Wireless communication methods and terminals for transmitting / receiving frames in wireless communication systems.

Abstract

The invention relates to a method for transmitting frames of a wireless communication system. A non-AP STA receives a signaling frame including a request type field from the AP and can receive a downlink frame or transmit an uplink frame according to the value of a specific field included in the signaling frame. Here, the request type field includes a specific field to denote the target wake time (TWT) for low-latency operation, and, if the value of the specific field is set to the first specific value, then the service period (SP) of the broadcast TWT is SP TWT for low-latency operation.

Description

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

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

[0002]

[0003] With the recent proliferation of mobile devices, wireless LAN (WLAN) technology, which can provide them with fast wireless Internet service, is attracting significant attention. WLAN technology utilizes short-range wireless communication technology to enable mobile devices such as smartphones, tablets, laptops, portable multimedia players, and embedded devices to wirelessly connect to the Internet at home, in businesses, or in specific service areas.

[0004] Since supporting the initial wireless LAN technology using the 2.4 GHz frequency, the Institute of Electrical and Electronics Engineers (IEEE) 802.11 has been commercializing or developing various technology standards. First, IEEE 802.11b supports communication speeds of up to 11 Mbps while using the 2.4 GHz band. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5 GHz band instead of the 2.4 GHz band, thereby reducing the impact of interference compared to the considerably crowded 2.4 GHz band. It also uses OFDM technology to increase communication speeds to up to 54 Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication range than IEEE 802.11b. And IEEE 802.11g, like IEEE 802.11b, uses the 2.4GHz band to achieve a communication speed of up to 54Mbps and satisfies backward compatibility, which has garnered considerable attention. It is also superior to IEEE 802.11a in terms of communication distance.

[0005] And to overcome the limitations of communication speed, which has been pointed out as a vulnerability in wireless LAN, there is IEEE 802.11n, a technical standard established. IEEE 802.11n aims to increase the speed and reliability of networks and extend the operating range of wireless networks. More specifically, IEEE 802.11n supports high throughput (HT) with data processing speeds of up to 540 Mbps or more, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology that uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates. In addition, this standard can use a coding method that transmits multiple redundant copies to increase data reliability.

[0006] As wireless LAN becomes more widespread and applications diversify, the need for new wireless LAN systems that support very high throughput (VHT) higher than the data processing speed supported by IEEE 802.11n has arisen. Among these, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) at the 5GHz frequency. Although the IEEE 802.11ac standard is defined only for the 5GHz band, early 11ac chipsets will also support operation in the 2.4GHz band to ensure backward compatibility with existing 2.4GHz band products. Theoretically, according to this specification, multi-station wireless LAN speeds can reach at least 1Gbps and a maximum single link speed of at least 500Mbps. This is achieved by extending the wireless interface concepts accepted in 802.11n, such as wider radio frequency bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256 QAM). In addition, there is IEEE 802.11ad, which transmits data using the 60 GHz band instead of the existing 2.4 GHz / 5 GHz. IEEE 802.11ad is a transmission standard that provides speeds of up to 7 Gbps using beamforming technology, making it suitable for streaming high-bitrate video such as large amounts of data or uncompressed HD video. However, the 60 GHz frequency band has a disadvantage in that it has difficulty passing through obstacles, so it can only be used between devices in short distances.

[0007] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard, which is a successor to 802.11ac and 802.11ad, is nearing development to provide high-efficiency and high-performance wireless LAN communication technology in high-density environments with densely packed APs and terminals. In an 802.11ax-based wireless LAN environment, high-frequency efficient communication must be provided indoors and outdoors in the presence of high-density stations and APs (Access Points), and various technologies have been developed to achieve this.

[0008] Additionally, development of new wireless LAN standards has begun to increase maximum transmission speeds to support new multimedia applications such as high-definition video and real-time gaming. The 7th generation wireless LAN standard, IEEE 802.11be (Extremely High Throughput, EHT), is currently under development with the goal of supporting transmission rates of up to 30 Gbps through wider bandwidths, increased spatial streams, and multi-AP cooperation in the 2.4 / 5 / 6 GHz bands. IEEE 802.11be proposes technologies such as a bandwidth of 320 MHz, multi-link operation, multi-Access Point (Multi-AP) operation, and retransmission operation (Hybrid Automatic Repeat Request, HARQ).

[0009] Multi-link operation can take a variety of forms, depending on its operating method and implementation method. Since problems not encountered in existing IEEE 802.11-based wireless LAN communication operations can arise, a detailed definition of the operating method for multi-link operation is necessary.

[0010] Meanwhile, the technology that serves as the background for the invention is written to promote understanding of the background for the invention, and may include content that is not a prior art already known to a person with ordinary skill in the field to which the technology belongs.

[0011]

[0012] The present invention is intended to provide a method, device and system for multi-link transmission operation using a wireless LAN, in order to efficiently perform transmission and reception operations of frames requiring low delay time by a wireless access point.

[0013] In addition, the present invention aims to provide a method, device and system for setting a section for limiting transmission and reception in order to transmit and receive frames requiring low delay time.

[0014] In addition, the present invention aims to provide a method, device and system for efficiently performing a frame transmission operation when a wireless access point or station cannot perform simultaneous transmission and reception operations on multiple links in a multi-link operation.

[0015] The technical problems to be achieved in this specification are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0016]

[0017] A multi-link device (MLD) of a wireless communication system includes a communication module; a processor for controlling the communication module, the processor receiving a beacon frame including a request type field from an AP, the request type field including 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, wherein 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.

[0018] Additionally, in the present invention, when the TWT SP for the low-delay operation is set, only frames requiring low delay can be transmitted during the TWT SP for the low-delay operation.

[0019] Additionally, in the present invention, the beacon frame further includes a quiet information element for protecting the TWT SP for the low-latency operation.

[0020] Additionally, in the present invention, the interval set by the quiet information element and the start time of the TWT SP for the low delay operation are the same.

[0021] In addition, in the present invention, if the interval set by the quiet information element overlaps with some or all of the TWT SP for the low-latency operation, some or all of the overlapping intervals set by the quiet information element are ignored.

[0022] Additionally, in the present invention, the interval set by the quiet information element is used for at least one STA to set the NAV.

[0023] Additionally, in the present invention, the NAV is set during the interval set by the quiet information element.

[0024] Additionally, 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 limited to transmission only in the form of a response frame for a downlink frame.

[0025] Additionally, 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 for which transmission of the frame is restricted by the TWT for the low-latency operation.

[0026] Additionally, in the present invention, when the non-AP STA configures a multi-link device (MLD), the MLD cannot transmit a frame through another link while receiving the beacon frame.

[0027] Additionally, in the present invention, the transmission operation of the frame is terminated before the start time of the TWT SP for the low-latency operation.

[0028]

[0029] According to one embodiment of the present invention, a frame requiring low delay can be efficiently transmitted.

[0030] Additionally, according to one embodiment of the present invention, a frame requiring low delay can be efficiently transmitted by setting a section that limits transmission of the frame.

[0031] According to the present invention, when supporting transmission and reception of frames requiring low latency in a wireless access point (AP) and an AP MLD including multiple wireless access points, a specific section is defined in which only transmission of frames requiring low latency is possible, and this is announced through a broadcast frame. When a wireless LAN station (STA) wishes to transmit and receive frames meeting the requirements, a negotiation process is performed with the AP or AP MLD to perform the corresponding operation. Here, information on the section requiring low latency is announced through a beacon frame or a probe response frame. Here, the method for announcing and negotiating the section requiring low latency is performed in a manner identical to or similar to the negotiation method of the TWT (Target Wake Time) operation. In order to efficiently perform the corresponding operation, the AP or AP MLD allows only terminals supporting the corresponding operation to access the link it operates. By using the low latency transmission operation, when a terminal or AP wishes to transmit a frame requiring low latency, the transmission and reception of the corresponding frame is stably performed, thereby increasing communication efficiency.

[0032] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention belongs from the description below.

[0033] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0034] Figure 2 illustrates a wireless LAN system according to another embodiment of the present invention.

[0035] Figure 3 shows the configuration of a station according to one embodiment of the present invention.

[0036] Figure 4 shows the configuration of an access point according to one embodiment of the present invention.

[0037] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0038] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0039] Figure 7 illustrates one embodiment of various standard generation-specific PPDU (PLCP Protocol Data Unit) formats.

[0040] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) PPDU formats and a method for indicating the same according to an embodiment of the present invention.

[0041] FIG. 9 is a structural diagram illustrating the internal hierarchical structure of an STA according to an embodiment of the present invention.

[0042] FIG. 10 is a conceptual diagram of an AP MLD and STA MLD structure performing multi-link operation according to an embodiment of the present invention.

[0043] FIG. 11 is a conceptual diagram illustrating a connection process between an AP MLD and a STA or STA MLD according to an embodiment of the present invention.

[0044] FIG. 12 is a first embodiment illustrating an operation for limiting a connection process of a terminal to perform a low-latency function according to an embodiment of the present invention.

[0045] FIG. 13 is a second embodiment illustrating an operation of limiting a terminal connection process to perform a low-latency function according to an embodiment of the present invention.

[0046] FIG. 14 is a block diagram illustrating a link state information element including transmission state information in a corresponding link according to an embodiment of the present invention.

[0047] FIG. 15 is a first embodiment illustrating the structure of a low-latency operation request frame requesting low-latency operation utilizing the TWT (Target Wake Time) function according to an embodiment of the present invention.

[0048] FIG. 16 is a second embodiment illustrating the structure of a low-latency operation request frame requesting low-latency operation utilizing a TWT function according to an embodiment of the present invention.

[0049] FIG. 17 is a block diagram illustrating a low-latency operation response frame that is a response to a request frame requesting low-latency operation utilizing a TWT function according to an embodiment of the present invention.

[0050] FIG. 18 is a first embodiment illustrating a process in which an AP or AP MLD and an STA perform low-latency operation utilizing a TWT function according to an embodiment of the present invention.

[0051] FIG. 19 is a second embodiment illustrating a process in which an AP or AP MLD and an STA perform low-latency operation utilizing a TWT function according to an embodiment of the present invention.

[0052] FIG. 20 illustrates an operation in which the TWT time is not protected for low-latency operation according to an embodiment of the present invention.

[0053] FIG. 21 illustrates an operation in which an AP MLD according to an embodiment of the present invention performs a low-latency operation by utilizing a TWT operation, and changes parameters at the same time.

[0054] FIG. 22 is an embodiment showing an operation of additionally transmitting a protection frame protecting the corresponding period at the start of the corresponding TWT time in order to protect the TWT time for low-latency operation by the AP MLD according to an embodiment of the present invention.

[0055] FIG. 23 is an embodiment illustrating a process in which an STA incapable of AP MLD and STR operation performs a low-latency operation utilizing a TWT function according to an embodiment of the present invention.

[0056] FIG. 24 is a conceptual diagram of an AP MLD and STA MLD structure performing multi-link operation according to an embodiment of the present invention.

[0057] FIG. 25 is a timing diagram illustrating a connection process and a negotiation process for multi-link operation between an AP MLD and a STA MLD according to an embodiment of the present invention.

[0058] FIG. 26 is a timing diagram illustrating a transmission method using multiple links according to an embodiment of the present invention.

[0059] FIG. 27 is an embodiment illustrating a frame transmission and reception operation between a receiving MLD that is incapable of STR operation and a transmitting MLD that is capable of STR operation in some or all links according to an embodiment of the present invention.

[0060] FIG. 28 is a first embodiment of an operation for protecting frame transmission and reception through an MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention.

[0061] FIG. 29 is a first embodiment illustrating the structure of an MU-RTS frame according to an embodiment of the present invention.

[0062] FIG. 30 is a second embodiment illustrating the structure of an MU-RTS frame according to an embodiment of the present invention.

[0063] FIG. 31 is a second embodiment of an operation for protecting frame transmission and reception through an MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention.

[0064] FIG. 32 is a third embodiment illustrating the structure of an MU-RTS frame according to an embodiment of the present invention.

[0065] FIG. 33 is a third embodiment of an operation for protecting frame transmission and reception through an MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention.

[0066] FIG. 34 is a fourth embodiment illustrating the structure of an MU-RTS frame according to an embodiment of the present invention.

[0067] FIG. 35 is an embodiment illustrating a channel reservation process through an MU-RTS frame and CTS frame exchange procedure during operation for multiple terminals according to an embodiment of the present invention.

[0068] FIG. 36 illustrates an operation in which a CTS frame is not transmitted for an MU-RTS frame in a specific 20 MHz channel according to an embodiment of the present invention.

[0069] FIG. 37 is a first embodiment of an operation of omitting transmission of an MU-RTS frame by imposing an additional condition in an AP MLD according to an embodiment of the present invention.

[0070] FIG. 38 is a second embodiment of an operation of omitting transmission of an MU-RTS frame by imposing an additional condition in an AP MLD according to an embodiment of the present invention.

[0071] FIG. 39 is an example of an operation for transmitting an MU-RTS frame according to additional conditions imposed by AP MLD according to an embodiment of the present invention.

[0072] FIG. 40 is a first embodiment of an operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz due to the operation of the corresponding STA MLD according to an embodiment of the present invention.

[0073] FIG. 41 is a second embodiment of an operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz due to the operation of the corresponding STA MLD according to an embodiment of the present invention.

[0074] FIG. 42 is a third embodiment of an operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz due to the operation of the corresponding STA MLD according to an embodiment of the present invention.

[0075] FIG. 43 is a first embodiment of an operation for continuing frame transmission even if a CTS frame is not received for an MU-RTS frame in a specific 20 MHz channel according to an embodiment of the present invention.

[0076] FIG. 44 is a second embodiment of an operation for continuing frame transmission even if a CTS frame is not received for an MU-RTS frame in a specific 20 MHz channel according to an embodiment of the present invention.

[0077] Figure 45 shows the operation of a soft AP according to an embodiment of the present invention.

[0078] FIG. 46 shows a non-STR soft AP multi-link device transmitting PPDUs on mandatory links and optional links according to an embodiment of the present invention.

[0079] FIG. 47 shows a non-STR soft AP multi-link device transmitting PPDUs on mandatory links and optional links according to an embodiment of the present invention.

[0080] FIG. 48 shows a non-STR soft AP multi-link device according to an embodiment of the present invention performing channel access in mandatory links and optional links.

[0081] FIG. 49 shows a non-STR soft AP multi-link device transmitting PPDUs on mandatory links and optional links according to an embodiment of the present invention.

[0082] FIG. 50 shows that transmission is performed independently on each of a plurality of links according to an embodiment of the present invention.

[0083] Figure 51 shows the operation of a multi-link device performing transmission on a non-STR link pair.

[0084] FIG. 52 shows an embodiment of the present invention applied when some of the multiple links on which an AP multi-link device operates are non-STR link pairs.

[0085] FIG. 53 illustrates a multi-link device operating on multiple links including non-STR link pairs according to an embodiment of the present invention.

[0086] FIG. 54 shows an operation of an AP multi-link device according to an embodiment of the present invention to couple with a station not included in the multi-link device.

[0087] FIG. 55 shows an operation of an AP multi-link device according to an embodiment of the present invention to couple with a station included in the multi-link device.

[0088] FIG. 56 shows a multi-link device according to an embodiment of the present invention performing transmission on a non-STR link pair based on a basic link.

[0089] FIG. 57 shows a multi-link device according to an embodiment of the present invention performing channel access for transmission on a non-STR link pair based on a basic link.

[0090] FIG. 58 shows a multi-link device according to an embodiment of the present invention performing channel access for transmission on a non-STR link pair based on a basic link.

[0091] FIG. 59 illustrates 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 both non-STR link pairs.

[0092] FIG. 60 illustrates 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 both non-STR link pairs.

[0093] FIG. 61 shows a 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 according to an embodiment of the present invention and the AP multi-link device performs transmission on one of the links.

[0094] FIG. 62 shows a 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 according to an embodiment of the present invention and an intra-BSS frame transmitted by another station is transmitted on one of the links.

[0095] FIG. 63 shows a 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 according to another embodiment of the present invention and an intra-BSS frame transmitted by another station is transmitted on one of the links.

[0096] Figure 64 is a flowchart showing an example of a method for transmitting a frame according to the present invention.

[0097] The terms used in this specification have been selected from widely used and current terms, taking into account the functions of the present invention. However, these terms may vary depending on the intentions of those skilled in the art, customs, or the emergence of new technologies. Furthermore, in certain cases, the applicant may arbitrarily select terms, in which case their meanings will be described in the description of the relevant invention. Therefore, it should be noted that the terms used in this specification should be interpreted based on their substantive meaning and the overall content of this specification, rather than simply their names.

[0098] Throughout the specification, when a component is said to be "connected" to another component, this includes not only cases where it is "directly connected," but also cases where it is "electrically connected" with another component in between. Furthermore, when a component is said to "include" a specific component, this does not exclude other components, but rather allows the inclusion of other components, unless specifically stated otherwise. Furthermore, the terms "more than" or "less than" based on a specific threshold may be appropriately replaced with "exceeds" or "less than", respectively, depending on the embodiment. In the following, fields and subfields may be used interchangeably in the present invention.

[0099] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0100] A wireless LAN system includes one or more Basic Service Sets (BSSs), which represent a collection of devices that have successfully synchronized and can communicate with each other. BSSs can generally be categorized as infrastructure BSSs and independent BSSs (IBSSs). Figure 1 illustrates an infrastructure BSS.

[0101] As illustrated in FIG. 1, the infrastructure BSS (BSS1, BSS2) includes one or more stations (STA1, STA2, STA3, STA4, STA5), an access point (AP-1, AP-2) that provides a distribution service, and a distribution system (DS) that connects multiple access points (AP-1, AP-2).

[0102] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium that complies with the IEEE 802.11 standard, and broadly includes both non-access point (AP) stations and access points (APs). In addition, the term "terminal" in this specification may refer to a non-AP STA or an AP, or both. A station for wireless communication includes a processor and a communication unit, and may further include a user interface unit and a display unit, depending on the embodiment. The processor may generate a frame to be transmitted through a wireless network or process a frame received through the wireless network, and may perform various other processes for controlling the station. In addition, the communication unit is functionally connected to the processor and transmits and receives frames through the wireless network for the station. In the present invention, a terminal may be used as a term that includes a user equipment (UE).

[0103] An Access Point (AP) is an entity that provides access to a distribution system (DS) via a wireless medium for stations associated with it. In an infrastructure BSS, communication between non-AP stations is in principle performed via the AP, but direct communication is also possible between non-AP stations when a direct link is established. Meanwhile, in the present invention, the AP is used as a concept including a Personal BSS Coordination Point (PCP), and in a broad sense, it can include concepts such as a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site controller. In the present invention, the AP may also be referred to as a base wireless communication terminal, and the base wireless communication terminal may be used as a term including, in a broad sense, an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal may include various types of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with multiple wireless communication terminals.

[0104] Multiple infrastructure BSSs can be interconnected via a distribution system (DS). Multiple BSSs connected via the distribution system are referred to as an Extended Service Set (ESS).

[0105] FIG. 2 illustrates an independent BSS, a wireless LAN system, according to another embodiment of the present invention. In the embodiment of FIG. 2, portions identical or corresponding to those in the embodiment of FIG. 1 will be omitted for duplicative description.

[0106] BSS3, illustrated in Figure 2, is an independent BSS and does not include an AP. Therefore, all stations (STA6, STA7) are not connected to an AP. An independent BSS does not allow access to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) can be directly connected to one another.

[0107] FIG. 3 is a block diagram showing the configuration of a station (100) according to one embodiment of the present invention. As illustrated, the station (100) according to the embodiment of the present invention may include a processor (110), a communication unit (120), a user interface unit (140), a display unit (150), and a memory (160).

[0108] First, the communication unit (120) transmits and receives wireless signals such as wireless LAN packets, and may be built into or externally installed in the station (100). According to an embodiment, the communication unit (120) may include at least one communication module using different frequency bands. For example, the communication unit (120) may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to one embodiment, the station (100) may include a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with an AP or an external station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (120) may operate only one communication module at a time or may operate 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 in an independent form, or the multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit (120) may represent an RF (Radio Frequency) communication module that processes RF (Radio Frequency) signals.

[0109] Next, the user interface unit (140) includes various types of input / output means provided in the station (100). That is, the user interface unit (140) can receive user input using various input means, and the processor (110) can control the station (100) based on the received user input. In addition, the user interface unit (140) can perform output based on a command of the processor (110) using various output means.

[0110] Next, the display unit (150) outputs an image on the display screen. The display unit (150) can output various display objects, such as content executed by the processor (110) or a user interface based on the control commands of the processor (110). In addition, the memory (160) stores a control program used in the station (100) and various data corresponding thereto. Such a control program may include a connection program required for the station (100) to connect to an AP or an external station.

[0111] The processor (110) of the present invention can execute various commands or programs and process data within the station (100). In addition, the processor (110) can control each unit of the above-described station (100) and control data transmission and reception between the units. According to an embodiment of the present invention, the processor (110) can execute a program for connection to an AP stored in the memory (160) and receive a communication setup message transmitted by the AP. In addition, the processor (110) can read information on the priority conditions of the station (100) included in the communication setup message and request connection to the AP based on the information on the priority conditions of the station (100). The processor (110) of the present invention may refer to the main control unit of the station (100), and according to an 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 or modulator and / or demodulator that modulates and / or demodulates wireless signals transmitted and received from the communication unit (120). The processor (110) controls various operations of transmitting and receiving wireless signals of the station (100) according to an embodiment of the present invention. A specific embodiment thereof will be described later.

[0112] The station (100) illustrated in FIG. 3 is a block diagram according to one embodiment of the present invention, and the blocks shown separately are logically distinguished elements of the device. Accordingly, the elements of the above-described device may be mounted as one chip or as multiple chips depending on the design of the device. For example, the processor (110) and the communication unit (120) may be implemented by being integrated into one chip or may be implemented as separate chips. In addition, in the embodiment of the present invention, some components of the station (100), such as the user interface unit (140) and the display unit (150), may be selectively provided in the station (100).

[0113] Fig. 4 is a block diagram illustrating the configuration of an AP (200) according to one embodiment of the present invention. As illustrated, the AP (200) according to the embodiment of the present invention may include a processor (210), a communication unit (220), and a memory (260). In Fig. 4, redundant descriptions of portions of the configuration of the AP (200) that are identical or corresponding to the configuration of the station (100) of Fig. 3 will be omitted.

[0114] Referring to FIG. 4, the AP (200) according to the present invention has a communication unit (220) for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit (220) of the AP (200) may also include a plurality of communication modules that utilize different frequency bands. That is, the AP (200) according to the embodiment of the present invention may include two or more communication modules for different frequency bands, such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP (200) may include a communication module that utilizes a frequency band of 7.125 GHz or higher and a communication module that utilizes a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with a station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (220) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the AP (200). In an embodiment of the present invention, the communication unit (220) may represent an RF communication module that processes an RF (Radio Frequency) signal.

[0115] Next, the memory (260) stores the control program used in the AP (200) and various data according to the control program. This control program may include a connection program that manages the connection of the station. In addition, the processor (210) controls each unit of the AP (200) and may control data transmission and reception between the units. According to an embodiment of the present invention, the processor (210) may execute a program for connection with a station stored in the memory (260) and transmit a communication setup message to one or more stations. At this time, the communication setup message may include information on the connection priority conditions of each station. In addition, the processor (210) performs connection setup according to a connection request from a station. According to one embodiment, the processor (210) may be a modem or a modulator and / or demodulator that modulates and demodulates a wireless signal transmitted and received from the communication unit (220). The processor (210) controls various operations of wireless signal transmission and reception of the AP (200) according to an embodiment of the present invention. Specific examples of this will be described later.

[0116] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0117] Referring to FIG. 5, the link between STA (100) and AP (200) is largely established through three stages: scanning, authentication, and association. First, the scanning stage is a stage in which STA (100) acquires access information of a BSS operated by AP (200). Methods for performing scanning include a passive scanning method in which information is acquired only by utilizing a beacon message (S101) periodically transmitted by AP (200), and an active scanning method in which STA (100) acquires access information by transmitting a probe request to AP (S103) and receiving a probe response from AP (S105).

[0118] The STA (100) that successfully receives wireless access information in the scanning step transmits an authentication request (S107a) and receives an authentication response from the AP (200) (S107b) to perform the authentication step. After the authentication step is performed, the STA (100) transmits an association request (S109a) and receives an association response from the AP (200) (S109b) to perform the association step. In this specification, association basically means wireless association, but the present invention is not limited thereto, and association in a broad sense may include both wireless association and wired association.

[0119] Meanwhile, an additional 802.1X-based authentication step (S111) and an IP address acquisition step (S113) via DHCP may be performed. In Fig. 5, the authentication server (300) is a server that processes STA (100) and 802.1X-based authentication, and may be physically connected to the AP (200) or may exist as a separate server.

[0120] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0121] A terminal performing wireless LAN communication performs carrier sensing before transmitting data to check whether the channel is busy. If a wireless signal above a certain strength is detected, the channel is determined to be busy, and the terminal delays access to the channel. This process is called clear channel assessment (CCA), and the level that determines whether the signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by the terminal is intended for the terminal, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected on the channel or a wireless signal with a strength lower than the CCA threshold is detected, the channel is determined to be idle.

[0122] When the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an Inter Frame Space (IFS) time, such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS may be used as a configuration to replace the existing DIFS (DCF IFS). Each terminal waits while decreasing the slot time by a random number determined for the terminal during the interval of the channel's idle state, and a terminal that has exhausted all of its slot time attempts to access the channel. The period during which each terminal performs the backoff procedure is called a contention window period.

[0123] If a specific terminal successfully accesses the channel, the terminal can transmit data through the channel. However, if the terminal attempting access collides with another terminal, the collided terminals are each assigned a new random number and perform a backoff procedure again. According to one embodiment, the random number newly assigned to each terminal may be determined within a range twice (2*CW) of the random number range (contention window, CW) previously assigned to the terminal. Meanwhile, each terminal performs the backoff procedure again in the next contention window period to attempt access, and at this time, each terminal performs the backoff procedure starting from the slot time remaining in the previous contention window period. In this way, each terminal performing wireless LAN communication can avoid collisions with each other for a specific channel.

[0124] 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. In addition, in the present invention, an AP STA may be referred to as an AP.

[0125] <Various PPDU format examples>

[0126] Fig. 7 illustrates examples of various standard generation-specific PPDU (PLCP Protocol Data Unit) formats. More specifically, Fig. 7(a) illustrates an embodiment of a legacy PPDU format based on 802.11a / g, Fig. 7(b) illustrates an embodiment of a HE PPDU format based on 802.11ax, and Fig. 7(c) illustrates an embodiment of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. In addition, Fig. 7(d) illustrates detailed field configurations of L-SIG and RL-SIG commonly used in the above PPDU formats.

[0127] Referring to FIG. 7(a), the preamble of a 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.

