Data transmission / reception method using transmission opportunity and wireless communication terminal using the same

Abstract

The present invention discloses an operating method and apparatus for a wireless communication terminal. Specifically, the wireless communication terminal according to the present invention can perform a first channel access procedure on a specific secondary subchannel included in a specific secondary channel. The entire bandwidth supported by the wireless communication terminal may consist of one primary channel and one or more secondary channels including the specific secondary subchannel. Thereafter, the wireless communication terminal can obtain a first transmission opportunity (TXOP) using the first channel access procedure, and the frequency range in which the first TXOP is obtained is limited to the specific secondary subchannel.

Description

[Technical Field]

[0001] The present invention relates to a method for acquiring transmission opportunities (TXOPs) and occupying channels to improve the efficiency of wireless LANs. [Background technology]

[0002] Recently, as the popularity of mobile devices has increased, wireless LAN technology, which can provide them with high-speed wireless Internet services, has been gaining attention. Wireless LAN technology is a technology that uses short-range wireless communication technology to enable mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, embedded devices, etc. to connect to the Internet wirelessly at home, in business, or in specific service areas.

[0003] Since supporting the initial wireless LAN technology using 2.4GHz z-wave, IEEE (Institute of Electronics Engineers) 802.11 has implemented or is currently developing standards for a variety of technologies. First, IEEE 802.11b uses frequencies in the 2.4GHz band and supports communication speeds of up to 11Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses frequencies in the 5GHz band instead of the 2.4GHz band, reducing the impact of interference compared to the significantly more congested 2.4GHz band. It also uses OFDM technology to improve communication speeds to a maximum of 54Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication distance than IEEE 802.11b. IEEE 802.11g has attracted considerable attention because it uses the same 2.4GHz band as IEEE 802.11b, achieving a maximum communication speed of 54Mbps and satisfying backward compatibility, but it also has an advantage over IEEE 802.11a in terms of communication distance.

[0004] IEEE 802.11n is a technical standard established to overcome the communication speed limitations that have been identified as a weakness of wireless LANs. IEEE 802.11n aims to increase network speed and reliability and extend the operating distance of wireless networks. Specifically, IEEE 802.11n supports high throughput (HT) with data processing speeds of up to 540 Mbps and is based on MIMO (Multiple Inputs and Multiple Outputs) technology, which uses multiple antennas on both the transmitter and receiver ends to minimize transmission errors and optimize data speed. This standard also uses a coding method that transmits multiple duplicate copies to increase data reliability.

[0005] As WLAN adoption continues to grow and its applications diversify, a need is emerging for new WLAN systems that support data throughput rates (Very High Throughput, VHT) higher than those supported by IEEE 802.11n. Among these, IEEE 802.11ac supports wide bandwidth (80MHz-160MHz) in the 5GHz frequency band. While the IEEE 802.11ac standard is defined only for the 5GHz band, initial 802.11ac chipsets are expected to support operation in the 2.4GHz band as well for backward compatibility with existing 2.4GHz products. Theoretically, this standard enables multi-station WLAN speeds of at least 1Gbps and maximum single-link speeds of at least 500Mbps. This is achieved by expanding the air interface concepts accepted by 802.11n, including wider radio frequency bandwidth (up to 160MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and denser modulation (up to 256QAM). IEEE 802.11ad is a method of transmitting data using the 60 GHz band instead of the conventional 24 GHz / 5 GHz band. IEEE 802.11ad is a transmission standard that uses beamforming technology to provide speeds of up to 7 Gbps, making it suitable for streaming large amounts of data and high-bitrate video, such as uncompressed HD video. However, the 60 GHz frequency band has the disadvantage of being difficult to pass through obstacles and can only be used between devices in close proximity.

[0006] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard is being developed and is nearing completion as the successor to 802.11ac and 802.11ad in order to provide high-efficiency and high-performance WLAN communication technology in high-density environments where APs and terminals are densely packed. In an 802.11ax-based WLAN environment, high-frequency-efficient communication must be provided both indoors and outdoors in the presence of a high density of stations and APs (Access Points), and various technologies are being developed to achieve this.

[0007] Additionally, development of new WLAN standards has begun to increase maximum transfer speeds to support new multimedia applications such as high-definition video and real-time games. IEEE 802.11be (Extremely High Throughput, EHT), the 7th generation WLAN standard, is currently being developed with the goal of supporting transmission rates of up to 30Gbps in the 2.4 / 5 / 6GHz bands through wider bandwidth, increased spatial streams, and multi-AP cooperation.

[0008] Recently, discussions have begun on ultra-high reliability (UHR) wireless LAN communication technology, which will be the next wireless LAN standard after 802.11be and will overcome the reliability issues that have been pointed out as limitations of wireless LAN. Standard development for ultra-high reliability wireless LAN standards is underway with the goal of supporting low-latency and low jitter in wireless LAN traffic with a high probability (e.g., 99.9999% or higher). Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide ultra-reliable wireless LAN services for new multimedia applications by enhancing the channel occupation method of wireless LANs.

[0010] The technical problems to be solved by the present specification are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention pertains from the following description. [Means for solving the problem]

[0011] In a non-AP (Access Point) multi-link device (MLD) including a plurality of stations according to the present invention, a processor performs a first channel access procedure on a specific secondary subchannel included in a specific secondary channel, the entire bandwidth supported by the wireless communication terminal is composed of one primary channel and one or more secondary channels including the specific secondary subchannel, and obtains a first transmission opportunity (TXOP) using the first channel access procedure, and the range on the frequency axis in which the first TXOP is obtained is limited to the specific subchannel.

[0012] In addition, in the present invention, the first channel access procedure is performed when the channel state of a primary subchannel included in the one primary channel is busy.

[0013] In addition, in the present invention, the primary channel access procedure is performed when the primary subchannel is occupied by an overlapping basic service set (OBSS) terminal.

[0014] Also, in the present invention, the processor transmits a trigger frame during the TXOP to one or more terminals, instructing them to transmit frames using a plurality of sub-channels that make up the specific sub-channel.

[0015] Also, in the present invention, when the one or more terminals operate on the one primary channel, the trigger frame instructs a change from the primary channel to the specific secondary channel.

[0016] Also, in the present invention, the one or more terminals do not support the bandwidth of the specific subchannel as an operating bandwidth, and the trigger frame includes a field instructing a change from the main channel to the specific subchannel.

[0017] In addition, in the present invention, the processor receives a frame for sharing a second TXOP from a specific terminal, and the second TXOP is obtained by a second channel connection procedure of the specific terminal on a primary subchannel included in the one primary channel.

[0018] In addition, in the present invention, the frequency range from which the second TXOP is acquired is a bandwidth supported by the specific terminal among the entire bandwidth, and the first TXOP and the second TXOP end at the same time.

[0019] The present invention also provides a method including the steps of: performing a first channel access procedure on a specific secondary subchannel included in a specific secondary channel, wherein the entire bandwidth supported by the wireless communication terminal is composed of one primary channel and one or more secondary channels including the specific secondary subchannel; and obtaining a first transmission opportunity (TXOP) using the first channel access procedure, wherein a range on a frequency axis in which the first TXOP is obtained is limited to the specific secondary channel. [Effects of the Invention]

[0020] An embodiment of the present invention can provide a wireless communication method for efficiently managing TXOPs and a wireless communication terminal using the same.

[0021] According to one embodiment of the present invention, a station can share (or transfer) a transmission opportunity (TXOP) that it has acquired with another station.

[0022] Furthermore, according to an embodiment of the present invention, a station can allocate a time period within the TXOP it has acquired to other stations.

[0023] Furthermore, according to one embodiment of the present invention, when a station has an opportunity to acquire a TXOP, it can assist other stations in acquiring the TXOP.

[0024] Furthermore, according to one embodiment of the present invention, a station can inherit / take over a TXOP acquired by another station and perform transmission and reception during the TXOP.

[0025] Additionally, in accordance with one embodiment of the present invention, a station may attempt to acquire a TXOP based on a frame transmitted by another station.

[0026] The effects obtained from the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a configuration of an access point according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating a process in which a STA establishes a link with an AP. [Figure 6] FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] 1A and 1B are diagrams illustrating various standard generation physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention. [Figure 8] FIG. 2 is a diagram showing an EHT / UHR PPDU format according to an embodiment of the present invention. [Figure 9] A diagram showing a transmission / TXOP protection method using RTS and CTS frames according to an embodiment of the present invention. [Figure 10] A diagram showing a transmission / TXOP protection method using MU-RTS frames and CTS frames in accordance with an embodiment of the present invention. [Figure 11] FIG. 2 is a diagram illustrating a format of a trigger frame according to an embodiment of the present invention. [Figure 12] A diagram showing the format of the Common Info field of a trigger frame in an embodiment of the present invention. [Figure 13] FIG. 10 is a diagram showing the format of a User Info field of a trigger frame according to an embodiment of the present invention. [Figure 14] FIG. 10 is a diagram showing an example of a frame exchange sequence between STAs performed during a TXOP according to an embodiment of the present invention. [Figure 15] 10 is a diagram showing an example of a frame exchange sequence in which a STA according to one embodiment of the present invention completes a backoff procedure and then transfers TXOP acquisition authority to another STA. [Figure 16] A figure showing an example of a frame exchange sequence for transferring TXOP acquisition authority after a backoff procedure of a STA according to one embodiment of the present invention and the NAV state of another STA. [Figure 17]1 is a diagram illustrating an example of a format of an initiating frame and a trigger frame according to an embodiment of the present invention. FIG. [Figure 18] A diagram showing an example of a TXOP sharing and bandwidth (BW) extension procedure between STAs in one embodiment of the present invention. [Figure 19] A diagram showing an example of a TXOP sharing procedure and a TXOP holder operation of a STA in one embodiment of the present invention. [Figure 20] A figure showing an example of a format for a frame for transferring TXOP acquisition authority or sharing TXOP in one embodiment of the present invention. [Figure 21] FIG. 10 is a diagram illustrating an example of a method for performing channel connection using a subchannel according to an embodiment of the present invention. [Figure 22] FIG. 10 is a diagram showing yet another example of a method for performing channel connection using a subchannel according to an embodiment of the present invention. [Figure 23] FIG. 1 illustrates an example of a method for initiating a channel access procedure using a sub-channel according to an embodiment of the present invention. [Figure 24] FIG. 2 illustrates an example of a method for obtaining a transmission opportunity (TXOP) using a shared TXOP according to an embodiment of the present invention. [Figure 25] FIG. 10 is a diagram illustrating an example of a format of a parameter set element for TXOP sharing according to one embodiment of the present invention. [Figure 26] 1 is a diagram illustrating an example of the configuration and connection state of an AP MLD and a non-AP MLD according to an embodiment of the present invention. [Figure 27] A diagram showing an example of elements for sharing a TXOP in one embodiment of the present invention. [Figure 28] A figure showing an example of a frame including elements for sharing a TXOP in one embodiment of the present invention. [Figure 29]A figure showing an example of a response frame format to a frame for sharing a TXOP in one embodiment of the present invention. [Figure 30] FIG. 10 is a diagram illustrating an example of a method for minimizing performance degradation of an overlapping basic service set (OBSS) of APs when expanding the bandwidth of a shared TXOP in accordance with one embodiment of the present invention. [Figure 31] FIG. 10 is a diagram illustrating an example of the operation of an AP when TXOP sharing between APs is performed and BW extension is performed during a shared TXOP according to an embodiment of the present invention. [Figure 32] FIG. 10 is a diagram illustrating an example of the operation of a station according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The terms used in this specification are generally used as widely as possible, taking into consideration the functions of the present invention. However, these may vary depending on the intentions of engineers in the relevant technical field, customs, or the emergence of new technologies. In addition, in certain cases, the applicant may have arbitrarily selected terms, and in such cases, the meanings thereof will be described in the relevant description of the invention. Therefore, it is made clear that the terms used in this specification should be interpreted not simply as names of terms, but based on the substantive meanings of the terms and the overall content of this specification.

[0029] Throughout the specification, when a component is "coupled" to another component, this includes not only when it is "directly coupled" to another component, but also when it is "electrically coupled" with another component in between. Furthermore, when a component "comprises" a specific component, this means that it may further include the other component, not excluding the other component, unless otherwise specified. In addition, limitations such as "greater than" or "less than" based on a specific threshold value may be appropriately replaced with "exceed" or "less than," respectively, depending on the embodiment.

[0030] Hereinafter, in the present invention, the terms field and subfield may be used interchangeably.

[0031] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention.

[0032] A wireless LAN system includes one or more Basic Service Sets (BSSs), which are a set of devices that can synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0033] As shown in FIG. 1, the infrastructure BSSs BSS1 and BSS2 include one or more stations STA1, STA2, STA3, STA4, and STA5, access points AP-1 and AP-2 that are stations providing distribution services, and a distribution system DS that connects multiple access points AP-1 and AP-2.

[0034] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard. In a broad sense, the term "station" encompasses not only non-AP stations but also APs. In this specification, the term "terminal" refers to either a non-AP or an AP, or both. A station for wireless communication includes a processor and a communication unit, and, depending on the embodiment, may further include a user interface unit and a display unit. The processor generates frames to be transmitted over a wireless network, processes frames received over the wireless network, and performs various other processes for controlling the station. The communication unit is functionally connected to the processor and transmits and receives frames over the wireless network for the station. In this specification, the term "terminal" encompasses user equipment (UE).

[0035] An access point (AP) is an entity that provides a connection to a distribution system (DS) via a wireless medium for associated stations. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP. However, if a direct link is established, direct communication is also possible between non-AP stations. Meanwhile, in the present invention, the term AP is used as a concept including a personal BSS coordination point (PCP), but in a broader sense, it also includes concepts such as a central controller, a base station (BS), a node B, a base transceiver system (BTS), or a site controller. In the present invention, an AP is also referred to as a base wireless communication terminal, but in a broader sense, the term base wireless communication terminal is used as a term including an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal includes various types of wireless communication terminals that allocate communication medium resources and perform scheduling for communication with multiple wireless communication terminals.

[0036] A plurality of infrastructure BSSs are connected to each other via a distribution system DS, and the plurality of BSSs connected via the distribution system are called an Extended Service Set (ESS).

[0037] 2 is a diagram showing an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of FIG. 2, the same or corresponding parts as those in the embodiment of FIG. 1 will not be described again.

[0038] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so none of the stations (STA6, STA7) are connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

[0039] 3 is a block diagram showing the configuration of a station 100 according to an embodiment of the present invention. As shown, the station 100 according to the embodiment of the present invention includes a processor 110, a communication unit 120, a user interface unit 140, a display unit 150, and a memory 160.

[0040] First, the communication unit 120 transmits and receives wireless signals such as WLAN packets and may be incorporated into or external to the station 100. According to an embodiment, the communication unit 120 may include at least one communication module using different frequency bands. For example, the communication unit 120 may include communication modules using different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to an embodiment, the station 100 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with an AP or an external station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 120 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the station 100. When the station 100 includes multiple communication modules, each communication module may be provided independently, or multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit 120 may represent a radio frequency (RF) communication module that processes RF signals.

[0041] Next, the user interface 140 includes various types of input / output means provided in the station 100. That is, the user interface unit 140 receives user input using various input means, and the processor 110 controls the station 100 based on the received user input. Also, the user interface unit 140 performs output based on instructions from the processor 110 using various output means.

[0042] Next, the display unit 150 outputs an image on a display screen. The display unit 150 outputs various display objects, such as content generated by the processor 110 or a user interface based on a control command from the processor 110. The memory 160 also stores control programs and various data used by the station 100. Such control programs include a connection program required for the station 100 to connect to an AP or an external station.

[0043] The processor 110 of the present invention executes various commands or programs to process data within the station 100. The processor 110 also controls each unit of the station 100 and controls the transmission and reception of data between the units. According to an embodiment of the present invention, the processor 110 executes a program for connection with an AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also reads information about the station 100's priorities contained in the communication setup message and requests connection to the AP based on the information about the station 100's priorities. The processor 110 of the present invention may refer to a main control unit of the station 100, or, depending on the embodiment, may refer to a control unit for individually controlling some components of the station 100, such as the communication unit 120. That is, the processor 110 may be a modem or a modulator and / or demodulator that modulates and demodulates wireless signals transmitted and received by the communication unit 120. The processor 110 controls various operations for transmitting and receiving wireless signals in the station 100 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0044] The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separate blocks indicate the logically separated elements of the device. Therefore, the above-described device elements may be implemented on a single chip or multiple chips depending on the device design. For example, the processor 110 and the communication unit 120 may be integrated into a single chip or implemented on separate chips. Furthermore, in embodiments of the present invention, some components of the station 100, such as the user interface unit 140 and the display unit 150, may be selectively provided in the station 100.

[0045] 4 is a block diagram showing the configuration of an AP 200 according to an embodiment of the present invention. As shown, the AP 200 according to the embodiment of the present invention includes a processor 210, a communication unit 220, and a memory 260. In FIG. 4, duplicated descriptions of parts of the configuration of the AP 200 that are the same as or correspond to the configuration of the station 100 in FIG. 3 will be omitted.

[0046] Referring to FIG. 4, the AP 200 according to the present invention includes a communication unit 220 for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit 220 of the AP 200 may also include multiple communication modules using different frequency bands. That is, the AP 200 according to the embodiment of the present invention may include two or more communication modules using different frequency bands, for example, 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with a station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 220 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the AP 200. In the embodiment of the present invention, the communication unit 220 may represent an RF (Radio Frequency) communication module that processes RF signals.

[0047] The memory 260 stores control programs used by the AP 200 and various data associated therewith. These control programs include a connection program that manages station connections. The processor 210 also controls each unit of the AP 200 and controls data transmission and reception between the units. According to an embodiment of the present invention, the processor 210 executes a program for connecting with a station stored in the memory 260 and transmits a communication setup message to one or more stations. The communication setup message includes information about connection preferences for each station. The processor 210 also performs connection setup in response to a station connection request. According to an embodiment, the processor 210 is a modem or a modulation / demodulation unit that modulates and demodulates wireless signals transmitted and received by the communication unit 220. The processor 210 controls various operations for transmitting and receiving wireless signals by the AP 200 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0048] FIG. 5 is a diagram illustrating a process in which a STA establishes a link with an AP.

[0049] 5, a link between the STA 100 and the AP 200 is established through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information for the BSS operated by the AP 200. There are two scanning methods: a passive scanning method in which the STA 100 acquires information using only a beacon message (S101) periodically transmitted by the AP 200, and an active scanning method in which the STA 100 transmits a probe request to the AP (S103) and receives a probe response from the AP (S105) to acquire connection information.

[0050] The STA 100 that has successfully received wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200 (S107b), and performs the authentication step. After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200 (S109b), and performs the association step. In this specification, association basically means wireless association, but the present invention is not limited to this, and association in a broad sense includes both wireless and wired association.

[0051] Meanwhile, an 802.1X-based authentication step (S111) and an IP address acquisition step via DHCP (S113) are additionally performed. In Fig. 5, server 300 is a server that processes 802.1X-based authentication with STA 100, and may be physically connected to AP 200 or may exist as a separate server.

[0052] FIG. 6 shows an example of a Carrier Sense Multiple Access (CSMA) / Collision Avoidance (CA) method used in wireless LAN communication.

[0053] A terminal performing wireless LAN communication performs carrier sensing to check whether a channel is occupied (busy) before transmitting data. If a wireless signal above a certain strength is detected, the channel is determined to be occupied (busy), and the terminal delays access to the channel. This process is called clear channel assessment (CCA), and the level used to determine whether a signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by a terminal is designated as the receiver, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected on the channel or a wireless signal with a strength lower than the CCA threshold is detected, the channel is determined to be idle.

[0054] If a channel is determined to be idle, each terminal having data to transmit performs a backoff procedure after an Inter Frame Space (IFS), such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. Depending on the embodiment, the AIFS may be used as an alternative to the existing DCF IFS (DIFS). Each terminal waits while decrementing a slot time equal to a random number determined for the terminal during the idle interval of the channel. A terminal that has used up its slot time attempts to access the channel. The period during which each terminal performs the backoff procedure is called a contention window period. The random number may be referred to as a backoff counter. The initial value of the backoff counter is set by an integer, which is a random number obtained by the terminal. If a terminal detects that a channel is idle during the slot time, the terminal may decrement the backoff counter by 1. If the backoff counter reaches 0, the terminal may be allowed to access the channel. Thus, a terminal may be allowed to transmit if the channel is idle during the AIFS time and the backoff counter slot time.

[0055] If a specific terminal successfully accesses the channel, it can transmit data on the channel. However, if a terminal attempting access collides with another terminal, the colliding terminals are assigned new random numbers and perform a backoff procedure again. According to one embodiment, the new random numbers assigned to each terminal may be determined within a range (2*CW) twice the random number range (contention window, CW) previously assigned to the terminal. Meanwhile, each terminal attempts access by performing a backoff procedure again in the next contention window period, and at this time, each terminal performs the backoff procedure starting from the slot time remaining in the previous contention window period. In this way, terminals communicating via a WLAN can avoid collisions between each other on a specific channel.

[0056] <Examples of various PPDU formats> FIG. 7 illustrates various standard generation physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0057] More specifically, Fig. 7(a) shows an example of a legacy PPDU format based on 802.11a / g, Fig. 7(b) shows an example of an HE PPDU format based on 802.11ax, Fig. 7(c) shows an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be, and Fig. 7(d) shows detailed field configurations of L-SIG and RL-SIG commonly used in the PPDU formats.

[0058] 7(a), the preamble of the legacy PPDU includes a Legacy Short Training field (L-STF), a Legacy Long Training field (L-LTF), and a Legacy Signal field (L-SIG). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as a legacy preamble.

[0059] Referring to FIG. 7(b), the preamble of the HE PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a High Efficiency Signal A field (HE-SIG-A), a High Efficiency Signal B field (HE-SIG-B), a High Efficiency Short Training field (HE-STF), and a High Efficiency Long Training field (HE-LTF) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF may be referred to as an HE preamble. The specific configuration of the HE preamble may vary depending on the HE PPDU format. For example, HE-SIG-B may only be used in the HE MU PPDU format.

[0060] 7(c), the preamble of the EHT PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a Universal Signal field (U-SIG), an Extremely High Throughput / Ultra High Reliability Signal A field (EHT / UHR-SIG-A), an Extremely High Throughput / Ultra High Reliability Signal B field (EHT / UHR-SIG-A), an Extremely High Throughput Short Training field (EHT-STF), and an Extremely High Throughput Long Training field (EHT-LTF). In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may vary depending on the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some of the EHT PPDU formats.

[0061] As such, the PPDU used in the UHR standard may have a format similar to that of the PPDU used in the EHT standard. The EHT PPDU format defined in 802.11be includes a U-SIG field that is intended to be commonly used across multiple WLAN generations. In this case, the PHY Version Identifier field of the U-SIG field included in the EHT PPDU may have a value of 0, and the PHY Version Identifier field of the U-SIG field included in the UHR PPDU may have a value other than 0, for example, 1. The EHT PPDU includes an Extremely High Throughput Short Training field (EHT-STF) in the STF field and an Extremely High Throughput Long Training field (EHT-LTF) in the LTF field. The UHR PPDU includes an Ultra High Reliability Short Training field (UHR-STF) in the STF field and an Ultra High Reliability Long Training field (UHR-LTF) in the LTF field.

[0062] The L-SIG field included in the PPDU preamble is configured with a total of 64 subcarriers using 64 FFT OFDM. Of these, 48 subcarriers, excluding guard subcarriers, DC subcarriers, and pilot subcarriers, are used for L-SIG data transmission. BPSK, Rate=1 / 2 MCS (Modulation and Coding Scheme) is applied to the L-SIG, so it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of the L-SIG.

[0063] Referring to FIG. 7(d), the L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field is composed of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the following transmission rates: 6, 9, 12, 18, 24, 36, 48, or 54 Mbps, which are a combination of a modulation scheme such as BPSK, QPSK, 16-QAM, or 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The combined information in the L_RATE and L_LENGTH fields indicates the total length of the PPDU. In the non-legacy PPDU format, the L_RATE field is set to the minimum rate of 6 Mbps.

[0064] The L_LENGTH field is in bytes, and a total of 12 bits are allocated to it, allowing it to signal up to 4095. It can indicate the length of the PPDU in combination with the L_RATE field. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0065] First, a legacy or non-legacy terminal analyzes the length of the PPDU using the L_LENGTH field as follows. When the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted in 4 us, which is the duration of one symbol of the 64 FFT. Therefore, by adding 3 bytes corresponding to the SVC field and Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of reference symbols for the 64 FFT after the L-SIG is obtained. The obtained number of symbols is multiplied by 4 us, which is the duration of one symbol, and then 20 us, which is required to transmit the L-STF, L-LTF, and L-SIG, is added to obtain the length of the PPDU, i.e., the reception time (RXTIME). This can be expressed as Equation 1 below.

[0066]

number

[0067] In this case, the value expressed by the following Equation 2 represents the smallest natural number greater than or equal to x.

[0068]

number

[0069] Since the maximum value of the L_LENGTH field is 4095, the length of the PPDU can be set to a maximum of 5.484 ms. A non-legacy terminal transmitting the PPDU must set the L_LENGTH field as shown in Equation 3 below.

[0070]

number

[0071] Here, TXTIME is the total transmission time constituting the PPDU, and is expressed as in the following Equation 4. In this case, TX represents the transmission time of X.

[0072]

number

[0073] Referring to the above formula, the length of the PPDU is calculated based on the rounded-up value of L_LENGTH / 3. Therefore, for any value of k, three different values ​​of L_LENGTH={3k+1, 3k+2, 3(k+1)} indicate the same PPDU length.

[0074] Referring to Figure 7(e), the Universal SIG (U-SIG) field continues to exist in EHT / UHR PPDUs and subsequent generation WLAN PPDUs, and serves to distinguish which generation of PPDU it is, including EHT / UHR. The U-SIG field can also facilitate spatial reuse of EHT / UHR and subsequent generation WLANs. The U-SIG is a 64 FFT-based OFDM 2 symbol and can transmit a total of 52 bits of information. Of these, 43 bits, excluding 9 CRC / Tail bits, are roughly divided into a Version Independent (VI) field and a Version Dependent (VD) field.

