Method and apparatus for preventing hidden node in service interval-based dynamic subchannel operation of wireless LAN

Abstract

In a wireless LAN system, a first STA may transmit a first ICF to a second STA, wherein the first ICF may instruct switching of an operating channel of the second STA, which carries out a DSO, from a primary subband to a DSO subband, carry out DSO frame exchange including transmission of the first ICF with the second STA in the DSO subband, and after a channel switching back time from the time point when the DSO frame exchange ends, carry out frame exchange with the second STA in the primary subband.

Description

Method and device for preventing hidden nodes in service segment-based dynamic sub-channel operation of wireless LAN

[0001] The present disclosure relates to a method and apparatus for preventing hidden node problems in service interval-based dynamic subchannel operation in a wireless local area network (WLAN).

[0002]

[0003] With the recent expansion of mobile device adoption, Wireless Local Area Network (WLAN) technology, capable of providing fast wireless communication services to these devices, is receiving significant attention. Based on short-range wireless communication technology, WLAN technology enables mobile devices such as smartphones, smart pads, laptop computers, portable multimedia players, and embedded devices to connect to the internet wirelessly.

[0004] Standards using wireless LAN technology are primarily developed by the IEEE (Institute of Electrical and Electronics Engineers) as the IEEE 802.11 standard. As the aforementioned wireless LAN technology has been developed and disseminated, applications utilizing wireless LAN technology have diversified, and a demand has arisen for wireless LAN technology that supports higher reliability.

[0005] As applications requiring higher reliability emerge, the IEEE 802.11bn standard, an Ultra High Reliability (UHR) wireless LAN technology, is being developed for single Basic Service Set (BSS) environments and / or redundant BSS environments. The goal of the IEEE 802.11bn standard may be to support improved data transmission speeds, enhanced latency performance, and reduced data error rates. Additionally, the IEEE 802.11bn standard can support low-power operation, peer-to-peer communication, and operations designed to increase channel utilization. It can also support a TXOP sharing method, where wireless LAN terminals share communication resources (transmit opportunities) between access points (APs). Furthermore, to increase the efficiency of communication resource utilization, the wireless LAN standard can support non-primary channel access (NPCA), which involves using a channel other than the primary channel when the primary channel is occupied. In addition, wireless LAN standards can support dynamic subband operation (DSO), a method that allows an AP to identify wireless LAN terminals that support only a narrower operating bandwidth than the AP's operating bandwidth within its BSS in order to increase the efficiency of utilizing communication resources, and to perform simultaneous transmission by allocating a portion of the operating bandwidth to a subchannel (DSO subband) rather than the primary subband that performs channel access.

[0006] When a DSO is used, media occupation by other wireless LAN networks may occur on the DSO subchannel, and the DSO may fail. Consequently, resource utilization efficiency in the wireless LAN network may not be improved; the following describes measures to address this issue.

[0007] Meanwhile, the technology forming the background of the invention is written to enhance understanding of the background of the invention and may include content that is not prior art already known to a person with ordinary knowledge in the field to which this technology belongs.

[0008]

[0009] The present disclosure relates to a method and apparatus for preventing hidden node problems in service interval-based dynamic subchannel operation in a wireless local area network (WLAN).

[0010] The present disclosure relates to a method and apparatus for suspending communication in a DSO subband and resuming communication in a main subband when a wireless LAN terminal performs a service interval-based DSO operation and the DSO subband is in use.

[0011] The present disclosure relates to a method and apparatus for minimizing frame collisions in a DSO subband by performing communication in a main subband when time interval-based DSO cannot be performed.

[0012] The technical problems to be solved in this disclosure are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this disclosure belongs from the description below.

[0013]

[0014] According to one embodiment of the present specification, a method of operation of a first station (STA) in a wireless LAN system may include the step of the first STA receiving a first initial control frame (ICF) from a second STA, wherein the first ICF indicates that the operating channel of the first STA performing a dynamic subband operation (DSO) is switched from a main subband to a DSO subband, the first STA performs a DSO frame exchange including the reception of the first ICF in the DSO subband with the second STA, and the first STA returns to the main subband after a channel switching back time from the time of termination of the DSO frame exchange, and switches to a state in which frame exchange with the second STA is possible in the main subband after the channel switching back time.

[0015] Additionally, according to one embodiment of the present specification, a first station (STA) in a wireless LAN system comprises at least one transceiver for transmitting and receiving signals, at least one processor for controlling at least one transceiver, and a memory for storing instructions that cause a non-AP STA to perform a specific operation by the at least one processor, wherein the specific operation is: the first STA receives a first initial control frame (ICF) from a second STA, wherein the first ICF instructs the first STA to switch the operation channel of the first STA performing a dynamic subband operation (DSO) from the main subband to the DSO subband, the first STA performs a DSO frame exchange including the reception of the first ICF in the DSO subband with the second STA, and the first STA returns to the main subband after a channel switching back time from the end of the DSO frame exchange, and can switch to a state where frame exchange with the second STA is possible in the main subband after the channel switching back time.

[0016] In addition, the following points may apply in common.

[0017] According to one embodiment of the present specification, frame switching in the main subband includes the operation of the first STA receiving an additional frame from the second STA, and the additional frame may include a second ICF indicating to switch the operation channel of the first STA from the main subband to the DSO subband.

[0018] In addition, according to one embodiment of the present specification, the end time of the DSO frame exchange may be a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' elapsed from the time of completion of reception of the first ICF performed in the DSO frame exchange when the first STA does not transmit a response frame for the first ICF.

[0019] In addition, according to one embodiment of the present specification, if the last frame received by the first STA in the DSO frame exchange is a frame that does not require an immediate response frame, the end time of the DSO frame exchange may be a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' elapsed from the time of completion of reception of the last received frame, and if the last frame received by the first STA in the DSO frame exchange is a frame that requires an immediate response frame, the end time of the DSO frame exchange may be a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' elapsed from the time of completion of transmission of the immediate response frame for the last received frame.

[0020] In addition, according to one embodiment of the present specification, the operating channel of the first STA may be switched from the DSO subband to the main subband within the channel switching back time from the end of the DSO frame exchange.

[0021] In addition, according to one embodiment of the present specification, when the DSO subband is occupied, the first STA may start operating channel switching after a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time when it completes receiving the first ICF, and switch to a state where frame exchange with the second STA is possible in the main subband after the channel switching back time.

[0022] Additionally, according to one embodiment of the present specification, the first STA further includes the step of performing a target wake time (TWT) negotiation to establish a service interval capable of communicating with the second STA, and the first STA supporting the DSO may be configured to monitor the reception of the first ICF within the service interval based on the TWT negotiation, or to operate in a DSO subband based on the reception of the first ICF.

[0023] In addition, according to one embodiment of the present specification, the first STA transmits a first ICR to the second STA instructing to switch the operating channel from the DSO subband to the main subband based on the occupancy status of the DSO subband within the service interval, and the time of completion of transmission of the first ICR is the time of termination of DSO frame exchange, and the first STA can perform frame exchange with the second STA.

[0024] Additionally, according to one embodiment of the present specification, a method of operation of a first station (STA) in a wireless LAN system may include the step of the first STA transmitting a first initial control frame (ICF) to a second STA, wherein the first ICF indicates that the operating channel of the second STA performing a dynamic subband operation (DSO) is switched from a main subband to a DSO subband, the first STA performs a DSO frame exchange including the transmission of the first ICF in the DSO subband with the second STA, and the first STA performs a frame exchange with the second STA in the main subband after a channel switching back time from the time of termination of the DSO frame exchange.

[0025] Additionally, according to one embodiment of the present specification, a first station (STA) in a wireless LAN system comprises at least one transceiver for transmitting and receiving signals, at least one processor for controlling at least one transceiver, and a memory for storing instructions that cause a non-AP STA to perform a specific operation by the at least one processor, wherein the specific operation is: the first STA transmits a first initial control frame (ICF) to a second STA, wherein the first ICF instructs the second STA, which performs a dynamic subband operation (DSO), to switch its operation channel from a main subband to a DSO subband, the first STA performs a DSO frame exchange with the second STA, including the transmission of the first ICF in the DSO subband, and the first STA may perform a frame exchange with the second STA in the main subband after a channel switching back time from the end of the DSO frame exchange.

[0026] In addition, according to one embodiment of the present specification, the first STA may be able to initiate a new transmit opportunity (TXOP) with the second STA in the main subband from the time when the second STA operates in the main subband after the channel switching back time from the time when the DSO frame exchange ends.

[0027] In addition, according to one embodiment of the present specification, if the first STA fails to acquire primitives based on frame reception for a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time of completion of transmission of the first ICF, it can confirm the failure of reception of the first ICR and confirm that the second STA operates in the main subband after the channel switching back time.

[0028] In addition, according to one embodiment of the present specification, when the DSO subband is occupied, the first STA may be considered to have started the operation channel switching of the second STA after a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time when the second STA completes receiving the first ICF, and the operation channel switching of the second STA to the main subband may be considered to have been completed after the channel switching back time.

[0029] Additionally, according to one embodiment of the present specification, the first STA further includes the step of performing a target wake time (TWT) negotiation to establish a service interval capable of communicating with the second STA, and the second STA supporting the DSO may be configured to operate in a DSO subband within the service interval based on the TWT negotiation.

[0030] Additionally, according to one embodiment of the present specification, the first STA further transmits the second ICF to the third STA operating in the main subband during the service interval, and if the first ICR reception from the second STA fails in the DSO subband and the second ICR reception from the third STA succeeds in the main subband, the first STA can perform frame exchange with the second STA in the main subband from the time when the operating channel of the second STA is switched to the main subband.

[0031] In addition, according to one embodiment of the present specification, when the transmission power of the second ICR received from the third STA in the main subband is greater than a preset value, the first STA confirms that the operating channel of the second STA is switched to the main subband, and can perform frame exchange with the second STA in the main subband from the time when the operating channel of the second STA is switched to the main subband.

[0032] Additionally, according to one embodiment of the present specification, the first STA further transmits a second ICF to the main subband in the service interval, wherein the second ICF is a frame requesting a response from the second STA and the third STA operating in the main subband, and if the first STA fails to receive the first ICR from the second STA in the DSO subband based on DSO subband occupancy and receives a response based on the second ICF from the second STA and the third STA in the main subband, the first STA may perform frame exchange with the second STA in the main subband after receiving the response from the second STA and the third STA in the main subband.

[0033]

[0034] According to the present disclosure, a method can be provided to prevent hidden node problems in service interval-based dynamic subchannel operation in a wireless local area network (WLAN).

[0035] According to the present disclosure, when a wireless LAN terminal performs a service interval-based DSO operation, if the DSO subband is in use, a method can be provided to stop communication in the DSO subband and resume communication in the main subband.

[0036] According to the present disclosure, a method can be provided to minimize frame collisions in the DSO subband by performing communication in the main subband when time interval-based DSO cannot be performed.

[0037] The technical problems to be solved in this disclosure are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this disclosure belongs from the description below.

[0038] The effects obtainable from the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present disclosure pertains from the description below.

[0039]

[0040] FIG. 1 is a diagram showing a communication node within a wireless LAN system to which the present disclosure applies.

[0041] FIG. 2 is a drawing showing a wireless LAN system to which the present disclosure is applied.

[0042] FIG. 3 is a diagram showing a wireless LAN network to which the present disclosure applies.

[0043] FIGS. 4a to 4c are drawings illustrating the wireless LAN service interval-based dynamic sub-channel operation applied to the present disclosure.

[0044] FIG. 5 is a diagram illustrating a hidden node prevention method during dynamic sub-channel operation based on a wireless LAN service interval applied to the present disclosure.

[0045] FIGS. 6a and 6b are drawings illustrating a subband response method during dynamic subband operation applied to the present disclosure.

[0046] FIG. 7 is a flowchart illustrating the operation of an STA in a wireless LAN to which the present disclosure applies.

[0047] FIG. 8 is a flowchart showing the operation of a STA in a wireless LAN to which the present disclosure applies.

[0048]

[0049] The present disclosure is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present disclosure to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present disclosure.

[0050] Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. Such terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present disclosure, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of a plurality of related described items or any of a plurality of related described items.

[0051] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0052] The terms used in this disclosure are used merely to describe specific embodiments and are not intended to limit this disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, terms such as “comprising” or “having” are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0053] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which this disclosure pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this disclosure.

[0054] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding of the present disclosure, the same reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0055] Below, a wireless communication system to which embodiments according to the present disclosure are applied will be described. The wireless communication system to which embodiments according to the present disclosure are applied is not limited to the details described below, and embodiments according to the present disclosure may be applied to various wireless communication systems. The wireless communication system may be referred to as a "wireless communication network."

