Master unit device and program

Abstract

To provide a master unit device and a program capable of operation in consideration of a slave unit that does not support a preamble puncturing technique.SOLUTION: A master unit device 1 communicates in either a first mode in which communication is performed using all sub-channels included in a sub-channel set consisting of multiple consecutive sub-channels used for communication by the master unit device that performs wireless LAN communication, or a second mode in which communication is performed using some of the sub-channels in the sub-channel set, and performs processing of disconnecting communication with a slave unit that has become unable to communicate in the second mode when communication in the second mode is started from a state in which communication in the first mode is being performed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a master device and a program for performing wireless LAN communication. [Background technology]

[0002] Recent wireless LAN standards divide the available frequency band into multiple subchannels, and establish a subchannel set by combining multiple consecutive subchannels, enabling communication using a wideband band. In this state, when interference occurs in one of the subchannels included in the subchannel set, a technology called preamble puncturing has been developed that ensures data transmission over as wide a bandwidth as possible by setting only the interfering subchannel not to be used for data transmission (e.g., Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-123698 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because preamble puncturing is a relatively new technology, even if the base station device, such as an access point, supports it, there are still some terminal devices communicating with the base station that do not support this technology.

[0005] In this case, if the parent device emits a signal using preamble puncturing technology, the child device cannot demodulate the signal, resulting in the problem of being unable to communicate with the parent device.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and one of its objects is to provide a base unit device and program that can operate in consideration of handset devices that do not support preamble puncturing technology. [Means for solving the problem]

[0007] One aspect of the present invention for solving the problems of the above-mentioned conventional examples is a parent device that performs wireless LAN communication, and includes communication means for performing communication in either a first mode in which communication is performed using all subchannels included in a subchannel set consisting of a plurality of consecutive subchannels used for the wireless LAN communication, or a second mode in which communication is performed using some of the subchannels of the subchannel set, and disconnection means for disconnecting communication with a child device that has been communicating in the first mode and is now unable to communicate in the second mode when communication in the second mode is started from a state in which communication in the first mode is performed.

[0008] In this way, the parent device of the present invention enables processing that takes into consideration child devices that do not support preamble puncturing technology, such as by disconnecting communication if there is a child device that cannot communicate in the preamble puncturing second mode, thereby giving the child device an opportunity to reconnect.

[0009] The disconnection means may be configured to disconnect the handset that was communicating in the second mode when a handset becomes unable to communicate in the second mode, or to disconnect communication only with the handset that becomes unable to communicate in the second mode when a handset becomes unable to communicate in the second mode.

[0010] According to the parent device in this example, by disconnecting communication with a child device that cannot communicate in the preamble-punctured second mode, the parent device is given an opportunity to reconnect, thereby enabling processing that takes into consideration child devices that do not support preamble-puncturing technology.

[0011] Furthermore, after the disconnection process is performed, a successive sub-channel may be set and communication using the set sub-channel may be started.

[0012] This base station device can resume communication with a handset that is unable to communicate in the preamble-punctured second mode in a band consisting of consecutive subchannels.

[0013] Furthermore, a parent device according to another aspect of the present invention may, after performing the disconnection process, set consecutive subchannels and start communication using the set subchannels, wherein the consecutive subchannels are different from a set of subchannels included in the subchannel set used for communication before the disconnection process.

[0014] According to this embodiment of the base unit device, communication with a handset that is unable to communicate in the preamble-punctured second mode can be resumed in a band consisting of consecutive subchannels different from the set of subchannels included in the subchannel set that was used for communication before the disconnection process.

[0015] When disconnecting communication in the second mode, a signal instructing the disconnection may be transmitted over the primary channel.

[0016] Another aspect of the present invention is a control method for a parent device performing wireless LAN communication, which performs communication in either a first mode in which communication is performed using all subchannels included in a subchannel set consisting of a plurality of consecutive subchannels used for the wireless LAN communication, or a second mode in which communication is performed using some subchannels of the subchannel set, and when communication in the second mode is started from a state in which communication in the first mode is performed, disconnects communication with a child device that is unable to communicate in the second mode. According to this aspect of the present invention, the parent device is controlled to disconnect communication when there is a child device that is unable to communicate in the preamble-punctured second mode, thereby enabling processing that takes into consideration child devices that do not support preamble puncturing technology, such as giving the child device an opportunity to reconnect.

