Wireless communication method using multi-link and wireless communication terminal using the same

Abstract

An object of the present invention is to provide a wireless communication method using multi-links and a wireless communication terminal using the same.SOLUTION: The present invention discloses a channel switching method and apparatus performed by a multi-linkDevice (MLD) including a plurality of stations respectively operating on a plurality of links in a wireless communication system. In detail, the MLD of the present invention may receive a frame including channel change information for a channel change from a 1AP of a primarylink among the plurality of links, and determine whether to perform a channel change of an STA connected to the 2AP through the one secondary link based on the channel change information.SELECTED DRAWING: Figure 20

Description

[Technical Field]

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

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

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

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

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

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

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

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

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

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

[0011] A multi-link device (MLD) according to the present invention, including a plurality of stations operating on a plurality of links, includes a processor, which receives a frame including channel change information for a channel change from a first AP of a primary link among the plurality of links, the plurality of links consisting of one of the primary link and at least one secondary link, the channel change information being used for a channel change of a second AP for one secondary link among the at least one secondary link, and determining whether to change a channel of a station connected to the second AP through the one secondary link based on the channel change information, and a field related to the timing of the channel change of the second AP included in the channel change information is set based on the first AP of the primary link.

[0012] In addition, in the present invention, the field related to the timing of the channel change of the second AP is set based on the target beacon transmission time (TBTT) and beacon interval (BI) of the primary link to the first AP.

[0013] In addition, in the present invention, the field related to the timing of the channel change of the second AP includes a switch time field indicating the time interval from the time the channel change starts until the first frame is transmitted through the changed channel, and / or a channel switch count field indicating the number of TBTTs remaining until the channel change starts.

[0014] In addition, in the present invention, the switch time field is recognized based on the time when a beacon frame in which the value of the channel switch count field related to the channel change of the second AP is set to “1” or “0” is transmitted from the first AP of the main link.

[0015] Also, in the present invention, if the value of the channel switch count field is 1, the channel change starts at the next TBTT of the first AP after the frame is transmitted, and if the value of the channel switch count field is 0, the channel change starts after the frame is transmitted.

[0016] In addition, in the present invention, the channel change information further includes a new channel number field indicating the number of the channel to be changed by the channel change.

[0017] In addition, in the present invention, the channel change information is included in at least one Per-STA profile sub-element included in the frame, and each of the at least one Per-STA profile sub-element includes information about other APs included in the same MLD.

[0018] In addition, in the present invention, the first AP and the second AP are non-simultaneous transmission and reception (NSTR) stations that do not support simultaneous transmission and reception within the same MLD.

[0019] Also, in the present invention, the processor performs a channel change for the station based on the channel change information, and receives a frame related to the completion of the channel change from the first AP or the second AP.

[0020] In addition, in the present invention, if the processor does not change the channel of the station connected to the second AP through the one secondary link based on the channel change information, it re-establishes a link with the AP MLD including the first AP and the second AP so that the MLD is connected only to the primary link of the first AP.

[0021] The present invention also provides a method including the steps of: receiving a frame including channel change information for a channel change from a first AP of a primary link among the plurality of links, the plurality of links consisting of one primary link and at least one secondary link, and the channel change information being used for a channel change of a second AP for one secondary link among the at least one secondary link; and determining whether to perform a channel change of a station connected to the second AP through the one secondary link based on the channel change information, wherein a field related to the timing of the channel change of the second AP included in the channel change information is set based on the first AP of the primary link. [Effects of the Invention]

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

[0023] The effects obtained from the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Figure 3]FIG. 2 is a diagram showing the configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a configuration of an access point according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating a process in which a STA establishes a link with an AP. [Figure 6] FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] 1 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1 illustrates various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention. [Figure 9] 1 shows a multi-link device according to an embodiment of the present invention; [Figure 10] 1 illustrates simultaneous transmission of different links in a multi-link operation according to an embodiment of the present invention. [Figure 11] 1 illustrates an example of the contents of a beacon frame transmitted by an AP in AP MLD and an example of a TBTT (target beacon transmission time) information field format included in an RNR (Reduced Neighbor Report) element according to one embodiment of the present invention. [Figure 12] 10 illustrates yet another example of a TBTT information field format according to an embodiment of the present invention. [Figure 13]10 illustrates an example of a TBTT information length subfield indicating a TBTT information field including an MLD AP TBTT offset subfield according to an embodiment of the present invention. [Figure 14] 10 illustrates an example of a Per-STA Profile subelement format according to an embodiment of the present invention. [Figure 15] 10 illustrates an example of a process in which a non-AP MLD set up with an NSTR (Non-Simultaneous Transmission and Reception) Soft AP MLD updates information on a non-primary link, according to one embodiment of the present invention. [Figure 16] 10 is a flowchart illustrating an example of a procedure in which a non-AP STA MLD associated with an NSTR AP MLD updates parameters of a non-primary link according to an embodiment of the present invention. [Figure 17] 10 shows an example of an element format according to an embodiment of the present invention. [Figure 18] 10 illustrates an example of a process in which an NSTR AP MLD defines a quiet interval for a non-primary according to an embodiment of the present invention. [Figure 19] 10 illustrates an example of a method for an NSTR AP MLD to perform a non-primary channel switch according to an embodiment of the present invention. [Figure 20] 10 is a flowchart illustrating an example of an operation of non-AP MLD according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The terms used in this specification are generally used as widely as possible, taking into consideration the functions of the present invention. However, these may vary depending on the intentions of engineers in the relevant technical field, customs, or the emergence of new technologies. In addition, in certain cases, the applicant may have arbitrarily selected terms, and in such cases, the meanings thereof will be described in the relevant description of the invention. Therefore, it is made clear that the terms used in this specification should be interpreted not simply as names of terms, but based on the substantive meanings of the terms and the overall content of this specification.

[0026] Throughout the specification, when a component is "coupled" to another component, this includes not only when it is "directly coupled" to another component, but also when it is "electrically coupled" with another component in between. Furthermore, when a component "comprises" a specific component, this means that it may further include the other component, not excluding the other component, unless otherwise specified. In addition, limitations such as "greater than" or "less than" based on a specific threshold value may be appropriately replaced with "exceed" or "less than," respectively, depending on the embodiment.

[0027] Hereinafter, in the present invention, the terms field and subfield may be used interchangeably.

[0028] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention.

[0029] A wireless LAN system includes one or more Basic Service Sets (BSSs), which are a set of devices that can synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0030] As shown in FIG. 1, the infrastructure BSSs BSS1 and BSS2 include one or more stations STA1, STA2, STA3, STA4, and STA5, access points AP-1 and AP-2 that are stations providing distribution services, and a distribution system DS that connects multiple access points AP-1 and AP-2.

[0031] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard. In a broad sense, the term "station" encompasses not only non-AP stations but also APs. In this specification, the term "terminal" refers to either a non-AP or an AP, or both. A station for wireless communication includes a processor and a communication unit, and may further include a user interface and a display unit, depending on the embodiment. The processor generates frames to be transmitted over a wireless network, processes frames received over the wireless network, and performs various other processes for controlling the station. The communication unit is functionally connected to the processor and transmits and receives frames over the wireless network for the station. In this specification, the term "terminal" encompasses user equipment (UE).

[0032] An access point (AP) is an entity that provides a connection to a distribution system (DS) via a wireless medium for associated stations. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP. However, if a direct link is established, direct communication is also possible between non-AP stations. Meanwhile, in the present invention, the term AP is used as a concept including a personal BSS coordination point (PCP), but in a broader sense, it also includes concepts such as a central controller, a base station (BS), a node B, a base transceiver system (BTS), or a site controller. In the present invention, an AP is also referred to as a base wireless communication terminal, but in a broader sense, the term base wireless communication terminal is used as a term including an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal includes various types of wireless communication terminals that allocate communication medium resources and perform scheduling for communication with multiple wireless communication terminals.

[0033] A plurality of infrastructure BSSs are connected to each other via a distribution system DS, and the plurality of BSSs connected via the distribution system are called an Extended Service Set (ESS).

[0034] 2 is a diagram showing an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of FIG. 2, the same or corresponding parts as those in the embodiment of FIG. 1 will not be described again.

[0035] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so none of the stations (STA6, STA7) are connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

[0036] 3 is a block diagram showing the configuration of a station 100 according to an embodiment of the present invention. As shown, the station 100 according to the embodiment of the present invention includes a processor 110, a communication unit 120, a user interface unit 140, a display unit 150, and a memory 160.

[0037] First, the communication unit 120 transmits and receives wireless signals such as WLAN packets and may be incorporated into or external to the station 100. According to an embodiment, the communication unit 120 may include at least one communication module using different frequency bands. For example, the communication unit 120 may include communication modules using different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to an embodiment, the station 100 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with an AP or an external station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 120 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the station 100. When the station 100 includes multiple communication modules, each communication module may be provided independently, or multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit 120 may represent a radio frequency (RF) communication module that processes RF signals.

[0038] Next, the user interface 140 includes various types of input / output means provided in the station 100. That is, the user interface unit 140 receives user input using various input means, and the processor 110 controls the station 100 based on the received user input. Also, the user interface unit 140 performs output based on instructions from the processor 110 using various output means.

[0039] Next, the display unit 150 outputs an image on a display screen. The display unit 150 outputs various display objects, such as a user interface, based on the contents processed by the processor 110 or the control commands of the processor 110. The memory 160 also stores control programs and various data used by the station 100. The control programs include a connection program required for the station 100 to connect to an AP or an external station.

[0040] The processor 110 of the present invention executes various commands or programs to process data within the station 100. The processor 110 also controls each unit of the station 100 and controls the transmission and reception of data between the units. According to an embodiment of the present invention, the processor 110 executes a program for connection with an AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also reads information about the station 100's preferences contained in the communication setup message and requests connection to the AP based on the information about the station 100's preferences. The processor 110 of the present invention may refer to a main control unit of the station 100, or, depending on the embodiment, may refer to a control unit for individually controlling some components of the station 100, such as the communication unit 120. That is, the processor 110 may be a modem that modulates and demodulates wireless signals transmitted and received by the communication unit 120, or a modulator and / or demodulator. The processor 110 controls various operations for transmitting and receiving wireless signals in the station 100 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0041] The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separate blocks indicate the logically separated elements of the device. Therefore, the above-described device elements may be implemented on a single chip or multiple chips depending on the device design. For example, the processor 110 and the communication unit 120 may be integrated into a single chip or may be implemented on separate chips. Furthermore, in embodiments of the present invention, some components of the station 100, such as the user interface unit 140 and the display unit 150, may be selectively included in the station 100.

[0042] 4 is a block diagram showing the configuration of an AP 200 according to an embodiment of the present invention. As shown, the AP 200 according to the embodiment of the present invention includes a processor 210, a communication unit 220, and a memory 260. In FIG. 4, duplicated descriptions of parts of the configuration of the AP 200 that are the same as or correspond to the configuration of the station 100 in FIG. 3 will be omitted.

[0043] Referring to FIG. 4, the AP 200 according to the present invention includes a communication unit 220 for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit 220 of the AP 200 may also include multiple communication modules using different frequency bands. That is, the AP 200 according to the embodiment of the present invention may include two or more communication modules using different frequency bands, for example, 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with a station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 220 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the AP 200. In the embodiment of the present invention, the communication unit 220 may represent an RF (Radio Frequency) communication module that processes RF signals.

[0044] The memory 260 stores control programs used by the AP 200 and various data associated therewith. These control programs include a connection program that manages station connections. The processor 210 also controls each unit of the AP 200 and controls data transmission and reception between the units. According to an embodiment of the present invention, the processor 210 executes a program for connecting with a station stored in the memory 260 and transmits a communication setup message to one or more stations. The communication setup message includes information regarding connection preferences for each station. The processor 210 also performs connection setup in response to a station connection request. According to an embodiment, the processor 210 is a modem or a modulation / demodulation unit that modulates and demodulates wireless signals transmitted and received from the communication unit 220. The processor 210 controls various operations for transmitting and receiving wireless signals by the AP 200 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0045] FIG. 5 is a diagram illustrating a process in which a STA establishes a link with an AP.

[0046] 5, a link between the STA 100 and the AP 200 is established through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information for the BSS operated by the AP 200. There are two scanning methods: a passive scanning method in which the STA 100 acquires information using only a beacon message S101 periodically transmitted by the AP 200, and an active scanning method in which the STA 100 transmits a probe request to the AP S103, receives a probe response from the AP S105, and acquires connection information.

[0047] The STA 100 that successfully receives wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200, and performs the authentication step (S107b). After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200, and performs the association step (S109b). In this specification, association basically means wireless association, but the present invention is not limited to this, and association in a broad sense includes both wireless association and wired association.

[0048] Meanwhile, an 802.1X-based authentication step S111 and an IP address acquisition step S113 via DHCP are additionally performed. In Fig. 5, server 300 is a server that processes 802.1X-based authentication with STA 100, and may be physically connected to AP 200 or may exist as a separate server.

[0049] FIG. 6 is a diagram showing a Carrier Sense Multiple Access (CSMA) / Collision Avoidance (CA) method used in wireless LAN communication.

[0050] A terminal performing WLAN communication performs carrier sensing to check whether a channel is occupied before transmitting data. If a wireless signal above a certain strength is detected, the channel is determined to be occupied, and the terminal delays access to the channel. This process is called Clear Channel Assessment (CCA), and the level that determines whether or not a signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by a terminal is identified as the receiver, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected from the channel or a wireless signal with strength below the CCA threshold is detected, the channel is determined to be idle.

[0051] If the channel is determined to be idle, each terminal having data to transmit performs a backoff procedure after an Inter Frame Space (IFS), such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS is used as a configuration replacing the conventional DCF IFS (DIFS). Each terminal waits while decrementing a slot time equal to a random number determined for the corresponding terminal during the idle interval of the channel, and a terminal that has exhausted all of its slot time attempts to access the corresponding channel. The period during which each terminal performs the backoff procedure is called a contention window period. In this case, the random number can be called a backoff counter. That is, the initial value of the backoff counter is set by an integer, which is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal can decrement the backoff counter by 1. If the backoff counter reaches 0, the terminal may be allowed to perform channel access on the corresponding channel. Therefore, if the channel is idle during the AIFS time and the backoff counter slot time, the terminal may be allowed to transmit.

[0052] If a specific terminal successfully accesses the channel, it transmits data over the channel. However, if the terminal attempting access collides with another terminal, the colliding terminals are assigned new random numbers and perform a backoff procedure again. According to one embodiment, the new random numbers assigned to each terminal are determined within a range (2*CW) twice the range of the random numbers previously assigned to the terminal (contention window, CW). Meanwhile, each terminal attempts access by performing a backoff procedure again in the next contention window period. At this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. In this way, terminals communicating over a wireless LAN can avoid collisions with each other on a specific channel.

[0053] <Examples of various PPDU formats>

[0054] Figure 7 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. More specifically, Figure 7(a) shows an example of a legacy PPDU format based on 802.11a / g, Figure 7(b) shows an example of an HE PPDU format based on 802.11ax, and Figure 7(c) shows an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Also, Figure 7(d) shows detailed field configurations of L-SIG and RL-SIG commonly used in the PPDU formats.

[0055] 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.

[0056] Referring to FIG. 7(b), the preamble of the HE PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a High Efficiency Signal A field (HE-SIG-A), a High Efficiency Signal B field (HE-SIG-B), a High Efficiency Short Training field (HE-STF), and a High Efficiency Long Training field (HE-LTF) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF can be referred to as an HE preamble. The specific configuration of the HE preamble may vary depending on the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0057] Referring to FIG. 7(c), the preamble of the EHT PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a Universal Signal field (U-SIG), an Extremely High Throughput Signal A field (EHT-SIG-A), an Extremely High Throughput Signal B field (EHT-SIG-A), an Extremely High Throughput Short Training field (EHT-STF), and an Extremely High Throughput Long Training field (EHT-LTF) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may vary depending on the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some EHT PPDU formats.

[0058] The L-SIG field included in the PPDU preamble is configured with a total of 64 subcarriers using 64 FFT OFDM. Of these, 48 subcarriers, excluding guard subcarriers, DC subcarriers, and pilot subcarriers, are used for L-SIG data transmission. BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, so it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of the L-SIG.

[0059] Referring to FIG. 7(d), the L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field is composed of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission rates of 6, 9, 12, 18, 24, 36, 48, or 54 Mbps, which is a combination of a modulation scheme such as BPSK, QPSK, 16-QAM, or 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The combined information in the L_RATE and L_LENGTH fields indicates the total length of the PPDU. In a non-legacy PPDU format, the L_RATE field is set to the minimum rate of 6 Mbps.

[0060] The unit of the L_LENGTH field is byte, and a total of 12 bits are allocated, allowing signaling up to 4095. In combination with the L_RATE field, the length of the PPDU can be indicated. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0061] First, a legacy or non-legacy terminal analyzes the length of the PPDU using the L_LENGTH field as follows. When the L_RATE field is set to 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted at 4 us, which is the duration of one symbol of the 64FFT. Therefore, by adding 3 bytes corresponding to the SVC field and the Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the amount of transmission of one symbol, the number of 64FFT reference symbols after the L-SIG is obtained. The obtained number of symbols is multiplied by 4 us, which is the duration of one symbol, and then 20 us, which is required to transmit the L-STF, L-LTF, and L-SIG, is added to obtain the length of the PPDU, i.e., the reception time (RXTIME). This can be expressed mathematically as shown in Equation 1 below.

[0062]

number

[0063] At this time,

number

[0064]

number

[0065] 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.

[0066]

number

[0067] 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.

[0068] Referring to Figure 7(e), the U-SIG (Universal SIG) field remains in the EHT PPDU and subsequent generation WLAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. The U-SIG is two 64FFT-based OFDM symbols and can transmit a total of 52 bits of information. Of these, 43 bits excluding 9 bits of CRC / tail are roughly divided into a VI (Version Independent) field and a VD (Version Dependent) field.

[0069] The VI bit will maintain its current bit configuration, so even if a subsequent generation PPDU is defined, current 11be UEs can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field consists of the PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits long and serves to sequentially distinguish between 11be and subsequent generations of WLAN standards. 11be has a value of 000b. The UL / DL field identifies whether the PPDU is an uplink or downlink PPDU. The BSS color represents a BSS identifier defined in 11ax and has a value of 6 or more bits. The TXOP represents the transmit opportunity duration (Transmit Opportunity Duration) transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without decoding the MPDU, and has a value of 7 or more bits.