[0075] The VI bit will maintain its current bit configuration in the future, so even if a subsequent generation PPDU is defined, current EHT / UHR UEs can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field consists of PHY version, UL / DL, BSS Color, TXOP, and Reserved fields. The PHY version ID field is 3 bits long and serves to sequentially distinguish EHT / UHR and subsequent generation WLAN standards by version. The PHY version ID field of an EHT (11be) PPDU has a value of 000b, and the PHY version ID field of a UHR PPDU has a value other than 000b. The UL / DL field distinguishes whether the PPDU is an uplink or downlink PPDU. BSS Color is a BSS-specific identifier defined in 11ax and has a value of 6 or more bits. TXOP refers to the Transmit Opportunity Duration transmitted in the MAC header, but by adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without decoding the MPDU, and has a value of 7 bits or more.

[0076] The EHT VD field is signaling information that is only useful for 11be version PPDUs and may consist of fields commonly used in any PPDU format, such as PPDU format and BW, and fields defined differently for each PPDU format. The PPDU format is a delimiter that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs.

[0077] The BW field signals five basic PPDU BW options: 20, 40, 80, 160 (80 + 80), and 320 (160 + 160) MHz (BWs that can be expressed in the form of an exponential power of 20 * 2 can be called basic BWs), as well as various remaining PPDU BWs formed by preamble puncturing. After signaling 320 MHz, it may be signaled with 80 MHz partially punctured. The punctured and modified channel shape may be signaled directly in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (e.g., a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signaling options are possible, so a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signalings are possible, so the puncturing mode can signal a maximum of 11.

[0078] The UHR VD field indicates signaling information useful only to the UHR PPDU. However, the information indicated by each field included in the VD field of the UHR PPDU may be the same as or more extended than the information indicated by a field that plays the same role as the VD field of the EHT (11be). For example, a field indicating a puncturing pattern included in the VD field of the UHR PPDU may indicate a wider variety of patterns than a field indicating a puncturing pattern included in the VD field of the EHT PPDU. Alternatively, the field indicating a puncturing pattern included in the VD field of the UHR PPDU may be analyzed in combination with the BW field. This allows for a wider variety of puncturing patterns to be indicated.

[0079] FIG. 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0080] The EHT / UHR PPDU format may be indicated by the PPDU Format field in the U-SIG field of the PPDU. Figure 8(a) shows an EHT / UHR SU PPDU according to an embodiment of the present invention. The EHT / UHR SU PPDU is a PPDU used for single-user transmission between an AP and a single station, and may include an EHT-SIG-A field for further signaling after the U-SIG.

[0081] 8(b) shows an EHT / UHR Trigger-based PPDU according to an embodiment of the present invention. The EHT / UHR Trigger-based PPDU is an uplink PPDU used for transmission in response to a trigger frame, and does not need to have a separate EHT / UHR-SIG-A field after the U-SIG.

[0082] 8(c) shows an EHT / UHR MU PPDU according to an embodiment of the present invention. The EHT / UHR MU PPDU is a PPDU used for transmission to one or more terminals. The EHT / UHR MU PPDU format may include an HE-SIG-B after the U-SIG field.

[0083] 8(d) shows an EHT / UHR ER SU PPDU according to an embodiment of the present invention. The EHT / UHR ER SU PPDU is used for single-user transmission to stations in an extended range. The EHT / UHR ER SU PPDU format allows the U-SIG to be repeated in time.

[0084] The EHT / UHR MU PPDU described in (c) of FIG. 8 may be used by an AP to perform downlink transmission to multiple stations. The EHT / UHR MU PPDU may include scheduling information for multiple stations to simultaneously receive the PPDU. The EHT / UHR MU PPDU may carry AID information of the recipient or sender of the PPDU using the user specific field of the EHT / UHR-SIG-B. A station receiving the EHT / UHR MU PPDU can perform spatial reuse based on the AID information obtained from the PPDU preamble. More specifically, the resource unit allocation (RA) field of the EHT / UHR-SIG-B may include information on the resource unit (RU) division pattern within a specific bandwidth (e.g., 20 MHz) in the frequency domain. Furthermore, information on the station assigned to each divided resource unit may be carried in the user specific field of the EHT / UHR-SIG-B. The user-specific field may include one or more user fields corresponding to each divided resource unit.

[0085] Among a plurality of divided resource units, an AID of a recipient or a sender may be inserted into a user field corresponding to a resource unit for data transmission. A pre-specified null STA ID may be inserted into a user field corresponding to the remaining resource units where no data transmission is performed.

[0086] Two or more PPDUs described in FIG. 8 may be indicated in the same PPDU format. For example, the value of the U-SIG PPDU format subfield indicating an EHT / UHR SU PPDU and the value of the U-SIG PPDU format subfield indicating an EHT / UHR MU PPDU may be the same.

[0087] Some fields or part of the information of the fields included in the above-described PPDU format may be omitted. This may be called a compression mode or a compressed mode.

[0088] <Wi-Fi Terminal Channel Access Method> Since a Wi-Fi terminal (AP, non-AP STA, etc.) communicates using an unlicensed band, before transmitting a frame, it checks whether the channel it intends to transmit on is being used by other devices. CSMA (Carrier Sense Multiple Access) is a channel access method in which a terminal attempting to transmit a packet performs carrier sense to check whether the channel is being used by other devices, and transmits only when it is determined (idle) that the channel is not being used by other devices. A terminal using CSMA can perform an operation of not attempting to transmit at least when it is confirmed that another device is using the medium (channel) (when it is determined to be busy), so that a previously started transmission can be protected from other devices.

[0089] However, multiple terminals that recognize that the medium is being occupied by another device will attempt to transmit a packet as soon as it is confirmed that the medium occupation by the other device has ended (the medium has changed to Idle), resulting in a transmission collision. That is, when a specific terminal attempts to transmit a packet, multiple other terminals simultaneously attempt to transmit packets, and the terminal that is supposed to receive the packet transmitted by the specific terminal is unable to correctly receive and decode the packet due to interference caused by the transmissions made by the other multiple terminals.

[0090] As mentioned above, CSMA / CA (CSMA with collision avoidance) is a channel access mechanism that prevents multiple terminals from simultaneously attempting packet transmission after detecting that the medium has changed to Idle. A terminal accessing the medium (channel) using CSMA / CA waits a random time before attempting transmission when the medium state it observes changes to Idle. The random time may be an aslot time (typically 9 us) equal to a random number (random backoff counter) generated by each terminal attempting to transmit. That is, terminals accessing the medium using CSMA / CA wait different random times before attempting transmission, which differs from the case when only CSMA is used. In this case, if a specific terminal that waited the shortest random time after the medium changed to Idle attempts transmission first, other terminals can recognize that the medium has been occupied (changed to Busy) by the specific terminal and can abort the channel access procedure. At this time, the specific terminal decreases its own maintained backoff counter by 1 every aslottime while the medium is kept idle, and can attempt transmission when the backoff counter reaches 0 or when aslottime has elapsed since the backoff counter reached 0. At this time, the specific terminal that has transmitted generates a new random number (new backoff counter) after completing transmission, and can attempt transmission when the new random number reaches 0 again or after it reaches 0.

[0091] The CSMA / CA and random backoff procedures briefly described above are applied to both DCF (Distributed Coordination Function) and EDCAF (Enhanced Distributed Channel Access), which are basic functions used when Wi-Fi terminals attempt channel access. Since these are well-known and widely used unlicensed band channel access methods, further detailed explanations will be omitted.

[0092] The DCF and EDCAF used by the MAC of a Wi-Fi terminal evaluate the channel status by considering not only the channel state (idle / busy) confirmed by each terminal itself through physical carrier sense (CS) but also the result of virtual CS. Even if the result of physical CS performed on a channel is idle, if the result of virtual CS is busy, the Wi-Fi terminal considers the channel state to be busy. Here, the virtual CS is a channel evaluation method that determines a channel as busy if the network allocation vector (NAV) is not 0. The NAV may be a value maintained for future traffic predicted to occupy the medium. Furthermore, when a Wi-Fi MAC receives an RTS / CTS frame, it sets its NAV (NAV count) based on the duration information of the received frame, e.g., the value of the duration field, and can maintain the NAV at a value other than 0 for the expected time the medium will be occupied after the RTS / CTS frame exchange. That is, the value maintained as the NAV decreases over time. If a specific MAC has a NAV value of 0, it may be interpreted as a state in which future traffic recognized by the specific MAC will no longer occupy the medium. If the NAV is 0, the MAC can determine the virtual CS result as idle. In this case, the Wi-Fi MAC can set its NAV based on duration values ​​obtained from other received MAC frames, as well as the RTS / CTS frame.

[0093] The channel evaluation method (determine the state of the medium) that takes into account both the physical CS and virtual CS results, briefly explained above, is also a well-known Wi-Fi MAC function, so a detailed explanation of it will be omitted.

[0094] <EDCAとTXOP> EDCA provides a mechanism for differentiating and managing traffic into four access categories (ACs) according to traffic characteristics. The four ACs are AC_VO (AC Voice), AC_VI (AC Video), AC_BE (AC Best Effort), and AC_BK (AC Background), and each AC may have a different contention window (CW), transmit opportunity (TXOP), and AIFSN parameters. Simply put, EDCA is a mechanism for differentiating the CW, TXOP, and AIFSN parameters for the four ACs and adjusting the transmission priority of traffic transmitted using each AC. To this end, EDCA can map traffic (MSDUs) to be serviced by a MAC to one of the four ACs according to traffic category (TC) or traffic stream (TS). The traffic mapped to one of the four ACs by EDCA is managed in four queues, one for each AC. The four queues may be logically, rather than physically, separated.

[0095] AC_VO is an AC that can be used for traffic that is vulnerable to transmission delays but does not have a large absolute volume of traffic, such as voice traffic, and has relatively small CW and AIFSN parameter values ​​to increase the probability of being served preferentially over traffic of other ACs. The TXOP parameter of AC_VO is limited to a smaller value than the TXOP parameters of other ACs, and only a shorter transmission time is guaranteed compared to other ACs.

[0096] AC_VI is an AC that can be used for traffic such as video, which is more tolerant of transmission delays than voice traffic but still requires low-delay transmission and must handle large amounts of traffic. AC_VI has larger CW and AIFSN parameter values ​​than AC_VO but smaller than other ACs, and in return, its TXOP is about twice as long as AC_VI.

[0097] AC_BE is an AC that can be used for traffic that is tolerant to transmission delays, and most general traffic except for voice data and streaming video data may be classified as AC_BE. AC_BE uses larger values ​​for CW and AIFSN parameters than AC_VO and AC_VI. Also, AC_BE does not have a separate TXOP. Therefore, traffic that falls under AC_BE cannot be used in a TXOP transmission sequence in which an ACK is received after transmitting a PPDU and then another PPDU is transmitted after SIFS.

[0098] AC_BK is an AC that can be used for traffic that is robust to transmission delays like AC_BE, but has a lower priority than BE traffic. AC_BK uses the same CW parameter value as AC_BE, but uses a larger AIFSN parameter value than AC_BE. Also, traffic that corresponds to AC_BK does not have a separate TXOP like AC_BE, and therefore cannot be used in a TXOP transmission sequence.

[0099] The four types of EDCA ACs are mapped to 802.1D UP (user priority), and the EDCA AC is determined by the UP value of traffic received via wire or the TID of MSDU indicated by an upper layer. In this case, if the TID of the MSDU indicates a value from 0 to 7, the value indicated by the TID may have a one-to-one correspondence with the UP.

[0100] In addition, the four types of EDCA ACs mentioned above have their default CW (CWmin, CWmax), AIFSN, and TXOP parameters defined in the standard. The parameter values ​​of each AC can be changed by the AP, and different values ​​can be used for each BSS.

[0101] Using the EDCA mechanism, Wi-Fi traffic is stored in one of four queues corresponding to four ACs, and may be transmitted to a destination device only if the AC containing the traffic wins a channel access contention with other ACs. In this case, each AC competes for channel access using its assigned access parameters (CW[AC], AIFSN[AC]), and the channel access contention behavior of each AC is the same as that of DCF. In this case, if a specific AC does not have any traffic to transmit in its queue, the specific AC does not need to participate in the contention.

[0102] However, as mentioned above, since the CW and AIFSN parameter values ​​used by each AC are different from each other, the AC_VO with the smallest CW and AIFSN parameters is more likely to win channel access contention with other ACs, and therefore the traffic of AC_VO is more likely to be served preferentially than the traffic of other ACs.

[0103] In addition, the EDCA mechanism specifies internal contention rules, such as when an internal collision occurs between ACs, the AC with the highest priority wins and increases the CW of the other AC that caused the collision, and rules for constructing a PPDU that includes traffic of other ACs rather than the AC that won the contention (primary AC).However, since these rules are not closely related to the proposal of the present invention, detailed explanations of them will be omitted.

[0104] As mentioned above, EDCA provides the EDCA Transmission Opportunity (TXOP) function as well as the function of operating differentiated ACs according to the type of traffic (frames, packets, etc.) to enhance QoS. EDCA TXOP refers to the time during which an EDCA Function (EDCAF) of a specific AC can control the medium without being disturbed by other devices when it obtains a channel access opportunity, i.e., when it becomes a TXOP holder. Here, EDCA TXOP may be limited by a TXOP limit advertised by the AP. The TXOP holder must ensure that its own transmission and the transmission of the response frame responded to by its own transmission can be completed within the TXOP limit.

[0105] A TXOP holder can transmit multiple frames (multiple PPDUs) during an EDCA TXOP interval. If each frame transmission occurs within the acquired TXOP interval, the TXOP holder can transmit multiple frames consecutively without performing a separate channel access procedure, such as a backoff procedure, between each frame transmission. If the multiple frames are MPDUs or A-MPDUs (Aggregated MAC protocol data units) that do not require immediate acknowledgment, the multiple frame transmissions may be performed at short interframe space (SIFS) or reduced interframe space (RIFS) intervals. If an MPDU or A-MPDU that requires immediate acknowledgment exists among the multiple frames, the TXOP holder can transmit the frame that requires immediate acknowledgment, receive an acknowledgment, and transmit the next frame after the SIFS interval.

[0106] In this case, traffic (packets, frames, etc.) of other ACs other than the specific AC that is the TXOP holder may also be transmitted within the TXOP acquired by the TXOP holder (specific AC) if certain conditions are met. The transmission of traffic of other ACs that are not the TXOP holder within the TXOP may be an operation due to TXOP sharing between ACs, and detailed content related to the certain conditions is omitted as it is not related to the present invention.

[0107] As described above, a TXOP holder can transmit consecutive frames without performing a separate channel access procedure within the TXOP. This may be achievable when other terminals understand and protect the TXOP section acquired by the TXOP holder. That is, in order for a TXOP holder to acquire medium control authority for an EDCA TXOP section, a procedure may be required to notify other terminals of the acquired TXOP section so that they can recognize it.

[0108] To this end, a terminal (AC) that has become a TXOP holder or starts transmission after completing the channel access procedure can attempt to allow other terminals to recognize the TXOP period by transmitting an RTS frame. In this case, the RTS frame refers to a frame in which the Type subfield (the fourth bit (B3) and the third bit (B2) of the Frame Control field of the MAC frame header) is set to 01b (Type = Control frame) and the Subtype subfield (the eighth bit (B7), the seventh bit (B6), the sixth bit (B5), and the fifth bit (B4) of the Frame Control field) is set to 1011b. Other terminals that receive an RTS frame from the TXOP holder can set their NAV based on duration-related information included in the RTS frame, for example, the value of the Duration field. The set NAV may be maintained at a value other than 0 for the time corresponding to the TXOP of the TXOP holder. However, a terminal designated as the destination device of the RTS frame must respond with a CTS frame instead of setting its NAV based on the information in the RTS frame. In this case, the destination device of the RTS frame sent to initiate a TXOP is the TXOP responder and must send a CTS frame in response to the RTS (SIFS after the RTS frame is received). The Duration field of the responding CTS frame is set to a value calculated by subtracting the CTS frame transmission time from the value indicated in the Duration field of the received RTS frame from the value indicated in the Duration field of the received RTS frame. A terminal receiving a CTS frame can set its NAV based on duration-related information (e.g., the value of the Duration field) included in the CTS frame.

[0109] Therefore, the NAV of the terminal that received the RTS frame from the TXOP holder and the terminal that received the CTS frame from the TXOP responder is set to 0 after the TXOP acquired by the TXOP holder is completed. This allows the Wi-Fi MAC mechanism to protect the TXOP holder and TXOP responder from unobstructed exchange of multiple frames during the TXOP.

[0110] However, if the TXOP holder transmits an RTS frame using a non-HT duplicate PPDU over the primary 80 MHz band, but the CTS frame (non-HT duplicate PPDU) received from the TXOP responder is only received in the primary 40 MHz band, the TXOP holder can use only the primary 40 MHz or a bandwidth less than the primary 40 MHz, e.g., the primary 20 MHz, for frame exchange during the acquired TXOP. The TXOP holder must set the CH_BANDWIDTH (a TXVECTOR parameter) of the PPDU it transmits to a value equal to or smaller than the CH_BANDWIDTH_IN-NON_HT (a RXVECTOR parameter) of the received CTS frame. In this case, the RTS frame may be an RTS frame that allows a CTS frame to be responded to in a BW smaller than the BW in which the RTS frame was transmitted. The RTS frame may be an RTS frame transmitted with DYN_BANDWIDTH_IN_NON_HT (a TXVECTOR parameter) set to Dynamic. If DYN_BANDWIDTH_IN_NON_HT is set to static and an RTS frame is sent by the TXOP holder, the TXOP responder must respond with a CTS frame in the same BW as the BW in which the RTS frame was received.

[0111] FIG. 9 illustrates a transmission / TXOP protection method using RTS and CTS frames according to an embodiment of the present invention.

[0112] Before transmitting a PPDU, the first station (STA1) transmits an RTS frame to the second station (STA2), which is the destination device of the PPDU. The second station (STA2) recognizes that the received RTS frame is an RTS frame targeted at itself and responds with a CTS frame after the SIFS.

[0113] After receiving the RTS frame transmitted by the first station (STA1), STA1_Neighbor, which is a neighboring station of the first station (STA1), sets the NAV based on the value indicated by the Duration field of the RTS frame. After receiving the CTS frame transmitted by the second station (STA2), STA2_Neighbor, which is a neighboring station of the second station (STA2), sets the NAV based on the information indicated by the Duration field of the CTS frame. After receiving the RTS / CTS frames, STA1_Neighbor and STA2_Neighbor determine that the virtual CS is busy while the set NAV (counter) remains a non-zero value and perform operations such as not decreasing the backoff counter. As a result, the neighboring terminals that receive the RTS / CTS frames do not attempt to transmit during the period when the NAV remains a non-zero value. Therefore, the first station (STA1) and the second station (STA2) can exchange the PPDU and Ack frames without being interfered with by neighboring terminals.

[0114] Even if there is a hidden relationship where signals from the first station (STA1) and STA2_Neighbor cannot be detected due to each other's transmissions, STA2_Neighbor can perform operations considering that the channel (channel, WM, Wireless medium) is in use while the first station (STA1) transmits the PPDU.

[0115] <TXOP Protection Using MU-RTS Trigger Frame> 11ax (6th generation Wi-Fi, Wi-Fi 6, HEW, High Efficiency WLAN) defines the MU-RTS Trigger / CTS frame exchange procedure, adding a feature that allows an AP to initiate a TXOP and protect the TXOP frame exchange procedure using the MU-RTS trigger frame (hereinafter referred to as MU-RTS or MU-RTS frame). The MU-RTS frame is a type of trigger frame. When an AP receives an MU-RTS frame and its AID12 (the 12 least significant bits of the association ID) is specified in the User field included in the MU-RTS frame, the AP simultaneously responds with a CTS frame. When an AP uses an MU-RTS frame to protect a TXOP, multiple stations respond with CTS frames, allowing the AP to protect the TXOP from each of the peripheral devices of multiple stations that are the destination of a Downlink Multi-User PPDU (DL MU PPDU). The MU-RTS frame can also be used to protect an Uplink Multi-User PPDU (UL MU PPDU). More specifically, before requesting a TB (Trigger based) PPDU from multiple stations using a trigger frame, the AP may transmit an MU-RTS frame, and multiple stations responding with the TB PPDU may respond with a CTS frame. In this case, the CTS frame responded by multiple stations may induce neighboring stations of each station to set NAVs that protect the TB PPDU and Ack frames (Ack, Block Ack, etc.) transmitted after the TB PPDU. As a result, legacy stations that cannot recognize (parse, decode) the trigger frame and the TB PPDU may not access the channel in the packet exchange order section (or TXOP) initiated by the trigger frame.

[0116] FIG. 10 illustrates a transmission / TXOP protection method using MU-RTS and CTS frames according to an embodiment of the present invention.

[0117] In the embodiment of Figure 10, before transmitting the MU PPDU, the AP transmits an MU-RTS frame to the first station (STA1) and the second station (STA2), which are the destination devices of the MU PPDU. The first station (STA1) and the second station (STA2) receive the MU-RTS frame and respond to the MU-RTS frame with their respective CTS frames after a SIFS.

[0118] After receiving the CTS frame transmitted by the first station (STA1), the neighboring station STA1_Neighbor sets its NAV based on the information indicated by the Duration field of the CTS frame. After receiving the CTS frame transmitted by the second station (STA2), the neighboring station STA2_Neighbor sets its NAV based on the information indicated by the Duration field of the CTS frame. After receiving the CTS frame, STA1_Neighbor and STA2_Neighbor determine that the Virtual Carrier Sense (Virtual CS) is busy and do not decrement the backoff counter while the set NAV (counter) remains non-zero. Therefore, neighboring terminals that receive a CTS frame do not attempt transmission while their NAV remains non-zero. This prevents interference from neighboring terminals between the AP transmitting the MU PPDU and the first station (STA1) and the second station (STA2) transmitting Ack frames.

[0119] The trigger frame mentioned above is a frame type defined in 11ax, and is a frame type in which the Type (4th bit (B3) and 3rd bit (B2)) and Subtype (8th bit (B7), 7th bit (B6), 6th bit (B5), and 5th bit (B4)) subfields of the Frame Control field are set to 01b and 0010b, respectively. A trigger frame is a Control Type frame in which the Type subfield of the Frame Control field is set to 01b, and a Subtype value of 0010 indicates a Trigger frame type. In 11ax, a trigger frame is defined so that an AP can request response frames from multiple stations at once, and an MU-RTS frame is used by an AP to request CTS frames from multiple stations (non-AP STAs). Trigger Types other than the MU-RTS frame include a basic trigger frame requesting a UL MU PPDU, a BRP trigger frame requesting a Beamforming Report (Beamforming Report Poll Tigger frame), an MU-BAR Tigger frame (BlockAck request), a BSRP trigger frame requesting a Buffer Status Report (Buffer Status Report Poll Tigger frame), a GCR MU-BAR trigger frame, a BQRP (Bandwidth Query Report Poll) trigger frame, and an NDP Feedback Report Poll (Poll) trigger frame. Trigger Types other than the MU-RTS frame are not relevant to the present invention, so detailed description will be omitted.

[0120] FIG. 11 shows a format of a trigger frame according to an embodiment of the present invention.

[0121] The trigger frame includes a MAC header including a Frame Control field, a Common Info field, a User Info List field, a Padding field, and an FCS field.

[0122] The Frame Control field includes Type and Subtype subfields, and a trigger frame has the values ​​of both subfields set to 01b and 0010b, respectively.

[0123] The Common Info field includes a Trigger Type subfield for indicating the type of trigger frame, a UL Length subfield for indicating the length of the UL transmission being responded to, etc., and the details thereof will be described in detail with reference to one embodiment of FIG. 12.

[0124] The User Info List field may include a User Info field containing information for indicating a target device of the trigger frame. In this case, the User Info field contains information on parameters, such as UL DCM or UL MCS, used when the target device transmits a response frame after receiving the trigger frame, depending on the type of the trigger frame, in addition to the information for indicating the target device. The details of the User Info field will be described in detail with reference to FIG. 13.

[0125] The Padding field is set to allow a station that receives a trigger frame time to prepare to transmit a response frame, such as a UL TB PPDU or CTS frame. The AP transmitting the trigger frame can adjust the length of the Padding field taking into account the performance of the destination device. In addition, in 11be (Wi-Fi 7, EHT), the end time of a PPDU containing a trigger frame may be added / adjusted to align it with other PPDUs, but a detailed description will be omitted.

[0126] The FCS (Frame Check Sequence) field includes a 32-bit CRC (Cyclic Redundancy Code) and is a value calculated including the MAC header and Frame Body field. The function and setting method of the FCS field of the trigger frame are the same as the function and setting method of the FCS field included in the conventional MAC frame. Further description thereof will be omitted.

[0127] FIG. 12 shows the format of the Common Info field of the trigger frame according to an embodiment of the present invention.

[0128] The Trigger Type subfield indicates the type (type, variant) of the trigger frame. If the value of the Trigger Type subfield is 0, it indicates a basic trigger frame. If the value of the Trigger Type subfield is 1, it indicates a Beamforming Report Poll (BFRP) trigger frame. If the value of the Trigger Type subfield is 2, it indicates an MU-BAR frame. If the value of the Trigger Type subfield is 3, it indicates an MU-RTS frame. If the value of the Trigger Type subfield is 4, it indicates a BSRP frame. If the value of the Trigger Type subfield is 5, it indicates a GCR MU-BAR frame. If the value of the Trigger Type subfield is 6, it indicates a Bandwidth Query Report Poll (BQRP) frame. If the value of the Trigger Type subfield is 7, it indicates an NDP Feedback Report Poll (NFRP) frame.

[0129] The UL Length subfield indicates the value to be set in the L-SIG LENGTH field of the TB PPDU responded to by the trigger frame.

