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 use of mobile devices has become more widespread, wireless LAN technology that can provide them with high-speed wireless Internet services has been attracting attention. Wireless LAN technology is a technology that enables mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, embedded devices, etc. to wirelessly connect to the Internet at home, in business, or in specific service areas based on short-distance wireless communication technology.

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

[0004] IEEE 802.11n is a technical standard established to overcome the communication speed limitations that have been pointed out as a weakness of wireless LAN. The purpose of IEEE 802.11n is to increase the speed and reliability of the network and to extend the operating distance of the wireless network. In detail, IEEE 802.11n supports a high throughput (HT) of up to 540Mbps or more in data processing speed, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology that 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 the use of wireless LANs becomes more widespread and applications using them become more diverse, the need for new wireless LAN systems to support data throughput rates (Very High Throughput, VHT) higher than those supported by IEEE 802.11n is emerging. Among them, IEEE 802.11ac supports wide bandwidth (80MHz~160MHz) at 5GHz frequency. Although the IEEE 802.11ac standard is defined only in the 5GHz band, it is expected that initial 11ac chipsets will also support operation in the 2.4GHz band for backward compatibility with existing 2.4GHz band products. Theoretically, this standard allows multi-station wireless LAN speeds of at least 1Gbps and maximum single link speeds of at least 500Mbps. This is done by extending the air interface concepts accepted by 802.11n, such as wider radio frequency bandwidth (up to 160MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high density modulation (up to 256QAM). Also, 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, and is suitable for streaming large amounts of data and high bitrate videos such as uncompressed HD video. However, the 60GHz frequency band has the disadvantage that it is 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 in the final stages as the WLAN standard after 802.11ac and 802.11ad 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, it is necessary to provide high-frequency efficient communication indoors / outdoors in the presence of high density stations and APs (Access Points), and various technologies are being developed to realize this.

[0007] In addition, new WLAN standards have begun to be developed to increase maximum transmission speeds to support new multimedia applications such as high-definition video and real-time games. IEEE 802.11be (Extremely High Throughput, EHT), the 7th generation WLAN standard, is currently being developed with the goal of supporting transmission rates of up to 30 Gbps through wider bandwidth in the 2.4 / 5 / 6 GHz bands, increased spatial streams, and multiple 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 the present invention is to provide a channel switching method for a station and an AP using multilink.

[0010] The technical problems to be achieved in this specification are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by a person 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 each operating on a plurality of links 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 channel switch announcement element for notifying the channel switching and / or class change of a second AP included in the AP MLD and / or a Max Channel Switch Time element related to a 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 according to a type of the AP MLD and / or a state of the channel switching, the first time being a maximum time from a last beacon frame transmitted from the second AP before the start of the channel switching to a first beacon frame on a new channel, and the second time being a time from a frame transmission 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 has been 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, the channel switch time field indicates the first time if it is before the channel switching begins.

[0014] In addition, in the present invention, the channel switch announcement element includes a new channel number field and a channel switch count field, the channel number field indicating the position of the new channel, and the channel switch count field indicating the number of TBTTs (Target Beacon Transmission Times) remaining until a 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] Also, in the present invention, the specific operation is resumption of a Basic Service Set (BSS) 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 in a primary link, and the second AP operates in a nonprimary link.

[0018] In addition, in the present invention, the channel switching state is determined according to 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, when the frame includes the maximum channel switch time element and 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 frame does not include the maximum channel switch time element, 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, comprising: 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 group consisting of a Channel Switch Announcement element for notifying a second AP of the channel switching and / or class change included in the AP MLD and / or a Max Channel Switch Time element associated with a 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 according to a type of the AP MLD and / or a state of the channel switching, the first time being a maximum time from a last beacon frame transmitted from the second AP before the start of the channel switching to a first beacon frame on a new channel, and the second time being a time from a transmission of the frame to a specific operation of the second AP on the new channel; and recognizing channel switching of the second AP based on the frame. Effect of the Invention

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

[0023] In addition, the channel change method according to an embodiment of the present invention has an effect of efficiently performing channel switching by clarifying the structure of a frame 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 description of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Diagram 2] FIG. 11 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing a configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing the configuration of an access point according to an embodiment of the present invention. [Diagram 5] 1 is a diagram illustrating a process in which a STA sets up 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 an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and a method for indicating the same according to an embodiment of the present invention. [Figure 9] 1 illustrates a multi-link device according to an embodiment of the present invention. [Figure 10] 1 illustrates a multi-link operation in which transmissions on different links are performed simultaneously according to an embodiment of the present invention. [Figure 11] 1 illustrates an example of the contents of a beacon frame transmitted by an AP in AP MLD and 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] 13 illustrates yet another example of a TBTT information field format according to an embodiment of the present invention. [Figure 13] 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. [Figure 14] 1 illustrates an example of a Per-STA Profile subelement format according to an embodiment of the present invention. [Figure 15]13 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] 11 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] 1 illustrates an example of an element format according to an embodiment of the present invention. [Figure 18] 13 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] 13 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 an ML (re)setup management method for channel switching according to one 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] 1 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] 1 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. [Diagram 25] 4 is a flowchart illustrating an example of a channel switching method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The terms used in this specification are selected as general terms that are currently widely used as much as possible in consideration of the functions of the present invention, but this may vary depending on the intentions, customs, or the emergence of new technologies of the engineers in the relevant technical field. In addition, in certain cases, the applicant may arbitrarily select terms, and in such cases, the meanings of the terms will be described in the description of the relevant invention. Therefore, it is clear that the terms used in this specification should be interpreted not simply as terms, but based on the substantial meanings of the terms and the contents of this specification as a whole.

[0029] Throughout the specification, when a certain component is "connected" to another component, this includes not only when it is "directly connected" to another component, but also when it is "electrically connected" with another component in between. Furthermore, when a certain component "includes" a specific component, this means that it may further include the other component, not excluding the other component, unless otherwise specified to the contrary. In addition, limitations such as "greater than" or "less than" based on a specific threshold value may be appropriately replaced with "greater than" or "less than" 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 (BSS), which are a set of devices that can successfully 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 which are stations providing a distribution service, and a distribution system DS which connects multiple access points AP-1 and AP-2.

[0034] A station (STA) is any device including a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard, and in a broad sense includes not only non-AP stations but also APs. In this specification, the term "terminal" refers to either a non-AP or an AP, or to both. A station for wireless communication includes a processor and a communication unit, and further includes a user interface unit and a display unit, etc., depending on the embodiment. The processor generates frames to be transmitted through a wireless network, processes frames received through 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 through the wireless network for the station. In the present invention, the term "terminal" is used to include a 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 a station associated therewith. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP, but when a direct link is set up, direct communication is possible between non-AP stations. Meanwhile, in the present invention, AP is used as a concept including a personal BSS coordination point (PCP), but in a broad sense, AP includes all 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, AP is also referred to as a base wireless communication terminal, but in a broad sense, the 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 in communication with a plurality of wireless communication terminals.

[0036] A plurality of infrastructure BSSs are connected to each other via a distribution system DS. In this case, a plurality of BSSs connected to each other via the distribution system is 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 which the same or corresponding parts in the embodiment of FIG. 2 are the same as or correspond to the embodiment of FIG.

[0038] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so all stations (STA6, STA7) are not connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

[0039] 3 is a block diagram showing a configuration of a station 100 according to an embodiment of the present invention. As shown in the figure, 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 wireless LAN packets, and may be built into or externally provided in the station 100. According to an embodiment, the communication unit 120 may include at least one communication module using different frequency bands. For example, the communication unit 120 may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to an embodiment, the station 100 may include a communication module using a frequency band of 7.125 GHz or more and a communication module using a frequency band of 7.125 GHz or less. Each communication module may perform wireless communication with an AP or an external station based on the wireless LAN standard of the frequency band supported by the communication module. The communication unit 120 may operate only one communication module at a time or operate multiple communication modules simultaneously according to the performance and requirements of the station 100. When the station 100 includes multiple communication modules, each communication module may be provided in an independent form, or multiple modules may be integrated into one chip. In an 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 a command from the processor 110 using various output means.

[0042] Then, 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 performed by the processor 110 or a control command of the processor 110. The memory 160 also stores control programs used by the station 100 and various data associated therewith. Such control programs include connection programs 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 transmission and reception of data between the units. According to an embodiment of the present invention, the processor 110 executes a program for connection to an AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also reads information on the priority conditions of the station 100 included in the communication setup message and requests a connection to the AP based on the information on the priority conditions of the station 100. The processor 110 of the present invention may refer to a main control unit of the station 100, or may refer to a control unit for individually controlling some components of the station 100, for example, the communication unit 120, depending on the embodiment. That is, the processor 110 may be a modem that modulates and demodulates a wireless signal transmitted and received from the communication unit 120, or a modulator and / or demodulator. The processor 110 controls various operations of transmitting and receiving wireless signals of the station 100 according to an embodiment of the present invention. A detailed embodiment of the present invention 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 are used to logically distinguish between elements of the device. Thus, the above-mentioned device elements may be mounted on one chip or multiple chips depending on the design of the device. For example, the processor 110 and the communication unit 120 may be integrated and embodied on one chip, or may be embodied on separate chips. In addition, in an embodiment of the present invention, some components of the station 100, such as the user interface unit 140 and the display unit 150, may be selectively provided in the station 100.

[0045] 4 is a block diagram showing a configuration of an AP 200 according to an embodiment of the present invention. As shown in the figure, 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, a duplicated description 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 a plurality of 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, any of 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with 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 operate multiple communication modules simultaneously according to the performance and requirements of the AP 200. In the embodiment of the present invention, the communication unit 220 may represent an RF communication module that processes RF (Radio Frequency) signals.

[0047] Next, the memory 260 stores control programs used in the AP 200 and various data associated therewith. Such control programs include a connection program for managing station connections. Also, the processor 210 controls each unit of the AP 200 and controls transmission and reception of data between the units. According to an embodiment of the present invention, the processor 210 executes a program for connection with a station stored in the memory 260 and transmits a communication setting message to one or more stations. At this time, the communication setting message includes information regarding connection priority conditions of each station. Also, the processor 210 performs connection setting in response to a connection request of a station. 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 of transmitting and receiving wireless signals of the AP 200 according to an embodiment of the present invention. A detailed embodiment thereof 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, the link between the STA 100 and the AP 200 is set up through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information of the BSS operated by the AP 200. There are two methods for performing scanning: 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 has successfully received wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200, and performs an 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 an association step (S109b). In this specification, association basically means wireless association, but the present invention is not limited thereto, 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, the server 300 is a server that processes 802.1X-based authentication with the STA 100, and may be physically connected to the 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 wireless LAN communication checks whether a channel is occupied by performing carrier sensing before transmitting data. If a wireless signal of a certain strength or more 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 the signal is detected is called the CCA threshold. If a wireless signal of a strength greater than the CCA threshold received by a terminal is received by the terminal, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected from the channel or a wireless signal of a strength less than the CCA threshold is detected, the channel is determined to be idle.

[0054] If the channel is determined to be in an idle state, each terminal having data to transmit performs a backoff procedure after an IFS (Inter Frame Space) according to the status of each terminal, for example, an AIFS (Arbitration IFS) or a PIFS (PCF IFS). In some embodiments, the AIFS is used as a configuration to replace the conventional DIFS (DCF IFS). Each terminal waits while decreasing a slot time of a random number determined for the corresponding terminal during an interval of the idle state of the channel, and a terminal that has exhausted all the slot time attempts to access the corresponding channel. In this manner, a section in which each terminal performs a backoff procedure is called a contention window section. At this time, the random number can be called a backoff counter. That is, an initial value of the backoff counter is set by an integer that is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal can decrease the backoff counter by 1. Also, if the backoff counter reaches 0, the terminal may be allowed to perform channel access on the corresponding channel. Thus, a terminal may be allowed to transmit if the channel is idle during the AIFS time and the backoff counter slot time.

[0055] If a specific terminal succeeds in accessing the channel, the terminal transmits data through 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 random numbers newly assigned to each terminal are determined within a range (2*CW) twice the range (contention window, CW) of the random numbers previously assigned to the terminal. Meanwhile, each terminal attempts access by performing a backoff procedure again in the next contention window period, and at this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. In this manner, each terminal performing wireless LAN communication can avoid collision with each other on a specific channel.

[0056] <Examples of various PPDU formats>

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

[0058] 7(a), the preamble of the legacy PPDU includes a legacy short training field (L-STF), a legacy long training field (L-LTF), and a legacy signal field (L-SIG). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as a legacy preamble.

[0059] Referring to FIG. 7(b), the preamble of the HE PPDU further includes a RL-SIG (Repeated Legacy Short Training field), a HE-SIG-A (High Efficiency Signal A field), a HE-SIG-B (High Efficiency Signal B field), a HE-STF (High Efficiency Short Training field), and a HE-LTF (High Efficiency Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF can be referred to as an HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, the 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 RL-SIG (Repeated Legacy Short Training field), a U-SIG (Universal Signal field), an EHT-SIG-A (Extremely High Throughput Signal A field), an EHT-SIG-A (Extremely High Throughput Signal B field), an EHT-STF (Extremely High Throughput Short Training field), and an EHT-LTF (Extremely High Throughput Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF can be called an EHT preamble. The specific configuration of the non-legacy preamble may be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some formats of the EHT PPDU format.

[0061] The L-SIG field included in the preamble of the PPDU is configured with a total of 64 subcarriers by applying 64 FFT OFDM. Of these, 48 subcarriers excluding the guard subcarriers, DC subcarriers, and pilot subcarriers are used for L-SIG data transmission. Since BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information configuration 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 speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which is a combination of a modulation method such as BPSK / QPSK / 16-QAM / 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The total length of the PPDU can be indicated by combining the information in the L_RATE field and the L_LENGTH field. In the non-legacy PPDU format, the L_RATE field is set to the minimum speed of 6 Mbps.

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

[0064] First, a method in which a legacy or non-legacy terminal analyzes the length of the PPDU using the L_LENGTH field is 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 one symbol duration of 64 FFT. Therefore, the number of 64 FFT reference symbols after the L-SIG is obtained by adding 3 bytes corresponding to the SVC field and the Tail field to the L_LENGTH field value and dividing it by 3 bytes, which is the transmission amount of one symbol. The length of the PPDU, i.e., the reception time (RXTIME), is obtained by multiplying the obtained number of symbols by 4 us, which is one symbol duration, and adding 20 us for the transmission of the L-STF, L-LTF, and L-SIG. This can be expressed as the following Equation 1.

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

[0072] The VI bit will maintain the current bit configuration, and even if a subsequent generation PPDU is defined, a current 11be terminal can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field is composed of PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits, and serves to sequentially distinguish 11be and subsequent generation WLAN standards by version. 11be has a value of 000b. The UL / DL field distinguishes whether the corresponding PPDU is an uplink / downlink PPDU. The BSS color means a BSS-specific identifier defined in 11ax, and has a value of 6 bits or more. The TXOP means a transmit opportunity duration that was transmitted in the MAC header, but by adding it to the PHY header, the length of the TXOP containing the corresponding PPDU can be inferred without decoding the MPDU, and has a value of 7 bits or more.