[0070] The VD field, which is signaling information useful only for 11be version PPDUs, may consist of fields commonly used in any PPDU format, such as the PPDU format and BW, as well as fields defined differently for each PPDU format. The PPDU format is a separator that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field broadly signals five basic PPDU BW options: 20, 40, 80, 160 (80 + 80), and 320 (160 + 160) MHz (BWs that can be expressed in the form of a power of 20 * 2 can be called basic BWs), as well as various remaining PPDU BWs formed by preamble puncturing. After signaling at 320 MHz, a portion of 80 MHz may be punctured. In addition, the punctured and modified channel shape may be signaled directly in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (for example, a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signalings are possible, so a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signalings are possible, so a maximum of 11 puncturing modes can be signaled.

[0071] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs may be signaled in the same PPDU format, and a field for distinguishing between MU PPDUs and SU PPDUs may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both SU PPDUs and MU PPDUs include an EHT-SIG field, but some fields not required for the SU PPDU may be compressed. In this case, the information of the compressed fields may be omitted or may have a reduced size compared to the size of the original fields included in the MU PPDU. For example, the SU PPDU may have a different configuration, such as the common fields of the EHT-SIG being omitted or replaced, or the user-specific fields being replaced or reduced to one.

[0072] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (such as the RA field) may be omitted depending on the value of the compression field.

[0073] When a portion of the EHT-SIG field of the SU PPDU is compressed, the information included in the compressed field may be signaled together in an uncompressed field (e.g., a common field). In the case of an MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of information signaled may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether the transmitted MU PPDU was sent to it. Therefore, the AP must transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols in the EHT-SIG field and / or the MCS, which is the modulation method. The EHT-SIG field may include information on the size and location of the RU assigned to each user.

[0074] In the case of an SU PPDU, a STA may be assigned multiple RUs, and the multiple RUs may be contiguous or discontinuous. If the RUs assigned to the STA are not contiguous, the STA can efficiently receive the SU PPDU only by recognizing punctured RUs in between. Therefore, the AP can transmit the SU PPDU including information on punctured RUs among the RUs assigned to the STA (e.g., puncturing pattern of the RUs). That is, in the case of an SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and the puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field can signal the type of discontinuous channels appearing within the bandwidth.

[0075] The type of signaled discontinuous channel is limited, and indicates the BW and discontinuous channel information of the SU PPDU in combination with the value of the BW field. For example, since the SU PPDU is a PPDU transmitted only to a single UE, the STA can recognize its allocated bandwidth from the BW field included in the PPDU and can recognize punctured resources within the allocated bandwidth from the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the UE can receive the PPDU in the remaining resource units other than the specific channel of the punctured resource units. In this case, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0076] The reason why only limited discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed for each 20 MHz subchannel, if puncturing is performed on a BW having multiple 20 MHz subchannels, such as 80, 160, or 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered discontinuous) must be signaled by expressing whether or not the remaining 15 20 MHz subchannels other than the primary channel are in use. Using 15 bits to signal the discontinuous channel type for single-user transmission can result in excessive signaling overhead when considering the low transmission rate of the signaling part.

[0077] This invention proposes a method for signaling the discontinuous channel type of the SU PPDU, illustrates the discontinuous channel type determined by the proposed method, and proposes a method for signaling the primary 160 MHz and secondary 160 MHz puncturing types in the 320 MHz BW configuration of the SU PPDU.

[0078] In addition, one embodiment of the present invention proposes a method of varying the PPDU configuration indicated by the preamble puncturing BW value depending on the PPDU format signaled in the PPDU format field. Assuming the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, a one-symbol EHT-SIG-A can be further signaled after the U-SIG, or EHT-SIG-A does not need to be signaled at all. Taking this into consideration, up to 11 puncturing modes must be fully signaled using only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B is further signaled after the U-SIG, so up to 11 puncturing modes can be signaled in a different manner than in the case of an SU PPDU. In the case of an EHT ER PPDU, the BW field is set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz bandwidth.

[0079] Figure 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. For an MU PPDU, SIG-B, a signaling field for simultaneous reception by multiple users, is required. SIG-B may be transmitted after the U-SIG without a separate SIG-A. For this purpose, the U-SIG must signal information for decoding SIG-B. These fields include the SIG-B MCS, SIG-B DCM, number of SIG-B symbols, SIG-B compression, and number of EHT-LTF symbols.

[0080] FIG. 8 illustrates various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and exemplary methods for indicating the same according to an embodiment of the present invention.

[0081] 8, a PPDU may be configured with a preamble and a data portion, and the format of one type, EHT PPDU, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 8(d) shows an example of an EHT ER SU PPDU format used for single-user transmission with STAs in an extended range. The EHT ER SU PPDU may be used for single-user transmission with STAs in a wider range than the EHT SU PPDU described in FIG. 8(a), and the U-SIG field may be repeated on the time axis.

[0086] The EHT MU PPDU described in (c) of Figure 8 can be used by the AP for downlink transmission to multiple STAs. In this case, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive the PPDU transmitted from the AP. The EHT MU PPDU can convey AID information of the receiver and / or sender of the transmitted PPDU to the STA through the user specific field of the EHT-SIG-B. Therefore, multiple terminals receiving the EHT MU PPDU can perform spatial reuse based on the AID information of the user specific field included in the preamble of the received PPDU.

[0087] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information regarding the configuration of resource units (e.g., the division type of resource units) in a specific bandwidth (e.g., 20 MHz) on the frequency axis. That is, the RA field may indicate the configuration of resource units divided by the bandwidth for transmitting the HE MU PPDU so that the STA can receive the PPDU. Information about the STA allocated (or designated) to each divided resource unit may be included in a user specific field of the EHT-SIG-B and transmitted to the STA. That is, the user specific field may include one or more user fields corresponding to each divided resource unit.

[0088] For example, among the multiple divided resource units, the user field corresponding to at least one resource unit used for data transmission may include the AID of the receiver or sender, and the user field corresponding to the remaining resource units not used for data transmission may include a previously set null STA ID.

[0089] For ease of explanation, the term frame or MAC frame may be used interchangeably with MPDU in this specification.

[0090] When a single wireless communication device communicates using multiple links, the communication efficiency of the wireless communication device can be improved. In this case, a link is a physical path and may be configured as a single wireless medium that can be used to transmit an MSDU (MAC service data unit). For example, when the frequency band of one link is being used by another wireless communication device, the wireless communication device can continue communication using another link. In this way, the wireless communication device can effectively use multiple channels. Furthermore, when a wireless communication device simultaneously communicates using multiple links, the overall throughput can be improved. However, existing wireless LANs are specified on the assumption that one wireless communication device uses one link. Therefore, a wireless LAN operation method for using multiple links is needed. A wireless communication method for a wireless communication device using multiple links will be described with reference to FIGS. 9 to 26. First, a specific embodiment of a wireless communication device using multiple links will be described with reference to FIG. 9.

[0091] FIG. 9 shows a multi-link device according to an embodiment of the present invention.

[0092] A multi-link device (MLD) may be defined for the wireless communication method using multiple links described above. The multi-link device may represent a device having one or more affiliated stations. Depending on a specific embodiment, the multi-link device may represent a device having two or more affiliated stations. The multi-link device may also exchange multi-link elements. The multi-link element includes information about one or more stations or one or more links. The multi-link element may include a multi-link setup element, which will be described later. In this case, the multi-link device may be a logical entity. Specifically, the multi-link device may have multiple affiliated stations. The multi-link device may be referred to as a multi-link logical entity (MLLE) or a multi-link entity (MLE). The multi-link device may have one medium access control service access point (SAP) up to a logical link control (LLC). The MLD may also have one MAC data service.

[0093] Multiple stations included in a multilink device can operate on multiple links. Also, multiple stations included in a multilink device can operate on multiple channels. Specifically, multiple stations included in a multilink device can operate on different links or different channels. For example, multiple stations included in a multilink device can operate on different channels, such as 2.4 GHz, 5 GHz, and 6 GHz.

[0094] The operation of the multilink device can be referred to as multilink operation, MLD operation, or multi-band operation. If the station associated with the multilink device is an AP, the multilink device can be referred to as AP MLD. If the station associated with the multilink device is a non-AP station, the multilink device can be referred to as non-AP MLD.

[0095] FIG. 9 shows the operation of communication between non-AP MLD and AP-MLD. Specifically, non-AP MLD and AP-MLD each communicate using three links. AP MLD includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). Non-AP MLD includes a first non-AP STA (non-AP STA1), a second non-AP STA (non-AP STA2), and a third non-AP STA (non-AP STA3). The first AP (AP1) and the first non-AP STA (non-AP STA1) communicate via a first link (Link1). The second AP (AP2) and the second non-AP STA (non-AP STA2) communicate via a second link (Link2). The third AP (AP3) and the third non-AP STA (non-AP STA3) communicate via a third link (Link3).

[0096] Multilink operation may include a multilink setup operation. Multilink setup corresponds to the association operation of the single-link operation described above and must be performed prior to frame exchange in the multilink. A multilink device can obtain information required for multilink setup from a multi-link setup element. Specifically, the multi-link setup element may include capability information related to the multilink. In this case, the capability information may include information indicating whether one of multiple devices included in the multilink device can transmit and the other devices can receive at the same time. The capability information may also include information about links available to each station included in the MLD. The capability information may also include information about channels available to each station included in the MLD.

[0097] Multilink configuration may be established through negotiation between peer stations. Specifically, multilink configuration may be established through communication between stations without communication with an AP. Multilink configuration may also be established through any one of the links. For example, even if the first to third links are established through multilink, multilink configuration may be established through the first link.

[0098] In addition, a mapping between a traffic identifier (TID) and a link may be configured. Specifically, frames corresponding to a specific TID value may be exchanged only through a pre-specified link. The mapping between a TID and a link may be configured on a directional basis. For example, when multiple links are configured between a first multilink device and a second multilink device, the first multilink device may be configured to transmit frames of the first TID to the multiple first links, and the second multilink device may be configured to transmit frames of the second TID to the first link. In addition, a default setting may exist for the mapping between TIDs and links. Specifically, if no additional settings are configured in the multilink configuration, the multilink device may exchange frames corresponding to TIDs on each link according to a default setting. In this case, the default setting may be that all TIDs are exchanged on any one link.

[0099] The TID will be described in detail. The TID is an ID for classifying traffic and data to support quality of service (QoS). The TID may be used and assigned in a layer higher than the MAC layer. The TID may indicate a traffic category (TC) or a traffic stream (TS). There may be 16 distinct TIDs. For example, the TID may be designated as any one of 0 to 15. Different TID values ​​may be designated depending on an access policy, a channel access method, or a medium access method. For example, when enhanced distributed channel access (EDCA) or hybrid coordination function contention-based channel access (HCAF) is used, the TID may be assigned a value ranging from 0 to 7. When EDCA is used, the TID may indicate a user priority (UP). In this case, the UP may be designated by the TC or the TS. The UP may be assigned in a layer higher than the MAC. Furthermore, when HCCA (HCF controlled channel access) or SPCA is used, the TID may be assigned a value in the range of 8 to 15. When HCCA or SPCA is used, the TID may indicate a TSID. Furthermore, when HEMM or SEMM is used, the TID may be assigned a value in the range of 8 to 15. When HEMM or SEMM is used, the TID may indicate a TSID.

[0100] UP and AC (access category) may be mapped. AC may be a label for providing QoS in EDCA. AC may be a label for indicating an EDCA parameter set. EDCA parameters or EDCA parameter sets are parameters used in EDCA channel contention. QoS stations can guarantee QoS using AC. AC may include AC_BK, AC_BE, AC_VI, and AC_VO. AC_BK, AC_BE, AC_VI, and AC_VO may indicate background, best effort, video, and voice, respectively. AC_BK, AC_BE, AC_VI, and AC_VO may be classified into lower-level ACs. For example, AC_VI may be further subdivided into AC_VI primary and AC_VI alternate. AC_VO may be further subdivided into AC_VO primary and AC_VO alternate. UP or TID may be mapped to an AC. For example, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI, AC_VI, AC_VO, and AC_VO, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI alternate, AC_VI primary, AC_VO primary, and AC_VO alternate, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may have decreasing priority in that order. That is, 1 may have a lower priority, and 7 may have a higher priority. Therefore, the order of priority may be AC_BK, AC_BE, AC_VI, and AC_VO. Also, AC_BK, AC_BE, AC_VI, and AC_VO can correspond to ACI (AC index) 0, 1, 2, and 3, respectively. Due to the characteristics of TID, the mapping between TID and link can represent the mapping between AC and link.The mapping between links and ACs can also represent the mapping between TIDs and links.

[0101] As described above, a TID may be mapped to each of multiple links. The mapping may specify the links through which traffic corresponding to a specific TID or AC can be exchanged. Furthermore, the TID or AC that can be transmitted for each transmission direction within a link may be specified. As described above, a default setting may exist for the mapping between TIDs and links. Specifically, if no additional settings are configured in the multilink configuration, the multilink device may exchange frames corresponding to the TID on each link according to the default setting. In this case, the default setting may be that all TIDs are exchanged on any one link. At any given time, any TID or AC may be mapped to at least one link. Management frames and control frames may be transmitted on all links.

[0102] When a link is mapped to a TID or AC, only data frames corresponding to the TID or AC mapped to the link may be transmitted on the link. Therefore, when a link is mapped to a TID or AC, frames not corresponding to a TID or AC not mapped to the link may not be transmitted on the link. When a link is mapped to a TID or AC, an ACK may also be transmitted based on the link to which the TID or AC is mapped. For example, a Block ACK agreement may be determined based on the mapping between the TID and the link. In yet another specific embodiment, the mapping between the TID and the link may be determined based on the Block ACK agreement. Specifically, a Block ACK agreement may be set for a TID mapped to a specific link.

[0103] The above-described TID-to-link mapping may ensure QoS. Specifically, a high-priority AC or TID may be mapped to a link where a relatively small number of stations are active or where channel conditions are good. The above-described TID-to-link mapping may also allow stations to remain in a power-saving state for a longer period of time.

[0104] FIG. 10 illustrates simultaneous transmission of different links in multi-link operation according to an embodiment of the present invention.

[0105] Depending on the implementation of the multi-link device, simultaneous operation of the multi-links may not be supported. For example, a multi-link device may support simultaneous transmission on multiple links, simultaneous reception on multiple links, or transmission on one link while receiving on another link. Reception or transmission on one link may affect reception or transmission on another link. Specifically, transmission on one link may interfere with other links. Interference from one link of a multi-link device affecting other links may be called internal leakage. The smaller the frequency spacing between links, the greater the internal leakage. If the internal leakage is not too large, transmission on one link can occur when transmission on another link. If the internal leakage is large, transmission on one link cannot occur when transmission on another link. This simultaneous operation of the multi-link device on multiple links may be called STR (simultaneous transmit and receive, simultaneous transmission and reception). For example, a multilink device transmitting on multiple links simultaneously, transmitting on one link while receiving on another link, or receiving on multiple links simultaneously can be referred to as STR.

[0106] On the other hand, if STR is not supported due to interference between multiple stations constituting an MLD, the STAs may be said to be in a non-STR relationship or NSTR relationship (a relationship in which STR is not supported).

[0107] In this case, whether two STAs (STA1 and 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).

[0108] Therefore, when an MLD operates STAs in a specific link pair, if STR is supported between the STAs operated in 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 in another link pair, if STR is not supported between the STAs operated in the other link pair, the other link pair may be considered as an NSTR link pair by the MLD.

[0109] In this way, whether STR is supported between STAs of an MLD is determined by whether the link pair on which these STAs operate is an STR link pair or an NSTR link pair. However, as described above, since the characteristics (such as shielding performance) of each MLD may differ from one another, a specific link pair may be considered as a link pair in which STR is supported for a specific MLD and as an NSTR link pair in which STR is not supported for another MLD.

[0110] In one embodiment of the present invention described below, for convenience of explanation, the STAs operated in the STR link pair of the MLD will be named (explicitly) as STR MLD STAs, and the STAs operated in the NSTR link pair of the MLD will be named (explicitly) as NSTR (and non-STR) MLD STAs. That is, in the embodiment described below, when a "non-STR MLD STA" is mentioned, it may be interpreted as referring to one of the two STAs operated in the NSTR link pair of the MLD, and when a "STR MLD STA" is mentioned, it may be interpreted as referring to one of the two STAs operated in the STR link pair of the MLD.

[0111] In addition, the NSTR MLD may include not only an MLD in which the STA of a specific MLD loses its receiving capability in relation to whether or not the STR is supported as described above, but also an MLD in which the hardware configuration of the MLD itself does not support simultaneous transmission / reception.

[0112] In other words, the hardware configuration of a multi-link device (MLD) may limit the hardware resources available to other STAs in the MLD when a specific STA in the MLD is transmitting or receiving. For example, if a specific MLD has a hardware configuration that supports processing of only one PPDU, when a specific STA in the MLD is receiving, the specific MLD cannot support Tx and Rx for other STAs in the MLD. Similarly, when a specific STA in the MLD is transmitting, the specific MLD cannot support Tx and Rx for other STAs in the MLD.

[0113] An MLD that can operate STAs on two or more links but can support transmission / reception for only one STA at a time may be called a Multi-link Single Radio MLD (MLSR MLD). Alternatively, an MLD operation mode that supports transmission / reception for only one STA may be called an Enhanced Multi-Link Single Radio (EMLSR) mode. An MLD operating in EMLSR mode may be a Multi-radio MLD or an Enhanced Single-radio MLD. An Enhanced Single-radio MLD supports data transmission / reception for only one link at a time, but may refer to a device that supports CCA and low-data-rate (e.g., encoded at 6 MHz or 24 MHz or less) PPDU transmission / reception for two or more links by including additional hardware (e.g., a low-cost PHY front end).