[0130] The More TF subfield indicates whether there are more trigger frames to be transmitted after the trigger frame containing the More TF subfield.

[0131] The CS Required subfield indicates whether the destination device of the trigger frame must perform CS when transmitting a response frame (Physical & Virtual CS, ED & NAV). If the value of the CS Required subfield is 1, a station that receives a trigger frame that includes the CS Required subfield must perform CS before transmitting a response frame for the trigger frame.

[0132] The UL BW subfield indicates the value of the BW field that a STA that responds with a TB PPDU after receiving a trigger frame must set in the preamble, for example, HE-SIG-A or U-SIG.

[0133] The GI and HE / EHT-LTF Type subfield indicates the GI (Guard interval) and HE (EHT)-LTF values ​​of the acknowledged TB PPDU.

[0134] The MU-MIMO HE(EHT)-LTF Mode subfield indicates information related to the HE(EHT)-LTF mode to be applied to the acknowledged TB PPDU.

[0135] If the value of the Doppler subfield is 0, the Number Of HE(EHT / UHR)-LTF Symbols And Midamble Periodicity subfield indicates the number of HE(EHT)-LTF symbols to be applied to the TB PPDU. If the value of the Doppler subfield is 1, the Number Of HE(EHT / UHR)-LTF Symbols And Midamble Periodicity subfield indicates information related to the number of HE(EHT)-LTF symbols and midamble periodicity.

[0136] The UL STBC subfield indicates whether STBC encoding should be applied to the TB PPDU, which is a response to a trigger frame containing the UL STBC subfield. If STBC encoding needs to be applied, the value of the UL STBC subfield is set to 1. The value of the UL STBC subfield in the trigger frame that triggers the EHT / UHR TB PPDU is reserved.

[0137] The LDPC Extra Symbol Segment subfield indicates whether an LDPC extra symbol segment should appear in a TB PPDU, which is a response to a trigger frame that includes the LDPC Extra Symbol Segment subfield. If the value of the LDPC Extra Symbol Segment subfield is 1, the TB PPDU, which is a response to a trigger frame that includes the LDPC Extra Symbol Segment subfield, includes an LDPC extra symbol segment.

[0138] The AP Tx Power subfield indicates a value related to the transmit power used by the AP that transmitted the trigger frame when transmitting the trigger frame. A station that receives the trigger frame can adjust the transmit power of a response frame to the trigger frame based on the value indicated by the AP Tx Power subfield.

[0139] The Pre-FEC Padding Factor and PE Disambiguity subfields indicate whether the Pre-FEC Padding Factor is 1, 2, 3, or 4, and information for clarifying the length of the PE (Packet Extension).

[0140] The UL Spatial Reuse subfield includes four Spatial Reuse subfields and indicates the value set in the Spatial Reuse field of a TB PPDU that is a response to a trigger frame that includes the UL Spatial Reuse subfield.

[0141] The Doppler subfield indicates whether a midamble is included in a TB PPDU, which is a response to a trigger frame that includes the Doppler subfield. A trigger frame that triggers an EHT / UHR TB PPDU may have the Doppler subfield value set to reserved. In this case, setting the subfield to reserved may indicate that a station operates without considering the presence and value of the Doppler subfield after receiving the trigger frame.

[0142] The Special User Info Field Present subfield indicates whether the AID12 subfield indicates a User Info field indicated by 2007 or a pre-specified value in the User Info field.

[0143] The Trigger Dependent Common Info subfield is a field that is included in the trigger frame only when the type of the trigger frame indicated in the Trigger Type field is a basic trigger frame or an NFRP trigger frame.

[0144] FIG. 13 shows the format of the User Info field of the trigger frame according to an embodiment of the present invention.

[0145] The AID12 subfield indicates information related to which station the User Info field including the AID12 subfield is for. A station having the same AID as the AID indicated by the AID12 subfield can determine that the trigger frame including the AID12 subfield includes the station as a destination device. In this case, the AID12 subfield may be set to 1 to 2006 when indicating one associated station (1 to 2007 when the trigger frame is an HE Trigger).

[0146] In this case, if the value of the AID12 subfield is 0, the AID12 subfield may indicate that one or more Random Access RUs (RA-RUs) are allocated to a station associated with the AP that transmitted the trigger frame. If the trigger frame received by a station associated with the AP that transmitted the trigger frame does not have a User Info field including an AID12 subfield indicating the station's AID, but has a User Info field with an AID12 subfield value of 0, the station may attempt to transmit a TB PPDU using the RA-RU.

[0147] Also, if the value of the AID12 subfield is 2045, the AID12 subfield may indicate that one or more Random Access RUs (RA-RUs) are allocated to stations that are not associated with the AP that transmitted the trigger frame. A station that is not associated with an AP may attempt to transmit a TB PPDU using the RA-RU if the trigger frame received by the station includes a User Info field with the AID12 subfield value of 2045.

[0148] Also, if the value of the AID12 subfield is 4095, a station receiving the trigger frame can determine that the padding field begins from the AID12 subfield, and the station does not need to attempt to parse the rest of the MAC frame after the AID12 subfield with a value of 4095.

[0149] Also, if the value of the AID12 subfield is 2046, the AID12 subfield can indicate that the User Info field including the AID12 subfield indicates information about an unallocated RU, which is an RU that has not been assigned to any station.

[0150] The RU Allocation subfield of trigger frames other than the MU-RTS trigger frame indicates the size and location information of the RU (Resource Unit) / MRU (Multiple Resource Unit) allocated to the destination device of the User Info field including the RU Allocation subfield. A station can determine the information of the RU / MRU allocated to the station by analyzing the RU Allocation subfield and the PS160 subfield included in the User Info field. A station can determine the information of the RU / MRU allocated to the station by analyzing the RU Allocation subfield and the PS160 and PS320 subfields included in the User Info field. In this case, the PS320 subfield indicates whether the allocated RU is included in the primary 320 MHz band or the secondary 320 MHz band within the 640 MHz band. The PS160 subfield indicates whether the RU allocated within the 320 MHz band (primary 320 MHz or secondary 320 MHz) indicated by the PS320 subfield is included in a 160 MHz band located higher on the frequency axis or a 160 MHz band located lower on the frequency axis. However, if the 320 MHz band indicated by the PS320 subfield is the primary 320 MHz, the information indicated by the PS160 subfield may indicate whether the RU is the primary 160 MHz or the secondary 160 MHz, rather than whether it is higher or lower on the frequency axis. Specifically, the 320 MHz band indicated by the PS320 subfield may be the primary 320 MHz. In this case, if the value of the PS160 subfield is 0, the PS160 subfield may indicate that the allocated RU is included in the primary 160 MHz band. In this case, if the value of the PS160 subfield is 1, the PS160 subfield may indicate that the allocated RU is included in the secondary 160 MHz band. In this case, the value of the PS160 subfield is an example.If the value of the PS160 subfield is 1, the PS160 subfield may indicate that the assigned RU is included in the primary 160 MHz band. If the value of the PS160 subfield is 0, the PS160 subfield may indicate that the assigned RU is included in the secondary 160 MHz band.

[0151] The method of indicating the location of the allocated RU within each 160 (and 320) MHz band indicated in this manner may be the same as or similar to the method of indicating the RU Allocation subfield of the trigger frame defined in the EHT.

[0152] The RU Allocation subfield of the MU-RTS frame indicates the channel on which the destination device in the User Info field responds with a CTS frame. Specifically, the RU Allocation subfield of the MU-RTS frame indicates whether the destination device transmits the CTS frame only on the primary 20 MHz channel or on the primary 40 MHz channel, primary 80 MHz channel, primary 160 MHz channel, 80+80 MHz channel, primary 320 MHz channel, or primary 640 MHz channel. In this case, an MRU represents an RU combining two or more RUs, and 52+26, 106+26, 484+242, 996+484, 996+484+242, 2x996+484, 3x996, 3x996+484, 4x996, and 4x996+4x996-tone size MRUs may be used in UHR.

[0153] The UL FEC Coding Type subfield indicates the code type of the TB PPDU being responded to. If the UL FEC Coding Type subfield has a value of 0 and a value of 1 for binary convolution coding (BCC), the UL FEC Coding Type subfield indicates low density parity check (LDPC).

[0154] The UL EHT / UHR-MCS subfield indicates the EHT / UHR-MCS to be applied to the TB PPDU transmission in response to the trigger frame.

[0155] The SS Allocation / RA-RU Information subfield may be used as the SS Allocation subfield if no RA-RU is allocated in the AID12 subfield. The 6 bits of the SS Allocation subfield may include a 4-bit Starting Spatial Stream subfield and a 2-bit Number Of Spatial Streams subfield. If the value of the AID12 subfield is 0, 2044, or 2045, the User Info field including the AID12 subfield indicates information about the RA-RU.

[0156] The UL Target Receive Power subfield indicates the predicted signal strength (power) value at which the TB PPDU, which is a response to the trigger frame, is received at the AP antenna. When a station transmits a TB PPDU, the station can adjust the transmission power of the TB PPDU according to the value of the UL Target Receive Power subfield. This allows the AP to receive the TB PPDU at the power it predicts.

[0157] The PS160 subfield, together with the RU Allocation subfield, indicates information about the location and size of the RU / MRU allocated by the User Info field containing the PS160 subfield.

[0158] The Trigger Dependent User Info (sub)field does not appear in the MU-RTS frame, so a detailed description is omitted.

[0159] <Limitations of existing channel access methods> As described above, in Wi-Fi, an AP can simultaneously instruct multiple non-AP STAs to transmit DL PPDUs by using a signaling field included in the preamble to indicate information related to the RUs that each non-AP STA should receive. Multiple non-AP STAs can also transmit UL PPDUs based on a trigger frame transmitted from the AP. This frame exchange sequence, in which the AP is centralized and multiple non-AP STAs communicate with each other, is an evolution of Wi-Fi wireless LAN technology devised to more efficiently use limited radio frequency resources.

[0160] However, there is a limitation in that AP operations such as transmitting a DL MU PPDU or using a trigger frame to instruct / trigger UL MU PPDU transmission can only be used when the AP has acquired a TXOP. When a non-AP STA acquires a TXOP, a one-to-one frame exchange sequence is performed in which the non-AP STA transmits a UL PPDU and the AP responds to it (Ack, Block Ack, etc.). This is the same frame exchange sequence used in older versions of WLAN. In other words, since the recently defined Wi-Fi standard's multi-user operation can only be used with a TXOP acquired by the AP, there is a limitation in that when a non-AP STA acquires a TXOP, it is difficult to expect improvements in WLAN utilization efficiency through MU operation.

[0161] When a non-AP STA obtains a TXOP, it is not possible to perform highly efficient MU operations (operations using DL MU PPDUs and UL MU PPDUs), and there are more limitations compared to when an AP obtains a TXOP.

[0162] For example, the amount of frequency resources available for frame exchange is limited. Generally, non-AP STAs have lower capabilities than APs, and therefore are likely to have a narrower operating bandwidth than APs. That is, the bandwidth of the TXOP acquired by a non-AP STA after channel access is higher than the bandwidth available for TXOP acquisition when the AP accesses the channel. For example, if an AP supports operation for a 320 MHz bandwidth, but a non-AP STA only supports operation for an 80 MHz bandwidth, the non-AP STA will only acquire a TXOP for 80 MHz before exchanging frames with the AP. In this case, the AP cannot utilize the capabilities it could have supported in the remaining 240 MHz of the 320 MHz bandwidth, excluding 80 MHz. This means that an opportunity to support service to more traffic is lost due to the TXOP acquired by the non-AP STA.

[0163] As another example, the number of spatial streams that can be used for frame exchange is limited. Generally, a non-AP STA has a configuration including fewer antennas than an AP, and therefore has a smaller number of available antennas than an AP. That is, even if there are available antennas remaining on the AP side, the non-AP STA is limited in its ability to perform more efficient operations using the available antennas during the time period in which it acquires a TXOP.

[0164] Even without the examples related to BW and number of antennas mentioned above, it is an easily understood fact that the expected utilization of TXOP acquired by an AP is higher than that of TXOP acquired by a non-AP STA, and detailed explanation of this will be omitted.

[0165] FIG. 14 shows an example of a frame exchange sequence between STAs performed during a TXOP according to an embodiment of the present invention.

[0166] 14, after obtaining channel access permission (completing the backoff procedure), the AP obtains a TXOP for 320 MHz by transmitting a CTS-to-self frame over the 320 MHz band. The AP may transmit a 320 MHz DL PPDU during the obtained TXOP and respond with a UL MU PPDU (TB PPDU) over the 320 MHz band using a trigger frame. That is, the AP performs MU operation using the 320 MHz band during its TXOP, and this process utilizes multiple antenna transmission / reception technology using the AP's eight antennas.

[0167] Meanwhile, after obtaining channel access permission, non-AP STAs transmit RTS frames over the 80 MHz band and receive CTS frames. Unlike the AP, which obtains a TXOP over the 320 MHz band, non-AP STAs only obtain a TXOP over the 80 MHz band due to capability limitations. The non-AP STA transmits an UL PPDU during the TXOP it obtains and receives a BA in response. In this process, operation is performed using only two spatial streams because the non-AP STA has only two antennas, while the AP has eight antennas.

[0168] As a result, the TXOPs acquired by the AP are efficiently utilized through MU PPDU exchange utilizing a wide bandwidth and a large number of antennas, whereas the TXOPs acquired by non-AP STAs are relatively inefficient as they utilize only a relatively narrow bandwidth and a small number of antennas.

[0169] That is, when an AP acquires a TXOP and performs UL / DL transmission, the UL / DL transmission can be performed more efficiently than when a non-AP STA acquires a TXOP and performs UL / DL transmission. Therefore, the present invention proposes a method for efficiently using a TXOP by a procedure for granting a right to acquire a TXOP or sharing an acquired TXOP between STAs.

[0170] Specifically, a STA (e.g., a non-AP STA or an AP) that has obtained a TXOP through the backoff procedure or that has already obtained a TXOP can share its obtained permission or TXOP with another STA (e.g., a non-AP STA or an AP) using a specific frame (e.g., an initiating frame). In this case, the other STA can send and receive PPDUs using the TXOP acquisition permission or the obtained TXOP. If a non-AP STA can share the TXOP acquisition permission or the obtained TXOP with an AP of an associated BSS. A non-AP STA can transmit its own information (e.g., connection category, TXOP length, buffer information related to the backoff procedure for TXOP acquisition) in a frame for obtaining a TXOP or sharing the obtained TXOP. The AP that has obtained a TXOP acquisition permission or shared a TXOP can send and receive PPDUs and can send a trigger frame to instruct the non-AP STA to perform uplink transmission. When an AP uses a trigger frame to instruct a non-AP STA that has TXOP acquisition authority or that shares a TXOP to perform uplink transmission, the user information field containing information such as the AID of the resource allocated to the corresponding non-AP STA may be located first among the user information fields included in the user specific field. When a non-AP STA that has TXOP acquisition authority or that shares a TXOP performs channel access, it can perform channel access using EDCA parameters regardless of the value of the MU-EDCA timer.

[0171] After the TXOP ends, the AP can select a new backoff counter for the channel connection within the contention window, where the size of the contention window for selecting the new backoff counter can be the minimum value or one of the contention window sizes for the current connection category.

[0172] The length of the TXOP shared in the present invention may be the same as or shorter than the length of the TXOP obtained by the sharing STA. That is, the STA can share all or part of the TXOP obtained by the backoff procedure.

[0173] Hereinafter, the method for obtaining the TXOP acquisition right or sharing the obtained TXOP according to the present invention may be applied not only to the method by which the non-AP STA shares with the AP, but also between non-AP STAs, between the AP and the non-AP STA, and between APs.

[0174] <AP channel access based on the start of non-AP STA> As described above, it can be seen that it is more advantageous for the AP to acquire the TXOP than for the non-AP STA to acquire the TXOP in order to efficiently utilize the radio resources, and it can be said that increasing the proportion of the AP acquiring the TXOP is important for the efficient utilization of the wireless LAN resources of the BSS and the entire network.

[0175] According to an embodiment of the present invention, after obtaining the channel access right, the non-AP STA can induce the AP to acquire the TXOP instead of itself acquiring the TXOP. That is, the non-AP STA can transfer / yield the TXOP acquisition opportunity it has obtained to the (associated) AP.

[0176] More specifically, the non-AP STA can perform a backoff procedure by DCF or EDCA to obtain the channel access right (complete the backoff procedure). Thereafter, the non-AP STA may cause the AP to acquire the TXOP by instructing the AP of the fact that it has obtained the channel access right according to a pre-agreed procedure. Through this process, based on the non-AP STA securing the channel access right, the AP can acquire the TXOP (become the TXOP holder).

[0177] A simple sequence of operations in which a non-AP STA accesses a channel and grants a TXOP acquisition opportunity to the AP is as follows (see 1. to 5. below; A, B, etc. indicate additional operations and considerations applicable to each sequence). However, the sequence of operations described below is merely one example, and the method by which the AP acquires a TXOP through a series of processes after the non-AP STA acquires a TXOP (channel access permission, i.e., completion of the backoff procedure) should be considered as the main idea of ​​the present invention. Furthermore, after the non-AP STA acquires a TXOP, a method in which the acquired TXOP is used in a similar manner to a TXOP in which the AP is the TXOP holder (i.e., the AP transmits a DL MU PPDU or transmits a trigger frame to solicit a UL MU PPDU response (soliciting), etc.), and a method in which the AP utilizes a BW larger than the BW of the TXOP acquired by the non-AP STA, etc., should be understood to be the same as the main function provided by the present invention, except that the entity that acquires the TXOP differs.

[0178] The procedure for an STA (AP or non-AP) to receive a TXOP from another STA (AP or non-AP STA) or receive a TXOP from another STA is as follows. Hereinafter, the procedure for an AP to receive a TXOP from a non-AP STA or receive a TXOP from another STA will be described. However, the present invention is not limited to this and may be applied to a TXOP receiving authorization or TXOP sharing procedure between STAs.

[0179] 1. The non-AP STA performs the backoff procedure using DCF or EDCA.

[0180] 2. After the backoff procedure is completed, the non-AP STA transmits a pre-promised frame to the associated AP to concede the TXOP acquisition opportunity to the AP, instead of transmitting a frame to initiate its own TXOP. (The associated AP refers to the AP of the BSS of which it is a member.)

[0181] 3. Upon receiving a TXOP initiating frame from a non-AP STA, the AP transmits a frame for TXOP acquisition on a channel that has been confirmed as IDLE by CCA within its own operating bandwidth.

[0182] 4. After the AP gets the TXOP, it sends a trigger frame.

[0183] 5. After the AP acquires the TXOP or when the TXOP is completed, it generates a new backoff counter.

[0184] (1. Execution of backoff procedure using DCF or EDCA) A non-AP STA can obtain TXOP acquisition permission through the backoff procedure. In this case, the non-AP STA can perform the backoff procedure using DCF, EDCA parameters, or MU EDCA parameters. When a non-AP STA attempts to obtain TXOP acquisition permission or share the obtained TXOP with an associated AP, it can perform the backoff procedure using EDCA parameters regardless of the value of the MU EDCA timer. In other words, a non-AP STA attempting to obtain TXOP acquisition permission or share the obtained TXOP with an associated AP can perform the backoff procedure using EDCA parameters even if the MU EDCA timer value is not '0' when performing the backoff procedure. In other words, a non-AP STA attempting to obtain TXOP acquisition permission or share the obtained TXOP with an associated AP can perform the backoff procedure using EDCA parameters at any time regardless of the value of the MU EDCA timer.

[0185] That is, a non-AP STA that intends to share a TXOP with the AP after acquiring it or that intends to yield the TXOP acquisition opportunity to the AP can access the channel using EDCA parameters regardless of the value of the MU-EDCA timer. Furthermore, even if a non-AP STA performs a backoff procedure through MU-EDCA, it can also yield the TXOP acquisition opportunity to the AP or share the acquired TXOP. Conventionally, when the MU-EDCA timer of a Wi-Fi non-AP STA is not 0, the non-AP STA must access the channel using MU-EDCA parameters. However, if the non-AP STA intends to yield the TXOP acquisition opportunity to the AP, it can perform the backoff procedure using EDCA parameters. This behavior may be considered so that a non-AP STA that yields the TXOP acquisition opportunity to the AP can have channel access privileges under the same conditions as legacy non-AP STAs that do not perform UL MU (Uplink Multi-User) operation when accessing the channel.

[0186] (2. Sending a frame for TXOP acquisition authority or TXOP sharing) After completing the backoff procedure, the non-AP STA may transmit a specific frame to grant (or share) the AP the right (or opportunity) to acquire the TXOP, instead of transmitting a frame to initiate the TXOP. In this case, the AP that receives the specific frame is the AP of the BSS to which the non-AP STA is a member, and the AP associated with the non-AP STA. The specific frame may be called an initiating frame, but may be called various other names. Alternatively, the initiating frame may be an existing frame, in which case the frame for granting the TXOP acquisition right may be configured in a different manner. For example, the initiating frame may be an RTS frame or a trigger frame. In this case, the RTX frame or trigger frame for granting the TXOP acquisition right may be configured in a different manner from the existing configuration method. For example, the format or field values ​​may be configured differently. In other words, the initiating frame may be classified as the same type (and subtype) of a frame as a conventional Wi-Fi-defined frame, but may be configured in a different manner when used to grant the AP the TXOP acquisition right it has acquired.

[0187] The initiation frame may include at least one of Duration / ID information, AC information, buffer status information, and / or at least one parameter related to PPDU transmission of the non-AP STA that has obtained TXOP acquisition permission (e.g., MCS, PPDU BW (RU size), PPDU length).

[0188] i. If the initiation frame is a CTS-to-AP frame, the CTS-to-AP frame refers to a CTS frame whose RA field is set to the MAC address of the AP. In this case, the Duration / ID of the CTS-to-AP frame may be set to a length that includes the trigger frame transmitted by the AP that received the initiation frame.

[0189] ii. The initiation frame may include information about an Access Category (AC) related to the backoff procedure for the non-AP STA to obtain TXOP acquisition permission and / or information related to the length of the TXOP that can be obtained after completing the backoff procedure. Regarding the information related to the TXOP length, the Duration / ID field of the initiation frame may be set to a length including a trigger frame transmitted by the AP that receives the initiation frame. That is, the Duration / ID field may be set to a value that takes into account the length of the trigger frame when the AP that is granted TXOP acquisition permission from the non-AP STA transmits the trigger frame. Alternatively, the information related to the TXOP length may be included and indicated in the frame body field of the initiation frame instead of the MAC header.

[0190] iii. The initiation frame may include information (e.g., buffer status information) related to the buffer status of the non-AP STA transmitting the initiation frame (i.e., granting permission to acquire the TXOP or sharing the acquired TXOP).

[0191] iv. The initiation frame may include information related to the parameters (e.g., MCS, PPDU bandwidth (RU size), PPDU length, etc.) that the non-AP STA transmitting the initiation frame (i.e., granting permission to acquire a TXOP or sharing an acquired TXOP) intends to use when transmitting an uplink PPDU.

[0192] v. The initiation frame may have a configuration including a user information field (the same (or similar) configuration as the user information field included in the trigger frame) that the non-AP STA intends to receive using the trigger frame. In this case, the AP may transmit a trigger frame including the same user information field as the user information field included in the initiation frame to at least one non-AP STA, including a non-AP STA that grants permission to acquire a TXOP or shares the acquired TXOP.

[0193] The start frame may be transmitted in a non-HT PPDU or a non-HT duplicated PPDU, i.e., a non-AP STA can transmit the start frame in a non-HT or non-HT duplicated PPDU.

[0194] The initiation frame may include information (e.g., channel state information) related to an idle channel confirmed by the non-AP STA transmitting the frame. More specifically, the initiation frame may include a field indicating the IDLE / BUSY status of each subchannel confirmed by the STA transmitting the frame. In this case, whether each subchannel is IDLE or BUSY may be information utilized by an AP transmitting a trigger frame after receiving the frame. For example, when allocating RUs to a STA that transmitted an initiation frame using a trigger frame, the AP may allocate RUs included in subchannels designated as IDLE by the STA. That is, when selecting RUs to allocate to a STA that transmitted an initiation frame, the AP may need to allocate RUs included in subchannels designated as IDLE by the STA that transmitted the frame.

[0195] The Duration / ID field of the initiation frame may be set in a predetermined manner. More specifically, the Duration / ID field of the initiation frame may be set to a value indicating a point before the start of a TB PPDU responded to by a trigger frame transmitted by the AP that received the initiation frame. That is, even if a second STA that received the initiation frame transmitted by a first STA sets a network allocation vector (NAV) based on the frame, the NAV is cleared when the second STA responds with a TB PPDU in response to the trigger frame transmitted by the AP. In this manner, the unassociated non-AP STA can respond with a TB PPDU to a random access RU (RA-RU) indicated by the trigger frame of the AP (through an UL OFDMA-based random access (UORA) procedure).

[0196] The Duration / ID field of the initiation frame may be set based on information previously instructed by the AP. That is, the AP may inform non-AP STAs of the value to be set in the Duration / ID field of the initiation frame using a Management frame. This value may be determined taking into account the time it takes for the AP to attempt to acquire a TXOP after receiving the initiation frame. For example, the AP may intend to adjust the length of a frame (e.g., an MU-RTS frame) to be transmitted to acquire a TXOP after receiving the initiation frame, and may inform the non-AP STAs of the Duration / ID field value determined taking into account the adjusted transmission length. As a more specific example, the AP may include padding in the initial frame transmitted after receiving the initiation frame, taking into account the mode transition time (eMLSR / low power mode => normal operation mode) of the non-AP STA, in consideration of non-AP STAs operating in eMLSR mode or low power listening mode. In this case, the time it takes for the AP to transmit the first trigger frame after acquiring a TXOP may be slightly longer than when a short initial frame (without padding) is transmitted. Therefore, in order to ensure MAC-level protection until the non-AP STA that transmitted the start frame sends a TB PPDU response to the trigger frame, the Duration / ID field value of the start frame must be appropriately adjusted, and for this purpose, the AP must publicly announce the Duration / ID field value. Alternatively, the AP may need to maintain the length of the initial frame to be transmitted after receiving the start frame at or below a predetermined length. In this case, the Duration / ID field value of the start frame is set in a predetermined manner, and the AP must adjust the initial frame sequence and length, etc., taking into account the time protected by the Duration / ID field value.

