JP7221772B2 - Beacon transmitting terminal, beacon receiving terminal and wireless communication system - Google Patents

Description

The present invention relates to a beacon transmitting terminal, a beacon receiving terminal, and a radio communication system that avoid an increase in communication delay time due to radio wave interference with other radio communication systems installed in the same vehicle or other vehicles.

Conventionally, there have been proposed methods for avoiding the occurrence of radio wave interference with radio devices of other radio communication systems.

For example, Patent Document 1 proposes a method in which a control device is arranged in a wireless network having one or more terminal devices, and the control device controls wireless communication using a plurality of frequency channels.

The controller includes a radio receiver, a quality determiner and a beacon generator. The radio receiving unit is capable of receiving radio signals of a plurality of frequency channels, and the quality determining unit determines usable frequency channels based on the reception state of the radio signals received by the radio receiving unit. Determine the order of use.

Then, the beacon generation unit generates a beacon including information on the order in which the frequency channels are used, and transmits the beacon to the terminal device. The channel setting unit of the terminal device that received the beacon sets the frequency channel to be used according to the use order information (see FIG. 17 (FIG. 14 of Patent Document 1)).

Also, in a superframe period consisting of an active period during which wireless communication can be performed and an inactive period during 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. 14 (FIG. 4 of Patent Document 1), FIG. 15 (FIG. 6 of Patent Document 1), and FIG. 16 (FIG. 6 of Patent Document 1).

Further, for example, Patent Literature 2 proposes a method by a system that performs communication by temporarily using a frequency band that is not assigned to itself. In other words, it is a method in which communication is performed by sharing a part of a license band assigned to a wireless communication system different from its own system. Specifically, before starting communication, first carrier sense is performed on predetermined L (L≧2) frequency bands, M frequency bands are selected from among them, and time slots are selected. second carrier sense is performed on M (L≧M≧2) frequency bands in the leading carrier sense section of, and a frequency band to be used for transmission is determined from unused frequency bands. (See FIG. 18 (FIG. 7 of Patent Document 2) and FIG. 19 (FIG. 8 of Patent Document 2)). At this time, if the frequency band used last time is among the final candidates, that frequency band is used. Alternatively, preferentially use a frequency band that has been used a large number of times.

The wireless terminal is equipped with a matched filter or the like, and calculates the correlation value between the same signal sequence as the known sequence stored in advance and the leading sequence of the received signal, and identifies the frequency band used for transmission. (See FIG. 20 (FIG. 9 of Patent Document 2)).

Further, for example, in Patent Document 3, in an autonomous decentralized wireless communication network that does not require a specific control station, in a communication environment in which a plurality of channels are prepared, channels are periodically opened in synchronization with reception of beacons. A method has been proposed in which, by changing the channel, communication can be performed using another communication channel even if the communication condition of a specific channel is poor.

In other words, if communication is performed while staying on the same channel, communication will not be possible if the communication condition of that channel is poor due to interference or the like. can avoid the influence of bad channels.

For this reason, 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 priority allocation section for communication, and after a certain period of time has passed, other wireless terminals can transmit (see FIG. 21 (see FIG. 3 of Patent Document 3). ), FIG. 22 (see FIG. 7 of Patent Document 3).

In addition, since the channel is regularly changed, a mechanism for determining and notifying the communication channel between terminals becomes unnecessary, and the operation becomes simple (see FIG. 23 (FIG. 13 of Patent Document 3)).

WO2010/007738 Japanese Patent Application Laid-Open No. 2007-300421 JP 2005-079985 A

However, according to the disclosures of Patent Document 1, Patent Document 2, and Patent Document 3, it is possible to independently avoid frequency bands that are subject to interference, and to avoid an increase in communication delay time when radio wave interference occurs for a long period of time. can be difficult.
Accordingly, an object of the present invention is to provide means for solving such problems.

In order to solve the above problems, the present invention employs the following configuration.
That is, the invention according to claim 1 is a beacon 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 sending terminal,
a beacon generation unit that generates a beacon;
a communication unit that transmits and receives data information and transmits the beacon;
a timer unit for timing 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 corresponding to the switching cycle of the communication channel;
The beacon generation unit causes the beacon to include time information measured by the timer unit as time synchronization information,
The communication unit transmits the beacon when the reception strength of the received signal is smaller than a predetermined value in a period that does not include the start timing and the end timing of the switching cycle of the communication channel,
The channel switching unit switches the communication channel based on the predetermined rule and resets the timer unit at the end timing of the switching cycle of the communication channel.

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 cycle, so it 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 communication channels in which radio wave interference has occurred for a long period of time.

In addition, even if the timing of the transmission frame of the beacon receiving terminal is shifted by a predetermined period, the beacon transmitting terminal and the beacon receiving terminal are synchronized by the time synchronization information for synchronizing the timer part of the beacon receiving terminal included in the beacon with the beacon transmitting terminal. It is possible to resynchronize between

In order to solve the above problem, the invention according to claim 2 is the beacon transmitting terminal according to claim 1, wherein the communication unit is configured to perform and transmitting the beacon when the received signal strength of the received signal is smaller than a predetermined value.

According to the above configuration, synchronization of the transmission frame is performed by the beacon in the middle of the transmission frame corresponding to the switching cycle of the communication channel. Synchronization becomes possible.

In order to solve the above-mentioned problems, the invention according to claim 3 is the beacon transmitting terminal according to claim 1 or 2, wherein a half of the switching cycle of the communication channel has passed during the transmission period of the data information. When the timing is included, the transmission period of the data information is divided, and the transmission period of the data information is set so that the transmission period of the data information does not include the timing when 1/2 of the switching cycle of the communication channel has passed. It is characterized by further including a data generator for dividing.

According to the above configuration, the transmission frame synchronization is controlled by the beacon in the middle of the transmission frame corresponding to the switching cycle of the communication channel. , beacons allow resynchronization.

In order to solve the above problems, the invention according to claim 4 is the beacon transmitting terminal according to any one of claims 1 to 3, wherein the communication unit has a communication channel switching period of 1/2. When the received signal strength of the received signal is equal to or greater than a predetermined value at the elapsed timing, the beacon is not transmitted, and when the received signal strength of the received signal becomes smaller than the predetermined value, the It is characterized by transmitting a beacon.

According to the above configuration, the beacon is not transmitted when the communication channel is interfered by another wireless communication system and when another wireless terminal of the own wireless communication system is transmitting data information. , it becomes possible to adaptively change the beacon transmission timing. Also, it becomes possible to effectively utilize the transmission frame.

