile unit receives a beacon signal of the group to which the mobile unit belongs. Only the data signal of the mobile unit will be transmitted during the data slot period allocated to the mobile unit. In a wireless communication system using a communication protocol characterized by being controlled, a plurality of data slots of a data period are allocated to each mobile unit in each group, and one beacon period followed by one beacon period When the data period is set as one cycle, the beacon stations of each group transmit a beacon signal according to a specified beacon interval, and after transmitting the beacon signal, set the number of groups existing outside the own group to 1. By stopping the transmission of the beacon signal by the period corresponding to the added number, a beacon station in the group other than the own group and the own group generates a period in which the transmission of the beacon signal is suspended , and each mobile unit Is the number of data slots corresponding to the number of data slots to which the mobile unit is allocated among the data slots. When a communication terminal is mounted and a data signal is transmitted in each assigned data slot, the data signal is transmitted using a different wireless communication terminal among the plurality of wireless communication terminals for each assigned data slot. to provide a wireless communication system, wherein to Rukoto.

According to a second aspect of the present invention, there is provided the wireless communication system according to the first aspect, wherein the group is a mobile communication network and the mobile is a vehicle.

  By using the data slot allocation method according to the present invention, it is possible to provide a good wireless communication system that does not cause a decrease in the efficiency of the communication channel even when the wireless environment deteriorates.

  In the technique disclosed in Patent Document 1 described above, a method of assigning a data channel to each terminal is used (see (7) in the description of Patent Document 1). However, in the present invention, as shown in FIG. By the data slot allocation method, good acquisition control of the communication channel is realized even in the wireless communication environment as shown in FIG.

  FIG. 1 is a block diagram showing a configuration of an embodiment of a radio communication terminal mounted on each mobile unit in the radio communication system of the present invention. The radio communication terminal 100 includes an antenna 11, a radio communication unit 12, a control unit 13, A memory 14 and an interface 15 are provided.

  The wireless communication unit 12 receives a beacon control frame and transmits / receives a data frame via the antenna 11 under a control of the control unit 13 according to a predetermined communication procedure. In addition, when the wireless communication terminal 100 is a representative wireless communication terminal described later, a beacon control frame and a data frame are transmitted and received.

  The control unit 13 has a microcomputer configuration including a CPU, a ROM (not shown), a program storage memory, an internal clock 131, and peripheral circuits. The control unit 13 controls the entire apparatus and means described below (in the embodiment, a program). In addition to execution control such as comparison of group ID information, priority determination, correction based on beacon time of internal clock, time synchronization with other groups, etc., communication channel by data slot allocation according to the present invention Perform acquisition control.

  In addition to the control program and communication protocol for controlling the entire wireless communication terminal, the program storage memory includes means (program) for performing communication control and necessary processing in the mobile wireless communication system of the present invention, and FIG. A beacon information table (not shown) in which information (for example, group ID, subgroup ID, etc.) included in the beacon control frame is tabulated and various setting values are stored.

  The memory 14 stores the beacon control frame and data frame received via the wireless communication unit 12 and the moving body data (movement speed, direction of travel, current position (coordinates), etc.) acquired via the interface 15 as a control unit. Store under 13 controls.

  The interface 15 converts the moving body data such as the moving speed, the direction of travel, the current position (coordinates), etc. acquired by the sensor provided in the moving body 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 moving body side (for example, when driving system control data is read from the memory 14, a driving system control unit (not shown) provided in the moving body. Send to)).

  Communication channels of each mobile group are acquired using beacon control frames. The beacon control frame has a function of assigning a communication channel for each wireless communication terminal in the group. This communication channel assignment function is a function for calculating an assignment time for transmitting a data frame in a data slot period assigned to each wireless communication terminal after receiving a beacon control frame having a data slot assignment belonging group ID. is there.

  Therefore, each wireless communication terminal in the group has a right to transmit a data frame only to a specific wireless communication terminal in each assigned data slot period, so that a data frame collision with another wireless communication terminal does not occur. 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.

  The beacon control frame is a special function given to the wireless communication terminal representing each group, and has a function of managing communication time (setting a reference time). This beacon control frame can be received by all wireless communication terminals (FIG. 1) regardless of the group to which the beacon belongs.

