Method and apparatus for preventing transmission failure in subchannel access operation of wireless LAN

Abstract

Provided are steps in which, in a wireless LAN system, a first STA detects OBSS transmission on a primary channel and sets an NAV on the primary channel during a TXOP corresponding to the transmission in the OBSS, the first STA not performing an NPCA operation and a second STA, connected to the first STA, supporting the NPCA operation and operating by switching an operating channel from the primary channel to an NPCA channel during the TXOP corresponding to the transmission in the OBSS, and in which a CF-End frame transmitted from the OBSS is received, the CF-End frame indicating truncation of the TXOP of the OBSS and release of the NAV on the primary channel, wherein channel access is performed on the primary channel at a time point determined on the basis of a time point at which the second STA returns to the primary channel or a time point at which the TXOP of the OBSS is scheduled to end, such that a frame can be transmitted to the second STA.

Description

Method and device for preventing transmission failure in sub-channel access operation of wireless LAN

[0001] The present disclosure relates to a method and apparatus for preventing frame transmission failure during a side-channel access 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 subchannel 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 communication resource utilization, and to perform simultaneous transmission by allocating a portion of the operating bandwidth to a subchannel (DSO channel) rather than the primary channel that performs channel access.

[0006] The following describes a method to prevent communication failures caused by terminals that do not support side-channel access operations while side-channel access operations are being performed.

[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 frame transmission failure during a side-channel access operation in a wireless local area network (WLAN).

[0010] The present disclosure relates to a method and apparatus for performing non-primary channel access (NPCA) operations based on detecting overlapping basic service set (OBSS) communication segments in a wireless LAN.

[0011] The present disclosure relates to a method and apparatus for preventing communication failure caused by terminals that do not support NPCA operation while NPCA operation is being performed in a wireless LAN.

[0012] The present disclosure relates to a method and apparatus for increasing the efficiency of communication resource utilization in a wireless LAN.

[0013] 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.

[0014]

[0015] According to one embodiment of the present specification, a method of operation of a first station (STA) in a wireless LAN system comprises the step of the first STA detecting an overlapping basic service set (OBSS) transmission on a main channel and setting a network allocation vector (NAV) on the main channel during a transmit opportunity (TXOP) corresponding to a transmission within the OBSS, wherein the first STA is a STA that does not perform non-primary channel access (NPCA) operations, and the second STA to which the first STA is connected is a STA that supports NPCA operations, wherein the operating channel is switched from the main channel to an NPCA channel during the TXOP corresponding to a transmission within the OBSS and operates, and receiving a contention-free (CF)-end frame transmitted from the OBSS, wherein the CF-End frame indicates the cutting of the TXOP of the OBSS and the release of the NAV on the main channel, and at a time determined based on the time of return of the second STA to the main channel or the scheduled time of termination of the TXOP of the OBSS, channel access is performed on the main channel to the second STA It may include a step of transmitting a frame.

[0016] Additionally, according to one embodiment of the present specification, a station (STA) in a wireless LAN system comprises at least one transceiver for transmitting and receiving signals, at least one processor for controlling the 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: detecting an overlapping basic service set (OBSS) transmission on the main channel and setting a network allocation vector (NAV) on the main channel during a transmit opportunity (TXOP) corresponding to the transmission within the OBSS, wherein the STA is a STA that does not perform non-primary channel access (NPCA) operations and another STA connected to the STA supports NPCA operations, wherein the operating channel is switched from the main channel to the NPCA channel during the TXOP corresponding to the transmission within the OBSS and operates, and receiving a contention-free (CF)-End frame transmitted from the OBSS, wherein the CF-End frame is for cutting off the TXOP of the OBSS and releasing the NAV on the main channel A frame can be transmitted to another STA by performing channel access on the main channel at a time determined based on the time of return to the main channel of another STA or the scheduled time of termination of the TXOP of the OBSS.

[0017] In addition, the following points may apply in common.

[0018] According to one embodiment of the present specification, when the first STA receives a CF-End frame, the first STA determines that the second STA has switched to the NPCA channel when the transmission of the OBSS satisfies a preset NPCA switching condition, maintains the NAV set based on the TXOP of the OBSS, and can transmit a frame by performing channel access on the main channel after the TXOP of the OBSS.

[0019] Additionally, according to one embodiment of the present specification, when the first STA receives a CF-End frame, the first STA releases the NAV and performs an enhanced distributed channel access (EDCA) TXOP acquisition procedure based on channel access, wherein the first STA determines that the second STA has switched to the NPCA channel when the transmission of the OBSS satisfies a preset NPCA switching condition, and waits for the EDCA backoff counter, which was reduced through the EDCA TXOP acquisition procedure during the TXOP of the OBSS, to be set to 0, or after repeating the EDCA backoff procedure and the EDCA TXOP acquisition procedure, transmits a frame from the main channel to the second STA after the TXOP of the OBSS.

[0020] Additionally, according to one embodiment of the present specification, when the first STA receives a CF-End frame, the first STA may release the NAV and attempt to transmit the frame to the second STA on the main channel by performing an enhanced distributed channel access (EDCA) TXOP acquisition procedure based on channel access.

[0021] Additionally, according to one embodiment of the present specification, if a frame transmission attempted by the first STA on the main channel fails, the first STA determines that the second STA has switched to the NPCA channel when the transmission of the OBSS satisfies a preset NPCA switching condition and maintains the channel access parameters, wherein the channel access parameters may include QSRC (QoS STA retry count) values ​​and CW (contention window) values ​​for each AC (access categories).

[0022] In addition, according to one embodiment of the present specification, when the second STA is a multi-link device (MLD) STA, the first link of the second STA is switched to and operated on the NPCA main channel, and the second link of the second STA is operated on the main channel, and when the first STA receives a CF-End frame, it can transmit a frame on the second link of the second STA operating on the main channel.

[0023] Additionally, according to one embodiment of the present specification, when the first STA receives a CF-End frame, it can perform frame transmission to a second STA including a radio chain operating for the NPCA main channel and a radio chain operating for the main channel.

[0024] Additionally, according to one embodiment of the present specification, if the first STA does not support NPCA operation or supports NPCA operation but disables NPCA operation, the first STA may not perform NPCA operation.

[0025] Additionally, according to one embodiment of the present specification, the first STA may be a non-AP STA or an AP STA.

[0026] 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 steps of: the first STA obtaining information indicating that an adjacent second STA activates an NPCA operation based on negotiation with a second STA; and the first STA obtaining a TXOP and transmitting data, wherein the channel occupied based on the TXOP obtained by the first STA overlaps with the main channel of the second STA, and the first STA may include the step of not transmitting a CF-End frame and maintaining media occupancy or leaving it idle until the end of the TXOP to protect the NPCA operation of the second STA, even if data transmission is completed earlier than the end of the TXOP.

[0027] In addition, according to one embodiment of the present specification, the first STA and the second STA are AP STAs, and the basic service set (BSS) of the first STA and the BSS of the second STA may overlap.

[0028] 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 steps of: the first STA detecting transmission of an OBSS in a main channel and switching the operating channel from the main channel to an NPCA channel as the transmission of the OBSS satisfies an NPCA switching condition; obtaining information regarding the TXOP cutting or early termination of the OBSS from at least one frame included in the transmission of the OBSS; determining a time to terminate operation in the NPCA channel and return to the main channel based on the obtained information; and returning to the main channel at the determined time and receiving a frame transmitted from a second STA in the main channel.

[0029] Additionally, according to one embodiment of the present specification, when an initial control frame (ICF) and an initial control response (ICR) exchange is performed within the OBSS, the first STA may determine the time to return from the NPCA channel to the main channel based on whether the ICF and ICR contain information related to TXOP cutting or early termination.

[0030] Additionally, according to one embodiment of the present specification, if the ICF and ICR do not contain information related to TXOP cutting, the cutting or early termination of the TXOP of the OBSS is not performed, the time at which the first STA returns from the NPCA channel to the main channel is determined after the TXOP of the OBSS, and the first STA can receive a frame from the second STA after the TXOP.

[0031] Additionally, according to one embodiment of the present specification, if the ICF and ICR contain information related to TXOP cutting, the cutting or early termination of the TXOP of the OBSS is performed, the time at which the first STA returns from the NPCA channel to the main channel is determined based on the cutting or early termination of the TXOP, and the first STA can receive a frame transmitted from the second STA on the main channel after returning to the main channel at the determined time.

[0032] Additionally, according to one embodiment of the present specification, among the ICF, ICR, and data frames exchanged within the OBSS, if the ICR is not receivable within the BSS containing the first STA and the ICF and data frames within the OBSS contain information related to TXOP truncation or early termination, the time at which the first STA returns from the NPCA channel to the main channel is determined based on the information related to TXOP truncation or early termination contained in the data frames, and the first STA can receive a frame transmitted from the second STA on the main channel after returning to the main channel at the determined time.

[0033]

[0034] According to the present disclosure, a method can be provided to prevent frame transmission failure during a side-channel access operation in a WLAN.

[0035] According to the present disclosure, a method for performing NPCA operation based on OBSS communication interval detection in a wireless LAN can be provided.

[0036] According to the present disclosure, a method can be provided to prevent communication failure caused by terminals that do not support NPCA operation while NPCA operation is being performed in a wireless LAN.

[0037] According to the present disclosure, a method for increasing the efficiency of communication resource utilization in a wireless LAN can be provided.

[0038] 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.

[0039] 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.

[0040]

[0041] FIG. 1 is a diagram showing a communication node within a wireless LAN system to which the present disclosure applies.

[0042] FIG. 2 is a drawing showing a wireless LAN system to which the present disclosure is applied.

[0043] FIG. 3 is a diagram illustrating a wireless LAN sub-channel access operation method and a sub-channel access operation applied to the present disclosure.

[0044] FIGS. 4a to 4d are drawings illustrating a method for preventing frame transmission failure during wireless LAN subchannel access operation applicable to the present disclosure.

[0045] FIGS. 5A and 5B are drawings illustrating a method for preventing frame transmission failure during wireless LAN subchannel access operation applicable to the present disclosure.

[0046] FIGS. 6a to 6c are drawings illustrating a method for preventing frame transmission failure during wireless LAN subchannel access operation applicable to the present disclosure.