[0017] Another aspect of the present invention is a communication system including a terminal and a base station device that communicates with the terminal over a wireless LAN, wherein the base station device communicates with the terminal over a wireless LAN in either a first mode in which communication is performed using all subchannels included in a subchannel set consisting of a plurality of consecutive subchannels used for the wireless LAN communication, or a second mode in which communication is performed using some subchannels of the subchannel set, and when communication in the second mode is started from a state in which communication in the first mode is performed, the base station device disconnects communication with a terminal that is unable to communicate in the second mode. According to this aspect of the present invention, the base station device can be controlled to disconnect communication when there is a terminal that is unable to communicate in the preamble-punctured second mode, thereby providing the terminal with an opportunity to reconnect, thereby enabling processing that takes into consideration terminals that do not support preamble puncturing technology.

[0018] Yet another aspect of the present invention is a program executed by a parent device that performs wireless LAN communication, which causes the parent device to function as: communication means for communicating in either a first mode in which communication is performed using all subchannels included in a subchannel set consisting of a plurality of consecutive subchannels used for the wireless LAN communication, or a second mode in which communication is performed using some of the subchannels of the subchannel set; and disconnection means for disconnecting communication with a child device that has been communicating in the first mode and is now unable to communicate in the second mode when communication in the second mode is started from a state in which communication in the first mode is performed.

[0019] According to this aspect of the present invention, the parent device is controlled to disconnect communication when there is a child device that cannot communicate in the preamble-punctured second mode, thereby enabling processing that takes into consideration child devices that do not support preamble-puncturing technology, such as giving the child device an opportunity to reconnect. [Effects of the Invention]

[0020] The base station device and program of the present invention enable operation that takes into consideration handset devices that do not support preamble puncturing technology. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a block diagram illustrating an example of a parent device according to an embodiment of the present invention. [Figure 2] 3 is a functional block diagram illustrating an example of a configuration realized by a control unit of a master device according to an embodiment of the present invention. FIG. [Figure 3] 5A and 5B are explanatory diagrams illustrating an example of the operation of the master device according to the embodiment of the present invention. [Figure 4] 4 is a flowchart illustrating an example of the operation of the master device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] An embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a master device 1 according to the embodiment of the present invention includes a control unit 11, a storage unit 12, a first communication unit 13, and a second communication unit 14. The master device 1 is also communicably connected to at least one slave device 2a, 2b, etc. Hereinafter, when it is not necessary to distinguish between the slave devices, they will be collectively referred to as a slave device 2. The slave device 2 is, for example, a smartphone or a personal computer, and transmits and receives data wirelessly to and from the master device 1.

[0023] The control unit 11 is a program-controlled device such as a CPU, and operates according to a program stored in the storage unit 12. In this embodiment, the control unit 11 controls the second communication unit 14 to communicate with the handset 2 in either a first mode in which communication is performed using all subchannels included in a subchannel set consisting of a plurality of consecutive subchannels, or a second mode (a mode in which communication is performed using a preamble puncturing technique) in which communication is performed using some of the subchannels in the subchannel set.

[0024] Furthermore, when communication in the first mode is discontinued and communication in the second mode is started, the control unit 11 checks whether any of the slave units that were communicating in the first mode have become unable to communicate in the second mode, and when the control unit 11 determines that any of the slave units has become unable to communicate in the second mode, it disconnects the communication.

[0025] In this embodiment, the communication means and disconnection means of the present invention are realized by the control unit 11. The operation of the control unit 11 will be described in detail later.

[0026] The storage unit 12 is a memory device or the like, and stores a program to be executed by the control unit 11. This program may be provided by being stored in a computer-readable and non-transitory recording medium, and may be copied and stored in the storage unit 12. The storage unit 12 also stores various parameter information required for the control unit 11 to execute the program, and also operates as a work memory for the control unit 11.

[0027] The first communication unit 13 is, for example, a wired network interface or the like, and is connected to a WAN (Wide Area Network) such as the Internet via a router or the like.

[0028] The second communication unit 14 is a wireless LAN interface, and transmits and receives data wirelessly to and from the slave device 2 in accordance with instructions input from the control unit 11.

[0029] Next, the operation of control unit 11 will be described. Control unit 11 in this embodiment controls second communication unit 14 to communicate with handset 2 wirelessly using a predetermined frequency band, and transmits information received from handset 2 to a server or the like connected to the WAN side via first communication unit 13. Control unit 11 also operates as a so-called access point, transmitting information received by first communication unit 13 from a server or the like connected to the WAN side to handset 2 via second communication unit 14.

