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

Abstract

To provide a wireless communication method efficiently using a multi-link and a wireless communication terminal using the same.SOLUTION: A multi-link device that includes a plurality of stations respectively operating on a plurality of links, and does not perform transmission and reception on a second link while performing frame exchange on a first link of the plurality of EMLSR links to which an enhancedmulti-linksingleradio (EMLSR) mode is applied, the multi-link device comprising: When a first station, which is one of a plurality of stations included in a multi-link device, performs frame exchange as a transmissionopportunity (TXOP) holder in a first link in an EMLSR mode, the processor terminates a TXOP for frame exchange before a time point earlier by a predetermined time, which is a delay time for the multi-link device to perform link switching, than a time point at which the multi-link device receives a beacon frame in a second link.SELECTED DRAWING: Figure 51

Description

[Technical Field]

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

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

[0003] Since supporting early wireless LAN technology using the 2.4 GHz frequency band, IEEE (Institute of Electronics Engineers) 802.11 has since implemented or is currently developing various other technology standards. IEEE 802.11b uses the 2.4 GHz frequency band and supports a maximum communication speed of 11 Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5 GHz frequency band instead of the 2.4 GHz band, reducing the impact of interference compared to the significantly more congested 2.4 GHz frequency band, and uses OFDM technology to improve communication speeds to a maximum of 54 Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication distance than IEEE 802.11b. IEEE 802.11g has attracted considerable attention because it uses the same 2.4GHz band as IEEE 802.11b, achieving a maximum communication speed of 54Mbps and satisfying backward compatibility, but it also has an advantage over IEEE 802.11a in terms of communication distance.

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

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

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

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

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

[0009] According to one embodiment of the present invention, a multilink device includes a plurality of stations operating on a plurality of links, and does not transmit or receive on a second link of the EMLSR links while performing frame exchange on a first link of the EMLSR links, the first link being a plurality of links to which the EMLSR mode is applied, in an EMLSR mode. The multilink device includes a transceiver unit and a processor. When a first station, one of the plurality of stations included in the multilink device, performs the frame exchange on the first link in the EMLSR mode as a TXOP (transmission opportunity) holder, the processor terminates a TXOP for the frame exchange before a time that is a predetermined time earlier than a time that the multilink device is to receive a beacon frame on the second link. The predetermined time may be a delay time for the multilink device to perform link switching.

[0010] The processor may receive an initial control frame that initiates the frame exchange on the first link in the EMLSR mode, and may not transmit a response frame to the initial control frame in order to receive the beacon frame on the second link.

[0011] If the frame exchange initiated by the initial control frame is not completed before a time earlier than the predetermined time from the time the multilink device receives the beacon frame on the second link, the processor does not transmit a response to the initial control frame, and if the frame exchange initiated by the initial control frame is completed before a time earlier than the predetermined time from the time the multilink device receives the beacon frame on the second link, the processor can transmit a response to the initial control frame.

[0012] The initial control frame may be a multi-user request to send (MU-RTS) frame or a buffer status report poll (BSRP).

[0013] The beacon frame may be a DTIM beacon.

[0014] The initial control frame may be transmitted at a pre-specified data rate using a pre-specified format.

[0015] The pre-designated time may be signaled by the multilink device.

[0016] The processor may signal a minimum duration of padding in an initial control frame required for the link switching, the initial control frame initiating frame exchange on the EMLSR link in the EMLSR mode, and the initial control frame may include padding corresponding to a time period equal to or longer than the minimum duration of padding. The EMLSR mode may be applied to only some of the links on which the stations included in the multilink device operate.

[0017] According to an embodiment of the present invention, an access point including a plurality of stations operating on a plurality of links, and configured to communicate with a multilink device in an enhanced multilink single radio (EMLSR) mode, which performs frame exchange on a first link of the EMLSR links while not transmitting or receiving on a second link of the EMLSR links, includes a transceiver unit and a processor. The processor transmits an initial control frame for initiating the frame exchange on the first link in the EMLSR mode, and terminates a TXOP for the frame exchange before a predetermined time earlier than the time when the multilink device is to receive a beacon frame on the second link. The predetermined time is a delay time for the multilink device to perform link switching.

[0018] The initial control frame may be a multi-user request to send (MU-RTS) frame or a buffer status report poll (BSRP).

[0019] The beacon frame may be a DTIM beacon.

[0020] The processor may transmit the initial control frame at a pre-specified data rate using a pre-specified format.

[0021] The pre-designated time may be signaled by the multilink device.

[0022] The processor may receive from the multilink device a minimum duration of padding in an initial control frame required for the link switching, and may include padding in the initial control frame corresponding to a time period equal to or longer than the minimum duration of padding. The EMLSR mode may be applied to only some of the links on which multiple stations included in the multilink device operate.

[0023] A method for operating a multilink device including a plurality of stations operating on a plurality of links, the method not transmitting or receiving on a second link of the EMLSR links while exchanging frames on a first link of the EMLSR links, the first link being a plurality of links to which an EMLSR mode is applied, in an EMLSR mode includes the step of, when a first station, one of the plurality of stations included in the multilink device, performs the frame exchange on the first link in the EMLSR mode as a TXOP (transmission opportunity) holder, terminating a TXOP for the frame exchange before a time that is a predetermined time earlier than a time that the multilink device receives a beacon frame on the second link, the predetermined time being a delay time for the multilink device to perform link switching.

[0024] The operating method may further include receiving an initial control frame in the EMLSR mode to initiate the frame exchange on the first link, and not transmitting a response frame to the initial control frame in order to receive the beacon frame on the second link.

[0025] The step of not transmitting a response frame to the initial control frame in order to receive the beacon frame on the second link may include a step of not transmitting a response to the initial control frame if the frame exchange initiated by the initial control frame is not completed before a time earlier than the time the multilink device receives the beacon frame on the second link by the predetermined time, and a step of transmitting a response to the initial control frame if the frame exchange initiated by the initial control frame is completed before a time earlier than the time the multilink device receives the beacon frame on the second link by the predetermined time.

[0026] The initial control frame may be a multi-user request to send (MU-RTS) frame or a buffer status report poll (BSRP). [Effects of the Invention]

[0027] An embodiment of the present invention provides a wireless communication method that efficiently uses multilinks and a wireless communication terminal that uses the same. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a configuration of an access point according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating a process in which a STA establishes a link with an AP. [Figure 6] FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] 1 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1 illustrates various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention. [Figure 9] 1 shows a multi-link device according to an embodiment of the present invention; [Figure 10] 1 illustrates simultaneous transmission of different links in a multi-link operation according to an embodiment of the present invention. [Figure 11] 10 illustrates the operation of a multi-link device when a link is changed according to one embodiment of the present invention. [Figure 12] 10 shows that, according to one embodiment of the present invention, when any one station in a non-STR multilink device is receiving, other stations in the non-STR multilink device are prohibited from accessing the channel. [Figure 13] 10 shows an operation of canceling channel access prohibition when it is confirmed that the intended recipient of a PPDU received by a station in a non-STR multilink device is not a station according to an embodiment of the present invention. [Figure 14] 10 shows a station according to an embodiment of the present invention accessing a channel after channel access prohibition is lifted. [Figure 15] 10 illustrates an operation of a station transmitting after channel access prohibition is lifted according to an embodiment of the present invention. [Figure 16] 10 illustrates transmissions based on the state of stations in a non-STR multilink device according to an embodiment of the present invention. [Figure 17] This shows the situation where interference or collision between links may occur. [Figure 18]10 illustrates an operation in which an STR multilink device stops transmission to a non-STR multilink device according to an embodiment of the present invention. [Figure 19] 10 shows how the STR multilink device processes the value of CW when it recognizes a transmission collision between links according to an embodiment of the present invention. [Figure 20] 10 illustrates an operation of an STR multilink device accessing a channel again after halting transmission to a non-STR multilink device according to an embodiment of the present invention. [Figure 21] 10 illustrates an 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. [Figure 22] 1 illustrates that multiple APs included in an STR multilink device transmit to multiple stations included in one non-STR multilink device according to an embodiment of the present invention. [Figure 23] According to an embodiment of the present invention, multiple APs included in an STR multilink device perform multiple transmissions with synchronized end of transmission to multiple stations included in one non-STR multilink device. [Figure 24] 1 illustrates multilink devices exchanging RTS / CTS frames according to an embodiment of the present invention. [Figure 25] 25 illustrates a hidden node problem that occurs in the RTS / CTS frame exchange procedure according to the embodiment described in FIG. 24. [Figure 26] 1 illustrates multilink devices exchanging RTS / CTS frames according to an embodiment of the present invention. [Figure 27] 10 shows that a multilink device transmits a response to a control frame exceptionally even when channel access is prohibited according to an embodiment of the present invention. [Figure 28] Indicates that a transmission for a station on a non-STR multilink device should be retransmitted. [Figure 29]10 shows that a control frame is transmitted on a link on which a station that is not prohibited from channel access operates, rather than on a link on which a station that is prohibited from channel access operates, according to an embodiment of the present invention. [Figure 30] 10 illustrates a multi-link device sending an ACK according to an embodiment of the present invention. [Figure 31] 10 shows an element field indicating information regarding support for receiving or transmitting a sink PPDU according to an embodiment of the present invention. [Figure 32] 1 illustrates a non-STR multi-link device operating in inter-link TXOP power save mode according to an embodiment of the present invention. [Figure 33] 10 illustrates that a station in a non-STR multilink device enters a power saving state while waiting to receive a sync PPDU according to an embodiment of the present invention. [Figure 34] 10 illustrates a state in which a station in a non-STR multilink device enters a power saving state while waiting to receive a sync PPDU according to yet another embodiment of the present invention. [Figure 35] 1 illustrates a connection between a single-radio multilink device and an AP multilink device according to an embodiment of the present invention. [Figure 36] 1 illustrates a single-radio multi-link device according to an embodiment of the present invention performing MIMO transmission. [Figure 37] 1 illustrates an operation of a single-radio multi-link device according to an embodiment of the present invention performing channel access taking into account a delay time of RF (radio frequency) chain change. [Figure 38] 10 shows a Capability element and an Operation element used by a single-radio multilink device according to an embodiment of the present invention. [Figure 39] 1 illustrates a single-radio multi-link device according to an embodiment of the present invention transmitting a PPDU using MIMO; [Figure 40] 1 illustrates a station and a single-radio multilink device according to an embodiment of the present invention performing an NDP sounding process. [Figure 41] 10 illustrates a station and a single-radio multilink device according to an embodiment of the present invention performing a feedback beamforming sounding sequence. [Figure 42] 1 illustrates a station and a single-radio multilink device according to an embodiment of the present invention performing an NDP sounding process. [Figure 43] The mapping relationship between UP and AC is shown. [Figure 44] 10 illustrates a multilink device transmitting traffic mapped to each station of the multilink device according to an embodiment of the present invention. [Figure 45] 1 illustrates a multi-link device exchanging frames by TID link mapping according to an embodiment of the present invention. [Figure 46] 10 shows that basic mapping between TIDs and links is set in an AP multilink device and a non-AP multilink device according to an embodiment of the present invention. [Figure 47] 10 shows that the mapping between TIDs and links is changed when the multi-link device according to the embodiment of the present invention activates the EMLSR mode. [Figure 48] 1 shows the format of a Multi-Link element according to an embodiment of the present invention. [Figure 49] 10 shows that the mapping between TIDs and links is changed when the multi-link device according to the embodiment of the present invention deactivates the EMLSR mode. [Figure 50] 10 illustrates a Multi-Link element signaling information regarding the length of padding in an initial control frame according to an embodiment of the present invention. [Figure 51] This shows that a multi-link device according to an embodiment of the present invention terminates a TXOP on a link where frame exchange is performed in EMLSR mode, taking into account a DTIM beacon received on an EMLSR link where frame exchange is not performed in EMLSR mode. DETAILED DESCRIPTION OF THE INVENTION

[0029] The terms used in this specification are generally used as widely as possible, taking into consideration the functions of the present invention. However, these may vary depending on the intentions of engineers in the relevant technical field, customs, or the emergence of new technologies. In addition, in certain cases, the applicant has arbitrarily selected terms, and in such cases, the meanings thereof will be described in the description of the relevant invention. Therefore, it is made clear that the terms used in this specification should be interpreted not simply as names of terms, but based on the substantive meanings of the terms and the overall content of this specification.

[0030] Throughout this specification, when a component is referred to as being "connected" to another component, this includes not only when the component is "directly connected" to another component, but also when the component is "electrically connected" to another component via another component in between. Furthermore, when a component is referred to as "comprising" a specific component, this does not mean that the component may exclude the other component, but may further include the other component, unless otherwise specified. In addition, limitations such as "greater than" or "less than" based on a specific critical value may be appropriately substituted with "exceeds" or "less than," respectively, depending on the embodiment.

[0031] Hereinafter, in the present invention, the terms field and subfield may be used interchangeably.

[0032] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention.

[0033] A wireless LAN system includes one or more Basic Service Sets (BSSs), which are a set of devices that can synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0034] As shown in FIG. 1, infrastructure BSSs BSS1 and BSS2 include one or more stations STA1, STA2, STA3, STA4, and STA5, access points AP-1 and AP-2 that are stations providing distribution services, and a distribution system DS that connects multiple access points AP-1 and AP-2.

[0035] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard. In a broad sense, the term "station" encompasses not only non-AP stations but also APs. In this specification, the term "terminal" refers to either a non-AP or an AP, or both. A station for wireless communication includes a processor and a communication unit, and may further include a user interface and a display unit, depending on the embodiment. The processor generates frames to be transmitted over a wireless network, processes frames received over the wireless network, and performs various other processes for controlling the station. The communication unit is functionally connected to the processor and transmits and receives frames over the wireless network for the station. In this specification, the term "terminal" encompasses user equipment (UE).

[0036] An access point (AP) is an entity that provides a connection to a distribution system (DS) via a wireless medium for associated stations. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP. However, if a direct link is established, direct communication is also possible between non-AP stations. Meanwhile, in the present invention, the term AP is used as a concept including a personal BSS coordination point (PCP), but in a broader sense, it also includes concepts such as a central controller, a base station (BS), a node B, a base transceiver system (BTS), or a site controller. In the present invention, an AP is also referred to as a base wireless communication terminal, but in a broader sense, the term base wireless communication terminal is used as a term including an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal includes various types of wireless communication terminals that allocate communication medium resources and perform scheduling for communication with multiple wireless communication terminals.

[0037] A plurality of infrastructure BSSs are connected to each other via a distribution system DS, and the plurality of BSSs connected via the distribution system are called an Extended Service Set (ESS).

[0038] 2 is a diagram showing an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of FIG. 2, the same or corresponding parts as those in the embodiment of FIG. 1 will not be described again.

[0039] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so none of the stations (STA6, STA7) are connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

[0040] 3 is a block diagram showing the configuration of a station 100 according to an embodiment of the present invention. As shown, the station 100 according to the embodiment of the present invention includes a processor 110, a communication unit 120, a user interface unit 140, a display unit 150, and a memory 160.

[0041] First, the communication unit 120 transmits and receives wireless signals such as WLAN packets and may be incorporated into or external to the station 100. According to an embodiment, the communication unit 120 may include at least one communication module using different frequency bands. For example, the communication unit 120 may include communication modules using different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to an embodiment, the station 100 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with an AP or an external station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 120 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the station 100. When the station 100 includes multiple communication modules, each communication module may be provided independently, or multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit 120 may represent a radio frequency (RF) communication module that processes RF signals.

[0042] Next, the user interface 140 includes various types of input / output means provided in the station 100. That is, the user interface unit 140 receives user input using various input means, and the processor 110 controls the station 100 based on the received user input. Also, the user interface unit 140 performs output based on instructions from the processor 110 using various output means.

[0043] Next, the display unit 150 outputs an image on a display screen. The display unit 150 outputs various display objects, such as a user interface, based on the contents processed by the processor 110 or the control commands of the processor 110. The memory 160 also stores control programs and various data used by the station 100. The control programs include a connection program required for the station 100 to connect to an AP or an external station.

[0044] The processor 110 of the present invention executes various commands or programs to process data within the station 100. The processor 110 also controls each unit of the station 100 and controls the transmission and reception of data between the units. According to an embodiment of the present invention, the processor 110 executes a program for connection with an AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also reads information about the station 100's preferences contained in the communication setup message and requests connection to the AP based on the information about the station 100's preferences. The processor 110 of the present invention may refer to a main control unit of the station 100, or, depending on the embodiment, may refer to a control unit for individually controlling some components of the station 100, such as the communication unit 120. That is, the processor 110 may be a modem that modulates and demodulates wireless signals transmitted and received by the communication unit 120, or a modulator and / or demodulator. The processor 110 controls various operations for transmitting and receiving wireless signals in the station 100 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0045] The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separate blocks indicate the logically separated elements of the device. Therefore, the above-described device elements may be mounted on a single chip or multiple chips depending on the device design. For example, the processor 110 and the communication unit 120 may be integrated into a single chip or may be mounted on separate chips. Furthermore, in embodiments of the present invention, some components of the station 100, such as the user interface unit 140 and the display unit 150, may be selectively provided in the station 100.

[0046] 4 is a block diagram showing the configuration of an AP 200 according to an embodiment of the present invention. As shown, the AP 200 according to the embodiment of the present invention includes a processor 210, a communication unit 220, and a memory 260. In FIG. 4, the same or corresponding parts of the configuration of the AP 200 as those of the station 100 in FIG. 3 will not be described again.

[0047] Referring to FIG. 4, the AP 200 according to the present invention includes a communication unit 220 for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit 220 of the AP 200 may also include multiple communication modules using different frequency bands. That is, the AP 200 according to the embodiment of the present invention may include two or more communication modules using different frequency bands, for example, 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with a station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 220 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the AP 200. In the embodiment of the present invention, the communication unit 220 may represent an RF (Radio Frequency) communication module that processes RF signals.

[0048] The memory 260 stores control programs used by the AP 200 and various data associated therewith. These control programs include a connection program that manages station connections. The processor 210 also controls each unit of the AP 200 and controls data transmission and reception between the units. According to an embodiment of the present invention, the processor 210 executes a program for connecting with a station stored in the memory 260 and transmits a communication setup message to one or more stations. The communication setup message includes information regarding connection preferences for each station. The processor 210 also performs connection setup in response to a station connection request. According to an embodiment, the processor 210 is a modem or a modulation / demodulation unit that modulates and demodulates wireless signals transmitted and received from the communication unit 220. The processor 210 controls various operations for transmitting and receiving wireless signals by the AP 200 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0049] FIG. 5 is a diagram illustrating a process in which a STA establishes a link with an AP.

[0050] 5, a link between the STA 100 and the AP 200 is established through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information for the BSS operated by the AP 200. There are two scanning methods: a passive scanning method in which the STA 100 acquires information using only a beacon message S101 periodically transmitted by the AP 200, and an active scanning method in which the STA 100 transmits a probe request to the AP S103, receives a probe response from the AP S105, and acquires connection information.

[0051] The STA 100 that successfully receives wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200, and performs the authentication step (S107b). After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200, and performs the association step (S109b). In this specification, association basically means wireless association, but the present invention is not limited to this, and association in a broad sense includes both wireless association and wired association.

[0052] Meanwhile, an 802.1X-based authentication step S111 and an IP address acquisition step S113 via DHCP are additionally performed. In Fig. 5, server 300 is a server that processes 802.1X-based authentication with STA 100, and may be physically connected to AP 200 or may exist as a separate server.

[0053] FIG. 6 is a diagram showing a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0054] A terminal performing WLAN communication performs carrier sensing to check whether a channel is occupied before transmitting data. If a wireless signal above a certain strength is detected, the channel is determined to be occupied, and the terminal delays access to the channel. This process is called Clear Channel Assessment (CCA), and the level that determines whether or not a signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold is received by the terminal and the terminal is the receiver, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected from the channel or a wireless signal with a strength below the CCA threshold is detected, the channel is determined to be idle.

[0055] If the channel is determined to be idle, each terminal having data to transmit performs a backoff procedure after an Inter Frame Space (IFS), such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS is used as a configuration replacing the conventional DCF IFS (DIFS). Each terminal waits while decrementing a slot time equal to a random number determined for the corresponding terminal during the idle interval of the channel, and a terminal that has exhausted all of its slot time attempts to access the corresponding channel. The period during which each terminal performs the backoff procedure is called a contention window period. In this case, the random number can be called a backoff counter. That is, the initial value of the backoff counter is set by an integer, which is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal can decrement the backoff counter by 1. If the backoff counter reaches 0, the terminal may be allowed to perform channel access on the corresponding channel. Therefore, if the channel is idle during the AIFS time and the backoff counter slot time, the terminal may be allowed to transmit.

[0056] If a specific terminal successfully accesses the channel, it transmits data over the channel. However, if the terminal attempting access collides with another terminal, the colliding terminals are assigned new random numbers and perform a backoff procedure again. According to one embodiment, the new random numbers assigned to each terminal are determined within a range (2*CW) twice the range of the random numbers previously assigned to the terminal (contention window, CW). Meanwhile, each terminal attempts access by performing a backoff procedure again in the next contention window period. At this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. In this way, terminals communicating over a wireless LAN can avoid collisions with each other on a specific channel.

[0057] <Examples of various PPDU formats>

[0058] Figure 7 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. More specifically, Figure 7(a) shows an example of a legacy PPDU format based on 802.11a / g, Figure 7(b) shows an example of an HE PPDU format based on 802.11ax, and Figure 7(c) shows an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Also, Figure 7(d) shows detailed field configurations of L-SIG and RL-SIG commonly used in the PPDU formats.

[0059] 7(a), the preamble of the legacy PPDU includes a Legacy Short Training field (L-STF), a Legacy Long Training field (L-LTF), and a Legacy Signal field (L-SIG). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as a legacy preamble.

[0060] Referring to FIG. 7(b), the preamble of the HE PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a High Efficiency Signal A field (HE-SIG-A), a High Efficiency Signal B field (HE-SIG-B), a High Efficiency Short Training field (HE-STF), and a High Efficiency Long Training field (HE-LTF) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF can be referred to as an HE preamble. The specific configuration of the HE preamble may vary depending on the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0061] Referring to FIG. 7(c), the preamble of the EHT PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a Universal Signal field (U-SIG), an Extremely High Throughput Signal A field (EHT-SIG-A), an Extremely High Throughput Signal B field (EHT-SIG-A), an Extremely High Throughput Short Training field (EHT-STF), and an Extremely High Throughput Long Training field (EHT-LTF) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may vary depending on the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some EHT PPDU formats.

[0062] The L-SIG field included in the PPDU preamble is configured with a total of 64 subcarriers using 64 FFT OFDM. Of these, 48 subcarriers, excluding guard subcarriers, DC subcarriers, and pilot subcarriers, are used for L-SIG data transmission. BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, so it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of the L-SIG.

[0063] Referring to FIG. 7(d), the L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field is composed of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission rates of 6, 9, 12, 18, 24, 36, 48, or 54 Mbps, which is a combination of a modulation scheme such as BPSK, QPSK, 16-QAM, or 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The combined information in the L_RATE and L_LENGTH fields indicates the total length of the PPDU. In a non-legacy PPDU format, the L_RATE field is set to the minimum rate of 6 Mbps.