[0047] FIG. 7 is a flowchart illustrating the operation of an 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] The following describes a method to prevent transmission efficiency from being detected due to transmission failure of wireless LAN nodes that do not support NPCA operation.

[0063] FIG. 3 is a diagram illustrating a wireless LAN sub-channel access operation method and a sub-channel access operation applied to the present disclosure.

[0064] Referring to FIG. 3, AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) may operate in a wireless LAN network. AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) may have a predetermined primary channel and a non-primary channel access (NPCA) primary channel. The primary channel may be a channel including the primary 20 MHz channel of the basic service set (BSS) configured by AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330). The primary 20 MHz channel may be a channel that must be occupied by all communications of the BSS, and all frame transmission and reception of the BSS may be performed by occupying the primary 20 MHz channel unless NPCA operations are performed. The NPCA main channel may be a channel configured within the BSS formed by AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330), and may be a channel predetermined as a channel set based on a 20 MHz channel different from the main 20 MHz channel included in the main channel described above. That is, the NPCA main channel may have a 20 MHz channel different from the main channel, and the 20 MHz channel is referred to as the NPCA main 20 MHz channel, but is not limited to such name or term. The BSS formed by the aforementioned AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) is referred to as BSS 1 in this disclosure, but this is for convenience of explanation only and is not limited thereto.Here, there may be another BSS that occupies the primary 20 MHz channel of the primary channel of BSS 1 (i.e., occupies the primary channel of BSS 1), and such BSS may be referred to as the OBSS (overlapping BSS) of BSS 1, but is not limited to such name or term.

[0065] Referring to FIG. 3, NPCA operations can be performed in a wireless LAN network. AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) (i.e., APs and STAs of BSS 1) can switch their operating channels to the NPCA main channel and operate when the main channel is occupied by another BSS (OBSS). For example, the OBSS may be a BSS composed of AP X and STA X. That is, when the main channel is occupied by AP X or STA X, AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) can operate on the NPCA main channel and perform channel access operations (e.g., EDCA (enhanced distributed channel access) backoff operations and EDCA TXOP (transmit opportunity) acquisition procedures) on the NPCA main 20 MHz channel. Here, the time during which the APs and STAs of BSS 1 can operate on the NPCA main channel may be the time corresponding to the interval during which the OBSS communicates on the main channel (i.e., the TXOP interval or the interval during which the basic NAV is set).

[0066] Specifically, APs and STAs of BSS 1 receive a frame of OBSS (e.g., PPDU (physical protocol data unit)), and if the received PPDU satisfies at least one of condition 1) or 2) of [NPCA Switching Conditions] below, they may switch the operating channel to the NPCA main channel and operate. In the following, the PPDU header may refer to the PPDU preamble, and the PPDU preamble may also refer to the PPDU header, and may not be limited to specific terms or names.

[0067] [NPCA Conversion Conditions]

[0068] 1) PHY-based NPCA: In the case where the NPCA STA receives a PPDU from the PCH (BSS primary channel) of the BSS and receives a PHY-RXSTART.indication primitive for an HE / EHT / UHR PPDU, satisfying all of the following conditions:

[0069] A. If a PPDU received by the NPCA STA from the BSS PCH is classified as an inter-BSS PPDU,

[0070] B. If at least one of the following conditions is satisfied:

[0071] i. In the case where the NPCA AP corresponding to the BSS to which the NPCA STA belongs has only PHY Header-based NPCA enabled, if the value of NPCA_PPDU_REM_DUR, a MAC (medium access control) variable of the received PPDU (or configured upon receiving the PPDU), is greater than the value indicated in the NPCA Minimum Duration Threshold field of the most recently received or transmitted NPCA for the BSS to which the NPCA STA belongs, or

[0072] ii. In the case where the NPCA AP of the BSS also enables MAC Header-based NPCA, if one or more of the NPCA_PHY_TXOP_REM_DUR or NPCA_PPDU_REM_DUR set from the received PPDU are greater than the aforementioned Threshold,

[0073] C. Where the bandwidth of the PPDU is determined to be 20, 40, 80, or 160 MHz by the NPCA STA, the bandwidth of the PPDU is based on the Bandwidth field within the PPDU's PHY preamble and the in-band channel allocation information indicated in the RU_ALLOCATION parameter contained in the RXVECTOR of the PHY-RXSTART.indication primitive associated with the PPDU, provided that the channel occupied by the PPDU does not overlap with the NPCA PCH,

[0074] D. When the intra BSS NAV of NPCA STA is 0,

[0075]

[0076] 2) MAC-based NPCA: All of the following conditions are satisfied

[0077] A. The NPCA STA receives all or part of a series of PPDUs separated by the SIFS (short interframe space) in the BSS PCH, wherein the reception of the first PPDU is the reception of a PPDU containing an initial control frame (ICF), which is the start frame of the control frame exchange, the reception of the second PPDU is the reception of a PPDU containing an initial control response frame (ICR), which is a response frame to the ICF (provided, the second PPDU may not have been received), and the reception of the third PPDU may be the case where at least one of PHY-RXSTART.indication and PHY-RXEARLYSIG.indication occurs in the NPCA STA upon receiving the preamble of a PPDU transmitted after the control frame exchange, and all of the following conditions are satisfied:

[0078] B. If a PHY-RXEARLYSIG.indication or PHY-RXSTART.indication primitive corresponding to the third PPDU described above is received from the PHY, and such reception occurs during the NPCA_START_TIMEOUT period starting from the time the MAC receives the PHY-RXEND.indication primitive for the first PPDU described above,

[0079] i. NPCA_START_TIMEOUT is '(2 x aSIFSTime) + (2 x aSlotTime) + aRxPHYStartDelay + ICR_Timeout',

[0080] 1. ICR_Timeout is the length value of the expected CTS frame when the ICF is an RTS or MU-RTS trigger frame, or

[0081] 2. ICR_Timeout is the value of the UL Length field of the BSRP trigger frame if the ICF is a BSRP trigger frame, and

[0082] C. If one of the above-described PPDU sequences is classified as an inter-BSS PPDU by NPCA STA,

[0083] D. If at least one of the following conditions is satisfied,

[0084] i. If the NPCA AP has enabled only PHY Header-based NPCA, and the NPCA_PPDU_REM_DUR MAC variable value of the third received PPDU (or configured upon receiving the PPDU) is greater than the value of the NPCA Minimum Duration Threshold field most recently received or transmitted for the BSS to which the NPCA STA belongs,

[0085] ii. If the NPCA AP has enabled MAC Header-based NPCA along with PHY Header-based NPCA, and the value of the NPCA_CFRAME_TXOP_REM_DUR MAC variable of the first PPDU (including ICF) among the aforementioned PPDU sequences (or set upon receiving the PPDU) is greater than the value of the NPCA Minimum Duration Threshold field most recently received or transmitted for the BSS to which the NPCA STA belongs,

[0086] E. If the bandwidth of the received PPDUs is identified by the NPCA STA as 20, 40, 80, or 160 MHz based on the bandwidth information specified in the received PPDU or the CH_BANDWIDTH_IN_NON_HT value, which is an RXVECTOR parameter of the received PPDU, and the channel occupied by the PPDUs does not overlap with the NPCA main channel,

[0087] i. If the control frame (e.g., ICF) is an RTS (request to send) frame within a non-HT (duplicate) PPDU, the RTS frame has a transmitter address (TA) field containing bandwidth information, and if the signaled bandwidth is one of 20, 40, 80, or 160 MHz,

[0088] ii. The channel occupied by a CTS (clear to send) frame within a non-HT (duplicate) PPDU is determined through the RTS frame or MU-RTS frame that elicited the corresponding CTS response.

[0089] F. When the intra BSS NAV of NPCA STA is 0,

[0090]

[0091] Here, if at least one of 1) or 2) is satisfied as a [NPCA switching condition], the APs and STAs of BSS 1 may switch their operating channels to the NPCA main channel and operate. The above-described MAC Header-based NPCA may mean performing NPCA operations by considering the TXOP time interval information of the MAC header or the MAC TXOP time interval information included in the PHY preamble. PHY Header-based NPCA may mean performing NPCA operations by considering the length of the PPDU, which is a PHY frame. The names of MAC Header-based NPCA and PHY Header-based NPCA may be referred to differently. For example, MAC Header-based NPCA may be referred to as MOPLEN NPCA and PHY Header-based NPCA may be referred to as PHYLEN NPCA, but are not limited to such embodiments. The time required to change the operation timing to the NPCA main channel may be the NPCA switching delay time, which may take Ts. The period during which the APs and STAs of BSS 1 operate on the NPCA main channel may be the 'OBSS communication period' of [NPCA switching condition]. The APs and STAs of BSS 1 may need to operate on the main channel again when the OBSS communication period ends. The transition time required for the APs and STAs of BSS 1 to switch back from the NPCA main channel to the main channel may be the NPCA switch back delay time, which may require Ts'. Ts and Ts' may be values ​​mutually negotiated by the AP and the STA supporting NPCA operation during the NPCA negotiation process. For example, Ts and Ts' may be set to the same time or different times and are not limited to a specific form.Therefore, the APs and STAs of BSS 1 may need to terminate transmission before time Ts from the end of the communication period of OBSS. In addition, the APs and STAs of BSS 1 may use the following three MAC variables to determine whether to switch the operating channel to the NPCA main channel.

[0092]

[0093] 1) NPCA_PPDU_REM_DUR :

[0094] The NPCA_PPDU_REM_DUR variable is set to the value obtained by subtracting the time difference between when the NPCA STA's PHY layer detected the first PPDU and generated the PHY-CCA.indication(BUSY) primitive and when it generated the PHY-RXSTART.indication primitive from the total length of the PPDU that the NPCA STA can identify in the PPDU header (e.g., the length of the PPDU indicated by the RXVECTOR generated upon receiving the PPDU or calculated from the indicated value, RXTIME). The NPCA_PPDU_REM_DUR variable indicates only the remaining PPDU length without the MAC layer's frame switching time interval information.

