JP2020010280A - Beacon transmission terminal, beacon reception terminal, and radio communications system - Google Patents

Abstract

To enable a communication system for avoiding increase in a communication delay time caused by radio wave interference with other radio communications systems mounted in the same vehicle and another vehicle.SOLUTION: A radio communications system takes one of a plurality of radio terminals as a beacon transmission terminal in predetermined order and takes the remaining radio terminals as a beacon reception terminal every time communication channel changeover is performed. The beacon transmission terminal includes: a beacon generation unit for generating a start beacon, an intermediate beacon, and an end beacon; a timer unit for clocking a channel changeover period; and a channel changeover unit for changing over a communication channel according to a predetermined rule. The beacon generation unit makes the start beacon include time synchronization information, makes the end beacon include channel changeover information, and generates an intermediate beacon including time information representing time at which a transmission request is generated when the transmission request is generated in an intermediate beacon transmission/reception section.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a beacon transmitting terminal, a beacon receiving terminal, and a wireless communication system that avoid an increase in communication delay time due to radio wave interference with another wireless communication system mounted in the same vehicle and another vehicle.

  2. Description of the Related Art Conventionally, a method for avoiding the occurrence of radio wave interference with a wireless device of another wireless communication system has been proposed.

For example, Patent Document 1 proposes a method in which a control device is arranged in a wireless network including one or more terminal devices, and the control device controls wireless communication using a plurality of frequency channels.
The control device includes a wireless reception unit, a quality determination unit, and a beacon generation unit. The wireless receiving unit is capable of receiving wireless signals of a plurality of frequency channels, and based on the reception state of the wireless signal received by the wireless receiving unit, determines a usable frequency channel by the quality determining unit, and Determine the order of use.
Then, the beacon generation unit generates a beacon including the use order information of the frequency channel, and transmits the beacon to the terminal device. The channel setting unit of the terminal device that has received the beacon sets the frequency channel to be used according to the use order information (see FIG. 19 (FIG. 14 of Patent Document 1)).
In a superframe period including an active period in which wireless communication can be performed and an inactive period in which wireless communication is not performed, the active period is divided into a plurality of beacon transmission periods, and beacons are periodically transmitted during the beacon transmission period. This is transmitted (see FIG. 16 (FIG. 4 of Patent Document 1), FIG. 17 (FIG. 6 of Patent Document 1), and FIG. 18 (FIG. 6 of Patent Document 1)).

In addition, for example, Patent Literature 2 proposes a system using a system in which communication is performed by temporarily using a frequency band that is not allocated to itself. That is, this is a system in which communication is performed by sharing a part of a license band allocated to a wireless communication system different from the own system. Specifically, before starting communication, the first carrier sense is performed for a predetermined number of L (L ≧ 2) frequency bands, and M frequency bands are selected from among them, and a time slot is selected. , The second carrier sense is performed on M (L ≧ M ≧ 2) frequency bands, and a frequency band to be used for transmission is determined from unused frequency bands. (See FIG. 20 (FIG. 7 of Patent Document 2) and FIG. 21 (FIG. 8 of Patent Document 2)). At this time, if the previously used frequency band is among the final candidates, that frequency band is used. Alternatively, a frequency band that is frequently used is preferentially used.
Note that the wireless terminal includes a matched filter or the like, calculates a correlation value between a signal sequence identical to a known sequence stored in advance and a leading sequence of a received signal, and specifies a frequency band used for transmission. (See FIG. 22 (FIG. 9 of Patent Document 2)).

Further, for example, in Patent Document 3, in a distributed autonomous wireless communication network that does not require a specific control station, a channel is periodically synchronized with reception of a beacon in a communication environment in which a plurality of channels are prepared. By changing the communication method, a method has been proposed in which communication can be performed on another communication channel even if the communication state of a specific channel is poor.
In other words, when communication is performed while staying on the same channel, communication cannot be performed if the communication condition of the channel is poor due to interference or the like. Of bad channels can be avoided.
Therefore, at the transmission timing of each wireless terminal, a beacon is transmitted before data transmission to synchronize the wireless terminals. Immediately after transmitting the beacon, the wireless terminal that transmitted the beacon is given a communication priority assignment section, and after a certain period of time, other wireless terminals can transmit (FIG. 23 (FIG. 3 of Patent Document 3)). ), FIG. 24 (see FIG. 7 of Patent Document 3)).
Further, since the channel is changed regularly, a mechanism for determining and notifying a communication channel between terminals is not required, and the operation is simplified (see FIG. 25 (FIG. 13 of Patent Document 3)).

International Publication No. 2010/007738 Japanese Patent Application Laid-Open No. 2007-300421 JP 2005-079985 A

However, according to the disclosures of Patent Literature 1, Patent Literature 2, and Patent Literature 3, it is possible to independently avoid a frequency band in which interference occurs and to avoid an increase in communication delay time when radio wave interference occurs for a long time. This can be difficult.
Therefore, an object of the present invention is to provide means for solving such a problem.

In order to solve the above problems, the present invention employs the following configuration.
That is, the invention according to claim 1 provides a beacon for a wireless communication system in which one of a plurality of wireless terminals is a beacon transmitting terminal in a predetermined order each time a communication channel is switched, and the remaining wireless terminals are beacon receiving terminals. A transmitting terminal,
A beacon generator that generates a start beacon, an intermediate beacon, and an end beacon;
A communication unit for transmitting and receiving the start beacon, data information, the intermediate beacon and the end beacon,
A timer unit that measures a communication channel switching cycle of the communication unit,
A channel switching unit that switches the communication channel of the communication unit according to a predetermined rule in accordance with the switching cycle of the communication channel,
The beacon generation unit includes the start beacon including timer information measured by the timer unit as time synchronization information, the end beacon including channel switching information indicating a timing of switching the communication channel, and transmitting and receiving an intermediate beacon. When a transmission request is generated in the section, it is time information indicating the time at which the transmission request is generated, and generates an intermediate beacon including the time information measured by the timer unit,
The communication unit transmits the start beacon before the start of transmission and reception of the data information, transmits the intermediate beacon when a transmission request is generated in an intermediate beacon transmission and reception section, and after the transmission and reception of the data information, Send an end beacon,
The channel switching unit, at the end of the communication channel switching cycle, while switching the communication channel based on the predetermined rule, reset the timer unit,
The intermediate beacon transmission / reception section is a period in which reception of a response signal to the data information from transmission of the data information over the communication channel cannot be completed before transmission of the end beacon.

According to the above configuration, the beacon transmitting terminal switches the communication channel based on a predetermined rule at the end of the communication channel switching period, so that the beacon transmission terminal autonomously avoids the communication channel that is a frequency band that is receiving interference. be able to. Therefore, it is possible to avoid an increase in communication delay time by avoiding a communication channel in which radio wave interference occurs for a long time.
Further, even if the timing of the transmission frame of the beacon receiving terminal is shifted by a predetermined period, time synchronization information for synchronizing the timer part of the beacon receiving terminal included in the start beacon with the beacon transmitting terminal, and channel switching included in the end beacon. The information allows resynchronization between the beacon transmitting terminal and the beacon receiving terminal.
Furthermore, when transmission / reception of data information is not completed in the transmission frame, the wireless terminal transmits an intermediate beacon in the intermediate beacon transmission / reception section, thereby shortening the communication delay time and effectively utilizing the transmission frame. Become. Further, by transmitting the intermediate beacon in advance, the period of the transmission / reception operation for the transmission request in the next communication channel can be omitted, so that the transmission frame can be effectively used.

  According to a second aspect of the present invention, in the beacon transmission terminal according to the first aspect, the beacon generation unit generates a transmission request included in the intermediate beacon transmitted and received by the communication unit. Based on the time information, the transmission order of the wireless terminal transmitting data information on the next communication channel is determined in the time order of the time information at which the transmission request occurred, and the transmission order information and the identification information of the wireless terminal are determined. Is included in the end beacon as transmission request information.

  According to the above configuration, the transmission order of the wireless terminals transmitting data information on the next communication channel is determined in the order of the time information of the time when the transmission request is generated, so that the wireless terminal having a long delay time is given priority first. Since the data information can be transmitted to the user, the delay time can be reduced.

In order to solve the above-mentioned problem, the invention according to claim 3 is the beacon transmission terminal according to claim 2, wherein, when the communication unit receives the end beacon of the immediately preceding communication channel, the beacon generation unit The transmission request information included in the end beacon as the transmission request information included in the start beacon,
If the communication unit cannot receive the end beacon of the last communication channel, the beacon generation unit, based on time information when a transmission request included in the intermediate beacon transmitted and received on the last communication channel, In the time order of the time information at which the transmission request occurred, the transmission order of the wireless terminal transmitting the data information is determined, and the transmission order information and the identification information of the wireless terminal are included in the start beacon as transmission request information. Features.

According to the above configuration, even when the beacon transmission terminal of the next communication channel cannot receive the end beacon, the beacon transmission terminal of the next communication channel that has received the intermediate beacon determines the transmission order of the wireless terminals. Then, it becomes possible to transmit the transmission order information in the start beacon.
Therefore, even if the end beacon receives interference, if the wireless terminal can transmit and receive the start beacon including the transmission order information, the delay time until the wireless terminal that has issued the transmission request transmits the data information can be reduced. Becomes possible.

  In order to solve the above-mentioned problem, the invention according to claim 4 is the beacon transmission terminal according to any one of claims 1 to 3, wherein the transmission is started when the transmission order of the beacon transmission terminal is first. After transmitting the beacon, the data information is transmitted without providing a waiting time.

  According to the above configuration, the wireless terminal can immediately transmit data information from the beginning of the transmission frame, so that the transmission frame can be effectively used. As an example, since transmission can be performed while skipping a contention window or the like employed in the CSMA / CA system, the time until the start of transmission can be shortened, and the transmission frame can be effectively used. Will be possible.

  In order to solve the above problem, the invention according to claim 5 is the beacon transmission terminal according to any one of claims 2 to 4, wherein the intermediate beacon further includes priority information indicating a priority of data information. The transmission order of the data information having the higher priority of the priority information is earlier than the transmission order of the data information having the lower priority of the priority information, and the data information having the same priority of the priority information is The transmission order is determined according to the time order of the time information at which the transmission request occurred.

