Description Title of Invention: WIRELESS COMMUNICATION APPARATUS, WIRELESS COMMUNICATION TERMINAL, WIRELESS COMMUNICATION METHOD, AND WIRELESS COMMUNICATION PROGRAM
Technical Field
[0001] The present invention relates to handover of wireless communication. Background Art
[0002] In a communication system of industrial equipment, it is repeated that a device called a master station notifies a plurality of devices called slave stations of a control amount of the industrial equipment and the plurality of slave stations notifies the master station of a state of the industrial equipment.
In this description, a time from the master station notifies the plurality of slave stations of the control amount until the master station receives notification of the state from all the plurality of slave stations, is referred to as a cycle time.
If this cycle time is short, it is possible to improve production efficiency caused by the industrial equipment and operation accuracy of the industrial equipment. [0003] Conventionally, although devices are wire-connected in the communication system of the industrial equipment, expectations for the wireless communication have been increasing in recent years due to easiness in a layout change and a demand for wire saving.
Considering convenience for a user upon adapting the wireless communication, it is preferable to realize a wireless system in an Industry-Science-Medical (ISM) band being a frequency band not requiring a license.
Among wireless systems in the ISM band, it is widely accepted to apply a wireless Local Area Network (LAN) system based on the IEEE802.11 standard capable

of high speed communication.
[0004] Incidentally, a packet error occurs in mobile communication if it takes time
for switching when a wireless child device switches a base station.
With regard to this point, Patent Literature 1 indicates a high speed handover method of a wireless LAN.
According to the method of Patent Literature 1, based on a connection history, it is possible to realize high speed handover by narrowing down access points to be connected from among several access points being handover candidates. Citation List Patent Literature
[0005] Patent Literature 1: JP 2009-49922 A Summary of Invention Technical Problem
[0006] However, when the high speed communication is required as in the communication system of the industrial equipment, the wireless communication is frequently performed in a wireless communication apparatus being a handover destination (a switching destination of wireless connection).
For this reason, a problem arises that, the handover is not completed before the wireless communication is completed in the wireless communication apparatus being the handover destination, and it takes time until a completion of the handover. [0007] The present invention mainly aims to solve a problem described above. The primary purpose of the present invention is to obtain a configuration in which a wireless communication terminal can switch a connection destination of wireless connection at high speed. Solution to Problem

[0008] A wireless communication apparatus according to the present invention includes:
a wireless reception unit to set first communication timing being timing for receiving a wireless frame from a first wireless communication terminal, among a plurality of wireless communication terminals, the first communication timing being wirelessly connected to the wireless communication apparatus and set second communication timing being timing for receiving a wireless frame from a second wireless communication terminal, among the plurality of wireless communication terminals, the second communication timing being wirelessly connected to other wireless communication apparatus other than the wireless communication apparatus, thereby receiving wireless frames; and
a switching control unit to, when the wireless reception unit receives the wireless frame from the second wireless communication terminal at the second communication timing, control to switch a connection destination of wireless connection of the second wireless communication terminal. Advantageous Effects of Invention
[0009] According to the present invention, a wireless communication apparatus performs switching control at a time of receiving a wireless frame from a second wireless communication terminal so that it is possible to switch a connection destination of wireless connection of a second wireless communication terminal at high speed. Brief Description of Drawings
[0010] Fig. 1 is a diagram illustrating a configuration example of a wireless communication system according to a first embodiment.
Fig. 2 is a diagram illustrating an outline of a functional configuration of a wireless communication parent device according to the first embodiment.

Fig. 3 is a diagram illustrating an outline of a functional configuration of a wireless communication child device according to the first embodiment.
Fig. 4 is a flowchart diagram illustrating an outline of an operation of the wireless communication parent device according to the first embodiment.
Fig. 5 is a flowchart diagram illustrating an outline of an operation of the wireless communication child device according to the first embodiment.
Fig. 6 is a flowchart diagram illustrating an outline of an operation of the wireless communication child device according to the first embodiment.
Fig. 7 is a diagram illustrating a detail of functional configuration of the wireless communication parent device according to the first embodiment.
Fig. 8 is a diagram illustrating a detail of a functional configuration of the wireless communication child device according to the first embodiment.
Fig. 9 is a diagram illustrating an example of a parent device management table of a wireless communication parent device 111 according to the first embodiment.
Fig. 10 is a diagram illustrating an example of the parent device management table of a wireless communication parent device 112 according to the first embodiment.
Fig. 11 is a diagram illustrating an example of a child device management table of a wireless communication child device 131 according to the first embodiment.
Fig. 12 is a diagram illustrating an example of the child device management table of a wireless communication child device 132 according to the first embodiment.
Fig. 13 is a diagram illustrating the child device management table of a wireless communication child device 133 according to the first embodiment.
Fig. 14 illustrates an example of a communication schedule between the wireless communication parent device 111 and wireless communication child devices 131 to 133 according to the first embodiment.

Fig. 15 illustrates an example of a communication schedule between the wireless communication parent device 112 and the wireless communication child devices 132 and 133 according to the first embodiment.
Fig. 16 illustrates an example of transmission timing of a response frame to the wireless communication parent device 111 by the wireless communication child device 133 according to the first embodiment.
Fig. 17 is a diagram illustrating an example of transmission timing of a disconnection frame to the wireless communication parent device 112 by the wireless communication child device 133 according to the first embodiment.
Fig. 18 is a diagram illustrating a hardware configuration example of the wireless communication parent device and the wireless communication child device according to the first embodiment. Description of Embodiments [0011] First Embodiment *** Description of System Configuration ***
Fig. 1 illustrates a configuration example of a wireless communication system according to the present embodiment.
As illustrated in Fig. 1, in the wireless communication system according to the present embodiment, a plurality of wireless communication parent device 111 and wireless communication parent device 112 is wire-connected to a master station 101 via anL2SW141andl42.
The L2SW 141 and L2SW 142 are layer 2 switches.
Wireless communication child devices 131 and 132 are wirelessly connected to the wireless communication parent device 111, and a wireless communication child device 133 is wirelessly connected to the wireless communication parent device 112.

That is, the wireless communication child devices 131 and 132 have established respective connection with the wireless communication parent device 111, and the wireless communication child device 133 has established connection with the wireless communication parent device 112.
Further, a slave station 121, a slave station 122, and a slave station 123 are wire-connected to the wireless communication child device 131, the wireless communication child device 132, and the wireless communication child device 133, respectively.
Among the wireless communication child devices, the wireless communication child device 131 is a fixed station, and the wireless communication child devices 132 and 133 are mobile stations.
[0012] As just described, in the communication system according to the present embodiment, the wireless communication parent device 111 and the wireless communication parent device 112 are wire-connected to one master station 101.
The wireless communication parent device 111 and the wireless communication parent device 112 operate at different wireless frequencies.
One or more wireless communication child devices are connected to each of the wireless communication parent device 111 and the wireless communication parent device 112.
The wireless communication parent device and the wireless communication child device communicate using Carrier Sense Multiple Access with Collision Detection (CSMA/CA).
Further, one slave station is wire-connected to the wireless communication child device. [0013] Each of the wireless communication parent device 111 and the wireless

communication parent device 112 corresponds to a wireless communication apparatus.
Further, each of the wireless communication child devices 131 to 133 corresponds to a wireless communication terminal.
The wireless communication child devices 131 and 132 are wirelessly connected to the wireless communication parent device 111 and correspond to first wireless communication terminals for the wireless communication parent device 111.
Further, the wireless communication child device 133 is wirelessly connected to the wireless communication parent device 112 and corresponds to a second wireless communication terminal for the wireless communication parent device 111.
On the other hand, since the wireless communication child device 133 is wirelessly connected to the wireless communication parent device 112, the wireless communication child device 133 corresponds to a first communication terminal for the wireless communication parent device 112.
Further, since the wireless communication child devices 131 and 132 are wirelessly connected to the wireless communication parent device 111, the wireless communication child devices 131 and 132 correspond to second wireless communication terminals for the wireless communication parent device 112.
Further, the wireless communication parent device 111 is a wireless communication parent device being connection destinations of wireless connection of the wireless communication child devices 131 and 132 and corresponds to a current wireless communication apparatus for the wireless communication child devices 131 and 132.
Further, the wireless communication parent device 112 is a wireless communication parent device being switching destinations of the wireless connection of the wireless communication child devices 131 and 132 and corresponds to a switching

destination wireless communication apparatus for the wireless communication child devices 131 and 132.
On the other hand, since the wireless communication parent device 112 is a wireless communication parent device being a connection destination of wireless connection of the wireless communication child device 133, the wireless communication parent device 112 corresponds to a current wireless communication apparatus for the wireless communication child device 133.
Further, since the wireless communication parent device 111 is a wireless communication parent device being a switching destination of the wireless connection of the wireless communication child device 133, the wireless communication parent device 111 corresponds to a switching destination wireless communication apparatus for the wireless communication child device 133.
Further, the wireless communication child device 131 being the fixed station corresponds to a fixed wireless communication terminal, and the wireless communication child devices 132 and 133 being the mobile stations correspond to mobile wireless communication terminals. [0014] *** Outline Description of Functional Configuration ***
Next, an outline of functional configurations of the wireless communication parent device 111 and the wireless communication parent device 112 will be described.
Fig. 2 illustrates the outline of the functional configurations of the wireless communication parent device 111 and the wireless communication parent device 112. [0015] A wireless transmission unit 21 transmits a communication frame by wireless communication.
The communication frame transmitted/received by the wireless communication is called a wireless frame.