[0095] 2) NPCA_PHY_TXOP_REM_DUR :

[0096] The NPCA_PHY_TXOP_REM_DUR variable is set to the value obtained by subtracting the time difference between when the NPCA STA's PHY layer detected the first PPDU and generated the PHY-CCA.indication(BUSY) primitive and when it generated the PHY-RXSTART.indication primitive from the sum of the total length of the PPDU that the NPCA STA can identify in the PPDU header (e.g., the length of the PPDU indicated by the RXVECTOR generated upon receiving the PPDU, or calculated from the indicated value, RXTIME) and the TXOP_DURATION value indicated in the PPDU header. Unless the TXOP_DURATION value is UNSPECIFIE (i.e., not indicated), the NPCA_PHY_TXOP_REM_DUR variable indicates the remaining transmission period of the received PPDU and the subsequent frame switching time period (e.g., remaining TXOP period).

[0097] 3) NPCA_CFRAME_TXOP_REM_DUR :

[0098] The NPCA_CFRAME_TXOP_REM_DUR variable can be set to the value of the duration / ID field of the MAC header of a control frame received by the NPCA STA. The NPCA_CFRAME_TXOP_REM_DUR variable indicates a frame exchange time interval (e.g., remaining TXOP interval) that is performed after the completion of transmission of the received frame (MAC frame) (e.g., completion of transmission of the PPDU containing the MAC frame).

[0099]

[0100] The APs and STAs of BSS 1 receive the PPDU of OBSS and can check the time length of the PPDU, which can be identified in the preamble of the OBSS PPDU. Additionally, the APs and STAs of BSS 1 can check the time length of the TXOP of OBSS in the preamble of the OBSS PPDU. The point in time when the APs and STAs of BSS 1 can check the time length of the OBSS PPDU may be the point in time when the PHY-RXSTART.indication primitive for the PPDU occurs. For example, this point in time may be T1, but is not limited to that name. At time T1, the MAC variable value may be set as follows.

[0101] - NPCA_PPDU_REM_DUR: Duration of PPDU - (Time elapsed from the occurrence of PHY-CCA.indication(BUSY) caused by PPDU to the occurrence of PHY-RXSTART.indication)

[0102] - NPCA_PHY_TXOP_REM_DUR : PPDU time length + TXOP time length included in PPDU - (Time elapsed from the occurrence of PHY-CCA.indication(BUSY) by PPDU to the occurrence of PHY-RXSTART.indication)

[0103] - NPCA_CFRAME_TXOP_REM_DUR : No effect

[0104]

[0105] Alternatively, the OBSS PPDU received by the APs and STAs of BSS 1 may include an Initial Control Frame (ICF) (e.g., RTS frame, CTS frame, MU-RTS trigger frame, BSRP trigger frame). The APs and STAs of BSS 1 can determine the time length of the OBSS TXOP from the duration field of the MAC header of the Initial Control Frame included in the OBSS PPDU. The point in time at which the time length of the OBSS PPDU can be determined may be the point in time when the PHY-RXEND primitive for the PPDU occurs; this point in time may be time T1, but is not limited to that designation. At time T1, the same MAC variable values ​​may be set as follows.

[0106] - NPCA_PPDU_REM_DUR: Duration of PPDU - (Time elapsed from the occurrence of PHY-CCA.indication(BUSY) caused by PPDU to the occurrence of PHY-RXSTART.indication)

[0107] - NPCA_PHY_TXOP_REM_DUR: Time length of PPDU + Time length of TXOP included in PPDU - (Time elapsed from the occurrence of PHY-CCA.indication(BUSY) by PPDU to the occurrence of PHY-RXSTART.indication)

[0108] - NPCA_CFRAME_TXOP_REM_DUR: The value of the duration field indicated by the MAC header of the initial control frame

[0109]

[0110] When using PHYLEN NPCA in BSS 1, the APs and STAs of BSS 1 can switch the operating channel to the NPCA main channel if, at time T1, the NPCA_PPDU_REM_DUR value is greater than the NPCA minimum duration threshold value most recently transmitted by the APs and STAs of BSS 1.

[0111] In addition, if MOPLEN NPCA is used in addition to PHYLEN NPCA in BSS 1, the APs and STAs of BSS 1 can switch the operating channel to the NPCA main channel if, at time T1, the NPCA_PHY_TXOP_REM_DUR value or NPCA_CFRAME_TXOP_REM_DUR value is greater than the NPCA minimum duration threshold value most recently transmitted by the APs and STAs of BSS 1.

[0112] Additionally, the NPCA timer may be a timer for the time it operates on the NPCA main channel. The NPCA timer may be a timer managed by the NPCA STA (the AP and STA of BSS 1). The NPCA timer may be set based on the value of the MAC variable described above. When the NPCA timer expires (when the timer value reaches 0), the NPCA STA must operate on the main channel again.

[0113] If the NPCA STA is unable to immediately switch the operating channel at time T1, the MAC variable described above may decrease the corresponding value at each time interval. Subsequently, when the NPCA STA switches the operating channel to the NPCA main channel, the NPCA timer may be set to the value obtained by subtracting the NPCA switching back delay time value, which is the time delay required to switch the operating channel from the NPCA main channel to the main channel for each NPCA STA, from the NPCA_PPDU_REM_DUR value when only PHYLEN NPCA is used in BSS 1. On the other hand, if MOPLEN NPCA is also used in BSS 1, the NPCA timer may be set to the value obtained by subtracting the NPCA switching back delay time value for each NPCA STA from the largest value among NPCA_PPDU_REM_DUR, NPCA_PHY_TXOP_REM_DUR, and NPCA_CFRAME_TXOP_REM_DUR.

[0114] As another example, unlike the wireless LAN network configuration described above, one can consider a case where the AP and non-AP STA 1 (320) of BSS 1 support NPCA operation, but the non-AP STA 2 (330) does not support NPCA operation. However, the non-AP STA 2 (330) can recognize that BSS 1 supports NPCA operation. For example, AP 1 (310) may include information indicating whether to use NPCA of BSS 1 in an ultra high reliability (UHR) operation element. The UHR operation element may be included in at least one of a beacon frame broadcast by AP 1 (310), an operating mode and parameters (UHR OMP), and a probe request frame transmitted by AP 1 (310). Therefore, non-AP STA 2 (330) can recognize that NPCA operation is used in BSS 1 even if non-AP STA 2 (330) does not support NPCA operation. In the above case, when AP 1 (310) and non-AP STA 1 (320) detect the communication interval of OBSS, they switch the operation channel from the main channel to the NPCA main channel to operate, but non-AP STA 2 (330) may not be able to switch the operation channel to the NPCA main channel and must operate on the main channel. Specifically, AP 1 (310), which is the AP of BSS 1, may be an AP that indicates NPCA operation capability through the NPCA Supported field of the UHR MAC capabilities element.AP 1 (310) can enable NPCA within BSS 1 and transmit a UHR operation element indicating NPCA enablement in order to indicate that NPCA is available within BSS 1, by including it in at least one of a beacon frame broadcast by AP 1 (310), a UHR OMP, and a probe request frame transmitted by AP 1 (310).

[0115] Here, non-AP STA 1 (320) may be a STA that supports NPCA. A STA that supports NPCA may be a STA that indicates NPCA operation is available through the NPCA Supported field of the UHR MAC capability element. On the other hand, a STA that does not support NPCA may be a STA that indicates NPCA operation is unavailable through the NPCA Supported field of the UHR MAC capability element. Alternatively, a STA that does not support NPCA may be a STA that does not use the UHR MAC capability element. Alternatively, a STA that does not support NPCA may be a STA that indicates NPCA operation is available but does not enable NPCA. Even if AP 1 (310) enables NPCA in BSS 1, the basic NPCA operation of non-AP STA 1 (320) may be disabled. That is, an STA that supports NPCA may not perform an NPCA operation until a separate NPCA operation is enabled. An STA that supports NPCA may send an OMP (operating mode and parameters) request frame to AP 1 (310) to enable an NPCA operation. The OMP request frame may include information indicating the channel switching time required for the NPCA operation (NPCA switching delay, NPCA switch back delay) and the enable / disable of the NPCA operation. The time when non-AP STA 1 (320) has completed sending the OMP request frame to AP 1 (310) (or, the time when the response frame to the OMP request frame sent by non-AP STA 1 (320) to AP 1 (310) (e.g.At the time when an Ack frame and an OMP response frame are received, non-AP STA 1 (320) can enable NPCA operation and perform NPCA operation.