[0114] In addition, as a variation of the EMLSR mode, Enhanced Multi-Link Multi-Radio (EMLMR) may be defined in which the MLD supports transmission / reception for each STA, but utilizes part of the RF chain used by a specific STA for transmission / reception for other STAs. EMLMR may have the same transmission / reception restriction characteristics as EMLSR when all of the RF chains used by the specific STA are utilized for transmission / reception for the other STAs. In other words, an MLD operating in EMLMR mode can operate to support transmission / reception for only one link (STA) at a specific time, regardless of whether STR is supported for the link, and this may be understood as an operation similar to that of an MLD operating in the EMLSR mode.

[0115] That is, the link of an MLD operating in EMLSR / EMLMR mode may be considered as an NSTR link pair.

[0116] In this case, the above-mentioned transmission / reception includes transmission / transmission and reception / reception, that is, it is not related to whether or not both links support STR / NSTR.

[0117] For ease of explanation, hereinafter, EMLSR / EMLMR MLD is used to mean an MLD that can only support transmission / reception for one STA at a specific time due to hardware constraints, and an MLD that can support transmission / reception for two or more STAs (processing capability unrelated to STR) but only supports high-speed data frame transmission / reception for one STA at a specific time as a type of operating mode.

[0118] The STR MLD operation that takes into account the performance limitations of the NSTR MLD provided by the above-described embodiment of the present invention can be directly utilized as the STR MLD operation for the MLSR MLD. For example, after an STR MLD STA transmits to a multi-link single radio MLD STA, if the STA determines that the transmission has failed or is predicted to fail due to the limited performance of the multi-link single radio MLD STA, the STA can cancel the transmission that is currently being performed or is about to be performed. In this case, the procedure for determining whether the transmission has failed due to the limited performance of the EMLSR / EMLMR MLD may be similar to the procedure for determining whether a transmission to an NSTR MLD STA has failed due to the limited performance of the NSTR MLD STA.

[0119] As mentioned above, a multilink device can support STR, or can support it with limitations. Specifically, a multilink device can support STR only under certain conditions. For example, if the multilink device operates with a single radio, the multilink device may not be able to perform STR. Also, if the multilink device operates with a single antenna, the multilink device may not be able to perform STR. Also, if an internal leak is detected to be greater than a predetermined magnitude, the multilink device may not be able to perform STR.

[0120] A station can exchange information about its STR capability with other stations. Specifically, a station can exchange information about whether or not the station has limitations on its ability to simultaneously transmit or receive on multiple links. Specifically, the information about whether or not the station has limitations on its ability to transmit or receive on multiple links can indicate whether or not the station will transmit or receive on multiple links simultaneously, or whether or not transmission and reception are simultaneous. Furthermore, the information about whether or not the station has limitations on its ability to transmit or receive on multiple links can be information indicated in stages. Specifically, the information about whether or not the station has limitations on its ability to transmit or receive on multiple links can 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 can 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 the frequency spacing between links that may affect internal leakage can be information indicating a stage indicating the relationship between the frequency spacing between links and the magnitude of internal leakage.

[0121] In FIG. 10, a first station (STA1) and a second station (STA2) are affiliated with one non-AP multilink device. A first AP (AP1) and a second AP (AP2) may also be affiliated with one non-AP multilink device. A first link (link1) is established between the first AP (AP1) and the first station (STA1), and a second link (link2) is established between the second AP (AP2) and the second station (STA2). In FIG. 10, the non-AP multilink device can perform limited STR. When the second station (STA2) transmits on the second link (Link2), the first station (STA1)'s reception on the first link (Link1) may be interrupted by the transmission on the second link (Link2). For example, in the following case, the first station (STA1)'s reception on the first link (Link1) may be interrupted by the transmission on the second link (Link2). The second station (STA2) transmits the first data (Data1) over the second link (Link2), and the first AP (AP1) transmits a response (Ack for Data1) to the first station (STA1). The second station (STA2) transmits the second data (Data2) over the second link (Link2). At this time, the transmission of the second data (Data2) and the transmission of the response (Ack for Data1) to the first data (Data1) may overlap. In this case, the transmission to the second station (STA2) over the second link (Link2) may cause interference to the first link (Link1). As a result, the first station (STA1) may not receive the response (Ack for Data1) to the first data (Data1).

[0122] The operation of the multilink device for channel access will be described below. The multilink operation without a specific description can follow the channel access procedure described in FIG.

[0123] A multilink device can perform channel access independently from multiple links. In this case, the channel access may be backoff-based channel access. When a multilink device performs channel access independently from multiple links and the backoff counters for multiple links reach zero, the multilink device can start transmission simultaneously from multiple links. In a specific embodiment, when one of the backoff counters for multiple links reaches zero and a predetermined condition is met, the multilink device can perform channel access not only for the link whose backoff counter has reached zero but also for other links whose backoff counters have not reached zero. Specifically, when one of the backoff counters for multiple links reaches zero, the multilink device can perform energy sensing on other links whose backoff counters have not reached zero. In this case, if energy greater than or equal to a predetermined value is not detected, the multilink device can perform channel access not only for the link whose backoff counter has reached zero but also for the link for which energy sensing has been performed. This allows the multilink device to start transmission simultaneously from multiple links. The threshold used for energy sensing may be smaller than the threshold used for determining whether to decrement the backoff counter. Furthermore, when determining whether to decrement the backoff counter, the multilink device can sense any type of signal, not just a WLAN signal. Furthermore, in the energy sensing described above, the multilink device can sense any type of signal, not just a WLAN signal. Internal leakage may not be detected as a WLAN signal. In such a case, the multilink device can detect signals detected due to internal leakage through energy sensing. Furthermore, as described above, the threshold used for energy sensing may be smaller than the threshold used when determining whether to decrement the backoff counter. Therefore, even while transmission is occurring on one link, the multilink device can decrement the backoff counter on another link.

[0124] Depending on the degree of interference between links used by the multilink device, the multilink device may determine whether stations operating on each link can operate independently. In this case, the degree of interference between links may be the magnitude of interference perceived by other stations in the multilink device when one station in the multilink device transmits on one of the links. If transmission on the first link of a first station in the multilink device causes interference of a predetermined magnitude or greater to a second station in the multilink device operating on the second link, the operation of the second station may be restricted. Specifically, reception or channel access of the second station may be restricted. If interference occurs, the second station may fail to decode a received signal due to the interference. Furthermore, if interference occurs, the second station may determine that the channel is in use when accessing the channel using backoff.

[0125] Furthermore, if the transmission of a first station in the multilink device through the first link causes interference of less than a predetermined magnitude to a second station in the multilink device operating through the second link, the first station and the second station can operate independently. Specifically, if the transmission of a first station in the multilink device through the first link causes interference of less than a predetermined magnitude to a second station in the multilink device operating through the second link, the first station and the second station can independently access the channel. Also, if the transmission of a first station in the multilink device through the first link causes interference of less than a predetermined magnitude to a second station in the multilink device operating through the second link, the first station and the second station can independently transmit or receive. If interference of less than a predetermined magnitude occurs, the second station can successfully decode the received signal even in the presence of interference. Also, if interference of less than a predetermined magnitude occurs, the second station can determine that the channel is idle when accessing the channel using backoff.

[0126] 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 a high RF (radio frequency) device may be smaller than the internal interference occurring in a multilink device including a low 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.

[0127] FIG. 10 shows how the magnitude of interference varies depending on the spacing between link frequency bands and the characteristics of the multilink devices. In the example of FIG. 10, a first multilink device (MLD#1) includes a first station (STA1)-1 operating on a first link (Link1) and a second station (STA1)-2 operating on a second link (Link2). A second multilink device (MLD#2) includes a first station (STA2)-1 operating on a first link (Link1) and a second station (STA2)-2 operating on a second link (Link2). The frequency spacing between the first link (Link1) and the second link (Link2) on which the first multilink device (MLD#1) operates is the same as the frequency spacing between the first link (Link1) and the second link (Link2) on which the second multilink device (MLD#2) operates. However, the magnitude of interference varies depending on the difference between the characteristics of the first multilink device (MLD#1) and the second multilink device (MLD#2). Specifically, the magnitude of interference generated in the second multilink device (MLD#2) may be greater than the magnitude of interference generated in the first multilink device (MLD#1). Considering that the magnitude of interference generated may differ depending on the characteristics of the multilink devices and that the presence or absence of STR support may differ depending on the multilink devices, information regarding whether STR is supported or not needs to be exchanged.

[0128] A multilink device may signal whether or not a station included in the multilink device supports STR. Specifically, an AP multilink device and a non-AP multilink device may exchange whether or not an AP included in the AP multilink device supports STR with whether or not a STA included in the non-AP multilink device supports STR. In this embodiment, an element indicating whether or not STR support is available may be used. The element indicating whether or not STR support is available may be referred to as an STR support element. The STR support element may indicate, by one bit, whether or not a station in the multilink device that transmitted the STR support element supports STR. Specifically, the STR support element may indicate, by one bit, whether or not each station included in the multilink device that transmitted the STR support element supports STR. 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. 1b The STR Support element may include a field having the following information: Stations operating in different frequency bands are assumed to support STR, and the STR Support element may omit signaling regarding the presence or absence of STR support between stations operating in different frequency bands. For example, a first station (STA1) operates on a first link of 2.4 GHz, and a second station (STA2) and a third station (STA3) operate on a second link of 5 GHz and a third link of 5 GHz, respectively. In this case, the STR Support element may indicate with one bit that STR is supported between the second station (STA2) and the third station (STA3). Alternatively, the STR Support element may include only one bit if the STR Support element signals two stations.

[0129] In a specific embodiment, the relationship between a link located at 2.4 GHz and a link located at 5 GHz or 6 GHz among the links of a multi-link device may always be determined as STR, and therefore, signaling regarding the presence or absence of STR between a link located at 2.4 GHz and a link located at 5 GHz or 6 GHz may be omitted.

[0130] In the above-described embodiments, the operation of a station in a multilink device may be replaced by the operation of the multilink device. Also, in the above-described embodiments, the operation of an AP may be replaced by the operation of a non-AP station, and the operation of a non-AP station may be replaced by the operation of an AP. Thus, the operation of an AP in a non-STR multilink device may be replaced by the operation of a non-AP station in a non-STR multilink device, and the operation of a non-AP station in an STR multilink device may be replaced by the operation of an AP in the STR multilink device. Also, the operation of a non-AP station in a non-STR multilink device may be replaced by the operation of an AP in a non-STR multilink device, and the operation of an AP in an STR multilink device may be replaced by the operation of a non-AP station in the STR multilink device.

[0131] Each AP included in the AP MLD can transmit a beacon frame on its own link. APs included in the AP MLD can transmit beacon frames for the same purposes and functions as APs in conventional Wi-Fi, and may also include in the beacon frame information indicating that the AP is included in the MLD, MLD level information (common information), and basic information of other APs included in the same MLD. In this case, the basic information of other APs may be included in the TBTT information field of the RNR element and transmitted in the beacon frame.

[0132] Beacon frames transmitted by AP MLD may contain only common information per MLD to prevent the size of the beacon frame from becoming too large (beacon bloating) due to information about multiple APs included in the same MLD being included in one beacon frame.

[0133] However, the NSTR Soft AP MLD can transmit beacon frames only through some of the APs it operates. For example, if the NSTR Soft AP MLD operates APs on two separate links and the two links are in an NSTR relationship with each other, the NSTR Soft AP MLD can transmit beacon frames through only one of the two links. In this case, the link through which the NSTR Soft AP MLD transmits beacon frames may be considered a primary link in the NSTR link pair of the NSTR Soft AP MLD. Meanwhile, the NSTR Soft AP MLD can operate links other than the primary link in the NSTR link pair as secondary links, and the secondary link may be a link through which beacon frames are not transmitted. The reason why the NSTR Soft AP MLD operates one link of the NSTR link pair as a primary link and at least one other link as a secondary link is to prevent problems that may occur when two separate APs operate independently in the NSTR link pair. Problems that may occur in an AP MLD operating an NSTR link pair will be described in more detail in conjunction with examples of operational restrictions 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, a link pair to which NSTR is applied can transmit beacon frames only on the primary link and cannot transmit beacon frames on the secondary link.

[0134] As described above, since the NSTR Soft AP MLD has the restriction of transmitting beacon frames only on the primary link, the NSTR Soft AP MLD may be allowed to include more information (related to APs on other links (non-primary)) in the beacon frames transmitted on the primary link compared to a general AP MLD. This may be a beacon frame configuration method devised to enable a non-AP MLD that also operates STAs on the secondary link to operate STAs on the secondary link based on information in a beacon frame received on the primary link.

[0135] For example, a primary link AP of an NSTR soft AP MLD may include a Per-STA Profile corresponding to an AP of a secondary link (of the same NSTR soft AP MLD) in the Multi-Link element of a beacon frame. In this case, the primary link AP of an NSTR soft AP MLD may not have any additional constraints when including a Per-STA Profile corresponding to an AP of a secondary link. The constraints refer to conditions under which a general AP MLD can include a Per-STA Profile in a beacon frame (such as an AP corresponding to a Per-STA Profile performing (extended) channel switching or channel quieting).

[0136] 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.

[0137] Referring to (a) of Figure 11, the beacon frame may include the same parameters and elements in legacy IEs as those included in the beacon frame disclosed in conventional Wi-Fi 802.11ax. For example, the legacy IEs of the beacon frame may include elements such as a timestamp field, a beacon interval field indicating the interval at which beacons are transmitted, TIM, DSSS parameter set, IBSS parameter set, country, channel switch announcement, extended channel switch announcement, wide bandwidth channel switch, transmit power envelope, supported operating classes, IBSS DFS, ERP information, HT capabilities, HT operation, VHT capability, VHT operation, S1G beacon compatibility, short beacon interval, S1G capability, S1G operation, HE capability, HE 6GHz band capability, HE operation, BSS color change announcement, and spatial reuse parameter set.

[0138] In this case, the setting method and meaning of the fields and elements included in the legacy IEs field are the same as the setting and meaning of the fields and elements of the same names included in the beacon frame disclosed up to conventional Wi-Fi 802.11ax.

[0139] The beacon frame may also include a Reduced Neighbor Report (RNR) element for indicating information about neighbor APs. The RNR element may be used to inform a station of information about neighbor APs, and the station may receive the beacon frame and recognize the neighbor APs based on the RNR element included in the beacon frame.

[0140] Specifically, the RNR element may include an element ID field, a length field, and a neighbor AP information field. Each neighbor AP information field may include a TBTT information header (2 octets), an operation class (1 octet), a channel number (1 octet), and a TBTT information set (variable length) field. In this case, the RNR element transmitted by the AP included in the AP MLD may include a TBTT information field format as shown in (b) of FIG. 11 to indicate basic information for other APs included in the same MLD. Unlike the TBTT information field of the RNR element transmitted by the AP in conventional Wi-Fi 802.11ax, the RNR element transmitted by the AP included in the EHT AP MLD may include an MLD parameter field.

[0141] The MLD parameter field may include an MLD ID, a link ID, and a Change Sequence subfield, as shown in (c) of Figure 11. In this case, when an AP MLD indicates information about another AP in the same MLD through a specific Neighbor AP Information field in an RNR element, the MLD ID subfield included in the specific Neighbor AP Information field can be set to 0. That is, the AP can set the MLD ID subfield to a specific value to inform a station that the Neighbor AP Information field is an AP included in the same AP MLD, and a station receiving the Neighbor AP Information field can recognize from the value of the MLD ID subfield that the AP corresponding to the Neighbor AP Information field is included in the same MLD as the AP that transmitted the Neighbor AP Information field.

[0142] The Link ID subfield may be a subfield indicating an index determined by the AP MLD to indicate a link operated by another AP to be indicated using neighbor AP information. The Change Sequence subfield may be a subfield used to indicate information related to an update (e.g., a Critical Update) related to the link of another AP. For example, if the value of the Change Sequence subfield is changed, a station receiving this can recognize that parameters related to the link of the corresponding AP have been updated and can request the updated parameters from the AP to update the corresponding parameters. In this case, if the AP MLD is an NSTR AP MLD, which is an MLD that does not support simultaneous transmission and reception (e.g., if the AP MLD is an NSTR mobile AP MLD or an NSTR soft AP MLD, i.e., if a mobile terminal operates as a soft AP MLD for tethering), the STA included in the STA MLD can perform a procedure to update parameters only on the primary link. That is, to update parameters of other links (e.g., non-primary links) to other neighbor APs other than the primary link of the AP MLD, frames for parameter update can be transmitted and received only via the primary link.

[0143] 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.

[0144] Furthermore, if the AP is an NSTR AP MLD that does not support simultaneous transmission and reception (e.g., an NSTR mobile AP MLD or an NSTR soft AP MLD, i.e., a mobile terminal or the like operates as a soft AP MLD for tethering, etc.), the NSTR AP MLD can transmit a beacon frame including information indicating that it is an NSTR AP MLD. For example, the NSTR AP MLD can set the value of a specific subfield included in the beacon frame to a specific value (e.g., '0' or '1'), and a non-AP STA MLD that receives the beacon frame can recognize that the AP MLD that transmitted the beacon frame is the NSTR AP MLD. Therefore, the specific subfield for indicating an NSTR AP MLD may be set to a value different from the specific value (e.g., '1' or '0') when not indicating an NSTR AP MLD (e.g., an STR AP MLD or another AP MLD, etc.).

[0145] A specific subfield for indicating NSTR AP MLD may be indicated together with a capability-related subfield (e.g., MLD level capability) in a beacon frame, or may be included in and transmitted in a neighbor AP information field associated with an AP of a non-primary link of the NSTR AP MLD. For example, a specific subfield for indicating NSTR AP MLD may be encoded and indicated together with a frequency separation for STR / AP MLD type indicator, which is a capability-related subfield. That is, the specific subfield may be encoded together with a frequency separation for STA / AP MLD type indicator indicating the distance for supporting STR, and indicated in a beacon frame. In this case, if the corresponding indicator indicates the type of AP MLD, a set value may indicate whether the AP MLD that transmitted the beacon frame is NSTR AP MLD or not (e.g., a value of '0' indicates not NSTR AP MLD, and a value of '1' indicates NSTR AP MLD).

[0146] 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.

