Method and wireless communication terminal for transmitting and receiving frames in wireless communication system

Abstract

To provide a method for transmitting frames in a wireless communication system.SOLUTION: A non-AP STA receives a beacon frame including a request type field from an AP and can receive a downlink frame or transmit an uplink frame depending on the value of a specific field included in the beacon frame. At this time, the request type field includes a specific field for indicating a target wake time (TWT) for low latency operation, and when the value of the specific field is set to a first specific value, a broadcast TWT service period (SP) is a TWT SP for the low latency operation.SELECTED DRAWING: Figure 64

Description

[Technical Field]

[0001] The present invention relates to wireless communication systems, and more particularly to a communication method, apparatus and system for transmitting and receiving frames requiring low latency operation. [Background technology]

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

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

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

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

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

[0007] Additionally, development of new WLAN standards has begun to increase maximum transmission speeds to support new multimedia applications such as high-definition video and real-time gaming. IEEE 802.11be (Extremely High Throughput, EHT), the seventh generation WLAN standard, is currently under development with the goal of supporting transmission rates of up to 30 Gbps through wider bandwidth in the 2.4 / 5 / 6 GHz bands, increased spatial streams, and multi-AP cooperation. IEEE 802.11be proposes technologies such as a 320 MHz bandwidth, multi-link operation, multi-AP (multi-access point) operation, and hybrid automatic repeat request (HARQ) retransmission.

[0008] Multi-link operation operates in various forms depending on its operation method and implementation method. In this case, problems that did not occur in conventional IEEE 802.11-based WLAN communication operations may occur, so a detailed definition of the operation method for multi-link operation is required.

[0009] On the other hand, the art that forms the background of the invention is created to enhance understanding of the background of the invention and includes content that is not prior art already known to those with ordinary skill in the field to which this technology belongs. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide a method, device and system for multi-link transmission using a wireless LAN, which allows a wireless access point to efficiently transmit and receive frames that require low latency.

[0011] Another object of the present invention is to provide a method, device and system for setting a section for limiting transmission and reception for transmitting and receiving frames that require low latency.

[0012] Another object of the present invention is to provide a method, apparatus, and system for efficiently performing frame transmission operations when a wireless access point or station is unable to perform simultaneous transmission and reception operations on multiple links during multi-link operation.

[0013] The technical problems to be solved by the present specification are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention pertains from the following description. [Means for solving the problem]

[0014] A multi-link device (MLD) of a wireless communication system includes a communication module; and a processor that controls the communication module, wherein the processor receives a beacon frame from an AP, the beacon frame including a request type field, the request type field including a specific field for indicating a target wake time (TWT) for low latency operation; receives a downlink frame or transmits an uplink frame according to a value of the specific field, and when the value of the specific field is set to a first specific value, a broadcast TWT service period (SP) is the TWT SP for the low latency operation.

[0015] Furthermore, in the present invention, when the TWT SP for the low-delay operation is set, only frames requiring low delay can be transmitted in the TWT SP for the low-delay operation.

[0016] In addition, in the present invention, the beacon frame further includes a quiet information element for protecting the TWT SP for the low latency operation.

[0017] In addition, in the present invention, the interval set by the quiet information element and the start time of the TWT SP for the low latency operation are the same.

[0018] In addition, in the present invention, when an interval set by the quiet information element overlaps with part or all of the TWT SP for the low latency operation, part or all of the overlapping interval set by the quiet information element is ignored.

[0019] In addition, in the present invention, the interval set by the quiet information element is used by at least one STA to set a NAV (Network Allocation Vector).

[0020] Also, in the present invention, the NAV is set in the interval set by the quiet information element.

[0021] Furthermore, in the present invention, when the value of the specific field is set to a second specific value, it indicates that the specific field is restricted to be transmitted only in the form of a response frame to a downlink frame.

[0022] In addition, in the present invention, the beacon frame further includes a parameter field including a broadcast TWT information field, and the broadcast TWT information field includes information related to a TID to which frame transmission is restricted by the TWT for the low latency operation.

[0023] Also, in the present invention, if the non-AP STA constitutes a multi-link device (MLD), the MLD cannot transmit frames on other links while receiving the beacon frame.

[0024] In addition, in the present invention, the frame transmission operation ends before the start time of the TWT SP for the low latency operation. [Effects of the Invention]

[0025] According to an embodiment of the present invention, frames requiring low delay can be transmitted efficiently.

[0026] Furthermore, according to an embodiment of the present invention, by setting a period during which frame transmission is restricted, frames requiring low delay can be transmitted efficiently.

[0027] According to the present invention, when a wireless access point (AP) and an AP MLD including multiple wireless access points support transmission and reception of frames requiring low latency, they define a specific interval that allows only transmission of frames requiring low latency and announce it in a broadcast frame. When a wireless LAN station (STA) attempts to transmit or receive a frame meeting the requirements, it negotiates with the AP or AP MLD to perform the operation. Here, information about the interval for low latency is announced in a beacon frame or a probe response frame. Here, the announcement and negotiation method for the interval for low latency is performed in a manner identical or similar to the negotiation method for Target Wake Time (TWT) operation. To perform the operation efficiently, the AP or AP MLD allows only connections of terminals that support the operation to be accepted by the link it operates. By using the low latency transmission operation, when a terminal or AP attempts to transmit a frame requiring low latency, the transmission and reception of the frame is stabilized, thereby improving communication efficiency.

[0028] The effects obtained from the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief explanation of the drawings]

[0029] [Figure 1]1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a configuration of an access point according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating a process in which a STA establishes a link with an AP. [Figure 6] FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] 1 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1 illustrates various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention. [Figure 9] 1 is a structural diagram showing the internal hierarchical structure of an STA according to an embodiment of the present invention. [Figure 10] 1 is a conceptual diagram showing the structure of an AP MLD and a STA MLD that perform a multi-link operation according to an embodiment of the present invention. [Figure 11] 1 is a conceptual diagram showing a connection process between an AP MLD and a STA or a STA MLD according to an embodiment of the present invention; [Figure 12] 1 is a first example illustrating an operation of restricting a terminal connection process to perform a low-latency function according to an embodiment of the present invention. [Figure 13] 10 is a second example illustrating an operation of restricting a terminal connection process to perform a low-delay function according to an embodiment of the present invention. [Figure 14] FIG. 2 is a block diagram illustrating a link status information element that contains information about the transmission status of the link in accordance with an embodiment of the present invention. [Figure 15] 1 is a first embodiment showing the structure of a low latency operation request frame for requesting a low latency operation using a TWT (Target Wake Time) function according to an embodiment of the present invention. [Figure 16] 10 is a second embodiment showing the structure of a low latency operation request frame for requesting low latency operation using a TWT function according to an embodiment of the present invention. [Figure 17] 10 is a block diagram showing a low latency operation response frame that is a response to a request frame requesting low latency operation using a TWT function according to an embodiment of the present invention. [Figure 18] 1 is a first embodiment showing a process in which an AP or AP MLD and a STA perform low latency operation using a TWT function according to an embodiment of the present invention. [Figure 19] 10 is a second embodiment showing a process in which an AP or AP MLD and a STA perform low latency operation using a TWT function according to an embodiment of the present invention. [Figure 20] FIG. 10 is a diagram illustrating an operation in which the TWT time is not protected for low latency operation according to an embodiment of the present invention. [Figure 21] 10 is a diagram illustrating an operation of changing parameters at the same time when an AP MLD according to an embodiment of the present invention performs low latency operation using TWT operation. [Figure 22] 10 is an example illustrating an operation of an AP MLD according to an embodiment of the present invention, in which the AP MLD further transmits a protection frame to protect a TWT time period at the start of the TWT time period in order to protect the TWT time period for low latency operation. [Figure 23] 10 is an example showing a process in which a STA that is not capable of AP MLD and STR operations performs low latency operations using TWT functions according to an embodiment of the present invention. [Figure 24] 1 is a conceptual diagram showing the structure of an AP MLD and a STA MLD that perform a multi-link operation according to an embodiment of the present invention. [Figure 25] 10 is a timing diagram illustrating a connection process and a negotiation process for a multi-link operation between an AP MLD and a STA MLD according to an embodiment of the present invention. [Figure 26]FIG. 2 is a timing diagram illustrating a transmission scheme using multiple links according to an embodiment of the present invention. [Figure 27] 10 is a diagram illustrating an operation in which a receiving MLD that is not capable of STR operation performs frame transmission and reception with a transmitting MLD that is capable of STR operation in a part or all of the links according to an embodiment of the present invention. [Figure 28] 10 illustrates a first embodiment of an operation for protecting frame transmission and reception by an MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention. [Figure 29] 1 is a first example showing a structure of an MU-RTS frame according to an embodiment of the present invention. [Figure 30] 10 is a second embodiment showing the structure of an MU-RTS frame according to an embodiment of the present invention. [Figure 31] 10 is a second embodiment of the operation of protecting frame transmission and reception by the MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention. [Figure 32] 10 is a third embodiment showing the structure of an MU-RTS frame according to an embodiment of the present invention. [Figure 33] 10 is a third embodiment of the operation of protecting frame transmission and reception by the MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention. [Figure 34] 4 is a fourth embodiment showing the structure of an MU-RTS frame according to an embodiment of the present invention. [Figure 35] 10 is an example showing a channel reservation process using an MU-RTS frame and CTS frame exchange procedure among operations for multiple terminals according to an embodiment of the present invention. [Figure 36] A diagram showing the operation of not transmitting a CTS frame for an MU-RTS frame on a specific 20 MHz channel in accordance with an embodiment of the present invention. [Figure 37] 10 is a first embodiment of an operation for omitting transmission of an MU-RTS frame by adding an additional condition in AP MLD according to an embodiment of the present invention. [Figure 38]10 is a second embodiment of the operation of omitting transmission of an MU-RTS frame by adding an additional condition in AP MLD according to an embodiment of the present invention. [Figure 39] 10 illustrates an example of an operation of transmitting an MU-RTS frame according to an additional condition given by AP MLD according to an embodiment of the present invention. [Figure 40] This is a first example of an operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz frequency by the operation of the STA MLD according to an embodiment of the present invention. [Figure 41] 10 is a second embodiment of the operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz frequency by the operation of the STA MLD according to the embodiment of the present invention. [Figure 42] 10 is a third embodiment of the operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz frequency by the operation of the STA MLD according to the embodiment of the present invention. [Figure 43] 10 is a first example of an operation for continuing frame transmission even if a CTS frame cannot be received in response to an MU-RTS frame on a specific 20 MHz channel according to an embodiment of the present invention. [Figure 44] 10 is a second example of an operation for continuing frame transmission even if a CTS frame cannot be received in response to an MU-RTS frame on a specific 20 MHz channel according to an embodiment of the present invention. [Figure 45] 1 illustrates the operation of a soft AP according to an embodiment of the present invention. [Figure 46] 10 shows a non-STR soft AP multi-link device according to an embodiment of the present invention transmitting PPDUs on a mandatory link and an optional link. [Figure 47] 10 shows a non-STR soft AP multi-link device according to an embodiment of the present invention transmitting PPDUs on a mandatory link and an optional link. [Figure 48] 10 illustrates a non-STR soft AP multi-link device according to an embodiment of the present invention performing channel access with a mandatory link and a selective link. [Figure 49]10 shows a non-STR soft AP multi-link device according to an embodiment of the present invention transmitting PPDUs on a mandatory link and an optional link. [Figure 50] 1 illustrates independent transmission on each of multiple links according to an embodiment of the present invention. [Figure 51] This shows the operation of a multilink device transmitting on a non-STR link pair. [Figure 52] This shows an embodiment of the present invention that is applied when some of the multiple links on which the AP multilink device operates are non-STR link pairs. [Figure 53] 1 illustrates that a multi-link device according to an embodiment of the present invention operates with multiple links including non-STR link pairs. [Figure 54] 10 illustrates an operation in which an AP multilink device according to an embodiment of the present invention associates with a station not included in the multilink device. [Figure 55] 10 illustrates an operation in which an AP multilink device according to an embodiment of the present invention associates with a station included in the multilink device. [Figure 56] 10 shows that a multi-link device according to an embodiment of the present invention transmits on a non-STR link pair based on a basic link. [Figure 57] 10 shows how a multi-link device according to an embodiment of the present invention performs channel access for transmission on a non-STR link pair based on a basic link. [Figure 58] 10 shows how a multi-link device according to an embodiment of the present invention performs channel access for transmission on a non-STR link pair based on a basic link. [Figure 59] 10 illustrates channel access of a multilink device according to an embodiment of the present invention when one non-AP multilink device is connected to all non-STR link pairs. [Figure 60] 10 illustrates channel access of a multilink device according to an embodiment of the present invention when one non-AP multilink device is connected to all non-STR link pairs. [Figure 61]This shows the transmission operation of a non-AP multi-link device when one non-AP multi-link device is connected to all links of a non-STR link pair of an AP multi-link device in an embodiment of the present invention and the AP multi-link device transmits through any one of the links. [Figure 62] This shows the transmission operation of a non-AP multi-link device when one non-AP multi-link device is connected to all links of a non-STR link pair of an AP multi-link device in an embodiment of the present invention, and an intra-BSS frame transmitted by another station is transmitted through one of the links. [Figure 63] This shows the transmission operation of a non-AP multi-link device when one non-AP multi-link device is connected to all links of a non-STR link pair of an AP multi-link device in yet another embodiment of the present invention, and an intra-BSS frame transmitted by another station is transmitted on one of the links. [Figure 64] 3 is a flow chart illustrating an example of a method for transmitting a frame according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The terms used in this specification are generally used as widely as possible, taking into consideration the functions of the present invention. However, these may vary depending on the intentions of engineers in the relevant technical field, customs, or the emergence of new technologies. In addition, in certain cases, the applicant may have arbitrarily selected terms, and in such cases, the meanings thereof will be described in the relevant description of the invention. Therefore, it is made clear that the terms used in this specification should be interpreted not simply as names of terms, but based on the substantive meanings of the terms and the overall content of this specification.

[0031] Throughout this specification, when a component is referred to as being "connected" to another component, this includes not only when the component is "directly connected" to the other component, but also when the component is "electrically connected" to the other component via another component therebetween. Furthermore, when a component is referred to as "comprising" a specific component, this does not mean that the component excludes the other component, but that the component may further include the other component, unless otherwise specified. Additionally, limitations such as "greater than" or "less than" based on a specific critical value may be appropriately substituted with "exceeds" or "less than," respectively, depending on the embodiment. Hereinafter, in the present invention, the terms "field" and "subfield" may be used interchangeably.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0055] If the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an Inter Frame Space (IFS), such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS is used as a configuration replacing the conventional DCF IFS (DIFS). Each terminal waits while decreasing a slot time by a random number determined for the corresponding terminal during the idle interval of the channel, and a terminal that has exhausted all slot times attempts to access the corresponding channel. The period during which each terminal performs the backoff procedure is called a contention window period.

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

[0057] Hereinafter, in the present invention, a terminal may be referred to as a non-AP STA, an AP STA, an AP, an STA, a receiving device, or a transmitting device, and the present invention is not limited thereto. Also, in the present invention, an AP STA may be referred to as an AP.

[0058] <Examples of various PPDU formats>

[0059] Figure 7 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. More specifically, Figure 7(a) shows an example of a legacy PPDU format based on 802.11a / g, Figure 7(b) shows an example of an HE PPDU format based on 802.11ax, and Figure 7(c) shows an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Also, Figure 7(d) shows detailed field configurations of L-SIG and RL-SIG commonly used in the PPDU formats.

[0060] 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.

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

[0062] Referring to FIG. 7(c), the preamble of the EHT PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a Universal Signal field (U-SIG), an Extremely High Throughput Signal A field (EHT-SIG-A), an Extremely High Throughput Signal B field (EHT-SIG-A), an Extremely High Throughput Short Training field (EHT-STF), and an Extremely High Throughput Long Training field (EHT-LTF) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may vary depending on the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some EHT PPDU formats.

[0063] The L-SIG field included in the PPDU preamble is configured with a total of 64 subcarriers using 64 FFT OFDM. Of these, 48 subcarriers, excluding guard subcarriers, DC subcarriers, and pilot subcarriers, are used for L-SIG data transmission. BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, so it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of the L-SIG.

[0064] Referring to FIG. 7(d), the L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field is composed of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission rates of 6, 9, 12, 18, 24, 36, 48, or 54 Mbps, which is a combination of a modulation scheme such as BPSK, QPSK, 16-QAM, or 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The combined information in the L_RATE and L_LENGTH fields indicates the total length of the PPDU. In a non-legacy PPDU format, the L_RATE field is set to the minimum rate of 6 Mbps.

[0065] The unit of the L_LENGTH field is bytes, and a total of 12 bits are allocated, allowing a maximum of 4095 to be signaled. In combination with the L_RATE field, it can indicate the length of the corresponding PPDU. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0066] First, a legacy or non-legacy terminal interprets the length of the corresponding PPDU using the L_LENGTH field as follows. When the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted during 4 us, which is one symbol duration of the 64FFT. Therefore, by adding the 3 bytes corresponding to the SVC field and Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of 64FFT reference symbols after the L-SIG is obtained. The obtained number of symbols is multiplied by 4 us, which is one symbol duration, and then 20 us, which is required to transmit the L-STF, L-LTF, and L-SIG, to obtain the length of the corresponding PPDU, i.e., the reception time (RXTIME). This can be expressed mathematically as shown in Equation 1 below.

[0067]

number

[0068] At this time,

number

[0069]

number

[0070] 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.

[0071]

number

[0072] 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.

[0073] Referring to Figure 7(e), the U-SIG (Universal SIG) field remains in the EHT PPDU and subsequent generation WLAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. The U-SIG is two 64FFT-based OFDM symbols and can transmit a total of 52 bits of information. Of these, 43 bits excluding 9 bits of CRC / tail are roughly divided into a VI (Version Independent) field and a VD (Version Dependent) field.

[0074] The VI bit will maintain its current bit configuration, so even if a subsequent generation PPDU is defined, current 11be UEs can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field consists of the PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits long and serves to sequentially distinguish between 11be and subsequent generations of WLAN standards. 11be has a value of 000b. The UL / DL field identifies whether the PPDU is an uplink or downlink PPDU. The BSS color represents a BSS identifier defined in 11ax and has a value of 6 or more bits. The TXOP represents the transmit opportunity duration (Transmit Opportunity Duration) transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without decoding the MPDU, and has a value of 7 or more bits.

[0075] The VD field, which is signaling information useful only for 11be version PPDUs, may consist of fields commonly used in any PPDU format, such as the PPDU format and BW, as well as fields defined differently for each PPDU format. The PPDU format is a separator that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field broadly signals five basic PPDU BW options: 20, 40, 80, 160 (80 + 80), and 320 (160 + 160) MHz (BWs that can be expressed in the form of a power of 20 * 2 can be called basic BWs), as well as various remaining PPDU BWs formed by preamble puncturing. After signaling at 320 MHz, a portion of 80 MHz may be punctured. In addition, the punctured and modified channel shape may be signaled directly in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (for example, a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signalings are possible, so a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signalings are possible, so a maximum of 11 puncturing modes can be signaled.

[0076] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs may be signaled in the same PPDU format, and a field for distinguishing between MU PPDUs and SU PPDUs may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both SU PPDUs and MU PPDUs include an EHT-SIG field, but some fields not required for the SU PPDU may be compressed. In this case, the information of the compressed fields may be omitted or may have a reduced size compared to the size of the original fields included in the MU PPDU. For example, the SU PPDU may have a different configuration, such as the common fields of the EHT-SIG being omitted or replaced, or the user-specific fields being replaced or reduced to one.

[0077] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (such as the RA field) may be omitted depending on the value of the compression field.

[0078] When a portion of the EHT-SIG field of the SU PPDU is compressed, the information included in the compressed field may be signaled together in an uncompressed field (e.g., a common field). In the case of an MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of information signaled may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether the transmitted MU PPDU was sent to it. Therefore, the AP must transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols in the EHT-SIG field and / or the MCS, which is the modulation method. The EHT-SIG field may include information on the size and location of the RU assigned to each user.

[0079] In the case of an SU PPDU, a STA may be assigned multiple RUs, and the multiple RUs may be contiguous or discontinuous. If the RUs assigned to the STA are not contiguous, the STA can efficiently receive the SU PPDU only by recognizing punctured RUs in between. Therefore, the AP can transmit the SU PPDU including information on punctured RUs among the RUs assigned to the STA (e.g., puncturing pattern of the RUs). That is, in the case of an SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and the puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field can signal the type of discontinuous channels appearing within the bandwidth.

[0080] The type of signaled discontinuous channel is limited, and indicates the BW and discontinuous channel information of the SU PPDU in combination with the value of the BW field. For example, since the SU PPDU is a PPDU transmitted only to a single UE, the STA can recognize its allocated bandwidth from the BW field included in the PPDU and can recognize punctured resources within the allocated bandwidth from the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the UE can receive the PPDU in the remaining resource units excluding specific channels of the punctured resource units. In this case, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0081] The reason why only limited discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed for each 20 MHz subchannel, if puncturing is performed on a BW having multiple 20 MHz subchannels, such as 80, 160, or 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered discontinuous) must be signaled by expressing whether or not each of the remaining 15 20 MHz subchannels excluding the primary channel is in use. Using 15 bits to signal the discontinuous channel type for single-user transmission can result in excessive signaling overhead when considering the low transmission rate of the signaling part.

[0082] This invention proposes a method for signaling the discontinuous channel type of the SU PPDU, shows 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.

[0083] In addition, one embodiment of the present invention proposes a method of varying the PPDU configuration indicated by the preamble puncturing BW value according to the PPDU format signaled in the PPDU format field. Assuming the length of the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, an EHT-SIG-A symbol of one symbol may be further signaled after the U-SIG, or no EHT-SIG-A may be signaled at all. Taking this into consideration, up to 11 puncturing modes must be signaled using only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B symbol is further signaled after the U-SIG, so up to 11 puncturing modes may be signaled in a different manner than in the SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz bandwidth.

[0084] Figure 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. For an MU PPDU, SIG-B, a signaling field for simultaneous reception by multiple users, is required. SIG-B may be transmitted after the U-SIG without a separate SIG-A. For this purpose, the U-SIG must signal information for decoding SIG-B. These fields include the SIG-B MCS, SIG-B DCM, number of SIG-B symbols, SIG-B compression, and number of EHT-LTF symbols.

[0085] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention.

[0086] 8, a PPDU may be configured with a preamble and a data portion, and the format of one type, EHT PPDU, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 8(d) shows an example of an EHT ER SU PPDU format used for single-user transmission with STAs in an extended range. The EHT ER SU PPDU may be used for single-user transmission with STAs in a wider range than the EHT SU PPDU described in FIG. 8(a), and the U-SIG field may be repeated on the time axis.

[0091] The EHT MU PPDU described in (c) of Figure 8 can be used by the AP for downlink transmission to multiple STAs. In this case, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive the PPDU transmitted from the AP. The EHT MU PPDU can convey AID information of the receiver and / or sender of the transmitted PPDU to the STA through the user specific field of the EHT-SIG-B. Therefore, multiple terminals receiving the EHT MU PPDU can perform spatial reuse based on the AID information of the user specific field included in the preamble of the received PPDU.

[0092] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information regarding the configuration of resource units (e.g., the division type of resource units) in a specific bandwidth (e.g., 20 MHz) on the frequency axis. That is, the RA field may indicate the configuration of resource units divided by the bandwidth for transmitting the HE MU PPDU so that the STA can receive the PPDU. Information about the STA allocated (or designated) to each divided resource unit may be included in a user specific field of the EHT-SIG-B and transmitted to the STA. That is, the user specific field may include one or more user fields corresponding to each divided resource unit.

[0093] For example, among the multiple divided resource units, the user field corresponding to at least one resource unit used for data transmission may include the AID of the receiver or sender, and the user field corresponding to the remaining resource units not used for data transmission may include a previously set null STA ID.

[0094] Two or more PPDUs shown in FIG. 8 can be indicated by a value indicating the same PPDU format. That is, two or more PPDUs can be indicated as the same PPDU format by the same value. For example, an EHT SU PPDU and an EHT MU PPDU can be indicated by the same value using the U-SIG PPDU format subfield. In this case, the EHT SU PPDU and the EHT MU PPDU can be distinguished depending on the number of STAs receiving the PPDU. For example, a PPDU received by only one STA may be identified as an EHT SU PPDU, and when the number of STAs is set so that two or more STAs can receive the PPDU, it may be identified as an EHT MU PPDU. In other words, two or more PPDU formats shown in FIG. 8 can be indicated using the same subfield value.

[0095] In addition, some of the fields or some information of the fields shown in Figure 8 may be omitted, and such a case where some of the fields or some information of the fields is omitted can be defined as a compression mode or a compressed mode.

[0096] Meanwhile, the AP and STA can request low latency operation for specific traffic requiring low latency. In this case, the traffic requiring low latency may be transmitted to the MAC layer as follows.

[0097] FIG. 9 is a structural diagram showing the internal hierarchical structure of an STA according to an embodiment of the present invention.

[0098] 9, the communication device included in the STA is composed of an application layer that performs various operations at the highest layer, a transport layer that ensures end-to-end transmission reliability, a network layer that searches for a path to a target communication node and transmits a signal in that direction, a data link layer that performs transmission operations in an end-to-end communication link, and a physical layer that actually performs transmission operations using physical signals. In this case, the data link layer may include LLC (Logical Link Control) and MAC (Medium Access Control).

[0099] Meanwhile, each layer can send data and additional parameters for data transmission to a layer above or below that layer through a Service Access Point (SAP). For example, the LLC layer can receive information about data, a source address, a destination address, etc. from a higher layer through a Link Service Access Point (LSAP). The MAC layer can transmit received data to a higher layer through a MAC SAP, and can receive data to be transmitted and additional parameters for data transmission from the higher layer.

[0100] In the hierarchical structure, if data to be transmitted requires low latency, the MAC layer can receive the data and related parameters from the upper layer in the form of an MA-UNITDATA.request. In this case, if the data to be transmitted requires low latency, the upper layer can include a corresponding indicator when transmitting the data to the MAC layer via the MAC SAP. For example, the MA-UNITDATA.request can include the fact that the data requires low latency. If the indicator for low latency is included, the MA-UNITDATA.request can include parameters as shown in Table 1 below.

[0101] [Table 1]

[0102] The parameters included in DA-UNITDATA.request can be as shown in Table 2 below.

[0103] [Table 2]

[0104] Alternatively, a separate traffic stream (TS) can be defined for data requiring low latency. In this case, in order to manage data corresponding to a specific TS, the required Quality of Service (QoS) information for the ID of the specific traffic stream can be received from the Station Management Entity (SME) through the MAC Layer Management Entity SAP (MLME SAP). In this case, the MAC layer can receive information about the TS from the SME in the form of an MLME-ADDTS.request.

[0105] Meanwhile, when an AP or STA supports a low-latency transmission operation for frames requiring low latency, an internal variable can be assigned to the terminal. For example, one of the Management Information Base (MIB) values indicating whether the low-latency operation is activated can be generated and managed within the terminal. In this case, the MIB value can be dot11rTWTActivated. In this case, the low-latency operation is an operation for transmitting latency-sensitive traffic (e.g., latency-sensitive traffic) or frames, and the latency-sensitive traffic or frames can be pre-configured traffic or frames. For example, the latency-sensitive traffic or frames can be indicated as latency-sensitive traffic or frames by a TID (or Access Category: AC).

