Wireless communication method using multilink and wireless communication terminal using the same

Abstract

The present invention discloses a channel switching method and device performed by a multi-link device (MLD) including a plurality of stations each operating on a plurality of links in a wireless communication system. Specifically, the MLD of the present invention receives a frame for channel switching from a first AP of an AP MLD including at least one AP (Access Point), and can recognize channel switching of other APs based on the received frame.

Description

[Technical Field]

[0001] The present invention relates to a wireless communication method using multilinks and a wireless communication terminal using the same. [Background technology]

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

[0003] Since supporting early wireless LAN technology using the 2.4 GHz frequency band, IEEE (Institute of Electronics Engineers) 802.11 has since implemented or is currently developing various other technology standards. IEEE 802.11b uses the 2.4 GHz frequency band and supports a maximum communication speed of 11 Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5 GHz frequency band instead of the 2.4 GHz band, reducing the impact of interference compared to the significantly more congested 2.4 GHz frequency band, and uses OFDM technology to improve communication speeds to a maximum of 54 Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication distance than IEEE 802.11b. IEEE 802.11g, like IEEE 802.11b, uses the 2.4GHz band and achieves a maximum transmission speed of 54Mbps, and has attracted considerable attention for its backward compatibility, but it also has an advantage over IEEE 802.11a in terms of communication distance.

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

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

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

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

[0008] An object of one embodiment of the present invention is to provide a wireless communication method using multilinks and a wireless communication terminal using the same.

[0009] Another object of an embodiment of the present invention is to provide a channel switching method for a station and an AP using multilink.

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

[0011] According to the present invention, a multi-link device (MLD) including a plurality of stations operating on a plurality of links respectively includes a processor, and the processor receives a frame for channel switching and / or class change from a first AP of an AP MLD including at least one AP, the frame including at least one of a Channel Switch Announcement element for notifying a second AP included in the AP MLD of the channel switching and / or class change and / or a Max Channel Switch Time element related to the time of the channel switching of the second AP, a Switch Time field included in the Max Channel Switch Time element indicates a first time or a second time depending on the type of the AP MLD and / or a state of the channel switching, the first time being the maximum time from the transmission of the last beacon frame transmitted from the second AP before the start of the channel switching to the first beacon frame on a new channel, and the second time being the time from the transmission of the frame to a specific operation of the second AP on the new channel, and the processor recognizes the channel switching of the second AP based on the frame.

[0012] Also, in the present invention, when the last beacon frame associated with the channel switching is transmitted, the channel switch time field indicates the second time, and the specific action is the transmission of the first beacon frame on the new channel.

[0013] Also, in the present invention, if the channel switching is before it starts, the channel switch time field indicates the first time.

[0014] In addition, in the present invention, the channel switch announcement element includes a new channel number field and a channel switch count field, where the channel number field indicates the position of the new channel, and the channel switch count field indicates the number of TBTTs (Target Beacon Transmission Times) remaining until the channel switch to the new channel.

[0015] Also, in the present invention, when the type of the AP MLD is a nonsimultaneous transmit and receive (NSTR) mobile AP MLD that does not support simultaneous transmission / reception, the channel switch time field indicates the second time.

[0016] In the present invention, the specific operation is the resumption of a BSS (Basic Service Set) operation of the second AP on the new channel.

[0017] Also, in the present invention, when the type of the AP MLD is NSTR mobile AP MLD, the first AP operates on a primary link, and the second AP operates on a non-primary link.

[0018] In addition, in the present invention, the channel switching state is determined depending on whether the channel switch announcement element or the maximum channel switch time element is included in the frame when the type of the AP MLD is NSTR mobile AP MLD.

[0019] In addition, in the present invention, if the frame includes the maximum channel switch time element but does not include the channel switch announcement element, the channel switching state is determined to be in progress.

[0020] Also, in the present invention, if the maximum channel switch time element is not included in the frame, the channel switching state is determined to be that the second AP has resumed the BSS operation.

[0021] The present invention also provides a method including: receiving a frame for channel switching and / or class change from a first AP of an AP MLD including at least one AP, the frame including at least one AP selected from a Channel Switch Announcement element for notifying a second AP included in the AP MLD of the channel switching and / or class change, the frame including at least one of a Channel Switch Announcement element for notifying the second AP of the channel switching and / or class change and / or a Max Channel Switch Time element related to the time of the channel switching of the second AP, a Switch Time field included in the Max Channel Switch Time element indicating a first time or a second time depending on a type of the AP MLD and / or a state of the channel switching, the first time being a maximum time from the transmission of a last beacon frame transmitted from the second AP before the start of the channel switching to the first beacon frame on a new channel, and the second time being a time from the transmission of the frame to a specific operation of the second AP on the new channel; and recognizing the channel switching of the second AP based on the frame. [Effects of the Invention]

[0022] An embodiment of the present invention provides a wireless communication method that efficiently uses multilinks and a wireless communication terminal that uses the same.

[0023] Furthermore, the channel change method according to an embodiment of the present invention has an advantage that channel switching can be performed efficiently by clarifying the structure of frames transmitted and received for channel switching.

[0024] In addition, by setting the frame configuration and the information indicated by the fields differently depending on whether the AP MLD supports STR or NSTR, it is possible to effectively perform channel switching depending on whether the AP MLD supports STR.

[0025] Furthermore, efficient channel switching enables efficient link management.

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

[0027] [Figure 1] 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a configuration of an access point according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating a process in which a STA establishes a link with an AP. [Figure 6] FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7]1 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1 illustrates various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention. [Figure 9] 1 shows a multi-link device according to an embodiment of the present invention; [Figure 10] 1 illustrates simultaneous transmission of different links in a multi-link operation according to an embodiment of the present invention. [Figure 11] 1 shows an example of the contents of a beacon frame transmitted by an AP in AP MLD and an example of a TBTT (target beacon transmission time) information field format included in an RNR (Reduced Neighbor Report) element according to one embodiment of the present invention. [Figure 12] 10 illustrates yet another example of a TBTT information field format according to an embodiment of the present invention. [Figure 13] 10 illustrates an example of a TBTT information length subfield indicating a TBTT information field including an MLD AP TBTT offset subfield according to an embodiment of the present invention. [Figure 14] 10 illustrates an example of a Per-STA Profile subelement format according to an embodiment of the present invention. [Figure 15]10 illustrates an example of a process in which a non-AP MLD set up with an NSTR (Non-Simultaneous Transmission and Reception) Soft AP MLD updates information on a non-primary link, according to one embodiment of the present invention. [Figure 16] 10 is a flowchart illustrating an example of a procedure in which a non-AP STA MLD associated with an NSTR AP MLD updates parameters of a non-primary link according to an embodiment of the present invention. [Figure 17] 10 shows an example of an element format according to an embodiment of the present invention. [Figure 18] 10 illustrates an example of a process in which an NSTR AP MLD defines a quiet interval for a non-primary according to an embodiment of the present invention. [Figure 19] 10 illustrates an example of a method for an NSTR AP MLD to perform a non-primary channel switch according to an embodiment of the present invention. [Figure 20] 1 illustrates an example of a method for managing ML (re)setup for channel switching according to an embodiment of the present invention. [Figure 21] 1 illustrates an example of a method for converting a single link operation based on channel switching according to an embodiment of the present invention. [Figure 22] 10 illustrates an example of a method for transitioning to an EMLSR mode based on channel switching according to an embodiment of the present invention. [Figure 23] 1 illustrates an example of a channel switching method according to an embodiment of the present invention. [Figure 24] 10 illustrates an example of a configuration of a beacon frame and a probe response frame for channel switching according to an embodiment of the present invention. [Figure 25] 1 is a flowchart illustrating an example of a channel switching method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0052] FIG. 6 is a diagram showing a Carrier Sense Multiple Access (CSMA) / Collision Avoidance (CA) method used in wireless LAN communication.

[0053] A terminal performing WLAN communication performs carrier sensing to check whether a channel is occupied before transmitting data. If a wireless signal above a certain strength is detected, the channel is determined to be occupied, and the terminal delays access to the channel. This process is called Clear Channel Assessment (CCA), and the level that determines whether or not a signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by a terminal is identified as the receiver, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected from the channel or a wireless signal with strength below the CCA threshold is detected, the channel is determined to be idle.

[0054] If the channel is determined to be idle, each terminal having data to transmit performs a backoff procedure after an Inter Frame Space (IFS), such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS is used as a configuration replacing the conventional DCF IFS (DIFS). Each terminal waits while decrementing a slot time equal to a random number determined for the corresponding terminal during the idle interval of the channel, and a terminal that has exhausted all of its slot time attempts to access the corresponding channel. The period during which each terminal performs the backoff procedure is called a contention window period. In this case, the random number can be called 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 can decrement the backoff counter by 1. If the backoff counter reaches 0, the terminal may be allowed to perform channel access on the corresponding channel. Therefore, if the channel is idle during the AIFS time and the backoff counter slot time, the terminal may be allowed to transmit.

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

[0056] <Examples of various PPDU formats>

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

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

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

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

[0061] The L-SIG field included in the PPDU preamble is configured with a total of 64 subcarriers using 64 FFT OFDM. Of these, 48 subcarriers, excluding guard subcarriers, DC subcarriers, and pilot subcarriers, are used for L-SIG data transmission. BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, so it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of the L-SIG.

[0062] Referring to FIG. 7(d), the L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field is composed of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission rates of 6, 9, 12, 18, 24, 36, 48, or 54 Mbps, which is a combination of a modulation scheme such as BPSK, QPSK, 16-QAM, or 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The combined information in the L_RATE and L_LENGTH fields indicates the total length of the PPDU. In a non-legacy PPDU format, the L_RATE field is set to the minimum rate of 6 Mbps.

[0063] The unit of the L_LENGTH field is byte, and a total of 12 bits are allocated, allowing signaling up to 4095. In combination with the L_RATE field, the length of the PPDU can be indicated. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0064] First, a legacy or non-legacy terminal analyzes the length of the PPDU using the L_LENGTH field as follows. When the L_RATE field is set to 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted at 4 us, which is the duration of one symbol of the 64FFT. Therefore, by adding 3 bytes corresponding to the SVC field and the Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the amount of transmission of one symbol, the number of 64FFT reference symbols after the L-SIG is obtained. The obtained number of symbols is multiplied by 4 us, which is the duration of one symbol, and then 20 us, which is required to transmit the L-STF, L-LTF, and L-SIG, is added to obtain the length of the PPDU, i.e., the reception time (RXTIME). This can be expressed mathematically as shown in Equation 1 below.

[0065]

number

[0066] At this time,

number

[0067]

number

[0068] Here, TXTIME is the total transmission time constituting the PPDU, and is expressed as the following equation 3. In this case, TX represents the transmission time of X.

[0069]

number

[0070] Referring to the above formula, the length of the PPDU is calculated based on the rounded up value of L_LENGTH / 3. Therefore, for any value of k, three different values ​​of L_LENGTH={3k+1, 3k+2, 3(k+1)} indicate the same PPDU length.

[0071] Referring to Figure 7(e), the U-SIG (Universal SIG) field remains in the EHT PPDU and subsequent generation WLAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. The U-SIG is two 64FFT-based OFDM symbols and can transmit a total of 52 bits of information. Of these, 43 bits excluding 9 bits of CRC / tail are roughly divided into a VI (Version Independent) field and a VD (Version Dependent) field.

[0072] The VI bit will maintain its current bit configuration, so even if a subsequent generation PPDU is defined, current 11be UEs can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field consists of the PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits long and serves to sequentially distinguish between 11be and subsequent generations of WLAN standards. 11be has a value of 000b. The UL / DL field identifies whether the PPDU is an uplink or downlink PPDU. The BSS color represents a BSS identifier defined in 11ax and has a value of 6 or more bits. The TXOP represents the transmit opportunity duration (Transmit Opportunity Duration) transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without decoding the MPDU, and has a value of 7 or more bits.

[0073] The VD field, which is signaling information useful only for 11be version PPDUs, may consist of fields commonly used in any PPDU format, such as the PPDU format and BW, as well as fields defined differently for each PPDU format. The PPDU format is a separator that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field broadly signals five basic PPDU BW options: 20, 40, 80, 160 (80 + 80), and 320 (160 + 160) MHz (BWs that can be expressed in the form of a power of 20 * 2 can be called basic BWs), as well as various remaining PPDU BWs formed by preamble puncturing. After signaling at 320 MHz, a portion of 80 MHz may be punctured. In addition, the punctured and modified channel shape may be signaled directly in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (for example, a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signalings are possible, so a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signalings are possible, so a maximum of 11 puncturing modes can be signaled.

[0074] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs may be signaled in the same PPDU format, and a field for distinguishing between MU PPDUs and SU PPDUs may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both SU PPDUs and MU PPDUs include an EHT-SIG field, but some fields not required for the SU PPDU may be compressed. In this case, the information of the compressed fields may be omitted or may have a reduced size compared to the size of the original fields included in the MU PPDU. For example, the SU PPDU may have a different configuration, such as the common fields of the EHT-SIG being omitted or replaced, or the user-specific fields being replaced or reduced to one.

[0075] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (such as the RA field) may be omitted depending on the value of the compression field.

[0076] When a portion of the EHT-SIG field of the SU PPDU is compressed, the information included in the compressed field may be signaled together in an uncompressed field (e.g., a common field). In the case of an MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of information signaled may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether the transmitted MU PPDU was sent to it. Therefore, the AP must transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols in the EHT-SIG field and / or the MCS, which is the modulation method. The EHT-SIG field may include information on the size and location of the RU assigned to each user.

[0077] In the case of an SU PPDU, a STA may be assigned multiple RUs, and the multiple RUs may be contiguous or discontinuous. If the RUs assigned to the STA are not contiguous, the STA can efficiently receive the SU PPDU only by recognizing punctured RUs in between. Therefore, the AP can transmit the SU PPDU including information on punctured RUs among the RUs assigned to the STA (e.g., puncturing pattern of the RUs). That is, in the case of an SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and the puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field can signal the type of discontinuous channels appearing within the bandwidth.

[0078] The type of signaled discontinuous channel is limited, and indicates the BW and discontinuous channel information of the SU PPDU in combination with the value of the BW field. For example, since the SU PPDU is a PPDU transmitted only to a single UE, the STA can recognize its allocated bandwidth from the BW field included in the PPDU and can recognize punctured resources within the allocated bandwidth from the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the UE can receive the PPDU in the remaining resource units other than the specific channel of the punctured resource units. In this case, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0079] The reason why only limited discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed for each 20 MHz subchannel, if puncturing is performed on a BW having multiple 20 MHz subchannels, such as 80, 160, or 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered discontinuous) must be signaled by expressing whether or not the remaining 15 20 MHz subchannels other than the primary channel are in use. Using 15 bits to signal the discontinuous channel type for single-user transmission can result in excessive signaling overhead when considering the low transmission rate of the signaling part.

[0080] This invention proposes a method for signaling the discontinuous channel type of the SU PPDU, illustrates the discontinuous channel type determined by the proposed method, and proposes a method for signaling the primary 160 MHz and secondary 160 MHz puncturing types in the 320 MHz BW configuration of the SU PPDU.

[0081] In addition, one embodiment of the present invention proposes a method of varying the PPDU configuration indicated by the preamble puncturing BW value depending on the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, an EHT-SIG-A symbol can be further signaled after the U-SIG, or no EHT-SIG-A can be signaled at all. Taking this into consideration, up to 11 puncturing modes must be fully signaled using only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B symbol is further signaled after the U-SIG, so up to 11 puncturing modes can be signaled in a different manner than in the case of an SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz bandwidth. Detailed puncturing patterns for each PPDU type will be described in detail below with reference to FIGS. 11 and 12.

[0082] Figure 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. For an MU PPDU, SIG-B, a signaling field for simultaneous reception by multiple users, is required. SIG-B may be transmitted after the U-SIG without a separate SIG-A. For this purpose, the U-SIG must signal information for decoding SIG-B. These fields include the SIG-B MCS, SIG-B DCM, number of SIG-B symbols, SIG-B compression, and number of EHT-LTF symbols.

[0083] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention.

[0084] 8, a PPDU may be configured with a preamble and a data portion, and the format of one type, EHT PPDU, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

[0085] 8(a) shows an example of an EHT SU PPDU format for a single STA. The EHT SU PPDU is a PPDU used for single user (SU) transmission between an AP and a single STA, and an EHT-SIG-A field for additional signaling may be located after the U-SIG field.

[0086] 8(b) shows an example of an EHT trigger-based PPDU format, which is an EHT PPDU transmitted based on a trigger frame. The EHT trigger-based PPDU is an EHT PPDU transmitted based on a trigger frame and is an uplink PPDU used for responding to the trigger frame. Unlike the EHT SU PPDU, the EHT PPDU does not have an EHT-SIG-A field after the U-SIG field.

[0087] 8(c) shows an example of an EHT MU PPDU format, which is an EHT PPDU for multiple users. The EHT MU PPDU is a PPDU used to transmit a PPDU to one or more STAs. In the EHT MU PPDU format, an HE-SIG-B field may be located after the U-SIG field.

[0088] 8(d) shows an example of an EHT ER SU PPDU format used for single-user transmission with STAs in an extended range. The EHT ER SU PPDU may be used for single-user transmission with STAs in a wider range than the EHT SU PPDU described in FIG. 8(a), and the U-SIG field may be repeated on the time axis.

[0089] The EHT MU PPDU described in (c) of Figure 8 can be used by the AP for downlink transmission to multiple STAs. In this case, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive the PPDU transmitted from the AP. The EHT MU PPDU can convey AID information of the receiver and / or sender of the transmitted PPDU to the STA through the user specific field of the EHT-SIG-B. Therefore, multiple terminals receiving the EHT MU PPDU can perform spatial reuse based on the AID information of the user specific field included in the preamble of the received PPDU.

[0090] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information regarding the configuration of resource units (e.g., the division type of resource units) in a specific bandwidth (e.g., 20 MHz) on the frequency axis. That is, the RA field may indicate the configuration of resource units divided by the bandwidth for transmitting the HE MU PPDU so that the STA can receive the PPDU. Information about the STA allocated (or designated) to each divided resource unit may be included in a user specific field of the EHT-SIG-B and transmitted to the STA. That is, the user specific field may include one or more user fields corresponding to each divided resource unit.

[0091] For example, among the multiple divided resource units, the user field corresponding to at least one resource unit used for data transmission may include the AID of the receiver or sender, and the user field corresponding to the remaining resource units not used for data transmission may include a previously set null STA ID.

[0092] For ease of explanation, the term frame or MAC frame may be used interchangeably with MPDU in this specification.

[0093] When a single wireless communication device communicates using multiple links, the communication efficiency of the wireless communication device can be improved. In this case, a link is a physical path and may be configured as a single wireless medium that can be used to transmit an MSDU (MAC service data unit). For example, when the frequency band of one link is being used by another wireless communication device, the wireless communication device can continue communication using another link. In this way, the wireless communication device can effectively use multiple channels. Furthermore, when a wireless communication device simultaneously communicates using multiple links, the overall throughput can be improved. However, existing wireless LANs are specified on the assumption that one wireless communication device uses one link. Therefore, a wireless LAN operation method for using multiple links is needed. A wireless communication method for a wireless communication device using multiple links will be described with reference to FIGS. 9 to 26. First, a specific embodiment of a wireless communication device using multiple links will be described with reference to FIG. 9.

[0094] FIG. 9 shows a multi-link device according to an embodiment of the present invention.

[0095] A multi-link device (MLD) may be defined for the wireless communication method using multiple links described above. The multi-link device may represent a device having one or more affiliated stations. Depending on a specific embodiment, the multi-link device may represent a device having two or more affiliated stations. The multi-link device may also exchange multi-link elements. The multi-link element includes information about one or more stations or one or more links. The multi-link element may include a multi-link setup element, which will be described later. In this case, the multi-link device may be a logical entity. Specifically, the multi-link device may have multiple affiliated stations. The multi-link device may be referred to as a multi-link logical entity (MLLE) or a multi-link entity (MLE). The multi-link device may have one medium access control service access point (SAP) up to a logical link control (LLC). The MLD may also have one MAC data service.

[0096] Multiple stations included in a multilink device can operate on multiple links. Also, multiple stations included in a multilink device can operate on multiple channels. Specifically, multiple stations included in a multilink device can operate on different links or different channels. For example, multiple stations included in a multilink device can operate on different channels, such as 2.4 GHz, 5 GHz, and 6 GHz.

[0097] The operation of the multilink device can be referred to as multilink operation, MLD operation, or multi-band operation. If the station associated with the multilink device is an AP, the multilink device can be referred to as AP MLD. If the station associated with the multilink device is a non-AP station, the multilink device can be referred to as non-AP MLD.

[0098] FIG. 9 shows the operation of communication between non-AP MLD and AP-MLD. Specifically, non-AP MLD and AP-MLD each communicate using three links. AP MLD includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). Non-AP MLD includes a first non-AP STA (non-AP STA1), a second non-AP STA (non-AP STA2), and a third non-AP STA (non-AP STA3). The first AP (AP1) and the first non-AP STA (non-AP STA1) communicate via a first link (Link1). The second AP (AP2) and the second non-AP STA (non-AP STA2) communicate via a second link (Link2). The third AP (AP3) and the third non-AP STA (non-AP STA3) communicate via a third link (Link3).

[0099] Multilink operation may include a multilink setup operation. Multilink setup corresponds to the association operation of the single-link operation described above and must be performed prior to frame exchange in the multilink. A multilink device can obtain information required for multilink setup from a multi-link setup element. Specifically, the multi-link setup element may include capability information related to the multilink. In this case, the capability information may include information indicating whether one of multiple devices included in the multilink device can transmit and the other devices can receive at the same time. The capability information may also include information about links available to each station included in the MLD. The capability information may also include information about channels available to each station included in the MLD.

[0100] Multilink configuration may be established through negotiation between peer stations. Specifically, multilink configuration may be established through communication between stations without communication with an AP. Multilink configuration may also be established through any one of the links. For example, even if the first to third links are established through multilink, multilink configuration may be established through the first link.

[0101] In addition, a mapping between a traffic identifier (TID) and a link may be configured. Specifically, frames corresponding to a specific TID value may be exchanged only through a pre-specified link. The mapping between a TID and a link may be configured on a directional basis. For example, when multiple links are configured between a first multilink device and a second multilink device, the first multilink device may be configured to transmit frames of the first TID to the multiple first links, and the second multilink device may be configured to transmit frames of the second TID to the first link. In addition, a default setting may exist for the mapping between TIDs and links. Specifically, if no additional settings are configured in the multilink configuration, the multilink device may exchange frames corresponding to TIDs on each link according to a default setting. In this case, the default setting may be that all TIDs are exchanged on any one link.

[0102] The TID will be described in detail. The TID is an ID for classifying traffic and data to support quality of service (QoS). The TID may be used and assigned in a layer higher than the MAC layer. The TID may indicate a traffic category (TC) or a traffic stream (TS). There may be 16 distinct TIDs. For example, the TID may be designated as any one of 0 to 15. Different TID values ​​may be designated depending on an access policy, a channel access method, or a medium access method. For example, when enhanced distributed channel access (EDCA) or hybrid coordination function contention-based channel access (HCAF) is used, the TID may be assigned a value ranging from 0 to 7. When EDCA is used, the TID may indicate a user priority (UP). In this case, the UP may be designated by the TC or the TS. The UP may be assigned in a layer higher than the MAC. Furthermore, when HCCA (HCF controlled channel access) or SPCA is used, the TID may be assigned a value in the range of 8 to 15. When HCCA or SPCA is used, the TID may indicate a TSID. Furthermore, when HEMM or SEMM is used, the TID may be assigned a value in the range of 8 to 15. When HEMM or SEMM is used, the TID may indicate a TSID.

[0103] UP and AC (access category) may be mapped. AC may be a label for providing QoS in EDCA. AC may be a label for indicating an EDCA parameter set. EDCA parameters or EDCA parameter sets are parameters used in EDCA channel contention. QoS stations can guarantee QoS using AC. AC may include AC_BK, AC_BE, AC_VI, and AC_VO. AC_BK, AC_BE, AC_VI, and AC_VO may indicate background, best effort, video, and voice, respectively. AC_BK, AC_BE, AC_VI, and AC_VO may be classified into lower-level ACs. For example, AC_VI may be further subdivided into AC_VI primary and AC_VI alternate. AC_VO may be further subdivided into AC_VO primary and AC_VO alternate. UP or TID may be mapped to an AC. For example, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI, AC_VI, AC_VO, and AC_VO, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI alternate, AC_VI primary, AC_VO primary, and AC_VO alternate, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may have decreasing priority in that order. That is, 1 may have a lower priority, and 7 may have a higher priority. Therefore, the order of priority may be AC_BK, AC_BE, AC_VI, and AC_VO. Also, AC_BK, AC_BE, AC_VI, and AC_VO can correspond to ACI (AC index) 0, 1, 2, and 3, respectively. Due to the characteristics of TID, the mapping between TID and link can represent the mapping between AC and link.The mapping between links and ACs can also represent the mapping between TIDs and links.

[0104] As described above, a TID may be mapped to each of multiple links. The mapping may specify the links through which traffic corresponding to a specific TID or AC can be exchanged. Furthermore, the TID or AC that can be transmitted for each transmission direction within a link may be specified. As described above, a default setting may exist for the mapping between TIDs and links. Specifically, if no additional settings are configured in the multilink configuration, the multilink device may exchange frames corresponding to the TID on each link according to the default setting. In this case, the default setting may be that all TIDs are exchanged on any one link. At any given time, any TID or AC may be mapped to at least one link. Management frames and control frames may be transmitted on all links.

[0105] When a link is mapped to a TID or AC, only data frames corresponding to the TID or AC mapped to the link may be transmitted on the link. Therefore, when a link is mapped to a TID or AC, frames not corresponding to a TID or AC not mapped to the link may not be transmitted on the link. When a link is mapped to a TID or AC, an ACK may also be transmitted based on the link to which the TID or AC is mapped. For example, a Block ACK agreement may be determined based on the mapping between the TID and the link. In yet another specific embodiment, the mapping between the TID and the link may be determined based on the Block ACK agreement. Specifically, a Block ACK agreement may be set for a TID mapped to a specific link.

[0106] The above-described TID-to-link mapping may ensure QoS. Specifically, a high-priority AC or TID may be mapped to a link where a relatively small number of stations are active or where channel conditions are good. The above-described TID-to-link mapping may also allow stations to remain in a power-saving state for a longer period of time.

[0107] FIG. 10 illustrates simultaneous transmission of different links in multi-link operation according to an embodiment of the present invention.

[0108] Depending on the implementation of the multi-link device, simultaneous operation of the multi-links may not be supported. For example, a multi-link device may support simultaneous transmission on multiple links, simultaneous reception on multiple links, or transmission on one link while receiving on another link. Reception or transmission on one link may affect reception or transmission on another link. Specifically, transmission on one link may interfere with other links. Interference from one link of a multi-link device affecting other links may be called internal leakage. The smaller the frequency spacing between links, the greater the internal leakage. If the internal leakage is not too large, transmission on one link can occur when transmission on another link. If the internal leakage is large, transmission on one link cannot occur when transmission on another link. This simultaneous operation of the multi-link device on multiple links may be called STR (simultaneous transmit and receive, simultaneous transmission and reception). For example, a multilink device transmitting on multiple links simultaneously, transmitting on one link while receiving on another link, or receiving on multiple links simultaneously can be referred to as STR.

