Method for transmitting and receiving data in wireless communication system, and wireless communication terminal using same

Abstract

The present invention provides a method and a device for operating a wireless communication terminal. Specifically, a wireless communication terminal according to the present invention may receive a physical layer protocol data unit (PPDU) from an overlapping basic service set (OBSS) access point (AP), which is not associated with the wireless communication terminal, in a primary channel of a bandwidth in which the wireless communication terminal operates. The preamble of the PPDU includes a transmission opportunity (TXOP) field and a duration field related to a TXOP duration configured by the OBSS AP. Thereafter, when a specific condition is satisfied, the wireless communication terminal may perform channel access by switching a channel from the primary channel of the bandwidth to a non-primary channel.

Description

Method for transmitting and receiving data in a wireless communication system and a wireless communication terminal using the same

[0001] The present invention relates to a channel access procedure in an overlapping operating channel.

[0002]

[0003] With the recent proliferation of mobile devices, wireless LAN (WLAN) technology, which can provide them with fast wireless Internet service, is attracting significant attention. WLAN technology utilizes short-range wireless communication technology to enable mobile devices such as smartphones, tablets, laptops, portable multimedia players, and embedded devices to wirelessly connect to the Internet at home, in businesses, or in specific service areas.

[0004] Since supporting the initial wireless LAN technology using the 2.4 GHz frequency, IEEE (Institute of Electrical and Electronics Engineers) 802.11 has been commercializing or developing various technology standards. First, IEEE 802.11b supports a communication speed of up to 11 Mbps while using the 2.4 GHz band. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5 GHz band instead of the 2.4 GHz band, thereby reducing the impact of interference compared to the considerably crowded 2.4 GHz band. It also uses OFDM (orthogonal frequency division multiplexing) technology to increase the communication speed to up to 54 Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication range than IEEE 802.11b. And IEEE 802.11g, like IEEE 802.11b, uses the 2.4GHz band to achieve a communication speed of up to 54Mbps and satisfies backward compatibility, which has garnered considerable attention. It is also superior to IEEE 802.11a in terms of communication distance.

[0005] And to overcome the limitations of communication speed, which has been pointed out as a vulnerability in wireless LAN, there is IEEE 802.11n, a technical standard established. IEEE 802.11n aims to increase the speed and reliability of networks and extend the operating range of wireless networks. More specifically, IEEE 802.11n supports High Throughput (HT) with data processing speeds of up to 540 Mbps or more, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology that uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates. In addition, this standard can use a coding method that transmits multiple redundant copies to increase data reliability.

[0006] As wireless LAN becomes more widespread and applications diversify, the need for new wireless LAN systems that support very high throughput (VHT) higher than the data processing speed supported by IEEE 802.11n has arisen. Among these, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) at the 5GHz frequency. Although the IEEE 802.11ac standard is defined only for 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 specification, multi-station wireless LAN speeds can reach at least 1Gbps and a maximum single-link speed of at least 500Mbps. This is achieved by extending the wireless interface concepts accepted in 802.11n, such as wider radio frequency bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256 QAM). In addition, there is IEEE 802.11ad, which transmits data using the 60 GHz band instead of the existing 2.4 GHz / 5 GHz. IEEE 802.11ad is a transmission standard that provides speeds of up to 7 Gbps using beamforming technology, making it suitable for streaming high-bitrate video such as large amounts of data or uncompressed HD video. However, the 60 GHz frequency band has a disadvantage in that it has difficulty passing through obstacles, so it can only be used between devices in short distances.

[0007] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard, which follows 802.11ac and 802.11ad as a wireless LAN standard, is nearing completion to provide high-efficiency and high-performance wireless LAN communication technology in high-density environments with densely packed APs and terminals. In an 802.11ax-based wireless LAN environment, high-frequency efficient 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 achieve this.

[0008] Additionally, development of new wireless LAN standards has begun to increase maximum transmission speeds to support emerging multimedia applications such as high-definition video and real-time gaming. 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 30 Gbps in the 2.4 / 5 / 6 GHz bands through wider bandwidth, increased spatial streams, and multi-AP cooperation.

[0009] Recently, discussions have begun on Ultra High Reliability (UHR) wireless LAN communication technology, a successor to the 802.11be standard, to overcome reliability issues that have been identified as limitations of wireless LAN. The UHR standard is currently under development with the goal of supporting low latency and low jitter in wireless LAN traffic with a high probability (e.g., greater than 99.9999%).

[0010]

[0011] The present invention aims to provide a method for improving channel accessibility for overlapping channels.

[0012] In addition, the present invention has a purpose of providing a method for performing a channel access procedure through a non-primary channel rather than a primary channel when the state of the primary channel (or primary channel) is busy.

[0013] The technical problems to be achieved in this specification are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0014]

[0015] In a non-AP (Access Point) multi-link device (MLD) including a plurality of stations according to the present invention, a processor includes a transceiver; and a processor, wherein the processor receives a preamble of an inter-BSS PPDU (Physical Layer Protocol Data Unit) from an OBSS (Overlapping Basic Service Set) AP (Access Point) that is not associated with the wireless communication terminal on a primary channel of a bandwidth in which the wireless communication terminal operates, the preamble of the inter-BSS PPDU including a TXOP field related to a transmission opportunity (TXOP) duration set by the OBSS AP, and when a specific condition is satisfied, switches the channel from the primary channel of the bandwidth to a non-primary channel, wherein the specific condition is whether a length of a remaining OBSS TXOP calculated based on the TXOP field or the duration field is greater than a minimum duration threshold value.

[0016] Additionally, in the present invention, the state of the primary channel is busy by the OBSS AP.

[0017] Additionally, in the present invention, the minimum duration threshold is a minimum value for the wireless communication terminal to switch the channel to the non-primary channel.

[0018] Additionally, in the present invention, the processor receives a management frame from an AP associated with the wireless communication terminal, wherein the management frame includes list information of adjacent APs.

[0019] Additionally, in the present invention, the list information includes BSS color information and / or MAC address of each of the APs.

[0020] Additionally, in the present invention, the channel switch to the non-primary channel is performed when the primary channel is occupied by one of the APs.

[0021] Additionally, in the present invention, the processor compares the BSS color information or MAC address of the inter-BSS PPDU with the BSS color information or MAC address included in the list information.

[0022] Additionally, in the present invention, it is determined whether the specific condition is satisfied by additionally considering the channel switch delay of the wireless communication terminal in addition to the length of the remaining OBSS TXOP.

[0023] Additionally, in the present invention, the processor transmits a primitive from the MAC layer to the PHY layer to perform the channel switch to the non-primary channel.

[0024] In addition, the present invention provides a method including the steps of receiving a Physical Layer Protocol Data Unit (PPDU) from an Overlapping Basic Service Set (OBSS) Access Point (AP) that is not associated with the wireless communication terminal on a primary channel of a bandwidth in which the wireless communication terminal operates, wherein a preamble of the PPDU includes a TXOP field and a Duration field related to a transmission opportunity (TXOP) duration set by the OBSS AP; and performing a channel access by switching a channel from the primary channel of the bandwidth to a non-primary channel when a specific condition is satisfied, wherein the specific condition is whether a specific value obtained based on a value indicated by the TXOP field or the Duration field is greater than a minimum duration threshold value.

[0025]

[0026] One embodiment of the present invention has the effect of efficiently performing channel access in an environment where operating channels overlap.

[0027] In addition, according to the present invention, by performing channel access through a plurality of BSSs operating in overlapping operating channels, even if the primary channel of a specific BSS among the plurality of BSSs is occupied by another device, channel access rights can be obtained through the primary channel of another BSS.

[0028] Additionally, according to one embodiment of the present invention, when the state of the primary channel is busy, a channel access procedure can be performed through a non-primary channel.

[0029] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention belongs from the description below.

[0030]

[0031] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0032] Figure 2 illustrates a wireless LAN system according to another embodiment of the present invention.

[0033] Figure 3 shows the configuration of a station according to one embodiment of the present invention.

[0034] Figure 4 shows the configuration of an access point according to one embodiment of the present invention.

[0035] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0036] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0037] FIG. 7 shows various standard generation-specific physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0038] Figure 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0039] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0040] FIG. 10 shows a transmission / TXOP protection method using an MU-RTS frame and a CTS frame according to an embodiment of the present invention.

[0041] Figure 11 shows a mapping table of user priority and access category.

[0042] Figure 12 shows an example of a channel connection procedure through a secondary channel when the state of the primary channel is busy.

[0043] Figure 13 illustrates an embodiment of a transmission length limitation of a PPDU transmitted after performing channel access through a subchannel.

[0044] FIG. 14 illustrates an embodiment of a method for limiting the length of a TXOP obtained through channel access via a subchannel.

[0045] FIG. 15 illustrates a method for an AP to manage a primary operating channel by obtaining TXOPs through primary and secondary channels according to one embodiment of the present invention.

[0046] FIG. 16 illustrates an example of a method for configuring an AP MLD including a primary AP and an auxiliary AP having overlapping operating channels and setting an operating channel, according to one embodiment of the present invention.

[0047] FIG. 17 illustrates an example of a procedure for an AP MLD to obtain a TXOP using a primary BSS and a secondary BSS, according to one embodiment of the present invention.

[0048] FIG. 18 illustrates an example of a format of an RNR element transmitted by an AP MLD to indicate an auxiliary AP, according to one embodiment of the present invention.

[0049] FIG. 19 illustrates a method in which a channel switch of an auxiliary BSS is instructed / performed together when a channel switch for a primary BSS is performed, according to one embodiment of the present invention.

[0050] FIG. 20 illustrates a configuration of an AP MLD including a primary AP and a secondary AP having continuous operating channels and a method for setting operating channels, according to one embodiment of the present invention.

[0051] FIG. 21 illustrates a channel access method of an MLD that operates STAs on two links having continuous operating channels, according to one embodiment of the present invention.

[0052] FIG. 22 illustrates an embodiment of a method for performing resource unit allocation to each STA using a resource unit allocation subfield and a resource unit allocation subfield indicated through a preamble of a PPDU and a method for indicating a content channel.

[0053] Figure 23 illustrates the ambiguity problem of allocation RU interpretation of an STA that receives a preamble on a subchannel.

[0054] FIG. 24 illustrates a method for an AP performing channel access through a subchannel to indicate BW and RU allocation information of a PPDU according to one embodiment of the present invention.

[0055] Figure 25 illustrates an embodiment of a transmission / TXOP protection method using an MU-RTS frame and a CTS frame.

[0056] Figure 26 illustrates the format of a trigger frame.

[0057] Figure 27 illustrates an example of the format of the common information field of a trigger frame.

[0058] Figure 28 illustrates an example of the format of the user information field of a trigger frame.

[0059] FIG. 29 illustrates an example of channel access in a non-primary channel when the primary channel is occupied according to one embodiment of the present invention.

[0060] FIG. 30 illustrates an example of the operation of STAs on a non-primary channel based on information related to OBSS transmitted from an AP according to an embodiment of the present invention.

[0061] FIG. 31 illustrates an example of a method for determining whether to perform an operation on a non-primary channel considering the TBTT of a BSS according to an embodiment of the present invention.

[0062] FIG. 32 illustrates an example of a channel access method according to reception of an RTS frame of an AP according to an embodiment of the present invention.

[0063] FIG. 33 illustrates another example of a channel access method according to reception of an RTS frame of an AP according to an embodiment of the present invention.

[0064] FIG. 34 illustrates an example of a method for transmitting a CTS-to-self frame based on reception of an RTS frame of an AP according to an embodiment of the present invention.

[0065] FIG. 35 illustrates an example of a method for setting information and NAV obtained by an STA based on reception of an OBSS PPDU according to an embodiment of the present invention.

[0066] FIG. 36 illustrates an example of a method for setting NAV and a method for using a subchannel when an STA receives an OBSS PPDU according to an embodiment of the present invention.

[0067] FIG. 37 illustrates an example of a primitive exchange procedure for channel access in a non-primary channel of an STA according to an embodiment of the present invention.

[0068] Figure 38 is a flowchart showing an example of a channel access procedure performed by a terminal according to one embodiment of the present invention.

[0069]

[0070] The terms used in this specification have been selected from widely used and current terms, taking into account the functions of the present invention. However, these terms may vary depending on the intentions of those skilled in the art, customs, or the emergence of new technologies. Furthermore, in certain cases, the applicant may arbitrarily select terms, in which case their meanings will be described in the description of the relevant invention. Therefore, it should be noted that the terms used in this specification should be interpreted based on their substantive meaning and the overall content of this specification, rather than simply their names.

[0071] Throughout the specification, when a component is said to be "connected" to another component, this includes not only the case where the component is "directly connected," but also the case where the component is "electrically connected" with another component intervening therebetween. Furthermore, when a component is said to "include" a particular component, this does not exclude the other component, but rather allows the inclusion of other components, unless specifically stated otherwise. Furthermore, the terms "more than" or "less than" based on a specific threshold value may be appropriately replaced with "more than" or "less than", respectively, depending on the embodiment.

[0072] Hereinafter, in the present invention, fields and subfields may be used interchangeably.

[0073] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0074] A wireless LAN system includes one or more Basic Service Sets (BSSs), which represent a collection of devices that have successfully synchronized and can communicate with each other. BSSs can generally be categorized as infrastructure BSSs and independent BSSs (IBSSs). Figure 1 illustrates an infrastructure BSS.

[0075] As illustrated in FIG. 1, the infrastructure BSS (BSS1, BSS2) includes one or more stations (STA1, STA2, STA3, STA4, STA5), an access point (AP-1, AP-2) that provides a distribution service, and a distribution system (DS) that connects multiple access points (AP-1, AP-2).

[0076] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium that complies with the IEEE 802.11 standard, and broadly includes both non-access point (AP) stations and access points (APs). In addition, the term "terminal" in this specification may refer to a non-AP STA or an AP, or 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, depending on the embodiment. The processor may generate a frame to be transmitted through a wireless network or process a frame received through the wireless network, and may perform various other processes for controlling the station. In addition, the communication unit is functionally connected to the processor and transmits and receives frames through the wireless network for the station. In the present invention, a terminal may be used as a term that includes a user equipment (UE).

[0077] 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 an infrastructure BSS, communication between non-AP stations is in principle performed via the AP, but direct communication is also possible between non-AP stations when a direct link is established. Meanwhile, in the present invention, the AP is used as a concept including a Personal BSS Coordination Point (PCP), and in a broad sense, it can 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 the base wireless communication terminal may be used as a term including, in a broad sense, an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal may include various types of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with multiple wireless communication terminals.

[0078] Multiple infrastructure BSSs can be interconnected via a distribution system (DS). Multiple BSSs connected via the distribution system are referred to as an Extended Service Set (ESS).

[0079] FIG. 2 illustrates an independent BSS, a wireless LAN system, according to another embodiment of the present invention. Parts of the embodiment of FIG. 2 that are identical or corresponding to those of the embodiment of FIG. 1 will not be redundantly described.

[0080] BSS3, illustrated in Figure 2, is an independent BSS and does not include an AP. Therefore, all stations (STA6, STA7) are not connected to an AP. An independent BSS does not allow access to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) can be directly connected to another.

[0081] FIG. 3 is a block diagram showing the configuration of a station (100) according to one embodiment of the present invention. As illustrated, the station (100) according to the 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).

[0082] First, the communication unit (120) transmits and receives wireless signals such as wireless LAN packets, and may be built into or externally installed 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 include 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 corresponding communication module. The communication unit (120) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the station (100). When the station (100) includes multiple communication modules, each communication module may be provided in an independent form, or multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit (120) may represent an RF (Radio Frequency) communication module that processes RF (Radio Frequency) signals.

[0083] 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 a command of the processor (110) using various output means.

[0084] Next, the display unit (150) outputs an image on 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 the control commands of the processor (110). In addition, the memory (160) stores a control program used in the station (100) and various data corresponding thereto. Such a control program may include a connection program required for the station (100) to connect to an AP or an external station.

[0085] 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 above-described station (100) and control data transmission and reception between the units. According to an embodiment of the present invention, the processor (110) can execute a program for connection to an AP stored in the memory (160) and receive a communication setup message transmitted by the AP. In addition, the processor (110) can read information on the priority conditions of the station (100) included in the communication setup message and request connection to the AP based on the information on 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 according to an embodiment, may refer to a control unit for individually controlling some components of the station (100), such as the communication unit (120). That is, the processor (110) may be a modem or 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 transmitting and receiving wireless signals of the station (100) according to an embodiment of the present invention. A specific embodiment thereof will be described later.

[0086] The station (100) illustrated in FIG. 3 is a block diagram according to one embodiment of the present invention, and the blocks shown separately are logically distinguished elements of the device. Accordingly, the elements of the above-described device may be mounted as one 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 by being integrated into one chip or may be implemented as separate chips. In addition, in the 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 selectively provided in the station (100).

[0087] Fig. 4 is a block diagram illustrating the configuration of an AP (200) according to one embodiment of the present invention. As illustrated, the AP (200) according to the embodiment of the present invention may include a processor (210), a communication unit (220), and a memory (260). In Fig. 4, redundant descriptions of portions of the configuration of the AP (200) that are identical or corresponding to the configuration of the station (100) of Fig. 3 will be omitted.

[0088] Referring to FIG. 4, the AP (200) according to the present invention has 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 that utilize different frequency bands. That is, the AP (200) according to the embodiment of the present invention may include two or more communication modules for different frequency bands, such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP (200) may include a communication module that utilizes a frequency band of 7.125 GHz or higher and a communication module that utilizes 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 corresponding communication module. The communication unit (220) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the AP (200). In an embodiment of the present invention, the communication unit (220) may represent an RF communication module that processes an RF (Radio Frequency) signal.

[0089] Next, the memory (260) stores the control program used in the AP (200) and various data according to the control program. This control program may include a connection program that manages the connection of the station. In addition, the processor (210) controls each unit of the AP (200) and may control data transmission and reception between the units. According to an embodiment of the present invention, the processor (210) may execute a program for connection with a station stored in the memory (260) and transmit a communication setup message to one or more stations. At this time, the communication setup message may include information on the connection priority conditions of each station. In addition, the processor (210) performs connection setup according to a connection request from a station. According to one embodiment, the processor (210) may be a modem or a modulator and / or demodulator that modulates and demodulates a wireless signal 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 examples of this will be described later.

[0090] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0091] Referring to FIG. 5, the link between STA (100) and AP (200) is largely established through three stages: scanning, authentication, and association. First, the scanning stage is a stage in which STA (100) acquires access information of the BSS operated by AP (200). Methods for performing scanning include a passive scanning method in which information is acquired only by utilizing a beacon message (S101) periodically transmitted by AP (200), and an active scanning method in which STA (100) acquires access information by transmitting a probe request to AP (S103) and receiving a probe response from AP (S105).

[0092] The STA (100) that successfully receives wireless access information in the scanning step transmits an authentication request (S107a) and receives an authentication response from the AP (200) (S107b) to perform the authentication step. After the authentication step is performed, the STA (100) transmits an association request (S109a) and receives an association response from the AP (200) (S109b) to perform the association step. In this specification, association basically means wireless association, but the present invention is not limited thereto, and association in a broad sense may include both wireless association and wired association.

[0093] Meanwhile, an additional 802.1X-based authentication step (S111) and an IP address acquisition step (S113) via DHCP may be performed. In Fig. 5, the authentication server (300) is a server that processes STA (100) and 802.1X-based authentication, and may be physically connected to the AP (200) or may exist as a separate server.

[0094] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0095] A terminal performing wireless LAN communication performs carrier sensing before transmitting data to check whether the channel is busy. If a wireless signal above a certain strength is detected, the channel is determined to be busy, and the terminal delays access to the channel. This process is called clear channel assessment (CCA), and the level that determines whether the signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by the terminal is intended for the terminal, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected on the channel or a wireless signal with a strength lower than the CCA threshold is detected, the channel is determined to be idle.

[0096] When the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an IFS (Inter Frame Space) time, such as AIFS (Arbitration IFS) or PIFS (PCF IFS), depending on the status of each terminal. In some embodiments, the AIFS may be used as a configuration to replace the existing DIFS (DCF IFS). Each terminal waits while decreasing the slot time by a random number determined for the terminal during the idle interval of the channel, and a terminal that has exhausted all slot times attempts to access the channel. The period during which each terminal performs the backoff procedure is called a contention window period. At this time, the random number may be referred to as a 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, if the backoff counter reaches 0, the terminal may be permitted to perform channel access on the corresponding channel. Accordingly, transmission by the terminal may be permitted if the channel is idle during the AIFS time and the slot time of the backoff counter.

[0097] 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 collided 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 twice (2*CW) of the random number range (contention window, CW) previously assigned to the terminal. Meanwhile, each terminal performs the backoff procedure again in the next contention window period to attempt access, and at this time, each terminal performs the backoff procedure starting from the slot time remaining in the previous contention window period. In this way, each terminal performing wireless LAN communication can avoid collisions with each other for a specific channel.

[0098] <Various PPDU format examples>

[0099] FIG. 7 shows various standard generation-specific physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0100] More specifically, FIG. 7(a) illustrates an embodiment of a legacy PPDU format based on 802.11a / g, FIG. 7(b) illustrates an embodiment of a HE PPDU format based on 802.11ax, and FIG. 7(c) illustrates an embodiment of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. In addition, FIG. 7(d) illustrates a detailed field configuration of L-SIG and RL-SIG commonly used in the above PPDU formats.

[0101] Referring to FIG. 7(a), the preamble of a legacy PPDU includes a legacy short training field (L-STF), a legacy long training field (L-LTF), and a legacy signal field (L-SIG). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as a legacy preamble.

[0102] 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 a 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.

[0103] Referring to FIG. 7(c), the preamble of the EHT PPDU additionally includes, in addition to the legacy preamble, an RL-SIG (Repeated Legacy Short Training field), a U-SIG (Universal Signal field), an EHT / UHR-SIG-A (Extremely High Throughput / Ultra High Reliability Signal A field), an EHT / UHR-SIG-A (Extremely High Throughput / Ultra High Reliability Signal B field), an EHT-STF (Extremely High Throughput Short Training field), and an EHT-LTF (Extremely High Throughput Long Training field). In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B can only be used in some of the EHT PPDU formats.

[0104] In this way, the PPDU used in the UHR standard may have a format similar to the PPDU format used in the EHT standard. This is because the EHT PPDU format defined in 802.11be includes a U-SIG field that multiple wireless LAN generations have agreed to use in common. At this time, the value of the PHY Version Identifier field of the U-SIG field included in the EHT PPDU may be 0, and the value of the PHY Version identifier field of the U-SIG field included in the UHR PPDU may have a non-zero value, such as 1. The EHT PPDU includes an EHT-STF (Extremely High Throughput Short Training field) field in the STF field, and an EHT-LTF (Extremely High Throughput Long Training field) field in the LTF field. The UHR PPDU includes a UHR-STF (Ultra High Reliability Short Training field) field in the STF field, and a UHR-LTF (Ultra High Reliability Long Training field) field in the LTF field.

[0105] The L-SIG field included in the PPDU preamble 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 L-SIG applies BPSK, Rate=1 / 2 Modulation and Coding Scheme (MCS), it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of L-SIG.

[0106] Referring to Fig. 7(d), L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field consists of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which combine modulation methods such as BPSK / QPSK / 16-QAM / 64-QAM and inefficiencies such as 1 / 2, 2 / 3, and 3 / 4. Combining the information in the L_RATE field and the L_LENGTH field can indicate the total length of the corresponding PPDU. In non-legacy PPDU formats, the L_RATE field is set to the minimum speed of 6 Mbps.

[0107] The L_LENGTH field is allocated in bytes, with a total of 12 bits, allowing for signaling up to 4095. In combination with the L_RATE field, it can indicate the length of the corresponding PPDU. At this time, legacy and non-legacy terminals may interpret the L_LENGTH field in different ways.

[0108] First, the method by which a legacy terminal or non-legacy terminal interprets the length of the 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 us, which is the duration of one symbol of 64 FFT. Therefore, by adding 3 bytes corresponding to the SVC field and Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of symbols based on 64 FFT after L-SIG is obtained. Multiplying the obtained number of symbols by 4 us, which is the duration of one symbol, and then adding 20 us required for transmission of L-STF, L-LTF, and L-SIG, the length of the PPDU, i.e., the reception time (RXTIME) is obtained. This can be expressed as a formula as shown in Mathematical Expression 1 below.

[0109]

[0110] 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 to a maximum of 5.484 ms. A non-legacy terminal transmitting the PPDU must set the L_LENGTH field as in Mathematical Expression 2 below.

[0111]

[0112] Here, TXTIME is the total transmission time that constitutes the corresponding PPDU, as shown in mathematical expression 3 below. In this case, TX represents the transmission time of X.

[0113]

[0114] Referring to the above formulas, the length of the PPDU is calculated based on the rounded 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.

[0115] Referring to Fig. 7(e), the U-SIG (Universal SIG) field continues to exist in EHT / UHR PPDUs and subsequent generation wireless LAN PPDUs, and serves to distinguish which generation of PPDU it is, including EHT / UHR. In addition, the U-SIG field can serve to facilitate spatial reuse of EHT / UHR and subsequent generation wireless LANs. U-SIG is an OFDM 2 symbol based on 64FFT and can convey a total of 52 bits of information. Of these, 43 bits, excluding the 9 bits of CRC / Tail, are largely divided into the VI (Version Independent) field and the VD (Version Dependent) field.

[0116] The VI bit maintains its current bit configuration in the future so that even if a subsequent generation PPDU is defined, current EHT / UHR terminals can obtain information about the PPDU through the VI fields of the PPDU. For this purpose, the VI field consists of PHY version, UL / DL, BSS Color, TXOP, and Reserved fields. The PHY version ID field is 3 bits and sequentially distinguishes EHT / UHR and subsequent generation wireless LAN standards by version. The PHY version ID field of the EHT (11be) PPDU has a value of 000b, and the PHY version ID field of the UHR PPDU has a value other than 000b. The UL / DL field distinguishes whether the PPDU is an uplink / downlink PPDU. BSS Color means an identifier for each BSS defined in 11ax and has a value of 6 bits or more. TXOP stands for 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 having to decode the MPDU, and has a value of 7 bits or more.

