Wireless communication method using non-primary channel access and wireless communication terminal using same

Abstract

Disclosed is a station for carrying out non-primary channel access (NPCA). The station comprises: a transmission / reception unit; and a processor. The processor carries out access on a non-primary channel, not a primary channel, when a predetermined condition is satisfied, and does not carry out non-primary channel access when an overlapping basic service set (OBSS) occupies the non-primary channel even if the predetermined condition is satisfied.

Description

Wireless communication method using non-primary channel access and wireless communication terminal using the same

[0001] The present invention relates to a wireless communication method that supports non-primary channel access and a wireless communication terminal using the same.

[0002] With the recent expansion of mobile device adoption, Wireless LAN technology, capable of providing fast wireless internet services to these devices, is gaining significant attention. Based on short-range wireless communication technology, Wireless LAN enables mobile devices—such as smartphones, smart pads, laptop computers, portable multimedia players, and embedded devices—to connect to the internet wirelessly in homes, businesses, or specific service areas.

[0003] Since supporting early wireless LAN technology using the 2.4GHz frequency, IEEE (Institute of Electrical and Electronics Engineers) 802.11 has been commercializing or developing standards for various technologies. First, IEEE 802.11b uses the 2.4GHz band and supports a maximum communication speed of 11Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5GHz band instead of the 2.4GHz band, thereby reducing the impact of interference compared to the significantly congested 2.4GHz band, and improved communication speeds to up to 54Mbps using OFDM technology. However, IEEE 802.11a has the disadvantage of a shorter communication range compared to IEEE 802.11b. IEEE 802.11g, like IEEE 802.11b, uses the 2.4GHz band frequency to achieve a maximum communication speed of 54Mbps and has received considerable attention for satisfying backward compatibility, and it also has an advantage over IEEE 802.11a in terms of communication distance.

[0004] In addition, IEEE 802.11n is a technical standard established to overcome the limitations on communication speed that have been pointed out as a vulnerability in wireless LANs. IEEE 802.11n aims to increase network speed and reliability, and to extend the operating range of wireless networks. More specifically, IEEE 802.11n supports High Throughput (HT) with a data processing speed of up to 540 Mbps or higher, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology, which uses multiple antennas at both the transmitter and receiver ends to minimize transmission errors and optimize data speeds. Furthermore, this standard allows for the use of coding schemes that transmit multiple redundant copies to enhance data reliability.

[0005] As the adoption of wireless LANs has increased and applications utilizing them have diversified, a need has arisen for new wireless LAN systems capable of supporting Very High Throughput (VHT) higher than the data processing speeds supported by IEEE 802.11n. Among these, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) in the 5GHz frequency band. Although the IEEE 802.11ac standard is defined only in the 5GHz band, early 11ac chipsets will also support operation in the 2.4GHz band to ensure backward compatibility with existing 2.4GHz band products. Theoretically, according to this standard, multi-station wireless LAN speeds can reach a minimum of 1Gbps, and maximum single-link speeds can reach a minimum of 500Mbps. This is achieved by extending the wireless interface concepts adopted in 802.11n, such as a wider wireless frequency bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256 QAM). Additionally, there is IEEE 802.11ad, which transmits data using the 60 GHz band instead of the existing 2.4 GHz / 5 GHz bands. IEEE 802.11ad is a transmission standard that provides speeds of up to 7 Gbps using beamforming technology, making it suitable for high-bitrate video streaming, such as large amounts of data or uncompressed HD video. However, the 60 GHz frequency band has the disadvantage of being difficult to penetrate through obstacles, limiting its use to only between devices in close proximity.

[0006] Meanwhile, as a wireless LAN standard following 802.11ac and 802.11ad, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard is in the final stages of development to provide high-efficiency and high-performance wireless LAN communication technology in high-density environments where APs and terminals are densely packed. In an 802.11ax-based wireless LAN environment, high frequency-efficiency communication must be provided indoors and outdoors in the presence of high-density stations and APs (Access Points), and various technologies have been developed to implement this.

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

[0008] Recently, discussions have begun on Ultra High Reliability (UHR) wireless LAN communication technology as a wireless LAN standard following 802.11be to overcome the reliability issues that have been pointed out as a limitation of wireless LANs. The Ultra High Reliability wireless LAN standard is currently under development with the goal of supporting low latency and low jitter for wireless LAN traffic with a high probability (e.g., over 99.9999%).

[0009] One embodiment of the present invention aims to provide a wireless communication method that supports non-primary channel access and a wireless communication terminal using the same.

[0010] A station performing non-primary channel access (NPCA) according to one embodiment of the present invention includes a transceiver; and a processor. The processor performs access on a non-primary channel other than a primary channel when a predetermined condition is satisfied, and does not perform non-primary channel access when the non-primary channel is occupied by an overlapping basic service set (OBSS) even when the predetermined condition is satisfied.

[0011] The processor may initiate transmission to the other station based on the NPCA switching delay between the station performing the NPCA and the other station. In this case, the NPCA switching delay may be the time required for switching between the primary channel and the non-primary channel.

[0012] The processor can start a transmission to the other station based on information regarding the NPCA switching delay transmitted by the other station.

[0013] The processor may defer transmission to the other station based on information regarding the NPCA switching delay transmitted by the other station.

[0014] When the processor delays transmission to the other station, it may not perform transmission to the other station even if it reaches backoff counter 0, and may acquire a new backoff counter.

[0015] When the processor acquires the new backoff counter, it can maintain the size of the previously used CW (contention window) and the QSRC (quality of service short retry counter).

[0016] If the processor recognizes a basic service set (BSS) color collision in the non-primary channel, it can transmit information about the BSS color collision in the non-primary channel to the access point (AP) to which the station is connected.

[0017] Information regarding BSS color collisions in the above non-primary channel may include information regarding the channel in which the BSS color collision was recognized.

[0018] The above-mentioned pre-specified conditions may include that the AP (access) operating the BSS to which the station belongs does not perform cooperative operations with the AP and other APs.

[0019] A method of operation of a station performing non-primary channel access (NPCA) according to an embodiment of the present invention includes: a step of performing access on a non-primary channel other than a primary channel when a predetermined condition is satisfied; and a step of not performing non-primary channel access when the non-primary channel is occupied by an overlapping basic service set (OBSS) even when the predetermined condition is satisfied.

[0020] The above operation method may include the step of starting transmission to the other station based on the NPCA switching delay between the station performing NPCA and the other station. In this case, the NPCA switching delay may be the time required for switching between the primary channel and the non-primary channel.

[0021] The step of starting transmission to the other station based on the NPCA switching delay of the other station may include the step of starting transmission to the other station based on information regarding the NPCA switching delay transmitted by the other station.

[0022] The step of initiating transmission to the other station based on the NPCA switching delay of the other station may include the step of delaying transmission to the other station based on information regarding the NPCA switching delay transmitted by the other station.

[0023] The step of delaying transmission to the other station may include the step of not performing transmission to the other station even if the backoff counter reaches 0 when delaying transmission to the other station, and acquiring a new backoff counter.

[0024] The step of acquiring the new backoff counter may include, when acquiring the new backoff counter, maintaining the size of the previously used CW (contention window) and maintaining the QSRC (quality of service short retry counter).

[0025] The above operation method may include the step of transmitting information about the BSS color collision in the non-primary channel to the access point (AP) to which the station is connected when the BSS color collision in the non-primary channel is recognized.

[0026] Information regarding BSS color collisions in the above non-primary channel may include information regarding the channel in which the BSS color collision was recognized.

[0027] The above-mentioned pre-specified conditions may include that the AP (access) operating the BSS to which the station belongs does not perform cooperative operations with the AP and other APs.

[0028] One embodiment of the present invention provides a wireless communication method that efficiently supports non-primary channel access and a wireless communication terminal using the same.

[0029] FIG. 1 shows a wireless LAN system according to one embodiment of the present invention.

[0030] FIG. 2 shows a wireless LAN system according to another embodiment of the present invention.

[0031] FIG. 3 shows the configuration of a station according to one embodiment of the present invention.

[0032] FIG. 4 shows the configuration of an access point according to one embodiment of the present invention.

[0033] Figure 5 schematically illustrates the process of a station establishing a link with an access point.

[0034] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0035] Figure 7 shows various standard generational PPDU (physical layer protocol data unit) formats according to an embodiment of the present invention.

[0036] FIG. 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0037] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0038] FIG. 10 shows a transmission / TXOP protection method using MU-RTS frames and CTS frames according to an embodiment of the present invention.

[0039] Figure 11 shows a mapping table of User priority and Access Category.

[0040] Figure 12 shows an example of a channel access procedure through a sub-channel when the state of the main channel is busy.

[0041] FIG. 13 illustrates an example of a transmission length limit for a PPDU transmitted after performing channel access through a sub-channel.

[0042] FIG. 14 illustrates an example of a method for limiting the length of a TXOP obtained through channel access via a sub-channel.

[0043] FIG. 15 illustrates a method for an AP to manage a main operation channel by acquiring a TXOP through a main channel and a sub-channel according to an embodiment of the present invention.

[0044] FIG. 16 illustrates an example of a configuration of an AP MLD including a primary AP and an auxiliary AP having overlapping operating channels and a method for setting an operating channel according to an embodiment of the present invention.

[0045] FIG. 17 illustrates an example of a procedure in which an AP MLD acquires a TXOP using a main BSS and an auxiliary BSS according to an embodiment of the present invention.

[0046] FIG. 18 illustrates an example of the format of an RNR element transmitted by an AP MLD to indicate an auxiliary AP according to an embodiment of the present invention.

[0047] FIG. 19 illustrates a method in which, according to one embodiment of the present invention, when a channel switch for a main BSS is performed, a channel switch of an auxiliary BSS is indicated / performed together.

[0048] FIG. 20 illustrates, according to one embodiment of the present invention, the configuration of an AP MLD including a main AP and an auxiliary AP having a continuous operation channel and a method for setting the operation channel.

[0049] FIG. 21 illustrates a channel connection method of an MLD operating an STA in two links having continuous operating channels according to an embodiment of the present invention.

[0050] FIG. 22 illustrates an embodiment of a method for assigning resource units to each STA using a resource unit assignment subfield indicated by the preamble of a PPDU and a method for indicating a content channel.

[0051] Figure 23 illustrates the ambiguity problem regarding the interpretation of the assigned RU of an STA that receives a preamble in a subchannel.

[0052] FIG. 24 illustrates a method in which an AP that performs channel access through a sub-channel indicates BW and RU allocation information of a PPDU according to one embodiment of the present invention.

[0053] FIG. 25 illustrates an embodiment of a transmission / TXOP protection method using a MU-RTS frame and a CTS frame.

[0054] Figure 26 illustrates the format of a trigger frame.

[0055] Figure 27 illustrates an example of the format of the common information field of a trigger frame.

[0056] Figure 28 illustrates an example of the format of the user information field of a trigger frame.

[0057] FIG. 29 shows an example of channel access in a non-primary channel when the primary channel is occupied according to an embodiment of the present invention.

[0058] FIG. 30 illustrates an example of the operation of STAs in a non-primary channel based on information related to OBSS transmitted from an AP according to an embodiment of the present invention.

[0059] FIG. 31 illustrates an example of a method for determining whether to perform operation in a non-primary channel considering the TBTT of a BSS according to an embodiment of the present invention.

[0060] FIG. 32 shows an example of a channel connection method according to the reception of an RTS frame of an AP according to an embodiment of the present invention.

[0061] FIG. 33 shows another example of a channel connection method according to the reception of an RTS frame of an AP according to one embodiment of the present invention.

[0062] FIG. 34 shows an example of a method for transmitting a CTS-to-self frame based on the reception of an RTS frame of an AP according to an embodiment of the present invention.

[0063] FIG. 35 shows an example of information obtained by STA and a NAV setting method based on the reception of OBSS PPDU according to an embodiment of the present invention.

[0064] FIG. 36 shows an example of a busy interval for a recognized channel in each of the STAs performing operations in non-primary channels according to an embodiment of the present invention.

[0065] FIG. 37 shows an example of the format of an element used for a channel access procedure in a non-primary channel according to an embodiment of the present invention.

[0066] FIG. 38 shows an example of a channel connection operation using a listening channel according to an embodiment of the present invention.

[0067] FIG. 39 illustrates an example of a method for performing MU-RTS / CTS protection for a band including a non-primary channel and a band including a listening channel according to an embodiment of the present invention.

[0068] FIG. 40 shows an example of operation in a non-primary channel according to an embodiment of the present invention.

[0069] FIG. 41 shows the format of the Common Info field of a MU-RTS TXS trigger frame according to an embodiment of the present invention and the values ​​that the TXOP Sharing Mode subfield can have.

[0070] FIG. 42 shows that, according to an embodiment of the present invention, an AP shares a TXOP for UL PPDU transmission with a non-AP station via a MU-RTS TXS trigger frame.

[0071] FIG. 43 shows that, according to an embodiment of the present invention, an AP shares a shared TXOP for transmitting UL PPDU and P2P PPDU to a station via a MU-RTS TXS trigger frame.

[0072] FIG. 44 shows a procedure between a shared AP and a shared AP according to an embodiment of the present invention.

[0073] FIG. 45 shows that, according to an embodiment of the present invention, a non-AP station determines whether to perform an NPCA operation based on a frame transmitted by an AP that is a TXOP holder.

[0074] FIG. 46 shows that, according to an embodiment of the present invention, a non-AP station determines whether to perform an NPCA operation based on frame exchange performed between a shareable AP that is a TXOP holder and an AP connected to the non-AP station.

[0075] Figure 47 shows the format of the HE Operation element and the BSS Color Information field.

[0076] Figure 48 shows the format of the BSS Color Change Announcement element that the AP transmits to change the BSS color of the BSS.

[0077] The terms used in this specification have been selected to be as widely used as possible, taking into account their functions in the present invention; however, these may vary depending on the intent, convention, or emergence of new technologies of those skilled in the art. In addition, in certain cases, terms have been arbitrarily selected by the applicant, and in such cases, their meanings will be described in the relevant description of the invention. Therefore, it should be noted that the terms used in this specification should be interpreted based on their actual meanings and the overall content of this specification, rather than merely their names.

[0078] Throughout the specification, when a configuration is described as being "connected" to another configuration, this includes not only cases where they are "directly connected" but also cases where they are "electrically connected" with other components interposed between them. Furthermore, when a configuration is described as "including" a specific component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. In addition, limitations such as "greater than or equal to" or "less than or equal to" based on a specific threshold value may be appropriately replaced with "greater than" or "less than," respectively, depending on the embodiment.

[0079] Hereinafter, in the present invention, fields and sub-fields may be used interchangeably.

[0080] FIG. 1 shows a wireless LAN system according to one embodiment of the present invention.

[0081] A wireless LAN system includes one or more Basic Service Sets (BSS), where a BSS represents a set of devices that can communicate with each other by successfully synchronizing. Generally, BSSs can be classified into infrastructure BSSs and independent BSSs (IBSS), and Figure 1 shows an infrastructure BSS.

[0082] As illustrated in FIG. 1, the infrastructure BSS (BSS1, BSS2) includes one or more stations (STA1, STA2, STA3, STA4, STA5), access points (AP-1, AP-2) that are stations providing distribution services, and a distribution system (DS) that connects multiple access points (AP-1, AP-2).

[0083] A Station (STA) is any device comprising a Medium Access Control (MAC) and a Physical Layer interface for a wireless medium that conforms to the specifications of the IEEE 802.11 standard, and in a broad sense includes both non-Access Point (non-AP) stations and Access Points (APs). Additionally, in this specification, the term "terminal" may be used to refer to a non-AP STA or an AP, or to refer to both. A station for wireless communication includes a processor and a communication unit, and may further include a user interface unit and a display unit, etc., depending on the embodiment. The processor generates frames to be transmitted over a wireless network or processes frames received over said wireless network, and may perform various other processing to control the station. Furthermore, the communication unit is functionally connected to said processor and transmits and receives frames over the wireless network for the station. In the present invention, the term "terminal" may be used to include user equipment (UE).

[0084] An Access Point (AP) is an entity that provides access to a Distribution System (DS) via a wireless medium for stations associated with it. In principle, communication between non-AP stations in an Infrastructure BSS is conducted via the AP, but direct communication between non-AP stations is possible if a direct link is established. Meanwhile, in the present invention, the term AP is used as a concept including a Personal BSS Coordination Point (PCP), and in a broader sense, it may include concepts such as a centralized controller, a Base Station (BS), a Node-B, a Base Transceiver System (BTS), or a site controller. In the present invention, the AP may also be referred to as a base wireless communication terminal, and in a broad sense, the term base wireless communication terminal may be used to include the AP, base station, eNB (eNodeB), and transmission point (TP). In addition, the base wireless communication terminal may include various types of wireless communication terminals that allocate medium resources and perform scheduling in communication with multiple wireless communication terminals.

[0085] Multiple infrastructure BSSs can be interconnected through a distribution system (DS). At this time, multiple BSSs connected through the distribution system are called an Extended Service Set (ESS).

[0086] FIG. 2 illustrates an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of FIG. 2, parts that are identical or corresponding to the embodiment of FIG. 1 are omitted from redundant description.

[0087] BSS3 shown in Fig. 2 is an independent BSS and does not include an AP, so all stations (STA6, STA7) are not 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) can be directly connected to one another.

[0088] FIG. 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 an embodiment of the present invention may include a processor (110), a communication unit (120), a user interface unit (140), a display unit (150), and a memory (160).

[0089] First, the communication unit (120) transmits and receives wireless signals such as wireless LAN packets and may be built into or externally provided in 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 of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to one embodiment, the station (100) may be equipped with a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with an AP or an external station according to the wireless LAN standard of the frequency band supported by the communication module. Depending on the performance and requirements of the station (100), the communication unit (120) may operate only one communication module at a time or operate multiple communication modules together simultaneously. When the station (100) includes a plurality of communication modules, each communication module may be provided in an independent form, or the plurality of modules may be integrated into a single chip. In an embodiment of the present invention, the communication unit (120) may represent an RF communication module that processes RF (Radio Frequency) signals.

[0090] Next, the user interface unit (140) includes various types of input / output means provided in the station (100). That is, the user interface unit (140) can receive user input using various input means, and the processor (110) can control the station (100) based on the received user input. In addition, the user interface unit (140) can perform output based on the commands of the processor (110) using various output means.

[0091] Next, the display unit (150) outputs an image to the display screen. The display unit (150) can output various display objects, such as content executed by the processor (110) or a user interface based on control commands of the processor (110). Additionally, the memory (160) stores a control program used in the station (100) and various data associated therewith. This control program may include a connection program necessary for the station (100) to establish a connection with an AP or an external station.

[0092] The processor (110) of the present invention can execute various commands or programs and process data within the station (100). In addition, the processor (110) can control each unit of the station (100) described above and control the transmission and reception of data between the units. According to an embodiment of the present invention, the processor (110) can execute a program for connection with an AP stored in memory (160) and receive a communication setting message transmitted by the AP. In addition, the processor (110) can read information regarding the priority conditions of the station (100) included in the communication setting message and request a connection to the AP based on the information regarding the priority conditions of the station (100). The processor (110) of the present invention may refer to the main control unit of the station (100), and, depending on the embodiment, may refer to a control unit for individually controlling a part of the station (100), such as a communication unit (120). That is, the processor (110) may be a modem or a modulator and / or demodulator that modulates and / or demodulates wireless signals transmitted and received from the communication unit (120). The processor (110) controls various operations of wireless signal transmission and reception of the station (100) according to an embodiment of the present invention. Specific embodiments thereof will be described later.

[0093] The station (100) illustrated in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separated blocks represent the elements of the device, logically distinguished. Accordingly, the elements of the device described above may be mounted as a single chip or as multiple chips depending on the design of the device. For example, the processor (110) and the communication unit (120) may be implemented as a single integrated chip or as separate chips. In addition, in an embodiment of the present invention, some components of the station (100), such as the user interface unit (140) and the display unit (150), may be optionally provided in the station (100).

[0094] FIG. 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 an embodiment of the present invention may include a processor (210), a communication unit (220), and a memory (260). In FIG. 4, redundant descriptions of parts of the configuration of the AP (200) that are identical to or corresponding to the configuration of the station (100) of FIG. 3 are omitted.

[0095] Referring to FIG. 4, the AP (200) according to the present invention is equipped with 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 a plurality of communication modules using different frequency bands. That is, the AP (200) according to the embodiment of the present invention may be equipped with two or more communication modules among different frequency bands, such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP (200) may be equipped with a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with a station according to the wireless LAN standard of the frequency band supported by the communication module. Depending on the performance and requirements of the AP (200), the communication unit (220) may operate only one communication module at a time or operate multiple communication modules together simultaneously. In an embodiment of the present invention, the communication unit (220) may represent an RF communication module that processes RF (Radio Frequency) signals.

[0096] Next, the memory (260) stores a control program used in the AP (200) and various data associated therewith. This control program may include a connection program that manages the connection of the station. Additionally, the processor (210) controls each unit of the AP (200) and can control the transmission and reception of data between the units. According to an embodiment of the present invention, the processor (210) executes a program for connection with a station stored in the memory (260) and can transmit a communication setting message for one or more stations. At this time, the communication setting message may include information regarding the connection priority conditions of each station. Additionally, the processor (210) performs connection settings according to the connection request of the station. According to one embodiment, the processor (210) may be a modem or a modulator and / or demodulator that modulates and demodulates wireless signals transmitted and received from the communication unit (220). The processor (210) controls various operations of wireless signal transmission and reception of the AP (200) according to an embodiment of the present invention. Specific embodiments thereof will be described later.

[0097] Figure 5 schematically illustrates the process of a station establishing a link with an access point.

[0098] Referring to FIG. 5, the link between STA (100) and AP (200) is established through three stages: scanning, authentication, and association. First, the scanning stage is a stage in which STA (100) obtains connection information of the BSS operated by AP (200). Methods for performing scanning include a passive scanning method, which obtains information by utilizing only beacon messages (S101) periodically transmitted by AP (200), and an active scanning method, in which STA (100) transmits a probe request to AP (S103) and receives a probe response from AP (S105) to obtain connection information.

[0099] STA (100), having successfully received wireless access information during the scanning phase, transmits an authentication request (S107a) and receives an authentication response from AP (200) (S107b) to perform an authentication step. After the authentication step is performed, STA (100) transmits an association request (S109a) and receives an association response from AP (200) (S109b) to perform an association step. In this specification, association basically refers to wireless association, but the present invention is not limited thereto, and association in a broad sense may include both wireless association and wired association.

[0100] Meanwhile, additionally, an 802.1X-based authentication step (S111) and an IP address acquisition step via DHCP (S113) may be performed. In FIG. 5, the authentication server (300) is a server that processes 802.1X-based authentication with the STA (100), and may exist by being physically coupled to the AP (200) or as a separate server.

[0101] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0102] A terminal performing wireless LAN communication performs Carrier Sensing before transmitting data to check whether the channel is busy. If a wireless signal of a certain strength or higher is detected, the channel is determined to be busy, and the terminal delays access to that channel. This process is called Clear Channel Assessment (CCA), and the level determining whether such a signal is detected is called the CCA threshold. If a wireless signal of a strength greater than the CCA threshold is received by the terminal and targets the terminal, the terminal processes the received wireless signal. Meanwhile, if no wireless signal is detected on the channel, or if a wireless signal of a strength lower than the CCA threshold is detected, the channel is determined to be idle.

[0103] When it is determined that the channel is idle, each terminal with data to transmit performs a backoff procedure after an Inter Frame Space (IFS) time, such as Arbitration IFS (AIFS) or PCF IFS (PIFS), depending on the situation of each terminal. According to an embodiment, the AIFS may be used as a configuration to replace the existing DCF IFS (DIFS). Each terminal waits by decreasing the slot time by a random number determined for that terminal during the interval of the channel's idle state, and the terminal that has exhausted all slot times attempts to access the channel. The period during which each terminal performs the backoff procedure in this manner is called the contention window period. At this time, the random number may be referred to as the backoff counter. That is, the initial value of the backoff counter is set by an integer, which is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal may decrease the backoff counter by 1. Additionally, when the backoff counter reaches 0, the terminal may be allowed to perform channel access on the corresponding channel. Thus, transmission by the terminal may be allowed when the channel is idle during the AIFS time and the slot time of the backoff counter.

[0104] If a specific terminal successfully accesses the channel, the terminal can transmit data through the channel. However, if the terminal attempting access collides with another terminal, the colliding terminals are each assigned a new random number and perform a backoff procedure again. According to one embodiment, the random number newly assigned to each terminal may be determined within a range (2*CW) that is twice the range of the random number (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, at which time each terminal performs the backoff procedure starting from the slot time remaining from the previous contention window period. In this way, each terminal performing wireless LAN communication can avoid collisions with each other regarding a specific channel.

[0105] <Examples of Various PPDU Formats>

[0106] Figure 7 shows various standard generational PPDU (physical layer protocol data unit) formats according to an embodiment of the present invention.

[0107] More specifically, FIG. 7(a) illustrates an example of a legacy PPDU format based on 802.11a / g, FIG. 7(b) illustrates an example of an HE PPDU format based on 802.11ax, and FIG. 7(c) illustrates an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Additionally, FIG. 7(d) shows the detailed field configuration of L-SIG and RL-SIG commonly used in the above PPDU formats.

[0108] Referring to FIG. 7(a), the preamble of the legacy PPDU includes L-STF (Legacy Short Training field), L-LTF (Legacy Long Training field), and L-SIG (Legacy Signal field). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as the legacy preamble.

[0109] Referring to FIG. 7(b), the preamble of the HE PPDU additionally includes RL-SIG (Repeated Legacy Short Training field), HE-SIG-A (High Efficiency Signal A field), HE-SIG-B (High Efficiency Signal B field), HE-STF (High Efficiency Short Training field), and HE-LTF (High Efficiency Long Training field) 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 the HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0110] Referring to FIG. 7(c), the preamble of the EHT PPDU additionally includes RL-SIG (Repeated Legacy Short Training field), U-SIG (Universal Signal field), EHT / UHR-SIG-A (Extremely High Throughput / Ultra High Reliability Signal A field), EHT / UHR-SIG-A (Extremely High Throughput / Ultra High Reliability Signal B field), EHT-STF (Extremely High Throughput Short Training field), and EHT-LTF (Extremely High Throughput Long Training field) in addition to the legacy preamble. 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 the EHT preamble. The specific configuration of the non-legacy preamble may be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B can be used in only some of the EHT PPDU formats.

[0111] As such, PPDUs used in the UHR standard can have a format similar to that of PPDUs used in the EHT standard. This is because the EHT PPDU format defined in 802.11be includes the U-SIG field, which is agreed upon for common use by multiple wireless LAN generations. In this case, the value of the PHY Version Identifier field within the U-SIG field included in the EHT PPDU is 0, while the value of the PHY Version Identifier field within the U-SIG field included in the UHR PPDU can be a non-zero value, such as 1. The EHT PPDU includes the EHT-STF (Extremely High Throughput Short Training field) in the STF field and the EHT-LTF (Extremely High Throughput Long Training field) in the LTF field. The UHR PPDU includes the UHR-STF (Ultra High Reliability Short Training field) in the STF field and the UHR-LTF (Ultra High Reliability Long Training field) in the LTF field.

[0112] The L-SIG field included in the preamble of the PPDU applies 64FFT OFDM and consists of a total of 64 subcarriers. Of these, 48 subcarriers, excluding the guard subcarrier, DC subcarrier, and pilot subcarrier, are used for L-SIG data transmission. Since the L-SIG applies a Modulation and Coding Scheme (MCS) of BPSK and Rate=1 / 2, it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information configuration of the L-SIG.

[0113] Referring to FIG. 7(d), the L-SIG includes the L_RATE field and the L_LENGTH field. The L_RATE field consists of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field represents a value among transmission speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which are a combination of modulation schemes such as BPSK / QPSK / 16-QAM / 64-QAM and buoyancy rates such as 1 / 2, 2 / 3, and 3 / 4. By combining the information from the L_RATE field and the L_LENGTH field, the total length of the corresponding PPDU can be indicated. In non-legacy PPDU formats, the L_RATE field is set to the minimum speed of 6 Mbps.

[0114] The L_LENGTH field is allocated a total of 12 bits in bytes, allowing it to signal up to 4095, and can represent the length of the corresponding PPDU in combination with the L_RATE field. In this case, legacy terminals and non-legacy terminals may interpret the L_LENGTH field in different ways.

[0115] First, the method by which legacy or non-legacy terminals interpret the length of the corresponding PPDU using the L_LENGTH field is as follows. If the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) can be transmitted during 4 µs, which is the duration of one symbol in a 64 FFT. Therefore, by adding the 3 bytes corresponding to the SVC and Tail fields to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of symbols based on the 64 FFT after L-SIG is obtained. By multiplying the obtained number of symbols by 4 µs, which is the duration of one symbol, and adding 20 µs, which is required for the transmission of L-STF, L-LTF, and L-SIG, the length of the corresponding PPDU, i.e., the receive time (RXTIME), is obtained. This can be expressed mathematically as Equation 1 below.

[0116]

[0117] At this time, represents the smallest natural number greater than or equal to x. Since the maximum value of the L_LENGTH field is 4095, the length of the PPDU can be set up to a maximum of 5.484ms. Non-legacy terminals transmitting the PPDU must set the L_LENGTH field as shown in Equation 2 below.

[0118]

[0119] Here, TXTIME is the total transmission time constituting the corresponding PPDU, as shown in Equation 3 below. In this case, TX represents the transmission time of X.

[0120]

[0121] Referring to the above formulas, 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.

[0122] Referring to Fig. 7(e), the U-SIG (Universal SIG) field continues to exist in EHT / UHR PPDUs and subsequent generations of wireless LAN PPDUs, and serves to distinguish which generation the PPDU belongs to, including EHT / UHR. Additionally, the U-SIG field can facilitate spatial reuse of EHT / UHR and subsequent generations of wireless LANs. U-SIG is a 64FFT-based OFDM 2 symbol that can transmit a total of 52 bits of information. Of these, 43 bits, excluding the 9 bits for CRC / Tail, are largely divided into the VI (Version Independent) field and the VD (Version Dependent) field.