[0106] Meanwhile, the AP may be an AP included in an AP Multi-link Device (MLD), and the STA may be an STA included in a STA MLD. The AP MLD and the STA MLD may be configured as described in FIG. 10.

[0107] FIG. 10 is a conceptual diagram showing the structure of an AP MLD and a STA MLD that perform a multi-link operation according to an embodiment of the present invention.

[0108] Referring to FIG. 10, an AP MLD (Multi-link Device) may be a device including one or more wireless access points (APs) and connected to a higher layer through one interface. That is, the AP MLD may be connected to a Logical Link Control (LLC) layer through one interface. Multiple APs included in the AP MLD may share some functions at the MAC layer. Each AP in the AP MLD may operate on a different link. An STA MLD may be a device including one or more non-AP STAs and connected to a higher layer through one interface. That is, the STA MLD may be connected to the LLC layer through one interface. Multiple STAs included in the STA MLD may share some functions at the MAC layer. The STA MLD may also be called a non-AP MLD. In this case, the AP MLD and the STA MLD can perform a multi-link operation, communicating using multiple individual links. That is, when the AP MLD includes multiple APs, each AP forms a separate link and can transmit and receive frames using multiple links with each UE included in the STA MLD. In this case, each link can operate in the 2.4 GHz, 5 GHz, or 6 GHz band, and each link can perform bandwidth expansion operation. For example, if AP MLD configures one link in the 2.4 GHz band and two links in the 5 GHz band, the 2.4 GHz band can transmit frames at a bandwidth of 40 MHz using the bandwidth expansion method, and each link using the 5 GHz band can transmit frames at a bandwidth of up to 320 MHz by utilizing the discontinuous bandwidth.

[0109] Meanwhile, due to interference issues within the device, the AP MLD or STA MLD may prevent one terminal in the MLD from receiving while another terminal is transmitting. This operation, in which one AP or terminal in the MLD transmits while another AP or terminal in the MLD receives, is called STR (Simultaneous Transmit and Receive). The AP MLD may be capable of STR operation for all links. Alternatively, STR operation may be disabled for some links of the AP MLD. An AP MLD may be connected to a terminal MLD capable of STR operation, or an MLD incapable of STR operation for some or all links. Furthermore, an AP included in an AP MLD may also be connected to terminals not belonging to the MLD (e.g., IEEE 802.11a / b / g / n / ac / ax terminals or IEEE 802.11be terminals that are not in MLD mode).

[0110] The AP MLD and STA MLD can perform a negotiation process for a multi-link operation. At this time, the negotiation process for a multi-link operation can be performed during the scanning and connection process described in Fig. 5. The AP MLD and STA MLD can perform a negotiation process for a multi-link use operation during the scanning and connection process described in Fig. 5. When the negotiation process for a multi-link operation is performed during the connection process, the AP MLD and STA MLD can operate as follows.

[0111] 11 is a conceptual diagram showing a connection process between an AP MLD and a STA or a STA MLD according to an embodiment of the present invention. In FIG. 11, the description of the connection process that overlaps with that described in FIG. 5 will be omitted.

[0112] Referring to FIG. 11, the AP MLD and the STA MLD may perform a negotiation process for multiple link operation during the scanning and connection process. For example, in the scanning process described in FIG. 5, an AP included in the AP MLD may transmit a beacon frame including an indicator indicating that multiple link operation is available, the number of available links, information on the multiple available links, etc. Alternatively, when the AP MLD transmits a probe response frame in the form of a broadcast frame, the probe response frame may include an indicator indicating that multiple link operation is available, information on the number of available links, the multiple available links, etc. A terminal belonging to the STA MLD may transmit a probe request frame including an indicator indicating that multiple link operation is available. When the STA MLD attempts to perform a negotiation process for multiple link operation, it may further request operation information from all APs belonging to the AP MLD. When a STA belonging to the STA MLD requests information on all APs belonging to the AP MLD, it may transmit a probe request frame including the request indicator. An AP belonging to the AP MLD can check the corresponding request indicator in the probe request frame and transmit a probe response frame including all parameters used for multi-link operation (e.g., information about the AP and beacon frame information transmitted from other APs belonging to the AP MLD). In this case, all the parameters may include the number of links available for multi-link operation, link information, etc.

[0113] The STA MLD, which has confirmed whether the AP MLD is to operate multiple links and the link information to be used during the scanning process, can perform a connection process with the AP MLD. At this time, the AP MLD and the STA MLD can simultaneously perform a negotiation process for multiple link operation. That is, a terminal (e.g., STA1) belonging to the STA MLD can send a connection request frame to an AP (e.g., AP1) belonging to the AP MLD, including an indicator indicating that the terminal's multiple link operation is available and a request indicator requesting the terminal to perform multiple link operation. The AP receiving the connection request frame from the terminal can check the indicator requesting multiple link operation. If multiple link operation is available, the AP can send a connection response frame to the terminal that allows the multiple link operation, including link information to be used for the multiple link operation and parameters to be used for each link. The parameters for the multiple link operation can include one or more of the bandwidth of each link to be used, the bandwidth expansion direction, the Target Beacon Transmission Time (TBTT), and whether STR operation is enabled. The AP MLD and STA MLD, in which the connection request frame and response frame are exchanged and the use of multiple link operation is confirmed, can perform frame transmission operations using multiple links through multiple APs included in the AP MLD and multiple terminals included in the STA MLD after the connection process.

[0114] Meanwhile, when an AP or AP MLD supports a low-latency transmission operation for frames requiring low latency, it may restrict the connection of only terminals capable of the operation to one or more links. That is, to efficiently perform the channel reservation process and transmission process for the low-latency operation, it may only allow the connection of terminals that can decode and understand the operation on a specific link. In this case, the low-latency transmission operation may be a low-latency transmission operation using the TWT operation. For example, when a reserved time for low-latency terminals, TWT SP (Target Wake Time Service Period), is included in a beacon frame and transmitted, STAs that support low-latency operation using the TWT function may not be able to perform a channel contention process for frame transmission unless they are the STAs reserved for the TWT SP time. On the other hand, STAs that do not support the function may perform a channel access process for frame transmission even in the TWT SP. In this case, a situation may occur in which the transmission of a frame reserved to be transmitted to the TWT SP is delayed or collided due to the channel access operation by a STA that does not support the low-latency function using the TWT operation. As a result, the required latency of a frame requiring low latency may not be met. To prevent this situation, the AP and AP MLD can designate a particular link to be used only by terminals that perform a channel reservation process with low latency operation.

[0115] On the other hand, if the AP or AP MLD specifies a link only for terminals that support low latency operation, it may reject a connection request from a STA that does not support the function as follows.

[0116] In this case, the low-latency operation is an operation for transmitting latency-sensitive traffic or frames, and the latency-sensitive traffic or frames may be previously configured traffic or frames. For example, the latency-sensitive traffic or frames may be indicated as latency-sensitive traffic or frames by a TID (or Access Category: AC). Alternatively, the latency-sensitive traffic or frames may refer to traffic or frames that should be transmitted within a certain delay time, and may be indicated by a TID (or Access Category: AC).

[0117] TWT allows STAs to manage their activities in a BSS by scheduling them to operate at different times to minimize contention and reduce the time STAs using power management modes need to stay awake. TWT operation may be individual TWT, which is individually configured by the AP, or broadcast TWT. That is, the AP can individually configure whether each STA will perform TWT operation, or can configure whether multiple STAs will perform TWT operation using broadcast TWT and transmit this information to non-AP STAs. When scheduled to perform TWT operation by the AP, non-AP STAs can perform TWT operation during the TWT service period (SP) interval.

[0118] In this case, the broadcast TWT operation can be referred to as a restricted TWT operation when used for low latency operation. That is, the broadcast TWT operation can be performed when a non-AP STA supports the restricted TWT operation according to a specific parameter of a capability element (e.g., when the specific element is set to '1') and the beacon frame is set as a frame for the restricted TWT operation according to a specific field of the beacon frame. In this case, the SP set for the broadcast TWT operation can be the SP for the restricted TWT operation.

[0119] In this case, limited TWT, which is a TWT operation for transmitting frames requiring low latency, may be used to support improved medium access protection and resource reservation for delay-sensitive traffic.

[0120] A non-AP STA for which a TWT SP has been set by an AP STA cannot transmit frames other than those negotiated by the individual TWT to the AP STA within the TWT SP.

[0121] Hereinafter, the restricted TWT operation for low latency operation may be referred to as TWT operation.

[0122] 12 is a first example showing an operation of restricting a terminal connection process to perform a low-latency function according to an embodiment of the present invention. In FIG. 12, the same processes as those described in FIG. 5 and FIG. 11 are omitted.

[0123] 12, an AP MLD may include multiple APs, and each AP may operate a link. In this case, the AP MLD may designate one or more of the operated links as links only for terminals that support low latency operation. For example, among the APs belonging to the AP MLD, the link operated by AP1 may be designated as a link only for terminals that support low latency operation. Alternatively, an AP not belonging to the AP MLD may be operated only for terminals that support low latency operation.

[0124] The AP or AP MLD may transmit a probe response frame, which is transmitted in the form of a beacon frame or a broadcast frame, including an indicator indicating whether low latency operation is supported. The low latency operation may be low latency operation using the TWT function described later in Figures 18 to 19 and 21 to 23.

[0125] For example, if the AP or AP MLD supports the low-latency operation, the field indicating whether the low-latency operation is supported may be set to 1 in the capability element included in the beacon frame and broadcast probe response frame and transmitted. Also, the beacon frame and broadcast probe response frame may include an indicator indicating that the link is for low-latency terminals only. For example, the beacon frame or broadcast probe response frame may include an EHT Operation information element, and the EHT Operation information element may include an indicator (e.g., an rTWT Required field) indicating that support for low-latency operation is required and transmitted. Alternatively, the IBSS STA subfield and ESS subfield values of the Capability information field in the beacon frame or broadcast probe response frame may both be set to 1, thereby preventing existing STAs that do not support low-latency operation from recognizing the BSS type of the AP. As another example, the beacon frame or broadcast probe response frame may further include an interworking information element, and an Access Network Type subfield in an Access Network Options field of the interworking information element may indicate that the corresponding link is a link for low-latency operation. A STA that does not support low-latency operation, among STA MLDs or STAs not belonging to the STA MLD, may check an indicator in the beacon frame or broadcast probe response frame indicating that the link is for low-latency terminals only, and the STA or STA MLD that checks the indicator may not perform an active scanning process and a connection process with the corresponding AP or AP MLD.

[0126] A STA MLD or a STA not belonging to the STA MLD can attempt scanning and connection with the AP or AP MLD as described in FIG. 5. For example, the STA MLD or STA can transmit a probe request frame to the AP or AP MLD. In this case, the STA or STA MLD can include function information supported by the STA or STA MLD in the probe request frame. For example, if the STA or STA MLD supports low latency operation, it can transmit the probe request frame with the indicator field supporting the function set to 1 in the capability element. On the other hand, if the STA or STA MLD does not support the function, it can transmit the probe request frame with the field indicating whether low latency operation is supported set to 0 in the capability element.

[0127] The AP or AP MLD can receive the probe request frame from the STA or STA MLD and can confirm whether the STA or STA MLD supports low-latency operation. If it is confirmed that the STA or STA MLD does not support low-latency operation, the AP or AP MLD may not transmit a probe response frame in response to the probe request frame. Alternatively, the AP or AP MLD can indicate that the AP is an AP that supports only low-latency UEs while transmitting a probe response frame in response to the probe request frame. The indicator indicating that the AP is an AP that supports only low-latency UEs may be the indicator indicating that the link is for low-latency UEs only. If the STA or STA MLD does not support low-latency operation, it can check the indicator indicating that the link is for low-latency UEs only in the probe response frame and not perform an association process with the AP or AP MLD.

[0128] Meanwhile, if a STA supports the low-latency operation or if it cannot decode the indicators in the beacon frame and probe response frame, the STA may transmit a connection request frame to an AP based on the scanning result as shown in FIG. 5. The AP that receives the connection request may transmit a connection response frame in response to the connection request frame. If the STA that transmitted the connection request frame supports the low-latency operation, the connection response frame may include an indicator that accepts the connection request. On the other hand, if the STA that transmitted the connection request frame does not support the low-latency operation, the connection response frame may include an indicator that rejects the connection request. In this case, the AP may indicate that the connection request has been rejected because the STA does not support the low-latency operation in the status code field of the connection response frame that rejects the connection request. For example, the AP may transmit a probe response frame by setting a field value (e.g., 133) that means LOW_LATENCY_SUPPORT_NEEDED in the status code field. If an AP included in the AP MLD rejects the connection request in response to the connection request frame, it may further include other link information to suggest connection to another link. Information about a general link that is not a link for the low latency terminal only may be transmitted in the form of a Neighbor Report information element, which may include at least one of a BSSID, a channel and operation class, and timing information.

[0129] A STA that receives a connection response frame including a rejection indicator from the AP can check the contents of the received connection response frame and determine that the connection request has been rejected. At this time, the STA can check the value of the status code field in the connection response frame to determine that the link requires support for low-latency operation, and can check whether or not a Neighbor Report information element is present in the connection response frame. If a Neighbor Report information element is included in the response frame, the STA can check its contents and determine the proposed BSS information. The STA can check other link information included in the Neighbor Report information element, move to a channel indicated by the information, and perform the connection process described in FIG. 5 or FIG. 11 with the AP of the link.

[0130] On the other hand, when the low latency operation is based on the TWT operation of the WLAN operation, the AP or AP MLD that configures a link only for the low latency terminal can exceptionally allow the connection of a terminal that supports the TWT function for low power operation. When allowing the connection of an existing WLAN terminal that supports the TWT function, the AP or AP MLD can accept or reject the connection request of the STA as follows.

[0131] 13 shows a second embodiment of the operation of restricting the access process of a terminal to perform a low-latency function according to an embodiment of the present invention. In FIG. 13, the same description as that of the access process in FIG. 5, FIG. 11, and FIG. 12 will be omitted.

[0132] 13, an AP MLD may include multiple APs, and each AP may operate a link. In this case, the AP MLD may designate one or more of the operated links as links only for terminals that support latency operation using the TWT function. For example, among the APs belonging to the AP MLD, the link operated by AP1 may be designated as a link only for terminals that support low latency operation using the TWT function. Alternatively, an AP not belonging to the AP MLD may be operated only for terminals that support low latency operation using the TWT function.

[0133] The AP or AP MLD may transmit a probe response frame transmitted in the form of a beacon frame or a broadcast frame, including an indicator indicating that it supports low-latency operation using the TWT function. For example, the AP or AP MLD may transmit a probe response frame in the form of a beacon frame or a broadcast frame, with an indicator indicating whether it supports low-latency operation using the TWT function set to 1 in the capability element in the beacon frame or broadcast probe response frame. Also, the AP or AP MLD may transmit a beacon frame or a broadcast probe response frame including an indicator indicating that the link is a link only for terminals that support the TWT operation. For example, the beacon frame or the broadcast probe response frame may include an EHT Operation information element, and the EHT Operation information element may include an indicator indicating that support of the TWT operation is required (e.g., a TWT Operation Required field, etc.). Alternatively, as described in FIG. 12, the AP or AP MLD may request support of the TWT function using the Capability information field or the Access Network Type subfield in the Access Network Options field of the interworking information element. In the case of a STA MLD or a STA not belonging to a STA MLD that does not support TWT operation, it can check an indicator indicating that the link is for terminals only that support the TWT function in the corresponding beacon frame or broadcast probe response frame, and the STA or STA MLD that checks the indicator does not need to perform an active scanning process and a connection process with the corresponding AP or AP MLD. Meanwhile, the AP or AP MLD can indicate that a STA or STA MLD that supports the TWT function itself but does not support low-latency operation using the TWT function needs to undergo a negotiation process for TWT operation by setting the TWT Required field in the HE Operation information element in the beacon frame or broadcast probe response frame to 1.

[0134] A STA MLD or a STA not belonging to the STA MLD can attempt scanning and connection with the AP or AP MLD as described in FIG. 5. For example, the STA MLD or STA can transmit a probe request frame to the AP or AP MLD. In this case, the STA or STA MLD can include, in the probe request frame, information on the capabilities supported by the STA or STA MLD. For example, if the STA or STA MLD supports TWT, it can transmit the probe request frame with an indicator field (e.g., TWT Requester Support field) supporting the capability set to 1 in the EHT Capability element. Also, if the STA or STA MLD supports low latency operation using the TWT function, it can transmit the probe request frame with an additional indicator supporting the capability set to 1. For example, it can transmit the probe request frame with an indicator field (e.g., TWT Requester Support field) supporting the capability set to 1 in the EHT Capability element. On the other hand, if the STA or STA MLD does not support the function, the fields indicating whether the TWT function is supported and whether low latency operation using the TWT function are supported in the HE capability element and EHT capability element in the probe request frame can be set to 0 and transmitted.

[0135] The AP or AP MLD can receive the probe request frame from the STA or STA MLD and can confirm whether the STA or STA MLD supports the TWT function and low-latency operation using the TWT function. If it is confirmed that the STA or STA MLD does not support the TWT function, the AP or AP MLD may not transmit a probe response frame in response to the probe request frame. Alternatively, the AP or AP MLD may transmit a probe response frame in response to the probe request frame and indicate that the AP needs to support the TWT function. The indicator indicating that support for the TWT function is required may be the indicator indicating that support for the TWT operation is required. If the STA or STA MLD does not support the TWT function, it can check the indicator requesting the TWT function in the probe response frame and not perform an association process with the AP or AP MLD. Meanwhile, the AP or AP MLD can indicate to a STA or STA MLD that supports the TWT function itself but does not support low-latency operation using the TWT function that a negotiation process for TWT operation is required by setting the TWT Required field to 1 in the HE Operation information element in the probe response frame.

[0136] Meanwhile, if a STA or STA MLD supports the TWT function or cannot decode the indicator in the beacon frame and probe response frame, the STA can transmit a connection request frame to the AP based on the scanning result as shown in FIG. 5. The AP that receives the connection request can transmit a connection response frame in response to the connection request frame. If the STA that transmitted the connection request frame supports the TWT operation, the connection response frame can include an indicator that accepts the connection request. In this case, by setting the TWT Required field to 1 in the HE Operation information element in the connection response frame, it can indicate to a STA or STA MLD that supports the TWT function but does not support low-latency operation using the TWT function that a negotiation process for TWT operation is required. On the other hand, if the STA that transmitted the connection request frame does not support the TWT operation, the connection response frame can include an indicator that rejects the connection request. In this case, the AP can indicate in the status code field of the connection response frame that the connection request was rejected because the STA does not support the TWT function. For example, a probe response frame may be transmitted by setting a field value (e.g., 134) meaning TWT_REQUESTER_SUPPORT_NEEDED in the status code field. If an AP included in the AP MLD rejects the connection request in response to the connection request frame, it may further include other link information to suggest connection to another link, as shown in FIG. 12. Information about a general link that is not a link exclusively for the low-latency UE may be transmitted in the form of a Neighbor Report information element. The Neighbor Report information element may include at least one of BSSID, channel and operation class, and timing information.

[0137] A STA that receives a connection response frame including a rejection indicator from the AP can check the contents of the received connection response frame and determine that the connection request has been rejected. At this time, the STA can check the value of the status code field in the connection response frame to determine that the link requires support for TWT operation, and can determine whether the connection response frame includes a Neighbor Report information element. If the response frame includes a Neighbor Report information element, the STA can check the contents as shown in FIG. 12 and perform a connection process with the AP indicated by the information element.

[0138] Meanwhile, the AP or AP MLD can set the TWT Required field in the HE Operation element to be transmitted to 1. In this case, if a STA MLD or a STA not belonging to the STA MLD supports the TWT function but does not support low-latency operation using the TWT function, it can recognize that a negotiation process for TWT operation is required after the connection process with the AP or AP MLD. As a result, the STA or STA MLD can negotiate for TWT operation with the AP during or after the connection process with the AP or AP MLD. After negotiating the TWT operation, it does not need to perform a frame transmission operation outside the negotiated TWT SP. On the other hand, if the STA or STA MLD supports both the TWT operation and low-latency operation using the TWT function, it does not need to perform a separate negotiation process for TWT operation after the connection process. In this case, the STA or STA MLD can confirm the TWT SP for low-latency operation transmitted by the AP in a beacon frame or a broadcast probe response frame, and can complete the frame transmission process before the start of the TWT SP. That is, a STA or STA MLD supporting low latency operation may not transmit frames during the TWT SP time for low latency operation unless negotiated with the AP in advance, i.e., the frame transmission operation may end before the start time of the TWT SP for low latency operation.

[0139] Meanwhile, an AP MLD or an AP not belonging to the AP MLD can measure information about frame transmission delay time for the link it operates. The information about the transmission delay time may be continuously updated and stored within the AP at regular intervals (e.g., 100 ms). An AP MLD supporting low-latency transmission operations can provide statistical information related to the transmission delay time of frames transmitted on each link operated by the AP MLD. That is, each AP belonging to the AP MLD can provide statistical information related to the transmission delay time of frames transmitted by the AP and other APs belonging to the same AP MLD. The statistical information may be transmitted in a beacon frame, probe response frame, access response frame, etc. transmitted by the AP MLD. If a STA checks the statistical information and receives a frame requesting low latency, it can perform an association process with an AP belonging to the AP MLD based on the information, according to the operations of FIGS. 5 and 12-13. Meanwhile, when there is a frame requiring low latency, the STA MLD that has checked the statistical information can perform a connection process with the AP MLD and a negotiation process for multi-link operation based on the information through the operations of Figures 5 and 11 to 13. Also, the STA MLD can determine through which link the frame requiring low latency should be transmitted based on the information.

[0140] The statistical information may be transmitted in the form of a Measurement Report information element. The information element related to the transmission delay time may be STA statistics with the Measurement type field of the Measurement Report information element set to 7, and may include the average channel access time (Access Delay) for each Access Category (AC) in the corresponding BSS. Alternatively, it may include information on the number of retransmissions according to each User Priority (UP) value. Alternatively, the Measurement Report information element may include the average transmission time and transmission success probability for each AC as follows:

[0141] FIG. 14 is a block diagram illustrating a link status information element that contains information about the transmission status of the link in accordance with an embodiment of the present invention.

[0142] Referring to FIG. 14, a Measurement Report information element including transmission status information on a link may include an element ID field, a length field, a field indicating the type of measured information, a field indicating the measurement period, a field indicating a measurement information group, and a field indicating measured data information. Here, the element ID field, the length field, and the field indicating the type of measured information may be set to the same or similar to those of STA statistics. The measurement group information field may be set to 17 to indicate that the information is information regarding the transmission delay time transmitted by the corresponding AP. The measurement information may include at least one of the average transmission time for all frames transmitted on the link, the average transmission time for each AC of frames transmitted on the link, the variance of the average transmission time for each AC of frames transmitted on the link, the top 95% of the transmission times for each AC of frames transmitted on the link, the transmission failure probability for all frames transmitted on the link, and the transmission failure probability for each AC of frames transmitted on the link. Here, the transmission time may be calculated from the time a frame to be transmitted by the corresponding AP is generated to the time an ACK frame is received upon completion of transmission of the frame. Alternatively, the transmission time may be calculated as the time from when the frame to be transmitted by the AP is generated to when an ACK frame is received upon completion of transmission of the frame to when the transmission or retransmission is completed before receiving the ACK. The transmission failure probability may be calculated as "(number of times transmission has failed due to exceeding the frame retransmission limit) / (number of times ACK for frame transmission has been received + number of times transmission has failed due to exceeding the frame retransmission limit)" during the measurement period.

[0143] Meanwhile, a STA or STA MLD that intends to transmit a frame requiring low latency can indicate information regarding the required latency for the frame to an AP or AP MLD. In this case, the frame having low latency may be identified as a specific traffic stream (TS). If the frame requiring low latency is data assigned to a specific TS, the STA or STA MLD can negotiate with the AP or AP MLD to add a TS to the data. For example, the STA can transmit a TS addition request frame to the AP to add a TS for traffic requiring low latency, and the AP can transmit a TS addition response frame in response to the TS addition request frame. Through the TS addition negotiation operation, the STA can transmit to the AP one or more of the latency information, data size, and requested transmission speed of the data of the TS to be added.

[0144] A STA or STA MLD that wishes to transmit a frame requesting low latency may negotiate with an AP or AP MLD to perform low latency operation. The negotiation process for low latency operation may be the same as or similar to the negotiation process for TWT operation. That is, when a request frame for low latency operation is transmitted from a STA to an AP, the request frame may be a TWT request frame. A response frame for low latency operation transmitted from an AP to a STA may be a TWT response frame.

[0145] Meanwhile, the low latency operation request frame may include information on the required latency for the frame to be transmitted, etc. When the low latency operation request frame includes the required latency and frame generation information, the low latency operation request frame is described below with reference to FIG.

[0146] FIG. 15 shows a first embodiment of a structure of a low latency operation request frame for requesting a low latency operation using a TWT (Target Wake Time) function according to an embodiment of the present invention.

[0147] Referring to FIG. 15, the frame requesting the low latency operation may be configured in the form of a TWT request frame. Accordingly, the request frame may include a TWT information element. The TWT information element included in the low latency operation request frame may include an element ID field, a length field, a control field, and a parameter field for the low latency operation using the TWT operation. It may include an NDP paging indicator field related to the channel measurement operation, a field indicating whether the TWT responder is willing to switch to PS mode, a field indicating the TWT negotiation type, a field indicating whether the TWT schedule is adjustable, and a field indicating the unit of the requested latency. Of the control fields, fields other than the field indicating the unit of the requested latency may be set to the same setting method as during negotiation for the broadcast TWT operation. For example, in the TWT request frame for the low latency operation, the NDP paging indicator field may be set to 0, and the field indicating whether the TWT responder is willing to switch to PS mode may be set to 0, thereby disabling the corresponding function. The TWT negotiation type field can be set to 3 to indicate that the frame is a request frame for negotiation of a broadcast TWT type, in which the TWT operation is a type in which a TWT SP for a low-latency UE is periodically transmitted in a beacon frame. The requested latency unit field indicates the unit of the maximum latency time requested on average by the frame requesting the low-latency operation. If this field is set to 0, 256 μs is displayed, and if this field is set to 1, 32 μs is displayed.

[0148] The parameter field for low latency operation using TWT operation may include one or more of a request type field, a field indicating the time when low latency traffic is expected to occur, a requested latency field, a significant digit field for the period of low latency based on the requested TWT operation, and a broadcast TWT information field.

[0149] The request type field may include a field indicating whether the frame is a TWT request frame, a TWT configuration instruction field, a trigger field, an operation type field, an operation method field in broadcast TWT time (or broadcast TWT SP), an index field for the period of the requested low latency time, and a field indicating that the TWT operation is a TWT for low latency operation. For example, the request type field may include a specific field indicating that the TWT operation according to the frame is a restricted TWT operation. Depending on the value of the specific field, frames that can be transmitted in the TWT SP according to the TWT operation may be restricted to specific frames for downlink frames, or the broadcast SP may be set as the restricted TWT SP. That is, if the value of the specific field (e.g., a broadcast TWT recommendation field) is '1', frames that can be transmitted in the TWT SP may be restricted to specific frames for downlink frames, and if the value of the specific field is '4', the broadcast TWT SP may be set as the restricted TWT SP.