[0064] The unit of the L_LENGTH field is byte, and a total of 12 bits are allocated, allowing signaling up to 4095. In combination with the L_RATE field, the length of the PPDU can be indicated. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0065] First, a legacy or non-legacy terminal analyzes the length of the PPDU using the L_LENGTH field as follows. When the L_RATE field is set to 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted at 4 us, which is the duration of one symbol of the 64FFT. Therefore, by adding 3 bytes corresponding to the SVC field and the Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the amount of transmission of one symbol, the number of 64FFT reference symbols after the L-SIG is obtained. The obtained number of symbols is multiplied by 4 us, which is the duration of one symbol, and then 20 us, which is required to transmit the L-STF, L-LTF, and L-SIG, is added to obtain the length of the PPDU, i.e., the reception time (RXTIME). This can be expressed mathematically as shown in Equation 1 below.

[0066]

number

[0067] At this time,

number

[0068]

number

[0069] Here, TXTIME is the total transmission time constituting the PPDU, and is expressed as the following equation 3. In this case, TX represents the transmission time of X.

[0070]

number

[0071] Referring to the above formula, the length of the PPDU is calculated based on the rounded up value of L_LENGTH / 3. Therefore, for any value of k, three different values ​​of L_LENGTH={3k+1, 3k+2, 3(k+1)} indicate the same PPDU length.

[0072] Referring to Figure 7(e), the U-SIG (Universal SIG) field remains in the EHT PPDU and subsequent generation WLAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. The U-SIG is two 64FFT-based OFDM symbols and can transmit a total of 52 bits of information. Of these, 43 bits excluding 9 bits of CRC / tail are roughly divided into a VI (Version Independent) field and a VD (Version Dependent) field.

[0073] The VI bit will maintain its current bit configuration, so even if a subsequent generation PPDU is defined, current 11be UEs can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field consists of the PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits long and serves to sequentially distinguish between 11be and subsequent generations of WLAN standards. 11be has a value of 000b. The UL / DL field identifies whether the PPDU is an uplink or downlink PPDU. The BSS color represents a BSS identifier defined in 11ax and has a value of 6 or more bits. The TXOP represents the transmit opportunity duration (Transmit Opportunity Duration) transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without decoding the MPDU, and has a value of 7 or more bits.

[0074] The VD field, which is signaling information useful only for 11be version PPDUs, may consist of fields commonly used in any PPDU format, such as the PPDU format and BW, as well as fields defined differently for each PPDU format. The PPDU format is a separator that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field broadly signals five basic PPDU BW options: 20, 40, 80, 160 (80 + 80), and 320 (160 + 160) MHz (BWs that can be expressed in the form of a power of 20 * 2 can be called basic BWs), as well as various remaining PPDU BWs formed by preamble puncturing. After signaling at 320 MHz, a portion of 80 MHz may be punctured. In addition, the punctured and modified channel shape may be signaled directly in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (for example, a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signalings are possible, so a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signalings are possible, so a maximum of 11 puncturing modes can be signaled.

[0075] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs may be signaled in the same PPDU format, and a field for distinguishing between MU PPDUs and SU PPDUs may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both SU PPDUs and MU PPDUs include an EHT-SIG field, but some fields not required for the SU PPDU may be compressed. In this case, the information of the compressed fields may be omitted or may have a reduced size compared to the size of the original fields included in the MU PPDU. For example, the SU PPDU may have a different configuration, such as the common fields of the EHT-SIG being omitted or replaced, or the user-specific fields being replaced or reduced to one.

[0076] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (such as the RA field) may be omitted depending on the value of the compression field.

[0077] When a portion of the EHT-SIG field of the SU PPDU is compressed, the information included in the compressed field may be signaled together in an uncompressed field (e.g., a common field). In the case of an MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of information signaled may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether the transmitted MU PPDU was sent to it. Therefore, the AP must transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols in the EHT-SIG field and / or the MCS, which is the modulation method. The EHT-SIG field may include information on the size and location of the RU assigned to each user.

[0078] In the case of an SU PPDU, a STA may be assigned multiple RUs, and the multiple RUs may be contiguous or discontinuous. If the RUs assigned to the STA are not contiguous, the STA can efficiently receive the SU PPDU only by recognizing punctured RUs in between. Therefore, the AP can transmit the SU PPDU including information on punctured RUs among the RUs assigned to the STA (e.g., puncturing pattern of the RUs). That is, in the case of an SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and the puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field can signal the type of discontinuous channels appearing within the bandwidth.

[0079] The type of signaled discontinuous channel is limited, and indicates the BW and discontinuous channel information of the SU PPDU in combination with the value of the BW field. For example, since the SU PPDU is a PPDU transmitted only to a single UE, the STA can recognize its allocated bandwidth from the BW field included in the PPDU and can recognize punctured resources within the allocated bandwidth from the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the UE can receive the PPDU in the remaining resource units excluding specific channels of the punctured resource units. In this case, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0080] The reason why only limited discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed for each 20 MHz subchannel, if puncturing is performed on a BW having multiple 20 MHz subchannels, such as 80, 160, or 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered discontinuous) must be signaled by expressing whether or not each of the remaining 15 20 MHz subchannels excluding the primary channel is in use. Using 15 bits to signal the discontinuous channel type for single-user transmission can result in excessive signaling overhead when considering the low transmission rate of the signaling part.

[0081] This invention proposes a method for signaling the discontinuous channel type of the SU PPDU, illustrates the discontinuous channel type determined by the proposed method, and proposes a method for signaling the primary 160 MHz and secondary 160 MHz puncturing types in the 320 MHz BW configuration of the SU PPDU.

[0082] In addition, one embodiment of the present invention proposes a method of varying the PPDU configuration indicated by the preamble puncturing BW value depending on the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, an EHT-SIG-A symbol can be further signaled after the U-SIG, or no EHT-SIG-A can be signaled at all. Taking this into consideration, up to 11 puncturing modes must be fully signaled using only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B symbol is further signaled after the U-SIG, so up to 11 puncturing modes can be signaled in a different manner than in the case of an SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz bandwidth. Detailed puncturing patterns for each PPDU type will be described in detail below with reference to FIGS. 11 and 12.

[0083] Figure 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. For an MU PPDU, SIG-B, a signaling field for simultaneous reception by multiple users, is required. SIG-B may be transmitted after the U-SIG without a separate SIG-A. For this purpose, the U-SIG must signal information for decoding SIG-B. These fields include the SIG-B MCS, SIG-B DCM, number of SIG-B symbols, SIG-B compression, and number of EHT-LTF symbols.

[0084] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention.

[0085] 8, a PPDU may be configured with a preamble and a data portion, and the format of one type, EHT PPDU, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

[0086] 8(a) shows an example of an EHT SU PPDU format for a single STA. The EHT SU PPDU is a PPDU used for single user (SU) transmission between an AP and a single STA, and an EHT-SIG-A field for additional signaling may be located after the U-SIG field.

[0087] 8(b) shows an example of an EHT trigger-based PPDU format, which is an EHT PPDU transmitted based on a trigger frame. The EHT trigger-based PPDU is an EHT PPDU transmitted based on a trigger frame and is an uplink PPDU used for responding to the trigger frame. Unlike the EHT SU PPDU, the EHT PPDU does not have an EHT-SIG-A field after the U-SIG field.

[0088] 8(c) shows an example of an EHT MU PPDU format, which is an EHT PPDU for multiple users. The EHT MU PPDU is a PPDU used to transmit a PPDU to one or more STAs. In the EHT MU PPDU format, an HE-SIG-B field may be located after the U-SIG field.

[0089] 8(d) shows an example of an EHT ER SU PPDU format used for single-user transmission with STAs in an extended range. The EHT ER SU PPDU may be used for single-user transmission with STAs in a wider range than the EHT SU PPDU described in FIG. 8(a), and the U-SIG field may be repeated on the time axis.

[0090] The EHT MU PPDU described in (c) of Figure 8 can be used by the AP for downlink transmission to multiple STAs. In this case, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive the PPDU transmitted from the AP. The EHT MU PPDU can convey AID information of the receiver and / or sender of the transmitted PPDU to the STA through the user specific field of the EHT-SIG-B. Therefore, multiple terminals receiving the EHT MU PPDU can perform spatial reuse based on the AID information of the user specific field included in the preamble of the received PPDU.

[0091] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information regarding the configuration of resource units (e.g., the division type of resource units) in a specific bandwidth (e.g., 20 MHz) on the frequency axis. That is, the RA field may indicate the configuration of resource units divided by the bandwidth for transmitting the HE MU PPDU so that the STA can receive the PPDU. Information about the STA allocated (or designated) to each divided resource unit may be included in a user specific field of the EHT-SIG-B and transmitted to the STA. That is, the user specific field may include one or more user fields corresponding to each divided resource unit.

[0092] For example, among the multiple divided resource units, the user field corresponding to at least one resource unit used for data transmission may include the AID of the receiver or sender, and the user field corresponding to the remaining resource units not used for data transmission may include a previously set null STA ID.

[0093] For ease of explanation, the term frame or MAC frame may be used interchangeably with MPDU in this specification.

[0094] When a single wireless communication device communicates using multiple links, the communication efficiency of the wireless communication device can be improved. In this case, a link is a physical path and may be configured as a single wireless medium that can be used to transmit an MSDU (MAC service data unit). For example, when the frequency band of one link is being used by another wireless communication device, the wireless communication device can continue communication using another link. In this way, the wireless communication device can effectively use multiple channels. Furthermore, when a wireless communication device simultaneously communicates using multiple links, the overall throughput can be improved. However, existing wireless LANs are specified on the assumption that one wireless communication device uses one link. Therefore, a wireless LAN operation method for using multiple links is needed. A wireless communication method for a wireless communication device using multiple links will be described with reference to FIGS. 9 to 26. First, a specific embodiment of a wireless communication device using multiple links will be described with reference to FIG. 9.

[0095] FIG. 9 shows a multi-link device according to an embodiment of the present invention.

[0096] A multi-link device (MLD) may be defined for the wireless communication method using multiple links described above. The multi-link device may represent a device having one or more affiliated stations. Depending on a specific embodiment, the multi-link device may represent a device having two or more affiliated stations. The multi-link device may also exchange multi-link elements. The multi-link element includes information about one or more stations or one or more links. The multi-link element may include a multi-link setup element, which will be described later. In this case, the multi-link device may be a logical entity. Specifically, the multi-link device may have multiple affiliated stations. The multi-link device may be referred to as a multi-link logical entity (MLLE) or a multi-link entity (MLE). The multi-link device may have one medium access control service access point (SAP) up to a logical link control (LLC). The MLD may also have one MAC data service.

[0097] Multiple stations included in a multilink device can operate on multiple links. Also, multiple stations included in a multilink device can operate on multiple channels. Specifically, multiple stations included in a multilink device can operate on different links or different channels. For example, multiple stations included in a multilink device can operate on different channels, such as 2.4 GHz, 5 GHz, and 6 GHz.

[0098] The operation of the multilink device can be referred to as multilink operation, MLD operation, or multi-band operation. If the station associated with the multilink device is an AP, the multilink device can be referred to as AP MLD. If the station associated with the multilink device is a non-AP station, the multilink device can be referred to as non-AP MLD.

[0099] FIG. 9 shows the operation of communication between non-AP MLD and AP-MLD. Specifically, non-AP MLD and AP-MLD each communicate using three links. AP MLD includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). Non-AP MLD includes a first non-AP STA (non-AP STA1), a second non-AP STA (non-AP STA2), and a third non-AP STA (non-AP STA3). The first AP (AP1) and the first non-AP STA (non-AP STA1) communicate via a first link (Link1). The second AP (AP2) and the second non-AP STA (non-AP STA2) communicate via a second link (Link2). The third AP (AP3) and the third non-AP STA (non-AP STA3) communicate via a third link (Link3).

[0100] Multilink operation may include a multilink setup operation. Multilink setup corresponds to the association operation of the single-link operation described above and must be performed prior to frame exchange in the multilink. A multilink device can obtain information required for multilink setup from a multi-link setup element. Specifically, the multi-link setup element may include capability information related to the multilink. In this case, the capability information may include information indicating whether one of multiple devices included in the multilink device can transmit and the other devices can receive at the same time. The capability information may also include information about links available to each station included in the MLD. The capability information may also include information about channels available to each station included in the MLD.

[0101] Multilink configuration may be established through negotiation between peer stations. Specifically, multilink configuration may be established through communication between stations without communication with an AP. Multilink configuration may also be established through any one of the links. For example, even if the first to third links are established through multilink, multilink configuration may be established through the first link.

[0102] In addition, a mapping between a traffic identifier (TID) and a link may be configured. Specifically, frames corresponding to a specific TID value may be exchanged only through a pre-specified link. The mapping between a TID and a link may be configured on a directional basis. For example, when multiple links are configured between a first multilink device and a second multilink device, the first multilink device may be configured to transmit frames of the first TID to the multiple first links, and the second multilink device may be configured to transmit frames of the second TID to the first link. In addition, a default setting may exist for the mapping between TIDs and links. Specifically, if no additional settings are configured in the multilink configuration, the multilink device may exchange frames corresponding to TIDs on each link according to a default setting. In this case, the default setting may be that all TIDs are exchanged on any one link.

[0103] The TID will be described in detail. The TID is an ID for classifying traffic and data to support quality of service (QoS). The TID may be used and assigned in a layer higher than the MAC layer. The TID may indicate a traffic category (TC) or a traffic stream (TS). There may be 16 distinct TIDs. For example, the TID may be designated as any one of 0 to 15. Different TID values ​​may be designated depending on an access policy, a channel access method, or a medium access method. For example, when enhanced distributed channel access (EDCA) or hybrid coordination function contention-based channel access (HCAF) is used, the TID may be assigned a value ranging from 0 to 7. When EDCA is used, the TID may indicate a user priority (UP). In this case, the UP may be designated by the TC or the TS. The UP may be assigned in a layer higher than the MAC. Furthermore, when HCCA (HCF controlled channel access) or SPCA is used, the TID may be assigned a value in the range of 8 to 15. When HCCA or SPCA is used, the TID may indicate a TSID. Furthermore, when HEMM or SEMM is used, the TID may be assigned a value in the range of 8 to 15. When HEMM or SEMM is used, the TID may indicate a TSID.

[0104] UP and AC (access category) may be mapped. AC may be a label for providing QoS in EDCA. AC may be a label for indicating an EDCA parameter set. EDCA parameters or EDCA parameter sets are parameters used in EDCA channel contention. QoS stations can guarantee QoS using AC. AC may include AC_BK, AC_BE, AC_VI, and AC_VO. AC_BK, AC_BE, AC_VI, and AC_VO may indicate background, best effort, video, and voice, respectively. AC_BK, AC_BE, AC_VI, and AC_VO may be classified into lower-level ACs. For example, AC_VI may be further subdivided into AC_VI primary and AC_VI alternate. AC_VO may be further subdivided into AC_VO primary and AC_VO alternate. UP or TID may be mapped to an AC. For example, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI, AC_VI, AC_VO, and AC_VO, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI alternate, AC_VI primary, AC_VO primary, and AC_VO alternate, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may have decreasing priority in that order. That is, 1 may have a lower priority, and 7 may have a higher priority. Therefore, the order of priority may be AC_BK, AC_BE, AC_VI, and AC_VO. Also, AC_BK, AC_BE, AC_VI, and AC_VO can correspond to ACI (AC index) 0, 1, 2, and 3, respectively. Due to the characteristics of TID, the mapping between TID and link can represent the mapping between AC and link.The mapping between links and ACs can also represent the mapping between TIDs and links.

[0105] As described above, a TID may be mapped to each of multiple links. The mapping may specify the links through which traffic corresponding to a specific TID or AC can be exchanged. Furthermore, the TID or AC that can be transmitted for each transmission direction within a link may be specified. As described above, a default setting may exist for the mapping between TIDs and links. Specifically, if no additional settings are configured in the multilink configuration, the multilink device may exchange frames corresponding to the TID on each link according to the default setting. In this case, the default setting may be that all TIDs are exchanged on any one link. At any given time, any TID or AC may be mapped to at least one link. Management frames and control frames may be transmitted on all links.

[0106] When a link is mapped to a TID or AC, only data frames corresponding to the TID or AC mapped to the link may be transmitted on the link. Therefore, when a link is mapped to a TID or AC, frames not corresponding to a TID or AC not mapped to the link may not be transmitted on the link. When a link is mapped to a TID or AC, an ACK may also be transmitted based on the link to which the TID or AC is mapped. For example, a Block ACK agreement may be determined based on the mapping between the TID and the link. In yet another specific embodiment, the mapping between the TID and the link may be determined based on the Block ACK agreement. Specifically, a Block ACK agreement may be set for a TID mapped to a specific link.

[0107] The above-described TID-to-link mapping may ensure QoS. Specifically, a high-priority AC or TID may be mapped to a link where a relatively small number of stations are active or where channel conditions are good. The above-described TID-to-link mapping may also allow stations to remain in a power-saving state for a longer period of time.

[0108] FIG. 10 illustrates simultaneous transmission of different links in multi-link operation according to an embodiment of the present invention.

[0109] Depending on the implementation of the multi-link device, simultaneous operation of the multi-links may not be supported. For example, a multi-link device may support simultaneous transmission on multiple links, simultaneous reception on multiple links, or transmission on one link while receiving on another link. Reception or transmission on one link may affect reception or transmission on another link. Specifically, transmission on one link may interfere with other links. Interference from one link of a multi-link device affecting other links may be called internal leakage. The smaller the frequency spacing between links, the greater the internal leakage. If the internal leakage is not too large, transmission on one link can occur when transmission on another link. If the internal leakage is large, transmission on one link cannot occur when transmission on another link. This simultaneous operation of the multi-link device on multiple links may be called STR (simultaneous transmit and receive, simultaneous transmission and reception). For example, a multilink device transmitting on multiple links simultaneously, transmitting on one link while receiving on another link, or receiving on multiple links simultaneously can be referred to as STR.

[0110] As mentioned above, a multilink device can support STR, or can support it with limitations. Specifically, a multilink device can support STR only under certain conditions. For example, if the multilink device operates with a single radio, the multilink device may not be able to perform STR. Also, if the multilink device operates with a single antenna, the multilink device may not be able to perform STR. Also, if an internal leak is detected to be greater than a predetermined magnitude, the multilink device may not be able to perform STR.

[0111] A station can exchange information about its STR capability with other stations. Specifically, a station can exchange information about whether or not the station has limitations on its ability to simultaneously transmit or receive on multiple links. Specifically, the information about whether or not the station has limitations on its ability to transmit or receive on multiple links can indicate whether or not the station will transmit or receive on multiple links simultaneously, or whether or not transmission and reception are simultaneous. Furthermore, the information about whether or not the station has limitations on its ability to transmit or receive on multiple links can be information indicated in stages. Specifically, the information about whether or not the station has limitations on its ability to transmit or receive on multiple links can be information indicating a stage indicating the magnitude of internal leakage. In a specific embodiment, the information indicating a stage indicating the magnitude of internal leakage can be information indicating a stage indicating the magnitude of interference caused by internal leakage. In yet another specific embodiment, the information indicating a stage indicating the frequency spacing between links that may affect internal leakage can be information indicating a stage indicating the relationship between the frequency spacing between links and the magnitude of internal leakage.

[0112] In FIG. 10, a first station (STA1) and a second station (STA2) are affiliated with one non-AP multilink device. A first AP (AP1) and a second AP (AP2) may also be affiliated with one non-AP multilink device. A first link (link1) is established between the first AP (AP1) and the first station (STA1), and a second link (link2) is established between the second AP (AP2) and the second station (STA2). In FIG. 10, the non-AP multilink device can perform limited STR. When the second station (STA2) transmits on the second link (Link2), the first station (STA1)'s reception on the first link (Link1) may be interrupted by the transmission on the second link (Link2). For example, in the following case, the first station (STA1)'s reception on the first link (Link1) may be interrupted by the transmission on the second link (Link2). The second station (STA2) transmits the first data (Data1) over the second link (Link2), and the first AP (AP1) transmits a response (Ack for Data1) to the first station (STA1). The second station (STA2) transmits the second data (Data2) over the second link (Link2). At this time, the transmission of the second data (Data2) and the transmission of the response (Ack for Data1) to the first data (Data1) may overlap. In this case, the transmission to the second station (STA2) over the second link (Link2) may cause interference to the first link (Link1). As a result, the first station (STA1) may not receive the response (Ack for Data1) to the first data (Data1).

[0113] The operation of the multilink device for channel access will be described below. The multilink operation without a specific description can follow the channel access procedure described in FIG.

[0114] A multilink device can perform channel access independently from multiple links. In this case, the channel access may be backoff-based channel access. When a multilink device performs channel access independently from multiple links and the backoff counters for multiple links reach zero, the multilink device can start transmission simultaneously from multiple links. In a specific embodiment, when one of the backoff counters for multiple links reaches zero and a predetermined condition is met, the multilink device can perform channel access not only for the link whose backoff counter has reached zero but also for other links whose backoff counters have not reached zero. Specifically, when one of the backoff counters for multiple links reaches zero, the multilink device can perform energy sensing on other links whose backoff counters have not reached zero. In this case, if energy greater than or equal to a predetermined value is not detected, the multilink device can perform channel access not only for the link whose backoff counter has reached zero but also for the link for which energy sensing has been performed. This allows the multilink device to start transmission simultaneously from multiple links. The threshold used for energy sensing may be smaller than the threshold used for determining whether to decrement the backoff counter. Furthermore, when determining whether to decrement the backoff counter, the multilink device can sense any type of signal, not just a WLAN signal. Furthermore, in the energy sensing described above, the multilink device can sense any type of signal, not just a WLAN signal. Internal leakage may not be detected as a WLAN signal. In such a case, the multilink device can detect signals detected due to internal leakage through energy sensing. Furthermore, as described above, the threshold used for energy sensing may be smaller than the threshold used when determining whether to decrement the backoff counter. Therefore, even while transmission is occurring on one link, the multilink device can decrement the backoff counter on another link.

[0115] Depending on the degree of interference between links used by the multilink device, the multilink device may determine whether stations operating on each link can operate independently. In this case, the degree of interference between links may be the magnitude of interference perceived by other stations in the multilink device when one station in the multilink device transmits on one of the links. If transmission on the first link of a first station in the multilink device causes interference of a predetermined magnitude or greater to a second station in the multilink device operating on the second link, the operation of the second station may be restricted. Specifically, reception or channel access of the second station may be restricted. If interference occurs, the second station may fail to decode a received signal due to the interference. Furthermore, if interference occurs, the second station may determine that the channel is in use when accessing the channel using backoff.

[0116] Furthermore, if the transmission of a first station in the multilink device through the first link causes interference of less than a predetermined magnitude to a second station in the multilink device operating through the second link, the first station and the second station can operate independently. Specifically, if the transmission of a first station in the multilink device through the first link causes interference of less than a predetermined magnitude to a second station in the multilink device operating through the second link, the first station and the second station can independently access the channel. Also, if the transmission of a first station in the multilink device through the first link causes interference of less than a predetermined magnitude to a second station in the multilink device operating through the second link, the first station and the second station can independently transmit or receive. If interference of less than a predetermined magnitude occurs, the second station can successfully decode the received signal even in the presence of interference. Also, if interference of less than a predetermined magnitude occurs, the second station can determine that the channel is idle when accessing the channel using backoff.

[0117] The degree of interference occurring between stations of a multilink device may vary depending on the interval between the frequency bands of the links on which the stations operate as well as the hardware characteristics of the multilink device. For example, the internal interference occurring in a multilink device including a high RF (radio frequency) device may be smaller than the internal interference occurring in a multilink device including a low RF device. Therefore, the degree of interference occurring between stations of a multilink device may be determined based on the characteristics of the multilink device.