[0117] The VD field of EHT is signaling information that is only useful for PPDUs of version 11be. It can be composed of fields that are commonly used in any PPDU format, such as PPDU format and BW, and fields that are defined differently for each PPDU format. The PPDU format is a delimiter that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs.

[0118] The BW field largely signals five basic PPDU BW options of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz (a BW that can be expressed in the form of an exponential of 20*2 can be called the basic BW), and various remaining PPDU BWs configured through Preamble Puncturing. In addition, some 80 MHz can be signaled in a punctured form after being signaled at 320 MHz. In addition, the punctured and modified channel form can be signaled directly in the BW field, or by using the BW field together with a field that appears after the BW field (for example, a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signaling is possible, so only a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signaling is possible, so the puncturing mode can signal up to 11.

[0119] The VD field of the UHR is a field that indicates signaling information that is only useful for the UHR PPDU. However, the information indicated by each field included in the VD field of the UHR PPDU may be identical to or more extended than the information indicated by the field that plays the same role as the VD field of the EHT (11be). For example, the field indicating the puncturing pattern included in the VD field of the UHR PPDU may indicate a wider variety of patterns than the field indicating the puncturing pattern included in the VD field of the EHT PPDU. Alternatively, the field indicating the puncturing pattern included in the VD field of the UHR PPDU may be interpreted in conjunction with the BW field. This allows for indicating a wider variety of puncturing patterns.

[0120]

[0121] Figure 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0122] 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 the U-SIG.

[0123] FIG. 8(b) illustrates an EHT / UHR Trigger-based PPDU according to an embodiment of the present invention. An 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 the U-SIG.

[0124] Figure 8(c) illustrates 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 a HE-SIG-B field after the U-SIG field.

[0125] Figure 8(d) illustrates an EHT / UHR ER SU PPDU according to an embodiment of the present invention. The EHT / UHR ER SU PPDU is used for single-user transmission to stations in an extended range. The EHT / UHR ER SU PPDU format allows the U-SIG to be repeated along the time axis.

[0126] The EHT / UHR MU PPDU described through (c) of FIG. 8 can be used by an AP to perform downlink transmission to multiple stations. At this time, the EHT / UHR MU PPDU can include scheduling information for multiple stations to simultaneously receive the PPDU. At this time, the EHT / UHR MU PPDU can convey AID information of the receiver or transmitter of the corresponding PPDU through the user specific field of EHT / UHR-SIG-B. A station that receives the EHT / UHR MU PPDU can 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 EHT / UHR-SIG-B can include information on a resource unit (RU) partitioning form in a specific bandwidth (e.g., 20 MHz) in the frequency domain. Additionally, information about the station assigned to each partitioned resource unit may be conveyed via a user-specific field of EHT / UHR-SIG-B. The user-specific field may include one or more user fields corresponding to each partitioned resource unit.

[0127] Among the multiple resource units divided, the AID of the receiver or sender may be inserted into the user field corresponding to the resource unit in which data transmission is performed. A pre-specified null STA ID may be inserted into the user field corresponding to the remaining resource units in which data transmission is not performed.

[0128] 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.

[0129] Some fields or some information within a field included in the format of the PPDU described above may be omitted. This may be referred to as compression mode or compressed mode.

[0130]

[0131] <Wi-Fi 단말의 채널 액세스 방법>

[0132] Wi-Fi terminals (APs, non-AP STAs, etc.) perform communication using unlicensed bands, so before transmitting a frame, they check whether the channel they want to transmit is in use by another device. CSMA (Carrier Sense Multiple Access) is a channel access method in which a terminal that wants to transmit a packet performs carrier sense to check whether the channel is in use by another device, and transmits only if the channel is determined to be idle. Since a terminal using CSMA can perform an action of not attempting transmission at least when it is determined that another device is using the medium (channel) (when it is determined to be busy), the transmission that was initiated first can be protected from other devices.

[0133] However, multiple terminals that recognize that the medium is occupied by another device experience a transmission collision by simultaneously attempting to transmit packets when it is confirmed that the medium occupation from the other device has ended (the medium has changed to Idle). That is, as multiple other terminals simultaneously attempt to transmit packets when a specific terminal attempts to transmit a packet, a terminal that is supposed to receive the packet transmitted by the specific terminal is unable to properly receive and decode the packet that it is supposed to receive due to interference caused by the transmissions performed by the multiple other terminals.

[0134] CSMA / CA (CSMA with collision avoidance) is a channel access mechanism that prevents multiple terminals from simultaneously attempting packet transmission when the medium has changed to Idle, as described above. Terminals accessing the medium (channel) using CSMA / CA attempt to transmit after waiting for a random amount of time when the state of the medium they observe changes to Idle. The random amount of time may be an aslottime (typically 9 microseconds) equal to a random number (random backoff counter) generated by each terminal attempting to transmit. In other words, terminals accessing the medium using CSMA / CA attempt to transmit after waiting for different random amounts of time, so they attempt to transmit at different times, unlike when CSMA alone is used. In this case, when a specific terminal that waited for the shortest random amount of time after the medium changed to Idle attempts to transmit first, other terminals can recognize that the medium has been occupied (changed to busy) by the specific terminal and abort the channel access procedure. At this time, the specific terminal may perform an operation of decreasing the backoff counter maintained by it by 1 every aslottime while the medium is maintained as Idle, and may attempt transmission when the backoff counter becomes 0, or when the aslottime has passed after the backoff counter becomes 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 may attempt transmission when the new random number becomes 0 again, or after it becomes 0.

[0135] The CSMA / CA and random backoff procedures briefly explained above are applied to DCF (Distributed coordination function) and EDCAF (Enhanced distributed channel access), which are the basic functions used by Wi-Fi terminals when attempting to access a channel. Since these are well-known and widely used unlicensed band channel access methods, a more detailed explanation will be omitted.

[0136]

[0137] The DCF and EDCAF utilized by the MAC of the Wi-Fi terminal evaluate the channel status by considering not only the channel status (idle / busy) confirmed by each terminal performing its own physical CS (Carrier Sense) but also the results of a virtual CS. In more detail, even if the result of the physical CS performed on the channel is idle, if the result of the virtual CS is busy, the Wi-Fi terminal considers the channel status to be busy. At this time, the Virtual CS is a channel evaluation method that determines the channel to be busy if the NAV (Network allocation vector) is not 0. The NAV may be a value maintained for future traffic that is predicted to occupy the medium. To explain in more detail, when the MAC of Wi-Fi receives an RTS / CTS frame, it can set the NAV (NAV count) based on the duration information of the received frame, for example, the value of the duration field, and maintain the NAV as a non-zero value for the expected time that 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 that the future traffic recognized by the specific MAC is no longer occupying the medium. If the NAV is 0, the MAC can determine the virtual CS result as Idle. At this time, the MAC of Wi-Fi can also set the NAV based on the duration value obtained from not only the RTS / CTS frame but also other received MAC frames.

[0138] The channel estimation method (determine the state of the medium) that considers the results of the physical CS and virtual CS briefly described above is also one of the well-known Wi-Fi MAC functions, so a detailed explanation is omitted.

[0139]

[0140] <EDCA와 TXOP>

[0141] EDCA provides a mechanism to differentiate and manage traffic into four types of ACs (access categories) according to the characteristics of the traffic. At this time, the 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 CW (contention window), TXOP (transmit opportunity), and AIFSN parameters. Simply put, EDCA is a mechanism that differentiates the CW, TXOP, and AIFSN parameters for the four types of ACs and controls the transmission priority of traffic transmitted using each AC. To this end, EDCA can map traffic (MSDU) that the MAC must service to one of the four ACs according to the TC (traffic category) or TS (traffic stream). At this time, the traffic mapped to one of the four ACs by EDCA is divided and managed into four queues for each AC. At this time, the four queues may be logically separated rather than physically separated.

[0142] AC_VO is an AC that can be utilized for traffic that is vulnerable to transmission delays, although the absolute volume of traffic, such as voice 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 relatively small value compared to the TXOP parameters of other ACs, ensuring only a shorter transmission time than other ACs.

[0143] AC_VI is an AC that is more delay-tolerant than voice traffic, but can still be utilized for traffic such as video that requires low-latency transmission and high traffic volume. AC_VI has larger CW and AIFSN parameter values ​​than AC_VO but smaller than other ACs, and its TXOP is approximately twice as long as AC_VI.

[0144] AC_BE is an AC that can be utilized for traffic that is robust to transmission delays, and most general traffic, excluding voice data and streaming video data, can be classified as AC_BE. AC_BE uses CW and AIFSN parameters with values ​​greater than AC_VO and AC_VI. In addition, AC_BE does not have a separate TXOP. Therefore, traffic corresponding to AC_BE cannot be utilized in the TXOP transmission sequence, which transmits a PPDU, receives an ACK in response, and then transmits a PPDU again after SIFS.

[0145] AC_BK, similar to AC_BE, is a delay-tolerant traffic, but can be utilized for lower-priority traffic than BE traffic. AC_BK utilizes the same CW parameter values ​​as AC_BE, and the AIFSN parameter values ​​are larger than those of AC_BE. In addition, traffic corresponding to AC_BK does not have a separate TXOP like AC_BE, so it cannot be utilized in the TXOP transmission sequence.

[0146] The four types of EDCA AC 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 through the wire or the TID of the MSDU indicated from the upper layer. At this time, if the TID of the MSDU indicates a value between 0 and 7, the value indicated by the TID can correspond one-to-one with the UP.

[0147] In addition, the four types of EDCA AC described above have default CW (CWmin, CWmax), AIFSN, and TXOP parameters defined in the standard, and the parameter values ​​of each AC can be changed by the AP, so that different values ​​can be used for each BSS.

[0148]

[0149] Using the EDCA mechanism, Wi-Fi traffic is stored in one of four queues corresponding to four ACs, and can be transmitted to the destination device only if the AC containing the traffic wins the channel access competition with other ACs. At this time, in the channel access competition between ACs, each AC competes using its assigned access parameters (CW[AC], AIFSN[AC]), and the channel access competition operation performed by each AC is identical to DCF. At this time, if a specific AC does not have any traffic to transmit in its queue, the specific AC may not participate in the competition.

[0150] However, as described above, since the CW and AIFSN parameter values ​​utilized by each AC are different, the AC_VO with the smallest CW and AIFSN parameters is more likely to win the channel access competition with other ACs, and thus the traffic of AC_VO is more likely to be serviced with priority over the traffic of other ACs.

[0151] In addition, the EDCA mechanism stipulates internal competition rules such as when an (internal) collision occurs between ACs, the AC with a higher priority wins, and increases the CW of the other AC that caused the collision, and rules for composing a PPDU including traffic from an AC other than the AC that won the competition (primary AC), but a detailed description is omitted because it is not closely related to the proposal of the present invention.

[0152] As described above, EDCA provides the EDCA TXOP (EDCA Transmission Opportunity) function along with the function of operating differentiated ACs according to the type of traffic (frames, packets, etc.) to enhance QoS. EDCA TXOP refers to the time during which the EDCAF (EDCA Function) of a specific AC can control the medium without being disturbed by other devices during the TXOP period (duration) when it obtains a channel access opportunity, i.e., becomes a TXOP holder. At this time, the EDCA TXOP may be limited by the TXOP limit advertised by the AP. The TXOP holder must ensure that its own transmission and the transmission of the response frame responded to by its own transmission can be terminated within the TXOP limit.

[0153] A TXOP holder can transmit multiple frames (multiple PPDUs) during an EDCA TXOP period. If the transmission of each frame is performed within the acquired TXOP period, the TXOP holder can transmit multiple frames continuously without performing a separate channel access procedure, such as a backoff procedure, between transmissions of each frame. At this time, if the multiple frames are MPDUs or A-MPDUs (Aggregated MAC protocol data units) that do not request an immediate ack, the transmission of the multiple frames can be performed at an interval of a short interframe space (SIFS) or a reduced interframe space (RIFS). At this time, if there is an MPDU or A-MPDU requesting an immediate ack among the multiple frames, the TXOP holder can transmit a frame requesting an immediate ack, receive the ack, and transmit the next frame after an SIFS.

[0154] At this time, traffic (packets, frames, etc.) of other ACs 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 other ACs other than the TXOP holder within the TXOP may be an operation due to TXOP sharing between ACs, and detailed information regarding the above-mentioned certain conditions is omitted because it is not related to the present invention.

[0155]

[0156] As described above, a TXOP holder can perform continuous frame transmission without performing a separate channel access procedure within the TXOP. This may be an operation that can be achieved when other terminals understand and protect the TXOP interval acquired by the TXOP holder. In other words, in order for the TXOP holder to acquire medium control authority for the EDCA TXOP interval, a procedure may be required to notify other terminals of the acquired TXOP interval so that they can recognize it.

[0157] To this end, a terminal (AC) that becomes a TXOP holder or initiates transmission after completing a channel access procedure may attempt to allow other terminals to recognize the TXOP section by transmitting an RTS frame. At this time, the RTS frame means a frame in which the Type subfield (the fourth bit (B3), the third bit (B2) of the Frame Control field) of the Frame Control field of the MAC frame header is set to 01b (Type = Control frame) and the Subtype subfield (the eighth bit (B7), the seventh bit (B6), the sixth bit (B5), the fifth bit (B4) of the Frame Control field) is set to 1011b. Another terminal that receives an RTS frame from a TXOP holder may set an 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 a time corresponding to the TXOP of the TXOP holder. However, the terminal indicated 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. At this time, the destination device of the RTS frame transmitted to start TXOP is a TXOP responder and must transmit a CTS frame in response to the RTS (SIFS after the RTS frame is received). At this time, 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. The terminals receiving the CTS frame can set the NAV based on information related to the duration included in the CTS frame (e.g., the value of the Duration field).

[0158] Therefore, the NAV of the terminal that received the RTS frame from the TXOP holder and the terminal that received the CTS frame from the TXOP responder are set to 0 after the TXOP acquired by the TXOP holder ends. This allows the Wi-Fi MAC mechanism to protect the TXOP holder and the TXOP responder from exchanging multiple frames without interruption during the TXOP.

[0159] However, if the TXOP holder transmits an RTS frame as a non-HT duplicate PPDU over the primary 80 MHz band, but the CTS frame (non-HT duplicate PPDU) responded to by the TXOP responder is responded to only in the primary 40 MHz band, the TXOP holder may use only the bandwidth of the primary 40 MHz or less than the primary 40 MHz, for example, the 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 shall 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 in a BW smaller than the BW in which the RTS frame was transmitted. An RTS frame may be an RTS frame transmitted with DYN_BANDWIDTH_IN_NON_HT (a type of TXVECTOR parameter) set to Dynamic. If DYN_BANDWIDTH_IN_NON_HT is set to Static and the RTS frame is transmitted from a TXOP holder, the TXOP responder may have to respond with a CTS frame with the same BW as the BW in which the RTS frame was received.

[0160]

[0161] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0162] Before transmitting a PPDU, the first station (STA1) transmits an RTS frame to the second station (STA2), which is the destination of the PPDU, and the second station (STA2) recognizes that the received RTS frame is an RTS frame destined for itself and responds with a CTS frame after SIFS.

[0163] STA1_Neighbor, a neighbor station of the first station (STA1), sets the NAV based on the value indicated by the Duration field of the RTS frame after receiving the RTS frame transmitted by the first station (STA1). STA2_Neighbor, a neighbor station of the second station (STA2), sets the NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the second station (STA2). STA1_Neighbor and STA2_Neighbor determine that the virtual CS is busy while the set NAV (counter) is maintained at a non-zero value after receiving the RTS / CTS frame, and perform actions such as not decreasing the backoff counter. As a result, the neighboring terminals that received the RTS / CTS frame do not attempt transmission during the period in which the NAV is maintained at a non-zero value. Therefore, the first station (STA1) and the second station (STA2) may not be disturbed by surrounding terminals while exchanging PPDU and Ack frames.

[0164] Even if the first station (STA1) and STA2_Neighbor are in a relationship where signals due to each other's transmissions are not detected (hidden), 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) transmits a PPDU.

[0165] Meanwhile, a Wi-Fi terminal (non-AP STA) can transmit an UL PPDU to the AP without directly acquiring a TXOP or performing channel access through DCF and EDCAF. More specifically, a non-AP STA can transmit an UL PPDU using its assigned RU after receiving a trigger frame transmitted by the AP. In this case, the UL PPDU is a TB (trigger-based) PPDU.

[0166] An STA that responds with a UL PPDU after receiving a trigger frame can obtain more transmission opportunities than an STA that does not transmit a UL PPDU based on the trigger frame because it can perform transmission without obtaining direct channel access opportunities through DCF and EDCAF. Therefore, an STA that transmits a UL PPDU through the trigger frame may cause a fairness issue in terms of channel access. To address 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 through the UL PPDU transmitted after receiving the trigger frame. Accordingly, an STA that transmits a UL PPDU through the trigger frame must perform channel access using the MU-EDCA parameter, not the EDCA parameter. MU-EDCA parameters include the size of the contention window for each of AC_VO, AC_VI, AC_BE, and AC_BK and parameters related to the MU EDCA timer, and the contention window included in MU-EDCA can be set to be larger than the parameters of EDCA. An STA that transmits a TB PPDU through a trigger frame and successfully transmits at least one MPDU performs channel access within the time period corresponding to the MU EDCA timer by performing channel access using the MU EDCA parameters rather than the EDCA parameters, thereby succeeding in channel access with a lower probability than an STA that uses the EDCA parameters.In this way, by lowering the channel accessibility of an STA that transmits a UL PPDU (TB PPDU) based on a trigger frame, the fairness problem in channel accessibility between an STA that transmits a UL PPDU without performing direct channel access and an STA that does not transmit a UL PPDU based on a trigger frame can be resolved / alleviated.

[0167] <MU-RTS 트리거 프레임을 이용한 TXOP 보호>

[0168] 11ax (6th generation Wi-Fi, Wi-Fi6, HEW, High Efficiency WLAN) defines the MU-RTS Trigger / CTS frame exchange procedure, and adds a function that enables the AP to start TXOP and protect the TXOP frame exchange procedure using the MU-RTS trigger frame (hereinafter referred to as MU-RTS, MU-RTS frame). The MU-RTS frame is a type of trigger frame. When the MU-RTS frame is received, the 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 the AP protects the TXOP using the MU-RTS frame, since multiple stations respond with CTS frames, the TXOP can be protected from the peripheral devices of each of the multiple stations that are the destination devices of the DL MU PPDU (Down link multi-user PPDU). In addition, the MU-RTS frame can be used to protect the UL MU PPDU. In more detail, before requesting a TB (Trigger based) PPDU from multiple stations through a trigger frame, the AP can transmit an MU-RTS frame to cause multiple stations that will respond to the TB PPDU to respond with a CTS frame. At this time, the CTS frames responded to by the multiple stations induce the surrounding stations of each station to set 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 stations STAs that cannot recognize (interpret, decode) the trigger frame and TB PPDU may not perform channel access during the packet exchange sequence period (or TXOP) initiated through the trigger frame.

[0169]

[0170] FIG. 10 shows a transmission / TXOP protection method using an MU-RTS frame and a CTS frame according to an embodiment of the present invention.

[0171] In the embodiment of FIG. 10, before transmitting an MU PPDU, the AP transmits an MU-RTS frame to the first station (STA1) and the second station (STA2), which are the destination devices of the MU PPDU, 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.

[0172]

[0173] STA1_Neighbor, a neighboring station of the first station (STA1), sets its NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the first station (STA1). STA2_Neighbor, a neighboring station of the second station (STA2), sets its NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the second station (STA2). STA1_Neighbor and STA2_Neighbor perform operations such as not decreasing the back-off counter, assuming that the Virtual CS (Virtual Carrier Sense) is busy while the NAV (counter) set after receiving the CTS frame remains at a non-zero value. Therefore, neighboring terminals that have received the CTS frame do not attempt to transmit during the period in which the NAV remains at a non-zero value. This allows the AP to transmit MU PPDUs and the first station (STA1) and the second station (STA2) to transmit Ack frames without being interrupted by surrounding terminals.

[0174] The trigger frame described above is a frame type defined in 11ax, and is a frame type 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. A trigger frame is a frame of Control Type in which the Type subfield of the Frame Control field is 01b, and the Subtype value 0010 indicates that it is a Trigger frame type. In 11ax, a trigger frame is defined so that an AP can request a response frame for multiple stations at once, and an MU-RTS frame is used so that an AP can request a CTS frame for multiple stations (non-AP STAs). Trigger Types other than the MU-RTS frame include the Basic Tigger frame requesting UL MU PPDU, the Beamforming Report Poll Tigger frame requesting Beamforming Report, the MU-BAR Tigger frame (BlockAck request), the BSRP trigger frame requesting Buffer Status Report, the GCR MU-BAR trigger frame, the Bandwidth Query Report Poll (BQRP) trigger frame, and the NDP Feedback Report Poll trigger frame. Trigger Types other than the MU-RTS frame are not related to the content of the present invention, so a detailed description thereof is omitted.

[0175] <Multi-link Device (MLD)>

[0176] In Wi-Fi 7's Extremely High Throughput (EHT), MLD is defined. MLD refers to a logical entity that includes one or more STAs. One or more APs (AP STAs) can be affiliated to an AP MLD, and one or more non-AP STAs can be affiliated to a non-AP (STA) MLD.

[0177] Each AP belonging to an AP MLD can operate an independent Basic Service Set (BSS), and the operating bandwidth (OS) and operating channel (Operating BW) of the BSSs operated by the APs can be different. 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. At this time, 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 on multiple Links.

[0178] Each MLD can have up to 15 STAs (AP STAs, non-AP STAs). That is, 15 APs can belong to an AP MLD, and the 15 APs each operate an independent BSS. At this time, each AP belonging to the AP MLD provides a service equivalent to a conventional Wi-Fi AP. That is, each AP belonging to the AP MLD can function as an independent AP and provide services to non-AP STAs (e.g., legacy non-AP STAs) that do not belong to the MLD. At this time, each AP belonging to the AP MLD operates in an independent Link, and the meaning of the Link only refers to the operating channel on which each AP operates, and does not mean a Link that distinguishes 2.4 / 5 / 6 GHz. That is, the first AP belonging to the AP MLD can operate in the first Link, and the second AP can operate in the second Link. At this time, it is possible for both the first link in which the first AP operates and the second link in which the second AP operates to be located in the 6 GHz band.

[0179] In addition, AP MLD and non-AP MLD 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, the procedure for performing Multi-Link setup between AP MLD and non-AP MLD is not important, so a detailed description thereof will be omitted.

[0180] When two MLDs are connected via multiple Links, the two MLDs can operate the traffic to be transmitted / received via each Link separately. This can be achieved by TID-to-Link mapping negotiation between the two MLDs or by applying the TID-to-Link mapping status indicated by the AP MLD. At this time, the TID-to-Link mapping status that the AP MLD indicates to the non-AP MLDs is indicated by the Management frame (e.g., Beacon, Probe Response frame) transmitted by the AP MLD, and the non-AP MLDs associated with the AP MLD via at least one Link must operate each Link according to the TID-to-Link mapping indicated 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 can be transmitted / received via 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, the AP MLD and the non-AP MLD must transmit / receive only MPDUs with TIDs 0 to 3 through Link 1, and must transmit / receive MPDUs with TIDs 4 to 7 through Link 2.

[0181] If the AP MLD does not indicate 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 the 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 transmit / receive MPDUs of all TIDs (TID = 0 to 7) on each Link.

[0182] Since Wi-Fi 8 (UHR, Ultra High Reliability) is expected to be developed based on Wi-Fi 7, the MLD concept, the connection procedure between MLDs, and the link operation method 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.

[0183] <MLD의 채널 접속>

[0184] Figure 11 shows a mapping table of user priority and access category.

[0185] Each STA belonging to the MLD performs channel access in the same manner as a conventional Wi-Fi terminal. More specifically, each STA performs channel access using Enhanced Distributed Channel Access (EDCA).

[0186] Channel access mechanism using EDCA is a commonly used method for channel access in unlicensed bands.

[0187] EDCA provides a mechanism to differentiate and manage traffic into four types of ACs (access categories) according to their characteristics. The 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 CW (contention window), TXOP (transmit opportunity), and AIFSN parameters. Simply put, EDCA is a mechanism to control the transmission priority of traffic transmitted using 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 the MAC must service to one of the four ACs according to the TC (traffic category) or TS (traffic stream). At this time, the traffic mapped to one of the four ACs by EDCA is divided and managed into four queues for each AC. At this time, the above four queues may not be physically separated, but rather logically 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 obtains channel access. Since the method by which an AC performs the backoff procedure to obtain channel access has already been described in Figure 6, a detailed description is omitted.

[0188] AC_VO is an AC that can be utilized for traffic vulnerable to transmission delays, although the absolute volume of traffic, such as voice 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 relatively small value compared to the TXOP parameters of other ACs, ensuring only a shorter transmission time than other ACs.

[0189] AC_VI is an AC that is more delay-tolerant than voice traffic, but can still be used for low-latency transmission and high-volume traffic, such as video. AC_VI has larger CW and AIFSN parameters than AC_VO but smaller than other ACs. However, its TXOP is about twice as long as AC_VI's.

[0190] AC_BE is an AC that can be utilized for traffic that is robust to transmission delays, and most general traffic, except for voice data and streaming video data, can be classified as AC_BE. AC_BE uses CW and AIFSN parameters with values ​​larger than AC_VO and AC_VI. In addition, AC_BE does not have a separate TXOP, and therefore cannot utilize the TXOP transmission sequence that transmits a PPDU, receives an ACK in response, and then transmits a PPDU again after SIFS.