  According to the above configuration, it is possible to transmit data information with high urgency with priority over other data information. As an example, when the wireless communication system is mounted on a vehicle or the like, the vehicle can control the vehicle smoothly by transmitting and receiving data information related to vehicle control with higher priority than data information related to entertainment such as music. Becomes possible.

  In order to solve the above problem, according to a sixth aspect of the present invention, in the beacon transmitting terminal according to any one of the first to fifth aspects, one of a plurality of wireless terminals is determined in advance each time the communication channel is switched. The beacon transmitting terminal to be a beacon transmitting terminal in the order described, among the wireless terminals included in the wireless communication system, the distance between the wireless terminals is within a predetermined range from the middle point on the longest line It is determined for wireless terminals.

  According to the above configuration, the wireless communication system of the present scheme can be smoothly operated by not using the wireless terminal that may have a bad communication environment as the beacon transmitting terminal. As an example, when a wireless communication system is mounted on a vehicle or the like, by using a wireless terminal arranged in the center of the vehicle as a beacon transmitting terminal, communication with wireless terminals arranged in front and rear of the vehicle is performed. The success rate can be increased and the wireless communication system can operate smoothly.

In order to solve the above problem, the invention according to claim 7 is configured such that each time a communication channel is switched, one of a plurality of wireless terminals is a beacon transmitting terminal in a predetermined order, and the remaining wireless terminals are a beacon receiving terminal. A beacon receiving terminal of a wireless communication system,
A beacon generator for generating an intermediate beacon,
A communication unit that receives a start beacon and an end beacon, and transmits and receives data information and the intermediate beacon,
A timer unit that measures a communication channel switching cycle of the communication unit,
A channel switching unit that switches the communication channel of the communication unit according to a predetermined rule in accordance with the switching cycle of the communication channel,
When the communication unit receives the start beacon, the timer unit sets time synchronization information included in the start beacon to the timer unit,
When the communication unit receives the termination beacon, the channel switching unit switches the communication channel after a predetermined period after receiving channel switching information indicating a timing of switching the communication channel included in the termination beacon. Reset the timer section,
The beacon generation unit, when a transmission request occurs in the intermediate beacon transmission / reception section, generates an intermediate beacon that is time information indicating a time when the transmission request is generated and includes the time information measured by the timer unit. ,
The intermediate beacon transmission / reception section is a period in which reception of a response signal to the data information from transmission of the data information over the communication channel cannot be completed before reception of the end beacon.

According to the above configuration, since the beacon receiving terminal switches the communication channel based on a predetermined rule at the end of the communication channel switching period, the beacon receiving terminal autonomously avoids the communication channel that is the frequency band that is receiving interference. be able to. Therefore, it is possible to avoid an increase in communication delay time by avoiding a communication channel in which radio wave interference occurs for a long time.
Further, even if the timing of the transmission frame of the beacon receiving terminal is shifted by a predetermined period, the timer section of the beacon receiving terminal is resynchronized with the beacon transmitting terminal with the time synchronization information included in the first start beacon of the transmission frame, and It becomes possible to resynchronize with the beacon transmitting terminal by the channel switching information included in the last end beacon.
Furthermore, when transmission / reception of data information is not completed in the transmission frame, the wireless terminal transmits an intermediate beacon in the intermediate beacon transmission / reception section, thereby shortening the communication delay time and effectively utilizing the transmission frame. Become. Further, by transmitting the intermediate beacon in advance, the period of the transmission / reception operation for the transmission request in the next communication channel can be omitted, so that the transmission frame can be effectively used.

  In order to solve the above-mentioned problem, the invention according to claim 8 is the beacon receiving terminal according to claim 7, wherein the transmission order of the beacon receiving terminal is the first based on the transmission order information included in the start beacon. In this case, after receiving the start beacon, data information is transmitted without providing a waiting time.

  According to the above configuration, the wireless terminal can immediately transmit data information from the beginning of the transmission frame, so that the transmission frame can be effectively used. As an example, since transmission can be performed while skipping a contention window or the like employed in the CSMA / CA system, the time until the start of transmission can be shortened, and the transmission frame can be effectively used. Will be possible.

  In order to solve the above problem, the invention according to claim 9 is the beacon receiving terminal according to any one of claims 6 to 8, wherein the communication unit is continuously connected to all communication channels, and the start beacon and the In a case where the end beacon is not received, the channel switching unit waits for reception of the start beacon or the end beacon on the communication channel set first in the communication channel switching order.

If the synchronization between the beacon receiving terminal and the beacon transmitting terminal is shifted by more than the transmission frame period, the beacon receiving terminal cannot receive the start beacon and the end beacon, so the period during which resynchronization with the beacon transmitting terminal cannot be performed is long. Is more likely to occur.
However, according to the above configuration, the beacon receiving terminal stops the switching operation of the communication channel and waits on the initial communication channel so that the beacon receiving terminal can receive the start beacon or the end beacon, and resynchronizes with the beacon transmitting terminal. It becomes possible.

  In order to solve the above problem, an invention according to claim 10 includes the beacon transmission terminal according to any one of claims 1 to 6 and the beacon reception terminal according to any one of claims 7 to 9. I do.

According to the above configuration, the beacon transmitting terminal and the beacon receiving terminal switch the communication channel based on a predetermined rule at the end of the communication channel switching period, so that the communication channel that is the frequency band that is receiving interference is changed. Can be avoided independently. Therefore, it is possible to avoid an increase in communication delay time by avoiding a communication channel in which radio wave interference occurs for a long time.
Further, even if the timing of the transmission frame of the beacon receiving terminal is shifted by a predetermined period, the timer section of the beacon receiving terminal is resynchronized with the beacon transmitting terminal with the time synchronization information included in the first start beacon of the transmission frame, and It becomes possible to resynchronize with the beacon transmitting terminal by the channel switching information included in the last end beacon.
Further, when transmission / reception of data information is not completed in the transmission frame, the wireless terminal sets an intermediate beacon transmission / reception section and transmits the intermediate beacon, thereby reducing communication delay time and effectively utilizing the transmission frame. Becomes possible. Further, by transmitting the intermediate beacon in advance, the period of the transmission / reception operation for the transmission request in the next communication channel can be omitted, so that the transmission frame can be effectively used.

  ADVANTAGE OF THE INVENTION According to this invention, while avoiding the communication channel which is a frequency band which is receiving interference autonomously, it becomes possible to avoid the increase of communication delay time when radio wave interference occurs for a long time.

  Further, when the transmission and reception of the data information and the response signal are not completed in one transmission frame, the wireless terminal sets an intermediate beacon transmission / reception section and transmits the intermediate beacon, thereby reducing the communication delay time and transmitting the transmission frame. It can be used effectively.

It is an example of the wireless communication network which comprises a wireless communication system. FIG. 3 is a block diagram illustrating a configuration example of hardware of a wireless terminal. FIG. 4 is a diagram illustrating a beacon transmission timing and a communication channel switching timing in the embodiment. It is a figure showing composition of a start beacon. It is a figure showing composition of an end beacon. FIG. 3 is a diagram illustrating a configuration example of a data frame. It is an example of the transmission frame of a beacon transmission terminal. 5 is a flowchart illustrating an initial operation after the wireless terminal is activated. It is the flowchart which showed the process after switching a communication channel. It is a flowchart at the time of a radio | wireless terminal operating as a beacon transmission terminal. It is a flowchart at the time of a radio | wireless terminal operating as a beacon transmission terminal. It is a flowchart at the time of a radio | wireless terminal operating as a beacon receiving terminal. It is a flowchart at the time of a radio | wireless terminal operating as a beacon receiving terminal. FIG. 4 is a diagram illustrating an example of a channel switching order when interference does not occur in a communication channel. It is a schematic diagram which shows resynchronization of a beacon receiving terminal by beacon reception. It is a schematic diagram which shows an intermediate beacon transmission / reception section. It is another example of the wireless communication network which comprises a wireless communication system. 13 is a diagram for describing Patent Document 1 which is a conventional technique. 13 is a diagram for describing Patent Document 1 which is a conventional technique. 13 is a diagram for describing Patent Document 1 which is a conventional technique. 13 is a diagram for describing Patent Document 1 which is a conventional technique. 11 is a diagram for describing Patent Document 2 which is a conventional technique. 11 is a diagram for describing Patent Document 2 which is a conventional technique. 11 is a diagram for describing Patent Document 2 which is a conventional technique. 11 is a drawing for explaining Patent Document 3 which is a conventional technique. 11 is a drawing for explaining Patent Document 3 which is a conventional technique. 11 is a drawing for explaining Patent Document 3 which is a conventional technique.

(Overview of wireless communication system)
In the wireless network composed of a plurality of wireless terminals according to the present embodiment, each wireless terminal performs communication by regularly switching two or more communication channels (frequency bands) to thereby perform frequency band interference. Can communicate independently. Each wireless terminal transmits a beacon at the beginning and end of a transmission frame in a preset beacon transmission order, and synchronizes with other wireless terminals. The channel switching cycle is predetermined, and as soon as the switching time is reached, each wireless terminal autonomously switches the frequency. Even if the synchronization signal by the beacon cannot be received, as described above, since each wireless terminal can independently switch the frequency, all wireless terminals can communicate on the same communication channel.

  Since the time spent in the communication channel is always constant, communication may not be completed before the communication channel is switched even if a transmission request is made immediately before switching the communication channel. In such a case, even if a transmission request occurs, the wireless terminal cannot start communication. Therefore, if a transmission request is issued even though communication cannot be terminated by the time the communication channel is switched, the wireless terminal that has issued the transmission request transmits an intermediate beacon, so that all wireless terminals have a transmission request. Notify that. Then, based on the information included in the intermediate beacon, the wireless terminal transmitting the end beacon determines in advance the order of the wireless terminals performing the transmission operation on the next communication channel. For example, when a plurality of transmission requests have occurred, the wireless terminal transmitting the end beacon determines the transmission order so that the wireless terminal having the earlier time at which the transmission request occurred can start the transmission operation preferentially. The transmission request occurrence time is based on the reception time of the start beacon immediately before the transmission request occurs. Also, the transmission order of the wireless terminals that have transmitted the intermediate beacon can be determined by the wireless terminal that transmits the start beacon after switching the communication channel, but the details will be described later.