  If the wireless communication terminal in each group is a beacon control frame of its own group, the internal clock is set according to the time information included therein. With this operation, time synchronization of wireless communication terminals belonging to the group can be performed, and further, the reception time of the next beacon control frame of the group can be predicted.

In addition, the representative wireless communication terminal of each group has a function of transmitting a beacon control frame at the time calculated from the internal clock 131 and the beacon interval at the start of operation as determined by the priority of the subgroup ID as described above. Yes. The hardware configuration of the representative wireless communication terminal may be the same as that in FIG. 1, and the beacon control frame transmission function of the wireless communication unit 12 is activated according to the priority order of the subgroup IDs with other wireless communication terminals in the group. It is different from the point that the function of the control unit 13 as a representative wireless communication terminal is active. That is, each wireless communication terminal has a normal mode that operates as a normal wireless communication terminal in the group and a representative mode that operates as a representative wireless communication terminal, and the switching between the normal mode and the representative mode is performed by the subgroup ID as described above. Determined by priority.
(Data slot assignment)
FIG. 2 is a diagram showing an example of allocation of a plurality of data slots. FIG. 2A is an example in which 2 slots are allocated to one mobile unit, and FIG. 2B is an example in which 5 slots are allocated to one mobile unit. is there.
By assigning a plurality of slots to each mobile body in this way, a plurality of communication opportunities can be created in one radio channel. Further, since each communication opportunity is separated in time (diversity different in time), the influence of the propagation path is generally different. In other words, since there are multiple communication opportunities within the acquired communication channel, there is an improvement effect (data quality improvement) against data loss such as deterioration of the communication environment.

  Each mobile unit is normally equipped with one wireless communication terminal, that is, one wireless communication terminal, so that one wireless communication terminal performs a plurality of wireless communications. However, each mobile unit has a plurality of wireless communication terminals. It may be mounted and communicate using a different wireless communication device for each slot assignment. In this way, even if one radio communication device breaks down, communication between the mobile units can be continued by another radio communication terminal mounted on the same mobile unit. Wireless communication can be realized.

  FIG. 3 is a flowchart showing a channel acquisition procedure of each wireless communication terminal between a plurality of mobile groups by the data slot allocation method according to the present invention, and FIG. 4 is a pause count control used in the channel acquisition procedure of FIG. FIG. 5 is a time chart showing communication channel acquisition by the data slot allocation method according to the present invention.

  In a wireless communication environment having a plurality of mobile groups arranged at short distances as shown in FIG. 8, it is most efficient for each group to acquire a communication right in order. In such a situation, in order to obtain the optimum communication right, as shown in the flowchart of FIG. 3, the number of groups other than the own group existing in the wireless communication area is monitored, and a certain group obtains the communication right once. It is effective to pause the transmission of the beacon signal and / or the data signal once in one cycle (beacon period + data period, hereinafter the same). In other words, when the group that acquired the communication right pauses the communication right acquisition work after the end of the communication, the other group can independently transmit the beacon signal and / or the data signal, and the communication right can be acquired. Become. This is because even when three or more groups exist in a wireless communication area, if one group of them stops transmitting beacons and / or data signals, the competitors will be reduced for other groups. Therefore, equality of channel acquisition is realized, and even when a mobile group comes close in a communication environment with poor visibility, the communication channel acquisition collision probability is reduced and the communication channel acquisition probability is increased.

With reference to the transmission suspension frequency control table in FIG. 4 and the time chart of each wireless communication terminal in FIG. 5 for an example in which two data slots are assigned to each wireless communication terminal as an example of a specific procedure of the above processing, FIG. The flowchart will be described. Here, the beacon transmission wireless communication terminal (A-1) and the beacon transmission wireless communication terminal (B-1) use the pause counter to determine whether or not to transmit a beacon.
That is, in FIG. 3, the control unit 13 of the beacon transmission wireless communication terminal (A-1) 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 S5. Proceed (step S1).