[0118] FIG. 10 shows how the magnitude of interference varies depending on the spacing between link frequency bands and the characteristics of the multilink devices. In the example of FIG. 10, a first multilink device (MLD#1) includes a first station (STA1)-1 operating on a first link (Link1) and a second station (STA1)-2 operating on a second link (Link2). A second multilink device (MLD#2) includes a first station (STA2)-1 operating on a first link (Link1) and a second station (STA2)-2 operating on a second link (Link2). The frequency spacing between the first link (Link1) and the second link (Link2) on which the first multilink device (MLD#1) operates is the same as the frequency spacing between the first link (Link1) and the second link (Link2) on which the second multilink device (MLD#2) operates. However, the magnitude of interference varies depending on the difference between the characteristics of the first multilink device (MLD#1) and the second multilink device (MLD#2). Specifically, the magnitude of interference generated in the second multilink device (MLD#2) may be greater than the magnitude of interference generated in the first multilink device (MLD#1). Considering that the magnitude of interference generated may differ depending on the characteristics of the multilink devices and that the presence or absence of STR support may differ depending on the multilink devices, information regarding whether STR is supported or not needs to be exchanged.

[0119] A multilink device can signal whether or not a station included in the multilink device supports STR. Specifically, an AP multilink device and a non-AP multilink device can exchange whether or not an AP included in the AP multilink device supports STR with whether or not a STA included in the non-AP multilink device supports STR. In this embodiment, an element indicating whether or not STR support is available may be used. The element indicating whether or not STR support is available may be referred to as an STR support element. The STR support element may indicate, with one bit, whether or not a station in the multilink device that transmitted the STR support element supports STR. Specifically, the STR support element may indicate, with one bit, whether or not each station included in the multilink device that transmitted the STR support element supports STR. In this case, if a station supports STR, the bit value may be 1, and if a station does not support STR, the bit value may be 0. If the multilink device that transmitted the STR support element includes a first station (STA1), a second station (STA2), and a third station (STA3), and the first station (STA1) and the third station (STA3) support STR, and the second station (STA2) does not support STR, the STR support element is 101. 1b The STR Support element may include a field having the following information: Stations operating in different frequency bands are assumed to support STR, and the STR Support element may omit signaling regarding the presence or absence of STR support between stations operating in different frequency bands. For example, a first station (STA1) operates on a first link of 2.4 GHz, and a second station (STA2) and a third station (STA3) operate on a second link of 5 GHz and a third link of 5 GHz, respectively. In this case, the STR Support element may indicate with one bit that STR is supported between the second station (STA2) and the third station (STA3). Alternatively, the STR Support element may include only one bit if the STR Support element signals two stations.

[0120] In a specific embodiment, the relationship between a link located at 2.4 GHz and a link located at 5 GHz or 6 GHz among the links of a multi-link device may always be determined as STR, and therefore, signaling regarding the presence or absence of STR between a link located at 2.4 GHz and a link located at 5 GHz or 6 GHz may be omitted.

[0121] In the above-described embodiments, the operation of a station in a multilink device may be replaced by the operation of the multilink device. Also, in the above-described embodiments, the operation of an AP may be replaced by the operation of a non-AP station, and the operation of a non-AP station may be replaced by the operation of an AP. Thus, the operation of an AP in a non-STR multilink device may be replaced by the operation of a non-AP station in a non-STR multilink device, and the operation of a non-AP station in an STR multilink device may be replaced by the operation of an AP in the STR multilink device. Also, the operation of a non-AP station in a non-STR multilink device may be replaced by the operation of an AP in a non-STR multilink device, and the operation of an AP in an STR multilink device may be replaced by the operation of a non-AP station in the STR multilink device.

[0122] FIG. 11 shows the operation of the multilink device when a link is changed according to one embodiment of the present invention.

[0123] When the frequency band of a link is changed, the STR assistance element may be exchanged. As described above, whether a station supports STR may vary depending on the distance between the frequency bands of the link, and whether a station supports STR may change when the frequency band of the link is changed. When the frequency band of the link is changed, at least one of a change in the center frequency of the link, a change in the bandwidth of the frequency band, and a 20 MHz primary channel may be included. The AP and the station may exchange the STR assistance element through a request and a response. In another specific embodiment, when the frequency band of the link is changed, the STR assistance element may be exchanged without a separate request. Furthermore, in the above embodiment, when the frequency band of the link is changed, the operating channel of the station may be changed.

[0124] If a station in a non-AP multilink device cannot perform STR, the station in the non-AP multilink device can request a link change from the AP. Specifically, the station in the non-AP multilink device can request at least one of a change in center frequency, a change in frequency band bandwidth, and a change in 20 MHz primary channel. The link change request may be transmitted to the AP through a link for which a change is requested. In yet another specific embodiment, the link change request may be transmitted to the AP through a link for which a change is not requested. In this case, the link change request may include information indicating the link for which a change is requested. The information indicating the link may be a number identifying the link. In this embodiment, the link change may be a change in an operating channel within a frequency band. The link change may also include information regarding a method for changing the link. Specifically, the link change request may indicate whether the center frequency of the link should be moved to a frequency higher than the current center frequency or a frequency lower than the current center frequency. In yet another specific embodiment, the link change request may implicitly indicate a change to a frequency band away from an adjacent link. The link change request may also indicate a reduction in link bandwidth. The link change request may also indicate a change in the location of the primary channel. Specifically, the link change request may indicate a change in the location of the primary channel to a channel in a lower frequency band or a channel in a higher frequency band than the location of the current primary channel. The AP that receives the link change request may change the link in response to the link change request. In a specific embodiment, the AP that receives the link change request may ignore the link change request.

[0125] In the embodiment of Figure 11, the second station (STA2) and the third station (STA3) of the non-AP multilink device are in a state where they cannot 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 changed third link (Link3) can send a change request to the third AP (AP3). In yet another specific embodiment, a station not operating on the third link (Link3) can send a change request to the AP that does not operate on the third link (Link3).

[0126] When an AP changes a link, the AP may broadcast information about the link change using a beacon frame. In this case, the information about the link change may include information about the link frequency. The information about the link frequency may include at least one of a change in the link center frequency, operating bandwidth, and primary channel. The information about the link change may also include information about the time of the link change. The link change may also be completed when a beacon including information about the link change is transmitted.

[0127] In Figure 11, the link on which the third station (STA3) operates is changed, and the third station (STA3) and the second station (STA2) can support STR. As described above, the non-AP multilink device can send an STR support element to the AP multilink device to signal whether or not it supports the changed STR.

[0128] The above-mentioned link change may not be allowed, or even if a link change occurs, STR may not be supported. Also, as in the embodiment of FIG. 11, an AP multilink device may support STR, but a non-AP multilink device may not support STR. This is because a relatively high-RF device is generally used in an AP multilink device, and a relatively low-RF device is generally used in a non-AP multilink device. Therefore, a method is needed to enable 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 will be described with reference to FIG. 12.

[0129] FIG. 12 shows that when any one station in a non-STR multilink device is receiving, other stations in the non-STR multilink device are prohibited from accessing the channel according to one embodiment of the present invention.

[0130] When transmission is performed on one link of a non-STR multilink device and reception is performed on another link of the non-STR multilink device, reception and transmission of the non-STR multilink device may fail. To solve this problem, when reception is performed on one link of the non-STR multilink device, channel access may be prohibited on the other links of the non-STR multilink device. Specifically, when reception is performed on one link of the non-STR multilink device, channel access backoff may be prohibited on the other links of the non-STR multilink device. This prevents transmission from starting on the other links of the non-STR multilink device when reception is performed on one link of the non-STR multilink device. In a specific embodiment, when reception begins on one link of the non-STR multilink device, channel access backoff may be prohibited on the other links of the non-STR multilink device. This may be set by a specific bit in memory, such as a channel access prohibition flag. Whether channel access is prohibited may be shared by memory within the multilink device. This embodiment allows channel access prohibition to be implemented without a separate frame exchange. For ease of explanation, unless otherwise specified, channel access prohibition as used herein refers to prohibiting channel access or transmission in order to protect the transmission or reception of non-STR multilink devices.

[0131] When channel access is prohibited, stations operating on the link where channel access is prohibited cannot perform a backoff procedure regardless of the NAV and CCA results. Furthermore, when channel access is prohibited, stations operating on the link where channel access is prohibited cannot transmit regardless of the NAV and CCA results. However, even if channel access is prohibited, stations operating on the link where channel access is prohibited can receive. Furthermore, the prohibition of channel access on the second link due to reception performed on the first link may be lifted when reception on the first link is completed. Specifically, the prohibition of channel access on the second link due to reception performed on the first link may be lifted when reception on the first link is completed. In yet another specific embodiment, the prohibition of channel access on the second link due to reception performed on the first link may be lifted when an ACK is transmitted after reception on the first link is completed. Specifically, the prohibition of channel access on the second link due to reception performed on the first link may be lifted when an ACK is transmitted after reception on the first link is completed. In yet another specific embodiment, channel access prohibition on the second link due to reception on the first link may be lifted when ACK transmission is completed after reception on the first link is completed. Also, immediately after the channel access prohibition is lifted, the station may immediately decrement the backoff counter without additional sensing. Here, additional sensing may refer to sensing performed during a DCF Interframe Space (DIFS). In yet another specific embodiment, if the channel is idle for a pre-specified time immediately before the channel access prohibition is lifted, the station may immediately decrement the backoff counter without additional sensing. Here, the pre-specified time may be any one of a PCF Interframe Space (PIFS), a DIFS, a Short Interframe Space (SIFS), and an Arbitration Interframe Space (AIFS).

[0132] In the embodiment of FIG. 12, a non-STR multi-link device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). When the second station (STA2) transmits on the second link (Link2) while the first station (STA1) receives, intra-device interference occurs. As described above, while the first station (STA1) operating on the first link (Link1) receives, the second station (STA2) is prohibited from accessing the channel on the second link (Link2). After the first station (STA1) completes reception on the first link (Link1), the channel access prohibition is lifted. Immediately after the channel access prohibition is lifted, the second station (STA2) can decrement its backoff counter value by 1, from 3 to 2, without additional sensing.

[0133] For convenience of illustration, in Fig. 12, Rx and Tx are represented by a single block (Tx solid line, Rx dotted line), and this single block may be understood to represent an operation including Tx / Ack reception and Rx / Ack transmission even if a separate Ack block is not shown. This may be equally applied to the drawings described later.

[0134] If a station determines that it is not the intended recipient of a PPDU it receives, it may discontinue receiving the PPDU. In such cases, the channel access unblocking operation of the multilink device becomes an issue. In this specification, the intended recipient is used synonymously with the destination station.

[0135] FIG. 13 shows an operation of canceling channel access prohibition when it is confirmed that the intended recipient of a PPDU received by a station in a non-STR multilink device is not a station according to an embodiment of the present invention.

[0136] If the station determines that it is not the intended recipient of the received PPDU, it can lift the channel access prohibition. The station can determine whether it is the intended recipient of the PPDU based on information indicating the recipient address in the signaling field of the PPDU. In this case, the information indicating the recipient address in the signaling field of the PPDU may be the value of the STA-ID field in the EHT-SIG field. Specifically, the station can determine whether the STA-ID field in the EHT-SIG field indicates 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 included in the PPDU. Specifically, the station can determine whether the RA field in the MAC frame included in the PPDU indicates the station. In FIG. 13, the non-STR multi-link device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). The first station (STA1) receives a PPDU. The first station (STA1) determines that it is not the intended recipient of the received PPDU and stops receiving the PPDU. At this time, the first station (STA1) can lift the channel access prohibition for the second station (STA2). Even if the channel access prohibition for the second station (STA2) is lifted, the channel access of the second station (STA2) may be delayed depending on the NAV set for the second station (STA2).

[0137] As shown in Figure 13, even if channel access prohibition is lifted, stations included in a non-STR multilink device often do not have a channel access opportunity compared to stations not included in the multilink device or stations included in the STR multilink device. Therefore, a method for compensating for channel access opportunities for stations included in a non-STR multilink device is needed to ensure fair competition with other stations. For example, immediately after channel access prohibition is lifted, a station whose channel access prohibition has been lifted may be allowed to decrement its backoff counter by more than 2. This will be described with reference to Figure 14.

[0138] FIG. 14 shows a station according to an embodiment of the present invention accessing a channel after channel access prohibition is lifted.

[0139] A station whose channel access prohibition has been lifted can decrement its backoff counter by 2 or more immediately after the channel access prohibition is lifted. This is to ensure fairness in channel access opportunities with other stations, since other stations have performed backoff procedures while the station's channel access was prohibited.

[0140] In yet another specific embodiment, a station whose channel access is prohibited can perform a channel access procedure to decrement the CCA (CSMA) and backoff counter while its channel access is prohibited. In FIG. 14, a non-STR multi-link device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). In FIG. 14, the second station (STA2) is prohibited from channel access while the first station (STA1) is receiving. In FIG. 14(a), while the second station (STA2) is prohibited from channel access, the second station (STA2) can perform a channel access procedure to decrement the CCA (CSMA) and backoff counter. In FIG. 14(a), while the second station (STA2) is prohibited from channel access, the second station (STA2) decrements its backoff counter because the channel of the second link (Link2) is idle.

[0141] In addition, a station whose channel access is prohibited can delay transmission without starting transmission even if its backoff counter reaches 0 while channel access is prohibited. In this case, the station can maintain the backoff counter value at 0. Furthermore, even if the station delays transmission, the station can maintain the CW value as it is. This is different from the station doubling the CW value because the channel it accesses is busy. This is because the reason for delaying transmission is not because the channel is determined to be busy. In Figure 14(b), while channel access of the second station (STA2) is prohibited, the second station (STA2) can perform a channel access procedure to decrement the CCA (CSMA) and backoff counter. In Figure 14(b), while channel access of the second station (STA2) is prohibited, the channel of the second link (Link2) is idle, so the second station (STA2) decrements the backoff counter. While the channel access of the second station (STA2) is prohibited, the backoff counter of the second station (STA2) reaches 0. The second station (STA2) delays transmission and resumes transmission after the channel access prohibition is lifted.

[0142] As described above, the channel access prohibition can include prohibiting a second station from transmitting when a first station in a non-STR multilink device is transmitting, and can also include prohibiting a second station from transmitting when a first station in a non-STR multilink device is receiving.

[0143] In the embodiment illustrated in Figure 14(b), if multiple stations are prohibited from channel access, there is a high possibility that the channel access prohibitions of multiple stations will be lifted simultaneously, causing multiple stations to attempt transmission simultaneously. Therefore, a method is needed to reduce the probability of transmission collisions. This will be explained in Figure 15.

[0144] FIG. 15 shows an operation of a station according to an embodiment of the present invention to transmit after channel access prohibition is lifted.

[0145] As described above, among multiple links operated by a non-STR multilink device, transmission may be performed on a first link and transmission may be prohibited on a second link. When the transmission on the first link is completed, transmission on the second link may begin by exchanging RTS / CTS frames. Therefore, when transmission is performed on a first link among multiple links operated by a non-STR multilink device, the non-STR multilink device may begin exchanging RTS / CTS frames on the second link. After the channel access prohibition of a station whose transmission has been delayed due to channel access prohibition is lifted, the station may begin exchanging RTS / CTS (request to send / clear to send) frames before starting the delayed transmission. At this time, if the station is unable to receive a CTS frame, it may be unable to start the delayed transmission. In the embodiment of FIG. 15(a), a station whose transmission has been delayed due to channel access prohibition transmits an RTS frame before starting the delayed transmission. The station begins the delayed transmission after receiving a CTS frame in response to the RTS frame.

[0146] In yet another specific embodiment, after a station whose transmission was delayed due to channel access prohibition is released, the station can transmit a frame including only a portion of the delayed transmission. In this case, after the station receives a response, e.g., an ACK, to the frame including only a portion of the delayed transmission, the station can transmit the remaining portion of the delayed transmission. If the station does not receive a response to the frame including only a portion of the delayed transmission, the station may not transmit the remaining portion of the delayed transmission. In this manner, the station initiates an RTS / CTS exchange or transmits only a portion of the delayed transmission after channel access prohibition is released because the collision probability of transmission after channel access prohibition is higher than that of general transmission. Therefore, the above-described embodiment may be mandatory for transmissions performed after channel access prohibition is released. In existing WLAN operations, the RTS / CTS frame is used to solve the hidden node problem and can be used based on the size of the transmission data. In the above-described embodiment, the RTS / CTS frame is used to prevent transmission collisions with stations attempting delayed transmissions to protect the transmission or reception of non-STR multilink devices.

[0147] As described above, when one station in a non-STR multilink device receives, transmissions by other stations in the non-STR multilink device may be restricted. Furthermore, when one station in a non-STR multilink device transmits, other stations in the non-STR multilink device may have difficulty accurately sensing the channel status of the link on which the station operates. Specifically, when a first station in a non-STR multilink device transmits, a second station in the non-STR multilink device may always determine that the channel status of the link on which the second station operates is busy. Therefore, even when the channel of the link on which the second station operates is idle, the second station may determine that the channel is busy due to intra-device interference. In this way, when a station that cannot determine the channel status due to intra-device interference or when one station in the non-STR multilink device is continuing to transmit is said to be in a blind state to other stations in the non-STR multilink device. Due to the above-described situation, a station in a blind state may have difficulty performing a backoff procedure and attempting transmission. In addition, due to the above-mentioned circumstances, it may be difficult for blind stations to start receiving or successfully decode the PPDU. Therefore, a transmission method that takes blind stations into consideration is required. This will be explained in FIG. 16.

[0148] FIG. 16 illustrates transmissions based on the state of stations in a non-STR multilink system according to an embodiment of the present invention.

[0149] A station attempting to transmit to a station in a non-STR multilink device can determine whether to transmit based on whether the station in the non-STR multilink device is in a blind state. In this case, the station attempting to transmit to a station in a non-STR multilink device may be a station included in the STR multilink device. Alternatively, the station attempting to transmit to a station in a non-STR multilink device may be an AP included in the 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 the station in the non-STR multilink device is in a blind state. The station attempting to transmit can determine whether other stations in the multilink device in which the station is included are transmitting to the non-STR multilink device. If other stations in the multilink device in which the station is included are receiving from the non-STR multilink device, the station can determine that the station in the non-STR multilink device receiving the station's transmission is in a blind state. In the embodiment of FIG. 16, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a 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 second station (STA2) is the subject of transmission to the second AP (AP2). 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.

[0150] Since the stations in the multi-link 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 performed explicitly.

[0151] A station does not need to transmit to a station in a blind state because, even if a station transmits to a station in a blind state, there is a high possibility that the station in the blind state will not be able to acknowledge reception or will not be able to decode the PPDU. In this case, the station can cancel transmission to the station in the blind state and transmit to another station.

[0152] When an STR multilink device transmits to a non-STR multilink device, the STR multilink device can transmit to the non-STR multilink device over multiple links. Specifically, when the STR multilink device transmits to the non-STR multilink device over a first link, the STR multilink device can begin transmitting to the non-STR multilink device over a second link. In this case, the STR multilink device can determine the length of the transmission over the second link based on the transmission to the non-STR multilink device. Specifically, the STR multilink device can determine the length of the transmission over the second link to the non-STR multilink device based on the length of the transmission over the first link to the non-STR multilink device. In a specific embodiment, the STR multilink device can simultaneously complete transmission over the first and second links. This is to prevent transmission to one of the stations in the non-STR multilink device from completing first, and to prevent transmission to another station in the non-STR multilink device from occurring while one of the stations in the non-STR multilink device is transmitting a response to the transmission, e.g., an ACK. The above-described embodiment allows multiple stations in the non-STR multilink device to simultaneously transmit responses to transmissions to multiple stations.

[0153] An STR multilink device cannot determine the status of stations included in non-STR multilink devices in real time. Therefore, even if an STR multilink device operates according to the embodiment described in FIG. 16, interference or transmission collisions may occur between links on which the non-STR multilink device operates. For example, in the embodiment of FIG. 16, the first AP (AP1) may begin transmitting to the first station (STA1) before recognizing that the second station (STA2) is transmitting to the second AP (AP2). In this way, the probability of inter-link interference or collisions may be greater than the probability of intra-link interference or transmission collisions. This is described in more detail in FIG. 17.

[0154] FIG. 17 shows a situation in which interference or collision between links may occur.

[0155] When a second station in a non-STR station multilink device starts transmitting to a second AP in the STR AP multilink device at the same time as a first AP in the STR AP multilink device starts transmitting to a first station in the non-STR station multilink device, a transmission collision between the links can occur. This is shown in Figure 17(a). As mentioned above, this can occur because the STR multilink device cannot determine the status of the stations included in the non-STR station multilink device in real time.

[0156] Furthermore, even if the transmission of the second station of the non-STR station multilink device to the second AP of the STR AP multilink device begins before the transmission of the first AP of the STR AP multilink device to the first station of the non-STR station multilink device, a transmission collision may occur between the links. This is shown in FIG. 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 transmitting. As such, since a transmission collision may occur even between stations that begin transmitting at different times, the probability of inter-device interference or transmission collision may be greater than the probability of intra-link interference or transmission collision. Furthermore, the longer the time it takes for the AP of the STR multilink device to identify the sender of the PPDU it receives, the greater the probability of inter-link interference or transmission collision. Therefore, a method to resolve this issue is needed. When one station of the STR multilink device is receiving, other stations of the STR multilink device may not be allowed to access the channel. However, if channel access is prohibited in this way, the purpose of implementing the STR function may be lost. Therefore, a method of operation that does not inhibit channel access for STR multilink devices is required, which is illustrated in FIG.

[0157] As described above, it may be important for the multilink device to quickly determine the station transmitting to the multilink device. The User field of the EHT-SIG of the EHT UL PPDU may indicate the identifier (STA-ID) of the station transmitting the EHT UL PPDU. Specifically, when the DL / UL field of the signaling field of the EHT PPDU indicates that the EHT PPDU is a UL PPDU, the User field of the EHT-SIG of the EHT PPDU may indicate the identifier of the station transmitting the EHT UL PPDU. The multilink device receiving the EHT PPDU can identify the station transmitting the EHT PPDU based on the User field of the EHT-SIG of the EHT UL PPDU. This allows the AP multilink device to determine the station transmitting the EHT UL PPDU, and the AP multilink device can determine the destination device of the transmission. Specifically, the AP multilink device can determine whether the intended transmission is likely to fail due to inter-link collision. Furthermore, if there is a high possibility that the transmission that the AP multilink device is attempting to perform will fail, the AP multilink device can delay the transmission that it is attempting to perform and perform another transmission.

[0158] FIG. 18 illustrates an operation in which an STR multilink device stops transmission to a non-STR multilink device according to one embodiment of the present invention.

[0159] If a station in an STR multilink device determines that a station in the non-STR multilink device is in a blind state while transmitting to a station in a non-STR multilink device, the STR multilink device can suspend transmission to the station in the blind state. Specifically, the STR multilink device can determine whether a station in the non-STR multilink device is in a blind state based on a value indicated as an STA(AID)-ID in the signaling field of a received PPDU or a TA (transmitting address) field of a MAC frame included in the received PPDU. In this case, the STA-ID may be a value indicating the station transmitting the UL PPDU in an UL PPDU. In a specific embodiment, the STR multilink device can determine that a second station included in the non-STR multilink device is in a blind state if a value indicated as an STA(AID)-ID in the signaling field of a received PPDU indicates a first station included in the non-STR multilink device. In addition, if the TA field of the MAC frame included in the received PPDU indicates a first station included in a non-STR multilink device, the STR multilink device can determine that a second station included in the non-STR multilink device is in a blind state. First, the operation of the station after transmission cancellation will be described.