[0147] As another example, the NSTR AP MLD may indicate that it is an NSTR AP MLD in an implicit manner rather than directly indicating that it is an NSTR AP MLD using a specific subfield. Specifically, the NSTR AP MLD may indicate that it is an NSTR AP MLD by indicating that it has two supportable links and at the same time indicating that it has an NSTR link pair. In this case, the NSTR AP MLD may set the Maximum Number Of Simultaneous Links subfield included in the beacon frame to 1 (or a predetermined value meaning 2) to indicate that it has two supportable links. In this case, the NSTR AP MLD may set the NSTR Link Pair Present subfield included in the beacon frame to 1 or 0 to indicate that it has an NSTR link pair.

[0148] The AP MLD can explicitly or implicitly inform the non-AP STA MLD that it is the NSTR AP MLD by transmitting a beacon frame according to the above-described method. The non-AP STA MLD can implicitly or explicitly determine from the received beacon frame whether the AP MLD that transmitted the beacon frame is the NSTR AP MLD. If the AP MLD that transmitted the beacon frame is the NSTR AP MLD (i.e., if the beacon frame indicates that the AP MLD is the NSTR AP MLD by an explicit or implicit method), the non-AP STA MLD can perform the procedure for association or setup with the NSTR AP MLD only on the link on which the beacon frame was received. In other words, the non-AP STA MLD can send and receive frames for association or setup with the NSTR AP MLD on the link on which the beacon frame was received (e.g., the primary link). For example, frames for association or configuration with an AP connected via a link other than the primary link included in the NSTR AP MLD may be transmitted only via the primary link. In this case, the (ML)(Re) association request frame transmitted by the Non-AP STA MLD may be transmitted via a link other than the primary link (non-primary link).

[0149] In this case, the NSTR AP MLD may not indicate information about the AP of the non-primary link in the RNR element of the beacon frame (transmitted on the primary link) to prevent the non-AP STA MLD from attempting a setup procedure on the non-primary link. That is, the beacon frame transmitted by the AP of the NSTR AP MLD may not include / indicate a neighbor AP information field for the AP of another link (in the same MLD). In this case, the non-AP STA MLD does not attempt to set up the NSTR AP MLD on the non-primary link after receiving the beacon frame because it cannot confirm information about the AP of the non-primary link. In this case, a non-AP STA MLD that receives a beacon frame from the NSTR AP MLD that does not include a neighbor AP information field for the AP of the non-primary link can implicitly recognize that the other AP is an NSTR AP MLD based on the fact that the number of simultaneously supported links of the AP that transmitted the beacon frame is two and information about other APs in the same MLD is not indicated, as described above.

[0150] Meanwhile, when a typical AP MLD receives an (ML) (Re) association request frame from a STA (MLD), it must transmit an (ML) association response frame over the link on which the (ML) association request frame was received. However, the NSTR AP MLD may be allowed to respond to an (ML) association request frame received over a non-primary link over the primary link (i.e., to send an (ML) association response frame over the primary link).

[0151] This may be an acceptable operation because, as described above, the NSTR AP MLD operation of transmitting on a non-primary link is somewhat limited compared to a general AP. Furthermore, the NSTR AP MLD has an operation restriction that when a response to an (ML) association response frame is transmitted on a non-primary link, it must also start transmitting on the primary link. This may be an operation restriction considered to prevent the AP of the primary link from entering a BLIND state, as considered in other embodiments of the present invention.

[0152] Therefore, when an NSTR AP MLD receives an (ML)(Re) association request frame over a non-primary link, it can respond with an (ML)(Re) association response frame over the primary link, or it can respond with an (ML)(Re) association response frame over both the primary and non-primary links simultaneously. That is, a STA MLD that sends an (ML)(Re) association request frame over a non-primary link of the NSTR AP MLD recognizes that the response to its request frame will be sent over the primary link, and can wait to receive an (ML)(Re) association response frame over the primary link.

[0153] The RNR element transmitted by the AP in the beacon frame may include a specific TBTT information field including an MLD Parameters field. In this case, if the MLD ID in the MLD Parameters field is set to '0', the STA MLD can recognize that the AP corresponding to the Neighbor AP Information field including the MLD Parameters field is included in the AP MLD that includes the AP that transmitted the beacon frame. In other words, the STA MLD can recognize that the Neighbor AP Information field indicates information about other APs included in the same AP MLD as the AP that transmitted the beacon frame. In this case, the method by which the STA MLD analyzes / acquires this information may be the same as or similar to the operation performed by a conventional STA after receiving an RNR element.

[0154] However, because an NSTR Soft AP does not transmit beacon frames via a non-primary link, it may be impossible to indicate information related to beacon frames of other APs (non-primary link APs) via the RNR element. Furthermore, because the NSTR Soft AP MLD does not transmit beacon frames via a non-primary link AP, it cannot support information related to beacon frames when indicating basic information about a non-primary link AP via the RNR element. For example, a non-primary link that does not transmit beacon frames does not have information corresponding to the TBTT information count, TBTT information length, and neighbor AP TBTT offset subfields that should be indicated in the RNR element. Therefore, when the NSTR Soft AP MLD transmits an RNR element via the primary link AP, it may be necessary to set the TBTT-related fields of the neighbor AP information field corresponding to the non-primary link AP to predetermined values.

[0155] The Neighbor AP TBTT Offset subfield of the TBTT Information field (see (b) of FIG. 11) indicates information related to the next TBTT of another AP to be indicated. That is, the Neighbor AP TBTT Offset subfield included in the Neighbor AP Information field may include information about the next TBTT of the AP corresponding to the Neighbor AP Information field. For example, when AP1 transmitting a beacon frame indicates information about AP2 using the RNR element (through the Neighbor AP Information field), the Neighbor AP TBTT Offset subfield corresponding to AP2 indicates how many TUs (Time Units, 1024 us) the next TBTT of AP2 differs from the previous TBTT of AP1. In this case, the value indicated in the Neighbor AP TBTT Offset subfield is a value obtained by rounding down the TBTT offset to the nearest integer. That is, when an AP indicates a value of 10 in the Neighbor AP TBTT Offset subfield of another AP, the next TBTT of the other AP may have a time interval of 10 TUs to less than 11 TUs based on the previous TBTT of the AP.

[0156] However, when an AP of a primary link of an NSTR Soft AP MLD sets a neighbor AP TBTT offset subfield (1-octet) corresponding to an AP of a non-primary link, it may need to set it to a preset value (e.g., 254 or 255). This may be because an NSTR Soft AP does not transmit a beacon frame on a non-primary link and is therefore unable to determine a target beacon transmission time (TBTT), which is a scheduled time for transmitting the next beacon frame. That is, a beacon frame transmitted by an NSTR Soft AP MLD on a primary link may need to set a neighbor AP TBTT offset subfield corresponding to an AP of a non-primary link to 254 and / or 255 using an RNR element. In this case, the neighbor AP TBTT offset subfield corresponding to the non-primary link may be present in a TBTT information field including an MLD parameters field in which the MLD ID subfield is set to 0.

[0157] Therefore, after receiving a beacon frame of an NSTR Soft AP MLD, if a non-AP STA MLD confirms that the TBTT information field in the specific neighbor AP information field of the RNR element included in the beacon frame has an MLD ID subfield of 0 and a TBTT offset subfield of 254 and / or 255, it can recognize that the specific neighbor AP information field is information about an AP (of the NSTR Soft AP MLD) operating on a non-primary link of the NSTR Soft AP MLD. Thus, if a non-AP STA MLD that has received a beacon frame of an NSTR Soft AP MLD confirms information about an AP MLD operating on a non-primary link of the NSTR AP MLD, it must not transmit a probe request frame or an ML probe request frame to the NSTR Soft AP MLD on a non-primary link.

[0158] Also, when the non-AP STA MLD recognizes that the received beacon frame is the beacon frame transmitted by the MLD, and the Neighbor AP TBTT Offset subfield corresponding to another AP of the same MLD as the AP (Reporting AP) that transmitted the beacon frame is indicated as 254 and / or 255, the non-AP STA MLD shall not transmit a probe request frame and an ML probe request frame to other APs.

[0159] Also, when the non-AP STA MLD recognizes that the received beacon frame is the beacon frame transmitted by the MLD, and the Neighbor AP TBTT Offset subfield corresponding to another AP of the same MLD as the AP (Reporting AP) that transmitted the beacon frame is indicated as 254 and / or 255, the non-AP STA MLD shall not transmit a probe request frame and an ML probe request frame to other APs.

[0160] <MLD AP TBTT Offset Indication>

[0161] In the above-described embodiment of the present invention, it was 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 with a preset value (254 and / or 255). However, the Neighbor AP TBTT Offset subfield may be indicated as 254 or 255 even when 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 grasped by the AP transmitting the beacon frame is 254 TU or more (254 TU or exceeding 254 TU), the AP can indicate the Neighbor AP TBTT Offset subfield corresponding to the other AP as 254 in the beacon frame. Also, when the AP transmitting the beacon frame cannot accurately grasp the TBTT offset of another AP, the AP can indicate the Neighbor AP TBTT Offset subfield corresponding to the other AP as 255.

[0162] However, since an AP in an MLD can always recognize the TBTT offset of other APs in the MLD, when using the RNR element to indicate (set) the neighbor AP TBTT offset subfield corresponding to another AP (in the same MLD), it must not indicate (set) it to 255.

[0163] Specifically, the Neighbor AP Information field included in the RNR element of the beacon frame may include a Neighbor AP TBTT Offset subfield indicating an offset between the times at which the beacon frames are transmitted. In this case, the Neighbor AP TBTT Offset subfield indicates an offset value between the time at which the beacon frame is transmitted and the time at which the next beacon frame is transmitted by the AP corresponding to the Neighbor AP TBTT Offset subfield among multiple APs included in the AP MLD (NSTR or STR AP MLD). In this case, the Neighbor AP TBTT Offset subfield cannot be set to a specific value under certain conditions.

[0164] For example, when the AP is included in the same AP MLD as the AP that transmitted the beacon frame, the neighbor AP TBTT offset subfield is not set to a specific value (e.g., "255"). In this case, the size of the neighbor AP TBTT offset subfield may be 8 bits, and in this case, the neighbor AP TBTT offset subfield is not set to the maximum value that can be indicated by the neighbor AP TBTT offset subfield (in the case of 8 bits, values ​​from 0 to 255 are respectively corresponding, and therefore the maximum offset that can be indicated by 8 bits may be 255). However, when the AP is not included in the same AP MLD as the AP that transmitted the beacon frame (for example, when the AP is a legacy AP), the neighbor AP TBTT offset subfield may be set to a specific value (e.g., "255").

[0165] In a similar embodiment, the neighbor AP TBTT offset subfield may be analyzed so that the set value varies depending on specific conditions.

[0166] For example, when the neighbor AP TBTT offset subfield is set to a specific value (eg, '254'), the set value may be analyzed to be different, such as '254' or greater than '254', depending on a specific condition.

[0167] Specifically, if the AP corresponding to the neighbor AP information field including the neighbor AP TBTT offset subfield is included in the same AP MLD as the AP that transmitted the beacon frame or in another MLD, and the neighbor AP TBTT offset subfield is set to a specific value (e.g., "254"), the station can interpret the value indicated by the neighbor AP TBTT offset subfield as 254 TUs. However, if the AP is not included in the same AP MLD as the AP that transmitted the beacon frame or in another MLD (e.g., if the AP is a legacy AP or an AP not included in the MLD), and the neighbor AP TBTT offset subfield is set to a specific value (e.g., "254"), the station can interpret the value indicated by the neighbor AP TBTT offset subfield as 254 TUs or more.

[0168] 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.

[0169] However, the neighbor AP TBTT offset subfield included in the conventional beacon frame is composed of one octet and is designed to be able to indicate only a TBTT offset corresponding to a maximum of 254TU. This may be a neighbor AP TBTT offset subfield design that compromises the overhead of the beacon frame and the information that can be indicated by excluding information support regarding cases where the AP has a TBTT offset of 254TU or more, considering the maximum TBTT offset that other APs can have ((2^16) or (2^16)-1TU when considering the configurable beacon interval).

[0170] However, when an AP MLD indicates information about other APs in the MLD using a beacon frame, it may include and transmit an additional MLD AP TBTT offset subfield to more accurately indicate the TBTT offset of the other AP. The MLD AP TBTT offset subfield may be included in the TBTT information field corresponding to other APs in the same MLD when the AP MLD transmits a beacon frame. In this case, if both the neighbor AP TBTT offset subfield and the MLD AP TBTT offset subfield are indicated in a specific TBTT information field, the neighbor AP TBTT offset subfield may be indicated with a preset value (which may be 254 or 255). The MLD AP TBTT offset subfield is a two-octet subfield and may be used to indicate the TBTT offset value when the TBTT offset between the AP (reporting AP) that transmitted the beacon frame and another AP (reported AP) in the same MLD exceeds 254TU. Furthermore, the MLD AP TBTT offset subfield may be included in the TBTT information field only when the TBTT offset of another AP in the same MLD exceeds 254 TU when the AP MLD transmits a beacon frame and the exact TBTT offset cannot be indicated in the existing neighbor AP TBTT offset subfield.

[0171] When the STA MLD checks a TBTT information field including an MLD AP TBTT offset subfield in an RNR element included in a beacon frame received from a specific AP, the STA can check the TBTT offset of the AP corresponding to the TBTT information field based on the value indicated in the MLD AP TBTT offset subfield. In this case, to determine whether the TBTT information field included in the beacon frame includes an MLD AP TBTT offset subfield, the STA may check based on the value of the TBTT information length subfield (located in the TBTT Information Header (sub) field of each neighbor AP information field) corresponding to each TBTT information field. That is, when the STA recognizes that the TBTT information field includes an MLD AP TBTT offset subfield based on the value of the TBTT Information Length subfield, the STA can check the TBTT offset of the AP corresponding to the TBTT information field based on the value indicated in the MLD AP TBTT offset subfield. In this case, when the MLD AP TBTT offset subfield of a specific TBTT information field indicates 0 or a preset value (or a value less than 254), the STA MLD can confirm the TBTT offset of the AP corresponding to the specific TBTT information field based on the value of the neighbor AP TBTT offset subfield.

[0172] FIG. 12 shows another example of a TBTT information field format according to an embodiment of the present invention.

[0173] 12, the TBTT information field may include an MLD AP TBTT offset subfield. The MLD AP TBTT offset subfield may be included only in beacon frames transmitted by APs of the AP MLD. Furthermore, the MLD AP TBTT offset subfield may be included only in TBTT information fields corresponding to other APs of the same MLD as the AP transmitting the beacon frame.

[0174] As an example, in a beacon frame transmitted by a specific AP in an AP MLD, to indicate that the TBTT offset of another AP in the same MLD is 300TU, the TBTT information field corresponding to the other AP may be used as a format including an MLD AP TBTT offset subfield. In this case, the neighboring AP TBTT offset subfield of the TBTT information field corresponding to the other AP may be indicated as 254 or 255, and the MLD AP TBTT offset subfield may be indicated as a value corresponding to 300TU (e.g., 300, 299, or (300-254)). In this case, the above-mentioned MLD AP TBTT offset subfield is a subfield name for illustrative purposes, and subfields with the same purpose may be defined with different names.

[0175] 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.

[0176] 13, the type of content included in the TBTT information field may be indicated by the TBTT information length subfield. The TBTT information length subfield may be a subfield included in a TBTT information header field present in a neighbor AP information field included in an RNR element. That is, the RNR element transmitted in a beacon frame may include multiple neighbor AP information fields, and the TBTT information fields included in each neighbor AP information field may have a structure including different amounts and types of content. In this case, since the TBTT information fields included in each neighbor AP information field may include different amounts and types of content, information regarding the content (and format) indicated by each TBTT information field is indicated by the TBTT information header field.

[0177] That is, the STA can parse each neighbor AP information field in the RNR element of the beacon frame received via the AP based on the information indicated in the TBTT information header. At this time, each parsed neighbor AP information field may indicate information about a neighbor AP or another AP of the same MLD. At this time, if the value of the TBTT information length subfield included in the TBTT information header field indicates a content configuration including an MLD AP TBTT offset subfield as shown in FIG. 13, the STA can determine the TBTT offset of the AP corresponding to the TBTT information field based on the value indicated in the MLD AP TBTT offset subfield.

[0178] Alternatively, a restriction may be applied that the AP MLD must manage the TBTT offset between the APs it operates so that it is not greater than 254 TU or not greater than 255 TU.

[0179] In this case, the AP MLD may need to adjust the beacon interval of the AP it operates on each link and / or the TBTT time (setting) of the BSS operated by each AP so that the TBTT time difference between APs belonging to the MLD does not exceed 254 TU or 255 TU. Here, the adjustment of the beacon interval and TBTT time is an example of a method for changing the TBTT interval of each AP in the MLD, and other implementations may be applied that adjust the TBTT offset so that it does not exceed a specific time value (254 TU or 255 TU). In addition, a method for the AP MLD to prevent the TBTT time difference between each AP it operates from exceeding a specific interval (254 TU or 255 TU) does not need to be defined separately.

[0180] In this way, when an AP MLD adjusts the TBTT time difference of each AP it operates to 254 TU or less or less than 255 TU, the neighbor AP TBTT offset subfield value transmitted to other APs in the same MLD in the RNR element transmitted by the specific AP in the beacon may indicate only a value of 253 or 254. Furthermore, when a specific AP MLD manages the TBTT time difference of the AP it operates to 254 or less or less than 255 TU, the neighbor AP TBTT offset subfield transmitted by a specific AP belonging to the specific AP MLD, and corresponding to other APs belonging to the same AP MLD (the specific AP MLD), may indicate (have) only a value of 254 or less.

[0181] As described above, when an AP MLD maintains the TBTT time difference between its APs at 254 TU or less or less than 255 TU, a non-AP STA may need to analyze the neighbor AP TBTT offset subfield of a beacon frame received from the AP of the AP MLD using a method different from the above-described analysis method. Here, the above-described analysis method may refer to an analysis method used when the value of the neighbor AP TBTT offset subfield is indicated as 254. That is, the above-described analysis method may analyze that the time interval between the previous TBTT of the Reporting AP and the next TBTT of the Reported AP (transmitted after the previous TBTT) is 254 TU or more when the value of the neighbor AP TBTT offset subfield is indicated as 254. Here, the other analysis method may analyze that the time interval between the previous TBTT of the Reporting AP and the next TBTT of the Reported AP (transmitted after the previous TBTT) is 254 TU or more but less than 255 TU when the value of the neighbor AP TBTT offset subfield is indicated as 254. Alternatively, another analysis method may be to analyze that when the value of the neighbor AP TBTT offset subfield is indicated as 254, the time interval between the previous TBTT of the Reporting AP and the next TBTT of the Reported AP (transmitted after the previous TBTT) is 254 TU.