  Information on the wireless terminal that performs the determined transmission operation is transmitted to all wireless terminals in an end beacon and a start beacon after the communication channel is switched. Immediately after the start beacon is transmitted / received, the wireless terminal starts the transmission operation based on the determined order. In this case, the time until the start of transmission can be reduced by skipping a contention window or the like adopted in the CSMA / CA (Carrier Sense Multiple Access / Collision Aidance) system. Also, in the CSMA / CA system, a transmitting wireless terminal is selected at random. However, according to this system, a wireless terminal having a long delay time can be preferentially transmitted first, so that the delay time can be reduced. As a basic operation of the wireless terminal, except for data transmission, Ack (Acknowledgment) transmission, and beacon transmission operation, the terminal always waits in a reception state and detects reception strength. Further, it is determined from the detected reception intensity whether it is data, a beacon, Ack, or the like, or interference.

  FIG. 1 illustrates a configuration example of a wireless communication network that configures the wireless communication system according to the present embodiment. In FIG. 1, the wireless terminals 11 to 20 constitute a wireless communication network 1000. The CSMA / CA system is assumed as the wireless communication system.

  FIG. 2 illustrates an example of a hardware block diagram of the wireless terminal 200 according to the present embodiment. The beacon transmitting terminal and the beacon receiving terminal described in the claims are realized as the wireless terminal 200. The wireless terminal 200 is a general computer including a communication unit 210, a determination unit 220, a control unit 230, an I / F (interface) unit 240, and an information recording unit 250. The functions shown in FIG. 2 are realized by a general computer executing the communication program. The control unit 230 is a CPU (Central Processing Unit). The control unit 230 executes processing in the wireless terminal 200 by reading and writing data stored in the information recording unit 250 and inputting and outputting data to and from the communication unit 210.

  The communication unit 210 includes a transmission / reception switching unit 211, a wireless transmission unit 212, and a wireless reception unit 213. When the wireless terminal 200 is in the transmission mode, the transmission / reception switching unit 211 connects the antenna and the wireless transmission unit 212. When the wireless terminal 200 is in the reception mode, the transmission / reception switching unit 211 connects the antenna and the wireless reception unit 213.

  The transmission / reception switching unit 211 switches the wireless terminal 200 to the transmission mode when transmitting data or a beacon, and switches the wireless terminal 200 to the reception mode otherwise.

  The wireless transmission unit 212 has a function of transmitting wireless signals such as data, a start beacon, an intermediate beacon, and an end beacon.

  The wireless reception unit 213 has a function of performing reception processing of wireless signals such as data received from another wireless terminal 200 via an antenna, a start beacon, an intermediate beacon, and an end beacon.

  Determination section 220 includes a reception strength determination section 221 and an interference determination section 222.

  The reception intensity determination unit 221 has a function of determining whether the power of the reception signal has exceeded a threshold level.

  The interference determination unit 222 has a function of determining whether the received signal exceeding the threshold level is from the own wireless communication system or from another wireless communication system. If the signal is a signal received by another wireless communication system, it is determined that interference has occurred in the current communication channel.

  The control unit 230 includes a beacon generation unit 231, a data generation unit 232, a beacon analysis unit 233, a channel switching unit 234, a data processing unit 235, and a timer unit 236. The control unit 230 transmits and receives data to and from the I / F (interface) unit 240, transmits and receives information to and from the information recording unit 250, transmits data and beacon information to the wireless transmitting unit 212, It receives data and beacon information.

  The beacon generation unit 231 starts a beacon when the own wireless terminal 200 transmits a beacon as a beacon transmission terminal based on the beacon transmission order information, the channel switching cycle information, and the timer information stored in the information recording unit 250. Alternatively, it has a function of generating and transmitting an end beacon. Further, when a transmission request is issued to the own wireless terminal 200 in the intermediate beacon transmission / reception section, a function of generating an intermediate beacon for transmitting information indicating that a transmission request has been issued to the own wireless terminal 200 to another wireless terminal 200 Having.

  In other words, when a transmission request is issued to the own wireless terminal 200 and transmission / reception of data information and transmission / reception of Ack for data information are not completed in the remaining period of the current communication channel, the beacon generation unit 231 sets the intermediate Generate a beacon. Details of the conditions for generating the intermediate beacon will be described later.

  The intermediate beacon includes identification information of the wireless terminal 200 transmitting the intermediate beacon, and time information at which the transmission request occurred. The time information at which the transmission request occurred is based on the reception time of the start beacon immediately before the transmission request occurred.

  In addition, the beacon transmitting terminal that has transmitted the start beacon receives the intermediate beacon, and, in order from the wireless terminal 200 having the earliest time at which the transmission request has occurred, reserves the right of which wireless terminal 200 to transmit on the next communication channel. Determine the information that you have. That is, the wireless terminal 200 that has transmitted the start beacon has determined the transmission order in the next communication channel of the wireless terminal 200 that has transmitted the intermediate beacon, and associated the transmission order information with the identification information of the wireless terminal 200. The transmission request information is included in the end beacon.

  The end beacon includes transmission request information in which transmission order information of the wireless terminal 200 on the next communication channel and identification information of the wireless terminal 200 are associated with each other, and channel switching information (CH switching) indicating channel switching timing. Information). Also, at the head of the end beacon, address information of the beacon transmitting terminal that transmitted the end beacon is added. The address information is identification information of the beacon transmitting terminal.

  Further, the start beacon includes transmission request information in which transmission order information of the wireless terminal 200 and identification information of the wireless terminal 200 on the communication channel through which the start beacon is transmitted and received, and synchronization between the wireless terminals 200 Time synchronization information for taking Also, at the beginning of the start beacon, address information of the beacon transmitting terminal that transmitted the start beacon is added. The address information is identification information of the beacon transmitting terminal.

  Here, the time synchronization information included in the start beacon may be timer information of a beacon transmitting terminal that transmitted the start beacon. The wireless terminal 200 that has received the start beacon writes the time synchronization information included in the start beacon to the timer unit 236 of the own wireless terminal 200. As a result, it becomes possible to synchronize between the beacon transmitting terminal that has transmitted the start beacon and the wireless terminal 200 that has received the start beacon.

  The data generation unit 232 has a function of generating data to be transmitted when a transmission request is issued from the I / F unit 240.

  The beacon analysis unit 233 extracts the above-described various beacon information included in the start beacon, the intermediate beacon, or the end beacon from the received start beacon, intermediate beacon, or the end beacon, and records the extracted information in the information recording unit 250. Has functions. In addition, as described above, the beacon analysis unit 233 of the beacon receiving terminal writes the time synchronization information extracted from the start beacon to the timer unit 236 to synchronize with the beacon transmission terminal.

  The channel switching unit 234 switches the communication channel after a lapse of a predetermined time after the reception of the channel switching information included in the termination beacon has been completed. The predetermined time is a time until the channel switching cycle of the beacon transmitting terminal ends. Therefore, the beacon transmitting terminal starts transmitting the end beacon so that the channel switching period ends after a predetermined time has elapsed from the transmission completion timing of the end beacon. The predetermined time can also be referred to as a channel switching grace period.

  Further, when the beacon receiving terminal cannot receive the end beacon, it reads the timer information stored in the information recording unit 250 and switches the communication channel when the channel switching period specified by the channel switching period information is reached. Do. When switching the communication channel, the channel switching unit 234 specifies the next communication channel to be changed based on the channel switching order information stored in the information recording unit 250, and switches the communication channel.

  The data processing unit 235 has a function of performing data processing on the received data and transmitting the data to the I / F unit 240.

  The timer unit 236 sets the channel switching cycle from the time when the communication channel is switched and the timer is reset to the time when the transmission and reception of the channel switching information included in the end beacon is completed and the communication channel is switched after the lapse of the channel switching grace period. Time as Here, the channel switching period is also the transmission frame length (Tms). The time measured by the timer unit 236 is recorded in the information recording unit 250 as timer information.

  Therefore, the transmission / reception of the end beacon is completed before the channel switching period by the channel switching grace period. Since the beacon transmission terminal recognizes the end beacon length, it starts transmission of the end beacon so that the transmission of the end beacon is completed before the channel switching period by the channel switching grace period. The channel switching grace period is predetermined in the wireless communication system, and all wireless terminals 200 included in the wireless communication system record the information in the information recording unit 250.

  The I / F unit 240 has an interface function with an external device. The external device can be any electronic device.

  The information recording unit 250 stores various information including timer information, transmission request information, channel switching cycle information, channel switching order information, and beacon transmission order information, and transmits and receives each information to and from the control unit 230. .

  The timer information records the elapsed time from the beginning of the channel switching cycle as time information in real time based on the time measured by the timer unit 236 in units of a predetermined channel switching cycle. When the wireless terminal 200 extracts the time synchronization information from the received start beacon, the wireless terminal 200 sets the time synchronization information in the timer unit 236 and transmits the start beacon, and the wireless terminal 200 that receives the start beacon. And synchronize with. That is, the timer unit 236 restarts counting from the time indicated by the time synchronization information, and records the counted time information in the information recording unit 250 as timer information.

  Further, after switching the communication channel, wireless terminal 200 resets and initializes timer section 236 (see FIG. 9). All the wireless terminals 200 keep time in units of the predetermined channel switching period, and when the start beacon and the end beacon cannot be received, the communication channel is automatically changed at the channel switching period. I do.

  Further, the transmission request information of the information recording unit 250 includes identification information of the wireless terminal 200 and transmission order information associated with the identification information of the wireless terminal 200. The transmission request information of the information recording unit 250 is the same as the transmission request information included in the end beacon or the start beacon.

  As described above, the transmission order is determined so that the wireless terminal 200 that has received the intermediate beacon can transmit in order from the wireless terminal 200 that has transmitted the intermediate beacon with the earliest time information at which the transmission request included in the intermediate beacon has occurred. The transmission request information may simply be arranged according to the transmission order of the identification information of the wireless terminal 200. Further, in the transmission request information, the time information at which the transmission request occurred may be recorded in association with the identification information of the wireless terminal 200 that transmitted the intermediate beacon.

  In the channel switching cycle information, information indicating a predetermined switching cycle of the communication channel is recorded. That is, the time (Tms) from the timing when the switching of the communication channel is completed to the timing when the transmission / reception of the channel switching information included at the end of the end beacon is completed and the channel is switched after the elapse of the channel switching grace period is recorded. I have.

  That is, as an example, the transmission frame length (Tms) is recorded in the information recording unit 250 as channel switching cycle information.