[0160] If a TXOP set for a station in a non-STR multilink device remains, the station that canceled transmission to the station in the non-STR multilink device can attempt transmission to stations other than the station in the non-STR multilink device. In this case, the station that canceled transmission to the station in the non-STR multilink device can transmit to stations other than the station in the non-STR multilink device without a separate backoff procedure. In a specific embodiment, if the channel is detected as idle for a pre-designated time period without a separate backoff procedure after canceling transmission to the station in the non-STR multilink device, the station that canceled transmission to the station in the non-STR multilink device can transmit to stations other than the station in the non-STR multilink device. In this case, the pre-designated time period may be any one of SIFS, PDIF, and DIFS.

[0161] When a station that has canceled a transmission to a station in a non-STR multilink device transmits to a station other than the station in the non-STR multilink device, the station that canceled the transmission to the station in the non-STR multilink device can transmit traffic with the same priority as the traffic of the canceled transmission or traffic with a higher priority. This is because transmitting traffic with a lower priority than the priority of the traffic used when accessing the channel for the canceled transmission would not be fair. In the above-mentioned embodiment, the station in the STR multilink device may be an AP.

[0162] A station that cancels transmission to a station in a non-STR multilink device can reset the TXOP it set. Specifically, a station that cancels transmission to a station in a non-STR multilink device can send a CF-End frame after canceling transmission, allowing other stations operating on the link scheduled for transmission to use the link.

[0163] In FIG. 18, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). The second station (STA2) is transmitting to the second AP (AP2). While transmitting to the first station (STA1), the first AP (AP1) determines that the first station (STA1) is in a blind state. Therefore, the first AP (AP1) suspends transmission to the first station (STA1). In FIG. 18(a), after suspending transmission to the first station (STA1), the first AP (AP1) transmits to stations other than the first station (STA1), as in the previously described embodiment. In FIG. 18(b), after suspending transmission to the first station (STA1), the first AP (AP1) transmits a CF-END frame as in the embodiment described below.

[0164] When a station suspends transmission, it may not transmit the next fragment after transmitting the fragment that was in transmission. In yet another specific embodiment, the station may immediately stop transmitting the packet that was in transmission.

[0165] In the above-described embodiment, when the STR multilink device suspends transmission to a station of a non-STR multilink device in a blind state and transmits to a station other than the station of the non-STR multilink device in a blind state, it is necessary to notify the other station that transmission to the other station is possible for stable reception. A method for this will be described. For convenience of explanation, the other station other than the station of the non-STR multilink device in a blind state will be referred to as the other station.

[0166] A station in an STR multilink device can insert the address of another station into a MAC frame. Specifically, the station in the 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 the address of the other station into a separate field. In yet another specific embodiment, the station in the device can insert the address of the other station into an EHT-SIG. Specifically, the station in the STR multilink device can insert the address of the intended recipient of the PPDU and the address of the other station into the User field of the signaling field of the PPDU. In this case, the address of the other station can be inserted after the address of the intended recipient of the PPDU in the User field of the signaling field of the PPDU.

[0167] In yet another specific embodiment, a station may monitor for reception of a PPDU for a predetermined time even after determining that the station is not the intended recipient of the received PPDU. Specifically, the station may monitor for continued reception of a PPDU for a predetermined time even after determining that the station is not the intended recipient of the received PPDU. This allows the station to determine whether PPDU transmission should be stopped and transmission to the station should begin. In this embodiment, if it is determined that PPDU transmission will continue for the predetermined time, the station may enter a doze state. If it is determined that PPDU transmission will not continue for the predetermined time, the station may remain in a wake-up state. At this time, if a new PPDU is received by the station, the station may decode the PPDU.

[0168] In yet another specific embodiment, a station transmitting a PPDU may insert information into the PPDU signaling that the transmission of the PPDU may be interrupted. The information signaling that the transmission of the PPDU may be interrupted may be a 1-bit subfield. For example, if the value of the subfield signaling that the transmission of the PPDU may be interrupted is 1, a station receiving the PPDU may determine that the transmission of the PPDU may be interrupted before the time indicated by the Length field of the signaling field of the PPDU and the Duration field of the MAC frame. If the station determines that the transmission of the PPDU may be interrupted before the time indicated by the Length field of the signaling field of the PPDU and the Duration field of the MAC frame, the station may postpone entering a power-saving state. Alternatively, a station transmitting a PPDU may insert information signaling that the transmission may be interrupted into a reserved field of the PPDU.

[0169] In this way, unnecessary channel occupation due to transmission cancellation or transmission interruption can be prevented.

[0170] When transmission is interrupted or postponed due to a transmission collision between links, the CW value used for channel access may be doubled, as in the case of a general transmission failure. When transmission is interrupted or postponed due to a transmission collision between links, unlike the case of a general channel access failure or transmission failure, the CW value used for channel access does not need to be doubled. That is, the station can maintain the CW value used for channel access as it is. Doubling the CW value increases the range of possible backoff counter values ​​and reduces the probability of transmission collision. This need can be reduced if the station can clearly recognize transmission collision between links. Also, when transmission is interrupted or postponed due to a transmission collision between links, doubling the CW value by the station may delay the transmission. However, when inter-link transmission collision and intra-link collision occur simultaneously, the station needs to double the CW value. This is described in FIG. 19.

[0171] FIG. 19 shows how the STR multilink device processes the value of CW when it recognizes a transmission collision between links according to an embodiment of the present invention.

[0172] As in the above-described embodiment, if a station cancels a transmission due to a transmission performed by a non-STR multilink device, the station can sense the channel state after canceling the transmission. If the channel is detected as not idle, the station can double the CW value. In this case, the doubling can be performed according to the embodiment described in FIG. 6. Alternatively, if the channel is detected as idle, the station can maintain the CW value. This embodiment is used because even if the channel is detected as idle, the possibility of intra-link transmission collision is low, so this is treated differently from a transmission attempt. Specifically, if an AP in an AP multilink device fails to transmit to a station in a non-STR multilink device, the AP in the AP multilink device can obtain a backoff counter in the CW without incrementing the CW. In this case, if a non-STR multilink device in the AP multilink device fails to transmit to a first station and a second station in the non-STR multilink device transmits, the AP in the AP multilink device can obtain a backoff counter in the CW without incrementing the CW. As described above, the AP multilink device can determine whether the second station of the non-STR multilink device is to transmit based on the transmitting station of the PPDU indicated by the signaling field of the PPDU or the station indicated by the TA field of the MAC frame included in the PPDU. In the above-described embodiment, when EDCA is applied, the procedures for CW adjustment and backoff counter generation may be performed for each AC.

[0173] In yet another specific embodiment, the STR multilink device can determine whether the transmission of a PPDU has failed based on whether a response to the PPDU has been received. In this case, the STR multilink device does not need to consider whether the station receiving the PPDU is included in a non-STR multilink device. For example, if a first station receiving the PPDU is included in a non-STR multilink device and the first station is unable to transmit a response to the PPDU because a second station in the non-STR multilink device is transmitting, the STR multilink device can still determine that the transmission of the PPDU has failed. Furthermore, if the STR multilink device's transmission of the PPDU has failed, the STR multilink device can increase the value of the CW to the next largest possible value. In this case, if the CW value is at its maximum value, the STR multilink device may maintain the CW value at the same value.

[0174] In another specific embodiment, when a channel is detected as being idle, the station may set the CW value to the minimum value (CW_min) of the traffic CW. This embodiment is intended to treat a case where a channel is detected as being idle as being the same as a successful transmission, since the possibility of a transmission collision occurring within the link is low. The station may apply the above embodiment to the CW of the AC of the traffic included in the canceled transmission.

[0175] Furthermore, when a station cancels transmission according to the above-described embodiment, the station may not increment the Retry Counter, which may include at least one of a long retry counter and a short retry counter.

[0176] In the above embodiments, canceling a transmission may include at least one of pausing the transmission and / or delaying the transmission before commencing the transmission.

[0177] If a station sends a CTS-to-Self frame before attempting to transmit and then cancels transmission, the station does not need to initiate an RTS / CTS frame exchange before attempting transmission after canceling transmission because the NAV has already been set by the CTS-to-Self frame. Also, if a station cancels transmission and still has a TXOP when it attempts to transmit again, the station can attempt transmission without a backoff procedure.

[0178] In FIG. 19, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). The second station (STA2) is transmitting to the second AP (AP2). While transmitting to the first station (STA1), the first AP (AP1) determines that the first station (STA1) is in a blind state. Therefore, the first AP (AP1) suspends transmission to the first station (STA1). In FIG. 19(a), the first AP (AP1) determines that the channel for the first link (Link1) is idle. At this time, there are no remaining TXOPs, so the first AP (AP1) accesses the channel using the backoff procedure. In Figure 19(b), the first AP (AP1) determines that the channel of the first link (Link1) is not idle. At this time, since there is a TXOP remaining, the first AP (AP1) attempts to transmit without a backoff procedure.

[0179] In the above-described embodiment, if the channel is detected as idle for a pre-specified time interval without a separate backoff procedure after canceling a transmission to a station in a non-STR multilink device, the station that canceled the transmission to the station in the non-STR multilink device can transmit to a station other than the station in the non-STR multilink device. In this case, the duration of the pre-specified time interval can be an issue. A station that receives a PPDU of a canceled transmission may fail to decode the PPDU. In this case, if the channel is detected as idle for an extended interframe space (EIFS), the station that fails to decode the PPDU can initiate a backoff procedure. Therefore, an issue arises as to whether the pre-specified time interval should be set to be longer than or equal to the EIFS. This will be described with reference to FIG. 20.

[0180] FIG. 20 illustrates an operation in which an STR multilink device performs channel access again after halting transmission to a non-STR multilink device according to an embodiment of the present invention.

[0181] As shown in Figure 20(a), the pre-specified time interval may be DIFS. This takes into consideration that a station in an STR multilink device acquires a channel access opportunity through a contention procedure and loses the acquired channel access opportunity due to transmission collision between links. In other words, since a station in an STR multilink device acquires a channel access opportunity through a contention procedure, it is given priority over other stations attempting channel access. When EDCA is applied, DIFS may be replaced with AIFS [AC].

[0182] In yet another specific embodiment, as shown in Figure 20(b), the pre-specified time interval may be EIFS, which is in consideration of the fact that the STR multilink device can assume that it has already used up its transmission opportunities and of fairness with other stations.

[0183] In another specific embodiment, as shown in FIG. 20(c), when the signaling field of the PPDU signals that transmission may be interrupted, the pre-specified time interval may be DIFS. Also, when a station receiving a PPDU detects that transmission of the PPDU has been interrupted, the station can detect whether the channel is idle using DIFS instead of EIFS. In this case, if the channel is detected as idle using DIFS, the station can initiate a backoff procedure. This embodiment can improve the performance of the entire network and ensure fairness between stations. When EDCA is applied, DIFS can be replaced with AIFS [AC].

[0184] As described above, the STR multilink device can recognize that a transmission collision between links may occur. Specifically, when a first station in the STR multilink device completes a backoff procedure, a second station in the STR multilink device may be receiving a PPDU. If the second station fails to complete decoding of the signaling field of the PPDU, the first station may not recognize that a transmission collision between links has occurred, but may determine that it is possible. In this case, the first station may insert information indicating that transmission may be interrupted into the PPDU to be transmitted, as described above. Furthermore, the NSTR multilink device may transmit a CTS-to-Self frame before transmitting to a non-STR multilink device for stable and efficient transmission. This will be described with reference to FIG. 21.

[0185] FIG. 21 illustrates an 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.

[0186] 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 a first station in the STR multilink device is receiving, the second station in the STR multilink device can transmit a CTS-to-Self frame before transmitting to the non-STR multilink device. This allows the second station to reserve a TXOP for transmission to the non-STR multilink device. Furthermore, before transmitting to the non-STR multilink device, the second station can determine whether a transmission for the first station is being transmitted from the non-STR multilink device. The second station can determine the destination station of a transmission based on whether a transmission for the first station is being transmitted from the non-STR multilink device. Specifically, if a transmission for the first station is not being transmitted from the non-STR multilink device, the second station can transmit to the non-STR multilink device. When a transmission for a first station is being sent from the non-STR multilink device, a second station may transmit to a station not included in the non-STR multilink device. For example, if the first station plans to transmit a SU-PPDU for a station in the non-STR multilink device, a MU-PPDU containing data for a station in the non-STR multilink device, or a PPDU containing a trigger frame that triggers a transmission for a station in the non-STR multilink device, the first station may cancel the planned transmission. In this case, the first station may attempt to transmit a SU-PPDU for a station other than a station in the non-STR multilink device, a MU-PPDU containing no data for a station in the non-STR multilink device, or a PPDU containing a trigger frame that does not trigger a transmission for a station in the non-STR multilink device.In this case, the first station can begin transmission after a time greater than SIFS from the time it transmits the CTS-to-Self frame. Specifically, the first station can begin transmission PIFS after transmitting the CTS-to-Self frame. The station that transmitted the CTS-to-Self frame must begin transmission SIFS after transmitting the CTS-to-Self frame. As in the above-described embodiment, when canceling a planned transmission and attempting a new transmission, processing time is required from the STR multilink device, such as generating a new MPDU to be transmitted. For this reason, exceptions to the regulations regarding the time interval between a CTS-to-Self frame and a transmission may be applied. In such an embodiment, the second station cannot transmit beyond the TXOP obtained by the CTS-to-Self frame.

[0187] In Figure 21, the STR multi-link device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The second AP (AP2) receives and schedules a transmission to a station in the non-STR multi-link device, so the first AP (AP1) transmits a CTS-to-Self frame before the scheduled transmission. As described above, the first AP (AP1) determines the destination station for transmission based on the determination of the station that transmitted the PPDU received by the second AP (AP2). In addition, the first AP (AP1) transmits after SIFS or PIFS from the time of transmitting the CTS-to-Self frame.

[0188] 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 an RTS / CTS frame exchange, the second station can acquire the TXOP only if the destination station is not blinded.

[0189] FIG. 22 illustrates a case in which multiple APs included in an STR multilink device transmit to multiple stations included in one non-STR multilink device according to an embodiment of the present invention.

[0190] Multiple stations included in one non-STR multilink device can receive simultaneously. This is because simultaneous reception by multiple stations causes relatively little interference. Figure 22 shows multiple stations included in one non-STR multilink device receiving simultaneously. In this case, to ensure stable operation of the non-STR multilink device, multiple APs included in the STR multilink device can perform multiple transmissions to multiple stations included in one non-STR multilink device, with the end of transmissions synchronized. This is described in Figure 23.

[0191] FIG. 23 shows an embodiment of the present invention in which multiple APs included in an STR multilink device perform multiple transmissions with synchronized end of transmission to multiple stations included in a single non-STR multilink device.

[0192] In non-STR links, when a multilink device transmits on one link, the multilink device can simplify the channel access procedure for transmissions on other links. Specifically, when a first station in the multilink device completes a backoff channel access procedure on the first link, if the channel is idle for a pre-specified time period in the link of a second station in the STR multilink device, the second station in the STR multilink device can begin transmission on the second link.

[0193] In a specific embodiment, when one station in an STR multilink device transmits to one station in a non-STR multilink device, the channel access procedure for other stations in the STR multilink device can be simplified. Specifically, when a first station in the STR multilink device completes a backoff channel access procedure for transmission to the first station in the non-STR multilink device, if the channel is idle for a pre-specified time period within the link of the second station in the STR multilink device, the second station in the STR multilink device can begin transmission to the second station in the non-STR multilink device. In this case, the pre-specified time period may be a PIFS. This operation may be applied when the first and second stations in the STR multilink device transmit to stations included in a single non-STR multilink device. In this embodiment, the first and second stations can begin transmission within a pre-specified time period. The pre-specified time period may be a slot time.

[0194] Furthermore, when a first station and a second station in an STR multilink device transmit to a station included in a single non-STR multilink device, the end of transmission of the first station and the second station may be synchronized. In this case, the synchronization of the end of transmission of the first station and the second station may mean that the transmission of the first station and the transmission of the second station end with a difference within a first pre-specified time interval. The first pre-specified time interval may mean within a slot boundary or a symbol boundary.

[0195] Multiple stations in a non-STR multilink device that receive synchronized transmission ends can simultaneously transmit subsequent transmissions, for example, responses. The responses can include an ACK. In conventional WLANs, subsequent transmissions are transmitted SIFS after reception. However, transmitting subsequent transmissions with a slight time difference between multiple transmissions that ended with a slight time difference can be more complex to implement than transmitting subsequent transmissions simultaneously. Therefore, as described above, multiple stations in a non-STR multilink device that receive synchronized transmission ends can simultaneously transmit subsequent transmissions. In this case, the interval between subsequent transmissions following at least one of the multiple transmissions whose transmission ends are synchronized may be the sum of SIFS and a time within a pre-specified time interval. Specifically, the transmission following the first transmission among the multiple transmissions whose transmission ends are synchronized may be transmitted at an interval that is the sum of SIFS and a time within a pre-specified time interval. In this case, the pre-specified time interval may be one of a slot time or a symbol length. Furthermore, the difference within a predetermined time interval may be the difference between the end of the last transmission among a plurality of transmissions whose end is synchronized and the first transmission among a plurality of transmissions whose end is synchronized.

[0196] In yet another specific embodiment, when multiple transmissions end with a time difference within a first pre-specified time interval, multiple stations receiving the transmission can transmit synchronized subsequent transmissions. The multiple subsequent transmissions with synchronized transmission ends can represent multiple subsequent transmissions transmitted with a time difference within a second pre-specified time interval. The difference within the second pre-specified time interval can be the difference between the end of the last completed transmission among the synchronized transmissions and the earliest completed transmission among the synchronized transmission ends. In this case, the second pre-specified time interval can be smaller than the first pre-specified time interval. A PPDU with synchronized transmission ends can be referred to as a sync PPDU.

[0197] In Figure 23, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). The first AP (AP1) and the second AP (AP2) synchronize the end of transmissions to the first station (STA1) and the second station (STA2), respectively. That is, after the first station (STA1) finishes transmission, the second station (STA2) finishes transmission within a time period pre-specified by the first station (STA1). The first station (STA1) and the second station (STA2) simultaneously send ACKs. At this time, the first station (STA1) transmits an ACK after the difference between the end of transmission to the first station (STA1) (SIFS) and the end of transmission to the first station (STA1) and the end of transmission to the second station (STA2).

[0198] This embodiment may be applied to transmissions for which the ACK policy is not set to No ACK. Specifically, it may also be applied when the ACK policy is not immediate. In a specific embodiment, when multiple stations in a multilink device receive transmissions whose end of transmission is synchronized, the multiple stations in the multilink device can simultaneously receive ACK requests and simultaneously transmit ACKs in response to the ACK requests. Multiple stations in a multilink device that receive transmissions for which the ACK policy is set to a value other than No ACK within a predetermined time period can simultaneously begin ACKs.

[0199] When non-STR multilink devices are present, they must be taken into consideration when transmitting RTS / CTS frames and CTS-to-Self frames to set TXOPs, as will be explained in Figures 24 to 29.

[0200] FIG. 24 shows multilink devices exchanging RTS / CTS frames according to an embodiment of the present invention.

[0201] Even when a non-STR multilink device exists, the RTS / CTS frame exchange procedure can follow the procedure defined in the existing WLAN. The RTS / CTS frame can be used to set the NAV of a station operating on another link. Specifically, a station that receives an RTS / CTS frame can transmit it to another station operating on a link other than the one it operates on and included in the multilink device in which it is included.

[0202] However, as in the previous embodiment, channel access or transmission may be restricted when a non-STR multilink device is present, which may prevent RTS / CTS transmission as shown in Figure 24. That is, a station planning to transmit to a first station in a non-STR multilink device may not attempt to exchange RTS / CTS frames if a second station in the non-STR multilink device is receiving.

[0203] In FIG. 24, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a 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) determines 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 this embodiment, a hidden node problem may occur, as will be described in FIG. 25.

[0204] FIG. 25 illustrates a hidden node problem that occurs in the RTS / CTS frame exchange procedure according to the embodiment described in FIG.

[0205] As described above, a station transmitting to a station in a non-STR multilink device may transmit without being able to exchange CTS / RTS. In this case, because a TXOP is not set for the other station, the other station may attempt to transmit, resulting in the station in the non-STR multilink device failing to transmit or receive. In the example of FIG. 25, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). Due to the first AP (AP1) transmitting to the first station (STA1), the second AP (AP2) was unable to send an RTS frame before transmitting. Therefore, a TXOP for the second AP (AP2) transmission is not set for the station operating on the second link (Link2). Therefore, when the second AP (AP2) transmits to the second station (STA2), a station in another BSS (OBSS STA) transmits on the second link (Link 2). As a result, the second station (STA2) fails to receive the transmission from the second AP (AP2). To solve this hidden node problem, the following embodiment may be applied.

[0206] In a specific embodiment, if any station in a non-STR multilink device is receiving, the station may not be allowed to transmit to any station in the non-STR multilink device. In yet another specific embodiment, if a station transmits to a first station in a non-STR multilink device and a second station in the non-STR multilink device is receiving, the station may transmit simultaneously with its transmission to the second station. If a station transmits to a first station in a non-STR multilink device and a second station in the non-STR multilink device is receiving, the station may synchronize the end of its transmission to the first station with the end of its transmission to the second station. Specifically, if a station transmits to a first station in a non-STR multilink device and a second station in the non-STR multilink device is receiving, the station may end its transmission to the first station simultaneously with its transmission to the second station. In such an embodiment, transmission to the second station may be performed by another station in the multilink device, including the station.

[0207] FIG. 26 shows multilink devices exchanging RTS / CTS frames according to an embodiment of the present invention.

[0208] In yet another embodiment of the present invention, if a first station in a multilink device continues transmitting to a third station in a non-STR multilink device, and a second station in the multilink device attempts to transmit an RTS frame to a fourth station in the non-STR multilink device, the first station may end 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. This allows TXOP tentative setup for frame exchange between the second and fourth stations. However, it may be difficult for the first station to end its transmission before the fourth station attempts to transmit the RTS frame.

[0209] In yet another embodiment of the present invention, if a second station in the multilink device attempts to transmit an RTS frame to a fourth station in the non-STR multilink device while a first station in the multilink device continues transmitting to a third station in the non-STR multilink device, the second station can transmit the RTS frame to the fourth station to coincide with the end of the first station's transmission to the third station. To do this, the second station can insert padding into the RTS frame. In this case, the RTS frame may have an RTS frame format that allows for flexible adjustment of the transmission length. For convenience of explanation, this RTS frame format is referred to as an ML (multilink)-RTS frame. The ML-RTS frame may include a pad field for padding. For example, the format of the ML-RTS frame may be the same as the RTS frame format shown in FIG. 26. In addition, the first station can insert padding into the transmission to the third station to coincide with the end of the RTS frame.

[0210] In the embodiment of Figure 26, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a 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) in synchronization with the end of the first AP's (AP1) transmission to the first station (STA1). Thereafter, when the first station (STA1) transmits an ACK to the first AP (AP1), the second station (STA2) transmits an ACK to the second AP (AP2). As a result, a TXOP for frame exchange between the second AP (AP2) and the second station (STA2) is established in the station operating on the second link channel.

[0211] In yet another specific embodiment, another frame for setting NAV may be substituted for the RTS / CTS frame. In the above-described embodiment, an ACK request frame may be transmitted instead of the RTS frame. The ACK request frame may include duration information related to the transmission end point. In addition, a frame including an ACK transmitted in response to the ACK request may also include duration information. In this case, the duration information of the frame including the ACK may be set according to the duration information of the ACK request frame.

[0212] Although the above-described embodiment has been described for RTS / CTS frame exchange, it may also be used for control frame exchange 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.

[0213] FIG. 27 shows that a multilink device transmits a response to a control frame exceptionally even when channel access is prohibited according to an embodiment of the present invention.