[0123] The VI bits maintain the current bit configuration in the future, allowing current EHT / UHR terminals to obtain information about a PPDU through its VI fields even when a subsequent generation of PPDUs is defined. To this end, the VI fields consist 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 versions of EHT / UHR and subsequent generation wireless LAN standards. The PHY version ID field of an EHT (11be) PPDU has a value of 000b, while the PHY version ID field of a UHR PPDU has a non-000b value. The UL / DL field distinguishes whether the PPDU is an uplink or downlink PPDU. The BSS Color refers to the BSS-specific identifier defined in 11ax and has a value of 6 bits or more. TXOP refers to the Transmit Opportunity Duration transmitted in the MAC header; by adding it to the PHY header, the length of the TXOP containing the corresponding PPDU can be inferred without the need to decode the MPDU, and it has a value of 7 bits or more.

[0124] The VD field of EHT contains signaling information useful only for PPDUs of version 11be, and can be composed of fields that are common to any PPDU format, such as PPDU format and BW, and fields that are defined differently for each PPDU format. PPDU format is a identifier that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), EHT ER (Extended Range) PPDUs, etc.

[0125] The BW field signals five basic PPDU BW options of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz (BWs expressible in the form of 20*2 powers can be referred to as basic BWs), as well as various remaining PPDU BWs configured through Preamble Puncturing. Additionally, a signal can be transmitted in a punctured form of 80 MHz after being signaled at 320 MHz. Furthermore, the punctured and modified channel form can be signaled directly in the BW field, or by utilizing the BW field together with fields appearing after it (e.g., fields within the EHT-SIG field). If the BW field is set to 3 bits, a total of 8 BW signals are possible, so a maximum of only 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signals are possible, so the puncturing mode can signal up to 11.

[0126] The VD field of the UHR is a field that 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 the field that performs the same role as the VD field of the EHT (11be). For example, the field indicating a puncturing pattern included in the VD field of the UHR PPDU may indicate a more diverse form of pattern than the 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 interpreted in combination with the BW field. Through this, a more diverse form of puncturing pattern may be indicated.

[0127]

[0128] FIG. 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0129] The EHT / UHR PPDU format can be indicated by the PPDU Format field of the U-SIG field of the PPDU. FIG. 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 additional signaling after U-SIG.

[0130] FIG. 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 may not have a separate EHT / UHR-SIG-A field after U-SIG.

[0131] FIG. 8(c) shows an EHT / UHR MU PPDU according to an embodiment of the present invention. An EHT / UHR MU PPDU is a PPDU used for transmission to one or more terminals. The EHT / UHR MU PPDU format may include HE-SIG-B after the U-SIG field.

[0132] FIG. 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. In the EHT / UHR ER SU PPDU format, U-SIG can be repeated in the time axis.

[0133] The EHT / UHR MU PPDU described through FIG. 8(c) can be used by an AP to perform downstream transmission to multiple stations. In this case, the EHT / UHR MU PPDU may include scheduling information for multiple stations to receive the PPDU simultaneously. In this case, the EHT / UHR MU PPDU may convey the AID information of the receiver or sender of the PPDU through the user-specific field of the EHT / UHR-SIG-B. A station that receives the EHT / UHR MU PPDU may perform a spatial reuse operation based on the AID information obtained from the preamble of the PPDU. More specifically, the resource unit allocation (RA) field of the EHT / UHR-SIG-B may include information regarding the resource unit (RU) partitioning form in a specific bandwidth (e.g., 20 MHz) in the frequency domain. Additionally, information on the station assigned to each partitioned resource unit may be transmitted through user-specific fields of EHT / UHR-SIG-B. User-specific fields may include one or more user fields corresponding to each partitioned resource unit.

[0134] Among the multiple divided resource units, the AID of the receiver or sender may be inserted into the user field corresponding to the resource unit where data transmission is performed. A pre-specified Null STA ID may be inserted into the user field corresponding to the remaining resource units where data transmission is not performed.

[0135] Two or more PPDUs described through FIG. 8 may be indicated by 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.

[0136] Some fields or parts of the information within the fields included in the PPDU format described earlier may be omitted. This may be referred to as compression mode or compressed mode.

[0137]

[0138] <Wi-Fi 단말의 채널 액세스 방법>

[0139] Since Wi-Fi terminals (APs, non-AP STAs, etc.) communicate using unlicensed bands, they check whether the channel they intend to transmit on is being used by another device before transmitting a frame. Carrier Sense Multiple Access (CSMA) is a channel access method in which a terminal intending to transmit a packet performs Carrier Sense to check whether the channel is being used by another device, and transmits only when it is determined that the channel is not being used by another device (i.e., is idle). Because a terminal using CSMA can perform an action of not attempting transmission when it is confirmed that another device is using the medium (channel) (when it is determined to be busy), transmissions that have already started can be protected from other devices.

[0140] However, multiple terminals that recognize that the medium has been occupied by another device experience a transmission collision by attempting to transmit packets simultaneously when it is confirmed that the media occupancy by the other device has ended (the medium changes to Idle). In other words, as multiple other terminals attempt to transmit packets at the same time as a specific terminal attempts to transmit a packet, the terminal required to receive the packet transmitted by the specific terminal is unable to properly receive and decode the packet due to interference caused by the transmissions performed by the other multiple terminals.

[0141] As described above, CSMA / CA (CSMA with collision avoidance) is a channel access mechanism that prevents multiple terminals from attempting packet transmission simultaneously upon detecting that the medium has changed to Idle. Terminals accessing the medium (channel) using CSMA / CA attempt transmission after waiting for a random amount of time when the observed state of the medium changes to Idle. This random amount of time may be an aslottime (typically 9 us) equal to a random number (random backoff counter) generated by each terminal attempting transmission. In other words, since terminals accessing the medium using CSMA / CA attempt transmission after waiting for different random amounts of time, they attempt transmission at different times, unlike when CSMA alone is used. At this time, if a specific terminal that has waited for the shortest random amount of time after the medium changes to Idle attempts transmission first, other terminals may stop the channel access procedure after realizing that the medium has been occupied (changed to busy) due to said specific terminal. At this time, the specific terminal may perform the operation of decreasing the backoff counter it maintains by 1 at every aslottime while the medium is kept in Idle, and attempt transmission when the backoff counter becomes 0, or when aslottime has passed after the backoff counter has become 0. At this time, the specific terminal that performed the transmission may generate a new random number (new backoff counter) after the transmission is finished, and attempt transmission when the new random number becomes 0 again, or after it becomes 0.

[0142] The CSMA / CA and random backoff procedures briefly explained above apply to both DCF (Distributed Coordination Function) and EDCAF (Enhanced Distributed Channel Access), which are the basic functions used by Wi-Fi terminals when attempting channel access. Since these are well-known and widely utilized methods for accessing unlicensed band channels, further detailed explanations will be omitted.

[0143]

[0144] The DCF and EDCAF utilized by the MAC of a Wi-Fi terminal evaluate the channel condition by considering not only the channel status (idle / busy status) confirmed by each terminal directly performing Physical Carrier Sense (CS), but also the results of Virtual CS. More specifically, even if the result of the Physical CS performed on the channel is idle, if the Virtual CS result is busy, the Wi-Fi terminal considers the channel status to be busy. In this case, the Virtual CS is a channel evaluation method that determines the channel as busy if the Network Allocation Vector (NAV) is not zero. The NAV may be a value maintained for future traffic predicted to occupy the medium. To explain in more detail, when a Wi-Fi MAC receives an RTS / CTS frame, it sets the NAV (NAV count) based on the duration information of the received frame, such as the value of the duration field, so that the NAV can be maintained as a non-zero value for the expected time during which the medium will be occupied after the RTS / CTS frame exchange. In other words, the value maintained as NAV decreases over time. If the NAV value of a specific MAC is 0, it can be interpreted as a state where future traffic perceived by the specific MAC no longer occupies the medium. If the NAV is 0, the MAC can determine the virtual CS result as Idle. In this case, the Wi-Fi MAC may set the NAV based on duration values ​​obtained from other received MAC frames, not just RTS / CTS frames.

[0145] The channel evaluation method (determine the state of the medium) that considers both the results of physical and virtual CS, briefly explained above, is also a well-known Wi-Fi MAC function, so a detailed explanation is omitted.

[0146]

[0147] <EDCA와 TXOP>

[0148] EDCA provides a mechanism for managing traffic by differentiating it into four types of access categories (ACs) based on traffic characteristics. These four types of ACs are AC_VO (AC Voice), AC_VI (AC Video), AC_BE (AC Best Effort), and AC_BK (AC Background), and each AC can have different contention window (CW), transmit opportunity (TXOP), and AIFSN parameters. Simply put, EDCA is a mechanism that controls the transmission priority of traffic transmitted by utilizing each AC by differentiating the CW, TXOP, and AIFSN parameters for the four types of ACs. To this end, EDCA can map traffic (MSDU) that a MAC must service to one of the four ACs based on the traffic category (TC) or traffic stream (TS). At this time, the traffic mapped to one of the four ACs by EDCA is divided and managed into four queues for each AC. In this case, the four queues may be logically separated queues rather than physically separated queues.

[0149] AC_VO is an AC that can be used for traffic that is vulnerable to transmission delays, such as voice traffic, where the absolute amount of traffic is not large. It has relatively small CW and AIFSN parameter values ​​to increase the probability of being serviced preferentially over traffic from other ACs. The TXOP parameter of AC_VO is limited to a value relatively smaller than the TXOP parameter of other ACs, so only a shorter transmission time than other ACs is guaranteed.

[0150] AC_VI is an AC that is more robust to transmission delay than voice traffic, but can be used for traffic such as video that still requires low-latency transmission and needs to handle a large amount of traffic. AC_VI has CW and AIFSN parameter values ​​that are larger than AC_VO but smaller than other ACs, and instead, TXOP is about twice as long as AC_VI.

[0151] AC_BE is an AC that can be used for traffic robust to transmission delay, and most general traffic, excluding voice data and streaming video data, can be classified as AC_BE. AC_BE uses larger values ​​for the CW and AIFSN parameters than AC_VO and AC_VI. Additionally, AC_BE does not have a separate TXOP. Therefore, traffic corresponding to AC_BE cannot be used in a TXOP transmission sequence in which a PPDU is transmitted, an ACK is received, and a PPDU is transmitted again after SIFS.

[0152] AC_BK is an AC that is robust to transmission delay, similar to AC_BE, but can be used for traffic with a lower priority than BE traffic. AC_BK uses the same CW parameter values ​​as AC_BE, and uses larger AIFSN parameter values ​​than AC_BE. Additionally, traffic corresponding to AC_BK does not have a separate TXOP, just like AC_BE, so it cannot be used in a TXOP transmission sequence.

[0153] The four types of EDCA ACs described above are mapped to the UP (user-priority) of 802.1D, and the EDCA AC is determined based on the UP value of the traffic received via wire or the TID of the MSDU indicated by the upper layer. In this case, if the TID of the MSDU indicates a value from 0 to 7, the value indicated by the TID can correspond one-to-one with the UP.

[0154] In addition, the default CW (CWmin, CWmax), AIFSN, and TXOP parameters for each of the four types of EDCA ACs described above are defined in the standard, and the parameter values ​​of each AC can be changed by the AP and different values ​​can be used for each BSS.

[0155]

[0156] When utilizing the EDCA mechanism, Wi-Fi traffic is stored in one of four queues corresponding to four ACs, and can be transmitted to a destination device only if the AC containing the traffic wins the channel access competition against another AC. In this case, during the channel access competition between ACs, each AC competes using the access parameters (CW[AC], AIFSN[AC]) assigned to it, and the channel access competition operation performed by each AC is the same as DCF. In this case, if a specific AC does not have any traffic to transmit in the queue, said specific AC may not participate in the competition.

[0157] However, as mentioned above, since the CW and AIFSN parameter values ​​utilized by each AC differ, the AC_VO with the smallest CW and AIFSN parameters has a high probability of winning the channel access competition against other ACs, and therefore, it is highly likely that the traffic of AC_VO will be served preferentially over the traffic of other ACs.

[0158] In addition, the EDCA mechanism stipulates internal competition rules, such as when an internal collision occurs between ACs, the AC with higher priority wins and increases the CW of the other AC that caused the collision, and rules for configuring PPDUs by including traffic from ACs other than the AC that won the competition (primary AC), but since these details are not significantly relevant to the proposal of the present invention, a detailed explanation is omitted.

[0159] As described above, EDCA provides the EDCA TXOP (EDCA Transmission Opportunity) function, along with the ability to operate differentiated ACs based on the type of traffic (frames, packets, etc.) to enhance QoS. EDCA TXOP refers to the time during which a specific AC's EDCAF (EDCA Function) can control the medium without interference from other devices during the TXOP duration when it acquires a channel access opportunity, that is, when it becomes a TXOP holder. At this time, the EDCA TXOP may be limited by a TXOP limit advertised by the AP. The TXOP holder must ensure that the transmission of their own transmission and the transmission of any response frames resulting from their transmission are completed within the TXOP limit.

[0160] A TXOP holder can transmit multiple frames (multiple PPDUs) during an EDCA TXOP interval. If the transmission of each frame is performed within the acquired TXOP interval, the TXOP holder can transmit multiple frames continuously without performing a separate channel access procedure, such as a backoff procedure, between the transmissions of each frame. In this case, if the multiple frames are MPDUs or A-MPDUs (Aggregated MAC protocol data units) that do not request an immediate ack, the transmission of multiple frames may be performed at SIFS (short interframe space) or RIFS (reduced interframe space) intervals. In this case, if there is an MPDU or A-MPDU among the multiple frames that requests an immediate ack, the TXOP holder can transmit the frame requesting the immediate ack, receive the ack, and then transmit the next frame after SIFS.

[0161] At this time, traffic (packets, frames, etc.) of an AC other than the specific AC that is the TXOP holder may also be transmitted together within the TXOP acquired by the TXOP holder (specific AC) when certain conditions are satisfied. The transmission of traffic of an AC other than the TXOP holder within the TXOP may be an operation due to TXOP sharing between ACs, and details regarding the above specific conditions are omitted as they are not relevant to the present invention.

[0162]

[0163] As described above, the TXOP holder can perform continuous frame transmission within the TXOP without performing a separate channel access procedure. This operation can be achieved when other terminals understand and protect the TXOP segment acquired by the TXOP holder. That is, in order for the TXOP holder to acquire medium control authority over the EDCA TXOP segment, a procedure to notify other terminals so that they can recognize the acquired TXOP segment may be necessary.

[0164] To this end, a terminal (AC) that has become a TXOP holder or has started transmission after completing the channel access procedure may attempt to enable other terminals to recognize the TXOP period by transmitting an RTS frame. At this time, the RTS frame refers to a frame in which the Type subfield of the Frame Control field of the MAC frame header (the fourth bit (B3) and third bit (B2) of the Frame Control field) is set to 01b (Type = Control frame), and the Subtype subfield of the Frame Control field (the eighth bit (B7), seventh bit (B6), sixth bit (B5), and fifth bit (B4) of the Frame Control field) is set to 1011b. Another terminal that receives the RTS frame from the TXOP holder may set a NAV based on information related to the duration included in the RTS frame, for example, the value of the Duration field. The set NAV may be maintained as a non-zero value for the duration corresponding to the TXOP of the TXOP holder. However, the terminal designated as the destination device of the RTS frame must respond with a CTS frame instead of setting the NAV based on the information in the RTS frame. In this case, the destination device of the RTS frame transmitted to initiate the TXOP is the TXOP responder, and must transmit a CTS frame as a response to the RTS (after the RTS frame is received and SIFS). In this case, the Duration field of the responding CTS frame is set to a value calculated as: the value indicated in the Duration field of the received RTS frame - the CTS frame transmission time - SIFS. Terminals that receive the CTS frame may set the NAV based on information related to the duration included in the CTS frame (e.g., the value of the Duration field).

[0165] Accordingly, 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 are set to 0 after the TXOP acquired by the TXOP holder is terminated. Through this, the Wi-Fi MAC mechanism can protect the TXOP holder and the TXOP responder from exchanging multiple frames during the TXOP without interference.

[0166] However, if the TXOP holder transmits an RTS frame as a non-HT duplicate PPDU across the primary 80 MHz band, but the CTS frame (non-HT duplicate PPDU) responded to by the TXOP responder is responded only in the primary 40 MHz band, the TXOP holder may use only the primary 40 MHz or a bandwidth less than the primary 40 MHz, e.g., primary 20 MHz, for frame exchange during the acquired TXOP. The CH_BANDWIDTH (a type of TXVECTOR parameter) of the PPDU transmitted by the TXOP holder must be set to a value equal to or smaller than the CH_BANDWIDTH_IN-NON_HT (a type of RXVECTOR parameter) of the received CTS frame. In this case, the RTS frame may be an RTS frame that allows the CTS frame to be responded to with a bandwidth smaller than the bandwidth in which the RTS frame was transmitted. The RTS frame may be an RTS frame transmitted with DYN_BANDWIDTH_IN_NON_HT (a type of TXVECTOR parameter) set to Dynamic. If the RTS frame is transmitted from the TXOP holder with DYN_BANDWIDTH_IN_NON_HT set to Static, the TXOP responder may respond with a CTS frame with the same BW as the BW at which the RTS frame was received.

[0167]

[0168] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0169] Before transmitting the PPDU, the first station (STA1) transmits an RTS frame to the second station (STA2), which is the destination device of the PPDU, and the second station (STA2) responds with a CTS frame after SIFS, after acknowledging that the received RTS frame is an RTS frame with itself as the destination device.

[0170] STA1_Neighbor, a neighbor station (Neighbor STA) of the first station (STA1), receives an RTS frame transmitted by the first station (STA1) and sets the NAV based on the value indicated by the Duration field of the RTS frame. STA2_Neighbor, a neighbor station of the second station (STA2), receives a CTS frame transmitted by the second station (STA2) and 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 actions such as not decreasing the backoff counter. Consequently, the neighbor terminal that receives the RTS / CTS frame does not attempt to transmit during the period in which the NAV remains a non-zero value. Therefore, the first station (STA1) and the second station (STA2) can be free from interference by surrounding terminals while exchanging PPDU and Ack frames.

[0171] Even if the first station (STA1) and STA2_Neighbor are in a hidden relationship where no signal is detected from each other's transmission, STA2_Neighbor can perform an operation that takes into account that the channel (channel, WM, Wireless medium) is in use while the first station (STA1) is transmitting a PPDU.

[0172] Meanwhile, a Wi-Fi terminal (non-AP STA) can transmit a UL PPDU to the AP without directly acquiring a TXOP or performing channel access via DCF and EDCAF. More specifically, the non-AP STA can transmit a UL PPDU using the RU assigned to it after receiving a trigger frame transmitted by the AP. In this case, the UL PPDU is a TB (trigger-based) PPDU.

[0173] A STA that responds with a UL PPDU after receiving a trigger frame can perform transmissions without acquiring direct channel access opportunities through DCF and EDCAF, and thus obtains more transmission opportunities compared to a STA that does not transmit a trigger frame-based UL PPDU; consequently, a STA that transmits a UL PPDU via a trigger frame may cause a fairness issue in terms of channel access. To resolve this fairness issue, 11ax defines a constraint that requires an HE non-AP STA to perform EDCAF using the MU (Multi-user)-EDCA parameter when it successfully transmits at least one MPDU via the UL PPDU transmitted after receiving a trigger frame. Accordingly, a STA that transmits a UL PPDU via a trigger frame must perform channel access using the MU-EDCA parameter instead of the EDCA parameter. The MU-EDCA parameters include parameters related to the size of the contention window for each of AC_VO, AC_VI, AC_BE, and AC_BK, as well as the MU-EDCA timer, and the contention window included in MU-EDCA can be set larger than the parameters of EDCA. An STA that has transmitted a TB PPDU via a trigger frame and has successfully transmitted at least one MPDU will succeed in channel access with a lower probability than an STA using EDCA parameters when performing channel access within the time interval corresponding to the MU-EDCA timer by utilizing the MU-EDCA parameters instead of the EDCA parameters.In this way, by reducing the channel accessibility of the STA that transmits the UL PPDU (TB PPDU) based on the trigger frame, the equity issue regarding channel accessibility between the STA that transmits the UL PPDU without performing direct channel access and the STA that does not transmit the UL PPDU based on the trigger frame can be resolved or mitigated.

[0174] <MU-RTS 트리거 프레임을 이용한 TXOP 보호>

[0175] In 11ax (6th generation Wi-Fi, Wi-Fi 6, HEW, High Efficiency WLAN), a MU-RTS Trigger / CTS frame exchange procedure is defined to add a feature that allows an AP to initiate a TXOP using a MU-RTS trigger frame (hereinafter referred to as MU-RTS, MU-RTS frame) and protect the TXOP frame exchange procedure. A MU-RTS frame is a type of trigger frame; upon receiving a MU-RTS frame, a station whose AID12 (the LSB 12 bits of the Association ID) is indicated in the User field included in the MU-RTS frame simultaneously responds with a CTS frame. When an AP protects a TXOP using a MU-RTS frame, multiple stations respond with CTS frames, thereby protecting the TXOP from the peripheral devices of each of the multiple stations that are the destination devices of a DL MU PPDU (Down-link multi-user PPDU). Additionally, MU-RTS frames can be used to protect an UL MU PPDU. More specifically, before requesting a Trigger-based PPDU (TB) from multiple stations via a trigger frame, the AP can transmit a MU-RTS frame to cause multiple stations responding to the TB PPDU to respond to a CTS frame. At this time, the CTS frames responded to by multiple stations induce the neighboring stations of each station to set up NAVs that protect the TB PPDU and the Ack frames (Ack, Block Ack, etc.) to be transmitted after the TB PPDU, thereby allowing legacy stations (STAs) that cannot recognize (interpret, decode) the trigger frame and the TB PPDU to not perform channel access during the packet switching sequence period (or TXOP) initiated by the trigger frame.

[0176]

[0177] FIG. 10 shows a transmission / TXOP protection method using MU-RTS frames and CTS frames according to an embodiment of the present invention.

[0178] In the embodiment of FIG. 10, prior to transmitting the MU PPDU, the AP transmits a MU-RTS frame to the first station (STA1) and the second station (STA2), which are the destination devices of the MU PPDU, and the first station (STA1) and the second station (STA2) receive the MU-RTS frame and, after SIFS, each respond to the MU-RTS frame with a CTS frame.

[0179]

[0180] After receiving the CTS frame transmitted by the first station (STA1), the neighboring station STA1_Neighbor sets the 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 the NAV based on the information indicated by the Duration field of the CTS frame. While the NAV (counter) set by STA1_Neighbor and STA2_Neighbor remains a non-zero value after receiving the CTS frame, the Virtual CS (Virtual Carrier Sense) determines it to be busy and performs actions such as not decreasing the back-off counter. Therefore, the neighboring terminal that received the CTS frame does not attempt to transmit during the period in which the NAV remains a non-zero value. This allows the AP to transmit MU PPDU and the first station (STA1) and the second station (STA2) to transmit Ack frames without being interfered with by surrounding terminals.

[0181] The trigger frame described above is a frame type defined in 11ax, in which the Type (fourth bit (B3) and third bit (B2)) and Subtype (eighth bit (B7), seventh bit (B6), sixth bit (B5), and fifth bit (B4)) subfields of the Frame Control field are set to 01b and 0010b, respectively. The trigger frame is a frame of the Control Type with the Type subfield of the Frame Control field being 01b, and the Subtype value 0010 indicates that it is a Trigger frame type. In 11ax, trigger frames are defined to allow an AP to request response frames from multiple stations at once, and MU-RTS frames are used for an AP to request CTS frames from multiple stations (non-AP STAs). Other Trigger Types, excluding the MU-RTS frame, include the Basic Trigger frame requesting UL MU PPDU, the BRP Trigger frame requesting a Beamforming Report (Beamforming Report Poll Trigger frame), the MU-BAR Trigger frame (BlockAck request), the BSRP Trigger frame requesting a Buffer Status Report (Buffer Status Report Poll Trigger frame), the GCR MU-BAR Trigger frame, the BQRP (Bandwidth Query Report Poll) Trigger frame, and the NDP Feedback Report Poll Trigger frame. Since other Trigger Types, excluding the MU-RTS frame, are not related to the content of the present invention, a detailed description is omitted.

[0182] Multi-link Device (MLD)

[0183] In Wi-Fi 7's EHT (Extremely High Throughput), MLDs are defined. An MLD refers to a logical entity containing one or more STAs, and an AP MLD may be affiliated with one or more APs (AP STAs), and a non-AP (STA) MLD may be affiliated with one or more non-AP STAs.

[0184] Each AP belonging to an AP MLD can operate an independent Basic Service Set (BSS), and the operating bandwidth (Operating BW) and operating channel of the BSSs operated by the APs may differ. When an AP MLD and a non-AP MLD are associated, setup can be performed between multiple APs belonging to a single AP MLD and multiple non-AP STAs belonging to a single non-AP MLD. In this case, since each AP belonging to the AP MLD operates a BSS on its own Link (Operating channel), the non-AP MLD associated with each of the multiple APs belonging to the single AP MLD is considered to have performed a Multi-Link setup. In other words, the AP MLD and non-AP MLD defined in Wi-Fi 7 can perform a Multi-Link setup connected across multiple Links.

[0185] Each MLD can have up to 15 STAs (AP STAs, non-AP STAs) attached. That is, 15 APs can be attached to an AP MLD, and each of the 15 APs operates an independent BSS. At this time, each AP attached to the AP MLD provides a level of service equivalent to that of a conventional Wi-Fi AP. In other words, each AP attached to the AP MLD functions as an independent AP and can perform services for non-AP STAs not attached to the MLD (e.g., legacy non-AP STAs). At this time, each AP attached to the AP MLD operates on a mutually independent Link, and the meaning of the Link refers only to the operating channel in which each AP operates, not a Link that distinguishes between 2.4 / 5 / 6 GHz. That is, the first AP attached to the AP MLD operates on the first Link, and the second AP can operate on the second Link. At this time, the first Link where the first AP is operated and the second Link where the second AP is operated can both be located in the 6 GHz band.

[0186] In addition, AP MLDs and non-AP MLDs can complete setup on multiple links through a Multi-Link setup procedure performed on a specific link. In this case, the Multi-Link setup procedure refers to the exchange of Multi-Link Probe Request / Response and Multi-Link Association Request / Response frames performed to establish a connection for one or more links. In the present invention, since the procedure for performing Multi-Link setup between AP MLDs and non-AP MLDs is not critical, a detailed description is omitted.

[0187] When two MLDs are connected via multiple links, it is possible for the two MLDs to operate the traffic transmitted and received through each link separately. This may be achieved through TID-to-Link mapping negotiations performed between the two MLDs or by applying the TID-to-Link mapping status instructed by the AP MLD. In this case, the TID-to-Link mapping status instructed by the AP MLD to non-AP MLDs is indicated by management frames (e.g., Beacon or Probe Response frames) transmitted by the AP MLD, and non-AP MLDs associated with the AP MLD through at least one link must operate their respective links in accordance with the TID-to-Link mapping instructed by the AP MLD. However, if a new TID-to-Link mapping negotiation is performed between the AP MLD and the non-AP MLD, the traffic (MPDU) of each TID may be transmitted and received through different links according to the method determined by the new TID-to-Link mapping negotiation. For example, if an AP MLD and a non-AP MLD are connected through two links, and TIDs 0 to 3 are mapped to Link 1 and TIDs 4 to 7 are mapped to Link 2, then the AP MLD and the non-AP MLD must transmit and receive only MPDUs with TIDs 0 to 3 through Link 1, and transmit and receive MPDUs with TIDs 4 to 7 through Link 2.

[0188] If the AP MLD has not indicated a separate TID-to-Link mapping state and there is no TID-to-Link mapping performed between the AP MLD and the non-AP MLD, the AP MLD and the non-AP MLD have a Default TID-to-Link mapping state. The Default TID-to-Link mapping state means that all TIDs are mapped to each Link, and in this case, the AP MLD and the non-AP MLD send and receive MPDUs of all TIDs (TID = 0 to 7) on each Link.

[0189] Since Wi-Fi 8 (UHR, Ultra High Reliability) is planned to be developed based on Wi-Fi 7, the MLD concept, connection procedures between MLDs, and methods of operating links through TID-to-Link mapping will still be inherited in Wi-Fi 8. In other words, it is possible for an AP belonging to an AP MLD to be a UHR STA, and it is also possible for a non-AP STA belonging to a non-AP MLD to be a UHR STA.

[0190] <MLD의 채널 접속>

[0191] Figure 11 shows a mapping table of User priority and Access Category.

[0192] Each STA belonging to the MLD performs channel access in the same way as conventional Wi-Fi terminals. More specifically, each STA performs channel access using EDCA (Enhanced Distributed Channel Access).

[0193] The channel access mechanism using EDCA is a commonly used method for accessing channels in the unlicensed band.

[0194] EDCA provides a mechanism for managing traffic by differentiating it into four types of access categories (ACs) based on their characteristics. These four types of ACs are AC_VO (AC Voice), AC_VI (AC Video), AC_BE (AC Best Effort), and AC_BK (AC Background), and each AC can have different contention window (CW), transmit opportunity (TXOP), and AIFSN parameters. Simply put, EDCA is a mechanism that controls the transmission priority of traffic transmitted by utilizing each AC by differentiating the CW, TXOP, and AIFSN parameters for the four types of ACs. To this end, EDCA can map traffic (MSDU) that a MAC must service to one of the four ACs according to the traffic category (TC) or traffic stream (TS). At this time, the traffic mapped to one of the four ACs by EDCA is distributed and managed across four queues for each AC. In this case, the four queues may be logically separated rather than physically separated. At this time, packets mapped to each AC and stored in the Transmission queue are transmitted when each AC completes the backoff procedure and acquires channel access rights. At this time, since the method by which an AC performs the backoff procedure to acquire channel access rights has been explained in Fig. 6, a detailed explanation is omitted.

