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

Abstract

The present invention discloses a traffic transmission method and apparatus performed by a first multi-link device (MLD) including a plurality of stations operating on a plurality of links in a wireless communication system. Specifically, the MLD of the present invention receives a beacon frame from a second MLD including a plurality of access points (APs) operating on the plurality of links, and transmits and receives data units based on the beacon frame. The beacon frame includes a multi-link traffic indication element indicating mapping of at least one traffic identifier (TID) among the plurality of TIDs for a buffered unit (BU) of the plurality of APs to the plurality of links, depending on whether mapping of the plurality of TIDs to the plurality of links is a default mapping for downlink or bidirectional.

Description

Technical Field

[0001] The present invention relates to a wireless communication method using multi-link and a wireless communication terminal using the same.

Background Art

[0002] Recently, with the growing popularization of mobile devices, Wireless LAN (WLAN) technology that can provide high-speed wireless Internet services to these devices has been attracting much attention. Wireless LAN technology is a technology that enables mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, embedded devices and the like to be wirelessly connected to the Internet in homes, enterprises or specific service providing areas based on short-range wireless communication technology.

[0003] IEEE (Institute of Electronics Engineers) 802.11 has put standards for various technologies into practical use or is developing such standards since it supported the early wireless LAN technology using the 2.4 GHz frequency band. First, IEEE 802.11b uses a frequency in the 2.4 GHz band and supports a maximum communication rate of 11 Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses a frequency in the 5 GHz band instead of the 2.4 GHz band, thereby reducing the influence of interference compared to the considerably congested 2.4 GHz band frequency, and uses OFDM technology to increase the communication rate up to 54 Mbps. However, IEEE 802.11a has a disadvantage that its communication distance is shorter than that of IEEE 802.11b. Then, IEEE 802.11g, same as IEEE 802.11b, uses a frequency in the 2.4 GHz band, implements a maximum communication rate of 54 Mbps, satisfies backward compatibility and thus attracted considerable attention, and also has an advantage over IEEE 802.11a in terms of communication distance.

[0004] Furthermore, IEEE 802.11n is a technical standard established to overcome the limitations in communication speed that had been pointed out as a vulnerability in wireless LANs. The purpose of IEEE 802.11n is to increase network speed and reliability and extend the operating range of wireless networks. Specifically, IEEE 802.11n supports high throughput (HT) with a data processing speed of up to 540 Mbps or more, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology, which uses multiple antennas at both the transmitter and receiver ends to minimize transmission errors and optimize data speed. In addition, this standard uses a coding method that transmits multiple duplicate copies to improve data reliability.

[0005] As the proliferation of wireless LANs accelerates and the applications using them diversify, there is a growing need for new wireless LAN systems that can support very high throughput (VHT) higher than the data processing speed supported by IEEE 802.11n. Among these, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) at the 5GHz frequency. Although the IEEE 802.11ac standard is defined only in the 5GHz band, early 11ac chipsets are expected to support operation in the 2.4GHz band for backward compatibility with older 2.4GHz band products. Theoretically, this standard allows for a minimum wireless LAN speed of 1Gbps and a maximum single-link speed of 500Mbps. This is achieved by extending the wireless interface concepts accepted in 802.11n, including wider radio frequency bandwidth (up to 160MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256QAM). Another method for transmitting data using the 60GHz band instead of the conventional 24GHz / 5GHz band is IEEE 802.11ad. IEEE 802.11ad is a transmission standard that uses beamforming technology to provide speeds of up to 7Gbps, making it suitable for streaming large amounts of data and high-bitrate video such as uncompressed HD video. However, the 60GHz frequency band has the disadvantage of being difficult to pass through obstacles, limiting its use to devices in short-range spaces.

[0006] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard has been developed and is nearing completion as a wireless LAN standard for 802.11ac and 802.11ad and beyond, to provide highly efficient and high-performance wireless LAN communication technology in high-density environments where access points (APs) and terminals are densely packed. In an 802.11ax-based wireless LAN environment, it is necessary to provide highly frequency-efficient communication indoors and outdoors in the presence of high-density stations and APs (Access Points), and various technologies have been developed to realize this.

[0007] Furthermore, in order to support new multimedia applications such as high-definition video and real-time games, development has begun on a new wireless LAN standard to increase the maximum transmission speed. The 7th generation wireless LAN standard, IEEE 802.11be (Extremely High Throughput, EHT), is being developed with the goal of supporting a maximum transmission rate of 30 Gbps in the 2.4 / 5 / 6 GHz band through wider bandwidth, increased spatial streams, and multiple AP coordination. [Overview of the project] [Problems that the invention aims to solve]

[0008] One embodiment of the present invention aims to provide a wireless communication method using multilink and a wireless communication terminal using the same.

[0009] The technical problems to be addressed herein are not limited to those mentioned above, and other technical problems not mentioned above will be clearly understood by those with ordinary skill in the art to which the present invention pertains from the following description. [Means for solving the problem]

[0010] In the wireless communication system according to the present invention, a terminal (non-AP STA) that transmits traffic includes a transmitting / receiving unit and a processor, the processor receiving beacon frames from a second MLD including a plurality of APs (Access Points) operating on each of the plurality of links, transmitting and receiving data units based on the beacon frames, and the beacon frames include a multi-link traffic indicator element that indicates the mapping between the plurality of links and at least one TID for the BUs (Buffered Units) of the plurality of APs, depending on whether the mapping between the plurality of traffic identifiers (TIDs) and the plurality of links is a default mapping for downlink or bidirectional.

[0011] Furthermore, in the present invention, the basic mapping means a state in which all of the multiple TIDs are mapped to each of the multiple links.

[0012] Furthermore, in the present invention, if the mapping between the plurality of TIDs and the plurality of links is not the basic mapping, the beacon frame includes the multiple link traffic indicator element.

[0013] Furthermore, in the present invention, when the mapping between the plurality of TIDs and the plurality of links is the basic mapping, the beacon frame does not include the multiple link traffic indicator element.

[0014] Furthermore, in the present invention, if the mapping between the plurality of TIDs and the plurality of links is not the basic mapping, and the beacon frame does not include the multiple link traffic indicator element, a PS-Poll frame for receiving the data unit is transmitted to the second MLD through the link corresponding to a specific TID among the plurality of links, which is at least one of the TIDs.

[0015] Furthermore, in the present invention, if at least one of the plurality of links constitutes an EMLSR link set in EMLSR (enhanced multi-link single radio) mode that supports transmission and reception on a single link only, and a specific link among the at least one link is removed, that specific link is removed from the EMLSR link set.

[0016] Furthermore, in the present invention, if the specific link among the at least one link is removed, and the number of remaining links among the at least one link excluding the specific link is 1 or 0, the EMLSR mode terminates.

[0017] Furthermore, in the present invention, the EMLSR mode terminates when the specific link is removed.

[0018] Furthermore, in the present invention, of the plurality of links, only one or more links mapped to at least one TID perform listening operations with the second MLD.

[0019] Furthermore, in the present invention, if the mapping relationship between the plurality of TIDs and the plurality of links is not the basic mapping relationship, and at least one TID is mapped to each of the plurality of links, the beacon frame does not include the multiple link traffic indicator element.

[0020] Further, the present invention provides a method comprising: receiving a beacon frame from a second MLD including a plurality of APs (Access Points) operating on each of the plurality of links; and transmitting and receiving data units based on the beacon frame, wherein the beacon frame includes a Multi-Link Traffic Indication element that indicates mapping between at least one TID among the plurality of TIDs for BUs (Buffered Units) of the plurality of APs and the plurality of links, depending on whether mapping between a plurality of traffic identifiers (TID) and the plurality of links is a default mapping for downlink or bidirectional. [Effects of the Invention]

[0021] One embodiment of the present invention provides a wireless communication method that efficiently uses multilinks and a wireless communication terminal using the same.

[0022] The effects obtainable from the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood from the following description by a person having ordinary knowledge in the technical field to which the present invention pertains. [Brief Description of the Drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating a wireless LAN system according to another embodiment of the present invention. [Figure 3] FIG. 3 is a diagram illustrating a configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram illustrating a configuration of an access point according to an embodiment of the present invention. [Figure 5] FIG. 5 is a diagram schematically illustrating a process in which an STA establishes a link with an AP. [Figure 6] This diagram illustrates the CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] Examples of various standard generational PPDU (PLCP Protocol Data Unit) formats are shown. [Figure 8] Examples of various EHT (Extremely High Throughput) PPDU (Physical Protocol Data Unit) formats and methods for specifying them according to embodiments of the present invention are shown. [Figure 9] This shows a multi-link device according to an embodiment of the present invention. [Figure 10] The embodiments of the present invention demonstrate that transmissions on different links occur simultaneously in multilink operation. [Figure 11] This illustrates the operation of a multilink device when the link is modified according to one embodiment of the present invention. [Figure 12] One embodiment of the present invention demonstrates that when one station of a non-STR multilink device is receiving, channel access for other stations of the non-STR multilink device is prohibited. [Figure 13] An embodiment of the present invention demonstrates the operation of releasing the channel access ban when it is confirmed that the intended recipient of the PPDU received by a station in a non-STR multilink device is not the station. [Figure 14] This example demonstrates that a station according to an embodiment of the present invention performs channel access after the channel access ban has been lifted. [Figure 15] This describes the operation of a station according to one embodiment of the present invention, which transmits after the channel access ban has been lifted. [Figure 16] An embodiment of the present invention demonstrates a transmission performed based on the status of a station in a non-STR multilink device. [Figure 17]This indicates a situation in which interference or collision may occur between links. [Figure 18] One embodiment of the present invention demonstrates the operation by which an STR multilink device ceases transmission to a non-STR multilink device. [Figure 19] This embodiment of the present invention demonstrates how an STR multilink device processes the CW value when it detects a transmission collision between links. [Figure 20] An embodiment of the present invention demonstrates the operation in which an STR multilink device performs channel access again after ceasing transmission to a non-STR multilink device. [Figure 21] An embodiment of the present invention demonstrates the operation in which an STR multilink device transmits a CTS-to-Self frame before transmitting to a non-STR multilink device. [Figure 22] This embodiment of the present invention demonstrates that multiple APs included in an STR multilink device transmit to multiple stations included in a single non-STR multilink device. [Figure 23] This embodiment of the present invention demonstrates that multiple APs included in an STR multilink device perform multiple transmissions with synchronized transmission termination to multiple stations included in a single non-STR multilink device. [Figure 24] An embodiment of the present invention demonstrates that a multilink device can exchange RTS / CTS frames. [Figure 25] Figure 24 illustrates the hidden node problem that occurs in the RTS / CTS frame exchange procedure according to the embodiment described. [Figure 26] An embodiment of the present invention demonstrates that a multilink device can exchange RTS / CTS frames. [Figure 27] Embodiments of the present invention demonstrate that a multilink device exceptionally transmits a response to a control frame even when channel access is prohibited. [Figure 28] This indicates that a transmission to a station from a non-STR multilink device will be retransmitted. [Figure 29]An embodiment of the present invention demonstrates that a control frame is transmitted on a link operated by a station that is not prohibited from channel access, rather than on a link operated by a station that is prohibited from channel access. [Figure 30] This embodiment of the present invention demonstrates that a multilink device transmits an ACK. [Figure 31] An embodiment of the present invention shows an element field that indicates information regarding sync PPDU reception support or transmission support. [Figure 32] This embodiment of the present invention demonstrates that a non-STR multilink device operates in inter-link TXOP (Inter-link TXOP) power saving mode. [Figure 33] This embodiment of the present invention demonstrates that a station of a non-STR multilink device enters a power-saving state while in standby mode for sync PPDU reception. [Figure 34] A further embodiment of the present invention demonstrates that a station of a non-STR multilink device enters a power-saving state while in standby mode for sink PPDU reception. [Figure 35] This shows the connection between a single-radio multilink device and an AP multilink device according to an embodiment of the present invention. [Figure 36] This example demonstrates that a single-radio multilink device according to an embodiment of the present invention performs MIMO transmission. [Figure 37] This example demonstrates how a single-radio multilink device according to an embodiment of the present invention performs channel access while taking into account the delay time of RF (radio frequency) chain changes. [Figure 38] The Capability element and Operation element used in a single-radio multilink device according to an embodiment of the present invention are shown. [Figure 39] This demonstrates that a single-radio multilink device according to an embodiment of the present invention transmits PPDU using MIMO. [Figure 40] This example demonstrates that a station and a single-radio multilink device according to an embodiment of the present invention perform an NDP sounding process. [Figure 41] This example demonstrates that a station and a single-radio multilink device according to an embodiment of the present invention perform a feedback beamforming sounding sequence. [Figure 42] This example demonstrates that a station and a single-radio multilink device according to an embodiment of the present invention perform an NDP sounding process. [Figure 43] This shows the mapping relationship between UP and AC. [Figure 44] An embodiment of the present invention demonstrates that a multilink device transmits traffic mapped to each station of the multilink device. [Figure 45] This embodiment of the present invention demonstrates that a multilink device performs frame replacement by TID link mapping. [Figure 46] This demonstrates that the AP multilink device and non-AP multilink device according to the embodiment of the present invention have basic mappings between TIDs and links. [Figure 47] This demonstrates that the mapping between TID and links is changed when the multilink device according to an embodiment of the present invention activates EMLSR mode. [Figure 48] The format of a Multi-Link element according to an embodiment of the present invention is shown. [Figure 49] This example demonstrates that when the multilink device according to an embodiment of the present invention deactivates the EMLSR mode, the mapping between the TID and the links is changed. [Figure 50] An embodiment of the present invention shows a Multi-Link element that signals information regarding the padding length of the initial control frame. [Figure 51] This embodiment of the present invention shows that, considering a DTIM beacon received on an EMLSR link where frame exchange does not occur in EMLSR mode, the TXOP terminates on a link where frame exchange does occur in EMLSR mode. [Figure 52]One embodiment of the present invention demonstrates the operation in which an EMLSR MLD changes to a receive (transmit / receive) support mode for other EMLSR links after the frame exchange procedure has been completed on a specific EMLSR link. [Figure 53] This document describes a TXOP (Frame Exchange Sequence) management method for an EMLSR link according to one embodiment of the present invention. [Figure 54] In one embodiment of the present invention, when an EMLSR MLD intends to receive a beacon / group address frame on an EMLSR link where a frame exchange procedure has already been performed, it exhibits an operation that does not switch to a listening operation. [Figure 55] Various EML Control field formats according to embodiments of the present invention are shown. [Figure 56] This invention describes a method for removing EMLSR links after performing TID-to-link mapping according to one embodiment of the present invention. [Figure 57] This invention describes a method for deactivating the EMLSR mode of a non-AP MLD after performing TID-to-link mapping according to one embodiment of the present invention. [Figure 58] One embodiment of the present invention demonstrates the operation of non-AP MLD and AP MLD when configuring an EMLSR link, taking into account the modified TID-to-Link mapping. [Figure 59] The table shows the analysis of the Transition Timeout instruction value and the instructed time. [Figure 60] One embodiment of the present invention demonstrates the operation of a non-AP MLD and an AP MLD when setting up an EMLSR link, taking into account the modified link configuration of the AP MLD. [Figure 61] This example shows a TID-to-Link mapping element that directs QMFs to be sent regardless of the link. [Figure 62] This example demonstrates how MLD operates after establishing a QMF policy through TID-to-Link mapping. [Figure 63]This shows one example of the format for a TID-to-Link mapping element. [Figure 64] This document describes a TID-to-Link mapping procedure according to one embodiment of the present invention. [Figure 65] This example shows a case where the initiating MLD instructs (or proposes) a TID, and the response MLD selectively responds to some TIDs during link mapping. [Figure 66] This describes how the initiating MLD responds by accepting the TID-to-Link mapping proposed in reverse from the response MLD. [Figure 67] This shows an unsolicited TID-to-Link mapping response frame sent from an AP MLD, and an example of the TID-to-Link mapping negotiation process between an AP MLD and a non-AP MLD. [Figure 68] This shows the TIM element format. [Figure 69] The first format of a multilink TIM element according to one embodiment of the present invention is shown. [Figure 70] This invention presents a method for indicating / analyzing multilink TIM elements using the first format of a multilink TIM element according to one embodiment of the present invention. [Figure 71] This document describes another method for indicating / analyzing a multilink TIM element using the first format of a multilink TIM element according to one embodiment of the present invention. [Figure 72] The second format of a multilink TIM element according to one embodiment of the present invention is shown. [Figure 73] This invention presents a method for indicating / analyzing multilink TIM elements using a second format of multilink TIM elements according to one embodiment of the present invention. [Figure 74] The third format of a multilink TIM element according to one embodiment of the present invention is shown. [Figure 75]This invention presents a method for indicating / analyzing multilink TIM elements using a third format of multilink TIM elements according to one embodiment of the present invention. [Figure 76] One embodiment of the present invention shows TIM elements and Multi-link TIM elements transmitted via MSDU. [Figure 77] This invention illustrates a method for indicating / setting AID-related information for a TIM element and a Multi-link TIM element according to one embodiment of the present invention. [Figure 78] One embodiment of the present invention demonstrates a method by which an AP MLD transmits a multilink TIM (Traffic Indication) element to a non-AP MLD. [Figure 79] This document shows one embodiment of the operation method of the MLD according to one embodiment of the present invention. [Modes for carrying out the invention]

[0024] The terminology used herein has been selected to the greatest extent possible from currently widely used general terms, taking into account the function of the present invention; however, this may differ depending on the intent, conventions, or emergence of new technologies of the articulate persons in the relevant field. In addition, in certain cases, the applicant has arbitrarily selected some terms, and in such cases, the meaning of these terms will be described in the relevant section of the invention description. Therefore, it should be made clear that the terms used herein are not merely names of terms, but should be interpreted based on the substantive meaning of the terms and the content of this specification as a whole.

[0025] Throughout the specification, when one component is described as being "connected" to another, this includes not only cases where they are "directly connected," but also cases where they are "electrically connected" with other components in between. Furthermore, when a component is described as "containing" a particular component, this means, unless otherwise stated, that it may contain other components rather than excluding them. In addition, limitations such as "greater than or equal to" or "less than or equal to" a specific critical value may be appropriately replaced by "greater than" or "less than" depending on the embodiment.

[0026] In the present invention, the terms "field" and "subfield" may be used interchangeably.

[0027] Figure 1 shows a wireless LAN system according to one embodiment of the present invention.

[0028] A wireless LAN system includes one or more Basic Service Sets (BSS), where a BSS represents a set of devices that have successfully synchronized and can communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0029] As shown in Figure 1, the infrastructure BSS BSS1, BSS2 includes one or more stations STA1, STA2, STA3, STA4, STA5, access points AP-1, AP-2 which are stations that provide distribution services, and a distribution system DS that connects multiple access points AP-1, AP-2.

[0030] A Station (STA) is any device that includes Medium Access Control (MAC) and a Physical Layer interface to a wireless medium in accordance with the IEEE 802.11 standard, and in a broad sense includes not only non-AP stations but also all access point (AP) stations. In this specification, "terminal" is used to refer to non-AP, AP, or both. A station for wireless communication includes a processor and a communication unit, and depending on the embodiment, further includes a user interface unit and a display unit, etc. The processor generates frames to be transmitted over the wireless network or processes frames received over the wireless network, and performs various other processing for controlling the station. The communication unit is functionally connected to the processor and sends and receives frames over the wireless network for the station. In this invention, "terminal" is used as a term that includes user equipment (UE).

[0031] An Access Point (AP) is an individual device that provides connectivity to a distribution system (DS) via a wireless medium for stations associated with it. In infrastructure BSS, communication between non-AP stations is generally conducted via APs, however, direct communication is possible between non-AP stations if a direct link is configured. In this invention, AP is used as a concept that includes PCP (Personal BSS Coordination Point), but in a broader sense, it includes all concepts such as central controllers, base stations (BS), node B, BTS (Base Transceiver System), or site controllers. In this invention, AP is also referred to as a base wireless communication terminal, but in a broader sense, base wireless communication terminal is used as a term that includes APs, base stations, eNBs (eNodeBs), and transmission points (TPs). Furthermore, base wireless communication terminals include various forms of wireless communication terminals that allocate and schedule communication medium resources in communication with multiple wireless communication terminals.

[0032] Multiple infrastructure BSSs are connected to each other via a distribution system DS. In this case, multiple BSSs connected via the distribution system are called an Extended Service Set (ESS).

[0033] Figure 2 shows an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of Figure 2, redundant explanations are omitted for parts that are the same as or corresponding to the embodiment of Figure 1.

[0034] As shown in Figure 2, BSS3 is an independent BSS and does not include APs, so all stations (STA6, STA7) are not connected to APs. 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 one another.

[0035] Figure 3 is a block diagram showing the configuration of station 100 according to one embodiment of the present invention. As shown, 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.

[0036] First, the communication unit 120 transmits and receives wireless signals such as wireless LAN packets and may be incorporated into the station 100 or provided externally. According to one 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 2.4GHz, 5GHz, 6GHz, and 60GHz. According to one embodiment, the station 100 may include a communication module using a frequency band of 7.125GHz or higher and a communication module using a frequency band of 7.125GHz or lower. Each communication module can perform wireless communication with an AP or external station based on the wireless LAN standard of the frequency band supported by the communication module. Depending on the performance and requirements of the station 100, the communication unit 120 may operate only one communication module at a time or operate multiple communication modules together simultaneously. When the station 100 includes multiple communication modules, each communication module may be provided in an independent form, or the multiple modules may be integrated as a single chip. In embodiments of the present invention, the communication unit 120 can represent an RF (Radio Frequency) communication module that processes RF signals.

[0037] Next, the user interface 140 includes various forms of input / output means provided in the station 100. In other words, 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. The user interface unit 140 also outputs based on instructions from the processor 110 using various output means.

[0038] Next, the display unit 150 outputs an image to the display screen. The display unit 150 outputs various display objects, such as content generated by the processor 110 or user interfaces based on control instructions from the processor 110. The memory 160 stores control programs used by the station 100 and various data associated with them. Such control programs include connection programs necessary for the station 100 to connect with APs or external stations.

[0039] The processor 110 of the present invention executes various instructions or programs and processes data within the station 100. The processor 110 also controls each unit of the station 100 and controls the transmission and reception of data between units. According to an embodiment of the present invention, the processor 110 executes a program for connection with the AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also reads information regarding the priority conditions of the station 100 contained in the communication setup message and requests a connection to the AP based on the priority conditions of the station 100. The processor 110 of the present invention may refer to the main control unit of the station 100, or, depending on the embodiment, may refer to a control unit for individually controlling a part of the station 100's configuration, such as the communication unit 120. In other words, the processor 110 may be a modem or a modulator and / or demodulator that modulates and demodulates the wireless signals transmitted and received from the communication unit 120. The processor 110 controls various operations of wireless signal transmission and reception of the station 100 according to an embodiment of the present invention. A detailed embodiment relating to this will be described later.

[0040] The station 100 shown in Figure 3 is a block diagram according to one embodiment of the present invention, and the separately shown blocks represent logically distinguished elements of the device. Therefore, the above-mentioned elements of the device are mounted on one chip or multiple chips depending on the device design. For example, the processor 110 and the communication unit 120 may be integrated and implemented on a single chip, or they may be implemented on separate chips. Furthermore, in the 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.

[0041] Figure 4 is a block diagram showing the configuration of AP200 according to one embodiment of the present invention. As shown, AP200 according to an embodiment of the present invention includes a processor 210, a communication unit 220, and a memory 260. In Figure 4, redundant explanations are omitted for parts of the AP200 configuration that are the same as or correspond to the configuration of station 100 in Figure 3.

[0042] Referring to Figure 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 Figure 3, the communication unit 220 of the AP 200 can also include a plurality of communication modules using different frequency bands. That is, the AP 200 according to an embodiment of the present invention can include two or more communication modules using different frequency bands, for example, 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 can 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 can communicate wirelessly with the station based on the wireless LAN standard of the frequency band supported by the communication module. Depending on the performance and requirements of the AP 200, the communication unit 220 can operate only one communication module at a time or operate multiple communication modules together simultaneously. In an embodiment of the present invention, the communication unit 220 can represent an RF (Radio Frequency) communication module that processes RF signals.

[0043] Next, the memory 260 stores the control program used by the AP200 and various data associated with it. Such a control program includes a connection program that manages the connection of stations. The processor 210 controls each unit of the AP200 and controls the transmission and reception of data between units. According to an embodiment of the present invention, the processor 210 executes the program for connecting with stations stored in the memory 260 and transmits a communication setting message to one or more stations. In this case, the communication setting message includes information regarding the connection priority conditions of each station. The processor 210 also performs connection settings in response to connection requests from stations. According to one embodiment, the processor 210 is a modem or modulation / demodulation unit that modulates and demodulates the wireless signals transmitted and received from the communication unit 220. The processor 210 controls various operations of wireless signal transmission and reception of the AP200 according to an embodiment of the present invention. A detailed embodiment relating thereto will be described later.

[0044] Figure 5 is a schematic diagram illustrating the process by which STA establishes a link with AP.

[0045] Referring to Figure 5, the link between STA100 and AP200 is established through three main steps: scanning, authentication, and association. First, the scanning step is the step in which STA100 obtains connection information for the BSS operated by AP200. There are two methods for performing scanning: passive scanning, which obtains information using only the beacon message S101 that AP200 periodically transmits, and active scanning, in which STA100 transmits a probe request S103 to the AP, receives a probe response S105 from the AP, and obtains connection information.

[0046] In the scanning step, STA100, having successfully received wireless connection information, transmits an authentication request (S107a), receives an authentication response from AP200 (S107b), and performs the authentication step. After the authentication step is performed, STA100 transmits an association request (S109a), receives an association response from AP200 (S109b), and performs the association step. In this specification, "association" basically means wireless coupling, but the present invention is not limited to this, and in a broad sense, coupling includes both wireless and wired coupling.

[0047] On the other hand, an additional 802.1X-based authentication step S111 and an IP address acquisition step S113 via DHCP are performed. In Figure 5, Server 300 is a server that processes authentication between STA100 and the 802.1X-based system, and may be physically connected to AP200 or exist as a separate server.

[0048] Figure 6 shows the CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0049] A terminal performing wireless LAN communication checks whether a channel is busy or not by performing carrier sensing before transmitting data. If a wireless signal above a certain strength is detected, the channel is determined to be busy, and the terminal delays access to that channel. This process is called Clear Channel Assessment (CCA), and the level at which the detection of the signal is determined is called the CCA threshold. If a wireless signal above the CCA threshold is received by the terminal and the terminal is the recipient, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected from the channel, or if a wireless signal below the CCA threshold is detected, the channel is determined to be idle.

[0050] If a channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after a time period determined by the status of each terminal, such as an IFS (Inter Frame Space), AIFS (Arbitration IFS), PIFS (PCF IFS), etc. In this embodiment, the AIFS is used as a replacement for the conventional DIFS (DCF IFS). Each terminal waits, decreasing a slot time equal to a random number determined for that terminal during the interval of idle state of the channel, and the terminal that has exhausted all of its slot time attempts to access the channel. The period in which each terminal performs this backoff procedure is called the competition window period. At this time, the random number can be called the backoff counter. That is, the initial value of the backoff counter is set by an integer, which is a random number acquired by the terminal. If a terminal senses that a channel is idle during the slot time, the terminal can decrease the backoff counter by 1. Also, when the backoff counter reaches 0, the terminal may be allowed to access the channel. Therefore, terminal transmission may be permitted when the channel is idle during the AIFS time and the backoff counter slot time.