[0056] FIG. 1 is a diagram showing a communication node within a wireless LAN system to which the present disclosure applies. Referring to FIG. 1, the communication node (100) may include at least one of a processor (110), memory (120), a transceiver (130), an input / output interface (140), a storage device (150), and a bus (160). For example, the communication node (100) may be an access point (AP), a station (STA), an access point multi-link device (MLD), or a non-AP MLD. However, the communication node may not be limited thereto and may be a node that performs communication with another node or device based on the configuration described above. For example, the operating channel bandwidth supported by the AP may be 20 MHz (megahertz), 80 MHz, 160 MHz, etc. The operating channel bandwidth supported by the station may be 20 MHz, 80 MHz, etc. However, it may not be limited thereto.

[0057] A processor (110) within a communication node (100) can control at least one of a memory (120), a transceiver (130), an input / output interface (140), and a storage device (150) for each component within the communication node. The memory (120) within the communication node (100) can store information regarding commands and instructions executed by the processor (110), and the transceiver (130) may refer to a transceiver, an RF (radio frequency) unit, an RF module, or other components that perform signal transmission and reception. The input / output interface (140) within the communication node (100) is an interface for input and output that can be linked with other interfaces and may further include a separate storage device (150). Each component within the communication node (100) can communicate with one another by being connected by a bus (160).

[0058] However, as an example, each component included in the communication node (100) may be connected via an individual interface or an individual bus centered on the processor (110), rather than via a common bus (160). The processor (1110) may also be connected via a dedicated interface to at least one of the memory (120), the transmission / reception device (130), the input / output interface device (140), and the storage device (150).

[0059] A processor (110) can execute a program command stored in at least one of a memory (120) or a storage device (150). The processor (110) may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present disclosure are performed. Each of the memory (120) and the storage device (150) may be composed of at least one of a volatile storage medium or a non-volatile storage medium. e.g., the memory (120) may be composed of at least one of read-only memory (ROM) or random access memory (RAM).

[0060] In the following, the relevant operations are described based on the wireless LAN terminal as a station (STA). In accordance with the terminology usage according to IEEE 802.11, STA can refer to both AP STAs operating as access points (APs) and non-AP STAs operating in connection with an AP. However, for the convenience of explanation, APs and non-AP STAs are distinguished below; this distinction is merely for convenience of explanation, and it is self-evident that operations regarding an AP can be applied to both AP STAs and non-AP STAs. Furthermore, it is self-evident that the non-AP STA operations described below can also be applied to both non-AP STAs and AP STAs.

[0061] FIG. 2 is a diagram illustrating a wireless LAN system to which the present disclosure applies. Referring to FIG. 2, the basic service set (BSS) of the wireless LAN system may include one AP (210) and a plurality of non-AP STAs (221, 222, 223, 224), and the plurality of non-AP STAs (221, 222, 223, 224) may be controlled by the AP (210). However, the wireless LAN system is not limited to a BSS, and an environment consisting only of non-AP STAs without a fixed service set or AP may also be considered, and is not limited to a specific form. Each wireless device within the wireless LAN system may include a MAC (medium access control) layer and a physical (PHY) layer, and communication between wireless devices may be performed. For convenience of explanation, the following description focuses on the AP and non-AP STA, but is not limited thereto. For example, the following items may apply equally to other communication nodes or devices and are not limited to a specific form.

[0062] If a wireless LAN terminal decides to operate in a DSO subband during a specific time interval, the terminal may revert to operating in the primary subband if the DSO subband is occupied; the operation for this purpose is described below. In other words, frame collisions can be minimized by having the wireless LAN terminal operate in the primary subband in situations where time-interval-based DSO cannot be performed. This can improve the resource utilization efficiency of the wireless LAN network, and the method for achieving this is described below.

[0063] FIG. 3 is a diagram showing a wireless LAN network to which the present disclosure applies.

[0064] Referring to FIG. 3, a wireless LAN network may be configured. However, this is not intended to limit the scope of application of the present invention and may be used to aid in understanding the operations to be described later, but it is not limited to a specific name. A wireless LAN terminal that performs wireless LAN communication may operate in the wireless LAN network. The wireless LAN terminal may perform the role of an access point (AP), and the wireless LAN terminal performing the above-described role may be referred to as an AP STA or an AP. Alternatively, the wireless LAN terminal may perform communication by being connected (associated) with an AP, and the wireless LAN terminal performing the above-described role may be referred to as a non-AP STA (or STA). In the following description, AP and non-AP STA are described based on STA 1 and STA 2, but this is for convenience of explanation only and is not limited thereto.

[0065] An AP and at least one STA connected to the AP (e.g., STA 1 and STA 2) can form a basic service set (BSS). The BSS may be a transmission range or communication area where the AP connects with a non-AP STA to perform communication. The AP may select a main subband to use for channel access within the BSS, and the main subband may be specified in a frame transmitted by the AP (e.g., Beacon frame, Probe Response frame, etc.). A non-AP STA can connect to the AP and access the channel using the main subband specified in a frame transmitted by the AP.

[0066] A wireless LAN terminal may have various operating bandwidths. For example, a wireless LAN terminal may have at least one operating bandwidth among 320 MHz, 160 MHz, 80 MHz, 40 MHz, and 20 MHz. The operating bandwidths of the aforementioned STA 1 and STA 2 may be more limited than the operating bandwidth of the AP. That is, the operating bandwidths of the aforementioned STA 1 and STA 2 may be smaller than the operating bandwidth of the AP. As a specific example, the AP may have an operating bandwidth of 320 MHz, and STA 1 and STA 2 may have at least one operating bandwidth among 160 MHz, 80 MHz, 40 MHz, and 20 MHz. That is, STA 1 and STA 2 may be operating at half or less of the operating bandwidth of the AP. However, this is for convenience of explanation only and is not limited thereto.

[0067] In addition, the wireless LAN terminal can perform enhanced distributed channel access (EDCA) operations. Although the EDCA operations of the wireless LAN terminal described below are based on those described below, they are not limited to such terms or names. Furthermore, the EDCA operations described below are not intended to limit the scope of application of the present disclosure.

[0068] A wireless LAN terminal (e.g., AP, STA 1, STA 2) can perform an enhanced distributed channel access (EDCA) operation. The EDCA operation may include at least one of a clear channel assessment (CCA) operation and an EDCA backoff procedure (hereinafter referred to as the backoff procedure). Specifically, the wireless LAN terminal can perform a CCA operation (hereinafter referred to as CCA) on a primary 20 MHz channel. CCA may be an operation to determine whether the channel is idle or busy. As detailed operations of CCA, a physical channel sensing (CS) in which the wireless LAN terminal detects a carrier transmitted on the channel and a virtual CS in which the network allocation vector (NAV) established through a successful frame exchange may be considered. A wireless LAN terminal can perform CCA for an amount of Inter-Frame Space (IFS) length (e.g., AIFS (Arbitration IFS)[AC]) determined by the type of frame to be transmitted (e.g., a frame with access category (AC) of VO, VI, BE, or BO).

[0069] Additionally, the wireless LAN terminal may invoke the EDCA backoff procedure. The backoff procedure may be a procedure performed to reduce the probability of collision between wireless LAN terminals. The backoff procedure may be a procedure performed by the EDCAF (EDCA function) corresponding to the type of frame to be transmitted within the wireless LAN terminal. The EDCAF of the wireless LAN terminal may invoke the backoff procedure when traffic to be transmitted occurs (e.g., when data is entered into the Transmit Queue of the AC corresponding to the EDCAF) and the channel is occupied. As another example, the EDCAF of the wireless LAN terminal may invoke the backoff procedure when it receives a separate instruction (e.g., when it receives an indicator instructing to start the backoff procedure via frame exchange).

[0070] When the EDCAF of a wireless LAN terminal initiates a backoff procedure, the EDCAF of the wireless LAN terminal may randomly select a backoff counter (BC) within [0, CW(contention window)[AC]] determined according to the associated AC. The BC value selected by the EDCAF associated with each AC may be the number of slots for which the EDCAF must perform CCA. If the channel is idle as a result of the CCA operation performed by the EDCAF on a slot-by-slot basis, the EDCAF may perform a BC reduction operation in each slot. Here, the slot length of the wireless LAN terminal used in the slot operation described above may vary. For example, a slot may consist of one or more AIFS[AC], EIFS[AC] (EIFS - DIFS - AIFSN[AC] Х aSlotTime + aSIFSTime - aRxTxTurnaroundTime) times or aSlotTime (e.g., 9us), but is not limited thereto. EDCAF can perform CCA according to the backoff procedure in slots corresponding to the selected BC value, and if the channel resulting from the CCA performed in a single slot is idle, it can decrease the BC by 1. If the CCA result channel is idle when the BC becomes 0, the wireless LAN terminal can perform frame transmission. For example, if the CCA result channel resulting from the backoff procedure is occupied, the wireless LAN terminal can maintain its BC at the current value for use in the next backoff procedure. When the channel transitions from an occupied state to an idle state, the wireless LAN terminal can perform the BC decrease procedure according to the EDCAF operation again.

[0071] The frame transmission procedure through EDCA operation may include the operation of performing CCA for AIFS[AC] in the primary channel and then waiting for a slot time until BC becomes 0, and the operation of performing frame transmission at the slot boundary of the slot where BC becomes 0 based on the decrease in BC. Here, the value indicated by AIFS[AC] may be the number of slots for performing CCA. Specifically, AIFS[AC] may be a time length of 'aSIFS(Short Inter-Frame Space)Time + AIFSN[AC](number specified per AC)* aSlotTime'.

[0072] The EDCAF may intend to access a wider bandwidth channel (broadband channel) including the main 20 MHz channel. To access the broadband channel, the EDCAF may perform CCA during AIFS[AC] on the main 20 MHz channel, wait for an additional slot time during which BC becomes 0, and then transmit a frame including the broadband channel where the result of the CCA operation performed prior to the PIFS (priority interframe space) time is idle at the slot boundary where BC becomes 0. For example, the EDCAF described above may intend to transmit a frame using only the main 20 MHz channel regardless of the CCA result of the broadband channel, and in the above case, the transmitted frame may be transmitted using only the main 20 MHz channel. The EDCA operation performed by the EDCAF within the wireless LAN terminal may be expressed as the EDCA operation performed by the wireless LAN terminal, but is not limited thereto.

[0073] In the aforementioned EDCA operation, the aforementioned main 20MHz channel may be a channel configured by the AP during the BSS configuration process. That is, it may be a channel indicated in a frame transmitted by the AP (e.g., beacon frame, probe response frame). Additionally, if the EDCAF within the wireless LAN terminal succeeds in accessing the channel as a result of performing an EDCA operation (TXOP acquisition procedure) on the main 20MHz channel, the EDCAF may transmit a frame of the corresponding AC (access category) using the successfully accessed channel (or bandwidth). The EDCAF within the wireless LAN terminal that transmitted the frame may acquire a transmit opportunity (TXOP). Here, the TXOP acquired by the EDCAF within the wireless LAN terminal may be expressed as the TXOP acquired by the wireless LAN terminal to which the EDCAF belongs. That is, the TXOP may be a time interval during which the aforementioned wireless LAN terminal can transmit at least one frame.

[0074] When multiple protection methods are used in TXOP, the time length of TXOP can be set to the time length from the time when the wireless LAN terminal (or the EDCAF of the corresponding AC within the wireless LAN terminal) completes the transmission of the first frame until the time indicated by the duration / ID field of the MAC (medium access control) header within the frame. That is, the wireless LAN terminal (or the EDCAF of the corresponding AC within the wireless LAN terminal) that transmitted the first frame can perform transmit and receive operations from the time when the first frame is completed until the time indicated by the duration / ID field of the MAC header within the first frame.

[0075] When a single protection method is used in a TXOP, regardless of the time length of the TXOP, the Duration / ID field of the MAC header of the frame transmitted by the wireless LAN terminal may indicate the expected length of the transmission of the response frame after the frame is transmitted. Here, the wireless LAN terminal may ensure that the exchange of frame(s) is completed within the acquired TXOP. The frame exchange may include the transmission of the wireless LAN terminal's frame and the response frame. Alternatively, if the ACK policy of the wireless LAN terminal's frame is No Ack, the frame exchange may not include the response frame because the wireless LAN terminal's frame is a frame that does not require a response frame.

[0076] The following describes the dynamic subband operation (DSO) of a wireless LAN terminal. However, this is not intended to limit the scope of application of the present disclosure and is intended to aid in understanding the operations described below, and is not limited to a specific form. Additionally, as an example, a DSO subchannel may be a DSO subband, and a primary channel may be a primary subband. Furthermore, a DSO subchannel may be referred to as a DSO subband, and is not limited to a specific term or name.

