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

Abstract

To provide a non-AP (accesspoint) multi-link device including a plurality of stations operating on a plurality of links, respectively.SOLUTION: The multi-link device includes a transceiver and a processor. The processor may be configured to receive a beacon frame including a TIM element and a Multi-LinkTraffic element from an AP multi-link device, and determine whether traffic for the non-AP multi-link device is buffered in the AP multi-link device based on a PartialVirtualBitmap subfield of the TIM element.SELECTED DRAWING: Figure 14

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 band and supports communication speeds of up to 11 Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5 GHz band instead of the 2.4 GHz band, reducing the impact of interference compared to the significantly more congested 2.4 GHz 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. It is also 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, IEEE 802.11ad is a method of transmitting data using the 60GHz band instead of the conventional 24GHz / 5GHz band. 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. [Means for solving the problem]

[0009] According to one embodiment of the present invention, a non-AP (access point) multilink device including a plurality of stations operating on a plurality of links includes a transceiver and a processor. The processor receives a beacon frame including a TIM element and a Multi-Link Traffic element from an AP multilink device and determines whether traffic for the non-AP multilink device is buffered in the AP multilink device based on a Partial Virtual Bitmap subfield of the TIM element. In this case, the Partial Virtual Bitmap subfield includes one or more first bits and one or more second bits, and a bit set to 1 among the one or more first bits indicates that traffic for the corresponding non-AP multilink device is buffered in the AP multilink device, and a bit set to 1 among the one or more second bits indicates that traffic for the corresponding non-AP station is buffered in the AP multilink device. When traffic for the non-AP multilink device is buffered in the AP multilink device, the processor determines, based on the Per-Link Traffic Indication List subfield of the Multi-Link Traffic element, which of the multiple links the traffic for the non-AP multilink device is buffered on, or which of the multiple links the AP multilink device recommends the non-AP multilink device retrieve traffic transmission from.In this case, the Per-Link Traffic Indication List subfield includes n Per-Link Traffic Indication Bitmap subfields, where n is the sum of the number of bits set to 1 among the one or more first bits and the number of bits set to 1 among the one or more second bits, and each of the n Per-Link Traffic Indication Bitmap subfields is mapped to a non-AP multilink device corresponding to a bit set to 1 among the one or more first bits and a non-AP station corresponding to a bit set to 1 among the one or more second bits, respectively.

[0010] The Per-Link Traffic Indication Bitmap subfields mapped to non-AP stations corresponding to the one or more second bits set to 1 may be set as reserved bits.

[0011] The value of the reserved bit may be zero.

[0012] If the non-AP multilink device successfully performs TID-to-link mapping with the AP multilink device and not all TIDs are mapped to all links, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device indicates whether traffic for the non-AP multilink device is buffered on each of the multiple links.

[0013] When a default mapping is applied to the link between the non-AP multilink device and the AP multilink device, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device may indicate which of the multiple links the non-AP multilink device recommends to direct traffic transmission to, where the default mapping is a mapping in which all TIDs are mapped to all links.

[0014] Among the bits in the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device, bits corresponding to links not configured by the AP multilink device or the non-AP multilink device may be set as reserved bits.

[0015] Among the bits of the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device, bits corresponding to disabled links of the non-AP multilink device may be set as reserved bits. The disabled links may be links where uplink and downlink transmissions are stopped.

[0016] The link IDs may be mapped in ascending order to bits in a Per-Link Traffic Indication Bitmap subfield that is mapped to the non-AP multi-link device.

[0017] When the AP that transmitted the beacon frame in the AP multilink device does not belong to a multiple BSSID set, the range of values ​​that the AP multilink device can assign as an association ID (AID) may be determined based on the value of a Group Addressed BU Indication Exponent subfield. The value of the Group Addressed BU Indication Exponent subfield may indicate the number of bits used to indicate buffered group address frames corresponding to APs other than the AP that transmitted the beacon frame in the AP multilink device.

[0018] If the AP that transmitted the beacon frame in the AP multilink device belongs to a multiple BSSID set, the range of values ​​that the AP multilink device can assign as an AID may be determined based on the value of the Group Addressed BU Indication Exponent subfield and a bitmap limit, where the bitmap limit may be 48 bits.

[0019] According to an embodiment of the present invention, an access point (AP) multilink device including a plurality of stations operating on a plurality of links includes a transceiver and a processor. The processor configures a TIM element and a Multi-Link Traffic element to be included in a beacon frame to be transmitted to a non-AP multilink device. The TIM element includes a Partial Virtual Bitmap subfield. The Partial Virtual Bitmap subfield includes one or more first bits and one or more second bits, where a bit set to 1 among the one or more first bits indicates that traffic for the corresponding non-AP multilink device is buffered in the AP multilink device, and a bit set to 1 among the one or more second bits indicates that traffic for the corresponding non-AP station is buffered in the AP multilink device. When traffic for the non-AP multilink device is buffered in the AP multilink device, the processor sets the Per-Link Traffic Indication List subfield of the Multi-Link Traffic element depending on which of the multiple links the traffic for the non-AP multilink device is buffered on, or which of the multiple links the AP multilink device recommends the non-AP multilink device retrieve traffic transmission from.

[0020] The processor transmits the beacon frame via the transceiver unit.

[0021] The Per-Link Traffic Indication List subfield includes n Per-Link Traffic Indication Bitmap subfields, where n is the sum of the number of bits set to 1 among the one or more first bits and the number of bits set to 1 among the one or more second bits. Each of the n Per-Link Traffic Indication Bitmap subfields is mapped to a non-AP multilink device corresponding to a bit set to 1 among the one or more first bits and a non-AP station corresponding to a bit set to 1 among the one or more second bits, respectively.

[0022] The processor may set a Per-Link Traffic Indication Bitmap subfield mapped to a non-AP station corresponding to a bit set to 1 among the one or more second bits as a reserved bit.

[0023] The value of the reserved bit may be zero.

[0024] If the non-AP multilink device successfully performs TID-to-link mapping with the AP multilink device and not all TIDs are mapped to all links, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device can indicate whether traffic for the non-AP multilink device is buffered on each of the multiple links.

[0025] When a default mapping is applied to the link between the non-AP multilink device and the AP multilink device, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device may indicate which of the multiple links the non-AP multilink device recommends to direct traffic transmission to. In this case, the default mapping may be a mapping in which all TIDs are mapped to all links.

[0026] The processor can set bits of the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device that correspond to links not configured by the AP multilink device or the non-AP multilink device as reserved bits.

[0027] The processor may set a bit corresponding to a disabled link of the non-AP multilink device among bits of a Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device as a reserved bit. The disabled link may be a link where uplink and downlink transmissions are stopped.

[0028] The link IDs may be mapped in ascending order to bits in a Per-Link Traffic Indication Bitmap subfield that is mapped to the non-AP multi-link device.

[0029] When the AP that transmitted the beacon frame in the AP multilink device does not belong to a multiple BSSID set, the range of values ​​that the AP multilink device can assign as an association ID (AID) may be determined based on the value of a Group Addressed BU Indication Exponent subfield. The value of the Group Addressed BU Indication Exponent subfield may indicate the number of bits used to indicate buffered group address frames corresponding to APs other than the AP that transmitted the beacon frame in the AP multilink device.

[0030] If the AP that transmitted the beacon frame in the AP multilink device belongs to a multiple BSSID set, the range of values ​​that the AP multilink device can assign as an AID may be determined based on the value of the Group Addressed BU Indication Exponent subfield and a bitmap limit, where the bitmap limit may be 48 bits.

[0031] A method for operating a non-AP (access point) multilink device including a plurality of stations operating on a plurality of links, includes the steps of receiving a beacon frame including a TIM element and a Multi-Link Traffic element from an AP multilink device; and determining whether traffic for the non-AP multilink device is buffered in the AP multilink device based on a Partial Virtual Bitmap subfield of the TIM element, the Partial Virtual Bitmap subfield including one or more first bits and one or more second bits, a bit set to 1 among the one or more first bits indicating that traffic for the non-AP multilink device corresponding to the bit is buffered in the AP multilink device, and a bit set to 1 among the one or more second bits indicating that traffic for the non-AP station corresponding to the bit is buffered in the AP multilink device; and, when traffic for the non-AP multilink device is buffered in the AP multilink device, determining whether traffic for the non-AP multilink device is buffered in the AP multilink device based on a Partial Virtual Bitmap subfield of the TIM element. The method includes determining, based on the List subfield, which of the plurality of links has buffered traffic for the non-AP multilink device, or which of the plurality of links the AP multilink device recommends the non-AP multilink device retrieve traffic transmission from.The Per-Link Traffic Indication List subfield includes n Per-Link Traffic Indication Bitmap subfields, where n is the sum of the number of bits set to 1 among the one or more first bits and the number of bits set to 1 among the one or more second bits, and each of the n Per-Link Traffic Indication Bitmap subfields is mapped to a non-AP multilink device corresponding to a bit set to 1 among the one or more first bits and a non-AP station corresponding to a bit set to 1 among the one or more second bits, respectively.

[0032] The Per-Link Traffic Indication Bitmap subfields mapped to non-AP stations corresponding to the one or more second bits set to 1 may be set as reserved bits. [Effects of the Invention]

[0033] An embodiment of the present invention provides a wireless communication method that efficiently uses multilinks and a wireless communication terminal that uses the same. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a diagram illustrating 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 an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same, according to an embodiment of the present invention. [Figure 9] 1 shows a multi-link device according to an embodiment of the present invention; [Figure 10] 1 illustrates a multi-link mapped by a TID-to-link mapping method according to an embodiment of the present invention. [Figure 11] 4 illustrates power management operations performed by a station according to an embodiment of the present invention. [Figure 12] 1 illustrates a format of a TIM element according to an embodiment of the present invention. [Figure 13] 1 shows a format of a Multi-Link Traffic element according to an embodiment of the present invention. [Figure 14] 10 illustrates how the Partial Virtual Bitmap subfield of the Multi-Link Traffic element and the TIM element signal buffered traffic to an AP multi-link device, according to an embodiment of the present invention. [Figure 15] 1 illustrates a method for configuring a Multi-Link Traffic element according to an embodiment of the present invention. [Figure 16] This shows a method for setting the Per-Link Traffic Bitmap subfield of the Multi-Link Traffic element when the link set in which an AP multi-link device operates is different from the link set in which a non-AP multi-link device communicating with the AP multi-link device operates, in accordance with an embodiment of the present invention. [Figure 17] 10 illustrates how the link indicated by the Per-Link Traffic Bitmap subfield is determined by TID-to-link mapping according to an embodiment of the present invention. [Figure 18] 10 illustrates a method for an AP multilink device to set a Per-Link Traffic Indication Bitmap subfield of a Multi-Link Traffic element according to yet another embodiment of the present invention. [Figure 19] 1 illustrates an EHT Operation element according to an embodiment of the present invention. [Figure 20] 1 shows a traffic indication virtual bitmap according to an embodiment of the present invention. [Figure 21] 1 shows a traffic indication virtual bitmap according to an embodiment of the present invention. [Figure 22] 1 illustrates signaling associated with a Multi-Link element and MediumSyncDelay according to one embodiment of the present invention. [Figure 23] 3 illustrates a multi-link setup process according to an embodiment of the present invention. [Figure 24] 10 illustrates the format of a Reduced Neighbor Report element according to an embodiment of the present invention. [Figure 25] 4 illustrates a method for setting an ID of a multi-link device according to an embodiment of the present invention. [Figure 26] A method for allocating AIDs to non-AP stations belonging to a multi-link device according to an embodiment of the present invention will now be described. [Figure 27] A method for allocating AIDs to non-AP stations belonging to a multi-link device according to an embodiment of the present invention will now be described. [Figure 28] 1 illustrates a TID-to-link mapping negotiation in which an AP multilink device sends a TID-to-link mapping request according to an embodiment of the present invention. [Figure 29]1 illustrates a TID-to-link mapping negotiation in which an AP multilink device sends a TID-to-link mapping request according to an embodiment of the present invention. [Figure 30] 10 illustrates TID-to-link mapping negotiation when a link set requesting TID-to-link mapping is different from a link set set in a TID-to-link mapping response according to an embodiment of the present invention. [Figure 31] 10 illustrates a method for a non-AP multilink device to determine traffic buffered in an AP multilink device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] 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.

[0036] 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.

[0037] Hereinafter, in the present invention, the terms field and subfield may be used interchangeably.

[0038] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention.

[0039] 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.

[0040] 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.

[0041] 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, depending on the embodiment, may further include a user interface unit and a display unit. 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).

[0042] 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.

[0043] 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).

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 for 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.

[0048] 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.

[0049] 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.

[0050] 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 priorities contained in the communication setup message and requests connection to the AP based on the information about the station 100's priorities. 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 or a modulator and / or demodulator that modulates and demodulates wireless signals transmitted and received by the communication unit 120. 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.

[0051] 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 implemented on separate chips. Furthermore, in some 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.

[0052] 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.

[0053] 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 can wirelessly communicate 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.

[0054] 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 by 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.

[0055] FIG. 5 is a diagram illustrating a process in which a STA establishes a link with an AP.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] FIG. 6 is a diagram showing a Carrier Sense Multiple Access (CSMA) / Collision Avoidance (CA) method used in wireless LAN communication.

[0060] 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 the signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by a terminal is designated 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 a strength below the CCA threshold is detected, the channel is determined to be idle.

[0061] 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 terminal during the idle interval of the channel, and a terminal that has exhausted all of its slot time attempts to access the 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 channel. Therefore, if the channel is idle during the AIFS time and the backoff counter slot time, the terminal may be allowed to transmit.

[0062] If a specific terminal successfully accesses the channel, it transmits data through the channel. However, if the terminal attempting access collides with another terminal, the colliding terminals are assigned new random numbers and perform a backoff procedure again. According to one embodiment, the 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 via a wireless LAN can avoid collisions with each other on a specific channel.

[0063] <Examples of various PPDU formats>

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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. Since BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, it may contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of the L-SIG.

[0069] 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.

[0070] 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.

[0071] 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 in 4 us, which is the duration of one 64 FFT symbol. Therefore, by adding 3 bytes corresponding to the SVC field and Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of 64 FFT 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 as Equation 1 below.

[0072]

number

[0073] At this time,

number

[0074]

number

[0075] 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.

[0076]

number

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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 using the same PPDU format, and a field for distinguishing between MU PPDUs and SU PPDUs may be located before the EHT-SIG field, requiring additional signaling. 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.

[0082] 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.

[0083] 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.

[0084] 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 the punctured RUs in between. Therefore, the AP can transmit the SU PPDU including information on the punctured RUs among the RUs assigned to the STA (e.g., the puncturing pattern of the RUs). 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] In addition, one embodiment of the present invention proposes a method of varying the PPDU configuration indicated by the preamble puncturing BW value depending on the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, an EHT-SIG-A symbol can be further signaled after the U-SIG, or no EHT-SIG-A can be signaled at all. Taking this into consideration, up to 11 puncturing modes must be fully signaled using only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B symbol is further signaled after the U-SIG, so up to 11 puncturing modes can be signaled in a different manner than in the case of an SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz bandwidth. Detailed puncturing patterns for each PPDU type will be described in detail below with reference to FIGS. 11 and 12.

[0089] 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.

[0090] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention.

[0091] 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 a PPDU is EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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 may 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 a 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.

[0097] 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 form 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.

[0098] 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 null STA ID that has already been set.

[0099] For ease of explanation, the term frame or MAC frame may be used interchangeably with MPDU in this specification.

[0100] 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 required. 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.

[0101] FIG. 9 shows a multi-link device according to an embodiment of the present invention.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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).

[0106] The multilink operation may include a multilink setup operation. The multilink setup corresponds to the association operation of the single-link operation described above and must be preceded by a frame exchange in the multilink. The multilink device can obtain information required for the multilink setup from the 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 the 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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 ACs. ACs 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 can be further subdivided into AC_VI primary and AC_VI alternate. AC_VO can 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.

[0111] 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.

[0112] 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.

[0113] 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 operating 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.

[0114] FIG. 10 illustrates a multi-link mapped by a TID-to-link mapping method according to an embodiment of the present invention.

[0115] Referring to Figure 10, as described in Figure 9, there may be a mapping relationship between TIDs and links. In addition, in the present invention, the mapping relationship between TIDs and links may be referred to as TID-to-link mapping, TID to link mapping, TID mapping, link mapping, etc. The TID may be a traffic identifier. The TID may also be an ID (identifier) ​​that classifies traffic, data, etc. to support quality of service (QoS).

[0116] Furthermore, the TID may be an ID used or assigned in a layer higher than the MAC layer. The TID can indicate TC (traffic categories) and TS (traffic streams). The TID may have 16 values, for example, values ​​from 0 to 15. The TID value used may differ depending on the access policy, channel access, or medium access method. For example, when EDCA (HCF (hybrid coordination function) contention-based channel access, enhanced distributed channel access) is used, the possible TID values ​​may be 0 to 7. When EDCA is used, the TID value may indicate UP (user priority), and the UP may be related to TC or TS. The UP may be a value assigned in a layer higher than the MAC layer. When HCCA (HCF controlled channel access) or SPCA is used, the possible TID values ​​may be 8 to 15. When HCCA or SPCA is used, the TID may indicate TSID. Furthermore, when HEMM or SEMM is used, the possible TID value may be 8 to 15. Furthermore, when HEMM or SEMM is used, TID may indicate TSID.

[0117] There may also be a mapping relationship between UP and access category (AC). An AC may be a label for providing QoS in EDCA or a label indicating a set of EDCA parameters. The EDCA parameters or a set of EDCA parameters may be used for channel connection. An AC may be used by a QoS STA.

[0118] The AC value may be set as one of AC_BK, AC_BE, AC_VI, and AC_VO. AC_BK, AC_BE, AC_VI, and AC_VO may represent background, best effort, video, and voice, respectively. Furthermore, AC_BK, AC_BE, AC_VI, and AC_VO can be further subdivided. For example, AC_VI may be further subdivided into AC_VI primary and AC_VI alternate. Furthermore, AC_VO may be further subdivided into AC_VO primary and AC_VO alternate. Furthermore, UP values ​​or TID values ​​may be mapped to AC values. For example, UP values ​​or TID values ​​1, 2, 0, 3, 4, 5, 6, and 7 may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI, AC_VI, AC_VO, and AC_VO, respectively. Alternatively, UP or TID values ​​1, 2, 0, 3, 4, 5, 6, and 7 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. UP or TID values ​​1, 2, 0, 3, 4, 5, 6, and 7 may have increasing 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. AC_BK, AC_BE, AC_VI, and AC_VO may correspond to AC indices (ACIs) 0, 1, 2, and 3, respectively.

[0119] Therefore, there may be a relationship between a TID and an AC. Therefore, the TID-to-link mapping of the present invention may be a mapping relationship between an AC and a link. Also, in the present invention, mapping a TID may mean mapping an AC, or vice versa.

[0120] According to one embodiment of the present invention, a TID may be mapped to each link of a multilink. For example, there may be a mapping of which links among multiple links a specific TID or a specific AC is allowed to transmit and receive on. Such mapping may be defined separately for each of the two directions of the link. As described above, a default setting may exist for the mapping between TIDs and links. For example, the mapping between TIDs and links may basically be such that all TIDs are mapped to a certain link. According to one embodiment, at a specific time, a certain TID or a certain AC may be mapped to at least one link. Furthermore, management frames or control frames may be transmitted on all links.

[0121] In the present invention, a data frame corresponding to a TID or AC mapped to a certain direction of a link may be transmitted, and a data frame corresponding to a TID or AC not mapped to a certain direction of a link may not be transmitted.

[0122] According to one embodiment, the TID-to-link mapping may also be applied to the acknowledgment. For example, a block ack agreement may be based on the TID-to-link mapping. Alternatively, the TID-to-link mapping may be based on the block ack agreement. For example, a block ack agreement may exist for a TID-to-link mapped TID.

[0123] TID-to-link mapping can provide QoS services. For example, by mapping a high-priority AC and TID to a link with good channel conditions or few STAs, data for that AC and TID can be transmitted faster. Alternatively, TID-to-link mapping can help STAs on a specific link save power (or enter a doze state).

[0124] 10, there may be an AP MLD including AP1 and AP2. There may also be a Non-AP MLD including STA1 and STA2. There may also be multiple links, Link1 and Link2, in the AP MLD. AP1 and STA1 may be associated via Link1, and AP2 and STA2 may be associated via Link2.

[0125] Therefore, Link1 may include a link transmitting from AP1 to STA1 and / or a link transmitting from STA1 to AP1, and Link2 may include a link transmitting from AP2 to STA2 and / or a link transmitting from STA2 to AP2. In this case, each link may be mapped with a TID and / or AC.

[0126] For example, all TIDs and all ACs may be mapped to Link1, a link for transmission from AP1 to STA1, and a link for transmission from STA1 to AP1. Also, only AC_VO or a TID corresponding to AC_VO may be mapped to Link2, a link for transmission from STA2 to AP2. Only data of mapped TIDs and / or ACs can be transmitted on the link. Data of TIDs or ACs not mapped to a link is not transmitted on the link.

[0127] FIG. 11 shows a power management operation performed by a station according to an embodiment of the present invention.

[0128] According to an embodiment of the present invention, a station can operate in a power save mode (PS). At this time, a station operating in the power save mode can switch between an awake state and a doze state. In the awake state, the station operates at full power. Also, in the awake state, the station can transmit and receive. In the power save state, the station may be restricted from transmitting and receiving. If a frame to be transmitted in the power save mode is buffered in the station, the station switches to the awake state; otherwise, the station can operate in the power save state. In the power save mode, the station can frequently switch between the awake state and the power save state. In the active mode, the station always maintains a state in which it can transmit and receive. That is, in the active mode, the station can always operate in the awake state.

[0129] As such, when a station operates in a power-saving mode, the station may be unable to receive. Therefore, the AP signals to the station that traffic to be transmitted is buffered, receives a response from the station, and then transmits. For convenience of explanation, the signaling by the AP to the station that traffic to be transmitted is buffered is referred to as a traffic indication. Also, signaling for traffic indication is referred to as traffic indication signaling. Traffic indication between the AP and the station may be performed as follows. In this specification, traffic may include any one of a frame, a BU, an MSDU, and an MPDU.