On the other hand, a communication frame transmitted/received by wired communication is called a wired frame.
The wireless transmission unit 21 transmits a response request frame being a wireless frame requesting a response.
In the below, in order to describe an example in which the wireless transmission unit 21 broadcasts the response request frame, the response request frame is also referred to as a broadcast frame.
Note that the wireless transmission unit 21 may multicast the response request frame. | [0016] A wireless reception unit 22 receives from the wireless communication child devices 131 to 133 a wireless frame responding to the broadcast frame transmitted by the wireless transmission unit 21.
The wireless frame received by the wireless reception unit 22 from the wireless communication child devices 131 to 133 in response to the response request I frame is, hereinafter, referred to as a response frame.
The wireless reception unit 22 sets first communication timing being timing
for receiving a response frame from the first wireless communication terminal and
second communication timing being timing for receiving a response frame from the
second wireless communication terminal, thereby receiving response frames.
) More specifically, the wireless reception unit 22 repeats a communication
cycle including n (n>l) number of first communication timing for receiving response
frames from n number of first wireless communication terminals and m (m>l) number
of communication timing for receiving response frames from m number of second
wireless communication terminals, thereby receiving response frames.
> As described above, in the wireless communication parent device 111, the

wireless communication child devices 131 and 132 correspond to the first wireless communication terminals, and the wireless communication child device 133 corresponds to the second wireless communication terminal (n=2, m=l).
Therefore, in the wireless reception unit 22 of the wireless communication parent device 111, the first communication timing is timing for receiving response frames from the wireless communication child devices 131 and 132, and the second communication timing is timing for receiving a response frame from the wireless communication child device 133.
On the other hand, in the wireless communication parent device 112, the wireless communication child device 133 corresponds to the first wireless communication terminal, and the wireless communication child devices 131 and 132 correspond to the second wireless communication terminals (n=l, m=2).
Therefore, in the wireless reception unit 22 of the wireless communication parent device 112, the first communication timing is timing for receiving a response frame from the wireless communication child device 133, and the second communication timing is timing for receiving response frames from the wireless communication child devices 131 and 132.
Note that a process performed by the wireless reception unit 22 is called a wireless reception process.
[0017] When the wireless reception unit 22 receives a response frame from the second wireless communication terminal at the second communication timing, a switching control unit 23 performs control to switch the connection destination of the wireless connection of the second wireless communication terminal.
That is, in the wireless communication parent device 111, when the wireless reception unit 22 receives the response frame from the wireless communication child

device 133 at the second communication timing, the switching control unit 23 performs control to switch the connection destination of the wireless connection of the wireless communication child device 133 from the wireless communication parent device 112 to the wireless communication parent device 111.
Further, in the wireless communication parent device 112, when the wireless reception unit 22 receives the response frame from the wireless communication child device 131 (or the wireless communication child device 132) at the second communication timing, the switching control unit 23 performs control to switch the connection destination of the wireless connection of the wireless communication child device 131 (or the wireless communication child device 132) from the wireless communication parent device 111 to the wireless communication parent device 112.
Note that a process performed by the switching control unit 23 is called a switching control process.
[0018] Next, an outline of functional configurations of the wireless communication child devices 131 to 133 according to the present embodiment will be described.
Fig. 3 illustrates the outline of the functional configurations of the wireless communication child devices 131 to 133 according to the present embodiment. [0019] A wireless reception unit 31 repeatedly receives a broadcast frame from the current wireless communication apparatus being a current connection destination of the wireless connection.
The wireless reception units 31 of the wireless communication child devices 131 and 132 repeatedly receive broadcast frames from the wireless communication parent device 111 being the current wireless communication apparatus.
Further, the wireless reception unit 31 of the wireless communication child device 133 repeatedly receives a broadcast frame from the wireless communication

parent device 112 being the current wireless communication apparatus.
Further, in a case where it is necessary to switch the connection destination of the wireless connection, the wireless reception unit 31 receives a broadcast frame from the switching destination wireless communication apparatus being the switching destination of the wireless connection.
The case where it is necessary to switch the connection destination of the wireless connection is, for example, a case where reception power of a wireless frame from the current wireless communication apparatus falls below a threshold value, or the like.
For example, when it is necessary to switch the connection destination of the wireless connection, the wireless reception units 31 of the wireless communication child devices 131 and 132 receive broadcast frames from the wireless communication parent device 112 being the switching destination wireless communication apparatus.
Further, when it is necessary to switch the connection destination of the wireless connection, the wireless reception unit 31 of the wireless communication child device 133 receives a broadcast frame from the wireless communication parent device 111 being the switching destination wireless communication apparatus. [0020] A communication timing detection unit 32 detects arrival of current communication timing being timing which repeatedly arrives and is for transmitting a wireless frame to the current wireless communication apparatus.
More specifically, the communication timing detection unit 32 detects the arrival of the current communication timing based on a time at which the wireless reception unit 31 receives the wireless frame from the current wireless communication apparatus.
Further, when it is necessary to switch the connection destination of the

wireless connection, the communication timing detection unit 32 detects arrival of switching destination communication timing being timing which repeatedly arrives and is for transmitting a wireless frame to the switching destination wireless communication apparatus.
More specifically, the communication timing detection unit 32 detects the arrival of the switching destination communication timing based on a time at which the wireless reception unit 31 receives the wireless frame from the switching destination wireless communication apparatus.
Note that the first communication timing and the second communication timing described above are classifications of communication timing recognized by the wireless communication parent devices 111 and 112, and the current communication timing and the switching destination communication timing are classifications of communication timing recognized by the wireless communication child devices 131 to 133.
For example, communication timing allocated for the wireless communication child device 131 to transmit a response frame to the wireless communication parent device 111 is recognized as the first communication timing by the wireless communication parent device 111 and recognized as the current communication timing by the wireless communication child device 131.
On the other hand, communication timing allocated for the wireless communication child device 133 to transmit a response frame to the wireless communication parent device 111 is recognized as the second communication timing by the wireless communication parent device 111 and recognized as the switching destination communication timing by the wireless communication child device 133.
Note that a process performed by the communication timing detection unit 32

is called a communication timing detection process.
[0021] A wireless transmission unit 33 transmits a response frame to the current wireless communication apparatus at the current communication timing detected by the communication timing detection unit 32.
Further, when it is necessary to switch the connection destination of the wireless connection, the wireless transmission unit 33 transmits a response frame to the switching destination wireless communication apparatus at the switching destination communication timing detected by the communication timing detection unit 32.
If the wireless transmission unit 33 transmits the response frame at the switching destination communication timing, the switching destination wireless communication apparatus starts an operation of switching the connection destination of the wireless connection upon receiving the response frame.
Note that a process performed by the wireless transmission unit 33 is called a wireless transmission process. [0022] *** Outline Description of Operation ***
Next, an outline of operations of the wireless communication parent devices 111 and 112 illustrated in Fig. 2 will be described.
Fig. 4 is a flowchart diagram illustrating the outline of the operations of the wireless communication parent devices 111 and 112.
In the below, although an operation example of the wireless communication parent device 111 will be described, an operation of the wireless communication parent device 112 is also the same as the operation described below.
Further, in the below, after transmitting a response request frame (a broadcast frame), the wireless communication parent device 111 waits for receiving response frames from the wireless communication child devices 131 and 132 being the first