[0182] This is because the TBTT time difference of each AP operated by AP MLD is adjusted by AP MLD to 254 TU or less or 255 TU or less, so the existing neighbor AP TBTT offset subfield has the meaning of "254 TU or more" and can be an analysis method that reflects the operating characteristics of AP MLD.

[0183] 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).

[0184] On the other hand, even when a non-AP STA receives a beacon frame from an AP with AP MLD, if the neighbor AP TBTT offset subfield included in the beacon frame that is not for an AP with the same AP MLD is indicated as 254, i.e., if the neighbor AP TBTT offset subfield for a legacy AP or an AP that is not MLD is indicated as 254, the non-AP STA must interpret this as indicating a TBTT offset of 254 TU or more.

[0185] In this case, the method by which the non-AP MLD distinguishes whether the specific neighbor AP TBTT offset subfield is for another AP of the same AP MLD may be based on information in the MLD Parameters subfield included in the same TBTT information field as the specific neighbor AP TBTT offset subfield. More specifically, if the MLD ID subfield value of the MLD Parameters subfield included in the same TBTT information field as the specific neighbor AP TBTT offset subfield is 0, the non-AP STA can interpret that the specific neighbor AP TBTT offset subfield is an AP of the same MLD as the AP that transmitted the beacon frame.

[0186] That is, when the neighbor AP TBTT offset subfield of the TBTT information field in which the MLD ID subfield value is 0 is indicated as 254, the non-AP STA can interpret that the neighbor AP TBTT offset subfield indicates a TBTT offset greater than or equal to 254 TU and less than 255 TU. In this case, the non-AP may further consider whether the beacon frame includes an ML element (whether the AP that transmitted the beacon frame is MLD) in order to analyze the neighbor AP TBTT offset subfield.

[0187] That is, if the MLD ID subfield value is not 0 (for example, 1 to 255) and the neighbor AP TBTT offset subfield of the TBTT information field is indicated as 254, the non-AP STA can interpret that the neighbor AP TBTT offset subfield indicates a TBTT offset of 254 TU or more.

[0188] <Non-primary link set-top and management>

[0189] As mentioned above, the NSTR AP MLD cannot transmit beacon frames, probe response frames, or ML (Multi-link) probe response frames on non-primary links. Therefore, a STA MLD that wishes to connect to the NSTR AP MLD must transmit ML probe request frames only on the link on which the NSTR AP MLD transmitted beacon frames.

[0190] The ML probe request frame transmitted by the STA of the EHT non-AP STA MLD may include EHT Capability information and a Multi-Link element in addition to the information included in the probe request frame transmitted by the conventional HE STA. In this case, the Multi-Link element included in the ML probe request frame can serve as a way for the MLD transmitting the ML probe request frame to request additional information about the AP of another link from the AP MLD.

[0191] For example, when transmitting an ML probe request frame, the non-AP STA MLD can request the AP MLD to further respond with complete or partial information about the APs of other links using the Multi-Link element of the ML probe request frame. That is, the non-AP STA MLD can request the AP MLD to transmit all or part of the parameters related to the links of other APs included in the same AP MLD to the AP receiving the ML probe request frame.

[0192] For example, if all or part of the parameters related to an AP connected via a non-primary link are updated, a station included in the non-AP STA MLD can request the AP connected via a primary link to transmit all or part of the updated parameters related to other APs of the non-primary link.

[0193] In this case, the complete information request / response means that the AP of the other link (Reported AP) is requested / responded to with the same level of information as the AP (Reporting AP) that responds with the ML probe response frame, and the partial information request / response means that only the information on the AP of the other link requested by the STA is responded to.

[0194] If the AP MLD that sent the beacon frame requests additional information about the AP of another link in the ML probe request frame received on a specific link, it can respond using an ML probe response frame to not only provide information about the AP of the specific link, but also the requested additional information about the AP of the other link.

[0195] In this case, when the STA MLD requests complete information about the AP of another link by transmitting an ML probe request frame on a specific link, the AP MLD must provide information about the AP of the other link at the same level as the information about the AP of the specific link using an ML probe response frame that responds on the specific link. In other words, the STA MLD that receives complete information about the AP of another link on a specific link can obtain the same level of information about the AP of the other link as when it directly receives an ML probe response from the AP of the other link.

[0196] In this case, if the STA MLD transmits an ML probe request frame over a specific link and requests partial information about the AP of another link, the AP MLD can provide only the requested information (requested element information) among the information about the AP of the other link using an ML probe response frame that responds over the specific link. In other words, the STA MLD that receives partial information about the AP of another link over a specific link can further obtain only the information it requested from the AP of the other link. In this case, the STA MLD that requests partial information about the AP of the other link can transmit an ML probe request frame including information indicating further information to be obtained (which may be indicated by the Requested element IDs field) together with the link ID corresponding to the other link. Therefore, if the ML probe request frame received over a specific link includes information indicating information about the other link (Request element IDs field), the AP MLD can further indicate the indicated information about the other link in the ML probe response frame.

[0197] In this case, when the STA MLD transmits an ML probe request frame on a specific link, it can set the Complete Profile subfield (in the Per-STA Control field included in the Multi-Link element) corresponding to the other link to 0 or 1 to indicate whether it requests complete information or partial information for the other link.

[0198] In this case, the additional information (Complete and Partial) for the other APs may be transmitted by a Per-STA profile included in the Multi-link element of the ML probe response frame. The Per-STA profile is a field that may be included zero or more times in the Multi-link element and may include information on other STAs (APs and non-AP STAs) that exist in the same MLD as the STA (AP and non-AP STA) that transmits the frame including the Multi-Link element. In this case, the Per-STA profile includes 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 the other STAs (APs and non-AP STAs) corresponding to (corresponding to) the Per-STA profile whose Complete Profile subfield is indicated as 1 can be obtained from the Per-STA profile. However, parameters / elements that mean the same information as the STA (AP and non-AP) that transmitted the Per-STA profile may be omitted according to inheritance rules. The inheritance rule may mean that if a parameter or element is not specified, the value of the same parameter or element (specified for other STAs (AP and non-AP)) that has already been specified is inherited and utilized to prevent repeated specification of the same parameter or element. That is, if a value of parameter1 is specified for STA1 and a value of parameter1 is not specified for STA2, the inheritance rule may interpret the value of parameter1 for STA2 as being the same as the value of parameter1 for STA1.

[0199] In this case, the Per-STA Profile subelement included in the Multi-link element transmitted by the NSTR AP MLD may not include a Beacon Interval subfield for indicating the interval at which beacons are transmitted. That is, when the NSTR AP MLD indicates a Per-STA Profile subelement corresponding to an AP of a non-primary link in the Multi-link element, the Beacon Interval Present subfield must be set to 0. This may be because an AP operating on a non-primary link of the NSTR AP MLD does not transmit beacon frames, and therefore there is no separate beacon frame period. That is, even if the Complete Profile subfield (in the Per-STA Control field) of the Per-STA Profile subelement (of the Probe Response and Association Response frames) corresponding to an AP of a non-primary link of the NSTR AP MLD is set to 1, the Beacon Interval Present subfield may be set to 0. That is, beacon interval information for the AP of a non-primary link is not present even when complete information is indicated.

[0200] 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 Per-STA profile corresponding to a non-primary link AP in the NSTR AP MLD may have a Complete Profile subfield (in the Per-STA Control field) indicated as 1, but a DTIM Info Present subfield indicated as 0.

[0201] That is, because beacons are not transmitted on non-primary links, even when a non-AP STA MLD requests all information (or all updated information) for other APs on non-primary links through the AP on the primary link of the AP MLD (i.e., when complete information is set to '1'), the beacon interval and DTIM information for the AP on 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 Per-STA profile subelement for the AP on the non-primary link included in the ML probe response frame.

[0202] In this case, even if all information (or all updated information) for other APs on non-primary links is requested, the AP MLD does not need to include the beacon interval and DTIM information for the APs on non-primary links in the ML probe response frame. Therefore, in this case, the AP MLD can transmit the beacon interval present subfield and the DTIM information present subfield set to a value (e.g., "0") indicating that the respective fields are not included.

[0203] Because the NSTR AP MLD does not transmit beacon frames to non-primary links, it does not need to indicate DTIM information and beacon interval information when indicating information about the AP of the non-primary link. That is, the NSTR AP MLD may need to always indicate 0 for the DTIM information present subfield in the Per-STA profile (more precisely, the STA Control field) corresponding to the AP of the non-primary link. That is, the NSTR AP MLD may need to always indicate 0 for the Beacon Interval Present subfield in the Per-STA profile corresponding to the AP of the non-primary link. Therefore, even when the NSTR AP MLD receives an ML probe request frame requesting complete information or an (ML)(Re) association request frame from a non-AP STA MLD, the NSTR AP MLD may need to always indicate 0 for the Beacon Interval Present subfield and the DTIM information present subfield in the Per-STA profile corresponding to the AP of the non-primary link.

[0204] Alternatively, since beacon frames are not transmitted to non-primary links, the NSTR AP MLD may need to set the Beacon Interval, DTIM Count, and DTIM Interval subfields in the Per-STA profile corresponding to the AP of the non-primary link to predetermined values. This may be an operation considered to maintain the same Per-STA profile configuration as a general AP MLD (e.g., STR AP MLD) when the NSTR AP MLD transmits (responds to) complete information for the AP of the non-primary link. That is, the STA MLD requests complete information for a specific link from the AP MLD using an ML probe request frame, and then the complete information for the AP of the specific link is expected to be returned in the response frame. In this case, if the complete information responded by the NSTR AP MLD has a different Per-STA profile configuration from the complete information responded by the STR AP MLD, the implementation complexity of the process by which the STA MLD obtains information according to the Per-STA profile may increase. Therefore, even if the AP of the non-primary link does not transmit a beacon frame, the NSTR AP MLD can use a Per-STA profile with the same configuration as the Per-STA profile used by the general AP MLD when responding with complete information for the non-primary link when responding with complete information. In this case, the Per-STA profile of the NSTR AP MLD corresponding to the AP of the non-primary link may have the Beacon Interval subfield, DTIM Count subfield, and DTIM Interval subfield set to predetermined values, respectively. For example, when transmitting complete information to the AP of the non-primary link, the NSTR AP MLD can set each bit of the Beacon Interval subfield of the non-primary link to all 0s, all 1s, or a predetermined method.For example, when the NSTR AP MLD transmits complete information for the AP of a non-primary link, it can set each bit of the DTIM Count subfield of the non-primary link to all 0s, all 1s, or a predetermined manner. For example, when the NSTR AP MLD transmits complete information for the AP of a 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.

[0205] Alternatively, because beacon frames are not transmitted on the non-primary link, the NSTR AP MLD may set the Beacon Interval, DTIM Count, and DTIM Interval subfields in the Per-STA profile corresponding to the AP of the non-primary link to values ​​associated with the beacon frame of the primary link. This may be considered to maintain the same Per-STA profile configuration, as described above. In this case, the Beacon Interval subfield, DTIM Count subfield, and DTIM Interval subfield in the Per-STA 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. For example, when transmitting complete information for the AP of the non-primary link, the NSTR AP MLD may set the Beacon Interval subfield of the non-primary link to a value indicating (meaning) the beacon interval of the primary link. For example, when transmitting complete information for the AP of the non-primary link, the NSTR AP MLD may set the DTIM Count subfield of the non-primary link to the DTIM Count value of the primary link. For example, when the NSTR AP MLD transmits complete information for the AP on the non-primary link, it can set the DTIM Interval subfield of the non-primary link to a value indicating the DTIM interval of the primary link.

[0206] Alternatively, because beacon frames are not transmitted to non-primary links, the NSTR AP MLD can set the Beacon Interval, DTIM Count, and DTIM Interval subfields of the Per-STA profile corresponding to the AP of the non-primary link to values ​​with specific purposes. Furthermore, the Beacon Interval subfield of the non-primary link may be set by the AP MLD to a value with specific purposes (a virtual beacon interval), for example, a value for calculation. Conventionally, the Wi-Fi beacon interval literally means a value related to the time interval between beacon frame transmissions, but is also used as a time unit for the operation of various BSSs. For example, the unit of a JointFailureTimeout primitive, a QueryFailureTimeout primitive, etc. is defined as a beacon interval, and the Listen Interval field, the PRAW Start Offset subfield, the AID Request Interval field, the AID Switch Count field, the AID Response Interval field, the Minimum Transmission Interval subfield, the Channel Quality Measurement Duration, the Color Switch Countdown (of the BSS Color Change Announcement element) subfield, etc. indicate their interval / duration using the beacon interval (or TBTT) as a basic unit. As such, the beacon interval has the meaning of a value related to the interval at which beacon frames are actually transmitted, and is also a value used as a unit in various primitives and fields. Therefore, even if beacon frames are not actually transmitted over non-primary links, the beacon interval for non-primary links may need to be defined (indicated, set) to be used as a unit in the above-mentioned primitives / subfields.

[0207] That is, even if a beacon frame is not transmitted over the non-primary link, the NSTR AP MLD can indicate the Beacon Interval subfield of the Per-STA profile corresponding to the AP of the non-primary link as the beacon interval value to be used as the time unit of the non-primary link. In this case, the non-AP MLD can recognize (check and calculate) the duration and interval of the above-mentioned primitives and fields (used as the beacon interval unit) based on the value indicated in the Beacon Interval subfield of the Per-STA profile corresponding to the AP of the non-primary link. In this case, the DTIM Interval subfield and DTIM Count subfield of the Per-STA profile corresponding to the AP of the non-primary link may also be set according to the BSS operation purpose of the AP MLD, and the non-AP MLD operating the STA over the non-primary link may need to operate based on the set values ​​when operating the STA over the non-primary link.

[0208] Meanwhile, the method of setting subfields (Beacon Interval, DTIM Count, DTIM Interval, etc.) related to non-primary link beacons of the NSTR AP MLD described above may be equally applied to other frames and subfields (transmitted on the primary link or non-primary link) containing information related to non-primary link beacons, as well as the Per-STA profile transmitted on the primary link.

[0209] In addition, a non-AP STA MLD attempting to associate with an NSTR AP MLD may need to use the beacon interval of the primary link of the NSTR AP MLD as the unit of the Listen Interval field transmitted while requesting setup for the primary link and non-primary links. That is, a non-AP STA MLD transmitting a Listen Interval field to an NSTR AP MLD must calculate and set the unit of the Listen Interval field as the beacon interval of the AP operating on the primary link of the NSTR AP MLD. In this case, the Listen Interval field may indicate information related to the period (time) at which at least one STA transitions to a wake state in order for the non-AP STA MLD performing multi-link (re)association to receive beacon frames. In this case, the Listen Interval field may indicate a value derived when the ListenInterval parameter is indicated in the MLME primitive.

[0210] In this case, when a non-AP STA MLD transmits a Listen interval field to another AP MLD (e.g., an STR AP MLD) other than the NSTR AP MLD, it may need to set the unit of the Listen interval field to the maximum value of the beacon interval of the link (AP) on which it intends to perform set-top. For example, when a non-AP STA MLD attempts to perform multi-link setup with the AP MLD and link 1 or link 2, the non-AP STA MLD may set the unit of the Listen interval field included in the ML association request frame to the larger of the beacon interval of link 1 (AP) and the beacon interval of link 2. That is, if the beacon interval of link 1 is 100 ms and the beacon interval of link 2 is 50 ms, the unit of the Listen interval subfield transmitted by the non-AP STA MLD may be in 100 ms units.

[0211] Generally, when an AP and a STA complete setup, the STA can learn and track (update) the AP's operating parameters and element changes by receiving a beacon frame transmitted by the AP. The beacon frame also provides information, including a timestamp field, for STAs within the BSS to synchronize their time.

[0212] However, since the NSTR AP MLD does not transmit beacon frames on non-primary links as mentioned above, the STA MLD set up with the NSTR AP MLD may need to perform separate operations to track (update) parameters / elements and maintain time synchronization for the non-primary links.

[0213] According to one embodiment of the present invention, a non-AP STA MLD combined with an NSTR AP MLD can check the change sequence (in the MLD parameter field of the RNR element) of the non-primary link after receiving a beacon frame over the primary link and transmit an ML Probe Request. In this case, the ML Probe Request frame transmitted by the non-AP STA MLD may be transmitted for the purpose of requesting changed parameter and element information of the non-primary link. In this case, the ML Probe Request frame may request complete information of the non-primary link by setting the complete profile of the Per-STA profile corresponding to the non-primary link (and the AP of the non-primary link) to 1. Alternatively, the ML Probe Request frame transmitted by the STA MLD for the purpose of updating parameters / elements of the non-primary link may request updated information, not complete / partial information, for the non-primary link.

[0214] In other words, even if multiple links are formed between the non-AP STA MLD and the AP MLD, frames for performing association, reassociation, and / or parameter update procedures may be transmitted only on the primary link. For example, if the STA recognizes that parameters for the AP of a non-primary link have been updated from a specific field (e.g., a change sequence or a BSS parameter change count subfield, etc.) that indicates whether the parameter update is for a link of another AP included in the neighbor AP information included in the beacon frame, the non-AP STA MLD can request transmission of the updated parameters on a primary link other than the non-primary link of the other AP. In other words, the non-AP MLD cannot transmit frames (e.g., probe request frames) for requesting updated parameters on a non-primary link.

[0215] As an example, after setting up with the NSTR AP MLD, the non-AP STA MLD requesting 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 Per-STA profile corresponding to the non-primary link to 1 in the ML Probe Request frame transmitted over the primary link. If the Updated Profile subfield is set to 1 in the Per-STA 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.

[0216] In this case, the Per-STA 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.