[0191] AC_BK, similar to AC_BE, is a delay-tolerant traffic, but can be utilized for lower-priority traffic than BE traffic. AC_BK utilizes the same CW parameter values ​​as AC_BE, and the AIFSN parameter values ​​are larger than those of AC_BE. Additionally, AC_BK, like AC_BE, does not have a separate TXOP, so it cannot utilize the TXOP transmission sequence.

[0192] The four types of EDCA AC 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 through the wire or the TID of the MSDU indicated from the upper layer. At this time, if the TID of the MSDU indicates a value between 0 and 7, the value indicated by the TID can correspond one-to-one with the UP.

[0193] The rules for mapping 802.1D UP and EDCA AC are described in the UP-to-AC mappings table shown in Figure 43.

[0194] In addition, the four types of EDCA AC described above have default CW (CWmin, CWmax), AIFSN, and TXOP parameters defined in the standard, and the parameter values ​​of each AC can be changed by the AP, so that different values ​​can be used for each BSS.

[0195] Using the EDCA mechanism, Wi-Fi traffic is stored in one of four queues corresponding to four ACs, and can be transmitted to the destination device only when the AC it is included in wins the channel access competition with another AC. At this time, in 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 identical to DCF. At this time, if a specific AC does not have any traffic to transmit in its queue, the specific AC may not participate in the competition.

[0196] However, as described above, since the CW and AIFSN parameter values ​​utilized by each AC are different, the AC_VO with the smallest CW and AIFSN parameters is more likely to win the channel access competition with other ACs, and thus the traffic of AC_VO is more likely to be serviced with priority over the traffic of other ACs.

[0197] In addition, the EDCA mechanism stipulates internal competition rules, such as when an (internal) collision occurs between ACs, the AC with a higher priority (see Fig. 11) wins, and increases the CW of the other AC that caused the collision, and rules for composing a PPDU including traffic from an AC other than the AC that won the competition (primary AC), but a detailed description is omitted because it is not closely related to the proposal of the present invention.

[0198] As described above, each STA belonging to an MLD performs channel access in the same manner as a conventional Wi-Fi terminal. That is, when observing each STA belonging to an MLD on each link, each STA belonging to an MLD performs channel access in the same manner as a non-MLD STA (QoS STA) that does not belong to an MLD performs channel access. This can be said to be a rule defined during the development of Wi-Fi 7, taking into account fairness with the existing non-MLD STAs operating on each link.

[0199] However, there is an exception defined for MLDs operating on Nonsimultaneous Transmit and Receive (NSTR) Link pairs. More specifically, STAs of MLDs operating on Nonsimultaneous Transmit and Receive (NSTR) Link pairs are allowed to defer transmission initiation after the backoff procedure has been completed in order to synchronize the transmission initiation timing with transmissions performed on other Links.

[0200] An NSTR link pair refers to a link pair that causes strong interference to the remaining links when the MLD performs transmission on a specific link among the link pairs on which the STA of the MLD operates. For example, if Link1 and Link2 are an NSTR link pair of a non-AP MLD, when non-AP STA1 of the non-AP MLD operating on Link1 performs transmission, non-AP STA2 of the non-AP MLD operating on Link2 experiences strong interference. Accordingly, non-AP STA2 cannot determine whether Link2 is IDLE / BUSY or normally receive the received PPDU while non-AP STA1 is performing transmission. In this case, the non-AP MLD has a problem that normal operation of the other link is impossible when transmission is performed on one link even though it operates STAs on two links. To alleviate this problem, Wi-Fi 7 introduced a mechanism that allows non-AP MLDs to initiate simultaneous transmission on an NSTR link pair. Briefly, the mechanism that can initiate simultaneous transmission is a mechanism that allows transmission to be initiated simultaneously on the first and second links by suspending 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.

[0201] Additionally, an exception rule is defined that allows a PPDU to be received on one Link of an NSTR link pair, and a response frame (e.g., a CTS frame) may not be responded to even if a frame requesting a response (e.g., an RTS frame) is received on the other Link of the NSTR link pair.

[0202] As described above, since an NSTR link pair is characterized by interference caused by transmissions performed by STAs operating on a specific Link that makes it impossible for STAs operating on other Links to operate normally (CCA and / or PPDU reception is impossible), 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 means a Link pair in which transmissions performed by each STA operating on each Link of the STR link pair do not affect STAs operating on other Links, and thus PPDU reception is possible on another Link while PPDU transmission is performed on a specific Link.

[0203] In this way, each link pair can be an STR link pair to a specific MLD or an NSTR link pair to another MLD depending on the interference shielding capability of each MLD. However, if the operating channels of a specific link pair overlap, the specific link pair cannot help but become an NSTR link pair regardless of the characteristics / performance of the MLD. Accordingly, in Wi-Fi 7, 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 operated in each link on which the setup is performed are regulated to not overlap with each other. In other words, the operating channels of each link on which an AP MLD and a non-AP MLD perform a multi-link setup do not overlap with each other.

[0204] <Primary channel (or main channel) dependency problem in conventional Wi-Fi channel access procedures>

[0205] MLD was introduced to 1) increase throughput by utilizing multiple links, and 2) obtain channel access more quickly by performing channel access procedures across multiple links than through a single link (by quickly obtaining access through one of the multiple links). However, this method of improving channel access opportunities by simultaneously performing channel access procedures across multiple links can incur significant power consumption as the number of links performing channel access procedures increases. While MLD can perform channel access procedures across multiple links to increase the probability (frequency) of channel access, it suffers from the power consumption associated with performing channel access procedures across multiple links. Therefore, using multiple links as a solution to increase channel access probability (frequency) is considered a limited solution, and a method is needed to increase the success probability (frequency) of the channel access procedure performed on each link. For example, to obtain channel access more quickly than through a single link, the channel access procedure can be performed across more than one link, but considering power consumption, the number of links can be limited. For example, if a channel access procedure cannot be performed on a 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 secondary channel) without waiting until the primary channel changes to an idle state.

[0206] Therefore, in order to support the development goal of Wi-Fi 8, which is 'Ultra High Reliability (UHR),' it is necessary to optimize the utilization of multiple links, which is a characteristic of MLD, as well as a method to support STAs operating on each link to obtain channel access opportunities in the best possible way.

[0207] In this context, it is necessary to analyze the channel accessibility issues of Wi-Fi terminals performing channel access on each link. The Wi-Fi standard has achieved significant throughput performance improvements over successive generations, and the Wi-Fi 7 standard, which is currently nearing standardization, supports throughput exceeding 30 Gbps. One of the reasons the Wi-Fi 7 standard can support extremely high throughput compared to legacy Wi-Fi standards is its wide operating bandwidth (BW). While conventional Wi-Fi terminals use a 20 MHz band as their operating bandwidth, Wi-Fi 7 operates with an operating bandwidth of up to 320 MHz. This means that the maximum throughput increase achieved solely by expanding the maximum operating bandwidth (BW) supported by the Wi-Fi standard amounts to a 16-fold increase. However, the maximum throughput of the Wi-Fi standard, which is increased by expanding the operating bandwidth, is merely a nominal figure and is unlikely to translate into actual performance improvements in Wi-Fi terminals.

[0208] In other words, despite the continuous expansion of the maximum supportable operating BW through the advancement of Wi-Fi terminals and standards, the impact on the actual performance of Wi-Fi terminals is relatively small. This is because the probability that the entire bandwidth included in the maximum operating BW will be identified as idle when the Wi-Fi terminal performs channel access is low, and the method by which the Wi-Fi terminal performs channel access has an excessively high dependency on the primary 20 MHz channel. Among these, the problem of the low probability of the entire wide bandwidth included in the operating BW being identified as idle may be an inherent problem because the frequency band in which the Wi-Fi terminal operates is an unlicensed band. In other words, it is natural for the medium to be occupied by other devices operating in the unlicensed band, and it is impossible to improve the channel access probability of the Wi-Fi terminal by improving this problem. However, the problem of excessively high Primary 20 MHz channel dependency is not a characteristic of Wi-Fi that was maintained for harmonious operation with heterogeneous devices, but rather a characteristic inherited in the process of maintaining the channel access technique traditionally used from existing Wi-Fi. To explain more specifically, the Wi-Fi standard was designed to perform channel access for a 40 MHz channel by extending the channel access technique used when the operating BW was 20 MHz.More specifically, the method for accessing a 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 the secondary 20 MHz channel has been identified as IDLE for the last PIFS (Priority Inter Frame Space, aSIFSTime (16 us) + aSlotTime (9 us)) at the time when the backoff procedure on the primary 20 MHz channel is completed. Similarly, the method for accessing the 80 MHz channel according to the method defined in the Wi-Fi standard is to perform access to the 80 MHz band (80 MHz band including the Primary 20 MHz, Secondary 20 MHz, and Secondary 40 MHz bands) if the Secondary 20 MHz channel and the Secondary 40 MHz channel have been identified as IDLE for the last PIFS (Priority Inter Frame Space, aSIFSTime (16 us) + aSlotTime (9 us)) when the backoff procedure is completed on the Primary 20 MHz channel. In this way, the Wi-Fi Wide Band Operation method for accessing subchannels identified as IDLE for the PIFS when the backoff procedure is completed on the Primary 20 MHz channel is applied in the same manner when accessing the 320 MHz BW defined in Wi-Fi 7. The reason why this method has been repeatedly used is because it enables wide bandwidth access in a more energy-efficient and less hardware-implementation manner by performing backoff on only one channel (primary channel) and determining whether other subchannels are accessible within a minimum time interval.

[0209] However, this method of channel access using a primary channel has a major drawback in that when the Primary 20 MHz channel on which the Wi-Fi terminal performs the backoff procedure is determined to be busy, even if all sub-channels except the Primary 20 MHz channel are available (not occupied by other devices), the backoff procedure of the Wi-Fi terminal cannot be completed, and thus channel access to wide idle sub-channels is also impossible.

[0210] As mentioned above, the issue of channel access of Wi-Fi terminals supporting wideband operation being limited depending on the CCA results of the Primary 20 MHz subchannel is not a new issue in UHR. However, UHR, which succeeds Wi-Fi 7 and supports ultra-wideband operation up to 320 MHz, may suffer greater losses due to the dependency on the Primary 20 MHz subchannel mentioned above compared to existing WiFi standards. Moreover, next-generation standards after UHR may also experience performance degradation issues due to the dependency on the Primary 20 MHz subchannel mentioned above. Therefore, it is clear that there is a need to resolve the channel access issue related to the Primary 20 MHz subchannel mentioned above.

[0211] For this reason, the present invention provides a method and procedure for a terminal supporting wideband 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.

[0212] For example, if a preamble of a PPDU is received through a Primary 20 MHz subchannel, and if CCA is performed based on the received preamble and the Primary 20 MHz subchannel is determined to be busy, a channel access procedure may be performed by selecting one of the non-Primary 20 MHz subchannels other than the Primary 20 MHz subchannel. In addition to the Primary 20 MHz subchannel, the other subchannel on which the channel access procedure is performed may be included in an operating channel that is the same as or different from the Primary 20 MHz.

[0213] Accessing channels that do not utilize the primary channel

[0214] As the simplest method to resolve the dependency problem on the aforementioned Primary 20 MHz sub-channel (hereinafter referred to as the P20 channel), a method of performing channel access using (through) a sub-channel (a non-primary channel (or sub-channel)) other than the P20 channel may be considered. At this time, performing channel access using (through) a non-primary channel means performing a backoff procedure based on whether the non-primary channel is idle / busy. At this time, there may be one or more non-primary channels on 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., the first non-primary channel or the second non-primary channel, etc.). At this time, the channels on which the terminal can perform the backoff procedure (i.e., the P20, the first non-primary channel, the second non-primary channel, the third non-primary channel, etc.) may be 20 MHz sub-channels included in different 80 MHz sub-blocks, respectively. That is, the first non-primary channel may be located in an 80 MHz subblock other than the 80 MHz subblock including the P20 channel. That is, when the terminal selects a backoff channel (non-primary channel) other than P20, the terminal must select another backoff channel (non-primary channel) from among the 20 MHz subchannels of the 80 MHz subblock (i.e., a subblock other than the Primary 80 MHz subblock) that does not include the P20 subchannel. At this time, each of the different backoff channels selected by the terminal may be located in a different 80 MHz subblock. That is, the first non-primary channel may be a subchannel located in an 80 MHz subblock other than the second non-primary channel.At this time, the selection restriction of non-primary channels related to the aforementioned 80 MHz subblock may only apply when the operating channel of the BSS is included in the 5 GHz or 6 GHz band.

[0215] At this time, channel access using a non-primary channel may be performed only during a time period in which 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) and PD, Virtual CCA. In addition, non-primary channel access may be limitedly permitted only to STAs (AP STAs, non-AP STAs) in which the P20 channel is BUSY and the frame identified on the P20 channel is not a frame destined for itself. Accordingly, the non-primary channel access procedure may be limitedly permitted only when the preamble of a PPDU received on the P20 channel is successfully detected or the MPDU is successfully decoded. Accordingly, the non-primary channel access procedure may be limitedly permitted only to STAs that have successfully received a frame received on the P20 channel.

[0216] 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 is transmitted from an overlapping BSS (OBSS), the STA can select one non-primary channel among 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 on which the channel access procedure is performed may be an idle state.

[0217] That is, backoff and channel access procedures using subchannels other than the P20 channel may be restricted to cases where the PPDU identified on the P20 channel is an OBSS PPDU. Accordingly, backoff and channel access procedures using other subchannels may be restricted to cases where the PPDU identified on the P20 channel is a PPDU whose destination is not the device that received the PPDU.

[0218] To this end, the backoff performing and channel accessing procedures using subchannels other than the P20 channel can be initiated after confirming whether the PPDU identified on the P20 channel is the destination device or OBSS by decoding the preamble of the PPDU to confirm the BSS Color of HE-SIG and / or U-SIG, confirming the STA-ID of EHT-SIG and / or UHR-SIG, or decoding the first MAC frame of the PPDU to confirm the destination device. That is, the STA can confirm 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 confirm the station identifier (STA-ID) included in the SIG field (e.g., HE-SIG-B, EHT-SIG, or UHR-SIG)) in order 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.

[0219] At this time, if the MAC addresses of the sender / receiver of a specific PPDU and the sender / receiver of the frame included in the PPDU are the APs with which it is associated, the specific PPDU can be distinguished as a PPDU (Intra-BSS PPDU) rather than an OBSS PPDU. At this time, a backoff procedure using a subchannel other than the P20 channel may need to be initiated after confirming whether the other subchannel is idle during DIFS. At this time, if the confirmed BSS Color is not its own BSS Color, the STA-ID and MAC frame decoding performed to specify the target device may be omitted. At this time, a method of confirming whether the other subchannel is idle may be to confirm by performing PHY CCA (Energy detection and / or Packet detection) performed for a preset period of time. At this time, the preset period of time may be PIFS (Priority Inter Frame Space), DIFS (Distributed Inter Frame Space), or MediumSync time. Here, MediumSync time can be a time interval with a different name, and it refers to the time that a device that intends to perform a backoff procedure on a non-primary channel (or secondary channel) must perform CCA to determine whether the medium is idle / busy. MediumSync time can be several milliseconds long and is shorter than MaxPPDU length (5.484 ms). A terminal that performs CCA using MediumSync time can set NAV using information contained in the PPDU (frame) received during the CCA.At this time, the NAV that the terminal sets based on the PPDU (frame) received on the S20 channel (a subchannel other than the primary 20 MHz channel) may be a NAV other than the two NAVs (Basic NAV, Intra-BSS NAV) used in conventional Wi-Fi. At this time, the other NAV is a timer set by the frame (PPDU) received through S20, and is a NAV used for Virtual CCA of the S20 channel when performing channel access through the S20 channel. That is, even if the other NAV is set by the frame (PPDU) received on the S20 channel and the value of the other NAV is not 0, the terminal can determine the result of the CCA performed on the P20 channel as IDLE. That is, the other NAV is a NAV for the S20 channel, not the P20 channel. At this time, the other NAV may be called a secondary NAV.

[0220] Therefore, if the terminal performing channel access via the S20 channel is an AP STA, the AP may need to manage both the basic NAV, which is set based on the frame (PPDU) received while occupying the primary 20 MHz subchannel, and the secondary NAV, which is set based on the frame (PPDU) received (i.e., received via the S20 channel) without occupying the primary 20 MHz subchannel. That is, the AP must perform a backoff procedure considering the basic NAV when performing channel access via the P20 channel, and must perform a backoff procedure considering the secondary NAV when performing channel access via the S20 channel. At this time, the secondary NAV may be a timer that is initialized to the 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 the Mediumsync time value at the same time as starting CCA for the S20 channel.

[0221] In addition, an STA that has performed frame exchange after performing channel access 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 another device when initiating a channel access procedure on the Primary 20 MHz subchannel after the frame exchange performed through the other subchannel is completed. At this time, a method for the STA to check whether the P20 channel is occupied by another BSS or another 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 acquired through the received PPDU (frame). In this case, the STA may resume the channel access procedure performed on the Primary 20 MHz subchannel when the set NAV is released (when the NAV timer becomes 0).

[0222] At this time, the backoff procedure using another subchannel can be compensated for the delayed time for 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 confirm the destination device (or BSS Color) of the PPDU identified in the P20 channel, an operation of decreasing the backoff counter used for channel access using a subchannel other than the P20 channel by 3 at once may be permitted. Alternatively, since channel access using a subchannel other than the P20 channel is an additional function that conventional devices do not utilize, the operation of decreasing the backoff counter all at once may not be permitted, but rather the backoff counter may be sequentially decremented by 1 after confirming the destination device of the PPDU identified in the P20 channel. In other words, compensation for the delayed backoff procedure may not be performed separately in the process of confirming the destination device of the PPDU identified in the P20.

[0223] In the embodiments of the present invention described below, the process of identifying the destination device of a PPDU received on the aforementioned P20 channel may be omitted for convenience of explanation. Therefore, even if not described separately, it should be understood that the channel access procedure performed using a subchannel other than the P20 channel includes the process of identifying the destination device of a PPDU received on the aforementioned P20 channel.

[0224] Figure 12 shows an example of a channel access procedure through a non-primary channel when the state of the primary channel is busy.

[0225] Referring to FIG. 12, if the CCA result of the Primary 20 MHz subchannel is determined to be busy, the terminal can perform channel access using a non-primary 20 MHz subchannel other than the Primary 20 MHz subchannel.

[0226] Specifically, an STA (AP STA, non-AP STA) constituting an MLD may perform channel access using a channel other than the P20 channel when the P20 channel is determined to be BUSY (e.g., when the P20 channel is determined to be busy based on the CCA result based on the preamble of the received PPDU). At this time, the operation of performing the channel access may be to perform a backoff according to the CCA result of the other channel. At this time, the backoff operation may be an operation of decreasing a backoff counter by 1 when the result of the CCA performed in each slot on the other channel is IDLE. In addition, the backoff operation may be an operation of maintaining the backoff counter without decreasing it when the result of the CCA performed in each slot on the other channel is BUSY.

[0227] The S20 channel that can be utilized for channel access using a 20 MHz subchannel other than the above-described P20 channel is not limited to a specific S20 channel, but multiple S20 channels can be utilized. For example, assuming that an STA performs 320 MHz operation as in the embodiment of FIG. 12, channel access may be possible not only through the S20_1 channel included in the Secondary 80 MHz subblock as illustrated in FIG. 12, but also through S20_2 and S20_3 included in the Secondary 160 MHz subblock. In this case, the number of S20 channels utilized for channel access by each STA 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 subchannel per 80 MHz subblock. At this time, each non-primary subchannel on which the STA performs backoff is a subchannel determined by the AP and is therefore indicated through a management frame transmitted by the AP. That is, the AP can indicate information on another subchannel (S20) on which backoff can be performed when the primary channel (P20) is busy through the management frame transmitted by the AP (e.g., Beacon, Probe Response, Association Response frame, etc.), and the other subchannel is one of the subchannels included in an 80 MHz subblock other than the Primary 80 MHz subblock.

[0228] Referring to Fig. 12 (a), the backoff counter used when performing channel access on the P20 channel and the backoff counter used when performing channel access on the S20 channel can exist and be managed separately. In this case, the backoff counter used by each channel can be changed to a new value as a backoff counter only when transmission is performed as a result of the channel access performed on each channel (when backoff is completed). In this case, changing to a new value means changing to a new backoff counter extracted using CW_min if the transmission is successful, or changing to a new backoff counter extracted using CW x 2 if the transmission fails. In other words, it does not mean an operation of decreasing the backoff counter as a result of the CCA. In this case, as described above, if there are multiple S20 channels performing channel access, the multiple S20 channels can have their own backoff counters. In this case, the backoff counter for each S20 channel may exist for each Access Category. That is, a terminal may need to manage a separate backoff counter for each AC for each S20 channel on which it can perform backoff. In other words, a terminal performing a backoff procedure through an S20 channel can internally perform a channel access procedure using four ACs.

[0229] Referring to Fig. 12 (b), all S20 channels performing channel access, including P20, can utilize a common backoff counter. As illustrated in Fig. 12 (b), as a result of the channel access operation performed on the P20 channel, the backoff counter is decreased from 5 to 3, and then the P20 channel is changed to BUSY. According to an embodiment proposed in the present invention, when the P20 channel is BUSY, the S20 channel can perform the channel access procedure, and as shown in Fig. 13 (b), the backoff counter that P20 reduced to 3 can continue to be decreased according to the CCA result performed on S20_1. If S20_1 is also determined to be BUSY while decreasing the backoff counter for channel access, the backoff counter can be maintained as is until a channel access using S20_2 is started, or until P20 to S20_1 are determined to be IDLE. At this time, if the channel connection using the above S20_2 is continued, it can be understood as an embodiment in which there are two or more S20 channels used for channel connection, and if the backoff counter is maintained until the above P20 to S20_1 are determined to be IDLE, it can be understood as an embodiment in which there is only one S20 channel used for channel connection.

[0230] <Restrictions on transmission through primary channels>

[0231] As described above, an STA (non-AP STA or AP) that constitutes an MLD (non-AP MLD or AP MLD) that operates 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 STA performs a CCA to perform the channel access procedure on the primary channel and the primary channel is found to be idle, the STA can perform the channel access procedure on the primary channel. However, if the CCA performed based on the preamble of the PPDU received on the primary channel determines that the primary channel is busy, the STA cannot perform the channel access procedure until the primary channel changes to idle. Therefore, in this case, the STA can select one of the non-primary channels that is in an idle state and perform the channel access procedure without waiting until the primary channel changes to idle.

[0232] In this way, an STA that performs a channel access procedure using a non-primary channel (S20 channel) rather than a primary channel may be restricted in the length of the PPDU it transmits. The PPDU transmission length restriction may be necessary for two reasons. In this case, the length of the PPDU transmitted after performing the backoff procedure on the S20 channel may be restricted so that it ends earlier than the end time of the PPDU recognized by the PPDU (and / or frame) confirmed on the P20 channel. 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 restricted 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 equal to or shorter than the length of the first PPDU. At this time, the length of the first PPDU to limit the length of the second PPDU can be confirmed by the length field included in the preamble of the first PPDU.

[0233] One reason why the above restriction is necessary may be to prevent problems that may occur when an OBSS device occupying the P20 channel terminates transmission while a transmission initiated using the S20 channel continues. More specifically, transmissions that occur after performing channel access through the S20 channel will be performed through subchannel(s) excluding the P20 channel, and during the transmission, the AP cannot provide any services, such as transmission / reception or scanning, for the P20 channel. Therefore, if the S20 transmission ends later than the OBSS PPDU identified on the P20 channel, the AP cannot identify and receive other STA UL PPDUs or OBSS PPDUs that may be identified on the P20 channel. In this case, in addition to the problem of not being able to receive the STA UL PPDU, the NAV setting by the OBSS PPDU cannot be performed, which may cause problems in the overall operation of the BBS. Another reason why the above PPDU transmission length restriction is necessary may be to alleviate fairness issues. If a length limit is not applied to transmissions made after performing channel access via the S20 channel, fairness issues may arise with conventional WiFi STAs that perform channel access only via the P20 channel. Therefore, in addition to limiting the number of S20 channels that can perform channel access via the aforementioned S20 channel, it may be necessary to alleviate fairness issues with conventional WiFi STAs by limiting the length of PPDUs transmitted through channel access via the S20 channel.

[0234] In addition, 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 a 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 the 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. In other words, an STA that performs channel access on a non-primary channel (S20 channel) rather than the primary channel (P20 channel) may be limited in the length of a TXOP obtained through the channel access procedure. For example, the length of a TXOP (second TXOP) acquired by an STA through a channel access procedure of a non-primary channel may be equal to or shorter than the length of a TXOP (first TXOP) based on a PPDU (first PPDU) of a primary channel. In this case, the length of the first TXOP may be acquired based on a TXOP field included in a preamble of the first PPDU.

[0235] The above TXOP length limitation may be necessary for two reasons. One aspect of the limitation may be to prevent a problem that may occur when the TXOP of an OBSS device occupying the P20 channel is terminated while the TXOP acquired using the S20 channel (a subchannel other than the primary 20 MHz channel) continues. More specifically, the TXOP acquired through the S20 channel is applied to the frequency range occupying the subchannel(s) excluding the P20 channel, and while frame exchange is performed using the TXOP, terminals may be in a state where they cannot perform transmission / reception, CCA, etc. for the P20 channel. Therefore, if the transmission of the S20 channel is terminated later than the TXOP of the OBSS confirmed on the P20 channel, terminals cannot confirm and receive other OBSS PPDUs that can be confirmed on the P20 channel. In this case, since the STA's UL PPDU cannot be received and NAV setting by OBSS PPDU cannot be performed, problems may occur in the overall operation of the BBS. Another aspect that requires the above PPDU transmission length limitation may be to alleviate fairness issues. If the length limitation of 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 through only the P20 channel. Therefore, in addition to limiting the number of S20 channels that can perform channel access through the aforementioned S20 channel, it may be necessary to alleviate the fairness issue with conventional Wi-Fi STAs by limiting the length of the TXOP obtained by channel access through the S20 channel.