[0077] DSO may be an operation used by an AP to increase channel efficiency. Specifically, the AP can identify non-AP STAs connected to the AP within the AP's BSS. The AP and the non-AP STAs connected to the AP can exchange information regarding maximum operating bandwidth during the connection process. For example, the maximum operating bandwidth of the non-AP STAs may be limited to the maximum operating bandwidth of the AP (e.g., when the AP's maximum operating bandwidth is 320 MHz while the non-AP STA's maximum operating bandwidth is 80 MHz). Here, when the AP transmits and receives data with a non-AP STA, the AP may limit the transmission bandwidth to the non-AP STA's maximum operating bandwidth (e.g., 80 MHz). In the above case, the remaining channel of the AP's maximum operating bandwidth (e.g., 320 MHz), excluding the 80 MHz bandwidth including the main subband, may not be used. Consequently, channel efficiency may be reduced.

[0078] An AP may use a DSO to increase channel efficiency in the above-described situation. An AP using a DSO may transmit an initial control frame (ICF) to non-AP STAs having a more limited operating bandwidth than the AP in the BSS. The ICF may include at least one of an operating channel switching indicator and an operating bandwidth indicator that instruct some of the non-AP STAs receiving the ICF to switch their operating channels to a subchannel (or DSO subchannel) or a subband (subband, or DSO subband). In this disclosure, 'operating channel switching' and 'channel switching' may be 'operating subband switching', 'subband switching', or 'band switching'. A DSO subband may refer to a channel located outside the operating bandwidth of a non-AP STA within the AP's operating bandwidth (the operating bandwidth of the BSS). The bandwidth location of the DSO subband may vary depending on at least one of the operating bandwidth and capability of each non-AP STA. Additionally, the DSO subband may be designated as a single unit in advance or multiple units may exist. For example, if the operating bandwidth of the AP is 160 MHz, the bandwidth of the DSO subband may be the AP's secondary 80 MHz channel. As another example, if the operating bandwidth of the AP is 320 MHz, the bandwidth of the DSO subband may be the AP's secondary 160 MHz channel or an 80 MHz channel included in the AP's secondary 160 MHz channel. Alternatively, if the operating bandwidth of the AP is 320 MHz, one of the AP's 320 MHz operating channels may be an 80 MHz channel, but is not limited to such embodiments. The operating channel switching indicator may be an indicator that indicates the target sub-channel (DSO subband) that the non-AP STA, which is the receiving target of the ICF, switches to.Additionally, the operating bandwidth indicator may be an indicator that indicates the operating bandwidth used by a non-AP STA, which is the recipient of the ICF, in a sub-channel (DSO sub-band). Specifically, the operating bandwidth indicator may be an indicator that indicates a position and bandwidth on the frequency based on a resource unit of OFDMA (orthogonal frequency division multiple access). As an example, the operating bandwidth indicator may indicate the index number of a resource unit indicating a DSO sub-band. As a specific example, the ICF may include a user info field, and the user info field of the ICF may include an indicator (e.g., an association identifier (AID)) of the STA that needs to switch the operating channel to the DSO sub-band. Additionally, the user info field of the ICF may include an RU index that occupies all or part of the DSO sub-band. A non-AP STA that receives at least one of the aforementioned operating channel switching indicator and operating bandwidth indicator may switch the operating channel to the sub-channel (DSO sub-band) indicated by the AP. The operating channel may refer to a channel used by a wireless LAN terminal to perform channel access, and may refer to at least one of a channel and bandwidth for transmitting and receiving data.

[0079] Here, the ICF can be a frame of various forms. For example, the ICF can be a Multi-User (MU) Request-To-Send (RTS) (MU-RTS) Trigger frame or a Buffer Status Report Poll (BSRP) Trigger frame, but is not limited to these and can be a frame of other forms. Additionally, the ICF can be a frame that is redundantly transmitted in 20 MHz increments across the entire channel or bandwidth over which the ICF is transmitted (e.g., a non-HT duplicate PPDU format frame). As another example, the ICF can be a frame that is transmitted to match at least one of the operating channel and operating bandwidth expected to be used by the receiving wireless LAN terminal.

[0080] Here, wireless LAN terminals (e.g., AP, non-AP STA) that support and participate in DSO operation may be referred to as DSO-supported wireless LAN terminals (DSO STA), but are not limited to such terms or names. A DSO non-AP STA may require an operating channel switching time to switch its operating channel to a sub-channel (DSO subband). The operating channel switching time may include a channel switching time (time Ts) required for a channel switching operation to switch the operating channel from the main subband to the sub-channel (DSO subband), and a channel switching back time (time Ts') required for a channel switching back operation to switch the operating channel from the sub-channel (DSO subband) to the main subband. The aforementioned operating mode switching times (at least one of the channel switching time and the channel switching back time) may vary depending on the performance of the DSO STA and the operating channel to be switched. A DSO STA may exchange information regarding its maximum operating bandwidth and operating channel switching time with other DSO STAs. For example, a non-AP STA that is a DSO STA can exchange information about its maximum operating bandwidth (e.g., 80 MHz operating bandwidth) and operating channel switching time with an AP that is a DSO STA. Through the above description, the AP that is a DSO STA and the non-AP STA that is a DSO STA can recognize each other's information about maximum operating bandwidth and operating capability switching time.

[0081] The DSO STA may be unable to perform transmit and receive operations during the operation channel switching time. That is, the DSO STA cannot perform frame transmission and reception during at least one of the channel switching time and the channel switching back time. Additionally, the DSO STA may not be able to perform operations for channel access (e.g., clear channel assessment (CCA)) during at least one of the channel switching time and the channel switching back time.

[0082] The aforementioned AP may add padding to the transmitted ICF to guarantee the operating channel switching time of the DSO STA. The padding may be used to extend the transmission time of the frame and may be included in at least one of the forms of fields, subfields, bits, and other forms within the frame. Additionally, the AP may add an Intermediate FCS to extend the padding length or to advance the start time of operation of the recipient wireless LAN terminal (e.g., the time when the DSO STA begins switching the operating channel). An Intermediate FCS may mean that all or part of the FCS (frame check sequence) field, which is a frame error detection code included at the end of the frame, is inserted in the middle of the frame in the form of a field or subfield. A wireless LAN terminal that receives the aforementioned Intermediate FCS can confirm the normal reception of the frame even in the middle of receiving the frame and can start subsequent operations (e.g., the operation of the DSO STA switching the operating channel).

[0083] The padding length within the ICF that the AP transmits to the non-AP STA can vary. For example, the padding length may be set to a time length equal to or longer than the time from the completion of receiving the MAC header of the ICF to the channel switching time of the non-AP STA. As another example, the padding length may be set to a time length equal to or longer than the time from the completion of receiving the Intermediate FCS to the channel switching time of the non-AP STA.

[0084] A non-AP STA that is a DSO STA can receive an ICF transmitted by the AP and can identify the operation channel switching indicator within the received ICF. Subsequently, the non-AP STA that is a DSO STA can successfully switch the operation channel to a sub-channel (DSO subband). In the above case, the non-AP STA can transmit an initial control response frame (ICR) to the AP after a Short Interframe Space (SIFS) time from the time the ICF reception ends. The ICR may be a frame transmitted by the non-AP STA using the bandwidth (e.g., 80 MHz) indicated in the operation channel (e.g., main subband, sub-channel (DSO subband)) indicated by at least one of the operation channel switching indicator and the operation bandwidth indicator. Here, the ICR may be a frame of various forms. For example, the ICR may be a Simultaneous Clear-To-Send (CTS) (S-CTS), Buffer Status Report (BSR), Multi-STA BlockAck, or QoS Null frame, but is not limited thereto and may be other types of frames. Additionally, the ICR may be a frame that is redundantly transmitted in 20 MHz increments across the entire channel or bandwidth where the ICR is transmitted (e.g., a non-HT duplicate PPDU format frame). Furthermore, the ICR may be a frame transmitted from the RU indicated by the ICR. As another example, the ICR may be a frame transmitted in accordance with at least one of the operating channel and operating bandwidth currently used by the wireless LAN terminal transmitting the ICR. That is, the ICR may be transmitted by occupying the entire DSO subband, or it may be transmitted from the available resources indicated by the AP's operating bandwidth indicator in the ICF.

[0085] The AP can receive an ICR transmitted by a non-AP STA that has successfully switched the operating channel on the channel indicated by at least one of the operating channel switching indicator and the operating bandwidth indicator. The AP can identify the non-AP STA that transmitted the ICR. The AP can transmit a frame (e.g., a data frame) to the non-AP STA that transmitted the ICR after receiving the ICR and SIFS time, using at least one of the channel and bandwidth where the ICR was transmitted. The non-AP STA that received the frame transmitted by the AP can transmit an acknowledgment frame (e.g., an Acknowledgement (ACK) frame, a Block Acknowledgement (BA) frame) to the AP using the bandwidth of the operating channel indicated by at least one of the operating channel switching indicator and the operating bandwidth indicator.

[0086] The aforementioned DSO may be performed for the duration indicated by the duration field of the MAC header of the ICF initially transmitted by the AP. The aforementioned DSO may be performed for the length of the TXOP acquired by the AP upon successful channel access through an EDCA operation. A DSO STA that has switched the operating channel to the DSO subband at the time of the end of the TXOP acquired by the AP may perform a channel switching back operation to switch its operating channel from the sub-channel (DSO subband) to the main subband. As another example, a DSO STA that has switched the operating channel to the DSO subband may begin changing the operating channel to the main subband if no frame is detected for a certain waiting time (e.g., aSIFSTime + aSlotTime + aRxPHYStartDelay) after the time the last frame transmission and reception was completed (e.g., if the DSO STA fails to generate the PHY-RXSTART.indication primitive). As an example, the DSO STA may switch the operating channel to the DSO subband and perform frame exchange with the AP (or DSO AP). Here, the DSO STA performs frame exchange with the AP in the DSO subband, and once the frame exchange is completed, it may begin changing the operating channel to the main subband after the aforementioned fixed waiting time. That is, the DSO STA performs frame exchange in the DSO subband, and if it does not detect the reception of an additional frame within a fixed time, it may begin switching the operating channel and change from the DSO subband to the main subband. Here, the DSO STA may change the operating channel during Ts' and operate again in the main subband after Ts'. That is, the DSO STA may operate again in the main subband after Ts', following a fixed waiting time after the point in time when it completed transmitting and receiving the last frame.

[0087] In the following, a service period (SP) based DSO method is described as an alternative operation method for the DSO of the wireless LAN terminal described above. Here, the operating bandwidth of the STA may be smaller than that of the AP. If the STA supports the DSO of the wireless LAN terminal described above, the STA can transmit and receive frames by receiving communication resources from the AP in a DSO subband outside the STA's operating bandwidth, rather than the main subband. The main subband may refer to the entire bandwidth channel of the STA, including the STA's main 20 MHz channel. The DSO subband may refer to a channel other than the STA's main subband that is included in the AP's operating bandwidth and can receive resources from the AP.

[0088] For example, if the operating bandwidth of the AP is 160 MHz, the DSO subband may be the AP's secondary 80 MHz channel. For another example, if the operating bandwidth of the AP is 320 MHz, the bandwidth of the DSO subband may be the AP's secondary 160 MHz channel or an 80 MHz channel included in the AP's secondary 160 MHz channel. Alternatively, if the operating bandwidth of the AP is 320 MHz, one of the AP's 320 MHz operating channels may be the DSO subband, but is not limited to such embodiments.

[0089] APs and STAs connected to the AP can negotiate a target wake time (TWT) with the AP. TWT may be an action to set a service period (SP), which is a communication interval during which the AP and STAs can communicate. When a TWT is negotiated between the AP and the STAs, the STAs that set the TWT may operate in a sleep state (e.g., in a doze state where frame transmission and reception are impossible) during periods other than the SP, and operate in a state where normal transmission and reception are possible (e.g., in an awake state where frame transmission and reception are possible) during the SP period. In other words, the period during which the STAs that set the TWT do not perform sleep operations is the SP, and the period during which they perform sleep operations may be a time interval other than the SP.