[0128] Referring to FIG. 7(b), the preamble of the HE PPDU additionally includes RL-SIG (Repeated Legacy Short Training field), HE-SIG-A (High Efficiency Signal A field), HE-SIG-B (High Efficiency Signal B field), HE-STF (High Efficiency Short Training field), and HE-LTF (High Efficiency Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF may be referred to as a HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0129] Referring to FIG. 7(c), the preamble of the EHT PPDU additionally includes, in addition to the legacy preamble, an RL-SIG (Repeated Legacy Short Training field), a U-SIG (Universal Signal field), an EHT-SIG-A (Extremely High Throughput Signal A field), an EHT-SIG-A (Extremely High Throughput Signal B field), an EHT-STF (Extremely High Throughput Short Training field), and an EHT-LTF (Extremely High Throughput Long Training field). In 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 be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some of the EHT PPDU formats.

[0130] The L-SIG field included in the PPDU preamble applies 64FFT OFDM and consists of a total of 64 subcarriers. Of these, 48 subcarriers, excluding the guard subcarrier, DC subcarrier, and pilot subcarrier, are used for L-SIG data transmission. Since L-SIG applies BPSK, Rate=1 / 2 Modulation and Coding Scheme (MCS), it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of L-SIG.

[0131] Referring to Fig. 7(d), L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field consists of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which combine modulation methods such as BPSK / QPSK / 16-QAM / 64-QAM and inefficiencies such as 1 / 2, 2 / 3, and 3 / 4. Combining the information in the L_RATE field and the L_LENGTH field can indicate the total length of the corresponding PPDU. In non-legacy PPDU formats, the L_RATE field is set to the minimum speed of 6 Mbps.

[0132] The L_LENGTH field is allocated in bytes, with a total of 12 bits, allowing for signaling up to 4095. In combination with the L_RATE field, it can indicate the length of the corresponding PPDU. At this time, legacy and non-legacy terminals may interpret the L_LENGTH field in different ways.

[0133] First, the method by which a legacy terminal or non-legacy terminal interprets the length of the PPDU using the L_LENGTH field is as follows. If the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) can be transmitted during 4 us, which is the duration of one symbol of 64 FFT. Therefore, by adding 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 symbols based on 64 FFT after L-SIG is obtained. Multiplying the obtained number of symbols by 4 us, which is the duration of one symbol, and then adding 20 us required for transmission of L-STF, L-LTF, and L-SIG, the length of the PPDU, i.e., the reception time (RXTIME) is obtained. This can be expressed as a formula as shown in Mathematical Expression 1 below.

[0134]

[0135] At this time, represents the smallest natural number greater than or equal to x. Since the maximum value of the L_LENGTH field is 4095, the length of the PPDU can be set to a maximum of 5.484 ms. A non-legacy terminal transmitting the PPDU must set the L_LENGTH field as in Mathematical Expression 2 below.

[0136]

[0137] Here, TXTIME is the total transmission time that constitutes the corresponding PPDU, as shown in mathematical expression 3 below. In this case, TX represents the transmission time of X.

[0138]

[0139] Referring to the above formulas, the length of the PPDU is calculated based on the rounded 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.

[0140] Referring to Fig. 7(e), the U-SIG (Universal SIG) field continues to exist in EHT PPDUs and subsequent generation wireless LAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. U-SIG is an OFDM 2 symbol based on 64FFT and can convey a total of 52 bits of information. Of these, 43 bits, excluding the 9 bits of CRC / Tail, are largely divided into the VI (Version Independent) field and the VD (Version Dependent) field.

[0141] The VI bit maintains its current bit configuration in the future so that even if a subsequent generation PPDU is defined, current 11be terminals can obtain information about the PPDU through the VI fields of the PPDU. To this end, the VI field consists of PHY version, UL / DL, BSS Color, TXOP, and Reserved fields. The PHY version field is 3 bits and sequentially distinguishes 11be and subsequent generation wireless LAN standards by version. For 11be, it has the value 000b. The UL / DL field distinguishes whether the PPDU is an uplink / downlink PPDU. BSS Color means an identifier for each BSS defined in 11ax and has a value of 6 bits or more. TXOP means the Transmit Opportunity Duration transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP including the PPDU can be inferred without having to decode the MPDU, and has a value of 7 bits or more.

[0142] The VD field is signaling information that is only useful for PPDUs of version 11be. It can be composed of fields that are commonly used in any PPDU format, such as PPDU format and BW, and fields that are defined differently for each PPDU format. The PPDU format is a delimiter that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field signals five basic PPDU BW options (a BW that can be expressed in the form of an exponential power of 20*2 can be called a basic BW) of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz, as well as various remaining PPDU BWs configured through Preamble Puncturing. In addition, after being signaled at 320 MHz, some 80 MHz can be signaled in a punctured form. Additionally, the punctured and modified channel shape can be signaled directly in the BW field, or can be signaled using the BW field together with a field appearing after the BW field (e.g., a field within the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signaling is possible, so only 3 puncturing modes can be signaled at most. If the BW field is 4 bits, a total of 16 BW signaling is possible, so a maximum of 11 puncturing modes can be signaled.

[0143] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs can be signaled in the same PPDU format, and a field to distinguish between MU PPDUs and SU PPDUs can be located before the EHT-SIG field, and additional signaling can be performed for this. Both SU PPDUs and MU PPDUs include the EHT-SIG field, but some fields that are not necessary in the SU PPDU may be compressed. In this case, the information in the compressed fields may be omitted or may have a reduced size compared to the original fields included in the MU PPDU. For example, in the case of the SU PPDU, the common field of the EHT-SIG may be omitted or replaced, or the user-specific field may be replaced or reduced to one, etc., and may have a different configuration.

[0144] Alternatively, the SU PPDU may further include a compression field indicating whether compression is performed, and some fields (e.g., RA field, etc.) may be omitted depending on the value of the compression field.

[0145] If part of the EHT-SIG field of the SU PPDU is compressed, information to be included in the compressed field may be signaled together in an uncompressed field (e.g., a common field, etc.). In the case of the MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of signaled information 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 allocated, and whether the transmitted MU PPDU was transmitted to itself. Therefore, the AP must include and 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 modulation method. The EHT-SIG field may include information on the size and location of the RU allocated to each user.

[0146] In the case of an SU PPDU, multiple RUs may be allocated to an STA, and the multiple RUs may or may not be consecutive. If the RUs allocated to the STA are not consecutive, the STA must recognize RUs that are punctured in the middle to efficiently receive the SU PPDU. Therefore, the AP may transmit information on punctured RUs among the RUs allocated to the STA in the SU PPDU (e.g., puncturing patterns 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 a puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field may signal the type of a discontinuous channel that appears within the bandwidth.

[0147] The form of the signaled discontinuous channel is limited, and the BW and discontinuous channel information of the SU PPDU are indicated in combination with the value of the BW field. For example, in the case of the SU PPDU, since it is a PPDU transmitted to only a single terminal, the STA can recognize the bandwidth allocated to it through the BW field included in the PPDU, and can recognize the punctured resource among the allocated bandwidth through the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the terminal can receive the PPDU in the remaining resource units except for a specific channel of the punctured resource unit. At this time, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0148] The reason why only a limited number of discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed on a per-20 MHz subchannel basis, if puncturing is performed on a BW with multiple 20 MHz subchannels, such as 80, 160, and 320 MHz, the discontinuous channel type (if only the edge 20 MHz is punctured, it is also considered discontinuous) must be signaled by individually indicating whether the remaining 15 20 MHz subchannels, excluding the primary channel, are used. Dedicating 15 bits to signaling the discontinuous channel type of single-user transmission can result in excessive signaling overhead considering the low data rate of the signaling portion.

[0149] The present invention proposes a technique for signaling the discontinuous channel type of an SU PPDU, and illustrates the discontinuous channel type determined according to the proposed technique. In addition, the present invention proposes a technique for signaling the puncturing types of the Primary 160 MHz and Secondary 160 MHz in a 320 MHz BW configuration of an SU PPDU, respectively.

[0150] In addition, one embodiment of the present invention proposes a technique for differentiating the configuration of a PPDU indicated by preamble puncturing BW values ​​according to the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits long, in the case of an EHT SU PPDU or a TB PPDU, an EHT-SIG-A of 1 symbol may be additionally signaled after the U-SIG, or EHT-SIG-A may not be signaled at all. Therefore, considering this, it is necessary to fully signal up to 11 puncturing modes through only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B is additionally signaled after the U-SIG, so up to 11 puncturing modes can be signaled in a different way from 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 band.

[0151] Figure 7(f) illustrates the configuration of the Format-specific field of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. In the case of the MU PPDU, the SIG-B signaling field for simultaneous reception by multiple users is essential, and SIG-B can be transmitted after the U-SIG without a separate SIG-A. To this end, 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 fields.

[0152] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) PPDU formats and a method for indicating the same according to an embodiment of the present invention.

[0153] Referring to FIG. 8, a PPDU can be composed of a preamble and a data portion, and the format of one type of EHT PPDU can be distinguished according to the U-SIG field included in the preamble. Specifically, whether the format of the PPDU is an EHT PPDU can be indicated based on the PPDU format field included in the U-SIG field.

[0154] Figure 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.

[0155] Figure 8 (b) shows an example of the 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 located after the U-SIG field.

[0156] Figure 8 (c) illustrates an example of the 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. The EHT MU PPDU format may include a HE-SIG-B field after the U-SIG field.

[0157] Fig. 8(d) illustrates 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 can 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 can be repeatedly positioned on the time axis.

[0158] The EHT MU PPDU described in (c) of FIG. 8 can be used by an AP for downlink transmission to multiple STAs. At this time, 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 transmit AID information of the receiver and / or transmitter of the PPDU transmitted through the user specific field of EHT-SIG-B to the STA. Accordingly, multiple terminals receiving the EHT MU PPDU can perform a spatial reuse operation based on the AID information of the user specific field included in the preamble of the received PPDU.

[0159] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information about the configuration of resource units (e.g., the partitioning form of resource units) in a specific bandwidth (e.g., 20 MHz, etc.) of the frequency axis. That is, the RA field may indicate the configuration of resource units partitioned in the bandwidth for transmission of the HE MU PPDU for the STA to receive the PPDU. Information about the STA allocated (or designated) to each partitioned resource unit may be included in the user-specific field of the EHT-SIG-B and transmitted to the STA. That is, the user-specific field may include one or more user fields corresponding to each partitioned resource unit.

[0160] For example, among the multiple resource units that are divided, a user field corresponding to at least one resource unit used for data transmission may include an AID of a receiver or a sender, and a user field corresponding to the remaining resource unit(s) that are not used for data transmission may include a preset null STA ID.

[0161] Two or more PPDUs illustrated in FIG. 8 can be indicated with a value indicating the same PPDU format. That is, two or more PPDUs can be indicated with the same PPDU format through the same value. For example, EHT SU PPDU and EHT MU PPDU can be indicated with the same value through the U-SIG PPDU format subfield. At this time, EHT SU PPDU and EHT MU PPDU can be distinguished by the number of STAs receiving the PPDU. For example, a PPDU received by only one STA can be identified as an EHT SU PPDU, and if the number of STAs is set so that two or more STAs receive it, it can be identified as an EHT MU PPDU. In other words, two or more PPDU formats illustrated in FIG. 8 can be indicated through the same subfield value.

[0162] In addition, among the fields illustrated in FIG. 8, some fields or some information of the fields may be omitted, and a case in which some fields or some information of the fields are omitted may be defined as compression mode or compressed mode.

[0163] Meanwhile, APs and STAs can request low-latency operation for specific traffic requiring low latency. In this case, the low-latency traffic can be forwarded to the MAC layer as follows:

[0164] FIG. 9 is a structural diagram illustrating the internal hierarchical structure of an STA according to an embodiment of the present invention.

[0165] Referring to FIG. 9, a communication device included in an 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 finds a path to a target communication node and transmits signals in that direction, a Data Link Layer that performs transmission operations in a terminal-to-terminal communication link, and a Physical Layer that performs transmission operations through actual physical signals. At this time, the Data Link Layer may include Logical Link Control (LLC) and Medium Access Control (MAC).

[0166] Meanwhile, each layer can send data and additional parameters for data transmission to its upper or lower layers through the Service Access Point (SAP). For example, the LLC layer can receive information about data, source address, destination address, etc. from the upper layer through the Link Service Access Point (LSAP). In addition, the MAC layer can forward received data to the upper layer through the MAC SAP and receive data to be transmitted and additional parameters for data transmission from the upper layer.

[0167] In the above hierarchical structure, if the data to be transmitted is data requiring low latency, the MAC layer can receive the data and related parameters from the upper layer in the form of MA-UNITDATA.request. At this time, if the data to be transmitted is data requiring low latency, the upper layer can include the corresponding indicator when transmitting the data to the MAC layer through the MAC SAP. For example, MA-UNITDATA.request can be transmitted by including an indication that the data requires low latency. If the indicator for the low latency is included, the MA-UNITDATA.request can include a meter as shown in Table 1 below.

[0168]

[0169] Each parameter included in DA-UNITDATA.request can be as shown in Table 2 below.

[0170]

[0171] Alternatively, a separate Traffic Stream (TS) can be defined for data requiring low latency. At this time, the Station Management Entity (SME) can receive the required Quality of Service (QoS) information for the ID of a specific Traffic Stream from the MAC Layer Management Entity SAP (MLME SAP) to manage the data corresponding to the specific TS. At this time, the MAC layer can receive information about the corresponding TS from the SME in the form of an MLME-ADDTS.request.

[0172] Meanwhile, if the AP or STA supports a low-latency transmission operation for a frame requiring low latency, an internal variable can be designated for 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. At this time, the MIB value can be dot11rTWTActivated. At this time, the low-latency operation is an operation for transmitting delay-sensitive traffic (e.g., latency-sensitive traffic) or frames, and the delay-sensitive traffic or frames can be preset traffic or frames. For example, the delay-sensitive traffic or frame can be indicated as delay-sensitive traffic or frames by the TID (or Access Category: AC).

[0173] Meanwhile, the AP may be an AP included in an AP MLD (Multi-link Device). The STA may be an STA included in an STA MLD. The AP MLD and STA MLD may be configured as described in FIG. 10 below.

[0174] FIG. 10 is a conceptual diagram of an AP MLD and STA MLD structure performing multi-link operation according to an embodiment of the present invention.

[0175] Referring to FIG. 10, 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 via a single interface. That is, the AP MLD may be connected to a Logical Link Control (LLC) layer via a single interface. Multiple APs included in the AP MLD may share some functions in the MAC layer. Each AP within 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 via a single interface. That is, a STA MLD may be connected to the LLC layer via a single interface. Multiple STAs included in the STA MLD may share some functions in the MAC layer. In addition, a STA MLD may be referred to as a non-AP MLD. In this case, the AP MLD and the STA MLD may perform a multi-link operation in which they communicate using a plurality of individual links. That is, when the AP MLD includes multiple APs, each AP can configure a separate link and perform frame transmission and reception operations using multiple links with each terminal included in the STA MLD. At this time, each link can operate in the 2.4 GHz, 5 GHz, or 6 GHz band, and each link can perform a bandwidth expansion operation. For example, when the AP MLD configures one link in the 2.4 GHz band and two links in the 5 GHz band, frame transmission can be performed with a bandwidth of 40 MHz through the bandwidth expansion method in the 2.4 GHz band, and frame transmission can be performed with a bandwidth of up to 320 MHz by utilizing a non-contiguous bandwidth in each link using the 5 GHz band.

[0176] Meanwhile, in the AP MLD or STA MLD, while one terminal in the MLD is performing a transmission operation, another terminal may not be able to perform a reception operation due to an interference problem within the device. In this way, the operation in which another AP or terminal in the MLD receives while one AP or terminal is performing a transmission operation is called STR (Simultaneous Transmit and Receive). The AP MLD may enable STR operation for all links. Alternatively, the STR operation may not be possible for some links of the AP MLD. A terminal MLD capable of STR operation may be connected to the AP MLD, and an MLD incapable of STR operation may be connected for some or all links. In addition, a terminal that does not belong to the MLD (for example, an IEEE 802.11a / b / g / n / ac / ax terminal or an IEEE 802.11be terminal that is not in the MLD format) may be additionally connected to an AP included in the AP MLD.

[0177] The above AP MLD and STA MLD can perform a negotiation process for multi-link operation. At this time, the negotiation process for 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 multi-link use operation during the scanning and connection process described in FIG. 5. When the negotiation process for multi-link operation is performed during the connection process, the AP MLD and STA MLD can operate as follows.

[0178] FIG. 11 is a conceptual diagram illustrating a connection process between an AP MLD and an STA or STA MLD according to an embodiment of the present invention. Any description of the connection process described in FIG. 11 and FIG. 5 will be omitted.

[0179] Referring to FIG. 11, the AP MLD and the STA MLD may perform a negotiation process for multi-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 multi-link operation is available, information on the number of available links, and information on multiple available links. Alternatively, when the AP MLD transmits a probe response frame in the form of a broadcast frame, the probe response frame may be transmitted including an indicator indicating that multi-link operation is available, information on the number of available links, and information on multiple available links. A terminal belonging to the STA MLD may transmit a probe request frame including an indicator indicating that multi-link operation is available. When the STA MLD intends to perform a negotiation process for multi-link operation, it may additionally request operation information for all APs belonging to the AP MLD. When an STA belonging to the STA MLD requests information on all APs belonging to the AP MLD, the probe request frame may be transmitted including the corresponding request indicator. An AP belonging to an 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 information about beacon frames transmitted from other APs belonging to the AP MLD). At this time, all of the parameters may include the number of links available for multi-link operation, link information, etc.

[0180] In the above scanning process, the STA MLD, which has confirmed whether the AP MLD operates in multi-link mode and the information on the links used, 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 multi-link operation. That is, any terminal (e.g., STA1) belonging to the STA MLD can send a connection request frame to any AP (e.g., AP1) belonging to the AP MLD, while sending an indicator indicating that the terminal's multi-link operation is available and a request indicator requesting that the terminal perform multi-link operation. The AP, which has received the connection request frame from the terminal, can confirm the indicator requesting multi-link operation, and if the AP is capable of multi-link operation, can transmit an connection response frame to the terminal, which includes link information to be used for multi-link operation and parameters used in each link, and allows multi-link operation. The parameters for the multi-link operation may include one or more of the bandwidth of each link used, the direction of bandwidth expansion, the Target Beacon Transmission Time (TBTT), and whether STR operation is performed. The AP MLD and STA MLD, in which the above connection request frame and response frame are exchanged and the use of multi-link operation is confirmed, can perform frame transmission operation using multiple links using multiple APs included in the AP MLD and multiple terminals included in the STA MLD after the connection process.

[0181]

[0182] Meanwhile, if the AP or AP MLD supports a low-latency transmission operation utilizing low-latency for frames requiring low latency, one or more links can be restricted to be accessed only by terminals capable of the operation. That is, in order to efficiently perform the channel reservation process and transmission process for the low-latency operation, only terminals that decode and understand the operation can be allowed to access a specific link. At this time, the low-latency transmission operation may be a low-latency transmission operation utilizing the TWT operation. For example, when transmitting a reservation time for a low-latency terminal by including the TWT SP (Target Wake Time Service Period) in a beacon frame, an STA that supports a low-latency operation utilizing the TWT function may not be able to perform a channel contention process for frame transmission if it is not an STA reserved for the corresponding TWT SP time. On the other hand, an STA that does not support the function can perform a channel access process for frame transmission even in the corresponding TWT SP. In this case, a situation may occur in which the transmission of a frame reserved to be transmitted to the corresponding TWT SP is delayed or collides due to a channel access operation by an STA that does not support the low-latency function utilizing the TWT operation. Accordingly, frames requiring low latency may not meet the required latency. To prevent this situation, the AP and AP MLD can designate specific links to be used only by terminals performing channel reservation procedures based on low latency operation.

[0183] Meanwhile, if the AP or AP MLD designates a link only for terminals that support low-latency operation, connection requests for STAs that do not support the function may be rejected as follows.

[0184] At this time, the low-latency operation is an operation for transmitting delay-sensitive traffic (e.g., latency-sensitive traffic) or frames, and the delay-sensitive traffic or frames may be preset traffic or frames. For example, the delay-sensitive traffic or frames may be indicated as delay-sensitive traffic or frames by the TID (or, Access Category: AC). Alternatively, the delay-sensitive traffic or frames may refer to traffic or frames that must be transmitted within a certain delay time, and may be indicated by the TID (or, Access Category: AC).

[0185] TWT allows STAs to manage their activity in the BSS by scheduling STAs to operate at different times to minimize contention and reduce the amount of time STAs using power management mode need to stay awake. TWT operation can be individual TWT or broadcast TWT, which is individually configured by the AP. That is, the AP can configure whether to perform the TWT operation individually for each STA or can transmit to non-AP STAs via broadcast TWT whether to perform the TWT operation for multiple STAs, and when a non-AP STA is scheduled to perform the TWT operation from the AP, the non-AP STA can perform the TWT operation during the interval of the TWT service period (SP).

[0186] At this time, the broadcast TWT operation may be referred to as a restricted TWT operation when used for low-latency operation. That is, the broadcast TWT operation may be performed as a restricted TWT operation when a non-AP STA supports the restricted TWT operation by a specific parameter of the capability element (for example, when a specific element is set to '1') and the beacon frame is set as a frame for the restricted TWT operation by a specific field of the beacon frame. At this time, the SP set for the broadcast TWT may be an SP for the restricted TWT operation.

[0187] At this time, limited TWT, which is a TWT operation for transmission of frames requiring low delay, can be used to support enhanced medium access protection and resource reservation for delay-sensitive traffic.

[0188] A non-AP STA for which a TWT SP has been set by an AP STA cannot transmit frames to the AP STA within the TWT SP except for frames agreed upon by individual TWTs.

[0189] Hereinafter, the limited TWT operation for low latency operation may be referred to as TWT operation.

[0190] FIG. 12 is a first embodiment illustrating an operation for limiting a terminal's connection process to perform a low-latency function according to an embodiment of the present invention. In FIG. 12, the connection process described in FIGS. 5 and 11 is omitted for brevity.

[0191] Referring to FIG. 12, an AP MLD may include multiple APs, each of which may operate a link. At this time, the AP MLD may designate one or more of the links it operates as a link exclusively for terminals supporting low-latency operation. For example, the link operated by AP 1 among the APs belonging to the AP MLD may be designated as a link exclusively for terminals supporting low-latency operation. Alternatively, an AP not belonging to the AP MLD may be operated exclusively for terminals supporting low-latency operation.

[0192] The above AP or AP MLD may transmit a probe response frame transmitted in the form of a beacon frame or broadcast frame, including an indicator indicating whether low-latency operation is supported. The low-latency operation may be a low-latency operation using the TWT function described in FIGS. 18 to 19 and 21 to 23 described below.

[0193] 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 the broadcast probe response frame and transmitted. In addition, an indicator indicating that the link is a link for low-latency terminals only may be included and transmitted in the beacon frame and the broadcast probe response frame. For example, the EHT Operation information element may be included in the beacon frame or the broadcast probe response frame, and an indicator (e.g., an rTWT Required field, etc.) indicating that support for the low-latency operation is required may be included in the EHT Operation information element and transmitted. Alternatively, the values ​​of both the IBSS STA subfield and the ESS subfield in the Capability information field in the beacon frame or the broadcast probe response frame may be set to 1 so that existing STAs that do not support the low-latency operation cannot recognize the BSS type of the AP. As another example, the beacon frame or broadcast probe response frame may additionally include an Interworking information element, and may indicate in the Access Network Type subfield of the Access Network Options field of the Interworking information element that the corresponding link is a link for low-latency operation. In the case of an STA that does not support low-latency operation among STA MLDs or STAs that do not belong to STA MLDs, an indicator indicating that the link is only for low-latency terminals may be checked in the beacon frame or broadcast probe response frame, and the STA or STA MLD that checks the indicator may not perform an active scanning process and an access process with the AP or AP MLD.

[0194] An STA MLD or an STA that does not belong to an STA MLD may attempt a scanning and connection process with the AP or AP MLD as described in FIG. 5. For example, the STA MLD or STA may transmit a probe request frame to the AP or AP MLD. At this time, the STA or STA MLD may 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, the indicator field supporting the function in the capability element in the probe request frame may be set to 1 and transmitted. On the other hand, if the STA or STA MLD does not support the function, the field indicating whether or not low-latency operation is supported among the capability elements in the probe request frame may be set to 0 and transmitted.

[0195] The AP or AP MLD can receive the probe request frame from the STA or STA MLD and check whether the STA or STA MLD supports the low-latency operation. If it is determined that the STA or STA MLD does not support the low-latency operation, the AP or AP MLD may not transmit a probe response frame as a response to the probe request frame. Alternatively, the AP or AP MLD may indicate that the AP supports only low-latency terminals while transmitting a probe response frame as a response to the probe request frame. The indicator indicating that the AP supports only low-latency terminals may be an indicator indicating that the link is only for the aforementioned low-latency terminals. If the STA or STA MLD does not support the low-latency operation, the indicator indicating that the link is only for low-latency terminals in the probe response frame may be checked and a connection process with the AP or AP MLD may not be performed.

[0196] Meanwhile, if the STA supports the low-latency operation or cannot decipher the indicators in the beacon frame and probe response frame, the STA may transmit a connection request frame to the AP based on the result of scanning 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 for accepting 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 for rejecting the connection request. In this case, the AP may indicate that the connection request is 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 probe response frame may be transmitted with the status code field set to a field value meaning LOW_LATENCY_SUPPORT_NEEDED (e.g., 133, etc.). If an AP included in the AP MLD rejects a connection request in response to a connection request frame, it may additionally transmit other link information to suggest connection to another link. Information about general links, not just links for low-latency terminals, may be transmitted in the form of a Neighbor Report information element. The Neighbor Report information element may include at least one of a BSSID, a channel and operation class, and timing information.

[0197] An 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 confirm that the connection request has been rejected. At this time, the STA can check the status code field value in the connection response frame to confirm that the corresponding link requires support for low-latency operation, and can check whether the corresponding 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 to confirm the proposed BSS information. The STA can check other link information included in the Neighbor Report information element, move to the channel indicated by the information, and perform the connection process described in FIG. 5 or FIG. 11 with the AP of the corresponding link.

[0198] Meanwhile, if the above-mentioned low-latency operation is based on the TWT operation of the wireless LAN operation, the AP or AP MLD that configures a link only for the low-latency terminal may exceptionally allow connection of a terminal that supports the TWT function for low-power operation. If connection of an existing wireless LAN terminal that supports the TWT function is allowed, the AP or AP MLD may accept or reject the connection request of the STA as follows.

[0199] FIG. 13 is a second embodiment illustrating an operation for limiting a terminal's connection process to perform a low-latency function according to an embodiment of the present invention. In FIG. 13, the same explanation as that described for the connection process in FIGS. 5, 11, and 12 is omitted.

[0200] Referring to FIG. 13, an AP MLD may include multiple APs, and each AP may operate a link. At this time, the AP MLD may designate one or more of the links it operates as a link only for terminals that support delay operation utilizing the TWT function. For example, the link operated by AP 1 among the APs belonging to the AP MLD may be designated as a link only for terminals that support low delay operation utilizing the TWT function. Alternatively, an AP not belonging to the AP MLD may be operated only for terminals that support low delay operation utilizing the TWT function.

