Method and apparatus for performing non-primary channel access operation in wireless LAN

Abstract

An operation method of a station (STA) in a wireless LAN system may comprise the steps of: receiving, by the STA, at least one frame from an overlapping basic service set (OBSS) while operating on a primary channel; identifying bandwidth information of a frame exchanged within the OBSS through the received at least one frame; determining, by means of the bandwidth information, whether or not to perform a non-primary channel access (NPCA) operation; and when performing the NPCA operation, switching, by the STA, a channel from the primary channel of the STA to an NPCA primary channel.

Description

Method and device for performing side channel access operation in wireless LAN

[0001] The present disclosure relates to a method and device for performing communication based on a non-primary channel (subchannel) in a wireless local area network (WLAN). Specifically, the present disclosure relates to a method for performing communication by performing a subchannel access operation after a WLAN terminal supporting a subchannel access operation receives a frame (OBSS frame) transmitted from an adjacent OBSS (overlapping basic service set), checking the transmission bandwidth of the OBSS frame to determine whether a subchannel is occupied, and then performing a subchannel access operation when receiving the frame. In addition, the present disclosure relates to a method for performing communication by taking into account a case where an access point (AP) and an STA have different channel states when using a subchannel.

[0002]

[0003] With the recent proliferation of mobile devices, wireless local area network (WLAN) technology, which can provide fast wireless communication services to these devices, is attracting significant attention. WLAN technology utilizes short-range wireless communication technology to enable mobile devices such as smartphones, tablets, laptops, portable multimedia players, and embedded devices to wirelessly access the Internet.

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

[0005] As applications requiring higher reliability arise, the IEEE 802.11bn standard, an Ultra High Reliability (UHR) wireless LAN technology, is being developed in a single Basic Service Set (BSS) environment and / or redundant BSS environments. The goals of the IEEE 802.11bn standard may support increased data transmission speed, improved latency performance, and improved data error rate. In addition, the IEEE 802.11bn standard may support low-power operation, peer-to-peer communication, and operations for increased channel utilization. In addition, the IEEE 802.11bn standard may support a TXOP sharing method in which wireless LAN terminals share a communication resource, a TXOP, between APs. In addition, the wireless LAN standard may support non-primary channel access (NPCA) operation and dynamic subchannel operation (DSO), which use a channel other than the primary channel when the primary channel is occupied, to increase the efficiency of communication resource utilization.

[0006] Below, a sub-channel access operation according to the transmission bandwidth of the OBSS and a sub-channel access method that considers different channel states of the AP and STA are described.

[0007] Meanwhile, the technology that serves as the background for the invention is written to promote understanding of the background for the invention, and may include content that is not a prior art already known to a person with ordinary skill in the field to which the technology belongs.

[0008]

[0009] The present disclosure relates to a method and device for performing a side-channel access operation in a wireless LAN.

[0010] The present disclosure relates to a method and device for enabling an AP to respond to an STA through a side channel or to stop a transmission attempt by an STA and perform a new communication operation on the side channel when performing side channel-based communication in a wireless LAN.

[0011] The present disclosure relates to a method and device for performing transmission and reception using a subchannel even when an AP and an STA recognize different channel states of the main channel and the subchannel.

[0012] The present disclosure relates to a method and device for determining whether to perform an NPCA operation based on whether the NPCA main channel is occupied after checking the entire transmission bandwidth of a frame received on a main 20 MHz channel by a wireless LAN terminal supporting an NPCA operation.

[0013] The present disclosure relates to a method and device for checking the transmission bandwidth of a frame received by a wireless LAN terminal supporting NPCA operation when a main 20 MHz channel is occupied by a frame exchanged within an OBSS, and determining whether to perform NPCA operation based on whether the main NPCA channel is occupied.

[0014] The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present disclosure belongs from the description below.

[0015]

[0016] According to one embodiment of the present specification, a method for operating a station (STA) in a wireless LAN system may include a step of receiving at least one frame from an overlapping basic service set (OBSS) while the STA operates on a primary channel, a step of checking bandwidth information of a frame exchanged within the OBSS through the at least one received frame, a step of determining whether to perform a non-primary channel access (NPCA) operation through the bandwidth information, and a step of the STA switching a channel from a primary channel of the STA to an NPCA primary channel when the NPCA operation is performed.

[0017] In addition, according to one embodiment of the present specification, in a wireless LAN system, a station (STA) includes at least one transceiver for transmitting and receiving a signal, at least one processor for controlling the at least one transceiver, and a memory for storing instructions for causing the STA to perform a specific operation by the at least one processor, wherein the specific operation includes: receiving at least one frame from an overlapping basic service set (OBSS) while operating on a primary channel, checking bandwidth information of frames exchanged within the OBSS through the received at least one frame, determining whether to perform a non-primary channel access (NPCA) operation through the bandwidth information, and when the STA performs the NPCA operation, switching a channel from the primary channel of the STA to the NPCA primary channel.

[0018] In addition, according to one embodiment of the present specification, in a method for operating an access point (AP) in a wireless LAN system, the method may include a step of receiving at least one frame from an overlapping basic service set (OBSS) while the AP operates on a primary channel, a step of checking bandwidth information of a frame exchanged within the OBSS through the received at least one frame, a step of determining whether to perform a non-primary channel access (NPCA) operation through the bandwidth information, and a step of the AP switching a channel from the AP's primary channel to an NPCA primary channel when the NPCA operation is performed.

[0019] In addition, according to one embodiment of the present specification, in a wireless LAN system, an access point (AP) includes at least one transceiver for transmitting and receiving a signal, at least one processor for controlling the at least one transceiver, and a memory for storing instructions for causing the AP to perform a specific operation by the at least one processor, wherein the specific operation comprises: receiving at least one frame from an overlapping basic service set (OBSS) while operating on a primary channel, checking bandwidth information of a frame exchanged within the OBSS through the received at least one frame, determining whether to perform a non-primary channel access (NPCA) operation through the bandwidth information, and when performing the NPCA operation, the AP can switch a channel from the primary channel of the AP to an NPCA primary channel.

[0020] Additionally, the following may be applied universally. However, for convenience of explanation, the description is based on STA, and may also be applied equally to AP.

[0021] According to one embodiment of the present specification, the STA can determine whether to perform an NPCA operation by checking the bandwidth information of frames exchanged within an OBSS through a sequence of physical layer protocol data units (PPDUs) exchanged at short interframe space (SIFS) intervals, and checking whether an NPCA primary channel is occupied through the bandwidth information of frames exchanged within the OBSS.

[0022] Additionally, according to one embodiment of the present specification, when the sequence of PPDUs includes a first PPDU including an initial control frame, a second PPDU including an initial control response, and a third PPDU including a data frame, and the STA switches the channel to the NPCA primary channel based on bandwidth information identified based on the sequence of PPDUs, the STA may switch the channel from the primary channel to the NPCA primary channel at the time of receiving the third PPDU.

[0023] Additionally, according to one embodiment of the present specification, the time point at which the third PPDU is received may be the time point at which the physical layer of the STA confirms the preamble of the third PPDU and transmits the primitive to the MAC layer of the STA.

[0024] Additionally, according to one embodiment of the present specification, the point in time at which the channel is switched from the primary channel to the NPCA primary channel after receiving the third PPDU may be a point in time after the third orthogonal frequency division multiplex (OFDM) symbol after receiving the L-SIG of the third PPDU.

[0025] Additionally, according to one embodiment of the present specification, the STA may receive some PPDUs among the first PPDU, the second PPDU, and the third PPDU in a sequence of PPDUs.

[0026] Additionally, according to one embodiment of the present specification, when an STA receives a third PPDU that does not occupy an NPCA primary channel after receiving a first PPDU that occupies an NPCA primary channel, the STA may perform an NPCA operation based on bandwidth information of the third PPDU.

[0027] Additionally, according to one embodiment of the present specification, when the STA acquires from the OBSS at least one of a first PPDU including a clear to send (CTS) to Self in a sequence of PPDUs and a second PPDU following the first PPDU and including a data frame to switch the channel to the NPCA primary channel, the STA may switch the channel from the primary channel to the NPCA primary channel at at least one of a time point of NPCA primary channel occupancy confirmation of the first PPDU including the CTS to Self or a time point based on reception of the second PPDU including the data frame.

[0028] Additionally, according to one embodiment of the present specification, the time based on reception of the second PPDU including the data frame may include at least one of a time when the physical layer of the STA confirms one of the PHY preamble of the second PPDU and the PHY header of the second PPDU and transmits a primitive to the MAC layer of the STA, and a time when the STA receives information including bandwidth information of the data frame and acquires information including bandwidth information.

[0029] Additionally, according to one embodiment of the present specification, when the STA acquires from the OBSS at least one of a first PPDU including a trigger frame (TF) and a second PPDU subsequent to the first PPDU and including a data frame in a sequence of PPDUs to switch the channel to the NPCA primary channel, the STA may switch the channel to the NPCA primary channel at at least one of a time point based on reception of the first PPDU including the TF or a time point based on reception of the second PPDU including the data frame.

[0030] In addition, according to one embodiment of the present specification, the time point based on reception of the first PPDU may include at least one of the time point at which the physical layer of the STA checks one of the PHY preamble and the PHY header of the first PPDU and transmits a primitive to the MAC layer of the STA, the time point at which the STA completely decodes the first PPDU, the time point at which the MAC (medium access control) header of the first PPDU is received, the time point at which the bandwidth through which the first PPDU is transmitted is checked to determine whether the NPCA primary channel is occupied, and the time point at which the bandwidth through which the data frame is transmitted is checked through bandwidth information included in the first PPDU, and the time point at which the physical layer of the STA checks one of the PHY preamble and the PHY header of the second PPDU and transmits a primitive to the MAC layer of the STA, and the time point at which the STA receives information including bandwidth information of the second PPDU and includes a time taken to acquire information including bandwidth information.

[0031] Additionally, according to one embodiment of the present specification, bandwidth information may be indicated to the STA by being included in at least one of a preamble of the PPDU, a PHY header of the PPDU, and a medium access control (MAC) header of the PPDU.

[0032]

[0033] According to the present disclosure, a method for performing a side-channel access operation in a wireless LAN can be provided.

[0034] According to the present disclosure, when performing side-channel-based communication in a wireless LAN, a method can be provided in which an AP responds to an STA through a side-channel so that the STA can operate in the side-channel or stops a transmission attempt by the STA and performs a new communication operation in the side-channel.

[0035] According to the present disclosure, a method can be provided for performing transmission and reception using a subchannel even when an AP and an STA recognize different channel states of a main channel and a subchannel.

[0036] According to the present disclosure, a method can be provided in which a wireless LAN terminal supporting NPCA operation determines whether to perform NPCA operation based on whether the NPCA main channel is occupied after checking the entire transmission bandwidth of a frame received on a main 20 MHz channel.

[0037] According to the present disclosure, when a main 20 MHz channel is occupied by a frame exchanged within an OBSS, a method can be provided for checking the transmission bandwidth of a frame received by a wireless LAN terminal supporting NPCA operation and determining whether to perform NPCA operation based on whether the NPCA main channel is occupied.

[0038] The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present disclosure belongs from the description below.

[0039] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned will be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the description below.

[0040]

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

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

[0043] Figure 3 is a diagram showing a wireless LAN network configuration applied to the present disclosure.

[0044] FIG. 4 is a diagram illustrating a wireless LAN subchannel communication instruction method considering different channel conditions applied to the present disclosure.

[0045] FIG. 5a and FIG. 5b are diagrams illustrating a wireless LAN subchannel communication resumption method applied to the present disclosure.

[0046] FIG. 6a and FIG. 6b are diagrams illustrating a method for initiating subchannel communication after wireless LAN communication interruption considering different channel conditions applied to the present disclosure.

[0047] FIG. 7a and FIG. 7b are diagrams showing a sub-channel access operation method according to the transmission bandwidth of a wireless LAN OBSS applied to the present disclosure.

[0048] FIG. 8 is a diagram illustrating a sub-channel access operation method according to the transmission bandwidth of a wireless LAN OBSS applied to the present disclosure.

[0049] FIG. 9 is a diagram illustrating a sub-channel access operation method according to the transmission bandwidth of a wireless LAN OBSS applied to the present disclosure.

[0050] FIG. 10 is a diagram illustrating a sub-channel access operation method according to the transmission bandwidth of a wireless LAN OBSS applied to the present disclosure.

[0051] FIG. 11 is a diagram illustrating a sub-channel access operation method according to the transmission bandwidth of a wireless LAN OBSS applied to the present disclosure.

[0052] Figure 12 is a flowchart showing the operation of STA in a wireless LAN applied to the present disclosure.

[0053] Figure 13 is a flowchart showing the operation of an AP in a wireless LAN applied to the present disclosure.

[0054]

[0055] This disclosure may be subject to various modifications and various embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the disclosure to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the disclosure.

[0056] While terms such as "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present disclosure, a first component may be referred to as a "second component," and similarly, a second component may also be referred to as a "first component." The term "and / or" includes a combination of multiple related items described herein or any of multiple related items described herein.

[0057] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0058] The terminology used in this disclosure is only used to describe specific embodiments and is not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0059] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this disclosure pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0060] 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 in describing the present disclosure, identical reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0061] 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 description below, and the embodiments according to the present disclosure can be applied to various wireless communication systems. The wireless communication system may be referred to as a "wireless communication network."

[0062] FIG. 1 is a diagram illustrating a communication node within a wireless LAN system to which the present disclosure applies. Referring to FIG. 1, a communication node (100) may include at least one of a processor (110), a 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 (AP) 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 other nodes or devices based on the above-described configuration. For example, the operating channel width supported by the AP may be 20 megahertz (MHz), 80 MHz, 160 MHz, etc. The operating channel width supported by the station may be 20 MHz, 80 MHz, etc. However, the present invention may not be limited thereto.

[0063] The processor (110) within the 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) as each component within the communication node. The memory (120) within the communication node (100) can store information on commands and instructions executed by the processor (110), and the transceiver (130) can refer to a transceiver, a radio frequency (RF) 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, can be linked with other interfaces, and can further include a separate storage device (150). Each component within the communication node (100) can be connected by a bus (160) to communicate with each other.

[0064] However, as an example, each component included in the communication node (100) may be connected through an individual interface or individual bus centered around the processor (110), rather than a common bus (160). The processor (1110) may be connected to at least one of the memory (120), the transmission / reception device (130), the input / output interface device (140), and the storage device (150) through a dedicated interface.

[0065] The processor (110) can execute program commands stored in at least one of the memory (120) and the storage device (150). The processor (110) may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which the methods according to embodiments of the present disclosure are performed. Each of the memory (120) and the storage device (150) may be configured with at least one of a volatile storage medium or a non-volatile storage medium. For example, the memory (120) may be configured with at least one of a read-only memory (ROM) or a random access memory (RAM).

[0066] FIG. 2 is a diagram illustrating a wireless LAN system to which the present disclosure applies. Referring to FIG. 2, a basic service set (BSS) of the wireless LAN system may include one AP (210) and multiple STAs (221, 222, 223, 224), and the multiple STAs (221, 222, 223, 224) may be controlled by the AP (210). However, the wireless LAN system is not limited to the BSS, and an environment consisting only of STAs without a defined 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 medium access control (MAC) layer and a physical (PHY) layer, and communication may be performed between the wireless devices. For the convenience of explanation, the following description focuses on APs and STAs, but may not be limited thereto. For example, the following may equally apply to other communication nodes or devices and are not limited to a specific form.

[0067] In a wireless LAN network, wireless LAN terminals can support side-channel access operations. When a non-AP STA (hereinafter, STA) performs side-channel access operations as a wireless LAN terminal, the STA's primary channel occupancy status may differ from that of the AP depending on the STA's location. Here, the communication method for transmitting data on the side-channel between the AP and the STA may be unclear, which may result in communication inefficiencies in the side-channel. For example, a specific STA may determine that the primary channel is idle, while the AP may determine that the primary channel is occupied and switch to the side-channel to operate. The specific STA may attempt to transmit a data frame in a band that includes the primary channel and the side-channel, but the AP cannot respond to the transmission because the primary channel is occupied. Therefore, side-channel communication operations in a wireless LAN may be inefficient. Taking the above-mentioned factors into account, the following describes a side-channel access method that considers different channel conditions.

[0068] In addition, a wireless LAN terminal supporting NPCA operation may need to check whether the NPCA primary channel is occupied in order to perform the NPCA operation, and may need to check the total transmission bandwidth (and / or channel) of a frame received on the primary 20 MHz channel. However, a wireless LAN terminal supporting NPCA operation may not be aware of the total transmission bandwidth of the received frame. For example, if the first frame received on the primary 20 MHz channel is a CTS (clear-to-send) frame, the wireless LAN terminal may not be aware of the total bandwidth in which the CTS frame was transmitted. Therefore, a wireless LAN terminal supporting NPCA operation may not be able to recognize whether the NPCA primary channel is occupied, and may not perform a channel switching operation to the NPCA primary channel. The wireless LAN terminal may not perform a transmission / reception operation until the time when transmission / reception operations on the primary 20 MHz channel become possible. In the above case, a terminal supporting NPCA operation may not be able to perform the NPCA operation regardless of whether the NPCA primary channel is occupied.

[0069] As another example, a terminal supporting NPCA operation may switch its operating channel to the NPCA primary channel if the primary 20 MHz channel is occupied, regardless of whether the NPCA primary channel is occupied. However, the NPCA primary channel may already be occupied, and transmission and reception operations on the NPCA primary channel may not be possible. In the above-described case, a terminal supporting NPCA operation may need to switch its operating channel from the NPCA primary channel back to the primary 20 MHz channel.

[0070] That is, if the total transmission bandwidth (and / or channel) of the frame received on the main 20 MHz channel cannot be confirmed before performing the NPCA operation, the wireless LAN terminal may not be able to perform the NPCA operation, which may cause a decrease in channel efficiency. In the following, a sub-channel access operation method considering the OBSS transmission bandwidth is described in consideration of the above. In addition, in the present invention, STA is used to refer to both non-AP STA and AP STA in the same way as the terminology is used according to IEEE 802.11. In the following, AP and non-AP STA are described separately for convenience of explanation, but STA can be used to refer to both non-AP STA and AP STA in the same way as the terminology is used according to IEEE 802.11.

[0071] FIG. 3 is a diagram illustrating a wireless LAN network configuration applicable to the present disclosure. Referring to FIG. 3, the wireless LAN network may be comprised of two or more basic service sets (BSSs). Each BSS may be comprised of an access point (AP) and a number of non-AP STAs (hereinafter, STAs) that are connected to the AP and perform data communication. Each BSS may operate on the same channel (or frequency). Furthermore, each BSS may share all or part of the channels on which it operates with other BSSs.

[0072] BSSs may have overlapping communication ranges. For example, data communication performed by one of multiple BSSs may be received by at least one other BSS. Conversely, the aforementioned BSS may receive data transmitted by at least one other BSS. Alternatively, the aforementioned BSS may not be able to receive data transmitted by at least one other BSS, but data transmission by at least one other BSS may occupy a portion of the total bandwidth in which the aforementioned BSS operates. Alternatively, data transmission performed by a BSS may occupy a portion of the total bandwidth in which at least one other BSS operates. That is, an environment in which BSSs overlap may be considered, and for convenience of description, the aforementioned BSS is referred to as a BSS below, and a BSS that overlaps a BSS with at least one other BSS is referred to as an OBSS (overlapping BSS). In the present disclosure, the operation of a BSS may be the operation of an AP or STA constituting the BSS. For example, when a BSS detects a frame transmission of an OBSS, it may refer to at least one of an AP and a STA of the BSS detecting a frame transmitted by at least one of the AP and the STA of the OBSS. When a BSS performs channel switching, it may refer to an operation in which at least one of an AP and a STA constituting the BSS performs channel switching. Below, a subchannel access method that takes different channel states into account is described.