In order to solve the above-mentioned problems, the invention according to claim 5 is the beacon transmitting terminal according to any one of claims 1 to 4, wherein the communication unit is configured such that the beacon transmission end timing is set to the communication channel. The beacon is not transmitted when the end timing of the switching cycle is exceeded.

According to the above configuration, by prioritizing the communication channel switching period over beacon transmission, it is possible to autonomously avoid the communication channel, which is the frequency band receiving interference. Also, since it may be possible to transmit a beacon in the next transmission frame, it is possible to resynchronize the beacon transmitting terminal and the beacon receiving terminal by means of the beacon.

In order to solve the above problems, the invention according to claim 6 is the beacon transmitting terminal according to any one of claims 1 to 5, wherein one of a plurality of wireless terminals is predetermined each time the communication channel is switched. The wireless terminal, which in turn becomes a beacon transmitting terminal, is the wireless terminal within a predetermined range from the midpoint on the line with the longest distance between the wireless terminals among the wireless terminals included in the wireless communication system. It is characterized by

According to the above configuration, it is possible to smoothly operate the wireless communication system according to the present method by not using a wireless terminal that may deteriorate the communication environment as a beacon transmitting terminal. As an example, when a wireless communication system is installed in a vehicle or the like, by using a wireless terminal placed in the center of the vehicle as a beacon transmitting terminal, communication with wireless terminals placed in the front and rear parts of the vehicle can be performed. It becomes possible to increase the success rate and operate the wireless communication system smoothly.

In order to solve the above-mentioned problems, the invention according to claim 7 sets one of a plurality of wireless terminals as a beacon transmitting terminal in a predetermined order each time a communication channel is switched, and the remaining wireless terminals as beacon receiving terminals. A beacon receiving terminal of a wireless communication system that
a communication unit that receives beacons and transmits and receives data information;
a timer unit for timing 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 corresponding to the switching cycle of the communication channel;
When the communication unit receives the beacon, the timer unit sets time synchronization information included in the beacon in the timer unit, and a communication channel switching cycle of the communication unit based on the set time synchronization information. and
The channel switching unit switches the communication channel based on the predetermined rule and resets the timer unit at the end timing of the switching cycle of the communication channel.

According to the above configuration, the beacon receiving terminal switches the communication channel based on a predetermined rule at the end of the communication channel switching cycle, so it 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 communication channels in which radio wave interference has occurred for a long period of time.

In addition, even if the timing of the transmission frame of the beacon receiving terminal is shifted by a predetermined period, the beacon transmitting terminal and the beacon receiving terminal are synchronized by the time synchronization information for synchronizing the timer part of the beacon receiving terminal included in the beacon with the beacon transmitting terminal. It is possible to resynchronize between

In order to solve the above problems, the invention according to claim 8 is the beacon receiving terminal according to claim 7, wherein when the communication unit does not continuously receive the beacon on all communication channels, the channel The switching unit is characterized in that it waits for reception of the beacon in a communication channel that is set first in the switching order of the communication channels.

If the synchronization between the beacon receiving terminal and the beacon transmitting terminal deviates by more than the period of the transmission frame, the beacon receiving terminal will not be able to receive the beacons, so there is a possibility that the period in which resynchronization with the beacon transmitting terminal will not be possible will be prolonged. increases.

However, according to the above configuration, the beacon receiving terminal stops the communication channel switching operation and waits in the initial communication channel, so that the beacon can be received and resynchronized with the beacon transmitting terminal. Become.

In order to solve the above problems, the invention according to claim 9 is the beacon receiving terminal according to claim 7 or 8, wherein the channel switching unit of the beacon receiving terminal newly participating in the wireless communication system is configured to: It is characterized by waiting for reception of the beacon in the communication channel that is set first in the communication channel switching order.

According to the above configuration, a wireless terminal that newly participates in the wireless communication system is added to the wireless network of the wireless communication system at any time by waiting for reception of a beacon in the communication channel that is set first in the communication channel switching order. It becomes possible to

In order to solve the above problems, the invention of a radio communication system according to claim 10,
A beacon transmitting terminal according to any one of claims 1 to 6,
A beacon receiving terminal is included in any one of claims 7 to 9.

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 cycle. can be avoided independently. Therefore, it is possible to avoid an increase in communication delay time by avoiding communication channels in which radio wave interference has occurred for a long period of time.

In addition, even if the timing of the transmission frame of the beacon receiving terminal is shifted by a predetermined period, the beacon transmitting terminal and the beacon receiving terminal are synchronized by the time synchronization information for synchronizing the timer part of the beacon receiving terminal included in the beacon with the beacon transmitting terminal. It is possible to resynchronize between

According to the present invention, it is possible to autonomously avoid a communication channel, which is a frequency band receiving interference, and to avoid an increase in communication delay time when radio wave interference occurs for a long period of time.

Furthermore, since transmission frame synchronization is achieved by a beacon in the middle of the transmission frame, resynchronization can be achieved by the beacon if the synchronization deviation of the transmission frame is within half of the transmission frame length.

It is an example of a wireless communication network that constitutes a wireless communication system. 3 is a block diagram showing an example hardware configuration of a wireless terminal; FIG. FIG. 4 is a diagram showing an example of beacon transmission timing and communication channel switching timing in the embodiment; It is a figure which shows the structural example of a beacon. 4 is a diagram showing a configuration example of a data frame; FIG. It is an example of a transmission frame of a beacon transmitting terminal. FIG. 11 is an example of a flowchart showing an initial operation after the wireless terminal is activated; FIG. FIG. 11 is an example of a flowchart showing processing after switching communication channels; FIG. FIG. 10 is an example of a flowchart when a wireless terminal operates as a beacon transmitting terminal; FIG. FIG. 10 is an example of a flowchart when a wireless terminal operates as a beacon transmitting terminal; FIG. FIG. 10 is an example of a flowchart when a wireless terminal operates as a beacon receiving terminal; FIG. FIG. 4 is a diagram showing an example of channel switching order; FIG. 4 is a schematic diagram showing resynchronization of a beacon receiving terminal by beacon reception; FIG. 10 is a schematic diagram showing another example of beacon transmission timing; It is drawing for demonstrating patent document 1 which is a prior art. It is drawing for demonstrating patent document 1 which is a prior art. It is drawing for demonstrating patent document 1 which is a prior art. It is drawing for demonstrating patent document 1 which is a prior art. It is drawing for demonstrating patent document 2 which is a prior art. It is drawing for demonstrating patent document 2 which is a prior art. It is drawing for demonstrating patent document 2 which is a prior art. It is drawing for demonstrating patent document 3 which is a prior art. It is drawing for demonstrating patent document 3 which is a prior art. It is drawing for demonstrating patent document 3 which is a prior art.

