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

Abstract

To efficiently provide a wireless communication method using multilink and wireless communication terminal using the same.SOLUTION: A multilink device includes a plurality of stations each operating on a plurality of links, and does not transmit or receive on a second link while exchanging frames on a first link of a plurality of EMLSR links to which an enhanced multi-link single radio (EMLSR) mode is applied. When a first station, which is one of a plurality of stations included in the multilink device, performs frame exchange on the first link in the EMLSR mode as a TXOP (transmission opportunity) holder, the processor terminates the TXOP for frame exchange before a point earlier than a point in time that the multilink device receives a beacon frame on the second link by a predetermined time, which is a delay time for the multilink device to perform link switching.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 use of mobile devices has become more widespread, wireless LAN technology that can provide them with high-speed wireless Internet services has been attracting attention. Wireless LAN technology is a technology that enables mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, embedded devices, etc. to wirelessly connect to the Internet at home, in business, or in specific service areas based on short-distance wireless communication technology.

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

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

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

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

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

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

[0009] According to one embodiment of the present invention, a multilink device includes a plurality of stations each operating on a plurality of links, and does not transmit or receive on a second link of an EMLSR link while performing frame exchange on a first link of the EMLSR link, which is a plurality of links to which an EMLSR mode is applied in an EMLSR mode, and includes a transceiver unit and a processor. When a first station, which is one of a 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 earlier than a time when the multilink device receives a beacon frame on the second link by a predetermined time. 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 initiating 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 pre-specified time from the time the multi-link 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 pre-specified time from the time the multi-link 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 predesignated 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, the initial control frame including padding corresponding to a duration equal to or greater than the minimum duration of padding. The EMLSR mode may be applied to only a portion 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 each operating on a plurality of links and communicating with a multilink device that does not transmit or receive on a second link of an EMLSR link while performing frame exchange on a first link of the EMLSR link, which is a plurality of links to which an EMLSR mode is applied, in an EMLSR mode includes a transceiver unit and a processor. The processor transmits an initial control frame for starting the frame exchange on the first link in the EMLSR mode, and terminates a TXOP for the frame exchange before a time earlier than a time when the multilink device is to receive a beacon frame on the second link by a predetermined time. 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 predesignated time may be signaled by the Multilink device.

[0022] The processor may receive from the multilink device a minimum duration of padding of an initial control frame required for the link switching, and may include padding in the initial control frame corresponding to a duration equal to or longer than the minimum duration of padding. The EMLSR mode may be applied to only a portion of the multiple 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 in a plurality of links, and not transmitting or receiving in a second link of an EMLSR link while exchanging frames in a first link of the EMLSR link, the first link being a plurality of links to which an EMLSR mode is applied in an EMLSR mode, includes the step of terminating a TXOP for the frame exchange before a time earlier than a time when the multilink device receives a beacon frame in the second link by a predetermined time when a first station, which is one of a plurality of stations included in the multilink device, performs the frame exchange in the first link as a TXOP (transmission opportunity) holder in the EMLSR mode, the time being a delay time for the multilink device to perform link switching.

[0024] The operating method may further include a step of receiving an initial control frame in the EMLSR mode to initiate the frame exchange on the first link, and a step of 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). Effect of the Invention

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

[0028] [Figure 1] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Diagram 2] FIG. 11 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing a configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing the configuration of an access point according to an embodiment of the present invention. [Diagram 5] 1 is a diagram illustrating a process in which a STA sets up a link with an AP. [Figure 6] FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] 1 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and a method for indicating the same according to an embodiment of the present invention. [Figure 9] 1 illustrates a multi-link device according to an embodiment of the present invention. [Figure 10] 1 illustrates a multi-link operation in which transmissions on different links are performed simultaneously according to an embodiment of the present invention. [Figure 11] 4 illustrates the operation of a multilink device when a link is changed according to one embodiment of the present invention. [Figure 12] According to one embodiment of the present invention, when any one station of a non-STR multilink device is receiving, channel access of other stations of the non-STR multilink device is prohibited. [Figure 13] 13 shows an operation of canceling channel access inhibition 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] 13 shows a station according to an embodiment of the present invention performing channel access after channel access prohibition is lifted. [Figure 15] 11 illustrates an operation of a station performing transmission after channel access prohibition is lifted according to an embodiment of the present invention. [Figure 16] 13 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 a situation where interference or collision between links may occur. [Figure 18]1 illustrates an operation of an STR multilink device ceasing transmission to a non-STR multilink device according to an embodiment of the present invention. [Figure 19] 13 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] 13 illustrates an operation of an STR multilink device performing channel access again after stopping transmission to a non-STR multilink device according to an embodiment of the present invention. [Figure 21] 13 illustrates an operation of an STR multilink device transmitting a CTS-to-Self frame before transmitting to a non-STR multilink device according to an embodiment of the present invention. [Figure 22] 1 shows that multiple APs included in a STR multi-link device transmit to multiple stations included in one non-STR multi-link device according to an embodiment of the present invention. [Diagram 23] According to an embodiment of the present invention, a plurality of APs included in an STR multilink device perform a plurality of transmissions, the end of which is synchronized, to a plurality of stations included in a single non-STR multilink device. [Figure 24] 1 illustrates multilink devices exchanging RTS / CTS frames according to an embodiment of the present invention. [Diagram 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 to a station on a non-STR multilink device should be retransmitted. [Figure 29]13 shows that, according to an embodiment of the present invention, a control frame is transmitted on a link in which a station not prohibited from channel access operates, rather than on a link in which a station prohibited from channel access operates. [Diagram 30] 4 illustrates a multi-link device sending an ACK according to an embodiment of the present invention. [Diagram 31] 13 shows an element field indicating information regarding support for receiving or transmitting a sink PPDU according to an embodiment of the present invention. [Diagram 32] 1 illustrates a non-STR multi-link device performing an inter-link TXOP power save mode operation according to an embodiment of the present invention. [Diagram 33] 1 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. [Diagram 34] 10 shows that 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. [Diagram 35] 3 illustrates a connection between a single-radio multi-link device and an AP multi-link device according to an embodiment of the present invention. [Diagram 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 multilink device according to an embodiment of the present invention performing channel access taking into account a delay time of changing an RF (radio frequency) chain. [Figure 38] 1 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] 4 illustrates a single-radio multi-link device according to an embodiment of the present invention transmitting a PPDU using MIMO. [Diagram 40] 1 illustrates a station and a single-radio multilink device according to an embodiment of the present invention performing an NDP sounding process. [Diagram 41] 1 illustrates a station and a single-radio multilink device according to an embodiment of the present invention performing a feedback beamforming sounding sequence. [Diagram 42] 1 illustrates a station and a single-radio multilink device according to an embodiment of the present invention performing an NDP sounding process. [Diagram 43] The mapping relationship between UP and AC is shown. [Diagram 44] 1 illustrates a multilink device transmitting traffic mapped to a station of the multilink device according to an embodiment of the present invention. [Diagram 45] 1 illustrates a multi-link device exchanging frames through TID link mapping according to an embodiment of the present invention. [Diagram 46] 13 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] 13 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 a format of a Multi-Link element according to an embodiment of the present invention. [Figure 49] 13 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] 1 illustrates a Multi-Link element for 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 PREFERRED EMBODIMENTS

[0029] The terms used in this specification are selected as common terms currently widely used as much as possible in consideration of the functions in the present invention, but this may vary depending on the intentions, customs, or the emergence of new technologies of the engineers in the relevant technical field. In addition, in certain cases, the applicant may arbitrarily select some terms, and in such cases, the meanings of the terms will be described in the description of the relevant invention. Therefore, it is clear that the terms used in this specification should be interpreted not simply as the names of terms, but based on the substantial meanings of the terms and the contents of this specification as a whole.

[0030] Throughout the specification, when a component is "connected" to another component, this includes not only when it is "directly connected" to another component, but also when it is "electrically connected" with another component in between. Furthermore, when a component "includes" a specific component, this means that it may further include the other component, not excluding the other component, unless otherwise specified to the contrary. In addition, limitations such as "greater than" or "less than" based on a specific critical value may be appropriately replaced with "more than" or "less than" 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 (BSS), which are a set of devices that can successfully synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[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 which are stations providing a distribution service, and a distribution system DS which connects multiple access points AP-1 and AP-2.

[0035] A station (STA) is any device including a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard, and in a broad sense includes not only non-AP stations but also APs. In this specification, the term "terminal" refers to either a non-AP or an AP, or both. A station for wireless communication includes a processor and a communication unit, and further includes a user interface unit and a display unit, etc., depending on the embodiment. The processor generates frames to be transmitted through a wireless network, processes frames received through 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 through the wireless network for the station. In the present invention, the term "terminal" is used to include a 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 a station associated therewith. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP, but when a direct link is set up, direct communication is possible between non-AP stations. Meanwhile, in the present invention, AP is used as a concept including a personal BSS coordination point (PCP), but in a broad sense, AP includes all concepts such as a central controller, a base station (BS), a node B, a base transceiver system (BTS), or a site controller. In the present invention, AP is also referred to as a base wireless communication terminal, but in a broad sense, the base wireless communication terminal is used as a term including an AP, a base station, an eNodeB (eNB), and a transmission point TP. In addition, the base wireless communication terminal includes various types of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with a plurality of wireless communication terminals.

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

[0038] 2 is a diagram showing an independent BSS, which is a wireless LAN system according to another embodiment of the present invention, in which the same or corresponding parts in the embodiment of FIG. 2 are the same as or correspond to the embodiment of FIG.

[0039] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so all stations (STA6, STA7) are not connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

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

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

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

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

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

[0046] 4 is a block diagram showing a configuration of an AP 200 according to an embodiment of the present invention. As shown in the figure, the AP 200 according to the embodiment of the present invention includes a processor 210, a communication unit 220, and a memory 260. In FIG. 4, a duplicated description of parts of the configuration of the AP 200 that are the same as or correspond to the configuration of the station 100 in FIG. 3 will be omitted.

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

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

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

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

[0051] The STA 100 that has successfully received wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200 (S107b), and performs an authentication step. After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200, and performs an association step (S109b). In this specification, association basically means wireless association, but the present invention is not limited thereto, 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, the server 300 is a server that processes 802.1X-based authentication with the STA 100, and may be physically connected to the AP 200 or may exist as a separate server.

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

[0054] A terminal performing wireless LAN communication performs carrier sensing before transmitting data to check whether a channel is occupied or not. If a wireless signal of a certain strength or more is detected, the channel is determined to be occupied and the terminal delays access to the channel. This process is called Clear Channel Assessment (CCA), and the level that determines whether or not the signal is detected is called the CCA threshold. If a wireless signal of a strength greater than 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 of a strength less than the CCA threshold is detected, the channel is determined to be idle.

[0055] If the channel is determined to be in an idle state, each terminal having data to transmit performs a backoff procedure after an IFS (Inter Frame Space) according to the status of each terminal, for example, an AIFS (Arbitration IFS) or a PIFS (PCF IFS). In some embodiments, the AIFS is used as a configuration to replace the conventional DIFS (DCF IFS). Each terminal waits while decreasing a slot time of a random number determined for the corresponding terminal during an interval of the idle state of the channel, and a terminal that has exhausted all the slot time attempts to access the corresponding channel. In this manner, a section in which each terminal performs a backoff procedure is called a contention window section. At this time, the random number can be called a backoff counter. That is, an initial value of the backoff counter is set by an integer that is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal can decrease the backoff counter by 1. Also, if the backoff counter reaches 0, the terminal may be allowed to perform channel access on the corresponding channel. Thus, a terminal may be allowed to transmit if the channel is idle during the AIFS time and the backoff counter slot time.

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

[0057] <Examples of various PPDU formats>

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

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

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

[0062] The L-SIG field included in the preamble of the PPDU is configured with a total of 64 subcarriers by applying 64 FFT OFDM. Of these, 48 subcarriers excluding the guard subcarriers, DC subcarriers, and pilot subcarriers are used for L-SIG data transmission. Since BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information configuration 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 speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which is a combination of a modulation method such as BPSK / QPSK / 16-QAM / 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The total length of the PPDU can be indicated by combining the information in the L_RATE field and the L_LENGTH field. In the non-legacy PPDU format, the L_RATE field is set to the minimum speed of 6 Mbps.

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

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

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

[0073] The VI bit will maintain the current bit configuration, and even if a subsequent generation PPDU is defined, a current 11be terminal can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field is composed of PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits, and serves to sequentially distinguish 11be and subsequent generation WLAN standards by version. 11be has a value of 000b. The UL / DL field distinguishes whether the corresponding PPDU is an uplink / downlink PPDU. The BSS color means a BSS-specific identifier defined in 11ax, and has a value of 6 bits or more. The TXOP means a transmit opportunity duration that was transmitted in the MAC header, but by adding it to the PHY header, the length of the TXOP containing the corresponding PPDU can be inferred without decoding the MPDU, and has a value of 7 bits or more.

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

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

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

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

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

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

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

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

[0082] In addition, in one embodiment of the present invention, a method is proposed in which the configuration of the PPDU indicated by the preamble puncturing BW value is different depending on the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits, in the case of EHT SU PPDU or TB PPDU, one symbol of EHT-SIG-A is further signaled after U-SIG, or EHT-SIG-A does not need to be signaled from the beginning, so that up to 11 puncturing modes must be completely signaled using only the BW field of U-SIG in consideration of this. However, in the case of EHT MU PPDU, EHT-SIG-B is further signaled after U-SIG, so up to 11 puncturing modes can be signaled in a different manner from SU PPDU. In the case of EHT ER PPDU, the BW field is set to 1 bit, and it is possible to signal whether the PPDU uses a 20 MHz or 10 MHz band. Detailed puncturing patterns for each PPDU type will be described in detail below with reference to FIG. 11 and FIG. 12.

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

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

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

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

[0090] The EHT MU PPDU described in (c) of FIG. 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 PPDU transmitted through the user specific field of the EHT-SIG-B to the STA. Therefore, multiple terminals receiving the EHT MU PPDU can perform spatial reuse based on the AID information of the user specific field included in the preamble of the received PPDU.

[0091] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information regarding a resource unit configuration (e.g., a resource unit division form) in a specific bandwidth (e.g., 20 MHz, etc.) on the frequency axis. That is, the RA field may indicate a resource unit configuration divided by a bandwidth for transmitting the HE MU PPDU so that the STA receives the PPDU. Information on the STA allocated (or designated) to each divided resource unit may be included in 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, a user field corresponding to at least one resource unit used for data transmission among the multiple divided resource units may include the AID of a receiver or sender, and a user field corresponding to the remaining resource units not used for data transmission may include a null STA ID that has already been set.