[0150] In this case, among the request type fields, fields other than the operation method field in broadcast TWT time, the exponent field for the period of the requested low latency time, the TWT field, and the field indicating that the TWT operation is a TWT for low latency operation may be set in the same format as the TWT information elements included in the existing broadcast TWT request frame.

[0151] The operation mode field in the broadcast TWT time is used when restricting frame transmission during the TWT SP time. For example, when restricting transmission during the TWT SP only in the form of a response frame to a downlink frame (e.g., an ACK or BlockAck frame to a downlink data frame, or an uplink frame transmitted in response to a trigger frame), the field can be set to 1.

[0152] In addition, this field can be set to 4 when requesting to limit the AC transmitted within the TWT SP period for the low-latency UE. This field can be set to 5 when requesting an additional protection operation (e.g., a Quiet Time Setup frame, an RTS frame, or an MU-RTS frame) to protect the TWT SP at the start point of the TWT SP for the low-latency UE. Alternatively, this field can be set to 6 when requesting that STA-to-STA communication be possible in the TWT SP. The exponent field for the requested low-latency period, together with the significant digits field for the low-latency period, can indicate the SP period for the requested TWT-based low-latency operation. For example, the SP period for the requested TWT-based low-latency operation can be expressed as "(significant digits field value for the low-latency period) × 2^(exponent field value for the low-latency period)." Furthermore, when the field indicating that the TWT operation is a TWT for low-latency operation is set to 1, it can indicate that the TWT information element is for low-latency operation.

[0153] That is, when a non-AP STA is scheduled for a TWT SP, it can only transmit and receive limited frames (e.g., frames that require low latency or are delay-sensitive) in the TWT SP, and cannot transmit or receive other frames, or it can transmit and receive only the limited frames with priority (e.g., the limited frames may have a higher priority).

[0154] Meanwhile, the field indicating the time when low-latency traffic is expected to occur may indicate the time when a frame requiring the low latency is expected to occur. The requested latency field is the maximum latency required for the frame, and together with the unit field for the requested latency, may indicate the required uplink and downlink latency for the frame of the same type. The broadcast TWT information field may be set in the same way as the field setting method in existing broadcast TWT operations. Alternatively, if the TWT operation request frame requests a TWT SP that is only permitted for a specific AC and ACs with higher priority (e.g., if the operation method field for the TWT time is set to 4), the broadcast TWT information field may include the AC or TID to be restricted instead of the broadcast TWT ID field.

[0155] That is, the broadcast TWT information field may include information related to the TID to which the transmission of the frame is restricted by the TWT for low latency operation.

[0156] Specifically, the Broadcast TWT Information field may include a field containing information related to the TID, which may include a Control field, a DL Bitmap (or a restricted TWT DL TID Bitmap) field, and a UL Bitmap (or a restricted TWT UL TID Bitmap) field.

[0157] The control field may include a DL bitmap valid field (or a DL TID bitmap valid field), a UL bitmap valid field (or a UL TID bitmap valid field), and a reserved field.

[0158] The DL Bitmap Valid field indicates the validity of the DL Bitmap field. When set to "0", it indicates that downlink frames for all TIDs are delay-sensitive traffic. When set to "1", it indicates that downlink traffic for TIDs corresponding to a value of "1" in the DL Bitmap is delay-sensitive traffic, and downlink traffic for TIDs corresponding to a value of "0" is delay-insensitive traffic.

[0159] The UL Bitmap Valid field indicates the validity of the UL Bitmap field, and when set to '0', it indicates that uplink frames for all TIDs are delay-sensitive traffic, and when set to '1', it indicates that uplink traffic for TIDs corresponding to a value of '1' in the UL Bitmap is delay-sensitive traffic, and uplink traffic for TIDs corresponding to a value of '0' is delay-insensitive traffic. Meanwhile, the information regarding the low latency time period based on the TWT operation may be set to a generation period of frames requiring low latency to be transmitted in the low latency operation.

[0160] Meanwhile, if TS negotiation for traffic requiring low latency is completed before the negotiation process for low latency operation using the TWT function, the negotiation process for low latency operation may not include the requested latency, etc. In this case, the low latency operation request frame may be configured as shown in FIG. 16, which will be described next.

[0161] 16 shows a second embodiment of the structure of a low latency operation request frame for requesting low latency operation using the TWT function according to an embodiment of the present invention. In FIG. 16, the same description as in FIG. 15 will be omitted.

[0162] 16, a delay operation request frame requesting low-latency operation using the TWT function may be configured similarly to a TWT operation request frame for negotiating broadcast TWT operation. Accordingly, the frame may include a TWT information element, which may include an element ID field, a length field, a control field, and a TWT parameter information field. In this case, the element ID field, the length field, and the control field may be set to the same as those set in the request frame for negotiating broadcast TWT.

[0163] The TWT parameter information field may include a request type field, a TWT field, the minimum time during which the STA remains awake among the TWT time fields, significant digits of the interval between TWT SPs, and broadcast TWT information. Among the request fields, fields other than the operation mode field in TWT time and the field indicating that the TWT operation is a TWT for low-latency operation may be set to the same as the existing broadcast TWT setting method. The operation mode field in TWT time and the field indicating that the TWT operation is a TWT for low-latency operation may be set as shown in FIG. 15. Alternatively, if the exchange of the TWT operation request frame is sent after a negotiation process for adding a TS, allocation of a TWT SP limited to a specific traffic stream ID (TSID) may be requested. In this case, the operation mode field in TWT time may be set to 7. An indication field indicating that the TWT request frame is a TWT request frame for low-latency operation may be added to the request field, as described in FIG. 15. The broadcast TWT information field may be set to the same as the low latency operation request frame using TWT described in Figure 15. Alternatively, if the TWT operation request frame requests the provision of a TWT SP limited to a specific TSID (e.g., if the operation method field in the TWT time is set to 7), the broadcast TWT information field may include the lowest 3 bits of the TSID for limitation instead of the broadcast TWT ID field.

[0164] Meanwhile, the AP or AP MLD can confirm the low latency operation using the TWT function from the content of the request frame, as shown in FIG. 15 or 16. It can allocate one of the broadcast TWTs allocated by the AP for low latency operation according to information such as the requested latency and traffic generation period confirmed from the request frame. Alternatively, it can generate a new broadcast TWT for only the traffic and allocate a TWT SP for low latency operation. When allocating a broadcast TWT in the above manner in response to a low latency operation request using the TWT operation, it can transmit a low latency operation response frame in response to the low latency operation request frame using the TWT operation. Alternatively, if the low latency operation request cannot be accepted, it can transmit a low latency operation response frame rejecting the request. In this case, the low latency operation response frame may be configured as follows:

[0165] 17 is a block diagram showing a low-latency operation response frame that is a response to a request frame requesting low-latency operation using the TWT function. In this case, the description of parts having the same configuration as the request frame requesting low-latency operation using the TWT function in FIGS. 15 and 16 may be omitted.

[0166] 17, the response frame for low latency operation using TWT may be configured similarly to the response frame for broadcast TWT operation. That is, it may include a TWT information element included in the response frame for broadcast TWT operation. The TWT information element may include an element ID field, a length field, a control field, and a TWT parameter information field. The element ID field, length field, and control field may be set to the same as those set in the response frame for broadcast TWT negotiation.

[0167] The TWT parameter information field may include a request type field, a TWT field, a minimum time during the TWT time that the STA remains awake, significant digits of the interval between TWT SPs, and broadcast TWT information. Among the request type fields, fields other than the operation mode field during TWT time and the field indicating that the TWT operation is a TWT for low-latency operation may be set identically to the existing broadcast TWT setting method. The field indicating that the TWT operation is a TWT for low-latency operation may be set identically to FIGS. 15 and 16. The operation mode field during broadcast TWT time is used when restricting frame transmission during the TWT SP time, as in FIGS. 15 and 16. For example, this field may be set to 1 when restricting transmission only in the form of a response frame to a downlink frame (e.g., an ACK or BlockAck frame for a downlink data frame, or an uplink frame transmitted in response to a trigger frame) in the negotiated TWT SP presented in the response frame. In addition, this field may be set to 4 when limiting the AC transmitted within the TWT SP period for the low-latency UE. This field may be set to 5 when an additional protection operation (e.g., a Quiet Time Setup frame, an RTS frame, or an MU-RTS frame) is to be performed at the start point of the TWT SP for the low-latency UE to protect the SP. This field may be set to 6 when allowing STA-to-STA communication in the TWT SP. Alternatively, when negotiation for the TWT operation is transmitted after the negotiation process for adding a TS, allocation of a TWT SP limited to a specific traffic stream ID (TSID) may be requested. In this case, the operation method field during the TWT time may be set to 7. As described with reference to FIGS. 15 and 16, an indication field indicating that the TWT request frame is a TWT request frame for low-latency operation may be added to the request field. The broadcast TWT information field may be set to the same as that of a response frame for the existing broadcast TWT negotiation.Alternatively, when restricting transmission of only frames having a priority equal to or higher than a specific AC during the TWT SP period for low latency operation (e.g., when the operation mode field for the TWT time is set to 4), the AC to be restricted may be further included in the broadcast TWT information field of the response frame. Alternatively, when restricting a specific TSID of frames that can be transmitted during the TWT SP (e.g., when the operation mode field for the TWT time is set to 7), the TSID for restriction may be further included in the broadcast TWT information field of the response frame.

[0168] The negotiation process and operation process of the low latency operation using the TWT operation using the low latency operation request frame and the low latency operation response frame may be performed as follows.

[0169] FIG. 18 shows a first embodiment of a process in which an AP or AP MLD and a STA according to an embodiment of the present invention perform a low-latency operation using the TWT function.

[0170] 18, the process of performing the low-latency operation for the TWT operation may include a step of confirming the low-latency operation capability between the STA and the AP, a step of negotiating the low-latency operation using the TWT operation by transmitting a low-latency operation request frame from the STA and a low-latency operation response frame from the AP, and a step of performing the low-latency operation by allocating TWT SPs for the low-latency operation to a broadcast probe response frame, a beacon frame, etc. In this case, before the step of negotiating the low-latency operation using the TWT operation, a step of negotiating to add a TS between the STA and the AP may be further included. In addition, after the step of negotiating the low-latency operation using the TWT operation, a step of negotiating to exchange the timing of a beacon frame to which the negotiated TWT SP is allocated by the STA may be further included.

[0171] The step of checking the low latency operation capability may be performed in a scanning and connection process between the AP or AP MLD and the STA or STA MLD. The scanning and connection process may be performed according to the processes shown in FIG. 5 and FIGS. 11 to 13. In this case, the AP and STA may transmit a capability element including an indicator indicating whether they support low latency operation using the TWT function. In addition, the AP or AP MLD may transmit a beacon frame, a probe response frame, or the like, including statistical information related to the transmission time of frames transmitted on all operating links. The statistical information may be a Measurement Report information element. Alternatively, the statistical information may be the Measurement Report information element shown in FIG. 14. The STA or STA MLD may check the statistical information transmitted by the AP or AP MLD and perform a connection process with the AP or AP MLD based on the information.

[0172] The process of negotiating to perform low-latency operation using TWT operation after the scanning and connection process may begin with a process in which the STA transmits a low-latency operation request frame using TWT operation to the AP. In this case, the low-latency operation request frame using TWT operation may be configured as shown in FIG. 15 or 16. The request frame may be an action frame. An AP supporting low-latency operation may receive the low-latency operation request frame using TWT operation from the STA and, based on the received content, may determine that the STA requests TWT SP allocation for a frame requiring low latency. If the AP can allocate a TWT SP corresponding to the request frame, the AP may transmit a low-latency operation response frame using TWT in response to the request frame. In this case, the TWT operation response frame may be configured as shown in FIG. 17.

[0173] Alternatively, when a STA and an AP negotiate to add a TS, the AP can transmit a low-latency operation response frame using an unrequested TWT operation to support the TS. In this case, after negotiating to add a TS, the STA can transmit a frame requesting low latency to the TWT SP without transmitting a separate request frame. In this case, if the STA does not perform low-latency operation based on the parameters included in the unrequested low-latency operation response frame, the STA can cancel the low-latency operation using a TWT release frame and transmit a low-latency operation request frame using a new TWT operation to request low-latency operation based on the TWT operation from the AP.

[0174] When the low-latency operation negotiation process using the TWT operation is completed, the AP may assign a broadcast TWT ID to the TWT SP assigned to the STA. The broadcast TWT ID may be received in the low-latency operation response frame described in FIG. 17. In this case, the same TWT ID may be assigned to multiple STAs. The low-latency operation method using the TWT operation may be performed similarly to the broadcast TWT operation method. That is, a TWT element including a broadcast TWT SP may be transmitted to all broadcast TWT IDs set in the AP in a beacon frame and a broadcast probe response frame. In this case, some broadcast TWT IDs may be TWT SPs for low-latency operation. A STA that has completed the low-latency operation negotiation using the TWT operation can check the broadcast TWT ID assigned by the low-latency operation response frame and can check the TWT parameter including the assigned broadcast TWT ID from the TWT element included in the beacon frame. It can transmit and receive frames requesting low latency at the time indicated by the TWT parameter. On the other hand, a STA that has not been assigned the broadcast TWT ID does not need to perform frame transmission operations in the TWT SP displayed in the TWT element if the TWT SP is confirmed as a TWT SP for low latency operation.

[0175] In this case, the TWT element may be transmitted by being included in a control frame or a management frame such as a beacon frame or a probe response frame.

[0176] To further protect the transmission of frames for low latency operation, the AP may further transmit an information element for protecting the time in the beacon frame. For example, when transmitting TWT SPs for low latency operation in the beacon frame, one or more Quiet information elements set to the same time for some or all of the TWT SPs for low latency operation may further be transmitted. Among the STAs that receive the Quiet information element, STAs that are not assigned a TWT SP at the same time may set their NAV at the time included in the Quiet information element and not transmit frames. If the TWT SP time indicated in the TWT parameter containing the assigned broadcast TWT ID matches the time in the received Quiet information element, the STA may ignore the Quiet information element and transmit frames at the time. This process allows a STA that is assigned a TWT SP for low latency operation to transmit frames requiring low latency at the time without interfering with other UEs.

[0177] That is, the beacon frame may further include a quiet information element for protecting the TWT SP. At least one non-AP STA not configured for TWT operation may set its NAV based on the quiet information element. In other words, at least one non-AP STA may not set its NAV and transmit a frame at the time indicated in the quiet information element. For example, at least one STA not configured for TWT operation may set its NAV to the same value as the time indicated by the quiet information element (or quiet element). Alternatively, a legacy STA (e.g., a VHT non-AP STA) may set its NAV to the same value as the time indicated by the quiet information element (or quiet element).

[0178] At this time, the quiet information element may be transmitted in a control frame and / or a management frame (for example, a probe response frame) in addition to a beacon frame.

[0179] When both the TWT SP and the quiet information element are configured and the interval configured by the quiet information element overlaps with part or all of the TWT SP for delay operation, the non-AP STA can ignore the overlapping part or all of the interval configured by the quiet information element. That is, the non-AP STA can operate as if the quiet interval, which is the interval configured by the quiet information element and overlaps with the limited TWT SP for low latency, does not exist.

[0180] The interval set by the quiet information element and the start time of the TWT SP for low latency operation may be the same. That is, if the interval set by the quiet information element and the TWT SP for low latency operation overlap, the interval set by the quiet information element and the start time of the TWT SP for low latency operation may be the same.

[0181] Meanwhile, after the negotiation process for low latency operation using the TWT function, a process of negotiating a transmission time of a beacon frame including the negotiated broadcast TWT ID between the STA and the AP may be further performed. This process may be performed by exchanging a broadcast TWT request frame and a broadcast TWT response frame. In this case, the TWT field may be set to the time when the beacon frame is transmitted. In this case, a field indicating the period between TWT SPs may be set to the period of the beacon frame including the corresponding broadcast TWT ID.

[0182] Meanwhile, a negotiation process for low latency operation using the TWT function may be performed during the connection process between the STA and the AP. Therefore, a STA that wants to perform low latency operation does not need to perform a separate negotiation process after connecting to the AP. In this case, the negotiation and operation process using the TWT operation may be performed as follows.

[0183] 19 is a second example of a process in which an AP or AP MLD and a STA perform low-latency operations using the TWT function according to an embodiment of the present invention. At this time, descriptions overlapping with those in FIG. 18 may be omitted.

[0184] 19, the process of performing the low-latency operation for the TWT operation may include a step of confirming the low-latency operation capability between the STA and the AP, a step of negotiating the low-latency operation using the TWT operation by transmitting a low-latency operation request frame from the STA and a low-latency operation response frame from the AP, and a step of performing the low-latency operation by allocating TWT SPs for the low-latency operation to a broadcast probe response frame, a beacon frame, etc. In this case, before the step of negotiating the low-latency operation using the TWT operation, a step of negotiating to add a TS between the STA and the AP may be further included. In addition, after the step of negotiating the low-latency operation using the TWT operation, a step of negotiating to exchange the timing of a beacon frame to which the negotiated TWT SP is allocated by the STA may be further included.

[0185] The step of checking the low latency operation capability may be performed during a scanning and connection process between an AP or AP MLD and a STA or STA MLD. The scanning and connection process may be performed according to the processes shown in FIG. 5 and FIGS. 11 to 13. In this case, the AP may transmit a beacon frame, a broadcast probe response frame, and a capability element in the probe response frame, including an indicator indicating whether the AP supports low latency operation using the TWT function. The STA may receive the beacon frame, the broadcast probe response frame, and the probe response frame and confirm that the AP supports low latency operation using the TWT operation. The AP or AP MLD may also transmit a beacon frame, a probe response frame, etc., including statistical information related to the transmission time of frames transmitted on all operated links. The statistical information may be a Measurement Report information element. Alternatively, the statistical information may be the Measurement Report information element shown in FIG. 14. Meanwhile, the STA may transmit a probe request frame and an access request frame including an indicator indicating whether the AP supports low latency operation using the TWT function in the capability element. The AP can confirm that the STA is performing low latency operation using TWT operation based on the probe request frame and connection request frame received from the STA.

[0186] A STA that has confirmed that the AP supports the function through a beacon frame, a broadcast probe response frame, and a probe response frame received from the AP may include a low-latency operation request indicator using the TWT function, requesting the use of the function, in a connection request frame when a frame requesting low latency occurs. In this case, the low-latency operation request indicator using the TWT function may be the TWT information element described with reference to FIG. 16 or 17. The AP may receive a connection request frame from the STA and check the low-latency operation request indicator using the TWT function included in the frame. The AP may confirm that the STA requests TWT SP allocation for a frame requesting low latency based on the content of the checked request indicator. If the AP can allocate a TWT SP corresponding to the request frame, the AP may transmit a connection response frame including a low-latency operation response indicator using the TWT as a response to the request frame. In this case, the low-latency response indicator using the TWT operation may be the TWT information element described with reference to FIG. 17.

[0187] Alternatively, if the AP determines from the probe request frame and connection request frame transmitted by the STA that the STA supports low-latency operation using the TWT function, the AP may transmit a low-latency operation response indicator using the unrequested TWT operation in the connection response frame. In this case, the STA may transmit a frame requesting low latency to the TWT SP without transmitting a separate request frame. In this case, if the STA does not perform low-latency operation based on the parameters included in the unrequested low-latency operation response frame, the STA may cancel the low-latency operation using a TWT cancel frame and transmit a low-latency operation request frame using a new TWT operation to request low-latency operation from the AP.

[0188] When the low-latency operation negotiation process using the TWT operation is completed, the AP may assign a broadcast TWT ID to the TWT SP assigned to the STA. The STA may receive the broadcast TWT ID through the low-latency operation response frame described in FIG. 17. At this time, the same TWT ID may be assigned to multiple STAs. Thereafter, the low-latency operation method using the TWT operation may proceed as shown in FIG. 18. That is, the TWT SP for the low-latency operation may be included in the beacon frame, and the negotiated low-latency operation may be performed using the TWT SP. In addition, to further protect the transmission of the frame for the low-latency operation, the AP may further transmit an information element for protecting the time in the beacon frame. After the negotiation process for the low-latency operation using the TWT function, a process of negotiating the transmission time of the beacon frame including the negotiated broadcast TWT ID between the STA and the AP may be further performed.

[0189] Meanwhile, during low latency operation using the TWT operation, if a terminal that is not capable of STR operation is connected to the link, the following problem may occur.

[0190] Figure 20 shows the operation when STR operation is not possible for AP MLD and STA MLD performing low latency operation, where the TWT information element is missed due to inability to receive beacon frames, and the TWT time for low latency operation is not protected.

[0191] Referring to FIG. 20, an AP MLD may include two or more APs. In this case, each AP can operate a separate link. For example, an AP MLD may include AP1 and AP2, where AP1 can operate on link 1 and AP2 on link 2. Meanwhile, a STA MLD may include STA1 and STA2. The STA MLD can perform a multi-link operation with the AP MLD using link 1 and link 2. In this case, the STA MLD may not be able to perform an STR operation on link 1 and link 2. That is, while STA1 of the STA MLD is transmitting a frame on link 1, STA2 may not be able to perform a channel sensing operation and a frame reception operation on link 2 due to interference caused by the transmission. Alternatively, while STA2 of the STA MLD is transmitting a frame on link 2, STA1 may not be able to perform a channel sensing operation and a frame reception operation on link 1 due to interference caused by the transmission.

[0192] The inability of STR operation in the STA MLD may interfere with low-latency transmission using the TWT operation. For example, when performing low-latency transmission using a TWT terminal over link 1, the TWT SP may be indicated in a beacon frame. In this case, if the STA MLD is performing frame transmission using link 2, it may not be able to receive the beacon frame transmitted over link 1 and may not be able to recognize the TWT SP for low-latency operation included in the beacon frame. STA1 of the STA MLD that cannot recognize the TWT SP for the low-latency terminal may perform a channel approach operation for frame transmission using the TWT SP, and transmission of frames requiring low latency in the TWT SP may not be protected.

[0193] To solve the above problem, AP MLD can simultaneously update TWT-related parameters for low latency operation as follows.

[0194] FIG. 21 is a diagram showing an operation in which parameters are changed at the same time when AP MLD performs low-latency operation using TWT operation.

[0195] Referring to FIG. 21, the parameter change time may be set to the same for all TWT SPs for low-latency UEs allocated by the AP MLD. For example, TWT SP-related parameters for low-latency UEs may be allowed to be changed only in a beacon frame including a Delivery Traffic Indication Map (DTIM). That is, the broadcast TWT maintenance fields of all TWT parameter information fields for low-latency UEs included in a TWT information element for allocating TWT SPs for low-latency UEs transmitted in a beacon frame may be set to the same value. TWT SPs for low-latency UEs may be generated periodically after the same time from the TBTT time, except for beacon frames (e.g., DTIM beacon frames) transmitted at the specific time point. Meanwhile, a STA MLD that is not capable of STR operation may not perform frame transmission operations on other links when a beacon frame (e.g., a DTIM beacon frame) transmitted at the specific time point is transmitted. Through this process, even if a STA MLD that is not capable of STR operation cannot receive a specific beacon frame, it can determine the TWT SP for low-latency UEs based on the content of the TWT information element included in a previously transmitted beacon frame.

[0196] That is, when a non-AP STA configures a multi-link device (MLD), the MLD cannot transmit frames on other links while receiving the beacon frame. In other words, if a STA included in a non-AP MLD successfully acquires a TXOP on one link of an STR link pair before the TBTT of the other link of the NSTR link pair, the STA must end the TXOP before the TBTT of the other link when it attempts to receive a beacon frame on the other link.

[0197] Alternatively, to solve the above problem, an additional protection frame can be transmitted at the beginning of the TWT SP to protect the TWT SP. The transmission operation of the protection frame may be performed as follows.

[0198] FIG. 22 illustrates an example of an operation in which AP MLD further transmits a protection frame at the start of a TWT time to protect the TWT time for low latency operation.

[0199] Referring to FIG. 22, to prevent terminals not assigned to the TWT SP for the low-latency terminal from transmitting frames during that time, an AP can transmit a reservation frame at the start of the TWT SP. The reservation frame may be an uncommitted Quiet Time setting frame. The Duration field value of the Quiet Time setting frame is specified as the TWT SP time, preventing STAs not negotiated in the TWT SP for the low-latency terminal from performing a channel contention process. Meanwhile, STAs negotiated with the AP to transmit frames in the TWT SP can transmit frames requiring low latency during that period.

[0200] Alternatively, the channel reservation process between the AP and the STA can be performed first in the TWT SP. For example, the AP may transmit an MU-RTS frame at the start of the TWT SP, and the assigned STA may transmit a CTS frame. In this case, the MU-RTS frame may include the AID of the STA assigned to the TWT SP. The NAV value set in the MU-RTS may be specified to extend until the end of the TWT SP. The STA assigned to the TWT SP can receive the MU-RTS frame and confirm that it intends to perform the channel reservation process using the MU-RTS frame. As a result, the multiple STAs can simultaneously transmit CTS frames in response to the MU-RTS frame. In this case, the end point of the NAV set in the transmitted CTS frame may be set to the end of the TWT SP. After the MU-RTS and CTS frame exchange procedure, the STA assigned to the TWT SP can transmit frames through a channel contention process. On the other hand, for STAs that are not assigned to the TWT SP, the NAV is set in the TWT SP and they do not need to perform frame transmission operations.

[0201] On the other hand, when a STA MLD that is not capable of STR operation performs low-latency operation using the TWT function, if it transmits frames on another link during the TWT SP time for low-latency operation, it may not be able to transmit frames requiring a low latency during that TWT SP time. In other words, if a frame transmission operation is performed on another link that is not capable of STR operation during that TWT SP time, the frame transmission operation requiring a low latency may not be able to be performed due to the influence of interference from that transmission. To solve this problem, when a STA MLD that performs low-latency operation using TWT is unable to perform STR operation, frame transmission on another link may be restricted as follows:

[0202] 23 illustrates an example of a process in which a STA that is not capable of AP MLD and STR operations performs low latency operation using the TWT function. In this case, the same content as that of FIG. 18 or FIG. 19 and FIG. 22 may be omitted.

[0203] Referring to FIG. 23, even a STA MLD that is not capable of STR operation can perform low-latency operation using the AP MLD and TWT function using some links. For example, the STA MLD can perform multi-link operation with the AP MLD using link 1 and link 2. In this case, the STA MLD may not be able to perform STR operation on link 1 and link 2. That is, while STA1 of the STA MLD is transmitting a frame on link 1, STA2 may not be able to perform channel sensing and frame reception on link 2 due to interference caused by the transmission. Alternatively, while STA2 of the STA MLD is transmitting a frame on link 2, STA1 may not be able to perform channel sensing and frame reception on link 1 due to interference caused by the transmission. In this case, the AP MLD can negotiate TWT operation for low-latency operation on link 1 with the STA MLD. The connection process and negotiation process for MLD operation may be performed in the manners of FIGS. 11 to 13. In this case, if the STA MLD wants to perform low latency operation using the TWT operation for some links, it can negotiate with the AP MLD to perform low latency operation using the TWT operation in the manner shown in Figures 18 and 19. For example, STA1 belonging to the STA MLD may negotiate with AP1 of the AP MLD to perform low latency operation using the TWT operation on link 1.