[0109] On the other hand, if STR is not supported due to interference between multiple stations that make up the MLD, the STAs may be said to have a non-STR relationship or an NSTR relationship (a relationship in which STR is not supported).

[0110] In this case, whether two STAs (STA1 or STA2) in the MLD support STR may depend on the distance between the link pair on which the STAs operate (Link1 on which STA1 operates and Link2 on which STA2 operates).

[0111] Therefore, when an MLD operates STAs on a specific link pair, if STR is supported between the two STAs operated on the specific link pair, the specific link pair may be considered as an STR link pair by the MLD. On the other hand, when an MLD operates STAs on different link pairs, if STR is not supported between the two STAs operated on the different link pairs, the different link pairs may be considered as an NSTR link pair by the MLD.

[0112] Whether STR is supported between STAs of an MLD is determined by whether the link pair on which these STAs operate is an STR link pair or an NSTR link pair. However, as described above, since the characteristics (such as shielding performance) of each MLD may differ from one another, a specific link pair may be considered to be a link pair in which STR is supported for a specific MLD and an NSTR link pair in which STR is not supported for other MLDs.

[0113] In one embodiment of the present invention described later, for convenience of explanation, the STAs operated in the STR link pair of the MLD are named (explicitly) as STAs of the STR MLD, and the STAs operated in the NSTR link pair of the MLD are named (explicitly) as STAs of the NSTR (and non-STR) MLD. That is, in the embodiment described later, when "STAs of the non-STR MLD" is used, it can be interpreted as referring to either one of the two STAs operated in the NSTR link pair of the MLD, and when "STAs of the STR MLD" is used, it can be interpreted as referring to either one of the two STAs operated in the STR link pair of the MLD.

[0114] In addition, NSTR MLD may refer to an MLD in which the STA of a specific MLD loses its receiving capability in relation to the presence or absence of STR support as described above, as well as an MLD in which the hardware configuration of the MLD itself does not support simultaneous transmission / reception.

[0115] In other words, the hardware configuration of a multi-link device (MLD) may be configured to limit the hardware resources available to other STAs in the MLD when a specific STA in the MLD is transmitting or receiving. For example, if a specific MLD has a hardware configuration that supports processing only one PPDU, when a specific STA in the specific MLD is performing Rx, the specific MLD cannot support Tx and Rx for other STAs in the MLD. Similarly, when a specific STA in the specific MLD is performing Tx, the specific MLD cannot support Tx and Rx for other STAs in the MLD.

[0116] Such a multi-link device, which can operate STAs on two or more links but can support transmission / reception for only one STA at a time, can be called a multi-link single radio MLD (MLSR MLD). Alternatively, an MLD operating mode that supports transmission / reception for only one STA can be called an enhanced multi-link single radio (EMLSR) mode. In this case, an MLD operating in EMLSR mode can be a multi-radio MLD or an enhanced single-radio MLD. An enhanced single-radio MLD supports data transmission / reception for only one link at a time, but can refer to a device that supports CCA and low-data-rate (e.g., encoded at 6 MHz or 24 MHz or less) PPDU transmission / reception for two or more links by including additional hardware (such as an inexpensive PHY front end).

[0117] In addition, as a variation of the EMLSR mode, Enhanced Multi-Link Multi-Radio (EMLMR) may be defined in which the MLD supports transmission / reception for each STA, but utilizes part of the RF chain used by a specific STA for transmission / reception for other STAs. In the case of EMLMR, if all of the RF chains used by the specific STA are utilized for transmission / reception for the other STAs, it may have the same transmission / reception restriction characteristics as EMLSR. In other words, an MLD operating in EMLMR mode can operate to support transmission / reception for only one link (STA) at a specific time, regardless of whether STR is supported for the link, and this may be understood as an operation similar to that of an MLD operating in the EMLSR mode.

[0118] That is, the link of an MLD operated in EMLSR / EMLMR mode may be considered to be an NSTR link pair.

[0119] At this time, the above-mentioned transmission / reception includes transmission / transmission and reception / reception, that is, it is not related to whether or not the two links support STR / NSTR.

[0120] For ease of explanation, hereinafter, EMLSR / EMLMR MLD is used to include an MLD that can only support transmission / reception for one STA at a specific time due to hardware constraints, and an MLD that can support transmission / reception for two or more STAs (processing capability unrelated to STR) but only supports high-speed data frame transmission / reception for one STA at a specific time as a type of operating mode.

[0121] The STR MLD operation taking into account the performance limitations of the NSTR MLD provided by the above-described embodiment of the present invention can be directly utilized as the STR MLD operation for the MLSR MLD. For example, after a STR MLD STA transmits to an MLSR MLD STA, if the STA determines that the transmission has failed or is predicted to fail due to the limited performance of the MLSR MLD STA, the STA can cancel the transmission that is currently being performed or is about to be performed. In this case, the procedure for determining whether the transmission has failed due to the limited performance of the EMLSR / EMLMR MLD may be similar to the procedure for determining whether a transmission to an NSTR MLD STA has failed due to the limited performance of the NSTR MLD STA.

[0122] As described above, a multilink device can support STR or can support it in a limited manner. Specifically, a multilink device can support STR only under certain conditions. For example, if the multilink device operates with a single radio, the multilink device may not be able to perform STR. Also, if the multilink device operates with a single antenna, the multilink device may not be able to perform STR. Also, if internal leakage is detected to be greater than a predetermined level, the multilink device may not be able to perform STR.

[0123] A station may exchange information regarding its STR capability with other stations. Specifically, a station may exchange information regarding whether or not the station has limitations on its ability to simultaneously transmit on multiple links or simultaneously receive on multiple links with other stations. Specifically, the information regarding whether or not the station has limitations on its ability to transmit or receive on multiple links may indicate whether or not the station can simultaneously transmit, receive, or transmit and receive on multiple links. Furthermore, the information regarding whether or not the station has limitations on its ability to transmit or receive on multiple links may be information indicated in stages. Specifically, the information regarding whether or not the station has limitations on its ability to transmit or receive on multiple links may be information indicating a stage indicating the magnitude of internal leakage. In a specific embodiment, the information indicating a stage indicating the magnitude of internal leakage may be information indicating a stage indicating the magnitude of interference caused by internal leakage. In yet another specific embodiment, the information indicating a stage indicating a frequency spacing between links that may affect internal leakage may be information indicating a stage indicating the relationship between the frequency spacing between links and the magnitude of internal leakage.

[0124] In FIG. 10, a first station (STA1) and a second station (STA2) are affiliated with one non-AP multilink device. A first AP (AP1) and a second AP (AP2) may also be affiliated with one non-AP multilink device. A first link (link1) is established between the first AP (AP1) and the first station (STA1), and a second link (link2) is established between the second AP (AP2) and the second station (STA2). In FIG. 10, the non-AP multilink device can perform limited STR. When the second station (STA2) transmits on the second link (link2), the first station (STA1)'s reception on the first link (link1) may be interfered with by the transmission on the second link (link2). For example, in the following case, the first station (STA1)'s reception on the first link (link1) may be interfered with by the transmission on the second link (link2). The second station (STA2) transmits the first data (Data1) over the second link (Link2), and the first AP (AP1) transmits a response (Ack for Data1) to the first station (STA1). The second station (STA2) transmits the second data (Data2) over the second link (Link2). At this time, the transmission of the second data (Data2) and the transmission of the response (Ack for Data1) to the first data (Data1) may overlap. In this case, the transmission to the second station (STA2) over the second link (Link2) may cause interference to the first link (Link1). As a result, the first station (STA1) may not receive the response (Ack for Data1) to the first data (Data1).

[0125] The operation of the multilink device for channel access will now be described. For multilink operations not specifically described, the channel access procedure explained in FIG.

[0126] A multilink device can perform channel access independently on multiple links. In this case, the channel access may be backoff-based channel access. When a multilink device performs channel access independently on multiple links and the backoff counters for the multiple links reach zero, the multilink device can start transmission simultaneously on the multiple links. In a specific embodiment, when one of the backoff counters for the multiple links reaches zero and a predetermined condition is met, the multilink device can perform channel access on the link whose backoff counter has reached zero as well as on other links whose backoff counters have not reached zero. Specifically, when one of the backoff counters for the multiple links reaches zero, the multilink device can perform energy sensing on other links whose backoff counters have not reached zero. In this case, if energy greater than or equal to a predetermined value is not detected, the multilink device can perform channel access on the link whose backoff counter has reached zero as well as on the link on which energy sensing has been performed. This allows the multilink device to start transmission simultaneously on multiple links. The threshold used for energy sensing may be smaller than the threshold used to determine whether to decrease the backoff counter. Furthermore, when determining whether to decrement the backoff counter, the multilink device can sense any type of signal, not just a WLAN signal. Furthermore, in the energy sensing described above, the multilink device can sense any type of signal, not just a WLAN signal. Internal outflow may not be detected as a WLAN signal. In such a case, the multilink device can sense the signal detected by the internal outflow through energy sensing. Furthermore, as described above, the threshold used for energy sensing may be smaller than the threshold used when determining whether to decrement the backoff counter. Therefore, even while transmission is occurring on one link, the multilink device can decrement the backoff counter on another link.

[0127] Depending on the degree of interference between links used by the multilink device, the multilink device may determine whether stations operating on each link can operate independently. In this case, the degree of interference between links may be the magnitude of interference perceived by other stations in the multilink device when one station in the multilink device transmits on one of the links. If transmission on the first link of a first station in the multilink device causes interference of a predetermined magnitude or greater to a second station in the multilink device operating on the second link, the operation of the second station may be restricted. Specifically, the reception or channel access of the second station may be restricted. If interference occurs, the second station may fail to decode a received signal due to the interference. Furthermore, if interference occurs, the second station may determine that the channel is in use when accessing the channel using backoff.

[0128] Furthermore, if the transmission of a first station in a multilink device through the first link causes interference to a second station in the multilink device operating through the second link less than a predetermined level, the first station and the second station can operate independently. Specifically, if the transmission of a first station in a multilink device through the first link causes interference to a second station in the multilink device operating through the second link less than a predetermined level, the first station and the second station can independently access the channel. Also, if the transmission of a first station in a multilink device through the first link causes interference to a second station in the multilink device operating through the second link less than a predetermined level, the first station and the second station can independently transmit or receive. If interference occurs less than a predetermined level, the second station can successfully decode the received signal even in the presence of interference. If interference occurs less than a predetermined level, the second station can determine that the channel is idle when accessing the channel using backoff.

[0129] The degree of interference occurring between stations of a multilink device may vary depending on the interval between the frequency bands of the links on which the stations operate as well as the hardware characteristics of the multilink device. For example, the internal interference occurring in a multilink device including expensive radio frequency (RF) equipment may be smaller than the internal interference occurring in a multilink device including inexpensive RF equipment. Therefore, the degree of interference occurring between stations of a multilink device may be determined based on the characteristics of the multilink device.

[0130] FIG. 10 shows that the magnitude of interference varies depending on the spacing between link frequency bands and the characteristics of the multilink devices. In the example of FIG. 10, a first multilink device (MLD#1) includes a first station (STA1-1) operating on a first link (Link1) and a second station (STA1-2) operating on a second link (Link2). A second multilink device (MLD#2) includes a first station (STA2-1) operating on a first link (Link1) and a second station (STA2-2) operating on a second link (Link2). The frequency spacing between the first link (Link1) and the second link (Link2) on which the first multilink device (MLD#1) operates is the same as the frequency spacing between the first link (Link1) and the second link (Link2) on which the second multilink device (MLD#2) operates. However, the magnitude of interference varies depending on the difference in characteristics between the first multilink device (MLD#1) and the second multilink device (MLD#2). Specifically, the magnitude of interference generated in the second multilink device (MLD#2) may be greater than the magnitude of interference generated in the first multilink device (MLD#1). Considering that the magnitude of interference generated may differ depending on the characteristics of the multilink devices and that the presence or absence of STR support may differ depending on the multilink device, information regarding the presence or absence of STR support needs to be exchanged.

[0131] A multilink device can signal whether or not a station included in the multilink device supports STR. Specifically, an AP multilink device and a non-AP multilink device can exchange whether or not an AP included in the AP multilink device supports STR with whether or not a STA included in the non-AP multilink device supports STR. In this embodiment, an element indicating whether or not STR is supported can be used. The element indicating whether or not STR is supported can be called an STR support element. The STR support element can indicate whether or not a station in the multilink device that transmitted the STR support element supports STR using one bit. Specifically, the STR support element can indicate whether or not each station included in the multilink device that transmitted the STR support element supports STR, one bit at a time. In this case, if a station supports STR, the bit value can be 1, and if a station does not support STR, the bit value can be 0. If the multilink device that transmitted the STR support element includes a first station (STA1), a second station (STA2), and a third station (STA3), and the first station (STA1) and the third station (STA3) support STR, but the second station (STA2) does not support STR, the STR support element is 101. 1bThe STR support element may include a field having the following information: Stations operating in different frequency bands are assumed to support STR, and the STR support element may omit signaling whether or not STR is supported between stations operating in different frequency bands. For example, a first station (STA1) operates on a first link of 2.4 GHz, and a second station (STA2) and a third station (STA3) operate on a second link of 5 GHz and a third link of 5 GHz, respectively. In this case, the STR support element may use one bit to indicate that STR is supported between the second station (STA2) and the third station (STA3). Alternatively, the STR support element may include only one bit if the STR support element signals two stations.

[0132] In a specific embodiment, the relationship between a link located at 2.4 GHz and a link located at 5 GHz or 6 GHz among the links of a multi-link device may always be determined as STR, and therefore, signaling regarding whether STR is supported for the link located at 2.4 GHz and the link located at 5 GHz or 6 GHz may be omitted.

[0133] In the above-described embodiments, the operation of a station in a multilink device may be replaced by the operation of the multilink device. Also, in the above-described embodiments, the operation of an AP may be replaced by the operation of a non-AP station, and the operation of a non-AP station may be replaced by the operation of an AP. Thus, the operation of an AP in a non-STR multilink device may be replaced by the operation of a non-AP station in a non-STR multilink device, and the operation of a non-AP station in an STR multilink device may be replaced by the operation of an AP in the STR multilink device. Also, the operation of a non-AP station in a non-STR multilink device may be replaced by the operation of an AP in a non-STR multilink device, and the operation of an AP in an STR multilink device may be replaced by the operation of a non-AP station in the STR multilink device.

[0134] Each AP included in the AP MLD can transmit a beacon frame on its own link. APs included in the AP MLD can transmit beacon frames for the same purposes and functions as APs in conventional Wi-Fi, and may also include in the beacon frame information indicating that the AP is included in the MLD, MLD level information (common information), and basic information of other APs included in the same MLD. In this case, the basic information of other APs may be included in the TBTT information field of the RNR element and transmitted in the beacon frame.

[0135] Beacon frames transmitted by AP MLD may contain only common information per MLD to prevent the size of the beacon frame from becoming excessively large (beacon bloating) due to information for multiple APs included in the same MLD being included in one beacon frame.

[0136] However, in the case of the NSTR Soft AP MLD, beacon frames can be transmitted through only some of the APs it operates. For example, if the NSTR soft AP MLD operates APs on two different links and the two links have an NSTR relationship with each other, the NSTR Soft AP MLD can transmit beacon frames through only one of the two links. In this case, the link through which the NSTR Soft AP MLD transmits beacon frames may be considered as the primary link of the NSTR link pair of the NSTR Soft AP MLD. Meanwhile, the NSTR Soft AP MLD may operate links other than the primary link of the NSTR link pair as secondary links, and the secondary link may be a link through which beacon frames are not transmitted. The reason why the NSTR Soft AP MLD operates one link of the NSTR link pair as the primary link and at least one other link as the secondary link may be to prevent problems that may occur when two different APs operate independently as an NSTR link pair. Problems that may occur in an AP MLD operating an NSTR link pair will be described in more detail below along with operational restriction examples applied to the NSTR Soft AP MLD and the STA MLD associated with the NSTR Soft AP MLD. That is, in a link pair to which NSTR is applied, beacon frames may be transmitted only on the primary link, and beacon frames may not be transmitted on the secondary link.

[0137] As described above, since the NSTR soft AP MLD has a restriction that beacon frames are transmitted only on the primary link, the NSTR soft AP MLD may be allowed to include more information (for APs of other links (non-primary)) in the beacon frames transmitted on the primary link compared to a general AP MLD. This may be a beacon frame configuration method devised to enable a non-AP MLD that operates STAs on the secondary link to operate STAs on the secondary link based on information in a beacon frame received on the primary link.

[0138] For example, the primary link AP of the NSTR Soft AP MLD may include a per-STA profile corresponding to the secondary link AP (of the same NSTR Soft AP MLD) in the Multi-Link element of the beacon frame. In this case, when the primary link AP of the NSTR Soft AP MLD includes a per-STA profile corresponding to the secondary link AP, there is no need for a separate constraint. The constraint means a condition under which a general AP MLD can include a per-STA profile in a beacon frame (such as an AP corresponding to a per-STA profile performing (extended) channel switching or channel quieting).

[0139] FIG. 11 shows an example of the contents of a beacon frame transmitted by an AP in AP MLD according to one embodiment of the present invention and an example of a TBTT (target beacon transmission time) information field format included in an RNR (Reduced Neighbor Report) element.

[0140] Referring to (a) of Figure 11, the beacon frame may include the same parameters and elements in legacy IEs as those included in the beacon frame disclosed in conventional Wi-Fi 802.11ax. For example, the legacy IEs of the beacon frame may include elements such as a timestamp field, a beacon interval field indicating the interval at which beacons are transmitted, TIM, DSSS parameter set, IBSS parameter set, country, channel switch announcement, extended channel switch announcement, wide bandwidth channel switch, transmit power envelope, supported operating classes, IBSS DFS, ERP information, HT capabilities, HT operation, VHT capability, VHT operation, S1G beacon compatibility, short beacon interval, S1G capability, S1G operation, HE capability, HE 6GHz band capability, HE operation, BSS color change announcement, and spatial reuse parameter set.

[0141] In this case, the setting method and meaning of the fields and elements included in the legacy IEs field are the same as the setting and meaning of the fields and elements of the same names included in the beacon frame disclosed up to conventional Wi-Fi 802.11ax.

[0142] The beacon frame may also include a Reduced Neighbor Report (RNR) element for indicating information about neighbor APs. The RNR element may be used to inform a station of information about neighbor APs, and the station may receive the beacon frame and recognize the neighbor APs based on the RNR element included in the beacon frame.

[0143] Specifically, the RNR element may include an element ID field, a length field, and a neighbor AP information field. Each neighbor AP information field may include a TBTT information header (2 octets), an operation class (1 octet), a channel number (1 octet), and a TBTT information set (variable length) field. In this case, the RNR element transmitted by the AP included in the AP MLD may include a TBTT information field format as shown in (b) of FIG. 11 to indicate basic information for other APs included in the same MLD. Unlike the TBTT information field of the RNR element transmitted by the AP in conventional Wi-Fi 802.11ax, the RNR element transmitted by the AP included in the EHT AP MLD may include an MLD parameter field.

[0144] The MLD parameter field may include an MLD ID, a link ID, and a Change Sequence subfield, as shown in (c) of Figure 11. In this case, when an AP MLD indicates information about another AP in the same MLD through a specific Neighbor AP Information field in an RNR element, the MLD ID subfield included in the specific Neighbor AP Information field can be set to 0. That is, the AP can set the MLD ID subfield to a specific value to inform a station that the Neighbor AP Information field is an AP included in the same AP MLD, and a station receiving the Neighbor AP Information field can recognize from the value of the MLD ID subfield that the AP corresponding to the Neighbor AP Information field is included in the same MLD as the AP that transmitted the Neighbor AP Information field.

[0145] The Link ID subfield may be a subfield indicating an index determined by the AP MLD to indicate a link operated by another AP to be indicated using neighbor AP information. The Change Sequence subfield may be a subfield used to indicate information related to an update (e.g., a Critical Update) related to the link of another AP. For example, if the value of the Change Sequence subfield is changed, a station receiving this can recognize that parameters related to the link of the corresponding AP have been updated and can request the updated parameters from the AP to update the corresponding parameters. In this case, if the AP MLD is an NSTR AP MLD, which is an MLD that does not support simultaneous transmission and reception (e.g., if the AP MLD is an NSTR mobile AP MLD or an NSTR soft AP MLD, i.e., if a mobile terminal operates as a soft AP MLD for tethering), the STA included in the STA MLD can perform a procedure to update parameters only on the primary link. That is, in order to update parameters of other links (e.g., non-primary links) to other neighbor APs other than the primary link of the AP MLD, frames for parameter update can be transmitted and received only via the primary link.

[0146] Hereinafter, in the present invention, the NSTR AP MLD can be referred to as an NSTR soft AP MLD or an NSTR mobile AP MLD.

[0147] Furthermore, if the AP is an NSTR AP MLD that does not support simultaneous transmission and reception (e.g., an NSTR mobile AP MLD or an NSTR soft AP MLD, i.e., a mobile terminal or the like operates as a soft AP MLD for tethering, etc.), the NSTR AP MLD can transmit a beacon frame including information indicating that it is an NSTR AP MLD. For example, the NSTR AP MLD can set the value of a specific subfield included in the beacon frame to a specific value (e.g., '0' or '1'), and a non-AP STA MLD that receives the beacon frame can recognize that the AP MLD that transmitted the beacon frame is the NSTR AP MLD. Therefore, the specific subfield for indicating an NSTR AP MLD may be set to a value different from the specific value (e.g., '1' or '0') when not indicating an NSTR AP MLD (e.g., an STR AP MLD or another AP MLD, etc.).

[0148] A specific subfield for indicating NSTR AP MLD may be indicated together with a capability-related subfield (e.g., MLD level capability) in a beacon frame, or may be included in and transmitted in a neighbor AP information field associated with an AP of a non-primary link of the NSTR AP MLD. For example, a specific subfield for indicating NSTR AP MLD may be encoded and indicated together with a frequency separation for STR / AP MLD type indicator, which is a capability-related subfield. That is, the specific subfield may be encoded together with a frequency separation for STA / AP MLD type indicator indicating the distance for supporting STR, and indicated in a beacon frame. In this case, if the corresponding indicator indicates the type of AP MLD, a set value may indicate whether the AP MLD that transmitted the beacon frame is NSTR AP MLD or not (e.g., a value of '0' indicates not NSTR AP MLD, and a value of '1' indicates NSTR AP MLD).

[0149] The method of utilizing the subfield indicating whether or not the AP MLD is an NSTR AP MLD may be a method of explicitly indicating whether or not the AP MLD is an NSTR AP MLD.

[0150] As another example, the NSTR AP MLD may indicate that it is an NSTR AP MLD in an implicit manner rather than directly indicating that it is an NSTR AP MLD using a specific subfield. Specifically, the NSTR AP MLD may indicate that it is an NSTR AP MLD by indicating that it has two supportable links and at the same time indicating that it has an NSTR link pair. In this case, the NSTR AP MLD may set the Maximum Number Of Simultaneous Links subfield included in the beacon frame to 1 (or a predetermined value meaning 2) to indicate that it has two supportable links. In this case, the NSTR AP MLD may set the NSTR Link Pair Present subfield included in the beacon frame to 1 or 0 to indicate that it has an NSTR link pair.

[0151] The AP MLD can explicitly or implicitly inform the non-AP STA MLD that it is the NSTR AP MLD by transmitting a beacon frame according to the above-described method. The non-AP STA MLD can implicitly or explicitly determine from the received beacon frame whether the AP MLD that transmitted the beacon frame is the NSTR AP MLD. If the AP MLD that transmitted the beacon frame is the NSTR AP MLD (i.e., if the beacon frame indicates that the AP MLD is the NSTR AP MLD by an explicit or implicit method), the non-AP STA MLD can perform the procedure for association or setup with the NSTR AP MLD only on the link on which the beacon frame was received. In other words, the non-AP STA MLD can send and receive frames for association or setup with the NSTR AP MLD on the link on which the beacon frame was received (e.g., the primary link). For example, frames for association or configuration with an AP connected via a link other than the primary link included in the NSTR AP MLD may be transmitted only via the primary link. In this case, the (ML)(Re) association request frame transmitted by the Non-AP STA MLD may be transmitted via a link other than the primary link (non-primary link).

[0152] In this case, the NSTR AP MLD may not indicate information about the AP of the non-primary link in the RNR element of the beacon frame (transmitted on the primary link) to prevent the non-AP STA MLD from attempting a setup procedure on the non-primary link. That is, the beacon frame transmitted by the AP of the NSTR AP MLD may not include / indicate a neighbor AP information field for the AP of another link (in the same MLD). In this case, the non-AP STA MLD does not attempt to set up the NSTR AP MLD on the non-primary link after receiving the beacon frame because it cannot confirm information about the AP of the non-primary link. In this case, a non-AP STA MLD that receives a beacon frame from the NSTR AP MLD that does not include a neighbor AP information field for the AP of the non-primary link can implicitly recognize that the other AP is an NSTR AP MLD based on the fact that the number of simultaneously supported links of the AP that transmitted the beacon frame is two and information about other APs in the same MLD is not indicated, as described above.

[0153] Meanwhile, when a typical AP MLD receives an (ML) (Re) association request frame from a STA (MLD), it must transmit an (ML) association response frame over the link on which the (ML) association request frame was received. However, the NSTR AP MLD may be allowed to respond to an (ML) association request frame received over a non-primary link over the primary link (i.e., to send an (ML) association response frame over the primary link).

[0154] This may be an acceptable operation because, as described above, the NSTR AP MLD operation of transmitting on a non-primary link is somewhat limited compared to a general AP. Furthermore, the NSTR AP MLD has an operation restriction that when a response to an (ML) association response frame is transmitted on a non-primary link, it must also start transmitting on the primary link. This may be an operation restriction considered to prevent the AP of the primary link from entering a BLIND state, as considered in other embodiments of the present invention.

[0155] Therefore, when an NSTR AP MLD receives an (ML)(Re) association request frame over a non-primary link, it can respond with an (ML)(Re) association response frame over the primary link, or it can respond with an (ML)(Re) association response frame over both the primary and non-primary links simultaneously. That is, a STA MLD that sends an (ML)(Re) association request frame over a non-primary link of the NSTR AP MLD recognizes that the response to its request frame will be sent over the primary link, and can wait to receive an (ML)(Re) association response frame over the primary link.

[0156] The RNR element transmitted by the AP in the beacon frame may include a specific TBTT information field including an MLD Parameters field. In this case, if the MLD ID in the MLD Parameters field is set to '0', the STA MLD can recognize that the AP corresponding to the Neighbor AP Information field including the MLD Parameters field is included in the AP MLD that includes the AP that transmitted the beacon frame. In other words, the STA MLD can recognize that the Neighbor AP Information field indicates information about other APs included in the same AP MLD as the AP that transmitted the beacon frame. In this case, the method by which the STA MLD analyzes / acquires this information may be the same as or similar to the operation performed by a conventional STA after receiving an RNR element.