[0073] As shown in the above-described Figure 3, an environment in which multiple BSSs exist in a wireless LAN network can be considered. The BSS can operate with a bandwidth of 40 MHz or more. The wireless LAN channel can be configured in units of 20 MHz. Therefore, when the BSS operates with a bandwidth of 40 MHz or more, the BSS can have at least two 20 MHz channels. For example, the BSS can operate with a total bandwidth of 160 MHz, and for the convenience of explanation, the following description assumes that the BSS operates with a total bandwidth of 160 MHz, but is not limited thereto. That is, the following matters can be equally applied when a bandwidth of 40 MHz or more is used. For example, the bandwidth of the BSS can vary from 40 MHz, 80 MHz, 160 MHz, 240 MHz, or 320 MHz. One 20 MHz channel among the entire operating bandwidth of the BSS can be designated as a primary 20 MHz channel. The primary 20MHz channel may be a basic channel used when at least one of the APs and STAs of the BSS performs channel access. At least one of the APs and STAs of the BSS may perform channel sensing (e.g., clear channel assessment (CCA)) and channel access operations based on the channel sensing (e.g., enhanced distributed channel access (EDCA) backoff operations and distributed coordination function (DCF) backoff operations)) on the primary 20MHz channel. In addition, depending on the channel bandwidth, there may exist primary / secondary 40MHz channels, primary / secondary 80MHz channels, or other primary / secondary channels other than the primary 20MHz channel.BSS can transmit frames with a wider bandwidth than 20 MHz (e.g. 40 MHz, 80 MHz, 160 MHz) depending on the channel access results on the main 20 MHz channel and the channel detection results on the primary / secondary channels.

[0074] Here, when the primary 20MHz channel is occupied by the OBSS, at least one of the APs and STAs of the BSS cannot transmit frames using the general channel access method. When at least one of the APs and STAs of the BSS supports the non-primary channel access (NPCA) operation, which is a side channel access operation, at least one of the APs and STAs of the BSS can transmit even when the primary 20MHz channel is occupied. For example, the side channel may be referred to as a non-primary channel, but may not be limited to a specific name. When at least one of the APs and STAs of the BSS supports the NPCA operation, at least one of the APs and STAs operates by switching the channel to a 20MHz channel different from the primary 20MHz channel that can perform channel access when the primary 20MHz channel is occupied. For example, a 20MHz channel that is different from the main 20MHz channel may be referred to as an NPCA main 20MHz channel, or a subchannel (NPCA channel), but may not be limited to a specific name. In addition, although the subchannel is indicated by the symbol 'Non-Primary' in the drawings of the present disclosure, it is not limited to that name. The subchannel may be selected within the operating frequency at which the BSS operates. If at least one of the APs and STAs of the BSS detects a transmission by the OBSS on the main 20MHz channel and confirms the communication section (e.g., a transmission opportunity (TXOP), or a physical layer protocol data unit (PPDU) transmission time section) during which the transmission is performed, at least one of the APs and STAs of the BSS may change the operating channel to the subchannel. That is, at least one of the APs and STAs of the BSS may change the channel on which channel sensing and channel access are performed to the subchannel, and perform the channel access operation on the subchannel.If at least one of the APs and STAs of the BSS succeeds in a channel access operation on a subchannel, at least one of the APs and STAs of the BSS that succeeded in the channel access operation on the subchannel can transmit a frame with a bandwidth wider than 20MHz (e.g., 40MHz, 80MHz, 160MHz) depending on the channel detection results of the subchannel and channels adjacent to the subchannel. That is, at least one of the APs and STAs of the BSS that succeeded in the channel access operation on the subchannel can obtain a TXOP, which is a communication section that can transmit multiple frames on the subchannel. At least one of the APs and STAs of the BSS that succeeded in the channel access operation on the subchannel must terminate the TXOP before the time when the communication section of the OBSS occupying the main 20MHz channel ends and must operate on the main 20MHz channel again.

[0075] The above-described sub-channel (e.g., NPCA sub-channel, NPCA Primary Channel) can be set at various locations within the operating bandwidth of the BSS. For example, the sub-channel can be set as a single 20 MHz channel within a bandwidth corresponding to half of the operating bandwidth of the BSS that does not include the primary channel among the channels included in the operating bandwidth of the BSS. As a specific example, if the operating bandwidth of the BSS is 320 MHz and there is a 160 MHz band including the primary channel and a 160 MHz band not including the primary channel, the sub-channel can be set as a single 20 MHz channel within the 160 MHz band that does not include the primary channel.

[0076] Here, as a condition for determining whether to perform the NPCA operation, an additional condition may be applied to perform the NPCA operation only when the bandwidth occupied by the PPDU (or frame) received from the OBSS is less than half of the operating bandwidth of the BSS. If the bandwidth occupied by the PPDU (or frame) received from the OBSS is 160 MHz and the operating bandwidth of the BSS is 320 MHz, a terminal supporting the NPCA operation that has received the PPDU (or frame) within the BSS may satisfy the condition for performing the NPCA operation.

[0077] In addition, each wireless LAN terminal (e.g., AP and STA) within a BSS may be affected by a different OBSS. For example, if AP 1 and STA 1 exist within a BSS, AP 1 may determine that the OBSS occupies the primary 20MHz channel or a wider channel (e.g., primary 40MHz, primary 80MHz, etc.) including the primary 20MHz channel, based on the channel access result and / or channel sensing result. Accordingly, AP 1 may change its operating channel to a subchannel and operate on the subchannel. That is, AP 1 may perform a channel access procedure on the subchannel to perform transmission or receive a frame transmitted by another STA on the subchannel. For example, the channel access procedure may be an EDCA procedure. Here, STA 1 may be affected by an OBSS different from AP 1. Accordingly, STA 1 may determine that the primary 20MHz channel is idle based on the channel access result and / or channel detection result, and may perform a channel access procedure on the primary 20MHz channel. Here, STA 1 may have succeeded in the channel access operation. For example, the maximum bandwidth supported by STA 1 may be 160MHz. However, this is for convenience of explanation and may not be limited thereto. STA 1 checks whether other channels are idle during the PIFS (priority interframe space) time from the time when the channel access operation is successful in order to perform transmission using a wide bandwidth. That is, STA 1 may check whether other channels are idle from the PIFS time before the backoff is successful until the time when the backoff is successful. STA 1 may transmit an RTS (request to send) frame to AP 1 on a wider channel (e.g., 160MHz channel) including the primary 20MHz channel on which the channel access operation was successful.For example, the RTS frame transmitted by STA 1 to AP 1 may be a frame transmitted in duplicate in units of 20 MHz channels in the form of a non-HT (high throughput) duplicated PPDU.

[0078] For example, a preamble in a non-HT PPDU format used for encoding an RTS frame may not have bandwidth information. Here, STA 1 may transmit by setting the transmitter address (TA) field of the MAC header to a bandwidth signaling TA value. The bandwidth signaling TA may be an operation of setting a portion of the MAC address of the transmitting terminal to a value modified in a preset manner. When the TA field is set to the bandwidth signaling TA value, some bits of the scrambling initialization of the 'SERVICE FIELD' may indicate channel bandwidth information on which the RTS frame is transmitted. Since AP 1 operates on a subchannel that does not include the main 20MHz channel using NPCA operation, it can receive the RTS frame only on NPCA-capable channels including the subchannel among the channels occupied by the RTS frame transmitted by STA 1. AP 1, which is performing NPCA operation, can determine that STA 1 is not performing NPCA operation if the TA of the RTS frame received from STA 1 is set to a bandwidth signaling TA and the channel bandwidth is set to a bandwidth including the main 20 MHz. In addition, the RTS frame transmitted by STA 1 to AP 1 can be received by other terminals within the transmission range of STA 1.

[0079] The bandwidth signaling TA of the RTS frame can be used in the same way during NPCA operation. Here, it may be difficult to distinguish between a situation where a terminal that is not performing NPCA operation transmits an RTS frame using the bandwidth signaling TA and a situation where a terminal performing NPCA operation transmits an RTS frame using the bandwidth signaling TA. For example, when a terminal transmits a frame using the bandwidth signaling TA during NPCA operation, one or more bits that are not used for bandwidth signaling among some bits of the scrambling initialization of the 'SERVICE FIELD' can be used as an indicator indicating that NPCA operation is in progress. As a specific example, when one or more bits of the field corresponding to 'B0 - B2' in the bits of the scrambling initialization field of the 'SERVICE FIELD' are activated, it can indicate that bandwidth signaling is performed during NPCA operation. That is, a terminal that receives a frame including the above-described indicator can recognize that the terminal that transmitted the frame is in NPCA operation. Here, channel expansion can be performed based on a subchannel with the NPCA main 20MHz channel. However, this is only one example and may not be limited thereto. The following Figures 4 to 7 describe a wireless LAN subchannel communication indication method that takes into account different channel conditions based on the above-described matters, and the above-described matters can be commonly applied.

[0080] FIG. 4 is a diagram illustrating a wireless LAN subchannel communication instruction method considering different channel conditions applied to the present disclosure. Referring to FIG. 4, as described above, a case in which AP 1 and STA 1 are affected by different OBSSs can be considered. In the case described above, STA 1 can operate on a primary 20MHz channel (i.e., BSS primary channel), and STA 1 can transmit frames in a wide bandwidth including the primary 20MHz. AP 1 can operate on the NPCA primary 20MHz channel (NPCA PCH) in NPCA operation, and the bandwidth of the frame transmitted by STA 1 can include the subchannel (NPCA PCH). That is, AP 1 operating on the subchannel (NPCA PCH) can receive a frame transmitted by STA 1 operating on the primary 20MHz channel on the subchannel (NPCA PCH), as described above.

[0081] For example, STA 1 may be an NPCA STA that supports NPCA operation but has not negotiated the use of NPCA operation with AP 1. Here, AP 1 may not respond to the RTS frame (401) transmitted by STA 1 that is operating on the main 20 MHz channel after receiving the RTS frame (401) transmitted by STA 1. That is, AP 1 may not transmit a CTS (clear to send) response to the RTS frame (401) transmitted by STA 1 that has not negotiated the use of NPCA operation.

[0082] As another example, STA 1 may be an NPCA STA that supports NPCA operation and may be an STA that has negotiated the use of NPCA operation with AP 1. AP 1 may transmit a CTS (clear to send) response after a short interframe space (SIFS) time after receiving the RTS frame (401) transmitted by STA 1. That is, AP 1 may transmit a CTS response to the RTS frame (401) transmitted by STA 1, which has negotiated the use of NPCA operation, including the main 20 MHz channel. The CTS frame (402) transmitted by AP 1 may be a frame that is transmitted in duplicate in units of 20 MHz in the form of a non-HT duplicated PPDU. The CTS response may be transmitted on channels on which the RTS frame (401) is transmitted among channels that can perform NPCA operation on a subchannel. Terminals other than STA 1 may also receive the CTS frame (402) transmitted by AP 1 to STA 1. Among the terminals other than AP 1 and STA 1, terminals that have received both the RTS frame (401) and the CTS frame (402) described above can completely recognize the value of the SIGNAL field by completely receiving the PHY header when receiving the CTS frame (402), and the PHY-RXSTART.indication primitive can be transferred from the PHY layer to the MAC layer to set the NAV (network allocation vector). Here, the length of the NAV to be set can be set to the duration value of the MAC header of the RTS frame (401) transmitted by STA 1.

[0083] The TXOP length indicated by the duration of the RTS frame MAC header transmitted by STA 1 may be longer than the point in time at which AP 1 completes the NPCA operation and must switch back to the primary 20MHz channel. In the above-described case, AP 1 may transmit the duration value of the CTS frame MAC header transmitted by setting it to a value shorter than the TXOP length indicated by the RTS frame (401) (e.g., only for the period in which AP 1 and STAs perform NPCA operation (the period in which the OBSS is busy on the primary channel). That is, the duration value of the CTS frame MAC header transmitted by AP 1 may be set to the end point of the NPCA operation period as a value including the switching time for switching the operating channel to operate on the primary 20MHz channel again after a series of frame exchanges are performed on the secondary channel from the end point of transmission of the CTS frame (402).

[0084] STA 1 can operate by switching the operating channel to the NPCA primary channel (or sub-channel, NPCA PCH) only when the time length indicated by the duration field of the CTS frame (401) transmitted by AP 1 is sufficiently long. For example, STA 1 can operate by switching the operating channel to the NPCA primary channel (NPCA PCH, sub-channel) only when the time length indicated by the duration field of the CTS frame is equal to or longer than the NPCA minimum duration threshold. The NPCA minimum duration threshold may be a time that takes into account the 'switching time for the NPCA STA to switch the operating channel to the sub-channel (NPCA PCH) + the time for exchanging one or more data in the sub-channel (NPCA PCH) + the switching time for returning to the primary 20 MHz channel in the sub-channel (NPCA PCH)', and may be a time that defines the minimum time for performing the NPCA operation. As another example, if STA 1 determines that the time length indicated by the duration field of the CTS frame transmitted by AP 1 is insufficient to perform data exchange on the subchannel (e.g., if the time length indicated by the duration of the CTS frame is less than the NPCA minimum duration threshold or is set to 0), STA 1 may operate on the main 20 MHz channel without switching to the subchannel (NPCA PCH).

[0085] A wireless LAN terminal that receives an RTS frame (401) transmitted by STA 1 can monitor reception of an additional frame during the NAVTimeout time after completing reception of the RTS frame (401). The NAVTimeout time may be a time for monitoring reception of a subsequent frame in order to confirm the set NAV by receiving a frame that sets the NAV (e.g., the RTS frame transmitted by STA 1). For example, the NAVTimeout may be (2 Х aSIFSTime) + (T_PREAMBLE + T_SIGNAL + UL_Length) + aRxPHYStartDelay + (2 Х aSlotTime) time. Here, the 'T_PREAMBLE + T_SIGNAL + UL_Length' time may be an initial control response (ICR) (e.g., CTS, Multi-STA BlockAck) transmission time. The wireless LAN terminal that receives the RTS frame (401) transmitted by STA 1 can confirm the NAV set by the RTS frame (401) by receiving the PHY-RXSTART.indication primitive generated by receiving an additional frame within the NAVTimeout time. Here, if the wireless LAN terminal that received the RTS frame (401) does not receive the PHY-RXSTART.indication primitive within the NAVTimeout time, the wireless LAN terminal can cancel the NAV set by receiving the RTS frame (401).

[0086] AP 1 may perform a method to prevent unnecessary NAV from being set in a side channel (NPCA PCH) due to the RTS frame (401) transmitted by STA 1. For example, when AP 1 receives the RTS frame (401) transmitted by STA 1, it may not transmit an additional frame for the NAVTimeout time from the time of completion of reception of the RTS frame (401). Accordingly, a wireless LAN terminal that has received the RTS frame (401) transmitted by STA 1 may not have received the PHY-RXSTART.indication primitive within the NAVTimeout time after completion of reception of the RTS frame (401), and may cancel the NAV set by the RTS frame (401). When AP 1 operating on the side channel (NPCA PCH) receives an RTS frame (401) and determines that the remaining NPCA operation time (NPCA_TIMER) after the NAVTimeout time is sufficient to exchange data on the side channel (NPCA PCH) (e.g., when the remaining NPCA_TIMER at the time when NAVTimeout has elapsed after receiving the RTS frame is equal to or longer than the NPCA Minimum Duration Threshold - the operation channel switching time to NPCA PCH), AP 1 can continue operating on the side channel (NPCA PCH).

[0087] As another example, if AP 1 receives an RTS frame (401) and determines that the remaining NPCA operation time (NPCA_TIMER) after the NAVTimeout time is insufficient to exchange data on the subchannel (NPCA PCH) (e.g., if the remaining NPCA_TIMER at the time when NAVTimeout has elapsed after receiving the RTS frame is shorter than the NPCA Minimum Duration Threshold - the operation channel switching time to NPCA PCH), AP 1 can return to the primary 20 MHz channel on the subchannel (NPCA PCH).

[0088] When STA 1 receives a CTS frame (402) on channels capable of NPCA including a subchannel, STA 1 may not recognize whether it received the CTS frame (402) on channels capable of NPCA including a subchannel for NPCA operation or whether there is a channel error and the CTS frame (402) was received only on some channels. Here, AP 1 may use the duration value of the CTS frame (402) as an indicator to indicate that the CTS frame (402) transmitted on channels capable of NPCA including a subchannel is an NPCA operation. For example, the duration may be set to indicate a general value in units of 32 μs. Alternatively, the duration value may be an even value. Here, AP 1 may set the duration value of the transmitted CTS frame (402) to an odd value, and the odd value may be used as an indicator indicating that the NPCA operation is. As another example, AP 1 may use a part of the MAC address (e.g., receiver address (RA)) of the receiving terminal of the CTS frame (402) as an indicator indicating NPCA operation by setting three bits of a specific pattern of values ​​(e.g., least significant bit (LSB) or most significant bit (MSB)) to '111', but may not be limited to the embodiment. When STA 1 receives a CTS frame (402) including an indicator indicating NPCA operation, it may recognize that it should perform NPCA operation, and thereafter, data transmission may be transmitted through channels capable of NPCA including subchannels (i.e., channels through which the CTS frame was received).

[0089] For example, as described above, STA 1 can transmit an RTS frame (401) to AP 1 using all available channels (e.g., 160MHz channel) including the primary 20MHz channel. However, AP 1 can transmit a CTS frame (402) in response to the RTS frame (401) using fewer channels (bandwidths) (e.g., 80MHz channels not including the primary 80MHz channel) than the channels (bandwidths) on which the RTS frame (401) was transmitted due to NPCA operation. Since the CTS frame (402) is repeatedly transmitted in 20MHz channel units, STA 1 can decode the CTS frame (402) only on the channel on which the CTS frame (402) transmitted by AP 1 was transmitted. STA 1 receives an indicator indicating NPCA operation within a successfully decoded CTS frame (402) (e.g., an indicator using a specific pattern in duration and / or RA) and can recognize that AP 1 is in NPCA operation. After receiving the indicator indicating NPCA operation, STA 1 can transmit data through NPCA-capable channels including subchannels (i.e., channels on which a CTS frame is received).

[0090] As another example, STA 1 can recognize that it is an NPCA operation by measuring the received power of the CTS frame (402) with or without an indicator indicating that it is an NPCA operation. STA 1 can transmit the RTS frame (401) using a specific power in a 160 MHz bandwidth. The channel gain, which is the degree to which the signal is attenuated between STA 1 and AP 1, can be recognized in the pre-negotiation stage or during operation. AP 1 can measure the received power of the RTS frame (401) received from STA 1 and then perform transmission using the corresponding pre-attenuation power (i.e., expected transmit power). Since the RTS frame (401) is transmitted using a channel in the 160 MHz band and the CTS frame (402) is transmitted using a channel in the 80 MHz band, the received power considering the gain (attenuation) may be half of the case where the CTS frame (402) could be received by transmitting it in 160 MHz. STA 1 can recognize that the CTS frame (402) is in NPCA operation when the reception power is as described above. STA 1 recognizes that the NPCA operation is in NPCA operation, and can then transmit data through channels capable of NPCA, including subchannels (i.e., channels that received the CTS frame).

[0091] STA 1 may not detect that the primary channel of the OBSS is busy, but may detect the energy (or power) of a weak OBSS. The above-described value may be an energy (or power) value that can recognize the presence of the OBSS. The energy level that determines the channel to be busy may be referred to as an ED (energy detection) threshold. Here, the currently measured energy of the primary channel is the primary channel energy (or power), and the energy (or power) level that can determine that the OBSS may exist may be the NPCA ED threshold. If the primary channel energy (or power) measured in the CCA before STA 1 transmits the RTS frame (401) is "ED (energy detection) threshold > Primary Channel Energy > NPCA ED threshold", STA 1 may recognize that AP 1 is operating NPCA.

[0092] STA 1, which receives a CTS frame (402) transmitted by AP 1, can recognize that AP 1 is operating in NPCA according to at least one of the above-described methods. If STA 1 receives a CTS frame (402) that can recognize that AP 1 is operating in NPCA, STA 1 can consider that it has successfully acquired TXOP regardless of whether the CTS frame of the main 20MHz channel is successfully received. Specifically, if STA 1 successfully receives the CTS frame (402) of the NPCA main 20MHz channel, STA 1 can consider that it has acquired TXOP and can determine the bandwidth of the TXOP by applying a channel extension rule based on the NPCA main 20MHz channel. STA 1 can receive the CTS frame (402) and transmit a data frame (403) to AP 1 after an SIFS time. As another example, STA 1 may determine that the time length indicated by the duration field of the CTS frame (402) after receiving the CTS frame (402) is equal to or longer than the NPCA minimum duration threshold described above. In the case described above, STA 1 may transmit a data frame (403) to AP 1 by switching the operating channel to a subchannel (NPCA PCH) after receiving the CTS frame (402). The length of the data frame (403) transmitted by STA 1 may be configured in consideration of the NPCA operable time interval indicated by the duration of the CTS frame MAC header. Here, the duration value of the data frame MAC header may be transmitted in accordance with the duration value of the received CTS frame.