[0195] AC_VO is an AC that can be used for traffic that is vulnerable to transmission delays, such as voice traffic, where the absolute amount of traffic is not large. It has relatively small CW and AIFSN parameter values ​​to increase the probability of being serviced preferentially over traffic from other ACs. However, the TXOP parameter of AC_VO is limited to a value relatively smaller than the TXOP parameter of other ACs, so only a shorter transmission time than other ACs is guaranteed.

[0196] AC_VI is an AC that is more robust to transmission delay than Voice traffic, but can be used for traffic such as Video that still requires low-latency transmission and needs to handle a large amount of traffic. AC_VI has CW and AIFSN parameter values ​​that are larger than AC_VO but smaller than other ACs, and instead, TXOP is about twice as long as AC_VI.

[0197] AC_BE is an AC that can be used for traffic robust to transmission delay, and most general traffic, excluding voice data and streaming video data, can be classified as AC_BE. AC_BE uses larger values ​​for the CW and AIFSN parameters than AC_VO and AC_VI. Additionally, AC_BE does not have a separate TXOP, and therefore cannot utilize the TXOP transmission sequence of transmitting a PPDU, receiving an ACK, and then transmitting a PPDU again after SIFS.

[0198] AC_BK is an AC that is robust to transmission delay, similar to AC_BE, but can be used for traffic with a lower priority than BE traffic. AC_BK uses the same CW parameter values ​​as AC_BE, and uses larger AIFSN parameter values ​​than AC_BE. Additionally, like AC_BE, AC_BK does not have a separate TXOP, so it cannot utilize the TXOP transmission sequence.

[0199] The four types of EDCA ACs described above are mapped to the UP (user-priority) of 802.1D, and the EDCA AC is determined based on the UP value of the traffic received via wire or the TID of the MSDU indicated by the upper layer. In this case, if the TID of the MSDU indicates a value from 0 to 7, the value indicated by the TID can correspond one-to-one with the UP.

[0200] The rules for mapping 802.1D UP and EDCA AC are explained by the UP-to-AC mappings table shown in Fig. 43.

[0201] In addition, the default CW (CWmin, CWmax), AIFSN, and TXOP parameters for each of the four types of EDCA ACs described above are defined in the standard, and the parameter values ​​of each AC can be changed by the AP and different values ​​can be used for each BSS.

[0202] When utilizing the EDCA mechanism, Wi-Fi traffic is stored in one of four queues corresponding to four ACs, and can be transmitted to a destination device only if the AC to which it belongs wins the channel access competition against other ACs. In this case, during the channel access competition between the ACs, each AC competes using the access parameters (CW[AC], AIFSN[AC]) assigned to it, and the channel access competition operation performed by each AC is the same as DCF. In this case, if a specific AC does not have any traffic to transmit in the queue, the specific AC may not participate in the competition.

[0203] However, as mentioned above, since the CW and AIFSN parameter values ​​utilized by each AC differ, the AC_VO with the smallest CW and AIFSN parameters has a high probability of winning the channel access competition against other ACs, and therefore, it is highly likely that the traffic of AC_VO will be serviced preferentially over the traffic of other ACs.

[0204] In addition, the EDCA mechanism stipulates internal competition rules, such as when an internal collision occurs between ACs, the AC with higher priority (see Fig. 11) wins and increases the CW of the other AC that caused the collision, and rules for configuring PPDUs including traffic from ACs other than the winning AC (primary AC), but since these details are not significantly related to the proposal of the present invention, a detailed explanation is omitted.

[0205] As described above, each STA belonging to an MLD performs channel access in the same way as conventional Wi-Fi terminals. That is, when observing each STA belonging to an MLD from each Link, each STA belonging to an MLD performs channel access in the same way that non-MLD STAs (QoS STAs) not belonging to an MLD perform channel access. This can be described as a rule defined when developing Wi-Fi 7, taking into account equity with existing non-MLD STAs operating on each Link.

[0206] However, there is an exception defined for MLDs operating on an NSTR (Nonsimultaneous transmit and receive) link pair. More specifically, the STA of an MLD operating on an NSTR (Nonsimultaneous transmit and receive) link pair is allowed to delay the start of transmission when the backoff procedure is completed in order to match the start time of transmission with transmissions performed on other links.

[0207] An NSTR link pair refers to a link pair among which an MLD's STA operates that causes strong interference to the remaining links when the MLD performs transmission on a specific link. For example, if Link 1 and Link 2 are an NSTR link pair of a non-AP MLD, when non-AP STA1 of the non-AP MLD operating on Link 1 performs transmission, non-AP STA2 of the non-AP MLD operating on Link 2 is subjected to strong interference. Consequently, while non-AP STA1 is performing transmission, non-AP STA2 is unable to determine whether Link 2 is idle or busy, or to receive incoming PPDU normally. In this case, the non-AP MLD faces the problem that, despite operating STAs on two links, normal operation of the other link is impossible when transmission is performed on one link. To mitigate this problem, Wi-Fi 7 introduced a mechanism that allows a non-AP MLD to initiate simultaneous transmission on an NSTR link pair. To briefly explain the mechanism for initiating simultaneous transmission, it is a mechanism that enables simultaneous initiation of transmission on the first and second links by delaying transmission until the backoff procedure performed on the second link is completed, even if the non-AP MLD has completed the backoff procedure on the first link.

[0208] In addition, an exception rule is defined to allow a response frame (e.g., CTS frame) not to be sent even if a frame requesting a response (e.g., RTS frame) is received from the other link of the NSTR link pair while a PPDU is being received on one of the links of the NSTR link pair.

[0209] As described above, since an NSTR link pair is characterized by the fact that interference caused by transmission performed by an STA operating on a specific link makes it impossible for an STA operating on another link to operate normally (inability to receive CCA and / or PPDU), the same link pair may be an NSTR link pair for a specific MLD and an STR link pair (Simultaneous transmit and receive) for another MLD. In this case, an STR link pair refers to a link pair in which the transmission performed by each STA operating on each link of the STR link pair does not affect an STA operating on another link, and thus allows for the reception of PPDU on another link while PPDU transmission is being performed on a specific link.

[0210] As such, each link pair can become an STR link pair for a specific MLD or an NSTR link pair for another MLD, depending on the interference shielding capability of each MLD. However, if the operating channels of a specific link pair overlap, the said specific link pair must inevitably become an NSTR link pair regardless of the characteristics / performance of the MLD. Accordingly, Wi-Fi 7 stipulates that when performing a Multi-Link setup in which an AP MLD and a non-AP MLD are connected through multiple links, the operating channels of the BSSs operating on each link where the setup is performed must be adjusted so that they do not overlap. In other words, the operating channels of each link where the AP MLD and the non-AP MLD perform the Multi-Link setup do not overlap.

[0211] <Problem of Primary Channel (or Main Channel) Dependency in Conventional Wi-Fi Channel Access Procedures>

[0212] The reasons for introducing MLD are: 1) to increase throughput by utilizing multiple links, and 2) to acquire channel access rights faster than performing channel access through a single link by executing channel access procedures across multiple links (acquiring rights quickly by performing channel access through one of the multiple links). However, the method of improving channel access opportunities by simultaneously executing channel access procedures on multiple links can lead to significant power consumption as the number of links performing the procedures increases. In other words, while MLD can perform channel access on multiple links to increase the probability (frequency) of channel access, it faces issues due to the power consumption required when performing channel access on multiple links. Therefore, using multiple links as a solution to increase the probability (frequency) of channel access can be considered a limited solution, and a method is needed to increase the success probability (frequency) of the channel access procedures performed on each link. For example, to acquire channel access rights faster than performing channel access through a single link, channel access procedures can be executed through one or more links, but a number of links below a certain limit may be used to account for power consumption. For example, if the channel access procedure cannot be performed on the primary channel, the channel access procedure can be performed by selecting one of the idle non-primary channels (such as a non-primary channel or a secondary channel) without waiting until the primary channel changes to an idle state.

[0213] Therefore, in order to support the development goal of Wi-Fi 8, 'Ultra High Reliability (UHR),' it is necessary not only to optimize the utilization of multiple links, which is a characteristic of MLD, but also to provide a method to support STAs operating on each link to obtain channel access opportunities in the best way.

[0214] In this context, it is necessary to analyze the channel accessibility issues of Wi-Fi terminals performing channel access on each link. Wi-Fi standards have achieved significant throughput performance improvements over successive generations, and the Wi-Fi 7 standard, which is currently in the final stages of standardization, supports throughput exceeding 30 Gbps. One of the reasons why the Wi-Fi 7 standard can support extremely high throughput compared to legacy Wi-Fi standards is its wide Operating Batch (OB) bandwidth. While conventional Wi-Fi terminals use a 20 MHz band as their Operating Batch, Wi-Fi 7 operates with an Operating Batch reaching up to 320 MHz. This means that the increase in maximum throughput achieved solely through the expansion of the maximum operating bandwidth supported by the Wi-Fi standard amounts to 16 times. However, the increased maximum throughput of the Wi-Fi standard resulting from the expansion of the Operating Batch is merely a nominal figure, and there are aspects where it is difficult to translate into actual performance improvements for Wi-Fi terminals.

[0215] In other words, despite the continuous expansion of the maximum supported operating bandwidth through the advancement of Wi-Fi terminals and standards, the impact on the actual performance of Wi-Fi terminals is relatively small. This is due to the low probability that the entire broadband included within the maximum operating bandwidth will be identified as idle at the time the Wi-Fi terminal establishes a channel, and the fact that the method by which Wi-Fi terminals establish channels involves an excessively high dependency on the Primary 20 MHz channel. Among these, the problem of the low probability that the entire wideband included in the operating bandwidth will be identified as idle may be an inherent issue stemming from the fact that the frequency band in which the Wi-Fi terminal operates is an unlicensed band. That is, it is natural for the medium to be occupied by other devices operating in the unlicensed band, and it is impossible to increase the probability of a Wi-Fi terminal establishing a channel by addressing this issue. However, the problem of excessive dependency on the primary 20 MHz channel is not a characteristic of Wi-Fi maintained for harmonious operation with heterogeneous devices, but rather a characteristic inherited from the process of maintaining the channel access method traditionally used in conventional Wi-Fi. To explain in more detail, the Wi-Fi standard was designed to perform channel access to a 40 MHz channel by extending the channel access method used when the operating BW was 20 MHz.More specifically, the method of accessing the 40 MHz channel according to the method defined in the Wi-Fi standard is to perform access to the 40 MHz band (40 MHz band including the Primary 20 MHz and Secondary 20 MHz bands) if, at the time the backoff procedure on the Primary 20 MHz channel is completed, the Secondary 20 MHz channel is identified as IDLE for the past PIFS (Priority Inter Frame Space, aSIFSTime (16 us) + aSlotTime (9 us)). Similarly, the method of accessing the 80 MHz channel according to the method defined in the Wi-Fi standard is to perform access to the 80 MHz band (an 80 MHz band including the Primary 20 MHz, Secondary 20 MHz, and Secondary 40 MHz bands) if, at the time the backoff procedure on the Primary 20 MHz channel is completed, the Secondary 20 MHz channel and Secondary 40 MHz channel are identified as IDLE during the past PIFS (Priority Inter Frame Space, aSIFSTime (16 us) + aSlotTime (9 us)). In this way, the Wi-Fi Wide Band Operation method of accessing subchannels identified as IDLE during the PIFS when the backoff procedure on the Primary 20 MHz channel is completed is applied in the same manner when accessing the 320 MHz BW defined in Wi-Fi 7. The reason this method has been repeatedly used is that it enables wide bandwidth access in a more energy-efficient and less burdensome way for hardware implementation by performing backoff on only one channel (primary channel) and determining whether other subchannels are accessible within a short time interval.

[0216] However, this method of channel access using a primary channel has a major disadvantage in that when the primary 20 MHz channel where the Wi-Fi terminal performs the backoff procedure is identified as idle, the backoff procedure of the Wi-Fi terminal cannot be completed even if all sub-channels excluding the primary 20 MHz channel are available (not occupied by other devices), and accordingly, channel access to wide idle sub-channels is also impossible.

[0217] As mentioned above, the problem of channel access being limited by the CCA result of the Primary 20 MHz subchannel for Wi-Fi terminals supporting broadband operation is not a new issue in UHR. However, in the case of UHR, which succeeds Wi-Fi 7 and supports ultra-broadband operation up to 320 MHz, the losses incurred due to the aforementioned dependency on the Primary 20 MHz subchannel may be greater than those of conventional Wi-Fi standards. Furthermore, next-generation standards following UHR may also experience performance degradation due to the aforementioned dependency on the Primary 20 MHz subchannel; therefore, it is clear that there is a need to resolve the channel access problem related to the aforementioned Primary 20 MHz subchannel.

[0218] For this reason, the present invention provides a method and procedure for a terminal supporting broadband operation to perform communication using a subchannel other than the Primary 20 MHz subchannel determined to be BUSY when the CCA result for the Primary 20 MHz subchannel is BUSY.

[0219] For example, if a preamble of a PPDU is received through a Primary 20 MHz subchannel and, as a result of performing a CCA based on the received preamble, it is determined that the Primary 20 MHz subchannel is busy, a channel access procedure may be performed by selecting one of the other subchannels (non-Primary 20 MHz subchannels) other than the Primary 20 MHz subchannel. The other subchannels where the channel access procedure is performed, other than the Primary 20 MHz subchannel, may be included in an operating channel that is the same as or different from the Primary 20 MHz.

[0220] Channel access that does not utilize the primary channel

[0221] As the simplest method to resolve the dependency issue regarding the aforementioned Primary 20 MHz sub-channel (hereinafter P20 channel), a method of performing channel access using (through) other sub-channels (non-primary channels (or sub-channels)) excluding the P20 channel may be considered. In this case, performing channel access using (through) a non-primary channel means performing a backoff procedure based on whether the non-primary channel is idle or busy. In this case, there may be one or more non-primary channels through which the terminal can perform the backoff procedure. That is, the terminal can perform the backoff procedure through the P20 channel or multiple non-primary channels (e.g., a first non-primary channel or a second non-primary channel, etc.). In this case, the channels through which the terminal can perform the backoff procedure (i.e., P20, the first non-primary channel, the second non-primary channel, the third non-primary channel, etc.) may each be 20 MHz sub-channels included in different 80 MHz subblocks. That is, the first non-primary channel may be located in an 80 MHz subblock other than the 80 MHz subblock containing the P20 channel. That is, when the terminal selects a different backoff channel (non-primary channel) excluding P20, it must select a different backoff channel (non-primary channel) from among the 20 MHz sub-channels of an 80 MHz subblock that does not contain the P20 sub-channel (i.e., a subblock excluding the Primary 80 MHz subblock). At this time, each different backoff channel selected by the terminal may be located in a different 80 MHz subblock. That is, the first non-primary channel may be a sub-channel located in an 80 MHz subblock different from the second non-primary channel.In this case, the selection restriction for the non-primary channel related to the aforementioned 80 MHz subblock may apply only when the operating channel of the BSS is included in the 5 GHz or 6 GHz band.

[0222] In this case, channel access using a non-primary channel may be performed only during the time interval when the P20 channel is determined to be BUSY. That is, channel access using a non-primary channel (hereinafter referred to as non-primary channel access) may be performed only when the P20 channel is determined to be Busy as a result of Physical CCA (ED, Energy detection), PD, and Virtual CCA. Additionally, non-primary channel access may be allowed only to STAs (AP STA, non-AP STA) for which the P20 channel is BUSY and the frame identified in the P20 channel is not a frame intended for itself as a destination device. Therefore, the above non-primary channel access procedure may be allowed only restrictively when the preamble of the PPDU received in the P20 channel is successfully detected or the MPDU is successfully decoded. Accordingly, the above non-primary channel access procedure may be allowed restrictively to STAs that have successfully received the frame received in the P20 channel.

[0223] That is, when an MLD (AP MLD or non-AP MLD) operates on one P20 and one or more non-primary channels, one of the STAs (AP or non-AP) constituting the MLD can perform a channel access procedure on the P20 channel. In this case, the STA can receive a preamble of a PPDU on the P20 channel and perform a CCA based on the preamble. If the CCA result determines that the P20 channel is busy and the PPDU received on the P20 channel was transmitted from an overlapping BSS (OBSS), the STA can select one of the one or more non-primary channels and perform a channel access procedure through the selected non-primary channel. The state of the non-primary channel where the channel access procedure is performed may be idle.

[0224] That is, backoff and channel access procedures using sub-channels other than the P20 channel may be limited to cases where the PPDU identified in the P20 channel is a PPDU of the OBSS. Therefore, backoff and channel access procedures using other sub-channels may be allowed restrictively only when the PPDU identified in the P20 channel is a PPDU that does not have the device receiving the PPDU as the destination device.

[0225] To this end, the backoff and channel connection procedure using a sub-channel other than the P20 channel may be initiated after decoding the preamble of the PPDU to check the BSS Color of HE-SIG and / or U-SIG, or the STA-ID of EHT-SIG and / or UHR-SIG, or decoding the first MAC frame of the PPDU to check the destination device or OBSS of the PPDU confirmed in the P20 channel. That is, the STA may check the BSS Color included in the SIG field (e.g., HE-SIG (HE-SIG-A or HE-SIG-B), or U-SIG) included in the preamble of the PPDU, or check the station identifier (STA-ID) included in the SIG field (e.g., HE-SIG-B, EHT-SIG or UHR-SIG) to determine whether the received PPDU was transmitted from the OBSS. Alternatively, the STA can identify the destination device by decoding the first MAC frame of the PPDU.

[0226] In this case, if the sender / receiver of a specific PPDU and the sender / receiver MAC addresses of the frame included in the PPDU are APs that have been associated with it, the specific PPDU may be classified as a PPDU (Intra-BSS PPDU) rather than an OBSS PPDU. In this case, a backoff procedure using sub-channels other than the P20 channel may need to be initiated after checking whether the other sub-channels are idle during DIFS. In this case, if the identified BSS Color is not its own BSS Color, STA-ID and MAC frame decoding performed to identify the destination device may be omitted. In this case, the method for checking whether the other sub-channels are idle may be to perform PHY CCA (Energy detection and / or Packet detection) for a preset time. In this case, the preset time may be PIFS (Priority Inter Frame Space), DIFS (Distributed Inter Frame Space), or MediumSync time. In this case, MediumSync time may be a time interval with a different name, and it refers to the time during which a device intended to perform a backoff procedure on a non-primary channel (or sub-channel) must perform CCA to determine whether the medium is IDLE or BUSY. MediumSync time can have a length of several milliseconds and is shorter than the MaxPPDU length (5.484 ms). A terminal performing CCA by applying MediumSync time can set the NAV using information contained in the PPDU (frame) received during the CCA execution.In this case, the NAV set by the terminal based on the PPDU (frame) received from the S20 channel (a sub-channel other than the Primary 20 MHz channel) may be a different NAV than the two NAVs (Basic NAV, Intra-BSS NAV) used in conventional Wi-Fi. In this case, the other NAV is a timer set by the frame (PPDU) received through S20, and is a NAV used for the Virtual CCA of the S20 channel when performing channel access through the S20 channel. That is, even if the value of the other NAV is not zero, the terminal can determine the result of the CCA performed on the P20 channel as IDLE, even if the other NAV is set by the frame (PPDU) received from the S20 channel. In other words, the other NAV is a NAV for the S20 channel, not the P20 channel. In this case, the other NAV can be referred to as a secondary NAV.

[0227] Therefore, if the terminal performing channel access via the S20 channel is an AP STA, the AP may need to manage both a basic NAV, which is set based on the received frame (PPDU) while occupying the Primary 20 MHz sub-channel, and a secondary NAV, which is set based on the received frame (PPDU) without occupying the Primary 20 MHz sub-channel (i.e., received via the S20 channel). In other words, when performing channel access via the P20 channel, the AP must perform a backoff procedure considering the basic NAV, and when performing channel access via the S20 channel, it must perform a backoff procedure considering the secondary NAV. At this time, the secondary NAV may be a timer that is initialized to a Mediumsync time value when the terminal performing channel access via the P20 channel decides to perform channel access via the S20 channel. That is, when the AP decides to perform channel access via the S20 channel, it may need to initialize the secondary NAV to a Mediumsync time value simultaneously with starting the CCA for the S20 channel.

[0228] Additionally, an STA that has performed a frame exchange after performing a channel connection through a subchannel other than the Primary 20 MHz subchannel may need to perform a procedure to check whether the Primary 20 MHz subchannel is occupied by another BSS or other device when initiating the channel connection procedure on the Primary 20 MHz subchannel after the frame exchange performed through the other subchannel is completed. At this time, the method by which the STA checks whether the P20 channel is occupied by another BSS or other device may be to perform a CCA for the P20 channel during the MediumSync time. At this time, if the STA receives a valid PPDU (frame) while performing the CCA during the MediumSync timer, the STA may set the NAV for the P20 channel based on the information obtained through the received PPDU (frame). In this case, the STA may resume the channel connection procedure performed on the Primary 20 MHz subchannel when the set NAV is released (when the NAV timer becomes 0).

[0229] At this time, a backoff procedure using another sub-channel can be compensated for the time delayed in decoding the preamble of the PPDU identified in the P20 channel or decoding the MAC frame. In one embodiment, if 3-slot time (e.g., 27 us) is consumed to identify the destination device (or BSS Color) of the PPDU identified in the P20 channel, an operation to reduce the backoff counter used for channel access using a sub-channel other than the P20 channel by 3 at once may be allowed. Alternatively, since channel access using a sub-channel other than the P20 channel is an additional function not utilized by conventional devices, the operation to reduce the backoff counter at once may not be allowed, and the counter may be reduced sequentially by 1 after identifying the destination device of the PPDU identified in the P20 channel. That is, compensation for the backoff procedure delayed during the process of identifying the destination device of the PPDU identified in P20 may not be performed separately.

[0230] In the embodiments of the present invention described below, the process of verifying the destination device of the PPDU received on the P20 channel described above may be omitted for convenience of explanation. Therefore, even if not separately described, a channel connection procedure performed using a sub-channel other than the P20 channel should be understood to include the process of verifying the destination device of the PPDU received on the P20 channel described above.

[0231] Figure 12 shows an example of a channel access procedure through a non-primary channel when the state of the primary channel is busy.

[0232]

[0233] *231 Referring to Figure 12, if the CCA result of the Primary 20 MHz subchannel is determined to be busy, the terminal may perform channel access using a non-Primary 20 MHz subchannel other than the Primary 20 MHz subchannel.

[0234] Specifically, the STAs (AP STA, non-AP STA) constituting the MLD may perform channel access using a channel other than the P20 channel when the P20 channel is determined to be BUSY (for example, when the P20 channel is determined to be BUSY based on the CCA result of the received PPDU preamble). At this time, the operation of performing channel access may be to perform backoff according to the CCA result of the other channel. At this time, the backoff operation may be an operation to decrease the backoff counter by 1 when the result of the CCA performed in each slot on the other channel is IDLE. Additionally, the backoff operation may be an operation to maintain the backoff counter without decreasing it when the result of the CCA performed in each slot on the other channel is BUSY.

[0235] The S20 channels that can be utilized for channel access using 20 MHz sub-channels other than the aforementioned P20 channel are not specified as specific S20 channels and multiple channels may be utilized. For example, as in one embodiment of FIG. 12, assuming that the STA performs 320 MHz operation, channel access using the S20_1 channel included in the Secondary 80 MHz subblock as illustrated in FIG. 12, as well as channel access through S20_2 and S20_3 included in the Secondary 160 MHz subblock, may be possible. In this case, the number of S20 channels utilized by each STA for channel access may be determined according to the capability of each STA, or may be limited to one or two specific S20 channels. However, the STA may perform backoff only on one non-primary sub-channel per 80 MHz subblock. At this time, each non-primary sub-channel for which the STA performs backoff is a sub-channel determined by the AP, and is therefore indicated through a management frame transmitted by the AP. That is, the AP can indicate information about another sub-channel (S20) for which backoff can be performed when the primary channel (P20) is busy through a management frame transmitted by itself (e.g., Beacon, Probe Response, Association Response frame, etc.), and said other sub-channel is one of the sub-channels included in an 80 MHz sub-block other than the Primary 80 MHz sub-block.

[0236] Referring to FIG. 12 (a), the backoff counter utilized when performing channel connection on the P20 channel and the backoff counter utilized when performing channel access on the S20 channel may exist and be managed separately. In this case, the backoff counter utilized by each channel may be changed to a new value only when transmission is performed (backoff is completed) as a result of the channel connection performed by each channel. At this time, changing to the new value means changing to a new backoff counter selected using CW_min if transmission is successful, or changing to a new backoff counter selected using CW x 2 if transmission fails. That is, it does not mean an operation to reduce the backoff counter as a result of CCA. At this time, as described above, if there are multiple S20 channels performing channel connection, the multiple S20 channels may each have a backoff counter. At this time, the backoff counter for each S20 channel may exist by Access Category. That is, the terminal may need to manage a backoff counter separately for each AC for each S20 channel capable of performing backoff. That is, a terminal performing a backoff procedure through an S20 channel may internally perform a channel connection procedure using four ACs.

[0237] Referring to FIG. 12 (b), all S20 channels performing channel connection, including P20, can utilize a common backoff counter. As illustrated in FIG. 12 (b), as a result of the channel connection operation performed in P20 channel, the backoff counter was reduced from 5 to 3, and subsequently, P20 channel was changed to BUSY. According to one embodiment proposed in the present invention, when P20 channel is BUSY, S20 channel can perform a channel connection procedure, and the backoff counter that P20 reduced to 3 can be continued to be reduced according to the CCA result performed in S20_1 as shown in FIG. 13 (b). If S20_1 is also determined to be BUSY while reducing the backoff counter for channel connection, the backoff counter can be maintained as is until channel connection using S20_2 starts, or until P20 to S20_1 is determined to be IDLE. At this time, if channel connection using S20_2 is continued, it is understood as an embodiment in which there are two or more S20 channels used for channel connection, and if a backoff counter is maintained until P20 to S20_1 is determined to be IDLE, it can be understood as an embodiment in which there is one S20 channel used for channel connection.

[0238] Restrictions on transmission through non-primary channels

[0239] As explained above, an STA (non-AP STA or AP) constituting an MLD (non-AP MLD or AP MLD) operating on one primary channel and one or more non-primary channels can attempt a channel access procedure on the primary channel. At this time, if the primary channel is idle as a result of the CCA performed by the STA to perform the channel access procedure on the primary channel, the channel access procedure can be performed on the primary channel. However, if the primary channel is determined to be busy as a result of the CCA performed based on the preamble of the PPDU received on the primary channel, the STA cannot perform the channel access procedure until the primary channel changes to idle. Therefore, in this case, the STA can perform the channel access procedure by selecting one of the one or more non-primary channels that is idle, without waiting until the primary channel changes to idle.

[0240] In this way, an STA that performs a channel access procedure using a non-primary channel (channel S20) rather than a primary channel may be subject to a limitation on the length of the transmitted PPDU. The limitation on the transmission length of the PPDU may be necessary in two aspects. In this case, the length of the PPDU transmitted after performing a backoff procedure on channel S20 may be limited so that it ends before the end time of the PPDU recognized by the PPDU (and / or frame) confirmed on channel P20. That is, when an STA that performs channel access on a non-primary channel transmits a PPDU (second PPDU) on the non-primary channel, the length of the PPDU transmitted on the non-primary channel may be limited to the length of the PPDU (first PPDU) received for CCA on the primary channel. For example, the length of the second PPDU may be the same as or shorter than the length of the first PPDU. In this case, the length of the first PPDU for limiting the length of the second PPDU may be determined by the length field included in the preamble of the first PPDU.

[0241] One aspect requiring the above limitation may be to prevent problems that could occur when the transmission of an OBSS device occupying the P20 channel ends while a transmission initiated using the S20 channel continues. More specifically, transmissions performed after channel access via the S20 channel will be carried out through sub-channel(s) excluding the P20 channel, and there is a problem in that the AP cannot provide any services, such as sending / receiving or scanning, for the P20 channel during the transmission. Therefore, if the transmission of S20 ends later than the OBSS PPDU identified on the P20 channel, the AP cannot identify or receive other STA UL PPDUs or OBSS PPDUs that may be identified on the P20 channel. In this case, along with the problem of not being able to receive the STA's UL PPDU, problems may arise in the overall operation of the BBS because NAV settings based on the OBSS PPDU cannot be performed. Another aspect requiring the above limitation on PPDU transmission length may be to mitigate fairness issues. If a length limit is not applied to the transmission that occurs after channel access is performed through the S20 channel, it may cause fairness issues with conventional WiFi STAs that perform channel access only through the P20 channel. Therefore, along with limiting the number of S20 channels that can perform channel access through the aforementioned S20 channel, it may be necessary to mitigate the fairness issues with conventional WiFi STAs by limiting the length of the PPDU transmitted through channel access via the S20 channel.

[0242] Additionally, a device that performs channel access using a non-primary channel (S20 channel) rather than a primary channel (P20 channel) may be limited in the length of the TXOP obtained after performing a backoff procedure on a sub-channel (S20) other than the Primary 20 MHz channel. In this case, the length of the TXOP obtained after performing a backoff procedure on the S20 channel may be limited to end earlier than the TXOP end time of the OBSS recognized by the PPDU (and / or frame) received on the P20 channel. That is, a STA that performs channel access on a non-primary channel (S20 channel) rather than a primary channel (P20 channel) may have the length of the TXOP obtained through the channel access procedure limited. For example, the length of the TXOP (2nd TXOP) obtained by the STA through the channel access procedure of the non-primary channel may be the same as or shorter than the length of the TXOP (1st TXOP) based on the PPDU (1st PPDU) of the primary channel. At this time, the length of the first TXOP can be obtained based on the TXOP field included in the preamble of the first PPDU.

