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

Abstract

To provide a non-AP (Access Point) multi-link device that includes a plurality of stations each operating on a plurality of links.SOLUTION: A multi-link device includes a transmitting / receiving unit and a processor. The processor receives a beacon frame including a TIM element and a multi-link traffic element from an AP multi-link device, and determines whether traffic for a non-AP multi-link device is buffered in the AP multi-link device based on a partial virtual bitmap 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 use of mobile devices has become more widespread, wireless LAN technology that can provide them with high-speed wireless Internet services has been attracting attention. Wireless LAN technology is a technology that enables mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, embedded devices, etc. to wirelessly connect to the Internet at home, in business, or in specific service areas based on short-distance wireless communication technology.

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

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

[0005] As the use of wireless LANs becomes more widespread and applications using them become more diverse, the need for new wireless LAN systems to support data throughput rates (Very High Throughput, VHT) higher than those supported by IEEE 802.11n is emerging. Among them, IEEE 802.11ac supports wide bandwidth (80MHz~160MHz) at 5GHz frequency. Although the IEEE 802.11ac standard is defined only in the 5GHz band, it is expected that initial 11ac chipsets will also support operation in the 2.4GHz band for backward compatibility with existing 2.4GHz band products. Theoretically, this standard allows multi-station wireless LAN speeds of at least 1Gbps and maximum single link speeds of at least 500Mbps. This is done by extending the air interface concepts accepted by 802.11n, such as wider radio frequency bandwidth (up to 160MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high density modulation (up to 256QAM). Also, there is IEEE 802.11ad, a method of transmitting data using the 60GHz band instead of the conventional 24GHz / 5GHz. IEEE 802.11ad is a transmission standard that uses beamforming technology to provide speeds of up to 7Gbps, and is suitable for streaming large amounts of data and high bitrate videos such as uncompressed HD video. However, the 60GHz frequency band has the disadvantage that it is difficult to pass through obstacles and can only be used between devices in close proximity.

[0006] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard is being developed and is in the final stages as the WLAN standard after 802.11ac and 802.11ad to provide high-efficiency and high-performance WLAN communication technology in high-density environments where APs and terminals are densely packed. In an 802.11ax-based WLAN environment, it is necessary to provide high-frequency efficient communication indoors / outdoors in the presence of high density stations and APs (Access Points), and various technologies are being developed to realize this.

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

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

[0009] According to an embodiment of the present invention, a non-AP (access point) multilink device including a plurality of stations each 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 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 indicates that traffic for the non-AP station corresponding to the bit is buffered in the AP multilink device. When traffic for the non-AP multi-link device is buffered in the AP multi-link 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 multi-link device is buffered on, or which of the multiple links the AP multi-link device recommends the non-AP multi-link device to 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] 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 may be set as a reserved bit.

[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 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 may indicate which of the multiple links is the link that the non-AP multilink device recommends to induce traffic transmission to, where the default mapping is a mapping in which all TIDs are mapped to all links.

[0014] Among the bits of 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 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 suspended.

[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 multilink 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 a buffered group address frame corresponding to an AP other than the AP that transmitted the beacon frame in the AP multilink device.

[0018] When 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 each operating on a plurality of links includes a transceiver and a processor. The processor sets 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. In this case, 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, and a bit set to 1 among the one or more first bits indicates 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 indicates that traffic for the non-AP station corresponding to the bit 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 a 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 to 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 a value obtained by adding 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.

[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 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 may indicate which of the multiple links is the link that the non-AP multilink device recommends to induce traffic transmission. 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 multilink 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 a buffered group address frame corresponding to an AP other than the AP that transmitted the beacon frame in the AP multilink device.

[0030] When 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 each 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 Partial Virtual Bitmap subfield including one or more first bits and one or more second bits, The method includes determining, based on the List subfield, which of the plurality of links has traffic buffered for the non-AP multilink device, or which of the plurality of links is a link that the AP multilink device recommends the non-AP multilink device to 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.

[0032] 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 may be set as a reserved bit. Effect of the Invention

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

[0034] [Figure 1] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Diagram 2] FIG. 11 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing a configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing a configuration of an access point according to an embodiment of the present invention. [Diagram 5] 1 is a diagram illustrating a process in which a STA sets up a link with an AP. [Figure 6]FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] 1 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same, according to an embodiment of the present invention. [Figure 9] 1 illustrates a multi-link device according to an embodiment of the present invention. [Figure 10] 4 illustrates a multi-link mapped by a TID-to-link mapping method according to an embodiment of the present invention. [Figure 11] 4 illustrates a power management operation 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] 13 illustrates how the Multi-Link Traffic element and the Partial Virtual Bitmap subfield of 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] 13 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] 13 illustrates a method for an AP multi-link device to set a Per-Link Traffic Indication Bitmap subfield of a Mut-Link Traffic element according to yet another embodiment of the present invention. [Figure 19] 1 shows 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. [Diagram 23] 4 illustrates a multi-link setup process according to an embodiment of the present invention. [Figure 24] 1 illustrates a format of a Reduced Neighbor Report element according to an embodiment of the present invention. [Diagram 25] 4 illustrates a method for setting an ID of a multilink 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 transmits 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 transmits a TID-to-link mapping request according to an embodiment of the present invention. [Diagram 30] 13 illustrates a TID-to-link mapping negotiation in a case where 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. [Diagram 31] 4 illustrates a method for a non-AP multi-link device to determine traffic buffered in an AP multi-link device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The terms used in this specification are selected as general terms currently widely used as much as possible in consideration of the functions in the present invention, but this may vary depending on the intentions, customs, or the emergence of new technologies of the technical experts in the field. In addition, in certain cases, the applicant may arbitrarily select terms, and in such cases, the meanings of the terms will be described in the description of the relevant invention. Therefore, it is clear that the terms used in this specification should be interpreted not simply as terms, but based on the substantial meanings of the terms and the contents of this specification as a whole.

[0036] Throughout the specification, when a certain component is "connected" to another component, this includes not only when it is "directly connected" to another component, but also when it is "electrically connected" with another component in between. Furthermore, when a certain component "includes" a specific component, this means that it may further include the other component, not excluding the other component, unless otherwise specified to the contrary. In addition, limitations such as "greater than" or "less than" based on a specific threshold value may be appropriately replaced with "greater than" or "less than" depending on the embodiment.

[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 (BSS), which are a set of devices that can successfully synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0040] As shown in FIG. 1, infrastructure BSS BSS1, BSS2 includes one or more stations STA1, STA2, STA3, STA4, STA5, access points AP-1, AP-2 which are stations providing a distribution service, and a distribution system DS which connects multiple access points AP-1, AP-2.

[0041] A station (STA) is any device including a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard, and in a broad sense includes not only non-AP stations but also APs. In this specification, the term "terminal" refers to either a non-AP or an AP, or both. A station for wireless communication includes a processor and a communication unit, and further includes a user interface unit and a display unit, etc., depending on the embodiment. The processor generates frames to be transmitted via a wireless network, processes frames received via 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 via the wireless network for the station. In the present invention, the term "terminal" is used to include a 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 a station associated therewith. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP, but when a direct link is set up, direct communication is possible between non-AP stations. Meanwhile, in the present invention, AP is used as a concept including a personal BSS coordination point (PCP), but in a broad sense, AP includes all concepts such as a central controller, a base station (BS), a node B, a base transceiver system (BTS), or a site controller. In the present invention, AP is also referred to as a base wireless communication terminal, but in a broad sense, the base wireless communication terminal is used as a term including an AP, a base station, an eNodeB (eNB), and a transmission point TP. In addition, the base wireless communication terminal includes various types of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with a plurality of wireless communication terminals.

[0043] A plurality of infrastructure BSSs are connected to each other via a distribution system DS. In this case, a plurality of BSSs connected to each other via the distribution system is called an Extended Service Set (ESS).

[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 all stations (STA6, STA7) are not connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

[0046] 3 is a block diagram showing a configuration of a station 100 according to an embodiment of the present invention. As shown in the figure, the station 100 according to the embodiment of the present invention includes a processor 110, a communication unit 120, a user interface unit 140, a display unit 150, and a memory 160.

[0047] First, the communication unit 120 transmits and receives wireless signals such as wireless LAN packets, and may be built into or externally provided in the station 100. According to an embodiment, the communication unit 120 may include at least one communication module using different frequency bands. For example, the communication unit 120 may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to an embodiment, the station 100 may include a communication module using a frequency band of 7.125 GHz or more and a communication module using a frequency band of 7.125 GHz or less. Each communication module may perform wireless communication with an AP or an external station based on the wireless LAN standard of the frequency band supported by the communication module. The communication unit 120 may operate only one communication module at a time or operate multiple communication modules simultaneously according to the performance and requirements of the station 100. When the station 100 includes multiple communication modules, each communication module may be provided in an independent form, or multiple modules may be integrated into one chip. In an embodiment of the present invention, the communication unit 120 may represent a radio frequency (RF) communication module that processes RF signals.

[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 a command from the processor 110 using various output means.

[0049] Then, the display unit 150 outputs an image on a display screen. The display unit 150 outputs various display objects such as a user interface based on the contents performed by the processor 110 or a control command of the processor 110. The memory 160 also stores control programs used by the station 100 and various data associated therewith. Such control programs include connection programs required for the station 100 to connect to an AP or an external station.

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

[0052] Fig. 4 is a block diagram showing a configuration of an AP 200 according to an embodiment of the present invention. As shown in the figure, the AP 200 according to the embodiment of the present invention includes a processor 210, a communication unit 220, and a memory 260. In Fig. 4, a duplicated description of parts of the configuration of the AP 200 that are the same as or correspond to the configuration of the station 100 in Fig. 3 will be omitted.

[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 a plurality of communication modules using different frequency bands. That is, the AP 200 according to the embodiment of the present invention may include two or more communication modules using different frequency bands, for example, any of 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with a station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 220 may operate only one communication module at a time or operate multiple communication modules simultaneously according to the performance and requirements of the AP 200. In the embodiment of the present invention, the communication unit 220 may represent an RF communication module that processes RF (Radio Frequency) signals.

[0054] Next, the memory 260 stores control programs used in the AP 200 and various data associated therewith. Such control programs include a connection program for managing the connection of stations. Also, the processor 210 controls each unit of the AP 200 and controls transmission and reception of data between the units. According to an embodiment of the present invention, the processor 210 executes a program for connection with a station stored in the memory 260 and transmits a communication setting message to one or more stations. At this time, the communication setting message includes information on the connection priority conditions of each station. Also, the processor 210 performs connection setting in response to a connection request of a station. According to an embodiment, the processor 210 is a modem or a modulation / demodulation unit that modulates and demodulates a wireless signal transmitted and received from the communication unit 220. The processor 210 controls various operations of transmitting and receiving wireless signals of the AP 200 according to an embodiment of the present invention. A detailed embodiment thereof will be described later.

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

[0056] 5, the link between the STA 100 and the AP 200 is set up through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information of the BSS operated by the AP 200. There are two methods for performing scanning: a passive scanning method in which the STA 100 acquires information using only a beacon message S101 periodically transmitted by the AP 200, and an active scanning method in which the STA 100 transmits a probe request to the AP S103, receives a probe response from the AP S105, and acquires connection information.

[0057] The STA100 that has successfully received wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200 (S107b), and performs an authentication step. After the authentication step is performed, the STA100 transmits an association request (S109a), receives an association response from the AP 200 (S109b), and performs an association step. 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, the server 300 is a server that processes 802.1X-based authentication with the STA 100, and may be physically connected to the AP 200 or may exist as a separate server.