[0116] Meanwhile, the communication period of the OBSS may be shortened compared to the initial period. For example, an initial frame and an initial response frame may be exchanged within the OBSS. Here, the initial frame may be referred to as an ICF, but is not limited thereto. For example, the ICF may be an RTS (request to send) frame (401), and the ICR may be a CTS (clear to send) frame (402). As another example, the ICF may be a BSRP (buffer status report poll) trigger frame, and the ICR may be a Multi-STA BlockAck frame. The duration field included in the RTS frame (401) and the CTS frame (402) may indicate the communication period of the OBSS (i.e., the communication period of the OBSS of the [NPCA transition condition] as the TXOP length of the OBSS). However, within the communication interval of the OBSS, frame exchange (e.g., exchange of a data frame (403) and a response frame (404) to the data frame) may end earlier than the end time of the communication interval of the OBSS indicated by the ICF and ICR, and a CF-End (contention free-end) frame (405) may be transmitted within the OBSS. The CF-End frame (405) may be a frame that releases the NAV (network allocation vector) set based on the RTS frame (401) and CTS frame (402) exchanged within the OBSS (e.g., initializing or updating the value of the NAV timer to 0). When the OBSS transmits the CF-End frame (405), the TXOP of the OBSS may be truncated, and the truncation of the TXOP may be an early termination of the TXOP. AP 1 (310) and non-AP STA 1 (320) can operate on the NPCA main channel when they receive the OBSS's ICF or both the ICF and ICR.Similar to the method of obtaining TXOP information based on ICF and ICR of the OBSS described above, the TXOP period of the OBSS can be indicated in the PPDU header of the OBSS. The NPCA_PHY_TXOP_REM_DUR described above can identify the TXOP of the OBSS using the TXOP_DURATION value included in the PPDU preamble of the OBSS. Accordingly, AP 1 (310) and non-AP STA 1 (320) can move the operating channel to the NPCA main channel if the value of the NPCA_PHY_TXOP_REM_DUR variable is greater than the NPCA minimum duration threshold. Subsequently, a CF-End (contention free-end) frame (405) can be transmitted within the OBSS. The CF-End frame (405) may be a frame that releases the NAV (network allocation vector) set based on frames exchanged within the OBSS. That is, it indicates the early termination of the TXOP of the OBSS. In the above case, since AP 1 (310) and non-AP STA 1 (320) operate on the NPCA main channel, they cannot determine whether the TXOP of OBSS has terminated early on the BSS main channel. Meanwhile, non-AP STA 2 (330) can set a NAV (e.g., Basic NAV) based on the OBSS's ICF or ICR, and can release the NAV upon receiving the OBSS's CF-End frame (405). That is, non-AP STA 2 (330) can release the NAV set based on the OBSS's ICF or ICR, or the reception of at least one frame other than the OBSS's ICF and ICR, upon receiving the OBSS's CF-End frame (405).The non-AP STA 2 (330) cannot transmit a frame because it detects the medium as occupied by virtual carrier detection (i.e., detecting the medium as occupied when the NAV timer value is not 0, and detecting the medium as idle when the NAV timer is 0) during the NAV setting period (i.e., during the period when the NAV timer value is not 0). However, when the NAV is released (i.e., when the NAV timer becomes 0), the virtual carrier detection can detect that the medium is no longer occupied. Here, if the non-AP STA 2 (330) detects the medium as occupied by physical carrier detection, the non-AP STA 2 (330) can perform channel access operations (e.g., EDCA backoff operation and EDCA TXOP acquisition procedure). Therefore, non-AP STA 2 (330) may attempt to transmit a frame (406) to AP 1 (310) to which non-AP STA 2 (330) is connected. However, since AP 1 (310) operates on the NPCA main channel, it may not be possible to receive the frame (406) from non-AP STA 2 (330). Consequently, non-AP STA 2 (330) may fail to transmit the frame (406), and the failure of non-AP STA 2 (330) to transmit the frame (406) may result in wasted frequency and time resources of the wireless LAN network. Additionally, since non-AP STA 2 (330) increases the channel access parameters (e.g., CW (contention window) [AC] and QSRC (QoS STA retry count) [AC]) for each access category, a frame transmission delay may occur during subsequent frame transmission. In addition, if the frame retransmission counter of non-AP STA 2 (330) reaches a certain threshold, frames may be discarded unnecessarily. Consequently, the performance of the wireless LAN network may be reduced. The following describes methods to solve the aforementioned problems.Here, the [NPCA switching conditions] described above may be applied commonly in the following, and the communication interval of the OBSS may be the TXOP interval of the OBSS, but is not limited thereto. Additionally, in the following, "a specific AP or STA supports NPCA" may mean that the NPCA operation capability of the AP or STA supports NPCA operation and simultaneously enables NPCA operation. On the other hand, "a specific AP or STA does not support NPCA" may be an AP or STA whose NPCA operation capability does not support NPCA operation. Alternatively, the AP or STA may refer to at least one of an AP or STA that supports NPCA operation but does not enable (i.e., disable) NPCA operation.

[0117] For example, if a frame received from OBSS by a non-AP STA (e.g., STA 2) matches at least one of the MAC variables NPCA_PPDU_REM_DUR, NPCA_PHY_TXOP_REM_DUR, and NPCA_CFRAME_TXOP_REM_DUR in FIG. 3, it can calculate at least one of these MAC variables in the same way as the NPCA STA. A non-AP STA (e.g., STA 2) can set an NPCA timer based on the above. For example, the NPCA timer of a non-AP STA 2 (330) can be set to the value NPCA_PPDU_REM_DUR if only PHYLEN NPCA is used in BSS 1. On the other hand, the NPCA timer of the non-AP STA 2 (330) may be set to the largest value among NPCA_PPDU_REM_DUR, NPCA_PHY_TXOP_REM_DUR and NPCA_CFRAME_TXOP_REM_DUR when MOPLEN NPCA is also used in BSS 1. The non-AP STA 2 (330) may not perform a channel access operation until the NPCA timer expires (when the value reaches 0). For example, the non-AP STA 2 (330) may not perform a channel access operation (and transmit a frame to which AP 1 (310), the AP to which STA 2 is connected, is the destination) until the NPCA timer expires, even if virtual carrier detection detects the medium as idle and physical carrier detection detects the medium as idle. The above operation means that the non-AP STA 2 (330) detects the medium as being occupied before the NPCA timer expires, or considers the frames in the transmission queue (e.g., frames to which AP 1 (310) is the destination) as non-existent before the NPCA timer expires, and considers the frames to be transmitted to occur after the NPCA timer expires.Alternatively, channel access operations may be performed repeatedly until the NPCA timer expires, and specific operations are described below.

[0118] FIGS. 4a to 4d are drawings illustrating a method for preventing frame transmission failure during wireless LAN subchannel access operation applicable to the present disclosure.

[0119] Referring to FIGS. 4a through 4d, AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) of BSS 1 according to FIG. 3 can be operated. Specifically, AP 1 (310) and non-AP STA 1 (320) support NPCA operation, and non-AP STA 2 (330) does not support NPCA operation, but it can be recognized that NPCA operation is used in BSS 1. However, this is for convenience of explanation only and is not limited thereto. The APs and STAs of BSS 1 (i.e., AP 1, non-AP STA 1, and non-AP STA 2) can receive at least one of the ICF and ICR of OBSS. AP 1 (310) and non-AP STA 1 (320) may operate by switching the operating channel to the NPCA main channel during the OBSS communication period identified in at least one of the ICF and ICR of the OBSS. Alternatively, AP 1 (310) and non-AP STA 1 (320) may operate by switching the operating channel to the NPCA main channel during the OBSS communication period identified based on the PPDU length information in the PPDU header identified by receiving the PPDU of the OBSS and the TXOP information of the OBSS. Here, since non-AP STA 2 (330) does not support NPCA operation, it may operate on the main channel without switching the operating channel to the NPCA main channel. However, if non-AP STA 2 (330) receives a frame in which at least one of the [NPCA transition conditions] conditions matches, non-AP STA 2 (330) recognizes that AP 1 (310) and non-AP STA 1 (320) are performing an NPCA operation, and can also recognize the period in which the NPCA operation is performed. For example, the communication period of OBSS may be terminated early by transmitting a CF-End frame (405) as described above.Here, even if non-AP STA 2 (330) receives a CF-End frame (405) from OBSS, it may not transmit a frame to AP 1 (310) during the period in which AP 1 (310) and non-AP STA 1 (320) perform NPCA operations. That is, if it is confirmed that frame reception is impossible because the frequency (channel) operating on which AP 1 (310), to which non-AP STA 2 (330) is connected, is different from that of non-AP STA 2 (330), non-AP STA 2 (330) may perform an operation to not transmit a frame within the communication period of OBSS of [NPCA switching condition]. As another example, non-AP STA 2 (330) may have a different method of handling cases where frame transmission fails in the above-described case. The communication interval of the OBSS described below may refer to the communication interval of the OBSS of the [NPCA transition condition] that is not terminated early. The communication interval of the OBSS that is terminated early is described as the 'communication interval of the terminated OBSS' or the 'communication interval of the early-terminated OBSS', but is not limited to these terms.

[0120] Referring to FIG. 4a, the non-AP STA 2 (330) can set up a NAV (e.g., Basic NAV) when it receives at least one of the ICF and ICR of the OBSS (or at least one that is not the ICF and ICR of the OBSS). The end time of the basic NAV of the non-AP STA 2 (330) may correspond to the end time of the communication period of the OBSS. Additionally, the non-AP STA 2 (330) can check whether the frame received from the OBSS is a frame that matches at least one of the [NPCA transition conditions]. If the non-AP STA 2 (330) sets up a basic NAV by receiving a frame from the OBSS that matches at least one of the [NPCA transition conditions], the non-AP STA 2 (330) can ignore the CF-End frame (405) when it receives the CF-End frame (405) from the OBSS. That is, the non-AP STA 2 (330) may ignore the CF-End frame (405) that releases the corresponding basic NAV and may not release the basic NAV. Specifically, if the non-AP STA 2 (330) determines that the received CF-End frame is an inter-BSS PPDU received from a BSS other than the BSS containing the non-AP STA 2 (330) (i.e., OBSS), the non-AP STA 2 (330) does not release the basic NAV.

[0121] Meanwhile, if the OBSS that sets the default NAV in the non-AP STA 2 (330) and the OBSS that transmits the CF-End frame are different from each other, the non-AP STA 2 (330) may not release the default NAV regardless of whether the OBSS that sets the default NAV and the OBSS that transmits the CF-End frame are different from each other. Alternatively, if the OBSS that sets the default NAV in the non-AP STA 2 (330) and the OBSS that transmits the CF-End frame are different from each other, the non-AP STA 2 (330) may release the default NAV when it receives the CF-End frame, and this is not limited to a specific form. Due to the NAV that terminates at the end of the communication period of the OBSS, the virtual carrier detection of the non-AP STA 2 (330) detects the medium as occupied during the communication period of the OBSS [NPCA transition condition], and thus cannot perform channel access operations. That is, the non-AP STA 2 (330) may be unable to transmit frames. The non-AP STA 2 (330) can release the NAV at the end of the communication period of the OBSS, and accordingly, the virtual carrier detection can detect the medium as idle. When the physical carrier detection of the non-AP STA 2 (330) also detects the medium as idle, the STA can perform channel access operations (e.g., EDCA backoff operation and EDCA TXOP acquisition procedure) to transmit a frame (407) to AP 1 (310). That is, non-AP STA 2 (330) can transmit a frame (407) by performing a channel access operation after the end of the communication period of OBSS. Since the end of the communication period of OBSS is the time when AP 1 (310) and non-AP STA 1 (320) operate on the main channel again, AP 1 (310) can receive the frame (407) of non-AP STA 2 (330) after that time.That is, the frame (407) of non-AP STA 2 (330) transmitted after the end of the communication period of OBSS can be received by AP 1 (310). Therefore, the transmission of the frame (407) of non-AP STA 2 (330) can be successful. As described above, unnecessary frame transmission failures by non-AP STA 2 (330) can be avoided.