[0130] When traffic to be transmitted to a station is buffered in an AP, the AP may transmit traffic indication signaling indicating that the traffic to be transmitted to the station has been buffered. In this specification, the traffic indication signaling may indicate that traffic has been buffered, and is not limited to traffic for a specific station, depending on the context. The traffic indication signaling may include at least one of a traffic indication map (TIM) element and a multi-link traffic element. The traffic indication signaling may be in a bitmap format. Specifically, the traffic indication signaling may indicate whether traffic corresponding to each bit of the bitmap has been buffered in the AP transmitting the bitmap. The traffic indication signaling may also indicate the recipient of the buffered traffic. For example, the traffic indication signaling may indicate that the buffered traffic corresponds to at least one of group addressed traffic, groupcast traffic, broadcast traffic, and individually addressed traffic. The bitmap may signal which group or station the traffic corresponds to depending on the position of the bit in the bitmap. A station can determine whether traffic corresponding to a group to which the station belongs is buffered in the AP or whether traffic for the station is buffered in the AP, depending on the position of the bit in the bitmap.

[0131] The traffic indication signaling may be transmitted based on a predetermined time point. Accordingly, a station in a power-save state may transition from a power-save state to an awake state based on the time point at which the traffic indication signaling is transmitted. The traffic indication signaling may be included in a beacon frame. Alternatively, the traffic indication signaling may be included in a TIM frame. Alternatively, the AP may periodically transmit the traffic indication signaling. Specifically, the AP may transmit the traffic indication signaling based on a target beacon transmission time (TBTT). However, if the channel is not idle (busy) at the TBTT, the AP may transmit the traffic indication signaling at a time point later than the TBTT. The station may remain awake at the TBTT to receive the traffic indication signaling. A beacon frame including the traffic indication signaling may not be transmitted exactly at the TBTT. Therefore, the station may remain awake for a certain period of time including the TBTT.

[0132] In the above embodiment, the traffic indication signaling is described as being transmitted by an AP and received by a station. In this case, the station may be a non-AP station. Also, the AP may be included in an AP multilink device, and the non-AP station may be included in a non-AP multilink device. Also, the traffic may represent a bufferable unit (BU) or a buffered BU.

[0133] An AP can send a DTIM (delivery TIM) before sending group-addressed traffic or broadcast traffic. DTIM is a type of TIM that indicates whether group-addressed traffic and broadcast traffic have been buffered in the AP. A beacon frame that includes a DTIM can be called a DTIM beacon frame. If a station receives a DTIM that indicates that group traffic for a group that includes the station is to be transmitted, the station can send signaling to the AP to indicate that it will receive the group traffic.

[0134] Upon receiving the traffic indication signaling, the station may transmit a signaling to retrieve transmission for the station. In this case, the signaling to retrieve transmission for the station may be at least one of a PS-Poll frame or a U-APSD trigger frame. Upon receiving the signaling to retrieve transmission for the station, the AP transmits buffered traffic to the station.

[0135] In FIG. 11, the first AP (AP1) includes a TIM in the beacon frame and transmits the beacon frame every TBTT. The TIM transmitted by the first AP (AP1) indicates that traffic for the first station (STA1) is buffered. The first station (STA1) transmits a PS-Poll frame and remains awake to receive traffic. The first AP (AP1) transmits the buffered traffic (Data to STA1) to the first station (STA1). The first station (STA1) receives the buffered traffic and can enter a power-saving state. The first station (STA1) can also remain awake when transmitting the next TIM.

[0136] Also, in FIG. 11, the first AP (AP1) transmits a DTIM every three beacon frames. Therefore, the DTIM interval is three beacon frames. At this time, the first station (STA1) operating in power save mode maintains an awake state every time a TIM is transmitted. After transmitting the DTIM beacon, the first AP (AP1) transmits broadcast traffic or group address traffic. If the DTIM indicates that the broadcast traffic or group address traffic to be received by the first station (STA1) is buffered, the first station (STA1) maintains an awake state to receive the broadcast traffic or group address traffic. This allows the first station (STA1) to stably receive broadcast traffic or group address traffic even in power save mode. The format of a TIM element that can be included in traffic indication signaling will be described with reference to FIG. 12.

[0137] FIG. 12 shows the format of a TIM element according to an embodiment of the present invention.

[0138] The TIM element includes the TIM described above. The TIM element may include at least one of an Element ID subfield, a Length subfield, a DTIM Count subfield, a DTIM Period subfield, a Bitmap Control subfield, and a Partial Virtual Bitmap subfield. The Element ID subfield, the Length subfield, the DTIM Count subfield, the DTIM Period subfield, and the Bitmap Control subfield each have a length of 1 octet, i.e., 8 bits. The Partial Virtual Bitmap subfield may have a variable length up to a maximum of 251 octets. The length of the Partial Virtual Bitmap subfield may be determined by the Bitmap Control field or the Bitmap Offset subfield of the Bitmap Control field.

[0139] The Element ID subfield indicates the ID of the element that contains it.

[0140] The Length subfield indicates the length of the element it is included in. Specifically, the Length subfield can indicate the length of the element excluding the Element ID subfield and the Length subfield.

[0141] The DTIM Count subfield indicates how many beacon frames are to be transmitted until the next DTIM. Specifically, the value of the DTIM Count subfield can indicate how many beacon frames are to be transmitted until the next DTIM, including the beacon frame in which the DTIM Count subfield is included. For example, a value of 0 in the DTIM Count subfield can indicate that the DTIM Count subfield is included in the DTIM beacon.

[0142] The DTIM Period subfield indicates the number of beacon frames transmitted during a DTIM. If all TIMs are DTIMs, the value of the DTIM Period subfield is set to 1.

[0143] The Bitmap Control subfield may include a Traffic Indicator subfield and a Bitmap Offset subfield. The Traffic Indicator subfield may be a 1-bit field, and the Bitmap Offset subfield may be a 7-bit field. The Traffic Indicator subfield may indicate whether group address traffic is buffered. Specifically, if group address traffic is buffered, the AP may set the value of the Traffic Indicator subfield to 1. Group address traffic may be traffic whose receiver AID is 0. The Bitmap Offset subfield indicates the starting point of the bit corresponding to the Partial Virtual Bitmap in the Traffic indication virtual bitmap. The AID (association ID) corresponding to the Partial Virtual Bitmap is determined by the Bitmap Offset subfield.

[0144] Each bit in the Partial Virtual Bitmap field indicates whether traffic to be transmitted to a station with an AID corresponding to that bit is buffered in the AP transmitting the TIM. When the value of a bit in the Partial Virtual Bitmap field is 1, it indicates that traffic to be transmitted to a station with an AID corresponding to that bit is buffered in the AP transmitting the TIM. When the value of a bit in the Partial Virtual Bitmap field is 0, it indicates that traffic to be transmitted to a station with an AID corresponding to that bit is not buffered in the AP transmitting the TIM. Therefore, when the value of a bit in the Partial Virtual Bitmap field is 1, a station receiving a TIM can determine that traffic to be transmitted to a station with an AID corresponding to that bit is buffered in the AP transmitting the TIM. When the value of a bit in the Partial Virtual Bitmap field is 0, a station receiving a TIM can determine that traffic to be transmitted to a station with an AID corresponding to that bit is not buffered in the AP transmitting the TIM. Furthermore, a station that receives a TIM can determine that traffic to be sent to a station with an AID not specified by the Partial Virtual Bitmap is not buffered in the AP that sends the TIM.

[0145] The TIM element may include a Traffic indication virtual bitmap subfield. In this case, the bit number in the Traffic indication virtual bitmap subfield may indicate the AID of the station corresponding to the bit. Specifically, a bit with bit number n in the Traffic indication virtual bitmap subfield indicates that a frame transmitted to a station with AID n is buffered in the AP transmitting the TIM element. Specifically, when the bit number in the Traffic indication virtual bitmap subfield is N, the bit may indicate whether traffic transmitted to a station with AID N or a group with Group ID N is buffered in the AP transmitting the TIM element. The TIM may include a Partial Virtual Bitmap subfield instead of the Traffic indication virtual bitmap subfield. The Partial Virtual Bitmap subfield is the Traffic indication virtual bitmap subfield with consecutive bits set to 0 omitted. The Partial Virtual Bitmap subfield may be the Traffic indication virtual bitmap subfield with the first consecutive bits or the last consecutive bits omitted from a set of consecutive bits set to 0 omitted. Specifically, the Partial Virtual Bitmap subfield may be bits from octet number N1 to N2 in the Traffic indication virtual bitmap subfield, where N1 may be the largest even number in the Traffic indication virtual bitmap subfield where bit numbers 1 to (N1*8-1) are all 0.N2 may be the smallest number in the Traffic indication virtual bitmap subfield where all bit numbers from (N2+1)*8 to 2007 are 0. This may be a method for configuring the Partial Virtual Bitmap subfield when multiple BSSID sets are not supported, i.e., when dot11MultiBSSIDImplemented is false. In this specification, the bit number n of a bitmap or subfield represents the (n+1)th bit of the bitmap or subfield.

[0146] When the values ​​of all bits in the Traffic indication virtual bitmap subfield except for the bit with bit number 0 are 0, the Partial Virtual Bitmap subfield has a length of 1 octet, and the values ​​of all bits in the Partial Virtual Bitmap subfield may be set to 0. In this case, the value of the Bitmap Offset field may be 0, and the value of the Length field may be set to 4.

[0147] Also, when the value of all bits in the Traffic indication virtual bitmap subfield is 0 and the value of all bits in the Bitmap Control subfield is 0, the TIM element may not include the Partial Virtual Bitmap field and the Bitmap Control field. In this case, the value of the Length field may be set to 2. Thus, the Bitmap Control field may be present in the TIM when the Partial Virtual Bitmap field is present.

[0148] When multiple BSSID sets are supported, i.e., when dot11MultiBSSIDImplemented is True, a method for configuring the Partial Virtual Bitmap subfield may be performed according to the following embodiment. When multiple BSSID sets are used, a management frame transmitted from an AP corresponding to a transmitted BSSID may include information for a BSS corresponding to a nontransmitted BSSID. In this case, the management frame may include at least one of a beacon frame and a probe response frame. The TIM element of a beacon frame transmitted from a transmitted BSSID may indicate whether an AP corresponding to a nontransmitted BSSID included in a multiple BSSID set including the transmitted BSSID buffers the frame. Taking this into consideration, a method for configuring the Partial Virtual Bitmap subfield will be described.

[0149] If the maximum number of BSSIDs that a multiple BSSID set can have is n, bits from bitmap number 1 to bitmap number (2^n-1) in the Traffic indication virtual bitmap subfield can indicate whether a group address frame is buffered in the AP transmitting the TIM element. In this case, the group address frame may be a frame buffered in an AP corresponding to a nontransmitted BSSID. Therefore, the group address frame is a group address frame of an AP or BSS corresponding to a nontransmitted BSSID. Each of bits from bitmap number 1 to bitmap number (2^n-1) in the Traffic indication virtual bitmap subfield can indicate whether a frame is buffered in the AP corresponding to that bit. In this case, bits in the Traffic indication virtual bitmap subfield with bit numbers greater than (2^n-1) indicate whether a frame transmitted to a station with AID n is buffered in the AP transmitting the TIM element. Therefore, an AP does not need to assign AIDs from 1 to (2^n-1). In this embodiment, bits corresponding to inactive nontransmitted BSSIDs may be set as reserved bits. In this case, the value of the reserved bits may be set to 0. The AP may also assign AIDs to stations with values ​​equal to or greater than 2^n. In this case, the AP may assign AIDs to stations from values ​​ranging from 2^n to 2007. The EHT AP may not assign 2007 as an AID. This range of AIDs that can be assigned is called an AID space. Transmitted BSSIDs and nontransmitted BSSIDs may share one AID space. In a specific embodiment, the EHT AP may not assign 2007 as an AID to a station.

[0150] The maximum number of BSSIDs, n, that a multiple BSSID set may have may be signaled in the multiple BSSID element, where n may be the value indicated by the MaxBSSID Indicator of the multiple BSSID element.

[0151] The following describes how to configure the Partial virtual bitmap subfield. The method for configuring the Partial virtual bitmap subfield may vary depending on the multiple BSSID set-related capabilities of the AP transmitting the TIM element. A non-S1G AP can configure the Partial virtual bitmap subfield using Method A or Method B. An S1G AP can configure the Partial virtual bitmap subfield using Method C. A non-HT AP, HT AP, VHT AP, HE AP, or EHT AP may all be a non-S1G AP. An S1G AP refers to an AP that operates in a frequency band below 1 GHz, while a non-S1G AP refers to an AP that operates in a frequency band above 1 GHz.

[0152] First, we will explain method A. The subfield of the partial virtual bitmap may be composed of bits with octet numbers 0 to N2 in the traffic indication virtual bitmap. N2 is the smallest number among the numbers that satisfy the condition that all bit values ​​from bit numbers (N2+1)*8 to 2007 in the traffic indication virtual bitmap are 0. If no N2 satisfies this condition, N2 is 250. In method A, the value of the Bitmap Offset field is 0. Also, the value of the Length field is N2+4.

[0153] Describe Method B. The subfield of the Partial virtual bitmap may be composed of bits from octet number 0 to (N0 - 1) of the Traffic indication virtual bitmap and bits from octet number N1 to N2 of the Traffic indication virtual bitmap. N0 may be the largest positive integer that satisfies (N0 * 8 - 2^n < 8). When N0 is odd, N1 may be an even number greater than N0 and the largest even number that satisfies that the values of bits from bit number N0 * 8 to (N1 * 8 - 1) are all 0. When there is no value greater than N0, N1 may be N0. Also, N2 may be the smallest positive integer that satisfies that the values of bits from bit number (N2 + 1) * 8 to 2007 of the Traffic indication virtual bitmap are all 0. When there is no N2 that satisfies this, N2 may be 250. In Method B, the value of the Bitmap Offset field is (N1 - N0) / 2. Also, the value of the Length field is (N0 + N2 - N1 + 4). When there is no buffered frame in any BSS corresponding to the transmitted BSSID and the nontransmitted BSSID, the length of the Partial Virtual Bitmap subfield is 1 octet, and the values of the bits of the Partial Virtual Bitmap subfield may all be set to 0. At this time, the value of the Bitmap Offset field is 0. Also, the value of the Length field is 4.

[0154] If no individually addressed frames are buffered in any of the BSSs corresponding to the transmitted and nontransmitted BSSIDs, and group addressed frames are buffered in one or more BSSs, the Partial virtual bitmap subfield may consist of bits from octet number 0 to (N0-1), where N0 is the largest positive integer such that (N0*8-2^n)<8.

[0155] It may be necessary for the multilink device to direct buffered traffic to each of the multiple links it operates on, as will be explained with reference to Figures 13 to 18.

[0156] FIG. 13 shows the format of a Multi-Link Traffic element according to an embodiment of the present invention.

[0157] APs operating in one multilink device can share an AID space. Specifically, one multilink device may have one AID space. In this case, when indicating buffered frames to an AP using the TIM element described in FIG. 12, a station may have difficulty determining which link the frame is buffered on. To solve this problem, a traffic indication signaling method is needed. Specifically, the multilink device can perform traffic indication signaling for each link. In a specific embodiment, the multilink device can perform traffic indication signaling for each station belonging to the multilink device. The TIM element transmitted by the multilink device can indicate whether there are buffered frames on each multilink operated by the multilink device. In this case, the TIM element transmitted by the multilink device is called a Multi-Link Traffic element.

[0158] A multi-link device can transmit a Multi-Link Traffic element in a beacon frame or a TIM frame, and the Multi-Link Traffic element may be included in a frame that includes a TIM element.

[0159] In FIG. 13, the Multi-Link Traffic element may include an Element ID subfield, a Length subfield, an Element ID Extension subfield, a Multi-Link Traffic Control subfield, and a Per-Link Traffic Indication List subfield.

[0160] The Element ID subfield is a one-octet field that indicates the ID of the element that contains it.

[0161] The Length subfield is a one-octet field that indicates the length of the element it is included in. Specifically, the Length subfield can indicate the length of the element excluding the Element ID subfield and the Length subfield.

[0162] The Element ID Extension subfield is a one-octet field that indicates a value that, when combined with the value of the Element ID subfield in which it is included, identifies the element.

[0163] The Multi-Link Traffic Control subfield is a 1-octet field and includes a Bitmap Size subfield and an AID Offset subfield. The Bitmap Size subfield is a 4-bit subfield and indicates the size of the Per-Link Traffic Indication Bitmap subfield. If the value of Bitmap Size is M, the size of the Per-Link Traffic Indication Bitmap subfield may be M+1. A Bitmap Size value of 0 is a reserved value.

[0164] The AID Offset subfield is an 11-bit subfield that indicates the starting position of the bit in the Traffic Indication virtual bitmap indicated by the Per-Link Traffic Indication List or Per-Link Traffic Indication Bitmap subfield. Therefore, the AID (association ID) corresponding to the Per-Link Traffic Indication List or Per-Link Traffic Indication Bitmap subfield is determined by the AID Offset subfield. If the value of AID Offset is K, the Per-Link Traffic Indication List or Per-Link Traffic Indication Bitmap subfield indicates bit number K of the Traffic Indication virtual bitmap first. Also, if the value of the AID Offset subfield is K, the smallest value of the AIDs corresponding to the Per-Link Traffic Indication List or Per-Link Traffic Indication Bitmap subfield is K. The Per-Link Traffic Indication List subfield is a variable-length field and may include one or more Per-Link Traffic Indication Bitmap subfields. When the value of the AID Offset subfield is K, each Per-Link Traffic Indication Bitmap subfield indicates the Traffic indication virtual bitmap starting from bit number K. The number of Per-Link Traffic Indication Bitmap subfields included in the Per-Link Traffic Indication List subfield may be the number of bits set to 1 among the bits corresponding to the AID of the non-AP multilink device in the Partial Virtual Bitmap.The plurality of Per-Link Traffic Indication Bitmap subfields may be Per-Link Traffic Indication List subfields, and may be sorted by AIDs corresponding to the Per-Link Traffic Indication Bitmap subfields. Specifically, the plurality of Per-Link Traffic Indication Bitmap subfields may be Per-Link Traffic Indication List subfields, and may be sorted in ascending order of AIDs corresponding to the Per-Link Traffic Indication Bitmap subfields.

[0165] When the value of the Bitmap Size field is m, the size of the Per-Link Traffic Indication Bitmap subfield is m+1 bits. When the TID-to-link mapping negotiation is successful, the bit of the Per-Link Traffic Indication Bitmap subfield indicates whether traffic to be transmitted to a non-AP station operating on the link corresponding to that bit is buffered. Specifically, when the value of a bit of the Per-Link Traffic Indication Bitmap subfield is 1, the bit of the Per-Link Traffic Indication Bitmap subfield may indicate that traffic to be transmitted to a non-AP station operating on the link corresponding to that bit is buffered. When the value of a bit of the Per-Link Traffic Indication Bitmap subfield is 0, the bit of the Per-Link Traffic Indication Bitmap subfield may indicate that traffic to be transmitted to a non-AP station operating on the link corresponding to that bit is not buffered. When the TID-to-link mapping is the default mapping, a bit in the Per-Link Traffic Indication Bitmap subfield may indicate whether to recommend retrieving buffered traffic transmission on the link corresponding to the bit. Specifically, when the value of a bit in the Per-Link Traffic Indication Bitmap subfield is 1, the bit in the Per-Link Traffic Indication Bitmap subfield may indicate that it is recommended to request transmission of buffered traffic on the link corresponding to the bit. When the TID-to-link mapping of a link corresponds to the default mapping, uplink and downlink transmissions on the link may be performed without TID restrictions. In addition, the default mapping is applied to links for which TID-to-link mapping negotiation has not been successfully completed.Therefore, if the TID-to-link mapping negotiation is successful, it can indicate the case where the TID-to-link mapping negotiation is successful and not all TIDs are mapped to all links.

[0166] The bits in the Per-Link Traffic Indication Bitmap subfield are mapped to links according to their bit numbers. Specifically, a bit in the Per-Link Traffic Indication Bitmap subfield with bit number n may be mapped to a link with link ID n. Furthermore, the Per-Link Traffic Indication List subfield may include a padding field. As a result, the Per-Link Traffic Indication List subfield may have a length in octets. The padding field may have a length of 0 to 7 bits.

[0167] The AP multilink device can transmit a frame including both a Multi-Link Traffic element and a TIM element, which may be a beacon frame. Figure 14 illustrates how the AP multilink device uses the Multi-Link Traffic element and the TIM element to signal buffered traffic to the AP multilink device.

[0168] FIG. 14 illustrates how the Partial Virtual Bitmap subfield of the Multi-Link Traffic element and the TIM element signal buffered traffic to an AP multi-link device according to an embodiment of the present invention.

[0169] The bit corresponding to the non-AP multilink device in the Partial Virtual Bitmap subfield or Traffic indication virtual bitmap of the TIM element transmitted by the AP multilink device may be set to 1. In this case, the non-AP multilink device can parse the Multi-Link Traffic element. Based on the Per-Link Traffic Indication Bitmap subfield corresponding to the non-AP multilink device in the Multi-Link Traffic element, the non-AP multilink device can determine which link the non-AP multilink device recommends retrieving buffered traffic from or which link the non-AP multilink device has buffered traffic on. As described in FIG. 13, if the TID-to-link mapping negotiation is successful, the non-AP multilink device can determine whether traffic to be transmitted to a station in the non-AP multilink device operating on the link corresponding to the bit is buffered based on the value of the bit in the Per-Link Traffic Indication Bitmap subfield corresponding to the non-AP multilink device. In addition, when the TID-to-link mapping is the default mapping, the non-AP multilink device can indicate whether or not to recommend that the AP multilink device request transmission of buffered traffic on the link corresponding to the bit, based on the value of the bit in the Per-Link Traffic Indication Bitmap subfield corresponding to the non-AP multilink device.

[0170] A non-AP multilink device may request the AP multilink device to transmit buffered traffic on links corresponding to bits set to 1 among bits in the Per-Link Traffic Indication Bitmap subfield corresponding to the non-AP multilink device. Specifically, if the TID-to-link mapping negotiation is successful, the non-AP multilink device may request the AP multilink device to transmit buffered traffic on links corresponding to bits set to 1 among bits in the Per-Link Traffic Indication Bitmap subfield corresponding to the non-AP multilink device. If the TID-to-link mapping is the default mapping, the non-AP multilink device may request the AP multilink device to transmit buffered traffic on one or more links, including links corresponding to bits set to 1 among bits in the Per-Link Traffic Indication Bitmap subfield corresponding to the non-AP multilink device. In such an embodiment, the non-AP multilink device may transmit a U-APSD trigger frame or a PS-Poll frame to request the AP multilink device to transmit buffered traffic. When a request for transmission of buffered traffic is received, the AP multilink device can transmit the buffered traffic to the non-AP multilink device, and when a request for transmission of buffered traffic is received, the AP multilink device can transmit a QoS Null frame in place of the buffered traffic.