[0201] The above 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 support for low-latency operation using the TWT function. For example, an indicator indicating whether or not low-latency operation using the TWT function is supported may be set to 1 in a capability element in the beacon frame or the broadcast probe response frame and transmitted. In addition, an indicator indicating that the corresponding link is a link only for terminals that support the TWT operation may be transmitted in the beacon frame or the broadcast probe response frame. For example, an EHT Operation information element may be included in the beacon frame or the broadcast probe response frame, and an indicator (e.g., a TWT Operation Required field, etc.) indicating that support for the TWT operation is required may be transmitted in the EHT Operation information element. Alternatively, as described in FIG. 12, support for the TWT function may be requested through an Access Network Type subfield in the Access Network Options field of the Capability information field or the Interworking information element. In the case of an STA that does not support TWT operation among STA MLD or STAs that do not belong to STA MLD, an indicator indicating that the link is for terminals that support TWT function only in the beacon frame or broadcast probe response frame can be checked, and the STA or STA MLD that checked the indicator may not perform the active scanning process and connection process with the AP or AP MLD.Meanwhile, the AP or AP MLD may set the TWT Required field to 1 in the HE Operation information element in the beacon frame or broadcast probe response frame to indicate that a negotiation process for TWT operation is required for an STA or STA MLD that supports the TWT function itself but does not support low-latency operation utilizing the TWT function.

[0202] An STA MLD or an STA that does not belong to an STA MLD may attempt a scanning and connection process with the AP or AP MLD as described in FIG. 5. For example, the STA MLD or STA may transmit a probe request frame to the AP or AP MLD. At this time, the STA or STA MLD may include information on functions supported by the STA or STA MLD in the probe request frame. For example, if the STA or STA MLD supports TWT, an indicator field (e.g., a TWT Requester Support field) supporting the function may be set to 1 in the HE capability element in the probe request frame and transmitted. In addition, if the STA or STA MLD supports a low-latency operation utilizing the TWT function, an indicator supporting the function may be additionally included in the probe request frame and transmitted. For example, an indicator field supporting the function may be set to 1 in the EHT capability element in the probe request frame and transmitted. On the other hand, if the STA or STA MLD does not support the function, the field indicating whether the TWT function is supported among the HE capability element and EHT capability element in the probe request frame and the field indicating whether low-latency operation using the TWT function is supported may be set to 0 and transmitted.

[0203] The AP or AP MLD can receive the probe request frame from the STA or STA MLD, and can check whether the STA or STA MLD supports the TWT function and the low-latency operation utilizing 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 as a response to the probe request frame. Alternatively, the AP or AP MLD may indicate that the AP requires support of the TWT function while transmitting a probe response frame as a response to the probe request frame. The indicator indicating that support of the TWT function is required may be an indicator notifying that support of the aforementioned TWT operation is required. If the STA or STA MLD does not support the TWT function, the indicator requesting the TWT function in the probe response frame may be checked, and a connection process with the AP or AP MLD may not be performed. Meanwhile, the AP or AP MLD may set the TWT Required field in the HE Operation information element in the probe response frame to 1 to indicate to an STA or STA MLD that supports the TWT function itself but does not support low-latency operation utilizing the TWT function that a negotiation process for TWT operation is required.

[0204] Meanwhile, if the STA or STA MLD supports the TWT function or cannot decipher the indicators in the beacon frame and probe response frame, the STA may transmit a connection request frame to the AP based on the result of scanning 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 TWT operation, the connection response frame may include an indicator for accepting the connection request. At this time, by setting the TWT Required field in the HE Operation information element in the connection response frame to 1, the STA or STA MLD that supports the TWT function itself but does not support low-latency operation utilizing the TWT function may be instructed 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 may include an indicator for rejecting the connection request. At this time, the AP may indicate in the status code field of the connection response frame that rejects the connection request that the connection request is rejected because the corresponding STA does not support the TWT function. For example, the probe response frame may be transmitted with the status code field set to a field value (e.g., 134) meaning TWT_REQUESTER_SUPPORT_NEEDED. If the AP included in the AP MLD rejects the connection request in response to the connection request frame, it may additionally include other link information and transmit it to suggest connection to another link, as shown in FIG. 12. Information about a general link, not a link for the low-latency terminal only, may be transmitted in the form of a Neighbor Report information element.The above Neighbor Report information element may include at least one of BSSID, channel and operation class, and timing information.

[0205] An 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 confirm that the connection request has been rejected. At this time, the STA can check the status code field value in the connection response frame to confirm that the link requires support for TWT operation, and can check 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.

[0206] Meanwhile, the AP or AP MLD may set the TWT Required field in the HE Operation element to be transmitted to 1. At this time, if an STA MLD or an STA that does not belong to the STA MLD supports the TWT function but does not support the low-latency operation utilizing the TWT function, it may be recognized that a negotiation process for the TWT operation is required after the connection process with the AP or AP MLD. Accordingly, the STA or STA MLD may perform a negotiation process for the TWT operation with the AP during or after the connection process with the AP or AP MLD. After negotiating the TWT operation, the frame transmission operation may not be performed at a time other than the negotiated TWT SP. Meanwhile, if the STA or STA MLD supports both the TWT operation and the low-latency operation utilizing the TWT function, a separate negotiation process for the TWT operation may not be performed after the connection process. At this time, the STA or STA MLD can check the TWT SP for low-latency operation transmitted by the AP in the beacon frame or broadcast probe response frame, and can terminate the frame transmission process before the start time of the corresponding TWT SP. That is, the STA or STA MLD supporting low-latency operation may not perform frame transmission during the TWT SP time for low-latency operation if it has not been negotiated with the AP in advance. In other words, the frame transmission operation may be terminated before the start time of the TWT SP for low-latency operation.

[0207] Meanwhile, an AP MLD or an AP that does not belong to an AP MLD can measure information about the frame transmission delay time for the link it operates. The transmission delay time can be continuously updated and stored within the AP at a certain time interval (e.g., 100 ms). In the case of an AP MLD that supports low-latency transmission operation, statistical information related to the transmission delay time of frames transmitted on each link operated by the AP MLD can be provided. That is, each AP belonging to an 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 can be transmitted as part of a beacon frame, a probe response frame, an access response frame, etc. transmitted by the AP MLD. An STA that has confirmed the statistical information can perform an access process with an AP belonging to the AP MLD through the operations of FIGS. 5 and 12 to 13 based on the information if there is a frame requiring a low latency time. Meanwhile, the STA MLD, which has verified the above statistical information, can, based on the information, if there is a frame requiring low latency, perform the connection process and the negotiation process for multi-link operation with the AP MLD through the operations of FIGS. 5 and 11 to 13. Furthermore, the STA MLD can determine, based on the information, through which link the frame requiring low latency will be transmitted.

[0208] The above 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 in which the Measurement type field of the Measurement Report information element is set to 7, and may include the average channel access time (Access Delay) by Access Category (AC) within 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 by AC, as follows.

[0209] FIG. 14 is a block diagram illustrating a link state information element including transmission state information in a corresponding link according to an embodiment of the present invention.

[0210] Referring to FIG. 14, a Measurement Report information element including transmission status information in a link may include an element ID field, a length field, a field indicating the format of measured information, a field indicating a measurement period, a field indicating a measurement information group, and a field indicating measured data information. At this time, the element ID field, the length field, the field indicating the format of measured information, etc. may be set to be the same as or similar to STA statistics. The measurement group information field may be set to 17 to indicate that it is information on a transmission delay time transmitted from the corresponding AP. The measurement information may include at least one of an average transmission time for all frames transmitted on the corresponding link, an average transmission time per AC of frames transmitted on the corresponding link, a variance of the average transmission time per AC of frames transmitted on the corresponding link, a top 95% value among the transmission times per AC of frames transmitted on the corresponding link, a transmission failure probability of all frames transmitted on the corresponding link, and a transmission failure probability per AC of frames transmitted on the corresponding link. At this time, the transmission time can be calculated from the time when the frame to be transmitted is generated in the corresponding AP to the time when the ACK frame is received upon completion of transmission of the corresponding frame. Alternatively, the transmission time can be calculated from the time when the frame to be transmitted in the corresponding AP is generated to the time when the ACK frame is received upon completion of transmission of the corresponding frame to the time when transmission or retransmission is completed before receiving the ACK. The transmission failure probability can be calculated as "(the number of times transmission failed due to exceeding the number of frame retransmission restrictions) / (the number of times ACKs for frame transmission were received + the number of times transmission failed due to exceeding the number of frame retransmission restrictions)" during the corresponding measurement period.

[0211] Meanwhile, an STA or STA MLD that wants to transmit a frame requiring low delay time can instruct the AP or AP MLD on information about the required delay time for the corresponding frame. At this time, the frame having the low delay time can be specified as a specific Traffic Stream (TS). If the frame requiring the low delay time is data allocated to a specific TS, the STA or STA MLD can perform a negotiation process with the AP or AP MLD to add a TS to the corresponding data. For example, the STA can transmit a TS addition request frame for adding a TS for traffic requiring low delay time to the AP, 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 at least one of the delay time information required by the data of the TS to be added, the data size, and the required transmission speed of the corresponding data.

[0212] An STA or STA MLD that wishes to transmit a frame requiring low latency may perform a negotiation process with an AP or AP MLD to perform low latency operation. The negotiation process for the low latency operation may be performed identically or similarly to the negotiation process for TWT operation. That is, when an STA transmits a request frame to an AP to perform low latency operation, the request frame may be a TWT request frame. A response frame for low latency operation transmitted from an AP to an STA may be a TWT response frame.

[0213] Meanwhile, the request frame for the low-latency operation may be transmitted including information on the required delay time for the frame to be transmitted. When the low-latency operation request frame includes the required delay time and frame generation information, the low-latency operation request frame is described in FIG. 15 below.

[0214] FIG. 15 is a first embodiment illustrating the structure of a low-latency operation request frame requesting low-latency operation utilizing the TWT (Target Wake Time) function according to an embodiment of the present invention.

[0215] Referring to FIG. 15, a 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 a low-latency operation utilizing a TWT operation. It may include an NDP Paging indicator field, which is a channel measurement operation-related field, a field indicating whether a TWT responder switches to PS mode, a field indicating the TWT negotiation type, a field indicating whether a TWT schedule can be adjusted, a field indicating a unit of a requested delay time, etc. Among the control fields, the remaining fields except for the field indicating the unit of the requested delay time may be set in the same manner as the setting method during negotiation for 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 a TWT responder switches to PS mode may be set to 0, thereby disabling the corresponding function. The field indicating the above TWT negotiation type can be set to 3 to indicate that the TWT operation is a request frame for negotiation in the form of broadcast TWT that periodically transmits TWT SP for low-latency terminals in a beacon frame. The unit field of the requested delay time indicates the unit of the maximum delay time required on average by the frame requesting the low-latency operation. If the field is 0, it can indicate a unit of 256 μs, and if it is 1, it can indicate a unit of 32 μs.

[0216] The parameter fields for low latency operations utilizing TWT operations may include one or more of a request type field, a field indicating when low latency traffic is expected to occur, a requested latency field, a valid number field for the period of low latency based on the requested TWT operation, and a broadcast TWT information field.

[0217] The above request type field may include a field indicating whether it is a TWT request frame, a TWT setup indication field, a trigger field, an operation type field, an operation method field during the broadcast TWT time (or, broadcast TWT SP), an index field for the period of the requested low-latency time, a field indicating that the corresponding TWT operation is a TWT for a low-latency operation, etc. For example, the request type field may include a specific field indicating that the TWT operation by the corresponding frame is a restricted TWT operation. At this time, depending on the value of the specific field, frames that can be transmitted during the TWT SP according to the TWT operation may be restricted to specific frames for downlink frames, or the broadcast SP may be set to the restricted TWT SP. That is, if the value of a specific field (e.g., a broadcast TWT recommendation field) is '1', frames that can be transmitted during 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 to the restricted TWT SP.

[0218] At this time, the remaining fields, excluding the operation method field during the broadcast TWT time among the request form fields, the index field TWT field for the cycle of the requested low-latency time, and the field indicating that the corresponding TWT operation is a TWT for low-latency operation, may be set in the same format as the TWT information element included in the existing broadcast TWT request frame.

[0219] The operation mode field during the above broadcast TWT time is used when frame transmission is to be restricted during the corresponding TWT SP time. For example, when transmission is to be restricted only to the form of a response frame for a downlink frame during the corresponding TWT SP (e.g., an ACK or BlockAck frame for a downlink data frame, or an uplink frame transmitted in response to a trigger frame), the field can be set to 1.

[0220] Also, when requesting to limit ACs transmitted within the TWT SP period for the corresponding low-latency terminal, the corresponding field may be set to 4. When requesting an additional protection operation (e.g., a Quiet Time Setup frame, an RTS frame, or an MU-RTS frame) to protect the SP at the start point of the TWT SP for the corresponding low-latency terminal, the corresponding field may be set to 5. Alternatively, when requesting to enable communication between STAs during the corresponding TWT SP, the corresponding field may be set to 6. The exponent field for the requested low-latency period may indicate the SP period for the requested TWT-based low-latency operation together with the significant digit field for the low-latency period described above. For example, the SP period for the requested TWT-based low-latency operation may be expressed as "(significant digit field value for the low-latency period) ㅧ2^(exponent field value for the low-latency period)". Additionally, the field indicating that the corresponding TWT operation is a TWT for low-latency operation can be set to 1 to indicate that the corresponding TWT information element is for low-latency operation.

[0221] That is, a non-AP STA may transmit and receive only limited frames (e.g., frames requiring low delay or delay-sensitive frames) during a TWT SP when a TWT SP is scheduled and may not transmit or receive other frames, or may transmit and receive the limited frames with priority (e.g., the limited frames may have a high transmission priority).

[0222] Meanwhile, the field indicating the point in time when low-latency traffic is expected to occur can indicate the point in time when a frame requesting the low-latency time is expected to occur. The requested delay time field is the maximum delay time required by the frame, and can indicate the requested delay time in the uplink and downlink for the frame of the type together with the unit field for the requested delay time described above. The broadcast TWT information field can be set in the same way as the field setting method in the existing broadcast TWT operation. Alternatively, when the TWT operation request frame requests a TWT SP that is permitted only for a specific AC and an AC with a higher priority than it (for example, when the operation method field during the TWT time is set to 4), the broadcast TWT information field can include the AC or TID to be restricted instead of the broadcast TWT ID field.

[0223] That is, the broadcast TWT information field may include information related to the TID for which transmission of frames is restricted by the TWT for low-latency operation.

[0224] Specifically, the broadcast TWT information field may include a field containing information related to a TID. The field containing information related to a TID may include a control field, a DL bitmap (or, restricted TWT DL TID bitmap) field, and an UL bitmap (or, restricted TWT UL TID bitmap) field.

[0225] 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.

[0226] The DL bitmap validity field is a field that 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 of a TID corresponding to a value of '1' in the DL bitmap is delay-sensitive traffic, and downlink traffic of a TID corresponding to a value of '0' is delay-insensitive traffic.

[0227] The UL bitmap validity field is a field that indicates the validity of the UL bitmap field. 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 of a TID corresponding to the value of '1' in the UL bitmap is delay-sensitive traffic and uplink traffic of a TID corresponding to the value of '0' is delay-insensitive traffic. Meanwhile, information on a low-latency time period based on the TWT operation can be set to the generation period of a frame that requires a low delay time to be transmitted in the corresponding low-latency operation.

[0228] Meanwhile, if TS negotiation for traffic requiring low latency has been completed prior to the negotiation process for low latency operation utilizing 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 below.

[0229] FIG. 16 is a second embodiment illustrating the structure of a low-latency operation request frame requesting low-latency operation utilizing the TWT function according to an embodiment of the present invention. In FIG. 16, the same description as in FIG. 15 is omitted.

[0230] Referring to FIG. 16, a delay operation request frame requesting a low-latency operation utilizing the TWT function can be configured similarly to a TWT operation request frame for negotiating a broadcast TWT operation. Accordingly, the frame can include a TWT information element, and the TWT information element can include an element ID field, a length field, a control field, and a TWT parameter information field. At this time, the element ID field, the length field, and the control field can be set identically to those set in the request frame for negotiating a broadcast TWT.

[0231] The above TWT parameter information field may include a request type field, a TWT field, a minimum time for which the STA maintains an awake state during the TWT time, a significant number of intervals between TWT SPs, and broadcast TWT information. Among the request fields, the remaining fields except for the operation mode field during the TWT time and the field indicating that the corresponding TWT operation is a TWT for low-latency operation may be set in the same manner as the existing broadcast TWT setting method. The operation mode field during the TWT time and the field indicating that the corresponding TWT operation is a TWT for low-latency operation may be set as shown in FIG. 15. Alternatively, when the exchange of the corresponding TWT operation request frame is transmitted after the negotiation process for adding a TS, the allocation of a TWT SP limited to a specific Traffic Stream ID (TSID) may be requested. In this case, the operation mode field during the TWT time may be set to 7. An indication field indicating that the corresponding 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 above broadcast TWT information field may be set identically to the low-latency operation request frame using TWT described in FIG. 15. Alternatively, if the TWT operation request frame requests provision of a TWT SP limited to a specific TSID (e.g., if the operation method field during the TWT time is set to 7), the above broadcast TWT information field may include the lower 3 bits of the TSID to be restricted instead of the broadcast TWT ID field.

[0232] Meanwhile, the AP or AP MLD can check the contents of the request frame for the low-latency operation utilizing the TWT function as illustrated in FIG. 15 or FIG. 16. Based on information such as the required delay time and traffic generation cycle identified in the request frame, one of the broadcast TWTs for the low-latency operation allocated by the AP can be allocated. Alternatively, a new broadcast TWT can be created only for the traffic and a TWT SP for the low-latency operation can be allocated. When the broadcast TWT is allocated in the above manner for a low-latency operation request utilizing the TWT operation, a low-latency operation response frame can be transmitted in response to the low-latency operation request frame utilizing the TWT operation. Alternatively, when the low-latency operation request cannot be accepted, a low-latency operation response frame rejecting the request can be transmitted. At this time, the low-latency operation response frame can be configured as follows.

[0233] Fig. 17 is a block diagram illustrating a low-latency operation response frame, which is a response to a request frame requesting low-latency operation utilizing the TWT function. At this time, a description of a part having the same configuration as the request frame requesting low-latency operation utilizing the TWT function in Figs. 15 and 16 may be omitted.

[0234] Referring to FIG. 17, the low-latency operation response frame utilizing the 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, the length field, and the control field may be set identically to those set in the response frame for negotiation of broadcast TWT.

[0235] The above TWT parameter information field may include a request type field, a TWT field, a minimum time for which the STA maintains an awake state during the TWT time, a significant number of intervals between TWT SPs, and broadcast TWT information. Among the request type fields, the remaining fields except for the operation method field during the TWT time and the field indicating that the corresponding TWT operation is a TWT for low-latency operation may be set in the same manner as the existing broadcast TWT setting method. The field indicating that the corresponding TWT operation is a TWT for low-latency operation may be set in the same manner as in FIGS. 15 and 16. The operation method field during the broadcast TWT time is used when it is desired to limit frame transmission during the corresponding TWT SP time, as shown in FIGS. 15 and 16. For example, when it is desired to limit transmission only to the form of a response frame for a downlink frame during the negotiated TWT SP presented in the corresponding response frame (e.g., an ACK or BlockAck frame for a downlink data frame, or an uplink frame transmitted in response to a trigger frame), the field may be set to 1. Also, when setting to limit the AC transmitted within the TWT SP period for the low-latency terminal, the field can be set to 4. When wanting to perform an additional protection operation (e.g., Quiet Time Setup frame, RTS frame, MU-RTS frame, etc.) to protect the SP at the start point of the TWT SP for the low-latency terminal, the field can be set to 5. Or, when allowing communication between STAs during the TWT SP, the field can be set to 6. Or, when the negotiation for the TWT operation is transmitted after the negotiation process for adding a TS, the allocation of a TWT SP limited to a specific Traffic Stream ID (TSID) can be requested. In this case, the operation method field during the TWT time can be set to 7.The request field may be further provided with an indication field indicating that the corresponding TWT request frame is a TWT request frame for low-latency operation, as described with reference to FIGS. 15 and 16. The broadcast TWT information field may be set to be the same as a response frame for existing broadcast TWT negotiation. Alternatively, if it is desired to restrict only frames having a priority higher than a specific AC to be transmitted during the TWT SP period for the corresponding low-latency operation (for example, if the operation mode field during the TWT period is set to 4), the AC to be restricted may be additionally included in the broadcast TWT information field of the response frame. Alternatively, if it is desired to restrict a specific TSID of a frame that can be transmitted to the corresponding TWT SP (for example, if the operation mode field during the TWT period is set to 7), the TSID to be restricted may be additionally included in the broadcast TWT information field of the response frame.

[0236] The negotiation process and operation process of low-latency operation utilizing TWT operation through the above low-latency operation request frame and low-latency operation response frame can be performed as follows.

[0237] FIG. 18 is a first embodiment illustrating a process in which an AP or AP MLD and an STA perform low-latency operation utilizing a TWT function according to an embodiment of the present invention.

[0238] Referring to FIG. 18, the process of performing a low-latency operation for the TWT operation may include a step of confirming the function of the low-latency operation in the STA and the AP, a step of negotiating a low-latency operation utilizing the TWT operation by transmitting a low-latency operation request frame in the STA and a low-latency operation response frame in the AP, and a step of performing the low-latency operation by allocating a TWT SP for the low-latency operation to a broadcast probe response frame and a beacon frame in the AP. At this time, a step of negotiating to add a TS to the STA and the AP may be additionally included before the step of negotiating the low-latency operation utilizing the TWT operation. In addition, a negotiation step for exchanging the timing of a beacon frame to which the negotiated TWT SP is allocated in the STA may be additionally included after the step of negotiating the low-latency operation utilizing the TWT operation.

[0239] The step of confirming the function of the above low-latency operation can be performed during the scanning and connection process between the AP or AP MLD and the STA or STA MLD. The scanning and connection process can be performed through the processes of FIGS. 5 and 11 to 13. At this time, the AP and STA can transmit an indicator indicating whether or not the low-latency operation using the TWT function is supported in the capability element. In addition, the AP or AP MLD can transmit statistical information related to the transmission time of the frame transmitted on the corresponding link for all links operated by the beacon frame and the probe response frame. The statistical information can be a Measurement Report information element. Alternatively, the statistical information can be a Measurement Report information element illustrated in FIG. 14. The STA or STA MLD can confirm 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.

[0240] After the scanning and connection process, the process of negotiating to perform a low-latency operation utilizing TWT operation can be initiated by the STA transmitting a low-latency operation request frame utilizing TWT operation to the AP. At this time, the low-latency operation request frame utilizing TWT operation can be configured as shown in FIGS. 15 and 16. The request frame can be an action frame. The AP supporting low-latency operation can receive the low-latency operation request frame utilizing TWT operation from the STA, and can confirm that the STA requests TWT SP allocation for a frame requiring a low latency time based on the received content. If the AP can allocate a TWT SP corresponding to the request frame, the AP can transmit a low-latency operation response frame utilizing TWT in response to the request frame. At this time, the TWT operation response frame can be configured as shown in FIG. 17.

[0241] Alternatively, if the STA and the AP have performed a negotiation process to add a TS, the AP may transmit a low-latency operation response frame using an unsolicited TWT operation to support the TS. In this case, the STA may transmit a frame requesting low latency to the corresponding TWT SP without transmitting a separate request frame after performing the negotiation to add the TS. At this time, if the STA does not want to perform the low-latency operation according to the parameters included in the unsolicited low-latency operation response frame, the STA may release the low-latency operation through a TWT release frame and transmit a low-latency operation request frame utilizing a new TWT operation to request the AP to perform a low-latency operation based on the TWT operation.

[0242] When the low-latency operation negotiation process utilizing the above TWT operation is completed, the AP can assign a broadcast TWT ID for the TWT SP to be assigned to the corresponding STA. The broadcast TWT ID can be received through the low-latency operation response frame described in FIG. 17. At this time, multiple STAs can be assigned the same TWT ID. The low-latency operation method utilizing the TWT operation can be performed similarly to the operation method of the broadcast TWT. That is, a TWT element including a broadcast TWT SP can be transmitted for all broadcast TWT IDs set in the corresponding AP in the beacon frame and the broadcast probe response frame. At this time, some broadcast TWT IDs can be TWT SPs for low-latency operation. The STA for which the low-latency operation negotiation through the TWT operation is completed can check the assigned broadcast TWT ID through the low-latency operation response frame, and can check the TWT parameter including the assigned broadcast TWT ID among the TWT elements included in the beacon frame. A frame requesting a low-latency time can be transmitted and received at the time indicated by the corresponding TWT parameter. On the other hand, an STA that has not been assigned the corresponding broadcast TWT ID may not perform frame transmission operations during the corresponding TWT SP when it is confirmed that the TWT SP indicated in the TWT element is a TWT SP for low-latency operation.

[0243] At this time, the TWT element can be transmitted by being included in a management frame such as a control frame or a beacon frame and a probe response frame.

[0244] At this time, in order to additionally protect the transmission of the frame for the low-latency operation, the AP may additionally transmit an information element for protecting the corresponding time in the beacon frame. For example, when transmitting a TWT SP for low-latency operation in the beacon frame, one or more Quiet information elements set to the same time may be additionally transmitted for some or all of the TWT SPs for low-latency operation among the plurality of TWT SPs. Among the STAs that have received the Quiet information element, an STA that has not been allocated a TWT SP at the same time may not perform frame transmission by setting a NAV during the time included in the Quiet information element. At this time, if the TWT SP time indicated by the TWT parameter including the allocated broadcast TWT ID matches the time of the received Quiet information element, the STA may ignore the Quiet information element and perform a frame transmission operation during the corresponding time. Through this process, an STA that has been allocated a TWT SP for low-latency operation can transmit a frame requiring a low latency time without interference from other terminals during the corresponding time.

[0245] That is, the beacon frame may further include a quiet information element to protect the TWT SP. At least one non-AP STA for which the TWT operation is not configured may set a NAV based on the quiet information element. In other words, at least one non-AP STA may not transmit a frame by setting a NAV during a time period indicated by the quiet information element. For example, at least one STA for which the TWT operation is not configured may set a NAV to a value equal to the time period indicated by the quiet information element (or quiet element). Alternatively, a legacy STA (e.g., a VHT non-AP STA, etc.) may set a NAV to a value equal to the time period indicated by the quiet information element (or quiet element).

[0246] At this time, the quiet information element may be transmitted in a beacon frame as well as a control frame and / or a management frame (e.g., a probe response frame).

[0247] Non-AP STAs may ignore some or all of the overlapping intervals set by the quiet information element when the TWT SP and the quiet information element are set together and the interval set by the quiet information element overlaps with some or all of the TWT SP for delay operation. That is, the non-AP STAs may operate as if the quiet interval, which is the interval set by the quiet information element that overlaps with the limited TWT SP for low delay, does not exist.

[0248] 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, when 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.

[0249] Meanwhile, after the negotiation process for low-latency operation utilizing the above TWT function, an additional process may be performed to negotiate the transmission time of a beacon frame including the broadcast TWT ID agreed upon between the STA and the AP. This process may be performed through the exchange of a broadcast TWT request frame and a broadcast TWT response frame. At this time, the TWT field may be set to the time at which the corresponding beacon frame is transmitted. At this time, the fields indicating the TWT SP interval may be set to the interval of the beacon frame including the corresponding broadcast TWT ID.