[0243] The above TXOP length limit may be necessary in two aspects. One aspect where the limit is necessary is to prevent problems that may occur when the TXOP of the OBSS device occupying the P20 channel ends while the TXOP acquired using the S20 channel (a sub-channel other than the Primary 20 MHz channel) persists. More specifically, the TXOP acquired through the S20 channel applies to the frequency range occupying the sub-channel(s) excluding the P20 channel, and while frame exchange is performed using the TXOP, terminals may be unable to perform transmission / reception, CCA, etc., on the P20 channel. Therefore, if the transmission of the S20 channel ends later than the TXOP of the OBSS identified on the P20 channel, terminals cannot identify and receive other OBSS PPDUs that can be identified on the P20 channel. In this case, problems may arise in the overall operation of the BBS because, along with the problem of not being able to receive the STA's UL PPDU, NAV settings via the OBSS PPDU cannot be performed. Another aspect requiring the above-mentioned limit on the PPDU transmission length may be to mitigate fairness issues. If a length limit on the TXOP obtained after performing channel access through the S20 channel is not applied, it may cause fairness issues with conventional Wi-Fi terminals that perform channel access only through the P20 channel. Therefore, along with limiting the number of S20 channels that can perform channel access through the aforementioned S20 channel, it may be necessary to mitigate fairness issues with conventional WiFi STAs by limiting the length of the TXOP obtained through channel access via the S20 channel.

[0244] FIG. 13 illustrates an example of a transmission length limit for PPDU transmitted after performing channel access through a non-primary channel.

[0245] Referring to FIG. 13, the length of the PPDU transmitted through the non-primary channel by the STA that performed the channel access procedure through the non-primary channel (S20 channel) rather than the primary channel (P20 channel) described above may be limited to be equal to or shorter than the length of the PPDU transmitted through the primary channel (e.g., the PPDU received by the STA through the primary channel for CCA).

[0246] Specifically, a situation is illustrated in which a terminal confirming that the P20 channel is BUSY completes a backoff procedure through the S20_1 channel and transmits a PPDU. At this time, the backoff counter of the backoff procedure performed on the S20_1 channel may be a backoff counter shared with the backoff counter used on the P20 channel, or it may be a separate backoff counter used for channel access through the S20_1 channel. Although the S20 channels are shown as being in the same 80 MHz subblock as the P20 channel in FIG. 13, the S20 channels that perform backoff when the P20 channel is BUSY may be located in an 80 MHz subblock different from the 80 MHz subblock containing the P20 channel.

[0247] Before initiating channel access through channel S20_1, the STA detects the preamble of the OBSS PPDU while attempting channel access through channel P20 and confirms that channel P20 is occupied (BUSY) by OBSS. In this situation, the STA can perform decoding on the preamble of the OBSS PPDU to determine how long the OBSS PPDU will last. At this time, the action performed by the STA after determining how long the OBSS PPDU will last may be to set the NAV. At this time, the STA can determine the duration of the OBSS PPDU by checking the L-SIG and Length fields of the detected preamble, or by using the value indicated by the TXOP field included in the U-SIG field and / or HE-SIG field of the OBSS PPDU. Alternatively, the STA can determine the duration of the OBSS PPDU based on the Duration / ID field of the MAC frame included in the PPDU.

[0248] Subsequently, the STA can determine the length of the PPDU transmitted after establishing a channel connection through the S20 channel based on the end time of the OBSS PPDU identified in the P20 channel. At this time, the length of the PPDU transmitted after establishing a channel connection through the S20 channel may be limited / adjusted so that it ends at or earlier than the predicted end time of the OBSS PPDU identified in the P20 channel. At this time, the method of limiting the length of the PPDU may be to adjust the end time of the Response frame expected to be responded to the PPDU so that it ends at or earlier than the end time of the OBSS PPDU. At this time, the Response frame refers to a PPDU including an ACK frame or a Block ACK frame, and a TB (Trigger-Based) PPDU, etc. In other words, the end time of the PPDU responded to by the PPDU may be limited so that it is earlier than or equal to the predicted end time of the OBSS PPDU identified in the P20 channel.

[0249] FIG. 14 illustrates an example of a method for limiting the length of a TXOP obtained through channel access via a non-primary channel.

[0250] Referring to FIG. 14, the length of a TXOP based on a PPDU transmitted through a non-primary channel (S20 channel) by an STA that has performed a channel access procedure through a non-primary channel other than the primary channel (P20 channel) described above may be limited to be equal to or shorter than the length of a TXOP based on a PPDU transmitted through the primary channel (e.g., a PPDU received by the STA through the primary channel for CCA).

[0251] Specifically, a situation is illustrated in which a terminal that has confirmed that the P20 channel is BUSY completes a backoff procedure through a sub-channel (S20 channel) included in a Secondary 80 MHz subblock and acquires a TXOP. At this time, the backoff counter of the backoff procedure performed through the S20 channel may be a backoff counter shared with the backoff counter used in the P20 channel, or it may be a separate backoff counter used when performing a backoff operation in a sub-channel included in the Secondary 80 MHz subblock.

[0252] A terminal intending to perform a backoff procedure via S20 when it is confirmed that the P20 channel is BUSY performs CCA on the S20 channel during a time interval corresponding to the MediumSync time to protect the communication of the OBSS, which may be in progress transmitting / receiving using the S20 channel. In FIG. 14, the state of S20 observed by the terminal during the time corresponding to the MediumSync time is IDLE, and therefore the terminal initiates a backoff procedure on the S20 channel.

[0253] When the terminal completes the backoff procedure performed through the S20 channel, the TXOP acquired by the terminal is set to terminate at the same time as the TXOP (OBSS TXOP) containing the frame (RTS / CTS frame of FIG. 14) transmitted by occupying the P20 channel. At this time, although the embodiment of FIG. 14 shows that the two TXOPs terminate at the same time, the TXOP acquired after performing backoff through the sub-channel included in the Secondary 80 MHz subblock may be set to terminate earlier than the OBSS TXOP.

[0254] When a terminal that acquires a TXOP after performing backoff through the S20 channel checks the TXOP length of the OBSS occupying the P20 channel, it may utilize the Duration / ID field of the (MU-)RTS and / or CTS and / or BSRP (Buffer Status Report Poll) / BSR (Buffer Status Report) frame received in the Primary 20 MHz subchannel. That is, when a frame transmitted by the STA of the OBSS is received through the Primary 20 MHz subchannel, the terminal checks the TXOP length of the OBSS based on the information indicated by the Duration / ID field of the received frame. In this case, the terminal sets the NAV corresponding to the Primary 20 MHz subchannel based on the confirmed length, and when acquiring a TXOP after completing the channel access procedure (backoff procedure) through the subchannel included in the Secondary 80 MHz subblock, it must adjust its own TXOP length so that the TXOP it acquired terminates simultaneously with or before the TXOP of the confirmed OBSS.

[0255] After the TXOP obtained through the S20 channel is terminated, the terminal performs CCA for the P20 channel during the interval corresponding to the MediumSync time to resume channel access through P20. If a valid frame (PPDU) is received before the time corresponding to the MediumSync time has elapsed, the terminal sets the NAV based on information obtained through the field related to the length of the received frame (PPDU), and can resume the channel access procedure through the P20 channel when the NAV is released. In the example of FIG. 14, P20 was observed in an IDLE state until the time corresponding to the MediumSync time had elapsed completely, and therefore the terminal resumed the channel access procedure after the time corresponding to the MediumSync time had expired.

[0256] <S20 채널(넌 프라이머리 채널)을 통한 채널 접속 절차의 제한>

[0257] A series of channel access procedures performed through the aforementioned S20 channel may be channel access procedures permitted only to AP STAs. In other words, channel access procedures through the S20 channel, rather than the P20 channel, may be channel access procedures that non-AP STAs cannot perform.

[0258] The reason the channel access procedure via the S20 channel is permitted only to AP STAs is that even among STAs belonging to a single BSS, the status of the P20 channel identified by each STA may differ. Assuming a situation where a first non-AP STA and a second non-AP STA are associated with a BSS operated by an AP, the first non-AP STA may recognize that the P20 channel is BUSY after receiving a PPDU transmitted from the OBSS, whereas the AP and the second non-AP STA may recognize that the P20 channel is IDLE because the said PPDU was not received. Additionally, there may be cases where the first non-AP STA fails to receive the PPDU that the second non-AP STA received. As such, the status of the P20 channel identified by each non-AP STA belonging to the same BSS may differ, and it is also possible for the status of the P20 channel identified by each STA to differ from the status of the P20 channel identified by the AP. In this case, even if a non-AP STA determines that channel P20 is busy and establishes a channel connection via channel S20 to transmit a UL PPDU, it is possible for the AP to determine that P20 is idle and continue the channel connection procedure on channel P20. In other words, if the AP confirms that channel P20 is idle, it is impossible for the AP to properly receive the PPDU transmitted by the non-AP STA after establishing a channel connection on S20. Furthermore, while a non-AP STA determines that channel P20 is busy and establishes a channel connection on channel S20 to transmit a UL PPDU, the AP may transmit a PPDU to the non-AP STA after completing the channel connection on channel P20. In this case, a problem arises where the non-AP STA is unable to properly process the PPDU received on P20 due to the PPDU transmission being performed on channel S20.As such, since the status of the P20 channel confirmed by each STA (AP STA and non-AP STA) belonging to the BSS may differ, each non-AP STA may be restricted from performing the channel access procedure on the S20 channel even if it determines that the P20 channel it has confirmed is in a BUSY state. However, when a non-AP STA determines that the P20 channel is in a BUSY state, it may need to wait for the reception of a PPDU that may be transmitted on the S20 channel.

[0259] In the case of an AP, after establishing a channel connection on the S20 channel, it may need to transmit a frame of a pre-configured format as the first frame transmitted after establishing the channel connection on the S20 channel in order to check whether the receiving device of the frames it intends to transmit is in a state where it can receive on the S20 channel. At this time, the pre-configured format may be an RTS (Request To Send), MU-RTS (Multi-User RTS), BSRP (Buffer Status Report Poll), or another type of trigger frame. That is, the AP may need to include the frame of the pre-configured format in the first PPDU transmitted after establishing a channel connection through the S20 channel.

[0260] That is, for an AP that performs a channel connection procedure on the S20 channel rather than the P20 channel, the format of the first frame transmitted after the channel connection procedure may be a pre-configured format. For example, for an AP that performs a channel connection procedure on the S20 channel, the very first frame transmitted after the channel connection procedure may be a frame that does not contain data. That is, since the channel of the STA associated with the AP may not yet have changed after the channel connection procedure, the AP may transmit a frame of a specific format that does not contain data as its very first frame after the channel connection procedure.

[0261] At this time, the frame of the above-mentioned pre-configured format transmitted by the AP is a frame requesting an immediate response frame from one or more STAs, and therefore when the AP transmits the frame of the above-mentioned pre-configured format, a response frame is received from the STAs that receive it.

[0262] When AP receives response frames in response to a frame of a pre-configured format that it has transmitted, it can recognize that the STAs that transmitted the response frames are STAs capable of receiving the PPDU transmitted through S20. Accordingly, after transmitting a frame of a pre-configured format, AP can transmit frames to the destination devices of the STAs that responded with response frames to the frame through the next PPDU.

[0263] As a more specific example, the AP may request a response frame from the first STA and the second STA through a frame of a preset format transmitted after performing a channel connection via S20. At this time, if a response frame is received from the first STA but not from the second STA, the AP may include an MPDU with the first STA as the destination device in the PPDU transmitted next, and may not include an MPDU with the second STA as the destination device. That is, if the AP does not receive a response frame for the frame of the preset format transmitted via S20 from a specific STA, it must not include an MPDU with the specific STA as the destination device (individually addressed) in the PPDUs transmitted through the channel connection.

[0264] <S20을 통한 채널 접속의 규범적 동작 제한>

[0265] All terminals communicating using unlicensed bands must perform normative channel access operations to ensure that each terminal can access the medium in a harmonious and equitable manner. The ETSI (European Telecommunications Standards Institute) BRAN (Broadband Radio Access Networks) committee has defined harmonized standards regarding channel access methods for terminals utilizing unlicensed bands, and since Wi-Fi terminals also perform operations using unlicensed bands, they must follow the standards defined by the ETSI BRAN. The EDCA mechanism, which is the channel access method used in conventional Wi-Fi, is defined as one of the normative channel access methods through the ETSI BRAN; therefore, conventional Wi-Fi terminals perform channel access through the normative operations defined by the ETSI BRAN.

[0266] Among the norms defined in relation to the EDCA mechanism, there is a regulation regarding the change of the channel (main operating channel) that performs the backoff operation through the EDCA mechanism. Specifically, the regulation states that a terminal performing channel access through EDCA must not change the main operating channel more than once per second. That is, when the channel performing the backoff procedure (main operating channel) is changed, a terminal performing channel access through EDCA must perform channel access using that channel for at least 1 second. At this time, the time taken to perform channel access using a specific sub-channel may be calculated based on the start time of transmission of the first PPDU among the PPDUs transmitted after performing channel access using the specific sub-channel. That is, if the start time of the first PPDU transmitted after the terminal changed the main operating channel to S20 is T1, the terminal may change the main operating channel to a sub-channel other than S20 (Primary 20 MHz sub-channel or another sub-channel) starting from the point in time when 1 second has elapsed from T1.

[0267] Accordingly, the channel connection operation via the S20 channel provided in the present invention may be utilized in a limited manner when the channel connection operation via the P20 channel is maintained for 1 second or more. Additionally, a terminal that has performed the channel connection operation via the S20 channel must attempt the channel connection operation via the S20 channel for 1 second or more, and it is possible to switch to performing channel connection via the P20 channel while maintaining the channel connection operation via the S20 channel for 1 second or more. At this time, the above 1 second is for illustrative purposes only, and it is also possible for the same operation / restriction to be performed by applying a different pre-agreed time length.

[0268] That is, in order for a terminal to perform a channel access procedure on a non-primary channel, it must attempt a channel access procedure on the primary channel for a certain period of time (e.g., 1 second), and subsequently, when performing a channel access procedure on a non-primary channel, it must attempt a channel access procedure on the non-primary channel for a certain period of time (e.g., 1 second). For example, when a terminal performs a channel access procedure on a non-primary channel, it must perform an operation (e.g., a channel access procedure) on the non-primary channel for a certain period of time (e.g., 1 second).

[0269] That is, non-AP STAs that recognize that the AP has established a channel connection via the S20 channel may perform actions treating the S20 channel as the primary channel until the AP can establish a channel connection via the P20 channel. In other words, non-AP STAs that recognize that the AP has established a channel connection via the S20 channel must establish a channel connection on the S20 channel or wait for the reception of PPDUs transmitted by the AP until the AP transitions to a state where it can establish a channel connection on the P20 channel. At this time, the AP may instruct the non-AP STAs using a Management frame (e.g., a Beacon frame) it transmits, providing information regarding the time when it established a channel connection via the S20 channel or the time when it can transition to establishing a channel connection via the P20 channel. That is, the AP may instruct the non-AP STAs through a Management frame it transmits, providing information regarding the time when it transitions to establishing a channel connection via the P20 channel during the time interval when it must establish a channel connection via the S20 channel. When Non-AP STAs receive a Management frame transmitted by an AP, if the Management frame contains information regarding the timing of when the AP switches to a channel connection operation through the P20 channel, they can determine whether the channel connection execution channel of the AP is the P20 channel or the S20 channel based on the indicated information.

[0270] FIG. 15 illustrates a method for an AP to manage a main operation channel by acquiring a TXOP through a primary channel and a non-primary channel according to an embodiment of the present invention.

[0271] Referring to Fig. 15, in a situation where OBSS1 and OBSS2 exist in the Primary 80 MHz subblock and Secondary 80 MHz subblock, respectively, the AP performs channel access through a channel not occupied by OBSS by changing the main operating channel. The following description explains the AP's channel access operation in chronological order (from left to right based on the diagram).

[0272] When AP acquires TXOP1, it obtains channel access rights by completing the channel access procedure performed through P20. Since the TXOP of OBSS2 is in progress in the Secondary 80 MHz subblock at the time AP acquires the TXOP, AP has acquired channel access rights only for the Primary 80 MHz, and therefore TXOP1 applies only to the Primary 80 MHz subblock. Subsequently, AP completes the channel access procedure again at P20 and acquires TXOP2, which is a TXOP for the 160 MHz band. After TXOP2 is terminated, while AP is performing the channel access procedure to acquire TXOP3, the TXOP of OBSS1 is acquired in a manner that occupies P20, which is AP's primary operating channel, and thus AP's backoff procedure is interrupted. At this time, AP recognizes that S20 is also occupied by the TXOP of OBSS2 and maintains the primary operating channel without changing it. However, after the first TXOP of OBSS1 ends, the TXOP of OBSS1 starts again before the channel connection procedure of the AP resumed is completed, and the AP decides to change the main operating channel to S20. At this time, the AP is able to change the main operating channel to S20 because the time it maintained P20 as the main operating channel was 1 second or longer than 1 second.

[0273] Accordingly, AP performs channel access via S20 and acquires TXOP3 while the second TXOP of OBSS1 is in progress. After the TXOP of OBSS2 ends, AP completes the channel access procedure performed in S20 and acquires TXOP4, which is a TXOP for the 160 MHz band. Subsequently, the channel access procedure performed by AP in S20 is interrupted as the TXOP of OBSS2 begins. At this time, AP confirms that P20 is IDLE and decides to change the primary operating channel to P20. At this time, AP is able to change the primary operating channel to P20 because the time it maintained S20 as the primary operating channel was 1 second or longer than 1 second.

[0274] Multi-subchannel access using multi-links

[0275] As previously mentioned, if the change of the primary operating channel is allowed only once per second according to the normative operation defined by the ETSI BRAN committee, it is difficult to consider the problem of dependency on the primary channel, which is the fundamental concept of the present invention, as fully resolved. This is because, after a specific terminal changes the primary operating channel, the availability of channel access is determined by whether the changed primary operating channel is IDLE / BUSY for at least one second. In other words, the problem of dependency on the primary channel possessed by the Wi-Fi terminal can be alleviated only once per second at most, and for the remaining time intervals, the same problem of dependency on the changed primary operating channel is retained. That is, the problem that must be solved through the present invention is not the problem of dependency on the primary 20 MHz sub-channel of the Wi-Fi terminal, but the problem of dependency on the primary operating channel of the Wi-Fi terminal (the channel used for channel access, the reference channel for performing the backoff procedure). Therefore, the method of changing the main operating channel from P20 channel to S20 channel, and then changing it again from S20 channel to P20 channel or another S20 channel, only provides the effect of changing the channel designated as the main operating channel, but does not resolve the limitation that channel access for the entire Operating BW is restricted when a specific 20 MHz sub-channel (main operating channel) is determined to be BUSY.

[0276] As a method to resolve the dependency issue regarding the designated primary operating channel (channel access, i.e., the channel performing the EDCA backoff procedure) as described above, a method to reduce the importance of the designated primary operating channel may be considered. As the simplest method to reduce the importance of the designated primary operating channel, designating multiple primary operating channels for a single operating channel may be considered. When multiple primary operating channels are designated for a single operating channel, the channel access dependency issue of the Wi-Fi terminal for each primary operating channel can be mitigated in proportion to the number of designated primary operating channels.

[0277] <Method for assigning multiple primary operation channels to a single operation channel>

[0278] The operating bandwidth supported by Wi-Fi standards has continuously increased, and the Wi-Fi 7 standard supports an operating bandwidth of up to 320 MHz. Even when accessing an operating channel with such a wide bandwidth (e.g., 40, 80, 160, 320 MHz channels), a Wi-Fi terminal can only perform channel access after completing the backoff procedure on the primary 20 MHz subchannel. At this time, since the backoff procedure can only be completed when the primary 20 MHz subchannel is determined to be IDLE, the Wi-Fi terminal cannot obtain access rights to the wide channel reaching the 320 MHz band when the primary 20 MHz subchannel is determined to be BUSY. This is due to the aforementioned dependency issue of the Wi-Fi terminal on the primary operating channel, and the reason conventional Wi-Fi standards have maintained a channel access procedure with such a dependency issue is to minimize the increase in complexity of the Wi-Fi terminal.

[0279] To explain the aforementioned ETSI regulation in more detail, the ETSI regulation defined two different normative channel access methods for wide-bandwidth (band exceeding 20 MHz). The first normative channel access method involves obtaining channel access rights by using EDCA (or a channel access mechanism operating under rules similar to EDCA) on each of the 20 MHz sub-channels included in the wide-bandwidth to be accessed, and simultaneously performing access to one or more 20 MHz channels for which channel access rights have been obtained. That is, a terminal performing channel access for a band exceeding 20 MHz can perform the channel access procedure at each 20 MHz and, upon completing the channel access procedure, access the 20 MHz channels for which channel access rights have been obtained. The second normative channel access method for wide-bandwidth defined in the ETSI regulation is to access other 20 MHz channels together when the result of a measurement performed for more than 25 µs is confirmed to be idle after completing the channel access procedure on one main operating channel (one 20 MHz channel). The method by which conventional Wi-Fi terminals access the 40 MHz, 80 MHz, 160 MHz, and 320 MHz bands utilizes the aforementioned second normative channel access method defined in the ETSI regulation.

[0280] If a Wi-Fi terminal uses the first prescriptive channel access method defined in the aforementioned ETSI regulation, the Wi-Fi terminal can access each subchannel determined to be IDLE within the Operating BW more flexibly without dependency issues on specific subchannels. However, performing a separate channel access procedure for each 20 MHz channel included within the Operating BW incurs significant costs in other aspects, such as increasing the hardware / operational complexity of the Wi-Fi terminal and making the energy consumption required for the channel access procedure excessive.

[0281] For this reason, the latest Wi-Fi standard, Wi-Fi 7, does not introduce a method of performing channel access on each 20 MHz sub-channel to access each 20 MHz sub-channel, but inherits the conventional Wi-Fi channel access method of performing channel access on the primary 20 MHz channel, which is the main operating channel, and performing channel access on other sub-channels that are determined to be IDLE when the channel access procedure on the primary 20 MHz channel is completed.

[0282] The method for configuring an overlapping operating channel of an MLD, described through the embodiments of the present invention described below, is a method that maintains the conventional Wi-Fi channel access method in which each terminal attempts to access a wide bandwidth channel using a main operating channel, while reducing dependency on the main operating channel.

[0283] Auxiliary AP / Link / BSS

[0284] As previously explained, in Wi-Fi 7, Multi-Link Devices (MLDs) are defined, and AP MLDs and non-AP MLDs can be in a Multi-Link Setup (ML-setup) state, where setup is performed through multiple links. In this case, the Operating channels of each link where the AP MLD and non-AP MLD perform setup must be set up without overlapping. When the AP MLD and non-AP MLD are set up through multiple links, the BSS of the AP (AP belonging to the AP MLD) operating on each of the multiple links must be a BSS that operates through non-overlapping frequency ranges.

[0285] However, the Operating Boundaries of each AP belonging to the AP MLD are permitted to overlap. The rules regarding the operating channels of the Multi-Link setup performed by the AP MLD and the non-AP MLD are explained with a simpler example as follows. The AP MLD may operate the 1st AP, 2nd AP, and 3rd AP at Link 1, Link 2, and Link 3, respectively. In this case, the operating channels of the two BSSs operated by the 1st AP and the 2nd AP overlap (partially or fully overlapped), and the operating channel of the BSS operated by the 3rd AP does not overlap with the operating channels of the BSS operated by the 1st AP and the 2nd AP. The above AP MLD performs ML setup with the non-AP MLD, allowing ML setup states such as [Link 1, Link 3] and [Link 2, Link 3], but not allowing ML setup states such as [Link 1, Link 2] and [Link 1, Link 2, Link 3]. This is because Link 1 and Link 2 among the links where the non-AP MLD performed setup have overlapping operating channels. To summarize, while the BSS operating channels of each AP operated by the AP MLD can overlap with each other, the BSS operating channels of multiple links where each non-AP MLD performed ML setup are not allowed to overlap with each other. This is because if the BSS operating channel of a specific link where the non-AP MLD performed ML setup overlaps with the BSS operating channel of another link where ML setup was performed, the BSS of the specific link and the other link act as OBSS (Overlapping BSS) to each other, resulting in BSSs that cannot be serviced simultaneously.

[0286] According to one embodiment of the present invention, an AP MLD may be configured to overlap the operating channels (channels where the AP operates the BSS) of two or more APs for the purpose of strengthening channel access for non-primary channels. In this case, one of the APs with overlapping operating channels may be configured as the primary AP, and the remaining APs may be configured as auxiliary APs. A method for performing channel access using the primary AP and auxiliary APs is described below.<Overlapping AP를 이용한 채널 접속> It is explained through.

[0287] In the following description of the present invention, the links in which the Primary AP and the auxiliary AP operate are named the Primary link and the auxiliary link, respectively, and the BSS operated by the Primary AP is named the Primary BSS, and the BSS operated by the auxiliary AP is named the auxiliary BSS. Since the operating channels of the Primary BSS and the auxiliary BSS overlap with each other, in the following description of the present invention, the two APs are described as having an Overlapping AP relationship.

[0288] The auxiliary AP operated by the AP MLD has a paired Primary AP, and the operating channels of the paired auxiliary AP and the Primary AP overlap. The Primary AP and the auxiliary AP support different levels of operation. For example, the Primary AP periodically transmits Beacon frames (including Beacon frames and / or other types of Management frames, Group addressed frames), while the auxiliary AP may not transmit Beacon frames (including Beacon frames and / or other types of Management frames, Group addressed frames). As another example, the Primary AP supports services for Legacy STAs (i.e., STAs following older standards other than Wi-Fi 8, such as Wi-Fi 7 and Wi-Fi 6), but the auxiliary AP may be restricted from performing services for Legacy STAs. Additionally, the BSS operated by the auxiliary AP (Auxiliary BSS) may be a BSS in which only STAs of the non-AP MLD to which the STAs that are members of the BSS operated by the Primary AP paired with the auxiliary AP (Primary BSS) belong.

[0289] In other words, for a non-AP MLD to be set up on a secondary link, it must also be set up on the primary link paired with the secondary link. That is, when a non-AP MLD requests setup for a secondary link from an AP MLD, it must also request setup for the primary link paired with the secondary link. In other words, a non-AP MLD must not transmit a frame (e.g., an Association Request frame) requesting setup only for the secondary link among the pair of primary and secondary links. However, if both the non-AP MLD and the AP MLD have already been set up via the primary link, the non-AP MLD may make an additional setup request for the secondary link to the AP MLD. In this case, the frame transmitted by the non-AP MLD to request the addition of the secondary link may be a Link Reconfiguration Request frame.

[0290] That is, only non-AP MLDs that are set up with the Primary link can be set up together with the auxiliary link paired with the Primary link.

[0291] That is, when an AP MLD receives a request for a Multi-Link setup from a non-AP MLD, if the non-AP MLD requests only the setup for the auxiliary link and does not request the setup for the Primary link paired with the auxiliary link, the AP MLD must not approve the setup for the auxiliary link. However, the non-AP MLD may request the AP MLD to set up only the Primary link among the paired Primary link and auxiliary link. In this case, if the non-AP MLD requests the setup for the Primary link and the third link together (requests ML setup), the AP MLD may perform the ML setup connected through the Primary link and the third link.

[0292] <Overlapping AP>

[0293] The reason an AP MLD operates two (Primary AP and Secondary AP) or two or more (Primary AP and First Secondary AP, Second Secondary AP, etc.) APs with overlapping operating channels is to perform channel access through the Primary 20 MHz channels of the BSS operated by each AP, and to support services to non-AP MLDs through the AP that has completed channel access. In this case, the Primary AP and Secondary AP may be APs using independent radios, or APs operating using a single radio. However, while the AP MLD performs channel access through the Overlapping APs, it performs channel access through only one AP at a specific time. In this context, performing channel access means executing a series of procedures for channel access, such as reducing the backoff counter according to EDCA rules.

[0294] There may be an implementation in which the Primary AP and the Secondary AP are configured using independent radios. In this case, while the Primary AP performs PPDU transmission through the Primary 20 MHz subchannel, the Secondary AP can receive other PPDUs through the Secondary channel (the primary channel of the Secondary BSS) or perform CCA, PD (Packet Detection), etc. Thus, the Secondary AP having an independent radio can have the capability to function as a general AP when it is not designated as a Secondary AP by the AP.

[0295] Additionally, it is possible to implement a configuration where the Primary AP and the Auxiliary AP share a single radio. In this case, when the Primary AP transmits a PPDU through the Primary 20 MHz sub-channel, the Auxiliary AP cannot perform transmission / reception, CCA, PD, etc., on its own primary channel (auxiliary channel). This is because if the radio commonly used by both APs is used for the operation of the Primary AP, there will be no radio available for the Auxiliary AP to use. In other words, the Primary AP and the Auxiliary AP are APs that exist only logically separated, but physically, they may be APs operated using a single device (radio, RF chain, antenna, etc.). The reason the AP MLD can operate multiple APs (Primary AP and Auxiliary APs) using a single radio in this way is that at a specific point in time, the radio is utilized for only one AP among the multiple APs. That is, the AP MLD may not support channel connection or PPDU transmission / reception for the Auxiliary APs at the time when the channel connection procedure is being performed by the Primary AP or PPDU transmission / reception is being performed. In addition, multiple APs share a single radio and operate in such a way that support for the Primary AP and other auxiliary APs is not required when performing channel access procedures or transmitting / receiving PPDUs through a specific auxiliary AP. That is, the AP MLD can perform Single-Radio Multi-Link operation for the Primary link and the auxiliary link.

[0296] At this time, an AP MLD operating on multiple links using a single radio may lose MediumSync for the remaining links while performing channel access or PPDU transmission / reception on a specific link among the multiple links. In this case, losing MediumSync means that the management of the NAV timer, which should have been managed by receiving other PPDUs (frames) transmitted / received on each link, was not performed. Therefore, an AP MLD that has lost MediumSync for the remaining links due to operations performed through a specific link may need to recover MediumSync before performing channel access on the other links. At this time, to recover MediumSync for the link that lost MediumSync, the AP MLD may perform CCA on the link that lost MediumSync for a period corresponding to the MediumSync time. Alternatively, to recover MediumSync for the link that lost MediumSync, the AP MLD may instruct a specific non-AP MLD to transmit a specific frame (e.g., a MediumSync Recovery frame) on the link that lost MediumSync. In this case, the non-AP MLD that has been instructed by the AP MLD to transmit the specific frame must transmit the specific frame to the AP MLD via the said link when it is determined that the link for which the AP MLD instructed the transmission of the specific frame is idle (idle as a result of PHY CCA and Virtual CCA). However, if the instructed link remains in a busy state from the time the transmission of the specific frame is instructed until the instructed time or a preset time has elapsed, the non-AP MLD may not transmit the specific frame to the AP MLD.