[0051] If a specific terminal successfully accesses the channel, it transmits data through the channel. However, if a terminal attempting access collides with another terminal, the colliding terminals are each assigned a new random number and perform a further backoff procedure. In one embodiment, the random number newly assigned to each terminal is determined within a range twice the range (competition window, CW) of the random number previously assigned to that terminal (2*CW). Meanwhile, each terminal attempts access again in the next competition window interval by performing a further backoff procedure, but this time, each terminal performs the backoff procedure from the slot time remaining in the previous competition window interval. In this way, each terminal performing wireless LAN communication can avoid collisions with each other for a specific channel.

[0052] <Examples of various PPDU formats>

[0053] Figure 7 shows examples of various standard generational PPDU (PLCP Protocol Data Unit) formats. More specifically, Figure 7(a) shows one example of a legacy PPDU format based on 802.11a / g, Figure 7(b) shows one example of an HE PPDU format based on 802.11ax, and Figure 7(c) shows one example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Figure 7(d) shows the detailed field configuration of L-SIG and RL-SIG commonly used in the aforementioned PPDU formats.

[0054] Referring to Figure 7(a), the legacy PPDU preamble includes L-STF (Legacy Short Training field), L-LTF (Legacy Long Training field), and L-SIG (Legacy Signal field). In embodiments of the present invention, the L-STF, L-LTF, and L-SIG can be referred to as the legacy preamble.

[0055] Referring to Figure 7(b), the HE PPDU preamble further includes RL-SIG (Repeated Legacy Short Training field), HE-SIG-A (High Efficiency Signal A field), HE-SIG-B (High Efficiency Signal B field), HE-STF (High Efficiency Short Training field), and HE-LTF (High Efficiency Long Training field) in addition to the legacy preamble. In embodiments of the present invention, RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF can be referred to as the HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0056] Referring to Figure 7(c), the EHT PPDU preamble further includes RL-SIG (Repeated Legacy Short Training field), U-SIG (Universal Signal field), EHT-SIG-A (Extremely High Throughput Signal A field), EHT-SIG-A (Extremely High Throughput Signal B field), EHT-STF (Extremely High Throughput Short Training field), and EHT-LTF (Extremely High Throughput Long Training field) in addition to the legacy preamble. In embodiments of the present invention, RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF can be referred to as the 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 in only some of the EHT PPDU formats.

[0057] The L-SIG field included in the PPDU preamble is configured with 64 FFT OFDM and consists of a total of 64 subcarriers. Of these, 48 subcarriers, excluding the guard subcarrier, DC subcarrier, and pilot subcarrier, are used for L-SIG data transmission. Since BPSK and a Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information configuration of the L-SIG.

[0058] Referring to Figure 7(d), L-SIG includes the L_RATE field and the L_LENGTH field. The L_RATE field consists of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which is a combination of a modulation scheme such as BPSK / QPSK / 16-QAM / 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. Combining the information from the L_RATE and L_LENGTH fields allows us to determine the total length of the PPDU. In non-legacy PPDU formats, the L_RATE field is set to the minimum speed of 6 Mbps.

[0059] The L_LENGTH field is measured in bytes, with a total of 12 bits allocated, allowing for signaling up to 4095. In combination with the L_RATE field, it can indicate the length of the PPDU. In this case, legacy and non-legacy terminals can parse the L_LENGTH field in different ways.

[0060] First, the method by which a legacy or non-legacy terminal analyzes the length of a PPDU using the L_LENGTH field is as follows: When the L_RATE field is set to 6Mbps, 3 bytes (i.e., 24 bits) may be transmitted in 4us, which is the symbol duration of one 64FFT. Therefore, by adding the 3 bytes corresponding to the SVC field and the Tail field to the L_LENGTH field value and dividing this by the transmission amount of one symbol, which is 3 bytes, the number of 64FFT reference symbols after L-SIG is obtained. After multiplying the obtained number of symbols by 4us, which is the symbol duration of one symbol, and then adding 20us, which is the transmission time for L-STF, L-LTF, and L-SIG, the length of the PPDU, i.e., the reception time (RXTIME), is obtained. This can be expressed mathematically as shown in Equation 1 below.

[0061]

number

[0062] At this time,

number

[0063]

number

[0064] Here, TXTIME is the total transmission time that constitutes the PPDU, as shown in Equation 3 below. In this case, TX represents the transmission time of X.

[0065]

number

[0066] 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 ​​L_LENGTH = {3k+1, 3k+2, 3(k+1)} indicate the same PPDU length.

[0067] Referring to Figure 7(e), the U-SIG (Universal SIG) field persists in EHT PPDUs and subsequent generations of wireless LAN PPDUs, playing a role in distinguishing which generation of PPDU it is, including 11be. The U-SIG is a 64FFT-based OFDM with two symbols, capable of transmitting a total of 52 bits of information. Of these, 43 bits, excluding the 9 bits of CRC / tail, are broadly divided into the VI (Version Independent) field and the VD (Version Dependent) field.

[0068] The VI bit maintains its current bit configuration, allowing current 11be terminals to obtain information about a PPDU from its VI field even when subsequent generations of PPDUs are defined. To this end, the VI field consists of the PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits and is responsible for sequentially distinguishing 11be and subsequent generations of wireless LAN standards by version. 11be has a value of 000b. The UL / DL field distinguishes whether the PPDU is an uplink or downlink PPDU. The BSS color represents the BSS identifier defined in 11ax and has a value of 6 bits or more. The TXOP represents the Transmit Opportunity Duration, which was transmitted in the MAC header, but by adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without decoding the PPDU, and it has a value of 7 bits or more.

[0069] The VD field may consist of the PPDU format as signaling information useful only for the 11be version of PPDU, fields that are common to any PPDU format such as BW, and fields that are defined differently depending on the PPDU format. The PPDU format is a divisor that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), EHT ER (Extended Range) PPDU, etc. The BW field broadly signals five basic PPDU BW options of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz (BW that can be expressed in the form of a power of 20*2 can be called a basic BW), and various remaining PPDU BWs composed of preamble puncturing. In addition, after being signaled at 320 MHz, some 80 MHz may be punctured and then signaled. Furthermore, the punctured and deformed channel shape may be signaled directly in the BW field, or it may be signaled using both the BW field and fields appearing after the BW field (for example, fields within 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.

[0070] Fields located after the BW field vary depending on the form and format of the PPDU. MU PPDUs and SU PPDUs may be signaled in the same PPDU format. A field to distinguish between MU PPDUs and SU PPDUs may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both SU PPDUs and MU PPDUs include an EHT-SIG field, but some fields unnecessary for the SU PPDU may be compressed. In this case, the information of the compressed fields may be omitted or have a reduced size compared to the original fields included in the MU PPDU. For example, in the case of a SU PPDU, the common fields of the EHT-SIG may be omitted or replaced, or user-specific fields may be replaced or reduced to one, resulting in a different configuration.

[0071] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (e.g., the RA field) may be omitted depending on the value of the compression field.

[0072] If a portion of the EHT-SIG field of an SU PPDU is compressed, the information contained in the compressed field may be signaled together with the uncompressed field (e.g., a common field). In the case of MU PPDUs, 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 know the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether or not the transmitted MU PPDU was sent to them. Therefore, the AP must transmit the EHT-SIG field with the above information included. To this end, the U-SIG field signals information for efficient transmission of the EHT-SIG field, which may be the number of symbols in the EHT-SIG field and / or the modulation method, MCS. The EHT-SIG field may include size and location information of the RU assigned to each user.

[0073] In the case of an SU PPDU, multiple RUs may be assigned to the STA, and these RUs may be consecutive or discontinuous. If the RUs assigned to the STA are not consecutive, the STA can efficiently receive the SU PPDU only if it recognizes the punctured RU in the middle. Therefore, the AP can transmit the SU PPDU including information about the punctured RUs among the RUs assigned to the STA (e.g., the puncturing pattern of the RUs). That is, in the case of an SU PPDU, the EHT-SIG field may contain a puncturing mode field that includes information on whether a puncturing mode was applied and the puncturing pattern shown in bitmap format or similar, and the puncturing mode field can signal the form of discontinuous channels appearing within the bandwidth.

[0074] The form of the signaled discontinuous channels is limited and, in combination with the value of the BW field, indicates the BW and discontinuous channel information of the SU PPDU. For example, in the case of an SU PPDU, since it is a PPDU transmitted to only one terminal, the STA can recognize the bandwidth allocated to it from the BW field included in the PPDU, and can recognize the punctured resources within the allocated bandwidth from the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the terminal can receive the PPDU with the remaining resource units excluding the specific channel of the punctured resource unit. At this time, the multiple RUs allocated to the STA may consist of different frequency bands or tones.

[0075] The reason only restricted forms of discontinuous channel configurations are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed on each 20MHz subchannel, when puncturing is performed on a bandwidth with multiple 20MHz subchannels, such as 80, 160, and 320MHz, in the case of 320MHz, the usage status of the remaining 15 20MHz subchannels (excluding the primary channel) must be represented, and the discontinuous channel configuration (if a configuration where only the end 20MHz is punctured is also considered discontinuous) must be signaled. Using 15 bits to signal the discontinuous channel configuration for single-user transmission in this way can result in excessive signaling overhead when considering the low transmission speed of the signaling portion.

[0076] This invention proposes a method for signaling the discontinuous channel configuration of an SU PPDU and illustrates the discontinuous channel configuration determined by the proposed method. Furthermore, it proposes a method for signaling the primary 160MHz and secondary 160MHz puncturing configurations of an SU PPDU in a 320MHz BW configuration.

[0077] Furthermore, 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 differs depending on the signaled PPDU format in the PPDU format field. Assuming that the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, one symbol of EHT-SIG-A is further signaled after U-SIG, or it is not necessary to signal EHT-SIG-A from the beginning. Taking this into consideration, it is necessary to fully signal up to 11 puncturing modes using only the BW field of U-SIG. However, in the case of an EHT MU PPDU, EHT-SIG-B is further signaled after U-SIG, so up to 11 puncturing modes can be signaled in a different way than in an SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20MHz or 10MHz bandwidth. Detailed puncturing patterns for each PPDU type will be described in detail in Figures 11 and 12.

[0078] Figure 7(f) shows the format-specific fields of the VD field when EHT MU PPDU is indicated in the U-SIG PPDU format field. 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 fields.

[0079] Figure 8 shows examples of various EHT (Extremely High Throughput) PPDU (Physical Protocol Data Unit) formats and methods for specifying them according to embodiments of the present invention.

[0080] Referring to Figure 8, a PPDU may consist of a preamble and a data portion, and one type of format, EHT PPDU, may be distinguished by a U-SIG field included in the preamble. Specifically, whether or not the PPDU format is an EHT PPDU may be indicated based on the PPDU format field included in the U-SIG field.

[0081] Figure 8(a) shows an example of the 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 may have an EHT-SIG-A field for additional signaling after the U-SIG field.

[0082] Figure 8(b) shows an example of an EHT trigger-based PPDU format, which is an EHT PPDU transmitted based on a trigger frame. An EHT trigger-based PPDU is an EHT PPDU transmitted based on a trigger frame and is an uplink PPDU used as a response to a trigger frame. Unlike an EHT SU PPDU, an EHT PPDU does not have an EHT-SIG-A field after the U-SIG field.

[0083] Figure 8(c) shows an example of the EHT MU PPDU format, which is an EHT PPDU for multiple users. An EHT MU PPDU is a PPDU used to send a PPDU to one or more STAs. In the EHT MU PPDU format, the HE-SIG-B field may be located after the U-SIG field.

[0084] Figure 8(d) shows an example of the EHT ER SU PPDU format used for single-user transmissions with STAs in an extended range. EHT ER SU PPDU may be used for single-user transmissions with STAs in a wider range than EHT SU PPDU described in Figure 8(a), and the U-SIG field may be repeatedly positioned on the time axis.

[0085] The EHT MU PPDU described in Figure 8(c) can be used by an AP to transmit downlink data to multiple STAs. In this case, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive PPDUs transmitted from the AP. The EHT MU PPDU can transmit the AID information of the recipient and / or sender of the PPDU transmitted through the user-specific field of EHT-SIG-B to the STAs. Therefore, multiple terminals that receive the EHT MU PPDU can perform spatial reuse operations based on the AID information in the user-specific field included in the preamble of the received PPDU.

[0086] Specifically, the resource unit allocation (RA) field in the HE-SIG-B field included in the HE MU PPDU may contain information about the configuration of resource units (e.g., resource unit division configuration) within a specific bandwidth on the frequency axis (e.g., 20 MHz). That is, the RA field can instruct the STA on the configuration of resource units divided by the bandwidth for transmitting the HE MU PPDU in order to receive the PPDU. Information about the STA allocated (or specified) to each divided resource unit may be included in the user-specific field of EHT-SIG-B and transmitted to the STA. That is, the user-specific field may contain one or more user fields corresponding to each divided resource unit.

[0087] For example, among the multiple divided resource units, the user field corresponding to at least one resource unit used for data transmission may contain the recipient's or sender's AID, while the user fields corresponding to the remaining resource units not used for data transmission may contain a previously set Null STA ID.

[0088] For the sake of clarity, the terms frame or MAC frame may be used interchangeably with MPDU in this specification.

[0089] When a single wireless communication device communicates using multiple links, the communication efficiency of the wireless communication device can be increased. In this case, a link is a physical path and may be configured as a single wireless medium that can be used to transmit an MSDU (MAC service data unit). For example, if the frequency band of 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 make effective use of multiple channels. Furthermore, when the wireless communication device communicates simultaneously using multiple links, the overall throughput can be increased. However, existing wireless LANs are defined on the premise that one wireless communication device uses one link. Therefore, a wireless LAN operation method for using multiple links is necessary. Referring to Figures 9 to 26, the wireless communication method for a wireless communication device using multiple links will be explained. First, using Figure 9, a specific form of a wireless communication device using multiple links will be explained.

[0090] Figure 9 shows a multi-link device according to an embodiment of the present invention.

[0091] A multi-link device (MLD) may be defined for the wireless communication method using the multiple links described above. A multi-link device can represent a device having one or more affiliated stations. In specific embodiments, a multi-link device can represent a device having two or more affiliated stations. A multi-link device can also exchange multi-link elements. A multi-link element contains information about one or more stations or one or more links. A multi-link element may include the multi-link setup element described later. In this case, the multi-link device may be a logical entity. Specifically, a multi-link device can have multiple affiliated stations. A multi-link device can be called an MLLE (multi-link logical entity) or an MLE (multi-link entity). A multi-link device can have one medium access control service access point (SAP) up to logical link control (LLC). An MLD can also have one MAC data service.

[0092] Multiple stations included in a multilink system can operate on multiple links. Furthermore, multiple stations included in a multilink system can operate on multiple channels. Specifically, multiple stations included in a multilink system can operate on different links or different channels. For example, multiple stations included in a multilink system can operate on different channels of 2.4GHz, 5GHz, and 6GHz.

[0093] The operation of a multilink device can be called multilink operation, MLD operation, or multi-band operation. Furthermore, if the station paired with the multilink device is an AP (Application Platform), the multilink device can be called an AP MLD (Application Platform Multilink). Conversely, if the station paired with the multilink device is a non-AP station, the multilink device can be called a non-AP MLD (Application Platform Multilink).

[0094] Figure 9 illustrates the communication operation between a non-AP MLD and an AP-MLD. Specifically, the non-AP MLD and AP-MLD communicate using three links each. The AP MLD includes the first AP (AP1), the second AP (AP2), and the third AP (AP3). The non-AP MLD includes the first non-AP STA (non-AP STA1), the second non-AP STA (non-AP STA2), and the third non-AP STA (non-AP STA3). The first AP (AP1) and the first non-AP STA (non-AP STA1) communicate via the first link (Link1). The second AP (AP2) and the second non-AP STA (non-AP STA2) communicate via the second link (Link2). The third AP (AP3) and the third non-AP STA (non-AP STA3) communicate via the third link (Link3).

[0095] Multilink operation can include a multilink setup operation. Multilink setup corresponds to the association operation of single-link operation described above and must be performed before frame exchange in multilink. A multilink device can obtain the information necessary for multilink setup from a multi-link setup element. Specifically, the multi-link setup element can include capability information related to multilink. In this case, capability information can include information indicating whether one of the multiple devices included in the multilink device can transmit and the other devices can receive simultaneously. Capability information can also include information about the links available to each station included in the MLD. Capability information can also include information about the channels available to each station included in the MLD.

[0096] Multilink configuration may be established through negotiations between peer stations. Specifically, multilink configuration may be performed through communication between stations without communication with the AP. Furthermore, multilink configuration may be established through any one of the links. For example, even if links 1 through 3 are configured via a multilink, the multilink configuration may be performed through link 1.

[0097] Furthermore, a mapping between TIDs (traffic identifiers) and links may be configured. Specifically, frames corresponding to a specific TID value may be exchanged only through pre-specified links. The mapping between TIDs and links may be configured in a directional-based manner. For example, if multiple links are configured between a first multilink device and a second multilink device, the first multilink device may be configured to send frames with a first TID to multiple first links, and the second multilink device may be configured to send frames with a second TID to the first links. Additionally, a default setting may exist for the mapping between TIDs and links. Specifically, if there are no additional settings in the multilink configuration, the multilink device can exchange frames corresponding to TIDs on each link according to the default setting. In this case, the default setting may be such that all TIDs are exchanged on any one link.

[0098] Let's explain TID in detail. TID is an ID used to classify traffic and data to support QoS (Quality of Service). TID may be used and assigned at layers higher than the MAC layer. TID can also indicate traffic category (TC) and traffic stream (TS). There may be 16 distinct TID values. For example, a TID may be specified as one of the values ​​from 0 to 15. Different TID values ​​may be specified depending on the access policy, channel access, or 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, TID can indicate user priority (UP). In this case, UP may be specified by TC or TS. UP may be assigned at layers higher than MAC. Furthermore, when HCCA (HCF controlled channel access) or SPCA is used, the TID value may be assigned in the range of 8 to 15. When HCCA or SPCA is used, TID can represent TSID. Furthermore, when HEMM or SEMM is used, the TID value may be assigned in the range of 8 to 15. When HEMM or SEMM is used, TID can represent TSID.

[0099] UP and AC (access category) may be mapped. AC may be a label for providing QoS in EDCA. AC may be a label for indicating an EDCA parameter set. EDCA parameters or EDCA parameter sets are parameters used in EDCA channel contention. QoS stations can guarantee QoS using AC. AC can also include AC_BK, AC_BE, AC_VI, and AC_VO. AC_BK, AC_BE, AC_VI, and AC_VO can indicate background, best effort, video, and voice, respectively. AC_BK, AC_BE, AC_VI, and AC_VO may also be classified into sub-ACs. For example, AC_VI can be subdivided into AC_VI primary and AC_VI alternate. Similarly, AC_VO can be subdivided into AC_VO primary and AC_VO alternate. UP or TID may also be mapped to AC. For example, each of 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, each of 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. Furthermore, the priority of 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be in that order from highest to lowest. That is, 1 may have a lower priority and 7 may have a higher priority. Therefore, the priority may be in the order of AC_BK, AC_BE, AC_VI, and AC_VO, from highest to lowest. Furthermore, AC_BK, AC_BE, AC_VI, and AC_VO can each correspond to ACI (AC index) 0, 1, 2, and 3, respectively. Due to these characteristics of TIDs, the mapping between TIDs and links can represent the mapping between ACs and links.Furthermore, the mapping between links and ACs can represent the mapping between TIDs and links.

[0100] As mentioned above, a TID may be mapped to each of multiple links. The mapping may specify which links can exchange traffic corresponding to a particular TID or AC. Additionally, TIDs or ACs that can be transmitted in different transmission directions within a link may be specified. As mentioned above, a default setting may exist for the mapping between TIDs and links. Specifically, in a multilink configuration where no additional settings are made, the multilink device can exchange frames corresponding to TIDs 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 always be mapped to at least one link. Management frames and control frames may be transmitted on all links.

[0101] When a link is mapped to a TID or AC, only data frames corresponding to the TID or AC mapped to that link may be transmitted on that link. Therefore, when a link is mapped to a TID or AC, frames that do not correspond to a TID or AC not mapped to that link do not need to be transmitted on that link. When a link is mapped to a TID or AC, the 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 TIDs and links. Furthermore, in other specific embodiments, the mapping between TIDs and links may be determined based on a block ACK agreement. Specifically, a block ACK agreement may be set for a TID mapped to a particular link.

[0102] The aforementioned mapping of TIDs to links may ensure QoS. Specifically, a relatively small number of stations may be operational, or higher-priority ACs or TIDs may be mapped to links with good channel conditions. Furthermore, the aforementioned mapping of TIDs to links may enable stations to maintain a power-saving state for longer periods.

[0103] Figure 10 shows that, according to an embodiment of the present invention, transmissions on different links are performed simultaneously in multilink operation.

[0104] The implementation of multilink devices does not always support simultaneous operation on multiple links. For example, a multilink device may support simultaneous transmission on multiple links, simultaneous reception on multiple links, or transmission on one link while receiving on another. Reception or transmission on one link may affect reception or transmission on other links. Specifically, transmission on one link may act as interference on other links. Interference from one link of a multilink device affecting other links can be called internal leakage. Internal leakage tends to increase as the frequency spacing between links decreases. If internal leakage is not too large, transmission on one link can occur while transmission is occurring on other links. If internal leakage is large, transmission on one link cannot occur while transmission is occurring on other links. Thus, simultaneous operation of multiple links by a multilink device can be called STR (simultaneous transmit and receive, simultaneous transmission and reception). For example, when a multilink device transmits on multiple links simultaneously, transmits on one link while receiving on another, or receives on multiple links simultaneously, this can be called STR (Simultaneous Transmission / Reception).

[0105] As mentioned earlier, multilink devices can support STR (Stroke Response) both fully and with limitations. Specifically, multilink devices can only support STR under certain conditions. For example, a multilink device may not be able to perform STR when operating as a single radio. Similarly, a multilink device may not be able to perform STR when operating as a single antenna. Furthermore, a multilink device may not be able to perform STR if internal leakage is detected to be above a predetermined level.

[0106] A station can exchange information with other stations regarding its STR capability. Specifically, a station can exchange information with other stations regarding whether there are limitations on its ability to transmit or receive on multiple links simultaneously. Specifically, information regarding limitations on the ability to transmit or receive on multiple links may indicate whether transmission or reception occurs simultaneously on multiple links, or whether transmission and reception occur simultaneously. Furthermore, information regarding limitations on the ability to transmit or receive on multiple links may be indicated in stages. Specifically, information regarding limitations on the ability to transmit or receive on multiple links may be information indicating stages indicating the magnitude of internal leakage. In a specific embodiment, information indicating stages indicating the magnitude of internal leakage may be information indicating stages indicating the magnitude of interference caused by internal leakage. In yet another specific embodiment, it may be information indicating stages indicating the frequency spacing between links that may affect internal leakage. Furthermore, information indicating stages indicating the magnitude of internal leakage may be information indicating the relationship between the frequency spacing between links and the magnitude of internal leakage in stages.

[0107] In Figure 10, the first station (STA1) and the second station (STA2) are affiliated to a single non-AP multilink device. Alternatively, the first AP (AP1) and the second AP (AP2) may also be affiliated to a single non-AP multilink device. A first link (link1) is established between the first AP (AP1) and the first station (STA1), and a second link (link2) is established between the second AP (AP2) and the second station (STA2). In Figure 10, the non-AP multilink device can perform STR (Signal Transmitting) to a limited extent. When the second station (STA2) transmits on the second link (Link2), reception by the first station (STA1) on the first link (Link1) may be interfered with by transmission on the second link (Link2). For example, in the following case, reception by the first station (STA1) on the first link (Link1) may be interfered with by transmission on the second link (Link2). On the second link (Link2), the second station (STA2) transmits the first data (Data1), and the first access point (AP1) transmits an acknowledgment (Ack for Data1) to the first station (STA1). On the second link (Link2), the second station (STA2) transmits the second data (Data2). At this time, the transmission timing of the second data (Data2) and the transmission timing of the acknowledgment (Ack for Data1) may overlap. In this case, the transmission to the second station (STA2) on the second link (Link2) may cause interference on the first link (Link1). Therefore, the first station (STA1) may not receive the acknowledgment (Ack for Data1) for the first data (Data1).

[0108] This section describes how a multilink device performs channel access. For multilink operations not specifically described, the channel access procedure shown in Figure 6 can be followed.

[0109] A multilink device can perform channel access independently from multiple links. In this case, the channel access may be backoff-based channel access. When the multilink device performs channel access independently from multiple links and the backoff counters reach 0 on multiple links, the multilink device can start transmitting on multiple links simultaneously. In a specific embodiment, when the backoff counter of any one of the links in the multilink reaches 0 and a predetermined condition is met, the multilink device can perform channel access on other links where the backoff counter has not reached 0, in addition to the link where the backoff counter reached 0. Specifically, when the backoff counter of any one of the links in the multilink reaches 0, the multilink device can sense energy on other links where the backoff counter has not reached 0. In this case, if no energy greater than a predetermined amount is sensed, the multilink device can perform channel access on the link where energy sensing was performed, in addition to the link where the backoff counter reached 0. This allows the multilink device to start transmitting on multiple links simultaneously. The size of the threshold used for energy sensing may be smaller than the size of the threshold used when deciding whether to decrease the backoff counter. Furthermore, when deciding whether to reduce the backoff counter, the multilink device can sense any form of signal, not just Wi-Fi signals. Also, in the energy sensing described above, the multilink device can sense any form of signal, not just Wi-Fi signals. Internal leakage may not be detected as a Wi-Fi signal. In such cases, the multilink device can detect the signal detected by internal leakage through energy sensing. Also, as mentioned above, the size of the threshold used for energy sensing can be smaller than the size of the threshold used when deciding whether or not to reduce the backoff counter. Therefore, even when transmission is taking place on one link, the multilink device can reduce the backoff counter on other links.

[0110] The degree of interference between links used by the multilink device may determine whether the stations operating on each link can operate independently. In this case, the degree of interference between links may be the magnitude of interference perceived by other stations of the multilink device when any one station of the multilink device transmits on any one link. If the transmission of the first station of the multilink device on the first link causes interference exceeding a predetermined magnitude to the second station of the multilink device operating on the second link, the operation of the second station may be restricted. Specifically, the reception or channel access of the second station may be restricted. When interference occurs, the second station may fail to decode the received signal due to the interference. Also, when interference occurs, the second station may determine that the channel is in use when using backoff for channel access.

[0111] Furthermore, if the transmission from the first station of a multilink device on the first link causes interference below a predetermined magnitude to the second station of the multilink device operating on the second link, the first and second stations can operate independently. Specifically, if the transmission from the first station of a multilink device on the first link causes interference below a predetermined magnitude to the second station of the multilink device operating on the second link, the first and second stations can independently access the channel. Also, if the transmission from the first station of a multilink device on the first link causes interference below a predetermined magnitude to the second station of the multilink device operating on the second link, the first and second stations can independently transmit or receive. When interference below a predetermined magnitude occurs, the second station can successfully decode the received signal even in the presence of interference. Also, when interference below a predetermined magnitude occurs, the second station can determine that the channel is idle when using backoff for channel access.

[0112] The degree of interference between stations in a multilink system can vary not only depending on the interval between the frequency bands of the links on which the stations operate, but also on the hardware characteristics of the multilink system. For example, internal interference in a multilink system that includes high-RF (radio frequency) equipment may be less than internal interference in a multilink system that includes low-RF equipment. Therefore, the degree of interference between stations in a multilink system may be determined based on the characteristics of the multilink system.