[0250] Meanwhile, the negotiation process for low-latency operation utilizing the TWT function can be performed during the connection process between the STA and the AP. Therefore, an STA seeking low-latency operation can avoid a separate negotiation process after connecting to the AP. In this case, the negotiation and operation process utilizing TWT operation can be performed as follows.

[0251] FIG. 19 is a second embodiment illustrating a process in which an AP or AP MLD and an STA perform low-latency operations utilizing the TWT function according to an embodiment of the present invention. In this case, any description overlapping with FIG. 18 may be omitted.

[0252] Referring to FIG. 19, the process of performing a low-latency operation for the TWT operation may be composed of a step of confirming the function of the low-latency operation in the STA and the AP, a step of negotiating a low-latency operation utilizing the TWT operation by transmitting a low-latency operation request frame in the STA and a low-latency operation response frame in the AP, and a step of performing the low-latency operation by allocating a TWT SP for the low-latency operation to a broadcast probe response frame and a beacon frame in the AP. At this time, a step of negotiating to add a TS to the STA and the AP may be additionally included before the step of negotiating the low-latency operation utilizing the TWT operation. In addition, a negotiation step for exchanging the timing of a beacon frame to which the negotiated TWT SP is allocated in the STA may be additionally included after the step of negotiating the low-latency operation utilizing the TWT operation.

[0253] The step of confirming the function of the above low-latency operation can be performed during the scanning and connection process between the AP or AP MLD and the STA or STA MLD. The scanning and connection process can be performed through the processes of FIGS. 5 and 11 to 13. At this time, the AP can transmit a beacon frame, a broadcast probe response frame, and an indicator indicating whether or not the low-latency operation using the TWT function is supported in a capability element in the probe response frame. The STA can receive the beacon frame, the broadcast probe response frame, and the probe response frame to confirm that the AP supports the low-latency operation using the TWT operation. In addition, the AP or AP MLD can transmit, including statistical information related to the transmission time of the frame transmitted on all links operated in the beacon frame and the probe response frame. The statistical information can be a Measurement Report information element. Alternatively, the statistical information may be a Measurement Report information element as illustrated in FIG. 14. Meanwhile, the STA may transmit an indicator indicating whether or not low-latency operation utilizing the TWT function is supported in the capability element of the probe request frame and the connection request frame. The AP may confirm that the STA performs the low-latency operation function utilizing the TWT operation through the probe request frame and the connection request frame received from the STA.

[0254] An STA that confirms that the AP supports the function through the beacon frame, broadcast probe response frame, and probe response frame received from the AP may include a low-latency operation request indicator utilizing the TWT function requesting the use of the function in an access request frame when a frame requiring low latency occurs. At this time, the low-latency operation request indicator utilizing the TWT function may be a TWT information element described in FIGS. 16 and 17. The AP may receive an access request frame from the STA and confirm the low-latency operation request indicator utilizing the TWT function included in the frame. The AP may confirm that the STA requests TWT SP allocation for the frame requiring low latency based on the contents of the confirmed request indicator. If the AP can allocate a TWT SP corresponding to the request frame, the AP may transmit an access response frame including a low-latency operation response indicator utilizing TWT as a response to the request frame. At this time, the low-latency response indicator utilizing the TWT operation may be a TWT information element described in FIG. 17.

[0255] Alternatively, if it is confirmed that the STA supports low-latency operation utilizing the TWT function through the probe request frame and connection request frame transmitted by the STA, the AP may transmit a low-latency operation response indicator using the TWT operation that was not requested 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. At this time, if the STA does not want to perform the low-latency operation according to the parameter included in the low-latency operation response frame that was not requested by the STA, the low-latency operation may be released through a TWT release frame, and a low-latency operation request frame utilizing a new TWT operation may be transmitted to request the low-latency operation to the AP.

[0256] When the low-latency operation negotiation process utilizing the above TWT operation is completed, the AP can allocate a broadcast TWT ID for the TWT SP to be assigned to the corresponding STA. The STA can receive the broadcast TWT ID through the low-latency operation response frame described in FIG. 17. At this time, multiple STAs can be allocated the same TWT ID. Thereafter, the low-latency operation method utilizing the TWT operation can proceed as shown in FIG. 18. That is, the TWT SP for the low-latency operation can be included in the beacon frame, and the negotiated low-latency operation can be performed in the TWT SP. In addition, in order to additionally protect the transmission of the frame for the low-latency operation, the AP can additionally transmit an information element for protecting the corresponding time in the beacon frame. After the negotiation process for the low-latency operation utilizing the TWT function, a process for negotiating the transmission time of the beacon frame including the broadcast TWT ID agreed upon between the STA and the AP can be additionally performed.

[0257] Meanwhile, if a terminal that cannot perform STR operation is connected to the link while performing a low-latency operation utilizing the above TWT operation, the following problem may occur.

[0258] Figure 20 illustrates an operation in which an AP MLD and an STA MLD performing low-latency operation cannot perform STR operation, and thus a TWT information element is missed due to failure to receive a beacon frame, and thus the TWT time for low-latency operation is not protected.

[0259] Referring to FIG. 20, an AP MLD may include two or more APs. In this case, each AP may operate a separate link. For example, the AP MLD may include AP 1 and AP 2, and AP 1 may operate on link 1 and AP 2 on link 2. Meanwhile, the STA MLD may include STA 1 and STA 2. The STA MLD may 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 STA 1 of the STA MLD performs a frame transmission operation on link 1, STA 2 may not be able to perform a channel sensing operation and a frame reception operation on link 2 due to the influence of interference caused by the transmission. Alternatively, while STA 2 of the above STA MLD is performing a frame transmission operation on link 2, STA 1 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.

[0260] The characteristic that STR operation is impossible in the STA MLD may interfere with the low-latency transmission operation using the TWT operation. For example, when performing a low-latency transmission operation using a TWT terminal in link 1, the corresponding TWT SP may be indicated in a beacon frame. At this time, when performing a frame transmission operation using link 2 in the STA MLD, the beacon frame transmitted in link 1 may not be received, and the TWT SP for the low-latency operation included in the beacon frame may not be recognized. STA 1 of the STA MLD that does not recognize the TWT SP for the low-latency terminal may perform a channel access operation for frame transmission in the TWT SP, and may not be able to protect the transmission of a frame requiring a low latency time in the TWT SP.

[0261] To solve the above problem, AP MLD can perform the update operation of TWT-related parameters for low-latency operation at the same time as follows.

[0262] Figure 21 illustrates an operation in which AP MLD performs a low-latency operation by utilizing TWT operation and changes parameters at the same time.

[0263] Referring to FIG. 21, the parameter change timing for all TWT SPs for low-latency terminals allocated in the AP MLD can be set to be the same. For example, parameters related to the TWT SP for low-latency terminals can be allowed to be changed only in a beacon frame containing a Delivery Traffic Indication Map (DTIM). That is, the broadcast TWT maintenance fields of all TWT parameter information fields for low-latency terminals included in the TWT information element for allocating the TWT SP for low-latency terminals transmitted in the beacon frame can be set to the same value. TWT SPs for low-latency terminals can be generated periodically after the same time from the TBTT timing, except for the beacon frame (e.g., the DTIM beacon frame) transmitted at the specific timing. Meanwhile, an STA MLD that is not capable of STR operation may not perform a frame transmission operation through another link when a beacon frame (e.g., a DTIM beacon frame) transmitted at the specific timing is transmitted. Through this process, even if a STA MLD that is not capable of STR operation does not receive a specific beacon frame, it can determine a TWT SP for a low-latency terminal based on the contents of a TWT information element included in a previously transmitted beacon frame.

[0264] That is, when a non-AP STA configures a multi-link device (MLD), the MLD cannot transmit frames through other links while receiving the beacon frame. In other words, when an STA included in a non-AP MLD successfully acquires a TXOP on one link of the NSTR link pair before the TBTT of the other link of the NSTR link pair, the STA must terminate the TXOP before the TBTT of the other link if it wants to receive a beacon frame on the other link.

[0265] Alternatively, to address the above issue, an additional protection frame may be transmitted at the start of the TWT SP to protect the TWT SP. The transmission operation of the protection frame may be performed as follows.

[0266] FIG. 22 is an embodiment illustrating an operation in which AP MLD additionally transmits a guard frame protecting the period at the start of the TWT time to protect the TWT time for low-latency operation.

[0267] Referring to FIG. 22, in order to prevent a terminal that is not assigned to a TWT SP for the low-latency terminal from transmitting frames at the corresponding time, an AP may transmit a reservation frame at the starting point of the corresponding TWT SP. The reservation frame may be an unscheduled Quiet Time setting frame. The Duration field value of the corresponding Quiet Time setting frame is designated as the corresponding TWT SP time, thereby preventing STAs that have not negotiated during the TWT SP for the low-latency terminal from performing a channel contention process. On the other hand, STAs that have negotiated with the AP to transmit frames during the corresponding TWT SP may transmit frames that require a low latency time during the corresponding period.

[0268] Alternatively, a channel reservation process between the AP and the corresponding STAs may be first performed in the TWT SP. For example, an operation may be performed in which the AP transmits an MU-RTS frame at the starting point of the TWT SP, and the assigned STAs transmit a CTS frame. At this time, the MU-RTS frame may include AIDs of the STAs assigned to the corresponding TWT SP. At this time, the NAV value set in the MU-RTS may be designated until the end time of the corresponding TWT SP. The STAs assigned to the TWT SP may receive the MU-RTS frame and confirm that they intend to perform a channel reservation process in the corresponding MU-RTS frame. Accordingly, the plurality of STAs may simultaneously transmit a CTS frame in response to the MU-RTS frame. At this time, the end time of the NAV set in the transmitted CTS frame may be set to the end time of the corresponding TWT SP. After the exchange procedure of the corresponding MU-RTS and CTS frames, STAs assigned to the TWT SP can perform frame transmission through a channel contention process. On the other hand, STAs not assigned to the TWT SP may not perform frame transmission operations during the TWT SP due to the NAV being set.

[0269] Meanwhile, when an STA MLD that is not capable of STR operation performs a low-latency operation utilizing the TWT function, if frame transmission is performed on another link during the TWT SP time for the low-latency operation, a frame requiring low latency may not be transmitted during the TWT SP time. That is, if a frame transmission operation is performed on another link that is not capable of STR operation during the TWT SP time, the transmission operation of a frame requiring low latency may not be performed due to the influence of interference caused by the transmission. To solve this, when an STA MLD that performs a low-latency operation utilizing TWT is not capable of STR operation, frame transmission on another link may be restricted as follows.

[0270] Figure 23 illustrates an embodiment of a process in which an STA incapable of AP MLD and STR operations performs low-latency operations utilizing the TWT function. In this case, any content overlapping with the descriptions of Figures 18 to 19 and Figure 22 may be omitted.

[0271] Referring to FIG. 23, even an STA MLD that is not capable of STR operation can perform low-latency operation utilizing the TWT function with the AP MLD using some links. For example, the STA MLD can perform multi-link operation with the AP MLD using Link 1 and Link 2. At this time, the STA MLD may not be able to perform STR operation on Link 1 and Link 2. That is, while STA 1 of the STA MLD performs a frame transmission operation on Link 1, STA 2 may not be able to perform a channel sensing operation and a frame receiving operation on Link 2 due to the influence of interference caused by the transmission. Alternatively, while STA 2 of the STA MLD performs a frame transmission operation on Link 2, STA 1 may not be able to perform a channel sensing operation and a frame receiving operation on Link 1 due to the influence of interference caused by the transmission. At this time, a TWT operation for low-latency operation on Link 1 of the AP MLD can be negotiated with the STA MLD. The above connection process and negotiation process for MLD operation can be performed in the manner of FIGS. 11 to 13. At this time, if the STA MLD wants to perform a low-latency operation utilizing TWT operation for some links, a negotiation process for performing a low-latency operation utilizing TWT operation with the AP MLD can be performed in the manner of FIGS. 18 to 19. For example, STA 1 belonging to STA MLD can negotiate with AP 1 of AP MLD to perform a low-latency operation utilizing TWT operation on link 1.

[0272] According to the above negotiated content, AP 1 belonging to AP MLD can assign a broadcast TWT ID to STA 1 and transmit a beacon frame including a TWT parameter indicated by the corresponding broadcast TWT ID. The TWT parameter may include a start time of the TWT SP. STA 1 of the STA MLD incapable of STR operation can receive the corresponding beacon frame and check 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, the TWT SP for low-latency operation corresponding to the assigned broadcast TWT ID can be inferred from the TBTT of the corresponding beacon frame based on the TWT SP included in the previously transmitted beacon frame.

[0273] STA 1 of STA MLD, which has recognized the TWT SP for the low-delay operation, may perform a frame transmission operation requiring a low delay time after the start time of the corresponding TWT SP. At this time, in order to prevent the transmission of the frame requiring the low delay time from being delayed, STA 1 operating on link 1 and STA 2, which is incapable of STR operation, may terminate the transmission operation of the frame being transmitted before the start time of the corresponding TWT SP. STA 2 may not perform frame transmission during the TWT SP time for the low-delay operation recognized by the corresponding STA MLD.

[0274] FIG. 24 is a conceptual diagram of an AP MLD and STA MLD structure performing multi-link operation according to an embodiment of the present invention.

[0275] 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 via a single interface. That is, the AP MLD may be connected to a Logical Link Control (LLC) layer via a single interface. Multiple APs included in the AP MLD may share some functions in the MAC layer. Each AP within 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 via a single interface. That is, a STA MLD may be connected to the LLC layer via a single interface. Multiple STAs included in the STA MLD may share some functions in the MAC layer. In addition, a STA MLD may be referred to as a non-AP MLD. In this case, the AP MLD and the STA MLD may perform a multi-link operation in which they communicate using a plurality of individual links. That is, when the AP MLD includes multiple APs, each AP can configure a separate link and perform frame transmission and reception operations using multiple links with each terminal included in the STA MLD. At this time, each link can operate in the 2.4 GHz, 5 GHz, or 6 GHz band, and each link can perform a bandwidth expansion operation. For example, when the AP MLD configures one link in the 2.4 GHz band and two links in the 5 GHz band, frame transmission can be performed with a bandwidth of 40 MHz through the bandwidth expansion method in the 2.4 GHz band, and frame transmission can be performed with a bandwidth of up to 320 MHz by utilizing a non-contiguous bandwidth in each link using the 5 GHz band.

[0276] Meanwhile, due to interference issues within the device for some or all of the APs or terminals belonging to the AP MLD or STA MLD, while one AP or terminal is performing a transmission operation, other APs or terminals in the same device may not be able to perform a reception operation. In this way, the operation in which another AP or terminal in the MLD receives while one AP or terminal is performing a transmission operation within the MLD is called STR (Simultaneous Transmit and Receive). The AP MLD may enable the STR operation for all links. Alternatively, the STR operation may not be possible for some links of the AP MLD. If the STR operation is impossible for some links, while one AP among the APs operating in the plurality of links is performing a transmission operation, other APs may not be able to perform a reception operation. An STA MLD capable of the STR operation may be connected to the AP MLD, and an STA MLD capable of the STR operation may be connected to some or all of the links. If a STA MLD is connected that does not support STR operation for some or all of the above links, reception operation may not be possible on other links while a terminal using the link is transmitting for the link for which STR operation is not possible in the STA MLD. In addition, terminals that do not belong to the MLD (e.g., IEEE 802.11a / b / g / n / ac / ax terminals) may be additionally connected to the AP included in the AP MLD.

[0277] FIG. 25 is a timing diagram illustrating a connection process and a negotiation process for multi-link operation between an AP MLD and a STA MLD according to an embodiment of the present invention.

[0278] Referring to FIG. 25, the AP MLD and the STA MLD may perform a negotiation process for multi-link usage 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 multi-link operation is available, information about the number of available links, information about multiple available links, and information about the AP operating the corresponding links. At this time, only a portion of the information about APs belonging to the AP MLD that do not transmit the corresponding beacon frame may be transmitted. At this time, the information about the APs that do not transmit the corresponding beacon frame may be transmitted in the form of a Reduced Neighbor Report (RNR) information element. At this time, 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 indicates an update status for parameters used by the corresponding AP, among the information about the AP included in the information element.

[0279] 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. In addition, some information about other APs belonging to the AP MLD (e.g., link ID, channel usage information, parameter update counter in the AP, etc.) can be confirmed. 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 illustrated in FIG. 5, and an AP belonging to the AP MLD can include an indicator indicating that multi-link operation is available in a probe response frame. In this case, the AP can additionally transmit the probe response frame including the number of links available for multi-link operation, link information, and information about the AP operating the link.

[0280] The above AP is an AP belonging to an AP MLD, and the STA MLD, which has confirmed some information about other APs belonging to the AP MLD, may transmit a multi-link probe request frame to the AP, requesting all information about other APs from the AP MLD, in order to perform a multi-link operation. The multi-link probe request frame may indicate necessary information about the AP that the STA MLD wishes to receive from the AP MLD. At this time, the necessary information may include one or more of an HT capability element, an HT operation element, a VHT capability element, a VHT operation element, a HE capability element, a HE operation element, an EHT capability element, an EHT operation element, a time point at which a beacon is transmitted (Target Beacon Transmission Time, TBTT), EDCA parameter setting information, information about the channel on which the AP operates, and information about the bandwidth supported by the AP. The STA MLD may request information about one or more specific APs in the multi-link probe request frame. Alternatively, the STA MLD may request information about all APs operated by the corresponding AP MLD.

[0281] The AP MLD may receive a multi-link probe request frame from the STA MLD, and may confirm that the STA MLD requests some or all of the information elements related to the operation of some or all of the APs belonging to the AP MLD. The AP MLD, which confirms the request information, may transmit to the STA MLD in the form of a multi-link probe response frame including the information requested by the STA MLD. At this time, information overlapping with information used by the AP transmitting the multi-link probe response frame may be omitted and transmitted. Meanwhile, since the multi-link probe response frame includes more information than the probe response frame in FIG. 5, the channel may be occupied for a longer period of time when the multi-link probe response frame is transmitted. Therefore, in order to prevent excessive channel occupation due to transmission of too many 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 may transmit a multi-link probe response frame containing information on all APs belonging to the AP MLD in the form of a broadcast frame. The multi-link probe response frame transmitted in the form of the broadcast frame may be transmitted over a specific period. At this time, if the multi-link probe response frame has been transmitted in the form of a broadcast frame within a specific time period before receiving the multi-link probe request frame from the STA MLD, the transmission of the multi-link probe response frame may not be performed. At this time, the specific time period may be after the time at which the STA belonging to the STA MLD transmits the probe request frame of FIG. 5.

[0282] The STA MLD, which 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 the connection process and negotiation process for multi-link operation with the AP MLD. At this time, the negotiation process for the multi-link operation can be performed during the connection process between the AP belonging to the AP MLD and the terminal belonging to the STA MLD. That is, any terminal belonging to the STA MLD (e.g., STA1) can send an connection request frame to any AP belonging to the AP MLD (e.g., AP1) while sending an indicator indicating that the terminal's multi-link operation is available and a request indicator requesting to perform the multi-link operation. At this time, the STA MLD can transmit the connection request frame including link information to be used in the AP MLD and capability information of the terminal related to the link (e.g., information indicating whether STR with other links is possible, the maximum transmittable bandwidth, or the maximum number of spatial streams that can be used, etc.). The AP, which has received the connection request frame from the terminal, can check the indicator requesting the multi-link operation, and if the AP is capable of the multi-link operation, can transmit to the terminal an connection response frame allowing the multi-link operation, including link information to be used for the multi-link operation and parameters used in each link. The parameters for the multi-link operation may include one or more of the link ID, MAC address, band, bandwidth extension direction, TBTT (Target Beacon Transmission Time), and STR operation of each link used. The AP MLD and STA MLD, in which the use of the multi-link operation is confirmed by exchanging the connection request frame and response frame, can perform a frame transmission operation using multiple links using multiple APs included in the AP MLD and multiple terminals included in the STA MLD after the connection process.

[0283] FIG. 26 is a timing diagram illustrating a transmission method using multiple links according to an embodiment of the present invention.

[0284] Referring to FIG. 28, the AP MLD and STA MLD, for which negotiation for the multi-link operation has been completed, can perform frame transmission and reception operations utilizing multiple links through a link-specific independent transmission method. When the multi-link operation is performed through the link-specific independent transmission method, each AP or terminal belonging to the AP MLD or STA MLD independently performs a channel competition process for frame transmission on each link and performs frame transmission on each link. At this time, the transmission start time and transmission end time of the frames transmitted on each link may not be the same. When the independent transmission method is performed, the TXOP (Transmission Opportunity) acquired through the channel competition process on each link can be independently obtained on each link.

[0285] When performing the above independent transmission method, there is an advantage in that each link can be operated more efficiently since channel access is performed independently for each link depending on the channel occupancy status. In this case, if the gap between the operating bands of each AP operating in the AP MLD is not wide enough to make STR operation impossible in the AP MLD or STA MLD, multi-link operation may not be performed using the above independent transmission method.

[0286] Meanwhile, if the receiving MLD is unable to perform STR operation on some or all links, the frame transmission and reception process using the link where the STR operation is impossible can be performed as follows.

[0287] FIG. 27 is an embodiment illustrating a frame transmission and reception operation between a receiving MLD that is incapable of STR operation and a transmitting MLD that is capable of STR operation in some or all links according to an embodiment of the present invention.

[0288] Referring to (a) of FIG. 27, when the STR operation is impossible in the MLD, the frame reception operation may not be performed in another link while frame transmission is being performed in one link. For example, AP1 and AP2 may belong to the AP MLD, and AP1 may operate link 1 and AP2 may operate link 2. STA1 and STA2 may belong to the STA MLD, and STA1 may be connected to AP1 and STA2 may be connected to AP2 through a negotiation process for multi-link operation. At this time, the STA MLD may not be able to perform the STR operation in links 1 and 2. That is, while STA1 is performing the frame transmission operation in link 1, STA2 may not be able to perform the frame reception operation in link 2. Conversely, while STA2 is performing the frame transmission operation in link 2, STA1 may not be able to perform the frame reception operation in link 1. The situation in which the STR operation is impossible may be due to interference within the device that occurs during the frame transmission operation in one link. Accordingly, if STA MLD is unable to perform STR operation on some links, channel sensing operation may not be performed on other links while performing frame transmission operation on one of the links. For example, while transmitting a frame to STA1 on link 1, STA2 on link 2 may not be able to perform channel sensing operation for frame transmission. Therefore, while STA1 is performing frame transmission on link 1, STA2 on link 2 may not be able to start frame transmission operation after channel contention process. That is, if STR operation is impossible on even one of the transmission MLD and the reception MLD on the link, multi-link communication operation through the independent transmission method in FIG. 11 may not be possible.

[0289] If the AP MLD or STA MLD in the above multiple links cannot perform STR operation (for example, if the bandwidth gap between links is not sufficient to perform multi-link operation), the AP MLD and STA MLD may perform multi-link operation in the form of simultaneous transmission operation as shown in (b) of FIG. 12. The simultaneous transmission operation may be performed through a process of aligning the transmission start time or transmission end time of the frames transmitted in each link to the same time. At this time, the transmission start time or transmission end time of the frame may be referred to as the transmission start time and transmission end time of the PPDU including the frame. That is, if the length of the frame transmitted by the AP or terminal to each link is different, padding or padding bits may be added and transmitted to align the corresponding transmission end times. In addition, the TXOP time for frame transmission in each link may be aligned to the same time. At this time, the multi-link operation in the form of simultaneous transmission may include a negotiation step for simultaneous transmission in multiple links and a step for performing simultaneous transmission using multiple links. The negotiation step for the above simultaneous transmission may include a step of simultaneously sending a request frame for obtaining a TXOP for simultaneous transmission to one or more links at the same time in an MLD having data to be transmitted (e.g., an AP MLD or a STA MLD), and a step of transmitting a response frame after a SIFS (Short Interframe Space) from a time when the MLD receiving the data has completed receiving the request frame. At this time, the response frame may be simultaneously transmitted on 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 the channel of one link is occupied during channel competition for performing simultaneous transmission operations, a channel access process for performing simultaneous transmission operations can be performed, or a frame transmission operation using only links with empty channels can be performed.

[0290] The channel access process for the above simultaneous transmission operation can be performed in various ways. For example, a backoff process can be performed on multiple links performing simultaneous transmission, carrier sensing can be performed on all links until the backoff value becomes 0 on all links, and if the carrier sensing results indicate that the channels of all links are empty, simultaneous transmission can be performed using multiple links. Alternatively, after performing a backoff operation on one link, if the channel of another link is empty for a specific period of time (e.g., AIFS, DIFS, or PIFS) before the backoff termination time, simultaneous transmission using multiple links can be performed by utilizing the link with the empty channel.

[0291] Meanwhile, if the transmitting MLD is unable to perform STR operation on the link, and the channel state of one or some links is busy while performing the channel access process for frame transmission in (b) of Fig. 10, one of the following methods may be used:

[0292] 1) After the occupancy period ends, perform carrier sensing on the channels of both links for a specific period of time (e.g., PIFS, AIFS, or AIFS+backoff time) to confirm that the channels of both links are empty, and then perform simultaneous transmission using the method of Fig. 12(b).

[0293] 2) Perform transmission operations only on links where the channel is empty.

[0294] When the operation of 2) above is performed, a backoff operation for frame transmission may not be performed until the end of transmission in the link performing transmission even after the occupancy time of the link in which the channel status was occupied has ended.

[0295] Meanwhile, if the transmitting MLD is capable of STR operation on the link and the receiving MLD is unable to perform STR operation on the link, and the channel state of one or some links is busy while performing the channel access process for frame transmission in (b) of Fig. 12, one of the following methods may be used:

[0296] 1) After the occupancy period ends, perform carrier sensing on the channels of both links for a specific period of time (e.g., PIFS, AIFS, or AIFS+backoff time) to confirm that the channels of both links are empty, and then perform simultaneous transmission using the method of Fig. 12(b).

[0297] 2) Perform transmission operations only on links where the channel is empty.

[0298] When the operation of 2) above is performed, frame transmission can be performed by independently performing a channel access process on the link after the occupancy time of the link in which the channel status was occupied has expired.

[0299] Meanwhile, if the transmitting MLD is capable of the STR operation and the receiving MLD is incapable of the STR operation on the corresponding link, the transmission start time and the transmission end time of frames transmitted from the transmitting MLD through multiple links may not be the same. That is, as shown in (c) of FIG. 12, after starting frame transmission on one link, the frame transmission operation can be independently performed after completing the channel contention process for frame transmission on the other link. For example, the AP MLD may be capable of the STR operation on links 1 and 2, and the STA MLD may be incapable of the STR operation on links 1 and 2. In this case, if the channel state of link 2 is busy during the channel access process for frame transmission in FIG. 12 (b), AP1 of the AP MLD can preferentially perform the frame transmission operation on link 1. Since the AP MLD is capable of the STR operation, AP2 on link 2 can perform the channel contention process for frame transmission even while AP1 is transmitting a frame on link 1. After completing the above channel contention process and channel access operation, AP2 can perform a frame transmission operation using link 2. Since STA MLD is not performing frame transmission on link 1, STA2 can receive the frame transmitted by AP2 on link 2. Meanwhile, if one or more of the frames transmitted by the transmitting MLD require an immediate response (e.g., a BlockAck frame, etc.) from the receiving MLD, transmission of the corresponding response frame may be performed while performing a reception operation on another link. In this case, the frame reception operation on the other link may not be performed smoothly due to the transmission of the response frame. To prevent this situation, if one or more of the frames transmitted by the transmitting MLD require transmission of a response frame, the transmission end times of the PPDUs including the frames transmitted on the multiple links may be identical.