[0297] FIG. 16 illustrates an example of a configuration of an AP MLD including a primary AP and an auxiliary AP having overlapping operating channels and a method for setting an operating channel according to an embodiment of the present invention.

[0298] Referring to Fig. 16(a), three AP MLDs belong to the AP MLD. In this case, AP1 functions as the Primary AP, and AP2 functions as an auxiliary AP paired with the Primary AP. AP3 is a general AP.

[0299] Referring to FIG. 16(b-1), the Primary AP and the auxiliary AP operate on exactly the same Operating channel (specific 320 MHz). However, the Primary 20 MHz sub-channel of the Primary AP is located in the lowest 20 MHz sub-channel within the Operating channel, and the Primary 20 MHz sub-channel of the auxiliary AP (auxiliary channel) is located in the highest 20 MHz sub-channel within the Operating channel.

[0300] Referring to Fig. 16(b-2), the operating channel of the auxiliary AP is included in the operating channel of the primary AP. However, even in this case, the primary 20 MHz sub-channel of the primary AP and the primary sub-channel (auxiliary channel) of the auxiliary AP are set to different 20 MHz.

[0301] Referring to Fig. 16(b-3), the operating channel of the auxiliary AP and the operating channel of the primary AP partially overlap. However, the primary 20 MHz sub-channel of the primary AP and the primary sub-channel (auxiliary channel) of the auxiliary AP are located in the band where the operating channels of the two APs overlap.

[0302] The embodiments of the present invention described below are based on the assumption that the operating channels of the Primary AP (BSS) and the Auxiliary AP (BSS) completely overlap with each other, as shown in FIG. 16 (b-1). However, operating channel configurations such as FIG. 16 (b-2) and (b-3) should also be understood as Primary / Auxiliary BSS operating channel configuration methods that can be used to improve accessibility to specific operating channel(s) using the method provided in the present invention.

[0303] <Overlapping AP를 이용한 채널 접속>

[0304] The AP MLD channel access procedure performed using a Primary BSS and an auxiliary BSS having an operating channel overlapping with the Primary BSS is as follows.

[0305] The Primary BSS and the Secondary BSS operate using the same operating channel (for example, both BSSs operate on the same 320 MHz channel). In this case, the Primary BSS and the Secondary BSS set different 20 MHz subchannels as the Primary 20 MHz subchannel. In this case, the operating channel of the Secondary BSS may be a subset of the operating channel of the Primary BSS.

[0306] The primary channel (auxiliary channel) of the auxiliary BSS may be located in an 80 MHz subblock other than the 80 MHz subblock where the primary channel of the primary BSS is located. That is, the 20 MHz sub-channel included in the primary 80 MHz subblock of the primary BSS cannot be set as the primary channel (auxiliary channel) of the auxiliary BSS.

[0307] If multiple auxiliary APs form an AP pair with a Primary AP, the multiple auxiliary APs must each have a primary channel (auxiliary channel) set in a different 80 MHz subblock. For example, if there are three auxiliary BSSs (auxiliary AP1, auxiliary AP2, auxiliary AP3) paired with a Primary BSS of 320 MHz BW, the three auxiliary BSSs must each have a primary channel (auxiliary channel1, auxiliary channel2, auxiliary channel3) set in the 80 MHz subblock corresponding to the lower frequency of the Primary BSS's Secondary 80 MHz subblock, the 80 MHz subblock corresponding to the lower frequency of the Secondary 160 MHz, and the 80 MHz subblock corresponding to the higher frequency of the Secondary 160 MHz.

[0308] If the Primary 20 MHz subchannel of the Primary BSS is determined to be IDLE, the AP MLD performs channel access through the Primary 20 MHz subchannel of the Primary BSS and then transmits a PPDU through the Primary AP. That is, for frames included in the PPDU transmitted through the Primary AP, the MAC address (TA) of the transmitting device is set to the MAC address (or BSSID) of the Primary AP. Additionally, the Address 3 field of a frame transmitted from the Primary BSS (transmitted by the Primary AP or by an STA that is a member of the Primary BSS) can be set to the BSSID of the Primary AP depending on the values ​​of the To DS and From DS subfields. Furthermore, for a frame transmitted by a non-AP STA that is a member of the Primary BSS, when the To DS and From DS subfields are 1 and 0, respectively, the Address 1 field (RA field) is set to the BSSID of the Primary BSS. In addition, for frames included in the PPDU transmitted through the Primary AP, the MAC address (RA) of the destination device is set to the MAC address of the non-AP STA operating on the Primary link among the non-AP STAs of the non-AP MLD. At this time, when the PPDU is transmitted as an HE / EHT / UHR PPDU, the BSS Color indicated by the preamble of the PPDU is set based on the ID of the BSS operated by the Primary AP. At this time, the auxiliary BSS remains in an inactive state during the period when channel access is performed through the Primary 20 MHz subchannel of the Primary BSS.

[0309] The fact that the auxiliary BSS remains in an inactive state means that PPDU transmission and reception are not performed through the auxiliary AP.

[0310] During the period when the auxiliary BSS remains in an inactive state, the auxiliary AP must not establish a channel connection through its primary channel (auxiliary channel). In this context, not establishing a channel connection means that the backoff counter managed for establishing a channel connection cannot decrease during the inactive time period.

[0311] An auxiliary AP configured with an independent radio may be able to perform PHY CCA or packet detection even during periods when it remains in an inactive state. In this case, the auxiliary AP can set the NAV for its primary channel (auxiliary channel) based on information obtained through the received PPDU (frame).

[0312] When the secondary AP performs the backoff procedure using the secondary channel, it is a situation where the backoff counter can be reduced according to the EDCA rule, and the backoff counter can be reduced only when the secondary AP is active. That is, even if it is a situation where the backoff counter can be reduced according to the EDCA rule, when the secondary AP is inactive, the secondary AP's backoff counter (more precisely, the backoff counter for each of the four Access Categories of the secondary AP) is not reduced.

[0313] A secondary AP may be unable to perform PHY CCA and PD operations when inactive. This may be because there is no available RF (Radio frequency front end) for the secondary AP to utilize when it is inactive. This situation can occur when the secondary AP is logically different from the primary AP but physically shares a single radio. In this case, the secondary AP may need to set NAV for the time interval corresponding to the MediumSync time when initiating channel connection. That is, even if no PPDU (frame) is received after initiating channel connection, the channel connection must be performed by treating the medium as BUSY (busy as a result of Virtual CCA) for the duration corresponding to the MediumSync time.

[0314] When a PPDU (frame) from another BSS is received through the Primary 20 MHz sub-channel of the Primary BSS, the AP MLD switches the Primary AP (BSS) to an inactive state and switches the auxiliary AP to an active state during the TXOP period of the other BSS identified through the received PPDU. However, if the state of the primary channel (auxiliary channel) of a specific auxiliary AP identified (determined) via PHY CCA in the situation where the PPDU of the other BSS is received is BUSY, the specific auxiliary AP may remain in an inactive state. If there is no IDLE auxiliary channel (primary channel of auxiliary APs paired with the Primary AP) identified via PHY CCA, the Primary AP may remain in an active state without being switched to an inactive state. In this case, the operation of the Primary AP switched to an inactive state may be the same or similar to the operation performed by the aforementioned auxiliary AP when it is in an inactive state.

[0315] The time interval during which the above Primary BSS remains in an inactive state may be until the TXOP of the above other BSS is terminated. The time interval during which the above Primary BSS remains in an inactive state may be until the time of termination of the PPDU of the above other BSS.

[0316] The time interval during which the above Primary BSS remains in an inactive state may be until a PPDU from another BSS is received through the auxiliary BSS.

[0317] The time interval during which the above Primary BSS remains in an inactive state may be until after the PPDU transmitted via the channel access performed through the primary channel (auxiliary channel) of the auxiliary BSS occupies the primary channel of the Primary AP.

[0318] The time interval during which the above Primary BSS remains in an inactive state may be limited to before the next TBTT (Target Beacon Transmission Time) of the Primary BSS. That is, at the time when the next TBTT of the Primary BSS arrives, the Primary BSS is in an active state and the auxiliary BSSs are in an inactive state.

[0319] The time interval during which the above Primary BSS remains in an inactive state may be limited to prior to the start of the Service Period (SP) of the Restricted Target Wake Time (R-TWT) operated by the Primary BSS. That is, at the time when the start of the R-TWT SP of the Primary BSS arrives, the Primary BSS is in an active state and the auxiliary BSSs are in an inactive state.

[0320] During the time the auxiliary AP (BSS) remains active, the AP MLD performs channel access through the primary channel (auxiliary channel) of the auxiliary BSS. Once the channel access procedure performed through the auxiliary channel is completed, the AP MLD transmits a PPDU through the auxiliary AP. That is, for frames included in the PPDU transmitted through the auxiliary AP, the MAC address (TA) of the transmitting device is set to the MAC address of the auxiliary AP. Additionally, the Address 3 field of a frame transmitted from the auxiliary BSS (transmitted by the auxiliary AP or by an STA that is a member of the auxiliary BSS) can be set to the BSSID of the auxiliary AP depending on the values ​​of the To DS and From DS subfields. Furthermore, for a frame transmitted by a non-AP STA that is a member of the auxiliary BSS, the Address 1 field (RA field) is set to the BSSID of the auxiliary BSS when the To DS and From DS subfields are 1 and 0, respectively. In addition, for frames included in the PPDU transmitted through the auxiliary AP, the MAC address (RA) of the destination device is set to the MAC address of the non-AP STA operating on the auxiliary link among the non-AP STAs of the non-AP MLD. At this time, when the PPDU is transmitted as an HE / EHT / UHR PPDU, the BSS Color indicated by the preamble of the PPDU is set based on the color of the BSS operated by the auxiliary AP. At this time, the color of the BSS operated by the auxiliary AP may be the same as the BSS color of the Primary AP. At this time, the Primary AP (BSS) remains in an inactive state during the period in which channel connection is performed through the primary channel (auxiliary channel) of the auxiliary AP (BSS).

[0321] The fact that the Primary BSS remains in an inactive state means that PPDU transmission and reception are not performed through the Primary AP.

[0322] During the period when the Primary BSS remains inactive, the Primary AP must not establish a channel connection through its primary channel. In this context, not establishing a channel connection means that the backoff counter managed for establishing a channel connection cannot decrease during the inactive time period.

[0323] A Primary AP configured with an independent radio may be able to perform PHY CCA or Packet Detection even during periods when it remains in an inactive state. In this case, the Primary AP can set the NAV for its primary channel based on information obtained through the received PPDU (frame).

[0324] When the Primary AP performs the backoff procedure using the primary channel, it is a situation where the backoff counter can be reduced according to the EDCA rule, and the backoff counter can be reduced only when the Primary AP is active. That is, even if the backoff counter can be reduced according to the EDCA rule, when the Primary AP is inactive, the Primary AP's backoff counter (more precisely, the backoff counter for each of the four Access Categories of the Primary AP) is not reduced.

[0325] The Primary AP may be unable to perform PHY CCA and PD operations when inactive. This may be because there is no available RF (Radio frequency front end) for the Primary AP to utilize when it is inactive. This situation can occur when the Primary AP is logically a different AP from the Secondary AP but physically shares a single radio in a configuration. In this case, the Primary AP may need to set the NAV for the time interval corresponding to the MediumSync time when initiating channel connection. That is, even if no PPDU (frame) is received after initiating channel connection, the channel connection must be performed by treating the medium as BUSY (busy as a result of Virtual CCA) for the duration corresponding to the MediumSync time.

[0326] A TXOP acquired by a secondary AP may need to be terminated earlier than the Primary BSS's TBTT. This is a restriction intended to ensure that the Primary AP can transmit a Beacon frame in accordance with the Primary BSS's TBTT. Therefore, the secondary AP must manage its TXOPs so that they terminate earlier than the Primary BSS's next TBTT. In this case, the secondary AP's TXOP may need to be terminated at least T earlier than the Primary BSS's TBTT. Here, T is a time interval that includes the time (delay) required for the inactive Primary AP (BSS) to transition to an active state. Here, T may be a time interval that includes the time required to recover MediumSync after the Primary AP transitions to an active state (e.g., MediumSync time).

[0327] TXOPs acquired by the secondary AP may need to be terminated earlier than the start time of the Primary BSS's R-TWT SP. This is a restriction intended to ensure that the Primary AP can perform channel access in alignment with the Primary BSS's R-TWT SP. Therefore, the secondary AP must manage its TXOPs so that they terminate earlier than the start time of the R-TWT SP operating on the Primary BSS. In this case, the secondary AP's TXOP may need to be terminated at least T earlier than the start time of the Primary BSS's R-TWT SP. Here, T is a time interval that includes the time (delay) required for the inactive Primary AP (BSS) to transition to an active state. Here, T may be a time interval that includes the time required to recover MediumSync after the Primary AP transitions to an active state (e.g., MediumSync time).

[0328] The operation in which the Primary AP and the auxiliary AP perform channel access according to the methods described in 1. to 4. above is a normative channel access operation in which each AP performs channel access through its own primary channel and does not change the channel (Primary operating channel) that performs channel access.

[0329] However, according to one embodiment of the present invention, the AP MLD can secure multiple access paths for a single operating channel by setting the operating channels of multiple APs in an overlapping form (overlapping and identically) and differentiating the main operating channels of each AP. Accordingly, when accessing a specific operating channel that operates multiple APs, the AP MLD can have lower main operating channel dependency than conventional Wi-Fi.

[0330] In this case, the APs belonging to a link pair (AP pair) composed of a Primary AP and auxiliary AP(s) have the characteristic that at a specific time, only one AP remains active, while the remaining APs remain inactive.

[0331] In this case, TBTT refers to the time agreed upon for the AP to transmit a Beacon frame. The AP periodically transmits Beacon frames through the primary channel of the BSS it operates, and the transmission period of the Beacon frame is the Beacon Interval. Therefore, each TBTT has a Beacon Interval interval.

[0332] In this case, the R-TWT SP is a type of Broadcast TWT and is a service interval for low-latency traffic introduced in the Wi-Fi 7 standard. During the R-TWT SP, low-latency traffic is processed preferentially. At this time, for each R-TWT SP, the ID of the traffic considered as low-latency traffic is designated by the AP. That is, when the R-TWT SP is operated in a specific BSS, traffic corresponding to the TID (Traffic ID) designated by the AP is serviced preferentially within the BSS during the R-TWT SP interval.

[0333] FIG. 17 illustrates an example of a procedure in which an AP MLD acquires a TXOP using a main BSS and an auxiliary BSS according to an embodiment of the present invention.

[0334] Referring to FIG. 17, the AP MLD performs channel access through the Primary 20 MHz sub-channel (P20) of the Primary BSS. That is, the Primary BSS is active, and the auxiliary BSS is inactive.

[0335] The AP MLD that acquired TXOP1 through the Primary BSS performs transmission and reception with the non-AP MLD through the Primary link. After TXOP1 is terminated, the AP MLD confirms that the Primary AP's P20 channel is occupied by the OBSS, switches the Primary AP to an inactive state, and switches the secondary AP to an active state.

[0336] The AP MLD establishes a channel connection through the primary channel (A20) of the auxiliary AP and acquires TXOP2. During TXOP2, the AP MLD performs transmission and reception with the non-AP MLD through the auxiliary link. At this time, TXOP2 terminated earlier than the TXOP of the OBSS acknowledged by the Primary AP.

[0337] When TXOP2 obtained through the auxiliary AP is terminated, AP MLD switches the Primary AP to an active state and switches the auxiliary AP to an inactive state to perform channel access through the Primary AP.

[0338] Afterwards, the AP MLD establishes a channel connection through the Primary AP's P20 and acquires TXOP3 when the channel connection is complete. During TXOP3, the AP MLD performs transmission and reception with the non-AP MLD through the Primary link, which is the active link.

[0339] <Overlapping AP들과 association한 non-AP MLD 동작>

[0340]

[0341] According to one embodiment of the present invention described above, the AP MLD can set the operating channels of a plurality of APs as overlapping operating channels and operate one of the plurality of APs as a Primary AP and the remaining APs as Auxiliary APs. In this way, when a specific AP is active in the overlapping operating channels, the other APs are kept in an inactive state, making it impossible to transmit or receive PPDUs. Furthermore, the inactive AP may be an AP in a state where not only the transmission or reception of PPDUs but also CCA (Virtual CCA and / or Physical CCA) is impossible.

[0342] Among the links where the Non-AP MLD has performed ML setup, if there is an inactive link (a link of an inactive AP), the Non-AP MLD must not transmit UL PPDU through said inactive link. This is because even if the Non-AP MLD transmits UL PPDU through an inactive link, the AP that is supposed to receive the UL PPDU does not support the reception of PPDU. In other words, the transmission of UL PPDU by the Non-AP MLD on an inactive link is a transmission that is bound to fail and can be understood as an unnecessary operation.

[0343] Therefore, among the links that have performed ML setup with AP MLD, if there are Primary links and auxiliary links, non-AP MLD may need to determine whether to perform transmission and / or channel access in a different way than the link where a regular AP (Regular AP) is operated when performing channel access through the Primary link or auxiliary link.

[0344] For example, a non-AP MLD must not perform UL PPDU transmission via EDCA on an auxiliary link of an AP MLD. Frames that a non-AP MLD can transmit on an auxiliary link may be limited to response frames for frames received from the auxiliary AP. In this case, the types of response frames transmitted by the non-AP MLD on the auxiliary link include at least one of a CTS frame transmitted after receiving an RTS / MU-RTS frame, a BSR frame transmitted after receiving a BSRP trigger frame, and a frame included in a TB PPDU transmitted after receiving a trigger frame.

[0345] The reason non-AP MLDs are restricted from performing transmissions via EDCA on secondary links may be that it is difficult for them to accurately determine whether the secondary AP is active or inactive. Therefore, instead of attempting to transmit UL PPDUs, which are likely to fail, non-AP MLDs may be restricted to transmitting UL PPDUs only when a frame requesting a response frame is received from the secondary AP.

[0346] However, there may be an exception allowing a non-AP MLD to transmit a UL PPDU after performing an EDCA channel access through an auxiliary link. As one example of the above exception, a non-AP MLD that has obtained information from an AP MLD that enables it to determine whether a specific auxiliary link is active may attempt to transmit a UL PPDU after performing a channel access through a non-AP STA operating on the specific auxiliary link (channel access using the EDCA mechanism, i.e., channel access performed independently rather than trigger-based channel access). The information that enables it to determine whether the specific auxiliary link is active may be information indicated through a frame transmitted via another AP belonging to the AP MLD. In this case, the information indicated via another AP belonging to the AP MLD may be information indicating which AP (which link) among the Primary AP and auxiliary APs is active. A non-AP MLD that performs channel access through a secondary link (channel access using the EDCA mechanism, or channel access performed independently rather than trigger-based channel access) may need to transmit the first frame transmitted from the secondary link as an RTS frame. In other words, the non-AP MLD may need to transmit an RTS frame as the first frame transmitted from the secondary link. If a CTS frame, which is a response to the RTS frame transmitted as the first frame, is not received from the AP, the non-AP MLD may not perform additional channel access to the secondary link.

[0347] Similar to AP MLD, non-AP MLD can use independent radios for the non-AP STA operated in the Primary and the non-AP STA operated in the Auxiliary, or it can operate the non-AP STAs of both links using a single radio.

[0348] That is, there may be an implementation in which the Primary non-AP STA and the Auxiliary non-AT STA are configured using independent radios. In this case, it is possible for the Primary non-AP STA to transmit and receive PPDUs through the Primary 20 MHz subchannel, while the Auxiliary non-AP STA receives other PPDUs through the Auxiliary channel (the primary channel of the Auxiliary BSS) or performs CCA, PD (Packet Detection), etc. An Auxiliary non-AP STA having such independent radios may have the capability to function as a general non-AP STA when associated with an AP that is not an Auxiliary AP (e.g., a Regular AP that is not a Primary or Auxiliary AP).

[0349] In addition, it is possible to implement a configuration in which the Primary non-AP STA and the Auxiliary non-AP STA share a single radio. In this case, when the Primary non-AP STA transmits / receives PPDU through the Primary 20 MHz subchannel, the Auxiliary non-AP STA cannot perform transmission / reception, CCA, PD, etc., on its own primary channel (auxiliary channel). This is because if the radio commonly used by the two non-AP STAs is used for the operation of the Primary non-AP STA, there will be no radio available for the Auxiliary non-AP STA to use. In other words, the Primary non-AP STA and the Auxiliary non-AP STA are non-AP STAs that exist only logically separated, but physically, they may be non-AP STAs operated using a single device (radio, RF chain, antenna, etc.). The reason a non-AP MLD can operate multiple non-AP STAs (a primary non-AP STA and auxiliary non-AP STAs) using a single radio in this manner is that, at a specific point in time among the multiple non-AP STAs, the radio is utilized for only one non-AP STA. In other words, the non-AP MLD may not support channel access or PPDU transmission / reception for auxiliary non-AP STAs when the channel access procedure is being performed or PPDU transmission / reception is being carried out by the primary non-AP STA. Furthermore, multiple non-AP STAs operate by sharing a single radio in such a manner that support for the primary non-AP STA and other auxiliary non-AP STAs is not required when PPDU transmission / reception is being performed through a specific auxiliary non-AP STA. That is, the non-AP MLD can perform single-radio multi-link operation for the primary link and the auxiliary link.

[0350] Meanwhile, a restriction may be applied to non-AP MLDs such that they can be set up on only one auxiliary link among the pairs of auxiliary links for each Primary link. For example, when there is a first Primary link and a first auxiliary link and a second auxiliary link which are pairs of the first Primary link, a specific non-AP MLD may have an ML setup state including the first Primary link and the first auxiliary link, or an ML setup state including the first Primary link and the second auxiliary link, and may not have an ML setup state including both the first auxiliary link and the second auxiliary link. That is, when there are multiple auxiliary links corresponding to a specific Primary link, a non-AP MLD may need to be set up through only one of the multiple auxiliary links.

[0351] A non-AP STA operating on a secondary link may need to terminate its TXOP before the next TBTT of the Primary link (TBTT of the Primary BSS) when it acquires a TXOP via EDCA. Since this is the same or similar operation as a secondary AP terminating its TXOP before the TBTT of the Primary BSS, a detailed explanation is omitted.

[0352] <Auxiliary AP Discovery>

[0353] As such, since auxiliary links (auxiliary APs, auxiliary BSSs) possess characteristics different from general APs and primary links, the AP MLD must indicate which of its affiliated APs is operating on the auxiliary link through the management frames it transmits. Furthermore, a non-AP MLD intending to perform ML setup with the AP MLD must receive the management frames transmitted by the AP MLD and determine, based on the information contained in the frames, whether each AP operated by the AP MLD is a general AP, a primary AP, or an auxiliary AP. For example, a non-AP MLD that receives a Beacon frame transmitted by a specific AP MLD and recognizes that a specific AP of that AP MLD is an auxiliary AP must not perform multi-link setup through that specific AP (auxiliary AP). In other words, the non-AP MLD must not transmit (ML) Probe Request frames and / or (ML) Association Request frames to the auxiliary AP.

[0354] One way for an AP MLD to indicate what type of AP each AP is through the management frames it transmits is by using the RNR element (Reduced Neighbor Report).

[0355] For example, the AP MLD can indicate that the AP corresponding to the Neighbor AP Information field configured / set in a different way from the Neighbor AP Information field corresponding to other APs (third AP (general AP) and Primary AP) among the Neighbor AP Information fields included in the RNR element it transmits is the auxiliary AP. A specific method by which the AP MLD indicates the auxiliary AP using the RNR element is explained in more detail through an embodiment of FIG. xx.

[0356] FIG. 18 illustrates an example of the format of an RNR element transmitted by an AP MLD to indicate an auxiliary AP according to an embodiment of the present invention.

[0357] Figure 18 (a) illustrates a Reduced Neighbor Report element format. A Reduced Neighbor Report element may include multiple Neighbor AP Information Fields, and the length of the element is indicated through the Length field.

[0358] The Neighbor AP Information Fields include a Neighbor AP Information field corresponding to each AP belonging to the AP MLD transmitting the element. However, the Neighbor AP Information field for the AP transmitting the RNR element is not included.

[0359] FIG. 18(b) illustrates a method for setting the Neighbor AP Information field corresponding to an auxiliary AP belonging to an AP MLD. Although the Neighbor AP Information Field is identical regardless of the nature of the corresponding AP, the settings of the TBTT Information Header and the size of the TBTT Information Set field may differ between a general AP and an auxiliary AP. More specifically, as shown in FIG. 18(b), in the Neighbor AP Information field corresponding to an auxiliary AP, the TBTT Information field Type of the TBTT Information Header field may be indicated as a non-zero value (e.g., 1 or 2). This is a setting method that is differentiated from the TBTT Information field Type of a general AP being indicated as 0. Additionally, in the Neighbor AP Information field corresponding to an auxiliary AP, the TBTT Information Length indicated in the TBTT Information Header field is set to 3. That is, the TBTT Information Set field is indicated to have a size of 3-octets. At this time, the MLD Parameters subfield is included in the TBTT Information Set field.

[0360] FIG. 18 (c) illustrates the MLD Parameters subfield format corresponding to an auxiliary AP. In the MLD Parameters subfield corresponding to the auxiliary AP, the link ID can be set to a value greater than the link ID of the general AP. That is, if there are multiple APs (Primary AP and general APs) and one auxiliary AP in the AP MLD, it is recommended that the link ID of the auxiliary AP be set to be greater than the link IDs of the other APs.

[0361] The MLD Parameters subfield corresponding to the auxiliary AP includes the Link ID of Primary Link subfield. The Link ID of Primary Link subfield is a subfield indicating the Link (Primary Link) ID of the Primary AP paired with the auxiliary AP. The Auxiliary Link Indication subfield is a subfield indicating whether the AP corresponding to the MLD Parameters subfield is an auxiliary AP, and is indicated as 1 when included in the MLD Parameters subfield corresponding to the auxiliary AP. The Separated Radio subfield is a subfield indicating whether the auxiliary AP corresponding to the MLD Parameters subfield is configured to have a radio independent of the Primary AP. That is, an auxiliary AP with the Separated Radio subfield set to a specific value (e.g., 1) can avoid losing medium sync for the primary channel (auxiliary channel) of the auxiliary BSS even when transmission / reception is performed through the Primary AP.

[0362] At this time, when non-AP MLDs receive an RNR element transmitted by an AP MLD, they can recognize that the Neighbor AP Information field corresponds to an auxiliary AP by checking the Neighbor AP Information field in the RNR element where the TBTT Information field Type is not 0. Alternatively, non-AP MLDs can recognize whether the AP corresponding to the MLD Parameters subfield is an auxiliary AP based on a specific bit included in the MLD Parameters subfield (auxiliary link indication in FIG. 18 (c)).

[0363] As another example, the AP MLD can indicate that the AP corresponding to the Per-STA Profile subelement configured / set in a different way is the auxiliary AP by configuring / setting the Per-STA Profile subelement corresponding to the auxiliary AP among the Per-STA Profile subelements included in the Multi-link element it transmits in a different way from the Per-STA Profile subelement corresponding to other APs (third AP (general AP) and Primary AP). The Per-STA Profile subelement configured / set in a different way may be such that the auxiliary AP is distinguished from the general AP by a subfield (bit) indicated by a specific value (e.g., 0 or 1) in the Per-STA Profile subelement corresponding to the general AP being set to a different value (e.g., 1 or 0) for the auxiliary AP.

[0364] A non-AP MLD that recognizes that a secondary AP is operational must not send a Probe Request frame to the AP MLD via the secondary link. In this case, the method by which the non-AP MLD recognizes that the secondary link is operational may be based on information indicated through a Management frame transmitted by the AP MLD.

[0365] Meanwhile, the AP MLD can change the AP functioning as the Primary AP among overlapping APs (Primary APs and Auxiliary APs). As a simple example, the AP that initially functioned as the Primary AP can be changed to an Auxiliary AP, and the AP that functioned as an Auxiliary AP can be changed to the Primary AP. There can be various reasons for the AP functioning as the Primary AP among the overlapping APs to be changed in this manner, and one reason may be that the AP MLD intends to change the channel through which Beacon frames are transmitted.

[0366] When an AP MLD intends to change the AP (link, BSS) that will function as the Primary AP (link, BSS) among the Overlapping APs (link, BSS), it must instruct the non-AP MLDs accordingly. At this time, the AP MLD may instruct information regarding the new Primary AP (an AP that is a secondary AP at the time the Management frame is transmitted) and / or information regarding the time when the Primary AP is changed, through a Management frame (e.g., a Beacon frame) that it transmits. At this time, the information instructed by the AP MLD through the Management frame may include the ID of the link where the secondary AP to be changed to the Primary AP is operating (i.e., the link ID of the secondary link). At this time, to indicate the time when the Primary AP is changed, the AP MLD may instruct the number of remaining TBTTs until said time of change. That is, if there are 5 TBTTs of the current Primary AP until the point at which the AP MLD intends to change the Primary AP, the AP MLD may set the value of the field related to the point at which the Primary AP is changed to based on the number of remaining TBTTs (e.g., 5 or 4 (5-1)). That is, if the AP MLD does not have any remaining TBTTs until the point at which the AP MLD intends to change the Primary AP, it sets the value of the field related to the point at which the Primary AP is changed to 1 or 0 and transmits it, and the next Beacon frame will be transmitted through the new Primary AP.