[0236] Figure 13 illustrates an embodiment of a transmission length limitation of a PPDU transmitted after performing channel access through a non-primary channel.

[0237] Referring to FIG. 13, the length of a PPDU transmitted by an STA through a non-primary channel (S20 channel) rather than the primary channel (P20 channel) described above when performing a channel access procedure may be limited to be equal to or shorter than the length of a PPDU transmitted on the primary channel (e.g., a PPDU received by the STA through the primary channel for CCA).

[0238] Specifically, a situation is illustrated in which a terminal, which has determined 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 in the S20_1 channel may be a backoff counter shared with the backoff counter used in the P20 channel, or may be a separate backoff counter utilized for channel access through the S20_1 channel. In Fig. 13, the S20 channels are illustrated as being in the same 80 MHz subblock as the P20 channel, but the S20 channels that perform a backoff when the P20 channel is BUSY may be located in a different 80 MHz subblock from the 80 MHz subblock that includes the P20 channel.

[0239] Before starting channel access through S20_1 channel, STA can detect preamble of OBSS PPDU while attempting channel access through P20 channel and confirm that P20 channel is occupied by OBSS (BUSY). In this situation, STA can perform decoding on preamble of OBSS PPDU and confirm how long OBSS PPDU will last. At this time, the operation of STA performed after confirming how long OBSS PPDU will last may be setting NAV. At this time, STA can check L-SIG and Length fields of detected preamble or confirm the duration of OBSS PPDU based on value indicated through TXOP field included in U-SIG field and / or HE-SIG field of OBSS PPDU. Alternatively, the STA can check the duration of the OBSS PPDU based on the Duration / ID field of the MAC frame included in the PPDU.

[0240] After this, the STA can determine the length of the PPDU to be transmitted after performing channel access through the S20 channel based on the end time of the OBSS PPDU confirmed on the P20 channel. At this time, the length of the PPDU to be transmitted after performing channel access through the S20 channel can be limited / adjusted to end earlier than or equal to the predicted end time of the OBSS PPDU confirmed on the P20 channel. At this time, a method of limiting the length of the PPDU may be such that the end time of the Response frame expected to be responded to the PPDU is adjusted to end earlier than or equal to the end time of the OBSS PPDU. At this time, the Response frame means a PPDU including an ACK frame or a Block ACK frame, a TB (trigger-based) PPDU, etc. In other words, the end time of the PPDU responded to by the PPDU can be limited to be earlier than or equal to the predicted end time of the OBSS PPDU confirmed on the P20 channel.

[0241] FIG. 14 illustrates an embodiment of a method for limiting the length of a TXOP obtained through channel access via a non-primary channel.

[0242] 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 performs a channel access procedure through a non-primary channel (P20 channel) rather than the primary channel described above may be limited to be equal to or shorter than the length of a TXOP based on a PPDU transmitted on the primary channel (e.g., a PPDU received by the STA through the primary channel for CCA).

[0243] Specifically, a situation is illustrated where a terminal that has determined that the P20 channel is BUSY completes a backoff procedure and acquires a TXOP through a subchannel (S20 channel) included in a secondary 80 MHz subblock. 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 may be a separate backoff counter used when performing a backoff operation in a subchannel included in the secondary 80 MHz subblock.

[0244] When a terminal determines that the P20 channel is BUSY and wishes to perform a backoff procedure through S20, it performs CCA on the S20 channel during a time period corresponding to the MediumSync time to protect communication of an OBSS that may be transmitting / receiving using the S20 channel. In Fig. 14, the state of S20 observed by the terminal during the time period corresponding to the MediumSync time is IDLE, and therefore the terminal initiates a backoff procedure on the S20 channel.

[0245] When the terminal completes the backoff procedure performed through the S20 channel, the TXOP acquired by the terminal is set to end at the same time as the TXOP (OBSS TXOP) that includes the frame (RTS / CTS frame of FIG. 14) transmitted by occupying the P20 channel. In this case, although the embodiment of FIG. 14 illustrates that the two TXOPs end at the same time, the TXOP acquired after performing the backoff through the subchannel included in the Secondary 80 MHz subblock may be set to end earlier than the OBSS TXOP.

[0246] After performing backoff through the S20 channel, the terminal that acquires the TXOP can 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 on the Primary 20 MHz subchannel when checking the TXOP length of the OBSS that occupied the P20 channel. That is, when a frame transmitted by an 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 through 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, completes the channel access procedure (backoff procedure) through the subchannel included in the Secondary 80 MHz subblock, and when acquiring a TXOP, the terminal must adjust its TXOP length so that the TXOP it acquired ends simultaneously with or before the TXOP of the confirmed OBSS.

[0247] After the TXOP acquired through the S20 channel is terminated, the terminal performs CCA for the P20 channel during the period corresponding to the MediumSync time to resume channel access through the P20. If a valid frame (PPDU) is received before the time corresponding to the MediumSync time elapses, the terminal sets the NAV based on the information acquired 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, the P20 was observed to be in an IDLE state until the time corresponding to the MediumSync time elapsed, and therefore, the terminal resumed the channel access procedure after the time corresponding to the MediumSync time expired.

[0248] <S20 채널(넌 프라이머리 채널)을 통한 채널 접속 절차의 제한>

[0249] The series of channel access procedures performed via the S20 channel described above may be channel access procedures permitted only to AP STAs. In other words, channel access procedures performed via the S20 channel, rather than the P20 channel, may be channel access procedures that non-AP STAs cannot perform.

[0250] The reason why the channel access procedure through the S20 channel is allowed only to AP STAs is because, even among STAs belonging to a single BSS, the status of the P20 channel confirmed by each STA may be different. Assuming that 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, but the AP and the second non-AP STA may recognize that the P20 channel is IDLE because the PPDU was not received. In addition, there may also be a case where the first non-AP STA does not receive the PPDU received by the second non-AP STA. In this way, the status of the P20 channel confirmed by each non-AP STA belonging to the same BSS may be different, and the status of the P20 channel confirmed by each STA and the status of the P20 channel confirmed by the AP may also be different. In this case, even if a non-AP STA that determines that the P20 channel is busy performs channel access through the S20 channel and transmits a UL PPDU, the AP may determine that the P20 is idle and still proceed with the channel access procedure on the P20 channel. In other words, the PPDU transmitted by the non-AP STA after performing channel access on the S20 channel cannot be normally received by the AP if the P20 channel confirmed by the AP is idle. Furthermore, while the non-AP STA that determines that the P20 channel is BUSY performs channel access on the S20 channel and transmits a UL PPDU, the AP may transmit a PPDU to the non-AP STA after completing the channel access on the P20 channel. In this case, the non-AP STA may have a problem in that it cannot normally perform a PPDU received on the P20 channel due to the PPDU transmission performed on the S20 channel.In this way, since the status of the P20 channel confirmed by each STA (AP STA and non-AP STA) belonging to the BSS may be different, each non-AP STA may be restricted from performing a channel access procedure on the S20 channel even if it determines that the P20 channel it has confirmed is in a BUSY state. However, the non-AP STA may have to wait for reception of a PPDU that may be transmitted on the S20 channel when it determines that the P20 channel is in a BUSY state.

[0251] In the case of an AP, after performing a channel connection on the S20 channel, in order to check whether the target device to receive the frames to be transmitted is capable of receiving on the S20 channel, a frame of a preset format may be transmitted as the first frame transmitted after performing a channel connection on the S20 channel. At this time, the preset format may be RTS (Request To Send), MU-RTS (Multi-User RTS), BSRP (Buffer Status Report Poll), or another type of trigger frame. In other words, the AP may have to transmit a frame of the preset format included in the first PPDU transmitted after performing a channel connection through the S20 channel.

[0252] That is, an AP that performs a channel access procedure on an S20 channel rather than a P20 channel may transmit a frame in a preset format for the first time after the channel access procedure. For example, an AP that performs a channel access procedure on an S20 channel may transmit a frame that does not contain data for the first time after the channel access procedure. That is, after the channel access procedure, the AP may transmit a frame in a specific format that does not contain data for the first time after the channel access procedure, since the channel of the STA associated with the AP may not have been changed yet.

[0253] At this time, the frame of the preset format transmitted by the AP is a frame that requests a response of an immediate response frame from one or more STAs, and therefore, when the AP transmits a frame of the preset format, a response frame is responded to by the STAs that receive it.

[0254] When the AP receives response frames in response to a frame of a preset format that it transmitted, it can recognize that the STAs that transmitted the response frames are STAs that can support reception of the PPDU transmitted via S20. Accordingly, after transmitting the frame of the preset format, the AP can transmit frames targeting the STAs that responded with the response frame to the frame through the next PPDU.

[0255] As a more specific example, after performing channel access via S20, the AP may request a response frame from the first STA and the second STA via a frame in a preset format that is transmitted. At this time, if the response frame is responded to from the first STA and the response frame is not responded to from the second STA, the AP may include an MPDU whose destination device is the first STA in the next transmitted PPDU, and may not include an MPDU whose destination device is the second STA. That is, if the AP does not receive a response frame for the frame in the preset format transmitted via S20 from a specific STA, the AP must not include an MPDU whose destination device is (individually addressed) the specific STA in the PPDUs transmitted via the channel access.

[0256] <S20을 통한 채널 접속의 규범적 동작 제한>

[0257] All terminals that perform communications using unlicensed bands must perform normative channel access operations to ensure that each terminal can access the medium in a harmonized and fair manner. The ETSI (European Telecommunications Standards Institute) BRAN (Broadband Radio Access Networks) committee has defined a harmonized standard regarding the channel access method of terminals that utilize unlicensed bands, and Wi-Fi terminals must also follow the standards defined by ETSI BRAN because they perform operations using unlicensed bands. 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 ETSI BRAN, and therefore conventional Wi-Fi terminals perform channel access through the normative operation defined by ETSI BRAN.

[0258] Among the standards defined in relation to the EDCA mechanism, there is a regulation regarding the change of the channel (primary operating channel) that performs the backoff operation through the EDCA mechanism. The specific regulation is that a terminal performing channel access through EDCA must not change the primary operating channel more than once per second. In other words, a terminal performing channel access through EDCA must perform channel access using the channel for at least 1 second when the channel performing the backoff procedure (primary operating channel) is changed. In this case, the time for performing channel access using a specific subchannel may be calculated based on the start time of transmission of the first PPDU transmitted among the PPDUs after performing channel access using the specific subchannel. In other words, if the start time of the first PPDU transmitted after the terminal changes the primary operating channel to S20 is T1, the terminal may change the primary operating channel to a subchannel other than S20 (primary 20 MHz subchannel or another subchannel) after 1 second has elapsed from T1.

[0259] Accordingly, the channel access operation via the S20 channel provided in the present invention may be limitedly usable when the channel access operation via the P20 channel is maintained for 1 second or more. In addition, a terminal that has performed a channel access operation via the S20 channel must attempt a channel access operation via the S20 channel for 1 second or more, and it is possible to switch to performing a channel access via the P20 channel while maintaining the channel access operation via the S20 channel for 1 second or more. In this case, the 1 second is for example only, and the same operation / restriction may be performed by applying another predetermined time length.

[0260] That is, in order for the terminal to perform a channel access procedure on a non-primary channel, the terminal must attempt the channel access procedure on the primary channel for a certain period of time (e.g., 1 s). Afterwards, when performing a channel access procedure on a non-primary channel, the terminal must attempt the channel access procedure on the non-primary channel for a certain period of time (e.g., 1 s). For example, when performing a channel access procedure on a non-primary channel, the terminal must perform an operation (e.g., the channel access procedure) on the non-primary channel for a certain period of time (e.g., 1 s).

[0261] That is, non-AP STAs that recognize that the AP has performed channel access through the S20 channel may have to perform operations considering the S20 channel as the default channel until the AP can perform channel access through the P20 channel. That is, non-AP STAs that recognize that the AP has performed channel access through the S20 channel must perform channel access on the S20 channel or wait to receive PPDUs transmitted from the AP until the AP switches to a state where it can perform channel access on the P20 channel. At this time, the AP can use the Management frame (e.g., Beacon frame) that it transmits to indicate to the non-AP STAs information related to the point in time when it performed channel access through the S20 channel or the point in time when it can switch to channel access operation through the P20 channel. That is, the AP can indicate information related to the point in time when it switches to channel access operation through the P20 channel during the time period when it must perform channel access through the S20 channel, through the Management frame that it transmits. When Non-AP STAs receive a Management frame transmitted by an AP, if the Management frame includes information related to the point in time when the AP switches to a channel access operation via a P20 channel, they can recognize whether the channel access execution channel of the AP is a P20 channel or an S20 channel based on the indicated information.

[0262] FIG. 15 illustrates a method for an AP to manage a primary operating channel by obtaining a TXOP through a primary channel and a non-primary channel, according to one embodiment of the present invention.

[0263] Referring to Figure 15, in a situation where OBSS1 and OBSS2 exist in the Primary 80 MHz subblock and the Secondary 80 MHz subblock, respectively, the AP performs channel access through a channel not occupied by the OBSS by changing the primary operating channel. The description below describes the channel access operation of the AP in chronological order (from left to right in the drawing).

[0264] When the AP acquires TXOP1, it acquires channel access by completing the channel attachment procedure performed through P20. Since the TXOP of OBSS2 is in progress in the secondary 80 MHz subblock at the time the AP acquires the TXOP, the AP acquires channel access only for the primary 80 MHz, and therefore TXOP1 is applied only to the primary 80 MHz subblock. After that, the AP completes the channel attachment procedure again in P20 and acquires TXOP2, which is a TXOP for the 160 MHz band. After TXOP2 is terminated, while the AP is performing the channel attachment procedure to acquire TXOP3, the TXOP of OBSS1 is acquired in the form of occupying P20, which is the AP's primary operating channel, and therefore the AP's backoff procedure is stopped. At this time, the AP recognizes that S20 is also occupied by the TXOP of OBSS2 and maintains the primary operating channel without changing it. However, before the channel association procedure of the AP that resumed after the first TXOP of OBSS1 ended is completed, the TXOP of OBSS1 starts again, and the AP decides to change the primary operating channel to S20. At this time, the AP is able to change the primary operating channel to S20 because the time it maintained P20 as the primary operating channel was 1 second or longer.

[0265] Accordingly, the AP performs channel access through S20 during the second TXOP of OBSS1 and acquires TXOP3. After the TXOP of OBSS2 ends, the AP completes the channel access procedure performed in S20 and acquires TXOP4, which is a TXOP for the 160 MHz band. After this, the channel access procedure performed by the AP in S20 is interrupted as the TXOP of OBSS2 starts. At this time, the AP confirms that P20 is idle and decides to change the primary operating channel to P20. At this time, the AP can change the primary operating channel to P20 because the time it maintained S20 as the primary operating channel was 1 second or longer.

[0266] <Multi-subchannel access using multi-link>

[0267] As mentioned above, if the primary operating channel is only allowed to be changed once per second according to the normative operation defined by the ETSI BRAN committee, it is difficult to say that the dependency problem on the primary channel, which is the basic idea of ​​the present invention, is completely resolved. This is because, after a specific terminal changes the primary operating channel, whether or not the channel can be accessed is determined based on whether the changed primary operating channel is idle / busy for at least one second. In other words, the dependency problem on the primary channel that the Wi-Fi terminal has can be alleviated only once per second at most, and the same dependency problem occurs on the changed primary operating channel for the remaining time interval. In other words, the problem to be solved through the present invention is not the dependency problem on the primary 20 MHz subchannel of the Wi-Fi terminal, but the dependency problem 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 primary operating channel from the P20 channel to the S20 channel and then again from the S20 channel to the P20 channel or another S20 channel only provides the effect of changing the channel designated as the primary operating channel, but does not resolve the limitation that channel access to the entire Operating BW is restricted when a specific 20 MHz subchannel (primary operating channel) is judged to be BUSY.

[0268] To address the dependency issue on the designated primary operating channel (i.e., the channel that performs the EDCA backoff procedure) described above, one may consider reducing the importance of the designated primary operating channel. The simplest way to reduce the importance of the designated primary operating channel is to designate multiple primary operating channels for a single operating channel. If multiple primary operating channels are designated for a single operating channel, the channel access dependency issue of a Wi-Fi terminal for each primary operating channel can be alleviated in proportion to the number of designated primary operating channels.

[0269] <How to specify multiple primary action channels for a single action channel>

[0270] The operating BW supported by the Wi-Fi standard has been continuously increasing, and the Wi-Fi 7 standard supports an operating BW of up to 320 MHz BW. Even when accessing an operating channel with such a wide BW (e.g., 40, 80, 160, 320 MHz channels), a Wi-Fi terminal can perform channel access only when it has completed the backoff procedure on the primary 20 MHz subchannel (the main operating channel). Since the backoff procedure can be completed only when the primary 20 MHz subchannel is determined to be IDLE, the Wi-Fi terminal cannot obtain access to a wide channel up to the 320 MHz band when the primary 20 MHz subchannel is determined to be BUSY. This is due to the dependency issue on the primary operating channel of the Wi-Fi terminal mentioned above, and the reason why the existing Wi-Fi standard has maintained a channel access procedure with this dependency issue is to minimize the increase in complexity of the Wi-Fi terminal.

[0271] To elaborate on the aforementioned ETSI regulation, the ETSI regulation defines two different normative channel access methods for wide-bandwidth (BW exceeding 20 MHz). The first normative channel access method is to obtain channel access rights using EDCA (or a channel access mechanism that operates under rules similar to EDCA) for each 20 MHz subchannel included in the wide-bandwidth to be accessed, and to simultaneously perform access to one or more 20 MHz channels for which channel access rights have been obtained. In other words, a terminal performing channel access for a band exceeding 20 MHz performs a channel access procedure for each 20 MHz subchannel separately, and can access the 20 MHz channels for which channel access rights have been obtained by completing the channel access procedure. The second normative channel access method for wide-bandwidth, defined in the ETSI regulation, is to simultaneously access other 20 MHz channels that have completed the channel access procedure on one primary operating channel (one 20 MHz channel) and that have been determined to be idle in measurements performed for more than 25 us. The method by which conventional Wi-Fi terminals access the 40 MHz, 80 MHz, 160 MHz, and 320 MHz bands utilizes the second normative channel access method defined in the ETSI regulation.

[0272] If a Wi-Fi terminal uses the first normative channel access method defined in the aforementioned ETSI regulation, the Wi-Fi terminal can more flexibly access each subchannel determined to be idle within the operating BW without the issue of dependency on a specific subchannel. However, performing a separate channel access procedure for each 20 MHz channel within the operating BW increases the hardware / operational complexity of the Wi-Fi terminal and incurs significant costs in other aspects, such as excessive energy consumption required for the channel access procedure.

[0273] For this reason, even in the latest Wi-Fi standard, Wi-Fi7, a method of performing channel access on each 20 MHz subchannel to access each 20 MHz subchannel was not introduced, but rather the channel access method of the existing Wi-Fi was inherited, which performs channel access on the Primary 20 MHz channel, which is the main operating channel, and performs channel access on other subchannels determined to be idle when the channel access procedure on the Primary 20 MHz channel is completed.

[0274] The overlapping operating channel configuration method of MLD described through the embodiments of the present invention described below is a method of maintaining the channel access method of conventional Wi-Fi in which each terminal attempts to access a channel for a wide bandwidth using a primary operating channel, while reducing the dependency on the primary operating channel.

[0275] Auxiliary AP / Link / BSS

[0276] As explained above, MLD (Multi-link Device) is defined in Wi-Fi7, and AP MLD and non-AP MLD can be in ML-setup (Multi-link setup) state where setup is performed through multiple links. At this time, the Operating channels of each link where AP MLD and non-AP MLD are setup must be set up in a non-overlapping state. At this time, when AP MLD and non-AP MLD are setup through multiple links, the BSS of the AP (AP belonging to AP MLD) operating in each of the multiple links must be a BSS operated through a non-overlapping frequency range.

[0277] However, the Operating BWs of each AP belonging to the AP MLD are allowed to overlap with each other. The rules in terms of the operating channels of the multi-link setup performed by the AP MLD and the non-AP MLD can be explained with a simpler example as follows. The AP MLD can operate the first AP, the second AP, and the third AP on Link 1, Link 2, and Link 3, respectively. At this time, the Operating channels of the two BSSs operated by the first and second APs overlap (partially or fully overlapped), and the Operating channel of the BSS operated by the third AP does not overlap with the Operating channels of the BSSs operated by the first and second APs. The AP MLD performs ML setup with the non-AP MLD, but allows ML setup states such as [Link 1, Link 3] and [Link 2, Link 3], and does not allow ML setup states such as [Link 1, Link 2] and [Link 1, Link 2, Link 3]. This is because, among the links on which the non-AP MLD performed setup, Link 1 and Link 2 have overlapping Operating channels. In summary, the BSS Operating channels of each AP operated by the AP MLD can overlap with each other, but the BSS Operating channels of multiple links on which each non-AP MLD performed ML setup are not permitted to overlap with each other. This is because, if the BSS Operating channel of a specific link on which the non-AP MLD performed ML setup overlaps with the BSS Operating channel of another link on which the ML setup was performed, the BSSs of the specific link and the other link act as OBSS (Overlapping BSS) and are BSSs that cannot provide service at the same time.

[0278] According to one embodiment of the present invention, AP MLD can set the operating channels (channels through which APs operate BSS) of two or more APs to overlap for the purpose of strengthening channel access to non-primary channels. At this time, among the APs whose operating channels overlap, one AP can be set as a primary AP, and the remaining APs can be set as secondary APs. A method for performing channel access using a primary AP and a secondary AP will be described later.<Overlapping AP를 이용한 채널 접속> is explained through .

[0279] In the following description of the present invention, the links through which the Primary AP and the Secondary AP operate are respectively named Primary Link and Secondary Link, the BSS through which the Primary AP operates is named Primary BSS, and the BSS through which the Secondary AP operates is named Secondary BSS. Since the operating channels of the Primary BSS and the Secondary BSS overlap, in the following description of the present invention, the two APs are expressed as having an Overlapping AP relationship.

[0280] A secondary AP operated by an AP MLD has a paired Primary AP, and the operating channels of the paired secondary AP and the Primary AP overlap. The Primary AP and the secondary AP support different levels of operation. For example, the Primary AP may periodically transmit Beacon frames (including Beacon frames and / or other types of Management frames, and Group-addressed frames), but the secondary AP may not transmit Beacon frames (including Beacon frames and / or other types of Management frames, and Group-addressed frames). For another example, the Primary AP may support services for legacy STAs (i.e., STAs that follow standards prior to Wi-Fi 8, such as Wi-Fi 7 and Wi-Fi 6), but the secondary AP may be restricted from performing services for legacy STAs. In addition, the BSS operated by the secondary AP (secondary BSS) may be a BSS in which only STAs of a non-AP MLD to which STAs that are members of the BSS (Primary BSS) operated by the Primary AP paired with the secondary AP belong may become members.

[0281] That is, in order for a non-AP MLD to be set up on a secondary link, it must be set up together with the primary link that is paired with the secondary link. In other words, when requesting the setup of a secondary link from the AP MLD, the non-AP MLD must also request the setup of the primary link that is paired with the secondary link. In other words, the non-AP MLD must not transmit a frame (e.g., an Association Request frame) that requests setup only for the secondary link among a pair of primary and secondary links. However, when the non-AP MLD and the AP MLD have already been set up through the primary link, the non-AP MLD may perform an additional setup request for the secondary link to the AP MLD. In this case, the frame that the non-AP MLD transmits to request the addition of the secondary link may be a Link Reconfiguration Request frame.

[0282] That is, only a non-AP MLD that is set up with a primary link can be set up with a secondary link that is paired with the primary link.

[0283] That is, when the AP MLD receives a request for a multi-link setup from a non-AP MLD, if the non-AP MLD only requests the setup for the secondary link and does not request the setup for the primary link that is paired with the secondary link, the AP MLD must not accept the setup for the secondary link. However, the non-AP MLD may request the AP MLD to set up only the primary link among the pair of primary and secondary links. In this case, if the non-AP MLD requests the setup for both the primary link and the third link (requests ML setup), the ML setup connected through the AP MLD, the primary link, and the third link can be performed.

[0284] <Overlapping AP>

[0285] The reason why AP MLD operates two (primary AP and auxiliary AP) or more than two APs (primary AP and first auxiliary AP, second auxiliary AP, etc.) 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 for non-AP MLDs through the AP that has completed channel access. At this time, the primary AP and the auxiliary AP may be APs that use independent radios or APs that are operated using a single radio. However, AP MLD performs channel access through overlapping APs, but performs channel access through only one AP at a specific time. At this time, performing channel access means performing a series of procedures for channel access, such as decreasing the backoff counter according to the EDCA rules.

[0286] There may be an implementation where the primary and secondary APs are configured with independent radios. In this case, the primary AP can transmit PPDUs over the primary 20 MHz subchannel, while the secondary AP can simultaneously receive other PPDUs received over the secondary channel (the primary channel of the secondary BSS) or perform CCA, PD (Packet Detection), etc. A secondary AP with such independent radios can have the capability to function as a regular AP when not designated as a secondary AP by the primary AP.

[0287] Also, an implementation where the Primary AP and the Secondary AP share a single radio may be possible. In this case, when the Primary AP transmits a PPDU through the Primary 20 MHz subchannel, the Secondary AP cannot perform transmission / reception, CCA, PD, etc. for its own primary channel (secondary channel). This is because if the radio commonly used by both APs is used for the operation of the Primary AP, there is no radio that can be used by the Secondary AP. In other words, the Primary AP and the Secondary AP are APs that exist only logically separately, and can be APs that are physically operated using a single device (radio, RF chain, antenna, etc.). The reason why the AP MLD can operate multiple APs (primary AP and secondary APs) using a single radio is because at a specific time, the radio is only utilized for one AP among the multiple APs. That is, AP MLD may not support channel access / PPDU transmission / reception for secondary APs when the channel access procedure is performed by the Primary AP or when PPDU transmission / reception is performed. In addition, when the channel access procedure is performed or PPDU transmission / reception is performed through a specific secondary AP, multiple APs share a single radio and operate in a way that does not require support for the Primary AP and other secondary APs. That is, AP MLD can perform Single-Radio Multi-link operation for the Primary link and the secondary link.