[0113] Figure 10 shows that the magnitude of interference varies depending on the interval between the frequency bands of the links and the characteristics of the multilink device. In the embodiment shown in Figure 10, the first multilink device (MLD#1) includes a first station (STA1)-1 operating on the first link (Link1) and a second station (STA1)-2 operating on the second link (Link2). The second multilink device (MLD#2) includes a first station (STA2)-1 operating on the first link (Link1) and a second station (STA2)-2 operating on the second link (Link2). The frequency interval between the first link (Link1) and the second link (Link2) in which the first multilink device (MLD#1) operates is the same as the frequency interval between the first link (Link1) and the second link (Link2) in which the second multilink device (MLD#2) operates. However, the magnitude of interference differs due to the difference between the characteristics of the first multilink device (MLD#1) and the characteristics of the second multilink device (MLD#2). Specifically, the magnitude of interference generated by the second multilink device (MLD#2) may be greater than the magnitude of interference generated by the first multilink device (MLD#1). Considering that the magnitude of interference may differ depending on the characteristics of the multilink devices, and that the availability of STR support may vary for each multilink device, it is necessary to exchange information regarding whether or not STR support is provided.

[0114] A multilink device can signal whether or not a station it includes provides STR support. Specifically, an AP multilink device and a non-AP multilink device can exchange whether or not an AP included in the AP multilink device provides STR support and whether or not a STA included in the non-AP multilink device provides STR support. In such an embodiment, an element indicating the presence or absence of STR support may be used. This element can be called an STR support element. The STR support element can indicate, with one bit, whether or not a station in the multilink device that transmitted the STR support element provides STR support. Specifically, the STR support element can indicate, one bit at a time, whether or not each station included in the multilink device that transmitted the STR support element provides STR support. In this case, the bit value may be 1 when the station provides STR support, and 0 when the station does not provide STR support. If the multilink device that transmits the STR support element includes a first station (STA1), a second station (STA2), and a third station (STA3), and the first station (STA1) and the third station (STA3) support the STR, but the second station (STA2) does not, then the STR support element is 101 1b The STR support element may include a field containing a bit. It is assumed that stations operating in different frequency bands support each other, and the STR support element may omit signaling for the presence or absence of STR support between stations operating in different frequency bands. For example, suppose the first station (STA1) operates on the 2.4GHz first link, and the second station (STA2) and third station (STA3) operate on the 5GHz second and third links, respectively. In this case, the STR support element can indicate with one bit that STR support is provided between the second station (STA2) and the third station (STA3). The STR support element may also contain only one bit if there are two stations to which the STR support element signals.

[0115] In a specific embodiment, the relationship between a link located at 2.4 GHz and a link located at 5 GHz or 6 GHz in a multilink device may always be considered a STR (Structured Link). Therefore, signaling for the presence or absence of a STR between the 2.4 GHz link and the 5 GHz or 6 GHz link may be omitted.

[0116] In the embodiments described above, what is described as the operation of a station in a multilink device may be replaced with the operation of a multilink device. Also, in the embodiments described above, the operation of an AP may be replaced with the operation of a non-AP station, and the operation of a non-AP station may be replaced with the operation of an AP. Therefore, the operation of an AP in a non-STR multilink device may be replaced with the operation of a non-AP station in a non-STR multilink device, and the operation of a non-AP station in an STR multilink device may be replaced with the operation of an AP in an STR multilink device. Furthermore, the operation of a non-AP station in a non-STR multilink device may be replaced with the operation of an AP in a non-STR multilink device, and the operation of an AP in an STR multilink device may be replaced with the operation of a non-AP station in an STR multilink device.

[0117] Figure 11 shows the operation of a multilink device when the link is changed according to one embodiment of the present invention.

[0118] The STR support element may be replaced when the link frequency bandwidth is changed. As mentioned above, the presence or absence of STR support at a station may depend on the distance between the link frequency bandwidths, and the presence or absence of STR support at a station may change when the link frequency bandwidth is changed. When the link frequency bandwidth is changed, this may include at least one of the following: a change in the link center frequency, a change in the bandwidth of the frequency band, and a 20MHz main channel. The AP and the station can replace the STR support element by request and response. Furthermore, in other specific embodiments, the STR support element may be replaced without further request when the link frequency bandwidth is changed. Also, in the embodiments described above, when the link frequency bandwidth is changed, this may include a change in the station's operating channel.

[0119] If a station of a non-AP multilink device is unable to perform a STR (Stroke Response), the station may request a link change from the AP (Application Platform). Specifically, the station may request a change to at least one of the following: a change in the center frequency, a change in the bandwidth of the frequency band, and a change in the 20 MHz main channel. The link change request may be transmitted to the AP through the link to which the change is requested. In yet another specific embodiment, the link change request may be transmitted to the AP through a link that is not to be changed. In this case, the link change request may include information indicating which link is to be changed. The information indicating the link may be a number that identifies the link. In such an embodiment, the link change may be a change in the operating channel within a single frequency band. The link change may also include information about how the link is changed. Specifically, the link change request may indicate moving the center frequency of the link to a higher frequency than the current center frequency, or moving the center frequency of the link to a lower frequency than the current center frequency. In yet another specific embodiment, the link change request may implicitly indicate a change to a frequency band that moves away from adjacent links. Furthermore, a link change request may indicate a reduction in link bandwidth. A link change request may also request a change in the location of the primary channel. Specifically, a link change request may indicate a change in the location of the primary channel to a channel in a lower or higher frequency band than the current primary channel location. An AP receiving a link change request may change the link in response to the request. In a specific embodiment, an AP receiving a link change request may also ignore it.

[0120] In the embodiment shown in Figure 11, the second station (STA2) and third station (STA3) of the non-AP multilink device are unable to support STR. The non-AP multilink device requests the AP multilink device to change the third link (Link3). Upon receiving the link change request, the AP multilink device changes the operating link of the third AP (AP3). At this time, the third station (STA3) operating on the third link (link3) to be changed can send a change request to the third AP (AP3). Furthermore, in other specific embodiments, a station that does not operate on the third link (link3) can send a change request to an AP that does not operate on the third link (link3).

[0121] When an AP changes links, it can broadcast information about the link change using a beacon frame. This link change information may include information about the link frequency. This information may include at least one of the following: changes to the link's center frequency, operating bandwidth, and primary channel. The link change information may also include information about the timing of the link change. Furthermore, the link change may be completed when the beacon containing the link change information is transmitted.

[0122] In Figure 11, the link on which the third station (STA3) operates is changed, and both the third station (STA3) and the second station (STA2) can support the STR. As mentioned earlier, the non-AP multilink device can transmit an STR support element to the AP multilink device and signal whether or not the STR support has been changed.

[0123] As mentioned above, link changes may not be permitted, or STR may not be supported even with a link change. Also, as shown in the embodiment in Figure 11, AP multilink devices may support STR, while non-AP multilink devices may not. This is because AP multilink devices generally use relatively high-RF equipment, while non-AP multilink devices generally use relatively low-RF equipment. Therefore, a method is needed for efficient communication between multilink devices even when one of the multilink devices does not support STR. In this case, STR can represent simultaneous transmission and reception. This is explained in Figure 12.

[0124] Figure 12 shows that, according to one embodiment of the present invention, when one station of the non-STR multilink device is receiving, channel access for other stations of the non-STR multilink device is prohibited.

[0125] When transmission occurs on one link of a non-STR multilink device and reception occurs on the other links, both reception and transmission may fail. To resolve this, channel access may be prohibited on the other links of the non-STR multilink device when reception occurs on one link. Specifically, when reception occurs on one link of the non-STR multilink device, backoff of channel access may be prohibited on the other links. This prevents transmission from starting on the other links of the non-STR multilink device when reception occurs on one link. In a specific embodiment, backoff of channel access may be prohibited on the other links of the non-STR multilink device when reception starts on one link. This may be set by a specific bit in memory, such as a channel access prohibition flag. The presence or absence of channel access prohibition may be shared by the memory inside the multilink device. Such an embodiment allows channel access prohibition to be implemented without separate frame exchange. For the sake of clarity, as used herein, channel access prohibition, unless otherwise specified, refers to prohibiting channel access or transmission in order to protect the transmission or reception of non-STR multilink equipment.

[0126] When channel access is prohibited, stations operating on the prohibited link cannot perform backoff procedures regardless of NAV and CCA results. Furthermore, when channel access is prohibited, stations operating on the prohibited link cannot transmit regardless of NAV and CCA results. However, even when channel access is prohibited, stations operating on the prohibited link can still receive. Additionally, a channel access prohibition on the second link due to reception on the first link may be lifted based on the completion of reception on the first link. Specifically, a channel access prohibition on the second link due to reception on the first link may be lifted when reception on the first link is completed. Furthermore, in other specific embodiments, a channel access prohibition on the second link due to reception on the first link may be lifted based on the point at which an ACK is sent after reception on the first link is completed. Specifically, a channel access prohibition on the second link due to reception on the first link may be lifted at the point at which an ACK is sent after reception on the first link is completed. In further specific embodiments, channel access prohibition on the second link due to reception on the first link may be lifted when the ACK transmission is completed after reception is completed on the first link. Also, immediately after the channel access prohibition is lifted, the station can immediately decrement the backoff counter without additional sensing. In this case, the additional sensing can represent sensing performed between DIFS (DCF Interframe Space). In yet another specific embodiment, immediately before the channel access prohibition is lifted, if the channel is idle for a predetermined time, the station can immediately decrement the backoff counter without additional sensing. In this case, the predetermined time may be one of PIFS (PCF Interframe Space), DIFS, SIFS (Short Interframe Space), and AIFS (Arbitration Interframe Space).

[0127] In the embodiment of FIG. 12, the non-STR multi-link device comprises a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). Intra-device interference occurs when the second station (STA2) performs transmission on the second link (Link2) while the first station (STA1) performs reception. As described above, channel access of the second station (STA2) performed on the second link (Link2) is prohibited while the first station (STA1) operating on the first link (Link1) performs reception. After the reception of the first station (STA1) on the first link (Link1) is completed, the channel access prohibition is lifted. Immediately after the channel access prohibition is lifted, the second station (STA2) can decrement the previous backoff counter value by 1 from 3 to 2 without additional sensing.

[0128] For convenience of expression, in FIG. 12, Rx and Tx are represented using a single block (Tx solid line, Rx dotted line), and it may be understood that the single block represents an operation including Tx / Ack reception and Rx / Ack transmission even if a separate Ack block is not shown. This may also be equally applied to the drawings described hereinafter.

[0129] When a station confirms that the intended receiver of a PPDU received by the station is not the station itself, the station may suspend reception of the PPDU. In such a case, the channel access prohibition lifting operation of the multi-link device becomes problematic. In the present specification, the intended recipient is used interchangeably with the target station.

[0130] FIG. 13 shows an operation of lifting channel access prohibition when it is confirmed that the intended receiver of a PPDU received by a station of a non-STR multi-link device is not the station itself according to an embodiment of the present invention.

[0131] If a station confirms that it is not the intended recipient of the PPDU it receives, it can lift the channel access ban. The station can determine whether it is the intended recipient of the PPDU based on the information indicating the recipient address in the PPDU's signaling field. In this case, the information indicating the recipient address in the PPDU's signaling field may be the value of the STA-ID field in the EHT-SIG field as described above. Specifically, the station can determine whether the STA-ID field in the EHT-SIG field points to the station. The station can also determine whether it is the intended recipient of the PPDU based on the value of the RA field in the MAC frame contained in the PPDU. Specifically, the station can determine whether the RA field in the MAC frame contained in the PPDU points to the station. In Figure 13, the non-STR multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The first station (STA1) receives the PPDU. The first station (STA1) determines that the intended recipient of the received PPDU is not the first station (STA1) and interrupts the reception of the PPDU. At this time, the first station (STA1) can lift the channel access ban on the second station (STA2). Even after the channel access ban on the second station (STA2) is lifted, channel access on the second station (STA2) may be delayed by the NAV set on the second station (STA2).

[0132] As shown in Figure 13, even after channel access restrictions are lifted, stations included in non-STR multilink devices often have fewer channel access opportunities than stations not included in multilink devices or stations included in STR multilink devices. Therefore, a method is needed to compensate for the channel access opportunities of stations included in non-STR multilink devices in order to ensure fair competition with other stations. For example, immediately after the channel access restriction is lifted, it may be permissible for a station whose channel access restriction has been lifted to reduce its backoff counter by 2 or more. This will be explained in Figure 14.

[0133] Figure 14 shows that a station according to an embodiment of the present invention performs channel access after the channel access prohibition is lifted.

[0134] A station whose channel access ban has been lifted can reduce its backoff counter by 2 or more immediately after the ban is lifted. This is to ensure fairness in channel access opportunities among stations, as other stations performed the backoff procedure while the station's channel access was banned.

[0135] In further specific embodiments, a station whose channel access is prohibited can perform a channel access procedure to reduce the CCA (CSMA) and backoff counter while channel access is prohibited. In Figure 14, a non-STR multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). In Figure 14, channel access for the second station (STA2) is prohibited while the first station (STA1) is receiving. In Figure 14(a), while channel access for the second station (STA2) is prohibited, the second station (STA2) can perform a channel access procedure to reduce the CCA (CSMA) and backoff counter. In Figure 14(a), while channel access for the second station (STA2) is prohibited, the channel on the second link (Link2) is idle, so the second station (STA2) reduces the backoff counter.

[0136] Furthermore, a station whose channel access is prohibited can delay transmission even if the backoff counter reaches 0 during the period when channel access is prohibited. In this case, the station can maintain the backoff counter value at 0. Also, even if the station delays transmission, the station can maintain the CW value as is. Therefore, this is differentiated from the station doubling the CW value because the channel it is accessing is busy. This is because the reason for the transmission delay is not that the channel was determined to be in use. In Figure 14(b), while channel access for the second station (STA2) is prohibited, the second station (STA2) can perform channel access procedures to reduce the CCA (CSMA) and backoff counter. In Figure 14(b), while channel access for the second station (STA2) is prohibited, the channel on the second link (Link2) is idle, so the second station (STA2) reduces the backoff counter. While channel access for Station 2 (STA2) is prohibited, Station 2's (STA2) backoff counter reaches 0. Station 2 (STA2) delays transmission and begins transmitting after the channel access prohibition is lifted.

[0137] As mentioned above, channel access prohibition may include prohibiting transmission to the second station when the first station of a non-STR multilink device is transmitting. Furthermore, channel access prohibition may also include prohibiting transmission by the second station when the first station of a non-STR multilink device is receiving.

[0138] In the embodiment described in Figure 14(b), if multiple stations have channel access prohibited, there is a high probability that the channel access prohibition will be lifted simultaneously for multiple stations, and multiple stations will attempt to transmit at the same time. Therefore, a method is needed to reduce the probability of transmission collisions. This will be explained in Figure 15.

[0139] Figure 15 shows the operation of a station according to one embodiment of the present invention, which transmits after the channel access ban is lifted.

[0140] As mentioned above, in a non-STR multilink device, transmission may occur on the first link while transmission is prohibited on the second link. If the transmission is completed on the first link, transmission on the second link may begin with RTS / CTS frame exchange. Therefore, when transmission occurs on the first link among the multiple links in which a non-STR multilink device operates, the non-STR multilink device can begin RTS / CTS frame exchange on the second link. After the channel access prohibition is lifted for a station whose transmission has been delayed due to channel access prohibition, the station can begin RTS / CTS (request to send / clear to send) frame exchange before starting the delayed transmission. At this time, if the station cannot receive a CTS frame, it may not be able to start the delayed transmission. In the embodiment shown in Figure 15(a), the station whose transmission has been delayed due to channel access prohibition sends an RTS frame before starting the delayed transmission. After the station receives a CTS frame as a response to the RTS frame, it starts the delayed transmission.

[0141] In another specific embodiment, after a station whose transmission has been delayed due to channel access prohibition has had its channel access prohibition lifted, the station can transmit a frame containing only a portion of the delayed transmission. In this case, after the station receives a response, such as an ACK, to the frame containing only a portion of the delayed transmission, the station can transmit the untransmitted portion of the delayed transmission. If the station does not receive a response to the frame containing only a portion of the delayed transmission, the station does not need to transmit the untransmitted portion of the delayed transmission. Thus, the reason why a station can start RTS / CTS exchange or transmit only a portion of the delayed transmission after channel access prohibition is lifted is because the probability of a collision in transmissions after channel access prohibition is higher than in general transmissions. Therefore, the above-described embodiment may be mandatory for transmissions made after channel access prohibition is lifted. In existing wireless LAN operations, RTS / CTS frames have been used to solve the hidden node problem and could be used based on the size of the transmitted data. In the above-described embodiment, the RTS / CTS frame is intended to prevent transmission collisions with stations attempting to perform delayed transmissions to protect the transmission or reception of non-STR multilink devices.

[0142] As mentioned above, when one station of a non-STR multilink device is receiving, transmission by other stations of the non-STR multilink device may be restricted. Also, when one station of a non-STR multilink device is transmitting, it may be difficult for other stations of the non-STR multilink device to accurately sense the channel status of the link on which the station is operating. Specifically, when the first station of a non-STR multilink device is transmitting, the second station of the non-STR multilink device may always determine that the channel status of the link on which the second station is operating is busy. For this reason, the second station may determine that the channel is in use due to internal interference, even when the channel on the link on which the second station is operating is idle. In this way, when a station cannot determine the channel status due to internal interference, or when one station of the non-STR multilink device is continuing to transmit, the other stations of the non-STR multilink device are said to be in a blind state. Due to the circumstances described above, a station in a blind state may find it difficult to attempt to transmit by performing a backoff procedure. Furthermore, stations in a blind state due to the aforementioned circumstances will likely have difficulty in initiating PPDU reception or successfully decoding it. Therefore, a transmission method that takes blind stations into consideration is necessary. This will be explained in Figure 16.

[0143] Figure 16 shows a transmission performed based on the status of a station in a non-STR multilink device according to an embodiment of the present invention.

[0144] A station attempting to transmit to a station in a non-STR multilink device can decide whether or not to transmit based on whether the non-STR multilink device station is blinded. In this case, the station attempting to transmit to a station in a non-STR multilink device may be a station included in an STR multilink device. Alternatively, the station attempting to transmit to a station in a non-STR multilink device may be an AP included in an AP multilink device, and the non-STR multilink device may be a non-AP multilink device. A station attempting to transmit to a station in a non-STR multilink device can determine whether or not the non-STR multilink device station is blinded. The station attempting to transmit can determine whether or not other stations in the multilink device that it includes are currently transmitting to the non-STR multilink device. If other stations in the multilink device that it includes are currently receiving from the non-STR multilink device, the station can determine that the non-STR multilink device station receiving the station's transmission is blinded. In the embodiment shown in Figure 16, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The second station (STA2) is transmitting to the second AP (AP2). Therefore, the second AP (AP2) can inform the first AP (AP1) that it is receiving from the second station (STA2). Specifically, the second AP (AP2) can inform the first AP (AP1) that the entity transmitting to the second AP (AP2) is the second station (STA2). In yet another specific embodiment, the second AP (AP2) can inform the first AP (AP1) that the second station (STA2) is currently transmitting.At this time, the first AP (AP1) can determine, based on the notification, that the first station (STA1) is in a blind state.

[0145] Since stations within a multilink device can operate via a common MAC, the information exchange between the first AP (AP1) and the second AP (AP2) described above may not be explicitly performed.

[0146] A station does not need to transmit to a station that is blind. This is because even if a station transmits to a blind station, there is a high probability that the blind station will not be able to disclose its reception or will not be able to decode the PPDU. In this case, the station can cancel the transmission to the blind station and transmit to another station.

[0147] When an STR multilink device transmits to a non-STR multilink device, the STR multilink device can transmit to the non-STR multilink device on multiple links. Specifically, when the STR multilink device transmits to a non-STR multilink device on the first link, the STR multilink device can start transmitting to the non-STR multilink device on the second link. At this time, the STR multilink device can determine the length of the transmission on the second link based on the fact that it is a transmission to a non-STR multilink device. Specifically, the STR multilink device can determine the length of the transmission to the non-STR multilink device on the second link based on the length of the transmission to the non-STR multilink device on the first link. In a specific embodiment, the STR multilink device can complete the transmission on the first link and the transmission on the second link simultaneously. This is to prevent transmission to other stations of the non-STR multilink device from occurring while a transmission to one of the non-STR multilink device stations is completed and that station is sending a response to the transmission, such as an ACK. In the embodiment described above, multiple stations of the non-STR multilink device can simultaneously send responses to transmissions to multiple stations.

[0148] STR multilink devices cannot determine the status of stations included in non-STR multilink devices in real time. Therefore, even if the STR multilink device operates as described in the embodiment in Figure 16, interference or transmission collisions may occur between links where non-STR multilink devices are operating. For example, in the embodiment in Figure 16, the first AP (AP1) may start transmitting to the first station (STA1) before the second station (STA2) recognizes that it is in the process of transmitting to the second AP (AP2). In this way, the probability of interference or collisions between links may be greater than the probability of interference or transmission collisions within a link. This will be explained in more detail in Figure 17.

[0149] Figure 17 shows a situation in which interference or collision between links may occur.

[0150] A transmission collision may occur between links when the transmission from the second station of a non-STR station multilink device to the second AP of an STR AP multilink device begins simultaneously with the transmission from the first AP of an STR AP multilink device to the first station of a non-STR station multilink device. This is shown in Figure 17(a). As mentioned above, this can occur because the STR multilink device cannot determine the state of stations included in the non-STR multilink device in real time.

[0151] Furthermore, even if the transmission from the second station of a non-STR station multilink device to the second AP of an STR AP multilink device begins earlier than the transmission from the first AP of an STR AP multilink device to the first station of a non-STR station multilink device, a transmission collision can still occur between links. This is shown in Figure 17(b). This is because it may take time for the second AP (AP2) to inform the first AP (AP1) that the second station (STA2) is performing a transmission. Thus, transmission collisions can occur even between stations that start transmitting at different times, so the probability of interference or a transmission collision between devices may be greater than the probability of interference or a collision within a link. Also, the longer the time it takes for an AP of an STR multilink device to identify the sender of the PPDU it receives, the greater the probability of interference or a transmission collision between links may become. Therefore, a method to resolve this is necessary. When one of the stations of an STR multilink device is performing a reception, other stations of the STR multilink device do not need to access the channel. However, if channel access is prohibited in this way, the meaning of the STR function may be lost. Therefore, an operating method that does not prohibit channel access is required for the STR multilink device. This is explained in Figure 18.

[0152] As mentioned above, it can be important for a multilink device to quickly determine which station is transmitting to it. The User field of the EHT-SIG in an EHT UL PPDU can indicate the identifier (STA-ID) of the station transmitting the EHT UL PPDU. Specifically, if the DL / UL field in the signaling field of the EHT PPDU indicates that the EHT PPDU is a UL PPDU, the User field of the EHT-SIG in the EHT PPDU can indicate the identifier of the station transmitting the EHT UL PPDU. A multilink device receiving an EHT PPDU can identify the station transmitting the EHT PPDU based on the User field of the EHT-SIG in the EHT UL PPDU. This allows the AP multilink device to determine which station is transmitting the EHT UL PPDU, and to determine the destination device for the transmission. Specifically, the AP multilink device can determine whether the transmission it is attempting is likely to fail due to an inter-link collision. Furthermore, if there is a high probability that the transmission that the AP multilink device is attempting to perform will fail, the AP multilink device may delay the transmission it is attempting and perform another transmission.

[0153] Figure 18 shows the operation in which an STR multilink device ceases transmission to a non-STR multilink device according to one embodiment of the present invention.

[0154] If a station in an STR multilink device determines that a station in a non-STR multilink device is blind while it is transmitting to that station, the STR multilink device can interrupt the transmission to the blind non-STR multilink device station. Specifically, the STR multilink device can determine whether a station in a non-STR multilink device is blind based on the value indicated as the STA(AID)-ID in the signaling field of the received PPDU or the TA (transmitting address) field of the MAC frame contained in the received PPDU. In this case, the STA-ID may be a value indicating the station transmitting the UL PPDU in the UL PPDU. In a specific embodiment, the STR multilink device can determine that a second station included in the non-STR multilink device is blind if the value indicated as the STA(AID)-ID in the signaling field of the received PPDU indicates a first station included in the non-STR multilink device. Furthermore, the STR multilink device can determine that a second station included in the non-STR multilink device is in a blind state if the TA field of the MAC frame contained in the received PPDU indicates a first station included in the non-STR multilink device. First, we will explain the operation of the station after transmission cancellation.

[0155] If a TXOP remains set on a station of a non-STR multilink device, a station that has canceled a transmission to that non-STR multilink device station may attempt to transmit to another station other than the said non-STR multilink device station. In this case, the station that canceled the transmission to the non-STR multilink device station can transmit to another station other than the non-STR multilink device station without a separate backoff procedure. In a specific embodiment, after canceling a transmission to a non-STR multilink device station, if the channel is detected as idle for a predetermined time interval without a separate backoff procedure, the station that canceled the transmission to the non-STR multilink device station can transmit to another station other than the non-STR multilink device station. In this case, the predetermined time interval may be any one of SIFS, PDIF, and DIFS.

[0156] A station that has canceled a transmission to a non-STR multilink device station may, when transmitting to other stations other than the non-STR multilink device station, transmit traffic with the same priority as the traffic for the canceled transmission, or traffic with a higher priority. This is because transmitting traffic with a lower priority than the traffic used for channel access for the canceled transmission would be unfair. In the embodiment described above, the STR multilink device station may be an AP.

[0157] A station that has canceled a transmission to a non-STR multilink station can initialize its configured TXOP. Specifically, a station that has canceled a transmission to a non-STR multilink station can send a CF-End frame after the cancellation. This allows other stations operating on the link that was scheduled to transmit to use the link.

[0158] In Figure 18, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The second station (STA2) is transmitting to the second AP (AP2). While the first AP (AP1) is transmitting to the first station (STA1), it determines that the first station (STA1) is in a blind state. Therefore, the first AP (AP1) interrupts the transmission to the first station (STA1). In Figure 18(a), after interrupting the transmission to the first station (STA1), the first AP (AP1) performs a transmission to a station other than the first station (STA1), as described in the embodiment above. In Figure 18(b), after interrupting transmission to the first station (STA1), the first AP (AP1) transmits a CF-END frame as described in the embodiment later.

[0159] When a station interrupts transmission, it does not need to send the next fragment after sending the fragment that was being transmitted. Furthermore, in other specific embodiments, the station may immediately stop transmitting the packet that was being transmitted.

[0160] In the embodiment described above, when an STR multilink device interrupts transmission to a non-STR multilink device station that is in a blind state and transmits to other stations other than the non-STR multilink device station that is in a blind state, it is necessary to inform the other stations that transmission to them may be taking place in order to ensure stable reception. The method for doing so will be described below. For the sake of explanation, other stations other than the non-STR multilink device station that is in a blind state will be referred to as "other stations".

[0161] A station in an STR multilink device can insert the addresses of other stations into MAC frames. Specifically, a station in an STR multilink device can insert the address of the intended recipient of the MAC frame into the RA (receiving address) of the MAC frame, and insert the address of another station into a separate field. In yet another specific embodiment, a station in the device can insert the address of another station into the EHT-SIG. Specifically, a station in an STR multilink device can insert the address of the intended recipient of the PPDU and the address of another station into the User field of the PPDU's signaling field. In this case, the address of the other station may be inserted after the address of the intended recipient of the PPDU in the User field of the PPDU's signaling field.