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

[0094] When one wireless communication device communicates using multiple links, the communication efficiency of the wireless communication device can be improved. In this case, the link is a physical path, and may be configured as one wireless medium that can be used to transmit MSDU (MAC service data unit). For example, when the frequency band of any one link is being used by another wireless communication device, the wireless communication device can continue to communicate using another link. In this way, the wireless communication device can effectively use multiple channels. Also, when the wireless communication device simultaneously communicates using multiple links, the overall throughput can be increased. However, the existing wireless LAN is specified on the premise that one wireless communication device uses one link. For this reason, a wireless LAN operation method for using multiple links is required. A wireless communication method of a wireless communication device using multiple links will be described with reference to Figs. 9 to 26. First, a specific form of a wireless communication device using multiple links will be described with reference to Fig. 9.

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

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

[0097] The stations included in the multilink device can operate on multiple links. Also, the stations included in the multilink device can operate on multiple channels. Specifically, the stations included in the multilink device can operate on different links or different channels. For example, the stations included in the multilink device can operate on different channels of 2.4 GHz, 5 GHz, and 6 GHz.

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

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

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

[0101] The multilink setting may be set by negotiation between peer stations. Specifically, the multilink setting may be set by communication between stations without communication with the AP. The multilink setting may be set through any one of the links. For example, even if the first link to the third link are set through the multilink, the multilink setting may be set through the first link.

[0102] Also, a mapping between a traffic identifier (TID) and a link may be set. Specifically, a frame corresponding to a specific TID value may be exchanged only through a link designated in advance. The mapping between a TID and a link may be set on a directional-based basis. For example, when a plurality of links are set between a first multilink device and a second multilink device, the first multilink device may be set to transmit a frame of a first TID to a plurality of first links, and the second multilink device may be set to transmit a frame of a second TID to the first link. Also, a default setting may exist for the mapping between a TID and a link. Specifically, when there is no additional setting in the multilink setting, the multilink device may exchange frames corresponding to a TID in each link according to a default setting. In this case, the default setting may be that all TIDs are exchanged in any one link.

[0103] The TID will be specifically described. The TID is an ID for classifying traffic and data to support QoS (quality of service). The TID may be used and assigned in a layer higher than the MAC layer. The TID may indicate a traffic category (TC) or a traffic stream (TS). The TID may be classified into 16 types. For example, the TID may be designated as one of 0 to 15. The TID value to be used may be designated differently depending on an access policy, a channel access, or a medium access method. For example, when EDCA (enhanced distributed channel access) or HCAF (hybrid coordination function contention based channel access) is used, the TID value may be assigned in the range of 0 to 7. When EDCA is used, the TID may indicate a user priority (UP). In this case, the UP may be designated by the TC or the TS. The UP may be assigned in a layer higher than the MAC. Also, 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. Also, 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 channel contention in EDCA. QoS stations can guarantee QoS using AC. AC may include AC_BK, AC_BE, AC_VI, and AC_VO. AC_BK, AC_BE, AC_VI, and AC_VO may indicate background, best effort, video, and voice, respectively. AC_BK, AC_BE, AC_VI, and AC_VO may be classified into lower ACs. For example, AC_VI may be subdivided into AC_VI primary and AC_VI alternate. AC_VO may be subdivided into AC_VO primary and AC_VO alternate. UP or TID may be mapped to AC. For example, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI, AC_VI, AC_VO, and AC_VO, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI alternate, AC_VI primary, AC_VO primary, and AC_VO alternate, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may have a higher priority in that order. That is, 1 may have a lower priority, and 7 may have a higher priority. Therefore, the priority may be higher in the order of AC_BK, AC_BE, AC_VI, and AC_VO. Also, AC_BK, AC_BE, AC_VI, and AC_VO may correspond to ACI (AC index) 0, 1, 2, and 3, respectively. Due to the characteristics of such a TID, the mapping between a TID and a link may represent the mapping between an AC and a link.Additionally, the mapping between links and ACs can represent the mapping between TIDs and links.

[0105] As described above, a TID may be mapped to each of a plurality of links. The mapping may be a designation of a link through which traffic corresponding to a particular TID or AC may be exchanged. Also, a TID or AC that may be transmitted for each transmission direction within a link may be designated. As described above, there may be a default setting for mapping between a TID and a link. Specifically, if there is no additional setting in the multilink setting, the multilink device may exchange frames corresponding to the TID on each link according to the default setting. In this case, the default setting may be that all TIDs are exchanged on any one link. At any given time, any TID or AC may be mapped to at least one link. Management frames and control frames may be transmitted on all links.

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

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

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

[0109] Depending on the implementation of the multilink device, simultaneous operation in the multilink may not be supported. For example, the multilink device may support simultaneous transmission in multiple links, simultaneous reception in multiple links, or transmission in one link and reception in another link. Reception or transmission in one link may affect reception or transmission in another link. Specifically, transmission in one link may act as interference in another link. Interference from one link of a multilink device acting on another link may be called internal leakage. The smaller the frequency interval between the links, the larger the internal leakage may be. If the internal leakage is not too large, transmission can be performed in another link when transmission is performed in one link. If the internal leakage is large, transmission cannot be performed in another link when transmission is performed in one link. In this way, the simultaneous operation of the multilink device in multiple links may be called STR (simultaneous transmit and receive, simultaneous transmission and reception). For example, a multilink device may transmit on multiple links simultaneously, transmit on one link while receiving on another link, or receive on multiple links simultaneously, all of which may be referred to as STR.

[0110] As mentioned above, the multilink device can support STR or can support it in a limited manner. Specifically, the 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 equal to or greater than a pre-specified magnitude, the multilink device may not be able to perform STR.

[0111] A station can exchange information on the STR capability of the station with other stations. Specifically, a station can exchange information on the presence or absence of a restriction on the capability of the station to simultaneously transmit on multiple links or simultaneously receive on multiple links with other stations. Specifically, the information on the presence or absence of a restriction on the capability of transmitting or receiving on multiple links can indicate whether the station transmits on multiple links simultaneously, receives on multiple links simultaneously, or transmits and receives simultaneously. In addition, the information on the presence or absence of a restriction on the capability of transmitting or receiving on multiple links may be information indicated in stages. Specifically, the information on the presence or absence of a restriction on the capability of transmitting or receiving on multiple links may be information indicating a stage indicating the magnitude of the internal leakage. In a specific embodiment, the information indicating a stage indicating the magnitude of the internal leakage may be information indicating a stage indicating the magnitude of interference generated by the internal leakage. In yet another specific embodiment, the information indicating a stage indicating a frequency interval between links that may affect the internal leakage may be information indicating a stage indicating the magnitude of the internal leakage. In addition, the information indicating a stage indicating the magnitude of the internal leakage may be information indicating a relationship between the frequency interval between the links and the magnitude of the internal leakage in stages.

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

[0113] The operation of the multilink device performing channel access will now be described. The multilink operation not specifically described can follow the channel access procedure described in FIG.

[0114] The multilink device may perform channel access independently from a plurality of links. In this case, the channel access may be a back-off based channel access. When the multilink device performs channel access independently from a plurality of links and the back-off counters reach 0 in the plurality of links, the multilink device may start transmission simultaneously from the plurality of links. In a specific embodiment, when any one of the back-off counters of the links of the multilink reaches 0 and a pre-specified condition is satisfied, the multilink device may perform channel access not only for the link whose back-off counter reaches 0 but also for other links whose back-off counters have not reached 0. Specifically, when any one of the back-off counters of the links of the multilink reaches 0, the multilink device may perform energy sensing in other links whose back-off counters have not reached 0. In this case, when energy equal to or greater than a pre-specified magnitude is not detected, the multilink device may perform channel access not only for the link whose back-off counter reaches 0 but also for the link whose energy sensing has been performed. In this way, the multilink device may start transmission simultaneously from the plurality of links. The threshold value used for energy sensing may be smaller than the threshold value used when determining whether to decrease the back-off counter. In addition, when determining whether to decrease the back-off counter, the multilink device can sense any type of signal, not just a WLAN signal. In addition, in the above-mentioned energy sensing, 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 sense a signal detected due to internal leakage by energy sensing. In addition, as described above, the threshold value used for energy sensing may be smaller than the threshold value used when determining whether to decrease the back-off counter. Therefore, even when transmission is being performed on one link, the multilink device can decrease the back-off counter on the other link.

[0115] Depending on the degree of interference between links used by the multilink apparatus, the multilink apparatus 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 sensed by other stations of the multilink apparatus when any one station of the multilink apparatus transmits on any one link. When the transmission of a first station of the multilink apparatus on the first link causes interference of a predetermined magnitude or more to a second station of the multilink apparatus operating on the second link, the operation of the second station may be restricted. Specifically, the reception or channel access of the second station may be restricted. When interference occurs, the second station may fail to decode a signal received due to the interference. Also, when interference occurs, the second station may determine that the channel is in use when the second station accesses the channel using backoff.

[0116] In addition, when the transmission of the first station of the multilink device through the first link generates interference of less than a pre-specified magnitude in the second station of the multilink device operating through the second link, the first station and the second station can operate independently. Specifically, when the transmission of the first station of the multilink device through the first link generates interference of less than a pre-specified magnitude in the second station of the multilink device operating through the second link, the first station and the second station can perform channel access independently. In addition, when the transmission of the first station of the multilink device through the first link generates interference of less than a pre-specified magnitude in the second station of the multilink device operating through the second link, the first station and the second station can perform transmission or reception independently. When interference of less than a pre-specified magnitude occurs, the second station can successfully decode the received signal even in the presence of interference. In addition, when interference of less than a pre-specified magnitude occurs, the second station can determine that the channel is idle when the second station accesses 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 that the magnitude of interference generated varies depending on the interval between the frequency bands of the links and the characteristics of the multilink device. In the embodiment of FIG. 10, the first multilink device (MLD#1) includes a first station (STA1)-1 operating on the first link (Link1) and a second station (STA1)-2 operating on the second link (Link2). The second multilink device (MLD#2) includes a first station (STA2)-1 operating on the first link (Link1) and a second station (STA2)-2 operating on the second link (Link2). The frequency interval between the first link (Link1) and the second link (Link2) in which the first multilink device (MLD#1) operates is the same as the frequency interval between the first link (Link1) and the second link (Link2) in which the second multilink device (MLD#2) operates. However, the magnitude of interference generated varies depending on the difference between the characteristics of the first multilink device (MLD#1) and the characteristics of the second multilink device (MLD#2). Specifically, the magnitude of interference generated 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] The multilink device may signal whether or not a station included in the multilink device supports STR. Specifically, the AP multilink device and the non-AP multilink device may exchange whether or not an AP included in the AP multilink device supports STR and whether or not an STA included in the non-AP multilink device supports STR. In this embodiment, an element indicating whether or not an STR is supported may be used. The element indicating whether or not an STR is supported may be called an STR support element. The STR support element may indicate whether or not an STR is supported by a station of the multilink device that transmits the STR support element by one bit. Specifically, the STR support element may indicate whether or not an STR is supported by each station included in the multilink device that transmits the STR support element by one bit. In this case, if the station supports STR, the bit value may be 1, and if the station does not support STR, the bit value may be 0. If the multilink device that transmitted the STR support element includes a first station (STA1), a second station (STA2), and a third station (STA3), and the first station (STA1) and the third station (STA3) support STR, and the second station (STA2) does not support STR, the STR support element is 101 1b It is assumed that stations operating in different frequency bands 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 in a first link of 2.4 GHz, and a second station (STA2) and a third station (STA3) operate in 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). Also, the STR support element may include only one bit when there are two stations to which the STR support element signals.

[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 the multi-link device may always be determined as an STR, and therefore, signaling regarding the presence or absence of an STR between the link located at 2.4 GHz and the link located at 5 GHz or 6 GHz may be omitted.

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

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

[0123] When the frequency band of the link is changed, the STR support element may be exchanged. As described above, the presence or absence of STR support of the station may change depending on the distance between the frequency bands of the link, and when the frequency band of the link is changed, the presence or absence of STR support of the station may change. 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 main channel may be included. The AP and the station may exchange the STR support element by a request and a response. In still another specific embodiment, when the frequency band of the link is changed, the STR support element may be exchanged without a separate request. Also, in the above embodiment, when the frequency band of the link is changed, it may include a change in the operating channel of the station.

[0124] When a station of a non-AP multilink device cannot perform STR, the station of the non-AP multilink device can request a link change to the AP. Specifically, the station of the non-AP multilink device can request at least one change of the center frequency, the bandwidth of the frequency band, and the 20 MHz primary channel. The link change request may be transmitted to the AP through a link for which the change is requested. In yet another specific embodiment, the link change request may be transmitted to the AP through a link for which the change is not requested. At this time, the link change request may include information indicating a link for which the change is requested. The information indicating a link may be a number identifying the link. In such an embodiment, the link change may be a change of an operating channel within one frequency band. Also, the link change may include information regarding a method of changing the link. Specifically, the link change request may indicate whether to move the center frequency of the link to a frequency higher than the current center frequency, or to move the center frequency of the link to 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 reducing the bandwidth of the link. The link change request may also request changing the position of the primary channel. Specifically, the link change request may indicate changing the position of the primary channel to a channel in a lower frequency band or a channel in a higher frequency band than the current position of the 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 FIG. 11, the second station (STA2) and the third station (STA3) of the non-AP multilink device are in a state in which STR cannot be supported. The non-AP multilink device requests the AP multilink device to change the third link (Link3). The AP multilink device, having received the link change request, changes the operating link of the third AP (AP3). At this time, the third station (STA3) operating on the third link (link3) to be changed can send a change request to the third AP (AP3). In yet another specific embodiment, a station that does not operate on the third link (link3) can send a change request to an AP that does not operate on the third link (link3).

[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 a frequency of the link. The information about the frequency of the link may include at least one of a change in a center frequency, an operating bandwidth, and a main channel of the link. In addition, the information about the link change may include information about a time point of the link change. In addition, the link change may 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 the presence or absence of changed STR support.

[0128] The above-mentioned link change may not be allowed or the STR may not be supported even if the link change occurs. Also, as in the embodiment of FIG. 11, the AP multilink device may support the STR, but the non-AP multilink device may not support the STR. This is because a relatively high RF device is generally used in the AP multilink device and a relatively low RF device is generally used in the non-AP multilink device. Therefore, a method is required for efficient communication even when one of the multilink devices does not support the STR during communication between the multilink devices. In this case, the STR may indicate that transmission and reception are performed simultaneously. This will be described with reference to FIG. 12.