[0197] If a non-AP STA does not receive a frame transmitted by the AP (a frame transmitted by the AP to acquire a TXOP or the frame following the start frame transmitted in a predetermined frame exchange sequence) within a predetermined time interval after transmitting a start frame, the non-AP STA must transmit a CF-END frame. This may be a procedure (transmission of a CF-END frame) for canceling the NAV of the STA whose NAV was set by the start frame when the procedure for transferring the TXOP to the AP by the start frame fails.

[0198] A non-AP STA must transmit a start frame if the time it acquires channel access permission (the time it completes the backoff procedure) is within the R-TWT SP (Restricted-TWT (target wake time) Service period). R-TWT SP is an SP set to prioritize low latency traffic transmission and is a type of Broadcast TWT. The start point of an R-TWT SP is characterized by having the same start point as the overlapping quiet interval (1 TU length).

[0199] A 20 MHz-only non-AP STA that only supports 20 MHz operation may be restricted to transmitting an initiation frame upon completing the backoff procedure. That is, a 20 MHz-only non-AP STA may be restricted to not be a TXOP holder and must transfer the TXOP to the AP. This may be an operational restriction on 20 MHz-only non-AP STAs that is considered to prevent the performance of the BSS from deteriorating due to the limited performance of the 20 MHz-only non-AP STAs.

[0200] (3. Obtain TXOP acquisition authority or attempt to acquire TXOP by an AP that shares TXOP) An AP that receives an initiation frame from a non-AP STA to be granted TXOP acquisition permission or to share an acquired TXOP can transmit a specific frame for TXOP acquisition on a channel within its operating bandwidth (BW) that is confirmed to be idle based on the results of CCA.

[0201] i. In this case, the method by which the AP determines whether each channel is IDLE through CCA may be based on the CCA result in PIFS after the start frame is received (including virtual CCA). In this case, the channel on which the start frame is received may be excluded from the determination of whether it is IDLE. Alternatively, the method by which the AP determines whether each channel is IDLE through CCA may be based on whether the channel maintains an IDLE state in PIFS or SIFS after the start frame is received (including virtual CCA). In this case, the channel on which the start frame is received may be excluded from the determination of whether it is IDLE. Alternatively, the method by which the AP determines whether each channel is IDLE through CCA may be based on whether the channel maintains an IDLE state in PIFS before the start frame is received (including virtual CCA).

[0202] ii. The AP may transmit a frame for TXOP acquisition on a channel (idle) other than the channel occupied by the PPDU containing the start frame received from the non-AP STA. That is, the AP's TXOP acquisition procedure may be performed using a PPDU with a larger BW than the PPDU containing the start frame. In this case, the AP's TXOP may be acquired for a BW larger than the BW in which the non-AP STA transmitted the start frame. Furthermore, even if the non-AP STA that transmitted the start frame determined the subchannel to be busy and did not transmit the start frame (a punctured channel included in the BW of the PPDU transmitted by the non-AP STA), the AP may determine the subchannel as idle and acquire the AP's TXOP. In this case, the AP does not allocate RUs of the subchannel (a subchannel not occupied by the start frame) to the non-AP STA, and can use the RUs for frame exchange with other non-AP STAs. However, even if the subchannel is determined to be idle by the AP, the AP does not attempt to acquire a TXOP for a subchannel determined not to be used in the BSS (disabled subchannel). After receiving an initiation frame, an AP attempting to acquire a TXOP for a BW larger than the BW of the PPDU containing the initiation frame must attempt BW extension taking into account the BW extension resolution and / or the ratio of IDLE subchannels to the additional BW. More specifically, an AP attempting to acquire a TXOP for a BW larger than the BW of the PPDU containing the initiation frame can attempt BW extension only if a certain ratio or more of the subchannels included in the extended BW are determined to be idle. In this case, the certain ratio may be, for example, 50%. For example, an AP receiving an initiation frame via an 80 MHz PPDU can attempt to acquire a TXOP for a 160 MHz BW only if two or more of the four subchannels included in the secondary 80 MHz BW are determined to be idle.That is, if only one of the four subchannels included in the secondary 80 MHz BW is determined to be idle, the AP must not attempt to acquire a TXOP for the 160 MHz BW. However, if six or more of the 12 subchannels included in the secondary 80 MHz and secondary 160 MHz bands are idle, the AP can attempt to acquire a TXOP for the 320 MHz band. However, even in this case, if fewer than four of the eight subchannels included in the secondary 160 MHz band are idle, the AP cannot attempt a BW extension for the secondary 160 MHz band. The above example considering a 50% ratio is for illustrative purposes only, and the specific ratio value can be changed to any other value. That is, whether or not the AP is allowed to extend the BW is determined based on whether the gain obtainable in the extended BW is sufficient, and the specific criteria for whether the gain is sufficient can be applied in any number of different ways or by any number of different criteria.

[0203] iii. The frame transmitted by the AP for TXOP acquisition may be a CTS-to-Self frame, an MU-RTS frame, an RTS frame, or a trigger frame.

[0204] iv. The PPDU including a frame for TXOP acquisition transmitted by the AP is transmitted SIFS or PIFS after the end of the PPDU including the start frame received from the non-AP STA. That is, the AP that receives the start frame transmits the frame for TXOP acquisition SIFS or PIFS later. In this case, the inter-frame space used when the AP transmits the frame for TXOP acquisition after receiving the start frame may be the same as the inter-frame space used by the AP to determine whether each subchannel is idle or busy. That is, the AP performs CCA (PHY CCA) and energy detection (ED) for its operating bandwidth in SIFS or PIFS immediately after receiving the start frame, and can perform channel access for subchannels determined to be idle.

[0205] v. The Duration / ID field of the frame for TXOP acquisition transmitted by the AP can be set based on the received initiation frame. For example, the Duration / ID field of the frame for TXOP acquisition transmitted by the AP can be set to a value equal to or smaller than the "Duration / ID field value of the initiation frame" minus "SIFS or PIFS" minus "length of the frame for TXOP acquisition transmitted by the AP." Alternatively, the AP may have to determine the length of the TXOP it attempts to acquire based on information indicated by other fields included in the initiation frame. That is, the length of the TXOP that the AP can acquire can be determined (limited) based on other fields (other than the Duration / ID field) included in the initiation frame.

[0206] The frame sent by the AP for TXOP acquisition must be sent in non-HT PPDU or non-HT duplicated PPDU format, i.e., after receiving the initiation frame, the AP must attempt to acquire the TXOP using non-HT or non-HT duplicated PPDU format.

[0207] (4. Trigger frame transmission by AP) When an AP receives an initiation frame transmitted by a non-AP STA and performs channel access to acquire a TXOP, the AP must transmit at least one trigger frame within the TXOP. In this case, the trigger frame may be a trigger frame that allocates an RU to the non-AP STA that transmitted the initiation frame and solicits a UL PPDU (TB PPDU). However, if the AP determines that the non-AP STA that transmitted the initiation frame does not need to transmit based on the information contained in the initiation frame, the AP may not transmit a trigger frame within the acquired TXOP.

[0208] When an AP transmits a trigger frame to a non-AP STA that transmitted an initiation frame, the AP may acquire a TXOP from the non-AP STA and then transmit a trigger frame to instruct at least one non-AP STA to perform uplink transmission within the acquired TXOP. In this case, the at least one non-AP STA may include a non-AP STA that has been granted TXOP acquisition permission or that has shared the acquired TXOP. If a trigger frame for uplink transmission is transmitted to a non-AP STA that has been granted TXOP acquisition permission or that has shared the acquired TXOP (hereinafter, a TXOP-sharing non-AP STA), the user information field for the TXOP-sharing non-AP STA may be located first among at least one user field included in the user identification field of the trigger frame. This is to compensate the non-AP STA that has granted the AP permission to acquire a TXOP or that has shared the acquired TXOP.

[0209] i. The trigger frame includes a user information field corresponding to the AID of the TXOP sharing non-AP STA that transmitted the start frame. Among the user information fields included in the trigger frame, the user information field corresponding to the TXOP sharing non-AP STA that transmitted the start frame may be indicated first (except for the special user information field (User Info field whose AID subfield is 2007 or a predetermined value)).

[0210] ii. The AP may set the User Info field for the TXOP sharing non-AP STA included in the trigger frame based on the information indicated by the start frame. That is, the User Info field corresponding to the non-AP STA that transmitted the start frame may be set based on various parameters (MCS, UL Length, BW / RU size information, etc.) included in the start frame. For example, the AP may set the UL Length subfield included in the trigger frame based on the information indicated by the TXOP sharing non-AP STA. If the non-AP STA indicates information related to the length of the TB PPDU that it intends to transmit, the AP may set the UL Length field of the trigger frame to be equal to the indicated length or to a length longer than the indicated length. When allocating RUs by a trigger frame transmitted during a TXOP acquired by receiving a start frame from a non-AP STA (when soliciting a TB PPDU response), the AP may prioritize scheduling of the STA that transmitted / will transmit the start frame. In this case, the AP may determine whether each STA is the STA that transmitted / scheduled to transmit the start frame based on whether a preset time has elapsed since the non-AP STA transmitted the start frame. Alternatively, the AP may determine whether each STA is the STA that transmitted / scheduled to transmit the start frame based on whether the STA sets a Capability or Operating element related to the start frame transmission to true (or 1). When allocating RUs to a TXOP-sharing non-AP STA that transmitted the start frame, the AP must allocate only RUs in the band occupied by the PPDU containing the start frame transmitted by the TXOP-sharing non-AP STA. In other words, the AP must not allocate RUs in the band not occupied by the start frame (or the PPDU containing the start frame) to the TXOP-sharing non-AP STA that transmitted the start frame.This may be an RU allocation restriction that takes into consideration that the band not occupied by the start frame (or the PPDU containing the start frame) is a band confirmed as BUSY by the non-AP STA that transmitted the start frame as a CCA result or a band outside the non-AP STA's operating bandwidth. Therefore, the size and location of the RU allocated to the non-AP STA that transmitted the start frame may be allocated differently from what the non-AP STA requested, depending on the CCA result of each subchannel confirmed by the AP.

[0211] vi. The AP must determine the location of the RU to be assigned to the TXOP-sharing non-AP STA that transmitted the start frame, taking into account the location of the primary 20MHz channel. More specifically, the AP must assign RUs within the primary 20MHz channel or including RUs on the primary 20MHz channel to the non-AP STA that transmitted the start frame.

[0212] (5. Backoff counter generation by AP) An AP that acquires a TXOP can generate (or select) a new backoff counter after acquiring the TXOP or when the TXOP ends. In this case, the AC for generating the backoff counter may be determined based on the AC indicated by the initiation frame. In other words, the backoff counter generated after acquiring the TXOP or when the TXOP ends may be the same (or similar) backoff counter for the AC indicated by the initiation frame. For example, if the AP confirms that AC_BE is indicated based on the information indicated by the initiation frame, it can generate a new backoff counter for AC_BE. When generating a new backoff counter, the AP must generate the new counter using the CW_min (minimum contention window) of the AC. Alternatively, when generating a new backoff counter, the AP must generate the new counter using the current CW of the AC. Alternatively, when acquiring a TXOP based on the initiation frame, the AP does not need to change the backoff counter of the EDCAF. Alternatively, the AC for which the AP generates a new backoff counter may be the AC with the smallest remaining backoff counter among all ACs. That is, when selecting an AC for which to regenerate a backoff counter, the AP can determine the AC for which to regenerate a backoff counter based on the backoff counter size of each AC. This can be understood as a backoff regeneration method that takes into account that the AP can use any AC in the process of performing channel access to transmit a trigger frame. In this case, if there are two or more ACs with the smallest backoff counters (i.e., two or more ACs have the same backoff counter), the AP can select one of the two ACs with the smallest backoff counters and regenerate the backoff counter for that AC. Alternatively, the AP can determine that the AC for which to generate a new backoff counter is any AC.This may also be a backoff regeneration method that takes into account that the AP can use any AC in the process of channel access to transmit a trigger frame. In the process of generating a new backoff counter, the AP can generate a new random number using CWmin and add the remaining backoff counter of the AC to determine a new backoff counter. That is, when the AP regenerates a new backoff counter when the backoff counter of AC[VO] is 2, it can determine the new backoff counter of AC[VO] as the value obtained by adding 2 to a random number (a natural number in the range of 0 to CWmin[VO]) generated using CWmin[VO].

[0213] FIG. 15 illustrates an example of a frame exchange sequence in which a STA according to an embodiment of the present invention completes a backoff procedure and then transfers the TXOP acquisition right to another STA.

[0214] Referring to Figure 15, after completing the backoff procedure, the non-AP STA obtains channel access permission for the 80 MHz band. Instead of obtaining a TXOP, the non-AP STA transmits an initiation frame to the AP. In this case, the initiation frame may have the same configuration as that described in Figure 14.

[0215] An AP that receives an initiation frame from a non-AP STA checks the CCA results of channels within its own operating bandwidth as well as the 80 MHz band where the initiation frame was received, and transmits a CTS-to-self frame to acquire a TXOP for the 320 MHz band. In one embodiment of Figure 15, some bands among the bands from which the AP acquired a TXOP were determined to be BUSY as a result of CCA and were punctured by the AP.

[0216] After sending a CTS-to-self frame, the AP sends a trigger frame to allocate RUs to one or more non-AP STAs. At this time, the AP allocates RUs in the band occupied by the PPDU containing the start frame to the non-AP STA that sent the start frame. Non-AP STAs that receive the trigger frame (including the non-AP STA that sent the start frame) respond with a TB PPDU, and the AP sends a BlockAck to indicate whether the reception was successful.

[0217] FIG. 16 illustrates an example of a frame exchange sequence for transferring TXOP acquisition authority after a backoff procedure of a STA according to an embodiment of the present invention and the NAV state of another STA.

[0218] Referring to Figure 16, non-AP STA1 transmits an initiation frame to the AP. At this time, non-AP STA1 is a non-AP STA that has obtained channel access permission (frame transmission permission) through the EDCA procedure. The initiation frame has a Duration / ID field setting for setting a NAV for a section that is transmitted after the AP obtains a TXOP or that includes a trigger frame transmitted to obtain a TXOP. Therefore, as shown in Figure 16, a NAV for the 40 MHz band in which the initiation frame is transmitted is set. In other words, the NAV of the STA that receives the frame within the 40 MHz band in which the initiation frame is transmitted is set.

[0219] In the situation shown in Figure 16, an AP that receives a 40 MHz start frame transmits a trigger frame to the 320 MHz band to attempt to acquire a TXOP, and the Duration / ID field of the trigger frame is set to the interval including the TB PPDU that is responded to by the trigger frame. Therefore, the NAV for the 320 MHz band is set by the trigger frame, and the AP can operate the TXOP without being interfered with by other STAs (such as OBSS STAs) within the acquired TXOP.

[0220] FIG. 17 shows an example of the format of an initiating frame and a trigger frame according to an embodiment of the present invention.

[0221] Referring to FIG. 17, a non-AP STA1 transmits an initiation frame to an AP, and the initiation frame includes a Duration field 1 and / or a Duration field 2. Duration field 1 includes information related to the length of a TXOP that the AP that received the initiation frame can acquire. Therefore, the AP acquires a TXOP based on information identified from Duration field 1 of the received initiation frame. In one embodiment of FIG. 17, it is considered that Duration field 1 directly indicates the length of a TXOP that can be acquired. When Duration field 1 indicates x, the TXOP duration of the AP is determined to be x. However, the information indicated in Duration field 1 may be information related to the access category (AC) used for channel access by the STA that transmitted the initiation frame or other types of information. Alternatively, the AP may acquire only TXOPs with lengths shorter than the TXOP length identified based on Duration field 1.

[0222] Furthermore, the start frame may include a User Info field. The User Info field included in the start frame may include information related to the configuration of the TB PPDU that the non-AP STA that transmitted the start frame intends to transmit. That is, the User Info field may include information related to the MCS to be applied to the TB PPDU, the size and / or location information of the RU to transmit the TB PPDU, the number of antennas (spatial streams) to be used, etc. The names of the fields used in the present invention are merely exemplary, and the field names may be different, or each piece of information described as being included in a field may be indicated by a separate field. Furthermore, information related to the length of the TB PPDU to be transmitted may be included, and Duration field 2 shown in one embodiment of FIG. 17 may be a field including information related to the response length of the TB PPDU. The information related to the response length of the TB PPDU may be a direct time length or the amount of traffic (queue size, buffer status, etc.) to be transmitted in the TB PPDU.

[0223] As a result, two different pieces of duration-related information (information related to the obtainable TXOP length and information related to the TB PPDU length) can be indicated in the initiation frame. At this time, at least one of the two different pieces of duration-related information can be indicated in the Duration / ID field of the MAC header. Alternatively, the two different pieces of duration-related information can be indicated in the frame body, and the Duration / ID field can be used for other purposes (such as NAV management of the OBSS).

[0224] In this case, the value indicated by Duration field 1 of the two different duration-related information may be greater than the value indicated by Duration field 2.

[0225] The AP acquires a TXOP based on the information included in the received initiation frame and then transmits a trigger frame. At this time, the length of the TXOP acquired by the AP is determined (limited) based on the duration-related information included in the initiation frame. In one embodiment of Figure 17, the AP acquires a TXOP with a length of x based on the x indicated in the Duration field 1 included in the initiation frame.

[0226] Furthermore, the AP transmits a trigger frame to the non-AP STA that transmitted the start frame based on the information included in the start frame. In one embodiment of Figure 17, the AP transmits a trigger frame in which the User Info field corresponding to AID12 of non-AP STA1 that transmitted the start frame is specified first, and the User Info field is set based on the information specified in the start frame. As a result, upon receiving the trigger frame, the non-AP STA that transmitted the start frame responds with a TB PPDU in the manner that it requested from the AP.

[0227] <Two-stage channel approach procedure> According to the above-described embodiment of the present invention, after a non-AP STA completes the backoff procedure, it can send an initiation frame to the AP to instruct the AP to start a TXOP acquisition procedure. In this case, the procedure in which the AP acquires a TXOP can be appropriately replaced with a procedure in which the AP shares the TXOP. That is, the above-described series of procedures can be changed to a procedure in which the non-AP STA, which is a TXOP holder, shares its TXOP with the AP by sending an initiation frame to the AP.

[0228] To put it simply, the way the TXOP sharing procedure is applied is as a series of steps in which a non-AP STA acquires a TXOP after completing the backoff procedure and shares the acquired TXOP with its own AP by sending an initiation frame.

[0229] In this case, the AP is allowed to perform operations during a shared TXOP similar to those performed when it is the TXOP holder. That is, the AP can perform operations such as transmitting a DL MU PPDU during a shared TXOP, transmitting a trigger frame to respond with a UL MU PPDU, or transmitting an RTS / MU-RTS frame to protect the subsequent frame exchange sequence. To this end, a series of operations defined to be performed by a TXOP holder in existing Wi-Fi may be allowed to be performed by an AP that shares a TXOP. That is, the AP can also transmit a CF-End frame to end the TXOP during a shared TXOP.

[0230] Therefore, the above-described TXOP acquisition opportunity transfer method can be appropriately modified into the following TXOP sharing procedure.

[0231] 1. A non-AP STA attempts to acquire a TXOP after performing a backoff procedure using DCF or EDCA.

[0232] 2. The non-AP STA that has acquired the TXOP sends a pre-agreed frame (hereinafter referred to as the TXOP sharing frame) to its associated AP to share the TXOP it has acquired with the AP (the associated AP means the AP of the BSS of which it is a member).

[0233] 3. An AP that receives a TXOP sharing frame from a non-AP STA attempts TXOP BW extension for channels within its own operating bandwidth that are confirmed as IDLE as a result of CCA.

[0234] 4. The AP utilizes the extended BW in the shared TXOP to transmit a Trigger frame or a DL (MU) PPDU.

[0235] 5. The AP can generate a new backoff counter after the shared TXOP has finished.

[0236] The operations and applicable restrictions in steps 1 to 5, in which a non-AP STA acquires a TXOP and shares it with the AP, are the same / similar to the TXOP transfer method described above, so a duplicated description will be omitted. However, since these operations are performed when the AP is not the TXOP holder, additional management methods for operations performed when the AP is not the TXOP holder may be applied as follows:

[0237] A non-AP STA (e.g., a second STA, a third STA) that recognizes that another non-AP STA (first STA) in the BSS is the TXOP holder can process frames transmitted after the AP shares the TXOP in the same way as it processes frames received during a TXOP in which the AP is the TXOP holder. That is, a non-AP STA can ignore the NAV (Intra-BSS NAV) during a TXOP shared by the AP. The AP can also ignore the NAV set by a non-AP STA that sent a TXOP sharing frame.

[0238] More specifically, a non-AP STA (e.g., the second or third STA) that is not the TXOP holder can respond to the RTS / MU-RTS frame transmitted by the AP even if it has set its NAV based on a frame transmitted by another non-AP STA (e.g., the first STA). That is, a non-AP STA (e.g., the second or third STA) that receives an RTS / MU-RTS frame transmitted by the AP during a TXOP shared by another non-AP STA (e.g., the first STA) can send a CTS response to the RTS / MU-RTS frame even if the TXOP holder it recognizes is not the AP. In this case, when a non-AP STA receives a frame requesting a response, such as an RTS / MU-RTS / Trigger frame received from the AP, the method for determining whether to respond may be determined based on whether the Virtual CCA result confirmed in basic NAV is IDLE. That is, a non-AP STA whose basic NAV is confirmed as IDLE (basic NAV is 0) can respond to an RTS / MU-RTS / Trigger frame transmitted by an AP even if its intra-BSS NAV is confirmed as Busy (intra-BSS NAV is not 0) and the TXOP holder is confirmed to be another STA other than the AP. This may be an additional exception to the existing Wi-Fi CTS frame response condition, which allows a first STA that receives an RTS frame to respond with a CTS frame only if the second STA that sent the RTS frame is confirmed to be the TXOP holder or if the NAV is 0 (i.e., if the NAV indicates idle).

[0239] For reference, intra-BSS NAV refers to a NAV set after receiving a PPDU classified as an intra-BSS PPDU, and basic NAV refers to a NAV set after receiving a PPDU not classified as an intra-BSS PPDU. Intra-BSS PPDU refers to a PPDU classified as an inter-BSS PPDU according to the intra-BSS and inter-BSS PPDU classification rules, and a classification method is defined using information such as a BSS color or an address field of a frame included in the PPDU. The intra-PPDU classification method is not related to the TXOP transfer / sharing for an AP provided by the present invention, so a detailed description will be omitted.

[0240] In other words, the TXOP holder of a TXOP is a non-AP STA, and the non-AP STA can transmit a frame in a pre-agreed format to the AP to share the TXOP it has acquired with the AP. An AP that receives a frame in the pre-agreed format from a non-AP STA may be allowed to perform operations similar to those performed when it is the TXOP holder during the TXOP of the non-AP STA. That is, the AP may perform operations such as transmitting a DL MU PPDU or a Trigger frame during the TXOP of the non-AP STA. Furthermore, when the AP receives a frame in the pre-agreed format from a non-AP STA, it may attempt to access an additional Idle subchannel other than the BW in which the non-AP STA acquired the TXOP. In this case, the channel access procedure performed by the AP after receiving the frame in the pre-agreed format (TXOP sharing frame) may be understood as a secondary channel access procedure for BW expansion. That is, the primary channel access procedure is a process in which a non-AP STA acquires a TXOP after completing a backoff procedure, and the secondary channel access procedure can refer to a BW extension procedure performed by an AP that receives a frame from a STA that has acquired a TXOP. At this time, it is easily understood that the CCA procedure performed to extend the BW and the operation of the AP during the shared TXOP may be similar to those at the time of TXOP transfer described above, and detailed description thereof will be omitted.

[0241] Furthermore, the above-described procedure can be utilized to share a TXOP with another AP when an AP completes the backoff procedure, as well as when a non-AP STA completes the backoff procedure. For example, after completing the backoff procedure, AP1 can transmit an initiation frame (or another frame transmitted for TXOP sharing) to instruct AP2 to perform a sharing operation in the same time period as the TXOP it acquired. In this case, AP2 can perform operations similar to those performed when it is the TXOP holder through the sharing operation. That is, AP2 can perform operations such as transmitting a DL PPDU or a Trigger frame to its associated STAs in the time period shared by AP1. Therefore, although the above-described and below-described embodiments of the present invention are described as procedures performed by a non-AP STA with its own AP after completing the backoff procedure, it should be understood that similar procedures may also be applied between APs.

[0242] FIG. 18 illustrates an example of a TXOP sharing and bandwidth (BW) extension procedure between STAs according to an embodiment of the present invention.

[0243] Referring to Figure 18, after completing the backoff procedure, the non-AP STA transmits an RTS frame to the AP and becomes a TXOP holder when it receives a CTS frame in response. The non-AP STA then transmits a TXOP sharing frame to the AP to share the TXOP it has acquired. The AP that receives the TXOP sharing frame performs CCA on its operating channel and attempts to extend the BW for subchannels determined to be IDLE. In this case, the AP performs the same operation as if it were the TXOP holder, even though the TXOP was not acquired by itself. In one embodiment of Figure 18, a procedure is shown in which the AP transmits a CTS-to-Self frame and a trigger frame to request a UL MU PPDU response.

[0244] FIG. 19 shows an example of a TXOP sharing procedure and a TXOP holder operation of a STA according to one embodiment of the present invention.

[0245] Referring to FIG. 19, after completing the backoff procedure, non-AP STA1 transmits an RTS frame to the AP and is responded with a CTS frame to become a TXOP holder. Then, non-AP STA1 transmits a TXOP sharing frame to the AP to share the TXOP.