[0157] However, because an NSTR Soft AP does not transmit beacon frames via a non-primary link, it may be impossible to indicate information related to beacon frames of other APs (non-primary link APs) via the RNR element. Furthermore, because the NSTR Soft AP MLD does not transmit beacon frames via a non-primary link AP, it cannot support information related to beacon frames when indicating basic information about a non-primary link AP via the RNR element. For example, a non-primary link that does not transmit beacon frames does not have information corresponding to the TBTT information count, TBTT information length, and neighbor AP TBTT offset subfields that should be indicated in the RNR element. Therefore, when the NSTR Soft AP MLD transmits an RNR element via the primary link AP, it may be necessary to set the TBTT-related fields of the neighbor AP information field corresponding to the non-primary link AP to predetermined values.

[0158] The Neighbor AP TBTT Offset subfield of the TBTT Information field (see (b) of FIG. 11) indicates information related to the next TBTT of another AP to be indicated. That is, the Neighbor AP TBTT Offset subfield included in the Neighbor AP Information field may include information about the next TBTT of the AP corresponding to the Neighbor AP Information field. For example, when AP1 transmitting a beacon frame indicates information about AP2 using the RNR element (through the Neighbor AP Information field), the Neighbor AP TBTT Offset subfield corresponding to AP2 indicates how many TUs (Time Units, 1024 us) the next TBTT of AP2 differs from the previous TBTT of AP1. In this case, the value indicated in the Neighbor AP TBTT Offset subfield is a value obtained by rounding down the TBTT offset to the nearest integer. That is, when an AP indicates a value of 10 in the Neighbor AP TBTT Offset subfield of another AP, the next TBTT of the other AP may have a time interval of 10 TUs to less than 11 TUs based on the previous TBTT of the AP.

[0159] However, when an AP of a primary link of an NSTR Soft AP MLD sets a neighbor AP TBTT offset subfield (1-octet) corresponding to an AP of a non-primary link, it may need to set it to a preset value (e.g., 254 or 255). This may be because an NSTR Soft AP does not transmit a beacon frame on a non-primary link and is therefore unable to determine a target beacon transmission time (TBTT), which is a scheduled time for transmitting the next beacon frame. That is, a beacon frame transmitted by an NSTR Soft AP MLD on a primary link may need to set a neighbor AP TBTT offset subfield corresponding to an AP of a non-primary link to 254 and / or 255 using an RNR element. In this case, the neighbor AP TBTT offset subfield corresponding to the non-primary link may be present in a TBTT information field including an MLD parameters field in which the MLD ID subfield is set to 0.

[0160] Therefore, after receiving a beacon frame of an NSTR Soft AP MLD, if a non-AP STA MLD confirms that the TBTT information field in the specific neighbor AP information field of the RNR element included in the beacon frame has an MLD ID subfield of 0 and a TBTT offset subfield of 254 and / or 255, it can recognize that the specific neighbor AP information field is information about an AP (of the NSTR Soft AP MLD) operating on a non-primary link of the NSTR Soft AP MLD. Thus, if a non-AP STA MLD that has received a beacon frame of an NSTR Soft AP MLD confirms information about an AP MLD operating on a non-primary link of the NSTR AP MLD, it must not transmit a probe request frame or an ML probe request frame to the NSTR Soft AP MLD on a non-primary link.

[0161] Also, when the non-AP STA MLD recognizes that the received beacon frame is the beacon frame transmitted by the MLD, and the Neighbor AP TBTT Offset subfield corresponding to another AP of the same MLD as the AP (Reporting AP) that transmitted the beacon frame is indicated as 254 and / or 255, the non-AP STA MLD shall not transmit a probe request frame and an ML probe request frame to other APs.

[0162] Also, when the non-AP STA MLD recognizes that the received beacon frame is the beacon frame transmitted by the MLD, and the Neighbor AP TBTT Offset subfield corresponding to another AP of the same MLD as the AP (Reporting AP) that transmitted the beacon frame is indicated as 254 and / or 255, the non-AP STA MLD shall not transmit a probe request frame and an ML probe request frame to other APs.

[0163] <MLD AP TBTT Offset Indication>

[0164] In the above-described embodiment of the present invention, it has been mentioned that a beacon frame transmitted by the NSTR Soft AP MLD may indicate a neighbor AP TBTT offset subfield corresponding to an AP of a non-primary link as a preset value (254 and / or 255). However, the neighbor AP TBTT offset subfield may be indicated as 254 or 255 even when the beacon frame does not correspond to an AP of a non-primary link of the NSTR Soft AP MLD. For example, if the TBTT offset of another AP recognized by the AP transmitting the beacon frame is 254 TU or more (254 TU or more than 254 TU), the AP may indicate the neighbor AP TBTT offset subfield corresponding to the other AP in the beacon frame as 254. Also, if the AP transmitting the beacon frame cannot accurately recognize the TBTT offset of the other AP, the AP may indicate the neighbor AP TBTT offset subfield corresponding to the other AP as 255.

[0165] However, since an AP in an MLD can always recognize the TBTT offset of other APs in the MLD, when using the RNR element to indicate (set) the neighbor AP TBTT offset subfield corresponding to another AP (in the same MLD), it must not indicate (set) it to 255.

[0166] Specifically, the Neighbor AP Information field included in the RNR element of the beacon frame may include a Neighbor AP TBTT Offset subfield indicating an offset between the times at which the beacon frames are transmitted. In this case, the Neighbor AP TBTT Offset subfield indicates an offset value between the time at which the beacon frame is transmitted and the time at which the next beacon frame is transmitted by the AP corresponding to the Neighbor AP TBTT Offset subfield among multiple APs included in the AP MLD (NSTR or STR AP MLD). In this case, the Neighbor AP TBTT Offset subfield cannot be set to a specific value under certain conditions.

[0167] For example, when the AP is included in the same AP MLD as the AP that transmitted the beacon frame, the neighbor AP TBTT offset subfield is not set to a specific value (e.g., "255"). In this case, the size of the neighbor AP TBTT offset subfield may be 8 bits, and in this case, the neighbor AP TBTT offset subfield is not set to the maximum value that can be indicated by the neighbor AP TBTT offset subfield (in the case of 8 bits, values ​​from 0 to 255 are respectively corresponding, and therefore the maximum offset that can be indicated by 8 bits may be 255). However, when the AP is not included in the same AP MLD as the AP that transmitted the beacon frame (for example, when the AP is a legacy AP), the neighbor AP TBTT offset subfield may be set to a specific value (e.g., "255").

[0168] In a similar embodiment, the neighbor AP TBTT offset subfield may be analyzed so that the set value varies depending on specific conditions.

[0169] For example, when the neighbor AP TBTT offset subfield is set to a specific value (eg, '254'), the set value may be analyzed to be different, such as '254' or greater than '254', depending on a specific condition.

[0170] Specifically, if the AP corresponding to the neighbor AP information field including the neighbor AP TBTT offset subfield is included in the same AP MLD as the AP that transmitted the beacon frame or in another MLD, and the neighbor AP TBTT offset subfield is set to a specific value (e.g., "254"), the station can interpret the value indicated by the neighbor AP TBTT offset subfield as 254 TUs. However, if the AP is not included in the same AP MLD as the AP that transmitted the beacon frame or in another MLD (e.g., if the AP is a legacy AP or an AP not included in the MLD), and the neighbor AP TBTT offset subfield is set to a specific value (e.g., "254"), the station can interpret the value indicated by the neighbor AP TBTT offset subfield as 254 TUs or more.

[0171] Generally, the reason why a conventional AP transmits TBTT offset information along with basic information about neighboring APs using a beacon frame may be to help a STA receiving a beacon frame quickly obtain basic information about other APs and receive beacon frames from other APs more efficiently using the confirmed TBTT offset information.

[0172] However, the neighbor AP TBTT offset subfield included in the conventional beacon frame is composed of one octet and is designed to be able to indicate only a TBTT offset corresponding to a maximum of 254TU. This may be a neighbor AP TBTT offset subfield design that compromises the overhead of the beacon frame and the information that can be indicated by excluding information support regarding cases where the AP has a TBTT offset of 254TU or more, considering the maximum TBTT offset that other APs can have ((2^16) or (2^16)-1TU when considering the configurable beacon interval).

[0173] However, when an AP MLD indicates information about other APs in the MLD using a beacon frame, it may include and transmit an additional MLD AP TBTT offset subfield to more accurately indicate the TBTT offset of the other AP. The MLD AP TBTT offset subfield may be included in the TBTT information field corresponding to other APs in the same MLD when the AP MLD transmits a beacon frame. In this case, if both the neighbor AP TBTT offset subfield and the MLD AP TBTT offset subfield are indicated in a specific TBTT information field, the neighbor AP TBTT offset subfield may be indicated with a preset value (which may be 254 or 255). The MLD AP TBTT offset subfield is a two-octet subfield and may be used to indicate the TBTT offset value when the TBTT offset between the AP (reporting AP) that transmitted the beacon frame and another AP (reported AP) in the same MLD exceeds 254TU. Furthermore, the MLD AP TBTT offset subfield may be included in the TBTT information field only when the TBTT offset of another AP in the same MLD exceeds 254 TU when the AP MLD transmits a beacon frame and the exact TBTT offset cannot be indicated in the existing neighbor AP TBTT offset subfield.

[0174] When the STA MLD checks a TBTT information field including an MLD AP TBTT offset subfield in an RNR element included in a beacon frame received from a specific AP, the STA can check the TBTT offset of the AP corresponding to the TBTT information field based on the value indicated in the MLD AP TBTT offset subfield. In this case, to determine whether the TBTT information field included in the beacon frame includes an MLD AP TBTT offset subfield, the STA may check based on the value of the TBTT information length subfield (located in the TBTT Information Header (sub) field of each neighbor AP information field) corresponding to each TBTT information field. That is, when the STA recognizes that the TBTT information field includes an MLD AP TBTT offset subfield based on the value of the TBTT Information Length subfield, the STA can check the TBTT offset of the AP corresponding to the TBTT information field based on the value indicated in the MLD AP TBTT offset subfield. In this case, when the MLD AP TBTT offset subfield of a specific TBTT information field indicates 0 or a preset value (or a value less than 254), the STA MLD can confirm the TBTT offset of the AP corresponding to the specific TBTT information field based on the value of the neighbor AP TBTT offset subfield.

[0175] FIG. 12 shows another example of a TBTT information field format according to an embodiment of the present invention.

[0176] 12, the TBTT information field may include an MLD AP TBTT offset subfield. The MLD AP TBTT offset subfield may be included only in beacon frames transmitted by APs of the AP MLD. Furthermore, the MLD AP TBTT offset subfield may be included only in TBTT information fields corresponding to other APs of the same MLD as the AP transmitting the beacon frame.

[0177] As an example, in a beacon frame transmitted by a specific AP in an AP MLD, to indicate that the TBTT offset of another AP in the same MLD is 300TU, the TBTT information field corresponding to the other AP may be used as a format including an MLD AP TBTT offset subfield. In this case, the neighboring AP TBTT offset subfield of the TBTT information field corresponding to the other AP may be indicated as 254 or 255, and the MLD AP TBTT offset subfield may be indicated as a value corresponding to 300TU (e.g., 300, 299, or (300-254)). In this case, the above-mentioned MLD AP TBTT offset subfield is a subfield name for illustrative purposes, and subfields with the same purpose may be defined with different names.

[0178] FIG. 13 illustrates an example of a TBTT information length subfield indicating a TBTT information field including an MLD AP TBTT offset subfield according to an embodiment of the present invention.

[0179] 13, the type of content included in the TBTT information field may be indicated by the TBTT information length subfield. The TBTT information length subfield may be a subfield included in a TBTT information header field present in a neighbor AP information field included in an RNR element. That is, the RNR element transmitted in a beacon frame may include multiple neighbor AP information fields, and the TBTT information fields included in each neighbor AP information field may have a structure including different amounts and types of content. In this case, since the TBTT information fields included in each neighbor AP information field may include different amounts and types of content, information regarding the content (and format) indicated by each TBTT information field is indicated by the TBTT information header field.

[0180] That is, the STA can parse each neighbor AP information field in the RNR element of the beacon frame received via the AP based on the information indicated in the TBTT information header. At this time, each parsed neighbor AP information field may indicate information about a neighbor AP or another AP of the same MLD. At this time, if the value of the TBTT information length subfield included in the TBTT information header field indicates a content configuration including an MLD AP TBTT offset subfield as shown in FIG. 13, the STA can determine the TBTT offset of the AP corresponding to the TBTT information field based on the value indicated in the MLD AP TBTT offset subfield.

[0181] Alternatively, a restriction may be applied that the AP MLD must manage the TBTT offset between the APs it operates so that it is not greater than 254 TU or not greater than 255 TU.

[0182] In this case, the AP MLD may need to adjust the beacon interval of the AP it operates on each link and / or the TBTT time (setting) of the BSS operated by each AP so that the TBTT time difference between APs belonging to the MLD does not exceed 254 TU or 255 TU. Here, the adjustment of the beacon interval and TBTT time is an example of a method for changing the TBTT interval of each AP in the MLD, and other implementations may be applied that adjust the TBTT offset so that it does not exceed a specific time value (254 TU or 255 TU). In addition, a method for the AP MLD to prevent the TBTT time difference between each AP it operates from exceeding a specific interval (254 TU or 255 TU) does not need to be separately defined.

[0183] In this way, when an AP MLD adjusts the TBTT time difference of each AP it operates to 254 TU or less or less than 255 TU, the neighbor AP TBTT offset subfield value transmitted to other APs in the same MLD in the RNR element transmitted by the specific AP in the beacon may indicate only a value of 253 or 254. Furthermore, when a specific AP MLD manages the TBTT time difference of the AP it operates to 254 or less or less than 255 TU, the neighbor AP TBTT offset subfield transmitted by a specific AP belonging to the specific AP MLD, and corresponding to other APs belonging to the same AP MLD (the specific AP MLD), may indicate (have) only a value of 254 or less.

[0184] As described above, when an AP MLD maintains the TBTT time difference between its APs at 254 TU or less or less than 255 TU, a non-AP STA may need to analyze the neighbor AP TBTT offset subfield of a beacon frame received from the AP of the AP MLD using a method different from the above-described analysis method. Here, the above-described analysis method may refer to an analysis method used when the value of the neighbor AP TBTT offset subfield is indicated as 254. That is, the above-described analysis method may analyze that the time interval between the previous TBTT of the Reporting AP and the next TBTT of the Reported AP (transmitted after the previous TBTT) is 254 TU or more when the value of the neighbor AP TBTT offset subfield is indicated as 254. Here, the other analysis method may analyze that the time interval between the previous TBTT of the Reporting AP and the next TBTT of the Reported AP (transmitted after the previous TBTT) is 254 TU or more but less than 255 TU when the value of the neighbor AP TBTT offset subfield is indicated as 254. Alternatively, another analysis method may be to analyze that when the value of the neighbor AP TBTT offset subfield is indicated as 254, the time interval between the previous TBTT of the Reporting AP and the next TBTT of the Reported AP (transmitted after the previous TBTT) is 254 TU.

[0185] This is because the TBTT time difference of each AP operated by AP MLD is adjusted by AP MLD to 254 TU or less or 255 TU or less, so the existing neighbor AP TBTT offset subfield has the meaning of "254 TU or more" and can be an analysis method that reflects the operating characteristics of AP MLD.

[0186] That is, when a non-AP STA receives a neighbor AP TBTT offset subfield for another AP in the same AP MLD via a beacon received from a specific AP in the AP MLD, if the value of the subfield is 254, it can analyze that the TBTT offset of the other AP is 254 TU or (greater than 254 TU and less than 255 TU).

[0187] On the other hand, even if a non-AP STA receives a beacon from an AP in AP MLD, if the Neighbor AP TBTT Offset subfield included in the beacon that is not for an AP in the same AP MLD is specified as 254, i.e., if the Neighbor AP TBTT Offset subfield for a Legacy AP or an AP that is not in MLD is specified as 254, the non-AP STA must interpret the beacon as specifying a TBTT offset of 254 TU or more.

[0188] In this case, the non-AP MLD may determine whether a specific Neighbor AP TBTT Offset subfield is for another AP of the same AP MLD based on information in the MLD Parameters subfield included in the same TBTT Information field as the specific Neighbor AP TBTT Offset subfield. More specifically, if the MLD ID subfield value of the MLD Parameters subfield included in the same TBTT Information field as the specific Neighbor AP TBTT Offset subfield is 0, the non-AP STA may interpret that the specific Neighbor AP TBTT Offset subfield is for an AP of the same MLD as the AP that transmitted the beacon frame.

[0189] That is, when the Neighbor AP TBTT Offset subfield of the TBTT Information field in which the MLD ID subfield value is 0 is indicated as 254, a non-AP STA can interpret that the Neighbor AP TBTT Offset subfield indicates a TBTT offset of 254 TUs or more and less than 255 TUs. In this case, the non-AP can further consider whether an ML element is included in the beacon frame (whether the AP that transmitted the beacon is MLD) in order to analyze the Neighbor AP TBTT Offset subfield.

[0190] That is, if the MLD ID subfield value is not 0 (for example, 1 to 255) and the Neighbor AP TBTT Offset subfield of the TBTT Information field indicates 254, the non-AP STA can interpret that the Neighbor AP TBTT Offset subfield indicates a TBTT offset of 254 TUs or more.

[0191] <Setting up and managing non-primary links>

[0192] As mentioned above, the NSTR AP MLD cannot transmit beacon frames, probe response frames, or ML (Multi-link) probe response frames on non-primary links. Therefore, a STA MLD that wishes to connect to the NSTR AP MLD must transmit ML probe request frames only on the link on which the NSTR AP MLD transmitted beacon frames.

[0193] The ML probe request frame transmitted by the STA of the EHT non-AP STA MLD may include EHT Capability information and a Multi-Link element in addition to the information included in the probe request frame transmitted by the conventional HE STA. In this case, the Multi-Link element included in the ML probe request frame can serve as a way for the MLD transmitting the ML probe request frame to request additional information about the AP of another link from the AP MLD.

[0194] For example, when transmitting an ML probe request frame, the non-AP STA MLD can request the AP MLD to further respond with complete or partial information about the APs of other links using the Multi-Link element of the ML probe request frame. That is, the non-AP STA MLD can request the AP MLD to transmit all or part of the parameters related to the links of other APs included in the same AP MLD to the AP receiving the ML probe request frame.

[0195] For example, if all or part of the parameters related to an AP connected via a non-primary link are updated, a station included in the non-AP STA MLD can request the AP connected via a primary link to transmit all or part of the updated parameters related to other APs of the non-primary link.

[0196] In this case, the complete information request / response means that the AP of the other link (Reported AP) is requested / responded to with the same level of information as the AP (Reporting AP) that responds with the ML probe response frame, and the partial information request / response means that only the information on the AP of the other link requested by the STA is responded to.

[0197] If the AP MLD that sent the beacon frame requests additional information about the AP of another link in the ML probe request frame received on a specific link, it can respond using an ML probe response frame to not only provide information about the AP of the specific link, but also the requested additional information about the AP of the other link.

[0198] In this case, when the STA MLD requests complete information about the AP of another link by transmitting an ML probe request frame on a specific link, the AP MLD must provide information about the AP of the other link at the same level as the information about the AP of the specific link using an ML probe response frame that responds on the specific link. In other words, the STA MLD that receives complete information about the AP of another link on a specific link can obtain the same level of information about the AP of the other link as when it directly receives an ML probe response from the AP of the other link.

[0199] In this case, if the STA MLD transmits an ML probe request frame over a specific link and requests partial information about the AP of another link, the AP MLD can provide only the requested information (requested element information) among the information about the AP of the other link using an ML probe response frame that responds over the specific link. In other words, the STA MLD that receives partial information about the AP of another link over a specific link can further obtain only the information it requested from the AP of the other link. In this case, the STA MLD that requests partial information about the AP of the other link can transmit an ML probe request frame including information indicating further information to be obtained (which may be indicated by the Requested element IDs field) together with the link ID corresponding to the other link. Therefore, if the ML probe request frame received over a specific link includes information indicating information about the other link (Request element IDs field), the AP MLD can further indicate the indicated information about the other link in the ML probe response frame.

[0200] In this case, when the STA MLD transmits an ML probe request frame on a specific link, it can set the Complete Profile subfield (in the Per-STA Control field included in the Multi-Link element) corresponding to the other link to 0 or 1 to indicate whether it requests complete information or partial information for the other link.

[0201] In this case, the additional information (Complete and Partial) for the other APs may be transmitted by the STA-specific profile included in the Multi-link element of the ML probe response frame. The STA-specific profile is a field included in the Multi-link element zero or more times, and may include information on other STAs (APs and non-AP STAs) that exist in the same MLD as the STA (AP and non-AP STA) that transmits the frame including the Multi-Link element. In this case, the STA-specific profile has a configuration including a Complete Profile subfield, and complete information (information at the same level as the STA (AP and non-AP) that transmits the frame including the Multi-Link element) of other STAs (APs and non-AP STAs) corresponding to (corresponding to) the STA-specific profile whose Complete Profile subfield is indicated as 1 can be obtained from the STA-specific profile. However, parameters / elements that mean the same information as the STA (AP and non-AP) that transmitted the STA-specific profile may be omitted according to inheritance rules. The inheritance rule may mean that if a parameter or element is not specified, the value of the same parameter or element (specified for other STAs (AP and non-AP)) that has already been specified is inherited and utilized to prevent repeated specification of the same parameter or element. That is, if a value of parameter1 is specified for STA1 and a value of parameter1 is not specified for STA2, the inheritance rule may interpret the value of parameter1 for STA2 as being the same as the value of parameter1 for STA1.

[0202] In this case, the per-STA profile subelement included in the Multi-link element transmitted by the NSTR AP MLD may not include a Beacon Interval subfield for indicating the interval at which beacons are transmitted. That is, when the NSTR AP MLD indicates a per-STA profile subelement corresponding to an AP of a non-primary link in the Multi-link element, the Beacon Interval Present subfield must be set to 0. This may be because an AP operating on a non-primary link of the NSTR AP MLD does not transmit beacon frames, and therefore there is no separate beacon frame period. That is, even if the Complete Profile subfield (in the Per-STA Control field) of the per-STA profile subelement (in the Probe Response and Association Response frames) corresponding to an AP of a non-primary link of the NSTR AP MLD is set to 1, the Beacon Interval Present subfield may be set to 0. That is, beacon interval information for the AP of a non-primary link is not present even when complete information is indicated.

[0203] Similarly, DTIM information (DTIM Count and DTIM Period information) for a non-primary link AP may not be present even when complete information is indicated. That is, for the STA-specific profile corresponding to a non-primary link AP in the NSTR AP MLD, even if the Complete Profile subfield (in the Per-STA Control field) is indicated as 1, the DTIM Info Present subfield may be indicated as 0.

[0204] That is, because beacons are not transmitted on non-primary links, even when a non-AP STA MLD requests all information (or all updated information) for other APs on non-primary links through the AP of the primary link of the AP MLD (i.e., when complete information is set to '1'), the beacon interval and DTIM information for the AP of the non-primary link may not be present in the ML probe response frame. That is, the beacon interval and DTIM information may not be included in the STA-specific profile subelement for the AP of the non-primary link included in the ML probe response frame.

[0205] In this case, even if all information (or all updated information) for other APs on non-primary links is requested, the AP MLD does not need to include the beacon interval and DTIM information for the APs on non-primary links in the ML probe response frame. Therefore, in this case, the AP MLD can transmit the beacon interval present subfield and the DTIM information present subfield set to a value (e.g., "0") indicating that the respective fields are not included.

[0206] Because the NSTR AP MLD does not transmit beacon frames to non-primary links, it does not need to indicate DTIM information and beacon interval information when indicating information about the AP of the non-primary link. That is, the NSTR AP MLD may need to always indicate 0 in the DTIM information present subfield of the STA-specific profile (more precisely, the STA Control field) corresponding to the AP of the non-primary link. That is, the NSTR AP MLD may need to always indicate 0 in the Beacon Interval Present subfield of the STA-specific profile corresponding to the AP of the non-primary link. Therefore, even when the NSTR AP MLD receives an ML probe request frame requesting complete information or an (ML)(Re) association request frame from a non-AP STA MLD, the NSTR AP MLD may need to always indicate 0 in the Beacon Interval Present subfield and the DTIM information present subfield of the STA-specific profile corresponding to the AP of the non-primary link.

[0207] Alternatively, since beacon frames are not transmitted to non-primary links, the NSTR AP MLD may need to set the Beacon Interval, DTIM Count, and DTIM Interval subfields in the STA-specific profile corresponding to the AP of the non-primary link to predetermined values. This may be an operation considered to maintain the same STA-specific profile configuration as a general AP MLD (e.g., STR AP MLD) when the NSTR AP MLD transmits (responds to) complete information for the AP of the non-primary link. That is, the STA MLD requests complete information for a specific link from the AP MLD using an ML probe request frame, and the complete information for the AP of the specific link is expected to be returned in a response frame. In this case, if the complete information responded by the NSTR AP MLD has a different STA-specific profile configuration from the complete information responded by the STR AP MLD, the implementation complexity of the process by which the STA MLD acquires information according to the STA-specific profile may increase. Therefore, even if the AP of the non-primary link does not transmit a beacon frame, the NSTR AP MLD can use a per-STA profile with the same configuration as the per-STA profile used by the general AP MLD when responding with complete information for the non-primary link when responding with complete information. In this case, the per-STA profile of the NSTR AP MLD corresponding to the AP of the non-primary link may have the Beacon Interval subfield, the DTIM Count subfield, and the DTIM Interval subfield set to predetermined values, respectively. For example, when transmitting complete information for the AP of the non-primary link, the NSTR AP MLD can set each bit of the Beacon Interval subfield of the non-primary link to all 0s, all 1s, or a predetermined method. For example, when transmitting complete information for the AP of the non-primary link, the NSTR AP MLD can set each bit of the DTIM Count subfield of the non-primary link to all 0s, all 1s, or a predetermined method.For example, when the NSTR AP MLD transmits complete information to the AP of the non-primary link, it can set each bit of the DTIM Interval subfield of the non-primary link to all 0s, all 1s, or a predetermined method.

[0208] Alternatively, because beacon frames are not transmitted on the non-primary link, the NSTR AP MLD may set the Beacon Interval, DTIM Count, and DTIM Interval subfields in the STA-specific profile corresponding to the non-primary link AP to values ​​associated with the beacon frame of the primary link. This may be considered to maintain the same STA-specific profile configuration, as described above. In this case, the Beacon Interval subfield, DTIM Count subfield, and DTIM Interval subfield in the STA-specific profile corresponding to the non-primary link AP of the NSTR AP MLD may be set to values ​​associated with the beacon frame transmitted on the primary link. For example, when transmitting complete information for the non-primary link AP, the NSTR AP MLD may set the Beacon Interval subfield of the non-primary link to a value indicating (meaning) the beacon interval of the primary link. For example, when transmitting complete information for the non-primary link AP, the NSTR AP MLD may set the DTIM Count subfield of the non-primary link to the DTIM Count value of the primary link. For example, when the NSTR AP MLD transmits complete information for the AP on the non-primary link, it can set the DTIM Interval subfield of the non-primary link to a value indicating the DTIM interval of the primary link.