[0300] Meanwhile, when performing frame transmission and reception operations between an AP and an STA, a channel reservation process may be performed to protect the frame transmission and reception operation. The channel reservation process may be performed through a process in which a transmitting STA that wishes to transmit a frame transmits an RTS (Request to Send) frame to a receiving STA, and the receiving STA transmits a CTS (Clear to Send). At this time, the receiving STA may perform a channel sensing operation for a SIFS time after receiving the RTS frame, and transmit a CTS only when the channel is idle.

[0301] Meanwhile, if an AP wishes to reserve a channel for multi-user transmission with multiple STAs, it may perform an exchange process of MU (Multi-user)-RTS frames and CTS frames. The exchange process of MU-RTS frames and CTS frames between the AP and multiple STAs may be performed as follows.

[0302] FIG. 28 is a first embodiment of an operation for protecting frame transmission and reception through an MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention.

[0303] Referring to FIG. 28, when an AP wants to transmit a frame to multiple STAs, it may perform an exchange procedure of an MU-RTS frame and a CTS frame before transmitting the frame in order to protect the frame transmission operation. The MU-RTS frame may be transmitted using one of the main 20 MHz channel, the main 40 MHz channel, the main 80 MHz channel, the main 160 MHz or 80+80 MHz channel, the main 240 MHz or the main 160+80 MHz channel, the main 320 MHz or 160+160 MHz channel. At this time, the MU-RTS may indicate the ID of the STA to transmit the CTS (e.g., Association ID), the channel on which each STA will transmit the CTS frame (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), etc. 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 FIG. 17, which will be described later. The MU-RTS frame may be a frame requesting simultaneous transmission of CTS frames from multiple STAs. At this time, the plurality of STAs may include HE STAs defined in IEEE 802.11ax and EHT STAs defined in IEEE 802.11be.

[0304] A plurality of STAs that receive an MU-RTS frame from an AP can check information included in the MU-RTS frame. The plurality of STAs can check information of the received MU-RTS frame and check an AID value included in one or more user information fields included in the corresponding MU-RTS frame. At this time, if the AID value matches an AID value allocated to the corresponding STA, the STA can check that the MU-RTS frame requests transmission of a CTS frame to the corresponding STA. The STA including the AID in the MU-RTS frame can perform a channel sensing operation for an SIFS time on a channel indicated by the MU-RTS frame after receiving the MU-RTS frame. At this time, the channel may be one of a main 20 MHz channel, a main 40 MHz channel, a main 80 MHz channel, a main 160 MHz / 80+80 MHz channel, a main 240 MHz / 160+80 MHz channel, and a main 320 MHz / 160+160 MHz channel. At this time, if the STA that received the MU-RTS frame is a HE STA, the bandwidth of the channel that transmits the CTS frame may be a maximum of 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 a physical detection, a virtual detection, and a NAV (Network Allocation Vector) confirmation process.

[0305] If the indicated channel is in a channel idle state for a SIFS time after receiving the MU-RTS frame from the STA, multiple STAs indicated in the MU-RTS frame can simultaneously transmit a CTS frame after the SIFS time after the end of transmission of the PPDU including the MU-RTS frame. At this time, the CTS frame can be transmitted in the indicated channel in the form of a non-HT PPDU or in the form of a non-HT duplicated PPDU that is repeated every 20 MHz band. At this time, the CTS frames transmitted by multiple STAs can be configured identically. Therefore, from the AP's perspective, a CTS frame can be received in each 20 MHz channel for the MU-RTS frame transmitted as in (a) of FIG. 28. At this time, the reception power of the CTS frame received in each 20 MHz channel can be different. When the AP receives a CTS frame in response to an MU-RTS, the AP can perform MU-OFDMA or MU-MIMO operation with multiple STAs based on the bandwidth of the received CTS frame.

[0306] Meanwhile, as described above, the transmission bandwidth of the CTS frame transmitted by the STA that received the MU-RTS frame may be different. For example, referring to (b) of FIG. 13, if the channel instructed to send the CTS frame in the MU-RTS frame is a primary 20 MHz channel, STA1 may transmit the CTS frame after performing channel sensing operation only on the primary 20 MHz channel. At this time, the CTS frame may be transmitted in the form of a non-HT PPDU. STA1 may receive a downlink frame within the 20 MHz channel after transmitting the CTS frame.

[0307] Referring to (c) of FIG. 28, if the channel instructed to send a CTS frame in the MU-RTS frame is a primary 40 MHz channel, the STA (e.g., STA2) indicated in the user information field of the MU-RTS frame can perform channel sensing operation only on the primary 40 MHz channel and then transmit a CTS frame. At this time, the CTS frame can be transmitted in the form of a non-HT duplicated PPDU. STA2 can receive a downlink frame within the 40 MHz channel after transmitting the CTS frame.

[0308] Referring to (d) of FIG. 28, if the channel instructed to send a CTS frame in the MU-RTS frame is a primary 80 MHz channel, the STA (e.g., STA3) indicated in the user information field of the MU-RTS frame can perform channel sensing operation only on the primary 80 MHz channel and then transmit the CTS frame. At this time, the CTS frame can be transmitted in the form of a non-HT duplicated PPDU. After transmitting the CTS frame, STA3 can receive a downlink frame within the 80 MHz channel.

[0309] The MU-RTS frame used in the above MU-RTS frame and CTS frame exchange procedure can be configured as follows.

[0310] FIG. 29 is a first embodiment illustrating the structure of an MU-RTS frame according to an embodiment of the present invention.

[0311] Referring to FIG. 29, an MU-RTS frame may be configured in the form of a trigger frame and may be configured with a common field and one or more user information fields. The common field may be configured with a trigger type field, an indication field indicating whether a trigger frame is additionally transmitted after the corresponding frame, a field indicating whether a carrier sensing operation is required at the receiving terminal, a bandwidth field of the uplink frame, a bandwidth extension field of the uplink frame, and a reservation 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 corresponding trigger frame is an MU-RTS frame. In addition, 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 corresponding MU-RTS frame is transmitted in a bandwidth of 160 MHz or less and the EHT STA does not set the user information field in a separate form. If the MU-RTS frame is transmitted with a bandwidth exceeding 160 MHz, it can be set to 10. The field indicating whether the carrier sensing operation is required can be set to 1 to instruct the STA that received the MU-RTS frame to perform the carrier sensing operation. The bandwidth field and the bandwidth extension field of the uplink frame can indicate the bandwidth of the CTS frame that the AP transmitting the MU-RTS frame wants to receive. That is, when multiple STAs transmit CTS frames in (a) of FIG. 13, the bandwidth of the CTS frame that the AP should finally receive can be indicated. The bandwidth field can be indicated as shown in Table 3 below.

[0312]

[0313] The bandwidth extension field is displayed only when the MURTS type field is not 00, and if the bandwidth field value is 2 or less, the bandwidth extension field is set to 0. If the bandwidth field value is 3, the bandwidth extension field can be set as shown in Table 4 below.

[0314]

[0315] Meanwhile, if the STA receiving the MU-RTS frame is a HE STA, the values ​​of the MURTS type field and the bandwidth extension field among the common fields of the MU-RTS frame may not be deciphered. Therefore, when the AP transmits the MU-RTS frame, the bandwidth at which the HE STA transmits the CTS frame may be indicated as a maximum of 160 MHz or 80+80 MHz regardless of the bandwidth extension field value. If the STA receiving the MU-RTS frame is an EHT STA, the bandwidth at which the CTS frame should be transmitted can be confirmed by checking both the bandwidth field and the bandwidth extension field values ​​of the MU-RTS frame.

[0316] The user information field may be configured differently depending on the MURTS type field value of the common field and whether the terminal receiving the MU-RTS frame is a 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) allocation field. When the MURTS type field is 10, if the user information field indicates a HE STA, it may be configured with a 12-bit AID field and an 8-bit RU (Resource Unit) allocation field. If the MURTS type field value is 10 and the user information field indicates an EHT STA, it may be configured with a 12-bit AID field and a 9-bit RU (Resource Unit) allocation field. Alternatively, the user information field may vary based on whether the receiving terminal is a HE STA or an EHT STA, regardless of the MURTS type field value. For example, if the user information field corresponds to a HE STA, the user information field may include a 12-bit AID field and an 8-bit RU allocation field. Additionally, 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 allocation field.

[0317] If the above RU (Resource Unit) allocation field consists of 8 bits, if the B0 value of the corresponding RU allocation field is 1, it can indicate that transmission of a CTS frame using a bandwidth of 160 MHz or 80+80 MHz is requested. If the B0 value, which is the least significant bit (LSB) of the RU allocation field, is 0, it can indicate that the STA indicated in the corresponding user field requests to transmit a CTS frame at 20 MHz, 40 MHz, or 80 MHz.

[0318] The transmission bandwidth and detailed location of the transmission band of the above CTS frame can be indicated in B7-B1 of the RU allocation field, i.e., the 7 upper bits of the RU allocation field. At this time, the B7-B1 value of the RU allocation field can be set as shown in Table 5 below.

[0319]

[0320] When the above RU allocation field is composed of 9 bits, B1-B0 of the above RU allocation field, i.e., the two least significant bits, can indicate the segment location of the 80 MHz band in which the corresponding CTS frame is transmitted when dividing a channel of 320 MHz bandwidth into four 80 MHz channel segments.

[0321] The transmission bandwidth of the above CTS frame and its location in the 80 MHz segment can be indicated in B8-B2 of the RU allocation field. At this time, the B8-B2 value of the RU allocation field can be set as shown in Table 6 below.

[0322]

[0323] Meanwhile, if the B8-B2 value indicates a 320 MHz or 160+160 MHz main channel, the B1-B0 value of the RU allocation field may be indicated as 11.

[0324] Meanwhile, if the length of the RU allocation field in the user information field transmitted to the EHT STA is to be maintained at 8 bits, the MU-RTS frame can be configured as follows.

[0325] Fig. 30 is a second embodiment illustrating the structure of an MU-RTS frame according to an embodiment of the present invention. At this time, description of parts identical or similar to the structure of the MU-RTS frame of Fig. 28 may be omitted.

[0326] Referring to FIG. 30, an MU-RTS frame may be configured in the form of a trigger frame and may be configured with a common field and one or more user information fields. The common field may be configured with a trigger type field, an indication field indicating whether a trigger frame is additionally transmitted after the corresponding frame, a field indicating whether a carrier sensing operation is required at the receiving terminal, a bandwidth field of the uplink frame, a bandwidth extension field of the uplink frame, and a reservation field. The common field may additionally include a MURTS type field. The configuration of the remaining fields excluding the MURTS type field may be configured in the same manner as the MU-RTS frame of FIG. 28. The MURTS type field may be set to 00 when the MU-RTS frame is transmitted in a bandwidth of 160 MHz or less and the EHT STA does not set a user information field in a separate form. When the MU-RTS frame is transmitted in a bandwidth exceeding 160 MHz, it may be set to 10.

[0327] The above user information field may be composed of a 12-bit AID field, an 8-bit RU allocation field, and a reservation field. When the AID field of the user information field indicates HE STA, or when the bandwidth field and the 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 be the same as the 8-bit RU allocation field of FIG. 13. That is, B0 of the RU allocation field indicates whether transmission is performed in a 160 MHz or 80+80 MHz bandwidth, and B7-B1 of the RU allocation field may be configured as shown in Table 3.

[0328] When the above MU-RTS frame is transmitted with 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 of the above RU allocation field, i.e., the two least significant bits, may indicate the segment location of the 80 MHz band in which the corresponding CTS frame is transmitted when dividing a channel of 320 MHz bandwidth into four 80 MHz channel segments.

[0329] The transmission bandwidth of the above CTS frame and its location in the 80 MHz segment can be indicated in B7-B2 of the RU allocation field. At this time, the B7-B2 value of the RU allocation field can be set as shown in Table 7 below.

[0330]

[0331] Meanwhile, if the B7-B2 value indicates a 320 MHz or 160+160 MHz main channel, the B1-B0 value of the RU allocation field may be indicated as 11.

[0332] The above MU-RTS frame and CTS frame exchange procedure can be performed using a main 20 MHz channel, a main 40 MHz channel, a main 80 MHz channel, a main 160 MHz / 80+80 MHz channel, a main 240 MHz / 160+80 MHz channel, a main 320 MHz / 160+160 MHz channel. Alternatively, if a specific 20 MHz channel other than the main 20 MHz channel is occupied, the 20 MHz channel may be emptied and only the remaining channels may be used. The MU-RTS frame and CTS frame exchange operation utilizing the operation of emptying some of the 20 MHz channels and transmitting frames (preamble puncturing operation) can be performed as follows.

[0333] FIG. 31 illustrates a second embodiment of an operation for protecting frame transmission and reception through an MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention. At this time, descriptions identical or similar to the operations of FIG. 28 may be omitted.

[0334] Referring to FIG. 31, an AP can simultaneously perform frame transmission and reception procedures with multiple STAs. The process of simultaneously transmitting and receiving frames with multiple STAs can be performed through MU-OFDMA or MU-MIMO operation. At this time, in order to protect the frame transmission and reception procedure, the AP can perform an exchange procedure of an MU-RTS frame and a CTS frame before transmitting the frame. The MU-RTS frame can be transmitted using one of 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, and a primary 320 MHz or 160+160 MHz channel. At this time, if one or more 20 MHz channels among the 20 MHz channels excluding the primary 20 MHz channel are occupied or if the 20 MHz channel is not to be used, the one or more 20 MHz channels may be vacated and the MU-RTS frame may be transmitted using only the remaining channels. That is, when transmitting an MU-RTS frame using the primary 80 MHz channel, the primary 160 MHz or 80+80 MHz channel, the primary 240 MHz or primary 160+80 MHz channel, the primary 320 MHz or 160+160 MHz channel, the MU-RTS frame may not be transmitted on a specific 20 MHz channel. For example, when transmitting an MU-RTS frame using the primary 80 MHz channel, if a 20 MHz channel within the secondary 40 MHz channel is occupied, the channel may be vacated and the MU-RTS frame may be transmitted using only the remaining channels.

[0335] The MU-RTS may indicate the ID of the STA to transmit the CTS (e.g., Association ID), the channel on which each STA will transmit the CTS frame (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), etc. In this case, an empty 20 MHz channel (punctured channel) on which the MU-RTS is not transmitted may be additionally indicated. The MU-RTS frame may be configured as illustrated 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. At this time, the plurality of STAs may include HE STAs defined in IEEE 802.11ax and EHT STAs defined in IEEE 802.11be.

[0336] Referring to (a) of FIG. 31, an AP can transmit an MU-RTS frame to multiple STAs, and receive a CTS frame simultaneously transmitted from the STAs after an SIFS time from the end time of transmission of a PPDU including the MU-RTS frame. The CTS frame may be repeatedly transmitted for each 20 MHz channel. The CTS frame may be in the form of a non-HT duplicated PPDU. At this time, the CTS frames transmitted by multiple STAs may be configured identically. Therefore, from the AP's perspective, a CTS frame can be received for each 20 MHz channel. At this time, the reception 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 can perform MU-OFDMA or MU-MIMO operation with multiple STAs based on the bandwidth of the received CTS frame.

[0337] Meanwhile, as described above, the transmission bandwidth of the CTS frame transmitted by the STA that received the MU-RTS frame may be different. For example, referring to (b) of FIG. 16, if the channel instructed to send the CTS frame in the MU-RTS frame is a primary 20 MHz channel, STA1 may perform a channel sensing operation only on the primary 20 MHz channel. The channel sensing operation may be performed during the SIFS time. If the primary 20 MHz channel is idle, the CTS frame may be transmitted. At this time, the CTS frame may be transmitted in the form of a non-HT PPDU. STA1 may receive a downlink frame within the 20 MHz channel after transmitting the CTS frame. At this time, the STA transmitting the CTS frame may be a HE STA or an EHT STA.

[0338] Referring to (c) of FIG. 31, if the channel instructed to send a CTS frame in an MU-RTS frame is a primary 40 MHz channel, an STA (e.g., STA2) indicated in the user information field of the MU-RTS frame can perform a channel sensing operation only on the primary 40 MHz channel. The channel sensing operation can be performed during an SIFS time. If the primary 40 MHz channel is idle, a CTS frame can be transmitted. At this time, the CTS frame can be transmitted in the form of a non-HT duplicated PPDU. After transmitting the CTS frame, STA2 can receive a downlink frame within the 40 MHz channel. At this time, the STA transmitting the CTS frame can be a HE STA or an EHT STA.

[0339] Referring to (d) of FIG. 31, if a channel instructed to send a CTS frame in an MU-RTS frame is a main 80 MHz channel and a specific 20 MHz channel is empty, an STA (e.g., STA3) indicated in the user information field of the MU-RTS frame may perform channel sensing operation only on channels other than the 20 MHz channel instructed to be empty among the main 80 MHz channels. If the channel is found to be idle as a result of channel sensing, a CTS frame may be transmitted. At this time, the CTS frame may be transmitted in the form of a non-HT duplicated PPDU. After transmitting the CTS frame, STA3 may receive a downlink frame within the channel on which the MU-RTS frame and the CTS frame were exchanged. The STA transmitting the CTS frame may be an EHT STA.

[0340] The MU-RTS frame used in the above MU-RTS frame and CTS frame exchange procedure may be configured by adding a field indicating a punctured channel to the existing MU-RTS frame. Alternatively, the MU-RTS frame may be configured as follows.

[0341] Fig. 32 is a third embodiment illustrating the structure of an MU-RTS frame according to an embodiment of the present invention. At this time, the portions configured identically to the MU-RTS frame of Fig. 29 may be omitted from description.

[0342] Referring to FIG. 32, an MU-RTS frame may be configured in the form of a trigger frame and may be configured with a common field and one or more user information fields. The common field may be configured with a trigger type field, an indication field indicating whether a trigger frame is additionally transmitted after the corresponding frame, a field indicating whether a carrier sensing operation is required at the receiving terminal, a bandwidth field of the uplink frame, a bandwidth extension field of the uplink frame, and a reservation field. The common field may additionally include a MURTS type field. In addition, the common field may additionally include a punctured channel field. In this case, the remaining fields except for 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 while emptying some 20 MHz channels. 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 MURTS punctured channel field may consist of 16 bits. In this case, each bit of the 16 bits may indicate one 20 MHz channel. Therefore, when the corresponding bit position is set to 0, it may indicate that an 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 may indicate that only the 20 MHz channel of the second lowest band is a punctured channel and frames are transmitted on other channels. In this case, the main 20 MHz channel may not be set to 1.

[0343] The user information field may be configured similarly to FIG. 29 or FIG. 30. For example, if the MU-RTS frame is transmitted in a bandwidth of 160 MHz or less and the MURTS type field of 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 configured as in Table 3. If the MU-RTS frame is transmitted in a bandwidth exceeding the 160 MHz band and the MURTS type field is 11, the RU allocation field in the user information field may be configured with 8 bits or 9 bits. If the RU allocation field is 9 bits, it may be configured as in FIG. 14. If the RU field is 8 bits, it may be configured as in FIG. 30.

[0344] An EHT STA that receives the MU-RTS frame from the AP can check the bandwidth field and bandwidth extension field to check the bandwidth on which the MU-RTS frame is transmitted if the MURTS type field is 11. The punctured channel field can be used to check the channel to be emptied when transmitting a CTS. In addition, the RU allocation field can be used to check the bandwidth on which the STA is to transmit. The interpretation method of the RU allocation field may vary depending on the bandwidth on which the MU-RTS frame is transmitted and the MURTS type field. An EHT STA that checks the RU allocation field and the punctured channel interpreted according to the bandwidth on which the MU-RTS frame is transmitted and the MURTS type field 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 allocation field.

[0345] Meanwhile, the HE STA that received the MU-RTS frame may not be able to decipher the punctured channel field. Therefore, the HE STA may transmit a CTS frame on the channel indicated in the RU allocation field without clearing the specific 20 MHz channel.

[0346] Meanwhile, during the exchange of the MU-RTS frame and CTS frame, the CTS frame can only be transmitted on one or more 20 MHz channels. In this case, the exchange operation of the MU-RTS and CTS frames can be performed as follows.

[0347] FIG. 33 illustrates a third embodiment of an operation for protecting frame transmission and reception through an MU-RTS frame and CTS frame exchange procedure between an AP and multiple STAs according to an embodiment of the present invention. At this time, descriptions identical or similar to the operations of FIG. 28 and FIG. 31 may be omitted.

[0348] Referring to FIG. 33, an AP can simultaneously perform frame transmission and reception procedures with multiple STAs. The process of simultaneously transmitting and receiving frames with multiple STAs can be performed through MU-OFDMA or MU-MIMO operation. At this time, in order to protect the frame transmission and reception procedure, the AP can perform an exchange procedure of an MU-RTS frame and a CTS frame before transmitting the frame. The MU-RTS frame can be transmitted using one of 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, and a primary 320 MHz or 160+160 MHz channel. At this time, if the channel status of the 20 MHz channel other than the main 20 MHz channel is occupied or if the 20 MHz channel is not to be used, only the 20 MHz channel can be emptied and transmission can be performed using the remaining channels. For example, when transmitting an MU-RTS frame using the main 80 MHz channel, if a 20 MHz channel within the secondary 40 MHz channel is occupied, the channel can be emptied and the MU-RTS frame can be transmitted using only the remaining channels.

[0349] The MU-RTS may indicate the ID of the STA to transmit the CTS (e.g., Association ID), the channel on which each STA will transmit the CTS frame, etc. The channel on which the CTS frame will be transmitted may be a specific 20 MHz channel or multiple 20 MHz channels. In this case, the multiple 20 MHz channels may have limited shapes. In addition, a punctured channel that is not used to transmit the MU-RTS may be additionally 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 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. At this time, the HE STA cannot be instructed to transmit a 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.

[0350] Referring to (a) of FIG. 33, an AP can transmit an MU-RTS frame to multiple STAs, and receive a CTS frame simultaneously transmitted from the STAs after an SIFS time from the end time of transmission of a PPDU including the MU-RTS frame. The CTS frame may be repeatedly transmitted for each 20 MHz channel. The CTS frame may be in the form of a non-HT duplicated PPDU. At this time, the CTS frames transmitted by multiple STAs may be configured identically. Therefore, from the AP's perspective, a CTS frame can be received for each 20 MHz channel. At this time, the reception 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 can perform MU-OFDMA or MU-MIMO operation with multiple STAs based on the bandwidth of the received CTS frame.

[0351] Meanwhile, as described above, the transmission bandwidth of the CTS frame transmitted by the STA that received the MU-RTS frame may be different. For example, referring to (b) of FIG. 18, if the channel instructed to send the CTS frame in the MU-RTS frame is a primary 20 MHz channel, STA1 may perform a channel sensing operation only on the primary 20 MHz channel. The channel sensing operation may be performed during the SIFS time. If the primary 20 MHz channel is idle, the CTS frame may be transmitted. At this time, the CTS frame may be transmitted in the form of a non-HT PPDU. STA1 may receive a downlink frame within the 20 MHz channel after transmitting the CTS frame. At this time, the STA transmitting the CTS frame may be a HE STA or an EHT STA.

[0352] Referring to (c) of FIG. 33, if the channel instructed to send a CTS frame in an MU-RTS 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 a channel sensing operation only on the 20 MHz channel. The channel sensing operation can be performed during the SIFS time. If the 20 MHz channel is idle, a CTS frame can be transmitted. At this time, the CTS frame can be transmitted in the form of a non-HT PPDU. After transmitting the CTS frame, STA2 can receive a downlink frame within the 20 MHz channel. At this time, the STA transmitting the CTS frame can be an EHT STA.

[0353] Referring to (d) of FIG. 33, if the channel instructed to send a CTS frame in an MU-RTS frame is a main 80 MHz channel and a specific 20 MHz channel is empty, the STA (e.g., STA3) indicated in the user information field of the MU-RTS frame can perform channel sensing operation only on the remaining channels except for the 20 MHz channel indicated as the main 80 MHz channel. If the channel is in an idle state as a result of channel sensing, the CTS frame can be transmitted. At this time, the CTS frame can be transmitted in the form of a non-HT duplicated PPDU. After transmitting the CTS frame, STA3 can receive a downlink frame within the channel on which the MU-RTS frame and the CTS frame were exchanged. The STA transmitting the CTS frame may be an EHT STA.

[0354] The MU-RTS frame used in the above MU-RTS frame and CTS frame exchange procedure may be a form in which the RU allocation field of the existing MU-RTS frame is modified to indicate multiple 20 MHz bands. In this case, a field indicating a punctured channel may be added to the MU-RTS frame and configured. Alternatively, the MU-RTS frame may be configured as follows.

[0355] Fig. 34 is a fourth embodiment illustrating the structure of an MU-RTS frame according to an embodiment of the present invention. At this time, the portions configured identically to the MU-RTS frame of Fig. 29 or Fig. 32 may be omitted from explanation.

[0356] Referring to FIG. 34, an MU-RTS frame may be configured in the form of a trigger frame and may be configured with a common field and one or more user information fields. The common field may be configured with a trigger type field, an indication field indicating whether a trigger frame is additionally transmitted after the corresponding frame, a field indicating whether a carrier sensing operation is required at the receiving terminal, a bandwidth field of the uplink frame, a bandwidth extension field of the uplink frame, and a reservation field. The common field may additionally include a MURTS type field. In this case, the remaining fields except for the field indicating the MURTS type field among the common fields may be set to be the same as in FIG. 14. The field indicating the MURTS type field may indicate that the MU-RTS frame is transmitted while emptying some 20 MHz channels. For example, the MURTS type field may be set to 11. Meanwhile, the common field may further include a punctured channel field. The above punctured field may be included when the MURTS type field is set to 11. If the above punctured channel field is included, the field may be set identically to the MU-RTS frame of FIG. 17.

[0357] The user information field may be configured differently depending on whether the terminal indicated by the field is a HE STA or an EHT STA. If the user information field indicates a HE STA, the user information field may be configured with a 12-bit AID field and an 8-bit RU allocation field. At this time, B0 of the RU allocation 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 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 allocation field. If the RU allocation field is 9 bits, B1-B0 of the RU allocation field may indicate the segment location of the 80 MHz band in which the main channel on which the CTS frame is transmitted is located when a channel with a 320 MHz bandwidth is divided into four 80 MHz channel segments. At this time, B0 can specify the location of the segment of the corresponding 80 MHz band. For example, if B0 is set to 0, it can indicate that the corresponding 80 MHz segment is contained within a 160 MHz channel of the lower band among the lower 320 MHz or 160+160 MHz main channels. If B0 is set to 1, it can indicate that the corresponding 80 MHz segment is contained within a 160 MHz channel of the higher band among the lower 320 MHz or 160+160 MHz main channels.

[0358] The transmission bandwidth of the above CTS frame and its location in the 80 MHz segment can be indicated in B8-B2 of the RU allocation field. At this time, the B8-B2 value of the RU allocation field can be set as shown in Table 8 below.