wireless communication terminals, and also waits for receiving a response frame from the wireless communication child device 133 being the second wireless communication terminal.
Note that a procedure illustrated in Fig. 4 corresponds to examples of a wireless communication method and a wireless communication program. [0023] When transmission timing of the response request frame arrives, the wireless transmission unit 21 broadcasts the response request frame (S401). [0024] Next, the wireless reception unit 22 determines a type of current communication timing (S402).
If the current communication timing is the first communication timing, that is, timing for receiving a response frame from the first wireless communication terminal, the wireless reception unit 22 performs a process of S403.
On the other hand, if the current communication timing is the second communication timing, that is, timing for receiving a response frame from the second wireless communication terminal, the wireless reception unit 22 performs a process of S408.
[0025] In S403, the wireless reception unit 22 determines whether or not the response frame is received from the first wireless communication terminal.
Then, when the response frame is received (YES in S403), the wireless reception unit 22 transfers the received response frame to an element (not illustrated in Fig. 2) that processes the response frame in the wireless communication parent device 111 (S404).
On the other hand, when the response frame is not received (NO in S403), the wireless transmission unit 21 retransmits the response request frame (S405).
When the response frame is not received even after the first communication

timing has completed (YES in S406), the wireless reception unit 22 performs an error process (S407).
In the error process, the wireless reception unit 22 notifies, for example, an element (not illustrated in Fig. 2) that manages a state of the wireless communication child device in the wireless communication parent device 111 that the response frame has not been received.
[0026] In S408, the wireless reception unit 22 determines whether or not the response frame from the second wireless communication terminal has been received.
Then, when the response frame has not been received (NO in S408), the wireless reception unit 22 performs an operation of S410.
On the other hand, when the response frame has been received at the second communication timing (YES in 408), the wireless reception unit 22 notifies the switching control unit 23 of the wireless communication child device being a transmission source of the response frame, and the switching control unit 23 performs a switching process (S409).
In a system configuration of Fig. 1, when the wireless reception unit 22 of the wireless communication parent device 111 has received the response frame from the wireless communication child device 133 at the second communication timing, the wireless communication parent device 111 processes to switch the connection destination of the wireless connection of the wireless communication child device 133 from the wireless communication parent device 112 to the wireless communication parent device 111.
[0027] In S410, the wireless reception unit 22 determines whether or not there is unprocessed communication timing.
When there is the unprocessed communication timing (YES in S410), the

wireless reception unit 22 performs operations S402 onwards on the unprocessed communication timing.
When there is no unprocessed communication timing (NO in S410), the wireless transmission unit 21 transmits the response request frame (S401). [0028] Next, an outline of operations of the wireless communication child devices 131 to 133 illustrated in Fig. 3 will be described.
Figs. 5 and 6 are flowchart diagrams illustrating the outline of the operations of the wireless communication child devices 131 to 133.
Fig. 5 is a flowchart diagram illustrating an operation at a time when each wireless communication child device transmits a response frame to the wireless communication parent device (the current wireless communication apparatus) being the current connection destination of the wireless connection.
Fig. 6 is a flowchart diagram illustrating an operation at a time when each wireless communication child device transmits a response frame to the wireless communication parent device (the switching destination wireless communication apparatus) being the switching destination, in order to switch the wireless communication parent device being the connection destination of the wireless connection.
Note that procedures illustrated in Figs. 5 and 6 correspond to examples of the wireless communication method and the wireless communication program. [0029] In Fig. 5, when the wireless reception unit 31 receives a response request frame transmitted from the wireless communication parent device being the connection destination of the wireless connection (YES in S501), the communication timing detection unit 32 determines whether or not the communication timing (the current communication timing) has arrived (S502).

The communication timing detection unit 32 determines that the communication timing has arrived at a time point when a prescribed waiting time has elapsed from a reception time of the response request frame.
If the communication timing has arrived (YES in S502), the wireless transmission unit 33 transmits a response frame in response to the response request frame to the wireless communication parent device being the connection destination of the wireless connection (S503).
[0030] In the wireless communication child devices 131 and 132, the wireless reception unit 31 receives the response request frame broadcasted from the wireless communication parent device 111 (S501).
In the wireless communication salve device 131, the communication timing detection unit 32 determines that the communication timing of the wireless communication child device 131 has arrived at a time point when a waiting time prescribed for the wireless communication child device 131 has elapsed from the reception time of the response request frame (YES in S502).
Then, the wireless transmission unit 33 transmits the response frame to the wireless communication parent device 111 (S503).
Likewise, in the wireless communication child device 132, the communication timing detection unit 32 determines that the communication timing of the wireless communication child device 132 has arrived at a time point when a waiting time prescribed for the wireless communication child device 132 has elapsed from the reception time of the response request frame (YES in S502).
Then, the wireless transmission unit 33 transmits the response frame to the wireless communication parent device 111 (S503).
Further, in the wireless communication child device 133, the wireless

reception unit 31 receives the response request frame broadcasted from the wireless communication parent device 112 (S501).
In the wireless communication child device 133, the communication timing detection unit 32 determines that the communication timing of the wireless communication child device 133 has arrived at a time point when a waiting time prescribed for the wireless communication child device 133 has elapsed from the reception time of the response request frame (YES in S502).
Then, the wireless transmission unit 33 transmits the response frame to the wireless communication parent device 112 (S5 03).
[0031] In Fig. 6, when it becomes necessary to switch the wireless communication parent device (YES in S601), the wireless reception unit 31 determines the wireless communication parent device being the switching destination of the wireless connection (S602).
Then, when the wireless reception unit 31 receives a response request frame from the wireless communication parent device being the switching destination (YES in S603), the communication timing detection unit 32 determines whether or not the communication timing (the switching destination communication timing) has arrived (S604).
The communication timing detection unit 32 determines that the communication timing has arrived at a time point when the prescribed waiting time has elapsed from the reception time of the response request fame.
If the communication timing has arrived (YES in S604), the wireless transmission unit 33 transmits a response frame in response to the response request frame to the wireless communication parent device being the switching destination (S605).

[0032] In the wireless communication child devices 131 and 132, when it is necessary to switch the wireless communication parent device (YES in S601), the wireless reception unit 31 determines the switching destination of the wireless connection as the wireless communication parent device 112 and receives the response request frame broadcasted from the wireless communication parent device 112 being the switching destination (S602 and S603).
In the wireless communication child device 131, the communication timing detection unit 32 determines that the communication timing of the wireless communication child device 131 has arrived at a time point when the waiting time prescribed for the wireless communication child device 131 has elapsed from the reception time of the response request frame (YES in S604).
Then, the wireless transmission unit 33 transmits the response frame to the wireless communication parent device 112 (S605).
Likewise, in the wireless communication child device 132, the communication timing detection unit 32 determines that the communication timing of the wireless communication child device 132 has arrived at a time point when the waiting time prescribed for the wireless communication child device 132 has elapsed from the reception time of the response request frame (YES in S604).
Then, the wireless transmission unit 33 transmits the response frame to the wireless communication parent device 112 (S605).
Further, in the wireless communication child device 133, when it is necessary to switch the wireless communication parent device (YES in S601), the wireless reception unit 31 determines the switching destination of the wireless connection as the wireless communication parent device 111 and receives the response request frame broadcasted from the wireless communication parent device 111 being the switching

destination (S602 and S603).
In the wireless communication child device 133, the communication timing detection unit 32 determines that the communication timing of the wireless communication child device 133 has arrived at a time point when the waiting time prescribed for the wireless communication child device 133 has elapsed from the reception time of the response request frame (YES in S604).
Then, the wireless transmission unit 33 transmits the response frame to the wireless communication parent device 111 (S605). [0033] *** Detailed Description of Functional Configuration ***
Next, details of functional configurations of the wireless communication parent devices 111 and 112 will be described.
Fig. 7 illustrates the details of the functional configurations of the wireless communication parent devices 111 and 112.
Note that, in the below, although a functional configuration of the wireless communication parent device 111 will be described, the description below will also be applied to the wireless communication parent device 112.
[0034] In Fig. 7, a parent device management table 201 is a table for managing identification information of the mobile station of the wireless communication child device in the wireless communication system, identification information of the fixed station connected to the wireless communication parent device 111, communication timing, and a connection state.
[0035] A wired frame reception unit 202 receives a wired frame. [0036] A wired frame analyzing unit 203 analyzes the wired frame received by the wired frame reception unit 202, thereby determining whether the wired frame received by the wired frame reception unit 202 is a wired frame from the master station 101 or a

wired frame from other wireless communication parent device 112.
When the wired frame is from the master station 101, the wired frame analyzing unit 203 notifies a wireless frame creation unit 204 of data included in the wired frame.
Further, when the wired frame is from other wireless communication parent device, the wired frame analyzing unit 203 notifies a connection management unit 210 of data included in the wired frame.
[0037] The wireless frame creation unit 204 creates a wireless frame for notifying the wireless communication child device of the data notified from the wired frame analyzing unit 203.
Further, the wireless frame creation unit 204 creates a wireless frame a transmission of which is instructed by a retransmission instruction unit 212. [0038] A wireless frame transmission unit 205 wirelessly transmits the wireless frame created by the wireless frame creation unit 204.
Further, the wireless frame transmission unit 205 notifies a communication timing control unit 211 of timing of having transmitted the wireless frame. [0039] A wireless frame reception unit 206 receives a wireless frame from the wireless communication child device.
[0040] A wireless frame analyzing unit 207 analyzes the wireless frame received by the wireless frame reception unit 206, thereby determining which of the wireless communication child devices has transmitted the wireless frame received by the wireless frame reception unit 206.
Further, when the wireless frame reception unit 206 does not receive the wireless frame, the wireless frame analyzing unit 207 notifies the communication timing control unit 211 that there is no reception of the wireless frame.