[0129] FIG. 12 shows that when any one station of a non-STR multilink device is receiving, other stations of 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 the 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, 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, backoff of channel access may be prohibited on the other links of the non-STR multilink device. This makes it possible to prevent 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 starts on one link of the non-STR multilink device, backoff of channel access may be prohibited on the other links of the non-STR multilink device. This may be set by a specific bit of a memory such as a channel access prohibition flag. This may be shared by a memory inside the multilink device to determine whether or not channel access is prohibited. With this embodiment, channel access prohibition can be implemented without a separate frame exchange. For ease of explanation, unless otherwise specified, channel access prohibition as used in this specification 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, a station operating on a link where channel access is prohibited cannot perform a back-off procedure regardless of the NAV and CCA results. Also, when channel access is prohibited, a station operating on a link where channel access is prohibited cannot transmit regardless of the NAV and CCA results. However, even if channel access is prohibited, a station operating on a link where channel access is prohibited can receive. Also, the channel access prohibition on the second link due to reception performed on the first link may be released based on the time when reception on the first link is completed. Specifically, the channel access prohibition on the second link due to reception performed on the first link may be released when reception on the first link is completed. In still another specific embodiment, the channel access prohibition on the second link due to reception performed on the first link may be released based on the time when an ACK is transmitted after reception on the first link is completed. Specifically, the channel access prohibition on the second link due to reception performed on the first link may be released based on the time when an ACK is transmitted after reception on the first link is completed. In yet another specific embodiment, the channel access prohibition in the second link due to reception in the first link may be released when the transmission of an ACK is completed after the reception is completed in the first link. Also, immediately after the channel access prohibition is released, the station may immediately decrement the back-off counter without additional sensing. In this case, the additional sensing may represent 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 released, the station may immediately decrement the back-off counter without additional sensing. In this case, 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, 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). When the second station (STA2) transmits on the second link (Link2) while the first station (STA1) receives, interference within the device occurs. As described above, while the first station (STA1) operating on the first link (Link1) receives, the channel access of the second station (STA2) on the second link (Link2) is prohibited. 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 reduce the previous 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 the single block may be understood as representing 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 the station determines that the intended recipient of the PPDU is not the station, the station may discontinue receiving the PPDU. In such a case, the channel access unblocking operation of the multilink device becomes problematic. In this specification, the intended recipient is used synonymously with the destination station.

[0135] FIG. 13 illustrates an operation of canceling channel access inhibition when it is determined 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] When the station confirms that the intended recipient of the PPDU it receives is not the station, the station can release the channel access prohibition. The station can determine whether the station 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 of the EHT-SIG field described above. Specifically, the station can determine whether the STA-ID field of the EHT-SIG field indicates the station. Also, the station can determine whether the station is the intended recipient of the PPDU based on the value of the RA field of the MAC frame included in the PPDU. Specifically, the station can determine whether the RA field of 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 due to the NAV set for the second station (STA2).

[0137] As shown in FIG. 13, even if channel access prohibition is lifted, stations included in a non-STR multilink device may 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 of stations included in a non-STR multilink device is required for 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 2 or more. This will be described in FIG. 14.

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

[0139] A station whose channel access prohibition has been released can decrement its backoff counter by 2 or more immediately after the channel access prohibition is released. This is to ensure fairness in channel access opportunities between the station and 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 of CCA (CSMA) and decrementing a back-off counter while 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, channel access of the second station (STA2) is prohibited while the first station (STA1) is receiving. In FIG. 14(a), while channel access of the second station (STA2) is prohibited, the second station (STA2) can perform a channel access procedure of CCA (CSMA) and decrementing a back-off counter. In FIG. 14(a), while channel access of the second station (STA2) is prohibited, the second station (STA2) decrements a back-off counter because the channel of the second link (Link2) is idle.

[0141] Also, a station whose channel access is forbidden can delay transmission without starting transmission even if the back-off counter reaches 0 while channel access is forbidden. In this case, the station can maintain the back-off counter value at 0. Also, 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 to which the station accesses is busy. This is because the reason for delaying transmission is not because it is determined that the channel is busy. In FIG. 14(b), while the channel access of the second station (STA2) is forbidden, the second station (STA2) can perform a channel access procedure of CCA (CSMA) and decrementing the back-off counter. In FIG. 14(b), while the channel access of the second station (STA2) is forbidden, the channel of the second link (Link2) is idle, so the second station (STA2) decrements the back-off 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 of a non-STR multilink device is transmitting, and can also include prohibiting a second station from transmitting when a first station of a non-STR multilink device is receiving.

[0143] In the embodiment illustrated in FIG. 14(b), when multiple stations are prohibited from channel access, the channel access prohibition of multiple stations is released at the same time, and multiple stations are likely to attempt transmission at the same time. Therefore, a method is required to reduce the probability of transmission collision. This will be explained in FIG. 15.

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

[0145] As described above, among the multiple links on which the non-STR multilink device operates, 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 be started by exchanging RTS / CTS frames. Thus, when transmission is performed on a first link among the multiple links on which the non-STR multilink device operates, the non-STR multilink device may start 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 start exchanging RTS / CTS (request to send / clear to send) frames before starting the delayed transmission. At this time, if the station cannot receive the CTS frame, it may not be able to start the delayed transmission. In the embodiment of FIG. 15(a), the station whose transmission has been delayed due to channel access prohibition transmits an RTS frame before starting the delayed transmission. After the station receives a CTS frame in response to the RTS frame, it starts the delayed transmission.

[0146] In yet another specific embodiment, after the channel access prohibition of a station whose transmission has been delayed due to the channel access prohibition is lifted, the station can transmit a frame including only a part of the delayed transmission. In this case, after the station receives a response, for example, an ACK, to the frame including only a part of the delayed transmission, the station can transmit the part of the delayed transmission that has not been transmitted. If the station does not receive a response to the frame including only a part of the delayed transmission, the station may not transmit the part of the delayed transmission that has not been transmitted. In this way, the station starts an RTS / CTS exchange after the channel access prohibition is lifted or transmits only a part of the delayed transmission because the collision probability of the transmission after the channel access prohibition is higher than that of a general transmission. Therefore, the above-mentioned embodiment may be mandatory for the transmission performed after the channel access prohibition is lifted. In the existing WLAN operation, 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-mentioned embodiment, the RTS / CTS frame is used to prevent transmission collision with a station that is attempting to perform a delayed transmission in order to protect the transmission or reception of a non-STR multilink device.

[0147] As described above, when any one station of the non-STR multilink device receives, the transmission of the other station of the non-STR multilink device may be restricted. In addition, when any one station of the non-STR multilink device transmits, it may be difficult for the other station of the non-STR multilink device to accurately sense the channel state of the link on which the station operates. Specifically, when a first station of the non-STR multilink device transmits, a second station of the non-STR multilink device may always determine that the channel state of the link on which the second station operates is busy. Therefore, even if 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 interference within the device. In this way, when a station that cannot determine the channel state due to interference within the device or any one station of the non-STR multilink device continues to transmit, it is said that the other station of the non-STR multilink device is in a blind state. Due to the above-mentioned situation, it may be difficult for a station that is in a blind state to perform a backoff procedure and attempt transmission. In addition, due to the above-mentioned circumstances, it may be difficult for stations in a blind state to start receiving or successfully decode the PPDU. Therefore, a transmission method that takes into account stations in a blind state is required. This will be described 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 that is about to transmit to a station of a non-STR multilink device can determine whether to transmit depending on whether the station of the non-STR multilink device is in a blind state. In this case, the station that is about to transmit to a station of a non-STR multilink device can be a station included in the STR multilink device. Also, the station that is about to transmit to a station of a non-STR multilink device can be an AP included in the AP multilink device, and the non-STR multilink device can be a non-AP multilink device. A station that is about to transmit to a station of a non-STR multilink device can determine whether the station of the non-STR multilink device is in a blind state. A station that is about to transmit can determine whether another station of the multilink device in which the station is included is transmitting to the non-STR multilink device. If another station of the multilink device in which the station is included is receiving from the non-STR multilink device, the station can determine that the station of the non-STR multilink device receiving the station's transmission is in a blind state. In the embodiment of FIG. 16, the STR AP 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 non-STR non-AP 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 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. This is 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 open 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 the STR multilink device transmits to the non-STR multilink device, the STR multilink device can transmit to the non-STR multilink device through multiple links. Specifically, when the STR multilink device transmits to the non-STR multilink device through the first link, the STR multilink device can start transmitting to the non-STR multilink device through the second link. At this time, the STR multilink device can determine the length of the transmission to be performed on 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 to the non-STR multilink device through the second link based on the length of the transmission to the non-STR multilink device through the first link. In a specific embodiment, the STR multilink device can simultaneously end the transmission on the first link and the transmission on the second link. This is to prevent the transmission to one of the stations of the non-STR multilink device from being terminated first and the transmission to another station of the non-STR multilink device from being performed while one of the stations of the non-STR multilink device transmits a response to the transmission, for example, an ACK. According to the above embodiment, multiple stations of the non-STR multilink device can simultaneously transmit responses to the transmission to multiple stations.

[0153] An STR multilink device cannot determine the state of a station included in a non-STR multilink device in real time. Therefore, even if an STR multilink device operates according to the embodiment described in FIG. 16, interference or transmission collision may occur between the links on which the non-STR multilink device operates. For example, in the embodiment of FIG. 16, the first AP (AP1) may start 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 interference or collision between links may be greater than the probability of interference or transmission collision within a link. This will be described in more detail in FIG. 17.

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

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

[0156] In addition, 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 starts earlier than 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 performing transmission. In this way, since a transmission collision occurs even between stations that start transmission at different times, the probability of occurrence of interference or transmission collision between devices may be higher than the probability of occurrence of interference or collision within a link. In addition, the probability of occurrence of interference or transmission collision between links may increase as the time for identifying the sender of the PPDU received by the AP of the STR multilink device is delayed. Therefore, a method for solving this is required. When one of the stations of the STR multilink device is performing reception, it is not necessary to perform channel access of the other stations of the STR multilink device. However, if channel access is prohibited in this way, the meaning of implementing the STR function may be lost. Therefore, a method of non-blocking channel access operation of the STR multilink device is required, which is illustrated in FIG.

[0157] As mentioned above, it may be important for the multilink device to quickly determine the station that transmits 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 that transmits 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 that transmits the EHT UL PPDU. The multilink device that receives the EHT PPDU may identify the station that transmits the EHT PPDU based on the User field of the EHT-SIG of the EHT UL PPDU. In this way, the AP multilink device may determine the station that transmits the EHT UL PPDU, and the AP multilink device may determine the destination device of the transmission. Specifically, the AP multilink device may determine whether the transmission that is to be performed is likely to fail due to an inter-link collision. Furthermore, if there is a high possibility that a 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 of an STR multilink device stopping transmission to a non-STR multilink device according to an embodiment of the present invention.

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

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

[0161] When a station that has cancelled a transmission to a station of a non-STR multilink device transmits to a station other than the station of the non-STR multilink device, the station that has cancelled a transmission to the station of the non-STR multilink device can transmit traffic having the same priority as the traffic of the cancelled transmission or traffic having a higher priority. This is because fairness is not achieved if traffic having a lower priority than the priority of the traffic used when accessing the channel for the cancelled transmission is transmitted. In the above embodiment, the station of the STR multilink device may be an AP.

[0162] A station that cancels transmission to a station in a non-STR multilink device can initialize the TXOP it has 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. This allows 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). The first AP (AP1) determines that the first station (STA1) is in a blind state while transmitting to the first station (STA1). 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 embodiment described above. 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 pauses 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 embodiment, when the STR multilink device stops transmission to a station of the non-STR multilink device in the blind state and transmits to other stations other than the station of the non-STR multilink device in the blind state, it is necessary to inform the other stations that transmission to the other stations may be performed in order to ensure stable reception. A method for this will be described. For convenience of explanation, the other stations other than the station of the non-STR multilink device in the blind state will be called other stations.

[0166] A station of the STR multilink device can insert the address of another station into a MAC frame. Specifically, the station of 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 of the device can insert the address of the other station into the EHT-SIG. Specifically, the station of 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, the station may monitor the reception of the PPDU for a pre-specified time even after it has determined that the station is not the intended recipient of the received PPDU. Specifically, the station may monitor whether the reception of the PPDU continues for a pre-specified time even after it has determined that the station is not the intended recipient of the received PPDU. This allows the station to determine whether the transmission of the PPDU is interrupted and the transmission to the station begins. In this embodiment, if it is determined that the transmission of the PPDU continues for a pre-specified time, the station may enter a doze state. If it is determined that the transmission of the PPDU does not continue for a pre-specified time, the station may remain in a wake-up state. At this time, if a new PPDU is received at 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 the power saving state. Also, a station transmitting a PPDU may insert information into a reserved field of the PPDU, signaling that the transmission may be interrupted.

[0169] In this way, it is possible to prevent unnecessary occupation of the channel due to transmission cancellation or interruption.

[0170] When transmission is interrupted or postponed due to a transmission collision between links, the value of the CW 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 a general channel access failure or transmission failure, the value of the CW used for channel access may not be doubled. That is, the station can maintain the value of the CW used for channel access as it is. The purpose of doubling the value of the CW is to increase the range of possible values ​​of the backoff counter and reduce the probability of a transmission collision. If the station can clearly recognize the transmission collision between links, this need may be reduced. Also, when transmission is interrupted or postponed due to a transmission collision between links, the station may double the value of the CW, which may delay the transmission. However, when a transmission collision between links and an intra-link collision occur simultaneously, the station needs to double the value of the CW. This will be described with reference to 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] When the station cancels the transmission due to the transmission performed in the non-STR multilink device as in the above-mentioned embodiment, the station can sense the channel state after canceling the transmission. When the channel is sensed not to be idle, the station can double the value of the CW. In this case, the doubling can be performed according to the embodiment described in FIG. 6. Also, when the channel is sensed to be idle, the station can maintain the value of the CW. This embodiment is for treating the channel as being idle differently from when the transmission is made because the possibility of a transmission collision occurring in the link is low even if the channel is sensed to be idle. Specifically, when the AP of the AP multilink device fails to transmit to the station of the non-STR multilink device, the AP of the AP multilink device can obtain the back-off counter in the CW without increasing the CW. In this case, when the non-STR multilink device of the AP multilink device fails to transmit to the first station and the second station of the non-STR multilink device transmits, the AP of the AP multilink device can obtain the back-off counter in the CW without increasing the CW. As described above, the AP multilink device can determine whether the second station of the non-STR multilink device transmits based on the transmitting station of the PPDU indicated by the signaling field of the PPDU or the station indicated by the TA field of the MAC frame included in the PPDU. In the above embodiment, when EDCA is applied, the procedure for CW adjustment and backoff counter generation may be performed for each AC.