[0090] In addition, there may exist TWT negotiations for low-latency frame transmission that are not for performing the aforementioned power-saving operations. TWT negotiations for low-latency frame transmission may be R(restricted)-TWT, but are not limited to this term or designation. When R-TWT is negotiated between APs and STAs, an R-TWT SP may be established. Before the start of the R-TWT SP, STAs that are not members of the R-TWT SP must cease communication. Within the R-TWT SP, the member STAs of the R-TWT SP and the AP may transmit low-latency frames preferentially. During the TWT negotiation process (including all types of TWT, such as general TWT and R-TWT), the AP may also conduct negotiations to allow STAs supporting DSO to perform DSO within the TWT SP. For example, the AP and STA may conduct TWT negotiations to allow STAs supporting DSO to operate in the DSO subband during the TWT SP period. Based on the above, at the start of the TWT SP interval, the STA may operate in the DSO subband, and this operation may be referred to as a service interval-based DSO (SP based DSO). That is, at a time Ts prior to the start of the TWT SP interval, the STA must perform a switching operation to the DSO subband, and at the start of the TWT SP interval, the STA may operate in the DSO subband. However, in the operation of the service interval-based DSO (SP based DSO), the DSO subband may be occupied by another wireless LAN terminal that is in a hidden node relationship with the AP. In the above case, the AP determines that the DSO subband is not occupied and establishes the service interval-based DSO (SP based DSO), but the STA operating in the DSO subband may detect energy from another wireless LAN terminal in the DSO subband and confirm that the channel is occupied.In the above-described case, even if the AP transmits a frame in the DSO subband, the STA operating in the DSO subband may not be able to receive the AP's frame. Alternatively, even if the STA operating in the DSO subband receives the AP's frame, it cannot transmit the frame because the DSO subband is occupied. Consequently, service interval-based DSO (SP-based DSO) operation cannot be performed smoothly. For example, if the AP cannot communicate with the STA that has configured the service interval-based DSO (SP-based DSO) and determines that the transmission of a frame sent in the DSO subband has failed, the AP may not transmit the frame in the DSO subband where the STA is operating. Furthermore, during the SP interval in which the STA is required to operate in the DSO subband, the STA can no longer receive frames from the AP and cannot transmit frames to the AP. In the above-described case, the STA may operate in the DSO subband unnecessarily. Therefore, when an STA performs a service segment-based DSO (SP-based DSO) operation, the STA may be made to operate again in the main subband if it detects that the DSO subband is occupied. Here, the TWT negotiation for establishing the service segment-based DSO (SP-based DSO) can be performed using the broadcast TWT method. That is, the AP can broadcast the TWT SP to multiple STAs by including a TWT element in a beacon frame. When the TWT negotiation for establishing the service segment-based DSO (SP-based DSO) is the broadcast TWT method, the service segment-based DSO (SP-based DSO) operation may be referred to as broadcast SST (subchannel selective transmission), but is not limited to such terms and names.

[0091] For example, if the STA and AP have negotiated service interval-based DSO (SP-based DSO) operation, ICF and ICR exchanges to perform frame exchange in the DSO subband may be unnecessary between the STA and AP. As another example, ICF and ICR exchanges may be necessary to transition the STA to the DSO subband or to check the communication availability of the STA in the DSO subband. The above may be the result of a prior negotiation that the service interval-based DSO (SP-based DSO) will operate in the DSO subband within the SP interval.

[0092] FIGS. 4a to 4c are drawings illustrating the wireless LAN service interval-based dynamic sub-channel operation applied to the present disclosure.

[0093] Referring to FIGS. 4a through 4c, a wireless LAN network composed of an AP, a non-AP STA 1 (310), and a non-AP STA 2 (320) may be the same as the wireless LAN network structure described in FIG. 3. Additionally, the wireless LAN terminal can obtain a TXOP if it succeeds in accessing the channel by performing the EDCA operation of the wireless LAN terminal described above. Meanwhile, the non-AP STA 2 (320) can support the DSO operation of the wireless LAN terminal described above and the service segment-based (SP-based) DSO operation of the wireless LAN terminal. That is, the AP and the non-AP STA 2 (320) can perform TWT negotiation, and the non-AP STA 2 (320) can identify the TWT SP. The non-AP STA 2 (320) can operate in the DSO subband at the TWT SP. As another example, the non-AP STA 2 (320) can perform DSO operations by receiving an ICF from the AP even when the TWT SP is not set or when it is not a TWT SP. Since the non-AP STA 2 (320) supports the DSO operations of the wireless LAN terminal described above, when the non-AP STA 2 (320) receives an ICF from the AP it is connected to, the non-AP STA 2 (320) can switch the operation channel to the DSO subchannel and operate. Even in the above case, the non-AP STA 2 (320) can perform the operations described below.

[0094] Meanwhile, non-AP STA 1 (310) may operate in the main subband without switching the operating channel from the TWT SP to the DSO subband. When the AP performs frame transmission from the TWT SP to the non-AP STA 2 (320), it may perform frame transmission using the DSO subband. For example, the non-AP STA 2 (320) operates by switching the operating channel from the TWT SP (hereinafter, SP) to the DSO subband. When the non-AP STA 2 (320) switches the operating channel to the DSO subband, the channel switching time, 'Ts', may be required. If the AP transmits a frame to the non-AP STA 2 (320) before the SP, the AP may need to terminate the transmission to the non-AP STA 2 (320) before the time Ts from the start of the SP. Alternatively, if there is a frame that the non-AP STA 2 (320) transmits to the AP prior to the SP, the non-AP STA 2 (320) may terminate the frame exchange (e.g., the exchange of a frame that STA 2 transmits to the AP and a response frame for the frame that non-AP STA 2 (320) transmits to the AP) before the start of the SP. Thus, the non-AP STA 2 (320) may operate in the DSO subband at the start of the SP. However, the non-AP STA 2 (320) may detect media occupancy in the DSO subband. For example, the non-AP STA 2 (320) may detect that the media is occupied by sensing energy according to physical CS (carrier sensing) in the DSO subband. Alternatively, non-AP STA 2 (320) can set a network allocation vector (NAV) corresponding to the frame and TXOP length information of the PHY preamble or MAC header of the frame received in the DSO subband according to the virtual CS in the DSO subband.Here, the non-AP STA 2 (320) may be considered to have the medium occupied until the NAV is terminated. Alternatively, the non-AP STA 2 (320) may use both the physical CS and the virtual CS to determine that the DSO subband is occupied. In the above case, the non-AP STA 2 (320) may not be able to receive the AP's frame in the DSO subband, or even if it receives the AP's frame, it may not be able to transmit a response frame. In the above case, the STA 2 may not operate in the DSO subband within the SP and may operate again in the main subband. The non-AP STA 2 (320) detecting that the DSO subband is occupied may be detecting that the RU assigned to the non-AP STA 2 (320), indicated by the AP's ICF, is occupied. For example, if the 20 MHz subchannel containing the RU directed by the AP is occupied, the non-AP STA 2 (320) can detect that the DSO subband is occupied.

[0095] For example, if non-AP STA 2 (320) receives an ICF and switches the operating channel to a DSO subband, and the DSO subband is detected to be occupied, non-AP STA 2 (320) may not transmit a response frame for the ICF. Here, non-AP STA 2 (320) may start switching the operating channel back to the main subband based on any of the following times. Here, one of the following times may be the end time of the DSO frame exchange. The AP and non-AP STA 2 (320) may determine one of the following times as the end time of the DSO frame exchange. That is, non-AP STA 2 (320) not transmitting a response frame for the ICF may mean that the DSO frame exchange has ended, and this may be one of the following times.

[0096] - Immediately after the AP completes receiving the ICF

[0097] - SIFS time (aSIFSTime) after the AP completes receiving the ICF

[0098] - After 'aSIFSTime + aSlotTime + aRxPHYStartDelay' time since the AP completes receiving the ICF

[0099]

[0100] The non-AP STA 2 (320) can start switching the operating channel from the DSO subband to the main subband and can operate again in the main subband before time Ts' is over. That is, it may take up to Ts' for the non-AP STA 2 (320) to switch the operating channel from the DSO subband to the main subband.

[0101] Meanwhile, the AP can acquire a TXOP capable of transmitting multiple frames by performing the EDCA backoff operation and EDCA TXOP acquisition procedure described in the EDCA operation of the wireless LAN terminal within the SP. The AP can transmit frames to non-AP STA 2 (320) using the DSO subband within the acquired TXOP. In the above case, the AP can determine that the DSO subband is not occupied. Alternatively, the AP can transmit frames to non-AP STA 2 (320) to perform frame transmission and reception with non-AP STA 2 (320) in the DSO subband regardless of whether the TWT SP has started.

[0102] Referring to FIG. 4a, the first frame transmitted by the AP in the TXOP may be an ICF (initial control frame, 401-1, 401-2). That is, the AP may transmit the ICF (401-1, 401-2) in the main subband and the DSO subband. For example, the ICF (401-1, 401-2) may be a request to send (RTS) frame, a multi-user (MU)-RTS trigger frame, or a buffer status report poll (BSRP) trigger frame, but is not limited thereto and may be other types of frames. The ICF (401-2) transmitted by the AP in the main subband may be a frame requesting a response frame from non-AP STA 1 (310) (e.g., an initial control response (ICR) frame, 402, which is a response frame to the ICF). Additionally, the ICF (401-1) transmitted by the AP in the DSO subband may be a frame requesting a response frame from non-AP STA 2 (320). As another example, the ICF transmitted by the AP in the main subband and the DSO subband is identical, and each of the multiple user information fields included in the ICF may request a response frame from non-AP STA 1 (310) and non-AP STA 2 (320) in the main subband and the DSO subband. The AP may initiate DSO frame exchange by transmitting the aforementioned ICF. Meanwhile, the ICF (401-1, 401-2) transmitted by the AP in the main subband and the DSO subband may include padding for the time Ts required for non-AP STA 2 (320) to operate from the main subband to the DSO main subband. Additionally, the ICF transmitted by the AP may include an indicator that instructs the non-AP STA 2 (320) to switch the operating channel from the main subband to the DSO subband.

[0103] non-AP STA 1 (310) can transmit a response frame (402) in the main subband. Here, non-AP STA 2 (320) may not be able to transmit a response frame in the DSO subband because it detects that the DSO subband is occupied and operates in the main subband again. Therefore, the AP receives the response frame (402) from non-AP STA 1 (310) in the main subband but may not receive the response frame from non-AP STA 2 (320) in the DSO subband. In the above case, the AP may attempt to transmit a frame using only the main subband within the acquired TXOP. Additionally, the AP may assume that non-AP STA 2 (320) is operating in the main subband because there was no response from non-AP STA 2 (320) in the DSO subband. Accordingly, after receiving the response frame (402) from non-AP STA 1 (310) in the main subband, the AP may transmit a downlink frame to both non-AP STA 1 (310) and non-AP STA 2 (320) or transmit a trigger frame (403) requesting an uplink frame. non-AP STA 2 (320) may operate in the main subband again at the time of returning to the main subband after the time of completion of receiving the ICF. If the AP does not receive the ICR, which is the response frame for the ICF (401-1), from non-AP STA 2 (320) (i.e., if the AP does not receive the ICR from the STA that instructed the AP to switch the operating channel to the DSO subband), the AP may be able to transmit a frame to non-AP STA 2 (320) at any of the following times after the time of completion of transmitting the ICF. That is, the AckTimeout time from the time the AP completes the transmission of the ICF (401-1) (the time when the PHY-RXEND.indication primitive occurs) (e.g.If the ICR is not received for a time (i.e., if the PHY-RXSTART.indication primitive or PHY-RXEARLYSIG.indication primitive associated with the ICR is not detected), the AP may be able to transmit a frame to non-AP STA 2 (320) at any of the following times from the time the ICF transmission is completed.

[0104]

[0105] - The point in time Ts' that has elapsed since the completion of ICF transmission, and thereafter

[0106] - The point in time after SIFS time (aSIFSTime) and Ts' time have elapsed from the time ICF transmission is completed, and thereafter

[0107] - The time after aSIFSTime + aSlotTime + aRxPHYStartDelay + Ts' has elapsed since the completion of ICF transmission, and thereafter.

[0108]

[0109] Here, regarding the time when aSIFSTime + aSlotTime + aRxPHYStartDelay + Ts has elapsed since the time of completion of ICF transmission and thereafter, the time when aSIFSTime + aSlotTime + aRxPHYStartDelay has elapsed since the time of completion of ICF transmission is the time when the non-AP STA 2 (320) starts switching the operating channel from the sub-channel (DSO subband) to the main subband, and this time is the time when the DSO frame exchange between the AP and the non-AP STA 2 (320) ends.