[0209] Alternatively, since beacon frames are not transmitted to non-primary links, the NSTR AP MLD can set the Beacon Interval, DTIM Count, and DTIM Interval subfields of the STA-specific profile corresponding to the AP of the non-primary link to values ​​with specific purposes. Furthermore, the Beacon Interval subfield of the non-primary link may be set by the AP MLD to a value with specific purposes (a virtual beacon interval), for example, a value for calculation. Conventionally, the Wi-Fi beacon interval literally means a value related to the time interval at which beacon frames are transmitted, but is also used as a time unit for the operation of various BSSs. For example, the unit of a JointFailureTimeout primitive, a QueryFailureTimeout primitive, etc. is defined as a beacon interval, and the Listen Interval field, the PRAW Start Offset subfield, the AID Request Interval field, the AID Switch Count field, the AID Response Interval field, the Minimum Transmission Interval subfield, the Channel Quality Measurement Duration, the Color Switch Countdown (of the BSS Color Change Announcement element) subfield, etc. indicate their interval / duration using the beacon interval (or TBTT) as a basic unit. As such, the beacon interval has the meaning of a value related to the interval at which beacon frames are actually transmitted, and is also a value used as a unit in various primitives and fields. Therefore, even if beacon frames are not actually transmitted over non-primary links, the beacon interval for non-primary links may need to be defined (indicated, set) to be used as a unit in the above-mentioned primitives / subfields.

[0210] That is, even if a beacon frame is not transmitted over the non-primary link, the NSTR AP MLD can indicate the Beacon Interval subfield of the STA-specific profile corresponding to the AP of the non-primary link as the beacon interval value to be used as the time unit of the non-primary link. In this case, the non-AP MLD can recognize (check and calculate) the duration and interval of the above-mentioned primitives and fields (used as the beacon interval unit) based on the value indicated in the Beacon Interval subfield of the STA-specific profile corresponding to the AP of the non-primary link. In this case, the DTIM Interval subfield and DTIM Count subfield of the STA-specific profile corresponding to the AP of the non-primary link may also be set according to the BSS operation purpose of the AP MLD, and the non-AP MLD operating the STA over the non-primary link may need to operate based on the set values ​​when operating the STA over the non-primary link.

[0211] Meanwhile, the method of setting subfields (Beacon Interval, DTIM Count, DTIM Interval, etc.) related to non-primary link beacons in the NSTR AP MLD described above may be equally applied to other frames and subfields (transmitted on the primary link or non-primary link) containing information related to non-primary link beacons, in addition to the STA-specific profile transmitted on the primary link.

[0212] In addition, a non-AP STA MLD attempting to associate with an NSTR AP MLD may need to use the beacon interval of the primary link of the NSTR AP MLD as the unit of the Listen Interval field transmitted while requesting setup for the primary link and non-primary links. That is, a non-AP STA MLD transmitting a Listen Interval field to an NSTR AP MLD must calculate and set the unit of the Listen Interval field as the beacon interval of the AP operating on the primary link of the NSTR AP MLD. In this case, the Listen Interval field may indicate information related to the period (time) at which at least one STA transitions to a wake state in order for the non-AP STA MLD performing multi-link (re)association to receive beacon frames. In this case, the Listen Interval field may indicate a value derived when the ListenInterval parameter is indicated in the MLME primitive.

[0213] In this case, when a non-AP STA MLD transmits a Listen interval field to another AP MLD (e.g., an STR AP MLD) other than the NSTR AP MLD, it may need to set the unit of the Listen interval field to the maximum value of the beacon interval of the link (AP) it is attempting to set up. For example, when a non-AP STA MLD attempts to perform multi-link setup with the AP MLD and link 1 or link 2, the non-AP STA MLD may set the unit of the Listen interval field included in the ML association request frame to the larger of the beacon interval of link 1 (AP) and the beacon interval of link 2. In other words, if the beacon interval of link 1 is 100 ms and the beacon interval of link 2 is 50 ms, the unit of the Listen interval subfield transmitted by the non-AP STA MLD may be in 100 ms units.

[0214] Generally, when an AP and a STA complete setup, the STA can learn and track (update) the AP's operating parameters and element changes by receiving a beacon frame transmitted by the AP. The beacon frame also provides information, including a timestamp field, for STAs within the BSS to synchronize their time.

[0215] However, since the NSTR AP MLD does not transmit beacon frames on non-primary links as mentioned above, the STA MLD set up with the NSTR AP MLD may need to perform separate operations to track (update) parameters / elements and maintain time synchronization for the non-primary links.

[0216] According to one embodiment of the present invention, a non-AP STA MLD combined with an NSTR AP MLD can check the change sequence (in the MLD parameter field of the RNR element) of the non-primary link after receiving a beacon frame over the primary link and transmit an ML Probe Request. In this case, the ML Probe Request frame transmitted by the non-AP STA MLD may be transmitted for the purpose of requesting changed parameter and element information of the non-primary link. In this case, the ML Probe Request frame may request complete information of the non-primary link by setting the complete profile of the STA-specific profile corresponding to the non-primary link (and the AP of the non-primary link) to 1. Alternatively, the ML Probe Request frame transmitted by the STA MLD for the purpose of updating parameters / elements of the non-primary link may request updated information, not complete / partial information, for the non-primary link.

[0217] In other words, even if multiple links are formed between the non-AP STA MLD and the AP MLD, frames for performing association, reassociation, and / or parameter update procedures may be transmitted only on the primary link. For example, if the STA recognizes that parameters for the AP of a non-primary link have been updated from a specific field (e.g., a change sequence or a BSS parameter change count subfield, etc.) that indicates whether the parameter update is for a link of another AP included in the neighbor AP information included in the beacon frame, the non-AP STA MLD can request transmission of the updated parameters on a primary link other than the non-primary link of the other AP. In other words, the non-AP MLD cannot transmit frames (e.g., probe request frames) for requesting updated parameters on a non-primary link.

[0218] As an example, after setting up with the NSTR AP MLD, a non-AP STA MLD requesting information for updating parameters / elements of a non-primary link can request the changed parameters / elements from the AP of the non-primary link by setting the Updated Profile subfield of the STA-specific profile corresponding to the non-primary link to 1 in the ML Probe Request frame transmitted over the primary link. If the Updated Profile subfield is set to 1 in the STA-specific profile (corresponding to the non-primary link) of the received ML Probe Request frame, the NSTR AP MLD can respond with an ML Probe Response frame including information (parameters and elements) of the changed non-primary link.

[0219] In this case, the STA-specific profile field of the ML probe request frame transmitted by the non-AP STA MLD may include an Updated Profile subfield and a Recorded Change Sequence subfield. The Recorded Change Sequence subfield indicates the latest Change Sequence value maintained by the non-AP STA MLD for the non-primary link, and the AP MLD can check / determine the type of Updated Information based on the value indicated by the Recorded Change Sequence subfield.

[0220] For example, the NSTR AP MLD may change Parameter 1 while increasing the Change Sequence number of the non-primary link from 100 to 101, and then change Parameter 2 while increasing the Change Sequence number from 101 to 102. In this case, the STA MLD can request updated information for the non-primary link by transmitting an ML probe request frame. In this case, if the non-AP STA MLD specifies the Recorded Change Sequence subfield as 100, the NSTR AP MLD can respond with an ML probe response frame that includes both Parameter 1 and Parameter 2, and if the non-AP STA MLD specifies the Recorded Change Sequence subfield as 101, the NSTR AP MLD can respond with an ML probe response frame that includes only Parameter 2.

[0221] In this case, the Non-AP STA MLD does not use a separate Updated Profile subfield to request an Updated Profile, but can indicate the Complete Profile subfield as 0. That is, the method by which the Non-AP STA MLD requests an Updated Profile may be to set the Complete Profile subfield to 0, and in this case, a separate Updated Profile subfield may not be included in the STA-specific profile.

[0222] FIG. 14 illustrates an example of a format of a Per-STA Profile subelement according to an embodiment of the present invention.

[0223] Referring to FIG. 14(a), a STA-specific profile sub-element may include a STA Control field. The STA Control field (see FIG. 14(b)) indicates information for indicating the type of fields included in the STA profile (see FIG. 14(a)) of the corresponding STA-specific profile sub-element. In this case, in a specific STA-specific profile sub-element transmitted by an AP MLD other than the NSTR AP MLD, if the Complete Profile sub-field of the STA Control field is set to 1, the MAC Address Present sub-field, Beacon Interval Present sub-field, and DTIM Information Present sub-field may all need to be set to 1. However, as described above, since the NSTR AP MLD does not transmit beacon frames to non-primary links, information related to beacon frames of non-primary links may not need to be indicated in the STA-specific profile sub-elements corresponding to non-primary links. That is, the profile sub-element for a specific STA (corresponding to an AP of a non-primary link) transmitted by the NSTR AP MLD may have the Complete Profile sub-field set to 1, but the Beacon Interval Present sub-field and the DTIM Information Present sub-field set to 0.

[0224] Also, as described in the above embodiment, a non-AP STA MLD transmitting an ML probe request frame to an NSTR AP MLD can request updated information of the non-primary link AP from the primary link AP by specifying 1 in the Updated Profile subfield of the STA Control field (included in the STA-specific profile subelement corresponding to the non-primary link AP). In this case, the non-AP STA MLD can specify a Recorded Change Sequence value, which is information related to the time when the non-AP STA MLD updated the non-primary link AP information, using the Recorded Change Sequence subfield (see FIG. 14(c)). In this case, the Recorded Change Sequence subfield may be a subfield included in the STA profile. After receiving an ML probe request frame of the non-AP STA MLD received via the primary link, the NSTR AP MLD can determine information of the non-primary link AP responding to the non-AP STA MLD by comparing the value of the Recorded Change Sequence subfield included in the ML probe request frame with the Change Sequence value of the current non-primary link AP.

[0225] FIG. 15 illustrates an example of a process in which a non-AP MLD set up with a Non-Simultaneous Transmission and Reception (NSTR) Soft AP MLD updates information about a non-primary link according to an embodiment of the present invention.

[0226] 15, after changing the parameters of AP2 operating on Link 2, which is a non-primary link, the NSTR AP MLD may indicate that the parameters of AP2 have been changed using a beacon frame transmitted by AP1 operating on Link 1, which is a primary link. In this case, the information that the parameters of AP2 have been changed may be indicated by indicating that the Change Sequence subfield value corresponding to AP2 in the RNR element included in the beacon frame transmitted by AP1 is increased by 1 from the value indicated in the immediately preceding beacon frame.

[0227] After receiving the beacon frame sent by AP1 through STA1, the non-AP STA MLD can recognize that the parameters of AP2 have been updated. The non-AP STA MLD can send an ML probe request frame through STA1 to obtain the changed parameter information of AP2.

[0228] The ML probe request frame transmitted by the non-AP STA MLD via STA1 may be configured to include a STA-specific profile sub-element corresponding to AP2 in the ML element, and the STA-specific profile sub-element may include an indicator indicating whether a complete profile or an updated profile is requested.

[0229] After receiving an ML probe request frame from STA1 on the primary link, the NSTR AP MLD can respond to STA1 by including the requested AP2 information (complete or updated information) in an ML probe response frame.

[0230] The non-AP STA MLD receives the requested AP2 information in an ML probe response frame from the NSTR AP MLD, and can complete the parameter update for the non-primary link to which the beacon frame is not transmitted by updating the parameters for AP2.

[0231] <Broadcast ML Probe Response>

[0232] According to one embodiment of the present invention, the NSTR AP MLD may transmit a broadcast ML probe response frame over the primary link when information related to an AP operating over a non-primary link is changed. When the non-AP STA MLD receives a broadcast ML probe response frame transmitted by the NSTR AP MLD over the primary link, it may need to update information related to the non-primary link (AP). In this case, the broadcast ML probe response frame may not be transmitted in response to an ML probe request frame transmitted by a specific STA, but may be an ML probe request frame transmitted by the NSTR AP MLD without a separate request.

[0233] The broadcast ML probe response frame includes a STA-specific profile subelement corresponding to the AP of the non-primary link and serves to help the non-AP STA MLD update changed parameters and elements of the non-primary link. Since the (Recorded) Change Sequence of the non-primary link maintained by each non-AP STA may be different from each other, the broadcast ML probe response frame may include complete information for the AP of the non-primary link. In this case, the broadcast ML probe response frame may be transmitted together with a DTIM beacon frame.

[0234] Therefore, a non-AP STA MLD may need to receive a broadcast ML probe response frame while receiving the next DTIM frame using a beacon frame if the Change Sequence Number corresponding to the AP of the non-primary link is different from the Change Sequence it maintains (recorded).

[0235] In this case, the parameter update procedure for the non-primary link using the above-mentioned broadcast ML probe response frame may be performed using a broadcast ML association response frame. In this case, the method of configuring the STA-specific profile sub-element of the broadcast ML association response frame and the procedure of updating the MLD of the receiving STA are the same as the embodiment of the above-mentioned broadcast ML probe response frame, and detailed description thereof will be omitted.

[0236] FIG. 16 is a flowchart illustrating an example of a procedure in which a non-AP STA MLD associated with an NSTR AP MLD updates parameters of a non-primary link according to an embodiment of the present invention.

[0237] After receiving a beacon frame over the primary link, the non-AP STA MLD checks the non-primary link Change Sequence (in the MLD Parameter field of the RNR element). If the checked non-primary link Change Sequence value differs from the Change Sequence value it maintains (recorded), the non-AP STA MLD can transmit an ML probe request frame over the primary link. In this case, the ML probe request frame may include a subfield indicating whether to request complete information or updated information from the AP of the non-primary link. In addition, an ML probe request frame requesting updated information may also include a subfield indicating the Change Sequence value it maintains (recorded). Thereafter, the non-AP STA MLD that receives an ML probe response frame from the AP MLD updates its parameters based on the non-primary link AP information included in the received ML probe response frame.

[0238] <Time synchronization management for non-primary links>

[0239] As mentioned above, the beacon frame transmitted by the AP not only conveys various parameters and element information but also helps STAs in the BSS to achieve time synchronization. The TimeStamp field included in the beacon frame indicates the timing synchronization function (TSF) timer value at the time when the data symbol containing the first bit of the TimeStamp field appears at the transmit antenna connector. STAs that receive the TimeStamp field can synchronize their own TSF timer with the AP based on the received TimeStamp field value.

[0240] In this way, the AP and STA can operate while maintaining time synchronization based on the TimeStamp value included in the beacon frame, and perform timing-based operations. However, NSTR AP MLD cannot transmit beacon frames on non-primary links, so among STAs in Non-AP STA MLD, STAs associated with a non-primary link AP in NSTR AP MLD must use a method other than beacon frames to maintain time synchronization with the AP.

[0241] To maintain time synchronization with the AP of the non-primary link of the NSTR AP MLD, associated non-AP STAs may need to use the TimeStamp in the TIM frame transmitted by the AP. Because the TIM frame includes a TimeStamp field with the same function as a beacon frame, STAs receiving a TIM frame from an AP of the non-primary link of the NSTR AP MLD may need to manage the TFS timer using the TimeStamp field included in the TIM frame. However, because the NSTR AP MLD may be restricted from starting transmission on a non-primary link without occupying the primary link, it may be necessary to simultaneously transmit a TIM frame on the non-primary link when transmitting a beacon frame on the primary link. In other words, non-AP STA MLDs associated with the NSTR AP MLD may need to prepare to receive TIM frames on the non-primary link in accordance with the TBTT of the primary link.

[0242] In yet another embodiment of the present invention, when the AP MLD is an NSTR AP MLD that does not support simultaneous transmission and reception, the same TSF timer may be used in each link for multiple APs included in the NSTR AP MLD, and the TSF timer used at this time may be the TSF timer of the primary link. That is, when the AP MLD is an NSTR AP MLD, links (non-primary links) for APs affiliated with the NSTR AP MLD can use the TSF timer of the primary link.

[0243] That is, the non-AP STA MLD combined with the NSTR Soft AP MLD may need to share the TSF timer of the primary link with the non-primary link. In other words, the non-AP STA MLD combined with the NSTR AP MLD does not have a separate TSF timer for the non-primary link (based on the NSTR Soft AP MLD) but can use the TSF timer managed using the primary link. That is, in one aspect of the present invention, the NSTR AP MLD and the non-AP STA MLD combined with the NSTR AP MLD can use an MLD-level (MLD unit, MLD common) timer. In this case, for stable operation of the NSTR AP MLD and the non-AP STA MLD combined with the NSTR AP MLD, it may be required that time synchronization between APs in the NSTR AP MLD and / or between STAs in the non-AP STA MLD combined with the NSTR AP MLD be maintained with an error below a predetermined value. For example, NSTR AP MLD may be required to maintain the timestamp difference (or the difference between timers) maintained between the AP of the primary link and the AP of the non-primary link at or below a predetermined value. For example, non-AP STA MLD combined with NSTR Soft AP MLD may be required to maintain the timestamp difference maintained between the STA of the primary link and the STA of the non-primary link at or below a predetermined value.

[0244] In other words, the TSF timer of the primary link may be maintained (or applied or used) the same for all links for APs included in or affiliated with the NSTR AP MLD. Also, the difference between the timestamp or TSF timer of any two APs included in or affiliated with the NSTR AP MLD may be limited to within a specific value (e.g., 30 us).

[0245] That is, the TSF timers of all APs included in or affiliated with the NSTR AP MLD may be the same, and the difference or clock drift between timestamps or TSF timers between two APs included in or affiliated with the AP MLD or NSTR AP MLD (e.g., an AP of a primary link and an AP of a non-primary link) may be limited to within a specific value (e.g., ±30 us), in which case the AP MLD or NSTR AP MLD can correct the timestamps or TSF timers so that the difference or clock drift between the TSF timers is within the specific value.

[0246] In addition, when a non-AP STA MLD combined with an NSTR AP MLD receives a TIM frame over a non-primary link, it may need to receive the next beacon frame transmitted over the primary link. More specifically, when a non-AP STA MLD receives a TIM frame through a non-primary link STA and the value indicated in the Check Beacon field in the TIM frame action field is different from the Check Beacon value it maintains, it may need to receive the next beacon frame transmitted over the primary link. In this case, the next beacon frame may refer to a beacon frame transmitted corresponding to the TBTT of the primary link that exists after the time the TIM frame was received over the non-primary link. In this case, receiving the next beacon frame may involve (include) updating parameters of the non-primary link using a STA-specific profile (corresponding to the AP of the non-primary link) included in the beacon frame. In this case, the parameters to be updated may be limited to parameters related to a critical update.

[0247] <Non-primary link channel switching and channel quieting procedures>

[0248] As described above, NSTR AP MLD does not transmit beacon frames on non-primary links, and therefore, the BSS operation based on the beacon frame transmission timing may be performed in a manner different from the BSS operation of general AP MLD.

[0249] Conventional Wi-Fi can change the operating channel frequency (operating frequency band) of a BSS through a procedure previously agreed upon between the AP and STA. This can be achieved using the conventional Extended Channel Switching (ECS) operation or the newly defined channel change mechanism in 11be. When an AP decides to change the operating channel of a BSS, it transmits a beacon frame, probe response frame, Extended Channel Switch Announcement frame, etc. to inform associated STAs that they can switch to a new channel and operating class while maintaining their association. In this case, the AP transmits an Extended Channel Switch Announce element in a beacon frame, and the Channel Switch Count field of the element indicates information about the number of subsequent beacon frame transmissions required before a channel switch (operating channel change) occurs. If the AP includes a MAX Channel Switch Time element in a beacon frame along with an Extended Channel Switch Announcement element, the AP must transmit the first beacon frame on the new channel within the Switch Time field (of the Max Channel Switch Time element). That is, the beacon frame transmitted on the new channel must be transmitted at a time interval smaller than the time interval indicated by the Switch Time field from the last beacon frame transmitted on the current channel.

[0250] Referring to the channel change operation of the conventional Wi-Fi BSS described above, the AP of the BSS can use a beacon frame transmitted on the current channel to indicate to the STA information about the new channel, information about the time when the channel change will occur, and information related to the time of the first beacon frame transmitted on the new channel. The STA of the BSS can complete the channel change while maintaining association with the AP by moving to the new channel during a predetermined time interval (the time interval indicated by the AP) based on the channel change-related information included in the beacon frame transmitted by the AP. As such, the channel change procedure of the conventional Wi-Fi BSS is performed in a manner in which information required for the channel change (e.g., channel switch mode, new operating class, new channel number, channel switch count) is provided by the beacon frame transmitted by the AP. Therefore, in the case of a BSS of a non-primary link of an NSTR AP MLD in which beacon frames are not transmitted, a channel change cannot be performed using the conventional channel change procedure.

[0251] In addition, when conventional Wi-Fi sets a quiet interval, information about the time period to which the quiet interval applies is indicated by elements (quiet element, quiet channel element) included in the beacon frame transmitted by the AP of the BSS, and similar to the channel change procedure, the non-primary link of the NSTR AP MLD, which does not transmit a beacon frame, cannot use the conventional quieting procedure to set the quiet interval.

[0252] According to one embodiment of the present invention, the NSTR AP MLD can indicate information required for switching the operating channel of the non-primary link (channel switching) and / or information required for setting the quiet interval through a beacon frame transmitted through the primary link. That is, the non-AP STA MLD associated with the NSTR AP MLD can operate based on information obtained through a beacon frame of the primary link to perform channel switching of the non-primary link. That is, the non-AP STA MLD associated with the NSTR AP MLD can obtain information related to the quiet interval of the non-primary link using a beacon frame of the primary link.

[0253] That is, in the case of STR AP MLD, APs included in the same AP MLD can periodically transmit beacon frames. In this case, these APs can include basic information for other APs in the beacon frames they transmit, and the basic information for other APs can include information related to channel changes of other APs (e.g., channel switch announcement element, extended channel switch announcement element, max channel switch element) and / or information for setting a quiet interval.

[0254] In this case, the channel switch guide element and the extended channel switch guide element may include a new channel number field and a channel switch count field indicating the number of the channel to be changed.

[0255] The Channel Switch Count field indicates the number of TBTTs until the STA that transmitted the Channel Switch Count field switches to a new channel. If the value of the Channel Switch Count field is set to '1', a channel switch occurs at the next TBTT. If the value of the Channel Switch Count field is set to '0', a channel switch may occur any time after the Channel Switch Count field is transmitted.

[0256] The channel switch guide element and the extended channel switch guide element may be transmitted in a channel switch guide frame, a beacon frame, and a probe response frame.

[0257] The station may further include a new operating class field in the extended channel switch guide element to indicate the operating class to which it is being changed.

[0258] The maximum channel switch time element may indicate a period during which a beacon may be transmitted on a changed channel from the time when channel switching begins. For example, if a channel change is successful, a station (e.g., an AP STA) that performed the channel change may transmit a beacon on a new changed channel within the time indicated by the maximum channel switch time element from the time when channel switching began.

[0259] In this case, the Max Channel Switch Time element may include a Switch Time field that indicates the interval for transmitting a beacon on the new channel.

[0260] Channel change information for changing the channels of other APs included in the same AP MLD may be transmitted by each AP under the assumption that the APs included in the same AP MLD periodically transmit beacons. However, APs included in the same AP MLD that support NSTR can transmit beacon frames only via the primary link. That is, only a specific AP among multiple APs included in the same AP MLD can transmit beacons via the primary link, and the remaining APs cannot transmit beacons. Therefore, in this case, even if the APs for the non-primary links do not transmit beacon frames, the APs for the primary links can transmit channel change information of the APs for the non-primary links by including it in a beacon frame.

[0261] More specifically, the NSTR AP MLD will have to include a STA-specific profile for the non-primary link AP in the primary link beacon frame (and (ML) probe response frame) when performing channel switching for the non-primary link or setting the quiet interval.

[0262] Figure 17 shows an example of the format of elements according to an embodiment of the present invention. Figure 17 shows an example of the format of each element described above.

[0263] Referring to FIG. 17, a (corresponding) STA-specific profile for an AP of a non-primary link may have a configuration including at least one of a Channel Switch Announcement element, an Extended Channel Switch Announcement element, a Max Channel Switch Time element, a Quiet element, and a Quiet Channel element.

[0264] The timing field of the element should be set based on the TBTT (Target Beacon Transmission Time) and Beacon Interval of the primary link.

[0265] Specifically, when an AP included in a general AP MLD transmits channel change information for other APs in a frame, elements for channel change of other APs (e.g., channel switch guide element, extended channel switch guide element, maximum channel switch time element, quiet element, quiet channel element, etc.) may be set and transmitted based on the AP performing the channel change rather than the AP transmitting the channel change information.

[0266] However, in the case of AP MLD supporting NSTR (NSTR AP MLD), only the AP for the primary link transmits beacon frames, and the AP for the non-primary link does not transmit beacon frames, so the channel change information and / or quiet interval information of the AP for the non-primary link may be set based on the AP for the primary link rather than the AP for the non-primary link.

[0267] Specifically, an AP configuring AP MLD may transmit a STA-specific profile including channel change information and / or quiet interval-related information for non-primary link APs via a primary link using a specific frame (e.g., a beacon frame). In this case, the channel change information and / or quiet interval-related information for non-primary link APs may be set based on the primary link AP.

[0268] For example, timing fields (e.g., time-related fields including duration-related fields (e.g., Switch Time, Quiet Duration fields, etc.) and point-in-time-related fields (e.g., Channel Switch Count, Quiet Count fields, etc.)) included in the channel switch guide element, extended channel switch guide element, quiet element, and / or quiet channel element should be applied by referring to the most recent TBTT and BI indicated in the corresponding element of the AP operating on the primary link.

[0269] A primary link AP in NSTR AP MLD must set the timing fields of the Channel Switch Announcement element, Extended Channel Switch Announcement element, Max Channel Switch Time element, Quiet element, and Quiet Channel element included in the STA-specific profile (included in the beacon frame and (ML) probe response frame) for non-primary link APs based on its own beacon interval and TBTT. Here, the timing fields are used to collectively refer to time-related fields including duration-related fields (switch time, Quiet Duration field, etc.) and time-point-related fields (channel switch count, Quiet Count field, etc.).

[0270] Therefore, the non-AP MLD combined with the NSTR AP MLD must receive a beacon frame from the AP of the NSTR AP MLD operating on the primary link, obtain information related to channel switching and / or quiet interval of the non-primary link from the STA-specific profile included in the beacon frame, and then analyze the information related to channel switching and / or quiet interval of the non-primary link based on the TBTT and BI (Beacon interval) of the primary link. Here, the STA-specific profile refers to the STA-specific profile corresponding to the AP of the non-primary link.