[0288] At this time, the AP MLD operating on multiple links using one radio may lose MediumSync for the remaining links while performing channel access or PPDU transmission / reception on a specific link among the multiple links. At this time, the loss of 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, the AP MLD that lost MediumSync for the remaining links due to an operation performed on a specific link may need to recover MediumSync before performing channel access on the other links. At this time, the AP MLD may need to perform CCA on the link that lost MediumSync for a time corresponding to the MediumSync time in order to recover MediumSync for the link that lost MediumSync. Alternatively, 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 order to recover MediumSync for the link that lost MediumSync. In this case, the non-AP MLD, which has been instructed to transmit the specific frame from the AP MLD, must transmit the specific frame to the AP MLD through the link when the link on which the AP MLD instructed to transmit the specific frame is determined to be idle (idle as a result of PHY CCA and Virtual CCA). If the instructed link remains busy until the instructed time or preset time elapses from the time when the transmission of the specific frame is instructed, the non-AP MLD may not transmit the specific frame to the AP MLD.

[0289] FIG. 16 illustrates an example of a method for configuring an AP MLD including a primary AP and an auxiliary AP having overlapping operating channels and setting an operating channel, according to one embodiment of the present invention.

[0290] Referring to Figure 16(a), three AP MLDs belong to the AP MLD. AP1 functions as the primary AP, AP2 functions as a secondary AP paired with the primary AP, and AP3 is a general AP.

[0291] Referring to Figure 16(b-1), the Primary AP and the Secondary AP operate on exactly the same Operating channel (specifically 320 MHz). However, the Primary 20 MHz subchannel of the Primary AP is located on the lowest 20 MHz subchannel within the Operating channel, and the Primary 20 MHz subchannel (secondary channel) of the Secondary AP is located on the highest 20 MHz subchannel within the Operating channel.

[0292] Referring to Fig. 16(b-2), the operating channel of the secondary AP is included in the operating channel of the primary AP. However, even in this case, the primary 20 MHz subchannel of the primary AP and the primary subchannel (auxiliary channel) of the secondary AP are set to different 20 MHz.

[0293] Referring to Figure 16(b-3), the operating channel of the secondary AP and the operating channel of the primary AP partially overlap each other. However, the primary 20 MHz subchannel of the primary AP and the primary subchannel (auxiliary channel) of the secondary AP are located in the band where the operating channels of the two APs overlap.

[0294] The embodiments of the present invention described below were written assuming a situation where the operating channels of the Primary AP (BSS) and the Secondary AP (BSS) completely overlap each other, as shown in FIG. 16 (b-1). However, it should be understood that operating channel configurations such as those shown in FIG. 16 (b-2) and (b-3) are also Primary / Secondary BSS operating channel configuration methods that can be used to improve accessibility to specific operating channel(s) using the method provided by the present invention.

[0295] <Overlapping AP를 이용한 채널 접속>

[0296] The AP MLD channel access procedure performed using the Primary BSS and the Secondary BSS with an operating channel overlapping the Primary BSS is as follows.

[0297] The primary BSS and secondary BSS operate on the same operating channel (e.g., both BSSs operate on the same 320 MHz channel). At this time, the primary BSS and secondary BSS each designate a different 20 MHz subchannel as the primary 20 MHz subchannel. It is possible for the secondary BSS's operating channel to be a subset of the primary BSS's operating channel.

[0298] The primary channel (auxiliary channel) of the secondary BSS may be located in an 80 MHz subblock other than the 80 MHz subblock in which the primary channel of the primary BSS is located. That is, a 20 MHz subchannel included in the primary 80 MHz subblock of the primary BSS cannot be set as the primary channel (auxiliary channel) of the secondary BSS.

[0299] If multiple auxiliary APs form an AP pair with the Primary AP, the multiple auxiliary APs must each have their primary channel (auxiliary channel) set to 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 their primary channel (auxiliary channel1, auxiliary channel2, auxiliary channel3) set to the 80 MHz subblock corresponding to the lower frequency among the Secondary 80 MHz subblock of the Primary BSS, the Secondary 160 MHz subblock, and the 80 MHz subblock corresponding to the higher frequency among the Secondary 160 MHz subblock.

[0300] 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 the PPDU through the Primary AP. That is, the frames included in the PPDU transmitted through the Primary AP have the MAC address (TA) of the transmitting device set to the MAC address (or BSSID) of the Primary AP. In addition, the Address 3 field of the frame transmitted from the Primary BSS (transmitted by the Primary AP or transmitted by an STA that is a member of the Primary BSS) may be set to the BSSID of the Primary AP depending on the values ​​of the To DS and From DS subfields. In addition, for the frame transmitted by a non-AP STA that is a member of the Primary BSS, the Address 1 field (RA field) is set to the BSSID of the Primary BSS when the To DS and From DS subfields are 1 and 0, respectively. In addition, the frames included in the PPDU transmitted through the Primary AP have the MAC address (RA) of the destination device 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, if the PPDU is transmitted as a HE / EHT / UHR PPDU, the BSS Color indicated through the preamble of the PPDU is set based on the ID of the BSS operated by the Primary AP. At this time, the secondary BSS is maintained in an inactive state during the period in which channel access is performed through the Primary 20 MHz subchannel of the Primary BSS.

[0301] The secondary BSS remains inactive, meaning that no PPDU transmission / reception is performed through the secondary AP.

[0302] During periods when the secondary BSS remains inactive, the secondary AP must not perform channel access on its primary channel (secondary channel). This non-performance of channel access means that the backoff counter managed for performing channel access cannot be decremented during the inactivity period.

[0303] A secondary AP with an independent radio may be able to perform PHY CCA or Packet Detection even during periods of inactivity. In this case, the secondary AP can set the NAV for its primary channel (secondary channel) based on information obtained through received PPDUs (frames).

[0304] When a secondary AP performs a backoff procedure using a secondary channel, it can decrement the backoff counter according to the EDCA rules, and it can only do so when the secondary AP is active. In other words, even if the backoff counter can be decremented according to the EDCA rules, the backoff counter of the secondary AP (more precisely, the backoff counter for each of the four Access Categories of the secondary AP) will not be decremented when the secondary AP is inactive.

[0305] When a secondary AP is inactive, it may not be able to perform PHY CCA and PD. This may be because there is no RF (Radio Frequency Front End) available to the secondary AP when it is inactive. This situation may occur when the secondary AP is logically different from the primary AP, but they physically share a single radio. In this case, the secondary AP may need to set the NAV for the time period corresponding to the MediumSync time when initiating a channel connection. In other words, even if no PPDU (frame) is received after initiating a channel connection, the channel connection must be performed by considering the medium as BUSY (busy as a result of Virtual CCA) during the MediumSync time.

[0306] When a PPDU (frame) of another BSS is received through the Primary 20 MHz subchannel of the Primary BSS, the AP MLD switches the Primary AP (BSS) to an inactive state and switches the secondary AP to an active state during the TXOP period of the other BSS confirmed through the received PPDU. However, in a situation where the PPDU of the other BSS is received, if the state of the primary channel (secondary channel) of a specific secondary AP confirmed (determined) through PHY CCA is BUSY, the specific secondary AP may be maintained in an inactive state. If there is no IDLE secondary channel (primary channel of the secondary APs paired with the Primary AP) confirmed through PHY CCA, the Primary AP may not be switched to an inactive state and may be maintained in an active state. In this case, the operation of the Primary AP switched to an inactive state may be the same / similar to the operation performed when the aforementioned secondary AP is in an inactive state.

[0307] The time period during which the Primary BSS remains inactive may be until the TXOP of the other BSS ends. The time period during which the Primary BSS remains inactive may be until the end time of the PPDU of the other BSS.

[0308] The time period during which the Primary BSS remains inactive may be until a PPDU from another BSS is received through the Secondary BSS.

[0309] The time period during which the Primary BSS remains inactive may be until after the PPDU transmitted through the channel access performed through the primary channel (auxiliary channel) of the auxiliary BSS occupies the primary channel of the Primary AP.

[0310] The time period during which the Primary BSS remains inactive may be limited to before the next TBTT (Target Beacon Transmission Time) of the Primary BSS. That is, when the next TBTT of the Primary BSS arrives, the Primary BSS is in an active state and the secondary BSSs are in an inactive state.

[0311] The time period during which the Primary BSS remains inactive may be limited to before the start time of the R-TWT (Restricted Target Wake Time) SP (Service period) operated by the Primary BSS. That is, when the start time of the R-TWT SP of the Primary BSS arrives, the Primary BSS is in an active state and the secondary BSSs are in an inactive state.

[0312] While the secondary AP (BSS) remains active, the AP MLD performs channel access through the primary channel (secondary channel) of the secondary BSS. When the channel access procedure performed through the secondary channel is completed, the AP MLD transmits a PPDU through the secondary AP. That is, the MAC address (TA) of the transmitting device in the frames included in the PPDU transmitted through the secondary AP is set to the MAC address of the secondary AP. In addition, the Address 3 field of the frame transmitted from the secondary BSS (transmitted by the secondary AP or transmitted by an STA that is a member of the secondary BSS) may be set to the BSSID of the secondary AP depending on the values ​​of the To DS and From DS subfields. In addition, in the frame transmitted by a non-AP STA that is a member of the secondary BSS, the Address 1 field (RA field) is set to the BSSID of the secondary BSS when the To DS and From DS subfields are 1 and 0, respectively. In addition, the frames included in the PPDU transmitted through the secondary AP have the MAC address (RA) of the destination device set to the MAC address of the non-AP STA operating on the secondary link among the non-AP STAs of the non-AP MLD. At this time, if the PPDU is transmitted as a HE / EHT / UHR PPDU, the BSS Color indicated through the preamble of the PPDU is set based on the color of the BSS operated by the secondary AP. At this time, the color of the BSS operated by the secondary AP may be the same as the BSS color of the Primary AP. At this time, the Primary AP (BSS) is maintained in an inactive state during the section in which channel access is performed through the primary channel (secondary channel) of the secondary AP (BSS).

[0313] The Primary BSS remains inactive, meaning that no PPDU transmission / reception is performed through the Primary AP.

[0314] During periods when the Primary BSS remains inactive, the Primary AP must not perform channel access on its primary channel. This non-performance of channel access means that the backoff counter managed for channel access cannot be decremented during the inactivity period.

[0315] A Primary AP with an independent radio may be able to perform PHY CCA or Packet Detection even during periods of inactivity. In this case, the Primary AP can set the NAV for its primary channel based on information obtained through received PPDUs (frames).

[0316] When the Primary AP performs a backoff procedure using the primary channel, it can decrease the backoff counter according to the EDCA rules, and it can only decrease the backoff counter when the Primary AP is active. In other words, even if the backoff counter can be decreased according to the EDCA rules, the backoff counter of the Primary AP (more precisely, the backoff counter for each of the four Access Categories of the Primary AP) will not be decreased when the Primary AP is inactive.

[0317] When the Primary AP is inactive, it may not be able to perform PHY CCA and PD. This may be because there is no RF (Radio Frequency Front End) available to the Primary AP when the Primary AP is inactive. This situation may occur when the Primary AP is logically different from the Secondary AP, but they physically share a single radio. In this case, the Primary AP may need to set the NAV for the time period corresponding to the MediumSync time when initiating a channel connection. In other words, even if no PPDU (frame) is received after initiating a channel connection, the channel connection must be performed by considering the medium as BUSY (busy as a result of Virtual CCA) during the time period corresponding to the MediumSync time.

[0318] The TXOP acquired by the secondary AP may be terminated earlier than the TBTT of the primary BSS. This is a restriction to ensure that the primary AP can transmit the beacon frame according to the TBTT of the primary BSS. Therefore, the secondary AP must manage its TXOP so that its TXOP is terminated earlier than the next TBTT of the primary BSS. At this time, the TXOP of the secondary AP may be terminated at least T earlier than the TBTT of the primary BSS. At this time, T is a time interval including the time (delay) required when the primary AP (BSS) in an inactive state transitions to an active state. At this time, T may be a time interval including the time required for the primary AP to recover MediumSync after transitioning to an active state (e.g., MediumSync time).

[0319] The TXOP acquired by the secondary AP may be terminated earlier than the start time of the R-TWT SP of the primary BSS. This is a restriction to ensure that the primary AP can perform channel access according to the R-TWT SP of the primary BSS. Therefore, the secondary AP must manage its TXOP so that its TXOP is terminated earlier than the start time of the R-TWT SP operated in the primary BSS. At this time, the TXOP of the secondary AP may be terminated at least T earlier than the start time of the R-TWT SP of the primary BSS. At this time, T is a time interval including the time (delay) required when the primary AP (BSS) in an inactive state transitions to an active state. At this time, T may be a time interval including the time required to recover MediumSync after the primary AP transitions to an active state (e.g., MediumSync time).

[0320] The operation of performing channel access by the Primary AP and the Secondary AP according to the above-described methods 1. to 4. is a normative channel access operation in which each AP performs channel access through its own primary channel and does not change the channel through which the channel access is performed (primary operating channel).

[0321] However, according to one embodiment of the present invention, AP MLD can secure multiple access paths for a single operating channel by setting the operating channels of multiple APs to overlap (overlapping and identical) and differentiating the primary operating channels of each AP. Accordingly, AP MLD can have a lower primary operating channel dependency than conventional Wi-Fi when accessing a specific operating channel that operates multiple APs.

[0322] At this time, the APs belonging to a link pair (AP pair) consisting of a Primary AP and Secondary AP(s) have the characteristic that at a certain point in time, only one AP remains active, and the remaining APs remain inactive.

[0323] Here, TBTT refers to the time the AP is scheduled to transmit a Beacon frame. The AP periodically transmits Beacon frames through the primary channel of its BSS, and the Beacon frame transmission cycle is the Beacon Interval. Therefore, each TBTT has a Beacon Interval interval.

[0324] At this time, R-TWT SP is a type of Broadcast TWT, and is a service section for low latency traffic introduced in the Wi-Fi 7 standard. During the R-TWT SP, low latency traffic is processed with priority. At this time, the ID of the traffic considered as low latency traffic for each R-TWT SP is indicated by the AP. That is, when R-TWT SP is operated in a specific BSS, the traffic corresponding to the TID (Traffic ID) indicated by the AP during the R-TWT SP section is serviced with priority within the BSS.

[0325] FIG. 17 illustrates an example of a procedure for an AP MLD to obtain a TXOP using a primary BSS and a secondary BSS, according to one embodiment of the present invention.

[0326] Referring to Figure 17, the AP MLD performs channel access through the Primary 20 MHz subchannel (P20) of the Primary BSS. That is, the Primary BSS is active and the Secondary BSS is inactive.

[0327] The AP MLD, which acquired TXOP1 through the Primary BSS, transmits and receives with the non-AP MLD through the Primary link. After TXOP1 ends, the AP MLD confirms that the P20 channel of the Primary AP is occupied by the OBSS, and switches the Primary AP to the inactive state and the Secondary AP to the active state.

[0328] The AP MLD establishes a channel connection via the secondary AP's primary channel (A20) and acquires TXOP2. During TXOP2, the AP MLD transmits and receives with the non-AP MLD via the secondary link. At this time, TXOP2 ends earlier than the TXOP of the OBSS confirmed by the primary AP.

[0329] When the TXOP2 acquired through the secondary AP is terminated, AP MLD switches the Primary AP to the active state and switches the secondary AP to the inactive state to perform channel access through the Primary AP.

[0330] Afterwards, the AP MLD performs channel access through the Primary AP's P20 and acquires TXOP3 when the channel access is completed. During TXOP3, the AP MLD transmits and receives with the non-AP MLD through the Primary link, which is an active link.

[0331] <Overlapping AP들과 association한 non-AP MLD 동작>

[0332]

[0333] According to one embodiment of the present invention described above, the AP MLD can set the operating channels of a plurality of APs to overlap operating channels, and operate one AP among the plurality of APs as a Primary AP and the remaining APs as Secondary APs. In this way, among the plurality of APs operating on the overlapped operating channels, when a specific AP is active, other APs remain inactive and cannot transmit / receive PPDUs. In addition, an AP in an inactive state may be an AP that cannot transmit / receive PPDUs as well as CCA (Virtual CCA and / or Physical CCA).

[0334] Among the links on which the non-AP MLD performed ML setup, if there is an inactive link (a link of an inactive AP), the non-AP MLD must not transmit a UL PPDU through the inactive link. This is because, even if the non-AP MLD transmits a UL PPDU through the inactive link, the AP, which is the entity that should receive the UL PPDU, does not support reception of the PPDU. In other words, the UL PPDU transmission by the non-AP MLD performed on the inactive link is a transmission that is obviously destined to fail and can be understood as an unnecessary operation.

[0335] Therefore, among the links that have performed AP MLD and ML setup, if there is a primary link and a secondary link, the non-AP MLD may need to determine whether to perform transmission and / or channel access in a different manner from the link on which a regular AP is operated when performing channel access through the primary link or the secondary link.

[0336] For example, a non-AP MLD must not transmit UL PPDUs via EDCA on a secondary link of an AP MLD. The frames that the non-AP MLD can transmit on the secondary link may be limited to response frames for frames received from the secondary AP. In this case, the types of response frames transmitted by the non-AP MLD on the secondary 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 frames included in a TB PPDU transmitted after receiving a trigger frame.

[0337] The reason why the non-AP MLD is restricted from transmitting via EDCA on the secondary link may be because it is difficult for the non-AP MLD to accurately determine whether the secondary AP is active or inactive. Therefore, instead of attempting to transmit a UL PPDU, which is likely to fail, the non-AP MLD can be restricted to transmitting a UL PPDU only when a frame requesting a response frame from the secondary AP is received.

[0338] However, there may be an exception that allows a non-AP MLD to transmit a UL PPDU after performing EDCA channel access through a secondary link. As an example of the exception, a non-AP MLD that obtains information from an AP MLD that allows it to determine whether a specific secondary link is active may perform channel access (channel access using an EDCA mechanism, i.e., channel access performed independently rather than trigger-based channel access) through a non-AP STA operating on the specific secondary link and then attempt to transmit a UL PPDU. The information that allows it to determine whether the specific secondary link is active may be information indicated through a frame transmitted through another AP belonging to the AP MLD. In this case, the information indicated through the other AP belonging to the AP MLD may be information indicating which AP (which link) among the Primary AP and the secondary APs is active. A non-AP MLD that performs channel access via a secondary link (channel access using the EDCA mechanism, channel access performed independently rather than trigger-based channel access) may need to transmit an RTS frame as the first frame transmitted on the secondary link. In other words, the non-AP MLD may need to transmit an RTS frame as the first frame transmitted on 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 on the secondary link.

[0339] Similar to AP MLD, non-AP MLD can use independent radios for the non-AP STA (Primary non-AP STA) operated in the Primary and the non-AP STA (Secondary non-AP STA) operated in the Secondary, or can operate the non-AP STAs of both links using one radio.

[0340] That is, there may be an implementation in which the Primary non-AP STA and the Secondary non-AT STA are configured using independent radios. In this case, the Primary non-AP STA can transmit / receive PPDUs through the Primary 20 MHz subchannel, while the Secondary non-AP STA can simultaneously receive other PPDUs received through the Secondary channel (the Primary channel of the Secondary BSS) or perform CCA, PD (Packet detection), etc. In this way, the Secondary non-AP STA with independent radios may have the capability to function as a general non-AP STA when associated with an AP that is not a Secondary AP (e.g., a Regular AP that is not a Primary / Secondary AP).

[0341] In addition, an implementation in which a primary non-AP STA and a secondary non-AP STA share a single radio may be possible. In this case, when the primary non-AP STA transmits / receives a PPDU through the primary 20 MHz subchannel, the secondary non-AP STA cannot perform transmission / reception, CCA, PD, etc. for its own primary channel (secondary 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 secondary non-AP STA. In other words, the primary non-AP STA and the secondary non-AP STA are non-AP STAs that exist only logically separately, and may be non-AP STAs that are physically operated using a single device (radio, RF chain, antenna, etc.). The reason why the non-AP MLD can operate multiple non-AP STAs (primary non-AP STA and auxiliary non-AP STAs) using one radio is because, at a specific point in time, the radio is utilized for only one non-AP STA among the multiple non-AP STAs. That is, the non-AP MLD may not support channel access / PPDU transmission / reception, etc. for auxiliary non-AP STAs when the channel access procedure is performed by the primary non-AP STA or PPDU transmission / reception is performed. In addition, when PPDU transmission / reception is performed through a specific auxiliary non-AP STA, multiple non-AP STAs share one radio and operate in a way that support for the primary non-AP STA and other auxiliary non-AP STAs is not required. That is, the non-AP MLD can perform single-radio multi-link operation for the primary link and the auxiliary link.

[0342] Meanwhile, a non-AP MLD may be subject to a restriction that it can only be setup with one auxiliary link among the pair 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 may have an ML setup state including the first Primary link and the second auxiliary link, but may not have an ML setup state including both the first auxiliary link and the second auxiliary link. In other words, when there are multiple auxiliary links corresponding to a specific Primary link, a non-AP MLD may only be setup with one auxiliary link among the multiple auxiliary links.

[0343] A non-AP STA operating on a secondary link may be required to terminate its TXOP before the next TBTT (the TBTT of the primary BSS) on the primary link when it has acquired a TXOP via EDCA. This is similar to the behavior of a secondary AP terminating its TXOP before the TBTT of the primary BSS, so a detailed description is omitted.

[0344] <Auxiliary AP Discovery>

[0345] In this way, since the auxiliary link (auxiliary AP, auxiliary BSS) is a link with different characteristics from the general AP and primary link, the AP MLD must indicate which of its affiliated APs is the AP operating on the auxiliary link through the management frames it transmits. In addition, the non-AP MLD that wants to perform ML setup with the AP MLD must, after receiving the management frame transmitted by the AP MLD, determine whether each AP operated by the AP MLD is a general AP, a primary AP, or a secondary AP based on the information contained in the management frame. For example, a non-AP MLD that recognizes that a specific AP of the specific AP MLD is a secondary AP by receiving a Beacon frame transmitted by a specific AP MLD must not perform multi-link setup through the specific AP (auxiliary AP). In other words, the non-AP MLD must not transmit an (ML) Probe Request frame and / or an (ML) Association Request frame to the secondary AP.

[0346] One way for the AP MLD to indicate what type of AP each AP is through the management frames it transmits could be by using the RNR element (Reduced Neighbor Report).

[0347] For example, the AP MLD can indicate that the AP corresponding to the Neighbor AP Information field configured / set in a different manner from the Neighbor AP Information fields corresponding to other APs (third AP (normal AP) and primary AP) among the Neighbor AP Information fields included in the RNR element it transmits is the secondary AP. The specific method by which the AP MLD indicates the secondary AP using the RNR element is described in more detail through an embodiment of FIG. xx.

[0348] FIG. 18 illustrates an example of a format of an RNR element transmitted by an AP MLD to indicate an auxiliary AP, according to one embodiment of the present invention.

[0349] Figure 18 (a) illustrates the Reduced Neighbor Report element format. The Reduced Neighbor Report element may include multiple Neighbor AP Information Fields, and the length of the element is indicated through the Length field.

[0350] The Neighbor AP Information Fields include a Neighbor AP Information field corresponding to each AP belonging to the AP MLD transmitting the corresponding element. At this time, the Neighbor AP Information field for the AP transmitting the RNR element is not included.

[0351] Figure 18 (b) illustrates a method for setting the Neighbor AP Information field corresponding to a secondary AP belonging to the AP MLD. The Neighbor AP Information Field is the same regardless of the characteristics of the corresponding AP, but the setting of the TBTT Information Header and the size of the TBTT Information Set field may differ between the normal AP and the secondary AP. More specifically, as illustrated in Figure 18 (b), in the Neighbor AP Information field corresponding to the secondary 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 the normal AP being indicated as 0. In addition, in the Neighbor AP Information field corresponding to the secondary 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 as having a size of 3 octets. At this time, the TBTT Information Set field includes the MLD Parameters subfield.

[0352] Figure 18 (c) illustrates the MLD Parameters subfield format corresponding to the secondary AP. The MLD Parameters subfield corresponding to the secondary AP may be set to a link ID greater than the link ID of the normal AP. That is, if there are multiple APs (primary AP and normal APs) and one secondary AP in the AP MLD, it is recommended that the link ID of the secondary AP be set to be greater than the link IDs of the other APs.

[0353] The MLD Parameters subfield corresponding to the secondary AP includes a 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 secondary AP. The Secondary Link Indication subfield is a subfield indicating whether the AP corresponding to the corresponding MLD Parameters subfield is a secondary AP, and is indicated as 1 when included in the MLD Parameters subfield corresponding to the secondary AP. The Separated Radio subfield is a subfield indicating whether the secondary AP corresponding to the corresponding MLD Parameters subfield is configured to have a radio independent of the primary AP. In other words, a secondary AP with the Separated Radio subfield set to a specific value (e.g., 1) can avoid losing medium sync for the primary channel (secondary channel) of the secondary BSS even when transmitting / receiving through the primary AP.

[0354] At this time, when non-AP MLDs receive the RNR element transmitted by the AP MLD, they can recognize that the Neighbor AP Information field corresponds to a secondary AP by checking the Neighbor AP Information field in which the TBTT Information field Type included in the RNR element is not 0. Alternatively, non-AP MLDs can recognize whether the AP corresponding to the MLD Parameters subfield is a secondary AP based on a specific bit included in the MLD Parameters subfield (secondary link indication in FIG. 18 (c)).