Further, when a wireless frame is received from a wireless communication child device wirelessly connected to the wireless communication parent device 111, the wireless frame analyzing unit 207 notifies a wired frame creation unit 208 of data included in the wireless frame.
Further, when the wireless frame is received from the wireless communication child device wirelessly connected to the wireless communication parent device 111, the wireless frame analyzing unit 207 notifies the connection management unit 210 of the wireless communication child device being the transmission source of the wireless frame.
[0041] The wired frame creation unit 208 creates a wired frame for notifying the master station 101 of the data notified from the wireless frame analyzing unit 207.
Further, the wired frame creation unit 208 creates, based on an instruction from the connection management unit 210, a wired frame for notifying the other wireless communication parent device 112 of a change in a connection state of the wireless communication child device.
[0042] A wired frame transmission unit 209 transmits the wired frame created by the wired frame creation unit 208 via wire.
[0043] The connection management unit 210 updates the connection state managed in the parent device management table 201 based on the data notified from the wired frame analyzing unit 203 and the data notified from the wireless frame analyzing unit 207.
Further, the connection management unit 210 notifies the communication timing control unit 211 of the updated connection state.
[0044] The communication timing control unit 211 generates communication timing for each wireless communication child device based on the transmission timing notified

from the wireless frame transmission unit 205.
Further, when there is no reception of the wireless frame from the wireless communication child device 131 or the wireless communication child device 132, the communication timing control unit 211 instructs the retransmission instruction unit 212 to retransmit the wireless frame.
[0045] Upon receiving a retransmission instruction from the communication timing control unit 211, the retransmission instruction unit 212 instructs the wireless frame creation unit 204 to retransmit the wireless frame.
[0046] In the configuration of Fig. 7, the wireless frame creation unit 204 and the wireless frame transmission unit 205 correspond to the wireless transmission unit 21 illustrated in Fig. 2.
That is, the wireless frame creation unit 204 generates a response request frame, and the wireless frame transmission unit 205 transmits the response request frame.
Further, the wireless frame reception unit 206, the wireless frame analyzing unit 207, and the communication timing control unit 211 correspond to the wireless reception unit 22 illustrated in Fig. 2.
That is, the wireless frame reception unit 206 receives a response frame, and the wireless frame analyzing unit 207 determines which of the wireless communication child devices has transmitted the response frame received by the wireless frame reception unit 206.
Further, the communication timing control unit 211 determines whether current communication timing is the first communication timing or the second communication timing.
Further, the connection management unit 210 corresponds to the switching

control unit 23 illustrated in Fig. 2.
That is, the connection management unit 210 switches the connection destination of the wireless connection of the second wireless communication child device by updating the connection state managed in the parent device management table 201.
[0047] Next, details of functional configurations of the wireless communication child devices 131 to 133 will be described.
Fig. 8 illustrates the details of the functional configurations of the wireless communication child devices 131 to 133.
[0048] In Fig. 8, a child device management table 301 manages identification information, a connection state, and communication timing of the wireless communication parent device being a connection candidate in the wireless communication system.
[0049] A wired frame reception unit 302 receives a wired frame from the slave station.
[0050] A wireless frame creation unit 303 creates a wireless frame for notifying of data included in the wired frame received by the wired frame reception unit 302.
Further, when a response control unit 308 instructs the wireless frame creation unit 303 to transmit a response, the wireless frame creation unit 303 creates a wireless frame for notifying of the response.
[0051] A wireless frame transmission unit 304 wirelessly transmits the wireless frame created by the wireless frame creation unit 303.
Further, when a wireless frequency switching unit 309 instructs the wireless frame transmission unit 304 to switch a frequency, the wireless frame transmission unit 304 switches the frequency at which the wireless frame is transmitted.

[0052] A wireless frame reception unit 305 receives a wireless frame from the wireless communication parent device.
Further, the wireless frame reception unit 305 transfers the received wireless frame to a wireless frame analyzing unit 306.
Further, the wireless frame reception unit 305 notifies the response control unit 308 of the reception power of the wireless frame.
Further, when the wireless frequency switching unit 309 instructs the wireless frame reception unit 305 to switch a frequency, the wireless frame reception unit 305 switches the frequency at which the wireless frame is received.
[0053] The wireless frame analyzing unit 306 analyzes the wireless frame transmitted from the wireless frame reception unit 305, thereby determining whether or not data included in the wireless frame is notified to the slave station.
When the data included in the wireless frame is notified to the slave station, the data is notified to a wired frame transmission unit 307.
Further, when the wireless frame analyzing unit 306 determines, as a result of analyzing the wireless frame transferred from the wireless frame reception unit 305, the wireless frame as the response request frame from the wireless communication parent device, the wireless frame analyzing unit 306 notifies the response control unit 308 that the response request frame has been received.
[0054] The wired frame transmission unit 307 transmits a wired frame for notifying the slave station of the data notified from the wireless frame analyzing unit 306. [0055] When the wireless frame analyzing unit 306 notifies the response control unit 308 that the response request frame from the wireless communication parent device has been received, the response control unit 308 detects the arrival of the communication timing allocated for the wireless communication child device.

Then, when the response control unit 308 detects the arrival of the communication timing, the response control unit 308 instructs the wireless frame creation unit 303 to transmit a response.
Further, based on the reception power notified from the wireless frame reception unit 305, the response control unit 308 determines whether or not it is necessary to switch a frequency. When it is necessary to switch the frequency, the response control unit 308 instructs the wireless frequency switching unit 309 to switch the frequency.
[0056] Based on an instruction from the response control unit 308 to switch the frequency, the wireless frequency switching unit 309 instructs the wireless frame transmission unit 304 to switch a transmission frequency of the wireless frame and instructs the wireless frame reception unit 305 to switch a reception frequency of the wireless frame.
[0057] In the configuration of Fig. 8, the wireless frame reception unit 305 and the wireless frequency switching unit 309 correspond to the wireless reception unit 31 illustrated in Fig. 3.
That is, the wireless frame reception unit 305 receives the wireless frame from the wireless communication parent device being the current connection destination of the wireless connection.
Then, when it becomes necessary to switch the wireless communication parent device, the wireless frequency switching unit 309 performs control to switch the reception frequency and searches for the wireless communication parent device being the switching destination of the wireless connection. The wireless frame reception unit 305 receives the wireless frame from the wireless communication parent device being the switching destination of the wireless connection.