(Overview of wireless communication system)
In a wireless network composed of a plurality of wireless terminals according to the present embodiment, each wireless terminal regularly switches between two or more communication channels (frequency bands) for communication, thereby reducing frequency bands that are subject to interference. can communicate autonomously. Each wireless terminal transmits a beacon in the middle of a transmission frame in a preset beacon transmission order to synchronize with other wireless terminals.

If there is a deviation in synchronization between wireless terminals, a beacon is used to correct the timer. A beacon is basically transmitted in the middle of a transmission frame, but if there is interference or transmission operations of other wireless terminals at the beacon transmission timing, beacon transmission is stopped until the channel becomes empty. If it is before the channel switching time, the beacon is transmitted immediately after the channel becomes vacant. By synchronizing the time between the wireless terminals by using the beacon in this way, it is possible to correct the time deviation of up to half the transmission frame.

The channel switching cycle is predetermined, and each wireless terminal autonomously switches the frequency as soon as the switching time comes. Even if the time synchronization signal by the beacon cannot be received, all the wireless terminals can communicate on the same communication channel because each wireless terminal can independently switch the frequency as described above.

As a basic operation of the wireless terminal, it always stands by in a reception state and detects the reception strength, except for data transmission, Ack (Acknowledgment) transmission, and beacon transmission. Also, from the detected reception strength, it is determined whether it is data, beacon, Ack, etc., or interference.

FIG. 1 shows a configuration example of a wireless communication network that constitutes the wireless communication system of this embodiment. In FIG. 1, wireless terminals 11 to 20 construct a wireless communication network 1000 . As a radio communication system, a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) system is assumed.

(Overview of wireless terminal)
FIG. 2 shows an example of a hardware block diagram of the wireless terminal 200 of this embodiment. A beacon transmitting terminal and a beacon receiving terminal described in the claims are implemented as a wireless terminal 200. FIG. Wireless terminal 200 is a general computer including communication section 210 , determination section 220 , control section 230 , I/F (interface) section 240 and information recording section 250 . A common computer executes a communication program to implement the functions shown in FIG. Also, the control unit 230 is a CPU (Central Processing Unit). The control unit 230 performs processing in the wireless terminal 200 by reading and writing data stored in the information recording unit 250 and inputting/outputting data with the communication unit 210 .

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

The wireless transmission unit 212 has a function of transmitting wireless signals such as data and beacons.

The radio reception unit 213 has a function of receiving data received from another radio terminal 200 through an antenna and radio signals such as beacons.

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

The reception strength determination section 221 has a function of determining whether or not the power of the received signal has exceeded a threshold level. The threshold level can be set to any value by the wireless communication system.

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 received signal is from another wireless communication system, it is determined that interference is occurring in the current communication channel.

Since received signals such as beacons and data information of its own wireless communication system include an ID (IDentification) unique to its own wireless communication system, the interference determination unit 222 can determine the received signal. Details will be described later.

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 transmission unit 212, and transmits data and beacon information from the wireless reception unit 213. Receives data and beacon information.

The beacon generation unit 231 uses the beacon transmission order information 252, the channel switching period information 253, and the timer information 251 stored in the information recording unit 250 to determine when the own wireless terminal 200 as a beacon transmitting terminal is to transmit a beacon. , has the ability to generate and transmit beacons.

Beacon 400 includes bit synchronization signal 410 , frame synchronization signal 420 , header 430 including a unique ID, source address 440 and time synchronization information 450 . The beacon 400 is transmitted in the middle of a transmission frame period during which the wireless terminal 200 as a beacon transmission terminal that transmits the beacon 400 transmits and receives data. The information contained in beacon 400 is detailed in FIG.

Note that the time synchronization information 450 included in the beacon 400 may be the timer information 251 of the beacon transmitting terminal that transmitted the beacon 400 . The radio terminal 200 that receives the beacon 400 writes the time synchronization information 450 included in the beacon 400 to the timer section 236 of its own radio terminal 200 . As a result, synchronization can be established between the beacon transmitting terminal that transmitted the beacon 400 and the wireless terminal 200 that received the beacon 400 .

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

In addition, when the data transmission period includes a timing at which 1/2 of the communication channel switching cycle has passed, the data generation unit 232 divides the data transmission period, and switches the communication channel during the data transmission period. It has a function of dividing the data transmission period so as not to include the timing when 1/2 of the cycle has elapsed.

The beacon analysis unit 233 has a function of extracting various kinds of beacon information included in the beacon 400 from the received beacon 400 and recording the extracted information in the information recording unit 250 . Also, as described above, the beacon analysis unit 233 of the beacon receiving terminal writes the time synchronization information 450 extracted from the beacon 400 to the timer unit 236 to synchronize with the beacon transmitting terminal.

The channel switching unit 234 reads the timer information 251 stored in the information recording unit 250, and switches the communication channel when the channel switching period specified by the channel switching period information 253 comes. When switching the communication channel, the channel switching unit 234 specifies the communication channel to be changed next based on the channel switching order information 254 stored in the information recording unit 250, and switches the communication channel.

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

The timer unit 236 counts the period from when the communication channel is switched and the timer is reset to when the communication channel is switched as a channel switching cycle. Here, as an example, the channel switching cycle is also the transmission frame length (Tms). The time measured by the timer section 236 is recorded in the information recording section 250 as timer information 251 .

Further, as described above, the radio terminal 200 that receives the beacon 400 writes the time synchronization information 450 included in the beacon 400 to the timer section 236 of its own radio terminal 200 . As a result, the wireless terminal 200 that is the beacon transmitting terminal that transmitted the beacon 400 and the wireless terminal 200 that is the beacon receiving terminal that received the beacon 400 can be synchronized.

The I/F section 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 251, beacon transmission order information 252, channel switching cycle information 253, and channel switching order information 254, and transmits/receives each information to/from the control unit 230. ing.

The timer information 251 records the elapsed time from the beginning of the channel switching cycle in real time as time information in units of predetermined channel switching cycles, based on the time measured by the timer section 236 . Also, when the wireless terminal 200 extracts the time synchronization information 450 from the received beacon 400, the time synchronization information 450 is set in the timer unit 236, and the wireless terminal 200 that transmitted the beacon 400 and the wireless terminal that received the beacon 400 Synchronize with terminal 200 . That is, the timer unit 236 restarts clocking from the time indicated by the time synchronization information 450 and records the clocked time information in the information recording unit 250 as the timer information 251 .

Furthermore, the radio terminal 200 resets and initializes the timer section 236 after switching the communication channel (see FIG. 8). All the wireless terminals 200 keep track of time in units of the channel switching cycle specified in advance, and when the beacon 400 cannot be received, the communication channel is automatically changed at the channel switching cycle.