[0355] As another example, the AP MLD can indicate that the AP corresponding to the Per-STA Profile subelement configured / configured in a different manner is a secondary AP by configuring / configuring the Per-STA Profile subelement corresponding to the secondary AP among the Per-STA Profile subelements included in the Multi-link element that it transmits in a different manner from the Per-STA Profile subelements corresponding to other APs (third AP (normal AP) and primary AP). The Per-STA Profile subelement configured / configured in a different manner may be such that a subfield (bit) that is indicated by a specific value (e.g., 0 or 1) in the Per-STA Profile subelement corresponding to the normal AP is set to a different value (e.g., 1 or 0) for the secondary AP, thereby distinguishing the secondary AP from the normal AP.

[0356] A non-AP MLD that recognizes that a secondary AP is in operation must not transmit a Probe Request frame to the AP MLD via the secondary link. In this case, the non-AP MLD may recognize that the secondary link is in operation based on information indicated in the Management frame transmitted by the AP MLD.

[0357] Meanwhile, the AP MLD can change the AP that functions as the primary AP among overlapping APs (primary AP and secondary APs). For example, an AP that initially functions as the primary AP can change to a secondary AP, and vice versa. There are various reasons why an AP that functions as the primary AP among overlapping APs might change, and one reason could be that the AP MLD wants to change the channel on which the beacon frame is transmitted.

[0358] When the AP MLD wants to change the AP (link, BSS) that will function as the Primary AP (link, BSS) among the Overlapping APs (links, BSS), it must instruct the non-AP MLDs to do so. At this time, the AP MLD can, through the Management frame (e.g., Beacon frame) that it transmits, indicate information about the new Primary AP (an AP that is a Secondary AP at the time of transmitting the Management frame) and / or information related to the point in time when the Primary AP is changed. At this time, the information that the AP MLD indicates through the Management frame can include the ID of the link on which the Secondary AP to be changed to the Primary AP is operated (i.e., the link ID of the Secondary link). At this time, the AP MLD can indicate the number of TBTTs remaining until the point in time when the Primary AP is changed in order to indicate the point in time when the Primary AP is changed. That is, if there are 5 TBTTs of the current Primary AP until the point at which the AP MLD wants to change the Primary AP, the AP MLD can set the value of the field related to the point at which the Primary AP is changed to a value (e.g., 5 or 4(5-1)) based on the number of remaining TBTTs. That is, if there is no TBTT remaining until the point at which the AP MLD wants to change the Primary AP, the AP MLD 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.

[0359] An AP MLD that wishes to change its 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 Primary AP is changed). At this time, the BSS Transition Management Request frame may be a frame that instructs non-AP STAs and non-AP MLDs that 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 a link designated as the Primary link is changed (and / or is scheduled to be changed) among a pair of Primary links (APs) and Secondary links (APs) having overlapping operating channels. A non-AP MLD that receives a BSS Transition Management frame Request with the Primary link Channel field set to 1 may interpret the BSS Transition Management Request frame not as indicating that the Primary BSS is being terminated, but as indicating that the Primary link (AP) and the Secondary link (AP) will be changed.At this time, the AP MLD must update the Neighbor AP Information field for the secondary link of the RNR element transmitted after the primary link and the secondary link are changed, and the Neighbor AP Information field for the primary link, taking into account the changed primary link.

[0360] Alternatively, the AP MLD may perform a Channel Switch to change the primary channel of the BSS operated by an AP functioning as a Primary AP (link) among multiple APs (links) having overlapping operating channels. At this time, the AP MLD may 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. At this time, the new primary channel is one of the subchannels included in the existing operating channel (BW). In this way, when the Channel Switch Announcement element is used to change the subchannel used by the Primary BSS as the primary channel without changing the operating channel, the new primary channel may be designated as the subchannel used by the secondary BSS, which is a pair of the Primary BSS, as the primary channel (auxiliary channel). If the primary channel of the new Primary BSS (indicated by the New Channel Number field) is a subchannel that the existing Secondary BSS used as a primary channel (secondary channel), the AP MLD must also transmit an (Extended) Channel Switch Announcement element that changes the primary channel (secondary channel) of the Secondary BSS. That is, the AP MLD that wants to change the primary channel of the Primary BSS to the primary channel (secondary channel) of the Secondary BSS may need to change the primary channel (secondary channel) of the Secondary BSS together to manage that the Primary BSS and the Secondary BSS do not use the same subchannel as a primary channel.A non-AP MLD that receives both an (Extended) Channel Switch Announcement element indicating a change in the primary channel of the Primary BSS from the AP MLD and an (Extended) Channel Switch Announcement element indicating a change in the primary channel (auxiliary channel) of the secondary BSS can recognize that the primary channels of the two BSSs will be switched. At this time, the two Channel Switch Announcement elements received together indicate the same value through the Channel Switch Count field. At this time, the Channel Switch Mode subfield of the Channel Switch Announcement element that the AP MLD transmits to change only the primary channel without changing the Operating channel of the Primary BSS can be set to a different value (for example, 2) than the value indicated when a general Channel Switch is performed (when the Operating channel is changed).

[0361] <Channel change of AP (link, BSS) pair with overlapping operating channels>

[0362] When changing the operating channel of multiple APs (primary AP and paired secondary 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 is commonly applied to multiple APs (primary AP and paired secondary APs) having overlapping operating channels. For example, if the operating channel of the primary BSS is changed from the first 320 MHz channel to the second 320 MHz channel through the Channel Switch Announcement element, the operating channel of the secondary BSS paired with the primary BSS is also changed from the first 320 MHz channel to the second 320 MHz channel. That is, when an operating channel change is instructed for a specific AP (e.g., primary AP) in overlapping operating channels (overlapping AP (link, BSS) pair), the operating channel change for another AP (e.g., secondary AP) can be implicitly instructed. Accordingly, when a non-AP MLD is instructed by the AP MLD to change the operating channel of the primary AP, the non-AP MLD can recognize that the operating channel of the secondary AP(s) paired with the primary AP is also changed to the same as that 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 AP MLD) transmitted after the completion of the Channel Switch of the Primary BSS.

[0363] FIG. 19 illustrates a method in which a channel switch of an auxiliary BSS is instructed / performed together when a channel switch for a primary BSS is performed, according to one embodiment of the present invention.

[0364] Referring to Figure 19, the Primary BSS and the Secondary BSS operate on an Operating channel whose initial Center Frequency is 'X'.

[0365] AP MLD includes the (Extended) Channel Switch Announcement element in the Beacon frame transmitted by the Primary AP to change the overlapping operating channel.

[0366] (Extended) Channel Switch Announcement element contains information about when the Primary BSS's Channel Switch starts and the new Operating channel.

[0367] 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 Channel Switch after transmitting Beacon#2. At this time, although the Channel Switch Announcement element for the secondary 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 secondary AP (BSS). This is because the secondary AP is an AP that is paired with the Primary AP that will perform the Channel Switch.

[0368] Therefore, when the Channel Switch of the Primary BSS starts, the Channel Switch of the Secondary BSS also starts, and the changed center frequency of the Primary BSS is the same as the changed center frequency of the Secondary BSS. In other words, the operating channels of the two BSSs remain overlapping even after the Channel Switch is completed.

[0369] The Primary AP transmits a Beacon#3 frame on the new operating channel, and Beacon#3 includes an RNR element indicating information about the new primary channel (auxiliary channel, A20 in Figure 19) of the secondary AP. Therefore, the non-AP MLD can check information about the new primary channel (auxiliary channel) of the secondary BSS by receiving the Beacon frame transmitted by the AP MLD after completing the Channel Switch of the Primary BSS.

[0370] <Features and Limitations of Auxiliary AP / Link / BSS>

[0371] As described above, AP MLD can operate multiple APs with overlapping operating channels to increase accessibility to a specific operating channel. One AP among the multiple APs functions as a primary AP, and the remaining AP(s) function as secondary APs. The primary AP transmits a beacon frame at every beacon interval and supports (ML) setup procedures with non-AP STAs and non-AP MLDs, supporting functions more similar to those of a general AP. On the other hand, a secondary AP is an AP with many limitations, such as not transmitting a beacon frame and not being able to be setup with a non-AP MLD that is not associated with the paired primary AP. This is because the reason AP MLD operates multiple APs with overlapping operating channels is to increase accessibility to the overlapping operating channels, and not to operate the secondary APs as general APs.

[0372] In this way, since the secondary 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 indicated through the primary AP and the parameters used by the primary AP in operating the secondary AP.

[0373] <TSF timer of auxiliary link>

[0374] As mentioned above, the secondary AP does not transmit the Beacon frame. The Beacon frame of Wi-F is a frame transmitted for various purposes, such as indicating various information that non-AP STAs associated with the AP transmitting the Beacon frame should recognize, and allowing non-AP STAs that are not associated to recognize the existence of the AP (discovery) as well as some information about other APs (Neighbor APs) adjacent to the AP. In addition, in 11be, by transmitting a multi-link element through the Beacon frame, it is expanded to include additional various information that non-AP MLDs should obtain, such as indicating information that the AP that transmitted the Beacon frame belongs to the AP MLD and information about other APs (links) belonging to the AP MLD.

[0375] The Timestamp field, one of the fields included in the Beacon frame, is a field that indicates a value related to the AP's timing synchronization function (TSF) timer. This field supports timing synchronization between the AP and non-AP STAs by adjusting their own TSF timers according to the AP's TSF timer value. All timing-based operations of the BSS are synchronized based on the AP's TSF timer, meaning that 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 own BSS, so non-AP STAs included in the secondary AP's BSS (secondary BSS) cannot 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.

[0376] According to one embodiment of the present invention, the secondary APs paired with the primary AP may have a common TSF timer. Alternatively, the TSF timers of the primary AP and the secondary 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 the Beacon frame transmitted by the primary AP. Therefore, the non-AP MLDs can maintain time synchronization with the secondary APs by receiving the Beacon frame transmitted by the primary AP.

[0377] <Mapping TID (Traffic ID) of auxiliary link>

[0378] As mentioned above, MLD is defined in Wi-Fi 7, and TID-to-link mapping negotiation can be performed between MLDs that have performed ML setup. As an example of a simple TID-to-link mapping, a non-AP MLD setup with an AP MLD over two links can negotiate 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 MPDUs / MSDUs with TIDs 0 to 3 over the first link, and MPDUs / MSDUs with TIDs 4 to 7 over 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 where TID-to-link mapping is not 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. At this time, the Default TID-to-link mapping mode is applied to both DL and UL directions.

[0379] In general, the TID-to-link mapping agreement between an AP MLD and a non-AP MLD can be freely established through the agreement between the two MLDs, except for the constraint that every TID must be mapped to at least one link. In other words, there is no constraint that only certain TIDs must be mapped to a specific link, or that certain TIDs must not be mapped to a specific link. However, this is valid only when all setup links are assumed to be links on which general APs operate, and if there are auxiliary links among the setup links, additional constraints may be applied.

[0380] According to one embodiment of the present invention, only TIDs mapped to a paired primary link can be mapped to a secondary link. Furthermore, TIDs mapped to a paired primary link can be identically mapped to a secondary link. That is, a TID that is not mapped to a paired primary link cannot be mapped to a secondary link. That is, the TID-to-link mapping state of a secondary link is identical to the TID-to-link mapping state of a paired primary link. The reason why a separate TID-to-link mapping constraint exists for a secondary link may be because the secondary link is a link that cannot be kept active simultaneously with the primary link.

[0381] To be more specific, the secondary link can be active only when the primary link is inactive, so 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 period when the primary link is inactive. This means that the TIDs that each MLD can transmit are limited depending on whether the active link is the primary link or the secondary link, which is a very inappropriate restriction for maintaining traffic flow. Therefore, by restricting the secondary link to always have the same TID mapped to the primary link, all TIDs can be transmitted through at least one setup link regardless of whether the primary link or the secondary link is active.

[0382] Therefore, when performing TID-to-link mapping, AP MLD and non-AP MLD must perform a TID-to-link mapping request that always maps the TID mapped to the primary link to the secondary link. At this time, the mapping constraints apply to both directions (DL / UL).

[0383] Alternatively, when the AP MLD and the non-AP MLD perform TID-to-link mapping, it may be considered that the TID mapping indicated for the primary link is applied equally to the secondary link, without separately indicating TID mapping information for the secondary link. That is, the AP MLD and the non-AP MLD may not perform a separate TID-to-link mapping agreement for the secondary link. In this case, the TID mapping status for the non-agreed secondary link may be applied identically to the TID mapping status agreed upon for the primary link paired with the secondary link. That is, the TID mapping for the secondary link is not directly indicated / negotiated, and the TID mapping for the primary link may be applied identically. This can be interpreted that the TID-to-link mapping agreement for the secondary link is implicitly performed / completed by the TID-to-link mapping agreement performed for the paired primary link.

[0384] <Traffic Indication of Auxiliary AP>

[0385] As described above, TID-to-link mapping negotiation can be performed between two MLDs associated through multiple links. If TID-to-link mapping negotiation has been performed between an AP MLD and a non-AP MLD, the AP MLD may need to consider the TID-to-link mapping negotiated with the non-AP MLD when indicating a traffic indication. Similarly, the non-AP MLD may also need to perform an MSDU reception operation considering the TID-to-link mapping when receiving a traffic indication from the AP MLD. The reason why the AP MLD and non-AP MLD must consider the TID-to-link mapping when indicating a traffic indication and receiving MSDUs is due to traffic transmission restrictions related to TID-to-link mapping. As described above for TID-to-link mapping, an MLD that has performed TID-to-link mapping negotiation with a peer MLD must transmit traffic to the peer MLD 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 non-default mode TID-to-link mapping 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 being queued.In other words, the non-AP MLD must transmit the PS-Poll frame only through the link through which the MSDU it is to receive can be transmitted. If the non-AP MLD transmits the PS-Poll frame on a link where the TID of the MSDU queued on the AP MLD side is not mapped to the DL direction, the non-AP MLD cannot receive the MSDU from the AP MLD. In this case, the non-AP MLD switches the link through which MSDU reception is impossible to Awake, which not only reduces PS efficiency but also causes a delay in MSDU transmission, making it difficult to effectively perform the operation / support of the PS mode.

[0386] Therefore, in order to avoid the problem of Queuing MSDU (BU) transmission impossibility due to TID-to-link mapping, the AP MLD must instruct each non-AP MLD through the TIM element whether there is a Queuing MSDU to be transmitted, and additionally instruct information regarding which link the MSDU should be transmitted on. At this time, for non-AP MLDs that have performed 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 the presence or absence of a Queuing MSDU may be performed. This may be because non-AP MLDs with default TID-to-link mapping states or links in which all TIDs are mapped in the DL direction can receive Queuing MSDUs without the problem of transmission impossibility due to TIDs by transmitting PS-Poll frames through the links to which all TIDs are mapped in order to receive Queuing MSDUs.

[0387] The AP MLD may transmit an element indicating a TID or link ID together with a TIM element to a non-AP MLD to indicate on which link the MSDU (BU, Queuing frame, etc.) should be transmitted. In this case, the element transmitted to indicate the TID or link ID to the non-AP MLD may be named a Multi-link TIM element (or Multi-link Traffic Indication element). The Multi-link TIM element indicates to each non-AP MLD, indicated by the TIM element as having a Queuing MSDU, information regarding whether or not the MSDU can be received on which link. If separate link-related information is not required for the non-AP MLD (if it is in the default TID-to-link mapping state or if TID-to-link mapping negotiation has been performed with a link to which all TIDs are mapped in the DL direction), separate link-related information may not be indicated in the Multi-link TIM element. Non-AP MLDs that are not instructed with separate link-related information via the multi-link TIM element must transmit PS-Poll frames on links to which all TIDs are mapped in the DL direction to receive BUs (queuing MSDUs). For non-AP MLDs that use the default TID-to-link mapping, it can be understood that there are no separate PS-Poll frame transmission link selection restrictions because all links have all TIDs mapped in the DL direction.

[0388] As described above, for the secondary link, the same TID as that mapped to the primary link is mapped. Therefore, traffic (MSDU / MPDU) of a TID that can be transmitted on the primary link according to the TID-to-link mapping status means that traffic can also be transmitted on the secondary link. In addition, a non-AP MLD that is set up through the secondary link is always set up through the primary link as well, and there is no non-AP STA that is associated only through the secondary link.

[0389] If the AP MLD indicates via the Multi-link Traffic Indication element that an MSDU queued on the AP MLD side can be received via the Primary link, it is self-evident that the 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.

[0390] 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, information about the secondary link may not be indicated. Instead, the 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.

[0391] In other words, each bit of the Per-link Traffic Indication Bitmap contained in the Multi-link Traffic Indication element transmitted by the AP MLD corresponds to the link ID of the general AP and / or the Primary AP, and 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.

[0392] A non-AP MLD that has been instructed by the AP MLD through the TIM (traffic indication map) element, 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 a secondary link paired with the specific primary link.

[0393] <BSS Color Setting of Auxiliary BSS>

[0394] 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 HE PPDU, U-SIG of 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. In addition, 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.

[0395] Therefore, when the Primary AP transmits the BSS Color Channel Announcement element to set the BSS color of the Primary BSS to a new value, the BSS color of the Secondary BSS is changed to the new value.

[0396] However, the Primary BSS and the Secondary BSS must be configured to have different BSSIDs. Setting the BSSIDs of the two BSSs to different values ​​means that the BSSIDs of the Primary BSS and the Secondary BSS are each randomly determined.

[0397] <Parameter update of auxiliary BSS>

[0398] As mentioned above, the secondary AP cannot transmit Beacon frames (and Probe response frames), and therefore cannot announce changes in the parameters of the secondary BSS to the member STAs of the secondary BSS.

[0399] Instead, parameter updates of the secondary BSS can be performed through management frames transmitted by the Primary AP paired with the secondary AP, or other APs belonging to the AP MLD. More specifically, when the parameters of the secondary BSS are updated, the AP MLD can indicate that the parameter update of the secondary BSS is in progress by using the update indication field corresponding to the secondary BSS (e.g., the BSS Parameter Change Count subfield (included in the MLD Parameters subfield corresponding to the secondary AP)) included in the RNR element included in the management frame transmitted by the AP MLD. In this case, the non-AP MLD can recognize that the parameters of the secondary BSS have changed through the received RNR element. Thereafter, the non-AP MLD can receive and update the parameters of the secondary BSS through the Per-STA Profile subelement of the secondary AP included in the Multi-link element transmitted by the AP MLD.

[0400] In addition, some present bits included in the Per-STA Profile subelement corresponding to the secondary AP must always be set to 0. The Beacon Interval Present subfield of the Per-STA Profile subelement corresponding to the secondary AP is set to 0. The TSF Offset Present subfield of the Per-STA Profile subelement corresponding to the secondary AP is set to 0. The DTIM Info Present subfield of the Per-STA Profile subelement corresponding to the secondary AP is set to 0. At this time, the reason why the three subfields are set to 0 is because the secondary AP does not transmit a Beacon frame and uses the TSF with the same value as the Primary AP. That is, since the information indicated when the Present subfields are indicated as 1 is information that is not defined for the secondary AP (BSS, link) or does not need to be indicated, the three Present subfields are always set to 0 for the secondary AP.

[0401] Certain operating parameters of the secondary BSS may depend on the operating parameters of the primary BSS. For example, the operating BW of the secondary BSS may change to be identical to the operating BW of the primary BSS when the operating BW of the primary BSS changes.

[0402] <How to operate the modified auxiliary link>

[0403] As described above, AP MLD and non-AP MLD may have an ML setup state that includes multiple links operating on overlapping operating channels for the purpose of improving accessibility to a specific operating channel.

[0404] Alternatively, instead of setting up multiple links with overlapping operating channels, a method may be utilized to set up multiple links with operating channels (bandwidths) located consecutively.

[0405] More specifically, the AP MLD and the non-AP MLD may seek to enhance channel accessibility for a continuous operating channel by establishing an ML setup connected through multiple links having continuous operating channels within a specific channel bandwidth. For example, the AP MLD and the non-AP MLD may seek to enhance accessibility for a specific 160 MHz channel by performing an ML setup through two links that each use two 80 MHz channels included in the specific 160 MHz channel as an operating channel. For another example, the AP MLD and the non-AP MLD may seek to enhance accessibility for a specific 320 MHz channel by performing an ML setup through two links that each use two 160 MHz channels included in the specific 320 MHz channel as an operating channel. As another example, an AP MLD and a non-AP MLD may wish to enhance accessibility to a particular 320 MHz channel by performing ML setup over four links that each use one of the four 80 MHz channels contained in that particular 320 MHz channel as an Operating channel.

[0406] In this case, when the AP MLD and / or the non-AP MLD performs transmission through the first STA (AP STA and / or non-AP STA) operating on the continuous Operating channel, the AP MLD may 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 on the first 80 MHz included in the specific 160 MHz, the AP MLD may perform a transmission synchronized with the second AP operating on the second 80 MHz included in the specific 160 MHz. In this case, the 80 MHz PPDUs transmitted by the first AP and the second AP, respectively, may be understood as the first segment and the second segment of the 160 MHz PPDU. At this time, the first segment means a PPDU transmitted in the first 80 MHz segment included in the specific 160 MHz, and the second segment means a PPDU transmitted in the second 80 MHz segment included in the specific 160 MHz. At this time, the fact that the AP MLD synchronizes the transmission of the first AP and the transmission of the second AP means that the transmission start time and the PPDU length of the PPDU transmitted through the first AP and the PPDU transmitted through the second AP are managed to be the same. In addition, when the first AP and the second AP transmit synchronized PPDUs, the TXOPs acquired by the first AP and the second AP can 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 synchronized PPDUs 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.

[0407] In addition, as described above, when a non-AP MLD performs transmission through a first STA (AP STA and / or non-AP STA) operating on a continuous Operating channel, it can perform an operation synchronized with the transmission of a second STA operating on the continuous Operating channel. In this case, 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.

[0408] Among multiple links having continuous operating channels, one link is set as the primary link, and the remaining links(s) are set as secondary links. The AP operating on the primary link periodically transmits a beacon frame, while the AP operating on the secondary link does not transmit a beacon frame. At this time, the primary link and secondary links operating on the continuous operating channel may be subject to the same / similar operating method as the primary link and secondary link operating on the overlapping operating channel described above. The same TID is mapped to the primary link and secondary link operating on the continuous operating channel, and the APs and STAs operating on the secondary link commonly use the TSF timer of the APs and STAs operating on the primary link.

[0409] FIG. 20 illustrates a configuration of an AP MLD including a primary AP and a secondary AP having continuous operating channels and a method for setting operating channels, according to one embodiment of the present invention.

[0410] Referring to Figure 20(a), three AP MLDs belong to the AP MLD. AP1 functions as the primary AP, AP2 functions as a secondary AP paired with the primary AP, and AP3 is a general AP.

[0411] Referring to Figure 20(b), the Primary AP and the Secondary AP operate on consecutive Operating channels (two 160 MHz channels located on a specific 320 MHz channel).

[0412] AP MLDs and non-AP MLDs connected through multiple links with continuous operating channels can communicate in the following manner.

[0413] 1. STAs (AP STAs and non-AP STAs) operating on each link (primary link and secondary link(s)) perform a backoff procedure via the primary channel of each link. STAs operating on the secondary link maintain a backoff counter of 0 when the backoff procedure is completed.

[0414] 2-1. When the backoff procedure of an STA (AP STA and non-AP STA) operating on the primary link is completed, the MLD including the STA initiates transmission through the primary link and the secondary link for which the backoff procedure has already been completed (including links completed simultaneously with the primary link). At this time, the MLD performs the transmissions performed on the primary link and the secondary link as synchronized transmissions.

[0415] 2-2. When the backoff procedure of an STA (AP STA and non-AP STA) operating on the primary link is interrupted, the MLD including the 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 when 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 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. At this time, the interruption of the backoff procedure means that the decrease of the backoff counter is stopped, such as when the primary channel is occupied by the OBSS.

[0416] 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 simultaneously by initiating synchronized transmission through the primary link and the secondary links for which the backoff procedure has already been completed.

[0417] If the backoff procedure of the primary link is interrupted, the MLD can initiate transmission through the secondary link, as described in 2-2 above. The MLD that initiates transmission through the secondary link terminates the TXOP acquired through the secondary link before the time at which the backoff procedure on the primary link is expected to resume (e.g., the time at which the NAV of the STA operating on the primary link is expected to become 0).

[0418] FIG. 21 illustrates a channel access method of an MLD that operates STAs on two links having continuous operating channels, according to one embodiment of the present invention.

[0419] Referring to Figure 21, a primary link and a secondary link, each having an 80 MHz operating BW, are operated within a specific 160 MHz channel.

[0420] The procedure for obtaining the first TXOP by MLD is as follows.

[0421] MLD first completes the channel access procedure (backoff procedure) on A20 of the secondary link (the Primary 20 MHz channel of the BSS operating on the secondary link), but does not initiate transmission on the secondary link. Instead, it performs an operation to maintain the backoff counter of the secondary link to 0 in order to perform transmission synchronized with the primary link. When MLD completes the channel access procedure on P20 of the primary link (the Primary 20 MHz channel of the BSS operating on the primary link), it initiates transmission not only through the primary link but also through the secondary link whose backoff counter is already 0. At this time, MLD performs synchronized transmission through the STAs of the primary and secondary links. At this time, the two 80 MHz PPDUs transmitted by MLD through the two links are indicated as having a BW field of 160 MHz, so that external terminals can recognize them as one 160 MHz PPDU.

[0422] The procedure for obtaining the second TXOP by MLD is as follows.

[0423] When MLD completes the channel access procedure (backoff procedure) on A20 of the secondary link (the primary 20 MHz channel of the BSS operating on the secondary link), it initiates transmission on the secondary link, considering that the primary link is occupied by the OBSS. At this time, the TXOP (or PPDU) initiated on the secondary link ends before the expected end of the TXOP of the OBSS occupying the primary link.

[0424] The procedure for obtaining the third TXOP by MLD is as follows.

[0425] When MLD completes the channel access procedure (backoff procedure) on P20 of the primary link, it initiates a TXOP on the primary link. After MLD initiates transmission on the primary link, it loses the CCA capability for the secondary link, and therefore the backoff counter of the secondary link may not decrease below 3. However, an MLD capable of performing CCA on the secondary link may also continuously decrease the backoff counter of the secondary link.