[0271] Meanwhile, after completing channel switching of the non-primary link using a beacon frame of the primary link (after completion of announcement and channel switching), the NSTR AP MLD must transmit a TIM frame (of the non-primary link) on the new channel within the time indicated by the Switch Time field (Max Channel Switch Time element). That is, after performing channel switching, the non-primary link AP of the NSTR AP MLD must transmit a TIM frame on the new channel. In this case, the non-primary link AP must transmit a TIM frame on the new channel within the time indicated by the Switch Time field after transmitting a beacon frame on the primary link with the Channel Switch Count subfield set to 1 (or 0). In this case, the Channel Switch Count field and the Switch Time field may be included in a STA-specific profile (corresponding to a non-primary AP) included in a beacon frame transmitted on the primary link. In this case, the TIM frame may be replaced with another frame transmitted on the new channel of the primary link or non-primary link. For example, after completing channel switching of the non-primary link, the NSTR AP MLD may transmit a beacon frame indicating information related to the completion of channel switching on the primary link. In this case, the beacon frame may be an additional beacon frame transmitted regardless of the TBTT. In this case, the beacon frame may be a beacon frame configured to include complete information for the non-primary link. For example, the beacon frame configured to include complete information for the non-primary link may be a beacon frame in which the Complete information subfield of the STA-specific profile corresponding to the AP of the non-primary link is set to 1.In this case, the primary link beacon frame transmitted after the channel switching of the non-primary link is completed should be transmitted within a predetermined time from the beacon frame transmitted before the channel switching started. In this case, the predetermined time may be the time indicated in the Switch Time field (of the Max Channel Switch Time element). Alternatively, the beacon frame may be a beacon frame including an indication related to the channel switching of the non-primary link. For example, the primary link beacon frame transmitted after the channel switching of the non-primary link is completed may include a Channel Switch Complete subfield. In this case, the Channel Switch Complete subfield may be a subfield included in the ML element. A specific Switch Complete subfield may be indicated as 1 when the channel switching of the AP corresponding to the STA-specific profile including the specific subfield is completed. That is, after completing the channel switching of the non-primary link, the AP should set the Channel Switch Complete subfield of the STA-specific profile (of the beacon frame) corresponding to the AP of the non-primary link to 1. At this time, the beacon frame related to the channel switching may be transmitted (utilized) for the same purpose even if the AP MLD is not the NSTR AP MLD, that is, even if the AP MLD is a general AP MLD.

[0272] The non-AP MLD combined with the NSTR AP MLD can perform operations that consider the channel switching of the non-primary link to be complete only when it receives a frame (a TIM frame or other frame of the non-primary link and / or a beacon frame indicating information related to the completion of the channel switching of the primary link) promised from the AP MLD after performing channel switching of the non-primary link on the primary link. That is, information about the channel switch for the AP of the non-primary link included in the AP MLD supporting NSTR (e.g., channel change information) may be transmitted by the AP of the primary link. In this case, even if the channel switch is completed, the AP of the non-primary link cannot transmit a beacon frame on the changed channel because it is not the primary link. Therefore, in this case, the AP of the non-primary link can transmit a TIM frame indicating the completion of the channel switch when the channel switch is completed, thereby informing stations of the non-AP MLD that the channel switch is completed. Alternatively, the AP of the primary link can transmit a beacon frame indicating that the channel switch to the AP of the non-primary link has been completed, thereby instructing the non-AP MLD station that the channel switch has been completed.

[0273] If the channel switching is considered to be incomplete, the non-AP STA MLD will consider the channel switching of the non-primary link to be canceled and will have to operate (revert to) the previous channel (before the channel switching took place).

[0274] Alternatively, the NSTR Soft AP MLD may set a specific subfield of a beacon frame transmitted on the primary link to a specific value while a non-primary link AP (the AP's BSS) is performing channel switching. More specifically, the beacon frame transmitted on the primary link by the NSTR Soft AP MLD may include a subfield that is maintained at 1 or 0 while the non-primary link AP is performing channel switching and is indicated as 0 or 1 during time periods when the non-primary link AP is not performing channel switching. That is, the NSTR Soft AP MLD must set the subfield based on whether the non-primary link AP is performing channel switching. In this case, the subfield may be a subfield included in the RNR element corresponding to the non-primary link AP or a STA-specific profile.

[0275] As described above, when the NSTR Soft AP MLD determines the value of the subfield based on whether the AP of the non-primary link is performing channel switching, a non-AP MLD associated with the NSTR Soft AP MLD can determine whether the channel switching of the non-primary link AP (BSS) is being performed based on the value of the subfield indicated in a beacon frame received on the primary link. That is, the non-AP MLD can determine that the AP of the non-primary link is performing channel switching by confirming that the subfield corresponding to the AP of the non-primary link is indicated as a specific value (e.g., 1) in a beacon frame received on the primary link. If the non-AP MLD confirms that the subfield corresponding to the AP of the non-primary link is not a specific value in a beacon frame received on the primary link, the non-AP MLD can determine that the AP of the non-primary link has completed the scheduled channel switching. In this case, the completion can mean that the channel switching operation indicated by the most recently received (extended) channel switching guide element corresponding to the non-primary link AP has been completed or canceled. If the subfield corresponding to the non-primary link AP is indicated as a non-specific value (a value other than the value indicated when channel switching is in progress), the non-AP MLD can consider that the non-primary link AP is operating in (or as) the operating channel / class indicated in the most recently received beacon frame (or probe response frame). When attempting to transmit an UL PPDU over the non-primary link, the non-AP MLD should transmit the UL PPDU based on whether the non-primary link AP is operating in its recognized channel (class).For example, Non-AP MLD can transmit an UL PPDU only when the subfield corresponding to the AP of a non-primary link is indicated as a non-specific value, whereas Non-AP MLD may consider that the AP of a non-primary link is performing channel switching and may not transmit an UL PPDU when the subfield corresponding to the AP of a non-primary link is indicated as a specific value.

[0276] As another method, the NSTR Soft AP MLD can maintain the Critical Update Flag of the beacon frame (or probe response frame) at 1 until the non-primary link AP (AP's BSS) completes channel switching. The NSTR Soft AP MLD helps the non-AP MLD to recognize the scheduled channel switching of the non-primary link by including an (extended) channel switching guidance element corresponding to the non-primary link AP in the beacon frame. In this case, the NSTR Soft AP MLD must set the Critical Update Flag subfield of the beacon frame to 1 when transmitting the (extended) channel switching guidance element in the beacon frame (transmitted on the primary link). The NSTR Soft AP MLD can make the non-AP MLD aware that the channel switching of the non-primary link is ongoing by maintaining the value of the Critical Update Flag subfield at 1 until the channel switching of the non-primary link is completed. In this case, the NSTR Soft AP MLD shall include an (extended) Channel Switch Announcement element (corresponding to the AP of the non-primary link) in the beacon frame until the AP of the non-primary link completes channel switching. In this case, when the AP of the non-primary link is performing channel switching, the NSTR Soft AP MLD shall indicate the Channel Switch Count subfield of the Channel Switch Announcement element corresponding to the AP of the non-primary link as 0. In this case, when the AP of the non-primary link is performing channel switching, the NSTR Soft AP MLD shall indicate the SwitchTime subfield of the Channel Switch Timing element corresponding to the AP of the non-primary link as the time value until the predicted completion of channel switching.In this case, the NSTR Soft AP MLD sets the SwitchTime subfield to a specific value (for example, 65535) so that it is not necessary to specify the channel switching completion time of the non-primary link AP.

[0277] As described above, if the NSTR Soft AP MLD maintains the value of the Critical Update Flag subfield at 1 when the AP of the non-primary link is switching channels, the non-AP MLD may not transmit a UL PPDU on the non-primary link when the value of the Critical Update subfield is 1. More specifically, if the Critical Update Flag subfield of a beacon (probe response) frame received from the NSTR Soft AP MLD is 1 and the Channel Switch Count subfield corresponding to the non-primary link AP is indicated as 0, the non-AP MLD may not transmit a UL PPDU on the non-primary link. Even more specifically, if the Critical Update Flag subfield of a beacon (probe response) frame received from the NSTR Soft AP MLD is 1 and the Switch Time subfield corresponding to the non-primary link AP is indicated as a non-zero value, the non-AP MLD may not transmit a UL PPDU on the non-primary link.

[0278] Alternatively, the NSTR Soft AP MLD can indicate that a non-primary link AP (the BSS of the AP) has completed channel switching by incrementing the value of the BSS Parameter Change Count subfield corresponding to the non-primary link AP. In this case, the BSS Parameter Change Count subfield refers to the BSS Parameters Change Count subfield in the MLD Parameters field of the TBTT Information field corresponding to the non-primary link AP. While a general AP MLD increments the value of the BSS Parameters Change Count subfield by 1 only when the AP parameter r corresponding to the BSS Parameters Change Count subfield is updated, the NSTR Soft AP MLD can also increment the BSS Parameters Change Count subfield corresponding to the non-primary link AP when channel switching is completed. This can be understood as incrementing the value of the BSS Parameters Change Count subfield as a method for indicating to the non-primary link AP that the instructed channel switching operation has been completed. When the non-AP MLD determines that channel switching of the non-primary link AP is scheduled / in progress, it can determine that the scheduled / in progress channel switching has been completed if the value of the BSS Parameters Change Count subfield is incremented by 1. In this case, the non-AP MLD can transmit an UL PPDU after determining that the scheduled / in progress channel switching has been completed. The operation of the non-AP MLD regarding the UL PPDU transmission conditions is the same as the other examples of the channel switching completion indication methods described above, and therefore, a description thereof will be omitted.

[0279] As another method, the NSTR Soft AP MLD can transmit a frame on the primary link including subfields indicating different values ​​when a non-primary link AP (the AP's BSS) is planning to switch channels, when channel switching is in progress, and when channel switching is complete. In this case, the frame may be a beacon frame. More specifically, when channel switching for a non-primary link AP is planned, the NSTR Soft AP MLD can indicate an (extended) Channel Switch Announcement element corresponding to the non-primary link AP and indicate a specific subfield to a specific value (e.g., 1). When channel switching for the non-primary link AP is initiated, the NSTR Soft AP MLD can set the specific subfield to a value other than the specific value (e.g., 2) until channel switching is complete. When channel switching for the non-primary link AP is completed, the NSTR Soft AP MLD can set the specific subfield to an initial value (e.g., 0). In this way, the NSTR Soft AP MLD sets the value of a specific subfield corresponding to a non-primary link AP to different values ​​when channel switching is scheduled, when channel switching is in progress, and when channel switching is completed (when channel switching is not scheduled), allowing an associated non-AP MLD to recognize the progress of channel switching of the non-primary link. The non-AP MLD can determine whether to transmit an UL PPDU over the non-primary link by checking the specific subfield included in a frame received over the primary link. For example, the non-AP MLD can transmit an UL PPDU only if the specific subfield most recently received is the initial value.

[0280] As another method, the non-AP MLD can determine whether the non-primary link AP has completed channel switching based on the primary link beacon frame received after the scheduled channel switching completion time of the non-primary link AP indicated (published) by the NSTR Soft AP MLD.

[0281] Furthermore, the non-AP MLD can determine whether the scheduled channel switching is complete by checking the Operating Channel / Class information of the non-primary link AP indicated in a beacon frame received on the primary link after the channel switching completion time of the non-primary link AP confirmed by an element related to channel switching. The method for checking the channel switching completion time of the non-primary link AP by the element related to channel switching may be to use the value indicated in the SwitchTime subfield of the Channel Switch Timing element. When the non-AP MLD confirms that the same information as the Operating Channel / Class for which channel switching was scheduled is indicated for the non-primary link AP in a beacon frame received after the scheduled channel switching completion time, it can determine that the non-primary link AP has completed the scheduled channel switching and transmit an UL PPDU. That is, the non-AP MLD can transmit an UL PPDU over the non-primary link when it receives a beacon frame (over the primary link) for the first time after the scheduled channel switching completion time of the non-primary link. In this case, the channel / class in which the non-AP MLD transmits the UL PPDU may be the operating channel / class of the non-primary link AP indicated in the first beacon frame.

[0282] In addition, NSTR AP MLD may not be able to perform channel switching of non-primary links. However, when NSTR AP MLD attempts to perform channel switching of non-primary links, it can release the non-primary link AP operating on the existing channel and operate as if a new non-primary link AP had been added on the new channel.

[0283] In yet another embodiment of the present invention, the NSTR AP MLD may be restricted from setting a quiet interval on a non-primary link. In this case, if a quiet interval is defined (set) for the primary link, the quiet interval for the non-primary link may be defined (set) to the same time interval as the quiet interval for the primary link. In other words, when the non-AP STA MLD combined with the NSTR AP MLD recognizes the quiet interval for the primary link, it can consider that a quiet interval for the same time interval is also set for the non-primary link.

[0284] In this way, the quiet element for the non-primary link transmitted in the beacon frame of the primary link may be set (instructed) by the NSTR AP MLD as follows:

[0285] 1. The Quiet Count field may be set to the number of TBTTs of the primary link remaining until the next quiet interval begins on the non-primary link.

[0286] 2. The Quiet Period field may be set to a value (in primary link beacon interval units) related to how many primary link beacon intervals the regular (periodic) quiet interval of the non-primary link defined by the Quiet element starts every (set to 0 if not a regular quiet interval).

[0287] 3. The Quiet Offset field may be set to a time value (in TU) associated with the offset at which the quiet interval of the non-primary link begins from the TBTT of the primary link identified by the Quiet Count subfield.

[0288] The (extended) Channel Switch Announcement element and Max Channel Switch Time element for the non-primary link transmitted in the beacon frame of the primary link may be set (instructed) by the NSTR AP MLD as follows:

[0289] 1. The Channel Switch Count field (of the Channel Switch Announcement element) may be set to information related to the number of remaining TBTTs of the primary link until channel switching of the non-primary link begins. If channel switching of the non-primary link AP begins in the next TBTT of the primary link, the Channel Switch Count field (associated with the non-primary link AP) of the beacon frame transmitted in this TBTT may be set to 1 or 0.

[0290] 2. The Switch Time field (of the Max Channel Switch Time element) may be set to a value corresponding to the maximum time difference between the primary beacon frame (the beacon frame with the Channel Switch Count field set to 1 or 0 in 1 above) transmitted in the TBTT immediately before the TBTT at which channel switching of the non-primary link began and the TIM frame transmitted on the new channel of the non-primary link after channel switching of the non-primary link is completed. For example, if the beacon interval of the primary link is 100 ms and the Switch Time field (for the non-primary link AP) is set to 200 ms, the non-primary link AP must transmit a TIM frame on the new channel within 200 ms from the time of transmitting the beacon frame of the primary link at which it initiated channel switching.

[0291] Therefore, after receiving a beacon frame over the primary link, the non-AP MLD combined with the NSTR AP MLD can obtain information about the quiet interval and channel switching time and duration of the non-primary link based on the information indicated in the STA-specific profile of the non-primary AP included in the beacon frame and the TBTT and beacon interval information of the primary link. In this case, the non-AP MLD can set (recognize and analyze) the start time of the quiet interval of the non-primary link based on the TBTT of the primary link. In this case, the non-AP MLD can recognize / analyze the channel switching time of the non-primary link based on the reception time of the beacon frame received over the primary link.

[0292] Conventionally, Wi-Fi non-AP STAs can choose whether to perform channel switching together with the AP to maintain association with the AP when the AP performs channel switching. However, a non-AP STA MLD associated with an NSTR AP MLD must perform channel switching on the non-primary link when the NSTR AP MLD performs channel switching on the non-primary link.

[0293] If a non-AP STA MLD that has performed ML setup with the NSTR AP MLD (i.e., ML setup using primary and non-primary links) decides not to perform channel switching of the non-primary link, the non-AP STA MLD will have to terminate (cancel or change) the ML setup with the NSTR AP MLD and change to a state set up with only the primary link (by termination and setup or re-setup).

[0294] That is, a non-AP MLD station that receives channel change information related to channel switching to a non-primary link AP from a primary link AP included in an AP MLD that supports NSTR can decide whether to switch channels together with the non-primary link AP.

[0295] If a station associated with an AP of a non-primary link decides to perform channel switching, the station moves to the changed channel and receives a specific frame (e.g., a TIM frame) from the AP of the non-primary link indicating that channel switching has been completed, or the AP of the primary link may receive a beacon frame indicating that channel switching of the AP of the non-primary link has been completed. The non-AP STA that receives the TIM frame or beacon frame can recognize that channel switching has been completed and can transmit and receive frames on the changed channel.

[0296] However, if a station associated with the AP of a non-primary link decides not to perform channel switching, the non-AP STA that does not perform channel switching may terminate (cancel or change) the multiple link configuration with the AP of the non-primary link. In this case, the link configuration between the AP and the non-AP STA of the non-primary link is cancelled, so that only the single link configuration of the primary link exists for the AP MLD and STA MLD.

[0297] If a non-AP STA that has a link established with the primary link AP does not perform channel switching to the primary link AP, the non-AP STA can choose whether to move to another BSS and establish a link with the AP of the other BSS.

[0298] Meanwhile, the NSTR Soft AP MLD must set the time interval for channel switching on the primary link to the quiet interval of the non-primary link BSS. This may be due to the constraint that the NSTR Soft AP MLD and a non-AP STA associated with the NSTR Soft AP MLD can occupy the non-primary link only when they occupy the primary link. When the NSTR Soft AP MLD performs channel switching for the primary link AP (BSS), the NSTR Soft AP MLD and associated non-AP MLD restrict communication not only on the primary link but also on the non-primary link. Therefore, when the NSTR Soft AP MLD performs channel switching for the primary link AP (BSS), it must specify the same time interval as the channel switching interval as the quiet interval of the non-primary link AP (BSS). Alternatively, even if the NSTR Soft AP MLD does not separately specify a quiet interval for the non-primary link, the non-AP MLD associated with the NSTR Soft AP MLD must not transmit UL PPDUs on the non-primary link from the start of channel switching of the primary link until the completion of channel switching (until the first beacon frame is received on the new channel of the primary link). In this case, the non-AP MLD can generate a new backoff counter when the backoff counter becomes 0 during the time period when no UL PPDUs are transmitted on the non-primary link. In this case, the new backoff counter may be the backoff counter generated using the current CW (Contention Window). In this case, counters related to retransmissions (such as the short retry count and long retry counter) remain unchanged.

[0299] Similarly, the NSTR Soft AP MLD should set the time interval set as the quiet interval in the primary link BSS as the quiet interval of the non-primary link BSS. This may be due to the restriction that the NSTR Soft AP MLD and a non-AP STA associated with the NSTR Soft AP MLD can occupy the non-primary link only when they occupy the primary link. When the NSTR Soft AP MLD sets the quiet interval for the primary link AP (BSS), the NSTR Soft AP MLD and associated non-AP MLD restrict communication on both the primary link and the non-primary link. Therefore, when the NSTR Soft AP MLD indicates (sets) the quiet interval for the primary link AP (BSS), it should indicate (set) the same time interval as the channel switching interval as the quiet interval of the non-primary link AP (BSS).

[0300] In this way, a non-AP MLD associated with an NSTR Soft AP MLD may not transmit UL PPDUs on the non-primary link when channel switching is being performed on the primary link or when the quiet interval of the primary link is set. Therefore, the non-AP MLD can perform power save operations on non-AP STAs operating on the non-primary link when channel switching on the primary link is being performed or the quiet interval is in progress. This may be a power save operation that uses the AP not transmitting DL PPDUs on the non-primary link when channel switching on the primary link is in progress or the quiet interval is in progress for non-AP STAs operating on the non-primary link. Furthermore, even if a non-AP STA operating on the non-primary link completes a channel access operation (e.g., an EDCA backoff operation), UL PPDU transmission on the non-primary link is restricted, so the non-AP MLD may decide to stop the channel access operation on the non-primary link. For example, when NSTR Soft AP MLD is performing channel switching or a quiet interval on the primary link, the non-AP MLD can suspend the channel access operation and / or CCA operation of the non-AP STA operating on the non-primary link. In this case, suspending the channel access operation and / or CCA operation can mean operating in a doze state in a power save mode.

[0301] Considering that a non-AP MLD STA has performed a power save operation (e.g., maintained a doze state) for a non-AP STA operating on a non-primary link, the NSTR Soft AP MLD can transmit an assistance frame on the non-primary link when the channel switching / quiet interval of the primary link ends. The assistance frame may be transmitted to guide the non-AP STA on the non-primary link to reset the NAVSyncDelay timer that was activated after the STA transitioned to awake. The assistance frame may be transmitted at a basic rate. The assistance frame may be transmitted simultaneously with the transmission of a beacon frame on the primary link. The NAVSyncDelay timer may refer to a timer associated with the time during which the STA transitioning from the doze state to awake must perform CCA to set its NAV.

[0302] FIG. 18 illustrates an example of a process in which an NSTR Soft AP MLD sets (defines) a quiet interval for a non-primary according to an embodiment of the present invention.

[0303] Referring to FIG. 18, the NSTR AP MLD operates AP1 and AP2 on the primary link and non-primary link, respectively, and is connected to STA1 and STA2 of the Non-AP STA MLD, respectively.

[0304] In order to set (define) a quiet interval (Quiet interval #1 in FIG. 18) for the non-primary link, the NSTR AP MLD can transmit a beacon frame transmitted via AP1 of the primary link including a Per-STA profile corresponding to AP2. The Per-STA profile corresponding to AP2 includes a Quiet element and indicates information related to the start time of the quiet interval (Quiet interval #1 in FIG. 18) in the Quiet Count and Quiet Offset fields. When the Quiet element is included in the first beacon frame (Beacon #1 in FIG. 18) of the primary link shown in FIG. 18, the Quiet Count field is set to 2 and the Quiet Offset field is set to a value indicating "x" TU (Time Unit, 1024 us), and in the second beacon frame (Beacon #2 in FIG. 18), the Quiet Count field is set to 1.

[0305] A non-AP STA MLD that receives the first and / or second beacon frame on the primary link can recognize that a quiet interval has been set (announced by the AP MLD) on the non-primary link by checking the Quiet element included in the Per-STA profile (corresponding to AP2) of the beacon frame, and that the quiet interval (Quiet interval #1 in Figure 18) begins when "x" TUs have elapsed since the TBTT corresponding to the third beacon frame.

[0306] As shown in Figure 18, the NSTR AP MLD can again include the Per-STA profile corresponding to AP2 in the beacon frame transmitted via AP1 on the primary link to further set (define) the next quiet interval (Quiet interval #2 in Figure 18) on the non-primary link. The sixth beacon frame (Beacon #6 in Figure 18) on the primary link shown in Figure 18 has the Quiet Count field set to 2 and the Quiet Offset field set to a value indicating 0TU (Time Unit, 1024 us), and the seventh beacon frame (Beacon #7 in Figure 18) has the Quiet Count field set to 1.

[0307] A non-AP STA MLD that receives the sixth and / or seventh beacon frame on the primary link can recognize that a quiet interval (Quiet interval #2) has been set (announced by the AP MLD) on the non-primary link by checking the Quiet element included in the Per-STA profile (corresponding to AP2) of the beacon frame, and that the quiet interval (Quiet interval #2) begins from the TBTT corresponding to the eighth beacon frame.

[0308] At this time, information about the length of the quiet interval is indicated by the Quiet Duration field indicated together with the Quiet element.

[0309] FIG. 19 illustrates an example of a method for an NSTR Soft AP MLD to perform a non-primary channel switch according to an embodiment of the present invention.

[0310] Referring to FIG. 19, the NSTR AP MLD operates AP1 and AP2 on the primary link and non-primary link, respectively, and is connected to STA1 and STA2 of the Non-AP STA MLD, respectively.

[0311] To change the non-primary link to a new channel, the NSTR AP MLD can include a Per-STA profile corresponding to AP2 (non-primary link) in a beacon frame transmitted via AP1 of the primary link. The Per-STA profile corresponding to AP2 includes an (Extended) Channel Switch Announcement element and a Max Channel Switch Time element, indicating information related to the time when a channel change begins and the time duration for transmitting a TIM frame on the new channel after the channel change. When the (Extended) Channel Switch Announcement element is included in the first beacon frame of the primary link (Beacon #1 in FIG. 19) shown in FIG. 19, the Channel Switch Count field is set to 2, and in the second beacon frame (Beacon #2 in FIG. 19) it is set to 1.

[0312] A non-AP STA MLD that receives the first and / or second beacon frame on the primary link can determine by checking the (Extended) Channel Switch Announcement element included in the Per-STA profile (corresponding to AP2) of the beacon frame that a channel change (to a new channel) of the non-primary link begins after receiving the second beacon frame and that AP2's TIM frame will be received on the new channel within "x" TUs from the time the second beacon frame is received. In this case, the new channel may be the channel corresponding to the value indicated in the New Channel Number field included in the (Extended) Channel Switch Announcement element. In this case, the "x" TUs may be the time value indicated in the Switch Time field included in the Max Channel Switch Time element included in the Per-STA profile (corresponding to AP2).

[0313] <Operation Restrictions of non-AP STA MLD Combined with NSTR AP MLD>

[0314] NSTR AP MLD is an AP MLD where the primary link and the non-primary link are NSTR link pairs. Therefore, during the transmission of a PPDU via the AP of the primary link, the AP of the non-primary link may go into the BLIND state. Conversely, when the AP of the non-primary link transmits, the AP of the primary link may go into the BLIND state. In this case, the AP of the NSTR AP MLD that has gone through the BLIND state may need to set the MediumSyncDelay to a pre-set value.

[0315] MediumSyncDelay is a single timer commonly applied to the EDCAF (EDCA Function) of the STA. When MediumSyncDelay is not 0, additional restrictions may be applied when the STA acquires a TXOP. At this time, the additional restrictions may be: (1) the first transmission attempt to obtain a TXOP must be an RTS frame; (2) only attempts to acquire a TXOP a pre-set number of times or less (until it decreases to 0) are allowed while MediumSyncDelay is applied; (3) utilize a CCA ED (energy detection) threshold that is stricter (lower: for example, -72dBm to -62dBm) than when MediumSyncDelay is 0. That is, a STA with a non-zero MediumSyncDelay value has more restrictions applied in TXOP acquisition compared to a STA with MediumSyncDelay equal to 0.

[0316] Therefore, even in the case of NSTR AP MLD, MediumSyncDelay must be applied when the AP enters a BLIND state, and in situations where AP channel access is restricted, it may be difficult to provide normal service to STAs in the BSS. The NSTR AP MLD determines one of the links of the NSTR link pair for which the AP operates as the primary link, thereby managing transmissions over non-primary links (links other than the primary link) in a manner that prevents the primary link from entering a BLIND state. For example, the NSTR AP MLD can manage the primary link from entering a BLIND state by transmitting over the non-primary link only when a transmission over the primary link is in progress. For this purpose, even if the NSTR AP MLD receives a frame requesting a response frame via the AP of the non-primary link, it does not need to respond with the requested response frame. In other words, the NSTR AP MLD can operate not to respond with a response frame even if it receives a frame requesting a response frame via the AP of the non-primary link. At this time, the reason why the NSTR AP MLD does not respond with a response frame via the AP of the non-primary link may be to prevent the AP of the primary link from entering a BLIND state.

[0317] As described above, the NSTR AP MLD can manage the operation (transmission) of APs operating on the primary link and / or non-primary links to establish a primary link and prevent the AP on the primary link from entering a BLIND state. Similarly, a non-AP STA MLD combined with the NSTR AP MLD may need to understand and operate according to the primary link management method of the NSTR AP MLD. For example, if the non-AP STA MLD determines that a response frame has not been received from the NSTR AP MLD on the non-primary link, it may not transmit a frame requesting a response on the non-primary link. Furthermore, if the non-AP STA MLD transmits a frame requesting a response on the non-primary link and then fails to receive a response from the NSTR AP MLD, it may not retransmit the frame requesting a response. For example, if the non-AP STA MLD transmits an RTS frame to the NSTR AP MLD on the non-primary link and fails to receive a CTS frame response, it may not retransmit the RTS frame. In this case, the Non-AP MLD does not need to attempt transmission to the NSTR AP MLD via the non-primary link until it receives a trigger frame via the non-primary link.