[0093] As described above, if STA 1 acquires a TXOP and AP 1 readjusts the duration value of the CTS frame to a different time point from the time point indicated by the duration value of the RTS frame and transmits it, STA 1 may consider the TXOP to be invalid after the time point corresponding to the duration value indicated in the CTS frame (402) transmitted by AP 1. Specifically, STA 1 may not attempt additional frame exchange with AP 1 after the time point described above. In addition, STA 1 may consider the time point described above as the time point at which the NPCA operation expires and may return to the main 20 MHz channel regardless of whether or not the TXOP remains. In addition, other terminals (e.g., STA 2) for which an intra-NAV (network allocation vector) (intra-NAV) is set by STA 1 may operate with the NPCA operation expiration time set to be longer than the NPCA operation expiration time, and may be required to return to the main 20MHz channel regardless of whether there are any remaining intra-NAVs. After returning to the main 20MHz channel through the above-described process, if an intra-NAV set in the NPCA main 20MHz channel remains, the intra-NAV may be deleted or invalidated.

[0094] As another example, if the bandwidth signaling TA of the RTS frame (401) received by STA 2 during NPCA operation from STA 1 does not include an indicator indicating that NPCA operation is in progress, STA 2 may not perform an intra-NAV setting operation. In the above-described case, if STA 2 sets the intra-NAV by AP 1's CTS frame transmission, the intra-NAV can normally perform the primary channel return operation because it is based on the readjusted duration value until the NPCA operation expiration time.

[0095] FIG. 5A and FIG. 5B are diagrams illustrating a wireless LAN subchannel communication resumption method applied to the present disclosure. As described above, FIG. 5A and FIG. 5B also consider a case where AP 1 and STA 1 are affected by different OBSSs. In the case described above, STA 1 can operate on a primary 20MHz channel (i.e., BSS primary channel), and STA 1 can transmit frames in a wide bandwidth including the primary 20MHz. AP 1 can operate on the NPCA primary 20MHz channel (NPCA PCH) in NPCA operation, and the bandwidth of the frame transmitted by STA 1 can include the subchannel (NPCA PCH). That is, AP 1 operating on the subchannel (NPCA PCH) can receive a frame transmitted by STA 1 operating on the primary 20MHz channel on the subchannel (NPCA PCH), as described above.

[0096] Referring to FIG. 5A, AP 1 can recognize an OBSS that STA 1 can detect. That is, AP 1 can recognize that STA 1 and the OBSS are hidden nodes from each other. Therefore, AP 1 can recognize that the OBSS occupying the main 20MHz channel is an OBSS that STA 1 cannot detect. Alternatively, AP 1 can recognize that STA 1 is not performing the NPCA operation through the bandwidth signaling TA of the RTS frame (405) as described above. Here, since STA 1 did not transmit the RTS frame (405) to perform the NPCA operation, AP 1 may not transmit a CTS frame to STA 1 through the NPCA channels including the subchannel. As another example, a case may be considered where AP 1 is operating on the main 20MHz channel and STA 1 is operating on the subchannel (NPCA PCH). In the above-described situation, AP 1 can transmit an RTS frame to STA 1 including the main 20 MHz. STA 1 may have received the RTS frame transmitted by AP 1 and may recognize that AP 1 and OBSS are hidden terminals from each other. Alternatively, STA 1 may recognize that AP 1 is not operating in a side channel (NPCA PCH) through the bandwidth signaling TA of the RTS frame received from AP 1. In the above-described case, STA 1 may not transmit a response frame (e.g., CTS) to the RTS frame transmitted by AP 1.

[0097] Since AP 1 is the receiver of the RTS frame (405) transmitted by STA 1, NAV may not be set. On the other hand, terminals that are not the receivers of the RTS frame (405) may wait for normal frame reception for a certain period of time (e.g., NAVTimeout) after receiving the RTS frame (405). Here, if other terminals receive normal frames within the NAVTimeout time (i.e., if they completely receive the PHY header of the frame and can completely recognize the value of the SIGNAL field), the PHY-RXSTART.indication primitives of the other terminals may be transferred from the PHY layer to the MAC layer, so that NAV (intra-NAV) may be set. Since AP 1 is the receiver of the RTS frame (405) and has not set the NAV, it uses a channel access procedure (e.g., EDCA procedure) even during the NAVTimeout time, and if channel access is successful, frame transmission may be possible.

[0098] If AP 1 successfully transmits a frame within the NAVTimeout time, terminals that are not the recipients of the RTS frame (405) can perform successful preamble decoding of the frame transmitted by AP 1 within the NAVTimeout time, and thus can set the NAV by transmitting the PHY-RXSTART.indication primitive from the PHY layer to the MAC layer.

[0099] The frame transmitted by AP 1 upon successful channel access may be an RTS frame (406) transmitted to another terminal (e.g., STA 2) other than STA 1 within the BSS. STA 2 may have its NAV set by the RTS frame (405) of STA 1 that it initially received and the RTS frame (PHY-RXSTART.indication) (406) transmitted by AP 1. Here, since the CTS frame (407) is an immediate response to the RTS frame (406), STA 2 may transmit the CTS frame (407) in response to the RTS frame (406) of AP 1. After receiving the CTS frame (407) from STA 2, AP 1 may transmit a data frame (408) to STA 2, and STA 2 may transmit a BA frame (409) as an immediate response.

[0100] Referring to FIG. 5b, AP 1 can recognize an OBSS that STA 1 can detect. That is, AP 1 can recognize that STA 1 and the OBSS are hidden nodes from each other. Therefore, AP 1 can recognize that the OBSS occupying the main 20MHz channel is an OBSS that STA 1 cannot detect. Here, since STA 1 did not transmit an RTS frame (410) to perform an NPCA operation, AP 1 may not transmit a CTS frame to STA 1 through NPCA channels including a subchannel.

[0101] Here, since AP 1 is the receiver of the RTS frame (410) transmitted by STA 1, NAV may not be set for AP 1. On the other hand, terminals that are not the receivers of the RTS frame (410) may wait for normal frame reception for a certain period of time (e.g., NAVTimeout) after receiving the RTS frame (410). If other terminals receive normal frames within the NAVTimeout time (i.e., completely receive the PHY header of the frame and completely know the value of the SIGNAL field), the PHY-RXSTART.indication primitive may be transmitted from the PHY layer to the MAC layer in other terminals to set the NAV. Since AP 1 is the receiver of the RTS frame (410) and has not set the NAV, channel access and frame transmission may be possible using the channel access procedure (e.g., EDCA procedure) even during the NAVTimeout time. If AP 1 successfully transmits a frame within the NAVTimeout time, terminals that are not the recipients of the RTS frame can perform successful preamble decoding of the frame transmitted by AP 1 within the NAVTimeout time, and thus can set the NAV by transmitting the PHY-RXSTART.indication primitive from the PHY layer to the MAC layer.

[0102] AP 1 can recognize that NAV is set in other terminals (e.g. STA 2) other than the receiver of the RTS frame (410) transmitted by STA 1, but can transmit an immediate response BA (BlockAck) and thus transmit a data frame (411) to STA 2. STA 2 can receive the data frame (411) transmitted by AP 1 because it is set as the receiver of the data frame (411) even though it has NAV set. For example, even in a situation where transmission is not possible because a NAV is set in one terminal, if a frame in which the receiver is set as itself requests an immediate response, the terminal that received the frame can ignore the NAV and transmit an immediate response reception response frame (BA, BlockAck). Therefore, STA 2 can transmit a BA (block acknowledgment) frame (412) to AP 1 as an immediate response to the received data frame (411).

[0103] Other terminals for which intra-NAV is set by STA 1 may operate with the NPCA operation expiration time taking precedence over the intra-NAV if the intra-NAV is set to be longer than the NPCA operation expiration time. That is, other terminals may have to return to the main 20MHz channel regardless of the remaining time of the intra-NAV. If other terminals return to the main 20MHz channel through the above-described process, other terminals may delete or invalidate the intra-NAV even if the intra-NAV set on the NPCA main 20MHz channel remains. As another example, if the bandwidth signaling TA of the RTS frame received by STA 2 during NPCA operation does not include an indicator indicating that NPCA is in operation, STA 2 may not perform the intra-NAV setting operation. In the above case, the NAV of the terminals is set based on the frame (e.g. RTS frame) transmitted by AP 1 during the NAVTimeout period, and since the frame transmitted by AP 1 is based on the readjusted duration value until the NPCA operation expires, the return to the primary channel operation can be performed normally.

[0104] Also, as an example, there may exist a wireless LAN terminal (e.g., STA x) that receives an RTS frame transmitted by STA 2 after receiving an RTS frame transmitted by STA 1 in the above-described FIGS. 5A and 5B. Here, STA x, which has received both RTS frames, may determine the NAV for the RTS frame of STA 1 as a result of receiving the RTS frame of STA 2 within the NAVTimeout time for the RTS frame of STA 1 that was received first. For example, if the determined NAV is longer than the time (e.g., NPCA_TIMER) that operates in the subchannel (NPCA PCH), STA x may return to the main 20 MHz channel when NPCA_TIMER expires even if there is an unexpired NAV. Additionally, STA x can release the set NAV by receiving an RTS frame from STA 1 on the subchannel (NPCA PCH) when it returns to the main 20 MHz channel at the time when NPCA_TIMER expires.

[0105] As another example, STA x may have encountered an error while receiving the RTS frame transmitted by STA 1, or may have simply detected energy exceeding a threshold. In the above-described situation, STA x may have to wait for an EIFS (extended interframe space) time from the time it has completed receiving the RTS frame with the error or the energy exceeding the threshold. Even in the above-described case, if the remaining NPCA_TIMER at the time of expiration of the EIFS time is insufficient to exchange new data (e.g., if the remaining NPCA_TIMER at the time of expiration of the EIFS applied due to the energy exceeding the threshold is shorter than the operating channel switching time to NPCA Minimum Duration Threshold - NPCA PCH), STA x may return to the primary 20 MHz channel at the time of expiration of the EIFS or the time of expiration of the NPCA_TIMER.

[0106] FIGS. 6A and 6B are diagrams illustrating a method for initiating subchannel communication after wireless LAN communication interruption considering different channel conditions applied to the present disclosure. FIGS. 6A and 6B also consider a case where AP 1 and STA 1 are affected by different OBSSs as described above. In the case described above, STA 1 can operate on a primary 20MHz channel (i.e., BSS primary channel), and STA 1 can transmit frames in a wide bandwidth including the primary 20MHz. AP 1 can operate on the NPCA primary 20MHz channel (NPCA PCH) in NPCA operation, and the bandwidth of the frame transmitted by STA 1 can include the subchannel (NPCA PCH). That is, AP 1 operating on the subchannel (NPCA PCH) can receive a frame transmitted by STA 1 operating on the primary 20MHz channel on the subchannel (NPCA PCH), as described above.

[0107] Referring to FIG. 6A, AP 1 may transmit a CF-END (contention free END) frame (415) as an immediate response to STA 1's RTS frame (413). That is, AP 1 may transmit a CF-END frame (414) through a 20 MHz channel in duplicate after a SIFS time after receiving the RTS frame (413). The CF-END frame (414) may be a frame that releases the NAV of all terminals that have received the CF-END frame (414). For example, when AP 1 receives a frame transmitted by STA 1 operating on the main 20 MHz channel on a side channel (NPCA PCH), AP 1 may release (or terminate) the NAV set by the frame transmitted by STA 1 by transmitting a CF frame (414).

[0108] Here, AP 1 may transmit its BSS color information in the CF-END frame (414) to prevent the basic NAV (inter-BSS NAV) (NAV set by OBSS in the above case) from being released by the CF-END frame (414). Terminals receiving the CF-END frame (414) may not release their NAVs if a CF-END frame (414) having a BSS color other than the BSS color to which they belong is received. Accordingly, the basic NAV set for terminals affected by OBSS may not be released. Terminals that are not the recipients of the RTS frame (413) can perform successful preamble decoding of the frame (CF-END frame) transmitted by AP 1 within the NAVTimeout time, and thus can set the NAV by transmitting the PHY-RXSTART.indication primitive from the PHY layer to the MAC layer. However, since they have decoded the CF-END frame, they can immediately release the set NAV. When AP 1, which is operating NPCA, transmits a CF-END frame (414) in response to a frame transmission from a terminal that is not operating NPCA, the duration value can be set to a non-zero value. Specifically, AP 1 can specify a duration value indicating the time point of termination of the NPCA operation. When STA 1 transmits an RTS frame (413) and receives a CF-END frame (414) on an NPCA operation channel after SIFS, STA 1 can recognize that AP 1 is operating NPCA and the time point of termination of the NPCA operation through the duration value. Here, STA 1 may be able to perform the NPCA operation immediately.

[0109] As another example, AP 1 may use a channel access procedure (e.g., EDCA procedure) to transmit a CF-END frame (414). AP 1 may perform a channel access operation for a NAVtimeout time after receiving an RTS frame (413) from STA 1 to transmit the CF-END frame (414).

[0110] The CF-END frame (414) transmitted by AP 1 may be transmitted as a non-HT Duplicated PPDU that is transmitted in duplicates in units of 20 MHz. If there is no response to the RTS frame (413) transmitted to AP 1, STA 1 may determine that transmission has failed and update the EDCA parameters (e.g., CW[AC], QSRC[AC], etc.). For example, CW (contention window) may be doubled and QSRC (QoS STA retry count) may be increased by 1. If STA 1 attempts retransmission using the updated EDCA parameters, the time required for channel access may be increased. The retransmission attempt may continue until AP 1 completes the NPCA operation and operates on the main 20 MHz channel again to send a response frame to STA 1. Therefore, the channel access inefficiency of STA 1 may increase. To prevent the above, STA 1 may not regard it as a transmission failure and may maintain the EDCA parameters without updating them when it receives the CF-END frame (414) transmitted by AP 1 as an immediate response to the RTS frame (413).

[0111] As another example, even if STA 1 receives a CF-END frame (414) transmitted through a channel access procedure (e.g., EDCA procedure) rather than an immediate response, STA 1 may not regard it as a transmission failure and may maintain the EDCA parameters without updating them. The above-described operation may also be applied only when the CF-END frame (414) is received within the NAVTimeout time.

[0112] AP 1, which transmitted the CF-END frame (414), can perform a channel access procedure (e.g., EDCA procedure) after transmitting the CF-END frame (414). All terminals that received the CF-END frame (414) can release their NAVs and perform a channel access operation if the BSS color of the CF-END frame (414) is the same as their own BSS color. AP 1 can succeed in the channel access operation and transmit a frame to another terminal (e.g., STA 2) that performed the NPCA operation within the BSS to obtain a new TXOP.

[0113] In FIG. 6A, if at least one of AP 1 that transmitted the CF-END frame (414) and NPCA STA (e.g., STA 2) that received the CF-END frame (414) determines that the remaining NPCA operation time (NPCA_TIMER) after transmitting or receiving the CF-END frame (414) is insufficient to exchange data on the NPCA primary channel (NPCA PCH), at least one of AP 1 that transmitted the CF-END frame (414) and NPCA STA (e.g., STA 2) that received the CF-END frame (414) may return to the primary 20 MHz channel. For example, if the remaining NPCA operation time (NPCA_TIMER) after transmitting or receiving a CF-END frame (414) is shorter than the NPCA minimum duration threshold, which is the minimum time for operating in the subchannel (NPCA PCH), at least one of AP 1 that transmitted the CF-END frame (414) and NPCA STA (e.g., STA 2) that received the CF-END frame (414) may return to the main 20 MHz channel at or after the completion of transmitting the CF-END frame (414). As another example, if the remaining NPCA operation time (NPCA_TIMER) after transmitting or receiving a CF-END frame (414) is shorter than the minimum time for operating in the subchannel (NPCA PCH), which is "NPCA minimum duration threshold - transition time to the subchannel (NPCA PCH)", at least one of AP 1 that transmitted the CF-END frame (414) and NPCA STA (e.g., STA 2) that received the CF-END frame (414) may return to the main 20 MHz channel at or after the completion of transmitting the CF-END frame (414). As another example, if the remaining NPCA operation time (NPCA_TIMER) after transmitting or receiving a CF-END frame (414) is shorter than the minimum time for operating in the subchannel (NPCA PCH), which is "NPCA minimum duration threshold - transition time to the subchannel (NPCA PCH)", at least one of AP 1 that transmitted the CF-END frame (414) and NPCA STA (e.g., STA 2) that received the CF-END frame (414) may return to the main 20 MHz channel at or after the completion of transmitting the CF-END frame (414)., minimum Number of Spatial Streams (NSS), minimum Modulation and Coding Scheme (MCS), minimum Bandwidth (BW), etc.) is transmitted and if the expected time to receive a response frame thereto is shorter than that, at least one of the AP 1 that transmitted the CF-END frame (414) and the NPCA STA (e.g., STA 2) that received the CF-END frame (414) may return to the main 20 MHz channel at or after the completion of transmission of the CF-END frame (414).

[0114] Referring to FIG. 6b, AP 1 may transmit a DS (defer signal, 415) as an immediate response to the RTS frame (413) of STA 1. The DS (415) may be a signal transmitted by a wireless LAN terminal (e.g., AP 1, STA 1) supporting P-EDCA (prioritized EDCA) to occupy a channel with high priority. For example, the wireless LAN terminal (e.g., AP 1, STA 1) may transmit the DS (415) at a certain time point (e.g., after DSAIFS [AC_VO]) when the CCA result channel was last switched from an occupied state to an idle state when voice traffic (e.g., AC_VO)) has undergone two or more retransmissions (e.g., when QSRC [AC_VO] is 2 or more), to preferentially occupy the channel. That is, DS (415) may be a signal transmitted by a wireless LAN terminal (e.g., AP 1, STA 1) to occupy a channel with high priority, and is not limited to the above-described example and may be used in various forms. DS (415) may be all or part of the preamble, and may be composed only of the beginning of the preamble and the L-SIG.

[0115] If the wireless LAN terminal decodes the preamble normally, the PHY-RXSTART.indication primitive can be transmitted from the PHY layer to the MAC layer in the wireless LAN terminal. Here, the wireless LAN terminal may set a NAV, and the NAV may be an unnecessary NAV. Here, in order to prevent unnecessary NAV setting, the 6 bits of the last SIGNAL TAIL of the signal field in the DS (415) may be set to '111111'. If the wireless LAN terminal receives the DS (415) in which the 6 bits of the last SIGNAL TAIL of the signal field in the DS (415) are set to '111111', the PHY-RXSTART.indication primitive may not be generated. In addition, in order to indicate that the DS (415) is transmitted in the NPCA operation, the value of the LENGTH of the signal field in the DS may be set to the NPCA operation time length and used as an NPCA indicator.

[0116] Terminals receiving the DS (415) transmitted according to the above-described operation cannot decode the DS (415) as a normal preamble. Therefore, the PHY-RXSTART.indication primitive may not be generated and the NAV may not be set for the terminals receiving the DS. As another example, if the terminals receive the DS (415) in which the 6 bits of the SIGNAL TAIL are set to '111111' as a new rule, the NAV may not be set and the channel access operation may be used to compete for frame transmission after receiving the DS (415).

[0117] As another example, the above-described DS (415) may be DS-CTS, which is a type of CTS. Specifically, the above-described DS-CTS may be in a non-HT duplicate format, may be transmitted at a data rate of 6 Mb / s, and a fixed value may be used for SCRAMBLER_INITIAL_VALUE. In addition, the receiver address (RA) field of the DS-CTS may be set to a unicast MAC address with OUI 00:0F:AC, and the remaining address bits may be set to any value. The value of the duration field of the DS-CTS may vary. For example, the value of the duration field of the DS-CTS may be set to 97 microseconds. The transmission time of at least one of the DS and the DS-CTS may vary. For example, the time of transmission of at least one of the DS and DS-CTS may be a time DSAIFS[AC_VO] elapsed from the last time the medium went from occupied to idle as a result of a CCA on a side channel (e.g., when an RTS frame was received successfully). The DSAIFS[AC_VO] time may be a slot boundary for transmitting at least one of the DS and DS-CTS, and the value may be AIFS[AC_VO] = AIFSN[AC_VO] * aSlotTime + aSIFSTime = 34 microseconds or a variety of values.