[0030] The control unit 11 of this embodiment also executes a program stored in the memory unit 12 to functionally realize a configuration including a communication control unit 21, an interference inspection unit 22, an inspection unit 23, and a disconnection control unit 24, as illustrated in FIG. 2.

[0031] As shown in FIG. 3, the communication control unit 21 divides a predetermined frequency band into non-overlapping sub-channels C1, C2, ... of 20 MHz each, and uses the sub-channels to perform wireless communication with the slave unit 2.

[0032] The communication control unit 21 controls the second communication unit 14 to set two consecutive (adjacent) sub-channels Ci, Ci+1 (i=1, 3, ...) as a pair to set a 40 MHz communication band. The control unit 11 also sets two adjacent 40 MHz communication bands as a pair to set an 80 MHz communication band. At this time, one 40 MHz communication band is set as the primary channel and the other as the secondary channel. Similarly, two consecutive (adjacent) 80 MHz communication bands are set as a pair to set a 160 MHz communication band, and one 80 MHz communication band is operated as the primary channel and the other as the secondary channel, ... thus forming communication bands of 40 MHz, 80 MHz, 160 MHz, ... (This mode is widely known as channel bonding, and detailed processing thereof will not be described here.)

[0033] Furthermore, the communication control unit 21 controls the second communication unit 14 to communicate with the handset 2 in either the first mode or the second mode. Specifically, when communicating in the first mode, the communication control unit 21 controls the second communication unit 14 as follows.

[0034] The communication control unit 21 controls the second communication unit 14 to communicate in the first mode under normal conditions (when there is no external interference on any of the subchannels to be used for communication) and to communicate with the handset 2 using a subchannel within a subchannel set consisting of multiple consecutive subchannels.

[0035] During communication in this first mode, the second communication unit 14 communicates with the slave device 2 at a bandwidth of 160 MHz using a subchannel set consisting of consecutive subchannels, for example, subchannels C1 to C8 (FIG. 3(a)). At this time, the communication control unit 21 uses, for example, subchannels C1 to C4 as primary channel PC and subchannels C5 to C8 as secondary channel SC.

[0036] On the other hand, if interference occurs in any of the subchannels used for communication in the first mode during communication in that mode, the communication control unit 21 starts communication in the second mode and controls the second communication unit 14 to disable the subchannel where the interference is occurring, as shown in Figure 3(b), and continue communication using subchannels from the subchannel set used in communication in the first mode, excluding the disabled subchannel (preamble puncturing). In this case, it is acceptable for the subchannels to be used to be discontinuous. Note that Figure 3(b) shows an example in which the third channel C3 is disabled.

[0037] When transitioning from the first mode to the second mode to communicate, the communication control unit 21 notifies the handset 2 that has been communicating in the first mode that it will transition to the second mode (notifying the channel to be used, etc.); however, this operation is widely known as preamble puncturing, and therefore a detailed explanation will be omitted here.

[0038] The interference inspection unit 22 checks whether interference is occurring for each of the subchannels (which may include unusable subchannels) included in the subchannel set used for communication by the communication control unit 21. Specifically, the interference inspection unit 22 performs carrier sense for each of the subchannels to check whether an external narrowband signal is interfering with the subchannel.

[0039] If there is a sub-channel that is determined to be interfering with, the interference inspection unit 22 outputs information identifying the sub-channel to the communication control unit 21, and causes the communication control unit 21 to start communication in the second mode.

[0040] Furthermore, when the interference detection unit 22 determines that no interference is occurring in all subchannels included in the subchannel set (including any subchannels that have been disabled), it causes the communication control unit 21 to communicate in the first mode. In this example, when the communication control unit 21 is communicating in the first mode (there are no disabled subchannels at this time), if it determines that no interference is occurring in all subchannels included in the subchannel set, the interference detection unit 22 ends the processing and causes the communication control unit 21 to continue communication in the first mode. Furthermore, when the communication control unit 21 is communicating in the second mode, the interference detection unit 22 may cause the communication control unit 21 to start communication in the first mode when it determines that no interference is occurring in all subchannels included in the subchannel set (because there are disabled subchannels at this time, all subchannels including the disabled subchannels).

[0041] After communication control unit 21 shifts from a state in which it is communicating in the first mode to a state in which it is communicating in the second mode, inspection unit 23 inspects whether any of handset units 2 that were communicating in the first mode have become unable to communicate in the second mode. This inspection can be performed by employing any of the widely known methods for inspecting the communication state, such as whether communication control unit 21 can receive a response from handset unit 2 within a predetermined time (timeout time) after sending a data packet to handset unit 2, indicating that the packet has been received.