When the pause counter = 0 in step S1, the control unit 13 of the wireless communication terminal (A-1) counts the type of group ID acquired from the received beacon. 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. 8, the number of groups is 2, and other than the own group) 4) (step S2). Based on this acquired value, the number of pauses is obtained from the pause count setting table 40 as shown in FIG. 4, and this is set as the beacon transmission pause count. The counter is set (in the example of FIG. 8, since the number of groups other than its own group = 1), the number of pauses 2 is obtained from the pause count setting table and set in the pause counter (step S3).

  And the control part 13 of a radio | wireless communication terminal (A-1) makes the radio | wireless communication part 12 transmit a beacon signal and a data signal, and complete | finishes a beacon transmission process (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).

  With the above operation, if a beacon signal is transmitted and a communication channel is acquired, acquisition of the communication channel can be stopped for a time corresponding to a period (beacon period + data period) corresponding to the number of beacon transmission suspensions. That is, in the example of the group in FIG. 8, the beacon transmission wireless communication terminal (A-1) transmits a beacon signal and a data signal every other time as shown in FIG. Further, the wireless communication terminal (A-2) of group A can transmit a data signal during this period. Similarly, the beacon transmission wireless communication terminal (B-1) also transmits a beacon signal and a data signal every other time. Group B wireless communication terminals (B-2) can transmit data signals during this period.

  Since the beacon transmission wireless communication terminal (A-1) and the beacon transmission wireless communication terminal (B-1) transmit the beacons alternately by changing the channel acquisition cycle, the communication channels are alternately switched as shown in FIG. Can be obtained. 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.

  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.

It is a block diagram which shows the structure of one Example of the radio | wireless communication terminal mounted in each mobile body in the radio | wireless communications system of this invention. It is a figure which shows the example of several data slot allocation. It is a flowchart which shows the channel acquisition procedure of each radio | wireless communication terminal between several mobile groups by the data slot allocation method by this invention. It is a figure which shows the example of a setting of the suspension frequency control table used by the channel acquisition procedure of FIG. 6 is a time chart showing communication channel acquisition by a data slot allocation method according to the present invention. It is explanatory drawing of the radio | wireless communication environment which is easy to produce a radio | wireless communication area overlap. It is a figure which shows the communication channel acquisition procedure in the mobile radio | wireless communications system by a prior art. It is a figure which shows an example of a radio | wireless communication area overlap. It is explanatory drawing of the channel collision at the time of the wireless area overlap of FIG.

Explanation of symbols

12 wireless communication unit 13 control unit 100 wireless communication terminal (beacon station, client station)
A, B Mobile group (group)
A-1, A-2, B-1, B-2 Mobile body (mobile body, vehicle)

Claims (2)

A wireless communication system in which a plurality of groups configured by performing wireless communication between a plurality of mobile units is set, and in each group, one mobile unit is assigned to a beacon station, and other mobile units belonging to the group 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 signal is transmitted from the beacon station of each group in the beacon period, and each mobile unit receives the beacon signal of the group to which the mobile unit belongs only during the data slot period allocated to the mobile unit. the wireless communication system using the communication protocol that will be controlled so as to transmit the data signal Stomach,
When a plurality of data slots in the data period are allocated to each mobile unit of each group and a beacon signal of a group to which the mobile unit belongs is received, the beacon station or client station of each group receives the data period. Transmitting a data signal in the plurality of data slots allocated to the own mobile body,
When one beacon period and one subsequent data period are combined into one cycle, the beacon stations of each group transmit beacon signals according to a specified beacon interval, and after transmitting the beacon signal, The beacon signal transmission is suspended for a period corresponding to the number of groups existing in 1 plus one, and beacon stations in groups other than the own group and the other group halt the transmission of beacon signals. Create a cycle ,
Each mobile unit is equipped with a number of wireless communication terminals corresponding to the number of data slots to which the mobile unit is allocated among the data slots, and when transmitting a data signal in each allocated data slot, Rukoto to transmit data signals using different wireless communication terminal ones of said plurality of wireless communication terminals to each of the allocated data slots,
A wireless communication system. The wireless communication system according to claim 1 , wherein the group performs wireless communication through a mobile communication network, and the mobile body is a vehicle.

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