[0426] <MU PPDU transmission / reception method for terminals performing nonprimary (secondary) channel access using a single link>

[0427] As described above, a channel access method using a non-primary channel can be considered as a method for improving the channel accessibility of a Wi-Fi STA, and in the case of MLD, a method for enhancing channel accessibility using the characteristics of MLD (such as the above-described Overlapping BSS) can be utilized. The commonality of the various channel access methods provided in the present invention is that a transmitting device does not perform channel access only through one 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.

[0428] In this way, since the transmitting device can initiate transmission on a channel other than the primary channel, the receiving device must also wait to receive a PPDU on a subchannel 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.

[0429] A PPDU transmitted by an STA (AP STA and non-AP STA) that has performed channel access through a non-primary channel is not transmitted by occupying the primary channel, but a PPDU transmitted by an STA that has performed channel access through the primary channel can be transmitted by occupying the non-primary channel. This is because the state of the primary channel determined by an STA that has performed channel access through a non-primary channel is always BUSY, and an STA that has performed channel access through the primary channel performs channel access through the primary channel regardless of the state of the non-primary channel.

[0430] Accordingly, when the state of the primary channel determined by the transmitting device is IDLE, the transmitting device can transmit a PPDU occupying both the primary channel and the non-primary channel, and the receiving device determined that the primary channel is BUSY can receive the PPDU via the non-primary channel. In other words, the device receiving the PPDU via the non-primary channel can receive both the PPDU transmitted by the transmitting device after performing channel access via the primary channel and the PPDU transmitted by the transmitting device after performing channel access via the non-primary channel, and can have difficulty interpreting which index of its RU (or MRU (Multiple-RU)) is indicated by the RU Allocation subfield of the received PPDU. In other words, the transmitting device and the receiving device can have different judgments regarding the state of the primary channel (IDLE or BUSY), and accordingly, the channel through which the transmitting device performed channel access and the channel through which the receiving device starts receiving the PPDU can be different from each other. The procedure by which a conventional Wi-Fi STA instructs and acquires RU Allocation information is briefly described through an embodiment of FIG. 22. Hereinafter, RU may be interpreted as a general term for not only conventional RUs such as 26, 52, 106, 242, 484, 996, 996 x N (N is a natural number greater than 2)-tone size RUs, but also MRUs (e.g., 52+26, 106+26, 484+242, 996+484-tone size RUs, etc.).

[0431] That is, the transmitting device may determine the primary channel and the non-primary channel to be idle, but the receiving device may determine the primary channel to be busy and the non-primary channel to be idle. In this case, the transmitting device may transmit a PPDU that occupies both the primary channel and the non-primary channel. However, the receiving device cannot receive the PPDU on the primary channel because the primary channel is busy, and can receive the PPDU through the non-primary channel. Since the receiving device received the PPDU through the non-primary channel, it can interpret the fields included in the PPDU (e.g., the RU allocation subfield, etc.) based on the non-primary channel. However, the transmitting device may 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 enable the receiving device to interpret the fields included in the PPDU based on the primary channel.

[0432] To this end, if the transmitting device transmits the PPDU using both the primary channel and the non-primary channel, the receiving device can interpret the fields included in the PPDU based on the primary channel even if the receiving device receives the PPDU on the non-primary channel.

[0433] In another embodiment of the present invention, instruction information indicating that a non-primary channel should interpret fields included in a PPDU based on a primary channel may be included in the PPDU and transmitted.

[0434] FIG. 22 illustrates an embodiment of a method for performing resource unit allocation to each STA using a resource unit allocation subfield and a resource unit allocation subfield indicated through a preamble of a PPDU and a method for indicating a content channel.

[0435] Figure 22 (a) represents a situation in which two 484-tone RUs and one 996-tone RU within the 160 MHz band are allocated to STAs A, B, C, and D. STA A and STA B are allocated RU#1 (484-tone size RU) located in the lowest frequency region, STA C is allocated RU#2 (484-tone size RU), and STA D is allocated RU#3 (996-tone size RU).

[0436] A transmitting device that transmits a PPDU that allocates RUs, as shown in Fig. 22 (a), indicates the RU configuration and information on the STA to which each RU is allocated, through a signaling field (e.g., HE / EHT / UHR SIG field) included in the DL PPDU. At this time, the signaling fields transmitted through each 20 MHz subchannel may include the same or different content channels.

[0437] 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 odd-numbered 20 MHz subchannels (see Fig. 22 (a)), and the RU Allocation subfields included in content channel #2 correspond to even-numbered 20 MHz subchannels (see Fig. 22 (a)).

[0438] Each RU Allocation subfield included in a content channel indicates RU information for each corresponding 20 MHz subchannel. More specifically, the first and second RU Allocation subfields included in content channel#1 indicate RU information corresponding to 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 20 MHz #2 and 20 MHz #4, respectively.

[0439] Referring to Fig. 22 (a), the 20 MHz #1 subchannel corresponds to RU#1, and therefore 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 information of the User to be allocated the corresponding RU, and among the User fields indicated after the RU Allocation subfields, the User field of the designated number is interpreted as having been allocated the RU indicated through the corresponding RU Allocation subfield.

[0440] In the example of Fig. 22 (b), the first RU Allocation subfield included in Content channel#1 indicates 1 User, and therefore RU#1 is allocated 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 allocated to STA C corresponding to the second User field included in Content channel#1.

[0441] Content channels #1 and #2 appear alternately in every 20 MHz band, and the specific indicated positions can be confirmed through (c) of FIG. 22. Therefore, an STA that wishes to check the position of the RU allocated to itself can receive two types of Content channels received through a specific 40 MHz band (e.g., Primary 40 MHz, Secondary 40 MHz, or a specific 40 MHz band included in the Secondary 80 / 160 MHz band), check whether the User field corresponding to itself is included in the Content channel, and then check the information of the RU indicated by the RU Allocation subfield corresponding to its User field, thereby obtaining the RU information allocated to itself. However, Content channels located in different 80 MHz Segments may include different contents 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 contents.

[0442] Figure 23 illustrates an ambiguity problem in the interpretation of an assigned RU by an STA that receives a preamble on a non-primary channel.

[0443] Case 1 and Case 2 of FIG. 23 illustrate the case of a DL MU PPDU transmitted by an AP that performed channel access on a primary 20 MHz channel and a DL MU PPDU transmitted by an AP that performed channel access on a secondary 20 MHz channel, respectively.

[0444] Case 1 occurs when the AP determines that the primary channel (primary 20 MHz subchannel) is IDLE and the STA determines that the primary channel is busy. Case 2 occurs when both the AP and the STA determine that the primary channel is busy.

[0445] In both Case 1 and Case 2, the STA waits for the reception of a PPDU through S20, receives a preamble, and by receiving the Content channel included in the preamble, confirms that the RU allocated to it is a 242-tone size RU located in the lowest frequency band.

[0446] 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 allocated to it is the RU corresponding to Case 1 or the RU corresponding to Case 2.

[0447] The following two methods can be used to resolve the ambiguity in the allocation RU interpretation of such a receiving device.

[0448] 1) First, when the receiving device checks the RU indicated through 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 transmitted it after performing channel access through the primary channel or after performing channel access through the non-primary channel. At this time, the different ways of interpreting the RU Allocation subfield mean that the frequencies that serve as a reference when interpreting the positions of the RUs indicated by the RU Allocation subfield are different. In other words, the subchannels to which a specific order of RU Allocation subfields indicated through the UHR-SIG (or EHT-SIG, HE-SIG) field corresponds may be different depending on whether the device that transmits the PPDU including the corresponding SIG field performed channel access through the primary channel or the non-primary channel.

[0449] 2) Second, the transmitting device can apply a setting to the signaling fields (e.g., Bandwidth, RU Allocation subfield, Puncturing information, etc.) of the PPDU transmitted after performing channel access on a non-primary channel, so as 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 can 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 can 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 performing channel access on the primary channel, regardless of which channel the device transmitting the received PPDU used to perform channel access.

[0450] As described in the first method above, the receiving device must determine whether the received PPDU was transmitted by a transmitting device that completed channel access through a primary channel or by a transmitting device that completed channel access through a non-primary channel, and interpret the RU Allocation subfield in different ways. In this case, the RU Allocation subfield means the RU Allocation subfield included in the Signaling field (e.g., included in the HE-SIG, EHT-SIG, UHR-SIG fields, etc.) located in the Preamble of the MU PPDU and / or the RU Allocation subfield located in the User field included in the trigger frame.

[0451] The method by which a receiving device determines on which channel a transmitting device has performed a channel connection and transmitted a PPDU may utilize direct information or indirect information indicated by the transmitting device.

[0452] 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 a specific field of the first PPDU in a manner different from a specific field of a second PPDU transmitted after performing channel access through the primary channel. At this time, the specific subfield may be a field included in a U-SIG (Universal SIG field). For example, an STA that transmits a PPDU after performing channel access through a primary channel may set a 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 that has received a PPDU may determine, based on the specific field, whether the device that transmitted the PPDU performed channel access through the primary channel and transmitted the PPDU or performed channel access through a non-primary channel and transmitted the PPDU.

[0453] According to another embodiment of the present invention, even if the transmitting device does not indicate whether the channel access was performed through a primary channel or a non-primary channel, it may be possible for the receiving device to independently determine the channel access method of the transmitting device. For example, a receiving device that receives an 80 MHz PPDU occupying a secondary 80 MHz segment from an STA (AP STA and non-AP STA) of a BSS with an operating BW of 160 MHz can recognize that the STA performed the channel access through a non-primary channel located in the secondary 80 MHz segment and then transmitted the 80 MHz PPDU. That is, the receiving device can obtain information on the channel on which the transmitting device performed the channel access based on the BW information of the received PPDU.

[0454] A receiving device of a PPDU interprets the RU Allocation subfield included in the received PPDU in the following manner based on whether the received PPDU was received from a device that performed Channel Access through a primary channel or from a device that performed Channel Access through a non-primary channel.

[0455] 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 manner as the RU Allocation subfield received on the primary channel.

[0456] 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 that uses the non-primary channel as a primary channel. That is, the receiving device that interprets the RU Allocation subfield received on the non-primary channel must interpret the received RU Allocation subfield by considering that the receiving device is a primary channel and that the 80 MHz segment including the non-primary channel is a Primary 80 MHz segment. In this process, when the receiving device interprets the position of the RU indicated through the RU Allocation subfield received on the non-primary channel, the receiving device can confirm the position of the RU allocated to itself by interpreting that the position of the RU indicated through the RU Allocation subfield has changed by a frequency offset between its own primary channel and the non-primary channel.

[0457] When the second method described above is used, the transmitting device sets the signaling fields of the PPDU in the same manner as when transmitting the PPDU after performing channel access through the primary channel when performing channel access through the non-primary channel. However, since the transmitting device performs secondary channel access during a time period in which the primary channel is determined to be busy, the PPDU transmitted after performing channel access through the non-primary channel is always transmitted without occupying the primary channel. In other words, when transmitting the PPDU after performing channel access on a non-primary channel, the transmitting device must transmit the PPDU in a form of puncturing the primary channel (in a form that does not occupy the primary channel).

[0458] For example, a transmitting device that performs channel access through a non-primary channel located in a secondary 80 MHz segment band because the primary channel is determined to be busy must set the BW field of the PPDU to 160 MHz when transmitting a PPDU through the secondary 80 MHz segment band and indicate that Preamble Puncturing is applied to the subchannel where the primary 20 MHz channel is located. At this time, a method of applying Preamble Puncturing to a subchannel located in the primary 20 MHz channel may be to puncture the primary 20 MHz subchannel or to puncture the entire band including the primary 20 MHz subchannel (e.g., the primary 40 MHz band or the primary 80 MHz segment, etc.).

[0459] That is, the limitation of conventional Wi-Fi that Preamble Puncturing should not be applied to the Primary 20 MHz subchannel may not be applied to PPDUs transmitted after performing channel access on a non-primary channel.

[0460] In this case, the receiving device can determine whether the transmitting device performed channel access through the primary channel or 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 performed channel access through the non-primary channel when the RU Allocation subfield of the received PPDU indicates that the RU located on the primary channel has been punctured. At this time, the RU Allocation subfield indicating that the RU has been punctured means the RU Allocation subfield interpreted as a 'Punctured 242-tone RU'. At this time, the 20 MHz subchannel indicated as the punctured 242-tone RU is a subchannel that is not occupied because puncturing has been applied to the PPDU.

[0461] However, when a receiving device obtains information about RUs allocated to it through the RU Allocation subfield included in the PPDU, the receiving device can interpret the RU Allocation subfield in the same way regardless of whether the channel used by the device transmitting the PPDU for channel access is a primary channel or a non-primary channel.

[0462] FIG. 24 illustrates a method for an AP performing channel access through a non-primary channel to indicate BW and RU allocation information of a PPDU according to one embodiment of the present invention.

[0463] Referring to Figure 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 through the U-SIG of the PPDU that the BW of the PPDU is 160 MHz. At this time, the indicated PPDU BW can be determined as a BW that includes the frequency band actually occupied by the PPDU and the primary channel.

[0464] Additionally, 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.

[0465] 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 confirm the RU allocated to it. The STA confirms that the subchannel corresponding to the RU Allocation subfield corresponding to its User field is the 20MHz #5 subchannel included in the Secondary 80 MHz Segment. Therefore, the STA can recognize that the RU allocated to it is the RU located in 20MHz #5. At this time, the STA can confirm that the RU allocated to it does not exist in the Primary 80 MHz segment by receiving the RU Allocation subfields corresponding to the Primary 80 MHz segment among the received RU Allocation subfields. That is, since the content channel includes an RU Allocation subfield indicating that the subchannel corresponding to the Primary 80 MHz segment has been punctured, the STA can clearly recognize that the band corresponding to the RU Allocation subfield corresponding to its User field is 20 MHz #5.

[0466] <Method for transmitting trigger frames and responding to trigger frames by terminals performing non-primary channel access procedures using a single link>

[0467] A trigger frame is a Wi-Fi control frame that triggers a response from the receiving device in the manner instructed / requested by the transmitting device. For example, an AP can instruct an STA to respond with a TB PPDU by sending a Basic trigger frame to the STA.

[0468] 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 that includes information that is commonly indicated to multiple STAs that will respond to the TB PPDU, such as the length of the TB PPDU, whether an additional trigger frame is transmitted, whether the Carrier sensing result should be considered when responding to the TB PPDU, and UL BW information that should be recorded in the BW field of the TB PPDU. The User Info field indicates information about the RU 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 itself.

[0469] In addition, the MU-RTS trigger frame that can be utilized for protection is also a type of trigger frame, and an AP that wants to transmit a DL MU PPDU can perform protection with multiple STAs at once by transmitting an MU-RTS frame that requests a CTS frame response from one or more STAs. A detailed description of the MU-RTS trigger frame is as follows.

[0470] MU-RTS is a type of trigger frame. When an MU-RTS trigger frame is received, STAs whose AID12 (LSB 12 bits of Association ID) is indicated in the User field included in the MU-RTS frame must simultaneously respond with a CTS frame. When the AP performs TXOP protection using the MU-RTS frame, since multiple STAs respond with the CTS frame, there is an advantage in that the TXOP can be protected from the adjacent devices of each of the multiple STAs that are the destination devices of the DL MU PPDU (Down link multi-user PPDU). In addition, the MU-RTS frame can also be used for the purpose of protecting the UL MU PPDU. In more detail, before requesting a TB (trigger based) PPDU from multiple STAs through the trigger frame, the AP can transmit an MU-RTS frame so that the multiple STAs that will respond with the TB PPDU respond with the CTS frame. At this time, the CTS frame responded to by the above multiple STAs serves to induce the neighbor STAs of each STA to set up NAVs that protect the TB PPDU and the Ack frame (Ack, Block Ack, etc.) to be transmitted after the TB PPDU, and through this, even legacy STAs that cannot recognize (interpret, decode) the trigger frame and TB PPDU may not perform channel access during the packet exchange sequence period (or TXOP) initiated by the trigger frame.

[0471] Figure 25 illustrates an embodiment of a transmission / TXOP protection method using an MU-RTS frame and a CTS frame.

[0472] Referring to FIG. 25, before transmitting an MU PPDU, the AP transmits an 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.

[0473] STA1_Neighbor, a neighbor STA of STA1, sets the NAV based on the information indicated in the Duration field of the CTS frame after receiving the CTS frame transmitted by STA1. STA2_Neighbor, a neighbor STA of STA2, sets the NAV based on the information indicated in the Duration field of the CTS frame after receiving the CTS frame transmitted by STA2. STA1_Neighbor and STA2_Neighbor consider that the Virtual CS (Virtual Carrier Sense) is busy while the NAV (counter) set after receiving the CTS frame remains at a non-zero value, and perform actions such as not decreasing the backoff counter. As a result, since the neighbor terminals that received the CTS frame do not attempt transmission during the period in which the NAV remains at a non-zero value, the AP may not be interrupted by the neighbor terminals while transmitting the MU PPDU and STA1 and STA2 respond with an Ack frame.

[0474] The trigger frame described above is a frame type defined in 11ax, and is a frame type 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. In other words, the trigger frame is a Control Type frame in which the Type subfield of the Frame Control field is 01, and the Subtype value 0010 is used to indicate that it is a trigger frame type. In 11ax, the trigger frame is defined so that an AP can request a response frame for multiple STAs at once, and the MU-RTS frame described above (a type of trigger frame) is used so that an AP can request a CTS frame for multiple STAs (non-AP STAs). Trigger types other than 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, and NDP Feedback Report Poll Tigger frame.

[0475] Figure 26 illustrates the format of a trigger frame.

[0476] The trigger frame is composed 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 for indicating the Type of the trigger frame, a UL Length subfield for indicating the length of the UL transmission to be responded to, and the details are described in detail through an embodiment of FIG. 27.

[0477] The User Info List field includes 0 or more User Info fields containing information for indicating the target device of the trigger frame. At this time, in addition to the information for indicating the target device, the User Info field also includes, depending on the Type of the trigger frame, parameter information (UL DCM, UL MCS, etc.) that the target device must utilize when transmitting a response frame after receiving the trigger frame. The details of the User Info field are described in detail through an embodiment of FIG. 28.

[0478] The padding field is added to ensure that the target devices of the trigger frame have time 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 target devices. In addition, in 11be (Wi-Fi 7, EHT), the end time of the PPDU including the trigger frame may be added / adjusted to align it with other PPDUs, but since it is not related to the content that the present invention intends to provide, a detailed description thereof is omitted.

[0479] The FCS (Frame Check Sequence) field contains a 32-bit CRC (Cyclic Redundancy Code), and is a calculated value including the MAC Header and Frame Body fields. The function and setting method of the FCS field of the trigger frame are the same as the function and setting method of the FCS field included in the conventional MAC frame, so a separate explanation is omitted.

[0480] Figure 27 illustrates an example of the format of the common information field of a trigger frame.

[0481] The trigger Type subfield (4 bits) is used to indicate the type (type, variant) of the trigger frame. If the trigger Type subfield is set to 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).

[0482] The UL Length subfield indicates the value that should be set in the L-SIG LENGTH field of the TB PPDU responded to via the trigger frame.

[0483] The More TF subfield is used to indicate whether there are more trigger frames to be transmitted after the corresponding trigger frame.

[0484] The CS Required subfield indicates whether the target device of the trigger frame must perform CS (Physical & Virtual CS, ED & NAV) when transmitting a response frame. An STA that transmits a response frame after receiving a trigger frame in which the CS Required subfield is set to 1 must perform CS.

[0485] The UL BW subfield indicates the BW value that STAs responding with a TB PPDU after receiving a trigger frame must indicate in the Preamble (e.g., HE-SIG-A or U-SIG).

[0486] 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 the Sharing mode when the MU-RTS trigger frame is used for TXOP sharing using the MU-RTS TXS (TXOP Sharing) trigger frame.

[0487] 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.

[0488] The Number Of HE / EHT-LTF Symbols subfield indicates the number of HE(EHT)-LTF symbols that should be applied to the TB PPDU when the Doppler subfield is indicated as 0, and indicates information related to the number of HE(EHT)-LTF symbols and the periodicity of the midamble when the Doppler subfield is indicated as 1.

[0489] The LDPC Extra Symbol Segment subfield indicates whether an LDPC extra symbol segment should appear in the responded TB PPDU. If the LDPC Extra Symbol Segment subfield is set to 1, an LDPC extra symbol segment must appear in the TB PPDU.

[0490] 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 with a response frame based on the value indicated in the AP Tx Power subfield.

[0491] The Pre-FEC Padding Factor and PE Disambiguity subfields indicate whether the Pre-FEC Padding Factor is 1, 2, 3, or 4, and provide information to clarify the length of the PE (Packet Extension).

[0492] 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.

[0493] The Doppler subfield indicates whether the TB PPDU to be responded to includes a midamble. However, the trigger frame responding with an EHT TB PPDU may have the Doppler subfield reserved. In this case, the subfield being reserved may mean that the STA responding with an EHT TB PPDU after receiving the trigger frame operates without considering the presence or setting of the subfield.

[0494] The HE / EHT P160 subfield indicates whether the responded TB PPDU is responded as a HE TB PPDU or an EHT TB PPDU on the channel corresponding to P160 MHz.

[0495] The Special User Info Field Present subfield indicates whether the User Info field with the AID12 subfield set to 2007 appears among the User Info fields.

[0496] The Trigger Dependent Common Info subfield is a field that appears only when the type of trigger frame indicated by the Trigger Type field is a Basic trigger frame or an NFRP trigger frame.

[0497] Figure 28 illustrates an example of the format of the user information field of a trigger frame.

[0498] Referring to FIG. 28, the AID12 subfield indicates information regarding which STA the corresponding User Info field is for. That is, an STA for which a value identical to its own AID is indicated in the AID12 subfield of a specific User Info field can recognize that the corresponding trigger frame includes itself as a target device. At this time, 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.

[0499] At this time, the AID12 subfield can be set to 0 when one or more RA-RU (Random Access RU) is to be allocated to associated STAs. That is, STAs associated with an AP can attempt to transmit TB PPDU using RA-RU if there is no User Info field of AID12 indicating its own AID in the received trigger frame and there is a User Info field indicating AID12 as 0.

[0500] At this time, the AID12 subfield can be set to 2045 or 2044 when one or more RA-RUs are to be allocated to unassociated STAs. That is, STAs that are not associated with an AP can attempt to transmit a TB PPDU using RA-RU if a User Info field in which AID12 is indicated as 2045 and 2044 exists in the received trigger frame. At this time, an STA that responds to a TB PPDU through RA-RU must respond with a HE TB PPDU when AID12 is indicated as 2045, and must respond with an EHT TB PPDU when AID12 is indicated as 2044.

[0501] At this time, the AID12 subfield can be set to a preset value such as 4095 or 4094, and if the AID12 subfield is indicated as a preset value, it means that the padding field starts from the corresponding AID12 subfield. That is, if the AID12 subfield of the trigger frame is indicated as a value (preset) indicating the start of the padding field, the STA can recognize that the padding field has started and not attempt to parse the remaining part of the MAC frame.

[0502] At this time, the User Info field in which the AID12 subfield is indicated as 2046 may include 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.

[0503] The RU Allocation subfield of trigger frames other than the MU-RTS trigger frame indicates the size and location information of the RU (Resource Unit) / MRU (Multiple Resource Unit) allocated to the destination device (STA indicated through 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 should respond to the CTS frame. More specifically, the RU Allocation subfield of the MU-RTS frame (in the User Info field) indicates whether the destination STA should respond to the CTS frame 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 (when transmitted by an EHT / UHR AP) channel. More specifically, the AP may indicate one of values ​​61 to 64 through B7-B1 of the RU Allocation subfield in the User Info field of the specific STA to indicate that the specific STA will respond to the CTS frame through Primary 20 MHz, may indicate 65 or 66 through B7-B1 of the RU Allocation subfield to indicate that the specific STA will respond to the CTS frame through Primary 40 MHz, may indicate 67 through B7-B1 of the RU Allocation subfield to indicate that the STA will respond to the CTS frame through Primary 80 MHz, and may indicate 68 through B7-B1 of the RU Allocation subfield to indicate that the STA will respond to the CTS frame through Primary 160 MHz.The instruction to respond to the CTS frame via the Primary 320 MHz channel is performed by indicating 69 via the B7-B1 above. At this time, the PS160 subfield of the User Info field, which instructs to respond to the CTS frame via the Primary 20 / 40 / 80 / 160 MHz, is set to 0, and the PS160 subfield of the User Info field, which instructs to respond to the CTS frame via the (Primary) 320 MHz, is set to 1.

[0504] The UL FEC Coding Type subfield indicates the code type of the TB PPDU to be responded to. 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).

[0505] The UL EHT-MCS subfield indicates the EHT-MCS to which the responding TB PPDU should be applied.

[0506] The SS Allocation / RA-RU Information subfield may be used as the RA-RU Information subfield when the AID12 subfield is not a value indicating that RA-RU is allocated, i.e., is indicated as 0, 2044, or 2045, and may be used as the SS Allocation subfield when the AID12 subfield is indicated 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 may be used as the 4 bit Starting Spatial Stream subfield and the 2 bit Number Of Spatial Streams subfield.

[0507] The UL Target Receive Power subfield indicates the predicted signal power at which the TB PPDU to be responded to will be received at the AP's antenna. Therefore, when an STA responds with a TB PPDU, it may need to adjust the transmit power of the TB PPDU based on the value of the UL Target Receive Power subfield so that the TB PPDU can be received at the power predicted by the AP.

[0508] The PS160 subfield is used together with the RU Allocation subfield and indicates information related to the location and size of the RU / MRU (Multiple-RU) allocated through the User Info field.

[0509] 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.

[0510] As described above, the AP transmits an MU-RTS frame, and indicates the STA that will respond to the CTS frame through the User Info field, and at the same time, indicates the band in which each STA must respond to the CTS frame, which includes the Primary 20 MHz channel.