[0246] At this time, after non-AP STA2 and the OBSS STA receive the RTS transmitted by non-AP STA1 or the CTS frame transmitted by the AP, they can recognize that the TXOP holder is non-AP STA1. Also, the NAV is set until the TXOP of non-AP STA1 ends.

[0247] After receiving the TXOP sharing frame from non-AP STA1, the AP performs the transmission of a trigger frame, which is one of the operations as a TXOP holder. The trigger frame is also a trigger frame that requests a response to the TB PPDU for non-AP STA2 in addition to non-AP STA1. Non-AP STA2 responds with the TB PPDU in a situation where it is confirmed that the TXOP holder is non-AP STA1. That is, non-AP STA2 can respond to the frame received from the AP while ignoring the NAV where non-AP STA1 is the TXOP holder.

[0248] The time interval for frame exchange during the shared TXOP by the AP is protected by the NAV of the OBSS STA set by the frame exchanged during the process where non-AP STA1 becomes the TXOP holder.

[0249] <Frame Format Utilized in the TXOP Start / Sharing Procedure> According to the above-described embodiment of the present invention, when a non-AP STA completes the backoff procedure, it can transmit a frame to the AP to transfer the TXOP acquisition opportunity. Also, after the non-AP STA acquires a TXOP, it can transmit a frame to share the acquired TXOP with the AP.

[0250] In this way, the behavior of a non-AP STA yielding a TXOP acquisition opportunity to an AP or sharing an acquired TXOP may be unfavorable from the viewpoint of the non-AP STA's operation. This is because, from the perspective of a non-AP STA, it is advantageous for the non-AP STA to acquire a TXOP and complete transmission of the frame it intends to transmit during the TXOP as quickly as possible, and the additional sequence performed to yield or share a TXOP is an unreasonable behavior with no expected gain. Therefore, a non-AP STA that yields a TXOP acquisition opportunity to an AP or shares an acquired TXOP with an AP should be adequately compensated.

[0251] The first consideration is that a non-AP STA that has completed the backoff procedure should be guaranteed the same frame processing capacity as if it had directly acquired and utilized a TXOP. That is, even if a non-AP STA transfers a TXOP acquisition opportunity to an AP or shares a TXOP it has acquired, it should be able to process the same amount of traffic as if it had directly acquired and utilized the TXOP. To achieve this, information related to the traffic and / or traffic volume that the non-AP STA intends to process must be indicated to the AP, and the AP must allocate sufficient resources to the non-AP STA based on the indicated information.

[0252] FIG. 20 illustrates an example of a format for a frame for transferring TXOP acquisition authority or TXOP sharing according to an embodiment of the present invention.

[0253] Referring to FIG. 20, the start frame may include a subfield related to TXOP limit or AC. The subfield related to TXOP limit or AC may be a field set based on the access category for which the non-AP STA transmitting the frame has completed the backoff procedure. The AP can determine the length of the acquired TXOP based on the information indicated in this field. When included in a TXOP sharing frame, the TXOP limit field may be a field used to indicate the duration of the TXOP that the non-AP STA wishes to share with the AP. The time indicated in this field must be the same as or earlier than the end time of the TXOP acquired by the non-AP STA.

[0254] The UL Length field indicates the frame length of the TB PPDU that the non-AP STA intends to transmit. After receiving a TXOP Start / Share frame, the AP that transmits a trigger frame to the non-AP STA must transmit a trigger frame with the UL Length field set to the same value as the UL Length field of the TXOP Start / Share frame.

[0255] The Number of Spatial Streams field indicates the number of spatial streams that the non-AP STA that transmitted the TXOP Start / Share frame intends to use when transmitting a TB PPDU. An AP that transmits a trigger frame to a non-AP STA after receiving a TXOP Start / Share frame must transmit trigger frames allocated to the non-AP STA for the number of spatial streams indicated in the Number of Spatial Streams field of the TXOP Start / Share frame. That is, when transmitting a trigger frame, the AP must set the SS Allocation subfield of the User Info field having an AID12 value indicating the non-AP STA to the same value as the Number of Spatial Streams field included in the TXOP Start / Share frame transmitted by the non-AP STA.

[0256] The MCS field indicates the MCS (Modulation and Coding Scheme) that the non-AP STA that transmitted the TXOP Start / Share frame intends to use when transmitting the TB PPDU. After receiving the TXOP Start / Share frame, the AP that transmits a trigger frame to the non-AP STA must transmit trigger frames assigned to the non-AP STA for the number of spatial streams indicated in the Number of Spatial Streams field of the TXOP Start / Share frame. That is, when transmitting a trigger frame, the AP must set the (HE / EHT / UHR) MCS field of the User Info field having the AID12 value indicating the non-AP STA to the same value as the MCS field included in the TXOP Start / Share frame transmitted by the non-AP STA.

[0257] The Buffer Status field indicates information related to the amount of buffered traffic held by the non-AP STA that sent the TXOP Start / Share frame. Alternatively, this field may be replaced with a field containing information related to the size and / or location of the BW or RU to which the non-AP STA intends to respond with the TB PPDU. In a trigger frame transmitted after receiving a TXOP Start / Share frame, the AP must set the RU Allocation subfield (and PS160, PS320 subfields, etc.) of the User Info field corresponding to the non-AP STA that sent the TXOP Start / Share frame based on the information indicated in the Buffer Status field of the TXOP Start / Share frame.

[0258] The Channel Info.Bitmap field indicates the IDLE / BUSY status of a subchannel confirmed when a non-AP STA that transmitted a TXOP start / shared frame accesses a channel. Each bit in the Channel Info.Bitmap field corresponds to a different subchannel, and is set to 1 (or 0) if the corresponding subchannel is confirmed as IDLE, and to 0 (or 1) if the corresponding subchannel is confirmed as BUSY. Among the bits in the Channel Info.Bitmap field, bits corresponding to subchannels for which the non-AP STA that sets the field cannot determine whether they are IDLE or BUSY are set in a predetermined manner. In this case, a method of setting a bit corresponding to a subchannel for which IDLE / BUSY cannot be determined may be to set the bit to the same value as the setting value of a bit corresponding to a BUSY subchannel. That is, if the Channel Info.Bitmap field consists of 16 bits corresponding to 16 20 MHz subchannels included in the 320 MHz band, a non-AP STA operating at 80 MHz indicates the Channel Info.Bitmap field by setting IDLE / BUSY for four subchannels (or three subchannels other than the primary 20 MHz subchannel) to 1 / 0, respectively, and setting IDLE / BUSY for the remaining 12 subchannels to 0. In the trigger frame transmitted after receiving a TXOP Start / Share frame, the AP must allocate to the non-AP STA only RUs included in the subchannels that the non-AP STA that transmitted the frame indicated as IDLE.

[0259] The second consideration is that a sufficient number of non-AP STAs that can perform the TXOP handover / sharing procedure provided by the present invention must be ensured. If there are no non-AP STAs that can perform the TXOP handover / sharing procedure among the non-AP STAs that are members of a BSS, the BSS cannot achieve the benefits intended by the present invention. Therefore, the AP can prioritize services for non-AP STAs that can support the TXOP handover / sharing procedure among the non-AP STAs that are members of the BSS, thereby encouraging non-AP STAs to actively support the TXOP handover / sharing procedure. In this process, the AP can prioritize scheduling (for DL / UL frame exchange) for non-AP STAs that support the TXOP handover / sharing procedure during a shared TXOP obtained through the TXOP handover / sharing procedure. In other words, the AP may be allowed to apply preferential scheduling to non-AP STAs that support the TXOP handover / sharing procedure (handing over a TXOP acquisition opportunity to a non-AP STA after it completes a backoff procedure) or TXOP sharing (sharing a TXOP obtained by a non-AP STA).

[0260] Although the above-described embodiment of the present invention was developed with consideration given to a non-AP STA transmitting a TXOP initiation / share frame to an associated AP, the same operation can also be performed between APs. In other words, after a first AP acquires a TXOP, it can transmit a TXOP share frame to a second AP to share the TXOP, and in this process, AP2 can extend the BW. Also, if the BW in which the first AP acquired the TXOP is smaller than the operating bandwidth of the second AP, the first AP can use the initiation frame it transmits to induce the second AP to perform frame exchange in the band in which the first AP itself could not acquire the TXOP. In this case, the TXOP share frame transmitted by the first AP to the second AP may be a frame classified as an MU-RTS type. In this case, the TXOP share frame transmitted by the first AP to the second AP may be a frame instructing the second AP about RUs not included in the BW acquired by the first AP itself.

[0261] The frame transmitted by a non-AP STA to an AP to share a TXOP may be an MU-RTS TXS (MU-RTS TXOP sharing) trigger frame. Here, the MU-RTS TXS trigger frame refers to a trigger frame in which the Triggered TXOP Sharing Mode subfield included in the Common Info field of the trigger frame is not 0. When a non-AP STA transmits an MU-RTS TXS trigger frame to an AP, it must include only one User Info field. Here, the User Info field may indicate TB PPDU-related parameters that the non-AP STA itself intends to receive from the AP, as discussed in the above-described embodiment of the present invention.

[0262] <Channel Access Procedure for Bandwidth (BW) Expansion> As described above, according to one embodiment of the present invention, when an AP receives a control frame (initiating frame and / or sharing frame) transmitted by a non-AP STA after obtaining channel access permission, the AP can attempt channel access to a bandwidth wider than the bandwidth in which the control frame was received. In other words, the AP that receives the control frame (initiating frame and / or sharing frame) transmitted by the non-AP STA can attempt access to a subchannel not occupied by the control frame.

[0263] However, an AP that accesses an additional subchannel other than the subchannel occupied by the control frame must go through a procedure to obtain access authority to that subchannel.

[0264] In the above-described embodiment, when an AP accesses an additional subchannel other than the subchannel on which a control frame is received, the AP may perform additional access to the subchannel when the subchannel is determined to be idle as a result of the CCA performed in SIFS or PIFS. This procedure for accessing an additional subchannel based on the result of the CCA performed in SIFS or PIFS may be considered similar to the procedure for a STA that has completed a backoff procedure on the primary channel to access the secondary channel, but it may cause fairness issues with different devices.

[0265] More specifically, some heterogeneous devices access each 20 MHz subchannel by performing an independent LBT (listen before talk, similar to the Wi-Fi backoff procedure) for each subchannel, and then access only the subchannels for which they have obtained channel access permission through LBT. Therefore, the AP's operation of performing only SIFS / PIFS CCA after receiving a control frame and then accessing additional subchannels can be said to be a somewhat aggressive channel access method compared to the heterogeneous devices.

[0266] In addition, similar to when Wi-Fi approaches a BW exceeding 20 MHz, other heterogeneous devices use a channel access method of accessing an additional subchannel determined to be IDLE when they have completed LBT (obtained channel access authority) on a specific 20 MHz subchannel (main channel). However, the condition for the other heterogeneous devices to access the additional subchannel is limited to when they have obtained channel access authority on the specific 20 MHz subchannel. Therefore, the act of accessing the additional subchannel when the AP receives a control frame may be recognized as an aggressive channel access method compared to the other heterogeneous devices.

[0267] Therefore, for harmonious operation with heterogeneous devices that share the unlicensed band, an AP that receives a control frame from a non-AP STA and accesses an additional subchannel according to one embodiment of the present invention must also access the additional subchannel after completing the backoff procedure.

[0268] The channel access method for BW extension, which will be described later, is a specific method for an AP to access additional subchannels in addition to the subchannel occupied by a control frame received from a non-AP STA, and can be performed without fairness issues with different devices. In this case, BW extension means obtaining channel access authority for a BW wider than the BW of a PPDU including a control frame, or obtaining channel access authority for additional subchannels rather than the subchannel occupied by the control frame. In other words, even if the BW obtained by an AP receiving a control frame is the same as the BW of a PPDU including the control frame, if the subchannels for which channel access authority is obtained are greater than the subchannels occupied by the control frame, the BW may be considered to be extended.

[0269] According to one embodiment of the present invention, when the entire bandwidth is composed of one primary channel block (or primary channel) and one or more secondary channel blocks (or secondary channels), a station (non-AP STA or AP) selects one of the one or more secondary channel blocks instead of a primary subchannel included in the primary channel block, and performs a channel access procedure using the secondary subchannels constituting the selected secondary channel block to obtain a TXOP. That is, the station can perform channel access using the secondary subchannel instead of the primary subchannel to obtain a TXOP.

[0270] In yet another embodiment of the present invention, when a TXOP is acquired using a secondary subchannel by the above method, the frequency axis range in which the TXOP is acquired may be limited to a subchannel block including the secondary subchannel in which the channel access procedure has been performed. That is, a station that has performed the channel access procedure using a secondary subchannel can only transmit and receive within the secondary channel block including the secondary subchannel in the acquired TXOP.

[0271] In yet another embodiment of the present invention, when a station (e.g., an AP or a non-AP STA) receives a TXOP (first TXOP) from another station (e.g., a non-AP STA or an AP), the station may perform a channel access procedure using the shared TXOP. However, if a primary subchannel of a primary channel block is occupied by another station (e.g., an OBSS STA) within the shared TXOP, the station cannot perform the channel access procedure using the primary subchannel. In this case, the station may select one secondary channel block from supported secondary channel blocks within the entire bandwidth, rather than the primary subchannel of the primary channel, and perform a channel access procedure using the secondary subchannel included in the selected secondary channel block to obtain a TXOP (second TXOP). In this case, the first TXOP may be used for frame transmission and reception up to the frequency range supported by the other station sharing the first TXOP on the frequency axis, but the frequency range on the frequency axis from which the second TXOP is obtained may be limited to the secondary channel including the secondary subchannel where channel access has been performed.

[0272] In yet another embodiment of the present invention, the second TXOP acquired by the above method may terminate at the same time as the first TXOP, and the second TXOP may be considered as a frequency axis extension of the first TXOP. That is, when the first TXOP is shared, a station can extend the frequency axis range of the first TXOP to the second TXOP by a channel access procedure using a secondary subchannel. In this case, other stations do not need to support a secondary channel for acquiring the second TXOP. For example, the total bandwidth may be 320 MHz, and the total bandwidth may be composed of one 80 MHz primary channel and 80 MHz and 160 MHz secondary channels. In this case, the 160 MHz secondary channel may be divided into a low 80 MHz channel and a high 80 MHz channel. In this case, one of the four 80 MHz bands may be a primary bandwidth (or primary channel) including a primary subchannel for channel access, and the remaining three may be secondary bandwidths (or secondary channels). A first station (e.g., an AP or non-AP STA) supports up to 320 MHz, while a second station supports only 160 MHz. The second station can perform a channel access procedure (first channel access procedure) on a primary subchannel of the primary band and obtain a TXOP (first TXOP) using the first channel access procedure to share with the first station. The first station can transmit and receive frames through the shared first TXOP. However, if the primary subchannel in the first TXOP is occupied by another station (e.g., an OBSS station), the first station cannot perform channel access or frame transmission and reception through the primary subchannel. Therefore, the first station can select an idle subband among the three subbands that is not occupied by a different station, change the channel to the selected subband, and perform a channel access procedure (second channel access procedure) on the secondary subchannel of the changed subband to obtain a TXOP (second TXOP).In this case, the frequency range on the frequency axis where the first TXOP is acquired is up to 160 MHz, which includes the main band that the second station can support, and the frequency range on the frequency axis where the second TXOP is acquired is up to 80 MHz, which is a sub-band including the sub-channel where the first station has made the second channel access (or up to a 160 MHz sub-channel including that sub-band). Also, the second TXOP may be considered as an extension of the first TXOP, and ends at the same time as the first TXOP.

[0273] In yet another embodiment of the present invention, when the first station acquires a TXOP by performing a channel access procedure in a subband that the second station does not support (e.g., the second station supports only the primary 160 MHz of 320 MHz, and the first station acquires a channel access in the low 80 MHz of the secondary 160 MHz), the first station can instruct the second station to move to the secondary 160 MHz to operate in order to change the operating channel of the second station. For example, the first station can transmit a frame (e.g., a trigger frame) instructing the second station to change the operating channel within the acquired second TXOP. The second station, upon receiving the frame, can move to the channel (e.g., the low 80 MHz of the secondary 160 MHz) instructed by the frame and receive or transmit a downlink frame instructed by the frame.

[0274] <Follow the backoff procedure for each of the 1.20MHz subchannels> In the channel access method according to this embodiment, an AP simultaneously performs a backoff procedure on multiple subchannels (including a primary channel) included in an operating bandwidth (BW), and when a control frame is received from a non-AP STA, the AP may perform channel access on a subchannel occupied by a PPDU including the control frame and an idle subchannel on which the backoff procedure has been completed. In this case, the simultaneous backoff procedure on multiple subchannels means that a separate backoff procedure is performed on each of the multiple subchannels, and these procedures are performed in parallel in time.

[0275] Specifically, an AP performs a backoff procedure on multiple subchannels included in the operating bandwidth. For example, an AP with an operating bandwidth of 80 MHz performs a backoff procedure on each of four 20 MHz subchannels included in the 80 MHz band. In this case, when the AP completes the backoff procedure on the primary 20 MHz channel, the AP can obtain channel access privileges for subchannels confirmed as idle among the four subchannels in the 80 MHz band according to conventional Wi-Fi operation.

[0276] However, even if the backoff procedure performed on a subchannel other than the primary 20 MHz channel is completed, the AP cannot access the other subchannel. This may be a restriction applied because the AP has not yet acquired channel access authority for the primary 20 MHz channel and is therefore unable to perform transmission that does not occupy the primary 20 MHz channel.

[0277] Therefore, the AP is in a state where it has acquired channel access permission for other subchannels (subchannels other than the primary 20 MHz subchannel) for which the backoff procedure has been completed (a state where the backoff procedure has been completed), and can perform an operation of waiting until it acquires access permission for the primary 20 MHz channel. In this case, when the backoff counter for backoff performed on subchannels other than the primary 20 MHz subchannel becomes 0, the AP can maintain the backoff counter at 0 until it acquires access permission for the main channel. In other words, the AP does not need to start transmission when the backoff counter for subchannels other than the primary 20 MHz subchannel is 0. In this case, the operation of the AP that has not started transmission can be continued until it acquires channel access permission for the primary 20 MHz channel.

[0278] As discussed in the above-described embodiment of the present invention, a non-AP STA that has acquired channel access permission can share its acquired TXOP with the AP by transmitting a control frame (TXOP sharing frame) to the AP. Since the non-AP STA performs the channel access procedure only in the Primary 20 MHz subchannel, the channel access permission acquired by the non-AP STA includes channel access permission for the Primary 20 MHz subchannel. Therefore, when the non-AP STA transmits a control frame to the AP to share its channel access permission for the Primary 20 MHz subchannel with the AP, the AP can begin accessing the Primary 20 MHz channel.

[0279] In this case, the AP accessing the main channel using the TXOP shared by the non-AP STA can also start channel access for the sub-channel for which it has already acquired channel access privileges (for which the backoff procedure has been completed). That is, when the non-AP STA accesses the main channel using the acquired TXOP, the AP can also start channel access for the additional sub-channel for which the backoff procedure has already been completed.

[0280] In other words, an AP extending the BW according to this embodiment performs the backoff procedure in parallel for each 20 MHz subchannel, and when the channel access authority for the main channel acquired by a non-AP STA is shared from the non-AP STA, the AP approaches the main channel using the shared authority, and then approaches other subchannels for which channel access authority has been acquired through the backoff procedure (the backoff procedure has been completed, the backoff counter is 0), thereby completing the channel access procedure for BW extension.

[0281] However, performing parallel backoff for each 20MHz subchannel can result in excessive power consumption for the AP during the channel access process. For example, an AP with a 320MHz operating bandwidth must perform a backoff procedure for each of the 16 20MHz subchannels to access the channel, which is expected to consume 16 times more power for the channel access procedure. This is likely because, unlike existing APs that perform CCA for other subchannels only after the backoff procedure for the primary 20MHz subchannel is completed, the parallel backoff operation requires a determination of the IDLE / BUSY state of each subchannel for each slot.

[0282] Therefore, the AP performs parallel backoff for each 20 MHz subchannel to secure channel access permission, but the period during which the parallel backoff is performed can be shortened. A specific method for shortening the period during which the AP performs parallel backoff may be to start the parallel backoff of the AP only when the AP receives a control frame transmitted by a non-AP STA.

[0283] Furthermore, the AP performs the backoff procedure only on the primary 20 MHz channel. However, when a control frame is received from a non-AP STA, the AP can initiate / perform a 20 MHz channel access procedure (backoff procedure) for each additional subchannel to obtain channel access permission for the additional subchannel. In this case, the non-AP STA can add padding to the PPDU containing the control frame it transmits, thereby helping the AP's backoff procedure (performed on a subchannel other than the primary channel) to be completed within the time secured by the padding. The amount of padding included may be a pre-set length or a length set based on a value instructed by the AP. In this case, the padding may be PHY and / or MAC padding. In this case, padding can refer to anything that can increase the PPDU length other than the control frame transmitted for TXOP sharing. That is, the non-AP STA can place the control frame in the first frame and aggregate other frames (UL traffic) to cause the other frames to play a role similar to padding.

[0284] Alternatively, the AP may perform a backoff procedure for a band larger than 20 MHz without performing a backoff procedure for each 20 MHz subchannel. For example, in addition to the backoff procedure for the primary 20 MHz subchannel, the AP may perform a backoff procedure for the secondary 80 MHz, the low 80 MHz of the secondary 160 MHz, and the high 80 MHz of the secondary 160 MHz. Therefore, the AP can obtain channel access privileges in 80 MHz units when accessing a band other than the primary 80 MHz band. This may be a channel access method that is considered because there may be a relatively large number of subchannels included in the operating bandwidth of the Wi-Fi AP, and performing a backoff procedure for each 20 MHz subchannel would excessively increase the operational complexity of the AP. That is, the AP can apply a single backoff procedure for bands larger than 20 MHz, thereby obtaining channel access privileges for bands larger than 20 MHz.

[0285] Alternatively, the AP may select a specific 20 MHz subchannel for performing the channel access procedure for each bandwidth and perform the channel access procedure (backoff procedure) on that subchannel. More specifically, the AP may select one 20 MHz subchannel for performing the channel access procedure for each of the four 80 MHz bands within the 320 MHz bandwidth. In this case, the primary 20 MHz subchannel must always be selected for the primary 80 MHz band among the four 80 MHz bands. Furthermore, when the AP operates in the 6 GHz band, the AP must perform the channel access procedure for each 80 MHz band on the channel that should be used as the primary in accordance with the 6 GHz rules. In this case, the channel that should be used as the primary in accordance with the 6 GHz rules refers to the scanning channel (PSD) preferred by the non-AP STA. In this case, the scanning channel preferred by the non-AP STA is one 20 MHz subchannel within each 80 MHz BW in the 6 GHz band, and the subchannel has a center frequency of (Channel starting frequency - 55 + (80xn)) MHz, where n is a value between 1 and 15.

[0286] In this case, if the channel access procedure performed in a specific 20 MHz subchannel of each 80 MHz band has already been completed, the AP can further access each 80 MHz IDLE channel when starting transmission on the primary 20 MHz channel. In this case, the AP's operation of starting transmission on the primary 20 MHz channel may be performed using a TXOP shared by a non-AP STA. If the channel access procedure performed in a specific 20 MHz subchannel of a specific 80 MHz band has not been completed, the AP cannot access the subchannel of the specific 80 MHz band when starting transmission on the primary 20 MHz channel. In this case, the method of selecting a specific 20 MHz subchannel (subchannel for which the channel access procedure is performed) for each 80 MHz band is merely an example; a specific 20 MHz subchannel may also be selected for each 160 MHz band or 320 MHz band. Even if a specific 20 MHz subchannel for which the channel access procedure is performed is selected not for each 80 MHz band but one for each other bandwidth, channel access permission for each IDLE subchannel can be obtained in the same or similar manner, and therefore, a repeated description will be omitted.

[0287] FIG. 21 shows an example of a method for performing channel connection using subchannels according to an embodiment of the present invention.

[0288] Referring to FIG. 21, after an AP receives a control frame from a non-AP STA, it can access the channel by utilizing an additional subchannel for which channel access authority is reserved.

[0289] Specifically, the AP and non-AP STAs perform a backoff procedure on the primary channel for channel access. A non-AP STA that completes the backoff procedure earlier than the AP transmits a control frame (Ctrl frame) to the AP. The control frame is a frame that the non-AP STA transmits to share the TXOP it has acquired with the AP.

[0290] At this time, the AP is performing backoff procedures for channel access not only on the main channel (P_20) but also on other sub-channels, and the backoff procedures on two sub-channels have already been completed (S_20 of S_40 and L_20 of S_40).

[0291] When an AP receives a control frame from a non-AP STA on the primary channel, it sends a response frame not only to the primary channel (P_20) occupied by the control frame, but also to additional sub-channels (S_20 of S_40 and L_20 of S_40) for which channel access privileges have already been secured (backoff procedures have been completed). At this time, the AP starts a TXOP on the sub-channels on which the AP sent the response frame, other than the primary channel occupied by the control frame. That is, the AP accesses the primary channel using the TXOP shared by the control frame sent by the non-AP STA, and at the same time as accessing the primary channel, it also accesses the additional sub-channels for which it has already completed the backoff procedures.

[0292] FIG. 22 shows yet another example of a method for performing channel connection using subchannels according to an embodiment of the present invention.

[0293] Referring to FIG. 22, after an AP receives a control frame from a non-AP STA, it can access the channel by utilizing an additional sub-channel for which channel access authority is reserved.

[0294] To avoid repetition, the same content as that described above in FIG. 21 may be omitted.

[0295] Specifically, the AP performs the backoff procedure not only on the primary 20 MHz channel but also on additional subchannels, which are part of the subchannels included in the AP's operating bandwidth.