  In the channel switching order information, a predetermined switching order of communication channels is recorded. That is, when no interference occurs in the communication channel, the wireless terminal 200 switches the communication channel in the channel switching order. For example, as shown in FIG. 12, the channel switching order is set so that all the communication channels prepared in one cycle are used once. When one cycle of the channel switching order ends, the wireless terminal 200 selects a communication channel again from the head of the channel switching order.

  In the beacon transmission order information, the order in which the wireless terminal 200 becomes the beacon transmission terminal is recorded. For example, if the identification information of the wireless terminals 200 is sequentially recorded in the beacon transmission order information, the wireless terminal 200 can recognize which wireless terminal 200 will be the beacon transmission terminal every time the communication channel is switched. When one cycle of the beacon transmission order ends, the wireless terminal 200 to be the beacon transmission terminal is determined again from the beginning of the beacon transmission order.

  All the wireless terminals 200 included in the wireless communication system are sequentially beacon transmission terminals, some wireless terminals 200 included in the wireless communication system are sequentially beacon transmission terminals, and beacon transmission terminals. The wireless terminal 200 may be fixed.

  For example, each time the communication channel is switched, a beacon transmission terminal that sets one of the plurality of wireless terminals 200 to a beacon transmission terminal in a predetermined order is a wireless terminal 200 among the wireless terminals 200 included in the wireless communication system. Is determined for the wireless terminal within a predetermined range from the midpoint on the longest line

  That is, the wireless communication system of the present system can be smoothly operated by not using the wireless terminal that may have a bad communication environment as the beacon transmitting terminal.

  As an example, when a wireless communication system is mounted on a vehicle or the like, by using a wireless terminal arranged in the center of the vehicle as a beacon transmitting terminal, communication with wireless terminals arranged in front and rear of the vehicle is performed. The success rate can be increased and the wireless communication system can operate smoothly. That is, the wireless communication system can be operated more stably by not using the wireless terminal 200 located at the periphery of the communicable range of the wireless communication system as the beacon transmission terminal.

  FIG. 3 is a diagram schematically showing a transmission cycle of a start beacon and an end beacon and a channel switching cycle.

  First, as a beacon transmitting terminal, the wireless terminal 11 transmits a start beacon on CH (Channel: Channel) 1, which is an initial communication channel arranged at the head of the channel switching order information, transmits and receives data, and performs an end beacon. Send The transmission from the transmission of the start beacon to the transmission of the end beacon is performed within Tms, which is the channel switching cycle. At this time, the wireless terminals 12 to 20 receive a start beacon and an end beacon on CH1 as beacon receiving terminals. Tms is also a transmission frame period which is a data transmission / reception period. Tms is a fixed period while the wireless communication system is operating.

  After the wireless terminal 11 transmits the end beacon, all the wireless terminals switch to CH2, and the wireless terminal 12, which is the next wireless terminal after the wireless terminal 11, becomes a beacon transmitting terminal and transmits a start beacon. Hereinafter, similarly, transmission and reception of the start beacon and the end beacon and switching of the communication channel are repeated.

  In FIG. 3, a start beacon and an end beacon are transmitted in a Tms cycle. After the transmission and reception of the end beacon is completed and the channel switching grace period has elapsed, the communication channel is changed, and the start beacon is transmitted after the communication channel is switched. As described above, the cycle time T is a transmission frame period, and is defined in advance in the wireless communication system. Further, the wireless communication system cannot change the specified period time T while the wireless terminal is operating.

  Further, in FIG. 3, ten wireless terminals from the wireless terminal 11 to the wireless terminal 20 are used, and the number of the wireless terminals does not change during the operation of the wireless terminals. That is, the wireless terminal is basically a fixed station, and does not consider the mobile station. Therefore, the increase or decrease in the number of wireless terminals in the wireless communication network is not considered, and the wireless terminals to be assigned as the wireless terminals 20 from the wireless terminal 11 must be defined first. Further, as described above, there are cases where all or some of the wireless terminals in the wireless communication system are sequentially beacon transmitting terminals, and cases where the beacon transmitting terminals are fixed.

  When the wireless terminal is not operating, the wireless communication system can newly add or reduce the number of wireless terminals. For example, when the wireless communication system adds one new wireless terminal, the wireless communication system assigns the newly added wireless terminal as the wireless terminal 21 in the next order of the wireless terminal 20 and the beacon of all wireless terminals. Information such as transmission order information is also updated.

  FIG. 3 shows a basic communication channel switching period. With the initial channel set to CH1, all wireless terminals simultaneously switch in the order of CH1, CH2, and CH3 at Tms intervals. Also, the beacon transmitting terminal that transmits the beacon may switch from the wireless terminal 11 to the wireless terminal 20 in order at the Tms cycle.

  In this case, it is desirable that all wireless terminals can be synchronized by beacons. However, even when a beacon cannot be received, communication channels are automatically switched at Tms intervals, so that it is possible to synchronize between wireless terminals.

  That is, if the beacon receiving terminal can receive the end beacon, the reception of the channel switching information of the end beacon is completed, and the beacon receiving terminal switches the communication channel after the elapse of the channel switching grace period. When the beacon receiving terminal cannot receive the end beacon, the communication channel is switched based on the timer information of the information recording unit 250.

  FIG. 4 shows a configuration diagram of the start beacon. The start beacon includes a source address, transmission request information, and time synchronization information. The start beacon is transmitted at the beginning of a transmission frame period in which the wireless terminal 200 as a beacon transmitting terminal that transmits a beacon transmits and receives data.

  The transmission source address is the address of the wireless terminal 200 that transmitted the start beacon.

  The transmission request information includes identification information of the wireless terminal 200 and transmission order information associated with the identification information of the wireless terminal 200. When the wireless terminal 200 that has received the start beacon has transmitted an intermediate beacon on the immediately preceding communication channel, the wireless terminal 200 performs a data transmission operation according to the transmission order information included in the start beacon.

  When the wireless terminal 200 transmitting the start beacon can receive the immediately preceding end beacon, the wireless terminal 200 transmits transmission request information included in the end beacon as transmission request information included in the start beacon.

  When the wireless terminal 200 transmitting the start beacon cannot receive the immediately preceding end beacon, the wireless terminal 200 creates transmission request information from the intermediate beacon received on the immediately preceding communication channel. In other words, the wireless terminal 200 transmitting the start beacon determines, in order from the wireless terminal 200 having the earliest time at which the transmission request occurred, the information indicating which wireless terminal 200 has the right to transmit on the current communication channel. I do. In other words, the wireless terminal 200 that transmitted the start beacon determines the transmission order of the wireless terminal 200 on the communication channel that transmitted the start beacon, and includes the identification information and the transmission order information of the wireless terminal 200 as transmission request information in the start beacon. No, it broadcasts the start beacon.

  As an example, the transmission request information may be such that the identification information of the wireless terminal 200 is merely arranged according to the transmission order.

  Further, as another example, a delimiter is arranged at the end of the source address information, identification information of the wireless terminal and a number as transmission order information are arranged after the delimiter, and a delimiter is arranged after the number. The identification information of the other wireless terminal 200 is arranged next to the delimiter, the number as the transmission order information of the other wireless terminal 200 is arranged next to the identification information of the other wireless terminal 200, and the delimiter is arranged next to the number. May be repeated. The number between the delimiters indicates the transmission order of the wireless terminal 200 specified by the identification information of the wireless terminal 200 between the delimiters. Further, time information at which a transmission request occurs between the delimiters may be included.

  The time synchronization information is timer information recorded in the information recording unit 250 of the wireless terminal 200 transmitting the start beacon. The wireless terminal 200 that has received the start beacon sets the timer unit 236 to the time indicated by the time synchronization information included in the start beacon, so that the wireless terminals 200 can synchronize with each other. When there is a deviation in synchronization between the wireless terminals 200, the time synchronization information enables resynchronization between the wireless terminal 200 that has transmitted the start beacon and the wireless terminal 200 that has received the start beacon.

  FIG. 5 shows a configuration diagram of the end beacon. The end beacon includes a source address, transmission request information, and channel (CH) switching information. The end beacon is transmitted by the beacon transmitting terminal at the end of the transmission frame.

  The source address is the address of the wireless terminal 200 as the beacon transmitting terminal that transmitted the end beacon.

  The transmission request information includes identification information of the wireless terminal 200 and transmission order information associated with the identification information of the wireless terminal 200. If the wireless terminal 200 that has received the end beacon has transmitted the intermediate beacon on the communication channel that has received the end beacon, the wireless terminal 200 performs a data transmission operation on the next communication channel according to the transmission order information. The wireless terminal 200 that has received the end beacon records the transmission request information included in the end beacon in the information recording unit 250.

  However, when the wireless terminal 200 receives the start beacon on the next communication channel, the wireless terminal 200 performs the transmission operation based on the transmission order information of the transmission request information of the start beacon.

  The channel (CH) switching information is timing information for switching to the next communication channel. After the transmission and reception of the channel (CH) switching information is completed and the channel switching grace period has elapsed, all the wireless terminals 200 switch to the next communication channel. Switch to the communication channel of.

  If there is a deviation in the synchronization between the wireless terminals 200, the channel (CH) switching information enables resynchronization between the wireless terminals 200. That is, if the beacon receiving terminal can receive the end beacon, the communication channel is switched at the timing of completion of receiving the channel (CH) switching information of the end beacon, so that the start timing of the communication channel is synchronized. The beacon receiving terminal resets the timer unit 236 at the timing when the communication channel is switched.

  FIG. 6 shows a configuration example of a data frame. At the beginning of the data frame, there is a bit synchronization signal for synchronization in units of bits, followed by a frame synchronization signal for synchronization in units of frames, and then an ID unique to the wireless communication system. There is a header that contains Following the header, there is a payload, which is the body of the data, and finally there is an error detection and correction code for detecting and correcting data errors. In the transmission and reception of data information in the intermediate beacon transmission and reception section, the data frame has a fixed length. The wireless communication system can set the data frame length to an arbitrary length.

  As shown in FIG. 6, since the data frame includes an ID unique to the wireless communication system, it is determined whether the wireless signal received by wireless terminal 200 is a wireless signal of the own wireless communication system by determining the unique ID of the wireless signal. It can be determined based on whether or not reception was successful.