[0204] According to the negotiated content, AP1 belonging to the AP MLD can assign a broadcast TWT ID to STA1 and transmit a beacon frame including TWT parameters indicated by the broadcast TWT ID. The TWT parameters may include the start time of the TWT SP. STA1 in the STA MLD that is not capable of STR operation can receive the beacon frame and confirm the TWT SP for low latency operation corresponding to the assigned broadcast TWT ID included in the received beacon frame. Alternatively, as described in FIG. 21, based on the TWT SP included in a previously transmitted beacon frame, the TWT SP for low latency operation corresponding to the assigned broadcast TWT ID can be inferred from the TBTT of the beacon frame.

[0205] STA1 of the STA MLD that recognizes the TWT SP for low latency operation can transmit frames requiring low latency after the start of the TWT SP. In this case, to prevent the transmission of the frames requiring low latency from being delayed, STA1 operating on link 1 and STA2 that is not capable of STR operation can terminate the transmission of frames that were transmitted before the start of the TWT SP. STA2 does not need to transmit frames during the TWT SP for low latency operation recognized by the STA MLD.

[0206] FIG. 24 is a conceptual diagram showing the structure of an AP MLD and a STA MLD that perform a multi-link operation according to an embodiment of the present invention.

[0207] Referring to FIG. 24, an AP MLD (Multi-link Device) may be a device including one or more wireless access points (APs) and may be a device connected to a higher layer through one interface. That is, the AP MLD may be connected to a Logical Link Control (LLC) layer through one interface. Multiple APs included in the AP MLD may share some functions at the MAC layer. Each AP in the AP MLD may operate on a different link. A STA MLD may be a device including one or more non-AP STAs and may be a device connected to a higher layer through one interface. That is, the STA MLD may be connected to the LLC layer through one interface. Multiple STAs included in the STA MLD may share some functions at the MAC layer. The STA MLD may also be called a non-AP MLD. In this case, the AP MLD and the STA MLD can perform a multi-link operation, communicating using multiple individual links. That is, when the AP MLD includes multiple APs, each AP forms a separate link and can transmit and receive frames using multiple links with each UE included in the STA MLD. In this case, each link can operate in the 2.4 GHz, 5 GHz, or 6 GHz band, and each link can perform bandwidth extension operation. For example, if AP MLD configures one link in the 2.4 GHz band and two links in the 5 GHz band, the 2.4 GHz band can transmit frames at a bandwidth of 40 MHz using the bandwidth extension method, and each link using the 5 GHz band can transmit frames at a bandwidth of up to 320 MHz by utilizing discontinuous bandwidth.

[0208] Meanwhile, due to interference issues within some or all of the APs or terminals belonging to the AP MLD or STA MLD, while one AP or terminal is transmitting, other APs or terminals in the same device may not be able to receive. This operation, in which one AP or terminal in an MLD receives while another AP or terminal in the MLD is transmitting, is called STR (Simultaneous Transmit and Receive). The AP MLD may be capable of STR operation for all links. Alternatively, STR operation may be disabled for some of the links of the AP MLD. If STR operation is disabled for some of the links, while one AP is transmitting among the APs operating on the multiple links, other APs may not be able to receive. An STA MLD capable of STR operation may be connected to an AP MLD, and an STA MLD incapable of STR operation may be connected to some or all of the links. If a STA MLD that is not capable of STR operation is connected to some or all of the links, while a terminal using the link that is not capable of STR operation is transmitting, the other links may not be able to receive. Also, terminals that do not belong to the MLD (e.g., IEEE 802.11a / b / g / n / ac / ax terminals) may be connected to the AP included in the AP MLD.

[0209] FIG. 25 is a timing diagram illustrating a connection process and a negotiation process for a multi-link operation between an AP MLD and a STA MLD according to an embodiment of the present invention.

[0210] Referring to FIG. 25, the AP MLD and the STA MLD may perform a negotiation process for a multiple link use operation during the scanning and connection process described in FIG. 5. For example, during the scanning process described in FIG. 5, an AP included in the AP MLD may transmit a beacon frame including an indicator indicating that a multiple link operation is available, the number of available links, the number of available links, and information on the AP operating the corresponding link. In this case, only a portion of the information on the APs belonging to the AP MLD that do not transmit the corresponding beacon frame may be transmitted. In this case, the information on the APs that do not transmit the corresponding beacon frame may be transmitted in the form of an RNR (Reduced Neighbor Report) information element. In this case, the RNR information element may include one or more of the link ID, channel, and operation class of the link operated by the corresponding AP, and a counter that notifies the update status of the parameters used by the corresponding AP, among the information on the AP included in the information element.

[0211] Meanwhile, a terminal belonging to the STA MLD can receive the beacon frame and confirm that the AP transmitting the beacon frame is an AP belonging to the AP MLD. The terminal can also confirm some information about other APs belonging to the AP MLD (e.g., link IDs, channel information, parameter update counters at the AP, etc.). Alternatively, a terminal belonging to the STA MLD can transmit a probe request frame including an indicator indicating that multi-link operation is available during the scanning process shown in FIG. 5, and an AP belonging to the AP MLD can transmit a probe response frame including an indicator indicating that multi-link operation is available. In this case, the AP can further transmit the probe response frame including the number of links available during multi-link operation, link information, and information about the AP operating the links.

[0212] If the AP belongs to the AP MLD, the STA MLD, having confirmed some information about other APs belonging to the AP MLD, can transmit a multi-link probe request frame to the AP, requesting all information about the other APs from the AP MLD in order to perform multi-link operation. The multi-link probe request frame can indicate necessary information for the AP that the STA MLD wishes to receive from the AP MLD. In this case, the necessary information may include one or more of the following: HT capability element, HT operation element, VHT capability element, VHT operation element, HE capability element, HE operation element, EHT capability element, EHT operation element, target beacon transmission time (TBTT), EDCA parameter setting information, channel information on which the AP operates, and bandwidth information supported by the AP. The STA MLD can request information about one or more specific APs in the multi-link probe request frame. Alternatively, the STA MLD can request information about all APs operated by the AP MLD.

[0213] The AP MLD can receive a multi-link probe request frame from the STA MLD and can confirm that the STA MLD requests some or all of the information elements related to the operation of the AP from some or all of the APs belonging to the AP MLD. After confirming the request information, the AP MLD can transmit the requested information to the STA MLD in the form of a multi-link probe response frame. Information that overlaps with information used by the AP transmitting the multi-link probe response frame may be omitted. Since the multi-link probe response frame contains more information than the probe response frame shown in FIG. 5, the transmission of the multi-link probe response frame may occupy the channel for a longer period of time. Therefore, to prevent excessive channel occupancy due to the transmission of excessive multi-link probe response frames, if a multi-link probe response frame has already been transmitted to a specific STA MLD, a response to a multi-link probe request frame received from the same STA MLD may not be transmitted. Meanwhile, the AP MLD can transmit a multi-link probe response frame in the form of a broadcast frame, including information of all APs belonging to the AP MLD. The multi-link probe response frame transmitted in the form of a broadcast frame may be transmitted at a specific interval or more. In this case, if a multi-link probe response frame has been transmitted in the form of a broadcast frame within a specific time period before receiving a multi-link probe request frame from the STA MLD, the multi-link probe response frame may not be transmitted. In this case, the specific time period may be after the time when the STA belonging to the STA MLD transmits the probe request frame of FIG. 5.

[0214] The STA MLD that receives the multi-link probe response frame from the AP MLD can check the operation parameters of each AP belonging to the AP MLD and perform a connection process and negotiation process for multi-link operation with the AP MLD. Here, the negotiation process for multi-link operation may be performed during the connection process between an AP belonging to the AP MLD and a terminal belonging to the STA MLD. That is, a terminal (e.g., STA1) belonging to the STA MLD can send an access request frame to an AP (e.g., AP1) belonging to the AP MLD, and can send an indicator indicating that the terminal's multi-link operation is available and a request indicator requesting that the terminal perform multi-link operation. Here, the STA MLD can send an access request frame to the AP MLD, including information on the link to be used and terminal capability information related to the link (e.g., information indicating whether STR with other links is possible, the maximum transmittable bandwidth, the maximum number of usable spatial streams, etc.). An AP that receives a connection request frame from the terminal can check an indicator requesting a multi-link operation, and if the AP is capable of a multi-link operation, can transmit a connection response frame to the terminal that allows the multi-link operation, including link information used for the multi-link operation and parameters used for each link. The parameters for the multi-link operation may include one or more of the link ID, MAC address, bandwidth, bandwidth expansion direction, Target Beacon Transmission Time (TBTT), and whether or not STR operation is enabled for each link used. After the connection request frame and response frame are exchanged and the use of the multi-link operation is confirmed, the AP MLD and STA MLD can perform a frame transmission operation using multiple links through the multiple APs included in the AP MLD and the multiple terminals included in the STA MLD after the connection procedure.

[0215] FIG. 26 is a timing diagram illustrating a transmission scheme using multiple links according to an embodiment of the present invention.

[0216] Referring to Figure 26, after completing the negotiation for the multi-link operation, the AP MLD and STA MLD can perform a frame transmission / reception operation using the multi-links using a link-specific independent transmission method. When the multi-link operation is performed using the link-specific independent transmission method, each AP or terminal belonging to the AP MLD or STA MLD independently performs a channel contention process for frame transmission on each link and transmits frames on each link. In this case, the transmission start and end times of frames transmitted on each link do not need to be the same. When the independent transmission method is performed, a transmission opportunity (TXOP) obtained through the channel contention process on each link may be obtained independently on each link.

[0217] The independent transmission method has the advantage that it can be performed more efficiently on each link because channel access is performed independently for each link depending on the channel occupancy state. However, if the interval between the operating bands of each AP operating in AP MLD is not wide enough, and STR operation is not possible in AP MLD or STA MLD, the independent transmission method may not be able to perform multiple link operation.

[0218] Meanwhile, when the STR operation is not possible on some or all of the links for the receiving MLD, the frame transmission / reception process using the link on which the STR operation is not possible may be performed as follows.

[0219] FIG. 27 shows an embodiment of a frame transmission / reception operation between a receiving MLD incapable of STR operation and a transmitting MLD capable of STR operation on a part or all of the link according to an embodiment of the present invention.

[0220] Referring to (a) of FIG. 27, if STR operation is not possible in the MLD, frame reception may not be possible on another link while a frame is being transmitted on another link. For example, AP1 and AP2 belong to the AP MLD, and AP1 can operate link 1, and AP2 can operate link 2. STA1 and STA2 belong to the STA MLD, and STA1 may be connected to AP1 and STA2 to AP2 through a negotiation process for multi-link operation. In this case, the STA MLD may be unable to perform STR operation on link 1 and link 2. That is, while STA1 is transmitting a frame on link 1, STA2 may be unable to receive a frame on link 2. Conversely, while STA2 is transmitting a frame on link 2, STA1 may be unable to receive a frame on link 1. The situation in which STR operation is not possible may be due to interference within the device that occurs during frame transmission on one link. As a result, if the STA MLD is unable to perform STR operation on some links, channel sensing may not be possible on other links while a frame is being transmitted on one of the links. For example, while STA1 is transmitting a frame via link 1, STA2 may not be performing channel sensing for frame transmission via link 2. Therefore, while STA1 is transmitting a frame via link 1, STA2 may not be able to start frame transmission via link 2 after a channel contention process. In other words, if STR operation is not possible on the link in either the transmitting MLD or the receiving MLD, multi-link communication operation via the independent transmission method shown in FIG. 11 may not be possible.

[0221] If the AP MLD or STA MLD cannot perform the STR operation on the multiple links (e.g., if the bandwidth gap between the links is insufficient for the multiple link operation), the AP MLD and STA MLD may perform the multiple link operation in the form of a simultaneous transmission operation, as shown in FIG. 12(b). The simultaneous transmission operation may be performed by aligning the transmission start time or transmission end time of a frame transmitted on each link. In this case, the transmission start time or transmission end time of a frame may be referred to as the transmission start time or transmission end time of a PPDU including the frame. That is, if the lengths of frames transmitted by an AP or a UE on each link are different, padding or padding bits may be added to align the transmission end points. In addition, the TXOP time for frame transmission on each link may be aligned. In this case, the simultaneous transmission type multiple link operation may include a negotiation step for simultaneous transmission on multiple links and a step of performing simultaneous transmission using multiple links. The negotiation for simultaneous transmission may include simultaneously transmitting request frames to one or more links to acquire a TXOP for simultaneous transmission from an MLD (e.g., AP MLD or STA MLD) having data to be transmitted, and transmitting a response frame from an MLD receiving the data after a Short Interframe Space (SIFS) from the time when the request frame is completely received. In this case, the response frame may be simultaneously transmitted from one or more links that received the request frame. The request frame may be a control frame. For example, the request frame may be an RTS or MU (Multi-user)-RTS frame, and the response frame may be a CTS frame. Meanwhile, if a channel of one link is occupied during channel contention for simultaneous transmission, a channel access procedure for simultaneous transmission may be performed, or a frame transmission operation may be performed using only the link with an available channel.

[0222] The channel approach process for the simultaneous transmission operation may be performed in various manners. For example, a backoff process may be performed on multiple links for simultaneous transmission, and carrier sensing may be performed on all links until the backoff values of all links reach 0. If the carrier sensing results show that channels on all links are free, simultaneous transmission may be performed using the multiple links. Alternatively, after performing a backoff operation on one link, if channels on other links are free during a specific time (e.g., AIFS, DIFS, or PIFS) before the end of backoff, simultaneous transmission may be performed using the free links of the channels.

[0223] On the other hand, if the STR operation is not possible for the transmitting MLD on the link, and the channel status of one or some of the links is busy during the channel access process for frame transmission in FIG. 10(b), one of the following methods can be used:

[0224] 1) After the occupancy period ends, carrier sensing is performed on the channels of both links at a specific time (e.g., PIFS, AIFS, or AIFS + backoff time) to confirm that the channels of both links are vacant, and then simultaneous transmission is performed using the method shown in Figure 27(b) above.

[0225] 2) Transmission operations are performed only on links with available channels.

[0226] When the operation 2) above is performed, it is not necessary to perform a backoff operation for frame transmission until the end of transmission on the link that transmits even after the end of the occupancy time of the link whose channel state was occupied.

[0227] Meanwhile, if the transmitting MLD is capable of STR operation on the corresponding link and the receiving MLD is not capable of STR operation on the corresponding link, and the channel status of one or some of the links is busy during the channel access procedure for frame transmission in FIG. 12(b), one of the following methods can be used:

[0228] 1) After the occupancy period ends, carrier sensing is performed on the channels of both links at a specific time (e.g., PIFS, AIFS, or AIFS + backoff time) to confirm that the channels of both links are vacant, and then simultaneous transmission is performed using the method shown in Figure 12(b) above.

[0229] 2) Transmission operations are performed only on links with available channels.

[0230] When the operation 2) is performed, after the end of the occupancy time of the link whose channel state is occupied, the channel access process can be independently performed on the link to transmit the frame.

[0231] Meanwhile, when the transmitting MLD is capable of STR operation and the receiving MLD is not capable of STR operation on the corresponding link, the start and end times of transmission of frames transmitted from the transmitting MLD over multiple links do not need to be the same. That is, as shown in FIG. 12(c), after starting frame transmission over one link, the frame transmission can be performed independently over the other links after completing the channel contention process for frame transmission over the other links. For example, the AP MLD may be capable of STR operation over Link 1 and Link 2, while the STA MLD may not be capable of STR operation over Link 1 and Link 2. In this case, as shown in FIG. 12(b), if the channel state of Link 2 is occupied during the channel access process for frame transmission, AP1 of the AP MLD can first transmit a frame over Link 1. Because the AP MLD is capable of STR operation, AP2 can perform a channel contention process for frame transmission over Link 2 while AP1 is transmitting a frame over Link 1. After completing the channel contention process and channel access process, AP2 can transmit a frame over Link 2. Since the STA MLD is not in the middle of transmitting a frame on link 1, STA2 on link 2 can receive the frame transmitted by AP2. Meanwhile, if one or more of the frames transmitted by the transmitting MLD request an immediate response (e.g., a BlockAck frame) from the receiving MLD, the transmission of the response frame may occur while a reception operation is being performed on another link. In this case, the transmission of the response frame may hinder the frame reception operation on the other link. To prevent this situation, if one or more of the frames transmitted from the transmitting MLD request the transmission of a response frame, the end times of transmission of PPDUs containing frames transmitted on the multiple links may be synchronized.

[0232] Meanwhile, when a frame transmission / reception operation is performed between an AP and a STA, a channel reservation process can be performed to protect the frame transmission / reception operation. The channel reservation process can be performed by a transmitting STA that intends to transmit a frame transmitting a Request to Send (RTS) frame to a receiving STA, and the receiving STA transmitting a Clear to Send (CTS). In this case, after receiving the RTS frame, the receiving STA performs a channel sensing operation during a SIFS time, and can transmit a CTS only if the channel is idle.

[0233] Meanwhile, when an AP intends to reserve a channel for multi-user transmission with multiple STAs, it may perform a process of exchanging MU (Multi-user)-RTS and CTS frames. The procedure for exchanging MU-RTS and CTS frames between the AP and multiple STAs may be performed as follows.

[0234] FIG. 28 shows a first embodiment of the operation for protecting frame transmission and reception by the MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention.

[0235] Referring to Figure 28, when an AP attempts to transmit a frame to multiple STAs, it may perform an MU-RTS frame and CTS frame exchange procedure before transmitting the frame to protect the frame transmission operation. The MU-RTS frame may be transmitted using one of the following channels: the primary 20 MHz channel, the primary 40 MHz channel, the primary 80 MHz channel, the primary 160 MHz or 80 + 80 MHz channel, the primary 240 MHz or primary 160 + 80 MHz channel, and the primary 320 MHz or 160 + 160 MHz channel. In this case, the MU-RTS may indicate the ID (e.g., Association ID) of the STA transmitting the CTS, the channel on which each STA transmits the CTS frame (e.g., the primary 20 MHz channel, the primary 40 MHz channel, the primary 80 MHz channel, the primary 160 MHz or 80 + 80 MHz channel, the primary 240 MHz or primary 160 + 80 MHz channel, and the primary 320 MHz or 160 + 160 MHz channel). The MU-RTS frame may be transmitted in the form of a trigger frame. Alternatively, the MU-RTS frame may be configured as shown in Fig. 14 or 17 (described later). The MU-RTS frame may be a frame requesting simultaneous transmission of CTS frames from multiple STAs. In this case, the multiple STAs may include HE STAs defined in IEEE 802.11ax and EHT STAs defined in IEEE 802.11be.

[0236] Multiple STAs receiving an MU-RTS frame from an AP can check the information included in the MU-RTS frame. The multiple STAs can check the information in the received MU-RTS frame and check the AID value included in one or more user information fields included in the MU-RTS frame. If the AID value matches the AID value assigned to the STA, the STA can check that the MU-RTS frame requests the STA to transmit a CTS frame. After receiving the MU-RTS frame, a STA that includes an AID in the MU-RTS frame can perform channel sensing within a SIFS on the channel indicated in the MU-RTS frame. The channel may be one of a primary 20 MHz channel, a primary 40 MHz channel, a primary 80 MHz channel, a primary 160 MHz / 80+80 MHz channel, a primary 240 MHz / 160+80 MHz channel, or a primary 320 MHz / 160+160 MHz channel. In this case, if the STA that received the MU-RTS frame is an HE STA, the maximum bandwidth of the channel that transmits the CTS frame may be 160 MHz or 80 + 80 MHz. If the STA that received the MU-RTS frame is an EHT STA, the maximum bandwidth of the channel that transmits the CTS frame may be 320 MHz or 160 + 160 MHz. The channel sensing operation may include physical sensing, virtual sensing, and NAV (Network Allocation Vector) confirmation processes.

[0237] If the indicated channel is idle during a SIFS time after a STA receives the MU-RTS frame, the multiple STAs indicated by the MU-RTS frame can simultaneously transmit CTS frames SIFS after the end of transmission of the PPDU containing the MU-RTS frame. The CTS frame may be transmitted in the indicated channel in the form of a non-HT PPDU or a non-HT duplicated PPDU, which is repeated every 20 MHz band. The CTS frames transmitted by the multiple STAs may be identical. Therefore, the AP can receive the CTS frame on each 20 MHz channel for the MU-RTS frame transmitted as shown in (a) of FIG. 28. The received power of the CTS frame received on each 20 MHz channel may be different. When the AP receives a CTS frame in response to the MU-RTS, the AP can perform MU-OFDMA or MU-MIMO operation with the multiple STAs based on the bandwidth of the received CTS frame.

[0238] Meanwhile, as described above, the transmission bandwidth of the CTS frame transmitted by the STAs that received the MU-RTS frame may vary. For example, referring to (b) of FIG. 13, if the channel instructed by the MU-RTS frame to transmit the CTS frame is the primary 20 MHz channel, STA1 can transmit the CTS frame after performing channel sensing only on the primary 20 MHz channel. In this case, the CTS frame may be transmitted in the form of a non-HT PPDU. After transmitting the CTS frame, STA1 can receive downlink frames within the 20 MHz channel.

[0239] Referring to (c) of Figure 28, if the channel instructed by the MU-RTS frame to send a CTS frame is the primary 40 MHz channel, the STA (e.g., STA2) indicated in the user information field of the MU-RTS frame can transmit a CTS frame after performing channel sensing only on the primary 40 MHz channel. In this case, the CTS frame can be transmitted in the form of a non-HT duplicated PPDU. After transmitting the CTS frame, STA2 can receive downlink frames within the 40 MHz channel.

[0240] Referring to (d) of Figure 28, if the channel instructed in the MU-RTS frame to send a CTS frame is the primary 80 MHz channel, the STA (e.g., STA3) indicated in the user information field of the MU-RTS frame can transmit a CTS frame after performing channel sensing only on the primary 80 MHz channel. In this case, the CTS frame can be transmitted in the form of a non-HT duplicated PPDU. After transmitting the CTS frame, STA3 can receive downlink frames within the 80 MHz channel.

[0241] The MU-RTS frame used in the MU-RTS frame and CTS frame exchange procedure may be configured as follows.

[0242] FIG. 29 shows a first embodiment of the structure of an MU-RTS frame according to an embodiment of the present invention.

[0243] Referring to FIG. 29, the MU-RTS frame may be configured in the form of a trigger frame and may include a common field and one or more user information fields. The common field may include a trigger type field, an indication field indicating whether another trigger frame will be transmitted after the frame, a field indicating whether a carrier sensing operation is required in the receiving terminal, an uplink frame bandwidth field, an uplink frame bandwidth extension field, and a reserved field. The common field may additionally include a MURTS type field. Alternatively, the MURTS type field may be included in the user information field. The trigger type field may be set to 3 to indicate that the trigger frame is an MU-RTS frame. Furthermore, if the trigger frame is an MU-RTS frame, the MURTS type field may be included in the trigger frame. The MURTS type field may be set to 00 if the MU-RTS frame is transmitted at a bandwidth of 160 MHz or less and the EHT STA does not separately configure a user information field. If the MU-RTS frame is transmitted at a bandwidth greater than 160 MHz, the MURTS type field may be set to 10. The field indicating whether carrier sensing operation is required can be set to 1 to instruct the STA that received the MU-RTS frame to perform carrier sensing operation. The bandwidth field and bandwidth extension field of the uplink frame can indicate the bandwidth of the CTS frame that the AP that transmits the MU-RTS frame intends to receive. That is, in Figure 13(a), when multiple STAs transmit CTS frames, they can indicate the bandwidth of the CTS frame that the AP must ultimately receive. The bandwidth field can be indicated as shown in Table 3 below.

[0244] [Table 3]

[0245] The Bandwidth Extension field is displayed only when the MURTS Type field is not 00, and when the Bandwidth field value is 2 or less, the Bandwidth Extension field is set to 0. When the Bandwidth field value is 3, the Bandwidth Extension field may be set as shown in Table 4 below.

[0246] [Table 4]

[0247] On the other hand, if the STA receiving the MU-RTS frame is an HE STA, the values of the MURTS type field and bandwidth extension field among the common fields of the MU-RTS frame may be indecipherable. Therefore, when the AP transmits the MU-RTS frame, the bandwidth for transmitting the CTS frame from the HE STA may be indicated as a maximum of 160 MHz or 80+80 MHz regardless of the value of the bandwidth extension field. If the STA receiving the MU-RTS frame is an EHT STA, it can determine the bandwidth for transmitting the CTS frame only by checking both the bandwidth field and bandwidth extension field values of the MU-RTS frame.

[0248] The user information field may be configured to differ depending on the MURTS type field value of the common field and whether the terminal receiving the MU-RTS frame is an HE STA or an EHT STA. When the MURTS type field value is 00, the user information field may be configured with a 12-bit AID field and an 8-bit RU (Resource Unit) assignment field. When the MURTS type field value is 10 and the user information field indicates an HE STA, the user information field may be configured with a 12-bit AID field and an 8-bit RU (Resource Unit) assignment field. When the MURTS type field value is 10 and the user information field indicates an EHT STA, the user information field may be configured with a 12-bit AID field and a 9-bit RU (Resource Unit) assignment field. Alternatively, the user information field may differ depending on whether the receiving terminal is an HE STA or an EHT STA, regardless of the MURTS type field value. For example, if the user information field corresponds to an HE STA, the user information field may include a 12-bit AID field and an 8-bit RU assignment field, and if the user information field corresponds to an EHT STA, the user information field may include a 12-bit AID field and a 9-bit RU assignment field.

[0249] When the RU (Resource Unit) allocation field is composed of 8 bits, if the B0 value of the RU allocation field is 1, it indicates that the STA requests transmission of a CTS frame using a 160 MHz or 80+80 MHz bandwidth. If the B0 value, which is the least significant bit (LSB) of the RU allocation field, is 0, it indicates that the STA indicated by the RU field requests transmission of a CTS frame at 20 MHz, 40 MHz, or 80 MHz.

[0250] The transmission bandwidth and detailed location of the transmission bandwidth of the CTS frame may be indicated by B7-B1 of the RU allocation field, i.e., the seven most significant bits of the RU allocation field. In this case, the values of B7-B1 of the RU allocation field may be set as shown in Table 5 below.

[0251] [Table 5]

[0252] When the RU allocation field consists of 9 bits, B1-B0, i.e., the two least significant bits, of the RU allocation field can indicate the segment position of the 80 MHz band in which the primary channel through which the CTS frame is transmitted is located when a 320 MHz bandwidth channel is divided into four 80 MHz channel segments.

[0253] The transmission bandwidth and location of the CTS frame in the 80 MHz segment may be indicated by B8-B2 of the RU allocation field, where the values of B8-B2 of the RU allocation field may be set as shown in Table 6 below.

[0254] [Table 6]

[0255] On the other hand, if the B8-B2 value indicates a 320 MHz or 160+160 MHz primary channel, the B1-B0 value of the RU allocation field may be indicated as 11.

[0256] Meanwhile, if the length of the RU allocation field in the user information field transmitted to the EHT STA is also to be maintained at 8 bits, the MU-RTS frame may be configured as follows.