[0073] The VD field may be composed of fields commonly used in any PPDU format, such as PPDU format and BW, which are signaling information useful only for PPDUs of the 11be version, and fields defined differently for each PPDU format. The PPDU format is a division factor that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), EHT ER (Extended Range) PPDU, etc. The BW field mainly signals five basic PPDU BW options of 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), and various remaining PPDU BWs formed by preamble puncturing. After being signaled at 320 MHz, some 80 MHz may be signaled in a punctured form. Also, the punctured and modified channel shape may be directly signaled in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (e.g., a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW 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. The MU PPDU and the SU PPDU may be signaled in the same PPDU format, and a field for distinguishing the MU PPDU from the SU PPDU may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both the SU PPDU and the MU PPDU include an EHT-SIG field, but some fields that are not necessary in the SU PPDU may be compressed. In this case, the information of the compressed field may be omitted or may have a reduced size compared to the size of the original field included in the MU PPDU. For example, in the case of the SU PPDU, the common field of the EHT-SIG may be omitted or replaced, or the user-specific field may be replaced or reduced to one, and may have a different configuration.

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

[0076] When a part 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, etc.). In the case of the 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 transmitted to itself. 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 of the EHT-SIG field and / or MCS, which is a modulation method. The EHT-SIG field may include the size and location information of the RU assigned to each user.

[0077] In the case of a 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 receive the SU PPDU efficiently only by recognizing the RUs punctured in between. Therefore, the AP can transmit the SU PPDU including information on the punctured RUs among the RUs assigned to the STA (e.g., the puncturing pattern of the RUs, etc.). That is, in the case of a 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 may signal the type of discontinuous channels that appear within the bandwidth.

[0078] The form of the 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, in the case of a SU PPDU, since it is a PPDU transmitted only to a single UE, the STA can recognize the bandwidth allocated to itself from the BW field included in the PPDU, and can recognize the punctured resources of 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 unit. In this case, the 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 SU PPDU. Since puncturing may be performed for each 20 MHz subchannel, if puncturing is performed for a BW having multiple 20 MHz subchannels such as 80, 160, and 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered as discontinuous) must be signaled by expressing whether or not the remaining 15 20 MHz subchannels other than the primary channel are used. In this way, using 15 bits to signal discontinuous channel types for single user transmission may result in excessive signaling overhead when considering the low transmission speed of the signaling part.

[0080] The present 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, in one embodiment of the present invention, a method is proposed in which the configuration of the PPDU indicated by the preamble puncturing BW value is different depending on the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits, in the case of EHT SU PPDU or TB PPDU, one symbol of EHT-SIG-A is further signaled after U-SIG, or EHT-SIG-A does not need to be signaled from the beginning, so that up to 11 puncturing modes must be completely signaled using only the BW field of U-SIG in consideration of this. However, in the case of EHT MU PPDU, EHT-SIG-B is further signaled after U-SIG, so up to 11 puncturing modes can be signaled in a different manner from SU PPDU. In the case of EHT ER PPDU, the BW field is set to 1 bit, and it is possible to signal whether the PPDU uses a 20 MHz or 10 MHz band. Detailed puncturing patterns for each PPDU type will be described in detail below with reference to FIG. 11 and FIG. 12.

[0082] FIG. 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates EHT MU PPDU. In the case of MU PPDU, SIG-B, which is a signaling field for simultaneous reception by multiple users, is required, and SIG-B may be transmitted after U-SIG without a separate SIG-A. For this purpose, U-SIG must signal information for decoding SIG-B. Such fields include 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 a method for indicating the same according to an embodiment of the present invention.

[0084] 8, a PPDU may be composed of a preamble and a data portion, and the format of an EHT PPDU, which is one type, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is an 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] Fig. 8(d) shows an example of an EHT ER SU PPDU format used for single-user transmission with an STA in an extended range. The EHT ER SU PPDU may be used for single-user transmission with a STA in a wider range than the EHT SU PPDU described in Fig. 8(a), and the U-SIG field may be repeatedly positioned on the time axis.

[0089] The EHT MU PPDU described in (c) of FIG. 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 PPDU transmitted through the user specific field of the EHT-SIG-B to the STA. 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 a resource unit configuration (e.g., a resource unit division form) in a specific bandwidth (e.g., 20 MHz, etc.) on the frequency axis. That is, the RA field may indicate a resource unit configuration divided by a bandwidth for transmitting the HE MU PPDU so that the STA receives the PPDU. Information on 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, a user field corresponding to at least one resource unit used for data transmission among the multiple divided resource units may include the AID of a receiver or sender, and a user field corresponding to the remaining resource units not used for data transmission may include a null STA ID that has already been set.

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

[0093] When one wireless communication device communicates using multiple links, the communication efficiency of the wireless communication device can be improved. In this case, the link is a physical path, and may be configured as one wireless medium that can be used to transmit MSDU (MAC service data unit). For example, when the frequency band of any one link is being used by another wireless communication device, the wireless communication device can continue to communicate using another link. In this way, the wireless communication device can effectively use multiple channels. Also, when the wireless communication device simultaneously communicates using multiple links, the overall throughput can be increased. However, the existing wireless LAN is specified on the premise that one wireless communication device uses one link. For this reason, a wireless LAN operation method for using multiple links is required. A wireless communication method of a wireless communication device using multiple links will be described with reference to Figs. 9 to 26. First, a specific form 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] For the wireless communication method using the above-mentioned multiple links, a multi-link device (MLD) may be defined. The multi-link device may represent a device having one or more affiliated stations. According to a specific embodiment, the multi-link device may represent a device having two or more affiliated stations. Also, the multi-link device may exchange a multi-link element. The multi-link element includes information on 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 called a multi-link logical entity (MLLE) or a multi-link entity (MLE). The multi-link device may have one MAC service access point (SAP) up to a logical link control (LLC). Also, the MLD may have one MAC data service.

[0096] The stations included in the multilink device can operate on multiple links. Also, the stations included in the multilink device can operate on multiple channels. Specifically, the stations included in the multilink device can operate on different links or different channels. For example, the stations included in the multilink device can operate on different channels of 2.4 GHz, 5 GHz, and 6 GHz.

[0097] The operation of the multilink device may be referred to as multilink operation, MLD operation, or multi-band operation. If a station associated with the multilink device is an AP, the multilink device may be referred to as AP MLD. If a station associated with the multilink device is a non-AP station, the multilink device may 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 through a first link (Link1). Also, the second AP (AP2) and the second non-AP STA (non-AP STA2) communicate through a second link (Link2). Also, the third AP (AP3) and the third non-AP STA (non-AP STA3) communicate through a third link (Link3).

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

[0100] The multilink setting may be set by negotiation between peer stations. Specifically, the multilink setting may be set by communication between stations without communication with the AP. The multilink setting may be set through any one of the links. For example, even if the first link to the third link are set through the multilink, the multilink setting may be set through the first link.

[0101] Also, a mapping between a traffic identifier (TID) and a link may be set. Specifically, a frame corresponding to a specific TID value may be exchanged only through a link designated in advance. The mapping between a TID and a link may be set on a directional-based basis. For example, when a plurality of links are set between a first multilink device and a second multilink device, the first multilink device may be set to transmit a frame of a first TID to a plurality of first links, and the second multilink device may be set to transmit a frame of a second TID to the first link. Also, a default setting may exist for the mapping between a TID and a link. Specifically, when there is no additional setting in the multilink setting, the multilink device may exchange frames corresponding to a TID in each link according to a default setting. In this case, the default setting may be that all TIDs are exchanged in any one link.

[0102] The TID will be specifically described. The TID is an ID for classifying traffic and data to support QoS (quality of service). 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). The TID may be classified into 16 types. For example, the TID may be designated as one of 0 to 15. The TID value to be used may be designated differently depending on an access policy, a channel access, or a medium access method. For example, when EDCA (enhanced distributed channel access) or HCAF (hybrid coordination function contention based channel access) is used, the TID value may be assigned in the range of 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. Also, 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. Also, 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 channel contention in EDCA. 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 ACs. For example, AC_VI may be subdivided into AC_VI primary and AC_VI alternate. AC_VO may be subdivided into AC_VO primary and AC_VO alternate. UP or TID may be mapped to 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 a higher priority in that order. That is, 1 may have a lower priority, and 7 may have a higher priority. Therefore, the priority may be higher in the order of AC_BK, AC_BE, AC_VI, and AC_VO. Also, AC_BK, AC_BE, AC_VI, and AC_VO may correspond to ACI (AC index) 0, 1, 2, and 3, respectively. Due to the characteristics of such a TID, the mapping between a TID and a link may represent the mapping between an AC and a link.Additionally, the mapping between links and ACs can represent the mapping between TIDs and links.

[0104] As described above, a TID may be mapped to each of a plurality of links. The mapping may be a designation of a link through which traffic corresponding to a particular TID or AC may be exchanged. Also, a TID or AC that may be transmitted for each transmission direction within a link may be designated. As described above, there may be a default setting for mapping between a TID and a link. Specifically, if there is no additional setting in the multilink setting, 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 the 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-mentioned 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 in operation or where channel conditions are good. The above-mentioned TID-to-link mapping may also allow stations to stay in a power saving state for a longer period of time.

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

[0108] Depending on the implementation of the multilink device, simultaneous operation in the multilink may not be supported. For example, the multilink device may support simultaneous transmission in multiple links, simultaneous reception in multiple links, or transmission in one link and reception in another link. Reception or transmission in one link may affect reception or transmission in another link. Specifically, transmission in one link may act as interference in another link. Interference from one link of a multilink device acting on another link may be called internal leakage. The smaller the frequency interval between the links, the larger the internal leakage may be. If the internal leakage is not too large, transmission can be performed in another link when transmission is performed in one link. If the internal leakage is large, transmission cannot be performed in another link when transmission is performed in one link. In this way, the simultaneous operation of the multilink device in multiple links may be called STR (simultaneous transmit and receive, simultaneous transmission and reception). For example, a multilink device may transmit on multiple links simultaneously, transmit on one link while receiving on another link, or receive on multiple links simultaneously, all of which may be referred to as STR.

[0109] On the other hand, when STR is not supported due to interference between multiple stations constituting an 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 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 two STAs operated on the different link pairs, the different link pairs may be considered as an NSTR link pair by the MLD.

[0112] In this way, whether STR is supported between STAs of MLDs is determined by whether the link pair in 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 each other, 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. In other words, in the embodiment described later, when it is referred to as "STAs of a non-STR MLD," it may be interpreted as referring to either one of the two STAs operated in the NSTR link pair of the MLD, and when it is referred to as "STAs of a STR MLD," it may 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 a 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 have a configuration in which, when a specific STA of an MLD is transmitting or receiving, the hardware resources available to other STAs of the MLD are limited. For example, if a specific MLD has a hardware configuration that supports only processing for one PPDU, when a specific STA of 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 of the specific MLD is performing Tx, the specific MLD cannot support Tx and Rx for other STAs in the MLD.

[0116] In this way, a multi-link device that can operate STAs on two or more links but can support transmission / reception for only one STA at a particular time can be called a multi-link single radio MLD (MLSR MLD). Alternatively, an operation mode in which an MLD supports transmission / reception for only one STA as one type of operation mode can be called an enhanced multi-link single radio (EMLSR) mode. In this case, an MLD operating in the EMLSR mode may be a multi-radio MLD or an enhanced single-radio MLD. 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-speed data rate (e.g., encoded at 6 MHz or 24 MHz or less) PPDU transmission / reception for two or more links by having a configuration including another hardware (such as an inexpensive PHY front end).

[0117] Also, as a modification of the EMLSR mode, EMLMR (Enhance Multi-Link Multi-Radio) may be defined in which the MLD supports transmission / reception for each STA, but uses 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 used for transmission / reception for the other STAs, it may have the same transmission / reception restriction characteristics as EMLSR. That is, the MLD operating in the EMLMR mode can operate to support only 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 the 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 has nothing to do with 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 particular 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 particular time as a type of operating mode.

[0121] The operation of the STR MLD considering the performance limitations of the NSTR MLD provided by the above-mentioned embodiment of the present invention can be directly utilized as the operation of the STR MLD for the MLSR MLD. As an example, after a STA of the STR MLD transmits to a STA of the MLSR MLD, when the STA determines that the transmitted transmission has failed or is expected to fail due to the limited performance of the MLSR MLD STA, the STA can cancel the transmission that is being performed or is about to be performed. In this case, the procedure of checking whether the transmission has failed due to the limited performance of the EMLSR / EMLMR MLD may be similar to the procedure of checking whether a transmission to a STA of the NSTR MLD has failed due to the limited performance of the NSTR MLD STA.

[0122] As described above, the multilink device can support STR or can support it in a limited manner. Specifically, the 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 equal to or greater than a predetermined level, the multilink device may not be able to perform STR.

[0123] A station may exchange information on the STR capability of the station with other stations. Specifically, a station may exchange information on the presence or absence of limitations on the ability of the station to simultaneously transmit on multiple links or simultaneously receive on multiple links with other stations. Specifically, the information on the presence or absence of limitations on the ability to transmit or receive on multiple links may indicate whether or not the ability to transmit or receive on multiple links is simultaneously transmitted or received on multiple links, or whether transmission and reception can be performed simultaneously. In addition, the information on the presence or absence of limitations on the ability to transmit or receive on multiple links may be information indicated in stages. Specifically, the information on the presence or absence of limitations on the 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 interval between links that may affect internal leakage may be information indicating a stage indicating the magnitude of internal leakage. In addition, the information indicating a stage indicating the magnitude of internal leakage may be information indicating a relationship between the frequency interval between links and the magnitude of internal leakage in stages.

[0124] In FIG. 10, a first station (STA1) and a second station (STA2) are affiliated to one non-AP multilink device. Also, a first AP (AP1) and a second AP (AP2) may be affiliated to 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 may perform STR in a limited manner. When the second station (STA2) transmits through the second link (Link2), the first station (STA1)'s reception through the first link (Link1) may be disrupted by the transmission through the second link (Link2). For example, in the following case, the first station (STA1)'s reception through the first link (Link1) may be disrupted by the transmission through the second link (Link2). The second station (STA2) transmits the first data (Data1) via 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) via the second link (Link2). At this time, the transmission time of the second data (Data2) and the transmission time of the response (Ack for Data1) to the first data (Data1) may overlap. At this time, the transmission to the second station (STA2) via the second link (Link2) may cause interference to the first link (Link1). As a result, the first station (STA1) may not be able to 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 described in FIG.

[0126] The multilink device can perform channel access independently on multiple links. In this case, the channel access may be back-off based channel access. When the multilink device performs channel access independently on multiple links and the back-off counters on the multiple links reach 0, the multilink device can start transmission simultaneously on the multiple links. In a specific embodiment, when any one of the back-off counters of the links of the multilink reaches 0 and meets a pre-specified condition, the multilink device can perform channel access on the link whose back-off counter has reached 0 as well as on other links whose back-off counters have not reached 0. Specifically, when any one of the back-off counters of the links of the multilink reaches 0, the multilink device can perform energy sensing on other links whose back-off counters have not reached 0. In this case, if energy equal to or greater than a pre-specified magnitude is not detected, the multilink device can perform channel access on the link whose back-off counter has reached 0 as well as on the link on which the energy sensing has been performed. This allows the multilink device to start transmission simultaneously on multiple links. The threshold value used for energy sensing may be smaller than the threshold value used when determining whether to decrease the back-off counter. In addition, when determining whether to decrease the back-off counter, the multilink device may sense any type of signal, not just a WLAN signal. In addition, in the above-mentioned energy sensing, the multilink device may sense any type of signal, not just a WLAN signal. An internal outflow may not be sensed as a WLAN signal. In such a case, the multilink device may sense the signal sensed by the internal outflow through energy sensing. In addition, as described above, the threshold value used for energy sensing may be smaller than the threshold value used when determining whether to decrease the back-off counter. Therefore, even when transmission is being performed on one link, the multilink device may decrease the back-off counter on the other link.