[0162] In another specific embodiment, the station can monitor PPDU reception for a predetermined time even after recognizing that the intended recipient of the received PPDU is not the station. Specifically, the station can monitor for a predetermined time whether PPDU reception continues even after recognizing that the intended recipient of the received PPDU is not the station. This allows the station to determine whether PPDU transmission has been interrupted and whether transmission to the station has begun. In such an embodiment, if it is determined that PPDU transmission will continue for the predetermined time, the station can enter a doze state. If it is determined that PPDU transmission will not continue for the predetermined time, the station can maintain a wake-up state. At this time, if a new PPDU is received by the station, the station can decode the PPDU.

[0163] In another specific embodiment, a station transmitting a PPDU may insert information into the PPDU that signals that the transmission of the PPDU may be interrupted. This information may be a 1-bit subfield. For example, if the value of the subfield that signals that the transmission of the PPDU may be interrupted is 1, a station receiving the PPDU can determine that the transmission of the PPDU may be interrupted before the time indicated by the Length field of the PPDU's signaling field and the Duration field of the MAC frame. If a station determines that the transmission of the PPDU may be interrupted before the time indicated by the Length field of the PPDU's signaling field and the Duration field of the MAC frame, the station may delay entering a power-saving state. Alternatively, a station transmitting a PPDU may insert information into the PPDU's reserved field that signals that the transmission may be interrupted.

[0164] In this way, canceling or interrupting transmissions can prevent unnecessary channel occupancy.

[0165] When transmission is interrupted or delayed due to a link-to-link transmit collision, the CW value used for channel access may be doubled, similar to a general transmit failure. However, when transmission is interrupted or delayed due to a link-to-link transmit collision, unlike a general channel access failure or transmit failure, the CW value used for channel access does not need to be doubled. In other words, the station can maintain the same CW value used for channel access. Doubling the CW value increases the range of possible values ​​for the backoff counter and reduces the probability of a transmit collision. This need may be reduced if the station can clearly recognize that it is a link-to-link transmit collision. Also, doubling the CW value when transmission is interrupted or delayed due to a link-to-link transmit collision may delay transmission. However, when a link-to-link transmit collision and an intra-link collision occur simultaneously, the station needs to double the CW value. This is explained in Figure 19.

[0166] Figure 19 shows how the CW value is processed when an STR multilink device detects a transmission collision between links according to an embodiment of the present invention.

[0167] As in the embodiment described above, if a station cancels a transmission due to a transmission made by a non-STR multilink device, it can sense the channel status after the transmission is canceled. If the station senses that the channel is not idle, it can double the CW value. In this case, the doubling can follow the embodiment described in Figure 6. Also, if the station senses that the channel is idle, it can maintain the CW value. Such embodiments are used because even if the channel is sensed to be idle, the possibility of a transmission collision in the link is low, so it is handled differently from when a transmission is successful. Specifically, if the AP of the AP multilink device fails to transmit to the station of the non-STR multilink device, the AP of the AP multilink device can obtain a backoff counter within CW without increasing CW. At this time, if the non-STR multilink device of the AP multilink device fails to transmit to the first station, and the second station of the non-STR multilink device transmits, the AP of the AP multilink device can obtain a backoff counter within CW without increasing CW. As described above, the AP multilink device can determine whether the second station of the non-STR multilink device transmits based on the transmitting station of the PPDU indicated by the PPDU's signaling field or the station indicated by the TA field of the MAC frame contained in the PPDU. In the embodiment described above, when EDCA is applied, the procedures for CW adjustment and backoff counter generation may be performed separately for each AC.

[0168] In other specific embodiments, the STR multilink device can determine whether or not it has failed to transmit a PPDU based on whether or not it has received a response to the PPDU. In this case, the STR multilink device does not need to consider whether or not the station receiving the PPDU is included in a non-STR multilink device. For example, even if the first station receiving the PPDU is included in a non-STR multilink device, and the second station of the non-STR multilink device transmits, preventing the first station from sending a response to the PPDU, the STR multilink device can still determine that it has failed to transmit the PPDU. Furthermore, if the STR multilink device fails to transmit a PPDU, it can increase the CW value to the next largest possible value among the possible CW values. In this case, if the CW value is at its maximum value, the STR multilink device may keep the CW value at the same value.

[0169] In another specific embodiment, if a channel is detected as idle, the station can set the CW value to the minimum CW value of the traffic (CW_min). This embodiment is used because, when a channel is detected as idle, the likelihood of a transmit collision in the link is low, and therefore it is treated the same as when a transmit is successful. The station can apply the above embodiment to the CW of the AC of the traffic included in the canceled transmit.

[0170] Furthermore, if the station cancels a transmission according to the embodiment described above, it does not need to increment the Retry Counter. In this case, the Retry Counter may include at least one of a long retry counter and a short retry counter.

[0171] In the above embodiment, canceling a transmission may include at least one of the following: interrupting the transmission or delaying the transmission before initiating it.

[0172] If a station sends a CTS-to-Self frame before attempting to transmit and then cancels the transmission, the station does not need to initiate RTS / CTS frame exchange before attempting to transmit again after the cancellation, because the NAV has already been set by the CTS-to-Self frame. Also, if a TXOP remains when the station attempts to transmit again after canceling the transmission, the station can attempt to transmit without a backoff procedure.

[0173] In Figure 19, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The second station (STA2) is transmitting to the second AP (AP2). The first AP (AP1) determines that the first station (STA1) is in a blind state while performing a transmission to the first station (STA1). Therefore, the first AP (AP1) interrupts the transmission to the first station (STA1). In Figure 19(a), the first AP (AP1) determines that the channel on the first link (Link1) is idle. At this time, since there are no TXOPs remaining, the first AP (AP1) accesses the channel using the backoff procedure. In Figure 19(b), the first AP (AP1) determines that the channel on the first link (Link1) is not idle. At this time, since TXOP remains active, the first AP (AP1) attempts to transmit without a backoff procedure.

[0174] In the embodiment described above, if a non-STR multilink device cancels a transmission to a station and then detects that the channel is idle for a predetermined time interval without a separate backoff procedure, the station that canceled the transmission to the non-STR multilink device can then transmit to other stations other than the non-STR multilink device station. At this time, the duration of the predetermined time interval can become an issue. A station that receives the PPDU of the canceled transmission may fail to decode the PPDU. At this time, if the channel is detected to be idle for the duration of EIFS (extended interframe space), the station that failed to decode the PPDU can initiate the backoff procedure. Therefore, the question arises as to whether to set the predetermined time interval to be longer than or the same as EIFS. This will be explained in Figure 20.

[0175] Figure 20 shows the operation in which an STR multilink device performs channel access again after ceasing transmission to a non-STR multilink device according to an embodiment of the present invention.

[0176] As shown in Figure 20(a), a pre-specified time interval may be DIFS. This takes into account that a station of an STR multilink device has gained a channel access opportunity through a race procedure and lost that channel access opportunity due to a transmit collision between links. In other words, because the station of the STR multilink device has gained a channel access opportunity through a race procedure, it is given priority over other stations performing channel access. When EDCA is applied, DIFS may be replaced with AIFS[AC].

[0177] In other specific embodiments, as shown in Figure 20(b), the predetermined time interval may be EIFS. This is because the STR multilink device may be considered to have already exhausted its transmission opportunities, and fairness with other stations is taken into consideration.

[0178] In further specific embodiments, as shown in Figure 20(c), when the signaling field of a PPDU signals that transmission may be interrupted, the pre-specified time interval may be DIFS. Also, when a station that receives a PPDU senses that the transmission of the PPDU has been interrupted, the station can sense whether the channel is idle or not using DIFS instead of EIFS. In this case, if the channel is detected as idle by DIFS, the station can initiate the backoff procedure. Such embodiments can improve the performance of the overall network and ensure fairness between stations. When EDCA is applied, DIFS may be replaced with AIFS[AC].

[0179] As mentioned above, an STR multilink device can recognize that a transmission collision between links may occur. Specifically, when the first station of the STR multilink device completes the backoff procedure, the second station of the STR multilink device may be receiving a PPDU. In this case, if the second station is unable to complete decoding the signaling field of the PPDU, the first station cannot recognize that a transmission collision between links has occurred, but can determine that it is possible. In this case, as mentioned above, the first station can insert information into the PPDU to be transmitted indicating that the transmission may be interrupted. Furthermore, an NSTR multilink device can transmit a CTS-to-Self frame before transmitting to a non-STR multilink device for stable and efficient transmission. This is explained in Figure 21.

[0180] Figure 21 shows the operation in which an STR multilink device transmits a CTS-to-Self frame before transmitting to a non-STR multilink device according to an embodiment of the present invention.

[0181] A station in an STR multilink device can transmit a CTS-to-Self frame before transmitting to a non-STR multilink device. Specifically, if a second station in an STR multilink device attempts to transmit to a non-STR multilink device while the first station of the STR multilink device is receiving, the second station can transmit a CTS-to-Self frame before transmitting to the non-STR multilink device. This allows the second station to secure a TXOP for transmission to the non-STR multilink device. Furthermore, the second station can determine whether the transmission to the first station is being sent from that non-STR multilink device before transmitting to it. The second station can determine the target station of the transmission based on whether the transmission to the first station is being sent from that non-STR multilink device. Specifically, if the transmission to the first station is not being sent from that non-STR multilink device, the second station can transmit to that non-STR multilink device. When a transmission to the first station is transmitted from the non-STR multilink device, the second station can transmit to stations not included in the non-STR multilink device. For example, if the first station plans to transmit a SU-PPDU to a station in the non-STR multilink device, an MU-PPDU containing data to a station in the non-STR multilink device, or a PPDU containing a trigger frame that triggers a transmission from a station in the non-STR multilink device, the first station can cancel the planned transmission. In this case, the first station can attempt to transmit a SU-PPDU to a station other than a station in the non-STR multilink device, an MU-PPDU that does not contain data to a station in the non-STR multilink device, or a PPDU containing a trigger frame that does not trigger a transmission from a station in the non-STR multilink device.In this case, the first station can begin transmitting after a time greater than SIFS from the time it transmitted the CTS-to-Self frame. Specifically, the first station can begin transmitting after PIFS from the time it transmitted the CTS-to-Self frame. The station that transmitted the CTS-to-Self frame must begin transmitting after SIFS from the time it transmitted the CTS-to-Self frame. As in the embodiment described above, processing time is required for the STR multilink device, such as generating the new MPDU to be transmitted, when a planned transmission is canceled and a new transmission is attempted. For this reason, an exception to the rule regarding the time interval between the CTS-to-Self frame and the transmission may be applied. In such an embodiment, as a general rule, the second station cannot transmit beyond the TXOP obtained by CTS-to-Self.

[0182] In Figure 21, the STR multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The second AP (AP2) receives data, and the first AP (AP1) plans to transmit to a station in the non-STR multilink device, so the first AP (AP1) transmits a CTS-to-Self frame before the planned transmission. As mentioned above, the first AP (AP1) determines the target station for transmission based on the judgment of the station that transmitted the PPDU received by the second AP (AP2). The first AP (AP1) also transmits after SIFS or PIFS from the time it transmits the CTS-to-Self frame.

[0183] The second station can initiate the RTS / CTS frame exchange procedure by sending an RTS frame instead of a CTS-to-Self frame. This allows the second station to achieve a similar effect to sending a CTS-to-Self frame. In the case of RTS / CTS frame exchange, the second station can only win a TXOP if the target station of the transmission is not blind.

[0184] Figure 22 shows that, according to an embodiment of the present invention, multiple APs included in an STR multilink device transmit to multiple stations included in a single non-STR multilink device.

[0185] Multiple stations included in a single non-STR multilink device can receive simultaneously. This is because simultaneous reception by multiple stations causes relatively little interference. Figure 22 illustrates that multiple stations included in a single non-STR multilink device can receive simultaneously. In this case, to ensure stable operation of the non-STR multilink device, the STR multilink device allows multiple APs included in the STR multilink device to send multiple transmissions to the multiple stations included in the single non-STR multilink device, with synchronized transmission termination. This is explained in Figure 23.

[0186] Figure 23 shows that, according to an embodiment of the present invention, multiple APs included in an STR multilink device perform multiple transmissions with synchronized transmission termination to multiple stations included in a single non-STR multilink device.

[0187] In a non-STR link, when a multilink device transmits on any one link, the multilink device can simplify the channel access procedure for transmission on other links. Specifically, when the first station of the multilink device completes the backoff channel access procedure on the first link, if a channel is idle for a predetermined time interval on the link of the second station of the STR multilink device, the second station of the STR multilink device can begin transmitting on the second link.

[0188] In a specific embodiment, when one station of an STR multilink device transmits to a station of a non-STR multilink device, the channel access procedure for other stations of the STR multilink device can be simplified. Specifically, when the first station of the STR multilink device completes the backoff channel access procedure for transmission to the first station of the non-STR multilink device, if the channel is idle for a predetermined time interval within the link of the second station of the STR multilink device, the second station of the STR multilink device can begin transmitting to the second station of the non-STR multilink device. In this case, the predetermined time interval may be PIFS. Such operation may be applied when the first and second stations of the STR multilink device transmit to a station included in a single non-STR multilink device. In such an embodiment, the first and second stations can begin transmitting within a predetermined time interval. The predetermined time interval may be slot time.

[0189] Furthermore, when the first and second stations of an STR multilink device transmit to a station included in a single non-STR multilink device, the end of transmissions by the first and second stations may be synchronized. In this case, the synchronization of the end of transmissions by the first and second stations can represent the end of transmissions by the first and second stations within a difference of a first predetermined time interval. This first predetermined time interval can represent a slot boundary or a symbol boundary.

[0190] Multiple stations of a non-STR multilink device that have received a synchronized transmission termination can simultaneously transmit a subsequent transmission, such as a response. In this case, the response may include an ACK. In conventional wireless LANs, the transmission following a reception is transmitted after SIFS from the reception. However, transmitting subsequent transmissions with a slight time difference to multiple transmissions that have terminated with a slight time difference can be more complex to implement than transmitting subsequent transmissions simultaneously. Therefore, as described above, multiple stations of a non-STR multilink device that have received a synchronized transmission termination can simultaneously transmit a subsequent transmission. In this case, the interval between transmissions following at least one of the multiple transmissions whose transmission termination is synchronized may be the sum of SIFS and the time within a predetermined time interval. Specifically, among the multiple transmissions whose transmission termination is synchronized, the transmission following the transmission that terminated first may be transmitted at an interval equal to the sum of SIFS and the time within a predetermined time interval from the transmission. In this case, the predetermined time interval may be either slot time or symbol length. Furthermore, the difference within a pre-specified time interval may be the difference between the end time of the last transmission to finish among multiple transmissions whose transmission ends simultaneously, and the end time of the first transmission to finish among multiple transmissions whose transmission ends simultaneously.

[0191] In another specific embodiment, if multiple transmissions are completed within a time difference in a first predetermined time interval, multiple stations that received the transmissions can then transmit synchronized subsequent transmissions. Multiple consecutive transmissions with synchronized completion can represent multiple consecutive transmissions transmitted within a second predetermined time interval. The difference within the second predetermined time interval may be the difference between the completion of the last transmission among the synchronized multiple transmissions and the transmission that completed first among the synchronized multiple transmissions. In this case, the second predetermined time interval may be smaller than the first predetermined time interval. Thus, PPDUs with synchronized transmission completion can be called sync PPDUs.

[0192] In Figure 23, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The first AP (AP1) and the second AP (AP2) synchronize the end of transmission to the first station (STA1) and the second station (STA2), respectively. That is, after the first station (STA1) ends its transmission, the second station (STA2) ends its transmission within a predetermined time interval from the first station (STA1). The first station (STA1) and the second station (STA2) send ACKs simultaneously. At this time, the first station (STA1) sends SIFS after the end of transmission to the first station (STA1), and then ACK after the difference between the end of transmission to the first station and the end of transmission to the second station (STA2).

[0193] Such embodiments may be applied to transmissions where the ACK policy is not set to No ACK. Specifically, they may also be applied when the ACK policy is not immediate response. In a specific embodiment, when multiple stations of a multilink device receive a transmission whose transmission end is synchronized, the multiple stations of the multilink device can simultaneously receive an ACK request and simultaneously send ACKs in response to the ACK request. Multiple stations of a multilink device that receive a transmission with an ACK policy set to a value other than No ACK within a predetermined time can simultaneously begin ACKing.

[0194] When a non-STR multilink device is present, it is necessary to consider the non-STR multilink device when transmitting RTS / CTS frames and CTS-to-Self frames to configure the TXOP. This is explained in Figures 24 to 29.

[0195] Figure 24 shows how a multilink device exchanges RTS / CTS frames according to an embodiment of the present invention.

[0196] Even when non-STR multilink equipment is present, the RTS / CTS frame exchange procedure can follow the procedure defined for existing wireless LANs. RTS / CTS frames may be used to configure the NAV of stations operating on other links. Specifically, a station that receives an RTS / CTS frame can operate on a link other than the one it is currently operating on and transmit it to other stations included in the multilink equipment that includes that station.

[0197] However, as in the embodiment described above, channel access or transmission may be restricted if a non-STR multilink device is present. For this reason, RTS / CTS may not be transmitted as shown in Figure 24. In other words, a station planning to transmit to the first station of a non-STR multilink device does not need to attempt RTS / CTS frame exchange if the second station of the non-STR multilink device is performing reception.

[0198] In Figure 24, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). When the first AP (AP1) transmits an RTS frame to the first station (STA1), channel access for the second station (STA2) is prohibited. The second AP (AP2) can determine that channel access for the second station (STA2) is prohibited. Therefore, the second AP (AP2) does not attempt to exchange RTS / CTS frames with the second station (STA2). In such an embodiment, a hidden node problem may occur. This will be explained in Figure 25.

[0199] Figure 25 shows the hidden node problem that occurs in the RTS / CTS frame exchange procedure according to the embodiment described in Figure 24.

[0200] As mentioned above, a station transmitting to a station in a non-STR multilink system may transmit without being able to perform CTS / RTS exchange. In this case, because TXOP is not set on other stations, other stations may attempt to transmit, and the station in the non-STR multilink system may fail to transmit or receive. In the embodiment shown in Figure 25, the STR AP multilink system includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink system includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). Due to the transmission by the first AP (AP1) to the first station (STA1), the second AP (AP2) was unable to transmit an RTS frame before transmission. Therefore, TXOP for transmission by the second AP (AP2) is not set on the station operating on the second link (Link2). Therefore, when the second AP (AP2) transmits to the second station (STA2), another BSS station (OBSS STA) transmits on the second link (Link2). As a result, the second station (STA2) fails to receive the transmission from the second AP (AP2). The following embodiment may be applied to solve this hidden node problem.

[0201] In a specific embodiment, if any one station of the non-STR multilink device is performing a receive operation, the station may not be permitted to transmit to any other station of the non-STR multilink device. In yet another specific embodiment, if a station transmits to a first station of the non-STR multilink device while a second station of the non-STR multilink device is performing a receive operation, the station may transmit simultaneously with the transmission to the second station. If a station transmits to a first station of the non-STR multilink device while a second station of the non-STR multilink device is performing a receive operation, the station may synchronize the end of the transmission to the first station with the end of the transmission to the second station. Specifically, if a station transmits to a first station of the non-STR multilink device while a second station of the non-STR multilink device is performing a receive operation, the station may end the transmission to the first station simultaneously with the transmission to the second station. In such an embodiment, the transmission to the second station may be performed by another station of the multilink device, including the station.

[0202] Figure 26 shows how a multilink device exchanges RTS / CTS frames according to an embodiment of the present invention.

[0203] In yet another embodiment of the present invention, if a first station of a multilink device is continuing to transmit to a third station of a non-STR multilink device, and a second station of the multilink device is attempting to transmit an RTS frame to a fourth station of a non-STR multilink device, the first station may terminate its transmission to the third station before the fourth station attempts to transmit the RTS frame. This allows the fourth station to transmit a CTS frame to the second station. Thus, a TXOP provisional setting for frame exchange between the second and fourth stations can be established. However, it may be difficult for the first station to terminate its transmission before the fourth station attempts to transmit the RTS frame.

[0204] In yet another embodiment of the present invention, if a second station of a multilink device attempts to transmit an RTS frame to a fourth station of a non-STR multilink device while a first station of a multilink device continues transmitting to a third station of a non-STR multilink device, the second station can transmit the RTS frame to the fourth station in sync with the end of the first station's transmission to the third station. To this end, the second station can insert padding into the RTS frame. In this case, the RTS frame may be in an RTS frame format that allows for flexible adjustment of the transmission length. For convenience of explanation, such an RTS frame format is referred to as an ML (multilink)-RTS frame. An ML-RTS frame may include a padded field for padding. For example, the format of an ML-RTS frame may be the same as the RTS frame format shown in Figure 26. The first station can also insert padding into its transmission to the third station in order to align the RTS frame with the end of its transmission.

[0205] In the embodiment shown in Figure 26, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The second AP (AP2) transmits an ML-RTS frame to the second STA (STA2) at the same time that the first AP (AP1) finishes transmitting to the first station (STA1). Subsequently, when the first station (STA1) sends an ACK to the first AP (AP1), the second station (STA2) sends an ACK to the second AP (AP2). This sets up a TXOP for frame exchange between the second AP (AP2) and the second station (STA2) at the station operating on the channel of the second link.

[0206] In other specific embodiments, other frames that set NAV may be exchanged instead of RTS / CTS frames. In the embodiments described above, ACK request frames may be sent instead of RTS frames. ACK request frames may include duration information associated with the end of transmission. Frames containing ACK that are sent in response to ACK requests may also include duration information. In this case, the duration information of the frame containing ACK may be set by the duration information of the ACK request frame.

[0207] Although the above-described embodiment was explained as being for RTS / CTS frame exchange, it may also be used for the exchange of control frames other than RTS / CTS frames. In this case, the control frame exchange may include the exchange of PS-Poll frames and response frames to PS-Poll.

[0208] Figure 27 shows that, according to one embodiment of the present invention, a multilink device exceptionally transmits a response to a control frame even when channel access is prohibited.

[0209] As described in the previously mentioned embodiment, channel access for some stations may be prohibited when a non-STR multilink device is present. Even if a station's channel access is prohibited, the station can still send a response to a control frame. Specifically, even if a station's channel access is prohibited, the station can still send a CTS frame as a response to an RTS frame.

[0210] Thus, when a response to a control frame is transmitted as an exception to channel access prohibition, the following embodiment may be applied. The first station transmits a response to a control frame as an exception to channel access prohibition. When the first station transmits a response to a control frame, the third station transmits to the second station, which is included in the multilink device that includes the first station. In such a case, the third station can retransmit to the first station. The third station can anticipate that the transmission to the second station will fail.

[0211] In the embodiment shown in Figure 27, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The first AP (AP) transmits to the first station (STA1). The second AP (AP2) transmits an RTS frame to the second station (STA2). Since the first station (STA1) receives the signal, channel access for the second station (STA2) is prohibited. However, as an exception to the channel access prohibition, the second station (STA2) transmits a CTS frame to the second AP (AP2). The first AP (AP1) can determine that there is a high probability that its transmission will fail due to the transmission of the CTS frame by the second station (STA2). Therefore, the first AP (AP1) retransmits to the first station (STA1). The retransmission method is explained in more detail in Figure 28.

[0212] Figure 28 shows the retransmission of a transmission to a station using a non-STR multilink device.

[0213] In the retransmission described in Figure 27, only a portion of the packets included in the initial transmission may be retransmitted. Specifically, a station performing retransmission can retransmit only a portion of the packets included in the initial transmission. The station performing retransmission can determine which packets to retransmit from the initial transmission based on the time interval in which the station receiving the CTS frame was received. Specifically, the station performing retransmission can determine which packets to retransmit from the packets included in the initial transmission that were transmitted in the time interval including the time interval in which the station receiving the CTS frame was received. In this case, the station performing retransmission can retransmit packets transmitted in the time interval including the time interval in which the station receiving the CTS frame was received, based on the propagation delay. Furthermore, in other specific embodiments, the station performing retransmission can retransmit all of the packets included in the initial transmission.

[0214] Furthermore, a station performing a retransmission can do so before receiving an ACK for the initial transmission. In this case, the station performing the retransmission can receive a Block ACK after the retransmission, indicating whether or not the initial transmission and the retransmission were received. For this reason, a station performing a retransmission can do so after the initial transmission but before SIFS. In another specific embodiment, a station that failed to receive a control frame sent as an exception to channel access prohibition can wait for the retransmission to be received without sending an ACK.

[0215] In the embodiment shown in Figure 28, the first AP (AP1) retransmits the fourth and fifth packets, taking into account the interval in which the second AP (AP2) receives the CTS frame and the transmit deal lay. After retransmission, the first AP (AP1) receives an ACK, which includes whether or not the retransmission was received.

[0216] Figure 29 shows that, according to an embodiment of the present invention, a control frame is transmitted on a link where a station that is not prohibited from channel access is operating, rather than on a link where a station that is prohibited from channel access is operating.

[0217] As illustrated in the embodiment in Figure 26, the end of transmission to multiple stations of a non-STR multilink device may be synchronized. However, this is difficult to implement as it may involve adjusting or regenerating MPDUs that have already been generated. Therefore, the multilink device may transmit control frames on links where stations that are not prohibited from channel access are operating, rather than on links where stations that are prohibited from channel access are operating. Specifically, the multilink device can transmit control frames through the links of the non-STR multilink device stations that are currently receiving from the multilink device. In this case, the control frame may be an RTS frame.

[0218] In the embodiment shown in Figure 29, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The first AP (AP1) transmits to the first station (STA1). Even if the second AP (AP2) successfully completes the backoff procedure, the second AP (AP2) cannot transmit to the second station (STA2) because the first station (STA1) is receiving the transmission sent from the first AP (AP1). At this time, the second AP (AP2) requests the first AP (AP1) to transmit an RTS frame that the second station (STA2) is receiving. At this time, the first AP (AP1) may include an RTS frame to be received by the second station (STA2) in the transmission that the first AP (AP1) is currently performing. In yet another specific embodiment, after the first AP (AP1) has finished the transmission that the first AP (AP1) is currently performing, the first AP (AP1) may transmit an RTS frame to be received by the second station (STA2) via the first link (Link1) after SIFS from the said transmission. The first station (STA1) receives the RTS frame to be received by the second station (STA2) and transmits the received RTS frame to the second station (STA2). The second station (STA2) performs CCA at PIFS. If the channel is idle at PIFS, the second station (STA2) transmits a CTS-to-Self frame. The first AP (AP1) may stop transmitting to the first station (STA1) during the time interval in which it is expected that the second station (STA2) will transmit a response to the RTS frame. Furthermore, while the second station (STA2) transmits a response to an RTS frame, the first station (STA1) can transmit an ACK for the received transmission. In yet another specific embodiment, while the second station (STA2) transmits a response to an RTS frame, the first station (STA1) can also transmit a response to an RTS frame.Figure 29 is provided to aid understanding of the explanation and may also be used for transmitting control frames other than RTS frames and CTS-to-Self frames. Furthermore, other time intervals other than PIFS may be used.

[0219] Figure 30 shows that a multilink device transmits an ACK according to an embodiment of the present invention.

[0220] A station in a multilink device can request a link to send an ACK to a station in a non-STR multilink device. Specifically, a station in a multilink device can request that an ACK be sent on a link other than the one used for transmission. In the embodiment shown in Figure 28, the first AP (AP1) of the STR multilink device sends a transmission (Tx(#2)) to the first station (STA1) of the non-STR multilink device. At this time, the first AP (AP1) requests that an ACK for the transmission (Tx(#2)) be sent on the second link (Link2). This is because the transmission (Tx(#2)) of the first AP (AP1) finishes before the transmission (Tx(#2)) of the second AP (AP2) to the second station (STA2), making it difficult to send an ACK for the transmission (Tx(#2)) of the first AP (AP1).