[0257] 30 shows a second example of the structure of the MU-RTS frame according to an embodiment of the present invention, in which the description of parts that are the same as or similar to the structure of the MU-RTS frame in FIG. 28 may be omitted.

[0258] Referring to FIG. 30, the MU-RTS frame may be configured in the form of a trigger frame and may include a common field and one or more user information fields. The common field may include a trigger type field, an indication field indicating whether a trigger frame is to be transmitted after the frame, a field indicating whether a carrier sensing operation is required in the receiving terminal, an uplink frame bandwidth field, an uplink frame bandwidth extension field, and a reserved field. The common field may further include a MURTS type field. The configuration of fields other than the MURTS type field may be the same as that of the MU-RTS frame of FIG. 28. The MURTS type field may be set to 00 if the MU-RTS frame is transmitted at a bandwidth of 160 MHz or less and the EHT STA does not set a separate user information field. The MURTS type field may be set to 10 if the MU-RTS frame is transmitted at a bandwidth of more than 160 MHz.

[0259] The user information field may consist of a 12-bit AID field, an 8-bit RU allocation field, and a reserved field. When the AID field of the user information field indicates a HE STA, or when the bandwidth field and bandwidth extension field of the common field indicate a bandwidth of 160 MHz or less and the MURTS type field is 00, the 8-bit RU allocation field may be set to the same as the 8-bit RU allocation field of Figure 13. That is, B0 of the RU allocation field indicates whether transmission is performed in 160 MHz or 80+80 MHz bandwidth, and B7-B1 of the RU allocation field may be configured as shown in Table 3.

[0260] When the MU-RTS frame is transmitted in a bandwidth exceeding 160 MHz and the MURTS type field is 10, the RU allocation field in the user information field indicating the EHT STA may be configured as follows: B1-B0, i.e., the two least significant bits, of the RU allocation field can indicate the segment position of the 80 MHz band in which the primary channel in which the CTS frame is transmitted is located when a 320 MHz bandwidth channel is divided into four 80 MHz channel segments.

[0261] The transmission bandwidth and location of the CTS frame in the 80 MHz segment may be indicated by B7-B2 of the RU allocation field, where the values of B7-B2 of the RU allocation field may be set as shown in Table 7 below.

[0262] [Table 7]

[0263] On the other hand, if the B7-B2 value indicates a 320 MHz or 160+160 MHz primary channel, the B1-B0 value of the RU allocation field may be indicated as 11.

[0264] The MU-RTS frame and CTS frame exchange procedure may be performed using the primary 20 MHz channel, the primary 40 MHz channel, the primary 80 MHz channel, the primary 160 MHz / 80+80 MHz channel, the primary 240 MHz / 160+80 MHz channel, or the primary 320 MHz / 160+160 MHz channel. Alternatively, when a specific 20 MHz channel is occupied except for the primary 20 MHz channel, the 20 MHz channel may be vacated and the procedure may be performed using only the remaining channels. The MU-RTS frame and CTS frame exchange operation utilizing the operation of vacating some 20 MHz channels to transmit frames (preamble puncturing operation) may be performed as follows.

[0265] 31 illustrates a second embodiment of the operation of protecting frame transmission and reception using the MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention. In this case, descriptions that are the same as or similar to the operation in FIG. 28 may be omitted.

[0266] Referring to Figure 31, an AP can simultaneously transmit and receive frames with multiple STAs. The simultaneous frame transmission and reception process with multiple STAs may be performed using MU-OFDMA or MU-MIMO operation. In this case, the AP may exchange MU-RTS and CTS frames before transmitting the frame to protect the frame transmission and reception process. The MU-RTS frame may be transmitted using one of the following channels: a primary 20 MHz channel, a primary 40 MHz channel, a primary 80 MHz channel, a primary 160 MHz or 80+80 MHz channel, a primary 240 MHz or primary 160+80 MHz channel, or a primary 320 MHz or 160+160 MHz channel. In this case, if one or more of the 20 MHz channels other than the primary 20 MHz channel are occupied or are not intended to be used, the AP can vacate the corresponding one or more 20 MHz channels and transmit the MU-RTS frame using only the remaining channels. That is, when transmitting an MU-RTS frame using the primary 80MHz channel, the primary 160MHz or 80+80MHz channel, the primary 240MHz or 160+80MHz channel, or the primary 320MHz or 160+160MHz channel, the MU-RTS frame does not need to be transmitted on a specific 20MHz channel. For example, when attempting to transmit an MU-RTS frame using the primary 80MHz channel, if one of the 20MHz channels in the secondary 40MHz channels is occupied, that channel can be vacated and the MU-RTS frame can be transmitted using only the remaining channels.

[0267] The MU-RTS may indicate the ID (e.g., Association ID) of the STA transmitting the CTS, the channel (e.g., primary 20 MHz channel, primary 40 MHz channel, primary 80 MHz channel, primary 160 MHz or 80+80 MHz channel, primary 240 MHz or primary 160+80 MHz channel, primary 320 MHz or 160+160 MHz channel) on which each STA transmits the CTS frame, etc. In this case, it may further indicate a 20 MHz channel (punctured channel) that is left vacant without transmitting the MU-RTS. The MU-RTS frame may be configured as shown in FIG. 17, which will be described later. The MU-RTS frame may be a frame requesting simultaneous transmission of CTS frames from multiple STAs. In this case, the multiple STAs may include HE STAs defined in IEEE 802.11ax and EHT STAs defined in IEEE 802.11be.

[0268] Referring to (a) of FIG. 31, an AP may transmit MU-RTS frames to multiple STAs and may receive CTS frames simultaneously transmitted from the STAs after a SIFS time from the end of transmission of the PPDU including the MU-RTS frame. The CTS frame may be repeatedly transmitted for each 20 MHz channel. The CTS frame may be a non-HT duplicated PPDU. In this case, the CTS frames transmitted by the multiple STAs may be identical. Therefore, the AP may receive the CTS frame in each 20 MHz channel. In this case, the received power of the CTS frame received for each 20 MHz channel may be different. When the AP receives a CTS frame in response to the MU-RTS, the AP may perform MU-OFDMA or MU-MIMO operation with the multiple STAs based on the bandwidth of the received CTS frame.

[0269] Meanwhile, as described above, the transmission bandwidth of the CTS frame transmitted from the STA that received the MU-RTS frame may vary. For example, referring to (b) of FIG. 16, if the channel instructed by the MU-RTS frame to transmit the CTS frame is the primary 20 MHz channel, STA1 can perform channel sensing only on the primary 20 MHz channel. The channel sensing operation may be performed in a SIFS time. If the primary 20 MHz channel is idle, STA1 can transmit a CTS frame. In this case, the CTS frame may be transmitted in the form of a non-HT PPDU. After transmitting the CTS frame, STA1 can receive downlink frames within the 20 MHz channel. In this case, the STA transmitting the CTS frame may be an HE STA or an EHT STA.

[0270] Referring to (c) of FIG. 31, when the channel instructed by the MU-RTS frame to transmit a CTS frame is the primary 40 MHz channel, the STA (e.g., STA2) indicated in the user information field of the MU-RTS frame can perform channel sensing only on the primary 40 MHz channel. The channel sensing operation may be performed in a SIFS time. A CTS frame can be transmitted when the primary 40 MHz channel is idle. In this case, the CTS frame may be transmitted in the form of a non-HT duplicated PPDU. STA2 can receive downlink frames within the 40 MHz channel after transmitting the CTS frame. In this case, the STA transmitting the CTS frame may be an HE STA or an EHT STA.

[0271] Referring to (d) of FIG. 31, if the channel instructed by the MU-RTS frame to transmit a CTS frame is a primary 80 MHz channel and a specific 20 MHz channel is vacant, the STA (e.g., STA3) designated in the user information field of the MU-RTS frame can perform channel sensing only on the corresponding primary 80 MHz channel other than the 20 MHz channel instructed to be vacant. If the channel sensing result indicates that the channel is vacant, the CTS frame can be transmitted. In this case, the CTS frame may be transmitted in the form of a non-HT duplicated PPDU. After transmitting the CTS frame, STA3 can receive downlink frames within the channel that exchanged the MU-RTS frame and the CTS frame. The STA transmitting the CTS frame may be an EHT STA.

[0272] The MU-RTS frame used in the MU-RTS frame and CTS frame exchange procedure may be configured by adding a field indicating a punctured channel to an existing MU-RTS frame, or the MU-RTS frame may be configured as follows.

[0273] 32 shows a third embodiment of the structure of an MU-RTS frame according to an embodiment of the present invention. In this case, the description of the parts configured the same as the MU-RTS frame in FIG. 29 may be omitted.

[0274] Referring to FIG. 32, the MU-RTS frame may be configured in the form of a trigger frame and may include a common field and one or more user information fields. The common field may include a trigger type field, an indication field indicating whether a trigger frame is to be transmitted after the frame, a field indicating whether a carrier sensing operation is required in the receiving terminal, an uplink frame bandwidth field, an uplink frame bandwidth extension field, and a reserved field. The common field may further include a MURTS type field. The common field may also include a punctured channel field. In this case, fields other than the MURTS type field and the punctured channel field may be set to the same as in FIG. 14. The field indicating the MURTS type field may indicate that the MU-RTS frame is transmitted with some 20 MHz channels vacant. For example, the MURTS type field may be set to 11. The punctured channel field may be included when the MURTS type field is set to 11. The punctured channel field of the MURTS may be configured to 16 bits. In this case, each bit of the 16 bits can indicate one 20 MHz channel. Therefore, when a corresponding bit position is set to 0, it indicates that the MU-RTS frame is transmitted on the 20 MHz channel corresponding to the bit position. For example, when only the second least significant bit (e.g., B1) of the 16 bits is set to 1 and the remaining bits are set to 0, it indicates that only the 20 MHz channel in the second lowest band is a punctured channel and that frames are transmitted on other channels. In this case, the primary 20 MHz channel does not need to be set to 1.

[0275] The user information field may be configured similarly to Figure 29 or Figure 30. For example, if the MU-RTS frame is transmitted in a bandwidth below 160 MHz and the MURTS type field in the common field is 11, B0 of the RU allocation field in the user information field indicates whether the bandwidth is 160 MHz or 80+80 MHz, and B7-B1 may be indicated as shown in Table 3. If the MU-RTS frame is transmitted in a bandwidth above 160 MHz and the MURTS type field is 11, the RU allocation field in the user information field may be configured with 8 or 9 bits. If the RU allocation field is 9 bits, it may be configured as shown in Figure 14. If the RU field is 8 bits, it may be configured as shown in Figure 30.

[0276] When an EHT STA receives the MU-RTS frame from the AP, if the MURTS type field is 11, it can check the bandwidth field and bandwidth extension field to determine the bandwidth in which the MU-RTS frame is transmitted. It can also check the channel to be vacated when transmitting a CTS from the punctured channel field. It can also check the bandwidth in which the STA should transmit from the RU assignment field. The interpretation method of the RU assignment field may vary depending on the bandwidth in which the MU-RTS frame is transmitted and the MURTS type field. After checking the RU assignment field and punctured channel interpreted according to the bandwidth in which the MU-RTS frame is transmitted and the MURTS type field, the EHT STA can vacate the 20 MHz channel indicated in the punctured channel field and transmit a CTS frame on the remaining channels according to the value indicated in the RU assignment field.

[0277] However, the HE STA receiving the MU-RTS frame may not be able to decipher the punctured channel field, and may transmit the CTS frame on the channel specified in the RU assignment field without leaving a specific 20 MHz channel free.

[0278] Meanwhile, in the process of exchanging the MU-RTS frame and the CTS frame, the CTS frame may be transmitted only on one or more 20 MHz channels. In this case, the exchange operation of the MU-RTS and CTS frames may be performed as follows.

[0279] 33 shows a third embodiment of the operation of protecting frame transmission and reception by exchanging MU-RTS and CTS frames between an AP and multiple STAs according to an embodiment of the present invention. In this case, descriptions that are the same as or similar to the operations in FIGS. 28 and 31 may be omitted.

[0280] Referring to Figure 33, an AP can simultaneously transmit and receive frames with multiple STAs. The simultaneous frame transmission and reception process with multiple STAs may be performed using MU-OFDMA or MU-MIMO operation. In this case, the AP may exchange MU-RTS and CTS frames before transmitting the frame to protect the frame transmission and reception process. The MU-RTS frame may be transmitted using one of the following channels: a primary 20 MHz channel, a primary 40 MHz channel, a primary 80 MHz channel, a primary 160 MHz or 80+80 MHz channel, a primary 240 MHz or primary 160+80 MHz channel, or a primary 320 MHz or 160+160 MHz channel. In this case, if a 20 MHz channel other than the primary 20 MHz channel is occupied or the 20 MHz channel is not intended to be used, the AP can vacate the 20 MHz channel and transmit using the remaining channels. For example, when attempting to transmit an MU-RTS frame using the primary 80 MHz channel, if one of the 20 MHz channels in the secondary 40 MHz channel is occupied, that channel can be left vacant and the MU-RTS frame can be transmitted using only the remaining channels.

[0281] The MU-RTS may indicate the ID (e.g., Association ID) of the STA transmitting the CTS, the channel on which each STA transmits the CTS frame, etc. The channel on which the CTS frame is transmitted may be a specific 20 MHz channel or multiple 20 MHz channels. In this case, the multiple 20 MHz channels may be limited in form. Furthermore, a 20 MHz channel (punctured channel) that is left vacant without transmitting the MU-RTS may be further indicated. The MU-RTS frame may be configured as shown in FIG. 34, which will be described later. The MU-RTS frame may be a frame requesting multiple STAs to simultaneously transmit CTS frames. In this case, the multiple STAs may include HE STAs defined in IEEE 802.11ax and EHT STAs defined in IEEE 802.11be. In this case, the HE STAs cannot be instructed to transmit the CTS frame on a channel other than the primary 20 MHz channel, primary 40 MHz channel, primary 80 MHz channel, primary 160 MHz channel, or primary 80+80 MHz channel.

[0282] Referring to (a) of FIG. 33, an AP may transmit MU-RTS frames to multiple STAs and may receive CTS frames simultaneously transmitted from the STAs after a SIFS time from the end of transmission of the PPDU including the MU-RTS frame. The CTS frames may be repeatedly transmitted for each 20 MHz channel. The CTS frames may be in the form of a non-HT duplicated PPDU. In this case, the CTS frames transmitted by the multiple STAs may be configured identically. Therefore, the AP may receive the CTS frames in each 20 MHz channel. In this case, the received power of the CTS frames received for each 20 MHz channel may differ. When the AP receives a CTS frame in response to the MU-RTS, the AP may perform MU-OFDMA or MU-MIMO operation with the multiple STAs based on the bandwidth of the received CTS frame.

[0283] Meanwhile, as described above, the transmission bandwidth of the CTS frame transmitted from the STA that received the MU-RTS frame may vary. For example, referring to (b) of FIG. 18, if the channel instructed by the MU-RTS frame to transmit the CTS frame is the primary 20 MHz channel, STA1 can perform channel sensing only on the primary 20 MHz channel. The channel sensing operation may be performed in a SIFS time. If the primary 20 MHz channel is idle, STA1 can transmit a CTS frame. In this case, the CTS frame may be transmitted in the form of a non-HT PPDU. After transmitting the CTS frame, STA1 can receive downlink frames within the 20 MHz channel. In this case, the STA transmitting the CTS frame may be an HE STA or an EHT STA.

[0284] Referring to (c) of FIG. 33, if the channel instructed in the MU-RTS frame to send a CTS frame is the second lowest 20 MHz channel, the STA (e.g., STA2) indicated in the user information field of the MU-RTS frame can perform channel sensing only on the 20 MHz channel. The channel sensing operation may be performed in a SIFS time. A CTS frame can be transmitted when the 20 MHz channel is idle. In this case, the CTS frame may be transmitted in the form of a non-HT PPDU. STA2 can receive downlink frames within the 20 MHz channel after transmitting the CTS frame. In this case, the STA transmitting the CTS frame may be an EHT STA.

[0285] Referring to (d) of FIG. 33, when the channel instructed by the MU-RTS frame to transmit a CTS frame is the primary 80 MHz channel and a specific 20 MHz channel is idle, the STA (e.g., STA3) designated in the user information field of the MU-RTS frame can perform channel sensing only on channels other than the primary 80 MHz channel and the designated 20 MHz channel. If the channel sensing result indicates that the channel is idle, the CTS frame can be transmitted. In this case, the CTS frame may be transmitted in the form of a non-HT duplicated PPDU. After transmitting the CTS frame, STA3 can receive downlink frames within the channel that exchanged the MU-RTS frame and the CTS frame. The STA transmitting the CTS frame may be an EHT STA.

[0286] The MU-RTS frame used in the MU-RTS frame and CTS frame exchange procedure may be a modified form of the existing MU-RTS frame in which the RU allocation field can indicate multiple 20 MHz bands. In this case, a field indicating a punctured channel may be added to the MU-RTS frame. Alternatively, the MU-RTS frame may be configured as follows:

[0287] Figure 34 shows a fourth embodiment of the structure of an MU-RTS frame according to an embodiment of the present invention. In this case, the description of the parts configured the same as the MU-RTS frame of Figure 29 or Figure 32 may be omitted.

[0288] Referring to FIG. 34, the MU-RTS frame may be configured in the form of a trigger frame and may include a common field and one or more user information fields. The common field may include a trigger type field, an indication field indicating whether a trigger frame is to be transmitted after the trigger frame, a field indicating whether a carrier sensing operation is required in the receiving terminal, an uplink frame bandwidth field, an uplink frame bandwidth extension field, and a reserved field. The common field may further include a MURTS type field. In this case, the fields in the common field other than the field indicating the MURTS type field may be set to the same as those in FIG. 14. The field indicating the MURTS type field may indicate that the MU-RTS frame is transmitted with some 20 MHz channels vacant. For example, the MURTS type field may be set to 11. Meanwhile, the common field may further include a punctured channel field. The punctured field may be included when the MURTS type field is set to 11. If the punctured channel field is included, the field may be set to the same as that of the MU-RTS frame of FIG.

[0289] The user information field may be configured differently depending on whether the terminal indicated by the field is an HE STA or an EHT STA. When the user information field indicates an HE STA, the user information field may be configured with a 12-bit AID field and an 8-bit RU assignment field. In this case, B0 of the RU assignment field indicates whether the bandwidth is 160 MHz or 80+80 MHz, and B7-B1 may be indicated as shown in Table 3. When the user information field indicates an EHT STA, the user information field may be configured with a 12-bit AID field and an 8-bit or 9-bit RU assignment field. When the RU assignment field is 9 bits, B1-B0 of the RU assignment field may indicate the segment position of the 80 MHz band where the primary channel through which the CTS frame is transmitted is located when a 320 MHz bandwidth channel is divided into four 80 MHz channel segments. In this case, B0 may specify the position of the segment of the 80 MHz band. For example, B0 set to 0 indicates that the 80 MHz segment is contained within the lower 160 MHz channel of either the lower 320 MHz or 160+160 MHz primary channel. B0 set to 1 indicates that the 80 MHz segment is contained within the higher 160 MHz channel of either the lower 320 MHz or 160+160 MHz primary channel.

[0290] The transmission bandwidth and location of the CTS frame in the 80 MHz segment may be indicated by B8-B2 of the RU allocation field, where the values of B8-B2 of the RU allocation field may be set as shown in Table 8 below.

[0291] [Table 8-1] [Table 8-2]

[0292] Values other than those in Table 8 for the RU allocation field may not be used.

[0293] On the other hand, if the B8-B2 values indicate a 320 MHz or 160+160 MHz primary channel, or if they indicate multiple RUs within 320 MHz or 160+160 MHz, the B1-B0 values in the RU allocation field may be indicated as 11.

[0294] On the other hand, when the RU allocation field is composed of 8 bits, B1-B0 of the RU allocation field can indicate the segment position of the 80 MHz band in which the main channel through which the CTS frame is transmitted is located when a 320 MHz bandwidth channel is divided into four 80 MHz channel segments.

[0295] The transmission bandwidth and location of the CTS frame in the 80 MHz segment may be indicated by B8-B2 of the RU allocation field. In this case, the values of B7-B2 of the RU allocation field may be set as shown in Table 9 below.

[0296] [Table 9-1] [Table 9-2]

[0297] Values other than those in Table 9 for the RU allocation field may not be used.

[0298] On the other hand, if the B8-B2 values indicate a 320 MHz or 160+160 MHz primary channel, or if they indicate multiple RUs within 320 MHz or 160+160 MHz, the B1-B0 values in the RU allocation field may be indicated as 11.

[0299] If the MURTS type field is 11, an EHT STA receiving the MU-RTS frame from the AP can check the bandwidth field and bandwidth extension field to determine the bandwidth on which the MU-RTS frame will be transmitted. The STA can also determine one or more 20 MHz channels on which the STA should transmit a CTS frame from the RU allocation field. The interpretation of the RU allocation field may vary depending on the type of terminal receiving the MU-RTS frame (e.g., HE STA or EHT STA) and the MURTS type field. An EHT STA that has checked the RU allocation field interpreted by the MURTS type field can transmit a CTS frame on one or more 20 MHz channels indicated in the RU allocation field. If a punctured channel field is added to the MU-RTS frame, the EHT STA can refer to the punctured channel field to transmit a CTS frame on one or more 20 MHz channels indicated in the RU allocation field.

[0300] On the other hand, the HE STA receiving the MU-RTS frame may not be able to decode the added punctured channel field, so the HE STA can transmit the CTS frame on the channel specified in the RU assignment field without vacating a specific 20 MHz channel.

[0301] Meanwhile, an indicator requesting transmission of a CTS frame on the primary 20 MHz channel may be added to the MU-RTS frame of Figure 19. When the indicator for transmitting a CTS frame on the primary 20 MHz channel is set, a STA that receives the MU-RTS frame can transmit a CTS frame on multiple 20 MHz channels including the primary 20 MHz channel even if the primary 20 MHz channel is not indicated in the RU allocation field.

[0302] Meanwhile, the MU-RTS frame and CTS frame exchange operation shown in Figure 13, Figure 16, or Figure 18 may also be performed between an AP belonging to an AP MLD and a terminal belonging to a STA MLD. In this case, the STA MLD may not be able to perform STR operations on some links. Therefore, the MU-RTS frame and CTS frame exchange operation can be initiated by transmitting an MU-RTS frame to a terminal belonging to the STA MLD on one link within the AP MLD, and to multiple terminals including other terminals in the STA MLD on other links. In this case, the operation between the AP MLD and the STA MLD may be performed as follows.

[0303] Figure 35 is an example showing a channel reservation process using an MU-RTS frame and CTS frame exchange procedure among operations for multiple terminals according to an embodiment of the present invention.

[0304] Referring to FIG. 35, even if some STAs cannot transmit a CTS frame for an MU-RTS frame transmitted from an AP belonging to an AP MLD due to the inability of STR operation for some STAs, when another STA transmits a CTS frame on the channel, the AP can perform a channel reservation process using an MU-RTS frame and CTS frame exchange procedure. For example, multiple APs may belong to an AP MLD. In this case, each AP can operate its own link. For example, AP1 and AP2 may belong to the AP MLD. AP1 can operate link 1, and AP2 can operate link 2. STAs not belonging to a STA MLD or STA MLD may be connected to an AP in the AP MLD. For example, STA1-1 and STA1-2 included in STA MLD1 may be connected to the AP MLD. In this case, STA1-1 may be connected to AP1, and STA1-2 may be connected to AP2. STA2-1 and STA2-2 included in STA MLD2 may be connected to AP1 and AP2, respectively. In this case, STR operation may be impossible for STA1-1 and STA1-2, which belong to STA MLD1. In other words, STA1-2 may not be able to receive while STA1-1 is transmitting on link 1. STR operation may be possible for STA2-1 and STA2-2, which belong to STA MLD2. Furthermore, STA3, which does not belong to STA MLD, may be connected to AP1.

[0305] 35(a), AP1 belonging to AP MLD can perform frame transmission / reception operations with multiple terminals connected to the AP. For example, AP1 can simultaneously transmit downlink frames to STA1-1, STA2-1, and STA3 using OFDMA operation. At this time, to protect the frame transmission / reception operations, AP1 can perform MU-RTS frame and CTS frame exchange procedures with the corresponding multiple terminals.

[0306] Meanwhile, when STR operation between APs belonging to AP MLD is possible, AP2 can independently perform channel access operation for frame transmission while AP1 is performing frame transmission / reception operation. After performing this channel access operation, frame transmission / reception operation with multiple terminals can be performed. For example, when AP2 has downlink data to transmit to multiple terminals, it can simultaneously transmit frames with STA1-2 and STA2-2 using downlink MIMO operation or downlink OFDMA operation. In this case, to protect the frame transmission / reception operation, it can transmit MU-RTS frames to the corresponding multiple terminals and attempt to perform an MU-RTS frame and CTS frame exchange procedure.

[0307] Referring to (b) of Figure 35, STA MLD1, which is incapable of STR operation on Link 1 and Link 2, receives a frame on Link 1, and therefore may not be able to transmit a CTS frame in response to the MU-RTS frame even if it receives the MU-RTS frame on Link 2. Referring to (c) of Figure 35, a STA that can transmit a CTS frame in response to the MU-RTS frame can transmit the CTS frame using the channel indicated by the MU-RTS. In this case, the STA that transmits the CTS frame may be a STA MLD that is not transmitting a frame on Link 1 at the time of receiving the CTS frame on Link 2, a STA MLD that is capable of STR operation on Link 1 and Link 2, or a STA that does not belong to a STA MLD. The operation of transmitting a CTS frame in response to the MU-RTS may be performed as shown in Figure 13, Figure 16, or Figure 18.

[0308] Referring to (a) of Figure 35, from the perspective of AP MLD, even if a CTS frame cannot be received from a STA of STA MLD that is not capable of STR operation in response to the transmitted MU-RTS frame, if another terminal instructed to transmit a CTS frame using the same band transmits a CTS frame, it can be determined that the exchange of the MU-RTS frame and the CTS frame has been successful. Therefore, AP2 of AP MLD can transmit downlink frames to terminals that were not able to transmit a CTS frame because they are not capable of STA operation. In this case, since a frame to be transmitted to a terminal that is not capable of STR operation is included, if a frame transmitted on Link 1 or Link 2 requests the transmission of a response frame (e.g., an ACK frame or a BlockAck frame), the transmission end times of the downlink frames transmitted on Link 1 and Link 2 may be the same.

[0309] On the other hand, referring again to (b) of Figure 35, STA1-2, which was unable to send a CTS response to the MU-RTS frame received on link 2 because STR operation was not possible, can receive the downlink frame transmitted by AP2 on that link if another terminal (e.g., STA2-2) transmits a CTS frame on that channel.

[0310] On the other hand, when an MLD that is not capable of the STR operation participates in the MU-RTS frame exchange process, it may not be able to send a CTS response to the received MU-RTS in the following situations, and there may be no CTS frame transmitted on a specific channel.

[0311] FIG. 36 is a diagram illustrating an operation in which a CTS frame for an MU-RTS frame is not transmitted on a specific 20 MHz channel according to an embodiment of the present invention.