In the channel switching period information 253, information indicating a predefined communication channel switching period is recorded.

That is, as an example, the transmission frame length (Tms) is recorded in the information recording section 250 as the channel switching period information 253 .

The channel switching order information 254 records a predetermined communication channel switching order. That is, the radio terminal 200 switches communication channels according to the channel switching order. For example, as shown in FIG. 11, the channel switching order is set so that all communication channels prepared in one cycle are used once. When one cycle of the channel switching order ends, the radio terminal 200 again selects a communication channel from the beginning of the channel switching order.

The beacon transmission order information 252 records the order in which the wireless terminal 200 becomes a beacon transmission terminal. For example, if the identification information of the wireless terminal 200 is recorded in order in the beacon transmission order information 252, the wireless terminal 200 can recognize which wireless terminal 200 will be the beacon transmitting terminal each time the communication channel is switched. . When one cycle of the beacon transmission order ends, the wireless terminal 200 that becomes the beacon transmission terminal again is determined from the beginning of the beacon transmission order.

Note that all the wireless terminals 200 included in the wireless communication system sequentially become beacon transmitting terminals, some wireless terminals 200 included in the wireless communication system sequentially become beacon transmitting terminals, and a beacon transmitting terminal In some cases, the wireless terminal 200 is fixed.

For example, a beacon transmitting terminal that selects one of the plurality of wireless terminals 200 as a beacon transmitting terminal in a predetermined order each time the communication channel is switched is one of the wireless terminals 200 included in the wireless communication system. is determined to be the wireless terminal 200 within a predetermined range from the midpoint on the line with the longest distance.

That is, by not using the wireless terminal 200, which is likely to deteriorate the communication environment, as a beacon transmitting terminal, it is possible to smoothly operate the wireless communication system of this scheme.

As an example, when a wireless communication system is mounted on a vehicle or the like, by using the wireless terminal 200 placed in the center of the vehicle as a beacon transmission terminal, communication with the wireless terminals 200 placed in the front and rear parts of the vehicle can be achieved. It becomes possible to increase the success rate of communication and operate the wireless communication system smoothly. In other words, the wireless communication system can be operated more stably by not using the wireless terminal 200 at the edge of the communicable range of the wireless communication system as a beacon transmitting terminal.

(Overview of operation of wireless communication system)
FIG. 3 is a diagram schematically showing a beacon transmission period and a channel switching period.

First, the wireless terminal 11 as a beacon transmitting terminal transmits and receives data on CH (channel: CHannel) 1, which is the initial communication channel arranged at the beginning of the channel switching order information 254, within Tms, which is the channel switching cycle, Then, beacon transmission is executed. Beacon transmission is performed when half the time of Tms, which is the channel switching period, has elapsed. At this time, the wireless terminals 12 to 20 receive beacons on CH1 as beacon receiving terminals. The wireless terminals 12 to 20 that have received the beacon are synchronized with the wireless terminal 11 that has transmitted the beacon based on the time synchronization information 450 included in the beacon. Tms is also a transmission frame period, which is a data transmission/reception period. Also, Tms is a fixed period during operation of the wireless communication system.

After T/2ms has passed since the wireless terminal 11 transmitted the beacon, all the wireless terminals switch to CH2, and the wireless terminal 12, which is the wireless terminal next to the wireless terminal 11, becomes the beacon transmitting terminal and transmits the beacon. Transmission and reception of beacons and switching of communication channels are repeated in the same manner.

In FIG. 3, beacons are transmitted and received at Tms intervals. Also, the communication channel is switched at Tms cycle. As described above, this periodic time T is the transmission frame period and is defined in advance in the wireless communication system. Also, the radio communication system cannot change the specified cycle time T while the radio terminal is in operation.

Furthermore, in FIG. 3, ten wireless terminals from wireless terminal 11 to wireless terminal 20 are used, and the number of wireless terminals does not change during operation of the wireless terminals. In other words, basically the wireless terminal is a fixed station, and the mobile station is not considered. Therefore, the increase or decrease in the number of wireless terminals within the wireless communication network is not taken into account, and wireless terminals to be assigned as wireless terminals 11 to 20 must first be defined. Moreover, as described above, there are cases where all or some of the wireless terminals in the wireless communication system become beacon transmitting terminals in order, and where the beacon transmitting terminals are fixed.

It is possible for the wireless communication system to add or remove wireless terminals when the wireless terminals are not in operation. For example, when one new wireless terminal is added to the wireless communication system, the wireless terminal newly added to the wireless communication system is assigned as the wireless terminal 21 in the order following the wireless terminal 20, and the beacon of all the wireless terminals is assigned. Information such as transmission order information is also updated.

FIG. 3 shows a basic communication channel switching cycle. With CH1 as the initial channel, all wireless terminals simultaneously switch in the order of CH1→CH2→CH3 at intervals of Tms. Also, beacon transmitting terminals that transmit beacons may be switched 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 be synchronized by beacons. However, even if the beacon cannot be received, the communication channel is automatically switched at intervals of Tms, so it is possible to synchronize the wireless terminals.

That is, if the beacon receiving terminal can receive the beacon, the reception of the time synchronization information 450 of the beacon is completed, and after T/2ms has passed, the beacon receiving terminal switches the communication channel. Also, when the beacon receiving terminal fails to receive the beacon, the communication channel is switched based on the timer information 251 of the information recording section 250 .

(Overview of beacon)
FIG. 4 illustrates an example configuration of a beacon 400 . Beacon 400 includes bit synchronization signal 410 , frame synchronization signal 420 , header 430 including a unique ID, source address 440 and time synchronization information 450 . In principle, the beacon 400 is transmitted in the middle of a transmission frame period during which the wireless terminal 200 as a beacon transmission terminal transmitting the beacon 400 transmits and receives data information.

A bit synchronization signal 410 and a frame synchronization signal 420 are signals for synchronizing with a beacon.

The unique ID included in header 430 is an ID unique to the wireless communication system. Therefore, the wireless terminal 200 that has received the beacon can determine whether or not the received beacon is the beacon of its own wireless communication system based on the unique ID included in the header.

The source address 440 is the address of the wireless terminal 200 that transmitted the beacon.

Time synchronization information 450 is timer information 251 recorded in information recording section 250 of wireless terminal 200 that transmits beacon 400 . The wireless terminals 200 that have received the beacon set the timer section 236 to the time indicated by the time synchronization information 450 included in the beacon, so that the wireless terminals 200 can be synchronized. If there is a deviation in synchronization between the wireless terminals 200, this time synchronization information 450 enables resynchronization between the wireless terminal 200 that transmitted the beacon 400 and the wireless terminal 200 that received the beacon 400. .