[0217] For example, the NSTR AP MLD may change Parameter 1 while increasing the Change Sequence number of the non-primary link from 100 to 101, and then change Parameter 2 while increasing the Change Sequence number from 101 to 102. In this case, the STA MLD can request updated information for the non-primary link by transmitting an ML probe request frame. In this case, if the non-AP STA MLD specifies the Recorded Change Sequence subfield as 100, the NSTR AP MLD can respond with an ML probe response frame that includes both Parameter 1 and Parameter 2, and if the non-AP STA MLD specifies the Recorded Change Sequence subfield as 101, the NSTR AP MLD can respond with an ML probe response frame that includes only Parameter 2.

[0218] In this case, the Non-AP STA MLD does not use a separate Updated Profile subfield to request an Updated Profile, but can indicate the Complete Profile subfield as 0. That is, the way in which the Non-AP STA MLD requests an Updated Profile is to set the Complete Profile subfield to 0, and in this case, a separate Updated Profile subfield may not be included in the Per-STA profile.

[0219] FIG. 14 illustrates an example of a format of a Per-STA Profile subelement according to an embodiment of the present invention.

[0220] Referring to FIG. 14(a), a Per-STA profile sub-element may include a STA Control field. The STA Control field (see FIG. 14(b)) indicates information for indicating the type of fields included in the STA profile (see FIG. 14(a)) of the Per-STA profile sub-element. In this case, in a specific Per-STA profile sub-element transmitted by an AP MLD other than the NSTR AP MLD, if the Complete Profile sub-field of the STA Control field is indicated as 1, the MAC Address Present sub-field, Beacon Interval Present sub-field, and 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 beacon frames to non-primary links, information related to beacon frames of non-primary links may not need to be indicated in the Per-STA profile sub-elements corresponding to non-primary links. That is, a specific Per-STA profile sub-element (corresponding to an AP of a non-primary link) transmitted by the NSTR AP MLD may have the Complete Profile sub-field indicated as 1, but the Beacon Interval Present sub-field and the DTIM Information Present sub-field indicated as 0.

[0221] Also, as described in the above embodiment, a non-AP STA MLD transmitting an ML probe request frame to an NSTR AP MLD can request updated information of the non-primary link AP from the primary link AP by specifying 1 in the Updated Profile subfield of the STA Control field (included in the Per-STA Profile subelement corresponding to the non-primary link AP). In this case, the non-AP STA MLD can specify a Recorded Change Sequence value, which is information related to the time when the non-AP STA MLD updated the non-primary link AP information, using the Recorded Change Sequence subfield (see FIG. 14(c)). In this case, the Recorded Change Sequence subfield may be a subfield included in the STA profile. After receiving an ML probe request frame of the non-AP STA MLD received via the primary link, the NSTR AP MLD can determine information of the non-primary link AP responding to the non-AP STA MLD by comparing the value of the Recorded Change Sequence subfield included in the ML probe request frame with the Change Sequence value of the current non-primary link AP.

[0222] FIG. 15 illustrates an example of a process in which a non-AP MLD set up with a Non-Simultaneous Transmission and Reception (NSTR) Soft AP MLD updates information about a non-primary link according to an embodiment of the present invention.

[0223] 15, after changing the parameters of AP2 operating on Link 2, which is a non-primary link, the NSTR AP MLD may indicate that the parameters of AP2 have been changed using a beacon frame transmitted by AP1 operating on Link 1, which is a primary link. In this case, the information that the parameters of AP2 have been changed may be indicated by indicating that the Change Sequence subfield value corresponding to AP2 in the RNR element included in the beacon frame transmitted by AP1 is increased by 1 from the value indicated in the immediately preceding beacon frame.

[0224] After receiving the beacon frame sent by AP1 through STA1, the non-AP STA MLD can recognize that the parameters of AP2 have been updated. The non-AP STA MLD can send an ML probe request frame through STA1 to obtain the changed parameter information of AP2.

[0225] The ML probe request frame transmitted by the non-AP STA MLD via STA1 may have a configuration in which a Per-STA profile sub-element corresponding to AP2 is included in the ML element, and the Per-STA profile sub-element may include an indicator indicating whether a complete profile or an updated profile is requested.

[0226] After receiving an ML probe request frame from STA1 on the primary link, the NSTR AP MLD can respond to STA1 by including the requested AP2 information (complete or updated information) in an ML probe response frame.

[0227] The non-AP STA MLD receives the requested AP2 information in an ML probe response frame from the NSTR AP MLD, and can complete the parameter update for the non-primary link to which the beacon frame is not transmitted by updating the parameters for AP2.

[0228] <Broadcast ML Probe Response>

[0229] According to one embodiment of the present invention, the NSTR AP MLD may transmit a broadcast ML probe response frame over the primary link when information related to an AP operating over a non-primary link is changed. When the non-AP STA MLD receives a broadcast ML probe response frame transmitted by the NSTR AP MLD over the primary link, it may need to update information related to the non-primary link (AP). In this case, the broadcast ML probe response frame may not be transmitted in response to an ML probe request frame transmitted by a specific STA, but may be an ML probe request frame transmitted by the NSTR AP MLD without a separate request.

[0230] The broadcast ML probe response frame includes a Per-STA profile subelement corresponding to the AP of the non-primary link and serves to help the non-AP STA MLD update changed parameters and elements of the non-primary link. Since the (Recorded) Change Sequence of the non-primary link maintained by each non-AP STA may be different from each other, the broadcast ML probe response frame may include complete information for the AP of the non-primary link. In this case, the broadcast ML probe response frame may be transmitted together with a DTIM beacon frame.

[0231] 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).

[0232] In this case, the parameter update procedure for the non-primary link using the above-mentioned broadcast ML probe response frame may be performed using a broadcast ML association response frame. In this case, the method of configuring the Per-STA 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.

[0233] 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.

[0234] After receiving a beacon frame over the primary link, the non-AP STA MLD checks the non-primary link Change Sequence (in the MLD Parameter field of the RNR element). If the checked non-primary link Change Sequence value differs from the Change Sequence value it maintains (recorded), the non-AP STA MLD can transmit an ML probe request frame over the primary link. In this case, the ML probe request frame may include a subfield indicating whether to request complete information or updated information from the AP of the non-primary link. In addition, an ML probe request frame requesting updated information may also include a subfield indicating the Change Sequence value it maintains (recorded). Thereafter, the non-AP STA MLD that receives an ML probe response frame from the AP MLD updates its parameters based on the non-primary link AP information included in the received ML probe response frame.

[0235] <Time synchronization management for non-primary links>

[0236] As mentioned above, the beacon frame transmitted by the AP not only conveys various parameters and element information but also helps STAs in the BSS to achieve time synchronization. The TimeStamp field included in the beacon frame indicates the timing synchronization function (TSF) timer value at the time when the data symbol containing the first bit of the TimeStamp field appears at the transmit antenna connector. STAs that receive the TimeStamp field can synchronize their own TSF timer with the AP based on the received TimeStamp field value.

[0237] In this way, the AP and STA can operate while maintaining time synchronization based on the TimeStamp value included in the beacon frame, and perform timing-based operations. However, NSTR AP MLD cannot transmit beacon frames on non-primary links, so among STAs in Non-AP STA MLD, STAs associated with a non-primary link AP in NSTR AP MLD must use a method other than beacon frames to maintain time synchronization with the AP.

[0238] To maintain time synchronization with the AP of the non-primary link of the NSTR AP MLD, associated non-AP STAs may need to use the TimeStamp in the TIM frame transmitted by the AP. Because the TIM frame includes a TimeStamp field with the same function as a beacon frame, STAs receiving a TIM frame from an AP of the non-primary link of the NSTR AP MLD may need to manage the TFS timer using the TimeStamp field included in the TIM frame. However, because the NSTR AP MLD may be restricted from starting transmission on a non-primary link without occupying the primary link, it may be necessary to simultaneously transmit a TIM frame on the non-primary link when transmitting a beacon frame on the primary link. In other words, non-AP STA MLDs associated with the NSTR AP MLD may need to prepare to receive TIM frames on the non-primary link in accordance with the TBTT of the primary link.

[0239] In yet another embodiment of the present invention, when the AP MLD is an NSTR AP MLD that does not support simultaneous transmission and reception, the same TSF timer may be used in each link for multiple APs included in the NSTR AP MLD, and the TSF timer used at this time may be the TSF timer of the primary link. That is, when the AP MLD is an NSTR AP MLD, links (non-primary links) for APs affiliated with the NSTR AP MLD can use the TSF timer of the primary link.

[0240] That is, the non-AP STA MLD combined with the NSTR Soft AP MLD may need to share the TSF timer of the primary link with the non-primary link. In other words, the non-AP STA MLD combined with the NSTR AP MLD does not have a separate TSF timer for the non-primary link (based on the NSTR Soft AP MLD) but can use the TSF timer managed using the primary link. That is, in one aspect of the present invention, the NSTR AP MLD and the non-AP STA MLD combined with the NSTR AP MLD can use an MLD-level (MLD unit, MLD common) timer. In this case, for stable operation of the NSTR AP MLD and the non-AP STA MLD combined with the NSTR AP MLD, it may be required that time synchronization between APs in the NSTR AP MLD and / or between STAs in the non-AP STA MLD combined with the NSTR AP MLD be maintained with an error below a predetermined value. For example, NSTR AP MLD may be required to maintain the timestamp difference (or the difference between timers) maintained between the AP of the primary link and the AP of the non-primary link at or below a predetermined value. For example, non-AP STA MLD combined with NSTR Soft AP MLD may be required to maintain the timestamp difference maintained between the STA of the primary link and the STA of the non-primary link at or below a predetermined value.

[0241] In other words, the TSF timer of the primary link may be maintained (or applied or used) the same for all links for APs included in or affiliated with the NSTR AP MLD. Also, the difference between the timestamp or TSF timer of any two APs included in or affiliated with the NSTR AP MLD may be limited to within a specific value (e.g., 30 us).

[0242] That is, the TSF timers of all APs included in or affiliated with the NSTR AP MLD may be the same, and the difference or clock drift between timestamps or TSF timers between two APs included in or affiliated with the AP MLD or NSTR AP MLD (e.g., an AP of a primary link and an AP of a non-primary link) may be limited to within a specific value (e.g., ±30 us), in which case the AP MLD or NSTR AP MLD can correct the timestamps or TSF timers so that the difference or clock drift between the TSF timers is within the specific value.

[0243] In addition, when a non-AP STA MLD combined with an NSTR AP MLD receives a TIM frame over a non-primary link, it may need to receive the next beacon frame transmitted over the primary link. More specifically, when a non-AP STA MLD receives a TIM frame through a non-primary link STA and the value indicated in the Check Beacon field in the TIM frame action field is different from the Check Beacon value it maintains, it may need to receive the next beacon frame transmitted over the primary link. In this case, the next beacon frame may refer to a beacon frame transmitted corresponding to the TBTT of the primary link that exists after the time the TIM frame was received over the non-primary link. In this case, receiving the next beacon frame may involve (include) updating parameters of the non-primary link using the Per-STA 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 associated with a critical update.

[0244] <Channel Switching and Channel Quieting Procedures for Non-Primary Links>

[0245] As described above, NSTR AP MLD does not transmit beacon frames on non-primary links, and therefore, the BSS operation based on the beacon frame transmission timing may be performed in a manner different from the BSS operation of general AP MLD.

[0246] Conventional Wi-Fi can change the operating channel frequency (operating frequency band) of a BSS through a procedure previously agreed upon between the AP and STA. This can be achieved using the conventional Extended Channel Switching (ECS) operation or the newly defined channel change mechanism in 11be. When an AP decides to change the operating channel of a BSS, it transmits a beacon frame, a probe response frame, an Extended Channel Switch Announcement frame, etc. to inform associated STAs that they can switch to a new channel and operating class while maintaining their association. In this case, the AP transmits an Extended Channel Switch Announce element in a beacon frame, and the Channel Switch Count field of the element indicates information about the number of subsequent beacon frame transmissions required before a channel switch (operating channel change) occurs. If the AP includes a MAX Channel Switch Time element in a beacon frame along with an Extended Channel Switch Announcement element, the AP must transmit the first beacon frame on the new channel within the Switch Time field (of the Max Channel Switch Time element). That is, the beacon frame transmitted on the new channel must be transmitted at a time interval smaller than the time interval indicated by the Switch Time field from the last beacon frame transmitted on the current channel.

[0247] Referring to the channel change operation of the conventional Wi-Fi BSS described above, the AP of the BSS can use a beacon frame transmitted on the current channel to indicate to the STA information about the new channel, information about the time when the channel change will occur, and information related to the time of the first beacon frame transmitted on the new channel. The STA of the BSS can complete the channel change while maintaining association with the AP by moving to the new channel during a predetermined time interval (the time interval indicated by the AP) based on the channel change-related information included in the beacon frame transmitted by the AP. As such, the channel change procedure of the conventional Wi-Fi BSS is performed in a manner in which information required for the channel change (e.g., channel switch mode, new operating class, new channel number, channel switch count) is provided by the beacon frame transmitted by the AP. Therefore, in the case of a BSS of a non-primary link of an NSTR AP MLD in which beacon frames are not transmitted, a channel change cannot be performed using the conventional channel change procedure.

[0248] In addition, when conventional Wi-Fi sets a quiet interval, information regarding the time period to which the quiet interval applies is indicated by elements (quiet element, quiet channel element) included in the beacon frame transmitted by the AP of the BSS, and similar to the channel change procedure, the non-primary link of the NSTR AP MLD, which does not transmit a beacon frame, cannot use the conventional quieting procedure to set the quiet interval.

[0249] According to one embodiment of the present invention, the NSTR AP MLD can indicate information required for changing the operating channel of the non-primary link (channel switching) and / or information required for setting the quiet interval through a beacon frame transmitted through the primary link. That is, the non-AP STA MLD associated with the NSTR AP MLD can operate based on information obtained through a beacon frame of the primary link to perform channel switching of the non-primary link. That is, the non-AP STA MLD associated with the NSTR AP MLD can obtain information related to the quiet interval of the non-primary link using a beacon frame of the primary link.

[0250] That is, in the STR AP MLD, APs included in the same AP MLD can periodically transmit beacon frames. In this case, these APs can include basic information about other APs in the beacon frames they transmit, and the basic information about other APs can include information related to channel changes of other APs (e.g., channel switch announcement element, extended channel switch announcement element, max channel switch element) and / or information for setting a quiet interval.

[0251] In this case, the channel switch guide element and the extended channel switch guide element may include a new channel number field indicating the number of the channel to be changed and a channel switch count field.

[0252] The Channel Switch Count field indicates the number of TBTTs until the STA that transmitted the Channel Switch Count field switches to a new channel. If the value of the Channel Switch Count field is set to '1', a channel switch occurs at the next TBTT. If the value of the Channel Switch Count field is set to '0', a channel switch may occur any time after the Channel Switch Count field is transmitted.

[0253] 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.

[0254] If the operating class is also changed, the station can send an extended channel switch guide element with a new operating class field indicating the changed operating class.

[0255] The maximum channel switch time element may indicate a period during which a beacon may be transmitted on a changed channel from the time when channel switching begins. For example, if a channel change is successful, a station (e.g., an AP STA) that performed the channel change may transmit a beacon on the new changed channel within the time indicated by the maximum channel switch time element from the time when channel switching began.

[0256] 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.

[0257] Such 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, in APs that support NSTR, the APs included in the same AP MLD can transmit beacon frames only via the primary link. That is, among multiple APs included in the same AP MLD, only a specific AP can transmit beacons via 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 channel change information of the AP for the non-primary link by including it in a beacon frame.

[0258] More specifically, the NSTR AP MLD may need to include a Per-STA profile for the non-primary link AP in the primary link beacon frame (and (ML) probe response frame) when changing channels or setting a quiet interval for the non-primary link.

[0259] Figure 17 shows an example of the format of elements according to an embodiment of the present invention. Figure 17 shows an example of the format of each element described above.

[0260] Referring to FIG. 17, the (corresponding) Per-STA profile for a non-primary link AP 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.

[0261] The timing field of the element may need to be set based on the target beacon transmission time (TBTT) and beacon interval of the primary link.

[0262] 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 that performs the channel change rather than the AP that transmits the channel change information.

[0263] However, in AP MLD supporting NSTR (NSTR AP MLD), only the AP for the primary link transmits beacon frames, and the AP for the non-primary link does not transmit beacon frames, so the channel change information and / or information regarding the quiet interval of the AP for the non-primary link may be set based on the AP for the primary link rather than the AP for the non-primary link.

[0264] Specifically, an AP configuring AP MLD may transmit a Per-STA Profile including channel change information and / or quiet interval-related information for non-primary link APs via a specific frame (e.g., a beacon frame) over a primary link. In this case, the channel change information and / or quiet interval-related information for non-primary link APs may be set based on the primary link AP.

[0265] 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 must be applied by referring to the most recent TBTT and BI indicated in the corresponding element of the AP operating on the primary link.

[0266] The AP of the primary link of the NSTR AP MLD may need to 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 Per-STA profile (included in the beacon frame and (ML) probe response frame) for the AP of the non-primary link based on its own beacon interval and TBTT. Here, the timing fields are used to collectively refer to time-related fields including duration-related fields (e.g., Switch Time, Quiet Duration fields) and time-point-related fields (e.g., Channel Switch Count, Quiet Count fields).

[0267] Therefore, the non-AP MLD combined with the NSTR AP MLD may receive a beacon frame from the AP of the NSTR AP MLD operating on the primary link, acquire information related to a channel change and / or a quiet interval of the non-primary link from the Per-STA profile included in the beacon frame, and then analyze the information related to a channel change and / or a quiet interval of the non-primary link based on the TBTT and Beacon interval (BI) of the primary link. Here, the Per-STA profile refers to a Per-STA profile corresponding to the AP of the non-primary link.