[0318] Furthermore, even if the non-AP MLD completes the channel access procedure of the non-primary link for UL transmission, it may postpone transmission on the non-primary link until the channel access procedure on the primary link is completed. In this case, the method by which the non-AP MLD postpones transmission on the non-primary link may be to suspend the backoff procedure performed by the STA of the non-primary link (more precisely, the EDCAF of the STA) until the backoff procedure performed by the STA of the primary link is completed. In this case, the method by which the non-AP MLD suspends the backoff procedure performed by the STA of the non-primary link may be to maintain a backoff counter at 0.

[0319] A non-AP STA MLD that has completed the channel access procedure on both the primary link and the non-primary link using the above method can perform simultaneous transmission (simultaneous UL PPDU transmission) on the primary link and the non-primary link. Here, "simultaneous transmission" means that the start times of each transmission are within a predetermined time interval. However, if only the channel access procedure on the primary link is completed and the channel access procedure on the non-primary link is not yet completed, the non-AP MLD can start PPDU transmission on the primary link only, or can start simultaneous transmission when the channel access procedure on the non-primary link is completed. That is, when transmitting to an NSTR AP MLD, the non-AP MLD can transmit using only the primary link, or can perform simultaneous transmission using the primary link and the non-primary link. However, a non-AP MLD may not be allowed to transmit PPDUs to an NSTR AP MLD using only the non-primary link.

[0320] In addition, non-AP MLD may require NSTR AP MLD to synchronize the end points of transmissions on both links when performing UL transmissions using both the primary link and the non-primary link. In this case, synchronizing the end points of transmissions may mean that transmissions on both links end within a predetermined time interval.

[0321] In addition, when NSTR AP MLD performs UL transmission using both the primary link and the non-primary link, the non-AP MLD may need to set whether the PPDUs transmitted on both links request a response frame. Furthermore, two UL PPDUs simultaneously transmitted by non-AP MLD on the primary link and the non-primary link may require both to request a response frame, or both to request a response frame. This restriction applies because if a response frame is only sent on a specific link as a result of UL transmission by non-AP MLD using both the primary link and the non-primary link, the AP operating on the other link of the NSTR AP MLD may enter a BLIND state. However, NSTR AP MLD does not need to send a response frame for both PPDUs if only one of two PPDUs received simultaneously (received on the primary link and the non-primary link, respectively) requests a response frame.

[0322] In addition, non-AP MLD may need to configure NSTR AP MLD so that when transmission is performed using both the primary link and the non-primary link, the TXOP of the non-primary link terminates at the same time as or earlier than the TXOP of the primary link. In other words, non-AP MLD may need to configure so that the TXOP of the non-primary link terminates at the same time as or earlier than the TXOP of the primary link. However, the non-primary link TXOP of the non-AP STA MLD may be allowed to terminate later than the TXOP of the primary link by a predetermined time interval.

[0323] In addition, the non-AP STA MLD can recognize that the NSTR AP MLD has experienced a BLIND state for an AP of a specific link and assist the AP in its operation. Furthermore, when the non-AP STA MLD recognizes that transmission has occurred on only one of the primary and non-primary links, it can determine that the AP of the other link that did not transmit must have experienced a BLIND state. In this case, the non-AP STA MLD can assist the AP in releasing the MediumSyncDelay (resetting it to 0) in consideration of the fact that the AP experiencing the BLIND state is restricted in channel access due to a non-zero MediumSyncDelay. In this case, the operation performed by the non-AP STA MLD may utilize the characteristic that MediumSyncDelay can be released when a NAV-configurable PPDU (including a valid MPDU) is received.

[0324] For example, after passing through the BLIND state, the non-AP STA MLD may transmit an Assist frame (a type of PPDU) capable of NAV setting to the AP of the NSTR AP MLD that is determined to have a non-zero MediumSyncDelay. Here, the Assist frame may refer to a frame included in a valid MPDU capable of NAV setting, regardless of the frame format. The condition under which the non-AP STA MLD transmits an Assist frame to the NSTR AP MLD over a specific link may be limited to when the state of the specific link confirmed by the non-AP STA MLD is in an IDLE state. Another condition under which the non-AP STA MLD transmits an Assist frame to the NSTR AP MLD may be limited to when the non-AP STA MLD is a non-AP STA MLD that has been explicitly or implicitly requested (instructed) by the NSTR AP MLD to transmit an Assist frame.

[0325] As mentioned above, non-AP MLD combined with NSTR Soft(mobile)AP MLD must operate taking into account the performance limitations of NSTR mobile AP MLD, resulting in more difficult operations than non-AP MLD combined with general AP MLD. For example, non-AP MLD combined with general AP MLD (AP MLD with only STR link pairs) can transmit PPDUs over two links by using independent channel access for each link, whereas non-AP MLD combined with NSTR mobile AP MLD must simultaneously start transmission over the primary and non-primary links, resulting in more difficult operations.

[0326] Therefore, non-AP MLDs that can perform multilink association (ML setup) with the NSTR mobile AP MLD may be limited to non-AP MLDs that support specific capabilities. Here, the specific capabilities may be related to the NSTR operation. That is, only non-AP MLDs that support the NSTR operation may be allowed to perform multilink association with the NSTR mobile AP MLD.

[0327] If a non-AP MLD that does not support NSTR operation (an MLD that supports only STR operation or only single-radio operation) attempts to associate with an NSTR mobile AP MLD, it must associate only with the primary link of the NSTR mobile AP MLD. In other words, a non-AP MLD that does not support NSTR operation cannot be associated with an NSTR mobile AP MLD simultaneously via both the primary link and non-primary link, but can only be associated via the primary link (single link association, single link setup). Therefore, a non-AP MLD that does not support NSTR operation must not send an association request frame to the NSTR mobile AP MLD requesting association including a non-primary link.

[0328] <Channel switching restrictions for non-AP MLDs that do not support NSTR operations>

[0329] According to the above-described embodiments of the present invention, the channel switching method and restrictions of NSTR Soft (mobile) AP MLD and non-AP MLD associated (associated) with NSTR mobile AP MLD have been described.

[0330] General AP MLDs that are not NSTR mobile AP MLDs support STR (simultaneous transmission and reception) for all link pairs, so they do not have another non-primary link. Therefore, each AP of the AP MLD can transmit beacon frames, probe response frames, etc. to the link (operating channel) on which it operates, and signal information related to channel switching to non-AP STAs. This means that each AP of the AP MLD can directly utilize the operations that conventional Wi-Fi APs have performed to change the operating channel of their BSS (or Operating Class). All non-AP STAs (all STAs of non-AP MLDs or STAs that are not MLDs) connected at each link can utilize the operations of non-AP STAs defined in conventional Wi-Fi to perform the channel switching instructed by the AP.

[0331] In addition, when a first AP (affected AP) belonging to a general AP MLD (AP MLD that is not a NSTR mobile AP MLD) transmits an (extended) Channel Switch element and a Max Channel Switch Time element in its beacon frame and (ML) probe response frame, other APs (reporting APs) belonging to the same AP MLD transmit the same elements in the STA-specific profile corresponding to the first AP. Therefore, a non-AP MLD that has performed AP MLD and ML setup can obtain information related to the channel switching instructed by the first AP by receiving the STA-specific profile for the first AP transmitted by the other AP, even without receiving a frame transmitted by the first AP. In this case, the timing field of the channel switching-related elements of the first AP transmitted by the other AP is set / interpreted based on the TBTT and BI of the first AP. This is because, unlike the non-primary link of NSTR mobile AP MLD, there is a TBTT and BI for the link of the first AP, and therefore, the channel switching information for the BSS of the first AP is set / interpreted based on the TBTT and BI of the BSS of the first AP, regardless of the link on which the information is received. Similarly, the MAX Channel Switch Time element for the BSS of the first AP is analyzed based on the transmission / reception time of the last beacon frame transmitted by the first AP, regardless of the link on which the element is received.

[0332] That is, when a general AP MLD other than an NSTR mobile AP MLD performs channel switching on a specific link, it signals information related to the channel switching of the specific link not only on the specific link but also on other links. Therefore, a non-AP MLD that has performed ML setup with a general AP MLD can obtain information related to channel switching more easily than when combined with an NSTR mobile AP MLD.

[0333] On the other hand, a non-AP MLD that has performed ML setup with a general AP MLD will have a new NSTR link pair after performing channel switching instructed by the AP MLD. This situation is caused by differences in hardware characteristics (such as interference screening ability) between the AP MLD and non-AP MLD, and may be because the AP MLD still supports STR for all link pairs even after channel switching, whereas the non-AP MLD cannot support STR for certain link pairs after channel switching.

[0334] As a simple example, AP MLD may support STR for a link pair that is 40 MHz apart (the operating channel separation distance between the two APs, or more specifically, the separation distance between the edges of the operating channels), while non-AP MLD may only support STR for link pairs that are 80 MHz or more apart. For example, if a non-AP MLD is initially connected through a first link and a second link that are 80 MHz apart, and the AP MLD performs channel switching for the first or second link, reducing the separation distance between the two links to 40 MHz, the AP MLD supports STR for the link pair that includes both links, but the non-AP MLD can no longer support STR. In this case, the link pair consisting of the first and second links becomes an NSTR link pair for the non-AP MLD after channel switching, and the non-AP MLD must support NSTR operation for the STAs operating on the NSTR link pair.

[0335] If a non-AP MLD that has an NSTR link pair as a result of channel switching instructed by the AP MLD, or that is expected to have an NSTR link pair after channel switching, does not support NSTR operation, the non-AP MLD will have to modify (disconnect or re-establish (ML)) the ML connection so that there are no NSTR-related link pairs among the links connected (set up, coupled) with the AP MLD. In other words, when a non-AP MLD that does not support NSTR operation has (or is expected to have) an NSTR link pair as a result of channel switching instructed by the AP MLD, it will have to change the state of its existing connection with the AP MLD so that there are no NSTR link pairs.

[0336] As a simple example of non-AP MLD operation, non-AP MLD may not perform channel switching as instructed by AP MLD and may instead perform an operation of disconnecting the AP of the link where channel switching has been performed (is to be performed). This may be a non-AP MLD operation selected to prevent the specific link and other links from entering an NSTR state due to the changed operating channel of the specific link. Alternatively, non-AP MLD may perform an operation of disconnecting the AP of other links that are predicted to be included in the NSTR link pair after the instructed channel switching is performed, rather than the link for which channel switching is instructed. This is another method of removing the NSTR link pair, and may be a non-AP MLD selection method that takes into account the capabilities of the link for which channel switching is instructed and the other links. In this case, the non-AP selection method that takes into account the capabilities may be an operation such as maintaining the link with the highest expected TPUT among the links of the NSTR link pair and tearing down the other links. As another method, the non-AP MLD can change the NSTR link pair to an STR link pair by changing the operating BW of the non-AP STA operating on the NSTR link pair. As such, since there are various methods for removing an NSTR link pair newly created (or expected to be created) by channel switching, various operations may be allowed depending on the selection of the non-AP MLD. However, a non-AP MLD that does not support NSTR operation must manage its connection state with the AP MLD to maintain a state in which it does not have an NSTR link pair.

[0337] In this case, the method by which the non-AP MLD predicts that a specific link pair will become an NSTR link pair may vary depending on the implementation. However, if the non-AP MLD indicates frequency separation distance information related to STR support to the AP MLD, the non-AP MLD should predict (evaluate) whether the link pair will become an NSTR link pair based on the separation distance information it indicates to the AP MLD. In this case, the frequency separation distance information related to STR support may be information that the non-AP MLD indicates to the AP MLD in the Frequency Separation For STR subfield included in the MLD Capabilities and operatings subfield.

[0338] As mentioned above, when the AP MLD instructs / performs channel switching, the non-AP MLD can change its connection state, such as releasing the link connected to the AP MLD. In this case, the non-AP MLD must instruct the AP MLD to change its connection state through the multi-link (re)setup procedure. The multi-link (re)setup procedure is performed by exchanging (re)association request / (re)association response frames between the non-AP MLD and the AP MLD. After the (ML) (re)setup procedure is completed, the non-AP MLD requests the setup of only those links that it wishes to maintain connection with the AP MLD through (re)association request frames.

[0339] However, a non-AP MLD that is connected to the AP MLD through only one link after the re-setup procedure must terminate the existing ML setup and perform a single-link association with the AP MLD. That is, if a non-AP MLD that was connected to the AP MLD through two or more links attempts to change to a state where it is connected to the AP MLD through only one link, the non-AP MLD must completely terminate its connection with the AP MLD (disconnect all links) and perform re-setup with a single link. In this case, the re-setup is a single-link setup, not a multi-link setup between MLDs. That is, the association request frame transmitted during the re-setup process does not include the per-STA profile of other STAs.

[0340] FIG. 20 illustrates an example of a method for managing ML (re)setup for channel switching according to an embodiment of the present invention.

[0341] 20, the AP MLD and the non-AP MLD that have performed multilink setup can perform MLD (re)setup to remove the NSTR link pair that is generated as a result of channel switching. In FIG. 20(a), before channel switching, the AP MLD and the non-AP MLD have completed multilink setup through Link1, Link2, and Link3.

[0342] The AP MLD instructed and performed channel switching to change the operating channel of Link2, and when the non-AP MLD performed the channel switching of Link2 instructed by the AP MLD, it determined that the separation distance between the frequencies of Link2 (Link2') and Link3 operating on the new operating channel was too close for it to support STR operation.

[0343] The non-AP MLD decides not to perform channel switching for Link2 and to disconnect STA2 from AP2 to prevent Link2' and Link3 from becoming an NSTR link pair. The non-AP MLD then enters a new type of multi-link setup state in which it is connected to the AP MLD only through the STR link pair Link1 and Link3 (see (b) of FIG. 20). At this time, the non-AP MLD may have performed ML (re)setup because it does not support NSTR operation.

[0344] FIG. 21 illustrates an example of a method for converting a single link operation based on channel switching according to an embodiment of the present invention.

[0345] Referring to FIG. 21, AP MLD and non-AP MLD with multi-link configuration may be converted to single link operation to eliminate NSTR link pairs generated as a result of channel switching.

[0346] Referring to Figure 21(a), before channel switching, the AP MLD and non-AP MLD are in a state where ML is set up through Link1 and Link2. The AP MLD instructs and executes channel switching to change the operating channel of Link2. When the non-AP MLD performs channel switching for Link2 as instructed by the AP MLD, it determines that the frequency separation distance between Link2 (Link2'), which operates on the new operating channel, and Link1 is too close for it to support STR operation. (Figure 21(b) shows the status of Link1 and Link2 as predicted (evaluated) by the non-AP MLD.)

[0347] For the purpose of avoiding operating the STA with the NSTR link pair, non-AP MLD terminates (Teardown, Disassociation) the MLD setup (the setup performed by MLD association) performed with the AP MLD and performs a new association. At this time, the non-AP that performs the new association does not operate as an MLD, but sets up with the AP in the same way as a single-radio non-AP STA.

[0348] After terminating the MLD setup, the non-AP that has performed the new setup is connected to the AP with a single link and operates as a single-radio non-AP STA that does not support all MLO (Multi-Link Operation).

[0349] <Channel Switching of non-AP MLD Supporting EMLSR Operation>

[0350] EMLSR (enhanced multi-link single radio) operation is an operation mode in which non-AP MLD supports listening for multiple EMLSR links (links in which STAs operating in EMLSR mode are operated), but frame exchange is performed with only one of the EMLSR links at a time. The EMLSR link pairs operated in EMLSR mode each perform a listening operation, and when frame exchange is performed on a specific EMLSR link, the RF chains of the other EMLSR links are used together in the frame exchange process of the specific EMLSR link. At this time, the listening operation means an operation that supports the reception of CCA (Clear Channel Assessment) and initial control frames. At this time, the initial control frame is a pre-agreed frame sent when the AP MLD attempts to perform frame exchange through one of the EMLSR links of the non-AP MLD, and means a frame transmitted in a non-HT (duplicate) PPDU format with one spatial stream.

[0351] When a STA operating on an EMLSR link pair receives a pre-promised frame from the AP MLD while listening, it aggregates the RF chains (Radio Frequency chains, Receive chains) used by each EMLSR link pair on the link where the pre-promised frame was received and uses them together in the frame exchange process performed after receiving the initial control frame. For example, if the first and second links are an EMLSR link pair operated in EMLSR mode, when an initial control frame is received on the first link, the RF chain used on the second link is also used in the frame exchange performed on the first link, and during this process, the second link is converted to a state where there is no RF chain. In other words, when a STA on a specific EMLSR link is performing a frame exchange, the STA operating on the EMLSR link pair has no RF to use for CCA and frame transmission / reception. Therefore, non-AP STAs operating on the EMLSR link pair cannot simultaneously participate in the frame exchange process. In other words, a non-AP STA operating on an EMLSR link pair can operate in EMLSR mode on an NSTR link pair even if it does not support NSTR operation, since the EMLSR link pair only exchanges frames with one link at a time.

[0352] Considering the operational characteristics of the EMLSR mode described above, a non-AP MLD that does not support NSTR operation and that has (or is expected to have) an NSTR link pair after performing channel switching instructed by an AP MLD can operate a non-AP STA operating on the NSTR link pair in EMLSR mode. In other words, a non-AP MLD that does not support NSTR operation can maintain a connection with the AP through a link pair that does not support STR by operating the NSTR link pair as an EMLSR link pair. This may be the operation of a non-AP MLD that does not support NSTR operation but supports EMLSR mode operation. In other words, a non-AP MLD with dot11EHTEMLSROptionImplemented set to true can operate a non-AP STA on the NSTR link pair even though it does not support NSTR operation by operating the NSTR link pair as an EMLSR link pair. In this case, the non-AP MLD may convert a non-AP STA operating in an NSTR link pair to the EMLSR mode by setting a bit corresponding to the NSTR link pair among bits in the EMLSR Link Bitmap subfield included in the EML Control field of an EML Operating Mode Notification frame to 1 and transmitting the frame to the AP. In this case, the non-AP MLD sets the EMLSR mode subfield of the same EMLSR Operating Mode Notification frame to 1. In addition, a non-AP MLD that does not support NSTR operation may operate an NSTR link pair as an EMLSR link pair if both its own and its associated AP MLD support EMLSR mode operation.That is, the non-AP MLD can operate the NSTR link pair as an EMLSR link pair without supporting NSTR operation and can operate a non-AP STA on the NSTR link pair only when the associated AP MLD supports EMLSR mode operation (only when the EML Capabilities Present subfield and EMLSR Support subfield of the Basic Multi-Link element received from the AP MLD are indicated as 1). In this case, operating a non-AP STA on the NSTR link pair means that a multilink connection state including the NSTR link pair can be maintained with the AP MLD.

[0353] FIG. 22 illustrates an example of a method for transitioning to EMLSR mode based on channel switching according to an embodiment of the present invention.

[0354] Referring to FIG. 22, the AP MLD and the non-AP MLD with multi-link setup may be converted to the EMLSR mode to remove the NSTR link pair generated as a result of channel switching.

[0355] Referring to Figure 22(a), before channel switching, the AP MLD and non-AP MLD are in a state where ML is set up through Link1 and Link2. The AP MLD commands and executes channel switching to change the operating channel of Link2. When the non-AP MLD performs channel switching for Link2 as commanded by the AP MLD, it determines that the separation distance between the frequencies of Link2 (Link2') operating on the new operating channel and Link1 is too close for it to support STR operation. (Figure 22(b) shows the state of Link1 and Link2 (Link2') predicted (evaluated) by the non-AP MLD.)

[0356] For the purpose of not supporting the NSTR operation, after determining to convert the STAs operating in the NSTR link pair to the EMLSR mode, the non-AP MLD instructs the AP MLD. After the operating mode of the non-AP MLD is changed, as shown in (c) of FIG. 22, the non-AP STA1 and non-AP STA2 of the non-AP MLD operate in the EMLSR mode in the EMLSR link pair.

[0357] <Operation of non-AP MLD that does not perform channel switching instructed by AP MLD>

[0358] Even if it is not a non-AP MLD that does not support the NSTR operation, each non-AP MLD can choose not to perform the channel switching operation of each link instructed by the AP MLD. This can be regarded as a natural selective operation of the non-AP MLD when considering that a conventional Wi-Fi non-AP STA does not have to perform the channel switching instructed by the AP.

[0359] Regarding the operation of a conventional Wi-Fi non-AP STA, when the non-AP STA decides not to perform the channel switching instructed by the AP, it can choose to move to another BSS or the like. In this case, the AP can recognize that the non-AP STA no longer operates in its BSS based on the fact that no frames are received from the non-AP STA for a certain period of time. That is, even without separate signaling (information, instructions, etc.) received from the non-AP STA, the AP can recognize that the non-AP STA is not performing channel switching and can terminate the association with the non-AP STA, such as deleting information about the non-AP STA.

[0360] On the other hand, if the non-AP MLD does not perform the channel switching instructed by the AP MLD, frame exchange with the non-AP MLD continues through other links other than the link where channel switching has been performed, and the connection between the AP MLD and the non-AP MLD does not end. In this case, the AP MLD may continue to attempt to transmit to the non-AP MLD through the link where channel switching has been performed, but because the non-AP MLD has not performed channel switching for that link, the AP MLD transmission attempt will repeatedly fail.

[0361] Such repeated transmission failures occur because the AP MLD is unaware that the non-AP MLD is not performing the channel switching that it instructed. Therefore, when the non-AP MLD decides not to perform the channel switching that the AP MLD instructed, it will have to signal (instruct, notify) this to the AP MLD.

[0362] Therefore, when the AP MLD and the non-AP MLD that has performed multi-link setup decide not to perform the channel switching instructed by the AP, the non-AP MLD will have to instruct the AP MLD to do so. At this time, the method by which the non-AP MLD instructs the AP MLD may be to terminate (teardown) the connection of the link for which the channel switching was instructed. That is, when the non-AP MLD decides not to perform the channel switching instructed by the AP MLD, it will have to perform (re)setup of the (ML) excluding the link for which the channel switching is to be performed. If the non-AP MLD is connected only to the AP MLD with two links, when it decides not to perform the channel switching instructed for one of the two links, it will have to terminate the connection with the AP MLD (MLD teardown, Disassociation) and perform single-link setup. At this time, the method of performing single-link setup is the same as the operation of the non-AP MLD that does not support the NSTR operation described above, and a detailed description thereof is omitted.

[0363] As another method, when the non-AP MLD decides not to perform the channel switching instructed by the AP MLD, it can move to another BSS. In this case, before moving to another BSS, the non-AP MLD can send a Disassociation frame to the AP MLD to which it is already associated.

[0364] <Method for Signaling the Progress / Completion of Channel Switching of NSTR Mobile AP MLD>

[0365] In yet another embodiment of the present invention, the AP MLD can transmit channel switching information of an AP where channel switching is performed to STAs of the non-AP MLD via another AP. That is, a reporting AP included in the AP MLD can include channel switching information of a reported AP, which is another AP, in a frame (e.g., a beacon frame or a probe response frame) and transmit the information to non-AP STAs of the non-AP MLD.

[0366] The channel switching information may include a channel switch announcement element (or an extended channel switch announcement element) and a maximum channel switch time element for announcing channel switching and / or class (operation class) changes, where the channel switch announcement element (or the extended channel switch announcement element) and the maximum channel switch time element may be included in whole, in part, or both.

[0367] If an operation class is to be changed, an extended channel switch announcement element may be used instead of a channel switch announcement element. When an extended channel switch announcement is used (i.e., when an extended channel switch announcement element is included in a frame), a maximum channel switch time element may always be included in the frame together with the extended channel switch announcement. In other words, when an extended channel switch announcement is included in a frame for an operation class change, a maximum channel switch time element may always be included in the frame. Hereinafter, in the present invention, a channel switch announcement element may also mean an extended channel switch announcement. In other words, a channel switch announcement element may be analyzed as an extended channel switch announcement depending on its use.

[0368] The channel switch announcement element may include a new channel number field and a channel switch count field.

[0369] The channel number field indicates the new channel location on which the reported AP will operate as a result of channel switching, and the channel switch count field indicates the number of TBTTs (Target Beacon Transmission Times) remaining until channel switching to the new channel.

[0370] The Max Channel Switch Time element includes a Switch Time field associated with the time of channel switching, and the Switch Time field may indicate information associated with the time when channel switching is completed.

[0371] In this case, the switch time field may indicate different values ​​depending on the type of AP MLD and / or whether channel switching has not yet started or is currently in progress.

[0372] Specifically, when the AP MLD is an STR AP MLD that supports simultaneous transmission and reception (STR type), the switch type field indicates the maximum time from the transmission of the last beacon frame transmitted from the reported AP before the start of channel switching to the first beacon frame on the new channel. In this case, the switch type field can indicate the above time until the transmission of the last beacon frame of the reported AP after channel switching. However, the switch type field included in a frame transmitted after the transmission of the last beacon frame of the reported AP after channel switching (i.e., after channel switching begins) indicates the time from the transmission of a frame including the switch time field to the first beacon frame on the new channel.

[0373] However, if the AP MLD is an NSTR AP MLD that does not allow simultaneous transmission and reception (NSTR type), the switch type field may indicate the time from when the reported AP transmits a frame including the switch time field to when the channel switching ends. In this case, the end point of the channel switching may be when the corresponding AP resumes BSS operation on a new channel.

[0374] If the AP MLD is an NSTR AP MLD that does not allow simultaneous transmission and reception (NSTR type), the switch type field indicates the time from when the reported AP transmits a frame including the switch time field to when channel switching is completed, so the time indicated by the switch time field may be different at each point in time. That is, the time indicated by the switch time field may gradually decrease each time a frame is transmitted.

[0375] If the AP MLD is the NSTR AP MLD, the AP MLD allows only APs operating on the primary link to transmit beacon frames, and does not allow APs operating on non-primary links to transmit beacons. Therefore, information related to channel switching of APs operating on non-primary links (e.g., channel switch announcement element and maximum channel switch time element) can only be transmitted by APs operating on the primary channel. Therefore, in the above-described channel switching operation, channel switching information of APs operating on non-primary links included in the AP MLD may be transmitted only by APs operating on the primary link.

[0376] In addition, non-AP STAs included in the non-AP MLD can recognize whether channel switching has started depending on whether the frame contains a channel switch announcement element and / or a maximum channel switch time element.

[0377] For example, a non-AP STA can determine that a channel switch has not yet occurred if a frame contains both a channel switch announcement element and a maximum channel switch time element. However, a non-AP STA can determine that a channel switching procedure is currently taking place if a received frame contains only a maximum channel switch time element and no channel switch announcement element.

[0378] If the received frame does not contain a maximum channel switch time element, the non-AP STA can determine that the channel switching procedure has ended. In this case, the end of the channel switching procedure may mean that the BSS operation of the reported AP is resumed on the new channel, as described above. In this case, the AP MLD may be the NSTR AP MLD or the STR AP MLD.

[0379] According to one embodiment of the present invention, the NSTR mobile AP MLD can indicate information related to channel switching of the non-primary link through a beacon and a (ML (Multi-Link)) probe response frame (hereinafter, a probe response frame) transmitted through the primary link. When a maximum channel switch time element related to channel switching of the non-primary link is utilized, the time indicated in the Switch Time field of the maximum channel switch time element is considered to indicate the time when channel switching of the non-primary link is expected to be completed, or the time when signaling indicating that channel switching has been completed is expected to be indicated on the primary link, or the time when a predetermined frame is transmitted on the non-primary link (e.g., a TIM frame).