[0110] In the present disclosure, the time point described above is referred to as the main subband return time, but is not limited to such term or name. For example, the time value of the aRxPHYStartDelay described above may be 20 us, but is not limited thereto. The time point described above may be the latest time point at which a STA returning from the DSO subband to the main subband (i.e., a STA that has switched the operating channel from the DSO subband by instructing the ICF to switch the operating channel to the DSO subband, but has not transmitted an ICR from the DSO subband and has returned to the main subband) can operate in the main subband again and transmit and receive frames. If there is a frame that the AP transmits to a STA (e.g., STA 1) other than the non-AP STA 2 (320) in the main subband, and the time of completion of the exchange of the frame (e.g., the time of completion of transmission of the frame if the frame does not require an immediate response frame, the time of completion of reception of the response frame if the frame requires an immediate response frame) is after the time of return of the non-AP STA 2 (320) to the main subband, the AP may be able to transmit a frame (e.g., data frame, ICF, trigger frame, etc.) to the non-AP STA 2 (320) in the main subband. Specifically, the AP may perform frame exchange by transmitting a frame to the non-AP STA 1 (310) in the main subband after the DSO frame exchange with the non-AP STA 2 (320) is completed. Here, if non-AP STA 2 (320) operates in the main subband after the frame exchange between AP and non-AP STA 1 (310) ends, AP may be able to transmit frames to non-AP STA 2 (320) in the main subband.

[0111] Meanwhile, if the time at which the frame exchange is completed is before the time when non-AP STA 2 (320) returns to the main subband, it may be impossible for the AP to transmit the frame from the main subband to non-AP STA 2 (320) even after completing the frame exchange with non-AP STA 1 (310) in the main subband. That is, the AP can transmit the frame from the main subband to non-AP STA 2 (320) at or after the time when non-AP STA 2 (320) returns to the main subband. Instead of transmitting the frame to non-AP STA 2 (320), the AP can transmit the frame to a STA other than non-AP STA 2 (320) and then transmit the frame to non-AP STA 2 (320). That is, the AP can transmit a frame to non-AP STA 2 (320) after the point in time when non-AP STA 2 (320) returns to the main subband within the acquired TXOP. Alternatively, the AP can acquire a new TXOP to transmit a frame to non-AP STA 2 (320) as follows.

[0112] Alternatively, the AP may initiate a channel access procedure (e.g., initiating an EDCA backoff procedure and an EDCA TXOP acquisition procedure) and, if the channel access operation is successful after the main subband return time of the non-AP STA 2 (320), transmit a frame to the non-AP STA 2 (320). On the other hand, if the channel access operation is terminated before the main subband return time of the non-AP STA 2 (320), the AP may repeat the channel access operation until the channel access operation is successful after the main subband return time of the non-AP STA 2 (320), or keep the backoff counter at 0 and transmit a frame to the non-AP STA 2 (320) at or after the main subband return time (e.g., immediately, or after any delay time).

[0113] In another channel access method, the AP may initiate a channel access procedure (e.g., initiating an EDCA backoff procedure and an EDCA TXOP acquisition procedure) at or after the non-AP STA 2 (320) returns to the main subband, and if the channel access operation is successful, transmit a frame to the non-AP STA 2 (320). In the above case, the AP may assume that there are no frames or packets destined for the non-AP STA 2 (320) in the AP's transmission queue before the non-AP STA 2 (320) operates in the main subband. Subsequently, the AP may assume that frames or packets destined for the non-AP STA 2 (320) are re-entered at or after the non-AP STA 2 (320) returns to the main subband, when the non-AP STA 2 (320) operates in the main subband.

[0114] The channel access operation described above may be performed within the acquired TXOP (i.e., within the interval where the acquired TXOP has not ended). In the case described above, the AP may not acquire a new TXOP even if the channel access operation is successful, and the AP may use the previously acquired TXOP as is. As another example, if the channel access operation is successful, the AP may acquire a new TXOP other than the previously acquired TXOP, or extend the previously acquired TXOP, and is not limited to a specific form. The AP can transmit a frame to the non-AP STA 2 (320) after the non-AP STA 2 (320) has returned to the main subband.

[0115] If there are no frames sent by the AP to a STA other than non-AP STA 2 (320), the AP cannot send frames to non-AP STA 2 (320) before the time of return to the main subband of non-AP STA 2 (320). For example, frames or packets destined for a STA other than non-AP STA 2 (320) (e.g., STA 1) may be lost due to the expiration of the lifetime of the AP's transmission queue, etc. In the above case, the AP can only send frames to non-AP STA 2 (320). Or, if the transmission of a packet destined for non-AP STA 1 (310) is successful (e.g., successful transmission over multiple links) for other reasons, the AP can only send frames to non-AP STA 2 (320), but is not limited to the above examples and there may be more examples. In the above case, the AP cannot perform additional frame exchange in the main subband and can perform a waiting or channel access operation to transmit a frame to non-AP STA 2 (320). That is, the AP can immediately transmit a frame to non-AP STA 2 (320) when non-AP STA 2 (320) returns to the main subband. The AP may be able to immediately transmit a frame within a previously acquired TXOP, but as described below, it may need to perform a new TXOP acquisition procedure to acquire a TXOP and transmit a frame to non-AP STA 2 (320). That is, the AP can start a channel access procedure (e.g., start an EDCA backoff procedure and an EDCA TXOP acquisition procedure) and transmit a frame to non-AP STA 2 (320) if the channel access operation is successful after non-AP STA 2 (320) returns to the main subband.On the other hand, if the channel access operation is terminated before the main subband return time of the non-AP STA 2 (320), the AP may repeat the channel access operation until the channel access operation is successful after the main subband return time of the non-AP STA 2 (320), or keep the backoff counter at 0 and then transmit a frame to the non-AP STA 2 (320) at or after the main subband return time (e.g., immediately, or after any delay time).

[0116] In another channel access method, the AP may initiate a channel access procedure (e.g., initiating an EDCA backoff procedure and an EDCA TXOP acquisition procedure) at or after the non-AP STA 2 (320) returns to the main subband, and if the channel access operation is successful, transmit a frame to the non-AP STA 2 (320). In the above case, the AP may assume that there are no frames or packets destined for the non-AP STA 2 (320) in the AP's transmission queue before the non-AP STA 2 (320) operates in the main subband. Subsequently, the AP may assume that frames or packets destined for the non-AP STA 2 (320) are re-entered at or after the non-AP STA 2 (320) returns to the main subband when the non-AP STA 2 (320) operates in the main subband.

[0117] The channel access operation described above can be performed within the acquired TXOP (i.e., within the interval where the acquired TXOP has not ended). In the case described above, the AP may use the previously acquired TXOP without acquiring a new TXOP even if the channel access operation is successful. As another example, if the channel access operation is successful, the AP may acquire a new TXOP other than the previously acquired TXOP or extend the previously acquired TXOP, but is not limited thereto. The AP can transmit a frame to the non-AP STA 2 (320) after the non-AP STA 2 (320) returns to the main subband.

[0118] Meanwhile, the AP can transmit a frame to a STA other than non-AP STA 2 (320) (e.g., STA 1 that has not switched the operating channel to the DSO main subband) without being restricted by the frame transmission timing based on the main subband return time.

[0119] That is, the operation of the AP according to the aforementioned main subband return time may be as follows.

[0120] 1. The AP transmits the ICF on the main subband and DSO subband, and the DSO non-AP STA switches the operating channel to the DSO subband.

[0121] 2. The DSO non-AP STA does not transmit the ICR for the ICF. The DSO non-AP STA operates as the main subband again at the point of returning to the main subband.

[0122] 3. If the AP needs to transmit a frame to a DSO non-AP STA, transmit the frame to the DSO non-AP STA after the main subband return time, which is the point in time when the DSO non-AP STA operates in the main subband.

[0123]

[0124] Meanwhile, the above-described operation is based on the operation in which the AP transmits a frame again to the non-AP STA 2 (320) in the main subband when the non-AP STA 2 (320) does not respond to the ICF transmitted by the AP to the non-AP STA 2 (320) in the DSO subband, but this may also apply after the AP and non-AP STA 2 (320) have performed an ICF and additional frame exchange in the DSO subband. For example, the non-AP STA 2 (320) in the DSO subband may respond to the ICF with an ICR. In the above-described case, the AP and non-AP STA 2 (320) in the DSO subband may perform at least one additional frame exchange. The last frame transmitted by the AP to the non-AP STA 2 (320) in the DSO subband may be a frame that does not require a response frame. In the above-described case, the AP may determine the time when 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed since the end of transmission of the last frame transmitted to non-AP STA 2 (320) as the end of the DSO frame exchange. As another example, the last frame transmitted by the AP to non-AP STA 2 (320) in the DSO subband may be a frame requesting an acknowledgment frame. The AP may determine the time when 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed since the time when the acknowledgment frame for the frame transmitted to non-AP STA 2 (320) has been received as the end of the DSO frame exchange. The time when non-AP STA 2 (320) returns to the main subband according to the above-described DSO frame exchange time is described later in FIG. 6a.Alternatively, if the AP does not request the reception of a response frame from the frame transmitted to non-AP STA 2 (320), the AP may determine the time when aSIFSTime + aSlotTime + aRxPHYStartDelay has elapsed since the end of transmission of the last frame transmitted to non-AP STA 2 (320) as the end of the DSO frame exchange. As another example, the last frame transmitted by the AP to non-AP STA 2 (320) in the DSO subband may be a trigger frame that allocates uplink resources to non-AP STA 2 (320). The AP may determine the time when aSIFSTime + aSlotTime + aRxPHYStartDelay has elapsed since the end of the uplink transmission of non-AP STA 2 (320) performed after the transmission of the trigger frame as the end of the DSO frame exchange. Alternatively, the AP may determine the time when 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed since the time when the AP completes transmitting its response frame regarding the time when the non-AP STA 2 (320) terminates the uplink after the trigger frame is transmitted. Alternatively, if the non-AP STA 2 (320) does not respond to the trigger frame, the AP may determine the time when the DSO frame exchange has elapsed since the time when the trigger frame is transmitted is transmitted and 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed. For example, the above-described time when the DSO frame exchange has terminated may be more varied.That is, when the AP and non-AP STA 2 (320) determine the time when normal completion of frame exchange in the DSO subband or the time when the transmission of the last frame completed by the AP is determined when no response frame for the frame is transmitted, the time when 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed since that time may be the time when DSO frame exchange ends. At the time when DSO frame exchange ends, non-AP STA 2 (320) may start switching the operating channel from the DSO subband to the main subband. The AP may not transmit a separate frame after receiving an ICR from non-AP STA 2 (320) in the DSO subband. In the above case, the AP may determine the time when DSO frame exchange ends as the time when 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed since the time when it completed receiving the ICR from non-AP STA 2 (320). The timing of the return of the main subband of non-AP STA 2 (320) according to the DSO frame exchange timing described above is described later in FIG. 6b.

[0125]

[0126] Here, the aforementioned 'aSIFSTime + aSlotTime + aRxPHYStartDelay' time may be the Tw time, and during the Tw time<Primary 전환> When the condition is met, it no longer operates in the DSO subband and can switch the operating channel to the main subband (or main subband). In addition to the point of return to the main subband of the non-AP STA 2 (320) described above, the following<Primary 전환> Conditions and<Primary 전환 - 수신> The timing of the return of the main subband of non-AP STA 2 (320) can be determined by the conditions.

[0127]

[0128] <Primary 전환>

[0129] If the MAC layer of non-AP STA 2 (320) has not received the PHY-RXSTART.indication primitive from the PHY layer and has not transmitted the PHY-TXSTART.request primitive, if the MAC layer of non-AP STA 2 (320) has not received the PHY-TXSTART.confirm primitive from the PHY layer, if there is no nonempty transmit queue in non-AP STA 1 (310), and if non-AP STA 2 (320) has not intended to transmit a frame or scheduled a transmission

[0130]

[0131] <Primary 전환> In the conditions, when the MAC layer of non-AP STA 2 (320) receives the PHY-RXSTART.indication primitive from the PHY layer, it may mean that non-AP STA 2 (320) detects a frame being received. When the MAC layer of non-AP STA 2 (320) sends the PHY-TXSTART.request primitive to the PHY layer, and the MAC layer of non-AP STA 2 (320) receives the PHY-TXSTART.confirm primitive from the PHY layer, it may mean that non-AP STA 2 (320) starts transmitting a frame.

[0132] However, non-AP STA 2 (320) receives the PHY-RXSTART.indication primitive within the Tw time.<Primary 전환> Even if the conditions are not met<Primary 전환 - 수신> If the conditions are met, it can operate by switching to the main subband instead of operating in the DSO subband.<Primary 전환> Without satisfying the conditions<Primary 전환 - 수신> If the conditions are not met, the non-AP STA 2 (320) can operate in the DSO subband without switching the operating channel to the main subband.