[0171] In the embodiment of FIG. 14, a legacy station before EHT or a station for which TID-to-link mapping is set as the default mapping is assigned an AID value smaller than K. A non-AP station for which TID-to-link mapping has been successfully negotiated is assigned an AID value equal to or greater than K. In the Traffic Indication Virtual Bitmap of FIG. 14, all bits smaller than bit number (N-1)*8 are set to 0. Therefore, the AP multilink device does not buffer traffic for stations with AIDs smaller than (N-1)*8. At least one bit of bits corresponding to bit number (N-1)*8 or greater is set to 1. N-1 is an even number, and N*8 is the value k. Therefore, the Partial Virtual Bitmap subfield begins with bit number (N-1)*8 of the Traffic Indication Virtual Bitmap. In this case, the value of the Bitmap Offset subfield of the Partial Virtual Bitmap subfield is set to (N-1) / 2. In addition, the values ​​of the bits in the Partial Virtual Bitmap subfield that correspond to AIDs (N-1)*8, (N-1)*8+2, (N-1)*8+3, k, k+2, and k+3 are set to 1.

[0172] As described above, the AID Offset subfield of the Multi-Link Traffic element can indicate the AID of the multi-link device corresponding to the leading one of the Per-Link Traffic Indication Bitmap subfields of the Multi-Link Traffic element. In Figure 14, the value of the AID Offset subfield is set to K. The Multi-Link Traffic element includes a Per-Link Traffic Indication Bitmap subfield corresponding to the multi-link device for which the Partial Virtual Bitmap subfield is set to 1. In Figure 14, the Multi-Link Traffic element includes Per-Link Traffic Indication Bitmap subfields for each of the stations or non-AP multi-link devices whose AIDs are k, k+2, and k+3. In this case, the Per-Link Traffic Indication Bitmap subfields are sorted in ascending order of AID.

[0173] The value of the Bitmap Size field of the Multi-Link Traffic element is 2. Therefore, the Per-Link Traffic Indication Bitmap subfield of the Multi-Link Traffic element includes 3 bits. In this case, the first bit (B0) of the Per-Link Traffic Indication Bitmap subfield is mapped to a link whose link ID is 0, the second bit (B1) is mapped to a link whose link ID is 1, and the third bit (B2) is mapped to a link whose link ID is 2.

[0174] As described above, default mapping is applied to the multilink device with AID value K, and TID-to-link mapping is successfully performed for the multilink devices with AID values ​​K+2 and K+3. Therefore, the Per-Link Traffic Indication Bitmap subfield corresponding to AID K indicates that a request for transmission of buffered traffic on the link with link ID 1 is recommended. Furthermore, the Per-Link Traffic Indication Bitmap subfield corresponding to AID K+2 indicates that the AP multilink device is buffering traffic on two links with link IDs 1 and 2. In this case, the traffic buffered on the link with link ID 1 and the traffic buffered on the link with link ID 2 may be the same or different. Furthermore, the Per-Link Traffic Indication Bitmap subfield corresponding to AID K+3 indicates that the AP multilink device is buffering traffic on the link with link ID 1.

[0175] However, it may not be guaranteed that the AIDs of non-AP multilink devices connected to the AP multilink device are assigned consecutively. Furthermore, AIDs of non-AP stations not included in the multilink device may be assigned between AIDs of non-AP multilink devices. In this case, it may be difficult for the non-AP multilink device to determine which AIDs are stations not included in the non-AP multilink device. Therefore, if the Multi-Link Traffic element does not include a Per-Link Traffic Bitmap subfield for stations not included in the non-AP multilink device, it may be difficult for the non-AP multilink device to parse the Per-Link Traffic Bitmap subfield. For example, in the embodiment of FIG. 14, AID K+1 is assigned to the non-AP multilink device, and the bit corresponding to AID K+1 in the Partial Virtual Bitmap subfield of the TIM element may have a value of 1. In this case, a non-AP multilink device with AID K+2 or K+3 cannot determine which of the three Per-Link Traffic Bitmap subfields is the Per-Link Traffic Bitmap subfield for that non-AP multilink device. Therefore, a method for configuring the Multi-Link Traffic element is required to resolve this issue. This will be explained with reference to FIG. 15.

[0176] FIG. 15 illustrates a method for configuring a Multi-Link Traffic element according to an embodiment of the present invention.

[0177] In an embodiment of the present invention, the AP multilink device may include a Per-Link Traffic Bitmap subfield for non-AP stations not included in the multilink device in the Multi-Link Traffic element. Specifically, the AP multilink device may include a Per-Link Traffic Bitmap subfield for non-AP stations in the Multi-Link Traffic element even if the non-AP station is not included in the multilink device, if the bit value of the Traffic Indication Bitmap subfield or the Partial Virtual Bitmap subfield corresponding to the non-AP station is 1. Therefore, the AP multilink device may include a Per-Link Traffic Bitmap subfield for all stations corresponding to a bit of the Traffic Indication Bitmap subfield or a bit of the Partial Virtual Bitmap subfield set to 1 in the Multi-Link Traffic element. For convenience of explanation, a station corresponding to a bit of the Traffic Indication Bitmap subfield or a bit of the Partial Virtual Bitmap subfield set to 1 is referred to as a station for which buffered traffic is indicated.

[0178] In this case, the AP multilink device can include a Per-Link Traffic Bitmap subfield for all stations to which buffered traffic is indicated in the Multi-Link Traffic element, regardless of whether the station to which buffered traffic is indicated belongs to the multilink device, whether it corresponds to a non-AP multilink device, or which AP or BSS it belongs to. The AP or BSS to which the station to which buffered traffic is indicated belongs can indicate whether the station to which buffered traffic is indicated belongs to a multiple BSSID set.

[0179] The AP multilink device can include the same number of Per-Link Traffic Bitmap subfields as the number of stations for which buffered traffic is indicated in the Multi-Link Traffic element. A method for the AP multilink device to set the Per-Link Traffic Bitmap subfields corresponding to stations that do not belong to the multilink device will be described.

[0180] The AP multilink device can set all bit values ​​in the Per-Link Traffic Bitmap subfield corresponding to stations that do not belong to the multilink device to 0. That is, the AP multilink device can set the bit values ​​in the Per-Link Traffic Bitmap subfield corresponding to stations that do not belong to the multilink device as reserved fields. In yet another specific embodiment, the AP multilink device can set the bit values ​​in the Per-Link Traffic Bitmap subfield corresponding to stations that do not belong to the multilink device to an arbitrary value. In yet another specific embodiment, the AP multilink device can set the bit values ​​in the Per-Link Traffic Bitmap subfield corresponding to stations that do not belong to the multilink device to 1. In this case, the non-AP multilink device can ignore the bit values ​​in the Per-Link Traffic Bitmap subfield corresponding to stations that do not belong to the multilink device. In yet another specific embodiment, the AP multilink device can set the bit values ​​in the Per-Link Traffic Bitmap subfield corresponding to stations that do not belong to the multilink device to 1. In yet another specific embodiment, the AP multilink device can set the value of the bit in the Per-Link Traffic Bitmap subfield corresponding to the link on which a station not belonging to the multilink device operates to 1, and set the value of the remaining bits to 0.

[0181] In the embodiment of Figure 15, the settings of the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfield may be the same as the settings of the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfield in Figure 14. However, in the embodiment of Figure 15, AID k and AID k+3 correspond to non-AP multilink devices. AID k+2 corresponds to a station not included in the multilink device. The Per-Link Traffic Bitmap subfields corresponding to AID k and AID k+3 of the Multi-Link Traffic element are set as in the embodiment of Figure 14. Because AID k+2 is a station not included in the multilink device, all bits of the Per-Link Traffic Bitmap subfield corresponding to AID k+2 of the Multi-Link Traffic element are set to 0.

[0182] The AID Offset subfield of the Multi-Link Traffic element may indicate bits after all bits corresponding to the Group ID and group address frame in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfield. In this case, the Group ID may include an AID value of 0. The Group ID may also include a bit number in the Traffic indication virtual bitmap corresponding to a multiple BSSID set, i.e., an AID corresponding to the bit number. The Group ID may also include a bit number in the Traffic indication virtual bitmap corresponding to a transmitted BSSID and a nontransmitted BSSID, i.e., an AID corresponding to the bit number. The Group ID may include values ​​corresponding to AID 0 to (2^n-1) when the maximum number of BSSIDs possible in a multiple BSSID set is 2^n. The AID Offset subfield may indicate values ​​after the value corresponding to AID 0 to (2^n-1) when multiple BSSID sets are used and the maximum number of BSSIDs possible in a multiple BSSID set is 2^n. The reason for setting the AID Offset field in this way is that group address frames are not limited to those transmitted on a specific link, and therefore there is little point in signaling them for each link.

[0183] According to yet another embodiment of the present invention, even if the AID Offset subfield indicates a bit in the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfield that is earlier than the bit indicating the Group ID, the Per-Link Traffic Indication Bitmap subfield corresponding to the Group ID may not be included in the Multi-Link Traffic element. Even if the AID Offset subfield indicates a bit in the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfield that is earlier than the bit indicating the Group ID, the Multi-Link Traffic element may only include Per-Link Traffic Indication Bitmap subfields corresponding to individual stations among the stations for which buffered traffic is indicated. Specifically, when the maximum number of configurable BSSIDs in a multiple BSSID set is 2^n, the AID Offset subfield may indicate a bit in the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfield that is earlier than the bit indicating the Group ID, corresponding to an AID that is (2^n-1) or less. In this case, the Multi-Link Traffic element may include only the Per-Link Traffic Indication Bitmap corresponding to the bits set to 1 among the bits of the Traffic indication virtual bitmap and the bits of the Partial Virtual Bitmap subfield corresponding to AID2^n.A station receiving the Multi-Link Traffic element can determine that the Multi-Link Traffic element contains only the Per-Link Traffic Indication Bitmap corresponding to the bits set to 1 among the bits of the Traffic indication virtual bitmap and the bits of the Partial Virtual Bitmap subfield corresponding to AID2^n.

[0184] According to yet another embodiment of the present invention, regardless of whether the AID Offset subfield indicates bits before the bit indicating the Group ID in the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfield, the Multi-Link Traffic element may include Per-Link Traffic Indication Bitmaps corresponding to all bits set to 1 after the bits indicated by the AID Offset subfield in the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfields. In this case, the AP multilink device may set the values ​​of the Per-Link Traffic Indication Bitmap fields corresponding to the bits of the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfields corresponding to the group address to a predetermined value. The predetermined value may be 0. In yet another specific embodiment, the AP multilink device may set the values ​​of the Per-Link Traffic Indication Bitmap fields corresponding to the bits of the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfields corresponding to the group address to any value. The AP multilink device can set the bit corresponding to the link through which the group address frame is transmitted to 1 and the remaining bits to 0 in the Per-Link Traffic Indication Bitmap field corresponding to the bits in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields corresponding to the group address.

[0185] Figure 16 shows a method for setting the Per-Link Traffic Bitmap subfield of the Multi-Link Traffic element when the link set in which an AP multi-link device operates in accordance with an embodiment of the present invention is different from the link set in which a non-AP multi-link device communicating with the AP multi-link device operates.

[0186] The link set in which an AP multilink device operates may differ from the link set in which a non-AP multilink device that communicates with the AP multilink device operates. For example, the AP multilink device may communicate with a first non-AP multilink device via links 1 to 3, and the AP multilink device may communicate with a second non-AP multilink device via links 1 and 2. In this case, the method for setting the Per-Link Traffic Bitmap subfield of the Multi-Link Traffic element may become an issue.

[0187] Even if the link set operated by the AP multilink device is different from the link set operated by a non-AP multilink device communicating with the AP multilink device, the AP can set the size of all Per-Link Traffic Indication Bitmap subfields included in the Multi-Link Traffic element to the same size and set the links mapped to each bit of all Per-Link Traffic Indication Bitmap subfields to the same size. Specifically, the AP multilink device can set the number of bits in all Per-Link Traffic Indication Bitmap subfields included in the Multi-Link Traffic element to a number greater than the number of links configured by the AP multilink device. This is because the link IDs configured by the AP multilink device may not start from 0 or the IDs of the multiple links may not be consecutive. For example, the AP multilink device can set the number of bits in all Per-Link Traffic Indication Bitmap subfields included in the Multi-Link Traffic element to the maximum number of links that the AP multilink device can configure. In yet another specific embodiment, the AP multilink device can set the number of bits of all Per-Link Traffic Indication Bitmap subfields included in the Multi-Link Traffic element to the value obtained by adding 1 to the maximum link ID value that the AP multilink device can set.

[0188] A problem may arise in how to set the value of a bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a link not established by the AP multilink device and a link not established by a non-AP multilink device corresponding to the Per-Link Traffic Indication Bitmap subfield. For convenience of explanation, a bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a link not established by the AP multilink device and a link not established by a non-AP multilink device corresponding to the Per-Link Traffic Indication Bitmap subfield is referred to as a no-link bit. The AP multilink device can set the value of the no-link bit to a pre-specified value. Therefore, the AP multilink device can set the bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a link not established by the AP multilink device or a non-AP multilink device to a pre-specified value. In this case, the pre-specified value may be 0. In yet another specific embodiment, the AP multilink device can set the value of the no-link bit to an arbitrary value. In this case, non-AP stations can ignore the value of the no-link bit.

[0189] In addition, the value of a bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a disabled link may be set to reserved. Specifically, the value of a bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a disabled link may be set to 0. In this case, a disabled link may be a link in which uplink and downlink transmissions are stopped. Specifically, a disabled link may be a link in which uplink and downlink transmissions of individual address frames are stopped. In this case, non-AP stations can ignore the value of the no-disabled bit.

[0190] In the embodiment of FIG. 16, as shown in FIG. 16(a), the AP multilink device (AP MLD) operates on the first link (Link 0) to the third link (Link 2). The first multilink device (MLD 1) and the AP multilink device (AP MLD) configure the first link (Link 0) to the third link (Link 2). The second multilink device (MLD 2) and the AP multilink device (AP MLD) configure the first link (Link 0) to the second link (Link 1). The AP multilink device (AP MLD) sets the number of bits in the Per-Link Bitmap subfield of the Multi-Link Traffic element to 3 bits. The Multi-Link Traffic element transmitted by the AP multilink device (AP MLD) includes Per-Link Bitmap subfields corresponding to the first multilink device (MLD 1), the first station (STA1), and the second multilink device (MLD 2). The AP multilink device (AP MLD) sets the value of the Per-Link Bitmap subfield corresponding to the first multilink device (MLD 1) according to the embodiment described in Figures 14 and 15. In addition, the AP multilink device (AP MLD) sets the value of the Per-Link Bitmap subfield corresponding to the first station (STA1) according to the embodiment described in Figure 15. The AP multilink device (AP MLD) sets the values ​​of the first bit (B0) and second bit (B1) of the Per-Link Bitmap subfield corresponding to the second multilink device (MLD 2) according to the embodiment described in Figures 14 and 15. In addition, the AP multilink device (AP MLD) sets the value of the third bit (B2) of the Per-Link Bitmap subfield corresponding to the second multilink device (MLD 2) to the pre-specified value 0, as described above.

[0191] In the above embodiment, it has been described that the bit number of a bit in the Per-Link Traffic Indication Bitmap subfield is the same as the ID of the link corresponding to that bit. Depending on a specific embodiment, the bit number of a bit in the Per-Link Traffic Indication Bitmap subfield may not be the same as the ID of the link corresponding to that bit. The link IDs of the links set by the AP multilink device that transmitted the Per-Link Traffic Indication Bitmap subfield may be mapped to the bit numbers of the bits in the Per-Link Traffic Indication Bitmap subfield in ascending order. The AP multilink device may set a link with an ID of 1 and a link with an ID of 3, and the Per-Link Traffic Indication Bitmap subfield may be a 2-bit field. In this case, the first bit (B0) of the Per-Link Traffic Indication Bitmap subfield is mapped to the link with an ID of 1, and the second bit (B1) is mapped to the link with an ID of 3.

[0192] FIG. 17 illustrates how the link indicated by the Per-Link Traffic Bitmap subfield is determined by TID-to-link mapping according to an embodiment of the present invention.

[0193] As described above, when the TID-to-link mapping negotiation is successful, a bit in the Per-Link Traffic Indication Bitmap subfield indicates whether traffic to be transmitted to a non-AP station operating on the link corresponding to the bit is buffered. Specifically, when the value of a bit in the Per-Link Traffic Indication Bitmap subfield is 1, the bit in the Per-Link Traffic Indication Bitmap subfield may indicate that traffic to be transmitted to a non-AP station operating on the link corresponding to the bit is buffered. When the value of a bit in the Per-Link Traffic Indication Bitmap subfield is 0, the bit in the Per-Link Traffic Indication Bitmap subfield may indicate that traffic to be transmitted to a non-AP station operating on the link corresponding to the bit is not buffered. When the TID-to-link mapping is the default mapping, the bit in the Per-Link Traffic Indication Bitmap subfield may indicate whether to recommend retrieving transmission of buffered traffic on the link corresponding to the bit. Specifically, when the value of a bit in the Per-Link Traffic Indication Bitmap subfield is 1, the bit in the Per-Link Traffic Indication Bitmap subfield may indicate that it is recommended to request transmission of buffered traffic on the link corresponding to that bit. If the TID-to-link mapping of a link corresponds to the default mapping, uplink and downlink transmissions on that link may be performed without TID restrictions. In addition, the default mapping is applied to links for which TID-to-link mapping negotiation has not been successfully completed or for which TID-to-link mapping negotiation has been torn down.

[0194] If the TID-to-link mapping negotiation is successful, it may indicate that the TID-to-link mapping is applied instead of the default mapping. Also, as described above, the TID-to-link mapping may be applied separately for each transmission direction. Therefore, in the above embodiment, if the TID-to-link mapping negotiation is successful, it may indicate that the TID-to-link mapping negotiation for downlink transmission is successful. Also, if the default mapping is applied, it may indicate that the TID-to-link mapping for downlink transmission is the default mapping.

[0195] In the example of Figure 17, the AP multilink device (AP MLD) and non-AP multilink device (non-AP MLD 1) successfully negotiate TID-to-link mapping. The AP multilink device (AP MLD) and non-AP multilink device (non-AP MLD 1) map TID value 0 to the uplink transmission of link 1 (link 0). The AP multilink device (AP MLD) and non-AP multilink device (non-AP MLD 1) also map TID values ​​1 to 7 to the uplink transmission of link 2 (link 1). In this case, the AP multilink device (AP MLD) and non-AP multilink device (non-AP MLD 1) apply default mapping to the downlink transmission of link 1 (link 0) and the downlink transmission of link 2 (link 1). Therefore, when the bit value of the Per-Link Traffic Indication Bitmap subfield transmitted by the AP multilink device (AP MLD) is 1, the non-AP multilink device (non-AP MLD 1) determines that the AP multilink device (AP MLD) recommends that the non-AP multilink device (non-AP MLD 1) request traffic transmission on the link corresponding to the bit set to 1. Since the bit value corresponding to the second link (link1) in the Per-Link Traffic Indication Bitmap subfield in FIG. 17(a) is 1, the non-AP multilink device (non-AP MLD 1) determines that it recommends that traffic transmission be requested on the second link (link1).

[0196] 17(b) shows a TID-to-Link Mapping element used for TID-to-link mapping negotiation. A multilink device can include the TID-to-Link Mapping element in a (Re)Association Request frame, a (Re)Association Response frame, a TID-To-Link Mapping Request frame, and a TID-To-Link Mapping Response frame. When a multilink device requests TID-to-link mapping, it can include the TID-to-Link Mapping element in a (Re)Association Request frame or a TID-To-Link Mapping Request frame. When a multilink device responds to a TID-to-link mapping request, it can include the TID-to-Link Mapping element in a (Re)Association Response frame or a TID-To-Link Mapping Response frame.

[0197] The TID-to-Link Mapping element may include an Element ID subfield, a Length subfield, an Element ID Extension subfield, a TID-To-Link Mapping Control subfield, and seven Link Mapping subfields corresponding to TIDs 0 to 7, respectively. The TID-To-Link Mapping Control subfield may include a Direction subfield, a Default Link Mapping subfield, a Reserved subfield, and a Link Mapping Presence Indicator subfield. The Direction subfield may indicate which transmission direction the TID-To-Link Mapping element including the Direction subfield indicates the mapping to be applied to. The Direction subfield may indicate at least one of downlink, uplink, and bidirectional link. The Default Link Mapping subfield may indicate whether the TID-To-Link Mapping element including the Default Link Mapping subfield is for TID-to-link mapping negotiation to apply default mapping. Specifically, the Default Link Mapping subfield may indicate whether the TID-To-Link Mapping element including the Default Link Mapping subfield is for TID-to-link mapping negotiation to apply default mapping to the transmission direction indicated by the Direction subfield.

[0198] Each bit of the Link Mapping Presence Indicator subfield may indicate whether the corresponding Link Mapping subfield is included in the TID-To-Link Mapping element. Each bit of the Link Mapping Presence Indicator subfield may be mapped to a Link Mapping subfield for a TID having a value similar to the bit index. That is, the nth bit (Bn-1) of the Link Mapping Presence Indicator subfield may be mapped to the Link Mapping subfield corresponding to TID n-1. The Link Mapping subfield indicates that the TID corresponding to the Link Mapping subfield is the target of TID-to-link mapping negotiation performed by the TID-to-Link Mapping element.

[0199] FIG. 18 illustrates a method for an AP multilink device to set a Per-Link Traffic Indication Bitmap subfield of a Multi-Link Traffic element according to yet another embodiment of the present invention.

[0200] In the embodiment described in FIG. 16, the Multi-Link Traffic element includes a Per-Link Traffic Indication Bitmap subfield for a station for which buffered traffic is indicated, regardless of whether the station for which buffered traffic is indicated is included in the multilink device. In yet another embodiment of the present invention, the Multi-Link Traffic element may include a Per-Link Traffic Indication Bitmap subfield for some of the stations for which buffered traffic is indicated, and may not include a Per-Link Traffic Indication Bitmap subfield for the remaining stations for which buffered traffic is indicated. In this case, the stations for which buffered traffic is indicated may be limited to stations for which buffered traffic is indicated after the bit corresponding to the AID indicated by the AID Offset subfield. Specifically, if the station for which buffered traffic is indicated in the Multi-Link Traffic element is not included in the multilink device, the AP multilink device may not include a Per-Link Traffic Indication Bitmap subfield for the station for which buffered traffic is indicated. This prevents the length of the Multi-Link Traffic element from becoming too long.