  FIG. 7 shows a transmission frame of the beacon transmission terminal X. The beacon transmitting terminal X transmits a start beacon at the beginning of a transmission frame and an end beacon at the end of the transmission frame. In other data transmission areas, a wireless terminal having a transmission request performs a transmission operation.

  Here, the transmission frame length (Tms) indicates a channel switching cycle. The transmission timing of the start beacon and the end beacon in the transmission frame is determined in advance by the wireless communication system.

  For example, the start beacon is transmitted with a delay of a predetermined rule time from the beginning of the transmission frame. This is because when synchronization is shifted between the wireless terminals 200, the timing at which the communication channels are switched may vary. The predetermined rule time is also referred to as a start beacon transmission grace period. Since the start beacon transmitting wireless terminal transmits the start beacon with a delay of the start beacon transmission grace period after the communication channel is switched, the probability that the wireless terminal 200 that is out of synchronization can receive the start beacon increases. Then, the wireless terminal 200 that has received the start beacon can resynchronize with the wireless terminal 200 that has transmitted the start beacon, based on the time synchronization information included in the start beacon.

  For example, if the switching timing of the communication channel of the wireless terminal 200 that could not receive the end beacon immediately before the start beacon is slightly delayed, and the start beacon is transmitted with a delay of the start beacon transmission grace period, the start beacon is transmitted. The probability of being received increases.

  The end beacon is transmitted such that the transmission / reception completion timing of the end beacon comes before the end of the transmission frame by the channel switching grace period. This is because, when the synchronization is shifted between the wireless terminals 200, the timing at which the communication channels are switched may vary. For example, the wireless terminal 200 in which the elapsed time of the timer information is earlier may not be able to receive the end beacon because the switching of the communication channel is earlier. However, if the transmission and reception completion timing of the end beacon is transmitted so as to be earlier than the end of the transmission frame by the channel switching grace period, the probability that the wireless terminal 200 that is out of synchronization can receive the end beacon increases. Then, the wireless terminal 200 that has received the end beacon can resynchronize with the wireless terminal 200 that has transmitted the end beacon, based on the channel switching information included in the end beacon.

  Note that the start beacon transmission grace period from the beginning of the transmission frame until the start beacon is transmitted and the channel switching grace period from the end of the transmission frame to the end of transmission and reception of the end beacon may be the same or different. , Any time can be set.

  If there is no transmission / reception of the intermediate beacon on the immediately preceding communication channel, a transmission right is given to all wireless terminals 200 after the start beacon is transmitted, and all wireless terminals 200 make a transmission request by CSMA / CA or the like. . Further, after the transmission of all the wireless terminals 200 that have made a transmission request by the intermediate beacon is completed, and before the intermediate beacon transmission / reception section described later, a transmission right is given to all the wireless terminals, and all the wireless terminals are assigned CSMA / A transmission request is made by a CA or the like.

  FIG. 8 is a flowchart illustrating an initial operation when the wireless terminal 200 is activated.

  In step S801, when the wireless terminals 200 are activated, each wireless terminal 200 sets a communication channel to an initial channel predetermined in the wireless communication system. This is performed by each wireless terminal 200 referring to the channel switching order information of the information recording unit 250 and setting the first communication channel of the channel switching order information as the initial channel. Next, the wireless terminal 200 proceeds to step S802.

  In step S802, it is determined whether the wireless terminal 200 is the initial wireless terminal 200 in the preset beacon transmission order. Since the beacon transmission order information is stored in the information recording unit 250, the wireless terminal 200 recognizes the identification information of the first wireless terminal 200 in the beacon transmission order information, and determines whether the wireless terminal 200 is the initial wireless terminal 200. Can be determined. When the wireless terminal 200 is the initial wireless terminal 200 (step S802: YES), the wireless terminal 200 proceeds to step S803, and when it is not the initial wireless terminal 200 (step S802: NO), the process proceeds to step S809.

  In step S803, before the beacon transmission terminal that is the initial wireless terminal 200 transmits the start beacon, the reception intensity determination unit 221 determines whether the reception intensity is detected. When the reception intensity is detected (step S803: YES), the initial wireless terminal 200 proceeds to step S804, and when the reception intensity is not detected (step S803: NO), the process proceeds to step S805.

  In step S804, if the reception strength is detected, the initial wireless terminal 200 cannot transmit the start beacon. Therefore, the initial wireless terminal 200 goes to step S803 again to wait on the initial channel until the reception strength is no longer detected. During the period in which the initial wireless terminal 200 communicates, the other wireless terminals 200 are not to communicate. Therefore, if the reception strength is detected, the initial wireless terminal 200 can determine that the received signal is a wireless signal from another wireless communication system and that interference has occurred in the communication channel.

  In step S805, since the reception strength has not been detected, the initial wireless terminal 200 transmits a start beacon, and proceeds to step S806.

  In step S806, the initial wireless terminal 200 waits until a predetermined period of the transmission frame set in advance elapses, and then proceeds to step S807.

  In step S807, before the initial wireless terminal 200 transmits the end beacon, the reception intensity determination unit 221 determines whether the reception intensity is detected. If the reception intensity has not been detected (step S807: NO), the initial wireless terminal 200 proceeds to step S808. When the reception intensity is detected (step S807: YES), the initial wireless terminal 200 does not transmit the end beacon. However, when the timer information recorded in the information recording unit 250 reaches the channel switching period, the channel switching unit 234 switches the communication channel based on the channel switching order information.

  In step S808, since the reception strength has not been detected, the initial wireless terminal 200 includes the necessary information in the end beacon and transmits the end beacon. Then, when the channel switching grace period has elapsed after the transmission of the end beacon has been completed, the channel switching unit 234 performs a process of switching the communication channel to the next channel based on the channel switching order information.

  In step S809, since the initial wireless terminal 200 is a beacon receiving terminal, it waits in a receiving state and determines whether a beacon has been received. If initial wireless terminal 200 has received a beacon (step S809: YES), initial wireless terminal 200 proceeds to step S811, and if it does not receive a beacon (step S809: NO), proceeds to step S810.

  In step S810, the initial wireless terminal 200, which is a beacon receiving terminal, proceeds to step S809 to wait on the initial channel until receiving a beacon.

  In step S811, the initial wireless terminal 200 that has received the beacon analyzes whether the received beacon is a start beacon. If the received beacon is a start beacon (step S811: YES), the initial wireless terminal 200 proceeds to step S812. If the received beacon is not the start beacon (step S811: NO), the received beacon is the end beacon, so the channel switching unit 234 of the initial wireless terminal 200 switches the communication channel to the next channel and ends the process. I do. The start beacon and the end beacon include beacon identification information.

  In step S812, since the received beacon is the start beacon, the initial wireless terminal 200 sets the timer unit 236 based on the time synchronization information included in the start beacon, and waits in the reception state until the transmission frame period ends. Next, the initial wireless terminal 200 proceeds to step S813.

  In step S813, the initial wireless terminal 200 determines whether an end beacon has been received. If the initial wireless terminal 200 receives the end beacon (step S813: YES), the communication channel is switched to the next channel after the channel switching grace period has elapsed, and the process ends. That is, when the reception of the channel switching information of the end beacon is completed, the channel switching unit 234 switches the communication channel to the next channel based on the channel switching order information after the channel switching grace period has elapsed, and ends the processing.

  If the initial wireless terminal 200 does not receive the end beacon (step S813: NO), at the end of the communication channel switching period, the channel switching unit 234 switches the communication channel based on the channel switching order information.

  The above operation is the initial operation at the time of activation of the wireless terminal 200. When the initial operation is completed, the transmission frame period has elapsed. At the time of the initial operation, transmission operations other than the beacon are not performed.

  FIG. 9 is a flowchart showing the processing after switching the communication channel. The communication channel to which the wireless terminal 200 switches can be determined by referring to the channel switching order information of the information recording unit 250.

  In step S901, the wireless terminal 200 resets the timer unit 236, sets the timer information of the information recording unit 250 to an initial value, and proceeds to step S902. As an example, the initial value is “0”.

  In step S902, it is determined whether or not the order in which the wireless terminal 200 transmits a beacon has come. When the order in which the wireless terminals 200 transmit beacons has come (step S902: YES), the process proceeds to process A, and when it is not in the order to transmit beacons (step S902: NO), the process proceeds to process B. . Whether or not the order in which the wireless terminals 200 transmit beacons can be determined by referring to the beacon transmission order information of the information recording unit 250.

  10A and 10B show a flowchart of the process A. Process A is a process flow in the case where the wireless terminal 200 transmits a beacon and functions as a beacon transmitting terminal.

  In step S1001, before the wireless terminal 200 transmits a start beacon, it is determined whether or not the reception strength determination unit 221 detects the reception strength. If the reception intensity has not been detected (step S1001: NO), the wireless terminal 200 proceeds to step S1002, and if the reception intensity has been detected (step S1001: YES), proceeds to step S1003 and waits for reception.

  In step S1002, since the reception intensity has not been detected, the wireless terminal 200 transmits a start beacon, proceeds to step S1003, and enters the reception mode. In this case, the transmission request information recorded in the information recording unit 250 is transmitted as the transmission request information included in the start beacon. Also, the timer information recorded in the information recording unit 250 is transmitted as time synchronization information included in the start beacon.

  In step S1003, since the wireless terminal 200 is in the reception mode, the reception intensity determination unit 221 determines whether the reception intensity is detected. If the reception intensity is detected (step S1003: YES), the wireless terminal 200 proceeds to step S1004, and if the reception intensity is not detected (step S1003: NO), the process proceeds to step S1007.

  In step S1004, since the reception strength has been detected, the wireless terminal 200 determines whether an ID unique to the wireless communication system is detected from the received signal. If a unique ID is detected (step S1004: YES), the wireless terminal 200 proceeds to step S1005, and if a unique ID is not detected (step S1004: NO), the process proceeds to step S1010.

  In step S1005, wireless terminal 200 determines whether data information has been successfully received from the received signal. When the wireless terminal 200 has successfully received the data information (step S1005: YES), the wireless terminal 200 proceeds to step S1006, and when the wireless terminal 200 has not been able to receive the data information normally (step S1005: NO), the process proceeds to step S1010. Proceed to.

  Since step S1006 is a case where the wireless terminal 200 has successfully received the data information, the wireless terminal 200 transmits an Ack signal to the wireless terminal 200 that has transmitted the data information, and proceeds to step S1010.