[0042] If, as a result of the above inspection, it is determined that any of the handset units 2 that were communicating in the first mode are now unable to communicate in the second mode, the inspection unit 23 instructs the disconnection control unit 24 to disconnect the handset unit 2.

[0043] When receiving the disconnection instruction from the inspection unit 23, the disconnection control unit 24 executes a disconnection process to disconnect the communication in the second mode with the slave unit 2. Specifically, this disconnection process can be performed by transmitting a Disassociation frame. In one example of the present embodiment, when receiving the disconnection instruction from the inspection unit 23, the disconnection control unit 24 transmits a Disassociation frame to all of the slave units 2 that have been communicating in the first mode (including the slave units 2 that are able to communicate in the second mode) to disconnect the communication.

[0044] In another example of the present embodiment, after the disconnection control unit 24 disconnects communication with the slave device 2, the communication control unit 21 may newly set a subchannel set consisting of consecutive subchannels (consecutive subchannels excluding the subchannel determined by the interference detection unit 22 to be causing interference) and start communication in the first mode using the newly set subchannel set. The width of the frequency band used in this communication in the first mode may be different from the width of the frequency band used in the communication in the first mode performed before the communication disconnection. For example, even if eight subchannels were used in the communication in the first mode performed before the communication disconnection, and communication was performed with a bandwidth of 160 MHz, interference may occur in one of the eight subchannels, causing a transition to communication in the second mode and subsequent disconnection. The number of subchannels included in the subchannel set that is set after the communication disconnection may be, for example, four. In this case, the communication bandwidth newly set after the disconnection is 80 MHz.

[0045] [Operation] The parent device 1 of this embodiment basically has the above configuration and operates as follows: In the following explanation, it is assumed that the parent device 1 has a preset SSID (Service Set IDentifier) ​​of "ID1".

[0046] As shown in Fig. 4, initially, the master device 1 groups consecutive subchannels C1 to C8 out of the 20 MHz subchannels C1, C2, ... into a subchannel set, sets a 160 MHz communication band using all the subchannels included in this subchannel set (S10), and performs communication over the wireless LAN using this communication band (S11: starts communication in the first mode). Note that, here, for example, as shown in Fig. 3(a), the master device 1 sets subchannels C1 to C4 as primary channel PC and subchannels C5 to C8 as secondary channel SC.

[0047] Then, handset devices 2a and 2b connect to base device 1 identified by "ID1" and start communication in the first mode (S12, S13). In the following explanation, handset device 2a is assumed to be a handset capable of communication compatible with preamble puncturing (i.e., capable of communication in the second mode), and handset device 2b is assumed to be a handset incompatible with preamble puncturing (i.e., not capable of communication in the second mode).

[0048] The parent device 1 acquires and stores information for identifying the child devices 2a and 2b (such as the MAC address of each child device 2).

[0049] After starting communication, the master device 1 checks whether interference is occurring for each subchannel included in the subchannel set used for communication (S14). If there is no interference in any of the subchannels (S14: No), communication continues in the first mode. On the other hand, if interference is occurring in any of the subchannels included in the subchannel set (S14: Yes), the master device 1 disables the subchannel where interference is occurring and starts communication in the second mode (communication using preamble puncturing) (S15). For example, if narrowband interference occurs within the 20 MHz band of subchannel C3, the master device 1 disables subchannel C3 and starts communication using subchannels C1, C2, and C4 to C8.

[0050] This communication signal can be decoded by handset 2a, which supports preamble puncturing, and communication can continue. However, handset 2b, which does not support preamble puncturing, cannot decode this signal, and handset 2b sets parent device 1, identified by SSID "ID1," as being unable to communicate.

[0051] After starting communication in the second mode, the master device 1 checks whether any of the slave devices 2a, 2b that have been communicating in the first mode have become unable to communicate in the second mode (S16). If there are no slave devices 2 that have become unable to communicate in the second mode (S16: No), the master device 1 continues communication in the second mode. In this case, the master device 1 may repeatedly execute the process of step S16.

[0052] Furthermore, after transitioning from the first mode to the second mode in this manner, the parent device 1 may check whether interference is occurring for each of the subchannels (including the subchannels that have been made unavailable) included in the subchannel set used in the first mode, and if there is no interference in any of the subchannels, it may set a communication band of 160 MHz using all the subchannels included in this subchannel set, and return to the first mode to continue communication.