[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 wireless LAN communication performs carrier sensing before transmitting data to check whether a channel is occupied or not. If a wireless signal of a certain strength or more is detected, the channel is determined to be occupied, and the terminal delays access to the channel. This process is called Clear Channel Assessment (CCA), and the level that determines whether the signal is detected is called the CCA threshold. If a wireless signal of a strength greater than the CCA threshold received by a terminal is set to the terminal as a 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 of a strength less than the CCA threshold is detected, the channel is determined to be idle.

[0061] If the channel is determined to be in an idle state, each terminal having data to transmit performs a backoff procedure after an IFS (Inter Frame Space) according to the status of each terminal, for example, an AIFS (Arbitration IFS) or a PIFS (PCF IFS). In some embodiments, the AIFS is used as a configuration to replace the conventional DIFS (DCF IFS). Each terminal waits while decreasing a slot time of a random number determined for the terminal during an interval of the idle state of the channel, and a terminal that has exhausted all the slot time attempts to access the channel. In this manner, a section in which each terminal performs a backoff procedure is called a contention window section. At this time, the random number can be called a backoff counter. That is, an initial value of the backoff counter is set by an integer that is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal can decrease the backoff counter by 1. Also, if the backoff counter reaches 0, the terminal may be allowed to perform channel access on the channel. Thus, a terminal may be allowed to transmit if the channel is idle during the AIFS time and the backoff counter slot time.

[0062] If a specific terminal succeeds in accessing the channel, the terminal transmits data through the channel. However, if the terminal attempting access collides with another terminal, the colliding terminals are assigned new random numbers and perform a backoff procedure again. According to one embodiment, the random numbers newly assigned to each terminal are determined within a range (2*CW) twice the range (contention window, CW) of the random numbers previously assigned to the terminal. Meanwhile, each terminal performs a backoff procedure again in the next contention window period to attempt access, and at this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. In this manner, each terminal performing wireless LAN communication can avoid collision with each other on a specific channel.

[0063] <Examples of various PPDU formats>

[0064] FIG. 7 shows an example of various standard generation PPDU (PLCP Protocol Data Unit) formats. More specifically, FIG. 7(a) shows an example of a legacy PPDU format based on 802.11a / g, FIG. 7(b) shows an example of a HE PPDU format based on 802.11ax, and FIG. 7(c) shows an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Also, FIG. 7(d) shows detailed field configurations of L-SIG and RL-SIG commonly used in the PPDU formats.

[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 RL-SIG (Repeated Legacy Short Training field), a HE-SIG-A (High Efficiency Signal A field), a HE-SIG-B (High Efficiency Signal B field), a HE-STF (High Efficiency Short Training field), and a HE-LTF (High Efficiency Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF can be referred to as an HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, the HE-SIG-B may be used only in the HE MU PPDU format.

[0067] Referring to FIG. 7(c), the preamble of the EHT PPDU further includes a RL-SIG (Repeated Legacy Short Training field), a U-SIG (Universal Signal field), an EHT-SIG-A (Extremely High Throughput Signal A field), an EHT-SIG-A (Extremely High Throughput Signal B field), an EHT-STF (Extremely High Throughput Short Training field), and an EHT-LTF (Extremely High Throughput Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF can be called an EHT preamble. The specific configuration of the non-legacy preamble may be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some formats of the EHT PPDU format.

[0068] The L-SIG field included in the preamble of the PPDU is configured with a total of 64 subcarriers by applying 64 FFT OFDM. Of these, 48 subcarriers excluding the guard subcarrier, DC subcarrier, and pilot subcarrier are used for data transmission of the L-SIG. 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 configuration 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 / 54 Mbps, which is a combination of a modulation method such as BPSK / QPSK / 16-QAM / 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The total length of the PPDU can be indicated by combining the information in the L_RATE field and the L_LENGTH field. In the non-legacy PPDU format, the L_RATE field is set to the minimum rate of 6 Mbps.

[0070] The unit of the L_LENGTH field is byte, and a total of 12 bits are allocated so that a maximum of 4095 can be signaled. The length of the corresponding PPDU can be indicated in combination with the L_RATE field. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0071] First, a method in which a legacy or non-legacy terminal analyzes the length of the PPDU using the L_LENGTH field is as follows. When the L_RATE field is set to 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted in 4 us, which is one symbol duration of 64 FFT. Therefore, the number of 64 FFT reference symbols after the L-SIG is obtained by adding 3 bytes corresponding to the SVC field and the Tail field to the L_LENGTH field value and dividing it by 3 bytes, which is the transmission amount of one symbol. The length of the PPDU, i.e., the reception time (RXTIME), is obtained by multiplying the obtained number of symbols by 4 us, which is one symbol duration, and adding 20 us for the transmission of the L-STF, L-LTF, and L-SIG. This can be expressed as the following Equation 1.

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

[0079] The VI bit will maintain the current bit configuration, and even if a subsequent generation PPDU is defined, a current 11be terminal can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field is composed of PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits, and serves to sequentially distinguish 11be and subsequent generation WLAN standards by version. 11be has a value of 000b. The UL / DL field distinguishes whether the corresponding PPDU is an uplink / downlink PPDU. The BSS color means a BSS-specific identifier defined in 11ax, and has a value of 6 bits or more. The TXOP means a transmit opportunity duration that was transmitted in the MAC header, but by adding it to the PHY header, the length of the TXOP containing the corresponding PPDU can be inferred without decoding the MPDU, and has a value of 7 bits or more.

[0080] The VD field may be composed of fields commonly used in any PPDU format, such as PPDU format and BW, which are signaling information useful only for PPDUs of the 11be version, and fields defined differently for each PPDU format. The PPDU format is a division factor that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), EHT ER (Extended Range) PPDU, etc. The BW field mainly signals five basic PPDU BW options of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz (BWs that can be expressed in the form of a power of 20*2 can be called basic BWs), and various remaining PPDU BWs formed by preamble puncturing. After being signaled at 320 MHz, some 80 MHz may be signaled in a punctured form. Also, the punctured and modified channel shape may be directly signaled in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (e.g., a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signalings are possible, so a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signalings are possible, so a maximum of 11 puncturing modes can be signaled.

[0081] The fields located after the BW field vary depending on the type and format of the PPDU. The MU PPDU and the SU PPDU may be signaled in the same PPDU format, and a field for distinguishing the MU PPDU from the SU PPDU may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both the SU PPDU and the MU PPDU include an EHT-SIG field, but some fields that are not necessary in the SU PPDU may be compressed. In this case, the information of the compressed field may be omitted or may have a reduced size compared to the size of the original field included in the MU PPDU. For example, in the case of the SU PPDU, the common field of the EHT-SIG may be omitted or replaced, or the user-specific field may be replaced or reduced to one, and may have a different configuration.

[0082] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (eg, the RA field, etc.) may be omitted depending on the value of the compression field.

[0083] When a part of the EHT-SIG field of the SU PPDU is compressed, the information included in the compressed field may be signaled together in an uncompressed field (e.g., a common field, etc.). In the case of the MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of information signaled may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether the transmitted MU PPDU was transmitted to itself. Therefore, the AP must transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols of the EHT-SIG field and / or MCS, which is a modulation method. The EHT-SIG field may include the size and location information of the RU assigned to each user.

[0084] In the case of a SU PPDU, a STA may be assigned multiple RUs, and the multiple RUs may be contiguous or discontinuous. If the RUs assigned to the STA are not contiguous, the STA can efficiently receive the SU PPDU only if it recognizes 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, etc.). That is, in the case of a SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and the puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field may signal the type of discontinuous channels that appear within the bandwidth.

[0085] The form of the signaled discontinuous channel is limited, and indicates the BW and discontinuous channel information of the SU PPDU in combination with the value of the BW field. For example, in the case of a SU PPDU, since it is a PPDU transmitted only to a single UE, the STA can recognize the bandwidth allocated to itself from the BW field included in the PPDU, and can recognize the punctured resources of the allocated bandwidth from the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the UE can receive the PPDU in the remaining resource units other than the specific channel of the punctured resource unit. In this case, the multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0086] The reason why only limited discontinuous channel types are signaled is to reduce the signaling overhead of SU PPDU. Since puncturing may be performed for each 20 MHz subchannel, if puncturing is performed for a BW having multiple 20 MHz subchannels such as 80, 160, and 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered as discontinuous) must be signaled by expressing whether or not the remaining 15 20 MHz subchannels other than the primary channel are used. In this way, using 15 bits to signal discontinuous channel types for single user transmission may result in excessive signaling overhead when considering the low transmission speed of the signaling part.

[0087] The present invention proposes a method for signaling the discontinuous channel type of the SU PPDU, illustrates the discontinuous channel type determined by the proposed method, and proposes a method for signaling the primary 160 MHz and secondary 160 MHz puncturing types in the 320 MHz BW configuration of the SU PPDU.

[0088] In addition, in one embodiment of the present invention, a method is proposed in which the configuration of the PPDU indicated by the preamble puncturing BW value is different depending on the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits, in the case of EHT SU PPDU or TB PPDU, one symbol of EHT-SIG-A is further signaled after U-SIG, or EHT-SIG-A does not need to be signaled from the beginning, so that up to 11 puncturing modes must be completely signaled using only the BW field of U-SIG in consideration of this. However, in the case of EHT MU PPDU, EHT-SIG-B is further signaled after U-SIG, so up to 11 puncturing modes can be signaled in a different manner from SU PPDU. In the case of EHT ER PPDU, the BW field is set to 1 bit, and it is possible to signal whether the PPDU uses a 20 MHz or 10 MHz band. Detailed puncturing patterns for each PPDU type will be described in detail below with reference to FIG. 11 and FIG. 12.

[0089] FIG. 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates EHT MU PPDU. In the case of MU PPDU, SIG-B, which is a signaling field for simultaneous reception by multiple users, is required, and SIG-B may be transmitted after U-SIG without a separate SIG-A. For this purpose, U-SIG must signal information for decoding SIG-B. Such fields include SIG-B MCS, SIG-B DCM, Number of SIG-B Symbols, SIG-B Compression, and Number of EHT-LTF Symbols.

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

[0091] 8, a PPDU may be composed of a preamble and a data portion, and the format of an EHT PPDU, which is one type, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is an EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

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

[0096] The EHT MU PPDU described in FIG. 8(c) 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 PPDU transmitted through a user specific field of the EHT-SIG-B to the STA. Therefore, multiple terminals receiving the EHT MU PPDU can perform spatial reuse based on the AID information of the user specific field included in the preamble of the received PPDU.

[0097] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information on the configuration of resource units (e.g., the division form of resource units) in a specific bandwidth (e.g., 20 MHz, etc.) 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 receives the PPDU. Information on the STA allocated (or designated) to each divided resource unit may be included in the 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, a user field corresponding to at least one of the divided resource units used for data transmission may include the AID of a receiver or sender, and a user field corresponding to the remaining resource units not used for data transmission may include a null STA ID that has already been set.

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

[0100] When one wireless communication device communicates using multiple links, the communication efficiency of the wireless communication device can be improved. In this case, the link is a physical path, and may be configured as one wireless medium that can be used to transmit MSDU (MAC service data unit). For example, when the frequency band of any one link is being used by another wireless communication device, the wireless communication device can continue to communicate using another link. In this way, the wireless communication device can effectively use multiple channels. Also, when the wireless communication device simultaneously communicates using multiple links, the overall throughput can be increased. However, the existing wireless LAN is specified on the premise that one wireless communication device uses one link. Therefore, a wireless LAN operation method for using multiple links is required. A wireless communication method of a wireless communication device using multiple links will be described with reference to Figs. 9 to 26. First, a specific form of a wireless communication device using multiple links will be described with reference to Fig. 9.