[0359]

[0360]

[0361] Values ​​other than those in Table 8 of the above RU allocation field may not be used.

[0362] Meanwhile, when the B8-B2 value indicates a 320 MHz or 160+160 MHz main channel, or indicates multiple RUs within 320 MHz or 160+160 MHz, the B1-B0 value of the RU allocation field may be indicated as 11.

[0363] Meanwhile, when the RU allocation field is composed of 8 bits, B1-B0 of the RU allocation field can indicate the segment location of the 80 MHz band in which the main channel in which the CTS frame is transmitted is located when dividing a channel of 320 MHz bandwidth into four 80 MHz channel segments.

[0364] The transmission bandwidth of the above CTS frame and its location in the 80 MHz segment can be indicated in B8-B2 of the RU allocation field. At this time, the B7-B2 values ​​of the RU allocation field can be set as shown in Table 9 below.

[0365]

[0366] Values ​​other than those in Table 9 of the above RU allocation field may not be used.

[0367] Meanwhile, when the B8-B2 value indicates a 320 MHz or 160+160 MHz main channel, or indicates multiple RUs within 320 MHz or 160+160 MHz, the B1-B0 value of the RU allocation field may be indicated as 11.

[0368] An EHT STA that receives the MU-RTS frame from an AP can check the bandwidth field and bandwidth extension field to check the bandwidth on which the MU-RTS frame is transmitted if the MURTS type field is 11. In addition, the STA can check one or more 20 MHz channels on which the STA should transmit a CTS frame through the RU allocation field. The interpretation method of the RU allocation field may vary depending on the type of the terminal receiving the MU-RTS frame (e.g., whether it is a HE STA or an EHT STA) and the MURTS type field. An EHT STA that checks the RU allocation field interpreted according to the MURTS type field can transmit a CTS frame on one or more 20 MHz channels indicated in the RU allocation field. At this time, if a punctured channel field is added to the MU-RTS frame, the EHT STA can refer to this to transmit the CTS frame on one or more 20 MHz channels indicated in the RU allocation field.

[0369] Meanwhile, the HE STA that received the MU-RTS frame may not be able to decipher the added punctured channel field. Therefore, the HE STA may transmit a CTS frame on the channel indicated in the RU allocation field without clearing the specific 20 MHz channel.

[0370] Meanwhile, an indicator requesting transmission of a CTS frame on a main 20 MHz channel may be added to the MU-RTS frame of FIG. 19. If the indicator for transmitting a CTS frame on the main 20 MHz channel is set, an STA that receives the MU-RTS frame may transmit a CTS frame on multiple 20 MHz channels including the main 20 MHz channel even if the main 20 MHz channel is not indicated in the RU allocation field.

[0371] Meanwhile, the MU-RTS frame and CTS frame exchange operation illustrated in FIG. 13, FIG. 16, or FIG. 18 may also be performed between an AP belonging to an AP MLD and a terminal belonging to a STA MLD. At this time, the STA MLD may not be able to perform STR operation in some links. Therefore, the MU-RTS frame and CTS frame exchange operation may be initiated by transmitting an MU-RTS frame to multiple terminals including other terminals of the STA MLD in one link within the AP MLD and the AP MLD in another link. At this time, the operation between the AP MLD and the STA MLD may be performed as follows.

[0372] FIG. 35 is an embodiment illustrating a channel reservation process through an MU-RTS frame and CTS frame exchange procedure during operation for multiple terminals according to an embodiment of the present invention.

[0373] Referring to FIG. 35, even if some STAs cannot transmit a CTS frame due to the characteristic that STR operation is not possible for an MU-RTS frame transmitted from an AP belonging to an AP MLD, if another STA transmits a CTS frame on the channel, the AP can perform a channel reservation process through an exchange procedure of MU-RTS frames and CTS frames. For example, multiple APs may belong to an AP MLD. At this time, each AP can operate its own link. For example, AP1 and AP2 may belong to an AP MLD. AP1 may operate link 1, and AP2 may operate link 2. STA MLD or STAs that do not belong to an STA MLD may be connected to an AP within the AP MLD. For example, STA1-1 and STA1-2 included in STA MLD1 may be connected to the AP MLD. At this time, 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. At this time, STA1-1 and 1-2 belonging to STA MLD1 may not be able to perform STR operation. That is, while STA1-1 is performing a transmission operation on link 1, STA1-2 may not be able to perform a reception operation. STA2-1 and STA2-2 belonging to STA MLD2 may be able to perform STR operation. In addition, STA3 not belonging to STA MLD may be connected to AP1.

[0374] Referring to (a) of Figure 35, AP1 belonging to the AP MLD can perform frame transmission and 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, in order to protect the frame transmission and reception operations, MU-RTS frame and CTS frame exchange procedures can be performed with the multiple terminals involved.

[0375] Meanwhile, if STR operation is possible between APs belonging to the AP MLD, AP2 can independently perform a channel access operation for frame transmission while AP1 is performing a frame transmission / reception operation. After performing the channel access operation, frame transmission / reception operation with multiple terminals can be performed. For example, if AP2 has downlink data to transmit to multiple terminals, it can simultaneously transmit frames by utilizing the downlink MIMO operation with STA1-2 and STA2-2 or by utilizing the downlink OFDMA operation. At this time, in order to protect the frame transmission / reception operation, it may attempt to transmit an MU-RTS frame to the multiple terminals and perform an exchange procedure of the MU-RTS frame and the CTS frame.

[0376] At this time, referring to (b) of FIG. 35, STA MLD1, which cannot perform STR operation on link 1 and link 2, may not transmit a CTS frame in response to the MU-RTS frame even if it receives the frame on link 2 because it is receiving the frame on link 1. At this time, referring to (c) of FIG. 35, an STA capable of transmitting a CTS frame in response to the MU-RTS frame may transmit the CTS frame using the channel indicated in the MU-RTS. At this time, the STA transmitting the CTS frame may be an STA MLD that is not transmitting the frame on link 1 at the time of receiving it on link 2, an STA MLD capable of STR operation on link 1 and link 2, or an STA that does not belong to the STA MLD. The operation of transmitting the CTS frame in response to the MU-RTS may be performed as in FIG. 13, FIG. 16, or FIG. 18.

[0377] Referring to (a) of FIG. 35, even if the AP MLD does not receive a CTS frame from an STA of an STA MLD that is incapable of STR operation for the transmitted MU-RTS frame, if another terminal that has been instructed to transmit a CTS frame using the same band transmits a CTS frame, the exchange of the MU-RTS frame and the CTS frame can be determined to be successful. Accordingly, AP2 of the AP MLD can transmit downlink frames even to terminals that are incapable of STA operation and thus have not transmitted a CTS frame. At this time, since the frame transmitted to the terminal that is incapable of STR operation is included, when the frame transmitted on link 1 or link 2 requests 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 coincide.

[0378] Meanwhile, referring again to (b) of FIG. 35, STA1-2, which is unable to transmit a CTS response to an MU-RTS frame received on link 2 due to the inability to perform STR operation, can receive a downlink frame transmitted by AP2 on the link when another terminal (e.g., STA2-2) transmits a CTS frame on the channel.

[0379] Meanwhile, if an MLD that is incapable of performing the above STR operation participates in the process of exchanging MU-RTS frames, a CTS response to the received MU-RTS may not be transmitted in the following situation, and thus, no CTS frame may be transmitted on a specific channel.

[0380] FIG. 36 illustrates an operation in which a CTS frame is not transmitted for an MU-RTS frame in a specific 20 MHz channel according to an embodiment of the present invention.

[0381] Referring to (a) of FIG. 36, when a channel extension operation as in FIG. 13 is performed to transmit an MU-RTS frame, if the extended channel includes only STAs receiving frames on a downlink in a link where the STR operation is not possible, a CTS frame may not be transmitted on the extended channel. That is, while the AP MLD is transmitting a frame on one link, the channel can be extended to perform an exchange operation of the MU-RTS frame and the CTS frame after completing a channel access operation on another link. At this time, the MU-RTS frame may be transmitted using one of the main 40 MHz channel, the main 80 MHz channel, the main 160 MHz or 80+80 MHz channel, the main 240 MHz or 160+80 MHz channel, or the main 320 MHz or 160+160 MHz channel. At this time, in the case of an STA that is capable of STR operation or is not receiving a frame from another link, a CTS frame for the received MU-RTS frame can be transmitted as in (c) of FIG. 20. On the other hand, in the case of an STA that is already receiving a frame from another link that is not capable of STR operation, a CTS frame may not be transmitted in response to the received MU-RTS as in (b) of FIG. 35. In this case, if the STAs that are instructed to transmit a CTS frame on the extension channel include only STAs that cannot transmit a CTS frame for the received MU-RTS frame as in (b) of FIG. 35, a CTS frame for the transmitted MU-RTS frame may not be transmitted on the extension channel. For example, AP1 and AP2 may belong to AP MLD. AP1 may operate link 1, and AP2 may operate link 2. STA MLD1 may include STA1-1 and STA1-2. STA MLD2 may include STA2-1 and STA2-2.STA1-1, STA2-1, and STA3 may be connected to AP1, and STA1-2 and STA2-2 may be connected to AP2. At this time, STA1-1 and STA1-2 of STA MLD1 may not be able to perform STR operation on link 1 and link 2. At this time, AP1 may transmit a downlink frame to STA1-1, STA2-1, and STA3 through a multi-user OFDMA operation. Alternatively, AP1 may transmit a downlink frame to STA1-1. AP1 may additionally perform an exchange procedure of an RTS frame or an MU-RTS frame and a CTS frame to protect the downlink frame. Meanwhile, while AP1 is performing frame transmission and reception operation with multiple terminals including STA1-1 or STA1-1, AP2 may complete a channel contention process for frame transmission on link 2.

[0382] At this time, AP2 may want to transmit a downlink frame to multiple terminals including STA1-2. For example, it may want to transmit a downlink frame to STA1-2 and STA2-2. At this time, in order to protect the transmission operation of the downlink frame, an MU-RTS frame and CTS frame exchange operation may be performed before transmitting the corresponding frame. The MU-RTS frame may be transmitted using the same bandwidth as the bandwidth of the downlink frame. For example, when the downlink frame is to be transmitted through a main 80 MHz channel, the MU-RTS frame may also be transmitted using the 80 MHz bandwidth. In the MU-RTS frame, the transmission bandwidth of the CTS frame transmitted by STA2-2 may be designated as the main 40 MHz channel, and the transmission bandwidth of the CTS frame transmitted by STA1-2 may be designated as the main 80 MHz channel. At this time, since STA1-1 is receiving a frame on link 1, STA1-2 may not be able to transmit a CTS frame as a response to the MU-RTS frame received on link 2. Meanwhile, STA2-2 may transmit a CTS frame as a response to the MU-RTS frame. Meanwhile, since AP2 received a CTS frame only in the 40 MHz band for the MU-RTS frame transmitted in the 80 MHz band, it may transmit a downlink frame using only the 40 MHz band. In other words, frame transmission and reception operations may not be performed on the secondary 40 MHz channel, not the primary 40 MHz channel, even if the actual channel is idle.

[0383] In addition, even when the exchange operation of MU-RTS frames and CTS frames is performed by emptying a specific 20 MHz channel as in FIG. 31 or FIG. 33, a situation may occur in which a CTS frame is not received for an MU-RTS frame transmitted for a specific 20 MHz channel. Referring to FIG. 36(b), AP1 and AP2 may belong to AP MLD as in FIG. 36(a), STA1-1 and STA1-2 may belong to STA MLD1, and STA2-1 and STA2-2 may belong to STA MLD2. At this time, AP1 and AP2 may operate link 1 and link 2, respectively, and STA1-1 and STA1-2 may not be able to perform STR operations on link 1 and link 2. At this time, AP1 may perform an operation of transmitting a downlink frame to multiple terminals including STA1-1 or STA1-1. During transmission of the frame, AP2 in link 2 may complete a channel access operation for frame transmission. At this time, AP2 may additionally perform an exchange operation of an MU-RTS frame and a CTS frame to protect the downlink frame to be transmitted. The receiving STA of the MU-RTS frame may be an STA that receives the downlink frame. For example, if AP2 wants to transmit a downlink frame to STA1-2 and STA2-2, it may transmit an MU-RTS frame to the corresponding terminals. At this time, AP2 may transmit the MU-RTS frame while clearing a specific 20 MHz band as in FIG. 16 or FIG. 18. STA1-2 and STA 2-2 that received the MU-RTS frame may transmit a CTS frame in response to the received MU-RTS frame. At this time, the CTS frame can be transmitted only on a channel that has been instructed to transmit the CTS frame in the MU-RTS frame, as shown in FIG. 18.At this time, STA1-2 may not be able to transmit a CTS frame for the MU-RTS frame because STA1-1 is receiving a frame on link 1. STA2-2 may transmit a CTS frame in response to the MU-RTS frame. At this time, if only STA1-2 is instructed to transmit the CTS frame for a specific 20 MHz channel, the 20 MHz channel may not be in a state in which CTS transmission is performed. AP2, which does not receive a CTS frame in response to the MU-RTS frame in the 20 MHz band, may empty the 20 MHz channel and transmit a downlink frame even if the 20 MHz channel is actually in an idle state. At this time, if the channel that did not receive the CTS response for the MU-RTS frame is the main 20 MHz channel, AP2 may not be able to transmit and receive downlink frames with STA1-2 and STA2-2 even if it receives a CTS frame for the MU-RTS frame on another channel. In addition, if the CTS response for the MU-RTS frame is received at least on the main 20 MHz channel, it may perform downlink frame transmission following the reception of the CTS response.

[0384] Alternatively, a phenomenon may occur in which the CTS frame for the MU-RTS frame is not transmitted when some of the STAs communicating with the AP temporarily change their primary channels. Referring to (c) of FIG. 36, in a situation in which the AP MLD transmits frames to the STA MLD1 and STA MLD2 as in (a) of FIG. 36, if the primary channel of STA2-2 has temporarily moved to a channel other than the primary channel of the AP before AP2 transmits the frame on link 2, the STA2-2 may transmit a CTS response to the received MU-RTS frame based on the primary channel of the STA2-2. For example, if it is instructed to transmit a CTS frame with a bandwidth of 40 MHz for the MU-RTS frame of FIG. 14 or FIG. 15, the STA2-2 may transmit a CTS frame using the primary 40 MHz channel of the STA2-2 in response to the MU-RTS frame received from the AP2. Meanwhile, the STA1-2 may use the same primary channel as the primary channel of AP2. At this time, the STA1-1 and STA1-2 are not capable of STR operation, and since the STA1-1 is receiving a frame on link 1, the STA1-2 may not be able to transmit a CTS frame in response to the received MU-RTS frame. At this time, if only STA1-2 is instructed to transmit the CTS frame for a specific 20 MHz channel, the 20 MHz channel may not be in a state where CTS transmission is not performed. At this time, if the channel that did not receive the CTS response for the MU-RTS frame is the primary 20 MHz channel, AP2 may not be able to transmit and receive downlink frames with STA1-2 and STA2-2 even if it receives a CTS frame on another channel for the MU-RTS frame.

[0385] In the present invention, when a downlink frame is transmitted to an STA belonging to an MLD where the STR operation is impossible and channel access is completed on another link, the frame is transmitted to another STA belonging to the MLD, and the downlink frame transmission operation can be performed as follows.

[0386] FIG. 37 is a first embodiment of an operation of omitting transmission of an MU-RTS frame by imposing an additional condition in an AP MLD according to an embodiment of the present invention.

[0387] Referring to FIG. 37, when the AP MLD is performing a frame transmission process on one link and the channel access operation for frame transmission on another link is completed, when transmitting a downlink frame including a terminal that cannot perform a CTS response to the transmission of the MU-RTS frame on the link, the transmission of the MU-RTS frame may be omitted. That is, even when 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 required, 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. STA MLD1 may include STA1-1 and STA1-2. STA MLD2 may include STA2-1 and STA2-2. STA1-1, STA2-1, and STA3 may be connected to AP1, and STA1-2 and STA2-2 may be connected to AP2. At this time, STA1-1 and STA1-2 of STA MLD1 may not be able to perform STR operation on link 1 and link 2. At this time, AP1 may transmit a downlink frame to STA1-1, STA2-1, and STA3 through a multi-user OFDMA operation. Alternatively, AP1 may transmit a downlink frame to STA1-1. AP1 may additionally perform an exchange procedure of an RTS frame or an MU-RTS frame and a CTS frame to protect the downlink frame. Meanwhile, while AP1 is performing frame transmission and reception operations with multiple terminals including STA1-1 or STA1-1, AP2 may complete a channel contention process for frame transmission on link 2. AP2 may want to transmit a downlink frame to multiple terminals including STA1-2.At this time, if at least one of the receiving STAs of the frame to be transmitted belongs to an STA MLD in which STR operation is impossible with link 1, and an STA belonging to the MLD is receiving a frame on link 1, the downlink frame can be transmitted without performing an exchange operation of an MU-RTS frame and a CTS frame. At this time, if the completion time of the channel contention process is before the end time of transmission of the CTS frame on link 1, even if the channel access operation on link 2 is completed, the channel sensing operation can be performed until the start time of the PPDU including the downlink frame on link 1, and then the frame transmission operation can be performed at that time.

[0388] Meanwhile, if the completion point of the channel competition process in the above link 2 occurs during the transmission time of the downlink frame in the above link 1, the following operation may be performed according to the remaining transmission time of the PPDU including the downlink frame in the link 1.

[0389] FIG. 38 is a second embodiment of an operation of omitting transmission of an MU-RTS frame by imposing an additional condition in an AP MLD according to an embodiment of the present invention.

[0390] Referring to FIG. 38, when an 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 there is a terminal that cannot perform a CTS response to the transmission of an MU-RTS frame on the corresponding link, the transmission of the MU-RTS frame may be omitted. At this time, if the time at which the channel access operation is completed is during the transmission time of a PPDU including a downlink frame on the other link, the transmission operations of the MU-RTS frame and CTS frame may be omitted and the downlink frame may be transmitted at the time at which the channel access is completed on the corresponding link. That is, even if the length of the PSDU (PHY Service Data Unit) 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 required, the MU-RTS frame and CTS frame exchange process may be omitted. For example, as in the above-described FIG. 22, while AP1 belonging to the AP MLD is performing frame transmission and reception operations with STA1-1 or multiple terminals 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. At this time, while AP1 is transmitting a PPDU including a downlink frame on link 1, AP2 may complete channel contention on link 2 and check the remaining transmission time of the PPDU transmitted on link 1 at the completion time. At this time, if the remaining transmission time of the PPDU transmitted on link 1 is longer than a specific time, AP2 may skip the exchange process of MU-RTS and CTS frames and transmit a downlink frame to the terminals including STA1-2. The specific time may be a value stored in the AP.Alternatively, the above specific time may be exchanged during the negotiation process for multi-link operation between AP MLD and STA MLD.

[0391] Meanwhile, if the channel contention completion point in the link 2 occurs during the transmission time of the downlink frame in the link 1, and the remaining transmission time of the PPDU being transmitted in the link 1 is within the specific time, the downlink frame may be transmitted as in FIG. 23, and the transmission end point of the PPDU including the frame may be aligned with the PPDU transmission end point in the link 1. Alternatively, the exchange process of the MU-RTS frame and the CTS frame may be performed as follows.

[0392] FIG. 39 illustrates an example of an operation for transmitting an MU-RTS frame according to additional conditions imposed by an AP MLD according to an embodiment of the present invention. At this time, any description overlapping with FIGS. 37 and 38 may be omitted.

[0393] Referring to FIG. 39, if a channel access operation for frame transmission on another link is completed while an AP MLD is transmitting a frame on one link, and the time from the completion time to the end time of PPDU transmission on the link that is already transmitting the frame is within a specific time, the AP MLD may perform an operation for transmitting an MU-RTS frame. For example, one of the APs belonging to the AP MLD (e.g., AP1) may transmit a downlink frame. At this time, the downlink frame may be transmitted to multiple terminals. For example, AP1 may operate on link 1 and transmit a downlink frame to STA1-1, STA2-1, and STA3. At this time, STA1-1 and STA1-2 belong to STA MLD1, and STA1-1 and STA1-2 may not be able to perform an STR operation. The above AP1 may complete a channel access operation for frame transmission in another AP (e.g., AP2) belonging to the same AP MLD that transmits a downlink frame in link 1. At this time, there may be multiple STAs of the frame to be transmitted in AP2, and at least one of them may be an STA that receives the frame in link 1. For example, the downlink frame transmitted by AP2 in link 2 may be transmitted to STA1-2 and STA2-2. At this time, if the remaining transmission time of the PPDU including the frame transmitted in link 1 is within a specific time at the time when the AP2 completes the channel access operation in link 2, AP2 may transmit the MU-RTS frame if the transmission operation of the MU-RTS frame is required according to the length of the PSDU to be transmitted. Alternatively, an exchange process of an MU-RTS frame and a CTS frame may be performed to protect the downlink frame to be transmitted by AP2. At this time, padding bits may be added to the MU-RTS frame to match the transmission end time with the downlink frame transmitted on link 1.Alternatively, a channel sensing operation may be additionally performed so that the transmission end time of the MU-RTS frame matches the PPDU transmission end time in the link 1.

[0394] Meanwhile, a plurality of STAs that have received the MU-RTS frame can confirm the MU-RTS frame, perform channel sensing on the channel indicated in the MU-RTS frame, and then transmit a CTS frame. The AP that has received the CTS frame can transmit a downlink frame to the plurality of STAs. At this time, if some STAs that cannot perform STR operation on the link 1 are transmitting an uplink response frame (e.g., a BlockAck frame), the downlink transmission can be delayed until the end time of transmission of the PPDU including the response frame on the link (e.g., link 1). At this time, a channel sensing operation can be performed during the delay time to determine whether the channel was occupied by another terminal during the delay time.

[0395] Meanwhile, if one or more terminals transmit a CTS frame in response to an MU-RTS frame on a specific channel, the AP can determine that the transmission operation of the MU-RTS frame has been successful. Accordingly, the following operation can be performed to induce one or more STAs to transmit a CTS frame on all 20 MHz band channels where the MU-RTS frame was transmitted.

[0396] FIG. 40 is a first embodiment of an operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz due to the operation of the corresponding STA MLD according to an embodiment of the present invention.

[0397] Referring to FIG. 40, when an AP belonging to an AP MLD wants to transmit a downlink frame to multiple terminals including an STA that cannot transmit a CTS frame due to a situation in which STR operation is impossible, the STA that cannot transmit the CTS frame can be instructed to transmit the CTS frame on a main 20 MHz channel or some channels including the main 20 MHz channel. At this time, the frame can be transmitted to other STAs on an extension channel. The other STAs can be instructed to transmit the CTS frame including the main channel and the extension channel. In other words, the other STAs can be made to 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 an AP MLD. AP1 may operate link 1, and AP2 may operate link 2. An STA MLD or an STA that does not belong to an STA MLD may be connected to an AP within 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. At this time, STA1-1 and STA1-2 belonging to STA MLD1 may not be able to perform STR operation. STA2-1 and STA2-2 belonging to STA MLD2 may be able to perform STR operation. In addition, STA3 may be additionally connected to AP1.

[0398] AP1 can transmit a downlink frame after completing a channel access operation on link 1. At this time, the downlink frame can be transmitted to STA1-1 or to multiple terminals including STA1-1. At this time, in order 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 additionally performed.

[0399] While AP1 is transmitting a downlink frame, AP2 may complete a channel access operation for transmitting a downlink frame. At this time, AP2 may have data to transmit to multiple STAs including STA1-2. At this time, AP2 may transmit a downlink frame to multiple terminals including STA1-2. At this time, the length of the PSDU including the downlink frame may exceed a specific length, so an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be required. At this time, the AP may transmit the MU-RTS frame to multiple STAs. At this time, an STA (e.g., STA1-2) that cannot transmit a CTS frame due to the presence or absence of the STR operation may be instructed to transmit a CTS frame on a main 20 MHz channel or some channels including the main channel. At this time, an STA capable of STR operation or an STA that is not receiving a frame on the link 1 can instruct to transmit a CTS frame on an extension channel among the channels on which an MU-RTS frame is transmitted. The STA capable of STR operation may be an STA belonging to an STA MLD capable of STR operation. Alternatively, it may be an STA belonging to an STA MLD that does not perform a frame reception operation on the link 1. Alternatively, it may be an STA that does not belong to an STA MLD. At this time, each STA can transmit the CTS frame according to the operation of FIG. 13 or FIG. 16. Accordingly, even if the STR operation is impossible and the STA1-2 cannot transmit a CTS frame, the AP2 can receive a CTS frame for the transmitted MU-RTS frame by having another STA transmit a CTS frame on multiple channels including the primary channel. AP2, which receives a CTS frame for the above MU-RTS frame, can determine that the transmission operation of the above MU-RTS frame was successful.Accordingly, the AP2 can transmit downlink frames to multiple terminals.

[0400] Meanwhile, if STR operation is impossible due to interference within the device, and some STAs cannot transmit CTS responses to received MU-RTS frames, other STAs can be requested to transmit CTS frames in the entire band as follows.

[0401] FIG. 41 illustrates a second embodiment of an operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz frequency due to the operation of the corresponding STA MLD according to an embodiment of the present invention. In this case, any description overlapping with FIG. 40 may be omitted.

[0402] Referring to FIG. 41, when an AP belonging to an AP MLD wants to transmit a downlink frame to multiple terminals including an STA that cannot transmit a CTS frame due to a situation in which STR operation is impossible, the AP may instruct an STA capable of CTS transmission to transmit a CTS frame in the entire band. For example, as shown in FIG. 25, STA MLD1, STA MLD2, and STA3 may be connected to the AP MLD. At this time, AP1 may complete a channel access operation on link 1 and transmit a downlink frame to multiple terminals including STA1-1. At this time, in order 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 additionally performed.

[0403] While AP1 is transmitting a downlink frame, AP2 may complete a channel access operation for transmitting a downlink frame. At this time, AP2 may have data to transmit to multiple STAs including STA1-2. At this time, AP2 may transmit a downlink frame to multiple terminals including STA1-2. At this time, the length of the PSDU including the downlink frame may exceed a specific length, and thus an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be required. At this time, the AP may transmit the MU-RTS frame to multiple STAs. At this time, a terminal that is not capable of STR operation may not be able to transmit a CTS frame, which is a response to the MU-RTS frame. If it is determined that some of the terminals are not able to transmit a CTS frame and thus will not transmit a CTS frame on a specific 20 MHz channel, AP2 may request other STAs capable of transmitting CTS frames to transmit CTS frames by including the corresponding channel. The above other STA may be an STA belonging to an STA MLD capable of STR operation. Alternatively, it may be an STA belonging to an STA MLD that does not perform a frame reception operation on the link 1. Alternatively, it may be an STA that does not belong to an STA MLD. For example, AP2 may transmit a downlink frame to STA2-2 only on the primary 40 MHz channel. At this time, it may transmit a downlink frame to STA1-2 on the secondary 40 MHz channel. At this time, since STA1-1 is receiving the frame, STA1-2 may not transmit a CTS frame in response to the MU-RTS. At this time, AP2 may request STA2-2 to transmit a CTS response to the MU-RTS frame using the entire band. STA2-2, which has received the MU-RTS frame, may transmit the CTS frame through all bands on which the MU-RTS frame was received.Accordingly, AP2 can receive a CTS frame for the transmitted MU-RTS frame. Upon receiving the CTS frame for the MU-RTS frame, AP2 can determine that the transmission operation of the MU-RTS frame has been successful. Accordingly, AP2 can transmit a downlink frame to multiple terminals.