[0380] Alternatively, a method of indicating whether channel switching of a non-primary link has been completed using the presence or absence of a maximum channel switch time element may be considered, the details of which will be described in one embodiment of the present invention below.

[0381] According to one embodiment of the present invention, the presence or absence of a maximum channel switch time element associated with a non-primary link AP can be used to indicate / interpret whether the non-primary link AP has completed channel / class switching.

[0382] More specifically, when an NSTR mobile AP MLD transmits an (extended) channel switching announcement element (extended channel switching announcement element and channel switching announcement element) for a non-primary link AP in a beacon frame and a (ML) probe response frame transmitted on the primary link, the NSTR mobile AP MLD must also include a Max Channel Switch Time element. In this case, beacons and probe response frames transmitted after the channel / class switching start point specified by the (extended) channel switching announcement element may not include the (extended) channel switching announcement element, but may continue to include only the Max Channel Switching element. In this case, the inclusion of the Max Channel Switch Time element may indicate that the channel / class switching of the non-primary link AP has not been completed, while the absence of the Max Channel Switch Time element may indicate that the channel / class switching of the non-primary link AP has been completed. That is, the non-AP MLD can interpret that channel switching of the non-primary link is completed (BSS operation is resumed) when the beacon and / or probe response frame received from the NSTR mobile AP MLD no longer contains a maximum channel switch time element corresponding to the non-primary link AP. In this case, the (extended) channel switching announcement element and maximum channel switch time element for the non-primary link AP may be included in the STA-specific profile corresponding to the non-primary link AP included in the beacon and probe response frame transmitted on the primary link. In this case, the maximum channel switch time element indicates the time (remaining time) that the non-primary link AP is expected / evaluated to resume service for the BSS on a new channel using the Switch Time field (in units of TU (1024 us)).In this case, the NSTR mobile AP MLD, which cannot indicate the prediction / evaluation time using the Max Channel Switch Time element, sets the Switch Time field to 0. In this case, the Max Channel Switch Time element may be continuously included in the beacon and probe response frames from the time the channel switching announcement element corresponding to the non-primary link AP is included in the beacon and probe response frame until BSS operation (service) is resumed after channel switching of the non-primary link AP is completed. That is, the Max Channel Switch Time element may also be included in the Per-STA profile subfield including the (extended) channel switching announcement element indicating 0 in the Channel Switching Count field. Meanwhile, the NSTR mobile AP MLD does not include the Max Channel Switching Time element corresponding to the non-primary link AP in the beacon frame and probe response frame transmitted after channel switching of the non-primary link is completed. In this case, the NSTR mobile AP MLD may transmit an unsolicited probe response frame that does not include the Max Channel Switch Time element in the STA-specific profile corresponding to the non-primary link AP when channel switching of the non-primary link is completed (when BSS operation is resumed). This may be an operation of the NSTR mobile AP MLD to allow the non-AP MLD that received the unsolicited probe response frame to recognize the completion of channel switching of the non-primary link more quickly. In this case, the unsolicited probe response frame may include complete information for the AP operating on the non-primary link. That is, the non-AP MLD that received the unsolicited probe response frame from the NSTR mobile AP MLD can obtain the same amount of information about the non-primary link AP as when the non-primary link transmits a probe response frame.

[0383] (Method of indicating whether non-primary link channel / class switching using maximum channel switch time element has been completed)

[0384] For the purpose of specific explanation, the operation of the NSTR mobile AP MLD, which transmits a channel switching announcement element or an extended channel switching announcement element to change the operating channel / class of an AP operating on a non-primary link, and the operation of the non-AP MLD, which receives the element and performs channel / class switching of the non-primary link, will be described in order.

[0385] NSTR Mobile AP MLD determines one of the links that the AP operates as a primary link and transmits beacons and (ML) probe response frames only through the primary link. In this case, other links that are not the primary link are non-primary links, and APs operating on non-primary links do not transmit beacons or probe response frames.

[0386] The NSTR Mobile AP MLD may attempt to change the operating channel / class of an AP operating on a non-primary link. In this case, the NSTR Mobile AP MLD transmits a beacon and probe response frame via the AP operating on the primary link, including a STA-specific profile corresponding to the AP of the non-primary link. In this case, the STA-specific profile includes an (extended) channel switching announcement element and a maximum channel switch time element.

[0387] The extended channel switching announcement element is used when changing an existing operating channel and / or operating class to a new channel and / or class, and the channel switching announcement element is used when changing an operating channel to a new channel. The (extended) channel switching announcement element also includes information specifying the time when channel / class switching will begin. More specifically, the channel switching count field included in the two elements indicates information related to when the channel / class switching indicated by the element will begin.

[0388] When an NSTR mobile AP MLD attempts to change the operating channel / class of an AP operating on a non-primary link, it transmits a STA-specific profile including an (extended) channel switching announcement element, along with a maximum channel switch time element. The maximum channel switch time element indicates information related to how long after the transmission / reception time of the frame (beacon or probe response frame) including the element, channel / class switching will be completed. For example, the maximum channel switch time element transmitted along with the channel switching time announcement element transmitted in the STA-specific profile corresponding to a specific non-primary link AP indicates the expected / estimated time until the channel switching indicated by the channel switching time announcement element is completed by the specific non-primary link AP. Completion of channel switching by the specific non-primary link AP may mean the same as the specific non-primary link AP resuming BSS operation (service) on a new channel.

[0389] In other words, the maximum channel switch time element that the NSTR mobile AP MLD transmits in the STA-specific profile corresponding to the non-primary link AP may indicate the time remaining until the non-primary link AP resumes BSS operation, rather than the time associated with the frame transmitted on a specific link.

[0390] In this case, in some implementations, the NSTR mobile AP MLD may be unable to evaluate / predict the time at which a non-primary link AP will resume BSS operation on a new operating channel / class. Alternatively, in some implementations, the NSTR mobile AP MLD may not want to evaluate / indicate the time at which a non-primary link AP will resume BSS operation on a new channel / class. In short, an NSTR mobile AP MLD that does not support indicating the time remaining until a non-primary link AP resumes BSS operation on a new operating channel / class can set the Switch Time field included in the Maximum Channel Switch Time element corresponding to the non-primary link AP to 0.

[0391] That is, if the NSTR mobile AP MLD sets the Switch Time field of the maximum channel switch time element corresponding to the non-primary link AP to 0, the maximum channel switch time element may indicate that the time to resume BSS operation on the new channel / class is unknown. Therefore, after receiving the maximum channel switch time element corresponding to the non-primary AP from the NSTR mobile AP MLD, the non-AP MLD confirms that the Switch Time field is set to 0 and must interpret that the time remaining until the BSS operation of the non-primary link AP indicated by the maximum channel switch time element is not 0 TU (1 TU is 1024 us) or later, but is undefined (Unknown).

[0392] Thus, when the NSTR mobile AP MLD intends to change the operating channel / class of an AP operating on a non-primary link, it transmits a beacon / probe response frame including an (extended) channel switching announcement element and a maximum channel switch time element.Then, at the time specified in the (extended) channel switching announcement element (the specified TBTT of the primary link), the AP operating on the non-primary link starts channel / class switching.

[0393] When an AP operating on a non-primary link starts channel / class switching, the service of the existing BSS is interrupted, and the non-AP MLD that was connected including the non-primary link also starts channel / class switching for the STA operating on the non-primary link (it may start switching first).

[0394] Even when a non-primary link AP is performing channel / class switching, the NSTR mobile AP MLD can transmit beacon / probe response frames via the AP operating on the primary link. A primary link beacon / probe response frame transmitted when a non-primary link AP is performing channel / class switching does not include an (extended) channel switching announcement element in the STA-specific profile corresponding to the non-primary link AP. However, a primary link beacon / probe response frame transmitted when a non-primary link AP is performing channel / class switching still includes a maximum channel switch time element in the STA-specific profile corresponding to the non-primary link AP. The maximum channel switch time element (more specifically, the Switch Time field) indicates the remaining time estimated / predicted for the non-primary link AP to complete channel / switching and resume BSS service (BSS operation). As described above, the maximum channel switch time element transmitted by an NSTR mobile AP MLD that does not support the estimation / prediction time indication has the Switch Time field set to 0. In this case, the maximum channel switch time element is included in the beacon / probe response frame from when the AP of the non-primary link initiates channel / class switching until the BSS operation is resumed after the initiated channel / class switching is completed.

[0395] Even if a probe response frame includes a STA-specific profile including an (extended) channel switching time element with the channel switching count field set to 0, the STA-specific profile may include a maximum channel switch time element.

[0396] The non-AP MLD, combined with the NSTR mobile AP MLD, can determine that a non-primary link AP is still performing channel / class switching based on the inclusion of a maximum channel switch time element in the per-STA profile sub-element corresponding to the non-primary link AP included in a beacon / probe response frame received on the primary link. The non-AP MLD can then determine that a non-primary link AP is still performing channel / class switching only if the per-STA profile sub-element containing the maximum channel switch time element does not contain an (extended) channel switching announcement element. This is because, if the per-STA profile sub-field corresponding to the non-primary link AP contains an (extended) channel switching announcement element along with a maximum channel switch time element, the maximum channel switch time element was transmitted before the non-primary link AP initiated channel / class switching.

[0397] The NSTR mobile AP MLD transmits beacon / probe response frames including a maximum channel switch time element in the STA-specific profile corresponding to the non-primary link AP while the non-primary link AP is performing channel / class switching, but does not include the maximum channel switch time element in beacon / probe response frames anymore after the non-primary link AP completes channel / class switching. In other words, when the non-primary link AP resumes BSS service (operation) on a new operating channel / class, the NSTR mobile AP MLD no longer transmits a maximum channel switch time element corresponding to the non-primary link AP in beacon / probe response frames transmitted on the primary link.

[0398] Therefore, the non-AP MLD associated with the NSTR mobile AP MLD can recognize that the ongoing channel / class switching of the non-primary link AP has been completed (BSS operation has resumed) based on the absence of a maximum channel switch time element corresponding to the non-primary link AP in the beacon / probe response frame received on the primary link.

[0399] That is, the Non-AP MLD can transmit a UL PPDU on the non-primary link when the most recently received beacon frame or (ML) probe response frame from the NSTR mobile AP MLD does not include a maximum channel switch time element for the non-primary link AP.

[0400] The non-AP MLD associated with the NSTR mobile AP MLD must not transmit an UL PPDU (Up-link Physical layer (PHY) Protocol Data Unit) from the time the non-primary link AP is instructed to start channel / class switching until the time the non-primary link AP recognizes that channel / class switching has been completed. This may be a UL PPDU transmission restriction that is applied because the BSS service is interrupted while the non-primary link AP is performing channel / class switching.

[0401] In this case, the time at which the AP of the non-primary link is instructed to start channel / class switching may be the time recognized by the (extended) channel switching announcement element (more specifically, the channel switching count field) included in the per-STA profile sub-element corresponding to the AP of the non-primary link. For example, if the channel switching count field of the (extended) channel switching announcement element included in the per-STA profile sub-element corresponding to the AP of the non-primary link is set to 1, the AP of the non-primary link may be instructed / interpreted to start channel switching at the next TBTT (TBTT of the primary link) after the element is transmitted. As another example, if the channel switching count field of the (extended) channel switching announcement element included in the per-STA profile sub-element corresponding to the AP of the non-primary link is set to 1, the AP of the non-primary link may be instructed / interpreted to start channel switching at any time after the frame including the element is transmitted. Here, "any time" refers to an unspecified time between the time of transmission / reception of the frame including the element and before the next TBTT (of the primary link).

[0402] In this case, the time at which the AP of the non-primary link recognizes that channel / class switching has been completed may be the time at which a beacon / probe response frame that does not include a maximum channel switch time element corresponding to the AP of the non-primary link is received on the primary link.

[0403] In this way, the non-AP MLD combined with the NSTR mobile AP MLD restricts UL PPDU transmission on the non-primary link until the channel / class switching of the non-primary link AP is completed. Therefore, the NSTR mobile AP MLD must operate so that the non-AP MLD recognizes the completion of the channel / class switching of the non-primary link as soon as possible. To this end, the NSTR mobile AP MLD can transmit an unsolicited probe response frame when the channel / class switching indicated for the non-primary link is completed. In this case, the unsolicited probe response frame does not include a maximum channel switch time element corresponding to the non-primary link AP. In this case, the unsolicited probe response frame includes complete information for the non-primary link AP. The inclusion of complete information in the unsolicited probe response frame means that all information indicated when the non-primary link AP transmitted a probe response frame can be indicated / obtained in the unsolicited probe response frame (transmitted on the primary link). When a non-AP MLD receives an unsolicited probe response frame sent by an NSTR mobile AP MLD on the primary link, it can recognize that the channel / class switching performed by the non-primary link AP has been completed (BSS service (operation) of the non-primary link AP), and can attempt to send an UL PPDU on the non-primary link before receiving the next beacon.

[0404] In addition, the NSTR mobile AP MLD can transmit an unsolicited probe response frame if the channel / class switching operation indicated in the (extended) channel switching announcement element fails, i.e., if the attempted switching operation ultimately fails. In this case, the probe response frame may include complete information for the non-primary link AP that attempted channel switching. The non-AP MLD that received the probe response frame can recognize that the channel switching operation indicated for the non-primary link AP has failed / cancelled based on the complete information indicated for the non-primary link AP.

[0405] In this case, the NSTR mobile AP MLD can transmit an (extended) channel switching announcement element that indicates the existing operating channel / class as a new channel / class using a STA-specific profile corresponding to the non-primary link AP in response to a channel switching failure. In other words, while switching is in progress to indicate a new channel / class other than the existing operating channel / class, the ongoing channel switching can be canceled by issuing an (extended) channel switching announcement element that indicates the channel / class before switching.

[0406] FIG. 23 illustrates an example of a channel switching method according to an embodiment of the present invention.

[0407] Referring to FIG. 23, the progress / completion of non-primary link channel switching may be indicated by a maximum channel switch time element.

[0408] Specifically, the NSTR mobile AP MLD operates AP1 and AP2 via a primary link and a non-primary link, respectively, and the non-AP STA MLD is connected to the NSTR mobile AP MLD via a primary link and a non-primary link.

[0409] The NSTR mobile AP MLD transmits an (extended) channel switching announcement element corresponding to the non-primary link (AP2) in the beacon frame and probe response frame transmitted on the primary link in order to change the operating channel (and / or operating class) of the BSS operated by AP2. Although not shown, this element is transmitted in a STA-specific profile sub-element corresponding to the non-primary link AP included in the beacon / probe response frame. In this case, the STA-specific profile sub-element also includes a maximum channel switch time element.

[0410] The first beacon (far left) shown in Figure 23 includes an (extended) Channel Switching Announcement element with the Channel Switching Count field set to 2 and a Maximum Channel Switch Time element with a Switch Time field indicating 'y' - 'x1'. Here, 'y' is the time when AP2 is evaluated / predicted to have completed switching to the new channel / class and resume BSS operation, and 'x1' is the time when the beacon frame containing this element (the first beacon in Figure 23) is transmitted / received. If the NSTR mobile AP MLD does not support the evaluation / prediction of 'y', the Switch Time field of the Maximum Channel Switch Time element is set / indicated to 0. After receiving the first beacon transmitted via the primary link via STA1, the Non-AP (STA) MLD can recognize that AP2 of the NSTR mobile AP MLD intends to switch to a new channel / class.

[0411] The second beacon shown in FIG. 23 includes an (extended) channel switching announcement element with the channel switching count field set to 1 and a maximum channel switch time element with a Switch Time field indicating 'y'-'x2'. Here, 'y' is the time when AP2 is evaluated / predicted to have completed switching to the new channel / class and resume BSS operation, and 'x2' is the time when the beacon frame containing this element (the second beacon in FIG. 23) is transmitted / received. If the NSTR mobile AP MLD does not support the evaluation / prediction of 'y', the Switch Time field of the maximum channel switch time element is set / indicated to 0. After receiving the second beacon transmitted via the primary link via STA1, the non-AP (STA) MLD confirms that the channel switching count field is set to 1, thereby recognizing that AP2 in the NSTR mobile AP MLD will begin switching to a new channel / class in the next TBTT of the primary link. If a probe response frame is transmitted from the NSTR mobile AP MLD between the first and second beacons, the (extended) channel switching announcement element and maximum channel switch time element for AP2 included in the probe response frame are set in the same manner as in the second beacon. The time indicated in the Switch Time field of the maximum channel switch time element included in the probe response frame is the difference between the time when the probe response frame is transmitted / received and the time when AP2 is evaluated / predicted to resume BSS operation on a new operating channel / class.

[0412] The third to sixth beacons seen in FIG. 23 do not include an (extended) channel switching announcement element, but only include a maximum channel switch time element. The maximum channel switch time element is set to a time value (difference value) from the time a beacon frame including the element in its Switch Time field is transmitted / received to the time AP2 is evaluated / predicted to resume BSS operation on a new operating channel / class. If a probe response frame transmitted by the NSTR mobile AP MLD is present between the third and sixth beacons, the Switch Time field of the maximum channel switch time element included in the probe response frame is set in the same manner as the Switch Time field of the maximum channel switch time element included in the third to sixth beacons. If it is determined that the beacon and (ML) probe response frame received from the NSTR Mobile AP MLD do not include an (extended) channel switching announcement element in the STA-specific profile for AP2, but only include a maximum channel switch time element, no UL PPDU is transmitted on the non-primary link (i.e., to AP2 via STA2).

[0413] When the NSTR mobile AP MLD completes the channel / class switching of AP2, which it previously announced using the first and second beacon frames, it transmits an Unsolicited (ML) Probe Response frame (Probe in FIG. 23) on the primary link. The Unsolicited Probe Response frame transmitted by the NSTR mobile AP MLD is a Probe Response frame transmitted by the NSTR mobile AP MLD even though it did not receive a Probe Request frame on the primary link. The Unsolicited Probe Response frame does not include a Maximum Channel Switch Time element in the STA-specific profile for AP2. The Non-AP (STA) MLD, which receives the Probe Response frame on the primary link, recognizes that the announced channel / class switching for the non-primary link (AP2) has been completed by AP2 based on the absence of a Maximum Channel Switch Time element in the STA-specific profile subelement for AP2. The Non-AP MLD can then attempt to transmit an UL PPDU to AP2 via STA2. That is, the Non-AP MLD transmits a UL PPDU on the non-primary link when the most recently received beacon frame or (ML) probe response frame from the NSTR mobile AP MLD does not include a maximum channel switch time element for the non-primary link AP.

[0414] <Non-primary link disablement>

[0415] As mentioned above, when the NSTR mobile AP MLD changes the operating channel and / or class of a non-primary link AP, UL PPDU transmission restrictions on the non-primary link may be applied to the non-AP MLD.

[0416] This restriction is taken into account because PPDU reception is not possible when a non-primary link AP is performing channel switching. More generally, UL PPDU transmission can be restricted for all APs undergoing channel switching. More specifically, when a general AP MLD AP, not an NSTR mobile AP MLD AP, performs channel switching, non-AP STAs (MLD STAs or general STAs) associated with that AP should not transmit UL PPDUs. Alternatively, even if a UL PPDU is transmitted, it cannot be received by the AP performing channel switching. Therefore, even if a separate restriction is not defined, a non-AP STA will not transmit a UL PPDU if it recognizes that the AP to which it is associated is performing channel switching.

[0417] In this way, an AP MLD, including the NSTR mobile AP MLD, cannot receive a PPDU transmitted on a specific link while the AP of the specific link is performing channel switching, and can therefore instruct its associated non-AP MLD not to transmit an UL PPDU on the specific link while the AP of the specific link is performing channel switching. In this case, the (NSTR mobile) AP MLD can designate the specific link undergoing channel switching as a disabled link. When a specific link is designated as a disabled link, non-AP STAs associated with the AP of the disabled link will not transmit an UL PPDU during the disabled period.

[0418] At this time, (NSTR mobile) AP MLD can guide non-AP STAs not to transmit UL PPDUs to the AP that is performing channel switching by indicating the link that performs channel switching as a disabled link.

[0419] <TID(Traffic identifier)-to-linkマッピングとリンクディセ-ブルメント>

[0420] MLDs may be associated through multiple links, and the multiple links can be used for different purposes to improve QoS or achieve operational goals. For example, two MLDs can be associated to send / receive large files or videos over 6 GHz, which has a wide bandwidth, and to exchange data and management frames that should be transmitted and received more stably over 2.4 GHz, which has a wide coverage.

[0421] In this way, the purpose for which the two MLDs connected through multiple links use each link may be determined by negotiation between the two MLDs, and TID-to-Link mapping may be used in this process.

[0422] TID-to-Link Mapping is a method of distinguishing the TIDs of frames transmitted on each link, and may be determined by agreement between both MLDs or by instruction from the AP MLD. If a specific TID is mapped only to a specific link and not to other links, frames having the specific TID can be transmitted only on the specific link and cannot be transmitted on the other links. In this case, TID-to-Link Mapping may be determined differently for each transmission direction (UL direction in the case of non-AP MLD, DL direction in the case of AP MLD).

[0423] As described above, only frames of TIDs mapped to a specific link can be transmitted on the specific link, and therefore, no frames can be exchanged on a link to which no TID is mapped. Thus, among the links connecting both MLDs, a link to which no TID is mapped can be called a disabled link, and frame exchange may not be performed on the disabled link.

[0424] (NSTR mobile) AP MLD can convert a specific link to a state in which there is no TID mapped to the specific link, i.e., a disabled link, during a channel switching period for the specific link. To this end, AP MLD can transmit a beacon and probe response frame containing an instruction to convert the specific link to a disabled state. More specifically, AP MLD can broadcast a TID-to-Link mapping instruction to disable the TID mapped to the specific link. In this case, non-AP MLDs receiving the TID-to-Link mapping instruction from AP MLD must follow the TID-to-Link mapping instructed by AP MLD. In this case, the AP MLD can indicate the TID-to-Link mapping by using a TID-to-Link mapping element. In this case, the TID-to-Link mapping element includes a link bitmap indicating link information to which each TID is mapped. As an example, a link bitmap corresponding to TID0 may be included to indicate link information to which TID0 is mapped, and each bit of the link bitmap (2 octets) may correspond to Link0 to Link14, respectively. In this case, if the bits corresponding to Link0 and Link1 (B0 and B1 of the link bitmap) are set to 1, TID0 is interpreted as being mapped to Link0.

[0425] In addition, the (NSTR mobile) AP MLD can indicate information about the time when the TID-to-Link mapping it specifies is applied and the duration for which it is maintained, and can indicate that the link is a disabled link using a Reduced Neighbor Report (RNR) element corresponding to the AP of the link disabled by the TID-to-Link mapping. More specifically, the AP MLD can indicate information about the time when the TID-to-Link mapping it specifies by broadcast is applied using a Mapping Switch Time field included in the TID-to-Link mapping element. In addition, the AP MLD can indicate information about the time when the TID-to-Link mapping it specifies by broadcast is applied using an Expected Duration field included in the TID-to-Link mapping element.

[0426] The Mapping Switch Time field is a field that indicates a value in TU units consisting of 2 octets, and after the time indicated in the Mapping Switch Time field of the TID-to-Link mapping element has elapsed, the TID-to-Link mapping indicated by the TID-to-Link mapping element is applied. That is, the TID-to-Link mapping element indicated by the AP MLD in the beacon / probe response frame includes information on the TID-to-Link mapping to be applied and information on the time when it is applied.

[0427] The Expected Duration field is a 3-octet field indicating a value in TU units, and indicates the length of time for which the TID-to-Link mapping indicated by the TID-to-Link mapping element is applied. That is, the TID-to-Link mapping element indicated by the AP MLD includes information on the TID-to-Link mapping to be applied and information on the duration of the application.

[0428] (NSTR mobile) AP MLD can indicate a specific link as a disabled link during a time period when the AP of the specific link performs channel switching so that the non-AP MLD does not transmit UL PPDUs on the specific link while the AP of the specific link performs channel switching. That is, AP MLD can indicate TID-to-Link mapping that disables the specific link during a time period when the AP of the specific link performs channel switching. That is, the TID-to-Link mapping function that disables a specific link can be used to prohibit UL PPDU transmission on a link during which channel switching is in progress.

[0429] More specifically, the (NSTR mobile) AP MLD broadcasts a TID-to-Link mapping element that indicates the time when the AP of a specific link starts channel switching in a Mapping Switch Time field and indicates the expected time period until the channel switching is completed in an Expected Duration field, thereby preventing the non-AP MLD from transmitting an UL PPDU to the AP of the specific link. In this case, the TID-to-Link mapping state indicated by the TID-to-Link mapping element is a state in which no TID is mapped to the specific link (i.e., the specific link is disabled).

[0430] However, there is a restriction that if the AP MLD changes a specific link to Disabled, the specific link must be changed to a non-Disabled state (i.e., enabled, available) after the time indicated in the Expected Duration field has elapsed or earlier. This may be an operational restriction of the AP MLD that allows a non-AP MLD that recognizes that a specific link will be changed to Disabled from the TID-to-Link mapping element indicated by the AP MLD to operate on the assumption that the specific link will be changed to an available state after the time indicated in the Expected Duration field of the TID-to-Link mapping element has elapsed.

[0431] For example, when a specific link is switched to disabled, the non-AP MLD can prepare for UL PPDU transmission before the end of the disabled maintenance period indicated by the Expected Duration, and if the AP MLD maintains the disabled state of the specific link for longer than originally indicated, the UL PPDU transmission of the non-AP MLD will fail. This means that the operation of the non-AP MLD may be inefficient due to incorrect information indication by the AP MLD.

[0432] As another example, if the AP MLD specifies a disabled period for a specific link longer than a specific value, a specific non-AP MLD may prefer to disassociate (tear down) the specific link rather than maintain the disabled state. However, the AP MLD uses the Expected Duration field to specify that the disabled state will be maintained only for a period shorter than the specific value, and the period maintained in the disabled state may be extended and maintained longer than the specific value. In this case, the non-AP MLD misses an opportunity to perform more efficient operations that meet its operational objectives due to the AP MLD's incorrect Expected Duration specification.

[0433] Therefore, an AP MLD that converts a specific link to disabled may be restricted to accurately notifying the time for which the specific link will be maintained in a disabled state using the Expected Duration field. However, the AP MLD can maintain the specific link in a disabled state only for a duration shorter than the disabled duration initially specified for the specific link. In this case, the AP MLD can further transmit an Expected Duration field that indicates an earlier time point than the time specified by the initially specified Expected Duration field. That is, the AP MLD can transmit a TID-to-Link mapping element that indicates an earlier time point (the end time of the disabled state) than the time specified in the Expected Duration field of the original TID-to-Link mapping element broadcast to convert the specific link to disabled. That is, the disabled maintenance duration of the specific link specified by the AP MLD may end earlier than the initially specified time point. On the other hand, AP MLD is restricted from maintaining a specific link in a disabled state for a period longer than the disabled period initially specified for the specific link. Therefore, AP MLD must not transmit a TID-to-Link mapping element that specifies a time later than the time (the end time of the disabled state) specified in the Expected Duration field of the TID-to-Link mapping element originally broadcast to convert the specific link to disabled.

[0434] An AP performing channel switching may encounter an unpredictable problem while switching to a new operating channel / class, and may need to change the channel / class switching that was in progress. For example, an AP that has performed channel switching to a new operating channel may detect a radar signal, satellite signal, etc. on the new operating channel and determine that it cannot operate on that channel. In this case, the AP must change the operating channel to another channel again, which results in the channel / class switching being completed later than the AP predicted. In other words, the completion time of channel / class switching may be a type of operation that cannot be accurately predicted.