[0173] In yet another specific embodiment, the STR multilink device may determine whether the transmission of the PPDU has failed based on whether a response to the PPDU has been received. At this time, the STR multilink device may not need to consider whether the station receiving the PPDU is included in the non-STR multilink device. For example, even if the first station receiving the PPDU is included in the non-STR multilink device and the first station cannot transmit a response to the PPDU because the second station of the non-STR multilink device transmits, the STR multilink device may determine that the transmission of the PPDU has failed. In addition, when the transmission of the PPDU of the STR multilink device has failed, the STR multilink device may increase the value of the CW to the next largest value among the values ​​that the CW value can have. At this time, when the value of the CW is the maximum value, the STR multilink device may maintain the value of the CW at the same value.

[0174] In yet another specific embodiment, when the channel is detected as being idle, the station may set the value of the CW to the minimum value (CW_min) of the traffic CW. This embodiment is for treating a case where the 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 traffic AC included in the canceled transmission.

[0175] In addition, when the 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 interrupting 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 to transmit after canceling transmission because the NAV has already been set by the CTS-to-Self frame. Also, if the station cancels transmission and then attempts to transmit again, and there is still a TXOP remaining, the station can attempt to transmit 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). The first AP (AP1) determines that the first station (STA1) is in a blind state while transmitting to the first station (STA1). Therefore, the first AP (AP1) stops transmitting to the first station (STA1). In FIG. 19(a), the first AP (AP1) determines that the channel of the first link (Link1) is idle. At this time, since there is no TXOP remaining, the first AP (AP1) accesses the channel by a backoff procedure. In Fig. 19(b), the first AP (AP1) determines that the channel of the first link (Link1) is not idle. At this time, since the TXOP remains, the first AP (AP1) attempts to transmit without a backoff procedure.

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

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

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

[0182] In yet another specific embodiment, as shown in Fig. 20(b), the pre-specified time interval may be EIFS, which is based on the consideration that the STR multilink device may consider that it has already exhausted its transmission opportunities and on the consideration 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 the transmission may be interrupted, the pre-specified time period may be DIFS. Also, when a station receiving the PPDU detects that the transmission of the PPDU is interrupted, the station may detect whether the channel is idle using DIFS instead of EIFS. In this case, when the channel is detected as idle using DIFS, the station may start a backoff procedure. This embodiment improves the performance of the entire network and ensures fairness between stations. When EDCA is applied, DIFS may 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 the first station of the STR multilink device completes the backoff procedure, the second station of the STR multilink device may be receiving a PPDU. In this case, if the second station cannot complete decoding of the signaling field of the PPDU, the first station cannot recognize that a transmission collision between links has occurred, but can determine that there is a possibility. In this case, the first station can insert information indicating that transmission may be interrupted into the PPDU to be transmitted, as described above. In addition, the NSTR multilink device can transmit a CTS-to-Self frame before transmitting to the 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 of the STR multilink device can transmit a CTS-to-Self frame before transmitting to the non-STR multilink device. Specifically, if a second station of the STR multilink device attempts to transmit to the non-STR multilink device while a first station of the STR multilink device is receiving, the second station of 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 secure a TXOP for transmission to the non-STR multilink device. Also, the second station can determine whether a transmission to the first station is transmitted from the non-STR multilink device before transmitting to the non-STR multilink device. The second station can determine the destination station of the transmission depending on whether a transmission to the first station is transmitted from the non-STR multilink device. Specifically, if a transmission to the first station is not 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 transmitted from the non-STR multilink device, a second station can transmit to a station not included in the non-STR multilink device. For example, when the first station plans to transmit a SU-PPDU for a station in the non-STR multilink device, a MU-PPDU including data for a station in the non-STR multilink device, and a PPDU including a trigger frame that triggers a transmission of a station in the non-STR multilink device, the first station can cancel the planned transmission. At this time, the first station can attempt to transmit a SU-PPDU for a station other than the station in the non-STR multilink device, a MU-PPDU including no data for a station in the non-STR multilink device, and a PPDU including a trigger frame that does not trigger a transmission of a station in the non-STR multilink device.In this case, the first station can start transmission after a time greater than SIFS from the time of transmitting the CTS-to-Self frame. Specifically, the first station can start transmission after PIFS from the time of transmitting the CTS-to-Self frame. The station that transmitted the CTS-to-Self frame must start transmission after SIFS from the time of transmitting the CTS-to-Self frame. As in the above-mentioned embodiment, when canceling a planned transmission and attempting a new transmission, processing time is required for the STR multilink device, such as generating a new MPDU to be transmitted. For this reason, an exception to the regulation on the time interval between the CTS-to-Self frame and transmission may be applied. In such an embodiment, the second station cannot transmit beyond the TXOP acquired by the CTS-to-Self in principle.

[0187] In FIG. 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). Since the second AP (AP2) receives and the first AP (AP1) plans to transmit to a station in the non-STR multi-link device, the first AP (AP1) transmits a CTS-to-Self frame before the planned transmission. As described above, the first AP (AP1) determines the destination station for transmission based on the judgment of the station that transmitted the PPDU received by the second AP (AP2). Also, the first AP (AP1) transmits after SIFS or PIFS from the time of transmitting the CTS-to-Self frame.

[0188] The second station can send an RTS frame instead of a CTS-to-Self frame to start the RTS / CTS frame exchange procedure. 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 only win the TXOP if the destination station is not in the blind state.

[0189] FIG. 22 illustrates a case in which multiple APs included in a 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 multiple stations receiving simultaneously causes relatively little interference. FIG. 22 shows multiple stations included in one non-STR multilink device receiving simultaneously. In this case, in the STR multilink device, multiple APs included in the STR multilink device can perform multiple transmissions with synchronized end of transmission to multiple stations included in one non-STR multilink device for stable operation of the non-STR multilink device. This will be described in FIG. 23.

[0191] FIG. 23 shows that, 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 a single non-STR multilink device.

[0192] In non-STR links, when a multilink device transmits on one of the links, the multilink device can simplify the channel access procedure for transmissions on the other links. Specifically, when a first station of 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 of the STR multilink device, the second station of the STR multilink device can start transmitting on the second link.

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

[0194] In addition, when a first station and a second station of an STR multilink device transmit to a station included in one 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 indicate 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 indicate within a slot boundary or within a symbol boundary.

[0195] A plurality of stations of a non-STR multilink device that receives a synchronized transmission end can simultaneously transmit a subsequent transmission, for example, a response. In this case, the response can include an ACK. In a conventional wireless LAN, a subsequent transmission after a reception is transmitted after a SIFS from the reception. However, transmitting a subsequent transmission with a slight time difference for a plurality of transmissions that have been completed with a slight time difference may be more complicated to implement than transmitting the subsequent transmissions simultaneously. Therefore, as described above, a plurality of stations of a non-STR multilink device that receives a synchronized transmission end can simultaneously transmit a subsequent transmission. In this case, the interval between the transmissions following at least one of the plurality of transmissions whose transmission ends are synchronized may be the sum of the SIFS and a time within a pre-specified time interval. Specifically, a transmission following a transmission that has been completed earlier among the plurality of transmissions whose transmission ends are synchronized may be transmitted at an interval obtained by adding the SIFS and a time within a pre-specified time interval from the transmission. In this case, the pre-specified time interval may be one of a slot time or a symbol length. In addition, the difference within a pre-specified time interval may be the difference between the end of the last transmission among multiple transmissions whose end is synchronized and the first transmission among multiple 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 may transmit synchronized subsequent transmissions. The multiple subsequent transmissions with synchronized transmission ends may represent multiple subsequent transmissions transmitted with a time difference within a second pre-specified time interval. Also, the difference within the second pre-specified time interval may be the difference between the end of the last completed transmission among the multiple synchronized transmissions and the first completed transmission among the multiple transmissions with synchronized transmission ends. In this case, the second pre-specified time interval may be smaller than the first pre-specified time interval. In this way, a PPDU with synchronized transmission ends may be called a sync PPDU.

[0197] In FIG. 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 transmission to the first station (STA1) and the second station (STA2), respectively. That is, after the first station (STA1) ends transmission, the second station (STA2) ends transmission within a time period previously designated by the first station (STA1). The first station (STA1) and the second station (STA2) simultaneously transmit ACK. 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 and the end of transmission to the second station (STA2).

[0198] Such an embodiment may be applied to transmissions where the ACK policy is not set to No ACK. In particular, it may also be applied when the ACK policy is not immediate response. In a particular embodiment, when multiple stations of a multilink device receive transmissions that are synchronized in their end of transmission, the multiple stations of the multilink device may simultaneously receive an ACK request and simultaneously transmit an ACK in response to the ACK request. Multiple stations of the multilink device that receive a transmission with an ACK policy set to a value other than No ACK within a pre-specified time period may begin ACKing simultaneously.

[0199] When a non-STR multilink device is present, the non-STR multilink device must be taken into consideration in the operation of transmitting an RTS / CTS frame and a CTS-to-Self frame to set a TXOP. This will be described with reference to Figures 24 to 29.

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

[0201] Even if a non-STR multilink device exists, the RTS / CTS frame exchange procedure can follow the procedure defined in the existing wireless LAN. 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 the frame to another station operating on a link other than the link on which the station operates and included in the multilink device in which the station is included.

[0202] However, as in the above embodiment, channel access or transmission may be restricted when a non-STR multilink device is present. This may result in failure to transmit RTS / CTS as shown in Fig. 24. That is, a station planning to transmit to a first station of a non-STR multilink device may not attempt to exchange RTS / CTS frames if a second station of 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), the second station (STA2) is prohibited from accessing the channel. The second AP (AP2) can determine that the second station (STA2) is prohibited from accessing the channel. Therefore, the second AP (AP2) does not attempt to exchange an RTS / CTS frame with the second station (STA2). In such an embodiment, a hidden node problem may occur. This 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. At this time, since TXOP is not set to other stations, other stations may attempt to transmit, causing stations in the non-STR multilink device to fail to transmit or receive. In the embodiment 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 transmission of the first AP (AP1) to the first station (STA1), the second AP (AP2) was unable to transmit an RTS frame before transmission. Therefore, a TXOP for the transmission of the second AP (AP2) is not set to 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 (Link2). As a result, the second station (STA2) fails to receive the transmission of the second AP (AP2). In order to solve this hidden node problem, the following embodiment may be applied.

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

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

[0208] In another embodiment of the present invention, when a second station of the multilink device is about to transmit an RTS frame to a fourth station of the non-STR multilink device while a first station of the multilink device is continuing to transmit to a third station of the non-STR multilink device, the first station may end transmission to the third station before the fourth station is about to transmit the RTS frame. This allows the fourth station to transmit a CTS frame to the second station. Thus, a TXOP tentative setting for frame exchange between the second station and the fourth station can be performed. However, it may be difficult for the first station to end transmission before the fourth station is about to transmit the RTS frame.

[0209] In yet another embodiment of the present invention, when a second station in the multilink device is about to transmit an RTS frame to a fourth station in the non-STR multilink device while a first station in the multilink device continues transmission to a third station in the non-STR multilink device, the second station can transmit the RTS frame to the fourth station in accordance with the end time of the first station's transmission to the third station. To this end, the second station can insert padding into the RTS frame. In this case, the RTS frame can be in an RTS frame format that allows the transmission length to be flexibly adjusted. For convenience of explanation, such an RTS frame format is called an ML (multilink)-RTS frame. The ML-RTS frame can include a pad field for padding. For example, the format of the ML-RTS frame can be the same as the RTS frame format shown in FIG. 26. Also, the first station can insert padding into the transmission to the third station in order to align the RTS frame with the end time of the transmission.

[0210] In the embodiment of FIG. 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 a first link (Link1) and a second station (STA2) operating on a second link (Link2). The second AP (AP2) transmits an ML-RTS frame to the second STA (STA2) in accordance with the end of the transmission of the first AP (AP1) to the first station (STA1). Then, 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 set in the station operating on the channel of the second link.

[0211] In yet another specific embodiment, another frame for setting NAV may be replaced instead of the RTS / CTS frame. In the above-mentioned embodiment, an ACK request frame may be transmitted instead of the RTS frame. The ACK request frame may include duration information related to a 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 an ACK may be set according to the duration information of the ACK request frame.

[0212] Although the above embodiment has been described for the exchange of RTS / CTS frames, it may also be used for the exchange of control frames other than RTS / CTS frames. In this case, the control frame exchange may include the exchange of PS-Poll frames and response frames to PS-Poll.

[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 exists, some stations may be prohibited from accessing the channel. Even if a station's channel access is prohibited, the station can still send a response to a control frame. Specifically, even if a station's channel access is prohibited, the station can still send a CTS frame 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 in which the first station is included. In this case, the third station can perform a retransmission to the first station. The third station can expect that the transmission to the second station will fail.

[0216] In the embodiment 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 a first link (Link1) and a second station (STA2) operating on a second link (Link2). The first AP (AP) transmits to the first station (STA1). The second AP (AP2) transmits an RTS frame to the second station (STA2). Since the first station (STA1) receives, the second station (STA2) is prohibited from accessing the channel. 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 (AP1) is likely to fail to transmit due to the CTS frame transmission of the second station (STA2). Therefore, the first AP (AP1) performs a retransmission to the first station (STA1). The retransmission method is described in more detail in FIG.

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

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

[0219] Also, a station performing retransmission can perform retransmission before receiving an ACK for a transmission. In this case, after performing retransmission, the station performing retransmission can receive a Block ACK indicating whether or not the initial transmission and the retransmission have been received. Therefore, the station performing retransmission can perform retransmission before a SIFS after the initial transmission. In yet another specific embodiment, a station that fails to receive due to a control frame transmitted as an exception to channel access prohibition can wait to receive the retransmission without transmitting an ACK.

[0220] In the embodiment of Fig. 28, the first AP (AP1) retransmits the fourth and fifth packets, taking into account the 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 including whether or not the retransmission was received.