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

[0102] For the wireless communication method using the above-mentioned multiple links, a multi-link device (MLD) may be defined. The multi-link device may represent a device having one or more affiliated stations. According to a specific embodiment, the multi-link device may represent a device having two or more affiliated stations. Also, the multi-link device may exchange a multi-link element. The multi-link element includes information on one or more stations or one or more links. The multi-link element may include a multi-link setup element, which will be described later. In this case, the multi-link device may be a logical entity. Specifically, the multi-link device may have multiple affiliated stations. The multi-link device may be called a multi-link logical entity (MLLE) or a multi-link entity (MLE). The multi-link device may have one MAC service access point (SAP) up to a logical link control (LLC). Also, the MLD may have one MAC data service.

[0103] The stations included in the multilink device can operate on multiple links. Also, the stations included in the multilink device can operate on multiple channels. Specifically, the stations included in the multilink device can operate on different links or different channels. For example, the stations included in the multilink device can operate on different channels of 2.4 GHz, 5 GHz, and 6 GHz.

[0104] The operation of the multilink device may be referred to as multilink operation, MLD operation, or multi-band operation. If a station associated with the multilink device is an AP, the multilink device may be referred to as AP MLD. If a station associated with the multilink device is a non-AP station, the multilink device may be referred to as non-AP MLD.

[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 through a first link (Link1). Also, the second AP (AP2) and the second non-AP STA (non-AP STA2) communicate through a second link (Link2). Also, the third AP (AP3) and the third non-AP STA (non-AP STA3) communicate through a third link (Link3).

[0106] The multi-link operation may include a multi-link setup operation. The multi-link setup corresponds to the association operation of the single-link operation described above, and must be performed prior to frame exchange in the multi-link. The multi-link device may obtain information required for the multi-link setup from the multi-link setup element. Specifically, the multi-link setup element may include capability information related to the multi-link. In this case, the capability information may include information indicating whether one of the multiple devices included in the multi-link device can transmit and the other devices can receive at the same time. In addition, the capability information may include information regarding links available to each station included in the MLD. In addition, the capability information may include information regarding channels available to each station included in the MLD.

[0107] The multilink setting may be set by negotiation between peer stations. Specifically, the multilink setting may be set by communication between stations without communication with the AP. The multilink setting may be set through any one of the links. For example, even if the first link to the third link are set through the multilink, the multilink setting may be set through the first link.

[0108] Also, a mapping between a traffic identifier (TID) and a link may be set. Specifically, a frame corresponding to a specific TID value may be exchanged only through a link designated in advance. The mapping between a TID and a link may be set on a directional-based basis. For example, when a plurality of links are set between a first multilink device and a second multilink device, the first multilink device may be set to transmit a frame of a first TID to a plurality of first links, and the second multilink device may be set to transmit a frame of a second TID to the first link. Also, a default setting may exist for the mapping between a TID and a link. Specifically, when there is no additional setting in the multilink setting, the multilink device may exchange frames corresponding to a TID in each link according to a default setting. In this case, the default setting may be that all TIDs are exchanged in any one link.

[0109] The TID will be specifically described. The TID is an ID for classifying traffic and data to support QoS (quality of service). The TID may be used and assigned in a layer higher than the MAC layer. The TID may indicate a traffic category (TC) or a traffic stream (TS). The TID may be classified into 16 types. For example, the TID may be designated as one of 0 to 15. The TID value to be used may be designated differently depending on an access policy, a channel access, or a medium access method. For example, when EDCA (enhanced distributed channel access) or HCAF (hybrid coordination function contention based channel access) is used, the TID value may be assigned in the range of 0 to 7. When EDCA is used, the TID may indicate a user priority (UP). In this case, the UP may be designated by the TC or the TS. The UP may be assigned in a layer higher than the MAC. 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 channel contention in EDCA. QoS stations can guarantee QoS using AC. AC may include AC_BK, AC_BE, AC_VI, and AC_VO. AC_BK, AC_BE, AC_VI, and AC_VO may indicate background, best effort, video, and voice, respectively. AC_BK, AC_BE, AC_VI, and AC_VO may be classified into lower ACs. For example, AC_VI may be subdivided into AC_VI primary and AC_VI alternate. AC_VO may be subdivided into AC_VO primary and AC_VO alternate. UP or TID may be mapped to AC. For example, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI, AC_VI, AC_VO, and AC_VO, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI alternate, AC_VI primary, AC_VO primary, and AC_VO alternate, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may have a higher priority in that order. That is, 1 may have a lower priority, and 7 may have a higher priority. Therefore, the priority may be higher in the order of AC_BK, AC_BE, AC_VI, and AC_VO. Also, AC_BK, AC_BE, AC_VI, and AC_VO may correspond to ACI (AC index) 0, 1, 2, and 3, respectively. Due to the characteristics of such a TID, the mapping between a TID and a link may represent the mapping between an AC and a link.Additionally, the mapping between links and ACs can represent the mapping between TIDs and links.

[0111] As described above, a TID may be mapped to each of a plurality of links. The mapping may be a designation of a link through which traffic corresponding to a particular TID or AC may be exchanged. Also, a TID or AC that may be transmitted for each transmission direction within a link may be designated. As described above, there may be a default setting for mapping between a TID and a link. Specifically, if there is no additional setting in the multilink setting, the multilink device may exchange frames corresponding to the TID on each link according to the default setting. In this case, the default setting may be that all TIDs are exchanged on any one link. At any given time, any TID or AC may be mapped to at least one link. Management frames and control frames may be transmitted on all links.

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

[0113] The above-mentioned TID-to-link mapping may ensure QoS. Specifically, a high priority AC or TID may be mapped to a link where a relatively small number of stations are in operation or where channel conditions are good. The above-mentioned TID-to-link mapping may also allow stations to stay in a power saving state for a longer period of time.

[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 Fig. 10, as described in Fig. 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 called TID-to-link mapping, TID to link mapping, TID mapping, link mapping, etc. The TID may be a traffic identifier. In addition, the TID may be an ID (identifier) ​​that classifies traffic, data, etc. to support quality of service (QoS).

[0116] Also, the TID may be an ID used or assigned in a layer higher than the MAC layer. The TID may indicate TC (traffic categories) and TS (traffic streams). The TID may have 16 values, and may be indicated as values ​​from 0 to 15, for example. The TID value used may differ depending on the access policy, channel connection, and medium access method. For example, when EDCA (HCF (hybrid coordination function) contention based channel connection, enhanced distributed channel connection) is used, the possible TID value 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. When HCCA (HCF controlled channel access) or SPCA is used, the possible TID value 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 a 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 the set of EDCA parameters may be used for a channel connection. An AC may be used by a QoS STA.

[0118] The value of AC 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. AC_BK, AC_BE, AC_VI, and AC_VO may be further subdivided. For example, AC_VI may be further subdivided into AC_VI primary and AC_VI alternate. AC_VO may be further subdivided into AC_VO primary and AC_VO alternate. UP 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. Also, 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 priority may increase in the order of AC_BK, AC_BE, AC_VI, and AC_VO. Also, AC_BK, AC_BE, AC_VI, and AC_VO may correspond to AC indexes (ACI) 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, the fact that a TID is mapped may mean that an AC is mapped, and vice versa.

[0120] According to an embodiment of the present invention, there may be a TID mapped to each link of a multilink. For example, there may be a mapping of which link among multiple links a specific TID or a specific AC is allowed to transmit or receive on. Also, such mapping may be defined separately for each of the two directions of the link. Also, as described above, there may be a default setting 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. Also, according to an embodiment, at a specific time, a certain TID or a certain AC may be mapped to at least one link. Also, a management frame or a control frame 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. Or, 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] By performing TID-to-link mapping, it is possible to provide QoS services. For example, by mapping a high-priority AC and TID to a link with a good channel condition or a small number of STAs, it is possible to transmit data of the AC and TID faster. Alternatively, by performing TID-to-link mapping, it is possible to help STAs of a particular 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 with Link1, and AP2 and STA2 may be associated with Link2.

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

[0126] For example, all TIDs and all ACs may be mapped to the link for transmission from AP1 to STA1 via Link1, and to the link for transmission from STA1 to AP1 via Link1. Also, only AC_VO or TID corresponding to AC_VO may be mapped to the link for transmission from STA2 to AP2 via Link2. Also, only data of the mapped TID and / or AC can be transmitted on the link. Also, data of TID or AC not mapped to the 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, and otherwise 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] In this way, when a station operates in a power saving mode, the station in the power saving state may not be able to receive. Therefore, the AP can signal to the station that traffic to be transmitted is buffered and receive a response thereto from the station to perform transmission. For convenience of explanation, the signaling by the AP to the station that traffic to be transmitted is buffered is called a traffic indication. Also, the signaling for the traffic indication is called a traffic indication signaling. The traffic indication between the AP and the station may be performed as follows. In this specification, the 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 traffic to be transmitted to the station is buffered. In this specification, the traffic indication signaling may indicate that traffic is buffered, 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 is buffered in the AP transmitting the bitmap. In addition, the traffic indication signaling may indicate a 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 the traffic corresponds to and which station the traffic corresponds to depending on the position of the bitmap bit. A station can determine whether traffic corresponding to a group in which the station is included is buffered in the AP or whether traffic for the station is buffered in the AP, depending on the position of a bit in the bitmap.

[0131] The traffic indication signaling may be transmitted based on a pre-specified time point. Thus, a station in a power saving state may be switched from a power saving 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. Also, the traffic indication signaling may be included in a TIM frame. Also, 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 maintain an awake state 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. Thus, the station may maintain an awake state 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 above 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. A DTIM is a type of TIM that indicates whether group-addressed traffic and broadcast traffic are buffered in the AP. A beacon frame that includes a DTIM can be called a DTIM beacon frame. If a station's received DTIM indicates that group traffic for a group that includes the station is to be sent, the station can send signaling to the AP to indicate that it will receive the group traffic.

[0134] The station that has received the traffic indication signaling can transmit a signaling to induce (retrieve) transmission to the station. In this case, the signaling to induce (retrieve) transmission to the station may be at least one of a PS-Poll frame or a U-APSD trigger frame. The AP that has received the signaling to induce (retrieve) transmission to the station transmits buffered traffic to the station.

[0135] In FIG. 11, the first AP (AP1) includes a TIM in the beacon frame and transmits a 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 the power saving 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. Thus, the first station (STA1) can stably receive the broadcast traffic or group address traffic even in the power saving mode. A format of a TIM element that may be included in the 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 lengths of the Element ID subfield, the Length subfield, the DTIM Count subfield, the DTIM Period subfield, and the Bitmap Control subfield are 1 octet, i.e., 8 bits. The Partial Virtual Bitmap subfield may have a variable length within 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 in which it is contained.