[0127] Depending on the degree of interference between the links used by the multilink apparatus, the multilink apparatus may determine whether stations operating on each link can operate independently. In this case, the degree of interference between the links may be the magnitude of interference sensed by other stations of the multilink apparatus when any one station of the multilink apparatus transmits on any one link. If the transmission of a first station of the multilink apparatus on the first link causes interference of a predetermined magnitude or more to a second station of the multilink apparatus 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 signal received due to the interference. Also, if interference occurs, the second station may determine that the channel is in use when the second station accesses the channel using backoff.

[0128] In addition, if the transmission of the first station of the multilink device at the first link causes interference of less than a pre-specified magnitude to the second station of the multilink device operating at the second link, the first station and the second station can operate independently. Specifically, if the transmission of the first station of the multilink device at the first link causes interference of less than a pre-specified magnitude to the second station of the multilink device operating at the second link, the first station and the second station can independently perform channel access. In addition, if the transmission of the first station of the multilink device at the first link causes interference of less than a pre-specified magnitude to the second station of the multilink device operating at the second link, the first station and the second station can independently perform transmission or reception. If interference of less than a pre-specified magnitude occurs, the second station can successfully decode the received signal even in the presence of interference. In addition, if interference of less than a pre-specified magnitude occurs, the second station can determine that the channel is idle when the second station accesses 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 an expensive RF (radio frequency) device may be smaller than the internal interference occurring in a multilink device including an inexpensive RF device. 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 generated varies depending on the interval between the frequency bands of the links and the characteristics of the multilink device. In the embodiment of FIG. 10, the first multilink device (MLD#1) includes a first station (STA1-1) operating on the first link (Link1) and a second station (STA1-2) operating on the second link (Link2). The second multilink device (MLD#2) includes a first station (STA2-1) operating on the first link (Link1) and a second station (STA2-2) operating on the second link (Link2). The frequency interval between the first link (Link1) and the second link (Link2) in which the first multilink device (MLD#1) operates is the same as the frequency interval between the first link (Link1) and the second link (Link2) in which the second multilink device (MLD#2) operates. However, the magnitude of interference generated differs depending on the difference between the characteristics of the first multilink device (MLD#1) and the characteristics of 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] The multilink device may signal whether or not the station included in the multilink device supports STR. Specifically, the AP multilink device and the non-AP multilink device may exchange whether or not the AP included in the AP multilink device supports STR and whether or not the STA included in the non-AP multilink device supports STR. In such an embodiment, an element indicating whether or not the STR is supported may be used. The element indicating whether or not the STR is supported may be called an STR support element. The STR support element may indicate whether or not the station of the multilink device that transmitted the STR support element supports STR by using one bit. Specifically, the STR support element may indicate whether or not each station included in the multilink device that transmitted the STR support element supports STR by one bit. In this case, if the station supports STR, the bit value may be 1, and if the station does not support STR, the bit value may 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, and 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 characteristics: Stations operating in different frequency bands are assumed to support STR, and the STR support element may omit signaling on the presence or absence of STR support between stations operating in different frequency bands. For example, a first station (STA1) operates in a first link of 2.4 GHz, and a second station (STA2) and a third station (STA3) operate in 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). Also, the STR support element may include only one bit when the number of stations to be signaled by the STR support element is two.

[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 the multi-link device may always be determined as STR, and therefore, signaling regarding the presence or absence of STR support 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-mentioned embodiment, the operation of the station of the multilink device may be replaced by the operation of the multilink device. Also, in the above-mentioned embodiment, the operation of the AP may be replaced by the operation of the non-AP station, and the operation of the non-AP station may be replaced by the operation of the AP. Therefore, the operation of the AP of the non-STR multilink device may be replaced by the operation of the non-AP station of the non-STR multilink device, and the operation of the non-AP station of the STR multilink device may be replaced by the operation of the AP of the STR multilink device. Also, the operation of the non-AP station of the non-STR multilink device may be replaced by the operation of the AP of the non-STR multilink device, and the operation of the AP of the STR multilink device may be replaced by the operation of the non-AP station of 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 further include information indicating that the AP is an MLD included in the MLD, MLD level information, common information, and basic information of other APs included in the same MLD in the beacon frame. 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] In a beacon frame transmitted by an AP MLD, only common information per MLD may be included in the beacon frame 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, the beacon frame can be transmitted only through some of the APs that it operates. As an example, when the NSTR soft AP MLD operates an AP on two different links and the two links have an NSTR relationship with each other, the NSTR Soft AP MLD can transmit a beacon frame only through one of the two links. In this case, the link through which the NSTR Soft AP MLD transmits a beacon frame may have a concept of a primary link among the NSTR link pairs of the NSTR Soft AP MLD. Meanwhile, the NSTR Soft AP MLD may operate other links than the primary link among the NSTR link pairs as a concept of a secondary link, and the secondary link may be a link that does not transmit a beacon frame. The reason why the NSTR Soft AP MLD operates one link among the NSTR link pairs as a primary link and at least one other link as a secondary link in this way may be to prevent problems that may occur when two different APs are independently operated as an NSTR link pair. Problems that may occur in the AP MLD operating the NSTR link pair will be described in more detail together with an operational restriction example applied to the NSTR Soft AP MLD and the STA MLD associated with the NSTR Soft AP MLD, which will be described later. That is, in the link pair to which the NSTR is applied, a beacon frame may be transmitted only on the primary link, and a beacon frame may not be transmitted on the secondary link.

[0137] As described above, since the NSTR soft AP MLD has a restriction that a beacon frame is transmitted only through 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 frame transmitted through the primary link compared to a general AP MLD. This may be a method of configuring a beacon frame devised so that a non-AP MLD that operates a STA also in a secondary link can operate a STA of the secondary link based on information of a beacon frame received through the primary link.

[0138] As an 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, it may not have 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, channel quieting, etc.).

[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 the Legacy IEs as those included in the beacon frame disclosed in conventional Wi-Fi 802.11ax. For example, the legacy IEs of a beacon frame may include elements such as a timestamp field, a beacon interval field indicating the interval at which a beacon is 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 6 GHz 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 in conventional Wi-Fi up to 802.11ax.

[0142] In addition, the beacon frame may 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 of the neighbor AP information fields 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 in order 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 FIG. 11. In this case, when the AP MLD indicates other AP information of the same MLD by the specific neighbor AP information field of the 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 the station that the neighbor AP information field is an AP included in the same AP MLD, and the 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 in which an index determined by the AP MLD is indicated to indicate a link operated by another AP to be indicated using the 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 a link of another AP. For example, when the value of the change sequence subfield is changed, a station receiving the change sequence subfield can recognize that a parameter related to the link of the corresponding AP has been updated, and can request the updated parameter from the AP to update the corresponding parameter. In this case, if the AP MLD is an NSTR AP 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., a mobile terminal operates as a soft AP MLD for tethering, etc.), the STA included in the STA MLD can perform a procedure for updating parameters only in a primary link. That is, in order to update parameters of other links (e.g., non-primary links) for other neighbor APs other than the primary link of the AP MLD, the frame for updating the parameters can be transmitted and received only through 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] Also, when the AP is an NSTR AP MLD that does not support simultaneous transmission and reception (e.g., when it is an NSTR mobile AP MLD or an NSTR soft AP MLD, i.e., when a mobile terminal 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 a beacon frame can recognize that the AP MLD that transmitted the beacon frame is the NSTR AP MLD. Therefore, the specific subfield for indicating that it is an NSTR AP MLD may be set to a value different from the specific value (e.g., "1" or "0") when not indicating the NSTR AP MLD (e.g., the STR AP MLD or another AP MLD, etc.).

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

[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 by an implicit method, rather than directly indicating that it is an NSTR AP MLD by a specific subfield. Specifically, the NSTR AP MLD may indicate that it has an NSTR link pair while indicating that it has two links that it can support, thereby implicitly indicating that it is an NSTR AP MLD. 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 pre-agreed value meaning 2) to indicate that it has two links that it can support. 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 inform the non-AP STA MLD that it is the NSTR AP MLD by an explicit or implicit method by transmitting a beacon frame by the above-mentioned method. The non-AP STA MLD can implicitly or explicitly recognize whether the AP MLD that transmitted the beacon frame is the NSTR AP MLD from the received beacon frame. 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 a procedure for association or setup with the NSTR AP MLD only on the link on which the beacon frame was received. That is, the non-AP STA MLD can transmit and receive frames for association or setup with the NSTR AP MLD on the link on which the beacon frame was received (e.g., 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, an (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] At this time, 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) in order 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 the neighbor AP information field for the AP of the other link (of the same MLD). In this case, the non-AP STA MLD may 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. At this time, the non-AP STA MLD that receives a beacon frame from the NSTR AP MLD that does not include the neighbor AP information field for the AP of the non-primary link can implicitly recognize that the other AP is the 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 of the same MLD is not indicated, as described above.

[0153] Meanwhile, in a typical AP MLD, when an (ML) (Re) association request frame is received from a STA (MLD), an (ML) association response frame must be transmitted on the link on which the (ML) association request frame was received. However, in the NSTR AP MLD, a response to an (ML) association request frame received on a non-primary link can be made on the primary link (i.e., an (ML) association response frame can be responded to on the primary link).

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

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

[0156] The RNR element transmitted by the AP in the beacon frame may include a specific TBTT information field including the MLD Parameters field. In this case, when the MLD ID of 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. That is, 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 / obtains this may be the same / similar to the operation that a conventional STA performs after receiving an RNR element.

[0157] However, since the NSTR Soft AP does not transmit a beacon frame through a non-primary link, it may be impossible to indicate information related to the beacon frame of another AP (non-primary link AP) through the RNR element. Furthermore, since the NSTR Soft AP MLD does not transmit a beacon frame through the non-primary link AP, it cannot support information related to the beacon frame when indicating the non-primary link AP basic information through the RNR element. For example, a non-primary link that does not transmit a beacon frame 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 through 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 a preset value.

[0158] The neighbor AP TBTT offset subfield of the TBTT information field (see FIG. 11(b)) is a subfield indicating 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 on the next TBTT of the AP corresponding to the neighbor AP information field. As an example, when AP1 transmitting a beacon frame indicates information on AP2 using the RNR element (by 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 has compared to 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 or more and less than 11 TUs based on the previous TBTT of the AP.

[0159] However, when the AP of the primary link of the NSTR Soft AP MLD sets the neighbor AP TBTT offset subfield (1-octet) corresponding to the AP of the non-primary link, it may need to set it to a preset value (e.g., 254 or 255). This may be because the NSTR Soft AP does not transmit a beacon frame to the non-primary link and is unable to determine a target beacon transmission time (TBTT), which is a scheduled time for transmitting the next beacon frame. That is, the beacon frame transmitted by the NSTR Soft AP MLD on the primary link may need to set the neighbor AP TBTT offset subfield corresponding to the AP of the non-primary link to 254 and / or 255 using the 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, when a non-AP STA MLD receives a beacon frame of an NSTR Soft AP MLD and checks a TBTT information field in which the MLD ID subfield is 0 and the TBTT offset subfield is specified as 254 and / or 255 in the specific neighbor AP information field of the RNR element included in the beacon frame, the non-AP STA MLD can recognize that the specific neighbor AP information field is information about an AP (of the NSTR Soft AP MLD) operated on a non-primary link of the NSTR Soft AP MLD. In this way, when a non-AP STA MLD that receives a beacon frame of an NSTR Soft AP MLD checks information about an AP MLD operated 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 when 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 when 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-mentioned embodiment of the present invention, it has been mentioned that the beacon frame transmitted by the NSTR Soft AP MLD can indicate the neighbor AP TBTT offset subfield corresponding to the AP of the non-primary link as a preset value (254 and / or 255). However, the neighbor AP TBTT offset subfield can be indicated as 254 or 255 even if it does not correspond to the AP of the non-primary link of the NSTR Soft AP MLD. As an example, when 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 can indicate the neighbor AP TBTT offset subfield corresponding to the other AP in the beacon frame as 254. Also, when the AP transmitting the beacon frame cannot accurately recognize the TBTT offset of the other AP, the AP can 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 offsets of other APs in the MLD, it should not indicate (set) 255 when indicating (setting) the neighbor AP TBTT offset subfield corresponding to another AP (in the same MLD) using the RNR element.

[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 when the beacon frame is transmitted. In this case, the neighbor AP TBTT offset subfield indicates an offset value between the time when the beacon frame is transmitted and the time when the next beacon frame is transmitted by the AP corresponding to the neighbor AP TBTT offset subfield among the 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 according to a specific condition.

[0167] For example, when the neighbor AP TBTT offset subfield 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, the values ​​from 0 to 255 are respectively corresponding, so the maximum offset that can be indicated by 8 bits may be 255). However, when the neighbor AP TBTT offset subfield 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 a value set therein may differ according to a specific condition.

[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', according to a specific condition.

[0170] Specifically, if an AP corresponding to a neighbor AP information field including a 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 indicate only a TBTT offset of up to 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 the case where a TBTT offset of 254TU or more is present when considering the maximum TBTT offset that other APs may have ((2^16) or (2^16)-1TU when considering the configurable beacon interval).

[0173] However, when the AP MLD indicates information about other APs in the MLD using a beacon frame, an additional MLD AP TBTT offset subfield may be included in the transmission to more accurately notify the TBTT offset of the other APs. 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, when the neighbor AP TBTT offset subfield and the MLD AP TBTT offset subfield are both indicated in a specific TBTT information field, the neighbor AP TBTT offset subfield may be indicated as a preset value (which may be 254 or 255). The MLD AP TBTT offset subfield is a subfield with a size of 2 octets, and may be used to indicate a TBTT offset value when the TBTT offset between the AP (Reporting AP) that transmits 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 existing neighbor AP TBTT offset subfield cannot indicate an accurate TBTT offset.

[0174] When the STA MLD checks the TBTT information field including the MLD AP TBTT offset subfield in the RNR element included in the 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, in order to know whether the TBTT information field included in the beacon frame includes the MLD AP TBTT offset subfield, the STA may check based on the value of the TBTT information length subfield (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 the 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 yet another example of a TBTT information field format according to an embodiment of the present invention.

[0176] 12, the TBTT information field may have a configuration including an MLD AP TBTT offset subfield. The MLD AP TBTT offset subfield may be included only in a beacon frame transmitted by an AP of the AP MLD. Also, the MLD AP TBTT offset subfield may be included only in a TBTT information field corresponding to another AP of the same MLD as the AP transmitting the beacon frame.

[0177] As an example, in a beacon frame transmitted by a specific AP of an AP MLD, in order to indicate that the TBTT offset of another AP of 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 neighbor 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 an example subfield name, and subfields having 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] Referring to FIG. 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 the TBTT information header field in the neighbor AP information field included in the RNR element. That is, the RNR element transmitted in the beacon frame may include a plurality of 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 through the AP based on the information indicated in the TBTT information header. At this time, each parsed neighbor AP information field may indicate information on 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 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.

[0181] Alternatively, a restriction may be applied such that an AP MLD must manage the TBTT offset between APs it operates so as not to exceed 254 TU or to exceed 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 254TU or 255TU. In this case, the adjustment of the beacon interval and the 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 as not to exceed a specific time value (254TU or 255TU). In addition, a method for the AP MLD to prevent the TBTT time difference of each AP it operates from exceeding a specific interval (254TU or 255TU) does not need to be defined separately.