[0221] Furthermore, for such ACK transmissions, the station can configure an implicit BAR and ACK policy to avoid sending an immediate response to the transmission. In yet another specific embodiment, the station can configure the ACK policy for transmissions to BlockAckReq. However, sending a Block ACK requires sending a BlockAckReq, which can result in channel access burden and transmission delay. Therefore, a new ACK policy is needed for multilink equipment.

[0222] A station in a multilink device can send both an ACK for a transmission it has received and an ACK for transmissions received by other stations in the same multilink device. Such an ACK transmission can be called ML (multilink)-ACK. Furthermore, ML-ACK may be set as the ACK policy. In the embodiment shown in Figure 30, the first AP (AP1) sets the ACK policy for transmission (Tx(#2)) to ML-ACK. After receiving transmission (Tx(#2)), the first station (STA1) does not send an ACK to the first AP (AP1). The second station (STA2) completes receiving the transmission from the second AP (AP2) and sends both an ACK to the second AP (AP2) for the transmission from the first AP (AP1) and an ACK for the transmission from the second AP (AP2). A non-STR multilink device may include a third station (STA3) in addition to the first station (STA1) and the second station (STA2), and an STR multilink device may include a third AP (AP3) in addition to the first AP (AP1) and the second AP (AP2). In this case, the ACK policy for transmissions from the second AP (AP2) to the second station (STA2) may also be set to ML-ACK. If the transmission from the third AP (AP3) to the third station (STA3) is completed later than the transmission from the second AP (AP2) to the second station (STA3), the third station (STA1) can send ACKs to the third AP (AP3) for the transmission from the first AP (AP1) to the first station (STA1), for the transmission from the second AP (AP2) to the second station (STA2), and for the transmission from the third AP (AP3) to the third station (STA3).

[0223] Such embodiments prevent inter-link interference that may occur due to ACK transmissions, even if transmissions to stations of non-STR multilink devices are not completed simultaneously. In the embodiments described above, the ACK policy may be set to BlockAck instead of ML-ACK. In yet another specific embodiment, the ACK policy may be set to No Ack instead of ML-ACK.

[0224] The number of links on which a multilink device acquires transmission opportunities may increase while it is transmitting traffic. In this case, the multilink device may transmit traffic that it intended to transmit on a link that acquired a transmission opportunity earlier, on a link that acquired a transmission opportunity later. In this case, the NAV set on the link on which the multilink device acquired a transmission opportunity earlier may be set to a value greater than the NAV required to transmit the traffic. If the NAV set on the link on which the multilink device acquired a transmission opportunity earlier is greater than the NAV required to transmit the traffic, the multilink device can reset the NAV by sending a CF-END frame after completing transmission on the link on which it acquired a transmission opportunity earlier.

[0225] The reception of the aforementioned sync PPDU and the signaling related to the reception of the sync PPDU are explained in Figures 31 to 34.

[0226] For the first station of a non-STR multilink device to receive the aforementioned sink PPDU, it must determine whether the second station, which has a non-STR relationship with the first station, has begun receiving the sink PPDU. Furthermore, the first station must continuously perform preamble detection (PD). Such operation by the first station may be unreasonable if channel access is prohibited due to reception by other stations in the non-STR multilink device. Therefore, the first station can enter a power-saving state under predetermined conditions. The sink PPDU may be transmitted within an existing TXOP. Therefore, the performance gain obtained by receiving the sink PPDU may be determined by the remaining length of the TXOP. Thus, the first station can determine whether to abandon receiving the sink PPDU based on its length. If the first station abandons receiving the sink PPDU, it can enter a power-saving state. This power-saving operation can be called inter-link TXOP PS (power save). A station that has entered a power-saving state via inter-link TXOP PS can wake up from power-saving mode to receive frames periodically transmitted from the AP, such as beacon frames, TIM frames, and DTIM frames. Furthermore, when TXOP ends, for example, when a CF-END frame is transmitted, a station that has entered a power-saving state via inter-link TXOP PS can wake up from power-saving mode.

[0227] The aforementioned TXOP may be modified to the duration indicated by the length field in the PPDU's signaling field and the Duration field in the MAC frame. Specifically, in the embodiment described above, the station can determine the time the PPDU occupies based on the duration indicated by the length field and the Duration field in the MAC frame.

[0228] A non-AP multilink device can signal to an AP multilink device information regarding the presence or absence of sink PPDU reception support and the conditions for sink PPDU support. The AP multilink device can also signal to the non-AP multilink device whether or not it provides support for AP multilink device sink PPDU transmission. In this case, the multilink device can signal the presence or absence of sink PPDU support on a per-multilink device basis. For example, an AP multilink device can signal the presence or absence of sink PPDU transmission support on a per-AP multilink device basis. Furthermore, in other specific embodiments, the multilink device can signal the presence or absence of sink PPDU support on a per-station basis. Specifically, an AP multilink device can signal the presence or absence of sink PPDU transmission support on a per-AP basis for each AP included in the AP multilink device. For example, an AP multilink device including a first AP, a second AP, and a third AP can instruct the first AP to provide sink PPDU transmission support, while the second AP and third AP do not.

[0229] When an AP multilink device associated with a non-AP multilink device signals that it will not support sink PPDU transmission, the non-AP multilink device's station can enter the aforementioned power-saving state of the inter-link PS while other non-AP multilink device stations are receiving. This is because the AP multilink device associated with the non-AP multilink device cannot transmit sink PPDU. At this time, the non-AP multilink device's station can determine how long to maintain the power-saving state based on the length of the PPDU received by other non-AP multilink device stations.

[0230] The presence or absence of transmit or receive support for the aforementioned sink PPDU may be determined not only by hardware performance but also by operational policies. Therefore, the presence or absence of transmit or receive support for the sink PPDU may be signaled not only by performance information but also by information regarding the operating mode. The signaling method for transmit or receive support for the sink PPDU will be specifically explained in Figure 31.

[0231] Figure 31 shows an element field that indicates information regarding sink PPDU reception support or transmission support according to an embodiment of the present invention.

[0232] As mentioned above, information indicating whether or not sync PPDU transmission support is available may be included in the element that indicates the station's capabilities. For convenience of explanation, the element that indicates the station's capabilities will be called the Capability element. The field in the Capability element that indicates whether or not sync PPDU transmission support is available will be called the Supporting Sync PPDU Tx subfield. In this case, the Capability element may be a Multi-Link element, which indicates multi-link capabilities. The Capability element may also be an EHT Capability element, which indicates EHT-related capabilities. Figure 31(a) shows an example of a Capability element.

[0233] When the value of the Supporting Sync PPDU Tx subfield is 1, Supporting Sync PPDU Tx can indicate that the station or multilink device indicated by the Supporting Sync PPDU Tx subfield supports the transmission of a sync PPDU. When the value of the Supporting Sync PPDU Tx subfield is 0, Supporting Sync PPDU Tx can indicate that the station or multilink device indicated by the Supporting Sync PPDU Tx subfield does not support the transmission of a sync PPDU. In addition, when a station not included in a multilink device transmits a Capability element, the Supporting Sync PPDU Tx subfield may signal information that is not unrelated to whether or not sync PPDU transmission is supported, or it may be used as a reserved field.

[0234] As mentioned above, information indicating whether or not sync PPDU reception support is available may be included in the element that indicates the station's operation-related information. For convenience of explanation, the element that indicates the station's operation-related information will be referred to as the Operation element. Furthermore, the field in the Operation element that indicates whether or not sync PPDU reception support is available will be referred to as the Supporting Sync PPDU Rx Disable subfield. Figure 31(b) shows an example of an Operation element. When the value of the Supporting Sync PPDU Rx Disabled subfield is 1, it can indicate that the station does not wish to receive sync PPDUs. Specifically, when the value of the Supporting Sync PPDU Rx Disabled subfield is 1, the Supporting Sync PPDU Rx Disabled subfield can indicate that the station sending the Supporting Sync PPDU Rx Disabled subfield does not wish to wait for sync PPDU reception. A multilink device with the Supporting Sync PPDU Rx Disabled subfield value set to 1 does not require the second station of the multilink device to perform PD and CCA while the first station of the multilink device is performing reception. An AP multilink device connected to a multilink device that sent the Supporting Sync PPDU Rx Disabled subfield does not simultaneously send PPDUs to multiple stations of the multilink device that sent the Supporting Sync PPDU Rx Disabled subfield. The PPDU may be an SU PPDU, Full BW MU PPDU, or OFDMA MU PPDU sent in one of the following formats: non-HT PPDU, HT PPDU, VHT PPDU, HE PPDU, or EHT PPDU. In this case, the AP multilink device must not send a response, such as a frame requesting an immediate response.The frame requesting a response may include at least one of RTS, MU-RTS (Multi-User RTS), a trigger frame, and BAR (Block Ack Request).

[0235] Further, the Operation element may include information related to the minimum length of a sync PPDU that can be received by the station or multilink device that transmitted the Operation element. In this case, the subfield indicating information related to the minimum length of a sync PPDU is referred to as a Remaining TXOP Threshold subfield. The Remaining TXOP Threshold subfield may indicate time. Further, the Remaining TXOP Threshold subfield may indicate the time in units of us, ms, or symbols. A multilink device coupled to the multilink device that transmitted the Remaining TXOP Threshold subfield may not be allowed to transmit a sync PPDU shorter than the length indicated by the Remaining TXOP Threshold subfield to the multilink device or station that transmitted the Remaining TXOP Threshold subfield.

[0236] Further, when the Remaining TXOP Threshold subfield is set to a predetermined value, this may indicate that the multilink device or station that transmitted the Remaining TXOP Threshold subfield does not support reception of sync PPDUs. The predetermined value may be a value indicating a time longer than the maximum time that can be indicated by the Remaining TXOP Threshold subfield. In still another specific embodiment, the predetermined value may be 0. When such an embodiment is applied, the Sync PPDU Rx Disable subfield may be omitted in the Operation element.

[0237] Furthermore, as explained in the above-described embodiment, the Sync PPDU Rx Disable subfield and the Remaining TXOP Threshold subfield can be signaled by the Operation element. The Sync PPDU Rx Disable subfield and the Remaining TXOP Threshold subfield may be signaled by elements other than the Operation element or by signaling information. Figures 32 to 34 illustrate an embodiment in which the inter-link TXOP power saving mode is performed by the signaling described in Figure 31.

[0238] Figure 32 shows that a non-STR multilink device operates in inter-link TXOP power saving mode according to an embodiment of the present invention.

[0239] If a non-STR multilink device signals that it will not support sink PPDU reception, the second station of the non-STR multilink device can enter a power-saving state while the first station of the non-STR multilink device is performing reception. In this case, the second station can maintain the power-saving state until the end of the TXOP indicated by the PPDU received by the first station. As mentioned above, the second station may anticipate receiving frames periodically transmitted from the AP before the end of the TXOP indicated by the PPDU received by the first station. In this case, the second station can wake up from the power-saving state before the end of the TXOP indicated by the PPDU received by the first station. As mentioned above, frames periodically transmitted from the AP may include at least one of beacon frames, TIM frames, and DTIM frames.

[0240] The second station can maintain a power-saving state even after the TXOP indicated by the PPDU received by the first station has ended. Specifically, the second station can determine whether or not to maintain a power-saving state after the TXOP indicated by the PPDU received by the first station has ended, based on information received from the AP to which the second station is connected. At this time, the information received from the AP to which the second station is connected may be NAV-related information. In addition, the information received from the AP to which the second station is connected may be operational information of the AP to which the first station is connected. If the NAV set by the second AP of the AP multilink device, which is currently transmitting to the second station of the non-AP multilink device, has not yet expired, the first AP of the AP multilink device can transmit information regarding the expected end time of transmission or reception and the expected expiration time of the NAV to the first station of the non-AP multilink device, which has signaled that it does not wish to receive a sink PPDU. If the NAV set by the second AP of an AP multilink device that is currently transmitting to the second station of a non-AP multilink device has not expired, the second AP may transmit or receive a PPDU from any one of the stations. If the NAV set by the second AP of an AP multilink device that is currently transmitting to the second station of a non-AP multilink device has not expired, the NAV may have been set on the second AP by a PPDU that the second station did not transmit.

[0241] In the embodiment shown in Figure 32, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The non-STR non-AP multilink device signals that it does not wish to receive a sink PPDU. The first AP (AP1) transmits to the first station (STA1). At this time, the second station (STA2) maintains a power-saving state until the end of the TXOP indicated by the PPDU transmitted by the first AP (AP1) to the first station (STA1).

[0242] Figure 33 shows that, according to an embodiment of the present invention, a station of a non-STR multilink device enters a power-saving state when waiting for sink PPDU reception.

[0243] The first station of a non-STR multilink device can enter the power-saving state of the inter-link TXOP if the remaining duration of the TXOP indicated by the PPDU being received by the first station is the same as or shorter than the length indicated by the Remaining TXOP Threshold subfield transmitted by the non-STR multilink device. At this time, before entering the power-saving state, i.e., if the remaining duration of the TXOP indicated by the PPDU being received by the first station is greater than the length indicated by the Remaining TXOP Threshold subfield transmitted by the non-STR multilink device, the second station can receive the sink PPDU transmitted to the second station. At this time, the second station can receive the sink PPDU. To do this, the second station can perform a PD (Planetary Debit) to determine whether the intended recipient of the received PPDU is the second station. Specifically, the second station can determine whether the AID indicated by the signaling field of the PPDU or the RA (Rating Authority) of the MAC frame included in the PPDU indicates the second station.

[0244] In the embodiment shown in Figure 33, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The non-STR non-AP multilink device signals that it desires to receive a sink PPDU. At this time, the non-STR non-AP multilink device also signals the minimum TXOP length required to receive the sink PPDU, "a". The first AP (AP1) transmits to the first station (STA1), and the second station (STA2) waits for the sink PPDU to be received. When the TXOP of the PPDU transmitted by the first AP (AP1) to the first station (STA1) is the same as or shorter than "a", the second station (STA2) enters an inter-link TXOP power saving state.

[0245] Figure 34 shows that, according to yet another embodiment of the present invention, a station of a non-STR multilink device enters a power-saving state when in standby mode for sink PPDU reception.

[0246] If a non-STR multilink device station is waiting to receive a sink PPDU and detects the transmission of a PPDU other than a sink PPDU from a BSS operated by an AP connected to the non-STR multilink device station, the non-STR multilink device station can enter an inter-link TXOP power-saving state. At this time, the station can determine that a PPDU that is not intended to be received by the station is not a sink PPDU. Furthermore, even if the station still has a minimum TXOP signaled by the station, if it detects the transmission of a PPDU other than a sink PPDU from a BSS operated by an AP connected to the non-STR multilink device station, the non-STR multilink device station can enter an inter-link TXOP power-saving state.

[0247] In the embodiment shown in Figure 34, the STR AP multilink device includes a first AP (AP1) operating on the first link (Link1) and a second AP (AP2) operating on the second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on the first link (Link1) and a second station (STA2) operating on the second link (Link2). The non-STR non-AP multilink device signals that it desires to receive a sink PPDU. At this time, the non-STR non-AP multilink device also signals the minimum TXOP length required to receive the sink PPDU, "a". The first AP (AP1) transmits to the first station (STA1), and the second station (STA2) waits for the sink PPDU to be received. The second station (STA2) senses that a PPDU that is not a sink PPDU is being transmitted from the BSS to which the second station belongs. Although the TXOP of the PPDU transmitted by AP1 to STA1 is greater than "a", STA2 enters an inter-link TXOP power saving state.

[0248] <Service Procedure for Multilink Single Radio Multilink Devices>

[0249] As mentioned above, the multilink device can operate adaptively, taking into account that the second station of the non-STR multilink device may become blind when the first station transmits. Specifically, if the multilink device determines that a station of the non-STR multilink device is blind, the multilink device may interrupt transmission to the non-STR multilink device station. In addition, a station of the non-STR multilink device may enter a doze state based on the operation of other stations of the non-STR multilink device, such as transmission and reception. This solves problems that may arise when the operation of one station of the non-STR multilink device restricts the operation of other stations.

[0250] As mentioned above, non-STR multilink devices cannot simultaneously transmit and receive due to internal interference. Furthermore, due to hardware configuration constraints, non-STR multilink devices cannot simultaneously transmit and receive. Specifically, when the first station of a non-STR multilink device transmits or receives, the second station may be restricted from using its transmitting / receiving unit. For example, a non-STR multilink device can only support one PPDU processing. In this case, when the first station of the non-STR multilink device transmits or receives, the second station cannot transmit or receive. A multilink device that includes multiple stations operating on multiple links, or that does not support simultaneous transmission or reception by multiple stations, is called a single-radio multilink device. Therefore, when any one station of a single-radio multilink device transmits or receives, the other stations cannot transmit or receive. Whether a multilink device operates as a single-radio multilink device depends on hardware constraints or operating mode definitions, as mentioned above. Therefore, in this specification, a single-radio multilink device can refer to a multilink device in which the operation of a station is limited by hardware constraints, as well as a multilink device in which the operation of a station is limited by the definition of the operating mode. Accordingly, a single-radio multilink device in this specification may include a multilink device that supports multiple stations of a multilink device transmitting or receiving simultaneously, but does not support multiple stations of a multilink device transmitting or receiving simultaneously under certain conditions. In this case, the certain conditions may include a specific time period.

[0251] Specifically, a multilink device can operate as a single-radio multilink device depending on its operating mode. For example, when a specific mode is deactivated, the multilink device transmits or receives on multiple links, and when the specific mode is activated, it can transmit or receive on only one of the multiple links during a specific time interval. In this case, when the specific mode is deactivated, the multilink device transmits or receives on multiple stations, and when the specific mode is activated, it can transmit or receive on only one of the multiple stations during a specific time interval. In this case, the specific time interval may include the time during which the multilink device performs frame exchange on any one of the links. Specifically, the specific time interval may be from the time the multilink device receives the initial control frame that initiates frame exchange on any one of the links until the end of said frame exchange. When a multilink device uses a single radio on a single link during a specific time interval of a specific mode, the specific mode can be called the EMLSR (enhanced multi-link single radio) mode. While a multilink device performs frame exchange on the first link of an EMLSR link (an EMLSR link consisting of multiple links to which EMLSR mode is applied), the multilink device does not transmit or receive on the second link of the EMLSR link. Furthermore, when a specific mode is used by a specific station of the multilink device for transmission or reception, and that station uses a portion of the RF chain used by that station to transmit or receive, the specific mode is called ELMR (enhanced multi-link multi-radio) mode. Specifically, in ELMR mode, when one station of the multilink device uses the entire RF chain of the other stations to transmit or receive, the operation of the multilink device may be the same as the operation of the multilink in EMLSR mode. Also, even when a multilink device operates in EMLSR mode, some of the multiple links on which the multilink device operates can operate without the restrictions imposed by EMLSR mode.When a multilink device operates in EMLSR mode, the links to which EMLSR mode applies may be only a portion of the links on which the multilink device operates. For example, when a multilink device operates on links 1 through 3, EMLSR mode or ELMMR mode may be applied only to links 1 and 2. Therefore, when a multilink device transmits or receives on link 1 during a specific time interval in EMLSR mode, the multilink device cannot transmit or receive on link 2. In this case, the multilink device can transmit or receive on link 3 without the restrictions imposed by EMLSR mode. For convenience of explanation, links to which EMLSR mode may apply, such as links 1 and 2, are referred to as EMLSR links, and links to which ELMMR mode may apply are referred to as ELMMR links. Transmitting or receiving using the RF chain of a specific station in EMLSR mode and ELMMR mode results in a change in the transmit, receive, or monitoring capabilities on the links on which the specific station operates. Therefore, embodiments of the present invention applied in the following description in relation to the EMLMR mode may be applied identically in relation to the EMLMR mode unless otherwise specified.

[0252] The embodiments described above regarding the operation of non-STR multilink devices are also applicable to the operation of single-radio multilink devices. Furthermore, the embodiments described above regarding the operation of a station that transmits and receives signals with a non-STR multilink station are also applicable to the operation of a station that transmits and receives signals with a single-radio multilink station. For example, if a station determines that it has failed to transmit to a single-radio multilink device on the first link due to transmission or reception by a single-radio multilink device on the second link, the station does not need to increase the CW channel access on the first link. Specifically, the station can apply the embodiment described in Figure 14. In this case, the method by which the station determines that it has failed to transmit to a single-radio multilink device on the first link due to transmission or reception by a single-radio multilink device on the second link may be similar to the method by which the station determines whether it has failed to transmit to a non-STR multilink station due to operational limitations of the non-STR multilink device.

[0253] Figure 35 shows the connection between a single-radio multilink device and an AP multilink device according to an embodiment of the present invention.

[0254] In this specification, the PHY backend refers collectively to the digital processors of the physical layer, including the processors that encode and decode the PPDU. The PHY frontend refers collectively to the analog baseband circuit, including the RF chain.

[0255] Multiple stations in a single-radio multilink device operate on different links. These stations may share a PHY backend. When any one of these stations transmits a PPDU, the PHY backend is used for encoding the PPDU. Therefore, the remaining stations cannot use the PHY backend at this time. Thus, although a single-radio multilink device includes multiple stations operating on different links, it can only transmit or receive on one link at a time.

[0256] However, a single-radio multilink device can perform channel access on multiple links. Specifically, a single-radio multilink device can perform monitoring on multiple links. Therefore, a single-radio multilink device can perform channel access on multiple links. In this case, monitoring can include channel sensing. Furthermore, channel sensing can include at least one of CCA (clear channel assessment) and PD (preamble detection). This allows the single-radio multilink device to reduce channel access delay. Specifically, even if the first station of the single-radio multilink device cannot perform channel access due to channel occupation by another radio communication device on the first link, the second station of the single-radio multilink device can perform the backoff procedure on the second link. In these embodiments, the single-radio multilink device may be a multilink device operating in EMLSR mode, as described above.

[0257] To support such embodiments, the PHY front end of a single-radio multilink device can assist with channel monitoring independently of the PHY backend. Furthermore, the PHY front end of a single-radio multilink device can assist with decoding of PPDU preambles independently of the PHY backend for PD purposes. Additionally, the PHY front end of a single-radio multilink device can assist with receiving frames transmitted by low MCS independently of the PHY backend. These frames transmitted by low MCS may include at least one of RTS frames and MU-RTS frames. Therefore, the PHY front end may include a MAC processor. Moreover, in such embodiments, the processing power of the PHY backend can be concentrated on encoding and decoding data frames.

[0258] In the embodiment of FIG. 35, the AP multi-link device includes a first AP (AP1) and a second AP (AP2). The single-radio multi-link device includes a first non-AP station (Non-AP STA1) and a second non-AP station (Non-AP STA2). The first AP (AP1) is connected to the first non-AP station (Non-AP STA1) via a first link Link1, and the second AP (AP2) is connected to the second non-AP station (Non-AP STA2) via a second link Link2. As in the foregoing embodiments, each of the first non-AP station (Non-AP STA1) and the second non-AP station (Non-AP STA2) independently performs channel access using a PHY front end.

[0259] A single-radio multi-link device can use the RF chain of a station that does not participate in transmission or reception for MIMO transmission. Specifically, when a first station of the single-radio multi-link device obtains a channel access opportunity, the first station can perform MIMO transmission using not only the RF chain used by the first station itself, but also the RF chain used by a second station of the single-radio multi-link device. This will be described with reference to FIG. 36.

[0260] FIG. 36 illustrates that a single-radio multi-link device according to an embodiment of the present invention performs MIMO transmission.

[0261] In the embodiment shown in Figure 36, the first station STA1 of the single-radio multilink device operates on the first link Link1, and the second station STA2 of the single-radio multilink device operates on the second link Link2. The first station STA1 performs channel access on the first link Link1, and the second station STA2 performs channel access on the second link Link2. If the first station STA1 successfully accesses the channel on the first link Link1, the first station STA1 performs 2x2 MIMO transmission on the first link Link1, using not only the RF chain used for channel access on the first link Link1, but also the RF chain used by the second station STA2 for channel access on the second link Link2.

[0262] Thus, when an RF chain operating on the second link is changed to operate on the first link, the single-radio multilink device cannot perform monitoring and channel access on the second link. Furthermore, when an RF chain that was changed to operate on the first link while operating on the second link returns to operating on the second link, the single-radio multilink device can perform channel access on the second link after waiting for a predetermined period of time. In this case, channel access by the single-radio multilink device on the second link may be restricted for a predetermined period of time from the completion of the RF change. Specifically, the single-radio multilink device can perform channel access on the second link after waiting for a predetermined period of time from the completion of the RF change. In this case, channel access may include a backoff procedure. Furthermore, the pre-specified time may be a pre-specified time that is applied when restrictions on channel access are necessary due to a period during which channel monitoring is impossible. Specifically, the pre-specified time may be NAVSyncdelay. Specifically, a single radio multilink device can perform a backoff procedure after waiting for NAVSyncdelay. This is because there is a high probability that the single radio multilink device will not be able to detect transmissions from other radio communication terminals on the second link during the period during which channel monitoring is impossible. In addition, when the link on which the RF chain operates is changed, a delay time may be required for the RF chain to start operating. Therefore, the single radio multilink device can perform channel access taking into account the delay time of the RF chain change. This is explained in Figure 37.Furthermore, for the sake of clarity, changing an RF chain that operates on one link to operate on another link will be referred to as an RF chain change. Also, a link change can refer to a change in the RF chain supported by that link. Specifically, an RF chain change can be described as a case where the first link supports the use of multiple RF chains but now supports the use of only one RF chain, or a case where the second link does not support the use of any RF chains but now supports the use of only one RF chain.

[0263] When a multilink device operates in the EMLSR mode or ELMMR mode described above, the transmit, receive, or monitoring capabilities of the link to which the EMLSR mode or ELMMR mode applies may be changed. This may cause the RF chain of the link to which the EMLSR mode or ELMMR mode applies to be reconfigured. The channel access restrictions described above may also be applied when a link is switched in EMLSR mode or ELMMR mode in this way. When link switching occurs on a link to which the EMLSR mode or ELMMR mode applies, channel access of the station to which the mode change applies among the stations of the multilink device may be restricted for a predetermined time from the time of reconfiguration. The predetermined time may be NAVSyncDelay or MediumSyncDelay. Even if the predetermined time has not elapsed, the channel access restriction of the multilink device may be released when a frame that allows NAV configuration is received. The predetermined time may also be the time indicated by the NAVSyncDelay parameter. In these embodiments, even before the predetermined time has elapsed from the time when link switching is completed, i.e., when monitoring capability is restored, a station can transmit a control frame to configure NAV and start frame exchange. The control frame used to configure the NAV may be at least one of an RTS frame and a MU-RTS frame. In the following description, link switching may include losing all or part of the link's transmit, receive, or monitor capability and then recovering it.

[0264] In this case, if the transmit, receive, or monitoring capability of the link to which EMLSR mode or EMLMR mode is applied is changed, this may include cases where the frequency bandwidth or center frequency of the RF chain is changed.

[0265] Furthermore, channel access restrictions on a multilink device may involve prohibiting transmission by the multilink device and causing the multilink device to perform CCA (Control Cross Access).

[0266] A station communicating with a single radio multilink device using MIMO may be a station of a multilink device. Specifically, a station communicating with a single radio multilink device using MIMO may be an AP included in a multilink device. Unless otherwise specified in this specification, a station communicating with a single radio multilink device using MIMO may be a station included in a multilink device. In this case, a station included in a multilink device may be an AP. Furthermore, what is described in this specification as the operation of a station of a multilink device may be a description of the operation of the multilink device.