[0201] In yet another specific embodiment, the AP multilink device may not include a Per-Link Traffic Indication Bitmap subfield for stations corresponding to a specific bit or later among the stations for which buffered traffic is indicated in the Multi-Link Traffic element. A station receiving the Multi-Link Traffic element can determine the last Per-Link Traffic Indication Bitmap subfield included in the Multi-Link Traffic element based on the Length subfield of the Multi-Link Traffic element. Therefore, even if the Multi-Link Traffic element does not include a Per-Link Traffic Indication Bitmap subfield for stations corresponding to a specific bit or later among the stations for which buffered traffic is indicated, the station receiving the Multi-Link Traffic element can correctly parse the Multi-Link Traffic element. In such an embodiment, the AP multilink device may assign a smaller value to the AID for the station included in the multilink device than the AID for the station not included in the multilink device.

[0202] In the example of Figure 18, the AID Offset of the Multi-Link Traffic element indicates an AID value of K. Stations indicated to have buffered traffic with an AID greater than K are the two multilink devices with AIDs K and K+2 and stations not included in the multilink devices with AIDs K+6 and K+7. The Multi-Link Traffic element includes Per-Link Traffic Indication Bitmap subfields for the two multilink devices with AIDs K and K+2.

[0203] In yet another specific embodiment, the Multi-Link Traffic element may include an AID Offset2 subfield. A station receiving the Multi-Link Traffic element can parse the Per-Link Traffic Indication Bitmap subfield of the Multi-Link Traffic element based on the AID Offset2 subfield. The AID Offset2 subfield can indicate which AID the last Per-Link Traffic Indication Bitmap subfield of the Multi-Link Traffic element corresponds to. In this case, the AID Offset2 subfield can indicate all AID values. In yet another specific embodiment, the AID Offset2 subfield can indicate the maximum AID value that can correspond to the last Per-Link Traffic Indication Bitmap subfield.

[0204] In yet another specific embodiment, the AID Offset2 subfield may indicate the AID corresponding to the last Per-Link Traffic Indication Bitmap subfield in units of a preset number. For example, when the value of the AID Offset2 subfield is n, the AID Offset2 subfield may indicate the AID corresponding to the last Per-Link Traffic Indication Bitmap subfield as 2^N, where N is an integer. In this embodiment, the AID Offset2 subfield may have a length of (11-N) bits.

[0205] When the value of the AID Offset2 subfield is n, the AID Offset2 subfield can indicate that the AID value is 2^N*n, where n is an integer. For example, AIDs can be indicated in units of 8. In this case, the AID Offset2 subfield can have a length of 8 bits. In this embodiment, the AID Offset2 subfield can indicate AIDs of 8, 16, 24, 32, etc. This allows the length of the AID Offset2 subfield to be defined to be less than 11 bits.

[0206] In yet another specific embodiment, the AID Offset2 subfield may indicate the AID in the same unit as the AID Offset subfield, thereby reducing the number of bits occupied by the AID Offset2 subfield and the AID Offset subfield.

[0207] In the above-described embodiment, one frame may include multiple Multi-Link Traffic elements. Specifically, in an AID list in which the AID values ​​of stations indicating buffered traffic having AIDs equal to or greater than the AID indicated by the AID Offset subfield are sorted in ascending order, the AP multilink device can generate Multi-Link Traffic elements including Per-Link Traffic Indication Bitmaps for one or more multilink devices corresponding to the AID values, from the first AID in the list up to the AID corresponding to a station not included in the multilink device, up to the excluded AIDs thereafter. In this case, the AIDs up to the excluded AIDs are excluded from the AID list, and the AP multilink device can generate Multi-Link Traffic elements including Per-Link Traffic Indication Bitmaps for one or more multilink devices corresponding to the AID values ​​up to the new excluded AID in the AID list. The AP multilink device can repeat this operation until the end of the AID list and generate further Multi-Link Traffic elements including Per-Link Traffic Indication Bitmaps for one or more multilink devices. As a result, even if an AID that is not included in the multi-link device is assigned between the AIDs of the multi-link device, the Multi-Link Traffic element includes a Per-Link Traffic Indication Bitmap subfield for the multi-link device, but does not need to include a Per-Link Traffic Indication Bitmap subfield that is not included in the multi-link device.

[0208] In this embodiment, the non-AP multilink device can ignore a Multi-Link Traffic element that does not include a Per-Link Traffic Indication Bitmap subfield corresponding to the AID of the non-AP multilink device. The non-AP multilink device can determine whether a Multi-Link Traffic element includes a Per-Link Traffic Indication Bitmap subfield corresponding to the AID of the non-AP multilink device based on at least one of the values ​​of the AID Offset subfield and the Length subfield of the Multi-Link Traffic element. The non-AP multilink device can determine whether a Multi-Link Traffic element includes a Per-Link Traffic Indication Bitmap subfield corresponding to the AID of the non-AP multilink device based on at least one of the values ​​of the AID Offset subfield and the AID Offset2 subfield of the Multi-Link Traffic element.

[0209] Also, in the above-described embodiment, if the non-AP multi-link device is not the station for which the buffered traffic is directed, the non-AP multi-link device can ignore the Multi-Link Traffic element.

[0210] A method for determining the AID space will be described with reference to Figures 19 to 21. First, the EHT Operation element will be described with reference to Figure 19.

[0211] FIG. 19 illustrates an EHT Operation element according to an embodiment of the present invention.

[0212] Figure 19(a) shows the format of the EHT Operation element, and Figure 19(b) shows the EHT Operation Parameters field. The EHT Operation element may include an Operation Parameters field. The Operation Parameters field may be a 1-octet field. The EHT Operation element may include an EHT Operation Information field. The EHT Operation Information field may have a size of 0, 3, or 5 octets. The EHT Operation Information field may include an EHT Operation Information field or a Disabled Subchannel Bitmap field.

[0213] The EHT Operation Parameters field may include an EHT Operation Information Present subfield, a Disabled Subchannel Bitmap Present subfield, a Group Addressed BU Indication Limit subfield, and a Group Addressed BU Indication Exponent subfield. The EHT Operation Information Present subfield may be a 1-bit field, the Disabled Subchannel Bitmap Present subfield may be a 1-bit field, the Group Addressed BU Indication Limit subfield may be a 1-bit field, and the Group Addressed BU Indication Exponent subfield may be a 1-bit field.

[0214] The EHT Operation Information Present subfield may indicate whether the EHT Operation element includes an EHT Operation Information subfield. If the value of the EHT Operation Information Present subfield is 0, the EHT Operation element may not include an EHT Operation Information subfield. That is, if the EHT Operation Information Present subfield is set to 0, the length of the EHT Operation Information subfield may be 0 octets. If the value of the EHT Operation Information Present subfield is 1, the EHT Operation element may include an EHT Operation Information field. In this case, the length of the EHT Operation Information subfield may be 3 or 5 octets.

[0215] The Disabled Subchannel Bitmap Present subfield can indicate whether the EHT Operation Information field includes a Disabled Subchannel Bitmap subfield. If the value of the Disabled Subchannel Bitmap Present subfield is 0, the EHT Operation Information subfield may not include the Disabled Subchannel Bitmap subfield. In this case, the size of the EHT Operation Information subfield may be 3 octets. If the value of the Disabled Subchannel Bitmap Present subfield is 1, the EHT Operation Information subfield may include the Disabled Subchannel Bitmap subfield. In this case, the size of the EHT Operation Information subfield may be 5 octets.

[0216] The Group Addressed BU Indication Limit subfield can indicate whether there are buffered group address frames for all nontransmitted BSSIDs in the multiple BSSID set and other APs belonging to the same AP multilink device, and whether there is a limit to indicate this in the TIM element. A specific setting method for the Group Addressed BU Indication Limit subfield can be as follows:

[0217] If at least one of the following conditions is met, the Group Addressed BU Indication Limit subfield may be set to 0; otherwise, the Group Addressed BU Indication Limit subfield may be set to 1.

[0218] - Condition 1. The AP (the AP sending the EHT Operation element) does not belong to a multiple BSSID set.

[0219] - Condition 2. The AP (AP transmitting the EHT Operation element, AP transmitting the beacon frame, or AP corresponding to the transmitted BSSID) belongs to a multiple BSSID set, and the number of bits required to indicate whether there are buffered group address frames corresponding to all non-transmitted BSSIDs and all other APs belonging to the same AP multilink device is not greater than 48 bits.

[0220] The Group Addressed BU Indication Exponent subfield can also indicate the number of bits (N) used to indicate buffered group address frames corresponding to other APs of the multilink device corresponding to each nontransmitted BSSID. The value of N is described further below.

[0221] In addition, the 48 bits mentioned above may be replaced with another number of bits. This may change the number of bits in the Traffic Indication Virtual Bitmap required to indicate group address traffic to other APs of the same multilink device as the AP with the nontransmitted BSSID. In the present invention, 48 bits or another number of bits may be referred to as a "bitmap limit."

[0222] FIG. 20 shows a traffic indication virtual bitmap according to an embodiment of the present invention.

[0223] The Traffic Indication Virtual Bitmap can indicate group address traffic corresponding to the AP of the multilink device, such as a transmitted BSSID, or the nontransmitted BSSID and the AP of the multilink device. A station receiving the Traffic Indication Virtual Bitmap can determine whether group address traffic is buffered in the AP (or BSS) to which the station is associated. The station can also use this to receive buffered group address traffic.

[0224] In an embodiment of the present invention, bits for group address traffic may be located first in the Traffic indication virtual bitmap, and bits for traffic individually addressed to a station or multilink device may be located after the bits for group address traffic.

[0225] An AP transmitting a TIM element can indicate buffered group address frames corresponding to other APs belonging to the multilink device to which the AP belongs. To indicate buffered group address frames corresponding to other APs belonging to the multilink device to which the AP belongs, N bits following the last bit used to indicate nontransmitted BSSIDs in the TIM element, Partial Virtual Bitmap subfield, or Traffic indication virtual bitmap may be used. If an AP does not belong to a multiple BSSID set, N bits following the first bit (B0) in the TIM element, Partial Virtual Bitmap subfield, or Traffic indication virtual bitmap can be used to indicate buffered group address frames corresponding to other APs included in the multilink device to which the AP belongs. In this case, each of the N bits is mapped in the order of link IDs, and each of the N bits can indicate whether a group address frame is buffered in the link mapped to the bit.

[0226] Bits X to X+N-1 of the Partial Virtual Bitmap subfield or Traffic indication virtual bitmap may indicate group address frames corresponding to the reporting AP (or the AP corresponding to the transmitted BSSID if the AP belongs to a multiple BSSID set) and other APs belonging to the multilink device to which the reporting AP belongs. In this case, the reporting AP represents the AP transmitting the TIM element. Also, X-1 may be the last bit used to indicate a nontransmitted BSSID in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap. If multiple BSSID sets are not used, X-1 may be 0. Also, N may be the N mentioned in the description of the EHT Operation element above. Specifically, if the AP transmitting the TIM element does not belong to a multiple BSSID set, X-1 may be 0. Also, N may be the N mentioned in the description of the EHT Operation element above. The value of N may be determined based on the Group Addressed BU Indication Exponent subfield. The value of N may be 2^(value of the Group Addressed BU Indication Exponent subfield + 1)-1. That is, if the value of the Group Addressed BU Indication Exponent subfield is 1, the value of N may be 2^(1+1)-1. That is, the value of N may be 3. Also, the N bits from bits X to X+N-1 may indicate whether group address traffic for each link is buffered in ascending order of the link ID. Of the N bits, the first n bits indicate group address frames corresponding to other APs of the AP multilink device to which the AP belongs, and the remaining bits may be set to 0.

[0227] The last bit indicating a nontransmitted BSSID in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap may be determined based on the theoretical maximum number of BSSIDs in the multiple BSSID set. When the theoretical maximum number of BSSIDs in the multiple BSSID set is 2^n, AIDs 1 to (2^n-1) are reserved for the AIDs of nontransmitted BSSIDs, and the last bit indicating a nontransmitted BSSID in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap may correspond to AID (2^n-1). Therefore, starting from bit 2^n of the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap, group address frames buffered in other APs of the multilink device to which the AP (reporting AP) of the transmitted BSSID belongs may be indicated.

[0228] In yet another specific embodiment of the present invention, the last bit indicating a nontransmitted BSSID in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap may be determined based on the actual bits used as the nontransmitted BSSID. When the maximum possible number of nontransmitted BSSIDs in the multiple BSSID set are not actually used, the last bit may be the last bit of the bits corresponding to the nontransmitted BSSID actually used in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap.

[0229] In FIG. 20, a Partial Virtual Bitmap subfield is configured using a portion of the Traffic indication virtual bitmap. Each bit in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields indicates whether there is buffered traffic to be transmitted to the station of the AID corresponding to that bit. In this case, the bit numbers of the bits in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields may be mapped to AID values. In FIG. 20, the first bit (B0) of the Traffic indication virtual bitmap is mapped to the transmitted BSSID. In yet another specific embodiment, the first bit (B0) of the Traffic indication virtual bitmap may be mapped to the reporting AP (AP transmitting the TIM element). That is, if the reporting AP belongs to a multiple BSSID set, the first bit (B0) of the Traffic indication virtual bitmap is mapped to the reporting AP or the transmitted BSSID. If the reporting AP does not belong to a multiple BSSID set, the first bit (B0) of the Traffic indication virtual bitmap is mapped to the reporting AP. The buffered traffic corresponding to the AP may be group address traffic.

[0230] In the embodiment of Figure 20, the second bit (B1) to the fourth bit (B3) of the Traffic Indication Virtual Bitmap are mapped to the nontransmitted BSSID. In this case, the aforementioned (X-1) is 3. Also, the fifth bit (B4) to the seventh bit (B6) of the Traffic Indication Virtual Bitmap may correspond to the reporting AP or other APs belonging to the AP multilink device to which the transmitted BSSID belongs. That is, in this case, the value of the Group Addressed BU Indication Exponent subfield is 1. Therefore, N is 3.

[0231] To indicate whether group address frames corresponding to other APs in the AP multilink device to which the AP corresponding to each nontransmitted BSSID belongs are buffered, the reporting AP can use N bits following the last bit (i.e., B X+N-1) in the TIM element, Partial Virtual Bitmap subfield, or Traffic indication virtual bitmap indicating whether group address traffic corresponding to other APs in the same AP MLD as the AP of the transmitted BSSID is buffered. Specifically, to indicate group address frames corresponding to other APs in the AP multilink device to which the AP corresponding to the kth nontransmitted BSSID belongs, the reporting AP can use the kth N bits following the last bit (i.e., B X+N-1) in the TIM element, Partial Virtual Bitmap subfield, or Traffic indication virtual bitmap indicating group address traffic corresponding to other APs in the AP multilink device to which the AP of the transmitted BSSID belongs. In this case, the N bits corresponding to each nontransmitted BSSID are mapped to N links in the order of the link IDs, and each of the N bits indicates whether a group address frame is buffered on the link corresponding to that bit.

[0232] The bits from bit number Y+(k-1)*N to bit number Y+k*N-1 in the Reporting Partial Virtual Bitmap subfield or Traffic indication virtual bitmap may indicate whether group address traffic corresponding to other APs in the AP multilink device to which the AP of the kth nontransmitted BSSID belongs is buffered. This embodiment may be applied only when the bit number is smaller than a pre-specified bit number. The pre-specified value may be determined based on the bitmap limit. The pre-specified value may be Y+(bitmap limit). In this case, k may start from 1 for the kth nontransmitted BSSID. Y-1 may be the last bit indicating whether group address frames corresponding to the AP multilink device to which the AP of the transmitted BSSID belongs are buffered. That is, Y-1 may be the same value as X+N-1. Furthermore, N may be the N mentioned in the embodiment related to the EHT Operation element. N may be determined based on the Group Addressed BU Indication Exponent subfield. N may be 2^(value of Group Addressed BU Indication Exponent subfield + 1) - 1. Also, in the TIM element, Partial Virtual Bitmap subfield, or Traffic indication virtual bitmap, N bits from bit numbers Y+(k-1)*N to Y+k*N-1 are mapped to N links in the order of link IDs, and each of the N bits indicates whether a group address frame has been buffered in the link corresponding to that bit. Among the N bits, the first n bits indicate whether a group address frame corresponding to another AP belonging to the AP multilink device to which the AP of the kth nontransmitted BSSID belongs has been buffered, and the remaining bits may be set to 0.

[0233] In Figure 20, Y is 7 and N is 3. Therefore, in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap, bit numbers 7+(k-1)*3 to 7+k*3-1 may indicate group address frames corresponding to other APs belonging to the AP multilink device to which the AP corresponding to the kth nontransmitted BSSID belongs. That is, in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap, bit numbers 7 to 9 indicate group address frames corresponding to other APs belonging to the AP multilink device to which the AP corresponding to the first nontransmitted BSSID belongs. In addition, the kth nontransmitted BSSID may be the nontransmitted BSSID corresponding to AID k.

[0234] The Traffic Indication Virtual Bitmap and Partial Virtual Bitmap subfields may include, as the portion corresponding to the group address frame, a portion corresponding to the reporting AP (or the transmitted BSSID if the reporting AP belongs to a multiple BSSID set), a portion corresponding to the nontransmitted BSSID (if the reporting AP belongs to a multiple BSSID set), a portion corresponding to other APs belonging to the AP multilink device to which the reporting AP belongs, and a portion corresponding to other APs belonging to the AP multilink device to which the AP with the nontransmitted BSSID belongs (if the reporting AP belongs to a multiple BSSID set). Also, the order in which each portion is included in the Traffic Indication Virtual Bitmap and Partial Virtual Bitmap subfields may be the same as the order mentioned.

[0235] According to the embodiment described in FIG. 14, the value of the AID Offset subfield may not indicate the portion corresponding to the group ID and group address frame in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields. That is, the value of the AID Offset subfield may indicate a value greater than the maximum value corresponding to the group ID and group address frame in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields. Alternatively, the value of the AID Offset subfield may indicate an individually addressed frame in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields. Alternatively, the value of the AID Offset subfield may indicate a value corresponding to a non-AP station or a non-AP multilink device in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields.

[0236] More specifically, in the embodiment described in Figure 14, the value of the AID Offset subfield is determined based on the maximum number of BSSIDs in the multiple BSSID set so that the value of the AID Offset subfield does not indicate the portion of the Traffic Indication Virtual Bitmap and Partial Virtual Bitmap subfields corresponding to the group address frame. According to the embodiments of Figures 19 and 20, the value of the AID Offset subfield may be determined by further considering other factors. This is because a larger number of bits in the Traffic Indication Virtual Bitmap and Partial Virtual Bitmap subfields can indicate the group address frame compared to the maximum number of BSSIDs that the multiple BSSID set can include.

[0237] According to an embodiment of the present invention, the range of values ​​that the AID Offset subfield can indicate may be determined based on the number of bits required to indicate a group address frame corresponding to another AP in the AP multilink device to which the AP corresponding to the transmitted BSSID or nontransmitted BSSID belongs. For example, the range of values ​​that the AID Offset subfield can indicate may be determined based on the maximum number of BSSIDs that the multiple BSSID set can include and the number of bits required to indicate a group address frame corresponding to another AP in the AP multilink device to which the AP corresponding to the transmitted BSSID or nontransmitted BSSID belongs. Furthermore, the range of values ​​that the AID Offset subfield can indicate may be determined based on the maximum number of BSSIDs that the multiple BSSID set can include, the number of bits required to indicate a group address frame corresponding to another AP in the AP multilink device to which the AP corresponding to the transmitted BSSID or nontransmitted BSSID belongs, and a bitmap limit.

[0238] According to an embodiment of the present invention, the AID Offset subfield may not be allowed to indicate a portion of the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields that corresponds to a group address frame, or the AID Offset subfield may indicate a portion of the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields that does not correspond to a group address frame.

[0239] In the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields, the portions corresponding to the Group address frame may include a portion corresponding to the reporting AP (or the transmitted BSSID if the reporting AP belongs to a multiple BSSID set), a portion corresponding to the nontransmitted BSSID (if the reporting AP belongs to a multiple BSSID set), a portion corresponding to other APs in the same AP MLD as the reporting AP, and a portion corresponding to other APs belonging to the AP multilink device to which the AP with the nontransmitted BSSID belongs (if the reporting AP belongs to a multiple BSSID set).

[0240] That is, the value of the AID Offset subfield may not be set to a value equal to or less than the smaller of (X-1) + N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs) + 1) and (X-1) + the bitmap limit (or either one of the values ​​if both values ​​are the same). The value of the AID Offset subfield may be set to a value greater than the smaller of (X-1) + N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs) + 1) and (X-1) + the bitmap limit (or either one of the values ​​if both values ​​are the same). As described above, (X-1) may be the last bit indicating a group address frame for an AP belonging to an AP multilink device to which the reporting AP or the AP corresponding to the transmitted BSSID belongs. That is, the AID Offset subfield may not be allowed to indicate a value equal to or less than min((X-1)+N*X, X-1+bitmap limit). The value of the AID Offset subfield may be set to a value greater than min((X-1)+N*X, X-1+bitmap limit). In this case, the above-mentioned content regarding N and bitmap limit has been omitted.

[0241] Another explanation for the same content is that (the maximum number of BSSIDs that a multiple BSSID set can contain) or (the number of BSSIDs in a multiple BSSID set) can be referred to as M. The value of the AID Offset subfield may not be set to the smaller of 1) M-1 plus M*N, or 2) M-1 plus N + bitmap limit. The value of the AID Offset subfield may be set to a value greater than the smaller of 1) M-1 plus M*N, or 2) M-1 plus N + bitmap limit. If the reporting AP does not belong to a multiple BSSID set, M may be 1.