[0140] The Length subfield indicates the length of the element it is included in. Specifically, the Length subfield may 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 may 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 may 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. The 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 of the Partial Virtual Bitmap field indicates whether traffic to be transmitted to a station of an AID corresponding to each bit is buffered in the AP that transmits the TIM. When the value of the bit of the Partial Virtual Bitmap field is 1, it can indicate that traffic to be transmitted to a station of an AID corresponding to the bit of the Partial Virtual Bitmap field is buffered in the AP that transmits the TIM. When the value of the bit of the Partial Virtual Bitmap field is 0, it can indicate that traffic to be transmitted to a station of an AID corresponding to the bit of the Partial Virtual Bitmap field is not buffered in the AP that transmits the TIM. Therefore, when the value of the bit of the Partial Virtual Bitmap field is 1, the station that receives the TIM can determine that traffic to be transmitted to a station of an AID corresponding to the bit of the Partial Virtual Bitmap field is buffered in the AP that transmits the TIM. When the value of the bit of the Partial Virtual Bitmap field is 0, the station that receives the TIM can determine that traffic to be transmitted to a station of an AID corresponding to the bit of the Partial Virtual Bitmap field is not buffered in the AP that transmits the TIM. In addition, a station that receives a TIM can determine that traffic to be sent to a station with an AID not indicated 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 number of the bit in the Traffic indication virtual bitmap subfield may indicate the AID of the station corresponding to the bit. Specifically, a bit with a 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 number of the bit 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. The TIM may include a Partial Virtual Bitmap subfield instead of the Traffic indication virtual bitmap subfield. The Partial Virtual Bitmap subfield is a subfield in which consecutive bits with a value of 0 are omitted in the Traffic indication virtual bitmap subfield. The Partial Virtual Bitmap subfield may be a subfield in which the first consecutive bits are omitted or the last consecutive bits are omitted from a set of consecutive bits with a value of 0 in the Traffic indication virtual bitmap subfield. 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 which bit numbers 1 to (N1*8-1) are all 0 in the Traffic indication virtual bitmap subfield.N2 may be the smallest number in which bit numbers (N2+1)*8 to 2007 in the Traffic indication virtual bitmap subfield are all 0. This may be a method of 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+1th bit among the bits of the bitmap or subfield.

[0146] When the values ​​of all bits in the Traffic indication virtual bitmap subfield are 0 except for the bit whose bit number is 0, the Partial Virtual Bitmap subfield may have 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 values ​​of all bits in the Traffic indication virtual bitmap subfield are 0 and the values ​​of all bits in the Bitmap Control subfield are 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 of 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 a transmitted BSSID buffers a frame. Taking this into consideration, a method of 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, the 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 an AP that transmits a 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 that corresponds to a nontransmitted BSSID. Each of the 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 an AP that corresponds to each bit. In this case, the bits in the Traffic indication virtual bitmap subfield with bit numbers greater than (2^n-1) indicate whether a frame to be transmitted to a station with an AID of n is buffered in an AP that transmits a TIM element. Therefore, the AP does not need to assign 1 to (2^n-1) as an AID. In such an embodiment, a bit corresponding to an inactive nontransmitted BSSID may be set as a reserved bit. In this case, the value of the reserved bit may be set to 0. Also, the AP may assign the AID of the station with a number equal to or greater than 2^n. In this case, the AP may assign the AID of the station from a value between 2^n and 2007. The EHT AP may not assign 2007 as an AID. The range in which AIDs may be assigned in this manner is called an AID space. The transmitted BSSID and the nontransmitted BSSID may share one AID space. In a specific embodiment, the EHT AP may not assign 2007 as an AID of the 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 a value indicated by the MaxBSSID Indicator of the multiple BSSID element.

[0151] A method for configuring the partial virtual bitmap subfield will be described. The method for configuring the partial virtual bitmap subfield may differ depending on the multiple BSSID set related function of the AP that transmits the TIM element. A non-S1G AP can configure the partial virtual bitmap subfield by method A or method B. Also, an S1G AP can configure the partial virtual bitmap subfield by method C. A non-HT AP, an HT AP, a VHT AP, a HE AP, and an EHT AP may all be non-S1G APs. An S1G AP refers to an AP that operates in a frequency band of 1 GHz or less, and a non-S1G AP refers to an AP that operates in a frequency band of more than 1 GHz.

[0152] First, method A will be described. The subfield of the partial virtual bitmap may be composed of bits from octet number 0 to N2 of the traffic indication virtual bitmap. N2 is the smallest number among the numbers that satisfy that all bit values ​​from bit number (N2+1)*8 to 2007 in the traffic indication virtual bitmap are 0. If there is no N2 that satisfies this, 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] Method B will be described. 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 the largest even number that satisfies N0 < N1 and that all the bit values from bit number N0 * 8 to (N1 * 8 - 1) are 0. When there is no value such that N1 > N0, N1 may be N0. Also, N2 may be the smallest positive integer that satisfies that all the bit values from bit number (N2 + 1) * 8 to 2007 of the Traffic indication virtual bitmap are 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 all the bit values of the Partial Virtual Bitmap subfield may 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 transmitted and nontransmitted BSSIDs and group addressed frames are buffered in one or more of the 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. This will be explained with reference to Figures 13 to 18.

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

[0157] APs operating in one multilink device can share the AID space. Specifically, one multilink device may have one AID space. In this case, when a buffered frame is indicated to an AP using the TIM element described in FIG. 12, it may be difficult for a station to determine which link the frame is buffered in. A traffic indication signaling method is needed to solve this problem. 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 is a buffered frame in each multilink for each multilink on which the multilink device operates. 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 the 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 contains 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 in which it is contained.

[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 contained, identifies the element.

[0163] The Multi-Link Traffic Control subfield is a 1-octet field and includes the Bitmap Size subfield and the 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. The value 0 of Bitmap Size is a reserved value.

[0164] The AID Offset subfield is an 11-bit subfield and indicates the start position of the bit of the Traffic indication virtual bitmap indicated by the Per-Link Traffic Indication List or Per-Link Traffic Indication Bitmap subfield. Therefore, the AID Offset subfield determines the AID (association ID) corresponding to the Per-Link Traffic Indication List or Per-Link Traffic Indication Bitmap subfield by the AID Offset subfield. When the value of the AID Offset is K, the Per-Link Traffic Indication List or Per-Link Traffic Indication Bitmap subfield indicates the bit number K of the Traffic indication virtual bitmap first. Also, when 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 field having a variable length 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 bit number K of the Traffic indication virtual bitmap first. 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.A 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, a 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 successfully performed, the bit of the Per-Link Traffic Indication Bitmap subfield indicates whether traffic to be transmitted to a non-AP station operating on a link corresponding to the bit is buffered. Specifically, when the value of the 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 a link corresponding to the bit is buffered. When the value of the 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 a link corresponding to the bit is not buffered. When the TID-to-link mapping is the default mapping, the bit of the Per-Link Traffic Indication Bitmap subfield may indicate whether to recommend retrieving the transmission of the buffered traffic on the link corresponding to the bit. Specifically, when the value of the bit of the Per-Link Traffic Indication Bitmap subfield is 1, the bit of the Per-Link Traffic Indication Bitmap subfield may indicate that it is recommended to request transmission of the buffered traffic on the link corresponding to the bit. When the TID-to-link mapping of a link corresponds to the default mapping, uplink transmission and downlink transmission performed on the link may be performed without TID restriction. In addition, the default mapping is applied to links for which the TID-to-link mapping negotiation has not been successfully performed.Thus, if the TID-to-link mapping negotiation is successful, it may 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 the bit numbers of the bits. Specifically, a bit in the Per-Link Traffic Indication Bitmap subfield with a bit number of n may be mapped to a link with a link ID of n. In addition, the Per-Link Traffic Indication List subfield may include a padding field. Thus, 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 may transmit a frame including both the Multi-Link Traffic element and the TIM element, where the frame may be a beacon frame. FIG. 14 illustrates how the AP multilink device may use 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 invention.

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

[0170] The non-AP multilink device may request the AP multilink device to transmit the buffered traffic on the link corresponding to the bit set to 1 among the bits of the Per-Link Traffic Indication Bitmap subfield corresponding to the non-AP multilink device. Specifically, when the TID-to-link mapping negotiation is successfully performed, the non-AP multilink device may request the AP multilink device to transmit the buffered traffic on the link corresponding to the bit set to 1 among the bits of the Per-Link Traffic Indication Bitmap subfield corresponding to the non-AP multilink device. When the TID-to-link mapping is the default mapping, the non-AP multilink device may request the AP multilink device to transmit the buffered traffic on one or more links including the link corresponding to the bit set to 1 among the bits of 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 the 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 the TID-to-link mapping is set as the default mapping is assigned an AID value smaller than K. A non-AP station for which negotiation regarding the TID-to-link mapping has been successfully performed is assigned an AID value equal to or larger 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 among bits corresponding to bits equal to or larger than bit number (N-1)*8 is set to 1. N-1 is an even number, and N*8 is a value of k. Therefore, the Partial Virtual Bitmap subfield first includes 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, among the bits in the Partial Virtual Bitmap subfield, the values ​​of the bits corresponding 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 FIG. 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 indicated by the Partial Virtual Bitmap subfield as 1. In FIG. 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 correspond to 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, the default mapping is applied to the multilink device with AID value K, and the 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 traffic buffered in the link with link ID 1 is recommended. Also, the Per-Link Traffic Indication Bitmap subfield corresponding to AID K+2 indicates that the AP multilink device is buffering traffic in two links with link IDs 1 and 2. In this case, the traffic buffered in the link with link ID 1 and the traffic buffered in the link with link ID 2 may be the same or different. Also, the Per-Link Traffic Indication Bitmap subfield corresponding to AID K+3 indicates that the AP multilink device is buffering traffic in the link with link ID 1.

[0175] However, it may not be guaranteed that the AIDs of the non-AP multilink device connected to the AP multilink device are assigned consecutively. In addition, the AIDs of the non-AP stations not included in the multilink device may be assigned to AIDs between the AIDs of the non-AP multilink device. 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 value of the bit corresponding to AID K+1 in the Partial Virtual Bitmap subfield of the TIM element may be 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 the non-AP multilink device. Therefore, a method for setting the Multi-Link Traffic element to solve this problem is required. This will be described with reference to FIG.

[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 a non-AP station 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 a non-AP station in the Multi-Link Traffic element even if the non-AP station is not included in the multilink device, when the value of the bit 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 the bit of the Traffic Indication Bitmap subfield or the bit of the Partial Virtual Bitmap subfield set to 1 in the Multi-Link Traffic element. For convenience of explanation, a station corresponding to the bit of the Traffic Indication Bitmap subfield or the bit of the Partial Virtual Bitmap subfield set to 1 is called a station to which buffered traffic is indicated.

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

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

[0180] The AP multilink device may set all the bit values ​​of the Per-Link Traffic Bitmap subfield corresponding to stations not belonging to the multilink device to 0. That is, the AP multilink device may set the bit values ​​of the Per-Link Traffic Bitmap subfield corresponding to stations not belonging to the multilink device as reserved fields. In yet another specific embodiment, the AP multilink device may set the bit values ​​of the Per-Link Traffic Bitmap subfield corresponding to stations not belonging to the multilink device to an arbitrary value. In yet another specific embodiment, the AP multilink device may set the bit values ​​of the Per-Link Traffic Bitmap subfield corresponding to stations not belonging to the multilink device to 1. In this case, the non-AP multilink device may ignore the bit values ​​of the Per-Link Traffic Bitmap subfield corresponding to stations not belonging to the multilink device. In yet another specific embodiment, the AP multilink device may set the bit values ​​of the Per-Link Traffic Bitmap subfield corresponding to stations not belonging 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 FIG. 15, the setting of the Traffic indication virtual bitmap and the setting of the Partial Virtual Bitmap subfield may be the same as the setting of the Traffic indication virtual bitmap and the setting of the Partial Virtual Bitmap subfield in FIG. 14. However, in the embodiment of FIG. 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 FIG. 14. Since 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 bits of the Traffic indication virtual bitmap and the bits of the Partial Virtual Bitmap subfield. In this case, the Group Id may include an AID value of 0. Also, the Group ID may include a bit number of the Traffic indication virtual bitmap corresponding to the multiple BSSID set, i.e., an AID corresponding to the bit number. Also, the Group ID may include a bit number of the Traffic indication virtual bitmap corresponding to the transmitted BSSID and the nontransmitted BSSID, i.e., an AID corresponding to the bit number. The Group ID may include a value corresponding to AID 0 to (2^n-1) when the maximum number of BSSIDs possible in the multiple BSSID set is 2^n. The AID Offset subfield may indicate a value after the value corresponding to AID 0 to (2^n-1) when a multiple BSSID set is used and the maximum number of BSSIDs possible in the multiple BSSID set is 2^n. The reason for setting the AID Offset field in this manner is that since group address frames are not limited to those transmitted on a specific link, there is little point in signaling them on a link-by-link basis.