[0296] The AP receives a control frame transmitted by a non-AP STA before the backoff procedure performed on the primary 20 MHz channel is completed, and thus, the non-AP STA shares a TXOP for the subchannel occupied by the control frame. The AP accesses the channel using the shared TXOP and simultaneously accesses an additional subchannel for which channel access permission has already been reserved. In this case, the AP may reserve channel access permission for the additional subchannel by accessing a subchannel determined to be IDLE by the result of CCA performed during the PIFS until it accesses the additional subchannel for which the backoff procedure has already been completed. That is, the AP accesses the primary channel using the TXOP shared by the control frame transmitted by the non-AP STA, and while accessing the primary channel, it simultaneously accesses the additional subchannel for which it has already completed the backoff procedure and performs PIFS access to the additional subchannel.

[0297] Therefore, the AP approaches the primary 80 MHz band occupied by the PPDU of the control frame transmitted by the non-AP STA using the TXOP shared by the non-AP STA, and at the same time, approaches the additional subchannels for which it has secured channel access privileges through the backoff procedure and PIFS CCA it performed on the additional subchannels. That is, the AP responds with a Resp frame for the control frame using not only the P_80 channel but also all of the remaining additional subchannels for which the channel access procedure has been completed (i.e., responding to the 320 MHz band in Figure 22).

[0298] FIG. 23 illustrates an example method for initiating a channel access procedure using a sub-channel according to one embodiment of the present invention.

[0299] Referring to FIG. 23, after the AP receives a control frame from a non-AP STA, it may initiate a channel access procedure to access an additional sub-channel.

[0300] To avoid repetition, the same content as described above in Figures 21 and 22 will be omitted.

[0301] Specifically, the AP and non-AP STAs perform a backoff procedure on the primary channel for channel access. The non-AP STA that completes the backoff procedure earlier than the AP transmits a control frame (Ctrl frame) to the AP. At this time, the PPDU including the control frame further includes padding.

[0302] Upon receiving a control frame from a non-AP STA, the AP initiates a backoff procedure for each additional subchannel not occupied by the control frame to secure channel access privileges for the additional subchannels. The backoff procedure initiated by the AP for each additional subchannel lasts for the time required for padding added to the PPDU containing the control frame, and the AP completes the backoff procedure for the S_20, L_20 of S_40, and H_20 of S_40 subchannels.

[0303] Therefore, the AP accesses the primary 20 MHz subchannel (P_20) occupied by the PPDU of the control frame transmitted by the non-AP STA using the TXOP shared by the non-AP STA, and simultaneously accesses the additional subchannels for which it has secured channel access privileges through the backoff procedure. That is, the AP responds with a Resp frame for the control frame using not only the P_20 channel but also all of the remaining additional subchannels for which the channel access procedure has been completed (i.e., responding to the 80 MHz band in Figure 23).

[0304] That is, the AP accesses the primary channel using the TXOP shared by the control frame transmitted by the non-AP STA, and at the same time, accesses the additional sub-channel on which it has already completed the backoff procedure.

[0305] <2. Perform channel access procedure in the TXOP section shared by the non-AP STA> Alternatively, the AP may perform a channel access procedure (backoff procedure) on the primary 20 MHz subchannel in a TXOP period shared by a non-AP STA, and upon completion of the channel access procedure (backoff procedure), the AP may access the primary 20 MHz subchannel and any additional subchannels confirmed as IDLE. That is, the AP may become the TXOP holder of a TXOP including the primary 20 MHz subchannel and any additional subchannels. In this case, when determining whether an additional subchannel other than the primary 20 MHz subchannel is IDLE / BUSY, the AP may make the determination based on the CCA results confirmed within PIFS (SIFS (16 us) + aSlotTime (9 us), i.e., 25 us) for each subchannel.

[0306] This channel access procedure may be achieved by the AP ignoring the NAV set in a frame transmitted by a non-AP STA during a TXOP shared by the non-AP STA. That is, when the AP receives a frame from the non-AP STA sharing the TXOP acquired by the non-AP STA, the AP can determine the virtual CCA result of the primary channel as IDLE (simply put, a CCA method that determines a STA as BUSY if the NAV is not 0) regardless of the NAV value set in the frame transmitted by the non-AP STA. That is, the AP can ignore the NAV set by the non-AP STA during the TXOP shared by the non-AP STA and perform the channel access procedure on the primary 20 MHz channel.

[0307] If the AP completes the channel access procedure on the primary 20 MHz channel during a TXOP shared by a non-AP STA with the AP (i.e., the backoff procedure is completed and channel access permission is obtained), the AP can attempt channel access to additional subchannels confirmed as IDLE, including the primary 20 MHz channel. In this case, the TXOP of the non-AP STA may be terminated and the TXOP of the AP may be initiated. In other words, the TXOP acquired by the non-AP STA is terminated and the TXOP of the AP is initiated when the AP completes the channel access procedure during the shared time.

[0308] This can be considered as an AP channel access method that is the same / similar to the channel access method in which other heterogeneous devices access additional subchannels that are determined to be IDLE when they complete LBT on a specific 20 MHz subchannel (main channel), except that the AP channel access can be performed within the TXOP acquired by a non-AP STA.

[0309] In other words, when a non-AP STA shares the TXOP it has acquired with an AP, it can be understood that it is sharing the TXOP taking into consideration that the AP's TXOP will begin after the AP has obtained channel access permission within the TXOP it has acquired.

[0310] In this case, the control frame (TXOP sharing frame) that a non-AP STA sends to the AP to share the TXOP it has acquired includes a function to guide the Wi-Fi STA that receives the frame to set its NAV. Therefore, other STAs that receive the control frame sent by a non-AP STA must determine that the Virtual CCA result of the primary 20MHz channel is BUSY until the NAV set by the frame is released (until it becomes 0), resulting in channel access restrictions.

[0311] In addition, if the AP receives a control frame (TXOP sharing frame) from a non-AP STA, it can send a response frame. In this case, the response frame sent by the AP includes a function that prompts the STA that received the response frame to set its NAV. Therefore, other STAs that receive the response frame sent by the AP must determine that the Virtual CCA result of the primary 20 MHz channel is BUSY until the NAV set by the frame is released (until it becomes 0), resulting in channel access being restricted.

[0312] That is, the channel access of STAs in the BSS and neighboring STAs is restricted by the NAV set by the control frame transmitted by the non-AP STA and the response frame transmitted by the AP, and only the AP can complete the channel access procedure by ignoring the NAV set by the non-AP STA (the STA that transmitted the control frame). Completing the channel access procedure means obtaining channel access permission by invoking the backoff procedure for channel access and performing operations such as decrementing the backoff counter (the backoff counter becomes 0).

[0313] In this case, the NAV set by the control frame transmitted by the non-AP STA may be set by a method identical or similar to the Duration / ID setting method considered in the above-described embodiment of the present invention, and a detailed description thereof will be omitted. However, when setting the Duration / ID field of the control frame, the non-AP STA may further consider the time it takes for the AP to complete the channel access procedure.

[0314] Furthermore, the AP can invoke / execute the backoff procedure only when the TXOP shared from the non-AP STA is longer than (or equal to or longer than) the previously committed time. That is, the AP may be restricted from invoking the backoff procedure and performing a series of operations to obtain channel access permission when the TXOP shared from the non-AP STA is shorter than (or shorter than or equal to) the previously committed time. Alternatively, a similar restriction may be applied to the non-AP STA. That is, the non-AP STA must transmit a control frame to share the TXOP to the AP only when the TXOP it can share with the AP is longer than the previously committed time.

[0315] Furthermore, if there is an additional subchannel confirmed as IDLE other than the subchannel occupied by the control frame received from the non-AP STA (i.e., if it is determined that there is an additional subchannel available for access), the AP may perform a channel access procedure to attempt to acquire its own TXOP. In other words, the AP may perform the channel access procedure during the TXOP shared from the non-AP STA only if it determines that it can secure the additional subchannel through the channel access procedure (e.g., invoking, proceeding, and completing the backoff procedure) performed during the shared TXOP. In this case, the AP may determine that there is an additional subchannel available for access by determining that at least one subchannel included in its operating bandwidth other than the subchannel occupied by the control frame received from the non-AP STA is accessible. In other words, when the AP receives a control frame and determines that at least one subchannel is accessible other than the subchannel occupied by the control frame, it may initiate a channel access procedure to acquire channel access permission for the additional subchannel.

[0316] In this case, the AP may determine whether there are any further accessible subchannels based on whether the CCA result of each subchannel identified in the PIFS before the control frame is received is IDLE. Alternatively, the AP may determine whether there are any further accessible subchannels based on whether the CCA result of each subchannel identified in the SIFS or PIFS immediately after the control frame is received is IDLE. In this case, the AP may apply other rules to determine whether each subchannel is accessible. What is important is that after determining whether each subchannel is accessible, the AP initiates the channel access procedure only when it is determined that additional subchannels other than the subchannel occupied by the control frame are accessible. The specific method for determining whether each subchannel is accessible is not important.

[0317] As described above, after receiving a control frame for TXOP sharing from a non-AP STA, the AP can determine whether to initiate a channel access procedure.

[0318] When the AP decides to access an additional subchannel by initiating a channel access procedure, and when it decides not to initiate a channel access procedure, it may operate in different ways so that the non-AP STA that sent the control frame is aware of this.

[0319] More specifically, after receiving the control frame, when the AP determines to access an additional subchannel by initiating a channel access procedure, it can transmit a first response frame to the non-AP STA as a response to the control frame. In this case, the first response frame may not only serve as a response to the received control frame, but also as a notification that the AP that responded with the first response frame will perform a channel access procedure. That is, when the non-AP STA that transmitted the control frame (TXOP sharing frame) receives the first response frame from the AP, it can recognize that the control frame has been successfully received by the AP and that the AP will initiate the channel access procedure. Therefore, the non-AP STA must not assume that its TXOP has ended and must not perform operations such as TXOP recovery. The first response frame may be an individually addressed frame or a broadcast (group addressed) frame transmitted to the non-AP STA that transmitted the control frame. This may be an addressing method that is considered because the first response frame may include a function that allows other STAs that receive the frame to recognize the operation intention of the AP that transmitted the first response frame. That is, the AP that transmitted the first response frame intends to perform a frame exchange sequence with STAs in its BSS by becoming a TXOP holder, and non-AP STAs (STAs that are members of the BSS) that receive the first response frame transmitted by its AP recognize that the AP's TXOP will soon begin and can prepare to participate in the frame exchange (e.g., remain in an awake state without switching to Doze). Therefore, since the first response frame transmitted by the AP not only serves as a response to the non-AP STAs that transmitted the control frame (TXOP sharing frame) but also has the function of notifying the existence of its own TXOP that will begin later, the AP can also transmit the frame as a broadcast (group-addressed) frame.However, even if the first response frame is sent in an individually addressed frame, member STAs of the BSS can recognize that the AP's TXOP is about to begin based on the format of the first response frame.

[0320] In this case, the format of the first response frame can be CTS or CTS-to-Self (RA addressed is set to the AP's MAC addressed). If the AP responds with a CTS-to-Self frame as the first response frame, the TXOP that the AP subsequently acquires is subject to the TXOP limit starting from the start of the CTS-to-Self frame transmission.

[0321] More specifically, when the AP determines not to initiate the channel access procedure after receiving the control frame, it may respond with a second response frame. In this case, if the AP transmits the second response frame, the AP can continue the frame exchange sequence using only the subchannel occupied by the control frame. This may be because the AP has determined that there are no more subchannels available for obtaining channel access permission within its operating bandwidth.

[0322] Therefore, when the AP determines not to initiate the channel access procedure after receiving a control frame, it can continue the frame exchange sequence using the subchannel occupied by the control frame and notify the non-AP STA of this by responding with a second response frame. In this case, the second response frame may be a trigger frame instructing a TB PPDU response. In this case, the trigger frame may be a trigger frame instructing the non-AP STA that transmitted the control frame (TXOP sharing frame) to respond with a TB PPDU. In this case, the second response frame may be an MU-RTS frame. A STA that receives the MU-RTS frame as the second response frame can respond with a CTS frame to the MU-RTS frame as the second response frame transmitted by the AP, even if the NAV set by the control frame is not 0. In other words, other non-AP STAs that have set their NAVs by a specific non-AP STA that shared a TXOP with the AP can ignore the NAV set by the specific non-AP STA when responding to a frame transmitted by the AP.

[0323] FIG. 24 illustrates an example method for obtaining a transmission opportunity (TXOP) using a shared TXOP according to one embodiment of the present invention.

[0324] Referring to FIG. 24, when a TXOP is shared from a non-AP STA, the AP can perform a backoff procedure within the shared TXOP to obtain the TXOP.

[0325] To avoid repetition, the same content as that described above with reference to FIGS. 21 to 23 may be omitted.

[0326] Specifically, the AP and non-AP STAs each perform a backoff procedure to obtain channel access privileges, and the non-AP STA completes the backoff procedure first. After completing the backoff procedure, the non-AP STA shares the TXOP it has obtained with the AP by sending a control frame to the AP.

[0327] After receiving the control frame sent by the non-AP STA, the AP sends a response frame to guide other STAs to set their NAVs. Then, the AP ignores the NAV set by the non-AP STA and invokes and completes the backoff procedure during the TXOP shared to itself.

[0328] An AP that completes the backoff procedure during a TXOP shared by a non-AP STA obtains channel access privileges for a subchannel that is confirmed as IDLE within PIFS from the time the backoff procedure is completed, and initiates its own TXOP for that subchannel.

[0329] At this time, other STAs can recognize that the channel access procedure has been interrupted by the NAV set by the control frame sent by the non-AP STA and / or the NAV set by the response frame sent by the AP, and that the AP has become the TXOP holder after receiving a frame to initiate its own TXOP.

[0330] As discussed in the above-described embodiment of the present invention, the operation of helping the AP initiate a TXOP after a non-AP STA has acquired channel access permission may be understood as a channel reservation or TXOP reservation operation performed by the non-AP STA to obtain a TXOP from the AP.

[0331] Also, in one embodiment of the present invention, although it is considered that the frame transmitted by the non-AP STA to share the TXOP with the AP is the MU-RTS TXS frame, the frame transmitted by the non-AP STA to allow the AP to acquire the TXOP may be another type of control frame. More specifically, the frame transmitted by the non-AP STA that has acquired the TXOP (acquired the channel access right) to allow the AP to perform the TXOP acquisition procedure may be a new type of trigger frame (a trigger frame of a type not defined in IEEE 802.11be, that is, EHT).

[0332] <Channel access procedure for TXOP sharing / start procedure> According to the procedure provided in the present invention, the AP can acquire the TXOP with the assistance of the Non-AP STA. That is, when the non-AP STA acquires the channel access right after completing the channel access procedure, the TXOP may be transferred / shared to the AP. An AP in an (associated) state combined with a plurality of non-AP STAs can acquire the TXOP every time at least one of the non-AP STAs acquires the channel access right, which may cause fairness issues with legacy BSSs and other BSSs that cannot utilize the procedure provided in the present invention.

[0333] To solve the fairness issue, the AP can instruct to apply different EDCA parameters from the general channel access procedure when the non-AP STA performs channel access to start the TXOP sharing / start procedure. That is, the AP can separately specify the EDCA parameters used for the TXOP sharing / start procedure in consideration of the presence of other BSSs, the number of STAs included in the BSS, etc., and instruct / induce the non-AP STA to follow them.

[0334] To this end, the AP can differentiate the EDCA parameters used when a non-AP STA approaches the channel to transmit a TXOP sharing / initiation frame by including a TXOP sharing EDCA parameter set element in a management frame (e.g., a beacon, a probe response, an association response frame, an operation mode instruction, etc.) transmitted by the AP. More specifically, the AP can indicate the EDCA parameters to be used when a non-AP STA intending to transmit an AP TXOP sharing / initiation frame performs a channel access procedure. The EDCA parameters may include at least one of CWmin, CWmax, and AIFSN. In this case, CWmin, CWmax, and AIFSN can be indicated for each access category (AC).

[0335] A non-AP STA that intends to transmit a TXOP Share / Start frame must access the channel using different CWmin, CWmax, and AIFSN parameters than when it does not intend to transmit a TXOP Share / Start frame.

[0336] For example, when a non-AP STA is instructed by the AP to transmit a TXOP start / shared frame, it must update its CWmin[AC], CWmax[AC], and AIFSN[AC] using the values ​​indicated by the TXOP Shared EDCA parameter set element, and when the AP instructs it not to transmit a TXOP start / shared frame, it must update its CWmin[AC], CWmax[AC], and AIFSN[AC] using the values ​​indicated by the EDCA parameter set element. However, if the MUEDCATimer[AC] is not 0 at the time the AP instructs it not to transmit a TXOP start / shared frame, the non-AP STA must update its CWmin[AC], CWmax[AC], and AIFSN[AC] using the values ​​indicated by the MU EDCA parameter set element.

[0337] Also, it is possible that the TXOP limit for each AC (Access Category) is indicated by the TXOP sharing EDCA parameter set element. At this time, the TXOP limit for each AC means the maximum length of the TXOP obtained by the EDCA of the corresponding AC. However, a non-AP STA that has obtained channel access authority by an AC for which the TXOP limit is indicated as 0 by the TXOP sharing EDCA parameter set element must always transmit the first frame as a TXOP sharing / start frame. That is, a non-AP STA whose EDCA for an AC with a TXOP limit of 0 is a TXOP holder must assist in starting the AP's TXOP (share the TXOP with the AP) by the first frame.

[0338] Also, if a non-AP STA that has transmitted a TXOP start / share frame to the AP cannot receive a response (e.g., a CTS frame) from the AP for the frame it has transmitted, it can attempt a TXOP recovery procedure. That is, when a response from the AP for the TXOP start / share frame is not made, the non-AP STA can perform procedures such as performing PIFS recovery, performing a new backoff procedure, or waiting until the TXNAV timer expires. This can be understood as a recovery procedure performed by the non-AP STA as a TXOP holder because the point at which no response from the AP for the TXOP start / share frame transmitted by the non-AP STA is made is the point at which the non-AP STA remains a TXOP holder.

[0339] <Signaling related to the TXOP sharing / start procedure> As described above, after a non-AP STA acquires a TXOP, the procedure of transferring the TXOP to the AP (i.e., transmitting a TXOP share / initiate frame) may be an operation that is performed only when required by the AP. If there is not much queued traffic on the AP side or if the AP does not intend to perform coordination operations with other APs, the AP may not intend to transmit using the TXOP acquired by the non-AP STA or to acquire a TXOP. Therefore, the AP can guide the non-AP STA to allow or not allow the non-AP STA to transmit a TXOP share / initiate frame to itself by informing the non-AP STA that it intends to acquire or share the TXOP.

[0340] That is, the AP can indicate to the STAs in the BSS whether it wishes to have a TXOP handed over (i.e., whether it wishes to receive a TXOP Share / Initiate frame), and this must be done in a pre-agreed manner between the AP and the STAs.

[0341] The method by which the AP instructs the non-AP STA to perform the TXOP sharing / initiation procedure may include at least one of the following methods.

[0342] The AP may use a beacon frame to indicate whether a non-AP STA that has obtained channel access permission during the time period up to the next TBTT (Target Beacon Transmit Time) should transmit a TXOP share / initial frame. If the AP does not use a specific beacon frame to indicate whether a TXOP share / initial frame should be transmitted or not, the instruction made by the beacon frame transmitted before the specific beacon frame may be interpreted as being maintained. That is, the AP may not indicate whether a TXOP share / initial frame should be transmitted in every beacon frame, but may use a beacon frame to indicate this instruction only when it intends to change the instruction regarding whether or not a TXOP share / initial frame should be transmitted. Therefore, if a first beacon frame includes an instruction regarding whether or not a TXOP share / initial frame should be transmitted and a second beacon frame does not include an instruction regarding whether or not a TXOP share / initial frame should be transmitted, the non-AP STA should interpret this as indicating that the same instruction made in the first beacon frame will continue to be maintained.

[0343] The AP can use a probe response frame and / or an association response frame to instruct whether to send a TXOP share / initiate frame. A non-AP STA that receives an instruction to send a TXOP share / initiate frame from the AP in a probe response / association response frame must send a TXOP share / initiate frame to the AP after completing the channel access procedure and obtaining channel access permission.

[0344] The AP can use the response frame sent to the non-AP STA to instruct the non-AP STA to send a TXOP share / initiation frame.

[0345] For example, when an AP receives an RTS frame from a non-AP STA, it can respond by setting a specific bit in a CTS frame for the RTS frame to a specific value (e.g., 1), thereby instructing the non-AP STA that sent the RTS frame to send a TXOP Share / Initiate frame. That is, if a specific bit in a CTS frame received in response to an RTS frame sent to the AP is set to a specific value, the non-AP STA must send a TXOP Share / Initiate frame to the AP. In this case, the specific bit in the CTS frame may be a bit included in the frame control field of the CTS frame. In this case, the specific bit may be one of the bits corresponding to the To DS, From DS, More Fragments, Retry, Power Management, More Data, Protected Frame, and +HTC subfields.

[0346] As another example, after receiving a frame from a non-AP STA, an AP can instruct the non-AP STA to transmit a TXOP share / initiate frame by setting a specific bit in the corresponding Ack / BlockAck frame to a specific value (e.g., 1). That is, the non-AP STA must transmit a TXOP share / initiate frame to the AP when a specific bit in the corresponding Ack / BlockAck frame from the AP is set to a specific value. In this case, the specific bit may be set for the above purpose only when the non-AP STA is the TXOP holder. In this case, the specific bit in the Ack / BlockAck frame may be a bit included in the frame control field. In this case, the specific bit may be one of the bits corresponding to the To DS, From DS, More Fragments, Retry, Power Management, More Data, Protected Frame, and +HTC subfields.

[0347] The AP can transmit an AP Priority Access Enable frame to instruct non-AP STAs to send TXOP Share / Initiate frames. The AP transmits the AP Priority Access Enable frame when it intends to take the initiative in managing TXOPs acquired within the BSS. When a non-AP STA receives this frame from its associated AP and acquires channel access privileges (TXOP), it must perform procedures to transfer the TXOP to the AP (e.g., by transmitting a TXOP Share / Initiate frame). The AP can then transmit an AP Priority Access Disable frame to instruct non-AP STAs not to transmit TXOP Share / Initiate frames. In this case, the AP Priority Access Enable frame may include information related to the time required to transmit a TXOP Share / Initiate frame. For example, if the AP specifies 100 ms in the AP Priority Access Enable frame, a non-AP STA must transmit a TXOP Share / Initiate frame to the AP if it acquires channel access privileges within 100 ms after receiving the frame. The AP Priority Access Disable frame is a frame that an AP transmits when it does not require the support of non-AP STAs, and when a non-AP STA receives this frame from its associated AP and obtains a channel access permission (TXOP), it does not perform the procedure to transfer the TXOP to the AP. The AP Priority Access Enable / Disable frame is a frame named for convenience of explanation, and other frames with the same or similar functions can be used for the same or similar purposes.

[0348] In this way, the AP can instruct / request non-AP STAs in the BSS to transmit TXOP share / initialization frames, or instruct / request them not to transmit TXOP share / initialization frames, depending on operational purposes. Non-AP STAs can decide whether to transmit TXOP share / initialization frames based on the most recently received instruction from the AP.

[0349] Furthermore, if the AP and non-AP STAs are devices that belong to a multi-link device (MLD), the AP's indication may be made by another AP in the MLD to which the AP belongs. For example, a beacon frame transmitted by AP2, which belongs to the same MLD as AP1, may be used to instruct a STA associated with AP1 whether to transmit a TXOP Share / Initiate frame. In this case, non-AP STA1 associated with AP1 can determine whether to transmit a TXOP Share / Initiate frame to AP1 based on information obtained from non-AP STA2, another STA in the MLD. The concept of MLD is explained in more detail in one embodiment of FIG. 26.

[0350] FIG. 25 illustrates an example of a format of a parameter set element for TXOP sharing according to one embodiment of the present invention.

[0351] 25, the TXOP shared EDCA parameter set element transmitted by the AP may include AC_BE Parameter Record, AC_BK Parameter Record, AC_VI Parameter Record, and AC_VO Parameter Record fields, where the AC_BE Parameter Record, AC_BK Parameter Record, AC_VI Parameter Record, and AC_VO Parameter Record fields of the TXOP shared EDCA parameter set element include AIFSN, CWmin, CWmax, and TXOP limit information to be used when a non-AP STA intending to transmit a TXOP sharing / initiation frame performs a channel access procedure.

[0352] The CWmin and CWmax values ​​are indicated by the 4-bit ECWmin and ECWmax subfields, respectively. ECWmin is 2 ECWmin The value -1 is set to the CWmin value to be specified. That is, the ECWmin subfield of the Parameter Record field that specifies CWmin as 15 is specified as 4. Similarly, ECWmax is set as 2. ECWmax = 1 value is set to the CWmax value to be specified. That is, the ECWmax subfield of the Parameter Record field that specifies CWmax as 1023 is specified as 10.

[0353] The TXOP Limit subfield indicates the maximum length of a TXOP obtained by the value of this parameter set.

[0354] FIG. 26 illustrates an example of the configuration and connection state of an AP MLD and a non-AP MLD according to an embodiment of the present invention.

[0355] An MLD is a logical entity to which one or more STAs belong. An MLD is an AP MLD in which each of the STAs belonging to it functions as an AP, and an MLD is a non-AP MLD in which each of the STAs belonging to it functions as a non-AP STA.

[0356] Each STA included in the MLD can operate on a different link (channel). That is, the STAs included in the MLD can operate on multiple different channels. For example, the STAs included in the MLD can operate using channels in different bands, such as 2.4 GHz, 5 GHz, and 6 GHz. This allows the MLD to gain channel access benefits and improve the performance of the entire network.

[0357] MLD operation can also be called multi-link operation, MLD operation, multi-band operation, etc. Existing WLANs operate using a single link, but MLD operation can utilize multiple links to gain more channel access opportunities and operate efficiently using multiple links taking into account channel conditions.

[0358] As shown in FIG. 26, two MLDs may be connected through a plurality of links. The AP MLD including AP1, AP2, and AP3 and the MLD non-AP MLD including non-AP STA1, non-AP STA2, and non-AP STA3 may be connected by three links respectively. When a plurality of links are connected between MLDs, in each link unit, the connection between the AP and the non-AP STA supports the same connection state as the connection state between single link devices. Also, information exchange using the MLD is possible between STAs belonging to the same MLD. Therefore, information received by AP1 can be transmitted to AP2, and information received by non-AP STA1 can also be transmitted to non-AP STA2.