[0242] This can also be explained separately for cases where the reporting AP belongs to a multiple BSSID set and cases where it does not. When the reporting AP belongs to a multiple BSSID set, the value of the AID Offset subfield cannot be set to a value less than N. Also, the value of the AID Offset subfield may be set to a value greater than N. When the reporting AP belongs to a multiple BSSID set, the AID Offset may not be set to the smaller of the value obtained by adding (X-1) to N * (the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs) and the value obtained by adding (X-1) to the bitmap limit (or, if both values ​​are the same, either value). The value of the AID Offset subfield may be set to a value greater than the smaller of (X-1) plus N*(number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs) and (X-1) plus the bitmap limit (or either one of them if both values ​​are the same). min(A,B) may be the smaller of A and B if the values ​​of A and B are different, or A=B if the values ​​of A and B are the same.

[0243] In the above embodiments, the number of nontransmitted BSSIDs or the number of BSSIDs in a multiple BSSID set may be the number of BSSIDs actually used in the multiple BSSID set, and the maximum number of nontransmitted BSSIDs or the maximum number of BSSIDs that a multiple BSSID set can include may be the maximum number that a multiple BSSID set can include based on the MaxBSSID Indicator value.

[0244] In the embodiments of Figures 19 and 20, the AID (association ID) space (for non-AP stations or non-AP MLD) may be limited. This is because the AID range assigned to group address frames has changed in the embodiments of Figures 19 and 20. The AID is assigned by the AP to the non-AP station (or non-AP multilink device). The AID may also be transmitted to the non-AP station (or non-AP multilink device) in an association response frame or a reassociation response frame.

[0245] In the existing IEEE 802.11 standard, an AP could assign AID values ​​from 1 to 2007 to non-AP stations. If an AP belongs to a multiple BSSID set, the AP cannot assign an AID value corresponding to a nontransmitted BSSID to a non-AP station. In other words, if an AP belongs to a multiple BSSID set, the AP cannot assign an AID value equal to or less than the maximum number of BSSIDs in the multiple BSSID set minus 1 to a non-AP station. In other words, the AP can assign an AID to a non-AP station within the range of (the maximum number of BSSIDs in the multiple BSSID set) to 2007.

[0246] Furthermore, the EHT standard may not allow an AP to assign 2007 as the AID for a non-AP station because the AID value 2007 is used to indicate the Special User Info field included in the trigger frame. That is, if the AP is not included in a multiple BSSID set, the AP can assign AIDs to non-AP stations in the range from 1 to 2006. If a multiple BSSID set is used, the AP can assign AIDs to non-AP stations in the range from (the maximum number of BSSIDs that the multiple BSSID set can include) to 2006.

[0247] Additionally, according to an embodiment of the present invention, the AID space may be limited based on the value of the Group Addressed BU Indication Exponent field or a bitmap limit.

[0248] In a specific embodiment, when an AP does not belong to a multiple BSSID set, the AP can assign AIDs to non-AP stations in the range of N+1 to 2006. When an AP belongs to a multiple BSSID set, the AP cannot assign AIDs to non-AP stations up to the smaller of (X-1) + N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs) + 1) and (X-1) + the bitmap limit (or, if both values ​​are the same, either one of these). That is, the AP can assign AIDs to non-AP stations in the range from the smaller of (X-1) + N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs) + 1) and (X-1) + the bitmap limit (or, if both values ​​are the same, either one of these) + 1 to 2006. Therefore, if an AP belongs to a multiple BSSID set, the AP can assign AIDs to non-AP stations in the range of 2^(MaxBSSID Indicator) + (2^(MaxBSSID Indicator)) * (2^(Group Addressed BU Indication Exponent subfield value + 1) - 1) to 2006.

[0249] If the AP does not belong to a multiple BSSID set, the AID space may be determined based on the value of the Group Addressed BU Indication Exponent subfield. If the AP belongs to a multiple BSSID set, the AID space may be determined based on the value of the MaxBSSID Indicator subfield and the value of the Group Addressed BU Indication Exponent subfield.

[0250] The MaxBSSID Indicator subfield may be included in a Multiple BSSID element or a Reduced Neighbor Report element, which may be included in a beacon frame, a probe response frame, an association response frame, or a reassociation response frame.

[0251] FIG. 21 shows a traffic indication virtual bitmap according to an embodiment of the present invention.

[0252] In still another embodiment of the present invention, (X-1) may be replaced with (Y-1) in the embodiments described with reference to Figures 19 and 20. Specifically, when adding a bitmap limit to (X-1), (X-1) may be replaced with (Y-1). The bitmap limit may be the number of the last bit that can indicate a group address frame among the bits corresponding to other APs belonging to the AP multilink device to which the AP corresponding to the transmitted BSSID belongs in the traffic indication virtual bitmap. Also, in the embodiments described below, (Y-1) may be replaced with (X-1).

[0253] As described above, the AP can extract a portion of the Traffic indication virtual bitmap to generate the Partial Virtual Bitmap subfield. Furthermore, each bit of the Traffic indication virtual bitmap or Partial Virtual Bitmap subfield can indicate whether traffic for the station of the AID corresponding to that bit is buffered. The bit number of the bits in the Traffic indication virtual bitmap or Partial Virtual Bitmap subfield may be mapped to the AID. The first bit (B0) of the Traffic indication virtual bitmap or Partial Virtual Bitmap subfield may be mapped to the transmitted BSSID. In yet another specific embodiment, the first bit (B0) of the Traffic indication virtual bitmap or Partial Virtual Bitmap subfield may be mapped to the reporting AP. If the reporting AP belongs to a multiple BSSID set, the first bit (B0) of the Traffic indication virtual bitmap is mapped to the reporting AP or the transmitted BSSID. If the reporting AP does not belong to a multiple BSSID set, the first bit (B0) of the Traffic indication virtual bitmap is mapped to the reporting AP.

[0254] In the embodiment of Figure 21, the second bit (B1) through the fourth bit (B3) of the Traffic Indication Virtual Bitmap may be mapped to the nontransmitted BSSID. In this case, the (X-1) value is 3. The fifth bit (B4) through the seventh bit (B6) of the Traffic Indication Virtual Bitmap may be mapped to the reporting AP or other APs belonging to the AP multilink device to which the transmitted BSSID belongs. In this case, the value of the Group Addressed BU Indication Exponent subfield may be set to 1. In this case, N is 3.

[0255] In the embodiment of FIG. 21, Y is 7, and N is 3. Therefore, bit number 7+(k-1)*3 to bit number 7+k*3-1 of the Traffic indication virtual bitmap indicate whether a group address frame corresponding to another AP of the AP multilink device to which the AP corresponding to the kth nontransmitted BSSID belongs is buffered. That is, bit eight (B7) to bit ten (B9) of the Traffic indication virtual bitmap indicate whether a group address frame corresponding to another AP of the AP multilink device to which the AP corresponding to the first nontransmitted BSSID belongs is buffered. In addition, the kth nontransmitted BSSID may be the nontransmitted BSSID corresponding to AID k.

[0256] The Traffic Indication Virtual Bitmap or Partial Virtual Bitmap subfield may include, as a portion corresponding to a group address frame, a portion corresponding to the reporting AP (or the transmitted BSSID when a multiple BSSID set is used), a portion corresponding to the nontransmitted BSSID (when a multiple BSSID set is used), a portion corresponding to other APs belonging to the AP multilink device to which the reporting AP belongs, and a portion corresponding to other APs belonging to the AP multilink device to which the AP with the nontransmitted BSSID belongs (when a multiple BSSID set is used). Also, the order in which each portion is included in the Traffic Indication Virtual Bitmap may be the same as the order mentioned.

[0257] In a specific embodiment, the AID space may be the same as the range of AIDs that can be indicated by the AID Offset subfield. The range of AIDs that cannot be assigned by an AP as an AID may be the same as the range of AIDs that cannot be indicated by the AID Offset subfield. The AID space may be a set of bit numbers of bits in the traffic indication virtual bitmap that cannot indicate that a group address frame is buffered. That is, the AID space may not include the bit numbers of bits in the traffic indication virtual bitmap that indicate that a group address frame is buffered. The AIDs that cannot be assigned by an AP as an AID may be a set of bit numbers of bits in the traffic indication virtual bitmap that indicate that a group address frame is buffered.

[0258] In a first embodiment of the AID space of the present invention, the AID space may be determined based on X or X-1. The AID space may be determined based on the maximum number of nontransmitted BSSIDs. Therefore, the AID space may be determined based on the Group Addressed BU Indication Exponent subfield. Specifically, the AID space may be determined based on (X-1) plus N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs)+1). For example, the minimum value of the AID space may be (X-1) plus N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs)+1)+1. The maximum value of the AID space may be 2006. (X-1) may be the bit number of the last bit used to indicate a nontransmitted BSSID in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap. If the reporting AP does not belong to a multiple BSSID set, X-1 is 0. If the reporting AP belongs to a multiple BSSID set, (X-1) is (2^(MaxBSSID Indicator value)-1). The MaxBSSID Indicator value can indicate the maximum number of BSSIDs in a multiple BSSID set. The maximum number of BSSIDs in a multiple BSSID set is 2^(MaxBSSID Indicator value).

[0259] In yet another specific embodiment, the minimum value of the AID space may be (X-1) plus N*X+1. If the reporting AP does not belong to a multiple BSSID set, the minimum value of the AID space may be N+1. If the reporting AP belongs to a multiple BSSID set, the minimum value of the AID space may be (X-1) plus N*((number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs)+1)+1. That is, if the AP belongs to a multiple BSSID set, the minimum value of the AID space may be (2^(MaxBSSID Indicator value)-1)+(2^(MaxBSSID Indicator value))*(2^(Group Addressed BU Indication Exponent subfield value+1)-1)+1. If an AP belongs to multiple BSSID sets, the minimum value of the AID space may be 2^((MaxBSSID Indicator value)+(Group Addressed BU Indication Exponent subfield value+1)).

[0260] In a second embodiment of the AID space of the present invention, the AID space may be determined based on a bitmap limit. In this case, the bitmap limit may be 48 bits. The AID space may be determined based on Y and the bitmap limit. Specifically, the AID space may be determined based on Y-1 and the bitmap limit. Specifically, the AID space may be determined based on the sum of Y-1 and the bitmap limit. In a specific embodiment, the minimum value of the AID space may be (Y-1) plus the bitmap limit value plus 1.

[0261] The above-mentioned Y may be replaced with X. Therefore, the AID space may be determined based on X and the bitmap limit. Specifically, the AID space may be determined based on X-1 and the bitmap limit. Specifically, the AID space may be determined based on the sum of X-1 and the bitmap limit. In a specific embodiment, the minimum value of the AID space may be (X-1) plus the bitmap limit value plus 1.

[0262] (Y-1) may be the last bit in the Traffic Indication Virtual Bitmap indicating a group address frame of the AP multilink device to which the AP corresponding to the transmitted BSSID belongs. That is, Y-1 may be the same value as X+N-1. Also, N is N described in the previous embodiment related to the EHT Operation element. N may be determined based on the value of the Group Addressed BU Indication Exponent subfield. N may be 2^(value of the Group Addressed BU Indication Exponent subfield + 1)-1. N may be a value obtained by subtracting 1 from the number of bits indicating a group address frame for one multilink device in the Traffic Indication Virtual Bitmap. Alternatively, N may be the number of bits indicating a group address frame corresponding to another AP of the multilink device to which the reporting AP, the transmitted BSSID, or the nontransmitted BSSID belongs. If the reporting AP does not belong to a multiple BSSID set, Y-1 may be N. If the reporting AP belongs to multiple BSSID sets, Y-1 may be X-1 + N. That is, if the reporting AP belongs to multiple BSSID sets, Y-1 may be ((maximum number of BSSIDs in the multiple BSSID set) - 1) + N.

[0263] The AP may not be permitted to assign AIDs corresponding to the bits after bit number (Y-1) in the Traffic Indication Virtual Bitmap to non-AP stations or non-AP multilink devices. That is, the AP may assign values ​​greater than (Y-1) + (bitmap limit) to non-AP stations or non-AP multilink devices. That is, in the embodiment of Figure 20, the AP may assign values ​​greater than 6 + 48, ie, 55 or greater, to AIDs of non-AP stations or non-AP multilink devices.

[0264] If the bit limit is 48, the AID values ​​that a reporting AP can assign may be (N+1) or more if the reporting AP does not belong to a multiple BSSID set, and may be (Y+48) or more if the AP belongs to a multiple BSSID set.

[0265] In a third embodiment related to the AID space of the present invention, the AID space may be determined based on the first and second embodiments. The AID space may be determined based on X, N, Y, the number of nontransmitted BSSIDs (or the maximum number of nontransmitted BSSIDs), and the bitmap limit. The minimum value of the AID space may be calculated by adding 1 to the smaller of the following values: (X-1) + N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs) + 1) and (Y-1) + the bitmap limit. The minimum value of the AID space may be min((X-1) + N*X, Y-1 + bitmap limit) + 1. In other words, the minimum value of the AID space may be min(X + N*X, Y + bitmap limit).

[0266] If the reporting AP does not belong to a multiple BSSID set, the minimum value of the AID space may be N+1. If the reporting AP belongs to a multiple BSSID set, the minimum value of the AID space may be the smaller of N+1 and Y + the bitmap limit. If the reporting AP belongs to a multiple BSSID set, the minimum value of the AID space may be 1 plus the smaller of (X-1) + N*((number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs) + 1) and (Y-1) + the bitmap limit. That is, if the reporting AP belongs to a multiple BSSID set, the minimum value of the AID space may be min(X+N*X, Y+bitmap limit). This may be expressed as follows: If the reporting AP belongs to a multiple BSSID set, the minimum value of the AID space may be min((a),(b)).

[0267] (a) (2^(MaxBSSID Indicator value) - 1) + (2^(MaxBSSID Indicator value)) * (2^(Group Addressed BU Indication Exponent subfield value + 1) - 1) + 1

[0268] (b) (Y-1) + (bitmap limit) + 1 = 2^(MaxBSSID Indicator value) - 1 + 2^(Group Addressed BU Indication Exponent subfield value + 1) - 1 + (bitmap limit) + 1 = 2^(MaxBSSID Indicator value) + 2^(Group Addressed BU Indication Exponent subfield value + 1) - 1 + (bitmap limit)

[0269] If the bitmap limit is 48 and the reporting AP does not belong to a multiple BSSID set, the minimum AID space is N + 1. If the bitmap limit is 48 and the reporting AP belongs to a multiple BSSID set, the minimum AID space may be min(Y + 48, Y + N * (number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs)).

[0270] If the reporting AP does not belong to a multiple BSSID set, the value of MaxBSSID Indicator in the formula applied when the reporting AP belongs to a multiple BSSID set can be set to 0, and the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs can be set to 0. In the above embodiment, the number of nontransmitted BSSIDs or the number of BSSIDs in a multiple BSSID set can indicate the number of BSSIDs actually used in the multiple BSSID set. Also, the maximum number of nontransmitted BSSIDs or the maximum number of BSSIDs that a multiple BSSID set can have can be determined based on the MaxBSSID Indicator value. A non-AP station can obtain the number of nontransmitted BSSIDs from the Multiple BSSID element. In yet another specific embodiment, a non-AP station can obtain the number of nontransmitted BSSIDs from an element or frame that indicates the maximum number of BSSIDs in a multiple BSSID set.

[0271] The bitmap limit may also be a pre-specified value. For example, the bitmap limit may be 48.

[0272] In the above-described embodiments, multiple BSSIDs or multiple BSSID sets may be replaced with co-located BSSIDs or co-located BSSID sets (co-located BSSID lists). A co-located BSSID may be a BSSID of a BSS that is physically located at the same location as the reporting BSS or reporting AP. A co-located BSSID may be a BSSID that corresponds to the same physical device as the reporting BSS or reporting AP.

[0273] The first embodiment of the AID space of the present invention has the advantage that when the number of BSSIDs in the multiple BSSID set is small or N is small, the number of bits indicating group address frames in the traffic indication virtual bitmap is small, resulting in a wide AID space. However, when the number of BSSIDs in the multiple BSSID set is large or N is large, the number of bits indicating group address frames in the traffic indication virtual bitmap is large, resulting in a narrow AID space. A wide or narrow AID space may mean a large or small number of stations or multilink devices that can be associated. Furthermore, the first embodiment of the AID space of the present invention may have the advantage of being simpler to calculate or implement than the third embodiment of the AID space of the present invention.

[0274] The second embodiment of the AID space of the present invention has the advantage that the number of bits used to indicate group address frames in the Traffic Indication Virtual Bitmap is limited and the AID space is wide, even when the number of BSSIDs in the multiple BSSID set is large or N is large. On the other hand, the second embodiment of the AID space of the present invention has the disadvantage that the AID space may be somewhat limited, even when the number of BSSIDs in the multiple BSSID set is small or N is small. Therefore, there may be AID values ​​that are not used as AIDs or to indicate group address frames. Furthermore, the second embodiment of the AID space of the present invention has the advantage that calculation or implementation is simpler than the third embodiment of the AID space of the present invention.

[0275] The third embodiment of the present invention relating to the AID space may have the advantage of combining the advantages of the first and second embodiments and reducing the disadvantages of the first and second embodiments, but may have the disadvantage of being more complex to calculate or implement than the first or second embodiments.

[0276] A method for setting up a multi-link will be described with reference to Figures 22 to 26. First, a Multi-Link element will be described with reference to Figure 22.

[0277] FIG. 22 illustrates signaling associated with a Multi-Link element and MediumSyncDelay according to one embodiment of the present invention.

[0278] A multilink device may perform multilink discovery and multilink setup using a multilink element. In this case, the multilink element may be included in a management frame. Specifically, the multilink element may be included in at least one of a beacon frame, a probe request frame, a probe response frame, an authentication frame, an association request frame, an association response frame, a reassociation request frame, and a reassociation response frame.

[0279] The Multi-Link element may include an Element ID subfield, a Length subfield, an Element ID Extension subfield, a Multi-Link Control subfield, a Common Info subfield, and a Link Info subfield. The Element ID subfield or the Element ID Extension subfield may indicate the ID of the element including the Element ID subfield or the Element ID Extension subfield. The Length subfield may indicate the length of the element including the Length subfield. The Multi-Link Control subfield may include a Type subfield and a Presence Bitmap subfield. The Type subfield may indicate the type of the Multi-Link element. The format of the Multi-Link element may also be determined based on the type of the Multi-Link element. The Presence Bitmap subfield may indicate whether subfields that can be included in the Multi-Link element are included. For example, the Presence Bitmap subfield may indicate whether subfields that can be included in the Common Info subfield included in the Multi-Link element are included. Subfields indicating whether the Presence Bitmap subfield is included in the Multi-Link element may include a MAC address subfield of the multi-link device, a Link ID Info subfield, a BSS Parameters Change Count subfield, a Medium Synchronization Delay Information subfield, an EML Capabilities subfield, and an MLD Capabilities subfield. The Medium Synchronization Delay Information subfield may include MediumSyncDelay and related information.

[0280] The Common Info subfield may contain information about multiple links or all links. The Common Info subfield may contain information commonly required or commonly applied to multiple links or all links. The Link Info subfield may contain information about the link corresponding to the Link Info subfield.

[0281] The information related to MediumSyncDelay indicates the value to be set as the duration of MediumSyncDelay and may have a default value. In certain situations, a multilink device can initialize the duration of MediumSyncDelay to a basic value. Also, if a multilink device (non-AP multilink device) does not receive information related to MediumSyncDelay from a peer multilink device (AP multilink device), the multilink device can set the duration of MediumSyncDelay to a default value. If a multilink device (non-AP multilink device) receives information related to MediumSyncDelay from a peer multilink device (AP multilink device), it can set the duration of MediumSyncDelay to a value indicated by the received information related to MediumSyncDelay.

[0282] In FIG. 22, the Medium Synchronization Delay Information subfield may include a Medium Synchronization Duration subfield, a Medium Synchronization OFDM ED Threshold subfield, and a Medium Synchronization Maximum Number Of TXOPs subfield.

[0283] The Medium Synchronization Duration subfield may indicate MediumSyncDelay. That is, the Medium Synchronization Duration subfield may indicate a value to set the MediumSyncDelay timer. For example, the Medium Synchronization Duration subfield may be an 8-bit field. Also, the Medium Synchronization Duration subfield may indicate a duration in 32us units. That is, when the Medium Synchronization Duration subfield is set to A, the time indicated by the Medium Synchronization Duration subfield may be A*32us.

[0284] The Medium Synchronization OFDM ED Threshold subfield may indicate a CCA threshold when MediumSyncDelay is applied. The CCA threshold indicated by the Medium Synchronization OFDM ED Threshold subfield may be the CCA ED threshold. That is, the Medium Synchronization OFDM ED Threshold subfield may indicate dot11MSDOFDMEDthreshold. The Medium Synchronization OFDM ED Threshold subfield may be a 4-bit field. The CCA threshold indicated by the Medium Synchronization OFDM ED Threshold subfield may be the value of the Medium Synchronization OFDM ED Threshold subfield plus -72, and the unit of the CCA threshold may be dBm. Therefore, when the value of the Medium Synchronization OFDM ED Threshold subfield is 0 or greater, the CCA threshold indicated by the Medium Synchronization OFDM ED Threshold subfield may be a value of -72 dBm or greater. Furthermore, the maximum value of the CCA threshold indicated by the Medium Synchronization OFDM ED Threshold subfield may be -62 dBm. In this case, the value of the Medium Synchronization OFDM ED Threshold subfield may be set in the range of 0 to 10. At this time, values ​​11 to 15 may be reserved for the Medium Synchronization OFDM ED Threshold subfield. That is, the value of the Medium Synchronization OFDM ED Threshold subfield is set to 0 to 10, and at this time, the Medium Synchronization OFDM ED Threshold subfield can indicate that the CCA threshold is -72 dBm to -62 dBm.That is, if the value of the Medium Synchronization OFDM ED Threshold subfield is x, the Medium Synchronization OFDM ED Threshold subfield can indicate that the CCA threshold is (x-72 dBM).

[0285] The Medium Synchronization Maximum Number Of TXOPs subfield may indicate MSD_TXOP_MAX. That is, the Medium Synchronization Maximum Number Of TXOPs subfield may indicate the maximum number of transmission attempts a station may make while MediumSyncDelay is applied. The Medium Synchronization Maximum Number Of TXOPs subfield may be a 4-bit field. In a specific embodiment, the value of the Medium Synchronization Maximum Number Of TXOPs subfield may be MSD_TXOP_MAX. In yet another specific embodiment, the value of the Medium Synchronization Maximum Number Of TXOPs subfield may be (MSD_TXOP_MAX+1). In yet another specific embodiment, the value of the Medium Synchronization Maximum Number Of TXOPs subfield may be (MSD_TXOP_MAX-1). Such an embodiment may be applied when the value of the Medium Synchronization Maximum Number Of TXOPs subfield is not set to the maximum value. If the value of the Medium Synchronization Maximum Number Of TXOPs subfield is set to the maximum value, e.g., 15 if the Medium Synchronization Maximum Number Of TXOPs subfield is a 4-bit field, the Medium Synchronization Maximum Number Of TXOPs subfield can indicate that a station is allowed to attempt an unlimited number of transmissions while MediumSyncDelay is applied.