[0122] As another example, the non-AP STA 2 (330) can set the NPCA timer based on the NPCA timer calculation method of the non-AP STA 2 (330) described above. The non-AP STA 2 (330) can release the NAV when it receives the CF-End frame (405) of the OBSS, but the virtual carrier detection can detect the medium as occupied until the NPCA timer expires. That is, the non-AP STA 2 (330) can detect the medium as idle based on the virtual carrier detection only when the NPCA timer expires. When the physical carrier detection of the non-AP STA 2 (330) also detects the medium as idle, the non-AP STA 2 (330) can perform a channel access operation (e.g., EDCA backoff operation and EDCA TXOP acquisition procedure) to transmit the frame to AP 1 (310). Here, the expiration time of the NPCA timer may be the time when AP 1 (310), to which non-AP STA 2 (330) is connected, operates again on the main channel. Alternatively, the expiration time of the NPCA timer may be the time when the TXOP of OBSS ends. That is, non-AP STA 2 (330) can transmit a frame after performing a channel access operation after the time when AP 1 (310) operates again on the main channel and after the end of the communication period of OBSS. As described above, unnecessary frame transmission failures by non-AP STA 2 (330) may not occur.

[0123] Referring to FIG. 4b, the non-AP STA 2 (330) can set up a NAV (e.g., Basic NAV) when it receives at least one of the ICF and ICR of the OBSS (or at least one that is not the ICF and ICR of the OBSS). The end time of the basic NAV of the non-AP STA 2 (330) may correspond to the end time of the communication period of the OBSS. Additionally, the non-AP STA 2 (330) can check whether the frame received from the OBSS is a frame that matches at least one of the [NPCA transition conditions]. If the frame received by the non-AP STA 2 (330) from the OBSS is a frame that matches at least one of the [NPCA transition conditions], the non-AP STA 2 (330) may consider that there are no frames in the transmission queue until the end time of the transmission period of the OBSS (or the expiration time of the NPCA timer of the STA 2). Therefore, the non-AP STA 2 (330) can perform a channel access operation after the default NAV is released and decrease the EDCA backoff counter. When the non-AP STA 2 (330) reaches 0, the EDCA Function (EDCA Function) may need to transmit a frame in the transmission queue at the slot boundary where the backoff counter is 0. Here, if the non-AP STA 2 (330) considers that there is no frame to transmit in the transmission queue, the non-AP STA 2 (330) may keep the backoff counter at 0 because there is no frame to transmit in the non-AP STA 2 (330)'s EDCAF. The non-AP STA 2 (330) may again consider that there is a frame to transmit in the transmission queue at the end of the transmission interval of the OBSS (or at the expiration of the STA 2's NPCA timer). That is, non-AP STA 2 (330) can be considered as having entered the transmission queue for the frame to be transmitted.When the non-AP STA 2 (330) considers that a frame to be transmitted has been entered into the transmission queue, and the medium is idle (e.g., both virtual carrier detection and physical carrier detection detect the medium as idle), the non-AP STA 2 (330) may wait for the AIFS (arbitration interframe space) [AC] time and immediately transmit the frame (408) to AP 1 (310). Here, the AIFS [AC] time may be a single slot with a backoff counter of 0, and transmitting the frame at the AIFS [AC] time may be transmitting the frame at the slot boundary with a backoff counter of 0.

[0124] As another example, non-AP STA 2 (330) can determine whether to transmit a frame by applying a randomly selected transmission probability value p between 0 and 1. non-AP STA 2 (330) may perform transmission if the randomly selected value exceeds a specific transmission probability threshold, and not perform transmission if it does not exceed it. Here, the specific transmission probability threshold may be a value specified by AP 1 (310). When non-AP STA 2 (330) considers that a frame to be transmitted has been entered into the transmission queue, if the medium is occupied (e.g., if the medium is occupied by either virtual carrier detection or physical carrier detection), non-AP STA 2 (330) can select a new backoff counter and perform a channel access operation according to the newly selected backoff counter (i.e., by decrementing the EDCA backoff counter and performing an EDCA TXOP acquisition procedure that causes EDCAF to decide to transmit the frame) to transmit the frame to AP 1 (310).

[0125] As another example, the non-AP STA 2 (330) may stop channel access operations after the default NAV is released. The above-described operation may mean that the non-AP STA 2 (330) stops decreasing the EDCA backoff counter. The non-AP STA 2 (330) may resume channel access operations after the end of the communication period of the OBSS (or, the expiration of the NPCA timer of the STA 2 described above). That is, the decrease of the EDCA backoff counter may resume. When the EDCA backoff counter reaches 0, the EDCAF of the non-AP STA 2 (330) may transmit a frame in the transmission queue at the slot boundary where the backoff counter reached 0, thereby allowing the non-AP STA 2 (330) to transmit a frame to AP 1 (310).

[0126] As another example, the non-AP STA 2 (330) may repeatedly perform channel access operations (an EDCA backoff operation to select an EDCA backoff counter and an EDCA TXOP acquisition procedure to decrement the EDCA backoff counter and allow the EDCAF to decide to transmit the frame) after the basic NAV is released. The non-AP STA 2 (330) may repeat the operation of decrementing the backoff counter within the transmission interval of the OBSS, and when the backoff counter reaches 0, not transmitting the frame, selecting a new backoff counter, and decrementing the backoff counter. In the above process, the CW[AC] and QSRC[AC] of the non-AP STA 2 (330) may not change. If the time when the backoff counter of non-AP STA 2 (330) reaches 0 is after the end time of the communication period of OBSS (or, the time when the NPCA timer of the STA 2 described above expires), non-AP STA 2 (330) can transmit a frame to AP 1 (310) at the slot boundary where the backoff counter reached 0.

[0127] In the operation related to FIG. 4b described above, non-AP STA 2 (330) can transmit a frame (408) after the end of the communication period of OBSS (or, the expiration time of the NPCA timer of STA 2 described above). Here, the end of the communication period of OBSS may be the time when AP 1 (310) and non-AP STA 1 (320) operate on the main channel again, and after that time, AP 1 (310) may be able to receive the frame of non-AP STA 2 (330). That is, the frame (408) of non-AP STA 2 (330) transmitted after the end of the communication period of OBSS can be received by AP 1 (310). Therefore, the transmission of the frame (408) of non-AP STA 2 (330) can be successful, and unnecessary frame transmission failures by non-AP STA 2 (330) may not occur.

[0128] Referring to FIG. 4c, the non-AP STA 2 (330) can set up a NAV (e.g., Basic NAV) when it receives at least one of the ICF and ICR of the OBSS (or at least one frame that is not the ICF and ICR of the OBSS). The end time of the basic NAV of the non-AP STA 2 (330) may correspond to the end time of the communication period of the OBSS. Additionally, the non-AP STA 2 (330) can check whether the frame received from the OBSS is a frame that matches at least one of the [NPCA transition conditions]. If the non-AP STA 2 (330) sets up a basic NAV by receiving a frame from the OBSS that matches at least one of the [NPCA transition conditions], the non-AP STA 2 (330) can release the basic NAV when it receives a CF-End frame (405) from the OBSS. non-AP STA 2 (330) can transmit a frame (409) to AP 1 (310) by releasing the basic NAV and performing a channel access operation (i.e., performing an EDCA backoff operation to select an EDCA backoff counter and an EDCA TXOP acquisition procedure to decrease the EDCA backoff counter and allow EDCAF to decide to transmit the frame). However, if the transmission of the frame (409) by non-AP STA 2 (330) is performed within the communication interval of OBSS, the transmission of the frame (409) by non-AP STA 2 (330) may fail.Here, when the transmission of a frame (409) by non-AP STA 2 (330) is performed within the communication interval of OBSS, and non-AP STA 2 (330) receives a frame from OBSS that matches at least one of the [NPCA switching conditions] and confirms the communication interval of OBSS, non-AP STA 2 (330) may not increase CW[AC] and QSRC[AC] even if the transmission of the frame (409) fails within the confirmed communication interval of OBSS (or, if the NPCA timer of the STA 2 described above has not expired). That is, although frame transmission failure by non-AP STA 2 (330) may occur, since non-AP STA 2 (330) does not increase the channel access parameters, non-AP STA 2 (330) may not suffer any disadvantage when accessing the channel.

[0129] As another example, referring to FIG. 4d, OBSS can exchange information with BSS 1 regarding whether to perform an NPCA operation. Specifically, the AP of OBSS (hereinafter referred to as OBSS AP) and AP 1 (310), which is the AP of BSS 1, can exchange information regarding whether to perform an NPCA operation. The aforementioned operation can be exchanged through at least one of a control frame, a management frame, a data frame, and other frames containing a MAPC (Multi-AP coordination) element, a Multi-Link element, and an OMP (operation mode and parameter) action field. That is, AP 1 (310) of BSS 1 and OBSS AP can exchange information regarding whether to perform the aforementioned NPCA operation based on a MAPC framework that exchanges and negotiates operation information through the MAPC element. Alternatively, operation information may be exchanged based on other elements or fields (e.g., Multi-Link element, OMP action field) other than the MAPC element within the MAPC framework. Alternatively, operational information regarding whether to perform the aforementioned NPCA operation between AP 1 (310) and OBSS AP can be exchanged via a separate inter-AP communication layer (e.g., SMD (seamless mobility domain)-ME (management entity)) rather than the MAPC framework. Among the examples of the separate inter-AP communication layer described above, the SMD is an area for management and information exchange within multiple APs, and is a group between APs or AP MLDs (multi-link devices). For example, AP 1 (310) and OBSS AP may belong to (or be linked to) the same SMD. In the above case, AP 1 (310) and OBSS AP can exchange operational information with each other through the SMD-ME.Operation information exchange within the SMD-ME may use SMD elements including SMD Information elements, but it is possible to use message formats that are not separately defined. The OBSS (i.e., the OBSS AP managing the transmission parameters of the OBSS and at least one non-AP STA connected to the OBSS AP) may not terminate the communication period (e.g., TXOP) of the OBSS early when it is confirmed that BSS 1 is performing an NPCA operation. That is, the OBSS may not cut the TXOP when BSS 1 is performing an NPCA operation. In the above case, the OBSS exchanges ICF and ICR on the main channel, and the non-AP STA 2 (330) may set a default NAV corresponding to the communication period of the OBSS. Here, the OBSS may not cut the TXOP and may not transmit a CF-End frame. Therefore, a situation in which the non-AP STA 2 (330) releases the default NAV corresponding to the communication period of the OBSS may not occur. For example, if the OBSS AP is a TXOP holder, the OBSS AP does not perform the operation to cut the TXOP when it is confirmed that AP 1 (310) is performing an NPCA operation. Additionally, the OBSS AP can instruct the non-AP STA of the OBSS not to cut the TXOP by transmitting a management frame (e.g., a management frame including a beacon frame, a probe response frame, etc.) containing an indicator that prevents at least one non-AP STA connected to the OBSS AP from cutting the TXOP.