Further, the response control unit 308 corresponds to the communication timing detection unit 32 illustrated in Fig. 3.
That is, the response control unit 308 detects the arrival of the communication timing for transmitting the wireless frame to the wireless communication parent device being the current connection destination of the wireless connection.
When it becomes necessary to switch the wireless communication parent device, the response control unit 308 detects the arrival of the communication timing for transmitting the wireless frame to the wireless communication parent device being the switching destination of the wireless connection.
Further, the wireless frame transmission unit 304 and the wireless frequency switching unit 309 correspond to the wireless transmission unit 33 illustrated in Fig. 3.
That is, the wireless frequency switching unit 309 sets the transmission frequency to a frequency of the wireless communication parent device being the switching destination of the wireless connection so that the wireless frame transmission unit 304 can transmit the wireless frame to the wireless communication parent device being the switching destination of the wireless connection.
Then, the wireless frame transmission unit 304 transmits the wireless frame to the wireless communication parent device being the switching destination of the wireless connection, at the communication timing with the wireless communication parent device being the switching destination of the wireless connection detected by the response control unit 308.
[0058] Next, the parent device management table 201 illustrated in Fig. 7 will be described.
The parent device management table 201 includes a wireless communication child device type, wireless communication child device identification information,

communication timing, and a connection state.
In the column of the wireless communication child device type, a type is indicated as to whether the wireless communication child device is a mobile station or a fixed station.
In the column of the wireless communication child device identification information, identification information of the wireless communication child device is indicated.
In the column of the connection state, it is indicated whether or not the wireless communication child device is wirelessly connected.
In the column of the communication timing, as described above, timing is indicated at which the wireless communication child device transmits a response frame in response to a response request frame transmitted by the wireless communication parent device.
Transmission order of the response frame is specified for each wireless communication child device. If response frames transmitted by all the wireless communication child devices have fixed length, the communication timing of each wireless communication child device can be identified from the transmission order of the response frame.
Further, in a case where response frame length is different depending on the wireless communication child device, the wireless communication timing of each wireless communication child device can be identified from a time required to transmit each response frame.
In the below, it is assumed that the response frames transmitted by all the wireless communication child devices have the fixed length and the communication timing of each wireless communication child device is identified from the transmission

order of the response frame.
Then, in the column of the communication timing of the parent device management table 201, the transmission order of the response frame of the wireless communication child device is described.
[0059] Fig. 9 illustrates an example of the parent device management table 201 of the wireless communication parent device 111.
Since the wireless communication child devices 131 and 132 are currently connected to the wireless communication parent device 111, the connection states with the wireless communication child devices 131 and 132 are connected and the connection state with the wireless communication child device 133 is disconnected. [0060] Fig. 10 illustrates an example of the parent device management table 201 of the wireless communication parent device 112.
Since the wireless communication child device 133 is currently connected to the wireless communication parent device 112, the connection state with the wireless communication child device 133 is connected and the connection state with the wireless communication child device 132 is disconnected.
Further, since the wireless communication child device 131 is the fixed station connected to the wireless communication parent device 111, information of the wireless communication child device 131 is not included in the parent device management table of the wireless communication parent device 112. [0061] Fig. 11 illustrates an example of the child device management table 301 of the wireless communication child device 131.
Further, Fig. 12 illustrates an example of the child device management table 301 of the wireless communication child device 132.
Furthermore, Fig. 13 illustrates an example of child device management table

301 of the wireless communication child device 133.
Since the wireless communication child device 131 is the fixed station, the connection candidate is only the wireless communication parent device 111 in Fig. 11.
On the other hand, since the wireless communication child devices 132 and 133 are the mobile stations, connection candidates are the wireless communication parent device 111 and the wireless communication parent device 112 in Figs. 12 and 13.
Since the wireless communication child device 132 is connected to the wireless communication parent device 111, the connection state with the wireless communication parent device 111 is connected and the connection state with the wireless communication parent device 112 is disconnected.
Further, since the wireless communication child device 133 is connected to the wireless communication parent device 112, the connection state with the wireless communication parent device 111 is disconnected and the connection state with the wireless communication parent device 112 is connected. [0062] *** Detailed Description of Operation ***
Next, a detail of operations of the wireless communication parent device illustrated in Fig. 7 and the wireless communication child device illustrated in Fig. 8 will be described.
[0063] Firstly, there will be described operations of the wireless communication parent device 111 and the wireless communication child devices 131 to 133 in a case where the wireless communication parent device 111 transmits a broadcast frame (a response request frame) in accordance with a communication schedule illustrated in Fig. 14.
In Fig. 14, the wireless communication parent device 111 transmits the broadcast frame (the response request frame) in a time slot 901, the wireless

communication child device 131 transmits a response frame to the wireless communication parent device 111 in a time slot 902, and the wireless communication child device 132 transmits a response frame to the wireless communication parent device 111 in a time slot 904.
A time slot 903 is communication timing for the wireless communication child device 133 to transmit a response frame to the wireless communication parent device 111. However, since the wireless communication child device 133 is wirelessly connected to the wireless communication parent device 112, normally (in a case where it is not necessary to switch the connection destination of the wireless connection), the wireless communication child device 133 does not transmit the response frame to the wireless communication parent device 111 in the time slot 903. [0064] In Fig. 14, the time slot 902 is communication timing for the wireless communication parent device 111 to receive the response frame from the wireless communication child device 132 wirelessly connected to the wireless communication parent device 111 and corresponds to the first communication timing.
Further, the time slot 902 is communication timing for the wireless communication child device 132 to transmit the response frame to the wireless communication parent device 111 being the current connection destination of the wireless connection and corresponds to the current communication timing.
The time slot 903 is communication timing for the wireless communication parent device 111 to receive the response frame from the wireless communication child device 133 wirelessly connected to the wireless communication parent device 112 and corresponds to the second communication timing.
Further, the time slot 903 is communication timing for the wireless communication child device 133 to transmit the response frame to the wireless

communication parent device 111 being the switching destination of the wireless connection and corresponds to the switching communication timing.
The time slot 904 is communication timing for the wireless communication parent device 111 to receive the response frame from the wireless communication child device 131 wirelessly connected to the wireless communication parent device 111 and corresponds to the first communication timing.
Further, the time slot 904 is communication timing for the wireless communication child device 131 to transmit the response frame to the wireless communication parent device 111 being the current connection destination of the wireless connection.
[0065] Firstly, there will be described a procedure in which the wireless communication parent device 111 transmits the broadcast frame (the response request frame) in the time slot 901.
[0066] In the wireless communication parent device 111, the wired frame reception unit 202 receives a broadcast frame transmitted via wired communication from the master station 101.
Next, the wired frame analyzing unit 203 analyzes the broadcast frame, and the wireless frame creation unit 204 creates the wireless frame (the response request frame).
Then, the wireless frame transmission unit 205 wirelessly transmits the wireless frame (the response request frame) created by the wireless frame creation unit 204.
At this time, the wireless frame transmission unit 205 notifies the communication timing control unit 211 of the transmission timing of the wireless frame (the response request frame).

Based on the transmission timing of the wireless frame (the response request frame) notified from the wireless frame transmission unit 205 and the transmission order described in the column of the communication timing in the parent device management table 201 (Fig. 9), the communication timing control unit 211 creates, for each wireless communication child device, the communication timing for receiving the response frame.
Then, the communication timing control unit 211 waits for reception of the response frame from the wireless communication child device. [0067] Next, there will be described a procedure in which the wireless communication child device 132 connected to the wireless communication parent device 111 transmits the response frame in the time slot 902.
[0068] In the wireless communication child device 132, the wireless frame reception unit 305 receives the wireless frame (the response request frame) from the wireless communication parent device 111 in the time slot 901.
Then, the wireless frame analyzing unit 306 analyzes the wireless frame received by the wireless frame reception unit 305 and transfers data included in the wireless frame to the wired frame transmission unit 307.
Then, the wired frame transmission unit 307 transmits a wired frame including the data included in the wireless frame, to the slave station 122.
The wireless frame analyzing unit 306 also notifies the response control unit 308 of reception of the wireless frame.
The response control unit 308 refers to the child device management table 301 (Fig. 10) and instructs the wireless frame creation unit 303 to transmit the response frame when the communication timing described in the child device management table 301 arrives.

Based on the reception time of the wireless frame (the response request frame) from the wireless communication parent device 111, the response control unit 308 detects the arrival of the communication timing of the wireless communication child device 132 in accordance with the transmission order described in the column of the communication timing in the child device management table 301.
The wireless frame creation unit 303 creates the response frame, and the wireless frame transmission unit 304 wirelessly transmits the response frame to the wireless communication parent device 111.
As a result of this, the wireless communication child device 132 transmits the response frame to the wireless communication parent device 111 in the time slot 902 of Fig. 14.
Further, upon receiving the wireless frame, the wireless frame reception unit 305 notifies the response control unit 308 of the reception power of the wireless frame. Here, the response control unit 308 determines that the reception power of the wireless frame is sufficiently large and determines that it is not necessary to switch a wireless connection destination.
[0069] The wireless communication child device 133 is not connected to the wireless communication parent device 111, and a reception frequency of the wireless frame reception unit 305 of the wireless communication child device 133 does not match a frequency of the wireless communication parent device 111.
Therefore, the wireless communication child device 133 does not receive the wireless frame (the response request frame) from the wireless communication parent device 111 in the time slot 901.
Therefore, the wireless communication child device 133 does not transmit the response frame to the wireless communication parent device 111 in the time slot 903.