[0359] Thereby, the AP MLD can transmit the change matters related to AP1 to non-AP STA1 via AP2. That is, as considered in one embodiment of the present invention, if AP2 instructs in Link2 that AP1 instructs the transmission of the TXOP sharing / start frame, non-AP STA1 can transmit the TXOP sharing / start frame to AP1 based on the information acquired by non-AP STA2 in Link2.

[0360] <Signaling of AP for the TXOP sharing procedure started by non-AP> As described above, the non-AP STA can transmit a specific frame (for example, a kind of control frame that can be named a TXOP sharing request frame (Sharing Request frame), which may be a trigger type frame)) to the AP in order to share the TXOP acquired by itself with the AP.

[0361] If there is no traffic that the AP intends to transmit on the AP side (i.e., the AP's transmission queue is empty) and there is no scheduled device known to the AP (i.e., a non-AP STA that should solicit a TB PPDU using a trigger frame), the AP may not have any action to take during the TXOP shared by the non-AP STA. In this case, the TXOP shared by the non-AP STA to the AP cannot be used for any purpose other than the non-AP STA's TB PPDU transmission, and therefore, it can be understood that unnecessary TXOP sharing has occurred.

[0362] Therefore, the AP can make an announcement to the non-AP STAs in the BSS regarding whether or not the TXOP should be shared. In this case, the announcement from the AP can be understood as an AP operation instructing the non-AP STAs whether or not to initiate the TXOP sharing procedure.

[0363] As a simple method for an AP to instruct a non-AP STA to perform TXOP sharing, the AP may instruct the non-AP STA to use the TXOP sharing procedure by transmitting a specific frame, element, or field. In this case, when the specific frame, element, or field received from the AP instructs the non-AP STA to share its acquired TXOP with the AP, the non-AP STA must share the acquired TXOP with the AP. That is, when the non-AP STA is instructed to perform TXOP sharing in the most recently received specific frame / element / field, it must share the TXOP with the AP if it acquires one. However, the non-AP STA may first transmit low-latency traffic using the acquired TXOP, taking into account the latency requirement of the traffic it intends to transmit, and then share the remaining TXOP with the AP. In this case, the non-AP STA sharing a TXOP with the AP means transmitting the TXOP share / initiation frame described above to the AP. That is, the term is used to encompass both a non-AP STA handing over a TXOP to an AP and initiating a TXOP acquisition procedure for the AP, and in one embodiment of the present invention described below, when a non-AP STA is described as "sharing" a TXOP it has acquired with an AP, it should be interpreted as encompassing both a TXOP being "handed over" to an AP and an AP's TXOP being "initiated" by a non-AP STA. That is, the TXOP of a non-AP STA being shared with an AP should be understood as the AP controlling (i.e., managing) the medium (i.e., transmitting a DL PPDU or requesting a TB PPDU response) during the time period (TXOP) for which the non-AP STA has obtained permission by completing a channel access procedure.

[0364] The method by which the AP instructs the non-AP STA whether the non-AP STA should perform TXOP sharing is described in more detail in one embodiment of FIG.

[0365] FIG. 27 illustrates an example of elements for sharing a TXOP according to one embodiment of the present invention.

[0366] The element that the AP sends to the non-AP STA to instruct whether the non-AP STA should share the acquired TXOP with the AP may have the format shown in FIG.

[0367] Specifically, as shown in Figure 27, the TXOP sharing element includes a TXOP Sharing Control field, and may further include a TXOP Sharing EDCA Parameter Set field.

[0368] In this case, whether the TXOP Shared EDCA Parameter Set field is further included in the TXOP Shared Element is indicated by the bit of the TXOP Shared EDCA Parameter Set included in the TXOP Sharing Control field. More specifically, the TXOP Shared EDCA Parameter Set field is included in the TXOP Shared Element when the bit of the TXOP Shared EDCA Parameter Set included in the TXOP Sharing Control field is set / indicated to 1.

[0369] The TXOP Sharing Control field includes a Policy subfield. The Policy subfield indicates whether a non-AP STA should share the acquired TXOP with the AP when it acquires the TXOP. If the Policy subfield of the TXOP sharing element sent by the AP indicates a specific value (e.g., 0), the non-AP STA does not need to share the TXOP with the AP when it acquires the TXOP. On the other hand, if the Policy subfield of the TXOP sharing element sent by the AP indicates another value (e.g., 1), the non-AP STA must share the TXOP with the AP when it acquires the TXOP. That is, the non-AP STA must transmit the TXOP Share / Initiate frame of the present invention described above to the AP. At this time, the non-AP STA must determine whether to share the TXOP based on the TXOP sharing element most recently received from the AP.

[0370] That is, the two types of policies indicated by the Policy subfield can be understood as normal and AP priority. That is, when the Policy subfield is indicated as the specific value (e.g., 0), the 'normal' policy is applied. In this case, the non-AP STA performs channel access using an existing channel access method (e.g., EDCA or DCF) and then performs the conventional frame exchange order. In this case, the conventional frame exchange order means that the non-AP STA does not share a TXOP with the AP and transmits an UL PPDU as a TXOP holder. On the other hand, when the Policy subfield is indicated as the other value (e.g., 1), the 'AP priority' policy is applied. In this case, the non-AP STA must obtain a TXOP and then share (transfer) the obtained TXOP to the AP.

[0371] On the other hand, when the "AP Preferred" policy is applied, a non-AP STA may perform a channel access procedure in a different manner than when the "General" policy is applied. Performing the channel access procedure in a different manner may mean using different values ​​for backoff-related parameters when performing channel access. That is, when the "General" policy is indicated, a non-AP STA performs channel access using parameters indicated in an EDCA parameter set element or an MU EDCA parameter set element. However, when the "AP Preferred" policy is indicated, a non-AP STA intending to initiate a TXOP sharing procedure must perform channel access using parameters indicated in the TXOP Shared EDCA Parameter Set field of a TXOP Sharing element or a TXOP Shared EDCA Parameter Set element included in a beacon frame, etc.

[0372] At this time, a non-AP STA that accesses the channel with the intention of initiating the TXOP sharing procedure performs channel access (EDCA) using the parameters (TXOP sharing EDCA parameters) indicated in the TXOP sharing EDCA parameter set field regardless of the MU EDCA timer value.

[0373] The R-TWT SP subfield indicates whether a TXOP acquired for an interval overlapping with the R-TWT SP should be shared with the AP. If the R-TWT SP subfield is set to a specific value (e.g., 0), a non-AP STA may not share the TXOP with the AP when it acquires a TXOP for an interval overlapping with the R-TWT SP. However, if the R-TWT SP subfield is set to another value (e.g., 1), the non-AP STA must share the TXOP acquired for an interval overlapping with the R-TWT SP with the AP. That is, for an interval overlapping with the R-TWT SP, the non-AP STA must ensure that the AP can control the medium (i.e., manage, for example, transmit a DL PPDU or solicit a TB PPDU). Therefore, if the R-TWT SP subfield is set to the other value (e.g., 1), the non-AP STA must share the TXOP obtained for the interval overlapping with the R-TWT SP with the AP regardless of the policy indicated in the Policy subfield.

[0374] In this case, the information indicated in the R-TWT SP subfield can be indicated in the Policy subfield. In other words, as in the example of FIG. 27, the Policy subfield and the R-TWT SP subfield are not indicated separately, and the Policy subfield can indicate whether or not to share the TXOP acquired for the interval overlapping with the R-TWT SP. That is, when the Policy subfield indicates a specific value (e.g., 2), it may be indicated / interpreted that the "AP priority" policy is applied to the R-TWT SP. That is, when the Policy subfield indicates the specific value (e.g., 2), the non-AP STA must decide whether or not to share the TXOP it acquired with the AP based on whether or not it overlaps with the R-TWT SP scheduled by the AP. In this case, if the TXOP it acquired overlaps with the R-TWT SP scheduled by the AP, the non-AP STA shares the TXOP with the AP. In this case, if the TXOP acquired by the non-AP STA does not overlap with the R-TWT SP scheduled by the AP, the non-AP STA does not need to share the TXOP with the AP.

[0375] The TXOP Shared EDCA Parameter Set field contains an EDCA parameter set to be used by a non-AP STA that performs channel access (EDCA) with the intention of TXOP sharing. The information contained in the TXOP Shared EDCA Parameter Set field may be similar to the information contained in the EDCA Parameter Set element and the MU EDCA Parameter Set element. More specifically, the TXOP Shared EDCA Parameter Set field may contain an ACI / AIFSN field, an ECWmin / ECWmax field, and a TXOP limit field. Although FIG. 27 shows that the TXOP Shared EDCA Parameter Set field contains one ACI / AIFSN, ECWmin / ECWmax, TXOP limit, and Shared TXOPlimit subfield, the TXOP Shared EDCA Parameter Set field may contain up to four ACI / AIFSN, ECWmin / ECWmax, TXOP limit, and Shared TXOPlimit subfields repeatedly. That is, the TXOP Shared EDCA Parameter Set field shown in FIG. 27 indicates that the ACI / AIFSN, ECWmin / ECWmax, TXOP limit, and Shared TXOPlimit subfields are included once each, and the same configuration can be included up to four times. In this case, the TXOP Shared EDCA Parameter Set field may indicate how many times the ACI / AIFSN, ECWmin / ECWmax, TXOP limit, and Shared TXOPlimit subfields are included in the TXOP Shared EDCA Parameter Set field. For example, the TXOP Shared EDCA Parameter Set Present subfield in one embodiment of FIG. 27 indicates whether the TXOP shared element containing the subfield includes a TXOP Shared EDCA Parameter Set field and may further indicate information related to the size of the TXOP Shared EDCA Parameter Set field (information related to how many times the ACI / AIFSN, ECWmin / ECWmax, TXOP limit, and Shared TXOPlimit subfields appear).

[0376] The ACI / AIFSN subfield, ECWmin / ECWmax, and TXOP limit subfields can be set and parsed in the same way as the fields of the same name included in the EDCA parameter set element of conventional Wi-Fi, so detailed explanations are omitted (see 9.4.2.28 (EDCA Parameter Set Element) of Draft P802.11REVme_D2.0).

[0377] The Shared TXOPlimit subfield indicates information related to the minimum time that must be observed when sharing a TXOP acquired by the AC (the access category indicated by the corresponding ACI / AIFSN subfield) with the AP. For example, if the ACI / AIFSN subfield indicates AC_VO and the corresponding Shared TXOPlimit subfield indicates 2 ms, a non-AP STA must share a TXOP acquired in AC_VO with the AP for at least 2 ms. That is, the Shared TXOPlimit subfield for a specific AC indicates the minimum time that a non-AP STA that acquired a TXOP through the specific AC must share with the AP. If the Shared TXOPlimit subfield for a specific AC is set to 0, the non-AP STA must transmit a TXOP share / initialization frame when attempting channel access (sending the first frame) through the specific AC. That is, an AC with a Shared TXOPlimit subfield set to 0 may mean that a non-AP STA must share a TXOP with the AP as soon as it acquires a TXOP through the AC.

[0378] The TXOP sharing element described in FIG. 27 may be transmitted in frames transmitted by the AP, and non-AP STAs must use the policies and parameters indicated in the most recently received TXOP sharing element.

[0379] If the information (value of each subfield) of the TXOP shared element indicated by the AP differs from the information indicated in the previously transmitted TXOP shared element, this may be considered a critical update to the BSS parameters. In other words, when the information indicated in the TXOP shared element is set to be different from the information indicated previously by the AP, the AP must take action considering this to be a critical update. In other words, the AP must increment the Check Beacon field value of the next TIM frame it transmits by 1.

[0380] FIG. 28 shows an example of a frame including an element for sharing a TXOP according to an embodiment of the present invention.

[0381] Referring to FIG. 28, the AP may transmit the TXOP sharing element using a Beacon, and / or a (ML) Probe Response, and / or a (Re)Association Response, and / or a TXOP Sharing Notification frame.

[0382] Non-AP STAs should follow the channel access policy indicated in the most recently received TXOP shared element, and if the "AP preferred" policy applies, they should perform the channel access procedure (EDCA) using the parameters indicated in the TXOP shared EDCA parameter set field.

[0383] The method of including elements in the Beacon, (ML) Probe Response, and (Re) Association Response frames is the same as the method of including various elements in the same frames in conventional Wi-Fi, and therefore a separate description will be omitted.

[0384] The TXOP Sharing Notification frame may be an Action frame that the AP sends to change instructions related to TXOP sharing. In this case, the TXOP Sharing Notification frame may be an Action No Ack frame. That is, a non-AP STA that receives the frame does not need to send a Response frame.

[0385] The Category field of the TXOP Sharing Notification frame is a field that indicates that the Action frame is a TXOP Sharing Notification frame, and a non-AP STA can recognize that the frame is a TXOP Sharing Notification frame when the Category field is set to a specific value.

[0386] The Category field of the TXOP Sharing Notification frame indicates that the Action frame is a (Protected) UHR Action frame. In this case, the value indicated by the Category field can be set to 38 to indicate that it is a UHR Action frame, or 39 to indicate that it is a Protected UHR Action frame.

[0387] The (Protected) UHR Action field of the TXOP Sharing Notification frame is a field that indicates that the Action frame is a TXOP Sharing Notification frame, and a non-AP STA can recognize that the frame is a TXOP Sharing Notification frame when the (Protected) UHR Action field is set to a specific value.

[0388] The Dialog Token field is set to a non-zero value and is used to distinguish this transaction from other transactions.

[0389] The TXOP Share field contains the TXOP Share element (see FIG. 27).

[0390] <Examples of various response frames> As described above, when a non-AP STA shares a TXOP with an AP through the TXOP Sharing / Initiation procedure, the AP may not have any operations it wishes to perform using the shared TXOP. In this case, the AP may transmit a response frame to the control frame (TXOP Sharing / Initiation frame) received from the non-AP STA to indicate that it does not need the TXOP to be shared. Furthermore, when the AP wishes to provide service to multiple non-AP STAs using the TXOP shared by the non-AP STA, the multiple non-AP STAs must prepare operations that take into account the AP's transmission to them.

[0391] That is, when an AP receives a control frame for TXOP sharing from a non-AP STA, the AP can instruct the other STA whether it will transmit / receive using the shared TXOP and / or prior information related to the operation to be performed using the shared TXOP. In this case, the instruction can be made by a response frame (TXOP sharing response frame) transmitted by the AP in response to the control frame.

[0392] The information that the AP indicates using the response frame can be broadly divided into two types: 1. Perform frame exchange order using the TXOP shared by the non-AP STA, and 2. There is no action that the non-AP STA intends to perform using the TXOP shared by the non-AP STA.

[0393] The method by which the AP indicates whether or not a non-AP STA will operate using a shared TXOP (hereinafter referred to as a shared TXOP) through a response frame may be to use the format of the response frame or to set a specific subfield (bit) included in the response frame to a specific value.

[0394] To explain the indication method using a frame format in more detail, when an AP intends to perform a subsequent operation using a shared TXOP (such as transmitting a DL MU PPDU or transmitting a trigger frame to request a UL TB PPDU response), it can send a TXOP share response frame in response to a TXOP share / initiate frame received from a non-AP STA. In this case, the TXOP share response frame may be a trigger frame or an MU-RTS (Trigger) frame. Alternatively, the TXOP share response frame may be a frame of another type of pre-agreed format. Therefore, after sending a TXOP share / initiate frame to the AP, a non-AP STA that receives a TXOP share response frame in response must not transmit during the remaining TXOP without triggering from the AP. In other words, when a non-AP STA receives a TXOP share response frame from the AP, it must perform an operation that recognizes that the AP has become the TXOP holder. In other words, it must set its NAV (Intra-BSS NAV, Basic NAV) based on the Duration / ID field value of the frame sent by the AP. In this case, when a non-AP STA receives a TXOP sharing response frame from the AP, it can abort the channel access procedure (keep the Virtual NAV busy) by setting its NAV timer to the same value as its remaining TXNAV timer. In this case, a non-AP STA can set its TXNAV to 0 when it receives a TXOP sharing response frame from the AP. TXNAV refers to a timer that the TXOP holder initializes to the value indicated in the Duration / ID field of the frame it most recently successfully transmitted. In this case, the successfully transmitted frame refers to a frame that is a received response frame to a frame.

[0395] When an AP does not intend to perform subsequent operations using the shared TXOP (such as sending a DL MU PPDU or sending a trigger frame to request a UL TB PPDU response), it can respond with a CTS frame in response to the TXOP Share / Initiate frame. That is, when a non-AP STA receives a CTS frame in response to a TXOP Share / Initiate frame it sent, it can recognize that the AP does not intend to use the TXOP it shared. In this case, the non-AP STA can use its remaining TXOP to perform operations such as sending a UL PPDU or a P2P PPDU. That is, when TXOP sharing with the AP is rejected (aborted), the non-AP STA can continue the operations it intended to perform during its TXOP as the TXOP holder.

[0396] To explain in more detail how to use a specific subfield (bit) included in the response frame, when an AP receives a TXOP Share / Initiate frame from a non-AP STA, the AP can set the specific subfield (bit) of the response frame in different ways depending on whether it intends to perform a subsequent operation using a shared TXOP. As a simple example, the AP can set the specific subfield to a specific value if it intends to transmit a DL MU PPDU or receive a UL TB PPDU using a shared TXOP, and can set the specific subfield to another value if there is no operation to be performed using a shared TXOP. Therefore, after transmitting a TXOP Share / Initiate frame to the AP, a non-AP STA can determine whether the AP intends to perform an operation using a shared TXOP based on the value of the specific subfield in the received response frame.

[0397] In this case, when the non-AP STA determines that the AP does not intend to operate using a shared TXOP, it can operate as a TXOP holder, such as by transmitting a UL PPDU or / and a P2P PPDU in the remaining TXOP, in the same manner as in the case of the indication method using the frame format described above.

[0398] In this case, when a non-AP STA recognizes from the specific subfield that the AP intends to operate using a shared TXOP, it must perform operations such as setting its NAV based on the frame sent by the AP and resetting its own TXNAV timer, just as in the case of the indication method using the frame format described above. That is, a non-AP STA that confirms that the AP intends to operate using a shared TXOP using a specific subfield of the TXOP Shared Response frame responded by the AP must function as if it were not a TXOP holder in the section corresponding to the shared TXOP.

[0399] In this way, an AP that receives a TXOP share / initiate frame can use the response frame to indicate whether it will operate using the Shared TXOP, and a non-AP STA that sent a TXOP share / initiate frame can determine whether it will function as a TXOP holder during the remaining TXOP based on the TXOP share response frame that is received in response.

[0400] Furthermore, the AP can use the TXOP Share Response frame to instruct the target non-AP STAs with which it intends to exchange frames using the Shared TXOP. That is, the AP can use the TXOP Share Response frame to issue instructions related to operations to be performed during the Shared TXOP to non-AP STAs other than the non-AP STA that sent the TXOP Share / Initiate frame. In this case, the AP can issue the same instruction not in the TXOP Share Response frame but in a frame transmitted following the TXOP Share Response frame (the next frame transmitted at an SIFS interval after the TXOP Share Response frame). The following description will be written assuming that an instruction to a non-AP STA is issued using the TXOP Share Response frame, but it should be understood that the same instruction can also be issued using a frame transmitted following the TXOP Share Response frame.

[0401] More specifically, the AP may use a TXOP sharing response frame to transmit information indicating non-AP STAs that intend to transmit / receive during a shared TXOP. In this case, the information indicating the non-AP STAs may refer to a field indicating the Association ID (AID) of the non-AP STA. That is, the AP may transmit one or more AID fields using the TXOP sharing response frame, and each AID field indicates the AID (e.g., AID11 or AID12) of the target non-AP STA that is to transmit a DL MU PPDU in the shared TXOP and / or the target non-AP STA that is to request a TB PPDU response using the trigger frame. Therefore, a non-AP STA whose AID is indicated in the TXOP sharing response frame transmitted by the AP (a response frame to a TXOP sharing / initiation frame transmitted by a specific non-AP STA) can recognize that the AP is transmitting a DL PPDU to it or requesting a TB PPDU response. In this case, the non-AP STA can wait for the DL PPDU reception and TB PPDU response scheduled to be performed later without switching to power save mode. The number of AID fields included in the TXOP Share Response frame is indicated by another (sub)field included in the TXOP Share Response frame. Here, the other field may be a control field. Therefore, the non-AP STA can recognize the number of AID fields included in the TXOP Share Response frame based on the value indicated in the control field (or another subfield (e.g., the Number Of AIDs subfield) included in the control field) of the received TXOP Share Response frame. Here, the control field may be set to the number of AID fields included in the TXOP Share Response frame minus 1. That is, in the control field of a TXOP Share Response frame including one AID field, the subfield associated with the number of AID fields may be set to 0.In this case, the control field may be set to the number of AID fields included in the TXOP Share Response frame. That is, in the control field of a TXOP Share Response frame including one AID field, the subfield corresponding to the number of AID fields may be set to 1. However, the AID of a specific non-AP STA that transmitted the TXOP Share / Initiate frame need not be indicated in the AID field. This may be an exception because the AP is expected to transmit at least one trigger frame to the specific non-AP STA (the non-AP STA that transmitted the TXOP Share / Initiate frame) during the Shared TXOP. That is, because the non-AP STA that transmitted the TXOP Share / Initiate frame is aware that it will receive at least one trigger frame from the AP during the Shared TXOP, the AP does not need to indicate the AID of the non-AP STA in the AID field.

[0402] Meanwhile, when operating using a shared TXOP, the AP may intend to change the operating channel of some non-AP STAs to the secondary channel in order to increase the utilization of the secondary channel.

[0403] As an example of the present invention, as described above, a station (e.g., an AP, etc.) can transmit a specific frame (e.g., a trigger frame, etc.) to cause other stations (e.g., non-AP STAs, etc.) to change their operating channels to channels that are not supported by the other stations, and the other stations that receive the specific frame can change their operating channels to the channel indicated by the specific frame and transmit and receive frames.

[0404] For example, if the total bandwidth is 320 MHz, the AP can support and use all 320 MHz, but a non-AP STA can support only the primary 160 MHz (or less) bandwidth and not support the remaining secondary 160 MHz. In this case, the operating bandwidth of the non-AP STA is the primary 160 MHz, and the remaining secondary 160 MHz is not supported by the non-AP STA, so the non-AP STA does not need to use the secondary 160 MHz. In order to use the secondary 160 MHz (e.g., to transmit or receive frames on the secondary 160 MHz), the AP can transmit a frame instructing the non-AP STA to change its operating bandwidth to the secondary 160 MHz, and the non-AP STA that receives the frame can change its operating bandwidth to the secondary 160 MHz instructed by the frame and operate.

[0405] In yet another embodiment of the present invention, in the above embodiment, the AP can acquire a TXOP on a secondary channel by the method described in "Channel Access Procedure for Bandwidth Expansion," and can perform a procedure for changing the operating bandwidth of a non-AP STA within the acquired TXOP.

[0406] As yet another embodiment of the present invention, the above-described method for changing the operating channel of a non-AP STA and the method for an AP to perform channel access on a secondary channel may be performed in conjunction with a method for sharing a TXOP. Specifically, a first STA (e.g., an AP or a non-AP STA) may receive a TXOP (first TXOP) from a second STA (e.g., a non-AP STA or an AP) through the above-described TXOP sharing procedure. In this case, the second STA supports only a Primary 160 MHz or a Primary 80 MHz subchannel of the total bandwidth of 320 MHz. The second STA may perform a channel access procedure (first channel access procedure) using the primary subchannel of the Primary 160 MHz or the Primary 80 MHz, thereby obtaining the first TXOP. The frequency range on the frequency axis within which the first TXOP is obtained may be up to the range of the Primary 160 MHz or the Primary 80 MHz. The first STA may transmit and receive frames within the shared first TXOP. However, if the primary subchannel of the Primary 160 MHz or Primary 80 MHz is occupied by another STA (e.g., an OBSS STA), the channel access procedure cannot be performed using the primary subchannel. Therefore, the first STA selects one of the remaining channels other than the Primary 160 MHz or Primary 80 MHz (e.g., the Secondary 160 MHz or the Secondary 80 MHz when the total bandwidth is 320 MHz), performs the channel access procedure (second channel access procedure) using a subchannel of the selected channel, and can obtain a TXOP (second TXOP). In this case, the frequency range in which the second TXOP is obtained may be limited to the channel in which the channel access procedure was performed (e.g., the Secondary 160 MHz or the Secondary 80 MHz), and the second TXOP may be considered as an extension of the first TXOP to the frequency band. Therefore, the second TXOP can end at the same time as the first TXOP.In this case, the first STA can transmit a specific frame (e.g., a trigger frame) to the other STA to change the operating channel of the other STA to the secondary 160 MHz or secondary 80 MHz where the second channel access procedure was performed. In this case, the other STA can support only the primary 160 MHz or primary 80 MHz, the same as or similar to the second STA. The other STA that receives the specific frame from the first STA can change its operating bandwidth to the secondary 160 MHz or secondary 80 MHz as a bandwidth extension, and can transmit and receive frames using the secondary 160 MHz or secondary 80 MHz.

[0407] For example, an AP may plan to operate the BW for frame exchange in a shared TXOP as 320 MHz. In this case, if all non-AP STAs attempting to transmit from the AP have set only the primary 160 MHz band as their operating BW, the AP cannot utilize the secondary 160 MHz band. The reason the operating BW of the non-AP STAs is limited to the primary 160 MHz may be because the operating bandwidth of the non-AP STAs is limited to 160 MHz. In this case, the AP may request some non-AP STAs to change to operate in the secondary 160 MHz band in order to utilize the secondary 160 MHz band. A non-AP STA requested by the AP to change to the secondary 160 MHz band can receive a DL PPDU or respond with a TB PPDU using an RU included in the secondary 160 MHz band until the frame exchange sequence with the AP is completed. That is, the non-AP STA does not support transmission / reception on the primary channel, but changes its operation mode to support transmission / reception on the secondary channel.