[0183] In this way, when the 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 of the same MLD in the RNR element transmitted by the specific AP in the beacon may indicate only a value of 253 or 254 or less. Furthermore, when the specific AP MLD manages the TBTT time difference of the AP it operates to 254 TU or less or less than 255 TU, the neighbor AP TBTT offset subfield transmitted by the specific AP belonging to the specific AP MLD, which corresponds 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 the AP MLD maintains the TBTT time difference of each AP operated by the non-AP STA to be equal to or less than 254TU or less than 255TU, the non-AP STA may need to analyze the neighbor AP TBTT offset subfield of the beacon frame received from the AP of the AP MLD in a manner different from the above-mentioned analysis method. In this case, the above-mentioned analysis method may mean an analysis method when the value of the neighbor AP TBTT offset subfield is indicated as 254. That is, the above-mentioned 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 equal to or greater than 254TU when the value of the neighbor AP TBTT offset subfield is indicated as 254. In this case, 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 equal to or greater than 254TU and less than 255TU 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 has been adjusted by AP MLD to less than 254 TU or less than 255 TU, 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 MLD is specified as 254, the non-AP STA must interpret this as indicating that a TBTT offset of 254 TU or more has been specified.

[0188] In this case, the method for determining whether a specific Neighbor AP TBTT Offset subfield is for another AP of the same AP MLD may be based on information of 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 can analyze that the specific Neighbor AP TBTT Offset subfield is 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 indicates 254, the non-AP STA can analyze 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 or not the beacon frame includes an ML element (whether or not the AP that transmitted the beacon is MLD) in order to analyze the Neighbor AP TBTT Offset subfield.

[0190] That is, when 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 be connected to the NSTR AP MLD must transmit (ML) probe request frames only on the link on which the NSTR AP MLD transmitted a beacon frame.

[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 play a role in which the MLD transmitting the ML probe request frame requests additional information on the AP of another link to the AP MLD.

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

[0195] For example, when 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 is requested / responded to mean 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, whereas the partial information is requested / responded to mean that only the information on the AP of the other link requested by the STA is responded to.

[0197] When additional information about APs of other links is requested in the ML probe request frame received on a particular link, the AP MLD that sent the beacon frame can respond using an ML probe response frame to not only provide information about the AP of the particular link, but also the requested additional information about the AP of the other link.

[0198] In this case, when the STA MLD transmits an ML probe request frame on a specific link and requests complete information on the AP of another link, the AP MLD must provide information on the AP of the other link at the same level as the information on 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 a response of complete information on the AP of another link on a specific link can obtain the same level of information on 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, when the STA MLD transmits an ML probe request frame on a specific link and requests partial information on the AP of another link, the AP MLD can provide only requested information (requested element information) among information on the AP of the other link using an ML probe response frame that responds on the specific link. In other words, the STA MLD that receives partial information on the AP of the other link on a specific link can further obtain only the information that it requested from the AP of the other link. In this case, the STA MLD that requests partial information on 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, when the ML probe request frame received on a specific link includes information indicating information on the other link (Request element IDs field), the AP MLD can further indicate the indicated information on the other link in the ML probe response frame.

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

[0201] In this case, the additional information (Complete and Partial) for the other AP 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 with 0 or more, and may include information of other STAs (AP 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 (AP and non-AP STAs) that correspond (correspond) to the STA-specific profile in which the 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 transmits 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 analyze that the value of parameter1 for STA2 is specified to be the same as the value of parameter1 for STA1.

[0202] At this time, the STA-specific profile subelement included in the Multi-link element transmitted by the NSTR AP MLD may have a configuration that does not include a Beacon Interval subfield for indicating the interval at which a beacon is transmitted. That is, when the NSTR AP MLD indicates a STA-specific 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 the AP operated in the non-primary link of the NSTR AP MLD does not transmit a beacon frame, and therefore there is no separate period of the beacon frame. That is, the STA-specific profile subelement (of the probe response and association response frames) corresponding to the AP of a non-primary link of the NSTR AP MLD may have a Beacon Interval Present subfield indicated as 0 even if the Complete Profile subfield (of the Per-STA Control field) is indicated as 1. That is, the beacon interval information for the AP of a non-primary link does not exist 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, the STA-specific profile corresponding to a non-primary link AP in the NSTR AP MLD may be indicated as 0 in the DTIM Info Present subfield even if the Complete Profile subfield (in the Per-STA Control field) is indicated as 1.

[0204] That is, since beacons are not transmitted on non-primary links, even if a non-AP STA MLD requests all information (or all updated information) for other APs of non-primary links through the AP of the primary link of the AP MLD (i.e., 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 of non-primary links is requested, the AP MLD does not need to include the beacon interval and DTIM information for the APs of 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] Since the NSTR AP MLD does not transmit a beacon frame to a non-primary link, 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 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 as 0. That is, the NSTR AP MLD may need to always indicate the Beacon Interval Present subfield in the STA-specific profile corresponding to the AP of the non-primary link as 0. Therefore, even if the NSTR AP MLD receives an ML probe request frame requesting complete information or receives an (ML)(Re) association request frame from a non-AP STA MLD, the NSTR AP MLD may need to always indicate the Beacon Interval Present subfield and the DTIM information present subfield in the STA-specific profile corresponding to the AP of the non-primary link as 0.

[0207] Alternatively, since the NSTR AP MLD does not transmit a beacon frame to the non-primary link, it may be necessary to set the subfields of Beacon Interval, DTIM Count, and DTIM Interval in the STA-specific profile corresponding to the AP of the non-primary link to a pre-promised value. 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, etc., and then the complete information for the AP of the specific link is expected to be responded to in the 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 of the STA MLD acquiring 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 STA-specific profile having the same configuration as the STA-specific profile used when the general AP MLD responds with complete information when responding with complete information for the non-primary link. In this case, the STA-specific profile of the NSTR AP MLD corresponding to the AP of the non-primary link may have a Beacon Interval subfield, a DTIM Count subfield, and a DTIM Interval subfield set to preset values, respectively. As an example, the NSTR AP MLD can set each bit of the Beacon Interval subfield of the non-primary link to all 0, all 1, or a predetermined method when transmitting complete information for the AP of the non-primary link. As an example, the NSTR AP MLD can set each bit of the DTIM Count subfield of the non-primary link to all 0, all 1, or a predetermined method when transmitting complete information for the AP of the non-primary link.For example, when the NSTR AP MLD transmits complete information for 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 manner.

[0208] Alternatively, since a beacon frame is not transmitted to 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 AP of the non-primary link to values ​​associated with the beacon frame of the primary link. This may be an operation 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 of the STA-specific profile corresponding to the AP of the non-primary link may be set to values ​​associated with the beacon frame transmitted on the primary link, respectively. As an example, 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 when transmitting complete information for the AP of the non-primary link. As an example, the NSTR AP MLD may set the DTIM Count subfield of the non-primary link to a value indicating (meaning) the beacon interval of the primary link when transmitting complete information for the AP of the non-primary link. As an example, the NSTR AP MLD may set the DTIM Count subfield of the non-primary link to the DTIM Count value of the primary link when transmitting complete information for the AP of the non-primary link. As an example, when the NSTR AP MLD transmits complete information for the AP of a non-primary link, it can set the DTIM Interval subfield of the non-primary link to a value indicating (meaning) the DTIM interval of the primary link.

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

[0210] That is, even if a beacon frame is not transmitted to 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 a beacon interval value to be used as a time unit of the non-primary link. In this case, the non-AP MLD can recognize (check, calculate) the duration and interval of the above-mentioned primitives and fields (used as a 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 the 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 on the non-primary link may need to operate based on the set value when operating the STA on the non-primary link.

[0211] Meanwhile, the method of setting subfields related to non-primary link beacons of the NSTR AP MLD described above (Beacon Interval, DTIM Count, DTIM Interval, etc.) 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 as well as STA-specific profiles transmitted on the primary link.

[0212] In addition, a non-AP STA MLD that wishes to associate with the 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 the non-primary link. That is, a non-AP STA MLD that transmits a Listen interval field to the NSTR AP MLD must calculate and set the unit of the Listen interval field as the beacon interval of an AP operating on the primary link of the NSTR AP MLD. In this case, the Listen interval field may be a field indicating information related to a period (time) at least one STA changes to a wake state in order for the non-AP STA MLD performing multi-link (re)association to receive a beacon frame. 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 the non-AP STA MLD transmits a Listen interval field to another AP MLD (e.g., STR AP MLD) other than the NSTR AP MLD, it may be necessary to set the unit of the Listen interval field to the maximum value of the beacon interval of the link (AP) that it is trying to set up. As an example, when the non-AP STA MLD is trying to perform a 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 value of the beacon interval of the 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 units of 100 ms.

[0214] Generally, when an AP and a STA complete the setup, the STA can learn and track (update) the operation parameters and element changes of the AP while receiving the beacon frame transmitted by the AP. The beacon frame also plays a role of providing information including the Timestamp field for the STA in the BSS to achieve time synchronization.

[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 additional operations to track (update) parameters / elements and maintain time synchronization for the non-primary links.

[0216] According to an embodiment of the present invention, the non-AP STA MLD combined with the 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 on 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 parameters 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 and transmitting it. Alternatively, the ML probe request frame transmitted by the STA MLD for the purpose of updating the 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 performed only on the primary link. For example, when the STA recognizes that parameters for the AP of a non-primary link have been updated from a specific field (e.g., change sequence or BSS parameter change count subfield, etc.) indicating whether or not the parameter for the link of another AP included in the neighbor AP information included in the beacon frame is an update, the non-AP STA MLD can request transmission of 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 a frame (e.g., a probe request frame, etc.) for requesting updated parameters on a non-primary link.

[0218] As an example, after setting up with the NSTR AP MLD, the non-AP STA MLD that requests information for updating parameters / elements of the 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 on the primary link. When the Updated Profile subfield is indicated as 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] As an 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 may further change Parameter 2 while increasing the Change Sequence number from 101 to 102. In this case, the STA MLD may request updated information of the non-primary link while transmitting an ML probe request frame. In this case, the NSTR AP MLD may respond with an ML probe response frame including both Parameter 1 and Parameter 2 when the non-AP STA MLD indicates that the Recorded Change Sequence subfield is 100, and may respond with an ML probe response frame including only Parameter 2 when the non-AP STA MLD indicates that the Recorded Change Sequence subfield is 101.

[0221] In this case, the Non-AP STA MLD does not use a separate Updated Profile subfield to request an Updated Profile, but may indicate the Complete Profile subfield as 0. That is, the method in 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 Per-STA Profile subelement format according to an embodiment of the present invention.

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

[0224] Also, as described in the above embodiment, the non-AP STA MLD transmitting the ML probe request frame to the NSTR AP MLD can request the AP of the primary link for updated information of the AP of the non-primary link by indicating the Updated Profile subfield of the STA Control field (included in the STA-specific profile subelement corresponding to the AP of the non-primary link) as 1. In this case, the non-AP STA MLD can indicate the Recorded Change Sequence value, which is information related to the time when the non-primary link AP information is updated, 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 the ML probe request frame of the non-AP STA MLD received via the primary link, the NSTR AP MLD can determine the information of the AP of the non-primary link 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 AP of the non-primary link.

[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 on a non-primary link according to an embodiment of the present invention.

[0226] 15, the NSTR AP MLD may indicate that the parameters of AP2 have been changed by using a beacon frame transmitted by AP1 operating on the primary link, link 1, after changing the parameters of AP2 operating on link 2, which is a non-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] Non-AP STA MLD can recognize the fact that the parameters of AP2 have been updated after receiving the beacon frame sent by AP1 through STA1. 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 to request a complete profile or an updated profile.

[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 information of AP2 (complete or updated information) in an ML probe response frame.

[0230] The non-AP STA MLD, which receives the requested information about AP2 from the NSTR AP MLD in an ML probe response frame, 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 an 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 operated 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 about 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 sub-element corresponding to the AP of the non-primary link, and plays a role in helping the non-AP STA MLD to 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 on the AP of the non-primary link. In this case, the broadcast ML probe response frame may be transmitted together with the 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 of 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 through the primary link, the non-AP STA MLD checks the Change Sequence (in the MLD Parameter field of the RNR element) of the non-primary link. If the checked Change Sequence value of the non-primary link is different from the Change Sequence value maintained (recorded) by the non-AP STA MLD, the non-AP STA MLD can transmit an ML probe request frame through the primary link. In this case, the ML probe request frame may include a subfield indicating whether to request complete information or updated information for the AP of the non-primary link. In addition, the ML probe request frame requesting updated information may also include a subfield indicating the Change Sequence value maintained (recorded) by the non-AP STA MLD. Thereafter, the non-AP STA MLD that has received a ML probe response frame from the AP MLD updates parameters based on the information of the AP of the non-primary link included in the responded ML probe response frame.

[0238] <Time Sync Management for Non-Primary Links>

[0239] As mentioned above, the beacon frame transmitted by the AP not only transmits various parameters and element information, but also helps the STAs in the BSS to synchronize time. The TimeStamp field included in the beacon frame indicates the TSF (timing synchronization function) timer value at the time when the data symbol containing the first bit of the TimeStamp field appears at the transmit antenna connector, and the STA that receives the TimeStamp field can synchronize its 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 that are associated with a non-primary link AP of NSTR AP MLD must use a method other than beacon frames to maintain time synchronization with the AP.

[0241] In order to maintain time synchronization with the AP of the non-primary link of the NSTR AP MLD, the associated non-AP STA may need to use the TimeStamp of the TIM frame transmitted by the AP. Since the TIM frame has a configuration including a TimeStamp field having the same function as a beacon frame, the STA that receives the TIM frame from the 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, since the NSTR AP MLD may be restricted from starting transmission on the non-primary link without occupying the primary link, it may be necessary to transmit a TIM frame on the non-primary link at the same time as transmitting a beacon frame on the primary link. In other words, the non-AP STA MLD associated with the NSTR AP MLD may need to prepare to receive a TIM frame 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, a link (non-primary link) for an AP 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 (NSTR Soft AP MLD reference) link, 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 to maintain time synchronization between APs of the NSTR AP MLD and / or between STAs of the non-AP STA MLD combined with the NSTR AP MLD to have an error less than 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 pre-promised / configured 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 pre-promised / configured value.

[0244] In other words, the TSF timer of the primary link may be maintained (or applied or used) the same for all links to APs included or affiliated in the NSTR AP MLD, and the difference between the timestamp or TSF timer of any two APs included or affiliated in 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 any two APs (e.g., an AP of a primary link and an AP of a non-primary link) included in or affiliated with the AP MLD or NSTR AP MLD may be limited to within a specific value (e.g., ±30 us), in which case the AP MLD or NSTR AP MLD can modify the timestamps or TSF timers so that the difference or clock drift of the TSF timers is within the specific value.

[0246] In addition, the non-AP STA MLD associated with the NSTR AP MLD may need to receive the next beacon frame transmitted through the primary link when it receives a TIM frame through the non-primary link. More specifically, when the non-AP STA MLD receives a TIM frame through the STA of the non-primary link 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 through the primary link. In this case, the next beacon frame may mean a beacon frame transmitted corresponding to the TBTT of the primary link that exists after the time point when the TIM frame is received through the non-primary link. In this case, the meaning of receiving the next beacon frame may be an operation that accompanies (includes) 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, the NSTR AP MLD does not transmit beacon frames on non-primary links, and therefore the BSS operation based on the transmission timing of the beacon frame may be performed in a manner different from the BSS operation of a general AP MLD.