(summary of data frame)
FIG. 5 shows a configuration example of a data frame 500. As shown in FIG. At the beginning of the data frame 500 is a bit synchronization signal 510 for synchronizing in units of bits, followed by a frame synchronization signal 520 for synchronizing in units of frames. There is a header 530 containing the ID of the . Next to the header is a payload 540 which is the body of the data, and finally an error detection and correction code 550 for detecting and correcting errors in the data. It is assumed that the data frame 500 has a fixed length in transmitting/receiving data information during the beacon transmission/reception period. The wireless communication system can set the data frame 500 length to any length.

As shown in FIG. 5, data frame 500 includes a unique ID of the wireless communication system. can be determined by whether or not it has been received.

(Example of beacon transmission timing)
FIG. 6 shows a transmission frame of wireless terminal X, which is a beacon transmitting terminal. A wireless terminal X, which is a beacon transmitting terminal, transmits a beacon 610 in the middle of a transmission frame. A wireless terminal 200 having a transmission request in the other data transmission areas 620 and 630 performs a transmission operation.

Here, as an example, the transmission frame length (Tms) indicates the channel switching period. Also, the transmission timing of the beacon 610 in the transmission frame is determined in advance by the wireless communication system.

That is, in principle, the beacon 610 is transmitted in the middle of the transmission frame, which is the channel switching period. However, as will be described later, the beacon 610 is not transmitted while receiving interference from other wireless communication systems and transmission signals from other wireless terminals 200 of the own wireless communication system.

(Overview of operation of wireless communication system)
FIG. 7 shows a flowchart showing the initial operation when the wireless terminal 200 is activated.

In step S701, when the wireless terminals 200 are activated, each wireless terminal 200 sets the communication channel to an initial channel predetermined in the wireless communication system. This is executed by each wireless terminal 200 referring to the channel switching order information 254 of the information recording unit 250 and setting the first communication channel in the channel switching order information 254 as the initial channel. Next, the wireless terminal 200 proceeds to step S702.

In step S702, it is determined whether or not the wireless terminal 200 is the initial wireless terminal 200 in the preset beacon transmission order. Since the beacon transmission order information 252 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 252, thereby identifying the wireless terminal 200 as the initial wireless terminal 200. It can be determined whether there is If the wireless terminal 200 is the initial wireless terminal 200 (step S702: YES), the wireless terminal 200 proceeds to step S703, and if not (step S702: NO), the wireless terminal 200 proceeds to step S707.

In step S703, before the beacon transmission terminal, which is the initial wireless terminal 200, transmits a beacon, the reception intensity determination unit 221 determines whether or not the reception intensity is detected. If the reception intensity is detected (step S703: YES), the initial wireless terminal 200 proceeds to step S704, and if the reception intensity is not detected (step S703: NO), it proceeds to step S705. The reception strength is a predetermined value and an arbitrary value set in the wireless communication system.

Since the initial wireless terminal 200 cannot transmit a beacon if the reception intensity is detected in step S704, the initial wireless terminal 200 waits on the initial channel until the reception intensity is no longer detected. It is agreed that other wireless terminals 200 do not communicate during the period in which the initial wireless terminal 200 communicates. Therefore, if the reception intensity is detected, the interference determination unit 222 of the initial wireless terminal 200 can determine that the received signal is a wireless signal from another wireless communication system and interference is occurring in the communication channel.

In step S705, since the reception intensity is not detected, the initial wireless terminal 200 transmits a beacon, and proceeds to step S706.

In step S706, when the timer information 251 recorded in the information recording unit 250 of the initial wireless terminal 200 reaches the channel switching period, the channel switching unit 234 switches the communication channel based on the channel switching order information 254.

In step S707, since the initial wireless terminal 200 is a beacon receiving terminal, it waits in the receiving state and determines whether or not it has received a beacon. If the initial wireless terminal 200 has received a beacon (step S707: YES), the initial wireless terminal 200 proceeds to step S709, and if not (step S707: NO), proceeds to step S708.

In step S708, the initial wireless terminal 200, which is a beacon receiving terminal, proceeds to step S707 to wait on the initial channel until receiving a beacon.

In step S709, the initial wireless terminal 200 sets the timer unit 236 based on the time synchronization information 450 included in the beacon, and proceeds to step S706.

The above operation is the initial operation when the wireless terminal 200 is activated, and when the initial operation is completed, the transmission frame period has passed. It should be noted that, during the initial operation, no transmission operation other than the beacon is performed. In addition, although the beacon is transmitted only once in order to synchronize between the wireless terminal 200 that transmitted the beacon and the wireless terminal 200 that received the beacon, the beacon may be transmitted multiple times only during the initial operation. .

FIG. 8 is a flowchart showing processing after switching communication channels. Note that which communication channel the wireless terminal 200 switches to can be determined by referring to the channel switching order information 254 of the information recording unit 250 .

In step S801, the wireless terminal 200 resets the timer section 236, initializes the timer information 251 in the information recording section 250, and proceeds to step S802. As an example, the initial value is "0".

In step S802, it is determined whether the wireless terminal 200 has come to transmit a beacon. If it is the wireless terminal 200's turn to transmit a beacon (step S802: YES), the process proceeds to process A. If it is not the wireless terminal's turn to transmit a beacon (step S802: NO), the process proceeds to process B. . Whether or not the radio terminal 200 has reached its turn to transmit a beacon can be determined by referring to the beacon transmission order information 252 of the information recording unit 250 .

9A and 9B show a flowchart of process A. FIG. Processing A is a processing flow when the wireless terminal 200 becomes a beacon transmitting terminal and functions as a beacon transmitting terminal.

In step S901, since the wireless terminal 200 is in the reception mode, the reception strength determination section 221 determines whether or not the reception strength is detected. If the reception intensity is detected (step S901: YES), the wireless terminal 200 proceeds to step S902, and if the reception intensity is not detected (step S902: NO), the wireless terminal 200 proceeds to step S905.

In step S902, since the reception strength is being detected, the wireless terminal 200 determines whether or not an ID unique to the wireless communication system is detected from the received signal. If the unique ID is detected (step S902: YES), the wireless terminal 200 proceeds to step S903, and if the unique ID is not detected (step S902: NO), proceeds to step S908.

In step S903, the wireless terminal 200 determines whether or not data information has been successfully received from the received signal. If the wireless terminal 200 has successfully received the data information (step S903: YES), the wireless terminal 200 proceeds to step S904; proceed to

Since step S904 is when 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 S908.