[0286] FIG. 23 illustrates a multi-link setup process according to an embodiment of the present invention.

[0287] In Figure 23, the AP multilink device includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). The non-AP multilink device (non-AP MLD) includes a first non-AP station (STA1), a second non-AP station (STA2), and a third non-AP station (STA3). The first AP (AP1) and the first non-AP station (STA1) operate on a first link (link1). The second AP (AP2) and the second non-AP station (STA2) operate on a second link (link2). The third AP (AP3) operates on a third link (link3).

[0288] The first AP (AP1) can transmit a Reduced Neighbor Report element to signal the presence of an AP Multilink Device (AP MLD) and AP Multilink Device (AP MLD)-related parameters. The Reduced Neighbor Report element transmitted by the first AP (AP1) can include information about the second AP (AP2) or the third AP (AP3). The Reduced Neighbor Report element can be included in a beacon frame or a probe response frame.

[0289] In addition, the first non-AP station (STA1) that receives a frame including a Reduced Neighbor Report element can recognize the AP or AP multilink device indicated by the Reduced Neighbor Report element. In this case, the first non-AP station (STA1) can transmit a probe request frame including a Multi-Link element to the first AP (AP1) to request information about the AP multilink device (AP MLD) or the multilink on which the AP multilink device (AP MLD) operates from the first AP (AP1). In this case, the Multi-Link element may include information about the non-AP multilink device or information about the AP included in the non-AP multilink device.

[0290] The first AP (AP1) may transmit a probe response frame to the non-AP station (STA1) in response to the probe request frame. In this case, the probe response frame may include a Multi-Link element. The Multi-Link element may include information about the AP multi-link device or information about the AP included in the AP multi-link device (AP MLD). Specifically, the Multi-Link element may include information requested by the first non-AP station (STA1).

[0291] A first non-AP station (STA1) may transmit an association request frame or a reassociation request frame to a first AP (AP1). The association request frame and the reassociation request frame may include a Multi-Link element. In this case, the Multi-Link element may include information about the link for which the non-AP multi-link device is to perform multi-link setup. For example, in FIG. 22, the Multi-Link element may include information about a first link (link1) and a second link (link2).

[0292] The first AP (AP1) may transmit an association response frame or a reassociation response frame to the first non-AP station (STA1). In this case, the association response frame and the reassociation response frame may include a Multi-Link element. In this case, the Multi-Link element may include information about the link on which multi-link setup is to be performed. The link on which multi-link setup is to be performed may be determined based on the link on which the non-AP multi-link device is to perform multi-link setup. In FIG. 22, the Multi-Link element may include information about the first link (link1) and the second link (link2) on which the first non-AP station (STA1) is to perform multi-link setup.

[0293] If the association response frame or reassociation response frame is successfully transmitted, it may be considered that the multi-link setup for the link indicated by the Multi-Link element included in the association response frame or reassociation response frame has been successfully performed.

[0294] FIG. 24 shows the format of a Reduced Neighbor Report element according to an embodiment of the present invention.

[0295] This will be explained by adding it to the Reduced Neighbor Report element explained in FIG.

[0296] A station or AP that transmits an element is called a reporting station or reporting AP. The station or AP pointed to by the element is called a reported station or reported AP. A station or AP that transmits a Reduced Neighbor Report element or a Multi-Link element is called a reporting station or reporting AP. The station or AP pointed to by a Reduced Neighbor Report element or a Multi-Link element is called a reported station or reported AP.

[0297] Referring to FIG. 24(a), the Reduced Neighbor Report element may include an Element ID subfield, a Length subfield, and one or more Neighbor AP Information subfields. The Element ID subfield may indicate the ID of an element. The Element ID subfield of the Reduced Neighbor Report element may indicate the ID of the Reduced Neighbor Report element. The Length subfield may indicate the size of the Reduced Neighbor Report element. For example, the Length subfield may indicate the length of the Reduced Neighbor Report element excluding the Element ID subfield and the Length subfield. That is, in the embodiment of FIG. 24(a), the Length subfield may indicate the length of the Neighbor AP Information subfield.

[0298] Each of the one or more Neighbor AP Information fields included in the Reduced Neighbor Report element may be the same as the Neighbor AP Information subfield shown in Figure 24(b). The Neighbor AP Information subfield may include a TBTT Information Header subfield, an Operating Class subfield, a Channel Number subfield, and a TBTT Information Set subfield.

[0299] The TBTT Information Header subfield may be a 2-octet field. The format of the TBTT Information Header subfield may be the same as that shown in Figure 24(c). The TBTT Information Header subfield may include a TBTT Information Field Type subfield, a Filtered Neighbor AP subfield, a Reserved subfield, a TBTT Information Count subfield, and a TBTT Information Length subfield. The TBTT Information Field Type subfield may be a 2-bit field, the Filtered Neighbor AP subfield may be a 1-bit field, the Reserved subfield may be a 1-bit field, the TBTT Information Count subfield may be a 4-bit field, and the TBTT Information Length subfield may be an 8-bit field.

[0300] The TBTT Information Field Type subfield, together with the TBTT Information Length subfield, identifies the TBTT Information subfield. The value of the TBTT Information Field Type subfield is set to 0, and the TBTT Information Field Type subfield values ​​1, 2, and 3 may be reserved values.

[0301] When the Filtered Neighbor AP subfield is not included in a probe response frame transmitted by a TVHT AP, the Filtered Neighbor AP subfield is set as a reserved field. This is reserved except when the Reduced Neighbor Report element is carried in a Probe Response frame transmitted by a TVHT AP. If the Filtered Neighbor AP subfield is included in a probe response frame transmitted by a TVHT AP and all BSSs of the APs in the Filtered Neighbor AP subfield correspond to a specific SSID, the value of the Filtered Neighbor AP subfield may be set to 1. Otherwise, the value of the Filtered Neighbor AP subfield may be set to 0.

[0302] The TBTT Information Count subfield may indicate the number of TBTT Information subfields included in the Neighbor AP Information subfield including the TBTT Information Count subfield. For example, the TBTT Information Count subfield may be set to a value obtained by subtracting 1 from the number of TBTT Information subfields included in the Neighbor AP Information subfield including the TBTT Information Count subfield.

[0303] The TBTT Information Length subfield may indicate the length of each TBTT Information subfield included in the Neighbor AP Information subfield including the TBTT Information Length subfield. Also, the TBTT Information Length subfield may indicate the configuration of each TBTT Information subfield included in the Neighbor AP Information subfield including the TBTT Information Length subfield. In this case, the TBTT Information Length subfield may indicate the length and configuration of each TBTT Information subfield.

[0304] The TBTT Information Set subfield may include one or more TBTT Information subfields.

[0305] The TBTT Information subfield may be the same as that shown in Figure 24(d). The TBTT Information subfield may include a Neighbor AP TBTT Offset subfield, a BSSID subfield, a Short SSID subfield, a BSS Parameters subfield, a 20MHz PSD subfield, and an MLD Parameters subfield. The size of each subfield may be the same as that shown in Figure 24(d). In this case, the subfields included in the TBTT Information subfield may be selectively included.

[0306] The Neighbor AP TBTT Offset subfield indicates the offset of the interval from the previous TBTT of the AP transmitting the Reduced Neighbor Report element to the next TBTT, rounded down to the nearest TU. If the value of the Neighbor AP TBTT Offset subfield is 254, it indicates that the offset is 254 TU or greater. If the value of the Neighbor AP TBTT Offset subfield is 255, it indicates that the offset value is unknown.

[0307] The BSSID subfield may indicate the BSSID.

[0308] The Short SSID subfield may indicate an SSID, specifically, abbreviated SSID information.

[0309] The BSS Parameters subfield may indicate information about the BSS, which may include information about BSS operation.

[0310] The 20MHz PSD subfield can indicate the maximum transmit power for the default category on the 20MHz primary channel. At this time, the 20MHz PSD subfield can indicate the maximum transmit power in dBm / MHz units. The value of the 20MHz PSD subfield is a signed integer, and a value of -128 in the 20MHz PSD subfield is a reserved value. A value of 127 in the 20MHz PSD subfield can indicate that there is no limit on the maximum transmit power for the default category. Also, when the value of the 20MHz PSD subfield, Y, is in the range of -127 to 126, the 20MHz PSD subfield can indicate that the maximum transmit power for the default category on the 20MHz primary channel is Y / 2 dBm / MHz.

[0311] The TBTT Information field configuration indicated by the value of the TBTT Information Length subfield may be as follows: If the value of the TBTT Information Length subfield is 1, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield. If the value of the TBTT Information Length subfield is 2, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield and the BSS Parameters subfield. If the value of the TBTT Information Length subfield is 4, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield and the MLD Parameters subfield. If the value of the TBTT Information Length subfield is 5, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield and the Short SSID subfield. If the value of the TBTT Information Length subfield is 6, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield, the Short SSID subfield, and the BSS Parameters subfield. If the value of the TBTT Information Length subfield is 7, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield and the BSSID subfield. If the value of the TBTT Information Length subfield is 8, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield, the BSSID subfield, and the BSS Parameters subfield.When the value of the TBTT Information Length subfield is 9, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield, the BSSID subfield, the BSS Parameters subfield, and the 20MHz PSD subfield. When the value of the TBTT Information Length subfield is 10, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield, the BSSID subfield, and the MLD Parameters subfield. When the value of the TBTT Information Length subfield is 11, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield, the BSSID subfield, and the Short SSID subfield. When the value of the TBTT Information Length subfield is 12, the TBTT Information subfield may include the TBTT Information subfield, the Neighbor AP TBTT Offset subfield, the BSSID subfield, the Short SSID subfield, and the BSS Parameters subfield. When the value of the TBTT Information Length subfield is 13, the TBTT Information subfield may include a Neighbor AP TBTT Offset subfield, a BSSID subfield, a Short SSID subfield, a BSS Parameters subfield, and a 20MHz PSD subfield. When the value of the TBTT Information Length subfield is 16, the TBTT Information subfield may include a Neighbor AP TBTT Offset subfield, a BSSID subfield, a Short SSID subfield, a BSS Parameters subfield, a 20MHz PSD subfield, and an MLD Parameters subfield.If the value of the TBTT Information Length subfield is 17 or greater, the TBTT Information subfield may include the following subfields in the preceding 16 octets: Neighbor AP TBTT Offset subfield, BSSID subfield, Short SSID subfield, BSS Parameters subfield, 20MHz PSD subfield, and MLD Parameters subfield. The remaining subfields of the TBTT Information subfield not mentioned above may be designated as reserved. That is, if the TBTT Information Length subfield is 4, 10, 16, or 17 or greater, the MLD Parameters subfield may be included.

[0312] The MLD Parameter subfield may be as shown in Figure 24(e). The MLD Parameters subfield may include an MLD ID subfield, a Link ID subfield, a BSS Parameters Change Count subfield, and a Reserved subfield. The MLD ID subfield may be an 8-bit field. The Link ID subfield may be a 4-bit field. The BSS Parameters Change Count subfield may be 8 bits. The Reserved subfield may be a 4-bit field.

[0313] The MLD ID subfield can indicate the ID of a multilink device, for example, an AP multilink device. The MLD subfield can indicate the ID of a multilink device corresponding to the TBTT Information subfield containing the MLD ID subfield. A specific setting method for the MLD ID subfield can be as shown in Figure 25.

[0314] The Link ID subfield may indicate the ID of the link corresponding to the reported AP. If the reported AP does not belong to a multi-link device or the reporting AP does not have related information, the link ID may be set to 15.

[0315] The BSS Parameters Change Count subfield may indicate a value to be incremented when a significant update occurs in the beacon frame of the reported AP. The value of the BSS Parameters Change Count subfield may be initialized to 0. The value of the BSS Parameters Change Count subfield may be incremented by 1 each time a significant update occurs in the AP or BSS corresponding to the BSS Parameters Change Count subfield. A significant update may include updating pre-specified parameters. The pre-specified parameters may include operation parameters. If the reported AP does not belong to a multilink device or the reporting AP does not have information about the multilink device to which the reported AP belongs, the value of the BSS Parameters Change Count subfield may be set to 255.

[0316] FIG. 25 illustrates a method for setting the ID of a multilink device according to an embodiment of the present invention.

[0317] The ID of the multilink device may be a value indicated by the MLD ID subfield described in FIG. 24. The MLD ID subfield may be 8 bits. The MLD ID subfield can indicate values ​​from 0 to 255. In an embodiment of the present invention, a reporting AP may represent an AP that sets and transmits the MLD ID subfield. A reported AP may represent an AP indicated by the MLD ID subfield or the TBTT Information subfield including the MLD ID subfield.

[0318] According to an embodiment of the present invention, the MLD ID subfield may be set as follows: The MLD ID subfield may indicate the ID of the AP multilink device to which the reported AP belongs. If the reported AP belongs to the AP multilink device to which the reporting AP belongs, the MLD ID subfield may be set to 0. If the reported AP belongs to a multilink device set to which a nontransmitted BSSID belongs that belongs to a multiple BSSID set, the value of the MLD ID subfield may be set to the same value as the value of the BSSID Index field of the Multiple BSSID-Index element of the nontransmitted BSSID profile corresponding to the nontransmitted BSSID. If the reported AP is part of another AP multilink device and the frame including the MLD ID subfield does not include a Multiple BSSID element, the value of the MLD ID subfield may be set to a value greater than 0 and less than 255. Furthermore, if the reported AP is part of a multilink device with other APs and the frame including the MLD ID subfield includes a Multiple BSSID element, the value of the MLD ID subfield may be set to a value greater than 2^n-1 and less than 255, where n is the value of the MaxBSSID Indicator subfield of the Multiple BSSID element. If the reported AP is not part of a multilink device or the reporting AP does not have information about the multilink device to which the reported AP belongs, the value of the MLD ID subfield may be set to 255. That is, if the reported AP belongs to the multilink device to which the reporting AP belongs, the value of the MLD ID subfield may be set to 0. Specifically, if the reported AP is not part of a multilink device or the reporting AP does not have information about whether the reported AP belongs to the multilink device, the value of the MLD ID subfield may be set to 255. That is, if the reported AP belongs to the multilink device to which the reporting AP belongs, the value of the MLD ID subfield may be set to 0.

[0319] In the embodiment of Figure 25, the reporting AP operates on the first link (link 1). The reporting AP belongs to the first multilink device, and the reporting AP transmits a Reduced Neighbor Report element and an MLD ID subfield. The first multilink device (MLD 1) operates on the first link (link 1), the second link (link 2), and the third link (link 3). In this case, the reporting AP sets the value of the MLD ID subfield corresponding to the AP operating on each of the second link (link 2) and the third link (link 3) to 0.

[0320] Alternatively, the reporting AP may transmit multiple BSSID elements along with the Reduced Neighbor Report element. In yet another specific embodiment, the reporting AP may not transmit multiple BSSID elements. In this case, if the reporting AP transmits multiple BSSID elements, it may indicate that the reporting AP belongs to a multiple BSSID set. Alternatively, if the reporting AP does not transmit multiple BSSID elements, it may indicate that the reporting AP does not belong to a multiple BSSID set.

[0321] According to an embodiment of the present invention, if the reported AP is included in the multiple BSSID set to which the reporting AP belongs, the value of the MLD ID subfield may be set to the BSSID index of the multiple BSSID set. Furthermore, if the reported AP belongs to a multilink device to which an AP that belongs to the multiple BSSID set to which the reporting AP belongs belongs, the value of the MLD ID subfield may be set to the BSSID index of the AP that belongs to the multiple BSSID set. If the reported AP belongs to a multilink device to which an AP with a nontransmitted BSSID that belongs to the multiple BSSID set to which the reported AP belongs belongs, the value of the MLD ID subfield may be set to the BSSID index of the reported AP.

[0322] The multiple BSSID set to which the reporting AP belongs may include APs operating on the first link (link 1) and belonging to the second multilink device (MLD 2). The second multilink device (MLD 2) may include APs operating on the first link (link 1) and APs operating on the second link (link 2). The reporting AP can set the MLD ID subfield values ​​corresponding to the APs operating on the first link (link 1) and the APs operating on the second link (link 2) belonging to the second multilink device (MLD 2) to the BSSID index of the reported AP. This is because the APs of the second multilink device (MLD 2) operating on the first link (link 1) and the APs of the second multilink device (MLD 2) operating on the second link (link 2) belong to the same multiple BSSID set as the reporting AP or belong to a multilink device included in the multiple BSSID set to which the reporting AP belongs.

[0323] When a reporting AP sends a multiple BSSID element, if the reported AP does not belong to the multilink device to which the reporting AP belongs, if the reported AP does not belong to the multiple BSSID set to which the reporting AP belongs, and if the reported AP does not belong to the multilink device to which an AP in the multiple BSSID set to which the reporting AP belongs belongs, the value of the MLD ID subfield may be set to a value greater than (2^n-1) and less than a pre-specified value.

[0324] Furthermore, when a reporting AP transmits a multiple BSSID element, if the reported AP does not belong to the multilink device to which the reporting AP belongs, if the reported AP does not belong to the multiple BSSID set to which the reporting AP belongs, or if the reported AP does not belong to the multilink device to which an AP in the multiple BSSID set to which the reporting AP belongs belongs, the value of the MLD ID subfield may be set to a value greater than (2^n-1) and less than a pre-specified value. This may be limited to cases where the reported AP belongs to the MLD. The pre-specified value may be the maximum value that the MLD ID subfield can indicate. The pre-specified value may be 255. Furthermore, n may be the MaxBSSID Indicator value corresponding to the multiple BSSID set to which the reporting AP belongs.

[0325] 25, the third multilink device (MLD3) may include an AP operating on the first link (link1) and an AP operating on the second link (link2). Furthermore, the AP belonging to the third multilink device (MLD3) and operating on the first link (link1) may not belong to the multiple BSSID set to which the reporting AP belongs. In this case, the values ​​of the MLD ID subfields for the AP belonging to the third multilink device (MLD3) and operating on the first link (link1) and the AP belonging to the third multilink device (MLD3) and operating on the second link (link2) may be set to values ​​greater than 2^n-1 and less than 255. This is because the AP belonging to the third multilink device (MLD3) and operating on the first link (link1) and the AP belonging to the third multilink device (MLD3) and operating on the second link (link2) do not belong to the multilink device to which the reporting AP belongs, and these two APs are not included in the multilink device to which the APs in the multiple BSSID set to which the reporting AP belongs belong.

[0326] If the reporting AP does not transmit multiple BSSID elements or if the reported AP does not belong to the same multi-link device as the reporting AP, the value of the MLD ID subfield may be set to a value greater than 0 and less than a pre-specified value. This may be limited to cases where the reported AP belongs to a multi-link device. The pre-specified value may be the maximum value that the MLD ID subfield can indicate. The pre-specified value may be 255.

[0327] Furthermore, if 1) the reported AP does not belong to a multilink device, 2) the reporting AP does not have information on whether the reported AP belongs to a multilink device, or 3) the reporting AP does not have information for setting the value of the MLD ID subfield, the reporting AP can set the value of the MLD ID subfield to a pre-specified value. In yet another specific embodiment, if 1) the reported AP does not belong to a multilink device, 2) the reporting AP does not have information on whether the reported AP belongs to a multilink device, or 3) the reporting AP does not have information for setting the value of the MLD ID subfield, the reporting AP can set the value of the MLD ID subfield to a value equal to or greater than a pre-specified value. The pre-specified value may be the maximum value that the MLD ID subfield can indicate. The pre-specified value may be 255.

[0328] In Figure 25, the fourth AP (AP4) operates on the first link (link1). At this time, the fourth AP (AP4) does not belong to any multilink device. Therefore, the reporting AP can set the value of the MLD ID subfield corresponding to the fourth AP (AP4) to 255.

[0329] A station can determine from which BSS a frame was transmitted based on the MAC address field in the MAC header of a received frame. Specifically, the station can determine whether the received frame was transmitted from the AP to which the station is associated or an AP belonging to the multiple BSSID set to which the AP to which the station is associated based on the MAC address field in the MAC header of the received frame. In a specific embodiment, the station can determine whether the received frame was transmitted from the AP to which the station is associated or an AP belonging to the multiple BSSID set to which the AP to which the station is associated based on the TA field in the MAC header of the received frame. In this case, if the TA field of the frame received by the station indicates the MAC address of the AP to which the station is associated or the MAC address of an AP belonging to the multiple BSSID set to which the AP to which the station is associated belongs, the station can determine that the received frame was transmitted from the AP to which the station is associated or an AP belonging to the multiple BSSID set to which the AP to which the station is associated belongs. If the TA field of a frame received by a station does not indicate the MAC address of the AP to which the station is associated and the MAC address of an AP belonging to the multiple BSSID set to which the AP to which the station is associated belongs, the station can determine that the received frame was transmitted from the AP to which the station is associated and an AP belonging to the multiple BSSID set to which the AP to which the station is associated belongs.

[0330] A station can determine to which AP a frame is to be transmitted based on the MAC address field in the MAC header of the received frame. In a specific embodiment, a station can determine whether a received frame is to be transmitted to the AP to which the station is associated or an AP belonging to the multiple BSSID set to which the AP to which the station is associated based on the RA field in the MAC header of the received frame. In this case, if the RA field of the frame received by the station indicates the MAC address of the AP to which the station is associated or the MAC address of an AP belonging to the multiple BSSID set to which the AP to which the station is associated, the station can determine that the received frame was transmitted to the AP to which the station is associated or an AP belonging to the multiple BSSID set to which the AP to which the station is associated. If the RA field of the frame received by the station does not indicate the MAC address of the AP to which the station is associated or the MAC address of an AP belonging to the multiple BSSID set to which the AP to which the station is associated, the station can determine that the received frame was transmitted to the AP to which the station is associated or an AP belonging to the multiple BSSID set to which the AP to which the station is associated.