[0312] Referring to (a) of Figure 36, when performing a channel extension operation as shown in Figure 13 to transmit an MU-RTS frame, if the STAs instructed using a CTS frame via an extension channel include only STAs receiving downlink frames on links where STR operation is not possible, the CTS frame does not need to be transmitted on the extension channel. That is, while the AP MLD is transmitting a frame on one link, it can complete a channel approach operation on another link and then extend the channel to exchange the MU-RTS frame and the CTS frame. In this case, the MU-RTS frame may be transmitted using one of the following channels: the primary 40 MHz channel, the primary 80 MHz channel, the primary 160 MHz or 80 + 80 MHz channel, the primary 240 MHz or 160 + 80 MHz channel, or the primary 320 MHz or 160 + 160 MHz channel. In this case, STAs that are capable of STR operation or are not receiving frames on other links can transmit a CTS frame in response to the received MU-RTS frame, as shown in (c) of Figure 20. On the other hand, a STA that has already received a frame on another link incapable of STR operation may be unable to transmit a CTS frame in response to the received MU-RTS frame, as shown in (b) of FIG. 35. In this case, if the STAs instructed to transmit a CTS frame on the extension channel include only STAs that are unable to transmit a CTS frame in response to the received MU-RTS frame, as shown in (b) of FIG. 35, the CTS frame in response to the transmitted MU-RTS frame may not be transmitted on the extension channel. For example, AP1 and AP2 may belong to an AP MLD. AP1 can operate link 1, and AP2 can operate link 2. STA1-1 and STA1-2 may belong to STA MLD1. STA2-1 and STA2-2 may belong to STA MLD2. STA1-1, STA2-1, and STA3 may be connected to AP1, and STA1-2 and STA2-2 may be connected to AP2. In this case, STA1-1 and STA1-2 of STA MLD1 may be unable to perform STR operation on link 1 and link 2.At this time, AP1 can transmit downlink frames to STA1-1, STA2-1, and STA3 through multi-user OFDMA operation. Alternatively, AP1 can transmit downlink frames to STA1-1. AP1 can further perform an RTS frame or MU-RTS frame and CTS frame exchange procedure to protect the downlink frames. Meanwhile, while AP1 is transmitting and receiving frames with STA1-1 or multiple terminals including STA1-1, AP2 can complete a channel contention process for frame transmission on Link 2.

[0313] At this time, AP2 may attempt to transmit downlink frames to multiple terminals including STA1-2. For example, AP2 may attempt to transmit downlink frames to STA1-2 and STA2-2. At this time, to protect the transmission operation of the downlink frames, an MU-RTS frame and a CTS frame exchange operation may be performed before the frame transmission. The MU-RTS frame may be transmitted using the same bandwidth as the downlink frame. For example, if the downlink frame is to be transmitted using the primary 80 MHz channel, the MU-RTS frame may also be transmitted using the 80 MHz bandwidth. The MU-RTS frame may specify the transmission bandwidth of the CTS frame transmitted by STA2-2 as the primary 40 MHz channel and the transmission bandwidth of the CTS frame transmitted by STA1-2 as the primary 80 MHz channel. At this time, because STA1-1 is receiving a frame on link 1, STA1-2 may not be able to transmit a CTS frame in response to the MU-RTS frame received on link 2. Meanwhile, STA2-2 may transmit a CTS frame in response to the MU-RTS frame. On the other hand, AP2 receives the CTS frame only in the 40 MHz band in response to the MU-RTS frame transmitted in the 80 MHz band, so it can transmit downlink frames using only the 40 MHz band. In other words, even if the secondary 40 MHz channel is idle, it may not be possible to transmit or receive frames in the secondary 40 MHz channel, not the primary 40 MHz channel.

[0314] Furthermore, even when the exchange operation of MU-RTS frames and CTS frames is performed by leaving a specific 20 MHz channel free as in Figure 31 or Figure 33, a situation may occur in which a CTS frame cannot be received in response to an MU-RTS frame transmitted on a specific 20 MHz channel. Referring to Figure 36(b), as in Figure 36(a), AP1 and AP2 may belong to AP MLD, STA1-1 and STA1-2 may belong to STA MLD1, and STA2-1 and STA2-2 may belong to STA MLD2. In this case, AP1 and AP2 may be able to operate Link 1 and Link 2, respectively, while STA1-1 and STA1-2 may not be able to perform STR operation on Link 1 and Link 2. In this case, AP1 may be able to transmit a downlink frame to STA1-1 or multiple terminals including STA1-1. During the transmission of this frame, AP2 may complete a channel approach operation for frame transmission on Link 2. At this time, AP2 can further exchange MU-RTS and CTS frames to protect the downlink frame it is trying to transmit. The receiving STA of the MU-RTS frame may be the STA that receives the downlink frame. For example, when AP2 attempts to transmit a downlink frame to STA1-2 and STA2-2, it can transmit an MU-RTS frame to the STAs. At this time, AP2 can transmit the MU-RTS frame by vacating a specific 20 MHz band as shown in FIG. 16 or FIG. 18. STA1-2 and STA2-2 that receive the MU-RTS frame can transmit CTS frames in response to the received MU-RTS frame. At this time, the CTS frame can only be transmitted on the channel instructed in the MU-RTS frame to transmit the CTS frame, as shown in FIG. 18. At this time, STA1-2 may not be able to transmit a CTS frame in response to the MU-RTS frame because STA1-1 is receiving a frame on link 1. STA2-2 can transmit a CTS frame in response to the MU-RTS frame.In this case, when only STA1-2 is instructed to transmit the CTS frame on a specific 20 MHz channel, the 20 MHz channel may be in a state where no CTS transmission is being performed. AP2, which fails to receive a CTS frame in response to the MU-RTS frame in the 20 MHz band, can leave the 20 MHz channel free to transmit a downlink frame, even if the 20 MHz channel is actually idle. In this case, if the channel on which the CTS response to the MU-RTS frame was not received is the primary 20 MHz channel, AP2 may not be able to transmit or receive downlink frames with STA1-2 and STA2-2 even if it receives a CTS frame on another channel in response to the MU-RTS frame. Furthermore, if the CTS response to the MU-RTS frame is received at least on the primary 20 MHz channel, it can transmit a downlink frame following the reception of the CTS response.

[0315] Alternatively, when some of the STAs communicating with the AP temporarily change their primary channel, a phenomenon may occur in which a CTS frame in response to the MU-RTS frame is not transmitted. Referring to (c) of Figure 36, in a situation where the AP MLD transmits frames to STA MLD1 and STA MLD2 as shown in (a) of Figure 36, if STA2-2's primary channel temporarily shifts to another channel other than the AP's primary channel before AP2 transmits a frame on link 2, STA2-2 can transmit a CTS response to the received MU-RTS frame based on its primary channel. For example, if the MU-RTS frame of Figure 14 or Figure 15 is instructed to transmit a CTS frame in a 40 MHz bandwidth, STA2-2 can transmit a CTS frame using its primary 40 MHz channel in response to the MU-RTS frame received from AP2. Meanwhile, STA1-2 can use the same primary channel as AP2's primary channel. In this case, STA1-1 and STA1-2 are unable to perform STR operations, and STA1-1 is receiving frames on link 1, so STA1-2 may not be able to transmit a CTS frame in response to the received MU-RTS frame. In this case, if only STA1-2 is instructed to transmit the CTS frame on a specific 20 MHz channel, the 20 MHz channel may be in a state where no CTS transmission is being performed. In this case, if the channel on which the CTS response to the MU-RTS frame was not received is the primary 20 MHz channel, AP2 may not be able to transmit or receive downlink frames with STA1-2 and STA2-2 even if it receives a CTS frame on another channel in response to the MU-RTS frame.

[0316] In the present invention, when a downlink frame is being transmitted to a STA belonging to an MLD in which the STR operation is not possible, and channel access is completed on another link to transmit a frame to another STA belonging to the MLD, the downlink frame transmission operation can be performed as follows.

[0317] FIG. 37 shows a first example of an operation for omitting transmission of an MU-RTS frame by adding an additional condition in AP MLD according to an embodiment of the present invention.

[0318] Referring to FIG. 37, when an AP MLD is performing a frame transmission process on one link and a channel access operation for frame transmission on another link is completed, if a downlink frame is transmitted to a UE that cannot send a CTS response to the transmission of the MU-RTS frame on the corresponding link, the transmission of the MU-RTS frame may be omitted. That is, even if the length of a PHY Service Data Unit (PSDU) to be transmitted on the corresponding link exceeds a specific value (e.g., dot11RTSThreshold) and transmission of an RTS frame or MU-RTS frame is requested, the MU-RTS frame and CTS frame exchange process may be omitted. For example, AP1 and AP2 may belong to the AP MLD. AP1 may operate link 1, and AP2 may operate link 2. STA1-1 and STA1-2 may belong to STA MLD1. STA2-1 and STA2-2 may belong to STA MLD2. STA1-1, STA2-1, and STA3 may be connected to AP1, and STA1-2 and STA2-2 may be connected to AP2. In this case, STA1-1 and STA1-2 of STA MLD1 may be unable to perform STR operation on Link 1 and Link 2. In this case, AP1 can transmit downlink frames to STA1-1, STA2-1, and STA3 through multi-user OFDMA operation. Alternatively, AP1 can transmit downlink frames to STA1-1. AP1 can further perform an RTS frame or MU-RTS frame and CTS frame exchange procedure to protect the downlink frames. Meanwhile, while AP1 is transmitting and receiving frames with STA1-1 or multiple UEs including STA1-1, AP2 may complete a channel contention process for frame transmission on Link 2. AP2 may attempt to transmit downlink frames to multiple UEs including STA1-2. In this case, if one or more of the receiving STAs of the frame to be transmitted belong to a STA MLD that is unable to perform STR operation on Link 1 and a STA belonging to the MLD is receiving a frame on Link 1, AP2 can transmit the downlink frame without exchanging MU-RTS and CTS frames.In this case, if the completion point of the channel contention process is before the end point of the transmission of the CTS frame on link 1, even if the channel approach operation is completed on link 2, the channel sensing operation can be performed up to the start point of the PPDU including the downlink frame on link 1, and then the frame transmission operation can be performed in accordance with that point.

[0319] On the other hand, if the completion point of the channel contention process on Link 2 occurs during the transmission time of the downlink frame on Link 1, the following operation can be performed depending on the remaining transmission time of the PPDU including the downlink frame on Link 1 as follows:

[0320] FIG. 38 shows a second embodiment of the operation of omitting transmission of an MU-RTS frame by adding an additional condition in AP MLD according to an embodiment of the present invention.

[0321] Referring to FIG. 38, when the AP MLD is performing an operation for frame transmission on one link and a channel access operation for frame transmission on another link is completed, if a UE that cannot send a CTS response to the transmission of the MU-RTS frame on the link is included, the transmission of the MU-RTS frame may be omitted. In this case, if the time when the channel access operation is completed is during the transmission time of a PPDU including a downlink frame on the other link, the downlink frame may be transmitted without transmitting the MU-RTS frame and CTS frame at the time when the channel access operation is completed on the link. In other words, even if the length of the PSDU (PHY Service Data Unit) to be transmitted on the link exceeds a specific value (e.g., dot11RTSThreshold) and transmission of an RTS frame or MU-RTS frame is requested, the MU-RTS frame and CTS frame exchange process may be omitted. For example, as shown in FIG. 22 above, while AP1 belonging to the AP MLD is transmitting and receiving frames with STA1-1 or multiple UEs including STA1-1, AP2 may complete a channel contention process for frame transmission on link 2. In addition, AP2 may have data to transmit to multiple STAs including STA1-2. While AP1 is transmitting a PPDU including a downlink frame over Link1, AP2 completes channel contention over Link2, and at the completion point, AP2 can check the remaining transmission time of the PPDU to be transmitted over Link1. If the remaining transmission time of the PPDU to be transmitted over Link1 is equal to or greater than a specific time, AP2 can skip the process of exchanging MU-RTS and CTS frames and transmit downlink frames to STAs including STA1-2. The specific time may be a value stored in the AP. Alternatively, the specific time may be exchanged during a negotiation process for multi-link operation between the AP MLD and the STA MLD.

[0322] On the other hand, if the completion point of the channel contention on Link 2 occurs during the transmission time of the downlink frame on Link 1 and the remaining transmission time of the PPDU being transmitted on Link 1 is within the specific time, the downlink frame can be transmitted as shown in Figure 23, and the transmission end point of the PPDU including the frame can be aligned with the PPDU transmission end point on Link 1. Alternatively, the MU-RTS frame and CTS frame exchange process can be performed as follows.

[0323] 39 shows an example of an operation of transmitting an MU-RTS frame according to an additional condition added in AP MLD according to an embodiment of the present invention. At this time, the description overlapping with that of FIGS. 37 and 38 may be omitted.

[0324] Referring to FIG. 39, if a channel access operation for frame transmission on another link is completed while the AP MLD is transmitting a frame on one link, and if the time from the completion of the channel access operation to the end of PPDU transmission on the link on which the frame is already being transmitted is within a specific time, the AP MLD can transmit an MU-RTS frame. For example, one AP (e.g., AP1) belonging to the AP MLD can transmit a downlink frame. In this case, the downlink frame may be transmitted to multiple UEs. For example, AP1 operates on link 1 and can transmit downlink frames to STA1-1, STA2-1, and STA3. In this case, STA1-1 and STA1-2 belong to STA MLD1, and STA1-1 and STA1-2 may not be able to perform the STR operation. AP1 can complete a channel access operation for frame transmission on another AP (e.g., AP2) belonging to the same AP MLD that transmits the downlink frame on link 1. In this case, there may be multiple STAs to which AP2 transmits the frame, and one or more of them may be STAs that receive the frame on link 1. For example, a downlink frame transmitted by AP2 on Link 2 may be transmitted to STA1-2 and STA2-2. At this time, if the remaining transmission time of a PPDU containing a frame to be transmitted on Link 1 is within a specific time when AP2 completes a channel approach operation on Link 2, AP2 may transmit the MU-RTS frame if a transmission operation of the MU-RTS frame is required according to the length of the PSDU to be transmitted. Alternatively, AP2 may perform an exchange process of an MU-RTS frame and a CTS frame to protect the downlink frame to be transmitted. At this time, padding bits may be added to the MU-RTS frame to align the transmission end point with the downlink frame transmitted on Link 1. Alternatively, a channel sensing operation may be further performed so that the transmission end point of the MU-RTS frame coincides with the transmission end point of the PPDU on Link 1.

[0325] Meanwhile, multiple STAs that receive the MU-RTS frame can check the MU-RTS frame and transmit a CTS frame after performing channel sensing on the channel indicated in the MU-RTS frame. The AP that receives the CTS frame can transmit a downlink frame to multiple STAs. In this case, if some STAs that are not capable of STR operation on Link 1 are transmitting an uplink response frame (e.g., a BlockAck frame), the AP can postpone downlink transmission until the end of transmission of the PPDU containing the response frame on that link (e.g., Link 1). In this case, the AP can perform channel sensing during the postponed time to check whether the channel is occupied by another terminal during that time.

[0326] On the other hand, if one or more STAs transmit a CTS frame in response to the MU-RTS frame on a specific channel, the AP can determine that the transmission of the MU-RTS frame was successful. Therefore, the AP can guide one or more STAs to transmit CTS frames on all 20 MHz band channels on which the MU-RTS frame was transmitted by the following operation.

[0327] FIG. 40 shows a first embodiment of the operation for avoiding a situation in which a CTS frame at a specific 20 MHz frequency is not transmitted by the operation of the STA MLD according to the embodiment of the present invention.

[0328] Referring to FIG. 40, when an AP belonging to an AP MLD attempts to transmit downlink frames to multiple terminals, including a STA that cannot transmit a CTS frame due to a situation where STR operation is not possible, the AP can instruct the STA that cannot transmit a CTS frame to transmit the CTS frame on the primary 20 MHz channel or a portion of channels including the primary 20 MHz channel. In this case, the AP can transmit the frame on an extension channel to other STAs. The other STAs can be instructed to transmit the CTS frame including the primary channel and the extension channel. That is, the other STAs may transmit the CTS frame including the band used by the STA that cannot transmit the CTS frame. For example, AP1 and AP2 may belong to the AP MLD. AP1 can operate link 1, and AP2 can operate link 2. STAs that do not belong to the STA MLD or the STA MLD may be connected to an AP in the AP MLD. For example, STA1-1 and STA1-2 included in STA MLD1 may be connected to AP1 and AP2, respectively. STA2-1 and STA2-2 included in STA MLD2 may be connected to AP1 and AP2, respectively. In this case, STA1-1 and STA1-2 belonging to STA MLD1 may not be able to perform STR operations. STA2-1 and STA2-2 belonging to STA MLD2 may be able to perform STR operations. Also, STA3 may be further connected to AP1.

[0329] AP1 can transmit a downlink frame after completing a channel access operation on Link 1. At this time, the downlink frame may be transmitted to STA1-1 or to multiple terminals including STA1-1. At this time, to protect the frame transmission operation on Link 1, an exchange operation of an RTS or MU-RTS frame and a CTS frame may be further performed.

[0330] While AP1 is transmitting a downlink frame, AP2 may complete a channel approach operation for transmitting the downlink frame. AP2 may have data to transmit to multiple STAs, including STA1-2. AP2 may transmit the downlink frame to multiple terminals, including STA1-2. If the length of the PSDU including the downlink frame exceeds a certain length, an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be requested. The AP may transmit the MU-RTS frame to multiple STAs. A STA (e.g., STA1-2) that cannot transmit a CTS frame due to the STR operation status may instruct the STA to transmit a CTS frame on the primary 20 MHz channel or some channels including the primary channel. A STA capable of STR operation or a STA that has not received a frame on Link 1 may instruct the STA to transmit a CTS frame on an extension channel among the channels on which the MU-RTS frame is transmitted. The STA capable of STR operation may belong to an STA MLD capable of STR operation. Alternatively, the STA may be a STA belonging to the MLD that does not perform frame reception operation on link 1. Alternatively, the STA may not belong to the STA MLD. In this case, each STA can transmit the CTS frame by the operation of FIG. 13 or 16. Therefore, even if STA1-2 cannot transmit a CTS frame because it is unable to perform STR operation, other STAs can transmit CTS frames on multiple channels including the main channel, allowing AP2 to receive a CTS frame in response to the transmitted MU-RTS frame. AP2, which receives a CTS frame in response to the MU-RTS frame, can determine that the transmission operation of the MU-RTS frame was successful. This allows AP2 to transmit downlink frames to multiple terminals.

[0331] On the other hand, if some STAs cannot send a CTS response to a received MU-RTS frame because STR operation is impossible due to interference within the device, they can request other STAs to send CTS frames over the entire bandwidth as follows.

[0332] 41 shows a second example of the operation for avoiding a situation where a CTS frame is not transmitted at a specific 20 MHz by the operation of the STA MLD according to the embodiment of the present invention. In this case, the description overlapping with that of FIG. 40 may be omitted.

[0333] 41, when an AP belonging to an AP MLD attempts to transmit downlink frames to multiple UEs, including a STA that cannot transmit a CTS frame due to a situation where the STR operation is not possible, the AP can instruct STAs that can transmit CTS frames to transmit CTS frames over the entire bandwidth. For example, as shown in FIG. 25, STA MLD1, STA MLD2, and STA3 may be connected to the AP MLD. In this case, AP1 can complete a channel access operation on Link 1 and transmit downlink frames to multiple UEs, including STA1-1. In this case, to protect the frame transmission operation on Link 1, an exchange operation of an RTS or MU-RTS frame and a CTS frame can be further performed.

[0334] While AP1 is transmitting a downlink frame, AP2 may complete a channel approach operation for transmitting the downlink frame. AP2 may have data to transmit to multiple STAs, including STA1-2. AP2 may transmit the downlink frame to multiple terminals, including STA1-2. If the length of the PSDU including the downlink frame exceeds a specific length, an exchange operation of an RTS frame or MU-RTS frame and a CTS frame may be requested. AP2 may transmit the MU-RTS frame to multiple STAs. A terminal that is not capable of STR operation may not be able to transmit a CTS frame in response to the MU-RTS frame. If some of the terminals are unable to transmit a CTS frame and it is determined that a CTS frame will not be transmitted on a specific 20 MHz channel, AP2 may request other STAs capable of transmitting a CTS frame to transmit a CTS frame on that channel. The other STAs may belong to a STA MLD capable of STR operation, or may belong to a STA MLD that does not receive frames on Link 1. Alternatively, the STA may not belong to the STA MLD. For example, AP2 can transmit downlink frames to STA2-2 only on the primary 40 MHz channel. In this case, it can transmit downlink frames to STA1-2 on the secondary 40 MHz channel. Since STA1-1 is receiving the frame, STA1-2 may not be able to transmit a CTS frame in response to the MU-RTS. In this case, AP2 can request that STA2-2 transmit a CTS response to the MU-RTS frame using the entire bandwidth. After receiving the MU-RTS frame, STA2-2 can transmit a CTS frame in all bandwidths in which the MU-RTS frame was received. This allows AP2 to receive a CTS frame in response to the MU-RTS frame it transmitted. After receiving the CTS frame in response to the MU-RTS frame, AP2 can determine that the transmission of the MU-RTS frame was successful. This allows AP2 to transmit downlink frames to multiple UEs.

[0335] Meanwhile, when the STA MLD that is not capable of STR operation is unable to perform STR operation only on some channels, the AP MLD can perform an operation to check whether a channel is available in each STA instead of exchanging an RTS or MU-RTS frame and a CTS. This operation may be performed by a process in which the AP transmits a Bandwidth Query Report Poll (BQRP) frame to multiple STAs and the multiple STAs transmit Bandwidth Query Report (BQR) frames. In this case, the channel on which each STA transmits the BQR frame may be different from the channel on which downlink data is transmitted. The process of checking whether a channel is available by transmitting a BQR frame may be performed as follows.

[0336] 42 shows a third embodiment of the operation for avoiding a situation where a CTS frame is not transmitted at a specific 20 MHz by the operation of the STA MLD according to the embodiment of the present invention. In this case, the description overlapping with that of FIGS. 40 and 41 may be omitted.

[0337] Referring to FIG. 42, when an AP belonging to an AP MLD attempts to transmit downlink frames to multiple UEs, including a STA that cannot transmit a CTS frame due to a situation where the STR operation is not possible, the AP may request each STA to check whether or not the channel is occupied for each 20 MHz channel, instead of performing a channel reservation process using the MU-RTS frame and the CTS frame. In this case, the channel status confirmed by the multiple STAs may be transmitted using a BQR frame. The frame requesting the BQR transmission may be a BQRP frame. For example, as shown in FIG. 25, STAs MLD1, MLD2, and STA3 may be connected to the AP MLD. In this case, AP1 completes a channel access operation on Link 1 and can transmit downlink frames to multiple UEs, including STA1-1. In this case, to protect the frame transmission operation on Link 1, an exchange operation of an RTS or MU-RTS frame and a CTS frame may be further performed.

[0338] While AP1 is transmitting a downlink frame, AP2 may complete a channel access operation for transmitting the downlink frame. AP2 may have data to transmit to multiple STAs including STA1-2. AP2 may transmit the downlink frame to multiple terminals including STA1-2. If the length of the PSDU including the downlink frame exceeds a specific length, an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be required. If STA1-2 is capable of STR operation with STA1-1 on a specific channel, AP2 may check whether the channel is occupied by multiple STAs receiving the downlink frame, instead of performing a channel protection operation using the MU-RTS frame transmission. The operation of checking the channel status of the multiple STAs can be performed by AP2 transmitting a request frame to the multiple STAs to check whether the channel is occupied for each 20 MHz channel. The request frame may be a frame requesting the multiple STAs to check the channel status. The request frame may be a Bandwidth Query Report Poll (BQRP) frame. The BQRP frame may be a frame requesting multiple STAs to transmit BQRs. Each STA may specify a channel on which to transmit the BQR. If STA1-2 can transmit frames on some channels, AP2 may specify the channel on which STA1-2 transmits the BQR frame.

[0339] The STAs that receive the BQRP frame from AP2 can confirm that the BQRP requests the transmission of a BQR frame. As a result, the STAs can perform channel sensing for all bands in which the STAs can operate. This allows them to confirm whether each 20 MHz channel is occupied. After confirming whether each 20 MHz channel is occupied, the STAs can transmit a BQR frame on the channel indicated in the BQRP frame. The PPDU in which the BQR frame is transmitted may be transmitted in the form of an HE TB PPDU or an EHT TB PPDU.

[0340] AP2, which receives BQR frames from the multiple STAs, can check whether each STA is occupying a channel for all bands. AP2 can transmit downlink frames through channels indicated as vacant in the BQR frames. In this case, the channel on which AP2 receives BQRs from each STA and the channel on which AP2 transmits downlink frames to the STAs may be different channels.

[0341] On the other hand, if STR operation is not possible due to interference within the device, and the AP is unable to receive a CTS frame for the MU-RTS frame transmitted by the AP on some channels other than the main channel, as shown in Figure 21, the AP can extend the channel and transmit the frame after receiving the CTS frame on some channels as follows.

[0342] 43 shows a first example of an operation for continuing frame transmission even if a CTS frame cannot be received for an MU-RTS frame on a specific 20 MHz channel according to an embodiment of the present invention. In this case, the description overlapping with that of FIG. 40 may be omitted.

[0343] 43, when an AP belonging to an AP MLD attempts to transmit downlink frames to multiple UEs, including a STA that cannot transmit a CTS frame due to a situation where the STR operation is not possible, the AP can instruct STAs that can transmit CTS frames to transmit CTS frames over the entire bandwidth. For example, as shown in FIG. 25, STA MLD1, STA MLD2, and STA3 may be connected to the AP MLD. In this case, AP1 can complete a channel access operation on Link 1 and transmit downlink frames to multiple UEs, including STA1-1. In this case, to protect the frame transmission operation on Link 1, an exchange operation of an RTS or MU-RTS frame and a CTS frame can be further performed.

[0344] While AP1 is transmitting a downlink frame, AP2 may complete a channel approach operation for transmitting the downlink frame. At this time, AP2 may have data to transmit to multiple STAs including STA1-2. At this time, AP2 can transmit the downlink frame to multiple terminals including STA1-2. At this time, if the length of the PSDU including the downlink frame is greater than or equal to a specific length, an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be requested. At this time, AP2 can transmit the MU-RTS frame to multiple STAs including STA1-2. Among the STAs that receive the MU-RTS frame, STAs that are capable of transmitting a CTS frame can transmit a CTS frame after performing carrier sensing on the channel indicated in the MU-RTS frame. At this time, STAs (e.g., STA1-2) that are unable to transmit a CTS frame in response to the MU-RTS frame due to inability of the STR operation may not be able to transmit a CTS frame in response to the MU-RTS frame. STA1-2 may be unable to transmit a CTS frame due to an inability to perform STR, and therefore may be unable to transmit a CTS frame on a specific 20 MHz channel in response to the transmitted MU-RTS. Meanwhile, after transmitting the MU-RTS frame to STA1-2, AP2 may recognize that transmission of a CTS frame on a specific 20 MHz channel is impossible due to the characteristics of STA1-2, which is unable to perform STR. In this case, even if a CTS frame is not received on the 20 MHz band, if a CTS frame is received on another band, AP2 may transmit a downlink frame using up to the 20 MHz band. For example, if AP2 instructs STA2-2 to transmit a CTS frame on the primary 40 MHz channel and instructs STA1-2 to transmit a CTS frame on the primary 80 MHz channel in response to the MU-RTS frame, AP2 may transmit a downlink frame to STA1-2 and STA2-2 using the 80 MHz channel even if it is unable to receive a CTS frame on the secondary 40 MHz channel.In this case, the AP2 may further perform a channel sensing operation for a specific time period for channels on which the CTS frame was not received. The channel sensing operation may include only an energy detection (ED) operation for checking a received energy level. In this case, the reference energy level for determining whether a channel is occupied during the ED operation may be set lower than the energy level for determining whether a channel is occupied during WLAN operation. For example, the reference energy level for determining whether a channel is occupied during the ED operation may be set to −82 dBm. The specific time period may be from the end of transmission of the MU-RTS frame to a time period before transmitting a downlink frame. Alternatively, the specific time period may be a specific IFS time period (e.g., SIFS, PIFS, or AIFS).