[0404] Meanwhile, if the STA MLD, which is incapable of the STR operation, is incapable of the STR operation only for some channels, the AP MLD may perform an operation of checking whether the channel is empty in each STA instead of the RTS or MU-RTS frame and CTS exchange operation. This operation may be performed through a process in which the AP transmits a BQRP (Bandwidth Query Report Poll) frame to multiple STAs, and the multiple STAs transmit a BQR (Bandwidth Query Report) frame. At this time, the channel through which each STA transmits the BQR frame may be different from the channel through which downlink data is transmitted. The process of checking whether the channel is empty through the operation of transmitting the BQR frame may be performed as follows.

[0405] FIG. 42 illustrates a third embodiment of an operation for avoiding a situation in which a CTS frame is not transmitted at a specific 20 MHz frequency due to the operation of the corresponding STA MLD according to an embodiment of the present invention. In this case, any description overlapping with FIG. 40 and FIG. 41 may be omitted.

[0406] Referring to FIG. 42, when an AP belonging to an AP MLD wants to transmit a downlink frame to multiple terminals including an STA that cannot transmit a CTS frame due to a situation in which STR operation is impossible, instead of a channel reservation process through an MU-RTS frame and a CTS frame, each STA may be requested to check whether a channel is occupied for each 20 MHz channel. At this time, the channel status confirmed by the multiple STAs may be transmitted through a BQR frame. The frame requesting the BQR transmission may be a BQRP frame. For example, as shown in FIG. 25, STA MLD1, STA MLD2, and STA3 may be connected to the AP MLD. At this time, AP1 may complete a channel access operation on link 1 and transmit a downlink frame to multiple terminals including STA1-1. At this time, in order 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 additionally performed.

[0407] While AP1 transmits a downlink frame, AP2 may complete a channel access operation for transmitting a downlink frame. At this time, AP2 may have data to transmit to multiple STAs including STA1-2. At this time, AP2 may transmit a downlink frame to multiple terminals including STA1-2. At this time, the length of the PSDU including the downlink frame may exceed a specific length, so an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be required. At this time, 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 through transmission of an MU-RTS frame. The operation of checking the channel status with the multiple STAs may 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 above request frame may be a frame requesting the plurality of STAs to check the channel status. The request frame may be a BQRP (Bandwidth Query Report Poll) frame. The BQRP frame may be a frame requesting the plurality of STAs to transmit a BQR. At this time, each STA may indicate a channel on which the BQR should be transmitted. At this time, if the STA1-2 can transmit frames on some channels, AP2 may designate the channel on which the STA1-2 transmits the BQR frame as the corresponding channel.

[0408] Multiple STAs that receive a BQRP frame from the AP2 can confirm that transmission of a BQR frame is requested through the BQRP. Accordingly, the multiple STAs can perform channel sensing for all bands in which the STAs can operate. Through this, it is possible to confirm whether each 20 MHz channel is occupied. Each STA that confirms whether each 20 MHz channel is occupied can transmit a BQR frame through the channel indicated in the BQRP frame. At this time, the PPDU in which the BQR frame is transmitted can be transmitted in the form of a HE TB PPDU or an EHT TB PPDU.

[0409] AP2, which receives BQR frames from the above-described multiple STAs, can check whether each STA occupies all bands. AP2 can transmit a downlink frame through a channel indicated as empty in the BQR frame. At this time, the channel through which AP2 receives BQRs from each STA and the channel through which it transmits the downlink frame to the corresponding STA may be different channels.

[0410] Meanwhile, if STR operation is impossible due to interference within the device and a CTS frame for an MU-RTS frame transmitted by an AP on some channels other than the main channel is not received as in Fig. 21, the AP can transmit the frame by expanding the channel after receiving a CTS frame on some channels as follows.

[0411] FIG. 43 illustrates a first embodiment of an operation for continuing frame transmission even when a CTS frame is not received for an MU-RTS frame on a specific 20 MHz channel according to an embodiment of the present invention. In this case, any description overlapping with FIG. 40 may be omitted.

[0412] Referring to FIG. 43, when an AP belonging to an AP MLD wants to transmit a downlink frame to multiple terminals including an STA that cannot transmit a CTS frame due to a situation in which STR operation is impossible, the AP may instruct an STA capable of CTS transmission to transmit a CTS frame in the entire band. For example, as shown in FIG. 25, STA MLD1, STA MLD2, and STA3 may be connected to the AP MLD. At this time, AP1 may complete a channel access operation on link 1 and transmit a downlink frame to multiple terminals including STA1-1. At this time, in order 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 additionally performed.

[0413] While AP1 transmits a downlink frame, AP2 may complete a channel access operation for transmitting a downlink frame. At this time, AP2 may have data to transmit to multiple STAs including STA1-2. At this time, AP2 may transmit a downlink frame to multiple terminals including STA1-2. At this time, the length of the PSDU including the downlink frame may exceed a specific length, so an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be required. At this time, AP2 may transmit an MU-RTS frame to multiple STAs including STA1-2. Among the STAs that have received the MU-RTS frame, an STA capable of transmitting a CTS frame may perform carrier sensing on a channel indicated in the MU-RTS frame and then transmit a CTS frame. At this time, an STA (e.g., STA1-2) that cannot transmit a CTS frame for the MU-RTS frame due to the STR operation being impossible may not transmit a CTS frame in response to the MU-RTS frame. Since STA1-2 cannot transmit a CTS frame due to the STR operation being impossible, a specific 20 MHz channel may not transmit a CTS frame for the transmitted MU-RTS. Meanwhile, AP2 may recognize that a CTS frame will not be transmitted in a specific 20 MHz channel due to the characteristic of STA1-2 that cannot perform the STR operation after transmitting the MU-RTS frame, including STA1-2. In this case, even if a CTS frame is not received in the 20 MHz band, if a CTS frame is received in another band, a downlink frame can be transmitted using up to the 20 MHz band.For example, if STA2-2 is instructed to transmit a CTS frame on a primary 40 MHz channel and STA1-2 is instructed to transmit a CTS frame on a primary 80 MHz channel in the MU-RTS frame, AP2 can transmit a downlink frame to STA1-2 and STA2-2 using the 80 MHz channel even if it does not receive a CTS frame on the secondary 40 MHz channel. At this time, AP2 can additionally perform a channel sensing operation for a specific period of time on a channel on which it did not receive a CTS frame. The channel sensing operation may include only an ED (Energy Detection) operation for checking a reception energy level. At this time, a reference energy level for determining that a channel is occupied during the ED operation may be set lower than an energy level for determining whether a channel is occupied during the wireless LAN 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 transmission of the downlink frame. Alternatively, the specific time may be a specific IFS time (e.g., SIFS, PIFS, or AIFS).

[0414] Meanwhile, AP2 may recognize that some of the STAs receiving the downlink frame may not receive the CTS frame even if they transmit the MU-RTS frame due to a specific reason in which STR is not possible. In this case, AP2 may omit the MU-RTS frame transmission process for the band in which the frame is transmitted to the corresponding STA, and perform the MU-RTS frame and CTS frame exchange procedure only for other bands.

[0415] FIG. 44 illustrates a second embodiment of an operation for continuing frame transmission even when a CTS frame is not received for an MU-RTS frame on a specific 20 MHz channel according to an embodiment of the present invention. In this case, descriptions overlapping with FIG. 40 and FIG. 43 may be omitted.

[0416] Referring to FIG. 44, when an AP belonging to an AP MLD wants to transmit a downlink frame to multiple terminals including an STA that cannot transmit a CTS frame due to a situation in which STR operation is impossible, the AP may instruct an STA capable of CTS transmission to transmit a CTS frame in the entire band. For example, as shown in FIG. 25, STA MLD1, STA MLD2, and STA3 may be connected to the AP MLD. At this time, AP1 may complete a channel access operation on link 1 and transmit a downlink frame to multiple terminals including STA1-1. At this time, in order 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 additionally performed.

[0417] While AP1 is transmitting a downlink frame, AP2 may complete a channel access operation for transmitting a downlink frame. At this time, AP2 may have data to transmit to multiple STAs including STA1-2. At this time, AP2 may transmit a downlink frame to multiple terminals including STA1-2. At this time, the length of the PSDU including the downlink frame may exceed a specific length, and thus an exchange operation of an RTS frame or an MU-RTS frame and a CTS frame may be required. At this time, AP2 may recognize that even if it transmits the MU-RTS frame including STA1-2, the CTS frame will not be transmitted on a specific 20 MHz channel because the STA1-2 is unable to perform an STR operation. In this case, AP2 may empty a channel on which it is recognized that the CTS frame will not be transmitted, and perform a channel reservation process through the exchange of MU-RTS frames and CTS frames only for other channels. For example, if AP2 transmits a downlink frame to STA2-2 on a primary 40 MHz channel and attempts to transmit a downlink frame to STA1-2 using a secondary 80 MHz channel, it may transmit an MU-RTS frame on the primary 40 MHz channel to receive a CTS frame. At this time, after AP2 receives the CTS frame on the primary 40 MHz channel, it may extend the channel usage to the primary 80 MHz channel and transmit frames to STA1-2 and STA2-2. At this time, AP2 may perform a channel sensing operation for the secondary 40 MHz channel for a specific period of time. The channel sensing operation may include only an ED (Energy Detection) operation for checking a reception energy level. At this time, a reference energy level for determining that a channel is occupied during the ED operation may be set lower than an energy level for determining whether a channel is occupied in a wireless LAN operation.For example, the reference energy level for determining whether the 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 transmission of the downlink frame. Alternatively, the specific time may be a specific IFS time (e.g., SIFS, PIFS, or AIFS).

[0418] Figure 45 shows the operation of a soft AP according to an embodiment of the present invention.

[0419] A soft AP may be an AP station. Furthermore, a soft AP may be an AP included in a multi-link device. In this case, the soft AP may be included in a non-STR multi-link device. When a soft AP is included in a non-STR multi-link device, such a multi-link device may be referred to as a non-STR soft AP multi-link device.

[0420] When a non-STR soft AP multi-link device operates on multiple links, the multiple links can be divided into mandatory links and optional links. Specifically, the multiple links can include at least one mandatory link. The operation of the non-STR soft AP multi-link device with a legacy station or a single-link station can be limited to being performed only on the mandatory link. Specifically, the association and authentication between the non-STR soft AP multi-link device and a legacy station or a single-link station can be limited to being performed on the mandatory link. In this case, the single-link station may be a station that cannot operate on multiple links.

[0421] The mandatory and optional links of a non-STR soft AP multi-link device can be designated by the non-STR soft AP multi-link device. Specifically, when a multi-link is set up between a non-STR soft AP multi-link device and a non-AP multi-link device, the mandatory and optional links can be established. For example, if a mandatory link is designated among multiple links, links other than the mandatory link can be optional links.

[0422] According to a specific embodiment, multiple links may be designated as mandatory links. In this case, the multiple links designated as mandatory links may be links capable of STR with each other. For example, the multiple links on which the non-STR soft AP multi-link device operates may include a first link and a second link, and the non-STR soft AP multi-link device may perform reception on the second link when performing transmission on the first link. In this case, the first link and the second link may be mandatory links. The mandatory links may be limited to being set identically for multiple devices communicating with the non-STR soft AP multi-link device. Specifically, it may not be permitted for multiple devices communicating with the non-STR soft AP multi-link device to be set with different mandatory links.

[0423] Additionally, the optional link of a non-STR soft AP multi-link device may only be used for communication between non-STR soft AP multi-link devices and multi-link devices. The optional link may not be used for communication between non-STR soft AP multi-link devices and legacy stations or single-link stations. Additionally, association and authentication between non-STR soft AP multi-link devices and multi-link devices may be performed on the mandatory link.

[0424] In the embodiment of FIG. 45, a non-STR soft AP multi-link device (Soft AP, non-STR AP MLD) operates on 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 multi-link device (Soft AP, non-STR AP MLD) communicates with the non-AP multi-link device (Non-AP MLD) via the second link (Link 2). Specifically, the non-STR soft AP multi-link device (Soft AP, non-STR AP MLD) performs connection and authentication with the non-AP multi-link device (Non-AP MLD) via the second link (Link 2). The non-STR soft AP multi-link device (Soft AP, non-STR AP MLD) communicates with a legacy station (Legacy STA) and a single link station (Single link STA) via the first link (Link 1). A non-STR Soft AP Multi-Link Device (Soft AP, non-STR AP MLD) performs association and authentication on the first link (Link 1) with legacy stations (Legacy STA) and single link stations (Single link STA).

[0425] The channel access method in a mandatory link may differ from the channel access method in an optional link. This is further explained in FIGS. 45 to 47.

[0426] FIG. 46 shows a non-STR soft AP multi-link device transmitting PPDUs on mandatory links and optional links according to an embodiment of the present invention.

[0427] When channel access is performed independently in the mandatory link and optional link as described above, a non-STR soft AP multi-link device may not be able to perform reception on the mandatory link when performing transmission on the optional link. To prevent this problem, whether to perform transmission on the optional link may be determined based on whether transmission is in progress on the mandatory link. The non-STR soft AP multi-link device may determine whether to perform transmission on the optional link based on whether transmission is in progress on the mandatory link. Specifically, when a non-STR soft AP multi-link device performs transmission, the non-STR soft AP multi-link device may mandatorily perform transmission on the mandatory link. In addition, a non-AP multi-link device connected to a non-STR soft AP multi-link device may determine whether to perform transmission on the optional link based on whether transmission is in progress on the mandatory link. Specifically, when a non-AP multi-link device connected to a non-STR soft AP multi-link device performs transmission, the non-AP multi-link device may mandatorily perform transmission on the mandatory link.

[0428] Therefore, a non-STR soft AP multi-link device can transmit on an optional link only when it transmits on a mandatory link. When a non-STR soft AP multi-link device does not transmit on a mandatory link, the non-STR soft AP multi-link device may not be permitted to transmit on an optional link.

[0429] When random backoff-based channel access is performed, the following embodiments may be applied. If the backoff counter on the optional link reaches 0 but the backoff counter on the mandatory link does not reach 0, the non-STR soft AP multi-link device may not perform transmission on the optional link. Specifically, the non-STR soft AP multi-link device may wait until the backoff counter on the mandatory link reaches 0. If the backoff counter on the optional link reaches 0 and the backoff counter on the mandatory link reaches 0 or transmission is being performed on the mandatory link, the non-STR soft AP multi-link device may start transmission on the optional link.

[0430] When channel access is performed based on the results of channel sensing for a fixed-length time interval, the following embodiments may apply. Even if a non-STR soft AP multi-link device detects that the channel of the optional link is idle for a predetermined time interval, it may not be permitted to start transmission on the optional link if no transmission is performed on the mandatory link. In this case, the predetermined time interval may be PIFS. In another specific embodiment, the non-STR soft AP multi-link device may perform channel access by performing channel sensing for a predetermined time interval on the optional link only when the non-STR soft AP multi-link device performs transmission on the mandatory link.

[0431] A non-STR soft AP multi-link device can align the end of a PPDU transmitted on a mandatory link with the end of a PPDU transmitted on an optional link. Simultaneously terminating transmission of multiple PPDUs can be referred to as aligning the ends of the PPDUs. In addition, if the difference between the transmission end times of multiple PPDUs is less than or equal to a threshold, the ends of the multiple PPDUs can be said to be aligned. In this case, the threshold can be a pre-specified value. Specifically, the threshold can be a value set based on SIFS. In addition, the threshold can be a value set based on the length of SIFS and signal extension. For example, the threshold can be a value obtained by dividing the sum of the lengths of SIFS and signal extension by 2. In this case, the threshold can be 8 us. A non-STR soft AP multi-link device can be allowed to not align the ends of PPDUs only if the PPDU transmitted on either of the mandatory link and the optional link does not include a frame that elicits an immediate response. Specifically, a non-STR soft AP multi-link device may align the end of a PPDU containing a frame inducing an immediate response with the end of a PPDU not containing a frame inducing an immediate response, or may configure the end of a PPDU containing a frame inducing an immediate response to precede the end of the PPDU containing a frame inducing an immediate response. For example, not aligning the ends of the PPDUs may result in the end of a PPDU not containing a frame inducing a response being the same as or precedes in time the end of a PPDU containing a frame inducing an immediate response.

[0432] In the embodiment of FIG. 46, the non-STR soft AP multi-link device includes a first AP (AP 1) and a second AP (AP 2). The first AP (AP 1) and the second AP (AP 2) each operate on a first link (Link 1), which is a mandatory link, and a second link (Link 2), which is an optional link. The first AP (AP 1) and the second AP (AP 2) are each associated with a first station (SAT 1) and a second station (STA 2) included in the non-STR multi-link device. When the second AP (AP 2) transmits data (Data 1) to the second station (STA2), if the first station (STA 1) transmits data (Data 2) to the first AP (AP 1), the first AP (AP 1) cannot receive the data (Data 2).

[0433] As in the embodiment described above, when a first AP (AP 1) and a second AP (AP 2) transmit PPDUs simultaneously, the ends of the first AP (AP 1) and the second AP (AP 2) PPDUs are aligned. When the first AP (AP 1) transmits a PPDU including data (Data 3) and the second AP (AP 2) transmits a PPDU including data (Data 4), the first AP (AP 1) and the second AP (AP 2) align the ends of the PPDUs. Furthermore, if a PPDU transmitted on either link does not include a frame that induces an immediate response, it may be permissible for the first AP (AP 1) and the second AP (AP 2) not to align the ends of the PPDUs. Since the data (Data 5) transmitted by the first AP (AP 1) does not induce an immediate response, the first AP (AP 1) may stop transmitting the PPDU before the PPDU transmitted by the second AP (AP 2).

[0434] The embodiments regarding channel access operations of the non-STR soft AP multi-link device described above can be equally applied to a non-AP multi-link device connected to a non-STR soft AP multi-link device.

[0435] In the above-described embodiments, if an exception is allowed where the ends of the PPDU are not aligned, a non-STR soft AP multi-link device may need to receive data from another link while transmitting a PPDU on one link. For example, as shown in FIG. 45, while a second AP (AP 2) is transmitting a PPDU containing data (Data 6), a first AP (AP 1) may receive a PPDU containing data (Data 7) from a first station. In this case, due to the transmission of the PPDU containing data (Data 6), the first AP (AP 1) may not be able to receive the PPDU containing data (Data 7). Therefore, a method may be needed in which PPDU reception is not interrupted on either link.

[0436]

[0437] FIG. 47 shows a non-STR soft AP multi-link device transmitting PPDUs on mandatory links and optional links according to an embodiment of the present invention.

[0438] A non-STR soft AP multi-link device may determine whether to align the ends of a PPDU based on whether the PPDU containing a frame inducing an immediate response is transmitted on the mandatory link or the optional link. Specifically, if the non-STR soft AP multi-link device transmits a PPDU containing a frame inducing an immediate response on the optional link, the non-STR soft AP multi-link device may need to align the ends of the PPDU transmitted on the mandatory link with the PPDU transmitted on the optional link. That is, if the non-STR soft AP multi-link device transmits a PPDU that does not contain a frame inducing an immediate response on the optional link, it may be acceptable for the non-STR soft AP multi-link device not to align the ends of the PPDU transmitted on the mandatory link with the PPDU transmitted on the optional link.

[0439] In the embodiment of FIG. 47, the non-STR soft AP multi-link device includes a first AP (AP 1) and a second AP (AP 2). The first AP (AP 1) and the second AP (AP 2) each operate on a first link (Link 1), which is a mandatory link, and a second link (Link 2), which is an optional link. The first AP (AP 1) and the second AP (AP 2) are each associated with a first station (SAT 1) and a second station (STA 2) included in the non-STR multi-link device. When the second AP (AP 2) transmits data (Data 1) to the second station (STA2), if the first station (STA 1) transmits data (Data 2) to the first AP (AP 1), the first AP (AP 1) cannot receive the data (Data 2). As in the embodiment described above, when the first AP (AP 1) transmits a PPDU including data (Data 1) that does not induce an immediate response on a required link, and the second AP (AP 2) transmits a PPDU including data (Data 2) that does induce an immediate response, the first AP (AP 1) and the second AP (AP 2) align the ends of the PPDUs. When the second AP (AP 2) transmits a PPDU that does not include data (Data 4) that does induce an immediate response, the first AP (AP 1) and the second AP (AP 2) do not align the ends of the PPDUs. Specifically, the second AP (AP 2) may terminate the transmission of the PPDU before the first AP (AP 1) terminates the transmission of the PPDU.

[0440] In the embodiments described above, the operation of the non-STR soft AP multi-link device may be the same as the operation of the communicating non-AP multi-link device.

[0441]

[0442] Even if a multi-link device sets up multiple links, it may not be able to support simultaneous transmission or reception on the multiple links. Such a multi-link device may transmit or receive on the multiple links under the condition that the multi-link device transmits or receives a limited type of frame or PPDU. In this case, the limited type of frame or PPDU may be a frame type, an MCS used for transmission, a number of special streams used for transmission, or a frequency bandwidth used for transmission. The operation of such a multi-link device may be referred to as enhanced multi-link operation. In enhanced multi-link operation, the multi-link device may concentrate the processing or transmission capabilities used for one or more links on one or more other links. A non-STR soft AP multi-link device may not perform enhanced multi-link operation. Specifically, enhanced multi-link operation may not be permitted on multiple links configured by a non-STR soft AP multi-link device. For example, a non-STR soft AP multi-link device may not configure enhanced multi-link operation of a multi-link device operating on multiple links configured by a non-STR soft AP multi-link device. Specifically, the non-STR soft AP multi-link device may signal that it rejects or does not support enhanced multi-link operation. This is because in enhanced multi-link operation, transmission cannot be performed on a mandatory link when transmission is performed on an optional link.

[0443]

[0444] FIG. 48 shows a non-STR soft AP multi-link device according to an embodiment of the present invention performing channel access in mandatory links and optional links.

[0445] While a non-STR soft AP multi-link device is performing reception on a selective link, the non-STR soft AP multi-link device may delay channel access on a mandatory link. This is because if the non-STR soft AP multi-link device performs transmission on a mandatory link while the non-STR soft AP multi-link device is performing reception on the selective link, reception on the selective link may be interrupted. A channel access defer may be a case where channel access is not performed during a defer period. Additionally, a channel access defer may be a case where transmission is not started even if a backoff counter reaches 0. Additionally, a non-STR soft AP multi-link device may defer channel access even before an identifier or address of a sender of a PPDU received on the selective link is identified. In this case, the channel access defer may continue until reception on the selective link is terminated.

[0446] In the embodiment of FIG. 48, a non-STR soft AP multi-link device includes a first AP (AP 1) and a second AP (AP 2). The first AP (AP 1) and the second AP (AP 2) each operate on a first link (Link 1), which is a mandatory link, and a second link (Link 2), which is an optional link. The first AP (AP 1) and the second AP (AP 2) are each associated with a first station (SAT 1) and a second station (STA 2) included in the non-STR multi-link device. The first AP (AP 1) transmits data (Data 1) that does not elicit an immediate response to the first station (STA 1), and the second AP (AP 2) transmits data (Data 2) that elicits an immediate response to the second station (STA 2). While the second AP (AP 2) receives a response to the data (Data 2) from the second station (STA 2), the first AP (AP 1) delays channel access. Additionally, the first AP (AP 1) transmits data (Data 3) to the first station (STA 1) to induce an immediate response, and the second AP (AP 2) transmits data (Data 4) to the second station (STA 2) to induce an immediate response. The first AP (AP 1) receives a response to the data (Data 3) from the first station (STA 1), and the second AP (AP 2) receives a response to the data (Data 4) from the second station (STA 2). While the second AP (AP 2) receives a response to the data (Data 4) from the second station (STA 2), the first AP (AP 1) delays channel access.

[0447] In another specific embodiment, a non-STR soft AP multi-link device may not transmit a PPDU containing a frame that induces an immediate response on an optional link while transmitting a PPDU that does not contain a frame that induces an immediate response on a mandatory link.

[0448]

[0449] FIG. 49 shows a non-STR soft AP multi-link device transmitting PPDUs on mandatory links and optional links according to an embodiment of the present invention.

[0450] If a non-STR soft AP multi-link device transmits a PPDU that does not include a frame that elicits an immediate response on both the mandatory link and the optional link, the non-STR soft AP multi-link device may terminate the PPDU transmission on the optional link no later than the PPDU transmission on the mandatory link. That is, the termination of the PPDU transmission on the optional link may be earlier than or equal to the termination of the PPDU transmission on the mandatory link. This is because if the PPDU transmission on the mandatory link is terminated before the PPDU transmission on the optional link, it may interrupt the transmission of a station transmitting on the mandatory link to the non-STR soft AP multi-link device.

[0451] In the embodiment of FIG. 49, the non-STR soft AP multi-link device includes a first AP (AP 1) and a second AP (AP 2). The first AP (AP 1) and the second AP (AP 2) each operate on a first link (Link 1), which is a mandatory link, and a second link (Link 2), which is an optional link. The first AP (AP 1) and the second AP (AP 2) each are associated with a first station (SAT 1) and a second station (STA 2) included in the non-STR multi-link device.

[0452] When a multi-link device communicating with a non-STR soft AP multi-link device transmits a PPDU that does not include a frame that elicits an immediate response on both the mandatory link and the optional link, the multi-link device may terminate transmission on the optional link before transmitting the PPDU on the mandatory link. This is because the non-STR soft AP multi-link device can still receive when another station transmits to the non-STR soft AP multi-link device on the optional link.

[0453]

[0454] An AP multi-link device and a non-AP multi-link device can negotiate the use of multi-links during the scanning and association processes described above with reference to FIG. 5. During the scanning process, an AP of an AP multi-link device can signal information about multiple links. Specifically, an AP of an AP multi-link device can include at least one of an indicator indicating that operation is possible on multiple links, the number of available links, and information about the multiple links in a beacon frame. In addition, a station of a non-AP multi-link device can signal information about multiple links during the scanning process. Specifically, a station of a non-AP multi-link device can include an indicator indicating that operation is possible on multiple links in a probe frame. In addition, a station of a non-AP multi-link device can include at least one of the number of available links and information about the multiple links in a probe frame.

[0455] During the scanning process, a non-AP multi-link device that has confirmed whether the AP multi-link device is operating multi-link and the link information used can perform a connection with the AP multi-link device. At this time, the AP multi-link device and the non-AP multi-link device can initiate a negotiation process for multi-link operation. The negotiation for multi-link operation can be performed during the connection process between the AP of the AP multi-link device and the station of the non-AP multi-link device. When the station of the non-AP multi-link device sends a connection request frame to the AP of the AP multi-link device, the station of the non-AP multi-link device can transmit an indicator indicating that multi-link operation is available and a request indicator requesting to perform multi-link operation. The AP that receives the connection request frame from the station can check the indicator requesting multi-link operation. At this time, if the AP is capable of multi-link operation, the AP can transmit an connection response frame to the station that allows multi-link operation, including link information to be used for multi-link operation and parameters used in each link. Parameters for multi-link operation may include at least one of a frequency band of each of the multiple links used in the multi-link operation, a bandwidth expansion direction of each of the frequency bands of the multiple links, a Target Beacon Transmission Time (TBTT), and whether STR operation is performed. An AP multi-link device and a non-AP multi-link device that have confirmed the use of multi-link operation by exchanging a connection request frame and a connection request response frame may perform a frame transmission operation using multiple links after the connection process.