[0053] On the other hand, in step S16, if any of the slave devices 2a, 2b that were communicating in the first mode has become unable to communicate in the second mode (S16: Yes), the master device 1 transmits a Disassociation frame to both of the slave devices 2a, 2b to disconnect the communication (S17). The master device 1 may send this signal for disconnection (here, the Disassociation frame) via the primary channel. In this example, since the slave device 2b has become unable to communicate, the process proceeds to step S17, and communication with both of the slave devices 2a, 2b is disconnected.

[0054] The master device 1 then establishes a new subchannel set consisting of consecutive subchannels (S18). The subchannel set established here is a set of consecutive subchannels different from the set of subchannels included in the subchannel set used for communication before the disconnection processing in step S17 (in the above example, the combination of subchannels C1 to C8, including the subchannel that was made unavailable). Specifically, the master device 1 uses consecutive subchannels that do not include the subchannel determined to be causing interference. In this example, since subchannel C3 is determined to be experiencing interference, the master device 1 establishes the subchannel set from subchannels C5 to C8 in step S18. The master device 1 then returns to step S11 (A) and establishes an 80 MHz communication band using the subchannel set established in step S18. The master device 1 then resumes communication in the first mode using the SSID "ID1."

[0055] Furthermore, at this time, the parent device 1 may send out a beacon signal guiding the subchannels included in the subchannel set set in step S18 to prompt the slave devices 2a and 2b, which disconnected communication in step S17, to resume communication. Alternatively, the parent device 1 may wait until it receives a probe request without sending out a beacon signal notifying the SSID. In this case, when the slave devices 2a and 2b send a probe request to the parent device 1 identified by "ID1" based on the history of previous communication, the parent device 1 will respond with a probe response. In this case, the slave devices 2a and 2b can resume communication.

[0056] Furthermore, the master device 1 may prompt the resumption of communication with the slave devices 2a and 2b, which were the previous communication partners, by sending a signal (such as a CSA frame) indicating that the sub-channel has been switched.

[0057] In these examples, since communication has been cut off once, both the slave devices 2a and 2b can now attempt to connect to the master device 1 anew, and communication is resumed.

[0058] On the other hand, by disconnecting communication in step S17, the slave devices 2a and 2b can connect to another master device. Therefore, the master device 1 of this embodiment may wait a period of time after disconnecting communication in step S17 before executing the processes in step S18 and thereafter, or may suspend operation for at least a certain period of time without executing steps S18 and thereafter.

[0059] In another example of the present embodiment, after communication is disconnected in step S17, the process may return to step S15 and communication may be resumed in the second mode. In this case, the slave device 2a may reconnect to the master device 1 and resume communication, and the slave device 2b may attempt to communicate with another master device.

[0060] [Example of disconnecting only the child devices that cannot communicate] In the explanation so far, when the disconnection control unit 24 receives a disconnection instruction from the inspection unit 23, it sends a Disassociation frame to all of the slave units 2 that were communicating in the first mode (including the slave units 2 that are able to communicate in the second mode) to disconnect the communication, but this embodiment is not limited to this example.

[0061] For example, when the control unit 11 of the parent device 1 receives a disconnection instruction from the inspection unit 23, the operation of the disconnection control unit 24 may be to send a Disassociation frame to disconnect communication only to a child device 2 that has been communicating in the first mode and that has been determined by the inspection unit 23 to be unable to communicate in the second mode.

[0062] In this example, only the handset 2 that supports preamble puncturing and is capable of communication in the second mode continues communication with the base device 1. At this time, the base device 1 may continue communication in the second mode. On the other hand, for handset 2 that does not support preamble puncturing, communication with the base device 1 of this embodiment is disconnected at this point, and the handset 2 will perform processing such as attempting to connect to another base device (a base device identified by an SSID different from the SSID used by the base device 1 at the time of disconnection).

[0063] [Example of setting up a new service] Furthermore, in this manner, when communication is cut off only with a slave unit 2 for which it is determined that communication in the second mode is no longer possible, the master unit 1 may start communication in the first mode corresponding to the slave unit 2 whose communication has been cut off in parallel (for example, in a time-division manner) with the ongoing communication in the second mode.

[0064] In this example, the parent device 1 generates a new SSID that is different from the SSID that the parent device 1 was using at the time of disconnection. Then, the parent device 1 sets a new subchannel set consisting of consecutive subchannels, similar to the process in step S18 of Fig. 4. Here too, the set subchannel set is consecutive subchannels that are different from the set of subchannels included in the subchannel set used for communication before the disconnection process (in the above example, the combination of subchannels C1 to C8 including the subchannel that was made unavailable).