[0249] In conventional Wi-Fi, the operating channel frequency (operating frequency band) of the BSS can be changed by a procedure previously agreed between the AP and the STA. In this case, the conventional ECS (Extended channel switching) operation can be used, or the channel change mechanism newly defined in 11be can be used. When the AP decides to change the operating channel of the BSS, it can transmit a beacon frame, a probe response frame, an Extended Channel Switch Announcement frame, etc., to inform the associated STAs that they can switch to a new channel and operating class while maintaining the 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 on how many beacon frames are transmitted before a channel switch (operating channel change) is performed. If the AP includes a MAX Channel Switch Time element in a beacon frame together 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 relative to 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 on the new channel, information on the time when the channel change is performed, 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 in a time period (time period indicated by the AP) determined based on the channel change related information included in the beacon frame transmitted by the AP. In this way, the channel change procedure of the conventional Wi-Fi BSS is performed in a manner in which information required for channel change (Channel Switch mode, new operating class, new channel number, channel switch count, etc.) is provided by the beacon frame transmitted by the AP, and therefore, in the case of a non-primary link BSS of the NSTR AP MLD in which a beacon frame is 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 regarding the time period to which the quiet interval is applied 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 an 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 by a beacon frame transmitted on the primary link. That is, the non-AP STA MLD associated with the NSTR AP MLD can operate based on information obtained by 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 by 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, each of these APs can transmit a beacon frame including basic information for other APs in the beacon frame that it transmits, and the basic information for other APs may 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 will occur at the next TBTT, and 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 guidance element and the extended channel switch guidance element may be transmitted in a channel switch guidance 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 has 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 begins.

[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] The channel change information for changing the channel 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, the APs included in the same AP MLD supporting NSTR can transmit beacon frames only through the primary link. That is, only a specific AP among the multiple APs included in the same AP MLD can transmit beacons through the primary link, and the remaining APs cannot transmit beacons. Therefore, in this case, even if the AP for the non-primary link does not transmit a beacon frame, the AP for the primary link can transmit the channel change information of the AP for the non-primary link by including it in the 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] Fig. 17 shows an example of the format of elements according to an embodiment of the present invention. Fig. 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 Target Beacon Transmission Time (TBTT) 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 a beacon frame, and the AP for the non-primary link does not transmit a beacon frame, so that the channel change information and / or quiet interval information of the AP for the non-primary link may be set based on the AP of the primary link rather than the AP of the non-primary link.

[0267] Specifically, an AP that configures an AP MLD may transmit a STA-specific profile including channel change information and / or quiet interval-related information for a non-primary link AP in 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 a non-primary link AP 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 to the corresponding element of the AP operating on the primary link.

[0269] A primary link AP of 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 the non-primary link AP based on its own beacon interval and TBTT. At this time, the timing fields are used to collectively refer to time-related fields including duration-related fields (switch time, Quiet Duration field, etc.) and time-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 operated in 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 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. In this case, the STA-specific profile refers to the STA-specific profile corresponding to the AP of the non-primary link.

[0271] Meanwhile, the NSTR AP MLD must transmit a TIM frame (of the non-primary link) on a new channel within the time indicated by the Switch Time field (Max Channel Switch Time element) after completing channel switching of the non-primary link using a beacon frame of the primary link (after completing announcement and channel switching). That is, the non-primary link AP of the NSTR AP MLD must transmit a TIM frame on a new channel after performing channel switching. At this time, the non-primary link AP must transmit a TIM frame on a new channel within the time indicated by the Switch Time field after a beacon frame with a Channel Switch Count subfield of 1 (or 0) is transmitted on the primary link. At this time, 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. At this time, the TIM frame may be replaced with another frame transmitted on a new channel of the primary link or non-primary link. As an example, the NSTR AP MLD may transmit a beacon frame indicating information related to the completion of channel switching in the primary link after completing channel switching of the non-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 having a configuration including complete information for the non-primary link. For example, the beacon frame having a configuration including 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.At this time, the primary link beacon frame transmitted after the channel switching of the non-primary link is completed should be transmitted within a time period previously agreed upon with the beacon frame transmitted before the channel switching is started. At this time, the previously agreed time may be a time indicated in a Switch Time field (of a 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. As an 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. At this time, the Channel Switch Complete subfield may be a subfield included in an ML element. The specific Switch Complete subfield may be a subfield that is 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 when the AP MLD is not the NSTR AP MLD, that is, by the general AP MLD.

[0272] The non-AP MLD combined with the NSTR AP MLD can perform an operation considering that the channel switching of the non-primary link is completed only when it receives a frame (the TIM frame of the non-primary link or other frame 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 the channel switching of the non-primary link in the primary link. That is, information on the channel switch for the AP of the non-primary link included in the AP MLD supporting NSTR (e.g., channel change information, etc.) may be transmitted from 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, when the channel switch is completed, the AP of the non-primary link can transmit a TIM frame indicating that the channel switch is completed, and can indicate to the station of the non-AP MLD that the channel switch is completed. Alternatively, the primary link AP can transmit a beacon frame indicating that a channel switch has been completed to the non-primary link AP, thereby instructing non-AP MLD stations that the channel switch has been completed.

[0273] If it is determined that the channel switching is not complete, the non-AP STA MLD will consider the channel switching of the non-primary link to be cancelled and will have to operate (revert to) on 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 while the non-primary link AP (the BSS of the AP) is performing channel switching to a specific value. 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 a time period 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 depending on whether the AP of the non-primary link is performing channel switching, the 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 by the beacon frame received on the primary link. That is, the non-AP MLD can recognize 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 the 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 the beacon frame received on the primary link, the non-AP MLD can recognize 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 (extended) channel switching guide element corresponding to the AP of the non-primary link most recently received is completed or canceled. When the subfield corresponding to the AP of the non-primary link 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 AP of the non-primary link is operating in (as) the operating channel / class indicated in the most recently received beacon frame (or probe response frame). When the Non-AP MLD is to transmit a UL PPDU on a non-primary link, it must transmit the UL PPDU based on whether the AP of the non-primary link is operating in its recognized channel (class).For example, Non-AP MLD can transmit a UL PPDU only when the subfield corresponding to a non-primary AP is indicated as a non-specific value, whereas Non-AP MLD may consider that the non-primary AP is performing channel switching and may not transmit a UL PPDU when the subfield corresponding to a non-primary AP 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 the probe response frame) at 1 until the non-primary link AP (the BSS of the AP) completes the 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 guide element corresponding to the AP of the non-primary link 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 guide element included in the beacon frame (transmitted on the primary link). The NSTR Soft AP MLD can make the non-AP MLD aware of the fact 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 should 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, the NSTR Soft AP MLD should indicate the Channel Switch Count subfield of the Channel Switch Announcement element corresponding to the AP of the non-primary link as 0 when the AP of the non-primary link is performing channel switching. In this case, the NSTR Soft AP MLD should 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 expected completion of channel switching when the AP of the non-primary link is performing channel switching.In this case, the NSTR Soft AP MLD sets the SwitchTime subfield to a specific value (eg, 65535) and does not need 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 to 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, the non-AP MLD may not transmit a UL PPDU on the non-primary link when the Critical Update Flag subfield of the 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. More specifically, the non-AP MLD may not transmit a UL PPDU on the non-primary link when the Critical Update Flag subfield of the beacon (Probe Response) frame received from the NSTR Soft AP MLD is 1 and the SwitchTime subfield corresponding to the non-primary link AP is indicated as a value other than 0.

[0278] As another method, the NSTR Soft AP MLD can indicate by incrementing the value of the BSS Parameter Change Count subfield corresponding to the non-primary link AP when the non-primary link AP (the BSS of the AP) completes channel switching. In this case, the BSS Parameter Change Count subfield means the BSS Parameters Change Count subfield in the MLD Parameters field of the TBTT Information field corresponding to the non-primary link AP. A general AP MLD increases 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, but the NSTR Soft AP MLD can also increase the BSS Parameters Change Count subfield corresponding to the non-primary link AP by 1 when channel switching is completed. This may be understood as increasing the value of the BSS Parameters Change Count subfield as a method for indicating that the instructed channel switching operation is completed for the non-primary link AP, and when the non-AP MLD determines that the channel switching of the non-primary link AP is scheduled / in progress, if the value of the BSS Parameters Change Count subfield is incremented by 1, the non-AP MLD can determine that the scheduled / in progress channel switching is completed. In this case, the non-AP MLD can transmit a UL PPDU after determining that the scheduled / in progress channel switching is completed. The operation of the non-AP MLD regarding the transmission condition of the UL PPDU is the same as the other channel switching completion indication method described above, and the description thereof will be omitted.

[0279] As another method, the NSTR Soft AP MLD can transmit a frame including a subfield indicating a different value on the primary link when the non-primary link AP (the BSS of the AP) is scheduled for channel switching, is performing channel switching, and has completed channel switching. In this case, the frame can be a beacon frame. More specifically, when channel switching for the non-primary link AP is scheduled, the NSTR Soft AP MLD can indicate a (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 started, 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 completed. 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), so that an associated non-AP MLD can recognize the progress of channel switching of the non-primary link. The non-AP MLD can determine whether to transmit a UL PPDU on a non-primary link by checking the specific subfield included in a frame received on a primary link. For example, the non-AP MLD can transmit a UL PPDU only if the specific subfield most recently received is an initial value.

[0280] As another method, the non-AP MLD can determine whether the non-primary link AP has completed channel switching based on a 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] In addition, the non-AP MLD can determine whether the scheduled channel switching is completed by checking the Operating channel / class information of the non-primary link AP indicated by 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 the channel switching. In this case, the method of checking the channel switching completion time of the non-primary link AP by the element related to the channel switching may be to use a 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 scheduled for channel switching 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 a UL PPDU. That is, the non-AP MLD can transmit a UL PPDU on the non-primary link when it receives a beacon frame (on 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 beacon frame for the first time.

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

[0283] In still another embodiment of the present invention, the NSTR AP MLD may be restricted so that the quiet interval cannot be set in the non-primary link. In this case, if there is a quiet interval defined (set) in the primary link, the quiet interval of the non-primary link may be defined (set) as the same time interval as the quiet interval of the primary link. In other words, when the non-AP STA MLD combined with the NSTR AP MLD recognizes the quiet interval of the primary link, it can be considered that the quiet interval is also set for the non-primary link for the same time interval.

[0284] In this way, the quiet element for the non-primary link transmitted in the beacon frame of the primary link may be set (indicated) 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 begins 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 how far 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 (indicated) 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 how many TBTTs of the primary link remain 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 (related to 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 (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 the channel switching of the non-primary link begins, and the TIM frame transmitted on the new channel of the non-primary link after the channel switching of the non-primary link is completed. As an example, when the beacon interval of the primary link is 100 ms, if 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 began channel switching.

[0291] Therefore, the non-AP MLD combined with the NSTR AP MLD can obtain information on the quiet interval and channel switching time and period of the non-primary link based on the information indicated by 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 after receiving the beacon frame on the primary link. At this time, the non-AP MLD can set (recognize, analyze) the start time of the quiet interval of the non-primary link based on the TBTT of the primary link. At this time, 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 on the primary link.

[0292] Conventionally, when an AP performs channel switching, a Wi-Fi non-AP STA can choose whether or not to perform channel switching together with the AP to maintain association with the AP. However, a non-AP STA MLD associated with an NSTR AP MLD will necessarily perform channel switching of 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 a non-primary link AP decides to perform channel switching, the station moves to the changed channel and receives a specific frame (e.g., a TIM frame) indicating that the non-primary link AP has completed channel switching, or the primary link AP may receive a beacon frame indicating that the non-primary link AP has completed channel switching. 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 setting with the AP of the non-primary link. In this case, the link setting between the AP of the non-primary link and the non-AP STA is cancelled, so that the AP MLD and the STA MLD have only a single link setting of the primary link.

[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 select whether or not 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 in the primary link as the quiet interval of the non-primary link BSS. This may be an operation that originates from the constraint that the non-primary link can be occupied only when the NSTR Soft AP MLD and the non-AP STA associated with the NSTR Soft AP MLD occupy the primary link. When the NSTR Soft AP MLD performs channel switching for the AP (BSS) of the primary link, the NSTR Soft AP MLD and the associated non-AP MLD restrict communication not only in the primary link but also in the non-primary link. Therefore, when the NSTR Soft AP MLD performs channel switching for the AP (BSS) of the primary link, 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 indicate the quiet interval of the non-primary link, the non-AP MLD associated with the NSTR Soft AP MLD should not transmit UL PPDU 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 perform an operation of generating a new backoff counter when the backoff counter becomes 0 during the time period in which the UL PPDU is not 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 retransmission (such as Short retry count and Long retry counter) are not changed.

[0299] Similarly, the NSTR Soft AP MLD will have to 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 an operation that originates from the constraint that the NSTR Soft AP MLD and the 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 a quiet interval for the AP (BSS) of the primary link, the NSTR Soft AP MLD and the associated non-AP MLD restrict communication on the non-primary link as well as the primary link. Therefore, when the NSTR Soft AP MLD indicates (sets) the quiet interval for the AP (BSS) of the primary link, it will have to 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, the non-AP MLD associated with the 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 a power save operation on the non-AP STA operating on the non-primary link when channel switching of the primary link is being performed or the quiet interval is in progress. This may be a power save operation using the fact that DL PPDU transmission from the AP of the non-primary link is not performed for the non-AP STA operating on the non-primary link when channel switching is in progress on the primary link or the quiet interval is in progress. Also, even if the non-AP STA operating on the non-primary link completes a channel access operation (e.g., a backoff operation of EDCA), the non-AP MLD can decide to stop the channel access operation performed on the non-primary link because UL PPDU transmission using the non-primary link is restricted. For example, non-AP MLD can suspend the channel access operation and / or CCA operation of non-AP STAs operating on a non-primary link when NSTR Soft AP MLD is performing channel switching or quiet interval on a 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 the STA of the Non-AP MLD has performed a power save operation (specifically, maintaining a doze state) for the non-AP STA operating on the 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 is completed. At this time, the assistance frame may be transmitted to induce (help) the non-AP STA of the non-primary link to reset the NAVSyncDelay timer that was activated after switching to awake. At this time, the assistance frame may be transmitted at a basic rate. At this time, the assistance frame may be a frame that is transmitted simultaneously when the beacon frame of the primary link is transmitted. At this time, the NAVSyncDelay timer may mean a timer related to the time that the STA that has switched from the doze state to awake must perform CCA to set the 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 associated with 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) in a non-primary link, the NSTR AP MLD can transmit a beacon frame transmitted through 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 time when the Quiet interval (Quiet interval#1 in FIG. 18) starts in 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, the Quiet Offset field is set to a value indicating "x" TU (Time Unit, 1024 us), and the Quiet Count field is set to 1 in the second beacon frame (Beacon#2 in FIG. 18).

[0305] The 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) starts when "x" TUs have elapsed since the TBTT corresponding to the third beacon frame.

[0306] As shown in Fig. 18, the NSTR AP MLD can again include the Per-STA profile corresponding to AP2 in the beacon frame transmitted via AP1 of the primary link in order to further set (define) the next quiet interval (Quiet interval#2 in Fig. 18) in the non-primary link. The sixth beacon frame (Beacon#6 in Fig. 18) of the primary link shown in Fig. 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 Fig. 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) is 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) starts from the TBTT corresponding to the eighth beacon frame.

[0308] At this time, information regarding the length of the quiet interval is indicated by a 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 associated with STA1 and STA2 of the Non-AP STA MLD, respectively.

[0311] In order to change the non-primary link to a new channel, the NSTR AP MLD can transmit a beacon frame transmitted via the primary link AP1 including a Per-STA profile corresponding to AP2 (non-primary link). The Per-STA profile corresponding to AP2 includes an (Extended) Channel Switch Announcement element and a Max Channel Switch Time element, and indicates information related to the time when the channel change starts and the time period during which the TIM frame is transmitted on the new channel after the channel change. When the (Extended) Channel Switch Announcement element is included in the first beacon frame (Beacon#1 in FIG. 19) of the primary link 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] The non-AP STA MLD that receives the first and / or second beacon frame on the primary link can determine that the channel change (to a new channel) of the non-primary link begins after receiving the second beacon frame by checking the (Extended) Channel Switch Announcement element included in the Per-STA profile (corresponding to AP2) of the beacon frame, and that the TIM frame of AP2 on the new channel will be received within 'x' TUs from the time the second beacon frame is received. In this case, the new channel may be a 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 a 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 Limitations of non-AP STA MLD Combined with NSTR AP MLD>

[0314] The NSTR AP MLD is an AP MLD where the primary link and the non-primary link are an NSTR link pair. Therefore, during the transmission of a PPDU via the AP of the primary link, the AP of the non-primary link may enter the BLIND state, and conversely, when the AP of the non-primary link transmits, the AP of the primary link may enter the BLIND state. In this case, the AP of the NSTR AP MLD that has passed through the BLIND state may need to set the MediumSyncDelay to a preset value.