[0268] Meanwhile, after completing a channel change of a non-primary link using a beacon frame of the primary link (after announcement and completion of the channel change), the NSTR AP MLD may need to 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). That is, after performing a channel change, the non-primary link AP of the NSTR AP MLD may need to transmit a TIM frame on a new channel. In this case, the non-primary link AP may need to 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 set to 1 (or 0) is transmitted on the primary link. In this case, the Channel Switch Count field and the Switch Time field may be included in a Per-STA profile (corresponding to a non-primary AP) included in a beacon frame transmitted on the primary link. In this case, the TIM frame may be replaced with another frame transmitted on a new channel of the primary link or non-primary link. For example, after completing a channel change for a non-primary link, the NSTR AP MLD may transmit a beacon frame indicating information related to the completion of the channel change for the primary link. In this case, the beacon frame may be an additional beacon frame transmitted regardless of the TBTT. In this case, the beacon frame may be a beacon frame configured to include complete information for the non-primary link. For example, the beacon frame configured to include complete information for the non-primary link may be a beacon frame in which the complete information subfield of the Per-STA profile corresponding to the AP of the non-primary link is set to 1.In this case, the primary link beacon frame transmitted after the channel change of the non-primary link is completed may need to be transmitted within a predetermined time from the beacon frame transmitted before the channel change began. In this case, the predetermined time may be the time indicated in the Switch Time field (of the Max Channel Switch Time element). Alternatively, the beacon frame may be a beacon frame including an indication related to the channel change of the non-primary link. For example, the primary link beacon frame transmitted after the channel change of the non-primary link is completed may include a Channel Switch Complete subfield. In this case, the Channel Switch Complete subfield may be a subfield included in the ML element. A specific Switch Complete subfield may be indicated as 1 when the channel change of the AP corresponding to the Per-STA profile including the specific subfield is completed. That is, after completing the channel change of the non-primary link, the AP may need to set the Channel Switch Complete subfield of the Per-STA profile (of the beacon frame) corresponding to the non-primary link AP to 1. In this case, the beacon frame related to the channel change may be transmitted (utilized) for the same purpose even if the AP MLD is not the NSTR AP MLD, that is, by the general AP MLD.

[0269] The non-AP MLD combined with the NSTR AP MLD can perform operations that consider the channel switching of the non-primary link to be complete only when it receives a frame (a TIM frame for the non-primary link, or other frames and / or a beacon frame indicating information related to the completion of the channel switching of the primary link) promised from the AP MLD after performing channel switching of the non-primary link on the primary link. That is, information about the channel switch for the AP of the non-primary link included in the AP MLD supporting NSTR (e.g., channel change information) may be transmitted by the AP of the primary link. In this case, even after the channel switch is completed, the AP of the non-primary link cannot transmit a beacon frame on the changed channel because it is not the primary link. Therefore, in this case, the AP of the non-primary link can notify stations of the channel switch completion by transmitting a TIM frame indicating the completion of the channel switch when the channel switch is completed. Alternatively, the AP of the primary link can send a beacon frame indicating that the channel switch to the AP of the non-primary link has been completed, thereby informing the non-AP MLD station that the channel switch has been completed.

[0270] If it is determined that the channel switching is not complete, the non-AP STA MLD may need to consider the channel switching of the non-primary link to be canceled and operate (return to) the previous channel (before the channel switching took place).

[0271] Alternatively, the NSTR Soft AP MLD may set a specific subfield of a beacon frame transmitted on the primary link while a non-primary link AP (the AP's BSS) 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 time periods when the non-primary link AP is not performing channel switching. That is, the NSTR Soft AP MLD may need to 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 Per-STA profile.

[0272] As described above, if the NSTR Soft AP MLD determines the value of the subfield based on whether a non-primary link AP is performing channel switching, a non-AP MLD associated with the NSTR Soft AP MLD can determine whether a non-primary link AP (BSS) is performing channel switching based on the value of the subfield indicated in a beacon frame received over the primary link. That is, the non-AP MLD can determine that a non-primary link AP is performing channel switching by confirming that the subfield corresponding to the non-primary link AP is indicated as a specific value (e.g., 1) in a beacon frame received over the primary link. If the non-AP MLD confirms that the subfield corresponding to the non-primary link AP is not a specific value in a beacon frame received over the primary link, the non-AP MLD can determine that the non-primary link AP has completed the scheduled channel switching. In this case, the meaning of "completed" may mean that the channel switching operation indicated by the last received (Extended) Channel Switching Announcement element corresponding to the non-primary link AP has been completed or canceled. If the subfield corresponding to the non-primary link AP is indicated as a value other than a specific value (a value other than the value indicated when channel switching is in progress), the non-AP MLD may consider that the non-primary link AP is operating in the operating channel / class indicated in the last received beacon frame (or probe response frame). When attempting to transmit an UL PPDU over the non-primary link, the non-AP MLD may need to transmit the UL PPDU based on whether the non-primary link AP is operating in the channel (class) it recognizes.For example, Non-AP MLD can transmit an UL PPDU only when the subfield corresponding to an AP of a non-primary link is indicated to have a value other than a specific value. On the other hand, when the subfield corresponding to an AP of a non-primary link is indicated to have a specific value, Non-AP MLD may consider that the AP of the non-primary link is performing channel switching and may not transmit an UL PPDU.

[0273] As another method, the NSTR Soft AP MLD can maintain the Critical Update Flag of the beacon frame (or Probe Response frame) at 1 until the non-primary link AP (AP's BSS) completes channel switching. The NSTR Soft AP MLD helps the non-AP MLD to recognize the scheduled channel switching of the non-primary link by including an (Extended) Channel Switching Announcement element corresponding to the non-primary link AP in the beacon frame. In this case, the NSTR Soft AP MLD must set the Critical Update Flag subfield of the beacon frame to 1 when transmitting the (Extended) Channel Switch Announcement element in the beacon frame (transmitted on the primary link). The NSTR Soft AP MLD can recognize the fact that 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 may need to 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, if the AP of the non-primary link is performing channel switching, the NSTR Soft AP MLD may need to indicate 0 in the Channel Switch Count subfield of the Channel Switch Announcement element corresponding to the AP of the non-primary link.In this case, if the AP of the non-primary link is performing channel switching, the NSTR Soft AP MLD may need to indicate the SwitchTime subfield of the Channel Switch Timing element corresponding to the AP of the non-primary link as the time value until the predicted completion of channel switching. In this case, the NSTR Soft AP MLD does not need to specify the completion time of the channel switching of the non-primary link AP by setting the SwitchTime subfield to a specific value (e.g., 65535).

[0274] As described above, if the NSTR Soft AP MLD maintains the value of the Critical Update Flag subfield at 1 when the AP of the non-primary link is switching channels, the non-AP MLD may not transmit a UL PPDU on the non-primary link if 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 if the Critical Update Flag subfield of a beacon (probe response) frame received from the NSTR Soft AP MLD is 1 and the Channel Switch Count subfield corresponding to the non-primary link AP is indicated as 0. Even more specifically, the non-AP MLD may not transmit a UL PPDU on the non-primary link if the Critical Update Flag subfield of a beacon (probe response) frame received from the NSTR Soft AP MLD is 1 and the Switch Time subfield corresponding to the non-primary link AP is indicated as a value other than 0.

[0275] Alternatively, the NSTR Soft AP MLD can indicate that a non-primary link AP (the BSS of the AP) has completed channel switching by incrementing the value of the BSS Parameter Change Count subfield corresponding to the non-primary link AP. In this case, the BSS Parameter Change Count subfield refers to the BSS Parameters Change Count subfield in the MLD Parameters field of the TBTT Information field corresponding to the non-primary link AP. While a general AP MLD increments the value of the BSS Parameters Change Count subfield by 1 only when the parameters of the AP corresponding to the BSS Parameters Change Count subfield are updated, the NSTR Soft AP MLD can also increment the BSS Parameters Change Count subfield corresponding to the non-primary link AP when channel switching is completed. This can be understood as incrementing the value of the BSS Parameters Change Count subfield as a method for indicating to the non-primary link AP that the instructed channel switching operation has been completed. When the non-AP MLD determines that channel switching of the non-primary link AP is scheduled / in progress, it can determine that the scheduled / in progress channel switching has been completed if the value of the BSS Parameters Change Count subfield is incremented by 1. In this case, the non-AP MLD can transmit an UL PPDU after determining that the scheduled / in progress channel switching has been completed. The operation of the non-AP MLD regarding the UL PPDU transmission conditions is the same as the other examples of the channel switching completion indication methods described above, and therefore, a description thereof will be omitted.

[0276] As another method, the NSTR Soft AP MLD can transmit a frame on the primary link including subfields indicating different values ​​when a non-primary link AP (the AP's BSS) is planning to perform channel switching, when channel switching is in progress, and when channel switching is completed. In this case, the frame may be a beacon frame. Furthermore, when channel switching for a non-primary link AP is planned, the NSTR Soft AP MLD can indicate an (Extended) Channel Switch Announcement element corresponding to the non-primary link AP and indicate a specific subfield to a specific value (e.g., 1). When channel switching for the non-primary link AP is initiated, the NSTR Soft AP MLD can set the specific subfield to a value other than the specific value (e.g., 2) until channel switching is 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), thereby allowing the associated non-AP MLD to recognize the progress of channel switching of the non-primary link. The non-AP MLD can determine whether to transmit an UL PPDU over the non-primary link by checking the specific subfield included in a frame received over the primary link. For example, the non-AP MLD can transmit an UL PPDU only if the last received specific subfield is the initial value.

[0277] As another method, the non-AP MLD can determine whether the non-primary link AP has completed channel switching based on the primary link beacon frame received after the scheduled channel switching completion time of the non-primary link AP indicated (published) by the NSTR Soft AP MLD.

[0278] Furthermore, the non-AP MLD can determine whether the scheduled channel switching has been completed by checking the Operating Channel / Class information of the non-primary link AP indicated in a beacon frame received on the primary link after the channel switching completion time of the non-primary link AP confirmed from a channel switching-related element. The method for checking the channel switching completion time of the non-primary link AP using the channel switching-related element may be to use the value indicated in the SwitchTime subfield of the Channel Switch Timing element. When the non-AP MLD confirms that the same information as the Operating Channel / Class for which channel switching was scheduled is indicated for the non-primary link AP in a beacon frame received after the scheduled channel switching completion time, it determines that the non-primary link AP has completed the scheduled channel switching and can transmit a UL PPDU. That is, when the non-AP MLD receives the first beacon frame (on the primary link) after the scheduled channel switching completion time of the non-primary link, it can transmit a UL PPDU on the non-primary link. In this case, the channel / class in which the non-AP MLD transmits the UL PPDU may be the operating channel / class of the non-primary link AP indicated in the first beacon frame.

[0279] In addition, NSTR AP MLD may not be able to perform channel switching of non-primary links. However, when NSTR AP MLD attempts to perform channel switching of non-primary links, it can release the non-primary link AP operating on the existing channel and operate as if a new non-primary link AP had been added on the new channel.

[0280] In yet another embodiment of the present invention, the NSTR AP MLD may be restricted from setting a quiet interval on a non-primary link. In this case, if a quiet interval is defined (set) for the primary link, the quiet interval for the non-primary link may be defined (set) to the same time interval as the quiet interval for the primary link. In other words, when the non-AP STA MLD combined with the NSTR AP MLD recognizes the quiet interval for the primary link, it can consider that a quiet interval for the same time interval is also set for the non-primary link.

[0281] In this way, the quiet element for the non-primary link transmitted in the beacon frame of the primary link may be set (instructed) by the NSTR AP MLD as follows:

[0282] 1. The Quiet Count field may be set to the number of TBTTs remaining on the primary link before the next quiet interval begins on the non-primary link.

[0283] 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).

[0284] 3. The Quiet Offset field may be set to a time value (in TU) related to how far the quiet interval of the non-primary link begins from the TBTT of the primary link identified by the Quiet Count subfield.

[0285] The (Extended) Channel Switch Announcement element and Max Channel Switch Time element for the non-primary link transmitted in the beacon frame of the primary link may be set (instructed) by the NSTR AP MLD as follows:

[0286] 1. The Channel Switch Count field (of the Channel Switch Announcement element) may be set to information related to the number of remaining TBTTs of the primary link until a channel change of the non-primary link begins. If a channel change of the AP of the non-primary link begins in the next TBTT of the primary link, the beacon frame transmitted in this TBTT may have the Channel Switch Count field (associated with the AP of the non-primary link) set to 1 or 0.

[0287] 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 (a 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 non-primary link channel change began and the TIM frame transmitted on the new channel of the non-primary link after the channel change of the non-primary link is completed. For example, if the beacon interval of the primary link is 100 ms and the Switch Time field (for the non-primary link AP) is set to 200 ms, the non-primary link AP must transmit a TIM frame on the new channel within 200 ms from the time of transmitting the primary link beacon frame at which it began the channel change.

[0288] Therefore, after receiving a beacon frame over the primary link, the non-AP MLD combined with the NSTR AP MLD can obtain information about the quiet interval and channel change time and duration of the non-primary link based on the information indicated in the non-primary AP's Per-STA profile included in the beacon frame, the TBTT and beacon interval information of the primary link. At this time, the non-AP MLD can set (recognize and analyze) the start time of the quiet interval of the non-primary link based on the TBTT of the primary link. At this time, the non-AP MLD can recognize / analyze the channel change time of the non-primary link based on the reception time of the beacon frame received over the primary link.

[0289] Conventionally, Wi-Fi non-AP STAs can choose whether to change channels together with the AP to maintain association when the AP changes channels. However, a non-AP STA MLD associated with an NSTR AP MLD may need to change the channel of the non-primary link whenever the NSTR AP MLD changes channels on the non-primary link.

[0290] 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 change the channel of the non-primary link, the non-AP STA MLD may need to terminate (cancel or change) the ML setup with the NSTR AP MLD and change it to a state set up only on the primary link (by setting up or resetting after termination).

[0291] That is, a non-AP MLD station that receives channel change information related to channel switching for 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.

[0292] 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) from the non-primary link AP indicating that channel switching has been completed, or the primary link AP may receive a beacon frame indicating that channel switching of the non-primary link AP has been completed. The non-AP STA that receives the TIM frame or beacon frame recognizes that channel switching has been completed and can transmit and receive frames on the changed channel.

[0293] On the other hand, 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 can terminate (cancel or change) the multiple link setup with the AP of the non-primary link. In this case, since the link setup between the AP of the non-primary link and the non-AP STA is cancelled, the AP MLD and STA MLD only exist for the single link setup of the primary link.

[0294] If a non-AP STA that has a link established with the primary link AP does not perform channel switching to the primary link AP, the non-AP STA can choose whether to move to another BSS and establish a link with the AP of the other BSS.

[0295] Meanwhile, the NSTR Soft AP MLD may need to set the time interval for channel switching on the primary link as the quiet interval for the non-primary link BSS. This may be due to the restriction that the non-primary link can be occupied only when the NSTR Soft AP MLD and a 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 primary link AP (BSS), the NSTR Soft AP MLD and associated non-AP MLD restrict communication not only on the primary link but also on the non-primary link. Therefore, when the NSTR Soft AP MLD performs channel switching for the primary link AP (BSS), it may need to specify the same time interval as the channel switching interval as the quiet interval for the non-primary link AP (BSS). Alternatively, even if the NSTR Soft AP MLD does not separately specify a quiet interval for the non-primary link, the non-AP MLD associated with the NSTR Soft AP MLD must not transmit UL PPDUs on the non-primary link from the start of channel switching of the primary link until the completion of channel switching (when the first beacon frame is received on the new channel of the primary link). In this case, the non-AP MLD may generate a new backoff counter when the backoff counter reaches 0 during a time period in which no UL PPDUs are transmitted on the non-primary link. In this case, the new backoff counter may be the backoff counter generated using the current CW (Contention Window). In this case, counters related to retransmissions (such as the short retry count and long retry counter) remain unchanged.

[0296] Similarly, the NSTR Soft AP MLD may need to set the time interval set as the quiet interval for the primary link BSS as the quiet interval for the non-primary link BSS. This may be due to the restriction that the NSTR Soft AP MLD and a non-AP STA associated with the NSTR Soft AP MLD can occupy the non-primary link only when they occupy the primary link. When the NSTR Soft AP MLD sets a quiet interval for the primary link AP (BSS), the NSTR Soft AP MLD and associated non-AP MLD restrict communication not only on the primary link but also on the non-primary link. Therefore, when the NSTR Soft AP MLD specifies (sets) the quiet interval for the primary link AP (BSS), it may need to specify (set) the same time interval as the channel switching interval as the quiet interval for the non-primary link AP (BSS).

[0297] In this way, a non-AP MLD associated with an NSTR Soft AP MLD may not transmit UL PPDUs over the non-primary link when channel switching is being performed over the primary link or when a quiet interval for the primary link is set. Therefore, the non-AP MLD can perform a power save operation for non-AP STAs operating over the non-primary link when channel switching over the primary link is being performed or a quiet interval is in progress. This can be a power save operation for non-AP STAs operating over the non-primary link by preventing DL PPDU transmission from the AP over the non-primary link when channel switching over the primary link is in progress or a quiet interval is in progress. Furthermore, even if a non-AP STA operating over the non-primary link completes a channel access operation (e.g., an EDCA backoff operation), UL PPDU transmission over the non-primary link is restricted, so the non-AP MLD can decide to stop the channel access operation over the non-primary link. For example, when NSTR Soft AP MLD is performing channel switching or a quiet interval on the primary link, the non-AP MLD can suspend the channel access operation and / or CCA operation of the non-AP STA operating on the non-primary link. In this case, suspending the channel access operation and / or CCA operation can mean operating in a doze state in a power save mode.

[0298] Considering that a non-AP MLD STA has performed a power saving operation (specifically, maintaining a Doze state) for a non-AP STA operating on a non-primary link, the NSTR Soft AP MLD can transmit an Assistance frame on the non-primary link when the channel switching / quiet interval of the primary link ends. The Assistance frame may be transmitted to guide (help) the non-AP STA on the non-primary link to reset the NAVSyncDelay timer that started after the STA transitioned to Awake. The Assistance frame may be transmitted at a basic rate. The Assistance frame may be transmitted simultaneously with the transmission of a beacon frame on the primary link. The NAVSyncDelay timer may refer to a timer related to the time when the STA transitioned from Doze to Awake should perform CCA to set its NAV.

[0299] 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.

[0300] Referring to FIG. 18, the NSTR AP MLD operates AP1 and AP2 on the primary link and non-primary link, respectively, and is connected to STA1 and STA2 of the Non-AP STA MLD, respectively.