[0183] According to another embodiment of the present invention, even if the AID Offset subfield indicates bits of the Traffic indication virtual bitmap and bits of the Partial Virtual Bitmap subfield before 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 bits of the Traffic indication virtual bitmap and bits of the Partial Virtual Bitmap subfield before the bit indicating the Group ID, the Multi-Link Traffic element may include only the Per-Link Traffic Indication Bitmap subfield corresponding to an individual station among the stations for which the buffered traffic is indicated. Specifically, when the maximum number of BSSIDs that can be set as the BSSIDs of the multiple BSSID set is 2^n, the AID Offset subfield may indicate bits of the Traffic indication virtual bitmap and bits of the Partial Virtual Bitmap subfield corresponding to an AID of (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 includes only Per-Link Traffic Indication Bitmap bits that correspond to AID2^n among the bits in the Traffic indication virtual bitmap and the bits in the Partial Virtual Bitmap subfield that are set to 1.

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

[0185] Figure 16 shows a method of 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 the AP multilink device operates may be different from the link set in which the non-AP multilink device that communicates with the AP multilink device operates. For example, the AP multilink device may communicate with the first non-AP multilink device via the first to third links, and the AP multilink device may communicate with the second non-AP multilink device via the first and second links. In this case, the method of setting the Per-Link Traffic Bitmap subfield of the Multi-Link Traffic element may be an issue.

[0187] Even if the link set in which the AP multilink device operates is different from the link set in which the non-AP multilink device that communicates with the AP multilink device operates, the AP can set the size of all Per-Link Traffic Indication Bitmap subfields included in the Multi-Link Traffic element to be the same, and set the links to which each bit of all Per-Link Traffic Indication Bitmap subfields maps to be the same. Specifically, 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 be greater than the number of links set by the AP multilink device. This is because the link IDs set 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 of 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 set. 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 a number obtained by adding 1 to the maximum link ID value that the AP multilink device can set.

[0188] A method for setting the value of a bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a link not set by the AP multilink device and a link not set by the non-AP multilink device corresponding to the Per-Link Traffic Indication Bitmap subfield may be problematic. For convenience of explanation, a bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a link not set by the AP multilink device and a link not set by the non-AP multilink device corresponding to the Per-Link Traffic Indication Bitmap subfield is called a no-link bit. The AP multilink device can set the value of the no-link bit to a pre-specified value. Thus, the AP multilink device can set the bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a link not set by the AP multilink device or the 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, the non-AP station can ignore the value of the no-link bit.

[0189] Also, the value of a bit in the Per-Link Traffic Indication Bitmap subfield corresponding to a disabled link may be set as 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. At this time, the disabled link may be a link in which uplink and downlink transmissions are stopped. Specifically, the disabled link may be a link in which uplink and downlink transmissions of individual address frames are stopped. At this time, non-AP stations may 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 with the first link (Link0) to the third link (Link2). The first multilink device (MLD 1) and the AP multilink device (AP MLD) set the first link (Link0) to the third link (Link2). The second multilink device (MLD 2) and the AP multilink device (AP MLD) set the first link (Link0) to the second link (Link1). The AP multilink device (AP MLD) sets the number of bits of 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 FIG. 14 and FIG. 15. Also, 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 FIG. 15. The AP multilink device (AP MLD) sets the values ​​of the first bit (B0) and the second bit (B1) of the Per-Link Bitmap subfield corresponding to the second multilink device (MLD 2) according to the embodiment described in FIG. 14 and FIG. 15. Also, 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 0, which is a pre-specified value, as described above.

[0191] In the above embodiment, it has been described that the bit number of the bit in the Per-Link Traffic Indication Bitmap subfield is the same as the ID of the link corresponding to the bit. In a specific embodiment, the bit number of the bit in the Per-Link Traffic Indication Bitmap subfield may not be the same as the ID of the link corresponding to the bit. Link IDs of links set by the AP multilink device that transmitted the Per-Link Traffic Indication Bitmap subfield may be mapped in ascending order to the bit numbers of the bits in the Per-Link Traffic Indication Bitmap subfield. 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 a method for determining the link indicated by the Per-Link Traffic Bitmap subfield 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, the bit of the Per-Link Traffic Indication Bitmap subfield indicates whether traffic to be transmitted to a non-AP station operating on a link corresponding to the bit is buffered. Specifically, when the value of the 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 a link corresponding to the bit is buffered. When the value of the 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 a link corresponding to the bit is not buffered. When the TID-to-link mapping is the default mapping, the bit of 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 the bit. When the TID-to-link mapping of a link corresponds to the default mapping, uplink transmission and downlink transmission on the link may be performed without TID restriction. In addition, the default mapping is applied to links where TID-to-link mapping negotiation has not been successfully performed or where 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 embodiment of FIG. 17, the AP multilink device (AP MLD) and the non-AP multilink device (non-AP MLD 1) successfully perform TID-to-link mapping negotiation. The AP multilink device (AP MLD) and the non-AP multilink device (non-AP MLD 1) map TID value 0 to the uplink transmission of the first link (link0). In addition, the AP multilink device (AP MLD) and the non-AP multilink device (non-AP MLD 1) map TID values ​​1 to 7 to the uplink transmission of the second link (link1). In this case, the AP multilink device (AP MLD) and the non-AP multilink device (non-AP MLD 1) apply default mapping to the downlink transmission of the first link (link0) and the downlink transmission of the second link (link1). 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 the non-AP multilink device (non-AP MLD 1) request traffic transmission on the second link (link1).

[0196] FIG. 17(b) shows a TID-to-Link Mapping element used for TID-to-link mapping negotiation. A multilink device may include a 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, the multilink device may include a 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, the multilink device may include a 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 Link Mapping subfield corresponding to that bit 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 such as a bit index. That is, the n-th bit (Bn-1) of the Link Mapping Presence Indicator subfield may be mapped to a 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 negotiation of TID-to-link mapping 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 Mulit-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, the AP multilink device may not include a Per-Link Traffic Indication Bitmap subfield for a station for which buffered traffic is indicated when the station for which buffered traffic is indicated in the Multi-Link Traffic element is not included in the multilink device. This can prevent 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 stations for which buffered traffic is indicated in the Multi-Link Traffic element. A station receiving the Multi-Link Traffic element may 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 Per-Link Traffic Indication Bitmap subfield for stations corresponding to a specific bit or later among stations for which buffered traffic is indicated is not included in the Multi-Link Traffic element, the station receiving the Multi-Link Traffic element may parse the Multi-Link Traffic element normally. In such an embodiment, the AP multilink device may assign a smaller value as the AID for a station included in the multilink device than the AID of a station not included in the multilink device.

[0202] In the embodiment of Figure 18, the AID Offset of the Multi-Link Traffic element indicates an AID value of K. Stations with buffered traffic indicated 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 may parse the Per-Link Traffic Indication Bitmap subfield of the Multi-Link Traffic element based on the AID Offset2 subfield. The AID Offset2 subfield may 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 may indicate all AID values. In yet another specific embodiment, the AID Offset2 subfield may indicate the maximum value of the AID that may correspond to the last Per-Link Traffic Indication Bitmap subfield.

[0204] In yet another specific embodiment, the AID Offset2 subfield may indicate an 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 an AID corresponding to the last Per-Link Traffic Indication Bitmap subfield as 2^N, where N is an integer. In such an 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 may indicate that the AID value is 2^N*n, where n is an integer. For example, the AID may be indicated in units of 8. In this case, the AID Offset2 subfield may have a length of 8 bits. In such an embodiment, the AID Offset2 subfield may 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 embodiment, one frame may include multiple Multi-Link Traffic elements. Specifically, in the AID list in which the AID values ​​of stations to which buffered traffic having AIDs equal to or greater than the AID indicated by the AID Offset subfield are arranged in ascending order, the AP multilink device may generate a Multi-Link Traffic element including a Per-Link Traffic Indication Bitmap for one or more multilink devices corresponding to the AID values ​​from the first AID in the list to the AID corresponding to the station not included in the multilink device to the excluded AID thereafter. In this case, the AIDs up to the excluded AID are excluded from the AID list, and the AP multilink device may generate a Multi-Link Traffic element including a Per-Link Traffic Indication Bitmap 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 may repeat this operation until the end of the AID list, and may further generate a Multi-Link Traffic element including a Per-Link Traffic Indication Bitmap 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 such an 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 the 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 the 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 embodiment, if the non-AP multilink device is not the station for which the buffered traffic is indicated, the non-AP multilink device can ignore the Multi-Link Traffic element.

[0210] A method for determining an 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 shows an EHT Operation element according to an embodiment of the present invention.

[0212] Figure 19(a) shows the format of an EHT Operation element, and Figure 19(b) shows an 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. When the value of the EHT Operation Information Present subfield is 0, the EHT Operation element may not include the EHT Operation Information subfield. That is, when the EHT Operation Information Present subfield is set to 0, the length of the EHT Operation Information subfield may be 0 octets. When 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 may indicate whether the EHT Operation Information field includes a Disabled Subchannel Bitmap subfield. When 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. When 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 a multiple BSSID set and other APs belonging to the same AP multilink device, and whether there is a limit to indicate them 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. An AP (AP transmitting an EHT Operation element, AP transmitting a beacon frame, or AP corresponding to a 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 nontransmitted 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 may 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] Also, the 48 bits mentioned above may be replaced with other bit numbers, which may change the number of bitmap bits required to indicate group address traffic to other APs of the same multilink device as the AP of the nontransmitted BSSID in the Traffic indication virtual bitmap. In the present invention, 48 bits or other bit numbers may be referred to as "bitmap limits."

[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 nontransmitted BSSID and the AP of the multilink device. A station that receives 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, in the Traffic indication virtual bitmap, bits for group address traffic may be located first, 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. In order 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 BSSID in the TIM element, Partial Virtual Bitmap subfield, or Traffic indication virtual bitmap may be used. If the AP does not belong to a multiple BSSID set, N bits following the first bit (B0) of 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 the Traffic indication virtual bitmap can indicate group address frames corresponding to the reporting AP (or the AP corresponding to the transmitted BSSID when 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 that transmits the TIM element. Also, X-1 may be the last bit used to indicate the nontransmitted BSSID in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap. If a multiple BSSID set is not used, X-1 may be 0. Also, N may be N mentioned in the description of the EHT Operation element above. Specifically, if the AP that transmits the TIM element does not belong to a multiple BSSID set, X-1 may be 0. Also, N may be N mentioned in the description of the EHT Operation element above. The N value may be determined based on the Group Addressed BU Indication Exponent subfield. The value of N may be 2^(value of Group Addressed BU Indication Exponent subfield+1)-1. That is, when 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, N bits from bit X to bit X+N-1 may indicate whether group address traffic for each link is buffered in ascending order of the link ID. Among 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 the 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 the nontransmitted BSSIDs, and the last bit indicating the 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, the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap may start indicating the group address frames buffered to other APs of the multilink device to which the AP (reporting AP) of the transmitted BSSID belongs, from bit 2^n.