[0367] An AP MLD that intends to change the Primary AP may transmit a BSS Transition Management Request frame through the existing Primary AP (the AP that will become the secondary AP after the change of the Primary AP). At this time, the BSS Transition Management Request frame may be a frame that instructs non-AP STAs and non-AP MLDs, which are connected (set up) only through the existing Primary AP, that the service of the BSS operated by the Primary AP will be terminated. At this time, the BSS Transition Management Request frame transmitted by the AP MLD may be a BSS Transition Management Request frame in which the Link Removal Imminent subfield is set to 0 and the Primary Link Change field is set to 1. The Primary Link Change field is a field that is set to 1 when the link designated as the Primary link changes (and / or is scheduled to change) among the pairs of Primary links (AP) and secondary links (AP) having an overlapping operating channel. A non-AP MLD that receives a BSS Transition Management frame Request in which the Primary link Channel field is set to 1 may interpret the BSS Transition Management Request frame not as the Primary BSS being terminated from service, but as an indication that the Primary link (AP) and the secondary link (AP) will be changed.In this case, the AP MLD must update the Neighbor AP Information field regarding the secondary link and the Neighbor AP Information field regarding the primary link of the RNR element transmitted after the primary and secondary links have changed, taking into account the changed primary link.

[0368] Alternatively, the AP MLD can perform a Channel Switch to change the primary channel of the BSS operated by the AP functioning as the Primary AP (link) among multiple APs (links) having overlapping operating channels. In this case, the AP MLD can transmit an (Extended) Channel Switch Announcement element to change the primary channel of the BSS operated by the Primary AP, and a new primary channel is indicated through the New Channel Number field included in the element. In this case, the new primary channel is one of the sub-channels included in the existing operating channel (BW). When the Channel Switch Announcement element is used to change the sub-channel used by the Primary BSS as the primary channel without changing the operating channel, it is possible for the new primary channel to be designated as the sub-channel used as the primary channel (auxiliary channel) by the auxiliary BSS that is a pair with the Primary BSS. If the primary channel of the new Primary BSS (indicated by the New Channel Number field) is a subchannel that was previously used as the primary channel (auxiliary channel) by the auxiliary BSS, the AP MLD must also transmit an (Extended) Channel Switch Announcement element that changes the primary channel (auxiliary channel) of the said auxiliary BSS. In other words, an AP MLD that intends to change the primary channel of the Primary BSS to the primary channel (auxiliary channel) of the auxiliary BSS may need to change the primary channel (auxiliary channel) of the said auxiliary BSS as well, thereby managing the situation so that the Primary BSS and the auxiliary BSS do not use the same subchannel as their primary channels.A non-AP MLD that receives together an (Extended) Channel Switch Announcement element instructing the change of the primary channel of the Primary BSS and an (Extended) Channel Switch Announcement element instructing the change of the primary channel (auxiliary channel) of the Auxiliary BSS from the AP MLD can recognize that the primary channels of the two BSSs will be swapped. At this time, the same value is indicated in the Channel Switch Count field of the two Channel Switch Announcement elements received together. At this time, the Channel Switch Mode subfield of the Channel Switch Announcement element transmitted by the AP MLD to change only the primary channel without changing the operating channel of the Primary BSS can be set to a value different from the value indicated when a normal Channel Switch is performed (when the operating channel is changed) (e.g., 2).

[0369] <Changing the channel of an AP (Link, BSS) pair with overlapping operation channels>

[0370] When changing the operating channel of multiple APs (Primary AP and paired auxiliary APs) having overlapping operating channels, the AP MLD can transmit only the (Extended) Channel Switch Announcement element for the Primary AP. That is, the Channel Switch Announcement element for the Primary AP (link, BSS) may be a Channel Switch Announcement element that applies commonly to multiple APs (Primary AP and paired auxiliary APs) having overlapping operating channels. For example, if the operating channel of the Primary BSS is changed from a first 320 MHz channel to a second 320 MHz channel through the Channel Switch Announcement element, the operating channel of the auxiliary BSS paired with the Primary BSS is also changed from the first 320 MHz channel to the second 320 MHz channel. In other words, for APs with overlapping operating channels (overlapping AP(link, BSS) pair), when an operating channel change is instructed for a specific AP (e.g., primary AP), an operating channel change for the other AP (e.g., secondary AP) may be implicitly instructed. Therefore, when a non-AP MLD receives an instruction from an AP MLD to change the operating channel of the Primary AP, it can perceive that the operating channels of the secondary AP(s) paired with the Primary AP are also changed to be identical to those of the Primary AP.At this time, the new primary channel (auxiliary channel) of the auxiliary AP(s) moved to the changed operating channel can be indicated through the RNR element included in the management frame (frame transmitted by the AP MLD) transmitted after the completion of the Primary BSS Channel Switch.

[0371] FIG. 19 illustrates a method in which, according to one embodiment of the present invention, when a channel switch for a main BSS is performed, a channel switch of an auxiliary BSS is indicated / performed together.

[0372] Referring to Fig. 19, the Primary BSS and the Auxiliary BSS operate in an Operating channel where the initial Center Frequency is 'X'.

[0373] AP MLD includes an (Extended) Channel Switch Announcement element in the Beacon frame transmitted by the Primary AP to change the overlapping operating channel.

[0374] The (Extended) Channel Switch Announcement element contains information about the time when the Primary BSS Channel Switch starts and the new Operating channel.

[0375] Since the Channel Switch Count value of the (Extended) Channel Switch Announcement element included in Beacon #1 is 2 and the Channel Switch Count value included in Beacon #2 is 1, the Primary AP starts the Channel Switch after transmitting Beacon #2. At this time, although the Channel Switch Announcement element for the auxiliary AP (BSS) is not directly included in Beacon #1 and Beacon #2, the same information as the Channel Switch information indicated for the Primary AP (BSS) is implicitly included in the auxiliary AP (BSS). This is because the auxiliary AP is the AP paired with the Primary AP that will perform the Channel Switch.

[0376] Therefore, when the Primary BSS channel switch starts, the Auxiliary BSS channel switch also starts simultaneously, and the changed center frequency of the Primary BSS is identical to the changed center frequency of the Auxiliary BSS. In other words, the operating channels of the two BSSs remain in an overlapping state even after the channel switch is completed.

[0377] The Primary AP transmits a Beacon #3 frame on a new operating channel, and Beacon #3 includes an RNR element indicating information about the new primary channel (auxiliary channel, A20 in Fig. 19) of the auxiliary AP. Therefore, the non-AP MLD can verify information about the new primary channel (auxiliary channel) of the auxiliary BSS by receiving the Beacon frame transmitted by the AP MLD after the Primary BSS completes its channel switch.

[0378] <Features and Limitations of Auxiliary APs / Links / BSSs>

[0379] As described above, an AP MLD can operate multiple APs with overlapping operating channels to increase accessibility to a specific operating channel. Among the multiple APs, one AP functions as the Primary AP, and the remaining AP(s), excluding the Primary AP, function as auxiliary APs. The Primary AP supports functions more similar to a general AP, such as transmitting a Beacon frame at every Beacon interval and supporting (ML) setup procedures with non-AP STAs and non-AP MLDs. On the other hand, the auxiliary AP is an AP with many restrictions, such as not transmitting a Beacon frame and being unable to be set up with a non-AP MLD that is not associated with the paired Primary AP. This is because the reason an AP MLD operates multiple APs with overlapping operating channels is to increase accessibility to the overlapping operating channels, and not to operate the auxiliary APs as general APs.

[0380] As such, since the auxiliary AP (link, BSS) is an AP that performs only limited operations and has a dependency on the primary AP (link, BSS), the AP MLD must utilize the information directed through the primary AP and the parameters used by the primary AP when operating the auxiliary AP.

[0381] <TSF timer in auxiliary link>

[0382] As mentioned above, auxiliary APs do not transmit Beacon frames. Wi-Fi Beacon frames are frames transmitted for various purposes, such as indicating various information that non-AP STAs associated with the AP transmitting the Beacon frame need to recognize, enabling non-AP STAs not associated with the AP to discover the existence of the AP, and even allowing them to recognize some information about other APs adjacent to the AP (Neighbor APs). Furthermore, in 11be, by transmitting a Multi-Link element through the Beacon frame, it has been expanded to include additional information that non-AP MLDs need to acquire, such as indicating that the AP transmitting the Beacon frame belongs to an AP MLD and even information about other APs (links) belonging to the AP MLD.

[0383] The Timestamp field, one of the fields included in a Beacon frame, indicates a value related to the AP's Timing Synchronization Function (TSF) timer. This field enables non-AP STAs to synchronize timing between the AP and non-AP STAs by adjusting their own TSF timers to match the AP's TSF timer value. All timing-based operations of a BSS are based on the AP's TSF timer; in other words, the AP functions as the timing master. Therefore, each non-AP STA must synchronize timing with the AP using the Timestamp field included in the Beacon frame transmitted by the AP. However, in the case of a secondary AP, it does not transmit a Beacon frame for its BSS. Consequently, non-AP STAs included in the secondary AP's BSS face the problem of being unable to synchronize time with the secondary AP. As a solution to this, it is possible to consider having the Primary BSS (AP, link) and the secondary BSS (AP, link) use a common TSF timer.

[0384] According to one embodiment of the present invention, a primary AP and a pair of auxiliary APs may have a common TSF timer. Alternatively, the TSF timers of the primary AP and the auxiliary APs may be the same. In this case, the value of the commonly used TSF timer is indicated to non-AP STAs (non-AP STAs and non-AP MLDs) through a Beacon frame transmitted by the primary AP. Accordingly, by receiving the Beacon frame transmitted by the primary AP, the non-AP MLD can maintain time synchronization with the auxiliary APs.

[0385] <Mapping TID (Traffic ID) of the auxiliary link>

[0386] As previously mentioned, MLDs are defined in Wi-Fi 7, and TID-to-link mapping consultation can be performed between MLDs that have undergone ML setup. As a simple example of TID-to-link mapping, a non-AP MLD set up via two links with an AP MLD can perform consultation with the AP MLD to map TID0 to TID3 to the first link and TID4 to TID7 to the second link. In this case, the non-AP MLD and the AP MLD transmit only MPDU / MSDU with TIDs 0 to 3 through the first link, and transmit MPDU / MSDU with TIDs 4 to 7 through the second link. At this time, it is possible to apply different TID-to-link mappings to the direction in which the AP MLD transmits (DL, Down link) and the direction in which the non-AP MLD transmits (UL, Up link). AP MLDs and non-AP MLDs for which TID-to-link mapping has not been performed have a Default TID-to-link mapping agreement state. The Default TID-to-link mapping state means that all TIDs are mapped to all setup links, i.e., all types of TIDs can be transmitted without restriction through all setup links. In this case, the Default TID-to-link mapping mode applies to both the DL and UL directions.

[0387] Generally, TID-to-link mapping agreements between an AP MLD and a non-AP MLD can be freely configured through agreement between the two MLDs, except for the constraint that every TID must be mapped to at least one link. In other words, there are no constraints requiring that only a specific TID be mapped to a specific link, or that a specific TID must not be mapped to a specific link. However, this is valid only when assuming that all setup links are links where a standard AP operates, and additional constraints may apply if there are auxiliary links among the setup links.

[0388] According to one embodiment of the present invention, only the TID mapped to the paired Primary link can be mapped to the auxiliary link. Furthermore, the TID mapped to the paired Primary link can be mapped identically to the auxiliary link. That is, the auxiliary link cannot have a TID that is not mapped to the paired Primary link. In other words, the TID-to-link mapping state of the auxiliary link is identical to the TID-to-link mapping state of the paired Primary link. The reason why a separate TID-to-link mapping constraint exists for the auxiliary link may be that the auxiliary link is a link that cannot maintain an active state simultaneously with the Primary link.

[0389] To explain in more detail, the secondary link can be active only when the primary link is inactive; therefore, the primary link remains inactive while transmission is being performed on the secondary link. If a specific TID is mapped only to the primary link and not to the secondary link, the TID not mapped to the secondary link becomes a TID that cannot be transmitted during the time interval when the primary link is inactive. This means that the TIDs that each MLD can transmit are restricted depending on whether the active link is the primary link or the secondary link, which is a highly inappropriate restriction for maintaining traffic flow. Therefore, by restricting the secondary link to always be mapped with the same TID as that mapped to the primary link, all TIDs must remain in a state where they can be transmitted through at least one setup link, regardless of whether the primary link or the secondary link is active.

[0390] Therefore, when AP MLDs and non-AP MLDs perform TID-to-link mapping, they must execute a TID-to-link mapping request in which the TID mapped to the Primary link is always mapped to the Secondary link. In this case, the constraints on the mapping apply to both directions (DL / UL).

[0391] Alternatively, when AP MLDs and non-AP MLDs perform TID-to-link mapping, one may consider that TID mapping information for auxiliary links is not separately specified, and that the TID mapping specified for the Primary link is applied identically to the auxiliary links. In other words, AP MLDs and non-AP MLDs may not perform separate TID-to-link mapping consultation for auxiliary links. In this case, the TID mapping status for the unconsented auxiliary links may be applied identically to the TID mapping status agreed upon for the Primary link paired with the auxiliary links. That is, the TID mapping for auxiliary links is not directly specified or consulted, and the TID mapping for the Primary link may be applied identically. This can be interpreted as the TID-to-link mapping consultation for the auxiliary links being implicitly performed or completed by the TID-to-link mapping consultation performed for the paired Primary links.

[0392] <Auxiliary AP Traffic Indication>

[0393] As mentioned above, TID-to-link mapping negotiations can be performed between two MLDs associated through multiple links. If a TID-to-link mapping negotiation is performed between an AP MLD and a non-AP MLD, the AP MLD may need to issue a traffic indication by considering the TID-to-link mapping negotiated with the non-AP MLD. Similarly, when the non-AP MLD receives a traffic indication from the AP MLD, it may need to perform an action to receive an MSDU by considering the TID-to-link mapping. The reason why AP MLDs and non-AP MLDs must consider the TID-to-link mapping when issuing traffic indications and receiving MSDUs is due to traffic transmission restrictions related to the TID-to-link mapping. As previously explained regarding TID-to-link mapping, when an MLD that has performed a TID-to-link mapping negotiation with a counterpart MLD performs transmission to that counterpart MLD, it must transmit the traffic only through the link to which the TID of the traffic to be transmitted is mapped. Therefore, if the AP MLD and the non-AP MLD have performed TID-to-link mapping in non-default mode for the DL direction, the AP MLD must transmit the MSDU to the non-AP MLD only through the link where the TID of the MSDU is mapped for the DL direction in order to transmit the MSDU that was queuing.In other words, a non-AP MLD must transmit PS-Poll frames only through a link where the MSDU it is to receive can be transmitted. If a non-AP MLD transmits a PS-Poll frame over a link where the TID of the MSDU queued to the AP MLD is not mapped to the DL direction, it cannot receive the MSDU from the AP MLD. In this case, the non-AP MLD switches the link where MSDU reception is impossible to Awake, which not only degrades PS efficiency but also causes MSDU transmission delays, making it difficult to effectively operate or support PS mode.

[0394] Therefore, to prevent the problem of being unable to transmit Queuing MSDU (BU) due to TID-to-link mapping, the AP MLD must instruct each non-AP MLD via the TIM element whether there is a Queuing MSDU to transmit, and additionally instruct information regarding which link the MSDU should be transmitted. At this time, for a non-AP MLD that has performed a TID-to-link mapping negotiation in which all TIDs are mapped in the DL (Down Link, the direction in which the AP transmits to the non-AP) direction for at least one link, no additional instructions other than whether there is a Queuing MSDU may be performed. This may be because a non-AP MLD in the default TID-to-link mapping state or a non-AP MLD with a link in which all TIDs are mapped in the DL direction can receive the Queuing MSDU without the problem of being unable to transmit due to TID by transmitting a PS-Poll frame through the link in which all TIDs are mapped to receive the Queuing MSDU.

[0395] A method by which an AP MLD instructs a non-AP MLD on which link the corresponding MSDU (BU, Queuing frame, etc.) should be transmitted may be to transmit an element indicating a TID or Link ID along with a TIM element. In this case, the element transmitted to instruct the non-AP MLD on the TID or Link ID may be named a Multi-Link TIM element (or Multi-Link Traffic Indication element). The Multi-Link TIM element instructs each non-AP MLD indicated by the TIM element as having a Queuing MSDU on which link the MSDU can be received. However, if a separate link-related information instruction is not required for the non-AP MLD (e.g., when the default TID-to-link mapping state is active or when a TID-to-link mapping negotiation has been performed with links where all TIDs are mapped in the DL direction), a separate link-related information may not be instructed in the Multi-Link TIM element. A non-AP MLD that is not instructed with separate link-related information via a multi-link TIM element must receive BU (queuing MSDUs) by transmitting a PS-Poll frame on a link where all TIDs are mapped for the DL direction. In the case of a non-AP MLD using default TID-to-link mapping, it can be understood that there is no restriction on selecting a separate PS-Poll frame transmission link because all links are mapped for all TIDs for the DL direction.

[0396] As described above, in the case of the secondary link, the same TID mapped to the Primary link is mapped. Therefore, depending on the TID-to-link mapping status, the traffic (MSDU / MPDU) of a TID that can be transmitted on the Primary link is traffic that can also be transmitted on the secondary link. Furthermore, a non-AP MLD set up via the secondary link is always set up via the Primary link as well, and there is no non-AP STA associated only through the secondary link.

[0397] If the Multi-Link Traffic Indication element transmitted by the AP MLD indicates that an MSDU queued at the AP MLD can be received via the Primary Link, it is self-evident that the said MSDU can also be received via the Secondary Link. Furthermore, it is self-evident that an MSDU that the AP MLD can transmit via the Secondary Link can also be transmitted via the Primary Link.

[0398] Therefore, when the AP MLD indicates that bufferable units (MSDUs) to be transmitted on each link are queued through the Multi-Link Traffic Indication element, it may not indicate information regarding the secondary link. Instead, traffic indication for the secondary link can be implicitly indicated through the traffic indication for the primary link. In this case, the link ID bitmap (Per-Link Traffic Indication Bitmap subfield) included in the Multi-Link Traffic Indication element transmitted by the AP MLD may not include a bit corresponding to the secondary link.

[0399] To summarize in other words, each bit of the Per-Link Traffic Indication Bitmap included in the Multi-Link Traffic Indication element transmitted by the AP MLD corresponds to the link ID of the general AP and / or Primary AP, but may not correspond to the link ID of the secondary AP. In other words, traffic indication for the secondary AP is not indicated by the AP MLD.

[0400] A non-AP MLD that is instructed by an AP MLD through a TIM (traffic indication map) element and a Multi-link Traffic Indication element that there is an MSDU to be received on a specific Primary link can attempt to receive a buffered BU from the AP MLD by transmitting a PS-Poll frame through the specific Primary link or an auxiliary link that is paired with the specific Primary link.

[0401] <Secondary BSS Color Settings>

[0402] The secondary BSS may be required to use the same BSS color as the primary BSS. That is, the AP MLD sets the BSS Color field (included in HE-SIG-A of the HE PPDU and U-SIG of the EHT / UHR PPDU) of the PPDU transmitted through the primary AP and the HE / EHT / UHR PPDU transmitted through the secondary AP to the same value. Additionally, the non-AP MLD must also set the BSS Color field of the PPDU transmitted from the primary BSS and the PPDU transmitted from the secondary BSS to the same value.

[0403] Therefore, when the Primary AP transmits a BSS Color Channel Announcement element to set the Primary BSS color to a new value, the BSS color of the Secondary BSS changes to the new value.

[0404] However, the Primary BSS and the Secondary BSS must be configured to have different BSSIDs. In this case, setting the BSSIDs of the two BSSs to different values ​​means determining the BSSID of the Primary BSS and the BSSID of the Secondary BSS, respectively, randomly.

[0405] <Auxiliary BSS parameter update>

[0406] As mentioned above, the auxiliary AP cannot transmit Beacon frames (and Probe response frames), and therefore cannot announce to the member STAs of the auxiliary BSS when the parameters of the auxiliary BSS change.

[0407] Instead, parameter updates of the auxiliary BSS can be performed through management frames transmitted by the Primary AP paired with the auxiliary AP, or by other APs belonging to the AP MLD. More specifically, when the parameters of the auxiliary BSS are updated, the AP MLD may indicate that the parameter update of the auxiliary BSS is proceeding by using an update instruction field corresponding to the auxiliary BSS (e.g., BSS Parameter Change Count subfield (included in the MLD Parameters subfield corresponding to the auxiliary AP)) in the RNR element included in the management frame it transmits. In this case, the non-AP MLD can recognize that the parameters of the auxiliary BSS have changed through the received RNR element. Subsequently, the non-AP MLD can receive and update the parameters of the auxiliary BSS through the Per-STA Profile subelement of the auxiliary AP included in the Multi-Link element transmitted by the AP MLD.

[0408] In addition, some present bits included in the Per-STA Profile subelement corresponding to the auxiliary AP must always be set to 0. The Beacon Interval Present subfield of the Per-STA Profile subelement corresponding to the auxiliary AP is set to 0. The TSF Offset Present subfield of the Per-STA Profile subelement corresponding to the auxiliary AP is set to 0. The DTIM Info Present subfield of the Per-STA Profile subelement corresponding to the auxiliary AP is set to 0. At this time, the reason the above three subfields are set to 0 is that the auxiliary AP does not transmit a Beacon frame and uses the same TSF value as the Primary AP. That is, since the information indicated when the above Present subfields are indicated as 1 is information that is not defined for or does not need to be indicated for the auxiliary AP (BSS, link), the above three Present subfields are always set to 0 for the auxiliary AP.

[0409] Certain parameters among the operating parameters of the auxiliary BSS may be dependent on the operating parameters of the primary BSS. For example, when the operating BW of the primary BSS changes, the operating BW of the auxiliary BSS may change to be the same as the operating BW of the primary BSS.

[0410] Modified Auxiliary Link Operation Method

[0411] As described above, AP MLD and non-AP MLD may have an ML setup state including multiple links operating in an overlapping operating channel for the purpose of improving accessibility to a specific Operating channel.

[0412] Alternatively, instead of setting up multiple links with overlapping operating channels, a method of setting up multiple links where the operating channels (bandwidth) are located consecutively can be utilized.

[0413] More specifically, AP MLDs and non-AP MLDs may enhance channel accessibility to consecutive operating channels by establishing an ML setup connected through multiple links having consecutive operating channels within a specific channel bandwidth. For example, AP MLDs and non-AP MLDs may enhance accessibility to a specific 160 MHz channel by performing an ML setup through two links that use each of the two 80 MHz channels included in a specific 160 MHz channel as an operating channel. As another example, AP MLDs and non-AP MLDs may enhance accessibility to a specific 320 MHz channel by performing an ML setup through two links that use each of the two 160 MHz channels included in a specific 320 MHz channel as an operating channel. As another example, AP MLD and non-AP MLD may enhance accessibility to the specific 320 MHz channel by performing ML setup through four links using each of the four 80 MHz channels included in the specific 320 MHz channel as an operating channel.

[0414] In this case, when the AP MLD and / or non-AP MLD performs transmission through the first STA (AP STA and / or non-AP STA) operating on the continuous operating channel, it can perform an operation synchronized with the transmission of the second STA operating on the continuous operating channel. For example, when the AP MLD transmits a PPDU through the first AP operating at the first 80 MHz included in the specific 160 MHz, it can perform a transmission synchronized with the second AP operating at the second 80 MHz included in the specific 160 MHz. At this time, the 80 MHz PPDUs transmitted by the first AP and the second AP, respectively, can be understood as the first segment and the second segment of the 160 MHz PPDU. In this case, the first segment refers to a PPDU transmitted from a first 80 MHz segment included in the specific 160 MHz, and the second segment refers to a PPDU transmitted from a second 80 MHz segment included in the specific 160 MHz. In this case, the meaning of the AP MLD synchronizing the transmission of the first AP and the transmission of the second AP is that the transmission start time and PPDU length of the PPDU transmitted through the first AP and the PPDU transmitted through the second AP are managed identically. Furthermore, when the first AP and the second AP transmit synchronized PPDUs, it is possible for the TXOPs acquired by the first AP and the second AP to also be synchronized. That is, when the AP MLD synchronizes and transmits 80 MHz PPDUs through the first AP and the second AP, respectively, it is possible for the two transmitted 80 MHz PPDUs to have the same form as a single 160 MHz PPDU. That is, when the AP MLD transmits a PPDU synchronized through the first AP and the second AP, the start time and length of the TXOP acquired by the first AP and the TXOP acquired by the second AP are set to be the same.

[0415] In addition, as described above, when a non-AP MLD performs transmission through a first STA (AP STA and / or non-AP STA) operating in a continuous operating channel, it can perform an operation synchronized with the transmission of a second STA operating in a continuous operating channel. At this time, a specific description of the synchronized transmission performed by the non-AP MLD is omitted as it is the same as in the case of the AP MLD described above.

[0416] Among multiple links having consecutive operating channels, one link is configured as the primary link, and the remaining links are configured as auxiliary links. The AP operating on the primary link periodically transmits Beacon frames, whereas the AP operating on the auxiliary link does not transmit Beacon frames. In this case, the same or similar operating methods as those for the primary link and auxiliary link operating on the aforementioned overlapping operating channel may be applied to the primary link and auxiliary link operating on the consecutive operating channel. The same TID is mapped to the primary link and auxiliary link operating on the consecutive operating channel, and the APs and STAs operating on the auxiliary link share the TSF timer of the APs and STAs operating on the primary link.

[0417] FIG. 20 illustrates, according to one embodiment of the present invention, the configuration of an AP MLD including a main AP and an auxiliary AP having a continuous operation channel and a method for setting the operation channel.

[0418] Referring to Fig. 20(a), three AP MLDs belong to the AP MLD. In this case, AP1 functions as the Primary AP, and AP2 functions as an auxiliary AP paired with the Primary AP. AP3 is a general AP.

[0419] Referring to Fig. 20(b), the Primary AP and the auxiliary AP operate on consecutive operating channels (two 160 MHz channels located in a specific 320 MHz channel).

[0420] AP MLDs and non-AP MLDs connected via multiple links having continuous operating channels can communicate in the following way.

[0421] 1. STAs (AP STA and non-AP STA) operating on each link (Primary link and auxiliary link(s)) perform a backoff procedure through the primary channel of each link. When the backoff procedure is completed, the STA operating on the auxiliary link keeps the backoff counter at 0.

[0422] 2-1. When the backoff procedure of the STA (AP STA and non-AP STA) operating on the Primary link is completed, the MLD containing the STA initiates transmission through the Primary link and the secondary link where the backoff procedure has already been completed (including the link where it was completed simultaneously with the Primary link). At this time, the MLD performs the transmission on the Primary link and the secondary link as a synchronized transmission.

[0423] 2-2. When the backoff procedure of an STA (AP STA and non-AP STA) operating on the Primary link is interrupted, the MLD containing the said STA performs transmission through the Secondary Link when the backoff procedure of the STA operating on the Secondary Link is completed. If, at the time the backoff procedure of the STA operating on the Primary Link is interrupted, the backoff procedure of the STA operating on the Secondary Link has already been completed and the backoff counter is being maintained at 0, the MLD must create a new backoff counter for the STA operating on the Secondary Link and then perform the backoff procedure. At this time, the Retry counter and CW (Contention Window) of the STA operating on the Secondary Link are not changed. In this case, the meaning of the backoff procedure being interrupted is that the decrease of the backoff counter has stopped, such as in a situation where the Primary Channel is occupied by OBSS.

[0424] That is, when the backoff procedure of the Primary link is completed, as a result of the above-described 2-1, the MLD can occupy consecutive Operating channels at once by initiating synchronized transmission through the Primary link and the auxiliary links for which the backoff procedure has already been completed.

[0425] If the backoff procedure of the Primary link is interrupted, the MLD may initiate transmission through the secondary link as described in 2-2 above. The MLD initiating transmission through the secondary link terminates the TXOP obtained through the secondary link before the time when the backoff procedure on the Primary link is expected to continue (e.g., the time when the NAV of the STA operating on the Primary link is expected to become 0).

[0426] FIG. 21 illustrates a channel connection method of an MLD operating an STA in two links having continuous operating channels according to an embodiment of the present invention.

[0427] Referring to FIG. 21, a primary link and an auxiliary link, each having an 80 MHz operating BW, are operated within a specific 160 MHz channel.

[0428]

[0429] *426 The procedure for obtaining the first TXOP by MLD is as follows.

[0430] The MLD first completes the channel access procedure (backoff procedure) on the A20 of the auxiliary link (the primary 20 MHz channel of the BSS operating on the auxiliary link) but does not initiate transmission on the auxiliary link; instead, it performs the operation of keeping the backoff counter of the auxiliary link at 0 to perform transmission synchronized with the primary link. When the channel access procedure is completed on the P20 of the primary link (the primary 20 MHz channel of the BSS operating on the primary link), the MLD initiates transmission not only through the primary link but also through the auxiliary link, where the backoff counter is already 0. At this time, the MLD performs transmission synchronized with the STAs of the primary link and the auxiliary link. At this time, the two 80 MHz PPDUs transmitted by the MLD through the two links are indicated as having a BW field of 160 MHz, so that external terminals can perceive them as a single 160 MHz PPDU.

[0431] The procedure for obtaining the second TXOP by MLD is as follows.

[0432] When the MLD completes the channel access procedure (backoff procedure) on the A20 of the auxiliary link (the Primary 20 MHz channel of the BSS operating on the auxiliary link), it initiates transmission on the auxiliary link, taking into account that the Primary link is occupied by the OBSS. At this time, the TXOP (or PPDU) initiated on the auxiliary link is terminated before the time when the TXOP of the OBSS occupying the Primary link is expected to terminate.

[0433] The procedure for obtaining the 3rd TXOP by MLD is as follows.

[0434] When the MLD completes the channel access procedure (backoff procedure) at P20 of the Primary link, it initiates a TXOP on the Primary link. After initiating transmission on the Primary link, the MLD loses the ability to perform CCA on the secondary link, and thus the Backoff counter of the secondary link may not decrease to 3 or less. However, an MLD capable of performing CCA on the secondary link may be able to continuously decrease the Backoff counter of the secondary link.