[0267] Figure 37 shows the operation of a single-radio multilink device according to an embodiment of the present invention, which performs channel access while taking into account the delay time of RF chain changes.

[0268] A single-radio multilink device can change the RF chain before the expected time of successful channel access. Specifically, the single-radio multilink device can change the RF chain a time period set based on the RF chain change delay time from the expected time of successful channel access. For example, the single-radio multilink device can change the RF chain a time period earlier than the expected time of successful channel access.

[0269] In the embodiment shown in Figure 37, the first station STA1 of the single-radio multilink device operates on the first link Link1, and the second station STA2 of the single-radio multilink device operates on the second link Link2. The first station STA1 performs channel access on the first link Link1, and the second station STA2 performs channel access on the second link Link2. If the first station STA1 successfully accesses the channel on the first link Link1, the first station STA1 performs 2x2 MIMO transmission on the first link Link1, using not only the RF chain used for channel access on the first link Link1, but also the RF chain used by the second station STA2 for channel access on the second link Link2. In the embodiment shown in Figure 37(a), the single-radio multilink device changes the RF chain by the RF chain switching delay from the expected time when successful channel access is expected (Expected Tx time).

[0270] In yet another specific embodiment, at the start of transmission after the single radio multilink device has changed the RF chain, the single radio multilink device can initiate RTS frame / CTS frame exchange. In yet another specific embodiment, at the start of transmission after the single radio multilink device has changed the RF chain, the single radio multilink device can transmit CTS-to-Self frames. Alternatively, the single radio multilink device can transmit frames of a relatively short length instead of CTS-to-Self frames. Such embodiments allow the single radio multilink device to obtain the time required for the RF chain change to be completed. Furthermore, unlike the previously described embodiments, such embodiments do not cause problems even if channel access is not successful at the predicted time.

[0271] In the embodiment shown in Figure 37(b), the single-radio multilink device starts transmitting via RTS frame / CTS frame exchange on the first link, Link1.

[0272] Figure 38 shows the Capability element and Operation element used in a single-radio multilink device according to an embodiment of the present invention.

[0273] A single-radio multilink device can transmit or receive by changing the RF chain, as explained in Figures 36 and 37. Alternatively, it can transmit or receive without changing the RF chain. The single-radio multilink device can choose whether or not to change the RF chain.

[0274] A single-radio multilink device can use the MIMO Rx support subfield of the Operation element to indicate whether to use the RF chains of other links when performing MIMO communication on that link. For example, if a single-radio multilink device sets the value of the MIMO Rx support subfield of the Operation element to 1, the MIMO Rx support subfield can indicate that MIMO reception will be performed using a number of spatial streams less than or equal to the value of the Max Rx spatial stream subfield of the Operation element. In this case, a station transmitting MIMO to the single-radio multilink device must perform MIMO transmission using a number of spatial streams less than or equal to the value of the Max Rx spatial stream subfield of the Operation element. In a specific embodiment, the format of the Operation element may be as shown in Figure 38(a).

[0275] Furthermore, a single-radio multilink device can signal the time required for RF chain changes using a Capability element. In this case, the switching latency subfield of the capability element can indicate the time required for RF chain changes. A station performing MIMO transmission to a single-radio multilink device must perform MIMO transmission taking into account the time required for RF chain changes. Specifically, a station performing MIMO transmission to a single-radio multilink device can start MIMO transmission after the time required for RF chain changes has elapsed from the initial transmission to the single-radio multilink device. In a specific embodiment, the format of the Capability element may be as shown in Figure 38(a).

[0276] When a single radio multilink device transmits or receives on the first link, it is not necessary for a station intending to transmit to the single radio multilink device to transmit on a link other than the first link. This is because the single radio multilink device cannot receive on a link other than the first link while it is transmitting or receiving on the first link. Specifically, in addition to the time while frames are being exchanged on the first link, it is not necessary for a station intending to transmit to the single radio multilink device to transmit on a link other than the first link until a certain amount of time has elapsed since the single radio multilink device completed the frame exchange sequence. Specifically, the completion of the frame exchange sequence may be determined based on the reception or transmission of the last frame of the frame exchange sequence. In this case, the frame exchange sequence may be performed on a link where multiple RF chains can be used. Specifically, the frame exchange sequence may be performed using MIMO. The certain amount of time may be determined based on the time required for RF chain changes. Specifically, the certain amount of time may be the time required for RF chain changes.

[0277] When the EMLSR mode of a multilink device is activated, transmission and reception are possible only on specific links among the multiple links to which the EMLSR mode of the multilink device is applied during a specific time period. Similarly, when the ELMMR mode of a multilink device is activated, transmission and reception become possible only on specific links among the multiple links to which the ELMMR mode of the multilink device is applied during a specific time period. Furthermore, as mentioned above, the RF chain may be reconfigured when the transmission, reception, or monitoring capability of the EMLSR mode or the link to which the ELMMR mode is applied is changed. This is to restore the monitoring capability on links that have lost all or part of their transmission, reception, or monitoring capability in the ELMMR mode or EMLSR mode. In other words, the RF chain is reconfigured to restore the monitoring or transmission / reception capability on the link to which the ELMMR mode or EMLSR mode is applied. Therefore, among the stations of the multilink device, a station attempting to transmit to a station operating on a link where transmit, receive, or monitoring capability has been restored, for example, a link where frame exchange is not taking place in EMLSR mode, cannot initiate frame exchange with the multilink device on the EMLMR link or EMLSR link during a predetermined time period from the time when the transmit, receive, or monitoring capability of the link is restored. In this case, the EMLMR link or EMLSR link may be limited to links where link switching, for example, the RF chain has been reset. In this case, the predetermined time may be a delay time for link switching. In this case, link switching can represent an operation to restore monitoring capability on a link that has lost monitoring capability. Specifically, the predetermined time may be set based on the time required for link switching, for example, an RF chain change. For such operation, the station performing frame exchange with the multilink device or the multilink device itself needs to be able to determine the link switching time.As mentioned above, a station or multilink device can determine the end of ELMMR mode or EMLSR mode. However, in the following description of the embodiment of the method for determining the end of mode, for the sake of clarity, the station will be the primary focus of the explanation. For the sake of clarity, ELMMR mode and EMLSR mode will be collectively referred to as EML mode. Also, ELMMR links and EMLSR links will be collectively referred to as EML links.

[0278] When a station performs a frame exchange on the first link, one of the EML links, it can set a timer for the end of the frame exchange on the second link, another EML link. For convenience of explanation, this timer will be referred to as the end-of-frame timer. In this case, the station can set the end-of-frame timer based on the Duration / ID field of the frame received from the multilink device entering EML mode. The station can determine that the end of the frame exchange corresponding to the timer is reached when the end-of-frame timer expires. The multilink device to which EML mode is applied can also set a timer for the end of the frame exchange. In this case, the multilink device can synchronize its end-of-frame timer with the station's end-of-frame timer. The multilink device can set the end-of-frame timer based on the Duration / ID field of the frame received from the AP.

[0279] The frame exchange completion point may be the point at which the frame exchange is completed in EML mode. In other specific embodiments, the frame exchange completion point may be the point at which the TXOP set to protect the frame exchange in EMLMR mode or EMLSR mode is terminated.

[0280] Therefore, when EML mode is applied, the station can determine the end of the frame exchange as the end of the TXOP set for the frames being exchanged. In this case, the end of the TXOP must be initiated before the TXOP is completed, and this may include the case where the TXOP has ended. A new backoff procedure must be initiated if neither the TXOP holder nor the TOXP responder has been able to occupy the channel for (aSIFSTime + aSlotTime) within the TXOP. aSIFSTime represents SIFS as defined in 802.11, i.e., 16us, and aSlotTime represents the unit time for channel sensing in EDCA and DCF, i.e., 9us. In the following description, aSIFSTime and aSlotTime are used in this sense unless otherwise specified. Specifically, in EML mode, the station can determine the end of the frame exchange as the time indicated by the Duration / ID field of the frame transmitted over the EML link has elapsed.

[0281] Furthermore, the station can determine the end of frame exchange when, after sending a response frame to the multilink device on an EML link where frame exchange takes place in EML mode, the link is detected as idle for a certain period of time. The station can receive a frame from the multilink device that does not require an immediate response frame. In this case, the station does not send a response frame. Therefore, the station can determine the end of frame exchange when, after receiving a frame that does not request a response frame from the multilink device on an EML link where frame exchange takes place in EML mode, the link is detected as idle for a certain period of time. Also, when the station receives a frame that requests a response frame, the station can determine the end of frame exchange when, after sending a response frame to the multilink device on an EML link where frame exchange takes place in EML mode, the link is detected as idle for a certain period of time. In these embodiments, the certain period of time may be PIFS + aRXPHYStartDelay. PIFS may be aSIFSTime + aSlotTime. Furthermore, aRXPHYStartDelay may be a delay time related to the time it takes for the MAC to recognize the fact after the PHY has started Rx operation. In this case, the station can determine the time when it has sent a response frame as the time when the PHY-TXEND.confirm primitive for the responded frame has occurred. Also, the time when the station receives a frame for which it does not request a response frame may be the time when the PHY-RXEND.indication primitive has occurred. These embodiments consider cases in conventional WLANs where the conditions for a TXOP holder to send consecutive frames within the TXOP are not met. That is, these embodiments determine that frame exchange is terminated when the TXOP holder fails to transmit and must attempt the backoff procedure again. In a specific embodiment, the TXOP may terminate as follows.

[0282] If the Ack Policy of a frame included in a received PPDU is "HETP Ack", a multilink device in EML mode must successfully receive the Tigger frame or TRS Control field included in the PPDU in order to send an Ack response. If the multilink device in EML mode fails to successfully receive the Trigger frame or TRS Control field, it will not be able to send a response even if it receives a frame requesting a response. In this case, the TXOP will terminate unless the station retransmits a frame requesting an immediate response.

[0283] AP multilink equipment is not permitted to transmit an initial control frame to a multilink equipment with EML mode applied during the RF switching change time of the multilink equipment with EML mode applied, from the TXOP time set to protect frames exchanged in EML mode. In other words, AP multilink equipment can transmit an initial control frame to a multilink equipment with EML mode applied after the RF switching change time of the multilink equipment with EML mode applied, from the TXOP time set to protect frames exchanged in EML mode.

[0284] Furthermore, the station can determine that the frame exchange is complete when it receives a CF-End frame on an EML link where frame exchange takes place in EML mode. In this case, the station can determine that it received the CF-End frame at the time the PHY-RXSTART.indication primitive is generated by the CF-End frame. In yet another specific embodiment, the station can determine that it received the CF-End frame at the time the PHY-RXEND.indication primitive is generated by the CF-End frame. In yet another specific embodiment, the station can determine that the frame exchange is complete from the time the CF-End frame is received until aSIFSTime. In this case, the station can determine that it received the CF-End frame at the time the PHY-RXSTART.indication primitive is generated by the CF-End frame. In yet another specific embodiment, the station can determine that it received the CF-End frame at the time the PHY-RXEND.indication primitive is generated by the CF-End frame.

[0285] As mentioned above, a station can set an end-time timer. When a station receives a CF-End frame, it can reset the end-time timer, i.e., set it to 0. In another specific embodiment, when a station receives a CF-End frame, it can set the end-time timer to a value less than 0. In this case, the value less than 0 may be the time corresponding to the transmission time (air time) of the CF-End frame. In this case, a station attempting to exchange frames with a multilink device to which EML mode was applied can immediately begin a new frame exchange upon receiving the CF-End frame.

[0286] The aforementioned transmission restriction due to link switching may only be applied to links that have lost the ability to transmit, receive, or monitor in EML mode, for example, links where no frame exchange occurred in EMLSR mode. In other words, the transmission restriction due to link switching does not need to be applied to links that have not lost the ability to transmit, receive, or monitor in EML mode, for example, links where frame exchange occurred in EMLSR mode. For example, if the EML links are the first and second links, and frame exchange occurs on the first link in EML mode, the transmission restriction may be applied only to the second link when the frame exchange on the first link is completed. Also, the transmission restriction does not need to be applied to the first link when link switching occurs.

[0287] When the above embodiment is applied, the multilink device that performed link switching needs to recover monitoring for links that have lost the ability to transmit, receive, or monitor in EML mode, for example, links where frame exchange did not occur in EMLSR mode, within a predetermined time from the end of frame exchange. In addition, a station, for example, the AP of an AP multilink device, can start frame exchange for multilink devices to which EML mode is applied on links that have lost the ability to transmit, receive, or monitor in EML mode, for example, EML links where frame exchange did not occur in EMLSR mode, after a predetermined time from the end of frame exchange.

[0288] A station using EML mode can transmit a frame indicating the end of frame exchange. This frame may be a CF-End frame. For example, a station that has completed frame exchange in EML mode can transmit a CF-End frame before the TXOP configured for frame exchange terminates. In this case, a multilink device that receives the CF-End frame can determine that the multilink device that transmitted the CF-End frame has completed frame exchange in EMLSR mode or EMLMR mode. This allows for faster frame exchange on links where transmission and reception were restricted by link switching.

[0289] Furthermore, in the frame exchange sequence immediately following an RF chain change, a station attempting to transmit to a single-radio multilink device can determine the format of the PPDU to be transmitted initially in the frame exchange sequence based on the time required for the RF chain change at the single-radio multilink device. Also, in the first frame exchange sequence following an RF chain change, a station attempting to transmit to a single-radio multilink device can determine the length of the padding used for the initial PPDU transmission based on the time required for the RF chain change at the single-radio multilink device. In this case, the padding may be either physical layer padding or MAC layer padding. Specifically, a station can set the padding of packets transmitted to a single-radio multilink device with a relatively short RF chain change time to be shorter than the padding of packets transmitted to a single-radio multilink device with a relatively long RF chain change time.

[0290] In further specific embodiments, padding may be inserted into the initial control frame, which is the first control frame transmitted during frame exchange in EMLSR mode. In this case, the padding length (duration) may be determined based on the link switching time. Specifically, the multilink device may insert padding into the initial control frame that is equal to or longer than the padding length corresponding to a time equal to or greater than the difference between the link switching time and (2x SIFS + CTS_time). In this case, CTS_time represents the time (air time) required to transmit the CTS frame. That is, the multilink device may insert padding into the initial control frame that is equal to or longer than the padding length corresponding to a time obtained by subtracting (2x SIFS + CTS_time) from the link switching time. In further specific embodiments, the multilink device may insert padding into the initial control frame that is equal to or longer than the padding length corresponding to a time equal to or greater than the difference between the link switching time and SIFS. A multilink device can insert padding into the initial control frame that is equal to or longer than the padding length corresponding to the time obtained by subtracting the SIFS from the link switching time.

[0291] In such embodiments, the multilink device supporting the EMLSR mode can signal the padding length (duration) of the initial control frame to the other multilink device. For example, in the embodiments described above, the multilink device supporting the EMLSR mode can signal the padding length of the initial control frame instead of the link switching time. In this case, the other multilink device can insert padding into the initial control frame that corresponds to a time longer than the signaled padding length. For example, the other multilink device can insert padding of the signaled padding length into the initial control frame.

[0292] These embodiments allow the multilink device to have time to set up the RF chain while the initial control frame padding is being transmitted.

[0293] Figure 39 shows that a single-radio multilink device according to an embodiment of the present invention transmits PPDU using MIMO.

[0294] A station attempting to transmit MIMO to a single radio multilink device can begin RTS / CTS frame exchange at the start of transmission after changing the RF chain. In this case, the RTS frame allows time for the RF chain to change and then protects the frame exchange. If it is determined that the RF chain change is not complete even after the RTS / CTS frame exchange, the station attempting to transmit MIMO to a single radio multilink device does not need to perform MIMO transmission. In this case, the station attempting to transmit MIMO to a single radio multilink device can transmit using a single spatial stream.

[0295] When a single radio multilink device transmits or receives on any one link, it cannot transmit or receive on any other link. Therefore, when a single radio multilink device transmits or receives on any one link, stations operating on other links can be considered blind. Consequently, when a single radio multilink device transmits or receives on any one link, an AP attempting to transmit to the single radio multilink device does not need to transmit to stations operating on other links. In this case, the AP attempting to transmit to the single radio multilink device may interrupt any transmission it is currently making to stations operating on other links.

[0296] When a single-radio multilink device transmits or receives on any one link, an AP that transmits to or interrupts transmission to a station of the single-radio multilink device does not need to increment the CW of the backoff procedure used for channel access for transmission. Subsequently, when the single-radio multilink device attempts to transmit to that station again, it can take the backoff counter within the previously used CW. This means that a station that transmits to or interrupts transmission to a station of the single-radio multilink device does not need to increment the CW of the backoff procedure used for channel access for transmission if a predetermined condition is met. The predetermined condition may be that, according to the embodiment described above, the station has determined that one of the stations of the single-radio multilink device is transmitting or receiving. Specifically, if the station determines that a station that transmits a PPDU received by another station in the multilink device that the station includes is included in the single-radio multilink device, the station can determine that one of the stations of the single-radio multilink device is transmitting. At this time, the station can determine the station transmitting the PPDU based on the identifier of the station transmitting the PPDU indicated by the signaling field of the PPDU. At this time, the station can determine which station of the single multilink device the STA-ID in the User field of the HE PPDU indicates. The station can also determine which station of the single multilink device the STA-ID in the User field of the EHT PPDU indicates. Furthermore, the station can determine which station of the single multilink device the TA field of the MAC frame contained in the PPDU indicates. The MAC frame may be any one of the MSDU, MPDU, or A-MPDU. This may be similar to the embodiment applied to transmission to a non-STR multilink device described earlier in Figure 19. Also, in the case of a channel access procedure to which EDCA is applied, the aforementioned CW can indicate the CW of the AC used for channel access.

[0297] Furthermore, if a transmission to another station of the single-radio multilink system fails due to a transmission or reception by any one station of the single-radio multilink system, the station that performed the transmission to the other station does not need to increment its retry counter. In this case, the retry counter may include at least one of a long retry counter and a short retry counter.

[0298] Furthermore, the aforementioned embodiment regarding maintaining the CW size does not necessarily apply when a station transmits an MU PPDU to multiple stations, including a station with a single radio multilink device. Specifically, if a station transmits an MU PPDU to multiple stations, including a station with a single radio multilink device, but does not receive a response from any of the stations, the station that transmitted the MU PPDU can increase the CW size. In this case, the station that transmitted the MU PPDU can increase the CW value to the next largest possible value among the possible CW values. If the CW value is at its maximum value, the station that transmitted the MU PPDU may keep the CW value at the same value.

[0299] In the embodiment shown in Figure 39, the single-radio multilink device includes a first station STA1 operating on the first link Link1 and a second station STA2 operating on the second link Link2. The station attempts to transmit to the first station STA1 using MIMO and successfully accesses the channel on the first link Link1, sending an RTS frame to the first station STA1. The first station STA1 sends a CTS frame in response to the RTS frame. The RF chain change of the single-radio multilink device is completed, and a PPDU is received using 2x2 MIMO. After the first station STA1 receives the PPDU, the single-radio multilink device changes the RF chain, and the second station STA2 waits for NAVSyncdelay from the time the RF chain was changed before starting channel access on the second link Link2.

[0300] <NDP (null data packet) transmission procedure for a single radio multilink device>

[0301] As mentioned earlier, a single-radio multilink device can perform MIMO by changing the link on which the RF chain operates. When the link on which the RF chain operates is changed, learning of the RF characteristics of the changed link is required before MIMO communication can begin.

[0302] Because the channel characteristics of the RF chain have not been learned, closed-loop beamforming may not be usable. Therefore, channel estimation may be necessary. Specifically, a single radio multilink device can perform channel estimation using the NDP sounding protocol. In an explicit NDP sounding sequence, the beamformer transmits an NDP announcement (NDPA) followed by an NDP. At this time, the interval between the NDPA and the NDP is SIFS. If the STA User Info list field of the NDPA indicates the station, the station, after receiving the NDP, transmits channel state information (CSI) feedback measured at the time of receiving the NDP to the beamformer.

[0303] At this time, RTS frame / CTS frame exchange may occur before the NDP sounding protocol is performed. Specifically, a single radio multilink device and a station attempting to initiate the NDP sounding protocol can transmit an RTS frame before transmitting an NDPA frame. For the sake of explanation, a single radio multilink device and a station attempting to initiate the NDP sounding protocol will be referred to as the NDP sounding protocol initiation station. The above embodiment allows the NDP sounding protocol initiation station to protect the NDP sounding sequence. This also allows time to be allocated for RF chain changes. Furthermore, the NDP sounding protocol initiation station can perform the MU-RTS frame / CTS frame exchange procedure instead of the RTS frame / CTS frame exchange procedure. Also, the NDP sounding protocol initiation station can perform trigger frame and response exchange of a different type than MU-RTS frames instead of the MU-RTS frame / CTS frame exchange procedure. Furthermore, in such embodiments, the NDP sounding protocol initiation station can transmit MU-RTS frames, trigger frames of a different type from MU-RTS frames, and NDPA frames in a pre-specified PPDU format. Specifically, the pre-specified PPDU format may be at least one of either a non-HT format or an HT format. In addition, the NDP sounding protocol initiation station can transmit MU-RTS frames, trigger frames of a different type from MU-RTS frames, and NDPA frames at a data rate below a pre-specified rate.

[0304] An NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence based on the time required for RF chain changes. An NDP sounding protocol initiation station can use a longer NDP sounding sequence when exchanging it with a single radio multilink device that has a relatively long RF chain change time, compared to when exchanging it with a single radio multilink device that has a relatively short RF chain change time. In this case, the NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence by omitting a portion of it. Furthermore, the NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence by adjusting the padding of the frames exchanged in the NDP sounding sequence. Additionally, the NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence by transmitting additional frames in the NDP sounding sequence. In this case, the padding may be physical layer padding or MAC layer padding. Therefore, in the embodiments described below, the padding may be the padding of the N-physical layer or the padding of the MAC layer.

[0305] Furthermore, when an NDP sounding protocol initiation station performs the NDP sounding protocol with multiple single-radio multilink devices, the NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence based on the longest time required for RF chain changes among the multiple single-radio multilink devices. The method for adjusting the length of the NDP sounding sequence is explained in Figures 40 to 42.

[0306] Figure 40 shows a station and a single radio multilink device according to an embodiment of the present invention performing an NDP sounding process.

[0307] As mentioned above, the NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence by adjusting the padding of the frames exchanged in the NDP sounding sequence. If the NDP sounding sequence includes RTS frame / CT frame exchange, the NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence by inserting padding into the RTS frame. Specifically, if the NDP sounding protocol initiation station determines that the RF chain change is not complete even after the RTS frame / CTS frame exchange, the NDP sounding protocol initiation station can insert padding into the RTS frame.

[0308] In another specific embodiment, if the NDP sounding protocol initiation station determines that the RF chain change is not complete even after the RTS frame / CTS frame exchange, the NDP sounding protocol initiation station can transmit an MU-RTS frame instead of an RTS frame. In this case, the NDP sounding protocol initiation station can insert padding into the MU-RTS frame.

[0309] In the embodiment described above, the NDP sounding protocol initiation station can determine whether the RF chain change will be completed after the RTS frame / CTS frame exchange based on whether the RF chain change is completed after a time equal to the length of the CTS frame plus 2 x SIFS has elapsed from the time the single radio multilink device completes receiving the RTS frame. The time of RTS reception completion may be one of the following: the time when the transmission of the PPDU containing the RTS frame begins, the time when the physical layer header of the PPDU completes transmitting the RTS frame, the time when the transmission of the PPDU containing the RTS frame is completed, or the time when the transmission of the RTS frame or the A-MPDU containing the RTS frame is completed. In addition, in the embodiment described above where the MU-RTS frame is used instead of the RTS frame, the MU-RTS frame may be applied instead of the RTS frame. Figure 40(a) shows that the NDPA frame, NDP frame, and feedback frame are exchanged after the RTS frame / CTS frame exchange according to the embodiment described above. At this time, the NDP sounding protocol initiation station performs MIMO transmission based on the received feedback frame.

[0310] Furthermore, the NDP sounding protocol initiation station may omit the transmission of NDPA frames in the NDP sounding sequence. In this case, the NDP sounding protocol initiation station and the single radio multilink device can discuss performing the NDP sounding protocol without transmitting NDPA frames. Therefore, the single radio multilink device station can wait for NDP reception without receiving NDPA frames. Specifically, the single radio multilink device station can signal that it can receive NDP without receiving NDPA using the Capability element. In a specific embodiment, the single radio multilink device station can set the NDPA compression support subfield of the Capability element to 1 to signal that it can receive NDP frames without receiving NDPA frames. Alternatively, the radio multilink device station can set the NDPA compression support subfield of the Capability element to 0 to signal that it cannot receive NDP frames without receiving NDPA frames. The NDP sounding protocol initiation station can decide whether or not to omit the transmission of NDPA frames. In this case, the NDP sounding protocol initiating station can omit the transmission of an NDPA frame in the NDP sounding sequence performed on a single radio multilink device that has received confirmation that it can receive an NDP frame without receiving an NDPA frame. Furthermore, this embodiment of omitting the transmission of an NDPA frame from the NDP sounding sequence is applicable only when the NDP sounding protocol initiating station transmits an NDP to a single station. In this case, if the NDP sounding protocol initiating station transmits an NDP to multiple stations, the transmission of an NDPA frame cannot be omitted. Figure 40(b) shows that, according to the embodiment described above, an NDP frame and a feedback frame are exchanged without an NDPA frame after the RTS frame / CTS frame exchange.At this time, the NDP sounding protocol initiation station performs MIMO transmission based on the received feedback frame.

[0311] In the embodiment described above, excessive overhead may occur because the NDP sounding sequence includes an NDPA frame, an NDP frame, and a control frame exchange before the feedback frame exchange. Furthermore, excessive overhead may occur even if the NDPA transmission is omitted. An implicit feedback beamforming sounding sequence may be performed to reduce this excessive overhead. This is explained in Figure 41.

[0312] Figure 41 shows a station and a single radio multilink device according to an embodiment of the present invention performing a feedback beamforming sounding sequence.

[0313] A frame exchange initiation station can omit not only NDPA frame transmission but also NDP frame transmission and feedback frame transmission. However, the frame exchange initiation station can measure the channel state while receiving PPDUs containing control frames, such as RTS frames, MU-RTS frames, and responses to different types of trigger frames. Based on the measured channel state, the frame exchange initiation station can acquire a steering matrix to be used for MIMO transmission. Specifically, the frame exchange initiation station can acquire a steering matrix based on the measured channel state. The frame exchange initiation station can perform MIMO transmission using the acquired steering matrix.

[0314] In such an embodiment, the frame change initiation station can insert padding into the control frame based on the time required for the RF chain change, as described above. Specifically, the frame change initiation station can insert padding into the control frame based on the time required for the RF chain change minus the SIFS.

[0315] Furthermore, the frame exchange initiation station can transmit a QoS data frame instead of a control frame. In this case, the single-radio multilink device can transmit an Ack frame or a Block Ack frame as a response to the QoS data frame.

[0316] Furthermore, in the embodiment described above, the frame exchange initiation station can set the TRQ (training request) bit of the control frame and QoS data frame to 1.

[0317] Furthermore, in the embodiment described above, even if the control frame is such that multiple stations can be set as receivers, like the MU-RTS frame, only one station may be set as the receiver of the control frame.