[0214] As described in the above embodiment, when a non-STR multilink device is present, channel access of some stations may be prohibited. Even if channel access of a station is prohibited, the station can still send a response to a control frame. Specifically, even if channel access of a station is prohibited, the station can still send a CTS frame in response to an RTS frame.

[0215] In this way, when a response to a control frame is transmitted as an exception to channel access denial, the following embodiment may be applied: A first station transmits a response to a control frame as an exception to channel access denial. When the first station transmits the response to the control frame, a third station transmits to a second station included in the multilink device including the first station. In this case, the third station can retransmit to the first station. The third station can predict that the transmission to the second station will fail.

[0216] In the example of FIG. 27, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a 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). Because the first station (STA1) receives, channel access for the second station (STA2) is prohibited. However, the second station (STA2) transmits a CTS frame to the second AP (AP2) as an exception to the channel access prohibition. The first AP (AP1) can determine that the first AP's (AP1's) transmission is likely to fail due to the second station's (STA2's) CTS frame transmission. Therefore, the first AP (AP1) retransmits to the first station (STA1). The retransmission method is described in more detail in FIG.

[0217] FIG. 28 shows the retransmission of a transmission to a station of a non-STR multilink device.

[0218] In the retransmission described in FIG. 27, only some of the packets included in the initial transmission may be retransmitted. Specifically, the station performing the retransmission may retransmit only some of the packets included in the initial transmission. The station performing the retransmission may determine some of the packets included in the initial transmission to be retransmitted based on the time interval in which the station performing the retransmission received the CTS frame. Specifically, the station performing the retransmission may determine, among the packets included in the initial transmission, packets transmitted in a time interval including the time interval in which the station performing the retransmission received the CTS frame as the packets to be retransmitted. In this case, the station performing the retransmission may retransmit packets transmitted in a time interval including the time interval in which the station performing the retransmission received the CTS frame based on the propagation delay. In yet another specific embodiment, the station performing the retransmission may retransmit all of the packets included in the initial transmission.

[0219] In addition, a station performing a retransmission can perform the retransmission before receiving an ACK for the transmission. In this case, after performing the retransmission, the station performing the retransmission can receive a Block ACK indicating whether the initial transmission and the retransmission were received. Therefore, the station performing the retransmission can perform the retransmission before a SIFS after the initial transmission. In yet another specific embodiment, a station that fails to receive a control frame transmitted as an exception to channel access prohibition can wait to receive a retransmission without transmitting an ACK.

[0220] 28, the first AP (AP1) retransmits the fourth and fifth packets, taking into account the time interval during which the second AP (AP2) receives the CTS frame and the transmission delay. After the retransmission, the first AP (AP1) receives an ACK indicating whether the retransmission was received or not.

[0221] FIG. 29 shows that a control frame is transmitted on a link on which a station whose channel access is not prohibited operates, rather than on a link on which a station whose channel access is prohibited operates, according to an embodiment of the present invention.

[0222] As in the embodiment described in FIG. 26, the end of transmission for multiple stations in a non-STR multilink device may be synchronized. However, this may require adjusting an already generated MPDU or generating an MPDU again, which is difficult to implement. Therefore, the multilink device may transmit a control frame over a link in which a station in which channel access is not prohibited operates, rather than a link in which a station in which channel access is prohibited operates. Specifically, the multilink device may transmit a control frame over a link in which a station in the non-STR multilink device is currently receiving from the multilink device. In this case, the control frame may be an RTS frame.

[0223] In the embodiment of FIG. 29, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a 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 a transmission from the first AP (AP1). At this time, the second AP (AP2) requests the first AP (AP1) to transmit an RTS frame with the second station (STA2) as the recipient. In this case, the first AP (AP1) may include an RTS frame for which the second station (STA2) is the recipient in the transmission currently being performed by the first AP (AP1). In yet another specific embodiment, after the first AP (AP1) finishes the transmission currently being performed by the first AP (AP1), the first AP (AP1) may transmit an RTS frame for which the second station (STA2) is the recipient via the first link (Link1) SIFS after the transmission. The first station (STA1) receives the RTS frame for which the second station (STA2) is the recipient and transmits the received RTS frame to the second station (STA2). The second station (STA2) performs CCA in the PIFS. If the channel is idle in the PIFS, the second station (STA2) transmits a CTS-to-Self frame. The first AP (AP1) may suspend transmission to the first station (STA1) during a time period in which the second station (STA2) is expected to transmit a response to the RTS frame. Also, while the second station (STA2) is transmitting a response to the RTS frame, the first station (STA1) can transmit an ACK for the received transmission. In yet another specific embodiment, while the second station (STA2) is transmitting a response to the RTS frame, the first station (STA1) can also transmit a response to the RTS frame.29 is provided to facilitate understanding of the explanation, and may be used for transmitting control frames other than RTS frames and CTS-to-Self frames. Also, time intervals other than PIFS may be used.

[0224] FIG. 30 shows a multi-link device sending an ACK according to an embodiment of the present invention.

[0225] A station in a multilink device can request a link for transmitting an ACK to a station in a non-STR multilink device. Specifically, a station in a multilink device can request that an ACK be transmitted over a link other than the link on which the transmission was made. In the example of FIG. 28, a first AP (AP1) in the STR multilink device transmits (Tx(#2)) to a first station (STA1) in a non-STR multilink device. At this time, the first AP (AP1) requests that an ACK for the transmission (Tx(#2)) be transmitted over the second link (Link2). This is because the first AP (AP1)'s transmission (Tx(#2)) to the second station (STA2) from the second AP (AP2) is completed before the first AP (AP1)'s transmission (Tx(#2)) to the second station (STA2) is completed, making it difficult to transmit an ACK for the first AP (AP1)'s transmission (Tx(#2)).

[0226] In addition, for such ACK transmission, the station can set an implicit BAR and ACK policy so as not to send an immediate response to the transmission. In yet another specific embodiment, the station can set the ACK policy for the transmission to BlockAckReq. However, in order to send a Block ACK, a BlockAckReq must be sent, which may result in channel access overhead and transmission delays. Therefore, a new ACK policy for multilink devices is needed.

[0227] A station in a multilink device can transmit both an ACK for a transmission received by the station and an ACK for a transmission received by another station included in the same multilink device. This type of ACK transmission can be called ML (multilink)-ACK. An ACK policy, ML-ACK, can also be configured. In the embodiment of FIG. 30, the first AP (AP1) configures the ACK policy for transmission (Tx(#2)) as ML-ACK. After receiving transmission (Tx(#2)), the first station (STA1) does not transmit an ACK to the first AP (AP1). After completing reception of the transmission from the second AP (AP2), the second station (STA2) transmits to the second AP (AP2) both an ACK for the transmission from the first AP (AP1) and an ACK for the transmission from the second AP (AP2). The non-STR multilink device may include a third station (STA3) in addition to the first station (STA1) and the second station (STA2), and the 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 transmissions from the third AP (AP3) to the third station (STA3) are completed later than transmissions from the second AP (AP2) to the second station (STA3), the third station (STA1) may transmit ACKs for transmissions from the first AP (AP1) to the first station (STA1), ACKs for transmissions from the second AP (AP2) to the second station (STA2), and ACKs for transmissions from the third AP (AP3) to the third station (STA3).

[0228] This embodiment can prevent interference between links that may occur due to ACK transmissions even if transmissions to stations in non-STR multilink devices are not completed simultaneously. In the above-described embodiment, the ACK policy may be set to BlockAck instead of ML-ACK. In yet another specific embodiment, the ACK policy may be set to NoAck instead of ML-ACK.

[0229] As a multilink device transmits traffic, the number of links that acquire transmission opportunities may increase. In this case, the multilink device may transmit traffic that was intended to be transmitted 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 where the multilink device acquired a transmission opportunity earlier may be set higher than the NAV required to transmit the traffic. If the NAV set on the link where the multilink device acquired a transmission opportunity earlier is higher than the NAV required to transmit the traffic, the multilink device can reset the NAV by transmitting a CF-END frame after completing transmission on the link that acquired a transmission opportunity earlier.

[0230] The above-mentioned reception of the Sync PPDU and signaling related to the reception of the Sync PPDU will be described with reference to FIGS.

[0231] In order for a first station in a non-STR multilink device to receive the Sync PPDU, it must determine whether a second station in a non-STR relationship with the first station has begun receiving the Sync PPDU. Furthermore, the first station must continuously perform preamble detection (PD). Considering that the first station receiving the Sync PPDU is denied channel access due to the reception activity of another station in the non-STR multilink device, this behavior of the first station may be unreasonable. Therefore, the first station can enter a power-saving state within pre-specified conditions. The Sync PPDU may be transmitted within an existing TXOP. Therefore, the performance gain obtained by receiving the Sync PPDU may be determined by the length of the remaining TXOP. Therefore, the first station can determine whether to give up receiving the Sync PPDU based on the length of the Sync PPDU. If the first station gives up receiving the Sync PPDU, the first station can enter a power-saving state. This power-saving operation can be referred to as inter-link TXOP power save (PS). A station that entered the power saving state in the inter-link TXOP PS can wake up from the power saving state to receive frames periodically transmitted from the AP, such as a beacon frame, a TIM frame, and a DTIM frame. Also, when the TXOP ends, for example, when a CF-END frame is transmitted, a station that entered the power saving state in the inter-link TXOP PS can wake up from the power saving state.

[0232] The above-mentioned TXOP may be changed to a period indicated by the length field of the signaling field of the PPDU and the duration field of the MAC frame. Specifically, in the above-mentioned embodiment, the station can determine the time occupied by the PPDU based on the period indicated by the length field and the duration field of the MAC frame.

[0233] A non-AP multilink device can signal to an AP multilink device information regarding whether it supports receiving a sink PPDU and the conditions for supporting the sink PPDU. Furthermore, an AP multilink device can signal to a non-AP multilink device whether it supports transmitting a sink PPDU. Here, the multilink device can signal whether it supports a sink PPDU for each multilink device. For example, an AP multilink device can signal whether it supports transmitting a sink PPDU for each AP multilink device. In yet another specific embodiment, a multilink device can signal whether it supports a sink PPDU for each station. Specifically, an AP multilink device can signal whether it supports transmitting a sink PPDU 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 indicate that the first AP supports transmitting a sink PPDU and that the second and third APs do not support transmitting a sink PPDU.

[0234] If an AP multilink device associated with a non-AP multilink device signals that it does not support sync PPDU transmission, a station in the non-AP multilink device can enter the inter-link PS power-saving state described above while another station in the non-AP multilink device is receiving. This is because the AP multilink device associated with the non-AP multilink device cannot transmit a sync PPDU. In this case, the station in the non-AP multilink device can determine the length of time to maintain the power-saving state based on the length of the PPDU received by the other station in the non-AP multilink device.

[0235] Whether the sync PPDU transmission or reception is supported may be determined based on hardware performance as well as operational policies. Therefore, whether the sync PPDU transmission or reception is supported may be signaled based on information on the operating mode as well as performance information. A method for signaling whether the sync PPDU transmission or reception is supported will be described in detail with reference to FIG. 31.

[0236] FIG. 31 shows an element field indicating information regarding support for receiving or transmitting a sink PPDU according to an embodiment of the present invention.

[0237] As described above, information indicating whether Sync PPDU transmission is supported may be included in an element indicating station capabilities. For ease of explanation, the element indicating station capabilities is called a Capability element. In addition, the field of the Capability element containing information indicating whether Sync PPDU transmission is supported is called a Supporting Sync PPDU Tx subfield. In this case, the Capability element may be a Multi-Link element indicating multi-link related capabilities. In addition, the Capability element may be an EHT Capability element indicating EHT-related capabilities. Figure 31(a) shows an example of a Capability element.

[0238] If the value of the Supporting Sync PPDU Tx subfield is 1, it may indicate that the station or multilink device indicated by the Supporting Sync PPDU Tx subfield supports sync PPDU transmission. If the value of the Supporting Sync PPDU Tx subfield is 0, it may indicate that the station or multilink device indicated by the Supporting Sync PPDU Tx subfield does not support sync PPDU transmission. Also, when a station not included in the multilink device transmits a Capability element, the Supporting Sync PPDU Tx subfield may signal information that is not unrelated to whether sync PPDU transmission is supported or may be used as a reserved field.

[0239] As described above, information indicating whether or not a station supports sync PPDU reception may be included in an element indicating station operation-related information. For ease of explanation, an element indicating station operation-related information is referred to as an Operation element. Furthermore, a field in the Operation element for information indicating whether or not a station supports sync PPDU reception is referred to as a Supporting Sync PPDU Rx Disable subfield. Figure 31(b) shows an example of an Operation element. When the Supporting Sync PPDU Rx Disabled subfield has a value of 1, it may indicate that the station does not want to receive a sync PPDU. Specifically, when the Supporting Sync PPDU Rx Disabled subfield has a value of 1, the Supporting Sync PPDU Rx Disabled subfield may indicate that the station transmitting the Supporting Sync PPDU Rx Disabled subfield does not want to wait for a sync PPDU to be received. In a multilink device that sets the Supporting Sync PPDU Rx Disabled subfield to 1, the second station of the multilink device does not need to perform PD and CCA while the first station of the multilink device is receiving. An AP multilink device connected to a multilink device that transmitted the Supporting Sync PPDU Rx Disabled subfield does not simultaneously transmit PPDUs to multiple stations of the multilink device that transmitted the Supporting Sync PPDU Rx Disabled subfield. The PPDU may be an SU PPDU, Full BW MU PPDU, or OFDMA MU PPDU transmitted in any one of non-HT PPDU, HT PPDU, VHT PPDU, HE PPDU, and EHT PPDU formats. In this case, the AP multilink device must not transmit a response, for example, a frame requesting an immediate response.The frame requesting a response may include at least one of an RTS, a Multi-User RTS (MU-RTS), a trigger frame, and a Block Ack Request (BAR).

[0240] The Operation element may also 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, a 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. The Remaining TXOP Threshold subfield may also be indicated in us, ms, or symbol units. A multilink device connected to the multilink device that transmitted the Remaining TXOP Threshold subfield may not be allowed to transmit a sync PPDU that is shorter than the length indicated by the Remaining TXOP Threshold subfield to the multilink device or station that transmitted the Remaining TXOP Threshold subfield.

[0241] Furthermore, if the Remaining TXOP Threshold subfield is set to a pre-specified value, it may indicate that the multilink device or station that transmitted the Remaining TXOP Threshold subfield does not support receiving Sync PPDUs. The pre-specified value may be a value indicating a time greater than the maximum time that the Remaining TXOP Threshold subfield can indicate. In yet another specific embodiment, the pre-specified value may be 0. When such an embodiment is applied, the Sync PPDU Rx Disable subfield may be omitted from the Operation element.

[0242] Also, in the above-mentioned embodiment, it has been described that 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 can be signaled by an element other than the Operation element or by signaling information. Figures 32 to 34 describe an embodiment in which the inter-link TXOP power save mode is performed by the signaling described in Figure 31.

[0243] FIG. 32 illustrates an inter-link TXOP power save mode operation in a non-STR multi-link device according to an embodiment of the present invention.

[0244] When a non-STR multilink device signals that it does not support sync PPDU reception, a second station in the non-STR multilink device can enter a power-save state while a first station in the non-STR multilink device is receiving. In this case, the second station can maintain the power-save state until the end of the TXOP indicated in the PPDU received by the first station. As described above, the second station can wake up from the power-save state before the end of the TXOP indicated in the PPDU received by the first station. As described above, the frame periodically transmitted from the AP can include at least one of a beacon frame, a TIM frame, and a DTIM frame.

[0245] The second station may maintain a power-saving state even after the end of the TXOP indicated by the PPDU received by the first station. Specifically, the second station may determine whether to maintain a power-saving state even after the end of the TXOP indicated by the PPDU received by the first station, based on information received from the AP to which the second station is connected. In this case, the information received from the AP to which the second station is connected may be NAV-related information. Also, the information received from the AP to which the second station is connected may be operation information of the AP to which the first station is connected. If the NAV set by the second AP of the AP multilink device currently transmitting to the second station of the non-AP multilink device has not yet expired, the first AP of the AP multilink device may transmit information regarding the expected end of the first AP's transmission or reception and the expected expiration of the NAV to the first station of the non-AP multilink device that signaled that it does not wish to receive a sync PPDU. If the NAV set by the second AP of the AP multilink device currently transmitting to the second station of the 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 the AP multilink device currently transmitting to the second station of the non-AP multilink device has not expired, the NAV may be set in the second AP by a PPDU not transmitted by the second station.

[0246] In the embodiment of Figure 32, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a 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 sync 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 in the PPDU transmitted by the first AP (AP1) to the first station (STA1).

[0247] FIG. 33 illustrates a non-STR multilink device station entering a power saving state while waiting to receive a sync PPDU according to an embodiment of the present invention.

[0248] A first station in a non-STR multilink device can enter a power-saving state for an inter-link TXOP if the remaining duration of the TXOP indicated in the PPDU being received by the first station in the non-STR multilink device is equal to or shorter than the duration indicated in the Remaining TXOP Threshold subfield transmitted by the non-STR multilink device. Before entering the power-saving state, a second station can receive a sync PPDU transmitted to the second station if the remaining duration of the TXOP indicated in the PPDU being received by the first station is greater than the duration indicated in the Remaining TXOP Threshold subfield transmitted by the non-STR multilink device. To do so, the second station can perform PD to determine whether the intended recipient of the received PPDU is the second station. Specifically, the second station can determine whether the AID indicated in the signaling field of the PPDU or the RA of the MAC frame included in the PPDU indicates the second station.

[0249] In the embodiment of Figure 33, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). The non-STR non-AP multilink device signals its desire to receive a sync PPDU. At this time, the non-STR non-AP multilink device also signals "a," the minimum TXOP length required to receive the sync PPDU. The first AP (AP1) transmits to the first station (STA1), and the second station (STA2) waits to receive the sync PPDU. If the TXOP of the PPDU transmitted by the first AP (AP1) to the first station (STA1) is equal to or shorter than "a," the second station (STA2) enters the inter-link TXOP power-save state.

[0250] FIG. 34 illustrates a station in a non-STR multilink device entering a power saving state while waiting to receive a sync PPDU according to yet another embodiment of the present invention.

[0251] If a station in a non-STR multilink device detects a PPDU other than a Sync PPDU from a BSS operated by an AP connected to the station in the non-STR multilink device while waiting to receive a Sync PPDU, the station in the non-STR multilink device can enter the inter-link TXOP power-saving state. In this case, the station can determine that a PPDU that is not the intended recipient of the station is not a Sync PPDU. Also, if a station detects a PPDU other than a Sync PPDU from a BSS operated by an AP connected to the station in the non-STR multilink device even if the minimum TXOP signaled by the station remains, the station in the non-STR multilink device can enter the inter-link TXOP power-saving state.

[0252] In the embodiment of FIG. 34, the STR AP multilink device includes a first AP (AP1) operating on a first link (Link1) and a second AP (AP2) operating on a second link (Link2). The non-STR non-AP multilink device includes a first station (STA1) operating on a first link (Link1) and a second station (STA2) operating on a second link (Link2). The non-STR non-AP multilink device signals its desire to receive a sync PPDU. At this time, the non-STR non-AP multilink device also signals the minimum TXOP length "a" required to receive the sync PPDU. The first AP (AP1) transmits to the first station (STA1), and the second station (STA2) waits to receive the sync PPDU. The second station (STA2) detects that a PPDU other than the sync PPDU is being transmitted from the BSS to which the second station belongs. Although the TXOP of the PPDU sent by the first AP (AP1) to the first station (STA1) is larger than 'a', the second station (STA2) enters the inter-link TXOP power saving state.

[0253] <Multilink Single Radio Multilink Device Service Procedure>

[0254] As described above, the multilink device can adaptively operate taking into account the possibility that a second station in a non-STR multilink device may be blinded due to transmission by a first station in the non-STR multilink device. Specifically, if the multilink device determines that a station in the non-STR multilink device is blinded, the multilink device may suspend transmission to the station in the non-STR multilink device. In addition, a station in the non-STR multilink device may enter a doze state based on the operation, e.g., transmission and reception, of another station in the non-STR multilink device. This solves problems that may occur when the operation of one station in the non-STR multilink device restricts the operation of other stations.

[0255] As mentioned above, due to intra-device interference, separate stations included in a non-STR multilink device cannot simultaneously receive and transmit. Furthermore, due to hardware configuration constraints of the non-STR multilink device, separate stations included in a non-STR multilink device cannot simultaneously receive and transmit. Specifically, when a first station in a non-STR multilink device transmits or receives, a second station in the non-STR multilink device may be restricted from using the transceiver. For example, a non-STR multilink device can only support single PPDU processing. In this case, when a first station in a non-STR multilink device transmits or receives, a second station in the non-STR multilink device 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 one station in the single-radio multilink device transmits or receives, the other stations in the single-radio multilink device cannot transmit or receive. The operation of a multilink device as a single-radio multilink device may be subject to hardware constraints or operating mode definitions, as mentioned above. Therefore, in this specification, the term "single-radio multilink device" may refer to a multilink device in which the operation of a station is limited by a hardware constraint, as well as a multilink device in which the operation of a station is limited by a defined operation mode. Therefore, the term "single-radio multilink device" in this specification may include a multilink device that supports simultaneous transmission or reception by multiple stations of the multilink device, but does not support simultaneous transmission or reception by multiple stations of the multilink device under specific conditions. In this case, the specific conditions may include a specific time point.

[0256] Specifically, a multilink device can operate as a single-radio multilink device depending on the operation mode. For example, when a specific mode is deactivated, the multilink device transmits or receives through multiple links, and when a specific mode is activated, the multilink device can transmit or receive through only one of the multiple links during a specific time period. When a specific mode is deactivated, the multilink device transmits or receives through multiple stations, and when a specific mode is activated, the multilink device can transmit or receive through only one of the multiple stations during a specific time period. The specific time period may include the time during which the multilink device exchanges frames through one of the links. Specifically, the specific time period may extend from when the multilink device receives an initial control frame initiating frame exchange through one of the links to the end of the frame exchange. When the multilink device uses a single radio on a single link during a specific time period of a specific mode, the specific mode may be referred to as an enhanced multi-link single radio (EMLSR) mode. While a multilink device exchanges frames on the first link of an EMLSR link, which is a set of multiple links to which the EMLSR mode is applied, the multilink device does not transmit or receive on the second link of the EMLSR link. Furthermore, when a specific station in the multilink device transmits or receives using some of the RF chains used by another station in the multilink device during a specific time period of the specific mode, the specific mode is called EMLMR (enhanced multi-link multi-radio) mode. Specifically, when one station in the multilink device transmits or receives using all of the RF chains of another station in the multilink device in the EMLMR mode, the operation of the multilink device may be the same as the operation of the multilink device in the EMLSR mode. Furthermore, even when the multilink device operates in the EMLSR mode, some of the multiple links on which the multilink device operates can operate without the restrictions imposed by the EMLSR mode.When a multilink device operates in EMLSR mode, the links to which the EMLSR mode is applied may be only a portion of the links on which the multilink device operates. For example, when the multilink device operates on links 1 to 3, the EMLSR mode or the EMLMR mode may be applied only to links 1 and 2. Therefore, when the multilink device transmits or receives on link 1 during a specific time period 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 the EMLSR mode can be applied, such as links 1 and 2, are referred to as EMLSR links, and links to which the EMLMR mode can be applied are referred to as EMLMR links. Transmitting or receiving using the RF chain of a specific station in EMLSR mode and EMLMR mode results in a change in the transmit, receive, or monitoring capabilities of the link on which the specific station operates. Therefore, embodiments of the present invention that are applied in connection with the EMLSR mode in the following description may be equally applied in connection with the EMLMR mode unless otherwise specified.