[0221] FIG. 29 shows that a control frame is transmitted on a link in which a station in which channel access is not prohibited operates, rather than on a link in which a station in which 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 of a non-STR multilink device may be synchronized. However, this is difficult to implement because it may require adjusting an already generated MPDU or generating an MPDU again. Therefore, the multilink device may transmit a control frame through 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 through 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) succeeds in the backoff procedure, the second AP (AP2) cannot transmit to the second station (STA2) because the first station (STA1) is receiving a transmission sent from the first AP (AP1). At this time, the second AP (AP2) requests the first AP (AP1) to transmit an RTS frame of which the second station (STA2) is the recipient. At this time, the first AP (AP1) may include an RTS frame in which the second station (STA2) is the recipient in the transmission being performed by the first AP (AP1). In yet another specific embodiment, after the first AP (AP1) finishes the transmission being performed by the first AP (AP1), the first AP (AP1) may transmit an RTS frame in which the second station (STA2) is the recipient through the first link (Link1) after SIFS from the transmission. The first station (STA1) receives the RTS frame in 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 stop transmission to the first station (STA1) in 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 description, and may be used for transmitting control frames other than the RTS frame and the CTS-to-Self frame. Also, time intervals other than the PIFS may be used.

[0224] FIG. 30 illustrates 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 to transmit an ACK to a station in a no-STR multilink device. Specifically, a station in a multilink device can request to transmit an ACK on a link other than the link on which the transmission was made. In the embodiment of FIG. 28, the first AP (AP1) of the STR multilink device transmits (Tx(#2)) to the first station (STA1) of the non-STR multilink device. At this time, the first AP (AP1) requests to transmit an ACK for the transmission (Tx(#2)) on the second link (Link2). This is because the first AP (AP1)'s transmission (Tx(#2)) to the second station (STA2) of the second AP (AP2) is completed before the first AP (AP1)'s transmission (Tx(#2)) to the second station (STA2), and it is determined that it is difficult to transmit an ACK for the first AP (AP1)'s transmission (Tx(#2)).

[0226] Also, 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 cause channel access burden and transmission delay. Therefore, a new ACK policy for the multilink device 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. Such an ACK transmission can be called ML (multilink)-ACK. In addition, ML-ACK may be set as an ACK policy. In the embodiment of FIG. 30, the first AP (AP1) sets the ACK policy for transmission (Tx(#2)) to ML-ACK. After receiving the transmission (Tx(#2)), the first station (STA1) does not transmit an ACK to the first AP (AP1). The second station (STA2) completes reception of the transmission transmitted from the second AP (AP2) and 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 multi-link device may include a third station (STA3) in addition to the first station (STA1) and the second station (STA2), and the STR multi-link 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 of the transmission from the second AP (AP2) to the second station (STA2) may also be set to ML-ACK. When the transmission from the third AP (AP3) to the third station (STA3) is completed later than the transmission from the second AP (AP2) to the second station (STA3), the third station (STA1) may transmit to the third AP (AP3) an ACK for the transmission from the first AP (AP1) to the first station (STA1), an ACK for the transmission from the second AP (AP2) to the second station (STA2), and an ACK for the transmission 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 of non-STR multilink devices are not completed simultaneously. In the above-mentioned 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 No Ack instead of ML-ACK.

[0229] While the 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 on which the multilink device acquired a transmission opportunity earlier may be set higher than the NAV required to transmit traffic. When the NAV is set higher than the NAV required to transmit traffic on the link on which the multilink device acquired a transmission opportunity earlier, 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 the first station of the non-STR multilink device to receive the above-mentioned Sync PPDU, it must determine whether the second station, which has a non-STR relationship with the first station, starts receiving the Sync PPDU. In addition, the first station must continuously perform preamble detection (PD). Considering that the first station receiving the Sync PPDU is prohibited from channel access due to the reception of other stations of the non-STR multilink device, such an operation of the first station may be unreasonable. Therefore, the first station can enter a power saving state within a pre-specified condition. 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. Such a power saving operation can be called inter-link TXOP power save (PS). A station that has 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 has 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] The non-AP multilink device may signal information regarding whether or not it supports sync PPDU reception and conditions for supporting sync PPDU to the AP multilink device. Also, the AP multilink device may signal whether or not it supports AP multilink device sync PPDU transmission to the non-AP multilink device. At this time, the multilink device may signal whether or not it supports sync PPDU for each multilink device. For example, the AP multilink device may signal whether or not it supports sync PPDU transmission for each AP multilink device. In still another specific embodiment, the multilink device may signal whether or not it supports sync PPDU for each station. Specifically, the AP multilink device may signal whether or not it supports sync PPDU transmission 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 may indicate that the first AP supports sync PPDU transmission and that the second AP and the third AP do not support sync PPDU transmission.

[0234] If an AP multilink device associated with a non-AP multilink device signals that it does not support sync PPDU transmission, a station of the non-AP multilink device can enter the power saving state of the inter-link PS described above while other stations of the non-AP multilink device are receiving. This is because the AP multilink device associated with the non-AP multilink device cannot transmit sync PPDUs. In this case, the station of 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 other stations of the non-AP multilink device.

[0235] Whether or not the sync PPDU transmission or reception is supported may be determined by an operation policy in addition to hardware performance. Therefore, whether or not the sync PPDU transmission or reception is supported may be signaled by information on an operating mode in addition to information on performance. A method of signaling whether or not the sync PPDU transmission or reception is supported will be described in detail with reference to FIG. 31.

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

[0237] As described above, the information indicating whether or not Sync PPDU transmission is supported may be included in an element indicating the station's capabilities. For convenience of explanation, the element indicating the station's capabilities is called a Capability element. In addition, a field of information indicating whether or not Sync PPDU transmission is supported in the Capability element is called a Supporting Sync PPDU Tx subfield. In this case, the Capability element may be a Multi-Link element that indicates capabilities related to multi-link. In addition, the Capability element may be an EHT Capability element that indicates EHT-related capabilities. An example of a Capability element is shown in FIG. 31(a).

[0238] If the value of the Supporting Sync PPDU Tx subfield is 1, the Supporting Sync PPDU Tx may indicate that the station or multilink device indicated by the Supporting Sync PPDU Tx subfield supports the transmission of the sync PPDU. If the value of the Supporting Sync PPDU Tx subfield is 0, the Supporting Sync PPDU Tx may indicate that the station or multilink device indicated by the Supporting Sync PPDU Tx subfield does not support the transmission of the sync PPDU. In addition, if a station not included in the multilink device transmits a Capability element, the Supporting Sync PPDU Tx subfield may signal information that is not related to the presence or absence of support for sync PPDU transmission or may be used as a reserved field.

[0239] As described above, the information indicating whether or not the sync PPDU reception is supported may be included in an element indicating operation-related information of a station. For convenience of explanation, the element indicating operation-related information of a station is referred to as an Operation element. In addition, a field of information indicating whether or not the sync PPDU reception is supported in the Operation element is referred to as a Supporting Sync PPDU Rx Disable subfield. FIG. 31(b) shows an example of an Operation element. When the value of the Supporting Sync PPDU Rx Disabled subfield is 1, it may indicate that the station does not want to receive the sync PPDU. Specifically, when the value of the Supporting Sync PPDU Rx Disabled subfield is 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 the reception of the sync PPDU. In a multilink device that sets the value of the Supporting Sync PPDU Rx Disabled subfield to 1, the second station of the multilink device may not perform PD and CCA while the first station of the multilink device is receiving. An AP multilink device connected to a multilink device that has transmitted the Supporting Sync PPDU Rx Disabled subfield may not transmit PPDUs simultaneously to multiple stations of the multilink device that has transmitted the Supporting Sync PPDU Rx Disabled subfield. The PPDU may be a SU PPDU, a Full BW MU PPDU, or an 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 may not transmit a frame requesting a response, for example, 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] Also, the Operation element may include information related to the minimum length of a sync PPDU that can be received by the station or multilink device that transmitted the Operation element. In this case, a subfield indicating information related to the minimum length of a sync PPDU is called a Remaining TXOP Threshold subfield. The Remaining TXOP Threshold subfield may indicate time. Also, the Remaining TXOP Threshold subfield may indicate in us, ms, or symbol units. A multilink device connected to a 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] Also, when 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 a Sync PPDU. 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 in the Operation element.

[0242] Also, in the above 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 may be signaled by an element other than the Operation element or by signaling information. In Figures 32 to 34, an embodiment in which the inter-link TXOP power save mode is performed by the signaling described in Figure 31 will be described.

[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 of the non-STR multilink device may enter a power saving state while a first station of the non-STR multilink device is performing reception. In this case, the second station may maintain the power saving state until the end of the TXOP indicated by the PPDU received by the first station. As described above, the second station may be in a state where the time at which the second station predicts reception of a frame periodically transmitted from the AP is before the end of the TXOP indicated by the PPDU received by the first station. In this case, the second station may wake up from the power saving state before the end of the TXOP indicated by the PPDU received by the first station. As described above, the frame periodically transmitted from the AP may include at least one of a beacon frame, a TIM frame, and a DTIM frame.

[0245] The second station can maintain the power saving state even after the end of the TXOP indicated by the PPDU received by the first station. Specifically, the second station can determine whether to maintain the 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. At this time, 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. When the NAV set by the second AP of the AP multilink device performing transmission to the second station of the non-AP multilink device has not expired, the first AP of the AP multilink device can transmit information on the expected end time of the transmission or reception of the first AP and the expected expiration time of the NAV to the first station of the non-AP multilink device that signaled that it does not want to receive the sync PPDU. If the NAV set by the second AP of the AP multilink device performing transmission 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 performing transmission 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 FIG. 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 a first link (Link1) and a second station (STA2) operating on a second link (Link2). The non-STR non-AP multilink device signals that it does not want to receive a sync PPDU. The first AP (AP1) transmits to the first station (STA1). The second station (STA2) then maintains a power saving state until the end of the TXOP indicated by the PPDU transmitted by the first AP (AP1) to the first station (STA1).

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

[0248] A first station of the non-STR multilink device can enter a power saving state of an inter-link TXOP when the remaining duration of a TXOP indicated by a PPDU being received by the first station of the non-STR multilink device is equal to or shorter than the length indicated by the Remaining TXOP Threshold subfield transmitted by the non-STR multilink device. At this time, before entering the power saving state, a second station can receive a sync PPDU transmitted to the second station when the remaining duration of a TXOP indicated by a PPDU being received by the first station is greater than the length indicated by the Remaining TXOP Threshold subfield transmitted by the non-STR multilink device. At this time, the second station can receive the sync PPDU. To this end, 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 by 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 FIG. 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 that it wishes 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. When 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 saving 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] When a station of a non-STR multilink device detects a PPDU other than a Sync PPDU from a BSS operated by an AP connected to the station of the non-STR multilink device while waiting to receive a Sync PPDU, the station of the non-STR multilink device can enter an 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. In addition, when a station detects a PPDU other than a Sync PPDU from a BSS operated by an AP connected to the station of the non-STR multilink device even if the minimum TXOP signaled by the station remains, the station of the non-STR multilink device can enter an 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 that it wishes 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 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 in consideration of the fact that the second station of the non-STR multilink device is in a blind state due to transmission by the first station of the non-STR multilink device. Specifically, when the multilink device determines that the station of the non-STR multilink device is in a blind state, the multilink device may suspend transmission to the station of the non-STR multilink device. In addition, the station of the non-STR multilink device may enter a doze state based on the operation, e.g., transmission and reception, of other stations of the non-STR multilink device. This can solve problems that may occur when the operation of one station of the non-STR multilink device restricts the operation of other stations.

[0255] As described above, in the non-STR multilink device, due to interference within the device, separate stations included in the non-STR multilink device cannot receive and transmit simultaneously. In addition, due to restrictions on the hardware configuration of the non-STR multilink device, separate stations included in the non-STR multilink device cannot receive and transmit simultaneously. Specifically, when a first station of the non-STR multilink device transmits or receives, a second station of the non-STR multilink device may be restricted from using the transceiver. For example, the non-STR multilink device can only support one PPDU processing. In this case, when a first station of the non-STR multilink device transmits or receives, a second station of the non-STR multilink device cannot transmit or receive. A multilink device that includes multiple stations each operating on multiple links or does not support multiple stations transmitting or receiving simultaneously is called a single-radio multilink device. Therefore, when any one station of the single-radio multilink device transmits or receives, the other stations of the single-radio multilink device cannot transmit or receive. The operation of the multilink device as a single-radio multilink device may be subject to hardware restrictions or operation mode definitions as described above. Therefore, in this specification, the single radio multilink device may refer to a multilink device in which the operation of a station is restricted by a hardware constraint, as well as a multilink device in which the operation of a station is restricted by a definition of an operation mode. Therefore, the single radio multilink device in this specification may include a multilink device that supports multiple stations of the multilink device to transmit or receive simultaneously, but does not support multiple stations of the multilink device to transmit or receive simultaneously under a specific condition. In this case, the specific condition may include a specific time point.

[0256] Specifically, the 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 only through a single link among the multiple links during a specific time period. At this time, 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 only through a single station among the multiple stations during a specific time period. At this time, the specific time period may include a time during which the multilink device exchanges frames through any one of the links. Specifically, the specific time period may be from when the multilink device receives an initial control frame that initiates frame exchange through any one of the links to the end of the frame exchange. When the multilink device uses a single radio with a single link during a specific time period of a specific mode, the specific mode may be called an enhanced multi-link single radio (EMLSR) mode. While the multilink device exchanges frames on the first link of the EMLSR link, which is a plurality of links to which the EMLSR mode is applied, the multilink device does not transmit or receive on the second link of the EMLSR link. In addition, when a part of the RF chain used by a particular station of the multilink device is used by another station of the multilink device to transmit or receive during a particular time period of the particular mode, the particular mode is called an EMLMR (enhanced multi-link multi-radio) mode. Specifically, when any one station of the multilink device transmits or receives using all of the RF chains of another station of 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. In addition, even if the multilink device operates in the EMLSR mode, some of the links on which the multilink device operates can operate without restrictions due to the EMLSR mode.When the multilink device operates in the EMLSR mode, the links to which the EMLSR mode is applied may be a part of the links on which the multilink device operates. For example, when the multilink device operates in the first to third links, the EMLSR mode or the EMLMR mode may be applied only to the first and second links. Therefore, when the multilink device transmits or receives in the first link during a specific time period in the EMSLR mode, the multilink device cannot transmit or receive in the second link. At this time, the multilink device can transmit or receive in the third link without any restriction due to the EMLSR mode. For convenience of explanation, a link to which the EMLSR mode can be applied, such as the first and second links, is called an EMLSR link, and a link to which the EMLMR mode can be applied is called an EMLMR link. Transmitting or receiving using the RF chain of a specific station in the EMLSR mode and the EMLMR mode results in a change in the transmission, reception, or monitoring capability of the link on which the specific station operates. Therefore, embodiments of the present invention that are applied in relation to the EMLSR mode in the following description may be equally applied in relation to the EMLMR mode, unless otherwise stated.