[0301] In order to set (define) a quiet interval (Quiet interval #1 in FIG. 18) for the non-primary link, the NSTR AP MLD can transmit a beacon frame transmitted via AP1 of the primary link including a Per-STA profile corresponding to AP2. The Per-STA profile corresponding to AP2 includes a Quiet element and indicates information related to the start time of the quiet interval (Quiet interval #1 in FIG. 18) in the Quiet Count and Quiet Offset fields. When the Quiet element is included in the first beacon frame (Beacon #1 in FIG. 18) of the primary link shown in FIG. 18, the Quiet Count field is set to 2 and the Quiet Offset field is set to a value indicating "x" TU (Time Unit, 1024 us), and in the second beacon frame (Beacon #2 in FIG. 18), the Quiet Count field is set to 1.

[0302] 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) begins when "x" TUs have elapsed since the TBTT corresponding to the third beacon frame.

[0303] 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 on the primary link to further set (define) the next quiet interval (Quiet interval #2 in Fig. 18) on the non-primary link. The sixth beacon frame (Beacon #6 in Fig. 18) on 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.

[0304] A non-AP STA MLD that receives the sixth and / or seventh beacon frame on the primary link can recognize that a quiet interval (Quiet interval #2) has been set (announced by the AP MLD) on the non-primary link by checking the Quiet element included in the Per-STA profile (corresponding to AP2) of the beacon frame, and that the quiet interval (Quiet interval #2) begins from the TBTT corresponding to the eighth beacon frame.

[0305] At this time, information regarding the length of the quiet interval is indicated in the Quiet Duration field indicated together with the Quiet element.

[0306] 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.

[0307] Referring to FIG. 19, the NSTR AP MLD operates AP1 and AP2 on the primary link and non-primary link, respectively, and is connected to STA1 and STA2 of the Non-AP STA MLD, respectively.

[0308] To change the non-primary link to a new channel, the NSTR AP MLD can include a Per-STA profile corresponding to AP2 (non-primary link) in a beacon frame transmitted via AP1 of the primary link. The Per-STA profile corresponding to AP2 includes an (Extended) Channel Switch Announcement element and a Max Channel Switch Time element, indicating information related to the time when a channel change begins and the time duration for transmitting a TIM frame on the new channel after the channel change. When the (Extended) Channel Switch Announcement element is included in the first beacon frame of the primary link (Beacon #1 in FIG. 19) shown in FIG. 19, the Channel Switch Count field is set to 2, and in the second beacon frame (Beacon #2 in FIG. 19) it is set to 1.

[0309] A non-AP STA MLD that receives the first and / or second beacon frame on the primary link can determine by checking the (Extended) Channel Switch Announcement element included in the Per-STA profile (corresponding to AP2) of the beacon frame that a channel change (to a new channel) of the non-primary link begins after receiving the second beacon frame and that AP2's TIM frame will be received on the new channel within "x" TUs from the time the second beacon frame is received. In this case, the new channel may be the channel corresponding to the value indicated in the New Channel Number field included in the (Extended) Channel Switch Announcement element. In this case, the "x" TUs may be the time value indicated in the Switch Time field included in the Max Channel Switch Time element included in the Per-STA profile (corresponding to AP2).

[0310] <Operation restrictions of non-AP STA MLD combined with NSTR AP MLD>

[0311] NSTR AP MLD is an AP MLD in which the primary link and the non-primary link are NSTR link pairs. Therefore, the AP of the non-primary link may be in the BLIND state while the PPDU is being transmitted via the AP of the primary link. Conversely, when the AP of the non-primary link transmits, the AP of the primary link may be in the BLIND state. In this case, the AP of the NSTR AP MLD that has gone through the BLIND state may need to set the MediumSyncDelay to a preset value.

[0312] MediumSyncDelay is a single timer that is commonly applied to the EDCAF (EDCA Function) of the STA. When MediumSyncDelay is not 0, additional restrictions may be applied when the STA acquires the TXOP. At this time, the additional restrictions may be: (1) the first transmission attempt to obtain the TXOP must be an RTS frame; (2) only attempts to acquire the TXOP a preset number of times or less (until it decreases to 0) are allowed while MediumSyncDelay is applied; (3) utilize a more stringent (lower: e.g., -72dBm to -62dBm) CCA ED (energy detection) threshold than when MediumSyncDelay is 0. That is, a STA with a non-zero MediumSyncDelay value is subject to more restrictions in acquiring the TXOP compared to a STA with MediumSyncDelay equal to 0.

[0313] Therefore, even in the case of NSTR AP MLD, MediumSyncDelay must be applied when the AP enters a BLIND state, and in situations where AP channel access is restricted, it may be difficult to provide normal service to STAs in the BSS. The NSTR AP MLD determines one of the links of the NSTR link pair for which the AP operates as the primary link, thereby managing transmissions over non-primary links (links other than the primary link) in a manner that prevents the primary link from entering a BLIND state. For example, the NSTR AP MLD can manage the primary link from entering a BLIND state by transmitting over the non-primary link only when a transmission over the primary link is in progress. For this purpose, even if the NSTR AP MLD receives a frame requesting a response frame via the AP of the non-primary link, it does not need to respond with the requested response frame. In other words, the NSTR AP MLD can operate not to respond with a response frame even if it receives a frame requesting a response frame via the AP of the non-primary link. At this time, the reason why the NSTR AP MLD does not respond with a response frame via the AP of the non-primary link may be to prevent the AP of the primary link from entering a BLIND state.

[0314] As described above, the NSTR AP MLD can manage the operation (transmission) of APs operating on the primary link and / or non-primary links to establish a primary link and prevent the AP on the primary link from entering a BLIND state. Similarly, a non-AP STA MLD combined with the NSTR AP MLD may need to understand and operate according to the primary link management method of the NSTR AP MLD. For example, if the non-AP STA MLD determines that a response frame has not been received from the NSTR AP MLD on the non-primary link, it may not transmit a frame requesting a response on the non-primary link. Furthermore, if the non-AP STA MLD transmits a frame requesting a response on the non-primary link and then fails to receive a response from the NSTR AP MLD, it may not retransmit the frame requesting a response. For example, if the non-AP STA MLD transmits an RTS frame to the NSTR AP MLD on the non-primary link and fails to receive a CTS frame response, it may not retransmit the RTS frame. In this case, the Non-AP MLD does not need to attempt transmission to the NSTR AP MLD via the non-primary link until it receives a trigger frame via the non-primary link.

[0315] Furthermore, even if the non-AP MLD completes the channel access procedure of the non-primary link for UL transmission, it may postpone transmission on the non-primary link until the channel access procedure on the primary link is completed. In this case, the method by which the non-AP MLD postpones transmission on the non-primary link may be to suspend the backoff procedure performed by the STA of the non-primary link (more precisely, the EDCAF of the STA) until the backoff procedure performed by the STA of the primary link is completed. In this case, the method by which the non-AP MLD suspends the backoff procedure performed by the STA of the non-primary link may be to maintain a backoff counter at 0.

[0316] A non-AP STA MLD that has completed the channel access procedure on both the primary link and the non-primary link using the above method can perform simultaneous transmission (simultaneous UL PPDU transmission) on the primary link and the non-primary link. Here, "simultaneous transmission" means that the start times of each transmission are within a predetermined time interval. However, if only the channel access procedure on the primary link is completed and the channel access procedure on the non-primary link is not yet completed, the non-AP MLD can start PPDU transmission on the primary link only, or can start simultaneous transmission when the channel access procedure on the non-primary link is completed. That is, when transmitting to an NSTR AP MLD, the non-AP MLD can transmit using only the primary link, or can perform simultaneous transmission using the primary link and the non-primary link. However, a non-AP MLD may not be allowed to transmit PPDUs to an NSTR AP MLD using only the non-primary link.

[0317] In addition, non-AP MLD may require NSTR AP MLD to synchronize the end points of transmissions on both links when performing UL transmissions using both the primary link and the non-primary link. In this case, synchronizing the end points of transmissions may mean that transmissions on both links end within a predetermined time interval.

[0318] In addition, when NSTR AP MLD performs UL transmission using both the primary link and the non-primary link, the non-AP MLD may need to set whether the PPDUs transmitted on both links request a response frame. Furthermore, two UL PPDUs simultaneously transmitted by non-AP MLD on the primary link and the non-primary link may require both to request a response frame, or both to request a response frame. This restriction applies because if a response frame is only sent on a specific link as a result of UL transmission by non-AP MLD using both the primary link and the non-primary link, the AP operating on the other link of the NSTR AP MLD may enter a BLIND state. However, NSTR AP MLD does not need to send a response frame for both PPDUs if only one of two PPDUs received simultaneously (received on the primary link and the non-primary link, respectively) requests a response frame.

[0319] In addition, non-AP MLD may need to configure NSTR AP MLD so that when transmission is performed using both the primary link and the non-primary link, the TXOP of the non-primary link terminates at the same time as or earlier than the TXOP of the primary link. In other words, non-AP MLD may need to configure so that the TXOP of the non-primary link terminates at the same time as or earlier than the TXOP of the primary link. However, the non-primary link TXOP of the non-AP STA MLD may be allowed to terminate later than the TXOP of the primary link by a predetermined time interval.

[0320] In addition, the non-AP STA MLD can recognize that the NSTR AP MLD has experienced a BLIND state for an AP of a specific link and assist the AP in its operation. Furthermore, when the non-AP STA MLD recognizes that transmission has occurred on only one of the primary and non-primary links, it can determine that the AP of the other link that did not transmit must have experienced a BLIND state. In this case, the non-AP STA MLD can assist the AP in releasing the MediumSyncDelay (resetting it to 0) in consideration of the fact that the AP experiencing the BLIND state is restricted in channel access due to a non-zero MediumSyncDelay. In this case, the operation performed by the non-AP STA MLD may utilize the characteristic that MediumSyncDelay can be released when a NAV-configurable PPDU (including a valid MPDU) is received.

[0321] For example, after passing through the BLIND state, the non-AP STA MLD may transmit an Assist frame (a type of PPDU) capable of NAV setting to the AP of the NSTR AP MLD that is determined to have a non-zero MediumSyncDelay. Here, the Assist frame may refer to a frame included in a valid MPDU capable of NAV setting, regardless of the frame format. The condition under which the non-AP STA MLD transmits an Assist frame to the NSTR AP MLD over a specific link may be limited to when the state of the specific link confirmed by the non-AP STA MLD is in an IDLE state. Another condition under which the non-AP STA MLD transmits an Assist frame to the NSTR AP MLD may be limited to when the non-AP STA MLD is a non-AP STA MLD that has been explicitly or implicitly requested (instructed) by the NSTR AP MLD to transmit an Assist frame.

[0322] FIG. 20 is a flowchart showing an example of the operation of non-AP MLD according to an embodiment of the present invention.

[0323] Referring to FIG. 20, an MLD consisting of a plurality of STAs can obtain channel change information for an AP of a non-primary link from an AP of a primary link of an AP MLD.

[0324] Specifically, a multi-link device (MLD) including multiple stations each operating on multiple links can receive a frame including channel change information for changing channels from a first AP of a primary link among the multiple links (S20010).

[0325] The multiple links may consist of one primary link and at least one secondary link (non-primary link), and the channel change information may be used for changing the channel of the second AP for one of the at least one secondary link.

[0326] Thereafter, the MLD can determine whether to change the channel of the station connected to the second AP through the one secondary link based on the channel change information (S33020).

[0327] In this case, a field related to the timing of the channel change of the second AP included in the channel change information may be set based on the first AP of the primary link.

[0328] The field related to the timing of the channel change of the second AP may be set based on the target beacon transmission time (TBTT) and beacon interval (BI) for the first AP of the primary link, and the field related to the timing of the channel change of the second AP may include a switch time field indicating the time interval from the time the channel change begins until the first frame is transmitted on the changed channel, and / or a channel switch count field indicating the number of TBTTs remaining until the channel change begins.

[0329] The switch time field may be recognized based on the time when a beacon frame is transmitted from the first AP of the main link, in which the value of the channel switch count field related to the channel change of the second AP is set to “1” or “0”.

[0330] If the value of the channel switch count field is 1, the channel change may begin at the first AP's next TBTT after the frame is transmitted, and if the value of the channel switch count field is 0, the channel change may begin after the frame is transmitted.

[0331] The channel change information may further include a new channel number field indicating the number of the channel to be changed by the channel change.

[0332] The channel change information is included in at least one Per-STA profile sub-element included in the frame, and each of the at least one Per-STA profile sub-element may include information about other APs included in the same MLD.

[0333] The first AP and the second AP are non-simultaneous transmission and reception (NSTR) stations that do not support simultaneous transmission and reception within the same MLD.

[0334] The MLD can perform a channel change for the station based on the channel change information and can receive a frame related to the completion of the channel change from the first AP or the second AP.

[0335] If the second AP is an AP operating on a non-primary link, and a non-AP STA associated with the second AP on the non-primary link decides not to perform channel switching, and channel switching is not performed, the non-AP STA that does not perform channel switching can terminate (release or change) the multiple link setup with the second AP on the non-primary link. In this case, since the link setup between the AP and the non-AP STA on the non-primary link is released, only a single link setup of the primary link exists for the AP MLD and STA MLD. Therefore, the AP MLD and STA MLD can re-establish the link to operate only on the primary link. That is, the AP MLD and STA MLD can re-establish the link to operate on a single link.

[0336] If a non-AP STA that has a link established with the first AP of the primary link does not perform channel switching for the first AP operating on the primary link, the non-AP STA of the first AP can choose whether to move to another BSS and establish a link with an AP of another BSS.

[0337] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical spirit or essential characteristics of the present invention. Therefore, the above-described embodiments should be understood to be illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed form, and similarly, each component described as a distributed type may be implemented in a combined form.

[0338] The scope of the present invention is indicated by the claims set forth below rather than by the above detailed description, and all modifications and variations that fall within the meaning and scope of the claims and their equivalents should be construed as being within the scope of the present invention.

Claims

1. A multi-link device (MLD) including a plurality of stations each operating on a plurality of links, The processor receiving a frame including channel change information for changing a channel from a first AP of a primary link among the plurality of links; The plurality of links are configured by one of the main links and at least one secondary link (non-primary link), the channel change information is used for a channel change of the second AP for one secondary link of the at least one secondary link; determining whether to change the channel of a station connected to the second AP through the one secondary link based on the channel change information; A field related to the timing of the channel change of the second AP included in the channel change information is set based on the first AP of the primary link.

2. 2. The MLD of claim 1, wherein the field related to the timing of the channel change of the second AP is set based on a target beacon transmission time (TBTT) and a beacon interval (BI) of the primary link to the first AP.

3. 2. The MLD of claim 1, wherein the fields related to the timing of the channel change of the second AP include a switch time field indicating a time interval from the start of the channel change until the first frame is transmitted through the changed channel, and / or a channel switch count field indicating the number of TBTTs remaining until the channel change starts.

4. The MLD of claim 3, wherein the switch time field is recognized based on the time when a beacon frame in which the value of the channel switch count field related to the channel change of the second AP is set to '1' or '0' is transmitted among beacon frames transmitted from the first AP of the primary link.

5. If the value of the channel switch count field is 1, the channel change begins at the first AP's next TBTT after the frame is transmitted; The MLD of claim 3 , wherein if the channel switch count field value is 0, the channel change begins after the frame is transmitted.

6. 4. The MLD according to claim 3, wherein the channel change information further includes a new channel number field indicating a number of a channel to be changed by the channel change.

7. the channel change information is included in at least one Per-STA profile sub-element included in the frame; The MLD of claim 1 , wherein each of the at least one Per-STA profile sub-element includes information about other APs included in the same MLD.

8. The MLD of claim 1, wherein the first AP and the second AP are non-simultaneous transmission and reception (NSTR) stations that do not support simultaneous transmission and reception within the same MLD.

9. The processor: The MLD according to claim 1 , further comprising: performing a channel change of the station based on the channel change information; and receiving a frame related to completion of the channel change from the first AP or the second AP.

10. The processor: The MLD of claim 1, wherein if the station connected to the second AP through the one secondary link does not change channels based on the channel change information, the MLD reestablishes a link with the AP MLD including the first AP and the second AP so that the MLD is connected only to the primary link of the first AP.

11. 1. A method performed by a multi-link device (MLD) including a plurality of stations operating on a plurality of links in a wireless communication system, the method comprising: receiving a frame including channel change information for changing a channel from a first AP of a primary link among the plurality of links; The plurality of links are configured by one of the main links and at least one secondary link (non-primary link), The channel change information is used for a channel change of a second AP for one secondary link of the at least one secondary link; and determining whether to change a channel of a station connected to the second AP through the one secondary link based on the channel change information, a field related to the timing of the channel change of the second AP included in the channel change information is set based on the first AP of the primary link.

12. 12. The method of claim 11, wherein the field related to the timing of the channel change of the second AP is set based on a target beacon transmission time (TBTT) and a beacon interval (BI) of the primary link to the first AP.

13. 12. The method of claim 11, wherein the fields related to the timing of the channel change of the second AP include a switch time field indicating a time interval from the start of the channel change until the first frame is transmitted through the changed channel, and / or a channel switch count field indicating the number of TBTTs remaining until the channel change starts.

14. The method of claim 13, wherein the switch time field is recognized based on the time when a beacon frame is transmitted from the first AP of the primary link, in which the value of the channel switch count field related to the channel change of the second AP is set to '1' or '0'.

15. If the value of the channel switch count field is 1, the channel change begins at the next TBTT of the first AP after the frame is transmitted; 14. The method of claim 13, wherein if the channel switch count field value is 0, the channel change begins after the frame is transmitted.

16. 14. The method of claim 13, wherein the channel change information further includes a new channel number field indicating a number of a channel to be changed by the channel change.

17. the channel change information is included in at least one Per-STA profile sub-element included in the frame; The method of claim 11 , wherein each of the at least one Per-STA profile sub-element includes information about other APs included in the same MLD.

18. The method of claim 11, wherein the first AP and the second AP are non-simultaneous transmission and reception (NSTR) stations that do not support simultaneous transmission and reception within the same MLD.

19. and further comprising: performing a channel change of the station based on the channel change information; The method of claim 11 , further comprising receiving a frame from the first AP or the second AP relating to the completion of the channel change.

20. 12. The method of claim 11, wherein if the station connected to the second AP through the one secondary link does not change channels based on the channel change information, link setup is performed again with an AP MLD including the first AP and the second AP so that the MLD is connected only to the primary link of the first AP.

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