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

[0316] Therefore, in the case of NSTR AP MLD, when the AP passes through the BLIND state, MediumSyncDelay must be applied, and in a situation where the channel access of the AP is restricted, it may be difficult to provide normal service to the STA of the BSS. The NSTR AP MLD can manage transmissions on a non-primary link (a link other than the primary link) in a manner that the primary link does not enter the BLIND state by determining one of the links of the NSTR link pair in which the AP operates as a primary link. As an example, the NSTR AP MLD can manage the primary link not to enter the BLIND state by transmitting on the non-primary link only when transmission is in progress on the primary link. For this purpose, the NSTR AP MLD does not need to respond with the requested response frame even if it receives a frame requesting a response frame through the AP of the non-primary link. That is, the NSTR AP MLD can perform an operation of not responding with a response frame even if it receives a frame requesting a response frame through 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 the AP operating on the primary link and / or the non-primary link in order to set up a primary link and prevent the AP of the primary link from being in a BLIND state. Similarly, the non-AP STA MLD combined with the NSTR AP MLD may need to understand the primary link management method of the NSTR AP MLD and operate. For example, when the non-AP STA MLD recognizes that a response frame is not responded to from the NSTR AP MLD on the non-primary link, it may not transmit a frame requesting a response of the response frame on the non-primary link. Also, when the non-AP STA MLD transmits a frame requesting a response of the response frame on the non-primary link and fails to receive a response of the response frame from the NSTR AP MLD, it may not retransmit the frame requesting a response of the response frame. For example, when 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] In addition, even if the non-AP MLD completes the channel access procedure of the non-primary link to perform UL transmission, the non-primary link transmission can be postponed until the channel access procedure is completed on the primary link. In this case, the method by which the non-AP MLD postpones the non-primary link transmission may be to stop 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 stops the backoff procedure performed by the STA of the non-primary link may be to maintain the backoff counter at 0.

[0319] In the above-mentioned method, the non-AP STA MLD that has completed the channel access procedure in both the primary link and the non-primary link can perform simultaneous transmission (simultaneous UL PPDU transmission) in the primary link and the non-primary link. In this case, the "simultaneous transmission" means that the time when each transmission starts is within a preset time interval. However, if only the channel access procedure in the primary link is completed and the channel access procedure in the non-primary link is not yet completed, the non-AP MLD can start PPDU transmission only in the primary link or can start simultaneous transmission when the channel access procedure in the non-primary link is completed. That is, when transmitting to the NSTR AP MLD, the non-AP MLD can perform transmission using only the primary link or perform simultaneous transmission using the primary link and the non-primary link. However, it is not necessary to allow the non-AP MLD to transmit PPDU to the 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 the transmissions on both links are completed within a preset time interval.

[0321] In addition, the non-AP MLD may need to set whether or not the PPDUs transmitted on both links request a response frame when performing UL transmission using both the primary link and the non-primary link in the NSTR AP MLD. Furthermore, the two UL PPDUs transmitted simultaneously by the non-AP MLD on the primary link and the non-primary link may both request a response frame, or both may need to request a response frame. This may be a restriction that is applied because if a response frame is only responded to on a specific link as a result of the UL transmission performed by the non-AP MLD using both the primary link and the non-primary link, the APs operating on other links of the NSTR AP MLD may be in a BLIND state. However, the NSTR AP MLD may not need to respond to all of the two PPDUs (received on the primary link and the non-primary link, respectively) that have been received simultaneously if only one of them is a PPDU that requests a response frame.

[0322] In addition, the non-AP MLD may need to configure the NSTR AP MLD so that the TXOP of the non-primary link ends at the same time as or earlier than the TXOP of the primary link when transmitting using both the primary link and the non-primary link. In other words, the non-AP MLD may need to configure so that the TXOP of the non-primary link ends 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 end later than the TXOP of the primary link by a point within a preset time interval.

[0323] In addition, the non-AP STA MLD can recognize that the NSTR AP MLD has experienced a BLIND state in the AP of a specific link and assist the AP in its operation. Furthermore, when the non-AP STA MLD recognizes that the NSTR AP MLD has transmitted only on one of the primary link and the non-primary link, it can recognize 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 (resetting to 0) MediumSyncDelay, considering that the AP experiencing the BLIND state is restricted from channel access due to a non-zero MediumSyncDelay. In this case, the operation performed by the non-AP STA MLD may be an operation using a characteristic that MediumSyncDelay can be released when a PPDU (including a valid MPDU) capable of NAV setting is received.

[0324] As an example, the non-AP STA MLD may transmit an Assist frame (a kind of PPDU) capable of NAV setting to the AP of the NSTR AP MLD that is determined to have a non-zero MediumSyncDelay after passing through the BLIND state. In this case, the Assist frame may mean a frame included in a valid MPDU capable of NAV setting, regardless of the frame format. In this case, the condition for the non-AP STA MLD to transmit an Assist frame to the NSTR AP MLD on 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. In this case, another condition for the non-AP STA MLD to transmit 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 is explicitly or implicitly requested (instructed) to transmit an Assist frame from the NSTR AP MLD.

[0325] As mentioned above, non-AP MLD combined with NSTR Soft(mobile)AP MLD must operate taking into consideration the performance limitations of NSTR mobile AP MLD, and as a result, it operates with higher difficulty than non-AP MLD combined with general AP MLD. As an example, non-AP MLD combined with general AP MLD (AP MLD with only STR link pair) can transmit PPDUs on two links by independent channel access on each link, but non-AP MLD combined with NSTR mobile AP MLD must start transmission on the primary link and non-primary link simultaneously, which makes it more difficult to operate.

[0326] Therefore, non-AP MLDs that can perform multi-link association (ML setup) with the NSTR mobile AP MLD may be limited to non-AP MLDs that support specific capabilities. In this case, 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 multi-link association with the NSTR mobile AP MLD.

[0327] If a non-AP MLD that does not support NSTR operation (MLD that supports only STR operation or supports 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 with a primary link and a non-primary link, but can only be associated with the primary link (single link association, single link setup). Therefore, a non-AP MLD that does not support NSTR operation must not transmit an association request frame to the NSTR mobile AP MLD to request association including a non-primary link.

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

[0329] According to the embodiments of the present invention described above, the channel switching methods and restrictions of NSTR Soft (mobile) AP MLD and non-AP MLDs 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 maximum channel switch time element in its beacon frame and (ML) probe response frame, another AP (reporting AP) belonging to the same AP MLD transmits 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 channel switching instructed by the first AP by receiving the STA-specific profile for the first AP transmitted by the other AP even if it does not receive a frame transmitted by the first AP. In this case, the timing field of the channel switching-related element 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 the 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] In other words, when a general AP MLD that is not an NSTR mobile AP MLD performs a channel switching operation 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, so that 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, the non-AP MLD that has performed ML setup with the general AP MLD will have a new NSTR link pair after performing channel switching instructed by the AP MLD. This situation is caused by the difference in hardware characteristics (interference shielding ability, etc.) between the AP MLD and the non-AP MLD, and the reason for this may be that the AP MLD still supports STR for all link pairs even after channel switching, whereas the non-AP MLD cannot support STR for a specific link pair after channel switching.

[0334] As a simple example, AP MLD may support STR for a link pair that is 40 MHz apart (the separation distance between the working channels of both APs, more specifically, the separation distance between the edges of the working channels), whereas non-AP MLD may only support STR for a link pair that is 80 MHz or more apart. If non-AP MLD is initially connected through a first link and a second link that have a separation distance of 80 MHz, and AP MLD performs channel switching for the first link or the second link, and the separation distance between the two links decreases to 40 MHz, AP MLD supports STR for the link pair including both links, whereas non-AP MLD cannot support STR any more. In this case, the link pair consisting of the first link and the second link becomes an NSTR link pair in non-AP MLD after channel switching, and non-AP MLD must support NSTR operation for 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 is expected to have an NSTR link pair after channel switching is performed does not support the NSTR operation, the non-AP MLD will have to modify (disconnect or re-setup) 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, a non-AP MLD that does not support the NSTR operation will have to change the connection state already established with the AP MLD so that there are no NSTR link pairs when it has (or is expected to have) an NSTR link pair as a result of channel switching instructed by the AP MLD.

[0336] As a simple example of the non-AP MLD operation, the non-AP MLD may perform an operation of disconnecting the AP of the link where the channel switching has been performed (will be performed) without performing the channel switching instructed by the AP MLD. This may be an operation of the non-AP MLD selected to prevent the specific link and other links from being in the NSTR state due to the changed operating channel of the specific link. Alternatively, the non-AP MLD may perform an operation of disconnecting the AP of the other link that is predicted to be included in the NSTR link pair after the instructed channel switching is performed, not the link where the channel switching is instructed. This is another method of removing the NSTR link pair, and may be a selection of the non-AP MLD considering the capabilities of the link where the channel switching is instructed and the other link. In this case, the selection method of the non-AP considering the capabilities may be an operation of maintaining the link with the higher 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 a STR link pair by changing the operating BW of the non-AP STA operating on the NSTR link pair. Since there are various methods for removing the 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 the NSTR operation must manage the connection state with the AP MLD to maintain a state in which it does not have an NSTR link pair.

[0337] At this time, 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, when the non-AP MLD indicates frequency separation distance information related to STR support to the AP MLD, the non-AP MLD must predict (evaluate) whether or not the link pair will become an NSTR link pair based on the separation distance information it indicates to the AP MLD. At this time, the frequency separation distance information related to the 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 ML re-setup procedure. The ML (re)setup procedure is performed by exchanging (re)association request / (re)association response frames between the non-AP MLD and the AP MLD, and after the (ML) (re)setup procedure is completed, the non-AP MLD requests setup with a (re)association request frame only for links that it wishes to maintain connection with the AP MLD.

[0339] However, a non-AP MLD connected to the AP MLD through only one link after the re-setup procedure must release the existing ML setup and perform single-link association with the AP MLD. That is, if a non-AP MLD connected to the AP MLD through two or more links is changed to a state connected to the AP MLD through only one link, the non-AP MLD must completely release its connection with the AP MLD (disconnect all links) and perform setup again with one 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 ML (re)setup management method for channel switching according to an embodiment of the present invention.

[0341] Referring to Figure 20, the AP MLD and the non-AP MLD that have performed the multi-link setup can perform ML (re)setup to remove the NSTR link pair that is generated as a result of channel switching. In Figure 20(a), before channel switching, the AP MLD and the non-AP MLD are in a state where the multi-link setup is completed 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 performs channel switching for Link2 instructed by the AP MLD, it determines that the separation distance between the frequencies of Link2 (Link2') and Link3 operating on the new operating channel is too close for it to support STR operation.

[0343] The Non-AP MLD decides not to perform channel switching for Link2 and to release the connection between STA2 and AP2 in order 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 pairs Link1 and Link3 (see FIG. 20(b)). At this time, the Non-AP MLD may have performed ML (re)setup since 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 FIG. 21(a), before channel switching, AP MLD and non-AP MLD are in a state of ML setup through Link1 and Link2. AP MLD instructs and executes channel switching to change the operating channel of Link2, and when non-AP MLD performs channel switching of Link2 instructed by 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. (FIG. 21(b) shows the state of Link1 and Link2 predicted (evaluated) by non-AP MLD.)

[0347] For the purpose of avoiding operating the STA with the NSTR link pair, the non-AP MLD terminates (Teardown, Disassociation) the MLD setup (the setup performed by MLD association) performed with the AP MLD and makes a new association. At this time, the non-AP that makes 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] The EMLSR (enhanced multi-link single radio) operation is an operation mode in which the non-AP MLD supports listening for multiple EMLSR links (links on which STAs operating in the 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 the 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 the non-HT (duplicate) PPDU format with one spatial stream.

[0351] When a STA operating in an EMLSR link pair receives a pre-promised frame from AP MLD during a listening operation, the STA aggregates the RF chains (Radio Frequency chains, Receive chains) used in 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 EMLSR link pairs operated in EMLSR mode, when the first link receives an initial control frame, the RF chain used in the second link is used together in the frame exchange performed in the first link, and in this process, the second link is converted to a state where there is no RF chain. That is, when a STA of a specific EMLSR link is performing frame exchange, the STA operating in the EMLSR link pair has no RF to use for CCA and frame transmission / reception, and therefore, non-AP STAs operating in the EMLSR link pair cannot participate in the frame exchange process at the same time. 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 above-mentioned operation characteristics of the EMLSR mode, a non-AP MLD that does not support the NSTR operation and has (or is expected to have) an NSTR link pair after performing channel switching instructed by the AP MLD can operate a non-AP STA operated in the NSTR link pair in the EMLSR mode. In other words, a non-AP MLD that does not support the NSTR operation can maintain a state of being connected to the AP through a link pair in which STR is not supported by operating the NSTR link pair as an EMLSR link pair. This may be an operation of a non-AP MLD that is possible when the non-AP MLD does not support the NSTR operation but supports the EMLSR mode operation. In other words, a non-AP MLD with dot11EHTEMLSROptionImplemented set to true can operate a non-AP STA in the NSTR link pair even though it does not support the NSTR operation by operating the NSTR link pair as an EMLSR link pair. In this case, the operation of the non-AP MLD to convert the non-AP STA operated in the NSTR link pair to the EMLSR mode may be to set a bit corresponding to the NSTR link pair among bits of the EMLSR Link Bitmap subfield included in the EML Control field of the EML Operating Mode Notification frame to 1 and transmit it 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, the condition for the non-AP MLD that does not support the NSTR operation to operate the NSTR link pair as the EMLSR link pair may be that both the self and the associated AP MLD support the EMLSR mode operation.That is, the non-AP MLD can operate the NSTR link pair as an EMLSR link pair and operate a non-AP STA on the NSTR link pair without supporting NSTR operation 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 binding 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 an EMLSR mode based on channel switching according to one embodiment of the present invention.

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

[0355] Referring to FIG. 22(a), before channel switching, AP MLD and non-AP MLD are in a state of ML setup through Link1 and Link2. AP MLD instructs and executes channel switching to change the operating channel of Link2, and when non-AP MLD performs channel switching of Link2 instructed by 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. (FIG. 22(b) shows the state of Link1 and Link2 (Link2') predicted (evaluated) by non-AP MLD.)

[0356] For the purpose of not supporting the NSTR operation, after determining to convert the STAs operating in an 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 Fig. 22 (c), the non-AP STA1 and non-AP STA2 of the non-AP MLD operate in the EMLSR mode in an 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 refrain from performing the channel switching operation for each link instructed by the AP MLD. This may 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 further, when the non-AP STA determines not to perform the channel switching instructed by the AP, it can choose to move to another BSS or the like. In this case, based on the fact that no frame is received from the non-AP STA for a certain period of time, the AP can recognize that the non-AP STA no longer operates in its own BSS. 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 end the association with the non-AP STA by deleting information about the non-AP STA.