[0435] <Method for transmitting / receiving MU PPDU for terminals performing nonprimary (secondary) channel access using a single link>

[0436] As described above, a channel access method using a non-primary channel can be considered as a method to improve the channel accessibility of Wi-Fi STA, and in the case of MLD, a channel accessibility enhancement method utilizing the characteristics of MLD (such as the aforementioned Overlapping BSS) can be utilized. The common feature of the various channel access methods provided in the present invention is that the transmitting device does not perform channel access only through a single primary channel, but performs channel access using another channel (such as a non-primary channel or a primary channel of an auxiliary link) when the primary channel is occupied by another device.

[0437] As such, since the transmitting device can initiate transmission through a channel other than the primary channel, the receiving device must also wait for PPDU reception on a sub-channel other than the primary channel (such as a non-primary channel or the primary channel of an auxiliary link) if the state of the primary channel it observes is BUSY.

[0438] PPDUs transmitted by STAs (AP STAs and non-AP STAs) that have established channel access through a non-primary channel do not occupy the primary channel for transmission, but PPDUs transmitted by STAs that have established channel access through a primary channel can occupy the non-primary channel for transmission. This is because the state of the primary channel determined by the STA that has established channel access through a non-primary channel is always BUSY, and the STA establishing channel access through the primary channel establishes channel access through the primary channel regardless of the state of the non-primary channel.

[0439] Therefore, if the state of the primary channel determined by the transmitting device is IDLE, the transmitting device may transmit a PPDU that occupies both the primary channel and the non-primary channel, and the receiving device determined that the primary channel is BUSY may receive the PPDU through the non-primary channel. That is, a device receiving a PPDU on the non-primary channel may receive both the PPDU transmitted by the transmitting device after establishing a channel connection through the primary channel and the PPDU transmitted by the transmitting device after establishing a channel connection through the non-primary channel, and may have difficulty interpreting which index RU (or MRU (Multiple-RU)) its own RU indicated by the RU Allocation subfield of the received PPDU is. In other words, the transmitting device and the receiving device may have different judgments regarding the state of the primary channel (IDLE or BUSY), and accordingly, the channel through which the transmitting device established a channel connection and the channel through which the receiving device began receiving the PPDU may be different. The procedure for a conventional Wi-Fi STA to direct and acquire RU Allocation information is briefly explained through an embodiment of FIG. 22. Hereinafter, RU can be interpreted as a general term for not only existing RUs such as 26, 52, 106, 242, 484, 996, 996 x N (N is a natural number greater than 2)-tone size RU, but also MRUs (e.g., 52+26, 106+26, 484+242, 996+484 -tone size RU, etc.).

[0440] That is, the transmitting device may determine that the primary channel and the non-primary channel are idle, whereas the receiving device may determine that the primary channel is busy and the non-primary channel is idle. In this case, the transmitting device can transmit a PPDU that occupies both the primary channel and the non-primary channel. However, since the primary channel is busy, the receiving device cannot receive the PPDU on the primary channel but can receive the PPDU through the non-primary channel. Because the receiving device received the PPDU through the non-primary channel, it can interpret the fields included in the PPDU (e.g., RU allocation subfield, etc.) based on the non-primary channel. However, the transmitting device can generate fields based on the primary channel and include them in the PPDU. Therefore, in this case, if the receiving device interprets the fields included in the received PPDU based on the non-primary channel, it may interpret the fields included in the PPDU differently from the transmitting device. Therefore, in this case, it is necessary to ensure that the receiving device interprets the fields included in the PPDU based on the primary channel.

[0441] To this end, when a transmitting device transmits a PPDU using both a primary channel and a non-primary channel, the receiving device can interpret the fields included in the PPDU based on the primary channel even if it receives the PPDU from the non-primary channel.

[0442] In another embodiment of the present invention, instruction information indicating that a non-primary channel interprets the fields included in the PPDU based on the primary channel may be included and transmitted in the PPDU.

[0443] FIG. 22 illustrates an embodiment of a method for assigning resource units to each STA using a resource unit assignment subfield indicated by the preamble of a PPDU and a method for indicating a content channel.

[0444] FIG. 22 (a) illustrates a situation in which two 484-tone RUs and one 996-tone RU included in the 160 MHz band are allocated to STAs A, B, C, and D. STAs A and B are allocated RU#1 (484-tone size RU) located in the lowest frequency range, STA C is allocated RU#2 (484-tone size RU), and STA D is allocated RU#3 (996-tone size RU).

[0445] As shown in FIG. 22 (a), a transmission device transmitting a PPDU that allocates RUs indicates the RU configuration and information of the STA allocated to each RU through a Signaling field (e.g., HE / EHT / UHR SIG field) included in the DL PPDU. At this time, the Signaling field transmitted through each 20 MHz subchannel may include the same or different Content channels.

[0446] FIG. 22 (b) illustrates the configuration of a Content channel. Each Content channel includes an RU Allocation subfield and a User field. At this time, the RU Allocation subfields included in Content channel #1 correspond to the odd-numbered 20 MHz sub-channels (see FIG. 22 (a)), and the RU Allocation subfields included in Content channel #2 correspond to the even-numbered 20 MHz sub-channels (see FIG. 22 (a)).

[0447] Each RU Allocation subfield included in the Content channel indicates RU information for the corresponding 20 MHz subchannel. More specifically, the first and second RU Allocation subfields included in Content channel #1 indicate RU information corresponding to the 20 MHz #1 and 20 MHz #3 subchannels, respectively, and the first and second RU Allocation subfields included in Content channel #2 indicate RU information corresponding to the 20 MHz #2 and 20 MHz #4, respectively.

[0448] Referring to FIG. 22 (a), the 20 MHz #1 sub-channel corresponds to RU#1, and thus the first RU Allocation subfield included in Content channel #1 indicates information about RU#1. At this time, the RU Allocation subfield also indicates the number of users to be allocated the corresponding RU, and among the User fields indicated after the RU Allocation subfields, the User field with a specified number is interpreted as having been allocated the RU indicated through the corresponding RU Allocation subfield.

[0449] In the example of Fig. 22 (b), the first RU Allocation subfield included in Content channel #1 indicates 1 User, and thus RU #1 is assigned to STA A corresponding to the first User field included in Content channel #1. Since the second RU Allocation subfield included in Content channel #1 indicates RU #2 corresponding to 20 MHz #3 and indicates 1 User, RU #2 is assigned to STA C corresponding to the second User field included in Content channel #1.

[0450] Content channels #1 and #2 appear alternately every 20 MHz band, and their specific indicated locations can be verified through Fig. 22 (c). Therefore, an STA wishing to determine the location of the RU assigned to it can obtain the RU information assigned to it by receiving two types of Content channels through a specific 40 MHz band (e.g., a specific 40 MHz band included in the Primary 40 MHz, Secondary 40 MHz, or Secondary 80 / 160 MHz band), checking whether the User field corresponding to it is included in the Content channel, and then verifying the RU information indicated by the RU Allocation subfield corresponding to its User field. However, Content channels located in different 80 MHz segments may contain different content even if they have the same index. For example, Content channel #1 indicated at 20 MHz #1 and Content channel #1 indicated at 20 MHz #5 may have different content.

[0451] Figure 23 illustrates the ambiguity problem regarding the interpretation of the assigned RU of an STA that receives a preamble in a non-primary channel.

[0452] Case 1 and Case 2 of FIG. 23 illustrate the cases of a DL MU PPDU transmitted by an AP that has established a channel connection on a Primary 20 MHz channel and a DL MU PPDU transmitted by an AP that has established a channel connection on a Secondary 20 MHz channel, respectively.

[0453] Case 1 is a situation that occurs when the AP determines that the primary channel (Primary 20 MHz sub-channel) is IDLE and the STA determines that the primary channel is Busy, and Case 2 is a situation that occurs when both the AP and the STA determine that the primary channel is Busy.

[0454] In both Case 1 and Case 2, the STA waits for reception of the PPDU via S20 and receives the preamble, and by receiving the Content channel included in the preamble, it confirms that the RU assigned to it is a 242-tone size RU located in the lowest frequency band.

[0455] However, in the case of Case 1 and Case 2, the location of the 242-tone size RU located in the lowest frequency band is different, and therefore the STA has a problem in that it cannot determine whether the RU assigned to it is the RU corresponding to Case 1 or the RU corresponding to Case 2.

[0456] The following two methods can be used to resolve the ambiguity in the interpretation of the assigned RU of such a receiving device.

[0457] 1) First, when the receiving device identifies the RU indicated by the RU Allocation subfield of the received PPDU, it interprets the RU Allocation subfield in different ways by considering whether the device that transmitted the received PPDU performed channel access through the primary channel or performed channel access through the non-primary channel. In this case, the different ways of interpreting the RU Allocation subfield mean that the reference frequency used when interpreting the location of the RU indicated by the RU Allocation subfield is different. That is, the sub-channel corresponding to a specific sequence of RU Allocation subfields indicated by the UHR-SIG (or EHT-SIG, HE-SIG) field may differ depending on whether the device transmitting the PPDU containing the corresponding SIG field performed channel access on the primary channel or on the non-primary channel.

[0458] 2) Secondly, the transmitting device may apply a setting to the signaling fields of the PPDU transmitted after performing channel access on a non-primary channel (e.g., Bandwidth, RU Allocation subfield, Puncturing information, etc.) to indicate that the band including the primary channel is punctured in the PPDU transmitted after performing channel access through the primary channel. That is, the transmitting device may set the signaling fields of the non-primary channel PPDU in the same way as the PPDU transmitted after performing channel access through the primary channel, but indicate that the band including the primary channel (e.g., Primary 80 MHz segment) is punctured. In this case, the receiving device can obtain the RU information allocated to it by interpreting the received PPDU as if it were transmitted by the device that performed channel access on the primary channel, regardless of which channel the transmitting device used to perform channel access.

[0459] As described in the first method above, the receiving device determines whether the received PPDU was transmitted by a transmitting device that has completed channel access through the primary channel or by a transmitting device that has completed channel access through the non-primary channel, and must interpret the RU Allocation subfield in different ways. In this case, the RU Allocation subfield refers to the RU Allocation subfield included in the Signaling field located in the Preamble of the MU PPDU (e.g., included in the HE-SIG, EHT-SIG, UHR-SIG fields, etc.) and / or the RU Allocation subfield located in the User field included in the trigger frame.

[0460] A method for a receiving device to determine whether a transmitting device has transmitted a PPDU after performing channel access on a certain channel may be to utilize direct or indirect information indicated by the transmitting device.

[0461] According to one embodiment of the present invention, an STA (AP STA and non-AP STA) that transmits a first PPDU after performing channel access through a non-primary channel may set the specific field of the first PPDU in a manner different from the specific field of the second PPDU transmitted after performing channel access through a primary channel. In this case, the specific subfield may be a field included in the U-SIG (Universal SIG field). For example, an STA that transmits a PPDU after performing channel access through a primary channel may set the specific field of the U-SIG to 0, and an STA that transmits a PPDU after performing channel access through a non-primary channel may set the specific field of the PPDU to a non-zero value. In this case, a device receiving the PPDU may determine, based on the specific field, whether the device transmitting the PPDU performed channel access through a primary channel and transmitted the PPDU, or performed channel access through a non-primary channel and transmitted the PPDU.

[0462] According to another embodiment of the present invention, even if the transmitting device does not indicate whether it has performed channel access through a primary channel or through a non-primary channel, it may be possible for the receiving device to determine the channel access method of the transmitting device on its own. For example, a receiving device that receives an 80 MHz PPDU occupying a secondary 80 MHz segment from a STA (AP STA and non-AP STA) of a BSS with an operating BW of 160 MHz can recognize that the STA transmitted the 80 MHz PPDU after performing channel access through a non-primary channel located in the secondary 80 MHz segment. That is, the receiving device can obtain information about the channel where the transmitting device performed channel access based on the BW information of the received PPDU.

[0463] The receiving device of the PPDU interprets the RU Allocation subfield included in the received PPDU in the following way, based on whether the received PPDU was received from a device that performed Channel Access through the primary channel or from a device that performed Channel Access through the non-primary channel.

[0464] First, when it is determined that the received PPDU was transmitted by a device that performed channel access on the primary channel, the receiving device interprets the RU Allocation subfield received on the non-primary channel in the same way as the RU Allocation subfield received on the primary channel.

[0465] Second, when it is determined that the received PPDU was transmitted by a device that performed channel access on a non-primary channel, the receiving device interprets the RU Allocation subfield received on the non-primary channel as if it were transmitted by a device using the non-primary channel as a primary channel. That is, the receiving device interpreting the RU Allocation subfield received on the non-primary channel must interpret the received RU Allocation subfield by considering that the receiving device is the primary channel and that the 80 MHz segment containing the non-primary channel is the primary 80 MHz segment. In this process, when the receiving device interprets the location of the RU indicated through the RU Allocation subfield received on the non-primary channel, it can confirm the location of the RU allocated to itself by interpreting that the location of the RU indicated through the RU Allocation subfield has changed by the frequency offset between its primary channel and the non-primary channel.

[0466] When the second method described above is used, the transmitting device configures the signaling fields of the PPDU in the same manner as when transmitting the PPDU after establishing a channel connection through the primary channel. However, since the transmitting device establishes a secondary channel connection during the time interval when the primary channel is determined to be busy, the PPDU transmitted after establishing a channel connection through the non-primary channel is always transmitted without occupying the primary channel. In other words, when the transmitting device transmits the PPDU after establishing a channel connection on the non-primary channel, it must transmit the PPDU in a form that punctures the primary channel (a form that does not occupy the primary channel).

[0467] For example, when a transmission device determines that the primary channel is busy and performs channel access through a non-primary channel located in the secondary 80 MHz segment band, when transmitting a PPDU through the secondary 80 MHz segment band, it must set the BW field of the PPDU to 160 MHz and indicate that Preamble Puncturing has been applied to the sub-channel where the primary 20 MHz channel is located. At this time, the method of applying Preamble Puncturing to the sub-channel located in the primary 20 MHz channel may be to puncture the primary 20 MHz sub-channel or to puncture the entire band including the primary 20 MHz sub-channel (e.g., the primary 40 MHz band or the primary 80 MHz segment).

[0468] That is, the conventional Wi-Fi constraint that Preamble Puncturing should not be applied to the Primary 20 MHz subchannel may not apply to PPDUs transmitted after performing channel access on a non-primary channel.

[0469] In this case, the receiving device can determine whether the transmitting device has performed channel access through the primary channel or through the non-primary channel based on the RU Allocation subfield included in the PPDU. More specifically, the receiving device can recognize that the device transmitting the PPDU has performed channel access through the non-primary channel when the RU Allocation subfield of the received PPDU indicates that the RU located in the primary channel has been punctured. At this time, the RU Allocation subfield indicating that the RU has been punctured refers to the RU Allocation subfield interpreted as 'Punctured 242-tone RU'. At this time, the 20 MHz sub-channel indicated as Punctured 242-tone RU is a sub-channel that is not occupied because puncturing has been applied to the PPDU.

[0470] However, when the receiving device obtains information about the RU allocated to it through the RU Allocation subfield included in the PPDU, it can interpret the RU Allocation subfield in the same way regardless of whether the channel used by the device that transmitted the PPDU for channel access is a primary channel or a non-primary channel.

[0471] FIG. 24 illustrates a method in which an AP that performs channel access through a non-primary channel directs BW and RU allocation information of a PPDU according to an embodiment of the present invention.

[0472] Referring to FIG. 24, the AP performs channel access through a non-primary channel and then transmits an 80 MHz PPDU occupying a secondary 80 MHz segment. At this time, the AP indicates that the BW of the PPDU is 160 MHz through the U-SIG of the PPDU. At this time, the indicated PPDU BW can be determined as the BW including the frequency band and primary channel occupied by the actual PPDU.

[0473] In addition, since the PPDU that the AP actually transmits does not occupy the Primary 80 MHz segment band, it does not allocate RUs through the RU Allocation subfields corresponding to the Primary 80 MHz segment band among the RU Allocation subfields included in the PPDU. At this time, the AP indicates that the corresponding subchannel is punctured through the RU Allocation subfield corresponding to the Primary 80 MHz segment.

[0474] An STA receiving a PPDU from an AP recognizes that the received PPDU is a PPDU of 160 MHz BW and checks the RU Allocation subfields to identify the RU assigned to it. The STA confirms that the subchannel corresponding to the RU Allocation subfield corresponding to its User field is the 20 MHz #5 subchannel included in the Secondary 80 MHz Segment. Therefore, the STA can recognize that the RU assigned to it is the RU located at 20 MHz #5. At this time, by receiving the RU Allocation subfields corresponding to the Primary 80 MHz segment among the received RU Allocation subfields, the STA can confirm that the RU assigned to it does not exist in the Primary 80 MHz segment. In other words, because the RU Allocation subfield indicating that the subchannel corresponding to the Primary 80 MHz segment has been punctured is included in the content channel, the STA can clearly recognize that the band corresponding to the RU Allocation subfield corresponding to its User field is 20 MHz #5.

[0475] Method for transmitting a trigger frame and responding to a trigger frame by terminals performing a non-primary channel access procedure using a single link

[0476] A trigger frame is a Wi-Fi control frame in which a response by a receiving device is performed in a manner instructed or requested by the transmitting device. For example, an AP can instruct a STA to respond with a TB PPDU by transmitting a Basic trigger frame to the STA.

[0477] The basic trigger frame includes a Common Info field and a User Info field, and a brief description of the Common Info field and the User Info field is as follows. The Common Info field is a field containing information commonly instructed to multiple STAs responding to the TB PPDU, such as the length of the TB PPDU, whether additional trigger frames are transmitted, whether carrier sensing results should be considered when responding to the TB PPDU, and UL BW information to be recorded in the BW field of the TB PPDU. The User Info field instructs the RU information to which each STA must respond to the TB PPDU, the FEC coding method, MCS information to be applied to the TB PPDU, DCM (dual carrier modulation), target Rx power information, etc., and each STA responds to the TB PPDU based on the information obtained through the User Info field corresponding to it.

[0478] In addition, the MU-RTS trigger frame, which can be utilized for protection, is also a type of trigger frame. An AP intending to transmit a DL MU PPDU can perform protection with multiple STAs simultaneously by transmitting a MU-RTS frame requesting a CTS frame response from one or more STAs. A detailed explanation of the MU-RTS trigger frame is as follows.

[0479] MU-RTS is a type of trigger frame, and STAs that receive a MU-RTS trigger frame and whose AID12 (the LSB 12 bits of the Association ID) is indicated in the User field included in the MU-RTS frame must simultaneously respond with a CTS frame. If the AP performs TXOP protection using a MU-RTS frame, there is an advantage in that TXOPs can be protected from adjacent devices of each of the multiple STAs that are the destination devices of the DL MU PPDU (Down-link multi-user PPDU) because multiple STAs respond with a CTS frame. Additionally, the MU-RTS frame can also be used for the purpose of protecting the UL MU PPDU. More specifically, before requesting a TB (trigger-based) PPDU from multiple STAs via a trigger frame, the AP can transmit a MU-RTS frame to cause the multiple STAs that will respond to the TB PPDU to respond with a CTS frame. At this time, the CTS frame responded to by the aforementioned multiple STAs serves to induce the neighbor STAs of each STA to set up a NAV that protects the TB PPDU and the Ack frame (Ack, Block Ack, etc.) to be transmitted after the TB PPDU, and through this, Legacy STAs that cannot recognize (interpret, decode) the trigger frame and the TB PPDU may not perform channel access during the packet switching sequence period (or TXOP) initiated by the trigger frame.

[0480] FIG. 25 illustrates an embodiment of a transmission / TXOP protection method using a MU-RTS frame and a CTS frame.

[0481] Referring to FIG. 25, prior to transmitting the MU PPDU, the AP transmits a MU-RTS frame to STA1 and STA2, which are the destination devices of the MU PPDU, and STA1 and STA2 receive the MU-RTS frame and respond with a CTS frame after SIFS.

[0482] STA1_Neighbor, the neighbor STA of STA1, receives the CTS frame transmitted by STA1 and sets the NAV based on the information specified in the Duration field of the CTS frame. STA2_Neighbor, the neighbor STA of STA2, receives the CTS frame transmitted by STA2 and sets the NAV based on the information specified in the Duration field of the CTS frame. STA1_Neighbor and STA2_Neighbor perform actions such as not decreasing the backoff counter, assuming that the Virtual CS (Virtual Carrier Sense) is busy while the NAV (counter) set after receiving the CTS frame remains a non-zero value. Consequently, since neighbor terminals that received the CTS frame do not attempt to transmit during the period when the NAV remains a non-zero value, the AP can be undisturbed by neighbor terminals while transmitting the MU PPDU and STA1 and STA2 respond with an Ack frame.

[0483] The aforementioned trigger frame is a frame type defined in 11ax, in which the Type (B3 B2) and Subtype (B7 B6 B5 B4) subfields of the Frame control field are set to 01 and 0010, respectively. That is, the trigger frame is a frame of Control Type with the Type subfield of the Frame control field being 01, and the Subtype value 0010 is used to indicate that it is a trigger frame type. In 11ax, trigger frames are defined so that an AP can request response frames from multiple STAs at once, and the aforementioned MU-RTS frame (a type of trigger frame) is used by the AP to request CTS frames from multiple STAs (non-AP STAs). Other trigger types, excluding MU-RTS, include Basic Tigger frame (UL MU PPDU request), Beamforming Report Poll Tigger frame (Beamforming Report request), MU-BAR Tigger frame (BlockAck request), Buffer Status Report Poll Tigger frame (Buffer Status Report request), GCR MU-BAR Tigger frame, Bandwidth Query Report Poll Tigger frame, NDP Feedback Report Poll Tigger frame, etc.

[0484] Figure 26 illustrates the format of a trigger frame.

[0485] A trigger frame consists of a MAC Header including a Frame Control field, a Common Info field, a User Info List field, a Padding field, and an FCS field. The Frame Control field includes Type and Subtype subfields, and in the trigger frame, the two subfields are set to 01 and 0010, respectively. The Common Info field includes a Trigger Type subfield to indicate the Type of the trigger frame, a UL Length subfield to indicate the length of the UL transmission being responded to, and other details are explained in detail through an embodiment of FIG. 27.

[0486] The User Info List field includes zero or one or more User Info fields containing information for indicating the target device of the trigger frame. In this case, in addition to the information indicating the target device, the User Info field includes parameter information (UL DCM, UL MCS, etc.) that the target device must utilize when transmitting a response frame after receiving the trigger frame, depending on the Type of the trigger frame. Detailed information regarding the User Info field is explained in detail through an embodiment of FIG. 28.

[0487] The padding field is added for the purpose of providing time for the destination devices of the trigger frame to prepare a response frame (e.g., UL TB PPDU, CTS frame, etc.) after receiving the trigger frame, and the AP transmitting the trigger frame can adjust the length of the padding field considering the performance of the destination devices. Additionally, in 11be (Wi-Fi 7, EHT), it may be added / adjusted to align the end time of a PPDU containing a trigger frame with other PPDUs, but a detailed explanation is omitted as this is not relevant to the content intended to be provided by the present invention.

[0488] The FCS (Frame Check Sequence) field contains a 32-bit CRC (Cyclic Redundancy Code) and is a value calculated by including the MAC Header and Frame Body fields. Since the function and setting method of the FCS field in a trigger frame are the same as the function and setting method of the FCS field included in a conventional MAC frame, a separate explanation is omitted.

[0489] Figure 27 illustrates an example of the format of the common information field of a trigger frame.

[0490] The trigger Type subfield (4-bit) is used to indicate the type (type, variant) of the trigger frame, and if the trigger Type subfield is 0, it indicates Basic; 1 indicates BFRP (Beamforming Report Poll); 2 indicates MU-BAR; 3 indicates MU-RTS; 4 indicates BSRP (Buffer Status Report Poll); 5 indicates GCR MU-BAR; 6 indicates BQRP (Bandwidth Query Report Poll); and 7 indicates NFRP (NDP Feedback Report Poll).

[0491] The UL Length subfield indicates the value that must be set in the L-SIG LENGTH field of the TB PPDU that is responded to through the trigger frame.

[0492] The More TF subfield is used to indicate whether there are more trigger frames to be transmitted after the corresponding trigger frame.

[0493] 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), and the STA transmitting the response frame after receiving a trigger frame in which the CS Required subfield is indicated as 1 must perform CS.

[0494] The UL BW subfield indicates the BW value that STAs responding to the TB PPDU after receiving a trigger frame must indicate to the Preamble (e.g., HE-SIG-A or U-SIG).

[0495] The GI And HE / EHT-LTF Type / Triggered TXOP Sharing Mode subfield indicates the GI (Guard interval) and HE(EHT)-LTF values ​​of the TB PPDU to be responded to, or is a subfield that indicates the Sharing mode when a MU-RTS trigger frame is used for TXOP sharing using a MU-RTS TXS (TXOP Sharing) trigger frame.

[0496] The MU-MIMO HE(EHT)-LTF Mode subfield indicates information regarding the HE(EHT)-LTF mode that should be applied to the TB PPDU to be responded to.

[0497]

[0498] *494Number Of HE / EHT-LTF Symbols subfield indicates the number of HE(EHT)-LTF symbols to be applied to the TB PPDU when the Doppler subfield is 0, and when the Doppler subfield is 1, it indicates information regarding the number of HE(EHT)-LTF symbols and the periodicity of the midamble.

[0499] The LDPC Extra Symbol Segment subfield indicates whether the LDPC extra symbol segment should appear in the TB PPDU being responded to, and if the LDPC Extra Symbol Segment subfield is indicated as 1, the LDPC extra symbol segment should appear in the TB PPDU.

[0500] The AP Tx Power subfield indicates a value related to the transmit power of the AP used when transmitting the trigger frame. The STA can perform Power Control when responding to a response frame based on the value indicated in the AP Tx Power subfield.

[0501] The Pre-FEC Padding Factor and PE Disambiguity subfields indicate information to clarify whether the Pre-FEC Padding Factor is 1 or 2, 3, or 4, and the length of the PE (Packet Extension).

[0502] The UL Spatial Reuse subfield consists of four Spatial Reuse subfields and indicates the values ​​to be set in the Spatial Reuse fields (HE-SIG-A) of the HE TB PPDU to be responded to.

[0503] The Doppler subfield indicates whether the TB PPDU to be responded to includes a midamble. However, the Doppler subfield may be reserved for the trigger frame that responds with an EHT TB PPDU. In this case, the meaning that the subfield is reserved may be that the STA responding with an EHT TB PPDU after receiving the trigger frame operates without considering the existence and setting value of the said subfield.

[0504] The HE / EHT P160 subfield indicates whether the TB PPDU being responded to is the HE TB PPDU or the EHT TB PPDU in the channel corresponding to P160 MHz.

[0505] The Special User Info Field Present subfield indicates whether the User Info field specified by the AID12 subfield as 2007 appears among the User Info fields.

[0506] The Trigger Dependent Common Info subfield is a field that appears only when the type of trigger frame specified by the Trigger Type field is a Basic trigger frame or an NFRP trigger frame.

[0507] Figure 28 illustrates an example of the format of the user information field of a trigger frame.

[0508] Referring to FIG. 28, the AID12 subfield indicates information regarding which STA the corresponding User Info field is associated with. That is, a STA in which the AID12 subfield of a specific User Info field is indicated with a value identical to its own AID can recognize that the corresponding trigger frame includes it as the destination device. In this case, the AID12 subfield can be set to 1 to 2006 (1 to 2007 in the case of an HE trigger) when indicating one associated STA.

[0509] In this case, the AID12 subfield can be set to 0 when assigning one or more RA-RUs (Random Access RUs) to associated STAs. That is, STAs associated with the AP may attempt to transmit TB PPDU using RA-RUs if, in the received trigger frame, there is no User Info field of AID12 where their AID is indicated, and there is a User Info field where AID12 is indicated as 0.

[0510] In this case, the AID12 subfield can be set to 2045 or 2044 when assigning one or more RA-RUs to unassociated STAs. That is, STAs not associated with an AP may attempt to send a TB PPDU using an RA-RU if a User Info field with AID12 indicated as 2045 or 2044 exists in the received trigger frame. In this case, the STA responding with the TB PPDU via the RA-RU must respond with a HE TB PPDU if AID12 is indicated as 2045, and may respond with an EHT TB PPDU if AID12 is indicated as 2044.

[0511] In this case, the AID12 subfield can be set to a preset value such as 4095 or 4094, and if the AID12 subfield is set to a preset value, it means that the padding field has started from that AID12 subfield. That is, if the AID12 subfield of the trigger frame is set to a value (preset) that indicates the start of the padding field, the STA recognizes that the padding field has started and may not attempt to parse the rest of the MAC frame.

[0512] At this time, the User Info field indicated by the AID12 subfield as 2046 may contain information about an unallocated RU. More specifically, when the AID12 subfield of a specific User Info field is indicated as 2046, the RU indicated by the RU Allocation subfield included in the specific User Info field may be an unallocated RU.

[0513]

[0514] The RU Allocation subfield of trigger frames other than the *509MU-RTS trigger frame indicates the size and location information of the RU (Resource Unit) / MRU (Multiple Resource Unit) allocated to the destination device (STA indicated via the AID12 subfield) of the corresponding User Info field. However, the RU Allocation subfield of the MU-RTS trigger frame is used to indicate the channel on which the destination device of the corresponding User Info field must respond to the CTS frame. More specifically, the RU Allocation subfield of the MU-RTS frame (of the User Info field) indicates whether the destination STA must respond to the CTS only on the Primary 20 MHz channel or on the Primary 40 MHz / Primary 80 MHz / Primary 160 MHz / 80 + 80 MHz / (Primary) 320 MHz (if transmitted by an EHT / UHR AP) channel when responding to the CTS frame. More specifically, the AP may indicate one of the values ​​from 61 to 64 through B7-B1 of the RU Allocation subfield in the User Info field of the specific STA to instruct the STA to respond to a CTS frame through the Primary 20 MHz, indicate 65 or 66 through B7-B1 of the RU Allocation subfield to instruct the STA to respond to a CTS frame through the Primary 40 MHz, indicate 67 through B7-B1 of the RU Allocation subfield to instruct the STA to respond to a CTS frame through the Primary 80 MHz, and indicate 68 to instruct the STA to respond to a CTS frame through the Primary 160 MHz.The instruction to respond to a CTS frame through the Primary 320 MHz channel is performed by indicating 69 through B7-B1 above. At this time, the PS160 subfield of the User Info field instructing to respond to a CTS frame through the Primary 20 / 40 / 80 / 160 MHz is set to 0, and the PS160 subfield of the User Info field instructing to respond to a CTS frame through the (Primary) 320 MHz is set to 1.