[0257] The above-mentioned embodiment regarding the operation of the non-STR multilink device can also be applied to the operation of the single radio multilink device. Also, the above-mentioned embodiment regarding the operation of the station that transmits and receives with the station of the non-STR multilink can also be applied to the operation of the station that transmits and receives with the station of the single radio multilink device. For example, when the station determines that the transmission to the single radio multilink device in the first link has failed due to the transmission or reception of the single radio multilink device in the second link, the station does not need to increase the CW of the channel access performed in the first link. Specifically, the station can apply the embodiment described in FIG. 14. In this case, the method of determining that the station has failed to transmit to the single radio multilink device in the first link due to the transmission or reception of the single radio multilink device in the second link can be similar to the method of determining whether the station has failed to transmit to the non-STR multilink station due to the operation restriction of the non-STR multilink device.

[0258] FIG. 35 illustrates 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 refers generally to the digital processors in the physical layer, including the processors that encode and decode the PPDU, and the PHY front-end refers generally to the analog baseband circuitry, including the RF chain.

[0260] The multiple stations of the single radio multilink device operate on different links. The multiple stations may share a PHY backend. In this case, when any one station transmits a PPDU, the PHY backend is used for encoding the PPDU. Therefore, the remaining stations of the multiple stations cannot use the PHY backend. Thus, the single radio multilink device includes multiple stations operating on different links, but can only transmit or receive on one link at a time.

[0261] However, the single radio multilink device can perform channel access in multiple links. Specifically, the single radio multilink device can perform monitoring in multiple links. Thus, the single radio multilink device can perform channel access in multiple links. At this time, the monitoring can include channel sensing. Also, the 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 performed in the first link, a second station of the single radio multilink device can perform a backoff procedure in the second link. In these embodiments, the single radio multilink device may be a multilink device operating in an EMLSR mode as described above.

[0262] To support such an embodiment, the PHY front-end of the single radio multi-link device may support channel monitoring independent of the PHY back-end. Also, the PHY front-end of the single radio multi-link device may support decoding of the preamble of the PPDU for PD independent of the PHY back-end. Also, the PHY front-end of the single radio multi-link device may support reception of frames transmitted by a low MCS independent of the PHY back-end. At this time, the frames transmitted by a low MCS may include at least one of an RTS frame and an MU-RTS frame. Therefore, the PHY front-end may include a MAC processor. Also, according to such an embodiment, the processing power of the PHY back-end may be intensively utilized for encoding and decoding of data frames.

[0263] In the embodiment of FIG. 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 above embodiment, each of the first non-AP station (Non-AP STA1) and the second non-AP station (Non-AP STA2) independently accesses a channel using a PHY front end.

[0264] The single radio multilink device can use the RF chain of a station that does not participate in transmission or reception for MIMO transmission. Specifically, when a first station of the single radio multilink device has a channel access opportunity, the first station can perform MIMO transmission using the RF chain used by the second station of the single radio multilink device in addition to the RF chain used by the first station. This will be described in FIG. 36.

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

[0266] In the embodiment of Fig. 36, a first station STA1 of the single radio multi-link device operates on a first link Link1, and a second station STA2 of the single radio multi-link device operates on a 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. When 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 and channel access in the second link. Also, when an RF chain changed to operate in the first link while operating in the second link operates in the second link again, the single radio multilink device can perform channel access in the second link after waiting for a pre-specified 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 and 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 pre-specified time. At this time, the channel access of the single radio multilink device in the second link may be restricted for a pre-specified 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 pre-specified time from the completion of the RF change. At this time, the channel access may include a back-off procedure. Also, the pre-specified time may be a pre-specified time that is applied when a restriction on channel access is necessary 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 cannot detect transmission of another wireless communication terminal performed on the second link due to a period during which channel monitoring was not possible. Also, when the link on which the RF chain operates is changed, a delay time for the RF chain to start operating may be necessary. Therefore, the single radio multilink device may perform channel access taking into account the delay time of 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 a change of an RF chain. Also, a change of a link may refer to a change of 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 a change of an RF chain.

[0268] When the multilink device operates in the above-mentioned 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. In this manner, the above-mentioned 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 the station to which the mode conversion is applied among the stations of the multilink device 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 released when a frame capable of setting the NAV is received. The pre-specified time may be a time indicated by the NAVSyncDelay parameter. In these embodiments, even before the pre-specified time has elapsed from the time when the link switching is completed, i.e., the time when the monitoring capability is restored, the station can transmit a control frame for setting the NAV to start frame exchange. The control frame that sets the NAV may be an RTS frame and / or a MU-RTS frame. In the following description, link switching may include losing and then recovering all or part of the transmission, reception or monitoring capabilities of the link.

[0269] At this time, when the transmission, reception or monitoring capability of a link to which the EMLSR mode or the EMLMR mode is applied is changed, this may include a case where 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 performs CCA.

[0271] A station that communicates with the single radio multilink device using MIMO may be a station of the multilink device. Specifically, a station that communicates with the single radio multilink device using MIMO may be an AP included in the multilink device. Unless otherwise specified in this specification, a station that communicates with the 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. Also, what is described in this specification as the operation of a station of the multilink device may represent the operation of the multilink device.

[0272] FIG. 37 illustrates 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 changing an RF chain.

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

[0274] In the embodiment of FIG. 37, the first station STA1 of the single radio multilink device operates in the first link Link1, and the second station STA2 of the single radio multilink device operates in the second link Link2. The first station STA1 performs channel access in the first link Link1, and the second station STA2 performs channel access in the second link Link2. When the first station STA1 succeeds in channel access in the first link Link1, the first station STA1 performs 2x2 MIMO transmission in the first link Link1 using the RF chain used in channel access in the first link Link1 and the RF chain used in channel access in the second link Link2 by the second station STA2. In the embodiment of FIG. 37(a), the single radio multilink device changes the RF chain to a time earlier than the time when the channel access is expected to be successful (Expected Tx time) by the delay time of RF chain change (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 start exchanging the RTS frame / CTS frame. 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 the CTS-to-Self frame. With this embodiment, the single radio multilink device can obtain the time it takes to complete the RF chain change. Also, unlike the above-mentioned embodiment, this embodiment does not cause a problem even if the channel access is not successful at the predicted time.

[0276] In the example of FIG. 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] As described in Figures 36 and 37, the single radio multilink device can transmit or receive by changing the RF chain. Also, the single radio multilink device can transmit or receive without changing the RF chain. The single radio multilink device can select whether to change the RF chain.

[0279] The single-radio multilink device may indicate in the MIMO Rx support subfield of the Operation element whether the RF chain of the other link is also used when performing MIMO communication in the link. For example, when the 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 the 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 that performs 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] In addition, the single-radio multilink device can signal the time required for RF chain switching in 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 that performs 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 that performs 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 the single radio multilink device transmits or receives on the first link, a station attempting to transmit to the single radio multilink device may not be allowed 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 transmitting or receiving on the first link. Specifically, a station attempting to transmit to the single radio multilink device may not be allowed to transmit on a link other than the first link until a certain time has elapsed since the single radio multilink device completed the frame exchange sequence, in addition to during the frame exchange on the first link. 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. At this time, the frame exchange sequence may be performed on a link capable of using a plurality of 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 the multi-link device is activated, transmission and reception are possible only in a specific link among a plurality of links to which the EMLSR mode of the multi-link device is applied in a specific time period. Also, when the EMLMR mode of the multi-link device is activated, transmission and reception are possible only in a specific link among a plurality of links to which the EMLMR mode of the multi-link device is applied in a specific time period. Also, 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 for recovering the monitoring capability of 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 reconfiguration of the RF chain is for recovering the monitoring or transmission and reception capability of a link to which the EMLMR mode or EMLSR mode is applied. Therefore, among the stations of the multilink device, a station that attempts to transmit to a station operating on a link where the transmission, reception or monitoring capability is restored, for example, where frame exchange is not performed in the EMLSR mode, cannot start frame exchange with the multilink device on the EMLMR link or the EMLSR link for a pre-specified time from the point in time when the transmission, reception or monitoring capability of the link is re-established. At this time, the EMLMR link or the EMLSR link may be limited to link switching, for example, a link where the RF chain is re-established. At this time, the pre-specified time may be a delay time for link switching. At this time, link switching may represent an operation for recovering the monitoring capability on a link that has lost the monitoring capability. Specifically, the pre-specified time may be set based on the time required for link switching, for example, changing the RF chain. For this operation, it is necessary for a station that exchanges frames with the multilink device or the multilink device to be able to determine the link switching time.As described above, a station or a multilink device can determine the end time of the EMLMR mode or the EMLSR mode, but for convenience of explanation, the following description of the embodiment of the end time determination method will be mainly based on the station. For convenience of explanation, the EMLMR mode and the EMLSR mode will be collectively referred to as the EML mode. Also, the EMLMR link and the EMLSR link will be collectively referred to as the EML link.

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

[0284] The frame exchange end point may be the time when the frame exchange is completed in the EML mode. In yet another specific embodiment, the frame exchange end point may be the time when the TXOP set to protect the frame exchange in the EMLMR mode or the EMLSR mode is ended.

[0285] Therefore, the station can determine the end of the TXOP set for the frame exchanged when the EML mode is applied as the end of the frame exchange. In this case, the end of the TXOP must invoke a new backoff procedure before the TXOP is completed, and may include the end of the TXOP. If none of the TXOP holder and the TOXP responder can occupy the channel during (aSIFSTime+aSlotTime) in the TXOP, the new backoff procedure must be initiated. aSIFSTime represents SIFS defined in 802.11, i.e., 16us, and aSlotTime represents the unit time for channel sensing in EDCA and DCF, i.e., 9us. In the following description, aSIFSTime and aSlotTime are used in this sense unless otherwise specified. Specifically, the station can determine the end of the frame exchange when the period indicated by the Duration / ID field of the frame transmitted on the EML link in the EML mode has elapsed.

[0286] Also, the station may determine the frame exchange end time when the link is detected as idle for a certain period of time after transmitting a response frame to the multilink device through the EML link where frame exchange is performed in the EML mode. The station may receive a frame that does not request an immediate response frame from the multilink device. At this time, the station does not transmit a response frame. Thus, the station may determine the frame exchange end time when the link is detected as idle for a certain period of time after receiving a frame that does not request a response frame from the multilink device through the EML link where frame exchange is performed in the EML mode. Also, when the station receives a frame that requests a response frame, the station may determine the frame exchange end time when the link is detected as idle for a certain period of time after transmitting a response frame to the multilink device through the EML link where frame exchange is performed in the EML mode. In these embodiments, the certain period of time may be PIFS+aRXPHYStartDelay. PIFS may be aSIFSTime+aSlotTime. Also, aRXPHYStartDelay may be a delay time related to the time it takes for the MAC to recognize the fact after the PHY starts the Rx operation. In this case, the station may determine that the time when the response frame is transmitted is the time when the PHY-TXEND.confirm primitive for the responded frame is generated. Also, the time when the station receives a frame that does not request a response frame may be the time when the PHY-RXEND.indication primitive is generated. These embodiments consider the case where the condition that the TXOP holder can transmit consecutive frames in the TXOP is not satisfied in the conventional WLAN. That is, it is an embodiment in which the frame exchange is determined to be terminated when the TXOP holder fails to transmit and must try the 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 EML mode multilink device must successfully receive the Trigger frame or TRS Control field included in the PPDU to perform an Ack response. If the EML mode multilink device 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 if the station does not retransmit the 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 required time of the multilink device to which the EML mode is applied from the TXOP time set to protect the frame 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 required time of the multilink device to which the EML mode is applied from the TXOP time set to protect the frame exchanged in the EML mode.

[0289] Also, the station may determine that the frame exchange end time is when it receives a CF-End frame on an EML link where frame exchange is performed in the EML mode. At this time, 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 the CF-End frame aSIFSTime before the time when it received the CF-End frame is the frame exchange end time. At this time, 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 that is 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 transmission, reception, or monitoring capabilities in EML mode, for example, links where frame exchange has not occurred in EMLSR mode. That is, the transmission restriction due to link switching may not be applied to links that have not lost transmission, reception, or monitoring capabilities in EML mode, for example, links where frame exchange has occurred in EMLSR mode. For example, when EML links are a first link and a second link, frame exchange occurs in the first link in EML mode, and frame exchange ends in the first link, the transmission restriction may be applied only to the second link. 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 has performed link switching must restore monitoring for a link that has lost transmission, reception, or monitoring capability in EML mode within a pre-specified time from the end of frame exchange, for example, a link for which frame exchange has not been performed in EMLSR mode. Also, a station, for example, an AP of an AP multilink device, can start frame exchange for a multilink device to which EML mode is applied, for a link that has lost transmission, reception, or monitoring capability in EML mode, for example, an EML link for which frame exchange has not been performed in EMLSR mode, after a pre-specified 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 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 a link where transmission and reception have been restricted by link switching.

[0294] In addition, in a frame exchange sequence immediately after changing the RF chain, a station that is going to transmit to the single radio multilink device can determine the format of the 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. In addition, in the first frame exchange sequence that starts after changing the RF chain, a station that is going to transmit to the single radio multilink device can determine the length of padding used for the PPDU transmission 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. At this time, the padding may be either padding of the physical layer or padding of the MAC layer. Specifically, the station can set the padding of a packet to be transmitted to the single radio multilink device, which takes a relatively short time to change the RF chain, to be shorter than the padding of a packet to be transmitted to the single radio multilink device, which 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 a control frame transmitted first in frame exchange in the EMLSR mode. At this time, the padding length 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 length of padding corresponding to a time equal to or greater than the difference between the required time for link switching and (2x SIFS+CTS_time). At this time, CTS_time indicates the time (air time) taken 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 length of padding corresponding to the link switching time minus (2x 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 length of padding corresponding to a time equal to or greater 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 greater than the length of padding corresponding to the link switching time minus the 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-mentioned 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 padding of the initial control frame is being transmitted.

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

[0299] A station that is going to perform MIMO transmission to a single radio multilink device can start exchanging RTS frames / CTS frames at the start of transmission after changing the RF chain. At this time, the RTS frame can secure time for the RF chain to change and then protect the frame exchange. If it is determined that the RF chain change is not completed even after exchanging the RTS frames / CTS frames, the station that is going to perform MIMO transmission to a single radio multilink device does not need to perform MIMO transmission. At this time, the station that is going to perform MIMO transmission to a single radio multilink device can perform transmission using a single spatial stream.