[0331] A station can determine whether a frame is an inter-BSS frame based on the MAC address field in the MAC header of the received frame. The MAC address field may include at least one of an RA field, a TA field, and a BSSID field. If none of the RA field, TA field, and BSSID field of a frame received by the station indicates the MAC address of the AP to which the station is associated or the MAC address of an AP belonging to the multiple BSSID set to which the AP to which the station is associated belongs, the station can determine the received frame as an inter-BSS frame. If at least one of the RA field, TA field, and BSSID field of the frame received by the station indicates the MAC address of the AP to which the station is associated or the MAC address of an AP belonging to the multiple BSSID set to which the AP to which the station is associated belongs, the station can determine the received frame as an intra-BSS frame.

[0332] In such an embodiment, the BSSID may be used instead of the MAC address of the AP.

[0333] If the BSS color included in the preamble of the PPDU received by the station is the same as the BSS color of the BSS to which the station belongs and the preamble of the PPDU received by the station indicates that it is for downlink transmission, the station can determine that the AP to which the station is associated or an AP belonging to the multiple BSSID set to which the AP to which the station is associated transmits the received PPDU. If the BSS color included in the preamble of the PPDU received by the station is different from the BSS color of the BSS to which the station belongs or the preamble of the PPDU received by the station does not indicate that it is for downlink transmission, the station can determine that the AP to which the station is associated or an AP belonging to the multiple BSSID set to which the AP to which the station is associated did not transmit the received PPDU.

[0334] A multiple BSSID set may be a set of multiple BSSs for which information about the BSSs can be signaled in a single beacon frame or a single probe response frame. Specifically, a set of BSSIDs indicated by a single multiple BSSID element may be called a multiple BSSID set. Furthermore, a single TIM element included in a single beacon frame or a single TIM frame may indicate frames buffered for multiple BSSIDs included in the multiple BSSID set. Furthermore, a single beacon frame or a single probe response frame may include multiple BSSID elements. The multiple BSSID element may signal information about multiple BSSs. The BSSID of the BSS from which the above-mentioned single beacon frame or probe response frame is transmitted is called the transmitted BSSID. The remaining BSSIDs in a multiple BSSID set, excluding the transmitted BSSID, are called nontransmitted BSSIDs. Furthermore, beacon frames or probe response frames may not be transmitted from BSSs corresponding to nontransmitted BSSIDs.

[0335] As described above, the maximum number of BSSIDs that a multiple BSSID set can include may be 2^n. Here, n may be a value signaled in the Multiple BSSID element. For example, n may be a value indicated by the MaxBSSID Indicator included in the Multiple BSSID element. A station receiving the Multiple BSSID element can determine the MAC addresses or BSSIDs of APs included in the multiple BSSID set based on the received Multiple BSSID element. Furthermore, multiple BSSID indexes may be mapped to each BSSID included in the multiple BSSID set. Therefore, the BSSIDs included in the multiple BSSID set may be identified by the BSSID index. The maximum value of the MaxBSSID Indicator may be 8.

[0336] However, there are cases where the value of the MLD ID subfield cannot be set in the above-described embodiment of the method for setting the MLD ID subfield.

[0337] In the above-described embodiment, if at least one of the pre-specified conditions is satisfied, the reporting AP may set the value of the MLD ID subfield to a pre-specified value. In another specific embodiment, if the pre-specified condition is satisfied, the reporting AP may set the value of the MLD ID subfield to a value equal to or greater than the pre-specified value. The pre-specified value may be the maximum value that the MLD ID subfield can represent. In this case, the pre-specified value may be 255. The pre-specified condition may include at least one of: 1) the reported AP does not belong to a multilink device; 2) the reporting AP does not have information on whether the reported AP belongs to a multilink device; and 3) the reporting AP does not have information for setting the value of the MLD ID subfield. In addition, the pre-specified condition may include the reported AP not being included in a multilink device to which an AP in the multiple BSSID set to which the reporting AP belongs belongs when the value of the MaxBSSID Indicator field corresponding to the reporting AP is the maximum value. Such a condition may be that the reporting AP transmits multiple BSSID elements. The maximum value of the MaxBSSID Indicator field may be 8.

[0338] When a reporting AP sends a multiple BSSID element, if the reported AP is an AP included in a multiple BSSID set that includes the reporting AP, or if the reported AP belongs to a multilink device to which an AP in a multiple BSSID set that includes the reporting AP belongs, the MLD ID subfield can be set to the BSSID index of the AP included in the multiple BSSID set. If the value of the MaxBSSID Indicator subfield is 8, the maximum number of BSSIDs that a multiple BSSID set can include is 2^8 = 256. Therefore, according to the above conditions, there can be no values ​​greater than 2^n-1 and less than 255.

[0339] In addition, when the value of the MaxBSSID Indicator subfield corresponding to the reporting AP is the maximum value, the reporting AP may not be able to set the value of the MLD ID subfield even if the reported AP belongs to a multilink device to which an AP in the multiple BSSID set to which the reporting AP belongs belongs. For example, the reporting AP cannot indicate a multilink device whose BSSID index is 255. The above-described embodiment allows the value of the MLD ID subfield to be set to 255. Therefore, when the value of the MLD ID subfield is 255, it is difficult to distinguish whether the 255 is set based on the BSSID index or a pre-specified value.

[0340] Therefore, the condition for setting the value of the MLD ID subfield to a predetermined value may further include that when the value of the MaxBSSID Indicator subfield corresponding to the reporting AP is the maximum value, the reported AP belongs to a multilink device to which an AP in the multiple BSSID set to which the reporting AP belongs belongs. In yet another specific embodiment, the use of 255 as a BSSID index in a multiple BSSID set may not be permitted.

[0341] Furthermore, according to the above-described embodiment, regardless of whether the reporting AP transmits multiple BSSID elements, it may be difficult for the reporting AP to set the value of the MLD ID subfield. For example, when the reporting AP indicates information about a large number of APs, it may be difficult for the reporting AP to set the value of the MLD ID subfield. Because the number of reported APs is greater than the number of configurable multilink device IDs, it may be impossible to identify the reported AP by the multilink device ID. For example, when the reporting AP transmits multiple BSSID elements and transmits information to more than (254-2^n+1) APs, it may be impossible to identify the reported AP by the limited range of multilink device IDs. When the reporting AP does not transmit multiple BSSID elements and transmits information to more than (254-1+1) APs, it may be impossible to identify the reported AP by the limited range of IDs. The conditions for setting the value of the MLD ID subfield to a pre-specified value may further include a case where the reported AP cannot be identified by an ID in a limited range.

[0342] To solve the above problem, the size of the MLD ID subfield can be set to more than 8 bits. In this case, the pre-specified value may be the maximum value that the MLD ID subfield can indicate. That is, if the size of the MLD ID subfield is N bits, the pre-specified value may be 2^N-1. For example, if the size of the MLD ID subfield is 9 bits, the pre-specified value may be 511. As another example, if the size of the MLD ID subfield is 16 bits, the pre-specified value may be 65535.

[0343] 26 and 27 illustrate a method for allocating AIDs to non-AP stations belonging to a multi-link device according to an embodiment of the present invention.

[0344] According to an embodiment of the present invention, one association ID (AID) may be assigned to a multilink device, that is, the AIDs of stations included in one multilink device may be the same.

[0345] AID allocation may be performed by an AP. For example, the AP may transmit the AID it has assigned to a non-AP STA. The non-AP STA can recognize that the AID received from the AP is the AID that corresponds to the non-AP STA. A non-AP station that receives a subfield containing an AID value assigned to the non-AP station can recognize that the subfield containing the AID value assigned to the non-AP station indicates a non-AP station.

[0346] The AID assigned to the non-AP station may be included in the association response frame or reassociation response frame. If multilink setup is performed after the AP assigns an AID to the non-AP station, the AID assigned to the non-AP station may be the AID assigned to the multilink device to which the non-AP station belongs.

[0347] The AID or information related to the AID may be included in the preamble of the PPDU. In this case, the PPDU preamble may use the AID to indicate that the intended recipient of the PPDU is a non-AP station corresponding to the AID. The PPDU preamble may use the AID to indicate that the sender of the PPDU is a non-AP station corresponding to the AID. As described above, the AID may also be used to indicate traffic. A frame may use the AID to indicate that a station corresponding to the AID is the recipient of the frame. For example, a trigger frame may use the AID to indicate the station that the trigger frame will trigger.

[0348] An AID assigned to a multilink device may not be allowed to be assigned to other stations or other multilink devices. In a specific embodiment, an AID assigned to a multilink device may not be allowed to be assigned to stations or multilink devices that operate on links other than the link used by the multilink device.

[0349] In Figure 26, the first multilink device (MLD 1) operates on the first link (Link 1) and the second link (Link 2). The second multilink device (MLD 2) operates on the third link (Link 3) and the fourth link (Link 4). In this case, X is assigned as the AID of the first multilink device (MLD 1). Therefore, X is not permitted to be assigned as the AID of the second multilink device (MLD 2), and Y is assigned instead.

[0350] In a specific embodiment of the present invention, an AP multilink device can reallocate an AID previously assigned to one multilink device to another station or another multilink device. If a pre-specified condition is met, the AP multilink device can reallocate an AID previously assigned to one multilink device to another station or another multilink device. In this case, the pre-specified condition may include multilink devices or stations commonly assigned an AID operating on different links. That is, the pre-specified condition may include multilink devices or stations commonly assigned an AID operating on non-overlapping links. In this case, stations or multiple multilink devices operating on a single link may not be permitted to be assigned the same AID. In yet another specific embodiment, multilink devices or stations commonly assigned an AID may operate on non-overlapping channels.

[0351] In Figure 27(a), a first multilink device (MLD 1) operates on a first link (Link 1) and a second link (Link 2). The AP multilink device assigns X as the AID of the station of the first multilink device (MLD 1). In this case, the AP multilink device can assign X as the AID of a first station (STA1) that does not belong to the first multilink device (MLD 1) and operates on a third link (Link 3) rather than the first link (Link 1) and the second link (Link 2).

[0352] In such an embodiment, if a frame contains information about multiple links, one AID assigned to multiple multilink devices or stations may cause confusion. To prevent this, information transmitted on any one link may apply to the station or multilink device operating on that link. For example, information transmitted on a first link may apply to a station or multilink with AID X operating on the first link, but may not apply to a station or multilink with AID X operating on a second link.

[0353] In Figure 27(b), beacon frames including TIMs are transmitted over both the first link (Link1) and the second link (Link2). At this time, the TIMs transmitted over both the first link (Link1) and the second link (Link2) indicate that traffic corresponding to AID X is buffered. The TIM transmitted over the first link (Link1) indicates that traffic for the multi-link device (MLD1) operating over the first link (Link1) has been buffered, and the TIM transmitted over the second link (Link2) indicates that traffic for the station (STA1) operating over the second link (Link2) has been buffered.

[0354] The TID-to-link mapping negotiation will be described with reference to FIGS.

[0355] FIG. 28 is a diagram showing TID-to-link mapping negotiation according to one embodiment of the present invention.

[0356] As described above, default mapping may be applied to a link for which no TID-to-link mapping has been performed. Also, if the TID-to-link mapping for a link for which TID-to-link mapping negotiation has been completed is torn down, default mapping may be applied to the link again.

[0357] TID-to-link mapping negotiation may be performed using a TID-to-link mapping request and a TID-to-link mapping response. Specifically, a multilink device may request TID-to-link mapping by transmitting a frame including a TID-To-Link Mapping element. In this case, the frame may include an association request frame, a reassociation request frame, and a TID-to-link mapping request frame. Thus, a non-AP station or a non-AP multilink device may request TID-to-link mapping by transmitting an association request frame, a reassociation request frame, or a TID-to-link mapping request frame. An AP or an AP multilink device may request TID-to-link mapping by transmitting a TID-to-link mapping request frame. A multilink device that receives a TID-to-link mapping request may respond to TID-to-link mapping by transmitting a frame including a TID-To-Link Mapping element. In this case, the frame may include an association response frame, a reassociation response frame, and a TID-to-link mapping response frame. Therefore, an AP or AP multilink device can respond to a TID-to-link mapping request by transmitting an association response frame, a reassociation response frame, or a TID-to-link mapping request frame. A non-AP station or non-AP station multilink device can respond to a TID-to-link mapping request by transmitting a TID-to-link mapping response frame.

[0358] A multilink device can initiate TID-to-link mapping by transmitting a TID-to-link mapping request. At this time, the multilink device can request default mapping by transmitting a frame including a TID-to-link element. A multilink device that receives a TID-to-link mapping request can accept TID-to-link mapping by transmitting a TID-to-link mapping response to the TID-to-link mapping request. At this time, a multilink device that receives a TID-to-link mapping request can accept TID-to-link mapping by transmitting a frame that does not include a TID-to-link Mapping element. In yet another specific embodiment, a multilink device that receives a TID-to-link mapping request can accept TID-to-link mapping by transmitting a frame including a TID-to-link Mapping element having the same content as the content of the TID-to-link Mapping element received from a non-AP multilink device.

[0359] Furthermore, a multilink device that has received a TID-to-link mapping request may reject the TID-to-link mapping by transmitting a TID-to-link mapping response to the TID-to-link mapping request. In this case, a multilink device that has received a TID-to-link mapping request may reject the TID-to-link mapping by transmitting a frame that does not include a TID-to-link Mapping element. In yet another specific embodiment, a multilink device that has received a TID-to-link mapping request may reject the TID-to-link mapping by transmitting a frame that includes a TID-to-link Mapping element having content different from the content of the received TID-to-link Mapping element. If the TID-to-link mapping is rejected, a default mapping may be applied to the link.

[0360] In this embodiment, the frames transmitted by the multilink device for the TID-to-link mapping request and response may include at least one of an association request frame, an association response frame, a reassociation request frame, a reassociation response frame, a TID-to-link mapping request frame, and a TID-to-link mapping response frame, as described above. Specifically, a multilink device that receives a TID-to-link mapping request may transmit a TID-to-link mapping response frame in response to the TID-to-link mapping request. In this case, a multilink device that receives a TID-to-link mapping request may insert a status code into the TID-to-link mapping response frame to accept or reject the TID-to-link mapping request. Specifically, a multilink device that receives a TID-to-link mapping request may set the status code of the TID-to-link mapping response frame to SUCCESS to accept the TID-to-link mapping request. In addition, a multilink device that receives a TID-to-link mapping request can reject the TID-to-link mapping request by setting the status code of the TID-to-link mapping response frame to REJECT or DENIED_TID_TO_LINK_MAPPING. In addition, a multilink device that receives a TID-to-link mapping request can reject the TID-to-link mapping request by setting the status code of the TID-to-link mapping response frame to PREFERRED_TID_TO_LINK_MAPPING_SUGGESTED. In this case, a multilink device that receives a TID-to-link mapping request can propose a preferred TID-to-link mapping while rejecting the TID-to-link mapping request. In addition, a multilink device that receives a TID-to-link mapping request can reject the TID-to-link mapping request by transmitting a TID-to-link mapping rejection frame.

[0361] The TID-To-Link Mapping element included in the TID-to-link matching request indicates the TID-to-link mapping that is the target of the TID-to-link mapping request. Also, the TID-To-Link Mapping element sent when accepting a TID-to-link mapping can indicate the accepted TID-to-link mapping. Also, the TID-To-Link Mapping element sent when rejecting a TID-to-link mapping can indicate a newly proposed TID-to-link mapping.

[0362] If the TID-to-link mapping request is accepted, the TID-to-link mapping included in the TID-to-link mapping request is set to the link that is the target of the TID-to-link mapping. If the TID-to-link mapping request is rejected, a default mapping may be applied to the link that is the target of the TID-to-link mapping.

[0363] Furthermore, for TID-to-link mapping negotiation, the TID-to-link mapping request frame and the TID-to-link mapping response frame may include a dialog token. The dialog token maps the TID-to-link mapping request frame and the TID-to-link mapping response frame. Specifically, if the value of the dialog token in the TID-to-link mapping request frame and the value of the dialog token in the TID-to-link mapping response frame are the same, the TID-to-link mapping response frame may be transmitted as a response to the TID-to-link mapping request frame. Therefore, when a multilink device that has received a TID-to-link mapping request frame transmits a TID-to-link mapping response frame, the multilink device can set the dialog token value of the TID-to-link mapping response frame to the dialog token value of the TID-to-link mapping request frame. When a multilink device transmits a TID-to-link mapping response frame without receiving a TID-to-link mapping request frame, the multilink device may set the dialog token value of the TID-to-link mapping response frame to a pre-specified value. In this case, the pre-specified value may be 0. That is, when a multilink device transmits an unsolicited TID-To-Link Mapping Response frame, the multilink device may set the dialog token value of the TID-to-link mapping response frame to a pre-specified value. A field indicating a dialog token in the TID-to-link mapping request frame and the TID-to-link mapping response frame may be a 1-octet field. The value of the dialog token may have any one of values ​​0 to 255.

[0364] If the capabilities of a multilink device support TID-to-link mapping, the multilink device can perform TID-to-link mapping. Furthermore, the capabilities of the multilink device may affect the extent to which the multilink device can perform TID-to-link mapping. For example, the capabilities of the multilink device may affect the number of TIDs that the multilink device can map to links or the number of applicable TID-link mapping combinations. The capabilities of a multilink device may indicate whether the multilink device can map to link sets where all TIDs are the same. The capabilities of a multilink device may also indicate how many link sets the multilink device can map a TID to.

[0365] In the embodiment of Figure 28, the AP multilink device (AP ML) includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). The non-AP multilink device (Non-AP MLD) includes a first non-AP station (Non-AP STA1) and a second non-AP station (Non-AP STA2). The non-AP multilink device (Non-AP MLD) transmits an association request frame including a TID-to-link Mapping element to the AP multilink device (AP ML). The AP multilink device (AP ML) transmits an association response frame including a TID-to-link Mapping element to the non-AP multilink device (Non-AP MLD) to accept or reject the TID-to-link mapping corresponding to the TID-to-link Mapping element. In addition, the non-AP multilink device (Non-AP MLD) can renegotiate the TID-to-link mapping by sending a TID-to-link mapping request frame to the AP multilink device (AP ML). At this time, the AP multilink device (AP ML) can accept or reject the TID-to-link mapping corresponding to the TID-to-link Mapping element by sending a TID-to-link mapping response frame to the non-AP multilink device (Non-AP MLD).

[0366] FIG. 29 illustrates a TID-to-link mapping negotiation in which an AP multilink device sends a TID-to-link mapping request according to an embodiment of the present invention.

[0367] The AP multilink device can transmit a TID-to-link mapping request using an association response frame, a reassociation response frame, and a TID-to-link mapping request frame. Specifically, the AP multilink device can initiate TID-to-link mapping negotiation using the association response frame, the reassociation response frame, and the TID-to-link mapping request frame. At this time, the AP multilink device can include a TID-to-link Mapping element in the association response frame, the reassociation response frame, and the TID-to-link mapping request frame. Specifically, the AP multilink device can initiate TID-to-link mapping negotiation by including a TID-to-link Mapping element in the association response frame, the reassociation response frame, and the TID-to-link mapping request frame. This is because the TID-to-link mapping request transmitted by a non-AP multilink device may be in a format not desired by the AP multilink device, and the AP may not transmit the TID-to-link mapping request transmitted from the non-AP multilink device. In addition, an AP multilink device can more easily grasp the overall network status than a non-AP multilink device and can determine an efficient TID-to-link mapping. Since the AP multilink device first transmits an association response frame or a reassociation response frame before completing the TID-to-link mapping negotiation, it can complete the multilink setup and reconfiguration. When a non-AP multilink device that receives a TID-to-link mapping request transmits a TID-to-link mapping response, the TID-to-link mapping negotiation is successfully completed.

[0368] The cases in which the AP multilink device can transmit a TID-to-link mapping request using an association response frame and a reassociation response frame may be limited. Specifically, if the association request frame does not request TID-to-link mapping, the AP multilink device can transmit a TID-to-link mapping request in the association response frame. If the association request frame does not include a TID-to-link Mapping element, the AP multilink device can determine that the association request frame does not request TID-to-link mapping. Also, if the reassociation request frame does not request TID-to-link mapping, the AP multilink device can transmit a TID-to-link mapping request in the reassociation response frame. If the reassociation request frame does not include a TID-to-link Mapping element, the AP multilink device can determine that the reassociation request frame does not request TID-to-link mapping. If the association request frame transmitted by the non-AP multilink device does not include a TID-to-link Mapping element, the non-AP multilink device can determine that the association response frame, which includes a TID-to-link Mapping element and is received in response to the association request frame, requests TID-to-link mapping. If the reassociation request frame transmitted by the non-AP multilink device does not include a TID-to-link Mapping element, the non-AP multilink device can determine that the reassociation response frame, which includes a TID-to-link Mapping element and is received in response to the reassociation request frame, requests TID-to-link mapping. This embodiment is because, if the association request frame includes a TID-to-link element and the association request frame includes a TID-to-link element, the non-AP multilink device may confuse the intention of including the TID-to-link element in the association response frame. The same applies to the reassociation request frame.

[0369] In this embodiment, the AP multilink device may not determine that the TID-to-link mapping has been successfully completed until it receives a TID-to-link mapping response from the non-AP multilink device. Therefore, the AP multilink device may operate using default mapping until it receives a TID-to-link mapping response from the non-AP multilink device. Furthermore, even if the AP multilink device receives an ACK for the association response frame or reassociation response frame, the AP multilink device may not determine that the TID-to-link mapping has been successfully completed.

[0370] According to the above-described embodiment, the non-AP multilink device can respond to the TID-to-link mapping request transmitted by the AP multilink device in an association frame or a reassociation frame. However, the non-AP multilink device must explicitly indicate that it will respond to the TID-to-link mapping request transmitted by the AP multilink device in an association frame or a reassociation frame. The non-AP multilink device can transmit a TID-to-link mapping response in a response frame to an association response frame requesting TID-to-link mapping or a reassociation response frame requesting TID-to-link mapping. In addition, the non-AP multilink device can set the dial log token value of the TID TID-to-link mapping response to the same value as the dialogue token value included in the association response frame requesting TID-to-link mapping or the reassociation response frame requesting TID-to-link mapping. However, the association response frame requesting TID-to-link mapping and the reassociation response frame requesting TID-to-link mapping do not need to include a dialogue token.