[0257] The above-described embodiments relating to the operation of a non-STR multilink device can also be applied to the operation of a single-radio multilink device. Furthermore, the above-described embodiments relating to the operation of a station transmitting and receiving to a non-STR multilink station can also be applied to the operation of a station transmitting and receiving to a station in a single-radio multilink device. For example, if a station determines that a transmission to the single-radio multilink device on the first link has failed due to transmission or reception by the single-radio multilink device on the second link, the station may not increase the CW for channel access on the first link. Specifically, the station may apply the embodiment described in FIG. 14. In this case, the method for determining that a transmission to the single-radio multilink device on the first link has failed due to transmission or reception by the single-radio multilink device on the second link may be similar to the method for determining whether a station has failed to transmit to a non-STR multilink station due to operational limitations of the non-STR multilink device.

[0258] FIG. 35 shows a connection between a single-radio multilink device and an AP multilink device according to an embodiment of the present invention.

[0259] In this specification, the PHY back end collectively refers to the digital processors in the physical layer, including the processors that encode and decode PPDUs, and the PHY front end collectively refers to the analog baseband circuitry, including the RF chain.

[0260] Multiple stations in a single-radio multilink device operate on different links. The multiple stations may share a PHY backend. In this case, when one station transmits a PPDU, the PHY backend is used to encode the PPDU. Therefore, the remaining stations cannot use the PHY backend. Therefore, although a single-radio multilink device includes multiple stations operating on different links, they can only transmit or receive on one link at a time.

[0261] However, the single-radio multilink device can perform channel access on multiple links. Specifically, the single-radio multilink device can perform monitoring on multiple links. Therefore, the 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 clear channel assessment (CCA) and preamble detection (PD). This allows the single-radio multilink device to reduce channel access delay. Specifically, even if a first station of the single-radio multilink device cannot perform channel access due to channel occupation by another wireless communication device on the first link, a second station of the single-radio multilink device can perform a 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.

[0262] To support this embodiment, the PHY front-end of the single radio multilink device can support channel monitoring independently of the PHY back-end. The PHY front-end of the single radio multilink device can also support decoding of a PPDU preamble for PD independently of the PHY back-end. The PHY front-end of the single radio multilink device can also support reception of frames transmitted with a low MCS independently of the PHY back-end. In this case, the frames transmitted with a low MCS can include at least one of an RTS frame and an MU-RTS frame. Therefore, the PHY front-end can include a MAC processor. This embodiment also allows the processing power of the PHY back-end to be concentrated on encoding and decoding data frames.

[0263] In the embodiment of Figure 35, the AP multilink device includes a first AP (AP1) and a second AP (AP2). The single-radio multilink 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 previous embodiment, the first non-AP station (Non-AP STA1) and the second non-AP station (Non-AP STA2) each independently access a channel using a PHY front end.

[0264] A single radio multilink device can use the RF chains of stations that do not participate in transmission or reception for MIMO transmission. Specifically, when a first station of the single radio multilink device obtains a channel access opportunity, the first station can perform MIMO transmission using not only the RF chain used by the first station but also the RF chain used by the second station of the single radio multilink device. This will be described with reference to FIG. 36.

[0265] FIG. 36 shows a single-radio multi-link device according to an embodiment of the present invention performing MIMO transmission.

[0266] 36, a first station STA1 of the single radio multi-link apparatus operates on the first link Link1, and a second station STA2 of the single radio multi-link apparatus 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 succeeds in channel access on the first link Link1, the first station STA1 performs 2x2 MIMO transmission on the first link Link1 using the RF chain used for channel access on the first link Link1 as well as the RF chain used by the second station STA2 for channel access on the second link Link2.

[0267] In this way, when an RF chain operating in the second link is changed to operate in the first link, the single radio multilink device cannot perform monitoring or channel access in the second link. Also, when an RF chain that was changed to operate in the first link while operating in the second link operates again in the second link, the single radio multilink device can perform channel access in the second link after waiting for a predetermined time. In this way, when an RF chain operating in the first link is changed to operate in the second link, the single radio multilink device cannot perform monitoring or channel access in the first link. Also, when the RF chain operates in the second link again, the single radio multilink device can perform channel access in the second link after waiting for a predetermined time. In this case, channel access of the single radio multilink device in the second link may be restricted for a predetermined time from the completion of the RF change. Specifically, the single radio multilink device can perform channel access in the second link after waiting for a predetermined time from the completion of the RF change. In this case, the channel access may include a backoff procedure. The pre-specified time may be a pre-specified time that is applied when channel access needs to be restricted due to a time when channel monitoring is not possible. Specifically, the pre-specified time may be NAVSyncDelay. Specifically, the single radio multilink device may 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 wireless communication terminals on the second link due to a period during which channel monitoring was not possible. Furthermore, 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 for changing the RF chain. This will be described with reference to FIG. 37.For ease of explanation, changing an RF chain operating in one link to operate in another link is referred to as an RF chain change. A link change may also refer to a change in an RF chain supported by a link. Specifically, a case where a first link supports the use of multiple RF chains but supports the use of one RF chain, or a case where a second link does not support the use of one RF chain but supports the use of one RF chain, may be referred to as an RF chain change.

[0268] When a multilink device operates in the above-described EMLSR mode or EMLMR mode, the transmission, reception, or monitoring capability may be changed in the link to which the EMLSR mode or EMLMR mode is applied. Accordingly, the RF chain of the link to which the EMLSR mode or EMLMR mode is applied may be re-established. The above-described channel access restriction may also be applied when the link is switched in the EMLSR mode or EMLMR mode. When link switching is performed in the link to which the EMLSR mode or EMLMR mode is applied, channel access of stations in the multilink device to which the mode change is applied may be restricted for a pre-specified time from the time of re-establishment. The pre-specified time may be NAVSyncDelay or MediumSyncDelay. Even if the pre-specified time has not elapsed, the channel access restriction of the multilink device may be lifted upon receiving a frame capable of setting the NAV. Alternatively, the pre-specified time may be the time indicated by the NAVSyncDelay parameter. In these embodiments, a station may transmit a control frame to set the NAV and start frame exchange even before the pre-specified time has elapsed since the link switching was completed, i.e., the monitoring capability was restored. The control frame that sets the NAV may be an RTS frame and / or an MU-RTS frame. In the following description, link switching may include losing and then recovering all or part of the transmit, receive, or monitoring capabilities of a link.

[0269] At this time, when the transmission, reception or monitoring capability of a link to which the EMLSR mode or EMLMR mode is applied is changed, this may include when the frequency band or center frequency of the RF chain is changed.

[0270] Also, the channel access restriction of the multilink device may be such that the multilink device is prohibited from transmitting and the multilink device performs CCA.

[0271] A station communicating with a single-radio multilink device using MIMO may be a station of the multilink device. Specifically, a station communicating with a single-radio multilink device using MIMO may be an AP included in the multilink device. Unless otherwise specified herein, a station communicating with a single-radio multilink device using MIMO may be a station included in the multilink device. In this case, the station included in the multilink device may be an AP. Furthermore, what is described herein as the operation of a station of the multilink device may represent the operation of the multilink device.

[0272] FIG. 37 shows an operation of a single-radio multilink device according to an embodiment of the present invention performing channel access taking into account the delay time of RF chain change.

[0273] The single-radio multilink device can change the RF chain before the time when successful channel access is expected. Specifically, the single-radio multilink device can change the RF chain a time period set based on the delay time for changing the RF chain before the time when successful channel access is expected. For example, the single-radio multilink device can change the RF chain at a time period that is earlier than the time when successful channel access is expected by the delay time for changing the RF chain.

[0274] In the example of Figure 37, a first station STA1 of the single radio multilink device operates on the first link Link1, and a 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 succeeds in channel access on the first link Link1, the first station STA1 performs 2x2 MIMO transmission on the first link Link1 using the RF chain used for channel access on the first link Link1 as well as the RF chain used by the second station STA2 for channel access on the second link Link2. In the example of Figure 37(a), the single radio multilink device switches RF chains to a time point that is earlier than the time point at which successful channel access is expected (Expected Tx time) by the RF chain switching delay.

[0275] In yet another specific embodiment, when the single radio multilink device starts transmission after changing the RF chain, the single radio multilink device can initiate an RTS frame / CTS frame exchange. In yet another specific embodiment, when the single radio multilink device starts transmission after changing the RF chain, the single radio multilink device can transmit a CTS-to-Self frame. Also, the single radio multilink device can transmit a frame having a relatively short length instead of a CTS-to-Self frame. This embodiment allows the single radio multilink device to obtain the time required to complete the RF chain change. Also, unlike the above-mentioned embodiment, this embodiment does not cause problems even if channel access is not successful at the predicted time.

[0276] In the example of Figure 37(b), a single radio multilink device begins transmission on the first link, Link1, with an RTS frame / CTS frame exchange.

[0277] FIG. 38 shows a Capability element and an Operation element used by a single-radio multilink device according to an embodiment of the present invention.

[0278] The single radio multilink device can transmit or receive by changing the RF chain as described in Figures 36 and 37. The single radio multilink device can also transmit or receive without changing the RF chain. The single radio multilink device can select whether to change the RF chain.

[0279] A single-radio multilink device may indicate in the MIMO Rx support subfield of the Operation element whether to use RF chains of other links when performing MIMO communication on the corresponding 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 may indicate that MIMO reception is performed using a number of spatial streams equal to or less than the value of the Max Rx spatial stream subfield of the Operation element. In this case, a station performing MIMO transmission to the single-radio multilink device must perform MIMO transmission using a number of spatial streams equal to or less than 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 FIG. 38(a).

[0280] Furthermore, the single-radio multilink device can signal the time required for RF chain switching using the Capability element. In this case, the switching latency subfield of the capability element can indicate the time required for RF chain switching. A station performing MIMO transmission to the single-radio multilink device must perform MIMO transmission taking into account the time required for RF chain switching. Specifically, a station performing MIMO transmission to the single-radio multilink device can start MIMO transmission after the time required for RF chain switching has elapsed since the first transmission to the single-radio multilink device. In a specific embodiment, the format of the Capability element may be as shown in FIG. 38(a).

[0281] When a single radio multilink device transmits or receives on a first link, a station attempting to transmit to the single radio multilink device may not be permitted 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 transmission or reception is taking place on the first link. Specifically, a station attempting to transmit to the single radio multilink device may not be permitted to transmit on a link other than the first link not only while frames are being exchanged on the first link but also until a certain time has elapsed since the single radio multilink device completed a 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 capable of using multiple RF chains. Specifically, the frame exchange sequence may be performed using MIMO. The certain time may be determined based on the time required for RF chain change. Specifically, the certain time may be the time required for RF chain change.

[0282] When the EMLSR mode of a multi-link device is activated, transmission and reception are possible only on a specific link among multiple links to which the EMLSR mode of the multi-link device is applied during a specific time period. Also, when the EMLMR mode of a multi-link device is activated, transmission and reception are possible only on a specific link among multiple links to which the EMLMR mode of the multi-link device is applied during a specific time period. As described above, when the transmission, reception, or monitoring capability of a link to which the EMLSR mode or EMLMR mode is applied is changed, the RF chain may be reconfigured. This is to restore monitoring capability to a link that has lost all or part of its transmission, reception, or monitoring capability in the EMLMR mode or EMLSR mode. That is, the RF chain is reconfigured to restore monitoring or transmission and reception capability to a link to which the EMLMR mode or EMLSR mode is applied. Therefore, a station in a multilink device that attempts to transmit to a station operating on a link where transmission, reception, or monitoring capabilities are restored, e.g., a station operating on a link where frame exchange is not being performed in EMLSR mode, cannot start frame exchange with the multilink device over the EMLMR link or EMLSR link for a pre-specified time from the point in time when the link's transmission, reception, or monitoring capabilities are re-established. In this case, the EMLMR link or EMLSR link may be limited to link switching, e.g., a link where the RF chain is re-established. In this case, the pre-specified time may be a delay time for link switching. In this case, link switching may represent an operation for restoring monitoring capabilities on a link that has lost monitoring capabilities. Specifically, the pre-specified time may be set based on the time required for link switching, e.g., changing the RF chain. For this operation to occur, the station exchanging frames with the multilink device or the multilink device itself must be able to determine the link switching time.As described above, a station or a multilink device can determine the end point of EMLMR mode or EMLSR mode. However, for convenience of explanation, the following description of an embodiment of the end point determination method will be centered on a station. For convenience of explanation, EMLMR mode and EMLSR mode will be collectively referred to as EML mode. Furthermore, EMLMR link and EMLSR link will be collectively referred to as EML link.

[0283] When a station exchanges frames over a first link, which is one of the EML links, the station may set a timer for the end of the frame exchange over a second link, which is also one of the EML links. For convenience of explanation, this timer is referred to as an end timer. In this case, the station may set the end timer based on the Duration / ID field of a frame received from a multilink device entering the EML mode. The station may determine that expiration of the end timer is the end of the frame exchange corresponding to the timer. A multilink device to which the EML mode is applied may also set a timer for the end. In this case, the multilink device may synchronize the end timer of the station with the end timer. The multilink device may set the end timer based on the Duration / ID field of a frame received from the AP.

[0284] The frame exchange end point may be the point at which the frame exchange is completed in EML mode. In yet another specific embodiment, the frame exchange end point may be the end point of a TXOP configured to protect the frame exchange in EMLMR mode or EMLSR mode.

[0285] Therefore, a station can determine the end of a TXOP set for a frame exchanged when the EML mode is applied as the end of a frame exchange. In this case, the end of a TXOP must invoke a new backoff procedure before the TXOP is completed, and may include the end of the TXOP. A new backoff procedure must be initiated if neither the TXOP holder nor the TXOP responder can occupy the channel within (aSIFSTime + aSlotTime) within the TXOP. aSIFSTime represents the SIFS defined in 802.11, i.e., 16 us, and aSlotTime represents the unit time for channel sensing in EDCA and DCF, i.e., 9 us. In the following description, aSIFSTime and aSlotTime are used with these meanings unless otherwise specified. Specifically, a station can determine the end of a frame exchange when the period indicated by the Duration / ID field of a frame transmitted over the EML link in the EML mode has elapsed.

[0286] Furthermore, a station may determine the end of frame exchange when it detects that a link is idle for a certain period of time after transmitting a response frame to a multilink device over an EML link where frame exchange is performed in EML mode. The station may receive a frame that does not request an immediate response frame from the multilink device. In this case, the station does not transmit a response frame. Therefore, a station may determine the end of frame exchange when it detects that a link is idle for a certain period of time after receiving a frame that does not request a response frame from the multilink device over an EML link where frame exchange is performed in EML mode. Furthermore, if the station receives a frame requesting a response frame, it may determine the end of frame exchange when it detects that a link is idle for a certain period of time after transmitting a response frame to a multilink device over an EML link where frame exchange is performed in EML mode. 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 that the PHY has started its Rx operation. In this case, the station may determine that the time it has transmitted a response frame is the time when a PHY-TXEND.confirm primitive for the responded frame is generated. Furthermore, the time when the station has received a frame that does not require a response frame may be the time when a PHY-RXEND.indication primitive is generated. These embodiments take into account cases in which the TXOP holder is unable to transmit consecutive frames within the TXOP in a conventional WLAN. That is, this is an embodiment in which frame exchange is determined to be terminated when the TXOP holder fails to transmit and must attempt a backoff procedure again. In a specific embodiment, the TXOP may be terminated as follows.

[0287] If the Ack Policy of the frame included in the received PPDU is "HETP Ack", the multilink device in EML mode must successfully receive the Trigger frame or TRS Control field included in the PPDU to send an Ack response. If the multilink device in EML mode does not successfully receive the Trigger frame or TRS Control field, the multilink device cannot send a response even if it receives a frame requesting a response frame. In this case, the TXOP ends unless the station retransmits a frame requesting an immediate response.

[0288] The AP multilink device is not permitted to transmit an initial control frame to the multilink device to which the EML mode is applied during the RF switching change time of the multilink device to which the EML mode is applied from the TXOP time set to protect frames exchanged in the EML mode. That is, the AP multilink device can transmit an initial control frame to the multilink device to which the EML mode is applied after the RF switching change time of the multilink device to which the EML mode is applied from the TXOP time set to protect frames exchanged in the EML mode.

[0289] Furthermore, a station may determine that the frame exchange end point is when it receives a CF-End frame on an EML link where frame exchange is performed in EML mode. In this case, the station may determine that it has received the CF-End frame at the time when a PHY-RXSTART.indication primitive is generated by the CF-End frame. In yet another specific embodiment, the station may determine that it has received the CF-End frame at the time when a PHY-RXEND.indication primitive is generated by the CF-End frame. In yet another specific embodiment, the station may determine that it has received a SIFSTime before the time when it received the CF-End frame is the frame exchange end point. In this case, the station may determine that it has received the CF-End frame at the time when a PHY-RXSTART.indication primitive is generated by the CF-End frame. In yet another specific embodiment, the station may determine that it has received the CF-End frame at the time when a PHY-RXEND.indication primitive is generated by the CF-End frame.

[0290] As mentioned above, a station can set the end timer. When a station receives a CF-End frame, the station can reset the end timer, i.e., set it to 0. In yet another specific embodiment, when a station receives a CF-End frame, the station can set the end timer to a value less than 0. In this case, the value less than 0 may be a time corresponding to the air time of the CF-End frame. In this case, a station attempting to exchange frames with a multilink device to which the EML mode is applied can start a new frame exchange immediately upon receiving the CF-End frame.

[0291] The transmission restriction due to link switching described above may be applied only to links that have lost their transmission, reception, or monitoring capabilities in EML mode, for example, links where frame exchange did not occur in EMLSR mode. In other words, the transmission restriction due to link switching may not be applied to links that have not lost their transmission, reception, or monitoring capabilities in EML mode, for example, links where frame exchange occurred in EMLSR mode. For example, if 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 frame exchange on the first link ends. Also, the transmission restriction may not be applied to the first link when link switching occurs.

[0292] When the above embodiment is applied, the multilink device that performed link switching must restore monitoring for the link that lost transmission, reception, or monitoring capability in EML mode within a predetermined time from the end of frame exchange, for example, a link where frame exchange was not performed in EMLSR mode. Also, a station, for example, an AP of an AP multilink device, can start frame exchange for the multilink device to which EML mode is applied, for the link that lost transmission, reception, or monitoring capability in EML mode, for example, an EML link where frame exchange was not performed in EMLSR mode, after a predetermined time from the end of frame exchange.

[0293] A station to which the EML mode is applied can transmit a frame indicating the end of frame exchange. In this case, the frame indicating the end of frame exchange can be a CF-End frame. For example, a station that has completed frame exchange in the EML mode can transmit a CF-End frame before the TXOP set for the frame exchange ends. 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 the EMLSR mode or the EMLMR mode. This can expedite frame exchange on links where transmission and reception were restricted due to link switching.

[0294] Furthermore, in a frame exchange sequence immediately after an RF chain change, a station attempting to transmit to a single radio multilink device can determine the format of a PPDU to be initially transmitted in the frame exchange sequence based on the time required to change the RF chain of the single radio multilink device. Furthermore, in the initial frame exchange sequence that begins after an RF chain change, a station attempting to transmit to a single radio multilink device can determine the length of padding to be used for the initial PPDU transmission in the frame exchange sequence based on the time required to change the RF chain of 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 shorter padding for packets to be transmitted to a single radio multilink device that takes a relatively short time to change the RF chain than for packets to be transmitted to a single radio multilink device that takes a relatively long time to change the RF chain.

[0295] In yet another specific embodiment, padding may be inserted into an initial control frame, which is the first control frame transmitted in frame switching in EMLSR mode. In this case, the padding duration may be determined based on the required time for link switching. Specifically, the multilink device may insert padding into the initial control frame with a length equal to or longer than the difference between the required time for link switching and (2×SIFS+CTS_time). Here, CTS_time indicates the air time required to transmit a CTS frame. That is, the multilink device may insert padding into the initial control frame with a length equal to or longer than the difference between the required time for link switching and (2×SIFS+CTS_time). In yet another specific embodiment, the multilink device may insert padding into the initial control frame with a length equal to or longer than the difference between the required time for link switching and SIFS. The multilink device can insert padding into the initial control frame with a length equal to or longer than the length of padding corresponding to the link switching time minus SIFS.

[0296] In such an embodiment, a multilink device supporting the EMLSR mode can signal the padding length of the initial control frame to a counterpart multilink device. For example, in the above-described embodiment, a multilink device supporting the EMLSR mode can signal the padding length of the initial control frame instead of the required time for link switching. In this case, the counterpart multilink device can insert padding corresponding to a time longer than the signaled padding length into the initial control frame. For example, the counterpart multilink device can insert padding of the signaled padding length into the initial control frame.

[0297] These embodiments allow the multilink device time to configure the RF chains while the initial control frame padding is transmitted.

[0298] FIG. 39 shows a single-radio multi-link device according to an embodiment of the present invention transmitting a PPDU using MIMO.

[0299] A station attempting to perform MIMO transmission to a single radio multilink device can start an RTS frame / CTS frame exchange at the start of transmission after changing the RF chain. At this time, the RTS frame can reserve time for the RF chain change and protect the frame exchange thereafter. If it is determined that the RF chain change is not complete even after the RTS frame / CTS frame exchange, the station attempting to perform MIMO transmission to a single radio multilink device does not need to perform MIMO transmission. In this case, the station attempting to perform MIMO transmission to a single radio multilink device can transmit using a single spatial stream.

[0300] When a single radio multilink device transmits or receives through one of the links, the single radio multilink device cannot transmit or receive through a link other than the link. Therefore, when a single radio multilink device transmits or receives through one of the links, stations operating through links other than the link can be considered to be in a blind state. Therefore, when a single radio multilink device transmits or receives through one of the links, an AP attempting to transmit to the single radio multilink device does not need to transmit to stations operating through links other than the link. In this case, the AP attempting to transmit to the single radio multilink device may suspend transmission to stations operating through links other than the link.

[0301] When a single radio multilink device transmits or receives on one of its links, an AP that transmits or halts transmission to a station in the single radio multilink device does not need to increase the CW of the backoff procedure used to access the channel for transmission. When the single radio multilink device subsequently attempts to transmit to the station again, it can count the backoff counter within the previously used CW. Thus, a station that transmits or halts transmission to a station in the single radio multilink device does not need to increase the CW of the backoff procedure used to access the channel for transmission if a pre-specified condition is met. The pre-specified condition may be that, according to the above-described embodiment, a station determines that one of the stations in the single multilink device is transmitting or receiving. Specifically, if a station determines that a station that transmitted a PPDU to be received by another station in the multilink device is included in the single multilink device, the station can determine that one of the stations in the single multilink device is transmitting. In this case, the station can determine the station transmitting the PPDU based on the station identifier indicated in the signaling field of the PPDU. At this time, the station can determine which station in the single multilink device the STA-ID in the User field of the EHT PPDU indicates. The station can also determine which station in the single multilink device the STA-ID in the User field of the EHT PPDU indicates. The station can also determine which station in the single multilink device the TA field of the MAC frame included in the PPDU indicates. The MAC frame may be any one of MSDU, MPDU, and A-MPDU. This may be similar to the embodiment applied to transmission to a non-STR multilink device described above with reference to FIG. 19. Furthermore, when EDCA is used as the channel access procedure, the CW described above may indicate the CW of the AC used for channel access.

[0302] In addition, if a transmission to another station in the single radio multilink device fails due to transmission or reception by any one station in the single radio multilink device, the station that transmitted to the other station in the single radio multilink device does not need to increment the retry counter, which may include at least one of a long retry counter and a short retry counter.