[0130] Meanwhile, the OBSS non-AP STA may not be able to perform the operation of truncation of TXOPs. The OBSS non-AP STA may not be able to interpret the indicator that prevents the aforementioned TXOP from being truncation. For example, if the OBSS non-AP STA is a non-AP STA using a wireless LAN standard that cannot interpret the indicator of a management frame transmitted by the OBSS AP (legacy non-AP STA), the non-AP STA may not be able to recognize the indicator that prevents the aforementioned TXOP from being truncation, and consequently may not be able to perform the operation of truncation of TXOPs. Alternatively, the OBSS AP may not have transmitted the indicator that prevents the TXOP from being truncation. Alternatively, the OBSS non-AP STA may not support not truncation of TXOPs. If at least one of the cases described above is established (occurs), and the OBSS non-AP STA is the TXOP holder, the OBSS non-AP STA may transmit a CF-End frame to perform TXOP truncation. That is, the TXOP of the OBSS non-AP STA is truncation. Meanwhile, the CF-End frame contains (indicates) the OBSS AP's BSSID (basic service set identifier). When the OBSS AP receives the CF-End frame from the OBSS non-AP STA, it is possible to respond to the CF-End frame. The OBSS AP may transmit a response frame to the CF-End frame after SIFS. An OBSS AP is a frame that can occupy the medium until the end of transmission of the first TXOP of the OBSS non-AP STA before the time length is truncated (e.g., physically occupying the medium until the end of transmission of the first TXOP, or virtual medium detection (e.g., NAV) information included in the MAC header or PPDU preamble (e.g.It is possible to transmit a response frame in which the value of the duration / ID field of the MAC header or the value of the TXOP_DURATION field of the PPDU preamble instructs the medium to be occupied until the end of the initial TXOP. Various frames may be used as response frames for the CF-End frame of the OBSS AP described above, excluding frames intended to release NAV like the CF-End frame. The OBSS AP performs medium occupancy during the initial TXOP period even if the TXOP of the OBSS non-AP STA is cut off.

[0131] In the above-described case, when non-AP STA 2 (330) detects the medium as idle through virtual carrier detection and physical carrier detection after the communication period of OBSS, it can perform a channel access operation (i.e., perform an EDCA backoff operation to select an EDCA backoff counter and an EDCA TXOP acquisition procedure to decrease the EDCA backoff counter and allow EDCAF to decide on frame transmission) and transmit a frame to AP 1 (310). Here, since the end point of the communication period of OBSS is the point when AP 1 (310) and non-AP STA 1 (320) operate on the main channel again, AP 1 (310) can receive the frame (410) of non-AP STA 2 (330) after that point. That is, the frame (410) of non-AP STA 2 (330) transmitted after the end point of the communication period of OBSS can be received by AP 1 (310). Therefore, the transmission of frames (410) by non-AP STA 2 (330) can be successful, and unnecessary frame transmission failures by non-AP STA 2 (330) can not occur.

[0132] Meanwhile, in FIGS. 4a and 4b, when non-AP STA 2 (330) receives a frame transmitted by AP 1 (310) while waiting for frame transmission to AP 1 (310) during the time interval corresponding to the OBSS TXOP on the BSS main channel, non-AP STA 2 (330) can confirm that AP 1 (310) is operating again on the BSS main channel. That is, non-AP STA 2 (330) no longer needs to wait for frame transmission to AP 1 (310) on the BSS main channel. non-AP STA 2 (330) can initialize at least one of the default NAV and NPCA timers on the BSS main channel. Alternatively, non-AP STA 2 (330) does not need to wait for the EDCA backoff counter to be set to zero or repeat. The non-AP STA 2 (330) can perform a transmission procedure (e.g., transmit the frame after performing at least one of the EDCA backoff procedure and the EDCA TXOP acquisition procedure, or transmit the frame immediately) for a frame transmitted to AP 1 (310).

[0133] As another example, in FIG. 4b, the non-AP STA 2 (330) may directly transmit communication data during the time interval when AP 1 (310) is operating on the NPCA main channel. That is, it may be possible for AP 1 (310) to transmit or receive frames to a non-destination STA. If there is a data frame that the non-AP STA 2 (330) can transmit to the non-destination STA of AP 1 (310), the non-AP STA 2 (330) does not need to keep the EDCA backoff counter at 0 or repeat backoff until AP 1 (310) operates on the main channel again, and the non-AP STA 2 (330) can transmit the data frame to the non-destination STA of AP 1 (310) when it acquires an EDCA TXOP.

[0134] FIGS. 5A and 5B are drawings illustrating a method for preventing frame transmission failure during wireless LAN subchannel access operation applicable to the present disclosure.

[0135] Referring to FIGS. 5a and 5b, AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) of BSS 1 according to FIG. 3 can be operated. Specifically, AP 1 (310) and non-AP STA 1 (320) support NPCA operation, and non-AP STA 2 (330) does not support NPCA operation, but it can be recognized that NPCA operation is used in BSS 1. However, this is for convenience of explanation only and is not limited thereto. The APs and STAs of BSS 1 (i.e., AP 1 and STA 1, STA 2) can receive at least one of the ICF and ICR of OBSS. AP 1 (310) and non-AP STA 1 (320) may operate by switching the operating channel to the NPCA main channel during the OBSS communication period identified in at least one of the ICF and ICR of the OBSS. Alternatively, AP 1 (310) and non-AP STA 1 (320) may operate by switching the operating channel to the NPCA main channel during the OBSS communication period identified based on the PPDU length information in the PPDU header identified by receiving the PPDU of the OBSS and the TXOP information of the OBSS. Here, since non-AP STA 2 (330) does not support NPCA operation, it may operate on the main channel without switching the operating channel to the NPCA main channel. However, if non-AP STA 2 (330) receives a frame in which at least one of the [NPCA transition conditions] conditions matches, non-AP STA 2 (330) recognizes that AP 1 (310) and non-AP STA 1 (320) are performing NPCA operations, and can recognize the period in which the NPCA operations are performed. For example, the communication period of OBSS may be terminated early by transmitting a CF-End frame (405) as described above. For example, the communication period of OBSS described below may indicate an OBSS communication period of [NPCA transition conditions] that was not terminated early.The communication interval of the OBSS that is terminated early is described as the 'communication interval of the terminated OBSS' or the 'communication interval of the early-terminated OBSS,' but is not limited to these terms.

[0136] The non-AP STA 2 (330) can set a NAV (e.g., basic NAV) by receiving at least one of the ICF and ICR of the OBSS. Alternatively, it can set a NAV by receiving at least one frame other than the ICF and ICR of the OBSS. Here, the end time of the basic NAV of the non-AP STA 2 (330) may correspond to the end time of the communication period of the OBSS. The non-AP STA 2 (330) can receive a CF-End frame (405) from the OBSS within the time period in which the basic NAV is set and release the basic NAV. When the basic NAV is released, the non-AP STA 2 (330) can transmit a frame to AP 1 (310) by performing a channel access operation (i.e., an EDCA backoff operation that selects an EDCA backoff counter and an EDCA TXOP acquisition procedure that decreases the EDCA backoff counter and causes the EDCAF to decide to transmit the frame).

[0137] For example, referring to FIG. 5a, AP 1 (310) can check both the NPCA main channel and the frames (411, 412) received on the main channel. Additionally, AP 1 (310) can transmit frames on both the NPCA main channel and the main channel. In the above case, AP 1 (310) can receive the frame (412) transmitted by non-AP STA 2 (330) to AP 1 (310) on the main channel, and AP 1 (310) can transmit a response frame (413) for the data frame (412) of non-AP STA 2 (330). Here, 'AP 1 (310) can transmit and receive on both the NPCA main channel and the main channel' may be one of the following two cases.

[0138] 1. AP 1 (310) is an AP belonging to an AP MLD (multi-link device), and AP 2 may also operate in the AP MLD. AP 1 (310) may be an AP where the AP MLD operates on the first link, and AP 2 may be an AP where the AP MLD operates on the second link. Therefore, when AP 1 (310) operates on the NPCA main channel, AP 2 can perform frame transmission and reception operations on the main channel of the first link. During the period when AP 1 (310) is performing NPCA operations, AP 2 may not be able to transmit or receive frames on the second link.

[0139] 2. A portion of the radio chain of AP 1 (310) may be used for transmitting and receiving frames on the main channel. In the above case, when AP 1 (310) is operating on the NPCA main channel, the number of spatial streams may be reduced, the modulation and coding index (MCS) may be lowered, and the transmittable frame format and bandwidth may be reduced. Here, at least one of the reduced MCS of AP 1 (310)—the number of spatial streams (NSS), transmittable frame format, operating bandwidth, and other values—may be indicated in a beacon frame that AP 1 (310) broadcasts to the STAs, or may be exchanged with the STAs connected to AP 1 (310) through a separate frame (e.g., an action frame).

[0140] In the case of using one of the above-described cases, the transmission of a frame sent by non-AP STA 2 (330) to AP 1 (310) on the main channel may not fail.