[0228] In yet another 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 are not actually used as the BSSIDs of the multiple BSSID set, the last bit may be the last bit among 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 part of the Traffic indication virtual bitmap. Each bit of the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfields indicates whether there is buffered traffic to be transmitted to a station of the AID corresponding to each bit. In this case, the bit number of the bits of the Traffic indication virtual bitmap and the Partial Virtual Bitmap subfields may be mapped to an AID value. 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 a reporting AP (AP that transmits a 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 FIG. 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 above-mentioned (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] The reporting AP can use N bits following the last bit (i.e., B X+N-1) indicating 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 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) indicating group address traffic corresponding to other APs in the AP multilink device to which the AP of the transmitted BSSID belongs in the TIM element, Partial Virtual Bitmap subfield, or Traffic indication virtual bitmap. 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 in the link corresponding to that bit.

[0232] The bits from bit number Y+(k-1)*N to bit number Y+k*N-1 of the Reporting Partial Virtual Bitmap subfield or the Traffic indication virtual bitmap may indicate whether group address traffic corresponding to other APs of 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 in the kth nontransmitted BSSID. Y-1 may be the last bit indicating whether a group address frame corresponding to the AP multilink device to which the AP of the transmitted BSSID belongs is buffered. That is, Y-1 may be the same value as X+N-1. Also, N may be N mentioned in the embodiment related to the EHT Operation element above. 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. In addition, in the TIM element, the Partial Virtual Bitmap subfield, or the Traffic indication virtual bitmap, N bits from bit number 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 is buffered in the link corresponding to each 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 is buffered, and the remaining bits may be set to 0.

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

[0234] The Traffic indication virtual bitmap and Partial Virtual Bitmap subfields may include, as a 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 of 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 above.

[0235] According to the embodiment described in FIG. 14, the value of the AID Offset subfield may not indicate a 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. Or, the value of the AID Offset subfield may indicate an individually addressed frame in the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields. Or, 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 FIG. 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 a portion of the Traffic indication virtual bitmap and Partial Virtual Bitmap subfields corresponding to the group address frame. According to the embodiment of FIG. 19-FIG. 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 a 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 of 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 of the AP multilink device to which the AP corresponding to the transmitted BSSID or nontransmitted BSSID belongs. In addition, 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 of 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 allowed to be set to a value equal to or less than the smaller value (if both values ​​are the same, either one of the values ​​obtained by adding (X-1) to N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs)+1) and the value obtained by adding (X-1) to the bitmap limit. The value of the AID Offset subfield may be set to a value greater than the smaller value (if both values ​​are the same, either one of the values ​​obtained by adding (X-1) to N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs)+1) and the value obtained by adding (X-1) to the bitmap limit. 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 an AP corresponding to a reporting AP or a 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 description regarding N and the bitmap limit has been omitted.

[0241] As another explanation for the same content, (the maximum number of BSSIDs that a multiple BSSID set can include) 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 allowed to be set to the smaller of 1) M-1 plus M*N, and 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, and 2) M-1 plus N+bitmap limit. If the reporting AP does not belong to a multiple BSSID set, M may be 1.

[0242] The same content can be explained separately for the case where the reporting AP belongs to a multiple BSSID set and the case where it does not. When the reporting AP belongs to a multiple BSSID set, the value of the AID Offset subfield is not set to N or less. 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 allowed to be set to the smaller value of (X-1) plus N*(number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs) and (X-1) plus the bitmap limit (if both values ​​are the same, either one of them). 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, and may be A=B if the values ​​of A and B are the same.

[0243] In the above embodiment, 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 may include may be the maximum number of BSSIDs that a multiple BSSID set may 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 the group address frame has been changed in the embodiments of Figures 19 and 20. The AID is assigned to the non-AP station (or non-AP multilink device) by the AP. 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 as the AID to a non-AP station. In other words, if an AP belongs to a multiple BSSID set, the AP cannot assign a value equal to or smaller than the maximum number of BSSIDs in the multiple BSSID set minus 1 as the AID 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] Also, the EHT standard may not allow an AP to assign 2007 as a non-AP station AID because the AID value 2007 is used to indicate the Special User Info field included in the trigger frame. That is, when the AP is not included in a multiple BSSID set, the AP can assign AIDs in the range of 1 to 2006 to non-AP stations. When a multiple BSSID set is used, the AP can assign AIDs in the range of (the maximum number of BSSIDs that the multiple BSSID set can include) to 2006 to non-AP stations.

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

[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 value (if both values ​​are the same, either one of the values ​​obtained by adding (X-1) to N*((number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs)+1) and (X-1) to a bitmap limit) as AIDs. That is, the AP can assign AIDs to non-AP stations in the range from the smaller value (if both values ​​are the same, either one of the values ​​obtained by adding (X-1) to N*((number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs)+1) and (X-1) to a bitmap limit) plus 1 to 2006. Therefore, when 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^(value of Group Addressed BU Indication Exponent subfield + 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, and 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. The Multiple BSSID element or the Reduced Neighbor Report element may be included in a beacon frame, a probe response frame, an association response frame, and 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 embodiment described in FIG. 19 and FIG. 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 last 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 embodiment described later, (Y-1) may be replaced with (X-1).

[0253] As described above, the AP may extract a portion of the Traffic indication virtual bitmap to generate a Partial Virtual Bitmap subfield. Also, each bit of the Traffic indication virtual bitmap or Partial Virtual Bitmap subfield may indicate whether traffic for a station of the AID is buffered for each bit. The bit number of the bits of 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 FIG. 21, the second bit (B1) to 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) to 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. Also, 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, the eighth bit (B7) to the tenth bit (B9) of the Traffic indication virtual bitmap can 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. Also, the kth nontransmitted BSSID may be a nontransmitted BSSID corresponding to AID k.

[0256] The Traffic indication virtual bitmap or Partial Virtual Bitmap subfield may include, as a portion corresponding to the 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 of 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 the AID Offset subfield can indicate. Also, the range that the AP cannot assign as an AID may be the same as the range of AIDs that the AID Offset subfield cannot indicate. Also, the AID space may be a set of bit numbers of bits that cannot indicate that a group address frame is buffered in the Traffic indication virtual bitmap. That is, the AID space may not include the bit number of the bit that indicates that a group address frame is buffered in the Traffic indication virtual bitmap. The AID that the AP cannot assign as an AID may be a set of bit numbers of bits that indicate that a group address frame is buffered in the Traffic indication virtual bitmap.

[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 a value obtained by adding N*((number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs)+1) to (X-1). For example, the minimum value of the AID space may be (X-1)+N*((number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs)+1)+1. In addition, 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. When 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] As mentioned above, Y may be replaced with X. Thus, 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 the 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 embodiment related to the EHT Operation element above. 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. Or, N may be the number of bits indicating a group address frame corresponding to another AP of the multilink device to which the AP corresponding to 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 a multiple BSSID set, Y-1 may be X-1+N. That is, if the reporting AP belongs to a multiple BSSID set, Y-1 may be ((maximum number of BSSIDs in the multiple BSSID set)-1)+N.

[0263] The AP may not be allowed 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 can assign values ​​greater than (Y-1) + (bitmap limit) to non-AP stations or non-AP multilink devices. That is, in the embodiment of FIG. 20, the AP can assign values ​​greater than 6 + 48, ie, 55 or more, to the 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 the AID values ​​that an AP can assign may be (Y+48) or more if the AP belongs to a multiple BSSID set.

[0265] In a third embodiment of the present invention related to the AID space, 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 a value obtained by adding 1 to the smaller value of a value obtained by adding (X-1) to N*((the number of nontransmitted BSSIDs or the maximum number of nontransmitted BSSIDs)+1) and a value obtained by adding (Y-1) to the bitmap limit. The minimum value of the AID space may be min((X-1)+N*X, Y-1+bitmap limit)+1. That is, 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+bitmap limit. If the reporting AP belongs to a multiple BSSID set, the minimum value of the AID space may be the smaller of (X-1) + N*((number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs)+1) and (Y-1) + bitmap limit plus 1. 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 value of the AID space is N+1. If the bitmap limit is 48 and the reporting AP belongs to a multiple BSSID set, the minimum value of the AID space may be min(Y+48, Y+N*(number of nontransmitted BSSIDs or maximum number of nontransmitted BSSIDs)).

[0270] When 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 a Multiple BSSID element. In yet another specific embodiment, a non-AP station can obtain the number of nontransmitted BSSIDs from an element or frame indicating the maximum number of BSSIDs in a multiple BSSID set.

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

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

[0273] In the first embodiment of the AID space of the present invention, 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, and the AID space is wide. 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, and the AID space is narrow. A wide or narrow AID space may mean a large or small number of stations or multilink devices that can be combined. In addition, the first embodiment of the AID space of the present invention may have an advantage that calculation or implementation is simpler than the third embodiment of the AID space of the present invention.

[0274] The second embodiment of the present invention regarding the AID space has an advantage that the number of bits used to indicate a group address frame 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, there is a disadvantage that the AID space may be limited to some extent 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 and are not used to indicate group address frames. In addition, the second embodiment of the present invention regarding the AID space has an advantage that it is easier to calculate or implement than the third embodiment of the present invention regarding the AID space.

[0275] The third embodiment of the present invention regarding 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 a multi-link will be described with reference to Fig. 22 to Fig. 26. First, a Multi-Link element will be described with reference to Fig. 22.

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

[0278] A multilink device may perform multilink discovery and multilink setup using a multilink element. At this time, 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 an ID of an element including the Element ID subfield or the Element ID Extension subfield. The Length subfield may indicate a length of an 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 a type of the Multi-Link element. Also, a format of the Multi-Link element may be determined based on the type of the Multi-Link element. The Presence Bitmap subfield may indicate whether a subfield that may be included in the Multi-Link element is included. For example, the Presence Bitmap subfield may indicate whether a subfield that may be included in the Common Info subfield included in the Multi-Link element is 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 include information about multiple links or all links. The Common Info subfield may include information commonly required or commonly applied to multiple links or all links. The Link Info subfield may include information about the link corresponding to the Link Info subfield.

[0281] The information related to MediumSyncDelay indicates a value to be set as the duration of MediumSyncDelay and may have a default value. In certain situations, a multilink device may 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 may 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 may 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 units of 32us. 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 a 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 a value obtained by adding −72 to the value of the Medium Synchronization OFDM ED Threshold subfield, 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 more, the CCA threshold indicated by the Medium Synchronization OFDM ED Threshold subfield may be a value of −72 dBm or more. 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 ​​of 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 that a station may attempt 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 a 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 transmission attempts while the 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 multi-link device includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). The non-AP multi-link 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). Also, the second AP (AP2) and the second non-AP station (STA2) operate on a second link (link2). Also, the third AP (AP3) operates on a third link (link3).

[0288] The first AP (AP1) may 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) may include information about the second AP (AP2) or the third AP (AP3). The Reduced Neighbor Report element may be included in a beacon frame or a probe response frame.

[0289] In addition, the first non-AP station (STA1) receiving 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 on 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 on the non-AP multilink device or information on 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 an AP multi-link device or information about an 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] The first non-AP station (STA1) may transmit an association request frame or a reassociation request frame to the 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 a 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 a link on which the multi-link configuration is to be performed. The link on which the multi-link configuration is to be performed may be determined based on the link on which the non-AP multi-link device is to perform the multi-link configuration. 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 the multi-link configuration.

[0293] If the association response frame or reassociation response frame is successfully transmitted, it may be deemed that multi-link setup for the link indicated by the Mulit-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 with reference to FIG.

[0296] A station or AP that transmits an element is called a reporting station or reporting AP. Also, a station or AP pointed to by an 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. A 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 an ID of an element. The Element ID subfield of the Reduced Neighbor Report element may indicate an ID of the Reduced Neighbor Report element. The Length subfield may indicate a 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 Fig. 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 FIG. 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. is reserved except when the Reduced Neighbor Report element is carried in a Probe Response frame transmitted by a TVHT AP. When the Filtered Neighbor AP subfield is included in a probe response frame transmitted by a TVHT AP and all BSSs of the AP 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 FIG. 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 FIG. 24(d). In this case, the subfields included in the TBTT Information subfield may be selectively included.