Since step S905 is for the case where the reception strength of the received signal is not detected, the wireless terminal 200 determines whether or not the wireless terminal 200 has a data information transmission request. If there is no data information transmission request (step S905: NO), the wireless terminal 200 proceeds to step S908. If there is a data information transmission request (step S905: YES), the wireless terminal 200 proceeds to step S906.

In step S906, the wireless terminal 200 transmits the data information because the reception strength is not detected and the wireless terminal 200 is requested to transmit the data information. The wireless terminal 200 then proceeds to step S907. Note that if the data information transmission period includes a timing when 1/2 of the channel switching cycle has elapsed, the communication unit 210 or the control unit 230 divides the data information transmission period, and divides the data information transmission period into It is also possible to divide the data information transmission period so as not to include the timing at which 1/2 of the channel switching cycle has elapsed.

In step S907, the wireless terminal 200 that has transmitted the data information checks whether or not Ack has been received. If the wireless terminal 200 that has transmitted the data information can receive the Ack, it is assumed that the transmission/reception communication of the data information has succeeded, and the process proceeds to step S908. Further, if the wireless terminal 200 that has transmitted the data information cannot receive the Ack, it is determined that the transmission/reception communication of the data information has failed, and the process proceeds to step S908.

In step S908, the wireless terminal 200 confirms the elapsed time. That is, the radio terminal 200 reads the timer information 251 and determines whether or not it is time to transmit the beacon. If it is not time to transmit a beacon (step S908: NO), the wireless terminal 200 proceeds to step S901 to transmit and receive data information. If it is time to transmit a beacon (step S908: YES), the wireless terminal 200 proceeds to step S909 to transmit a beacon. Here, an example of the time at which the beacon should be transmitted is the middle of the same channel switching period as the transmission frame, and is the time when 1/2 of the channel switching period has elapsed. Note that since a beacon transmission period is necessary to transmit a beacon, step S908 is executed before a time equal to 1/2 of the channel switching period has elapsed, taking into account the beacon transmission period.

In step S<b>909 , the wireless terminal 200 determines whether or not the reception intensity is detected by the reception intensity determination section 221 . If the reception intensity is detected (step S909: YES), the wireless terminal 200 proceeds to step S916, and if the reception intensity is not detected (step S909: NO), the wireless terminal 200 proceeds to step S910.

In step S910, the wireless terminal 200 determines whether or not a beacon has been transmitted. If the wireless terminal 200 has transmitted a beacon (step S910: YES), the wireless terminal 200 proceeds to step S913, and if not (step S910: NO), proceeds to step S911.

In step S<b>911 , the wireless terminal 200 writes the timing information of the timer unit 236 to the timer information 251 of the information recording unit 250 to update the timer information 251 . The wireless terminal 200 then proceeds to step S912.

In step S912, the wireless terminal 200 transmits a beacon. The beacon contains time synchronization information including updated timer information of wireless terminal 200, which is the beacon transmitting terminal. Next, the wireless terminal 200 proceeds to step S919.

In step S913, since the reception strength of the received signal is not detected and the beacon has already been transmitted, the wireless terminal 200 determines whether or not the wireless terminal 200 has a data information transmission request. If there is no data information transmission request (step S913: NO), the wireless terminal 200 proceeds to step S919. If there is a data information transmission request (step S913: YES), the wireless terminal 200 proceeds to step S914.

In step S914, the wireless terminal 200 transmits the data information because the reception strength is not detected and the wireless terminal 200 is requested to transmit the data information. The wireless terminal 200 then proceeds to step S915.

In step S915, the wireless terminal 200 that has transmitted the data information checks whether or not Ack has been received. If the wireless terminal 200 that has transmitted the data information can receive the Ack, it is assumed that the transmission/reception communication of the data information has succeeded, and the process proceeds to step S919. If the wireless terminal 200 that has transmitted the data information cannot receive the Ack, it is determined that the transmission/reception communication of the data information has failed, and the process proceeds to step S919.

In step S916, since the reception strength is being detected, the wireless terminal 200 determines whether or not an ID unique to its own wireless communication system is detected from the received signal. If the unique ID is detected (step S916: YES), the wireless terminal 200 proceeds to step S917, and if the unique ID is not detected (step S916: NO), proceeds to step S919.

In step S917, the wireless terminal 200 determines whether or not data information has been successfully received from the received signal. If the wireless terminal 200 has successfully received the data information (step S917: YES), the wireless terminal 200 proceeds to step S918. The process proceeds to step S919.

Since step S918 is when 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 S919.

In step S<b>919 , the wireless terminal 200 determines whether or not the elapsed time recorded in the timer information 251 of the information recording unit 250 has reached the channel switching cycle recorded in the channel switching cycle information 253 . If the elapsed time has not reached the channel switching cycle (step S919: NO), the wireless terminal 200 proceeds to step S909, and if the elapsed time has reached the channel switching cycle (step S919: YES), the wireless terminal 200 switches communication channels. That is, when the timer information 251 recorded in the information recording section 250 of the radio terminal 200 reaches the channel switching period, the channel switching section 234 switches the communication channel based on the channel switching order information 254 .

FIG. 10 shows a flowchart of process B. FIG. Process B is a process flow when wireless terminal 200 functions as a beacon receiving terminal.

In step S<b>1001 , the wireless terminal 200 determines whether or not the reception strength is detected by the reception strength determination section 221 . If the reception intensity is detected (step S1001: YES), the wireless terminal 200 proceeds to step S1002, and if the reception intensity is not detected (step S1002: NO), the wireless terminal 200 proceeds to step S1007.

In step S1002, since the reception strength is being detected, the wireless terminal 200 determines whether or not an ID unique to its own wireless communication system is detected from the received signal. If the unique ID is detected (step S1002: YES), the wireless terminal 200 proceeds to step S1003, and if the unique ID is not detected (step S1002: NO), the wireless terminal 200 proceeds to step S1010.

In step S1003, since the received signal includes an ID unique to its own wireless communication system, the wireless terminal 200 determines whether the received signal is a beacon or data information. If the received signal is a beacon (step S1003: YES), the wireless terminal 200 proceeds to step S1004, and if the received signal is not a beacon (step S1003: NO), the wireless terminal 200 proceeds to step S1005. An ID unique to the own wireless communication system is determined in advance in the wireless communication system and recorded in information recording section 250 of wireless terminal 200 .

In step S1004, since the beacon is detected, the wireless terminal 200 establishes time synchronization based on the time synchronization information 450 included in the beacon. That is, the wireless terminal 200 that has received the beacon sets the time synchronization information 450 included in the beacon in the timer section 236 . Since the time synchronization information 450 included in the beacon is also the time information of the timer unit 236 of the wireless terminal 200 that transmitted the beacon, the wireless terminal 200 that transmitted the beacon and the wireless terminal 200 that received the beacon can be synchronized. becomes possible.