[0118] As another example, the DS may be transmitted using channel access operation via EDCA rather than an immediate response to the RTS frame, similar to the CF-END frame transmission in FIG. 6A. The DS transmitted by AP 1 may be transmitted in 20MHz units. If there is no response to the RTS frame transmitted to AP 1, STA 1 may determine that the transmission has failed and update the EDCA parameters (e.g., CW[AC], QSRC[AC], etc.). For example, CW may be doubled and QSRC may be increased by 1. Here, if STA 1 attempts retransmission using the updated EDCA parameters, the time required for channel access may be increased, and the above-described retransmission attempt may continue until AP 1 completes the NPCA operation and operates on the main 20MHz channel again to send a response frame to STA 1. Therefore, the channel access inefficiency of STA 1 may increase. To prevent the above, STA 1 may not consider it a transmission failure and may keep the EDCA parameters without updating them when it receives the DS transmitted by AP 1 as a response frame to the RTS frame.

[0119] As another example, even if STA 1 receives a DS using EDCA, STA 1 may not regard it as a transmission failure and may maintain the EDCA parameters without updating them. The above-described operation may be applied only when the DS is received within the NAVTimeout time. AP 1, which transmitted the DS, may perform a simplified contention procedure after the DS transmission. The simplified contention procedure may be a channel access operation using at least one of a short latency (e.g., PIFS, etc.) and a short contention window. In other words, the simplified contention procedure may be a procedure for quickly transmitting frames in a limited-length NPCA interval. As another example, AP 1 may perform a channel access operation using EDCA operation after the DS transmission. AP 1 may acquire a new TXOP by transmitting a frame to another terminal (e.g., STA 2) performing NPCA operation within the BSS using one of the channel access methods.

[0120] In the above-described FIGS. 4 to 6b, the RTS frame transmitted by the wireless LAN terminal (e.g., AP 1, STA 1, STA 2) may be an initial control frame (ICF). For example, frames that can be ICF may be RTS, MU (multi user)-RTS, basic trigger (TF), BSRP (buffer status report poll), and other frames, and may not be limited to a specific form. In addition, the CTS frame transmitted by the wireless LAN terminal (e.g., AP 1, STA 1, STA 2) may be an initial control response (ICR) frame, and frames that can be ICR may be CTS, data, BSR (buffer status report), Multi-STA BlockAck, and other frames, and may not be limited to a specific form. In addition, in cases where the RTS frame transmitted by the wireless LAN terminal (e.g., AP 1, STA 1, STA 2) in FIGS. 4 to 6b is an ICF, the NAVTimeout time to wait after receiving the ICF may be (2 Х aSIFSTime) + (T_PREAMBLE + T_SIGNAL + UL_Length) + aRxPHYStartDelay + (2 Х aSlotTime) time. Here, the 'T_PREAMBLE + T_SIGNAL + UL_Length' time may be the transmission time of the ICR.

[0121] AP 1 and AP 2 exist as wireless LAN terminals that constitute a BSS (basic service set), and STA 1 and STA 2 may exist as non-AP STAs (hereinafter, STAs). STA 1 may be (re)associated with AP 1, and STA 2 may be (re)associated with AP 2. Here, AP 1 may constitute BSS 1, and AP 2 may constitute BSS 2. BSS 1 and BSS 2 may be OBSSs with overlapping transmission ranges therebetween. That is, a frame transmitted by a wireless LAN terminal (e.g., AP 1, STA 1) within BSS 1 may be received by a wireless LAN terminal (e.g., AP 2, STA 2) within BSS 2. Conversely, a frame transmitted by a wireless LAN terminal (e.g., AP 2, STA 2) within BSS 2 can be received by a wireless LAN terminal (e.g., AP 1, STA 1) within BSS 1.

[0122] A wireless LAN terminal (e.g., AP 1, AP 2, STA 1, STA 2) can perform an enhanced distributed channel access (EDCA) operation. The EDCA operation can perform at least one of a clear channel assessment (CCA) operation and an EDCA backoff procedure (hereinafter, referred to as the backoff procedure). Specifically, the wireless LAN terminal can perform a CCA operation (hereinafter, referred to as CCA) on a primary 20 MHz channel. The CCA may be an operation to determine whether the channel is idle or busy. For example, as a detailed operation of the CCA, there may exist a physical CS (channel sensing) that detects a carrier transmitted on the channel and a Virtual CS that determines whether a network allocation vector (NAV) set through successful frame exchange is set. A wireless LAN terminal can perform CCA for a set IFS (inter-frame space) length (e.g., AIFS (arbitration IFS)[AC], etc.) depending on the type of frame to be transmitted (e.g., a frame with an access category (AC) of VO, VI, BE, or BO).

[0123] A wireless LAN terminal can initiate an EDCA backoff procedure (hereinafter, referred to as the backoff procedure). The backoff procedure may be a procedure performed to reduce the probability of collision between wireless LAN terminals. The backoff procedure may be a procedure performed by an EDCA function (EDCAF) corresponding to the type of frame to be transmitted within the wireless LAN terminal. The EDCAF of the wireless LAN terminal can initiate the backoff procedure when traffic to be transmitted has arrived (e.g., when data is entered into the transmit queue of an AC corresponding to the EDCAF) and the channel is busy. As another example, the EDCAF of the wireless LAN terminal can initiate the backoff procedure when a separate instruction exists (e.g., when an instruction indicating to initiate the backoff procedure is received through frame exchange).

[0124] When the EDCAF of a WLAN terminal initiates a backoff procedure, the EDCAF of the WLAN terminal can randomly select a backoff counter (BC) within a predetermined [0, CW (contention window)[AC]] according to the associated AC (access category). The BC value selected by the EDCAF associated with each AC can be the number of slots for which the EDCAF must perform CCA. If the channel is idle as a result of the CCA operation performed by the EDCAF on a slot-by-slot basis, the EDCAF can perform a BC decrease operation in each slot. For example, the slot length of the WLAN terminal used in the slot operation can vary. As a specific example, the slot length can be composed of one or more AIFS[AC] or EIFS[AC] (EIFS - DIFS - AIFSN[AC] Х aSlotTime + aSIFSTime - aRxTxTurnaroundTime) times or aSlotTime (e.g. 9 us). EDCAF can perform CCA according to the backoff procedure in slots corresponding to the selected BC value. EDCAF can decrease the BC by 1 if the channel resulting from the CCA performed in one slot is idle. The wireless LAN terminal can perform frame transmission if the channel resulting from the CCA performed when the BC becomes 0 is idle. For example, if the channel resulting from the CCA performed according to the backoff procedure is occupied, the wireless LAN terminal can maintain its BC at the current value for use in the next backoff procedure. Afterwards, the wireless LAN terminal can perform the BC decrease procedure according to the EDCAF operation again when the channel transitions from occupied to idle.

[0125] The frame transmission procedure through EDCA operation may be a procedure to perform CCA during AIFS[AC] on the main 20 MHz channel, wait for an additional slot time when BC becomes 0, and then perform frame transmission at the slot boundary when BC becomes 0. The value indicated by AIFS[AC] may be the number of slots during which CCA is performed. Specifically, AIFS[AC] may be a time length equal to aSIFS (short inter-frame space) time + AIFSN[AC] (a number specified per AC) * aSlotTime.

[0126] EDCAF may want to access a wider bandwidth channel (wideband channel) including the main 20 MHz channel. To access the wideband channel, EDCAF performs CCA during AIFS[AC] on the main 20 MHz channel, waits for an additional slot time when BC becomes 0, and then transmits a frame including the wideband channel for which the result of the CCA operation performed is idle for a period of time equal to the PIFS (priority interframe space) time before the slot boundary where BC becomes 0. Here, EDCAF may want to transmit the frame using only the main 20 MHz channel regardless of the CCA result of the wideband channel, and in the above-described case, the transmitted frame may be transmitted using only the main 20 MHz channel. The EDCA operation performed by EDCAF in a wireless LAN terminal can be expressed as an EDCA operation performed by a wireless LAN terminal (e.g., AP 1, AP 2, STA 1, STA 2).

[0127] The primary 20 MHz channel described in the EDCA operation may be a channel set by the AP during the BSS configuration process. The primary 20 MHz channel may be a channel indicated in a frame transmitted by the AP (e.g., a beacon frame, a probe response frame, etc.). As another example, the primary 20 MHz channel described in the EDCA operation may be an NPCA primary channel negotiated by an AP supporting NPCA operation with a non-AP STA supporting NPCA operation connected to it. In other words, when a WLAN terminal supporting NPCA operation performs NPCA operation, the EDCA operation may be performed on the NPCA primary channel, not the primary 20 MHz channel.

[0128] If the EDCAF in the wireless LAN terminal succeeds in channel access as a result of performing the EDCA operation on at least one of the main 20 MHz channel and the NPCA main channel, the EDCAF can transmit a frame of the corresponding AC (access category) using the channel (or bandwidth) on which the channel access was successful. The EDCAF in the wireless LAN terminal that transmitted the frame can obtain a transmit opportunity (TXOP). The TXOP obtained by the EDCAF in the wireless LAN terminal can be expressed as the TXOP obtained by the wireless LAN terminal to which the EDCAF belongs. The time length of the TXOP can be set to the time length from the time point of completion of the transmission of the frame initially transmitted by the wireless LAN terminal (or the EDCAF of the corresponding AC in the wireless LAN terminal) to the time point indicated by the duration / ID field of the MAC header in the frame. That is, the wireless LAN terminal that transmitted the first frame (or the EDCAF of the corresponding AC in the wireless LAN terminal) can perform transmission and reception operations from the time of completion of the first frame transmission to the time indicated by the Duration / ID field of the MAC header in the first frame.

[0129] In addition, the wireless LAN terminals (e.g., AP 1, AP 2, STA 1, STA 2) may be wireless LAN terminals that support non-primary channel access (NPCA) operation. The NPCA operation may be an operation in which the wireless LAN terminal switches the operating channel to an NPCA primary channel (or sub-channel) negotiated with other wireless LAN terminals in the BSS in advance when the channel is occupied as a result of CCA performed on the primary 20 MHz channel, and performs the above-described EDCA operation on the NPCA primary channel. For example, at least one of AP 1 and STA 1 in BSS 1 may have received a frame transmitted by at least one of AP 2 and STA 2 in BSS 2 on the primary 20 MHz channel. In the above case, at least one of AP 1 and STA 1 may perform an NPCA operation to switch its operating channel from the main 20 MHz channel to the NPCA main channel and then perform an EDCA operation (e.g., CCA, backoff procedure, etc.) on the NPCA main channel. When a wireless LAN terminal performs an NPCA operation, a switching time may be required for switching the operating channel (switching from the main 20 MHz channel to the NPCA main channel or from the NPCA main channel to the main 20 MHz channel). For example, the switching time may vary depending on the implementation performance of the terminal. A wireless LAN terminal performing an NPCA operation may perform an EDCA operation on the main 20 MHz channel or the NPCA main channel after the switching time described above when performing the NPCA operation.

[0130] When AP 1 in BSS 1 wants to activate NPCA operation in the BSS 1, AP 1 can transmit a management frame including an indicator indicating that the NPCA operation is activated. For example, the management frame can be any one of a beacon frame, a probe / association response frame, an ultra high reliability operation management frame (UHR OMN), and other frames, but may not be limited to a specific form. As another example, STA 1 connected to AP 1 can transmit the aforementioned management frame to AP 1 to indicate that the NPCA operation is enabled. As another example, AP 1 and STA 1 connected to AP 1 can negotiate the activation of the NPCA operation through an exchange of management frames between them. When AP 1 receives a frame transmitted from an OBSS, AP 1 can transmit the aforementioned management frame including minimum TXOP length information for performing the NPCA operation. STA 1 associated with AP 1 can transmit an indicator indicating whether it can perform NPCA operation by including it in a probe / association request frame. In addition, an STA capable of performing NPCA operation can change whether to activate NPCA operation and can transmit a frame (e.g., Management frame) including an indicator indicating whether to activate NPCA operation to AP 1 to indicate whether to participate in NPCA operation. The indicator indicating whether to activate NPCA operation can be included in the header of the MAC frame. Specifically, the indicator indicating whether to activate NPCA operation can be included in the A-control field. More specifically, the indicator indicating whether to activate NPCA operation can be included in one subfield of the OM Control field.In the present disclosure, a terminal supporting the NPCA operation may be a terminal that has instructed AP 1 to activate the NPCA operation through an indicator indicating whether to activate the NPCA operation. For example, if AP 1 has activated the NPCA operation and STA 1 belonging to BSS 1 has activated the NPCA operation, a condition may be added that a TXOP must be initiated through a control frame exchange in a predefined format. Specifically, if the NPCA operation is activated and a TXOP longer than a specific length is initiated, a control frame exchange may be required. The control frame in the predefined format may be a frame including information on a bandwidth or occupied channel used in the TXOP.

[0131] In addition, when a wireless LAN terminal (e.g., AP 1, AP 2, STA 1, STA 2) receives a frame (e.g., PPDU) on its main 20 MHz channel, the wireless LAN terminal may set a network allocation vector (NAV) using the value of the duration / ID field in the MAC header of the frame received by the wireless LAN terminal if the value of the RA (receiver address) field in the MAC header of the received frame is different from its own MAC address. The value of the duration / ID field in the MAC header of the frame received by the wireless LAN terminal may be set to the length of time until the end of TXOP of the wireless LAN terminal transmitting and / or receiving the frame. That is, the NAV set by the wireless LAN terminal may be set to the length of time from the above-described frame reception completion time until the end of TXOP of the wireless LAN terminal transmitting or receiving the frame. Here, the NAV set by the wireless LAN terminal may be an intra-BSS NAV or a basic NAV. The intra-BSS NAV may be a NAV set when a wireless LAN terminal receives an intra-BSS PPDU transmitted within a BSS. On the other hand, the default NAV may be a NAV set when a wireless LAN terminal receives an inter-BSS PPDU transmitted between BSSs. As another example, the default NAV may be a NAV set when a PPDU that cannot be classified as an intra-BSS PPDU or an inter-BSS PPDU is received. Non-AP STAs (e.g., STA 1, STA 2) may need to manage both the intra-BSS NAV and the default NAV described above. On the other hand, APs (e.g., AP 1, AP 2) may manage at least one of the inter-BSS NAV and the default NAV.

[0132] A wireless LAN terminal (e.g., AP 1, AP 2, STA 1, STA 2) can classify a received PPDU as an inter-BSS PPDU. For example, if the BSS_COLOR value of the RXVECTOR parameter of the PPDU received by the wireless LAN terminal is not 0 and the BSS_COLOR value does not match the BSS Color value of the BSS to which the wireless LAN terminal is currently connected, the wireless LAN terminal can classify the received PPDU as an inter-BSS PPDU. As another example, if a PPDU received by a wireless LAN terminal is a VHT (very high throughput) PPDU and the PARTIAL_AID (association ID) value of the RXVECTOR parameter is different from the BSSID of the BSS to which the wireless LAN terminal is currently connected, if the PARTIAL_AID value of the RXVECTOR parameter is different from the BSSID of the BSS to which the wireless LAN terminal is currently connected, if the PARTIAL_AID value of the RXVECTOR parameter is different from the BSSIDs of other BSSs belonging to the same multiple BSSID set or co-hosted BSSID set, and if the GROUP_ID of the RXVECTOR parameter is 0, the wireless LAN terminal can classify the received PPDU as an inter-BSS PPDU based on at least one of the following.As another example, if a PPDU received by a wireless LAN terminal is a VHT (very high throughput) PPDU, and the 5th to 8th bits of the PARTIAL_AID value of the RXVETOR parameter are not the same as the lower 4 bits (4 Least Significant Bits) of the BSS Color value announced from the BSS to which the wireless LAN terminal belongs and whose dot11PartialBSSColorImplemented value is True, and the GROUP_ID of the RXVECTOR parameter is 63, and the Partial BSS Color field of the most recently received HE Operation element is 1, the wireless LAN terminal may classify the received PPDU as an inter-BSS PPDU based on at least one of the following:

[0133] As another example, if a PPDU received by a wireless LAN terminal is a VHT MU (multi-user) PPDU or a HE (high efficiency) MU PPDU, the UPLINK_FLAG value of the RXVECOR parameter is 0, and the wireless LAN terminal receiving the PPDU is an AP, the wireless LAN terminal may classify the received PPDU as an inter-BSS PPDU. As another example, if the PPDU received by the wireless LAN terminal carries one frame, and is not identical to the BSSID of the BSS to which the wireless LAN terminal is connected, and is not identical to the BSSIDs of other BSSs belonging to the same multiple BSSID set or co-hosted BSSID set and is not a wildcard BSSID, the wireless LAN terminal may classify the received PPDU as an inter-BSS PPDU based on at least one of the following: As another example, if a PPDU received by a wireless LAN terminal carries a frame that does not include a BSSID field, but has both an RA field and a TA field, and the values ​​of the RA field and the TA field are not the same as the BSSIDs of other BSSs belonging to the same multiple BSSID set or co-hosted BSSID set, the wireless LAN terminal may classify the received PPDU as an inter-BSS PPDU. In the above case, the value of the Individual / Group bit in the TA field of the received PPDU may be set to 0 before the comparison between fields. The above conditions are inter-BSS PPDU judgment conditions, and a wireless LAN terminal that receives a PPDU that matches even one of the above conditions may update its basic NAV.

[0134] If a PPDU received by a wireless LAN terminal includes a control frame, and the control frame does not have a TA field but has an RA field (e.g., in the case of a CTS frame), the wireless LAN terminal may determine the PPDU as an intra-BSS PPDU if the address of a previously stored TXOP holder matches the address indicated in the RA field, and if the address indicated in the RA field is the address of the BSS to which the wireless LAN terminal is currently associated, or the address of the multiple BSSID set or co-hosted BSSID set to which the currently associated BSS belongs. For example, the above may be some of the determination conditions for an intra-BSS PPDU, but may not be limited thereto.

[0135] If the RA field of the CTS frame is not a BSSID and is different from the address of the previous TXOP holder, the PPDU containing the CTS frame may not meet any of the inter-BSS PPDU judgment conditions and may also differ from some of the intra-BSS PPDU judgment conditions described above. In the above cases, the PPDU may not be judged as either an intra-BSS PPDU or an inter-BSS PPDU. If the wireless LAN terminal receives a PPDU that cannot be judged as either an intra-BSS PPDU or an inter-BSS PPDU, the wireless LAN terminal may set the default NAV based on the PPDU.

[0136] In addition, a wireless LAN terminal supporting NPCA operation can perform frame transmission and reception operation on a channel (or bandwidth) including the NPCA primary channel until the primary 20 MHz channel state is expected to be idle after performing the NPCA operation. For example, when at least one of AP 1 and STA 1 receives a frame transmitted by at least one of AP 2 and STA 2, at least one of AP 1 and STA 1 can set a default NAV using the value of the duration / ID field in the MAC header of the received frame. The end time of the default NAV can be the same as the end time of the TXOP acquired by AP 2 or STA 2. At least one of AP 1 and STA 1 can switch its operating channel from the NPCA primary channel to the primary 20 MHz channel in accordance with the TXOP end time (default NAV end time) of at least one of AP 2 and STA 2.

[0137] The above-described NPCA primary channel (e.g., NPCA secondary channel, NPCA Primary Channel) can be set at various locations within the operating bandwidth of the BSS. For example, the secondary channel can be set as a single 20 MHz channel within a bandwidth corresponding to half of the operating bandwidth of the BSS that does not include the primary channel among the channels included in the operating bandwidth of the BSS. As a specific example, if the operating bandwidth of the BSS is 320 MHz, and there is a 160 MHz band including the primary channel and a 160 MHz band not including the primary channel, the secondary channel can be set as a single 20 MHz channel within the 160 MHz band that does not include the primary channel.