[0306] The Neighbor AP TBTT Offset subfield can indicate 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 can indicate that the offset is 254 TU or more. If the value of the Neighbor AP TBTT Offset subfield is 255, it can indicate that the offset value is unknown.

[0307] The BSSID subfield may indicate the BSSID.

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

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

[0310] The 20 MHz PSD subfield can indicate the maximum transmission power for the default category in the 20 MHz primary channel. In this case, the 20 MHz PSD subfield can indicate the maximum transmission power in dBm / MHz. The value of the 20 MHz PSD subfield is a signed integer, and the value of -128 in the 20 MHz PSD subfield is a reserved value. The value of 127 in the 20 MHz PSD subfield can indicate that there is no limit on the maximum transmission power for the default category. Also, when the value of the 20 MHz PSD subfield, Y, is in the range of -127 to 126, the 20 MHz PSD subfield can indicate that the maximum transmission power for the default category in the 20 MHz 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: When the value of the TBTT Information Length subfield is 1, the TBTT Information subfield may include the Neighbor AP TBTT Offset subfield. When 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. When 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. When 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. When 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 a Neighbor AP TBTT Offset subfield and a BSSID subfield. If the value of the TBTT Information Length subfield is 8, the TBTT Information subfield may include a Neighbor AP TBTT Offset subfield, a BSSID subfield, and a 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 Parameter 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, 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 a MLD Parameters subfield.If the value of the TBTT Information Length subfield is 17 or more, the TBTT Information subfield may include the following subfields in the previous 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, i.e., the MLD Parameters subfield may be included if the TBTT Information Length subfield is 4, 10, 16, or 17 or more.

[0312] The MLD Parameter subfield may be as shown in FIG. 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 including the MLD ID subfield. A specific setting method of the MLD ID subfield can be as shown in FIG.

[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 increased 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 increased by 1 each time a significant update occurs in the AP or BSS corresponding to the BSS Parameters Change Count subfield. The significant update may include an update of 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 may indicate a value from 0 to 255. In the embodiment of the present invention, the reporting AP may represent an AP that sets and transmits the MLD ID subfield. The 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 in 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 propyl 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. Also, if the reported AP is part of another AP multilink device 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 has no information about the multilink device of the reported AP, 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 has no 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 FIG. 25, the reporting AP operates on the first link (link1). 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) also operates on the first link (link1), the second link (link2), and the third link (link3). At this time, the reporting AP sets the values ​​of the MLD ID subfields corresponding to the APs operating on the second link (link2) and the third link (link3) to 0.

[0320] Also, the reporting AP may transmit multiple BSSID elements together with the Reduced Neighbor Report element. In yet another specific embodiment, the reporting AP may not transmit multiple BSSID elements. In this case, when the reporting AP transmits multiple BSSID elements, the reporting AP may belong to a multiple BSSID set. Also, when the reporting AP does not transmit multiple BSSID elements, the reporting AP may 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. Also, 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 of 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 (link1) and belonging to the second multilink device (MLD 2). The second multilink device (MLD 2) may include APs operating on the first link (link1) and APs operating on the second link (link2). The reporting AP may set the value of the MLD ID subfield corresponding to the APs operating on the first link (link1) belonging to the second multilink device (MLD 2) and the APs operating on the second link (link2) 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 (link1) and the APs of the second multilink device (MLD 2) operating on the second link (link2) 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] In addition, when the 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, and if the reported AP does not belong to the multilink device to which an AP of 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 the case 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. In addition, n may be a 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 (ink2). In addition, 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 value of the MLD ID subfield 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 a value 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 and 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] In addition, 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 above-mentioned 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 above-mentioned MLD ID subfield, the reporting AP can 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 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] The station can determine from which BSS the frame is transmitted based on the MAC address field of the MAC header of the received frame. Specifically, the station can determine whether the received frame is transmitted from the AP to which the station is associated or an AP belonging to the multiple BSSID to which the AP to which the station is associated belongs based on the MAC address field of the MAC header of the received frame. In a specific embodiment, the station can determine whether the received frame is transmitted from the AP to which the station is associated or an AP belonging to the multiple BSSID to which the AP to which the station is associated belongs based on the TA field of 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 is 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] The station can determine which AP the frame is sent to based on the MAC address field of the MAC header of the received frame. In a specific embodiment, the station can determine whether the received frame is sent to the AP to which the station is associated or to an AP belonging to the multiple BSSID to which the AP to which the station is associated based on the RA field of 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 belongs, the station can determine that the received frame is sent to the AP to which the station is associated or to an AP belonging to the multiple BSSID set to which the AP to which the station is associated belongs. 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 belongs, the station can determine that the received frame is sent to the AP to which the station is associated and to an AP belonging to the multiple BSSID set to which the AP to which the station is associated belongs.

[0331] A station can determine whether a frame is an Inter-BSS frame based on a MAC address field of a 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 an 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 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 an 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 the received frame as an Intra-BSS frame.

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

[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 indicates that the preamble of the PPDU received by the station 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 has transmitted 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 does not indicate that the preamble of the PPDU received by the station 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 has not transmitted the received PPDU.

[0334] A multiple BSSID set may be a set of multiple BSSs in 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 multiple BSSID element may be called a multiple BSSID set. Also, a TIM element included in a beacon frame or a TIM frame may indicate frames buffered in multiple BSSIDs included in the multiple BSSID set. Also, a single beacon frame or a single probe response frame may include a multiple BSSID element. 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 a transmitted BSSID. The remaining BSSIDs in the multiple BSSID set, excluding the transmitted BSSID, are called nontransmitted BSSIDs. Also, a beacon frame or a probe response frame may not be transmitted in a BSS corresponding to a nontransmitted BSSID.

[0335] As described above, the maximum number of BSSIDs that a multiple BSSID set may 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 may determine the MAC addresses or BSSIDs of APs included in the multiple BSSID set based on the received Multiple BSSID element. Also, each of the multiple BSSID indexes may be mapped to each of the BSSIDs included in the multiple BSSID set. Thus, 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 regarding the method for setting the MLD ID subfield.

[0337] In the above 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 a maximum value that the MLD ID subfield can indicate. 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 that the reported AP is not included in a multilink device to which an AP of 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 a 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 the reporting AP transmits a multiple BSSID element, if the reported AP is an AP included in a multiple BSSID set including the reporting AP, or if the reported AP belongs to a multilink device to which an AP of the multiple BSSID set including 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 the multiple BSSID set can include can be 2^8=256. Therefore, according to the above conditions, there can be no value 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 of the multiple BSSID set to which the reporting AP belongs belongs. For example, the reporting AP cannot indicate a multilink device with a BSSID index of 255. The above-mentioned 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 value is 255 set based on the BSSID index or 255 set based on a pre-specified value.

[0340] Therefore, the condition for setting the value of the MLD ID subfield to a pre-specified value may further include that when the value of the MaxBSSID Indicator subfield corresponding to the reporting AP is a maximum value, the reported AP belongs to a multi-link device to which an AP of 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] In addition, according to the above-described embodiment, the reporting AP may have difficulty in setting the value of the MLD ID subfield regardless of whether the reporting AP transmits multiple BSSID elements. For example, when the reporting AP indicates information on a large number of APs, the reporting AP may have difficulty in setting the value of the MLD ID subfield. Since the number of reported APs is greater than the number of configurable multilink device IDs, the reported AP may not be identified by the ID of the multilink device. For example, when the reporting AP transmits multiple BSSID elements and the reporting AP transmits information to more than (254-2^n+1) APs, the reported AP may not be identified by the ID of the multilink device in a limited range. When the reporting AP does not transmit multiple BSSID elements and the reporting AP transmits information to more than (254-1+1) APs, the reported AP may not be identified by the ID in a limited range. 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 may 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, when the size of the MLD ID subfield is N bits, the pre-specified value may be 2^N-1. For example, when the size of the MLD ID subfield is 9 bits, the pre-specified value may be 511. As yet another example, when the size of the MLD ID subfield is 16 bits, the pre-specified value may be 65535.

[0343] 26 and 27 illustrate a method of 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, an AID allocated by an AP may be transmitted to a non-AP STA. A non-AP STA may recognize that an AID received from an AP is an AID corresponding to the non-AP STA. A non-AP station that receives a subfield including an AID value allocated to a non-AP station may recognize that the subfield including an AID value allocated 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 the 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. Also, as described above, the AID may be used for traffic indication. 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 that the multilink device uses.

[0349] In Figure 26, a first multilink device (MLD 1) operates with a first link (Link 1) and a second link (Link 2). Also, a second multilink device (MLD 2) operates with a third link (Link 3) and a fourth link (Link 4). At this time, X is assigned as the AID of the first multilink device (MLD 1). Therefore, it is not permitted to assign X as the AID of the second multilink device (MLD 2), and Y is assigned instead.

[0350] In a specific embodiment of the present invention, the AP multilink device may reallocate the AID assigned to any one of the multilink devices to another station or another multilink device. When a pre-specified condition is met, the AP multilink device may reallocate the AID assigned to any one of the multilink devices to another station or another multilink device. In this case, the pre-specified condition may include that the multilink devices or stations to which one AID is commonly assigned operate on different links. That is, the pre-specified condition may include that the multilink devices or stations to which one AID is commonly assigned operate on non-overlapping links. In this case, a station or multiple multilink devices operating on one link may not be allowed to be assigned one AID. In yet another specific embodiment, the multilink devices or stations to which one AID is commonly assigned 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 a 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, when a frame includes 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 be applied to a station or multilink device operating on that link. For example, information transmitted on a first link may be applied to a station or multilink with AID X operating on the first link, and may not be applied to a station or multilink with AID X operating on the second link.

[0353] In Fig. 27(b), a beacon frame including a TIM is transmitted on each of the first link (Link1) and the second link (Link2). At this time, the TIM transmitted on both the first link (Link1) and the second link (Link2) indicates that traffic corresponding to AID X is buffered. The TIM transmitted on the first link (Link1) indicates that traffic for the multi-link device (MLD 1) operating on the first link (Link1) has been buffered, and the TIM transmitted on the second link (Link2) indicates that traffic for the station (STA1) operating on 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, a default mapping may be applied to a link for which no TID-to-link mapping has been performed. Also, when a TID-to-link mapping is torn down for a link for which TID-to-link mapping negotiation has been completed, the default mapping may be applied to the link again.

[0357] The TID-to-link mapping negotiation may be performed by a TID-to-link mapping request and a TID-to-link mapping response. Specifically, the multilink device may transmit a frame including a TID-To-Link Mapping element to perform a TID-to-link mapping request. 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 transmit an association request frame, a reassociation request frame, or a TID-to-link mapping request frame to request TID-to-link mapping. An AP or an AP multilink device may transmit a TID-to-link mapping request frame to request TID-to-link mapping. The multilink device that has received the TID-to-link mapping request may transmit a frame including a TID-To-Link Mapping element to perform a TID-to-link mapping response. 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 the 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 a non-AP station multilink device can respond to the TID-to-link mapping request by transmitting a TID-to-link mapping response frame.

[0358] The multilink device may initiate TID-to-link mapping by transmitting a TID-to-link mapping request. At this time, the multilink device may transmit a frame including a TID-to-link element to request a default mapping. The multilink device that has received the TID-to-link mapping request may transmit a TID-to-link mapping response to the TID-to-link mapping request to accept the TID-to-link mapping. At this time, the multilink device that has received the TID-to-link mapping request may transmit a frame that does not include a TID-to-link Mapping element to accept the TID-to-link mapping. In yet another specific embodiment, the multilink device that has received the TID-to-link mapping request may transmit 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 the non-AP multilink device to accept the TID-to-link mapping.