[0070] In the wireless communication child device 131, the same operation as the
wireless communication child device 132 is performed, and the wireless communication
child device 131 transmits the response frame to the wireless communication parent
device 111 in the time slot 904.
[0071] Next, there will be described an operation at a time when the wireless
communication parent device 111 receives the response frame from the wireless
communication child device.
[0072] In the wireless communication parent device 111, the wireless frame
reception unit 206 receives the response frame from the wireless communication child
device 132 in the time slot 902.
The wireless frame analyzing unit 207 analyzes the response frame received by the wireless frame reception unit 206, thereby recognizing that the response frame has been received from the wireless communication child device 132.
The wireless frame analyzing unit 207 notifies the communication timing control unit 211 that the response frame has been received from the wireless communication child device 132.
The communication timing control unit 211 confirms that the response frame from the wireless communication child device 132 has been received in the time slot 902 and waits for the response frame from the wireless communication child device 133.
Note that when the wireless frame reception unit 206 has not received the response frame from the wireless communication child device 132 in the time slot 902, the communication timing control unit 211 notifies the retransmission instruction unit 212 that the response frame from the wireless communication child device 132 has not been received.
Then, the retransmission instruction unit 212 notifies the wireless frame

creation unit 204 to retransmit the response request frame to the wireless communication child device 132.
The wireless frame creation unit 204 outputs the response request frame to the wireless frame transmission unit 205, and the wireless frame transmission unit 205 retransmits the response request frame via unicast, to the wireless communication child device 132.
[0073] As described above, since the wireless communication child device 133 is currently connected to the wireless communication parent device 112, the wireless communication child device 133 does not transmit the response frame in the time slot 903.
Therefore, the wireless communication parent device 111 does not receive the response frame in the time slot 903.
Since the communication timing control unit 211 does not receive the response frame in the time slot 903, the communication timing control unit 211 refers to the parent device management table 201.
With reference to the parent device management table 201, the communication timing control unit 211 confirms that the wireless communication child device 133 to which the time slot 903 is allocated is disconnected to the wireless communication parent device 111.
Then, the communication timing control unit 211 decides not to retransmit the response request frame to the wireless communication child device 133 and waits for reception of the next response frame from the wireless communication child device 131. [0074] In the wireless communication parent device 111, the wireless frame reception unit 206 receives the response frame from the wireless communication child device 131 in the time slot 904.

Note that since an operation of the wireless communication parent device 111 in the time slot 904 is the same as an operation of the wireless communication parent device 111 in the time slot 902, the description thereof will be omitted. [0075] Next, there will be described operations of the wireless communication parent device 112 and the wireless communication child devices 131 to 133 in a case where the wireless communication parent device 112 transmits a broadcast frame (a response request frame) in accordance with a communication schedule illustrated in Fig. 15.
In Fig. 15, the wireless communication parent device 112 transmits the broadcast frame (the response request frame) in a time slot 1001, and the wireless communication child device 133 transmits a response frame to the wireless communication parent device 112 in a time slot 1003.
A time slot 1002 is communication timing for the wireless communication child device 132 to transmit a response frame to the wireless communication parent device 112. However, since the wireless communication child device 132 is wirelessly connected to the wireless communication parent device 111, normally (in a case where it is not necessary to switch the connection destination of the wireless connection), the wireless communication child device 132 does not transmit the response frame to the wireless communication parent device 112 in the time slot 1003.
Further, since the wireless communication child device 131 is the fixed station that is wirelessly connected to the wireless communication parent device 111 and is not wirelessly connected to the wireless communication parent device 112, the communication timing for the wireless communication child device 131 is not set for the wireless communication parent device 112.
Therefore, in the wireless communication parent device 112, there is no delay caused by waiting for a response frame from the wireless communication child device

131.
[0076] In Fig. 15, the time slot 1002 is communication timing for the wireless communication parent device 112 to receive the response frame from the wireless communication child device 132 wirelessly connected to the wireless communication parent device 111 and corresponds to the second communication timing.
Further, the time slot 1002 is communication timing for the wireless communication child device 132 to transmit the response frame to the wireless communication parent device 112 being the switching destination of the wireless connection and corresponds to the switching communication timing.
Further, the time slot 1003 is communication timing for the wireless communication parent device 112 to receive the response frame from the wireless communication child device 133 wirelessly connected to the wireless communication parent device 112 and corresponds to the first communication timing.
Further, the time slot 1003 is communication timing for the wireless communication child device 133 to transmit the response frame to the wireless communication parent device 112 being the current connection destination of the wireless connection and corresponds to the current communication timing.
Note that an operation in a case where the wireless communication parent device 112 receives the response frame from the wireless communication child device 133 in the time slot 1003 is the same as an operation in a case where the wireless communication parent device 111 receives the response frame from the wireless communication child device 132 in the time slot 902 of Fig. 14.
Further, an operation in a case where the wireless communication parent device 112 does not receive the response frame from the wireless communication child device 133 in the time slot 1003 is the same as an operation in a case where the wireless

communication parent device 111 does not receive the response frame from the wireless
communication child device 132 in the time slot 902 of Fig. 14.
[0077] Next, there will be described an operation of the wireless communication
child device 133 to perform handover from the wireless communication parent device
111 to the wireless communication parent device 112.
[0078] In the wireless communication child device 133, when the response control
unit 308 is notified, from the wireless frame reception unit 305, of the reception power
of the response request frame from the wireless communication parent device 112, the
response control unit 308 compares the notified reception power with the threshold
value.
Then, when the reception power of the response request frame from the wireless communication parent device 112 falls below the threshold value, the response control unit 308 instructs, while the wireless frame transmission unit 304 and the wireless frame reception unit 305 are not communicating, the wireless frequency switching unit 309 to search for other wireless communication parent device.
The wireless frequency switching unit 309 sequentially switches a reception frequency of the wireless frame reception unit 305.
Then, when the wireless frame reception unit 305 receives a response request frame from the wireless communication parent device 111 with a reception output equal to or larger than the threshold value, the wireless frame transmission unit 304 transmits a response frame to the wireless communication parent device 111 at communication timing for the wireless communication child device 133 to transmit a response frame to the wireless communication parent device 111.
[0079] Fig. 16 illustrates a communication schedule at a time when the wireless communication child device 133 transmits a response frame to the wireless

communication parent device 111.
In Fig. 16, a time slot 1101 is communication timing for the wireless communication parent device 111 to transmit a response request frame.
A time slot 1102 is communication timing for the wireless communication child device 132 to transmit a response frame to the wireless communication parent device 111.
A time slot 1103 is communication timing for the wireless communication child device 133 to transmit a response frame to the wireless communication parent device 111.
A time slot 1104 is communication timing for the wireless communication child device 131 to transmit a response frame to the wireless communication parent device 111.
The wireless communication child device 133 transmits the response frame to the wireless communication parent device 111 in the time slot 1103, thereby switching the connection destination of the wireless connection from the wireless communication parent device 112 to the wireless communication parent device 111.
At this time, the response control unit 308 of the wireless communication child device 133 changes the connection states in the child device management table 301 to "connected" for the wireless communication parent device 111 and "disconnected" for the wireless communication parent device 112. [0080] When the wireless communication parent device 111 receives the response frame from the wireless communication child device 133 in the time slot 1103, the wireless frame analyzing unit 306 notifies the connection management unit 210 of the wireless communication child device 133 being the transmission source of the response frame.