[0435] For the same reason, when the AP MLD indicates the time that the AP of a specific link expects to complete channel switching using the Expected Duration field (of the TID-to-Link mapping element), channel switching may not be completed at the time indicated by the Expected Duration field due to external variables. This may be due to a delay in the scheduled channel / class switching procedure due to an external factor, rather than a change in the time at which the AP MLD changes the specific link to Disabled. Therefore, the AP MLD may be allowed to extend the Disabled maintenance time of the specific link when changing the specific link to Disabled in response to channel switching of the specific link. On the other hand, the AP MLD should not extend the Disabled maintenance time of the specific link unless changing the specific link to Disabled in response to channel switching of the specific link. In other words, the specific link should be maintained in Disabled only for a period that is shorter than or the same as the originally specified maintenance time.

[0436] Therefore, the AP MLD can set the Expected Duration field indicating a later time point than the previously indicated time point only in the TID-to-Link mapping element that indicates the link where channel switching is in progress as a disabled link. That is, the AP MLD can transmit a TID-to-Link mapping element in which the Expected Duration field is set indicating a later time point than the time indicated in the Expected Duration field of the initially transmitted TID-to-Link mapping element in order to indicate the link where channel switching is in progress as a disabled link. In this case, the TID-to-Link mapping information (relationship between link and TID) indicated in the two TID-to-Link mapping elements is the same.

[0437] When the AP MLD uses the Max Channel Switching Time element in the process of performing channel switching of a specific link, the AP MLD can indicate the same time point as the time point indicated by the Max Channel Switching Time element using the Expected Duration field of the TID-to-Link mapping element that indicates channel switching of the specific link in a disable link. In other words, when both the TID-to-Link mapping element and the Max Channel Switching Time element are used in connection with channel / class switching of a specific link, the Expected Duration field of the TID-to-Link mapping element and the Switch Time field of the Max Channel Switching Time element indicate the same time point.

[0438] Thus, when the AP MLD indicates a link undergoing channel switching as a disabled link, the RNR element (included in the beacon and probe response frame) transmitted by the AP MLD may indicate that the Disabled Link Indication subfield of the MLD parameters corresponding to the link undergoing channel switching is set to 1. After channel switching of a specific link is completed, the non-AP MLD confirms that the Disabled Link Indication subfield corresponding to the specific link in the RNR element is set to 0, and can recognize that the AP of the specific link has completed channel switching. That is, after confirming that the Disabled Link Indication subfield corresponding to the specific link is set to 0, the non-AP MLD can transmit a UL PPDU to the AP of the specific link. <Simultaneous Channel / Class Switching of Primary and Non-Primary Links> The NSTR mobile AP MLD can simultaneously change the operating channel / class of the primary and non-primary links, depending on operational purposes, or initiate channel / class switching of the primary link while channel / class switching of the non-primary link is in progress. However, since beacon / probe response frames cannot be transmitted on the primary link when channel / class switching of the primary link is in progress, initiation of channel / class switching of non-primary links while channel / class switching of the primary link is in progress may be restricted. For reference, in the above and below descriptions of the present invention, for convenience, the terms "primary link operating channel" and "non-primary link operating channel" are used interchangeably, and these terms are used interchangeably to mean the operating channel of an AP operated on the primary link and the operating channel of an AP operated on a non-primary link, respectively. In addition, the term "channel switch announcement element" is an abbreviation for the (extended) channel switch announcement element, and "channel switching" may be an abbreviation for channel / class switching.

[0439] As mentioned above, the NSTR mobile AP MLD determines / designates one of the two links over which it operates the AP as the primary link and the other link as the non-primary link. The NSTR mobile AP MLD transmits beacon frames and probe response frames only over the primary link, and non-AP MLDs attempting to associate with the NSTR mobile AP MLD must perform the association procedure only over the primary link, so the primary link plays a very important role in the BSS operation of the NSTR mobile AP MLD.

[0440] Therefore, NSTR mobile AP MLD can designate and operate as the primary link the link that is easier to use as the primary link out of the two links it operates (primary link and non-primary link).If a link that has been previously designated and operated as a non-primary link is determined to be better than the link previously operated as a primary link, NSTR mobile AP MLD can change the existing non-primary link to the primary link and change the existing primary link to the non-primary link.

[0441] In this case, the NSTR mobile AP MLD can use the (extended) channel switch announcement element for the primary link to specify the new operating channel of the primary link as the operating channel of the existing non-primary link, and at the same time, use the (extended) channel switch announcement element for the non-primary link to specify the new operating channel of the non-primary link as the operating channel of the existing primary link. In other words, by specifying the new operating channels for the primary link and non-primary link as the operating channels of the existing non-primary link and primary link, respectively, the operating channels of the primary link and non-primary link can be swapped (switched) with each other.

[0442] When changing the primary link by switching the operating channels of the primary link and non-primary link, NSTR mobile AP MLD can complete channel switching for both links by changing the role of the AP that was operating on the existing primary link to an AP that operates on the non-primary link, and changing the role of the AP that was operating on the existing non-primary link to an AP that operates on the primary link, instead of actually performing channel switching.

[0443] However, when the NSTR mobile AP MLD transmits a channel switch announcement element for the primary link and the non-primary link for the purpose of switching (swapping) the primary link and the non-primary link, a restriction may be applied that the channel switch of both links should be initiated simultaneously. This restriction may be considered to prevent the operating channels of the NSTR mobile AP MLD's primary link and non-primary link from overlapping at a particular moment.

[0444] To achieve this, the NSTR mobile AP MLD must set the channel switch count fields of two channel switch announcement elements transmitted to switch between the primary link and non-primary links to the same value. More specifically, when the NSTR mobile AP MLD transmits two channel switch announcement elements in a beacon or probe response frame to switch between the primary link and non-primary links, it must set the switch time fields included in the two channel switch announcement elements to the same value. Of the two channel switch announcement elements, the element for the primary link is located outside the ML element (Multi-Link element) of the beacon / probe response frame, and the element for the non-primary link is located within the STA-specific profile for the non-primary link (AP) included in the ML element of the beacon / probe response frame.

[0445] Furthermore, when the NSTR mobile AP MLD has the purpose of switching between the primary link and the non-primary link, it will have to start advertising the channel switch announcement elements for the primary link and the non-primary link at the same time. That is, the channel switch announcement elements for the primary link and the non-primary link that the NSTR mobile AP MLD sends to switch between the primary link and the non-primary link should always be indicated together.

[0446] In addition, when the NSTR mobile AP MLD has the purpose of switching between the primary link and the non-primary link, the two Max Channel Switch Time elements for the primary link and the non-primary link must indicate the same time point. That is, the Max Channel Switch Time element for the primary link (more specifically, the Switch Time field) must indicate the same time point as the Max Channel Switch Time element for the non-primary link (more specifically, the Switch Time field).

[0447] Even when switching between the primary link and non-primary links as described above does not occur, the NSTR mobile AP MLD can transmit a beacon / probe response frame that includes both an (extended) channel switch announcement element for the primary link and an (extended) channel switch announcement element for the non-primary link. As an example, the NSTR mobile AP MLD can include an (extended) channel switch announcement element in the STA-specific profile for the non-primary link to advertise a channel / class switch for the non-primary link, but can also include an (extended) channel switch announcement element corresponding to the primary link in the beacon / probe response frame to advertise a channel / class switch for the primary link. In other words, the NSTR mobile AP MLD can include an (extended) channel switch announcement element corresponding to the primary link and an (extended) channel switch announcement element corresponding to the non-primary link in a single beacon / probe response frame. In this case, the two (extended) channel switch announcement elements may be advertisements related to independent channel switching procedures, rather than for the purpose of switching between primary and non-primary links.

[0448] However, the NSTR mobile AP MLD has a restriction that when a single beacon / probe response frame includes both an (extended) channel switch announcement element corresponding to the primary link and an (extended) channel switch announcement element corresponding to a non-primary link, the value indicated in the channel switch count field of the (extended) channel switch announcement element corresponding to the primary link must be set to a value equal to or greater than the value indicated in the channel switch count field of the (extended) channel switch announcement element corresponding to the non-primary link. This restriction may be intended to prevent the value of the channel switch count field of the (extended) channel switch announcement element for the primary link from reaching 1 before the value of the channel switch count field of the (extended) channel switch announcement element for the non-primary link.

[0449] Furthermore, if the (extended) channel switch announcement element with the smaller channel switch count value among two (extended) channel switch announcement elements included in a single beacon / probe response frame corresponds to the primary link, no more beacon frames are transmitted on the primary link after the channel switch count field of the (extended) channel switch announcement element corresponding to the primary link is set to 1, and therefore no more (extended) channel switch announcement elements corresponding to non-primary links can be transmitted. That is, if the channel switch count field value corresponding to the primary link is smaller than the channel switch count field value corresponding to the non-primary link, no more (extended) channel switch announcement elements corresponding to the non-primary link can be transmitted on the primary link, i.e., the countdown associated with the start of a channel switch for the non-primary link cannot be completed.

[0450] Therefore, when the NSTR mobile AP MLD includes both an (extended) channel switch announcement element for the primary link and an (extended) channel switch announcement element for the non-primary links in a single beacon / probe response frame, the channel switch count field value of the (extended) channel switch announcement element for the primary link must be set to be equal to or greater than the channel switch count field value of the (extended) channel switch announcement element for the non-primary links. As mentioned above, the two channel switch count field values ​​may be set to the same when the NSTR mobile AP MLD has the purpose / intent of switching the operating channels of the primary link and non-primary links. Furthermore, even when changing the operating channel / class of the primary link from a first operating channel / class to a second operating channel / class and simultaneously changing the operating channel / class of the non-primary link from a third operating channel / class to a fourth operating channel / class, the channel switch count fields for both links may still be set to the same value.

[0451] FIG. 24 illustrates an example of a configuration of a beacon frame and a probe response frame for channel switching according to an embodiment of the present invention.

[0452] 24, a beacon / probe response frame may include both an (extended) channel switch announcement element corresponding to the primary link and an (extended) channel switch announcement element corresponding to a non-primary link. The (extended) channel switch announcement element corresponding to the primary link is indicated (included) in a position that is not inside the Multi-Link element, and the value of the channel switch count field is set to 'x'. The (extended) channel switch announcement element corresponding to a non-primary link is indicated (included) in a STA-specific profile sub-element corresponding to the non-primary link included in the Multi-Link element, and the value of the channel switch count field is set to 'y'.

[0453] In this way, when a single beacon / probe response frame contains both (extended) channel switch announcement elements for the primary link and non-primary links, the value of the channel switch count field corresponding to the primary link is set to be equal to or greater than the value of the channel switch count field corresponding to the non-primary link.

[0454] At this time, the values ​​of the two channel switch count fields, 'x' and 'y', are set to the same value when the NSTR mobile AP MLD attempts to switch the operating channels of the primary link and non-primary link to each other.

[0455] Alternatively, in another method, when the countdown using the (extended) channel switch announcement element corresponding to the non-primary link is interrupted due to the initiation of a channel switch for the primary link, the NSTR mobile AP MLD and non-AP MLD can be considered to have initiated channel switching for the non-primary link in accordance with the virtual TBTT predicted when the (extended) channel switch announcement element corresponding to the non-primary link reaches 0.

[0456] Furthermore, if the channel switch count field value of the (extended) channel switch announcement element corresponding to the non-primary link in the last beacon frame transmitted by the AP of the primary link before initiating channel switching is 2 (at this time, the channel switch count field value of the (extended) channel switch announcement element corresponding to the primary link is 1), the NSTR mobile AP MLD may initiate a channel / class switch of the non-primary link 2 × beacon interval after the TBTT at which the beacon frame was transmitted. In other words, the NSTR mobile AP MLD and non-AP MLD can initiate or determine that a channel switch of the non-primary link has been initiated if a time equal to the value of the last channel switch count field instructed / instructed for the non-primary link × beacon interval (the beacon interval of the primary link) has elapsed after the TBTT at which the beacon frame including the channel switch count field was transmitted.

[0457] This may be an operation in which a virtual beacon frame is considered to have been transmitted in a virtual TBTT (which exists for each beacon interval) even if no further beacon frames are transmitted on the primary link due to a channel switch initiated on the primary link. In this case, each virtual beacon frame is considered to indicate a value in the channel switch count field corresponding to the non-primary link that is 1 less than the value in the previous (virtual) beacon frame. Therefore, when channel switching is not performed on the primary link, it can be determined that a channel switch of the non-primary link has been initiated / started at the point in time when it is determined (calculated, predicted) that the value in the channel switch count field corresponding to the non-primary link reaches 0.

[0458] <Non-AP MLD operation without channel / class switching performed on the primary link>

[0459] When the NSTR mobile AP MLD announces channel / class switching for a non-primary link, the non-AP MLD can decide not to perform the specified channel / class switching and tear down the non-primary link. In this case, the non-AP MLD can perform / initiate a multi-link re-setup procedure to tear down the non-primary link. Alternatively, the non-AP MLD can terminate the ML setup with the NSTR mobile AP MLD and establish a new single-link association with the primary link. In other words, a non-AP MLD that chooses not to perform the announced channel / class switching for a non-primary link can transition to a state where it is connected to the NSTR mobile AP MLD only via the primary link.

[0460] When the NSTR mobile AP MLD announces channel / class switching for the primary link, the non-AP MLD can decide not to perform the specified channel / class switching and in this case, can disassociate from the NSTR mobile AP MLD. In this case, disassociation means that all connections between the primary link and the non-primary link are torn down. In other words, when the NSTR mobile AP MLD announces channel / class switching for the primary link, the non-AP MLD can decide to move to another AP or another AP MLD without performing the specified channel / class switching. In this case, the non-AP MLD that decides not to perform the specified channel / class switching must send a disassociation frame to the NSTR mobile AP MLD.

[0461] Unlike when selecting not to perform announced channel / class switching for a non-primary link, the reason why the connection with the NSTR mobile AP MLD must be terminated when announced channel / class switching for a primary link is not performed is because the BSS operated by the NSTR mobile AP MLD is highly dependent on the primary link. In other words, a non-AP STA connected only through a non-primary link, excluding the primary link, and the NSTR mobile AP MLD cannot exchange frames normally, which may result in limitations on maintaining the connection excluding the primary link.

[0462] However, the non-AP MLD may receive a frame requesting a response frame from the NSTR mobile AP MLD before starting / completing a move to another AP or another AP MLD. This may occur because the NSTR mobile AP MLD is unaware that it has decided to move to another AP or another AP MLD without performing channel switching. That is, after announcing channel / class switch information for the primary link, the NSTR mobile AP MLD may send a frame requesting a response frame to the non-AP MLD without acknowledging that the non-AP MLD has decided not to perform the channel switch. In this case, the non-AP MLD may implicitly inform the NSTR mobile AP MLD that it has decided not to perform a channel / class switch by not responding to the frame received from the NSTR mobile AP MLD.

[0463] Therefore, according to one embodiment of the present invention, a non-AP MLD that has determined not to perform a channel / class switch announced by an NSTR mobile AP MLD for the primary link may not respond to a frame received from the NSTR mobile AP MLD. The time at which the non-AP MLD does not respond to the received frame may be when it has determined not to perform a channel / class switch (when the determination is maintained). The time at which the non-AP MLD does not respond to the received frame may be after channel / class switching of the primary link has been initiated, when it has determined not to perform a channel / class switch. In this case, even when it has determined not to perform a channel / class switch, the non-AP MLD can respond to a frame received before the channel / class switch is initiated (before the next TBTT after a beacon frame with a channel switch count field set to 1 is transmitted). Also, since frames received from the NSTR mobile AP MLD after an announced channel / class switch for the primary link has been initiated are received on the non-primary link, a restriction applied to the non-AP MLD may be that it must not respond to frames (sent by the NSTR mobile AP MLD) received on the non-primary link when it has decided not to perform a channel / class switch for the primary link.

[0464] <NSTR mobile AP MLDのトリガーフレーム> NSTR mobile AP MLD transmits a trigger frame like regular AP MLD and allows non-AP STAs (and non-AP MLDs) to transmit UL PPDUs. In this case, the UL PPDU transmitted by each STA may be a TB PPDU based on orthogonal frequency division multiplexing (OFDMA).

[0465] More specifically, 802.11ax (Wi-Fi 6), the conventional Wi-Fi standard, employs OFDMA, and each frequency resource (RU, Resource Unit) transmitting a DL PPDU from an AP can be targeted to a different STA. The DL PPDU includes information related to which STA each RU is assigned in the HE SIGNAL field. Each STA receives the HE SIGNAL field to obtain information related to whether or not it has an assigned RU, the RU's location, the applied MCS, etc., and can then receive the data transmitted to it in the DL PPDU. Similarly, OFDMA is also employed for UL PPDUs, and the AP transmits a trigger frame to enable multiple STAs to simultaneously transmit UL PPDUs. The trigger frame includes information instructing each STA on the RU transmitting the UL PPDU, the MCS to be applied, the transmission length, etc. After receiving the trigger frame from the AP, if a non-AP STA has an assigned RU, it transmits the traffic it wishes to transmit to the AP via UL in the manner instructed by the trigger frame. In this case, the UL PPDU that the non-AP STA transmits after receiving the trigger frame is called a TB PPDU (Trigger-Based PPDU (physical layer protocol data unit)).

[0466] The AP can use the trigger frame to allocate RUs to non-AP STAs associated with itself, as well as to allocate RUs that can be used by non-AP STAs that are not associated with itself (i.e., unassociated STAs). When the AP allocates RUs that can be used by non-AP STAs that are not associated with itself, the non-AP STAs that are not associated with the AP can attempt to associate with the AP, such as by transmitting a probe response frame in the RU.

[0467] For example, a non-AP STA that receives a beacon frame or a FILS discovery frame transmitted by an AP to which it is not associated may attempt to associate with the AP. In this case, the non-AP STA may attempt channel access using EDCA to transmit a probe request frame to the AP. However, the non-AP STA may receive a trigger frame transmitted by the AP before completing the channel access procedure. If the non-AP STA identifies an RU assigned in the trigger frame that is permitted for use by STAs not associated with the AP, it can transmit a probe request frame to the AP using the RU. That is, the non-AP STA can transmit the probe request frame it intended to transmit by responding with a TB PPDU using an RU that is permitted for access by non-associated non-AP STAs. In this case, the RU that the AP permits access by unassociated STAs using the trigger frame may be an RU whose assigned device AID is specified as 2045. At this time, the RU whose AID of the allocation target device is designated as 2045 is an RU called a Random Access Resource Unit (RA-RU) in the conventional Wi-Fi standard.

[0468] Considering the use of RUs for Unassociated STAs described above, it can be seen that RUs for Unassociated STAs should not be allocated when the NSTR mobile AP MLD transmits a trigger frame over a non-primary link. Furthermore, if the NSTR mobile AP MLD allocates RUs for Unassociated STAs using a trigger frame transmitted over a non-primary link, the Unassociated STA may respond with a probe request frame. This may be considered as an unnecessary transmission considering that the NSTR mobile AP MLD does not support association over a non-primary link. Alternatively, even if an Unassociated RU is allocated, there may be no non-AP STAs attempting to transmit a probe request frame to the AP over the non-primary link because there are no beacon / FILS discovery / probe response frames transmitted over the non-primary link of the NSTR mobile AP MLD, resulting in the waste of RUs.

[0469] As a result, the NSTR mobile AP MLD must not indicate an (RA-)RU for an unassociated STA when transmitting a trigger frame through an AP operating on a non-primary link. That is, the NSTR mobile AP MLD must not allocate an RU whose AID is indicated as 2045 when transmitting a trigger frame through an AP operating on a non-primary link. That is, the NSTR mobile AP MLD must not indicate the AID12 subfield as 2045 when transmitting a trigger frame through an AP operating on a non-primary link.

[0470] In this case, the AID12 subfield is a subfield included in the User Info field included in the trigger frame, and indicates the AID of the device to which the RU allocated based on the RU Allocation subfield of the User Info field is assigned. If the AID12 subfield of a specific User Info field is set to 0, the device to which the RU allocated based on the RU Allocation subfield of the User Info field is assigned is an unspecified associated STA. If the AID12 subfield of a specific User Info field is set to a value between 1 and 2007, the device to which the RU allocated based on the RU Allocation subfield of the User Info field is assigned is an STA having the same AID as the value indicated by the AID12 subfield. If the AID12 subfield of a specific User Info field is set to 2054, the device to which the RU allocated based on the RU Allocation subfield of the User Info field is assigned is an unspecified unassociated STA. If the AID12 subfield of a specific User Info field is set to 2046, the RU indicated based on the RU Allocation subfield of the User Info field is an unallocated RU that has not been allocated to any STA. If the AID12 subfield of a specific User Info field is set to 4095, it indicates that a Padding field appears after the User Info field. Settings where the AID12 subfield value is 2008 to 2044 or 2047 to 4094 are Reserved.

[0471] Furthermore, the EHT AP can specify the format of the TB PPDU to be responded to using the trigger frame. The TB PPDU format that can be specified is either the HE TB PPDU or the EHT TB PPDU. Since the EHT STA supports the function of the HE STA, the EHT AP can specify that the TB PPDU should be responded to in the HE TB PPDU format by the HE STA (not the EHT STA) and all EHT STAs. The TB PPDU format specified by the AP can be specified based on at least one of B54 and / or B55 included in the Common Info field of the trigger frame. A trigger frame in which both B54 and B55 in the Common Info field are set to 1 can be a trigger frame instructing a response with an HE TB PPDU. That is, a STA assigned an RU in a trigger frame in which both B54 and B55 are set to 1 must perform UL transmission using the HE TB PPDU format.

[0472] The reason why the EHT AP is allowed to selectively respond with the HE TB PPDU and the EHT TB PPDU is to allow the EHT AP to simultaneously allocate RUs to the HE STA and the EHT STA and simultaneously respond with TB PPDUs. As an example, the EHT AP can transmit a trigger frame for the purpose of allocating RUs to all of the HE STAs and EHT STAs associated with it. In this case, the EHT AP can receive the HE TB PPDUs simultaneously responded from the HE STA and the EHT STA at once by instructing the EHT STA to respond with the HE TB PPDU format.

[0473] On the other hand, when the EHT AP transmits a trigger frame that allocates RUs only to EHT STAs, it does not need to instruct them to respond with an HE TB PPDU because all STAs t...

Claims

1. A station (STA) of a multi-link device (MLD), a transmitter / receiver; a processor, the multilink device includes at least one station; The processor: Receive a specific frame for channel switching and / or class switching from a first AP (Access Point) of an AP MLD including at least one AP; The specific frame includes a Per-STA profile subelement corresponding to the second AP included in the AP MLD, The STA-specific profile sub-element includes at least one of i) a channel switch announcement element for informing channel switching and / or class switching, and / or ii) a maximum channel switch time element associated with the time of the channel switching of the second AP, determining whether the channel switching and / or the class switching of the second AP is completed based on the per-STA profile sub-element; Whether the channel switching and / or the class switching is completed is determined based on whether the STA-specific profile sub-element includes at least one of the channel switch announcement element and the maximum channel switch time element. The station is configured as follows.

2. A station as described in claim 1, wherein if the STA-specific profile sub-element includes the maximum channel switch time element but does not include the channel switch announcement element, it is determined that the channel switching and / or class switching of the second AP has not been completed after channel switching has started.

3. A station as described in claim 1, wherein when the STA-specific profile subelement does not include the maximum channel switch time element, it is determined that the channel switching and / or class switching of the second AP is completed and that BSS (Basic Service Set) operation of the second AP is resumed.

4. 2. The station of claim 1, wherein the maximum channel switch time element includes a switch time field related to the time from completion of the channel switching to transmission of a first beacon frame or resumption of BSS operation on a new channel.

5. A station as described in claim 4, wherein the switch time field included in the maximum channel switch time element of the last beacon frame indicates the time between the transmission time of the last beacon frame transmitted by the second AP and the transmission time of the first beacon frame on the new channel when the last beacon frame is transmitted by the second AP on the current channel.

6. The station of claim 4, wherein the switch time field indicates the time between the transmission time of the particular frame including the maximum channel switch time element and the transmission time of the first beacon frame on the new channel when the last beacon frame on the current channel is transmitted by the second AP.

7. 5. The station of claim 4, wherein the switch time field indicates a time difference between a transmission time of the particular frame including the maximum channel switch time element and a time until the BSS operation on the new channel is resumed when the AP MLD is a nonsimultaneous transmit and receive (NSTR) mobile AP MLD that does not support simultaneous transmission / reception.

8. The channel switch announcement element includes a new channel number field and a channel switch count field; the new channel number field indicates the number of the new channels; 5. The station of claim 4, wherein the channel switch count field indicates the number of Target Beacon Transmission Times (TBTTs) remaining before initiating a channel switch on the new channel.

9. A method for a station (STA) of a multi-link device (MLD) in a wireless communication system to receive a frame, comprising: receiving a specific frame for channel switching and / or class switching from a first AP (Access Point) of an AP MLD including at least one AP, The specific frame includes a Per-STA profile subelement corresponding to the second AP included in the AP MLD, The STA-specific profile sub-element includes at least one of i) a channel switch announcement element for informing channel switching and / or class switching, and / or ii) a maximum channel switch time element associated with the time of the channel switching of the second AP; determining whether the channel switching and / or the class switching of the second AP is completed based on the per-STA profile sub-element, and determining whether the channel switching and / or the class switching has been completed based on whether the STA-specific profile sub-element includes at least one of the channel switch announcement element and the maximum channel switch time element.

10. The method described in claim 9, wherein if the STA-specific profile subelement includes the maximum channel switch time element but does not include the channel switch announcement element, it is determined that the channel switching and / or class switching of the second AP has not been completed after channel switching has started.

11. The method described in claim 9, wherein if the STA-specific profile subelement does not include the maximum channel switch time element, it is determined that the channel switching and / or class switching of the second AP is completed and it is determined that BSS (Basic Service Set) operation of the second AP will resume.

12. 10. The method of claim 9, wherein the maximum channel switch time element includes a Switch Time field related to the time from completion of the channel switching to transmission of a first beacon frame or resumption of BSS operation on a new channel.

13. The method described in claim 12, wherein the switch time field included in the maximum channel switch time element of the last beacon frame indicates the time between the transmission time of the last beacon frame transmitted by the second AP and the transmission time of the first beacon frame on the new channel when the last beacon frame is transmitted by the second AP on the current channel.

14. 13. The method of claim 12, wherein the switch time field indicates the time between the transmission time of the particular frame including the maximum channel switch time element and the transmission time of the first beacon frame on the new channel when the last beacon frame on the current channel is transmitted by the second AP.

15. 13. The method of claim 12, wherein the switch time field indicates a time difference between a transmission time of the particular frame including the maximum channel switch time element and a time until the BSS operation on the new channel is resumed when the AP MLD is a nonsimultaneous transmit and receive (NSTR) mobile AP MLD that does not support simultaneous transmission / reception.

16. The channel switch announcement element includes a new channel number field and a channel switch count field; the new channel number field indicates the number of the new channels; The method of claim 12 , wherein the channel switch count field indicates the number of Target Beacon Transmission Times (TBTTs) remaining before initiating a channel switch on the new channel.

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