[0515] The UL FEC Coding Type subfield indicates the code type of the TB PPDU to be responded to, and if the UL FEC Coding Type subfield is 0, it indicates BCC (binary convolution coding), and if it is 1, it indicates LDPC (low density parity check).

[0516] The UL EHT-MCS subfield indicates the EHT-MCS to be applied to the TB PPDU being responded to.

[0517] The SS Allocation / RA-RU Information subfield is used as the RA-RU Information subfield when the AID12 subfield is not a value indicating that RA-RU has been allocated, i.e., when it is specified as 0, 2044, or 2045, and can be used as the SS Allocation subfield when the AID12 subfield is specified as a value other than 0, 2044, or 2045. When used as the SS Allocation subfield, the 6-bits corresponding to the SS Allocation subfield can be used as the Starting Spatial Stream subfield 4-bits and the Number Of Spatial Streams subfield 2-bits.

[0518] The UL Target Receive Power subfield indicates the predicted signal power value at which the TB PPDU to be responded will be received at the AP's antenna side. Therefore, when the STA responds to a TB PPDU, it may need to adjust the transmission power of the TB PPDU according to the value of the UL Target Receive Power subfield so that its TB PPDU can be received at the power predicted by the AP.

[0519] The PS160 subfield is used in conjunction with the RU Allocation subfield and indicates information regarding the location and size of the RU / MRU (Multiple-RU) allocated through the corresponding User Info field.

[0520] However, UL EHT-MCS, UL FEC Coding Type, UL DCM, SS Allocation / RA-RU Information, and UL Target Receive Power fields are not used in the MU-RTS trigger frame. In other words, they are Reserved subfields.

[0521] As described above, the AP transmits a MU-RTS frame and, through the User Info field, indicates the STA to respond to the CTS frame, and at the same time, indicates the band to which each STA must respond to the CTS frame as a band including the Primary 20 MHz channel.

[0522] However, if the non-primary channel access method provided in the present invention is utilized, the AP may perform channel access through the non-primary channel and then transmit a MU-RTS frame through channels excluding the Primary 20 MHz channel. In this case, the STA that responds with a CTS frame after receiving the MU-RTS frame must also respond with the CTS frame in a manner that does not occupy the Primary 20 MHz channel.

[0523] Therefore, an AP transmitting a MU-RTS frame after performing channel access on a non-primary channel must receive a CTS frame in response via the User Info field

[0524] This is a different operation from the conventional method where a Wi-Fi STA performs transmission only while occupying the Primary 20 MHz channel. Therefore, a STA that receives a MU-RTS frame from an AP that has established channel access through a non-primary channel must respond with a CTS frame in a form that does not occupy the primary channel.

[0525] However, as previously explained, an AP that transmits a MU-RTS frame and instructs the STA on the channel to respond to a CTS frame has a limitation in that it can only indicate channel types that occupy a Primary 20 MHz channel, such as Primary 20 / 40 / 80 / 160 / 320 MHz. Therefore, in order to allow an AP that transmits a MU-RTS frame after performing channel access through a non-primary channel to instruct the response of a CTS frame that occupies only the non-primary channel, more information than that in the existing MU-RTS trigger frame may need to be utilized between the AP / STA performing the non-primary channel operation. In this case, the aforementioned more information may refer to information about the channel used by the AP for channel access and / or more diverse instruction methods for instructing the STA on the channel to respond to a CTS frame.

[0526] According to one embodiment of the present invention, an AP transmitting a trigger frame may indicate whether it has performed channel access through a primary channel or through a non-primary channel. More specifically, the trigger frame may include a subfield that is indicated by different values ​​when transmitted by an AP that has performed channel access on a Primary 20 MHz channel and when transmitted by an AP that has performed channel access on a non-primary channel (another 20 MHz sub-channel excluding the Primary 20 MHz channel).

[0527] By setting a specific subfield included in the Common Info field of the trigger frame to a specific value, the AP can indicate to the STAs receiving the trigger frame that it has transmitted the trigger frame after performing channel access through the primary channel. When the AP performs channel access through a non-primary channel, it can set the specific subfield to a different value to indicate that it has not performed channel access through the primary channel. In this case, if the specific subfield has a size of 1 bit, the specific subfield may be set to 0 to indicate that the AP has performed channel access on the primary channel, or set to 1 to indicate that the AP has performed channel access on a channel other than the primary channel. At this time, if the specific subfield has a size of 2 bits, the specific subfield may be indicated as 0 to indicate that the AP has performed channel access in the primary channel, set to 1 to indicate that the AP has performed channel access through the first non-primary channel, set to 2 to indicate that the AP has performed channel access through the second non-primary channel, and set to 3 to indicate that the AP has performed channel access through the third non-primary channel. At this time, the first, second, and third non-primary channels may be sub-channels located in different 80 MHz segments.

[0528] When an AP specifies information regarding the channel it accessed through the Common Info field of a trigger frame, the STA must interpret the RU Allocation subfield included in its User Info field based on the information regarding the channel accessed by the AP. In other words, to determine the frequency band for which it will respond to a CTS frame, the STA that receives the MU-RTS frame must utilize both the channel information used for channel access specified by the AP through the Common Info field and the information specified through the RU Allocation subfield of its User Info field. Briefly explaining how the STA utilizes the information specified in the Common Info field and the information specified through the RU Allocation subfield, it may obtain the bandwidth for which the CTS frame must be responded to through the RU Allocation subfield and identify the location of the sub-channel to which the CTS frame must be responded based on the information specified in the Common Info field.

[0529] For example, when the RU Allocation subfield included in the User Info field of the STA is indicated as a value meaning Primary 80 MHz, if the channel accessed by the AP is indicated as Primary 20 MHz channel, the STA responds with a CTS frame through the Primary 80 MHz channel, and if the channel accessed by the AP is indicated as a non-primary channel, the STA responds with a CTS frame in the 80 MHz channel located in the 80 MHz segment containing the non-primary channel.

[0530] Alternatively, the AP can specify all frequency band and location information for each STA to respond to a CTS frame through the User Info field of each STA. That is, the AP can specify a RU that does not include a Primary 20 MHz channel by setting the RU Allocation subfield included in the User Info field to a value other than 61 to 69. For example, the AP can specify to respond to a CTS frame on one of the four 20 MHz sub-channels located in the Secondary 80 MHz segment by setting the RU Allocation subfield to 71 to 74, specify one of the two 40 MHz channels located in the Secondary 80 MHz segment by setting the RU Allocation subfield to 75 and 76, or specify a Secondary 80 MHz channel by setting it to 77. That is, the RU Allocation subfield included in the User Info field of the MU-RTS trigger frame can have the function of indicating a frequency range excluding the Primary 20 MHz channel.

[0531] Alternatively, the RU Allocation subfield may use the conventional setting method as is, but by having the RU Allocation subfield interpreted in combination with other subfields indicated in the User Info field, the AP may instruct the STA to respond to a CTS frame in a band other than the Primary 20 MHz channel. For example, the AP may indicate a value corresponding to 20 MHz through the RU Allocation subfield (e.g., 61 to 64) and indicate a first 80 MHz segment through the specific subfield, thereby instructing the STA to respond to a CTS frame through a specific 20 MHz subchannel located in the first 80 MHz segment. That is, the STA can determine the subchannels to which it must respond to a CTS frame by combining the indicated segment information and the indicated CTS frame response BW information.

[0532]

[0533] Efficient Operation Methods for Non-Primary Channel Access (NPCA)

[0534] The two channel access methods described in the present invention, 1) a channel access method using an auxiliary link and 2) a channel access method using a sub-channel other than a primary channel, are different channel access methods that can be used to achieve the same purpose. These two channel access methods differ in whether the STA performing the channel access changes the channel on which the channel access procedure (e.g., EDCA) is performed, or whether the channel on which the channel access procedure is performed is changed by changing the link in the active state.

[0535] In other words, both channel access methods are essentially the same in that they achieve the same effect by performing channel access by switching to another sub-channel (non-primary channel) excluding the primary channel when the primary channel is occupied. Therefore, the method for efficiently utilizing both channel access methods is also the same. Below, the efficient operation method for non-primary channel access proposed in the present invention can be applied to both the non-primary channel access method in which a single STA changes the channel performing channel access from the primary channel to another sub-channel (e.g., a non-primary channel or a sub-channel) rather than changing from the primary channel to the primary channel, and the channel access method using Overlapping BSS (the method using the primary link and auxiliary link described above). However, for the convenience of explanation, the efficient operation method for non-primary channel access described below will focus on the method in which a single STA (AP and / or non-AP STA) performs channel access using another sub-channel by switching to a sub-channel other than the primary channel. That is, the conditions for performing the non-primary channel access method described below can be applied in the same way as the conditions for switching the primary link to an inactive state and switching the secondary link to an active state. That is, the operation / decision method of the STA performing the non-primary channel access described below can be applied in the same way to the operation / decision method of the MLD using the Overlapping BSS.

[0536] A STA performing non-primary channel access can improve its channel access capability by performing channel access procedures through a subchannel other than the primary channel, even if the primary channel is occupied by an OBSS. However, when performing channel access procedures on a subchannel other than the primary channel, it must perform procedures to protect transmissions by other STAs that may be proceeding first on that subchannel (e.g., applying a Medium sync time), and is subject to the restriction that the TXOP acquired after completing the channel access procedure must be terminated at the same time as or earlier than the TXOP of the OBSS occupying its primary channel.

[0537] In other words, if the primary channel is occupied by an AP of another OBSS or a non-AP STA and is in a busy state, the STA can improve channel access capability by switching the channel to another sub-channel (sub-channel or non-primary channel) within the same bandwidth and performing the channel access procedure on that channel. Additionally, since it can resolve the issue where other sub-channels within the bandwidth cannot be used due to the primary channel being occupied, the channel can be used efficiently. In this case, to protect the operation of other STAs on the switched sub-channel, the STA must perform the channel access procedure on the switched channel within the TXOP set on the primary channel. Therefore, if the channel access procedure cannot be performed within the TXOP, the STA cannot perform the channel access procedure on the switched sub-channel. Accordingly, to determine whether the channel access procedure can be performed on the switched sub-channel, the STA can determine the remaining length of the TXOP set based on the frame transmitted from an AP of another OBSS or a non-AP STA on the primary channel prior to channel switching. Additionally, after receiving a frame, the STA can determine whether the received frame is a frame transmitted from an associated AP or a frame transmitted from an unassociated AP before determining the remaining duration of the TXOP. At this time, the STA can determine the remaining duration of the TXOP set on the primary channel based on the values ​​of the TXOP field or the duration field included in the received frame.

[0538] Therefore, an STA performing non-primary channel access must perform many additional operations (e.g., applying a medium sync time, changing the operating frequency from the primary channel to another subchannel) compared to when performing channel access on the primary channel, whereas the length of the TXOP obtainable through non-primary channel access may be more limited. In other words, considering the cost incurred to perform non-primary channel access, a situation may arise where the length of the TXOP obtainable through non-primary channel access is too short, and in this case, it may be more advantageous for the STA not to perform non-primary channel access. Therefore, even an STA capable of performing non-primary channel access may not always perform non-primary channel access when the primary channel is occupied by OBSS.

[0539] As explained above, if the STA determines that the primary channel of the bandwidth is occupied by the OBSS AP, it may switch channels to another sub-channel (non-primary channel) of the bandwidth. At this time, the STA can determine whether the frame (or PPDU) it has received is a frame transmitted by the OBSS AP (i.e., whether it is an inter-BSS frame or an intra-BSS frame). For example, it can determine whether the received frame is a frame transmitted by the OBSS AP through the BSS color information or MAC address of the received frame.

[0540] If the received frame is a frame transmitted from the OBSS AP, the primary channel is occupied by the OBSS AP and is in a busy state, so the STA cannot perform the channel access procedure on the primary channel. Therefore, the STA can perform the channel access procedure by switching the channel to a non-primary channel within the bandwidth described above.

[0541] At this time, the STA may determine whether to perform a non-primary channel connection based on the TXOP length of the OBSS occupying the primary channel. More specifically, the STA may perform a non-primary channel connection only when the TXOP length of the OBSS occupying its primary channel is longer than a specific value (Threshold) (or equal to or longer than). At this time, the length of the OBSS TXOP considered by the STA may refer to the length from the time it recognizes the OBSS TXOP until the time the OBSS TXOP ends. That is, the STA's decision is made based on the remaining time length of the OBSS TXOP remaining at the time of determining whether to perform a non-primary channel connection, rather than the total length of the OBSS TXOP. At this time, the method by which the STA obtains the remaining time length of the OBSS TXOP may be based on the NAV (network allocation vector) set based on the frame transmitted by the OBSS STAs, or based on the time indicated by the TXOP field included in the preamble of the OBSS PPDU.

[0542] At this time, the STA may decide whether to perform a non-primary channel connection based on the PPDU length of the OBSS occupying the primary channel. More specifically, the STA may perform a non-primary channel connection only if the PPDU length of the OBSS occupying its primary channel is longer than a specific value (Threshold) (or equal to or longer than). At this time, the length of the OBSS PPDU considered by the STA may refer to the total length of the OBSS PPDU or the length of time remaining from the time it recognizes the OBSS PPDU until the end of the said OBSS PPDU. That is, the STA may decide to perform a non-primary channel connection if the total length of the OBSS PPDU it has identified is longer than a specific value (Threshold), or if the length of the remaining OBSS PPDU from the time it recognizes the OBSS PPDU is longer than a specific value (Threshold). At this time, STA can obtain information on the total length of the OBSS PPDU or the remaining time length until the end of the OBSS PPDU from the RXVECTOR parameter generated by the OBSS PPDU. Since the specific process of obtaining information related to the length of the OBSS PPDU from the RXVECTOR parameter is explained through the embodiments of the present invention described later, a detailed explanation is omitted.

[0543] In other words, when an STA receives a PPDU from another STA (an AP or non-AP STA), it can determine whether the received PPDU is an intra-BSS PPDU transmitted from the BSS to which it belongs or an inter-BSS PPDU transmitted from a BSS to which it does not belong (an OBSS) based on the information contained in the received PPDU (e.g., BSS color, BSSID, or MAC address). If the received PPDU is an inter-BSS PPDU, the STA can confirm through CCA operations that the primary channel of the band in which it operates is occupied, and in this case, it cannot perform frame exchange (or channel access procedure) on the primary channel. Therefore, the STA can perform frame exchange or channel access by switching the channel to a channel other than the primary channel of the bandwidth in which it operates (e.g., a non-primary channel). In this case, for the STA to perform channel switching to another channel, the TXOP set by the received PPDU (or the TXOP set by another OBSS) must remain sufficient for channel switching and frame exchange (or channel connection). To determine this, the STA may compare a specific value associated with the received PPDU with a minimum duration threshold. If the specific value is greater than (or greater than or equal to) the minimum duration threshold, the STA may switch the channel to another channel to perform frame exchange or channel connection procedures.

[0544] At this time, a specific value associated with the received PPDU may be either the length of the received PPDU or the duration of the remaining TXOP. The length of the received PPDU may be the total length of the PPDU transmitted from the OBSS or the length of the remaining PPDU from the time the STA recognizes the PPDU, and the length of the remaining PPDU may be obtained based on the length field and rate field included in the PPDU. The duration of the remaining TXOP may refer to the length of the remaining TXOP from the time the STA recognizes the PPDU transmitted from the OBSS, and may be obtained by adding the length of the remaining PPDU to the value of the TXOP field included in the PPDU.

[0545] Alternatively, the STA may recognize the total length of the PPDU or the length of the remaining PPDU by the RXVECTOR parameter, which is generated in the PHY layer by the received PPDU and transmitted to the MAC layer. The embodiments described below explain specific values ​​based on the remaining TXOP duration, but may also be performed based on the total length of the PPDU or the length of the remaining PPDU as well as the remaining TXOP duration.

[0546] A specific value may be a value indicated by the AP through a Management frame transmitted by the AP (e.g., a Beacon frame and / or Probe Response frame and / or Association Response frame and / or a Management frame indicating whether to utilize a non-primary channel connection (a type of Operating Mode Notification frame)). Alternatively, the specific value may be a preset value (e.g., 1 ms or 2 ms, etc.).

[0547] At this time, the method for determining the TXOP length of the OBSS that the STA occupies the primary channel may be to use the value indicated through the TXOP field included in the Preamble of the received PPDU (e.g., HE-SIG-A or U-SIG) or the Duration / ID field of the MAC Header.

[0548] In this case, the STA can recognize the duration of the TXOP remaining after the reception of the frame based on the duration field or TXOP field included in the received frame. That is, the STA can recognize the remaining duration from the end of the received frame to the end of the TXOP set by the OBSS based on the value indicated by the duration field or TXOP field included in the frame. Accordingly, the STA can determine whether it can perform a channel access procedure by switching to a non-primary channel within the set TXOP based on the remaining duration, and if it is determined that channel switching and a channel access procedure (or frame exchange) can be performed within the remaining duration, it can perform a channel access procedure (or frame exchange) by switching to a non-primary channel. At this time, the STA may determine whether channel switching and channel access procedures can be performed within the remaining duration by comparing the remaining duration (or the total length of the PPDU or the length of the remaining PPDU, etc.) with a threshold value; if the remaining duration is greater than (or equal to or greater than) the threshold value, it may be determined that channel switching and channel access procedures can be performed. For example, if the value obtained by adding the value indicated by the TXOP field or the duration field to the duration of a frame (e.g., a received PPDU) is greater than the threshold value, the STA may determine that channel access procedures on a non-primary channel are possible. At this time, the length of the frame (or the duration of the PPDU) may be obtained based on the length field and rate field included in the frame. At this time, the threshold value may represent the minimum duration for the STA to perform channel switching and channel access.

[0549] Alternatively, the method by which an STA determines whether to perform channel access on a non-primary channel may be based on the length of the TXOP that it judges it can obtain through channel access on the non-primary channel, rather than based on the length of the TXOP of the OBSS occupying the primary channel. That is, the STA can decide to perform channel access on the non-primary channel only when the length of the TXOP that it can obtain through channel access on the non-primary channel is longer than a specific value (Threshold) (or equal to or longer than). In this case, while performing channel access procedures on a sub-channel other than the primary channel, if the length of the TXOP that can be obtained through channel access on the non-primary channel becomes shorter than a specific value (calculated based on the end time of the TXOP of the OBSS occupying the primary channel), the STA may switch back to the primary channel and perform channel access procedures. That is, if the STA fails to complete the channel access procedure of the non-primary channel before a specific time from the time the TXOP of the OBSS occupying its primary channel ends, it may abandon the non-primary channel access and switch back to the channel access procedure using the primary channel.

[0550] The method based on the length of the OBSS TXOP described above and the method based on the length of the TXOP that can be obtained are different methods for determining whether the TXOPs obtainable through non-primary channel access are sufficient (whether they are sufficiently efficient). An STA that decides whether to attempt non-primary channel access can use one of the two methods or both methods together to make a final decision on whether to perform non-primary channel access.

[0551] Additionally, in the process of determining whether to perform the channel access procedure in the non-primary channel, the STA may decide whether to switch to the non-primary channel operation by considering the switching delay or transition delay required to switch to the non-primary channel operation. More specifically, even if the STA is indicated that the TXOP of the OBSS occupying its primary channel is maintained for a longer time than the threshold, it may not switch to the non-primary channel operation mode if the time available to operate in the non-primary channel is shorter than the threshold when considering the time required to switch to the non-primary channel operation mode. That is, the STA may decide whether to switch to the non-primary channel operation mode based on whether the remaining 'time length of OBSS TXOP - Transition delay' is longer than (or longer than or equal to) the threshold.

[0552] For example, to determine whether the channel access procedure in the non-primary channel described above is possible, the STA may additionally consider a switching delay or a transition delay. That is, in the process of comparing a threshold value with a value obtained based on the value indicated by the duration field or TXOP field included in the received frame (or PPDU) (e.g., the value indicated by the TXOP field or duration field plus the duration of the PPDU), the threshold value may be set to the value obtained by adding the switching delay or a transition delay to the minimum value for performing channel switching and channel access procedures.

[0553] FIG. 29 shows an example of channel access in a non-primary channel when the primary channel is occupied according to an embodiment of the present invention.

[0554] Referring to FIG. 29, when the primary channel is busy due to a TXOP set by OBSS, the STA can perform a channel access procedure by switching the channel to a non-primary channel (sub-channel). FIG. 29 illustrates the channel status and channel access procedure verified from the perspective of an STA capable of performing non-primary channel access.

[0555] Before completing the backoff procedure on the primary channel (P20), the STA receives an RTS / CTS frame that the OBSS STA exchanges to initiate OBSS TXOP1. Based on the information contained in the received frame, the STA can determine that the remaining time length of OBSS TXOP1 is longer than the threshold value. Since the length of OBSS TXOP1 is sufficiently long, the STA performs a channel access procedure through a channel other than the primary channel (S20_1 in FIG. 29), acquires the TXOP, and performs frame exchange.

[0556] The STA that terminated its own TXOP before OBSS TXOP1 terminated performs the channel access procedure again through the primary channel (P20 in FIG. 29), and OBSS TXOP2 starts before the backoff procedure is completed. The STA confirms that the length of the OBSS TXOP2 it identified is shorter than the threshold value, and instead of performing the channel access procedure on a channel other than the primary channel, it waits for OBSS TXOP2 to terminate on the primary channel. Afterward, when OBSS TXOP2 terminates, it continues the channel access procedure on the primary channel.

[0557] As described above, it is possible to determine whether performing a non-primary channel connection is efficient or inefficient depending on the length of the TXOP that can be obtained through the non-primary channel connection, and the STA can determine whether to perform a non-primary channel connection based on the result of the determination.

[0558] Another type of inefficiency that can occur due to non-primary channel access arises when the primary channel status identified by the AP and the non-AP STA differs. As previously explained, the adjacent STAs of the AP and the non-AP STA may differ, and there are cases where the signal of an OBSS occupying the AP's primary channel is not received by a specific non-AP STA. Additionally, there may be cases where the signal of an OBSS occupying a specific non-AP STA's primary channel is not received by the AP.

[0559] As such, when the primary channel status confirmed by the AP differs from the primary channel status confirmed by the non-AP STA, the channels on which the AP and the non-AP STA perform channel access may differ. For example, the AP determines that the primary channel is IDLE and transmits a PPDU after completing channel access on the primary channel, but the non-AP STA determines via OBSS that the primary channel is BUSY and may be performing the channel access procedure on a subchannel other than the primary channel or waiting to receive a PPDU from the AP. Similarly, the non-AP STA determines that the primary channel is IDLE and transmits a PPDU after completing channel access on the primary channel, but the AP determines via OBSS that the primary channel is BUSY and may be performing the channel access procedure on a subchannel other than the primary channel or waiting to receive a PPDU. As such, when the AP and non-AP STA have different views of the primary channel, PPDU transmission fails due to channel mismatch between the transmitting and receiving devices.

[0560] This is a new problem that arose due to the introduction of non-primary channel access procedures, which was not experienced by conventional Wi-Fi STAs that operated only through primary channels. Therefore, in order to maximize the benefits and minimize losses from non-primary channel access, situations in which such problems occur must be reduced. However, the fact that the channel environments of STAs operating in different locations differ is a natural phenomenon caused by the characteristic that the range of wireless transmission signals is limited, and therefore, the phenomenon in which the judgments of two STAs regarding a specific channel may differ cannot be resolved.

[0561] However, based on information exchanged in advance between two STAs, a specific STA may be helped to determine the point in time when another STA has the same view as itself. As a simple example, if a specific STA has instructed another STA in advance that a signal transmitted by STA1 will be received by it, the other STA can anticipate that while it is receiving STA1's signal, STA1's signal will also be received by the specific STA. That is, based on the information provided by the specific STA, it is possible for the other STA to confirm that it has the same view as the specific STA at a specific point in time.

[0562] According to one embodiment of the present invention, an AP can instruct a non-AP STA on information related to an adjacent BSS (Overlapping), and the non-AP STA can determine whether to perform a non-primary channel connection (moving to a subchannel other than the primary channel for performing channel access procedures and / or listening (e.g., performing CCA and PD (Preamble / Packet detection), etc.) based on the information instructed by the AP. That is, the AP can transmit information about the adjacent OBSS to the associated non-AP STAs by including it in a management frame. For example, the AP can transmit a list of OBSS APs in a management frame, and when performing a non-primary channel connection operation, the non-AP STA can perform the non-primary channel connection procedure described above if the AP that transmitted the frame is included in the list information of the management frame based on the information related to the AP included in the received frame (or PPDU). That is, when a PPDU is transmitted from an OBSS AP, a non-AP STA can compare the AP-related information (BSS color information or MAC address) included in the PPDU with the list information included in the management frame. If the AP-related information is included in the list information, the non-AP STA can perform the channel access procedure on the non-primary channel as described above.

[0563] Specifically, the AP may notify non-AP STAs of information (a kind of list) regarding OBSSs capable of occupying its primary channel (i.e., OBSSs that change the state of the AP's primary channel to busy). In this case, the information regarding OBSSs that the AP notifies non-AP STAs of may be the BSS color information of the OBSSs and / or the MAC address of the Neighbor AP operating the said OBSS. In this case, the number of Neighbor APs indicated by the AP in relation to non-primary channel access may be smaller than the number of APs indicated by the AP through the RNR element (Reduced Neighbor Report) of the beacon frame. This is because the Neighbor APs indicated by the AP in relation to non-primary channel access are limited to APs operating BSSs capable of occupying the AP's primary channel.

[0564] A non-AP STA that receives information regarding an OBSS from an AP can determine whether to switch to non-primary channel operation (performing channel access procedures using a subchannel other than the primary channel and / or listening for reception on a subchannel other than the primary channel) by checking whether the OBSS occupying its primary channel when its primary channel is switched to BUSY is an OBSS included in the list of OBSS instructed by the AP.

[0565] Specifically, a non-AP STA may decide to perform non-primary channel operation when its primary channel is occupied by an OBSS and the color of the OBSS is included in the OBSS color list designated by the AP. That is, the non-AP STA can know that the OBSS that changed the state of its primary channel to B...

Claims

1. At a station performing non-primary channel access (NPCA), Transmitter / receiver; and Includes a processor, The above processor If pre-specified conditions are satisfied, access is performed on a non-primary channel instead of a primary channel, and Even if pre-specified conditions are satisfied, if the non-primary channel is occupied by the overlapping basic service set (OBSS), non-primary channel access is not performed. Station.

2. In Paragraph 1, The above processor Based on the NPCA switching delay between the station performing NPCA and the other station, start transmission to the other station, and The above NPCA switching delay is the time required for switching between the primary channel and the non-primary channel. Station.

3. In Paragraph 2, The above processor Starting transmission to the other station based on information regarding the NPCA switching delay transmitted by the other station Station.

4. In Paragraph 2, The above processor Deferring transmission to the other station based on information regarding the NPCA switching delay transmitted by the other station Station.

5. In Paragraph 4, The above processor When delaying transmission to the other station, even if the backoff counter reaches 0, the transmission to the other station is not performed, and a new backoff counter is acquired. Station.

6. In Paragraph 5, The above processor When acquiring the new backoff counter mentioned above, the size of the previously used CW (contention window) is maintained, and Maintaining the QSRC (quality of service short retry counter) Station.

7. In Paragraph 1, The above processor When a basic service set (BSS) color collision is detected in the above non-primary channel, the station transmits information about the BSS color collision in the above non-primary channel to the access point (AP) to which the station is connected. Station.

8. In Paragraph 8, Information regarding BSS color collisions in the above non-primary channel includes information regarding the channel in which the BSS color collision was recognized. Station.

9. In Paragraph 1, The above-mentioned pre-specified condition includes that the AP (access) operating the BSS to which the station belongs does not perform cooperative operations with the AP and other APs. Station.

10. In a method of operation of a station performing non-primary channel access (NPCA), A step of performing access on a non-primary channel rather than a primary channel if a pre-specified condition is satisfied; and A step including not performing non-primary channel access when the non-primary channel is occupied by the overlapping basic service set (OBSS) even if a pre-specified condition is satisfied. Method of operation.

11. In Paragraph 10, The above method of operation The method includes the step of initiating transmission to the other station based on the NPCA switching delay between the station performing NPCA and the other station, and The above NPCA switching delay is the time required for switching between the primary channel and the non-primary channel. Method of operation.

12. In Paragraph 11, The step of starting transmission to the other station based on the NPCA switching delay of the other station A step comprising initiating transmission to the other station based on information regarding the NPCA switching delay transmitted by the other station. Method of operation.

13. In Paragraph 11, The step of starting transmission to the other station based on the NPCA switching delay of the other station A step of deferring transmission to the other station based on information regarding the NPCA switching delay transmitted by the other station. Method of operation.

14. In Paragraph 13, The step of delaying transmission to the other station mentioned above When delaying transmission to the other station, the method includes the step of not performing transmission to the other station even if the backoff counter reaches 0, and acquiring a new backoff counter. Method of operation.

15. In Paragraph 14, The step of acquiring the new backoff counter mentioned above When acquiring the new backoff counter, the step of maintaining the size of the previously used CW (contention window) as is, and including the step of maintaining a QSRC (quality of service short retry counter). Method of operation.

16. In Paragraph 10, The above method of operation When a basic service set (BSS) color collision is detected in the non-primary channel, the method includes the step of transmitting information about the BSS color collision in the non-primary channel to the access point (AP) to which the station is connected. Method of operation.

17. In Paragraph 16, Information regarding BSS color collisions in the above non-primary channel includes information regarding the channel in which the BSS color collision was recognized. Method of operation.

18. In Paragraph 10, The above-mentioned pre-specified condition includes that the AP (access) operating the BSS to which the station belongs does not perform cooperative operations with the AP and other APs. Method of operation.

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