[0408] As in the above example, the operation of a non-AP STA changing its operating BW to a secondary channel instead of the primary channel of a BSS may be similar to the Subchannel Selective Transmission (SST) operation defined in IEEE 11ax. However, there may be a difference in that when the AP transmits a frame instructing the non-AP STA to change to the secondary channel, the non-AP STA operates on the instructed secondary channel only during the consecutive frame exchange sequence that includes the frame. Here, the consecutive frame exchange sequence refers to the frame exchange sequence performed within a single TXOP. Here, each frame (PPDU) in the consecutive frame exchange sequence has a SIFS or PIFS interval.

[0409] Thus, when a non-AP STA changes its operation mode to support transmission / reception in another band (a band including a secondary channel) that does not include the primary channel, a required time may be required depending on the non-AP STA's capability. That is, each non-AP STA may have a required time required to change to the secondary channel operation mode, and the operation mode change time may be indicated as the non-AP STA's capability during association between the AP and the non-AP STA. In this case, the value indicated by the non-AP STA according to its capability may be the transition time required to change to the secondary channel operation mode and / or the minimum padding field length to be included in a frame (a frame transmitted by the AP) instructing the change to the secondary channel operation mode. Therefore, when an AP instructs a specific non-AP STA to change to the secondary channel operation mode, the AP must operate taking into account the time required for the specific non-AP STA to change to the secondary channel operation mode. That is, when an AP instructs a specific non-AP STA to change to a secondary channel operation mode, the AP must include a padding field equal to or longer than the minimum padding field length indicated by the specific non-AP STA in the frame transmitted to instruct the change. In this case, the padding field may refer to a field included after the AID field indicating the AID of the specific non-AP STA.

[0410] In this way, the AP can instruct the non-AP STA to switch to the secondary channel operation mode, and the non-AP STA can exchange frames on the secondary channel by switching to the secondary channel operation mode when instructed by the AP. To this end, the AP and the non-AP STA can negotiate the secondary channel operation mode in advance. More specifically, the AP can request the non-AP STA to activate the secondary channel operation mode, and the non-AP STA can operate by changing the secondary channel operation mode only if the non-AP STA accepts the request. Furthermore, the AP can instruct the non-AP STA regarding information about the secondary channel to which the non-AP STA should move, and the non-AP STA can accept the secondary channel instructed by the AP or instruct the AP to use another secondary channel. Once agreement on the secondary channel is reached between the AP and the non-AP STA, the non-AP STA can switch to a state in which it can operate on the agreed-upon secondary channel when it switches to the secondary channel operation mode.

[0411] Therefore, if the AID of another non-AP STA operating in the secondary channel operation mode is indicated using a TXOP Share Response frame transmitted after receiving a TXOP Share / Initiate frame transmitted from a specific non-AP STA, the other non-AP STA may switch to the operation mode for the secondary channel previously negotiated with the AP. That is, the TXOP Share Response frame transmitted by the AP not only indicates the target non-AP STA that intends to transmit / receive using the Shared TXOP, but also indicates the secondary channel operation mode switch of the indicated non-AP STA. In this case, the AP may set a specific bit (or a specific subfield) included in the TXOP Share Response frame to a predetermined value to indicate whether the TXOP Share Response frame indicates a switch to the secondary channel operation mode. For example, the AP may set the Secondary Subchannel Operation subfield included in the response frame to 1 to indicate that the non-AP STA whose AID is indicated in the AID field included in the TXOP Share Response frame should switch to the secondary channel operation mode. If the Secondary Subchannel Operation subfield of the TXOP Sharing Response frame is set to 0, the non-AP STA will not switch to the secondary channel operation mode even if its own AID is indicated in the AID field.

[0412] FIG. 29 illustrates an example of a response frame format to a frame for sharing a TXOP according to an embodiment of the present invention.

[0413] The Duration / ID field of the TXOP Share / Initiate frame indicates a time later than the time indicated by the Duration / ID field of the TXOP Share / Initiate frame received by the AP. That is, the time indicated by the Duration / ID field of the TXOP Share / Initiate frame transmitted in response to the TXOP Share / Initiate frame is a time later than the time indicated by the Duration / ID field of the TXOP Share / Initiate frame. This Duration / ID field setting rule is designed to allow a STA that sets its NAV after receiving a TXOP Share / Initiate frame to reset its NAV after receiving the TXOP Share / Initiate frame. A STA that resets its NAV after receiving a TXOP Share / Initiate frame recognizes that the STA that sent the TXOP Share / Initiate frame, i.e., the AP, is the TXOP holder. To this end, a non-AP STA that sends a TXOP Share / Initiate frame must set the Duration / ID field of the TXOP Share / Initiate frame to a value smaller than a specific value (the maximum value that can be indicated considering the TXOP limit). In this case, a non-AP STA transmitting a TXOP Share / Initiate frame must set the Duration / ID field to a preset value. The preset value may be a value designated by the AP or a standard to be set in the Duration / ID field of the TXOP Share / Initiate frame. However, when an AP transmits a TXOP Share Response frame indicating that it does not intend to use a Shared TXOP, the Duration / ID field of the TXOP Share Response frame may be set to indicate the same time as the time indicated by the Duration / ID field of the TXOP Share / Initiate frame.

[0414] The Accept / Refuse field indicates whether the AP that received the TXOP Share / Initiate frame intends to operate using a Shared TXOP. If the Accept / Refuse field is set to a specific value (e.g., 1), it indicates that the AP plans to use the Shared TXOP, i.e., to take over the Shared TXOP. If the Accept / Refuse field is set to another value (e.g., 0), it indicates that the AP does not plan to use the Shared TXOP. In this case, the non-AP STA that sent the TXOP Share / Initiate frame can function as a TXOP holder (i.e., send UL PPDUs and / or P2P PPDUs, receive Ack / BlockAck frames, etc.) during the remaining TXOP.

[0415] The following fields are included only in the response frame sent by the AP to instruct it to use Shared TXOP.

[0416] The Secondary Subchannel Operation field indicates whether non-AP STAs that support the secondary channel operation mode, among those whose AIDs are specified using the TXOP Share Response frame, should switch to the secondary channel operation mode. If the Secondary Subchannel Operation field is set to 1, non-AP STAs that support the secondary channel operation mode among those whose AIDs are specified in the AID field, must switch to the secondary channel operation mode. If the Secondary Subchannel Operation field is set to 0, even non-AP STAs whose AIDs are specified in the AID field can participate in subsequent frame exchange sequences without switching to the secondary channel operation mode. In this case, the Secondary Subchannel Operation field may be meaningful only for non-AP STAs that support the secondary channel operation mode and have completed negotiation with the AP regarding secondary channel operation. In other words, non-AP STAs that do not support the secondary channel operation mode among non-AP STAs do not perform any separate operation depending on the value of the Secondary Subchannel Operation field.

[0417] The control field indicates the number of AID fields included in the TXOP Share Response frame. The control field may be set to the number of AID fields minus 1. Alternatively, the control field may be set to the number of AID fields.

[0418] The AID field indicates the AID of a non-AP STA that the AP transmitting the TXOP sharing response frame intends to transmit / receive during the Shared TXOP. Therefore, a non-AP STA whose AID is indicated in the AID field must operate considering that during the Shared TXOP, the AP may transmit at least one DL PPDU to it or transmit at least one trigger frame (i.e., request a TB PPDU response). That is, during the period corresponding to the Shared TXOP, it must not transition to the Doze state and must maintain the Awake state.

[0419] The padding field is a field set based on the minimum padding length indicated by a non-AP STA that changes to the secondary channel operation mode. More specifically, among the non-AP STAs whose transition to the secondary channel operation mode is indicated by the TXOP sharing response frame, the padding field is set to a length equal to or longer than the length indicated by the non-AP STA that indicated the largest minimum padding length. As an example, when the minimum padding lengths indicated by three non-AP STAs whose secondary channel operation mode transitions are performed by a specific TXOP sharing response frame are 10 us, 20 us, and 30 us respectively, the AP sets the padding field of the TXOP sharing response frame to have a length of 30 us or longer than 30 us.

[0420] <BW Extension Rules for Harmonious Operation with Overlapping BSS> According to an embodiment of the present invention described above, an AP that has received a TXOP sharing / start frame from a non-AP STA can approach a subchannel confirmed as Idle among the subchannels not occupied by the received TXOP sharing / start frame. At this time, as mentioned, the AP must call / perform / complete an additional backoff procedure during the Shared TXOP to obtain the access right to approach the subchannel confirmed as Idle.

[0421] Thus, even if an AP performs an additional backoff procedure during a shared TXOP to obtain access permission for an idle subchannel, a fairness issue may arise regarding the operation of extending the BW while the TXOP is in progress. As a simple example, after a non-AP STA shares a TXOP obtained for an 80 MHz (Primary 80 MHz) band with the AP, the AP accesses an additional 80 MHz band (Secondary 80 MHz) to operate using the 160 MHz band. This may result in interference with the channel access of an overlapping BSS (basic service set) operating in the additional 80 MHz band. According to one embodiment of the present invention, the AP performs an additional backoff procedure to obtain access permission for a secondary channel and confirms that the CCA result for the additional subchannel is IDLE, thereby ensuring fair contention. However, for legacy BSSs that do not have an opportunity for BW extension, such an operation may still be considered unreasonable.

[0422] Therefore, an AP attempting to obtain channel access permission for additional BW (BW and idle subchannels) during a shared TXOP can further protect the OBSS's operating channel to minimize OBSS performance degradation. As a simple example, an AP obtaining channel access permission for additional BW during a shared TXOP must access only idle subchannels that do not correspond to the OBSS's operating BW. In other words, an AP attempting channel access for additional BW during a shared TXOP may not attempt channel access for subchannels included in the OBSS's operating BW, even if the subchannel is confirmed as idle. However, OBSS-related restrictions do not apply to AP access to channels occupied by a TXOP share / initiate frame. In this context, channel access during a shared TXOP refers to the channel access procedure performed after an AP receives a TXOP share / initiate frame and responds with a TXOP share response frame.

[0423] That is, when the AP extends the BW during a shared TXOP, it may not approach subchannels included in the OBSS's operating BW. In this case, the AP may perform preamble puncturing to avoid approaching subchannels included in the OBSS's operating BW. Preamble puncturing refers to a method of transmitting a signal without transmitting it on specific subchannels (subchannels that are not intended to be occupied) in order to not occupy some of the subchannels included in the PPDU BW. For example, when an STA transmits a 320 MHz PPDU to which preamble puncturing is applied, the STA may transmit in a manner that does not occupy a specific 80 MHz band within the 320 MHz band spanned by the 320 MHz PPDU. In this case, the 320 MHz PPDU signal is not detected in the specific 80 MHz band. Since the preamble puncturing technology is a conventional technology introduced in 11ax and 11be, further detailed description thereof will be omitted.

[0424] If the channel access of an AP extending its BW during a Shared TXOP is restricted to all subchannels included in the OBSS's operating BW, the performance gain obtained by the AP's BW extension procedure may be significantly limited. To solve this problem, an AP extending its BW during a Shared TXOP must be allowed to access a specific subchannel under certain conditions, even if the subchannel is included in the OBSS's operating BW.

[0425] For example, an AP extending its BW during a shared TXOP may be permitted to access subchannels other than the primary channel of the OBSS. More specifically, an AP extending its BW during a shared TXOP may access a secondary channel of the OBSS if the secondary channel is identified as idle. However, access to the primary channel of the OBSS is not permitted even if it is identified as idle as a result of CCA. In this case, the primary channel of the OBSS refers to a channel including the primary 20 MHz subchannel of the OBSS. That is, the primary channel of the OBSS may be the primary 20 MHz subchannel of the OBSS. That is, the primary channel of the OBSS may be two subchannels corresponding to the primary 40 MHz of the OBSS. That is, the primary channel of the OBSS may be four subchannels corresponding to the primary 80 MHz of the OBSS.

[0426] As another example, an AP extending its BW during a shared TXOP may be permitted to access subchannels included in the OBSS's operating BW, but may be recommended to perform multi-AP coordination operations taking into account the requirements of the OBSS. In this case, an AP extending its BW during a shared TXOP may perform channel access to the OBSS's operating BW and, if necessary, perform multi-AP coordination operations to share a resource unit (RU) or TXOP with the OBSS. Multi-AP operations refer to a series of operations in which APs exchange mutual requirement information and harmoniously share and use frequency resources and / or TXOPs in consideration of each other's requirements. In this case, an AP that allocates (shares) frequency resources or allocates (shares) TXOPs to other APs may be called a sharing / coordinating AP. In the above-described embodiment of the present invention, it may be understood that the AP that extends the BW during the Shared TXOP functions as a sharing / coordinating AP and allocates (shares) RUs (frequency resources, resource units) and / or TXOPs to the APs of the OBSS, thereby performing the operation of extending the BW in a manner that minimizes performance degradation of the OBSS.

[0427] In this case, an AP extending the BW during a shared TXOP may attempt to extend the BW for an IDLE subchannel according to different rules depending on whether the OBSS is a legacy BSS or a UHR BSS. For example, if the OBSS is a legacy BSS, the AP may not access subchannels included in the operating BW of the legacy BSS. If the OBSS is a UHR BSS, the AP may allocate (share) an RU / TXOP to the UHR BSS, which is the OBSS, through multi-AP operation. Also, even if the OBSS is a UHR BSS, if multi-AP operation with the OBSS is not performed, the AP may not access subchannels included in the operating BW of the OBSS. In other words, if a UHR BSS that does not perform multi-AP operation is an OBSS, the operating BW of the UHR BSS must be considered in the same way as a legacy BSS.

[0428] FIG. 30 illustrates an example of a method for minimizing performance degradation of an overlapping basic service set (OBSS) of APs when expanding the bandwidth of a shared TXOP in one embodiment of the present invention.

[0429] Referring to the Operating BW of the BSSs in Figure 30, the operating BW of the BSS, which is 320 MHz, includes four 80 MHz segments, corresponding to 80_1 to 80_4. In this case, the operating BW of the UHR BSS, which is an OBSS, is the third and fourth 80 MHz segments, and the operating BW of the legacy BSS, which is an OBSS, is the fourth 80 MHz segment.

[0430] After receiving the Ctrl frame (TXOP Share / Initiate frame) sent by the non-AP STA, the AP responds with a response frame (TXOP Share Response frame). The AP initiates an additional channel access procedure (Channel Access during Shared TXOP) to occupy only the Primary 80MHz band for the Ctrl frame and operate using a wider BW during Shared TXOP.

[0431] The AP confirms that all 320 MHz bands included in the operating BW of its own BSS are idle, but does not approach the fourth 80 MHz segment because it is included in the operating BW of the Legacy OBSS. In this case, the AP transmits a 320 MHz PPDU and punctures the subchannel corresponding to the fourth 80 MHz segment to avoid approaching the fourth 80 MHz segment.

[0432] The AP obtains channel access privileges for the first, second, and third 80MHz segment bands by transmitting an M-AP coordination frame to the bands corresponding to the first, second, and third 80MHz segments. However, the AP considers the requirements of the UHR BSS and allocates (shares) RUs located in the primary 80MHz band of the UHR BSS (the third 80MHz segment of the BSS) to the AP of the UHR BSS.

[0433] As described above, the embodiments of the present invention are designed with a non-AP STA transmitting a TXOP initiation / share frame to an associated AP in mind, but the same operation can also be performed between APs. In other words, after a first AP acquires a TXOP, it can transmit a TXOP share frame to a second AP to share the TXOP, and in this process, AP2 can extend its BW. Also, if the BW in which the first AP acquired the TXOP is smaller than the operating BW of the second AP, the first AP can use its TXOP initiation frame to induce the second AP to perform frame exchange in the band in which the first AP was unable to acquire the TXOP. In this case, the TXOP share frame transmitted by the first AP to the second AP may be a frame classified as an MU-RTS type. In this case, the frame transmitted by the first AP to the second AP may be a frame transmitted for multi-AP operation.

[0434] However, when TXOP sharing is performed between these two APs, TXOP sharing may only be performed for bands where the operating BWs of both APs overlap. As an example, when AP1 uses a 320 MHz band including a first 160 MHz band and a second 160 MHz band as its operating BW, and AP2 uses a 320 MHz band including a second 160 MHz band and a third 160 MHz band as its operating BW, the band in which the first AP can share a TXOP with the second AP may be limited to the second 160 MHz band. This may be because the first AP cannot obtain channel access permission for the third 160 MHz band included in the operating BW of the second AP. Therefore, when TXOP sharing is performed between these two APs, TXOP sharing may only be performed for frequency regions where the operating BWs of both APs overlap. In this case, the above-mentioned AP2 can obtain channel access permission for the third 160 MHz band by performing additional channel access during the shared TXOP allocated (shared) by AP1. The method by which AP2 performs additional channel access during the time allocated (shared) by AP1 may be performed in the same / similar manner as the AP performs additional channel access during the time allocated (shared) by a non-AP STA, and detailed description thereof will be omitted.

[0435] In addition, a condition for a specific AP to share a TXOP with another AP is that the primary 20 MHz channel of the other AP must be present within the operating BW of the specific AP. This is because if the primary 20 MHz channel of the other AP is not included within the operating BW of the specific AP, the other AP cannot receive a frame (e.g., a TXS trigger frame) transmitted by the specific AP.

[0436] FIG. 31 illustrates an example of the operation of an AP when TXOP sharing between APs is performed and BW extension is performed during a shared TXOP according to an embodiment of the present invention.

[0437] Referring to Figure 31, the operating BW of AP1 is 160 MHz corresponding to the first 80 MHz segment and the second 80 MHz segment, and the operating BW of AP2 is a 320 MHz band including the first 80 MHz segment, the second 80 MHz segment, the third 80 MHz segment, and the fourth 80 MHz segment.

[0438] AP1 acquires a TXOP by transmitting a CTS-to-Self frame to the first 80 MHz segment, which is its own primary 80 MHz band. AP1 then transmits a control frame (TXS trigger frame in FIG. 31) to AP2 to share (allocate) the TXOP it has acquired. At this time, the control frame transmitted by AP1 to AP2 occupies only the first 80 MHz segment, so AP2 also responds with a response frame occupying only the first 80 MHz segment, and as a result, a TXOP for the 80 MHz corresponding to the first 80 MHz segment is allocated to AP2.

[0439] AP2 invokes / performs / completes a new backoff procedure to obtain access permission for a wider bandwidth during the shared TXOP. This allows AP2 to further obtain channel access permission for the second, third, and fourth 80 MHz segments that are determined to be idle. AP2 functions as a TXOP holder for these four 80 MHz segments during the shared TXOP. That is, during the time allocated by AP1 (shared TXOP), AP2 can exchange frames with STAs in its own BSS using not only the first 80 MHz segment to which AP1 assigned (shared) the TXOP, but also the second, third, and fourth 80 MHz segments for which AP2 obtained channel access permission through the channel access procedure performed by AP2 using the shared TXOP. During the shared TXOP allocated (shared) by AP1, AP2 can transmit DL PPDUs occupying its entire operating BW (320 MHz) and receive TB PPDUs. In other words, a trigger frame can be used to allocate RUs in the 320 MHz band.

[0440] FIG. 32 shows an example of the operation of a station according to an embodiment of the present invention.

[0441] Referring to FIG. 32, a station may perform a channel access procedure over a secondary channel rather than the primary channel.

[0442] Specifically, the station may perform a first channel access procedure on a specific secondary subchannel included in a specific secondary channel (S32010). In this case, the entire bandwidth supported by the wireless communication terminal may be configured with one primary channel and one or more secondary channels including the specific secondary subchannel.

[0443] Thereafter, the station may acquire a first transmission opportunity (TXOP) using a first channel access procedure (S32020). At this time, the first channel access procedure and the first TXOP may be a channel access and a TXOP using the aforementioned sub-channel, and the range on the frequency axis in which the first TXOP is acquired may be limited to the specific sub-sub-channel.

[0444] The first channel access procedure may be performed when the channel state of a primary subchannel included in one primary channel is busy and / or when the primary subchannel is occupied by an overlapping basic service set (OBSS) terminal.

[0445] During a TXOP, a station can transmit a trigger frame to one or more terminals to instruct them to transmit frames using a plurality of subchannels that make up the specific subchannel.

[0446] When one or more terminals operate on the one primary channel, the trigger frame can instruct a change from the primary channel to the specific secondary channel. Also, when the one or more terminals do not support the bandwidth of the specific secondary channel as an operating bandwidth, the trigger frame can include a field instructing a change from the primary channel to the specific secondary channel.

[0447] The station may receive a frame for sharing a second TXOP from a specific terminal, and the second TXOP may be obtained by a second channel access procedure of the specific terminal on a primary subchannel included in the one primary channel.

[0448] The range on the frequency axis from which the second TXOP is acquired may be the entire bandwidth, and the end points of the first TXOP and the second TXOP may be the same.

[0449] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. Therefore, the above-described embodiments should be understood to be illustrative in all respects and not restrictive. For example, each component described as a single component may be implemented in a distributed form, and similarly, distributed components may be implemented in a combined form.

[0450] The scope of the present invention is indicated by the appended claims rather than the above detailed description, and all modifications and variations that fall within the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims

1. A first terminal, Transmitter and receiver, Includes a processor, The aforementioned processor, The second terminal receives an ICF (initial control frame) to determine whether it intends to share the transmission opportunity (TXOP) acquired by the second terminal. The second terminal transmits a response frame in response to the ICF, the response frame including a specific field indicating whether it intends to participate in the TXOP to perform frame exchange, The second terminal is configured to receive a trigger frame for sharing the TXOP when the specific field is set to a value indicating the intention to participate in the TXOP in order to perform the frame exchange. The frequency resources to be shared for the TXOP are determined based on the overlap between the first Basic Service Set (BSS) band of the first terminal and the second BSS band of the second terminal. Terminal 1.

2. The processor further, It is configured to perform frame exchange with one or more stations (STAs) associated with the first terminal within the frequency resource, The ICF includes AC information indicating the Access Category (AC) used by the second terminal to obtain the TXOP, The frame replacement is performed based on the AC information. The first terminal according to claim 1.

3. The first primary 20 MHz channel of the first terminal is included in the second BSS band of the second terminal. The first terminal according to claim 1.

4. The first primary 20MHz channel of the first terminal is the same as the second primary 20MHz channel of the second terminal. The first terminal according to claim 3.

5. The processor further, It is configured to negotiate with the STA associated with the first terminal regarding a specific operating mode for switching the operating subband of the STA from a first subband including the primary channel to a second subband, The first subband and the second subband are located within the frequency resources of the first BSS band. Conducting the aforementioned negotiations To transmit information providing the second subband to the STA, The STA includes receiving a first frame from the STA that accepts the second subband provided or a second frame that requests a different subband within the frequency resources of the first BSS band, The first terminal according to claim 1.

6. The first frame receiving the provided second subband is transmitted by the STA on the condition that the STA is ready to operate on the provided second subband. The first terminal according to claim 5.

7. The particular operating mode is enabled after the first frame receiving the second subband provided has been transmitted by the STA. The first terminal according to claim 6.

8. The processor further, The system is configured to receive capability information from the STA indicating the minimum padding field length required for the STA to switch to the second subband in the specific operating mode. The first terminal according to claim 5.

9. A method performed by a first terminal, The second terminal receives an ICF (initial control frame) in order to determine whether there is an intention to share the transmission opportunity (TXOP) acquired by the second terminal, The second terminal transmits a response frame in response to the ICF, wherein the response frame includes a specific field indicating whether there is an intention to share the TXOP for frame exchange. The second terminal receives a trigger frame for sharing the TXOP when the specific field is set to a value indicating the intention to share the TXOP in order to perform the frame exchange, The frequency resources to be shared for the TXOP are determined based on the overlap between the first Basic Service Set (BSS) band of the first terminal and the second BSS band of the second terminal, including the following: method.

10. Further comprising performing frame exchange with one or more stations (STAs) associated with the first terminal within the frequency resource, The ICF includes AC information indicating the Access Category (AC) used by the second terminal to obtain the TXOP, The frame replacement is performed based on the AC information. The method according to claim 9.

11. The first primary 20 MHz channel of the first terminal is included in the second BSS band of the second terminal. The method according to claim 9.

12. The first primary 20MHz channel of the first terminal is the same as the second primary 20MHz channel of the second terminal. The method according to claim 11.

13. Further comprising negotiating with the STA associated with the first terminal regarding a specific operating mode for switching the operating subband of the STA from a first subband including a primary channel to a second subband, The first subband and the second subband are located within the frequency resources of the first BSS band. Conducting the aforementioned negotiations To transmit information providing the second subband to the STA, The STA includes receiving a first frame from the STA that accepts the second subband provided or a second frame that requests a different subband within the frequency resources of the first BSS band, The method according to claim 9.

14. The first frame receiving the provided second subband is transmitted by the STA on the condition that the STA is ready to operate on the provided second subband. The method according to claim 13.

15. The particular operating mode is enabled after the first frame receiving the second subband provided has been transmitted by the STA. The method according to claim 14.

16. Further comprising receiving capability information from the STA indicating the minimum padding field length required for the STA to switch to the second subband in the particular operating mode, The method according to claim 13.

17. The processor further, The system is configured to transmit a frame to the STA within the frequency resource of the first BSS band, instructing the STA to perform the specific operating mode. The frame includes a padding field having a length equal to or greater than the minimum padding field length. The first terminal according to claim 8.

18. The processor further, After the aforementioned specific operating mode is performed, the system is configured to perform frame exchange with the STA on the second subband within the frequency resource of the first BSS band. The first terminal according to claim 17.

19. Further comprising transmitting a frame to the STA in the frequency resource of the first BSS band instructing the STA to perform the particular operating mode, The frame includes a padding field having a length equal to or greater than the minimum padding field length. The method according to claim 16.

20. After the specific operating mode is performed, further comprising performing the frame exchange with the STA on the second subband within the frequency resource of the first BSS band, The method according to claim 19.

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