[0138] Here, as a condition for determining whether to perform the NPCA operation, an additional condition may be applied to perform the NPCA operation only when the bandwidth occupied by the PPDU (or frame) received from the OBSS is less than half of the operating bandwidth of the BSS. When the bandwidth occupied by the PPDU (or frame) received from the OBSS is 160 MHz and the operating bandwidth of the BSS is 320 MHz, a terminal supporting the NPCA operation that has received the PPDU (or frame) within the BSS may satisfy the condition for performing the NPCA operation. Here, the above-described matters may be equally applied to FIGS. 7a to 11 below.

[0139] Additionally, at least one of AP 1 and STA 1 may perform an operation (hereinafter, OBSS occupied channel confirmation operation) to check the channel (or bandwidth) on which frames (e.g., RTS frames, CTS frames, Data frames, trigger frames, etc. transmitted by AP 2 and / or STA 2) exchanged within the OBSS (e.g., BSS 2) are transmitted in order to perform NPCA operation.

[0140] In a method for confirming the channel (or bandwidth) through which a frame exchanged within an OBSS is transmitted, when at least one of AP 1 and STA 1 receives a frame exchanged within the OBSS, at least one of AP 1 and STA 1 may perform CCA in the entire operating bandwidth including the main 20 MHz channel at the start time of frame reception (e.g., the entire 160 MHz bandwidth if the entire operating bandwidth supported by at least one of AP 1 and STA 1 is 160 MHz), and may recognize the channel (e.g., bandwidth) through which the frame is transmitted by confirming the channel that is in an occupied state as a result of the CCA performance. Hereinafter, the start time of frame reception may be the time when PHY-RXSTART.indication is received from the physical layer to the MAC layer. Hereinafter, the method for confirming the channel (or bandwidth) through which a frame exchanged within the OBSS described above is referred to as the first method.

[0141] In a method of confirming a channel (or bandwidth) through which a frame exchanged within an OBSS is transmitted, when at least one of AP 1 and STA 1 receives a frame exchanged within an OBSS, at least one of AP 1 and STA 1 may recognize a channel through which the frame is transmitted by confirming an occupied channel as a result of CCA performed on the entire operating bandwidth including a primary 20 MHz channel for a certain period of time (e.g., PIFS time) before the time at which reception of the frame is completed. Alternatively, at least one of AP 1 and STA 1 may recognize a channel through which the frame is transmitted by confirming an occupied channel as a result of CCA performed on the entire operating bandwidth including a primary 20 MHz channel for a certain period of time (e.g., PIFS time) after the time at which reception of the frame starts. The CCA may be a CCA that senses which channel is an occupied channel by performing energy detection in units of 20 MHz channels. The time length of the CCA performed in the above-described manner may vary from one slot time (e.g., 9 μs), SIFS time, PIFS (priority interframe space) time, total transmission time of the received frame, and other times, and may not be limited to a specific form. Hereinafter, the method of confirming the channel (or bandwidth) through which the frames exchanged within the above-described OBSS were transmitted is referred to as the second method.

[0142] In addition, as a method of confirming the channel (or bandwidth) through which the frames exchanged within the OBSS were transmitted, if at least one of AP 1 and STA 1 can always decode the frames received within its own operating bandwidth in units of 20 MHz, at least one of AP 1 and STA 1 can recognize the channel through which the frames were transmitted by confirming the channel through which the received frames were successfully decoded after receiving the frames exchanged within the OBSS. Hereinafter, the method of confirming the channel (or bandwidth) through which the frames exchanged within the OBSS described above were transmitted is referred to as the third method.

[0143] In order to determine the channel (or bandwidth) on which frames exchanged within the OBSS are transmitted, AP 1 and AP 2 may share information about each other's operating channels. That is, AP 1 and AP 2 may be coordinated APs (C-APs). The shared information may include bandwidth information in frames transmitted from each BSS, and when a terminal in a different BSS receives a frame, the terminals can mutually know which channel the frame occupies. In addition, AP 1 and AP 2, which are C-APs, may inform each other that NPCA operation is available in the BSSs they have configured. AP 1 and AP 2, which are C-APs, may transmit frames exchanged in their BSSs including information about the bandwidth (or channel) on which the current frame is transmitted. For example, AP 2 may recognize that NPCA operation can be used in BSS 1 configured by AP 1, and information about the bandwidth (or channel) on which the current frame is transmitted may be included in a frame transmitted by at least one of AP 2 and STA 2. At least one of AP 1 and STA 1 may, after receiving the frame exchanged in the OBSS, use the information about the bandwidth (or channel) included in the frame to determine the channel on which the frame was transmitted. When AP 1 and AP 2 are C-APs, they may share at least one of an operating channel, a primary channel, an NPCA primary channel, and minimum TXOP length information for performing NPCA operation with each other. In addition, the above-described information may be shared with terminals within the BSS via beacon frames. Therefore, when STA 1 belonging to AP 1 and BSS 1 initiates a TXOP to induce NPCA operation by occupying the primary channel of BSS 2 in a C-AP relationship, a condition may be added that the TXOP must be initiated through an exchange of control frames in a predefined format.Specifically, if at least one of AP 1 and STA 1 of BSS 1 occupies the primary channel of BSS 2 or occupies the NPCA primary channel of BSS 2 and additionally initiates a TXOP exceeding the minimum TXOP length for performing the NPCA operation of BSS 1, the control frame exchange may be required. The control frame of the above-described predefined format may be a frame including information on the bandwidth or occupied channel used in the TXOP. The AP and STA included in BSS 2 may determine whether to perform the NPCA operation based on the information in the control frame. For example, if a frame transmitted from BSS 1 in a C-AP relationship is a control frame of the above-described predefined format and exceeds the minimum TXOP length for the NPCA operation, the NPCA operation may be performed by recognizing that it is a TXOP that does not occupy the NPCA primary channel. For example, information about the operating bandwidth (or channel) may vary. Information about the operating bandwidth (or channel) may be a bandwidth signaling TA. As another example, information about the operating bandwidth (or channel) may be a bandwidth signaling RA. A conventional RA (receiver address) may indicate the MAC address of a wireless LAN terminal that is the recipient of the frame. On the other hand, a bandwidth signaling RA may be an RA that uses several bits of the RA to indicate the bandwidth. As another example, information about the operating bandwidth (or channel) may be included in the form of a field (e.g., U-SIG, etc.), subfield, bit, etc. in the PHY preamble and / or PHY header. Hereinafter, a method for confirming the channel (or bandwidth) through which a frame exchanged within the above-described OBSS is transmitted is referred to as the fourth method.

[0144] When at least one of AP 1 and STA 1 initially receives a frame (e.g., RTS frame, MU-RTS (Multi User RTS) frame, CTS frame, CTS-to-Self frame, Trigger Frame (TF), etc.) from the OBSS in order to determine the channel (or bandwidth) on which the frames exchanged within the OBSS are transmitted, at least one of AP 1 and STA 1 may set a NAV using the value of the Duration / ID field in the MAC header of the frame initially received from the OBSS. At least one of AP 1 and STA 1 may wait for reception of a subsequent frame for a NAVTimeout period to confirm the NAV set by the frame initially received from the OBSS. The NAVTimeout period may be "(2 x aSIFSTime) + CTS_Time + aRxPHYStartDelay + (2 x aSlotTime)". At least one of AP 1 and STA 1 may cancel the NAV set to the frame initially received from the OBSS if no subsequent frame is received during the NAVTimeout period. At least one of AP 1 and STA 1 may confirm the NAV set to the RTS frame or the MU-RTS frame if at least one of AP 1 and STA 1 receives a subsequent frame during the NAVTimeout period. At least one of AP 1 and STA 1 may perform CCA in units of 20 MHz over its entire operating bandwidth during the NAVTimeout period. That is, at least one of AP 1 and STA 1 may perform CCA over its entire operating bandwidth after receiving the frame initially received from the OBSS to determine the channel (or bandwidth) over which the subsequent frame (e.g., CTS frame, Data frame, etc.) received during the NAVTimeout period was transmitted.If at least one of AP 1 and STA 1 determines whether a subsequent frame is received during the NAV Timeout, at least one of AP 1 and STA 1 may determine frame reception by receiving a PHY preamble and / or a PHY header in the subsequent frame. As a method of determining a channel (or bandwidth) over which a frame exchanged within an OBSS is transmitted, at least one of AP 1 and STA 1 may determine frame reception through energy detection of the subsequent frame. As another example, at least one of AP 1 and STA 1 may determine reception of the subsequent frame if the MAC layer receives a PHY-RXSTART.indication primitive transmitted from the physical layer to the MAC layer after detecting a PPDU and successfully decoding the preamble. Hereinafter, the method of determining a channel (or bandwidth) over which a frame exchanged within the OBSS described above is transmitted is referred to as the fifth method.

[0145] As a method for confirming the channel (or bandwidth) through which a frame exchanged within an OBSS is transmitted, at least one of AP 1 and STA 1 can confirm transmission bandwidth information in the received OBSS frame. At least one of AP 1 and STA 1 can recognize that the frame does not occupy the NPCA primary channel if the transmission bandwidth is smaller than the gap between the primary channel and the NPCA primary channel. For example, the bandwidth of the received frame may be smaller than the difference in center frequencies between the primary channel and the NPCA primary channel. If the bandwidth of the received frame is 80 MHz, the difference between the center frequency of the primary channel and the center frequency of the NPCA primary channel may be 160 MHz. In the above case, at least one of AP 1 and STA 1 can recognize that the received frame including the primary channel does not occupy the NPCA primary channel. Hereinafter, the method for confirming the channel (or bandwidth) through which a frame exchanged within the OBSS is transmitted is referred to as the sixth method.

[0146] As a method of confirming the channel (or bandwidth) on which the frames exchanged within the OBSS are transmitted, the physical layer (PHY layer) of at least one AP and STA supporting VHT (very high throughput) among the IEEE 802.11 protocols can recognize that there is a PPDU to be received if it receives a valid PHY preamble and / or PHY header including the main 20 MHz channel. The physical layer can confirm the scrambling sequence present in the service field of the PHY header of the received PPDU. Here, the physical layer can interpret specific bits of the scrambling sequence (e.g., bits 5, 6, and 7 out of the first 7 bits of the scrambling sequence) as bits indicating information on the bandwidth on which the PPDU is transmitted. If it is determined that the PPDU has been received correctly, the physical layer can include the information on the bandwidth on which the PPDU is transmitted in the RXVECTOR and transmit it to the medium access control layer (MAC layer). For example, the bandwidth information transmitted by the PPDU may be included in the RXVECTOR in the form of the CH_BANDWIDTH_IN_NON_HT parameter. The MAC layer can check the bandwidth information received by the PPDU by checking the RXVECTOR transmitted by the physical layer. For example, if the TA (transmitting address) of the MAC header of the MAC frame in the received PPDU is a bandwidth signaling TA (e.g., if the TA of the received MAC frame is a individually designated address and the Individual / Group bit is set to 1), the PPDU included in the RXVECTOR may determine that the received bandwidth information is valid. Accordingly, when the MAC layer receives a frame in which the TA is set to the bandwidth signaling TA, the MAC layer can recognize the bandwidth transmitted by the received PPDU using the bandwidth information included in the RXVECTOR. Hereinafter, the method of checking the channel (or bandwidth) transmitted by the frames exchanged within the above-described OBSS is referred to as the seventh method.

[0147] As a method of determining the channel (or bandwidth) through which frames exchanged within an OBSS are transmitted, at least one of the AP and the STA may have additionally received a frame (response frame) transmitted immediately in response to the frame after initially receiving the frame exchanged within the OBSS. However, although the transmission bandwidth of the initially received frame may be recognized, the transmission bandwidth of a response frame received thereafter may not be recognized. For example, at least one of the AP and the STA may have received a (MU-)RTS frame transmitted from the OBSS, and thereafter received a CTS frame transmitted in response to the (MU-)RTS. In the above case, at least one of the AP and the STA may recognize the bandwidth through which the (MU-)RTS frame was transmitted using the above-described method. For example, when the TA field of the (MU-)RTS frame is a bandwidth signaling TA, at least one of the AP and the STA may recognize the bandwidth through which the RTS frame was transmitted. However, since the CTS frame does not have a TA field, the bandwidth through which the CTS frame was transmitted cannot be recognized by the above-described method. Therefore, if at least one of the AP and the STA has received the (MU-)RTS frame initially exchanged within the OBSS, and the TA of the (MU-)RTS frame is a bandwidth signaling TA, the bandwidth information (e.g., CH_BANDWIDTH_IN_NON_HT parameter) in the RXVECTOR transmitted by the physical layer to the MAC layer as a result of receiving the subsequently received CTS frame (the CTS frame transmitted in response to the (MU-)RTS frame) can be determined to be valid. Therefore, at least one of the AP and the STA can recognize the transmission bandwidth of the CTS frame transmitted within the OBSS. Hereinafter, the method of confirming the channel (or bandwidth) through which the frame exchanged within the OBSS was transmitted will be referred to as the eighth method.The first to eighth methods described above can be applied equally to FIGS. 7a to 11 below, and are referred to as each method below for convenience of explanation.

[0148] In addition, as an example, AP 2 (or STA 2) configuring BSS 2 can access the channel through the above-described EDCA operation on the main 20 MHz channel of BSS 2 and transmit the first frame to STA 2 (or AP 2). That is, AP 2 (or STA 2) can perform an EDCA operation (e.g., a CCA operation and / or an EDCA backoff procedure) on the main 20 MHz channel after traffic to be transmitted to STA 2 (or AP 2) (e.g., downlink (DL) traffic or uplink (UL) traffic) arrives, and can transmit the first frame to STA 2 (or AP 2) using the main 20 MHz channel and / or an operating bandwidth (or channel) including the main 20 MHz channel through the EDCA operation performed on the main 20 MHz channel. AP 2 (or STA 2) that transmitted the first frame can obtain a TXOP.

[0149] The first frame transmitted by the above-mentioned AP 2 (or STA 2) may be an RTS frame. The TA (transmit address) field value of the RTS frame MAC header may be a bandwidth signaling TA. Here, the existing TA may indicate the MAC address of the wireless LAN terminal that transmitted the frame. On the other hand, the bandwidth signaling TA may use several bits of the TA to indicate the bandwidth. AP 2 (or STA 2) may use the bandwidth signaling TA of the RTS frame transmitted on the main 20 MHz channel of BSS 2 to indicate to STA 2 (or AP 2) information about the bandwidth (e.g., 40 MHz, 80 MHz, 160 MHz, 80+80 MHz, 320 MHz, etc.) of a frame expected to be transmitted subsequently (e.g., Data frame). STA 2 (or AP 2), which receives the RTS frame transmitted by AP 2 (or STA 2), can transmit a CTS frame to AP 2 (or STA 2) after an SIFS period after receiving the RTS frame. AP 2 (or STA 2), which receives the CTS frame transmitted by STA 2 (or AP 2), can receive the CTS frame and transmit a data frame to STA 2 (or AP 2) using the bandwidth over which the CTS frame was transmitted after an SIFS period. STA 2 (or AP 2), which receives the data frame transmitted by AP 2 (or STA 2), can receive the data frame and respond by transmitting a BlockAck (BA) frame to AP 2 (or STA 2) after an SIFS period.

[0150] When at least one of the AP and the STA receives a frame (e.g., a PPDU transmitted within a BSS), there may be various ways to check the bandwidth information transmitted in the received frame. For example, when at least one of the AP and the STA receives a valid preamble during the initial primary 20 MHz channel sensing, the AP and the STA may check the bandwidth information included in the received PPDU (e.g., bandwidth information included in a PHY header). For example, the bandwidth information may be bandwidth information included in a scrambling sequence of a service field included in a PHY header. As another example, the bandwidth information may be bandwidth information included in a MAC header, but may not be limited to a specific form. At least one of the AP and the STA may recognize the transmission bandwidth of the received frame through the bandwidth information described above. At least one of the AP and the STA may transmit a frame in response to the received frame by setting the transmission bandwidth of the frame to the bandwidth indicated by the bandwidth information of the received frame. However, if at least one of the AP and the STA cannot transmit the entire bandwidth of the received frame depending on the timing of transmitting the response frame or the channel status of the bandwidth of the bandwidth of the received frame (e.g., busy state), the AP and the STA may transmit using a bandwidth (channel) narrower than the bandwidth of the received frame. Here, the above-described matters can be equally applied to FIGS. 7a to 9.

[0151] FIGS. 7A and 7B are diagrams illustrating a sub-channel access operation method according to a transmission bandwidth of a wireless LAN OBSS applied to the present disclosure. Referring to FIGS. 7A and 7B , at least one of AP 1 and STA 1 may have received a frame exchanged between AP 2 and STA 2 described above on a primary 20 MHz channel of BSS 1. At least one of AP 1 and STA 1 may recognize that the received frame is a frame (i.e., an inter-BSS PPDU) transmitted within the OBSS (e.g., BSS 2). At least one of AP 1 and STA 1 may check the occupancy status of the NPCA primary channel in order to perform an NPCA operation. That is, if at least one of AP 1 and STA 1 has received a frame occupying the primary 20 MHz channel from the OBSS and the above-described frame satisfies the condition for performing the NPCA operation, and the NPCA primary channel is not occupied, the NPCA operation may be performed. Here, at least one of AP 1 and STA 1 may have received at least one of the CTS frame (602) and the BA frame (604) among the frames exchanged between AP 2 and STA 2. At least one of the above-described CTS frame (602) and the BA frame (604) may not include bandwidth information. Therefore, at least one of AP 1 and STA 1 may not be able to recognize the entire bandwidth over which the frame received from the OBSS is transmitted, and may not be able to recognize whether the NPCA primary channel is occupied by the frame received from the OBSS.

[0152] Referring to FIG. 7A, at least one of AP 1 and STA 1 may not have received the RTS frame (601) and may have only received the CTS frame (602). The CTS frame (602) is a frame transmitted from the OBSS, and at least one of AP 1 and STA 1 may confirm the CTS frame (602) and set a basic NAV. Here, the CTS frame (602) may not include information on the bandwidth to be transmitted. Therefore, if at least one of AP 1 and STA 1 does not receive both the RTS frame (601) and the CTS frame (602) transmitted from the OBSS, it cannot recognize information on the bandwidth (or channel) occupied by the OBSS. Here, at least one of AP 1 and STA 1 may not be able to recognize whether the bandwidth (or channel) occupied by the OBSS occupies an NPCA primary channel and may therefore not perform an NPCA operation. That is, if at least one of AP 1 and STA 1 receives only the CTS frame (602), at least one of AP 1 and STA 1 cannot recognize the bandwidth occupied by the OBSS, and thus, upon receiving the CTS frame (602), sets the default NAV but transitions to the NPCA primary channel and operates on the primary channel without performing the NPCA operation.

[0153] As another example, when the CTS frame (602) does not include bandwidth information, at least one of AP 1 and STA 1 may perform one or more of the first, second, third, fourth, fifth and sixth methods described above to determine whether the channel on which the CTS frame (602) is transmitted includes a subchannel (or NPCA main channel) by checking the transmitted channel (or bandwidth). When the channel on which the CTS frame (602) is transmitted includes a subchannel (or NPCA main channel), at least one of AP 1 and STA 1 may not perform an NPCA operation. At least one of AP 1 and STA 1 may wait without performing a transmission or reception operation on the main 20 MHz channel until the TXOP end time of AP 2 or STA 2 (i.e., the basic NAV end time). At least one of AP 1 and STA 1 may perform the EDCA operation described above on the primary 20 MHz channel at the end of the TXOP of AP 2 or STA 2 (the end of the primary NAV).

[0154] Referring to FIG. 7B, at least one of AP 1 and STA 1 may not have received the RTS frame (605) and may have only received the CTS frame (606). At least one of AP 1 and STA 1 may confirm the CTS frame (606) transmitted from the OBSS and set a default NAV. Here, the CTS frame (606) may not include information on the bandwidth to be transmitted. Therefore, when at least one of AP 1 and STA 1 does not receive both the RTS frame (605) and the CTS frame (606) transmitted from the OBSS, at least one of AP 1 and STA 1 may not be able to recognize information about the bandwidth (or channel) occupied by the OBSS and may not be able to recognize whether the bandwidth (or channel) occupied by the OBSS occupies an NPCA primary channel, and thus may not perform the NPCA operation. That is, if at least one of AP 1 and STA 1 receives only the CTS frame (606), at least one of AP 1 and STA 1 receives the CTS frame (606) and sets the default NAV, but cannot recognize the bandwidth occupied by the OBSS and thus transitions to the NPCA primary channel and operates on the primary channel without performing the NPCA operation.