[0511] 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 an MU-RTS frame through channels other than 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 form that does not occupy the Primary 20 MHz channel.

[0512] Therefore, an AP that transmits an MU-RTS frame after performing channel access on a non-primary channel must respond with a CTS frame through the User Info field.

[0513] This is a different operation from the conventional Wi-Fi STA, which only performs transmission while occupying the Primary 20 MHz channel. Therefore, an STA that receives an MU-RTS frame from an AP that performs channel access through a non-primary channel must respond with a CTS frame that does not occupy the primary channel.

[0514] However, as explained above, an AP that transmits an MU-RTS frame and instructs an STA on a channel to respond to a CTS frame has a limitation in that it can only instruct a channel type that occupies the Primary 20 MHz channel, such as Primary 20 / 40 / 80 / 160 / 320 MHz. Therefore, in order to allow an AP that performs channel access through a non-primary channel and then transmits an MU-RTS frame to instruct a response to a CTS frame that only occupies the non-primary channel, more information than 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 more information may mean information on the channel that the AP used for channel access and / or more diverse instruction methods for instructing a channel on which the STA will respond to the CTS frame.

[0515] 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 a non-primary channel. More specifically, the trigger frame may include a subfield that is indicated with a different value when transmitted by an AP that has performed channel access through a primary 20 MHz channel and when transmitted by an AP that has performed channel access through a non-primary channel (a 20 MHz subchannel other than the primary 20 MHz channel).

[0516] By setting a specific subfield included in the Common Info field of the trigger frame to a specific value, the AP can indicate to STAs receiving the trigger frame that it has transmitted the trigger frame after performing channel access through the primary channel. When the AP has performed channel access through a non-primary channel, the AP can indicate that it has not performed channel access through the primary channel by setting the specific subfield to a different value. At this time, if the specific subfield has a size of 1 bit, the specific subfield can be indicated as 0 to indicate that the AP has performed channel access on the primary channel, and can be 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 set to 0 to indicate that the AP performed channel access on the primary channel, set to 1 to indicate that the AP performed channel access through the first non-primary channel, set to 2 to indicate that the AP performed channel access through the second non-primary channel, and set to 3 to indicate that the AP performed channel access through the third non-primary channel. At this time, the first, second, and third non-primary channels may be subchannels located in different 80 MHz segments.

[0517] When the AP indicates information related to the channel on which it performed Channel Access through the Common Info field of the trigger frame, the STA must interpret the RU Allocation subfield included in its User Info field based on the information about the channel on which the AP performed Channel Access. In other words, the STA that receives the MU-RTS frame must utilize both the channel information used for channel access indicated by the AP through the Common Info field and the information indicated through the RU Allocation subfield of its User Info field to confirm the frequency band on which it will respond to the CTS frame. Briefly, a method for the STA to utilize the information indicated in the Common Info field and the information indicated through the RU Allocation subfield may be to obtain the bandwidth on which it should respond to the CTS frame through the RU Allocation subfield, and to confirm the location of the subchannel on which the CTS frame should be responded based on the information indicated in the Common Info field.

[0518] 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 on which the AP performed Channel Access is indicated as the Primary 20 MHz channel, the STA responds with a CTS frame through the Primary 80 MHz channel, and if the channel on which the AP performed Channel Access is indicated as the non-primary channel, the STA responds with a CTS frame on the 80 MHz channel located in the 80 MHz segment that includes the non-primary channel.

[0519] Alternatively, the AP can indicate both the frequency band and location information on which each STA will respond to the CTS frame through the User Info field of each STA. That is, the AP can indicate an RU that does not include the 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 indicate that the CTS frame will be responded to on one of the four 20 MHz subchannels located in the Secondary 80 MHz segment by setting the RU Allocation subfield to 71 to 74, can indicate 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 can indicate the 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 may have the function of indicating a frequency range excluding the Primary 20 MHz channel.

[0520] Alternatively, the RU Allocation subfield may be configured using the conventional method, but the AP may instruct the STA to respond to the CTS frame in a band other than the Primary 20 MHz channel by interpreting the RU Allocation subfield in combination with other subfields indicated in the User Info field. For example, the AP may indicate a value corresponding to 20 MHz (e.g., 61 to 64) through the RU Allocation subfield and indicate a first 80 MHz segment through the specific subfield, thereby instructing the STA to respond to the CTS frame through a specific 20 MHz subchannel located in the first 80 MHz segment. That is, the STA may determine the subchannels on which it should respond to the CTS frame by combining the indicated segment information and the indicated CTS frame response BW information.

[0521]

[0522] <Efficient Operation Method of Non-Primary Channel Access (NPCA)>

[0523] 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 subchannel other than a primary channel, are different channel access methods that can be used to achieve the same purpose. The difference between these two channel access methods lies in whether the STA performing the channel access changes the channel on which the channel access procedure is performed (e.g., EDCA) or whether the channel on which the channel access procedure is performed is changed by changing an active link.

[0524] That is, both channel access methods are essentially the same in that they perform channel access by performing channel switching to a subchannel (non-primary channel) other than the primary channel when the primary channel is occupied, thereby having the same effect. Therefore, the methods for efficiently utilizing the two channel access methods are also the same. Hereinafter, the efficient operation method of 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 through which it performs channel access from the primary channel to another subchannel (e.g., a non-primary channel or subchannel) rather than changing the channel 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 of non-primary channel access described below will be mainly explained in the context of the method in which a single STA (AP and / or non-AP STA) performs channel access by using another subchannel through channel switching to a subchannel other than the primary channel. That is, the conditions for performing the non-primary channel access method described below can be applied identically to the conditions for switching the primary link to an inactive state and switching the secondary link to an active state. That is, the operation / judgment method of the STA performing the non-primary channel access described below can be applied identically to the operation / judgment method of the MLD using the overlapping BSS.

[0525] An STA performing non-primary channel access can improve its channel access capability by performing a channel access procedure through a subchannel other than the primary channel even when the primary channel is occupied by an OBSS. However, when performing a channel access procedure on a subchannel other than the primary channel, a procedure must be performed to protect transmissions of other STAs that may be in progress on the subchannel first (e.g., applying Mediumsync time), and after completing the channel access procedure, the STA must terminate the acquired TXOP at the same time as or earlier than the TXOP of the OBSS that occupied its primary channel.

[0526] That is, when the primary channel is occupied by an AP or non-AP STA of another OBSS and is busy, the STA can switch the channel to another sub-channel (sub-channel or non-primary channel) within the same bandwidth and perform a channel access procedure on the channel, thereby improving the channel access capability. In addition, since the problem of other sub-channels in the bandwidth not being used due to the primary channel being occupied can be resolved, the channel can be used efficiently. In this case, in order to protect the operations of other STAs in the switched sub-channel, the STA must perform the channel access procedure on the switched channel within the TXOP configured in 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. Therefore, the STA can determine the remaining length of the configured TXOP based on a frame transmitted from an AP or non-AP STA of another OBSS on the primary channel before channel switching to determine whether the channel access procedure can be performed on the switched sub-channel. Additionally, after receiving a frame, the STA may determine whether the received frame is a frame transmitted from an AP associated with it or an AP not associated with it before determining the remaining duration of the TXOP. At this time, the STA may determine the remaining duration of the TXOP set on the primary channel based on the value of the TXOP field or duration field included in the received frame.

[0527] Therefore, an STA performing a non-primary channel connection must perform many additional operations (e.g., applying Mediumsync time, changing the operating frequency from the primary channel to another subchannel, etc.) compared to performing a channel connection on the primary channel, whereas the TXOP length that can be obtained through the non-primary channel connection may be further limited. In other words, considering the cost consumed to perform a non-primary channel connection, a situation may arise where the TXOP length that can be obtained through the non-primary channel connection is too short, and in this case, it may be more advantageous for the STA not to perform the non-primary channel connection. Therefore, even an STA with the capability to perform a non-primary channel connection may not always perform the non-primary channel connection when the primary channel is occupied by the OBSS.

[0528] As explained above, if the STA determines that the primary channel of the bandwidth is occupied by the OBSS AP, the STA can perform channel switching to another sub-channel (non-primary channel) of the bandwidth. At this time, the STA can determine whether the frame (or PPDU) it 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 from the OBSS AP through the BSS color information or the MAC address of the received frame.

[0529] If the received frame is a frame transmitted from an OBSS AP, the primary channel is occupied by the OBSS AP and is therefore 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 to a non-primary channel within the bandwidth described above.

[0530] At this time, the STA can 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 can perform a non-primary channel connection only when the TXOP length of the OBSS occupying its primary channel is longer than (or equal to or longer than) a specific value (threshold). At this time, the length of the OBSS TXOP considered by the STA may mean the length from the time when the STA recognizes the OBSS TXOP to the time when the OBSS TXOP ends. In other words, 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 a NAV (network allocation vector) set based on a frame transmitted by the OBSS STAs, or on a time indicated by a TXOP field included in the preamble of the OBSS PPDU.

[0531] At this time, the STA can decide whether to perform non-primary channel access based on the PPDU length of the OBSS that occupies the primary channel. More specifically, the STA can perform non-primary channel access only when the PPDU length of the OBSS that occupies its primary channel is longer than (or equal to or longer than) a specific value (Threshold). At this time, the length of the OBSS PPDU considered by the STA may mean the total length of the OBSS PPDU or the remaining time from the time when the STA recognizes the OBSS PPDU to the end of the OBSS PPDU. That is, the STA can decide to perform non-primary channel access if the total length of the OBSS PPDU that it has confirmed is longer than a specific value (Threshold), or to perform non-primary channel access if the length of the remaining OBSS PPDU from the time when the STA recognizes the OBSS PPDU is longer than a specific value (Threshold). At this time, the 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. The specific process of obtaining information related to the length of the OBSS PPDU from the RXVECTOR parameter is described through the embodiments of the present invention described later, so a detailed description is omitted.

[0532] In other words, when a PPDU is received from another STA (AP or non-AP STA), the STA can recognize whether the received PPDU is a PPDU transmitted from the BSS to which it belongs (intra-BSS PPDU) or a PPDU transmitted from a BSS to which it does not belong (inter-BSS PPDU) based on information included 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 that the primary channel of the bandwidth in which it operates is occupied through the CCA operation, and in this case, the STA 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, etc.). In this case, in order for the STA to perform channel switching to another channel, the TXOP set by the received PPDU (TXOP set by another OBSS) must be sufficiently left for channel switching and frame exchange (or channel access). To determine this, the STA can 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 can perform a frame exchange or channel access procedure by switching to another channel.

[0533] At this time, a specific value related to 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 the rate field included in the PPDU. The duration of the remaining TXOP may mean 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.

[0534] Alternatively, the STA can recognize the total length of the PPDU or the length of the remaining PPDU by the RXVECTOR parameter generated at the PHY layer by the received PPDU and transmitted to the MAC layer. The following embodiments describe a specific value based on the remaining TXOP duration, but it may be performed based on the total length of the PPDU or the length of the remaining PPDU as well as the remaining TXOP duration.

[0535] The specific value may be a value indicated by the AP via a Management frame transmitted by the AP (e.g., a Beacon frame and / or a Probe Response frame and / or an Association Response frame and / or a Management frame (a type of Operating Mode Notification frame) indicating whether to utilize a non-primary channel connection). Alternatively, the specific value may be a preset value (e.g., 1 ms or 2 ms, etc.).

[0536] At this time, the method for the STA to check the TXOP length of the OBSS that occupies the primary channel may be to use the value indicated through the TXOP field included in the Preamble (e.g. HE-SIG-A or U-SIG) of the received PPDU or the Duration / ID field of the MAC Header.

[0537] In this case, the STA can recognize the duration of the remaining TXOP after 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 time of the received frame to the end time 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 channel switching to a non-primary channel within the set TXOP based on the remaining duration, and if it is determined that channel switching and the channel access procedure (or frame exchange) can be performed within the remaining duration, the STA can perform the channel access procedure (or frame exchange) by channel switching to a non-primary channel. At this time, the STA may compare the remaining duration (or the total length of the PPDU or the length of the remaining PPDU, etc.) with a threshold value to determine whether channel switching and channel access procedures can be performed within the remaining duration. 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 the frame (e.g., the received PPDU) is greater than the threshold value, the STA may determine that the channel access procedure on the non-primary channel is possible. At this time, the length of the frame (or the duration of the PPDU) may be obtained based on the length field and the rate field included in the frame. At this time, the threshold value may mean the minimum duration for the STA to perform channel switching and channel access.

[0538] Alternatively, the method for determining whether an STA performs a channel access on a non-primary channel may be performed based on the length of the TXOP that it determines it can obtain through channel access on the non-primary channel, rather than based on the TXOP length of the OBSS occupying the primary channel. That is, the STA may determine to perform a channel access on the non-primary channel only if the length of the TXOP that it can obtain through channel access on the non-primary channel is longer than (or equal to or longer than) a specific value (threshold). In this case, while performing a channel access procedure on a subchannel other than the primary channel, if the length of the TXOP that it can obtain through non-primary channel access becomes shorter than the specific value (calculated based on the end point of the TXOP of the OBSS occupying the primary channel), the STA may switch back to the primary channel and perform the channel access procedure. That is, if an STA fails to complete the channel access procedure of a non-primary channel before a certain time from the end of the TXOP of the OBSS that occupies its primary channel, the STA may give up access to the non-primary channel and switch back to the channel access procedure using the primary channel.

[0539] 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 acquired are different methods for determining whether the TXOP that can be acquired through non-primary channel access is sufficient (whether it is sufficiently efficient). An STA that decides whether to attempt non-primary channel access can use one or both methods together to make the final decision on whether to perform non-primary channel access.

[0540] Additionally, when determining whether to perform a channel access procedure on a non-primary channel, the STA may consider the switching delay or transition delay for switching to the non-primary channel operation to determine whether to switch to the non-primary channel operation. More specifically, even if the STA is instructed that the TXOP of the OBSS occupying its primary channel is maintained for a time longer than a threshold, if the time it takes for the STA to switch to the non-primary channel operation mode is shorter than the threshold, the STA may not switch to the non-primary channel operation mode. In other words, the STA may determine whether to switch to the non-primary channel operation mode based on whether the remaining 'time length of the OBSS TXOP - Transition delay' is longer than (or longer than or equal to) the threshold.

[0541] For example, in order to determine whether a channel access procedure is possible in the non-primary channel described above, the STA may additionally consider a switching delay or a transition delay. That is, the STA may compare a value obtained based on a value indicated by a duration field or a TXOP field included in a received frame (or PPDU) (e.g., a value obtained by adding the duration of the PPDU to the value indicated by the TXOP field or the duration field value) with a threshold value, and the threshold value may be set to a value obtained by adding the switching delay or a transition delay to a minimum value for performing channel switching and channel access procedures.

[0542] FIG. 29 illustrates an example of channel access in a non-primary channel when the primary channel is occupied according to one embodiment of the present invention.

[0543] Referring to Figure 29, an STA can perform a channel access procedure by switching to a non-primary channel (secondary channel) when the primary channel is in a busy state due to a TXOP set by the OBSS. Figure 29 illustrates the channel status and channel access procedure confirmed from the perspective of an STA capable of performing non-primary channel access.

[0544] Before completing the backoff procedure on the primary channel (P20), the STA receives the RTS / CTS frame exchanged by the OBSS STA 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 a 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 then performs frame exchange.

[0545] An STA that terminates its own TXOP before OBSS TXOP1 terminates performs a 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 OBSS TXOP2 it has confirmed is shorter than the threshold value, and instead of performing a channel access procedure on a channel other than the primary channel, it waits for OBSS TXOP2 to terminate on the primary channel. Afterwards, when OBSS TXOP2 terminates, the channel access procedure continues on the primary channel.

[0546] As described above, it is possible to determine whether performing a non-primary channel connection is efficient or inefficient depending on the length of a TXOP that can be obtained through the non-primary channel connection, and the STA can decide whether to perform the non-primary channel connection based on the determination result.

[0547] Another type of inefficiency that can arise from non-primary channel access occurs when the AP and non-AP STAs perceive different primary channel states. As previously explained, the neighboring STAs of an AP and a non-AP STA may be different, and signals from an OBSS occupying the AP's primary channel may not be received by certain non-AP STAs. Furthermore, signals from an OBSS occupying the primary channel of a specific non-AP STA may not be received by the AP.

[0548] In this case, if the primary channel status confirmed by the AP and the primary channel status confirmed by the non-AP STA are different, the channels on which the AP and the non-AP STA perform channel access may be different. For example, the AP may determine that the primary channel is IDLE and transmit a PPDU after completing channel access on the primary channel, but the non-AP STA may determine that the primary channel is BUSY due to the OBSS and may be performing a 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 may determine that the primary channel is IDLE and transmit a PPDU after completing channel access on the primary channel, but the AP may determine that the primary channel is BUSY due to the OBSS and may be performing a channel access procedure on a subchannel other than the primary channel or waiting to receive a UL PPDU. In this way, when the AP and non-AP STA have different views of the primary channel, PPDU transmission fails due to channel mismatch issues between the transmitting and receiving devices.

[0549] This is because the introduction of the non-primary channel access procedure has introduced a new problem that was not experienced by existing Wi-Fi STAs that operated only through the primary channel. Therefore, the situations in which such problems occur must be reduced to maximize the benefits and minimize losses that can be obtained from non-primary channel access. However, the fact that the channel environments of STAs operating in different locations are different is a natural phenomenon that occurs due to the limited reach of wireless transmission signals. Therefore, the phenomenon in which two STAs may have different judgments about a specific channel is an unresolvable phenomenon.

[0550] However, based on information previously exchanged between two STAs, it is possible to help a specific STA determine a point in time when another STA has the same view as itself. For a simple example, if a specific STA has previously indicated to another STA that it has received a signal transmitted by STA1, the other STA can anticipate that the signal of STA1 will also be received by the specific STA while it is receiving the signal of STA1. That is, based on the information provided by the specific STA, the other STA can determine that it and the specific STA have the same view at a specific point in time.

[0551] According to one embodiment of the present invention, an AP may indicate information related to an adjacent BSS (Overlapping) to a non-AP STA, and the non-AP STA may determine whether to perform a non-primary channel access (move to a subchannel other than the primary channel for performing a channel access procedure and / or waiting for reception (e.g., performing CCA and PD (Preamble / Packet detection)) based on the information indicated to the AP. That is, the AP may transmit information on adjacent OBSS to associated non-AP STAs by including it in a management frame. For example, the AP may transmit a management frame including list information on OBSS APs, and when the non-AP STA performs a non-primary channel access operation, if the AP that transmitted the frame is included in the list information of the management frame, the non-AP STA may perform the non-primary channel access procedure described above based on 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 list information includes AP-related information, the non-AP STA can perform a channel access procedure on a non-primary channel as described above.

[0552] Specifically, the AP can notify non-AP STAs of information (a kind of list) related to OBSSs that can occupy its primary channel (i.e., OBSSs that change the primary channel status of the AP to busy). At this time, the information related to OBSSs that the AP notifies to non-AP STAs may be BSS color information of the OBSSs and / or the MAC address of a neighbor AP that operates the OBSS. At this time, the number of neighbor APs that the AP indicates in relation to non-primary channel access may be smaller than the number of APs that the AP indicates through the RNR element (Reduced Neighbor Report) of the beacon frame. This is because the neighbor APs that the AP indicates in relation to non-primary channel access are limited to APs that operate a BSS that can occupy the AP's primary channel.

[0553] A non-AP STA that has received information related to an OBSS from an AP can determine whether to switch to non-primary channel operation (performing a channel access procedure using a subchannel other than the primary channel and / or waiting to receive 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 included in the OBSS list indicated by the AP.

[0554] 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 indicated by the AP. That is, the non-AP STA can know that the OBSS that changed the state of its primary channel to BUSY is the OBSS that also changed the state of the AP's primary channel to BUSY, and it is expected that the AP will also switch to non-primary channel operation when the non-AP STA switches to non-primary channel operation.

[0555] That is, the prior information about the OBSS transmitted by the AP through the management frame can be used by the non-AP STA to determine whether the OBSS occupying its primary channel causes the AP to initiate non-primary channel operation. If the OBSS occupying its primary channel is an OBSS not included in the list information transmitted by the AP, the non-AP STA must not switch to non-primary channel operation. In this case, the AP also must not switch to non-primary channel operation if the primary channel is occupied by an OBSS not included in the list information of the OBSS transmitted by the AP.

[0556] The process by which an AP acquires / instructs information about an OBSS and determines whether or not each non-AP STA performs non-primary channel operation based on the instructed information can be summarized as follows.

[0557] 1) When a PPDU transmitted while occupying its own primary channel is received, the AP records the information of the OBSS that transmitted the PPDU. At this time, the OBSS information recorded by the AP may be BSS color information of the OBSS or the MAC address of the AP operating the OBSS. i) For the BSS color information, the AP can obtain it through the BSS color field (included in the SIG field (e.g., HE-SIG-A or U-SIG, etc.)) of the received PPDU (e.g., HE PPDU, EHT PPDU, UHR PPDU). ii) The MAC information can be obtained through the TA or RA field (included in the MAC header) of the MAC frame included in the received PPDU (e.g., HE PPDU, EHT PPDU, UHR PPDU).

[0558] 2) The AP can notify the list information, which is information of the OBSS that switches the state of its primary channel to busy, through the frame it transmits. At this time, i) the OBSS information may be BSS color information of each OBSS and / or the MAC address of the AP that operates the OBSS. ii) The AP can indicate the BSS information through the beacon frame and / or notification frame (e.g., Operating Mode Notification frame) it transmits. At this time, the Notification frame may be a frame that indicates whether the AP is going to perform non-primary channel access.

[0559] 3) A non-AP STA may perform a non-primary channel access operation based on the list information (e.g., color information or MAC address) of OBSSs transmitted from the AP through a management frame. For example, i) a non-AP STA may perform a non-primary channel access operation if the BSS color of the OBSS that occupies its primary channel or the MAC address of the OBSS AP matches the BSS color or MAC address included in the list information obtained from the AP. ii) However, a non-AP STA may not perform the non-primary channel access operation if the BSS color of the OBSS that occupies its primary channel or the MAC address of the OBSS AP does not match the BSS color or MAC address included in the list information obtained from the AP.

[0560] 4) The AP manages the information of the OBSS that switches the primary channel to a busy state (i.e., the OBSS that occupies the primary channel) by applying a timeou...

Claims

1. As a wireless communication terminal, Transmitter and receiver; and Contains a processor, The above processor, Receive a preamble of an inter-BSS PPDU (Physical Layer Protocol Data Unit) on a primary channel of a bandwidth in which the wireless communication terminal operates from an OBSS (Overlapping Basic Service Set) AP (Access Point) that is not associated with the wireless communication terminal, The preamble of the above inter-BSS PPDU includes a TXOP field related to the transmission opportunity (TXOP) duration set by the OBSS AP, When a specific condition is satisfied, the channel is switched from the primary channel of the above bandwidth to a non-primary channel. The above specific condition is a wireless communication terminal wherein the length of the remaining OBSS TXOP calculated based on the TXOP field or the duration field is greater than a minimum duration threshold value.

2. In paragraph 1, A wireless communication terminal whose primary channel status is Busy by the OBSS AP.

3. In paragraph 1, The wireless communication terminal is a wireless communication terminal whose minimum duration threshold is the minimum value for switching a channel to the non-primary channel.

4. In the first paragraph, the processor, Receive a management frame from an AP associated with the above wireless communication terminal, The above management frame is a wireless communication terminal including list information of neighboring APs.

5. In paragraph 4, The above list information is a wireless communication terminal including BSS color information and / or MAC address of each of the APs.

6. In paragraph 4, A wireless communication terminal in which a channel switch to the above non-primary channel is performed when the primary channel is occupied by one of the above APs.

7. In the fourth paragraph, the processor, A wireless communication terminal that compares the BSS color information or MAC address of the inter-BSS PPDU with the BSS color information or MAC address included in the list information.

8. In paragraph 1, A wireless communication terminal, wherein the above specific condition is determined by additionally considering the channel switch delay of the wireless communication terminal in addition to the length of the remaining OBSS TXOP.

9. In the first paragraph, the processor, A wireless communication terminal that transmits a primitive from the MAC layer to the PHY layer to perform the channel switch to the above non-primary channel.

10. In a method performed by a wireless communication terminal, the method comprises: A step of receiving a preamble of an inter-BSS PPDU (Physical Layer Protocol Data Unit) on a primary channel of a bandwidth in which the wireless communication terminal operates from an OBSS (Overlapping Basic Service Set) AP (Access Point) that is not associated with the wireless communication terminal; The preamble of the inter-BSS PPDU includes a transmission opportunity (TXOP) field related to the duration set by the OBSS AP; and Including a step of switching a channel from the primary channel of the bandwidth to a non-primary channel when a specific condition is satisfied, The above specific condition is a method in which the length of the remaining OBSS TXOP calculated based on the TXOP field or the duration field is greater than a minimum duration threshold value.

11. In clause 10, The state of the above primary channel is Busy by the above OBSS AP.

12. In paragraph 10, The above minimum duration threshold is a method in which the wireless communication terminal switches a channel to the non-primary channel.

13. In the 10th paragraph, the method, Further comprising a step of receiving a management frame from an AP associated with the above wireless communication terminal, A method in which the above management frame includes list information of neighboring APs.

14. In paragraph 13, A method wherein the above list information includes BSS color information and / or MAC address of each of the APs.

15. In paragraph 13, A method in which a channel switch to the above non-primary channel is performed when the primary channel is occupied by one of the above APs.

16. In the 13th paragraph, the method, A method further comprising the step of comparing the BSS color information or MAC address of the inter-BSS PPDU with the BSS color information or MAC address included in the list information.

17. In paragraph 10, A method for determining whether the above specific condition is satisfied by additionally considering the channel switch delay of the wireless communication terminal in addition to the length of the remaining OBSS TXOP.

18. In the 10th paragraph, the method, A method further comprising the step of transmitting a primitive from the MAC layer to the PHY layer to perform the channel switch to the non-primary channel.

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