The connection management unit 210 changes the connection state of the wireless communication child device 133 in the parent device management table 201 to "connected".
Further, the connection management unit 210 instructs the wired frame creation unit 208 to create a connection notification frame notifying the wireless communication parent device 112 that the wireless communication child device 133 has connected to the wireless communication parent device 111.
The wired frame creation unit 208 creates the connection notification frame.
Then, the wired frame transmission unit 209 broadcasts the connection notification frame.
Furthermore, the connection management unit 210 broadcasts a dummy frame whose transmission source is the wireless communication child device 133 via the wired frame creation unit 208 and the wired frame transmission unit 209 in order to make the L2SW 141 andl42 to learn a path of a unicast frame of the wireless communication child device 133.
Note that the connection management unit 210 may transmit a wired frame integrating the above connection notification frame and the dummy frame. [0081] In the wireless communication parent device 112, the wired frame reception unit 202 receives the connection notification frame transmitted from the wireless communication parent device 111.
The wired frame analyzing unit 203 analyzes the connection notification frame and determines that the connection notification frame is a wired frame from the wireless communication parent device 111.
Then, the wired frame analyzing unit 203 notifies the connection management unit 210 of data (data indicating that the wireless communication child device 133 has

connected to the wireless communication parent device 111) included in the connection notification frame.
The connection management unit 210 changes the connection state of the wireless communication child device 133 in the parent device management table 201 to "disconnected".
Further, the connection management unit 210 notifies the communication timing control unit 211 that the wireless communication child device 133 is disconnected to the wireless communication parent device 112.
The communication timing control unit 211 is notified that the wireless communication child device 133 is disconnected. Thus, even if not receiving the response frame from the wireless communication child device 133, the communication timing control unit 211 does not instruct the retransmission instruction unit 212 to retransmit the response request fame to the wireless communication child device 133. [0082] *** Description of Effects of Embodiment ***
As described above, in the present embodiment, in addition to the communication timing for receiving the response frame from the wireless communication child device connected to the wireless communication parent device, the wireless communication parent device is provided with the communication timing for receiving the response frame from the wireless communication child device connected to the other wireless communication parent device.
Therefore, according to the present embodiment, it is possible for the wireless communication parent device to perform a switching control at a time when receiving the response frame from the wireless communication child device connected to the other wireless communication parent device, thereby completing the handover at high speed. [0083] *** Appendix ***

In the above, there has been described a procedure in which the wireless communication child device 133 transmits the response frame to the wireless communication parent device 111 being the switching destination of the wireless connection.
Alternatively, the wireless communication child device 133 may transmit the response frame to the wireless communication parent device 111 after transmitting a disconnection frame to the wireless communication parent device 112. [0084] When the reception power of the response request frame received from the wireless communication parent device 112 falls below the threshold value, the wireless frequency switching unit 309 of the wireless communication child device 133 sequentially switches the reception frequency of the wireless frame reception unit 305 and searches for the other wireless communication parent device.
When the reception power from the wireless communication parent device 111 is stronger than that of the wireless communication parent device 112, the response control unit 308 of the wireless communication child device 133 makes the wireless frame creation unit 303 to create the disconnection frame at the communication timing for transmitting the response frame to the wireless communication parent device 112 and makes the wireless frame transmission unit 304 to transmit the disconnection frame. [0085] Fig. 17 illustrates a communication schedule at a time when the wireless communication child device 133 transmits the disconnection frame to the wireless communication parent device 112.
In Fig. 17, a time slot 1201 is communication timing for the wireless communication parent device 112 to transmit a response request frame.
A time slot 1202 is communication timing for the wireless communication child device 132 to transmit a response frame to the wireless communication parent

device 112.
A time slot 1203 is communication timing for the wireless communication child device 133 to transmit a response frame to the wireless communication parent device 112.
The wireless communication child device 133 transmits the disconnection frame to the wireless communication parent device 112 in the time slot 1203.
The disconnection frame is a wireless frame that requests the wireless communication parent device 112 to switch the wireless connection to the wireless communication parent device 111.
In the wireless communication child device 133, after transmitting the disconnection frame, the wireless frequency switching unit 309 changes a transmission frequency of the wireless frame transmission unit 304 and a reception frequency of the wireless frame reception unit 305 to a frequency used by the wireless communication parent device 111.
Then, the response control unit 308 waits for reception of a wireless frame from the wireless communication parent device 111.
[0086] In the wireless communication parent device 112 which has received the disconnection frame from the wireless communication child device 133, the connection management unit 210 changes the connection state of the wireless communication child device 133 in the parent device management table 201 to "disconnected".
Furthermore, the connection management unit 210 transmits a handover notification frame notifying the handover of the wireless communication child device 133 to the wireless communication parent device 111, via the wired frame creation unit 208 and the wired frame transmission unit 209. [0087] When the wireless communication parent device 111 receives the handover

notification frame from the wireless communication parent device 112, the connection management unit 210 changes the connection state of the wireless communication child device 133 in the parent device management table 201 to "connected".
Further, when there is no response frame received from the wireless communication child device 133, the connection management unit 210 notifies the communication timing control unit 211 to retransmit the response request frame to the wireless communication child device 133.
Further, the connection management unit 210 broadcasts a dummy frame whose transmission source is the wireless communication child device 133 via the wired frame creation unit 208 and the wired frame transmission unit 209 in order to make the L2SW 141 and 142 to learn a path of a unicast frame of the wireless communication child device 133.
Furthermore, in order to check whether or not the wireless communication child device 133 is connected to the wireless communication parent device 111, the connection management unit 210 instructs the wireless frame creation unit 204 to create a dummy frame addressed to the wireless communication child device 133.
Based on an instruction of the connection management unit 210, the wireless frame creation unit 204 creates the dummy frame and the wireless frame transmission unit 205 unicasts the dummy frame to the wireless communication child device 133. [0088] As described above, the wireless communication child device notifies the currently connected wireless communication parent device of disconnection of the wireless connection and the wireless communication parent device being the switching destination of the wireless connection.
In this case, the wireless communication parent device being a handover destination can also perform retransmission control of the wireless communication child

device so that a frame arrival rate at the wireless communication parent device being the
handover destination is improved.
[0089] *** Description of Hardware Configuration Example ***
Lastly, a hardware configuration example of the wireless communication parent devices 111 and 112 and the wireless communication child devices 131 to 133 will be described with reference to Fig. 18.
The wireless communication parent devices 111 and 112 and the wireless communication child devices 131 to 133 are computers.
The wireless communication parent devices 111 and 112 and the wireless communication child devices 131 to 133 include hardware such as a processor 1901, an auxiliary storage device 1902, a memory 1903, a communication device 1904, an input interface 1905, and a display interface 1906.
The processor 1901 is connected to other hardware via a signal line 1910 and controls these other hardware.
The input interface 1905 is connected to an input device 1907.
The display interface 1906 is connected to a display 1908. [0090] The processor 1901 is an Integrated Circuit (IC) to perform processing.
The processor 1901 is, for example, a Central Processing Unit (CPU), a Digital Signal Processor (DSP), or a Graphics Processing Unit (GPU).
The auxiliary storage device 1902 is, for example, a Read Only Memory (ROM), a flash memory, or a Hard Disk Drive (HDD).
The memory 1903 is, for example, a Random Access Memory (RAM).
The communication device 1904 includes a receiver 19041 that receives data and a transmitter 19042 that transmits data.
The communication device 1904 is, for example, a communication chip or a

Network Interface Card (NIC).
The input interface 1905 is a port to which a cable 1911 of the input device 1907 is connected.
The display interface 1906 is a port to which a cable 1912 of the display 1908 is connected.
The input device 1907 and the display 1908 are, for example, a touch panel. [0091] In the auxiliary storage device 1902, programs are stored by which functions of "units" illustrated in Figs. 2, 3, 7, and 8 are implemented.
These programs are loaded into the memory 1903, read into the processor 1901, and executed by the processor 1901.
Furthermore, the auxiliary storage device 1902 also stores an Operating System (OS).
Then, at least a part of the OS is loaded into the memory 1903, and the processor 1901 executes the programs each of which implements the functions of the "units" while executing the OS.
In Fig. 18, one processor 1901 is illustrated, but the wireless communication parent devices 111 and 112 and the wireless communication child devices 131 to 133 may include a plurality of processors 1901.
Then, the plurality of processors 1901 may cooperatively execute the programs to implement the functions of the "units".
Further, the memory 1903, the auxiliary storage device 1902, or a register or a cash memory in the processor 1901 stores information, data, a signal value, and a variable value indicating the result of processing performed by the "units".
Further, the programs to implement the functions of the "units" are stored in a storage medium such as a magnetic disk, a flexible disk, an optical disk, a compact disk,

a Blu-ray (registered trademark) disk, or a DVD.
[0092] The "units" may be provided using "processing circuitry".
Further, the "units" may be read as "circuits", "steps", "procedures", or "processes".
The "circuits" and the "processing circuitry" are each a concept including not only the processor 1901, but also other types of processing circuits such as a logic IC, a Gate Array (GA), an Application Specific Integrated Circuit (ASIC), or a Field-Programmable Gate Array (FPGA). Reference Signs List
[0093] 21: wireless transmission unit; 22: wireless reception unit; 23: switching control unit; 31: wireless reception unit; 32: communication timing detection unit; 33: wireless transmission unit; 101: master station; 111: wireless communication parent device; 112: wireless communication parent device; 121: slave station; 122: slave station; 123: slave station; 131: wireless communication child device; 132: wireless communication child device; 133: wireless communication child device; 141: L2SW; 142: L2SW; 201: parent device management table; 202: wired frame reception unit; 203: wired frame analyzing unit; 204: wireless frame creation unit; 205: wireless frame transmission unit; 206: wireless frame reception unit; 207: wireless frame analyzing unit; 208: wired frame creation unit; 209: wired frame transmission unit; 210: connection management unit; 211: communication timing control unit; 212: retransmission instruction unit; 301: child device management table; 302: wired frame reception unit; 303: wireless frame creation unit; 304: wireless frame transmission unit; 305: wireless frame reception unit; 306: wireless frame analyzing unit; 307: wired frame transmission unit; 308: response control unit; and 309: wireless frequency switching unit