[0155] As another example, when the CTS frame (606) does not include bandwidth information, at least one of AP 1 and STA 1 may perform at least one of the first, second, third and fourth methods described above to determine that the channel on which the CTS frame (606) is transmitted does not include an NPCA primary channel (or subchannel) by checking the transmitted channel (or bandwidth). Accordingly, at least one of AP 1 and STA 1 may switch its operating channel from the primary 20 MHz channel to the NPCA primary channel at the time of completion of the OBSS occupied channel checking operation. At least one of AP 1 and STA 1 may perform an EDCA operation on the NPCA primary channel after a switching time required for switching the operating channel to the NPCA primary channel, and may transmit a frame using a channel (or bandwidth) including the NPCA primary channel.

[0156] As another example, the EDCA operation performed on the NPCA primary channel can only be performed by the AP. Therefore, AP 1 can access the channel through the EDCA operation on the NPCA primary channel and transmit the first frame to STA 1, which is expected to have performed the NPCA operation using the channel that successfully accessed the channel. The length of time indicated by the Duration / ID field in the MAC header of the frame initially transmitted by AP 1 to STA 1 may be the TXOP end time (basic NAV end time) of AP 2 or STA 2. That is, the end time of the TXOP acquired by at least one of AP 1 and STA 1 using the NPCA primary channel may be the same as the TXOP end time (basic NAV end time) of AP 2 or STA 2. At least one of AP 1 and STA 1 may switch its operating channel from the NPCA primary channel to the primary 20 MHz channel at the end of the TXOP of AP 2 or STA 2 (the end of the default NAV) after performing frame exchange in the TXOP acquired from the NPCA primary channel. At least one of AP 1 and STA 1 may perform EDCA operations on the primary 20 MHz channel after a switching time required for switching the operating channel to the primary 20 MHz channel.

[0157] FIG. 8 is a diagram illustrating a sub-channel access operation method according to a transmission bandwidth of a wireless LAN OBSS applied to the present disclosure. Referring to FIG. 8, at least one of AP 1 and STA 1 can receive a frame exchanged between AP 2 and STA 2 on a main 20 MHz channel of BSS 1. At least one of AP 1 and STA 1 can recognize that the received frame is a frame (i.e., an inter-BSS PPDU) transmitted within the OBSS (e.g., BSS 2). Here, at least one of AP 1 and STA 1 may need to check the occupancy status of the NPCA main channel in order to perform an NPCA operation. However, at least one of AP 1 and STA 1 may have received at least one of an RTS frame (607) and a data frame (609) among the frames exchanged between AP 2 and STA 2. For example, at least one of AP 1 and STA 1 may not receive a CTS frame among the frames exchanged by AP 2 and STA 2. At least one of AP 1 and STA 1 may be aware of the entire bandwidth to be transmitted when receiving an RTS frame (607) from the OBSS, but may not be aware of the bandwidth to be used for transmitting a data frame (609) when not receiving a CTS frame (608). Here, at least one of AP 1 and STA 1 may not be able to recognize whether the NPCA primary channel is occupied by a frame received from the OBSS.

[0158] For example, if at least one of AP 1 and STA 1 receives only an RTS (or MU-RTS) frame (607) from the OBSS, at least one of AP 1 and STA 1 may determine whether the NPCA primary channel is occupied based on bandwidth information included in the RTS (or MU-RTS) frame (607). If at least one of AP 1 and STA 1 determines that the NPCA primary channel is occupied through the RTS (or MU-RTS) frame (607), at least one of AP 1 and STA 1 may not perform the NPCA operation. On the other hand, if at least one of AP 1 and STA 1 determines that the NPCA primary channel is not occupied based on bandwidth information included in the RTS (or MU-RTS) frame (607), at least one of AP 1 and STA 1 may perform the NPCA operation.

[0159] As another example, at least one of AP 1 and STA 1 may determine whether to perform an NPCA operation through the method of checking the transmission bandwidth of frames exchanged in the above-described OBSS. Referring to FIG. 8, at least one of AP 1 and STA 1 may perform an operation corresponding to the fifth method by checking the transmitted channel (or bandwidth) after receiving the RTS frame (607). That is, at least one of AP 1 and STA 1 may receive the RTS frame (607), obtain bandwidth information used for transmission and reception in the RTS frame (607), and then perform CCA in units of 20 MHz on its own operating bandwidth (or channel) during the NAVTimeout period.

[0160] Here, at least one of AP 1 and STA 1 may have received a data frame (609) during the NAVTimeout period. At least one of AP 1 and STA 1 may check the channel (or bandwidth) through which the data frame (609) was transmitted (or both the RTS frame and the channel through which the data frame was transmitted) and may check that the NPCA primary channel is not occupied.

[0161] At least one of AP 1 and STA 1 can determine whether a frame exchanged in an OBSS occupies an NPCA primary channel based on channel allocation information of a frequency band in which at least one of AP 1 and STA 1 operates and the sequence of PPDUs exchanged between AP 2 and STA 2 at SIFS intervals. Specifically, at least one of AP 1 and STA 1 can determine whether an NPCA primary channel is occupied based on bandwidth information indicated in the PPDUs (e.g., bandwidth information included in either a PHY header or a MAC header) or bandwidth information of a PPDU obtained from a CH_BANDWIDTH_IN_NON_HT parameter value of an RXVECTOR received as a result of receiving the PPDUs during a series of transmissions of a first PPDU including an initial control frame (ICF) (e.g., RTS), a second PPDU including an initial control response (ICR) (e.g., CTS) (the second PPDU may not be received), and a third PPDU (e.g., a PPDU including a data frame) as a sequence of PPDUs exchanged between AP 2 and STA 2. If at least one of AP 1 and STA 1 determines that the NPCA primary channel is not occupied based on bandwidth information of the received PPDU, at least one of AP 1 and STA 1 may switch its operating channel from the primary 20 MHz channel to the NPCA primary channel at the time of receiving a third PPDU including a data frame (609). At least one of AP 1 and STA 1 may initiate a channel switching operation for the NPCA operation and perform the NPCA operation after the switching time.

[0162] The time at which at least one of AP 1 and STA 1 switches to the NPCA primary channel may be the time (e.g., NHT switch time) at which the physical layer checks the preamble of the received PPDU and transmits PHY-RXEARLYSIG.indication primitive or PHY-RXSTART.indication primitive to the MAC layer as a result of receiving the third PPDU in a series of transmissions of the first PPDU, the second PPDU, and the third PPDU exchanged between AP 2 and STA 2 as a sequence of PPDUs, and the MAC layer receives it. For example, the time at which the physical layer of the wireless LAN terminal checks the preamble of the received PPDU and transmits PHY-RXEARLYSIG.indication primitive or PHY-RXSTART.indication primitive to the MAC layer may be the time after the third OFDM (orthogonal frequency division multiplex) symbol after receiving the L-SIG of the PPDU. That is, at least one of AP 1 and STA 1 can switch to the NPCA primary channel at a preset point in time based on the result of receiving the third PPDU.

[0163] The point in time at which at least one of the above-described AP 1 and STA 1 switches to the NPCA primary channel may be the point in time at which the terminal (e.g., AP 1, STA 1) switching to the NPCA primary channel confirms the third OFDM symbol after receiving the L-SIG of the PPDU, regardless of whether the PHY of the terminal (e.g., AP 1, STA 1) switching to the NPCA primary channel transmits the PHY-RXEARLYSIG.indication primitive or the PHY-RXSTART.indication primitive to the MAC, or a point in time thereafter. That is, even if the PHY of the terminal (e.g., AP 1, STA 1) switching to the NPCA primary channel has not performed the process of transmitting the primitive to the MAC, the point in time at which the terminal (e.g., AP 1, STA 1) switching to the NPCA primary channel acquires the bandwidth information included in the PPDU at that point in time may be the point in time thereafter.

[0164] The aforementioned point in time may be a point in time when at least one of AP 1 and STA 1 confirms that a valid TXOP is set in the OBSS by receiving the third PPDU even if it has not received ICR (CTS) after receiving only ICF (RTS). That is, even in a situation where at least one of AP 1 and STA 1 has received an RTS frame, if it determines that the third PPDU does not occupy the NPCA primary channel by the aforementioned method at the time of receiving the third PPDU including a data frame, it may switch the operating channel to the NPCA primary channel. At least one of AP 1 and STA 1 may perform an EDCA operation on the NPCA primary channel after a switching time required for switching the operating channel to the NPCA primary channel, and may transmit a frame using a channel (or bandwidth) including the NPCA primary channel.

[0165] As another example, the EDCA operation performed on the NPCA primary channel can only be performed by the AP. Therefore, AP 1 can access the channel through the EDCA operation on the NPCA primary channel and transmit the first frame to STA 1, which is expected to have performed the NPCA operation using the channel that successfully accessed the channel. The length of time indicated by the Duration / ID field in the MAC header of the frame initially transmitted by AP 1 to STA 1 may be the TXOP end time (basic NAV end time) of AP 2 or STA 2. That is, the end time of the TXOP acquired by at least one of AP 1 and STA 1 using the NPCA primary channel may be the same as the TXOP end time (basic NAV end time) of AP 2 or STA 2. At least one of AP 1 and STA 1 may switch its operating channel from the NPCA primary channel to the primary 20 MHz channel at the end of the TXOP of AP 2 or STA 2 (the end of the default NAV) after performing frame exchange in the TXOP acquired from the NPCA primary channel. At least one of AP 1 and STA 1 may perform EDCA operations on the primary 20 MHz channel after a switching time required for switching the operating channel to the primary 20 MHz channel.

[0166] Referring to FIG. 8, when either AP 1 or STA 1 fails to receive the second PPDU transmitted in response to the first PPDU during a series of transmissions of the first PPDU (e.g., (MU-)RTS), the second PPDU (e.g., CTS) and the third PPDU (e.g., Data) exchanged between AP 2 and STA 2 of the OBSS in the sequence of the PPDUs, and performs a switch to the NPCA primary channel at or after the time of starting to receive the third PPDU (e.g., the time of receiving the third OFDM symbol after receiving the L-SIG of the third PPDU, etc.), the length of time for performing a wireless LAN operation (e.g., EDCA channel access operation, frame exchange operation, etc.) on the NPCA primary channel may take into account the length of the transmission time of the PPDU indicated by the LENGTH field in the PHY preamble and / or PHY header of the third PPDU. For example, in the above-described situation, the length of time that either AP 1 or STA 1 operates on the NPCA primary channel may be a time calculated as [the end time of reception of the third PPDU indicated by the LENGTH field in the PHY preamble and / or PHY header of the third PPDU - (the start time of switching to the NPCA primary channel - the time required to switch from the NPCA primary channel to the primary channel (e.g., NPCA switch back delay)]. That is, the length of time that either AP 1 or STA 1 operates on the NPCA primary channel may be equal to or shorter than the end time of transmission of the third PPDU.

[0167] FIG. 9 is a diagram illustrating a sub-channel access operation method according to a transmission bandwidth of a wireless LAN OBSS applied to the present disclosure. Referring to FIG. 9, at least one of AP 1 and STA 1 may have received a frame exchanged between AP 2 and STA 2 on a main 20 MHz channel of BSS 1, and may recognize that the received frame is a frame (i.e., inter-BSS PPDU) transmitted within the OBSS (e.g., BSS 2). At least one of AP 1 and STA 1 may need to check the occupancy status of the NPCA main channel in order to perform an NPCA operation. At least one of AP 1 and STA 1 may have received all of the control frames exchanged between AP 2 and STA 2 for data transmission. That is, at least one of AP 1 and STA 1 may have received both an RTS frame (610) and a CTS frame (611). At least one of AP 1 and STA 1 may be able to recognize the bandwidth from the RTS frame (610) received from the OBSS, but may not be able to recognize the entire bandwidth used to transmit the data frame (612) because the CTS frame (611) does not contain information on the entire bandwidth used for transmission and reception. In addition, at least one of AP 1 and STA 1 may not be able to recognize whether the NPCA primary channel is occupied by the data frame (612) to be transmitted by the OBSS.

[0168] Here, at least one of AP 1 and STA 1 may not be able to determine information about the entire bandwidth over which the CTS frame (611) was transmitted in the CTS frame (611). At least one of AP 1 and STA 1 may determine whether to perform an NPCA operation based on information about the entire bandwidth (or / and channel) over which the RTS (or MU-RTS) frame (610) was transmitted, which is a frame that requests immediate transmission of the CTS frame (611) received prior to the CTS frame (611) as a response frame. For example, if it is determined that the bandwidth (or / and channel) over which the RTS (or MU-RTS) frame was transmitted includes an NPCA primary channel, at least one of AP 1 and STA 1 may not perform the NPCA operation.

[0169] Referring to FIG. 9, at least one of AP 1 and STA 1 may receive a CTS frame (611) after receiving an RTS frame (610). Even when at least one of AP 1 and STA 1 receives a CTS frame (611), if the bandwidth at which STA 2 or AP 2 that transmitted the CTS frame (611) can receive a data frame (612) (i.e., the total bandwidth that STA 2 or AP 2 can support) is smaller than the bandwidth indicated in the RTS frame (610), the bandwidth at which the CTS frame (611) is transmitted may be smaller than the bandwidth indicated in the RTS frame (610). In the case described above, when at least one of AP 1 and STA 1 receives a frame, at least one of AP 1 and STA 1 may perform one or more of the first method, the second method, the third method, the fourth method, the fifth method, the sixth method, the seventh method, and the eighth method described above as a method of checking the transmitted channel (or bandwidth) to check the channel (or bandwidth) on which the data frame (612) is to be transmitted. For example, at least one of AP 1 and STA 1 may perform the seventh method and the eighth method described above, and may check the channel (or bandwidth) on which the RTS frame (610) is transmitted and the channel (or bandwidth) on which the CTS frame (611) is transmitted after receiving the RTS frame (610). Here, the RTS frame (610) received by at least one of AP 1 and STA 1 may occupy the NPCA primary channel. However, a response frame (e.g., CTS frame) of an RTS frame (610) received by at least one of AP 1 and STA 1 may be transmitted using a channel (or bandwidth) less than the transmission channel (or bandwidth) of the RTS frame (610). Therefore, the NPCA primary channel may not be occupied by the OBSS.At least one of AP 1 and STA 1 may perform one or more of the first, second, third, fourth, fifth, sixth, seventh, and eighth methods for checking the transmitted channel (or bandwidth) after receiving the RTS frame (610) to check the transmitted channel (or bandwidth) of a frame (e.g., a CTS frame, a Data frame, etc.) transmitted subsequent to the RTS frame (610). For example, at least one of AP 1 and STA 1 may perform the eighth method described above to check the transmitted channel (or bandwidth) of a frame (e.g., a CTS frame, a Data frame, etc.) transmitted subsequent to the RTS frame (610). As a result of the method for checking the transmitted channel (or bandwidth), at least one of AP 1 and STA 1 may check that the frame transmitted subsequent to the RTS frame (610) occupied the NPCA primary channel. In the above case, at least one of AP 1 and STA 1 may not perform the NPCA operation. That is, at least one of AP 1 and STA 1 may wait without performing transmission / reception operations on the main 20 MHz channel until the TXOP end time (basic NAV end time) of AP 2 or STA 2. At least one of AP 1 and STA 1 may perform the EDCA operation on the main 20 MHz channel at the TXOP end time (basic NAV end time) of AP 2 or STA 2.

[0170] As another example, at least one of AP 1 and STA 1 may determine that a frame transmitted subsequent to an RTS frame (610) as a result of the method of determining the transmitted channel (or bandwidth) does not occupy the NPCA primary channel. Accordingly, at least one of AP 1 and STA 1 may switch its operating channel from the primary 20 MHz channel to the NPCA primary channel at the time of completion of the OBSS occupied channel determination operation. At least one of AP 1 and STA 1 may perform an EDCA operation on the NPCA primary channel after a switching time required for switching the operating channel to the NPCA primary channel, and may transmit the frame using a channel (or bandwidth) including the NPCA primary channel.

[0171] As another example, the EDCA operation performed on the NPCA primary channel can only be performed by the AP. Therefore, AP 1 can access the channel through the EDCA operation on the NPCA primary channel and transmit the first frame to STA 1, which is expected to have performed the NPCA operation using the channel on which the channel access was successful. The time length indicated by the Duration / ID field in the MAC header of the frame initially transmitted by AP 1 to STA 1 may be the TXOP end time (Basic NAV end time) of AP 2 or STA 2. That is, the end time of the TXOP acquired by at least one of AP 1 and STA 1 using the NPCA primary channel may be the same as the TXOP end time (Basic NAV end time) of AP 2 or STA 2. At least one of AP 1 and STA 1 may switch its operating channel from the NPCA primary channel to the primary 20 MHz channel at the end time of the TXOP of AP 2 or STA 2 (the end time of the Basic NAV) after performing frame exchange in the TXOP acquired from the NPCA primary channel. At least one of AP 1 and STA 1 may perform the EDCA operation on the primary 20 MHz channel after a switching time required for switching the operating channel to the primary 20 MHz channel.

[0172] As another example, at least one of AP 1 and STA 1 may have confirmed that the CTS frame (611) received subsequently after receiving the RTS frame (610) transmitted from BSS 2 did not occupy the NPCA primary channel by checking the transmitted channel (or bandwidth). At least one of AP 1 and STA 1 may have set a NAV using the duration field value of the MAC header of at least one of the RTS frame (610) and the CTS frame (611) after receiving the RTS frame (610) and the CTS frame (611) transmitted from BSS 2. At least one of AP 1 and STA 1 may store the duration field value (the time length of the TXOP). Here, the set NAV may indicate the time length of the TXOP during which transmission is performed by AP 2 and STA 2 that exchanged the RTS frame (610) and the CTS frame (611).

[0173] In addition, even if at least one of AP 1 and STA 1 confirms that the NCPA primary channel is not occupied by checking the transmission bandwidth of the CTS frame (611), the operating channel may not be immediately switched to the NPCA primary channel. Specifically, at least one of AP 1 and STA 1 may wait to receive a third frame (e.g., Data frame) received after receiving the CTS frame (611). At least one of AP 1 and STA 1 may have received the third frame and confirmed that the third frame does not occupy the NPCA primary channel. In the above case, at least one of AP 1 and STA 1 may switch the operating channel to the NPCA primary channel at the time when it confirms that the third frame does not occupy the NPCA primary channel. At least one of AP 1 and STA 1 may perform the NPCA operation by using the time length information (i.e., the time length of TXOP) indicated by the NAV set by receiving the first received RTS frame (610) and CTS frame (611), rather than the transmission time length of the PPDU indicated by the PPDU Duration field of the PHY header of the PPDU including the third frame, even though the NPCA operation was performed after receiving the third frame. Alternatively, at least one of AP 1 and STA 1 may perform the NPCA operation by setting the stored Duration field value as the NPCA operation period.

[0174] Another way to determine whether the NPCA primary channel is occupied is to receive an RTS frame (610) transmitted from BSS 2, and then determine that the RTS frame (610) occupies the NPCA primary channel, and then fail to determine that the CTS frame (611) received thereafter does not occupy the NPCA primary channel. Alternatively, at least one of AP 1 and STA 1 may receive only the RTS frame (610) and not the CTS frame (611), and thus may recognize that the NPCA primary channel is occupied through the bandwidth information of the RTS frame (610). Alternatively, at least one of AP 1 and STA 1 may receive only the CTS frame (611) and may not recognize whether the NPCA primary channel is occupied. However, in the above-described case, at least one of AP 1 and STA 1 may store the duration information received through at least one of the RTS frame (610) and the CTS frame (611). That is, the time length of TXOP can be stored. At least one of AP 1 and STA 1 can receive the third frame (e.g., Data frame) and set the default NAV by confirming that the third frame is an inter-BSS PPDU. Here, at least one of AP 1 and STA 1 can perform the NPCA operation by confirming that the third frame does not occupy the NPCA primary channel and satisfying the NPCA execution condition. Even if at least one of AP 1 and STA 1 performs the NPCA operation after receiving the third frame, the NPCA operation can be performed using the time length information (i.e., the time length of TXOP) indicated by the NAV set by receiving the first received RTS frame (610) and CTS frame (611), not the transmission time length of the PPDU indicated by the PPDU Duration field of the PHY header of the PPDU including the third frame. Alternatively, the NPCA operation can be performed by setting the NPCA operation period with the stored Duration field value.