  Step S1007 is a case where the reception intensity of the received signal is not detected, and thus the wireless terminal 200 determines whether the wireless terminal 200 itself has a data information transmission request. When there is no data information transmission request, or when the own wireless terminal 200 is not in the transmission order in the transmission request information transmitted in the start beacon (step S1007: NO), the wireless terminal 200 proceeds to step S1010. If there is a data information transmission request and the own wireless terminal 200 is in the transmission order in the transmission request information transmitted in the start beacon (step S1007: YES), the wireless terminal 200 proceeds to step S1008. . Furthermore, even when there is a data information transmission request and all the transmissions of the wireless terminal 200 included in the transmission request information transmitted in the start beacon have been completed (step S1007: YES), the wireless terminal 200 is Proceed to step S1008.

  Step S1008 is a state where there is data information to be transmitted to the wireless terminal 200, so the wireless terminal 200 transmits the data information and proceeds to step S1009. In this case, when the transmission order of the own wireless terminal 200 is the first in the transmission request information transmitted in the start beacon, the operation regarding the contention window or the like is skipped and the data information is transmitted. For example, when the transmission order of the own wireless terminal 200 is No. 1, the wireless terminal 200 transmits the data information immediately after transmitting the start beacon.

  In step S1009, wireless terminal 200 determines whether or not an Ack signal for the transmitted data information has been received. If wireless terminal 200 does not receive the Ack signal, wireless terminal 200 sets a retransmission flag and proceeds to step S1010, and if an Ack signal is received, clears the retransmission flag and proceeds to step S1010. As an example, the retransmission flag is represented by one bit, and setting the retransmission flag to “1” is referred to as setting the retransmission flag, and setting the retransmission flag to “0” is referred to as clearing the retransmission flag. If the retransmission flag is set, a transmission request is generated in steps S1007 and S1012.

  In step S1010, the wireless terminal 200 checks the elapsed time. That is, wireless terminal 200 transmits data information within the remaining data frame period, and confirms whether an Ack for the transmitted data information can be received. If there is no transmittable time during which data information can be transmitted and Ack can be received (step S1010: NO), the wireless terminal 200 proceeds to step S1011. If there is a transmittable time (step S1010: YES), the wireless terminal 200 proceeds to step S1003 to transmit and receive data information.

  In step S1011, wireless terminal 200 determines whether or not reception intensity is detected by reception intensity determination section 221. When the reception intensity is detected (step S1011: YES), the wireless terminal 200 proceeds to step S1014, and when the reception intensity is not detected (step S1011: NO), the process proceeds to step S1012.

  In step S1012, wireless terminal 200 determines whether there is a transmission request. If there is a transmission request to wireless terminal 200 (step S1012: YES), wireless terminal 200 proceeds to step S1013, and if there is no transmission request (step S1012: NO), proceeds to step S1016.

  In step S1013, the wireless terminal 200 transmits an intermediate beacon. The intermediate beacon includes, as transmission request information, identification information of the wireless terminal 200 that has generated the transmission request and time information indicating the time at which the transmission request has occurred.

  In step S1014, the wireless terminal 200 determines whether an intermediate beacon has been received. If the wireless terminal 200 has received the intermediate beacon (step S1014: YES), the wireless terminal 200 proceeds to step S1015, and if not received (step S1014: NO), proceeds to step S1016.

  In step S1015, the wireless terminal 200 records the identification information of the wireless terminal 200 included in the intermediate beacon and the time information indicating the time at which the transmission request occurred in the information recording unit 250.

  If the wireless terminal 200 has not received another intermediate beacon, the transmission request in which the transmission order of the wireless terminal 200 specified by the identification information of the wireless terminal 200 included in the intermediate beacon received in step S1014 is the first The information is recorded in the information recording unit 250.

  When the wireless terminal 200 has already received another intermediate beacon, the wireless terminal 200 determines the transmission order from the wireless terminal 200 whose time information indicating the time at which the transmission request recorded in the information recording unit 250 is earlier, and transmits the information. The information is recorded in the information recording unit 250 as request information. For example, the wireless terminal 200 sets the transmission order of the wireless terminal 200 having the earliest transmission request time to the first, and the transmission order of the wireless terminal 200 having the second earliest transmission request time to the second. Set. As described above, the wireless terminal 200 preferentially determines the transmission order in the order of the time when the transmission request is generated.

  In step S1016, the wireless terminal 200 checks the elapsed time. That is, the wireless terminal 200 checks whether or not the intermediate beacon transmission / reception section in which the intermediate beacon can be transmitted / received has elapsed. When the intermediate beacon transmission / reception section has elapsed, it is time to transmit an end beacon. If the intermediate beacon transmission / reception section has elapsed (step S1016: YES), the wireless terminal 200 proceeds to step S1017. If the intermediate beacon transmission / reception section has not elapsed (step S1016: NO), the wireless terminal 200 proceeds to step S1011.

  In step S1017, wireless terminal 200 determines whether or not reception intensity is detected by reception intensity determination section 221. When the reception intensity is not detected (step S1017: NO), the wireless terminal 200 proceeds to step S1018. When the reception strength is detected (step S1017: YES), the wireless terminal 200 performs the channel change process without transmitting the end beacon. In this case, at the end of the communication channel switching cycle, the channel switching unit 234 switches the communication channel based on the channel switching order information.

  In step S1018, since there is no interference in the communication channel, the wireless terminal 200 transmits a termination beacon, and performs a channel switching process after a lapse of a channel switching grace period. The above is the processing flow of the processing A.

  11A and 11B show a flowchart of the processing B. Process B is a process flow when the wireless terminal 200 functions as a beacon receiving terminal.

  Since step S1101 is immediately after the wireless terminal 200 switches the communication channel, the wireless terminal 200 determines whether or not a start beacon has been received from the beacon transmitting terminal. If wireless terminal 200 has received the start beacon (step S1101: YES), wireless terminal 200 proceeds to step S1102, and if not received the start beacon (step S1101: NO), proceeds to step S1103.

  In step S1102, the beacon analyzer 233 of the wireless terminal 200 analyzes information included in the start beacon. That is, wireless terminal 200 rewrites the transmission request information of information recording section 250 to the transmission request information included in the start beacon, and sets timer section 236 to the time synchronization information included in the start beacon. The wireless terminal 200 that has transmitted the intermediate beacon on the immediately preceding communication channel can recognize the transmission order by referring to the rewritten transmission request information.

  In step S1103, since the wireless terminal 200 is in the reception mode, the reception intensity determination unit 221 determines whether the reception intensity is detected. If the reception intensity is detected (step S1103: YES), the wireless terminal 200 proceeds to step S1104, and if the reception intensity is not detected (step S1103: NO), the process proceeds to step S1107.

  In step S1104, since the reception intensity has been detected, the wireless terminal 200 determines whether an ID unique to the wireless communication system is detected from the received signal. If a unique ID is detected (step S1104: YES), the wireless terminal 200 proceeds to step S1105, and if a unique ID is not detected (step S1104: NO), the process proceeds to step S1110.

  In step S1105, wireless terminal 200 determines whether data information has been successfully received from the received signal. If the wireless terminal 200 has successfully received the data information (step S1105: YES), the wireless terminal 200 proceeds to step S1106, and if the wireless terminal 200 has not been able to receive the data information normally (step S1105: NO), step S1110. Proceed to.

  Since step S1106 is a case where the wireless terminal 200 has successfully received the data information, the wireless terminal 200 transmits an Ack signal to the wireless terminal 200 that transmitted the data information, and proceeds to step S1110.

  Step S1107 is a case in which the reception intensity based on the reception signal is not detected, and thus the wireless terminal 200 determines whether or not the wireless terminal 200 itself has a data information transmission request. If there is no data information transmission request, or if the own wireless terminal 200 is not in the transmission order in the transmission request information received in the start beacon (step S1107: NO), the wireless terminal 200 proceeds to step S1110. If there is a data information transmission request and the own wireless terminal 200 is in the transmission order in the transmission request information received in the start beacon (step S1107: YES), the wireless terminal 200 proceeds to step S1108. . Furthermore, even when there is a data information transmission request and all the transmissions of the wireless terminal 200 included in the transmission request information received in the start beacon have been completed (step S1107: YES), the wireless terminal 200 also transmits Proceed to step S1108.

  In step S1108, there is data information to be transmitted to the wireless terminal 200, so the wireless terminal 200 transmits data information, and proceeds to step S1109. In this case, if the transmission order of the own wireless terminal 200 is the first in the transmission request information received in the start beacon, the operation regarding the contention window or the like is skipped and the data information is transmitted. For example, when the transmission order of the own wireless terminal 200 is the first, the wireless terminal 200 transmits the data information immediately after receiving the start beacon.

  In step S1109, wireless terminal 200 determines whether or not an Ack signal for the transmitted data information has been received. If wireless terminal 200 does not receive the Ack signal, wireless terminal 200 sets a retransmission flag and proceeds to step S1110, and if an Ack signal is received, clears the retransmission flag and proceeds to step S1110. As an example, the retransmission flag is represented by one bit, and setting the retransmission flag to “1” is referred to as setting the retransmission flag, and setting the retransmission flag to “0” is referred to as clearing the retransmission flag. If the retransmission flag is set, a transmission request is generated in steps S1107 and S1112.

  In step S1110, the wireless terminal 200 checks the elapsed time. That is, wireless terminal 200 transmits data information within the remaining data frame period, and confirms whether an Ack for the transmitted data information can be received. If there is no transmittable time for transmitting the data information and receiving the Ack (step S1110: NO), the wireless terminal 200 proceeds to step S1111. If there is a transmittable time (step S1110: YES), the wireless terminal 200 proceeds to step S1103 to transmit and receive data information.

  In step S1111, the wireless terminal 200 determines whether or not the reception intensity is detected by the reception intensity determination unit 221. If the reception intensity is detected (step S1111: YES), the wireless terminal 200 proceeds to step S1114. If the reception intensity is not detected (step S1111: NO), the process proceeds to step S1112.

  In step S1112, the wireless terminal 200 determines whether the wireless terminal 200 has a transmission request. If there is a transmission request to wireless terminal 200 (step S1112: YES), wireless terminal 200 proceeds to step S1113, and if there is no transmission request (step S1112: NO), proceeds to step S1116.