In step S1005, the wireless terminal 200 determines whether or not the data information was successfully received from the received signal. If the wireless terminal 200 has successfully received the data information (step S1005: YES), the wireless terminal 200 proceeds to step S1006; proceed to

Since step S1006 is when 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 S1010.

Since step S1007 is for the case where the reception strength of the received signal is not detected, the wireless terminal 200 determines whether or not the wireless terminal 200 has a data information transmission request. If there is no data information transmission request (step S1007: NO), the wireless terminal 200 proceeds to step S1010. If there is a data information transmission request (step S1007: YES), the wireless terminal 200 proceeds to step S1008.

In step S1008, the wireless terminal 200 transmits the data information because the reception strength is not detected and the wireless terminal 200 is requested to transmit the data information. The wireless terminal 200 then advances to step S1009.

In step S1009, the wireless terminal 200 that has transmitted the data information checks whether or not Ack has been received. If the wireless terminal 200 that has transmitted the data information can receive the Ack, it is assumed that the transmission/reception communication of the data information has succeeded, and the process proceeds to step S1010. If the wireless terminal 200 that has transmitted the data information fails to receive the Ack, it is determined that the transmission/reception communication of the data information has failed, and the process proceeds to step S1010.

In step S<b>1010 , the wireless terminal 200 determines whether or not the elapsed time recorded in the timer information 251 of the information recording unit 250 has reached the channel switching cycle recorded in the channel switching cycle information 253 . If the elapsed time has not reached the channel switching cycle 253 (step S1010: NO), the wireless terminal 200 proceeds to step S1001, and if the elapsed time has reached the channel switching cycle (step S1010: YES), Terminal 200 switches channels. That is, when the timer information 251 recorded in the information recording section 250 of the radio terminal 200 reaches the channel switching period, the channel switching section 234 switches the communication channel based on the channel switching order information 254 .

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

FIG. 11 is a diagram showing the switching order indicated by the channel switching order information 254 recorded in the information recording unit 250. The communication channels are switched in the order of CH1→CH2→CH3. Any number of communication channels may be used as long as the number is two or more. In addition, the order of channel switching need only be uniformly defined for all wireless terminals 200, and the order of channel switching can be arbitrarily set by the wireless communication system. Similarly, the initial channel may 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 section 250 as channel switching order information 254 .

If the wireless terminal 200 fails to receive the beacon for the specified number of times in succession, it stops switching the communication channel, returns to the initial channel, and waits on the initial channel until it can receive the beacon. The prescribed number of times can be set to any value by the wireless communication system. Also, the specified number of times is recorded in the information recording section 250 .

For example, if the wireless terminal 200 fails to receive a beacon on any communication channel in the order of CH3, CH1, and CH2, it returns to the initial channel, CH1, and waits until it can receive a beacon.

In this manner, even if the wireless terminals 200 are completely out of synchronization for some reason, the wireless terminals 200 can be synchronized again by waiting on the initial channel.

(Method for Correcting Synchronization Deviation)
Next, a method for correcting synchronization deviation will be described.
Since each radio terminal 200 has a timer section 236, it can switch frequency channels regularly at a predetermined channel switching period (Tms). However, basically, each wireless terminal 200 is synchronized by receiving a beacon.

On the other hand, in addition to the case where the wireless terminal 200 cannot receive the 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 the shift of the clock frequency of the timer section 236 or the like.

Therefore, FIG. 12 shows a procedure for resynchronization by beacon reception.

FIG. 12 is a diagram showing a case where the channel switching timing from CH1 to CH2 of beacon receiving terminal 1202 is too early. In this case, beacon receiving terminal 1202 receives a beacon at normal timing on channel switching destination CH2, and by setting timer section 236 of beacon receiving terminal 1202 to beacon time synchronization information 450, other wireless terminals 200 can be resynchronized with That is, since the time synchronization information 450 is included at the end of the beacon, the beacon receiving terminal 1202 rewrites the timer section 236 with the time synchronization information 450 of the beacon when the reception of the beacon is completed. As a result, the beacon transmitting terminal 1201 that transmitted the beacon and the beacon receiving terminal 1202 that received the beacon are synchronized. In this way, the channel switching timing to CH3 is synchronized at timing 1210 between the beacon transmitting terminal 1201 that transmitted the beacon and the beacon receiving terminal 1202 that received the beacon.

The beacon receiving terminal 1203 in FIG. 12 shows a case where the channel switching timing from CH1 to CH2 is too late. In this case, the beacon receiving terminal 1203 can receive the beacon at normal timing on CH2, which is the channel switching destination. Therefore, the beacon receiving terminal 1203 uses the time synchronization information 450 included at the end of the beacon to rewrite the timer section 236 with the time synchronization information 450 of the beacon upon completion of beacon reception. As a result, the beacon transmitting terminal 1201 that transmitted the beacon and the beacon receiving terminal 1203 that received the beacon are synchronized. That is, the channel switching timing to CH3 is synchronized at timing 1210 between the beacon transmitting terminal 1201 that transmitted the beacon and the beacon receiving terminal 1203 that received the beacon.

As shown in FIG. 12, when a deviation within 1/2 of the channel switching period (Tms), which is the length of a transmission frame determined in advance, occurs, the wireless terminal 200 switches to the channel to which it has switched. It is possible to resynchronize with another wireless terminal 200 by receiving a beacon at . If synchronization is lost for a time equal to or longer than half Tms, as described above, wireless terminal 200 waits on the initial channel until a beacon can be received.

(Beacon transmission timing)
FIG. 13 shows beacon transmission timing. As shown in FIG. 6, wireless terminal X, which is a beacon transmitting terminal, basically transmits a beacon 610 in the middle of a transmission frame, and wireless terminals 200 that generate transmission requests in other data transmission areas 620 and 630 Perform transmission operation. However, it is assumed that interference signals from other wireless communication systems and transmission data within the wireless communication network 1000 overlap with the transmission timing of the beacon 610 . In that case, as shown in FIG. 13, wireless terminal 200 waits until the reception strength falls below a predetermined threshold, and transmits beacon 1310 after the reception strength falls below the predetermined threshold. The wireless terminal 200 transmitting the beacon 1310 records the time information of the timer section 236 in the timer information 251 of the information recording section 250, and updates the timer information 251 as the time synchronization information 450 of the beacon 1310. to send. In the wireless terminal 200 transmitting the beacon, if the timing at which the reception intensity falls below the predetermined threshold reaches the channel switching time, the wireless terminal 200 switches the communication channel without transmitting the beacon 1310 .