Claims
[Claim 1] A wireless communication apparatus comprising:
a wireless reception unit to set first communication timing being timing for receiving a wireless frame from a first wireless communication terminal, among a plurality of wireless communication terminals, the first wireless communication terminal being wirelessly connected to the wireless communication apparatus and second communication timing being timing for receiving a wireless frame from a second wireless communication terminal, among the plurality of wireless communication terminals, the second wireless communication terminal being wirelessly connected to other wireless communication apparatus other than the wireless communication apparatus, thereby receiving wireless frames; and
a switching control unit to, when the wireless reception unit receives the wireless frame from the second wireless communication terminal at the second communication timing, control to switch a connection destination of wireless connection of the second wireless communication terminal. [Claim 2] The wireless communication apparatus according to Claim 1,
wherein the wireless reception unit repeats a communication cycle including n (n>l) number of first communication timing for receiving wireless frames from n number of first wireless communication terminals wirelessly connected to the wireless communication apparatus and m (m>l) number of second communication timing for receiving wireless frames from m number of second wireless communication terminals wirelessly connected to the other wireless communication apparatus, thereby receiving wireless frames. [Claim 3] The wireless communication apparatus according to Claim 1,

wherein when the wireless reception unit receives the wireless frame from the second wireless communication terminal at the second communication timing, the switching control unit performs control to switch a connection destination of wireless connection of the second wireless communication terminal from the other wireless communication apparatus to the wireless communication apparatus. [Claim 4] The wireless communication apparatus according to Claim 1, further comprising
a wireless transmission unit to transmit a response request frame being a wireless frame requesting a response, before the first communication timing and the second communication timing start,
wherein the wireless reception unit, at the first communication timing, receives a response frame being a wireless frame responding to the response request frame from the first wireless communication terminal,
at the second communication timing, does not receive a response frame from the second wireless communication terminal when the second wireless communication terminal does not need to switch a connection destination of wireless connection, and receives the response frame from the second wireless communication terminal when the second wireless communication terminal needs to switch the connection destination of the wireless connection. [Claim 5] The wireless communication apparatus according to Claim 4,
wherein the wireless transmission unit, at the second communication timing, does not retransmit the response request frame even when the wireless reception unit does not receive the response frame from the second wireless communication terminal, and at the first communication timing, retransmits the response request frame when the wireless reception unit does not receive the response frame from the first wireless

communication terminal.
[Claim 6] The wireless communication apparatus according to Claim 1,
wherein the switching control unit, at the first communication timing, performs control to switch a connection destination of wireless connection of the first wireless communication terminal, when the wireless reception unit receives from the first wireless communication terminal, a wireless frame requesting to switch the connection destination of the wireless connection . [Claim 7] The wireless communication apparatus according to Claim 2,
wherein in a case where a mobile wireless communication terminal wirelessly connected to the other wireless communication apparatus and a fixed wireless communication terminal wirelessly connected to the other wireless communication terminal are included in the m number of second wireless communication terminals,
the wireless reception unit sets the second communication timing for the mobile wireless communication terminal but does not set the second communication timing for the fixed wireless communication terminal. [Claim 8] A wireless communication terminal comprising:
a communication timing detection unit to detect arrival of a current communication timing being timing which repeatedly arrives and is for transmitting a wireless frame to a current wireless communication apparatus being a current connection destination of wireless connection, and also to detect arrival of switching destination communication timing being timing which repeatedly arrives and is for transmitting a wireless frame to a switching destination wireless communication apparatus being a switching destination of the wireless connection when it is necessary to switch a connection destination of the wireless connection; and
a wireless transmission unit to transmit a wireless frame to the current

wireless communication apparatus at the current communication timing detected by the communication timing detection unit, and also to transmit a wireless frame to the switching destination wireless communication apparatus at the switching destination communication timing detected by the communication timing detection unit when it is necessary to switch the connection destination of the wireless connection. [Claim 9] The wireless communication terminal according to Claim 8, further comprising
a wireless reception unit to receive a wireless frame repeatedly from the current wireless communication apparatus and also to receive a wireless frame from the switching destination wireless communication apparatus when it is necessary to switch a connection destination of wireless connection,
wherein the communication timing detection unit detects arrival of the current communication timing based on a time at which the wireless reception unit receives a wireless frame from the current wireless communication apparatus, and
detects arrival of the switching destination communication timing based on a time at which the wireless reception unit receives a wireless frame from the switching destination wireless communication apparatus. [Claim 10] The wireless communication terminal according to Claim 8,
wherein the wireless transmission unit, at the current communication timing, transmits a wireless frame requesting to switch a connection destination of wireless connection to the switching destination wireless communication apparatus, to the current wireless communication apparatus, in place of transmitting a wireless frame to the switching destination wireless communication apparatus at the switching destination communication timing, when it is necessary to switch the connection destination of the wireless connection.

[Claim 11] The wireless communication terminal according to Claim 8,
wherein the communication timing detection unit detects arrival of the switching destination communication timing, when it is necessary to switch a connection destination of wireless connection since reception power of a wireless frame from the current wireless communication apparatus falls below a threshold value. [Claim 12] A wireless communication method comprising:
by a wireless communication apparatus being a computer, setting first communication timing being timing for receiving a wireless frame from a first wireless communication terminal, among a plurality of wireless communication terminals, the first wireless communication terminal being wirelessly connected to the wireless communication apparatus and second communication timing being timing for receiving a wireless frame from a second wireless communication terminal, among the plurality of wireless communication terminals, the second wireless communication terminal being wirelessly connected to other wireless communication apparatus other than the wireless communication apparatus, thereby receiving wireless frames; and
when the wireless reception unit receives the wireless frame from the second wireless communication terminal at the second communication timing, controlling to switch a connection destination of wireless connection of the second wireless communication terminal. [Claim 13] A wireless communication method comprising:
by a wireless communication terminal being a computer, detecting arrival of a current communication timing being timing which repeatedly arrives and is for transmitting a wireless frame to a current wireless communication apparatus being a current connection destination of wireless connection,

and also to detect arrival of switching destination communication timing being timing which repeatedly arrives and is for transmitting a wireless frame to a switching destination wireless communication apparatus being a switching destination of the wireless connection when it is necessary to switch a connection destination of the wireless connection; and
transmitting a wireless frame to the current wireless communication apparatus at the current communication timing, and also to transmit a wireless frame to the switching destination wireless communication apparatus at the switching destination communication timing when it is necessary to switch the connection destination of the wireless connection.
[Claim 14] A wireless communication program to cause a wireless communication apparatus being a computer to execute:
a wireless reception process to set first communication timing being timing for receiving a wireless frame from a first wireless communication terminal, among a plurality of wireless communication terminals, the first wireless communication terminal being wirelessly connected to the wireless communication apparatus and second communication timing being timing for receiving a wireless frame from a second wireless communication terminal, among the plurality of wireless communication terminals, the second wireless communication terminal being wirelessly connected to other wireless communication apparatus other than the wireless communication apparatus, thereby receiving wireless frames; and
a switching control process to, when the wireless frame is received from the second wireless communication terminal at the second communication timing, control to switch a connection destination of wireless connection of the second wireless communication terminal.

[Claim 15] A wireless communication program to cause a wireless communication terminal being a computer to execute:
a communication timing detection process to detect arrival of a current communication timing being timing which repeatedly arrives and is for transmitting a wireless frame to a current wireless communication apparatus being a current connection destination of wireless connection, and also to detect arrival of switching destination communication timing being timing which repeatedly arrives and is for transmitting a wireless frame to a switching destination wireless communication apparatus being a switching destination of the wireless connection when it is necessary to switch a connection destination of the wireless connection; and
a wireless transmission process to transmit a wireless frame to the current wireless communication apparatus at the current communication timing detected by the communication timing detection process, and also to transmit a wireless frame to the switching destination wireless communication apparatus at the switching destination communication timing detected by the communication timing detection process when it is necessary to switch the connection destination of the wireless connection.