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

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

[0302] In addition, when a transmission to another station of the single-radio multilink device fails due to transmission or reception of any one station of the single-radio multilink device, the station that transmitted to the other station of the single-radio multilink device does not need to increase the Retry counter. In this case, the Retry counter may include at least one of a Long retry counter and a Short retry counter.

[0303] Also, when a station transmits an MU PPDU to multiple stations including a station of a single radio multilink device, the above-described embodiment regarding maintaining the size of the CW may not be applied. Specifically, when a station transmits an MU PPDU to multiple stations including a station of a single radio multilink device but fails to receive a response from any of the multiple 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 value of the CW to the next largest value among the values ​​that the CW value can have. When the value of the CW is the maximum value, the station that transmitted the MU PPDU may maintain the same value of the CW.

[0304] In the embodiment of FIG. 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 the first station STA1 attempts to transmit using MIMO, the station succeeds in channel access 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 of the single radio multilink device is completed and the PPDU is received using 2x2MIMO. After the first station STA1 receives the PPDU, the single radio multilink device changes the RF chain, and the second station STA2 waits for NAVSyncdelay from the time of changing the RF chain and then starts channel access on the second link Link2.

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

[0306] As described above, the single radio multi-link device can perform MIMO by changing the link in which the RF chain operates. When the link in which the RF chain operates is changed, it is necessary to learn the RF characteristics of the changed link before MIMO communication.

[0307] Since the channel characteristics of the RF chain have not been learned, closed-loop multiple antenna technology (beamforming) may not be available. Therefore, channel estimation may be required. Specifically, a single radio multilink device may 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). At this time, the interval between the NDPA and the NDP is SIFS. When a station receives an NDPA, if the STA User Info list field of the NDPA indicates a station, the station receives the NDP and then transmits channel state information (CSI) feedback measured when receiving the NDP to the beamformer.

[0308] At this time, an RTS frame / CTS frame exchange may be performed before the NDP sounding protocol is performed. Specifically, a station that is to start the NDP sounding protocol with a single radio multilink device may transmit an RTS frame before transmitting an NDP frame. For convenience of explanation, a station that is to start the NDP sounding protocol with a single radio multilink device is called an NDP sounding protocol initiation station. According to the above-described embodiment, the NDP sounding protocol initiation station can protect the NDP sounding sequence. This also allows time required for changing the RF chain to be secured. Also, the NDP sounding protocol initiation station can perform an MU-RTS frame / CTS frame exchange procedure instead of an RTS frame / CTS frame exchange procedure. Also, the NDP sounding protocol initiation station can exchange a trigger frame of a type different from the MU-RTS frame and a response to the trigger frame instead of an MU-RTS frame / CTS frame exchange procedure. In addition, in such an embodiment, the NDP sounding protocol initiating station can transmit the MU-RTS frame, the trigger frame of a type different from the MU-RTS frame, and the NDPA frame 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. In addition, the NDP sounding protocol initiating station can transmit the MU-RTS frame, the trigger frame of a type different from the MU-RTS frame, and the NDPA frame at a pre-specified data rate or lower.

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

[0310] In addition, when the NDP sounding protocol initiation station performs the NDP sounding protocol with multiple single-radio multilink devices, the NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence based on the longest time required 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 illustrates 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 initiation station can adjust the length of the NDP sounding sequence by adjusting the padding of frames exchanged in the NDP sounding sequence. When the NDP sounding sequence includes an RTS frame / CT frame exchange, the NDP sounding protocol initiation station can adjust the length of the NDP sounding sequence by inserting padding into the RTS frame. Specifically, when the NDP sounding protocol initiation station determines that the RF chain change is not completed even after the RTS frame / CTS frame exchange, the NDP sounding protocol initiation 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 embodiment, the NDP sounding protocol initiating station can determine whether the RF chain change is completed even after the RTS frame / CTS frame exchange based on whether the RF chain change is not completed after the time of the RTS frame reception completion time of the single radio multilink device plus 2 x SIFS has elapsed. Also, the RTS reception completion time may be one of the start time of the transmission of the PPDU including the RTS frame, the time of the physical layer header of the PPDU including the RTS frame, the completion time of the transmission of the PPDU including the RTS frame, and the completion time of the transmission of the RTS frame or the A-MPDU including the RTS frame. Also, in the above embodiment in which the MU-RTS frame is used instead of the RTS frame, the MU-RTS frame may be applied instead of the RTS frame. FIG. 40(a) shows that the NDPA frame, the NDP frame, and the feedback frame are exchanged after the RTS frame / CTS frame exchange according to the above embodiment. At this time, the NDP sounding protocol initiating station performs MIMO transmission based on the received feedback frame.

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

[0316] In the above 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. Also, excessive overhead may occur even if the NDPA transmission is omitted. In order to reduce the excessive overhead, an implicit feedback beamforming sounding sequence may be performed. This will be 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 not only an NDPA frame transmission but also an NDP frame transmission and a feedback frame transmission. In this case, 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, and a response to a trigger frame of a type different from the MU-RTS frame. The frame exchange initiating station may obtain a steering matrix to be used for MIMO transmission based on the measured channel state. Specifically, the frame exchange initiating station may obtain a steering matrix based on the measured channel state. The frame exchange initiating station may perform MIMO transmission using the obtained 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] Also, 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] Also, 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 including an MU-RTS frame, and the frame exchange initiating station measures a channel state while receiving a PPDU including 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 state, 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. After that, 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 in SISO (single input single output).

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

[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 for changing the RF chain of the single radio multilink device. Specifically, the NDP sounding protocol initiating station can delay the MIMO transmission start time to the time when the RF chain change of the single radio multilink device is completed. For example, if the RF chain change is not completed during the exchange of a response frame to the control frame / control frame, for example, 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 manner, 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 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 is completed during the exchange of a control frame / response frame to the control frame based on the time it takes 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 in the frame exchange sequence using SISO. For convenience of explanation, in the explanation 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 called a frame exchange sequence execution station. That is, when a single radio multilink device transmits using SISO, the frame exchange sequence execution station may not be allowed to transmit the remaining frames in the frame exchange sequence using MIMO. Specifically, when a single radio multilink device transmits an ACK for the transmission of the frame exchange sequence execution station using SISO, the frame exchange sequence execution station can transmit the remaining frames in the frame exchange sequence using SISO. At this time, the ACK can include an ACK frame and a BA frame. Therefore, when a single radio multilink device transmits an ACK for the transmission of the frame exchange sequence execution station using SISO, the frame exchange sequence execution station cannot transmit the remaining frames in the frame exchange sequence using MIMO.

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

[0331] In the embodiment of FIG. 42(b), SISO is also used until PPDU transmission after RTS frame and CTS frame exchange. Since RF chain change is completed after PPDU reception, the first station STA1 of the single radio multilink device transmits a BA frame using MIMO (2x2). Since 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, the NDP sounding protocol initiating station transmits a PPDU using MIMO (2x2) after receiving a BA frame transmitted using MIMO (2x2).

[0332] Despite the increase in transmission speed of WLAN, transmission delay is still a problem for some services. In particular, WLAN operated in unlicensed bands is inconvenient for operating services that require low-latency transmission because it is difficult to predict the time required for traffic transmission. EDCA has been introduced to solve this problem. A station supporting EDCA is called a QoS station, an AP supporting EDCA is called a QoS AP, and a BSS supporting EDCA is called a QoS BSS. For convenience of explanation, a QoS AP is called an AP, a QoS station is called a station, and a QoS BSS is called a BSS. In EDCA, traffic is classified into four access categories (ACs) according to characteristics. In this case, the four ACs are AC_VO (AC Voice), AC_VI (AC Video), AC_BE (AC Best effort), and AC_BK (AC Background). In the above-mentioned backoff procedure, the AC determines the value of a parameter related to CW. The AC may also determine the maximum value of TXOP. The AC may also determine the value of an 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 vulnerable to transmission delays, but does not have a large absolute amount of traffic like voice traffic, and is mapped with relatively small CW and AIFSN parameter values. However, the maximum TXOP value of AC_VO has a relatively smaller value than the maximum TXOP value 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 process a large amount 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 about 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 into AC_BE. The CW and AIFSN parameters of AC_BE are mapped with values ​​larger than the CW and AIFSN parameters of AC_VO and the CW and AIFSN parameters of AC_VI. Also, no other TXOP maximum value is mapped to AC_BE. Transmission using consecutive transmission sequences is not permitted 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 greater than the AIFSN parameter of AC_BE. Also, no other TXOP maximum value is mapped to AC_BK. Transmission using consecutive transmission sequences is not permitted 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 on the wire or the TID of the MSDU specified 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 can correspond one-to-one 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 CW parameters (CWmin, CWmax), AIFSN parameters, and TXOP max for an AC 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 that corresponds to the AC of the traffic. 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 apply HCF controlled channel access (HCCA) for QoS management. HCCA provides a centralized / hybrid coordinator function to guarantee TS (Traffic Stream) QoS for applications that must be serviced periodically (such as voice and video). Other functions such as Service Period Channel Access (SPCA) and dynamic allocation of service period may also be used. However, this is only available for DMG stations.

[0339] A method for enhancing QoS for a multilink device may be needed. Separate transmit queues may be used for each link of the multilink device. In this case, the queues may be logically independent. When traffic is mapped to each link, the QoS of the traffic may 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 FIG. 44, the AP multi-link device (AP MLD) includes the first AP (AP1) to the fourth AP (AP4). Also, the non-AP multi-link device (Non-AP MLD) includes the first station (non-AP STA1) to the fourth station (non-AP STA4). The first station (non-AP STA1) to the fourth station (non-AP STA4) operate on the first link (Link1) to the fourth link (Link1), respectively. The first AP (AP1) to the fourth AP (AP4) operate on the first link (Link1) to the fourth link (Link1), respectively. At this time, traffic is mapped to each of the first AP (AP1) to 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 an 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. In addition, the performance and operating bandwidth of each station may differ. Therefore, the bandwidth and MCS of the PPDU containing the traffic may change depending on which traffic the multilink device maps to which link.

[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 an operating channel of 40 MHz. If the fourth AP (AP4) operates in the 6 GHz band, the fourth AP (AP4) can operate an operating channel of up to 320 MHz. The AP multilink device (AP MLD) can map traffic that requires a large amount of processing 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 characteristics of the traffic. This can enhance the QoS of traffic transmission.

[0343] In order to finely subdivide the QoS reinforcement, a TID may be mapped to each link, and each link may prioritize transmission of traffic corresponding to the TID mapped to that link. This will be described with reference to FIG.

[0344] FIG. 45 shows a multi-link device exchanging frames by TID link mapping according to an embodiment of the present invention.

[0345] Traffic transmitted in 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 contained in the MAC frame. In this case, the QoS control field may include a TID service field. The TID identifies the traffic contained in the MSDU or fragment or A-MSDU of the MAC frame. The TID corresponds to UP (user priorities) or TSID (traffic stream identifier). The TID service field is a total of 4-bit field and can indicate values ​​from 0 to 15. If the value of the TID subfield is any one of 0 to 7, the value of the TID subfield indicates the UP of the MSDU contained in the frame body of the MAC frame including the TID subfield. The MAC frame is processed by the MAC entity using an AC parameter corresponding to UP according to EDCA. If the value of the TID subfield is any one of 8 to 15, the value of the TID subfield indicates the TSID of the MSDU contained in the frame body of the MAC frame including 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. If the 7th and 8th bits of the Access Policy subfield are set to 10, the UP of the TSID may be indicated in the User Priority field of the TCLAS. b 11 indicates EDCA if b If so, indicate HCCA.

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

[0347] A TID may be mapped to each of a plurality of links on which a multilink device operates. At this time, the multilink device may signal information on the TID mapped to each link to a multilink device associated with the multilink device. At this time, 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, frame exchange may be performed 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, frame exchange may be performed on each link according to a default mapping between the TID and the link.

[0348] When a multilink device maps a TID to a link, the multilink device must map all TIDs to one or more links. In a specific embodiment, the multilink device transmits a frame including traffic corresponding to a TID mapped to the link through the link, and may not allow transmission of a frame including traffic corresponding to a TID not mapped to the link. 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, a TID mapped to an uplink and a TID mapped to a downlink in one link may be different. Thus, when a first multilink device and a second link device are connected through a first link and a second link, 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 ​​that are 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, the remaining TID values ​​other than TID values ​​0-3 may be mapped to the second link. In yet another specific embodiment, the second link may be allowed to transmit traffic corresponding to all TIDs.

[0351] Furthermore, the mapping between TIDs and links may be changed during operation other than when the multilink devices are first connected. When the multilink device disassociates a station of a specific link, the multilink device may change the mapping between TIDs and links. In this case, the multilink device may disassociate a station when the station of a specific link enters a power saving mode. Furthermore, the multilink device may request a change in the mapping between TIDs and links from the other multilink device. For example, when TID values ​​0 to 3 are mapped to the first link, the non-AP multilink device may request the AP multilink device to map TID values ​​0 to 3 to the second link. Specifically, when the multilink device has difficulty in guaranteeing the QoS of the traffic mapped to the link, the multilink device may request a change in the mapping between TIDs and links from the other multilink device.

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

[0353] A method for signaling mapping between TIDs and links will be described. A multilink device can signal mapping between TIDs and links using a TID-to-Link Mapping element. The TID-to-Link Mapping element may include a Link ID field. The Link ID field indicates a link that the TID-to-Link Mapping element signals. In addition, the TIDs Info field indicates information about a TID mapped to a link indicated by the Link ID field. The TIDs Info field may include a field indicating a value of a TID mapped to a link indicated by the Link ID field. In this case, the TIDs Info field may include a bitmap indicating a value of a TID mapped to a link indicated by the Link ID field. In this case, each bit of the bitmap is mapped to a specific TID, and when a bit is set to 1, it can indicate that a TID corresponding to the bit is mapped to a link indicated by the Link ID field.