[0133]

[0134] <Primary 전환 - 수신>

[0135] If the MAC layer of STA 2 receives the PHY-RXSTART.indication primitive from the PHY layer, and the recipient of the received frame is not STA 1, or

[0136] If the MAC layer of STA 2 receives the PHY-RXSTART.indication primitive from the PHY layer and the received frame is a trigger frame, or

[0137] If the received trigger frame does not allocate a RU (resource unit) for STA 2, or,

[0138] If the MAC layer of STA 2 receives the PHY-RXSTART.indication primitive from the PHY layer and the received frame is a CTS (clear to send) frame, or

[0139] If the receiver address (RA) of the CTS frame is not the address of the AP to which STA 2 is connected, the AP may transmit a frame to STA 2 in the main subband at a time when Ts', the switching back time of STA 2, has elapsed from the end of the DSO frame exchange, or thereafter.

[0140]

[0141] That is, the time Ts' elapsed after the end of the DSO frame exchange may be the time of return to the main subband of the non-AP STA 2 (320). After receiving a frame from the AP in the DSO subband, if the received frame is a frame that does not require a response frame, the non-AP STA 2 (320) may start returning to the main subband if no primitives occur based on frame detection such as PHY-RXSTART.primitive for a time of 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time the frame is received. If the received frame is a frame that requires a response frame, the non-AP STA 2 (320) may start returning to the main subband if no primitives occur based on frame detection such as PHY-RXSTART.primitive for a time of 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time the response frame is transmitted. The non-AP STA 2 (320) may not respond to a frame received from the AP if the received frame requests a response frame but the DSO subband is detected to be occupied or if an error is detected in the frame received from the AP. In the above case, the non-AP STA 2 (320) may start returning to the main subband if no primitive occurs based on frame detection such as PHY-RXSTART.primitive for a time of 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time the frame is received. It takes time Ts', which is the switching back time, for the non-AP STA 2 (320) to return from the DSO subband to the main subband.

[0142] Even when the AP receives a response frame for the ICF from non-AP STA 2 (320) and performs additional frame exchange in the DSO subband, the AP may perform an operation to transmit a frame from the main subband to non-AP STA 2 (320) after a certain delay time from the time of return to the main subband of non-AP STA 2 (320) or the time of return to the main subband of non-AP STA 2 (320) as described above, or perform an operation to transmit a frame to non-AP STA 2 (320) at or after the time of return to the main subband of non-AP STA 2 (320) through frame transmission or channel access operations, and the operation may be the same or similar to the operation in the case where the response frame for the ICF is not received.

[0143] The AP cannot transmit frames to the non-AP STA 2 (320) prior to the non-AP STA 2 (320)'s return to the main subband. When the AP retransmits an ICF instructing the non-AP STA 2 (320) to transition to the DSO subband, it may transmit it at or after the non-AP STA 2 (320)'s return to the main subband. That is, the AP may transmit an ICF that causes the non-AP STA 2 (320) to switch the operating channel from the main subband to the DSO subband at or after the non-AP STA 2 (320)'s return to the main subband. Accordingly, the AP can initiate a DSO frame exchange (a frame exchange initiated by an ICF that switches the operating channel to a DSO subband) or a DSO TXOP (initiated by the transmission of an ICF that switches a non-AP STA (e.g., STA 2) to a DSO subband, or a TXOP including the transmission of an ICF that switches a non-AP STA to a DSO subband).

[0144] Meanwhile, the non-AP STA 2 (320) can perform frame transmission and reception in the main subband again at or after the time of returning to the main subband. That is, the non-AP STA 2 (320) can receive a frame from the AP in the main channel at or after the time of returning to the main subband and transmit a response frame for the frame received from the AP. Alternatively, the non-AP STA 2 (320) can perform a channel switching operation (e.g., switching the operating channel from the main subband to the DSO subband) based on the frame received from the AP.

[0145] In FIG. 4a, the AP can transmit a trigger frame (403) that allocates uplink resources to non-AP STA 1 (310) and non-AP STA 2 (320) in the main subband. That is, the AP may attempt to communicate with non-AP STA 2 (320) in the main subband, rather than the DSO subband. Non-AP STA 1 (310) and non-AP STA 2 (320) can transmit uplink frames to the AP based on the uplink resources allocated by the AP's trigger frame (403). Thus, even if the DSO subband is occupied and unusable, the AP and non-AP STA 2 (320) can perform frame transmission and reception.

[0146] Referring to FIG. 4b, the first frame transmitted by the AP in the TXOP may be an ICF (initial control frame, 401-1, 401-2). That is, the AP may transmit the ICF (401-1, 401-2) in the main subband and the DSO subband. For example, the ICF (401-1, 401-2) may be a request to send (RTS) frame, a multi-user (MU)-RTS trigger frame, or a buffer status report poll (BSRP) trigger frame, but is not limited thereto and may be other types of frames. The ICF (401-2) transmitted by the AP in the main subband may be a frame requesting a response frame from non-AP STA 1 (310) (e.g., an initial control response (ICR) frame, 402, which is a response frame to the ICF). Additionally, the ICF (401-1) transmitted by the AP in the DSO subband may be a frame requesting a response frame from non-AP STA 2 (320). non-AP STA 1 (310) may transmit a response frame (402) in the main subband. Since non-AP STA 2 (320) detects the DSO subband as occupied and operates back in the main subband, it may not be able to transmit a response frame in the DSO subband. The AP receives the response frame (402) from non-AP STA 1 (310) in the main subband but may not receive the response frame from non-AP STA 2 (320) in the DSO subband. Here, the AP can confirm that the reception power of the response frame received in the main subband is high. For example, the AP can confirm that the reception power of the response frame received in the main subband is higher than a preset value.If no response frame is received in the DSO subband and the reception power of the response frame is high in the main subband (or, if the reception power of the response frame is high in the main subband), the AP can confirm that non-AP STA 2 (320) is operating in the main subband. Therefore, the AP can attempt to transmit a frame using only the main subband within the acquired TXOP. Additionally, since there was no response from non-AP STA 2 (320) in the DSO subband and the reception power of the response frame (402) in the main subband was high, the AP can consider that non-AP STA 2 (320) is operating in the main subband. Therefore, after receiving the response frame (402) of non-AP STA 1 (310) in the main subband, the AP can transmit a downlink frame to both non-AP STA 1 (310) and non-AP STA 2 (320) or transmit a trigger frame (403) requesting an uplink frame. In FIG. 4b, the AP can transmit a trigger frame (403) that allocates uplink resources to non-AP STA 1 (310) and non-AP STA 2 (320) in the main subband. That is, the AP may attempt to communicate with non-AP STA 2 (320) in the main subband, rather than the DSO subband. non-AP STA 1 (310) and non-AP STA 2 (320) can transmit uplink frames to the AP based on the uplink resources allocated by the AP's trigger frame (403). Thus, even if the DSO subband is occupied and unusable, the AP and non-AP STA 2 (320) can perform frame transmission and reception.

[0147] Referring to FIG. 4c, the first frame transmitted by the AP in the TXOP may be an ICF (initial control frame, 404-1, 404-2). That is, the AP may transmit the ICF (404-1, 404-2) in the main subband and the DSO subband. The ICF (404-1, 404-2) may be a request to send (RTS) frame, a multi-user (MU)-RTS trigger frame, or a buffer status report poll (BSRP) trigger frame, but is not limited thereto and may be other types of frames. The ICF (404-2) transmitted by the AP in the main subband may be a frame requesting a response frame (e.g., an initial control response (ICR) frame, which is a response frame to the ICF) from non-AP STA 1 (310) and non-AP STA 2 (320). For example, the ICF (404-2) may be a trigger frame that allocates a resource unit (RU), which is an orthogonal frequency division multiple access (OFDMA) resource such as a BSRP trigger frame. Here, a portion of the RU may be allocated to non-AP STA 1 (310), and another portion of the RU may be allocated to non-AP STA 2 (320). In the above case, non-AP STA 1 (310) and non-AP STA 2 (320) may transmit an ICR, which is a response frame, according to the RU indicated by the AP's ICF (404-2). The ICF (404-1) transmitted by the AP in the DSO subband may be a frame requesting a response frame from non-AP STA 2 (320). The AP may request a response frame from the non-AP STA 2 (320) even in the ICF (404-2) transmitted in the main subband, and the above operation may be to determine whether the non-AP STA 2 (320) is operating in the DSO subband or in the main subband.Here, if non-AP STA 2 (320) is unable to operate in the DSO subband, non-AP STA 2 (320) can transmit a response frame (405-2) based on the AP's ICF (404-2) in the main subband. Additionally, non-AP STA 1 (310) can also transmit a response frame (405-1) in the main subband. Since non-AP STA 2 (320) detects that the DSO subband is occupied and operates again in the main subband, it can transmit a response frame (405-2) in the main subband without transmitting a response frame in the DSO subband. The AP can verify both the response frame (405-1) of non-AP STA 1 (310) and the response frame (405-2) of non-AP STA 2 (320) received in the main subband. In the above-described case, the AP can confirm that non-AP STA 2 (320) is operating in the main subband. Therefore, after receiving the response frame (405-1) of non-AP STA 1 (310) in the main subband, the AP can transmit a downlink frame to both non-AP STA 1 (310) and non-AP STA 2 (320) in the main subband, or transmit a trigger frame (406) requesting an uplink frame. In FIG. 4c, the AP can transmit a trigger frame (406) allocating uplink resources to non-AP STA 1 (310) and non-AP STA 2 (320) in the main subband. That is, the AP may attempt to communicate with non-AP STA 2 (320) in the main subband rather than the DSO subband. non-AP STA 1 (310) and non-AP STA 2 (320) can transmit uplink frames to the AP based on the uplink resources allocated by the AP's trigger frame (406). Thus, even if the DSO subband is occupied and unusable, the AP and non-AP STA 2 (320) can perform frame transmission and reception.

[0148] FIG. 5 is a diagram illustrating a hidden node prevention method during dynamic sub-channel operation based on a wireless LAN service interval applied to the present disclosure.

[0149] Referring to FIG. 5, a wireless LAN network composed of an AP, a non-AP STA 1 (310), and a non-AP STA 2 (320) may be the same as the wireless LAN network structure described in FIG. 3. Additionally, the wireless LAN terminal can obtain a TXOP if it successfully accesses the channel by performing the EDCA operation of the wireless LAN terminal described above. Meanwhile, the non-AP STA 2 (320) can support the DSO operation of the wireless LAN terminal described above and the service segment-based (SP-based) DSO operation of the wireless LAN terminal. That is, the AP and the non-AP STA 2 (320) can perform TWT negotiation, and the non-AP STA 2 (320) can identify the TWT SP. The non-AP STA 2 (320) can operate in the DSO subband from the TWT SP. Meanwhile, the non-AP STA 1 (310) can operate in the main subband without switching the operation channel from the TWT SP to the DSO subband. When AP performs frame transmission from TWT SP to non-AP STA 2 (320), AP may perform frame transmission using the DSO subband. non-AP STA 2 (320) may operate by switching the operating channel from TWT SP (hereinafter, SP) to the DSO subband. When non-AP STA 2 (320) switches to the DSO subband, a channel switching time of 'Ts' may be required. When AP transmits a frame to non-AP STA 2 (320) before SP, AP may need to terminate transmission to non-AP STA 2 (320) before time Ts from the start of SP. Alternatively, if there is a frame that non-AP STA 2 (320) transmits to the AP prior to the SP, non-AP STA 2 (320) may terminate the frame exchange (e.g., the exchange of a frame that STA 2 transmits to the AP and a response frame for the frame that non-AP STA 2 (320) transmits to the AP) before time Ts from the start of the SP.Accordingly, the non-AP STA 2 (320) can operate in the DSO subband at the start of the SP. However, the non-AP STA 2 (320) can detect media occupancy in the DSO subband. For example, the non-AP STA 2 (320) can detect that the media is occupied by sensing energy according to the physical CS (carrier sensing) in the DSO subband. Alternatively, the non-AP STA 2 (320) can set a network allocation vector (NAV) corresponding to the frame and TXOP length information in the PHY preamble or MAC header of the frame received in the DSO subband according to the virtual CS in the DSO subband. Here, the non-AP STA 2 (320) can consider the media to be occupied until the NAV ends. Alternatively, the non-AP STA 2 (320) can confirm that the DSO subband is occupied by using both the physical CS and the virtual CS. In the above case, non-AP STA 2 (320) may not be able to receive the AP's frame in the DSO subband, or may not be able to send a response frame even if the AP's frame is received.

[0150] Meanwhile, the AP can acquire a TXOP capable of transmitting multiple frames by performing the EDCA backoff operation and EDCA TXOP acquisition procedure described in the EDCA operation of the wireless LAN terminal within the SP. The AP can transmit frames to non-AP STA 2 (320) using the DSO subband within the acquired TXOP. In the above case, the AP can determine that the DSO subband is not occupied.