[0175] In addition to the RTS frame (610) and the CTS frame (611) described above, if there are PPDUs transmitted before the third frame within the same TXOP as the TXOP of the third frame being received, and the duration information of the MAC layer is confirmed through the PPDUs transmitted before the third frame, but the conditions for performing the NPCA operation are not satisfied, and the NPCA operation is performed through the third frame, the time information for determining the NPCA operation execution period may have priority over the duration information of the MAC layer confirmed through the PPDUs transmitted before the third frame, but may not be limited thereto.

[0176] At least one of AP 1 and STA 1 may switch its operating channel from the main 20 MHz channel to the NPCA primary channel when it is confirmed that the third frame does not occupy the NPCA primary channel. At least one of AP 1 and STA 1 may perform an EDCA operation on the NPCA primary channel after a switching time required for switching the operating channel to the NPCA primary channel. At least one of AP 1 and STA 1 may perform frame transmission using a bandwidth that is not occupied by the OBSS among the channels (or bandwidths) including the NPCA primary channel in the operating bandwidth of the BSS. At least one of AP 1 and STA 1 may receive an RTS frame (610) and a CTS frame (611) for a time length indicated by a Duration / ID field in a MAC header and may be an OBSS TXOP end time (Basic NAV end time) indicated by a NAV set by receiving the RTS frame (610) and the CTS frame (611). That is, at least one of AP 1 and STA 1 can perform frame transmission and reception operations on the NPCA primary channel until the OBSS TXOP ends and then return to the primary channel.

[0177] As another example, at least one of AP 1 and STA 1 may set the time length indicated by the Duration / ID field in the MAC header in the frame initially transmitted to a time point excluding the NPCA Switch back delay time length, which is the time for at least one of AP 1 and STA 1 to return from the NPCA primary channel to the primary channel from the OBSS TXOP end point (Basic NAV end point) indicated by the set NAV by receiving the RTS frame (610) and the CTS frame (611). That is, at least one of AP 1 and STA 1 may return to the primary channel at the time point when the OBSS TXOP ends after performing frame transmission and reception operations on the NPCA primary channel.

[0178] At least one of AP 1 and STA 1 can check the channel (or bandwidth) on which the data frame is transmitted (or all of the channels on which the RTS frame, the CTS frame, and the data frame are transmitted) and can check that the NPCA primary channel is not occupied. Specifically, a method for determining whether a frame exchanged in an OBSS occupies the NPCA primary channel (NPCA PCH) can be performed based on channel allocation information of a frequency band on which at least one of AP 1 and STA 1 operates and a sequence of PPDUs exchanged between AP 2 and STA 2 at SIFS intervals. Specifically, at least one of AP 1 and STA 1 can determine whether the NPCA primary channel (NPCA PCH) is occupied based on the bandwidth information indicated in the PPDUs (e.g., bandwidth information included in either a PHY header or a MAC header) or the bandwidth information of the PPDU obtained from the CH_BANDWIDTH_IN_NON_HT parameter value of the RXVECTOR received as a result of receiving the PPDUs during a series of transmissions of a first PPDU including an ICF (e.g., RTS), a second PPDU including an ICR (e.g., CTS) (in the case of FIG. 9, at least one of AP 1 and STA 1 also received the second PPDU) and a third PPDU (e.g., a PPDU including a Data frame) as a sequence of PPDUs exchanged between AP 2 and STA 2. If at least one of AP 1 and STA 1 determines that the PPDU does not occupy the NPCA PCH, at least one of AP 1 and STA 1 may switch its operating channel from the main 20 MHz channel to the NPCA main channel at the time when it confirms reception of a third PPDU containing a data frame on the transmitted channel (or bandwidth). That is, it may initiate a channel switching operation for NPCA operation and perform the NPCA operation after the switching time.

[0179] The time point at which at least one of AP 1 and STA 1 switches to the NPCA primary channel (NPCA PCH) may be the time point (e.g., NHT switch time) at which the PHY layer checks the preamble of the received PPDU and transmits PHY-RXEARLYSIG.indication primitive or PHY-RXSTART.indication primitive to the MAC layer as a result of receiving the third PPDU in a series of transmissions of the first PPDU, the second PPDU, and the third PPDU exchanged between AP 2 and STA 2, and the MAC layer receives it. For example, the time point at which the physical layer of the wireless LAN terminal checks the preamble of the received PPDU and transmits PHY-RXEARLYSIG.indication primitive or PHY-RXSTART.indication primitive to the MAC layer may be the time point after the third OFDM (orthogonal frequency division multiplex) symbol after receiving the L-SIG of the PPDU. That is, at least one of AP 1 and STA 1 can switch to the NPCA primary channel at a preset point in time based on the result of receiving the third PPDU.

[0180] The point in time at which at least one of the above-described AP 1 and STA 1 switches to the NPCA primary channel may be the point in time at which the terminal (e.g., AP 1, STA 1) switching to the NPCA primary channel confirms the third OFDM symbol after receiving L-SIG of the PPDU, regardless of whether the PHY of the terminal (e.g., AP 1, STA 1) switching to the NPCA primary channel transmits the PHY-RXEARLYSIG.indication primitive or PHY-RXSTART.indication primitive to the MAC, or a point in time thereafter. That is, even if the PHY has not performed the process of transmitting the primitive to the MAC, the point in time at which the terminal (e.g., AP 1, STA 1) switching to the NPCA primary channel acquires the bandwidth information included in the PPDU at that point in time may be the point in time thereafter.

[0181] The aforementioned point in time may be the point in time when at least one of AP 1 and STA 1 confirms that a valid TXOP is set in the OBSS by receiving the third PPDU even if it has not received ICR (CTS) after receiving only ICF (RTS). That is, even in a situation where at least one of AP 1 and STA 1 has received both the RTS frame and the CTS frame, if it determines that the third PPDU does not occupy the NPCA primary channel (NPCA PCH) by the aforementioned method at the point in time when it receives the data frame, it may perform an operation channel switching operation to the NPCA primary channel (NPCA PCH).

[0182] FIG. 10 is a diagram illustrating a sub-channel access operation method according to a transmission bandwidth of a wireless LAN OBSS applied to the present disclosure. Referring to FIG. 10, AP 2, which configures BSS 2, can access a channel through an EDCA operation on a main 20 MHz channel of BSS 2 and transmit an initial frame to STA 2. That is, AP 2 can perform an EDCA operation (e.g., a CCA operation and / or an EDCA backoff procedure) on the main 20 MHz channel after traffic (e.g., DL) to be transmitted to STA 2 arrives. In addition, AP 2 can perform an initial frame transmission to STA 2 using at least one of the main 20 MHz channel and an operating bandwidth (or channel) including the main 20 MHz channel through the EDCA operation performed on the main 20 MHz channel. AP 2, which transmitted the initial frame, can obtain a TXOP. When AP 2 wants to transmit DL traffic to STA 2, the first frame transmitted by AP 2 may be a CTS-to-Self frame (613) to set the NAV before transmitting to STA 2. The CTS-to-Self frame has the same structure as the CTS frame, but is a frame in which the RA is set to its own address. After transmitting the CTS-to-Self frame (613), AP 2 may transmit a data frame (614) to STA 2 after SIFS. STA 2, which receives the data frame (614) transmitted by AP 2, may receive the data frame (614) and, after SIFS time, may respond by transmitting a BlockAck (BA) frame (615) to AP 2 using the bandwidth on which the data frame (614) was transmitted.

[0183] At least one of AP 1 and STA 1 may have received a CTS-to-Self frame (613) transmitted by AP 2 on the main 20 MHz channel of BSS 1 and may recognize that the received frame is a frame (i.e., an Inter-BSS PPDU) transmitted within an OBSS (e.g., BSS 2). At least one of AP 1 and STA 1 may need to check the occupancy status of the NPCA main channel in order to perform an NPCA operation. At least one of AP 1 and STA 1 may have received a CTS-to-Self frame (613) transmitted first by AP 2 among the frames transmitted by at least one of AP 2 and STA 2. Here, at least one of AP 1 and STA 1 may not be aware of the entire bandwidth over which the frame received from the OBSS is transmitted, and may not be aware of whether the NPCA main channel is occupied by the frame received from the OBSS.

[0184] Referring to FIG. 10, at least one of AP 1 and STA 1 may perform at least one of the first, second, third and fourth methods for checking the transmitted channel (or bandwidth) described above after receiving the CTS-to-Self frame (613). At least one of AP 1 and STA 1 may check whether the CTS-to-Self frame (613) occupies the NPCA primary channel as a result of the OBSS occupied channel checking operation. If the CTS-to-Self frame (613) occupies the NPCA primary channel, at least one of AP 1 and STA 1 may not perform the NPCA operation. That is, at least one of AP 1 and STA 1 may wait without performing a transmission / reception operation on the primary 20 MHz channel until the TXOP end time (Basic NAV end time) of AP 2 or STA 2. At least one of AP 1 and STA 1 may perform EDCA operation on the primary 20 MHz channel at the end of TXOP of AP 2 or STA 2 (end of Basic NAV).

[0185] As another example, at least one of AP 1 and STA 1 may determine that the NPCA primary channel is not occupied after performing at least one of the first, second, third, and fourth methods for checking the transmitted channel (or bandwidth) described above after receiving the CTS-to-Self frame (613). Accordingly, at least one of AP 1 and STA 1 may switch its operating channel to the NPCA primary channel (NPCA PCH) after performing at least one of the first, second, third, and fourth methods for checking the transmitted channel (or bandwidth) described above.

[0186] Here, the timing at which at least one of AP 1 and STA 1 switches its operating channel to the NPCA primary channel (NPCA PCH) may vary. For example, at least one of AP 1 and STA 1 may switch its operating channel from the primary 20 MHz channel to the NPCA primary channel at the timing at which it determines that the CTS-to-Self frame (613) does not occupy the NPCA primary channel (NPCA PCH). As another example, at least one of AP 1 and STA 1 may receive a PPDU corresponding to a frame (e.g., Data frame) transmitted subsequent to the CTS-to-Self frame (613) after confirming that the CTS-to-Self frame (613) does not occupy the NPCA primary channel (NPCA PCH) or without confirming whether the NPCA primary channel (NPCA PCH) is occupied, and transmit a PHY-RXEARLYSIG.indication primitive or a PHY-RXSTART.indication primitive to the MAC layer by confirming the preamble of the PPDU received by the PHY layer, and the MAC layer may receive the PHY-RXEARLYSIG.indication primitive at the time (e.g., NHT switch time). If it is determined that a frame (e.g., a Data frame) transmitted subsequent to the CTS-to-Self frame (613) at that time does not occupy the NPCA primary channel (NPCA PCH), at least one of AP 1 and STA 1 may switch its operating channel from the primary 20 MHz channel to the NPCA primary channel. The determination of whether the above-described NPCA primary channel (NPCA PCH) is occupied may not be performed if it is determined that the CTS-to-Self frame (613) does not occupy the NPCA primary channel (NPCA PCH).At least one of AP 1 and STA 1 may perform EDCA operation on the NPCA primary channel after a switching time required for switching the operating channel to the NPCA primary channel, and may transmit a frame using a channel (or bandwidth) including the NPCA primary channel.

[0187] As another example, the EDCA operation performed on the NPCA primary channel can only be performed by the AP. Therefore, AP 1 can access the channel through the EDCA operation on the NPCA primary channel and transmit the first frame to STA 1, which is expected to have performed the NPCA operation using the channel that successfully accessed the channel. The length of time indicated by the Duration / ID field in the MAC header of the frame initially transmitted by AP 1 to STA 1 may be the TXOP end time (Basic NAV end time) of AP 2 or STA 2. That is, the end time of the TXOP acquired by at least one of AP 1 and STA 1 using the NPCA primary channel may be the same as the TXOP end time (Basic NAV end time) of AP 2 or STA 2. At least one of AP 1 and STA 1 may switch its operating channel from the NPCA primary channel to the primary 20 MHz channel at the end of the TXOP of AP 2 or STA 2 (at the end of the Basic NAV) after performing frame exchange in the TXOP acquired from the NPCA primary channel. At least one of AP 1 and STA 1 may perform EDCA operations on the primary 20 MHz channel after a switching time required for switching the operating channel to the primary 20 MHz channel.

[0188] As another example, another method of checking the channel (or bandwidth) on which a frame transmitted in the OBSS was transmitted may be considered to determine whether NPCA operation can be performed when a CTS-to-Self frame (613) is received. Specifically, the bandwidth information contained in the frame may be checked by receiving a frame (e.g., a Data frame or an MU-RTS frame) transmitted after a certain period of time (e.g., SIFS time, PIFS time, etc.) after receiving the CTS-to-Self frame (613). More specifically, the operation of checking the channel on which the frames exchanged within the OBSS were transmitted may be performed using the same method or a modified or combined method. As an example, at least one of AP 1 and STA 1 may have received the CTS-To-Self frame (613) transmitted by AP 2 and may check the transmission bandwidth information of a frame (e.g., a Data frame) transmitted subsequent to the CTS-To-Self frame (613). The fifth method described above can be performed with some modifications as a method of checking the transmission bandwidth of a data frame. That is, the NAVTimeout waiting time applied to confirm the NAV after the first received frame (e.g., CTS-To-Self) may not be applied, and the bandwidth of a subsequent frame (e.g., Data frame) received within a certain period of time (e.g., SIFS time, PIFS time, etc.) after the reception of the first frame can be checked. If it is determined as a result of checking the bandwidth information of a frame (e.g., Data frame) transmitted subsequent to the CTS-To-Self frame (613) that the NPCA primary channel is not occupied, at least one of AP 1 and STA 1 can perform an NPCA operation by performing an NPCA channel switching operation. On the other hand, a frame (e.g.,, Data frame) is determined to be occupied, at least one of AP 1 and STA 1 may operate on the main 20 MHz channel without performing NPCA channel switching operation.

[0189] FIG. 11 is a diagram illustrating a sub-channel access operation method according to a transmission bandwidth of a wireless LAN OBSS applied to the present disclosure. Referring to FIG. 11, AP 2, which configures BSS 2, can access a channel through an EDCA operation on a main 20 MHz channel of BSS 2 and transmit an initial frame to STA 2. That is, AP 2 recognizes that there is a data frame to be received from STA 2, and can perform an EDCA operation (e.g., a CCA operation and / or an EDCA backoff procedure) on the main 20 MHz channel to allocate UL (uplink) resources for STA 2 to use for transmission to AP 2. AP 2 can transmit an initial frame to STA 2 using at least one of the main 20 MHz channel and an operating bandwidth (or channel) including the main 20 MHz channel through the EDCA operation performed on the main 20 MHz channel. AP 2, which transmitted the initial frame, can obtain a TXOP.

[0190] Here, when AP 2 wants to allocate UL resources to STA 2, the first frame transmitted by AP 2 may be a trigger frame (TF, 616). STA 2, which receives the TF (616) transmitted by AP 2, may transmit a data frame (617) to AP 2 after receiving the TF (616) and SIFS time. The data frame (617) transmitted by STA 2 to AP 2 may be a UL Trigger Based PPDU (UL TB PPDU). AP 2, which receives the data frame (617) transmitted by STA 2, may receive the data frame and, after SIFS time, may respond by transmitting a BlockAck (BA) frame (618) to STA 2 using the bandwidth in which the data frame (617) was transmitted.

[0191] At least one of AP 1 and STA 1 may have received a TF (616) transmitted by AP 2 on the main 20 MHz channel of BSS 1 and may recognize that the received frame is a frame transmitted within an OBSS (e.g., an Inter-BSS PPDU). Here, at least one of AP 1 and STA 1 may need to check the occupancy status of the NPCA main channel in order to perform an NPCA operation. At least one of AP 1 and STA 1 may have received a TF (616) initially transmitted by AP 2 among the frames transmitted by at least one of AP 2 and STA 2. At least one of AP 1 and STA 1 may recognize the entire bandwidth over which the TF received from the OBSS is transmitted, and may recognize whether the NPCA main channel is occupied by the frame received from the OBSS.

[0192] Referring to FIG. 11, at least one of AP 1 and STA 1 can receive TF (616), check channel (or bandwidth) information included in TF (616), and confirm that the NPCA primary channel has been occupied for frame transmission and reception. In the above-described case, at least one of AP 1 and STA 1 may not perform the NPCA operation. That is, at least one of AP 1 and STA 1 may wait without performing transmission and reception operations on the primary 20 MHz channel until the TXOP end time (Basic NAV end time) of AP 2 or STA 2. At least one of AP 1 and STA 1 may perform the EDCA operation on the primary 20 MHz channel at the TXOP end time (Basic NAV end time) of AP 2 or STA 2.

[0193] As another example, at least one of AP 1 and STA 1 can check the channel (or bandwidth) information included in TF (616) to confirm that TF (616) does not occupy the NPCA primary channel. Accordingly, at least one of AP 1 and STA 1 can receive TF (616) and switch its operating channel to the NPCA primary channel (NPCA PCH). The time point at which at least one of AP 1 and STA 1 switches its operating channel to the NPCA primary channel (NPCA PCH) may vary. As an example, at least one of AP 1 and STA 1 can switch its operating channel from the primary 20 MHz channel to the NPCA primary channel at the time point at which it completes receiving at least one of the HE-SIG-A and U-SIG fields of the PHY header of the PPDU including TF (616) (e.g., HE switch time). The time at which at least one of the HE-SIG-A and U-SIG fields of the PHY header of the PPDU is received may be the time at which the PHY verifies the preamble of the PPDU corresponding to the received TF (616) and transmits the PHY-RXEARLYSIG.indication primitive or the PHY-RXSTART.indication primitive to the MAC layer and the MAC layer receives it (e.g., NHT switch time). As another example, the time at which the operating channel is switched from the main 20 MHz channel to the NPCA main channel may be the time at which the TF (616) is fully decoded and the common info field and the user info field information are verified to determine whether the NPCA main channel (NPCA PCH) is occupied and whether there is sufficient time to perform the NPCA operation.At least one of AP 1 and STA 1 may perform EDCA operation on the NPCA primary channel after a switching time required for switching the operating channel to the NPCA primary channel, and may transmit a frame using a channel (or bandwidth) including the NPCA primary channel.

[0194] As another example, the EDCA operation performed on the NPCA primary channel can only be performed by the AP. Therefore, AP 1 can access the channel through the EDCA operation on the NPCA primary channel and transmit the first frame to STA 1, which is expected to have performed the NPCA operation using the channel that successfully accessed the channel. The length of time indicated by the Duration / ID field in the MAC header of the frame initially transmitted by AP 1 to STA 1 may be the TXOP end time (Basic NAV end time) of AP 2 or STA 2. That is, the end time of the TXOP acquired by at least one of AP 1 and STA 1 using the NPCA primary channel may be the same as the TXOP end time (Basic NAV end time) of AP 2 or STA 2. At least one of AP 1 and STA 1 may switch its operating channel from the NPCA primary channel to the primary 20 MHz channel at the end of the TXOP of AP 2 or STA 2 (at the end of the Basic NAV) after performing frame exchange in the TXOP acquired from the NPCA primary channel. At least one of AP 1 and STA 1 may perform EDCA operations on the primary 20 MHz channel after a switching time required for switching the operating channel to the primary 20 MHz channel.

[0195] Another method for determining whether NPCA operation can be performed when TF (616) is received is to check the channel (or bandwidth) through which a frame transmitted in the OBSS is transmitted, by receiving a frame (e.g., Data frame) transmitted after a certain period of time (e.g., SIFS time, PIFS time, etc.) after the TF, and checking the bandwidth information included in the frame. Specifically, the operation of checking the channel through which the frames exchanged within the OBSS are transmitted as described above can be performed by the same method or by some variation or combination thereof. For example, at least one of AP 1 and STA 1 may have received TF (616) transmitted by AP 2 and may check the transmission bandwidth information of a frame (e.g., Data frame) transmitted subsequent to TF (616). The fifth method described above can be performed with some variation as a method for checking the transmission bandwidth of a data frame (617). That is, the NAVTimeout waiting time applied to confirm the NAV after receiving the first received frame (e.g., TF) may not be applied, and the bandwidth of the subsequent frame (e.g., Data frame) received within a certain period of time (e.g., SIFS time, PIFS time, etc.) after receiving the first frame may be checked.