[0354] In the embodiment of FIG. 45, the AP multilink device (AP MLD) plans to transmit traffic with TIDs 0 to 3 on the first link (Link1) among traffic to be transmitted to the non-AP multilink device (non-AP MLD). The AP multilink device (AP MLD) signals to the non-AP multilink device (non-AP MLD) that it will map TID values ​​0 to 3 to the first link (Link1) and TID values ​​4 to 7 to the second link (Link2) using the TID-to-Link Mapping element. The TID-to-Link Mapping element includes two Link ID fields indicating the first link and the second link, respectively, and includes two TIDs Info fields indicating information on the TIDs mapped to the first link and the information on the TIDs mapped to the second link, respectively. In addition, the TIDs Info fields may include 7 bits indicating TIDs 0 to 7, respectively. For example, 8 bits of the TIDs info subfield may be 11110000 to indicate TIDs 0 to 3. b and the 8 bits of the TIDs info subfield are set to 00001111 to indicate TIDs 4 through 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 each of the Min TID field and the Max TID field is 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 only signals for the TIDs mapped to the first link, and the TIDs mapped to the second link may be implicitly signaled. Specifically, since the TID-to-Link Mapping element explicitly signals that TIDs 0 through 7 are mapped to the first link, the TID-to-Link Mapping element can implicitly signal that the remaining TIDs are mapped to the second link.

[0356] A non-AP multilink device accepts the mapping between TIDs and links 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 by 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 by 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 applies when another mapping between TIDs and links is not configured. In the embodiment of Figure 46, the basic mapping between TIDs and links is that all TIDs and TSIDs are mapped to links.

[0360] In the above-mentioned EML mode, frame exchange is performed only on one of multiple links, so the QoS improvement effect 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 allowed 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 mapping request between TIDs and links, a counterpart multilink device may reject the mapping request between TIDs and links. In yet another specific embodiment, when a multilink device to which the EML mode is applied transmits a mapping request between TIDs and links, the counterpart multilink device may not transmit a response to the mapping request 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 may 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 TIDs and links may be applied to the EML links among the links in which the multilink device operates. In this case, basic mapping between TIDs and links may be performed without a separate negotiation.

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

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

[0366] In the embodiment of FIG. 47, the AP multilink device (AP MLD) includes (affiliates) a first AP (AP1) and a second AP (AP2), and the non-AP multilink device (STA MLD) includes a first station (STA1) and a second station (STA2). The first AP (AP1) and the first station (STA1) operate on 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 map 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 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 (Link1), and map TID values ​​0 to 7 to the second link (Link2). At this time, the non-AP multilink device (STA MLD) can transmit 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 described with reference to FIG. 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 the non-AP multilink device to activate the 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 the EMLSR mode. In this case, the AP multilink device and the non-AP multilink device can activate the EMLSR mode.

[0369] Using FIG. 49, a description will be given of the mapping setting between TIDs and links when the EML mode is activated and then deactivated.

[0370] FIG. 49 shows that the mapping between TIDs and links is changed when the multilink 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 renegotiate the mapping between TIDs and links.

[0372] In the embodiment of FIG. 49, the AP multilink device (AP MLD) includes a first AP (AP1) and a second AP (AP2), and the non-AP multilink device (STA MLD) includes a first station (STA1) and a second station (STA2). 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 in the first link (Link1), and the second AP (AP2) and the second station (STA2) operate in 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 the non-AP multilink device (STA MLD) map TID values ​​0 to 7 to the first link (Link1) and map TID values ​​0 to 7 to the second link (Link2). The EMLSR mode is deactivated in the non-AP multilink device (STA MLD). The AP multilink device (AP MLD) and the non-AP multilink device (STA MLD) apply the TID and link mapping applied before the EMLSR mode was activated to the first link (Link1) and the second link (Link2). That is, 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 map TID values ​​4 to 7 to the second link (Link2).

[0373] As described above, the AP multilink device may 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 a trigger frame of an MU-RTS frame or 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 may 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 may transmit a BSR frame as a response frame. Depending on the type of trigger frame, the type of response frame to the trigger frame may differ, and the time required to transmit the response frame may vary. Therefore, the non-AP multilink device may set the length of the initial control frame based on the type of the initial control frame. In this case, the padding may be for securing time for reconfiguring the RF chain, as described above.

[0374] When 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-CTStime-SIFS). When 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-BSRtime-SIFS). In this case, the BSRtime may be a time required for transmitting the BSR frame, for example, air time. Also, the BSRtime may be a value determined on the assumption 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 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 may 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 may determine the length of the padding of the BSRP trigger frame based on the value of the UL Length subfield of the Common Info field of the BSRP trigger frame.

[0375] As described above, the multilink device to which the EML mode is applied may signal the duration of the RF chain change. The AP multilink device may determine the length of padding in the initial control frame based on the signaled duration of the RF chain change. The AP multilink device may 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, the multilink device to which the EML mode is applied may 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 that signals 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 is signaled the padding length of the initial control frame, the AP multilink device may determine the padding length of the initial control frame according to the signaled padding length. Specifically, the AP multilink device may include padding of a length equal to or longer than the signaled padding length in the initial control frame. At this time, 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. At this time, when the AP multilink device transmits an initial control frame other than the MU-RTS frame, for example, a BSRP trigger frame, the AP multilink device may include padding of a length other than the signaled padding length in the initial control frame. The AP multilink device may 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 of a length equal to or longer than the signaled padding length plus the padding length corresponding to (CTStime - 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 time required 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 according to the back-calculated time required for RF chain change, because the signaled padding length is a value determined based on the time required for RF chain change.

[0379] The length of the padding mentioned above 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, due to link switching performed in the EML mode, some of the EML links may lose the transmission, reception or monitoring capability. In this case, the monitoring may include at least one of CCA and PD (preamble detection). In addition, even if the multilink device performs link switching to recover the transmission, reception or monitoring capability in a link, the multilink device may not be able to transmit, receive or monitor in the link for a pre-specified time from the link switching point. Specifically, the pre-specified time may be determined based on the required time for link switching of the multilink device in which the EML mode is activated. In a specific embodiment, the pre-specified time 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 in the EML link with a multilink device supporting the EML mode may manage TXOP in consideration of frame exchange of the multilink device in the EML mode. In addition, a multilink device supporting the EML mode may also manage TXOP in the EML link in consideration of frame exchange of 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, some of the EML links may lose the ability to transmit, receive, or monitor due to link switching performed in the EML mode. For example, when frame switching is performed in one of the EMLSR links in the EMLSR mode, the multilink device cannot transmit, receive, or monitor the remaining links of the EMLSR links. In this case, the monitoring may include at least one of CCA and PD (preamble detection). In addition, even if the multilink device performs link switching to recover the ability to transmit, receive, or monitor in a link, the multilink device may not be able to transmit, receive, or monitor in the link for a pre-specified time from the start of link switching. In this case, the pre-specified time may be a delay time for link switching. Specifically, the pre-specified time may include a time period during which the RF chain of the multilink device supporting the EML mode is changed. A station exchanging frames in the EML link with a multilink device supporting the EML mode can manage TXOPs in consideration of frame exchange of the multilink device in the EML mode. In addition, a multilink device supporting the EML mode can also manage TXOPs in the EML link in consideration of frame exchange of the multilink device in the EML mode.

[0383] When a multilink device in which the EML mode is activated needs to receive a specific frame in a first link that has lost the transmission, reception or monitoring capability of an EML link in the EML mode, for example, in which frame exchange is not performed in the EMLSR mode, the multilink device in the EML mode or a station exchanging frames with the multilink device in the EML mode can terminate a TXOP for the frame exchange in a second link, which is one of the EML links and in which frame exchange is performed, based on the time of receiving a specific frame in the first link. For convenience of explanation, a multilink device in which the EML mode is activated is referred to as a multilink device, and a station exchanging frames with a multilink device in which the EML mode is activated is referred to as a station. In this case, when the multilink device is a holder of a TXOP, the station is a TXOP responder. Also, when the multilink device is a responder of a TXOP, the station is a TXOP holder. In a state in which the EML mode is activated, the TXOP of the second link may be terminated earlier than a time that is a predetermined time from the time when the multilink device is about 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 a time required for changing the RF chain of the multi-link device. In a specific embodiment, the pre-specified time may be a 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. Also, the time when the specific frame is to be received may be the TBTT. The multi-link device or station may terminate the TXOP for frame exchange in the second link that has been performing frame exchange in the EML mode based on the time when the specific frame is received in the first link.Also, when the station is a TXOP holder, the station can terminate the TXOP in the second link based on the information indicating that the multilink device is going to receive a specific frame in the first link. At this time, the information indicating that the multilink device is going to receive a specific frame in the first link can be signaled in a manner agreed upon between the multilink device and the station. The information indicating that the multilink device is going to receive a specific frame in the first link can be information signaling that the beacon frame of the first link is a DTIM beacon frame. When the station is a TXOP holder and the beacon received in the first link is a DTIM beacon, the station can terminate the TXOP in the second link based on the information indicating that the multilink device is going to receive a specific frame in the first link.

[0384] Even if a multilink device to which the EML mode is applied 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 to which the EML mode is applied receives an initial control frame at a first link of the EML links, the multilink device may not transmit a response frame to the initial control frame in order to receive a specific frame at a second link of the EML links. For example, even if a multilink device to which the EML mode is applied receives an initial control frame at a first link of the EML links, if a frame exchange initiated by the initial control frame is not completed before a time earlier than a time that is a predetermined time from a time when a specific frame is to be received at a second link of the EML links, the multilink device may not transmit a response frame to the initial control frame at the first link. If a frame exchange initiated by the initial control frame is completed before a time earlier than a time that is a predetermined time from a time when a specific frame is to be received at a second link, the multilink device may transmit a response frame to the initial control frame at the first link. In these embodiments, the initial control frame may be an MU-RTS frame, an ML-RTS frame, or a BSRP trigger frame, as described above. Even if the initial control frame is an MU-RTS frame or an ML-RTS frame and a multilink device to which the 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 frame exchange. This is an exception to the requirement that a station must 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 the 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] The non-AP multi-link device with the EMLSR activated includes a first station (STA1) and a second station (STA2). The first station (STA1) operates on a first link (Link1), and the second station (STA2) operates on a second link (Link2). The first station (STA1) receives an RTS frame from the first AP on the first link (Link1) and transmits a CTS frame in response to the RTS frame. The first station (STA1) receives a PPDU from the first AP on the first link (Link1). At this time, the first AP terminates the TXOP at a time earlier than the time of receiving a beacon frame scheduled on the second link (Link2) by the time required for the RF change of the non-AP multi-link device. As described above, the termination of the TXOP at a time earlier than the time of receiving a beacon frame scheduled on the second link (Link2) by the time required for the RF change of the non-AP multi-link device may be applied in the same manner when the first station (STA1) acquires a TXOP.

[0386] When a multilink device in which the EMLSR mode is activated receives a beacon frame, the EMLSR multilink device does not need to change the RF chain because the beacon frame is not transmitted by MIMO. When a multilink device in which the EMLSR mode is activated receives a beacon frame on the first link, the multilink device in which the EMLSR mode is activated can perform at least one of monitoring and channel access on the second link. In this case, even if the multilink device completes a channel access procedure on 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 only at a pre-specified data rate on the second link. In this case, the pre-specified data rate may be any one of 6 Mbps, 12 Mbps, and 24 Mbps.

[0387] In addition, a station that is attempting to exchange frames with a multilink device activated in the EMLSR mode may not be permitted to start a frame exchange procedure on a second link that is one of the EMLSR links when the multilink device receives a specific frame on a first link that is one of the EMLSR links. A station that is attempting to exchange frames with a multilink device activated in the EMLSR mode may not be permitted to transmit an initial control frame on a second link that is one of the EMLSR links when the multilink device receives a specific frame on a first link that 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, etc. Also, although the method, apparatus and system of the present invention have been described in relation to a specific embodiment, some or all of the components and operations of the present invention can be embodied 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. The features, structures, effects, etc. exemplified in each embodiment can be combined or modified in other embodiments by a person having ordinary skill in the art to which the embodiment belongs. Therefore, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

[0390] The above description focuses on the embodiments, but these are merely illustrative and do not limit the present invention. Those skilled in the art will understand that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the present embodiment. For example, each component specifically illustrated in the embodiments can be modified. Furthermore, differences related to such modifications and applications should be interpreted as being included in the scope of the present invention as defined in the appended claims. [Explanation of symbols]

[0391] 100 Stations 110 Processor 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, the multi-link device being configured to, in an enhanced multi-link single radio (EMLSR) mode, perform frame exchange on a first link of the EMLSR link corresponding to a plurality of links to which the EMLSR mode is applied, while not performing transmission and reception on a second link of the EMLSR link, A transceiver unit, and A processor is included. 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 a frame exchange initiated by the initial control frame is not expected to be completed before a pre-specified time earlier than a time when 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 if a frame exchange initiated by the initial control frame is expected to be completed before a time earlier than the time that the multi-link device intends to receive the beacon frame on the second link by the pre-specified time; the predetermined time corresponds to a delay time for the multilink 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.

2. 2. The multi-link device according to claim 1, wherein the initial control frame is transmitted at a pre-specified data rate using a pre-specified format.

3. 2. The multi-link device of claim 1, wherein said predesignated time is signaled by said multi-link device.

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

5. An access point that includes a plurality of stations each operating on a plurality of links, and communicates with a multi-link device that does not transmit or receive on a second link of an enhanced multi-link single radio (EMLSR) link while exchanging frames on a first link of the EMLSR link corresponding to a plurality of links to which the EMLSR mode is applied, in an EMLSR mode, A transceiver unit, and A processor is included. 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 equal to or greater than the minimum length of padding; configured to transmit the initial control frame; if a frame exchange initiated by the initial control frame is not expected to be completed before a pre-specified time earlier than a time when 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 if a frame exchange initiated by the initial control frame is expected to be completed before a time earlier than the pre-specified time from a time at which the multi-link device intends to receive the beacon frame on the second link; the predetermined time corresponds to a delay time for the multilink 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, the access point.

6. The processor, 6. The access point of claim 5, configured to transmit the initial control frame at a pre-specified data rate using a pre-specified format.

7. 6. The access point of claim 5, wherein said predesignated time is signaled by said multilink device.

8. The access point according to claim 5 , wherein the EMLSR mode is applied to only a portion of the plurality of links on which the plurality of stations included in the multilink device operate.

9. A method for operating a multi-link device including a plurality of stations each operating on a plurality of links, the method being for, in an enhanced multi-link single radio (EMLSR) mode, not transmitting or receiving on a second link of an EMLSR link while exchanging frames on a first link of the EMLSR link corresponding to a plurality of links to which the EMLSR mode is applied, comprising: 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 pre-specified 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 that the multilink device intends to receive the beacon frame on the second link by the pre-specified time; the predetermined time corresponds to a delay time for the multilink 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.

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