  In step S1113, the wireless terminal 200 transmits an intermediate beacon. The intermediate beacon includes, as transmission request information, identification information of the wireless terminal 200 that has generated the transmission request and time information indicating the time at which the transmission request has occurred.

  In step S1114, wireless terminal 200 determines whether or not an intermediate beacon has been received. If the wireless terminal 200 has received the intermediate beacon (step S1114: YES), the wireless terminal 200 proceeds to step S1115, and if not received (step S1114: NO), proceeds to step S1116.

  In step S1115, the wireless terminal 200 records the identification information of the wireless terminal 200 included in the intermediate beacon and the time information indicating the time at which the transmission request occurred in the information recording unit 250.

  If another intermediate beacon has not been received, the transmission request information in which the transmission order of the wireless terminal 200 specified by the identification information of the wireless terminal 200 included in the intermediate beacon received in step S1114 is the first is recorded. Recorded in the section 250.

  When the wireless terminal 200 has already received another intermediate beacon, the wireless terminal 200 determines the transmission order from the wireless terminal 200 whose time information indicating the time at which the transmission request recorded in the information recording unit 250 is earlier, and transmits the information. The information is recorded in the information recording unit 250 as request information. For example, the wireless terminal 200 sets the transmission order of the wireless terminal 200 having the earliest transmission request time to the first, and the transmission order of the wireless terminal 200 having the second earliest transmission request time to the second. Set. As described above, the wireless terminal 200 preferentially determines the transmission order in the order of the time when the transmission request is generated.

  In step S1116, the wireless terminal 200 checks the elapsed time. That is, the wireless terminal 200 checks whether or not the intermediate beacon transmission / reception section in which the intermediate beacon can be transmitted / received has elapsed. When the intermediate beacon transmission / reception section has elapsed, it is time to transmit an end beacon. If the intermediate beacon transmission / reception section has elapsed (step S1116: YES), the wireless terminal 200 proceeds to step S1117, and if the intermediate beacon transmission / reception section has not elapsed (step S1116: NO), proceeds to step S1111.

  In step S1117, wireless terminal 200 determines whether or not an end beacon is received. When the end beacon is received (step S1117: YES), the wireless terminal 200 proceeds to step S1118. If the end beacon has not been received (step S1117: NO), wireless terminal 200 performs a channel change process. In this case, at the end of the communication channel switching cycle, the channel switching unit 234 switches the communication channel based on the channel switching order information.

  In step S1118, wireless terminal 200 records transmission request information included in the end beacon in information recording section 250. Next, a channel change process is performed. The above is the processing flow of the processing B.

(Overview of channel switching order)
Next, an outline of the channel switching order will be described with reference to FIG.

  FIG. 12 is a diagram illustrating the switching order indicated by the channel switching order information recorded in the information recording unit 250, and the communication channels are switched in the order of CH1, CH2, and CH3. The number of communication channels may be any number as long as it is two or more. In addition, the channel switching order only needs to be uniformly defined for all wireless terminals 200, and the channel switching order can be arbitrarily set by the wireless communication system. Similarly, the initial channel only needs to be uniformly defined for all wireless terminals 200, and any communication channel may be the initial channel. The channel switching order is recorded in the information recording unit 250 as channel switching order information.

When the wireless terminal 200 has failed to receive the start beacon and the end beacon continuously for the specified number of times, it stops switching the communication channel, returns to the initial channel, and returns to the initial channel until the start beacon or the end beacon can be received. Wait on the channel. The specified number of times can be set to an arbitrary value by the wireless communication system.
For example, when the wireless terminal 200 cannot receive the start beacon and the end beacon in any of the communication channels in the order of CH3, CH1, and CH2, the wireless terminal 200 returns to the initial channel CH1 until it can receive the start beacon and the end beacon. Wait.

(How to correct the synchronization gap)
Next, a method of correcting a synchronization shift will be described.
Since each wireless terminal 200 has the timer unit 236, the frequency channel can be regularly switched at a predetermined channel switching period (Tms) including a transmission / reception period of a start beacon and a transmission / reception period of an end beacon. . However, synchronization is basically achieved by receiving a start beacon and an end beacon.

  On the other hand, in addition to the case where the wireless terminal cannot receive a beacon due to interference or the like, there is a possibility that the channel switching timing may be too early or too late due to a shift in the clock frequency of the timer unit 236 or the like.

  FIG. 13 shows a procedure of resynchronization by receiving a beacon.

  The beacon receiving terminal 1301 in FIG. 13 is a diagram illustrating a case where the channel switching timing from CH1 to CH2 is too early. In this case, the beacon receiving terminal 1301 receives the start beacon at the normal timing on the channel switching destination CH2, and sets the timer unit 236 of the beacon receiving terminal 1301 to the time synchronization information of the start beacon, so that the other wireless terminal 200 and can be resynchronized. That is, since the time synchronization information is included at the end of the start beacon, the beacon receiving terminal 1301 rewrites the timer unit 236 to the time synchronization information of the start beacon upon completion of reception of the start beacon. As a result, synchronization is established between the wireless terminal 200 that has transmitted the start beacon and the wireless terminal 200 that has received the start beacon.

  The beacon receiving terminal 1302 of FIG. 13 is a diagram illustrating a case where the channel switching timing from CH1 to CH2 is too late. In this case, the beacon receiving terminal 1302 can receive the end beacon at normal timing on the channel switching destination CH2. Therefore, based on the CH switching information included at the end of the end beacon, beacon receiving terminal 1302 can switch to CH3 after the lapse of the channel switching grace period from the completion of the reception of the end beacon and resynchronize with another wireless terminal. .

  As shown in FIG. 13, when a deviation occurs within a channel switching period (Tms), which is a predetermined transmission frame length, the wireless terminal 200 transmits a start beacon or a termination beacon on a channel to which the wireless terminal 200 has been switched. By receiving the beacon, resynchronization with another wireless terminal 200 is possible. If the synchronization is lost for a time equal to or longer than Tms, as described above, the wireless terminal 200 waits on the initial channel until a beacon can be received.

  FIG. 14 shows an intermediate beacon transmission / reception section in which transmission / reception of an intermediate beacon is possible. The intermediate beacon transmission / reception section is a period during which transmission of data information and reception of a response signal to the data information on the communication channel cannot be completed before transmission / reception of the end beacon. In FIG. 14, the transmittable / receivable section of the intermediate beacon is, for convenience, a theoretical period from when the wireless terminal 200 transmits data information to when the reception of the Ack transmitted by the other wireless terminal 200 that has received the data information can be completed. The period is shown as a fixed length.

  The reason is that, in practice, the synchronization between the wireless terminals 200 hardly coincides completely in units of clocks of the CPU, and there is a high possibility that a wireless signal transmission delay or the like will occur. The period is a transmission / reception section of the intermediate beacon.

  As described above, all wireless terminals 200 set the above-described predetermined fixed-length intermediate beacon transmission / reception section. Then, when a transmission request is issued to the wireless terminal 200 while the timer information indicates the intermediate beacon transmission / reception section, the intermediate beacon is transmitted in order to transmit data information on the next communication channel without transmitting data information. Send

  The intermediate beacon includes identification information of the wireless terminal 200 transmitting the intermediate beacon, and time information at which the transmission request occurred. The time information at which the transmission request occurred is based on the reception time of the start beacon immediately before the transmission request occurred.

  The beacon transmitting terminal that has transmitted the start beacon receives the intermediate beacon, and sequentially determines which wireless terminal 200 has the right to transmit on the next communication channel, starting with the wireless terminal 200 having the earliest time at which the transmission request occurred. Is determined. That is, the wireless terminal 200 that has transmitted the start beacon has determined the transmission order in the next communication channel of the wireless terminal 200 that has transmitted the intermediate beacon, and associated the transmission order information with the identification information of the wireless terminal 200. The transmission request information is transmitted in the end beacon.

  If the beacon transmitting terminal of the next communication channel can receive the transmission request information of the end beacon of the beacon transmission terminal of the previous communication channel, the transmission request information is included in the start beacon and broadcast.

  However, when the beacon transmission terminal of the next communication channel cannot receive the transmission request information of the end beacon of the beacon transmission terminal of the previous communication channel, the transmission request information is newly generated.

  That is, the beacon transmitting terminal of the next communication channel newly creates transmission request information based on the intermediate beacon received on the previous communication channel, and broadcasts the transmission request information by including the transmission request information in the start beacon.

As described above, according to the present embodiment. Each wireless terminal can operate independently without installing a control station.
In addition, since all wireless terminals regularly change frequency channels for communication, there is no need to wait for a long time on the same frequency channel, and there is no need to carry out carrier sensing in all frequency bands before starting communication.
Further, since the frequency band used is unified for all wireless terminals, it is not necessary to estimate the frequency band used for transmission by correlation.
Furthermore, even when there is a transmission request other than the beacon transmission terminal, priority transmission can be performed using the intermediate beacon, so that all wireless terminals can communicate efficiently.
Further, even when only a specific wireless terminal receives interference, the channel is automatically switched, so that it is possible to synchronize with another wireless terminal by receiving a beacon at the channel switching destination.
Further, since synchronization is performed between the first and last two beacons of the transmission frame, any deviation within the transmission frame length can be re-synchronized with the beacon. Further, even when synchronization is completely lost, the mobile station waits on the initial channel, so that re-synchronization with another wireless terminal becomes possible.

(Modification 1)
In FIG. 1, all wireless terminals are included in the wireless communication network. However, as shown in FIG. 15, there may be wireless terminals that cannot directly communicate. In this case, a wireless communication network can be formed by using the relay transmission.

  For example, a case will be described in which the wireless terminal 11 belonging to the wireless communication network 1501 is a beacon transmitting terminal. The wireless terminal 14 receiving the start beacon and / or the end beacon transmitted by the wireless terminal 11 relays the start beacon and / or the end beacon to the wireless terminals 15 to 20 that do not belong to the wireless communication network 1501. Alternatively, the wireless terminal 12 or 13 that has received the start beacon and / or the end beacon transmitted by the wireless terminal 11 relays and transmits to the wireless terminals 15 to 17, and the wireless terminal 17 transmits the start beacon and / or the wireless terminals 18 to 20 to the wireless terminals 18 to 20. Relay the end beacon.