[0318] In the embodiment shown in Figure 41(a), the frame exchange initiation station transmits a MU-RTS frame with the TRQ field set to 1. The frame exchange initiation station transmits a PPDU containing the MU-RTS frame, and measures the channel state while receiving a PPDU containing a CTS frame, which is the response to the MU-RTS frame. Based on the acquired channel state, the frame exchange initiation station obtains a steering matrix and uses the acquired steering matrix to perform MIMO transmission. In the embodiment shown in Figure 41(b), the frame exchange initiation station transmits an RTS frame instead of a MU-RTS frame. This may occur if the time required for RF chain change is shorter than SIFS. Subsequently, the frame exchange initiation station and the station of the single-radio multilink device operate in the same manner as in the embodiment shown in Figure 41(a), except that in the embodiment shown in Figure 41(b), the station of the single-radio multilink device transmits a BA frame in SISO (single input single output).

[0319] In the frame exchange sequence that takes place immediately after an RF chain change, the final frame exchange may be performed in SISO (single input single output) (1x1). Specifically, a station of a single radio multilink device can transmit the last frame of the frame exchange sequence that takes place immediately after an RF chain change in SISO (1x1). Also, if there are no frames remaining to transmit or receive in MIMO in the frame exchange sequence that takes place immediately after an RF chain change, a station of a single radio multilink device can change the RF chain. Specifically, a station of a single radio multilink device can begin changing the RF chain before transmitting the last frame of the frame exchange sequence that takes place immediately after an RF chain change.

[0320] Figure 42 shows a station and a single radio multilink device according to an embodiment of the present invention performing an NDP sounding process.

[0321] An NDP sounding protocol initiation station can determine the MIMO transmission initiation time based on the time required for RF chain changes in a single radio multilink device. Specifically, the NDP sounding protocol initiation station can delay the MIMO transmission initiation time to the time when the RF chain change of the single radio multilink device is completed. For example, if the RF chain change is not completed during control frame / response frame exchange, such as RTS frame / CTS frame or MU-RTS frame / CTS frame exchange, the NDP sounding protocol initiation station can delay the MIMO transmission initiation time. Specifically, the NDP sounding protocol initiation station can transmit the first PPDU sent after the control frame / response to the control frame using SISO.

[0322] If the RF chain change is not completed in this manner, MIMO transmission from the NDP sounding protocol initiating station does not need to be permitted. Furthermore, the explicit and implicit NDP sounding protocols mentioned above do not need to be permitted before the RF chain change is complete.

[0323] Furthermore, the NDP sounding protocol initiation station can determine whether the RF chain change is complete during the exchange of control frames / response frames to control frames, based on the time it takes for the RF chain change to occur as indicated by the Capability element transmitted by the single radio multilink device.

[0324] When a single radio multilink device transmits using SISO, a station that has performed a frame-exchange sequence on a link that supports the use of multiple RF chains can transmit the remaining frames from that frame-exchange sequence using SISO. For convenience of explanation, in the description relating to this embodiment, a station that has performed a frame-exchange sequence on a link that supports the use of multiple RF chains will be referred to as a frame-exchange sequence execution station. That is, when a single radio multilink device transmits using SISO, the frame-exchange sequence execution station is not permitted to transmit the remaining frames from that frame-exchange sequence using MIMO. Specifically, when a single radio multilink device transmits an ACK to the transmission of the frame-exchange sequence execution station using SISO, the frame-exchange sequence execution station can transmit the remaining frames from that frame-exchange sequence using SISO. In this case, the ACK may include ACK frames and BA frames. Therefore, when a single radio multilink device transmits an ACK to the transmission of the frame-exchange sequence execution station using SISO, the frame-exchange sequence execution station cannot transmit the remaining frames from that frame-exchange sequence using MIMO.

[0325] In the embodiments shown in Figures 42(a) and 42(b), the RF chain change of the single radio multilink device was not completed even during the RTS frame and CTS frame exchange. Therefore, in the embodiment shown in Figure 42(a), SISO is used even after the RTS frame and CTS frame exchange until the PPDU and BA frame are transmitted. When the NDP sounding protocol initiation station receives an ACK frame, it determines that the RF chain change is complete. At this time, the NDP sounding protocol initiation station starts the sounding protocol using MIMO (2x2).

[0326] Furthermore, in the embodiment shown in Figure 42(b), SISO is used from the RTS frame and CTS frame exchange until PPDU transmission. Since the RF chain change is completed after PPDU reception, the first station STA1 of the single-radio multilink device transmits a BA frame using MIMO(2x2). Because the first station STA1 of the single-radio multilink device transmits a BA frame using MIMO(2x2), the NDP sounding protocol initiation station determines that MIMO(2x2) transmission is permitted. Therefore, after receiving the BA frame transmitted using MIMO(2x2), the NDP sounding protocol initiation station transmits a PPDU using MIMO(2x2).

[0327] Despite the increase in WLAN transmission speeds, transmission delay remains a problem for some services. In particular, WLANs operating on unlicensed bandwidth are unsuitable for operating services that require low-latency transmission because it is difficult to predict the time it takes to transmit traffic. EDCA has been introduced to address this problem. A station that supports EDCA is called a QoS station, an AP that supports EDCA is called a QoS AP, and a BSS that supports EDCA is called a QoS BSS. For the sake of explanation, QoS APs will be referred to as APs, QoS stations as stations, and QoS BSSs as BSSs. In EDCA, traffic is classified into four ACs (access categories) based on its characteristics. These four ACs are AC_VO (AC Voice), AC_VI (AC Video), AC_BE (AC Best Effort), and AC_BK (AC Background). In the backoff procedure described above, the AC determines the values ​​of the CW parameters. The AC may also determine the maximum value of TXOP. Furthermore, the AC may determine the value of the AIFSN parameter. This may adjust the priority of traffic transmission for each AC. Traffic may be mapped to four ACs based on either a TC (traffic category) or a TS (traffic stream). The traffic mapped to the four ACs is managed by four queues, each operated separately for each AC.

[0328] AC_VO is an AC for traffic that is not as large in absolute volume as voice traffic but is vulnerable to transmission delay, and is mapped to relatively small CW and AIFSN parameter values. However, the maximum TXOP value for AC_VO is relatively smaller than the maximum TXOP value for other ACs. AC_VI is an AC for video traffic that is more tolerant of transmission delay than voice traffic but requires low-latency transmission and must handle a large volume of traffic. AC_VI is mapped to CW and AIFSN parameter values ​​that are larger than AC_VO but smaller than the CW and AIFSN parameters for other ACs. The maximum TXOP value for AC_VO is approximately twice as long as the maximum TXOP value for AC_VI. AC_BE is an AC for traffic that is tolerant of transmission delay, and most general traffic other than voice data and streaming video data may be classified as AC_BE. The CW and AIFSN parameters for AC_BE are mapped to larger values ​​than the CW and AIFSN parameters for AC_VO and AC_VI. Furthermore, no other TXOP maximum value is mapped to AC_BE. Transmission using a continuous transmit sequence is not permitted for AC_BE. AC_BK is an AC for traffic that is as tolerant of transmit delay as AC_BE, but has a lower priority than BE traffic. AC_BK is mapped to the same CW parameter values ​​as AC_BE, and the AIFSN parameter value is mapped to a value greater than the AIFSN parameter of AC_BE. Furthermore, no other TXOP maximum value is mapped to AC_BK. Transmission using a continuous transmit sequence is not permitted for AC_BK.

[0329] The four ACs mentioned above are mapped to 802.1D UP (user-priority), and the EDCA AC is determined by the UP value of the wired traffic or the TID of the MSDU indicated from the upper layer. In this case, if the TID of the MSDU indicates a value between 0 and 7, the value indicated by the TID can correspond one-to-one with UP.

[0330] Figure 43 shows the mapping relationship between UP and AC.

[0331] The default CW parameters (CWmin, CWmax), AIFSN parameters, and TXOP maximum values ​​for each of the four ACs are defined by the 802.11 standard. The AC's CW parameters (CWmin, CWmax), AIFSN parameters, and TXOP maximum values ​​can be changed by the AP, and different values ​​may be used for each BSS. EDCA places traffic in the queue corresponding to the traffic's AC among the four queues. Channel access conflicts occur between the four ACs, and the traffic of the AC that wins the conflict is transmitted. AC-specific access parameters (CW[AC], AIFSN[AC]) are used in channel access conflicts. In this case, the channel access operation is the same as the DCF channel access operation.

[0332] As mentioned above, since channel access parameter values ​​differ for each AC, transmission priority can be applied separately for each AC.

[0333] In addition to EDCA, the 802.11 MAC protocol may also apply HCCA (HCF controlled channel access) for QoS management. HCCA provides a centralized / hybrid coordinator function to ensure TS (Traffic Stream) QoS for applications that must be serviced periodically (such as voice and video). Other functions such as SPCA (Service Period Channel Access) and dynamic allocation of service period may also be used. However, this is only available for DMG stations.

[0334] A method for enhancing QoS for multilink devices may be necessary. Independent transmit queues may be used for each link in the multilink device. In this case, the queues may be logically independent. When traffic is mapped to each link, the QoS of the traffic can be enhanced. This will be explained using Figure 44.

[0335] Figure 44 shows that, according to an embodiment of the present invention, a multilink device transmits traffic mapped to each station of the multilink device.

[0336] In Figure 44, the AP multilink device (AP MLD) includes (affiliated) APs 1 through 4 (AP4). The non-AP multilink device (Non-AP MLD) includes stations 1 through 4 (non-AP STA1 through non-AP STA4). Each of stations 1 through 4 operates on links 1 through 4 (Link1 through Link1). Each of APs 1 through 4 operates on links 1 through 4 (Link1 through Link1). In this case, traffic is mapped to each of APs 1 through 4 (AP4) separately. AC_BK is mapped to AP1 (1st AP), AC_BE is mapped to AP2 (2nd AP), AC_VI is mapped to AP3 (3rd AP), and AC_VO is mapped to AP4 (4th AP). As a result, in the AP Multilink Device (AP MLD), traffic corresponding to AC_BK is transmitted at AP1 (1st AP), traffic corresponding to AC_BE is transmitted at AP2 (2nd AP), traffic corresponding to AC_VI is transmitted at AP3 (3rd AP), and traffic corresponding to AC_VO is transmitted at AP4 (4th AP). The channel quality and load conditions of each link may differ. Also, the performance and operating bandwidth of each station may differ. Therefore, the bandwidth and MCS of the PPDU containing the traffic may change depending on which traffic the multilink device maps to which link.

[0337] For example, if the first AP (AP1) of an AP Multilink Device (AP MLD) operates in the 2.4GHz band, AP1 can operate a 40MHz operating channel. If the fourth AP (AP4) operates in the 6GHz band, AP4 can operate a maximum of 320MHz operating channel. The AP Multilink Device (AP MLD) can map traffic requiring high processing volume and low-latency transmission to AP4. The multilink device can map traffic to each of its multiple links, taking into account the characteristics of the traffic. This enhances the QoS of traffic transmission.

[0338] To further refine QoS enhancements, each link may be mapped to a TID, and traffic corresponding to the TID mapped to that link may be given priority. This will be explained using Figure 45.

[0339] Figure 45 shows an embodiment of the present invention in which a multilink device performs frame replacement by TID link mapping.

[0340] Traffic transmitted over a WLAN is identified by a TID. MAC frames, such as data frames or QoS data frames, signal the TID of the traffic they contain using the TID service field. The QoS control field may include the TID service field. The TID identifies the traffic contained in the MSDU, fragment, or A-MSDU of the MAC frame. The TID also corresponds to UP (user priorities) or TSID (traffic stream identifier). The TID service field is a 4-bit field and can represent values ​​from 0 to 15. When the value of the TID subfield is one of 0 to 7, the value of the TID subfield indicates the UP of the MSDU contained in the frame body of the MAC frame containing the TID subfield. The MAC frame is processed by EDCA using the AC parameter corresponding to UP in the MAC entity. When the value of the TID subfield is one of 8 to 15, the value of the TID subfield indicates the TSID of the MSDU contained in the frame body of the MAC frame containing the TID subfield. MAC frames are processed by the MAC entity using parameters corresponding to UP for the TSID, as indicated in the User Priority service field of the TS Info field in the TSPEC. UP for the TSID may be indicated in the User Priority field of the TCLAS. The Access Policy for the TSID is indicated by the Access Policy field in the TS Info subfield. The 7th and 8th bits of the Access Policy subfield are set to 10. b In that case, EDCA is shown, 11 b This indicates HCCA.

[0341] When a multilink device maps a TS's TID to a link, it can obtain information about the TS's UP and the alternate queue used for TS transmission from the Intra-Access Priority field of the Intra-Access Category Priority element of the ADDTS Request frame used when generating the TS. The multilink device can then use the obtained information about the UP and alternate queue when transmitting traffic corresponding to the TS's TID.

[0342] A TID may be mapped to each of the multiple links on which a multilink device operates. In this case, the multilink device can signal information about the TID mapped to each link to an associated multilink device. Upon receiving the signal, the multilink device can accept or reject the link mapping with the TID. If an agreement on the mapping between the TID and the links cannot be reached, frame exchange may be performed on each link without TID restrictions. Furthermore, in other specific embodiments, if an agreement on the mapping between the TID and the links cannot be reached, frame exchange may be performed on each link using the default mapping between the TID and the links.

[0343] When a multilink device maps TIDs to links, the multilink device must map all TIDs to one or more links. In a specific embodiment, the multilink device may transmit frames containing traffic corresponding to TIDs mapped to a link, and may not be permitted to transmit frames containing traffic corresponding to TIDs not mapped to a link. The mapping between TIDs and links may be performed separately for each multilink device. Furthermore, the mapping between TIDs and links may be mapped according to the transmission direction. For example, the TIDs mapped to the uplink and the TIDs mapped to the downlink may be different on a single link. Therefore, when a first multilink device and a second link device are connected via the first and second links, the first multilink device can map TID values ​​0 to 3 to the first link, and the second multilink device can map TID values ​​4 to 7 to the first link.

[0344] In this specification, mapping between TID and links may be replaced by mapping between AC and links, or mapping between UP and links, or mapping between TC and links, or mapping between TS and links.

[0345] Furthermore, any remaining TID values ​​not explicitly specified in the TID-to-link mapping may be mapped to the remaining links. For example, if it is signaled that TID values ​​0-3 are mapped to the first link, any remaining TID values ​​other than 0-3 may be mapped to the second link. In other specific embodiments, the transmission of traffic corresponding to all TIDs may be permitted on the second link.

[0346] Furthermore, the mapping between TIDs and links may be changed during operation, in addition to being initially linked between multilink devices. When a multilink device disassociates a station on a specific link, the multilink device can change the mapping between TIDs and links. In this case, the multilink device can disassociate a station when the station on a specific link enters power-saving mode. A multilink device can also request a peer multilink device to change the mapping between TIDs and links. For example, if TID values ​​0-3 are mapped to the first link, a non-AP multilink device can request an AP multilink device to map TID values ​​0-3 to the second link. Specifically, if a multilink device finds it difficult to guarantee QoS for the traffic mapped to a link, it can request a peer multilink device to change the mapping between TIDs and links.

[0347] Furthermore, if a multilink device rejects a TID-to-link mapping request, the multilink device that sent the TID-to-link mapping request may be restricted for a predetermined time from requesting the same TID-to-link mapping again that it had previously requested. This is to prevent repeated TID-to-link mapping requests. In this case, the predetermined time may be a time indicated by the AP. Specifically, the AP multilink device can signal the predetermined time using BSS operation parameters.

[0348] This section describes how to signal the mapping between TIDs and links. A multilink device can signal the mapping between TIDs and links using a TID-to-Link Mapping element. The TID-to-Link Mapping element may include a Link ID field. The Link ID field indicates the link that the TID-to-Link Mapping element signals. The TIDs Info field indicates information about the TID mapped to the link indicated by the Link ID field. The TIDs Info field may include a field that shows the value of the TID mapped to the link indicated by the Link ID field. In this case, the TIDs Info field may include a bitmap that shows the value of the TID mapped to the link indicated by the Link ID field. In this case, each bit of the bitmap is mapped to a specific TID, and when a bit is set to 1, it can indicate that the TID corresponding to that bit is mapped to the link indicated by the Link ID field.

[0349] In the embodiment shown in Figure 45, the AP multilink device (AP MLD) plans to transmit traffic with TIDs 0-3 to the non-AP multilink device (non-AP MLD) via the first link (Link1). The AP multilink device (AP MLD) signals the non-AP multilink device (non-AP MLD) to map TID values ​​0-3 to the first link (Link1) and TID values ​​4-7 to the second link (Link2) using a TID-to-Link Mapping element. The TID-to-Link Mapping element includes two Link ID fields, one indicating the first link and the other the second link, and two TIDs Info fields, one indicating information about the TID mapped to the first link and the other indicating information about the TID mapped to the second link. The TIDs Info fields may each contain 7 bits indicating TIDs 0 through 7. For example, to indicate TIDs 0-3, the 8 bits of the TIDs info subfield may be 11110000. b Set to 00001111 to indicate TID4-7, the 8 bits of the TIDs info subfield are set to 00001111 b It may be set to this.

[0350] In further specific embodiments, the TIDs Info field may include a Min TID field and a Max TID field. The Min TID field indicates the minimum value of the TIDs mapped to the link corresponding to the TIDs Info field, and the Max TID field indicates the maximum value of the TIDs mapped to the link corresponding to the TIDs Info field. Each of the Min TID field and the Max TID field may be a 3-bit or 4-bit field. For example, if both the Min TID field and the Max TID field are 3 bits, and the TIDs Info field indicates a value between 0 and 3, then the Min TID field is set to 000 and the Max TID field is set to 011 bIt may be set to this. As mentioned above, the TID-to-Link Mapping element may signal only for TIDs mapped to the first link, and implicitly signal for TIDs mapped to the second link. Specifically, since the TID-to-Link Mapping element explicitly signals that TIDs 0 through 7 are mapped to the first link, the TID-to-Link Mapping element can implicitly signal that the remaining TIDs are mapped to the second link.

[0351] Non-AP multilink devices accept the mapping between TIDs and links indicated by the TID-to-Link Mapping element.

[0352] When multiple TIDs are mapped to a single link, and multiple TIDs correspond to two or more ACs, the multilink device can differentiate the ACs and transmit traffic using EDCA. For example, if a TID corresponding to AC_VO and a TID corresponding to AC_BK are mapped to the first link, the multilink device can use EDCA to transmit traffic corresponding to AC_VO with priority over traffic corresponding to AC_BK. Furthermore, every TID must be mapped to at least one link, and the multilink device does not need to allow mapping requests between links for TIDs that are not mapped to any link.

[0353] Figure 46 shows that the basic mapping between TID and links has been set up in the AP multilink device and the non-AP multilink device according to the embodiment of the present invention.

[0354] As mentioned above, the basic mapping between TIDs and links is applied when no other mapping between TIDs and links is configured. In the example shown in Figure 46, the basic mapping between TIDs and links maps all TIDs and TSIDs to the links.

[0355] In the aforementioned EML mode, frame exchange occurs on only one of the multiple links. Therefore, the QoS improvement effect sought from the mapping between TID and links may not apply to multilink devices operating in EML mode. For this reason, a TID-to-link mapping that takes this into account is necessary. This will be explained using Figures 47 to 51.

[0356] Figure 47 shows that the mapping between TID and links is changed when the multilink device according to an embodiment of the present invention activates the EMLSR mode.

[0357] Multilink devices to which EML mode is applied may not be permitted to perform TID-to-link mapping. Basic TID-to-link mapping may be applied to multilink devices to which EML mode is applied. In this case, multilink devices to which EML mode is applied cannot negotiate for TID-to-link mapping. When a multilink device to which EML mode is applied sends a TID-to-link mapping request, the other multilink device may reject the TID-to-link mapping request. Furthermore, in other specific embodiments, when a multilink device to which EML mode is applied sends a TID-to-link mapping request, the other multilink device does not need to send a response to the TID-to-link mapping request. In this case, the multilink device to which EML mode is applied does not need to perform TID-to-link mapping only for EML links. Therefore, even a multilink device to which EML mode is applied can perform TID-to-link mapping for links to which EML mode is not applied.

[0358] Furthermore, if a multilink device whose EML mode is not activated performs TID mapping to a link, and the EML mode of the multilink device is activated, the basic mapping between TID and the link may be applied to the EML link among the links on which the multilink device operates. In this case, the basic mapping between TID and the link may be performed without further negotiation.

[0359] Similarly, a multilink device connected to a multilink device with EML mode activated can also apply TID and basic link-to-link mapping to the EML link.

[0360] The multilink device can re-associate to activate EML mode. At this time, the multilink device can initialize the information for link operation. At this time, the multilink device can initialize the mapping between the link and TID.

[0361] In the embodiment shown in Figure 47, the AP multilink device (AP MLD) includes a first AP (AP1) and a second AP (AP2), and the non-AP multilink device (STA MLD) includes a first station (STA1) and a second station (STA2). The first AP (AP1) and the first station (STA1) operate on the first link (Link1), and the second AP (AP2) and the second station (STA2) operate on the second link (Link2). The AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) map TID values ​​from 0 to 3 to the first link (Link1) and TID values ​​from 4 to 7 to the second link (Link2). EMLSR mode is activated in the non-AP multilink device (STA MLD), and EMLSR mode is applied to both the first link (Link1) and the second link (Link2). At this time, the AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) apply a basic mapping between TIDs and links. That is, the AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) map TID values ​​from 0 to 7 to the first link (Link1) and map TID values ​​from 0 to 7 to the second link (Link2). At this time, the non-AP multilink device (STA MLD) can send a (Re)Association Request frame to activate EMLSR mode. At this time, the (Re)Association Request frame may include a Multi-Link element. The Multi-Link element will be explained using Figure 48.

[0362] Figure 48 shows the format of a Multi-Link element according to an embodiment of the present invention.

[0363] As mentioned above, the (Re)Association Request frame sent by a non-AP multilink device to activate EMLSR mode may include a Multi-Link element. In this case, the non-AP multilink device can set the EMLSR mode subfield of the Common Info field of the Multi-Link element to 1. In this case, the Common Info field of the Multi-Link element may be in Basic variant format. An AP multilink device that receives the Multi-Link element from a Non-AP multilink device can recognize that the Non-AP multilink device is attempting to activate EMLSR mode. In this case, both the AP multilink device and the Non-AP multilink device can activate EMLSR mode.

[0364] Using Figure 49, we will explain the mapping settings between TID and links when EML mode is activated and then deactivated.

[0365] Figure 49 shows that the mapping between the TID and the link is changed when the multilink device according to an embodiment of the present invention deactivates the EMLSR mode.

[0366] When EML mode is deactivated, the TID-to-link mapping used before EML mode was activated may be applied again. In this case, the multilink device does not need to negotiate the TID-to-link mapping again.

[0367] In the embodiment shown in Figure 49, the AP multilink device (AP MLD) includes a first AP (AP1) and a second AP (AP2), and the non-AP multilink device (STA MLD) includes a first station (STA1) and a second station (STA2). EMLSR mode is activated in the non-AP multilink device (STA MLD), and EMLSR mode is applied to both the first link (Link1) and the second link (Link2). The first AP (AP1) and the first station (STA1) operate on the first link (Link1), and the second AP (AP2) and the second station (STA2) operate on the second link (Link2). The AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) apply TID and basic mapping between links. In other words, the AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) map TID values ​​from 0 to 7 to the first link (Link1) and TID values ​​from 0 to 7 to the second link (Link2). The EMLSR mode is deactivated in the non-AP multilink device (STA MLD). The AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) apply the TID and link mapping that was applied before the EMLSR mode was activated to the first link (Link1) and the second link (Link2). In other words, the AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) map TID values ​​from 0 to 3 to the first link (Link1) and TID values ​​from 4 to 7 to the second link (Link2).

[0368] As mentioned above, an AP multilink device can send an initial control frame to a multilink device with EML mode activated in order to transmit. In this case, the initial control frame may be an MU-RTS frame or a trigger frame for another variant. The trigger frame for another variant may be an ML-RTS frame, which is an RTS frame for multilink. A non-AP multilink device that has received a trigger frame for another variant can send a response frame to that other variant's trigger frame. Specifically, the initial control frame may be a BSRP (buffer status report poll) trigger frame. In this case, a non-AP multilink device that has received a BSRP trigger frame can send a BSR frame as the response frame. The type of response frame to a trigger frame differs depending on the type of trigger frame, and the time required to send the response frame may vary. Therefore, a non-AP multilink device can set the length of the initial control frame based on the type of initial control frame. In this case, the padding may be to allow time for RF chain resetting, as mentioned above.

[0369] If the initial control frame is a MU-RTS frame, the MU-RTS frame may include padding that is equal to or longer than (RF switching latency - SIFS - CTStime - SIFS). If the initial control frame is a BSRP trigger frame, the BSRP trigger frame may include padding that is equal to or longer than (RF switching latency - SIFS - BSRtime - SIFS). In this case, BSRtime may be the transmission time of the BSR frame, for example, airtime. Alternatively, BSRtime may be a value determined assuming that the BSR frame is transmitted at a specific data rate. In yet another specific embodiment, a non-AP multilink device can determine the length of the padding of the trigger frame based on the value of the UL Length subfield in the Common Info field of the trigger frame. This is because the station receiving the trigger frame determines the length of the PPDU, which includes the response frame to the trigger frame, based on the value of the UL Length subfield in the Common Info field. Specifically, a non-AP multilink device may include padding in the trigger frame that is equal to or longer than (RF switching latency - SIFS - UL length (response frame length) indicated in the trigger frame - SIFS) time. If the initial control frame is a BSRP trigger frame, the non-AP multilink device may determine the length of the padding in the BSRP trigger frame based on the value of the UL Length subfield in the Common Info field of the BSRP trigger frame.

[0370] As mentioned above, a multilink device to which EML mode is applied can signal the duration of the RF chain change. An AP multilink device can determine the length of the padding in the initial control frame based on the signaled duration of the RF chain change. The AP multilink device can include padding in the initial control frame that corresponds to a duration equal to or longer than the signaled duration of the RF chain change. In yet another specific embodiment, a multilink device to which EML mode is applied can signal the padding length of the initial control frame. This will be illustrated with reference to Figure 50.

[0371] Figure 50 shows a Multi-Link element that signals information regarding the padding length of the initial control frame according to an embodiment of the present invention.

[0372] When a multilink device to which EML mode is applied is signaled the padding length of the initial control frame, the AP multilink device can determine the padding length of the initial control frame based on the signaled padding length. Specifically, the AP multilink device can include padding in the initial control frame that is equal to or longer than the signaled padding length. In this case, the padding length may be signaled separately for each type of trigger frame. In a specific embodiment, the signaled padding length may be the padding length that should be included in the MU-RTS frame. In this case, when the AP multilink device transmits an initial control frame that is not a MU-RTS frame, for example, a BSRP trigger frame, the AP multilink device can include padding of a length other than the signaled padding length in the initial control frame. The AP multilink device can determine the padding length of the initial control frame based on the difference between the transmission airtime of the CTS frame and the transmission airtime of the response frame to the initial control frame, and the signaled padding length. The AP multilink device can insert padding into the initial control frame that is equal to or longer than the length of the signaled padding plus a padding length corresponding to (CTStime - the transmission time of the response frame to the initial control frame (airtime)).

[0373] In yet another specific embodiment, the AP multilink device can calculate the time required for an RF chain change based on the length of the signaled padding. In this case, the AP multilink device can determine the length of padding included in the initial control frame based on the calculated time required for the RF chain change, because the length of the signaled padding is a value determined based on the time required for the RF chain change.

[0374] The padding length mentioned above may be signaled by the Multi-Link element. In the embodiment shown in Figure 50, the Multi-Link element includes an EMLSR Delay field indicating the padding length of the initial control frame.