[0151] The first frame transmitted by the AP in the TXOP may be an ICF (initial control frame, 407-1, 407-2). That is, the AP may transmit the ICF (407-1, 407-2) in the main subband and the DSO subband. The ICF may be a request to send (RTS) frame, a multi-user (MU)-RTS trigger frame, or a buffer status report poll (BSRP) trigger frame, but is not limited to these and may be a frame of another type. The ICF (407-2) transmitted by the AP in the main subband may be a frame requesting a response frame from non-AP STA 1 (310) (e.g., an initial control response (ICR) frame, 408, which is a response frame to the ICF). The ICF (407-1) transmitted by the AP in the subchannel may be a frame requesting a response frame from non-AP STA 2 (320). non-AP STA 1 (310) may transmit a response frame (408-2) in the main subband. non-AP STA 2 (320) may transmit a response frame (408-1) to the AP's ICF, even though the DSO subband is detected as occupied, as this is considered an exception. Alternatively, the CS required bit of the ICF (407-1) transmitted by the AP in the DSO subband may be set to 0. If the STA receives an ICF with the CS required bit set to 0, the STA may receive the ICF regardless of whether the channel is occupied or idle in the CS (carrier sensing) and transmit a response frame after SIFS. Here, the response frame (408-1) to the AP's ICF may indicate that the non-AP STA 2 (320) 'cannot be used because the DSO subband is occupied'. For example, in FIG. 5, non-AP STA 2 (320) is the occupied section of the DSO subband (e.g.If the end time and remaining length of the NAV set in the DSO subband can be confirmed, the response frame (408-1) to the ICF (407-1) may also indicate the occupied period of the DSO subband. The non-AP STA 2 (320) can operate in the main subband after transmitting the response frame (408-1) to the ICF (407-1) in the DSO subband.

[0152] When the AP receives a response frame (408-1) for an ICF (407-1) from non-AP STA 2 (320), and the response frame indicates that the DSO subband is occupied and cannot be used, the AP can confirm that non-AP STA 2 (320) is operating in the main subband after the transmission of the response frame (408-1) from non-AP STA 2 (320). Therefore, after the AP receives the response frame (408-2) from non-AP STA 1 (310) in the main subband, it can transmit a downlink frame in the main subband to both non-AP STA 1 (310) and non-AP STA 2 (320), or transmit a trigger frame (409) requesting an uplink frame. The time at which the AP transmits a trigger frame (409) to non-AP STA 1 (310) and non-AP STA 2 (320) in the main subband may be at least after time Ts' after receiving a response frame (408-2) in the DSO subband. The AP may transmit a trigger frame (409) that allocates uplink resources to non-AP STA 1 (310) and non-AP STA 2 (320) in the main subband. That is, the AP may attempt to communicate with non-AP STA 2 (320) in the main subband rather than the DSO subband. non-AP STA 1 (310) and non-AP STA 2 (320) may transmit uplink frames to the AP based on the uplink resources allocated by the AP's trigger frame (409). Therefore, even if the DSO subband is occupied and cannot be used, the AP and non-AP STA 2 (320) can perform frame transmission and reception.

[0153] Meanwhile, if the response frame (408-1) transmitted by non-AP STA 2 (320) to the AP’s ICF (407-1) indicates the occupied period of the DSO subband, non-AP STA 2 (320) can operate on the DSO subband again if the occupied period of the DSO subband has ended and the SP has not ended. The AP can check the occupied period of the DSO subband from the response frame (408-1) of non-AP STA 2 (320), and if the occupied period of the DSO subband has ended and the SP has not ended, it can transmit a frame to non-AP STA 2 (320) again.

[0154]

[0155] FIGS. 6a and 6b are drawings illustrating a subband response method during dynamic subband operation applied to the present disclosure.

[0156] Referring to FIGS. 6a and 6b, a wireless LAN network composed of an AP, a non-AP STA 1 (310), and a non-AP STA 2 (320) may be the same as the wireless LAN network structure described in FIG. 3. Here, the non-AP STA 1 (310) connected to the AP may not support DSO operation. On the other hand, the AP and the non-AP STA 2 (320) connected to the AP may support DSO operation. Here, the AP may transmit an ICF (410) in the DSO subband and the main subband. The ICF (410) may allocate an RU corresponding to the DSO subband to the non-AP STA 2 (320) and an RU corresponding to the main subband to the non-AP STA 1 (310). Here, since the non-AP STA 2 (320) performs a DSO operation, the ICF (410) may include a padding field that allows the non-AP STA 2 (320) to move the operating channel from the main subband to the DSO subband. The length of the padding field may be set to a time length corresponding to or greater than the DSO padding delay of the non-AP STA 2 (320). After moving the operating channel to the DSO subband, the non-AP STA 2 (320) may perform carrier sensing (including both virtual and physical carrier sensing) during SIFS. Here, the DSO subband may be detected as occupied (e.g., the channel containing the DSO subband, such as 20 MHz, 40 MHz, 80 MHz, 160 MHz, and 320 MHz, may be detected as occupied, or the subchannel constituting the RU indicated by the AP in the ICF may be detected as occupied). For example, consider the case where the basic NAV timer value of the non-AP STA 2 (320) is not 0 or the physical CS result of the non-AP STA 2 (320) is in a occupied state. The basic NAV timer described above may be referred to as the basic NAV below, and is not limited to a specific term or name.The default NAV timer is a timer whose value decreases over time and can be expired or initialized when the value becomes 0. The non-AP STA 2 (320) can detect that the medium is occupied at a point (or interval) when the default NAV timer is not 0 (i.e., when it has not expired (or interval)), and the above-described operation may be a virtual CS operation. The default NAV timer may be a timer used commonly in both the main subband and the DSO subband. However, it may be possible for the default NAV timer to be managed separately for the main subband and the DSO subband, and is not limited to a specific form. When the DSO subband is occupied, the non-AP STA 2 (320) may need to perform a separate operation to transmit an ICR (411-1), which is a response frame to the ICF (410), in the DSO subband.

[0157] When the non-AP STA 2 (320) is busy with the DSO subband, the non-AP STA 2 (320) may include an indicator in the ICR (411-1) that the non-AP STA 2 (320) transmits to the AP indicating that the DSO subband is busy. For example, if the ICR (411-1) is a Multi-STA BlockAck frame, the per AID TID info field of the Multi-STA BlockAck frame may be used to indicate that the DSO subband is busy. For example, the non-AP STA 2 (320) may indicate through the ICR (411-1) whether the channel is busy due to a physical CS, whether the channel is busy due to a virtual CS, and at least one of the default NAV timer residual value of the non-AP STA 2 (320). Here, the non-AP STA 2 (320) may transmit an ICR (411-1) when the DSO subband is occupied, ignoring the case where the CS required bit of the common info field of the ICF (410) received from the AP is 1. Specifically, the case where the CS required bit is 1 may be an indicator instructing the non-AP STA 2 (320) to perform channel detection based on the physical CS and virtual CS during SIFS after the ICF transmission is complete. The non-AP STA 2 (320) may transmit an ICR regardless of whether the DSO subband is occupied when the CS required field value of the common info field of the ICF is 0. That is, the case where the CS required field value is 0 may be an indicator instructing the non-AP STA 2 (320) not to perform channel detection during SIFS after the ICF transmission is complete. Based on the above, the AP may receive the ICR from the non-AP STA 2 (320).

[0158] Referring to FIG. 6a, when the AP receives the ICR (411-1) of the non-AP STA 2 (320), it can transmit additional frames (e.g., downlink frame, trigger frame, 412) to the non-AP STA 2 (320). Here, the AP can determine the frames to be transmitted subsequently based on the ICR information received from the non-AP STA 2 (320). If the ICR of the non-AP STA 2 (320) indicates the occupation of the DSO subband based on at least one of the virtual CS and physical CS, the AP can first transmit a downlink frame (412) to the non-AP STA 2 (320). Additionally, the AP may transmit the PPDU (a PPDU containing a downlink frame) to the non-AP STA 2 (320) by increasing the transmission power or lowering the modulation and coding scheme (MCS) index so that the non-AP STA 2 (320) can receive the frame without error. Specifically, if the MCS index of the PPDU is increased, the frame transmission speed increases, but the frame may become more vulnerable to interference. On the other hand, if the MCS index of the PPDU is lowered, the frame transmission speed decreases, but the frame may become more robust against interference. That is, if the non-AP STA 2 (320) detects the occupancy status of the DSO subband, the AP may transmit the PPDU more robustly. Alternatively, the AP may transmit a trigger frame requesting an uplink frame to the non-AP STA 2 (320). The AP can transmit the trigger frame to the non-AP STA 2 (320) by setting the CS required field value of the common info field to 0. That is, the AP can cause the non-AP STA 2 (320) to ignore the DSO subband occupancy status and transmit the uplink frame.For example, the transmission of the robust PPDU described above may not be performed when the non-AP STA 2 (320) indicates the occupancy status of the DSO subband based only on the virtual CS. The non-AP STA 2 (320) can perform frame transmission and reception (e.g., downlink and uplink frame transmission and reception) in the AP and DSO subband.

[0159] When non-AP STA 2 (320) completes frame transmission and reception, non-AP STA 2 (320) may wait for the Tw time described above. The time when the Tw time has elapsed from the time when frame transmission and reception is completed is the time when non-AP STA 2 (320) begins switching the operating channel from the DSO subband to the main subband, and this time may be the time when the DSO frame exchange between the AP and non-AP STA 2 (320) ends, as described above.

[0160] During Tw time<Primary 전환> or the condition is satisfied<Primary 전환> Although the conditions were not met<Primary 전환 - 수신> If the condition is satisfied, the non-AP STA 2 (320) can be switched back to the main subband. Here, when the non-AP STA 2 (320) switches the operating channel from the DSO subchannel to the main subband, a time Tt may be required, and Tt may be the switching back delay time described above.

[0161] As another example, the AP may transmit an additional ICF that causes the non-AP STA 2 (320) to switch back to the main subband instead of performing frame exchange with the non-AP STA 2 (320) in the DSO subband. When the AP receives the initial ICR of the non-AP STA 2 (320) and the DSO subband is indicated as occupied, the AP may assign a RU index of the user info field to the non-AP STA 2 (320) to operate in the main subband and transmit an ICF that adds a padding field corresponding to the longer of the DSO padding delay or DSO transition delay of the non-AP STA 2 (320), or the longer value. When the non-AP STA 2 (320) receives the ICF, it may switch the operating channel from the DSO subband to the main subband. The non-AP STA 2 (320) can transmit an ICR to the AP in the main subband after SIFS time from the time the ICF is received. The AP can perform frame transmission and reception with the non-AP STA 2 (320) in the main subband.

[0162] Referring to FIG. 6b, when the AP receives the ICR (411-1) of the non-AP STA 2 (320), it can transmit additional frames (e.g., downlink frames, trigger frames, etc.) to the non-AP STA 2 (320). However, the non-AP STA 2 (320) may not detect the frames transmitted by the AP because the physical CS of the non-AP STA 2 (320) is occupied (i.e., due to transmission energy from another terminal). As another example, the AP receives the ICR (411-1) of the non-AP STA 2 (320) and knows that the DSO subband of the non-AP STA 2 (320) is occupied. Therefore, the AP does not transmit frames to the non-AP STA 2 (320) from the DSO subband. Therefore, the non-AP STA 2 (320) may not be able to detect a frame received from the AP in the DSO subband after transmitting the ICR. The non-AP STA 2 (320) may initiate the aforementioned Tw time after transmitting the ICR. During the Tw time, the non-AP STA 2 (320)<Primary 전환> or the condition is satisfied<Primary 전환> Although the conditions were not met<Primary 전환 - 수신> If the condition is satisfied, the operating channel can be switched back to the main subband. Here, non-AP STA 2 (320) may take time Tt when switching the operating channel from the DSO subband to the main subband. If the PHY-RXSTART.indication primitive does not occur within time Tw, non-AP STA 2 (320) may operate back in the main subband after time Tw and time Tt have elapsed from the time of completion of ICR transmission.

[0163] Referring to FIGS. 6a and 6b, the AP's ICF may indicate whether the AP performs uplink resource allocation in the DSO subband (or performs only downlink frame transmission). If the AP's ICF transmits an ICF indicating that only downlink frame transmission is performed in the DSO subband, the non-AP STA 2 (320) may transmit an ICR to the AP even if the DSO subband is occupied. If the AP's ICF transmits an ICF indicating that uplink resource allocation is performed in the DSO subband, the non-AP STA 2 (320) may not transmit an ICR to the AP if the DSO subband is occupied. Alternatively, if the non-AP STA 2 (320) does not transmit an ICR to the AP, a main subband return operation may be performed. Alternatively, non-AP STA 2 (320) may transmit an ICR in the DSO subband when it receives an ICF from the AP that indicates that uplink resource allocation is performed in the DSO subband.