[0359] Also, the multilink device receiving the 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. At this time, the multilink device receiving the 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, the multilink device receiving the TID-to-link mapping request may reject the TID-to-link mapping by transmitting a frame including 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, the multilink device that has received the TID-to-link mapping request may transmit a TID-to-link mapping response frame in response to the TID-to-link mapping request. At this time, the multilink device that has received the 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, the multilink device that has received the 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. Also, the multilink device receiving the TID-to-link mapping request may 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. Also, the multilink device receiving the TID-to-link mapping request may 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, the multilink device receiving the TID-to-link mapping request may propose a preferred TID-to-link mapping while rejecting the TID-to-link mapping request. Also, the multilink device receiving the TID-to-link mapping request may 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. In addition, the TID-To-Link Mapping element sent when accepting a TID-to-link mapping can indicate the accepted TID-to-link mapping. In addition, the TID-To-Link Mapping element sent when rejecting a TID-to-link mapping can indicate a new 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] Also, for the TID-to-link mapping negotiation, the TID-to-link mapping request frame and the TID-to-link mapping response frame may include a dialogue token. The dialogue token maps the TID-to-link mapping request frame and the TID-to-link mapping response frame. Specifically, when the value of the dialogue token of the TID-to-link mapping request frame and the value of the dialogue token of 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 may set the dialogue token value of the TID-to-link mapping response frame to the dialogue token value of the TID-to-link mapping request frame. When the multilink device transmits a TID-to-link mapping response frame without receiving a TID-to-link mapping request frame, the multilink device may set a dialogue 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 the multilink device transmits an unsolicited TID-To-Link Mapping Response frame, the multilink device may set a dialogue token value of the TID-to-link mapping response frame to a pre-specified value. A field indicating a dialogue 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 dialogue token may have any one of values ​​0 to 255.

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

[0365] In the embodiment of FIG. 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 may 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 may initiate a TID-to-link mapping negotiation using an association response frame, a reassociation response frame, and a TID-to-link mapping request frame. At this time, the AP multilink device may 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 may initiate a 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 the non-AP multilink device may be in a form not desired by the AP multilink device, and the TID-to-link mapping request transmitted from the non-AP multilink device may not be transmitted. In addition, the AP multilink device can easily grasp the entire network status and determine an efficient TID-to-link mapping compared to a non-AP multilink device. In this case, the AP multilink device can complete the multilink setup and re-setup since it first transmits an association response frame or a re-association response frame before completing the TID-to-link mapping negotiation. When the non-AP multilink device that receives the TID-to-link mapping request transmits a TID-to-link mapping response, the TID-to-link mapping negotiation is successfully completed.

[0368] 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 restricted. 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. When 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 may determine that the association response frame, which includes the TID-to-link Mapping element and is received in response to the association request frame, requests TID-to-link mapping. When 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 may determine that the reassociation response frame, which includes the 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. This also applies to the reassociation request frame.

[0369] Also, in such an embodiment, the AP multilink device may not determine that the TID-to-link mapping is successfully completed until it receives a TID-to-link mapping response from the non-AP multilink device. Therefore, the AP multilink device may operate according to default mapping until it receives a TID-to-link mapping response from the non-AP multilink device. Also, 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 is 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 the association frame or reassociation frame. However, the non-AP multilink device must clearly indicate that it responds to the TID-to-link mapping request transmitted by the AP multilink device in the association frame or 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 a TID-to-link mapping or a reassociation response frame requesting a 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 be equal to the dialogue token value included in the association response frame requesting a TID-to-link mapping or the reassociation response frame requesting a TID-to-link mapping. However, the association response frame requesting a TID-to-link mapping and the reassociation response frame requesting a TID-to-link mapping may not 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 above-mentioned TID-to-Link Mapping Control field. Specifically, the response indication field may be included in a reserved field of the above-mentioned TID-to-Link Mapping Control field. 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 may determine whether the TID-to-link Mapping element requests TID-to-link mapping based on the response indication field.

[0372] Since the non-AP multilink device transmits a TID-to-link mapping response frame as a response to an association request frame or a reassociation request frame, the AP multilink device needs to distinguish which frame the TID-to-link mapping response frame is a response to. Specifically, when the non-AP multilink device transmits a TID-to-link mapping response frame as a response to an association request frame or a reassociation request frame, the non-AP multilink device may set the value of the dialogue token of the TID-to-link mapping response frame to a random value. Also, if the value of the dialogue token of the TID-to-link mapping response frame is the same as the value of the dialogue token of 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 of the TID-to-link mapping response frame is different from the value of the dialogue token of 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 association request frame or the 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 set to a pre-specified value, the AP multilink device may 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 pre-specified value. In this case, the pre-specified 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 and 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 a 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 a 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 the association response frame or reassociation response frame based on the value of the Link Mapping field for the TID of the received TID-to-link mapping response frame. Specifically, if the value of the Link Mapping field for the TID of the received TID-to-link mapping response frame is the same as 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 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 the association response frame or reassociation response frame. Specifically, the received TID-to-link mapping response frame may include Link Mapping fields for multiple TIDs. In this case, if all the Link Mapping field values ​​included in the TID-to-link mapping response frame are the same as all the Link Mapping field values ​​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 Link Mapping field value for the TID of the TID-to-link mapping response frame received by the AP multilink device is different from the Link Mapping field value 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 Link Mapping field for the TID of the TID-to-link mapping response frame received by the AP multilink device includes at least one of the values ​​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 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 a TID-to-link mapping negotiation in a case where 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.

[0378] The link set for which the TID-to-link mapping is requested in the association request frame or the 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 the reassociation response frame. For example, the association request frame or the reassociation request frame may request TID-to-link mapping for three links, and the association response frame or the reassociation response frame may set TID-to-link mapping for two links. In addition, the link sets being different from each other may include different settings of the link sets. Specifically, the link sets being different from each other may include different operating channels of the link sets. In addition, the link sets being different from each other may include different configurations of the link sets.

[0379] In some embodiments of Figure 28, when the 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 set up 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 that requests the TID-to-link mapping in the association request frame or the reassociation request frame may be different from the link set for which the TID-to-link mapping is to be set up in the association response frame or the reassociation response frame.

[0380] Therefore, in another embodiment of the present invention, when an AP multilink device receives an association request frame or a reassociation request frame including a TID-to-link Mapping element and the association request frame or the reassociation request frame attempts to set a link set different from the link set of the multilink to be set, the AP multilink device may transmit an association response frame or a reassociation response frame that does not include a TID-to-link Mapping element. In this way, the AP multilink device may 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 the AP multilink device receives an association request frame or a reassociation request frame including a TID-to-link Mapping element and transmits an association response frame or a reassociation response frame that sets a link set different from the link set of the multilink that the association request frame or the reassociation request frame is to set, the AP multilink device may transmit an association response frame or a reassociation response frame that does not include a TID-to-link Mapping element. Also, when the non-AP multilink device transmits an association request frame or a reassociation request frame including a TID-to-link Mapping element and receives an association response frame or a reassociation response frame that sets a link set different from the link set of the multilink that the association request frame or the reassociation request frame is to set, the non-AP multilink device may determine that the TID-to-link mapping request is rejected even if the received association response frame or the reassociation response frame does not include a TID-to-link Mapping element. In this case, a default mapping may be applied to the AP multilink device and the non-AP multilink device.

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

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

[0384] FIG. 31 illustrates a method for a non-AP multi-link device to determine traffic buffered in an AP multi-link 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). At this time, 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 non-AP multilink device corresponding to the bit is buffered in the AP multilink device. Also, one or more second bits set to 1 may indicate that traffic for the non-AP station corresponding to the bit is buffered in the AP multilink device. A specific format and setting of the Partial Virtual Bitmap subfield may follow the embodiments described in FIG. 13 to FIG. 18.

[0387] When traffic for a non-AP multilink device is buffered in the AP multilink device, it is possible to determine 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 on, based on a Per-Link Traffic Indication List subfield of a Multi-Link Traffic element. The Per-Link Traffic Indication List subfield may include n Per-Link Traffic Indication Bitmap subfields, where n is a value obtained by adding 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. In addition, each of the n Per-Link Traffic Indication Bitmap subfields may be 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. 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 of the second bits set to 1. In this case, the value of the reserved bit may be 0.

[0389] 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, the Per-Link Traffic Indication Bitmap subfield mapped to the non-AP multilink device may indicate whether traffic for the non-AP multilink device is buffered on each of the multiple links. Also, when a default mapping is applied to the 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 may indicate which of the multiple links is the link that the non-AP multilink device recommends to induce traffic transmission. In this case, the default mapping may be such that all TIDs are mapped to all links.

[0390] Among bits of the Per-Link Traffic Indication Bitmap subfield mapped to a non-AP multilink device, bits corresponding to links not set by the AP multilink device or the non-AP multilink device may be set as reserved bits. Also, among bits of 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 communication, the present invention is not limited thereto and may be equally applied to other communication systems such as cellular communication, etc. Also, although the method, apparatus and system of the present invention have been described in relation to specific embodiments, some or all of the components and operations of the present invention may be embodied 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 having ordinary skill in the art to which the embodiment belongs. Therefore, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

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

[0395] 100 Stations 110 Processor 120 Communications Department 140 User Interface Section 150 display units 160 Memory 200 APs (Access Points) 210 Processor 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 transmitting / receiving unit; 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; 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; When traffic for the non-AP multilink device is buffered in the AP multilink device, determine which of the multiple links is a link for which traffic for the non-AP multilink device is buffered, or which of the multiple 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; 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, 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; 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 according to claim 1, wherein the value of the reserved bit is zero.

3. 2. The non-AP multilink device of claim 1, wherein 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.

4. 4. The non-AP multilink device of claim 3, 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.

5. 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; 4. The non-AP multi-link device according to claim 3, wherein the disabled link is a link in which uplink and downlink transmissions are stopped.

6. 4. The non-AP multi-link device of claim 3, wherein IDs of the multiple links are mapped in ascending order to bits of the Per-Link Traffic Indication Bitmap subfield that are mapped to the non-AP multi-link device.

7. 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 Addressed 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.

8. 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; 8. The non-AP multilink device of claim 7, wherein the bitmap limit is 48 bits.

9. An AP (access point) multilink device including a plurality of stations each operating on a plurality of links, A transmitter / receiver unit; Processor and Including, The processor, A traffic indication map (TIM) element and a multi-link traffic element are configured to be 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 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, a Per-Link Traffic Indication List subfield of the Multi-Link Traffic element is set according to which of the multiple links is a link for which traffic for the non-AP multilink device is buffered, or which of the multiple links is a link for which the AP multilink device recommends retrieving traffic transmission to the non-AP multilink device; Transmitting the beacon frame via the transceiver unit; 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, 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; 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.

10. 10. The AP multilink device according to claim 9, wherein the value of the reserved bit is zero.

11. 10. The AP multilink device of claim 9, wherein when 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 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.

12. The processor, The AP multilink device of claim 11, 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.

13. 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 11 , wherein the disabled link is a link in which uplink and downlink transmissions are stopped.

14. 12. The AP multilink device of claim 11, wherein IDs of the multiple links are mapped in ascending order to bits of the Per-Link Traffic Indication Bitmap subfield that are mapped to the non-AP multilink device.

15. 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 Addressed BU Indication Exponent subfield; 10. The AP multilink device of claim 9, 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.

16. 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; 16. The AP multilink device of claim 15, wherein the bitmap limit is 48 bits.

17. 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 for 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, 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; 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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