[0196] If it is determined that the NPCA primary channel is not occupied as a result of checking the bandwidth information of the frame (e.g., Data frame) transmitted subsequent to TF (616), at least one of AP 1 and STA 1 may perform an NPCA operation by performing an NPCA channel switching operation. If it is determined that the NPCA primary channel is occupied as a result of checking the bandwidth of the frame (e.g., Data frame) transmitted subsequent to TF (616), at least one of AP 1 and STA 1 may operate on the primary 20 MHz channel without performing the NPCA channel switching operation.

[0197] In addition, as another method of checking the channel (or bandwidth) on which a frame transmitted from the OBSS is transmitted to determine whether an NPCA operation can be performed when receiving a TF (616), a method of checking bandwidth information included in the TF may be performed. The TF (616) may be a frame transmitted to trigger UL transmission. In the above case, the STA receiving the TF (616) may include a common info field and a user info field in the MAC header of the TF (616) to allocate radio resources to be used for UL transmission. Specifically, the common info field may include an uplink bandwidth (UL Bandwidth) field. The uplink bandwidth field may be a field included for the purpose of checking the total bandwidth of radio resources to be used for UL transmission by the receiver terminal (e.g., STA 2) of the TF (616). For example, the uplink bandwidth field may indicate at least one bandwidth among 20, 40, 80, 160, 80+80, and 320 MHz. In addition, the user information field may include an Association Identifier (AID) field of the receiving terminal and an RU allocation field indicating radio resources (e.g., channels) allocated to the corresponding terminal. The RU allocation field may indicate radio resources to be used for UL transmission in a relative position based on the bandwidth indicated in the UL bandwidth field. For example, if the uplink bandwidth field indicates 80 MHz and the first bit of the RU allocation field is 0 and the remaining bits indicate 61, it may indicate to use the lowest 20 MHz channel of the 80 MHz bandwidth indicated by the uplink bandwidth. Consequently, the receiving terminal (e.g., STA 2) of the TF (616) can check the information in the uplink bandwidth field and the RU allocation field allocated to it to confirm the radio resources allocated to it.

[0198] At least one of AP 1 and STA 1 can check the uplink bandwidth field included in TF (616) to check the entire bandwidth over which TF (616) was transmitted. In addition, a method of checking the uplink bandwidth field of TF as a method of checking the entire bandwidth over which TF (616) was transmitted may be additionally performed, together with a method of checking the CCA result within the time at which TF (616) was transmitted (e.g., a first method of checking the channel over which frames exchanged in OBSS were transmitted). The bandwidth indicated by the uplink bandwidth field of TF (616) may indicate the bandwidth over which a frame (e.g., data frame (617)) transmitted in response to TF (616) is transmitted. If it is determined as a result of checking the bandwidth information of TF (616) that the NPCA primary channel is not occupied, at least one of AP 1 and STA 1 may perform an NPCA operation by performing an NPCA channel switching operation. If at least one of AP 1 and STA 1 determines whether the NPCA primary channel (NPCA PCH) is occupied by checking the bandwidth information (e.g., UL Bandwidth, RU Allocation, etc.) in the MAC header of TF (616), at least one of AP 1 and STA 1 may switch its operating channel to the NPCA primary channel (NPCA PCH) at the time of receiving the MAC header of TF (616) (e.g., at the time of completing reception of the Common Info field, User Info field, etc.). Here, if it is determined as a result of checking the bandwidth of TF (616) that the NPCA primary channel is occupied, at least one of AP 1 and STA 1 may operate on the primary 20 MHz channel without performing the NPCA channel switching operation.

[0199] In the present disclosure, the RTS frame and the CTS frame may be used as examples of control frames. Specifically, the RTS frame may be referred to as a control frame or an initial control frame (ICF), and the CTS frame may be referred to as a control frame or an initial response frame or an initial control response frame (ICR), and are not limited to a specific form. The RTS frame (ICF) and the CTS frame (ICR) are control frames exchanged before transmitting a data frame, and the frame format may be configured as a Non-HT PPDU format or a HE / EHT / UHR PPDU format. In the case of a Non-HT PPDU format, both the RTS frame and the CTS frame must be received and it must be confirmed that the NPCA primary channel is not occupied using the bandwidth confirmation method presented in the present disclosure, so that the NPCA operation can be performed by transitioning to the NPCA primary channel. In the case where the RTS frame (ICF) and the CTS frame (ICR) are configured in the HE / EHT / UHR PPDU format, if it is confirmed that the occupied bandwidth does not occupy the NPCA primary channel using the bandwidth information included in the frame when only one of them is received, the NPCA operation can be performed by transitioning to the NPCA primary channel. Alternatively, in the case where the RTS frame (ICF) and the CTS frame (ICR) are configured in the HE / EHT / UHR PPDU format, if it is confirmed that the occupied bandwidth does not occupy the NPCA primary channel using the bandwidth information of the frame that sets the default NAV among the received RTS frame (ICF) or CTS frame (ICR) or data frame, the NPCA operation can be performed by transitioning to the NPCA primary channel.

[0200] In addition, in the present disclosure, the NAVTimeout time may be a time for monitoring the reception of a subsequent frame to confirm the established NAV by receiving a frame that sets the NAV (e.g., RTS exchanged in OBSS). For example, the NAVTimeout may be (2 Х aSIFSTime) + (T_PREAMBLE + T_SIGNAL + UL_Length) + aRxPHYStartDelay + (2 Х aSlotTime) time. Here, the 'T_PREAMBLE + T_SIGNAL + UL_Length' time may be the transmission time of a frame subsequent to the frame that sets the ICR (e.g., CTS, Multi-STA BlockAck) or the NAV. A wireless LAN terminal (e.g., AP 1, STA 1) that has received an RTS frame exchanged in OBSS may confirm the established NAV by receiving the RTS frame if it receives a PHY-RXSTART.indication primitive generated by receiving an additional frame within the NAVTimeout time. For example, a wireless LAN terminal that has received an RTS frame can cancel the set NAV by receiving the RTS frame if it does not receive the PHY-RXSTART.indication primitive within the NAVTimeout time.

[0201] FIG. 12 is a flowchart illustrating an operation of an STA in a wireless LAN applied to the present disclosure. Referring to FIG. 12, an STA may receive at least one frame from an OBSS while operating on a primary channel. (S1210) The STA may check bandwidth information of frames exchanged within the OBSS through the received at least one frame. (S1220) Thereafter, the STA may determine whether to perform an NPCA operation through the bandwidth information. (S1230) When performing an NPCA operation, the STA may switch the channel from the STA's primary channel to the NPCA primary channel. (S1240) Here, the STA may check bandwidth information of frames exchanged within the OBSS through a sequence of PPDUs (physical layer protocol data units) exchanged at short interframe space (SIFS) intervals, and may determine whether to perform an NPCA operation by checking whether the NPCA primary channel is occupied through the bandwidth information of the frames exchanged within the OBSS. For example, the sequence of PPDUs may include a first PPDU including an initial control frame, a second PPDU including an initial control response, and a third PPDU including a data frame. When the STA switches the channel to the NPCA primary channel based on bandwidth information identified based on the sequence of PPDUs, the STA may switch the channel from the primary channel to the NPCA primary channel at the time of receiving the third PPDU. Here, the time of receiving the third PPDU may be the time at which the physical layer of the STA identifies the preamble of the third PPDU and transmits the primitive to the MAC layer of the STA. As another example, the time at which the channel is switched from the primary channel to the NPCA primary channel after the time of receiving the third PPDU may be the time after the third orthogonal frequency division multiplex (OFDM) symbol after receiving the L-SIG of the third PPDU.As another example, the STA may receive some of the first PPDU, the second PPDU, and the third PPDU in a sequence of PPDUs. In addition, if the STA receives the third PPDU that does not occupy the NPCA primary channel after receiving the first PPDU that occupies the NPCA primary channel, the STA may perform the NPCA operation based on the bandwidth information of the third PPDU.

[0202] As another example, when an STA acquires from an OBSS at least one of a first PPDU including CTS (clear to send) to Self and a second PPDU subsequent to the first PPDU and including a data frame in a sequence of PPDUs and switches the channel to an NPCA primary channel, the STA may switch the channel from the primary channel to the NPCA primary channel at at least one of a time point at which the NPCA primary channel occupancy of the first PPDU including CTS to Self is confirmed or a time point based on reception of the second PPDU including a data frame. Here, the time point based on reception of the second PPDU including a data frame may include at least one of a time point at which a physical layer of the STA confirms either a PHY preamble of the second PPDU or a PHY header of the second PPDU and transmits a primitive to a MAC layer of the STA, and a time point including a time point at which the STA receives information including bandwidth information of the data frame and acquires information including bandwidth information.

[0203] As another example, when an STA switches to an NPCA primary channel by acquiring from an OBSS at least one of a first PPDU including a trigger frame (TF) and a second PPDU following the first PPDU and including a data frame in a sequence of PPDUs, the STA may switch to the NPCA primary channel at at least one of a time point based on reception of the first PPDU including the TF or a time point based on reception of the second PPDU including the data frame. Here, the time based on reception of the first PPDU may include at least one of the time when the physical layer of the STA checks either the PHY preamble or the PHY header of the first PPDU and transmits a primitive to the MAC layer of the STA, the time when the STA completely decodes the first PPDU, the time when the MAC (medium access control) header of the first PPDU is received, the time when the bandwidth through which the first PPDU is transmitted is checked to determine whether the NPCA primary channel is occupied, and the time when the bandwidth through which the data frame is transmitted is checked through bandwidth information included in the first PPDU. In addition, the time based on reception of the second PPDU may include at least one of the time when the physical layer of the STA checks either the PHY preamble or the PHY header of the second PPDU and transmits a primitive to the MAC layer of the STA, and the time when the STA receives information including bandwidth information of the second PPDU and includes a time taken to acquire information including bandwidth information. Here, bandwidth information may be indicated to the STA by being included in at least one of the preamble of the PPDU, the PHY header of the PPDU, and the MAC (medium access control) header.

[0204] FIG. 13 is a flowchart illustrating the operation of an AP in a wireless LAN applied to the present disclosure. Referring to FIG. 13, the AP may receive at least one frame from an OBSS while operating on a primary channel. (S1310) The AP may check the bandwidth information of frames exchanged within the OBSS through the received at least one frame. (S1320) Thereafter, the AP may determine whether to perform an NPCA operation through the bandwidth information. (S1330) When performing an NPCA operation, the AP may switch the channel from the AP's primary channel to the NPCA primary channel. (S1340) Here, the AP may check the bandwidth information of frames exchanged within the OBSS through a sequence of PPDUs (physical layer protocol data units) exchanged at short interframe space (SIFS) intervals, and may determine whether to perform the NPCA operation by checking whether the NPCA primary channel is occupied through the bandwidth information of the frames exchanged within the OBSS. For example, the sequence of PPDUs may include a first PPDU including an initial control frame, a second PPDU including an initial control response, and a third PPDU including a data frame. When the AP switches the channel to the NPCA primary channel based on bandwidth information identified based on the sequence of PPDUs, the AP may switch the channel from the primary channel to the NPCA primary channel at the time of receiving the third PPDU. Here, the time of receiving the third PPDU may be the time at which the physical layer of the AP identifies the preamble of the third PPDU and transmits the primitive to the MAC layer of the AP. As another example, the time at which the channel is switched from the primary channel to the NPCA primary channel after the time of receiving the third PPDU may be the time after the third orthogonal frequency division multiplex (OFDM) symbol after receiving the L-SIG of the third PPDU.As another example, the AP may receive some PPDUs among the first PPDU, the second PPDU, and the third PPDU in a sequence of PPDUs. Furthermore, if the AP receives the third PPDU, which does not occupy the NPCA primary channel, after receiving the first PPDU, which occupies the NPCA primary channel, the AP may perform the NPCA operation based on the bandwidth information of the third PPDU.

[0205] As another example, when the AP acquires from the OBSS at least one of a first PPDU including CTS (clear to send) to Self and a second PPDU following the first PPDU and including a data frame in a sequence of PPDUs and switches the channel to the NPCA primary channel, the AP may switch the channel from the primary channel to the NPCA primary channel at at least one of a time point at which the first PPDU including CTS to Self occupancy of the NPCA primary channel is confirmed or a time point based on reception of the second PPDU including the data frame. Here, the time point based on reception of the second PPDU including the data frame may include at least one of a time point at which the physical layer of the AP verifies either a PHY preamble of the second PPDU or a PHY header of the second PPDU and transmits a primitive to the MAC layer of the AP, and a time point including a time point at which the AP receives information including bandwidth information of the data frame and acquires information including bandwidth information.

[0206] As another example, when the AP switches to the NPCA primary channel by acquiring from the OBSS at least one of a first PPDU including a trigger frame (TF) and a second PPDU following the first PPDU and including a data frame in a sequence of PPDUs, the AP may switch to the NPCA primary channel at at least one of a time point based on reception of the first PPDU including the TF or a time point based on reception of the second PPDU including the data frame. Here, the time based on reception of the first PPDU may include at least one of the time when the physical layer of the AP checks either the PHY preamble or the PHY header of the first PPDU and transmits a primitive to the MAC layer of the AP, the time when the AP decodes the entire first PPDU, the time when the MAC (medium access control) header of the first PPDU is received, the time when the bandwidth through which the first PPDU is transmitted is checked to determine whether the NPCA primary channel is occupied, and the time when the bandwidth through which the data frame is transmitted is checked through bandwidth information included in the first PPDU. In addition, the time based on reception of the second PPDU may include at least one of the time when the physical layer of the AP checks either the PHY preamble or the PHY header of the second PPDU and transmits a primitive to the MAC layer of the AP, and the time when the AP receives information including bandwidth information of the second PPDU and includes a time taken to acquire information including bandwidth information. Here, bandwidth information may be indicated to the AP by being included in at least one of the preamble of the PPDU, the PHY header of the PPDU, and the MAC (medium access control) header.

[0207] The methods according to the present disclosure may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc., 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 may be known and available to those skilled in the art of computer software. Examples of the computer-readable medium include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Examples of program instructions include not only machine language codes generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The above-described hardware devices 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 disclosure has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

[0208]

[0209] The above may also apply to other systems.

Claims

1. In the operation method of a station (STA) in a wireless LAN system, A step of receiving at least one frame from an overlapping basic service set (OBSS) while the STA is operating on a primary channel; A step of checking bandwidth information of frames exchanged within the OBSS through at least one received frame; A step of determining whether to perform NPCA (non-primary channel access) operation through the above bandwidth information; and An operating method, comprising a step of the STA switching a channel from the primary channel of the STA to an NPCA primary channel when performing the above NPCA operation.

2. In paragraph 1, An operating method in which the STA determines whether to perform the NPCA operation by checking the bandwidth information of frames exchanged within the OBSS through a sequence of PPDUs (physical layer protocol data units) exchanged at SIFS (short interframe space) intervals and checking whether the NPCA main channel is occupied through the bandwidth information of frames exchanged within the OBSS.

3. In paragraph 2, The sequence of the above PPDUs includes a first PPDU containing an initial control frame, a second PPDU containing an initial control response, and a third PPDU containing a data frame, An operating method in which, when the STA switches the channel to the NPCA primary channel based on the bandwidth information confirmed based on the sequence of the PPDUs, the STA switches the channel from the primary channel to the NPCA primary channel at the time of receiving the third PPDU.

4. In paragraph 3, The operating method is such that the time point at which the third PPDU is received is the time point at which the physical layer of the STA confirms the preamble of the third PPDU and transmits a primitive to the MAC layer of the STA.

5. In paragraph 3, An operating method, wherein the point in time at which the channel is switched from the primary channel to the NPCA primary channel after receiving the third PPDU is a point in time after the third OFDM (orthogonal frequency division multiplex) symbol after receiving the L-SIG of the third PPDU.

6. In paragraph 3, An operating method in which the STA receives some PPDUs among the first PPDU, the second PPDU, and the third PPDU in a sequence of the PPDUs.

7. In paragraph 6, An operating method in which, when the STA receives the third PPDU that does not occupy the NPCA primary channel after receiving the first PPDU that occupies the NPCA primary channel, the STA performs the NPCA operation based on bandwidth information of the third PPDU.

8. In paragraph 2, An operating method, wherein when the STA acquires from the OBSS at least one of a first PPDU including a CTS (clear to send) to Self in the sequence of the PPDUs and a second PPDU subsequent to the first PPDU and including a data frame and switches the channel to the NPCA primary channel, the STA switches the channel from the primary channel to the NPCA primary channel at at least one of a time point of confirmation of NPCA primary channel occupancy of the first PPDU including the CTS to self or a time point based on reception of the second PPDU including the data frame.

9. In paragraph 8, A method of operation, wherein the time based on reception of the second PPDU including the data frame includes at least one of a time when the physical layer of the STA confirms one of the PHY preamble of the second PPDU and the PHY header of the second PPDU and transmits a primitive to the MAC layer of the STA, and a time including a time taken for the STA to receive information including bandwidth information of the data frame and obtain the information including the bandwidth information.

10. In paragraph 2, An operating method, wherein when the STA acquires from the OBSS at least one of a first PPDU including a trigger frame (TF) in the sequence of the PPDUs and a second PPDU subsequent to the first PPDU and including a data frame and switches the channel to the NPCA primary channel, the STA switches the channel to the NPCA primary channel at at least one of a time point based on reception of the first PPDU including the TF or a time point based on reception of the second PPDU including the data frame.

11. In paragraph 10, The time based on the reception of the first PPDU includes at least one of the time when the physical layer of the STA confirms one of the PHY preamble and PHY header of the first PPDU and transmits a primitive to the MAC layer of the STA, the time when the STA decodes the entire first PPDU, the time when the MAC (medium access control) header of the first PPDU is received, the time when the bandwidth through which the first PPDU is transmitted is confirmed to determine whether the NPCA primary channel is occupied, and the time when the bandwidth through which the data frame is transmitted is confirmed through bandwidth information included in the first PPDU. An operating method according to claim 1, wherein the time based on the reception of the second PPDU includes at least one of a time when the physical layer of the STA confirms one of the PHY preamble and the PHY header of the second PPDU and transmits a primitive to the MAC layer of the STA, and a time when the STA receives information including bandwidth information of the second PPDU and obtains the information including the bandwidth information.

12. In paragraph 1, An operating method in which the bandwidth information is included in at least one of the preamble of the PPDU, the PHY header of the PPDU, and the MAC (medium access control) header and is indicated to the STA.

13. In a wireless LAN system, at a station (STA), At least one transceiver for transmitting and receiving signals; At least one processor controlling at least one transceiver; and A memory storing instructions that cause the STA to perform a specific operation by at least one processor, The above specific actions are: Receive at least one frame from an overlapping basic service set (OBSS) while operating on a primary channel, Check the bandwidth information of the frames exchanged within the OBSS through at least one frame received, Determine whether to perform NPCA (non-primary channel access) operation through the above bandwidth information, and When the STA performs an NPCA operation, the STA switches the channel from the primary channel of the STA to the NPCA primary channel.

14. In the operating method of an access point (AP) in a wireless LAN system, A step of receiving at least one frame from an overlapping basic service set (OBSS) while the AP is operating on a primary channel; A step of checking bandwidth information of frames exchanged within the OBSS through at least one received frame; A step of determining whether to perform NPCA (non-primary channel access) operation through the above bandwidth information; and An operating method, comprising a step of the AP switching a channel from the primary channel of the AP to an NPCA primary channel when performing the above NPCA operation.

15. In a wireless LAN system, at the access point (AP), At least one transceiver for transmitting and receiving signals; At least one processor controlling at least one transceiver; and A memory storing instructions that cause the AP to perform a specific operation by at least one processor, The above specific actions are: Receive at least one frame from an overlapping basic service set (OBSS) while operating on a primary channel, Check the bandwidth information of the frames exchanged within the OBSS through at least one frame received, Determine whether to perform NPCA (non-primary channel access) operation through the above bandwidth information, and When performing the above NPCA operation, the AP switches the channel from the primary channel of the AP to the NPCA primary channel.

Images