[0371] Therefore, the TID-to-link Mapping element may include a response indication field indicating that the element is a response to the TID-to-link mapping request. In this case, the response indication field may be included in the TID-to-Link Mapping Control field described above. Specifically, the response indication field may be included in the reserved field of the TID-to-Link Mapping Control field described above. For example, the response indication field may be any one of the fourth bit (B3) to the eighth bit (B8) of the TID-to-Link Mapping Control field. A multilink device that receives the TID-to-link element can determine whether the TID-to-link Mapping element requests TID-to-link mapping based on the response indication field.

[0372] Because a non-AP multilink device transmits a TID-to-link mapping response frame in response to an association request frame or a reassociation request frame, the AP multilink device must distinguish which frame the TID-to-link mapping response frame is a response to. Specifically, when a non-AP multilink device transmits a TID-to-link mapping response frame in response to an association request frame or a reassociation request frame, the non-AP multilink device may set the value of the dialogue token in the TID-to-link mapping response frame to a random value. Also, if the value of the dialogue token in the TID-to-link mapping response frame is the same as the value of the dialogue token in the TID-to-link mapping request frame transmitted by the AP multilink device, the TID-to-link mapping response frame may be a response to the TID-to-link mapping request frame. Also, if the value of the dialogue token in the TID-to-link mapping response frame is different from the value of the dialogue token in the TID-to-link mapping request frame transmitted by the AP multilink device, the TID-to-link mapping response frame may be a response to an association request frame or a reassociation request frame.

[0373] In yet another specific embodiment, when the AP multilink device transmits a TID-to-link mapping request in an association response frame or a reassociation response frame, the value of the dialogue token of the TID-to-link mapping response frame transmitted in response to the TID-to-link mapping request may be set to a pre-specified value. In this case, the pre-specified value may be 0, 1, or 255. When the AP multilink device transmits a TID-to-link mapping request in an association frame or a reassociation frame and receives a TID-to-link mapping response frame having a dialogue token value equal to the pre-specified value, the AP multilink device can determine that the received TID-to-link mapping response frame is a response to the transmitted TID-to-link mapping request.

[0374] In yet another specific embodiment, when the AP multilink device transmits a TID-to-link mapping request in an association response frame or a reassociation response frame, the status code of the TID-to-link mapping response frame transmitted in response to the TID-to-link mapping request may be a predetermined value. In this case, the predetermined status code value may be different from the status code value of the TID-to-link mapping response frame transmitted in response to the TID-to-link mapping request transmitted by the multilink device in a frame other than the association frame or the reassociation frame. Thus, the AP multilink device can determine whether the received TID-to-link mapping response frame is a response to the TID-to-link mapping request transmitted by the AP multilink device in the association response frame or the reassociation response frame based on the status code of the received TID-to-link mapping response frame. Specifically, if the status code of the received TID-to-link mapping response frame is a pre-specified value, the AP multilink device can determine that the received TID-to-link mapping response frame is a response to the TID-to-link mapping request sent by the AP multilink device in an association response frame or a reassociation response frame.

[0375] In yet another specific embodiment, the AP multilink device may determine whether the received TID-to-link mapping response frame is a response to the TID-to-link mapping request transmitted by the AP multilink device in an association response frame or a reassociation response frame based on the value of the Link Mapping field for the TID in the received TID-to-link mapping response frame. Specifically, if the value of the Link Mapping field for the TID in the received TID-to-link mapping response frame is the same as the value of the Link Mapping field for the TID in the TID-to-link mapping request transmitted by the AP multilink device in an association response frame or a reassociation response frame, the AP multilink device may determine that the received TID-to-link mapping response frame is a response to the TID-to-link mapping request transmitted by the AP multilink device in an association response frame or a reassociation response frame. Specifically, the received TID-to-link mapping response frame may include Link Mapping fields for multiple TIDs. In this case, if the values ​​of all Link Mapping fields included in the TID-to-link mapping response frame are the same as the values ​​of all Link Mapping fields of the TID-to-link mapping request transmitted by the AP multilink device in the association response frame or reassociation response frame, the AP multilink device can determine that the received TID-to-link mapping response frame is a response to the TID-to-link mapping request transmitted by the AP multilink device in the association response frame or reassociation response frame.If the value of the Link Mapping field for the TID in the TID-to-link mapping response frame received by the AP multilink device is different from the value of the Link Mapping field for the TID in the TID-to-link mapping request transmitted by the AP multilink device in the association response frame or reassociation response frame, the AP multilink device does not need to transmit an ACK for the received TID-to-link mapping response frame.In addition, if the Link Mapping field for the TID of the TID-to-link mapping response frame received by the AP multilink device includes at least one value of the Link Mapping field for the TID of the TID-to-link mapping request transmitted by the AP multilink device in the association response frame or reassociation response frame, the AP multilink device does not need to transmit an ACK for the received TID-to-link mapping response frame. In addition, if the TID-to-link mapping response frame received by the AP multilink device does not include any Link Mapping field for the TID of the TID-to-link mapping request transmitted by the AP multilink device in the association response frame or reassociation response frame, or if the value of the Link Mapping field of the TID-to-link mapping response frame received by the multilink device is different from the value of the Link Mapping field for the TID of the TID-to-link mapping request transmitted by the AP multilink device in the association response frame or reassociation response frame, the AP multilink device does not need to transmit an ACK for the received TID-to-link mapping response frame. The above-described embodiment is also applicable to the case where the TID-to-link mapping request is not transmitted in the association response frame or the reassociation response frame.

[0376] In the embodiment of Figure 29, the AP multilink device (AP ML) includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). The non-AP multilink device (Non-AP MLD) includes a first non-AP station (Non-AP STA1) and a second non-AP station (Non-AP STA2). The non-AP multilink device (Non-AP MLD) transmits an association request frame that does not include a TID-to-link Mapping element to the AP multilink device (AP ML). The AP multilink device (AP ML) transmits an association response frame that includes a TID-to-link Mapping element to the non-AP multilink device (Non-AP MLD) to request a TID-to-link mapping corresponding to the TID-to-link Mapping element. At this time, the non-AP multilink device (Non-AP MLD) transmits a TID-to-link mapping response frame to the AP multilink device (AP ML) to accept the TID-to-link mapping request.

[0377] FIG. 30 illustrates TID-to-link mapping negotiation when a link set requesting TID-to-link mapping is different from a link set established by a TID-to-link mapping response according to an embodiment of the present invention.

[0378] The link set for which the TID-to-link mapping is requested in the association request frame or reassociation request frame may be different from the link set for which the TID-to-link mapping is to be set in the association response frame or reassociation response frame. For example, the association request frame or reassociation request frame may request TID-to-link mapping for three links, and the association response frame or reassociation response frame may set TID-to-link mapping for two links. Different link sets may also mean different link set configurations. Specifically, different link set configurations may mean different operating channels for the link sets. Different link sets may also mean different link set configurations.

[0379] 28, when an AP multilink device receives an association request frame or a reassociation request frame including a TID-to-link Mapping element, the AP multilink device may establish a multilink by transmitting an association response frame or a reassociation response frame that does not include a TID-to-link Mapping element. However, as described above, the link set for which the TID-to-link mapping is requested in the association request frame or the reassociation request frame may differ from the link set for which the TID-to-link mapping is to be established in the association response frame or the reassociation response frame.

[0380] Therefore, in yet another embodiment of the present invention, if an AP multilink device receives an association request frame or a reassociation request frame including a TID-to-link Mapping element and attempts to establish a link set different from the link set of the multilink that the association request frame or the reassociation request frame is attempting to establish, the AP multilink device can transmit an association response frame or a reassociation response frame that does not include a TID-to-link Mapping element. This allows the AP multilink device to reject the TID-to-link mapping. In this case, a default mapping may be applied to the AP multilink device and the non-AP multilink device.

[0381] When an AP multilink device receives an association request frame or reassociation request frame including a TID-to-link Mapping element and transmits an association response frame or reassociation response frame that sets a link set different from the link set of the multilink that the association request frame or reassociation request frame is attempting to establish, the AP multilink device may transmit an association response frame or reassociation response frame that does not include a TID-to-link Mapping element. Also, when a non-AP multilink device transmits an association request frame or reassociation request frame including a TID-to-link Mapping element and receives an association response frame or reassociation response frame that sets a link set different from the link set of the multilink that the association request frame or reassociation request frame is attempting to establish, the non-AP multilink device may determine that the TID-to-link mapping request has been rejected even if the received association response frame or reassociation response frame does not include a TID-to-link Mapping element. In this case, default mapping may be applied to the AP multilink device and the non-AP multilink device.

[0382] In yet another specific embodiment, when an AP multilink device receives an association request frame or a reassociation request frame including a TID-to-link Mapping element and attempts to establish a link set different from the link set of the multilink that the association request frame or the reassociation request frame attempts to establish, the AP multilink device may transmit an association response frame or a reassociation response frame including a TID-to-link Mapping element. In this case, the TID-to-link Mapping element included in the association response frame or the reassociation response frame may indicate the TID-to-link mapping proposed by the AP multilink device. In this case, the operation of the non-AP multilink device may be the same as the embodiment described in FIG. 28.

[0383] In the above-described embodiment, for convenience of explanation, the operation of the multilink device has been described. However, the operation of the multilink device may also be performed by a station included in the multilink device.

[0384] FIG. 31 illustrates a method for a non-AP multilink device to determine traffic buffered in an AP multilink device according to an embodiment of the present invention.

[0385] The non-AP multilink device receives a beacon frame including a beacon frame from the AP multilink device (S3101).

[0386] The non-AP multilink device determines whether traffic for the non-AP multilink device is buffered in the multilink device based on the Partial Virtual Bitmap subfield of the TIM element (S3103). In this case, the Partial Virtual Bitmap subfield includes one or more first bits and one or more second bits, and one or more first bits set to 1 may indicate that traffic for the corresponding non-AP multilink device is buffered in the AP multilink device. Also, one or more second bits set to 1 may indicate that traffic for the corresponding non-AP station is buffered in the AP multilink device. Specific formats and settings of the Partial Virtual Bitmap subfield may follow the embodiments described with reference to FIGS. 13 to 18.

[0387] When traffic for a non-AP multilink device is buffered in the AP multilink device, the AP multilink device can determine, based on the Per-Link Traffic Indication List subfield of the Multi-Link Traffic element, which of a plurality of links the traffic for the non-AP multilink device is buffered on, or which of the plurality of links the AP multilink device recommends the non-AP multilink device to retrieve traffic transmission from. The Per-Link Traffic Indication List subfield may include n Per-Link Traffic Indication Bitmap subfields, where n is the sum of the number of bits set to 1 among the one or more first bits and the number of bits set to 1 among the one or more second bits. Furthermore, each of the n Per-Link Traffic Indication Bitmap subfields may be mapped to a non-AP multilink device corresponding to one or more first bits set to 1 and a non-AP station corresponding to one or more second bits set to 1, respectively. Additionally, multiple link IDs may be mapped in ascending order to bits in the Per-Link Traffic Indication Bitmap subfield that are mapped to non-AP multi-link devices.

[0388] In addition, a reserved bit may be set in the Per-Link Traffic Indication Bitmap subfield mapped to a non-AP station corresponding to one or more second bits set to 1. In this case, the value of the reserved bit may be 0.

[0389] When a non-AP multilink device successfully performs TID-to-link mapping with an AP multilink device and not all TIDs are mapped to all links, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device can indicate whether traffic for the non-AP multilink device is buffered on each of the multiple links. Also, when default mapping is applied to links between the non-AP multilink device and the AP multilink device, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device can indicate which of the multiple links the non-AP multilink device recommends for traffic transmission. In this case, the default mapping may map all TIDs to all links.

[0390] Among the bits in the Per-Link Traffic Indication Bitmap subfield mapped to a non-AP multilink device, bits corresponding to links not configured by the AP multilink device or non-AP multilink device may be set as reserved bits. Also, among the bits in the Per-Link Traffic Indication Bitmap subfield mapped to a non-AP multilink device, bits corresponding to disabled links of the non-AP multilink device may be set as reserved bits. In this case, a disabled link may be a link in which uplink and downlink transmissions are stopped.

[0391] A specific Per-Link Traffic Indication List subfield of the Multi-Link Traffic element may be as described with reference to FIGS.

[0392] Although the present invention has been described above with reference to wireless LAN communications, the present invention is not limited thereto and may be equally applied to other communications systems such as cellular communications. Furthermore, although the method, apparatus, and system of the present invention have been described in connection with specific embodiments, some or all of the components and operations of the present invention may be implemented using a computer system having a general-purpose hardware architecture.

[0393] The features, structures, effects, etc. described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to one embodiment. Furthermore, the features, structures, effects, etc. exemplified in each embodiment can be combined or modified in other embodiments by a person skilled in the art to which the embodiment belongs. Therefore, content related to such combinations and modifications should be interpreted as being included within the scope of the present invention.

[0394] The above description has focused on the embodiments, but these are merely illustrative and do not limit the present invention. Those skilled in the art will recognize that various modifications and applications not exemplified above are possible within the scope of the essential characteristics of the present invention. For example, each component specifically illustrated in the embodiments can be modified and implemented. Differences related to such modifications and applications should be construed as being included within the scope of the present invention as defined by the appended claims. [Explanation of symbols]

[0395] 100 Stations 110 processors 120 Communications Department 140 User Interface Section 150 display units 160 memory 200 APs (Access Points) 210 processors 220 Communications Department 260 memory

Claims

1. A non-AP (access point) multi-link device including a plurality of stations each operating on a plurality of links, a transmitter / receiver; Processor and Including, The processor: Receive a beacon frame including a TIM (Traffic Indication Map) element and a Multi-Link Traffic element from the AP multilink device; and determining whether traffic for the non-AP multilink device is buffered in the AP multilink device based on a Partial Virtual Bitmap subfield of the TIM element, the Partial Virtual Bitmap subfield including one or more first bits and one or more second bits, wherein a bit set to 1 among the one or more first bits indicates that traffic for a non-AP multilink device corresponding to the bit among the one or more first bits is buffered in the AP multilink device, and a bit set to 1 among the one or more second bits indicates that traffic for a non-AP station not belonging to any of the multilink devices corresponding to the bit among the one or more second bits is buffered in the AP multilink device; When traffic for the non-AP multilink device is buffered in the AP multilink device, determine, based on a Per-Link Traffic Indication List subfield of the Multi-Link Traffic element, which of the plurality of links is the link on which traffic for the non-AP multilink device is buffered, or which of the plurality of links is the link for which the AP multilink device recommends retrieving traffic transmission to the non-AP multilink device; The Per-Link Traffic Indication List subfield includes n Per-Link Traffic Indication Bitmap subfields; n is equal to the sum of the number of the one or more first bits that are set to 1 and the number of the one or more second bits that are set to 1; Each of the n Per-Link Traffic Indication Bitmap subfields is mapped to the non-AP multilink device corresponding to a bit set to 1 among the one or more first bits and the non-AP station corresponding to a bit set to 1 among the one or more second bits, respectively; When the non-AP multilink device successfully performs TID-to-link mapping with the AP multilink device and all TIDs are not mapped to all links in the TID-to-link mapping, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device indicates whether traffic for the non-AP multilink device is buffered on each of the multiple links; The Per-Link Traffic Indication Bitmap subfield mapped to the non-AP station corresponding to the bit set to 1 among the one or more second bits is set as a reserved bit, and the value of the reserved bit is 0; The one or more first bits and the leading bit of the one or more second bits of the Partial Virtual Bitmap subfield correspond to an association ID (AID) indicated by an AID Offset field of the Multi-Link Traffic element; Non-AP multi-link device.

2. 2. The non-AP multilink device of claim 1, wherein among the bits of the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device, bits corresponding to links not set by the AP multilink device or the non-AP multilink device are set as reserved bits.

3. Among the bits of the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device, bits corresponding to disabled links of the non-AP multilink device are set as reserved bits; The non-AP multi-link device of claim 1, wherein the disabled link is a link in which uplink and downlink transmissions are stopped.

4. 2. The non-AP multi-link device according to claim 1, wherein IDs of the plurality of links are mapped in ascending order to bits of the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multi-link device.

5. When the AP that transmitted the beacon frame in the AP multilink device does not belong to a multiple BSSID set, a range of values ​​that the AP multilink device can assign as an AID is determined based on a value of a Group Address BU Indication Exponent subfield; 2. The non-AP multilink device of claim 1, wherein a value of the Group Addressed BU Indication Exponent subfield indicates a number of bits used to indicate buffered group address frames corresponding to an AP other than the AP that transmitted the beacon frame in the AP multilink device.

6. 6. The non-AP multilink device of claim 5, wherein when the AP that transmitted the beacon frame in the AP multilink device belongs to the multiple BSSID set, a range of values ​​that the AP multilink device can assign as an AID is determined based on a value of the Group Address BU Indication Exponent subfield and a bitmap limit, and the bitmap limit is 48 bits.

7. An AP (access point) multi-link device including a plurality of stations each operating on a plurality of links, a transmitter / receiver; Processor and Including, The processor: and configuring a TIM (Traffic Indication Map) element and a Multi-Link Traffic element included in a beacon frame transmitted to a non-AP multilink device, the TIM element including a Partial Virtual Bitmap subfield, the Partial Virtual Bitmap subfield including one or more first bits and one or more second bits, a bit set to 1 among the one or more first bits indicating that traffic for a non-AP multilink device corresponding to the bit among the one or more first bits is buffered in the AP multilink device, and a bit set to 1 among the one or more second bits indicating that traffic for a non-AP station not belonging to any of the multilink devices corresponding to the bit among the one or more second bits is buffered in the AP multilink device; When traffic for the non-AP multilink device is buffered in the AP multilink device, a Per-Link Traffic Indication List subfield of the Multi-Link Traffic element is set according to which link among the plurality of links the traffic for the non-AP multilink device is buffered on, or which link among the plurality of links the AP multilink device recommends the non-AP multilink device to retrieve traffic transmission from, and Transmitting the beacon frame via the transceiver; The Per-Link Traffic Indication List subfield includes n Per-Link Traffic Indication Bitmap subfields; n is equal to the sum of the number of the one or more first bits that are set to 1 and the number of the one or more second bits that are set to 1; Each of the n Per-Link Traffic Indication Bitmap subfields is mapped to the non-AP multilink device corresponding to a bit set to 1 among the one or more first bits and the non-AP station corresponding to a bit set to 1 among the one or more second bits, respectively; When the non-AP multilink device successfully performs TID-to-link mapping with the AP multilink device and all TIDs are not mapped to all links in the TID-to-link mapping, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device indicates whether traffic for the non-AP multilink device is buffered on each of the multiple links; When a default mapping is applied to a link between the non-AP multilink device and the AP multilink device, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device indicates which of the multiple links is a link that the non-AP multilink device recommends for inducing traffic transmission; The default mapping is a mapping in which all TIDs are mapped to all links; The Per-Link Traffic Indication Bitmap subfield mapped to the non-AP station corresponding to the bit set to 1 among the one or more second bits is set as a reserved bit, and the value of the reserved bit is 0; The one or more first bits and the leading bit of the one or more second bits of the Partial Virtual Bitmap subfield correspond to an association ID (AID) indicated by an AID Offset field of the Multi-Link Traffic element; AP multilink device.

8. the processor: The AP multilink device according to claim 7, wherein among the bits of the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device, bits corresponding to links not set by the AP multilink device or the non-AP multilink device are set as reserved bits.

9. the processor: Among bits of the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device, bits corresponding to disabled links of the non-AP multilink device are set as reserved bits; The AP multi-link device according to claim 7 , wherein the disabled link is a link in which uplink and downlink transmissions are stopped.

10. 8. The AP multilink device according to claim 7, wherein IDs of the plurality of links are mapped in ascending order to bits of the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device.

11. When the AP that transmitted the beacon frame in the AP multilink device does not belong to a multiple BSSID set, a range of values ​​that the AP multilink device can assign as an AID is determined based on a value of a Group Address BU Indication Exponent subfield; 8. The AP multilink device of claim 7, wherein a value of the Group Addressed BU Indication Exponent subfield indicates a number of bits used to indicate buffered group address frames corresponding to an AP other than the AP that transmitted the beacon frame in the AP multilink device.

12. 12. The AP multilink device of claim 11, wherein when the AP that transmitted the beacon frame in the AP multilink device belongs to the multiple BSSID set, a range of values ​​that the AP multilink device can assign as an AID is determined based on a value of the Group Address BU Indication Exponent subfield and a bitmap limit, and the bitmap limit is 48 bits.

13. A method for operating a non-AP (access point) multi-link device including a plurality of stations each operating on a plurality of links, comprising: receiving a beacon frame including a Traffic Indication Map (TIM) element and a Multi-Link Traffic element from an AP multi-link device; determining whether traffic for the non-AP multilink device is buffered in the AP multilink device based on a Partial Virtual Bitmap subfield of the TIM element, the Partial Virtual Bitmap subfield including one or more first bits and one or more second bits, a bit set to 1 among the one or more first bits indicating that traffic for a non-AP multilink device corresponding to the bit among the one or more first bits is buffered in the AP multilink device, and a bit set to 1 among the one or more second bits indicating that traffic for a non-AP station not belonging to any of the multilink devices corresponding to the bit among the one or more second bits is buffered in the AP multilink device; determining, when traffic for the non-AP multilink device is buffered in the AP multilink device, which of the plurality of links is a link on which traffic for the non-AP multilink device is buffered, or which of the plurality of links is a link for which the AP multilink device recommends retrieving traffic transmission to the non-AP multilink device, based on a Per-Link Traffic Indication List subfield of the Multi-Link Traffic element; Including, The Per-Link Traffic Indication List subfield includes n Per-Link Traffic Indication Bitmap subfields; n is equal to the sum of the number of the one or more first bits that are set to 1 and the number of the one or more second bits that are set to 1; Each of the n Per-Link Traffic Indication Bitmap subfields is mapped to the non-AP multilink device corresponding to a bit set to 1 among the one or more first bits and the non-AP station corresponding to a bit set to 1 among the one or more second bits, respectively; When the non-AP multilink device successfully performs TID-to-link mapping with the AP multilink device and all TIDs are not mapped to all links in the TID-to-link mapping, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device indicates whether traffic for the non-AP multilink device is buffered on each of the multiple links; The Per-Link Traffic Indication Bitmap subfield mapped to the non-AP station corresponding to the bit set to 1 among the one or more second bits is set as a reserved bit, and the value of the reserved bit is 0; The one or more first bits and the leading bit of the one or more second bits of the Partial Virtual Bitmap subfield correspond to an association ID (AID) indicated by an AID Offset field of the Multi-Link Traffic element; How it works.

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