[0345] Meanwhile, the AP2 can recognize that some of the STAs receiving the downlink frame cannot receive the CTS frame even if they transmit the MU-RTS frame due to the fact that they are unable to perform STR. In this case, the AP2 can omit the MU-RTS frame transmission process for the band in which the AP2 transmits frames to the STAs and perform the MU-RTS and CTS frame exchange procedure only for the other bands, as follows:

[0346] Figure 44 shows a second example of the operation of continuing frame transmission even if a CTS frame cannot be received for an MU-RTS frame on a specific 20 MHz channel according to an embodiment of the present invention. In this case, the description overlapping with Figures 40 and 43 may be omitted.

[0347] 44, when an AP belonging to an AP MLD attempts to transmit downlink frames to multiple UEs, including a STA that cannot transmit a CTS frame due to a situation where the STR operation is not possible, the AP can instruct STAs that can transmit CTS frames to transmit CTS frames over the entire bandwidth. For example, as shown in FIG. 25, STA MLD1, STA MLD2, and STA3 may be connected to the AP MLD. In this case, AP1 can complete a channel access operation on Link 1 and transmit downlink frames to multiple UEs, including STA1-1. In this case, to protect the frame transmission operation on Link 1, an exchange operation of an RTS or MU-RTS frame and a CTS frame can be further performed.

[0348] While AP1 is transmitting a downlink frame, AP2 may complete a channel access operation for transmitting the downlink frame. AP2 may have data to transmit to multiple STAs, including STA1-2. AP2 can transmit the downlink frame to multiple terminals, including STA1-2. If the length of the PSDU including the downlink frame exceeds a certain length, an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be required. Even if AP2 transmits the MU-RTS frame to STA1-2, it may recognize that STA1-2 cannot transmit a CTS frame on a specific 20 MHz channel because STA1-2 is unable to perform an STR operation. In this case, AP2 may clear the channel recognized as being unable to transmit a CTS frame and perform a channel reservation process using an MU-RTS frame and a CTS frame exchange only on other channels. For example, if AP2 transmits a downlink frame to STA2-2 using the primary 40 MHz channel and a downlink frame to STA1-2 using the secondary 80 MHz channel, it may transmit an MU-RTS frame to the primary 40 MHz channel and receive a CTS frame. After receiving the CTS frame on the primary 40 MHz channel, AP2 may extend the used channel to the primary 80 MHz channel and transmit frames to STA1-2 and STA2-2. AP2 may perform a channel sensing operation on the secondary 40 MHz channel for a specific time. The channel sensing operation may include only an energy detection (ED) operation that checks the received energy level. The reference energy level for determining whether a channel is occupied during the ED operation may be set lower than the energy level for determining whether a channel is occupied during WLAN operation. For example, the reference energy level for determining whether a channel is occupied during the ED operation may be set to −82 dBm. The specific time may be from the end of transmission of the MU-RTS frame to the time before transmitting a downlink frame.Alternatively, the specific time may be a specific IFS time (eg, SIFS, PIFS, or AIFS).

[0349] FIG. 45 illustrates the operation of a soft AP according to an embodiment of the present invention.

[0350] A soft AP may be an AP station. Alternatively, a soft AP may be an AP included in a multilink device. In this case, the soft AP may be included in a non-STR multilink device. When a soft AP is included in a non-STR multilink device, such a multilink device can be called a non-STR soft AP multilink device.

[0351] When a non-STR soft AP multilink device operates with multiple links, the multiple links can be divided into mandatory links and optional links. Specifically, the multiple links may include at least one mandatory link. Operation between a non-STR soft AP multilink device and a legacy station or a single-link station may be restricted to only the mandatory link. Specifically, association and authentication between a non-STR soft AP multilink device and a legacy station or a single-link station may be restricted to only the mandatory link. In this case, a single-link station may be a station that cannot operate with multiple links.

[0352] The required links and optional links of a non-STR soft AP multilink device may be specified by the non-STR soft AP multilink device. Specifically, the required links and optional links may be set when a multilink is set up between a non-STR soft AP multilink device and a non-AP multilink device. For example, if a required link is specified among multiple links, the links other than the required link may be optional links.

[0353] Depending on the specific embodiment, multiple links may be designated as required links. In this case, the multiple links designated as required links may be links that can perform STR with each other. For example, the multiple links on which a non-STR soft AP multilink device operates may include a first link and a second link, and when the non-STR soft AP multilink device transmits through the first link, it can receive through the second link. In this case, the first link and the second link may be required links. The required links may be restricted to be set identically for multiple devices communicating with the non-STR soft AP multilink device. Specifically, it may not be permitted for different required links to be set for multiple devices communicating with the non-STR soft AP multilink device.

[0354] In addition, the selective link of a non-STR soft AP multilink device may be used only for communication between non-STR soft AP multilink devices and other multilink devices. The selective link may not be used for communication between a non-STR soft AP multilink device and a legacy station or a single link station. In addition, association and authentication between a non-STR soft AP multilink device and other multilink devices may be performed using the mandatory link.

[0355] In the embodiment of Figure 45, a non-STR soft AP multilink device (Soft AP, non-STR AP MLD) operates over a first link (Link 1) and a second link (Link 2). The first link (Link 1) is a mandatory link, and the second link (Link 2) is an optional link. The non-STR soft AP multilink device (Soft AP, non-STR AP MLD) communicates with a non-AP multilink device (Non-AP MLD) over the second link (Link 2). Specifically, the non-STR soft AP multilink device (Soft AP, non-STR AP MLD) connects to and authenticates with the non-AP multilink device (Non-AP MLD) over the second link (Link 2). The non-STR soft AP multilink device (Soft AP, non-STR AP MLD) communicates with legacy stations (Legacy STAs) and single link stations (Single link STAs) over the first link (Link 1). The non-STR soft AP multi-link device (Soft AP, non-STR AP MLD) connects and authenticates with a legacy station (Legacy STA) and a single link station (Single link STA) via the first link (Link 1).

[0356] The channel access method for the mandatory link and the optional link may be different, as further explained in Figures 45-47.

[0357] FIG. 46 shows a non-STR soft AP multi-link device according to an embodiment of the present invention transmitting PPDUs on mandatory links and optional links.

[0358] When channel access is performed independently for the required link and the selective link, when a non-STR soft AP multilink device transmits via the selective link, it may not be able to receive via the required link. To prevent this problem, whether to transmit via the selective link may be determined depending on whether transmission is being performed via the required link. A non-STR soft AP multilink device can determine whether to transmit via the selective link based on whether transmission is being performed via the required link. Specifically, when a non-STR soft AP multilink device transmits, the non-STR soft AP multilink device can mandatory transmit via the mandatory link. Furthermore, a non-AP multilink device connected to a non-STR soft AP multilink device can determine whether to transmit via the selective link based on whether transmission is being performed via the mandatory link. Specifically, when a non-AP multilink device connected to a non-STR soft AP multilink device transmits, the non-AP multilink device can mandatory transmit via the mandatory link.

[0359] Therefore, a non-STR soft AP multilink device can transmit on a selective link only when transmitting on a required link. When a non-STR soft AP multilink device does not transmit on a required link, the non-STR soft AP multilink device may not be allowed to transmit on a selective link.

[0360] When random backoff-based channel access is performed, the following embodiment may be applied. If the backoff counter for the selective link reaches 0 but the backoff counter for the required link has not yet reached 0, the non-STR soft AP multilink device does not need to transmit on the selective link. Specifically, the non-STR soft AP multilink device can wait until the backoff counter for the required link reaches 0. When the backoff counter for the selective link reaches 0, the non-STR soft AP multilink device can start transmitting on the selective link if the backoff counter for the required link has reached 0 or if transmission is currently being performed on the required link.

[0361] The following embodiment may be applied when channel access is performed based on the results of channel sensing during a fixed-length time interval. Even if a non-STR soft AP multilink device detects that the channel of a selective link is idle during a pre-specified time interval, if no transmission is occurring on the required link, the non-STR soft AP multilink device may not be allowed to start transmission on the selective link. In this case, the pre-specified time interval may be PIFS. In yet another specific embodiment, the non-STR soft AP multilink device may perform channel sensing and channel access on the selective link during a pre-specified time interval only when the non-STR soft AP multilink device is transmitting on the required link.

[0362] A non-STR soft AP multilink device can align the ends of PPDUs transmitted through a mandatory link and the ends of PPDUs transmitted through an optional link. Ending the transmission of multiple PPDUs simultaneously can be referred to as aligning the ends of PPDUs. Furthermore, the ends of multiple PPDUs are said to be aligned when the difference between the end times of the transmission of multiple PPDUs is smaller than, or smaller than, or equal to a threshold value. In this case, the threshold value may be a predetermined value. Specifically, the threshold value may be a value set based on the SIFS. Furthermore, the threshold value may be a value set based on the length of the SIFS and the signal extension. For example, the threshold value may be a value obtained by dividing the sum of the length of the SIFS and the signal extension by 2. In this case, the threshold value may be 8 us. Only when a PPDU transmitted through either the mandatory link or the optional link does not contain a frame inducing an immediate response, the non-STR soft AP multilink device may be allowed to not align the ends of PPDUs. Specifically, the non-STR soft AP multilink device can be configured to align the end of a PPDU including a frame inducing an immediate response with the end of a PPDU not including a frame inducing an immediate response, or to place the end of a PPDU including a frame inducing an immediate response before the end of a PPDU including a frame inducing an immediate response. For example, in the case where the ends of PPDUs are not aligned, the end of a PPDU not including a frame inducing a response may be the same as or come earlier in time than the end of a PPDU including a frame inducing an immediate response.

[0363] In the embodiment of Figure 46, the non-STR soft AP multi-link device includes a first AP (AP1) and a second AP (AP2). Each of the first AP (AP1) and the second AP (AP2) operates with a first link (Link1), which is a mandatory link, and a second link (Link2), which is an optional link. Each of the first AP (AP1) and the second AP (AP2) is coupled to a first station (SAT1) and a second station (STA2) included in the non-STR multi-link device. When the second AP (AP2) transmits data (Data1) to the second station (STA2), if the first station (STA1) transmits data (Data2) to the first AP (AP1), the first AP (AP1) cannot receive the data (Data2).

[0364] As in the above-described embodiment, when the first AP (AP1) and the second AP (AP2) simultaneously transmit PPDUs, the first AP (AP1) and the second AP (AP2) align the ends of the PPDUs. When the first AP (AP1) transmits a PPDU containing data (Data3) and the second AP (AP2) transmits a PPDU containing data (Data4), the first AP (AP1) and the second AP (AP2) align the ends of the PPDUs. Also, if a PPDU transmitted over one link does not include a frame inducing an immediate response, the first AP (AP1) and the second AP (AP2) may be allowed to not align the ends of the PPDUs. Because the data (Data5) transmitted by the first AP (AP1) does not induce an immediate response, the first AP (AP1) can stop transmitting its PPDU before the PPDU transmitted by the second AP (AP2).

[0365] The above-described embodiment regarding the channel access operation of the non-STR soft AP multilink device may be equally applied to a non-AP multilink device connected to a non-STR soft AP multilink device.

[0366] In the above-described embodiments, if the exception of PPDU end alignment is allowed, a non-STR soft AP multi-link device may need to receive data on another link while transmitting a PPDU on one link. For example, as shown in FIG. 45, while a second AP (AP2) is transmitting a PPDU containing data (Data6), a first AP (AP1) may receive a PPDU containing data (Data7) from a first station. In this case, the transmission of the PPDU containing data (Data6) may prevent the first AP (AP1) from receiving the PPDU containing data (Data7). Therefore, a method may be needed to prevent PPDU reception on one link from being interrupted.

[0367] FIG. 47 shows a non-STR soft AP multi-link device according to an embodiment of the present invention transmitting PPDUs on mandatory links and optional links.

[0368] A non-STR soft AP multilink device may determine whether to align the ends of PPDUs based on whether a PPDU including a frame inducing an immediate response is transmitted through a mandatory link or a selective link. Specifically, when a non-STR soft AP multilink device transmits a PPDU including a frame inducing an immediate response through a selective link, the non-STR soft AP multilink device may need to align the ends of the PPDUs transmitted through the mandatory link and the selective link. That is, when a non-STR soft AP multilink device transmits a PPDU that does not include a frame inducing an immediate response through a selective link, the non-STR soft AP multilink device may be allowed to not align the ends of the PPDUs transmitted through the mandatory link and the selective link.

[0369] In the embodiment of Figure 47, the non-STR soft AP multi-link device includes a first AP (AP1) and a second AP (AP2). Each of the first AP (AP1) and the second AP (AP2) operates with a first link (Link1), which is a mandatory link, and a second link (Link2), which is an optional link. Each of the first AP (AP1) and the second AP (AP2) is coupled to a first station (SAT1) and a second station (STA2) included in the non-STR multi-link device. When the second AP (AP2) transmits data (Data1) to the second station (STA2), if the first station (STA1) transmits data (Data2) to the first AP (AP1), the first AP (AP1) cannot receive the data (Data2). As in the above-described embodiment, when the first AP (AP1) transmits a PPDU including data (Data1) that does not induce an immediate response on the required link and the second AP (AP2) transmits a PPDU including data (Data2) that induces an immediate response, the first AP (AP1) and the second AP (AP2) align the ends of the PPDUs. When the second AP (AP2) transmits a PPDU that does not include data (Data4) that induces an immediate response, the first AP (AP1) and the second AP (AP2) do not align the ends of the PPDUs. Specifically, the second AP (AP2) may finish transmitting its PPDU before the first AP (AP1) finishes transmitting its PPDU.

[0370] In the above-described embodiment, the operation of the non-STR soft AP multilink device may be the same as the operation of the communicating non-AP multilink device.

[0371] Even if a multilink device sets up multiple links, it may not be able to support simultaneous transmission or reception on the multiple links. Such a multilink device can transmit or receive on the multiple links provided that it transmits or receives a restricted type of frame or PPDU. In this case, the restricted type of frame or PPDU may be limited in the frame type, MCS used for transmission, number of special streams used for transmission, and frequency bandwidth used for transmission. Such multilink device operation can be referred to as enhanced multilink operation. In enhanced multilink operation, the multilink device may concentrate processing or transmission capabilities used for one or more links on one or more other links. A non-STR softAP multilink device may not perform enhanced multilink device operation. Specifically, enhanced multilink device operation may not be permitted for multiple links set up by a non-STR softAP multilink device. For example, a non-STR softAP multilink device may not set enhanced multilink device operation for a multilink device operating on multiple links set up by a non-STR softAP multilink device. Specifically, non-STR SoftAP multilink devices may be signaled as rejecting or not supporting enhanced multilink operation because transmissions on required links are not possible when transmissions are made on selective links in enhanced multilink operation.

[0372] FIG. 48 shows a non-STR soft AP multi-link device according to an embodiment of the present invention performing channel access with a mandatory link and a selective link.

[0373] While a non-STR soft AP multilink device is receiving on a selective link, the non-STR soft AP multilink device can defer channel access on a required link. This is because if a non-STR soft AP multilink device transmits on a required link while receiving on a selective link, reception on the selective link may be disrupted. Channel access deferral may mean not attempting channel access during the deferral period. Channel access deferral may also mean not starting transmission even if the backoff counter reaches 0. A non-STR soft AP multilink device can defer channel access even before the sender identifier or address of a PPDU received on the selective link is identified. In this case, channel access deferral may continue until reception on the selective link is completed.

[0374] In the embodiment of Figure 48, the non-STR soft AP multi-link device includes a first AP (AP1) and a second AP (AP2). Each of the first AP (AP1) and the second AP (AP2) operates with a first link (Link1), which is a mandatory link, and a second link (Link2), which is an optional link. Each of the first AP (AP1) and the second AP (AP2) is coupled to a first station (STA1) and a second station (STA2) included in the non-STR multi-link device. The first AP (AP1) transmits data (Data1) to the first station (STA1) that does not require an immediate response, and the second AP (AP2) transmits data (Data2) to the second station (STA2) that requires an immediate response. The first AP (AP1) postpones channel access while the second AP (AP2) receives a response to the data (Data2) from the second station (STA2). In addition, the first AP (AP1) transmits data (Data3) to the first station (STA1) to induce an immediate response, and the second AP (AP2) transmits data (Data4) to the second station (STA2) to induce an immediate response. The first AP (AP1) receives a response to the data (Data3) from the first station (STA1), and the second AP (AP2) receives a response to the data (Data4) from the second station (STA2). While the second AP (AP2) receives the response to the data (Data4) from the second station (STA2), the first AP (AP1) postpones channel access.

[0375] In yet another specific embodiment, a non-STR soft AP multi-link device may not transmit a PPDU including a frame inducing an immediate response on a selective link while transmitting a PPDU not including a frame inducing an immediate response on a required link.

[0376] FIG. 49 shows a non-STR soft AP multi-link device according to an embodiment of the present invention transmitting PPDUs on mandatory links and optional links.

[0377] When a non-STR soft AP multilink device transmits a PPDU that does not contain a frame that induces an immediate response on both the required link and the selective link, the non-STR soft AP multilink device can end the PPDU transmission on the selective link at the same time as the PPDU transmission on the required link. That is, in this case, the end of the PPDU transmission on the selective link can be earlier than or the same as the end of the PPDU transmission on the required link. This is because if the PPDU transmission on the required link ends before the PPDU transmission on the selective link, it may interfere with the transmission of a station transmitting to the non-STR soft AP multilink device on the required link.

[0378] In the embodiment of Figure 49, the non-STR soft AP multi-link device includes a first AP (AP1) and a second AP (AP2). Each of the first AP (AP1) and the second AP (AP2) operates with a first link (Link1) that is a mandatory link and a second link (Link2) that is an optional link. Each of the first AP (AP1) and the second AP (AP2) is coupled to a first station (SAT1) and a second station (STA2) included in the non-STR multi-link device.

[0379] When a multilink device communicating with a non-STR SoftAP multilink device transmits a PPDU that does not contain a frame that induces an immediate response on both the mandatory link and the selective link, the multilink device can complete transmission on the selective link before transmitting the PPDU on the mandatory link. In this case, even if another station transmits to the non-STR SoftAP multilink device on the selective link, the non-STR SoftAP multilink device can receive.

[0380] An AP multilink device and a non-AP multilink device can negotiate the use of multilinks during the scanning and association process described in FIG. 5 above. During the scanning process, the AP of the AP multilink device can signal information about multiple links. Specifically, the AP of the AP multilink device can include in a beacon frame at least one of an indicator indicating that it is capable of operating with multiple links, the number of available links, and information about the multiple links. Also, during the scanning process, a station of a non-AP multilink device can signal information about multiple links. Specifically, a station of a non-AP multilink device can include in a probe frame an indicator indicating that it is capable of operating with multiple links. Also, a station of a non-AP multilink device can include in a probe frame at least one of the number of available links and information about the multiple links.

[0381] A non-AP multilink device that has confirmed the availability of multilink operation and the link information used by the AP multilink device during the scanning process can establish a connection with the AP multilink device. At this time, the AP multilink device and the non-AP multilink device can begin a negotiation process for multilink operation. Negotiation for multilink operation may occur during a connection process between the AP of the AP multilink device and a station of the non-AP multilink device. When a station of the non-AP multilink device sends a connection request frame to the AP of the AP multilink device, the station of the non-AP multilink device can send an indicator indicating that multilink operation is available and a request indicator requesting multilink operation. The AP that receives the connection request frame from the station can check the indicator requesting multilink operation. At this time, if multilink operation is possible for the AP, the AP can send a connection response frame to the station that allows multilink operation, including link information used for multilink operation and parameters used for each link. The parameters for the multilink operation may include at least one of the frequency bands of each of the multiple links used in the multilink operation, the bandwidth expansion direction of each of the frequency bands of the multiple links, a Target Beacon Transmission Time (TBTT), and whether or not the STR operation is enabled. After the connection process, the AP multilink device and the non-AP multilink device, which have exchanged a connection request frame and a connection request response frame and confirmed the use of the multilink operation, can perform a frame transmission operation using the multiple links.

[0382] FIG. 50 illustrates independent transmission over each of multiple links according to an embodiment of the present invention.

[0383] After completing negotiation for multilink operation, the AP multilink device and the non-AP multilink device can transmit and receive independently for each link or simultaneously for multiple links. When multiple links are transmitted and received independently, the AP of the AP multilink device and the non-AP station of the non-AP multilink device independently compete for the channel for transmission. Therefore, the start and end times of transmission for each link do not need to be the same. In addition, the transmission opportunity (TXOP) acquired in the channel access procedure for each link can also be acquired independently.

[0384] In the embodiment of Figure 50, the AP multi-link device (AP MLD) includes a first AP (AP1) and a second AP (AP2), and the first AP (AP1) and the second AP (AP2) operate on a first link (Link1) and a second link (Link2), respectively. The non-AP multi-link device (STA MLD) includes a first station (STA1) and a second station (STA2), and the first station (STA1) and the second station (STA2) operate on a first link (Link1) and a second link (Link2), respectively. The first AP (AP1) and the second AP (AP2) independently access the channel on the first link (Link1) and the second link (Link2). The first station (STA1) and the second station (STA2) also independently access the channel on the first link (Link1) and the second link (Link2), respectively. Therefore, an AP multilink device (AP MLD) and a non-AP multilink device (STA MLD) can transmit on one link while receiving on the other link.

[0385] This embodiment can improve transmission efficiency for individual links. However, if a non-AP multilink device or an AP multilink device does not support STR, such independent channel access for each of the multiple links may not be permitted. If a non-AP multilink device or an AP multilink device does not support STR, another embodiment may be applied. This will be described in FIG. 50.

[0386] FIG. 51 shows the operation of a multilink device transmitting on a non-STR link pair.

[0387] A non-STR multilink device that does not support STR cannot receive on any other link when transmitting on one link. Therefore, if a non-STR multilink device independently accesses channels on each of the multiple links, a transmission failure may occur. In the embodiment of FIG. 50(a), an AP multilink device (AP MLD) includes a first AP (AP1) and a second AP (AP2), each of which operates on a first link (Link1) and a second link (Link2). A non-AP multilink device (STA MLD) includes a first station (STA1) and a second station (STA2), each of which operates on a first link (Link1) and a second link (Link2). While the first station (STA1) is transmitting an uplink (UL frame) to the first AP (AP1), the second station (STA2) may have difficulty communicating with the second AP (AP2).

[0388] When a non-STR link pair exists, a multilink device transmitting on the non-STR link can align the start and end times of transmission of frames transmitted on the non-STR link pair. The start and end times of transmission of a frame may be the start and end times of transmission of a PPDU containing the frame. To this end, the multilink device can use padding or padding bits. Negotiation for simultaneous transmission may be performed. Negotiation for simultaneous transmission may include frame exchange to acquire TXOPs for simultaneous transmission. Specifically, a multilink device can transmit request frames on multiple links for which it has acquired TXOPs. A multilink device that receives a request frame can transmit a response frame at a short interframe space (SIFS) interval after the request frame. The request frame may be a control frame. The request frame may also be a request to send (RTS) frame or a multi-user (MU)-RTS frame. The response frame may also be a clear to send (CTS) frame. If any link is not idle when transmitting the request frame or response frame described above, the multilink device can transmit the request frame or transmission frame through an idle link among the multiple links. In the embodiment of FIG. 50(b), as described in FIG. 50(a), the first AP (AP1) and the second AP (AP2) operate on the first link (Link1) and the second link (Link2), respectively. Also, the first station (STA1) and the second station (STA2) operate on the first link (Link1) and the second link (Link2), respectively. Since the non-AP multilink device is a non-STR multilink device, the first AP (AP1) and the second AP (AP2) simultaneously transmit and receive frames. The first AP (AP1) and the second AP (AP2) simultaneously transmit request frames to secure a TXOP. The first station (STA1) and the second station (STA2) simultaneously transmit response frames in response to the request frame.Thereafter, the first AP (AP1) and the second AP (AP2) exchange frames with the first station (STA1) and the second station (STA2) within the reserved TXOP.

[0389] However, due to different channel conditions of the multiple links, transmissions may not start simultaneously on the non-STR link pair. Taking this into consideration, multiple stations transmitting to a non-STR multi-link device can align the ends of their PPDUs. Specifically, multiple stations transmitting to a non-STR multi-link device can align the ends of their PPDUs even if they cannot align the starts of their PPDUs. Also, as described above, if one of the PPDUs transmitted on a non-STR link pair does not contain a frame inducing an immediate response, the ends of the other PPDUs do not need to be aligned with the ends of the PPDUs that do not contain a frame inducing an immediate response. In the embodiment of FIG. 50(b), as described in FIG. 50(a), the first AP (AP1) and the second AP (AP2) operate on the first link (Link1) and the second link (Link2), respectively. Also, the first station (STA1) and the second station (STA2) operate on the first link (Link1) and the second link (Link2), respectively. Because the non-AP multilink device is a non-STR multilink device, the first AP (AP1) and the second AP (AP2) align the ends of the PPDUs when they transmit PPDUs simultaneously. If the first AP (AP1) transmits a PPDU that does not contain a frame that induces an immediate response, the first AP (AP1) and the second AP (AP2) do not align the ends of the PPDUs. If the first AP (AP1) and the second AP (AP2) transmit PPDUs simultaneously, the first AP (AP1) and the second AP (AP2) align the ends of the PPDUs.

[0390] The aforementioned non-STR link pair refers to a link pair for which STR is not possible. A non-STR link group refers to a non-STR link group in which multiple links include a non-STR link pair. An embodiment applied when some of the multiple links on which an AP multilink device operates are non-SRT link pairs will be described in Figure 51.

[0391] FIG. 52 shows an embodiment of the present invention that is applied when some of the multiple links on which an AP multilink device operates are non-STR link pairs.

[0392] A multilink device may be associated with a station that is not included in the multilink device. In this case, it is difficult for the station that is not included in the multilink device to determine whether transmission is occurring on another link. Furthermore, when stations included in different multilink devices communicate in a non-STR link pair, it is difficult for the stations included in the different multilink devices to determine whether transmission is occurring on a link other than the link on which the station is operating. Figure 51 shows a non-STR AP multilink device communicating with a first station (STA1) and a second station (STA2) that are not included in the multilink device. In the example of Figure 51(a), a first AP (AP1) and a second AP (AP2) attempt channel access on the first link (Link1) and the second link (Link2), respectively. The first AP (AP1) succeeds in channel access and begins a frame exchange sequence by initiating RTS frame transmission. The second AP (AP2) fails channel access and is unable to begin the frame exchange sequence. As described above, the second AP (AP2) is unable to determine whether transmission is occurring on the first link. When the first AP (AP1) transmits data to the first station (STA1) via the first link (Link1), the second station (STA2) can perform uplink transmission. In the example of FIG. 51(b), the first station (STA1) successfully accesses the channel and begins the frame exchange sequence by initiating RTS frame transmission. The second station (STA2) successfully accesses the channel and attempts uplink transmission. While the first AP (AP1) is receiving data transmitted by the first station (STA1) via the first link (Link1), the second station (STA2) may complete transmission via the second link (Link2). At this time, because the first AP (AP1) is receiving data transmitted by the first station (STA1) via the first link (Link1), the second AP (AP2) cannot transmit a response to the transmission of the second station (STA2). Furthermore, the second STA (STA2) cannot confirm whether the transmission transmitted by the second station (STA2) was successful. An embodiment for preventing such a frame exchange failure will be described with reference to FIG.