[0303] Furthermore, when a station transmits an MU PPDU to multiple stations, including a station in a single radio multilink device, the above-described embodiment regarding maintaining the CW size may not apply. Specifically, if a station transmits an MU PPDU to multiple stations, including a station in a single radio multilink device, but fails to receive a response from any of the stations, the station that transmitted the MU PPDU may increase the size of the CW. In this case, the station that transmitted the MU PPDU may increase the CW value to the next largest possible value. If the CW value is the maximum value, the station that transmitted the MU PPDU may maintain the same CW value.

[0304] In the embodiment of Figure 39, the single radio multilink device includes a first station STA1 operating on a first link Link1 and a second station STA2 operating on a second link Link2. When attempting to transmit to the first station STA1 using MIMO, the station successfully accesses the channel on the first link Link1 and transmits an RTS frame to the first station STA1. The first station STA1 transmits a CTS frame in response to the RTS frame. The RF chain change in 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 NAVSyncdelay from the time of the RF chain change before beginning channel access on the second link Link2.

[0305] <NDP (null data packet) transmission procedure for single-radio multilink devices>

[0306] As described above, a single-radio multi-link 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 be performed.

[0307] Since the channel characteristics of the RF chain have not been learned, closed-loop multi-antenna technology (beamforming) may not be available. Therefore, channel estimation may be required. Specifically, a single-radio multilink device can perform channel estimation using an NDP sounding protocol. In an explicit NDP sounding sequence, a beamformer transmits an NDP after transmitting an NDP announcement (NDPA). The interval between the NDPA and the NDP is SIFS. After receiving the NDP, if the STA User Info list field in the NDPA indicates a station, the station receives the NDP and then transmits channel state information (CSI) feedback measured at the time of receiving the NDP to the beamformer.

[0308] In this case, an RTS frame / CTS frame exchange may be performed before the NDP sounding protocol is performed. Specifically, a station that intends to initiate the NDP sounding protocol with a single radio multilink device may transmit an RTS frame before transmitting an NDP A frame. For convenience of explanation, a station that intends to initiate the NDP sounding protocol with a single radio multilink device is referred to as an NDP sounding protocol initiating station. According to the above-described embodiment, the NDP sounding protocol initiating station can protect the NDP sounding sequence. This also ensures time required for RF chain change. Furthermore, the NDP sounding protocol initiating station may perform an MU-RTS frame / CTS frame exchange procedure instead of the RTS frame / CTS frame exchange procedure. Furthermore, the NDP sounding protocol initiating station may exchange trigger frames of types different from the MU-RTS frame and responses to the trigger frames instead of the MU-RTS frame / CTS frame exchange procedure. In this embodiment, the NDP sounding protocol initiating station can transmit MU-RTS frames, trigger frames of types different from the MU-RTS frames, and NDPA frames in a pre-specified PPDU format. Specifically, the pre-specified PPDU format can be at least one of a non-HT format and an HT format. The NDP sounding protocol initiating station can transmit MU-RTS frames, trigger frames of types different from the MU-RTS frames, and NDPA frames at a pre-specified data rate or lower.

[0309] The NDP sounding protocol initiating station can adjust the length of the NDP sounding sequence based on the time required for RF chain change. The NDP sounding protocol initiating station can use a longer NDP sounding sequence when exchanging an NDP sounding sequence with a single-radio multilink device having a relatively long RF chain change time compared to when exchanging an NDP sounding sequence with a single-radio multilink device having a relatively short RF chain change time. In this case, the NDP sounding protocol initiating station can adjust the length of the NDP sounding sequence by omitting a portion of the NDP sounding sequence. The NDP sounding protocol initiating station can also adjust the length of the NDP sounding sequence by adjusting padding of frames exchanged in the NDP sounding sequence. The NDP sounding protocol initiating station can also 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. The padding may also be MAC layer padding. Therefore, in the embodiments described below, the padding may be N physical layer padding or MAC layer padding.

[0310] Furthermore, when an NDP sounding protocol initiating station performs an NDP sounding protocol with multiple single-radio multilink devices, the NDP sounding protocol initiating station can adjust the length of the NDP sounding sequence based on the longest time required to change the RF chains of the multiple single-radio multilink devices. A method for adjusting the length of the NDP sounding sequence will be described with reference to Figures 40 to 42.

[0311] FIG. 40 shows a station and a single-radio multilink device according to an embodiment of the present invention performing an NDP sounding process.

[0312] As described above, the NDP sounding protocol initiating station can adjust the length of the NDP sounding sequence by adjusting the padding of frames exchanged in the NDP sounding sequence. If the NDP sounding sequence includes an RTS frame / CTS frame exchange, the NDP sounding protocol initiating station can adjust the length of the NDP sounding sequence by inserting padding into the RTS frame. Specifically, if the NDP sounding protocol initiating station determines that the RF chain change is not complete even after the RTS frame / CTS frame exchange, the NDP sounding protocol initiating station can insert padding into the RTS frame.

[0313] In yet another specific embodiment, if the NDP sounding protocol initiating station determines that the RF chain change is not completed even after the RTS frame / CTS frame exchange, the NDP sounding protocol initiating station can transmit an MU-RTS frame instead of an RTS frame, and in this case, the NDP sounding protocol initiating station can insert padding into the MU-RTS frame.

[0314] In the above-described embodiment, the NDP sounding protocol initiating station can determine whether the RF chain change is complete even after the RTS frame / CTS frame exchange, based on whether the RF chain change is not completed after the time (2 x SIFS plus the length of the CTS frame) has elapsed from the time when the RTS frame is completely received by the single-radio multilink device. The RTS reception completion time may be one of the following: the start time of transmission of a PPDU including an RTS frame; the time when the physical layer header of the PPDU including the RTS frame is completely transmitted; the completion time of transmission of a PPDU including an RTS frame; or the completion time of transmission of an RTS frame or an A-MPDU including an RTS frame. In addition, in the above-described embodiment in which an MU-RTS frame is used instead of an RTS frame, an MU-RTS frame may be applied instead of the RTS frame. Figure 40(a) shows that an NDPA frame, an NDP frame, and a feedback frame are exchanged after the RTS frame / CTS frame exchange according to the above-described embodiment. At this time, the NDP sounding protocol initiating station performs MIMO transmission based on the received feedback frame.

[0315] In addition, the NDP sounding protocol initiating station may omit transmitting an NDPA frame in the NDP sounding sequence. In this case, the NDP sounding protocol initiating station and the single-radio multilink device can negotiate to perform the NDP sounding protocol without transmitting an NDPA frame. Therefore, a station in the single-radio multilink device can wait for NDP reception without receiving an NDPA frame. Specifically, a station in the single-radio multilink device can signal that it can receive NDP without receiving an NDPA frame using the Capability element. In a specific embodiment, a station in the single-radio multilink device can signal that it can receive NDP frames without receiving an NDPA frame by setting the NDPA compression support subfield of the Capability element to 1. Alternatively, a station in the radio multilink device can signal that it cannot receive NDP frames without receiving an NDPA frame by setting the NDPA compression support subfield of the Capability element to 0. The NDP sounding protocol initiating station can decide whether to omit transmitting an NDPA frame. In this case, the NDP sounding protocol initiating station can omit transmitting an NDPA frame in the NDP sounding sequence to a single radio multilink device that has received the signal that it can receive an NDP frame without receiving an NDPA frame. This embodiment of omitting transmitting an NDPA frame from the NDP sounding sequence is applicable only when the NDP sounding protocol initiating station transmits an NDP to one station. However, if the NDP sounding protocol initiating station transmits an NDP to multiple stations, transmitting an NDPA frame cannot be omitted. Figure 40(b) shows that an NDP frame and a feedback frame are exchanged without an NDPA frame after exchanging an RTS frame / CTS frame according to the above-described embodiment.At this time, the NDP sounding protocol initiating station performs MIMO transmission based on the received feedback frame.

[0316] In the above-described embodiment, excessive overhead may occur because the NDP sounding sequence includes an NDPA frame, an NDP frame, and a control frame exchange before a feedback frame exchange. Even if the NDPA transmission is omitted, excessive overhead may occur. To reduce the excessive overhead, an implicit feedback beamforming sounding sequence may be performed. This is described in FIG. 41.

[0317] FIG. 41 shows a station and a single-radio multilink device according to an embodiment of the present invention performing a feedback beamforming sounding sequence.

[0318] A frame exchange initiating station that initiates a frame exchange may omit transmitting an NDP frame and a feedback frame in addition to transmitting an NDPA frame. In this case, however, the frame exchange initiating station may measure a channel state while receiving a PPDU including a control frame, for example, an RTS frame, an MU-RTS frame, or a response to a trigger frame of a different type than the MU-RTS frame. The frame exchange initiating station may acquire a steering matrix to be used for MIMO transmission based on the measured channel state. Specifically, the frame exchange initiating station may acquire a steering matrix based on the measured channel state. The frame exchange initiating station may perform MIMO transmission using the acquired steering matrix.

[0319] In such an embodiment, the frame exchange initiating station may insert padding into the control frame based on the time it takes to change the RF chain, as described above. Specifically, the frame exchange initiating station may insert padding into the control frame based on the time it takes to change the RF chain minus SIFS.

[0320] In addition, the frame exchange initiating station can transmit a QoS data frame instead of a control frame, and the single-radio multilink device can transmit an Ack frame or a Block Ack frame in response to the QoS data frame.

[0321] In addition, in the above-described embodiment, the frame switching initiating station can set the TRQ (training request) bit to 1 in the control frame and the QoS data frame.

[0322] Furthermore, in the above-described embodiment, even in the case of a control frame, such as an MU-RTS frame, in which multiple stations can be set as recipients, only one station may be set as the recipient of the control frame.

[0323] In the embodiment of FIG. 41(a), the frame exchange initiating station transmits an MU-RTS frame with the TRQ field set to 1. The frame exchange initiating station transmits a PPDU containing the MU-RTS frame, and measures the channel condition while receiving a PPDU containing a CTS frame, which is a response to the MU-RTS frame. The frame exchange initiating station obtains a steering matrix based on the obtained channel condition and performs MIMO transmission using the obtained steering matrix. In the embodiment of FIG. 41(b), the frame exchange initiating station transmits an RTS frame instead of an MU-RTS frame. This may be the case when the time required for RF chain change is shorter than SIFS. Thereafter, the frame exchange initiating station and the station of the single-radio multilink device operate in the same manner as in the embodiment of FIG. 41(a). However, in the embodiment of FIG. 41(b), the station of the single-radio multilink device transmits a BA frame using SISO (single input single output) transmission.

[0324] The last frame exchange in the frame exchange sequence performed immediately after the RF chain change may be performed in SISO (single input single output) (1x1) format. Specifically, a station in a single radio multilink device can transmit the last frame of the frame exchange sequence performed immediately after the RF chain change in SISO (1x1) format. Also, if there are no frames remaining to be transmitted or received via MIMO in the frame exchange sequence performed immediately after the RF chain change, the station in a single radio multilink device can change the RF chain. Specifically, a station in a single radio multilink device can start changing the RF chain before transmitting the last frame of the frame exchange sequence performed immediately after the RF chain change.

[0325] FIG. 42 shows a station and a single-radio multilink device according to an embodiment of the present invention performing an NDP sounding process.

[0326] The NDP sounding protocol initiating station can determine the MIMO transmission start time based on the time required to change the RF chain of the single radio multilink device. Specifically, the NDP sounding protocol initiating station can delay the MIMO transmission start time until the RF chain change of the single radio multilink device is completed. For example, if the RF chain change is not completed during the exchange of a response frame to a control frame / control frame, such as an RTS frame / CTS frame or an MU-RTS frame / CTS frame, the NDP sounding protocol initiating station can delay the MIMO transmission start time. Specifically, the NDP sounding protocol initiating station can transmit the first PPDU to be transmitted after the response to the control frame / control frame using SISO.

[0327] In this way, if the RF chain change is not completed, MIMO transmission of the NDP sounding protocol initiating station may not be permitted, and the aforementioned explicit and implicit NDP sounding protocols may also not be permitted before the RF chain change is completed.

[0328] In addition, the NDP sounding protocol initiating station can determine whether the RF chain change will be completed during the exchange of control frames / response frames to the control frames based on the time required for the RF chain change indicated by the Capability element transmitted by the single-radio multilink device.

[0329] 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 of the frame exchange sequence using SISO. For convenience of explanation, in the description related to this embodiment, a station that has performed a frame exchange sequence on a link that supports the use of multiple RF chains is referred to as a frame exchange sequence executing station. That is, when a single radio multilink device transmits using SISO, the frame exchange sequence executing station may not be allowed to transmit the remaining frames of the frame exchange sequence using MIMO. Specifically, when a single radio multilink device transmits an ACK for a transmission by a frame exchange sequence executing station using SISO, the frame exchange sequence executing station can transmit the remaining frames of the frame exchange sequence using SISO. In this case, the ACK can include an ACK frame and a BA frame. Therefore, when a single radio multilink device transmits an ACK for a transmission by a frame exchange sequence executing station using SISO, the frame exchange sequence executing station cannot transmit the remaining frames of the frame exchange sequence using MIMO.

[0330] In the embodiments of Figures 42(a) and 42(b), the RF chain change of the single-radio multilink device is not completed even during the exchange of the RTS and CTS frames. Therefore, in the embodiment of Figure 42(a), SISO is used even for PPDU and BA frame transmission after the exchange of the RTS and CTS frames. When the NDP sounding protocol initiating station receives the ACK frame, it determines that the RF chain change is complete. At this time, the NDP sounding protocol initiating station starts the sounding protocol using MIMO (2x2).

[0331] In the embodiment of Figure 42(b), SISO is also used up to PPDU transmission after the RTS frame and CTS frame exchange. Since the RF chain change is completed after the PPDU is received, 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 initiating station determines that MIMO(2x2) transmission is permitted. Therefore, after receiving the BA frame transmitted using MIMO(2x2), the NDP sounding protocol initiating station transmits a PPDU using MIMO(2x2).

[0332] Despite the increase in WLAN transmission speeds, transmission delays remain a problem for some services. In particular, WLANs operating in unlicensed bands are inconvenient for operating services that require low-latency transmissions because it is difficult to predict the time required for traffic transmission. EDCA was introduced to address this issue. A station supporting EDCA is referred to as a QoS station, an AP supporting EDCA is referred to as a QoS AP, and a BSS supporting EDCA is referred to as a QoS BSS. Hereinafter, for convenience of explanation, a QoS AP will be referred to as an AP, a QoS station as a station, and a QoS BSS as a BSS. In EDCA, traffic is classified into four access categories (ACs) based on their characteristics. The 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 value of parameters related to the CW. The AC may also determine the maximum TXOP value. The AC may also determine the value of the AIFSN parameter. This allows the priority of traffic transmission for each AC to be adjusted. Traffic may be mapped to four ACs for each traffic category (TC) or traffic stream (TS). The traffic mapped to the four ACs is managed in four queues operated for each AC.

[0333] AC_VO is an AC for traffic that is sensitive to transmission delays but does not have a large absolute volume like voice traffic, and is mapped with relatively small CW and AIFSN parameter values. However, the maximum TXOP value of AC_VO is relatively smaller than the maximum TXOP values ​​of other ACs. AC_VI is an AC for video traffic that is more resistant to transmission delays than voice traffic but requires low-delay transmission and must handle a large volume of traffic. AC_VI is mapped with CW and AIFSN parameter values ​​that are larger than AC_VO but smaller than the CW and AIFSN parameters of other ACs. The maximum TXOP value of AC_VO is approximately twice as long as the maximum TXOP value of AC_VI. AC_BE is an AC for traffic that is resistant to transmission delays, and most general traffic other than voice data and streaming video data may be classified as AC_BE. The CW and AIFSN parameters of AC_BE are mapped with larger values ​​than the CW and AIFSN parameters of AC_VO and AC_VI. Also, a different TXOP maximum value is not mapped to AC_BE. Transmission using a continuous transmission sequence is not allowed in AC_BE. AC_BK is an AC for traffic that is tolerant to transmission delays like AC_BE, but has a lower priority than BE traffic. AC_BK is mapped with the same CW parameter value as AC_BE, and with an AIFSN parameter value that is larger than the AIFSN parameter of AC_BE. Also, a different TXOP maximum value is not mapped to AC_BK. Transmission using a continuous transmission sequence is not allowed in AC_BK.

[0334] The four ACs are mapped to 802.1D UP (user priority), and the EDCA AC is determined by the UP value of the traffic received via wire or the TID of the MSDU indicated by the upper layer. In this case, when the TID of the MSDU indicates a value from 0 to 7, the value indicated by the TID has a one-to-one correspondence with the UP.

[0335] FIG. 43 shows the mapping relationship between UP and AC.

[0336] The default CW parameters (CWmin, CWmax), AIFSN parameters, and TXOP max for each of the four ACs are defined in the 802.11 standard. The AC's CW parameters (CWmin, CWmax), AIFSN parameters, and TXOP max can be changed by the AP, and different values ​​may be used for each BSS. In EDCA, traffic is stored in one of the four queues corresponding to the traffic's AC. Channel access contention occurs between the four ACs, and the traffic of the AC that wins the contention is transmitted. In channel access contention, AC-specific access parameters (CW[AC], AIFSN[AC]) are used. In this case, the channel access operation is the same as that of DCF.

[0337] As described above, since the channel access parameter values ​​are different for each AC, transmission priority may be applied for each AC.

[0338] In addition to EDCA, the 802.11 MAC protocol may also employ HCF controlled channel access (HCCA) for QoS management. HCCA provides a centralized / hybrid coordinator function to guarantee TS (Traffic Stream) QoS for applications that require periodic service (such as voice and video). Other features include Service Period Channel Access (SPCA) and dynamic allocation of service periods. However, these are only available for DMG stations.

[0339] A method for enhancing QoS for a multilink device may be needed. Independent transmission queues may be used for each link of the multilink device. In this case, the queues may be logically independent. When traffic is mapped by link, the QoS of the traffic can be enhanced. This will be described with reference to FIG. 44.

[0340] FIG. 44 illustrates a multilink device transmitting traffic mapped to each station of the multilink device according to an embodiment of the present invention.

[0341] In Figure 44, the AP multilink device (AP MLD) includes the first AP (AP1) through the fourth AP (AP4). Also, the non-AP multilink device (Non-AP MLD) includes the first station (non-AP STA1) through the fourth station (non-AP STA4). The first station (non-AP STA1) through the fourth station (non-AP STA4) operate on the first link (Link1) through the fourth link (Link1), respectively. The first AP (AP1) through the fourth AP (AP4) operate on the first link (Link1) through the fourth link (Link1), respectively. In this case, traffic is mapped to each of the first AP (AP1) through the fourth AP (AP4) by AC. AC_BK is mapped to the first AP (AP1), AC_BE is mapped to the second AP (AP2), AC_VI is mapped to the third AP (AP3), and AC_VO is mapped to the fourth AP (AP4). Thus, in the AP multilink device (AP MLD), traffic corresponding to AC_BK is transmitted by the first AP (AP1), traffic corresponding to AC_BE is transmitted by the second AP (AP2), traffic corresponding to AC_VI is transmitted by the third AP (AP3), and traffic corresponding to AC_VO is transmitted by the fourth AP (AP4). The channel quality and load status of each link may differ. Furthermore, the performance and operating bandwidth of each station may differ. Therefore, the bandwidth and MCS of the PPDU containing the traffic may vary depending on which traffic the multilink device maps to which link.

[0342] For example, if the first AP (AP1) of an AP multilink device (AP MLD) operates in the 2.4 GHz band, the first AP (AP1) can operate on a 40 MHz operating channel. If the fourth AP (AP4) operates in the 6 GHz band, the fourth AP (AP4) can operate on a maximum 320 MHz operating channel. The AP multilink device (AP MLD) can map traffic that requires high throughput and low latency transmission to the fourth AP (AP4). The multilink device can map traffic to each of the multiple links taking into account the traffic characteristics. This improves the QoS of traffic transmission.

[0343] In order to finely divide the QoS reinforcement, a TID may be mapped to each link, and priority may be given to the transmission of traffic corresponding to the TID mapped to that link on each link. This will be explained using FIG. 45.

[0344] FIG. 45 shows how a multilink device exchanges frames using TID link mapping according to an embodiment of the present invention.

[0345] Traffic transmitted over a WLAN is identified by a TID. A MAC frame, such as a data frame or a QoS data frame, uses a TID service field to signal the TID of the traffic included in the MAC frame. The QoS control field may include the TID service field. The TID identifies the traffic included in an MSDU, fragment, or A-MSDU of the MAC frame. The TID corresponds to a UP (user priorities) or a TSID (traffic stream identifier). The TID service field is a 4-bit field and can represent values ​​from 0 to 15. If the value of the TID subfield is one of 0 to 7, the value of the TID subfield indicates the UP of the MSDU included in the frame body of the MAC frame containing the TID subfield. The MAC frame is processed by the MAC entity using AC parameters corresponding to the UP according to EDCA. If the value of the TID subfield is one of 8 to 15, the value of the TID subfield indicates the TSID of the MSDU included in the frame body of the MAC frame containing the TID subfield. The MAC frame is processed by the MAC entity using parameters corresponding to the UP of the TSID indicated in the User Priority service field of the TS Info field of the TSPEC. The UP of the TSID may be indicated in the User Priority field of the TCLAS. The Access Policy of the TSID is indicated by the Access Policy field of the TS Info subfield. The 7th and 8th bits of the Access Policy subfield are set to 10. b EDCA is indicated if b If so, it indicates HCCA.

[0346] When a multilink device maps a TS TID to a link, it can obtain information about the UP of the TS and the alternate queue to be used for TS transmission from the Intra-Access Priority field of the Intra-Access Category Priority element of the ADDTS Request frame used to generate the TS. The multilink device can use the obtained information about the UP and alternate queue when transmitting traffic corresponding to the TS TID.

[0347] A TID may be mapped to each of multiple links operated by a multilink device. In this case, the multilink device may signal information about the TID mapped to each link to associated multilink devices. In this case, the multilink device receiving the signaling may accept or reject the link mapping with the TID. If no agreement is reached on the mapping between the TID and the link, frames may be exchanged on each link without TID restrictions. In yet another specific embodiment, if no agreement is reached on the mapping between the TID and the link, frames may be exchanged on each link using a default mapping between the TID and the link.

[0348] 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 transmits frames containing traffic corresponding to the TIDs mapped to the links through the links, and may not transmit frames containing traffic corresponding to TIDs not mapped to the links. Mapping between TIDs and links may be performed for each multilink device. Furthermore, mapping between TIDs and links may be performed for each transmission direction. For example, the TID mapped to the uplink and the TID mapped to the downlink of a link may be different. Therefore, when a first multilink device and a second link device are connected via the first and second links, the first multilink device may map TID values ​​0 to 3 to the first link, and the second multilink device may map TID values ​​4 to 7 to the first link.

[0349] In this specification, the mapping between TID and link may be replaced with the mapping between AC and link, or the mapping between UP and link, or the mapping between TC and link, or the mapping between TS and link.

[0350] Additionally, remaining TID values ​​not explicitly indicated in the mapping between TIDs and links may be mapped to the remaining links. For example, if it is signaled that TID values ​​0-3 are to be mapped to the first link, remaining TID values ​​other than TID values ​​0-3 may be mapped to the second link. In yet another specific embodiment, transmission of traffic corresponding to all TIDs may be permitted on the second link.