[0141] As another example, referring to FIG. 5b, AP 1 (310) can check both the NPCA main channel and the frames (414, 415) received on the main channel. However, AP 1 (310) may only be able to transmit frames on the NPCA main channel. In the above case, AP 1 (310) may receive the frame (415) transmitted by non-AP STA 2 (330) to AP 1 (310) on the main channel, but may not be able to transmit a response frame. Since AP 1 (310) did not transmit a response frame, non-AP STA 2 (330) determines that the transmission of the frame (415) failed and may increase the channel access parameters CW[AC] and QSRC[AC]. AP 1 (310) can transmit a response frame for a data frame (415) transmitted by non-AP STA 2 (330) after the end of the communication period of OBSS. When non-AP STA 2 (330) receives the response frame from AP 1 (310), it can set CW[AC] and QSRC[AC] to their values ​​before incrementing or initialize them (e.g., initialize CW[AC] to the value of CWmin[AC] and initialize QSRC[AC] to 0). As another example, AP 1 (310) can receive a frame transmitted by non-AP STA 2 (330) on the main channel, so it can recognize that non-AP STA 2 (330) has transmitted a frame. AP 1 (310) can transmit a Trigger Frame after performing a channel access procedure to allow non-AP STA 2 (330) to retransmit a frame after the end of the communication period of OBSS. non-AP STA 2 (330) can receive the Trigger Frame from AP 1 (310) and, after SIFS, transmit the frame using the resources allocated in the Trigger Frame. After receiving the above-mentioned frame, AP 1 (310) can transmit a response Frame to non-AP STA 2 (330) after SIFS.

[0142] FIGS. 6a to 6c are drawings illustrating a method for preventing frame transmission failure during wireless LAN subchannel access operation applicable to the present disclosure.

[0143] Referring to FIGS. 6a through 6c, AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) of BSS 1 according to FIG. 3 can be operated. Specifically, AP 1 (310) and non-AP STA 1 (320) support NPCA operation, and non-AP STA 2 (330) does not support NPCA operation, but it can be recognized that NPCA operation is used in BSS 1. However, this is for convenience of explanation only and is not limited thereto. The APs and STAs of BSS 1 (i.e., AP 1 and STA 1, STA 2) can receive at least one of the ICF and ICR of OBSS. AP 1 (310) and non-AP STA 1 (320) may switch the operating channel to the NPCA main channel during the OBSS communication period identified in at least one of the ICF and ICR of the OBSS. Here, since non-AP STA 2 (330) does not support NPCA operation, it may operate on the main channel without switching the operating channel to the NPCA main channel. However, if non-AP STA 2 (330) receives a frame in which at least one of the [NPCA switching conditions] conditions is met, non-AP STA 2 (330) may recognize that AP 1 (310) and non-AP STA 1 (320) are performing NPCA operation and may recognize the period in which the NPCA operation is performed.

[0144] Referring to FIGS. 6a and 6b, AP 1 (310) and non-AP STA 1 (320) can receive the ICF (416) and ICR (417) of the OBSS. AP 1 (310) and non-AP STA 1 (320) can check whether the ICF (416) and ICR (417) of the OBSS contain information related to TXOP truncation. TXOP truncation of the OBSS may mean that transmission is to be terminated before a transmission-unable period due to in-device coexistence (IDC) of the OBSS STA. Alternatively, TXOP truncation of the OBSS may mean that transmission is to be terminated before the R (restricted)-TWT (target wake time) SP of the OBSS or the R-TWT SP that the OBSS must protect, but is not limited thereto.

[0145] Referring to FIG. 6a, AP 1 (310), non-AP STA 1 (320) and non-AP STA 2 (330) receive the ICF (416) and ICR (417) of the OBSS and can confirm that the ICF (416) and ICR (417) do not contain information regarding TXOP truncation. AP 1 (310) and non-AP STA 1 (320) can perform NPCA operations during the communication period of the OBSS indicated in the ICF (416) and ICR (417) (i.e., the untruncation of the OBSS TXOP). The communication period of the OBSS on the main channel is not terminated early, and the non-AP STA 2 (330) operating on the main channel without moving to the NPCA main channel can transmit a frame by performing a channel access operation after the communication period of the OBSS has ended (i.e., by performing an EDCA backoff operation to select an EDCA backoff counter and an EDCA TXOP acquisition procedure to decrease the EDCA backoff counter and allow EDCAF to decide to transmit the frame). Since the end point of the OBSS communication period is the point when AP 1 (310) and non-AP STA 1 (320) operate on the main channel again, AP 1 (310) can receive frames from non-AP STA 2 (330) after that point. That is, frames (418) from non-AP STA 2 (330) transmitted after the end point of the communication period of the OBSS can be received by AP 1 (310). Therefore, the transmission of the frame (418) of non-AP STA 2 (330) can be successful.

[0146] Referring to FIG. 6b, AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) receive the ICF (416) and ICR (417) of the OBSS, and can see that the ICF (416) and ICR (417) contain information regarding TXOP truncation. For example, the end time of the OBSS TXOP indicated by the duration field value indicated in the ICR (417) may be shorter than the end time of the OBSS TXOP indicated by the duration field value indicated in the ICF (416). In the above case, AP 1 (310) and non-AP STA 1 (320) can perform an NPCA operation during the communication period of the OBSS that is terminated early (i.e., the truncation of the OBSS TXOP) indicated in the ICR (417). The communication period of the OBSS on the main channel may be terminated early. Accordingly, the OBSS can cut off the TXOP of the OBSS by sending a CF-End frame (421) after completing the exchange of the ICF (416), ICR (417), data frame (419), and response frame (420). AP 1 (310) and non-AP STA 1 (320) can operate on the main channel at the time when the OBSS cuts off the TXOP (i.e., the time when the communication period of the OBSS is terminated early). When non-AP STA 2 (330) receives the CF-End frame (421) of the OBSS, it can release the default NAV corresponding to the communication period of the OBSS that was not terminated early, which is set based on the ICF (416) sent by the OBSS.Here, since the time when AP 1 (310) is operating on the main channel and the time when non-AP STA 2 (330) releases the basic NAV coincide, when non-AP STA 2 (330) operating on the main channel after that time performs a channel access operation (i.e., an EDCA backoff operation to select an EDCA backoff counter and an EDCA TXOP acquisition procedure to decrease the EDCA backoff counter and cause EDCAF to decide to transmit the frame) and transmits a frame, AP 1 (310) can receive the frame (422) of non-AP STA 2 (330). Therefore, the frame transmission of non-AP STA 2 (330) can be successful.

[0147] Referring to FIG. 6c, AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) can receive only the ICF (416) of the OBSS. For example, AP 1 (310), non-AP STA 1 (320), and non-AP STA 2 (330) can receive only the ICF (416) of the OBSS due to IDC and may not receive the ICR (417). Here, if AP 1 (310) and non-AP STA 1 (320) of the BSS 1 receive only the ICF (416) of the OBSS, they may not operate on the NPCA main channel. Subsequently, AP 1 (310) and non-AP STA 1 (320) can receive the data frame (419) of the OBSS and confirm that the communication period of the OBSS has ended early. For example, the end time of the TXOP of the OBSS indicated in the OBSS data frame (419) may be shorter than the end time of the TXOP of the OBSS indicated by the duration field value indicated in the ICF (416). The remaining length of the TXOP of the OBSS may be indicated in the TXOP field of the PHY preamble of the OBSS data frame (419). Alternatively, the remaining length of the TXOP of the OBSS may be indicated through the MAC header duration field of the OBSS data frame (419). In the above case, AP 1 (310) and non-AP STA 1 (320) may perform an NPCA operation during the communication period of the OBSS indicated in the data frame (419) (i.e., the cut TXOP of the OBSS). That is, the communication period of the OBSS on the main channel may be terminated early. OBSS can cut off the TXOP of OBSS by sending a CF-End frame (421) after completing the exchange of ICF (416), ICR (417), data frame (419), and response frame (420). AP 1 (310) and non-AP STA 1 (320) can operate on the main channel at the time when OBSS cuts off the TXOP (i.e., when the communication period of OBSS ends early).When non-AP STA 2 (330) receives the CF-End frame (421) of the OBSS, it can release the default NAV corresponding to the communication interval of the OBSS that was not terminated early, which is set via the ICF (416) transmitted by the OBSS. Here, since the time when AP 1 (310) operates on the main channel and the time when non-AP STA 2 (330) releases the default NAV coincide, when non-AP STA 2 (330) operating on the main channel after that time performs a channel access operation (i.e., an EDCA backoff operation to select the EDCA backoff counter and an EDCA TXOP acquisition procedure to decrease the EDCA backoff counter and cause the EDCAF to decide to transmit the frame) and transmits the frame (423), AP 1 (310) can receive the frame from non-AP STA 2 (330). Therefore, the transmission of the frame (423) of non-AP STA 2 (330) can be successful.

[0148] 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 detects an overlapping basic service set (OBSS) transmission in the main channel and can set a network allocation vector (NAV) in the main channel during a transmit opportunity (TXOP) corresponding to the transmission within the OBSS (S710). Here, the first STA is a STA that does not perform non-primary channel access (NPCA) operations, and the second STA connected to the first STA is a STA that supports NPCA operations, so that during the TXOP corresponding to the transmission within the OBSS, the operating channel can be switched from the main channel to the NPCA channel to operate. After that, the first STA can receive a contention-free (CF)-end frame transmitted from the OBSS (S720). Here, the CF-End frame can indicate the cutting of the TXOP in the OBSS and the release of the NAV in the main channel. After that, the first STA can transmit a frame to the second STA by performing channel access on the main channel at a time determined based on the time of return to the second STA's main channel or the scheduled time of termination of the OBSS's TXOP (S730). Here, when the first STA receives a CF-End frame, the first STA determines that the second STA has switched to the NPCA channel if the transmission of the OBSS satisfies a preset NPCA switching condition, maintains the NAV set based on the OBSS's TXOP, and can transmit a frame by performing channel access on the main channel after the OBSS's TXOP.

[0149] Additionally, when the first STA receives a CF-End frame, the first STA may release NAV and perform an enhanced distributed channel access (EDCA) TXOP acquisition procedure based on channel access. If the transmission of the OBSS satisfies a preset NPCA switching condition, the first STA determines that the second STA has switched to the NPCA channel and waits for the EDCA backoff counter, which was reduced through the EDCA TXOP acquisition procedure during the OBSS TXOP, to be set to 0, or after repeatedly performing the EDCA backoff procedure and the EDCA TXOP acquisition procedure, transmits a frame from the main channel to the second STA after the OBSS TXOP.