  In this manner, by using the relay transmission, one wireless communication network can be formed by the wireless communication network 1501, the wireless communication network 1502, and the wireless communication network 1503.

(Modification 2)
When a wireless communication network is formed in a vehicle, the above-described communication control method can be adopted for all wireless terminals in the vehicle. As a result, it is possible to construct a wireless communication network that can cope with interference from other wireless communication systems outside the vehicle and interference from other wireless terminals and wireless devices brought into the same vehicle. In addition, the above-described communication control method can be similarly applied to a wireless device in a factory or the like regardless of the inside of the vehicle. In addition, a method other than the CSMA / CA method can be adopted as the wireless communication method.

(Modification 3)
As described above, the intermediate beacon includes the identification information of the wireless terminal 200 that transmits the intermediate beacon, and the time information at which the transmission request occurred, and the time information at which the transmission request occurred indicates the time information immediately before the transmission request occurred. Based on the reception time of the start beacon. However, the priority can be included in the data information for which the transmission request has occurred. For example, in wireless communication in a vehicle, the wireless terminal 200 needs to transmit data information related to vehicle control earlier than data information such as music data. In such a case, it is preferable that the wireless terminal 200 grant the transmission right in accordance with the importance of the data information rather than granting the transmission right on the next communication channel in the order of the time when the transmission request is generated. For this purpose, the intermediate beacon preferably includes information on the priority.

  For example, the wireless terminal 200 includes the priority information bit in the intermediate beacon, sets the priority information bit to “1” for a transmission request with a high priority, and sets the priority information bit for a transmission request with a low priority. Set the bit to “0” and transmit the intermediate beacon.

  The wireless terminal 200 that has received the intermediate beacon determines the transmission order from the transmission requests whose priority information bits are set to “1” in the order in which the transmission requests occurred. Next, the wireless terminal 200 that has received the intermediate beacon determines the transmission order in the order of the generation time of the transmission request from among the transmission requests whose priority information bits are set to “0”.

  As described above, the wireless terminal 200 can reduce the delay of important data information such as control information by including the priority information of the data information for which the transmission request has occurred in the intermediate beacon. Note that the priority information does not need to be one bit, and the priority information can be composed of a plurality of bits and three or more priorities can be set.

(Modification 4)
In the third modification, the priority information bit is added to the intermediate beacon. However, the emergency information bit having the highest priority can be added to the intermediate beacon.

  For example, in order to avoid a situation related to a vehicle accident or the like, it may be necessary to transmit and receive data information for controlling the vehicle with the highest priority. In such a case, the emergency information bit is included in the intermediate beacon, the emergency information bit is set to “1” for the transmission request with the highest priority, and the emergency information bit is set to “0” for the other transmission requests. To transmit an intermediate beacon.

  The wireless terminal 200 that has received the intermediate beacon preferentially determines the transmission order of the transmission request in which the emergency information bit is set to “1”. Therefore, the wireless terminal 200 in which the emergency information bit is set to “1” can preferentially transmit data information on the next communication channel.

  In this way, the emergency information bit enables data information for controlling the vehicle to be preferentially transmitted and received in order to avoid a situation related to a vehicle accident or the like.

(Modification 5)
In the embodiment, as illustrated in FIG. 3, an example has been mainly described in which all the wireless terminals 200 included in the wireless communication system sequentially become the beacon transmission terminals based on the beacon transmission order information. However, only some of the wireless terminals 200 included in the wireless communication system may be beacon transmitting terminals.

  For example, the radio waves of the wireless terminal 200 at the front or rear of the vehicle may not easily reach the wireless terminal 200 at the rear or front of the vehicle. In such a case, if the state in which the start beacon and the end beacon cannot be received continues, a synchronization shift is likely to occur, and a communication delay may occur.

  Therefore, among the wireless terminals 200 included in the wireless communication system, only the wireless terminal 200 within a predetermined range from the midpoint on the line where the distance between the wireless terminals 200 is the longest can be set as the beacon transmission terminal.

  In the wireless communication system, the predetermined range can be set to an arbitrary value. As an example, in the wireless communication system, the predetermined range can be set to 1 / n (n is a natural number of 3 or more) of the vehicle length. In this way, by using only the wireless terminal 200 located at the center of the vehicle as the beacon transmitting terminal, the beacon receiving terminal can easily receive the start beacon and the end beacon, and suppress the occurrence of communication delay. Further, only the wireless terminal 200 having the best communication state among the wireless terminals 200 in the center of the vehicle can be the beacon transmitting terminal. For example, only the wireless terminal 200 having the largest CNR (Carrier to Noise Ratio) in the wireless communication system may be a beacon transmitting terminal.

  Although various embodiments have been described above, some or all of the embodiments may be combined to form a new embodiment.

  INDUSTRIAL APPLICABILITY The present invention is extremely useful when used in a wireless network that performs communication control to avoid an increase in communication delay time due to radio interference with another wireless communication system.

200 wireless terminal 210 communication unit 211 transmission / reception switching unit 212 wireless transmission unit 213 wireless reception unit 220 determination unit 221 reception intensity determination unit 222 Interference determination unit 230 Control unit 231 Beacon generation unit 232 Data generation unit 233 Beacon analysis unit 234 Channel switching unit 235 Data processing unit 236 Timer Unit 240: I / F (interface) unit 250: Information recording unit

Claims (10)

A beacon transmission terminal for a wireless communication system in which one of a plurality of wireless terminals is a beacon transmission terminal in a predetermined order each time a communication channel is switched and the remaining wireless terminals are beacon reception terminals,
A beacon generator that generates a start beacon, an intermediate beacon, and an end beacon;
A communication unit for transmitting and receiving the start beacon, data information, the intermediate beacon and the end beacon,
A timer unit that measures a communication channel switching cycle of the communication unit,
A channel switching unit that switches the communication channel of the communication unit according to a predetermined rule in accordance with the switching cycle of the communication channel,
The beacon generation unit includes the start beacon including timer information measured by the timer unit as time synchronization information, the end beacon including channel switching information indicating a timing of switching the communication channel, and transmitting and receiving an intermediate beacon. When a transmission request is generated in the section, it is time information indicating the time at which the transmission request is generated, and generates an intermediate beacon including the time information measured by the timer unit,
The communication unit transmits the start beacon before the start of transmission and reception of the data information, transmits the intermediate beacon when a transmission request is generated in an intermediate beacon transmission and reception section, and after the transmission and reception of the data information, Send an end beacon,
The channel switching unit, at the end of the communication channel switching cycle, while switching the communication channel based on the predetermined rule, reset the timer unit,
The beacon transmission terminal, wherein the intermediate beacon transmission / reception section is a period in which reception of a response signal to the data information from transmission of the data information over the communication channel cannot be completed before transmission of the end beacon.   The beacon generation unit, based on the time information when the transmission request is included in the intermediate beacon transmitted and received by the communication unit, based on the time information of the time when the transmission request occurred, the data information in the next communication channel The beacon transmitting terminal according to claim 1, wherein the transmitting order of the transmitting wireless terminal is determined, and information of the transmitting order and identification information of the wireless terminal are included in the end beacon as transmission request information. If the communication unit has received the end beacon of the immediately preceding communication channel, the beacon generation unit, as transmission request information included in the start beacon transmission request information included in the end beacon,
If the communication unit cannot receive the end beacon of the last communication channel, the beacon generation unit, based on time information when a transmission request included in the intermediate beacon transmitted and received on the last communication channel, In the time order of the time information at which the transmission request occurred, the transmission order of the wireless terminal transmitting the data information is determined, and the transmission order information and the identification information of the wireless terminal are included in the start beacon as transmission request information. The beacon transmission terminal according to claim 2, wherein   4. The transmission method according to claim 1, wherein when the transmission order of the beacon transmitting terminal becomes the first, after transmitting the start beacon, the data information is transmitted without providing a waiting time. Beacon transmission terminal.   The intermediate beacon further includes priority information indicating the priority of the data information, and the priority information of the data information having a higher priority than the transmission order of the data information having a lower priority of the priority information. The transmission order is determined according to the time order of the time information at which the transmission request occurred, wherein the transmission order is earlier and the data information having the same priority of the priority information is determined. 2. A beacon transmission terminal according to item 1.   Each time the communication channel is switched, the beacon transmitting terminal that sets one of the plurality of wireless terminals in a predetermined order as a beacon transmitting terminal, among the wireless terminals included in the wireless communication system, The beacon transmitting terminal according to any one of claims 1 to 5, wherein the wireless terminal is determined with respect to the wireless terminal within a predetermined range from a midpoint on the longest line. A beacon receiving terminal of a wireless communication system in which one of a plurality of wireless terminals is a beacon transmitting terminal in a predetermined order each time a communication channel is switched and the remaining wireless terminals are beacon receiving terminals,
A beacon generator for generating an intermediate beacon,
A communication unit that receives a start beacon and an end beacon, and transmits and receives data information and the intermediate beacon,
A timer unit that measures a communication channel switching cycle of the communication unit,
A channel switching unit that switches the communication channel of the communication unit according to a predetermined rule in accordance with the switching cycle of the communication channel,
When the communication unit receives the start beacon, the timer unit sets time synchronization information included in the start beacon to the timer unit,
When the communication unit receives the termination beacon, the channel switching unit switches the communication channel after a predetermined period after receiving channel switching information indicating a timing of switching the communication channel included in the termination beacon. Reset the timer section,
The beacon generation unit, when a transmission request occurs in the intermediate beacon transmission / reception section, generates an intermediate beacon that is time information indicating a time when the transmission request is generated and includes the time information measured by the timer unit. ,
The beacon receiving terminal, wherein the intermediate beacon transmission / reception section is a period in which reception of a response signal to the data information from transmission of the data information over the communication channel cannot be completed before reception of the end beacon.   Based on the information on the transmission order included in the start beacon, if the transmission order of the beacon receiving terminal becomes the first, after receiving the start beacon, transmitting data information without providing a waiting time The beacon receiving terminal according to claim 7, wherein   If the communication unit does not receive the start beacon and the end beacon continuously on all communication channels, the channel switching unit uses the communication channel set at the beginning of the switching order of the communication channel, the start beacon. 9. The beacon receiving terminal according to claim 7, wherein the terminal waits for reception of the end beacon. A beacon transmission terminal according to any one of claims 1 to 6,
A wireless communication system comprising: the beacon receiving terminal according to claim 7.