As described above, according to this embodiment, . Each wireless terminal 200 can operate independently without installing a control station.

In addition, since all the wireless terminals 200 regularly change the frequency channel for communication, there is no need to wait for a long time on the same frequency channel, and there is no need to perform carrier sense for all frequency bands before starting communication.

Furthermore, since the frequency band used is the same for all wireless terminals 200, there is no need to estimate the frequency band used for transmission by correlation.

Furthermore, even if only a specific wireless terminal 200 receives interference, the frequency channel is automatically switched, so synchronization with other wireless terminals 200 can be achieved by receiving the beacon at the channel switching destination. Also, even if synchronization is completely lost, the initial channel is used for standby, so resynchronization with another wireless terminal 200 is possible.

Furthermore, since the beacon in the middle of the transmission frame is used for synchronization, the beacons 610 and 1310 can resynchronize if the deviation is within half the length of the transmission frame. Also, when an interference signal or the like is detected at the beacon transmission timing, synchronization can be achieved by shifting the transmission timing of the beacon 1310 . In addition, even when synchronization is completely lost as described above, resynchronization with another wireless terminal 200 is possible because the initial channel is on standby.

(Modification 1)
When building a wireless communication network in a vehicle, the communication control method described above can be adopted for all the wireless terminals 200 in the vehicle. As a result, it is possible to construct a wireless communication network 1000 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 wireless devices in factories and the like, regardless of whether they are installed in a vehicle. It should be noted that the wireless communication system can adopt a system other than the CSMA/CA system.

(Modification 2)
In the embodiment, as shown in FIG. 3, an example was mainly described in which all wireless terminals 200 included in the wireless communication system become beacon transmitting terminals in order based on the beacon transmission order information 252 . However, there are cases where only some wireless terminals 200 included in the wireless communication system become beacon transmitting terminals.

For example, radio waves from the wireless terminal 200 at the front or rear of the vehicle may have difficulty reaching the wireless terminal 200 at the rear or front of the vehicle. In such a case, if the beacons 610 and 1310 cannot be received for a period of time, synchronization deviation is likely to occur, and communication delays may occur.

Therefore, among the wireless terminals 200 included in the wireless communication system, only the wireless terminals 200 within a predetermined range from the midpoint on the line with the longest distance between the wireless terminals 200 can be the beacon transmitting terminals.

The wireless communication system can set the predetermined range to any value. As an example, the wireless communication system can set the predetermined range to 1/n of the vehicle length (n is a natural number of 3 or more). In this way, by using only the wireless terminal 200 in the center of the vehicle as a beacon transmitting terminal, the beacon receiving terminals can easily receive the beacons 610 and 1310, thereby suppressing communication delays. Alternatively, only the wireless terminal 200 with the best communication state among the wireless terminals 200 in the center of the vehicle can be used as the beacon transmitting terminal. For example, only the wireless terminal 200 with the highest CNR (Carrier to Noise Ratio) or the lowest BER (Bit Error Rate) in the wireless communication system can be the beacon transmitting terminal.

(Modification 3)
Wireless terminals 200 that do not transmit beacons 610, 1310 can be added into the wireless communication network 1000 at any time. When a new wireless terminal 200 is added to the wireless communication network 1000, the newly added wireless terminal 200 waits on the initial channel as an initial operation, receives the beacons 610 and 1310, and establishes time synchronization.

Although various embodiments have been described above, some or all of these embodiments can be combined to form new embodiments.

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 wave 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 strength 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 251 Timer information 252 Beacon transmission order information 253 Channel switching period information 254 Channel switching order information 500 Data frame 450 Time synchronization information 400, 610, 1310 Beacon 1201 Beacon transmitting terminal 1202, 1203 Beacon receiving terminal

Claims (10)

A beacon transmitting terminal of a wireless communication system in which one of a plurality of wireless terminals is set as 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 generation unit that generates a beacon;
a communication unit that transmits and receives data information and transmits the beacon;
a timer unit for timing 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 corresponding to the switching cycle of the communication channel;
The beacon generation unit causes the beacon to include time information measured by the timer unit as time synchronization information,
The communication unit transmits the beacon when the reception strength of the received signal is smaller than a predetermined value in a period that does not include the start timing and the end timing of the switching cycle of the communication channel,
The beacon transmitting terminal, wherein the channel switching unit switches the communication channel based on the predetermined rule and resets the timer unit at the end timing of the switching cycle of the communication channel. The communication unit is characterized by transmitting the beacon when the reception strength of the received signal is smaller than a predetermined value in a period including a timing when 1/2 of the switching cycle of the communication channel has passed. The beacon transmission terminal according to claim 1. If the transmission period of the data information includes a timing at which 1/2 of the switching period of the communication channel has passed, the transmission period of the data information is divided, and the communication channel is switched during the transmission period of the data information. 3. The beacon transmission terminal according to claim 1, further comprising a data generation unit that divides the transmission period of the data information so as not to include the timing when 1/2 of the cycle has elapsed. The communication unit receives the received signal without transmitting the beacon when the received signal strength of the received signal is equal to or greater than a predetermined value at the timing after 1/2 of the switching cycle of the communication channel has passed. 4. The beacon transmitting terminal according to any one of claims 1 to 3, wherein the beacon is transmitted when the intensity becomes smaller than a predetermined value. 5. The communication unit according to any one of claims 1 to 4, wherein the communication unit does not transmit the beacon when the beacon transmission end timing exceeds the communication channel switching period end timing. beacon transmitting terminal. Each time the communication channel is switched, one of the plurality of wireless terminals becomes a beacon transmitting terminal in a predetermined order. is the wireless terminal within a predetermined range from the 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 communication unit that receives beacons and transmits and receives data information;
a timer unit for timing 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 corresponding to the switching cycle of the communication channel;
When the communication unit receives the beacon, the timer unit sets time synchronization information included in the beacon in the timer unit, and a communication channel switching cycle of the communication unit based on the set time synchronization information. and
The beacon receiving terminal, wherein the channel switching unit switches the communication channel based on the predetermined rule and resets the timer unit at the end timing of the switching cycle of the communication channel. When the communication unit does not continuously receive the beacon on all communication channels, the channel switching unit waits for reception of the beacon on the communication channel set first in the communication channel switching order. 8. A beacon receiving terminal according to claim 7. 8. The channel switching unit of the beacon receiving terminal newly participating in the wireless communication system waits for reception of the beacon in a communication channel that is set first in the communication channel switching order. 9. The beacon receiving terminal according to 8. A beacon transmitting terminal according to any one of claims 1 to 6,
A wireless communication system comprising the beacon receiving terminal according to any one of claims 7 to 9.

Images