[0150] Additionally, when the first STA receives a CF-End frame, the first STA may release NAV and attempt to transmit a frame from the main channel to the second STA by performing an enhanced distributed channel access (EDCA) TXOP acquisition procedure based on channel access. Additionally, if the frame transmission attempted by the first STA on the main channel fails, the first STA may determine that the second STA has switched to the NPCA channel and maintain the channel access parameters if the transmission of the OBSS satisfies a preset NPCA switching condition. Here, the channel access parameters may include QoS STA retry count (QSRC) values ​​and contention window (CW) values ​​for each access category (AC).

[0151] Additionally, if the second STA is an MLD (multi-link device) STA, the first link of the second STA is switched to operate on the NPCA main channel, and the second link of the second STA is operated on the main channel. When the first STA receives a CF-End frame, it can transmit a frame on the second link of the second STA operating on the main channel. Additionally, when the first STA receives a CF-End frame, it can perform frame transmission to the second STA, which includes a radio chain operating for the NPCA main channel and a radio chain operating for the main channel. Additionally, if the first STA does not support NPCA operation or supports NPCA operation but has disabled NPCA operation, the first STA may not perform NPCA operation. Additionally, the first STA may be a non-AP STA or an AP STA.

[0152] As another example, the first STA may obtain information indicating that the adjacent second STA activates NPCA operation based on negotiation with the second STA. Subsequently, the first STA may obtain a TXOP and transmit data. Here, the channel occupied by the first STA based on the TXOP obtained may overlap with the second STA's main channel. Subsequently, even if data transmission is completed earlier than the end time of the TXOP, the first STA may not transmit a CF-End frame and may maintain media occupancy or leave it idle until the end time of the TXOP to protect the second STA's NPCA operation. Here, the first STA and the second STA are AP STAs, and the basic service set (BSS) of the first STA and the BSS of the second STA may overlap.

[0153] As another example, the first STA may detect the transmission of an OBSS on the main channel and, as the transmission of the OBSS satisfies the NPCA switching condition, switch the operating channel from the main channel to the NPCA channel. Information regarding the TXOP cutting or early termination of the OBSS may be obtained from at least one frame included in the transmission of the OBSS. Afterward, the first STA determines a time to terminate the operation on the NPCA channel and return to the main channel based on the obtained information, and at the determined time, returns to the main channel and receives a frame transmitted from the second STA on the main channel.

[0154] Here, when an initial control frame (ICF) and an initial control response (ICR) exchange is performed within the OBSS, the first STA can determine the time to return from the NPCA channel to the main channel based on whether the ICF and ICR contain information related to TXOP cutting or early termination. Additionally, if the ICF and ICR do not contain information related to TXOP cutting, the cutting or early termination of the TXOP of the OBSS is not performed, and the time to return from the NPCA channel to the main channel of the first STA is determined after the TXOP of the OBSS, and the first STA can receive a frame from the second STA after the TXOP. Additionally, if the ICF and ICR contain information related to TXOP cutting, the cutting or early termination of the TXOP of the OBSS is performed, and the time at which the first STA returns from the NPCA channel to the main channel is determined based on the cutting or early termination of the TXOP, and the first STA can receive a frame transmitted from the second STA on the main channel after returning to the main channel at the determined time.

[0155] Additionally, among the ICF, ICR, and data frames exchanged within the OBSS, if the ICR cannot be received within the BSS containing the first STA and the ICF and data frames within the OBSS contain information related to TXOP cutting or early termination, the time at which the first STA returns from the NPCA channel to the main channel is determined based on the information related to TXOP cutting or early termination contained in the data frames, and the first STA can receive a frame transmitted from the second STA on the main channel after returning to the main channel at the determined time.

[0156] 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.

[0157]

[0158] 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 first STA detects an overlapping basic service set (OBSS) transmission on the main channel and sets a network allocation vector (NAV) on the main channel during a transmit opportunity (TXOP) corresponding to the transmission within the OBSS, wherein the first STA is a STA that does not perform non-primary channel access (NPCA) operations, and the second STA to which the first STA is connected is a STA that supports NPCA operations, and the operating channel is switched from the main channel to the NPCA channel during the TXOP corresponding to the transmission within the OBSS; A step of receiving a CF (contention free)-end frame transmitted from the OBSS, wherein the CF-End frame indicates the cutting of the TXOP of the OBSS and the release of the NAV in the main channel; and A method of operation comprising the step of transmitting a frame to the second STA by performing channel access on the main channel at a time determined based on the time of return of the second STA to the main channel or the scheduled time of termination of the TXOP of the OBSS.

2. In Paragraph 1, A method of operation in which, when the first STA receives the CF-End frame, the first STA determines that the second STA has switched to the NPCA channel when the transmission of the OBSS satisfies a preset NPCA switching condition, maintains the NAV set based on the TXOP of the OBSS, and performs the channel access on the main channel after the TXOP of the OBSS to transmit the frame.

3. In Paragraph 1, A method of operation in which, when the first STA receives the CF-End frame, the first STA releases the NAV and performs an enhanced distributed channel access (EDCA) TXOP acquisition procedure based on the channel access, wherein the first STA determines that the second STA has switched to the NPCA channel when the transmission of the OBSS satisfies a preset NPCA switching condition, and waits for the EDCA backoff counter reduced through the EDCA TXOP acquisition procedure during the TXOP of the OBSS to be set to 0, or after repeating the EDCA backoff procedure and the EDCA TXOP acquisition procedure, transmits the frame from the main channel to the second STA after the TXOP of the OBSS.

4. In Paragraph 1, A method of operation in which, when the first STA receives the CF-End frame, the first STA releases the NAV and performs an EDCA (enhanced distributed channel access) TXOP acquisition procedure based on the channel access to attempt to transmit the frame to the second STA on the main channel.

5. In Paragraph 4, A method of operation in which, if the frame transmission attempted by the first STA on the main channel fails, the first STA determines that the second STA has switched to the NPCA channel when the transmission of the OBSS satisfies a preset NPCA switching condition, and maintains channel access parameters, wherein the channel access parameters include QSRC (QoS STA retry count) values ​​and CW (contention window) values ​​for each AC (access categories).

6. In Paragraph 1, A method of operation in which, when the second STA is an MLD (multi-link device) STA, the first link of the second STA is switched to and operated on the NPCA main channel, the second link of the second STA is operated on the main channel, and when the first STA receives the CF-End frame, the frame is transmitted on the second link of the second STA operating on the main channel.

7. In Paragraph 1, A method of operation in which the first STA, upon receiving the CF-End frame, performs the frame transmission to the second STA, which includes a radio chain operating for the NPCA main channel and a radio chain operating for the main channel.

8. In Paragraph 1, A method of operation in which, if the first STA does not support the NPCA operation or supports the NPCA operation but disables the NPCA operation, the first STA does not perform the NPCA operation.

9. In Paragraph 1, A method of operation in which the first STA is a non-AP STA or an AP STA.

10. A method of operation of a first station (station, STA) in a wireless LAN system, A step of the first STA obtaining information indicating that an adjacent second STA activates an NPCA operation based on negotiation with the second STA; The method includes the step of the first STA acquiring a TXOP and transmitting data, wherein the channel occupied by the first STA based on the acquired TXOP overlaps with the main channel of the second STA; and A method of operation comprising the step of the first STA maintaining media occupancy or leaving it idle until the end of the TXOP without transmitting a CF-End frame to protect the NPCA operation of the second STA, even if the data transmission is completed earlier than the end of the TXOP.

11. In Paragraph 10, A method of operation in which the first STA and the second STA are AP STAs, and the BSS (basic service set) of the first STA and the BSS of the second STA overlap.

12. In a method of operation of a first station (station, STA) in a wireless LAN system, The step of the first STA detecting the transmission of an OBSS in the main channel, and switching the operating channel from the main channel to the NPCA channel as the transmission of the OBSS satisfies the NPCA switching condition; A step of obtaining information regarding the TXOP truncation or early termination of the OBSS from at least one frame included in the transmission of the OBSS; A step of determining a time to terminate the operation in the NPCA channel and return to the main channel based on the information obtained above; and A method of operation comprising the step of returning to the main channel at the determined time and receiving a frame transmitted from the second STA on the main channel.

13. In Paragraph 12, A method of operation in which, when an initial control frame (ICF) and an initial control response (ICR) exchange is performed within the above OBSS, the first STA determines the time to return from the NPCA channel to the main channel based on whether the ICF and the ICR contain information related to TXOP cutting or early termination.

14. In Paragraph 13, A method of operation in which, if the ICF and the ICR do not include information related to the TXOP cutting, the cutting or early termination of the TXOP of the OBSS is not performed, the time at which the first STA returns from the NPCA channel to the main channel is determined after the TXOP of the OBSS, and the first STA receives the frame from the second STA after the TXOP.

15. In Paragraph 13, A method of operation in which, if the ICF and the ICR contain information related to the TXOP cutting, the cutting or early termination of the TXOP of the OBSS is performed, the time at which the first STA returns from the NPCA channel to the main channel is determined based on the cutting or early termination of the TXOP, and the first STA returns to the main channel at the determined time and receives the frame transmitted from the second STA in the main channel.

16. In Paragraph 12, If, among the ICF, ICR, and data frames exchanged within the above OBSS, the ICR is unreceiveable within the BSS containing the first STA, and the ICF and data frames within the above OBSS contain information related to the TXOP truncation or early termination, A method of operation in which the time at which the first STA returns from the NPCA channel to the main channel is determined based on information related to the TXOP truncation or early termination included in the data frame, and the first STA returns to the main channel at the determined time and receives the frame transmitted from the second STA in the main channel.

17. In a wireless LAN system, regarding a 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: Detecting an overlapping basic service set (OBSS) transmission on the main channel, and setting a network allocation vector (NAV) on the main channel during a transmit opportunity (TXOP) corresponding to the transmission within the OBSS, wherein the STA is a STA that does not perform non-primary channel access (NPCA) operations, and another STA connected to the STA supports NPCA operations, and the operating channel is switched from the main channel to the NPCA channel during the TXOP corresponding to the transmission within the OBSS. Receive a CF (contention free)-End frame transmitted from the above OBSS, wherein the CF-End frame instructs the cutting of the TXOP of the above OBSS and the release of NAV in the main channel, and A STA that transmits a frame to the other STA by performing channel access on the main channel at a time determined based on the time of return of the other STA to the main channel or the scheduled time of termination of the TXOP of the OBSS.

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