[0065] For example, the master device 1 may use consecutive subchannels that do not include the subchannel determined to be interfering. When performing time-division communication with the ongoing second mode communication, the channels included in the newly established subchannel set may overlap with the subchannels used in the second mode communication. For example, if subchannel C3 is experiencing interference, a new subchannel set is established, including subchannels C5 through C8, with a communication bandwidth of 80 MHz. The master device 1 then begins communication in the first mode using the newly created SSID, while sharing the frequency band in a time-division manner with the original SSID communication (second mode communication, i.e., communication using preamble puncturing).

[0066] In this way, the disconnected handset 2 that does not support preamble puncturing can reconnect to the base device 1 identified by the newly set SSID and communicate in the first mode. In this case, the base device 1 may also send a beacon signal indicating the subchannel to prompt the disconnected handset 2 that does not support preamble puncturing to resume communication. The base device 1 may also send a signal (such as a CSA frame) indicating that the subchannel has been switched to prompt the previous communication partner, the handset 2 that does not support preamble puncturing, to resume communication.

[0067] [Effects of the embodiment] According to this embodiment, it is possible to perform operations that take into consideration handset units that do not support preamble puncturing technology. [Explanation of symbols]

[0068] 1 parent device, 2 child device, 11 control unit, 12 storage unit, 13 first communication unit, 14 second communication unit, 21 communication control unit, 22 interference inspection unit, 23 inspection unit, 24 disconnection control unit.

Claims

1. A base unit for wireless LAN communication, a communication means for performing communication in either a first mode in which communication is performed using all subchannels included in a subchannel set consisting of a plurality of consecutive subchannels used for the wireless LAN communication, or a second mode in which communication is performed using some of the subchannels of the subchannel set; a disconnection means for disconnecting communication with a slave unit that has become unable to communicate in the second mode when communication in the second mode is started from a state in which communication in the first mode is being performed; A parent device including:

2. 2. The base unit according to claim 1, The disconnecting means is a base unit that, when a handset that has become unable to communicate in the second mode is found, disconnects the handset that has been communicating in the second mode.

3. 2. The base unit according to claim 1, The disconnecting means is a base unit that, when there is a handset that is unable to communicate in the second mode, disconnects communication only with the handset that is unable to communicate in the second mode.

4. 4. The base unit according to claim 2 or 3, After performing the disconnection process, the master device sets a successive sub-channel and starts communication using the set sub-channel.

5. 4. The base unit according to claim 2 or 3, After the disconnection process is performed, a successive sub-channel is set and communication using the set sub-channel is started; The master device, wherein the consecutive sub-channels are different from the set of sub-channels included in the sub-channel set used for communication before the disconnection process.

6. The base unit according to any one of claims 1 to 3, When disconnecting communication in the second mode, the master device transmits a signal instructing the disconnection on the primary channel.

7. A method for controlling a master device that performs wireless LAN communication, comprising: communication is performed in either a first mode in which communication is performed using all subchannels included in a subchannel set consisting of a plurality of consecutive subchannels used for the wireless LAN communication, or a second mode in which communication is performed using some of the subchannels of the subchannel set; A control method for a parent device that disconnects communication with a child device that has become unable to communicate in the second mode when communication in the second mode is started from a state in which communication in the first mode is being performed.

8. A communication system including a slave device and a master device that performs wireless LAN communication with the slave device, The parent device is communication with the slave device in either a first mode in which communication is performed using all sub-channels included in a sub-channel set consisting of a plurality of consecutive sub-channels used for the wireless LAN communication, or a second mode in which communication is performed using some of the sub-channels of the sub-channel set; A communication system that, when communication in the second mode is started from a state in which communication in the first mode is being performed, disconnects communication with a slave unit that has become unable to communicate in the second mode.

9. A program executed by a parent device that performs wireless LAN communication, a communication means for performing communication in either a first mode in which communication is performed using all subchannels included in a subchannel set consisting of a plurality of consecutive subchannels used for the wireless LAN communication, or a second mode in which communication is performed using some of the subchannels of the subchannel set; a disconnection means for disconnecting communication with a slave unit that has become unable to communicate in the second mode when communication in the second mode is started from a state in which communication in the first mode is being performed; A program that causes the parent device to function as a

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