[0393] FIG. 53 illustrates a multi-link device operating with multiple links including non-STR link pairs according to an embodiment of the present invention.

[0394] When a multilink device operates with multiple links including non-STR link pairs, the multilink device can designate at least one of the multiple links as a basic link. In this case, the basic link may be the required link described above. The multilink device can designate one of the multiple links as a basic link. Links other than the basic link among the multiple links can be called extended links.

[0395] When a non-AP multilink device attempts to connect to a link included in a non-STR link pair, the AP multilink device can guide the non-AP multilink device to connect to all links included in the non-STR link pair. Also, when a station not included in the non-AP multilink device attempts to connect to a link included in the STR link pair, the AP multilink device can guide the station not included in the non-AP multilink device to connect to a link included in the STR link pair.

[0396] In yet another specific embodiment, the AP multilink device may allow a station not included in the non-AP multilink device to connect only via the basic link. A station not included in the non-AP multilink device may connect to the AP multilink device only via the basic link of the AP multilink device.

[0397] In the embodiment of Figure 53, a non-STR AP multilink device (non-STR AP MLD) operates with a first link (Link1), a second link (Link2), and a third link (Link3), which are STR-capable link pairs. The first link (Link1) and the second link (Link2) are a non-STR link pair, the first link (Link1) and the third link (Link3) are an STR-capable STR link pair, and the second link (Link2) and the third link (Link3) are an STR-capable STR link pair. The non-STR AP multilink device (non-SRT AP MLD) designates the first link (Link1) and the third link (Link3) as basic links. In this case, a third station (STA3), which is not included in the multilink device, may be connected to the non-STR multilink device (non-STR AP MLD) via the first link (Link1) or the third link (Link3). A third station (STA3) that is not included in the multilink device does not have to be connected to the non-STR multilink device (non-STR AP MLD) via the first link (Link1) or the second link (Link2). The non-STR multilink device (non-STR AP MLD) can induce the third station (STA3) to be connected to the non-STR multilink device (non-STR AP MLD) via the third link (Link3).

[0398] In the above-described embodiment, the channel load of the basic link may increase excessively. To prevent this, the number of links included in the non-STR link pair can be limited. In this case, the number of links included in the non-STR link pair may be two.

[0399] In the above embodiment, during negotiation for multilink operation, the AP multilink device can induce connection to a basic link, as illustrated in FIG.

[0400] FIG. 54 shows the operation of an AP multilink device according to an embodiment of the present invention when it joins with a station not included in the multilink device.

[0401] When a station not included in the multilink device requests a connection to the AP multilink device via an extension link, the AP multilink device may reject the connection request from the station. Specifically, when a station not included in the multilink device transmits a probe request frame to the AP multilink device, the AP multilink device may not transmit a probe response frame to the station. Also, when a station not included in the multilink device transmits a connection request frame to the AP multilink device via an extension link, the AP multilink device may transmit a connection response frame to the station, the connection response frame including an indicator rejecting the connection request. The connection response frame may include a field indicating a status code for proposing a connection to another link. For example, the status code for proposing a connection to another link may be 82. The connection response frame may also include information about the link for which the connection is proposed. The information about the link for which the connection is proposed may be in the form of a Neighbor Report information element. The Neighbor Report information element may include at least one of an SSID, a channel, an operation class, and timing information. The link for which the connection is proposed may be a basic link included in the STR link pair. A station not included in the multilink can attempt to connect to a link proposed by the AP multilink device based on information about the link proposed by the AP multilink device.

[0402] The AP multilink device can also transmit beacon frames simultaneously via the extension link and the basic link. The AP multilink device can also transmit beacon frames via the extension link in a format that cannot be decoded by stations not included in the multilink device. Specifically, for example, the IBSS STA subfield and the ESS subfield in the Capability information field in the beacon frame can both be set to 1. In this case, stations not included in the multilink device cannot decode the beacon and cannot transmit an association request based on the beacon frame. In this embodiment, the AP multilink device can also transmit beacon frames via the basic link included in the non-STR link pair in a format that cannot be decoded by stations not included in the multilink device. The AP multilink device can also set some fields of the BSS load information element of the beacon frame transmitted via the extension link to predetermined values. In this case, the AP multilink device can set the BSS load information element of the beacon frame transmitted via the extension link to indicate the maximum channel utilization rate. The AP multilink device can also set the BSS load information element transmitted via the extension link to indicate the maximum number of connected stations. A station receiving such a beacon frame may determine that it is not possible to establish a connection over the extended link or that establishing a connection would reduce efficiency, and may not attempt to establish a connection. In yet another specific embodiment, the AP multilink device may not transmit a beacon frame over the extended link.

[0403] The above-described embodiment may be applied to a basic link included in a non-STR link pair as well as an extended link. For example, the AP multilink device may transmit a connection denial frame even if a station not included in the multilink transmits an connection request frame on a basic link included in a non-STR link pair.

[0404] In the embodiment of FIG. 54, a station (STA) not included in the multilink device transmits a probe request frame to a second AP (AP2) operating in the extended link. At this time, the second AP (AP2) does not transmit a probe response frame to the station (STA). The station (STA) not included in the multilink device transmits an association request frame to the second AP (AP2) operating in the extended link. At this time, the second AP (AP2) transmits an association response frame including a status code rejecting the association to the station (STA). At this time, the association response frame may include information regarding the link on which the third AP (AP3) or the first AP (AP1) operates, as described above. The station (STA) transmits an association request frame to the third AP (AP3) based on the information regarding the link on which the third AP (AP3) operates.

[0405] FIG. 55 illustrates an operation in which an AP multilink device according to an embodiment of the present invention associates with a station included in the multilink device.

[0406] A non-AP multilink device can request information about links for multilink operation from an AP multilink device using a probe request frame. Specifically, the probe request frame may include an indicator requesting link information for multilink operation. An AP multilink device that receives a probe request frame including information about links for multilink operation can transmit a probe response frame including information about links for multilink operation to a non-AP multilink device. The information about links for multilink operation may include at least one of information about STR link pairs, information about non-STR link pairs, and information about basic links. The non-AP multilink device can obtain information about links for multilink operation from the probe response frame.

[0407] A non-AP multilink device can transmit a multilink operation request to an AP multilink device using an association request frame. The association request frame may include an indicator indicating that multilink operation is requested. Upon receiving the multilink operation request, the AP multilink device can determine whether to accept the multilink operation. Specifically, if the association request frame includes an indicator indicating that multilink operation is requested, the AP multilink device can determine whether to accept the multilink operation. In a specific embodiment, the AP multilink device can determine whether the non-AP multilink device requests a connection via a non-STR link pair or a basic link of a non-STR link pair. Furthermore, the AP multilink device can determine whether the non-AP multilink device requests a connection via multiple links. If the non-AP multilink device requests a connection via an unavailable link, the AP multilink device can reject the connection request from the non-AP multilink device. Specifically, when a non-AP multilink device requests connection via an extended link of a non-STR link pair, the AP multilink device can reject the connection request from the non-AP multilink device. Also, when a non-AP multilink device requests connection via only some of the links of a non-STR link pair, the AP multilink device can reject the connection request from the non-AP multilink device. The multilink device can reject the connection request from the non-AP multilink device by transmitting a connection response frame indicating a connection rejection. Also, the multilink device can transmit a connection response frame indicating a link different from the link the non-AP multilink device requested connection via.

[0408] In the embodiment of Figure 55, a non-AP multilink device (STA MLD) transmits a probe request frame to an AP multilink device (AP MLD). The probe request frame includes an indicator (Multi-link Capabilities Indication) requesting link information for multilink operation. The AP multilink device (AP MLD) transmits a probe response frame including link information for multilink operation to the non-AP multilink device (STA MLD). The non-AP multilink device (STA MLD) acquires link information for multilink operation. The non-AP multilink device (STA MLD) transmits an association request frame including information for multilink negotiation to the AP multilink device (AP MLD). The AP multilink device (AP MLD) transmits an association response frame to the non-AP multilink device (STA MLD) indicating whether or not to accept multilink operation.

[0409] When a multilink device transmits on a non-STR link pair, transmission on the extended link may be restricted depending on whether transmission is performed on the basic link, as will be described in FIG.

[0410] FIG. 56 shows a multilink device according to an embodiment of the present invention transmitting over a non-STR link pair based on a basic link.

[0411] As described above, a basic link may be designated when an AP multilink device communicates with a station not included in the multilink device via a non-STR link pair, or when an AP multilink device and a station in the multilink device communicate via only some of the links in a non-STR link pair. The multilink device can perform independent channel access only via the basic link. Specifically, the multilink device can also transmit via the extended link under the condition that it transmits via the basic link. Therefore, if the basic link is occupied, transmission by the multilink device via the extended link may not be permitted. The multilink device may be an AP multilink device or a non-AP multilink device.

[0412] In the embodiment of FIG. 56, the AP multilink device includes a first AP (AP1) and a second AP (AP2). The first AP (AP1) and the second AP (AP2) operate on a first link (Link1) and a second link (Link2), respectively. The non-AP multilink device includes a first station (STA1) and a second station (STA2). The first station (STA1) and the second station (STA2) operate on a first link (Link1) and a second link (Link2), respectively. A third station (STA3), which is not included in the multilink, is connected to the first AP (AP1) via the first link. When the first station (STA1) does not transmit on the first link (Link1), the second station (STA2) cannot transmit on the second link (Link2). When the first station (STA1) transmits on the first link (Link1), the second station (STA2) transmits on the second link (Link2).

[0413] The operation of performing channel access before transmission in such an embodiment is illustrated in FIG.

[0414] FIG. 57 shows how a multilink device according to an embodiment of the present invention performs channel access for transmission on a non-STR link pair based on a basic link.

[0415] When a multilink device has successfully accessed a random backoff-based channel on the basic link, and when the extension link is idle for a predetermined consecutive time interval after the basic link has been successfully accessed, the multilink device can simultaneously transmit on the basic link and the extension link. The predetermined time interval may be PIFS. Alternatively, the predetermined time interval may be AIFS. In yet another specific embodiment, when a multilink device has successfully accessed a random backoff-based channel on the basic link, and the extension link is also idle for the same amount of time as the basic link is idle, the multilink device can simultaneously transmit on the basic link and the extension link. The multilink device may be an AP multilink device or a non-AP multilink device.

[0416] If channel access is successful on the basic link but the extension link is not idle, the AP multilink device does not need to transmit. In yet another specific embodiment, if channel access is successful on the basic link but the extension link is not idle, the AP multilink device can initialize the backoff counter value on the basic link and restart channel access. This operation can also be applied to non-AP multilink devices.

[0417] The embodiment of Figure 57 embodies the channel access operation of the embodiment of Figure 55. When a first station (STA1) successfully accesses the channel on the first link (Link1), which is the basic link, and a second station (STA2) also successfully accesses the channel on the first link (Link1), it determines whether the second link (Link2) has been idle for a predetermined time period. Since the second link (Link2) has been idle for a predetermined time period since the first link (Link1) successfully accesses the channel, the first station (STA1) and the second station (STA2) transmit simultaneously.

[0418] Yet another channel access method applicable to non-STR link pairs is described in FIG.

[0419] FIG. 58 shows how a multilink device according to an embodiment of the present invention performs channel access for transmission on a non-STR link pair based on a basic link.

[0420] In a non-STR link pair, a multilink device can independently perform random backoff-based channel access. In this case, if the backoff counter for the first link reaches 0 but the backoff counter for the second link has not yet reached 0, the multilink device can wait without starting transmission. Specifically, even if the backoff counter for the first link reaches 0, the multilink device may not start transmission until the backoff counter for the second link reaches 0. In this case, the multilink device can simultaneously transmit on the first and second links when the backoff counter for the second link reaches 0. If the first link is detected as the basic link and the second link is not idle, the multilink device can transmit only on the first link. Furthermore, even if the multilink device successfully accesses the channel only on the extension link, the multilink device may not be allowed to transmit only on the extension link. The multilink device may be an AP multilink device or a non-AP multilink device.

[0421] In the example of Figure 58, even if the backoff counter on the second link (Link2) reaches 0, the second station (STA2) waits without starting transmission because the first station (STA1) did not succeed in channel access on the first link (Link1), which is the basic link. When the first station (STA1) succeeds in channel access on the first link (Link1), which is the basic link, the first station (STA1) and the second station (STA2) transmit simultaneously.

[0422] A channel access execution method when one non-AP multi-link device is connected to all non-STR link pairs will be described with reference to FIGS.

[0423] FIG. 59 shows channel access of a multilink device according to an embodiment of the present invention when one non-AP multilink device is connected to all non-STR link pairs.

[0424] In a non-STR link pair, a multilink device can independently perform random backoff-based channel access. In this case, if the backoff counter of the first link reaches 0 but the backoff counter of the second link has not yet reached 0, the multilink device can maintain the backoff counter at 0 without starting transmission. Specifically, even if the backoff counter of the first link reaches 0, the multilink device does not need to start transmission until the backoff counter of the second link reaches 0. In this case, the multilink device can simultaneously transmit on the first and second links when the backoff counter of the second link reaches 0.

[0425] In the example of Figure 59, even if the backoff counter of the second link (Link2) reaches 0, the second station (STA2) does not start transmission and maintains the backoff counter at 0 because the first station (STA1) did not succeed in channel access on the first link (Link1), which is the basic link. When the first station (STA1) succeeds in channel access on the first link (Link1), which is the basic link, the first station (STA1) and the second station (STA2) transmit simultaneously.

[0426] In an STR link pair, multilink devices can independently perform random backoff-based channel access. A multilink device can begin transmission on one of the links only after first successfully accessing the channel on that link. However, when a multilink device transmits a PPDU containing an immediate response, the multilink device can align the ends of PPDUs transmitted on multiple links.

[0427] In the above-described embodiment, when the multilink device has successfully accessed a channel on one of the links and is waiting for the backoff procedure of the other links to be completed, the multilink device can perform channel sensing on the link that has successfully accessed the channel. At this time, if the channel on the link that has successfully accessed the channel is detected as not being idle, the multilink device can restart the channel access procedure on that channel. The operation of the multilink device when the multilink device has successfully accessed a channel on one of the links and has detected that the channel on the link that has not successfully accessed the channel is not being idle is described with reference to FIG. 60.

[0428] FIG. 60 shows channel access of a multi-link device according to an embodiment of the present invention when one non-AP multi-link device is connected to all non-STR link pairs.

[0429] In a non-STR link pair, if a multilink device successfully accesses a channel on the first link and detects that the channel on the second link is not idle, the multilink device can transmit on the first link. In this case, the multilink device can determine whether to start transmission on the first link based on the type of signal occupying the second link. Specifically, if the signal occupying the second link is a frame transmitted from another BSS, the multilink device can transmit on the first link. In yet another specific embodiment, if the signal occupying the second link is a frame transmitted from another BSS, the multilink device can maintain a backoff counter value of 0 on the first link. In this case, the multilink device can simultaneously transmit PPDUs on the first and second links when the second link becomes idle.

[0430] In this embodiment, the multilink device can determine whether the signal occupying the second link is a frame transmitted from another BSS based on the MAC address field of the received frame. If at least one of the MAC address fields of the received frame indicates the address of the AP to which the multilink device is connected, the multilink device can determine that the frame is an intra-BSS frame. Also, if the BSSID field of the received frame indicates the address of the AP to which the multilink device is connected, the multilink device can determine that the frame is an intra-BSS frame. Also, the multilink device can determine whether the signal occupying the second link is a frame transmitted from another BSS based on the BSS color indicated in the received PPDU. In this case, the PPDU can indicate the BSS color using the BSS color field or the Group ID field and Partial AID field of the signaling field.

[0431] If the signal occupying the second link is not a Wi-Fi signal, the multilink device may not transmit on the first link and may maintain the backoff counter at 0. In yet another specific embodiment, if the signal occupying the second link is not a Wi-Fi signal, the multilink device may transmit on the first link.

[0432] In the embodiment of Figure 60, the AP multilink device includes a first AP (AP1) and a second AP (AP2). Each of the first AP (AP1) and the second AP (AP2) operates on a non-STR link pair, a first link (Link1) and a second link (Link2). The non-AP multilink device also includes a first station (STA1) and a second station (STA2). Each of the first station (STA1) and the second station (STA2) operates on the first link (Link1) and the second link (Link2). Each of the first station (STA1) and the second station (STA2) independently accesses the channel on the first link (Link1) and the second link (Link2). If the first link (Link1) is not idle and the second station (STA2) successfully accesses the channel on the second link (Link2), the second station (STA2) can transmit on the second link (Link2).

[0433] When a multilink device attempts to transmit multiple PPDUs over a non-STR link pair, one of the links may be occupied by a frame transmitted from the BSS to which the station of the multilink device belongs. A method for performing channel access for the multilink device in this case will be described with reference to Figures 61 to 63.

[0434] Figure 61 shows the transmission operation of a non-AP multi-link device when one non-AP multi-link device is connected to all links of a non-STR link pair of an AP multi-link device in an embodiment of the present invention and the AP multi-link device transmits via one of the links.

[0435] As described above, according to one embodiment of the present invention, the AP multilink device can accept a connection only if the non-AP multilink device requests connection to all non-STR link pairs. In this case, the non-AP multilink device can independently access the channel for each non-STR link pair. While the AP multilink device is transmitting on one of the non-STR link pairs, the non-AP multilink device does not need to transmit on the other links.

[0436] In the embodiment of Figure 61, the AP multilink device includes a first AP (AP1) and a second AP (AP2). The first AP (AP1) and the second AP (AP2) each operate on a non-STR link pair, a first link (Link1) and a second link (Link2). The non-AP multilink device also includes a first station (STA1) and a second station (STA2). The first station (STA1) and the second station (STA2) each operate on the first link (Link1) and the second link (Link2). The first station (STA1) and the second station (STA2) each independently access the channel on the first link (Link1) and the second link (Link2). While the first AP (AP1) is transmitting on the first link (Link1), the second station (STA2) does not transmit on the second link (Link2).

[0437] Figure 62 shows the transmission operation of a non-AP multi-link device when one non-AP multi-link device is connected to all links of a non-STR link pair of an AP multi-link device in an embodiment of the present invention and an intra-BSS frame transmitted by another station is transmitted on one of the links.

[0438] As described above, according to one embodiment of the present invention, the AP multilink device can accept a connection only if the non-AP multilink device requests connection to all of the non-STR link pairs. In this case, the non-AP multilink device can independently access the channel for each of the non-STR link pairs. If an Intra-BSS frame transmitted by another station is detected on one of the non-STR links, the non-AP multilink device can transmit on the other link. In this case, the non-AP multilink device can transmit only PPDUs that do not include frames inviting an immediate response. In addition, the non-AP multilink device can transmit until the transmission on the other link is expected to end. The non-AP multilink device can predict the end of transmission based on the value of the Length field in the L-SIG field of the PPDU.

[0439] In the embodiment of FIG. 62, the AP multilink device includes a first AP (AP1) and a second AP (AP2). The first AP (AP1) and the second AP (AP2) each operate on a non-STR link pair, a first link (Link1) and a second link (Link2). The non-AP multilink device also includes a first station (STA1) and a second station (STA2). The first station (STA1) and the second station (STA2) each operate on the first link (Link1) and the second link (Link2). The first station (STA1) and the second station (STA2) each independently access the channel on the first link (Link1) and the second link (Link2). A station other than the first station (STA1) transmits an Inter-BSS frame on the first link (Link1). At this time, the second station (STA2) transmits a PPDU on the second link (Link2) that does not include a frame inducing an immediate response. At this time, the second station (STA2) continues transmission until the other stations finish transmitting Inter-BSS frames.

[0440] Figure 63 shows the transmission operation of a non-AP multi-link device when one non-AP multi-link device is connected to all links of a non-STR link pair of an AP multi-link device in yet another embodiment of the present invention, and an intra-BSS frame transmitted by another station is transmitted on one of the links.

[0441] As described above, according to one embodiment of the present invention, the AP multilink device can accept a connection only if the non-AP multilink device requests a connection to all non-STR link pairs. In this case, the non-AP multilink device can independently access channels in each non-STR link pair. If an Intra-BSS frame transmitted by another station is detected on one of the non-STR links, the non-AP multilink device can transmit on the other link. In this case, even when the non-AP multilink device transmits a PPDU including a frame inducing an immediate response, the non-AP multilink device may need to complete the transmission before the end of the transmission of the Intra-BSS frame transmitted by the other station. Specifically, when the non-AP multilink device transmits a PPDU including a frame inducing an immediate response, the non-AP multilink device can align the end of the PPDU of the Intra-BSS frame transmitted by the other station with the end of the PPDU transmitted by the non-AP multilink device. The non-AP multilink device can predict the end of transmission based on the value of the Length field in the L-SIG field of the PPDU.

[0442] In the embodiment of Figure 63, the AP multilink device includes a first AP (AP1) and a second AP (AP2). The first AP (AP1) and the second AP (AP2) each operate on a non-STR link pair, a first link (Link1) and a second link (Link2). The non-AP multilink device also includes a first station (STA1) and a second station (STA2). The first station (STA1) and the second station (STA2) each operate on the first link (Link1) and the second link (Link2). The first station (STA1) and the second station (STA2) each independently access the channel on the first link (Link1) and the second link (Link2). A station other than the first station (STA1) transmits an Inter-BSS frame on the first link (Link1). At this time, the second station (STA2) transmits a PPDU on the second link (Link2) that does not include a frame inducing an immediate response. At this time, the second station (STA2) continues transmission until the other stations finish transmitting Inter-BSS frames.

[0443] In the embodiments described in Figures 61 to 63, if the sender address in the MAC Address field of the Intra-BSS frame is the same as the address of the AP to which the station is connected, the station in the non-AP multilink device can determine that the frame is an Intra-BSS frame transmitted by another station. Also, if the PPDU including the Intra-BSS frame indicates uplink transmission, the station in the non-AP multilink device can determine that the frame is an Intra-BSS frame transmitted by another station. The determination of whether the frame is an Intra-BSS frame may be performed using the same operation as described above.

[0444] FIG. 64 is a flowchart illustrating an example of a method for transmitting frames according to the present invention.

[0445] 64, a non-AP STA may receive a beacon frame including a request type field from an AP STA (S64010). The request type field may include a specific field for indicating a target wake time (TWT) for low latency operation, and when the value of the specific field is set to a first specific value, the broadcast TWT service period (SP) is the TWT SP for the low latency operation.

[0446] Thereafter, the non-AP STA receives downlink frames or transmits uplink frames according to the value of the specific field (S64020). That is, when a TWT SP is scheduled, the non-AP STA transmits and receives only limited frames (e.g., frames requiring low latency or that are latency-sensitive) in the TWT SP, and cannot transmit or receive other frames, or can transmit and receive only the limited frames with priority (e.g., the limited frames may have a higher priority).

[0447] When the TWT SP for low latency operation is set, only frames requiring low latency can be transmitted in the TWT SP for low latency operation.

[0448] The beacon frame may further include a quiet information element f...

Claims

1. A non-AP (Access Point) STA (station) of a wireless communication system, communication module; a processor for controlling the communication module; The processor: Receive a beacon frame including a request type field from the AP; The request type field includes a specific field for indicating a target wake time (TWT) for low latency operation; Receive a downlink frame or transmit an uplink frame according to the value of the specific field; If the value of the specific field is set to a first specific value, the broadcast TWT service period (SP) is the TWT SP for the low latency operation, STA.

2. The STA according to claim 1 , wherein, when the TWT SP for the low-latency operation is configured, only frames requiring low latency can be transmitted in the TWT SP for the low-latency operation.

3. The STA of claim 1 , wherein the beacon frame further includes a quiet information element for protecting the TWT SP for the low-latency operation.

4. The STA of claim 3 , wherein an interval set by the quiet information element and a start time of the TWT SP for the low latency operation are the same.

5. 4. The STA of claim 3, wherein, when an interval set by the quiet information element overlaps with part or all of the TWT SP for the low latency operation, the overlapping part or all of the interval set by the quiet information element is ignored.

6. The STA of claim 3 , wherein the interval set by the quiet information element is used by at least one STA to set a NAV.

7. The STA of claim 6 , wherein the NAV is set at the interval set by the quiet information element.

8. The STA of claim 1 , wherein when the value of the specific field is set to a second specific value, the specific field indicates that transmission is restricted only in the form of a response frame to a downlink frame.

9. the beacon frame further includes a parameter field including a broadcast TWT information field; The STA of claim 1 , wherein the broadcast TWT information field includes information related to a TID to which frame transmission is restricted by the TWT for the low latency operation.

10. 2. The STA of claim 1, wherein when the non-AP STA configures a multi-link device (MLD), the MLD cannot transmit frames on other links while receiving the beacon frame.

11. The STA of claim 1 , wherein a frame transmission operation ends before a start time of a TWT SP for the low latency operation.

12. A method for a non-AP STA to transmit a frame in a wireless communication system, comprising: receiving a beacon frame including a request type field from an AP, The request type field includes a specific field for indicating a target wake time (TWT) for low latency operation; and receiving a downlink frame or transmitting an uplink frame according to a value of the specific field, If the value of the specific field is set to a first specific value, a broadcast TWT service period (SP) is the TWT SP for the low latency operation.

13. The method of claim 12, wherein when the TWT SP for low latency operation is configured, only frames requiring low latency can be transmitted in the TWT SP for low latency operation.

14. The method of claim 12 , wherein the beacon frame further includes a quiet information element for protecting the TWT SP for the low latency operation.

15. The method of claim 14 , wherein an interval set by the quiet information element and a start time of the TWT SP for the low latency operation are the same.

16. 15. The method of claim 14, wherein if an interval set by the quiet information element overlaps with some or all of the TWT SP for the low latency operation, the overlapping part or all of the interval set by the quiet information element is ignored.

17. The method of claim 14 , wherein the interval set by the quiet information element is used by at least one STA to set a NAV.

18. The method of claim 17 , wherein the NAV is set at the interval set by the quiet information element.

19. The method of claim 12 , wherein when the value of the specific field is set to a second specific value, the specific field indicates that transmission is restricted only in the form of a response frame to a downlink frame.

20. the beacon frame further includes a parameter field including a broadcast TWT information field; The method of claim 12 , wherein the broadcast TWT information field includes information related to a TID to which transmission of frames is restricted by the TWT for the low latency operation.

21. 13. The method of claim 12, wherein when the non-AP STA configures a multi-link device (MLD), the MLD cannot transmit frames on other links while receiving the beacon frame.

22. The method of claim 12 , wherein a frame transmission operation ends before a start time of a TWT SP for the low latency operation.

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