[0456] FIG. 50 shows that transmission is performed independently on each of a plurality of links according to an embodiment of the present invention.

[0457] AP multi-link devices and non-AP multi-link devices that have completed negotiation for multi-link operation can independently transmit and receive on each link or simultaneously transmit and receive on multiple links. When transmission and reception are performed independently on each link, the AP of the AP multi-link device and the non-AP station of the non-AP multi-link device independently compete for transmission channels. Therefore, the transmission start and end times on each link may not be the same. In addition, the transmission opportunity (TXOP) acquired in the channel access procedure of each link can also be obtained independently.

[0458] In the embodiment of FIG. 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) each operate in a first link (Link 1) and a second link (Link 2). 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) each operate in a first link (Link 1) and a second link (Link 2). The first AP (AP1) and the second AP (AP2) each independently perform channel access in the first link (Link 1) and the second link (Link 2). The first station (STA1) and the second station (STA2) each also independently perform channel access in the first link (Link 1) and the second link (Link 2). Therefore, an AP multi-link device (AP MLd) and a non-AP multi-link device (STA MLD) can perform reception on one link while performing transmission on the other link.

[0459] These embodiments can improve transmission efficiency on individual links. However, if a non-AP multi-link device or an AP multi-link device does not support STR, channel access performed independently on each of the multiple links may not be permitted. If a non-AP multi-link device or an AP multi-link device does not support STR, other embodiments may be applicable. These are described in detail with reference to FIG. 50.

[0460]

[0461] Figure 51 shows the operation of a multi-link device performing transmission on a non-STR link pair.

[0462] A non-STR multi-link device that does not support STR cannot perform reception on another link when performing transmission on one link. Therefore, if a non-STR multi-link device independently performs channel access on each of multiple links, a transmission failure may occur. In the embodiment of FIG. 50(a), 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 (Link 1) and a second link (Link 2), 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 (Link 1) and a second link (Link 2), respectively. While the first station (STA1) performs an uplink transmission (UL frame) to the first AP (AP1), it may be difficult to perform communication between the second station (STA2) and the second AP (AP2).

[0463] When a non-STR link pair exists, a multi-link device performing transmission on a non-STR link can align the transmission start time and the transmission end time of a frame transmitted on the non-STR link pair. The transmission start time and the transmission end time of the frame may be the transmission start time and the transmission end time of a PPDU including the frame. For this purpose, the multi-link device may use padding or padding bits. For such simultaneous transmission, negotiation for simultaneous transmission may be performed. The negotiation for simultaneous transmission may include frame exchange to obtain a TXOP for simultaneous transmission. Specifically, the multi-link device may transmit a request frame on multiple links from which to obtain a TXOP. The multi-link device receiving the request frame may transmit a response frame at a short interframe space (SIFS) interval from the request frame. The request frame may be a control frame. In addition, the request frame may be a request to send (RTS) frame or a multi-user (MU)-RTS frame. In addition, the response frame may be a clear to send (CTS) frame. When one of the links is not idle during transmission of the request frame or response frame as described above, the multi-link device can transmit the request frame or transmission frame on 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) each operate on the first link (Link 1) and the second link (Link 2). In addition, the first station (STA1) and the second station (STA2) each operate on the first link (Link 1) and the second link (Link 2). Since the non-AP multi-link device is a non-STR multi-link device, the first AP (AP1) and the second AP (AP2) transmit frames simultaneously and receive frames simultaneously.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 frames. Thereafter, within the secured TXOP, the first AP (AP1) and the second AP (AP2) exchange frames with the first station (STA1) and the second station (STA2).

[0464] However, since the channel statuses of multiple links are different, transmissions may not start simultaneously on non-STR link pairs. Considering this, multiple stations that perform transmissions to non-STR multi-link devices can align the ends of PPDUs. Specifically, multiple stations that perform transmissions to non-STR multi-link devices can align the ends of PPDUs even if they cannot align the starts of PPDUs. In addition, as described above, if one of the PPDUs transmitted on a non-STR link pair does not include a frame that induces an immediate response, the end of the other PPDU may not be aligned with the end of the PPDU that does not include a frame that induces 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) each operate on the first link (Link 1) and the second link (Link 2), respectively. In addition, the first station (STA1) and the second station (STA2) operate on the first link (Link 1) and the second link (Link 2), respectively. Since the non-AP multi-link device is a non-STR multi-link device, the first AP (AP1) and the second AP (AP2) align the ends of the PPDU when transmitting PPDUs simultaneously. If the first AP (AP1) transmits a PPDU that does not include a frame that induces an immediate response, the first AP (AP1) and the second AP (AP2) do not align the ends of the PPDU. If the first AP (AP1) and the second AP (AP2) transmit a PPDU simultaneously, the first AP (AP1) and the second AP (AP2) align the ends of the PPDU.

[0465] The non-STR link pairs described above represent link pairs for which STR is not possible. A non-STR link group represents multiple links included in the non-STR link group that include non-STR link pairs. An embodiment applicable when some of the multiple links on which an AP multi-link device operates are non-SRT link pairs is described with reference to FIG. 51.

[0466]

[0467] FIG. 52 shows an embodiment of the present invention applied when some of the multiple links on which an AP multi-link device operates are non-STR link pairs.

[0468] A multi-link device can associate with a station that is not included in the multi-link device. In this case, it is difficult for a station that is not included in the multi-link device to determine whether transmission is performed on a different link. In addition, when stations included in different multi-link devices perform communication in a non-STR link pair, it is difficult for the stations included in different multi-link devices to determine whether transmission is performed on a link other than the link on which the station is operating. FIG. 51 illustrates a non-STR AP multi-link device communicating with a first station (STA1) and a second station (STA2) that are not included in the multi-link device. In the embodiment of FIG. 51(a), the first AP (AP1) and the second AP (AP2) attempt channel access on the first link (Link 1) and the second link (Link 2), respectively. The first AP (AP1) succeeds in channel access and initiates a frame exchange sequence starting with an RTS frame transmission. The second AP (AP2) fails in channel access and cannot initiate the frame exchange sequence. As described above, the second AP (AP2) cannot determine whether transmission is performed on the first link. When the first AP (AP1) transmits data to the first station (STA1) on the first link (Link 1), the second station (STA2) can perform uplink transmission. In the embodiment of FIG. 51(b), the first station (STA1) succeeds in channel access and starts a frame exchange sequence starting with an RTS frame transmission. The second station (STA2) succeeds in channel access and attempts uplink transmission. While the first AP (AP1) is receiving data transmitted by the first station (STA1) on the first link (Link 1), the second station (STA2) can complete transmission on the second link (Link 2). At this time, since the first AP (AP1) is receiving data transmitted by the first station (STA1) on the first link (Link 1), the second AP (AP2) cannot transmit a response to the transmission of the second station (STA2).Additionally, the second STA (STA2) cannot confirm the success or failure of the transmission transmitted by the second station (STA2). An embodiment for preventing such frame exchange failure is described in FIG. 53.

[0469]

[0470] FIG. 53 illustrates a multi-link device operating on multiple links including non-STR link pairs according to an embodiment of the present invention.

[0471] When a multi-link device operates on multiple links, including non-STR link pairs, the multi-link device may designate at least one of the multiple links as the primary link. The primary link may be the mandatory link described above. The multi-link device may designate one of the multiple links as the primary link. Links other than the primary link among the multiple links may be referred to as extended links.

[0472] When a non-AP multi-link device attempts to connect to a link included in a non-STR link pair, the AP multi-link device can induce the non-AP multi-link device to connect to all links included in the non-STR link pair. Furthermore, when a station not included in the non-AP multi-link device attempts to connect to a link included in a STR link pair, the AP multi-link device can induce the station not included in the non-AP multi-link device to connect to a link included in the STR link pair.

[0473] In another specific embodiment, the AP multi-link device may allow connections from stations not included in the non-AP multi-link device only on the primary link. Stations not included in the non-AP multi-link device may connect to the AP multi-link device only on the primary link of the AP multi-link device.

[0474] In the embodiment of FIG. 53, a non-STR AP multi-link device (non-STR AP MLD) operates on 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 non-STR link pairs, the first link (Link1) and the third link (Link3) are STR-capable STR link pairs, and the second link (Link2) and the third link (Link3) are STR-capable STR link pairs. The non-STR AP multi-link device (non-SRT AP MLD) designates the first link (Link1) and the third link (Link3) as default links. At this time, a third station (STA3) that is not included in the multi-link device can be connected to the non-STR multi-link device (non-STR AP MLD) on the first link (Link1) or the third link (Link3). A non-STR multi-link device (non-STR AP MLD) cannot be connected to a non-STR multi-link device (non-STR AP MLD) on the first link (Link1) or the second link (Link2). The non-STR multi-link device (non-STR AP MLD) can induce the third station (STA3) to be connected to the non-STR multi-link device (non-STR AP MLD) on the third link (Link3).

[0475] In the embodiments described above, the channel load on the primary link may become excessively high. To prevent this, the number of links included in a non-STR link pair may be limited. In this case, the number of links included in a non-STR link pair may be two.

[0476] In the embodiments described above, in negotiations for multi-link operation, the AP multi-link device can induce a connection to the primary link. This is described in FIG. 53.

[0477]

[0478] FIG. 54 shows an operation of an AP multi-link device according to an embodiment of the present invention to couple with a station not included in the multi-link device.

[0479] When a station that is not included in the multi-link device sends a connection request to the AP multi-link device on an extended link, the AP multi-link device may reject the connection request from the station. Specifically, when a station that is not included in the multi-link device sends a probe request frame to the AP multi-link device, the AP multi-link device may not send a probe response frame to the station. Furthermore, when a station that is not included in the multi-link device sends a connection request frame to the AP multi-link device on an extended link, the AP multi-link device may send a connection response frame that includes an indicator for rejecting the connection request to the station. At this time, the connection response frame may include a field indicating a status code proposing connection to another link. For example, the status code proposing connection to another link may be 82. Furthermore, the connection response frame may include information about the link proposing connection. At this time, the information about the link proposing connection 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 and operation class, and timing information. The link proposing the connection may be the primary link included in the STR link pair. Stations not included in the multi-link may attempt to connect to the link proposed by the AP multi-link device based on information about the link proposed by the AP multi-link device.

[0480] In addition, the AP multi-link device can transmit a beacon frame simultaneously on the extended link and the primary link. In addition, the AP multi-link device can transmit a beacon frame in a form that cannot be decoded by a station that is not included in the multi-link device in the extended link. Specifically, for example, the values ​​of both the IBSS STA sub-field and the ESS sub-field in the Capability information field in the beacon frame can be set to 1. At this time, a station that is not included in the multi-link device cannot decode the beacon and thus cannot transmit a connection request based on the beacon frame. In this embodiment, the AP multi-link device can transmit a beacon frame in a form that cannot be decoded by a station that is not included in the multi-link device even in the primary link included in a non-STR link pair. In addition, the AP multi-link device can set some fields of the BSS load information element of the beacon frame transmitted in the extended link to a predetermined value. At this time, the AP multi-link device can set the BSS load information element of the beacon frame transmitted in the extended link to indicate a maximum channel usage rate. Additionally, the AP multi-link device may configure the BSS load information element transmitted on the extended link to indicate a maximum number of connected stations. A station receiving a beacon frame configured in this manner may determine that it is unable to connect on the extended link or that connecting would be inefficient, and may therefore not attempt to connect. In another specific embodiment, the AP multi-link device may not transmit a beacon frame on the extended link.

[0481] The embodiments described above can be applied not only to extended links but also to basic links included in non-STR link pairs. For example, an AP multi-link device can transmit a frame rejecting a connection even if a station not included in the multi-link transmits a connection request frame on the basic link included in the non-STR link pair.

[0482] In the embodiment of FIG. 54, a station (STA) not included in the multi-link device transmits a probe request frame to a second AP (AP2) operating on an extended link. At this time, the second AP (AP2) does not transmit a probe response frame to the station (STA). A station (STA) not included in the multi-link device transmits a connection request frame to a second AP (AP2) operating on an extended link. At this time, the second AP (AP2) transmits a connection response frame including a status code for rejecting the connection to the station (STA). At this time, the connection response frame may include information about a link on which a third AP (AP3) or a first AP (AP1) operates, as described above. The station (STA) transmits a connection request frame to the third AP (AP3) based on the information about the link on which the third AP (AP3) operates.

[0483]

[0484] FIG. 55 shows an operation of an AP multi-link device according to an embodiment of the present invention to couple with a station included in the multi-link device.

[0485] A non-AP multi-link device can request information about a link for multi-link operation from an AP multi-link device using a probe request frame. Specifically, the probe request frame can include an indicator requesting link information for multi-link operation. An AP multi-link device that receives a probe request frame including information about a link for multi-link operation can transmit a probe response frame including information about a link for multi-link operation to the non-AP multi-link device. The information about a link for multi-link operation can include at least one of information about a STR link pair, information about a non-STR link pair, and information about a default link. The non-AP multi-link device can obtain information about a link for multi-link operation from the probe response frame.

[0486] A non-AP multi-link device can transmit a multi-link operation request to an AP multi-link device using a connection request frame. The connection request frame can include an indicator indicating that a multi-link operation is requested. An AP multi-link device that receives a multi-link operation request can determine whether the multi-link operation can be accepted. Specifically, if the connection request frame includes an indicator indicating that a multi-link operation is requested, the AP multi-link device can determine whether the multi-link operation can be accepted. In a specific embodiment, the AP multi-link device can determine whether the non-AP multi-link device requests a connection in a non-STR link pair or whether the non-AP multi-link device requests a connection in a primary link of a non-STR link pair. In addition, the AP multi-link device can determine whether the non-AP multi-link device requests a connection in multiple links. If the non-AP multi-link device requests a connection in an unavailable link, the AP multi-link device can reject the connection request of the non-AP multi-link device. Specifically, if the non-AP multi-link device requests a connection in an extended link of a non-STR link pair, the AP multi-link device can reject the connection request of the non-AP multi-link device. Additionally, if a non-AP multi-link device requests a connection only on some of the links of a non-STR link pair, the AP multi-link device may reject the connection request of the non-AP multi-link device. The multi-link device may reject the connection request of the non-AP multi-link device by transmitting an association response frame indicating rejection of the connection. Additionally, the multi-link device may transmit an association response frame indicating a different link from the link to which the non-AP multi-link device requested a connection.

[0487] In the embodiment of FIG. 55, a non-AP multi-link device (STA MLD) transmits a probe request frame to an AP multi-link device (AP MLD). The probe request frame includes an indicator (Multi-link Capabilities Indication) requesting link information for multi-link operation. The AP multi-link device (AP MLD) transmits a probe response frame including link information for multi-link operation to the non-AP multi-link device (STA MLD). The non-AP multi-link device (STA MLD) obtains link information for multi-link operation. The non-AP multi-link device (STA MLD) transmits a connection request frame including information for multi-link negotiation to the AP multi-link device (AP MLD). The AP multi-link device (AP MLD) transmits to the non-AP multi-link device (STA MLD) whether to accept multi-link operation using a connection response frame.

[0488]

[0489] When a multi-link device performs transmission on a non-STR link pair, transmission on the extended link may be restricted depending on whether transmission is performed on the primary link. This is explained in FIG. 55.

[0490] FIG. 56 shows a multi-link device according to an embodiment of the present invention performing transmission on a non-STR link pair based on a basic link.

[0491] As described above, when a station other than the AP multi-link device and the multi-link device communicate in a non-STR link pair, or when the stations of the AP multi-link device and the multi-link device communicate only on some links of the non-STR link pair, a primary link may be designated. The multi-link device can perform independent channel access only on the primary link. Specifically, the multi-link device can also perform transmission on the extended link under the condition that it performs transmission on the primary link. Therefore, if the primary link is occupied, transmission of the multi-link device on the extended link may not be permitted. The multi-link device may be an AP multi-link device or a non-AP multi-link device.

[0492] In the embodiment of FIG. 56, the AP multi-link device includes a first AP (AP 1) and a second AP (AP 2). The first AP (AP 1) and the second AP (AP 2) operate on a first link (Link 1) and a second link (Link 2), respectively. In addition, the non-AP multi-link device includes a first station (STA 1) and a second station (STA 2). The first station (STA 1) and the second station (STA 2) operate on a first link (Link 1) and a second link (Link 2), respectively. In addition, a third station (STA3) that is not included in the multi-link is connected to the first AP (AP1) on the first link. If the first station (STA 1) does not transmit on the first link (Link 1), the second station (STA 2) cannot transmit on the second link (Link 2). When the first station (STA 1) performs transmission on the first link (Link 1), the second station (STA 2) performs transmission on the second link (Link 2).

[0493] In this embodiment, the operation of performing channel access before performing transmission is described through FIG. 57.

[0494]

[0495] FIG. 57 shows a multi-link device according to an embodiment of the present invention performing channel access for transmission on a non-STR link pair based on a basic link.

[0496] If a multi-link device succeeds in random backoff-based channel access on a primary link and is idle continuously for a predetermined time period on an extended link after successfully accessing the primary link, the multi-link device can perform transmissions simultaneously on the primary link and the extended link. The predetermined time period may be PIFS. Alternatively, the predetermined time period may be AIFS. In another specific embodiment, if a multi-link device succeeds in random backoff-based channel access on a primary link and is idle continuously for as long as the primary link is idle, the multi-link device can perform transmissions simultaneously on the primary link and the extended link. The multi-link device may be an AP multi-link device or a non-AP multi-link device.

[0497] If the extended link is not idle even after successful channel access on the primary link, the AP multi-link device may not perform transmission. In another specific embodiment, if the extended link is not idle even after successful channel access on the primary link, the AP multi-link device may reset the value of the backoff counter on the primary link to resume channel access. This operation may also be applied to non-AP multi-link devices.

[0498] The embodiment of Fig. 57 specifies the channel access operation in the embodiment of Fig. 55. When the first station (STA1) succeeds in channel access on the first link (Link 1), which is the basic link, the second station (STA2) determines whether the second link (Link 2) has been idle continuously for a predetermined time period when the channel access on the first link (Link 1) succeeds. Since the second link (Link 2) has been idle continuously for a predetermined time period when the channel access on the first link (Link 1) succeeds, the first station (STA1) and the second station (STA2) perform transmission simultaneously.

[0499] Another channel access method applicable to non-STR link pairs is described in FIG. 57.

[0500]

[0501] FIG. 58 shows a multi-link device according to an embodiment of the present invention performing channel access for transmission on a non-STR link pair based on a basic link.

[0502] In a non-STR link pair, a multi-link device can independently perform random backoff-based channel access. At this time, the multi-link device may wait without starting transmission if the backoff counter in the second link has not reached 0 even if the backoff counter in the first link reaches 0. Specifically, the multi-link device may not start transmission until the backoff counter in the second link reaches 0 even if the backoff counter in the first link reaches 0. At this time, the multi-link device may perform transmission on the first and second links simultaneously when the backoff counter in the second link reaches 0. If the first link is the primary link and the second link is detected to be non-idle, the multi-link device may perform transmission only on the first link. In addition, even if the multi-link device succeeds in channel access only on the extended link, the multi-link device may not be permitted to perform transmission only on the extended link. The multi-link device may be an AP multi-link device or a non-AP multi-link device.

[0503] In the embodiment of FIG. 58, the second station (STA2) waits without starting transmission because the first station (STA1) failed to successfully access the channel on the first link (Link 1), which is the primary link, even if the backoff counter reaches 0 on the second link (Link 2). When the first station (STA1) succeeds in successfully accessing the channel on the first link (Link 1), which is the primary link, the first station (STA1) and the second station (STA2) perform transmission simultaneously.

[0504]

[0505] A method for performing channel access when one non-AP multi-link device is connected to both non-STR link pairs is described through FIGS. 59 to 60.

[0506] FIG. 59 illustrates 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 both non-STR link pairs.

[0507] In a non-STR link pair, a multi-link device can independently perform random backoff-based channel access. At this time, even if a backoff counter reaches 0 in a first link, the multi-link device can keep the backoff counter at 0 without starting transmission if the backoff counter does not reach 0 in a second link. Specifically, even if the backoff counter reaches 0 in the first link, the multi-link device may not start transmission until the backoff counter reaches 0 in the second link. At this time, the multi-link device can perform transmission simultaneously in the first link and the second link when the backoff counter reaches 0 in the second link.

[0508] In the embodiment of FIG. 59, the second station (STA2) does not start transmission and maintains the backoff counter at 0 even when the backoff counter reaches 0 in the second link (Link 2) because the first station (STA1) did not succeed in channel access in the first link (Link 1), which is the primary link. When the first station (STA1) succeeds in channel access in the first link (Link 1), which is the primary link, the first station (STA1) and the second station (STA2) perform transmission simultaneously.

[0509] In a STR link pair, a multi-link device can independently perform random backoff-based channel access. The multi-link device can initiate transmission on any link that first successfully accesses that link. However, if the multi-link device transmits a PPDU containing an immediate response, the multi-link device can align the ends of the PPDUs transmitted on multiple links.

[0510] In the embodiments described above, when a multi-link device successfully accesses a channel on one link and waits for the backoff procedure of another link to be completed, the multi-link device may perform channel sensing on the link in which the channel access was successful. At this time, if the channel is detected as not idle on the link in which the channel access was successful, the multi-link device may restart the channel access procedure on that channel. The operation of the multi-link device when the multi-link device successfully accesses a channel on one link and detects that the channel is not idle on the link in which the channel access was unsuccessful is described with reference to FIG. 60.

[0511]

[0512] FIG. 60 illustrates 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 both non-STR link pairs.

[0513] In a non-STR link pair, if a multi-link device successfully accesses a channel on the first link and detects that the channel is not idle on the second link, the multi-link device may perform transmission on the first link. At this time, the multi-link device may determine whether to start transmission on the first link depending on the type of signal that occupies the second link. Specifically, if the signal that occupies the second link is a frame transmitted from another BSS, the multi-link device may perform transmission on the first link. In another specific embodiment, if the signal that occupies the second link is a frame transmitted from another BSS, the multi-link device may maintain the backoff counter value at 0 on the first link. At this time, the multi-link device may transmit PPDUs simultaneously on the first link and the second link when the second link becomes idle.

[0514]

[0515] In these embodiments, the multi-link device can determine whether a 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 multi-link device is connected, the multi-link device can determine that the frame is an intra-BSS frame. In addition, if the BSSID field of the received frame indicates the address of the AP to which the multi-link device is connected, the multi-link device can determine that the frame is an intra-BSS frame. In addition, the multi-link device can determine whether a signal occupying the second link is a frame transmitted from another BSS based on the BSS color indicated by the received PPDU. In this case, the PPDU can indicate the BSS color through the BSS color field or the Group ID field and the Partial AID field of the signaling field.

[0516] If the signal occupying the second link is not a Wi-Fi signal, the multi-link device may not perform transmission on the first link and may keep the backoff counter at 0. In another specific embodiment, if the signal occupying the second link is not a Wi-Fi signal, the multi-link device may perform transmission on the first link.

[0517] In the embodiment of FIG. 60, the AP multi-link device includes a first AP (AP 1) and a second AP (AP 2). The first AP (AP 1) and the second AP (AP 2) each operate on a first link (Link 1) and a second link (Link 2), which are non-STR link pairs. In addition, the non-AP multi-link device includes a first station (STA 1) and a second station (STA 2). The first station (STA 1) and the second station (STA 2) each op...

Claims

1. In a non-AP (Access Point) station (STA) of a wireless communication system, Communication module; comprising a processor controlling the above communication module; The above processor, Receive a beacon frame including a request type field from the AP, The above request type field includes a specific field to indicate a target wake time (TWT) for low latency operation, Receive a downlink frame or transmit an uplink frame depending on the value of the above specific field. When the value of the above specific field is set to the first specific value, the broadcast TWT service period (SP) is a STA that is a TWT SP for the low-latency operation.

2. In paragraph 1, An STA that can transmit only frames requiring low delay during the TWT SP for the low delay operation when the TWT SP for the low delay operation is set.

3. In paragraph 1, The STA wherein the above beacon frame further includes a quiet information element for protecting the TWT SP for the low latency operation.

4. In paragraph 3, The interval set by the above quiet information element and the start time of the TWT SP for the low latency operation are the same STA.

5. In paragraph 3, An STA that ignores a part or all of the overlapping interval set by the quiet information element and a portion or all of the TWT SP for the low-latency operation when the interval set by the quiet information element overlaps.

6. In paragraph 3, The interval set by the above quiet information element is an STA that is used by at least one STA to set the NAV.

7. In paragraph 6, The above NAV is an STA set during the interval set by the above quiet information element.

8. In paragraph 1, An STA indicating that when the value of the above specific field is set to a second specific value, the above specific field is restricted from transmission only in the form of a response frame for a downlink frame.

9. In paragraph 1, The above beacon frame further includes a parameter field including a broadcast TWT information field, The above broadcast TWT information field is a STA that includes information related to a TID whose transmission of frames is restricted by the TWT for the low-latency operation.

10. In paragraph 1, When the above non-AP STA configures a multi-link device (MLD), the MLD is an STA that cannot transmit frames through other links while receiving the beacon frame.

11. In paragraph 1, STA whose frame transmission operation is terminated before the start time of TWT SP for the above low-latency operation.

12. In a method for a non-AP STA to transmit a frame in a wireless communication system, A step of receiving a beacon frame including a request type field from an AP; The above request type field includes a specific field to indicate a target wake time (TWT) for low latency operation; and Receive a downlink frame or transmit an uplink frame depending on the value of the above specific field. A method wherein a broadcast TWT service period (SP) is a TWT SP for the low-latency operation, when the value of the above specific field is set to a first specific value.

13. In paragraph 12, A method in which only frames requiring low delay can be transmitted during the TWT SP for the low delay operation when the TWT SP for the low delay operation is set.

14. In paragraph 12, A method wherein the beacon frame further includes a quiet information element for protecting the TWT SP for the low latency operation.

15. In paragraph 14, The interval set by the above quiet information element and the start time of the TWT SP for the low latency operation are the same method.

16. In paragraph 14, A method in which, 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 intervals set by the quiet information element is ignored.

17. In paragraph 14, The interval set by the above quiet information element is a method used by at least one STA to set the NAV.

18. In paragraph 17, A method in which the above NAV is set during the interval set by the above quiet information element.

19. In paragraph 12, A method for indicating that, when the value of the above specific field is set to a second specific value, transmission of the above specific field is restricted to only the form of a response frame for a downlink frame.

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

21. In paragraph 12, A method in which, when the non-AP STA configures a multi-link device (MLD), the MLD cannot transmit a frame through another link while receiving the beacon frame.

22. In paragraph 12, A method in which the transmission operation of a frame is terminated before the start time of a TWT SP for the above low-latency operation.

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