[0164] FIG. 7 is a flowchart illustrating the operation of an STA in a wireless LAN to which the present disclosure applies. Referring to FIG. 7, a first STA may receive a first initial control frame (ICF) from a second STA (S710). Here, the first ICF may indicate that the operation channel of the first STA, which performs a dynamic subband operation (DSO), is switched from the main subband to the DSO subband. The first STA may perform a DSO frame exchange with the second STA in the DSO subband, including the reception of the first ICF (S720). Afterward, the first STA returns to the main subband after a channel switching back time from the end of the DSO frame exchange, and may perform a frame exchange with the second STA in the main subband after the channel switching back time (S730). For example, the first STA may be a non-AP STA and the second STA may be an AP STA, but is not limited thereto. Here, frame switching in the main subband includes the operation of the first STA receiving an additional frame from the second STA, and the additional frame may include a second ICF indicating that the operation channel of the first STA is switched from the main subband to the DSO subband.

[0165] Additionally, if the first STA does not transmit a response frame for the first ICF, the end time of the DSO frame exchange may be a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' elapsed from the time of completion of reception of the first ICF performed in the DSO frame exchange. Additionally, if the last frame received by the first STA in the DSO frame exchange is a frame that does not require an immediate response frame, the end time of the DSO frame exchange may be a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' elapsed from the time of completion of reception of the last received frame. On the other hand, if the last frame received by the first STA in the DSO frame exchange is a frame that requires an immediate response frame, the end time of the DSO frame exchange may be a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' elapsed from the time of completion of transmission of the immediate response frame for the last received frame. Additionally, the operating channel of the first STA may be switched from the DSO subband to the main subband within the channel switching back time from the time the DSO frame exchange ends. Additionally, if the DSO subband is occupied, the first STA may start the operating channel switching after a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time it completes receiving the first ICF, and switch to a state where frame exchange with the second STA is possible in the main subband after the channel switching back time. Additionally, the first STA may perform a TWT (target wake time) negotiation to establish a service interval capable of communicating with the second STA. Here, the first STA supporting the DSO may be configured to monitor the reception of the first ICF within the service interval based on the TWT negotiation, or to operate in the DSO subband based on the reception of the first ICF.

[0166] Additionally, the first STA may transmit a first ICR to the second STA instructing to switch the operating channel from the DSO subband to the main subband based on the occupancy status of the DSO subband within the service interval. Here, the time of completion of transmission of the first ICR is the time of termination of DSO frame exchange, and the first STA may perform frame exchange with the second STA.

[0167] FIG. 8 is a flowchart showing the operation of a STA in a wireless LAN to which the present disclosure applies.

[0168] Referring to FIG. 8, the first STA may transmit a first initial control frame (ICF) to the second STA (S810). Here, the first ICF may indicate that the operating channel of the second STA, which performs a dynamic subband operation (DSO), is switched from the main subband to the DSO subband. After that, the first STA may perform a DSO frame exchange with the second STA in the DSO subband, which includes the transmission of the first ICF (S820). After that, the first STA may perform a frame exchange with the second STA in the main subband after a channel switching back time from the end of the DSO frame exchange (S830). For example, the first STA may be an AP STA and the second STA may be a non-AP STA, but is not limited thereto. The first STA may be able to initiate a new transmit opportunity (TXOP) with the second STA in the main subband from the time when the second STA operates in the main subband after the channel switching back time from the time when the DSO frame exchange ends. Additionally, if the first STA fails to acquire primitives based on frame reception for a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time when the transmission of the first ICF is completed, it may confirm the failure of reception of the first ICR and confirm that the second STA operates in the main subband after the channel switching back time. Additionally, if the DSO subband is occupied, the first STA may consider that the operation channel switching of the second STA begins after a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time when the second STA completes reception of the first ICF, and that the operation channel switching of the second STA to the main subband is completed after the channel switching back time.Additionally, the first STA performs a target wake time (TWT) negotiation to establish a service interval capable of communicating with the second STA, and the second STA supporting the DSO may be configured to operate in the DSO subband within the service interval based on the TWT negotiation. Additionally, the first STA further transmits the second ICF to the third STA operating in the main subband during the service interval, and if the first ICR reception from the second STA in the DSO subband fails and the second ICR reception from the third STA in the main subband succeeds, the first STA may perform frame exchange with the second STA in the main subband from the time when the second STA's operating channel is completely switched to the main subband. In addition, if the transmission power of the second ICR received from the third STA in the main subband is greater than a preset value, the first STA confirms that the operating channel of the second STA has been switched to the main subband, and can perform frame exchange with the second STA in the main subband from the time when the switching of the operating channel of the second STA to the main subband is completed. In addition, the first STA can further transmit the second ICF to the main subband during the service interval. Here, the second ICF is a frame requesting a response from the second STA and the third STA operating in the main subband, and if the first STA fails to receive the first ICR from the second STA in the DSO subband based on DSO subband occupancy, and receives a response based on the second ICF from the second STA and the third STA in the main subband, the first STA can perform frame exchange with the second STA in the main subband after receiving the responses from the second STA and the third STA in the main subband.

[0169] The methods according to the present disclosure may be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc., either alone or in combination. The program instructions recorded on the computer-readable medium may be those specifically designed and configured for the present disclosure, or they may be those known and available to those skilled in the art of computer software. Examples of computer-readable media include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. Examples of program instructions include machine code, such as that produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter, etc. The hardware devices described above may be configured to operate as at least one software module to perform the operations of the present disclosure, and vice versa. Although the present invention has been described with reference to the embodiments above, those skilled in the art will understand that various modifications and changes can be made to the present disclosure without departing from the spirit and scope of the disclosure as set forth in the following claims.

[0170]

[0171] The above-mentioned matters may also be applied to other systems.

Claims

1. In a method of operation of a first station (station, STA) in a wireless LAN system, The step of the first STA receiving a first initial control frame (ICF) from the second STA, wherein the first ICF instructs the first STA performing a dynamic subband operation (DSO) to switch its operation channel from the main subband to the DSO subband; The step of the first STA performing a DSO frame exchange including reception of the first ICF in the DSO subband with the second STA; and A method of operation comprising the step of the first STA returning to the main subband after a channel switching back time from the end point of the DSO frame exchange, and switching to a state in which frame exchange with the second STA is possible in the main subband after the channel switching back time.

2. In Paragraph 1, A method of operation in which the frame exchange in the main subband includes the operation of the first STA receiving an additional frame from the second STA, and the additional frame includes a second ICF indicating to switch the operation channel of the first STA from the main subband to the DSO subband.

3. In Paragraph 1, A method of operation in which the termination point of the above DSO frame exchange is a point in time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed from the point of completion of reception of the first ICF performed in the DSO frame exchange when the first STA does not transmit a response frame for the first ICF.

4. In Paragraph 1, If the last frame received by the first STA in the DSO frame exchange is a frame that does not require an immediate acknowledgment frame, the end time of the DSO frame exchange is the time after a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed from the time of completion of reception of the last received frame, and A method of operation in which, if the last frame received by the first STA in the DSO frame exchange is a frame requesting an immediate response frame, the end time of the DSO frame exchange is a time when a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' has elapsed from the time of completion of transmission of the immediate response frame for the last received frame.

5. In Paragraph 1, A method of operation in which the operating channel of the first STA is switched from the DSO subband to the main subband within the channel switching back time from the end point of the above DSO frame exchange.

6. In Paragraph 1, A method of operation in which, when the above DSO subband is occupied, the first STA starts an operation channel switching after a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time when the reception of the first ICF is completed, and switches to a state in which frame exchange with the second STA is possible in the main subband after the channel switching back time.

7. In Paragraph 1, A method of operation in which the first STA further includes the step of performing a TWT (target wake time) negotiation to establish a service interval capable of communicating with the second STA, and the first STA supporting the DSO is configured to monitor the reception of the first ICF within the service interval based on the TWT negotiation, or to operate in the DSO subband based on the reception of the first ICF.

8. In Paragraph 7, A method of operation in which the first STA transmits a first ICR to the second STA instructing to switch the operating channel from the DSO subband to the main subband based on the occupancy status of the DSO subband within the service interval, the time of completion of transmission of the first ICR is the time of termination of the DSO frame exchange, and the first STA performs the frame exchange with the second STA.

9. In a method of operation of a first station (station, STA) in a wireless LAN system, A step in which the first STA transmits a first initial control frame (ICF) to the second STA, wherein the first ICF instructs the second STA, which performs a dynamic subband operation (DSO), to switch its operation channel from the main subband to the DSO subband; The step of the first STA performing a DSO frame exchange including the transmission of the first ICF in the DSO subband with the second STA; and A method of operation comprising the step of the first STA performing a frame exchange with the second STA in the main subband after a channel switching back time from the end point of the DSO frame exchange.

10. In Paragraph 9, A method of operation in which the first STA can initiate a new transmit opportunity (TXOP) with the second STA in the main subband from the time when the second STA operates in the main subband after the channel switching back time from the end time of the DSO frame exchange.

11. In Paragraph 9, A method of operation in which the first STA checks for a failure to receive the first ICR if it fails to acquire a primitive based on frame reception for a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time of completion of transmission of the first ICF, and checks that the second STA operates in the main subband after the channel switching back time.

12. In Paragraph 9, A method of operation in which, when the above DSO subband is occupied, the first STA starts the operation channel switching of the second STA after a time corresponding to 'aSIFSTime + aSlotTime + aRxPHYStartDelay' from the time when the second STA completes receiving the first ICF, and considers the operation channel switching of the second STA to the main subband to be completed after the channel switching back time.

13. In Paragraph 9, A method of operation in which the first STA further includes the step of performing a TWT (target wake time) negotiation to establish a service interval capable of communicating with the second STA, and the second STA supporting the DSO is configured to operate in the DSO subband within the service interval based on the TWT negotiation.

14. In Paragraph 13, A method of operation in which the first STA further transmits a second ICF to a third STA operating in the main subband during the service interval, and if reception of the first ICR from the second STA fails in the DSO subband and reception of the second ICR from the third STA succeeds in the main subband, the first STA performs the frame exchange with the second STA in the main subband from the time when the operating channel of the second STA is completely switched to the main subband.

15. In Paragraph 14, A method of operation in which, when the transmission power of the second ICR received from the third STA in the main subband is greater than a preset value, the first STA confirms that the operating channel of the second STA is switched to the main subband, and performs the frame exchange with the second STA in the main subband from the time when the operating channel of the second STA is switched to the main subband.

16. In Paragraph 13, The first STA further transmits a second ICF to the main subband in the service interval, wherein the second ICF is a frame requesting a response from the second STA and a third STA operating in the main subband, and A method of operation in which, if the first STA fails to receive the first ICR from the second STA in the DSO subband based on the DSO subband occupation, and receives a response based on the second ICF from the second STA and the third STA in the main subband, the first STA receives the responses of the second STA and the third STA in the main subband and then performs the frame exchange with the second STA in the main subband.

17. In a wireless LAN system, in a first station (station, STA), At least one transceiver for transmitting and receiving signals; At least one processor controlling the above-mentioned at least one transmitting and receiving unit; and It includes a memory that stores instructions for the non-AP STA to perform a specific operation by the above at least one processor, and The above specific operation is: The first STA receives a first initial control frame (ICF) from the second STA, wherein the first ICF instructs the first STA performing a dynamic subband operation (DSO) to switch its operation channel from the main subband to the DSO subband, and The first STA performs DSO frame switching with the second STA, including reception of the first ICF in the DSO subband, and A first STA that returns to the main subband after a channel switching back time from the end point of the DSO frame exchange, and switches to a state where frame exchange with the second STA is possible in the main subband after the channel switching back time.

18. In a first station (STA) of a wireless LAN system, At least one transceiver for transmitting and receiving signals; At least one processor controlling the above-mentioned at least one transmitting and receiving unit; and It includes a memory that stores instructions for the non-AP STA to perform a specific operation by the above at least one processor, and The above specific operation is: The first STA transmits a first initial control frame (ICF) to the second STA, wherein the first ICF instructs the second STA, which performs a dynamic subband operation (DSO), to switch its operation channel from the main subband to the DSO subband, and The first STA performs DSO frame switching with the second STA, including the transmission of the first ICF in the DSO subband, and A first STA that performs frame exchange with the second STA in the main subband after the channel switching back time from the end point of the DSO frame exchange.

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