[0360] On the other hand, if the non-AP MLD has not performed channel switching as 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, so the connection between the AP MLD and the non-AP MLD does not end. In this case, the AP MLD can continue to attempt to transmit to the non-AP MLD through the link where channel switching has been performed, but since 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 are a problem that arises because the AP MLD does not know that the non-AP MLD is not performing the channel switching that it has instructed, and therefore when the non-AP MLD decides not to perform the channel switching that the AP MLD has instructed, it will have to signal (instruct, announce) this to the AP MLD.

[0362] Therefore, when the AP MLD and the non-AP MLD that has performed a 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 an (ML) (re)setup excluding the link for which the channel switching is to be performed. If the non-AP MLD is connected to the AP MLD by only 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 a single-link setup. At this time, the method of performing the 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, the non-AP MLD can send a Disassociation frame to the AP MLD to which it is already associated before moving to another BSS.

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

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

[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 neither.

[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, and 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. That is, 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 together. Hereinafter, in the present invention, a channel switch announcement element may also mean an extended channel switch announcement. That is, 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 position on which the reported AP operates as a result of channel switching, and the channel switch count field indicates the number of TBTTs (Target Beacon Transmission Time) 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, which 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 allows simultaneous transmission and reception (STR type), the switch type field indicates the maximum time from 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 last beacon frame of the reported AP is transmitted in channel switching. However, the switch type field included in the frame transmitted after the last beacon frame of the reported AP is transmitted in channel switching (i.e., after channel switching begins) indicates the time from the 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 the time when the corresponding AP resumes the BSS operation on the 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 a frame including the switch time field is transmitted by the reported AP 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 the AP operating on the primary link to transmit a beacon frame, and does not allow the AP operating on the non-primary link to transmit a beacon. Therefore, information related to channel switching of the AP operating on the non-primary link (e.g., a channel switch announcement element and a maximum channel switch time element, etc.) can be transmitted only by the AP operating on the primary channel. Therefore, in the above-mentioned channel switching operation, the channel switching information of the AP operating on the non-primary link included in the AP MLD may be transmitted only by the AP 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 includes a channel switch announcement element and / or a maximum channel switch time element.

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

[0378] If the non-AP STA does not include the maximum channel switch time element in the received frame, it can determine that the channel switching procedure is completed. In this case, the completion 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 by a beacon and a (ML (Multi-Link)) probe response frame (hereinafter, a probe response frame) transmitted on 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 indicates the time when channel switching of the non-primary link is expected to be completed, or the time when signaling indicating that channel switching is completed is expected to be indicated on the primary link, or the time when a frame previously promised on the non-primary is transmitted (e.g., a TIM frame).

[0380] Alternatively, a method of indicating whether or not 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 or not the non-primary link AP has completed channel / class switching.

[0382] More specifically, when the NSTR mobile AP MLD transmits a beacon frame and a (ML) probe response frame on the primary link, it must also include a (extended) channel switching announcement element (extended channel switching announcement element and channel switching announcement element) for a non-primary link AP. In this case, the beacon and probe response frames transmitted after the channel / class switching start time specified by the (extended) channel switching announcement element may not include the (extended) channel switching announcement element, and may continue to include only the Max channel switching element. In this case, if the Max channel switch time element is included, it may mean that the channel / class switching of the non-primary link AP has not been completed, and if the Max channel switch time element is not included, it may mean that the channel / class switching of the non-primary link AP has been completed. That is, the non-AP MLD can be interpreted as completing channel switching of the non-primary link (BSS operation is resumed) when the beacon and / or probe response frame received from the NSTR mobile AP MLD does not include any more maximum channel switch time elements corresponding to the AP of the non-primary link. 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 (TU (1024 us) unit).At this time, the NSTR mobile AP MLD, which cannot indicate the prediction / evaluation time using the maximum channel switch time element, sets the Switch Time field to 0. At this time, the maximum channel switch time element may be continuously included in the beacon and probe response frame from when the channel switching announcement element corresponding to the non-primary link AP is included in the beacon and probe response frame until the BSS operation (service) is resumed after the channel switching of the non-primary link AP is completed. That is, the maximum 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 the channel switching of the non-primary link is completed. At this time, the NSTR mobile AP MLD may transmit an unsolicited probe response frame that does not include the maximum channel switch time element in the STA-specific profile corresponding to the non-primary link AP when the channel switching of the non-primary link is completed (when the 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 operated by 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 for 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 has been completed using the maximum channel switch time element)

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

[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. At this time, 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 which case the NSTR Mobile AP MLD transmits a beacon and probe response frame transmitted via an AP operating on a primary link, including a STA-specific profile corresponding to the AP of the non-primary link. At this time, 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 utilized 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 further includes information specifying the time when channel / class switching is to be started. 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 is to be started.

[0388] The NSTR mobile AP MLD that wants to change the operating channel / class of the AP operated in the non-primary link transmits a STA-specific profile including a (extended) channel switching announcement element together with a maximum channel switch time element. At this time, 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, the channel / class switching is completed. For example, the maximum channel switch time element transmitted together with the channel switching time announcement element transmitted in the STA-specific profile corresponding to the specific non-primary link AP indicates the expected / evaluated time until the channel switching indicated by the channel switching time announcement element is completed by the specific non-primary link AP. At this time, the 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 transmitted by the NSTR mobile AP MLD in a 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 a frame transmitted on a specific link.

[0390] In this case, the NSTR mobile AP MLD in some implementations may be unable to evaluate / predict the time when the non-primary link AP resumes BSS operation on the new operating channel / class. Alternatively, the NSTR mobile AP MLD in some implementations may not want to evaluate / indicate the time when the non-primary link AP resumes BSS operation on the new channel / class. In short, the NSTR mobile AP MLD that does not support indicating the time remaining until the non-primary link AP resumes BSS operation on the new operating channel / class may 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, when 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 not indicate the time when the BSS operation will be resumed on the new channel / class (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 that confirms that the Switch Time field is set to 0 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 resumed is not 0 TU (1 TU is 1024 us) or later, but is undefined (Undefined, Unknown).

[0392] Thus, when the NSTR mobile AP MLD intends to change the operating channel / class of the AP operating on the 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 (specific 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 the AP of the non-primary link is performing channel / class switching, the NSTR mobile AP MLD can transmit a beacon / probe response frame through the AP operating in the primary link. The beacon / probe response frame of the primary link transmitted when the AP of the non-primary link is performing channel / class switching does not include the (extended) channel switching announcement element in the STA-specific profile corresponding to the AP of the non-primary link. However, the beacon / probe response frame of the primary link transmitted when the AP of the non-primary link is performing channel / class switching still includes the maximum channel switch time element in the STA-specific profile corresponding to the AP of the non-primary link. At this time, the maximum channel switch time element (more specifically, the Switch Time field) indicates the remaining time that is evaluated / predicted when the AP of the non-primary link completes channel / switching and resumes the BSS service (BSS operation). At this time, the maximum channel switch time element transmitted by the NSTR mobile AP MLD that does not support the indication of the evaluation / prediction time as described above 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 AP resumes BSS operation 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 recognize that the 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 the beacon / probe response frame received on the primary link. In this case, the non-AP MLD can analyze that the non-primary link AP is still performing switching only when the (extended) channel switching announcement element is not present in the per-STA profile sub-element including the maximum channel switch time element. This is because when the (extended) channel switching announcement element is included in the per-STA profile sub-field corresponding to the non-primary link AP together with the maximum channel switch time element, the maximum channel switch time element is transmitted before the non-primary link AP starts channel / class switching.

[0397] While the AP of the non-primary link is performing channel / class switching, the NSTR mobile AP MLD transmits a beacon / probe response frame including a maximum channel switch time element in the STA-specific profile corresponding to the AP of the non-primary link, but does not include the maximum channel switch time element in the beacon / probe response frame any more after the AP of the non-primary link completes channel / class switching. In other words, when the AP of the non-primary link resumes BSS service (operation) on a new operating channel / class, the NSTR mobile AP MLD does not transmit the maximum channel switch time element corresponding to the AP of the non-primary link in the beacon / probe response frame transmitted on the primary link any more.

[0398] Therefore, the non-AP MLD combined 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 fact that the beacon / probe response frame received on the primary link does not contain a maximum channel switch time element corresponding to the non-primary link AP.

[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 when the non-primary link AP is instructed to start channel / class switching to the time when the non-primary link AP recognizes that the channel / class switching is 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 when the AP of the non-primary link is instructed to start channel / class switching may be a time recognized by a (extended) channel switching announcement element (more specifically, a channel switching count field) included in a STA-specific profile sub-element corresponding to the AP of the non-primary link. As an example, if the channel switching count field of the (extended) channel switching announcement element included in the STA-specific 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 STA-specific 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. In this case, "any time" means an unspecified time existing 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 is restricted from transmitting UL PPDUs on the non-primary link until the channel / class switching of the non-primary link AP is completed, and therefore the NSTR mobile AP MLD must operate so that the non-AP MLD knows as soon as possible that the channel / class switching of the non-primary link is completed. For this purpose, 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. At this time, the unsolicited probe response frame does not include a maximum channel switch time element corresponding to the non-primary link AP. At this time, the unsolicited probe response frame includes complete information for the non-primary link AP. The meaning that the unsolicited probe response frame includes complete information means that all information indicated when the non-primary link AP transmits 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 a UL PPDU on the non-primary link before the next beacon is received.

[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 can 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 as a response to the channel switching failure. In other words, while switching is being performed to indicate a new channel / class other than the existing operating channel / class, the (extended) channel switching announcement element that indicates the channel / class before switching is indicated, so that the channel switching being performed can be canceled.

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

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

[0408] Specifically, the NSTR mobile AP MLD operates AP1 and AP2 on 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 a beacon frame and a probe response frame transmitted on the primary link including an (extended) channel switching announcement element corresponding to the non-primary link (AP2) in order to change the operating channel (and / or operating class) of the BSS operated by AP2. At this time, although not shown, the element is transmitted in a STA-specific profile sub-element corresponding to the non-primary link AP included in the beacon / probe response frame. At this time, the STA-specific profile sub-element also includes a maximum channel switch time element.

[0410] The first beacon (leftmost) seen in FIG. 23 includes an (extended) channel switching announcement element with the channel switching count field set to 2 and a maximum channel switch time element indicating 'y'-'x1' in the Switch Time field. In this case, 'y' is the time when AP2 is evaluated / predicted to complete switching to a new channel / class and resume BSS operation, and 'x1' is the transmission / reception time of the beacon frame (first beacon in FIG. 23) including the element. If the NSTR mobile AP MLD does not support evaluation / prediction for 'y', the Switch Time field of the maximum channel switch time element is set / indicated to 0. After receiving the first beacon transmitted on 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 seen 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'. In this case, 'y' is the time when AP2 is evaluated / predicted to complete switching to a new channel / class and resume BSS operation, and 'x2' is the transmission / reception time of a beacon frame (second beacon in FIG. 23) including the element. If the NSTR mobile AP MLD does not support evaluation / prediction for 'y', the Switch Time field of the maximum channel switch time element is set / indicated to 0. After receiving the second beacon transmitted on the primary link via STA1, the Non-AP (STA) MLD can recognize that AP2 of the NSTR mobile AP MLD will start switching to a new channel / class in the next TBTT of the primary link by checking that the channel switching count field is set to 1. At this time, 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 the maximum channel switch time element for AP2 included in the probe response frame are set in the same manner as in the second beacon. At this time, 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 it is evaluated / predicted that AP2 will resume BSS operation on a new operating channel / class.

[0412] The third to sixth beacons confirmed 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 when a beacon frame including the element in the Switch Time field is transmitted / received to the time when AP2 is evaluated / predicted to resume BSS operation on a new operating channel / class. In this case, if there is a probe response frame transmitted by the NSTR mobile AP MLD 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 confirmed 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, the UL PPDU is not transmitted on the non-primary link (i.e., to AP2 via STA2).

[0413] When the channel / class switching of AP2 announced using the first and second beacon frames is completed, the NSTR mobile AP MLD transmits an Unsolicited (ML) probe response frame (Probe in FIG. 23) on the primary link. At this time, 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 the NSTR mobile AP MLD 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 that receives the Probe Response frame on the primary link recognizes that the channel / class switching announced for the non-primary link (AP2) has been completed by AP2 based on the fact that the Maximum Channel Switch Time element is not included in the STA-specific profile subelement for AP2. The Non-AP MLD can then attempt to transmit a 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 is a restriction that is taken into consideration because a non-primary link AP cannot receive PPDUs while performing channel switching, and more generally, UL PPDU transmission to all APs undergoing channel switching may be restricted. More specifically, when a general AP MLD AP, not an NSTR mobile AP MLD AP, performs channel switching, a non-AP STA (MLD STA or general STA) associated with the AP should not transmit UL PPDUs. Alternatively, even if a UL PPDU is transmitted, the AP performing channel switching cannot receive it, so even if a separate restriction is not defined, it is clear that 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, since an AP MLD including an NSTR mobile AP MLD cannot receive a PPDU transmitted on a specific link while an AP of the specific link is performing channel switching, it can instruct its associated non-AP MLD not to transmit a UL PPDU on the specific link while an AP of the specific link is performing channel switching. In this case, the (NSTR mobile) AP MLD can designate the specific link performing channel switching as a disabled link. When a specific link is designated as a disabled link, a non-AP STA associated with the AP of the disabled link will not be allowed to transmit a UL PPDU in the disabled section.

[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 that the link performing channel switching is 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 may be used for different purposes to improve QoS or achieve operational goals. For example, both MLDs may be committed to sending / receiving large files or videos at 6 GHz, which has a wide BW, and to exchanging data and management frames that should be transmitted and received more stably at 2.4 GHz, which has a wide coverage.

[0421] In this manner, 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 TID of a frame to be transmitted on each link, and may be determined by agreement between both MLDs or by instruction of AP MLD. If a specific TID is mapped only to a specific link and not to other links, a frame having the specific TID may 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 of the directions in which both MLDs transmit (UL direction in the case of non-AP MLD, DL direction in the case of AP MLD).

[0423] As described above, since only frames of TIDs mapped to a specific link can be transmitted on the specific link, no frames may be exchanged on a link to which no TID is mapped. In this manner, among the links to which both MLDs are connected, 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 where there is no TID mapped to the specific link, i.e., a disabled link, during a section where channel switching of the specific link is in progress. To this end, AP MLD can transmit a beacon and a probe response frame including an instruction for converting the specific link to a disabled state. More specifically, AP MLD can broadcast a TID-to-Link mapping instruction to make the TID mapped to the specific link non-existent. In this case, non-AP MLD that receives the TID-to-Link mapping instruction from AP MLD should follow the TID-to-Link mapping instructed by AP MLD. In this case, the method in which the AP MLD instructs the TID-to-Link mapping may be to use a TID-to-Link mapping element. In this case, the TID-to-Link mapping element has a configuration including a link bitmap that indicates link information to which each TID is mapped. As an example, to indicate the link information to which TID0 is mapped, a link bitmap corresponding to TID0 may be included, and each bit of the link bitmap (2 octets) may correspond to Link0 to Link14, respectively. In this case, when 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, (NSTR mobile) AP MLD can indicate information on the time when the TID-to-Link mapping specified by itself is applied and the duration of the duration, and can indicate that the link is a disabled link by using a Reduced Neighbor Report (RNR) element corresponding to the AP of the link disabled by the TID-to-Link mapping. More specifically, AP MLD can indicate information on the time when the TID-to-Link mapping specified by itself is applied by using a Mapping Switch Time field included in the TID-to-Link mapping element. In addition, AP MLD can indicate information on the time when the TID-to-Link mapping specified by itself is applied by 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 composed 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 length of time to be applied.