[0351] Furthermore, the mapping between TIDs and links may change during operation, not just when a multilink device is first connected. When a multilink device disassociates a station from a specific link, the multilink device can change the mapping between TIDs and links. In this case, the multilink device can disassociate a station from a specific link when the station enters a power-saving mode. A multilink device can also request a change in the mapping between TIDs and links from a peer multilink device. For example, if TID values ​​0 to 3 are mapped to the first link, a non-AP multilink device can request the AP multilink device to map TID values ​​0 to 3 to the second link. Specifically, if a multilink device has difficulty guaranteeing the QoS of traffic mapped to a link, the multilink device can request a change in the mapping between TIDs and links from a peer multilink device.

[0352] In addition, if a multilink device rejects a TID-to-link mapping request, the multilink device that sent the TID-to-link mapping request may be limited for a pre-specified time from requesting the same TID-to-link mapping as the previously requested TID-to-link mapping again. This is to prevent repeated TID-to-link mapping requests. In this case, the pre-specified time may be a time specified by the AP. Specifically, the AP multilink device may signal the pre-specified time in the BSS operation parameters.

[0353] A method for signaling a mapping between a TID and a link will be described. A multilink device can signal a mapping between a TID and a link 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 signaled by the TID-to-Link Mapping element. In addition, 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 indicating 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 indicating 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 may indicate that the TID corresponding to that bit is mapped to the link indicated by the Link ID field.

[0354] In the example of FIG. 45, the AP multilink device (AP MLD) plans to transmit traffic with TIDs 0 to 3 to the non-AP multilink device (non-AP MLD) on the first link (Link 1). The AP multilink device (AP MLD) signals to the non-AP multilink device (non-AP MLD) using the TID-to-Link Mapping element to map TID values ​​0 to 3 to the first link (Link 1) and TID values ​​4 to 7 to the second link (Link 2). The TID-to-Link Mapping element includes two Link ID fields indicating the first and second links, respectively, and two TIDs Info fields indicating information about the TIDs mapped to the first link and the information about the TIDs mapped to the second link, respectively. Furthermore, each TIDs Info field may include 7 bits indicating TIDs 0 to 7. For example, to indicate TIDs 0 to 3, 8 bits of the TIDs info subfield are set to 11110000. b and 8 bits of the TIDs info subfield are set to 00001111 to indicate TIDs 4 to 7. b may be set to

[0355] In yet another specific embodiment, 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 the Min TID field and the Max TID field are each 3 bits and the TIDs Info field indicates 0 to 3, the Min TID field is set to 000 and the Max TID field is set to 011. bAs mentioned above, the TID-to-Link Mapping element signals only the TIDs mapped to the first link, and the TIDs mapped to the second link may be implicitly signaled. Specifically, because 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.

[0356] A non-AP multilink device accepts the mapping between TID and link indicated by the TID-to-Link Mapping element.

[0357] When multiple TIDs are mapped to one link and the multiple TIDs correspond to two or more ACs, the multilink device can differentiate the ACs using EDCA and transmit traffic. For example, when a TID corresponding to AC_VO and a TID corresponding to AC_BK are mapped to a first link, the multilink device can transmit traffic corresponding to AC_VO with priority over traffic corresponding to AC_BK using EDCA. In addition, all TIDs must be mapped to at least one link, and the multilink device may not accept a mapping request between a TID and a link if any TID is not mapped to any link.

[0358] FIG. 46 shows that basic mapping between TIDs and links is set in an AP multilink device and a non-AP multilink device according to an embodiment of the present invention.

[0359] 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 of Figure 46, the basic mapping between TIDs and links is that all TIDs and TSIDs are mapped to links.

[0360] In the EML mode described above, frame exchange is performed only on one of multiple links, so the QoS improvement effect that is expected to be obtained from the mapping between TID and links may not be applied to a multi-link device operating in the EML mode. Therefore, a mapping between TID and links that takes this into consideration is required. This will be explained using Figures 47 to 51.

[0361] FIG. 47 shows that the mapping between TIDs and links is changed when the multi-link device according to the embodiment of the present invention activates the EMLSR mode.

[0362] A multilink device to which the EML mode is applied may not be permitted to perform mapping between TIDs and links. A basic mapping between TIDs and links may be applied to a multilink device to which the EML mode is applied. In this case, a multilink device to which the EML mode is applied cannot negotiate for mapping between TIDs and links. When a multilink device to which the EML mode is applied transmits a request for mapping between TIDs and links, the other multilink device may reject the request for mapping between TIDs and links. In yet another specific embodiment, when a multilink device to which the EML mode is applied transmits a request for mapping between TIDs and links, the other multilink device may not transmit a response to the request for mapping between TIDs and links. In this case, a multilink device to which the EML mode is applied may not perform mapping between TIDs and links only for EML links. Therefore, even a multilink device to which the EML mode is applied can perform mapping between TIDs and links for links to which the EML mode is not applied.

[0363] In addition, when a multilink device in which the EML mode is not activated performs TID mapping on a link, and the EML mode of the multilink device is activated, basic mapping between TID and link may be applied to the EML link among the links in which the multilink device operates. In this case, basic mapping between TID and link may be performed without a separate negotiation.

[0364] Similarly, a Multilink device connected to a Multilink device in which EML mode is activated can also apply basic mapping between TID and link to the EML link.

[0365] The Multilink device can re-associate to activate EML mode. At this time, the Multilink device can initialize information for link operation. At this time, the Multilink device can initialize the mapping between links and TIDs.

[0366] In the embodiment of Figure 47, the AP multilink device (AP MLD) is affiliated with a first AP (AP1) and a second AP (AP2), and the non-AP multilink device (STA MLD) is affiliated with a first station (STA1) and a second station (STA2). The first AP (AP1) and the first station (STA1) operate on a first link (Link1), and the second AP (AP2) and the second station (STA2) operate on a second link (Link2). The AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) map TID values ​​0 to 3 to the first link (Link1) and TID values ​​4 to 7 to the second link (Link2). The EMLSR mode is activated in the non-AP multilink device (STA MLD), and the 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 the basic mapping between TID and link. That is, the AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) map TID values ​​0 to 7 to the first link (Link 1) and TID values ​​0 to 7 to the second link (Link 2). At this time, the non-AP multilink device (STA MLD) can send a (Re)Association Request frame to activate the 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.

[0367] FIG. 48 shows the format of a Multi-Link element according to an embodiment of the present invention.

[0368] As described above, the (Re)Association Request frame transmitted by a non-AP multilink device to activate EMLSR mode may include a Multi-Link element. In this case, the non-AP multilink device may 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 the Basic variant format. An AP multilink device that receives a 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, the AP multilink device and the non-AP multilink device can activate EMLSR mode.

[0369] Using FIG. 49, the mapping setting between TID and link when the EML mode is activated and then deactivated will be described.

[0370] FIG. 49 shows that the mapping between TIDs and links is changed when the multi-link device according to the embodiment of the present invention deactivates the EMLSR mode.

[0371] When the EML mode is deactivated, the mapping between TIDs and links used before the EML mode was activated may be applied again, and the multilink device may not need to negotiate the mapping between TIDs and links again.

[0372] In the embodiment of Figure 49, the AP multilink device (AP MLD) is affiliated with a first AP (AP1) and a second AP (AP2), and the non-AP multilink device (STA MLD) is affiliated with a first station (STA1) and a second station (STA2). The EMLSR mode is activated in the non-AP multilink device (STA MLD), and the 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 basic mapping between TIDs and links. That is, the AP multilink device (AP MLD) and non-AP multilink device (STA MLD) map TID values ​​0 to 7 to the first link (Link 1) and TID values ​​0 to 7 to the second link (Link 2). EMLSR mode is deactivated in the non-AP multilink device (STA MLD). The AP multilink device (AP MLD) and non-AP multilink device (STA MLD) apply the TID-to-link mapping that was applied before EMLSR mode was activated to the first link (Link 1) and second link (Link 2). That is, the AP multilink device (AP MLD) and non-AP multilink device (STA MLD) map TID values ​​0 to 3 to the first link (Link 1) and TID values ​​4 to 7 to the second link (Link 2).

[0373] As described above, an AP multilink device can transmit an initial control frame to transmit to a multilink device in which the EML mode is activated. In this case, the initial control frame may be an MU-RTS frame or a trigger frame of another variant. The trigger frame of another variant may be an ML-RTS frame, which is an RTS frame for multilink. A non-AP multilink device that receives a trigger frame of another variant can transmit a response frame to the trigger frame of another variant. Specifically, the initial control frame may be a buffer status report poll (BSRP) trigger frame. In this case, a non-AP multilink device that receives a BSRP trigger frame can transmit a BSR frame as a response frame. The type of response frame to the trigger frame varies depending on the type of trigger frame, and the time required to transmit the response frame may vary. Therefore, the non-AP multilink device can set the length of the initial control frame based on the type of initial control frame. In this case, padding may be added to ensure time for reconfiguration of the RF chain, as described above.

[0374] If the initial control frame is an MU-RTS frame, the MU-RTS frame may include padding corresponding to a time equal to or longer than (RF switching latency - SIFS - CTS time - SIFS). If the initial control frame is a BSRP trigger frame, the BSRP trigger frame may include padding corresponding to a time equal to or longer than (RF switching latency - SIFS - BSR time - SIFS). In this case, BSR time may be the time required to transmit the BSR frame, such as air time. Also, BSR time may be a value determined assuming that the BSR frame is transmitted at a specific data rate. In yet another specific embodiment, the non-AP multilink device may determine the length of the padding of the trigger frame based on the value of the UL Length subfield of the Common Info field of the trigger frame. This is because the station receiving the trigger frame determines the length of the PPDU including the response frame to the trigger frame based on the value of the UL Length subfield of the Common Info field. Specifically, the non-AP multilink device can include padding in the trigger frame that corresponds to a time equal to or longer than (RF switching latency - SIFS - UL length (length of response frame) indicated in the trigger frame - SIFS). If the initial control frame is a BSRP trigger frame, the non-AP multilink device can 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.

[0375] As described above, a multilink device employing the EML mode can signal the duration of an RF chain change. The AP multilink device can determine the length of 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 time equal to or longer than the signaled duration of the RF chain change. In yet another specific embodiment, a multilink device employing the EML mode can signal the length of padding in the initial control frame. This will be described with reference to FIG. 50.

[0376] FIG. 50 illustrates a Multi-Link element signaling information regarding the length of padding in an initial control frame according to an embodiment of the present invention.

[0377] When a multilink device to which the EML mode is applied receives a signal indicating the padding length of an 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 of a length equal to or longer than the signaled padding length in the initial control frame. In this case, the padding length may be signaled according to the type of trigger frame. In a specific embodiment, the signaled padding length may be the length of padding to be included in the MU-RTS frame. In this case, when the AP multilink device transmits an initial control frame other than an MU-RTS frame, such as 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 airtime of the CTS frame and the 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 signaled padding length plus the padding length corresponding to (CTS time - the airtime required to transmit the response frame to the initial control frame).

[0378] In yet another specific embodiment, the AP multilink device may back-calculate the required time for RF chain change based on the signaled padding length. In this case, the AP multilink device may determine the length of padding included in the initial control frame based on the back-calculated required time for RF chain change, because the signaled padding length is a value determined based on the required time for RF chain change.

[0379] The length of the aforementioned padding may be signaled in the Multi-Link element. In the embodiment of Figure 50, the Multi-Link element includes an EMLSR Delay field that indicates the length of the padding in the initial control frame.

[0380] As described above, link switching performed in the EML mode may cause some links of the EML link to lose their transmission, reception, or monitoring capabilities. In this case, monitoring may include at least one of CCA and preamble detection (PD). Even if a multilink device performs link switching to restore its transmission, reception, or monitoring capabilities on a link, the multilink device may be unable to transmit, receive, or monitor on the link for a pre-specified time period from the link switching point. Specifically, the pre-specified time period may be determined based on the time required for link switching of the multilink device in which the EML mode is activated. In a specific embodiment, the pre-specified time period may include a time period during which the RF chain of the multilink device in which the EML mode is activated is changed. A station exchanging frames on an EML link with a multilink device supporting the EML mode can manage TXOPs taking into account frame exchanges by the multilink device in the EML mode. Furthermore, a multilink device supporting the EML mode can also manage TXOPs on the EML link taking into account frame exchanges by the multilink device in the EML mode. This will be described with reference to FIG. 51.

[0381] Figure 51 shows that a multi-link device according to an embodiment of the present invention terminates a TXOP on a link where frame exchange is performed in EMLSR mode, taking into account a DTIM beacon received on an EMLSR link where frame exchange is not performed in EMLSR mode.

[0382] As described above, link switching performed in the EML mode may cause some of the EML links to lose their transmission, reception, or monitoring capabilities. For example, when frame exchange occurs in one of the EMLSR links in the EMLSR mode, the multilink device cannot transmit, receive, or monitor the remaining EMLSR links. In this case, monitoring may include at least one of CCA and preamble detection (PD). Even if the multilink device performs link switching to restore its transmission, reception, or monitoring capabilities on a link, the multilink device may be unable to transmit, receive, or monitor the link for a pre-specified time period from the start of the link switching. In this case, the pre-specified time period may be a delay time for link switching. Specifically, the pre-specified time period may include a time period during which the RF chain of the multilink device supporting the EML mode is changed. A station exchanging frames on the EML link with a multilink device supporting the EML mode can manage TXOPs taking into account the frame exchange of the multilink device in the EML mode. In addition, a multilink device supporting the EML mode can also manage TXOPs on the EML link taking into account the frame exchange of the multilink device in the EML mode.

[0383] When a multilink device in EML mode has lost the ability to transmit, receive, or monitor an EML link in EML mode, for example, when a first link in EML mode where frame exchange is not occurring is required, the multilink device in EML mode or a station exchanging frames with the multilink device in EML mode can terminate a TXOP for the frame exchange in a second link where frame exchange is occurring, which is one of the EML links, based on the time of reception of the specific frame in the first link. For convenience of explanation, a multilink device in EML mode is referred to as a multilink device, and a station exchanging frames with a multilink device in EML mode is referred to as a station. In this case, when the multilink device is the holder of a TXOP, the station is the TXOP responder. Conversely, when the multilink device is the responder of a TXOP, the station is the TXOP holder. When EML mode is activated, a TXOP for the second link may be terminated a predetermined time earlier than the time when the multilink device attempts to receive a specific frame in the first link. At this time, the pre-specified time may be determined based on a link switching delay of the multi-link device. Specifically, the pre-specified time may be determined based on the time required for changing the RF chain of the multi-link device. In a specific embodiment, the pre-specified time may be the time required for changing the RF chain of the multi-link device. At this time, the specific frame may be a frame that is periodically received. Specifically, the specific frame may be a beacon frame. In a specific embodiment, the specific frame may be a DTIM beacon frame. Furthermore, the time at which the specific frame is to be received may be the TBTT. The multi-link device or station may terminate the TXOP for the frame exchange on the second link that has been performing frame exchange in EML mode based on the time at which the specific frame is received on the first link.Furthermore, when a station is a TXOP holder, the station can terminate a TXOP on the second link based on information indicating that the multilink device is going to receive a specific frame on the first link. In this case, the information indicating that the multilink device is going to receive a specific frame on the first link can be signaled in a predetermined manner between the multilink device and the station. The information indicating that the multilink device is going to receive a specific frame on the first link can be information signaling that the beacon frame on the first link is a DTIM beacon frame. When a station is a TXOP holder and the beacon received on the first link is a DTIM beacon, the station can terminate a TXOP on the second link based on information indicating that the multilink device is going to receive a specific frame on the first link.

[0384] Even if a multilink device applying the EML mode receives an initial control frame, the multilink device may not transmit a response frame to the initial control frame. Specifically, even if a multilink device applying the EML mode receives an initial control frame on a first link of the EML links, the multilink device may not transmit a response frame to the initial control frame because it will receive a specific frame on a second link of the EML links. For example, even if a multilink device applying the EML mode receives an initial control frame on a first link of the EML links, if the frame exchange initiated by the initial control frame does not end before a predetermined time earlier than the time when the specific frame is to be received on the second link of the EML links, the multilink device may not transmit a response frame to the initial control frame on the first link. If the frame exchange initiated by the initial control frame ends before a predetermined time earlier than the time when the specific frame is to be received on the second link, the multilink device may transmit 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. When the initial control frame is an MU-RTS frame or an ML-RTS frame and a Multilink device to which EML mode is applied receives the initial control frame, the Multilink device does not need to transmit a CTS frame in response to the initial control frame. This allows the Multilink device to refuse to start a frame exchange. This is an exception to the requirement that a station transmit a CTS frame when it receives an MU-RTS frame or an RTS frame in existing WLAN operation. Specifically, even if a Multilink device to which EML mode is applied receives an initial control frame on a first link, which is one of the EML links, the Multilink device does not need to transmit a response frame to the initial control frame for frame exchange to be performed on a second link.

[0385] A non-AP multilink device with EMLSR activated 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). The first station (STA1) receives an RTS frame from the first AP via Link1 and transmits a CTS frame in response to the RTS frame. The first station (STA1) receives a PPDU from the first AP via Link1. In this case, the first AP terminates the TXOP at a time earlier than the scheduled time of receiving the beacon frame via Link2 by the time required for the RF change of the non-AP multilink device. This termination of the TXOP at a time earlier than the scheduled time of receiving the beacon frame via Link2 by the time required for the RF change of the non-AP multilink device may also be applied when the first station (STA1) acquires a TXOP, as described above.

[0386] When a multilink device activated in EMLSR mode receives a beacon frame, the EMLSR multilink device does not need to change RF chains because the beacon frame is not transmitted via MIMO. When a multilink device activated in EMLSR mode receives a beacon frame over the first link, the multilink device activated in EMLSR mode can perform at least one of monitoring and channel access over the second link. In this case, even if the multilink device completes the channel access procedure over the second link, it may not be allowed to transmit. In yet another specific embodiment, the multilink device can perform at least one of transmission and reception over the second link only at a pre-specified data rate. In this case, the pre-specified data rate may be any one of 6 Mbps, 12 Mbps, and 24 Mbps.

[0387] Furthermore, a station attempting to exchange frames with a multilink device activated in EMLSR mode may not be permitted to initiate a frame exchange procedure on a second link, which is one of the EMLSR links, when the multilink device receives a specific frame on a first link, which is one of the EMLSR links. A station attempting to exchange frames with a multilink device activated in EMLSR mode may not be permitted to transmit an initial control frame on a second link, which is one of the EMLSR links, when the multilink 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 groupcast frame or a group-addressed frame, for example, a beacon frame. Specifically, the beacon frame may be a DTIM beacon frame.

[0388] Although the present invention has been described above with reference to wireless LAN communication, the present invention is not limited thereto and can be equally applied to other communication systems such as cellular communication. Furthermore, although the method, apparatus, and system of the present invention have been described in relation to specific embodiments, some or all of the components and operations of the present invention can be implemented by a computer system having a general-purpose hardware architecture.

[0389] The features, structures, effects, etc. described in the above embodiments are included in at least one embodiment of the present invention and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects, etc. exemplified in each embodiment can be combined or modified in other embodiments by a person skilled in the art to which the embodiment belongs. Therefore, content related to such combinations and modifications should be interpreted as being included within the scope of the present invention.

[0390] Although the above description has focused on the embodiments, these are merely examples and are not intended to limit the present invention. Those skilled in the art will appreciate that various modifications and applications not exemplified above are possible within the scope of the essential characteristics of the present invention. For example, each component specifically illustrated in the embodiments can be modified. Furthermore, differences related to such modifications and applications should be construed as being included within the scope of the present invention as defined by the appended claims. [Explanation of symbols]

[0391] 100 Stations 110 processors 120 Communications Department 140 User Interface Section 150 display units 160 memory 200 AP 210 processor 220 Communications Department 260 memory

Claims

1. A multi-link device including a plurality of stations each operating on a plurality of links, wherein in an enhanced multi-link single radio (EMLSR) mode, a first link of the EMLSR links corresponding to the plurality of links to which the EMLSR mode is applied is exchanged with a first link of the EMLSR links while a second link of the EMLSR links is not transmitted or received, a transceiver, and a processor; The processor: configured to signal a minimum duration of padding of an initial control frame required for link switching, the initial control frame initiating the frame exchange on the first link in the EMLSR mode; the processor is configured to receive the initial control frame including padding corresponding to a time period equal to or greater than a minimum length of the padding; If the frame exchange initiated by the initial control frame is not expected to be completed before a time earlier than a time that is a predetermined time from a time that the multi-link device intends to receive a beacon frame on the second link, the processor does not transmit a response to the initial control frame; the processor is configured to transmit a response to the initial control frame when a frame exchange initiated by the initial control frame is expected to be completed before a time earlier than the time at which the multi-link device intends to receive the beacon frame on the second link by the predetermined time; the predetermined time corresponds to a delay time for the multi-link device to perform link switching; The initial control frame is a multi-user request to send (MU-RTS) trigger frame or a buffer status report poll (BSRP) trigger frame, and is transmitted at a pre-specified data rate using a pre-specified format; The pre-specified time is signaled by the multi-link device.

2. 2. The multi-link device according to claim 1, wherein the EMLSR mode is applied to only some of the links on which the stations included in the multi-link device operate.

3. An access point that includes a plurality of stations that operate on a plurality of links, and that communicates with a multi-link device in an enhanced multi-link single radio (EMLSR) mode, wherein the access point does not transmit or receive on a second link of the EMLSR links while exchanging frames on a first link of the EMLSR links corresponding to the plurality of links to which the EMLSR mode is applied, a transceiver, and a processor; The processor: configured to receive from the multi-link device a minimum duration of padding of an initial control frame required for link switching, the initial control frame initiating the frame exchange on the first link in the EMLSR mode; the processor including, in the initial control frame, padding corresponding to a time period equal to or greater than the minimum length of the padding; configured to transmit the initial control frame; If the frame exchange initiated by the initial control frame is not expected to be completed before a time earlier than a time that is a predetermined time from a time that the multi-link device intends to receive a beacon frame on the second link, the processor does not receive a response to the initial control frame; the processor is configured to receive a response to the initial control frame when a frame exchange initiated by the initial control frame is expected to be completed before a time earlier than the time at which the multi-link device intends to receive the beacon frame on the second link by the predetermined time; the predetermined time corresponds to a delay time for the multi-link device to perform link switching; The initial control frame is a multi-user request to send (MU-RTS) trigger frame or a buffer status report poll (BSRP) trigger frame, and is transmitted at a pre-specified data rate using a pre-specified format; The pre-designated time is signaled by the multilink device, an access point.

4. The access point according to claim 3 , wherein the EMLSR mode is applied to only some of the links on which the stations included in the multi-link device operate.

5. 1. A method for operating a multi-link device including a plurality of stations operating on a plurality of links, the method including, in an enhanced multi-link single radio (EMLSR) mode, performing frame exchange on a first link of the EMLSR links corresponding to the plurality of links to which the EMLSR mode is applied, while not performing transmission and reception on a second link of the EMLSR links, signaling a minimum duration of padding in an initial control frame required for link switching, the initial control frame initiating the frame exchange on the first link in the EMLSR mode; receiving the initial control frame including padding corresponding to a time period equal to or greater than a minimum length of the padding; not transmitting a response to the initial control frame if a frame exchange initiated by the initial control frame is not expected to be completed before a time earlier than a time that is a predetermined time from a time that the multi-link device intends to receive a beacon frame on the second link; transmitting a response to the initial control frame when a frame exchange initiated by the initial control frame is expected to be completed before a time earlier than the time when the multi-link device intends to receive the beacon frame on the second link by the predetermined time; the predetermined time corresponds to a delay time for the multi-link device to perform link switching; The initial control frame is a multi-user request to send (MU-RTS) trigger frame or a buffer status report poll (BSRP) trigger frame, and is transmitted at a pre-specified data rate using a pre-specified format; The method of operation wherein the pre-designated time is signaled by the multilink device.

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