[0375] As mentioned above, link switching performed in EML mode may result in the loss of transmit, receive, or monitor capability on some EML links. In this case, monitoring may include at least one of CCA and PD (preamble detection). Furthermore, even if a multilink device performs link switching to restore transmit, receive, or monitor capability on a link, the multilink device may be unable to transmit, receive, or monitor on that link for a predetermined period of time from the time of link switching. Specifically, the predetermined period may be determined based on the time required for link switching of the multilink device in which EML mode is activated. In a specific embodiment, the predetermined period may include the time interval during which the RF chain of the multilink device in which EML mode is activated is changed. A multilink device supporting EML mode and a station exchanging frames on an EML link can manage TXOP considering the frame exchange of the multilink device in EML mode. Similarly, a multilink device supporting EML mode can manage TXOP on an EML link considering the frame exchange of the multilink device in EML mode. This will be explained using Figure 51.

[0376] Figure 51 shows that a multilink device according to an embodiment of the present invention terminates TXOP on a link where frame exchange occurs in EMLSR mode, taking into account DTIM beacons received on an EMLSR link where frame exchange does not occur in EMLSR mode.

[0377] As mentioned above, link switching performed in EML mode may cause some links in the EML link to lose transmit, receive, or monitor capability. For example, if frame exchange occurs on one of the EMLSR links in EMLSR mode, the multilink device will not be able to transmit, receive, or monitor on the remaining EMLSR links. In this case, monitoring may include at least one of CCA and PD (preamble detection). Furthermore, even if the multilink device performs link switching to restore transmit, receive, or monitor capability on a link, the multilink device may not be able to transmit, receive, or monitor on that link for a predetermined period of time from the start of the link switching. In this case, the predetermined period may be a delay time for link switching. Specifically, the predetermined period may include a time interval in which the RF chain of the multilink device supporting EML mode is changed. A multilink device supporting EML mode and a station exchanging frames on an EML link can manage TXOP considering the frame exchange of the multilink device in EML mode. Similarly, a multilink device supporting EML mode can manage TXOP on an EML link considering the frame exchange of the multilink device in EML mode.

[0378] In EML mode, a multilink device with EML mode activated needs to receive a specific frame on a first link that has lost transmit, receive, or monitor capability in EML mode, for example, a first link where frame exchange is not taking place in EMLSR mode. In EML mode, the multilink device or a station exchanging frames with a multilink device in EML mode can terminate the TXOP for that frame exchange on a second link, which is one of the EML links where the frame exchange is taking place, based on the time the specific frame is received on the first link. For convenience of explanation, a multilink device with EML mode activated will be referred to as the multilink device, and a station exchanging frames with a multilink device with EML mode activated will be referred to as the station. In this case, if the multilink device is the TXOP holder, the station is the TXOP responder. Also, if the multilink device is the TXOP responder, the station is the TXOP holder. With EML mode activated, the TXOP on the second link may need to be terminated a predetermined time earlier than the time the multilink device attempts to receive a specific frame on the first link. In this case, the predetermined time may be determined based on the link switching delay of the multilink device. Specifically, the predetermined time may be determined based on the time required to change the RF chain of the multilink device. In a specific embodiment, the predetermined time may be the time required to change the RF chain of the multilink device. In this case, the specific frame may be a frame that is received periodically. Specifically, the specific frame may be a beacon frame. In a specific embodiment, the specific frame may be a DTIM beacon frame. Also, the time when the specific frame is to be received may be TBTT. The multilink device or station may terminate the TXOP for frame exchange on the second link, which was performing frame exchange in EML mode, based on the time when the specific frame was received on the first link.Furthermore, if the station is a TXOP holder, the station may terminate the TXOP on the second link based on information indicating that the multilink device is scheduled to receive a specific frame on the first link. In this case, the information indicating that the multilink device is scheduled to receive a specific frame on the first link may be signaled in a manner agreed upon between the multilink device and the station. The information indicating that the multilink device is scheduled to receive a specific frame on the first link may be information signaling that the beacon frame on the first link is a DTIM beacon frame. If the station is a TXOP holder and the beacon received on the first link is a DTIM beacon, the station may terminate the TXOP on the second link based on information indicating that the multilink device is scheduled to receive a specific frame on the first link.

[0379] Even if a multilink device to which EML mode is applied receives an initial control frame, the multilink device does not need to send a response frame to the initial control frame. Specifically, even if a multilink device to which EML mode is applied receives an initial control frame on the first link of the EML links, the multilink device does not need to send a response frame to the initial control frame in order to receive a specific frame on the second link of the EML links. For example, even if a multilink device to which EML mode is applied receives an initial control frame on the first link of the EML links, if the frame exchange initiated by the initial control frame does not finish by a predetermined time earlier than the time when it attempts to receive a specific frame on the second link of the EML links, the multilink device does not need to send a response frame to the initial control frame on the first link. If the frame exchange initiated by the initial control frame finishes by a predetermined time earlier than the time when it attempts to receive a specific frame on the second link, the multilink device can send a response frame to the initial control frame on the first link. In these embodiments, the initial control frame may be an MU-RTS frame, an ML-RTS frame, or a BSRP trigger frame, as described above. Even if a multilink device to which EML mode is applied receives an initial control frame that is either a MU-RTS frame or an ML-RTS frame, the multilink device does not need to send a CTS frame in response to the initial control frame. This allows the multilink device to refuse to initiate frame exchange. This is an exception to the rule in existing wireless LAN operation that a station must send a CTS frame when it receives a MU-RTS frame or an RTS frame. Specifically, even if a multilink device to which EML mode is applied receives an initial control frame on the first link, which is one of the EML links, the multilink device does not need to send a response frame to the initial control frame for frame exchange to take place on the second link.

[0380] A non-AP multilink device with activated EMLSR includes a first station (STA1) and a second station (STA2). The first station (STA1) operates on the first link (Link1), and the second station (STA2) operates on the second link (Link2). On the first link (Link1), the first station (STA1) receives an RTS frame from the first AP and transmits a CTS frame as a response to the RTS frame. The first station (STA1) receives a PPDU from the first AP on the first link (Link1). At this time, the first AP terminates the TXOP earlier than the scheduled beacon frame reception time on the second link (Link2) by the time required for the non-AP multilink device's RF change. This termination of the TXOP earlier than the scheduled beacon frame reception time on the second link (Link2) by the time required for the non-AP multilink device's RF change can also be applied when the first station (STA1) acquires the TXOP, as mentioned above.

[0381] When a multilink device with EMLSR mode activated receives a beacon frame, the EMLSR multilink device does not need to change the RF chain because the beacon frame is not transmitted in MIMO. When a multilink device with EMLSR mode activated receives a beacon frame on the first link, the multilink device with EMLSR mode activated can perform at least one of monitoring and channel access on the second link. In this case, even if the multilink device has completed the channel access procedure on the second link, it is not permitted to transmit. In yet another specific embodiment, the multilink device can perform at least one of transmitting and receiving on the second link only at a predetermined data rate. In this case, the predetermined data rate may be one of 6 Mbps, 12 Mbps, or 24 Mbps.

[0382] Further, a station that intends to exchange frames with a multi-link device in which EMLSR mode is activated may not be permitted to start a frame exchange procedure on a second link, which is one of the EMLSR links, when the multi-link device receives a specific frame on a first link, which is one of the EMLSR links. A station that intends to exchange frames with a multi-link device in which EMLSR mode is activated may not be permitted to transmit an initial control frame on a second link, which is one of the EMLSR links, when the multi-link device receives a specific frame on a first link, which is one of the EMLSR links. In this case, the specific frame may be a group-cast frame or a group-addressed frame, for example, a beacon frame. Specifically, the beacon frame may be a DTIM beacon frame.

[0383] <Receiving beacon frame by EMLSR MLD>

[0384] The EMLSR MLD may not perform an RF switching operation when receiving a beacon frame. This may be because beacon frames are generally not transmitted via MIMO. That is, the EMLSR MLD does not need to perform RF switching when receiving a beacon frame, and therefore, even when receiving a beacon frame on a specific link, the EMLSR MLD can perform monitoring (listening operation) and / or channel access operation for other links.

[0385] However, even when the EMLSR MLD performs reception without performing an RF switching operation for a specific link (as in the above example of beacon frame reception), operation and / or performance on other links may be restricted while reception is performed on the specific link.

[0386] As an example, when the EMLSR MLD is receiving a beacon frame on a specific link, channel access may be restricted even if the channel access procedure has been completed on another link. Alternatively, transmission and / or reception on another link performed while the EMLSR MLD is receiving a beacon frame on a specific link may be performed only at basic rates (6, 12, 24 Mbps).

[0387] This is because the EMLSR MLD does not perform RF switching for the operation of the specific link, so it may still be capable of transmission / reception and channel access operations on other links, but the operation on the other links may be restricted by the resources required for the operation on the specific link.

[0388] In addition, as described above, when the EMLSR MLD is receiving a frame (e.g., a beacon frame) on a specific link, operations on other links may be restricted. Therefore, a device (terminal) that intends to initiate a packet exchange procedure with the EMLSR MLD may be restricted from initiating the packet exchange procedure while the EMLSR MLD is performing a (beacon frame) reception operation. More specifically, when the EMLSR MLD is receiving a beacon frame (or a groupcast (group addressed) frame) on a specific link, the AP MLD may be prohibited from transmitting an initial control frame to the EMLSR MLD via another link. This may be a restriction applied because it is clear that the EMLSR MLD that has received the initial control frame cannot perform an RF switching operation after receiving the initial control frame (since the RF of another link is being used to receive the beacon frame). In this case, the beacon frame may be a DTIM beacon frame.

[0389] <EMLSR Operation and TXOP Management Method Considering the Operation Intention of EMLSR MLD>

[0390] The aforementioned TXOP management method, which takes RF switching delay into consideration, assumes that when an EMLSR MLD intends to receive a beacon frame / group-addressed frame scheduled for a specific EMLSR link, it will immediately prepare for reception on that specific EMLSR link as soon as the TXOP on other links terminates.

[0391] In short, an EMLSR MLD may, instead of switching to listening operation (a state that supports CCA etc. for the EMLSR link) after completing a packet exchange sequence (frame exchange, frame exchange sequence) on a specific EMLSR link, immediately prepare to receive frames scheduled on other EMLSR links (e.g., frames destined for beacons / groups). In this case, preparing to receive on other EMLSR links after completing frame exchange on a specific EMLSR link means a series of operations to utilize the transmission / reception functions for at least one RF chain and non-initial control frames (frames other than initial control frames) used on the specific EMLSR link on the other EMLSR link. This may be an exception to the operational restriction that an EMLSR MLD must switch to listening operation for an EMLSR link when the frame exchange sequence it was performing / participating in on the EMLSR link is completed. In other words, an EMLSR MLD must switch to listening mode for an EMLSR link when the frame exchange sequence it was performing / participating in on a particular EMLSR link has finished, but it does not need to switch to listening mode for an EMLSR link when it intends to receive frames destined for a beacon / group on another EMLSR link. In this case, instead of switching to listening mode for an EMLSR link, the EMLSR MLD can operate to provide RX support to the other EMLSR link.

[0392] Furthermore, when an EMLSR MLD has finished a frame exchange sequence that it was performing / participating in on a particular EMLSR link, if it intends to receive other frames that are scheduled to be received on the same EMLSR link, it can maintain a receive support state for the same EMLSR link without switching to listening operation. This is another exception to the operational restriction that requires switching to listening operation, and will be explained in more detail in one embodiment of the present invention described later.

[0393] Furthermore, if an EMLSR MLD intends to initiate a frame exchange sequence on a particular EMLSR link after a frame exchange sequence it was performing or participating in on that EMLSR link has finished, it may continue to perform channel access procedures to that EMLSR link without switching to listening operation. This may be a further exception to the operational restriction that requires switching to listening operation.

[0394] Alternatively, an EMLSR MLD may receive an initial control frame again on a specific EMLSR link while in the process of switching to listening mode after determining that a frame exchange sequence it was performing / participating in on that link has ended. This can occur when the EMLSR MLD is able to assist in receiving initial control frames on some EMLSR links during an EMLSR transition operation. In this case, the EMLSR MLD can cancel the EMLSR transition operation (the transition operation to listening mode) it was performing in order to assist in the frame exchange sequence on the specific EMLSR link where the initial control frame was received again. In other words, an EMLSR MLD that receives an initial control frame while in the process of performing an EMLSR transition after determining that a frame exchange sequence has ended does not need to perform a transition to listening mode.

[0395] Alternatively, an EMLSR MLD that receives an initial control frame while transitioning to listening mode after determining that a frame exchange sequence it was performing / participating in on a specific EMLSR link has finished does not need to send a response to the received initial control frame. For example, an EMLSR MLD that receives an initial control frame, such as a MU-RTS or BSRP trigger frame, does not need to send a response frame to the received initial control frame if it is in the process of transitioning to listening mode.

[0396] Thus, since an EMLSR MLD in the process of transitioning to listening mode does not need to respond to an initial control frame, an initial control frame transmission restriction may be applied to the AP. In other words, the AP may not transmit an initial control frame to an EMLSR MLD in the process of transitioning to listening mode. In this case, the method by which the AP determines whether a particular EMLSR MLD is in the process of transitioning to listening mode may be based on whether the frame exchange sequence performed with the particular EMLSR MLD has been determined to have ended by the particular EMLSR MLD, and whether the EMLSR Transition Delay (as instructed by the particular EMLSR MLD) has elapsed. More specifically, the AP can determine that a particular EMLSR MLD is in the process of transitioning to listening mode if, after the conditions for determining that the frame exchange sequence in which the particular EMLSR MLD participated has been ended by the particular EMLSR MLD have been met, the EMLSR Transition Delay has not elapsed. If the time equivalent to the EMLSR conversion delay has elapsed, the AP can determine that the EMLSR MLD has completed its conversion to listening mode.

[0397] If the affiliated STA operating on a specific EMLSR link is a TXOP holder, the EMLSR MLD can immediately begin preparing to utilize the resources used on that specific EMLSR link (such as processing power and hardware resources like RF chains) on other EMLSR links as soon as the TXOP is terminated. On the other hand, if the STA of a specific EMLSR link is a TXOP responder (when the AP has started the frame exchange procedure), the EMLSR MLD can begin preparing to utilize the resources used on that specific EMLSR link on other EMLSR links when it determines that the frame exchange on that specific EMLSR link has ended (for example, when the next frame is not received from the AP until aSIFSTime + aSlotTime + aRxPHYStartDelay has elapsed after responding to a response frame).

[0398] The AP MLD should begin preparing to receive on other EMLSR links only after confirming that the EMLSR MLD has completed the frame exchange sequence on a specific EMLSR link. Therefore, the AP MLD must complete the frame exchange sequence with the EMLSR MLD (on the specific EMLSR link) at least aSIFSTime + aSlotTime + aRxPHYStartDelay + EMLSR switching delay (RF switching back latency) earlier than frames destined for beacons / groups transmitted on other EMLSR links. In this case, the AP MLD only needs to follow the frame exchange sequence termination rule described above if it is expected that the EMLSR MLD will receive frames destined for beacons / groups transmitted on other EMLSR links. In this case, aSIFSTime + aSlotTime + aRxPHYStartDelay is the time it takes for the EMLSR MLD to determine the end of the frame exchange sequence. In this case, since the AP MLD does not know the aRxPHYStartDelay of the EMLSR MLD, it can determine the end of the frame exchange sequence by assuming that its own aRxPHYStartDelay and the EMLSR MLD's aRxPHYStartDelay are the same. However, since aRxPHYStartDelay generally has a small time interval of 1us to 2us, it is possible for the AP to ignore aRxPHYStartDelay (considering only aSIFSTime + aSlotTime + EMLSR conversion delay) when determining the end of the frame exchange sequence.

[0399] Figure 52 shows an example of how, according to one embodiment of the present invention, the EMLSR MLD changes to a receive (transmit / receive) support mode for other EMLSR links after the frame exchange procedure is completed on a specific EMLSR link.

[0400] Referring to Figure 52, the EMLSR MLD operates STA1 and STA2 on Link 1 and Link 2, respectively. The AP transmits a MU-RTS frame as the initial control frame on Link 1, and the EMLSR MLD responds with a CTS frame via STA1, and then receives the PPDU transmitted from the AP using two RF chains.

[0401] After receiving a PPDU from the AP, the EMLSR MLD, upon confirming that no additional PPDUs have been received in aSIFSTime+aSlotTime+aRxPHYStartDelay, determines that the frame exchange sequence on link 1 has ended.

[0402] After the frame exchange sequence on Link 1 is complete, the EMLSR MLD immediately switches to receive mode for Link 2 instead of switching to listening mode in order to receive frames destined for beacon frames / groups on Link 2. However, since frames destined for beacon frames / groups are not transmitted in MIMO, the receive operation supported on Link 2 may be supported using only one RF chain.

[0403] In Figure 52, the AP MLD anticipated that the EMLSR MLD would attempt to receive a beacon frame / group-bound frame scheduled for Link 2's TBTT, and terminated the Link 1 TXOP (frame exchange sequence) by aSIFSTime + aSlotTime + aRxPHYStartDelay + EMLSR conversion delay (RF switching back delay) earlier than the Link 2 TBTT to allow (induce) the EMLSR MLD to begin its receive assistance (preparation) operation for Link 2.

[0404] In one example, an EMLSR MLD may not be required to immediately change its operation to support a frame exchange sequence for another EMLSR link while it is supporting a frame exchange sequence for a specific EMLSR link, or it may not be permitted to immediately change the frame exchange sequence support link in order to reduce the operational complexity of a non-AP MLD operating in EMLSR mode and the AP MLD servicing the non-AP MLD. In other words, if an EMLSR MLD intends to support a frame exchange sequence for another EMLSR link while it is supporting a frame exchange sequence for a specific EMLSR link, it may need to first switch to a listening operation for each EMLSR link (a state that supports CCA, initial control frame reception, etc.) after the frame exchange sequence on the specific EMLSR link is completed, and then prepare to support the frame exchange sequence (transmit / receive support) for the other EMLSR link. In this case, an EMLSR MLD that intends to receive frames destined for a beacon / group on another EMLSR link can switch to a receive (or transmit / receive) support mode for the other EMLSR link once the frame exchange sequence performed on the specific EMLSR link is completed, without having to receive another initial control frame on the other link.

[0405] In this case, the AP MLD must manage the frame exchange sequences (and / or TXOPs) of other links, taking into account all the time required for the EMLSR MLD to switch to listening operation and the time required to support reception on the specific link, before transmitting frames destined for the beacon (and its associated TBTT (Target Beacon Transmit Time)) / group on the specific link. In this case, the AP MLD may need to further consider the time it takes for the EMLSR MLD to determine the end of the frame exchange sequence (e.g., aSIFSTime + aSlotTime + aRxPHYStartDelay, or PIFS + aRxPHYStartDelay, or PIFS(aSIFSTime + aSlotTime)). However, the AP MLD can only apply the frame exchange sequence management method described above when it is expected that the EMLSR MLD will receive frames destined for the beacon / group scheduled on the particular link. If the AP MLD expects that multiple EMLSR MLDs (e.g., TXOP responders) participating in the frame exchange sequence on other links will receive frames destined for the beacon / group scheduled on the particular link, the AP MLD must terminate the frame exchange sequence on the other link, taking into account the EMLSR MLD that requests the largest preparation time among the multiple EMLSR MLDs (e.g., the one that has indicated the largest value as the EMLSR conversion delay (RF switching back latency)). Alternatively, the AP MLD may consider the multiple EMLSR MLDs Instead of considering the largest EMLSR conversion delay of the MLDs, the frame exchange sequence of the other links may be terminated by considering the largest EMLSR conversion delay of all associated EMLSR MLDs.As a further alternative, the AP MLD may terminate the frame exchange sequence on the other link by considering the largest EMLSR conversion delay among all EMLSR MLDs currently participating in the frame exchange sequence on the other link, rather than considering the largest EMLSR conversion delay among multiple EMLSR MLDs (EMLSR MLDs that participated in the frame exchange sequence on the other link and are expected to receive frames destined for a specific link's beacon / group). In this case, the AP MLD behavior described above and further alternatives is provided to allow the AP MLD to determine the termination point of the frame exchange sequence in a simpler way, taking into account the operational complexity of the AP MLD.

[0406] Similarly, when an EMLSR MLD attempts to receive a frame destined for a beacon / group on a specific EMLSR link, it must terminate any TXOPs operating on other EMLSR links in advance, taking into account the time required to assist in frame reception on the specific EMLSR link. In this case, after terminating the TXOPs on the other EMLSR links, the EMLSR MLD must terminate the TXOPs on the other EMLSR links, taking into account the time required to switch to listening operation for each EMLSR link and the time required to assist in frame reception for the specific EMLSR link. For example, when an EMLSR MLD attempts to receive a DTIM beacon destined for a specific EMLSR link, the EMLSR MLD may need to terminate the TXOPs on other EMLSR links at least (time to switch to listening operation + time to switch operation to assist in frame reception on the specific link) earlier, based on the TBTT associated with the DTIM beacon.

[0407] However, if the frame that an EMLSR MLD is trying to receive on a particular EMLSR link is receivable in listening mode, the EMLSR MLD can terminate earlier by the time it takes to switch the TXOP on other EMLSR links to listening mode (RF switching back delay, EMLSR switching delay). In other words, if different EMLSR MLDs support different operations on a particular EMLSR link that is in listening mode, the different EMLSR MLDs may apply different criteria to the time it takes to terminate the TXOP operating on other EMLSR links. For example, if a first EMLSR MLD supports beacon frame reception on a link that is in listening mode, the first EMLSR MLD can terminate earlier by considering only the time it takes to switch the TXOP on other links to listening mode, whereas if a second EMLSR MLD does not support beacon frame reception on a link that is in listening mode, the second EMLSR MLD must terminate the TXOP on other links earlier by considering the time it takes to switch to listening mode plus the time it takes to change operations to support beacon frame reception.

[0408] Therefore, a non-AP MLD can instruct an AP MLD on Capability information related to whether or not it can receive a beacon frame (or any frame other than the initial control frame) while maintaining the EMLSR link in listening mode. In this case, the Capability information related to the reception of the beacon frame may be indicated as "support" by indicating a specific bit in the EML Capabilities subfield (included in the Multi-Link element) transmitted by the non-AP MLD as 1, and as "do not support" by indicating a specific bit as 0.

[0409] Furthermore, a non-AP MLD may be capable of assisting in the reception of beacon frames (or other frames besides the initial control frame) during listening operations for only one EMLSR link that has been pre-arranged with the AP MLD. This means that while a non-AP MLD assists in listening operations for each EMLSR link, it can maintain a state in which it assists in the reception of general frames (other frames including beacons and group-addressed frames, in addition to the initial control frame) for a specific EMLSR link. This operation may be achieved by a non-AP MLD operating in EMLSR mode utilizing its transmit / receive assistance capability for one pre-arranged EMLSR link while no frame exchange sequence is taking place on other EMLSR links.

[0410] In this case, even while in listening mode, the non-AP MLD will assist in frame reception for the predetermined EMLSR link. Therefore, when attempting to receive a frame destined for a beacon / group on the predetermined EMLSR link, it may terminate the frame exchange sequence on other links, considering only the time required to switch to listening mode. Similarly, if the AP MLD anticipates that the EMLSR MLD will receive a frame destined for a beacon / group on the predetermined link, it may manage the frame exchange sequences on other links, considering only the time required for the EMLSR MLD to switch to listening mode. Furthermore, when the AP MLD transmits a frame destined for a group that the EMLSR MLD is to receive, it may transmit the group frame through a specific link that the EMLSR MLD has promised to assist in general frame reception while in listening mode.

[0411] In this case, the non-AP MLD can include Link ID information in the EML Capabilities subfield (included in the Multi-Link element) that it sends to the AP MLD in order to instruct the AP about the link that supports the reception (send / receive) of general frames in the listening operation state. For example, the EML Capabilities subfield may have a configuration that includes a Link ID subfield. In this case, if a value corresponding to a specific link is indicated in the Link ID subfield, the specific link may be the link that the non-AP supports the reception of general frames during listening operation.

[0412] Figure 53 shows a TXOP (frame exchange sequence) management method for an EMLSR link according to one embodiment of the present invention.

[0413] Referring to Figure 53, the EMLSR MLD operates STA1 and STA2 on Link 1 and Link 2, respectively. The AP transmits a MU-RTS frame as the initial control frame on Link 1, and the EMLSR MLD responds with a CTS frame via STA1, and then receives the PPDU transmitted from the AP using two RF chains.

[0414] After receiving a PPDU from the AP, if the EMLSR MLD confirms that no additional PPDUs are received within aSIFSTime+aSlotTime+aRxPHYStartDelay, it determines that the frame exchange sequence on link 1 has ended.

[0415] After the frame exchange sequence on Link 1 is completed, the EMLSR MLD intends to receive frames destined for beacons / groups on Link 2. To do this, it switches to listening mode to receive frames destined for beacons / groups on Link...

Claims

1. A first multilink device (MLD) including multiple stations, Transmitter / receiver unit, Processor and Includes, The aforementioned processor, A second MLD, which includes multiple access points (APs), receives a beacon frame, and the second MLD is associated with one or more other MLDs, including the first MLD. Processing the received beacon frame, It is configured in such a way, The beacon frame includes a multilink traffic indicator element based on the satisfaction of both 1) a first condition and 2) a second condition. The first condition is that, with respect to the first MLD among the one or more other MLDs, there exists a first link between the second MLD and the first MLD to which a first traffic identifier (TID) is mapped but a second TID is not mapped. The second condition is that the second MLD has a bufferable unit (BU) buffered relative to the first MLD, the BU having the second TID, in a first multilink device.

2. The first multilink device according to claim 1, wherein the beacon frame further includes a traffic indicator map (TIM) element relating to whether or not the BU(or BU) exists for the first MLD.

3. The processor, when the presence of the BU of the first MLD is indicated by the TIM element, i) if the multiple link traffic indicator element is not present in the beacon frame, or ii) if the multiple link traffic indicator element is present in the beacon frame and the multiple link traffic indicator element does not include link information of the first MLD, the first multilink device according to claim 2, configured to transmit a PS-Poll frame for reception of the BU to the second MLD via any of the activated links of the first MLD.

4. The first multilink device according to claim 3, wherein the processor is configured to receive a frame for the BU from the second MLD based on the PS-Poll frame.

5. A frame transmission and reception method performed in a first multilink device (MLD) including multiple stations, wherein the method is: A step of receiving a beacon frame from a second MLD which includes multiple access points (APs), wherein the second MLD is associated with one or more other MLDs which include the first MLD, The steps include processing the received beacon frame, Includes, The beacon frame includes a multilink traffic indicator element based on the satisfaction of both 1) a first condition and 2) a second condition. The first condition is that, with respect to the first MLD among the one or more other MLDs, there exists a first link between the second MLD and the first MLD to which a first traffic identifier (TID) is mapped but a second TID is not mapped. The second condition is that the second MLD has a bufferable unit (BU) buffered relative to the first MLD, the BU having the second TID, the method.

6. The method according to claim 5, wherein the beacon frame further includes a traffic indicator map (TIM) element relating to whether or not the BU(or BU)BU)(BU)(BU)(BU)(BU)(BU)(BU)(BU)

7. When the presence of the BU of the first MLD is indicated by the TIM element, The method according to claim 6, further comprising the step of transmitting a PS-Poll frame for reception of the BU to the second MLD via an activated link if i) the multiple link traffic indicator element is not present in the beacon frame, or ii) the multiple link traffic indicator element is present in the beacon frame and the multiple link traffic indicator element does not include link information of the first MLD.

8. The method according to claim 7, further comprising the step of receiving a frame for the BU from the second MLD based on the PS-Poll frame.

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