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

[0429] More specifically, the (NSTR mobile) AP MLD broadcasts a TID-to-Link mapping element indicating the time when the AP of a specific link starts channel switching in a Mapping Switch Time field and indicating the expected time period until the channel switching is completed in an Expected Duration field, thereby preventing the non-AP MLD from transmitting a 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 there is no TID 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 specified in the Expected Duration field has elapsed or earlier. This may be an operation restriction of the AP MLD to allow a non-AP MLD that recognizes that a specific link is changed to Disabled from a TID-to-Link mapping element specified by the AP MLD to operate on the assumption that the specific link will be changed to an available state after the time specified 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, non-AP MLD can prepare UL PPDU transmission in advance before the end of the disabled maintenance period indicated by Expected Duration, and if AP MLD maintains the disabled state of the specific link longer than initially indicated, the UL PPDU transmission of non-AP MLD will fail. This means that the operation of non-AP MLD may be inefficient due to erroneous information indication of AP MLD.

[0432] As another example, when an AP MLD specifies a disabled period of 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 specific link in a disabled state. However, the AP MLD specifies, using the Expected Duration field, that the disabled state is 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 a more efficient operation that meets the operational purpose due to the erroneous Expected Duration specification of the AP MLD.

[0433] Therefore, the AP MLD that converts a specific link to disabled may be restricted to accurately notify the time during which the specific link will be maintained in disabled state using the Expected Duration field. However, the AP MLD can maintain the specific link in a disabled state only for a period shorter than the disabled period initially specified for the specific link. In this case, the AP MLD can further transmit an Expected Duration field indicating a time earlier than the time indicated by the initially specified Expected Duration field. That is, the AP MLD can transmit a TID-to-Link mapping element indicating a time earlier than the time (disabled state end time) indicated by the Expected Duration field of the initially broadcasted TID-to-Link mapping element to convert the specific link to disabled state. That is, the disabled maintenance period of the specific link specified by the AP MLD may end earlier than the initially specified time. 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, and therefore AP MLD must not transmit a TID-to-Link mapping element that indicates a time later than the time (the end time of the disabled state) specified in the Expected Duration field of the original TID-to-Link mapping element broadcast to switch the specific link to disabled.

[0434] For an AP performing channel switching, a situation may arise where an unpredictable problem is discovered while switching to a new operating channel / class, and the AP must change the channel / class switching that was in progress. As an example, an AP that has performed channel switching to a new operating channel may determine that it cannot operate on that channel after detecting a radar signal, satellite signal, etc., on the new operating channel. In this case, the AP must change the operating channel to another channel again, resulting in the channel / class switching being completed at a later time 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 when the AP of a specific link expects to complete channel switching using the Expected Duration field (of the TID-to-Link mapping element), the channel switching may not be completed at the time indicated by the Expected Duration field due to an external variable. This may be the result of the scheduled channel / class switching procedure being delayed by an external factor, not the time when 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 the 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 the specific link is changed to Disabled in response to the channel switching of the specific link. That is, the specific link should be maintained in Disabled only for a period shorter than or equal to the initially indicated maintenance time.

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

[0437] In the process of performing channel switching of a specific link, when the AP MLD uses the Max channel switching time element, the AP MLD can indicate the same time as the time 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 the disable link. In other words, when both the TID-to-Link mapping element and the Max channel switching time element are used in relation to 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.

[0438] In this way, when the AP MLD indicates a link where channel switching is in progress 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 where the channel switching is in progress is 1. After completing channel switching of a specific link, the non-AP MLD can recognize that the AP of the specific link has completed channel switching by confirming that the Disabled Link Indication subfield corresponding to the specific link is indicated as 0 in the RNR element. That is, the non-AP MLD that has confirmed that the Disabled Link Indication subfield corresponding to the specific link is set to 0 can transmit a UL PPDU to the AP of the specific link. <Simultaneous Channel / Class Switching of Primary Link and Non-Primary Link> The NSTR mobile AP MLD can simultaneously change the operating channel / class of the primary link and non-primary link according to an operational purpose, or can start channel / class switching of the primary link when channel / class switching of the non-primary link is in progress. However, when channel / class switching of the primary link is in progress, a beacon / probe response frame cannot be transmitted on the primary link, so that channel / class switching of a non-primary link may be restricted from being started when channel / class switching of the primary link is in progress. For reference, in the above and below descriptions of the present invention, the expressions of the primary link operating channel and the non-primary link operating channel are used interchangeably for convenience, and these expressions are used to mean the operating channel of an AP operated on the primary link and the operating channel of an AP operated on the non-primary link, respectively. In addition, the part written as a channel switch announcement element is an abbreviation of an (extended) channel switch announcement element, and channel switching may be an abbreviation of channel / class switching.

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

[0440] Therefore, NSTR mobile AP MLD can designate / 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 the link that was previously determined / 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 a primary link and attempt to change the existing primary link to a 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 a new operating channel of the primary link as the operating channel of the existing non-primary link, and at the same time, can use the (extended) channel switch announcement element for the non-primary link to specify a 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 the non-primary link as the operating channels of the existing non-primary link and the primary link, respectively, the operating channels of the primary link and the non-primary link can be swapped 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 an AP that was operating with the existing primary link to an AP that operates with the non-primary link, and changing the role of an AP that was operating with the existing non-primary link to an AP that operates with 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 may be a restriction taken into consideration to prevent the operating channels of the primary link and the non-primary link of the NSTR mobile AP MLD from overlapping the same channel at a particular moment.

[0444] For this purpose, the NSTR mobile AP MLD must set the channel switch count fields of the two channel switch announcement elements transmitted for the purpose of switching between the primary link and the non-primary link to the same value. More specifically, when the NSTR mobile AP MLD transmits two channel switch announcement elements in the beacon and probe response frame for the purpose of switching between the primary link and the non-primary link, it must set the switch time fields included in the two channel switch announcement elements to the same value. In this case, among 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, i.e., 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] Also, 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 shall indicate the same time point, i.e., the Max Channel Switch Time element for the primary link (more specifically, the Switch Time field) shall 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 if the primary link and non-primary link switching is not performed as described above, the NSTR mobile AP MLD can transmit a beacon / probe response frame including both the (extended) channel switch announcement element for the primary link and the (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 further 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 a primary link and a non-primary link.

[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 a primary link and an (extended) channel switch announcement element corresponding to a non-primary link, the value indicated by 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 by the channel switch count field of the (extended) channel switch announcement element corresponding to the non-primary link. This restriction may be to prevent the value of the channel switch count field of the (extended) channel switch announcement element for the primary link from reaching 1 earlier than 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 having a smaller channel switch count value among the 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 indicated as 1, and therefore, a problem occurs in which the (extended) channel switch announcement element corresponding to the non-primary link cannot be transmitted any more. 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, a problem occurs in which the (extended) channel switch announcement element corresponding to the non-primary link cannot be transmitted any more on the primary link, i.e., a problem occurs in which the countdown associated with the channel switch start time of the non-primary link cannot be completed.

[0450] Therefore, when the NSTR mobile AP MLD includes both the (extended) channel switch announcement element for the primary link and the (extended) channel switch announcement element for the non-primary link 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 link. In this case, as described above, when the two channel switch count field values ​​are set to be equal, this may be when the NSTR mobile AP MLD has the purpose / intention of switching the operating channels of the primary link and the non-primary link to each other. In addition, even when changing the operating channel / class of the primary link from the first operating channel / class to the second operating channel / class and simultaneously changing the operating channel / class of the non-primary link from the third operating channel / class to the fourth operating channel / class, the channel switch count fields for both links may still be allowed to 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 a primary link and an (extended) channel switch announcement element corresponding to a non-primary link. The (extended) channel switch announcement element corresponding to a primary link is indicated (included) at a position not inside a 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 manner, when a single beacon / probe response frame includes both (extended) channel switch announcement elements for the primary link and the 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 links.

[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 the non-primary link to each other.

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

[0456] Furthermore, if the channel switch count field value of the (extended) channel switch announcement element corresponding to the non-primary link is 2 in the last beacon frame transmitted by the AP of the primary link before starting channel switching (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 start a channel / class switch of the non-primary link at a time point 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 start or determine that a channel switch of the non-primary link has started if a time period equal to the value of the last channel switch count field instructed / instructed for the non-primary link×beacon interval (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 of considering a virtual beacon frame to have been transmitted in a virtual TBTT (which exists every 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 previous (virtual) beacon frame, and 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 / initiated at the point in time when it is determined (calculated, predicted) that the value of 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 in this case, can tear down the connection of the non-primary link. In this case, the non-AP MLD can perform / start a multi-link re-setup procedure to tear down the connection of the non-primary link. Alternatively, the non-AP MLD can disassociate the ML setup with the NSTR mobile AP MLD and make a new single-link association with the primary link. In other words, the non-AP MLD that has selected not to perform the announced channel / class switching for the non-primary link can switch to a state where it is connected to the NSTR mobile AP MLD only with 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 with the NSTR mobile AP MLD. In this case, the 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 not to perform the specified channel / class switching and move to another AP or another AP MLD. In this case, the non-AP MLD that has decided not to perform the specified channel / class switching must send a Disassociation frame to the NSTR mobile AP MLD.

[0461] The reason why the connection with the NSTR mobile AP MLD must be terminated when the announced channel / class switching for the primary link is not performed, unlike when the announced channel / class switching for the non-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, the non-AP STA and the NSTR mobile AP MLD connected only through the non-primary link, excluding the primary link, cannot exchange frames normally, and therefore the connection except for the primary link is restricted from being maintained.

[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 unable to recognize 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 transmit a frame requesting a response frame to the non-AP MLD without recognizing 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 a primary link may not respond to a frame received from the NSTR mobile AP MLD. In this case, the time when 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). In this case, the time when the non-AP MLD does not respond to the received frame may be when it has determined not to perform a channel / class switch after the channel / class switching of the primary link has started. In this case, even in a situation where 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 started (before the next TBTT after the beacon frame with the 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 should 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> The NSTR mobile AP MLD transmits a trigger frame like a 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 that is responded to on an OFDMA (orthogonal frequency division multiplexing) basis.

[0465] More specifically, 802.11ax (Wi-Fi6), which is a conventional Wi-Fi, introduces OFDMA, and each frequency resource (RU, Resource Unit) to which the AP transmits DL PPDU 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, and each STA can receive data transmitted to itself included in the DL PPDU by obtaining information related to whether or not there is an RU assigned to it, the location of the RU, the applied MCS, etc. by receiving the HE SIGNAL field. Similarly, OFDMA is also introduced in the UL PPDU, and the AP transmits a trigger frame to enable multiple STAs to transmit UL PPDUs simultaneously. The trigger frame includes information instructing each STA on the RU that transmits the UL PPDU, the MCS to be applied, the transmission length, etc. After receiving the trigger frame from the AP, if there is an RU assigned to it, the non-AP STA transmits the traffic to be transmitted to the AP via UL in a 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 not only allocate RUs to non-AP STAs associated with itself, but also allocate RUs that can be used by non-AP STAs not associated with itself (i.e., unassociated STAs). When the AP allocates RUs that can be used by non-AP STAs not associated with itself, the non-AP STAs not associated with the AP can attempt a procedure to associate with the AP, such as 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 that is not associated with the non-AP STA 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, and when the non-AP STA checks an RU that is permitted to be used by a STA that is not associated with the AP among the RUs allocated in the trigger frame, the non-AP STA may transmit a probe request frame to the AP using the RU. That is, the non-AP STA may transmit the probe request frame that it intended to transmit by responding with a TB PPDU using an RU that is permitted for a non-AP STA that is not associated to approach. In this case, the RU that the AP allows for another STA (unassociated STA) that is not associated to approach using the trigger frame may be an RU whose assigned device AID is specified as 2045. At this time, the RU to which the AID of the allocation target device is designated as 2045 is...

Claims

1. A station (STA) of a multi-link device (MLD), A transmitting / receiving unit; a processor; The multilink device includes at least one station; The processor, Receive a frame for channel switching and / or class change from a first AP of an AP MLD including at least one AP; The frame includes at least one of a channel switch announcement element for informing the second AP of the channel switching and / or class change included in the AP MLD and / or a maximum channel switch time element associated with the time of the channel switching of the second AP, A switch time field included in the maximum channel switch time element indicates a first time or a second time according to the type of the AP MLD and / or the state of the channel switching; The first time is a maximum time from the last beacon frame transmitted from the second AP before the channel switching is started to the first beacon frame in a new channel, the second time is a time from the transmission of the frame to a specific operation of the second AP on the new channel; A station recognizes the channel switching of the second AP based on the frame.

2. the channel switch time field indicating the second time when the last beacon frame associated with the channel switching was transmitted; 2. The station of claim 1, wherein the specific action is the transmission of a first beacon frame on the new channel.

3. 2. The station of claim 1, wherein the channel switch time field indicates the first time if it is before the channel switching begins.

4. The channel switch announcement element includes a new channel number field and a channel switch count field; the channel number field indicates the location of the new channel; 2. The station of claim 1, wherein the channel switch count field indicates a number of Target Beacon Transmission Times (TBTTs) remaining until a channel switch to the new channel.

5. The station of claim 1 , wherein if 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.

6. The station of claim 5 , wherein the specific operation is a resumption of a Basic Service Set (BSS) operation of the second AP on the new channel.

7. The station of claim 1 , wherein if the type of the AP MLD is NSTR mobile AP MLD, the first AP operates as a primary link and the second AP operates as a nonprimary link.

8. The station of claim 1 , wherein the state of the channel switching is determined according to 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.

9. 9. The station of claim 8, wherein the channel switching state is determined to be in progress if the frame includes the maximum channel switch time element and does not include the channel switch announcement element.

10. The station of claim 8 , wherein if the frame does not include the maximum channel switch time element, the channel switching state is determined to be that the second AP has resumed the BSS operation.

11. A method for receiving a frame by a station (STA) of a multi-link device (MLD) in a wireless communication system, comprising: 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 includes at least one of a channel switch announcement element for informing the second AP of the channel switching and / or class change included in the AP MLD and / or a maximum channel switch time element associated with the time of the channel switching of the second AP, A switch time field included in the maximum channel switch time element indicates a first time or a second time according to the type of the AP MLD and / or the state of the channel switching; The first time is a maximum time from the last beacon frame transmitted from the second AP before the channel switching is started to the first beacon frame in a new channel, the second time being a time from when the frame is transmitted to a specific operation of the second AP on the new channel; and recognizing channel switching of the second AP based on the frame.

12. the channel switch time field indicating the second time when the last beacon frame associated with the channel switching was transmitted; The method of claim 11 , wherein the particular action is the transmission of a first beacon frame on the new channel.

13. The method of claim 11 , wherein the channel switch time field indicates the first time if it is before the channel switching begins.

14. The channel switch announcement element includes a new channel number field and a channel switch count field; the channel number field indicates the location of the new channel; The method of claim 11 , wherein the channel switch count field indicates a number of Target Beacon Transmission Times (TBTTs) remaining until a channel switch to the new channel.

15. The method of claim 11 , wherein if 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.

16. The method of claim 15, wherein the specific action is a resumption of a Basic Service Set (BSS) operation of the second AP on the new channel.

17. The method of claim 11 , wherein if the type of the AP MLD is NSTR mobile AP MLD, the first AP operates as a primary link, and the second AP operates as a non-primary link.

18. The method of claim 11 , wherein the state of the channel switching is determined according to whether the frame includes the channel switch announcement element or the maximum channel switch time element when the type of the AP MLD is NSTR mobile AP MLD.

19. 20. The method of claim 18, wherein the channel switching state is determined to be in progress if the frame includes the maximum channel switch time element and the channel switch announcement element is not included.

20. The method of claim 18 , wherein if the frame does not include the maximum channel switch time element, the channel switching state is determined to be that the second AP has resumed the BSS operation.

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